[Gasification] Gasification Digest, Vol 8, Issue 6

[Anand Karve]

Improving the charcoal kiln
By Dr.A.D.Karve
President, Appropriate Rural Technology Institute,
Maninee Apartments, Survey No. 13, Dhayarigaon,
Pune 411 041

Because there was a good demand for charcoal from the general public,
our Institute started looking at the process of charring in order to
remove the drawbacks in the traditional system. On the one hand, we
wanted to offer an alternative to wood as the raw source of  charcoal,
and on the other, we wanted to eliminate, or at least reduce the
atmospheric pollution that the traditional process leads to.
The objective of saving wood was achieved by us by using agricultural
waste as the source of charcoal. One can use all forms of dry
agricultural waste, such as straw of cereal grains, and also stalks of
plants like cotton, castor, pigeonpea, soybean, mustard, castor, etc.
but in order to sustain a commercial operation, the raw material must
be available throughout the year.  Agricultural waste is however
available only seasonally, at the time of harvest. This problem was
solved by us by using sugarcane leaves. India produces sugarcane on
about 1.5 million hectares. It is harvested continuously, throughout
the dry part of the year. After harvest, a hectare of sugarcane leaves
about 10 tons of dry leaves lying in the field. Being highly lignified
and silicified, they do not have any use for the farmer, and therefore
the sugarcane leaves, called trash, are burned by the farmer in the
field itself.  Leaf litter of plantation crops like rubber, mango,
cashewnut and even the dry leaves from urban avenue trees can be used
as raw material for this activity.
In order to tackle the problem of atmospheric pollution, our Institute
produced two improved models of the charcoal kiln. One of the models
made use of the oven and retort process, whereas the other model was
based on the top-lit, updraft gasifier stove that our Institute is
propagating under the brand name “Agni”.  Agricultural waste is light
in weight. Transporting such material from a large number of small
farms to a centrally located kiln is costly. Therefore, both the kilns
developed by ARTI are portable. It is the kiln that is moved around
and only the char, representing just 20 to 30% of the original
biomass, is transported to a central briquetting facility.
The kiln based on the oven-and-retort principle consists of a
cylindrical structure (about 150 cm wide and 100 cm tall), made of
sheet iron. This structure is called the oven. It consists of two
compartments, one above the other. About 5 kg trash is placed into the
basal compartment of the oven. Cylindrical metallic containers, called
retorts, filled with 3 kg trash each, are then placed into the upper
compartment of the oven. The retorts are about 37.5 cm wide and 60 cm
tall, and provided with a tightly fitting lid, which has a hole in its
centre. The retorts are placed upside down into the oven and the
spaces between the retorts are stuffed with trash. The oven is then
closed with a sheet metal lid, which has a built-in chimney. The trash
lying underneath the retorts (in the lower compartment of the oven) is
ignited to heat the retorts. This action starts the process of
pyrolysis of the material contained in the retorts. The pyrolysis gas
generated inside the retorts emerges out of the holes in their lids.
It too burns, adding to the process heat. The process of pyrolysis is
over by the time the trash underneath and around the retorts has
burned out. This process is free of pollution because the pyrolysis
gases are burned inside the kiln itself and the formation of carbon
monoxide is also avoided in this process.
 The kiln designed after a top-lit, updraft gasifier stove, consists
of a metallic barrel of 200 litre capacity. Its basal part is provided
with a few air holes, similar to the traditional kiln, but there is
also a long chimney placed on its top. Air gaps have been provided
also at the base of the chimney. The barrel is loosely filled with
biomass and the same is ignited from the top, and the lid with the
chimney is placed over it. When fire is started in the barrel, the
draft created by the chimney sucks not only primary air through the
basal holes, but it also sucks secondary air into the chimney to cause
complete combustion of the pyrolysis gas and also of carbon monoxide.
Combustion of these gases takes place inside the tall chimney, so that
none of the polluting gases enters the atmosphere.
The char generated in both the kilns is powdery. Therefore, it has to
be mixed with a binder and extruded into briquettes, which can then be
used as fuel in a household brazier or in an industrial burner.


On Thu, Apr 14, 2011 at 11:29 PM, GF <gfwhell at aol.com> wrote:
> I have always thought that a pile of leaves posses considerable
> thermal energy, probably equaling the equivalent of 1kw per sw yard if the
> surface area of each leaf were noted.
> If this pile of leaves were compressed into pellets for pyrolization, what
> gasifier design would be needed to extract this potential energy?
> I have about 50 trees which have an ever increasing molting rate. I clear up
> this crap and need somewhere sensible to put it. ( sensible comments only
> please)
> If all this debris can be gasified, there is surely a market for the needed
> apparatus.
>
> GF