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A national laboratory of the U.S. Department of Energy 

Office of Energy Efficiency & Renewable Energy 

National Renewable Energy Laboratory 

Innovation for Our Energy Future 

Technical Report Large-Scale Pyrolysis Oil 

NREL/TP-510-37779 Production: A Technology November 2006 

Assessment and Economic 

Analysis 

M. Ringer, V. Putsche, and J. Scahill 

NREL is operated by Midwest Research Institute Battelle Contract No. DE-AC36-99-GO10337 
Technical Report

NREL/TP-510-37779 

November 2006

Large-Scale Pyrolysis Oil 

Production: A Technology

Assessment and Economic 

Analysis 

M. Ringer, V. Putsche, and J. Scahill 

Prepared under Task No. BB06.7510 

National Renewable Energy Laboratory

1617 Cole Boulevard, Golden, Colorado 80401-3393 

303-275-3000 • www.nrel.gov

Operated for the U.S. Department of Energy

Office of Energy Efficiency and Renewable Energy

by Midwest Research Institute • Battelle 

Contract No. DE-AC36-99-GO10337
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Executive Summary 

Pyrolysis is one of a number of possible paths for converting biomass to higher value products. 

As such, this technology can play a role in a biorefinery model to expand the suite of product 

options available from biomass. The intent of this report is to provide the reader with a broad 

perspective of pyrolysis technology as it relates to converting biomass substrates to a liquid “biooil” product, and a detailed technical and economic assessment of a fast pyrolysis plant 

producing 16 tonne/day of bio-oil. 

The international research community has developed a considerable body of knowledge on the 

topic over the last twenty-five years. The first part of this report attempts to synthesize much of 

this information into the relevant issues that are important to advancing pyrolysis technology to 

commercialization. The most relevant topics fall under the following categories: 

1) Technical requirements for converting biomass to high yields of liquid bio-oil 

2) Reactor designs capable of meeting technical requirements 

3) Bio-oil stability issues and recent findings that address the problem 

4) Product specifications and standards that need to be established 

5) Applications for using bio-oil in existing or modified end use devices 

6) Environmental, safety, and health issues 

For the bio-oil plant technical and economic analysis, the process is based on fast pyrolysis, 

which is composed of five major processing areas: feed handling and drying, pyrolysis, char 

combustion, product recovery, and steam generation. An ASPEN model was developed to 

simulate the operation of the bio-oil production plant. Based on a 550 tonne/day biomass (wood 

chips, 50% by mass water content) feed, the cost of the bio-oil for a fully equity financed plant 

and 10% internal rate of return is $7.62/GJ on a lower heating value (LHV) basis. 

i 
Table of Contents 

Executive Summary......................................................................................................................... i 

1. Introduction............................................................................................................................. 1 

2. Production of Bio-oil .............................................................................................................. 5 

2.1 Heat Transfer Requirements ........................................................................................... 5 

2.2 Biomass Feedstock Preparation ...................................................................................... 6 

2.3 Reactor Designs Capable of Achieving Fast Pyrolysis Conditions................................ 7 

2.3.1 Bubbling Fluidized Bed .......................................................................................... 8 

2.3.2 Circulating Fluidizing Bed...................................................................................... 9 

2.3.3 Ablative Pyrolysis................................................................................................. 11 

2.3.4 Vacuum Pyrolysis ................................................................................................. 12 

2.3.5 Rotating Cone Pyrolysis Reactor.......................................................................... 13 

2.4 Pyrolysis Vapor (Bio-oil) Recovery ............................................................................. 13 

2.5 Char and Particulate Separation.................................................................................... 14 

3. Properties of Bio-oil.............................................................................................................. 16 

3.1 Chemical Nature of Bio-oil........................................................................................... 16 

3.2 Physical Properties of Bio-oil (Stability)...................................................................... 19 

3.3 Physical Properties (Re-vaporization) .......................................................................... 20 

3.4 Environmental / Health................................................................................................. 21 

4. Uses for Bio-oil..................................................................................................................... 23 

4.1 Combustion................................................................................................................... 23 

4.2 Diesel Engines .............................................................................................................. 23 

4.3 Combustion Turbines.................................................................................................... 24 

4.4 Bio-Oil Standards and Specifications ........................................................................... 25 

4.5 Upgrading Bio-oil Properties to Higher Value Products .............................................. 27 

5. Prior Investigations of Bio-Oil Production Costs ................................................................. 29 

6. Wood Chip Pyrolysis Facility Economic Analysis............................................................... 31 

6.1 Design Basis and Process Description.......................................................................... 31 

6.2 Model Description ........................................................................................................ 35 

6.3 Material and Energy Balance Results........................................................................... 36 

6.4 Economic Basis............................................................................................................. 36 

6.5 Capital Costs ................................................................................................................. 37 

ii 
iii 

6.6 Operating Costs............................................................................................................. 37 

6.7 Economic Analysis ....................................................................................................... 38 

6.8 Capital Cost Results...................................................................................................... 39 

6.9 Operating Cost Results ................................................................................................. 41 

6.10 Financial Analysis Results............................................................................................ 41 

6.11 Discussion..................................................................................................................... 41 

6.12 Sensitivity Studies......................................................................................................... 42 

6.13 Upgrading of Crude Bio-Oil ......................................................................................... 43 

6.14 Limitations of the Analysis........................................................................................... 44 

7. Conclusions and Recommendations ..................................................................................... 45 

7.1 Current State-of-the-Art for Fast Pyrolysis of Biomass ............................................... 45 

7.2 Recommendations for Advancing Fast Pyrolysis Technology..................................... 47 

References..................................................................................................................................... 51 

Appendix A: ASPEN Plus® Model Implementation / Mass Balances ........................................ 57 

List of Figures 

Figure 1. Process Schematic for a Bubbling Fluidized Bed Pyrolysis Design ............................... 9 

Figure 2. Process Schematic for a Circulating Fluidized Bed Pyrolysis Design .......................... 10 

Figure 3. Schematic of the NREL Vortex Reactor Fast Pyrolysis Reactor Design...................... 11 

Figure 4. Molecular Beam Mass Spectrometer Scans of Pyrolysis Product Profile at Different 

Temperatures Using the Same Pine Wood Sample ...................................................................... 18 

Figure 5. Fast Pyrolysis Block Flow Diagram.............................................................................. 32 

Figure 6. Proposed Heavy Bio-Oil Upgrading Process ................................................................ 43 

Figure 7. Bio-Oil Production and Upgrading Cost Goals............................................................. 50 

List of Tables

Table 1. Worldwide Biomass Pyrolysis Units ................................................................................ 3 

Table 2. Properties of Bio-oil from Various Feedstocks .............................................................. 17 

Table 3. Proposed Specifications for Various Grades of Bio-oil.................................................. 26 

Table 4. Bio-oil Production Cost/Selling Price............................................................................. 30 

Table 5. Design Basis ................................................................................................................... 33 
Table 6. Total Project Investment Factors .................................................................................... 37 

Table 7. Unit Costs ....................................................................................................................... 38 

Table 8. Employee Requirements................................................................................................. 38 

Table 9. Installed Equipment Costs .............................................................................................. 40 

Table 10. Total Project Investment............................................................................................... 41 

Table 11. Crude Bio-oil Sensitivity Studies ................................................................................. 43 

Table 12. Worldwide Current Biomass Pyrolysis Operating Plants............................................. 47 

iv 
1. Introduction 

The vast stores of biomass available in the domestic United States have the potential to displace 

significant amounts of fuels that are currently derived from petroleum sources. Energy security, 

energy flexibility, and rural and urban job development are other drivers that support the use of 

biomass to produce fuels, chemicals, and other products. The loss of traditional biomass-based 

industries such as lumber and paper to overseas markets make it increasingly important to 

develop this domestic resource. The rationale is even more compelling if one considers the 

benefits of forest thinning to forest health and fire issues in the arid West. Proposed fuel 

reduction activities would involve removing enormous amounts of biomass that have no current 

market value. The only realistic market capable of consuming this volume of material is energy 

and/or commodity chemicals. The primary question of “what is the best way to convert biomass 

into higher value products” is then raised. 

Pyrolysis is one of a number of possible paths by which we can convert biomass to higher value 

products. As such, this technology can play a role in a biorefinery model to expand the suite of 

product options available from biomass. The intent of this report is to provide the reader with a 

broad perspective of pyrolysis technology as it relates to converting biomass substrates to a 

liquid “bio-oil” product, and a detailed technical and economic assessment of a fast pyrolysis 

plant producing 16 tonne/day of bio-oil. 

The international research community has developed a considerable body of knowledge on 

pyrolysis over the last twenty-five years. The first part of this report attempts to synthesize much 

of this information into the relevant issues that are important to advancing pyrolysis technology 

to commercialization. The most relevant topics fall under the following categories: 

1) Technical requirements to effect conversion of biomass to high yields of liquid bio-oil 

2) Reactor designs capable of meeting technical requirements 

3) Bio-oil stability issues and recent findings that address the problem 

4) Product specifications and standards need to be established 

5) Applications for using bio-oil in existing or modified end use devices 

6) Environmental, safety, and health issues. 

The first two categories above represent topics that are well established and accepted in the 

research community. There is little argument on requirements for producing bio-oil in high 

yields. The principal technical requirement is to impart a very high heating rate with a 

corresponding high heat flux to the biomass. When exposed to this environment, thermal energy 

cleaves chemical bonds of the original macro-polymeric cellulose, hemicellulose, and lignin to 

produce mostly oxygenated molecular fragments of the starting biomass. These fragments have 

molecular weights ranging from a low of 2 (for hydrogen) up to 300-400. The lower molecular 

weight compounds remain as permanent gases at ambient temperature while the majority of 

compounds condense to collectively make up what is called bio-oil at yields up to 70 wt%. This 

70 wt% also includes the water formed during pyrolysis in addition to moisture in the biomass 

feed that ends up as water in bio-oil. The yield of permanent gas is typically 10-15 wt% with the 

balance of the weight produced as char. 

1 
A number of reactor designs have been explored that are capable of achieving the heat transfer 

requirements noted above. They include: 

• Fluidized beds, both bubbling and circulating 

• Ablative (biomass particle moves across hot surface like butter on a hot skillet) 

• Vacuum 

• Transported beds without a carrier gas 

Of these designs, the fluidized and transported beds appear to have gained acceptance as the 

designs of choice for being reliable thermal reaction devices capable of producing bio-oil in high 

yields. 

Categories 3, 4, and 5 have important relationships to each other. The stability of the bio-oil 

product is critical to the design of end use devices such as burners, internal combustion (IC) 

engines, and turbines. As with devices that operate on petroleum-based fuels, these devices are 

designed to function properly with consistent fuel properties. To gain marketplace acceptance of 

bio-oils, the consumer must have confidence that this fuel will perform reliably in a given piece 

of equipment and not have deleterious effects on the equipment. The generally accepted way of 

providing this level of confidence is to establish a set of specifications for bio-oil that every 

producer would be required to meet. This, of course, needs to be done in concert with the 

designers and manufacturers of the end use application devices. One of the key specification 

issues is the level of char fines remaining in the bio-oil. While char is known to be a primary 

catalytic influence on the long-term stability of the oil, it is not known how it can be removed in 

a cost effective manner. The difficulty is tied to the sub-micron size of these char fines. In many 

respects the issue of “clean up” of char fines from the bio-oil can be considered analogous to the 

cleaning of tars and particulates from gasifier product streams. Both are critical technical hurdles 

that must be overcome before the technology gains widespread commercial acceptance. 

The last category concerns environmental, safety, and health issues. These issues are important 

to both the producer and consumer of bio-oils. The producer must have a good understanding of 

the toxicity of bio-oil so as to design and build in the appropriate engineering controls for 

protecting plant operating personnel. Information about these issues is also required to meet the 

requirements of commerce with respect to transportation and consumer right-to-know safety 

issues. 

Current pyrolysis systems are relatively small from a process industries throughput standpoint. 

The table below illustrates this point. Some of the mobile systems that are currently under 

development or were demonstrated in the late 1980s have capacities of about 5 tons /day, which 

is similar to some of stationary units noted below. The implication here is that this technology is 

still in its early development stages from a standpoint of its commercialization status. The Red 

Arrow plants can be considered commercial but they are focused on high value flavoring 

compounds that have limited markets. Large-scale systems to serve energy markets have not yet 

achieved commercial status. 

2 
Table 1. Worldwide Biomass Pyrolysis Units 

Reactor Design Capacity (Dry 

Biomass Feed) 

Organization or 

Company 

Products 

Fluidized bed 400 kg/hr (11 

tons/day) 

DynaMotive, Canada Fuel 

250 kg/hr (6.6 

tons/day) 

Wellman, UK Fuel 

20 kg/ hr (0.5 

tons/day) 

RTI, Canada Research / Fuels 

Circulating Fluidized 

Bed 

1500 kg/hr (40 

tons/day) 

Red Arrow, WI 

Ensyn design 

Food flavorings / 

chemicals 

1700 kg/hr (45 

tons/day) 

Red Arrow, WI 

Ensyn design 

Food flavorings / 

chemicals 

20 kg/hr (0.5 

tons/day) 

VTT, Finland 

Ensyn design 

Research / Fuels 

Rotating Cone 200 kg/hr (5.3 

tons/day) 

BTG, Netherlands Research / Fuels 

Vacuum 3500 kg/hr (93 

tons/day) 

Pyrovac, Canada Pilot scale 

demonstration / Fuels 

Other Types 350 kg/hr (9.3 

tons/day) 

Fortum, Finland Research / Fuels 

The application of heat in the absence of oxygen is well recognized as a method for breaking 

down the complex polymeric constituents of biomass (cellulose, hemicellulose, and lignin) to 

simpler molecular fragments. Some of the earliest recorded uses of this technique were in Egypt 

to produce pitch for water sealing boats and as an embalming agent. In more recent times, before 

the advent of the petrochemical industry, a number of chemicals such as methanol, phenol, 

carboxylic acids, and furfural were derived from the pyrolysis liquids generated during charcoal 

manufacturing. These were rather crude techniques and little effort was expended in trying to 

improve the yields or selectivity of the compounds of choice since charcoal was the primary 

product. In the late 1960s and early 1970s pioneering research in understanding the fundamental 

mechanisms of thermal processes as applied to biomass substrates began in earnest [1,2]. After 

the global petroleum supply restrictions in the early 1970s, and the subsequent price increases, 

the use of biomass as a source of energy saw renewed interest. This interest accelerated the 

research and development of thermal processes and investigators began to gain a better 

understanding of how the various components of biomass break down in high temperature 

environments [3]. By this time the community of researchers investigating thermochemical 

conversion pathways had grown substantially. In October 1980, a workshop sponsored by the 

Solar Energy Research Institute (SERI) —forerunner to the National Renewable Energy 

Laboratory (NREL)—was held at Copper Mountain CO. The workshop brought together most of 

the people who had been doing research in biomass pyrolysis. In retrospect this “Specialists’ 

3 
Workshop on Fast Pyrolysis of Biomass” could be considered a watershed event that began 

extensive networking among researchers in this field. This then set the stage for rapid 

advancement of the chemical science and engineering that would be crucial in developing 

biomass fast pyrolysis into a commercial technology. The years from 1980 to 1990 can be 

considered the golden era of biomass pyrolysis development with many advances made by U.S. 

and Canadian research teams. By the end of the 90s Europe had taken the lead in advancing 

biomass fast pyrolysis technology. With the wide number of researchers involved in developing 

biomass pyrolysis, liquid products have taken on a variety of descriptors such as: biomass (or 

wood) pyrolysis oils, biocrude oils, wood oil, pyroligneous tar, liquid wood, biomass pyrolysis 

liquids, or simply bio-oil. For the remainder of this report the term bio-oil will be used for the 

liquid product. 

4 
2. Production of Bio-oil 

2.1 Heat Transfer Requirements 

Three primary products are obtained from pyrolysis of biomass. They are char, permanent gases, 

and vapors; that at ambient temperature condense to a dark brown viscous liquid. While 

pyrolysis of biomass has been practiced in some form for thousands of years, it wasn’t until 

recently that the relationship between heat transfer rates into the biomass and product 

distribution yields were well understood. The practice of charcoal manufacture from biomass is 

generally referred to as a slow pyrolysis process based on the rate in which heat is imparted to 

the biomass. The distribution of products between liquid, char, and gas on a weight basis for this 

“slow” pyrolysis is approximately 30%, 35%, and 35% respectively, whereas under “fast 

pyrolysis” conditions the product distribution is dramatically altered and shifts the distribution 

primarily to a liquid bio-oil product. Under these conditions bio-oil yields of liquid, char, and gas 

are 75%, 12%, and 13% respectively [4]. It is generally recognized that two primary processing 

steps are required to meet the conditions for fast pyrolysis. They are: 

• Very high heat flux to the biomass with a corresponding high heating rate of the biomass 

particle. 

• The heat transfer to the biomass must occur in a very short time period with immediate 

quenching following product formation. 

The rate of the heat transfer to the particle needs to be between 600-1000 W/cm

2

 [5]. Some 

unpublished work done at SERI (now NREL) in the early 1980s indicated that the heat of 

pyrolysis (energy required to thermally break the macro polymer bonds) was relatively low, on 

the order of 230 KJ/kg. The reproducibility of the data was not very good so the accuracy of this 

number is questionable. Other published data report numbers as high as 1000 KJ/kg [6], which 

sheds some light on the relative magnitude of energy required for converting solid biomass to a 

liquid. For comparison, the amount of energy needed to reform methane to hydrogen is about 

750 MJ/Kg. Even at the higher value these numbers imply that once the reaction vessels are 

brought up to temperature the amount of energy required to actually break apart the biomass is 

not significant. The energy needed to carry out this transformation is readily available in the coproducts of pyrolysis gas and/or char. 

Applying this heat to the macro-polymer components making up biomass will result in their 

cleaving into smaller fragments. Because of the oxygen present in these fragments, they tend to 

be unstable above 400°C and will continue to undergo chemical change unless they are thermally 

quenched. Hence, very short residence times are required in the thermal reaction zone, ideally 

only a few hundred milliseconds. These thermal breakdown reactions are very complex and have 

not been well characterized, but it is thought that many free radical-type compounds are present 

in the promptly formed products. We know however, that if not rapidly quenched these 

compounds can crack further into smaller molecular weight fragments and/or polymerize into 

larger fragments, both at the expense of fragments making up the desired liquid product [7,3]. 

The combination of these processing requirements, a short residence time, and immediate 

cooling of the vapors, can be thought of in terms of a “cracking severity” (combined effect of 

temperature and time), which generally defines the optimized operating parameters. Even though 

the “cracking severity” has the major impact on pyrolysis vapors, there are other factors that can 

5 
also influence the nature and yield of the pyrolysis products. For example, the amount of inert 

gas present in the reaction environment will determine the partial pressure of the resulting 

fragments and therefore affect the rate of their polymerization. It is also well known that mineral 

matter present in the biomass exhibits catalytic effects for both cracking and polymerization 

[8,9]. 

Because most forms of biomass are composed of lignin, cellulose, hemicellulose, and 

extractives; the thermal breakdown fragments from each of these will be chemically different 

and therefore affected differently by the cracking severity as well as any catalytic effects from 

mineral matter present in a given type of biomass. However, even with all the variables involved 

in producing bio-oil it is interesting to note that if oils are prepared from different biomass 

substrates and the amount of moisture in the resulting bio-oil is relatively constant then the 

heating value of the oil is relatively uniform at about 17 MJ/kg. If one compares this to the 

heating value of the starting biomass at 18 MJ/kg it is apparent that fast pyrolysis is primarily a 

process of changing the physical state of biomass from a solid to a liquid. However this needs to 

viewed from the context that approximately 25% of the starting biomass weight has been lost 

during the conversion process. But this only tells part of the story. Closer inspection of the 

resulting liquids reveals a complex yet rich mixture of compounds that may also serve chemical 

markets in addition to a useful form of energy. 

2.2 Biomass Feedstock Preparation 

To achieve the high bio-oil yields of fast pyrolysis it is also necessary to prepare the solid 

biomass feedstock in such a manner that it can facilitate the required heat transfer rates. There 

are three primary heat transfer mechanisms available to engineers in designing reaction vessels: 

convection, conduction, and radiation. To adequately exploit one or more of these heat transfer 

mechanisms as applied to biomass fast pyrolysis requirements, it is necessary to have a relatively 

small particle for introduction to the reaction vessel. This ensures a high surface area per unit 

volume of particle. Because of small linear dimensions the whole particle achieves the desired 

temperature in a very short residence time. 

Another reason for small particles is the physical transition of biomass as it undergoes pyrolysis 

when char develops at the surface. Char has insulating properties that impede the transfer of heat 

into the center of the particle and therefore runs counter to the requirements needed for fast 

pyrolysis. The smaller the particle the less of an affect this has on heat transfer. Comminution 

(size reduction) of biomass however requires energy, and this in turn adds to the overall 

processing cost. As would be expected, the smaller the desired size the more expense added to 

the feedstock preparation costs. To put this in perspective, a study conducted by Himmel et al. 

[10] in 1985 showed that reducing biomass to particles in the size range of 2.5 mm to 250 micron 

would add $1.80/ton to $5.60/ton respectively. These operating costs were based on a 7 cents / 

kW-hr cost of power to drive the mill. Since feedstock cost is a primary driver in the cost of 

producing bio-oils, it is important to keep these feed preparation costs low. In the early days of 

fast pyrolysis development researchers thought that particle sizes of a few hundred microns were 

needed to facilitate the high heat transfer rates. However, more recent practical experience has 

demonstrated this is not the case, but sizes of approximately 2 mm are still necessary [4]. 

Moisture in the biomass is another feedstock preparation consideration. Any moisture present in 

the feed will simply vaporize and then re-condense with the bio-oil product. As we will discuss 

later in Section 4.4, the amount of moisture in the bio-oil product will impact the resulting 

6 
quality of these liquids. It should also be noted that water is formed as part of the 

thermochemical reactions occurring during pyrolysis. If bone-dry biomass is subjected to the 

thermal requirements for fast pyrolysis the resulting bio-oil will still contain 12-15 wt% water. 

This is thought to be a result of dehydration of carbohydrates and possibly free radical reactions 

occurring with the hydrogen and oxygen in the high temperature (500°C) pyrolysis environment. 

So water in the starting biomass will simply add to this base amount in the final bio-oil product. 

At 2.3 MJ/kg, the latent heat of evaporation of water is substantial and points out another 

important consideration with respect to drying the biomass feed prior to pyrolysis. Moisture in 

the feed becomes a heat sink and competes directly with the heat available for fast pyrolysis. 

Ideally it would be desirable to have little or no moisture in the starting biomass feed but 

practical considerations make this unrealistic. Commercial wood chip dryers, having reasonable 

throughput capacities, have lower limits of moisture that are difficult to exceed without risking 

volatile organic chemical (VOC) emissions and fires starting in the dryers. Additional costs are 

also incurred as the moisture is driven to levels approaching zero, so in practice a balance must 

be sought. Moisture levels of 5-10 wt% are generally considered acceptable for the pyrolysis 

process technologies currently in use. As with the particle size, the moisture levels in the 

feedstock biomass are a trade off between the cost of drying and the heating value penalty paid 

for leaving the moisture in. 

2.3 Reactor Designs Capable of Achieving Fast Pyrolysis 

Conditions 

During the last twenty-five years of fast pyrolysis development a number of different reactor 

designs have been explored that meet the heat transfer requirements noted above while also 

attempting to address the cost issues of size reduction and moisture content of the feed. These are 

described in more detail in a comprehensive survey published by Bridgewater and Paecocke [11] 

and fall under the following general categories: 

• Fluidized bed 

• Transported bed 

• Circulating fluid bed 

• Ablative (vortex and rotating blade) 

• Rotating cone 

• Vacuum 

The rotating blade type of ablative reactor along with the rotating cone and vacuum pyrolysis 

reactors do not require an inert carrier gas for operation. When issues of product vapor collection 

and quality are considered, the lack of a carrier gas when conducting fast pyrolysis can be a real 

advantage. This is because the carrier gas tends to dilute the concentration of bio-oil fragments 

and enhances the formation of aerosols as the process stream is thermally quenched. This in turn 

makes recovery of the liquid oil more difficult. Another disadvantage is that high velocities from 

the carrier gas entrain fine char particles from the reactor, which then are collected with the oil as 

it condenses. As we will discuss in sections 2.5 and 3.2 these char fines have a deleterious effect 

7 
on the bio-oil quality. A general discussion of the advantages and disadvantages of each reactor 

design follows. 

2.3.1 Bubbling Fluidized Bed 

Bubbling fluidized bed reactors have been used in petroleum and chemical processing for over 

fifty years and therefore have a long operating history. As reactor designs, they are characterized 

as providing high heat transfer rates in conjunction with uniform bed temperatures, both being 

necessary attributes for fast pyrolysis. By selecting the appropriate size for the bed fluidizing 

media, the gas flow rate can be established such that gas/vapor residence time in the freeboard 

section above the bed can be set to a desired value, generally between 0.5-2.0 seconds. 

Experience has shown that an operating temperature of 500° -550°C in the bed will usually result 

in the highest liquid yields at about 0.5 sec residence time, however larger systems can operate at 

a somewhat lower temperature and a longer residence time. The temperatures may also vary 

depending on the type of biomass being processed. The largest units in operation are a 200 kg/hr 

unit by Union Fenosa in Spain and a 400 kg/hr unit by DynaMotive in Canada. Both were 

designed and constructed based on the Waterloo Fast Pyrolysis Process developed at the 

University of Waterloo and designed by its spin-off company Resource Transforms International 

in Canada. 

Because of their long history of service and inherently simple operating design, this type of 

reactor is considered to be very reliable and virtually trouble free as a system capable of 

conducting fast pyrolysis of biomass. There are however, some practical constraints that must be 

taken into account when considering this design for larger-scale reactors. The reactor throughput 

depends on the amount and efficiency of heat supply. Some bubbling beds operate in an 

adiabatic regime with all the process heat supplied by the preheated fluidizing gas, which in 

many instances is recycled pyrolysis gas. This simplifies the reactor design but usually results in 

a smaller throughput. Better performance is obtained when the reactor sand is indirectly heated 

by the use of fired tubes. DynaMotive uses natural gas to heat their pilot reactor but larger-scale 

commercial units will need to integrate combustion of char and gas byproducts to supply the 

necessary heat. Direct heating using flue gases is not recommended because it can result in 

smaller oil yields due to oxidation from excess air in the flue gases. 

In principle, the bubbling bed is “self cleaning,” which means that byproduct char is carried out 

of the reactor with the product gases and vapors. However, in practice this requires using 

carefully sized feedstock with a relatively narrow particle size distribution. If biomass particles 

are too large the remaining char particles (after pyrolysis) may have too much mass to be 

effectively entrained out of the reactor with the carrier gas and product vapors. The density of 

this char will be less than that of the fluidizing media and, consequently, this char will “float” on 

top of the bed. In this location it will not experience enough turbulence with the bed media to 

undergo attrition into smaller particles that will eventually leave the reactor. Another issue with 

having the char on top of the bed is that it will have a catalytic influence on the vapors as they 

pass through it on their way out of the bed. This can affect the yields and the chemical nature of 

the resulting liquid product. On the other hand, if fines are present in the feed, then the feed must 

be introduced lower in the bed otherwise the fines will be quickly entrained out of the bed before 

complete pyrolysis can occur. In general, char accumulation in the bed should be prevented. The 

design should include a means for skimming and discharging char from the top of the bed. If this 

is not done the feed will need to be carefully screened to obtain a narrow particle size 

8 
distribution. This in turn will add considerably to the feedstock preparation costs. A schematic of 

a typical fluidized bed is shown below in Figure 1. 

Biomass 

Char 

Recycle gas 

Fluid Bed Reactor

Cyclone 

Bio-Oil 

Quench Cooler

Secondary Recovery 

Recycle Gas Heater 

Figure 1. Process Schematic for a Bubbling Fluidized Bed Pyrolysis Design 

Some design considerations in bubbling fluidized bed systems: 

• Heat can be applied to the fluid bed in a number of different ways that offer flexibility for 

a given process. 

• Vapor residence time is controlled by the carrier gas flow rate 

• Biomass feed particles need to be less than 2-3 mm in size 

• Char can catalyze vapor cracking reactions so it needs to be removed from the bed 

quickly 

• Char can accumulate on top of the bed if the biomass feed is not sized properly, 

provisions for removing this char may be necessary

• Heat transfer to bed at large scales has not been demonstrated. 

2.3.2 Circulating Fluidizing Bed 

This reactor design also is characterized as having high heat transfer rates and short vapor 

residence times which makes it another good candidate for fast pyrolysis of biomass. It is 

somewhat more complicated by virtue of having to move large quantities of sand (or other 

fluidizing media) around and into different vessels. This type of solids transport has also been 

practiced for many years in refinery catalytic cracking units, so it has been demonstrated in 

9 
commercial applications. Circulating bed technology has been extensively applied to biomass 

pyrolysis by Ensyn Technologies under the name of Rapid Thermal Processing (RTP). Other 

organizations involved in developing this type of pyrolysis technology are CRES (Greece) and 

ENEL (Italy). Various system designs have been developed with the most important difference 

being in the method of supplying heat. Earlier units were based on a single indirectly heated 

reactor, cyclone, and standpipe configuration, where char was collected as a byproduct. Later 

designs incorporated a dual reactor system such as that operated by ENEL in Italy. In this design 

the first reactor operates in pyrolysis mode while the second one is used to burn char in the 

presence of the sand and then transfer the hot sand to the pyrolysis vessel. Such an option has 

advantages but also is more challenging because of solids transport and temperature control 

(overheating of sand in the combustor) in the system. Sand flow rate is also 10-20 times greater 

than the biomass feed rate and there is a high energy cost in moving this sand around the loop. 

Feed particles sized for a circulating bed system must be even smaller than those used in 

bubbling beds. In this type reactor the particle will only have 0.5-1.0 seconds (s) residence time 

in the high heat transfer pyrolysis zone before it is entrained over to the char combustion section 

in contrast to the bubbling bed where the average particle residence time is 2-3 s. For relatively 

large particles this would not be enough time to transport heat to the interior of the particle. This 

is especially true as a char layer develops on the outside surface, which acts as an insulating layer 

preventing further penetration of heat. The movement of sand and particles through the system 

causes abrasion of this char layer but mostly at the elbows and bends where there is more 

forceful interaction between the particles and sand. The incompletely pyrolyzed larger particles 

will end up in the char combustor where they will simply be burned. Consequently, if larger feed 

particles are used, the oil yield will be reduced due to combustion of incompletely pyrolyzed 

particles. Particles in the 1-2 mm are the desired size range. A schematic of this type of pyrolysis 

system is shown below in Figure 2. 

Biomass 

Hot Sand 

Sand + Char 

Flue Gas 

Product Gas 

Recycle Gas 

Air 

Bio-Oil 

CFB Pyrolysis Reactor 

Cyclone 

Co

mbustor

Quench Cooler

Secondary Recovery 

Figure 2. Process Schematic for a Circulating Fluidized Bed Pyrolysis Design 

10 
2.3.3 Ablative Pyrolysis 

The vortex reactor was developed at SERI (now NREL) from 1980 until 1996 [12,13] to exploit 

the phenomena of ablation. In this approach the biomass particle is melted / vaporized from one 

plane or side of its aspect ratio. This design approach had the potential to use particle sizes up to 

20 mm in contrast to the 2 mm particle size required for fluidized bed designs. Biomass particles 

were accelerated to very high velocities by an inert carrier gas (steam or nitrogen) and then 

introduced tangentially to the vortex (tubular) reactor. Under these conditions the particle was 

forced to slide across the inside surface of the reactor at high velocities. Centrifugal force at the 

high velocities applied a normal force to the particle against the reactor wall. The reactor wall 

temperature was maintained at 625°C, which effectively melted the particle in a fashion similar 

to butter melting on a hot skillet. Vapors generated at the surface were quickly swept out of the 

reactor by the carrier gases to result in vapor residence times of 50-100 milliseconds. So this 

design was also able to meet the requirements for fast pyrolysis and demonstrated yields of 65% 

liquids. A schematic of this design is shown in Figure 3. 

In practice it was necessary to incorporate a solids recycle loop close to the exit of the reactor to 

re-direct larger incompletely pyrolyzed particles back to the entrance to insure complete 

pyrolysis of the biomass. Particles could escape the reactor only when they were small enough to 

become re-entrained with the vapor and gases leaving the reactor. While the solids recycle loop 

was able to effectively address the issue of insuring all particles would be completely pyrolyzed 

it also resulted in a small portion of the product vapors being recycled into the high temperature 

zone of the reactor. This portion of vapors effectively had a longer residence time at the 

pyrolysis reactor temperature and most likely resulted in cracking of the product to gases thus 

resulting in slightly lower yields compared to other fluidized bed designs. 

Biomass 

Inert Gas 

700°C 

Gas 

Bio-Oil 

Ejector 

Nozzle 

Char 

Solids Recycle Loop 

Vortex Reactor 625°C 

Liquid

Cooling

Cyclone 

Figure 3. Schematic of the NREL Vortex Reactor Fast Pyrolysis Reactor Design 

11 
Other design issues with the vortex reactor were: 

• High entering velocities of particles into the reactor caused erosion at the transition from 

linear to angular momentum. 

• Excessive wear was also realized in the recycle loop. Both wear problems were 

exacerbated when inert tramp material (stones, etc.) were introduced with the feed. 

• There were uncertainties about the scalability of the design related to maintaining high 

particle velocities throughout the length of the reactor. The high velocities are necessary 

for centrifugal force to maintain particle pressure against the reactor wall. The high 

sliding velocity and constant pressure of the particle against the 600°C reactor wall are 

necessary to achieve the high heat transfer requirements for fast pyrolysis. 

Because of these issues the vortex reactor design concept was abandoned in 1997. 

2.3.4 Vacuum Pyrolysis 

Pyrovac in Québec, Canada has developed a vacuum pyrolysis process for converting biomass to 

liquids [14]. While this is a slow pyrolysis process (lower heat transfer rate) it generates a 

chemically similar liquid product because the shorter vapor residence time reduces secondary 

reactions. However, the slow heating rates also result in lower bio-oil yields of 30-45 wt% 

compared to the 70 wt% reported with the fluid bed technologies. The process itself is very 

complicated mechanically, involving a moving metal belt that carries the biomass into the high 

temperature vacuum chamber. There are also mechanical agitators that periodically stir the 

biomass on the belt; all of this mechanical transport is being done at 500°C. These design 

features are expected to have high investment and maintenance costs. Operating at a vacuum 

requires special solids feeding and discharging devices to maintain a good seal at all times. 

Heating efficiency is low and, in this particular design, unnecessarily complex in the use of a 

burner and an induction heater with molten salts as a heat carrier. Even with these drawbacks 

vacuum pyrolysis does have several advantages: 

• It produces a clean oil (no or very little char) without using hot vapor filtration (this 

technique is discussed later in section 2.5). 

• Liquid product condensation is easier than for fluidized bed or entrained flow 

technologies (higher vapor concentration, less, if any, aerosol formation). 

• It can use larger feed particles than fluidized bed processes; up to 2-5 cm. 

• The lignin-derived fraction of the oil can be of a lower molecular weight than that from 

fast pyrolysis processes, which may have advantages if extracting this component for 

phenolic type chemicals. 

• Eliminates the requirement to sweep vapors out of the reaction vessel by a carrier gas 

through vacuum assistance. The lack of a carrier gas appears to be a key factor in 

minimizing aerosol formation. 

However, vacuum pyrolysis technology also has serious drawbacks for producing liquids, 

especially for fuel applications because of the high yields required: 

12 
• It is a slow pyrolysis process that will not be able to provide oil yields as high as fast 

heating rate processes (vacuum pyrolysis has demonstrated yields of 47% organics and 

17% water from spruce, 35% organics and 20% water from bark). 

• It generates more water than other fast pyrolysis processes. In the Pyrovac plant the 

condensates are collected as two fractions, the second one being heterogeneous. Based on 

the published yields, after mixing these fractions the whole bark oil will contain 36% 

water and the wood oil 28% water, which can both result in phase separation. 

• It generates liquid effluents as volatile material that is not collected in the scrubbers but 

absorbed in the liquid ring compressor pump. These would need to be recycled back to 

the scrubbers. 

This process was successfully scaled up to 3000 kg/hr in 2000 but lack of markets for the bio-oil 

generated from this unit made continued operation untenable and operations were discontinued 

in 2002. 

2.3.5 Rotating Cone Pyrolysis Reactor 

The Rotating Cone Pyrolysis Reactor has been under development at the University of Twente in 

The Netherlands since the early 1990s. Recent activities have involved scale up of the system to 

200 kg/hr [15]. This technology is analogous to the transported bed design (circulated fluidized 

bed) in that it co-mingles hot sand with the biomass feed to affect the thermal pyrolysis 

reactions. The primary distinction is that centrifugal force resulting from a rotary cone is used for 

this transport instead of a carrier gas. The biomass feed and sand are introduced at the base of the 

cone while spinning causes centrifugal force to move the solids upward to the lip of the cone. As 

the solids spill over the lip of the cone, pyrolysis vapors are directed to a condenser. The char 

and sand are sent to a combustor where the sand gets re-heated before introducing at the base of 

the cone with the fresh biomass feed. This design has demonstrated yields of 70% on a consistent 

basis. Advantages of this design are: 

• It does not require a carrier gas for pyrolysis (but it does for sand transport) which makes 

bio-oil product recovery easier 

• The transport dynamics of the sand and biomass are not as aggressive as in the Ensyn 

Rapid Thermal Processing (RTP) circulating fluid bed process therefore reducing wear 

problems 

Some disadvantages for this process design are: 

• The integrated process is complex, involving a rotating cone, a bubbling bed for char 

combustion, and pneumatic transport of sand back to the reactor 

• Scale up issues are uncertain 

2.4 Pyrolysis Vapor (Bio-oil) Recovery 

Once the pyrolysis vapors are generated in the reaction vessel it is a critical processing 

requirement that they be thermally quenched from the high reaction temperatures. This is 

important to preserve the compounds that comprise the bio-oil; otherwise many of these 

compounds will further crack to permanent gases or polymerize to char. 

13 
Upon cooling, the pyrolysis vapors have a tendency to form aerosols, which are submicron 

droplets. This phenomenon is enhanced if large amounts of carrier gas are present with the oil 

vapors when condensation occurs. Because of their size these droplets are very difficult to 

separate from the permanent gas stream. A number of techniques have been used over the years 

with the most effective probably being liquid spray scrubbing. Simple column scrubbers and 

venturi scrubbers have both been used successfully. The key to these devices is generating spray 

droplets that are very small so they can effectively collide with the bio-oil aerosol droplets. 

Venturi scrubbers can also be effective but a high-pressure drop (>10 kPa) penalty must be paid, 

and this pressure loss may not be available from the process. Electrostatic precipitators have also 

been used successfully [16] for capturing pyrolysis aerosols but they can be tricky to operate and 

are more expensive than simple scrubbers. 

Devices such as mist eliminators and coalescing filters are very effective in removing liquid 

mists and aerosols from gas streams but they are not practical for the pyrolysis processes 

described above because particulates are present along with the aerosol. The particulates will 

rapidly plug the small openings in these devices. 

Staged condensation with a series of shell and tube heat exchangers has also been used but this 

was only about 90% efficient in capturing bio-oil aerosols. While not quite as efficient in 

capturing aerosols as the spray scrubber, the staged system [14] had the advantage of collecting 

the liquids as fractions or “thermal cuts”. This may have some advantages if one is seeking to 

extract certain compounds from the whole oil such as in a bio-refinery application. 

2.5 Char and Particulate Separation 

Char is one of the co-products produced during the conversion of biomass to bio-oil. Because of 

the relatively low reaction temperatures (500o-600oC) employed during pyrolysis, all of the 

mineral matter in the starting biomass ends up being sequestered in the char. This phenomenon 

has some benefits in offering techniques to effectively manage the minerals in biomass but can 

also impact the quality of the resulting bio-oil. Work done at NREL in the mid 1990s [17] 

showed that char played a major role in the long-term stability of bio-oils. This role will be 

discussed in more detail in the section on Properties of Bio-oil, but for now the discussion will 

focus on char and particulate removal techniques applied during the pyrolysis processing steps. 

Ideally it would be desirable to separate the char while it is in the vapor stream before the vapor 

is cooled and condensed to a liquid. All of the processes described above attempt to do this by 

using cyclone separators at the exit of the high temperature reaction vessel. Proper design of 

cyclones specifies the required entering velocities, vortex finder length & diameter, cone angle, 

etc. for a given particle loading in the gas stream. When designed properly for optimum 

separation efficiency, the pressure drop across the cyclone needs to be at least 1.5 kPa. The 

limitation on cyclones, however, has to do with the particle size (or actually particle mass). They 

are not very effective on particles below 2-3 microns and all pyrolysis processes generate char 

particles under this size. The exception to this would be the vacuum pyrolysis system developed 

by PyroVac. Since this process does not involve carrier gas and sand attrition of the char, there is 

little to no entrainment of char with the vapor stream in this design. Instead the char is 

mechanically transported out of the reaction vessel. So in practice, almost all pyrolysis processes 

produce bio-oils that contain a certain level of char fines. 

14 
In the early 1990s NREL began a research effort to use hot gas filtration in lieu of cyclones in an 

attempt to remove essentially all of the char before condensing the pyrolysis vapors to liquids 

[18]. The approach was to use conventional baghouse type filters that were modified for biomass 

pyrolysis operation. These modifications involved reducing the volume and therefore the 

residence time that the vapors would spend in the high-temperature bag-house filter. The 

objective was to minimize cracking of the vapors to gases during filtration of char fines and 

therefore maximize bio-oil yields. The baghouse operating temperature was reduced to as low as 

390°C to also minimize cracking of product vapors. This temperature is approximately where 

many of the compounds present in bio-oil will begin to condense so this was effectively the 

lower limit for hot vapor filtration. Although it was possible to remove almost all of the char 

with this technique it was fraught with difficulties. The char cake became very difficult to 

remove from the filter elements after a relatively short period of operation. There was also 

evidence of chemical reactions as indicated by a measured temperature rise across the filter 

elements. Both cracking and polymerization reactions among the various compounds in bio-oil 

are likely to have occurred as the pyrolysis vapors passed through the char cake on the filter 

elements [19]. It is suspected that polymerization reactions were responsible for bonding char 

particles together in the cake, making it difficult to remove from the filter elements. These 

reactions undoubtedly contributed to oil yield losses of 10%-15% observed when doing hot gas 

filtration. However, this loss should be weighed against a dramatic improvement in the quality of 

the resultant oil. This is especially true with respect to long term stability, which will be 

discussed in the next section on bio-oil properties. 

15 
3. Properties of Bio-oil 

The properties of bio-oil can encompass a broad range of parameters because of the complex 

nature of this material. Even if one is able to perfectly reproduce all of the processing conditions 

necessary to produce bio-oil, the biomass feed, itself, can influence the nature of the final 

product. Not only are there differences between types of biomass species but also where a 

particular species is grown can affect things such as the composition of mineral matter present. 

Given this non-uniformity in the starting material and the high temperature reactive environment 

to which the prompt biomass vapor fragments are exposed during pyrolysis, it is not unusual to 

see variations in many of the physio-chemical properties of bio-oil. For some applications, the 

small variations will be of little consequence, but in situations where it is desirable to use bio-oil 

in devices that have been designed to operate on hydrocarbon fuels, some of these properties will 

make operation difficult or simply not feasible. 

3.1 Chemical Nature of Bio-oil 

Based on the Ultimate Analysis, the chemical formula for wood can be represented by CH1.4O0.6. 

What this formula implies is that on a weight basis wood is composed of almost 42% oxygen. 

When biomass under goes pyrolysis, bonds are cleaved to produce fragments of the original 

macro polymers: cellulose, hemicellulose, and lignin. During this process most of the original 

oxygen is retained in the fragments that collectively comprise bio-oil. Research reports that biooil contains 45-50 wt% oxygen [20], but this is thought to be related to water content. Proximate 

analysis of bio-oil gives a chemical formula of CH1.9O 0.7 which represents about 46% oxygen. 

The oxygen difference between the original biomass and the bio-oil is related to how the oxygen 

is coupled to compounds in the permanent gases and the amount tied up as water in the oil. The 

oxygen in bio-oil is embodied in most of the more than 300 compounds that have been identified 

[21] in bio-oil. Given the limitations of analytical techniques used to identify and quantify many 

of the higher molecular weight species, it is probably safe to assume there are many more 

compounds than those already identified. 

We can classify these compounds into five broad categories [22]: hydroxyaldehydes, 

hydroxyketones, sugars, carboxylic acids, and phenolics. The phenolic compounds are present as 

oligimers having molecular weights ranging from 900 to 2500 [23]. These phenolics are 

primarily derived from the lignin component of biomass. A more detailed classification of 

compounds can be found [24, 25] that classifies compounds under the following categories: 

acids, alcohols, aldehydes, esters, ketones, phenols, guaiacols, syringols, sugars, furans, alkenes, 

aromatics, nitrogen compounds, and misc. oxygenates. While there is a rich mixture of known 

compounds in bio-oil, the vast majority are found in low concentrations. The highest 

concentration of any single chemical compound (after water) is hydroxyacetaldehyde at levels up 

to 10 wt%. This is followed by acetic and formic acids, at about 5 wt% and 3 wt%, respectively. 

This is the primary reason why bio-oils exhibit a pH in the range of 2.0-3.0. 

Table 2 lists the chemical properties of bio-oils produced from three different types of biomass: 

birch, pine, and poplar [26]. The birch and pine were produced at VTT in Finland using a 

circulating fluidized bed reactor while the poplar was produced in a vortex reactor at NREL. The 

column labeled “various” is a compilation of over 150 bio-oil samples produced from a variety 

of feedstocks by different organizations, so a range is given here. We should point out that the 

wide range of some of these properties is tied to certain processing methods employed by the 

16 
particular organization producing the oils. For example some producers may not have used bone 

dry feed as a starting material and the additional moisture ends up in the oil. This is clearly seen 

in the range of moisture contents for the various samples whereas the samples produced at VTT 

and NREL both used bone-dry feed. It is interesting to note that bio-oils from birch and poplar, 

both hardwoods, have identical moisture contents even though they were made in different 

laboratories with different reactor designs. Both reactor designs however employ similar heating 

rates and residence times. A similar issue applies for the mineral matter, which is a function of 

the amount of char permitted to carry over to the condensation system where the oils are 

recovered. The hot gas filtered oils produced at NREL clearly show the link between char 

content and minerals. In other production runs using the same poplar feedstock but employing 

cyclone separators instead of a baghouse filter, alkali metal levels of up to 300 ppm were 

measured. 

Table 2. Properties of Bio-oil from Various Feedstocks 

Property Birch Pine Poplar Various 

Solids (wt%) 0.06 0.03 0.045 0.01-1 

PH 2.5 2.4 2.8 2.0-3.7 

Water (wt%) 18.9 17.0 16.8 15-30 

Density (kg/m3) 1.25 1.24 1.20 1.2-1.3 

Viscosity, cSt @ 50°C 28 28 13.5 13-80 

LHV (MJ/kg) 16.5 17.2 17.3 13-18 

Ash (wt%) 0.004 0.03 0.007 0.004-0.3 

CCR (wt%) 20 16 N/M 14-23 

C (wt%) 44.0 45.7 48.1 32-49 

H (wt%) 6.9 7.0 5.3 6.9-8.6 

N (wt%) <0.1 <0.1 0.14 0.0-0.2 

S (wt%) 0.00 0.02 0.04 0.0-0.05 

O (wt%) 49.0 47.0 46.1 44-60 

Na + K (ppm) 29 22 2 5-500 

Ca (ppm) 50 23 1 4-600 

Mg (ppm) 12 5 0.7 N/M 

Flash Point (°C) 62 95 64 50-100 

Pour Point (°C) -24 -19 N/M -36 -9 

It is also possible to manipulate the chemistry of bio-oils by changing the thermal conditions in 

which they are produced or carrying out the pyrolysis in the presence of catalysts (see section 

4.5). Increasing the cracking severity (time/temperature relationship) is known to alter the 

chemical profile of the resulting oils. Elliot [26] described the relationship between compound 

classes and the temperature to which the vapors were exposed to before quenching. That 

relationship is described in the example shown below. 

17 
18 

Mixed Phenolic Alkyl Heterocyclic Polycyclic 

 Aromatic HC 

 Larger 

Oxygenates Ethers Phenolics Ethers PAH PAH 

400° C 500° C 600° C 700° C 800° C 900° C

This relationship is also shown below in a series of molecular beam scans taken at different 

temperatures when using a common Pine biomass sample. As the temperature is increased, alkyl 

groups are split off aromatic compounds until eventually the aromatics condense into polycyclic 

aromatic hydrocarbons at the higher temperatures. Even though the desired high yields are 

realized at the lowest cracking severities, this thermal chemistry shows the potential for altering 

the chemical nature of bio-oils by shifting the temperature.

Figure 4. Molecular Beam Mass Spectrometer Scans of Pyrolysis Product Profile at Different 

Temperatures Using the Same Pine Wood Sample 

Given the complex nature and number of different compounds making up bio-oil, it is not 

unreasonable to expect that one could effect some separation of compounds by exploiting the 

temperature profile on the quenching or condensation end of the process. Another approach to 

selectively producing specific compound classes was demonstrated by Pakdel et al. [27] by what 
they called “fractional pyrolysis.” This involved ramping up the pyrolysis temperature in stages 

and collecting the products before ramping to the next temperature. In this manner they were 

able to almost double the amount of phenolic compounds produced compared to a conventional 

approach of simply ramping straight up to the final pyrolysis temperature. Again this 

demonstrates the potential of manipulating the product slate by creative application of the 

heating profile. 

3.2 Physical Properties of Bio-oil (Stability) 

One of the primary attributes of converting solid biomass to a liquid bio-oil is the ability to store 

bio-oil until needed for immediate energy use. In the early development stages of this technology 

the long-term storability of bio-oils was plagued by major problems; the principal one being a 

slow gradual increase in the viscosity of the freshly produced oils. This phenomenon also occurs 

with petroleum derived fuels but at a much slower rate. To put this in perspective, hydrocarbon 

fuels can be stored for periods of up to six months while bio-oils appear to have a shelf life of 

weeks or at most a few months depending on properties of the oil. However, recent studies 

(described below) have demonstrated that this shelf life can be greatly extended. Another 

significant issue observed in bio-oils was phase changes that appeared to coincide with the 

increase in viscosity. These can result in heavy molecular weight tars, sludges, waxes, and water 

as multiple phases in what originally started as a single-phase product. Since combustion 

burners, injector nozzles, and other end use devices are designed to operate with liquids that have 

consistent properties this became a major technical challenge to overcome to gain acceptance by 

end users of these oils. 

Considerable effort was expended in the early 1990s and continues today to understand the 

mechanisms of this undesirable phenomenon. Much of the pioneering effort was done at NREL 

where both fundamental mechanisms were explored; and controlled studies were conducted to 

measure the rates of changing viscosity as a function of temperature. At the same time, work was 

being done to develop methods of removing char from pyrolysis vapors prior to condensing the 

vapors to liquid bio-oil. These efforts coincided to provide a considerable base of knowledge 

about bio-oil stability and revealed methods to address the problem. 

The production of bio-oils from fast pyrolysis is a thermodynamically non-equilibrium process. 

The short residence times in the high temperature zone of the process followed by rapid thermal 

quenching results in a liquid product that is also not at equilibrium. The many oxygenated 

compounds present in bio-oil then attempt to achieve equilibrium during storage resulting in 

additional chemical reactions. These reactions cause increases in the average molecular weight 

and consequently increase the viscosity of the oil. As with most chemical reactions temperature 

increases the rate at which these reactions occur. The co-solubility of many of the compounds is 

also impacted by these reactions, which also adversely affect the viscosity. With the “soup” of 

various chemical compounds present in bio-oil and the low pH it is not surprising that chemical 

reactions occur within the bio-oil. 

A major finding however was the influence of char on these reactions. Agblevor et al. [28,29] 

clearly showed that char fines present in the bio-oil had a major impact on the rate at which 

viscosity increased in these oils. In one experiment a freshly produced sample of pyrolysis oil 

was spiked with 5 wt% of char produced from the same biomass feed. Dramatic increases in the 

19 
viscosity of this oil sample were observed in a few days time and within a month the sample was 

solidified. Additional studies [30] identified the reason for this interaction of char on the rate of 

viscosity increase. X-Ray Photoelectron Spectroscopy (XPS) analysis of char particles revealed 

that the mineral matter sequestered in the char was randomly distributed within the char particle 

but a substantial amount was also exposed at the surface. The mineral matter is primarily 

composed of alkali (Na and K) and alkali earth (Ca and Mg) metals. The alkali metal potassium 

is a known catalyst for influencing char forming reactions during the pyrolysis step [31]. Not 

only is the alkali metal present on the surface of the char particles but the particles themselves 

are very small. Agblevor et al. [30] showed that over 90% of the char particles in bio-oils that 

used a cyclone for separation were less than 1 micron in size. This small size distribution implies 

a large surface area available for alkali exposure to the many compounds present in the oils. 

Also during the 1990s, other researchers at NREL were developing hot vapor techniques to filter 

biomass pyrolysis vapors prior to cooling and condensation [19]. This work resulted in 

producing bio-oils that had very low levels of char and consequently alkali metal content, on the 

order of only a few ppm total alkalis. This char-free oil displayed remarkable stability 

characteristics compared to other bio-oils produced with the same feedstock but employing 

cyclone separators for the char removal. Indeed, samples of this hot vapor filtered oil were still 

fluid in 2003 after storage at ambient temperature in closed containers for seven years. This 

corroborates the work of Agblevor et al linking char (alkali) as the catalyzing agent for 

promoting the molecular building reactions tied to viscosity increases in these oils. 

In 1997 Diebold and Czernik [32] investigated the addition of various solvents (including water) 

to bio-oils in an attempt to chemically interrupt molecular building reactions suspected of 

occurring between known compounds in bio-oil. Acetalization and esterification reactions 

induced by alcohol addition in the presence of mineral acids has been reported in the literature by 

Radlein et al. [33] to support this idea. The Diebold and Czernik work investigated various 

addition levels of methanol, ethanol, ethyl acetate, MiBK, acetone, and combinations of these. 

The findings were very promising, showing a strong effect in slowing the rate of aging of biooils both at ambient and elevated temperature. The study also indicated that adding the solvent 

when the oils were freshly produced had a more favorable impact than when added to older aged 

samples. Methanol showed the greatest benefit when added at 10 wt% levels; reducing the aging 

rate by a factor of 17! Fortuitously it was also the least expensive of all the solvents 

investigated. Adding a solvent also improves the quality of bio-oil by reducing its viscosity and 

increasing the heating value. For more detail on the issue of bio-oil stability the reader is referred 

to Diebold [34] who prepared a comprehensive report on this topic in January 2000. 

Based on these two studies it appears there are demonstrated methods to stabilize biomass 

pyrolysis oils. Although filtration to remove the char before oil recovery was demonstrated, it 

also revealed difficulties with the technique that precluded the use of conventional filtration 

equipment. It also resulted in a yield loss penalty of about 10 wt%. 

3.3 Physical Properties (Re-vaporization) 

Another property of bio-oils that is closely tied to the complex chemical composition is the 

inability to revaporize the oils from a liquid state. Unlike hydrocarbon fuels that can be heated to 

develop a distillation curve, the complex and oxygenated nature of the compounds in bio-oil 

prevent this. As bio-oils are heated to increasingly higher temperatures the volatiles are first 

driven off, followed by water and soon the remaining compounds begin to polymerize. The result 

20 
is that 40%-60% of the original starting material will remain as a solid. This property of the oil 

will cause potential difficulties in fuel processing devices that require pre-heating of the fuel. In a 

closed system, such as a diesel injector loop, the volatiles and water will be preserved which can 

minimize this problem but as noted above, any residual char in the oil will exacerbate the 

problem. Little research effort has been devoted to solving this problem of re-volatilizing bio-oil 

liquids. 

3.4 Environmental / Health 

Given the large number of compounds in bio-oil, it obviously raises concerns about the human 

health and environmental effects of this material. As reported earlier in this document, more than 

300 specific compounds have been identified in biomass pyrolysis oil and some of those 

compounds are known carcinogens such as benzene and phenanthrene. In addition there are 

many compounds in bio-oil that have not been identified and their toxicity or health effects are 

not known by the research community developing biomass fast pyrolysis technologies. Because 

this is an important issue to the eventual commercialization of this technology, researchers began 

to investigate the health effects of bio-oil in the mid 1980s. Elliot [26] used the Ames test to look 

at the mutagenic activity of bio-oil as a function of the thermal severity of the process used to 

generate the oils. With the low temperature “primary” oils, produced in the range of 500° -

600°C no mutagenic activity was observed. However, when the bacteria were exposed to oils 

produced at the highest severity a marked increase in mutagenicity occurred. When other 

investigators conducted similar studies with samples of bio-oil produced using different biomass 

feedstocks and different processes, they saw mixed results. Scott [35] exposed two different 

strains of bacteria to two separate bio-oil samples and also saw mixed results. One strain showed 

mutagenicity and the other did not. In a later series of Ames tests [36] with two separate bio-oil 

samples produced at NREL using a hardwood and a softwood; both samples displayed 

mutagenic activity but only slightly when compared to a benzo(a)pyrene standard. These results 

were considered to be inconclusive. 

Elliot conducted additional studies with mammals using a subset of the same bio-oil samples 

used for the Ames test. Diluted samples of oil were applied to the skin of mice genetically bred 

to be susceptible to cancer. The low severity “primary” oil showed no statistically significant 

difference compared to controls that were only painted with the dilutent acetone. However, 

exposure to the higher severity oils definitely showed a positive carcinogenic response. The two 

oils from the Waterloo process used for the Ames test were also tested with ovary cell cultures 

from Chinese hamsters for chromosome damage. Over narrow ranges of dilution, both of these 

samples exhibited damage to the cells [35]. 

While some of these tests were inconclusive others showed a clear potential carcinogenic effect. 

The oils produced at a lower cracking or thermal severity appear to be relatively benign but as 

the severity goes up the cancer promoting activity also increases. If one refers to Figure 4, this is 

consistent with the experience seen in the coal tar industry where exposure to polycyclic 

aromatic hydrocarbons (PAH) was correlated with high incidence of cancer. These same PAHs 

can be made with biomass under severe cracking conditions. Fortunately the production of high 

yields of bio-oil requires process operating conditions based on the lowest cracking severity. 

21 
When investigating the health aspects of fast pyrolysis processes, the focus was entirely on the 

liquid product because some of the identified compounds are known carcinogens. The char from 

many of the processes used for fast pyrolysis can be attrited to very small sizes and some portion 

is likely to be in the PM 10 and PM 2.5 size range. This refers to particles in the 10 and 2.5 

micron size range that pose unique respiratory hazards. Given that these particles are coentrained with the organic vapors it is realistic to expect that some compounds become adsorbed 

on the surface. To protect workers in an emerging pyrolysis industry, and comply with OSHA 

reporting requirements, it would be prudent to include health and safety assessment of the char in 

any future toxicology studies. 

The low pH of bio-oils is also a potential environmental and safety issue. In the studies reported 

in the literature there was no reference to investigations of damaging effects of physical contact 

with acidic bio-oil. In studies where mammals were dosed by application of oil to the skin the 

primary objective was to evaluate the cancer promoting potential of these liquids. With a pH of 

2.0-2.5 the oil is likely to have damaging effects to the eyes but this has not been conclusively 

established by controlled studies. 

Work done by Piskorz and Radlein [37] used respirometry techniques to show that bio-oil readily 

biodegrades in soils at rates significantly higher than hydrocarbon fuels. This was also true for 

biodegradation in water but neutralizing the oil first enhanced this process. Neutralizing the biooil was not necessary to see the biodegradability in soil. The low pH of these oils, however, 

would obviously have detrimental effects on aquaculture in the event of a large spill in a river, 

lake, or stream. Given how often one hears of hydrocarbon fuel tanker truck spills in rivers and 

streams next to roadways, it would be inevitable for this to happen with bio-oils as well. 

Another environmental / health issues relates to the design and operation of the pyrolysis plant or 

biorefinery producing the bio-oils. Fugitive emissions from the collection, transfer, and further 

processing would need to be carefully controlled. Fugitive emissions from drying the biomass 

feed also need to be carefully controlled. Because of the large number of compounds present it is 

possible that some operating personnel may develop chemical sensitivities to vapors or liquids 

they are exposed to. Modern process design usually takes this into consideration but critical 

HAZOPs analysis should be applied to key processing steps where the potential exists. 

22 
4. Uses for Bio-oil 

Bio-oil has the potential for multiple applications. These can range from a variety of combined 

heat and power options to the extraction of selected chemicals. Use as a substitute for 

hydrocarbon fuels in conventional prime movers to produce electricity or generate steam has 

been demonstrated but has not been commercially adopted. This is primarily due to lower cost 

for petroleum-based fuels compared to bio-oils. However, in some applications with more 

sophisticated prime movers such as internal combustion engines and aeroderivitive turbines, 

quality issues with the oil must still be addressed. Upgrading of bio-oils to higher value 

transportation fuels requires de-oxygenation and reforming of most of the compounds present in 

the bio-oil. Because of the large amount of oxygen present there will be a loss in mass (or 

volume) yield but this will be balanced against higher heating values. Overviews of these 

applications are provided below. 

4.1 Combustion 

Sandia National Laboratory [37,38] conducted fundamental single droplet combustion studies of 

bio-oils produced at NREL, including hot gas filtered oil. Despite the major differences between 

petroleum fuels compared to bio-oil, the burnout time for bio-oil was comparable to #2 fuel oil. 

The bio-oil however demonstrated a sequential burnout ending with formation and subsequent 

burnout of cenosphere particles. This property may present problems with soot formation during 

combustion. Also unique to the bio-oil was micro-explosion of the droplet as it transitioned 

through the combustion sequence. The phenomenon of the micro-explosion was also observed to 

be different depending on the cracking severity in which the oil was produced. It is not known if 

this droplet micro-explosion will cause combustion problems in large burner applications or 

impact the resulting combustion products. Full-scale combustion tests on bio-oil conducted in 

flame tunnels at MIT [39] and CANMET [40] did not show fundamental differences in 

combustion behavior compared to #2 fuel oil. However, the NOx, CO, and particulate emissions 

from bio-oil were higher. Other studies in Europe [41,42] have reported similar findings with a 

clear correlation of the emissions to the quality of the bio-oil, in particular the residual char fines 

content. 

4.2 Diesel Engines 

Medium and slow speed diesel engines are known for their ability to run on low quality fuels, 

even such fuels as coal slurries. In the early 1990s researchers began investigating the use of biooils in these engines. Solantausta [43] conducted pioneering work in this area using a high-speed 

single cylinder engine with a compression ratio of 15:1. It was very difficult to get the bio-oil to 

auto-ignite without substantial amounts of nitrated ignition additives. In addition, carbon 

deposits formed at the injectors causing plugging problems. Additional studies conducted on 

larger scale medium speed engines, equipped with pilot fuel capabilities, showed more promise 

[44]. While auto-ignition was not a problem it was difficult to maintain proper adjustment on the 

injectors, and excessive wear and corrosion were seen in the injector loop. Much of this was 

attributed to the acidity and particulate matter in the oil. Additional testing was done at the 

University of Kansas and MIT using the very clean hot gas filtered oil produced at NREL. When 

Suppes [45] at the University of Kansas blended methanol and a cetane enhancer with these 

clean oils they exhibited performance characteristics similar to conventional diesel fuel. If high 

23 
compression ratios are employed, the solvent blended oils would even perform well in highspeed engines. At MIT, Shihadeh [46] showed that the clean oils had much better combustion 

characteristics (shorter ignition delay, faster burn out, and less coking) than non-filtered oil. He 

also demonstrated that these clean oils would auto-ignite if the combustion air were preheated to 

55°C. More recently [47], testing of emulsions of diesel fuel and bio-oil at 50:50 blends were 

successfully demonstrated as an alternative way to get around the auto ignition problem. 

With only minor modifications to the engines, these early results indicate that bio-oils have the 

potential to replace conventional diesel fuel in low to moderate speed stationary diesel engines. 

The difficulties encountered with wear and corrosion appears to be solvable with proper 

selection of materials for key components and improved particulate removal from the oil. 

4.3 Combustion Turbines 

Combustion turbines are a well-established technology that offers the potential of producing 

power (and heat) at relatively high efficiencies. They are primarily fueled on petroleum 

distillates or natural gas but if properly designed, in conjunction with appropriate fuel 

specifications, they should be able to operate on any fuel including bio-oil. Of critical importance 

in these devices is particulates and alkali metal content in the fuel. This is especially important if 

sulfur is also present due to alkali sulfate formation during the combustion process. Alkali 

sulfates will stick to and aggressively corrode the turbine blades. Fortunately, biomass is very 

low in sulfur but it does contain alkali (K and Na) and alkali earth (Ca and Mg) metals that are 

sequestered in the char during pyrolysis. A small portion of this char is typically entrained with 

pyrolysis vapors and captured with the bio-oil product. Consequently one of the key issues to 

using bio-oils in combustion turbines is the effective removal of char from the oil. The acidic 

nature, low heating value, and higher viscosity properties of bio-oil can be addressed by 

appropriate design and material selection in the turbine. 

Since 1995, Orenda Aerospace Corp. (Canada) has been investigating the use of bio-oils in a 

combustion turbine application. They have selected a turbine designed by Mashproekt in the 

Ukraine because of its robust design for low quality fuels. It also employs advanced coating in 

the entire hot section of the turbine to protect against alkali contaminants. Andrews et al [48] 

tested this 2.5 MW turbine on bio-oil fuel (after starting on diesel) and ran it through its full 

operating range from idle to full power without any difficulties. Measured emissions on bio-oil 

were lower for NOx, SOx, and HC but higher for particulates. The higher particulates may have 

been due to higher levels of char in the bio-oil but this property was not measured. Orenda has 

recently started to market this turbine for bio-oil applications, which implies they feel confident 

about the performance of the Mashproekt turbine operating on bio-oil fuel. 

Strenziok et al. [49], at the University of Rostock in Germany, tested a smaller commercial 75 

kW turbine on bio-oils. In this demonstration the combustion chamber was modified to enable 

dual fuel operation with diesel and bio-oil. Under dual fuel operation they were able to achieve 

73% of the full output power that would have been obtained from diesel alone. The ratio of fuel 

blend was 40% bio-oil and 60 % diesel. When compared to straight diesel operation the CO and 

HC emissions were higher while the NOx was lower. 

As with diesel engine applications, these early results show that it is indeed possible to operate 

turbines on bio-oil fuels. These results were achieved with only minor modifications of existing 

24 
equipment and little effort was expended in tailoring the oil properties specifically for turbine 

operation. 

4.4 Bio-Oil Standards and Specifications 

The petroleum and automobile industries have a long history of working together in a symbiotic 

relationship to develop the fuels and engines that work in concert to provide reliable, efficient, 

and clean service. As with many engineering designs there are compromises that must be made 

because of conflicting performance objectives. For example internal combustion engines can be 

designed to be more efficient than they currently are by increasing the compression ratio of the 

engine. This in turn requires the petroleum industry to produce fuels with higher octane levels. 

Chemical engineers learned that a relatively easy and inexpensive way to do this is by adding 

tetra-ethyl lead. Environmental engineers however recognized the pervasive increases of lead in 

the environment, along with the long-term health costs tied to its continued use. After restricting 

this method of octane enhancement, the petroleum industry was forced to develop other ways to 

increase octane levels in motor fuels. The alternate approaches are not as effective as tetra-ethyl 

lead so the internal combustion engine designer also had to compromise on the upper limits of 

compression ratio. Cost of course also plays a major role in these design considerations. This is a 

good example of the importance of developing good technical relationships between the fuel 

producer and the end user of that fuel. 

The situation with the auto / petroleum industry can also be applied to the emerging bio-oil 

industry. The examples noted above with pioneering efforts to utilize bio-oil in various prime 

movers, and even relatively simple combustion burners, demonstrates the need for 

standardization of bio-oil properties. If there was a uniform set of standard specifications for biooil, designers of the various end use devices could select the appropriate materials and make the 

necessary design changes to achieve much better performance than what has already been 

demonstrated. Commercial acceptance of biomass pyrolysis technology will demand that these 

specifications be established. Unfortunately there has been little progress in this area over the 

years. 

To a large extent the petroleum industry has laid the foundation for what a set of standards and 

specifications should be based on. Because there are also quality variations in petroleum 

hydrocarbons, the industry has established separate specifications for a number of different 

grades of hydrocarbon fuels. The higher grades of course command a premium price and a 

similar situation would be expected with bio-oil grades. The specifications for petroleum fuels 

are established by an independent organization such as ASTM in the United States and similar 

organizations in other countries. These organizations also get involved in 

developing/establishing the methods and protocols used for quantifying the specification 

property. The specifications are usually based on the end use requirements of the consumer for 

the given fuel and typically are concerned with such things as the ability to properly atomize, 

flash points or ignition temperatures, energy content (LHV), and qualities that have 

environmental impacts such as sulfur content. 

In 1996 the Pyrolysis Activity of the International Energy Agreement under Task XIII proposed 

a series of specifications for bio-oil [51] that were modeled after the ASTM specifications for 

hydrocarbon fuels. The proposed specifications attempted to mimic as much as possible the key 

25 
properties established for petroleum fuels that have major design considerations for end use 

devices. This was intentionally done to require the least effort on the part of the manufacturer of 

end use equipment to accommodate bio-oil fuels. The proposed specifications from this 

document are listed in Table 3. 

Table 3. Proposed Specifications for Various Grades of Bio-oil [51] 

Property Light Bio-oil 

(~ASTM #2) 

Light-Medium Bio-oil 

(~ASTM #4) 

Medium Bio-oil 

(~PORL 100) 

Heavy Bio-oil 

(~CAN #6) 

Viscosity, cSt 1.9-3.4 FO 

1.9-4.1 D 

1.9-4.1 GT 

@40° C 

5.5-24 

@40° C 

17-100 

@50° C 

100-638 

@50° C 

Ash, wt% 0.05 FO 

D 

0.01 GT 

0.05 FO 

0.01 D 

0.10 FO 0.10 FO 

Pour point, °C min Report Report Report Report 

Conradson carbon, 

wt% 

Report Report Report Report 

Max. 0.1 μm filtered 

ethanol insol. solids, 

wt% 

0.01 FO 0.05 0.10 0.25 

Accelerated aging 

rate @90° C, cSt/hr 

Report Report Report Report 

Water, wt% of wet 

oil, max 

32 32 32 32 

LHV, MJ/L min, wet 

oil 

18 18 18 Report 

C, wt% dry 

H, wt5 dry 

O, wt% dry 

S , wt% dry 

N, wt5 dry 

K+ Na, ppm 

Report 

“ 

“ 

Max 

Max. 

Report 0.5 GT 

Report 

“ 

“ 

Max. 

Max. 

Report 

Report 

“ 

“ 

.2 Max. 

.3 Max 

Report 

Report 

“ 

“ 

.4 max. 

.4 max 

Report 

Phase stability @ 

20° C after 8 hr @ 

90° C 

Single phase Single phase Single phase Single phase 

Flash point, ° C 

minimum 

52 55 60 60 

Density, kg/m3 Report Report Report Report 

26 
As with petroleum type fuels, these specifications are structured around viscosity and ash 

content, because these have significant impacts on end use devices. Requirements for pour point 

will generally be site specific depending on the climate but the information is necessary for the 

end user to determine storage requirements such as heating to maintain flow properties. While 

the water content may seem high, this is the amount that would be expected if the feedstock were 

dried to 8 wt% moisture. Because the water content of bio-oil can vary depending on feedstock 

and operating conditions it is expected that bio-oil will be sold based on the LHV. These are 

initial proposals for bio-oil specifications and adjustments to these values are likely to occur as 

more experience is gained in using these fuels in various end use devices. 

4.5 Upgrading Bio-oil Properties to Higher Value Products 

As noted in the previous section, bio-oil quality can be improved to move it into a different grade 

and therefore command a higher price for the producer. The simplest and least expensive 

methods involve adding solvents or limited amounts of water to bring the bio-oil into the desired 

viscosity range. If solvents such as alcohols are used, added benefits accrue by adjusting the 

heating value and gaining improved long term storage properties. Solids in the form of ash and 

attrited fluidizing media can be removed by filtration, either hot (vapor phase) or after the oil has 

been condensed. This processing step will add complexity and additional operating costs to the 

final product. We should point out that while filtration has been demonstrated, both approaches 

have inherent difficulties that will require additional development before they can be considered 

commercially viable. These physical upgrading techniques can improve the quality of the neat, 

as produced, bio-oil but will still require the designer of end use equipment to make significant 

modifications to address the chemical properties of bio-oil, including acidity and low heating 

values because of high oxygen content. 

If bio-oils could be upgraded chemically to produce a product that looked more like petroleum 

hydrocarbons then the end use device would require little to no modification. This would be the 

fastest way to gain acceptance of biomass-based fuels into the existing infrastructure. This 

approach essentially involves de-oxygenation and subsequent reforming of the remaining 

hydrocarbons. Two approaches have been explored for chemical upgrading of these oils: 

catalytic cracking and catalytic hydrotreating. 

Diebold and Scahill [52] and others investigated in situ cracking of promptly formed biomass 

pyrolysis vapors over zeolite cracking catalysts. A number of zeolite cage sizes along with 

different doping metals were explored but the standard Mobile ZSM-5 catalyst developed for the 

methanol to gasoline process gave the best results. Oxygen is rejected in the form of H2O, CO2, 

and CO and the remaining hydrocarbons are re-arranged to form mostly aromatic type 

hydrocarbons because of the shape selectivity of zeolite catalysts for these types of 

hydrocarbons. Although conversion efficiencies of 42 wt% are theoretically possible, in practice 

only about half of this value was obtained in C2 + hydrocarbons. High coking rates on the 

catalyst (up to 15 wt%) were a major contributor to the low yield. 

An alternate approach using catalytic hydrotreating showed more promise. Elliott et al [53] and 

others have been developing this approach to chemical upgrading. Early work using low-activity 

sulfided catalysts, showed that it was necessary to carry out the hydrotreating in two steps. The 

first step (at lower temperature) initially stabilized the more reactive lower molecular weight 

compounds, which was followed by higher temperature more aggressive hydrotreating of the 

more stable phenolic compounds. This effort resulted in higher yields than those seen for 

27 
catalytic cracking but also produced a similar highly aromatic product composition. Although 

aromatics have a relatively high-octane level, which makes these compounds good for gasoline 

blending stocks, other toxicity issues limit their concentration in present fuel specifications to 

about 3 wt%. Current work in this area is focused on a number of improvements in hydrotreating 

catalysts with the following objectives: 

• Optimize the catalytic processing for the properties of a given bio-oil or bio-oil fraction 

feedstock 

• Explore the efficiency and selectivity of these newly developed, non-sulfided catalysts, 

which can be operated at lower temperatures 

• Direct the selectivity to produce de-oxygenated higher value (but less aromatic) 

transportation fuels in addition to chemical co-products 

• Improve the hydrogen utilization for the process 

• Establish the process economics with the improved catalysts 

Other catalytic methods of upgrading bio-oil to hydrocarbon gases were demonstrated in the late 

1980s. Researchers at the University of Waterloo in Canada [54] demonstrated that by using a 

catalyst in lieu of the sand in a fluidized bed pyrolysis reactor they were able to produce methane 

in relatively high yields. Using different catalysts in this fashion resulted in different 

hydrocarbon products. 

More recent work at NREL is focused on developing processes to reform bio-oil to hydrogen 

using conventional steam reforming catalysts. Yields of greater than 80% of theoretical have 

been demonstrated [55]. However, the current economics are favorable only if higher value coproducts are produced in conjunction with the hydrogen. 

These examples show the potential for catalytic manipulation of bio-oil to produce gaseous 

hydrocarbons or hydrogen that could be used as feed streams for other biorefinery products. 

28 
5. Prior Investigations of Bio-Oil Production Costs 

Islam and Ani [56] studied the cost of producing crude bio-oil and catalytically treated bio-oil 

based upon data from a 0.3 kg/h pilot plant. Both Fluidized Bed Fast Pyrolysis (FBFP) and FBFP 

with Catalytic Treatment were examined at 100 kg/hr and 1,000 kg/hr scales using rice husks. 

The base feed cost was $20/ton. The system was operated at 3,120 hours/year (10 hours/day). 

The interest rate on capital was 10%. The electricity cost was $0.04/kWh. Notable cost 

assumptions for this analysis were: (1) an extremely low labor rate of $1.00/hr for Malaysia and 

(2) feed preparation costs were not included. Sensitivities were performed around feedstock cost, 

labor cost, equipment cost, and char credit. The estimated crude bio-oil price was $0.38/kg for 

the 100 kg/hr plant and $0.18/kg for the 1,000 kg/hr plant. The total capital investments were 

$97,000 and $389,000 for the 100 kg/hr and 1,000 kg/hr plants, respectively. The authors 

identified feedstock cost, equipment cost, and operating labor as important variables. 

A study done at the University of New Hampshire [57] looked at the conversion of low-grade 

wood chips to bio-oil, primarily for use as a substitute for No. 2 fuel oil. The study looked at 

using a DynaMotive fast pyrolysis reactor design at 100, 200, and 400 metric tonne/day wet 

wood feed rates. The base feed cost was $18/wet ton at 45% moisture. The electricity cost was 

$0.065/kWh. The plant operated 24 hours/day, 330 days/year (7,920 hours/year). The bio-oil cost 

was calculated to be $1.21/gal, $0.99/gal, and $0.89/gal for 100, 200, and 400 wet tonne/day 

plant sizes. The total capital costs were $6.6 million, $8.8 million, and $14 million, respectively. 

Cole Hill Associates and DynaMotive compared the University of New Hampshire results with 

similar studies. The bio-oil costs for the Cole Hill and DynaMotive studies ranged from 

$0.77/gal to $1.05/gal of bio-oil. 

Cottom and Bridgwater [58] performed an analysis of a generic flash pyrolysis process using 

correlations from the University of Waterloo. Their base case was sized at 1,000 tonnes/day 

using 7% moisture wood at $43.2/dry tonne. The resulting crude bio-oil price was $78.4/ton of 

bio-oil. A sensitivity analysis was done that showed the effect of feedstock cost on bio-oil cost, 

but no details of other cost assumptions were provided. No capital costs were provided. The 

authors noted feedstock cost as an important cost driver. 

NREL [59,60] performed an analysis of the cost of bio-oil production in the early 1990s. The 

base case design for this study was 900 dry tonne/day of 50% moisture wood. The total capital 

investment for this facility was $46 million and the bio-oil selling price was $0.11/kg for a 15% 

after-tax internal rate of return. The operating hours were 8,000 per year. The feed stock cost was 

$44/dry tonne. Some sensitivities were done regarding plant size, capital cost, return on 

investment, feedstock cost, online availability, and different approaches to debt financing. 

Important cost variables identified were financing method, feedstock cost, plant availability, 

plant size, and depreciation schedule. 

Solantausta et al. [61] reviewed 11 different pyrolysis variations looking at wood, peat, and straw 

as possible feedstocks. The base case feedstock prices were $30/tonne, $20/tonne, and 

$42.50/dry for wood, peat, and straw, respectively. The base case process size was 1,000 

tonne/day dry biomass feed. The electricity price was assumed to be $0.065/kWh and the capital 

was financed at 10% interest. With these assumptions, the crude bio-oil price ranged from 

$117/ton to $488/ton of bio-oil. The total capital costs for the different 1,000 tonne/day plants 

29 
ranged from $44-$143 million. Graphs showing the sensitivity to biomass cost and capital 

recovery were included. 

Arthur J. Power and Associates, Inc. also completed a feasibility study for the conversion of 

1,000 tpd of biomass to bio-oil in 1991 for SERI (now NREL) [62]. In that report, a 15% pre-tax 

return on investment was used with 100% equity financing, $0.037/kWh electricity price, and 

$40/dry ton wood price. The total capital investment for the 1,000 dry tpd plant was $37 million. 

The estimated cost of the bio-oil produced was $0.044/lb. A sensitivity case was also done for a 

250 dry tpd plant, resulting in a bio-oil cost of $0.039/lb with a total capital investment of $14 

million. Other sensitivity calculations included varying the feed cost, the rate of return on capital, 

and the product yield for the two different plant sizes. 

Table 4 lists the plant size, feedstock price, estimated bio-oil cost, and capital investment as 

reported in the various reports. Where applicable, the crude bio-oil values were reported instead 

of the upgraded product price. No attempt was made to adjust these costs to current dollars or put 

all the costs on a consistent basis. For one of the studies [62], a higher biomass purchase price 

was assumed with the larger plant sizes. 

Table 4. Bio-oil Production Cost/Selling Price 

Plant Size 

(tonne/d) 

Feed Cost 

($/dry tonne) 

Feed 

Cost 

($/GJ)

1 

Bio-Oil 

Cost 

($/kg) 

Bio-Oil 

Cost 

($/gal)

1 

Bio-Oil Cost 

($/GJ)

1 

Total Capital 

Investment 

Source 

2.4 $22 $1.10 $0.38 $1.73 $21.20 $97,000 [56] 

24 $22 $1.10 $0.18 $0.82 $10.10 $389,000 [56] 

100 $36 $1.80 $0.26 $1.21 $14.50 $6.6 million [57] 

200 $36 $1.80 $0.21 $0.99 $11.70 $8.8 million [57] 

400 $36 $1.80 $0.19 $0.89 $10.60 $14 million [57] 

1,000 $46.50 $2.33 $0.09 $0.41 $5.00 (Not given) [58] 

1,000 $44 $2.20 $0.11 $0.50 $6.10 $46 million [59] 

250 $44 $2.20 $0.11 $0.50 $6.10 $14 million [60] 

1,000 $20-$42.50 $1.00­

$2.13 

$0.13­

$0.54 

$0.59­

$2.46 

$7.30-$30.00 $44-143 

million 

[61] 

250 $11 $0.55 $0.10 $0.46 $5.60 $14 million [62] 

1,000 $44 $2.20 $0.09 $0.41 $5.00 $37 million [62] 

1 Assumes 20 MJ/kg HHV for wood, 17.9 MJ/kg HHV of bio-oil and 4.55 kg/gal density of bio-oil. [57, 63] 

30 
6. Wood Chip Pyrolysis Facility Economic Analysis 

A preliminary Stage 1 analysis was conducted for a wood chip pyrolysis facility producing biooils (i.e., bio-crude). Material and energy balances were developed using ASPEN Plus® 12.1 and 

an economic analysis was conducted based on ASPEN ICARUS Questimate® 11.1 and standard 

NREL economic protocols. 

6.1 Design Basis and Process Description 

The production of bio-oil from biomass is based on the fast pyrolysis process, which is 

composed of five major processing areas: feed handling and drying, pyrolysis, char combustion, 

product recovery, and steam generation. Figure 1 is a block flow diagram of a fast pyrolysis 

process. 

In the feed handling section, the biomass is reduced in size to <1-5 mm and dried to 5%-10% 

moisture. It is then sent to pyrolysis where it is heated to 400-500oC in an oxygen-deficient 

atmosphere to degrade the biomass into a mix of gases, bio-oils, and char. Char is removed using 

high-efficiency cyclones and is combusted to fuel the pyrolysis reaction. To maximize the yield 

of bio-oils, the reaction is rapidly quenched through heat exchange or direct liquid (e.g., water or 

recycled bio-oils) injection. The bio-oils are present in the gas stream as aerosols and require 

scrubbers and/or wet electrostatic precipitators for efficient capture. After cleaning, some of the 

clean pyrolysis gases are recycled to fluidize the bed and the remaining gases are combusted for 

process heat. Where feasible, heat is recovered from the pyrolysis gases to generate steam for 

electricity production. 

31 
Figure 5. Fast Pyrolysis Block Flow Diagram 

Exhaust Gas Exhaust Net Electricity 

Recycle Carrier Gas 

Gas Clea

Oil Rec

Process Electricity 

Feed Handling and 

Drying Pyrolysis Steam Cycle 

Wood 

Char Combustion 

Combustion Air 

Ash 

32 
The pyrolysis facility was modeled using numerous assumptions and data sources. The following 

table summarizes the key design parameters and their sources. 

Table 5. Design Basis 

Parameter Value Source 

Feedstock

 Type

 Moisture Content 

 Cost 

 Throughput 

 Particle size 

Wood Chips 

50% 

$30/dry ton 

550 dry tons/day 

3-45 mm 

Engineering judgment 

[64] 

[64] 

[64] 

[65] 

Feedstock Composition (wt%, dry)

 Carbon

 Hydrogen 

 Oxygen

 Nitrogen 

 Sulfur 

 Chlorine

 Ash 

50.93% 

6.05% 

41.93% 

0.17% 

0.0% 

0.0% 

0.92% 

Original feedstock composition 

in model; modified to eliminate 

S based on engineering 

judgment 

Pyrolysis Design

 Pyrolysis Type

 Temperature 

 Air Carrier Ratio

 Feed Moisture Content 

 Ground Particle Size 

Bubbling Fluidized Bed 

500 oC 

2.75 lb air/lb pyrolysis 

feed 

7% 

< 3 mm 

Engineering judgment 

Original model 

[66] 

[67/68] 

[67/68] 

Yields (Dry Basis) 

 Oil 

Water 

 Char and Ash 

 Gas 

59.9% 

10.8% 

16.2% 

13.1% 

[67/68] 

Large-scale facility 

33
Table 5. Design Basis 

Parameter Value Source 

Oil Representative Components 

(lb/100 lb wood)

 C2H4O2

 C3H6O2

 C7H8O2

 C8H10O3

 CH2O2

 C10H12O3

 C6H6O 

C7H8

 C5H4O2

 C6H6 

Projected Overall bio-oil 

composition (wt%)

 Carbon

 Hydrogen 

 Oxygen 

Target Overall bio-oil composition 

(wt%) 

 Carbon

 Hydrogen 

 Oxygen 

5.93 

7.31 

0.61 

3.80 

3.41 

16.36 

0.46 

2.27 

18.98 

0.77 

59.27 

6.03 

34.69 

55-58% 

5.5-7.0% 

35-40% 

Estimated values 

Spreadsheet results 

[67/68] 

Gas Composition (lb/100 lb dry wood)

 CO2

 CO

 CH4

 C2H4

 H2

 C3H6

 NH3 

5.42 

6.56 

0.035 

0.142 

0.588 

0.152 

0.0121 

Elemental balance 

From the ratios of the earlier 

model 

Material balance – all N in 

feed 

34
Several of these assumptions, particularly the yields, require further explanation. The overall 

yields of the major streams: bio-oil, char, gas, and reaction water were taken from Bridgwater et 

al. [67/68] and are based on the dry feedstock. The composition of these major streams is highly 

variable. In fact, over 200 compounds have been identified in the bio-oil alone [69]. The original 

model, developed by Gregoire [60] used pseudo-components to represent the bio-oils, but it was 

since changed, but not documented, to have the representative components listed in the table 

above. 

The exact distribution of these components was not found, but a range of typical values for biooil was obtained by Bridgwater et al. [67/68]. The yields of the representative compounds were 

manipulated until the analysis approximated that found in Bridgwater et al. [67/68]. No effort 

was made to ensure that other important properties of the bio-oil (e.g., density and LHV) 

matched that of the mixture of components. However, all of the economic calculations are based 

on a typical bio-oil densities and LHVs and so this should not be a concern. If a better 

representation of the composition of the bio-oil is obtained, the slate and distribution of the 

components should be modified. 

Similarly, the exact composition of the gaseous product varies depending upon the operating 

conditions and the feedstock. In this case, the number of components is much lower and the 

relative concentrations are better known. To estimate the dry gas composition, we assumed that 

all of the nitrogen in the fuel converted to ammonia. The remaining gaseous product was 

apportioned in the same ratios as the original model. 

Finally, the composition of char is variable. For this analysis, we determined char composition 

based on an elemental balance using the assumed feedstock composition and the slate of 

products. All ash was assumed to be present in the char. The heat of combustion of char was then 

determined using an IGT estimation correlation presented in Domalski et al. [70]: 

HHV = 146.58C + 568.78H - 51.53(O+N) - 6.58A + 29.45S in Btu/lb 

Where C - % carbon 

H - % hydrogen 

O - % oxygen 

N - % nitrogen 

A - % ash 

S - % sulfur 

From this, the standard heat of formation is calculated. The density and heat capacity of the char 

were assumed the same as elemental carbon. 

6.2 Model Description 

An ASPEN Plus® model was developed for the pyrolysis process, based largely on the work by 

Gregoire [60]. Significant design changes include: 

• Elimination of steam generation for sale 

• Combining all steam generated into a single steam drum, similar to the Combi System by 

Clayton Industries [71]. 

35
• Substitution of condensing turbine for original turbine 

• Modification of process parameters to correspond to literature values rather than in-house 

data 

• Changed pyrolysis type to fluidized bed vs. ablative 

• Increased carrier gas rate to 2.75 lb/lb feed for fluidized bed vs. 1.3 lb/lb feed for ablative 

• Addition of power requirements for size reduction 

• Modification of quench section to include a scrubber and wet electrostatic precipitator 

(WESP) after heat recovery 

• Recycle of cooled product as the scrubbing medium in the quench section. 

Other modeling changes included: 

• Removal of several unit operation models by simplifying the modeling methodology 

• Modification for heat flow design convention and heat integration design-specs 

• Use of characteristic components instead of pseudo-components 

• Elimination of unused components 

• Conversion of non-conventional components (e.g., ash) to conventional solids (e.g., SiO2) 

• Addition of utility flowsheet 

• Modification of flash specifications to account for free water. 

The modeling changes had only small effects on the overall material and energy balances. In 

general, they only simplified the model and increased its utility. 

6.3 Material and Energy Balance Results 

Using the assumptions outlined above, the overall material and energy balances were completed 

for the process. The mass balances for the model are included with the ASPEN model write-up 

in Appendix A. 

The facility produces 16,091 kg/hr of bio-crude with a moisture content of 23.6%. It also 

produces almost 4,900 kW of electricity, but uses roughly 80% of that value for recycle gas 

compression (2,600 kW) and feedstock size reduction (1,400 kW). The net electricity output for 

the facility is 588 kW. 

6.4 Economic Basis 

The economic analysis for the pyrolysis process is based on standard NREL analysis protocol 

and the most recent NREL ethanol economic analysis [72]. The basis for the capital and 

operating costs as well as the financial calculations are addressed in this section. 

All costs were projected in 2003$. 

36
6.5 Capital Costs 

Using the material and energy balance as well as standard sizing procedures in Perry’s Chemical 

Engineers’ Handbook [73] and similar references, each major piece of equipment was sized. The 

equipment and setting charges for each component were then estimated primarily using ASPEN 

ICARUS Questimate® Version 11.1. For non-standard equipment (e.g., the pyrolysis unit), other 

methods such as comparison with other similar equipment were employed. Each of these nonstandard methods is discussed in the capital cost results section. 

Installation factors were applied for each component type based on the most recent NREL 

ethanol economic analysis [72]. After estimating the equipment costs, a contingency factor of 

35% was applied to project the total equipment costs. This conservative contingency factor was 

designed to account for any miscellaneous equipment left out of the analysis, uncertainty in the 

analysis due to its early stage of development, and the conceptual nature of the analysis. 

Using the total equipment cost, the total project investment (TPI) was projected using a factored 

method based on the methodology used in the most recent NREL ethanol economic analysis 

[72]. Table 6 outlines the factors used. 

Table 6. Total Project Investment Factors 

Component Basis 

Total Equipment Cost

 Warehouse 

 Site Development 

Questimate® and Literature 

1.5% of Equipment Costs 

9% of ISBL 

Total Installed Cost (TIC) Sum of Above 

Indirect Costs 

 Field Expenses 

Home Office & Construction 

Fee 

Project Contingency 

20% of TIC 

25% of TIC 

3% of TIC 

Total Capital Investment (TCI) Sum of Above 

Other Costs (Startup) 10% of TCI 

Total Project Investment Sum of Above 

6.6 Operating Costs 

Annual costs were projected for both variable and fixed operating costs. Variable operating costs 

are incurred for feedstock and incidental chemicals such as cooling tower chemicals. Unit 

operating costs were obtained from the literature or similar NREL studies. Unit costs for the 

cooling tower chemicals and boiler feed water chemicals were obtained from the most recent 

NREL ethanol economic analysis [72]. 

Table 7 summarizes the unit costs associated with these items. 

37
Table 7. Unit Costs 

Input Unit Cost Source 

Wood chip feedstock $30/dry ton Bain 2003 

Cooling tower chemicals $1.00/lb Ruth 2003 

Boiler feed water 

chemicals 

$1.03/lb Ruth 2003 

Fixed operating costs, composed of labor, maintenance, overhead, taxes and insurance were also 

determined. The number, expertise, and salaries of personnel required to operate the facility was 

estimated based on NREL experience. Salaries were scaled using the Bureau of Labor Statistics’ 

labor index for Chemical and Allied Trade Workers [74]. 

Table 8 summarizes the salaries and number of employees required. 

Table 8. Employee Requirements 

Employee Number Required Annual Salary 

Plant/General Manager 1 $121,600 

Plant Engineer 1 $79,000 

Maintenance Supervisor 1 $72,940 

Lab Manager/Chemist 1 $60,780 

Shift Supervisor 4 $45,000 

Maintenance Tech 5 $34,000 

Shift Operators 20 $30,400 

Administrative Assistants 2 $24,300 

The remaining fixed operating costs were calculated as percentages of the total labor cost or 

capital costs. 

• Overhead/maintenance – 60% of labor [72] 

• Maintenance – 2% of equipment [72] 

• Insurance and taxes – 1.5% of total installed capital [72] 

6.7 Economic Analysis 

The economic viability of the process is evaluated using a discounted-cash flow-rate of return 

(DCFROR) calculation. An internal rate of return (IRR) of 10% was specified for a plant life of 

20 years and straight-line depreciation over 7 years. The plant will be constructed over a 3-year 

period with capital outlays of 8%, 60%, and 32% each year. Working capital is estimated at 5% 

of the fixed capital investment and the start-up period is projected to be six months. These 

assumptions are from the Bain [64] analysis. 

38
6.8 Capital Cost Results 

A majority of the equipment costs were determined using ASPEN Icarus Questimate® 11.1. 

Two large component costs, the pyrolysis system and the feed handling system were estimated 

using other cost quotes. 

As noted earlier, the pyrolysis unit is a non-standard unit operation. Although there are numerous 

commercial pyrolysis units, most of these units are slow pyrolysis units and as such, may not be 

directly applicable to the proposed fast pyrolysis unit. The cost for the pyrolysis system was 

estimated from a fluidized bed boiler system designed by Energy Products of Idaho [75]. The 

heat recovery equipment would likely be the most similar between the systems (e.g., both are 

composed of air preheater, economizer, and superheater) and was thus used as the basis for 

scaling. The cost of the pyrolysis system was projected to be $3.8 million based on the steam 

flow rates of the two systems with a 0.6 equipment cost exponent. 

This estimate should be conservative based on several factors. The pyrolysis chamber should be 

significantly smaller than the combustion chamber of a fluidized bed boiler based on the lower 

gas flow rates in the pyrolysis system. The steam pressure and temperature for the EPI system is 

higher (950 psi) than that for the pyrolysis system (620 psi). Finally, the EPI cost quote included 

NOx and SO2 control and other systems that may not be required for the pyrolysis system. 

The cost of the wood feed handling system was estimated from the Gregoire [59] report and 

scaled up to 2003$. The system has provisions for rail car or truck delivery and accommodates 4 

weeks of storage. Rocks and tramp metal are removed using a flume and two front-end loaders 

are used to feed the wood chips to the process conveyor. Additional small metal pieces are 

removed with a magnet. The Gregoire [59] report estimated the cost of this system at $400,000. 

For this analysis, the cost is projected at a little more than $450,000. 

Solids handling within the facility was estimated using Questimate® based on the design 

presented in Bridgwater et al. [65]. This design includes screening, re-chipping of oversized 

components, drying, grinding, screening, and re-grinding of overs. 

The costs for the WESP and scrubber were estimated from literature values [76]. The power 

requirement for the WESP was estimated at 5.17E-4 kW/acfm [76]. 

The equipment costs were developed assuming a minimum of sparing. In general, each pump has 

a spare, but other unit operations were designed without redundancy. Table 9 summarizes the 

installed equipment costs by unit area. 

39
Table 9. Installed Equipment Costs 

Plant Area Installed Equipment Cost 

($ Million) 

A1000- Feedstock Handling and Drying $5.57 

A2000 – Pyrolysis $3.92 

A3000 – Quench $1.94 

A4000 – Heat Recovery $1.14 

A5000 – Product Recovery and Storage $0.80 

A6000 – Recycle $1.38 

A7000 – Steam and Power Production $3.16 

A9000 – Utilities $3.13 

Equipment Contingency – 35% $7.37 

Total Installed Equipment Cost $28.41 

Using the installed equipment costs and the factors outlined in Table 6, the TPI was estimated at 

$46.1 million. Table 10 provides a breakdown of the TPI. 

40
Table 10. Total Project Investment 

Component Cost 

Total Equipment Cost 

Warehouse 

 Site Development 

$28,410,567 

$426,159 

$826,448 

Total Installed Cost (TIC) $29,663,173 

Indirect Costs

 Field Expenses

 Home Office & Construction Fee 

 Project Contingency 

$5,932,635 

$7,415,793 

$889,895 

Total Capital Investment (TCI) $43,901,497 

Other Costs (Startup) $4,390,150 

Total Project Investment $48,291,646 

6.9 Operating Cost Results 

Variable operating costs were determined from the material and energy balance. The largest 

variable operating cost, by far is the feedstock at $5.5 million annually. Make-up water and 

miscellaneous chemicals have negligible costs. Waste treatment, both water and solid, contribute 

almost $1 million to the annual costs. After accounting for plant electricity demands, the facility 

has a net export of 4.70 MM kWh of electricity annually, resulting in a revenue stream of $0.21 

million. Overall variable operating costs are thus estimated at $6.13 million annually. 

Labor costs were estimated as outlined earlier in Table 10 and resulted in a direct labor cost of 

$1.34 million. An additional $800,000 was estimated for overhead labor charges. 

At 2% of the equipment and TPI costs, respectively, the costs for maintenance and 

insurance/taxes are estimated at $568,000 and $724,000. The total fixed operating costs are thus 

estimated at $3.4 million and the total operating costs are roughly $9.6 million. 

The operating cost spreadsheet is provided in Appendix B. 

6.10 Financial Analysis Results 

A DCFROR analysis was conducted using the parameters outlined earlier. The selling price of 

the bio-oil was projected to be $7.62/GJ, LHV. 

6.11 Discussion 

As discussed in Section 4.4 of this report, pyrolysis oils have several concerns including their 

shelf life, high ash content, volatility, heat content, and their overall quality. Table 3 showed 

some proposed specifications for the various grades of bio-oil. 

41
The IEA Bioenergy Pyrolysis committee, which developed the specifications in Table 3, focused 

on four grades of fuel oil: #2, #4, #5, and #6 corresponding to similar petroleum-based distillate 

and residual fuels. The committee does not believe that pyrolysis oils will be able to meet the 

viscosity, volatility and residue specifications for #1 fuel oil and so they did not develop 

specifications for these oils [77]. ASTM #2 fuel oil is also considered a volatile fuel as the 

specifications are not as strict as for #1 fuel oil. In addition, applications using ASTM #2 fuel oil 

generally have some preheating, which would likely also be required for an IEA #2 fuel oil [77]. 

Three example bio-oils were highlighted in the Diebold [77] report; one that had been upgraded 

with hot gas filtration and two that had only cyclones. The two oils using cyclones only generally 

met the proposed IEA specifications for #6 heavy bio-oil; they failed to meet only the flash 

point, LHV, and filtered solid specs [77]. The upgraded bio-oil (i.e., via hot gas filtration) met 

the flash point and filtered solid specifications for the IEA #6 heavy bio-oil oil and almost 

achieved the LHV. This oil closely parallels the #4 specification. With further upgrading to 

remove alkali and other solids, it could meet the IEA #2 light bio-oil specification. The #2 

specification is important as this type of fuel could likely be used in applications such as gas 

turbines without significant equipment modifications. 

The IEA committee did not include shelf life as a specification, but the literature shows that this 

is a concern. To account for these differences, it is assumed that pyrolysis oils, as currently 

produced have a value similar to #6 residual fuel oil and that the ultimate goal is to develop a 

fuel oil that meets the specifications of #2 fuel oil and will have a shelf life of at least 6 months. 

Thus, when evaluating process improvements, the product oil will be referred to as either IEA #6 

heavy bio-oil or IEA #2 light bio-oil and their values will be assigned based on this specification. 

The market values of the petroleum fuel oils that correspond to the two end points of the 

proposed fuel oil specifications (i.e., #2 and #6) differ considerably. In fact, in 2000, distillate 

fuel (#2) sold for $9.30/MM Btu ($10.12/GJ) while residual fuel oil (#6) sold for less than half of 

that at $4.50/MM Btu ($4.75/GJ), on an LHV basis [78]. Residual oil is generally used as an 

industrial heating oil and distillate oil is used for residential heating, power generation, or for 

vehicles. For this study, only non-highway uses of distillate are considered. The markets for both 

oils are significant. In 2001, over 12,400 million gallons of residual fuel oil and 22,900 million 

gallons of non-highway distillate fuel oil was purchased in the United States [79]. 

Although this analysis is portraying these oils as IEA #2 light bio-oil and IEA #6 heavy bio-oil, it 

is critical to note that the pyrolysis oils are not fungible with petroleum fuels (e.g., #2 distillate 

and #6 residual fuel oils). A separate fuel handling and transport system must thus be developed. 

In addition, the fuel specifications proposed by the IEA committee have not been accepted by 

conventional standards organizations (e.g., ASTM) and many properties of bio-oils will never be 

equivalent to their petroleum-based counterparts (e.g., heating value). However, the proposed 

comparison should provide a useful method to assess the potential for fuel upgrading and to 

provide appropriate cost goals and markets. 

6.12 Sensitivity Studies 

Several sensitivity studies were conducted and the cost barriers were identified. From this, 

researchers devised a roadmap of the improvements necessary to be cost competitive with 

petroleum fuels. It is envisioned that there will be parallel development efforts, focusing on the 

low-end IEA #6 heavy bio-oil and the higher-end IEA #2 light bio-oil markets. 

42
Based on the above analysis as well as the earlier analysis by Bain [64], the following sensitivity 

studies were conducted in series to determine their cumulative effect and whether the #6 fuel oil 

goal of $4.75/GJ, LHV based on the current price of #6 residual fuel oil was feasible. Table 11 

summarizes the results of these analyses. 

Table 11. Crude Bio-oil Sensitivity Studies 

Sensitivity Study Resulting Bio-Oil Cost 

Increase facility size to 2000 dtpd $5.65/GJ (LHV) 

Increase bio-oil yield; 59.9% to 70% $4.84/GJ (LHV) 

Reduce contingency factor; 35% to 10% $4.44/GJ (LHV) 

As shown in the table, the cost goal of $4.75/GJ, LHV appears to be feasible for a larger facility, 

decreased capital costs and an increase in bio-oil yield. None of these achievements is 

unreasonable. The 70% bio-oil yield has been achieved and the capital contingency factor should 

decrease as the equipment becomes better specified [66]. In addition, the facility size of 2000 

dtpd is well within the projected range of biomass facility sizes. Finally, while the stated goal for 

the crude IEA #6 fuel oil is that for #6 residual fuel oil, the actual value of the IEA #6 bio-oil 

may be higher due to its extremely low sulfur content. In general, residual oils have sulfur 

contents of > 1% [80]. 

6.13 Upgrading of Crude Bio-Oil 

Bio-oil can be upgraded through both chemical (e.g., hydrotreating) and physical (e.g., filtering) 

methods into chemicals and fuels. If the bio-oil can be upgraded to an ASTM #2-type fuel oil, 

suitable for use in residential heating or power production (e.g., gas turbines), it would likely 

demand a price that is double that of the crude pyrolysis oil. 

NREL researchers have proposed a process to upgrade the crude bio-oil, which involves a direct 

solvent (e.g., ethanol or methanol) quench, scrubbing, a wet ESP, and bio-oil filtration [66]. 

Figure 6 provides a block flow diagram of the proposed upgrading process. 

Char 

Cyclone

Scrubber 

Liquid Filtration Wet ESP 

Cold Solvent (e.g. 

ethanol,methanol) 

Pyrolysis 

Vapors 

IEA #2 Light 

Bio-Oil 

To Recycle 

Figure 6. Proposed Heavy Bio-Oil Upgrading Process 

43
The proposed process is relatively simple, adding only a solvent quench and liquid filtration to 

the current design. The solvent should help stabilize the product and the filtration can remove 

fine solids. It is not clear if the design would also impact the current heat integration/steam 

generation design. If the solvent quench can be employed after the heat recovery, then it will not 

be impacted. Further research and analysis is required to test the feasibility of this design. In 

addition, it is not clear that it would meet the proposed #2 IEA specifications. In fact, reviewers 

of this report are skeptical that the proposed process would improve the volatility of the oil 

sufficiently for use in #2 fuel oil applications and would employ a chemical modification [81]. 

Costs for this process were not estimated, as it is not clear whether this process is feasible and 

will achieve the proposed IEA specifications for a refined bio-oil. However, all of the unit 

operations are based on standard equipment and no exotic chemicals are employed. 

The actual potential for this technology is tremendous. Assuming that, based on the analysis 

above, the crude bio-oil can be produced for the current residual fuel oil price of $4.75/GJ, LHV, 

then the proposed upgrading process would have an allowable cost of over $5/GJ, LHV to meet 

the $10.12/GJ, LHV cost goal for IEA #2 light bio-oil. Although the margin of error is relatively 

high given the scope of this analysis, the tremendous potential increase in product value (i.e., > 

100%) for the upgrade is attractive. In fact, even if none of the projected process improvements 

for the current crude bio-oil design are implemented, the upgrading process, if successful, has an 

allowable cost of $2.50/GJ, LHV (i.e., $10.12/GJ-$7.62/GJ). 

6.14 Limitations of the Analysis 

The current analysis has several limitations, many due to the lack of current laboratory data as 

well as the conceptual nature of the analysis itself. The following is a summary of the most 

significant limitations of this analysis. 

• Lack of current data 

• Untested, proposed design for bio-oil upgrading 

• Quench section design with heat recovery may be infeasible due to the rapid quenching 

required (i.e., Ensyn uses direct quench without heat recovery) 

• Fungibility issues and the resulting storage and distribution system requirements of biooil have not been addressed 

• Large contingency factor due to the large uncertainty 

• Proposed development approach is based on proposed fuel standards that have not been 

accepted by traditional standardization bodies (e.g., ASTM) 

44
7. Conclusions and Recommendations 

Researchers have learned much about the science and engineering of pyrolysis of biomass 

especially in the last twenty-five years. This knowledge base has contributed to rapid advances in 

process hardware design improvements in addition to a broad understanding of the physical and 

chemical properties of the resulting bio-oil product during the same time period. Even with these 

advances, significant technical and economic challenges remain to be addressed before fast 

pyrolysis technology gains commercial acceptance. The following section will summarize the 

current state-of-the-technology, where it needs to go, and suggested paths to get it there. 

7.1 Current State-of-the-Art for Fast Pyrolysis of Biomass 

The method to produce bio-oils in high yield is well established. Numerous researchers 

throughout the world, using a variety of biomass feedstocks and a number of uniquely different 

reactor designs, have demonstrated this. As long as the thermal requirement of imparting high 

heat fluxes to the biomass immediately followed by rapid thermal quenching of the resulting 

vapors is followed, product yields and the chemical nature of the bio-oil product will be 

reasonably consistent. This will be true regardless of the specific reactor design or its relative 

size. Scale up to commercial size plants has yet to be demonstrated and there are questions 

related to being able to get enough heat into the reaction vessel. There may be other reasons to 

select one particular reactor design over another based on certain operating conditions that 

impact another processing step; but the thermal “cracking severity” or time / temperature 

relationship is the overriding principle to employ in any reactor design. 

The requirements needed to produce a bio-oil that has a reasonably long shelf life (equivalent to 

petroleum fuels) is also fairly well established. The principle technical issue here is producing oil 

containing little or no char. A substantial body of evidence has implicated the alkali metal 

sequestered in the char as a catalytic agent for promoting polymerization reactions between 

certain compounds known to be present in the bio-oil. While it is understood that this is an 

important issue for bio-oil stability, it is not known how to remove the char effectively and 

inexpensively. The challenge is primarily related to the very small (sub-micron) size of the char 

fines. Complementary to the absence of char fines for improving the storage stability is the 

addition of alcohol or other solvents. Based on the known types of compounds present in bio-oil 

and the chemical reactions between alcohols and some of these compounds, a convincing 

argument can be made that these reactions tie up the compounds suspected of undergoing 

polymerization reactions. The combination of these two approaches is expected to result in a biooil product capable of having a shelf life of up to six months. 

Although the need to remove char fines from the bio-oil is recognized by the biomass pyrolysis 

community, there is not a consensus in how this can be done easily at a reasonable cost. 

Filtration at elevated temperatures before condensing the bio-oil vapors to liquids created major 

operational problems. Vapors passing through the char cake captured on the filter surface are 

exposed to the same alkali metal in the char that has been linked to the polymerization reactions 

thought responsible for impacting long term stability in the liquid oils. In fact evidence of vapor 

phase polymerization reactions occurring within the char cake on the filters was observed. The 

consequence of this polymerization was a bonding of the char particles making up the cake on 

the filter surface. This bonding then made removal of the char cake from the filter very difficult. 

The polymerization is also thought to contribute to a yield loss of approximately 10% of the 

45
product bio-oil. Filtering liquid bio-oil after condensation has its own set of problems. As 

particulate is collected on the filter surface, the viscous bio-oil passing through the particulate 

cake tends to agglomerate the char fines into a thick sludge. As the sludge is removed from the 

filter to recover pressure drop, a considerable amount of bio-oil is also rejected with the sludge. 

So this strategy also results in a yield loss. As with gasification and the need to clean up the 

synthesis gas product from tars and particulates, a similar analogy applies to bio-oil. These are 

both difficult technical challenges that do not lend themselves to easy solutions. This is a critical 

technical challenge because of the link to both stability of the bio-oil and the need to meet 

stringent specification standards for particulate and alkali metal content. 

It is imperative to establish a set of standard specifications for bio-oils that have broad 

acceptance in the international community. Without this set of specifications designers and 

manufacturers of burners, IC engines, and turbines will not know how to design their equipment 

to accommodate the properties of this new fuel. At this point in time a set of standards has been 

proposed but no formal acceptance has been established between producers, users, and 

organizations involved with developing methods and protocols for measuring each specification. 

Preliminary studies of the health effects of bio-oil indicate that when produced at the relatively 

moderate temperature (500°C) used for fast pyrolysis conditions, the oils are not overly toxic. 

However these studies were preliminary in nature and some of the data showed inconclusive 

results. More definitive answers to the health and safety aspects of bio-oil will be required before 

this product can gain widespread public acceptance. In addition to the oils, the char produced as 

a byproduct also needs to be assessed from a chronic exposure standpoint. This information will 

be critical in both gaining public acceptance of the use of bio-oil and in designing plants to 

minimize chronic exposure to these materials. Along with the health aspects of working with 

bio-oil the effects on the environment also need to be better understood. Little to no effort has 

been expended in this area to date. The impact of a major spill of bio-oil on land and /or aquatic 

systems needs to be assessed. 

It is possible to upgrade bio-oil to hydrocarbon-like fuels through catalytic hydrotreating or 

cracking. These processes remove the oxygen in bio-oil and then reform the remaining carbon 

and hydrogen into hydrocarbon compounds. The yield of liquid product is reduced substantially 

because of efficiency losses and the fact that much of the mass of the original bio-oil is oxygen 

that gets rejected in the form of carbon oxides or water. Yields are lower when doing catalytic 

cracking instead of hydrotreating. In both cases the resulting hydrocarbon product is dominated 

by aromatic compounds, which have limits for blending into motor fuels. Methods for 

redirecting the type of hydrocarbons produced will need to be developed. Upgrading the bio-oil 

to a hydrocarbon fuel would be the fastest way to gain acceptance of biomass pyrolysis-based 

fuels into the existing market. We expect that the resulting product would be used directly in 

prime movers that have been designed for hydrocarbon fuels with little or no modification. 

Moderate scale fast pyrolysis plants have gained enough operating experience that reasonably 

good economic data is available to assess the economic viability of this emerging technology. No 

large scale plants have been built to date. This is primarily due to the lack of demand for the 

pyrolysis product. There have been modest size pilot plants built and operated at a number of 

locations worldwide. These have mostly been for demonstration purposes and are listed in the 

table below. The two plants at Red Arrow WI can be considered commercial operations but they 

are producing food flavoring compounds and there is a limited market for those products. Larger 

scale plants needed for producing fuels have yet to be developed from a commercial status. 

46
Table 12. Worldwide Current Biomass Pyrolysis Operating Plants 

Reactor Design Capacity 

(Dry Biomass Feed) 

Organization or Company 

Fluidized bed 400 kg/hr (11 tons/day) DynaMotive, Canada 

250 kg/hr (6.6 tons/day) Wellman, UK 

20 kg/ hr (0.5 tons/day) RTI, Canada 

Circulating Fluidized Bed 1500 kg/hr (40 tons/day) Red Arrow, WI; Ensyn design 

1700 kg/hr (45 tons/day) Red Arrow, WI; Ensyn design 

20 kg/hr (0.5 tons/day) VTT, Finland; Ensyn design 

Rotating Cone 200 kg/hr (5.3 tons/day) BTG, Netherlands 

Vacuum 3500 kg/hr (93 tons/day) Pyrovac, Canada 

Other Types 350 kg/hr (9.3 tons/day) Fortum, Finland 

A technoeconomic analysis using discounted cash flow methodology (10% IRR, 100% equity 

financing) on a bio-oil production facility showed that heavy bio-oil (i.e., IEA #6 heavy bio-oil) 

is projected to have a selling price of roughly $7.62/GJ, LHV. The facility analyzed produced 

16,091 kg/hr of bio-crude with a moisture content of 23.6%. The feed rate to the pyrolyzer was 

550 dry tones/day. The pyrolysis reactor was modeled using yields from Bridgewater, et al. 

[67/68]. 

The pyrolysis unit also produced almost 4,900 kW of electricity, but used roughly 80% of that 

value for recycle gas compression (2,600 kW) and feedstock size reduction (1,400 kW). The net 

electricity output for the facility was 588 kW. 

7.2 Recommendations for Advancing Fast Pyrolysis Technology 

There are a number of barriers that must be overcome to advance the technology of biomass fast 

pyrolysis. They can be listed as follows: 

• No universally accepted specifications or standards for bio-oil 

• Bio-oil quality and reproducibility must be established, especially with respect to storage 

stability of the oil 

• Effects on the environment and safety and health of production personnel potentially 

exposed to bio-oil needs to be established. This need is also present for consumers using 

the product. 

• Public acceptance or perception may be an issue, particularly if the health and safety 

issues are unknown. Odor is another issue related to public acceptance. Bio-oil has a 

strong smoky smell that is unlikely to be masked by other compounds. 

• A near term technical barrier is lack of adequate supplies of bio-oil for long term testing 

in burners and prime movers for power generation. There are currently a limited number 

of sources for bio-oil production and little support for funding bio-oil production runs. 

47
• A policy barrier is the need to secure long term supplies of the biomass resource. This is a 

ubiquitous problem for all biomass utilization technologies and will prevent the flow of 

investment capital unless it can be resolved. A minimum of a guaranteed ten year supply 

will be necessary to create a favorable investment climate. 

The first two barriers are somewhat related in that if the appropriate specifications are 

established for key properties of the oil then the oil stability and quality will be enhanced. Given 

what is already known about char fines and their relationship to storage stability, their effective 

removal should be a priority. One approach worth investigating would be to add alcohol solvents 

to the bio-oil prior to doing liquid filtration. Adding the alcohol will reduce the viscosity to the 

point where sludge buildup on the filter surface may no longer present a problem. Previous 

studies have shown that addition of the alcohol solvent is more effective in stabilizing oils when 

it is added shortly after the oils are produced. An approach that should be explored is adding the 

alcohol solvent directly into the hot bio-oil vapor stream. Two benefits could possibly result 

from this method of addition. Vaporization of the alcohol will have a cooling effect on the hot 

vapor stream, which is desirable from a standpoint of quenching the thermal reactions from 

pyrolysis and preserving the biomass fragments that comprise the liquid product. Addition of the 

alcohol at this location in the process would provide a small amount of residence time in an 

elevated temperature zone to enhance the reactivity of alcohol with some of the reactive 

compounds in bio-oil. This may further improve the stability over what has already been 

observed with the addition of alcohol to liquid bio-oil. There may also be benefits of cocondensing the alcohol solvent with bio-oil vapors to minimize the formation of aerosols during 

cooling. 

Establishing a moisture specification for bio-oil will require the producer to dry the biomass feed 

to a certain level prior to pyrolysis. This requirement can be set to levels that insure bio-oil will 

always remain a single phase. What currently happens in practice is that various organizations 

make their own determination as to the moisture content of the starting feed. This results in a 

wide range of moisture contents for bio-oil produced by different organizations. 

It will be necessary to stay involved the international pyrolysis research community in 

developing specifications for bio-oil. The best vehicle in which to do this would be the 

International Energy Agency. Indeed, the first set of standards promulgated for bio-oil was done 

through the Pyrolysis Activity under Task XIII within the IEA. There continues to be a lot of 

activity in developing protocols and standard methods for measuring the properties of bio-oil in 

the European biomass pyrolysis community. This is even being done in collaboration with 

equipment manufacturers. The United States should re-engage with this activity. An organization 

such as ASTM also needs to be brought into the loop to provide credibility to the final 

specifications and methods for measuring them. The manufacturers of the end use equipment 

also must be involved in establishing these specifications. NREL and PNNL both have extensive 

experience in analyzing bio-oils and can provide technical assistance in developing the 

measuring protocols. 

A better understanding of the environmental impacts along with safety and health issues of 

exposure to bio-oil needs to occur. This analysis should also include particle size distribution and 

toxic compounds that may be adsorbed on the surface of particles for the char, particularly the 

fines.. Having this information will be critical in gaining public acceptance of bio-oil as a new 

fuel source. These studies should be more rigorous and therefore more definitive than the 

preliminary studies previously conducted. They also need to include biodegradability of the oil in 

48
soils and an assessment of the impacts on aquaculture resulting from a major spill in a river or 

lake. 

Collaborative activities with the U.S. Department of Agriculture (USDA) Forest Service should 

continue because of their close connection with the biomass resource and the need to establish 

long-term access to this resource by investors willing to provide capital for the emerging 

conversion technologies. The Forest Service also conducts R&D on biomass harvesting and size 

reduction equipment. There may be opportunities to guide this development toward equipment 

that can be multi-purpose with respect to feed preparation for biomass conversion technology. 

An example would be equipment that could simultaneously grind and dry the biomass, thus 

reducing process feed costs. 

Upgrading of bio-oil to hydrocarbon fuels or high value chemical products should continue. 

Since the performance characteristics, toxicity, and public acceptance of these types of fuel are 

well known this will present the fastest path to market for biomass based transportation fuels. 

Additional opportunities should be explored in catalytic manipulation of the promptly formed 

pyrolysis vapors. All technologies employing heat transfer media (fluid or transported beds) lend 

themselves to this approach by replacing the transfer media with a catalyst. Some effort has been 

expended in this area in the past so it may offer novel pathways to chemicals or other fuels from 

biomass pyrolysis. The University of Waterloo in Canada demonstrated (69) an example of this 

approach during the late 1980s where they conducted pyrolysis of biomass in the presence of 

hydrogen with a catalyst as the fluidizing media. They were able to convert the carbon in 

biomass primarily to methane at very high yields. At the time methane was an inexpensive 

commodity fuel so there was little commercial interest. However, recent trends in the supply / 

demand dynamics of natural gas are changing this situation and may offer new opportunities to 

exploit this technology. 

The technoeconomic analysis also showed that research on upgrading the bio-oil should 

continue. For example, in order for pyrolysis oil to be cost competitive with #6 fuel oil and to 

compete in the industrial heating market, further cost reductions are necessary. Potential areas 

for improvement include increased yields, larger facility sizes, and reduced pyrolysis unit capital 

costs. With further research and development, it is likely that the cost goal of $4.75/GJ, LHV for 

this grade of bio-oil is achievable. 

Developing a higher-value bio-oil (e.g., IEA #2 light bio-oil) will require some type of gas 

cleanup or liquid fuel upgrade. This higher value oil could be used in applications such as gas 

turbines without extensive equipment modifications. This trade-off should be explored using 

studies such as Thamburaj [82]. 

NREL researchers have proposed a simple bio-oil upgrading process that may cost effectively 

convert the crude bio-oil into a gas turbine fuel with properties similar to a #2 distillate. Due to 

the large cost differential between residual ($4.75/GJ, LHV) and distillate ($10.12/GJ, LHV) fuel 

oils, there is an attractive economic incentive for evaluating this process. For the current bio-oil 

design, the upgrading process has an allowable cost of $2.5/GJ, LHV to meet the proposed cost 

goal of $10.12/GJ, LHV and if the projected crude oil process improvements are achieved, the 

allowable cost doubles to $5/GJ, LHV. 

Figure 7 summarizes these results graphically. 

49
$12.00 

$10.00 

$8.00 

$6.00 

$4.00 

$2.00 

$0.00 

Current 

Process 

$7.62 

$2.50 

$5.65 

$4.47

$4.84 

$5.28 

$4.75 

$5.37 

$10.12/GJ, LHV Cost goal for IEA #2 Bio-oil 

Allow able Cost for Upgrading 

IEA #6 Heavy Bio-Oil 

2000 dtpd 70% Bio- Decrease 

plant Oil yield capital 

costs 

$/

G

J, L

H

V

Process Improvements 

Figure 7. Bio-Oil Production and Upgrading Cost Goals 

50
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56
Appendix A: ASPEN Plus® Model Implementation / Mass

Balances

57
The ASPEN Plus® pyrolysis model is divided into eight flowsheets: 

• A1000 – Feed Handling and Drying 

• A2000 – Pyrolysis 

• A3000 – Quench 

• A4000 – Heat Recovery 

• A5000 – Product Recovery and Storage 

• A6000 – Recycle 

• A7000 – Steam and Power Production 

• A9000 – Utilities 

Each of these areas will be briefly discussed and flow diagrams from ASPEN Plus® will be 

presented. The flow diagrams show only those unit operations modeled in ASPEN Plus®. 

Equipment used for operations such as conveyance, size reduction, and storage are generally not 

included in the model. The power requirements of this equipment, however, are included and are 

modeled as work streams in the utility section, A9000. Also, costs for all of the equipment are 

included in the economic analysis. 

The mass for each section is included with each of the flow diagrams. 

A1.1 A1000 – Feed Handling and Drying 

Figure A1 shows the flowsheet for the feed drying area. Two unit operation models, a heater and 

a flash, model the wood chip dryer. The wood chip feed (1001) is milled and dried (DR-1001) 

using the preheated flue gases (1002) from the secondary condenser (HX-3002). The outlet 

moisture content is controlled to 7% [68] using a design-spec AIRDRY. The evaporated water 

(1004) is flashed in DR1001FL and sent off the flowsheet. The dried wood chips (1005) are sent 

to Pyrolysis (A2000). 

All of the necessary heat for drying is supplied from gases heated from the condensing pyrolysis 

vapors (A3000). Due to convergence issues, the recycle stream (1007) was broken. However, the 

model ensures that the heat added to the recycle is more than sufficient to heat the incoming 

dryer air (1002). 

The feed handling section has several pieces of equipment, (e.g., conveyors) which are not 

modeled in ASPEN Plus®. In fact, one of the most significant energy demands is the feedstock 

grinder. The power requirements to grind the wood to < 2 mm are estimated at 50 kWh/ton [83] 

and are calculated in the utility section (A9000). 

58
1001 

1002 

1003 

QDR1001 

1005 A2000 

1004 

DR-1001 

DR1001FL 

1007 

A3

CC-1001 

3008 

Figure A1 A1000 – Feedstock Handling and Drying 
 1001 1002 1003 1004 1005 1007 3008 

Mass Flow kg/hr 

N2 0.0 267209.0 267209.0 267209.0 0.0 264954.0 264954.0 

O2 0.0 81135.4 81135.4 81135.4 0.0 81194.4 81194.4 

H2 0.0 0.0 0.0 0.0 0.0 0.0 0.0 CO 0.0 0.0 0.0 0.0 0.0 0.0 0.0 

CO2 0.0 0.0 0.0 0.0 0.0 161.6 161.6 

H2O 20789.6 0.0 20789.6 19222.5 1567.2 2315.4 2315.4 

H3N 0.0 0.0 0.0 0.0 0.0 0.0 0.0 CH4 0.0 0.0 0.0 0.0 0.0 0.0 0.0 C2H4 0.0 0.0 0.0 0.0 0.0 0.0 0.0 C3H6-2 0.0 0.0 0.0 0.0 0.0 0.0 0.0 

AR 0.0 0.0 0.0 0.0 0.0 4498.6 4498.6 

C2H4O2-1 0.0 0.0 0.0 0.0 0.0 0.0 0.0 C3H6O2-D 0.0 0.0 0.0 0.0 0.0 0.0 0.0 C7H8O2-E 0.0 0.0 0.0 0.0 0.0 0.0 0.0 

C8H10O3 0.0 0.0 0.0 0.0 0.0 0.0 0.0

 CH2O2 0.0 0.0 0.0 0.0 0.0 0.0 0.0 

C10H12O3 0.0 0.0 0.0 0.0 0.0 0.0 0.0 

C6H6O 0.0 0.0 0.0 0.0 0.0 0.0 0.0 C7H8 0.0 0.0 0.0 0.0 0.0 0.0 0.0 C5H4O2 0.0 0.0 0.0 0.0 0.0 0.0 0.0 C6H6 0.0 0.0 0.0 0.0 0.0 0.0 0.0

 CHAR 0.0 0.0 0.0 0.0 0.0 0.0 0.0 

ASH 0.0 0.0 0.0 0.0 0.0 0.0 0.0 

WOOD 20789.6 0.0 20789.6 0.0 20789.6 0.0 0.0 

Total Flow kg/hr 41579.3 348344.4 369134.0 367566.8 1567.2 353123.9 353123.9 
Temperature C 25.0 200.0 110.0 52.0 52.0 200.3 200.3 

Pressure psi 20.0 20.0 20.0 20.0 20.0 14.8 14.8 Enthalpy MJ/hr -427852.3 62125.2 -336599.0 -247680.0 -118056.0 30515.2 30515.2 

Table A1. Mass Balance for Section A1000 
A1.2 A2000 – Pyrolysis 

As shown in Figure A2, the dried wood chips are fluidized (MX-2001) using recycled pyrolysis 

vapors (6008) at 200oC in a 2.75:1 gas-to-feed ratio. The fluidizing gas rate is maintained with 

the design spec GASSPLT that controls the split in SP-6001. The solid/gas mixture is heated 

(HX-2001) to the pyrolysis temperature of 500oC using heat from the char combustor (CB-4001). 

The pyrolysis unit is modeled as an RSTOIC reactor. All of the incoming wood is converted to 

gas (e.g., CO, H2), water, ash, char, or biocrude constituents (e.g., C2H4O2). As noted in the 

design basis, the yield of biocrude is estimated at 59.9% of the dry wood feed. Heat for pyrolysis 

(QPY-2001) is supplied from the char combustor (CB-4001). The hot mix of solids, liquids and 

gases are sent to a bank of high efficiency cyclones (CY-2001) where the solids (e.g., ash and 

char) are separated (2005) from the gases and biocrude liquids (2004). 

A1.3 A3000 – Quench 

The pyrolysis reaction is rapidly quenched and the biocrude vapors are condensed in a series of 

two condensers: HX-3001 and HX-3002 shown in Figure A3. The first condenser is used to 

generate 515-psig steam (3010), which is then sent to the steam drum (V-7001). A design-spec 

BOILSTM is used to control the amount of steam generated. No biocrude is condensed from this 

stage. 

In the second condenser (HX-3002), air (3007) is used as the cooling medium. The heated 

(200oC) air is recycled back to the feedstock dryer (DR-1001). A design-spec, AIRFLOW1, 

controls the airflow to achieve the specified outlet temperature. 

Any remaining aerosols in the vapor stream are removed in a scrubber (SC-3001) and wet ESP 

(ES-3001). The recovered liquids are sent to Product Recovery (A5000). The cleaned vapors 

(3006) are sent to Recycle (A6000) for recycle as the fluidizing medium. 

A1.4 A4000 – Heat Recovery 

The first unit operation in the heat recovery section (Figure A4) is the char and gas combustor 

(CB-4001). In reality, this combustor will be integral to the pyrolysis unit, but for modeling 

purposes, it is broken out. The combustor supplies the heat (QHX-2001) to preheat the feed/gas 

mixture (2001) before pyrolysis as well as the pyrolysis reactor (QPY-2001). A design-spec 

COMBADIA manipulates the temperature of the combustor to ensure adiabatic (i.e., QCB-4001 

= 0) combustion. The combustor is modeled as an RSTOIC reaction, with ASPEN Plus® 

calculating the appropriate reactions; complete combustion is assumed. 

Combustion air (4010) is combined with recycled product gases (2006) prior to the combustor. 

The amount of combustion air is maintained at 15% excess and is controlled with design-spec 

COMBAIR. 

62
2005 

2006 

6006 

MIXER 

MX-2002 

A6000 

A1000 

6008 

MIXER 

2001 

MX-2001

1005

2002 2003 CY-2001

HX-2001+ PY-2001

2004

Figure A2 

A2000 - Pyrolysis 

A3000 
 1005 2001 2002 2003 2004 2005 2006 6006 

Mass Flow kg/hr 

N2 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 O2 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 H2 0.0 2614.0 2614.0 2737.2 2737.1 0.0 123.1 123.1 26CO 0.0 28919.3 28919.3 30283.0 30281.5 0.0 1362.2 1362.2 289CO2 0.0 23953.2 23953.2 25080.1 25081.5 0.0 1128.3 1128.3 239

H2O 1567.2 1571.5 1571.5 3818.6 3818.5 0.0 0.2 0.2 

H3N 0.0 911.6 911.6 954.6 954.5 0.0 42.9 42.9 9CH4 0.0 154.1 154.1 161.3 161.3 0.0 7.3 7.3 C2H4 0.0 628.6 628.6 658.2 658.2 0.0 29.6 29.6 6C3H6-2 0.0 0.0 0.0 31.7 31.7 0.0 0.0 0.0 AR 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 

 C2H4O2-1 0.0 0.3 0.3 1232.6 1232.6 0.0 0.0 0.0 

C3H6O2-D 0.0 0.3 0.3 1520.6 1520.5 0.0 0.0 0.0 C7H8O2-E 0.0 0.0 0.0 127.5 127.5 0.0 0.0 0.0 C8H10O3 0.0 0.0 0.0 791.0 791.0 0.0 0.0 0.0 CH2O2 0.0 0.2 0.2 708.5 708.5 0.0 0.0 0.0 C10H12O3 0.0 0.0 0.0 3400.2 3400.2 0.0 0.0 0.0 

C6H6O 0.0 0.0 0.0 96.7 96.7 0.0 0.0 0.0 C7H8 0.0 0.1 0.1 472.9 472.9 0.0 0.0 0.0 C5H4O2 0.0 0.9 0.9 3944.5 3944.5 0.0 0.0 0.0 C6H6 0.0 0.0 0.0 160.3 160.3 0.0 0.0 0.0 CHAR 0.0 0.0 0.0 3176.6 0.0 3176.6 3176.6 0.0 ASH 0.0 0.0 0.0 191.2 0.0 191.2 191.2 0.0 

WOOD 20789.6 20789.6 20789.6 0.0 0.0 0.0 0.0 0.0 

Total Flow kg/hr 1567.2 58754.0 58754.0 79547.4 76179.2 3367.8 9429.4 2693.7 57
Temperature C 52.0 454.4 500.0 500.0 500.0 500.0 499.5 105.6 7

Pressure psi 20.0 20.0 20.0 20.0 20.0 20.0 20.0 45.0 Enthalpy MJ/hr -118056.0 -380690.3 -372838.6 1179320.0 -372270.0 1551570.0 1536357.0 -15211.3 -2626

Table A2. Mass Balance for Section A2000. 
3006 

5005 A5000 

3020

6001 Q A6000 

ES-3001 MS-3001

QHX3001X 

3005

HX-3001­ 3010 3009

3021 A5000 

HX-3002+ 3003

SC-3001 2004 3002

HX-3001+ 3004 A5000 

QHX3002 

A2000 

QHX-3001 

A7000 

A9000

3007 3008

HX-3002­

A1000 

CP-3001

Figure A3 

WCP-3001 A3000 - Quench 
2004 3002 3003 3004 3005 3006 3007 3008 3009 3010 3020 

Mass Flow kg/hr N2 0.0 0.0 0.0 0.0 0.0 264954.0 264954.0 264954.0 0.0 0.0 0.0 

O2 0.0 0.0 0.0 0.0 0.0 81194.4 81194.4 81194.4 0.0 0.0 0.0 

 H2 2737.1 2737.1 2737.1 0.0 2737.1 0.0 0.0 0.0 0.0 0.0 2737.1 

CO 30281.5 30281.5 30281.5 0.0 30281.5 0.0 0.0 0.0 0.0 0.0 30281.5 CO2 25081.5 25081.5 25081.5 0.0 25081.5 161.6 161.6 161.6 0.0 0.0 25081.5 H2O 3818.5 3818.5 3818.5 0.0 4491.6 2315.4 2315.4 2315.4 1470.9 1470.9 4.5 

H3N 954.5 954.5 954.5 0.0 954.5 0.0 0.0 0.0 0.0 0.0 954.5 CH4 161.3 161.3 161.3 0.0 161.3 0.0 0.0 0.0 0.0 0.0 161.3 C2H4 658.2 658.2 658.2 0.0 658.2 0.0 0.0 0.0 0.0 0.0 658.2 C3H6-2 31.7 31.7 31.7 29.8 7.5 0.0 0.0 0.0 0.0 0.0 0.0 

AR 0.0 0.0 0.0 0.0 0.0 4498.6 4498.6 4498.6 0.0 0.0 0.0 C2H4O2-1 1232.6 1232.6 1232.6 1160.1 290.0 0.0 0.0 0.0 0.0 0.0 0.3 

C3H6O2-D 1520.5 1520.5 1520.5 1431.1 357.8 0.0 0.0 0.0 0.0 0.0 0.4 C7H8O2-E 127.5 127.5 127.5 120.0 30.0 0.0 0.0 0.0 0.0 0.0 0.0 

C8H10O3 791.0 791.0 791.0 744.5 186.1 0.0 0.0 0.0 0.0 0.0 0.2 CH2O2 708.5 708.5 708.5 666.8 166.7 0.0 0.0 0.0 0.0 0.0 0.2 C10H12O3 3400.2 3400.2 3400.2 3200.2 800.0 0.0 0.0 0.0 0.0 0.0 0.8 C6H6O 96.7 96.7 96.7 91.0 22.7 0.0 0.0 0.0 0.0 0.0 0.0 

C7H8 472.9 472.9 472.9 445.0 111.3 0.0 0.0 0.0 0.0 0.0 0.1 

C5H4O2 3944.5 3944.5 3944.5 3712.3 928.1 0.0 0.0 0.0 0.0 0.0 0.9 

C6H6 160.3 160.3 160.3 150.9 37.7 0.0 0.0 0.0 0.0 0.0 0.0 

CHAR 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 ASH 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 

WOOD 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 

Total Flow kg/hr 76179.2 76179.2 76179.2 11751.7 67303.7 353123.9 353123.9 353123.9 1470.9 1470.9 59881.6 
Temperature C 500.0 470.0 35.0 33.1 33.1 15.0 16.0 200.3 30.0 242.1 33.1 

Pressure psi 20.0 20.0 20.0 20.0 20.0 14.7 14.8 14.8 515.0 515.0 20.0 Enthalpy MJ/hr -372270.0 -376540.0 -442880.0 -42921.3 -421880.0 -36184.4 -35824.5 30515.2 -23544.2 -19275.6 -345170.0 

Table A3. Mass Balance for Section A3000. 
Figure A4 

A4000 – Heat Recovery 

QHX-2001 

A2000 

2006 

A2000 

QPY-2001 

A2000 

4010 4011 

WCP-4001 

A9000 

4012 

4001 

4004 

4002 

4005 

4000 

4003 

4006 

4007 

QHX4002 

A7000 

QHX

A

QCB-4001 

Q 

4013 

4014 

CP-4001 

MIXER 

MX-4002 

CY-4001 

MS-4001 

MIXER 

MX-4001 

HX-4001+ 

HX-4002+ HX

CB-4001 

SP-4002 
2006 4000 4001 4002 4003 4004 4005 4006 4007 4008 4009 4010 4

Mass Flow kg/hr 

N2 0.0 0.0 37351.3 0.0 0.0 37351.3 37351.3 37351.3 37351.3 37351.3 37351.3 37351.3 373O2 0.0 0.0 2349.6 0.0 0.0 2349.6 2349.6 2349.6 2349.6 2349.6 2349.6 11446.2 114

H2 123.1 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 

CO 1362.2 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 CO2 1128.3 0.0 12780.9 0.0 0.0 12780.9 12780.9 12780.9 12780.9 12780.9 12780.9 22.8 H2O 0.2 3316.1 2492.0 0.0 3316.1 2492.0 2492.0 2492.0 2492.0 2492.0 2492.0 326.4 3

H3N 42.9 0.0 42.9 0.0 0.0 42.9 42.9 42.9 42.9 42.9 42.9 0.0 CH4 7.3 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 

C2H4 29.6 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 C3H6-2 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0  AR 0.0 0.0 634.2 0.0 0.0 634.2 634.2 634.2 634.2 634.2 634.2 634.2 6C2H4O2-1 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 C3H6O2-D 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 C7H8O2-E 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 C8H10O3 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 CH2O2 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 C10H12O3 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 C6H6O 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 C7H8 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 C5H4O2 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 C6H6 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0  CHAR 3176.6 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 

ASH 191.2 0.0 191.2 191.2 191.2 0.0 0.0 0.0 0.0 0.0 0.0 0.0 

WOOD 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 
6061.6 3316.1 55842.2 191.2 3507.3 55650.9 55650.9 55650.9 55650.9 55650.9 55650.9 49780.9 497

Total Flow kg/hr Temperature C 499.5 25.0 1796.6 1796.6 60.0 1796.6 1796.6 982.1 792.4 402.9 155.0 25.0 Pressure psi 20.0 20.0 14.8 14.8 14.8 14.8 14.8 14.8 14.8 14.8 14.8 14.7 Enthalpy MJ/hr 1536357.0 -53170.9 -28218.3 -2334.4 -55505.3 -25883.9 -25883.9 -86183.3 -99468.0 -125220.0 -140330.0 -4597.1 -45

Table A4. Mass Balance for Section A4000. 
The hot (> 1850oC) combustion products are sent to a cyclone (CY-4001) where ash and noncombusted solids are removed (4002). The temperature of the solids is reduced to 60oC through 

the addition of process water (4000). The addition of the water is controlled by H2OQUENH. A 

rotary filter (SP-4002) is used to separate the solids from the quench water. Both waste streams 

are sent off the flowsheet. The quench water (4013) is sent to wastewater treatment while the 

solids (4014) are landfilled. 

The clean, hot flue gases (4004) are sent through a series of heat exchangers to recover heat for 

the process. The first exchanger, HX-4001+, is used to preheat the recycled product gases in HX6002. The next three exchangers, HX-4002+ - HX-4004+, simulate the process side of a typical 

steam production system comprised of a superheater, economizer, and boiler feed water heater. 

These exchangers are coupled with the steam side of several exchangers in the steam production 

area (A7000). 

The superheater is modeled as HX-4002+ (process side) coupled to HX-7003 (steam side). The 

515 psig-saturated steam (7004 and 3010) is superheated to 620oC prior to introduction into the 

steam turbine. The outlet temperature of the process side is manipulated by design-spec 

AIRPRHT to provide enough heat for superheating the steam. Additionally, if outside air is 

needed for the dryer (7006), it is heated here. 

The economizer is modeled as HX-4003+ (process side) coupled to HX-7002). The design-spec 

ECOMZER manipulates the flue gas temperature to vaporize all of the inlet water to HX-7002. 

The boiler water preheater is modeled by coupling HX-4004+ and HX-7001. The flue gas outlet 

(4009) temperature is specified at 155oC. The boiler feed water (7001) rate is manipulated by the 

design-spec H2ORECY. 

A1.5 A5000 – Product Recovery and Storage 

The Product Recovery and Storage flowsheet, shown in Figure A5, is very simple and consists of 

a mixer (MX-5001), a pump (P-5001), and a cooler (HX-5001). The mixer combines products 

recovered from areas A3000 and A6000. It is pumped to the cooler (HX-5001), where it is 

cooled to 20 oC using cooling water. 

The area will also include a storage tank (T-7001), sized for 7 days storage, and a product 

transfer pump (P-7002). These are not modeled, but are included in the equipment costs. 

A1.6 A6000 – Recycle 

As shown in Figure A6, vapors (6001) from the initial product condensation steps in A3000 are 

sent to a tertiary condenser (HX-6001) where chilled water is used to cool the stream to 7oC, 

resulting in further product recovery. The chilled stream is flashed (FL-6001) and the condensed 

product is sent to A5000, Product Recovery and Storage where it is combined with additional 

product. 

The flashed vapor stream (6004) is compressed for recycle as a fluidizing medium. The amount 

of gas required for fluidization is estimated at 2.75 lb gas/lb pyrolysis feed [66] and is controlled 

by the design-spec GASSPLT, which specifies the split of recycle gas (6007) in SP-6001. The 

recycle gas is heated to 700oC in HX-6002 using heat from the char combustor flue gas (CB4001) in the air preheater, HX-4001. This heat transfer is controlled with design-spec AIRPRHT. 

The vapors that are not needed for fluidization (6006) are recycled back to Heat Recovery, 

A4000, to provide heat for the process. 

72
A1.7 A7000 – Steam and Power Production 

Many of the unit operations and much of the logic in this area (Figure A7) have already been 

discussed in A4000 and will not be repeated here. Steam from the economizer (HX-7002) and 

the waste heat recovery boiler (HX-3001) are combined in the steam drum, V-7001, and sent to 

the steam turbine, TB-7001. Here, power is generated in a condensing turbine with an outlet 

pressure of 1.47 psig. Over 5,000 kW of electrical power is generated. The turbine outlet (7011) 

is condensed in the turbine condenser (CD-7001) with cooling water. Blowdown (7013) is 

estimated at 3% of the steam system requirement. This blowdown value is used to determine the 

steam system make-up. 

A1.8 A9000 – Miscellaneous Utilities 

The miscellaneous utilities flowsheet shown in Figure A8 is basically a summary flowsheet that 

calculates the total utilities (e.g., cooling water, power) for the other flowsheets. 

The overall power requirements for the facility are calculated in MX-9000. This block sums all 

of the power demands from the modeled pumps and compressors as well as the solids handling 

equipment that were not specifically modeled. The power requirements for the solids handling 

equipment are specified in the FORTRAN block MISCPOW and are based on the Questimate® 

equipment specifications. Each power demand, except grinding, is scaled from the dry wood feed 

rate (1001). The grinding power demand (50 kWh/ton) is scaled from the total dried wood rate 

(1005). 

The cooling tower is sized based on a supply temperature of 16 oC and a maximum temperature 

rise of 8oC. The heat demands from the turbine condenser (9002) and the product cooler (9004) 

are summed in MX-9001 and an overall cooling water demand is projected (9005). 

The pyrolysis system also requires chilled water to recover product in the tertiary condenser. The 

chilled water system is designed for a –18 ̊C supply temperature and a –12  ̊C return 

temperature. 

Process water is also required for quenching and other uses. The overall process water demand is 

calculated as the sum of the quench water (4000) and boiler blowdown (7013). The facility will 

also require process and instrument air. These utilities were not included in the ASPEN Plus® 

model, but their capital costs will be included in the economic analysis. 

73
A3000 3004

5001 5002 

A9000 WP-5001

QHX-5001 

A6000 6003

MIXER P-5001 HX-5001

T-5001 

HX-500

A9000 9004

A3000 5005

A3000 3021

QHX5001X 

Q 

Figure A5 
 3004 3021 5001 5002 5003 5004 5005 6003 9003 90

Mass Flow kg/hr 

N2 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 O2 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 H2 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 CO 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 CO2 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 

H2O 0.0 4487.1 4487.2 4487.2 4487.2 3814.2 673.1 0.0 14804.8 14804H3N 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 CH4 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 C2H4 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 C3H6-2 29.8 7.5 37.3 37.3 37.3 31.7 5.6 0.0 0.0 

AR 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 

 C2H4O2-1 1160.1 289.7 1449.8 1449.8 1449.8 1232.4 217.5 0.0 0.0 

C3H6O2-D 1431.1 357.4 1788.5 1788.5 1788.5 1520.2 268.3 0.0 0.0 C7H8O2-E 120.0 30.0 150.0 150.0 150.0 127.5 22.5 0.0 0.0 

C8H10O3 744.5 185.9 930.6 930.6 930.6 791.0 139.6 0.2 0.0 CH2O2 666.8 166.5 833.4 833.4 833.4 708.4 125.0 0.0 0.0 C10H12O3 3200.2 799.2 4000.2 4000.2 4000.2 3400.2 600.0 0.8 0.0 C6H6O 91.0 22.7 113.7 113.7 113.7 96.7 17.1 0.0 0.0 

C7H8 445.0 111.1 556.2 556.2 556.2 472.8 83.4 0.0 0.0 
C5H4O2 3712.3 927.2 4639.5 4639.5 4639.5 3943.6 695.9 0.0 0.0 

C6H6 150.9 37.7 188.6 188.6 188.6 160.3 28.3 0.0 0.0 

 CHAR 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 

ASH 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 

WOOD 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 

Total Flow kg/hr 11751.7 7422.1 19175.0 19175.0 19175.0 16298.7 2876.2 1.0 14804.8 14804Temperature C 33.1 33.1 35.7 35.9 25.0 -6.4 -6.4 7.0 21.1 3Pressure psi 20.0 20.0 26.0 40.0 40.0 40.0 40.0 20.0 15.0 1Enthalpy MJ/hr -42921.3 -81619.8 -124530.0 -124530.0 -125530.0 -106700.0 -18829.4 -2.9 -237660.0 -23666

Table A5. Mass Balance for Section A5000. 
CP-6001 

6006 

A2000 

A3000 6001

QHX-

A40

6003 

A5000 

6002 

QHX-6001 

6004 

6005 

6007 

HX-6001 

FL-6001 FSPLIT 

SP-6001 

HX-6002+ 

HX-6001­

QHX6001X Q 

9006 9007 

Figure A6

A6000 – Product Storage
 6001 6002 6003 6004 6005 6006 6007 6008 9006 

Mass Flow kg/hr 

N2 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 O2 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 

H2 2737.1 2737.1 0.0 2737.1 2737.1 123.1 2614.0 2614.0 0.0 CO 30281.5 30281.5 0.0 30281.5 30281.5 1362.2 28919.3 28919.3 0.0 CO2 25081.5 25081.5 0.0 25081.5 25081.5 1128.3 23953.2 23953.2 0.0 

H2O 4.5 4.5 0.0 4.5 4.5 0.2 4.3 4.3 64197.7 64H3N 954.5 954.5 0.0 954.5 954.5 42.9 911.6 911.6 0.0 CH4 161.3 161.3 0.0 161.3 161.3 7.3 154.1 154.1 0.0 C2H4 658.2 658.2 0.0 658.2 658.2 29.6 628.6 628.6 0.0 C3H6-2 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 AR 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 

C2H4O2-1 0.3 0.3 0.0 0.3 0.3 0.0 0.3 0.3 0.0 

C3H6O2-D 0.4 0.4 0.0 0.4 0.4 0.0 0.3 0.3 0.0 C7H8O2-E 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 C8H10O3 0.2 0.2 0.2 0.0 0.0 0.0 0.0 0.0 0.0 CH2O2 0.2 0.2 0.0 0.2 0.2 0.0 0.2 0.2 0.0 C10H12O3 0.8 0.8 0.8 0.0 0.0 0.0 0.0 0.0 0.0 

C6H6O 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 C7H8 0.1 0.1 0.0 0.1 0.1 0.0 0.1 0.1 0.0 
C5H4O2 0.9 0.9 0.0 0.9 0.9 0.0 0.9 0.9 0.0 

C6H6 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 CHAR 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 ASH 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 

WOOD 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 

Total Flow kg/hr 59881.6 59881.6 1.0 59880.6 59880.6 2693.7 57186.9 57186.9 64197.7 64Temperature C 33.1 7.0 7.0 7.0 105.6 105.6 105.6 700.0 4.0 Pressure psi 20.0 20.0 20.0 20.0 45.0 45.0 45.0 45.0 15.0 Enthalpy MJ/hr -345170.0 -347650.0 -2.9 -347650.0 -338140.0 -15211.3 -322930.0 -262630.0 -1035900.0 -1033

Table A6. Mass Balance for Section A6000. 
A4000 A4000 

QHX4004 

A3000 

A4000 

A9000 

7012

HX-7002 

QHX4002 

WP-7001 WTB7001 

QHX4003 

3010

TB7001

7005 HX-7003 CD-7001 B

7011

7003 7004

P-7001 HX-7001­

Q QHX7001X 

Q QHX7003X 

Q QCD7001

9001

QCD7001- 

QCD7001X 

Q 

7001 7002 

Figure A7

A7000 – Product Storage
3010 7001 7002 7003 7004 7005 7011 7012 7013 7014 90

Mass Flow kg/hr 

N2 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 O2 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 H2 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 

CO 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 CO2 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 H2O 1470.9 14106.5 14106.5 14106.5 14106.5 15577.4 15577.4 15577.4 467.3 15110.0 585

H3N 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 

CH4 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 C2H4 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 C3H6-2 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 

AR 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 

C2H4O2-1 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 

 C3H6O2-D 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 

C7H8O2-E 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 

 C8H10O3 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 

CH2O2 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 

 C10H12O3 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 

C6H6O 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 C7H8 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 
C5H4O2 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 

C6H6 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 CHAR 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 

ASH 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 

WOOD 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 

Total Flow kg/hr 1470.9 14106.5 14106.5 14106.5 14106.5 15577.4 15577.4 15577.4 467.3 15110.0 5851Temperature C 242.1 30.0 31.1 242.0 242.1 620.0 50.3 50.3 50.3 50.3 2Pressure psi 515.0 20.0 515.0 515.0 515.0 515.0 1.5 1.5 1.5 1.5 1Enthalpy MJ/hr -19275.6 -225850.0 -225720.0 -210610.0 -184860.0 -190850.0 -208740.0 -247880.0 -7436.3 -240440.0 -939270

Table A7. Mass Balance for Section A7000. 
A6000 

WCP-6001 

9002 

A7000 

9004 A5000 

9005 

W-9000 

W 

W-9001

W 

A3000 WCP-3001

A4000 WCP-4001

WP-5001 A5000 

W 

MIXER 

MX-9000 

MIXER 

MX-9001 

Figure A8

A9000 – Product Storage
0 0

0 0

0 0

0 0

0 0

0 0

9005 

Mass Flow kg/hr 9003 

9004 

N2 0 

O2 0 0 0 H2 0 0 0 CO 0 CO2 0 0 0 H2O 14804.79 14804.79 599912 H3N 0 CH4 0 0 0 C2H4 0 0 0

 C3H6-2 0 

AR 0 0 0 C2H4O2-1 0 0 0

 C3H6O2-D 0 

C7H8O2-E 0 0 0 

C8H10O3 0 0 0 CH2O2 0

 C10H12O3 0 0 0 

C6H6O 0 0 0 

C7H8 0 0 0 
0 0

0 0

15 15

C5H4O2 0 0 0 

C6H6 0 

CHAR 0 0 0 

ASH 0 0 0 

WOOD 0 

Total Flow kg/hr 14804.79 14804.79 599912 Temperature C 21.11111 35.11111 35.00334 Pressure psi 15 Enthalpy MJ/hr -237660 -236660 -9590200 

Table A8. Mass Balance for Section A9000. 
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November 2006 

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Technical Report 

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Large-Scale Pyrolysis Oil Production: A Technology Assessment 

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M. Ringer; V. Putsche, J. Scahill 

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BB067510 

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A broad perspective of pyrolysis technology as it relates to converting biomass substrates to a liquid bio-oil product 

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pyrolysis, bio-oil; biorefinery 

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