February 2005 • NREL/SR-510-37581 

TSS Consultants 

For the City of Gridley, California 

Gridley, California 

Gridley Ethanol Demonstration 

Project Utilizing Biomass 

Gasification Technology: Pilot 

Plant Gasifier and Syngas 

Conversion Testing 

August 2002—June 2004 

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
February 2005 • NREL/SR-510-37581 

Gridley Ethanol Demonstration 

Project Utilizing Biomass 

Gasification Technology: Pilot 

Plant Gasifier and Syngas 

Conversion Testing 

August 2002—June 2004 

TSS Consultants 

For the City of Gridley, California 

Gridley, California 

NREL Technical Monitor: M. Ruth 

Prepared under Subcontract No. ZCO-2-32065-01 

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
This publication was reproduced from the best available copy 

submitted by the subcontractor and received no editorial review at NREL 

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iii

TABLE OF CONTENTS 

I. PURPOSE OF THE REPORT......................................................................... 1

II. RELATED EVALUATION STUDIES........................................................ 1

III. BACKGROUND ................................................................................................ 1

A. RICE STRAW BURNING REDUCTION ACT OF 1991..................................................... 1 

B. THE PROPOSED GRIDLEY ETHANOL DEMONSTRATION PROJECT............................... 2 

C. GRIDLEY ETHANOL PROJECT OBJECTIVES ................................................................ 3 

D. BIOMASS GASIFICATION BASICS ............................................................................... 3 

IV. EXPERIMENTAL PLAN............................................................................... 4

V. DESCRIPTION OF THE PEARSON PILOT PLANT 

TECHNOLOGY........................................................................................................... 6

A. PILOT PLANT LOCATION ........................................................................................... 6 

Figure V-1 Regional Map of Mississippi................................................................. 7

Figure V-2 Local Map for Aberdeen, Mississippi and Location of Pearson 

Technologies Site ........................................................................................................ 7

Figure V-3 Aerial Photo of Pearson Technology Site (c. 1996).............................. 8

Figure V-4 Photo of Pearson Technology Site (May 2003) ..................................... 8

B. PEARSON TECHNOLOGY DESCRIPTION ...................................................................... 9 

C. DETAILED PROCESS DESCRIPTION........................................................................... 10 

Figure V-5. Pearson Technologies Process Flow Diagram................................... 11

D. FEEDSTOCK HANDLING SYSTEM ............................................................................. 12 

Figure V-6. Feeder for the Verdyol Bale Breaker ................................................... 14

Figure V-7. Conveyor from the Bale Breaker to the Hammer Mill......................... 14

Figure V-8. Schutte-Buffalo Hammer Mill at Verdyol Mulch of Canada................ 15

VI. ENERGY AND MASS BALANCE ANALYSES ................................. 16

A. RICE STRAW PROPERTIES........................................................................................ 16 

B. SYNGAS ENERGY BALANCE ANALYSES .................................................................. 16 

Table VI-1. Energy Content of Syngas Constituents................................................ 18

C. SYSTEM CARBON BALANCE ANALYSES (EXPERIMENTAL)...................................... 19 

D. ETHANOL MASS BALANCE ANALYSES (EXPERIMENTAL)........................................ 19 

Table VI-2. Physical Properties of Ethanol............................................................. 20

Figure VI-1. Determination of Ethanol Mass Balances (Experimental) ................ 21

E. ETHANOL MASS BALANCE ANALYSES (OPTIMIZED) ............................................... 21 

Table VI-3. The Composition of Syngas That Would Result from the ..................... 22

Conversion of all CO2 to CO .................................................................................... 22

Figure VI-2. Determination of Ethanol Mass Balances (Optimized) ..................... 23

F. ETHANOL MASS BALANCE ANALYSES (THEORETICAL)........................................... 23 

VII. CONCLUSIONS AND RECOMMENDATIONS .............................. 24

A. THE PILOT CONVERSION SYSTEM ........................................................................... 24 
iv

B. FEEDSTOCK CHARACTERISTICS THAT HAVE A NEGATIVE IMPACT ON THE CATALYST

....................................................................................................................................... 24 

C. CATALYST PERFORMANCE ...................................................................................... 25 

D. OTHER ISSUES: PEARSON FISCHER-TROPSCH PERFORMANCE IN CONVERTING 

SYNGAS TO ETHANOL .................................................................................................... 25 

E. FEEDSTOCK HANDLING PROBLEMS ......................................................................... 25 

F. CONDITIONS RECOMMENDED FOR THE PROPOSED DEMONSTRATION PLANT .......... 26 

G. ENERGY AND MASS BALANCE ANALYSES .............................................................. 27 

Table VII-1. Thermal Energy Efficiencies for the Conversion of Rice Straw to 

Various Products Using the Pearson Technologies System ..................................... 28

VIII. REFERENCES.............................................................................................. 30
 1

GRIDLEY ETHANOL DEMONSTRATION PROJECT 

UTILIZING BIOMASS GASIFICATION TECHNOLOGY 

PILOT PLANT GASIFIER AND SYNGAS 

CONVERSION TESTING

I. PURPOSE OF THE REPORT

This report is in response to Task 3 of the National Renewable Energy Laboratory 

(NREL) Subcontract No. ZCO-2-32065-01, that describes the Pearson Technologies 

Pilot Plant Gasifier and Syngas Conversion Testing for converting California rice straw 

into syngas and then the syngas into ethanol. The report on this task of the NREL 

Subcontract is part of an overall evaluation of using a modified Pearson Pilot Plant for 

processing rice straw into syngas and ethanol and the application of the Pearson 

technology for building a Demonstration Plant at Gridley. The Demonstration Plant 

would be located in the recently developed City of Gridley Industrial Park in Gridley, 

California (“Gridley”). This report also includes information on the feedstock 

preparation, feedstock handling, feedstock performance, catalyst performance, ethanol 

yields and potential problems identified from the pilot scale experiments. 

II. RELATED EVALUATION STUDIES

The evaluation of the Pearson technology, using rice straw for a proposed Demonstration 

Project at Gridley, is being conducted through this initial NREL subcontract that overlaps 

with a more comprehensive evaluation under a related Department of Energy (DOE) 

Subcontract that is developing a feasibility study using information from this pilot plant 

data. The DOE Study includes milestones and go/no-go decisions as to proceeding with 

the proposed Demonstration Plant using the Pearson technology at the Gridley site. 

III. BACKGROUND

A. Rice Straw Burning Reduction Act of 1991

Approximately 500,000 acres of rice are harvested annually in California, resulting in 

the availability of approximately 1 million bone dry tons (BDT) of rice straw 

annually. The Rice Straw Burning Reduction Act of 1991 (AB 1378) mandated a 

reduction in rice straw burning by the year 2000 to no more than 25% of the planted 

acreage. The California rice straw burning phase-down has proceeded as required by 

the statutes, with growers burning less than the statute limitations. Other open field 

burning laws and regulations further limit the actual rice straw acreage burned 
 2

annually. The total rice acreage burned annually has declined from 303,000 acres in 

1992, the first year of the phase-down, to slightly less than 72,000 acres in 2002. 

The State of California enacted legislation in 1997 (SB 318 -Rice Straw 

Demonstration Project), to modify existing law to provide a pause in the phase down 

of rice straw burning. This legislation was necessary because anticipated commercial 

technologies that could utilize significant amounts of rice straw had not yet 

developed. This legislation established a fund to provide cost-sharing grants for the 

development by demonstration projects for new rice straw technologies. Since its 

establishment in 1997, the California Air Resources Board (CARB) has awarded $5 

million in funds to 10 recipients for demonstration and commercialization projects 

through the Rice Straw Demonstration Project Grant Fund. 

The Gridley Ethanol Project, through the efforts of the Rice Straw Cooperative, was 

able to take advantage of the program and received $380,000 as a 50% cost sharing 

grant to collect, transport and store 18,000 BDT of rice straw for this project during 

2000 and 2001. This grant allowed the Rice Straw Cooperative the opportunity to 

gain valuable experience in developing and operating a rice straw collection 

infrastructure. 

These grants were intended to support diversion of 50% or more of rice straw 

produced toward off-field uses by 2000, the legislative goal. Off-field uses could 

include, but were not limited to, the production of energy and fuels, construction 

materials, pulp, paper, and livestock feed. New technologies had not yet been 

sufficiently developed to achieve this goal. CARB reports that only 3–5 % 

(approximately 18,000 tons) of the rice straw grown in California is currently used 

off-field. The primary uses to date have been for cattle feed and for erosion control.

B. The Proposed Gridley Ethanol Demonstration Project

Gridley is located in the heart of California’s rice growing area and its economy is 

uniquely dependent on rice production and markets. In addition, Gridley operates a 

municipal utility, with responsibility for delivering electrical power to the 

community. The Gridley community, including local rice growers, initiated the 

Gridley Ethanol Project to solve a major rice straw disposal problem and help 

maintain the economic viability in Butte County and the greater Sacramento Valley. 

The proposed Gridley Ethanol Project will utilize rice straw to produce ethanol for 

the transportation fuel markets.

A viable market alternative to the disposal of rice straw will reduce the alternative 

disposal costs of the phase-down of rice straw burning for rice growers. One of the 

more promising technologies for producing a high value product is to convert rice 

straw into ethanol. The current technology utilized by Pearson Technologies, Inc. 

(Pearson) has the theoretical potential to annually produce 20 million gallons of 

ethanol from 113,000 BDT of rice straw, co-host process heat and/or electricity. 
 3

In the fall of 1997, a group of Butte County rice growers, the Gridley Vice Mayor, 

Tom Sanford, and TSS Consultants (TSS) began to evaluate the feasibility of a rice 

straw-to-ethanol facility. During March 1998, the Butte County rice growers formed 

the Rice Straw Cooperative to provide supplies of rice straw to potential commercial 

users. The goal of this Cooperative was to find a reliable market for the rice straw in 

Butte County and to develop the infrastructure and methods to collect and transport 

the rice straw to a location where it can be economically converted to products. To 

date, members of the Cooperative have baled over 45,000 tons of rice straw over a 

six-year period to gain knowledge and evolve the infrastructure and techniques 

needed to collect and store rice straw. 

The site for the proposed Gridley Ethanol Project is within the Gridley’s newly 

established Gridley Industrial Park. A 14.74 acre parcel located in the northeastern 

portion of the industrial park has been selected for the construction of this facility. 

Given the anticipated footprint of the ethanol production facility and associated 

infrastructure, it is estimated that approximately one month’s rice straw feedstock will 

be stored on this site. The supply plan envisions rice grower site storage at a few 

locations within the Butte County area. 

C. Gridley Ethanol Project Objectives

The primary objectives of the Gridley Ethanol Project are to: 

(a) Help preserve the Community’s agriculture economy in Butte County and 

adjacent areas. 

(b) Support continued rice farming in the Sacramento Valley by providing a practical 

straw disposal alternative to burning. 

(c) Create jobs, a new tax base and economic development in the Sacramento Valley. 

(d) Comply with the environmental legislative mandates to phase out most of the 

open field rice straw burning. 

(e) Annually produce up to 20 million gallons of ethanol, a clean transportation fuel, 

which can reduce tail-pipe emissions from California’s older in-use vehicles. 

D. Biomass Gasification Basics

A critical factor in the high-energy efficiency of the overall process is that of the 

gasifier (primary reformer). When any fuel is completely burned, all of its potential 

energy, or heating value (designated HP) in units of Btu/lb, is released as sensible 

(“can be felt”) heat (designated HS) that can be recovered for immediate use in a 

boiler, for example. In most established gasification processes, a fuel (wood or coal) 

is partially burned, leaving some gaseous products, while releasing a smaller amount 

of sensible heat, carried by the high temperature product gases. An established use 

for simple gasification is to pass the hot product gases directly to a closely coupled 
 4

boiler or gas turbine, to do useful work, like generating electricity. Here the overall 

efficiency is defined as HP of product gases + HS carried by gases) / (HP of fuel). For 

a well-designed system, the overall efficiency may approach that of a well-designed 

solid fueled boiler. The advantage of such designs is to use efficient gas-fired boilers 

or turbines with solid fuels. 

When steam is injected into such a gasifier, it reacts with the burning solid fuel, to 

produce more of the gaseous product, the primary reaction being carbon (C) plus 

water (H2O), yielding hydrogen (H2) and carbon monoxide (CO). This reaction is 

endothermic, consuming part of the sensible heat of combustion, HS, in effect 

converting it to more fuel value, HP, in the product gas. The sensible heat consumed 

in these reactions is a heat of reaction (designated HR), which reduces the overall 

efficiency, as a price paid for a richer fuel or syngas product. Overall thermal 

efficiencies of gasifiers are in the range of 50% to 75%. “Directly heated” is defined 

as that air or oxygen used to burn part of the fuel to provide the heat of reaction, HR. 

“Probably” means simply that most published results are based on developmental 

projects, in which engineering efforts to optimize process heat recovery are still 

relegated to future, hypothetical commercial plant designs. Published pilot plant 

results also have a common tendency to ignore the external heat supplied by electric 

heaters applied as an afterthought on pipes and reactors to offset heat loses inherent in 

small, non-optimized system designs. 

The Pearson system appears to handle heat recovery very well by recovering heat 

from the cooling of syngas and using that heat to help produce super-heated steam for 

the gasifier and for the gas straw dryer. 

IV. EXPERIMENTAL PLAN

Pearson has invested more than ten years of effort in developing their biomass to ethanol 

conversion technologies. Wood waste has been used as the primary biomass feedstock 

for this development process. The accomplishments and knowledge gained from these 

prior efforts was applied in this NREL subcontract to determine the differences in the 

chemical and physical properties of the rice straw compared to wood on: 

1. Biomass Processing – Rice straw is a very fibrous material that contains 15-17% 

silica, which is problematic in the physical processing of the straw. The first 

objective was to explore and test rice straw processing equipment that can 

produce material that has a diameter of less than 3/16”. 

2. Gasification and Reforming – The second objective was to determine if the silica 

would adversely affect the performance of the gasifier and to compare the syngas 

composition from the conversion of rice straw to wood. 
 5

3. Syngas Cleaning – The next objective was to determine if there are any particular 

problems associated with the removal of particles, water-soluble contaminants, 

Benzene, Toluene and Xylene (BTX), and high molecular weight hydrocarbons. 

4. Ethanol Production – The fourth objective was to determine the yield of ethanol 

from rice straw derived syngas. 

5. Task 2 Bench-Scale Tests – These gasification tests were used to help re-design 

the pilot plant for the efficient conversion of rice straw. 

A description of the Experimental Plan for testing Gridley rice straw in the Pearson Pilot 

Plant facility located in Aberdeen, Mississippi is presented below: 

1. Gridley would provide part of the funding to modify the existing Pilot Plant to run 

rice straw as a raw material. The funding source was the NREL Subcontract that 

provided up to $400,000 through a Sub-Tier Subcontract between Gridley and 

Pearson. Appendix C reflects the equipment purchased and installed under this 

Sub-Tier Subcontract. If the costs exceed the projected budget, Pearson agreed to 

cover the additional costs. 

2. Pearson has carried out more than ten years of Pilot Plant research and 

development, resulting in the accumulation of a large body of experimental data 

on the conversion of wood wastes to alcohols. The Task 2 bench scale tests 

produced qualitatively and quantitatively similar syngas from both wood and rice 

straw. On an ash free and moisture free basis, there were no significant chemical 

differences in syngas derived from rice straw wood from the Pilot Plant. As a 

result, original modifications to the Pilot Plant, developed as a result of the studies 

with wood, were retained. Exceptions to this include potential changes in the 

feedstock processing system, the dryer unit, and the Fischer-Tropsch (F-T) 

catalyst would be made using the same basic Pilot Plant processes. In addition, 

parts would be replaced, as needed and better instrumentation would be installed 

to better evaluate the results of the rice straw runs in the modified Pilot Plant. 

3. Gridley would provide the rice straw for the Pilot Plant run, using actual rice 

straw from the surrounding rice growing area in California. Approximately 34 

tons of Gridley area rice straw would be shipped to the Aberdeen, Mississippi 

Pilot Plant site. 

4. Specifications for running the rice straw through the Pilot Plant would be 

determined. Initially, the specifications used for processing wood wastes would 

be used: 3/16” minus particle size. Alternative rice straw handing and processing 

equipment would be evaluated for use in the Pilot Plant to process the rice straw. 

5. Pearson will provide Gridley with the technical data from processing the rice 

straw through the Pilot Plant to produce syngas and ethanol. The technical data 

will include energy and mass material balances of converting the rice straw into 
 6

syngas, and the syngas into ethanol. In the cases where the Pilot Plant cannot 

measure the processes on-line, estimates or calculated data will be provided and 

noted in the data. 

6. Gridley and its technical Sub-Tier Subcontractor, TSS, will evaluate the results of 

the technical data from the Pilot Plant run and identify: 

• Any specific feedstock characteristics that have a negative impact on the 

catalysts and any additional equipment required in the process design due to 

feedstock characteristics. 

• Provide a description of feedstock preparation, handling, and performance in 

the Pilot Plant. 

• Describe the catalyst performance in converting the syngas produced from 

rice straw into alcohols. 

• Describe problems that were identified in running the rice straw through the 

Pilot Plant, which might be significant in scaling up the Pearson technology to 

a Gridley Ethanol Demonstration Plant. 

• Describe the choice of conditions that would be used in scaling the Pilot Plant 

technology up to the Gridley Ethanol Demonstration Plant. 

V. DESCRIPTION OF THE PEARSON PILOT PLANT 

TECHNOLOGY

A. Pilot Plant Location

The Pearson facility is located in Aberdeen, Mississippi. Its physical location is 20088 

Norm Connell Drive, Aberdeen, MS 39730. It is located in the City of Aberdeen 

industrial park (the Aberdeen Port Facility) adjacent to the Tennessee-Tombigbee 

Waterway. 
 7

Figure V-1 Regional Map of Mississippi 

Figure V-2 Local Map for Aberdeen, Mississippi and Location of Pearson 

Technologies Site
 8

Figure V-3 Aerial Photo of Pearson Technology Site (c. 1996) 

Figure V-4 Photo of Pearson Technology Site (May 2003)

Pearson 

Technology 

Facility Area 
 9

B. Pearson Technology Description

Stan Pearson, the founder of Pearson Technologies, Inc., has carried out research 

efforts to develop technologies for the conversion of biomass material into syngas and 

the syngas into ethanol since the early 1990’s. As a result, Pearson has developed a 

system for the production of syngas, electrical power and ethanol using a unique 

combination of gasification and steam reforming processes. In addition, Pearson 

developed proprietary F-T catalysts to convert syngas to ethanol. 

The Pearson process is a versatile process for converting biomass material to syngas 

and/or liquid fuel products by a combination of steam reforming (gasification) of solid 

feed and a F-T series of gas reforming steps. The specific design converts ground 

waste wood, sawdust or rice straw into fuel grade ethanol as its end product. 

Wood or straw, as received, is dried to a moisture content of about 15%, and ground 

fine enough (~ 3/16”) to be fed, along with superheated steam, into a gas-fired primary 

reformer. The reformer is externally heated, so that the product gas is not diluted by 

nitrogen from the combustion air. Air is also removed from the injected rice straw to 

minimize dilution of the syngas product with nitrogen. The organic material in the 

feedstock is efficiently gasified (>98% conversion efficiency), leaving only the 

inorganic materials (ash). The raw syngas then passes through a series of five different 

cleaning steps to remove any ash or tars (e.g. heavy hydrocarbons) that could be 

detrimental to downstream catalyst beds or processing equipment. 

The clean gas is next compressed to a high pressure, and passed through the series of 

F-T reaction stages, where the ratio of H2 to CO is adjusted to an optimum for reaction 

to ethanol. During this process, surplus H2, methane (CH4), and carbon dioxide (CO2) 

are separated using a Pressure Swing Absorption system (PSA) and recycled to 

appropriate points in the process. As a result, there are no by-product vent streams, so 

that up to 100% of the feed C content can be converted theoretically to syngas and or 

ethanol. The emissions are surplus water, mainly as clean vapor from the cooling 

steps. Multiple alcohols are produced and sent to a distillation column for separating 

the ethanol from methanol, water and other (higher molecular weight) alcohols. The 

final product is 95% ethanol, which can be run through a silica gel column to produce 

a 99% fuel grade ethanol. 

F-T technology has been in commercial use for decades, in the chemical and refining 

industries, most notably to produce gasoline and diesel fuel from syngas produced by 

coal gasification. The process design differences among F-T products are primarily a 

result of changes to process pressure, temperature and use of custom catalysts, to 

adjust chemical reactions and produce the desired product. Pearson has spent years 

developing proprietary catalysts to maximize ethanol production in this process. The 

operating temperatures and pressures are also proprietary information, developed over 

recent years of research by Pearson. 
 10

The overall process used standard chemical engineering design practice from the 

chemical industry, to maximize recovery of excess heat and generate the required 

steam, minimizing natural gas consumption. A proprietary design for the gasifier 

resolves earlier problems with indirect feed heating, provides the heat of reaction to 

convert wood (cellulose and lignin) to syngas, without having to burn the wood or 

straw and dilute the syngas with nitrogen. This, plus pressurized operation, results in 

smaller gas volumes and much smaller equipment. Even though this results in higher 

unit costs of high-pressure vessels and piping, the overall effect is lower total 

equipment costs. Another critical design feature is the use of multiple, redundant gas 

cleaning operations, to protect the downstream systems (e.g. catalysts) in the event of 

gasifier malfunctions. 

C. Detailed Process Description

Based on an abbreviated flow sheet received from Pearson, plus additional verbal 

information, the Pilot Plant process flow diagram (Figure V-5) was developed to 

describe the process in more detail, and to confirm the essential validity of the original 

assumptions. Complete material and energy balances are not however possible here, 

because many process parameters, such as temperatures and pressures, are proprietary 

and not cleared for presentation in this document. 

This process is unique in being substantially more complex in the number of 

processing steps, than other biomass to syngas and ethanol conversion technologies. 

This additional complexity is in the following areas: 

1. Drying of the rice straw to ~15% moisture and the subsequent addition of 

moisture as super-heated steam to the gasifier/reformer. 

2. The injection of used oil from the oil scrubber into the gasifier/reformer. 

3. The PSA system for removal of CO2 from the syngas. 

4. The addition of un-reacted H2 and CO from the catalyst to the compressor. 

5. The addition of fractionated methanol from the distillation column to H2 and CO 

in the compressor. 

6. The addition of fractionated water and other alcohols from the distillation column 

into the process feed water used for super-heated steam production. 
 11

Figure V-5. Pearson Technologies Process Flow Diagram 

This following section is a detailed description for each step of the Pilot Plant process 

flow diagram illustrated in Figure V-5. The straw is received at a moisture level of 15-

65% and ground to particles of 3/16” or less and then dried to approximately 15% 

water content. 

The processed rice straw is injected into the gasifier/reformer with super-heated steam. 

The super-heated steam also contains some recycled water and other alcohols from 

storage tanks. The rice straw-feeding device is a commercially available unit that is 

complementary to Pearson’s proprietary configuration of the gasifier. 

The gasifier is indirectly heated by burning natural gas, so that the product gas is not 

diluted by nitrogen from the natural gas combustion product stream. The feeder, the 

gasifier and all downstream components operate at a pressure high enough to result in 

a substantial reduction in the size of piping, vessels and other components. 

Silica, metal oxides, traces of elemental C and higher molecular weight hydrocarbons 

are collected as ash. 

The hot, raw syngas is cooled in the steam production/heat recovery system and the 

recovered heat is used to produce super-heated steam and lower-grade heat for drying 

the rice straw. 

The partially cooled gas then passes through a cyclone to remove particles that are 

greater than 5-10 um in size and then through a High Efficiency Particulate Air 

(HEPA) filter to remove particles down to about 0.5 um. It then passes through a 

counter-current water scrubber where water-soluble components are removed. The 

cooled syngas gas is further cleaned by scrubbing with a circulating stream of light 

petroleum oil, which absorbs BTX and heavier hydrocarbons that may have been 

formed during gasification. A small amount of oil is periodically sent to the gasifier to 

keep the oil from becoming saturated with BTX and higher molecular weight 

Rice Straw 

Processing 

Rice Straw 

Gasification Ash 

Syngas

FischerTropsch 

Catalyst

Ethanol, other 

alcohols, and 

Water 
 12

hydrocarbons. At this point, the clean, dry gas is about half CO2 by weight, the rest 

being a mixture of H2, CO, methane and ethane. 

It is not possible that the F-T catalyst could produce a single product (ethanol in this 

case) with one pass. Therefore, in order to increase the yield of ethanol, it is necessary 

to separate the products (methanol) by distillation and re-introduce the methanol with 

the H2 and CO at the compression stage. According to the Pearson team, the nearly 

complete conversion of the methanol to ethanol may require recycling up to 7 or 8 

times. 

These products are cooled and collected in a condenser and fractionated using a 

distillation column into three fractions: 1) methanol, 2) ethanol (95%) and an aqueous 

solution of the remaining alcohols. The excess H2 and CO is separated from the 

aqueous phase and recycled back to the compressor. 

The flow diagram shows no water entering the process except for the moisture in the 

rice straw. Recycled water, condensed from the various process streams, appears to be 

adequate to generate the steam needed. However, there are also some cooling water 

requirements not shown, and all or most of the water will be combined at a cooling 

tower, where most of the excess process heat will be rejected, with substantial 

evaporation losses. Thus a small but highly variable supply of make-up water will be 

available if required. 

D. Feedstock Handling System

Gridley shipped two truckloads of rice straw to the Pearson Pilot Plant. The rice straw 

was left uncovered during this winter, causing the moisture to increase from 15% to 

40-60+%. This created additional challenges in processing the rice straw at these 

moisture levels. However, this is reflective of the actual problems of rice straw being 

harvested late in the summer/fall season and subjected to rain before being covered. 

For Pearson’s system, the rice straw must be processed through a hammer mill with a 

3/16” screen. Pearson purchased and tested two different feedstock units that 

processed the rice straw into 3/16” minus form for the gasifier unit. 

1. Schutte-Buffalo Equipment 

Pearson first selected and purchased a hammer mill manufactured by SchutteBuffalo (Schutte) located in Buffalo, NY. Schutte has manufactured size 

reduction equipment since 1928. TSS contacted Schutte to find locations 

where Schutte hammer mills were successfully processing straw. After 

research by Schutte, they could locate only one company processing straw 

with their hammer mill. This company is Verdyol Mulch of Canada 

(Verdyol) located in Cookstown, Ontario, approximately one hour north of 

Toronto. Verdyol has been a leading manufacturer of erosion control products 
 13

since 1976. The hammer mill purchased by Verdyol is used for processing 

wheat straw to create a mulch product. 

Verdyol uses a bale breaker to preprocess the straw before it is fed into the 

hammer mill (Figure V-6). They have successfully processed wheat straw 

through their hammer mill while using a 1 - inch screen to produce a product 

ranging in size from 1⁄2 to 2 inches in length (Figures V-7 and V-8). They 

have had limited experience using a 3/16th inch screen as Pearson would 

require. They found that production was very slow and the screen had a 

tendency to plug. 

In order to achieve optimum throughput with the hammer mill, Tom Warren, 

President of Schutte recommended that straw be preprocessed to lengths 

ranging from 30 – 40% of the width of the opening of the hammer mill to 

increase the likelihood that the material will flow freely and not bridge. In the 

case of the Model 2410 hammer mill purchased by Pearson with an opening 

10 inches wide, this would equal straw lengths of 3 – 4 inches. Feeding straw 

into a hammer mill with this limited opening is not conducive to optimum 

production. 

The manufacturer’s estimate of production through this hammer mill is 80 – 

85 pounds per horsepower (HP)/hour through a 3/16” inch screen with air 

pulling the material through. Without air, the production would be reduced 

significantly. The hammer mill purchased by Pearson was a 25 HP system. It 

is estimated that production could be as high as 2,000 pounds per hour or as 

low as 500 pounds per hour. 

This unit worked on low moisture (15%) rice straw, but bridging problems 

occurred on the higher moisture straw. If this unit were to be used on the Pilot 

Plant, it would probably require drying the straw before being processed 

through the Schutte unit as the rice straw with higher moisture content would 

likely bridge and clog trying to enter the rice straw processing input system. 
 14

Figure V-6. Feeder for the Verdyol Bale Breaker 

Figure V-7. Conveyor from the Bale Breaker to the Hammer Mill 
 15

Figure V-8. Schutte-Buffalo Hammer Mill at Verdyol Mulch of Canada 

2. Marathon Equipment 

After limited success utilizing the Schutte hammer mill, Pearson selected a 

similar sized grinder manufactured by Marathon Equipment (Marathon) 

located in Vernon, Alabama. The feed opening is 10” x 11”, operated with a 

25 HP motor and utilizing a 3/16th inch screen. Pearson took a large bale of 

rice straw (approximately 900 lbs.) to Marathon for evaluating with their 

processing equipment. Marathon modified some of their equipment and 

produced a unit that was tested and installed at the Pilot Plant. This Marathon 

unit readily processed the rice straw, even at the very high moisture rates of 

40 – 60%, into 3/16” minus material without clogging and without requiring 

pre-drying of the rice straw to 15% moisture or less. 

TSS’s observation of the end product indicated that the Marathon grinder 

worked well in processing rice straw utilizing a 3/16th inch screen size. 

Production data was not available from the manufacturer; however, TSS 

estimates that the production through this grinder should be similar to the 

Schutte hammer mill. 
 16

Marathon announced as of January 30, 2004, they have discontinued the 

manufacture of all size reduction equipment. TSS contacted Marathon about 

the availability of spare parts. They indicated that they would be available for 

some time and that any structural components could be manufactured. 

There is still a need to evaluate the scale-up of the Marathon unit and other 

similar processing systems that would be viable in a full-scale commercial 

facility. This is being done as part of the DOE Feasibility Study Subcontract. 

VI. ENERGY AND MASS BALANCE ANALYSES

This section describes results from the 400 lbs/hr (4.8 ton/day) pilot system developed for 

validation of their bench scale system (1). Energy, C mass, and total mass balance 

analyses are presented for the conversion of rice straw to electrical energy and/or ethanol. 

This analysis is based upon experimental data reported by Pearson to TSS. Theoretical 

calculations are used to estimate energy, C mass and total mass balances in those cases 

where experimental data is not available. 

A. Rice Straw Properties

The rice straw was received from the City of Gridley. The percent weight (wgt%) of 

organic material, inorganic material and water is 72%, 17% and 11%, respectively. 

Silica comprises 85-90% of the inorganic materials. The elemental composition (wgt 

%) of the organic material is 51% C, 5% H, and 44% O (Simmons, 2000). The 

energy content of the rice straw as received was 5,650 BTU/lb. The system described 

in this report used 9,600 lbs of rice straw as received. The rice straw is 72% organic 

material, of which 51% is C. Therefore, the mass of C in the biomass is 3,524 

lbs/day. 

B. Syngas Energy Balance Analyses

Water is added as superheated steam (0.18 lbs water/1.00 lbs rice straw) to optimize 

the chemistry of gasification. The steam reacts with the heated straw to enhance the 

production of CO and H2 as given in Equation VI-1. 

C + H2O → H2 + CO Eq. VI-1 

This reaction is endothermic (requires heat), consuming part of the sensible heat of 

combustion, but in effect converting the syngas products to a higher heating value. 
 17

The primary reformer is externally heated to minimize dilution with nitrogen. The 

reformer plays an important role in sustaining a high-energy efficiency for the overall 

system. 

The thermal efficiency of the Pearson system was estimated to be 70%. At this 

efficiency, the actual energy output is 3.80 x 10+7 BTU/day (5.42 x 10+7 BTU/day x 

0.70). Since the energy content of the syngas was 322 BTU/ft3

, then the syngas 

output was 1.18 x 10+5 ft3/day. Therefore, the mass of the syngas generated each day 

is 9,886 lbs as derived from the following calculation, where 13.66 g/mole is the 

average molecular weight of the syngas:

(1.18 x10+5 ft3

)(28.3 L/ft3)(13.66 g/mole)/(22.4 L/mole)(206 g/lbs) = 9,886 lbs. 

Excess H2, CH4 and CO2 are separated and recycled to appropriate points in the 

process. As a result, there are no by-product vent streams, so that 100% of the C in 

the rice straw could be theoretically converted to ethanol. The only emissions are 

clean water vapor generated from the cooling steps. 

The theoretical energy output of the system for the production of syngas is 54.2 

MMBTU if all of the organic material in the rice straw could be converted to syngas 

with 100% efficiency. External energy is needed to run the system. Natural gas (9.76 

MMBTU) and electricity (2.71 MMBTU) comprise the external energy requirement. 

The Pearson system utilizes heat recovered from the gasifier and ethanol production 

to help provide energy for system operation. The energy recovered and reused from 

the gasifier (16.6 MMBTU) and the exothermic production of ethanol over the F-T 

catalyst (6.7 MMBTU) results in 23.3 MMBTU of recovered energy that is 

effectively re-used for the processes. 

There are a number of processes in which energy can be lost. These processes 

include heat lost to the environment (assumed to be less than 1.0 MMBTU), 

endothermic energy required for chemical processes, and other energy losses, such as 

friction and gas expansion. Additional energy demands need to be factored in for a 

commercial sized system. Such energy demands include heating and cooling 

processes that are not reflected in the Pilot Plant, a major network of steam and water 

lines plus a variety of heat exchangers in a commercial size plant, a venting of surplus 

CO2 to the atmosphere, etc. Even though these energy demand values are not known, 

their impact will be reflected in the percent (%) energy efficiency for syngas 

production. Therefore, the total energy losses and energy demand for a scaled up, 

commercial system are not included in the energy balance analysis. 

The energy content of the syngas can be determined by determining its composition 

and volume. Hydrogen and CO are low energy constituents with energy contents of 

301 BTU/ft3 and 353 BTU/ft3, respectively, at conditions of standard temperature and 

pressure (Table VI-2). 
 18

Table VI-1. Energy Content of Syngas Constituents 

Methane: 1000 BTU/ft3 @STP 

Hydrogen: 301 BTU/ft3 @STP 

Carbon Monoxide: 353 BTU/ft3 @STP 

The energy content of the syngas is determined from equation VI-2 by multiplying the mole% 

of each constituent in the syngas by the energy content of each respective constituent. 

CH4 + H2 + CO + (>C1) HC’s = 322 BTU/ft3

(0.07)(1000) (0.63)(301) (0.12)(353) (0.02)(1000) (Eq. VI-2)

The resulting energy content of the syngas is 322 BTU/ft3. This is a typical value for 

syngas derived from the gasification of biomass. 

In this manner the energy content of the syngas was determined to be 47.0 MMBTU. 

Since no electricity was generated from this system, there is no recovered heat and. 

Therefore, the energy content of the syngas will be 47.0 MMBTU. 

The efficiency for heat recovery from the primary process is determined from 

Equation VI-3.

(Recovered Energy) / (Energy Input + Recovered Energy) = 25.9% (Eq. VI-3) 

The energy efficiency for syngas production is determined from Equation VI-4. 

Energy Efficiency for Syngas Production = (Energy Content of Products/Energy 

Input) = 70.5% (Eq. VI-4) 

Therefore, the total energy efficiency of the primary process is (25.9% + 70.5%) or 

96.4%.

A calculation was carried out to determine the thermal energy efficiency for the 

production of electricity using a reciprocating internal combustion (IC) engine. The 

average thermal efficiency for a modern IC engine generator, operating on syngas 

fuel with an energy content of 300 BTU/ft3

 or higher, is 40%. Therefore, the thermal 

efficiency can be determined from Equation VI-5 and the values for energy content of 

syngas and energy input. 

Energy Content of Electricity = Conversion of Syngas to Electricity = (Energy 

Content of Syngas)*(0.40) = 18.8 MMBTU (Eq. VI- 5)

Energy Efficiency for Electricity Production = Energy Content of Electricity/Energy 

Input = 28.2% 
 19

C. System Carbon Balance Analyses (Experimental)

Ethanol is produced from the reaction of H2 and CO in the presence of a F-T type 

catalyst developed by the Pearson group. 

Since the yield of ethanol in the F-T process is dependent upon the ratio of H2 to CO 

as shown in Equation VI-6, it is necessary that this ratio be optimized. 

2CO + 4H2 → H-CH2-CH2OH + H2 O (Eq. VI-6)

Pearson found that the H2/CO ratio can be adjusted somewhat by changing the 

residence time of gaseous products in the reformer. This is in part due to the chemical 

kinetics and thermodynamics of the water-gas shift reaction in Equation VI-7. 

CO + H2 O ↔ CO2 + H2 (Eq. VI-7)

However, the syngas composition data shows that the H2/CO ratio still needs to be 

adjusted. Therefore, a PSA unit (Quest Air Technologies, Burnaby BC, Canada) was 

recently added to help control the H2/CO ratio. 

Since CO represents 24.6 wgt% of the total syngas C, then the total ethanol C that can 

be produced is calculated from Equation VI-8. 

Carbon Content of Ethanol (experimental) = (24.6% C)(Carbon Content of Syngas -

3,524 lbs/day) = 867 lbs/day (Eq. VI- 8)

The C content of other syngas constituents is determined from Equation VI-9 where 

the C content of these other constituents represents 73.5 wgt% of the total C. 

Carbon Content of Methane (experimental) = (75.4 wgt% C)(Carbon in Syngas -

3,524 lbs/day) = 2657 lbs/day (Eq. VI- 9) 

The mass of C in the biomass (3,524 lbs/day calculated in VI-A) is in excellent 

agreement with the total mass of C calculated from the syngas composition (3,560 

lbs/day), a 99% agreement. The mass of C in the biomass (3,524 lbs/day) will be 

used for all subsequent calculations. 

D. Ethanol Mass Balance Analyses (Experimental)

The total mass and volume of ethanol is calculated from the physical data for ethanol 

in Table VI-4 and equation VI-10. 
 20

Table VI-2. Physical Properties of Ethanol 

Density (Specific Gravity) 0.789 g/cc 

Mass/Gallon 2.99 Kg/gallon 

Mass/Gallon 6.57 lbs/gallon 

Carbon Content 52.2 wgt% 

Energy Density 75,551 BTU/gallon 

Energy Density 11.5 MMBTU/kg 

Energy Density 5.22 MMBTU/lb 

Since the C content of ethanol is 52.2 wgt%, then the maximum amount of ethanol 

that can be produced from the experimentally produced syngas is 1996 lbs/day or 

303.8 gallons/day. Therefore, the yield of ethanol per ton of rice straw feedstock is 

303.8 gallons/day) / (4.8 tons/day of rice straw) or 63.3 gallons/ton. 

M9 (1,042 lbs/day) / (0.522) = 1996 lbs/day (Eq. VI-10) 

 = 303.8 gallons/day 

 = 63.3 gallons/ton of rice straw 

The energy content for this volume of ethanol is calculated and tabulated in Figure 

VI-4 as follows: 

Energy Content of Ethanol Produced = (303.8 gallons/day)(75,551BTU/gallon) 

 = 22.95 MMBTU 

Therefore the % energy efficiency for ethanol production is: 

Energy Content of Ethanol/Energy Input*100 or 34.5% 

Figure VI-1 summarizes the results of the experimental ethanol mass balance 

analyses. 
 21

Figure VI-1. Determination of Ethanol Mass Balances (Experimental) 

M1

(Mass Input)

M3 & M4 (Mass of 

Emissions and Ash)

M5 (Mass of Primary 

Products-Syngas)

M9

(Mass of Ethanol)

M1 (6,910 lbs/day) 

(Organic Mass Input) = 

M2 (9,600 lbs/day) 

*(0.72) (Feedstock Mass 

x %Organics/100)

 

M5 (9,886 lbs/day) 

(Mass of Syngas) = 

M1 (6,910 lbs/day) 

(Organic Mass Input) + 

M3 (2,976 lbs/day) 

(Addition of H and O 

from Water) - 

M4 (Not Known) 

(Mass of Carbon 

Compounds in Ash)

M9 (1,996 lbs/day) 

(Mass of Ethanol) = 

M7 (5,730 lbs/day) 

(Mass of Secondary 

Products) - 

M6 (2,778 lbs/day) 

(Mass of CO and H2 used 

for Ethanol Production 

(100% Conversion) - 

M8 (0.0) 

(Mass of Syngas Used 

as a Process Fuel)

E. Ethanol Mass Balance Analyses (Optimized)

If the ratio of H2/CO can be adjusted by the water-shift reaction (Equation VI-11) to 

produce additional CO from the CO2, then CO would represents 67.8% of the total C 

present in the syngas (Table VI-3) that could optimally be converted to ethanol. 

Therefore, the total ethanol that can be produced optimally is calculated from 

Equation VI-11. 

Carbon Content of Ethanol (optimized) = (68.3% C)(3,524 lbs/day) = 2406 lbs/day 

 (Eq.VI-11) 
 22

Table VI-3. The Composition of Syngas That Would Result from the 

Conversion of all CO2 to CO

Component Mole % Weight % C Weight%1 C Weight%2 

Methane 8.4 10.4 7.8 16.7 

Hydrogen 55.7 8.6 0.0 0.0 

Carbon Monoxide 33.4 72.4 31.0 67.8 

C2-C4 Hydrocarbons 

(Assumes average 

molecular weight = 44) 

2.5 8.5 7.0 15.5 

Carbon Dioxide <1% <1% <1% <1% 

Nitrogen <1% <1% <1% <1% 

 

Total 100 100 45.8 100 

1 Expressed as weight% of total syngas mass 

2 Expressed as weight% of total carbon in syngas

The total mass and volume of ethanol is calculated from the physical data for ethanol in 

equation VI-12. 

Carbon Content of Ethanol (2,393 lbs/day) / (0.552 wgt% C) = 4336 lbs/day (M9) 

 = 704.7 gallons/day 

 = 137.4 gallons/ton 

 (Eq. VI-12)
 23

Figure VI-2 summarizes the results of the optimized ethanol mass balance analyses. 

Figure VI-2. Determination of Ethanol Mass Balances (Optimized) 

M1

(Mass Input)

M8 

(Mass of Air Emissions)

M5 

(Mass of Primary ProductsSyngas)

M9

(Mass of Ethanol)

M1 (9,600 lbs/day) 

(Mass Input) = 

M2 (9,600 lbs/day) 

(Feedstock Mass)

 

M5 (7,872 lbs/day) 

(Mass of Syngas) = 

M1 (9,600 lbs/day) 

(Mass Input) - 

M3 (Assume 0.0 

lbs/day) 

(Mass of Emissions) -

M4 (1,728 lbs/day) 

(Mass of Ash)

M9 (4,336 lbs/day) 

(Mass of Ethanol) = 

M5 (7,872 lbs/day) 

(Mass of Syngas) -

M7 (3,536 lbs/day) 

(Mass of Secondary 

Products)= 

M6 (4,336 lbs/day) 

(Mass of CO and H2)

F. Ethanol Mass Balance Analyses (Theoretical)

If the CH4 and C2-C4 hydrocarbons could also be converted to CO and H2 in the 

proper ratios, then the theoretical yield of ethanol can be calculated from Equation VI13. 

M9 (theoretical) = (100% C)(3,530 lbs/day)/(0.552 wgt% C) (Eq. VI-13) 

 = 6395 lbs/day

 = 6395 lbs/day/6.57 lbs/gallon = 973.4 gallons/day 

 = 973.4/4.8 tons = 202.8 gallons/ton
 24

VII. CONCLUSIONS AND RECOMMENDATIONS

Key conclusions and recommendations from this NREL contracted study are summarized 

in this section as follows. 

A. The Pilot Conversion System

The Pearson conversion system has been designed with standard chemical industry 

engineering practices. This design maximizes the recovery of process heat to 

generate the required steam and minimizes natural gas consumption. Its pressurized 

operation results in smaller gas volumes and thus smaller conversion vessels, which 

can significantly reduce the capital investment in the Demonstration Plant. 

B. Feedstock Characteristics That Have a Negative Impact on the Catalyst

There are potential problems in gasifying rice straw that could create problems in the 

F-T unit that produces alcohol. Following are the potential problem areas and finding 

from the Pilot Plant tests: 

1. The first potential problem is specific to rice straw as a raw material, in that 

there is a range of 9–19% silica in the California rice straw. Based on 

previous sampling done by TSS and others, the average silica content is 17%. 

In the Pearson Pilot Plant, this silica was removed in the gasification stage and 

was not incorporated into the syngas produced by the Pearson gasifier. 

Samples of the silica removed were taken and tested by a contract analytical 

laboratory. These samples are being further evaluated for use in commercial 

markets as part of the DOE Subcontract. The conclusion from running the 

rice straw through the Pearson gasifier is that silica is removed at an early 

stage before it reaches the F-T unit. It is not anticipated to be a problem with 

the F-T conversion of the syngas to alcohols.

2. Although it wasn’t detected, the syngas from the Pearson gasifier unit could 

produce some minimal volumes of particulate matter, oils and tars. Pearson 

has designed multiple cleanup systems in the pilot plant that would be used in 

the proposed Gridley Ethanol Demonstration Plant. These were removed by 

the following configuration of equipment that processed the syngas from the 

gasifier before the syngas proceeded to the F-T unit: 

a. A bag house and a cyclone were installed behind the gasifier to remove 

particulate matter. 

b. Both a water scrubber and an oil scrubber were installed behind the 

cyclone to remove any remaining oils and tars that could have 

contaminated the catalyst in the F-T unit. 

c. Three guard beds were installed to remove any remaining contaminants 

from the syngas before it enters the first reactor in the F-T unit. 
 25

All of these mitigation equipment systems are off the shelf technology from the coal 

gasification, oil refineries and power plant industries, where they are used for similar 

contaminant cleanup in producing their respective products. These cleanup 

equipment systems would be built into the proposed Gridley Demonstration Plant 

design. 

C. Catalyst Performance

The results of using the mitigation equipment referenced in Section B above, was that 

the syngas entering the F-T unit appeared to have no contaminants or poisons to 

interact with the catalyst during the Pilot Plant operation of producing alcohol from 

the syngas. The alcohols were produced in the F-T unit without observable 

deterioration of the catalyst. However, longer-term continuous runs of the F-T unit 

are needed to determine rates of deterioration of the catalyst. Some of the syngas 

from the rice straw processed in the Pearson gasifier was collected and stored in 

pressure canisters for longer-term runs with the catalyst to determine longer-term 

deterioration of the catalyst from any minor volumes of contaminants that may have 

been incorporated in the syngas. A smaller bench scale F-T unit was constructed for 

this longer term run. After more than 3,048 hours of continuous catalyst operation, 

no catalyst deterioration was detected for the conversion of syngas to alcohols. 

D. Other issues: Pearson Fischer-Tropsch Performance in Converting Syngas 

to Ethanol

In reviewing the existing Pearson Pilot Plant run of the rice straw, there is a problem 

in that the F-T unit produces a mixture of alcohols, rather than pure ethanol. The 

Pilot Plant has not been modified to allow recycling of these the other alcohols and 

their subsequent conversion to ethanol. Thus, it is TSS’s opinion that more 

development work will be needed before the Pearson technology can be scaled up to a 

commercial operation. 

E. Feedstock Handling Problems

Gridley shipped two truckloads of rice straw to the Pearson Pilot Plant. The rice 

straw was left uncovered during this winter, causing the moisture to increase from 

15% to 40-60+%. This created additional challenges in processing the rice straw at 

these moisture levels. 

Pearson purchased and tested two different feedstock-processing units that processed 

the rice straw into 3/16” minus form for the gasifier unit. The first unit was a Schutte 

unit. This unit worked on low moisture (15%) rice straw, but bridging problems 

occurred on the higher moisture straw. If this unit were to be used on the Pilot Plant, 
 26

it would have required drying the straw before being processed through the Schutte 

unit and rice straw with higher moisture content would likely bridge and clog trying 

to enter the rice processing unit. 

A second unit, custom made by Marathon was evaluated and purchased. This 

Marathon unit readily processed the rice straw, even at the very high moisture rates of 

40 – 60%, into 3/16” minus material without clogging and without pre-drying of the 

rice straw to 15% moisture or less. There is still a need to evaluate the scale-up of the 

Marathon unit and other similar processing systems that would be viable in a fullscale commercial facility. This is being done as part of the DOE Feasibility Study 

Subcontract. 

F. Conditions Recommended For the Proposed Demonstration Plant

Based on the results of evaluating the technical data from the Pearson Pilot Plant 

running rice straw, the following conditions are recommended for the proposed 

Gridley Ethanol Demonstration Project: 

1. The gasifier module unit does not have to be scaled up to a larger size; rather 

the modules would be replicated to reach the desired size of the 

Demonstration Plant. This is a common practice in the chemical industry, to 

pilot test the exact commercial module that would be used in a commercial 

facility. This eliminates the significant scale-up risk from smaller units to 

multiple size vessels. 

2. Although the gasifier and F-T units will be replicated modules of the Pilot 

Plant, the front end rice straw receiving, breakdown and processing systems 

should be scaled up to provide central processing to the gasification modules. 

Further analysis should be done to determine whether the rice straw 

processing train should be one or a few separate systems feeding into the 

various gasification modules. 

3. The increasing costs of natural gas and electricity suggests that further 

evaluations of the tradeoff in using part of the syngas to produce electricity 

and or process steam and heat should be conducted to determine if it is more 

cost effective. Such an economic analysis should be carried out for various 

production scenarios as the proposed City of Gridley site. 

4. The F-T catalyst is expensive and the lifetime of this catalyst needs to be 

evaluated over sufficient periods of operating time. Pearson is continuing to 

run the rice straw derived syngas to better evaluate catalyst deterioration. The 

results should be available before completing the DOE Feasibility Study 

Subcontract. 
 27

5. The major economic driver appears to be cost of raw material. The syngas 

derived from rice straw and wood waste showed negligible differences in 

chemical composition when compared on an ash-free and moisture free basis. 

Since the delivered cost of rice straw is typically higher than some forms of 

wood wastes, it is recommended that further economic and operational 

analysis be carried out to determine the benefits of mixing wood waste with 

rice straw. 

6. A more comprehensive evaluation needs to be carried out to determine if the 

mixture of alcohols generated from the F-T catalyst could be sold to a 

refinery, or if the only marketable product would be a fuel-grade ethanol. 

Since existing oil refineries have the capacity to do large scale conversion of 

the multiple alcohols potentially at significantly lower costs in their larger 

facilities than in the smaller demonstration units, there may be an economic 

tradeoff to reducing the capital investment and operating costs in a second 

reactor in the F-T unit. This should be investigated in scaling this technology 

up to the Gridley Ethanol Demonstration Project size. This will be evaluated 

in the DOE Feasibility Study Subcontract. 

7. During the term of this NREL contract, the market place has changed 

significantly, particularly in the areas of wholesale prices of natural gas and 

gasoline. These new wholesale energy prices make renewable technologies, 

such as the Pearson technology, more competitive as a substitute for natural 

gas or as an extender of gasoline. In addition to use of ethanol as an 

oxygenate, the gasoline distributors are interested in gasoline extenders that 

can reduce their wholesale price of gasoline. This is a new potential market 

opportunity that is being evaluated in the DOE Feasibility Study Subcontract. 

8. Recent discussions with Pearson have indicated they will make available a 

process engineering study, which will further elaborate on the commercial 

viability of the Pearson technology. This process engineering study will be 

evaluated in the DOE Feasibility Study Subcontract. 

G. Energy and Mass Balance Analyses

Table VII-1 summarizes the results of the energy and mass balance study for the 

conversion of rice straw to syngas, and the conversion of the syngas to electricity or 

ethanol. 
 28

Table VII-1. Thermal Energy Efficiencies for the Conversion of Rice Straw to 

Various Products Using the Pearson Technologies System 

Products Syngas Recovered 

Heat (from 

gasifier)

Electricity 

(IC Engine) 

Combined 

Heat/Power 

(CHP) 

Ethanol 

Thermal 

Efficiency 

(%)

70.5% 

(Experimental)

25.9% 

(Experimental)

28.2% 

(Theoretical)

42.3% 

(Theoretical) 

34.5% 

(Experimental)

74.7% 

(Optimized) 

110.3% 

(Theoretical)

The thermal efficiency for conversion of the rice straw to syngas was found to be 

70.5%. Another 24.9% of thermal energy (as heat) is recovered and used for the 

conversion system. Pearson has previously reported that the hot gas efficiency or 

higher heating value (HHV) was 89% and the cold gas efficiency or lower heating 

value (LLV) was 81% for studies carried out for the conversion of wood.

The thermal energy efficiency was calculated for the possible production of 

electricity using a reciprocating IC engine running at 40% thermal efficiency on the 

syngas mixture, optimized for engine operation. It was determined that the 

theoretical thermal efficiency for electricity production would be 28.2% (70.5% x 

40.0%). 

Assuming that a reciprocating IC engine with a combined heat and power capability 

(CHP) can operate at 60% thermal efficiency, then the resulting CHP thermal 

efficiency is 42.3% (70.5% x 60.0%). 

Table VII-1 summarizes the production of ethanol from syngas using three scenarios. 

These scenarios assume that all of the CO in the syngas is converted to ethanol with 

100% efficiency. 

Scenario 1 is for the production of ethanol from the syngas generated experimentally 

from the gasification of rice straw. Ethanol (63.3 gallons/ton of rice straw) will be 

produced with a mass efficiency of 28.9% and a thermal energy efficiency of 34.5%. 

Scenario 2 is for the production of ethanol from syngas that has been optimized for 

the production of H2 and CO. In this case, ethanol (137.4 gallons/ton of rice straw) 

will be produced with a mass efficiency of 67.8% and a thermal efficiency of 74.7%. 
 29

Scenario 3 is the theoretical (maximum) efficiency for the production of ethanol from 

the syngas. Ethanol (202.8 gallons/ton) will be produced if 100% of the C in the rice 

straw can be converted to ethanol C with 100% thermal efficiency (Scenario 3). 

It may be possible to produce ethanol with a mass and energy efficiency somewhere 

between that of Scenario 1 and Scenario 2 with optimized chemical engineering and 

design practices. 

The theoretical energy efficiency (Scenario 3) analyses provided a value of 110.3%. 

This is a reasonable theoretical efficiency since several measurements and physical 

parameters were used to derive this value. It is also possible that since this efficiency 

is dependent upon the input energy to the system (energy content of biomass, external 

electrical and external heat from natural gas), then it could be that more external 

(electricity and/or natural gas) energy could have been input into the system than 

expected. 

The lower ethanol yields of the experimental pilot plant levels versus the higher 

yields reflected in the optimized and theoretical scenarios summarized above would 

likely result in a significant stream of surplus CO2 will be vented to the atmosphere. 
 30

VIII. References

Simmons, M.D., “Fundamental Properties of Rice Straw in Comparison with 

Softwoods,” ESPM 286 Final Report, University of California – Davis” (Dec. 21, 2000). 
F1146-E(12/2004) 

REPORT DOCUMENTATION PAGE Form Approved 

OMB No. 0704-0188

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currently valid OMB control number. 

PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ORGANIZATION.

1. REPORT DATE (DD-MM-YYYY)

February 2005 

2. REPORT TYPE

Subcontract Report 

3. DATES COVERED (From - To)

August 2002 - June 2004 

5a. CONTRACT NUMBER

DE-AC36-99-GO10337 

5b. GRANT NUMBER

4. TITLE AND SUBTITLE

Gridley Ethanol Demonstration Project Utilizing Biomass 

Gasification Technology: Pilot Plant Gasifier And Syngas 

Conversion Testing 

5c. PROGRAM ELEMENT NUMBER

5d. PROJECT NUMBER

NREL/SR-510-37581 

5e. TASK NUMBER

 

6. AUTHOR(S)

TSS Consultants for City of Gridley, California 

5f. WORK UNIT NUMBER

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

City of Gridley, California (TSS Consultants) 

2724 Kilgore Road 

Rancho Cordova, CA 95670) 

8. PERFORMING ORGANIZATION 

REPORT NUMBER

ZCO-2-32065-01 

10. SPONSOR/MONITOR'S ACRONYM(S)

NREL 

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)

National Renewable Energy Laboratory 

1617 Cole Blvd. 

Golden, CO 80401-3393 11. SPONSORING/MONITORING 

AGENCY REPORT NUMBER

NREL/SR-510-37581 

12. DISTRIBUTION AVAILABILITY STATEMENT

National Technical Information Service 

U.S. Department of Commerce 

5285 Port Royal Road 

Springfield, VA 22161 

13. SUPPLEMENTARY NOTES

NREL Technical Monitor: M. Ruth 

14. ABSTRACT (Maximum 200 Words)

This report is part of an overall evaluation of using a modified Pearson Pilot Plant for processing rice straw into 

syngas and ethanol and the application of the Pearson technology for building a Demonstration Plant at Gridley. This 

report also includes information on the feedstock preparation, feedstock handling, feedstock performance, catalyst 

performance, ethanol yields and potential problems identified from the pilot scale experiments 

15. SUBJECT TERMS

Gridley; ethanol; gasification; rice straw; Pearson; syngas 

16. SECURITY CLASSIFICATION OF: 19a. NAME OF RESPONSIBLE PERSON 

a. REPORT 

Unclassified 

b. ABSTRACT 

Unclassified

c. THIS PAGE 

Unclassified

17. LIMITATION 

OF ABSTRACT

UL 

18. NUMBER 

OF PAGES 

19b. TELEPHONE NUMBER (Include area code)

Standard Form 298 (Rev. 8/98) 

Prescribed by ANSI Std. Z39.18