Using Life-Cycle Assessment to 

Evaluate Environmental Impacts 

of 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–262

December

2018

Used with permission from Schatz Energy Research Center
Abstract

This report presents a life-cycle impact assessment analysis 

of near-woods processing of post-harvest forest residues 

into wood briquettes as an alternative to other fuels such 

as propane in residential heating systems. The study was 

part of the Waste to Wisdom project with a broader goal 

of evaluating the feasibility of using semimobile biomass 

conversion technologies to overcome the barriers of 

valorizing woody biomass residues for renewable energy 

and material production. The cradle-to-grave system 

boundary included feedstock procurement, hauling, 

feedstock preparation, production of briquetted biomass 

from forest residues, briquette transportation (distribution), 

and heat generation at the residential wood stove (use 

phase) life-cycle stages. The feedstock preparation stage 

contributed the most to the global warming (GW) impact 

of the near-woods wood briquette production supply 

chain. This was because of the drying process, which 

contributed 72% of the overall GW impact. Near-woods 

biomass conversion using wood gasifier as the power source 

was favorable compared with the other scenarios, which 

included diesel power and in-town processing of forest 

residues using grid electricity. The overall decrease in GW 

impact was 33%, after taking into account the avoided pile 

and burn emissions. Thus, substituting propane with wood 

briquettes in heating systems provided greenhouse gas 

reduction while aiding forest restoration activities.

Keywords: bioenergy, biomass densification, briquette, postharvest forest residues, life-cycle assessment

Acknowledgments

This material is based upon 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 U.S. Forest Service Research 

Participation Program administered by the Oak Ridge 

Institute for Science and Education through an interagency 

agreement between the U.S. Department of Energy and the 

U.S. Department of Agriculture 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 ..............................................1

Life-Cycle Inventory Analysis.............................................9

Life-Cycle Impact Assessment ..........................................13

Life-Cycle Interpretation ...................................................17

Conclusions, Limitations, and Recommendations.............18

External Review.................................................................20

References..........................................................................20

December 2018

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

assessment to evaluate environmental impacts of briquette production 

from forest residues. General Technical Report FPL-GTR-262. Madison, 

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

Laboratory. 22 p.

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Using Life-Cycle Assessment to Evaluate 

Environmental Impacts of 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

This study evaluates environmental sustainability of using 

post-harvest forest residues in the briquetting process, where 

biomass conversion takes place close to the harvest site, 

for solid biofuel production using the life-cycle assessment 

(LCA) tool. The objective was to assess and document 

life-cycle environmental impacts associated with briquetted 

biomass production from post-harvest forest residues and 

the use of briquetted biomass as a solid biofuel for domestic 

heating. This 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 covered a cradle-to-grave 

system boundary for the wood briquette production 

supply chain. The system boundary started at feedstock 

procurement (woody biomass collection) and included six 

life-cycle stages: feedstock procurement, hauling, feedstock 

preparation, production of briquetted biomass from forest 

residues, product transportation (distribution), and heat 

generation at the residential wood stove (use phase). 

The feedstock procurement stage included processing 

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

life-cycle stage, which is located at the near-woods 

processing site, included chipping, screening, and 

(propane-fueled forced) drying unit processes.

The operational data used in this study were developed by 

other subtasks under the Waste to Wisdom (WTW) project 

(www.wastetowisdom.com). Feedstock procurement 

and feedstock preparation data were based on field data 

collected and experimental studies performed in 2015 by 

Humboldt State University, Arcata, California, USA. The 

primary data for the briquetter relied on the operational runs 

of the 200-kg/h distributed-scale briquetting unit collected 

from the production site in Big Lagoon, California, USA, in 

2015 near a major commercial harvesting site. This included 

data for the dryer and briquetting processes.

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 (USEPA 2012), and the system was modeled using 

the SimaPro 8.5 LCA software package (PRéConsultants 

bv, Amersfoort, the Netherlands). The functional unit in 

this study was defined as 1 MJ of useful thermal energy 

produced for domestic heating, including any efficiencies 

lost.

The results of the comparative analysis revealed that a 

notable reduction in global warming (GW) impact can be 

achieved by substituting wood briquettes produced from 

post-harvest forest residues using near-woods biomass 

conversion operation for propane. Although the postharvest forest residues were field-dried to 20% moisture 

content (MC) before being collected, the contribution 

analysis showed that the drying unit process had the 

highest contribution to the overall GW impact, about 72% 

contribution, followed by other feedstock preparation 

processes: chipping and screening. Overall, most GW 

impact (about 82%) resulted from the feedstock preparation 

life-cycle stage. More specifically, propane consumption 

during the drying process was responsible for the large 

contribution of the drying process to the overall GW impact. 

Conversely, the contribution of densification (briquetting) 

and use phases were minor, about 1%. When alternative 

scenarios were considered, near-woods operation using 

wood gasifier power was identified to be the scenario with 

the best environmental performance. Not unexpectedly, 

sensitivity analysis showed that MC of the incoming 

feedstock used in the briquetter system was revealed to 

have a substantial effect on the resulting environmental 

impacts. This was caused by the greater heat demand for the 

dryer when high MC feedstock was used, which resulted 

in increased propane consumption. Thus, lowering the 

amount of force-drying would have the greatest influence on 

lowering environmental impacts, especially for greenhouse 

gas (GHG) mitigation efforts.

Definition of Goal and Scope

Study Goals

The aim of this study was to evaluate environmental 

sustainability of briquetting (densifying) post-harvest forest 

residues for solid biofuel production. A cradle-to-grave LCA 
General Technical Report FPL–GTR–262

2

was performed to assess the environmental sustainability 

of producing wood briquettes from forest residues near 

the point of harvesting logs (i.e., near-woods). The LCA 

analysis was performed at plant and unit process level in 

accordance with ISO 14040 and ISO 14044 LCA standards 

(ISO 2006a, 2006b).

Currently, there is growing demand for biomass-based 

renewable energy to decrease the use of fossil fuels and 

to mitigate GHG emissions (Tilman and others 2009, 

Lippke and others 2012, Jakes and others 2016). Therefore, 

this study was performed to evaluate the environmental 

footprint and to obtain more insight into the life-cycle 

impacts of producing wood briquettes as an alternative 

low-carbon energy source. To evaluate the environmental 

performance and competitiveness of the studied system, 

the briquette production system was evaluated against 

the propane production system for energy substitution. 

The wood briquettes from forest residues are designed to 

replace firewood in wood heating systems. This study was 

conducted with funding support from a BRDI grant, which 

is a collaborative initiative between DOE and USDA.

Intended Application

This study assessed and documented life-cycle 

environmental performance associated with the briquetted 

biomass production from post-harvest forest residues. 

Briquetting improves the quality of biomass allowing 

easier transportation and storage of the product compared 

with wood logs (Bergman and Zerbe 2008). In addition, 

briquettes have higher calorific value and volume density, 

have lower MC, and provide more consistent, efficient, 

and longer burn compared with wood logs (Canadian 

Biomass Magazine 2010, Grover and Mishra 1996). 

Briquettes made from biomass are a solid renewable 

energy source that can be burned in domestic hot water 

boilers and wood furnaces and stoves for space heating as 

an energy substitute for propane or cordwood (Roy and 

Corscadden 2012). Valorization of forest residues, which 

are a byproduct of commercial harvesting operations, for 

biofuel production may result in considerable environmental 

and economic benefits. Briquetting technology can be used 

for transformation of forest residues to a (solid) bioenergy 

carrier, which may be used to substitute for fossil fuels. This 

can allow for mitigation of GHG emissions. Therefore, the 

intended application of this study was to provide credited 

data and enhance knowledge about environmental aspects 

associated with conversion of forest residues to bioenergy 

carriers using a decentralized small-scale briquetting process 

at life-cycle level. The assessment also included comparison 

of wood briquette production with production of traditional 

fuel, i.e., propane, to demonstrate the environmental benefits 

that may be achieved through substitution of traditional 

energy sources. The results of this study may promote 

production of forest-based bioenergy using the briquetting 

process.

Motivation

The increase in demand for and consumption of energy 

resources, environmental sustainability initiations, and 

new policies to combat climate change are major drivers 

for establishing renewable energy sources (USEIA 2017b, 

IEA 2017). Energy consumption in the Organization for 

Economic Cooperation and Development (OECD) countries 

is expected to increase 9% between 2015 and 2040, whereas 

the expected increase is 41% in nonOECD countries 

(USEIA 2017b). 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 (US 

Congress 2007).

Biomass is considered a promising feedstock for renewable 

energy production. Currently in the United States, the 

forest biomass, i.e., slash, resulting from commercial 

logging operations is often left on site to decay or is burned 

(USDOE 2011, USEPA 2007). In the United States, there 

is good potential for forest residues as wood waste to be 

utilized as a renewable energy source (Oswalt and others 

2014). About 93 million dry metric tons of forest removals 

are generated in the United States annually, 73% of which 

is the result of logging residues (Smith and others 2009, 

USDOE 2011). According to the 2016 Billion-Ton Report 

baseline scenario (assuming moderate growth in housing 

starts and low growth in biomass for energy), about 84 

million dry metric tons (93 million dry tons) of forest 

residues and whole-tree biomass from commercial timber 

harvesting and thinning operations will be available in 

2022 at US$60 per dry metric ton (USDOE 2016). Also, 

increasing wildfire frequency and intensity are growing 

concerns, especially in the western United States, and 

forest residues left on site increase the risk of wildfires 

and spreading of diseases (USDA Forest Service 2005, 

Dennison and others 2014, Giuntoli and others 2015). 

Many forestland management agencies in the United States 

encourage biomass removal as a means to reduce fire hazard 

(Loeffler and others 2010). Potential benefits of removing 

forestry residues from public lands include reducing the risk 

of catastrophic fires and preventing diseases from spreading 

(USDA Forest Service 2005, Giuntoli and others 2015).

The motivation for undertaking this study was to evaluate 

environmental viability of valorization of post-harvest 

forest residues, in combination with a briquetter, to 

produce a bioenergy carrier. The use of forest residues 

as biomass feedstock has the potential to decrease fossil 

fuel dependence while eliminating fossil-fuel-based GHG 

emission. 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 decrease dependence on 

fossil fuels (U.S. Senate 2005, U.S. Congress 2007).
Using Life-Cycle Assessment to Evaluate Environmental Impacts of Briquette Production from Forest Residues

3

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

Deconstruction Upgrading

Conversion

Biomass

production

Feedstock

logistics

Feedstock supply

Distribution End use

Bioenergy infrastructure

Production of biomass fuels and products can lower the 

requirement for oil and gasoline imports while supporting 

the growth of agriculture, forestry, and rural economies 

(Naik and others 2010, USDOE 2016, USEIA 2017c). This 

study was part of a USDOE-funded BRDI project called 

Waste to Wisdom (www.wastetowisdom.com) in which 

the team performed an investigation of biomass feedstock 

logistics, near-woods product production, distribution, and 

end-use, focusing on integrating three biomass conversion 

systems that used post-harvest forest residues near the 

woods where the timber harvest occurred, hence the term 

near-woods (Han and others 2018, Bergman and others 

2018). This study focused only on briquetting raw woody 

biomass.

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 subjected to third-party critical 

review (ISO 2006a, 2006b). 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 decrease fire risk (Loeffler and others 2010). 

The removal of biomass for biofuel production may be of 

interest to forestland managers because this may assist them 

to overcome costs associated with biomass fuel treatment 

for decreasing fire hazard.

This study presented an environmental evaluation of 

briquetted biomass production in the United States as a 

potential low-carbon solid biofuel product that could replace 

fossil fuels. This may help industries or residential energy 

users achieve GHG emission reductions. Furthermore, this 

study may also be of interest to consumers that have basic 

environmental concerns.

Scope of the Study

The scope of this LCA study covered cradle-to-grave 

feedstock procurement and preparation, hauling, production 

of briquetted biomass from forest residues, distribution, 

and heat generation from domestic heating systems. The 

system boundaries begin at the collection and biomass 

conversion of forest residues to briquetted biomass near 

the forest and end at the grave, i.e., combustion in a wood 

stove for space heating. The life-cycle level environmental 

impacts of briquetted biomass production from post-harvest 

forest residues were evaluated and compared with propane 

production from crude oil as the reference supply chain for 

heating fuel. An LCA for propane was constructed from 

peer-reviewed literature and other secondary sources. Forest 

residues are 100% wood; therefore, the terms forest residues 

and wood are used interchangeably in this report.

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 included any efficiency loss to 

generate the 1 MJ of heat and was based on higher heating 

value (HHV). HHV is used to convert volume or mass basis 

of a fuel to its energy value. HHV represents the energy 

content of a fuel with the combustion products such as 

water vapor brought to 25 oC, whereas lower heating value 

(LHV) omits the energy consumed to vaporize water held in 

the native energy form or produced during the combustion 

process. HHV (gross heat content) is the preferred method 

used in the United States (USEIA 2017a). The input and 

output flows were standardized based on the selected FU.

System Boundary

This study evaluated two functionally compatible energy 

carriers, i.e., briquetted (densified) biomass and propane, 

with different production processes by making use of the 

LCA tool. The typical life cycle of a biomass-to-bioenergy 

supply chain starts at biomass production and ends at the 

end user (Fig. 1).

The system boundary of the briquetter system investigated 

is provided in Figure 2. This study performed a cradleto-grave LCA in which the life-cycle stages of briquetted 

biomass production included feedstock procurement, 

hauling, feedstock preparation (chipper, screener, and 

dryer), briquetting, distribution, and the use phase. The 

biomass feedstock supplied to the system was post-harvest 

forest residue, which is generated during commercial 

timber harvesting operations and treated as a waste product. 

Because forest residues are a waste product, which are 

typically left to decay or burnt on site, it was assumed 

that they do not have an environmental burden. Therefore, 
General Technical Report FPL–GTR–262

4

Figure 3. System boundary for propane production supply chain.

Heat

Raw material 

extraction 

(crude oil)

Processing Distribution Combustion 

in furnace

the cradle-to-grave system boundary does not include the 

previous life-cycle stages associated with harvesting and 

generation of forest residues. The cradle starts at the point 

of collection or extraction of post-harvest forest residues. 

Because of insufficient information on the briquetting 

technology investigated, manufacturing, maintenance, and 

disposal of equipment used in the system were considered 

outside the scope of the LCA. This is in line with the 

propane production system, which also excludes those 

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 stops at 

the useful heat produced from the residential furnace for 

domestic heating purposes (Corma and others 2018, USEIA 

2017c, LTS 2017, Johnson 2012).

In this study, various system configurations were analyzed 

to evaluate the effect of process variation and logistics on 

life-cycle impacts of the briquette production supply chain. 

The system description of briquetting plant processes along 

with the inputs and emissions to and from the system is 

provided in Figure 4.

The feedstock used in this study was obtained from 

commercial timber harvesting operations in the western 

United States, specifically Washington, Oregon, and 

California. Logging slash residues were used as the input 

biomass feedstock. These residues included tree tops, limbs, 

chunks, and branches, which are byproducts of commercial 

harvesting operations. The feedstock procurement 

stage (woody biomass collection) included processing 

(delimbing), sorting, and loading. All electricity and heat 

necessary for the remote system was generated on site 

using a wood gasifier and propane burner, respectively. The 

system components are described in the following sections 

in detail.

Feedstock Procurement

The biomass feedstock received was the waste from 

commercial timber harvesting operations and was composed 

of tree tops, limbs, branches, etc. Pulp logs made up part 

of the biomass feedstock because of the lack of nearby 

markets, which is not historically typical. In this study, 

the term logging slash was used when referring to forest 

residues. Because the logging slash was left in the forest 

for air-drying for 1 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 

the post-harvest forest residues. 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., near-woods 

biomass conversion technology (BCT) site). Primary data 

from five commercial harvesting sites in the western United 

States were used for modeling the biomass procurement 

T

Heat

Feedstock

procurement

System boundary

T

Feedstock

preparation

Biomass

collection Chipper Screener Dryer

Briquette

Briquetter Forest

residues

Combustion

Figure 2. System boundary for briquetted biomass production supply chain (T, transportation).
Using Life-Cycle Assessment to Evaluate Environmental Impacts of Briquette Production from Forest Residues

5

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

supply chain (T, transportation).

model: Port Angeles, Washington; Warm Springs, Oregon; 

Oakridge, Oregon; Lakeview, Oregon; Quincy, California. 

Average transport distance traveled from the primary 

landing to the BCT site for the five regions investigated was 

about 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 briquetting 

into bioenergy products. The lubricant consumption data for 

hydraulic oils, general lubricants, and fuel consumption of 

chipper and screener were based on the tests performed by 

Humboldt State University (HSU), which were generated as 

a part of the WTW project (Oneil and others 2017).

In this study, a variety of feedstocks were tested for certain 

characteristics for the WTW project. Feedstocks used 

were sourced from Redwood (Sequoioideae), Douglas-fir 

(Pseudotsuga menziesii), Tanoak (Lithocarpus densiflorus), 

and mixed conifer species. The characteristics of the 

feedstock used for biomass conversion are provided in 

Table 1.

Densification (Briquetting)

Wood chips were densified into briquettes using an RUF200 

model briquetter (RUF Briquetting Systems, Zaisertshofen, 

Germany). The briquetter used hydraulic cylinders for 

compressing the feedstock and had a capacity of 200 kg 

feedstock per hour. The woody biomass feedstock was fed 

into a hopper, then transferred to a pressing chamber via a 

screw conveyor (Fig. 5). Finally, the compressed 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 

(briquetting) phase to improve binding characteristics. For 

the system under investigation, no binder addition occurred. 

The characteristics of the briquette fuel produced after 

biomass conversion are provided in Table 2.

Transportation

Environmental burdens resulting from transportation of 

materials from the harvesting site (distribution) and from 

manufacturers to the briquetting site were considered in this 

study. The briquetter was located in Big Lagoon, California, 

USA, and transportation of briquettes to the end-user for 

residential heating was included in the inventory. It was 

assumed that the briquettes produced for use in the closest 

town were transported via tractor trailer fueled by diesel. 

Post-harvest 

forest residues

Feedstock 

procurement

Chipper

Screener

Dryer

Combustion

Heat

Briquetter

T

T

Lubricants

Diesel

Lubricants

Diesel

Lubricants

Diesel

Propane Flue gas

Flue gas

Electricity

Resources

Emissions 

to air, 

water, 

land
General Technical Report FPL–GTR–262

6

Table 2—Properties of briquettes produced

Property Valuea

Moisture content (%) wbb 6.13 (15.60)

Average density (kg/m3) 861.67 (8.07)

Energy density (MJ/kg) HHVc 17.78 (1.89)

Durability (%) 95.98 (2.11)

a

Coefficient of variation (%) values are provided in parentheses.

b

wb, wet basis.

c

HHV, higher heating value.

Cabinet

Hopper

Precharger

Mould change cylinder

Briquette outlet

Figure 5. RUF briquetter machine (photo used with permission from RUF Briquetting Systems, 

Zaisertshofen, Germany).

Table 1—Properties of feedstock used for bioconversion

Sample ID Type

Moisture content

(%)

Bulk density

(kg/m3)

S1 Redwood, chip, mediuma 6.5 —

S2 Douglas-fir, chip, smallb 6.3 187.07

S3 Douglas-fir, chip, medium 6.3 174.46

S4 Tanoak, chip, small 4.2 194.47

S5 Tanoak, chip, medium 6.5 196.07

S6 Conifer, chip, medium 6.9 180.92

a

Medium chips: 0.75 to 2 in.

b

Small chips: ≤0.75 in.
Using Life-Cycle Assessment to Evaluate Environmental Impacts of Briquette Production from Forest Residues

7

Additionally, environmental impact resulting from the 18.8-

km weighted-average transportation of biomass feedstock to 

the briquetting site was taken into account. Transportation 

tends to be a limiting economic factor when hauling woody 

biomass but not a limiting environmental factor (Giuntoli 

and others 2015, Ranta and others 2016, Kylili and others 

2016).

Combustion

Use-phase data came 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 typical freestanding 

wood stove that was not U.S. Environmental Protection 

Agency (EPA) certified (Schrader Woodstoves, Harrisburg, 

Pennsylvania, USA) using 2.4 m of single-walled stove 

pipe followed by 2.4 m of insulated double-walled 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 Investigated

In this study, alternative system configurations were 

investigated at the cradle-to-grave level (Table 3). The 

effects of logistical options, such as locating the BCT site at 

a remote location close to the harvest site or close to town 

with access to grid electricity, were investigated.

In addition, alternative options for the electricity source 

were compared. The briquetter unit was considered to be 

a mobile unit for near-woods operations because it can 

easily be transported between forest operation sites. This 

allows processing of the forest residues closer to the primary 

landing before the bioenergy product is shipped to the user. 

Two remote power generation technologies were taken into 

account: a woody biomass gasification generator set and 

a diesel generator set. These were compared with a local 

grid electricity mix that was used when biomass conversion 

operations took place in town instead of close to the 

harvest site. These two alternatives showed that as distance 

increased from the point of harvesting, speed increased 

because the type of transportation could be on-road versus 

off-road (i.e., in the forest). The off-road transportation was 

the same for both scenarios. For the two in-town scenarios, 

distribution distance of briquettes was not taken into 

consideration because the biomass conversion operation 

took place close to users. Power Pallet-PP20 biomass 

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

an engine generator rated at 20 kWe was tested for remote 

power generation (All Power Labs 2016). The power source 

used in the base scenario was a woody biomass gasifier 

generator set (genset), and as an alternative scenario, a 

diesel power generator was investigated to evaluate the 

effect of the power source used on the environmental impact 

results. In addition, the effect on the results was evaluated 

from a scenario of transferring forest residues to an in-town 

facility where grid electricity was used as opposed to an onsite operation for biomass conversion. 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 resulting from 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 where 

two or more functions are delivered. The only product of 

the system under investigation was briquetted biomass. 

For this reason, allocation was not required in the 

densification process. For the other life-cycle phases 

including multifunctional processes such as the screening 

process, mass allocation was used in line with the North 

American Structural and Architectural Wood Products 

product category rule, which suggests use of economic 

allocation when the difference in revenues is more than 10% 

(FPInnovations 2015). In this case, differences between the 

economic values of the products were less than 10%. Mass 

allocation was used in the propane system model. Thus, the 

allocation approach was consistent between the two product 

systems.

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, 50% moisture content feedstock, in-town operation (2-h travel distance) with grid power

S7 1 MJ heat, near-woods operation with wood gasifier power with pile and burn credit
General Technical Report FPL–GTR–262

8

Assumptions and Limitations

Wood is composed of many compounds in addition to its 

solid components, including volatile organic compounds 

(VOCs). VOCs are considered hazardous air pollutants. 

VOC emissions from wood occur when it is freshly cut. 

In this study, VOC emissions that occurred during drying 

of the fresh biomass feedstock were taken into account. 

Because the biomass was field-dried to a MC of about 

20% on a wet basis, it was assumed, when the biomass 

was received at the dryer unit, that 20% of the VOCs were 

emitted during drying, whereas the remaining 80% had 

been emitted in the forest. In addition, the data on heat 

requirement during 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). Tracking material flow was important for 

verifying mass balance of product systems. Mass loss during 

the densification process was negligible. Therefore, it was 

assumed that there was no mass loss at the briquetter.

The EPA released a second draft of Framework for 

Assessing Biogenic CO2 Emissions from Stationary Sources 

that provides an analytical methodology on 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 carbon 

neutral, which is 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.

Life-Cycle Impact Assessment Method and 

Types of Impacts

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

categories examined in this study included 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). All impact categories covered in the TRACI 

method were considered in this study (Bare 2011, USEPA 

2012). 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, and more research will be required 

to establish them. Site-specific data are required because 

of the unique properties of location, meteorology, and 

existing ecosystems (USEPA 2012). Therefore, 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 to be waste. As 

mentioned earlier, forest residues are commonly left on 

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

method. For this reason, we did not consider the growth of 

the tree that generates the forest residues to be within the 

system boundaries. Consequently, we did not evaluate the 

land-use impacts.

Among the available methods for LCIA, TRACI was 

used in this study (Bare 2011). TRACI is a midpoint level 

impact assessment model developed by the EPA and is 

specifically representative for the United States using input 

parameters consistent with U.S. conditions. LCIA results are 

relative expressions and do not predict impacts on category 

endpoints or the exceeding of thresholds, safety margins, or 

risks.

Data Quality

The data were collected in line with the data quality criteria 

addressed by ISO 14044 to ensure quality and reliability. 

The details are provided in the following sections.

Geographical and Time-Related Coverage

Quantitative data on mass and energy flows of the 

briquetting system were based on the operational data of 

core processes in the year 2015. The unit was located and 

operated in northern California, USA. Woody biomass 

collection and feedstock preparation data were obtained 

from field-based data and experimental studies, in 2015, 

performed as a part of the WTW project (Bisson and Han 

2016, Kizha and Han 2016). The field data on the feedstock 

procurement stage was 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 from the 

Ecoinvent v.2.2 data set (LTS 2017, PRé Consultants 2017, 

NREL 2012). The U.S. LCI Database is based on regional 

conditions and represents U.S. circumstances.

Precision

Variance could not be calculated because this study 

was based on a single data set, not on an industry level. 

However, process-specific data were provided 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 briquetter 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 briquetting technology used is current and 

representative, and the product it produces is compatible 
Using Life-Cycle Assessment to Evaluate Environmental Impacts of Briquette Production from Forest Residues

9

with other products in the market. The internal process 

(mechanical and hydraulic presses) and inputs (binding 

agents) can be different depending on the technology and 

feedstock used, but the final product is the same.

Reproducibility

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

generated in this study were provided in detail to allow 

other LCA practitioners to reproduce the results presented in 

this study.

Data Sources

Feedstock procurement and preparation data were obtained 

from Oneil and others (2017) and were based on field data 

and experimental studies performed as part of the WTW 

project (Bisson and Han 2016, Kizha and Han 2016, Kizha 

and others 2018). The primary data for the briquetter relied 

on the operational runs of the mobile briquetting unit. All 

relevant quantitative data (input–output flows) associated 

with the unit processes were collected from the production 

site in Big Lagoon, California. This included operational 

data for the dryer and briquetting processes. These data 

included input–output mass and energy flows and physical 

properties of the feedstock received by the systems and 

characteristics of the final product, briquetted biomass. The 

secondary data such as supply of electricity, manufacturing 

of the chemicals, transport, and waste disposal came from 

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, and Shaobo Liang, PhD, 

Postdoctoral Research Fellow, USDA Forest Service, 

Forest Products Laboratory.

The main aims of the review panel, as outlined by 

ISO 14044, were to ensure that (1) the methods were 

scientifically and technically valid, (2) the methods were 

consistent with ISO 14044, (3) the data were appropriate 

and reasonable in light of the goal of the study, (4) the 

interpretations reflected the limitations, and (5) the report 

is transparent and consistent.

Value Choices

In this study, only the 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. Thus, 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. Endpoint-level impact assessment analysis 

combines midpoint impacts under the three areas of 

protection: natural environment, human health, and 

natural resources. Endpoint analysis allows the results 

to be presented with a single-score result, which allows 

easier interpretation and communication of LCA results 

with nonLCA experts and easier comparison of the 

environmental impact of different products or scenarios. 

The optional weighting step based on value choices allows 

a single-score result of the LCA analysis, yet it introduces 

more assumptions to the analysis, leading to more 

uncertainties.

Life-Cycle Inventory Analysis

The cradle-to-grave system boundary of the briquetting 

plant includes feedstock procurement (processing such as 

delimbing, sorting, and loading), feedstock preparation 

(chipping, screening, and drying), briquetting (densification) 

of forest residues, product transportation, and combustion of 

the briquettes in wood stoves for domestic heating. Biomass 

procurement data were provided by the WTW project. All 

relevant material and energy flows associated with the unit 

processes included in the cradle-to-grave system boundary 

of briquette production were collected to develop a cradleto-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 starts at the extraction 

of crude oil and stops at the useful heat produced at the 

residential furnace used for domestic heating. The propane 

product system includes four major life-cycle stages: crude 

oil extraction, propane production, propane distribution, 

and propane use. Crude oil extraction, propane production, 

and propane distribution data came from DATASMART 

database in which combustion data were retrieved from 

literature (LTS 2017, Johnson 2012). Johnson (2012) 

evaluated the existing data sources for residential heating 

systems using propane LCI and generated integrated data 

for propane combustion emission factors (Table 4).

Cradle-to-Grave Life-Cycle Inventory of 

the Briquetting System

All primary data related to the inputs and outputs of the 

processes were obtained by on-site measurements at 

the near-woods briquetter plant. The field experiments 

were performed in Big Lagoon, California, in 2015 on 

an old sawmill site using seven feedstock samples from 

four different species and two different chip sizes. The 

characteristics of the briquettes produced from seven 
General Technical Report FPL–GTR–262

10

different feedstocks are provided in Table 5. The material 

and energy inputs and outputs for production of 1 MJ of 

energy from wood briquettes are provided in the following 

sections.

Feedstock Procurement

Table 6 shows the cradle-to-gate input and output flows 

for feedstock procurement processes along with hauling 

for 1 bone-dry metric ton (BDT) of wood chips. Feedstock 

procurement processes and hauling were adopted from the 

forest operations model developed by Oneil and others 

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

on the operational data generated in 2015 (Bisson and 

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

The feedstock procurement stage includes woody biomass 

collection, sorting, and delimbing as well as the loading and 

transportation of the collected forest residues to the BCT 

site using a dump truck.

Feedstock Preparation

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

including chipping, screening, and drying processes are 

provided in Table 7. Screening and chipping data were 

adopted from the forest operations model developed by 

Oneil and others (2017).

Forced-drying was applied before the briquetting process to 

decrease the MC of the biomass feedstock. Thermal energy 

required for forced-drying the input biomass was provided 

from a thermal oxidizer using propane as fuel. Electricity 

consumption in the dryer process came from the belt 

conveyor used (Beltomatic, Norris Thermal Technologies, 

Tippecanoe, Indiana, USA). The use of the dryer was based 

on the MC of the incoming biomass feedstock. For better 

system efficiency, forced-drying was required if the MC of 

the incoming feedstock was higher than 15% (Nemeth and 

others 2012). Although the feedstock was left in the forest 

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

before the briquetting process to decrease the MC below 

15%. Biomass conversion tests were performed using 

various feedstock MCs to identify the optimum MC, which 

for average feedstock after the drying process was about 

6.13±0.96% for the experimental runs with high-quality 

product. Thermal energy required for forced-drying of 

the input biomass was provided from propane fuel. Heat 

requirement of the drying process was assumed to be 

5 MJ/kg water removed, and system efficiency was 80% 

(Adams and others 2015).

Table 4—Propane combustion 

emission factors (Johnson 2012)

Compounda Emissions(mg/kWh)

CH4 3.7

CO 31.9

CO2, fossil 227,200

N2O 0.4

NOx 169.2

PM10 1.2

SOx 0.7

NMVOC 6.2

a

PM, particulate matter; NMVOC, 

nonmethane volatile organic compound.

Table 5—Properties of briquettes produced using the feedstock tested for analysis

ID Type

Average briquette mass

(kg)

Average density

(kg/m3)

Moisture content

(%)

Durability

(%)

S1 Redwood, chip, smalla 0.73 897.9 NAb 79

S2 Redwood, chip, mediumc 0.70 831.0 8.1 97

S3 Douglas-fir, chip, small 0.81 930.1 6.6 97

S4 Douglas-fir, chip, medium 0.74 862.6 5.7 96

S5 Tanoak, chip, small 0.79 943.7 5.1 98

S6 Tanoak, chip, medium 0.77 753.7 7.5 93

S7 Conifer, chip, medium 0.75 848.8 6.7 95

a

Small chips: ≤0.75 in.

b

Data not available.

c

Medium chips: 0.75 to 2 in.
Using Life-Cycle Assessment to Evaluate Environmental Impacts of Briquette Production from Forest Residues

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Table 6—Cradle-to-gate input–output flow analysis for feedstock 

procurement of one bone-dry metric ton of wood chips

Process 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 kg 0.696 Alanya-Rosenbaum and others 2018

Hauling

Transportation km 18.77 Oneil and others 2017

Table 7—Gate-to-gate input–output flow analysis for feedstock preparation 

of one bone-dry metric ton of wood chips

Process Unit Value Source

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 kWh 7.14 Alanya-Rosenbaum and others 2018

Propane L 44.4 Engineering calculations

Volatile organic compounds g 174 Alanya-Rosenbaum and others 2018

Waste heat MJ 491 Engineering calculations

Drying wood results in VOC emissions, which were 

accounted for in the analysis. This analysis assumed freshly 

cut wood to be on the conservative side and tracked any 

VOCs emitted during field-drying in the forest as well 

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

emitted during field-drying, because they occur at lower 

concentrations and over 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 the 

Milota (2013) findings, emission levels mainly depend on 

the species and are higher for drying fresh woody biomass 

than for drying aged material. He concluded that only 10% 

to 20% of total hydrocarbon emissions occur below 20% 

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

emissions were emitted during the drying process, whereas 

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

Densification and Use Phases

Table 8 shows the environmental inputs and outputs for 

the densification and use phases. It is assumed that the 

briquettes were stored and sold in 15-kg-capacity plastic 

bags with low-density polyethylene (LDPE) (Laschi and 

others 2016). Overall efficiency of the wood stove was 

about 72%. Stack emissions from burning briquettes were 

obtained from WTW project combustion tests and were 

complemented by literature data.

Results of Life-Cycle Inventory Analysis

The results of the LCI analysis per 1 MJ of thermal 

energy generated for domestic heating from combusting 

wood briquettes are presented in Tables 9 and 10. Table 9 

presents the cradle-to-grave primary energy consumption 

and contribution of different fuel sources to the briquette 

production supply chain. Total primary energy use was 
General Technical Report FPL–GTR–262

12

Table 8—Environmental input and output flows for densification and use phases 

for a briquetting system

Process Unit Value Source

Densification phase

Briquetter

 Electricity kWh/BDTa 33.8 Alanya-Rosenbaum and others 2018

 Lubricants mL/BDT 4.99 Alanya-Rosenbaum and others 2018

Packaging

 LDPEb packaging g/BDT 0.67 Laschi and others 2016

Distribution km 90.2 Oneil and others 2017

Use phase

Combustion

 CO2 (biogenic) g/MJ input 85.43 Operational data

 CH4 g/MJ input 0.004 Khalil and others 2013

 NOx g/MJ input 0.038 Operational data

 CO g/MJ input 5.064 Operational data

 Volatile organic compounds g/MJ input 0.764 Operational data

 SO2 g/MJ input 0.007 Khalil and others 2013

 PM2.5c g/MJ input 0.035 Operational data

 PM10 g/MJ input 0.217 Operational data

a

BDT, bone-dry metric ton.

b

LDPE, low-density polyethylene.

c

PM, particulate matter.

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

combusting wood briquettes

Primary energy consumption 

(MJ/MJ heat)

Fuel Percentage Total

Feedstock 

procurement

Feedstock 

preparation Densification Transportation

Use phase 

(combustion)

Renewable fuel use

Wood fuel 45.8 1.08E–01 0.00E+00 1.88E–02 8.92E–02 0.00E+00 0.00E+00

Nonrenewable fuel use

Gas, natural, in ground 2.4 5.74E–03 4.00E–04 4.80E–03 6.60E–05 4.76E–04 0.00E+00

Coal, in ground 1.6 3.80E–03 2.65E–04 3.18E–03 4.19E–05 3.17E–04 0.00E+00

Oil, crude, in ground 49.6 1.17E–01 8.17E–03 9.77E–02 1.29E–03 9.78E–03 0.00E+00

Uranium 0.5 1.17E–03 8.20E–05 9.82E–04 1.30E–05 9.80E–05 0.00E+00

Renewable energy sources

Hydro <1.0 1.42E–04 2.13E–06 1.14E–04 1.06E–05 1.55E–05 0.00E+00

Wind <1.0 5.92E–05 4.13E–06 4.94E–05 6.52E–07 4.93E–06 0.00E+00

Solar <1.0 8.90E–07 6.21E–08 7.44E–07 9.82E–09 7.42E–08 0.00E+00

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

Total 100.0 2.36E–01 8.92E–03 1.26E–01 9.06E–02 1.07E–02 0.00E+00

Total, by percentage 100 3.8 53.3 38.4 4.5 0.0
Using Life-Cycle Assessment to Evaluate Environmental Impacts of Briquette Production from Forest Residues

13

0.236 MJ per MJ heat generated. The feedstock preparation 

stage was responsible for the majority of primary energy 

with about 53% contribution, followed by the densification 

stage (38%). Type of primary energy source used was 

dominated by wood fuel and crude oil. Most wood fuel 

was used for electricity production during the densification 

process, followed by feedstock preparation. This was caused 

by the wood-gasifier-based electricity consumption in these 

processes. Most of the fossil energy was from propane 

and diesel consumption during drying and transportation, 

respectively, which is extracted as crude oil from the 

ground as the primary energy source before conversion. 

The contribution of other renewable energy sources to total 

energy consumption, including geothermal, solar, hydro, 

and wind, was minor because of the lower renewable source 

in the electricity grid used in propane production.

Table 10 also provides values for the energy and material 

resource consumption. Total fossil energy use was 0.13 MJ/

MJ heat, used mainly for force-drying of wood chips to 

desired MC. Total renewable energy was 0.11 MJ/MJ heat 

coming primarily from the biomass gasifier. Nonrenewable 

material resources were minor (less than about 10–6). Solid 

waste generated consisted of packaging waste.

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 the TRACI v2.1 

method are documented in this section. Cradle-to-grave 

assessment analyzed environmental impacts associated 

with the wood briquette production supply chain and 

compared them with a fossil fuel alternative, i.e., propane. 

In addition, the effect of alternative scenarios considering 

different power sources, logistics, and feedstock properties 

on the impact results were evaluated using cradle-to-grave 

analysis.

Cradle-to-Grave Life-Cycle Analysis Results

Environmental impact assessment results associated with 

generating heat from wood briquettes in 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 were for the original scenario tested, in which 

the briquetter was operated near the woods close to the 

feedstock source and powered using a biomass gasifier. 

The drying process had the greatest impact in the GW, 

smog, carcinogenics, noncarcinogenics, ecotoxicity, and 

fossil fuel depletion categories.

Environmental impact assessment results associated with 

generating heat at the propane furnace are presented in 

Table 14. The production stage was responsible for the 

majority of the impact for all impact categories except 

GW, followed by the combustion stage. Contribution of

the distribution stage to overall impact was minor.

Table 10—Resources consumed and waste generated per 1 MJ of thermal energy generated for domestic heating 

from combusting wood briquettes

Resources and waste Unit Total

Feedstock 

procurement

Feedstock 

preparation Densification Transportation

Use phase 

(combustion)

Total primary energy 

consumption

MJ 2.36E–01 8.92E–03 1.26E–01 9.06E–02 1.07E–02 0.00E+00

Nonrenewable fossil MJ 1.26E–01 8.84E–03 1.06E–01 1.39E–03 1.06E–02 0.00E+00

Nonrenewable nuclear MJ 1.17E–03 8.20E–05 9.82E–04 1.30E–05 9.80E–05 0.00E+00

Renewable (solar, 

wind, hydroelectric, 

and geothermal)

MJ 2.02E–04 6.32E–06 1.64E–04 1.13E–05 2.05E–05 0.00E+00

Renewable (biomass) MJ 1.08E–01 0.00E+00 1.88E–02 8.92E–02 0.00E+00 0.00E+00

Material resources 

consumption (nonfuel 

resources)

Renewable materials kg 9.22E–02 9.09E–02 2.27E–04 1.07E–03 1.63E–07 0.00E+00

Fresh water L 9.36E–04 6.54E–05 7.83E–04 1.03E–05 7.81E–05 0.00E+00

Waste generated

Solid waste kg 4.87E–08 0.00E+00 0.00E+00 0.00E+00 0.00E+00 4.87E–08
General Technical Report FPL–GTR–262

14

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

propane furnace for domestic heating from combusting propane

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 the 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
Using Life-Cycle Assessment to Evaluate Environmental Impacts of 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 

wood briquettes

Impact category Unita Feedstock procurement Hauling

Chipping/

screening Drying Briquetter Packaging Distribution

Use

phase

Ozone depletion kg CFC-11 eq 1.11E–12 2.22E–13 1.61E–12 1.17E–11 1.75E–13 1.08E–15 1.10E–12 0.00E+00

Global warming kg CO2 eq 6.08E–04 1.99E–04 8.84E–04 6.70E–03 9.93E–05 1.08E–07 6.61E–04 1.24E–04

Smog kg O3 eq 4.87E–04 3.21E–05 3.78E–04 4.06E–04 1.01E–04 3.12E–09 1.05E–04 1.70E–03

Acidification kg SO2 eq 8.00E–06 1.05E–06 1.16E–05 1.64E–05 3.64E–06 2.29E–10 3.65E–06 4.67E–05

Eutrophication kg N eq 6.14E–07 8.73E–08 8.94E–07 2.24E–06 2.19E–07 7.72E–10 3.38E–07 2.34E–06

Carcinogenics CTUh 1.01E–11 2.01E–12 1.47E–11 1.06E–10 1.59E–12 1.42E–15 1.00E–11 0.00E+00

Noncarcinogenics CTUh 9.93E–11 1.98E–11 1.44E–10 1.04E–09 1.56E–11 3.86E–14 9.87E–11 0.00E+00

Respiratory 

effects

kg PM2.5 eq 1.58E–07 1.62E–08 2.30E–07 2.95E–07 1.11E–07 9.19E–12 5.63E–08 5.21E–05

Ecotoxicity CTUe 2.54E–03 5.08E–04 3.70E–03 2.67E–02 4.00E–04 4.51E–06 2.53E–03 0.00E+00

Fossil fuel 

depletion

MJ

surplus

1.17E–03 2.35E–04 1.71E–03 1.23E–02 1.85E–04 5.08E–07 1.17E–03 0.00E+00

a

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

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.

Comparison of the GW impact results per megajoule of 

heat generated from propane and wood briquettes and the 

contribution percentages of the different processes to the 

overall impact for the wood briquette supply chain are 

presented in Figures 6 and 7. Wood briquette production 

was performed as a near-woods operation using woodfueled gasifier power. Environmental impacts associated 

with domestic heat generated through a propane furnace and 

a propane system supplemented with a wood furnace using 

briquette fuel were compared. Comparative data showed 

that 50% and 80% substitution of heat from propane with 

wood briquettes resulted in 45% and 72% reduction in the 

GW impact, respectively.

The contribution analysis revealed that a large portion of 

the GW impact resulted from drying processes (72%), with 

chipping and screening following. The large contribution 

of the drying process resulted from the propane used for 

heat generation for forced-drying. Converesly, contribution 

of densification (briquetting) and use phases were minor 

and the use phase for the propane scenario was the major 

contributor to GW impact that resulted from fossil-fuelbased GHG emissions (i.e., propane combustion emissions).

Alternative System Configurations 

Life-Cycle Impact Assessment

The LCIA results of alternative scenarios considered 

are evaluated in this section. The GW impact resulting 

from different scenarios and the process contribution 

to the overall impact are presented in Figure 8. When 

effect of using different power sources to support dryer 

and briquetter processes on the overall GW impact were 

compared at cradle-to-grave level, gasifier power (S1) 

generation outperformed diesel electricity (S2) and grid 

electricity (S3) scenarios. Displacing diesel-based power 
General Technical Report FPL–GTR–262

16

Figure 6. Comparison of global warming per 1 MJ of thermal energy 

generated for domestic heating from 100% propane (S0), propane 

system supplemented with 50% of the heat generated from a wood 

stove burning wood briquettes (S0+S1), and propane system 

supplemented with 80% of the heat generated from a wood stove 

burning wood briquettes (S0+S1).

Figure 7. Contribution of processes to overall global warming impact 

for the wood briquette production system per 1 MJ of thermal energy 

generated by the wood stove.

0

20

40

60

80

100

S0 50% S1 80% S1

g CO2 equivalent/MJ heat

Wood briquette

Propane

94.4

51.8

26.3

Chipping/screening (10%)

Drying (72%)

Hauling (2%)

Feedstock procurement (7%)

Briquetter (1%)

Packaging (0%)

Distribution (7%)

Use phase (1%)
Using Life-Cycle Assessment to Evaluate Environmental Impacts of Briquette Production from Forest Residues

17

and grid power generation with gasifier power resulted in a 

26% and 15% decrease, respectively, in GW impact. Grid 

power access scenarios, S3 and S4, are in-town operation 

scenarios for which the feedstock was hauled to town 

before the biomass preparation and biomass conversion 

processes occurred. Two different distances were evaluated 

to investigate the effect of hauling distance on the results 

when the biomass feedstock was processed in town. In these 

scenarios, an increase in the contribution of hauling to the 

overall impact was observed with longer transportation 

of feedstock. The contribution of hauling to GW impact 

increased from 2% to 9% when feedstock was transported 

to town with a limitation of 2-h travel distance (S3) before 

biomass conversion, whereas it increased to 18% when 

travel distance was assumed to be 4 h. The increase in 

hauling distance resulted in 1.7 g CO2 equivalent increase 

in GW impact per megajoule heat generated for 2-h hauling. 

Scenario analysis also showed that use of feedstock with 

high MC, 50% in this case, was the least favorable of the 

alternative scenarios (S5, S6). For near-woods operations, 

using green post-harvest residues (with 50% MC) instead 

of air-dried feedstock with around 20% MC resulted in 

about four times higher GHG emissions. This was caused 

by increased propane consumption to meet the dryer 

heat demand. About 33% GHG reduction occurred with 

conversion of the post-harvest forest residues to briquettes 

for heat generation mainly because of avoided methane 

emissions from pile and burning (S7).

The effect of using different power sources for meeting the 

electricity demand for the dryer and briquetter processes 

on the impact was investigated and presented for OD, 

smog, acidification, eutrophication, and fossil fuel impact 

assessment categories (Fig. 9). The results of the analysis 

revealed that, at the cradle-to-grave level, using on-site 

wood gasifier power generation improved the environmental 

performance of the system compared with on-site diesel 

electricity and grid electricity in all impact categories 

except for smog impact. The difference was notable in the 

OD impact category for which displacing diesel power 

generation and electricity with a gasifier resulted in 26% 

and 47% decreases, respectively.

Pile and burn credits resulted in substantial benefits 

particularly in the human health impact categories (Fig. 10). 

Environmental benefits of the avoided pile-and-burn 

emissions were notable in the carcinogenic and respiratory 

effects impact categories. The respiratory effects impact 

category was dominated by emissions from use phase, 

whereas the major contributor to the rest of the human 

health impact categories was drying process because of the 

propane consumed.

Life-Cycle Interpretation

The interpretation section evaluates results for the LCI or 

the LCIA, or both, in line with the defined goal and scope. 

The midpoint analysis results are presented and discussed 

Figure 8. Contribution of processes to overall global warming impact per 1 MJ of thermal energy generated for 

seven 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% MC feedstock, nearwoods operation with wood gasifier power; S6: 1 MJ heat, 50% MC feedstock, in-town operation (2-h travel 

distance) with grid power; S7: 1 MJ heat, near-woods operation with wood gasifier power with pile and burn credit. g CO2 equivalent/MJ heat

Total

Use phase (combustion)

Distribution

Briquetter

Feedstock preparation

Hauling

Feedstock procurement

Pile and burn

0

5

10

–5

15

20

25

30

35

40

S1 S2 S3 S4 S5 S6 S7

7.0

38.5

36.8

12.3

11.0

12.6

9.3
General Technical Report FPL–GTR–262

18

in the previous section, which included scenario analysis. In 

this part of the report, results from the additional parameterbased sensitivity analysis are addressed as part of the 

interpretation. Additional components include conclusions, 

limitations, and recommendations.

A parameter-based sensitivity analysis was conducted in 

addition to the scenario analysis performed in this section. 

The sensitivity of the GW impact was examined using 

key parameters including briquetter electricity demand, 

dryer propane consumption, and distribution and hauling 

distances. The effect of 25% variation of these parameters 

on the resulting GW impact is presented in Figure 11. 

Key parameters that had great influence on the impact 

assessment results were investigated through sensitivity 

analysis. The performed sensitivity analysis showed that 

dryer propane consumption was a key parameter with great 

influence on variation in the GW impact. Distribution 

distance also had some influence on the impact. This 

reveals the importance of dryer heat requirement and energy 

consumption data to decrease the uncertainty resulting from 

parameters used. Similarly, scenario analysis showed that 

the MC of the incoming feedstock had notable effect on the 

resulting environmental impact.

Conclusions, Limitations, and 

Recommendations

This study provided a comprehensive cradle-to-grave 

LCA of the wood briquette production supply chain. The 

environmental performance of using post-harvest forest 

residues in a near-woods briquetting process for solid 

biofuel production was investigated. Briquetting occurred 

near the point of harvesting to decrease transporting 

distance of the forest residues. Results indicated that 

the GW impact was highly dependent on drying process 

efficiency during wood briquette production; therefore, 

use of high-efficiency dryer systems is crucial to improve 

environmental performance of the supply chain. Using fielddried feedstock with lower MC resulted in considerable 

decrease of GW impact, which showed the importance of 

developing and using different techniques for decreasing the 

MC of biomass feedstock, such as air-drying. Alternatively, 

use of biomass as a fuel source for the drying system 

can be investigated to examine its effect on the overall 

environmental impact of the system, which may mitigate the 

GW impact of the drying process. Data on heat requirements 

of 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.

Substitution of fossil fuel products with renewable energy 

products consistently shows GHG emission reduction 

potential (Panwar and others 2011, Ellabban and others 

2014, Baul and others 2017, Gustavsson and others 2017). 

In particular, this study showed that substituting wood 

briquettes produced from widely available forest residues 

for propane for domestic heating reduced GHG emissions. 

In addition, for remote power generation, GHG emissions 

were lower when a biomass gasifier genset was substituted 

for a diesel generator. When in-town grid electricity was 

used at 2-h distance instead of near-woods bioenergy 

production systems using power from an on-site wood 

gasifier, the GW impact increased by 15%. Using postharvest residues as biofuel instead of using the typical pile 

and burn approach notably lowered resulting environmental 

impact.

Figure 9. Summary of the comparative life-cycle impact assessment (LCIA) results for 

three power sources (grid, diesel, and gasifier electricity) for the briquetter system. Impact in LCIA (%)

0

10

20

30

40

50

60

70

80

90

100

1 MJ heat, grid

1 MJ heat, diesel 

1 MJ heat, wood gasifier

Fossil fuel

depletion

Ozone depletion Smog Acidification Eutrophication
Using Life-Cycle Assessment to Evaluate Environmental Impacts of Briquette Production from Forest Residues

19

Figure 10. The toxicity impact category results for generating 1 MJ of thermal output for the scenarios investigated.

Figure 11. Sensitivity of key parameters on global warming impact.

Hauling

Distribution

Electricity briquetter

Dryer propane use

–1.70 –1.20 –0.70 –0.20

g CO2

 equivalent/MJ heat

0.30 0.80 1.30 1.80

Process contribution (%)

Pile and burn

Combustion

Distribution

Briquetter

Drying

Chipping/screening

Hauling

Feedstock procurement

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

0

10

20

30

40

50

60

70

80

90

100

–100

–90

–80

–70

–60

–50

–40

–30

–20

–10

–150

–140

–130

–120

–110

Carcinogenics Noncarcinogenics Respiratory effects Ecotoxicity
General Technical Report FPL–GTR–262

20

External Review

The external review process was intended to ensure 

consistency between the completed LCA and the principals 

and requirements of the international standards on LCA 

(ISO 2006a). The independent external review was 

performed by James Salazar, M.S., Principal of Coldstream 

Consulting, and Shaobo Liang, PhD, Postdoctoral Research 

Fellow, USDA Forest Service, Forest Products Laboratory.

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