Inleakage is often overlooked as an operating problem. In some instances, it can be beneficial
to ESP performance, but in most cases its effect is detrimental. Inleakage may occur
within the process itself or in the ESP and is caused by leaking access doors, leaking ductwork,
and even open sample ports.
Inleakage usually cools the gas stream, and can also introduce additional moisture. Air
inleakage often causes localized corrosion of the ESP shell, plates, and wires. The temperature
differential also can cause electrical disturbances (sparking) in the field. Finally, the
introduction of ambient air can affect the gas distribution near the point of entry. The primary
entrance paths are through the ESP access and hopper doors. Inleakage through hopper
doors may reentrain and excessively cool the dust in the hopper, which can cause both
reentrainment in the gas stream and hopper pluggage. Inleakage through the access doors
is normally accompanied by an audible in-rush of air.
Inleakage is also accompanied by an increase in gas volume. In some processes, a certain
amount of inleakage is expected. For example, application of Lungstrom regenerative air
heaters on power boilers or recovery boilers is normally accompanied by an increase in
flue gas oxygen. For utility boilers the increase may be from 4.5% oxygen at the inlet to
6.5% at the boiler outlet. For other boilers the percentage increase may be smaller when
measured by the O2 content, but 20 to 40% increases in gas volumes are typical and the
ESP must be sized accordingly. Excessive gas volume due to air inleakage, however, can
cause an increase in emissions due to higher velocities through the ESP and greater reentrainment
of particulate matter. For example, at a kraft recovery boiler, an ESP that was
designed for a superficial velocity of just under 6 ft/s was operating at over 12 ft/s to handle
an increased firing rate, increased excess air, and inleakage downstream of the boiler.
Because the velocities were so high through the ESP, the captured material was blown off
the plate and the source was unable to meet emission standards.
Table summarizes the problems associated with electrostatic precipitators, along with
corrective actions and preventive measures.
to ESP performance, but in most cases its effect is detrimental. Inleakage may occur
within the process itself or in the ESP and is caused by leaking access doors, leaking ductwork,
and even open sample ports.
Inleakage usually cools the gas stream, and can also introduce additional moisture. Air
inleakage often causes localized corrosion of the ESP shell, plates, and wires. The temperature
differential also can cause electrical disturbances (sparking) in the field. Finally, the
introduction of ambient air can affect the gas distribution near the point of entry. The primary
entrance paths are through the ESP access and hopper doors. Inleakage through hopper
doors may reentrain and excessively cool the dust in the hopper, which can cause both
reentrainment in the gas stream and hopper pluggage. Inleakage through the access doors
is normally accompanied by an audible in-rush of air.
Inleakage is also accompanied by an increase in gas volume. In some processes, a certain
amount of inleakage is expected. For example, application of Lungstrom regenerative air
heaters on power boilers or recovery boilers is normally accompanied by an increase in
flue gas oxygen. For utility boilers the increase may be from 4.5% oxygen at the inlet to
6.5% at the boiler outlet. For other boilers the percentage increase may be smaller when
measured by the O2 content, but 20 to 40% increases in gas volumes are typical and the
ESP must be sized accordingly. Excessive gas volume due to air inleakage, however, can
cause an increase in emissions due to higher velocities through the ESP and greater reentrainment
of particulate matter. For example, at a kraft recovery boiler, an ESP that was
designed for a superficial velocity of just under 6 ft/s was operating at over 12 ft/s to handle
an increased firing rate, increased excess air, and inleakage downstream of the boiler.
Because the velocities were so high through the ESP, the captured material was blown off
the plate and the source was unable to meet emission standards.
Table summarizes the problems associated with electrostatic precipitators, along with
corrective actions and preventive measures.
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