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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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