In a Zigzag kiln, fuel is fed continuously through the fuel feed holes provided at the top of the kiln, by a single fireman standing on the top of the kiln. Usually two firemen are deployed in a shift who feed fuel alternately. The fuel is fed in six chambers of the brick setting simultaneously. In each chamber, there are two rows of fuel feed holes, so in total, there are 12 rows of fuel feed holes (about 80–130 feed holes) in the firing zone.
The fuel is fed sequentially in six chambers, starting from fuel-feed holes of chamber-1 and going up to chamber-6. This cycle is repeated continuously in the firing zone.
One chamber consists of five lines/rows of brick setting. There are two rows of fuel feed holes in each chamber. These are usually provided in the second and fourth lines of the brick setting in a chamber in the direction of air flow as shown in the figure above (for double zigzag brick setting).
Usually solid fuels such as coal, firewood, sawdust, and agriculture residues are used in a Zigzag kiln. Ideally, the type of fuel or fuel mixture used depends on the temperature to be maintained inside the chambers. An example of fuel mixtures being used in a better-operated Zigzag kiln located in North India is shown in the figure above.
In a Zigzag kiln, fuel is fed in crushed form (less than 5 mm). Fuel is fed continuously through the fuel feed holes by a single fireman. Spoons of different sizes are used for feeding different fuels depending on fuel density. Sawdust requires large spoon because of its low density. Medium-sized spoon is used for feeding the mixture of sawdust and coal. Small-sized spoon is used for feeding coal. Generally, 200–400 g fuel is fed per spoon.
In a Zigzag kiln, the fireman starts feeding fuel in chamber-1 from one end of the trench, and goes across the trench width to feed all the holes till he reaches the opposite end of chamber-1. The fireman then comes back to the starting end and starts feeding fuel in chamber-2 in the same manner. This sequence is repeated for other chambers till feeding is complete in chamber-6 to complete one feeding cycle. The new feeding cycle is again started from chamber-1.
Typically, in a Zigzag kiln (for all production capacities), three chambers are fired per day (fire travels about 18 feet (~5.5 m) in 24 hours). In every eight hours, a new chamber along the direction of fire travel is opened for fuel feeding.