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Biomass torrefaction VGB PowerTech 7 l 2015

Author

Kurzfassung

Torrefizierte Biomasse – das perfekte CO2 neutrale Kohlesubstitut erlangt Marktreife Biomasseveredelung zur Herstellung eines kohleähnlichen Brennstoffs zählt seit Langem zur den FuE-Themen. Die heutige Reife der Tor-

Versorgung mit CO2-neutralem Brennstoff in industriellem Maßstab.

-tion der Mahlenergie und verbesserter Wasser-beständigkeit führt. Flexibilität hinsichtlich

-zugsgebiete der Verbraucher und reduzieren Sensitivität gegen Änderungen einzelner Kos-tenfaktoren.

-

---

-erungstests steht zur Verfügung. Die Reduktion

-

-

feuerungen.

-

l

Torrefied biomass: The perfect CO2 neutral coal substitute is maturingMichael Wild

Michael WildWild & Partner LLC, Principal Intern. Biomass Torrefaction Council-IBTC, President Vienna/Austria

What is torrefaction and why to do it?Torrefaction is a thermal pre-treatment

technology intended to upgrade lingo-

cellulosic biomass to a higher quality and

more attractive biofuel. In the torrefaction

process, biomass is heated to a tempera-

atmosphere with low oxygen concentra-

tions, so that all moisture is removed. Dur-

ing the torrefaction process, the biomass

partly devolatilises leading to a decrease

in mass, but the initial energy content of

in the solid product so that the energy den-

sity of the biomass becomes higher than

the original biomass, which makes it more

attractive for i.e. transportation.

A typical mass and energy balance for

of the mass is retained as a solid product,

is converted into torrefaction gas which

biomass. Ideally, the energy contained in

these released volatiles equates to the heat-

ing requirements of the process. A thermal

achieved.

depend on the process conditions coming

into play (reaction temperature, residence

time and biomass properties) and on the

composition of the biomass resource, be-

cause the content of hemicellulose, cellu-

the product distribution. While organically

bound chlorine is reduced by torrefaction

the ash properties of the feedstock remain

almost unchanged.

Mainly caused by the removal of oxy-

gen, torrefaction strongly impacts on the

properties of the solid product. During

of the original biomass material is largely

destroyed through the breakdown of the

hemicellulose structure so that the end

product is brittle and mills itself very easily

(Ta b l e 1).

Torrefaction can be applied to any lignocel-

lulose type of biomass and some designs of

the diversity of feedstock. In this respect,

torrefaction can also offer an opportunity

for cheaper feedstock such as by-product

streams, forestry or plantation residues or

agricultural-material. However, in order to

allow the use of these resources, individual

testing is required. Most of the practical ex-

perience today is based on woody biomass

both in torrefaction itself and test combus-

tion.

Why torrefaction?Torrefaction brings many important ad-

vantages by overcoming traditional limi-

2

neutrality advantage:

–

increase in energy density and water re-

sistance,

– broader feedstock basis – geographically

and types of raw material,

– almost no biodegradation of product

when stored,

– large variety of applications,

– -

–

– superior water resistance to wood pel-

lets,

–

– can be made to meet clients’ require-

ments,

– helps developing the market towards

commoditisation and

Tab. 1. Properties of transportable biomass and competing fossil fuel.

Fresh wood Wood pellets Torrefied pellets Coal

Moisture (%) 35 to 50 7 to 10 1 to 5 10 to 15

Calorific value (GJ/T) 9 to 12 16 to 18 19 to 23 23 to 28

Bulk density (T/m3) 0.2 to 0.25 0.6 to 0.68 0.65 to 0.75 0.8 to 0.85

Energy density (GJ/m3) 2 to 3 9.6 to 12.2 12.4 to 17.3 18.4 to 23.8

Acidity (pH)

Ash (% by wt) 0.4 to 2 0.4 to 2.5 9.7 to 20.2

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VGB PowerTech 7 l 2015 Biomass torrefaction

– 2 footprint along the supply

chain.

Despite the fact that some companies

might have overpromised in terms of pro-

ject implementation time, with today’s in-

stalled capacity and test burn experience

producers are ready to accept orders for

both test burn volumes and term contracts.

TechnologiesThere is an array of technologies to roast/

superdry/devolatilise biomass. In basically

the same way as in all other process steps

in biomass processing, a number of reac-

tor designs are available for torrefaction as

well. Screw conveyers, rotary drums (even-

tually combined with microwave), moving

beds, vibrating belts or torbed are the most

typical reactor types implemented.

-

for a torrefaction technology to become

-

the energy from the feedstock and – last

but by far not least – mechanical compres-

variables. A typical setup of an integrated

torrefaction plant would consist of a feed-

stock pre-processing unit (shredding, chip-

ping etc.), a drying unit, the torrefaction

reactor, a product milling and a mechani-

cal compression (pelleting, briquetting)

unit. In most cases, energy supply is inte-

grated in the plant setup, very often con-

suming also the torgases. In some cases,

drying and torrefaction are carried out

within one device.

The choice of the reactor type and inte-

feedstock and volumes to be processed, by

location of implementation and local elec-

tricity costs.

All this is valid for stand-alone torrefaction

plants of which the job it is to convert low-

cost raw biomass into an internationally

tradable product. Alternative setups may

include torrefaction reactors integrated

in the pre-processing line of a coal power

plant simply treating biomass prior to its

milling in the coal mills or the torrefac-

tion of already pelletised biomass. The lat-

technology or products available on the

market. There is, however, a disadvantage:

the higher transportation costs because of

the reduced bulk density.

Most technology developers and suppliers

have overcome the technical and integra-

of the complete process. If open issues still

remain, they can be located in the area of

outdoor storage, trade permissions and

implementation of full-scale consumption

(F i g u r e 1).

According to factors such as time, temper-

ature and residence time, biomass can be

temperatures. Directly connected to the

of the resulting product. Theoretically,

(depending on feedstock).

Current situationAfter several years of technology develop-

ment, demonstration plant operation and

test burns, a number of renowned compa-

nies are now ready to set-up their technol-

ogy as systems or component suppliers re-

industrial scale projects. Most of the initia-

and in North America. Yet Asian companies

have recently become very active as well, if

one takes into account the creation of value

from the enormous stream of agricultural

by-products in the region (F i g u r e 2).

Torrefaction has the potential to become

an important biomass pre-treatment tech-

nology, thereby improving the biomass to

a high-quality solid fuel with good charac-

teristics in energy density, homogeneity,

grindability and hydrophobic behaviour.

Still the sector is in its optimisation phase,

and the bulk of this optimisation can be

done only in co-operation with consum-

ing partners. Further large-scale testing

in power plants and heat applications is

required to adjust some of the parameters

-

-

faction degree, feedstock and resulting ash

composition, geometrical form, durability

and water resistance are just some of the

variables to be adjusted to clients’ require-

ments. The minimum requirements for

are available from several producers, in

several shapes and at different torrefaction

levels.

Costs and the technology choiceThe multitude of torrefaction technologies

is a big advantage of the torrefaction sector

in respect to other thermal treatment tech-

nologies. However, this should be of no real

importance for the consumer who is only

interested in consistency of the product

and availability of this consistent product

from a number of sources. It falls within

the producer’s abilities to implement the

best technology available to transform the

available feedstock into the desired prod-

uct. The multitude of technologies will

help in optimising costs in processing.

and sustainability setup, the energy bal-

ance of a torrefaction plant will only be

marginally worse than that of a wood pel-

let plant. However, some extra heat losses

and electricity consumption will appear.

-

Torgas handling

Torgas utilisation

Continuous torrefaction

Predictability and consistency of product

Densification

Feedstock flexibility

Safety in plant

Indoor storage

Outdoor storage

Standardisation of product

Safety along supply chain

Trade registrations and permissions

Co-firing trials

Co-firing burn tests

Co-firing full scale

Heat application trials

Heat application acceptance

Done

Done

Done

Mostly done

In optimisation

Mostly done

Done

Done

In optimisation

In progress

In progress

In progress

Done

In progress

In progress

In progress

Open

Fig. 1. Torrefaction implementation thermometer (Source: Michael Wild).

Fig. 2. Torrefaction Products (Source: Andritz AG).

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Biomass torrefaction VGB PowerTech 7 l 2015

ing costs in respect to wood pellet produc-

tion.

F i g u r e 3 is to illustrate the potential sav-

ings along the value chain compared to

costs caused by wood pellets. It is based

on identical feedstock to be processed by

this, leaving aside the possibility to process

lower value (priced) feedstock into a fuel

by torrefaction.

Despite the fact that the torrefaction stage

represents an additional unit operation

in the processing of biomass causing ad-

ditional capital and operating costs, there

are savings elsewhere in the biomass sup-

ply chain which offset the aforementioned

drawbacks. The advantages of torrefaction

are particularly salient in the logistics and

storage areas. The additional investments

related to torrefaction represent less than

the associated logistic cost reduction. In

fuel preparation at the power plant the tor-

or co-milling in existing coal mills is pos-

sible in many cases as proven by the test

burns. Therefore, little new infrastructure

-

especially at power plants which have not

yet invested in wood pellet infrastructure.

Experience in co-firing torrefied biomass with coal

plants have been undertaken, thereby co-

combusting several thousands of tonnes

from different producers. Although in-

dividual results are not to be published

in detail, the results of these successful

plants can be summarised as follows:

–

–

were acknowledged,

– the performance of the material in the

mill and in the burners was excellent,

pellets,

– the emissions performance was satisfac-

tory – no difference to wood pellets,

– burner performance was excellent, bet-

ter than any wood pellet fuel to date.

No need for support fuels (needed with

wood pellets),

– fuel preparation costs approximately

– improvements in performance of the

expected (dust formation, full water re-

sistance).

Trading torrefied biomasses

in the technologies and production capa-

bilities, there is no certainty concerning

logistics regulation as well as health and

safety regulation.

for solid biofuels. Final discussions are al-

ready taking place in 2015.

-

on 4.2. no self heating properties. Hence

-

Technical/safety characteristics of the

from those of normal biomass dust, but

are clearly more reactive than coal dust.

however, result in good chances to produce

more dust in handling and, therefore, extra

care shall be taken in not allowing dust to

pile up.

A company that “places the substance

-

tion and hence needs to be registered. The

the torrefaction industry and Sea to Sky

have formed a consortium to clarify the

exemption possibility or registration ne-

-

Issues being optimised Mechanical compression by pelleting or

briquetting did prove harder than ex-

feedstock as is the quality of the resulting

product.

water resistance (weather ability) which

is the one core area providing room for

biomass is a completely hydrophobic mate-

water-resistant today, because cracks and

geometrical structure. This reduces the

durability of the pellets or briquettes.

What is the impact on daily business with

pellets/briquettes, the top layer, if weath-

ered for weeks, will weaken and reduce du-

rability. There will thus be no complete dis-

integration as observed with wood pellets.

Binders and additives in the mechanical

compression process will help increase wa-

ter resistance. In co-operation with the con-

suming power plants, this further test will

be carried out to make sure that eventual

binders do not represent a disadvantage.

Further testing in heat applications is on

the agenda of almost all producers and re-

120 %

100 %

80 %

60 %

40 %

20 %

0 %

Wood pellets

Torrefied pellets

Raw

mat

eria

l

Prim

ary

trans

port

Mfg

cos

t ful

ly lo

aded

Seco

ndar

y tra

nspo

rt &

load

ing

Ship

ping

Unlo

adin

g &

terc

iary

tran

spor

t

Stor

age

at p

ower

pla

nt

Pre-

com

busti

on p

roce

ssin

g (1

0 y)

Cos

t CIF

per

GJ

Cos

t CPT

per

GJ

Cos

ts at

com

busti

on in

take

per

GJ

Rela

tive

cost

Fig. 3. Cost torrefied vs white pellets (Source: Michael Wild).

Fig. 4. ACB torrefied briquettes stored in open area (Source: ACB GmbH).

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VGB PowerTech 7 l 2015 Biomass torrefaction

pellet furnaces have basically proved the

viability. However, they have also shown

that adjustments in air-management and

the control system are needed before being

put on the market (F i g u r e 4).

IBTC, a cooperation platform to accelerate progressThe International Biomass Torrefaction

platform for companies, organisations and

individuals dedicated to the promotion of

allows discussion of common interests

without competition and facilitates com-

panies´ synergy to overcome the barriers

that hinder the market development.

-

rier for the power and the heat market, un-

dertake studies and projects to increase the

depth of knowledge and gain permissions

products, and to spread the concerns of the

industry to the outside world.

Here are some of the burning topics in

– product quality standards currently un-

-

mittee 238 WG2,

– -

rial,

–

– other transport and safety requirements.

as fully supporting members. l

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