U.S. patent application number 09/255712 was filed with the patent office on 2001-11-22 for method for operating a power plant including a co2 process.
Invention is credited to FRUTSCHI, HANS ULRICH, WETTSTEIN, HANS.
Application Number | 20010042367 09/255712 |
Document ID | / |
Family ID | 8235964 |
Filed Date | 2001-11-22 |
United States Patent
Application |
20010042367 |
Kind Code |
A1 |
FRUTSCHI, HANS ULRICH ; et
al. |
November 22, 2001 |
METHOD FOR OPERATING A POWER PLANT INCLUDING A CO2 PROCESS
Abstract
In a method for operating a power plant by means of a CO.sub.2
process, isentropic compression first takes place, subsequently an
isobaric heat supply, then isentropic expansion, and finally
isobaric heat discharge. The CO.sub.2 process broken down here
takes place with internal combustion, a fuel (21) and the oxygen
(18) necessary for oxidization being supplied. After the charging
of the CO.sub.2 circuit (23) has been carried out, the excess
CO.sub.2 formed from combustion is discharged continuously, in that
this gas is led through a cooler (14), in which said gas is
condensed. In order to dispose of this condensed CO.sub.2 (15),
there are available here, for example, the possibilities of storing
this CO.sub.2 on the ocean floor or of introducing the condensed
CO.sub.2 into a worked-out deposit of natural gas.
Inventors: |
FRUTSCHI, HANS ULRICH;
(RINIKON, CH) ; WETTSTEIN, HANS; (FISLISBACH,
CH) |
Correspondence
Address: |
BURNS DOANE SWECKER & MATHIS L L P
POST OFFICE BOX 1404
ALEXANDRIA
VA
22313-1404
US
|
Family ID: |
8235964 |
Appl. No.: |
09/255712 |
Filed: |
February 23, 1999 |
Current U.S.
Class: |
60/772 |
Current CPC
Class: |
Y02E 20/34 20130101;
Y02E 20/344 20130101; Y02T 10/12 20130101; Y02T 10/16 20130101;
F02C 1/10 20130101; F01K 21/047 20130101; F01K 21/042 20130101 |
Class at
Publication: |
60/39.02 |
International
Class: |
F02C 007/00 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 25, 1998 |
EP |
98 810 154.9 |
Claims
What is claimed as new and desired to be secured by Letters Patent
of the United States is:
1. A method for operating a power plant by means of a CO.sub.2
process, the method consisting of isentropic compression, isobaric
and/or isochoric heat supply, isentropic expansion and isobaric
and/or isochoric heat discharge, wherein the CO.sub.2 process is
operated with internal combustion, and wherein, in addition to a
fuel (21), the oxygen (18) necessary for oxidation is also
supplied.
2. The method as claimed in claim 1, wherein, in cooperation with
the process, excess water (25) and CO.sub.2 (15) are condensed out
and are separated from the process.
3. The method as claimed in claims 1 and 2, wherein the degree of
charging of the process and, consequently, its power are regulated
by the separation of CO.sub.2 at an appropriate rate.
4. The method as claimed in claim 1, wherein the power plant is
started up by the connection of an air startup flap (7) acting
upstream of compression.
5. The method as claimed in claim 2, wherein a CO.sub.2 part
quantity extracted from the process is condensed out in a cooler
(14).
6. The method as claimed in claim 5, wherein parasitic gases (16)
occurring in the process are separated out from the cooler (14)
downstream of the latter.
7. A setup for carrying out the method as claimed in one or more of
claims 1-6, the power plant being capable of being operated by
means of a circulation gas, wherein the power plant consists of a
gas turbine with a closed or quasi closed circuit, and wherein the
gas turbine has at least one compressor unit (1), one combustion
chamber (3), one turbine (2) and one generator (4).
8. The setup as claimed in claim 7, wherein the compressor unit (1)
has at least one intermediate cooler (28).
9. The setup as claimed in claim 7, wherein the compressor unit (1)
has means for isothermal cooling.
10. The setup as claimed in claims 5 and 7, wherein the cooler for
condensing out the CO.sub.2 is arranged on the outflow side of the
compressor unit.
11. The setup as claimed in claim 7, wherein a cooler or heat
exchanger (24) for separating a water quantity (25) occurring in
the process is arranged on the outflow side of the turbine.
12. The setup as claimed in one of claims 7-11, wherein at least
one steam circuit (31, 34, . . . ) operated in cooperation with the
exhaust gases from the turbine is arranged on the outflow side of
the gas turbine.
13. The setup as claimed in claim 12, wherein the steam circuit
consists at least of a waste-heat steam generator (31) and at least
one steam turbine (32).
14. The setup as claimed in one of claims 7-13, wherein the gas
turbine is based on sequential firing.
15. The setup as claimed in claim 14, wherein the gas turbine
consists of a compressor unit, of a first combustion chamber acting
downstream of the compressor unit, of a first turbine acting
downstream of the first combustion chamber, of a second combustion
chamber acting downstream of the first turbine and of a second
turbine acting downstream of the second combustion chamber, and
wherein the second combustion chamber is designed as a
spontaneously igniting combustion chamber.
16. The setup as claimed in claim 15, wherein the turbomachines are
arranged on a common rotor shaft.
17. The setup as claimed in claim 15, wherein the second combustion
chamber is equipped with vortex-generating elements.
18. A setup for carrying out the method as claimed in one or more
of claims 1-6, the power plant being capable of being operated by
means of a circulation gas, wherein the power plant consists of at
least one combustion chamber (3), one turbine (2) and one generator
(4), wherein a water pump (58) compresses the circulation gas (23)
in cooperation with an injector (60), wherein a recuperator (64) is
arranged on the outflow side of the turbine, wherein the compressed
circulation gas (63) flows through the recuperator, and wherein a
quantity of circulation gas (67) is separated and can be condensed
out upstream of the recuperator.
19. The setup as claimed in claim 18, wherein the water pump (58)
is driven by the turbine (2).
20. The setup as claimed in claim 18, wherein the circulation gas
can be compressed isothermally by a water atomization device, in
that this water atomization device mixes the circulation gas to be
compressed with atomized water drops, so that a water/circulation
gas mixture is obtained, wherein this water/circulation gas mixture
enters a chamber, in which the water is separated from the
compressed circulation gas, and wherein this circulation gas can be
supplied through a further duct directly or indirectly to the
combustion chamber (3).
21. The setup as claimed in claim 20, wherein the water atomization
device is a high-pressure water injector.
22. A setup for carrying out the method as claimed in one or more
of claims 1-6, the power plant being capable of being operated by
means of a circulation gas, wherein the power plant is a piston
engine (69/70) capable of being operated by spontaneous or spark
ignition.
23. The setup as claimed in claim 22, wherein the piston engine is
a four-stroke internal combustion engine.
24. The setup as claimed in claim 22, wherein the circulation gas
can be extracted, as required, from a storage volume (71).
25. The setup as claimed in claim 22, wherein the excess
circulation gas can be extracted from the cycle (80) at a suitable
point for further condensation.
26. The setup as claimed in claim 7, 18 or 22, wherein the charging
pressure of the power plant can be regulated by an appropriate
metering of the extraction of the excess circulation gas.
27. The method as claimed in claim 1, wherein the compression and
expansion developed quasi-insentropic.
28. The setup as claimed in claim 9, wherein the cooling developed
quasi-isothermal.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a method for operating a
CO.sub.2 plant according to the preamble of claim 1. The invention
also relates to setups for carrying out this method.
[0003] 2. Discussion of Background
[0004] Internal combustion engines burn their fuel in compressed
atmospheric air and mix their combustion gases intimately with this
air and with the residual oxygen which has not been utilized. At
the same time, the fuels, which almost always contain carbon,
generate, inter alia, CO.sub.2 which is a greenhouse gas. Extended
use of fossil fuels nowadays releases CO.sub.2 quantities which are
internationally recognized as a risk to the world climate. An
intensive search for CO.sub.2-free technologies is therefore
already in progress.
[0005] The supply of energy is, at the present time, determined by
the use of fossil fuel energies in internal combustion engines, the
highly diluted CO.sub.2 being disposed of into the atmosphere.
[0006] It would be obvious to separate the CO.sub.2 from the
exhaust gases and dispose of it by condensation, separation and
sealing it off from the atmosphere. However, the large volume flow
makes it impossible to put such a procedure into practice.
[0007] Another known possibility is for cooled exhaust gases to be
recirculated into the intake of internal combustion engines. This
can be carried out to such an extent that the oxygen in the air is
just used up. In this case, however, the exhaust gas still remains
mixed with the atmospheric nitrogen and the CO.sub.2 separation
problem is therefore only marginally reduced.
[0008] Furthermore, all air-operated internal combustion engines
also generate nitric oxides which act as air pollutants and the
production of which requires costly measures to combat it.
SUMMARY OF THE INVENTION
[0009] Accordingly, one object of the invention, as defined in the
claims, is to provide a novel method and a setup of the type
initially mentioned, to dispose in an environmentally friendly way
of the CO.sub.2 which occurs, and, at the same time, here, the
object of the invention is to eliminate the atmospheric nitric
oxides which likewise occur.
[0010] The essential advantages of the invention are to be seen in
that a method is proposed here, in which the CO.sub.2 is discharged
in pure form and under pressure for the purpose of subsequent
condensation.
[0011] In this case, the method proceeds from a CO.sub.2 process
with internal combustion, in which, in order to heat the CO.sub.2
mass located in the circuit, said heating preferably being carried
out by means of a gaseous fuel, only that necessary oxygen quantity
which is required for oxidizing this very fuel is supplied.
[0012] The degree of charging and, consequently, the power of the
process can be regulated continuously by means of an appropriate
extraction of CO.sub.2 from the circuit at a suitable point.
[0013] Subsequently, by condensing out the CO.sub.2 separated from
the process, that state of aggregation of this gas is then brought
about, at which the CO.sub.2 occurring can easily be disposed of in
an environmentally friendly way, particularly as regards the
greenhouse problem.
[0014] Another essential advantage of the invention is to be seen
in that the method can be carried out by means of several types of
gas turbine setups, the setup described in each case constituting a
specific optimum solution as a function of the predetermined
parameters.
[0015] Another essential advantage of the invention is to be seen
in that it provides a remedy against the fact that all
air-breathing internal combustion engines also generate nitric
oxides which act as air pollutants and the production of which
requires costly measures to combat it, not least in light of the
internationally restrictive laws on permissible pollutant
emissions. Since no atmospheric nitrogen enters the flame in the
recirculation mode with pure oxygen, NO.sub.x is also not
generated. Admittedly, if the fuel carries bound nitrogen with it,
a slight formation of NO.sub.x must be expected. However, since the
excess gas represents a much smaller quantity than the exhaust gas
in the air mode, its retreatment is simpler and less expensive.
[0016] Advantageous and expedient developments of the solutions
according to the invention for achieving the object are defined in
the further claims.
[0017] Exemplary embodiments of the invention are explained in more
detail below with reference to the drawings. All the features not
essential for an immediate understanding of the invention have been
omitted. Identical elements are given the same reference symbols in
the various figures. The direction of flow of the media is
indicated by arrows.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] A more complete appreciation of the invention and many of
the attendant advantages thereof will be readily obtained as the
same becomes better understood by reference to the following
detailed description when considered in connection with the
accompanying drawings, wherein:
[0019] FIG. 1 shows a gas turbine with a closed circuit, with heat
exchangers for the separation of water and CO.sub.2,
[0020] FIG. 2 shows a gas turbine according to FIG. 1 with
additional compression intermediate cooling,
[0021] FIG. 3 shows a gas turbine with a closed circuit and with a
steam circuit,
[0022] FIG. 4 shows a setup according to FIG. 3 with additional
compression intermediate cooling,
[0023] FIG. 5 shows a setup according to FIG. 3, a plurality of
steam turbines being integrated into the steam circuit,
[0024] FIG. 6 shows a setup according to FIG. 4, a plurality of
steam turbines being integrated into the steam circuit,
[0025] FIG. 7 shows a further gas turbine setup with a plurality of
recuperators and intermediate coolers,
[0026] FIG. 8 shows a gas turbine process with an isothermal
compressor and with recuperation,
[0027] FIG. 9 shows a piston engine process with a final purpose
according to one of the preceding setups.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0028] Referring now to the drawings, wherein like reference
numerals designate identical or corresponding parts throughout the
several views, FIG. 1 shows a gas turbine with a closed circuit.
This gas turbine or gas turbo set consists, in terms of assemblies,
of a compressor unit 1, of a generator 4 coupled to this compressor
unit, of a turbine 2 coupled to the compressor unit and of a
combustion chamber 3 acting between the compressor unit 1 and
turbine 2. The turbomachines 1 and 2 can be coupled by means of a
common shaft 5. The circuit medium 6, which is sucked in by the
compressor unit 1 and which is predominantly CO.sub.2, flows, after
compression has taken place, into the combustion chamber 3, in
which the heat treatment of this medium is carried out, said medium
then acting as hot gases 10 on the turbine 2. For startup, the
compressor unit 1 may also, via a starting flap 7, suck in air 8,
the nitrogen of which is discharged successively via an outlet flap
40 as said nitrogen is displaced by CO.sub.2 which occurs. Whilst,
after compression, the main fraction of the compressed circulation
gas 9 is supplied to the combustion chamber 3, as already stated, a
first secondary stream 11 is introduced as a coolant into the
cooling paths of the assemblies to be cooled. Here, in this setup,
the combustion chamber 3 and turbine 2 are the components primarily
to be cooled, and cooling can be carried out in closed and/or open
flow paths. A second secondary stream 12 of the order of magnitude
of 4-8% of the entire compressed circulation gas is additionally
branched off. In this case, this compressed CO.sub.2 has the
pressure which is necessary for condensation. Via a valve 13, which
performs the function of an excess gas valve, this CO.sub.2
fraction is discharged from the closed circuit. This circulation
gas consists predominantly of CO.sub.2, but may possibly also
contain parasitic gases which have been entrained with the oxygen
and fuel and, during startup, with air, as well as transformation
products of said gases, for example NO.sub.x. After the CO.sub.2
has condensed in a cooler 14, this condensed CO.sub.2 mass flow 15
is discharged in order to be disposed of, for example and/or
preferably on the ocean floor or into a worked-out deposit of
natural gas.
[0029] This disposal at a suitable location by suitable means
constitutes a quick and lasting solution to the problem of the
greenhouse effect caused by the constant emission of gaseous
CO.sub.2 into the atmosphere. In addition, the parasitic gases are
likewise separated in cooperation with said cooler 14, and this
very small mass flow 16 may be subjected to further separation or
be discharged into the atmosphere. As regards the operation of the
combustion chamber 3, the oxygen quantity 18 produced in an air
separation plant 17 is recompressed in a compressor 19 and
introduced via a regulating member 20 to the combustion chamber 3.
In parallel with this, a fuel 21, which is appropriately
coordinated via a regulating member 22 and which is preferably
natural gas, or else other hydrocarbons or CO or mixtures of these,
also flows into the combustion chamber 3, the heat treatment of the
compressed circulation gas 9 being carried out by means of the
added oxygen quantity 18. The hot gas coming from the combustion
chamber is subsequently expanded into the downstream turbine 2. In
respect of the closed circuit shown here, the exhaust gases 23
flowing out of the turbine 2 are led through a heat exchanger 24
before being supplied once again for the compression which has
already been described. The water 25 which occurs is separated from
this heat exchanger 24 via a regulating member 26.
[0030] The setup shown here is, strictly, a quasi closed circuit
which is designed to be pressure resistant, vacuum resistant
circuit routing also being possible in various operating modes. By
the excess gas valve 13 being throttled or opened, the circuit is
charged or discharged automatically, the circulating mass flow and
the power increasing correspondingly. When this valve 13 is opened,
the pressure in the circuit falls, and the vacuum may be generated
in the return. The plant has approximately constant efficiency in
the entire pressure mode, that is to say in a design pressure range
with respect to the return of 0.5 to 5 bar in the power range of
10-100%. In the lower pressure range, the condensation temperature
in the heat exchanger 24 falls, thus also causing the efficiency to
rise slightly. The undesirable power losses which are known from
stationary gas turbines and which occur with an increasing
installation height and an increasing intake temperature are
thereby avoided. If the plant is possibly operated with the excess
being discharged into the atmosphere, overall efficiency is further
improved by also utilizing its excess pressure in a turbine with
additional power output. In this respect, reference is made in
detail to the description of the following figures.
[0031] FIG. 2 differs from FIG. 1 in that, here, one or more
intermediate cooling stages are carried out in cooperation with
compression. Such intermediate cooling stages during compression
are considered to be process improvements which are provided for
the purpose of an efficiency rise and/or a power increase. In this
case, intermediate cooling results in a flattening of the
efficiency curve and is particularly useful in plants with high
pressure ratios. The intermediate cooling illustrated here is the
simplest possible setup, in that the circulation medium 6 to be
compressed flows, downstream of a first precompressor stage 1a/27,
through an intermediate cooler 28. The intermediately compressed
and cooled medium 29 is subsequently finish compressed in a second
compressor stage 1b. This intermediate cooling may also be designed
in such a way that a condensed part quantity 30 of the CO.sub.2 can
already be discharged here. Further intermediate cooling, which
results in a considerable rise in the efficiency of the plant and
better condensing-out of the CO.sub.2 to be discharged, can be
achieved by aiming for isothermal or quasi-isothermal cooling in
the region of the compression process. For this purpose, water
injections are carried out in the compressor, these being arranged
in each case in the plane of the guide blading and extending over
the entire height of the compressor duct through which the flow
passes. This measure makes it possible to dispense with additional
components having pressure losses, this precaution resulting in the
possibility of injecting the water according to the particular
flow. These water injections are maintained, in terms of quantity,
in such a way that water is added in each case to the compression
process only to an extent such that the steam/CO.sub.2 mixture
which occurs does not exceed the water saturation line during
compression, and that the intermediately compressed CO.sub.2 is
cooled down until at least all the injected water condenses out
and, after being purified, can be used again as injection water.
This procedure makes it possible to have virtually no water
consumption. The remaining method steps of this setup according to
FIG. 2 correspond to the statements made with regard to FIG. 1.
[0032] FIG. 3 shows a gas turbo set with a steam circuit. Here too,
an essential feature of this setup is that the gas turbo set
operates in a closed circuit. The exhaust gases 23 from the turbine
2 flow through a waste-heat steam generator 31, in which the
counterflow of a water quantity 33 provided by a feed pump
generates a steam quantity 34 which is used mainly for acting on a
steam turbine 32. The expanded steam is subsequently introduced via
a regulating member 36 into the combustion chamber 3, and, if
required, a part quantity 37 of this expanded steam is branched off
downstream of said regulating member 36 and introduced into the
turbine 2. This introduction is preferably employed for cooling the
parts of this turbomachine which are subjected to high thermal load
and is then fed into the flow. The turbine power thereby rises, and
the circulation gas, here CO.sub.2, additionally enriched with
steam, generates additional steam, with the result that the power
density, in turn, rises sharply. Finally, if the entire steam 34
from the waste-heat steam generator 31 is injected into said
assemblies of the gas turbo set, there is in the end no need for
said steam turbine 32, and the plant becomes simpler and more
cost-effective, with an efficiency which is only a few percentage
points lower. Reference is made here, in particular, to setups with
STIG. At the same time, the efficiency can be further improved if
the steam in the waste-heat steam generator 31 is generated at as
high a pressure as possible and is discharged via a steam turbine
with power output to the main shaft 5 of the gas turbo set or to a
separate generator not illustrated in any more detail. Such a setup
is shown and described in more detail with reference to FIGS. 5 and
6. A part quantity 39 of the circulation gas 38 cooled in the
waste-heat steam generator 31, said part quantity being regulated
via an outlet flap 40, is branched off upstream of the heat
exchanger 24 belonging to the closed or quasi closed circuit.
[0033] FIG. 4 starts from a basic setup according to FIG. 3 and, as
regards intermediate cooling in the region of the compressor unit
1, follows FIG. 2. The statements made in respect of the two
figures mentioned are also applicable here and are an integral part
of this FIG. 4.
[0034] FIG. 5 is based closely on FIG. 3, here the steam turbine
41, operating in cooperation with the waste-heat steam generator
31, being coupled to the main shaft 5 of the gas turbo set, the
power output taking place directly. The steam 42 expanded from this
steam turbine 41 is introduced (reference 44) via a regulating
member 43 into the combustion chamber 3 and/or into the turbine 2.
The power density thereby rises sharply. This steam may, of course,
also be introduced at other locations in the circuit of the gas
turbo set. Furthermore, it is possible, by means of this steam 42,
for those parts of said assemblies 2/3 which are subjected to high
thermal load to be cooled in the closed and/or open flow path. In
this case, it must be said that the steam 34 can be generated
directly at the necessary pressure or else can be expanded to a
higher pressure and then, via the regulating member 43 already
mentioned or correspondingly via the steam turbine 41, to the
pressure level required for injection. The setup shown here has,
for the charged mode, additional extraction of an exhaust gas
quantity 47 from the waste-heat steam generator 31 and extraction
of a further exhaust gas quantity 45 downstream of the waste-heat
steam generator 31. Both exhaust gas quantities 45/47 act on an
expander 46 and, after this, are discharged 48, their reuse being
ensured specifically in each individual case. For example, an
optimum pressure for charging the circuit can be set via this
expander 46, and, in such a case, quantity regulation must be
provided. By means of this pressure regulation, if required,
interdependent regulation of the pressure of the main steam
quantity 34 can also be achieved.
[0035] The setup just described may also be designed along the
lines of a combined plant, the gas turbine circuit shown according
to this FIG. 5, whether with or without intermediate cooling,
forming the basic setup for a combined plant, one of these being
disclosed in EP-0,767,290 A1, and this publication forming an
integral part of the present description.
[0036] FIG. 6 starts from a basic setup according to FIG. 5 and, as
regards intermediate cooling in the region of the compressor unit
1, follows FIG. 2. The statements made with regard to the two
figures mentioned are also applicable here and are an integral part
of this FIG. 6.
[0037] The gas turbo set according to one of FIGS. 1 to 6 can be
readily replaced by a sequentially fired plant according to
EP-0,620,362 A1, this publication forming an integral part of the
present description.
[0038] FIG. 7 shows a partly closed gas turbine process which is
charged with CO.sub.2 and which is operated in such a way that the
fuel 21, here as CH.sub.4, and the associated oxidant 18, here as
O.sub.2, are supplied to the combustion chamber 3, the aim here,
too, being to separate at a suitable location the excess CO.sub.2
which has occurred and the H.sub.2O. The separated high-pressure
CO.sub.2 can then easily be condensed by cooling
(T.sub.k=31.degree. C., p.sub.k=74 bar), thus making it possible to
dispose of it easily on the ocean floor. CO.sub.2 is a relatively
heavy gas. Its specific heat changes, in the semiideal gas state,
from c.sub.p 0.84 at 15.degree. C. to c.sub.p=1.235 kJ/kg.degree.
C., so that the isentropic exponent .kappa. falls from 1.29 at
15.degree. C. to .kappa.=1.181 at 1000.degree. C. This property
results in very high pressure ratios for maximum specific work and
maximum efficiency. The values are above those for air by a factor
of 4. It is therefore advantageous, in such a setup, to provide for
the introduction of an intermediate cooler and a recuperator. A low
pressure ratio of about 5 at 700.degree. C. is then obtained here.
Furthermore, in these terms, it must be remembered that, because of
the substantially lower sound velocity of CO.sub.2, as compared
with air, in particular the compressor must be designed for a lower
circumferential velocity than is normally customary for air. In
FIG. 7, the first precompressor stage 1a (LP compressor) is still
in the undistorted gas, whilst the downstream intermediate cooler
50 is near the gas/steam/liquid boundary curve and, as a function
of pressure, has extremely high specific heat. The precompressed
circulation medium 27 then flows through a recuperator 51 and,
subsequently, the intermediate cooler 50 already mentioned, before
it flows into the second compressor stage 1b, in which final
compression is carried out. In cooperation with this intermediate
cooler 50, the excess CO.sub.2 from the process can be extracted in
liquid form in a very simple way by means of moderate further
cooling or heat discharge. Advantageously, for this intended use,
the isobaric section in the region of the intermediate cooler 50
can be displaced into the wet zone, so that the excess CO.sub.2 is
then already condensed. For this purpose, it is necessary to have
available cold cooling water which, if possible, is at a
temperature of less than 20.degree. C. The finally compressed
circulation gas 12 then flows via parallel lines 54, 55 through
recuperators 51, 53, likewise connected in parallel, in which
combined intermediate preheating takes place. Final preheating of
the circulation gas 56 then takes place in a downstream recuperator
52, through which the exhaust gases 23 from the turbine 2 flow.
Furthermore, these exhaust gases 23 are also relevant to the
recuperator 53 already mentioned, whereas the recuperator 51,
connected in parallel to the lastmentioned recuperator 53, has only
the precompressed circulation gas 27 flowing through it. On the
outflow side of the recuperators 52, 53, through which the exhaust
gases 23 flow, a further intermediate cooler 49 is arranged, before
the cooled circulation gas 57 flows into the precompressor stage 1a
again, the result of this being, then, that the circuit is
considered to be closed.
[0039] FIG. 8 shows a gas turbine process with a downstream steam
circuit, here the setup being extended by an isothermal compressor
and recuperation. Here, in a preferred version, this setup makes
use of an isothermal compressor 49 operated by pressurized water or
a gradient. On account of its intensive heat exchange, this
isothermal compressor can at the same time perform the function of
the recooler. There is therefore no need for a bladed conventional
compressor. In such an isothermal compressor which is preferably
used, circulation gas can be converted into a precompressed state
within the framework of isothermal compression, in which the
circulation gas can be comparatively highly compressed, without
reaching high compression temperatures, so that, in the extreme
case, said gas is available directly for driving the gas turbine,
at least with a conventional compressor being avoided and therefore
without the need to drive the compressor by means of the turbine.
This isothermal compression ensures that the maximum possible heat
supply does not decrease with an increasing pressure ratio. The
power density therefore remains high even in the case of a high
pressure ratio. Moreover, recuperation is always possible. It is,
of course, possible to deliver isothermally precompressed
circulation gas to a conventional high-pressure compressor stage.
Such an isothermal compressor then offers improved properties as
regards utilizing the waste heat from the exhaust gases emerging
from the turbine, especially since the temperature level of the
highly compressed air, after it has emerged from a high-pressure
compressor stage possibly located downstream of isothermal
compression, is lower than in the case of compressors of
conventional gas turbine plants. In a preferred version of this
isothermal compressor, in combination with an energy-generating gas
turbine, as may be gathered from FIG. 7, a vertically running flow
duct is provided, which has an upper inlet region and a lower
outlet region, the diameter of the flow duct being greater in the
region of the inlet than the diameter in the region of the outlet.
Arranged in the inlet region of the flow duct is a water-atomizing
nozzle arrangement which generates as great a number of very small
water drops as possible in a large quantity. In the case of water
atomization in the inlet region of the flow duct, it is likewise
necessary to ensure that the atomized water is thoroughly mixed
with the circulation gas. Due to gravitation, the circulation
gas/water mixture generated in this way falls through the flow
duct, the inner contour of which is designed in such a way that the
region near the inlet orifice has a largely uniform cross-sectional
area along the vertical extent of the flow duct, so that the
velocities of the flow of the circulating gas and of the falling
cloud of drops are equated as quickly as possible by pulse
transmission. As soon as the circulation gas/water mixture has
reached a specific falling velocity of 6 to 12 m/s, the cross
section of the flow duct decreases in the direction of fall, so
that the relative velocity difference between the cloud of drops
and the circulation gas remains approximately constant. Without
being braked, the cloud of drops would be accelerated downward by
gravitational acceleration. The velocity v would increase quickly
according to the formula v={square root}{square root over
(2g(x+x.sub.0))}, g denoting the gravitational acceleration and x
being the downwardly directed coordinate. x.sub.0 is the constant
which corresponds approximately to the starting point of the free
falling movement. If the circulation gas were also to execute a
free fall, the cross-sectional area of the compression well would
have to obey the law of conservation of volume A={square
root}{square root over ({x.sub.0/(x+x.sub.0)}.cndot.A.sub.0)},
A.sub.0 denoting the cross-sectional area at the start of the fall
well and A the cross-sectional area at any point. However, the
cross section of the fall well is narrowed somewhat more slowly, as
compared with the lastmentioned formula. In this case, the profile
of the narrowing is selected as just sufficient to ensure that the
braking action of the circulation gas on the cloud of drops leads
to a constant relative velocity difference between the drops and
the circulation gas. Thus, as a result of the reduction in flow
cross section, the circulation gas enclosed between the water drops
experiences, according to Bernoulli, a pressure increase which
corresponds to isothermal compression. Finally, the isothermally
compressed circulation gas/water mixture passes through the outlet
orifice of the flow duct into a collecting tank or high-pressure
chamber which is provided directly at the outlet orifice and in
which water is separated from the compressed circulation gas.
[0040] Such isothermal compression is explained in more detail with
reference to the example according to FIG. 8, this being based on a
driven water supply instead of on the process described above.
[0041] As regards the technical and physical aspects of CO.sub.2 as
a circulation gas in terms of temperature and pressure for optimum
condensation, reference is made to the statements relating to FIG.
7.
[0042] Here, in contrast to the statements made above, the
provision of the compressed circulation gas is initiated by a water
pump 58 which is located on the turbine rotor shaft 5, that is to
say is driven by the turbine 2. The water 59, brought to pressure,
flows into an injector 60, in which compression of the exhaust gas
23 from the turbine 2, said exhaust gas previously having been
cooled by means of a recuperator 64, takes place. The expanded
water 65 then flows from here back into the pump 58 again. Air 61
flowing via a regulating member 62 is simultaneously provided, in
this injector, for starting the process. The compressed circulation
gas 63 then flows through the recuperator 64, already mentioned,
and there absorbs the heat discharged by the exhaust gases 23,
before said gas then flows as treated circulation gas 66 into the
combustion chamber. A part quantity 67 of the circulation gas 63
compressed in the injector is branched off upstream of the
recuperator 64 and led through a cooler 14, in which the
condensation of the CO.sub.2 takes place in the way already
described. The discharge 15 of the condensed CO.sub.2 and of the
parasitic gases 16 is subsequently carried out. The remaining
elements of this figure correspond to the setup according to FIG.
5, here the steam line 47 from the recuperator 64 also being
equipped with a regulating member 68.
[0043] FIG. 9 shows a setup which is based on a piston engine
69/70. Engines having a multipiston system may, of course, also be
used here. During the intake stroke, the piston 70 moves upward,
and a recirculation gas is sucked in from the line 74 and/or from
the storage volume 71, during the start itself air 72 being sucked
in from the surroundings. These operations during intake or
starting are controlled by means of corresponding regulating
members 73, 75. During the compression phase, the piston 70 closes
(piston 70 downward). In the course of the work cycle, the
separately compressed fuel 78 is injected by means of the
regulating member 79 and oxygen 76 by means of the regulating
member 77 in a near-stoichiometric ratio, being ignited
spontaneously or by spark, depending on the pressure ratio, with
the result that expansion (piston 70 upward) is initiated. During
subsequent ejection, the piston 70 moves downward; in the operating
mode with recirculation, only the valve 81 to the cooler is open.
During starting, first the piston engine is started up and ignited
and then the exhaust gas valve 85 is throttled, with the result
that the recirculation line 80 and its branch 84 are supplied with
exhaust gas. The air intake valve 73 is also gradually throttled
and recirculation is enriched with circulation gas predominantly
consisting of CO.sub.2. Finally, the two valves 73, 85, which are
operatively connected during starting, are closed completely and
the engine is in the recirculation mode. The excess circulation
gas, namely CO.sub.2, can be extracted from the cycle basically in
two ways: at the lowest pressure level via a line 82, which is
provided with a regulating member 83 and which branches off from
the ejection string, or by means of a valve, not shown in any more
detail in the figure, which is arranged upstream of the cooler 24.
Another possibility for extracting the excess circulation gas from
the cycle is to branch it off under pressure in a suitable section
of the compression cycle, recool it and condense it. The
circulation gas extracted in this case contains only a little water
to be discharged, insofar as the setup has good dewatering 25/26
downstream of the cooler 24. In contrast to a conventional plant,
this piston engine does not require any charging in order to
achieve a power increase. If less excess gas is extracted from the
closed or quasi closed circuit, the process pressure in the return
through the line 74 and in the storage volume 71 rises
automatically, and vice versa. As already mentioned, the engine
present here also needs a hydrocarbon or hydrogen as fuel and,
correspondingly, also oxygen, either in the pure form or as
oxygen-enriched air. In the case of operation with relatively pure
oxygen, no nitrogen enters the flame, with the result that NO.sub.x
formation, known in piston engines, is eliminated completely.
[0044] Obviously, numerous modifications and variations of the
present invention are possible in the light of the above teachings.
It is therefore to be understood that, within the scope of the
appended claims, the invention may be practiced otherwise than as
specifically described herein.
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