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CHARCOAL PRODUCTION PROCESSES

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CHARCOAL PRODUCTION PROCESSES Powered By Docstoc
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INDUSTRIAL PRODUCTION OF CHARCOAL
By:      Morten Grønli, SINTEF Energy Research, N-7465 Trondheim, Norway
         Phone: + 47 73 59 37 25, Fax: + 47 73 59 28 89: E-mail: Morten.Gronli@energy.sintef.no

INTRODUCTION                                                and lignin content of the feedstock, that is, higher
Based on our relatively cheap (and clean) hydroelectric     lignin content gives higher charcoal yield /2/. Between
power, Norway has become the largest producer of            30 and 60% of the energy content of the feedstock will
silicon and ferrosilicon in Europe. Silicon is produced     be accumulated in the charcoal after carbonisation
industrially by reduction of silicon dioxide by carbon      (depending on charcoal yield). Chemicals (methanol,
in arc furnaces according to the idealised reaction: SiO2   acetic acid, smoke flavours, etc.) can be extracted from
(s) + 2C (s) = Si (s) + 2CO (g). Very high purity silicon   the pyroligneous liquid. However, these are only
is used to manufacture semiconductors and photo-            “niche” products and usually the pyroligneous liquid is
voltaic cells. Silicon is also used as an alloy in the      burnt together with the gases to provide heat for the
production of steel, cast iron, aluminium, and other        carbonisation. Surplus energy can be used for pre-
metals. The major reduction materials (carbon sources)      drying the feedstock or to produce hot water or steam
currently being used are mineral coal and coke.             in boilers for heating purposes.
Although, some charcoal and woodchips are already
being used, charcoal is now becoming increasingly           CHARCOAL PRODUCTION PROCESSES
important as it is derived from one of the few sources      There are more than one hundred concepts and
of carbon capable of regeneration.                          methods to produce charcoal. Three types of heating to
                                                            initiate the carbonisation and maintain high tempera-
In 1997, the Norwegian Ferroalloy Producers                 tures during the processes are generally used (see
Association, founded by the major ferrosilicon              Figure 1) /1/:
producers of Norway (Elkem ASA, FESIL ASA,
Tinfos Jernverk AS) initiated a five year research          •   Internal heating. Part of the raw material is burnt
project which aims to increase the use of charcoal in           under controlled air flow.
the Norwegian ferroalloy industry and thereby reduce        •   External heating. The retort is heated from the
the emissions of CO2 as required by the Kyoto-                  outside and no oxygen enters the reactor.
protocol. Most of the charcoal used today (∼ 60.000         •   Heating with recirculated gas. Part of the
tons/year) is imported from Asia and South-America.             pyroligneous vapours are burnt in an external com-
The crude, traditional methods of charcoal making,              bustion chamber and directed into the reactor
which are still widely used in these countries, are             where it is in direct contact with the raw material.
inefficient and strongly pollute the environment. As
part of this project, we are studying the feasibility of
charcoal production in Norway by modern carboni-
sation techniques from our own biomass resources.

Modern literature on charcoal-making is scarce, and
comprehensive literature has not appeared since
Emrich presented his survey in 1985 /1/. We made a
current-state-of-the-art review of industrial carboni-
sation processes to identify which companies are active
in the manufacturing of equipment for charcoal
production. This review is based on information
(brochures, etc.) gathered from these companies.


THE PROCESS OF CARBONISATION
Charcoal is manufactured from biomass by pyrolysis in
large kilns or retorts. By-products are pyroligneous
liquid and gases (i.e. volatile matter). The yield of the
different reaction products varies with biomass species
and heating conditions. Larger particle sizes and slow
heating favour the formation of charcoal by enhancing
the contact time of the volatiles with the solid carbon
product. Volatiles are not stable at elevated tempera-
tures in the presence of charcoal, or decomposing solid
biomass. They adsorb onto the surface of the solid and
quickly carbonise, releasing water, carbon dioxide, and
methane as by-products. Fundamental research has also
shown that there is a correlation between charcoal yield                Figure 1. Heating systems /1/.
                                                                                                                    2


In the following, some charcoal processes utilising
these principles of heating will be described.


INTERNAL HEATING

In this category one finds the kilns which are made of
concrete or brick. The kiln design is simple and the
investment costs are usually low. The most commonly
used technology are the Missouri kiln, the Argentine
kiln and the Brazilian (beehive) kiln. For discussion
purpose, the Missouri kiln which is widespread in
developed countries will be described. The Missouri
Kiln is made of poured concrete and has rectangular or
square shape with a volume capacity of 180 m3 or more
                                                                        Figure 3. CML 12 F UNIT /3/.
(see Figure 2) /1/.The kiln must be properly loaded
with round wood or sawmill slabs, and doors at each
end allows the use of front-end loaders for charging
                                                            EXTERNAL HEATING
and discharging. Along each side of the kiln are four
chimneys with air vents, and on the roof there are six to
                                                            The VMR oven consists of two retorts (R1 & R2) and a
eight air vents which can be sealed during the cooling
                                                            central combustion chamber (see Figure 4). A vessel
period. In the centre of the kiln, are laid brands from
                                                            charged with wood lumps is placed in R1 with a fork-
previous burns partially charred and dried in order to
                                                            lift. Each vessel has a volume capacity of approxi-
ignite the kiln. Part of the wood are burnt within the
                                                            mately 4.5 m3. The first vessel is heated using external
kiln to carbonise the reminder. The charcoal yield from
                                                            energy (gas or fuel oil). After pyrolysis has started, the
a Missouri kiln may vary from 20 to 30% depending on
                                                            pyroligneous vapours are conveyed to the combustion
operational conditions and feedstock used. The cycle
                                                            chamber and burnt, to give energy for heating of the
time varies from 7 days to more than 30 days in a
                                                            second vessel which has been placed in R2. The
warm climate.
                                                            external heat source (gas or oil burner) is switched off.
                                                            After carbonisation has ended in R1, the vessel with
                                                            charcoal is taken out of the oven and replaced with a
                                                            new one charged with wood. The vessel with hot
                                                            charcoal is covered with a lid and set aside to cool.
                                                            Hence, the VMR system is an alternating system, that
                                                            is, pyroligneous vapours from one retort are burnt to
                                                            give energy for heating of the other one. The total
                                                            carbonisation time for one vessel is 8-12 hours and the
                                                            charcoal yield is 30-32%, both being dependent on the
                                                            moisture content and feedstock used. One plant with 12
                                                            VMR ovens, run on a 24-hours basis, has a production
                                                            capacity of 6-7.000 tons/year and need 3 workers per
              Figure 2. Missouri Kiln /1/.                  shift /4/.
The CML carbonisation system consists of 4 to 12 steel
retorts (lined with refractory concrete) connected to a
central combustion chamber through ductings. These
are partial combustion, direct draught retorts with a
volume capacity of 16.5 m3, each. Wood is charged at
the top and the charcoal is discharged at the bottom.
Air intake is controlled by manual valves placed on the
bottom and lower periphery of the retorts, while
pyrolysis vapours are sucked out from the top. Each
retort is mounted on a balance, which allows con-
tinuous monitoring of mass loss and control of the
process. The total cycle time for one batch is 22 to 24
hours, with 1 hour for charging/discharging, 6 to 8
hours for carbonisation and 14 to 15 hours for cooling.
The charcoal yield is 22-24% depending on feedstock
used. The central combustion chamber makes it easy to
recover heat from the system. One plant with 12 CML
retorts (see Figure 3) has a production capacity of 2-                      Figure 4. VMR-oven /4/
3.000 tons/year and need 4-5 workers in total /3/.
                                                                                                                   3


HEATING WITH RECIRCULATED GAS                                bustion chamber. One part of the combustion gases is
                                                             conditioned and re-injected in the middle of the retort,
Another batch process is the Degussa (Reichert)              to serve as a heating medium for drying/carbonisation.
process (see Figure 5) /5/. The centre piece of this         Another part is cooled and re-injected at the bottom of
process is the large retort with a volume capacity of        the retort to serve as a cooling medium for charcoal.
100 m3 (H=8.5m; D=5m). Both the top and bottom are           The CISR process, shown in Figure 6 /8/ is somewhat
conical, but only the bottom cone is brick lined. The        simpler and is not equipped with a system for by-
retort is fed by a belt conveyer from the top. After         product recovery.
charging, the main heating pipe is opened to let hot
gases into the interior. During the cycle, which takes
16-20 hours, the carbonisation zone moves slowly
down to the bottom. On its way out, the pyroligneous
vapours pass through the uncarbonised feed, taking off
the moisture. After leaving the retort from the top, the
condensable fraction (tars, water vapour, etc.) is
removed in coolers and scrubbers. The non-con-
densable fraction goes to a heat exchanger, where it is
heated to the necessary temperatures of carbonisation
(450-550°C). Excess gas is discharged, burnt and used
for heating the heat exchanger and pre-drying of the
feedstock. Charcoal is discharged from the bottom and
fall into air-tight bunkers for cooling. The Degussa
process is used and owned by Chemviron Carbon in
Bodenfelde, Germany. They produce around 24.000
tons/year of charcoal from beech wood in 7 retorts.
Typical charcoal yield obtained from beech wood is
34%. Approximately 500 tons/year of very pure acetic
acid is recovered in a 19 stage process and sold to the
electronic industry. In addition, smoke flavours are
produced and sold to the food industry /6, 7/.




                                                             Figure 6. Lambiotte CISR carbonisation process /8/.

                                                             The retort is heated by an internal combustion device
                                                             which burns part of the pyroligneous vapours. In the
                                                             lower part of the retort, a second gas circulating cools
                                                             the charcoal before it leaves the converter. This gas
                                                             stream is refrigerated and washed in a scrubber. Since
                                                             Lambiotte is a continuous process, the quality and
                                                             homogeneity of the feedstock are crucial. The wood
                                                             pieces should not vary in size and the moisture content
             Figure 5. Degussa process /5/                   should not exceed 25% (wet basis). There are several
                                                             Lambiotte carbonisation plants in Europe. The largest
The Lambiotte carbonisation process is a continuous          one is Usine Lambiotte in Premery, France. This plant
process. The retort has the shape of a vertical cylinder     is based on the SIFIC process and produces 25.000
(H=18 to 33m; D=4.3m) with a fed opening at the top          tons/year of charcoal from oak wood in two retorts.
and a discharge cone at the bottom /8/. Wood is              Acetic acid and some other chemicals are recovered
transported to the top of the retort by a hoist and enters   from the pyroligneous liquid. Excess gas is used for
the retort through a lock-hopper. On its way down, the       pre-drying the wood in two shaft furnaces (H=20m;
wood passes three zones, that is, the drying, the            D=3m) /9/.
carbonisation and the cooling zone. Two different
heating systems exist for the Lambiotte process, the         Lurgi has developed a carbonisation process which is
SIFIC (French) and the CISR (Belgian) system. Both           quite similar to the Lambiotte process. The retort is
systems have two closed gas-loops, one for the               divided into an upper carbonisation zone and a lower
drying/carbonisation stage and one for the cooling           cooling zone, each with its own re-circulating gas
stage. The SIFIC process can be run with by-product          stream. Gas for the carbonising zone is distributed
recovery. Pyroligneous vapours are taken out from the        across the middle of the retort and flow upwards.
top of the retort, the condensable fraction is trapped in    Pyroligneous vapours leave the retort at the top and is
coolers and scrubbers before the gas is burnt in a com-      delivered to a specially designed incinerator for staged
                                                                                                                        4


combustion. In the first stage, the retort gas is burnt at   (dry basis). The pyroligneous vapours are burnt in an
near stoichiometric conditions. In the second stage,         external combustion chamber. The combustion gases
more air is added to ensure complete combustion              are separated in three parts. One part is conditioned and
before release to the atmosphere. About one third of         sent to the pre-drying chamber where it is in direct
the combustion gases are withdrawn and conditioned           contact with the raw material. Another part is sent to
(550-700°C) to serve as rinse gas for the carbonisation.     the carbonisation chamber where it heats indirectly the
Excess combustion gases from the second stage are            wood through a heat exchanger placed in the tunnel. A
conveyed via a stack to the atmosphere, however,             third part is cooled and used as a cooling medium for
waste heat recovery can be installed. The gas                the charcoal The total residence time within the tunnel
circulation loop in the lower zone of the retort is          is 25-35 hours depending on moisture content and
designed to sufficiently cool the charcoal descending        feedstock used. In Italy, there several O.E.T Calusco
from the upper zone, and flows counter-current to the        plants. The largest plants are placed in Milazzo and
charcoal. The heated cooling gas is directly re-cooled       Mortera, each with a production capacity of 6.000
by water in a scrubber before it enters the retort in the    tons/year of charcoal /11/.
bottom. The largest Lurgi charcoal plant forms part of
a Silicon Metal Complex (SIMCOA) in Bunbury,
Western-Australia (see Figure 7), and produces 27.000
tons/year of charcoal in two retorts from local Jarrah
hardwood /10/.




                                                                   Figure 8. Principle drawing of the O.E.T Calusco
                                                                                carbonisation process.


                                                             REFERENCES

                                                             /1/       Emrich, W. ‘Handbook of Charcoal Making.
                                                                       The Traditional and Industrial Methods’. D.
                                                                       Reidel Pub. Co.,Hingham, MA, 1985 pp 296.

                                                             /2/       Antal, M. J., S. G. Allen, X. Dai, B. Shimizu,
                                                                       M. S. Tam and M. Grønli. ’Attainment of the
                                                                       Theoretical Yield of Carbon from Biomass’.
                                                                       Paper submitted to Ind. Eng. Chem. Res, May
                                                                       2000.

                                                             /3/       Information received from CML, France

                                                             /4/       Information received from B. V. Carbo
                                                                       Engineering VMR, Netherlands

                                                             /5/       Brocksiepe, H.-G. ‘Charcoal’ In: Ullmann’s
  Figure 7. Lurgi’s charcoal plant in Bunbury, West-                   Encyclopedia of Industrial Chemistry, Fifth
                    Australia /10/.                                    edition, Vol A6.
The last process that will be described is the O.E.T         /6/       Marushewski, H. ‘Analysis of slow pyrolysis
Calusco (former Carbolisi) carbonisation process. A                    liquids’ Presentation given at PyNe Workshop,
principle drawing is shown in Figure 8. Wood is                        Montpellier, April 1999.
transported by trolleys through a horizontal tunnel. The
tunnel, 45m long, is U-shaped so that the entrance of        /7/       PyNe Newsletter, Issue 4
trolleys loaded with wood and the exit of trolleys
loaded with charcoal occurs at the same side of the          /8/       Information received from S. A. Lambiotte &
reactor. The tunnel is divided in three chambers where                 Cie S. A., Belgium
the wood successively undergoes 1) pre-drying; 2)
carbonisation; and 3) cooling. Each chamber is               /9/       Information received from Mr. Mares, Usine
separated by slide doors. The trolleys, each with a                    Lambiotte, France
volume capacity of 12 m3, are lined with perforated
steel sheets, travel on wheels, and are connected with a     /10/      Information received from Lurgi, Germany
mechanical towing system to move them along
specially laid tracks inside the tunnel. The carboni-        /11/      Information received from Impianti Trattamento
sation process is energetically self-sufficient as long as             Biomasse (I.T.B), Italy
the moisture content of the feedstock is below 45-50%
                                         5


MANUFACTURERS OF CHARCOAL
PROCESSES

CML
Route de Port Galland
01360 Loyettes
FRANCE
Phone: + 33 472 939 616
Fax: + 33 472 939 617
E-mail: CML.LOY@wanadoo.fr

B. V. Carbo Engineering VMR
P.O.Box 260
7640 AG Wierden
THE NETHERLANDS
Phone: + 31 546 549 129
Fax: + 31 546 549 229

S. A. Lambiotte & Cie S. A.
18, av, des Aubépines
B-1180 Brussels
BELGIUM
Phone: + 32 2 374 44 65
Fax: + 32 2 375 31 55
E-mail: mail@lambiotte.com

Lurgi Umwelt GmbH
Lurgiallee 6
60295 Frankfurt am Main
GERMANY
Phone: + 49 69 58 08 0
Fax:     + 49 69 58 08 26 28

Impianti Trattamento Biomasse (I.T.B.)
Via Vitt. Emanuele, 815
24033 Calusco d’ Adda
ITALY
Phone: + 39 35 791 800
Fax: + 39 35 794 068

				
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