METHOD FOR THERMAL TRANSFORMATION OF BIOMASS

PROCEDE DE TRANSFORMATION THERMIQUE DE LA BIOMASSE

English Abstract

The inventive method for thermal transformation of biomass comprises the
following: the material is loaded into a converter, the material is pyrolysed
at a temperature of 650 ~C to 950 ~C and in the atmosphere of a reducing gas,
steam is supplied after pyrolysis and a fixed residual is abstracted. The
reducing gas is obtained by burning hydrocarbon fuel with a coefficient of air
consumption .alpha. ranging from 0.85 to 1.1 and mixing burned products with
pyrolysis gases of the biomass at a correlation of (1-3): 1. The inventive
method for transforming biomass makes it possible to use the biomass as a
clean ecological fuel and produce activated charcoal possessing a high
specific surface of a value of 280 to 500 ml/100g.

French Abstract

L'invention concerne un procédé de transformation thermique de la biomasse qui consiste à charger un matériau dans le convertisseur, le pyrolyser à une température comprise entre 650 ·C et 950 ·C dans le milieu du gaz réducteur, envoyer la vapeur après pyrolyse et précipiter les résidus solides. Le procédé se caractérise en ce que le gaz réducteur est obtenu par la combustion d'hydrocarbures dont l'indice de consommation de l'air .alpha. est compris entre 0,85 et 1,1, et par le mélange des produits de combustion avec des gaz de pyrolyse de la biomasse selon un rapport des produits de combustion de (1-3): 1. Le procédé de transformation de la biomasse permet d'utiliser la biomasse en tant que combustible écologiquement propre et de produire en même temps du charbon actif ayant une surface spécifique importante comprise entre 280 à 500 ml/100g.

Claims

5
CLAIMS
1. A method for thermal biomass processing, comprising charging the material
in a
converter, pyrolyzing said material at a temperature ranging between 650 and
950°C in the
medium of a reducing gas, feeding of steam after the pyrolysis reaction has
been completed,
and isolating the resultant solid residue, CHARACTERIZED in that said reducing
gas is
prepared by combusting a hydrocarbon fuel at an air consumption factor a
ranging from 0.85
to 1.1, and by mixing the resultant combustion products together with the
biomass pyrolysis
gases, the ratio between said gases and said combustion products being (1-
3):1.
2. The method of claim 1, CHARACTERIZED in that saturated steam is fed at a
temperature ranging from 105 and 140°C, and a weight percentage ratio
between said
saturated steam and the material being processed is equal to (0.1-0.25):1.

Description

n' ~ i
CA 02395432 2002-06-17
1
METHOD FOR THERMAL TRANSFORMATION OF BIOMASS
Technical Field
The present invention relates generally to thermal pyrolysis; more
specifically it
concerns a method for thermal biomass processing.
Background Art
Known in the present state of the art is a method for thermal processing of
vegetable-
origin materials comprising preparing charcoal resulting from pyrolysis (cf.
RF Pat.
N~ 2,039,078 A).
However, the method in question suffers from too high a power consumption rate
due
to heat transfer through the wall, a long-time pyrolysis reaction, and a low
charcoal adsorption
activity (40-SO ml/100 g).
Another method for thermal processing of vegetable-origin materials is known
to
comprise loading the material, its pyrolysis, and discharging the solid
residue (i.e:, charcoal)
(c~ USSR Patent Ns 1,808,003 A).
However, the method also suffers from too high a power consumption rate of the
process (steam-to-bone-dry wood ratio being (0.6-1.6):l at 400 to
800°C), and a low
2 0 absorbing activity of the resultant charcoal (40 to 50 mi1100 g).
A method for thermal processing of a biomass is also known, said method being
conducting at 650 to 950°C in the medium of a reducing gas resulting
from combusting a
hydrocarbon fuel at an air consumption factor a of from 0.4 to 0.85) (cf. RF
Pat. Ne 2,124,547
A).
However, the method also suffers from a high power consumption rate and
inadequately high activity of the resultant charcoal (not over 250 ml/100 g).
Disclosure of the Invention
It is a principal object of the present invention to provide a method for
thermal
processing of a biomass, capable of reducing power consumption rate thereof
and enhancing
adsorption activity of the resultant charcoal.

n'
CA 02395432 2002-06-17
2
Said object is accomplished due to the fact that in a method for thermal
processing of
a biomass, comprising loading the material in a converter, pyrolyzing said
material at a
temperature ranging between 650 and 950°C in the medium of a reducing
gas, feeding of
steam after the pyrolysis reaction has been completed, and isolating the solid
residue, said
reducing gas being prepared by combusting a hydrocarbon fuel at an air
consumption factor a
ranging from 0.85 to 1.1, and mixing the resultant combustion products
together with the
biomass pyrolysis gases, the ratio between said gases and said combustion
products being (1-
3):1.
Said object is accomplished also due to the fact that once the pyrolysis
reaction has
been completed, saturated steam is fed at a temperature ranging from 105 and
140°C and a
weight percentage ratio between said saturated steam and the material under
processing equal
to (0.1-0.25):1.
Brief Description of the Drawings
In what follows the present invention is explained in the disclosure of an
exemplary
embodiment thereof given by way of illustration to be taken in conjunction
with the
accompanying drawing representing a flowsheet diagram of the method for
thermal
processing of a biomass, according to the present invention.
2 0 Best Method of Carrying Out the Invention
It is common knowledge that the principal reagents of the reducing gas are H~,
CO,
CO2, HaO, CH4, C~Ha, C"Hm and hence the rate of the pyrolysis reaction depends
(at the same
temperature) on the volume concentration of said gas components. The
composition of the
reducing gas may be changed depending on the air consumption factor involved
in
2 5 combusting a hydrocarbon fuel, the higher said factor the higher heat
evolution and the
content of H~0 and COZ in the fuel combustion products. It has been
established by the
inventors, the biomass pyrolysis gases emerging from the converter at 220-
350°C, contain the
same components as the combustion gases (with the factor a of from 0.85 to 1.1
) fed from the
generator for the biomass pyrolysis. Merging the flows of the combustion
products with the
3 0 pyrolysis gases results in heat recovery to the process and increased
concentration of the
reagents indispensable for the biomass pyrolysis reaction, namely, HBO, CO,
CO~, H~, CH,,. It
is due to recycling the pyrolysis gases into the process that the power
consumption rate of the
process is much reduced.

CA 02395432 2002-06-17
3
The limit weight ratio of the pyrolysis gases and the fuel combustion
products, viz, (1-
3):1 has been found experimentally upon processing the various vegetable-
origin materials,
the lower limit being conditioned by providing the highest pyrolysis
temperatures, and the
upper limit, by providing the lowest temperatures.
The fact that completing the pyrolysis reaction is followed by feeding
saturated steam
at a ratio of (0.1-0.25):1 makes it possible to cool the activated charcoal
and enhance
adsorption activity thereof (i.e., the iodine value and optical transmission
of the toluene
extract). Feeding saturated steam at a ratio below 0.1:1 fails to considerably
increase the
iodine value, whereas with the steam feeding ratio above 0.25:1 the iodine
value is increased
but the yield of activated charcoal is badly affected. When preparing
activated charcoal it is
expedient that saturated steam has a temperature of from 105 to 140°C.
Use of saturated
steam makes possible removing the remainder of the hydrocarbon residues.
disposed on the
charcoal surface in order to prepare charcoal having a 99.7 to 100-percent
optical transmission
of the toluene extract.
The appended Drawing represents a flowsheet diagram of the method for thermal
processing of a biomass. Shown in the diagram are: converter 1, generator 2,
mixer 3, cooled
bin 4, air blower 5, and gas blower 6. Arrow A indicates the direction of
charging the
biomass, arrow B, the direction of steam feeding, arrow C, the direction of
discharge of the
solid residue, and arrow D, the direction of feed of pyrolysis gases to the
boiler.
2 0 The method is carried into effect as follows. The pre-dried biomass is
continuously
charged from a feed hopper (not shown) through an air-tight feeder into the
converter 1
appearing as a metal housing lined from inside with a refractory material
resistant to a
reducing medium. A reducing gas is fed in a counterflow to the material
through a branch-
pipe and a system of openings (not shown). The reducing gas is prepared b
mixing the
2 5 combustion products arriving from the generator 2, and the biomass
pyrolysis gases picked off
by the gas blower 6 from the converter 1 at a temperature of 230-350°C,
and fed to the mixer
3. The remainder pyrolysis gases are fed for combustion in heat-generating
apparatus (e.g.,
such as boilers). Saturated steam is fed at 105-140°C to the converter
1 downstream along the
direction of feed of the material to withdraw a majority of the heat from
activated charcoal
3 0 and at the same time cleans its surface from the remainder hydrocarbons.
Then the cooled
activated charcoal is from the lower portion of the converter 1 to the bin 4
cooled by the air
blower 5, wherefrom the heated air is fed to the generator 2 for fuel
combustion. The resultant
activated charcoal has a specific surface area (with respect to iodine)
ranging from 280 to 500
m1/100 g and a density of from 140 to 180 kg/m3.

CA 02395432 2002-06-17.
4
Example
Waste products of the wood-working industry first are divided to a particle
size of
from 15 to 35 mm, then dried and heated by a reducing gas prepared by
intermixing the
products of combusting a hydrocarbon fuel in the generator at a factor a equal
to 0.8, and the
pyrolysis gases, the ratio between said gases and the combustion products
being 2.8:1. The
time of the pyrolysis reaction is 25 min. Saturated steam having a temperature
of 110°C is fed
to the lower portion of the converter l, the ratio between the steam and the
material being
processed being 0.1:1. The yield of activated charcoal is 24.8%, a specific
surface area (with
respect to iodine) equals 286 m1/100 g, optical transmission of the toluene
extract, 99.7%, and
charcoal density, 173 kglm3. The remainder of the pyrolysis gases are fed by
the gas blower
to the boiler furnace to be combusted there together with an additional amount
of fuel fed
thereto. The smoke fumes are free from 3-4-benzopyrene and carbon monoxide,
the content of
nitrogen oxides thereof being 34 mg/m3.
The herein-proposed method for biomass processing makes possible using a
biomass
1.5 as a pollution-free fuel, as well as for simultaneous production of
activated charcoal having
high specific surface area.
Industrial Applicability
2 0 The present invention can find application in the forestry engineering
industry for
salvage of wood waste products, as well as in farming practice for salvage, in
particular,
straw, stalks and cops of maize and helianthus, and also husks of millet,
rice, cotton, and the
like,