Power plants – Combustion products used as motive fluid – Process
Reexamination Certificate
2000-12-05
2003-07-29
Kim, Ted (Department: 3746)
Power plants
Combustion products used as motive fluid
Process
C060S039120, C060S039182, C122S00700A
Reexamination Certificate
active
06598399
ABSTRACT:
This application claims priority under 35 U.S.C. §§119 and/or 365 to Appln. No. 100 01 997.8 filed in Germany on Jan. 19, 2000; the entire content of which is hereby incorporated by reference.
FIELD OF THE INVENTION
The present invention relates to the field of power plant technology. It concerns an integrated power plant and a method of operating such an integrated power plant.
BACKGROUND OF THE INVENTION
The present invention relates to the field of power plant technology. It concerns an integrated power plant according to the preamble of claim
1
and a method of operating such an integrated power plant.
An integrated power plant of the type referred to has been disclosed by the article by G. Bauer et al.
SUMMARY OF THE INVENTION
“Das Verbund-Kraftwerk—eine neue Variante des kombinierten Kraftwerks” [The integrated power plant—a new variant of the combined-cycle power plant], VGB Kraftwerkstechnik 73, No. 2, pp. 120-121 (1993).
A conventional coal-fired power plant (for example a hard-coal-fired power plant) essentially comprises a coal-fired steam generator, a condensing turbine and a condensate/feedwater heater. Such an exemplary coal-fired power plant forms the right-hand part of the integrated power plant
10
shown in FIG.
1
and consists of those plant parts which are designated by the reference numerals
21
to
50
(with the exception of reference numeral
43
). The thermal circuit diagram shows a water/steam circuit
49
with simple reheating (reheater
22
), a three-cylinder steam turbine
26
with a high-pressure stage
27
, an intermediate-pressure stage
28
and a low-pressure stage
29
, and regenerative heating with a condensate heater
37
and a feedwater heater
31
.
The preheated feedwater passes into the steam generator
21
. The live steam generated is delivered to the high-pressure stage
27
, is then reheated, and is then expanded in the stages
28
and
29
. The steam turbine
26
drives a generator
30
. A condenser
42
is arranged downstream of the low-pressure stage
29
of the steam turbine
26
. The resulting condensate is pumped by a condensate pump
41
through the condensate heater
37
into a feedwater tank/deaerator
33
. From there, a feedwater pump
32
pumps the feedwater through the feedwater heater
31
into the steam generator
21
.
The coal-fired steam generator
21
receives crushed coal via a mill
24
and fresh air, which is necessary for the combustion, via a forced-draft fan
36
. The resulting flue gas is cleaned after flowing through the steam generator
21
and delivered to the environment via a stack. A hot flue-gas NOx-reduction unit (high-dust DeNOx)
23
is provided as the first exhaust-gas cleaning stage. Further cooling of the flue gases is effected in an air heater
25
. Provided downstream of it is an electrostatic precipitator
34
. The induced-draft fan
35
then delivers the flue gases to a flue-gas desulfurization unit
39
. A regenerative flue-gas heater
38
may also be arranged in between.
It is essential with regard to the invention that the flue-gas temperature of such a conventional steam generator or boiler depends on the load to a very high degree, and that, at the same time, the flue-gas NOx-reduction units, frequently used nowadays, in a high-dust circuit require a certain temperature range of about 320° C. (280° C.) to 400° C. for the flue gas.
Another known type of power plant is the so-called combined-cycle power plant in which a gas-turbine set and a conventional coal-fired power plant are interconnected on the flue-gas side. In this case, the advantages of a combination of the gas-turbine cycle and the Rankine cycle are utilized by utilizing the waste heat and the residual-oxygen content of the gas-turbine exhaust gas. The gas turbine in this case is used, as it were, as a forced-draft fan for the conventionally fired steam generator. During normal operation, the gas turbine exhaust gas serves the coal firing as an oxygen carrier. If the gas turbine is shut down or has failed, the steam generator and steam turbine can continue to be operated by a back-up forced-draft fan and an adequately dimensioned steam and flue-gas air heater. Such a combined-cycle power plant is described or shown, for example, in EP-B1-0 591 163 or VGB Kraftwerkstechnik 71, No. 2, page 84 (1991).
However, on account of the type of coupling, the flue-gas-side interconnection of the gas-turbine set and the conventional coal-fired power plant in the case of the combined-cycle power plant has disadvantages, which have then led to the concept of the integrated power plant, in which the coupling between gas-turbine set with heat-recovery boiler and coal-fired power plant is restricted to the water/steam circuit. Various possibilities of this coupling between heat-recovery boiler and water/steam circuit are disclosed in the publication mentioned at the beginning.
If selective catalytic reduction (SCR), which is preferred nowadays, according to the high-dust method is now used in such an integrated power plant for the flue-gas NOx reduction of the coal-fired steam generator, care must be taken to ensure that the temperatures remain within the abovementioned temperature range of the catalyst (approx. 280° C. or 320° C. to 400° C.) even at part load. To this end, the following additional measures have been disclosed hitherto:
the economizer (for heating the feedwater) arranged upstream of the catalyst contains a bypass, so that less heat is extracted from the flue gas when required by opening the bypass;
a bypass is provided for the flue gas, via which bypass the economizer is bypassed when required and the heat extraction from the flue gas can thus be reduced;
a start-up part-load heat exchanger, which relieves the load on the economizer, is used for the feedwater heating.
These are measures which are exclusively intended to keep the flue-gas temperature (at part load) upstream of the catalyst at a high level by relieving (reducing) the flue-gas-side heat absorption in the economizer.
In principle, the load on the economizer of the steam generator may be relieved by proportional heating and evaporation of feedwater in the heat-recovery boiler in those circuit variants of the integrated power plants with (at least proportional) live-steam generation. This helps to improve a part-load behavior of the conventional steam generator with regard to the flue-gas NOx-reduction unit. However, these measures must be regarded as being restricted in their potential. There is in any case no such improvement in other circuit variants.
The object of the invention is therefore to provide an integrated power plant having a flue-gas NOx-reduction unit according to the “high-dust” method, which power plant has an improved part-load behavior with regard to the flue-gas NOx reduction irrespective of the respective coupling between heat-recovery boiler and water/steam circuit, and to specify a method of operating it.
The essence of the invention is to keep the flue-gas temperature upstream of the flue-gas NOx-reduction unit within the predetermined temperature range by specifically feeding some of the gas-turbine exhaust gas to the stream generator even at part load of the same.
The object is achieved by all the features of claims
1
and
9
together. The essence of the invention is to keep the flue-gas temperature upstream of the flue-gas NOx-reduction unit within the predetermined temperature range by specifically feeding some of the gas-turbine exhaust gas to the steam generator even at part load of the same.
A first development of the invention is characterized in that means for setting or controlling the branched-off portion of the exhaust gases coming from the gas-turbine set are provided, and in that the setting or control means comprise a damper arranged in the branch line and a damper arranged in the exhaust-gas duct leading from the heat-recovery boiler to a stack. As a result, it is possible in a simple manner, for various part-load cases, to in each case optimally set the proportion of the added gas-turbine exhaust gases with regard
Alstom (Switzerland Ltd
Burns Doane Swecker & Mathis L.L.P.
Kim Ted
LandOfFree
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