Power plants – Combustion products used as motive fluid – Process
Reexamination Certificate
2000-08-31
2002-08-27
Kim, Ted (Department: 3746)
Power plants
Combustion products used as motive fluid
Process
C060S039094, C060S039463
Reexamination Certificate
active
06438963
ABSTRACT:
BACKGROUND
The field of the invention relates to gas turbines, and, in particular but not limited, to liquid fuel injection systems for industrial gas turbines.
Industrial gas turbines are often capable of alternatively running on liquid and gaseous fuels, e.g., natural gas. These gas turbines have fuel supply systems for both liquid and gas fuels. The gas turbines generally do not burn both gas and liquid fuels at the same time. Rather, when the gas turbine burns liquid fuel, the gas fuel supply is turned off. Similarly, when the gas turbine burns gaseous fuel, the liquid fuel supply is turned off. Fuel transitions occur during the operation of the gas turbine as the fuel supply is switched from liquid fuel to gaseous fuel, and vice versa.
Gas turbines that burn both liquid and gaseous fuel require a liquid fuel purge system to clear the fuel nozzles in the combustors of liquid fuel. The liquid fuel supply system is generally turned off when a gas turbine operates on gaseous fuel. When the liquid fuel system is turned off, the purge system operates to flush out any remaining liquid fuel from the nozzles of the combustor and provide continuous cooling airflow to the nozzles.
FIG. 1
, shows schematically a gas turbine
100
having liquid fuel system
102
and a liquid fuel purge system
104
. The gas turbine is also capable of running on a gas, such as natural gas, and includes a gaseous fuel system
106
. Other major components of the gas turbine include a main compressor
108
, a combustor
110
, a turbine
112
and a controller
114
. The power output of the gas turbine is a rotating turbine shaft
116
, which may be coupled to a generator that produces electric power.
In the exemplary industrial gas turbine shown, the combustor may be an annular array of combustion chambers, i.e., cans
118
, each of which has a liquid fuel nozzle
120
and a gas fuel nozzle
122
. The combustor may alternatively be an annular chamber. Combustion is initiated within the combustion cans at points slightly downstream of the nozzles. Air from the compressor
108
flows around and through the combustion cans to provide oxygen for combustion. Moreover, water injection nozzles
111
are arranged within the combustor
110
to add energy to the hot combustion gases and to cool the combustion cans
118
.
FIG. 2
shows a conventional liquid fuel purge system
104
for a liquid fuel system. When the gas turbine
100
operates on natural gas (or other gaseous fuel), the liquid fuel purge system
104
blows compressed air through the nozzles
120
of the liquid fuel
102
system to purge liquid fuel and provide a flow of continuous cooling air to the liquid fuel nozzles
120
.
The air used to purge the liquid fuel system is supplied from a dedicated motor (M) controlled purge compressor
128
. The purge compressor boosts the compression of air received from the main compressor
108
via compressor discharge
202
. A compressor air pre-cooler
164
, separator
166
and filter
168
arrangement is used to treat the compressor air before it is boosted by the purge compressor
128
. A tuning orifice
132
meters the flow of purge. The purge air from the purge compressor is routed through piping
130
, a strainer
162
, a Tee
137
that splits the purge airflow between the liquid fuel purge system
104
and a water purge system
126
. A liquid fuel purge multiport valve
138
routes the boosted pressure purge air to each of the liquid fuel nozzles
120
. The multiport valve is controlled by a solenoid
139
that is operated by the controller
114
. At each combustion chamber, end cover check valves
147
prevent liquid fuel from back flowing into the purge system. In addition, the purge compressor provides air through another tuning orifice
133
to an atomizing air manifold
134
and to the atomizing air ports of the liquid fuel nozzles
120
.
The liquid fuel check valves
165
, at least one for each combustion chamber, isolate the liquid fuel supply
172
during purge operations and prevent purge air from back-flowing into the liquid fuel system. By preventing purge air from entering the liquid fuel system, the check valves avoid air-fuel interfaces with the fuel supply.
When the liquid fuel purge system
104
is initiated, a solenoid controlled soft purge valve
140
is open simultaneously with the multiport valve
138
by a common solenoid valve
139
. The soft purge valve
140
opening rate is mechanically controlled by a metering valve in an actuation line (not shown). The soft purge valve opens over a relatively long duration of time to minimize load transients resulting from the burning of residual liquid fuel blown out into the combustor from the purge system piping
142
and the liquid fuel nozzles. The soft purge valve
140
is a low flow rate valve, to reduce the boosted pressure purge air flowing from the purge compressors. After the soft purge valve has been opened a predetermined period of time, a high flow purge valve
144
is opened to allow the boosted purge air to flow at the proper system pressure ratio. The high flow purge valve may be a two-way ball valve
144
.
The above-described piping, valves, purge compressor and other components of the liquid fuel purge system are complicated and cumbersome. The system requires controlled opening of several valves, multiport valves, metering tuning orifices, check valves, all of which require maintenance and are possible failure points. If the purge system fails, component failures will likely go undetected until turbine operation is ultimately affected, at which time the turbine must be taken off-line and serviced. To avoid having to take a gas turbine off-line due to a purge system failure, the conventional wisdom has been to add more purge system components and to add a backup system to the main purge system.
For example, if the purge compressor
128
fails, then air for the purge systems is supplied from an atomizing air compressor
150
and cooled in a purge air cooler
152
. When the atomizing air compressor operates to provide air for the purge systems, then motor (M) operated valves
154
,
156
, are closed to reduce flow and pressure, and air is routed through the purge cooler at the appropriate pressure and temperature. In addition, motor operated valve
158
is opened to provide a surge protection feedback loop. The operation of these valves
154
,
156
and
158
controls the air flow to and from the atomizing air compressor
150
.
Purge air from the atomizing air or purge air compressor passes through a strainer
162
to remove contaminants from the purge air and protect the contaminant sensitive components from start up and commissioning debris. The purge cooler
152
is in addition to the precooler
164
, separator
166
and filter
168
used to cool air from the main compressor
108
.
The previously-described conventional liquid fuel purge system has long suffered from several disadvantages and is prone to failure. To overcome the disadvantages of prior systems, the conventional wisdom has been to regularly redesign the components of the purge system, especially those components, e.g., check valves
147
and multiport valve
138
, that are prone to failure due to contaminants in the purge air.
Check valves do not provide optimal isolation of the purge and fuel systems. When they fail in an open position, purge check valves allow fuel to leak into the purge system. When purge check valves fail closed, purge air does not reach the fuel nozzles, and nozzle coking and melting can occur. When a fuel check valve fails in a closed position, it prevents fuel flow to a nozzle and can create pressure head differences in the fuel system between the combustors. Failure of the fuel check valves (either open or closed) may also lead to ignition and cross-fire failures and damage to the fuel system upstream of the fuel check valves. When they fail in an open position, fuel check valves may allow purge air to bubble into the fuel system. Check valve failures lead to serious combustion problems and may force the gas turbine to be shut down for rep
Iasillo Robert Joseph
Kaplan Howard Jay
Morawski Christopher John
Schroeder Troy Joseph
Traver Robert Scott
General Electric Company
Kim Ted
Nixon & Vanderhye P.C.
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