Note: Descriptions are shown in the official language in which they were submitted.
The present invention relates to a process for generating
mechanical energy as defined in the preamble to patent claim 1,
and to an apparatus for carrying out this process.
In most thermal generating stations, in order to generate
electrical energy, superheated steam is first produced in boilers
by the combustion of fossil fuels; this superheated steam is
expanded inside steam tu~bines and converted into mechanical
energy thereby. The steam turbines are coupled to electrical
generators, so that this mechanical energy is converted into
electrical energy. The latter occurs at a level of efficiency
that is clearly above 90~. In contrast to this, the degree of
efficiency with which the energy that is chemically bound within
the fuel that is used into mechanical energy is very modest, for
the degree of efficiency of the turbines themselves amounts at
most to 37% in the case of large turbines, and losses in the
boiler must also be accepted. For this reason, in many
instances, up to now only approximately 35~ of the heat that is
liberated during combustion can be used effectively for the
generation of electricity, whereas approximately 65~ of the waste
heat is lost, or could only be used for heating purposes.
Recently, it has been possible to achieve a considerable increase
in the overall degree of efficiency in that, in order to convert
the thermal energy into mechanical energy, a combination of gas
turbines and steam turbines is used, the hot combustion gases
being first expanded in gas turbines, when the heat from the
exhaust gases of these gas turbines is used to generate steam for
the steam turbines. Additional possibilities for improvement are
that~the expanded steam that flows out of a steam turbine is, in
each instance, passed back into the combustion chamber of the
preceding gas turbine, thereby generating a greater volume flow
to drive the gas turbine. These measures have made it possible
to increase the overall degree of efficiency of the conversion of
thermal energy into mechanical energy to an order of magnitude of
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approximately 48 to 50% in the case of large generating
facilities (above 50 MW).
A combined gas/steam turbine process of this kind is described,
for example, in DE 33 31 153 Al. Conventional ~'flowing~ fuels,
i.e., liquid or gaseous hydrocarbons, are used to generate the
required hot combustion gases for gas turbines. In order to
avoid the formation of nitrogen oxides to the greatest extent
possible, the combustion chamber temperature is lowered by
introducing some of the steam that is generated with the heat of
the gas turbine exhaust gases into the combustion chamber. At a
total power output of 300 MW, the degree of efficiency that can
be achieved for this process is said to be 48~.
The journal VGB Kraftwerkstechnik [Power Station Technology], 66,
No. 5, May 1988, pp. 451 - 458, describes a combined gas/steam
turbine process that is used in conjunction with coal
gasification. The combustible gas that is generated in the coal
gasification process is burned in part with compressed air in a
first combustion chamber after having been scrubbed. One part of
the hot combustion gases that are generated by doing this is
first used for superheating the steam for the coal gasification
and for heating the allothermic coal gasification itselS, before
these gases are expanded in a first gas turbine that, in its
turn, drives a compressor for the required combustion air. The
other part of the combustible gas that is produced during the
coal gasification is burned in a second combustion chamber and
immediately thereafter is expanded in a second gas turbine that
is coupled to an additional compressor for the combustion air
that is required in the second combustion chamber and to an
electrical~generator to generate electrical energy. The expanded
turbine exhaust gas from the second gas turbine is used for steam
generation before being passed to the atmosphere together with
the expanded exhaust gas from the first gas turbine (c~mpressor
drive turbine). This steam is expanded in a ~team turbine that
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lS similarly coupled to a generator, in order to generate
electrical energy. After partial expansion, some of the steam is
uncoupled from the steam turbine and then, after the previously
discussed superheating by the combustion gases from the first
combustion chamber, is used for coal gasification.
Coal is used as the initial fuel in these known systems, and this
is made useable for a gas turbine process in that it is first
gasified. This conversion is urgently required from the
technical standpoint because of the ash fraction that is produced
during combustion and that would destroy a gas turbine. In
contrast to this, fuels that are based on hydrocarbon compounds
can be in either liquid or gaseous form, contain no ash fraction
and, for this reason, can be used directly in a combined
gas/steam turbine process without any problem. A characteristic
of these known systems is that the combustion gases move in two
sub-flows that are initially completely independent of each other
and are used for different sub-processes before they are used
together to generate steam at the end of the process. The net
degree of efficiency of this apparatus is said to be
approximately 42%, with the internal energy requirement for
carrying out the process amounting to approximately 7.5%.
Another combined gas/steam turbine process for generating
electrical energy, in which, initially, coal gasification i6
carried out, is described in US 4,478,039. Here, the gas that is
generated is burned under pressure in a combustion chamber. The
resulting~hot combustion gases are then expanded in a gas turbine
that drives an electrical generator and a compressor for
compressing the combustion air. The expanded turbine exhaust gas
is~addltionally used for heating the coal gasification plant and
for~generating steam for the steam turbine process. The steam
turbine also~drives an electrical generator. This document makes
to~;reference to the use of starting fuels that are based on
hydrocarbon compounds.
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ln addition, DE 37 40 86~ Al describes a process and an apparatus
for recovering hydrogen, a gaseous initial fuel, i.e., a
hydrocarbon compound, being converted in steam reformation to a
gas that is enriched with and has an absolute heating value that
is elevated relative to the mass flow of the initial fuel.
In this context, ~'absolute heat value" is not understood to be a
unit of a heating value that is related to a unit of weight, as
is usually the case. Rather, what is meant here is the total
quantity of combustion heat that is contained in a specific
quantity of the initial fuel, or in a quantity of the converted
fuel, and which results through the endothermic conv~rsion of the
same quantity of initial fuel. In the case of steam reformation,
because of the steam fraction that is added during the
conversion, the total quantity of the converted fuel is of
necessity considerably enlarged relative to the origina} quantity
of the starting fuel, so that the heat value that is based on
weight is smaller than was previously the case, even through the
quantity of heat released during the combustion of the converted
fuel has become greater.
The crude gas that is produced by this process according to DE 37
40 865 A1 is treated in a purification stage (e.g. a pressure
alternation absorption apparatus) in order to produce a pure
hydrogen gas, in which the impurities ~e.g. CO, CO2, H20, non-
converted hydrocarbons) are separated off and removed in the form
of a flow of exhaust gas. This combustible flow of exhaust gas
that, of necessity, also contains certain residual fractions of
the hydrogen gas, is burned with compressed air after compression
in a compressor to a higher pressure than combustion gas, e.g.,
in the~heating chamber of the indirectly heated steam reformer.
Because of the extensive separation of the hydrogen from the
crude~gas, the absolute thermal value of the flow of exhaust gas
from~the purification stage falls considerably, relative to the
absolute thermal value of the crude gas, and still lies beneath
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that of the starting fuel that is used. For this reason, in many
instances it is necessary to burn a partial flow of the starting
fuel directly at the same time, when the steam reformer is being
heated. After heating the steam reformer, the resulting
combustion exhaust gas is passed on, as a moderator gas, to lower
the temperature in a combustion chamber in which a part flow of
the starting fuel is burned with compressed air. The flow of
combustion exhaust gases that emerges from this combustion
chamber is then expanded in a gas turbine. The gas turbine
provides the compressor drive energy that is required in this
process, and also makes it possible to generate electrical energy
by means of a generator that is connected to it.
In this known process, the conversion of the starting fuel is
effected only because of the fact that the intention is to
produce hydrogen that is required for any applications beyond the
scope of this process. DE 37 40 865 A1 contains no indications
to the effect that such an endothermic fuel conversion could also
be advantageous, were the converted fuel to be burned
subsequently for purposes of generating mechanical energy. The
combustion of the converted fuel that is used in this known
process is thus effected only to make use of a secondary product.
In this connection, it is important to emphasize that during the
combustion only one part of the original combustible component
originally contained in the converted fuel is present, because
the hydrogen fraction that accounts for the major part of the
absolute thermal value has to a large extent been separated off
prior to this. For this reason, the purely theoretical ratio of
the generated useable mechanical or electrical energy to the
quantity of chemically bound energy contained in the starting
fuel that is used, less than lo~, is extremely small.
EP 0 318 122 A2, that forms the generic concept, describes a
process and an apparatus for generating mechanical energy from
gaseous fuels, in which the mechanical energy, which can be used,
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~or example, for generating electricity, is produced by means of
a gas turbine alone. This gas turbine, which is provided in
particular for a power range of 50-3000 KW, achieves an
efficiency of approximately 42% relative to the thermal energy
used (the lower thermal value). To this end, provision is made
for the fact that combustion air is first compressed in a
compressor. The compressed combustion air is then heated in an
exhaust gas heat exchanger, passed through a first gas turbine,
which drives only the compressor, partially expanded, and then
passed to a combustion chamber, within which fuel is burned with
this combustion air. The hot exhaust gas that results from this
combustion drives a second gas turbine that supplies the
mechanical energy that is actually useable. The exhaust gas that
flows out of the second turbine, and which is still hot, is used
to drive the exhaust gas heat exchanger that is used to heat the
compressed combustion air.
Fina}ly, US 31 67 913 describes yet another apparatus, which
incorporates a single combustion chamber that is arranged ahead
of the compressor turbine, i.e., ahead of the high pressure
stagé, of the turbine system. Such high pressure systems require
that the combustion chambers be designed to handle high
pressures.
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In addition, in order to increase the efficiency o~ the turbine,
every~effort is made to achieve high combustion temperatures,
with the result that more injurious substances result. Because
of the great~compression of the combustion air, there are high
temperatures~in~th- compressed combustion air, and these have to
be taken~into account when the exhaust gas heat exchanger is
being~designed. All of these factors increase not only the cost
of the~apparatus~; they also downgrad~ the overall efficiency of
the system.
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I~ is the task of the present invention to so develop a process
and an apparatus of this kind that the efficiency of the
conversion of the energy (lower thermal value) contained in a
fuel that is based on C-H compounds into mechanical energy in
small plants (50-3000 KW) is greater than 50%, and in large
plants is at least 55%. In the following, the expression
"efficiency" will always be understood to be the "mechanical"
efficiency, i.e., the ratio of the generated useable mechanical
energy from the turbine to the energy of the starting fuel that
is used (based on the lower thermal value ~u)~
With respect to this process, this problem has been solved by the
distinguishing features of patent claim l. Advantageous
developments of this process ~re distinguished by the features of
the sub-claims 2 to 13. An installation according to the present
inventio~ for carrying out this process incorporates the features
set out in patent claim 14, and this can be configured more
advantageously by using the distinguishing features set out in
sub-claims 15 to 21.
An important innovative step is that the configuration that is
known from EP 0 310 122 A2 has been supplemented by a reactor for
an endothermic chemical reaction, in which the fuel that is used
(starting fuel) is-converted into a higher value fuel that is
ultimately burned with the compressed air from the compressor.
When this is done, the thermal energy for operating the reactor
is preferably recovered from the exhaust gas heat of tha exhaust
gases that flow out of the gas turbine in which the usable `
mechanical energy is produced. However, other flows of hot gas
within the process can be used to heat the reactor. In the event
that the exhaust gas is used for the reactor, this additionally
cooled gas can be use, for example, in an exhaust gas heat
exchanger in order to heat the compressed combustion air.
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The conversion of the starting fuel means that, as in a heat
pump, waste heat from the exhaust gas from the gas turbine or
another flow of heat can, as it were, be raised to a higher
"potential temperature level," so that this heat can b~ better
used, technically speaking, than heat at a lower temperature.
This "raising" of the temperature level takes place in the form
of an elevated absolute thermal value of the new fuel (e.g., H2
and C0) formed within the reactor from the original fuel ~e.g.,
natural gas).
The procedure and the apparatus according to the present
invention make it possible to trap the waste heat that results in
the process systematically and use it in an effective manner. In
this connection, it is a particular advantage to carry out the
endothermic reaction for generating the higher value fuel, which
can be carried out in particular as steam reformation, e.g., from
natural gas, at a comparatively low temperature. Normally, this
steam reformation ls carried out at an industrial scale only at
temperatures in the range of 780 - sOoC. According to the
present invention, it is more expedient that an upper temperature
limit of 760 c, or better still, of 700 or even 650-C, is not
exceeded.
The disadvantage that with the lower temperature, one has to
accept some downgrading of the conversion rate of the original
fuel, which is to say an increase in the proportion of non-
converted fuel, is more than made up for by the advantage of
improved utilization of the waste heat from the gas turbine or
the heat of another flow of hot gas from the process during
reactor heating, and the reduction of the temperature of the
f~esh steam that is required for the endothermic reaction. ~he
reduced temperature level also entails advantages for the costs
of a plant according to the present invention, for the thermal
d-mands~ on the fuels that are used are lower than in the prior
a:rt.
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Also of very great importance is the fact that the combustion of
the fuel can be influenced, e.g., by injecting water or water
steam into the system's combustion chamber or chambers such that
nitrogen oxides are either not formed or else formed in very
small quantities. The flame temperature is restricted to values
of at most 1700C (adiabatic flame temperature~ and the inlet
temperature into the gas turbine is kept to at most 1250-C, so
that the operation of the process according to the present
invention is possible in a particularly environmentally benign
manner without the need for any costly nitrogen removal
apparatus. All of this is made possible by the integration of
the fuel conversion and the generation of mechanical energy from
the heat that is liberated by the combustion of the fuel, as
provided for by the present invention. This means that such
effective utilization of the waste heat flow is possible that a
degree of efficiency previously regarded as unachievable has been
achieved. Typical values lie in the range of 50-70%, in which
connection smaller facilities are to ~e placed in the lower
range, and larger facilities are to be placed in the upper part
of the range. The plants according to the present invention are
particularly well suited for the decentralized, i.e., local,
generation of electricity, and thus offer the additional
advantage that losses caused by the transmission of energy over
great distances and/or by the transformation of current can be
largely avoided. In the case of large generating stations, these
losses have been found to amount to approximately 10% of the
electrical energy that is produced.
Two main variants are to be regarded as particularly preferred
~for the process according to the present invention. In one of
these main variants, as has already been described heretofore,
the compressed combustion air is heated in an exhaust gas heat
exchanger prior to being introduced into the combustion chamber,
the waste gas heat exchanger being supplied with the waste gas
f~rom the gas turbine that produces the useable mechanical energy.
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It is preferred that this waste gas heat exchanger be configured
as a recuperator.
The greater the quantity of heat per unit time that i5 to be
exchanged within this recuperator, the more rapidly the
construction volume of this heat exchanger aggregate increases.
In the case of major installations of the kind according to the
present invention (in the power range from approximately 50-80
MW), the recuperator is extremely large in comparison to
conventional system parts, and is correspondingly costly. For
this reason the second main variant of the invention, in which
there is no recuperator, is preferred for larger installations.
In the second main variant, the exhaust gas from the gas turbine
is used for the production of steam, (optionally after heating
the reactor for the fuel conversion). This steam is superheated
by means of a flow of hot gas that is present in the process, and
then expanded in a steam turbine in order to generate additional
mechanical energy, as is known from the so-called "combined
cycle" power stations. Certainly, the efficiency of the process
in such major installations is somewhat lower than in a version
of the installation according to the first main variant, but the
installation costs are significantly lower.
The present invention will be described in greater detail below
on the basis of examples shown in the drawings appended hereto.
These drawings show the following:
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Figure l:~a system with a recuperator;
~; ~ Figure 2:~a~system w1th a steam turbine.
; In~the~embodiment of the present invention that is shown in
figure~l~combustion air is drawn in through a line 9, by a
aompressor~;3a of a compressor unit 3 that also incorporates a
second~compressor 3b. The compressed combustion air is subjected
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to intermediate cooling in a cooler 4 and then compressed to a
still higher pressure in a second compressor 3b. ~oth
compressors 3a and 3b are coupled mechanically by way of the
shafts 24, 25 to a compressor drive gas turbine unit 2. The
compressed combustion air is passed from the second compressor 3b
through a line 10 into an exhaust gas heat exchanger 8 that is
configured as a recuperator and from there it passes through a
line 11 into a first combustion chamber 5 after being heated by
indirect heat exchange.
Some of the fuel that has been formed from a starting fuel by
means of an endothermic reaction passes into the combustion
chamber 5 through the fuel feed line 20, and this is then burned
in the combustion chamber 5. The resulting hot gas mixture that,
in addition to the combustion products, also contains excess
combustion air, passes through the hot gas feed line 12 to the
compressor drive gas turbine unit 2, where it is partially
expanded while giving off the drive energy that is required for
the compressor unit 3, and thus cools down somewhat when this is
done. Then, this gas mixture, which is still hot, passes through
the hot gas feed line 13 into a second combustion chamber 6, into
which fuel is also introduced through a branch line off the fuel
feed line 20, and is then burned with the excess air, so that the
exhaust gas is once again brought to a higher temperature.
The hot exhaust gas that results from this combustion passes
through a hot gas line 14 to a gas turbine 1 that generates
useable mechanical energy and, after expansion, it passes from
there through the exhaust gas line 15. The compressor drive gas
turbine unit 2 and the gas turbine 1 can be arranged on a common
shaft and, under some circumstances, can even be configured as a
~; singIe turbine aggregate in order to simplify the overall
installation. It is also possible to have these driven in part
~ by the gas turbine 1 if there are several compressor ~tages.
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qnis makes it possible to achieve an optimal match of the
compressor and the turbines.
The adiabatic flame temperature can be kept below 1700-C, and the
inlet temperature into the gas turbine 1 can be kept to
approximately 1250', and in many instances at even lower values
of up to 800-C, by injecting water or water steam, for example,
into the combustion chambers S and 6; at these temperatures no
noteable quantities of nitrogen oxides are formed. In this
connection, the present invention also provides a major advantage
in that the formation of nitrogen oxide can be significantly
reduced in that, in place of the starting fuel, the converted
fuel, which has a higher absolute thermal value, which results in
the endothermic reaction, is burned in place of the starting
fuel. This means that from the very beginning (depending on the
air surplus) there is an adiabatic flame temperature that is 300
to 550-C lower than the adiabatic flame temperature during
combustion of the starting fuel.
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It is also possible to burn the fuel that is introduced in a
single combustion chamber 5, so that the combustion chamber 6 can
be eliminated. When two combustion chambers are used, the
measures aimed at reducing the flame temperatures can also be
~confined to the second combustion chamber 6, for the nitrogen
oxides that are formed in the first combustion chamber will be
decomposed to a very great extent by the effect of heat during
the subsequent second combustion. This means that, in the first
combustion, work can be done with higher exhaust gas temperatures
and, because of this, under favourable conditions for the
compressor drive gas turbine with respect to the highest possible
turblne~efficiency, without this ultimately leading to higher N0
contents.~ The controlled temperature management is thus of
particular~importance in the first instance for the last
combust~ion~stage.
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Ihe mechanical energy that lS produced during expansion withln
the turbine 1 is available for use on the output shaft 26 and can
be used, for example, to drive a generator 6 to produce
electrical current. The exhaust gas that has been cooled
somewhat during expansion, but which is still hot, passes through
the exhaust gas line 15 into the hot area of the indirectly
heated reactor 7 for the endothermic reaction. `
Because of this endothermic reaction, which can take place as
steam reformation, for example, a new fuel with an elevated
absolute thermal value is generated from the starting fuel that
has a specific absolute thermal value. For the case of steam
reformation from natural gas that is introduced, for example,
through the fuel feed line 18, a steam feed 19 leading into the
reaction space of the reactor 7 is shown.
As a rule, it is useful to mix the steam with the fuel before
this. The new fuel that is generated, which consists of a
mixture of H2, C0, C02 non-converted CH4 and steam, is passed
along the feed line 20 from the reaction chamber and into the
combustion chambers 5 and 6, where it is burned, as described
above. It is, of course, also possible to mix part of the
starting fuel into the higher-value fuel in order to optimize the
combustion processes (temperature, mass flow) within the
combustion chambers 5 and 6. When this is done, it is most
expedient to use a mixture with at least 50~, and preferably even
more than 60% of the unconverted fuel. The smaller the amount of
unconverted fuel that is contained, the more the efficiency will
be réduced, according to tendency. The principle to the effect
that--taken all in all--the fuel that is burned has a higher
thermal-value than the starting fuel, is maintained in each case.
Some of~the higher value fuel can, of course, be decoupled from
the process and used in other processes.
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During the steam reformation of natural gas (essentially CH4)
that has been discussed above, the absolute thermal value of the
fuel is increased by approximately 30~. In the case of
hydrogenation of the starting fuel--toluol--the thermal value
increase amounts to approximately 15~. In place of steam
reformation, the endothermic reaction can be in the form of de-
hydrogenation, for example. In the case of ethane as a starting
fuel, this would result in a thermal value increase of
approximately 10-20%, and in the case of methanol by
approximately 20-30%. A further example for an endothermic
reaction is the steam cracking of some hydrocarbon compounds
(e.g., biogas, LPG, naphtha and kerosene).
This last-named possibility is interesting because it permits the
alternating utilization of a number of different fuels to
generate the mechanical energy, without the gas turbine having to
be adjusted for a new fuel each time a different fuel is used.
The endothermic reaction is, as far as possible, to be carried
out at temperatures below 780C or be~ter still, below 700-C.
The exhaust gas that is used for heating leaves the hot area of
the reactor 7 through the exhaust gas line 16, when it i5 still
at a relatively high temperature and, according to the present
invention, is used, for example, for heating the exhaust gas heat
exchanger 8, with which the ~ompressed combustion air is heated.
Finally, the cooled gas passes out of the exhaust gas heat
exchanger through the exhaust gas line 17.
In the case of an endothermic reaction in which the use of steam
is necessary, the process according to the present invention can
be operated as a closed system insofar as this steam can be
generated by using the heat that is available in the individual
hot volume flows. In order to achieve an even higher overall
efficiency for the process, at least one part of the reguired
fresh steam can also be introduced from any ~team source, from
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outside the reactor 7. In the lay-out diagra~, steam generators
21, 22, 23 have been drawn in with dashed lines at the locations
in question as options, and these can be operated alternatively
or simultaneously. The steam generator 21 is installed at the
end of the system, in the exhaust gas line 17, and for this
reason can only generate steam of a relatively low temperature.
A heat exchanger that is used to pre-heat the starting fuel (or a
fuel/steam mixture) or to pre-heat the feed water for the steam
generator could also be installed at this point.
A further possible place for the steam generator 22 is between
the exhaust gas heat exchanger 8 and the reactor 7 in the exhaust
gas line 16.
A preferred arrangement is to incorporate the steam generator 23
between the compressor drive gas turbine unit 2 and the second
combustion chamber 6, for this arrangement has a positive effect
in the sense of reducing the combustion temperature in the
combustion chamber 6. If a plurality of steam generators 21 to
~23 i8 installed at the same time, these can be so arranged one
behind the other that one (for example 21) generates steam at a
relatively low temperature, and this steam i8 then superheated to
a higher temperature in another (e.g. 22 and/or 23).
Fundamentally, the waste heat that occurs as a result of
intèrmediate~cooling during compres~sion of the combustion air can
be used in the cooler 4 to generate steam.
In the~ lay-out diagram shown in figure 1, the reactor 7 is
installed in~the exhaust gas line 15, 16 of the gas turbine 1.
Nowever, it is also possible to provide for reactor heating with
a~flow of~hot gas that is produced earlier in the process. For
this~reason, the~reactor 7 could, in principle, be incorporated
in the~lines 11, 12~, 13, or 14. Because of a temperature
reduction~;in the~hot~gas flow, the turbine efficiency of the
turbines ~I, or~2~r-apaot~valy, is reduced but, however~ NO~
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formation is also reduced at the same time. For this reason, the
process parameters must be matched to each other in order to
achieve the optimal effect.
In order to make it possible to start the system up from cold,
when neither a hot gas flow nor sufficient converted fuel are
available for use, as an alternative or simultaneously, provision
can be made for the fact that the original fuel (e.g., natural
gas) can be introduced in the combustion chamber 5 and the hot
area of the reactor 7 and there burned, at least on a temporary
basis.
The corresponding separate fuel feed lines (not shown herein) can
be switched on briefly should the thermal output that is
available in these aggregates be momentarily inadequate. Because
of this, the overall operation of the installation is extremely
simple to control. In addition, in order to provide better
control and to optimize the overall system, provision can also be
made for some of the energy produced in the gas turbine 2 for the
compressor drive to be utilized as useable mechanical energy
outside the system.
Figure 2 is a schematic representation of the second main variant
of the process according to the present invention. In this
drawing, components of the system that perform the same functions
as in figure 1 bear the same reference numbers as in figure 1.
For this reason, the statements made with respect to figure 1
apply to figure 2 as well, so that only the differences between
the two variants will be discussed in greater detail below.
The essential difference compared to figure 1 is the fact that
the heat exchanger 8, which is configured as a recupterator for
pre-heating the combustion air, has been eliminated, and in place
of this there is a system to generate superheated steam that is
used in a steam turbine 31 in order to produce mechanical energy.
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This steam generating system consists of a boiler 30 and a steam
superheater 28.
The steam boiler 30 is heated with the residual heat from the
exhaust gases that leave the gas turbine 1, once these gases have
passed through the heating chamber of the reactor 7 and given up
additional heat in so doing. The steam that is generated passes
through the line 37 to the superheater 29 and from there through
the line 38 to the steam inlet side of the steam turbtne 31. The
expanded steam passes from the steam turbine 31 into a condenser
32. The condensate pump 33 delivers the condensed water into a
de-gassing apparatus 34.
From there, the prepared boiler water is moved by the boiler feed
pump 35 through a line into the boiler 30. Thus, the steam/water
system is a largely closed circulatory system. Water losses that
take place are made up by a water feed system (not shown herein).
These water losses occur, in particular, when, as is shown in
fi~ure 2 by a dashed line 36, steam is decoupled from the high
pressure section of the steam turbine 31 and introduced into the
combustion chambers 5 and 6 to control the temperature and
increase the mass flow. The line 19, which is also optional, can
decouple steam from the circulating system in the same way and
introduce this into the reaction chamber of the reactor 7.
However, this steam could be generated in another part of the
system, as has already been discussed in connection with figure
1, or else supplied from outside the system. The water that is
required to replenish the steam/water circulation system can be
obtained by recovering condensate from the exhaust gas line 17.
For purposes of completeness, it should be mentioned that the
feed line for introducing th~ compressed combustion air into the
first combustion chamber 5 in figure 2 is numbered 27 and the hot
gas line from the steam superheater 29 to the second combustion
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chamber 6 is numbered 28. In principle, the fact that the
reactor 7 can be incorporated at another location in the hot gas
lines also applies to the process variant that is shown in figure
2. A preferred solution for this is that the positions of the
reactor 7 and of the steam superheater 2~ can be exchanged with
each other.
A further advantageous configuration of the present in~ention
(not shown in figures 1 and 2) relates to the utilization of the
hot exhaust gas that is expanded in the gas turbine 1. In the
normal course of events, this exhaust gas still contains a
considerable 2 content because combustion is effected with an
excess of 2- For this reason, this can be used, for example, as
a cathode gas for the 2 supply of a fuel cell system in which
electrical current is generated.
In fuel cell systems of this type, it is advantageous that
cathode gas be introduced at a temperature that corresponds to
the operating temperature of the fuel cells. Depending on the
type of fuel cell system, the operating temperature lies at
another level. Accordingly, the fuel cell system i9 incorporated
at a suitable point in the exhaust gas line 15, 16, 17, i.e., the
cooling of the expanded exhaust gas during heating of other media
flows that are required in the process according tc the present
invention (air pre-heating, steam generation, reformer heating)
is carried out approximately up to the level that corresponds to
the operating temperature that is desired in each instance, and
then the flow of exhaust gas or a part thereof is introduced into
the cathode chamber of the fuel cell system. The fuel cell
system can be supplied with fuel by any H2 gas source (e.g.,
pipeline or gas accumulator). A partial flow of a gas enriched
with H2, produced in the reactor 7, could also be introduced into
the anode chamber of the fuel cell system.
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The effectiveness of the process according to the present
invention is described in greater detail below, on the basis o~
an embodiment. A system diagram that corresponds to figure 1 has
been used in order to do this. The heat exchanger 21 was used to
generate steam and to pre-heat natural gas, whereas the heat
exchanger 22 served to superheat the steam/natural gas mixture,
before this mixture was passed to the steam reformer 7. The
natural gas that was used as the starting fuel was at a line
pressure of 20 bar and the water that was used was at a
temperature of approximately 15C. The steam~carbon [sic] ratio
(mol/mol) amounted to 2Ø For the remainder, the process
parameters were selected in accordance with the following tabular
compilation. In the interests of clarity, the same reference
numbers are used here as in figure 1.
- Low pressure compressor (3a) inlet temperature 15 D C
Outlet temperature 1~0C
Outlet pressure 4.5 bar
- High pressure compressor (3b) inlet temperature 25C
Outlet temperature 203~C
Outlet pressure 20 bar
- Recuperator (8)
Temperature rise in the combustion air 357C
Temperature drop of the exhaust gas 327C
- Combustion chamber (5)
Temperature rise during combustion 6~0C
- Compressor drive turbine (2)
Inlet temperature 1250C
Pressure ratio at the turbine 2.8
Outlet temperature 970-
- Combustion chamber (6)
Temperature rise during combustion 280OC
- Gas turbine (1)
Inlet temperature 1250'C
Pressure ratio at the gas turbine 6.4
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Outlet temperature 780-C
- Generator (6) to generate electrical
currPnt; power output 3200 KW~
- Steam reformer (7)
Inlet temperature of superheated fuel/
steam mixture 550 C
Outlet temperature of the exhaust gas 647 C
Outlet temperature of the product gas 720-C
- Fuel/steam superheater (22)
Inlet temperature fuel/steam mixture 249 C
Outlet temperature of the exhaust gas 610 n C
- Fuel pre-heater/steam generator (21)
Outlet temperature of the exhaust gas 227-C
During the steam reformation of the natural gas that consists
essentially of methane, some 12~ of the methane fraction was not
converted and was burned in the combustion chambers 5 and 6 in
its original form. With the exception of the energy for
compression of the natural gas, which was available at sufficient
line pressure, the total energy requirement for the process was
covered by the process itself, so that there was no additional
energy brought in from outside the system. The overall
efficiency achieved thereby, i.e., the ratio of the generated
electrical energy to the quantity of energy used from fuel on th~
basis of the lower thermal value amounted to 65%, and was thus
was at an order of magnitude not previously achieved. When this
was done, the exhaust gas that was discharged into the
environment was characterized by a very low content of nitrogen
oxides, without any additional nitrogen removel measures being
required in order to achieve this.
The major advantage that is achieved by the present invention is
the fact that it not only makes possible a drastic increase in
efficiency during the generation of mechanical energy, using
fuels that are based on hydrocarbon compounds, but also the fact
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that this can be connected with a reduction in the content of
injurious substances in the exhaust gas that i5 generated. In
addition, there is the fact that, because of the special
suitability of systems according to the present invention for
decentralized generation of electricity, the losses that are
incurred by moving electrical energy over long distances, using
conventional technology of the sort found in large generating
stations, and during the transformation of the current, are
largely avoided.
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