What is a Fixed Chimney Bull’s Trench Kiln (FCBTK)?
Fixed Chimney Bull’s Trench Kiln (FCBTK) technology is the most popular technology for the production of bricks in India, Bangladesh, Nepal, and Pakistan.
The main reasons for its popularity are:
Low construction cost
Availability of trained manpower for operation
No need of electricity for its operation.
History of FCBTK
FCBTK is a modified version of the Bull’s trench kiln (BTK) introduced in India by a British engineer W. Bull in 1876. Initially it had movable metal chimneys, which were placed ahead of the fire on the brick setting and were moved as the firing progressed. This technology was modified to the more efficient and less polluting FCBTK. Consequent to a regulatory ban in India on the use of moving chimney kilns during the 1990s, there was a large-scale shift to FCBTK. This was followed by similar regulations in Bangladesh and Nepal.
What are the main characteristics/features of FCBTK technology?
The main characteristics/ features of FCBTK technology are as given below.
It has an oval or circular shape in which the chimney is located at the centre and the bricks are fired in the space around the chimney, between the central part of the kiln (called miyana) and the outer wall. This space is called ‘trench’ or ‘dug’.
It is a continuous moving-fire kiln in which the fire burns continuously and moves in a closed circuit through the bricks stacked in the trench.
The draught required for the flow of air in the kiln is created by the chimney.
The bricks are stacked in the kiln in ‘column-blade’ brick setting in which the bricks are stacked in vertical columns in a row along the width of the trench. The rows of brick columns are arranged one ahead of the other in the direction of air flow.
The air flows through the passages left in between the brick columns in a straight-line path.
Usually, solid fuels such as coal, wood, saw dust, and agriculture residues are used in FCBTKs.
The size (footprint) of the kiln is generally 75–100 feet (20–30 m) in width and 250–400 feet (75–120 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 is the typical performance of FCBTK technology?
The performance of FCBTK technology in terms of energy consumption, product quality, and pollutant emissions is given below.
Specific energy consumption (SEC) of FCBTK technology: 1.1–1.5 MJ/kg of fired bricks.
Typically, about 60% of the bricks produced in FCBTK 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 150 to1250 mg/Nm3 or about 1.18 g/kg of fired bricks.
What are the advantages and disadvantages of FCBTK technology?
Being a continuous kiln, it has better heat recovery features and is more efficient as compared to intermittent kilns.
Low cost of the technology.
Higher fuel consumption compared to other efficient continuous kilns because of incomplete combustion and heat losses in the kiln.
Only about 60% of the bricks produced are of Class-1 quality.
Relatively higher PM emission compared to other continuous kiln technologies.