Note: Descriptions are shown in the official language in which they were submitted.
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PROCESS AND APPARATUS FOR PRODUCING BIOCARBON
FIELD OF THE INVENTION
The invention relates to the process defined
in the preamble of claim 1 and to the apparatus de-
fined in the preamble of claim 13 for producing a bio-
carbon product.
BACKGROUND OF THE INVENTION
Known from the prior art are different proc-
esses and apparatuses for producing energy products
from different kinds of raw stock by combustion tech-
nology. It is known to use wood in order to produce
energy.
In addition, known form the prior art is the
production of biocarbon, e.g. charcoal, by charring.
Wood-based charcoal has become the focus of great in-
terest in Europe, China and the USA, as CO2 emissions
of coal-fired power stations and coke plants are tried
to be reduced. Conventionally, shaft, rotary or multi-
layer kilns are used in order to produce charcoal.
Typically, woodchips are fed to the apparatus e.g. in
a chip size of 2 to 8 cm, dried to the moisture of 10
to 25 %, and charred at a temperature of 200 to 320 C
for approximately 20 to 30 minutes.
A problem in using wood in the production of
energy is that it cannot be fed to large power station
boilers in large proportions without significant
changes in the devices, e.g. in the carbon boiler and
feeder lines. In burning wood and charcoal, the prob-
lem in power boilers that produce electricity is often
the high ash content of wood fuels and thereby the
contamination of the boiler and the increase of the
corrosion risk, as well as the after-treatment of ash.
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A functional fluidized-bed charring process
and apparatus that are applicable for the production
of biocarbon have not been developed before. For exam-
ple, the fact that it is difficult e.g. to separate a
product formed from wood and the fluidized-bed mate-
rial has been conceived as a problem. Another problem
has been the light structure of the product which has
disturbed stable operation of a fluidized-bed reactor.
Known from publications US 2003/0221363, US
2009/0151251 and EP 2017325 is the production of a
biocarbon-type product from biomass. The processes of
the publications seem to be based mainly on prelimi-
nary treatment of the raw stock for the production of
a synthesis gas or a pyrolysis liquid.
OBJECTIVE OF THE INVENTION
An objective of the invention is to disclose
a new type of a process and apparatus for producing a
biocarbon product.
SUNIl4ARY OF THE INVENTION
The process and apparatus according to the
invention for producing a biocarbon product are char-
acterized by what is presented in the claims.
The invention is based on a process for pro-
ducing a biocarbon product from bio-based raw stock.
According to the invention the bio-based raw stock is
sorted by removing in the raw stock the undesired
fraction in terms of the production of biocarbon from
the desired fraction of the raw stock which is used
for the production of biocarbon, the desired fraction
of the raw stock is fed to a fluidized-bed reactor in
order to produce biocarbon, the undesired fraction of
the raw stock is fed to a combustion boiler disposed
in connection with the fluidized-bed reactor. in order
to produce energy fractions, a heat transfer material,
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preferably solid heat transfer particles, to be used
in the fluidized-bed reactor is warmed up, e.g.
heated, in the combustion boiler, and the warmed-up,
such as heated, heat transfer material is led to the
fluidized-bed reactor, the bio-based raw stock is
heated in the fluidized-bed reactor in oxygen-free
conditions to a temperature of 220 to 350 C in the
presence of the heat transfer material in order to
form a solid biocarbon product, and the heat transfer
material is circulated from the fluidized-bed reactor
to the combustion boiler in order to warm up, such as
heat, and purify the heat transfer material.
In addition, the invention is based on an ap-
paratus corresponding to the process for producing a
biocarbon product from bio-based raw stock. According
to the invention the apparatus includes a fluidized-bed
reactor in order to produce a biocarbon product and a
combustion boiler in order to produce energy fractions
and warm up a heat transfer material, these two being
integrated together, and sorting means for the bio-
based raw stock in order to sort the bio-based raw
stock into a desired and undesired (19) fraction in
terms of the production of biocarbon, feeding means in
order to feed the desired fraction of the raw stock to
the fluidized-bed reactor, and feeding means in order
to feed the undesired fraction of the raw stock to the
combustion boiler, means for leading the warmed-up heat
transfer material from the combustion boiler to the
fluidized-bed reactor, means for separating the heat
transfer material from the biocarbon product that has
been formed, and means for circulating the heat trans-
fer material back to the combustion boiler in order to
warm up and purify the heat transfer material.
A biocarbon product in this context means a
product to be utilized as biocarbon. The biocarbon
product may be in this context any biocarbon product,
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biocarbon, biocarbon fraction, biocarbon product frac-
tion or equivalent. The biocarbon may be formed from
suitable raw stock, and binders and/or additives may or
may not be added to it.
The process according to the invention oper-
ates in the temperature range of 220 to 350 C as an
atmospheric pressure process and in oxygen-free state.
At higher temperatures, biocarbon grades that only in-
clude a small amount of volatile matter may be pro-
duced, e.g. for coke plants. The biocarbon product be-
ing formed is always substantially in a solid state.
Preferably, the bio-based raw stock is cured in order
to form the biocarbon product. In one embodiment the
bio-based raw stock may be dried before curing to the
moisture of approximately 10 to 15 The drying may
be performed by utilizing waste heat of the apparatus
or the plant.
Preferably the fluidized-bed reactor to be
used for the production of biocarbon is combined with
the combustion boiler which is used to produce energy
and preferably to warm up and/or purify the heat
transfer material, to treat the possible residual
fractions developed in the production of biocarbon
and/or to produce energy from lower-grade starting ma-
terial. The combustion boiler may be a separate com-
bustion boiler for the production of energy or a com-
bustion boiler of the power station or equivalent. In
one embodiment the fluidized-bed reactor designated
for the production of biocarbon is a supplementary ap-
paratus in the boiler of the power station. In addi-
tion, the annual variations of the combustion boiler,
e.g. a traditional CHP power station, may be utilized
by the integrated fluidized-bed reactor and combustion
boiler connection, so that during summer time when low
energy demand, such as low steam load, prevails, a
large biocarbon production capacity is provided.
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The energy fractions to be formed in the com-
bustion boiler may include heat, electricity, steam,
combustion gases or the equivalent. The heat may be
bound e.g. to the heat transfer material and conducted
by the heat transfer material to a desired destina-
tion.
In a preferred embodiment heat is brought to
the production of a biocarbon product by the solid
heat transfer material. In addition, heat may be
brought to the production of the biocarbon product by
fluidizing the fluidized bed with hot oxygen-free or
low-oxygen circulating gases or combustion gases of
the boiler. Also, the use of superheated steam is pos-
sible as a heat-bearing material.
The solid heat transfer material, preferably
in the form of particles, may be heated to a desired
temperature of 300 to 1000 in the combustion boiler
and/or outside the boiler, e.g. by guiding the heat
transfer material through a separate heat exchanger
and warming it up by hot combustion gases. The combus-
tion gases may come from the combustion boiler or any
suitable thermal reactor.
In one embodiment of the invention the heat
transfer material is led into contact with the bio-
based raw stock in the fluidized-bed reactor in order
to provide direct transfer of heat. In one embodiment
the heat transfer material acts at the same time as
the fluidized-bed material of the fluidized-bed reac-
tor either alone or with another bed material.
In one embodiment of the invention the heat
transfer material is led to a heat exchanger provided
inside the fluidized-bed reactor. In this case, suit-
able bed material is used in the fluidized-bed reactor
as the fluidized-bed material, or the fluidized bed is
formed only by the bio-based raw stock. In one, alter-
native embodiment the heat transfer material is led to
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a separate heat transfer material bed or heat transfer
bed, e.g. a woodchip bed or equivalent, of the fluid-
ized-bed reactor.
The transfer of heat from the heat transfer
material to the bio-based raw stock may take place di-
rectly by the heat transfer material or indirectly
through a heat exchanger or other separate heat trans-
ferring means accommodated within the fluidized bed.
In one embodiment a heat transfer material
selected from the group of sand, magnetite, ash blend
and their combinations is used.
In using hot sand or equivalent solid heat
transfer material in the production of biocarbon, a
higher heat transfer, typically approximately 100 to
180 W/m2K, than that of the conventional reactor de-
vices designated for the production of charcoal, is
substantially achieved.
In one embodiment of the invention the heat
transfer material is separated from the biocarbon
product that has been formed, and it is circulated to
the combustion boiler.
In a preferred embodiment the biocarbon prod-
uct that has been formed is substantially lighter than
the fluidized-bed material and/or the heat transfer
material, and it is separated in connection with the
fluidization to the top of the fluidized bed so as to
be removed as a concentrate without a significant
amount of the bed material and/or the heat transfer
material escaping with the cured biocarbon product. By
adjusting the fluidization rate close to the minimum
fluidization rate of the bed material, the separation
of the biocarbon product form the mixture may be en-
hanced. In one embodiment also mechanical screening or
centrifugal force may be utilized in order to separate
the cured biocarbon. product. Magnetic separation may
be used with magnetic materials, e.g. the heat trans-
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fer material. In one embodiment a separator may be
provided either in the fluidized-bed reactor or there-
after in order to separate the biocarbon product from
the heat transfer material and/or the bed material. In
one embodiment part of the separated biocarbon product
is returned to the bottom of the fluidized-bed reac-
tor.
In one embodiment of the invention the bio-
based raw stock is selected from the group of: wood,
wood-based raw stock, straw, different herbaceous bio-
masses, biosludge, other solid biomass materials and
other types of bio-based raw stock and their combina-
tions. In addition to the fraction that is undesired
for the production of the bio-based raw stock and es-
pecially biocarbon, it is possible to burn in the com-
bustion boiler peat, lignite, wood, waste materials
and/or equivalent raw stock. The combustion boiler
produces energy for the fluidized-bed reactor, e.g.
from the undesired raw stock and/or other starting ma-
terials.
In one embodiment of the invention the bio-
based raw stock is heated in the fluidized-bed reactor
with a dwell time of less than 30 minutes, more pref-
erably less than 20 minutes, and most preferably less
than 5 minutes, in order to form a solid biocarbon
product. By the present invention, even a dwell time
of less than 5 min is reached instead of the dwell
time of 20 to 30 min of the conventional shaft kilns.
This implies smaller and less expensive fluidized-bed
reactors for the production of biocarbon. In addition,,
the dwell time may be influenced by the particle size
of the feed. For example, for the homogeneous carboni-
zation of wood it is required that the inner part of
the woodchip particle reaches the desired end tempera-
ture. The temperature profile of the particle on its
surface and inside of it may be described as a func-
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tion of the particle size and the heat-transfer coef-
ficient.
In one embodiment the bio-based raw stock is
crushed to a desired particle size before it is fed to
the fluidized-bed reactor.
In one embodiment of the invention the bio-
based raw stock is dried before producing the biocar-
bon product, preferably with energy obtained from the
combustion boiler and/or by energy fractions, e.g.
combustion gas or steam, or by the combustion gas de-
veloped in the process using direct or indirect trans-
fer of heat.
The drying of the bio-based raw stock may be
performed in the fluidized-bed reactor designated for
the production of biocarbon or in a separate reactor
or drier. When the raw stock is dried in a separate
drier, the evaporated water is separated from the
product flow of the drier, e.g. in a cyclone, and the
dried bio-based raw stock is thereafter fed to the
fluidized-bed reactor in order to produce biocarbon.
The fluidized-bed reactor and the drier may be con-
nected in series. Depending on the temperature used in
the drier, the odorous gases may be burnt in the com-
bustion boiler. In one embodiment the bio-based raw
stock is dried by mixing it with heated heat transfer
material or bed material of the fluidized-bed reactor
before leading the mixture to the production of bio-
carbon.
Production, i.e. a production step, of biocar-
bon or a biocarbon product means in this context spe-
cifically treatment of the bio-based raw stock in the
fluidized-bed reactor in order to form a biocarbon
product.
In one embodiment of the invention the bio-
based raw stock is washed before producing the biocar-
bon product in order to lower the ash content. In one
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embodiment ECN Torwash technology may be utilized in
washing the raw stock. In this case, the bio-based raw
stock, e.g. herbaceous biomass, may be washed by
steam/hot water of the combustion boiler, whereupon 80
to 90 % of the problematic ash components may be re-
duced. The reduction is lower with logging waste. In
an alternative embodiment the raw stock may be washed
by a hot water washing.
In one embodiment of the invention the appara-
tus includes sorting means for the bio-based raw stock.
By the invention, the best raw stock may be sorted for
the production of biocarbon and the undesired raw
stock may be sorted for burning in order to form en-
ergy. The integrated connection of the fluidized-bed
reactor to the combustion boiler, e.g. a combustion
boiler of the power station, gives a possibility to
classify the biomaterial coming to the station accord-
ing to the ash content or the content of harmful mate-
rials. The intention is to lead only the low-ash, low-
alkali and low-chlorine raw stock to the production of
biocarbon. Correspondingly, the less favorable and un-
desired fraction of the bio-based raw stock, e.g. the
needles, the bark and the equivalent, may be led di-
rectly to the combustion boiler for the production of
energy.
In one embodiment the apparatus includes a
classifier in order to sort the bio-based raw stock
into a desired and undesired fraction in terms of the
production of biocarbon. By the classifier, the de-
sired fraction is guided to the production of biocar-
bon and the undesired fraction is guided to the com-
bustion boiler. The operation of the classifier may be
based on density, mechanical screening, color differ-
ence measurement or determination of the chemical com-
position, e.g. on an NIR infra-red detector. The clas-
sifier provides for the production of different bio-
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carbon grades from different kinds of raw stock ac-
cording to the end use requirements of the biocarbon.
Typically, in power stations that use carbon and have
high primary steam values, high ash, alkali or chlo-
rine contents are not allowed.
In one embodiment of the invention the resid-
ual and/or minor flows formed in the production of the
biocarbon product are burnt in the combustion boiler in
order to produce energy fractions. The odorous gases
and other residual flows of the process may be burnt
in the combustion boiler. Preferably, energy fractions
are fed from the combustion boiler to the fluidized-
bed reactor in the form of the heat transfer material,
steam, heat and/or electricity.
In the production of biocarbon, water vapor
as well as organic compounds and gases that are evap-
orable at a low temperature evaporate from the bio-
based raw stock, e.g. wood. The heat based on conden-
sation of the gases may be recovered, e.g. to district
heating water or steam circuit of the boiler, and/or
the gas flow may be led to the combustion boiler to be
burnt. This way, possible odor problems are avoided.
In addition, valuable chemicals may be utilized from
the condensate.
In one embodiment of the invention the solid
biocarbon fraction that has been formed is treated
further by pelletizing, e.g. graining, granulating or
in an equivalent manner, in order to form a biocarbon
product. In one embodiment the biocarbon fraction is
pelletized using a binder.
In one embodiment of the invention binders
and/or additives, e.g. materials that ameliorate the
weatherproofness, are added to the biocarbon product
that has been formed in order to provide the final
biocarbon product. In one embodiment suitable binders
are added to biocarbon for binding the ash compounds
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that cause corrosion or scorification and/or in order
to form pellets. Before pelletizing the biocarbon to
form a biocarbon product, additives that ameliorate
the weatherproofness of the product, such as olefine
plastics that are unqualified for recycling, e.g. from
package waste, may be added to the biocarbon in addi-
tion to the optional binder. It is also possible to
add e.g. lime to the biocarbon product for desulphuri-
zation of the power stations.
In one embodiment the fluidized-bed reactor
is selected from the group of reactors based on a s-
pouted bed and a bubbling bed and their different com-
binations, where the heavier bed material may be re-
moved, if desired, from the bottom of the bed, and the
lighter biocarbon may be removed as overflow from the
top of the reactor. The cured biocarbon product may be
circulated either in the internal circulation (spouted
bed) or external circulation (bubbling bed) of the
fluidized-bed reactor in order to control the dwell
time of the treatment.
The combustion boiler may be any kind of a
boiler known per se, either a large size class power
station boiler or a small combustion boiler. If it is
a typical district heat producing unit, the seasonal
variations of energy load are significant. Heat power
would be available especially in the summer, in the
time of low heat demand, for large-scale and in the
winter for smaller-scale biocarbon production.
The apparatus according to the invention may
be integrated in connection with a large power sta-
tion, e.g. of over 50t/h, corresponding to a power
station of 250MWpa, or in connection with a smaller
combustion boiler,,e.g. in pellet factories.
The biocarbon product according to the inven-
tion may be used in the production of heat energy,
e.g. as a substituent for coal.
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Important advantages are achieved by the proc-
ess and the apparatus according to the invention in
comparison with the prior art.
Thanks to the invention, biocarbon of a good
quality may be formed cost-effectively. Thanks to the
invention, it is possible to utilize different types
of raw stock and raw stock components which may not
have been utilized cost-effectively before.
By the invention, a substantially better
transfer of heat and power density of the reactor are
achieved in the production of biocarbon than in the
known biocarbon production processes. In addition, the
integration of biocarbon and the combustion boiler of-
fers important advantages in the treatment and drying
of raw stock as well as treatment of different resid-
ual and minor flows. Additionally, higher efficiency
is reached, because essentially all the minor flows
can be utilized.
By the invention, energy products, such as en-
ergy fractions, are provided as additional products
cost-effectively and with low production costs. Alter-
natively, different value added products, such as bio-
carbon products, are simultaneously provided by the in-
vention in addition to the principal energy products,
which increases the cost-effectiveness of the process.
The process and the apparatus according to
the invention are substantially less expensive in pro-
duction costs than the known biocarbon production
processes, and the obtained product is a granulated
biocarbon fuel that is purer and richer in energy than
before.
LIST OF FIGURES
Fig. 1 presents one process apparatus accord-
ing to the invention as a schematic plan.
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DETAILED DESCRIPTION OF THE INVENTION
In the following, the invention will be de-
scribed by means of a detailed exemplary embodiment
with reference to the accompanying figure 1.
Example 1
This example describes the production of a
biocarbon product by the process according to the in-
vention and the apparatus according to Fig. 1. The in-
tegrated process and apparatus presented herein are
used in order to produce a biocarbon product and energy
fractions at the same time.
The apparatus of Fig. 1 includes a fluidized-
bed reactor 1 for the production of biocarbon and a
combustion boiler.2 for the production of energy frac-
tions and warming up and purifying of heat transfer
material, these two being integrated together. Fur-
thermore, the apparatus includes a classifier 3 for
bio-based raw stock in order to sort the bio-based raw
stock in terms of the production of biocarbon into a
desired 18 fraction, e.g. wood pieces, woodchips and
dust, and undesired 19 fraction, e.g. bark and needles,
as well as feeding means (not presented in the figure)
in order to feed the desired fraction 18 of the raw
stock to the fluidized-bed reactor 1 and feeding means
(not presented in the figure) in order to feed the un-
desired fraction 19 to the combustion boiler 2. The
apparatus includes a drier 5, wherein the fraction of
the bio-based raw stock selected for the production of
biocarbon is dried by hot combustion gases 16 to the
moisture of approximately 10 to 15 % at a temperature
of 40 to 100 C before feeding the raw stock to the
fluidized-bed reactor 1. The bio-based raw stock may
also be washed, if desired, before the production of
the biocarbon product in order to lower.the ash con-
tent.
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In addition, the apparatus includes means for
leading a heat transfer material 6 that has been hea-
ted in the combustion boiler from the combustion boi-
ler 2 to the fluidized-bed reactor 1. In this appara-
tus the heated heat transfer material 6 is led to the
raw stock 18 selected for the production of the bio-
carbon product in the fluidized-bed reactor, i.e. to
be in contact with the raw stock, in order to provide
direct transfer of heat from the heat transfer mate-
rial to the raw stock. In the fluidized-bed reactor 1
the raw stock 18 is heated by the heat transfer mate-
rial 6 in oxygen-free conditions to a temperature of
220 to 350 C in order to form a solid biocarbon prod-,
uct. In the fluidized-bed reactor there may be fluid-
ized-bed sand in addition to the heat transfer mate-
rial in order to form the fluidized bed, or alterna-
tively the heat transfer material may act alone as the
fluidized-bed material, forming the fluidized bed.
The apparatus includes a separator cyclone 4
in order to separate the biocarbon product 9 and 10
from the heat transfer material 7 and the fluidized-
bed material 8 after the formation of the biocarbon
product. Part of the separated biocarbon product 9 is
returned to the bottom of the fluidized-bed reactor 1.
The rest of the biocarbon 10 is led to pelletizing in
order to form biocarbon pellets, wherein binders and
desired additives may be added to the biocarbon prod-
uct. In addition, the apparatus includes means for
circulating the heat transfer material 7 back to the
combustion boiler 2 in order to heat and purify the
heat transfer material.
A desired type of raw stock 17 may be fed to
the combustion boiler 2 in addition to the fraction 19
rejected from the production of biocarbon in order to
form energy fractions. In addition, a possibility to
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feed air to the combustion boiler (not presented in
the figure) may be provided in the combustion boiler.
From the separator cyclone- 4, the combustion
gases 11 are circulated via a filter 12 to the combus-
tion boiler 2 as a combustion gas flow 13 in order to
form energy fractions, to the fluidized-bed reactor 1
as a combustion gas flow 15 and/or to the drier 5 as a
combustion gas flow 16 in order to dry the raw stock,
and/or are led out of the process 14.
The process and the apparatus according to the
invention are applicable in different embodiments for
use in the production of most different types of bio-
carbon products from most different types of raw stock.
The invention is not limited merely to the
examples referred to above; instead, many variations
are possible within the scope of the inventive idea
defined by the claims.
