1-High exhaust temperature: Vacuum drops or maintains at lower side due to high exhaust steam temperature flow into steam condenser. This high exhaust temperature is mainly due to 1-Operation of Turbine at lower loads 2-More clearance in labyrinth seals 3-Not operating exhaust hood sprays 4-More load on condenser 5-Breaking of ejector U loop 2-Low circulating cooling water flow Vacuum in condenser reduces due to inadequate cooling water flow through steam condenser. This is mainly due to; 1-Problems associated with pumps 2-Air pockets in pipe line 3-Leakages in cooling water line 4-Stuck of discharge valve of pump 3-High cooling water temperature at condenser inlet Higher cooling water temperature at condenser inlet results into reduction of vacuum due to poor heat transfer from steam to water 4-Poor heat transfer in condenser Very less or poor heat transfer in steam condenser reduces vacuum to very low level resulting into high exhaust temperature &am
Why does boiler back
fire?
Following potential situations may cause back fire in biomass
or bagasse fired boilers
1-Sudden trip of ID fans or closing of fans suction or
discharge dampers:
If there is no interlock on ID fans trip to FD fans, a very
huge back fire occurs in boiler which has potential to cause damages to the
Boiler & operators.
Sudden closure of ID fans suction or discharge dampers will cause
same back fire as above.
2-Malfunctioning of pneumatic dampers positioner may cause
closure of ID fans dampers resulting into huge back fire in Boiler
3-APH tubes jam : Area required for the flue gas flow is equals to Boiler
capacity/9. Due to accumulation of ash in tubes, the flue gas flow area gets
reduce. This situation causes backfire
This situation occurs if Boiler is run at lower load for
long time without bypassing APH for FD/SA air, as at lower load flue gas
temperature will be less, which get condense in APH tubes.
4-Higher moisture in the fuel: If the fuel has higher moisture
that required, then there will be more requirement of combustion air, while
maintaining this air fuel mixture back fire may occur.
5-Frequent variation in fuel moisture : This is experienced in
sugar plants due to variation in bagasse moisture at mill outlet due to
variation in imbibition water added to extract juice from cane.
Upon continuous variation of fuel moisture it become very difficult
for operator to maintain balanced draught in furnace.
6-Improper spreading of fuel : Due to this furnace may
experience bed heap combustion of fuel, due to this there will not be uniform distribution
of bottom combustion air causing boiler back fire.
7-Sudden drop of boiler load: Due to this boiler air fuel
ratio & draught system gets disturbed causing boiler back fire.
8-Fouling in Super heater coils : Higher moisture in fuel
cause accumulation of bagasse & unburnt on super heater coils, which blocks
the flue gas path causing boiler back fire
9-Accumulation & deposition of ash in ESP fields: This
situation causes more resistance to flow of flue gas.
10-Improper air fuel mixture during start up & shutdowns may
cause boiler back fire
11-Air leakage into & out of the system : Due to the air
ingress & flue gas leakages, it becomes very difficult for operator to
maintain balanced draught.
12.Leakage or puncture of water wall tubes: Leakage or puncture of water wall tubes will result into high furnace pressure
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