Using Life-Cycle Assessment to 

Evaluate Environmental Impacts 

of Torrefied Briquette Production 

from Forest Residues

Sevda Alanya-Rosenbaum

Richard Bergman

United States Department of Agriculture

Forest

Service

Forest Products

Laboratory

General Technical Report

FPL–GTR–263

December

2018

Used with permission from Schatz Energy Research Center
Abstract

This report presents life-cycle impact assessment 

analysis of near-woods processing of post-harvest forest 

residues (a biomass raw material) into torrefied wood for 

bioenergy production. The study was part of the Waste to 

Wisdom project with a broader goal of evaluating the use 

semimobile biomass conversion technologies to optimize 

biomass logistics, thereby overcoming the barriers of 

valorizing woody biomass residues for renewable energy 

and material production. Cradle-to-grave analysis of 

the torrefied briquettes (TOB) supply chain included 

feedstock procurement, hauling, feedstock preparation 

and bioconversion (torrefaction and densification) stages, 

product transportation (distribution), and combustion of 

TOB in domestic wood stoves for heat generation. The 

results showed that a large portion of the global warming 

(GW) impact of the TOB supply chain resulted from the 

torrefaction process (59%) followed by the drying process 

with about 24% of the contribution. The large contribution 

of these processes resulted from propane use. Comparative 

analysis showed that 50% substitution of propane used in 

domestic heating with TOB resulted in a 41% decrease in 

GW impact. The near-woods operation resulted in a 55% 

lower GW impact compared with transporting the feedstock 

to an in-town facility with access to grid electricity.

Keywords: torrefaction, biomass densification, briquette, 

bioenergy, post-harvest forest residues, life-cycle assessment

Acknowledgments

This material is based on work supported by a grant 

from the U.S. Department of Energy under the Biomass 

Research and Development Initiative program: Award 

Number DE-EE0006297. This research was supported 

in part by an appointment to the USDA Forest Service 

Research Participation Program administered by the Oak 

Ridge Institute for Science and Education (ORISE) through 

an interagency agreement between the U.S. Department 

of Energy and the USDA Forest Service. ORISE is 

managed by Oak Ridge Associated Universities (ORAU) 

under DOE contract number DE-AC05-06OR23100. All 

opinions expressed in this report are the authors’ and do not 

necessarily reflect the policies and views of USDA, DOE, or 

ORAU/ORISE.

Contents

Executive Summary.............................................................1

Definition of Goal and Scope ..............................................2

Life-Cycle Inventory Analysis...........................................10

Life-Cycle Impact Assessment ..........................................16

Life-Cycle Interpretation ...................................................21

References..........................................................................22

December 2018

Alanya-Rosenbaum, Sevda; Bergman, Richard. 2018. Using life-cycle 

assessment to evaluate environmental impacts of torrefied briquette 

production from forest residues. General Technical Report FPL-GTR-263. 

Madison, WI: U.S. Department of Agriculture, Forest Service, Forest 

Products Laboratory. 24 p.

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Using Life-Cycle Assessment to Evaluate 

Environmental Impacts of Torrefied 

Briquette Production from Forest Residues

Sevda Alanya-Rosenbaum, Postdoctoral Research Fellow

Richard Bergman, Supervisory Research Wood Scientist

USDA Forest Service, Forest Products Laboratory, Madison, Wisconsin, USA

Executive Summary

The goal of this study was to assess environmental 

sustainability of near-woods processing of post-harvest 

forest residues as a feedstock in torrefied briquette (TOB) 

production and its use as biofuel for domestic heating. 

To quantify the impact associated with the torrefied 

briquette supply chain, USDA Forest Service, Forest 

Products Laboratory, scientists developed a cradle-togate life-cycle inventory (LCI) and performed a life-cycle 

assessment (LCA) analysis. The study was funded by the 

U.S. Department of Energy (DOE) and U.S. Department 

of Agriculture (USDA) through a Biomass Research and 

Development Initiative (BRDI) grant.

The scope of this LCA study included six main lifecycle stages: feedstock procurement, hauling, feedstock 

preparation, biomass conversion (torrefaction and 

briquetting), transportation (distribution), and heat 

generation at a residential wood stove (use phase). 

The feedstock procurement stage included processing 

(delimbing), sorting, and loading. The feedstock preparation 

stage included processes used to achieve the feedstock 

specifications required for the biomass conversion stage: 

chipping, screening, and drying of the feedstock. The 

operational data used in this study were developed by 

other subtasks under the Waste to Wisdom project (www.

wastetowisdom.com). These data include feedstock 

procurement and preparation processes, torrefaction, 

densification (briquetting), and woody biomass gasification 

generator set (genset). Biomass collection and feedstock 

preparation data were based on field data and experimental 

studies performed by Humboldt State University (HSU) 

(Arcata, California, USA) in 2015. This included data for 

the dryer and briquetting processes. The primary data for the 

torrefaction and briquetting processes relied on operational 

runs of the demonstration-scale torrefaction unit at Samoa, 

California, USA, in 2016.

The cradle-to-grave LCA was performed using the Tool 

for the Reduction and Assessment of Chemical and Other 

Environmental Impacts (TRACI) v2.1 impact assessment 

method. The system was modeled using the SimaPro 8.5 

LCA software package. The data were normalized using the 

functional unit, which was defined as 1 MJ of useful thermal 

energy produced for residential heating.

Alternative system configurations were investigated at the 

cradle-to-grave level for evaluation of the effect of nearwoods versus in-town processing of forest residues. Two 

remote power generation technologies were taken into 

account: a woody biomass gasification genset and a diesel 

generator. Effect of moisture content of incoming feedstock 

on the resulting impact was also investigated.

The following list shows the main conclusions of the study 

based on the life-cycle impact assessment results:

• Scenario analyses indicated that the most favorable 

scenario for near-woods processing of forest residues 

was using on-site woody biomass gasification genset 

for power.

• Near-woods operation using woody biomass gasification 

genset to meet the electricity demand of torrefaction, 

briquetter, and dryer processes showed major reductions 

in greenhouse gas (GHG) emissions compared with using 

a diesel generator or using grid electricity from in-town 

operations. Near-woods operation using diesel power was 

proven to be the least favorable alternative.

• When nonrenewable power source options were 

compared, diesel power had the worst environmental 

performance, even though longer hauling distances for 

in-town operations resulted in higher global warming 

impact from the hauling process.

• Global warming impact was highly dependent on drying 

process and torgas management at TOB production. For 

better environmental performance, the following are 

recommended: high-efficiency drying systems, field-dried 

feedstock with low moisture content (MC), and efficient 

recovery systems from displacing propane with torgas, 

especially in the drying process.
General Technical Report FPL–GTR–263

2

Definition of Goal and Scope

Study Goals

The goal of this study was to assess environmental 

sustainability of the processing of forest residues near the 

point of harvesting logs (i.e., near-woods) as a feedstock in 

TOB production. To quantify the impact of the TOB supply 

chain on the environment and to address environmental 

impacts associated with each process involved, a cradle-tograve LCA was performed. The evaluation was performed at 

plant and unit process levels in accordance with ISO 14040 

and ISO 14044 LCA standards (ISO 2006a, 2006b). The 

study was conducted with funding support from a BRDI 

grant, which is a collaborative initiative between the DOE 

and USDA.

The main function of the torrefaction process was to 

generate a solid biobased fuel that can be an alternative 

to nonrenewable fossil fuels. To evaluate environmental 

performance and obtain more insight into the environmental 

competitiveness of torrefied wood as a biobased fuel 

substitute, a comparison was made with a residential 

propane heating system.

Intended Application

This study assessed and documented the environmental 

burden and benefits associated with TOB production 

from forest residues at life-cycle level. Torrefaction is 

a promising technology for production of a sustainable 

energy carrier that can be used in existing infrastructure. 

Yet, its market penetration is still in the initial stages 

and information on its application is limited (Nhuchhen 

and others 2104). Therefore, the intended application of 

this study was to provide credited data and enhance our 

knowledge on environmental aspects associated with 

conversion of forest residues to bioenergy carriers using the 

torrefaction process at a life-cycle level. Torrefaction allows 

production of a renewable and carbon-neutral solid biomass 

energy resource (Hektor and others 2016, Miner and others 

2014). Hence, the assessment also includes comparison 

of the torrefied wood production with use of traditional 

fuel, i.e., propane, for domestic heating to evaluate its 

environmental performance compared with traditional fossil 

energy sources. The results of this study may promote the 

production of forest-based bioenergy using the torrefaction 

process.

Motivation

Today, the radical increase in demand for and consumption 

of energy resources, environmental sustainability initiations, 

and new policies to combat climate change are major drivers 

for establishing new renewable energy sources (USEIA 

2016). Mitigation of GHG emissions and achieving energy 

independence via reducing the nation’s dependence on fossil 

fuels are major challenges that can be overcome by adopting 

use of renewable energy sources.

Currently in the United States, about 93 million dry metric 

tons of forest removals are generated annually, 73% of 

which are the result of logging residues (USDOE 2011). The 

forest removals represent the removed portion of standing 

timber, which include roundwood products, logging 

residues, and other removals from growing stock and other 

sources (USDOE 2011). Forest residues resulting from 

commercial logging operations, which are often left on site 

to decay or be burned, can potentially be used by biomass 

conversion technologies to produce biofuels (USDOE 2011, 

USEPA 2007). Overstocked forests increase wildfire risk. 

Forest thinning and removal of post-harvest forest residues 

may help mitigate wildfires (Giuntoli and others 2015, 

Loeffler and others 2017). With the torrefaction process, 

forest residues can be eliminated and converted to a highquality renewable energy source that can replace fossil fuels.

The motivation for undertaking this study was to evaluate 

environmental viability of using post-harvest forest residues, 

in combination with a torrefaction process, to produce a 

high-quality bioenergy carrier. The use of forest residues 

as biomass feedstock has the potential to reduce fossil fuel 

dependence. Moreover, this study aimed to support the 

national policy on GHG emission reductions and promote 

national energy security by investigating the viability of 

alternative renewable energy sources that may reduce 

dependence on fossil fuels.

Intended Audience

The results of this study are intended to be used in 

comparative assertions and disclosed to the public. Thus, 

this LCA study was subject to third-party critical review. 

Another intended audience is researchers working on LCA 

analysis of biomass conversion of forest residues. The 

results may also be interesting for professionals representing 

governmental interests related to decision-making in 

renewable energy policies. The removal of forest residues 

might be required in forest management practices to reduce 

fire risk (Loeffler and others 2010). Removal of biomass 

for biofuel production may be of interest to forest land 

managers because this may assist them to overcome costs 

associated with biomass fuel treatment for reducing fire 

hazards.

The final Clean Power Plan rule released by the U.S. 

Environmental Protection Agency (EPA) requires 

approximately 32% reduction in electricity sector carbon 

emissions by 2030 compared with CO2 emission levels in 

2005 (Ohio EPA 2015). Torrefied wood has properties that 

are comparable with coal and can replace coal in power 

plants.

This study presents an environmental evaluation of 

torrefied wood production in the United States as a lowcarbon biofuel product with the potential to replace coal 

in power plants or propane in residential heating systems. 

Furthermore, this study will be of interest to consumers that 
Using Life-Cycle Assessment to Evaluate Environmental Impacts of Torrefied Briquette Production from Forest Residues

3

have environmental concerns regarding their residential 

heating systems.

The Scope of the Study

The scope of this LCA included cradle-to-grave stages 

of feedstock procurement and preparation, hauling, nearwoods production of TOB from post-harvest forest residues, 

distribution, and combustion of TOB in domestic wood 

stoves for heat generation. The system boundaries covered 

procurement, hauling, preparation, biomass conversion of 

forest residues to TOB, and distribution and ended at the 

grave, i.e., combustion in wood stoves for residential space 

heating. The life-cycle level impacts of TOB production 

were evaluated and compared with propane as a reference 

fossil fuel source. Propane is the most common fossil 

fuel energy source used in the studied area for domestic 

heating in rural areas. The heat production from propane for 

domestic heating was considered as the reference supply 

chain. The LCA for propane was constructed from peerreviewed literature and other secondary sources.

Functional Unit

The functional unit (FU) in LCA analyses can be defined 

in terms of system input or output depending on the goal 

of the study. It should be based on a unit that allows valid 

comparison of different alternatives. The FU in this study 

was defined as 1 MJ of useful thermal energy produced for 

residential heating.

The FU includes any efficiency loss to generate the 1 MJ 

of heat and was based on the higher heating value (HHV). 

HHVs are used to convert volume or mass basis of a fuel 

to its energy value. HHVs represent the energy content of 

a fuel with the combustion products such as water vapor 

brought to 25 oC, whereas lower heating value (LHV) 

ignores the energy produced by the combustion of hydrogen 

in fuel. HHV (gross heat content) is the preferred method 

used in the United States (USEIA 2017).

System Boundary

This study evaluated two energy carriers, torrefied 

briquettes and propane, with different production processes, 

by making use of the LCA tool. The life cycle of a biomassto-bioenergy supply chain typically starts at the feedstock 

supply stage where biomass production occurs followed by 

biomass conversion. It ends at the user where the biofuel is 

used for energy production (Fig. 1).

The system boundary of the torrefaction system investigated 

is provided in Figure 2. The life-cycle stages of TOB 

production include feedstock procurement, feedstock 

preparation, biomass conversion, and use (combustion). 

Feedstock preparation and biomass conversion processes 

occurred at the biomass conversion technology (BCT) site. 

Disposal or beneficial use of the ash generated was left 

outside the scope of this study. In addition, disposal of ash 

would be hard to determine in rural areas because it is likely 

to be spread onto fields and woods. Because of insufficient 

Figure 1. Biomass-to-bioenergy supply chain (USDOE 2014).

Deconstruction Upgrading

Conversion

Biomass

production

Feedstock

logistics

Feedstock supply

Distribution End use

Bioenergy infrastructure

Figure 2. Cradle-to-grave system boundary for torrefied wood production supply chain (T, transportation).

Heat

T

Feedstock

procurement

System boundary

T

Feedstock

preparation

Torrefaction

Biomass

collection Chipper Screener Dryer

Combustor Densification

Torrefaction Cooling Forest

residues

Combustion Torrefied

briquette
General Technical Report FPL–GTR–263

4

Flue gas

Post-harvest 

forest residues

Feedstock 

procurement

Chipper/

screener

Torrefied

briquettes

Dryer Combustor

Torrefaction

Cooling

Densification

Combustion

T

T

Lubricants

Diesel

Electricity Flue gas

Condensate

Nitrogen

Propane

Lubricants

Diesel

1 MJ

Resources

Emissions 

to air, 

water, 

Condenser/ land

filter

information on the torrefaction technology investigated, the 

manufacturing, maintenance, and disposal of equipment 

used in the system are considered outside the scope of this 

LCA, which is in line with the propane production system 

that also excludes these elements.

The cradle-to-grave system boundary of the propane 

production system is provided in Figure 3. The system 

boundary starts at the extraction of crude oil and ends at the 

useful heat produced at the residential furnace for domestic 

heating.

Figure 4 shows the torrefied briquette supply chain 

processes along with the inputs to and emissions from the 

system. Input biomass feedstock was post-harvest logging 

residue, which is a byproduct of commercial harvesting 

operations. The field-dried feedstock was sourced from 

timber harvesting operations in the western United States, 

specifically Washington, Oregon, and California.

The Waste to Wisdom (WTW) project (www.

wastetowisdom.com) investigated integrated harvesting 

and near-woods biomass conversion of post-harvest 

Figure 3. Cradle-to-grave system boundary for propane production supply chain.

Heat

Raw material 

extraction 

(crude oil)

Processing Distribution Combustion 

in furnace

Figure 4. Cradle-to-grave process flow diagram of near-woods torrefied briquette production supply chain 

(T, transportation).
Using Life-Cycle Assessment to Evaluate Environmental Impacts of Torrefied Briquette Production from Forest Residues

5

forest residues to produce high-quality feedstock with 

low contamination and uniform-sized feedstock (Kizha 

and Han 2016, Bergman and others 2018, Han and others 

2018). The feedstock procurement stage included biomass 

processing, sorting, and loading. Processed tree tops from 

integrated timber harvesting operations were used as 

feedstock biomass for the biomass conversion technology. 

Sorting and processing (delimbing) were used to generate 

processed tree tops. Feedstock preparation was performed to 

achieve necessary feedstock specifications for the biomass 

conversion process. This included chipping, screening, 

and drying. The unit processes of the biomass conversion 

system included torrefaction, cooling, and densification. 

In the briquetting process, torrefied biomass was densified 

into briquettes. All electricity and heat necessary for 

the system was generated on site using either a woody 

biomass gasification generator set (genset) or a diesel 

power generator. The system components are subsequently 

described in detail.

Feedstock Procurement

The biomass feedstock received was a waste product of 

commercial timber harvesting operations composed of tree 

tops, limbs, and branches. Pulp logs made up part of the 

biomass feedstock because of the lack of near-by markets, 

which is not historically typical. In this study, the term 

logging slash was used interchangeably when referring to 

forest residues. Because the logging slash was left in the 

forest for air-drying for one year before collection, it had an 

MC (wet basis) of 17% to 23% (Kizha and others 2018). At 

the feedstock procurement stage, this biomass feedstock was 

processed (delimbed) and sorted (Kizha and Han 2016). To 

improve the quality of the bioenergy product, tree tops and 

pulp logs were delimbed for further processing to generate 

post-harvest forest residues. In this study, branches were not 

used in biomass conversion. Then, the post-harvest residues 

were collected at the primary landing and loaded onto a 

dump truck for shuttling to the secondary landing (i.e., the 

near-woods BCT site). Primary data from five commercial 

harvesting sites in the western United States were used for 

modeling biomass procurement: Port Angeles, Washington; 

Warm Springs, Oregon; Oakridge, Oregon; Lakeview, 

Oregon; and Quincy, California. The average transport 

distance traveled from the primary landing to the BCT site 

for the five regions investigated was nearly 18.8 km (Oneil 

and others 2017). Transport distance, lubricant, and fuel 

consumption for the processing, sorting, and loading data 

were from field experiments performed as a part of the 

WTW project (Kizha and Han 2016, Oneil and others 2017).

Feedstock Preparation

Feedstock preparation included chipping, screening, and 

drying to achieve the specifications required for feedstock 

to be torrefied and briquetted into bioenergy products. The 

lubricant consumption data for chipping equipment, which 

consisted of hydraulic oils, general lubricants, and fuel 

consumption of chipper and screener, were based on tests 

performed by HSU. These were generated as a part of the 

WTW project (Oneil and others 2017). Details of the forest 

operations model and the equipment used for feedstock 

preparation are provided in Oneil and others (2017).

In this study, feedstocks were sourced from Tanoak 

(Notholithocarpus densiflorus). Forced-drying was applied 

before the torrefaction process to decrease the MC of the 

biomass feedstock. The use of the dryer was based on the 

target MC of the biomass feedstock (Li and others 2012). 

Torrefaction tests were performed using various feedstock 

MCs to identify the optimum MC for the highest quality 

product (Severy and others 2018). The characteristics of the 

feedstock after the preparation stage are provided in Table 1.

Torrefaction

Torrefaction is a thermal pretreatment process that adds 

value to the biofuel produced, given that the product is 

hydrophobic, has high energy and bulk density, and has 

increased grindability compared with nonthermally treated 

biomass. The biomass feedstock is heated in a virtually 

oxygen-free environment to a temperature of approximately 

200 to 300 °C (Tumuluru and others 2011). These 

characteristics make it a suitable bioenergy carrier with 

specifications equivalent to coal (Nunes and others 2014, 

Proskurina and others 2017).

For the WTW project, a semimobile, electrically heated, 

screw-type, demonstration-scale torrefaction process 

(Biogreen, ETIA Group, Compiègne, France, and Norris 

Thermal Technologies, Tippecanoe, Indiana, USA) was 

used, which processed about 0.5 metric tons wood chips 

per hour. A piping and instrumentation diagram of the 

torrefaction unit used is provided in Figure 5. The reactor 

temperature was at about 275 °C, and to provide the 

required inert conditions during the torrefaction process, 

nitrogen gas was introduced to the process for purging. 

Nitrogen used for purging was negligible because it was 

needed only at the start of the operation. Nitrogen and 

gas were shut off when the reactor reached a steady state 

temperature. As noted in Table 1, the MC of the biomass 

input was about 9%. The torrefaction unit included 

condensation and filtration, which were used to remove 

contaminants from the gases released during torrefaction 

(torgas), which can potentially damage combustion 

equipment when torgas is used (i.e., propane burner or 

Table 1—Properties of feedstock before torrefaction

Property Value

Moisture content (%) wba 9.34

Ash content (%) dbb 3.4

Volatile matter (%) db 81

Higher heating value (MJ/kg db) 19.6

a

wb, wet basis.

b

db, dry basis.
General Technical Report FPL–GTR–263

6

thermal oxidizer). The byproducts of condensation and 

filtration were condensate (bio-oil) and tar, respectively. 

The bio-oil generated was acidic (pH of about 2). It was 

neutralized using sodium hydroxide (NaOH) and disposed 

to a municipal sewage system. During the testing, the torgas 

generated at the torrefaction unit was flared. But, in the LCA 

analysis, torgas was assumed to be used to support dryer 

energy requirement. Because of the low energy content 

of the torgas, flaring was supplemented with propane fuel 

to initiate and maintain optimum combustion. In the LCA 

analysis, various scenarios were investigated to evaluate the 

environmental burden resulting from different applications. 

Use of torgas for thermal energy generation was one of the 

scenarios investigated. In this specific scenario, torgas was 

assumed to be combusted as a substitute for propane where 

its exhaust (flue) gases supplied heat for the dryer.

The characteristics of the TOB fuel after biomass conversion 

are provided in Table 2.

Densification

Torrefied wood was densified into briquettes using a 

RUF lignum model briquetter (RUF Briquetting Systems, 

Zaisertshofen, Germany) (RUF Briquetting Systems 2016). 

The briquetter used hydraulic cylinders, which consumed 

electricity, for compressing the feedstock (Fig. 6). The 

torrefied wood chips were fed into a hopper, then transferred 

to a pressing chamber via a screw conveyor. Finally, 

the compressed torrefied wood was ejected as finished 

briquettes. Finished briquette dimensions were 63 mm wide 

by 150 mm long by 109 mm high (Severy 2018). Binding 

agents may be used in the densification process to improve 

binding characteristics. For the system under investigation, 

no binder was used.

Transportation

Transportation including that for raw materials and the final 

product (distribution) was considered in this study. Average 

transport distance traveled from the primary landing to 

the BCT site for the five regions investigated was 18.8 km 

(Oneil and others 2017). The transportation of TOB to end 

user for residential heating was included in the inventory. 

It was assumed that the briquettes were transported to 

the closest town for use and that tractor trailers fueled by 

diesel were used for transportation. As part of this study, 

transportation sensitivity analysis was conducted and results 

are shown in a later section. In addition, transportation of 

other materials from manufacturers to the BCT site were 

considered in this study.

Combustion

Use-phase data comes from the combustion tests conducted 

to simulate the use phase of the briquettes produced. 

Test results were provided by Schatz Energy Research 

Center, HSU. Each test was conducted in a freestanding 

Figure 5. Biogreen torrefaction unit (Severy and others 2018).

Table 2—Properties of the torrefied briquette 

product

Property Value

Moisture content (%) wba 0.6

Ash content (%) dbb 2.5

Volatile matter (%) db 71

Higher heating value (MJ/kg db) 23.0

a

wb, wet basis.

b

db, dry basis.
Using Life-Cycle Assessment to Evaluate Environmental Impacts of Torrefied Briquette Production from Forest Residues

7

non-EPA-certified wood stove (Schrader Woodstoves, 

Harrisburg, Pennsylvania, USA) using 2.4 m of singlewalled stove pipe followed by 2.4 m of insulated, doublewalled chimney pipe to replicate residential installation. 

Burn tests were performed by modifying EPA Method 28 – 

Certification and Auditing of Wood Heaters (USEPA 2017).

Alternative System Configurations

Alternative system configurations were investigated at the 

cradle-to-grave level for evaluating the effect on various 

changes in the supply chain (Table 3). The torrefaction 

unit was designed to be a semimobile unit to perform 

near-woods operations, allowing biomass conversion 

to occur close to the source and allowing the unit to be 

transported between forest operation sites. This allows 

processing of the low-density forest residues closer to the 

primary landing before the high-density bioenergy product 

is shipped to the user. Near-woods processing required 

remote power generation because the selected BCT site had 

no access to grid electricity. Two remote power generation 

technologies were taken into account: a woody biomass 

gasification genset and a diesel generator. Using the same 

feedstock to produce the torrefied wood briquettes, the 

Power Pallet-PP20 biomass gasifier (All Power Labs, 

Berkeley, California, USA) (All Power Labs 2016) with 

an engine generator rated at 20 kWe was tested for remote 

power generation. The woody biomass gasifier genset was 

selected as the base case with a diesel power generator 

as the alternative scenario to investigate the effect of the 

power source used on the environmental impact results. 

Diesel was supplied by an on-site fuel tank to run the diesel 

generator. In addition, the impact of logistics on the results 

Table 3—A review of the scenarios investigated

Scenario Description

S0 Propane production system

S1 1 MJ heat, near-woods operation with wood gasifier power

S2 1 MJ heat, near-woods operation with diesel power

S3 1 MJ heat, in-town operation (2-h travel distance) with grid power

S4 1 MJ heat, in-town operation (4-h travel distance) with grid power

S5 1 MJ heat, 50% moisture content feedstock, near-woods operation with wood gasifier power

S6 1 MJ heat, near-woods operation with wood gasifier power with pile and burn credit

Figure 6. RUF briquetter machine (photo used with permission from RUF Briquetting Systems, 

Zaisertshofen, Germany).

Cabinet

Hopper

Precharger

Mould change cylinder

Briquette outlet
General Technical Report FPL–GTR–263

8

were evaluated with a scenario that considered transferring 

forest residues to an in-town facility where grid electricity 

was used for biomass conversion as opposed to the on-site 

operation. The effect of MC of incoming feedstock was 

also examined. It was assumed that the feedstock received 

was not air-dried in the forest and had 50% MC, wet basis 

(MCwb).

A scenario considering the environmental credit from 

avoided pile-and-burn emissions as a result of converting 

forest residues to solid biofuel was also analyzed. It was 

assumed that only 50% of the residue was burnt. The 

combustion emissions profile from pile and burn was 

adopted from Pierobon and others (2014).

Allocation Procedure

Allocation is required for multi-output systems in which two 

or more functions are delivered. The major product of the 

system under investigation was TOB, whereas torgas was 

the coproduct. Energy allocation was used for accounting 

for the burden between the torgas and torrefied chips. Mass 

allocation was used in the propane system model.

Assumptions and Limitations

Volatile organic compound (VOC) emissions, which occur 

during drying of the fresh biomass feedstock, were taken 

into account. Because the biomass was field-dried and the 

MC was around 20% on a wet basis when received at the 

dryer unit, it was assumed that 20% of the VOC was emitted 

during the dryer and the rest, 80%, was emitted at the forest. 

Because exact emission VOC data from tanoak were not 

available, white oak was used as a proxy (Beakler and 

others 2007).

Torrefaction is an emerging technology. Because 

of insufficient information on this technology, the 

manufacturing, maintenance, and disposal of equipment 

used in the system were considered outside the scope of 

the LCA. For consistency, the propane production system 

excluded these elements as well.

At the use phase, propane and torgas were assumed to be 

combusted with 95% combustion efficiency (McNamee 

and others 2016). In addition, data on heat requirements at 

the dryer process were not available through experimental 

runs performed; therefore, it was retrieved from literature as 

5 MJ/kg water removed (Adams and others 2015). All mass 

and energy flows were accounted for in this study without 

applying cutoff criteria. Mass loss at the densification 

process was negligible. Therefore, it was assumed that there 

was no mass loss at the briquetter.

EPA released a second draft of Framework for Assessing 

Biogenic CO2 Emissions from Stationary Sources that 

provides an analytical methodology on the evaluation of 

net atmospheric contribution of biogenic carbon dioxide 

(CO2) emissions from production, processing, and use of 

biogenic material at stationary sources (USEPA 2015). 

Yet, accounting for emissions of biogenic CO2 from 

stationary sources is still under evaluation. In this study, 

CO2 emissions from woody biomass in the system under 

investigation was considered biogenic and thus carbonneutral, in line with the Intergovernmental Panel on Climate 

Change (IPCC) approach (IPCC 2006, 2014). Regardless, 

biogenic CO2 emissions were reported along with fossil 

GHG emissions.

For propane combustion data, a literature source (Johnson 

2012) was used instead of DATASMART, which is based 

on the U.S. LCI Database, because the literature source 

compared data from different databases and sources, 

evaluated the data, and provided an integrated dataset based 

on the most reliable data available.

Life-Cycle Impact Assessment Methodology and 

Types of Impacts

For the life-cycle impact assessment (LCIA), the 

impact categories examined in this study include global 

warming (GW) (kg CO2-eq), acidification (kg SO2-eq), 

eutrophication (kg N-eq), ozone depletion (OD) (kg 

chlorofluorocarbons-11-eq), smog formation (kg O3-eq), 

human health (CTUh), respiratory effects (kg PM2.5 eq), 

ecotoxicity (CTUe), and fossil fuel depletion (MJ). Among 

the available methods for the LCIA, the TRACI method was 

used in this study (Bare 2011, USEPA 2012). The system 

was modeled using the SimaPro 8.5 LCA software package 

(PRé Consultants 2017). TRACI is a midpoint-level impact 

assessment model developed by EPA and is representative 

for the United States with input parameters consistent with 

U.S. conditions. All impact categories covered in the TRACI 

method were considered in this study. Resource depletion 

categories including water scarcity, land occupation, and 

land transformation are not included in the TRACI method. 

These categories are listed for future inclusion, but they 

require more research to establish since site-specific data 

are required because of the unique properties of location, 

meteorology, and existing ecosystems (USEPA 2012). Thus, 

these impact categories were not taken into consideration 

in this study. Forest residues are generated as a byproduct 

of commercial harvesting operations and are considered 

waste. As mentioned, forest residues are commonly left 

on the forest floor to decay or cleared using pile-and-burn 

methods. For this reason, we didn’t consider the growth of 

the tree that generates the forest residues within the system 

boundaries. Consequently, the authors did not evaluate the 

land use impacts.

Data Quality

The data were collected in line with the data quality 

requirements addressed by ISO 14044 to ensure quality and 

reliability. Details are provided in the following sections.

Geographical and Time-Related Coverage

Quantitative data on mass and energy flows of the 

demonstration-scale torrefaction system and forest 
Using Life-Cycle Assessment to Evaluate Environmental Impacts of Torrefied Briquette Production from Forest Residues

9

operations were based on the operational data of core 

processes for the years 2015 and 2016. The torrefaction 

unit was located and operated in northern California. The 

field data on the feedstock procurement stage were based 

on forest operations in three western states: Washington, 

Oregon, and California. Secondary data were derived from 

peer-reviewed literature and LCI databases including the 

DATASMART database, which is an integrated database 

complementing the U.S. LCI database using U.S. Ecoinvent 

processes using underlying Ecoinvent v.2.2 datasets (LTS 

2017, PRé Consultants 2017, NREL 2012). The U.S. LCI 

database is based on regional conditions and represents U.S. 

circumstances.

Precision

No variance can be calculated because this study was based 

on a single dataset not on an industry level. However, 

process-specific data were collected and analyzed wherever 

possible.

Completeness, Consistency, and Uncertainty

The quality of the data used in the analyses is crucial to 

accurately represent the systems investigated. Therefore, 

mass and energy balances for the TOB production were 

developed based on field data to assure reliability of the 

data used. In addition, sensitivity and scenario analyses 

were conducted to address completeness, consistency, and 

uncertainty issues relevant to the data used.

Representativeness

The torrefaction technology used here is current and 

representative technology and creates a product that is 

comparable with other products in the market. The internal 

process of torrefying feedstock can be different depending 

on the technology used, but the final product is similar. 

Torrefaction is a thermochemical process that occurs in 

the following temperatures: 200 to 300 °C for increased 

energy density and decreased volatile matter and MC of the 

product.

Reproducibility

The methods used, the input and output data, and the LCI 

generated in this study are provided in detail to allow other 

LCA practitioners to reproduce the results presented in this 

report.

Data Sources

Feedstock procurement data were obtained from Oneil 

and others (2017). The data came from five commercial 

harvesting sites located in the western United States: Port 

Angeles, Washington; Warm Springs, Oregon; Oakridge, 

Oregon; Lakeview, Oregon; and Quincy, California. Average 

transport distance traveled from the primary landing to 

the BCT site and BCT site to the closest town was based 

on the data derived from the operations in the five regions 

investigated. Feedstock preparation data were based on 

field data and experimental studies performed as a part of 

the WTW project in 2015 (Bisson and Han 2016, Kizha and 

Han 2016, Kizha and others 2018).

The primary data for the torrefaction processes rely on the 

operational runs of the demonstration-scale torrefaction unit. 

A semimobile electrically heated screw-type demonstrationscale torrefaction unit with 0.5 metric tons wood chips per 

hour processing capacity was used. All relevant quantitative 

data (input–output flows) associated with the unit processes 

were collected from the production site. These include 

data for the dryer, torrefaction, densification processes, 

and woody biomass gasification genset. The data included 

input–output mass and energy flows, air emissions resulting 

from the torrefaction process, physical properties of the 

feedstock received by the systems, and characteristics of the 

final product, i.e., torrefied briquettes. Secondary data such 

as supply of electricity, manufacturing of the chemicals, 

transport, and waste disposal came from the DATASMART 

database and peer-reviewed literature (LTS 2017).

Type of Critical Review

Because of the comparative nature of this study and its 

intention to be disclosed to the public, as required by 

ISO 14044, a critical review was conducted by a panel of 

experts. The review panel for this study was composed 

of two LCA experts: James Salazar, M.S., Principal of 

Coldstream Consulting (Vancouver, British Columbia, 

Canada), and Shaobo Liang, PhD, Postdoctoral Research 

Fellow, USDA Forest Service, Forest Products Laboratory.

The main goals of the review panel, as outlined by ISO 

14044, are to ensure that (1) the methods are scientifically 

and technically valid, (2) the methods are consistent with 

ISO 14044, (3) the data are appropriate and reasonable 

in light of the goal of the study, (4) the interpretations 

reflect the limitations and study goal, and (5) the report is 

transparent and consistent.

Value Choices

In this study, midpoint-level impact assessment was 

performed using the TRACI 2.1 method (Bare 2011, 

USEPA 2012). Midpoint-level analysis was used to express 

results from the impact assessment. Value judgments 

from weighting were avoided because impact category 

results were neither ranked based on their importance nor 

aggregated to obtain a single score.

Although not considered for this study, endpoint results 

can be performed at the inventory stage or obtained by 

aggregation of midpoint-level impact category results 

by assigning numerical weighting factors based on their 

importance. The endpoint-level impact assessment analysis 

aggregates midpoint impacts under the three areas of 

protection: natural environment, human health, and natural 

resources. Endpoint analysis allows the results to be 

presented using a single score result, which allows easier 

interpretation and communication of LCA results with 
General Technical Report FPL–GTR–263

10

nonLCA experts and comparison of the environmental 

impact of different products or scenarios. The optional 

weighting step based on value choices allows for obtaining 

a single score result of LCA analysis, yet it introduces more 

assumptions to the analysis, leading to greater uncertainties.

Life-Cycle Inventory Analysis

Cradle-to-grave system boundary of the TOB supply chain 

included feedstock procurement (processing, sorting, 

and loading), hauling, feedstock preparation (chipping, 

screening, and drying), biomass conversion (torrefaction 

and densification), transportation (distribution), and the 

use phase (combustion at domestic wood stoves). Biomass 

procurement and preparation data were provided by the 

WTW project. All relevant material and energy flows 

associated with the unit processes included in the cradle-tograve system boundary of TOB production were collected to 

develop a cradle-to-grave LCI. The study conformed to ISO 

14040 and ISO 14044 LCA standards.

Cradle-to-Grave Life-Cycle Inventory of the 

Propane System

The cradle-to-grave system boundary for the propane 

system began at the extraction of crude oil and ended at 

the useful heat produced at the residential furnace for 

domestic heating. The propane product system included 

four major life-cycle stages: crude oil extraction, propane 

production, distribution, and use phase. Crude oil extraction, 

propane production, and distribution data came from the 

DATASMART database for which combustion data were 

retrieved from literature. Johnson (2012) evaluated the 

existing data sources for residential heating systems that use 

propane and generated an integrated data set for propane 

combustion emission factors (Table 4).

Cradle-to-Grave Life-Cycle Inventory of the 

Torrefaction System

The cradle-to-grave LCI for the torrefaction system was 

developed using all the primary data related to the inputs 

and outputs of the processes included in the system 

boundary. Data were obtained by on-site measurements at 

the torrefaction plant near-woods field experiments. LCI 

for different life-cycle stages are provided in the following 

section.

Feedstock Procurement

Table 5 shows the cradle-to-gate input and output flows for 

feedstock procurement including processing (delimbing), 

sorting, and loading along with hauling for one bone-dry 

metric ton (BDT) of wood chips. The feedstock procurement 

stage along with hauling the forest residue were adopted 

from the forest operations model developed by Oneil and 

others (2017). The Oneil and others (2017) model was based 

on the operational data generated in 2015 (Bisson and Han 

2016, Kizha and Han 2016, Kizha and others 2018).

Feedstock Preparation

Gate-to-gate input and output flows of feedstock preparation 

including chipping, screening, and drying are provided in 

Table 6. Screening and chipping data were adopted from 

the forest operations model developed by Oneil and others 

(2017) and were modeled based on the operational data 

generated in 2015 (Bisson and Han 2016, Kizha and Han 

2016, Kizha and others 2018).

Thermal energy required for drying the input biomass was 

provided from torgas, which was supplemented by propane 

fuel for ignition and continuous combustion. About 31% 

of the torgas generated at the torrefaction unit was directed 

to the dryer as heat supply. Electricity consumption in the 

dryer process occurred from the belt conveyor (Beltomatic, 

Norris Thermal Technologies). The drying process was 

modeled based on the operational data generated in 2015.

Although the feedstock was left in the forest and field-dried 

to 20±3% MC, feedstock was force-dried using torgas and 

propane before torrefaction to achieve the desired product 

quality. A value below 25% MC was suggested by the 

manufacturer for desired product quality. However, average 

feedstock MC after the drying process was about 9.3%, 

which provided an optimum product (Severy and others 

2018). Process data for heat consumed in the drying process 

were not available. Therefore, heat requirements of the 

drying process were assumed to be 5 MJ/kg water removed 

(Adams and others 2015). Torrefaction gases (torgas) were 

assumed to be combusted to provide heat for the dryer and 

were also assumed to have 95% combustion efficiency 

(McNamee and others 2016). Heating content of torgas after 

the condensation stage was about 3.7±0.03 kJ/L, and its 

combustion was supplemented by propane to start ignition 

and maintain effective combustion.

Drying wood results in VOC emissions, which was 

accounted for in the analysis. Assuming freshly cut wood, 

this analysis conservatively tracked any VOCs emitted 

during field-drying of the forest residues as well as 

Table 4—Propane combustion 

emission factors (Johnson 2012)

Emissionsa Value(mg/MJ)

CH4 1.03

CO 8.86

CO2, fossil 63,111

N2O 0.11

NOx 47.00

PM10 0.33

SO2 0.19

NMVOC 1.72

a

PM, particulate matter; NMVOC, nonmethane 

volatile organic compounds.
Using Life-Cycle Assessment to Evaluate Environmental Impacts of Torrefied Briquette Production from Forest Residues

11

during the forced-drying. It would be expected that VOCs 

emitted during field-drying, because they occur at lower 

concentrations and for a far longer period, would be less 

harmful to the environment. The VOC emission data were 

derived from literature for the species used in this study 

(Beakler and others 2007, Milota and Lavery 1998, Milota 

and Mosher 2008, Milota 2013). According to Milota 

(2013), emission levels mainly depend on the species and 

are higher for drying fresh woody biomass compared with 

drying aged material. Milota (2013) concluded that only 

10% to 20% of the total hydrocarbon emissions occur below 

20% MC. In this study, it was assumed that 20% of the VOC 

emissions were emitted during forced-drying, whereas the 

rest (80%) were emitted in the forest during field-drying.

Biomass Conversion and Use Phases

The material and energy inputs and outputs for TOB 

production and use phases are provided in Table 7. The 

data were provided for biomass conversion processes: 

torrefaction and briquetting (densification), along with the 

use phase. Use-phase data, including stack emissions from 

burning TOB that were obtained from the WTW project 

combustion tests and data, were complemented by literature 

data. Overall, efficiency of burning TOB in the wood stove 

was 76%. It was assumed that the briquettes were stored and 

sold in 15-kg-capacity plastic bags made from low-density 

polyethylene (LDPE) (Laschi and others 2016).

Table 5—Cradle-to-gate input–output flow analysis for procuring material for 

one bone-dry metric ton of wood chips

Category Unit Value Source

Feedstock procurement

Processing

 Diesel L 1.0115 Oneil and others 2017

 Lubricants L 0.0182 Oneil and others 2017

Sorting

 Diesel L 0.346 Oneil and others 2017

 Lubricants L 0.006 Oneil and others 2017

Loading

 Diesel L 0.708 Oneil and others 2017

 Lubricants L 0.013 Oneil and others 2017

Volatile organic compounds g 8.54 Alanya-Rosenbaum and others 2018

Hauling

Transportation km 18.77 Oneil and others 2017

Table 6—Cradle-to-gate input–output flow analysis for one bone-dry metric ton 

of wood chips

Category Unit Value Source

Feedstock procurement

Chipper

 Diesel L 0.5461 Oneil and others 2017

 Lubricants L 0.0098 Oneil and others 2017

Screener

 Diesel L 1.5939 Oneil and others 2017

 Lubricants L 0.0287 Oneil and others 2017

Dryer

Electricity Wh 7.14 Alanya-Rosenbaum and others 2018

Propane L 20.9 Engineering calculations

Volatile organic compounds g 2.13 Alanya-Rosenbaum and others 2018

Torgas m3 212 Process data

Waste heat MJ 391 Engineering calculations
General Technical Report FPL–GTR–263

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Table 8 presents the concentration of compounds in the 

flue gas generated as a result of torgas combustion. Torgas 

combustion was supplemented by propane to start ignition 

and maintain combustion.

Life-Cycle Inventory Analysis

The results of the LCI analysis per 1 MJ of thermal energy 

generated for domestic heating from combusting TOB are 

presented in Tables 9 and 10. Total primary energy used 

to produce 1 MJ of heat from TOB at a domestic wood 

stove was 1.34 MJ (Table 9). The majority of the overall 

primary energy consumption was from wood fuel with about 

82.7% contribution. This was caused by high electricity 

consumption in the torrefaction process, 75.2% contribution, 

in which the power source used was a wood gasifier genset. 

Contribution of other renewable energy sources to total 

primary energy was minor. Most of the fossil energy was 

derived from propane and diesel consumption during torgas 

combustion and transportation, respectively, which was 

captured as crude oil as the primary energy source before 

conversion (Table 10). Nonrenewable material resource use 

was minor (less than about 10–6 MJ).

Table 7—Input–output flows of torrefied briquette (TOB) production and usea

Category Unit Value Source

Torrefaction

Inputs

 Dry wood chip kg db/MJ torrefied chips 0.063 Operational data

 Lubricants mL/MJ torrefied chips 0.002 Operational data

 Electricity kWh/MJ torrefied chips 0.019 Operational data

 NaOH g/MJ torrefied chips 0.667 Operational data

Outputs

 Bio-oil L/MJ torrefied chips 0.011 Operational data

 Torgas m3/MJ torrefied chips 0.043 Operational data

Briquetter

Electricity kWh/MJ TOB 0.0037 Operational data

Lubricants mL/MJ TOB 0.00019 Operational data

Packaging

LDPE packaging g/BDT 0.632 Laschi and others 2016

Distribution

Distribution km 90.200 Oneil and others 2017

Combustion (use phase)

CO2 (biogenic) g/MJ TOB 76.873 Operational data

CH4 g/MJ TOB 0.002 Khalil and others 2013

NOx g/MJ TOB 0.028 Operational data

CO g/MJ TOB 3.476 Operational data

VOC g/MJ TOB 0.730 Operational data

SO2 g/MJ TOB 0.008 Khalil and others 2013

PM2.5 g/MJ TOB 0.014 Operational data

PM10 g/MJ TOB 0.104 Operational data

a

LDPE, low-density polyethylene; BDT, bone-dry ton; VOC, volatile organic compounds; 

PM, particulate matter.

Table 8—Flue gas composition of torgas combustion

Category Unit Value Source

Inputs

Torgas L 1 Operational data

Propane L 9.9E–05 Operational data

Outputs

CO2

(biogenic)

mg 1,654 Operational data/

engineering calculations

CH4 mg 0.0836 Operational data/

engineering calculations

C2H6 mg 0.0412 Operational data/

engineering calculations

C3H8 mg 0.0282 Operational data/

engineering calculations

NOx mg 0.0503 Nanou and others 2016
Using Life-Cycle Assessment to Evaluate Environmental Impacts of Torrefied Briquette Production from Forest Residues

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Table 9—Cumulative primary energy consumption per 1 MJ of thermal energy generated for domestic heating from combusting torrefied briquettes

Primary energy consumption 

(MJ/MJ heat)

Fuel Percentage Total

Feedstock 

procurement

Feedstock 

preparation Torrefaction Densification Transportation

Use phase 

(combustion) Packaging

Renewable fuel use

Wood fuel 82.7 1.11E+00 0.00E+00 6.36E–02 8.67E–01 1.76E–01 0.00E+00 0.00E+00 0.00E+00

Nonrenewable fuel use

Gas, natural, in ground 1.4 1.84E–02 4.54E–04 3.53E–03 1.39E–02 1.25E–04 3.84E–04 0.00E+00 2.28E–06Coal, in ground 1.0 1.31E–02 3.01E–04 2.38E–03 1.01E–02 8.19E–05 2.56E–04 0.00E+00 9.86E–08Oil, crude, in ground 14.6 1.95E–01 9.27E–03 6.38E–02 1.11E–01 2.52E–03 7.88E–03 0.00E+00 4.98E–07Uranium 0.3 3.75E–03 9.30E–05 7.22E–04 2.83E–03 2.53E–05 7.90E–05 0.00E+00 3.05E–08

Renewable energy sources 

Hydro <1.0 4.87E–04 1.21E–05 9.38E–05 3.67E–04 3.28E–06 1.03E–05 0.00E+00 3.96E–09

Wind <1.0 1.89E–04 4.69E–06 3.64E–05 1.43E–04 1.27E–06 3.98E–06 0.00E+00 1.54E–09

Solar <1.0 2.89E–06 7.05E–08 5.50E–07 2.19E–06 1.92E–08 5.99E–08 0.00E+00 2.47E–11Geothermal <1.0 0.00E+00 0.00E+00 0.00E+00 0.00E+00 0.00E+00 0.00E+00 0.00E+00 0.00E+00

Total 100.0 1.34E+00 1.01E–02 1.34E–01 1.01E+00 1.79E–01 8.61E–03 0.00E+00 2.91E–06Total, by percentage 100 0.8 10.0 75.2 13.4 0.6 0.0 0.0
General Technical Report FPL

–GTR–263

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Table 10—Resources consumed and waste generated per 1 MJ of thermal energy generated for domestic heating from combusting torrefied briquettesResources and waste Unit Total

Feedstock 

procurement

Feedstock 

preparation Torrefaction Densification Transportation

Use phase 

(combustion) Packaging

Total primary energy consumption

MJ 1.34E+00 1.01E–02 1.34E–01 1.01E+00 1.79E–01 8.61E–03 0.00E+00 2.91E–06

Nonrenewable fossil MJ 2.26E–01 1.00E–02 6.97E–02 1.35E–01 2.73E–03 8.52E–03 0.00E+00 2.88E–06Nonrenewable nuclear MJ 3.75E–03 9.30E–05 7.22E–04 2.83E–03 2.53E–05 7.90E–05 0.00E+00 3.05E–08Renewable (solar,wind, hydroelectric, and geothermal)

MJ 6.79E–04 1.68E–05 1.31E–04 5.12E–04 4.58E–06 1.43E–05 0.00E+00 5.52E–09

Renewable (biomass) MJ 1.11E+00 0.00E+00 6.36E–02 8.67E–01 1.76E–01 0.00E+00 0.00E+00 0.00E+00

Material resources consumption (nonfuel resources)

Renewable materials kg 1.16E–01 1.03E–01 7.61E–04 1.04E–02 2.10E–03 1.32E–07 0.00E+00 0.00E+00Fresh water L 3.01E–03 7.42E–05 5.77E–04 2.28E–03 2.01E–05 6.30E–05 0.00E+00 0.00E+00

Waste generated

Solid waste kg 3.60E–08 0.00E+00 0.00E+00 0.00E+00 0.00E+00 0.00E+00 0.00E+00 3.60E–08
Using Life-Cycle Assessment to Evaluate Environmental Impacts of Torrefied Briquette Production from Forest Residues

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Table 11—Cumulative primary energy consumption per 1 MJ of thermal energy generated at propane furnace 

for domestic heating

Primary energy consumption

(MJ/MJ heat)

Fuel Percentage Total Production Transportation Combustion

Renewable fuel use

Wood fuel 0.0 0.00E+00 0.00E+00 0.00E+00 0.00E+00

Nonrenewable fuel use

Gas, natural, in ground 4.5 6.51E–02 6.51E–02 4.56E–05 0.00E+00

Coal, in ground 3.0 4.34E–02 4.33E–02 4.45E–05 0.00E+00

Oil, crude, in ground 91.4 1.34E+00 1.34E+00 9.44E–10 0.00E+00

Uranium 1.0 1.42E–02 1.34E–02 7.89E–04 0.00E+00

Renewable energy sources

Hydro <1.0 1.74E–03 1.74E–03 1.22E–06 0.00E+00

Wind <1.0 6.75E–04 6.75E–04 4.72E–07 0.00E+00

Solar <1.0 1.02E–05 1.01E–05 7.11E–09 0.00E+00

Geothermal <1.0 0.00E+00 0.00E+00 0.00E+00 0.00E+00

Total 100.0 1.46E+00 1.46E+00 8.80E–04 0.00E+00

Total, by percentage 100 99.9 0.1 0.0

Table 12—Resources consumed and waste generated per 1 MJ of thermal energy generated at propane furnace 

for domestic heating

Resources and waste Unit Total Production Transportation Combustion

Total primary energy 

consumption

MJ 1.46E+00 1.46E+00 8.80E–04 0.00E+00

Nonrenewable fossil MJ 1.44E+00 1.44E+00 9.01E–05 0.00E+00

Nonrenewable nuclear MJ 1.42E–02 1.34E–02 7.89E–04 0.00E+00

Renewable (solar,

wind, hydroelectric, 

and geothermal)

MJ 2.43E–03 2.42E–03 1.70E–06 0.00E+00

Renewable (biomass) MJ 0.00E+00 0.00E+00 0.00E+00 0.00E+00

Material resources 

consumption (nonfuel 

resources)

Nonrenewable materials kg 4.29E–05 4.28E–05 3.00E–08 0.00E+00

Renewable materials kg 2.24E–05 2.23E–05 1.56E–08 0.00E+00

Fresh water L 1.07E–02 1.07E–02 7.48E–06 0.00E+00

Waste generated

Solid waste kg 0.00E+00 0.00E+00 0.00E+00 0.00E+00
General Technical Report FPL–GTR–263

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The GW impact results per megajoule of heat generated 

through various scenarios was compared. These scenarios 

included propane furnace, Scenario 0 (S0), and propane 

system supplemented with TOB at two different 

percentages. Scenario 1 (S1) is presented in Figure 8. 

Comparative data showed that 50% and 80% substitution of 

propane with torrefied wood briquettes resulted in 41% and 

66% reduction in GW impact, respectively.

Alternative System Configurations 

Life-Cycle Assessment

Results of the comparative analysis of alternative scenarios 

investigated for GW impact are provided in Figure 9. 

Total GW impact of producing 1 MJ of heat from TOB 

combustion at a wood stove was nearly 17 g CO2 eq. for 

the base scenario (S1). Analysis showed that near-woods 

operation using diesel power as the remote (off-grid) 

power generation source was the least favorable alternative 

scenario (S2). Using a diesel generator instead of a wood 

gasifier genset for remote power generation resulted 

in 308% higher GHG emissions. Similarly, biomass 

conversion of forest residues close to the biomass source 

using gasifier genset instead of transporting the feedstock a 

2-hour (S3) or 4-hour (S4) drive (maximum) to an in-town 

facility with access to grid electricity decreased the GW 

impact by 55% and 57%, respectively. High feedstock MC 

scenario resulted in a 55% increase in total GW impact 

(S5), because of increased propane consumption at the 

dryer process. Using feedstock with higher MC resulted in 

a 6% increase in GW impact of the hauling process. Higher 

propane consumption was caused by increased torgas use 

and additional propane requirements because of higher heat 

demand at the dryer. In S1, some portion of the torgas was 

used to generate heat for the dryer, whereas the remaining 

was flared at the torrefaction process. In S5, total torgas 

produced was used in the drying process instead of flaring at 

the torrefaction process. This shifted environmental burden 

from the torrefaction process to the feedstock preparation 

stage, mainly the drying process, because more torgas was 

used in the drying process and torgas combustion itself 

requires support by propane. Accounting for the benefits of 

heat generation through controlled burn compared with pile 

and burn (S6) resulted in a 19% decrease in resulting GW 

impact.

The effects of using different power sources, for meeting the 

electricity demand for the dryer, briquetter, and torrefaction 

processes, on the resulting environmental impact is 

presented in Figure 10. Comparative results are presented 

for OD, smog, acidification, eutrophication, and fossil 

fuel depletion impact assessment categories. The results 

of the analysis revealed that, at the cradle-to-grave level, 

using wood-gasifier-based power generation improved the 

environmental performance of the system compared with 

diesel electricity and grid electricity in all impact categories 

except smog. The difference was notable in the OD and 

eutrophication impact categories.

The results of the LCI analysis per 1 MJ of thermal energy 

generated for domestic heating from combusting propane 

are presented in Tables 11 and 12. Total primary energy 

used to produce 1 MJ of heat was 1.46 MJ. The majority of 

primary energy consumption was from crude oil with about 

91.4% contribution.

Life-Cycle Impact Assessment

The results of the LCIA performed using TRACI v2.1 are 

documented in this section. The cradle-to-grave assessment 

analyzed environmental impacts associated with TOB 

production supply chain and compared with a fossil 

fuel alternative (i.e., propane). In addition, the effects of 

alternative scenarios with different power sources, logistics, 

and feedstock properties on the impact results were 

evaluated.

Cradle-to-Grave Life-Cycle Assessment 

Results of Torrefied Briquette Supply Chain

The environmental impact assessment results associated 

with generating heat from wood briquettes at wood stoves 

are presented in Table 13 for 10 impact categories: GW, 

acidification, eutrophication, OD, smog formation, human 

health (carcinogenics and noncarcinogenics), respiratory 

effects, ecotoxicity, and fossil fuel depletion. The results 

presented here are for the same conditions in which the 

demonstration-scale system was operated near the woods 

and torrefaction and briquetting occurred at the BCT site 

close to the feedstock source and was powered using a 

wood gasifier genset as the base scenario. The drying 

process was heated by a portion of the torgas combustion 

(31%). The remaining torgas was flared at the torrefaction 

unit. Propane was used to achieve ignition and complete 

combustion of torgas, which caused the torrefaction 

process to have the highest impacts for the categories of 

OD, GW, eutrophication, carcinogenics, noncarcinogenics, 

ecotoxicity, and fossil fuel depletion.

Process contributions to the overall GW impact for the 

TOB supply chain are presented in Figure 7. Contribution 

analysis revealed that a large portion of the GW impact 

resulted from torrefaction and drying processes with 59% 

and 24% contributions, respectively. As expected, the high 

contribution of these processes resulted from propane use. 

In the base scenario, torgas was used to provide heat to the 

drying process. Yet, because of the low energy content of 

torgas, combustion was supplemented with propane for 

ignition and steady burn.

Environmental impact assessment results associated with 

generating heat from a propane furnace are presented in 

Table 14. The production stage was responsible for the 

majority of the impact for all impact categories except 

for GW. This was followed by the combustion stage. 

Contribution of the distribution stage to overall impact 

was minor.
Using Life-Cycle Assessment to Evaluate Environmental Impacts of Torrefied Briquette Production from Forest Residues

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Table 13—Environmental performance of 1 MJ of thermal energy generated for domestic heating from combusting torrefied briquettesImpact category Unita

Feedstock 

procurement Hauling

Chipping/

screening Drying Torrefaction Briquetter Distribution Combustion Packaging

Ozone depletion kg CFC-11 eq 1.26E–12 2.51E–13 1.83E–12 1.31E–11 1.46E–10 3.42E–13 8.17E–13 0.00E+00 8.02E–16Global warming kg CO2 eq 6.89E–04 2.26E–04 1.00E–03 4.02E–03 9.82E–03 1.96E–04 4.89E–04 7.57E–05 8.02E–08Smog kg O3 eq 2.98E–04 3.64E–05 4.29E–04 3.24E–04 1.46E–03 1.99E–04 7.80E–05 4.61E–03 2.31E–09Acidification kg SO2 eq 9.07E–06 1.20E–06 1.32E–05 1.33E–05 5.87E–05 7.18E–06 2.70E–06 3.59E–05 1.69E–10Eutrophication kg N eq 6.97E–07 9.90E–08 1.01E–06 1.62E–06 6.85E–06 4.30E–07 2.51E–07 1.61E–06 5.72E–10Carcinogenics CTUh 1.15E–11 2.28E–12 1.67E–11 6.31E–11 1.63E–10 3.11E–12 7.41E–12 0.00E+00 1.05E–15Noncarcinogenics CTUh 1.13E–10 2.25E–11 1.64E–10 6.27E–10 1.70E–09 3.06E–11 7.31E–11 0.00E+00 2.86E–14Respiratory effects kg PM2.5 eq 1.79E–07 1.84E–08 2.61E–07 2.70E–07 1.63E–06 2.18E–07 4.17E–08 2.13E–05 6.81E–12Ecotoxicity CTUe 2.88E–03 5.77E–04 4.20E–03 1.58E–02 3.72E–02 7.83E–04 1.88E–03 0.00E+00 3.34E–06Fossil fuel depletion MJ surplus 1.33E–03 2.66E–04 1.94E–03 7.28E–03 1.72E–02 3.61E–04 8.65E–04 0.00E+00 3.76E–07aCFC, chlorofluorocarbons; CTUh, comparative toxicity units humans; PM, particulate matter; CTUe, comparative toxicity units ecotoxicity.
General Technical Report FPL–GTR–263

18

Figure 7. Contribution of processes to the overall global warming 

impact of the torrefied briquette production system.

Table 14—Environmental performance of 1 MJ of thermal energy generated for domestic 

heating from propane combustion

Impact category Unita Production Distribution Combustion

Ozone depletion kg CFC-11 eq 1.81E–10 1.27E–13 0.00E+00

Global warming kg CO2 eq 1.62E–02 7.65E–05 7.81E–02

Smog kg O3 eq 2.05E–03 1.96E–05 1.45E–03

Acidification kg SO2 eq 1.52E–04 7.24E–07 4.09E–05

Eutrophication kg N eq 2.85E–05 5.22E–08 2.57E–06

Carcinogenics CTUh 1.64E–09 1.15E–12 0.00E+00

Noncarcinogenics CTUh 1.62E–08 1.13E–11 0.00E+00

Respiratory effects kg PM2.5 eq 2.39E–06 1.08E–08 5.32E–07

Ecotoxicity CTUe 4.16E–01 2.91E–04 0.00E+00

Fossil fuel depletion MJ surplus 1.92E–01 1.34E–04 0.00E+00

a

CFC, chlorofluorocarbons; CTUh, comparative toxicity units humans; PM, particulate matter; CTUe, comparative 

toxicity units ecotoxicity.

Chipping/screening (6%)

Drying (24%)

Hauling (1%)

Feedstock procurement (4%)

Briquetter (1%)

Distribution (3%)

Use phase (combustion) (0%)

Torrefaction (59%)
Using Life-Cycle Assessment to Evaluate Environmental Impacts of Torrefied Briquette Production from Forest Residues

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0

20

40

60

80

100

Production

Pile and burn

Use phase (combustion)

Distribution

Briquetter

Torrefaction

Feedstock preparation

Hauling

Feedstock procurement

S0 50% S1 80% S1

g CO2 equivalent/MJ heat

94.4

55.4

32.1

Total

Figure 8. Comparison of the global warming impact results per megajoule of heat generated 

through a propane furnace, Scenario 0 (S0), and a propane system supplemented with torrefied 

briquettes (50% and 80%), Scenario 1 (S1).

g CO2 equivalent/MJ heat

Pile and burn

Total

Use phase (combustion)

Distribution

Briquetter

Torrefaction

Feedstock preparation

Hauling

Feedstock procurement

0

–10

10

20

30

40

50

60

S1 S2 S3 S4 S5 S6

16.5

50.8

36.8 38.2 37.1

13.9

Figure 9. Contribution of processes to overall global warming impact per megajoule of thermal 

energy generated for six scenarios investigated. S1: 1 MJ heat, near-woods operation with wood 

gasifier power; S2: 1 MJ heat, near-woods operation with diesel power; S3: 1 MJ heat, in-town 

operation (2-h travel distance) with grid power; S4: 1 MJ heat, in-town operation (4-h travel 

distance) with grid power; S5: 1 MJ heat, 50% moisture content feedstock, near-woods operation 

with wood gasifier power; S6: 1 MJ heat, near-woods operation with wood gasifier power with 

pile-and-burn credit. 
General Technical Report FPL–GTR–263

20

Impact category (%)

0

10

20

30

40

50

60

70

80

90

100

1 MJ heat, grid 2 h

1 MJ heat, diesel 

1 MJ heat, gasifier

Fossil fuel

depletion

Ozone depletion Smog Acidification Eutrophication

Figure 10. Summary of comparative life-cycle impact assessment results for three power sources 

(grid, diesel, and gasifier electricity) for the torrefied briquette production system.

Figure 11. The toxicity impact category results for generating 1 MJ of thermal output for the scenarios investigated. Process contribution (%)

Pile and burn

Use phase (combustion)

Distribution

Briquetter

Torrefaction

Feedstock preparation

Hauling

Feedstock procurement

0

10

20

30

40

50

60

70

80

90

100

–100

–90

–80

–70

–60

–50

–40

–30

–20

–10 1 MJ heat, gasifier

1 MJ heat, diesel1 MJ heat, grid 2 h1 MJ heat, pile and burn1 MJ heat, gasifier1 MJ heat, diesel1 MJ heat, grid 2 h1 MJ heat, pile and burn1 MJ heat, gasifier1 MJ heat, diesel1 MJ heat, grid 2 h1 MJ heat, pile and burn1 MJ heat, gasifier1 MJ heat, diesel1 MJ heat, grid 2 h1 MJ heat, pile and burn

Carcinogenics Noncarcinogenics Respiratory effects Ecotoxicity
Using Life-Cycle Assessment to Evaluate Environmental Impacts of Torrefied Briquette Production from Forest Residues

21

Conclusions, Limitations, and 

Recommendations

This study provides a comprehensive cradle-to-grave LCA 

of the TOB production supply chain investigating the 

environmental performance of using post-harvest forest 

residues with torrefaction and briquetting processes for 

biofuel production. Using torrefied briquettes for energy 

production instead of fossil fuel alternatives was revealed to 

be preferable for GHG emission reduction. Major benefits 

were observed consistent with recent studies investigating 

the use of torrefied wood as a substitute for natural gas for 

heat production and coal for electricity production (Majer 

and others 2015).

Near-woods bioenergy production systems using power 

from an on-site wood gasifier genset showed better 

environmental performance than did the fossil fuel 

alternatives (on-site diesel and in-town grid electricity). 

For remote power generation, GHG emissions were about 

three times lower when a woody biomass gasifier genset 

was substituted for a diesel generator. In-town operation 

with grid electricity supply was a better option compared 

with remote operation using a diesel generator. Use of 

post-harvest residues as biofuel as opposed to the typical 

pile-and-burn practice showed a notable environmental 

advantage in GW and toxicity impact categories. Data on 

heat requirements at the dryer process were not available. 

Therefore, data were retrieved from literature using a 

conservative approach. As the sensitivity analysis revealed, 

drying parameters had a great influence on the impact 

assessment results. Therefore, drying data that rely on 

operational runs would improve the quality of the analysis.

Results indicated that GW impact was highly dependent on 

torgas management in the torrefaction process and on heat 

demand in the drying processes. This was mainly because 

of the low energy content of torgas, which required use 

Figure 11 presents the toxicity impact category results: 

human health (carcinogenics and noncarcinogenics), 

respiratory effects, and ecotoxicity. Using a wood gasifier 

as the power source for near-woods operation showed better 

performance compared with diesel and grid electricity 

alternatives for toxicity impact categories. Pile-and-burn 

credits resulted in substantial benefits particularly in 

human health impact categories. Environmental benefits 

of the avoided pile-and-burn emissions were notable in 

the respiratory effects impact category, mainly because of 

avoided particulate matter emissions.

Life-Cycle Interpretation

The interpretation section evaluates results for either the 

LCI or the LCIA, or both, in line with the defined goal 

and scope. The midpoint analysis results are presented and 

discussed in the previous section, which included scenario 

analysis. In this part of the report, results from the additional 

parameter-based sensitivity analysis are addressed as 

part of the interpretation. Additional components include 

conclusions, limitations, and recommendations.

Completeness, Sensitivity, and 

Consistency Checks

Results of the parameter-based sensitivity analysis are 

presented in Figure 12. The sensitivity of the GW impact 

was examined for 25% variation in key parameters 

including briquetter and torrefier electricity demand, 

distribution and hauling distances, and propane supplement 

used for torgas combustion. The sensitivity analysis 

performed showed that propane supplement was a key 

parameter with great influence on variation in the GW 

impact, followed by electricity consumption of the 

torrefaction process. This reveals the importance of dryer 

heat requirement and energy consumption data to decrease 

the uncertainty resulting from parameters used.

Hauling

Distribution

Electricity briquetter

Electricity torrefier

Torgas propane use

–3.20 –2.20 –1.20 –0.20

g CO2

 equivalent/MJ heat

0.80 1.80 2.80

Figure 12. Sensitivity of key parameters on global warming impact.
General Technical Report FPL–GTR–263

22

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External Review

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