Dr. N. Subramanian
Bricks are traditional building materials which hold a lot of importance in Indian architecture. Brick manufacture in India and also in some parts of the world still use the traditional firing technique. After China, India is the second largest manufacturer of bricks, producing over 10 percent of the global production, and has about 140,000 brick-making enterprises, which accounts for 250 billion brick masonry units (www.proptiger.com). The industry employs about 15 million workers and consumes over 35 million tons of coal annually.
In developed countries, the simple kilns have been replaced by continuous tunnel kilns that produce millions of high-quality bricks in less time. For India’s brick industry to survive, it should modernize its kilns.
The Ministry of Housing and Urban Affairs (HUA) is examining whether it can ban use of burnt-clay bricks in its construction projects, a move aimed to boost environment-friendly products. If the Government bans burnt clay bricks, it would be a big blow to the brick-kiln industry. The National Green Tribunal (NGT) too had ordered that digging of earth for making bricks without prior environment clearance (EC), be banned.
These moves are because traditional brick-kilns cause air pollution as they use coal in the brick-making process. In October 2018, the Supreme Court empowered Environment Pollution (Prevention and Control) Authority (EPCA) to ensure that all brick-kilns implement the “zig-zag” technology, as specified by the Ministry of Environment and Forests, which can reduce emissions by 80 percent.
This article presents a review of the various kiln technologies and suggests that the vertical shaft brick kiln (VSBK) should be used as an alternative to the polluting traditional kilns. By adopting VSKB, the huge manpower engaged in this industry will not only safeguard their livelihood but can also live in better workplaces with limited pollution.
Classification of Brick Kilns
Brick kilns first started in pits and walls were added later. A chimney stack was added to improve the air flow or draught of the kiln, and to help burn the fuel more completely. Several variations have been invented over the years with varying degrees of efficiency and cost. The different types of brick kiln technologies that are used around the world, include the following (Akinshipe and Kornelius, 2017): 1. Clamp kiln 2. Up-draught kiln (UDK) 3. Down-draught kiln (DDK) 4. Bull’s trench kiln (BTK) which can have movable or fixed chimney 5. Zig-zag kiln 6. Hoffman (annular) kiln 7. Vertical shaft brick kiln (VSBK) and 8. Tunnel kiln.
The less popular types include the Habla kiln (an energy efficient variant to the Zig-zag kiln invented in Germany), the Igloo or Beehive kiln (used in Zimbabwe), the Kondagaon kiln, and the Bhadrawati kiln (Akinshipe and Kornelius, 2017). Other less common kilns include the modified clamp kilns such as the Scove kiln and the Scotch kiln.
There two types of brick kilns based on the production process and based on the flow of air in the kilns.
Classification Based on Production Process
The two basic types are Intermittent kilns and Continuous kilns (Fig. 1).
In intermittent kilns, bricks are fired in batches and can be further sub-divided into two categories: without chimney, which do not have any stack/chimney to guide the flue gases (examples: Clamp, Scove and Scotch kilns), and with chimney, which have a stack/chimney to create draught for releasing the flue gases at a higher level in the atmosphere (Examples: Downdraught kiln and climbing kilns). In both types, bricks and fuel are stacked in layers and the entire batch is fired at once. After the fire dies down, the bricks are allowed to cool. The kiln is then emptied, refilled again with raw bricks, and a new fire is started for the next batch of bricks. Thus, the heat contained in the hot flue gases, in the fired bricks and in the kiln structure is lost. These kilns have low fuel efficiency and pollute the atmosphere.
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