Power plants – Combustion products used as motive fluid
Reexamination Certificate
2000-06-12
2002-02-26
Koczo, Michael (Department: 3746)
Power plants
Combustion products used as motive fluid
C060S039550
Reexamination Certificate
active
06349536
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a water injection manifold device and an operation method thereof. The water injection manifold device can create a low NOx combustion by water injection into a combustor in an industrial gas turbine in the process of operation and stop thereof. The manifold device is designed particularly to have such a multifunction that water supplied into the combustor for reducing combustion temperature is prevented from coming into the gas turbine with water head existing still after a stop of the water supply. In addition, high temperature high pressure combustion gas in a turbine cylinder is prevented from coming reversely into the water injection manifold of which inner pressure is lowered by stop of water supply when dust accumulation occurs in a drain valve.
2. Description of the Prior Art
In order to realize a low NOx combustion in an oil mono-fuel combustor or an oil/gas dual-fuel combustor used in an industrial gas turbine, the flame temperature is usually reduced by mixing water into fuel or injecting water into the combustion zone.
As one example to reduce flame temperature in the oil mono-fuel combustor, the applicant here has heretofore disclosed an invention by the Japanese patent application No. Hei 11 (1999)-159756 titled, “Oil firing DLN (Dry Low NOx) combustor”.
An oil firing premix type DLN combustor in a gas turbine comprises a water injection control device for controlling the flow rate of water to be injected into fuel corresponding to fuel flow rate. A pilot fuel system and main fuel A, B systems, including a fuel flow control valve, for fuel supply and a water injection system in the main fuel A, B systems, including a water flow detector and a water injection flow control valve, are provided, and the valves are controlled via a water injection flow control circuit so as to control water injection rate.
In this control circuit, a fuel flow control signal, a water flow detected signal and planned value signals on turbine cylinder pressure and injection water supply pressure are inputted so that valve openings are computed beforehand in proportion to the oil fuel flow rate and then the values so computed are corrected by a feedback signal from the detector. Thus, the valves are controlled so that the water injection rate may be controlled quickly corresponding to the oil fuel flow rate and so that NOx quantity generated by the combustion may be reduced.
Next, NOx reduction in a diffusion type combustor of a liquid mono-fuel gas turbine or a liquid/gas dual-fuel gas turbine in the prior art will be described with reference to
FIGS. 3
to
5
.
FIG. 3
is a partial view of the gas turbine having a water injection manifold in the prior art, wherein an upper half of
FIG. 3
shows a cross sectional view and a lower half thereof shows an outside side view. In
FIG. 3
, there is provided a water injection manifold
2
formed by a master pipe in an annulus of 5 to 6 m diameter surrounding a turbine cylindrical body near a plurality of combustors
1
. The combustors
1
are arranged in ten to twenty or more pieces thereof in the turbine circumferential direction. In operation, water is injected into flames in each of the combustors
1
so as to lower combustion temperature thereby to reduce NOx generation in the combustor
1
.
FIG. 4
is a block diagram of the water injection manifold
2
. As shown there, a water supply pipe
3
is connected to the water injection manifold
2
. A compressed air pipe
4
is connected directly to the water supply pipe
3
, and a drain pipe
5
and a plurality of branch pipes
6
are also connected to the water supply pipe
3
via the water injection manifold
2
. The water supply pipe
3
is for supplying therethrough a high pressure water of as a high pressure as 53 to 70 kg/cm
2
g, which is a total nozzle differential pressure of about 40 to 50 kg/cm
2
g for water holes
16
of small diameter, to be described later with respect to
FIG. 6
, and combustion gas pressure of 13 to 20 kg/cm
2
g in the combustor
1
and in the turbine cylinder. By such arrangement, water is injected from the water injection manifold
2
into flames in the combustor
1
so as to lower an adiabatic flame temperature thereby to reduce the NOx quantity in the combustion gas, as mentioned above, and while the gas turbine is stopped, the water in the water injection manifold
2
is drained.
A water injection pump
7
, a flow control valve
8
and a shut-off valve
9
are interposed in the water supply pipe
3
. A sweep air supply valve
10
and a check valve
11
are interposed in the compressed air pipe
4
so that compressed air may be supplied through the compressed air pipe
4
as sweep air for preventing clogging of the water holes.
The drain pipe
5
, being interposed with a drain valve
12
on the way, is connected to a lower end portion of the water injection manifold
2
so that water in the water injection manifold
2
may be drained when no water injection into the combustor
1
is needed.
Between the water injection manifold
2
and each of the combustors
1
, there is provided the branch pipe
6
of at least ten mm diameter with neither a valve or similar item being specifically interposed therein.
As may be understood by the description of an injection nozzle
17
with respect to
FIG. 6
, when an oil firing operation is stopped, fuel oil may trail down on the injection nozzle
17
to the water holes
16
to be carbonized under a high temperature environment there, which may result in causing a clogging of the water holes
16
. Hence, in order to prevent the clogging, when the oil firing operation is stopped, the sweep air supply valve
10
is opened so that the fuel oil which has so trailed to the water holes
16
may be blown off into the combustor
1
.
Usually, in the prior art water injection device as mentioned above, operation is done such that when the gas turbine is ignited, the water injection is started at no load or at a certain low load and the water supply is increased as the load is increased thereby to lower the gas turbine adiabatic flame temperature and to make the outlet NOx quantity as low and as uniform as possible, because the NOx quantity is increased as the adiabatic flame temperature becomes higher.
On the other hand, when the gas turbine is stopped, as the load is lowered from the full load, the water supply is reduced. As soon as the fuel is stopped, the drain valve
12
is opened so that water remaining in the water injection manifold
2
may be drained instantly by the pressure of 6 to 10 kg/cm
2
g of the combustion gas remaining in the combustor
1
and turbine cylinder.
FIG. 5
is a graph showing examples of liquid fuel heat input and gas fuel heat input according to load state in the gas turbine of FIG.
3
. The above operation of the water injection device will be described with reference to FIG.
5
.
In case the gas turbine is operated from no load at the time of ignition to the full load by oil firing only, as shown by the rightward arrow along the horizontal axis, the water supply is increased from point a at no load to point e at the full load as the liquid fuel heat input is increased. In other words, the water supply is increased as the oil firing load is increased, like a→b→c→d→e. If the load is lowered from the full load, as shown by the leftward arrow along the horizontal axis, the water supply is reduced as the load decreases, like e→d→c→b→a.
Also, if the gas turbine is operated by oil and gas firing, (i) as one case, the gas firing operation is done from no load to a certain load, for example B load, and then the operation is changed to the oil firing up to the full load, that is, the water supply is increased as the load is increased, like g→h→i. If the load is lowered from the full load to no load, i→h→g, the oil fuel heat input is first reduced so that the load is lowered from the full load to B load, then the gas fuel heat input is reduced so that the lo
Koczo Michael
Mitsubishi Heavy Industries Ltd.
Wenderoth , Lind & Ponack, L.L.P.
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