Torrefied Wood from Temperate & Tropical Species: Advantages & Prospects
J.P. BOURGEOIS and JACQUELINE DOAT
Abstract
This
paper gives the results obtained by the thermo-condensation of a few tropical
and temperate woods with
special reference to energetic yields and potential
uses of this new product, called "torrefied wood".
Upgrading of biomass by means of
torrefaction
Pentananunt, R. Rahman, A.N.M.M. and Bhattacharya, S.C.
Asian Institute of Technology, Bangkok, Thailand
Energy, Vol.15, No.12, pp.1175-1179 (1990)
Abstract
We present results on upgrading of wood and briquettes by means of torrefaction. The torrefied products showed significantly less smoking
during; combustion and a relatively faster rate of combustion. The weight and energy
yields of torrefied wood are 66.7 to 83.3 and 76.5 to 89.6%, respectively: the corresponding values for sawdust briquettes are
76.3 to 93.8 and 83.1 to 95.3%, respectively.
Fuel wood is often difficult to use because of its poor combustion characteristics, e.g.,
(low heating value, variable moisture content which is often high, hydroscopic nature, smoking
during combustion, etc. For domestic and a number of other applications, wood is often
upgraded to charcoal. The charcoal-making process is, however, grossly
inefficient, with the product containing only about 55% of the energy of the original raw material in well-managed,
commercial operations and as little as 20% in traditional processes.
Torrefaction or roasting appears to be an attractive option to upgrading wood to a product
which retains about 90% of its energy and can be substituted for charcoal in a variety
of applications. The important advantages of torrefied wood include high energy yield and
hydrophobicity so that it does not regain moisture during storage.
Developments
on Torrefied Wood: An Alternative to Charcoal for Reducing Deforestation
Abstract
Prospects for torrefied wood, with its
specific properties and high-energy yield, are potentially very promising:
 | in industry, where its use as a reducer
should compare favorably with the use of charcoal, as the cost of low yields when compounded by high wood prices is reflected in rising charcoal production costs. |
| in the domestic fuel sector, where there
is evidence to show that torrefied wood may be more competitive than charcoal in developed countries and in the larger urban centers in arid zones where a correlative reduction in pressures on threatened woodland ecosystems would ensue. |
Bench unit for biomass residues torrefaction
Fonseca Felfli, F, Luengo, C.A., Bezzon G. and Beaton Soler,
P. (1998),
Abstract
A bench unit for biomass torrefaction was designed to improve energy properties of agricultural and
forest residues. In some applications, torrefied residues may substitute firewood and charcoal, reducing costs and
environmental impacts during forest exploitation. The unit is composed basically by two chambers, one for combustion
and other one for thermal treatment. The combustion chamber supplies thermal energy for the
process, by burning biomass residues. Hot vapors and gases produced in the torrefaction
chamber are recirculated and burnt in the
combustion chamber, improving overall energy efficiency and avoiding atmospheric pollution. Torrefied products of
several experiments have presented low moisture and hydrophobic nature. According to the process conditions and
properties of the starting material, the fixed carbon content of the products ranged from 25 to 40% and the overall yield
from 70 to 90%. Also, the average calorific value was near 23 MJ/kg, which is an intermediate value between biomass
and charcoal. Torrefied biomass presents good quality for combustion and gasification purposes, with
favorable characteristics for storage and transportation, mainly because of its low moisture, high density and hydrophobic nature.
European
Community Demonstration projects for energy saving and alternative energy
sources.
Wood
roasting unit: Aim
of the project
The
project consisted of building a wood roasting unit and demonstrating on an
industrial scale that the roasting process is technically and economically
viable. Roasted wood is
obtained by subjecting wood to thermo-condensation at a temperature of between
250 and 300° C. It is therefore an intermediate product between wood and
charcoal. It has most of the advantages of both products.
Other references:
RWEDP Report No. 23 REGIONAL WOOD ENERGY DEVELOPMENT PROGRAMME
IN ASIA
GCP/RAS/154/NET Proceedings OF THE INTERNATIONAL WORKSHOP ON BIOMASS
BRIQUETTING NEW DELHI, INDIA (3-6 APRIL 1995).
Carbonization & Torrefaction of Briquettes
Carbonization
Charcoal is a premium fuel widely used in many developing countries to meet household as well
as a variety of other needs. It is however often difficult, if not impossible, to find a sufficient supply
of firewood for charcoal making. Substitution of wood charcoal by biocoal, which is charcoal
obtained from agricultural and forestry residues, appears to be an attractive option to alleviate the
traditional fuel crisis faced by many developing countries.
Biomass briquettes can be carbonized to produce charcoal briquettes. The carbonization process
can be carried out in kilns similar to conventional brick and metal kilns used for making charcoal
from wood. In a test run of an industrial plant in Thailand, the yield of charcoal from sawdust
briquettes on ash-and moisture-free basis was found to be about 35%. In a study carried out at
the Asian Institute of Technology (Bhattacharya and Bhattacharya, 1989) using a 2 cubic meter
brick kiln, the yield was found to be in the range of 33.5 to 41.3%.
Torrefaction
Charcoal making is a rather inefficient process, with the product containing only about 55% of the
energy of the original raw material in well-managed, commercial operations and as little as 20%
in traditional processes. Low temperature carbonization of biomass to obtain roasted or "torrefied"
products is a relatively recent development. During the process wood has been reported to lose
only 7 to 10% of its energy content while losing up to 30% of its weight. Torrefied products can
substitute charcoal in a number of applications (Bourgeois and Doat, 1985). A study by
Pentananunt et al. (1990) showed the weight and energy yields of torrefied wood to be
66.7 to 83%
and 76.5 to 89.6%, respectively. The corresponding values for sawdust briquettes were
76.3 to 93.8 and
83.1 to 95.3%, respectively. Torrefied briquettes have superior combustion characteristics as
compared with ordinary briquettes. Thus, combustion tests showed that the torrefied briquettes,
particularly of rice husk, were easier to ignite and burned much faster with less smoke compared
with ordinary briquettes.
Fonseca Felfli, F, Luengo, C.A., Bezzon G., Beaton Soler, P.
and Suros Mora, W.(1998),
A numerical model for biomass
torrefaction, Biomass for Energy and Industry, Proceedings of the
International Conference, Würzburg, Germany, 8-11 June 1998, Ed. by Kopetz,
Weber, Palz, Chartier and Ferrero, C.A.R.M.E.N., Rimpar Germany, 1998, p.1596-1599.
Abstract
For a good design and operation of a biomass torrefaction plant, the influence of heat
transfer, temperature, particle shape and size in the process must be analyzed. This analysis would allow to estimate process condition and results,
like temperature range, particle density and size, overall yield, residence time, and final products composition. A study of the
influence of these parameters in the torrefaction of a biomass briquette is presented. A
numerical model was developed for determination of best process conditions. The study of the physical and
chemical process during torrefaction involves the
formation of three main species: gas, tar and char. The model also analyses heat
transfer by convection and conduction, the convective transport of gaseous species and overall mass balance, considering physical
properties variation during the thermo chemical reactions. Different briquette shapes can be used in this model, based on the ratio between diameter and
length. The influence of heat transfer coefficient and temperature in the results is shown, defining best
conditions for heat transfer, temperature and total time, based on the weight yield and properties of the final products.
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