JPH0318006B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field] The present invention relates to an open cycle gas turbine system using methanol-based fuel, which improves thermal efficiency by effectively recovering waste heat from turbine exhaust. [Prior art] Unlike petroleum, methanol does not contain sulfur, heavy metals, alkali metals, solid substances, etc., so when used as fuel for gas turbines, it does not damage gas turbines and does not cause environmental pollution problems. It has excellent advantages such as not causing any problems.
Therefore, methanol can be said to be ideal as a fuel for gas turbines. Conventionally, obtaining motive power or electric power using such a gas turbine using methanol as fuel has been widely studied. In general, there are various types of gas turbine systems, but the one most commonly used today consists of an air compressor, a combustor, and a turbine. It is directly connected to the turbine. In this case, the difference between the recovered power of the turbine and the power consumed by the air compressor is the net output. The compressed air is used to burn fuel in a combustor, and the combustion gases are expanded to atmospheric pressure in a turbine and then released into the atmosphere. A gas turbine system in which the working fluid does not circulate is generally called an open cycle gas turbine system. The thermal efficiency of such open cycle gas turbine systems can be improved by increasing the turbine inlet temperature and the turbine inlet to outlet pressure ratio. However, in reality, due to the heat resistance of the materials that make up the turbine and the limits of cooling technology for its components, the turbine inlet temperature is currently only 1100°C, and for aircraft engines it is only about 1300°C. . Until now, technology has been developed to raise the turbine inlet temperature to 1500°C, but it is thought that improvements in this area have reached a saturation point. There is also a limit to the pressure ratio between the inlet and outlet of the turbine (hereinafter simply referred to as pressure ratio), and if this upper limit is exceeded, the thermal efficiency will actually decrease. This pressure ratio, which provides the highest thermal efficiency, tends to increase as the turbine inlet temperature increases. However, the pressure ratio in practical use is lower than the pressure ratio that achieves the highest thermal efficiency due to cost considerations, and at a temperature of 1100°C,
4. For aircraft applications where the turbine inlet temperature is 1300℃,
It ranks 20th. Among the gas turbine systems at the current technological level as described above, a simple open cycle gas turbine system that uses petroleum distillate as fuel has a power generation end of the high calorific value standard (hereinafter referred to as HHV standard) at a turbine inlet temperature of 1100°C. Thermal efficiency is approximately 32% (Yukawa et al.; Thermal and Nuclear Power Generation Vol. 31,
No. 12, 1369, 1680). Conventionally, in order to improve the thermal efficiency of the open cycle gas turbine system, so-called combined cycle gas turbines have been developed, in which a Rankine cycle system is used in which the waste heat of the exhaust gas of the turbine is used to generate steam to drive a steam turbine. The system has been put into practical use. The power generation frost thermal efficiency of a combined cycle gas turbine system using regular oil distillate as fuel is approximately 43% based on the HHV standard when the turbine inlet temperature is 1100°C (Yukawa et al., Thermal and Nuclear Power Generation Vo31, No. 12,
1369, 1980). On the other hand, a so-called chain cycle gas turbine system has also been developed in which the steam cycle of the above-mentioned combined cycle gas turbine system is also an open cycle (Japanese Patent Publication No. 54-34865
Publication No.). The shaft end thermal efficiency of this chain cycle gas turbine system that uses petroleum distillate as fuel is:
At a turbine inlet temperature of 1100°C and a pressure ratio of 14,
Approximately 45% based on low calorific value standards (hereinafter referred to as LHV standards)
becomes. This gas turbine system does not require a steam turbine or a condenser, has low construction costs, is simpler than a combined cycle system, has the advantages of easy operation and maintenance, and is highly reliable. Furthermore, its thermal efficiency is on the same level as a combined cycle gas turbine system at a turbine inlet temperature of 1100°C. In the simple open cycle gas turbine system, combined cycle gas turbine system, and chain cycle gas turbine system described above, it is possible to use methanol-based fuel instead of petroleum distillate fuel, but in this case, , the thermal efficiency is about the same or slightly higher. By the way, as mentioned earlier, methanol
In addition to having properties superior to petroleum as a fuel, it also has a temperature below the exhaust gas temperature of a gas turbine (approximately 300℃).
It has the chemical property of undergoing an endothermic reaction in the presence of a catalyst. Attempts have been made to utilize this chemical property to improve the thermal efficiency of gas turbine systems. This endothermic reaction of methanol involves
There is a decomposition reaction of methanol and a reforming reaction between methanol and water. Its chemical formula and endothermic amount are as shown below. [Decomposition reaction] CH ₃ OH→CO+2H ₂ -21.7kca/mol [Reforming reaction] CH ₃ OH+H ₂ O→CO ₂ +3H ₂ -11.8kca/mol Utilizing the endothermic reaction of methanol to increase the thermal efficiency of the gas turbine system For, methanol,
First, it is vaporized using gas turbine exhaust waste heat, and in the case of a decomposition reaction, it is used as is, or in the case of a reforming reaction, steam that is also generated from the waste heat is mixed with this methanol vapor, and then a heat exchange type that is filled with a catalyst is used. An endothermic reaction is carried out in the reactor to increase the heat of the methanol fuel, and the endothermic reaction product gas, which has been heated up, is then combusted in the combustor of the gas turbine system and supplied to the turbine inlet. In this specification, a gas turbine system that utilizes the endothermic reaction of methanol caused by a reforming reaction is referred to as a reforming gas turbine system. In this reforming gas turbine system, the LHV standard shaft end thermal efficiency of the gas turbine system when the gas obtained from the endothermic reactor is further heated to 493°C is:
At a turbine inlet temperature of 1176℃, it is approximately 44% (C.
W.James; “Proceeding, Intersociety of
Energy Conversion Engineering Conference”
14th, Vo. 2, 1979). Shaft end thermal efficiency of the reforming gas turbine system 44
% is not much different from the generating end thermal efficiency of the combined cycle gas turbine, which is 43%. Therefore, a system has been proposed that combines a reforming gas turbine system and the above-mentioned combined cycle gas turbine system (hereinafter referred to as a reforming combined cycle gas turbine system). The LHV standard shaft end thermal efficiency of this system is approximately 53 at a turbine inlet temperature of 1176°C.
% (CWJanes; “Proceeding
Intersociety of Energy Conversion
Engineering Conference”14th, Vo2;
1979). Next, the thermal efficiency of each of the above gas turbine systems is summarized as shown in Table 1.

〔the purpose〕

The present invention overcomes the aforementioned drawbacks of the prior art and provides a system that is simpler than reforming combined cycle gas turbine systems, thereby avoiding increased construction costs, facilitating operation and maintenance, and increasing reliability. Moreover, it is an object of the present invention to provide an open cycle gas turbine system using methanol-based fuel that can achieve thermal efficiency equivalent to that obtained with a reformed combined cycle gas turbine system. [Structure] According to the present invention, in an open gas turbine system using methanol-based fuel that includes an air compressor, a combustor, and a turbine, a methanol vaporizer that vaporizes methanol using a part of the turbine exhaust waste heat; A boiler that vaporizes boiler feed water into steam using a portion of the waste heat, and an endothermic reactor that causes an endothermic reaction of the vaporized methanol or a mixture of the vaporized methanol and a portion of the water vapor using a portion of the waste heat. , a steam superheater for superheating the steam generated in the boiler with a part of the waste heat, and piping for guiding endothermic reaction product gas from the endothermic reactor to the combustor via a heater as the case may be; a combustion gas/steam mixer for mixing combustion gas from the combustor and superheated steam from the superheater; and a duct for guiding the combustion gas/steam mixture from the mixer to the turbine; a first waste heat recovery system consisting of the steam superheater and a heater provided as the case may be for heating the endothermic reaction product gas; a second waste heat recovery system consisting of the reactor; and the boiler. and a third waste heat recovery system consisting of the methanol vaporizer and the third waste heat recovery system are arranged in series in the order of the waste heat recovery systems along the flow direction of the gas turbine exhaust gas. be done. The main features of the gas turbine system of the present invention are:
In summary, a methanol vaporizer vaporizes methanol using a portion of turbine exhaust waste heat, a boiler vaporizes boiler feed water, and a mixture of vaporized methanol or vaporized methanol and a portion of the water vapor generated in the boiler is subjected to an endothermic reaction. an endothermic reactor that generates an endothermic reaction product gas, a superheater that superheats the remaining steam from the boiler from which the steam to be mixed with the vaporized methanol is extracted, and a heater that heats the endothermic reaction product gas. At the same time, the remaining steam obtained from the boiler is superheated by a part of the waste heat, and the superheated steam obtained is used to burn the endothermic reaction product gas without passing through the endothermic reactor and combustor. The point is that it is directly mixed with gas and supplied to the turbine. In the gas turbine system of the present invention, the gas turbine inlet temperature can be lowered and the excess air rate of the combustor can be reduced, so the power consumption of the air compressor for obtaining compressed air is reduced. As a result, increasing the net power output of the turbine,
The thermal efficiency of the system can be improved to almost the same level as that of the reforming combined cycle gas turbine system, which is currently considered the most thermally efficient system. Furthermore, the gas turbine system of the present invention does not require cooling equipment such as a steam turbine, a condenser, and a chilled water tower, compared to the above-mentioned modified combined cycle gas turbine system, and the equipment cost is low, as well as its operation. It has various advantages such as being very easy to maintain. Furthermore, it has better thermal efficiency than a chain cycle gas turbine system, and also has the characteristics that the amount of boiler feed water is less due to the endothermic reaction. Note that the methanol endothermic reaction in this specification refers to a reaction that chemically changes methanol into a compound with a larger calorific value than methanol, and such endothermic reactions include methanol decomposition reactions and methanol decomposition reactions. Modification reactions are included. When comparing a methanol decomposition reaction and a reforming reaction, the former recovers a larger amount of waste heat and has a higher thermal efficiency, but carbon deposition is more likely to occur than the latter. Therefore, from the viewpoint of carbon precipitation, the latter is more advantageous, and the latter can also be effectively utilized as an endothermic reaction in the present invention.
Furthermore, both the methanol decomposition reaction and the reforming reaction described above are carried out in the presence of a catalyst, and commercially available catalysts or conventionally known catalysts can be used as the catalyst. Moreover, the endothermic reaction product gas as used herein means the reaction product gas obtained by the endothermic reaction. Furthermore, the methanol-based fuel as used herein means methanol or a fuel containing methanol as a main component. Next, one example of the gas turbine system of the present invention will be explained with reference to FIG. In FIG. 1, 1 is a turbine, and 2 and 3 are an air compressor and a generator, respectively, which are coaxially attached to the turbine. 4 and 4' indicate the flue through which the turbine exhaust gas passes. 5 is a steam superheater, 6 is an endothermic reaction product gas heater, 7 is an endothermic reactor, 8 is a boiler, 9 is a methanol vaporizer, and 10 is a water preheater, all of which are installed in the flue 4 of the turbine exhaust. will be placed in The high-temperature exhaust gas discharged from the turbine 1 is at atmospheric pressure or pressurized to about 200 mmH ₂ O to 1000 mmH ₂ O above atmospheric pressure, and is released into the atmosphere through the flues 4 and 4'. The waste heat possessed by the exhaust gas is recovered by each of the equipment installed in the flue 4 described above. That is, water is supplied through line 20, which is preheated in water preheater 10 and then sent to deaerator 11, where the degassed gas is separated through line 22. The degassed water is sent to the boiler 8 by the boiler feed water pump 12, where it is vaporized and extracted as steam through a line 25. On the other hand, methanol is supplied to the methanol vaporizer 9 through a line 26, and vaporized methanol is extracted through a line 27. The vaporized methanol extracted from the methanol vaporizer 9 through the line 27 is transferred to the steam/methanol mixer 39 via the line 28 branched from the line 25.
After passing through line 29 to reactor 7 where it undergoes an endothermic reaction, the product gas is withdrawn through line 30 where it undergoes further endothermic reaction. Generated gas heater 6
combustor 31 through line 31.
sent to. On the other hand, steam extracted from the boiler 8 through the line 25 and passing through the line 32 is sent to the steam superheater 5, where it is superheated, and then extracted through the line 33 as superheated steam. Endothermic reaction product gas is supplied to the combustor 13 through a line 31, and compressed air obtained by compressing air from a line 34 with an air compressor 2 is supplied through a line 35. The endothermic reaction product gas is combusted through the combustor 13 via line 36.
extracted from. This combustion gas is mixed with superheated steam from a line 33 in a combustion gas/steam mixer 38, and then supplied to the turbine 1 to drive the turbine 1. A part of this turbine driving force is used for air compression by the air compressor 2, and the remainder becomes the net output, which is used to drive the generator 3 to generate electricity or used as a power source. . In the gas turbine system of the present invention, the type of the boiler 8 may be either a drum water tube type or a once-through type with natural circulation or forced circulation, and the type of the methanol vaporizer 9 may also be either a drum water tube type or a once-through type. . As the endothermic reactor, a multi-tubular heat exchange type reactor can be installed inside the flue, and a fixed bed type reactor can be used outside the flue. If a fixed bed reactor is used, a heat exchanger is installed in the flue and the water/methanol mixture is forced to circulate between the heat exchanger and the fixed bed reactor. In the present invention, it has been found that in order to obtain a gas turbine system with maximum thermal efficiency, the arrangement order of the equipment group for recovering turbine exhaust waste heat is very important. That is, in the present invention, a first waste heat recovery system includes a steam superheater 5 and an endothermic reaction product gas heater 6, a second waste heat recovery system includes an endothermic reactor 7, a boiler 8, and a methanol vaporizer. A third waste heat recovery system consisting of 9 is arranged in series in the order of the waste heat recovery system along the flow direction of the turbine exhaust gas. In this case, the arrangement of the steam superheater 5 and endothermic reaction product gas heater 6 in the first waste heat recovery system and the arrangement of the boiler 8 and methanol vaporizer 9 in the third waste heat recovery system are arbitrary. In addition to series arrangement, parallel arrangement can be adopted.
In addition, the pinch temperature difference on the high temperature side of the first waste heat recovery system is
The temperature is preferably around 60°C, and the pinch temperature difference on the low temperature side of the third waste heat recovery system is preferably around 30°C. In the gas turbine system shown in FIG. 1, the water preheater 10 does not necessarily need to be installed in the flue, and the endothermic reaction product gas heater 6 is not necessarily required. In particular, when the water/methanol mixing ratio is 0, the endothermic reaction becomes a methanol decomposition reaction, and the reaction product gas consists of a mixture of carbon monoxide and hydrogen, causing a carbon precipitation reaction in the heater 6. In this case, it is better not to heat the endothermic reaction product gas as there is a risk of blockage. Further, in FIG. 1, the boiler 8 and methanol vaporizer 9 are shown as being of the drum water tube type, and the flue is shown as being horizontal, but the boiler 8 and the methanol vaporizer 9 are shown as having a once-through flow. The flue may be of the vertical type. The boiler feed water sent to the water preheater via line 20 is advantageously ion-exchanged water, which is similar to normal low-pressure boiler feed water.
In addition, a methanol preheater is installed in the flue.
It is also possible to send preheated methanol to the metal vaporizer 9. The gas turbine system of the present invention is operated by the flow system as described above, and the boiler 8
When steam is generated in a turbine, the steam pressure needs to be higher than the turbine inlet pressure. The amount of steam generated is preferably the maximum amount that can be obtained from gas turbine exhaust waste heat. Practically speaking, the amount of water vapor is at most about 6 times the mole of vaporized methanol. Also endothermic reactor 7
The amount of water vapor mixed with part of the water vapor generated in the boiler 8 through the line 28 is 0 to 1 mole of methanol.
The proportion is preferably 2 moles, and if it exceeds this range, the combustibility of the endothermic reaction product gas obtained from the reactor 7 will deteriorate, which is not preferable. Note that when the steam mixing ratio to vaporized methanol is zero, a methanol decomposition reaction takes place in the reactor 7, and when the steam mixing ratio is set to a molar ratio of 1 or more, the methanol decomposition reaction takes place in the reactor 7.
In this case, the methanol reforming reaction proceeds smoothly. The reaction temperature in the endothermic reactor 7 is selected so that the methanol conversion rate is 90% or more, and is generally about 250 to 300°C, depending on the pressure. line 32
The maximum amount of steam sent to the combustion gas/steam mixer 38 via the steam superheater 5 through the line 33 is typically the methanol 1 supplied.
Per mole, it is about 6 moles in the case of methanol decomposition reaction, and about 5 to 4 moles in the case of methanol reforming reaction, and it is preferable that as much steam as possible is sent to the mixer 38. Further, it is preferable that the temperature of the combustion gas/steam mixture is as high as possible within the permissible temperature range at the turbine inlet, and for this purpose, the capacity of the air compressor is selected to be as small as possible. [Example] Next, the present invention will be explained in more detail with reference to Examples. Example In the gas turbine system shown in FIG. 1, the LHV standard (low calorific value standard) shaft end thermal efficiency was calculated. In this case, the atmospheric pressure is 1 atm, the atmospheric temperature is 15°C, the turbine back pressure is 1 atm, the polytropic efficiency of the air compressor is 87%, and the adiabatic efficiency of the turbine is 90%.
%, the combustion efficiency was 100%, and each pressure loss in the combustor and combustion gas/steam mixer was 0%. Regarding turbine inlet temperature, 800℃, 1100℃ and
The temperature was set at 1400°C, and the turbine inlet/outlet pressure ratios were set at 8, 14, 20, and 30. Table 2 shows the LHV standard axial thermal efficiency and other specifications when a methanol reforming reaction with a water/methanol molar ratio of 1 is used, and Table 3 shows a methanol decomposition reaction with a water/methanol molar ratio of 0. in case of
Shows LHV standard shaft end thermal efficiency and other specifications.

【table】

[Table] The thermal efficiency shown in Tables 2 and 3 above uses the turbine back pressure at atmospheric pressure for convenience, but in reality, taking into account the pressure loss due to equipment installed in the flue, it is calculated using atmospheric pressure. Usually, a high back pressure of about 200 to 1000 mmH ₂ O is selected. In this case, the thermal efficiency is lower than in the case of atmospheric back pressure, but the reduction in thermal efficiency is shown in the following table.

[Table] Also, for convenience, the thermal efficiency shown in Tables 2 and 3 above is calculated assuming that the pressure loss of the combustor and combustion gas/steam mixer is 0% of the pressure ratio.
In reality, there is a pressure loss of 2-4%. Table 5 shows the decrease in thermal efficiency when this pressure loss is taken into consideration.

〔effect〕

As is clear from comparing the thermal efficiency of the gas turbine system of the present invention shown in Tables 2 and 3 above with the thermal efficiency of the conventional system shown in Table 1,
Regarding the thermal efficiency of the gas turbine system of the present invention, when using a methanol reforming reaction, the LHV standard shaft end thermal efficiency is approximately 52% at a turbine inlet temperature of 1100°C and a pressure ratio of 14, which is the same as that of a reforming combined cycle gas turbine. It can be said that it is almost the same as the system (note that the turbine inlet temperature in Table 1 is 1171℃). In the case of methanol decomposition reaction, the thermal efficiency is approximately 53% under the same conditions, which is also the same thermal efficiency as the reforming combined cycle gas turbine system.
Additionally, this thermal efficiency is 46% for the combined cycle gas turbine system and 45% for the shaft end thermal efficiency for the chain cycle gas turbine system.
%, shaft end thermal efficiency of reforming gas turbine system 44%
The thermal efficiency is higher than either value, and the shaft-end thermal efficiency of a gas turbine system that combines methanol vaporization using turbine exhaust waste heat and a chain cycle is approximately 50%, so it is better than this. The reason why the gas turbine system of the present invention is able to achieve high thermal efficiency is due to the combination of its sophisticated waste heat recovery system. That is, a first waste heat recovery system consisting of a steam superheater and an endothermic reaction product gas heater, a second waste heat recovery system consisting of a reactor, and a third waste heat recovery system consisting of a boiler and a methanol vaporizer are: They are arranged in series in that order along the flow direction of the turbine exhaust gas. FIG. 2 shows a diagram showing the relationship between the temperature of the waste heat system and the amount of heat transfer under the same criteria as the conditions of operation No. 2 in Table 2 above. In this diagram, line -A shows waste heat recovery from the turbine exhaust, and the turbine exhaust has an exhaust temperature of 635
°C to a flue emission temperature of 121 °C. on the other hand,
Line-5 is waste heat recovery in the steam superheater 5, line-6 is waste heat recovery in the endothermic reaction product gas heater 6, line-7
is waste heat recovery in the endothermic reactor 7, line -8 is waste heat recovery in the boiler 8, line -9 is waste heat recovery in the methanol vaporizer 9, and line -10 is waste heat recovery in the water preheater 10. are shown respectively. As shown in this diagram, in the case of the present invention, heat recovery equipment is arranged in a specific order, and waste heat recovery is performed at multiple temperature levels corresponding to each heat recovery equipment. It is understood that the exergy loss is decreasing. The gas turbine system of the present invention exhibits high thermal efficiency as described above, is significantly simpler than a reforming combined cycle gas turbine system, has low construction costs, and has low system operation and
It is easy to maintain and has extremely high system reliability. Furthermore, in the case of the system of the present invention,
Excess air rate is lower than normal gas turbines,
Although the temperature of the combustion gas is somewhat high, it is not in the temperature/time range where it is immediately cooled by water vapor and nitrogen oxides increase. Therefore, a denitrification oxide device is not required or its load can be greatly reduced. In the system of the present invention, it is necessary to reduce the capacity of the air compressor compared to a normal gas turbine. This can be easily implemented by Considering that the system of the present invention has a simple equipment system, low construction cost, and easy operation and maintenance, it is preferably applied as a small-output power generation system, and in particular, by applying it to distributed power generation, it can be It is also possible to improve efficiency.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of an open cycle gas turbine system of the present invention. 1...Turbine,
2... Air compressor, 3... Generator, 4,4'...
Flue, 5... Steam superheater, 6... Endothermic reaction product gas heater, 7... Endothermic reactor, 8... Boiler, 9... Methanol vaporizer, 10... Water preheater, 13... Combustion vessel. FIG. 2 is a diagram showing the relationship between the temperature (° C.) of the waste heat recovery system and the amount of heat transfer when the methanol reforming reaction is used. Line-A...Turbine exhaust waste heat recovery line,
Line-5...Waste heat recovery line in steam superheater 5, line-
6...Waste heat recovery line at the endothermic reaction product gas heater 6, line -7...Waste heat recovery line at the endothermic reactor 7, line -8...Waste heat recovery line at the boiler 8, line -9 ……
Waste heat recovery line in methanol vaporizer 9, line -10...
...Waste heat recovery line in the water preheater 10.

Claims (1)

[Claims] 1. In an open cycle gas turbine system using methanol-based fuel consisting of an air compressor, a combustor, and a turbine, there is a methanol vaporizer that vaporizes methanol using a portion of the turbine exhaust waste heat, and a methanol vaporizer that vaporizes methanol using a portion of the waste heat. A boiler that vaporizes boiler feed water into water vapor, an endothermic reactor that causes an endothermic reaction of the vaporized methanol or a mixture of the vaporized methanol and a portion of the water vapor using a portion of the waste heat, and the water vapor generated in the boiler. a steam superheater for superheating the endothermic reactor with a part of the waste heat, and a pipe for guiding endothermic reaction product gas from the endothermic reactor to the combustor via a heater as the case may be; a combustion gas/steam mixer for mixing combustion gas and superheated steam from the superheater; a duct for guiding the combustion gas/steam mixture from the mixer to the turbine; a first waste heat recovery system consisting of a heater for heating the gas produced by the endothermic reaction disposed therein; a second waste heat recovery system consisting of the endothermic reactor; the boiler and the methanol vaporizer. A third waste heat recovery system comprising: and a third waste heat recovery system are arranged in series in the order of the waste heat recovery systems along the flow direction of the gas turbine exhaust gas.