Method for operating a gas turbine
View Patent ↗A method for operating a gas turbine includes supplying fuel via at least one control valve regulated using an open-loop control system based on a predetermined load setpoint value. A valve stroke control command (s cmd ) is generated based on a fuel mass flow control command (m cmd ) using a mass flow-valve stroke converter. The valve stroke control command (s cmd ) is compared with a valve stroke limit value (min{s lim1 , s lim2 }) using a variable pressure regulator. A load limit value is generated if the valve stroke control command (s cmd ) exceeds the valve stroke limit value (min{s lim1 , s lim2 }) to reduce the load setpoint value. Operation of the gas turbine is stabilized using a low limit value (x lim ) of a pressure drop ratio (x), wherein the pressure drop ratio (x) is a quotient of a pressure drop (dp) which occurs at the control valve and of a pressure (p 1 ) upstream of the control valve.
1. A method for operating a gas turbine, the gas turbine including a compressor for compressing air, a combustion chamber for combusting a gaseous fuel with the compressed air so as to form a hot gas and a turbine for expanding the hot gas, the method comprising:
regulating a supply of the gaseous fuel based on a predetermined load setpoint value via at least one control valve using an open-loop control system, the regulating including:
generating a valve stroke control command (S cmd ) based on a fuel mass flow control command (m cmd ) using a mass flow-valve stroke converter;
comparing the valve stroke control command (S cmd ) with a valve stroke limit value (min{s lim1 , s lim2 }) using a variable pressure regulator;
generating a load limit value if the valve stroke control command (S cmd ) exceeds the valve stroke limit value (min{s lim1 , s lim2 }) so as to reduce the load setpoint value; and
stabilizing operation of the gas turbine by using a low limit value (X lim ) of a pressure drop ratio (x), wherein the pressure drop ratio (x) is a quotient of a pressure drop (dp) which occurs at the at least one control valve and of a pressure (p 1 ) upstream of the at least one control valve.
2. The method as recited in claim 1 , wherein the valve stroke limit value (min{s lim1 , s lim2 }) is a minimum of a first valve stroke limit value and a second valve stroke limit value, the first valve stroke limit value (s lim1 ) being predefined and the second valve stroke limit value (s lim2 ) being calculated based on the low pressure drop ratio limit value (x lim ) using
s
lim
2
=
f
-
1
(
K
v
)
=
f
-
1
(
m
cmd
N
1
·
F
p
·
p
1
·
Y
x
s
·
M
Z
·
T
)
wherein m cmd is the fuel mass flow control command to the control valve, N 1 is a constant, F p is a constant piping geometry factor, f −1 (K v ) is a control valve characteristic, M is the fuel gas molecular weight, Z is a compressibility factor of the fuel gas and Y is an expansion factor according to the equation
Y
=
1
-
x
s
3
F
r
x
T
,
wherein x s =F(x lim , F r x T ), and
F
r
=
k
g
k
a
apply, with k g being the isentropic coefficient for the gaseous fuel and k a being the isentropic coefficient for air.
3. The method as recited in claim 2 , wherein x s =min{x lim ,F r x T }.
4. The method as recited in claim 2 , wherein x s =min{x,F r x T } and wherein
x
=
max
{
dp
p
1
,
x
lim
-
0.01
}
so as to limit a sensitivity of the mass flow-valve stroke conversion relative to a pressure measurement.
5. The method as recited in claim 1 , wherein a value of the low pressure drop ratio limit value (x lim ) is between 0.09 and 0.11.
6. The method as recited in claim 1 , wherein the at least one control valve includes a plurality of control valves, and wherein the load setpoint value is reduced if the valve stroke control command (s cmd ) exceeds the valve stroke limit value (min{s lim1 , s lim2 }) in one of the plurality of control valves.