Prevalent Misconceptions Regarding Construction and Operation of a Zigzag Kiln
Greentech Knowledge Solutions Private Limited (GKSPL) and Bihar State Pollution Control Board (BSPCB) has jointly conducted several workshops on “Design, construction and operation of a Zigzag Kiln” across different districts of Bihar during the 2018-19. During workshops, we have observed that there are many fundamental misconceptions prevalent among kiln owners and masons regarding construction and operation of a Zigzag kiln. Here we have tried to clear up the most widespread misconceptions in a very clear manner with short explanations.
“Zigzag kiln” is a completely new design of kiln for brick production.
It must be clear in everybody’s mind that “Zigzag kiln” is NOT a completely new design of brick kiln and it is similar in many ways to traditional “oval shape” Bull’s trench brick kiln. Zigzag kiln is just an “improved version” of traditional kiln. The main difference between oval-shape Bull’s trench kiln and Zigzag kiln is the brick-setting pattern and hence, the fuel feeding/firing method. Applying the improved brick-layout design in a Zigzag kiln, air/hot-gases are provided more time to exchange heat with bricks which is the main reason of its better performance compared to conventional kiln.
- Is it necessary to change the shape of kiln from oval to rectangular while upgrading from traditional kiln to Zigzag kiln?
Yes, it is RECOMMENDED for a Zigzag kiln to have a rectangular shape to properly employ improved brick-setting pattern and thus to obtain better performance compared to traditional kiln.
- “Zigzag kiln” and “High-draught kiln” are two different kiln designs.
Zigzag kiln refers to a kiln in which air/hot-gases does NOT flow “mostly” in a straight line (unlike in traditional oval-shape kiln) along the length of trench.Zigzag kilns can be of two types:
- Natural-draught Zigzag kiln: In this type draught is created naturally within the kiln with the help of chimney.
- Induced-draught or High-draught Zigzag kiln: In this type draught is created artificially within the kiln with the help of fan and chimney.
- There are separate types of chimneys for natural-draught and induced-draught or high-draught Zigzag kilns.
Chimney type is SAME for both natural-draught and high-draught Zigzag kiln. The cross-section of chimney can be either circular or square in both types of Zigzag kiln. For a given daily production capacity and brick-setting design, chimney internal diameter and height changes according to the type of Zigzag kiln.
- In a Zigzag kiln, a new design of chimney called “Zigzag chimney” is required to be installed.
It is absolutely WRONG to say that a new type of chimney called “Zigzag chimney” is essential to run any Zigzag kiln. If for a given daily production capacity and brick-setting design the required internal width, height and quality is met by the existing chimney, the same chimney can used to operate the Zigzag kiln.
- To operate a Zigzag kiln, only the chimney having square cross-section will work.
It is NOT necessary for a chimney to have square cross-section to operate any Zigzag kiln. The cross-section of chimney can be either circular or square in both the types of Zigzag kilns.
- State pollution control board will only allow the chimney having square cross-section to operate a Zigzag kiln.
There is NO demand from state pollution control board to compulsorily install chimney having square cross-section to operate a Zigzag kiln. Both circular and square cross-sectional chimney are permitted to run any Zigzag kiln.
- There are strict orders from state pollution control board that the height of new or retrofitted chimney must be greater than the existing one.
Central or state pollution control board ONLY specifies the “minimum height” of chimney as per the type of Zigzag kiln. If the existing, new or retrofitted chimney is meeting the required minimum height criteria for a given Zigzag kiln type, pollution control board will allow it to operate. According to draft notification published on March 16, 2018 by “Ministry of Environment, Forest and Climate Change”, the minimum height requirements for Zigzag kiln are as follows:
- In an induced-draught or high-draught kiln only “single Zigzag type” brick setting will work.
Since in an induced-draught or high-draught kiln the required draught is created artificially with the help of fan, ANY type of brick setting viz. single, double or triple Zigzag can be employed satisfactorily.
- When using a fan in induced-draught or high-draught Zigzag kiln, it is compulsory to increase the height of chimney.
If the chimney is meeting the “minimum height criteria” set by central or state pollution control board and the chimney’s internal width and height is meeting the design criteria for the required daily production capacity, it is NOT compulsory to increase the height of chimney.
- In a Zigzag kiln, the brick-setting design is completely different from the design used in traditional oval-shape Bull’s trench kilns.
Brick-setting design in a Zigzag is NOT VERY different form the setting employed in conventional oval-shape Bull’s trench kiln. The basic pattern of stacking bricks in “rows” along the width of trench with each row containing several “brick columns” is same in both traditional and improved kilns. To increase the time required for heat exchange between bricks and hot-gases/air, some rows in Zigzag kilns are made differently (like a wall) to allow air/hot gases to flow past them only through few spaces left in the wall. (For more details, refer knowledge briefs a). How is setting of bricks done in a natural-draught kiln, b). How is setting of bricks done in an induced-draught Zigzag kiln).
- Is it compulsory to install platform and ladder on the chimney for emission measurements?
Yes, it is COMPULSORY to install platform and ladder on the chimney as per the criteria set by central/state pollution control board to facilitate the kiln’s emission measurements. (For more details, refer knowledge brief – What are the good practices for the construction of masonry chimney of a Zigzag kiln?).
The writer is a Consultant at
Greentech Knowledge Solutions Pvt. Ltd. New Delhi