U.S. patent number 3,738,103 [Application Number 05/066,257] was granted by the patent office on 1973-06-12 for power plant process.
This patent grant is currently assigned to Metallgesellschaft Aktiengesellschaft. Invention is credited to Ernst Kapp, Paul Rudolph.
United States Patent |
3,738,103 |
Rudolph , et al. |
June 12, 1973 |
POWER PLANT PROCESS
Abstract
In a turbine power plant, fluid hydrocarbon fuel is first
cracked with steam under pressure; the cracked compressed gas is
then expanded in a gas turbine to perform work and thereafter
burned in a boiler to generate steam to drive a steam turbine. The
cracked, compressed gas may also be expanded to an intermediate
pressure in a gas turbine to perform work, combusted under
pressure, the combusted, compressed gas expanded in a second gas
turbine to perform work and then fed to a boiler where the heat of
the combusted gas is utilized to generate stem to drive a steam
turbine. The cracked, compressed gas may also be fully expanded in
a gas turbine to perform work and thereafter combusted and a
portion of the hot combustion gas therefrom is fed to a boiler to
generate steam to drive a steam turbine and the balance is recycled
to an externally heated cracker and then to the boiler.
Inventors: |
Rudolph; Paul (Bad Homburg,
DT), Kapp; Ernst (Frankfurt am Main, DT) |
Assignee: |
Metallgesellschaft
Aktiengesellschaft (Frankfurt am Main, DT)
|
Family
ID: |
5744300 |
Appl.
No.: |
05/066,257 |
Filed: |
August 24, 1970 |
Foreign Application Priority Data
|
|
|
|
|
Sep 1, 1969 [DT] |
|
|
P 19 44 307.3 |
|
Current U.S.
Class: |
60/649;
60/39.182; 60/672; 208/130; 60/772; 60/655; 208/125; 252/373 |
Current CPC
Class: |
C01B
3/38 (20130101); F01K 3/188 (20130101); C01B
3/22 (20130101); F02C 3/20 (20130101); C01B
3/386 (20130101); C01B 3/36 (20130101); Y02P
20/129 (20151101) |
Current International
Class: |
F01K
3/00 (20060101); C01B 3/22 (20060101); C01B
3/36 (20060101); C01B 3/38 (20060101); F02C
3/20 (20060101); C01B 3/00 (20060101); F01K
3/18 (20060101); F01k 025/08 (); F01k 023/00 ();
F01k 023/10 (); F01k 023/14 () |
Field of
Search: |
;60/37,39,38,40,50,108,1,39.12,39.71,39.18 ;208/130,132 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Schwadron; Martin P.
Assistant Examiner: Ostrager; Allen M.
Claims
What is claimed is:
1. Power plant process comprising
a. cracking a fluid hydrocarbon fuel with steam and/or air under
pressure to form a gaseous mixture high in carbon monoxide and
hydrogen;
b. expanding the cracked compressed gaseous mixture from (a) in a
gas turbine to perform work;
c. thereafter combusting the expanded gaseous mixture from (b) to
produce combustion gases; and
d. feeding at least a portion of the combustion gases from (c) to a
boiler to generate steam to drive a steam turbine.
2. Process of claim 1 wherein said fuel is catalytically
cracked.
3. Process of claim 1 wherein said fuel is thermally cracked.
4. Process of claim 1 wherein the balance of the combustion gases
from (c) is fed to an indirectly heated cracker wherein said fluid
hydrocarbon fuel is cracked and then to a boiler to generate steam
to drive a steam turbine.
Description
BACKGROUND
The present invention relates to a power plant process in which
hydrocarbon-containing, liquid or gaseous fuels are fired.
Steam boiler power plants have been fired for years with solid
fuels; more recently, liquid or gaseous fuels have been fired in
such plants. Power plant processes using gas turbines have been
restricted to the use of liquid and/or gaseous fuels. Such fuels
are generally burned with a large surplus of air in a combustion
chamber which precedes the gas turbine, to which the hot flue gas
is admitted. Two-stage power plant processes are known in which two
gas turbines are used and the gas for driving the second gas
turbine is produced from the high-oxygen exhaust gas of the first
gas turbine by afterburning said exhaust gas together with added
gaseous or liquid fuels.
SUMMARY
It has been found that the power plant process using gas turbines
and liquid or gaseous (fluid) hydrocarbons as fuel may be improved
if the feed fuel is thermally or catalytically cracked with steam
and/or oxygen (air), and, if desired, with carbon dioxide and under
a pressure which is higher than the operating pressure in the
combustion chamber, to form a mixture of carbon monoxide and
hydrogen. This cracked gas is then expanded to perform work in a
gas turbine to the inlet pressure of the succeeding power plant
process. This succeeding power plant process may be carried out in
a gas turbine power plant or a steam boiler plant and begins in
either case in a combustion chamber which produces hot combustion
gas.
THE DRAWINGS
FIG. 1 is a flow diagram illustrating the power plant process of
this invention;
FIG. 2 is a flow diagram illustrating an alternate embodiment of
the power plant process of this invention; and
FIG. 3 is a flow diagram illustrating another alternate embodiment
of the power plant process of this invention.
DESCRIPTION
The feed hydrocarbons may be thermally or catalytically cracked
with steam in an endothermic reaction with an indirect supply of
heat, e.g., in a tubular heater. Alternatively, the cracking may be
effected in an autothermic process with steam and an addition of
oxygen or air or mixtures thereof and carbon dioxide may also be
admixed to the feed mixture.
The power plant process according to the invention is characterized
in that the fuel before being burnt is cracked with steam and under
a pressure which is higher than the pressure in the combustion
chamber to produce a gas which is high in CO and H.sub.2 and is
expanded to perform work in a gas turbine before it is admitted to
the combustion chamber. The fuel consists preferably of hydrocarbon
mixtures which can be cracked with steam by the known steam
reforming process and are either available at a pressure which is
higher than the pressure in the combustion chamber or can be
pressurized to said elevated pressure.
At first glance, the operation according to the invention may seem
to involve an uneconomical complication of the power plant process.
A calculation surprisingly shows, however, that the quantity of
heat required in the power plant process according to the invention
for the generation of electric power is distinctly lower than in
comparable known power plant processes.
This advantage is probably due to the fact that the gas produced by
a cracking of hydrocarbons has a substantially larger volume than
the feed materials fuel and steam and any added oxygen, air or
carbon dioxide.
It is apparent from the following reaction equations that in the
least favorable case, in which methane is used, this increase in
volume is by a factor of 2:
Ch.sub.4 + 1/2 o.sub.2 = co + 2h.sub.2 (partial oxidation,
exothermic)
Ch.sub.4 + h.sub.2 o = co + 3h.sub.2 (cracking with steam,
endothermic)
Ch.sub.4 + co.sub.2 =2co + 2h.sub.2 (endothermic)
This factor F increases as the C number of the
hydrocarbon-containing fuel is increased. The following equations
are applicable to ethane:
C.sub.2 H.sub.6 + O.sub.2 = 2CO + 3H.sub.2 F = 2.5 C.sub.2 H.sub.6
+ 2H.sub.2 O = 2CO +F = 2.23 C.sub.2 H.sub.6 + 2CO.sub.2 = 4CO +
3H.sub.2 F = 2.23
the following equations are applicable to butane:
C.sub.4 H.sub.10 + 20.sub.2 = 4CO + 5H.sub.2 F = 3 C.sub.4 H.sub.10
+ 4H.sub.2 O = 4CO + 9H.sub.2 F = 2.6 C.sub.4 H.sub.10 + 4CO.sub.2
= 8CO +F = 2.6 2
the factors range from 2.6 to 3.
Liquid hydrocarbons can be pressurized to a higher pressure by a
pump having a capacity which corresponds to the liquid volume. The
work of compression is required to pressurize gaseous hydrocarbons
to that higher pressure unless said gases are available under a
sufficiently elevated pressure, such as is the case, e.g., with
natural gas and with some exhaust gases from refineries.
When the primary cracked gas, which consists mainly of carbon
monoxide and hydrogen, has been expanded to perform work, the
expanded gas may be supplied in the process according to the
invention to a steam boiler power plant or a turbine power plant.
Both embodiments are shown by way of Example in FIGS. 1 to 3 in
flow schemes.
In the plant according to FIG. 1, the process of the invention
involves expansion of a cracked gas produced under pressure prior
to being fed to a steam turbine power plant.
In the plant shown in FIG. 2, the power plant to which the cracked
gas produced under pressure is admitted is a gas turbine power
plant.
In the plant shown in FIG. 3, hydrocarbons are cracked in an
indirectly heated tubular heater, which is succeeded by a steam
turbine power plant.
The plant according to FIG. 1 comprises a cracking reactor 4, a gas
turbine 6, which drives an air compressor 7 and an electric
generator 8, a steam boiler 11, a steam turbine 12 provided with a
condenser 13, and an electric generator 14.
In this case, the cracking reactor consists of a shaft furnace
which is filled with a cracking catalyst, e.g., a nickel catalyst
on a magnesia support.
The feed hydrocarbons used as a fuel are subjected to autothermic
cracking with steam, which is extracted by a conduit 3 from a
medium-pressure outlet of the stem turbine 12, and with an addition
of air. The fuel itself is supplied through conduit 1. Air is
pressurized in the compressor 7 to the pressure in the cracking
reactor and is supplied through conduit 2 to the reactor 4 to
supply the heat required for the endothermic crack reaction. Fuel,
steam and air are mixed in known manner as or before they enter the
cracking reactor.
The cracked gas produced in the cracking reactor 4 is conducted
through conduit 5 to the turbine 6 and expanded in the latter to
the ambient pressure. The work performed by the turbine is expended
in the air compressor 7 and the electric generator 8. The cracked
gas which has been expanded and cooled flows from turbine 6 through
a conduit 17 to the combustion chamber of the steam boiler 11 and
is burnt therein with air which has been preheated in known manner
by a utilization of waste heat and is supplied through conduit 9.
The flue gas is exhausted through conduit 10. The steam which is
generated in the steam boiler 11 flows in conduit 16 to a
multi-stage steam turbine 12, from which part of the steam is
extracted behind the first stage under the pressure which is
required to crack the fuel in the reactor 4. The remaining steam is
expanded to ambient pressure in the second stage of the steam
turbine 12 and is then condensed in the condensor 13.
In the embodiment shown in FIG. 2, the inserted fuel is cracked
under a much higher pressure so that the cracked gas which has been
expanded can be burnt under a higher pressure.
The plant shown in FIG. 2 consists of a cracking reactor 104, a
first gas turbine 106 used to expand the cracked gas, a combustion
chamber 112, a second gas turbine 113 fed with flue gas, a waste
heat boiler 116, a steam turbine 118 provided with a condensor 119,
air compressors 114 and 107 and electric generators 108, 115,
120.
The hydrocarbons fed as a fuel are supplied into the cracking
reactor 104 through conduit 101. The air which is required for
autothermic cracking is sucked through conduit 121 by the first
compressor 114, precompressed by the latter to the mean pressure in
the combustion chamber, and conducted through a conduit 122 and a
waste heat boiler 111, in which the heat of compression is utilized
to produce the steam for the cracking reaction. Part of the
precompressed air is branched off behind the waste heat boiler 111
by a conduit 109 and supplied to the combustion chamber 112 of the
second gas turbine. The other part is supplied in conduit 123 to
the second compressor 107, in which the air is compressed to the
pressure of the cracking reaction and discharges the compressed air
through conduit 102 to the cracking reactor 104, the steam for the
cracking reaction is supplied from waste heat boiler 111 through
conduit 103 to cracking reactor 104. The cracked gas produced under
pressure flows from the cracking reactor in conduit 105 to the
first gas turbine 106, in which the gas is expanded to an
intermediate pressure to perform work. The work is performed in the
second air compressor 107 and the electric generator 108.
The cracked gas which has been expanded to intermediate pressure
flows from the gas trubine 106 through the conduit 124 to the
combustion chamber 112 of the second gas turbine and is burnt in
the latter with precompressed air from conduit 109. The resulting
hot combustion flue gas is conducted in conduit 110 to the second
gas turbine 113 and is expanded therein to ambient pressure with
performance of work. The work performed in the gas turbine 113 is
expanded in the first air compressor 114 and the electric generator
115.
The exhaust gas from the second gas turbine is conducted through
conduit 125 to the waste heat boiler 116 and is passed from the
latter through conduit 110 to the chimney.
The steam produced in waste heat boiler 116 is passed in conduit
117 to the steam turbine 118 and is deposited behind the same in
condenser 119. The steam turbine 118 drives the electric generator
120.
The plant shown in FIG. 3 consists of a cracking reactor 204, a gas
turbine 206, which drives an electric generator 208, a steam boiler
211 and a steam turbine 212, which is provided with a condenser 213
and drives an electric generator 214. In this case, the cracking
reactor 204 is an externally heated tubular heater, the tubes of
which are filled with a cracking catalyst, e.g., a nickel catalyst
on an alumina support, Hence, the hydrocarbons fed as fuel are
cracked with steam and with a supply of sensible heat.
Steam is extracted through a conduit 202 from an
intermediate-pressure outlet of the steam turbine 212. Fuel is fed
through conduit 201. Hot flue gas is supplied through conduit 203
and caused to flow around the cracking tubes to deliver part of its
sensible heat. The cracked gas produced in the cracking reactor 204
is supplied through conduit 205 to the turbine 206, which drives
the electric generator 208. The cracked gas which has been expanded
in the turbine flows through a conduit 215 to a combustion chamber
207, in which it is burnt with air from conduit 209. Part of the
flue gas flows through conduit 216 directly to the steam boiler
211. The remaining flue gas is conducted in conduit 203 to the
cracking reactor 204 and when it has delivered part of its sensible
heat is also supplied to the steam boiler 211 through 217. The
cooled flue gas is exhausted from the steam boiler through conduit
218. The steam which has been generated flows through conduit 210
into the turbine 212, in which part of the steam is extracted
behind the first expansion stage and supplied through conduit 202
to the cracking reactor 204. The remaining steam is completely
expanded and condensed in condenser 213. The turbine drives the
electric generator 214.
The invention will now be explained more fully with reference to
the following examples:
EXAMPLE 1
In the embodiment shown in FIG. 1, 1.17 standard cubic meters
methane 1 having a net calorific value corresponding to 10,000
kilocalories are catalytically cracked under a pressure of 10
kilograms per square centimeter absolute pressure and at a
temperature of 820.degree.C in a cracking under 4 supplied with 4
standard cubic meters air 2 and 0.754 standard cubic meters steam
3. 7.43 standard cubic meters moist gas 5 are thus formed, which
has the following composition:
CO.sub.2 5.6% by volume CO 10.1% by volume H.sub.2 30.3of by volume
% by 2 42.7% by volume H.sub.2 O 11.3% by volume Total: 100.0% by
volume
The calorific value is 1086 kilocalories per standard cubic meter.
This gas is admitted at 820.degree.C to the gas turbine 6, where it
is expanded to ambient pressure with utilization of the temperature
gradient to 390.degree.C. In this operation, the turbine performs
work corresponding to 1.33 kWh. 0.45 kWh being expended in the air
compressor 7, 0.88 kWh of electric energy are generated in the
electric generator 8.
The gas exhausted from the turbine has the following heat
content:
Heat due to calorific value 8060 kilocalories Sensible heat 965
kilocalories Total: 9025 kilocalories The expanded gas is burnt
with 7.2 standard cubic meters of air 9 to produce 13.13 standard
cubic meters of flue gas 10, the heat of which is used to generate
steam in a steam boiler 11. The steam drives the steam turbine 12,
which is provided with a condenser 13. The steam turbine 12 drives
the electric generator 14, which generates electric power.
A good steam process requires 2,200 kilocalories per kWh if all
losses are taken into account
Heat available in the gas 9025 kilocalories Heat content of
generated steam 410 kilocalories From the remainder of 8615
kilocalories,
8615:2200 = 3.92 kWh are generated. The total air requirement 15 of
this operation is 11.2 standard cubic meters.
In the overall process, 10,000 kilocalories are converted into 3.92
+ 0.88 = 4.80 kWh. The heat rate of 10,000 : 4.8 = 2,080
kilocalories per kWh is lower than the figure of 2,200 kilocalories
per kWh in the known process used for a comparison.
EXAMPLE 2
In the embodiment shown in FIG. 2, 1.17 standard cubic meters of
methane 101 are also cracked in the cracking unit 104, which is
supplied with 4 standard cubic meters air 102 and 0.754 standard
cubic meters steam 103, In this case, cracking is effected under a
pressure of 40 kilograms per square centimeter absolute pressure
and at 820.degree.C on a catalyst.
Under these conditions, the cracked gas contains methane in view of
equilibrium requirements so that a small additional amount of
methane passes through the cracking unit without being changed
therein. This additional amount of methane has not been taken into
account in the calculation because it does not change the basic
process. The above reference to 1.17 standard cubic meters of
methane thus relates only to the methane which is completely
cracked to form also 7.43 standard cubic meters of gas 105 having
the same composition as in Example 1.
The pressure is reduced to 10 kilograms per square centimeter
absolute pressure in a gas turbine 106 so that a temperature of
540.degree.C. is obtained and 0.88 kWh are generated, 0.27 kWh of
which are expended in the air compressor 107 so that 0.61 kWh of
electric energy are generated in the electric generator 108. The
steam required in the cracking unit is generated in this case in
the waste heat boiler 111 from feed water heated with waste heat
from the compressed air.
The gas is then burnt in the combustion chamber 112 with a total of
43.3 standard cubic meters of air 109 to produce 49.23 standard
cubic meters flue gas 110, which at a temperature of 820.degree.C
enters the second gas turbine 113 and is expanded therein to
ambient pressure, whereby a temperature of 390.degree.C is
obtained. This results in a generation of 8.75 kWh, of which 5.25
kWh are expended in the air compressor 114 to compress 43.3 + 4.0
standard cubic meters of air to a pressure of 10 kilograms per
square centimeter absolute pressure so that 3.5 kWh of electric
energy are generated in the generator 115.
The exhaust gases are cooled to 100.degree.C in a succeeding waste
heat boiler 116 so that additional 6.7 kilograms of steam 117 under
a pressure of 10 kilograms per square centimeter absolute pressure
are generated. A steam turbine 118 provided with a condenser 119
drives the lectric generator 120, which generates 1.14 kWh of
electric energy. The electric energy produced in the overall
process thus amounts to
0.61 + 3.50 + 1.14 = 5.25 kWh
so that the heat rate is 1,900 kilocalories per kWh. The total air
requirement 121 amounts to 47.3 standard cubic meters.
EXAMPLE 3
A true comparison process may be carried out in the plant of FIG.
2. This comparison process begins in the combustion chamber 112 and
comprises burning the 1.17 standard cubic meters methane directly
with 54.4 standard cubic meters air 109 to produce 55.5 standard
cubic meters flue gas 110, which is admitted to the gas turbine 113
at a temperature of 820.degree.C.
As the flue gas is expanded to ambient pressure in the gas turbine
113, the temperature drops to 390.degree.C and 9.85 kWh are
generated. 6.05 kWh are expended in the air compressor 114 so that
the electric generator 115 generates 3.80 kWh of electric
energy.
The flue gas is again cooled in the waste heat boiler 116 to
generate 7.5 kilograms steam 117 under a pressure of 10 kilograms
per square centimeter absolute pressure. This steam is used to
generate 1.28 kWh by means of a steam turbine 118, provided with
the condenser 119, and of the electric generator 120.
The electric energy produced in the overall process thus amounts
to
3.80 + 1.28 = 5.08 kWh.
The heat rate of 1,970 kilocalories per hour is higher than in the
process according to the invention. The air requirement is also
correspondingly higher.
EXAMPLE 4
In the embodiment shown in FIG. 3, 1.17 standard cubic meters
methane 201 having a heat content of 10,000 kilocalories due to the
net calorific value, are catalytically cracked under a pressure of
10 kilograms per square centimeter absolute pressure and at
820.degree.C in a tubular cracking unit 204 supplied with 3.06
standard cubic meters H.sub.2 O 202 and with flue gas 203. The flue
gas supplied to the cracking unit delivers 4,050 kilocalories to
the cracking reaction, which results in the formation of 6.57
standard cubic meters of moist gas 205 having the following
composition:
CO.sub.2 5.1% CO 12.7% H.sub.2 58.5% H.sub.2 O 23.7%
the calorific value is 1,886 kilocalories per standard cubic meter.
This gas is admitted at 820.degree.C to the gas turbine 206, where
it is expanded to ambient pressure. The turbine performs work
amounting to 1.18 kWh, and this work is expended in the electric
generator 208 to generate electric energy. The expended gas
exhausted from the gas turbine is burnt in a combustion chamber 207
supplied with 11.2 standard cubic meters air, whereby 15.34
standard cubic meters of hot flue gas are produced. 6.86 standard
cubic meters of that flue gas are supplied through conduit 203 to
cracking unit 204 and leave the latter by conduit 217 at about
900.degree.C and are further utilized in the steam boiler 211. The
remaining 8.57 standard cubic meters of flue gas directly enter the
steam boiler. The steam generated in the steam boiler drives the
steam turbine 212, which is provided with a condenser 213. The
steam turbine 212 drives the electric generator 214, which
generates electric energy.
At 820.degree.C., the cracked gas has the following heat
content:
Heat due to calorific value 12,400 kilocalories Sensible heat 1,870
kilocalories Total: 14,270 kilocalories
Of that heat, 1,014 kilocalories are consumed in the gas turbine so
that the cracked gas supplied to the combustion chamber contains
13,256 kilocalories. The same heat quantity is contained in the
flue gas because the air temperature is assumed to be 0.degree.C.
As 4,050 kilocalories are delivered from the flue gas to the
cracking unit, the remainder which is available for the steam
boiler amounts to 9,204 kilocalories. The steam delivered from the
turbine 212 to the cracking unit has a heat content of 1,660
kilocalories so that the remainder which is available to generate
electric energy amounts to 7,546 kilocalories and can be used in a
good steam power process to generate 7,546:2,200 = 3.40 kWh.
In the overall process, 10,000 kilocalories are converted into 1.18
+ 3.40 = 4.58 kWh and the heat rate of 2,180 kilocalories per kWh
is still slightly lower than the figure of 2,200 kilocalories per
kWh in the known comparison process.
* * * * *