Power plants – Combustion products used as motive fluid – Process
Reexamination Certificate
2001-01-12
2002-09-17
Casaregola, Louis J. (Department: 3746)
Power plants
Combustion products used as motive fluid
Process
C060S039182, C060S039500
Reexamination Certificate
active
06449954
ABSTRACT:
BACKGROUND
1. Field of the Invention
The present invention relates to the field of combined cycle power stations (combined plant). It relates to a process for the recovery of water which arises in a combined plant, and also to a combined cycle power station.
2. Related Art
Combined cycle power stations normally burn natural gas, which produces water vapor during combustion. 1 kg of natural gas burns to about 2 kg of water and also CO
2
. The flue gas with the water contained therein is usually discharged through a chimney at elevated temperatures, without the water being used to advantage. The same also holds for water or steam, which in other cases is injected or sprayed in during combustion and thus becomes a component of the flue gas. On the other hand, water already forms an increasingly valuable resource at the present time.
The simplified diagram of an exemplary combined cycle power station from the state of the art is reproduced in FIG.
1
. The combined cycle power station
10
essentially comprises a gas turbine plant
11
, a waste heat boiler (heat recovery steam generator HRSG)
33
, and a steam turbine
25
, which are connected together. The gas turbine plant
11
consists of a compressor
14
and a turbine
17
, which are arranged on a rotor
16
, and also a combustion chamber
15
. In operation, the compressor
14
sucks in air through an air inlet
12
, compresses it, and delivers the compressed air to the combustion chamber
15
, where it enters combustion as combustion air, together with a liquid or gaseous fuel
19
(e.g., natural gas) which is fed in through a fuel supply duct
21
. In addition, water or steam
36
can be injected or sprayed into the combustion chamber
15
to reduce the combustion temperature. The hot combustion gases are conducted from the combustion chamber
15
into the turbine
17
, where they set the rotor
16
in rotation. The flue gas
42
exiting the turbine
17
is then conducted through the waste heat boiler
33
for the production of steam, where it flows in succession through a superheater
40
, an evaporator
39
, and a preheater (economizer)
34
, and gives up heat stepwise. The cooled flue gas
42
finally leaves the waste heat boiler
33
and is usually, possibly after a flue gas cleaning, discharged from a chimney.
The superheater
40
, evaporator
39
and preheater
34
are connected in series as part of a water/steam circuit, in which the steam turbine is also connected. The exhaust steam from the steam turbine
25
passes into a condenser
26
and condenses there. The condensate is pumped by a condensate pump
28
, possibly with the addition of additional water
27
, through a feed water duct
29
to a feed water container
30
with degasser. The degassed condensate is then pumped as feed water
32
through the preheater
34
by a boiler feed pump
31
, and as pressurized feed water
35
to a steam drum
37
with the connected evaporator
39
. The steam then passes to the superheater
40
, where it is superheated, and finally drives the steam turbine
25
as superheated steam
41
. Both the steam turbine
25
and also the gas turbine plant
11
respectively drive a generator
13
or
24
which produces electrical current. Means for the recovery of water or water vapor contained in the flue gas are not provided here.
SUMMARY OF THE INVENTION
The invention therefore has as an object to provide a process and also a combined cycle power station with which the water contained in the flue gas is recovered and can be advantageously reused.
An aspect of the invention involves configuring the combined cycle power station and conducting the process so that the water is condensed out of the flue gas after leaving the waste heat boiler and is separated in liquid form.
A first preferred embodiment of the process according to the invention is characterized in that the flue gas is expanded for condensing the water out, with output of work. The expansion is preferably carried out by means of a utilization turbine. In particular, the waste heat boiler is operated for this purpose at a pressure exceeding the ambient air pressure by several bar, preferably 2-5 bar, and the flue gas is brought to the ambient air pressure by the subsequent expansion. Alternatively to this, the waste heat boiler can be operated at about the ambient pressure with respect to the flue gas, the flue gas subsequently being expanded into a vacuum, and the flue gas being compressed again to ambient air pressure after the separation of water. In both cases, the water is separated from the flue gas particularly during the expansion or in the utilization turbine itself, and/or in a droplet separator following the expansion or the utilization turbine.
A second preferred embodiment of the process according to the invention is characterized in that the waste heat boiler is operated with respect to the flue gas at a pressure exceeding the ambient air pressure by several bar, preferably 2-5 bar, in that the water is condensed out of the flue gas on cold surfaces after leaving the waste heat boiler, in particular on the cold tubes of a heat exchanger, and in that the dewatered flue gas is brought to the ambient air pressure by a subsequent expansion; here also, the expansion is preferably carried out by means of a utilization turbine.
A preferred embodiment of the combined cycle power station according to the invention is distinguished in that the means for condensation and separation comprise means for the expansion of the flue gas, preferably in the form of a utilization turbine.
A first development of this embodiment is characterized in that the expansion means or the utilization turbine is followed by a droplet separator.
A second development of this embodiment is characterized in that the expansion means comprises a utilization turbine working in vacuum, and that a compressor follows the utilization turbine.
A third development of this embodiment is characterized in that condensation means, particularly in the form of a heat exchanger, is arranged between the waste heat boiler and the expansion means.
REFERENCES:
patent: 4434613 (1984-03-01), Stahl
patent: 5761896 (1998-06-01), Dowdy et al.
patent: 5771678 (1998-06-01), Shouman
Alstom (Switzerland Ltd
Burns Doane Swecker & Mathis L.L.P.
Casaregola Louis J.
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