Gas Turbine Handbook : Principles and Practices

244 Gas Turbine Handbook: Principles and Practices
9 ppm thermal NO x
emissions in the laboratory using 100% syngas
with head end steam injection. An additional benefit of the compressor
air-blown gasifier is the retention in the cycle of N 2
which helps
with NO x
control. Syngas has an ammonia content which contributes
to the overall NO x
output. Testing will also determine the ammonia
to NO x
conversion rates.
Compressor Air Extraction
The most efficient way to provide air to the gasifier is to bleed
compressor discharge air from the gas turbine. The MS6001FA has
the capacity to supply high bleeds, in excess of 20% of compressor
flow. This allows plant simplification in that an air blown gasifier
can be used, supplied with compressor discharge air. Additionally, no
turbo-machinery changes are required. Extraction flow can be supplied
to the gasifier at all conditions from full speed no load to full
load. This is particularly important in the event of a load trip because
the gas turbine can still supply the gasifier even though fuel to the
gas turbine has been cut back. This allows an orderly turn-down of
the gasifier to match gas turbine fuel demand.
Compressor discharge air is extracted through casing ports.
The ports incorporate a metering orifice designed to limit the flow to
a level that does not cause operability problems for the gas turbine
compressor. The extraction pressure is increased by a boost compressor
which delivers the flow to the gasifier. As a supplement to the inlet
bleed heat surge protection function already existing in the control
system, the gas turbine is protected by a blow-off valve from excessive
back-pressure caused by gasifier or boost compressor problems.
It is important in the design of the extraction and syngas delivery
system to minimize pressure drops. Extraction and delivery
pressures losses are a very powerful driver in the sizing of the boost
compressor. High losses can double the size of the boost compressor,
raising initial cost and reducing net power output over the life of the
plant. To minimize the losses GE is developing a unique low pressure
drop fuel control system for this application. (Figure 14-7, View of
MS6001FA Combustor Case Extraction Manifold.)
Control System
The overall plant is controlled by a Distributed Control System
(DCS). The Mk. V Speedtronic ® turbine control systems interfaces