a review on advances of torrefaction technologies - bimal.pdf

7/24/2019 A review on advances of torrefaction technologies - Bimal.pdf

http://slidepdf.com/reader/full/a-review-on-advances-of-torrefaction-technologies-bimalpdf 1/21

REVIEW ARTICLE

A review on advances of torrefaction technologies

for biomass processing

Bimal Acharya & Idris Sule & Animesh Dutta

Received: 17 April 2012 /Revised: 1 July 2012 /Accepted: 30 July 2012 /Published online: 20 September 2012# Springer-Verlag 2012

Abstract Torrefaction is a thermochemical pretreatment

process at 200 – 300 °C in an inert condition which trans-

forms biomass into a relatively superior handling, milling,co-firing and clean renewable energy into solid biofuel. This

increases the energy density, water resistance and grindabil-

ity of biomass and makes it safe from biological degradation

which ultimately makes easy and economical on transpor-

tation and storing of the torrefied products. Torrefied bio-

mass is considered as improved version than the current

wood pellet products and an environmentally friendly future

alternative for coal. Torrefaction carries devolatilisation,

depolymerization and carbonization of lignocellulose com-

ponents and generates a brown to black solid biomass as a

productive output with water, organics, lipids, alkalis, SiO2,

CO2, CO and CH4. During this process, 70 % of the mass isretained as a solid product, and retains 90 % of the initial

energy content. The torrefied product is then shaped into

pellets or briquettes that pack much more energy density

than regular wood pellets. These properties minimize on the

difference in combustion characteristics between biomass

and coal that bring a huge possibility of direct firing of

biomass in an existing coal-fired plant. Researchers are

trying to find a solution to fire/co-fire torrefied biomass

instead of coal in an existing coal-fired based boiler with

minimum modifications and expenditures. Currently avail-

able torrefied technologies are basically designed and tested

for woody biomass so further research is required to addresson utilization of the agricultural biomass with technically

and economically viable. This review covers the torrefaction

technologies, its’ applications, current status and future rec-

ommendations for further study.

Keywords Torrefaction . Bioenergy . Coal-fired plant

NomenclatureBO2 Bio-dioxide (like carbon dioxide)

CV Calorific value

GHG Green house gas

LCA Life cycle analysis

SCD Screw conveyors dryers

TB Torrefied biomass

VOC Volatile organic compounds

1 Introduction

Carbon-offset programs to limit the amount of GHG emis-

sion have not only dominated the global warming discus-

sions but also the continuous rise in world populations has

increased the energy demand in a more unsustainable fash-

ion. As a result, this has spearheaded the increasing demand

for clean and sustainable sources of energy. For instance,

Europe established a cap-and-trade system in 2005 that

limits CO2 emissions from about 50% of industry to reach

its emission target as dictated by the Kyoto Protocol [1].

Furthermore, fossil fuels like petroleum, natural gas or coal,

which are the main sources of energy in most industrialized

nations, are major contributor to global warming through the

GHG emissions, and their sources are depleting. For in-

stance, coal-fired plants use most coal and produce most

of the fossil fuel air pollution, and for each ton of carbon

burned, 3.67 tons of CO2 is generated. The emission is not

only damaging to the environment but also to the human

health. The global use of carbon causes emission of approx-

imately 7 billiontons/year, and it is projected to reach 14 bil-

liontons/year by 2050 [1]. These global challenges have

triggered an increase in the adoption of alternative sources

of energy, including renewable sources.

B. Acharya : I. Sule : A. Dutta (*)

School of Engineering, University of Guelph,

Guelph, ON, Canada

e-mail: [email protected]

Biomass Conv. Bioref. (2012) 2:349 – 369

DOI 10.1007/s13399-012-0058-y



Consequently, as one of the game changer, bio-energy

has been discovered to be one of the key renewable energy

initiatives to substantially reduce GHG emissions and con-

tribute enormously to sustainable energy generation for

electricity and industrial applications. Renewable energy is

derived from natural resources that may be replenished

unlike fossil fuels. Biomass energy products are referred to

as bio-energy, which can be in the form of solid (bio-solids),liquid (bio-oil) or gas (bio-gas).

Despite the tremendous popularity gained by biomass

energy in the recent years, the fraction of its utilization in

producing energy remains insignificant in the overall source

of energy production in industrialized nations. This can be

due to several factors, including the limitation associated

with its properties [2]. The variations in biomass feedstock

cause several challenges during the conversion process,

including excess smoke during combustion and low com-

bustion efficiency. Torrefaction, a biomass pretreatment pro-

cess, has been found to improve biomass combustible

properties [2, 3]. Torrefaction is partially an endothermic pro ces s tha t req uires hea t the rma l dec omp osi tio n and

requires approximately 0.6 – 1 MJ/kg based on scale and ener-

gy balance of the overall process and product in terms of

higher heating value [4]. Since the main changes in biomass

due to torrefaction include the decomposition of hemicellu-

lose and partial depolymerization of lignin and cellulose,

torrefied biomass (TB) has higher content of carbon, lower

mass and higher calorific value (CV) than the raw biomass [4].

The temperature and residence time of torrefaction process

must be precisely controlled to ensure higher energy efficien-

cy of the biomass conversion process [5].

Hence, the main objectives of this paper is to provide

updates on the torrefaction research activities which mainly

include (a) issues with biomass and its components and

component analysis procedure; (b) torrefaction and its

chemistry, reaction, kinetics, process integration, torrefied

fuel characteristics, technology used and recent develop-

ment; (c) application of torrefaction technologies in pelleti-

zation, combustion/co-firing, gasification and emission and

(d) economics and further research potential for energy

application.

2 Biomass fuel

According to Yoshida et al. [6], the word “ biomass” origi-

nally meant the total mass of living matter within a given

unit of environmental area, but more recently, it has also

been described as plant material, vegetation or agricultural

waste used as an energy source. Tumuluru et al. [7] also

defined biomass materials as a composite of carbohydrate

polymers with a small amount of inorganic matter and low

molecular weight with extractable organic constituents.

Generally, biomass is a biological or organic material,

which can serve as source of renewable energy through

thermal or biochemical conversion processes. It can also

be classified as carbon-based material, which composed of

mixture of organic molecules including hydrogen, oxygen,

nitrogen and small quantities of atoms including alkali,

alkaline, earth and heavy metals. Because biomass are

organic materials which encompasses all living matter,their energy contents are obtained from the sunlight and

stored in form of chemical energy that is then converted

into heat energy through thermal or biochemical process-

es. A good illustration of biomass as one of the source of

renewable energy is wood, which is obtained from trees.

Trees absorb sunlight and CO2 from the atmosphere dur-

ing photosynthesis to make cellulose from sugars; conse-

quently, the cellulose, which contains stored chemical

energy, releases this energy as heat when combusted and

the CO2 liberated as off-gas is approximately equivalent to

the amount absorbed during photosynthesis process.

Hence, biomass can be greenhouse gas emission neutral[8]. Unlike fossil fuels, biomass is a renewable source of

energy that can be replenished and add zero net green-

house gas to the atmosphere.

2.1 Biomass challenges

Biomass materials have several limitations that limit their

utilization for energy generations. This can be due to many

factors, including their physical and chemical properties [2].

Some of these challenges include low heating value, high

moisture content, hygroscopicity, excess smoke during com-

bustion, low energy density, higher alkali contents and low

combustion efficiency [9].

These limitations greatly impact not only the combustion

performances but also the biomass-to-energy supply chain

logistics due to costly handling and transportation of bio-

mass. As a result, biomass materials must be treated to

overcome these challenges and make them suitable for

energy use.

2.2 Biomass components

The three main polymeric constituent of biomass are hemi-

cellulose, cellulose and lignin, and generally, they cover,

respectively, 20 – 40, 40 – 60 and 10 – 25 wt.% for a lignocel-

lulosic biomass [10, 11]. Figure 1 shows the polymer struc-

ture of a woody biomass.

2.2.1 Cellulose

Cellulose, a linear polymer that makes up about 45 % of the

dry weight of wood, is composed of D-glucose subunits linked

together to form long chains (elemental fibrils), which are

350 Biomass Conv. Bioref. (2012) 2:349 – 369



further linked together by hydrogen bonds and Van der Waals

forces. The cellular fibre formed by several micro-fibrils com-ing together can either be crystalline or amorphous [12].

Furthermore, cellulose is a high molecular weight polymer

that makes up the fibres in lignocellulosic materials, and its

degradation starts anywhere from 240 to 350 °C because of

high resistance of its crystalline structure to thermal depoly-

merization owns to its strength [7]. The waters held in the

amorphous regions of the cellulosic wall rupture the structure

when converted into steam as a result of thermal treatment [7].

2.2.2 Hemicelluloses

Hemicellulose is a complex carbohydrate polymer with a lower molecular weight than cellulose and makes up 25 –

30 % of total dry weight of wood. It consists of D-xylose, D-

mannose, D-galactose, D-glucose, L-arabinose, 4-O-methyl-

glucuronic, D-galacturonic and D-glucuronic acids [12]. The

principal component of hardwood hemicellulose is glucuro-

noxylan whereas glucomannan is predominant in softwood

[12]. In contrast to cellulose, hemicelluloses are easily hydro-

lysable polymers and do not form aggregates. It consists of

shorter polymer chains with 500 – 3,000 sugar units as com-

pared to the 7,000 – 15,000 glucose molecules per polymer seen

in cellulose [7]. Thermal degradation of hemicellulose occurs

between the temperature of 130 – 260 °C, with the majority of

weight loss occurring above 180 °C [13, 14]. Hemicellulose

produces less tars and char due to its low degradation temper-

ature range compared to that of the cellulose [7].

2.2.3 Lignin

Lignin along with cellulose is the most abundant polymer in

nature [12]. Lignin is an unstructured and highly branched

polymer that fil ls the spaces in the cell wall betw een

cellulose, hemicellulose and pectin components [7]. It is

covalently bonded to hemicellulose and thereby exhibits

mechanical strength on the cell wall. It is relatively hydro-

phobic and aromatic in nature and decomposes between 280

and 500 °C when subjected to a thermal treatment [ 13, 14].

Lignin is difficult to dehydrate and thus converts to more

char than cellulose or hemicelluloses [7].

3 Overview of torrefaction

Torrefaction is a method to improve biomass properties for

energy generation. In literature, it is defined as a thermal

treatment process through which biomass is heated between

temperature of 200 – 300 °C in an inert condition and at a

relatively low residence time. Historically, torrefaction princi-

ple became known in relation to wood pretreatment in the

1930s in France [25] when the production of torrefied wood

(TW) was researched for use in gasifier, not until the 1980s

when there is an interest in substituting charcoal for TW inmetallurgic processing plant that first torrefaction demonstra-

tion plant was built in France by a French company, Pechiney,

to produce TW of 12,000 tons/acre [3]. During torrefaction,

the biomass properties are changed to better fuel character-

istics for combustion and gasification applications. The torre-

fied products show relatively similar characteristics as coal

[3]. Torrefaction combined with densification provides an

energy dense fuel of 20 to 25 GJ/ton [3].

Torrefied materials exhibit following characteristics:

1. Hydrophobic behaviour: TB has hydrophobic character-

istics owning to the destruction of its O – H bond struc-

ture, hence making it incapable to retain or absorb

moisture. Although no standardized test exists yet for

validating hydrophobic properties of torrefied biomass,

Bergman et al. [5] demonstrated hydrophobic test by

immersing torrefied fuel in water for 2 h, drained and

measured weight changes.

2. Inhibiting biological decomposition: stopping biologi-

cal decomposition like rotten

3. Improved grindability: Torrefied biomass has improved

grindability. This leads to more efficient co-firing in

existing coal-fired power stations or entrained-flow gas-

ification for the production of chemicals and transpor-

tation fuels. TB is more brittle owing to its higher C/H

and C/O ratios, hence provides enhanced pulverize

characteristics and requires far less energy for grinding

compared to that of raw biomass [3, 13, 14].

4. Higher heating value: Torrefaction increases the cal-

orific value of biomass and as a result increases

their energy density [5, 15]. Densification increases

the bulk and volumetric density of biomass. Hence,

a combination of torrefaction and pelletization

Fig. 1 Polymer structure of a woody biomass (source: [16])

Biomass Conv. Bioref. (2012) 2:349 – 369 351



processes produce torrefied pellets, which pilot-scale

experiments have shown to have better handling

than biomass pellets due to its hydrophobicity

[17 – 19]. Torrefaction process causes dehydration

that initiates and propagates cracks in the lignocel-

lulosic structure (e.g. wood), as a result induces

porosity and density changes [20]. Increased poros-

ity, due to more particle voids, decreases particlesize but inevitably increases the particle density and bulk

density [21]. Generally, density varies in a different way

depending on wood species during temperature treatment

[20, 22], and the changes with respect to torrefaction

might not be very significant [23]. The particle density

of torrefied pine chips (TPC) and torrefied logging resi-

dues (TLR) did not change compared to that of untreated

biomass; while the bulk density of TPC particles de-

creased until the torrefaction temperature of 250 °C then

increased up to the torrefaction temperature of 300 °C, no

significant change occurs in TLR compared to the un-

treated sample [22, 24, 25].5. Particle sizes and distribution of torrefied biomass: Pul-

verized torrefied biomass exhibit more uniform and

smaller particle sizes compared to that of pulverized

raw biomass [22, 26].

3.1 What is torrefaction?

Although the definitions exhibit similarities in terms of

torrefaction processes, the operating temperature range dif-

fers from studies to studies depending on the biomass types

that were researched. [3, 16, 27, 28] defined the torrefaction

temperature range from 200 to 300 °C; Prins et al. [29] and

Pimchuai et al. [30] defined temperature between 230 and

300 °C; meanwhile, Arias et al. [13] defined temperature

range between 220 and 300 °C, and [31 – 33] defined tem-

perature range between 225 and 300 °C. Studies have shown

that biomass exhibit different behaviour to thermal treat-

ment owing to their types, origin and properties [2]; hence,

the initiation of biomass decomposition depends on the type

of biomass. In order to develop a more general definition of

torrefaction, an experimental study on a range of biomass

types will be required to determine the temperature at which

a biomass sample is torrefied. This may be exemplified by

hydrophobicity, i.e. the operating temperature and residence

time when the torrefied biomass seizes to absorb water.

Although the typical definition that mostly occur in pub-

lished journals is “the thermal pretreatment method carried

out between the operating temperature of 200 °C and 300 °C

under inert condition and relatively short reactor residence

time and slow heating rate less than 50 °C/min” [2]. It is

carried out under conditions of atmospheric pressure and in

the presence of a minimum amount of oxygen in order to

avoid spontaneous combustion. Recently, a number of

researchers including present authors have carried out torre-

faction research at different oxygen concentrations. P.

Rousset et al. [27] in their study showed that the different

oxygen concentrations did not significantly affect the com-

position of the solid by-product for low temperatures. An

oxygen concentration of 6 % apparently shows better char-

acterisations on grindability and hydrophobicity tests of

torrefied biomass [34]. Therefore, torrefaction of biomasscan be defined as a thermochemical pre-treatment process in

an oxygen reduced condition at a temperature range from 200

to 300 °C for a shorter residence time that maximizes the

solids content and enhances its hydrophobic characteristics.

The torrefaction process involves the decomposition of

biomass during which various types of volatiles are liberat-

ed, and the final product is a solid fuel generally called

torrefied biomass or torrefied fuel [2, 3, 5].

3.2 Torrefaction process

The pre-conversion of biomass using torrefaction involvesthree main steps: chopping, drying and torrefaction

(roasting) [31, 32] as shown in Fig. 2. During torrefaction

process, biomass is fed into a chopper to reduce them into

fine or more uniform particles. The chopped biomass then

goes through the drying section to remove the moisture and

then fed into the torrefaction reactor [33, 35]. The moisture

liberated during drying composed of both condensable and

non-condensable gases and volatiles as stated in Fig. 3 [29,

36]. The higher the temperature of torrefaction, the higher

the combustion heat of the waste volatiles gas liberated

during the process.

After a complete devolatilisation of the biomass, the final

solid product that remains is often referred to as torrefied

biomass or char [3, 37]. The improved combustible proper-

ties of biomass after torrefaction result in an attractive solid

fuel for combustion and gasification processes. Further-

more, the improved grindability of torrefied biomass makes

it advantageous for pelletization, which facilitates storage,

transportation and co-combustion of biomass with coal [3,

38]. During torrefaction process, biomass undergoes series

of decomposition reactions that cause the liberation of gas-

eous products including volatile organic compounds. In

particular, the C, H, O compositions of the biomass become

altered, and the H/C (or O/C) ratio decreases because it loses

its hydrogen and oxygen in more proportion compared to

carbon [3, 5]. The decomposition of biomass polymer struc-

ture during torrefaction causes the destruction of its hydrox-

yl (OH) group and making it incapable to form hydrogen

bond with water and hence loses its tendency to absorb

water [5, 17, 39]. As a result, torrefied biomass is non-

polar molecular structure, which is practically hydrophobic

[27]. During torrefaction process, biomass undergoes two-

stage processes: drying and torrefaction. During drying,




biomass loses majority of its moisture at temperature around

110 °C, and further increase of treatment temperature ini-

tiates the decomposition of its polymeric structure, predom-

inantly, hemicellulose. At torrefaction temperature between

250 and 300 °C [3, 5, 17, 27], high significance of decom-

position occurs in hemicellulose and relatively slight de-

composition in lignin and cellulose. Consequently,

majority of biomass weight loss is attributable to the de-composition of hemicellulose into volatile compound. Since

only slight devolatilisation occurs in lignin and cellulose,

torrefied biomass retains majority of its energy content [5].

According to Bergman et al., the typical process of torre-

faction retains around 70 % of its mass which contains

around 90 % of its initial; hence, around 30 % of the mass

containing only 10 % of energy content of the biomass is

converted into torrefaction gases (i.e. the volatile organic

compounds released as flue gas). This is illustrated in Fig. 4.

Prior to torrefaction process, chopping of biomass feed-

stock into uniform sizes may be required depending on the

feedstock type and properties. Particle size has significant effect in torrefaction reactions according to Ciolkosz and

Wallace [40], especially when large biomass feedstock is

being processed. Although no definite sizes are recommen-

ded for biomass in torrefaction process by most studies, the

sizes can be based on processing equipment and biomass

properties. In the torrefaction experiments conducted by

Prins et al. [41] on deciduous wood (beech and willow),

coniferous wood (larch) and straw, the particle sizes used

were in the range of 0.7 to 2.0 mm in all cases, except for

straw where it was less than 5 mm. Furthermore, according

to Ciolkosz and Wallace [40], most studies to date only

examined torrefaction of ground material (or pellets) and

have not studied the complicating factors that the torrefac-

tion of larger material may introduce. Most studies agree

that temperature parameter has more significant effect in

enhancing the combustible properties of biomass than resi-

dence time [2, 5, 16]. According to Bergman and Kiel [3],

the torrefaction products are classified based on their state at

room temperature. The products in the solid phase are dark

brown-coloured carbon-rich char with traces of ash; those in

gas phase are referred to as non-condensable or permanent

gases.

3.3 Torrefaction kinetics

Prins et al. [41] explored the weight loss kinetic of torrefiedwood and concluded that the kinetics of torrefaction occurs

in two steps reactions: hemicellulose decomposition and

cellulose decomposition. And since hemicellulose decom-

position occurs faster than the cellulose decomposition, it

contributes significantly towards the overall mass yield of

torrefied wood. Due to these different fractions, biomass can

decompose in different way under various conditions. Bio-

mass undergoes four stages during torrefaction process:

moisture evaporation, hemicellulose decomposition, lignin

decomposition and cellulose decomposition [42].

3.4 Torrefaction mechanism

During torrefaction process, the thermal decomposition of

biomass causes numerous reactions to occur through their

polymer/cell structure. The decomposition process was well

documented in Bridgeman et al. [2] as seen in Fig. 5. At low

torrefaction temperatures, decomposition occurs in the

hemicellulose structure by means of a limited devolatilisa-

tion and carbonization; meanwhile, in the lignin and cellu-

lose structure, a minor decomposition occurred. Figure 5

shows that hemicellulose undergoes extensive thermal

decomposition between 200 and 300 °C while only limited

devolatilisation and carbonization occurred in the lignin and

cellulose structure.

It can also be noted that the transition from one decom-

position regime occurs at narrow temperature range for

hemicellulose while the transitions for lignin and cellulose

occur over at wide temperature range. Hence, it can be

concluded that hemicellulose is the most reactive polymer

Fig. 2 Basic principle concept

for directly heated, two stage

torrefaction with gas recycling

[5, 9]




constituent of biomass, and it is attributed to the significant mass loss in biomass during torrefaction [3, 16, 27].

Temperature has a significant effect in the degree of

decomposition of biomass. In the process of heating ligno-

cellulosic materials, the decomposition of the polymer struc-

ture of the material undergoes stages of decomposition

regimes as seen in Fig. 6 due to increasing temperature.

At temperature between 200 and 280 °C, only hemicellu-

lose has undergone depolymerization with limited devolatili-

sation reactions while in lignin and cellulose, these reactions

are still occurring. After majority of the moisture has been

removed at temperature between 100 and 120 °C, the signif-

icant weight loss of biomass is attributable to depolymeriza-

tion and limited devolatilisation of the hemicellulose during

torrefaction process (between temperature of 200 and 300 °C).

Hence, since only slight depolymerization and devolatilisation

reaction occur in lignin and cellulose during torrefaction,

majority of the energy content remains in the torrefied

products. Furthermore, in a study on the torrefaction impact on lignocellulosic structure of biomass, Rousset et al. [27]

concluded that the slight weight loss that occurred in biomass

at temperature of 230 °C was attributed to slight decomposi-

tion of hemicellulose, and at temperature around 260 °C,

severe decomposition of hemicellulose and slight of lignin

contributed to massive biomass weight loss. These conclu-

sions were similar to those from [3, 16, 17, 27, 43]. Rousset et

al. [27] went further to categorize the temperature range for

thermal decomposition of hemicellulose as 150 to 350 °C,

cellulose as 275 to 350 °C and lignin as 250 to 500 °C. During

decomposition of lignocellulosic polymer structure, other im-

portant parameter is the residence time, which accounts for the

transition periods that exist from a decomposition regime to

another. For instance, the transition period from the depoly-

merization regime to devolatilisation regime is shorter for

hemicellulose due to its high reactivity and lower temperature

range [3, 16] than that of the lignin and cellulose. This

explains why during torrefaction process, increase in resi-

dence time decreases the mass yield of biomass [2, 3, 5]

because of more devolatilisation that occurs at specified oper-

ating temperature for a span of time. However, temperature

effect is more significant to weight loss of biomass compared

to that of the residence time [5].

3.5 Effect of temperature and residence time on product

characteristics

Torrefaction treatment improves the combustible (physical

and chemical) properties of biomass, and the characteristics

of torrefied products depend on the biomass properties and

the operating temperature and residence time used in the

treatment. The main characteristics of torrefied products are

as listed in Section 3. Generally, biomass density varies in a

Fig. 3 Products formed during

torrefaction process (source: [5])

Torrefaction(200-

300°C)

Torrefied Gasas Loss

30%M

+10%E

BiomassFeed Stock

input

100%M

+100%E

TorrefiedBiomass

70%M

+90%E

Fig. 4 Mass and energy and energy balance of a typical torrefaction

process ( M = mass and E = energy) [5]




different way depending on wood species and temperature

treatment [23, 44]. According to Bourgeois et al. [44], the

particle density of TPC and TLR did not change compared

to that of untreated biomass, while the bulk density of TPC

particles decreased until the torrefaction temperature of

250 °C but then rose after 250 °C to the torrefaction

temperature of 300 °C; however, no significant change

occurred in TLR compared to the untreated sample [24,

25, 44]. Table 1 below summarizes the comparison in fuel

properties and handling characteristics of raw wood, wood

pellets, torrefied wood pellets, coal and charcoal.

Bergman et al. [3, 5] further examined the CV of the

torrefaction gas experimentally, while mass and energy

balance thermal process efficiency, auto-thermal operationand combustibility of the torrefaction gas were investi-

gated by means of process simulations. In their studies,

the yield of reaction water varied between 5 and 15 %

weight, resulting in a concentration of 50 – 80 wt.% in the

torrefaction gas (excluding free water from the feed

stock). It is found that the major difference between

charcoal and torrefied wood is the volatile content. Vol-

atiles are lost during charcoal production, which also

means a possible loss of energy. On the other hand,

during torrefaction, most of the volatiles are retained. It

is also recommended that every form of carbonization be

avoided during torrefaction. From the data, torrefied pel-lets have product characteristics, like handling, milling

and transport requirements, similar to coal. Torrefied

pellets all ow for higher co-fir ing percent ages up to

40 % due to matching fuel properties with coal, and they

can use the existing equipment setup for coal.

The reaction water yield increased with residence time

and temperature, while its concentration decreased. Conse-

quently, the relative contribution of combustible products

increases with increased temperature and residence time as

Fig. 6 Stages in the heating of moist biomass as translation of energy requirement [3]

Fig. 5 Decomposition regimes of lignocellulosic material during ther-

mal treatment [17]




does the CV, which ranges from 5.3 to 16.2 MJ/Nm3.

Despite the high water content of the torrefaction gas, the

CV value is relatively high. It can be compared to produce

gas from air blown biomass gasification (4 – 7 MJ/Nm3) and

syngas from an indirectly heated gasification process (15 –

20 MJ/Nm3). Based on this comparison, the torrefaction gas

should be combustible and can play an important role in the

torrefaction process [3, 24, 44]. Typical experimental resultsfor torrefaction mass and energy yields and gas-phase com-

position for willow are given in Fig. 7.

The temperature and residence time have effect on the

properties of torrefied biomass. From the data analysis, it is

found that percentage of mass yield decreases with the

increase in the temperature. Similarly, with the increase in

the residence time, the percentage of mass yield decreases

slightly. Hence, the net effect of temperature rise has signif-

icant effect on the percentage of mass yield rather than the

residence time. It is observed that raw biomass has the

highest properties of moisture retaining capacity while the

torrefied biomass at the highest temperature has the least hygroscopic behaviours [45, 46]. From the literature [7], if

we compare the conversion of agricultural residues of rice

straw and rape stalk with woody biomass, the solid to liquid

conversion of the former is much higher than that of the

latter under the same temperature and residence time. This is

because of the higher volatile matter contents in the agricul-

tural residues and hemicellulose decomposition temperature

range. Bridgeman et al. also concluded similar findings

where mass yield in dry ash free was 55.1, 61.5 and

72.0 % for wheat straw, reed canary grass and willow,

respectively, at 290 °C for 30 min residence time. The

calorific value of TB increases with increase in treatment

temperature and residence time [5, 16], and this can be

explained by the fact that TB has lost its moisture content

and its oxygen – carbon or hydrogen – carbon ratio reduces

with increasing temperature

Torrefied biomass produces more uniform and smooth

particle sizes compared to untreated biomass because of

their brittleness, which is similar to that of coal, and this

behaviour is supported by their lower energy consumption

during grinding [20, 44]. In their experiment to examine the

particle size and particle size distribution of a torrefied pine

chips and logging residues, Phanphanich and Mani [22]

found out that the mean particle size of ground torrefied biomass decreased with increase in torrefaction temperature.

Consequently, torrefaction of biomass not only decreased

the specific energy required for grinding but also decreased

the average particle size of ground biomass. Furthermore,

they concluded that the particle size distribution curves of

torrefied biomass produces smaller particles than that of

untreated biomass, and their results were comparable to

the studies by Mani [21]. Cumulative percent passing curve

also showed the similar behaviour for torrefied biomass.

3.6 Technology

Torrefaction is based on thermal drying principle; there are

many established and patented potential methods for carry-

ing out torrefaction of biomass, which are majorly based on

different drying equipment. However, there exist several

challenges which have made it hitherto difficult to run a full

commercial scale torrefaction plant; one of these challenges

is the complex characteristics of biomass and ability to

control operating conditions that will improve the quality

of torrefied products at low costs. There are two principles

of heat contact during a drying process: directly heated

drying and indirectly heated drying. In the directly heated

driers, biomass is brought in contact with the heat carrier,

which can either be hot steam or hot air. However, in

indirectly heated dryer, biomass is not in direct contact with

heat carrier [3, 47, 48]. Many drying technology can be

modified to meet the specifications of a torrefaction reactor.

Table 1 Summary of torrefied pellets properties versus coal (source: [64])

Parameters Wood Wood pellet Torrefied pellets Coal

Moisture content (wt.%) 30 – 40 7 – 10 1 – 5 10 – 15

Calorific value (MJ/kg) 9 – 12 15 – 16 20 – 24 23 – 28

Volatiles (% db) 70 – 75 70 – 75 55 – 65 15 – 30

Fixed carbon (% db) 20 – 25 20 – 25 28 – 35 50 – 55

Bulk density (kg/m3) 200 – 250 550 – 750 750 – 850 800 – 850

Volumetric energy density (GJ/m3) 2.0 – 3.0 7.5 – 10.4 15.0 – 18.7 18.4 – 23.8

Dust explosibility Average Limited Limited Limited

Hydroscopic properties Hydrophilic Hydrophilic Hydrophobic Hydrophobic

Biological degradation Yes Yes No No

Milling requirements Special Special Classic Classic

Handling properties Special Easy Easy Easy

Transport cost High Average Low Low




These include rotary drum dryer, fluidized bed dryer, belt

dryer, conveyor dryer, screw (auger) dryer, microwave dryer

and multiple hearth furnace dryer (or turbo dryer):

(a) Rotary drum reactor consists of a rotating drum, which

rotates about a fixed point via a rotating shaft and can

either be configured in an inclined or vertical position.

Most widely used type is the directly heated single pass

in which hot gas (or steam) is contacted with biomass

in a rotating drum. The rotating drum causes the bio-

mass particles to tumble through hot gas to promote

heat and mass transfer [49]. In addition, hot steam can

be used as heat carrier in a rotary drum dryer. The

feedstock (biomass) normally flows co-currently with

the hot carrier through the reactor to facilitate drying.

Moreover, if contamination is not a concern in the

reactor, hot flue gas can be fed into reactor to supple-

ment for energy source for the operation.

(b) Fluidization is one of the most commonly used techni-

ques and found to have widespread applications for dry-

ing of solid particulates. The techniques require high-

velocity hot gas stream that creates a “fluid bed” with

special hydrodynamics and heat and mass transfer char-

acteristics [50]. Fluidized bed drying offers many advan-

tages, including fast drying and high thermal efficiency

with uniform and closely controllable bed temperature

[51]. It offers good mixing and ease of combining several

processes [51]. However, its fast drying advantage is not

ideal for torrefaction because torrefaction requires a slow

and controllable drying rate (i.e. slow pyrolysis). The

disadvantages, however, include high-pressure drop,

abrasion of the solids causing erosive surfaces, bed height

control to accommodate the height for fluidization and

the height allowed by the pressure drop, and restriction in

particle sizes and size distribution [50].

(c) A moving bed chemical reactor is characterized by the

movement of both solid and fluid phase during chemical

reaction and the operation may be countercurrent, co-

current or cross flow depending upon the relative direc-

tions of fluid and solid [52, 53]. The moving bed tech-

nique, especially on its application in agricultural dryers,has become popular owing to its lower investment, lower

energy consumption, less mechanical damage to the

seeds [54], high heat transfer rate, good hold time for

temperature, fast drying [3], low pressure drop [52] and

good plug flow. The design can be compact, highly

efficient and flexible to combine with other reactors

(e.g. fluidized bed) to optimize their applications.

(d) A screw conveyor consists of a helical flight fastened

around a pipe or solid shaft that is mounted within a

tubular or U-shaped trough; hence, when the screw

rotates, material heaps up in front of the advancing

flight and is pushed through the trough [55]. Varioustypes of screw configurations have been reported to

handle variety of materials and flow rate requirements

[55]. The screw conveyor dryer consists of a jacketed

conveyor in which material is simultaneously heated

and dried through heating medium such as hot steam or

a high-temperature heat transfer medium such as pot

oil and fused salt [55]. The heat carrier may be through

a hollow flight and shaft (indirect contact) to provide

greater heat transfer area with minimum space require-

ments [55]. Screw conveyors dryers have utilities in

many industrial applications, including agricultural,

food, chemical, pharmaceutical and pyrolytic process

of coal [55 – 57]. Some of the advantages are their

application for drying wide range of solid particles

ranging from fine powder to lumpy, sticky and fibrous

materials [44, 58]. Waje et al. [55] found their average

value of heat transfer rates to be between 42 and

105 Wm−2°C−1. Some of the disadvantages are high

cost of maintenance due to several moving parts, low

heat transfer rate [3] and not recommended for materi-

als that have tendency to cause fouling [55].

(e) Microwave heating is very attractive for various chem-

ical processes as it produces efficient internal heating

for chemical reactions, even under exothermic condi-

tions [48], and has become a widely accepted non-

conventional energy source for performing organic

synthesis [59]. In addition, microwave heating pro-

vides shorter residence time, prevents undesirable sec-

ondary reactions that lead to formation of impurities

and provides volumetric heating with good penetration

depth [48, 60]. Two most common frequencies allocat-

ed for material heating are 915 and 2,450 MHz for

industrial, scientific and medical applications [61].

Torrefaction

(32 minutesat 260°C)

Gas PhaseComponents

CO=0.1%CO2=3.3%

H2O=89.3%Acetic Acid=4.8%

Furfural=0.2%Methanol=1.2%

Formic Acid=0.1%

Remainder=1.0%

Feed: Willow

Size: 10-30mm

LHV=14.8MJ/

kg

MC =14.4%

(wb)

Fixed

Carbon=16.8%

Torrefied

Willow

Size: 10-30mm

LHV=18.5MJ/

kg

MC =1.9%

(wb)

Mass yield=75.3%

Energy Yield

Fig. 7 Experimental results of torrefaction of willow [6]




Several advantage of microwave drying comes from

volumetric heating rather than surface heating and

since the electromagnetic energy is dissipated directly

in the dried material, heat losses are considerably re-

duced [50]. However, some of the drawbacks of mi-

crowave heating technology are inability to process

fines and allow scale up of operation [26] and inability

to provide uniform heating.(f ) M u ltiple h e arth fu rn a ce (M HF ) is a v e rtica l

refractory-lined cylindrical steel shell reactor, which

contains circular hearths that rotate in horizontal

plane about a centre shaft installed with rabble arms

that moves in spiral path across each hearth [62].

The materials that enter the top hearth pass through

a drop hole to the hearth below. The retention time

of the materials in the multiple hearths can be from

0.5 to 3 h depending on the shaft speed and on the

number of hearths [62]. In some operations, com-

bustion of charged-elements supplies the heat, while

in other cases, it is furnished with combustion of auxiliary fuel by direct or indirect firing [63].

According to Dangtran et al. [62], a multiple hearth

furnace is divided into three zones: The upper zones

(or the drying zone) is where raw materials undergo

drying to remove moisture; the middle hearth zone

(or the combustion zone) is where the dried materi-

als are exposed to the combustible reactions at high

temperatures; hence, the residence time is usually

short; and the lower hearths (or the cooling zone)

where the products are cooled and its heat is trans-

ferred to the incoming combustion air/steam. Some

benefits of MHF are their capacity to: allow wide

range of processing conditions including mode of

heat transfer (co-current, counter-current or cross

flow), control temperature and residence time, pro-

vide high heat and mass transfer and ensure good

mixing [62, 63]. MHF drawbacks, however, are

their sensitivity to change in feed characteristics,

sealing issues and high cost of maintenance due

multiple moving parts.

Torrefaction is still an evolving technology, and many

technologies, which are based on the drying techniques

adopted for industrial processes such as in the agricul-

tural and mining industries, have been proposed by

many research institutes and technologies developers

across the Europe and North America. Although few

companies have claimed to develop torrefaction technol-

ogies that can be operated commercially, no proven

commercial application exists yet. Overview of various

torrefaction reactor technologies has been documented

in torrefaction review papers and conference presenta-

tions [26, 64] and these reviews include the lists of

companies, their reactor technologies and the principal

developers. Consequently, to compare the aforemen-

tioned reactor technologies as potential candidates for

torrefaction, the reactor technology must be proven and

versatile enough to accommodate all the operating con-

ditions, including the capacity to: control temperature

and residence time, accommodate wide range of feed

stocks, accommodate the heat integration system to takeadvantage of energy recirculation to supplement the

process heat, accommodate scale-up of operations, en-

hance mixing, provide uniform heating, provide high

heating rate, enhance mass and heat transfer and process

large and small particles. Ranking these different reactor

technologies will be based on the above criteria via

decision matrix. Table 2 below shows the total rating

of each potential reactor technology for torrefaction

operation based on decision matrix principles. The tech-

nology that scored the highest is the fluidized bed

following by the multiple hearth furnace. These ratings

are slightly different from those from Ferro et al. [46]due to the consideration of moving parts. Moving parts

may lead to high cost of maintenance or unnecessary

interruptions of plant operations.

3.7 Recent development

According to Kleinschmidt [64], torrefaction technology is

in the process of commercialization even though the tech-

nology and quality are still surrounded by many maturities

and uncertainties. EU is leading on the execution of the

torrefaction in the world. Energy Center of the Netherland

is one of the first to recognize the potential of torrefaction

for biomass to energy purposes. Initial small scale research

was started in 2002 – 2003. Based on the small-scale re-

search, 25 tons of torrefied material was produced in 2008

from poplar chips, softwood/hardwood mixture and agricul-

tural residues at 220 – 280 °C. European utilities Essent

B.Vm DELTA N.V. had taken the risk to produce torrefied

bio-product and supply to the other utilities RWE Innogy for

long-term basis. This brings new rays of hopes on the

commercialization of torrefaction technology [65, 66]. It is

expected that developmental stages in Europe will lead to

gear the momentum of commercialization of torrefaction in

the North America and other world.

There are more than 50 development projects under way

in European Union out of which more than ten projects were

targeted to be in production before end of 2011, but none of

the literatures confirms these claims. One of the projects of

Canada was from The Centre for Energy Advancement

through Technological Innovation (CEATI) program [67].

CEATI evaluated most promising torrefaction/carboniza-

tion/steam explosion/microwave technologies and provided

critical assessment of the leading sources/vendors that offer




the best short- and long-term technology/project potential to

determine the economic viability of beneficiated fuels and to

determine the technical viability of beneficiated fuels based

on actual testing, comprehensive lab analysis, 1 MW pilot

test burns, 150 MW full scale and 100 % beneficiated

biomass test burns. The tentative project timeline was to

initiate in March 2010 and Energy Research Center of the

Netherland (ECN) was selected for lab test.

According to Dana et al. [68], several manufacturers and

researchers are developing torrefaction units for commercial

use. Integro Earth Fuels, LLC reports that their torrefaction

process reduces 20 – 30 % of the mass while retaining 90 %

of its energy. Their torrefaction process operates in the

temperature range of 240 – 270 °C. The company anticipates

producing 4,000 tons of torrefied biomass each month in the

pilot plant. Knowledge gained from the pilot plant was

intended to develop a full-sized torrefaction facility [69].

Heating values of the final product range from 9,500 to

11,000 Btu/lb. Southern pine species have an energy value

of approximately 8,500 Btu/Lb (dry weight). Under this

torrefaction process, the energy value from a dry ton of

wood would be reduced from 8,500 to 7,650 Btu/lb (a

10 % loss); however, there are mass losses associated with

the process. If the mass reduction from the process is 20 %,

the final product has an increased energy value of 9,563 Btu/

lb or a 12.5 % increase in energy value. Thermya, a French

engineering company, has developed a continuous torrefac-

tion process called TORSPYD. In April 2010, World Bio-

energy News reported that Thermya was the only European

company to offer an industrially proven, fully operational,

continuous biomass torrefaction process [70]. The system is

reported to operate in the lower range of temperatures

reported for torrefaction. TORSPYD processing operates

in temperatures ≤240 °C, a soft thermal treatment. Unit

capacities can range from 100 to 5,000 kg/h. The final

product is called bio-coal and is marketed as a coal substi-

tute to be co-fired with coal or used in industrial boilers for

producing electricity. The bio-coal can also be used in pellet

manufacture and eliminates the need for sawdust [70]. Agri-

Tech Producers, LLC, a company based in South Carolina,

is reported to be nearing the completion of a commercial-

grade torrefaction machine. Using technology developed at

North Carolina State University, their process operates in a

low-oxygen environment at temperatures ranging from 300

to 400 °C. The first built plant was named as the Torre-Tech

5.0. The production rate of this machine was 5 tons of

torrefied wood/h. Researchers in the Netherlands are con-

tinuing to research on a torrefaction process that began in

the 1980s by a French aluminium company. Originally, the

process was used to produc e metal from metal oxides.

Today, the current process is called TOP for torrefaction and

pelletization. Early results in 2005 (Bergman and Kiel) indi-

cated that a commercial scale plant could produce 60 –

100 greenktons/year (approximately 66,000 – 110,000 green

tons/year) of high-energy torrefied pellets. Researchers indi-

cate that TOP pellets could be delivered to power plants at a

lower cost/Btu as compared to standard wood pellets. They

attribute some of the cost savings to the pelletization process,

but the majority of the savings is attributed to transportation

logistics from transporting an energy dense product.

In 2009, Natural Fuels Industries, Inc. of Calgary, AB,

Canada announced plans to build biomass processing plants

in Georgia (USA) and Brazil. The company planned to pro-

duce bio-coal briquettes using torrefaction technology. The

briquettes could be shipped to European markets. In their

initial announcement [67], they stated that there is a

Table 2 Comparison of potential torrefaction technologies [9, 69 – 72]

Torrefierstechnology

Mode of heating

Status criteria

Rotary drumreactor

Direct Proven technology, minimum heat transfer, high heating rate, medium temperature control, good residencetime control, excellent heating integration, enhanced mixing, large size tolerance, high moving parts, goodfouling,, little scaling problem

Fluidized bedreactor

Direct Proven technology, enhanced heat transfer, high heating rate, medium temperature control, medium residencetime control, excellent scalability, excellent heating integration, excellent uniform heating materials,enhanced mixing

Moving bedreactor

Direct Under development, enhanced heat and transfer, high heating rate, medium temperature control, goodresidence time control, excellent heating integration, enhanced mixing, good fouling

Screw conveyor Direct Indirect Proven technology, enhanced heat and transfer, high heating rate, medium temperature control, good residencetime control, excellent heating integration, enhanced mixing, large size tolerance, high moving parts, best fouling and scaling

Microwave Direct Indirect Under R&D, enhanced heat and transfer, high heating rate, good temperature control, good residence timecontrol

Multiple hearthfurnace

Direct Proven technology, enhanced heat and transfer, high heating rate, medium temperature control, good residencetime control, excellent heating integration, enhanced mixing, large size tolerance, high moving parts, perfect scaling and best scalability




tremendous demand from European and American pulverized

coal plants for bio-coal to meet cap and trade regulations and

renewable portfolio standards for power generation. Recent

project around the world is stated in the “Appendix”.

Kiel et al. [19] developed BO2 technology under the

umbrella of ECN for biomass upgrading into commodity

fuel, a technology that combines torrefaction and pelletiza-

tion processes to produce products called torrefied pellets(BO2 pellets™). BO2 pellets™ possess the benefits of both

process but with higher bulk density (1.5 – 2 times conven-

tional pellets) and calorific values and can be produced from

a broad range of biomass streams, such as woodchips,

agricultural residues and various residues from the food

and feed processing industry [6, 19].

The BO2 technology consists of three main process steps:

drying, torrefaction and pelletization. The drying and pelleti-

zation components are conventional technologies that are

commercially available. The innovative part in the BO2 tech-

nology is the torrefaction step. The central element in this step

is a directly heated moving bed torrefaction reactor in which biomass is heated using recycled torrefaction gases which has

been re-pressurized to compensate for the pressure drop in the

recycle loop and of the heating of the recycle gas to deliver the

required heat demand in the torrefaction reactor [19].

Kiel et al. [6, 19] provides the summary of the test results

(Table 3) showing the comparison of “BO2 Pellets™” prop-

erties against those from raw wood chips, wood pellets and

torrefied woods. Moreover, there is high expectation of

strong growth in pelleting equipment and will continue to

project through the future; also the use of briquetting densi-

fication will continue, although on a smaller scale than

pelleting. Overall, with any densification process, reliable

control of process variables and feedstock properties is

essential to good results.

AMANDUS KAHL is a German-based company and one

of the leading manufacturers of pellet equipment from small

to industrial scale. KAHL pelleting plants have been applied

successfully for compacting organic products of different

particle sizes, moisture contents and bulk densities. Their

pelleting presses are designed for array of feedstock charac-

teristics as seen in Fig. 8. Available pelleting presses consist

of a drive power of 3 to 500 kW and a throughput between

0.3 and 8 tons/h. KAHL recently developed pellet press

equipment with 15 to 20 tons/h capacity.

4 Application

The high fuel quality of torrefied biomass makes it veryattractive for combustion and gasification applications which

are summarized from [3, 9 – 74] (http://www.ecotechenergy-

group.com/index.php/alternative-energy ). Due to high calorif-

ic values, the thermal energies of the combustion and

gasification system can be improved significantly [5, 19]. The

other applications include (a) biomass solid fuel (acting as coal)

for thermal power plant to generate heat and electricity; (b) co-

firing in pulverized boilers; (c) co-gasification in entrained-flow

gasifier (biofuels production); (d) good-quality fuels for domes-

tic and commercial use; (e) pellets, briquettes used as fuels; (f)

small-scale pellet boilers/stoves and (g) high-quality fuel for

advanced bioenergy application [74].

4.1 Pelletization

Kumar et al. [75] conducted a detail study in western

Canada on the cost to produce biomass power by direct

combustion; they concluded that transportation was the

second-most factor that influence the net cost of operation.

One of the techniques that can address these limitations is

to densify biomass materials into pellets, briquettes or

cubes [76]. Methodology of simple pelletization process

is given in Fig. 9.

Densification increases the bulk density of biomass from

an initial bulk density (including baled density) between 40

and 200 kg/m3 to approximately bulk density of 600 to

800 kg/m3 [44, 77, 78]. Hence, densification of biomass

materials could reduce the costs of transportation, handling

and storage. Because of uniform shape and sizes, densified

products can be easily handled using the standard handling

and storage equipment and can be easily adopted in direct

combustion or co-firing with coal, gasification, pyrolysis

and in other biomass-based conversion processes [76].

Table 3 Comparison of BO2

pellet properties [19] Properties (typical values) Wood chips Torrefied wood Wood pellets BO2 pellet

Moisture wt.%) 35 0 10 3

LHV (kJ/kg)

Dry 17.7 20.4 17.7 20.4

As received 10.5 20.4 15.6 19.9

Bulk density

kg/m3 475 230 650 750

MJ/m3 5.0 4.7 10.1 14.9


http://www.ecotechenergygroup.com/index.php/alternative-energy







Table 4 below shows the summary of commercial scale

pellet mill specifications from four different manufacturers.

With pelletization being the most popular densification pro-

cess, integrating it with torrefaction process can even in-

crease their properties, including their volumetric densities.

Although there have been many advancements made to

densification equipment to improve their throughputs and

their performances, the technology still remains the same.

More recently, research has discovered a biomass treatment

process that combines the densification (pelletization) and

torrefaction to increase the bulk density and the calorific

value of biomass.

4.2 Combustion and co-firing

The most important application of biomass is in the co-firing

of pulverized coal boilers. In this application, biomass has to

be fed to the reactor as a powder, which is costly and

achievable only at very low capacity in classical coal mills.

Due to this limitation, wood pellets are currently the state-

of-the-art for co-firing, as they consist of sufficiently small

particles. But wood pellets also have some limitations in

terms of energy content and moisture content which create

problems during storage and transportation [79]. Torrefied

biomass, because it is energy dense and hydrophobic in

nature, can be a good replacement for wood pellets in co-

firing and gasification plants. The high fuel quality of torre-

fied biomass makes it very attractive for combustion and

gasification applications. Due to high calorific values, the

thermal energies of the combustion and gasification system

can be improved significantly. However, data are lacking on

milling, handling, storing, transporting and combusting.

Almost complete combustion is possible with torrefied bio-mass for heat generation which ultimately can lead for elec-

tricity generation, centralized heating system etc. [7, 80].

4.3 Gasification

The main application of torrefied biomass (wood) is as a

renewable fuel for combustion or gasification. Prins et al.

[72] studied the possibility of more efficient biomass

gasification via torrefaction in different systems: air-

blown circulating fluidized bed gasification of wood,

wood torrefaction and circulating fluidized bed gasifica-

tion of torrefied wood and wood torrefaction integratedwith entrained flow gasification of torrefied wood. Gasi-

fication is a process that converts biomass into carbon

mon ox ide , h yd ro g en a nd c arb on d io xid e. T his is

achieved by reacting the material at high temperatures

(>700 °C), without combustion, with a controlled amount

of oxygen and/or steam. The resulting gas mixture is

called syngas (from synthesis gas or synthetic gas) or

producer gas and is itself a fuel. The power derived from

gasification of biomass and combustion of the resultant

gas is considered to be a source of renewable energy; the

gasification of fossil fuel-derived materials such as plastic

is not considered to be renewable energy.

The advantage of gasification is that using the syngas

is potentially more efficient than direct combustion of the

original biomass because it can be combusted at higher

temperatures or even in fuel cells, so that the thermody-

namic upper limit to the efficiency defined by Carnot ’s

rule is higher or not applicable. Syngas may be burned

directly in gas engines, used to produce methanol and

hydrogen, or converted via the Fischer – Tropsch process

into synthetic fuel. Gasification can also begin with ma-

terial which would otherwise have been disposed of such

as biodegradable waste. In addition, the high-temperature

process refines out corrosive ash elements such as chlo-

ride and potassium, allowing clean gas production from

otherwise problematic fuels. Gasification of fossil fuels is

currently widely used on industrial scales to generate

electricity.

Gasification of biomass that in many ways is a more

efficient use of the feedstock is nowadays an interesting

alternative to combustion for many industries but is still

limited. Tar production is a major drawback of woody

gasification in any convention gasifier which is leading

Fig. 8 Pictures of raw and pelletized materials (source: http://www.

akahl.de/akahl/files/Prospekte/Prospekte_englisch/1322_Strohpell_

10e.pdf )

Drying Torrefaction

Cooling

Densification

TOP pellets

Fig. 9 Methodology for torrefaction and palatalization process [5]


http://www.akahl.de/akahl/files/Prospekte/Prospekte_englisch/1322_Strohpell_10e.pdf








towards the application of torrefied woody biomass. Other

disadvantages are the relatively low energy content and its

hydroscopic character. Additionally, Prins et al. have shown

that higher gasification efficiency can be achieved by fuels

with lower O/C ratio by thermochemical process. Torrefac-

tion is a process that effectively lowering the O/C ratio of

biomass in a simple way and lowers the power cost during

milling and transportation cost. The output product in the

form of powder greatly enhances the feeding properties.

Although extensive studies have been made on the solid

product and its application of gasification, limited publica-

tions has been made on the utilization of torrefied product in

existing thermochemical process [8, 79].

5 Emission

Biomass could reduce pollutants emitted in power pro-

duction. Burning biomass is generally carbon neutral;

net carbon emissions would be zero and that would

help control global warming. This is one of the major

concerns of the industrialized nation. Many countries

are planning to replace coal-fired plant by biomass to

minimize the greenhouse gas effect. Torrefied biofuel

will be much safer and environmentally friendly than

the present fossil fuels.

However, from the torrefaction process, the output

product contains gaseous, volatiles, organic acids and

primary tars. This needs to be minimized by capturing

gaseous and liquid products of the process, and the

remaining emissions consists only of CO2, H2O, NO x

and So x. NO x emissions can be negligible due to low

temperature, and SO x emissions can be considered as

zero due to least sulphur contents of the lignocellulosic

biomass. Condensed tars are a major concerned on the

application of torrefied biomass. As the temperature

increases during torrefaction, the tar formation also in-

creased exponentially. This issue needs to be addressed

very carefully. According to Kleinschmidt [64], test

results have shown that even after combustion, the flue

gas contains some organic compounds like hydrogen

fluorides, sulphides and nitrates that need to be removed

before emitting the flue gas. This needs additional care

on flue gas. Bag filters and ceramic filters with an

absorbent are suggested to minimize the emissions.

The emissions of biomass torrefaction are not expected

to be a major technical challenge, but reduction on the

ash, chlorine, sulphur and alkaline production should be

minimized.

6 Storage behaviour

Solid biofuels usually have porous moisture and are

prone to off-gassing and self-heating caused by chemi-

cal oxidation and microbiological activity. During stor-

age, chemical – microbial reactions take place because of

the presence of moisture on it. Tumuluru et al. [7]

concluded that high storage temperatures of 50 °C can

r es ul t i n h ig h C O a nd C O2 e mis s ion s , a n d th e

Table 4 Summary specifications of four different wood/sawdust pellet [6, 19]

Company La Meccanica NOVA Pellet Kerry Die Amandus Kahl

Model CLM 800 P LG N-Plus B-Mass 800 60 – 1250

Roller quantity 2 Unknown 6 4 – 5

Drive power (KW) Up to 280 160 450 3 – 500

Energy consumption Unknown Unknown Unknown 40 – 60 kWh/t

Capacity (T/H) 2.3 – 3 Up to 2.5 10 15 – 20

Operation mode Continuous Continuous Continuous Continuous

Weight (kg) 10,800 7,500 Unknown 9,370

Roll diameter (mm) Unknown 245 250 450

Motor speed (rpm) 750 Unknown 1,490 Unknown

Roller speed (m/s) 6.5 – 7.5 Variable Variable 2.5

Die diameter (mm) Unknown 580 840 175 – 1,250

Input density Unknown Unknown Unknown 150

Output density (kg/m3) Unknown Unknown Unknown 550 – 650

Feedstock moisture Unknown 8 – 12 % Unknown 12 – 15 wt.%

Feedstock size Unknown 0.5 – 1.5 mm Unknown 4 mm

Pellet moisture 9 – 12 wt.% Unknown Unknown 12 wt.%

Pellet diameter (mm) 6 6 8 2 – 30




concentrations of these off-gases can reach up to 1.7

and 6 % for 60 days of storage period. These emissions

were also found sensitive to relative humidity and prod-

uct moisture content [81]. Torrefied biomass or pellets

are superior to the regular raw pellets as they are

hydrophobic in nature, and moisture uptake is almost

negligible even under severe storage conditions. The

storage issues like off-gassing and self-heating may bevery low in torrefied biomass as most of the solid,

liquid and gaseous products, which are chemically and

microbiologically active, are removed during the torre-

faction process. Some studies conducted by researchers

at the University of British Columbia, Vancouver, Can-

ada on off-gassing from torrefied wood chips indicated

that CO and CO2 emissions were very low, nearly one

third of the emissions from regular wood chips. Cost

analysis shipping, trucking, storage and others are

shown in Fig. 10 [82].

7 Economic potential

To analyse the details of net profit of torrefaction, the

impact of the process on the all steps of the value chain

is to be discussed. The segments of benefits are trans-

port, storage, carbon neutral and production. Higher en-

ergy density, condensation, pelletization and dried mass

of the torrefied products make economic benefit on the

transportation. Hydrophobic behaviour of torrefied bio-

mass can be successfully stored outdoors, thus obviating

the need for an enclosed storage bin or building but

further studied is required on this issue. However, it

should be noted that, in dry climates, wood chips have

been successfully stored in large outdoor piles. The rel-

ative fuel losses (shrinkage) during storage are not well-

known but can be expected to be higher for outdoor

storage. Comparisons of shrinkage losses of torrefied

versus raw biomass are needed for different storage con-

ditions and climates. Utilization benefits are related to the

higher energy content, lower oxygen content and

(probable) lower moisture content, relative to unprocessed

biomass. Torrefied biomass is expected to perform as

well or better than raw biomass for many bioenergy

applications, including combustion, gasification and fuel

production applications [83]. Enhanced conversion and

utilization, when compared to the other steps in the

supply chain, probably provide the most significant op-

portunity for cost savings (followed by transport costs).

Torrefied biomass is believed to be a superior solid fuel

for combustion, especially when co-fired with coal due to

its higher energy density and coal-like handling proper-

ties. Torrefied biomass is also expected to provide advan-

tages as a fuel for thermochemical processing, due to the

removal of acids and oxygen. Gasification using torrefied

biomass allows for improved flow properties of the feed-

stock, increased levels of H2 and CO in the resultingsyngas and improved overall process efficiencies [66,

83]. Torrefaction combined with pelletization provides a

lower cost fuel for power or fuel production when com-

pared to pelletizing alone, with cost savings ranging from

4 to 16 %, depending on the end use of the biomass.

Figure 10 shows supply chain costs for several scales

and processing options for biomass, indicating that pel-

letizing of torrefied biomass significantly reduces costs,

that larger-scale operations are more cost efficient and

that integrated torrefaction and pelletizing is less costly

than pelletizing alone. Zwart et al. conclude that, while

torrefaction is one of the most cost-effective options for

supply of overseas biomass, modifications to the supply

chain, such as the centralized processing of raw feed-

stock, can result in similar reductions in overall costs.

According to Van der Stelt et al. [42], the torrefaction

step represents an additional unit operation in the bio-

mass utilization chain. The attendant capital and operat-

ing costs, as well as conversion losses, are, however,

offset by savings elsewhere. Recent cost estimates for

the ECN torrefaction technology indicate that the total

capital investment of a standalone 75 ktons/year plant

will be in the range 6.1 to 7.3 MV. The assumed feed-

stock is wet softwood chips. The plant consists of a

conventional rotary drum for drying the biomass, ECN

torrefaction technology and conventional grinding equip-

ment and pellet mill. No feedstock preparation (e.g.

chipping) before drying was included. At 75 ktons/year

production rate (design), the total production costs are

calculated at 37 V/ton product (2.0 V/GJ), produced from

a feedstock with 35 % moisture content. At 50 and 25 %

moisture content, this is 50 V/ton (2.6 V/GJ) and 34 V/

ton (1.9 V/GJ) of product, respectively. The moisture

Fig. 10 Delivery costs of pelletized biomass (numbers indicate nom-

inal capacity of system (dry kilotons of raw biomass feedstock per year

[28]))




content is one of the most influential parameters of the

torrefaction process as it predominantly determines the

energy input of the process. These data represent the

added cost for the torrefaction process without pre-

processing of pre-drying process of biomass.

8 Research gaps

There exists several gaps in the development of torrefaction

technologies and its maturities, and there is need for con-

tinued research and development to characterize and opti-

mize this promising option for bioenergy feedstock

processing for the application of next generation fuel prior

to the depletion of fossil fuels. Governments, private

parties and universities are investing a lot in the field of

biomass applications. Several achievements are still under

the scope of laboratory. The most challenging is to see the

laboratory experiment in the commercial applications. For

this, in-depth study on chemical reactions and its network,composition and application of tar, char and ash has yet to

be established, in part due to the complex chemical nature

of the feedstock. The health and safety issues on torrefac-

tion process and its product applications is another area of

further study [28]. Environmental effect, storage behaviour

of torrefied biomass, energy analysis of the torrefied prod-

ucts, temperature effect, heating values due to different

temperature, practical reactors, residue management, syn-

gas management, molecular level analysis and effective

transportation possibilities are few areas of research on

the torrefaction process.

According to Chew and Doshi [8], torrefaction of

biomass as a thermochemical treatment has the potential

to contribute to energy demand of the world. In the

recent years, torrefaction studies on various agricultural

prod ucts asso ciat ed with fuel prop erties have shown

promising result. However, due to the complexity and

variety of agricultural residues, all the process parame-

ters have yet to be derived. Torrefaction process output

solely depends on the polymeric structure of biomass.

Detailed investigation is still required on polymeric

structure. Future work can look into the possibility of

deriving indicative parameter to define process parame-

ter for torrefaction based on the polymeric structure of

the feedstock. Further research should focus on the

possibil ity of utilizing the by-products to improve the

overall efficiency of torrefaction. Another area of study

could be the kinetic analysis for torrefaction. Future

work should concentrate on different kinetic analysis

approaches to validate reliability and consistency of

the kinetic information.

A primary goal of torrefaction of biomass is to in-

crease its energy density such that biomass transporta-

tion cost can be minimized. In terms of this attribute of

torrefaction, appropriate reactor selection is important

parameters. Energy yield is important when torrefaction

is carried out at the point of use or at the end of its

major transportation. Identifying reactor for specific pur-

poses with specific properties could be another area of study. Similarly, the emission effect from the torrefied

biomass is still under the further study.

9 Conclusions

In major universities and green energy industries, inten-

sive research on torrefaction of biomass materials is in

progress. Almost all countries have expressed concerned

on the global warming and shifted towards the optimum

utilization of GHG energy [84]. Torrefaction improves

the physical, chemical and theological characteristics of bio mas s materi als . Torre fied bio mas s is a gro up of

products resulting from the partially controlled and iso-

thermal pyrolysis of biomass occurring at the 200 – 300 °

C temperature range. The most common torrefaction

reactions include devolatilisation and carbonization of

hemicelluloses in first steps and depolymerization and

devolatilisation of lignin and cellulose in other step.

Torrefaction of the biomass helps in developing a uni-

form feedstock with minimum moisture content and less

affected by atmospheric environment. Torrefaction of

biomass improves energy density, homogeneity, grind-

ability and pelletability performance. Similarly ultimate

and proximate analysis gives moisture contents; ash

contents; volatile matters; carbon content; oxygen, hy-

drogen, nitrogen and sulphur contents; CV content and

biochemical composition. Lignin helps for better bind-

ing in process of pelletization. During torrefaction, the

biomass loses most of the low energy content of the

material which includes water, organics and lipids and

gases, H2, CO, CO2 and CH4, C xH y , toluene and ben-

zene. Torrefaction can keep the biomass for a long time

without biological degradation due to the chemical re-

arrangement of structures. Torrefied biomass can be

used as an upgraded solid fuel in electric power plants

and gasification plants. Torrefied biomass provides al-

ternative source of coal in the future for all coal based

plants by replacing carbon neutral energy dense torre-

fied pallets. Torrefied biomass can directly mill and co-

fire with coals. The typical calorific value of torrefied

biomass is in the range of 18 – 22 MJ/kg. The product is

brittle and easily breaks down in small particles. Also, it




is less sensitive to degradation due to hydrophobic

nature. The volumetric energy density of torrefied pel-

lets is nearly 16 GJ/Nm3 compared to nearly 10 GJ/m3

of wood pallets. But torrefaction alone cannot signifi-

cantly reduce sulphur, chlorine and alkali concentrations

of the biomass.

The present technologies mainly concentrate on process-

ing of wood chips for narrow bandwidth of particle size.Agricultural residues are still a challenge because it ignites

easily, has a low bulk density and has long fibres. Till this

date, only results from pilot plants are available. It will be a

challenge for developers to develop a full commercial tor-

refaction plant, which incorporates the necessary design and

process modification for good commercial performance.

Although some experience has been gained with pilot test-

ing, real operational data will reveal the performance of the

torrefaction process. The trade-off between energy yield,

product quality and production cost is important. The prod-

uct needs to be validated by large co-firing trials. This can

be seen only after the commercial application. Most torre-faction developers are small companies with a limited fi-

nancial base. Convincing investors are needed to finance the

necessary R&D, and an up-scaling effort is a real challenge.

A dominant torrefaction concept will emerge out of a large

variety of technologies and initiatives to commercially pro-

vide biomass according to the specifications. Product stan-

dardization is needed to make the market more transparent

and reliable. The urgency and quality of demand is signifi-

cantly higher than the supply. Torrefaction suppliers are

facing the challenge to scale-up their first commercial dem-

onstration plant in a rapid pace.

The combination of torrefaction and densification

offers the opportunity to produce high-quality second-

generation fuel pellets from a wide range of biomass

feed stocks. Due to their high energy density, hygro-

scopic nature and easy grindability, BO2 pellets have the

potential to become a major commodity fuel with ex-

cellent properties for co-firing applications, for biofuels

pro duct ion via high-tempera ture gasifi cation and for

small-scale combustion applications. Moreover, the hy-

groscopic nature makes the pellets highly resistant to

biological degradation and spontaneous heating, which

leads to large advantages in transport, handling and

storage. Significant cost savings can be achieved

throughout the biomass-to-energy chain when compared

to state-of-the-art wood pellets. Econcern and Chemfo

jointly have set up the first commercial plant at a scale

of approximately 70 ktonnes/year BO2 pellets in the

Netherland. After the production from this plant, it can

be expected that torrefaction will have new dimension

and applications in the commercial market [85, 86].

Torrefied wood is being used in different proposes

from the long time. The hydrophobic and brittle prop-

erties of torrefied wood make it compatible with coal or

as a coal replacement. In order for torrefied wood to

compete in the coal market, the cost of producing

torrefied wood, from the stump to the delivery point,

must not exceed the price of coal deliveries. Other

potential uses of torrefied wood include industrial boil-ers, residential heating, co-firing of thermal plants and

for backyard grilling. From the perspective of the log-

ging and timber industry, literature indicates that raw

material can vary in size and can include thin and thick

chips and even larger wood chunks. Depending on the

equipment design and considering characteristics such as

pre-drying, processing temperature and reaction time, it

appears that feed stocks for the torrefaction process

could be produced by utilizing different types of wood

processing equipment which are available in the present

commercial or residential applications.

From the above study, the following recommendationsare made for further exploration on the commercialization

of the biomass energy applications using torrefaction pro-

cess: (1) further analysis of heating value and residence

time for particular biomass during torrefaction processes;

(2) energy analysis during the process of torrefaction and

densifications processes; (3) in-depth study on the calcu-

lation of activation energy required during the degradation

of different chemical components of biomass; (4) molec-

ular level analysis on the torrefaction; (5) study of the

severity of the torrefaction process based on colour

changes using the different types of colorimeter; (6) stud-

ies on cost-effective transportation of torrefied biomass

fuels; (7) effect of temperature on the different chemical

bonds of biomass structure; (8) commercial viability on

the integrated processes of torrefaction and densifications;

(9) study of storage condition of different torrefied bio-

mass at different environmental conditions; (10) study of

finding out of suitable reactor for yielding the highest

energy and the best qualify biofuel from the torrefaction;

(11) studies on the proper management and handling of

residues from the torrefaction; (12) designing of an effi-

cient, robust, fuel flexible, scalable and cost-effective tor-

r e f ac t i on d e mo n st r a ti o n p l an t f o r c o mm e r ci a l

application; (13) identify the extent if any of risk for

self-ignition and biological degradation of torrefied

bio mass while stored; (14 ) asses s the pot ential for

slagging/agglomeration of fluidized bed and corrosion

and fouling of super heater/economizer tubes and (15)

LCA analysis of torrefied biomass and its application

to power generation and/or making ethanol/biodiesel

[2, 7, 87 – 91].




Appendix: Overview of torrefaction projects

(source: [64])

Table 5 Overview of torrefaction projects (source: [64])

Company Demotechnology

Supplier Location (s) Prod.capacity(tons/year)

ESD of operation

Comments

3RAgrocarbon(Hungary)

Rotary kiln(3R pyrolysis

biochar)

Unknown Unknown Unknown Unknown Pyrolysis unit that can also perform torrefaction

4Energy Invest.(Belgium)

Unknown StramproyGreen Tech.(the Netherlands)

Amel (Belgium) 40,000 Q4 2010 Contract with StramproyGreen Tech Terminated inJune 2010; Renogen SA,to take full control of

project

Agri-Tech ProducersLLC (USA/SC)

Belt conveyor Kuster ZimaCorporation(USA/SC)

Unknown Unknown 2010

Andritz(Austria) Unknown Unknown Unknown ~50,000 Unknown Torrefaction processfor biomass: develop process for medium sized plant (~50,000 tons/year) pilot plant under construction

Atmosclear (Switzerland)

Rotary drum CDS (UK) Latvia, New Zealand,USA

50,000 Q4 2010

BioEnergyDevelopment (Sweden)

Rotary drum Unknown Ö-vik (Sweden) 25,000 –

30,0002011/

2012

Biogreen Energy(France)

Screw conveyor ETIA (France) Unknown Unknown Unknown No recirculation of thenon-condensable fractionof the Tor-Gas, hence thesystem could be energy

consumingBiolake BV

(the Netherlands)Screw conveyor Unknown Eastern Europe 5,000 –

10,000Q4 2010

CDS (UK) Rotary kiln Unknown Unknown Unknown Unknown

CMI (NESA) Multiple heathfurnace

EBES AG (Austria) Rotary drum Andritz (T) Frohnleiten(Australia)

10,000 2011

ECN (the Netherlands) Moving bed Unknown Unknown Unknown Unknown

FoxCoal B.V. (the Netherlands)

Screw conveyor Unknown Winschoten(the Netherlands)

35,000 2012

Integro Earth Fuels,LLC (USA/NC)

TurboDryer Wyssmont (USA/NC)

Roxboro, NC 50,000 2010

New Earth Renewable

Energy Fuels, Inc.(US/WA)

Fixed bed/

pyrovac

Pyrovac Group

(Canada/QU)

Unknown Unknown Unknown

Rotawave Ltd. (UK) Microwaveheating

Group’s Vikoma Terrace, B.C, Canada 110,000 Q4 2011

Stramproy GreenInvestment B.V.(the Netherlands)

Oscillating belt conveyor

StramproyGreen Tech.(the Netherlands)

Sreenwijk(the Netherlands)

45,000 Q3 2010

Thermya (France) Moving bed Lantec Group (SP) San Sebastian (SP) 20, 000 2011

Topell Energy B.V.(the Netherlands)

Torbed Torftech Inc (UK) Duiven(the Netherlands)

60,000 Q4 2010

Torr-Coal B.V. Rotary drum Unknown Dilsen-Stokkem(Belgium)

35,000 Q3 2010




References

1. United Nations (UN). Kyoto protocol to the United Nations frame-

work convention on climate change [Online]. Available at: http://

unfccc.int/resource/docs/

2. Bridgeman TG, Jones JM, Shield I, Williams PT (2008) Torrefac-

tion of reed canary grass, wheat straw and willow to enhance solidfuel qualities and combustion properties. J Fuels 87:844 – 856

3. Bergman, PCA, and Kiel JHA (2005) Torrefaction for biomass

upgrading. In: 14th European Biomass Conference & Exhibition,

Paris, France, 17 – 21 October

4. Paoluccio AJ, Smith RS, Modesto CA (2006) U.S. patent applica-

tion for “Method and apparatus for biomass torrefaction, manufac-

turing a storable fuel from biomass and producing offsets for the

combustion products of fossil fuels and combustible article of

manufacture,” Docket no. 60/747,803

5. Bergman PCA, Boersma AR, Zwart RWH, and Kiel JHA (2005)

Torrefaction for biomass co-firing in existing coal-fired power

stations. Report ECN-C-05-013, ECN

6. Kiel JHA (2007) Torrefaction for biomass upgrading into com-

modity fuels. In: Proceedings of the IEA Bioenergy Task 32

Workshop on Fuel Storage, Handling and Preparation and System

Analysis for Biomass Combustion Technologies. Berlin, Germany

7. Tumuluru JS, Shahab Sokhansanj J, Wright CT, and Boardman RD

(2010) Biomass torrefaction process review and moving bed tor-

refaction system model development. Oak Ridge National Labo-

ratory, INT/EXT-10019569 and INL/CON-10-18636

8. Chew JJ, Doshi V (2011) Recent advances in biomass pretreatment

— torrefaction fundamentals and technology. Renew Sust Energ

Rev 15(2011):4212 – 4222

9. Tumuluru JS, Sokhansanj S, Hess JR, Wright CT, Boardman RD

(2011) A review on biomass torrefaction process and product

properties for energy applications. Ind Biotechnol 7:384 – 401

10. McKendry P (2002) Energy production from biomass (part1):

overview of biomass. Biores Technol 83:37 – 46

11. Yang H, Yan R, Chen H, Zheng C, Lee DH, Liang DT (2005) In-

depth investigation of biomass pyrolysis based on three major

components: hemicellulose, cellulose and lignin. Energy Fuel

20:388 – 393

12. Pérez J, Muñoz-Dorado J, Rubia T, Martínez J (2002) Biodegra-

dation and biological treatments of cellulose, hemicellulose and

lignin: an overview. Int Microbiol 5(2):53 – 63

13. Arias B, Pedida C, Fermoso J, Plaza MG, Rubiera F, Pis JJ (2008)

Influence of torrefaction on the grindability and reactivity of

woody biomass. Fuel Process Technol J 89(2):169 – 175

14. Bridgeman TG, Jones JM, Williams A, Waldron DJ (2010) An

investigation of the grindability of two torrefied energy crops. Fuel

J 89(12):3911 – 3918

15. Sadaka S, Negi S (2009) Improvements of biomass physical and

thermochemical characteristics via torrefaction process. Environ

Prog Sustain Energy, AlChE J 28(3):427 – 434

16. Jeffries TW (1994) Biodegradation of lignin and hemicelluloses.

In: Ratledge C (ed) Biochemistry of microbial degradation.

Kluwer, Dordrecht, pp 233 – 277

17. Uslu A, Faaij APC, Bergman PCA (2008) Pre-treatment technol-

ogies, and their effect on international bioenergy supply chainlogistics. Techno-economic evaluation of torrefaction, fast pyroly-

sis and pelletization. Elsevier Energy 33:1206 – 1223

18. Wang G, Luo Y, Deng J, Kuang J, Zhang Y (2011) Pretreatment of

biomass by torrefaction. Chin Sci Bull 56:1442 – 1448

19. Kiel JHA, Verhoeff F, Gerhauser H, and Meuleman B (2008) BO2

Technology for biomass upgrading into solid fuel-pilot scale test-

ing and market implementation. Energy Research Centre of the

Netherlands (ECN), Petten

20. Repellin V, Govin A, Rolland M, Guyonne R (2010) Energy

requirement for fine grinding of torrefied wood. Biomass Bioen-

ergy J 34(7):923 – 930

21. Mani S (2010) Integrating biomass torrefaction with thermo-

chemical conversion processes. In: Proceedings of the Annual

Meeting of AIChE, Nashville, TN. Nov 8 – 13, 2009, Paper #

160229, [online materials]. http://www.aicheproceedings.org/

2009/Fall/data/papers/Paper160229.pdf

22. Phanphanich M, Mani S (2010) Impact of torrefaction on the

grindability and fuel characteristics of forest biomass. Biores Tech-

nol J 102(2):1246 – 1253

23. Almeida G, Brito JO, Perre P (2010) Alterations in energy prop-

erties of eucalyptus wood and bark subjected to torrefaction: the

potential of mass loss as a synthetic indicator. Biores Technol J 101

(24):9778 – 9784

24. Bergman PCA, Boersma AR, Kiel JHA, Prins MJ, Ptasinski KJ,

and Janssen FGGJ (2005) Torrefied biomass for entrained-flow

gasification of biomass. Report ECN-C--05-026, ECN

25. Bioenergy Update (2000) vol. 2 No. 4 https://www.bioenergyupdate.

com/magazine/security/NL0400/bioenergy_update_april_2000.htm

26. Govin A, Repellin V, Rolland M, and Duplan J (1988) Effect of

torrefaction on grinding energy requirement for thin wood particle

production [online materials]. http://hal.archives-ouvertes.fr/docs/

00/46/23/39/PDF/AG-SFGP09.pdf

27. Rousset P, Davrieux F, Macedo L, Perré P (2011) Characterisation

of the torrefaction of beech wood using NIRS: combined effects of

temperature and duration. Biomass Bioenergy J 35(3):1219 – 1226

28. Chen W, Kuo P (2011) Torrefaction and co-torrefaction character-

ization of hemicellulose, cellulose and lignin as well as torrefaction

of some basic constituents in biomass. Energy J 36(2):803 – 811

29. Prins MJ, Ptasinski KJ, Janssen FJJG (2006) More efficient bio-

mass gasification via torrefaction. Energy Fuels J 31(15):3458 –

3470

Table 5 (continued)

Company Demotechnology

Supplier Location (s) Prod.capacity(tons/year)

ESD of operation

Comments

Torrefaction SystemInc. (USA)

Unknown Bepex International(USA/MN)

Unknown Unknown 2013

Vattenfall (Sweden) Moving bed Unknown Unknown Unknown Unknown

WPAC (Canada) Unknown Unknown Unknown 35, 000 2011

Zilkha BiomassEnergy (USA)

Unknown Unknown Crockett, TX (USA) 40,000 Q4 2010

ESD estimated starting date


http://unfccc.int/resource/docs/


http://www.aicheproceedings.org/2009/Fall/data/papers/Paper160229.pdf


https://www.bioenergyupdate.com/magazine/security/NL0400/bioenergy_update_april_2000.htm


http://hal.archives-ouvertes.fr/docs/00/46/23/39/PDF/AG-SFGP09.pdf












30. Pimchuai A, Dutta A, Basu P (2010) Torrefaction of agricultural

residue to enhance combustible properties. Energy Fuel J 24

(9):4638 – 4645

31. Jenkins BM, Baxter LL, Miles TR Jr (1998) Combustion proper-

ties of biomass. Fuel Process Technol 54:17 – 46

32. Yan W, Acharjee TC, Coronella CJ, Vásquez VR (2009) Thermal

pretreatm ent of lignocellulosic biomass. Environ Prog Sustain

Energy 28:435 – 440

33. Waje SS, Patel AK, Thorat BN, Mujumdar AS (2006) An exper-

imental study of the thermal performance of a screw conveyor dryer. Dry Technol 24(3):293 – 301

34. Sule I (2012) Torrefaction behaviour of agricultural biomass and

their commercial feasibilities, M.A.Sc. Thesis, University of

Guelph

35. Pipatmanomai S (2011) Overview and experiences of biomass

fluidized bed gasification in Thailand. J Sustain Energy Environ

Spec Issue 29 – 11

36. Koukios EG (1993) Progress in thermochemical, solid state

refining of biofuels: from research to commercialization. In:

Bridgwater AV (ed) Advances in thermochemical biomass con-

version, Proceedings of the International Conference, 11 – 15

May 1992, Vol. 2. Blackie Academic& Professional, London,

pp 1678 – 1693

37. Ciolkosz D, Wallace R (2011) A review of torrefaction for bioen-

ergy feedstock production. Biofuels Bioprod Bioref. doi:10.1002/ bbb.275

38. Chen W-H, Hsu H-C, Lu K-M, Lee W-J, Lin T-C (2011) Thermal

pretreatment of woo(Lauan) block by torrefaction and its influence

on the properties of the biomass. Energy 36:3012 – 3021

39. Chen W-H, Cheng W-Y, Lu K-M, Huang Y-PA (2011) In evalua-

tion on improvement of pulverized biomass property for solid fuel

through torrefaction. Appl Energy 88:3636 – 3644

40. Ciolkosz D, Wallace R (2011) A review of torrefaction for bioenergy

feedstock production. Biofuels, Bioprod Biorefin 5(3):317 – 329

41. Prins MJ, Ptasinski KJ, Janssen FJJG (2006) Torrefaction of wood:

part 1. Weight loss kinetics. J Anal Appl Pyrolysis 77:28 – 34

42. Van der Stelt MJC, Gerhauser H, Kiel JHA, Ptasinski KJ (2011)

Biomass upgrading by torrefaction for the production of biofuels: a

review. Biomass Bioenergy 35:3748 – e3762

43. Acharjee TC, Coronella CJ, Vasquez VR (2011) Effect of thermal

pretreatment on equilibrium moisture content of lignocellulosic

biomass. Biores Technol J 102(7):4849 – 4854

44. Bourgeois J, Bartholin MC, Guyonnet R (1989) Thermal treatment

of wood: analysis of the obtained product. Wood Sci Technol

23:303 – 310

45. Deng J, Wang G-J, Kuang J-H, Zhang Y-L, Luo Y (2009) Pre-

treatment of agricultural residues for co-gasification via torrefac-

tion. J Anal Appl Pyrolysis 86:331 – 337

46. Ferro DT, Vigouroux V, Grimm A, Zanzi R (2004) Torrefaction of

agricultural and forest residues. Cubasolar 2004. Guantánamo,

Cuba

47. Felfli FF, Luengo CA, Soler PB, Rocha JD (2004) Mathematical

modelling of woods and briquettes torrefaction. In: Proceedings of

the 5th Encontro de Energia no Meio Rural, Campinas, Spain,

October 19 – 2. http://www.feagri.unicamp.br/energia/agre2004/

Fscommand/PDF/Agrener/Trabalho%205.pdf

48. Leonelli C, Mason TJ (2010) Microwave and ultrasonic process-

ing: now a realistic option for industry. Chem Eng Process J 49

(9):885 – 900

49. Amos WA (1998) Report on biomass drying technology. National

Renewable Energy Laboratory, report no. NREL/TP-570-25885.

http://www.nrel.gov/docs/fy99osti/25885.pdf

50. Kudra T, Mujumdar AS (2002) Advanced drying technologies.

Marcel Dekker, New York, pp 69 – 70, 81 – 83, and 335 – 336

51. Chandran AN, Rao SS, Varma YBG (1990) Fluidized bed drying

of solids. AlChE J 36(1):29 – 38

52. Marb CM, Vortmeyer D (1988) Multiple steady states of a cross

flow moving bed reactor. Chem Eng Sci 43(4):811 – 819

53. Linghong Z, Chunbao CX, Pascale C (2010) Overview of recent

advances in thermo-chemical conversion of biomass. Energy

51:969 – 982

54. Barrozo MAS, Murata VV, Assis AJ, Freire JT (2006) Modeling of

drying in moving bed. Drying Technology 24:269 – 279

55. Waje SS, Patel AK, Thorat BN, Mujumdar AS (2007) Study of

residence time distribution in a pilot-scale screw conveyor dryer.

Dry Technol 25(1):249 – 25956. Tsamba AJ, Yang W, Blasiak W (2006) Pyrolysis characteristics

and global kinetics of coconut and cashew nut shells. Fuel Process

Technol 87:523 – 530

57. Shafizadeh F, Chin Peter PS (1977) Thermal deterioration of

wood. Wood technology: chemical aspects. American Chemical

Society, Washington, DC, pp 57 – 81

58. Shu-de Q, Fang-Zhen G, Dong-li Z (1996)The study on performance

of twin screw conveyor. Dry Technol 14(7and 8):1859 – 1870

59. De la Hoz A, Díaz-Ortiz A, Moreno A (2005) Microwaves in

organic synthesis. Thermal and non-thermal microwave effects.

Chem Soc Rev 34:164 – 178

60. Miura M, Kaga H, Sakurai A, Kakuchi T, Takahashi K (2004)

Rapid pyrolysis of wood block by microwave heating. J Anal Appl

Pyrolysis 71:187 – 199

61. Salem AA, Ani FN (2011) Microwave induced pyrolysis of oil palm biomass. Biosource Technol J 102(3):3388 – 3395

62. Dangtran KY, Mullen JF and Mayrose DT (2000) A comparison of

fluid bed and multiple hearth biosolids incineration. In: The 14th

Annual Residuals & Sludge Management Conference

63. FGC Group (2010) http://www.fgcgroupllc.com/multiple_hearth_

furnaces.html. Accessed 30 May 2011

64. Kleinschmidt CP (2011) Overview of international develop-

ments in torrefaction. Bio-energy Trade, Torrefaction work-

s h o p , h t t p : / / w w w. b i o e n e r g y t r a d e. o r g / d o w n l o a d s /

grazkleinschmidtpaper2011.pdf

65. Mosier N, Wyman C, Dale B, Elander R, Lee YY, Holtzapple M et

al (2005) Features of promising technologies for pretreatment of

lignocellulosic biomass. Bioresour Technol 96:673 – 686

66. IEA Bioenergy (2010) Technology roadmaps. International Energy

Agency (IEA), Paris

67. Helwig T, Jannasch R, Samson R, DeMaio A, Caumartin D (2010)

Agricultural biomass residue inventories and conversion systems

for energy production in Eastern Canada. Prepared for Natural

Resources — Canada [online material]. http://www.reapCanada.com/

online_library/feedstockbiomass/7Agricultural%20Biomass%

20Residue%20Inventories%20and%20Conversion..Samson%

20et%20al.%202002.pdf

68. Dana Mitchell, Tom Elder (2010) Fueling the future. In: 2010

Council on Forest Engineering Annual Meeting June 6 – 9; Devall

Drive, Auburn, Alabama

69. White RH, Dietenberger MA (2001) Wood products: thermal

degradation and fire. In: The encyclopedia of materials: science

and technology. Elsevier Applied Science, Amsterdam

70. Twidell J, Weir T (2005) Biomass and biofuels. In: Renewable

energy resources, 2nd edn. Spon, London, pp 351 – 99

71. Hakansson K (2007) Torrefaction and gasification of hydrolysis

residue. MSc thesis, Umea Institute of Technology

72. Prins MJ, Ptasinski KJ, Janssen FJJG (2003). Thermodynamics of

gas-char reactions: first and second law analysis. Chem Eng Sci 58

(13 – 16):1003 – 1011

73. Josheph J James (2010) Creating power from biomass: torrefaction a

key facilitating technology. http://www1.eere.energy.gov/biomass/

biomass2010/pdfs/biomass2010_plenary2_james.pdf

74. Kaliyan N, Vance Morey R (2009) Factors affecting strength and

durability of densified biomass products. Biomass Bioenergy

33:337 – 359


http://dx.doi.org/10.1002/bbb.275


http://www.feagri.unicamp.br/energia/agre2004/Fscommand/PDF/Agrener/Trabalho%205.pdf



http://www.fgcgroupllc.com/multiple_hearth_furnaces.html


http://www.bioenergytrade.org/downloads/grazkleinschmidtpaper2011.pdf


http://www.reapcanada.com/online_library/feedstockbiomass/7Agricultural%20Biomass%20Residue%20Inventories%20and%20Conversion..Samson%20et%20al.%202002.pdf




http://www1.eere.energy.gov/biomass/biomass2010/pdfs/biomass2010_plenary2_james.pdf



















75. Kumar A, Cameron JB, Flynn PC (2003) Biomass power cost and

optimum plant size in Western Canada. Biomass Bioenergy J 24

(6):445 – 464

76. Nalladurai KR, Vance M (2009) Factors affecting strength and

durability of densified biomass products. Biomass Bioenergy 33

(3):337 – 359

77. Holley CA (1983) The densification of biomass by roll briquetting.

In: Proceedings of the Institute for Briquetting and Agglomeration

(IBA), Vol. 18, No., pp 95 – 102

78. Obernberger I, Thek G (2004) Physical characterization and chem-ical composition of densified biomass fuels with regard to their

combustion behavior. Biomass Bioenergy 27(6):653 – 669

79. McMullen J, Fasina OO, Wood CW, Feng Y (2005) Storage and

handling characteristics of pellets from poultry litter. Appl Eng

Agric 21(4):645 – 651

80. Couhert C, Salvador S, Commandré JM (2009) Impact of

torrefaction on syngas production from wood. Fuel 88:2286 –

2290

81. Kuang X, Tumuluru JS, Bi XT, Lim CJ, Sokhansanj S, Melin S

(2009) Rate and peak concentrations of off-gas emissions in stored

wood pellets — sensitivities to temperature, relative humidity, and

headspace volume. Ann Occup Hyg 53(8):789 – 796

82. Zwart RWJ, Boerrigter H, Drift AVD (2006) The impact of

biomass pretreatment on the feasibility of overseas biomass con-

version to Fischer-Tropsch products. Energy Fuel J 20(5):2192 – 2197

83. Svoboda K, Pohoř elý M, Hartman M, Martinec J (2009) Pretreat-

ment and feeding of biomass for pressurized entrained flow gasi-

fication. Fuel Process Technol J 90(5):629 – 635

84. Douglas B (2010) Canada report on bioenergy [Online

Material]. http://www.canbio.ca/documents/publications/

canadacountryreport2009.pdf

85. Felfli FF, Luengo CA, Suárez JA, Beatón PA (2005) Wood bri-

quette torrefaction. Energy Sustain Dev 9:19 – 22

86. Gilbert P, Ryu C, Sharifi V, Swithenbank J (2009) Effect of process

parameters on pelletization of herbaceous crops. Fuel 88:1491 – 1497

87. UNEP (2010) Global trends in green energy 2009: new power

capacity from renewable sources tops fossil fuels again in US,

Europe. REN 21

88. Lam PS, Sokhansanj S, Bi XT, Lim CJ (2012) Colorimetry applied

to steam-treated biomass and pellets made from western Douglas

Fir ( Pseudotsuga menziesii, L.). Trans ASABE 55(2):673 – 678

89. Magalhaes A, Petrovic D, Rodriguez A, Putra Z, Thielemans G

(2009) Techno economic assessment of biomass pre-conversion

processes as a part of biomass-to-liquids line-up. Biofuels, Bioprod

Bioref 3:584 – 600

90. Rosillo-Calle F (2007) Biomass assessment handbook — bioenergy

for a sustainable environment, 1st edn. Earthscan, London

91. Rousset P, Turner I, Donnot A, Perré P (2006) The choice of a low

temperature pyrolysis model at the microscopic level for use inamacroscopic formulation. Ann For Sci 63:213 – 229


http://www.canbio.ca/documents/publications/canadacountryreport2009.pdf




a review on advances of torrefaction technologies - bimal.pdf

Documents