In a Zigzag Kiln, air flows in a zigzag path. Zigzag Kilns are an improvement over Fixed Chimney Bull’s Trench Kilns (FCBTK), in which air flows in a straight-line path. The zigzag air flow considerably improves the combustion of fuel and heat transfer in a Zigzag Kiln, because of which its performance is better than an FCBTK.
The zigzag firing concept was first used in the Buhrer Kiln, which was patented in 1868 by Jacob Buhrer of Switzerland. The Buhrer Kiln was similar to a Hoffmann Kiln in construction. The main innovation was the zigzag path of air flow. The zigzag path increased the distance travelled by air in the kiln and created turbulence. A fan was used to induce the necessary draught for the air flow.
The zigzag firing concept was later used in Habla Kilns, which were widely used in Germany between the first and second World Wars. They were also popular in Australia. In India, the Zigzag Kiln was first introduced by the Central Building Research Institute (CBRI) during the early 1970s, which was later replicated in Bangladesh and Nepal. These kilns were called Induced/High Draught Zigzag Kilns as they used a fan to create draught for air flow in the kiln.
In the past 40 years, many modifications have happened to the original design and several different variations of High Draught Zigzag Kilns can be found in the field. In recent years, some brick makers have modified the brick setting and practices and are successfully operating the kiln with the natural draught of the chimney without using a fan.
The main characteristics/ features of Zigzag Kiln technology are as given below.
In Zigzag Kilns, air flows in a zigzag path. There can be one, two, or three parallel zigzag air flow streams in a kiln. Accordingly, the air flow and the brick setting are called single, double, or triple zigzag air flow and single, double, or triple zigzag brick setting, respectively.
Depending upon the trench width and the draught available in the kiln, single, double, or triple zigzag brick setting is practised in the kiln. For the same trench width, the draught required for air flow in a single zigzag brick setting is higher than that required in double and triple zigzag brick setting. Also, the draught requirement increases with increase in trench width. Now-a-days, in some of the bigger kilns, quadruple zigzag brick setting is also practised in which there are four parallel zigzag air flow streams.
Zigzag kilns are of two types.
Natural Draught Zigzag Kiln | Induced Draught Zigzag Kiln |
Draught for air flow |
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Chimney creates the draught required for the air flow. | Fan creates the draught required for the air flow. |
Role of chimney |
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To create necessary draught as well as to expel the flue gases at a certain height as required under environment rules. | Mainly to expel the flue gases at a certain height as required under environment rules. |
Chimney height |
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Taller chimney (130–150 feet high); height of the chimney is usually determined by draught requirement. | Height of the chimney is relatively lower (80–90 feet); height is usually determined by environment rules. |
Kiln draught |
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Kiln operates at lower draught (6–8 mm water column). | Kiln operates at higher draught (30–50 mm water column). |
Zigzag setting |
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Usually double or triple zigzag brick settings are practised. | Usually single zigzag brick setting is practised. |
Setting density |
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Relatively loose brick setting (no. of bricks per unit volume is lower). | Relatively denser brick setting (no. of bricks per unit volume is higher). |
Electricity/diesel requirement |
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Not required in the operation of the kiln. | Required in the operation of the kiln (to power fan). |
The performance of Zigzag Kiln technology in terms of energy consumption, product quality, and pollutant emission is given below.
Zigzag Kilns have several advantages over the traditional FCBTKs: