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Seeking to make fire without smoke

N. Gopal Raj

It is how humans have cooked food and heated their homes across the ages — by burning wood, dry leaves, straw, and other crop residues as well as animal dung. Unfortunately, even now “more than three billion people still burn wood, dung, coal and other traditional fuels inside their homes,” says the World Health Organisation. “The resulting indoor air pollution is responsible for more than 1.5 million deaths a year — mostly of young children a nd their mothers. Millions more suffer every day with difficulty in breathing, stinging eyes and chronic respiratory disease.”

“The inefficient burning of solid fuels on an open fire or traditional stove indoors creates a dangerous cocktail of hundreds of pollutants, primarily carbon monoxide and small particles” but also many other health-damaging chemicals, noted the WHO in a brochure it published last year.

The National Sample Survey found that 86 per cent of rural households in India as well as more than one in five of urban households relied primarily on firewood, woodchips or dung cakes for their cooking fuel in 1999-2000. The WHO estimates that more than 407,000 deaths occurred in India during 2002 that were due to causes attributable to solid fuel use.

In such a situation, efficient biomass-burning cooking stoves that belch out less smoke would be hugely beneficial. Designing such stoves that are also able to gain public acceptance is, however, quite a challenge.

People burn dung cakes, various kinds of wood, cotton stalks and so on in stoves, pointed out Anand Karve who heads the Appropriate Rural Technology Institute (ARTI), a Pune-based NGO that he was instrumental in establishing. In a village, the fuel that is used in the chulha changes seasonally and the pot also varies depending what is being cooked. “Our local chulha is neither pot-specific nor fuel-specific,” which reduces their efficiency, he remarked.

The Union Government’s Ministry of New and Renewable Energy supported a National Programme on Improved Chulhas that began in 1986-87 and lasted till 2002. By 2001-2002, 338 lakh improved chulhas had been supplied under the programme.

The national programme spread awareness about improving cooking practices and the importance of keeping out smoke, according to K.S. Jagadish, a retired professor of the Indian Institute of Science. But the impact of the programme in terms of reducing fuel consumption may have been only marginal, remarked Dr. Jagadish, who participated in stove design efforts at the Institute and for a time headed its ASTRA (Application of Science and Technology for Rural Areas) programme.

Stoves needed to be precisely configured in order to burn efficiently and even small changes in the design parameters could affect their performance, he told this correspondent. However, the people who were trained to build the improved chulhas did not understand this requirement adequately and often produced stoves that were different from what was conceived. Besides, the stoves did not adequately take into account the sort of fuel that families were used to or the cultural practices involved in cooking, said Dr. Jagadish.

Now, there are private initiatives under way to develop and sell high quality biomass-burning stoves. The new stoves use a variety of techniques to boost efficiency and reduce air pollution. In addition, their designers are trying to make them as appealing as possible to the public.

A unit of the Aprovecho Research Center, a small non-profit technical organisation based in Oregon in the United States that has specialised in designing and popularising all sorts of biomass stoves, has been working out of Puducherry in order to develop high quality wood stoves. The current focus was on Tamil Nadu and Karnataka where the vast majority of people relied on burning wood, said Mouhsine Serrar, head of Aprovecho India.

In order to reduce firewood consumption and emissions, the organisation’s stove designs sought to improve the efficiency of combustion, according to Dr. Serrar. But, in addition, it was necessary to transfer the heat produced as efficiently as possible to the cooking vessel. For that, the stoves had to be designed so that hot gases from the burning wood flowed past the vessel as fast possible. In addition, the heat transfer could be maximised by having a skirt around the pot so that its sides as well as the bottom were exposed to the hot gases, he added

The biggest challenge, however, was making sure that those doing the cooking liked the stoves, he said. With cleaner combustion, less tar was deposited on the pots which could then be cleaned more readily. The new stoves could also be lit more quickly and easily. For lowering the heat (as when simmering food as it was being cooked), it was possible to have just one stick burning without smouldering.

Scientists at the Indian Institute of Science’s Combustion, Gasification & Propulsion Laboratory have opted for a different approach. Their cooking stove is based on the gasification principle.

When wood and other solid fuels were heated, a mix of volatile substances in them escaped as gases, said H.S. Mukunda, who has been closely involved in the stove’s development. If the generation of volatile substances and their combustion occurred erratically, then smoke and soot was produced, as often happened in a conventional wood stove. To overcome this problem, the gasifier stove used a battery-powered fan to produce a controlled stream of air that kept the biomass burning smoothly, thus generating gaseous volatiles at a uniform rate, and then ensured that those volatiles were completely burnt.

Before cooking began, the stove is filled with small pellets made from agricultural residues. The pellets are lit at the top and, with air from the fan coming in through the bottom, the flame propagates steadily downwards. The volatile gases produced are burnt with more air introduced near the top of the stove.

At a village near Madurai in Tamil Nadu, two women belonging to a joint family showed this correspondent their shiny gasifier stove. In a matter of minutes, they had filled the pellets and got the stove going. Afterwards, they showed how little soot had got deposited on the vessel and how easily that soot could be removed. Much of the daily cooking was now being done on the stove, said N. Muneeswari of Aviyur village.

The major problem with burning biomass was that shape, size, and other characteristics such as the fuel’s moisture and ash content could vary widely, said Prof. Mukunda. The pellets, on the other hand, could be produced from a wide range of crop residues, which could be dried and mixed suitably for the lowest cost and to give the best burn characteristics. The size and shape of the fuel could also be controlled.

ARTI based in Pune too has developed gasifier-based stoves. Gasification technology makes it possible to avoid indoor air pollution by burning wood very cleanly, agrees Priyadarshini Karve, the organisation’s project coordinator and one of the directors of its commercial affiliate. Dr. Karve worked on designing a gasifier stove that ran on sawdust as a M.Sc. research project. ‘Vivek,’ as the stove came to be named, did not have a big market potential but was useful wherever sawdust was easily available, she said.

In-house teams at ARTI created the ‘Sampada’ stove that uses woodchips or wood pieces as fuel. With this stove, it was possible to keep adding fuel even after it had been lit. The ‘Agni’ stove, intended for use in restaurants and by roadside vendors, was designed in association with a U.S. scientist, Paul Anderson, said Dr. Karve. ARTI’s gasifier stoves do not use fans to provide forced convection as that would increase cost and also raise maintenance issues.

In addition, there was a lot of agricultural waste of low-density, such as sugarcane trash, groundnut shells, and even dry leaves that could be used as a clean fuel once it had been converted into charcoal, said Dr. Karve. ARTI has established ways to produce charcoal briquettes and also designed a charcoal-based cooker.

The efforts of Aprovecho India and ARTI to create and popularise more efficient and less polluting stoves suited for local conditions are being supported by Shell Foundation, an independent charity registered in the U.K. that was established by the Shell Group to promote sustainable development globally. The Foundation wanted to establish a value chain involving stove designers, manufacturers, and distribution networks that would sell five million biomass-burning stoves in India over five years, said Ajit Abraham, manager in India of the charity’s programme to combat indoor air pollution. The Foundation’s role was only to act as catalyst and it would receive none of the proceeds from the stove sales, he added.

The Indian Institute of Science’s technology for a gasifier stove was taken by BP Energy India Limited. The Institute scientists and the company then worked together to produce a market-ready design. The ‘Oorja’ stove underwent commercial trials in Tamil Nadu and Maharashtra. With more than 25,000 stoves sold, the company says that it is “scaling up the business in India with the objective of reaching hundreds of thousands of Indian households.”

Would people be prepared to pay a higher price in order to buy a better biomass-burning cooking stove? It was not a question of price alone but of what people were getting in return, believes Dr. Karve. Rural people would be willing to pay for a good stove that they felt gave a quality of energy similar to kerosene or LPG, she says.

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