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FBC BOILER – BIOMASS FUELSAutomatic Combustion Control with Manual Fuel/Air Ratio Adjustment

FDFAN

ID

FAN

OVERFIREAIR

FAN

SCREW

FEEDER(S)

STEAM

DRUM

FDFAN

ID

FAN

OVERFIREAIR

FAN

SCREW

FEEDER(S)

STEAM

DRUM

 

SYSTEM DESCRIPTION

Boiler MasterThe boiler master control loop receives the drum pressure signal from the drum pressuretransmitter and compares it to the operator-entered setpoint. The controller modulates its outputin order to eliminate any difference between the signal and the setpoint. The output of the

controller represents the boiler demand for steam, and is sent to the variable speed drives on thefeeders or distributors if automatic feed control is used. It is also sent to the fuel/air ratio station.The operator may adjust the setpoint in automatic or place the controller in manual to fire theboiler manually. The controller rejects to Manual on bad signal quality. A high/low pressure alarmis shown.

Fuel/Air Ratio AdjustmentThe fuel-air ratio is determined by a lookup table entered into the controller during commissioningonce the combustion test has been performed. The means of trimming, or fine-tuning, the fuel-airratio is provided via a faceplate display on the controller which allows the operator to enter avalue for the fuel-air ratio, based on observation and/or a sample from a portable combustibles orO2 analyzer. This value will modify the demand for airflow by multiplying the position signal fromthe boiler master with a correction factor, limited to +/-10% for safety. The signal is sent to the

fuel-air ratio lookup table and then to the VFD on the FD Fan. It is also sent to the furnacepressure control loop as a feedforward adjustment.

Furnace PressureThe furnace pressure control loop receives the signal from the furnace pressure transmitter,compares it to the operator-entered setpoint and generates a correction signal. The total air flowdemand output from the fuel/air ratio is characterized in order to linearize the FD to ID speed orposition, and is then added as a feedforward signal to the furnace pressure control output. Theresult is sent to the VFD on the ID Fan.

MicroMod Automation, Inc.75 Town Centre Dr.

Rocheste,r NY 14623 USA

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Overfire AirThe overfire air control loop receives its input signal from the boiler master control loop, adjustedas a ratio of the main air flow via a 10-point lookup table. It compares this signal to an operator-entered setpoint and generates an output signal to the overfire air (OFA) fan.

TA

∆PID

A

FURNACE

PRESS

f(x)

∑X

0 - 100%-0.90 TO +1.10

A

K±

FUEL/AIRADJUST

f(x)

ATA

±

STEAM

PRESSURE

FUELDMD

FEEDERS

f(x)

ATA

±

F(x)

VFD

ID FAN

F(x)

VFD

FD FAN

F(x)

VFD

OVERFIRE AIR FAN

FUELvs.

AIR

FD

vs.ID

TA TA

∆PID

∆PID

AA

FURNACE

PRESS

f(x)f(x)

∑∑XX

0 - 100%-0.90 TO +1.10

AA

K±

FUEL/AIRADJUST

f(x)f(x)

ATAA

±±

STEAM

PRESSURE

FUELDMD

FEEDERS

f(x)f(x)

ATA ATA

±±

F(x)F(x)

VFD

ID FAN

F(x)F(x)

VFD

FD FAN

F(x)F(x)

VFD

OVERFIRE AIR FAN

FUELvs.

AIR

FD

vs.ID

 

MicroMod Automation, Inc.75 Town Centre Dr.

Rocheste,r NY 14623 USA