Coal charging and coal properties in fixed chimnery kiln
Another area of kiln operation which requires attention is coal feeding operation. At present coal is generally fed intermittently, with
intervals between two successive feeding operation ranging from 20 minutes to 50 minutes. At any given time, coal is generally fed in 2
to 3 rows, and due to heavy charging of coal, black smoke can be observed coming out during and just after the coal feeding operation.
When a fairly large charge of coal is fed , smoking is liable to occur for two reasons: (1) the coal bed is deepened and the diffusion of air
into the coal becomes difficult (figure 7) ; (2) the addition of cold fuel reduces the temperature of the fuel bed, some times below the
ignition temperature of the fuel resulting in incomplete combustion. Hence, it becomes important to feed coal in small quantities,
continuously, instead of heavy intermittent charging which is followed now. For achieving better combustion, following actions are
suggested: a) increase in number of fuel feeding lines from 2-3 to 3-5 ; b) continuous charging, instead of intermittent charging, which
can be achieved either by the use of mechanical stoker or in case of manual operation by allowing only one person to charge at a time;
c) following the feed pattern shown in figure 8; d) using small size spoons for fuel feeding (500 -700 g/spoon).
The other factor which affect combustion is the particle size of the fuel. The time for combustion of solid fuel depends on particle size.
The practice of feeding large sized fuel particles and lumps results in wastage. In general the particle size should be less them 10 mm for
getting good efficiency.