THE BRICK INDUSTRY

KILN TECHNOLOGY

The basic concept of brick kiln technology in developing countries has changed little over the past thousands of years. Brick making is an ancient technology. Bricks are made, dried, fired and cooled.

Kilns first started in pits, walls were then added. The addition of a chimney stack, improved the air flow or draw of the kiln, thus burning the fuel more completely. Several variations have been invented over the years with varying degrees of efficiency and cost.

Brick kilns fall into one, or both, of the following categories:

Intermittent

Kilns are sealed and the internal temperature increased according to a schedule. After the firing process is complete, both the kiln and bricks are cooled. The kiln is left to cool sufficiently before the bricks can be removed. Due to the relative ease and cost of construction these are the kilns types primarily used in developing countries.

Continuous (or Tunnel)

There are two types of continuous kilns:

• Tunnel kiln - the bricks are moved through a stationary fire zone, like a train in a tunnel.
• Continuous kiln - the bricks remain stationary and the fire moves through the kiln with assistance or help of a chimney or by a suction fan.

Both types are long structures in which only the central portion is directly heated. The same result can be achieved with both types of kilns.

The main difference is the tunnel kiln is vastly more expensive to build however it saves on labour costs and can be highly automated, bricks can be made and burnt without being touched by human hands.

KILN TYPES

The following kilns are most commonly in use today:

Clamp Kiln – ANCIENT TECHNOLOGY 4,000 B.C.
The most commonly used kiln in the developing world. These kilns have a devastating impact both on the environment and workers. Generally built with four brick walls like a room, then green bricks are stacked inside. They are inefficient in fuel, labour intensive and highly polluting. They are only operated in intermittent mode. To produce higher brick production clamp kilns are frequently built, grouped and operated in clusters.

Hoffman Kiln – INVENTED GERMANY 1858 – KNOWN ALSO AS CHINESE HYBRID HOFFMAN OR FIXED CHIMNEY KILN
These kilns have a large permanent arched masonry and an expensive tall masonry chimney of about 30 metres. They must operate in continuous mode. Used in Australia from 1883 until approximately 1985.

Tunnel Kiln – INVENTED GERMANY 1877
Most common in developed countries, since their invention tunnel kilns have now become highly automated and are for large brick production. Bricks move mechanically through a long stationary fire zone. They have minimal labour requirements but a very high capital cost. They must be operated in continuous mode and require a guaranteed electricity supply. One such plant built in New South Wales in 1993 cost $40 million, one currently proposed for Perth will be over $75 million.

Bull's Trench Kiln – INVENTED ENGLAND 1876
Movable Bull's Trench Kiln is commonly used in India and many developing countries. This kiln uses movable metal chimneys which are lifted and man-handled by a team of workers into different positions as the fire moves through the kiln. Has very high emissions, dispersed over a wide area, working conditions are hazardous. Although banned in many areas is still used. The Improved Bull's Trench Kiln has a permanent, fixed brick chimney over 30 metres high. The chimney requires skilled bricklayers to construct and is costly to build. The kiln can only be operated in continuous mode. It has no roof and cannot be used during the monsoon season.

Vertical Shaft Kiln – INVENTED CHINA 1958
Reasonably fuel efficient however the kiln is limited due to a low throughput. Green bricks are loaded into the shaft and therefore must be hauled up a ramp to the top of the kiln.

Habla Zig-Zag Kiln – INVENTED GERMANY 1927
The Habla Zig-Zag Kiln is the most fuel efficient kiln yet invented and the cheapest to build. It features a long fire zone advanced by a suction fan. The Habla Zig-Zag Kiln consumes less fuel, uses less mechanical energy and requires far less capital outlay with almost no maintenance. It also has a roof resulting in improved working conditions, the potential of water being collected and longer operational time during monsoon conditions. The Habla Zig-Zag Kiln is ideally suited to both large scale continuous brick making operations and to small semi-continuous village applications in developing countries.

THE PROCESS

Brick making consists of the following processes:

• Winning – digging for clay
• Preparation – preparing the clay for shaping
• Shaping – moulded using various mould types and methods, by hand or by machine
• Drying – open air, hot floor, chamber, tunnel, etc
• Firing – various kiln methods including Bull’s Trench, Clamp, Habla, Hoffman, Tunnel, etc.
• Quality Control – sorted into grades, e.g. firsts, seconds, soft (reburn)
• Dispatch – Sales

THE BRICK MARKET

The brick making industry in developing countries is most often the industry of the very poor and under-privileged. There are approximately 300,000 polluting brick kilns throughout the developing world with over 100,000 of these estimated to be in India alone.

The brick industry in India is the third largest user of coal, over 30 million tonnes per year. The majority of Indian kilns are Clamp Kilns.

In China the brick industry is claimed to be the fourth largest user of coal. It is estimated that the worldwide handmade brick production in developing countries is 1,266 billion bricks per annum, split into three main regions:

• China - 700 billion bricks – 55.3%
• India – 144 billion bricks – 11.3%
• Asia, Africa, South America & Mexico – 422 billion bricks – 33.4%

In contrast, worldwide machine made brick production using automated kilns, is approximately 125 billion bricks, with Australia’s brick production accounting for only 2 billion of this total.

The UK produces 4 billion, the USA 8 billion and China 100 billion. Other developed countries produce approximately 11 billion.