Gas Turbine Inlet Bleed Heating

Operation of the gas turbine with reduced minimum IGV settings can be used to extend the Premix operating region from 75%-Base load to 50%- Base load. Reducing the minimum IGV angle allows the combustor to operate at a firing temperature high enough to support premix operation.

Inlet bleed heating, (IBH), through the use of recirculated compressor discharge airflow, is necessary when operating with reduced IGV angles. Inlet heating protects the compressor from stall by relieving the discharge pressure and by increasing the inlet air stream temperature.

The inlet bleed heat system regulates compressor discharge bleed flow through a control valve and into a manifold located in the compressor inlet air stream. The control valve varies the inlet heating air flow as a function of IGV angle. At minimum IGV angles the inlet bleed flow is controlled to a maximum of 5.0% of the total compressor discharge flow. As the IGV's are opened at higher loads, the inlet bleed flow will proportionally decrease until shut off. The IBH control valve is monitored for its ability to track the command set point. If the valve command set point differs from the actual valve position by a prescribed amount for a period of time, an alarm will annunciate to warn the operator. If the condition persist for an extended amount of time, the inlet bleed heat system will be tripped and the IGV's minimum reference will be raised to the default value.

The IBH system monitors the temperature rise in the compressor inlet airflow. This temperature rise serves as an indication of bleed flow. Failure to detect a sufficient temperature rise in a set amount of time will cause the inlet bleed heat system to be tripped and an alarm annunciated. See schematic diagram in bleed heating system.