In both natural zig-zag eent Bhatta and induced draft zigzag kilns, the setting of green bricks is done in chambers. In natural draft kilns, depending upon the width of the trench, bricks can be stacked to achieve single, double, or triple zigzag patterns. In induced draft kilns, bricks are mostly stacked in a denser single zigzag pattern. In the Gali, bricks are set in a straight line,
as in an FCBTK kiln.
Brick setting in chambers in a zig-zag eent Bhatta
In a natural draft zigzag kiln, bricks are set in five lines in each chamber. A gap of five inches is maintained between adjacent lines for the flow of air. The width of a column of green bricks caries with the width of the trench and the production capacity of the kiln. For a trench width of 33 feet and a daily brick production of 44,000 bricks (and triple zigzag pattern),
two columns of four bricks, two columns of 10 bricks, and 12 columns of six bricks are recommended.
In induced draft brick kilns, the size of each chamber is around six feet. Bricks are set in six lines in each chamber; the length of each line is equal to the length of a brick. A three-inch gap is maintained between adjacent lines to help airflow. Green bricks are stacked in columns, the width of which depends on the width of the trench and production capacity.
For a trench width of 33 feet and a daily brick production of 55,000, two columns of four bricks, four columns of six bricks, and 10 columns of seven bricks are recommended.
The chimney is the most important and costly section of a kiln structure. Hence, chimney
design is of prime concern for all kiln owners.
In natural draft brick kilns, the temperature difference between the air inside and outside the kiln creates a draft inside the kiln, which is crucial in the processes of thermodynamics and aerodynamics of the kiln. The production capacity of a kiln depends on the chimney height.
For a daily production of 44,000 bricks, a chimney height of 145 feet is recommended.
A square chimney is faster to construct, and therefore, we have described the construction of a 145-feet-high square chimney in this section.
WICKET GATE OR DWARI ZIG ZAG KILN
Wicket gates are provided in the outer wall of the kiln for transportation of bricks in and out of the kiln. There is no consistent design methodology to define size, positioning, and a number of wicket gates (dwarfs) in zigzag kilns. The width of the wicket gates should be sufficient for loaded vehicles to move in and out of the kiln. Smaller and fewer wicker gates reduce heat loss from the kiln.
The following considerations must be taken into account while designing a wicker gate:
• Heat loss must be minimized
• It should be easy to transport green bricks into and fired bricks out of the kiln
• It should be easy and to transport green bricks into the dug efficiently using any mode
of transport, either human, animal, electric cars or trucks
We propose a total of six-wicket gates (three on either side) for an 11-feet-long outer wall. No
wicket gates have been proposed in the Gali area.
The common practice is to close wicket gates with a two-brick-thick (18 inches) wall with mud plaster. Heat loss and air leakage from such constructions are significant. Therefore,
some progressive kiln owners construct two 18 inch brick walls with a four-inch gap in the middle filled with ash, for better insulation. This is also our recommendation.