TM 5-810-15
the aeration valves. The aeration control is
air temperature at the burner outlet to the selected
normally only required during start-up and are
temperature. A low limit select limits the fuel to the
manually controlled.
available primary air flow through the duct burner.
(7) Sorbent (limestone) feeder control.
When in-bed lances are utilized the fuel flow
The sorbent feeder control provides the proper
setpoint is compared to the actual fuel flow to
amount of sorbent to capture the SO2 generated in
modulate the burner valve. Position of the fuel
the combustion process. The sorbent feeder control
valve is limited by a low selector to the available air
is shown in figure 9-9. Sorbent feeder speed
flow to the combustor. The warmup burner and in-
controls the sorbent flow to the combustor. The
bed lance control is shown in figure 9-10.
i. Oxygen trim. Boiler efficiency can be im-
volumetric rate of sorbent delivered to the
combustor is directly related to feeder speed.
proved by minimizing excess air levels. Excess air
Feeder speed setpoint is based on SO2 in the stack
is required to ensure complete combustion and
flue gases, modified by oxygen in the flue gas, total
optimum heat release from the fuel. However
fuel flow and a correction factor. The SO2
excess air adds to heat loss and reduces boiler
measurement is provided by a flue gas analyzer or
thermal efficiency. Oxygen trim controls are used
analyzers, total fuel flow is taken from the main
to operate the boiler at low excess air levels. An
fuel feeders and oxygen from the flue gas O2
oxygen analyzer is installed to monitor the amount
analyzer. The setpoint value is compared to the
of oxygen in the boiler flue gas. The signal from the
actual sorbent (limestone) flow. A low limit is
analyzer is used to correct the combustion air flow
applied to the controller output to prevent the
to maintain the proper oxygen level in the flue gas
exiting the boiler. The boiler manufacturer*s
value from falling below a minimum value.
(8) Warmup burner control. A gas/oil fired
recommendations for flue gas oxygen content
burner or in-bed lances are utilized to warm the bed
versus boiler load for optimum boiler efficiency
material to the value where main fuel combustion
should be used to establish the proper oxygen
occurs. When gas/oil fire burners are utilized they
content in the flue gas at all boiler loads. Oxygen
normally are placed in the primary air duct. Fuel
trim controls applied to a parallel metering system
flow is regulated by a controller comparing primary
9-10
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