Pottery kilns are notorious polluters. But the introduction of the rat-trap wall brick masonry technique is drastically reducing fuel consumption and resulting in incremental savings to boot.
Potters have been an intrinsic part of India’s cultural warp and weft. The humble potter is the common thread that connects the mitti ka kulhar (clay teacup) in which piping hot tea is cherished in winters and the surahi (clay cup) that is used to keep drinking water cool in summers. As such earthenware is ubiquitous in Indian homes, potters also play a vital role in India’s grassroot economy.
The potters laboriously collect the clay, pound the lumps into a fine powder, and then knead it painstakingly into a mouldable dough, so that it can be given the desired shape on the pottery wheel. The wares are then fired in a kiln.
The traditional kilns or furnaces used by the potter community, however, suffers from several major drawbacks. The low firing temperatures usually yields poor quality and discoloured products that easily break.
Also, the low furnace efficiency results in high fuel consumption and pollution. Even though high efficiency pottery kilns are being used in the organised sector, they are too expensive to be used by potters working in the small-scale sector.
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That’s why IIT Delhi (IIT), along with Rural Technology Action Group (RuTAG), stepped in to address these concerns.
IIT’s energy audit threw up some interesting findings. It found that a very large fraction of energy gets absorbed by the kiln walls and the floor, and another major fraction of the energy escapes into the atmosphere. Thus, only a small fraction is absorbed by the pottery to be fired. For instance, firing a 600 kg load of pottery in a single batch in a traditional kiln required 10 times its mass to be heated because the walls and the floor of the kiln too got heated. Drawing inspiration from the building construction techniques in countries that have colder climates, IIT Delhi modified the kiln on the concept of rat trap bonding.
The innovation reduced the total mass of bricks being heated by introducing air gaps in the outer and inner walls of the kiln using a channel of bricks. This rat-trap type of construction technique created a low-cost insulating medium that minimised heat absorption by the walls and heat loss to the environment.
Similar air gaps were created between the ground and the floor of the furnace on which firing actually happens. The thickness of the walls was also reduced.
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Minimising the energy absorbed by the floor and the walls of the furnace meant more heat retention, thus increasing ware temperatures during firing. That too with no additional fuel input.
In fact, the rat-trap bonding technique cut down the fuel consumption required to fire per kg of pottery by 50 percent. Considering that wood is one of the main fuels used for firing the kilns, a 50 percent saving per batch will result in incremental savings of firewood at the national level.
The new design also substantially increased the proportion of energy going to the pottery from 7 percent to 17 percent, while energy lost to walls and floor decreased from 35 percent to 30 percent.
These savings essentially translate into higher incomes for the potters who, reportedly, constitute the second poorest group in the country.
The design also solves the problem of smoky combustion. The traditional kilns create a lot of pollution because they require rapid refuelling due to the use of biomass such as fuelwood, crop stalks and husk which burn off fast. Since the kilns are not scientifically designed for adequate air supply, rapid feeding results in smoky combustion of the fuel. The new kiln design, on the other hand, by virtue of providing primary air for combustion, minimises smoke emissions during firing.
The modified kiln design also uses up to 10 percent fewer bricks than the traditional kiln. It also offsets the additional construction cost of providing a grate below the firing area. At an estimated cost Rs 30,000, the improved kiln includes excavation, brick masonry, and labour charges. It also improves the productivity and incomes of the potters.
Five units have been disseminated so far to Bharatpur in Rajasthan, Khurrampur in Haryana and Bhuj in Gujarat. The intervention indeed exemplifies the thrust placed by the Government of India on upgrading the rural industrial sector.
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Rural Technology Action Group (RuTAG) was conceptualized as a mission by the Office of the Principal Scientific Advisor (PSA) to the Government of India to provide a higher level of science and technology intervention and support for development and dissemination of appropriate technologies for rural areas. It is located in eight IITs (Bombay, Delhi, Guwahati, Kanpur, Kharagpur, Madras, Roorkee, Ropar). It identifies the technology needs for rural areas, available technology solutions and problems encountered in adopting the existing technology at grass root level; find technology solutions through government agencies , S&T institutions, S&T NGOs, academic institutes, corporate sectors and other voluntary agencies; and disseminate refined technology to rural areas.
The lead image on top shows potters crafting clayware using traditional techniques passed down through generations.
