Power plants – Combustion products used as motive fluid – Multiple fluid-operated motors
Reexamination Certificate
2000-09-07
2002-06-18
Casaregola, Louis J. (Department: 3746)
Power plants
Combustion products used as motive fluid
Multiple fluid-operated motors
C122S00700A
Reexamination Certificate
active
06405525
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the field of power plant technology. It concerns a combination power plant with an injection device for injecting water into the live steam according to the preamble of claim
1
. Such a combination power plant is known, for example, from applicant's document DE-A1-195 45 668.
BACKGROUND OF THE INVENTION
In combined gas/steam power plants or combination power plants in which the hot waste gases of one or more gas turbine(s) are used to generate steam in the water/steam cycle of one or more steam turbine(s), the steam temperature depends greatly on the load of the gas turbine(s) and the environmental conditions. In order to be able to flexibly adapt the steam temperature of the live steam to the requirements of the steam turbine(s), water—if necessary—is injected into the live steam, so that the temperature of the live steam may be reduced, more or less, as needed. The simplified schematic of such an (exemplary) combination power plant as currently used is shown in FIG.
1
. The combination power plant
10
comprises a gas turbine system
11
(shown for simplicity's sake as a function block), a steam turbine
13
with high pressure stage
14
, medium pressure stage
15
, and low pressure stage
16
, a waste heat steam generator
25
with various evaporation and heat exchanger devices, a feed water container
18
, and a condensation device
17
(also shown only as a function block). In the example, the gas turbine system
11
and the steam turbine
13
drive a common generator
12
. The waste heat steam generator
25
of the example comprises three evaporators, i.e. a low pressure evaporator
27
, a medium pressure evaporator
30
, and a high pressure evaporator
34
. Each of the three evaporators
27
,
30
,
34
adjoins a corresponding steam drum, i.e. a low pressure steam drum
28
, a medium pressure steam drum
31
, and a high pressure steam drum
35
, from which the condensate in each case is pumped by means of recirculation pumps
40
,
41
, and
42
to the adjoining evaporator. Hot waste gases that are discharged from the gas turbine system
11
(arrows in
FIG. 1
) flow through the waste heat steam generator
25
from the bottom to the top. At the cold, upper end of the waste heat steam generator
25
, a low pressure preheating stage (low pressure economizer)
26
is provided. Between the evaporators
27
and
30
is a medium pressure preheating stage (medium pressure economizer)
29
. A high pressure preheating stage (high pressure economizer)
32
is located between evaporators
30
and
34
. Also located between evaporators
30
and
34
is a medium pressure superheater
33
. And finally, at the hot, lower end of the waste heat steam generator
25
, a high pressure superheater
37
and an intermediate superheater (“reheater”) are provided. The internal construction of waste heat steam generator
25
is therefore similar to the one in U.S. Pat. No. 5,647,199. The function of the system according to
FIG. 1
can be described as follows: Feed water is pumped from the feed water container
18
via one of two possible ways by a first feed water pump
19
through a first feed water line
21
to the waste heat steam generator
25
, and is heated there consecutively in preheating stages
26
,
29
, and
32
. The preheated feed water flows into the high pressure steam drum
35
, and is evaporated in the connected high pressure evaporator
34
. The resulting steam from high pressure steam drum
35
is superheated in the following superheater
37
, and is fed as live steam via a live steam line
51
to the high pressure stage
14
of the steam turbine
13
. After flowing through the high pressure stage
14
, additional steam from the medium pressure steam drum
31
that has been superheated in the superheater
33
is added to this steam before it is reheated in the intermediate superheater
36
, and it is then passed via a hot steam line
52
to the medium pressure stage
15
. The medium pressure steam drum
31
is hereby supplied by a second feed water pump
20
via a second feed water line
22
with feed water that is preheated in the two preheating stages
26
and
29
. The low pressure steam drum
28
is also supplied by the second feed water line
22
with feed water that is preheated in the first preheating stage
26
. The steam from the low pressure steam drum
28
is supplied via the medium pressure steam line to the medium pressure stage
15
of the steam turbine
13
. After the steam has consecutively passed through the medium pressure stage
15
and the low pressure stage
16
, it is condensed in an condensation device
17
, and the condensate pumped back into the feed water container
18
. As previously mentioned, the temperature of the steam in the live steam line
51
and hot steam line
52
depends greatly on the discharge temperature of the gas turbine system
11
. To make it possible that the steam temperature can be changed without intervening in the operation of the gas turbine system
11
, injection devices
38
and
39
that can be used to inject water into the steam and thus to reduce the steam temperature have been provided in each of lines
51
and
52
. The injection devices
38
and
39
receive their water via corresponding supply lines
23
and
24
from the feed water lines
21
and
22
, in which the required injection pressure is already present due to the feed water pumps
19
,
20
.
During operation of the system, it may occur that—in order to improve the start-up behavior—the steam temperature is adjusted down in a controlled manner at certain time intervals by injecting water, while no water needs to be injected at other time intervals. This means that the injection devices
38
,
39
are only required intermittently. This operation results in high loads due to alternating stresses within the injection devices
38
,
39
installed in the hot steam stream. During injection operation they are brought to a temperature close to that of the injected water which, in order to have a sufficient initial pressure (see
FIG. 1
) is removed directly from the (approximately 60° C. cool) feed water. In contrast, the injection devices
38
,
39
are brought to steam temperature between the periods of the injection operation, whereby said steam temperature can easily be above 500° C. and up to 600° C. in modern systems. These thermal and thermo-mechanical alternating stresses can result in premature breakage of components of the injection devices. In principle, the situation could be somewhat improved if preheated water were removed for injection from the preheating stages
26
,
29
,
32
of the waste heat steam generator
25
. But with this procedure, the water in supply lines
23
,
24
also remains cold in most cases until it reaches injection devices
38
,
39
, since the lines are not located within the warm waste gas stream. This means that at the beginning of the injection process, first cold water flows through the injection devices
38
,
39
and results in thermal stresses. Although the extent and duration of these stresses are limited, they are large enough to pose a serious risk of breakage.
DESCRIPTION OF THE INVENTION
It is therefore the objective of the invention to modify a combination power plant of the above-mentioned type in such a way that the described disadvantages are avoided, and, in particular, so that the thermal stresses in the injection device(s) are reduced to such an extent that breakage due to alternating stresses can be largely avoided. This objective is realized with the entirety of the characteristics of claim
1
. The core of the invention is that the mechanical stresses induced by temperature differences are reduced to a harmless level by preheating the injection water or maintaining its temperature up to a short distance from the injection devices or injection nozzles. A first preferred embodiment of this combination power plant according to the invention is characterized in that the steam turbine comprises a high pressure stage and a medium pressure stage, that t
Droux Francois
Froehlich Ursula
Krieg Hansueli
Mueller Peter
Reinhard Jurgen
Alstom
Burns Doane Swecker & Mathis L.L.P.
Casaregola Louis J.
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