Upload
john-taulo
View
216
Download
0
Embed Size (px)
Citation preview
7/31/2019 Coalstove Newsletter Article
1/3
Experiment testing of Top Lit Updraft Coal Stove for
Domestic use in Malawi
by John L Taulo, Deputy Director (Research and Development)
Introduction
Combustion of biomass remains the prevalent energy source for cooking and heating of rural
households in Malawi, where more than 84.7% of the countrys population resides (Kambewa
and Chiwaula, 2010). Approximately 11 million rural people in Malawi still use biomass for
cooking, where fuelwood represents approximately 88% of energy used by rural households and
95.4% of total energy use in rural communities (NSO, 2009). Cooking is then often done over
open fires, which are highly inefficient transferring only 5-10% of the fuel energy to the cooking
pot. The adverse health and socio-economic implications of this form of energy supply are
enormous, with women and children at particular risk. The burden of biomass fuel collection andprocessing for cooking also falls mainly upon women and children (mainly girls), who spend
significant time gathering fuel resources every day.
Steadily rising firewood consumption for cooking purposes results in deforestation of large areas
creating severe ecological problems. In order to protect the environment it is urgently required to
utilize alternative methods for cooking purposes. Therefore, providing a clean cooking energy
option for these households will yield enormous gains in terms of health and socio-economic
welfare of the weakest and the most vulnerable sections of society. At the same time, the cleaner
combustion in these devices will greatly reduce the products of incomplete combustion which
are greenhouse pollutants, thus helping combat climate change.
This study aims at using locally available materials to develop a more efficient, affordable and
safe coal-burning stove in which the use of the stove will result in lesser consumption rates of
fuel and reduce the indoor air pollution. The stove in the present study follows the principle of
producing combustible gases, primarily carbon monoxide, from coal by burning it with limited
amount of air. The coal is burnt just enough to convert the fuel into char and allow the oxygen in
the char at a higher temperature to produce combustible carbon monoxide (CO), hydrogen (H2),
and methane. Other gases, like carbon dioxide (CO2) and water vapour (H2O) which are not
combustible, are also produced during gasification. By controlling the air supply with a small
fan, the amount of air necessary to gasify coal is achieved.
TLUD Coal Stove
The TLUD stove (see Fig.1) consists of a cylindrical reactor, an outer cylinder, a gas burner, and
a fan. The cylindrical reactor having a diameter of 15 cm and a height of 49 cm is where the fuel
is gasified. It is made of 1.6 mm mild steel sheet and is provided with grate at the bottom for the
passage of primary air. The grate is made of 12 mm diameter deformed bars with 10 mm
7/31/2019 Coalstove Newsletter Article
2/3
spacing. The outer cylinder serves as stove body and as burner support. The gas burner is where
the gas generated from the reactor, mixed with preheated air, and is ignited. The fan is attached
to the stove body and is used to supply the air needed for gasification. The primary air enters
from the bottom end of the reactor with the use of a 12 cm, 15- watt computer fan. The
secondary air, on the other hand, enters the reactor through 16 holes on top of the stove casing
having a diameter of 20 mm and is mixed with the gas generated at the small holes located at the
upper portion of the burner. Combustible gases are burned in the plate burner consisting of 40
and 45 holes at the inner and outer circles, respectively, with 10-mm diameter.
Results
Modified University of California water boiling test (WBT) version 4.12 was used for testing the
stove. Burn rate and stove efficiency were determined together with emission factors for carbon
dioxide (CO2), carbon monoxide (CO), nitric oxide (NO) and hydrocarbons(HC). Compared tothe three stone fire, the coal stove exhibited a higher burn rate (25.57 g/min (1.534 kg h -1)) but
lower efficiency. The average computed thermal efficiency of the stove was 18.3%. The CO and
CO2 emission was in the range 9 ppm to 5480ppm (10.32-6279 mg/m3) and 1700 ppm to 23, 500
ppm (3060-42,300 mg/m3), respectively. The coal stove recorded mean CO, CO2, HC and NO
emission factors of 1.658, 125.2, 0.197 and 0.236 g kg -1, respectively. The emissions and
concentrations of carbon monoxide met an emission standard of a CO: CO2 ratio of
7/31/2019 Coalstove Newsletter Article
3/3
this study a more efficient coal-burning stove was designed, fabricated and the thermal
performance of the stove was compared with that of a traditional stove. The results obtained
showed that the combustion of coal in the stove was very slow, resulting in a slow temperature
increase in the pot. The coal stove can be operated at power outputs ranging from 1.578 to 18.93
kW at efficiency of approximately 18.3%. The study also showed that the power output of the
fire influences the efficiency and emission characteristics of the stove; decreased combustion
efficiency could lead to more or less complete combustion and emit more products of incomplete
combustion (PICs).
Further studies are also needed to explore the relationship between the efficiencies estimated
above and the actual rate of household fuel consumption. An integrated assessment of
greenhouse gas emissions, thermal efficiency, and health impacts can provide more balanced,
fair, and complete evaluation of the stove than only considering one of these parameters. It
seems, however, that the design of the coal stove must be improved before it can be promoted as
a reliable fuel-saving intervention. The domestic use of coal on a massive scale should not be
considered until a more fuel efficient and cleaner burning stove is designed. The work atMIRTDC is underway to perfect this technology by performing extensive experiments on
various models.