JP2001241304A - Combined power generation system utilizing gas pressure energy - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a combined power generation system wherein utilities such as steam and water are unnecessary, an operation and maintenance are easy, and high power generation output and a power generating efficiency are achieved by recovering gas pressure energy which is not utilized beforehand. SOLUTION: The combined power generation system is provided with a gas turbine 1, an expansion turbine 7 serving fuel gas as an operating fluid, a power generator 4 driven by those turbines, and exhaust heat recovering/gas heater 12 for recovering exhaust heat from the gas turbine 1 and for heating the fuel gas which flows into the expansion turbine 7 using exhaust heat.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power generation system, and more particularly to a combined power generation system using gas turbine power generation and expansion turbine power generation using gas pressure energy for use in a fuel gas decompression facility or the like. About.

[0002]

2. Description of the Related Art Compared to steam power generation, gas turbine power generation has the advantages that it is easy to perform large load fluctuations, sudden start / stop, and has excellent load adjustment functions. Due to its lowness, in Japan,
Although it was used during peak times of power demand, it was rarely used as a regular power generation facility. However, as a means to improve the overall power generation efficiency of power generation by gas turbines,
Combined cycle power generation of gas turbines and steam power plants has emerged, and has now become the mainstream of natural gas-fired power generation.

There are several types of combined cycle power generation systems, and the simplest and most widely used system is a system called an exhaust heat recovery system, and as shown in FIG. To the exhaust heat recovery boiler 2, recovering the heat of the exhaust gas to generate steam, using this steam to drive the steam turbine 3, and driving the generator 4 with the gas turbine 1 and the steam turbine 3. It is. In the figure, reference numeral 5 denotes a condenser for condensing steam.

On the other hand, in order to transport fuel gas economically and efficiently, fuel gas such as city gas and natural gas is delivered to a transport pipeline at high pressure. This high-pressure fuel gas is reduced to a pressure required by a demand destination near a gas demand area. Conventionally, this pressure reduction operation has been generally performed by a pressure reduction valve of a governor station (pressure reduction equipment). Utilizing all or a part of this fuel gas decompression process for power generation using an expansion turbine to recover pressure energy as electric power (hereinafter, referred to as gas pressure recovery power generation) requires the use of pressure energy that has not been used until now. Is useful and useful. Gas pressure recovery power generation that supplies high-pressure fuel gas as a working fluid to an expansion turbine has been conventionally known as LNG.
(Liquefied natural gas) is being implemented mainly at bases. In this power generation facility, as shown in FIG. 5, LNG pressurized by a pump is vaporized by a vaporizer 6, and the gas is decompressed and expanded by an expansion turbine 7, thereby driving a generator 4 to generate electric power. Since the temperature is lowered during the decompression and expansion, the gas temperature is further raised to a predetermined temperature by the gas heater 8, and then the fuel gas is supplied to the demand destination. L
The NG terminal is generally located on the coast, and often uses a large amount of seawater as a heat source in the vaporizer 6 and the gas heater 8.

[0005] As another example of the gas pressure recovery power generation at the time of fuel gas decompression as described above, when a district heating / cooling facility or a business power generation facility is close to a city gas governor station, the location condition is taken advantage of. Some of them perform gas pressure recovery power generation separately from main power generation by gas engines and gas turbines. FIG. 6 shows an example of such a system, in which gas turbine combined cycle power generation (right side) and gas pressure recovery power generation in which the expansion turbine 7 is operated by utilizing the pressure energy at the time of decompression of city gas and the generator 9 is driven by that power (Left side). The city gas is heated by the preheater 10 and then supplied to the expansion turbine 7,
The temperature of the city gas discharged from is supplied to the demand destination as a predetermined temperature. For heating city gas, low-pressure steam supplied from an exhaust heat boiler 2 for recovering exhaust heat of exhaust gas from a gas turbine combined cycle power generation is used. In the figure, reference numeral 11 denotes a condenser for condensing steam. In addition, Japanese Patent Application Laid-Open No. Hei 7-21 describes power generation using an expansion turbine at a governor station for city gas.
No. 7800.

[0006]

The root of the power supply and demand is currently supported by large-scale power plants because of its high power generation efficiency and economy. These large-capacity thermal and nuclear power plants are often constructed far away from cities and industrial areas where power demand is high, due to location constraints, etc., and are often transmitted endlessly over long distances. In the process of losing a lot of energy, there are many problems in energy security.
In addition, large-scale power plants located in such remote areas are expected to have much more heat demand to collect heat and power even if they collect waste heat from power generation and aim to further improve thermal efficiency. Can not. Under these circumstances, the development of small and medium-sized distributed power generation facilities close to the power demand area is important to complement large-scale power plants that can handle base loads. However, for example, in the case of distributed power generation facilities installed in areas other than the coast, it is often difficult to obtain utilities such as water and steam from the outside, and sufficient personnel such as large-scale facilities cannot be expected. Simple and independent facilities that do not require external water intake are required. In addition, high power generation efficiency is required.

[0007] As described above, in ordinary gas turbine power generation, a composite heat engine is used in which a gas turbine (Preyton cycle) and a steam turbine (Rankine cycle) are combined, and the operating temperature range is widened from high to low. It has improved the total power generation efficiency to the highest level of the current thermal power generation system. Gas turbines
Except for special cases such as those with an intercooler, cooling water is usually unnecessary, but when combined cycle power generation is configured, a large amount of cooling water is required for the condenser of the steam turbine. Although it is possible in principle to use a cooling tower or an air-cooled condenser for condensing water, it is not practical because a large space is required for the installation space. In addition, external boiler water supply is required, and hot drainage to the outside is also generated. Therefore, conventional combined cycle power generation requires a large site for that purpose, and in addition to operation management of the prime mover itself, operation control of the boiler and water treatment (condensation / water supply treatment and boiler water treatment) are required. Therefore, operation and maintenance are more complicated than single gas turbine power generation, and many personnel are required.

On the other hand, providing gas pressure recovery power generation for supplying a high-pressure fuel gas as a working fluid to an expansion turbine in a decompression facility of a fuel gas supply pipeline is effective use of pressure energy which has not been used before. Useful for
The above-described decompression facility close to the gas demand area is generally considered to be close to the power demand area, and it is desirable to install a power generation facility here in terms of power transmission efficiency.

However, there are few practical examples of gas pressure recovery power generation at the time of transporting fuel gas, except for some installation examples described above. One of the technical problems preventing the spread is the problem of securing a heat source. That is, the gas depressurization process at the pressure reducing valve is approximately isenthalpy expansion, while that at the expansion turbine is close to isentropic change. During this expansion process, the gas works on the generator,
The temperature of the fuel gas exhausted from the expansion turbine drops significantly. In the case of fuel gas conduits, if the gas temperature drops below 0 ° C, problems such as freezing and frozen soil in the conduits and surrounding facilities will occur.
It is necessary to keep the gas temperature below 0 ° C. In addition, when the temperature of the gas decreases significantly, some of the gas components may be condensed.In addition, when natural gas contains a certain amount of water or more, hydrate is generated and conduits or pipes are formed. There is also a risk of instrument blockage. For this reason, a gas heater is required on either or both of the upstream side and the downstream side of the pressure reduction step by the expansion turbine. Therefore, it has been difficult to put the gas pressure recovery power generation system into practical use unless a heat source such as seawater, hot water, or steam is in the facility or can be easily supplied and used.

The present invention has been made in order to solve the above-mentioned problems when the conventional combined cycle power generation and gas pressure recovery power generation are used as a distributed power generation facility.
In particular, assuming that it is used as a part or all of the fuel gas decompression equipment, there is no need for utilities such as steam and water, and operation and maintenance are simple, and energy that has not been used so far is used. By collecting high power output,
It is an object of the present invention to provide a combined power generation system using gas pressure energy capable of achieving power generation efficiency.

[0011]

SUMMARY OF THE INVENTION A power generation system according to the present invention includes a gas turbine, an expansion bin using a fuel gas as a working fluid, a generator driven by these turbines, and a waste heat from the gas turbine. Waste heat recovery / heating the fuel gas flowing into the expansion turbine using the waste heat.
And a gas heater. The exhaust heat recovery / gas heater warms the high-pressure fuel gas flowing into the expansion turbine and also heats the low-pressure fuel gas discharged from the expansion turbine. .
The gas turbine further includes an intake air cooler that takes in the cold heat of the low-pressure side fuel gas discharged from the expansion turbine and cools the intake air flowing into the gas turbine.

Further, the exhaust heat recovery / gas heater is configured to exchange heat between the exhaust gas from the gas turbine and the fuel gas. Further, a common generator is driven by the gas turbine and the expansion turbine. Further, a part of the fuel gas used as the working fluid of the expansion turbine is used as the fuel of the gas turbine.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 Most of the exhaust heat of the gas turbine is exhausted as exhaust gas heat. Therefore, in order to improve the thermal efficiency of gas turbine power generation, it is important to efficiently recover exhaust heat of exhaust gas. As seen in the conventional combined cycle power generation that combines a gas turbine and a steam turbine, a general method of recovering waste heat is to generate steam in a waste heat boiler. Is not available and the thermal efficiency remains significantly lower. In the present embodiment, the exhaust heat recovery /
In the gas heater, heat is exchanged between the exhaust gas of the gas turbine and the fuel gas flowing into the expansion turbine to improve the thermal efficiency of gas turbine power generation to about the same level as that of combined cycle power generation, and to reduce the recovered heat. It is used for heating gas required for power generation of the expansion turbine. At this time, the temperature of the fuel gas discharged from the expansion turbine is set to a temperature that does not adversely affect the downstream side (generally 0 ° C. or more).
In the exhaust heat recovery / gas heater, the fuel gas flowing into the expansion turbine is heated to a predetermined temperature.

In general, the temperature of exhaust gas from a gas turbine is as high as about 500 ° C. as compared with other prime movers, while the temperature of fuel gas flowing into an expansion turbine is almost the same as the ambient temperature. Even in the case of direct heat exchange with gas, it is possible to recover waste heat more efficiently than in the case of conventional combined cycle power generation. In other words, the exhaust gas temperature at the exhaust heat boiler outlet in the case of combined cycle power generation is usually determined by the saturated steam temperature at the operating pressure of the boiler, and a multi-pressure boiler or economizer is used to further improve the heat recovery rate. However, the temperature of exhaust gas at the exhaust heat boiler outlet after exhaust heat recovery is usually about 150 to 100 ° C. On the other hand, the temperature of the fuel gas flowing into the expansion turbine is almost the same as the temperature of the exhaust gas, and the temperature difference between the fuel gas and the exhaust gas is large. When the temperature is set to 100 ° C. or 100 ° C. or lower, more heat can be recovered, so that the thermal efficiency of gas turbine power generation can be improved.

FIG. 1 is a configuration diagram of a combined power generation system of gas turbine power generation and gas pressure recovery power generation according to Embodiment 1 of the present invention. In the gas turbine 1 including the compressor, the combustor, and the turbine, the fuel gas for the gas turbine is mixed with the air compressed by the compressor and the combustor and burns,
Generates power when the combustion gas expands in the turbine,
The generator 4 is driven. Then, the high-temperature exhaust gas that has exited the turbine of the gas turbine 1 is introduced into the exhaust heat recovery / gas heater 12, exchanges heat with the fuel gas, is cooled, and is then discharged into the atmosphere. On the other hand, on the side of the expansion turbine 7, high-pressure fuel gas such as city gas is introduced into the exhaust heat recovery / gas heater 12, which is heated by heat exchange with the exhaust gas. to go into. Expansion turbine 7
Generates power when the fuel gas adiabatically expands, and drives the generator 4. The fuel gas exiting the expansion turbine 7 is supplied to a demand destination as a low-pressure fuel gas.

Embodiment 1 FIG. Next, a specific example of the power generation system according to Embodiment 1 will be introduced as Example 1. The type of fuel gas, pressure and temperature conditions for operating the expansion turbine are as follows. Fuel gas type: City gas 13A High-pressure side fuel gas Pressure: 40 kg / cm ² G, temperature: 24 ° C. Low-pressure side fuel gas pressure: 6 kg / cm ² G, temperature: 5 ° C. Gas turbine 1 with an output rating of 1000 kW class and the above The system shown in FIG. 1 is configured by using the expansion turbine 7 using city gas as a working fluid and the exhaust heat recovery / gas heater 12, and the exhaust gas temperature at the outlet of the exhaust heat recovery / gas heater 12 is 100 ° C.
The results are shown below, comparing the city gas consumption and output when operating with setting to be as follows. The power generation efficiency is the ratio of the amount of generated power to the lower calorific value of the fuel gas consumed by the gas turbine.

System of Embodiment 1 Gas turbine power generation alone Gas turbine fuel consumption 402 Nm ³ / h 402 Nm ³ / h Flow rate of working fluid 74,900 Nm ³ / h 0 Nm ³ / h Generator output 4149 kw 1003 kW Power generation efficiency 89.4% 21.6%

As described above, expansion turbine power generation using city gas as a working fluid and gas turbine power generation are combined,
By using the exhaust gas heat from the gas turbine 1 recovered by the exhaust heat recovery / gas heater 12 to heat the city gas flowing into the expansion turbine 7, the thermal efficiency of the gas turbine power generation is improved, and Efficient recovery of pressure energy
Can be achieved simultaneously without utilities such as steam and water. In addition,
In the first embodiment, the temperature of the city gas exiting the exhaust heat recovery / gas heater 12 and entering the expansion turbine 7 is increased to about 97 ° C.

Embodiment 2 FIG. 2 is a configuration diagram of a combined power generation system of gas turbine power generation and gas pressure recovery power generation according to Embodiment 2 of the present invention. This is the same as the system configuration of FIG. 1 except for the flow channel configuration of the working gas on the expansion turbine side including the exhaust heat recovery / gas heater.
That is, both the high-pressure fuel gas introduced into the expansion turbine 7 and the low-pressure fuel gas emitted from the expansion turbine 7 are heated at the front stage and the rear stage of the exhaust heat recovery / gas heater 12, respectively. I have.

As the exhaust gas temperature at the outlet of the exhaust heat recovery / gas warmer 12 is lowered, the amount of heat recovery can be increased and the thermal efficiency can be improved. Expensive. However, the second embodiment
The high-pressure fuel gas on the inlet side of the expansion turbine 7 at the front stage of the exhaust heat recovery / gas heater 12 and the low-pressure fuel gas on the outlet side of the expansion turbine 7 at the rear stage of the exhaust heat recovery / gas heater 12 By adopting a configuration in which the fuel gas is heated, the efficiency of heat exchange can be improved. That is, if the gas temperature on the inlet side of the expansion turbine 7 is set lower than that in the first embodiment, the gas temperature on the outlet side of the expansion turbine 7 becomes lower than that in the first embodiment. Since the temperature difference between the gas and the exhaust gas in the gas heater 12 is large, the efficiency of exhaust heat recovery is improved, and effective heat efficiency can be obtained with a smaller heat transfer area.

Incidentally, actually, the exhaust heat recovery / gas heater 1
The lower limit of the exhaust gas temperature at the two outlets is regulated by the heat transfer tube corrosion problem. In the case of fuel gas containing no sulfur, such as general city gas, the problem of sulfuric acid corrosion does not occur, but caution must be exercised in carbonic acid corrosion due to CO ₂ and moisture in the exhaust gas. For this reason, when passing relatively low-temperature gas through the heat transfer tubes, keep the outer surface temperature of the heat transfer tubes above the water dew point,
Consideration must be given to using a corrosion-resistant material for the low-temperature heat transfer tubes. However, since gas turbines require a large amount of cooling air, the excess air ratio is high, so the water dew point of exhaust gas is considerably lower than that of other prime movers, and the temperature of the heat transfer tube outer surface must be kept above the water dew point. Is easy.

Embodiment 2 FIG. The same gas turbine as in the first embodiment,
The power generation system shown in FIG. 2 is implemented by using an expansion turbine, a generator, fuel gas of the same type and the same inlet / outlet pressure and temperature conditions, and further using an exhaust heat recovery / gas cooler 12 according to the second embodiment. The same generator output as in Example 1 was obtained, and the exhaust gas temperature at the outlet of the exhaust heat recovery / gas heater 12 was set to 100 ° C., the same as in Example 1. In this case, the temperature of the high-pressure side fuel gas exiting the exhaust heat recovery / gas heater 12 and entering the expansion turbine 7 is about 70 ° C., and
The temperature of the low-pressure side fuel gas exiting the expansion turbine 7 and entering the exhaust heat recovery / gas heater 12 is about -19 ° C.
The temperature is lower than in the case of Therefore, the heat transfer area of the heat exchanger of the exhaust heat recovery / gas heater 12 is about 11 times that of the heat exchanger of the first embodiment because the heat recovery efficiency of the exhaust heat recovery / gas heater 12 is improved. %, The exhaust heat recovery / gas heater 12 can be made smaller, and equipment costs can be reduced.

Embodiment 3 FIG. FIG. 3 is a configuration diagram of a combined power generation system of gas turbine power generation and gas pressure recovery power generation according to Embodiment 3 of the present invention. This is because the low-pressure side fuel gas discharged from the expansion turbine 7 is once introduced into the intake air cooler 13 to exchange heat with the air supplied to the gas turbine 1, thereby lowering the temperature of the air supplied to the gas turbine 1. 1 is the same as the system configuration of FIG. 1 except that the fuel gas is heated by the intake air cooler 13 and then supplied to a demand destination.

The gas turbine 1 has a characteristic that its maximum output depends on the temperature of the air to be taken in. If the intake temperature is high, the maximum output will decrease. However, by introducing the low-temperature fuel gas at the outlet side of the expansion turbine 7 into the intake air cooler 13 to lower the intake air temperature of the gas turbine 1 in this way, a large output such as during the daytime in summer when the atmospheric temperature is high can be obtained. Even when required, it is possible to maintain the output of the gas turbine 1 and prevent a decrease in power supply. Next, this embodiment will be described.

Embodiment 3 and Embodiment 4. The system of FIG. 1 in which the gas temperature of the gas turbine 1 is 35 ° C. using the same gas turbine, expansion bin, and generator as in the first embodiment is referred to as a third embodiment. On the other hand, as shown in FIG. 13 and the system in which the intake temperature of the gas turbine 1 was set to 17 ° C. was set as Example 4 and the fuel gas consumption and the maximum output of these systems were compared. The conditions of the fuel gas for operating the expansion turbine are as follows. Fuel gas type: city gas 13A High-pressure side fuel gas Pressure: 40 kg / cm ² G, temperature: 35 ° C. Low-pressure side fuel gas pressure: 6 kg / cm ² G, temperature: 5 ° C. Also, the flow rate of fuel gas flowing into the expansion turbine 7 Was the same in Example 3 and Example 4. As a result, the maximum output of the generator was improved by 4.3% in the case of the power generation in Example 4 (the system in FIG. 3) in which the intake air was cooled as described below.

System of Embodiment 3 System of Embodiment 4 Gas turbine intake temperature 35 ° C. 17 ° C. Gas turbine fuel consumption 377 Nm ³ / h 419 Nm ³ / h Generator output 4026 kW 4199 kW

In the fourth embodiment, the exhaust heat recovery / gas heater 1
The temperature of the fuel gas exiting from 2 and entering the expansion turbine 7 is about 9
It is assumed that the temperature of the exhaust gas at the outlet of the exhaust heat recovery / gas heater 12 is 180 ° C., and the temperature of the fuel gas exiting the expansion turbine 7 and entering the intake air cooler 13 is about 1 ° C. If the temperature is, for example, about 1 ° C., the temperature of the fuel gas entering the expansion turbine 7 and the temperature of the fuel gas exiting the expansion turbine 7 and entering the intake air cooler 13 can be further reduced. The maximum output of the generator can be improved.

Although the embodiments of the present invention have been described in detail, the combination of the gas turbine generator and the expansion turbine generator includes a case where each turbine drives a separate generator, and a case where each turbine There are two types: a single-shaft type that drives one common generator. In each of the above embodiments, the single-shaft type is shown, but the present invention can also use a system for driving different generators. However, in the case of a single-shaft type, there is a feature that a single generator is used as a common unit, the installation space for the equipment is reduced, and a large generator is driven to increase the generator efficiency. In the case of a single-shaft type, the expansion turbine can be used as a starter when starting the gas turbine.
Another feature is that a starting device for the gas turbine is not required. In each of the above embodiments, the expansion turbine 7
Can be installed in a plurality of stages so that their input / output flow paths are connected in series to further increase the power generation efficiency. Further, a speed reducer is installed between each turbine and the generator as needed.

Further, in each of the above embodiments, the exhaust heat recovery / gas heating device performs heat exchange between gases. However, the exhaust heat recovery device and the gas heating device are separately provided, and the liquid is interposed therebetween. Indirect heat exchange in which the heat medium is circulated is also possible. In that case,
The overall heat transfer coefficient of the heat exchanger can be larger than that of heat exchange between gases, but the equipment becomes large because separate heat exchangers are required.

Further, in the present invention, the fuel gas for operating the expansion turbine is city gas, natural gas (LN
G (including vaporized G) can be used. At that time, it is convenient to take in and use a part of the fuel gas as the working fluid for the expansion turbine as the fuel used in the gas turbine.

[0031]

As described in detail above, the present invention provides
A combined power generation system is configured with a gas turbine generator, an exhaust heat recovery / gas heater, and an expansion turbine generator to recover exhaust heat from gas turbine power generation and use it for heating the working fluid of the expansion turbine. This eliminates the need for utilities other than fuel gas such as steam and water, simplifies the operation and maintenance of the system, and recovers unused gas pressure energy to increase power generation output and output. This has the effect of achieving power generation efficiency.

[Brief description of the drawings]

FIG. 1 is a first embodiment of the present invention (Examples 1 and 3);
Configuration diagram of the power generation system according to FIG.

FIG. 2 is a configuration diagram of a power generation system according to Embodiment 2 (Example 2) of the present invention.

FIG. 3 is a configuration diagram of a power generation system according to Embodiment 3 (Example 4) of the present invention.

FIG. 4 is a configuration diagram of a conventional combined cycle power generation system.

FIG. 5 is a configuration diagram of a conventional power generation system using an expansion turbine.

FIG. 6 is a configuration diagram of a conventional combined cycle power generation system using an expansion turbine.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Gas turbine 4 Generator 7 Expansion turbine 12 Exhaust heat recovery / Gas heater 13 Intake cooler

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F02C 7/143 F02C 7/143 7/224 7/224 (72) Inventor Yoshiki Moriyama Marunouchi, Chiyoda-ku, Tokyo 1-1-2, Nihon Kokan Co., Ltd. (72) Inventor Mitsuru Tanaka 1-2-1, Marunouchi, Chiyoda-ku, Tokyo F-Term, Nihon Kokan Co., Ltd. 3G081 BA02 BA11 BB00 BB06 BC07 DA21

Claims (6)

[Claims] 1. A gas turbine, an expansion cylinder using fuel gas as a working fluid, a generator driven by these turbines, and recovering exhaust heat from the gas turbine and using the exhaust heat to perform the expansion. A combined power generation system utilizing gas pressure energy, comprising: an exhaust heat recovery / gas heater for heating fuel gas flowing into a turbine. 2. The exhaust heat recovery / gas heater warms a high-pressure fuel gas flowing into the expansion turbine and also heats a low-pressure fuel gas discharged from the expansion turbine. The power generation system according to claim 1, wherein 3. The power generation system according to claim 1, further comprising an intake air cooler for taking in cold energy of the low-pressure side fuel gas discharged from the expansion turbine to cool intake air flowing into the gas turbine. system. 4. The exhaust heat recovery / gas heater according to claim 1, wherein heat exchange is performed between exhaust gas from the gas turbine and the fuel gas. The described power generation system. 5. The gas turbine and the expansion turbine drive a common generator.
The power generation system according to any one of claims 1 to 4. 6. The power generation system according to claim 1, wherein a part of a fuel gas used as a working fluid of the expansion turbine is used as fuel for the gas turbine.