Power plants – Combustion products used as motive fluid – With safety device
Reexamination Certificate
2001-02-13
2002-05-14
Thorpe, Timothy S. (Department: 3746)
Power plants
Combustion products used as motive fluid
With safety device
Reexamination Certificate
active
06385961
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a gas turbine fuel system and more specifically to a gas turbine fuel system comprising a fuel oil distribution control system, a fuel oil purge system, a purging air supply system and a fuel nozzle wash system in which, fuel oil distribution is controlled to be done uniformly to a plurality of fuel nozzles with enhanced reliability of fuel distribution, and residual oil in fuel pipings and nozzles, when gas turbine operation is changed over to gas fuel from oil fuel, is purged effectively so that a load change caused by burning of the residual oil at the time of purging is prevented.
2. Description of the Prior Art
FIG. 9
is a block diagram-of an entire gas turbine fuel system comprising therein a fuel oil supply system, a fuel oil purge system, a purging air supply system and a compressor outlet wash system in the prior art. In
FIG. 9
, a combustor X comprises therein a plurality, about 20 pieces for example, of fuel nozzles X
1
, X
2
disposed along an inner periphery thereof. The fuel nozzles X
1
are supplied with fuel gas from a fuel gas supply system and the fuel nozzles X
2
are supplied with fuel oil from a fuel oil supply system G. The gas and oil are changed over to either one thereof to be supplied into the combustor X for combustion. The fuel oil supply system G, as mentioned, is a system for supplying therethrough fuel oil and a fuel oil purge system H is a system for purging oil remaining in the piping system or fuel nozzles when the fuel is changed over to gas from oil. A purging air supply system J supplies therethrough a purging air into the fuel oil purge system H. A compressor outlet wash system K is a system for injecting water into a compressor outlet for washing this compressor outlet which communicates with the combustor. Description will be made further on each of the above systems.
The fuel oil supply system G will be described first. In the gas turbine, a stable combustion is required for a wide range of fuel flow rates from ignition to power output. Especially, in the low fuel flow rate range at the time of ignition etc., there is only a small differential pressure of the fuel nozzles in the combustor, which results in an unstable combustion. In recent gas turbines there are provided a large number of fuel nozzles, of about 20 pieces, and there arises an imbalance in the fuel flow rate due to the influence of the head difference between upper ones and lower ones of the fuel nozzles, which are vertically disposed. For this reason, a flow divider is provided so that fuel is divided to be supplied uniformly to each of the fuel nozzles. But this flow divider is not necessarily of a sufficient reliability, and troubles in the fuel system are thereby often caused.
FIG. 10
is a diagrammatic view of the fuel oil supply system G in the prior art. In
FIG. 10
, fuel oil is flow rate controlled by a flow control valve
11
to then flow through a piping
12
and enter a flow divider
80
to be divided there to flow through a plurality of pipings
82
of about 20 pieces and to be supplied into each of the fuel nozzles X
2
of the combustor X. The gas turbine fuel nozzles X
2
are disposed in about 20 pieces along a circumference and there is a head difference of about 4 m between the nozzles of upper positions and those of lower positions. This head difference produces an imbalance in the fuel flow rate, especially in the low fuel flow rate range at the time of ignition. For this reason, the flow divider
80
is provided, but this flow divider
80
is constructed such that a spiral shaft is disposed in a cylindrical body, and while this shaft is rotated, fuel oil flows into the cylindrical body to be divided to flow through each of the plurality of pipings
82
uniformly. A motor
81
is operated only during the operation start time for ensuring a smooth start of rotation of the flow divider
80
.
FIG. 11
is a view showing a relation between load transition (fuel flow rate) and system differential pressure in the prior art gas turbine, wherein as load increases, fuel flow rate increases from gas turbine ignition time t
0
to rated speed (no load) arrival time t
1
, and further to time t
2
when the system differential pressure, including nozzle differential pressure, comes to a necessary nozzle differential pressure V
1
. That is, during the time T from t
0
to t
2
, the system differential pressure does not reach the necessary nozzle differential pressure V
1
, but reaches V
2
at time t
2
to increase more thereafter. Accordingly, the nozzle differential pressure is low during the time shown by T, and if there is a head difference between the plurality of fuel nozzles, there occurs an imbalance of fuel flow rates between each of the fuel nozzles, hence the flow divider
80
is operated so that the imbalance of the fuel oil between each of the fuel nozzles may be eliminated. But this flow divider
80
has a very small gap between the inner rotational body and the stationary portion for its function, and this makes control of foreign matter difficult and has often been a cause of trouble in the fuel system.
Next, the fuel oil purge system H will be described.
FIG. 12
is a diagrammatic view of the fuel oil purge system in the prior art at the time when the gas turbine fuel is changed over. In
FIG. 12
, numeral
1
designates a flow control valve in a fuel gas system, numeral
2
designates a piping therefor, numeral
3
designates a fuel gas distributor, which distributes the fuel gas to the plurality of fuel nozzles X
1
and numeral
4
designates a plurality of pipings, which supply therethrough the fuel gas from the fuel gas distributor
3
to the respective fuel nozzles X
1
.
Numeral
11
designates a flow control valve in a fuel oil system, numeral
12
designates a piping therefor, numeral
13
designates a header, which distributes the fuel oil from the piping
12
to the plurality of fuel nozzles X
2
and numeral
14
designates a plurality of pipings, which are connected to the header
13
and supply therethrough the fuel oil distributed by the header
13
to the respective fuel nozzles X
2
. Numeral
26
designates a purging air system piping, numeral
25
designates an opening/closing valve, numeral
23
designates a drain valve piping and numeral
24
designates an opening/closing valve therefor. Combustor X comprises therein the fuel nozzles X
1
, X
2
.
In the mentioned system so constructed, while the operation is done with the fuel oil being burned, the fuel oil flowing through the flow control valve
11
and the piping
12
is distributed by the header
13
to flow through the plurality of pipings
14
to the respective fuel nozzles X
2
. The fuel oil so distributed is injected into the combustor X from the fuel nozzles X
2
for combustion.
When the operation is done with the fuel being changed over to gas from oil, the flow control valve
11
is closed and the fuel gas is led instead into the piping
2
to be supplied to the fuel nozzles X
1
through the fuel gas distributor
3
and the piping
4
. In this case, the previous fuel oil remains as it is in the pipings
12
,
14
, and this fuel oil, if left there, is carbonized to stick there, with a fear of causing blockage of the pipings and nozzles. Hence, it is necessary to remove such residual oil when the fuel is changed over to gas.
Thus, the opening/closing valve
25
is opened so that purging air
40
is led into the piping
12
from the purging air system piping
26
. The purging air
40
enters the header
13
through the piping
12
to then flow through the pipings
14
to the fuel nozzles X
2
to be blown into the combustor X. Thereby, the fuel oil which remains in the piping
12
, header
13
, pipings
14
and fuel nozzles X
2
is all discharged into the combustor X. This purging of the residual oil is done while the operation is continued with the fuel gas being supplied and burned in the combustor X. But there is a considerable quantity of such residual oil itself in the piping
12
Mitsubishi Heavy Industries Ltd.
Rodriguez William H
Thorpe Timothy S.
Wenderoth , Lind & Ponack, L.L.P.
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