Knowledge Brief

Why is the performance of a Zigzag Kiln better than a Fixed Chimney Bull’s Trench Kiln (FCBTK)?

In a Zigzag Kiln, there is (1) less consumption and wastage of solid fuel, (2) improvement in the quantity of good quality bricks, (3) reduction in air pollution, and (4) higher revenue compared to an FCBTK.

There are three main reasons for the better performance of a Zigzag Kiln compared to FCBTK:

1. Better combustion of solid fuel
2. Better heat exchange between hot gases or air and bricks
3. Uniform temperature across the cross-section of the kiln.

Why is the combustion of solid fuel better in a Zigzag Kiln?

In a Zigzag Kiln, the combustion of solid fuel is better because of the following reasons:

1. Zigzag flow path
2. Firing crushed solid fuel
3. Long firing path
4. Feeding smaller quantity of solid fuel
5. Continuous feeding of solid fuel.

1. Zigzag flow path

In a Zigzag Kiln, air and hot gases move in a zigzag manner in which there are repeated changes in the direction of flow. Due to the turbulence created by the zigzag movement of air in the firing zone, the mixing of solid fuel and air is better in a Zigzag Kiln than in an FCBTK. Better mixing results in rapid, proper, stable, and complete combustion.

2. Firing crushed solid fuel

Crushed solid fuel or very small pieces of solid fuel are fired in a Zigzag Kiln. Feeding solid fuel of such form in small quantities results in better mixing of fuel and air. When the mixing of fuel and air is good, complete combustion of fuel takes place leading to the release of more heat from the solid fuel. Because of the smaller size of solid fuel particles, the generation of heat is also more uniform. Further, there is negligible accumulation of unburnt solid fuel at the bottom of the kiln.

3. Long firing path

In a Zigzag Kiln, the length of the firing zone and firing path are much more than in an FCBTK. The volatiles released from solid fuel travel a longer length and have longer residence time in the combustion zone where the temperature is high. Thus, there is sufficient time for proper mixing of volatiles with air, and for solid fuel particles to get heated and reach ignition temperature. Hence, there is near complete combustion of solid fuel in a Zigzag Kiln.

4. Feeding smaller quantity of solid fuel

Smaller spoons are used for feeding solid fuel in a Zigzag Kiln. As only a small amount of solid fuel is fed into the firing zone in every feed, sufficient amount of air is available for the complete combustion of solid fuel.

5. Continuous feeding of solid fuel

Due to continuous feeding of solid fuel in the firing zone, the generation of heat is gradual, uniform, and continuous. Therefore the resultant temperature in each chamber is more uniform and consistent in a Zigzag Kiln compared to an FCBTK. These conditions aid better combustion of solid fuel.

What are the benefits due to better combustion of solid fuel in a Zigzag Kiln?

Due to better combustion of solid fuel in a Zigzag Kiln, there is less consumption and wastage of solid fuel, and reduction in air pollution compared to an FCBTK.

Why is the heat exchange between hot gases and bricks better in a Zigzag Kiln?

In a Zigzag Kiln, air and hot gases move in a zigzag manner in which there are repeated changes in the direction of flow. Due to the turbulence created by the zigzag movement, the rate of heat transfer between air or hot gases and bricks is higher. This higher rate of heat transfer results in better heat exchange.

What are the benefits due to better heat exchange between gases and bricks in a Zigzag Kiln?

Due to better heat exchange between hot gases and bricks in a Zigzag Kiln, there is less consumption of solid fuel, and improvement in the quantity of good quality bricks compared to an FCBTK. Higher production of good quality bricks results in higher revenue in a Zigzag Kiln.

Why is the temperature uniform across the cross-section of the kiln in a Zigzag Kiln?

Due to continuous feeding of solid fuel in a Zigzag Kiln, the generation of heat is gradual, uniform, and continuous. This leads to more uniform and consistent temperature in each chamber.

In an FCBTK, large lumps of coal fed in the kiln burn mostly on the kiln floor and a large part of the heat generation takes place at the bottom of the kiln. In a Zigzag Kiln, small solid fuel particles and small quantity of solid fuel per spoon ensure that most of the solid fuel stays and burns on the ledges provided at different heights, resulting in uniform temperature from the top to the bottom of the kiln.

The turbulence caused due to the zigzag flow also helps in uniform heat distribution.

What are the benefits due to uniform temperature across the cross-section of the kiln in a Zigzag Kiln?

Due to uniform temperature across the cross-section of the kiln in a Zigzag Kiln, there is improvement in the production of good quality bricks. Production of higher quantity of good quality bricks generates higher revenue for the owner of a Zigzag Kiln.