What is a Zigzag Kiln?
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.
History of Zigzag Kilns
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.
What are the main characteristics/features of Zigzag Kiln technology?
The main characteristics/ features of Zigzag Kiln technology are as given below.
- Zigzag Kilns are of rectangular shape. The bricks are fired in the space (called 'trench' or 'dug') between the rectangular central part of the kiln (called miyana) and the rectangular outer wall of the kiln.
- The chimney can be located either at the centre of the kiln or on any side of the kiln.
- It is a continuous moving-fire kiln in which the fire burns continuously and moves in a closed rectangular circuit through the bricks stacked in the trench.
- The draught required for the flow of air in the kiln is created either by the chimney or by a fan.
- In Zigzag Kilns, the bricks are stacked in a manner such that distinct chambers are formed in the brick setting. In alternate chambers, the openings for the flow of air through the brick setting are provided in such a way that it causes zigzag flow of air in the kiln.
- Usually, solid fuels such as coal, wood, saw dust, and agriculture residues are used in Zigzag Kilns.
- The size (footprint) of the kiln is generally 65–100 feet (20–30 m) in width and 200–250 feet (60–75 m) in length.
- Typical production capacity: 20,000–50,000 bricks per day.
- Capital investment required: Rs 30 lakh to Rs 50 lakh (excluding the cost of land and working capital).
- Area of land required: 4–6 acres (15,000–25,000 square metres) excluding the land required for excavation of clay.
- Seasonal operation: the kiln operates during the dry season only.
What are various types of zigzag brick setting being practised in Zigzag Kilns?
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.
What are the types of Zigzag kilns?
Zigzag kilns are of two types.
- Natural Draught Zigzag Kiln (NDZK), in which the draught required for air flow in the kiln is created by the chimney.
- Induced or High Draught Zigzag Kiln (IDZK), in which a fan is used to create the draught for air flow in the kiln.
What are the differences between Natural Draught Zigzag Kilns and Induced Draught Zigzag Kilns?
Natural Draught Zigzag Kiln
Induced Draught Zigzag Kiln
Draught for air flow
Chimney creates the draught required for the air flow.
Fan creates the draught required for the air flow.
Role of chimney
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.
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 operates at lower draught (6–8 mm water column).
Kiln operates at higher draught (30–50 mm water column).
Usually double or triple zigzag brick settings are practised.
Usually single zigzag brick setting is practised.
Relatively loose brick setting (no. of bricks per unit volume is lower).
Relatively denser brick setting (no. of bricks per unit volume is higher).
Not required in the operation of the kiln.
Required in the operation of the kiln (to power fan).
What is the typical performance of Zigzag Kiln technology?
The performance of Zigzag Kiln technology in terms of energy consumption, product quality, and pollutant emission is given below.
- Specific energy consumption (SEC) of Zigzag kiln technology: 0.95–1.15 MJ/kg of fired bricks.
- Usually, over 80% of the bricks produced in a Zigzag kiln are of Class-1 quality. The remaining are either over-burnt, under-burnt or breakages.
- The emission of particulate matter (PM) in the flue gases is in the range of 30 to 250 mg/Nm3 or about 0.23 g/kg of fired bricks.
What are the main advantages of Zigzag Kiln technology?
Zigzag Kilns have several advantages over the traditional FCBTKs:
- About 20%–25% savings in fuel consumption.
- Better product quality – over 80% bricks are of Class-1 quality.
- Substantial reduction in carbon dioxide (CO2) and PM emissions.