Agriculture Reference
In-Depth Information
During coal-raffinate firing freeboard temperature was higher than bed temperature but in
the case of gas-raffinate co-firing it was vice versa.It may be possible that with coal-raffinate
co-firing there might be potentially more unburned combustibles in the bed region compared
to gas-raffinate co-firing and the combustion of these unburned combustibles could have
proceeded to the freeboard region. This indicates the burning of raffinate in the bed with gas
firing. It picks heat from the sand to get ignited. With coal firing, as coal is already burning
above the bed, it picks up heat from the flame above the bed and at least part of it starts
burning above the bed.
The figure shows that just before the raffinate feed was stopped both bed and freeboard
temperatures started increasing and bed pressure started declining before a sudden dip which
was thought to be the condition of onset of agglomeration and raffinate feed was
stopped.Afterraffinate feed was stopped, bed temperature kept on increasing which could be
due to two reasons. Firstly, as the bed pressure was very low indicating that most of the bed
was agglomerated and slumped, there was lesser sand available to be fluidized and to absorb
heat from the hot flue gas coming from the bottom consequently bed temperature observed to
be increased. Secondly, increase in the bed temperature may be probably due to increased
combustion chamber temperature. It was observed that air flow was increased itself, possibly
due to lesser resistance offered by bed as lesser sand was available to be fluidized as a result
of agglomeration. As gas flow also increases with air flow proportionally due to the constant
air/fuel ratio control system, a higher gas flow might have increased combustion chamber
temperature. This higher combustion chamber could be responsible for higher bed
temperature. It is possible that both of these factors are acting simultaneously and the increase
in bed temperature is the net effect of the two.
1000
500
900
450
800
400
700
350
600
300
500
250
Bed Temperature
Freeboard temperature
Bed pressure
400
200
300
150
200
100
Raffinate on
Raffinate off
100
50
0
0
0.0
0.5
1.0
1.5
2.0
2.5
Time (hrs)
Figure 12. Bed behaviour during co-combustion of natural gas and raffinate.
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