JP2011032954A - Combined power generation system using cold of liquefied gas - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an LNG vaporizing facility not requiring seawater for vaporization of LNG and a small highly-efficient power generation system, by applying a Rankine cycle using carbon dioxide as working fluid for vaporization of the LNG and using the exhaust heat of a small gas turbine as a high heat source. <P>SOLUTION: This power generation system 1 includes: the gas turbine 2 using LNG as fuel; an exhaust heat recovery boiler 21 recovering the exhaust heat of the gas turbine; a carbon dioxide turbine 3 providing power from the carbon dioxide heated in the exhaust heat recovery boiler; and a condenser condensing exhausted carbon dioxide of the carbon dioxide turbine. The condenser is arranged in an LNG line, uses the exhausted carbon dioxide as the heat source used for the LNG vaporization, and also circulates the exhausted carbon dioxide after use to the exhaust heat recovery boiler. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a combined power generation system that uses cold heat of liquefied gas such as liquefied natural gas (hereinafter referred to as LNG).

Usually, a large amount of seawater is used when LNG of extremely low temperature (about -162 ° C) is vaporized and heated to room temperature. In order to effectively use the cold energy, several LNG cold power generation systems have already been installed. The cold power generation is a Rankine cycle in which the low heat source is LNG cold heat Q _L (the latent heat of LNG and sensible heat from about −162 ° C. to room temperature), and the high heat source is the calorific value Qh of seawater. A = Qh−Q _L is derived from the system. Recoverable energy. However, in the conventional power generation system for the temperature difference between the high heat source and a low heat source is relatively low, Qh of moving heat, expensive power plants is recovered power A i.e. power generation amount as compared to the Q _L is relatively small The spread is small. The seawater amount required, if not including the cryogenic energy storage, is a considerable amount of heat Q _L, by adopting the cryogenic energy storage becomes heat Qh correspond, rather, there is a disadvantage that the amount of sea water is increased.

  Therefore, in order to effectively use such waste heat and cold energy instead of cold power generation, for example, a vaporizer that vaporizes liquefied fuel, a heater that heats the fuel vaporized by the vaporizer, and a heater A steam generator that generates water vapor by evaporating water using the combustion gas of the heated fuel, a steam turbine that is driven by the steam generated by the steam generator, and a condensate that condenses the water vapor that drives the steam turbine And recovering heat from the combustion gas used to generate water vapor in the steam generator by vaporizing the liquefied fuel with the cooling water (hot waste water) used for cooling in the condenser. There is a power generation system that is used to heat fuel in a heater (see Patent Document 1).

JP 2005-98240 A

  However, in the above apparatus, LNG at an extremely low temperature (about −162 ° C.) exchanges heat with air at substantially room temperature, so that energy is transferred at a large temperature difference, and cold energy recovery with a large exergy loss is achieved. In addition, it is difficult to heat design a heat exchange system including countermeasures against frost generation by heat exchange between LNG and air at a very low temperature. In addition, there is an operational difficulty that the vaporization facility for supplying natural gas to a large power plant does not function unless the large power plant is in operation.

The present invention has been devised in view of such problems of the prior art, and is a relatively small gas turbine that uses LNG cold heat as a low heat source and consumes fuel gas of about 5% of the amount of LNG to be vaporized. LNG vaporization equipment that does not require seawater by applying a Rankine cycle that uses CO ₂ as a working fluid, with the exhaust heat of the heat source as a high heat source, and a cold power generation system with a lower unit price than conventional cold power generation It is an object.

A first invention made to solve the above-mentioned problems is that a gas turbine using liquefied gas as fuel, a first generator driven by the gas turbine, and heating CO ₂ with exhaust gas of the gas turbine an exhaust heat recovery apparatus for recovering exhaust heat by a CO ₂ turbine for obtaining power from CO ₂ which has been heated in the exhaust heat recovery device, a second generator driven by said CO ₂ turbine, the CO ₂ turbine A condenser for condensing the CO ₂ exhausted from the exhaust, the condenser using the exhausted CO ₂ as a heat source for vaporization of the liquefied gas, and the exhaust heat recovery device used in the condenser a structure to heat the CO ₂ after being.

According to a second aspect of the present invention, a plurality of the capacitors are provided in the liquefied gas flow path according to the pressure level of the liquefied gas, and the plurality of capacitors have different CO2 temperatures from the CO ₂ turbine. ₂ can be supplied.

Further, passing the third invention, by the CO ₂ passing through the forward passage of CO ₂ leading to the condenser from the CO ₂ turbine, the return flow path of the CO ₂ leading from said capacitors to said exhaust heat recovery device the CO ₂ can be further provided with a configuration of the heater for heating the for.

Further, as a fourth invention, the exhaust heat recovery device has a first flow path through which the exhaust CO ₂ adjacent to each other through a heat transfer wall and a second flow path through which the exhaust gas passes, The exhaust CO ₂ receives heat from the exhaust gas while passing from the inflow portion to the discharge portion of the first flow path, and the first flow path is located at the intermediate portion between the inflow portion and the discharge portion. injection channels for injecting at least a portion of the CO ₂ can be configured to provided.

According to the first aspect of the invention, the heat for vaporizing LNG is used as the low heat source of the Rankine cycle using CO ₂ as the working fluid, so that seawater necessary for vaporizing LNG is not necessary. In addition, by utilizing the exhaust gas energy of a small gas turbine that provides power for the station as a high heat source for the CO ₂ Rankine cycle, the steam condenser is more compact than a combined cycle that combines a steam turbine. In addition, there is an excellent effect that a small-scale high-efficiency combined cycle power generation system that does not require cooling water such as seawater can be realized.
In addition, according to the second aspect of the present invention, it is possible to optimize the heat exchange temperature condition in each capacitor to more effectively utilize the cold heat of the liquefied gas, and to improve the efficiency of the Rankine cycle using CO ₂ as the working fluid. Can be improved.
Further, according to the third aspect, it is possible to appropriately adjust the temperature and pressure in the circulating CO _2, it is possible to improve the efficiency of the Rankine cycle in which the CO ₂ and the working fluid.
According to the fourth aspect of the invention, the temperature of CO ₂ in each part (inflow part, intermediate part, exhaust part) in the exhaust heat recovery device is appropriately controlled by appropriately controlling the amount of CO ₂ injected from the injection pipe. Profile can be optimized and highly efficient heat exchange can be performed.

It is a lineblock diagram showing the outline of the power generation system concerning an embodiment. It is a principal part detail drawing which changes and shows a part of electric power generation system of FIG.

The configuration of the power generation system according to the embodiment of the present invention will be described below with reference to FIG. In FIG. 1, the direction of the flow of CO ₂ or LNG is indicated by arrows.

The power generation system 1 includes a gas turbine 2 that uses vaporized LNG as fuel, and a CO ₂ turbine 3 that uses exhaust gas from the gas turbine 2 as a heat source, and is driven by the gas turbine 2 and the CO ₂ turbine 3, respectively. Electric power is generated by the generator 4 and the second generator 5. In this power generation system 1, LNG stored in the LNG tank 6 is transported through the LNG line 8 at a predetermined flow rate (here, 100 t / hr) by the LNG pump 7, and a plurality (here, The temperature is raised and vaporized stepwise by two capacitors Ca and Cb. A predetermined amount (here 4.6 t / hr) of the vaporized LNG is sent to the gas turbine 2, and the remaining amount (here 95.4 t / hr) is supplied to the city gas branched from the LNG line 8. It is sent to the pipe 9.

In this power generation system 1, CO ₂ is condensed by a low temperature heat source due to LNG vaporization, and thermal energy from the exhaust gas of the gas turbine 2, which is a high temperature heat source, is supplied to the CO ₂ whose density has been increased. Through such a process, CO _2, which is a working fluid in which energy is stored, rotates the CO ₂ turbine 3 to generate power.

  In the gas turbine 2, a part of the LNG vaporized by the condenser Ca · Cb and the combustion air compressed by the axial compressor 11 are sent to the combustor 12 where the LNG mixed with the compressed air is supplied. Burn. The axial-flow turbine 13 is rotated by the kinetic energy of the high-temperature and high-pressure combustion gas generated by the combustion. The first generator 4 is connected to the output shaft 2a of the gas turbine 2, and converts the rotational force of the output shaft 2a into electric power (here, an output of about 20 MW).

Further, the gas turbine 2 is provided with an exhaust heat recovery boiler 21 as a countercurrent heat exchanger for recovering the exhaust heat. In the exhaust heat recovery boiler 21, exhaust gas (combustion gas) supplied from the gas turbine 2 to the flue (second flow path) of the boiler body, and a heat transfer tube (first flow path) 22 disposed in the flue. Heat exchange is performed with CO ₂ flowing through the heat transfer wall. Although details are not shown, a plurality of heating units including heat transfer tube groups are provided in the boiler body, and efficient heat exchange between the exhaust gas and CO ₂ is possible.

CO ₂ turbine 3, the exhaust heat recovery boiler 21 is heated the CO 2 _(i.e., the exhaust heat of the gas turbine 2) while the high heat source, cold heat at the time of LNG gasification and low-temperature heat source, the CO ₂ High-efficiency power generation (here, about 15 MW output) is performed by the second generator 5 connected to the output shaft 3a by the Rankine cycle as the working fluid. In the CO ₂ turbine 3, turbine blades (not shown) are rotated by the high-temperature and high-pressure CO ₂ kinetic energy supplied from the exhaust heat recovery boiler 21.

The CO ₂ turbine 3 is connected with a plurality (here, two systems) of outgoing pipes La and Lb for transporting the extracted or discharged CO ₂ (hereinafter referred to as exhaust CO ₂ ) to the capacitors Ca and Cb. ing. Exhaust CO ₂ having different temperatures and pressures is supplied from the CO ₂ turbine 3 to the outgoing pipes La and Lb in accordance with the temperature rise and vaporization conditions of the LNG in the capacitors Ca and Cb. The downstream sides of the forward pipes La and Lb are connected to the return pipes Ma and Mb via capacitors Ca and Cb, respectively. The return pipe Ma is provided with a high-pressure feed pump 31, and the downstream side of the return pipe Ma is connected to the exhaust heat recovery boiler 21. The return pipe Mb is provided with a low-pressure condensate pump 32, and the downstream side of the return pipe Mb is connected to a capacitor Ca.

A plurality of heaters Ha1 and Ha2 and a plurality of heaters Hb1 and Hb2 are provided on the outward line La and the outward line Lb, respectively. These heaters Ha1, Ha2, Hb1, and Hb2 are relatively high-temperature exhaust CO ₂ that is supplied from the CO ₂ turbine 3 to the condenser Ca · Cb, and is relatively circulated from the condenser Ca · Cb to the exhaust heat recovery boiler 21. A regeneration cycle is realized by exchanging heat with the low-temperature exhaust CO ₂ . The CO ₂ transported by the return pipe Ma is sequentially introduced into the heater Hb1 and the heater Ha1, and is exchanged with the CO ₂ transported by the forward pipe Lb / La, and then returned to the exhaust heat recovery boiler 21. Similarly, CO ₂ transported by the return pipe Mb is sequentially introduced into the heater Hb2 and the heater Ha2, and after being heat-exchanged with CO ₂ transported by the forward pipe Lb / La, it is introduced again into the capacitor Ca. .

  Next, the details of the operation of the power generation system 1 will be described with reference to FIG. The power generation stem 1 shown in FIG. 2 is the same system as the power generation system 1 shown in FIG. 1 except that some changes have been made to the number, arrangement, and the like of the condenser, the heater, and the LNG pump. It is. 2, the same components as those in FIG. 1 are denoted by the same reference numerals and detailed description thereof is omitted.

In the power generation system 1, in the exhaust heat recovery boiler 21, the exhaust gas supplied from the gas turbine 2 is introduced from one side of the boiler body as a heating fluid and flows in the horizontal direction in FIG. On the other hand, CO ₂ is introduced into the downstream portion of the exhaust heat recovery boiler 21 (that is, the low temperature portion of the exhaust gas flow) as a heat receiving fluid so as to oppose the exhaust gas flow, and the upstream portion (that is, the exhaust gas flow of the exhaust gas flow). Sent to the high temperature part). CO ₂ enters a supercritical state (ie, a critical temperature of 31 ° C. and a critical pressure of 7.38 MPa or more) by heat exchange with the exhaust gas, and finally obtained high-temperature and high-pressure (here, temperature: 507 ° C., pressure: 20 MPaA). ) CO ₂ is introduced into the CO ₂ turbine 3. CO ₂ in the supercritical state, because of their small volume change as compared with the case of vapor, it is possible to realize a compact equipment with a relatively simple structure.

The CO ₂ turbine 3 is connected with a plurality of (here, four systems) outbound pipes La, Lb, Lc, and Ld for transporting the exhaust CO ₂ to the capacitors Ca and Cb. Here, the temperature and pressure of the exhaust CO ₂ from the CO ₂ turbine 3 are the highest in CO ₂ (here, temperature: 366 ° C., pressure: 6.1 MPaA) introduced into the outbound pipe La, and hereinafter, the outbound pipe Lb. CO ₂ (here, temperature: 306 ° C., pressure: 3.5 MPaA), CO ₂ (here, temperature: 234 ° C., pressure: 1.68 MPaA) introduced into the outgoing pipe Lb, and outgoing pipe Lb The lower temperature and the lower pressure are achieved in the order of CO ₂ introduced (here, temperature: 165 ° C., pressure: 0.74 MPaA).

The downstream sides of the outgoing pipes La, Lb, Lc, and Ld are connected to the return pipes Ma, Mb, Mc, and Md via capacitors Ca, Cb, Cc, and Cd, respectively. The capacitors Ca, Cb, Cc, and Cd are sequentially arranged from the downstream side of the LNG line 8 (that is, the high temperature side of the LNG flow) to the upstream side (that is, the low temperature side of the LNG flow). Valves V1 to V4 for adjusting the flow rate of CO ₂ are provided on the return pipes Ma and Mc and the branch pipes Md1 and Md2, respectively.

  The return pipe Ma is connected to the capacitor Cb. The return pipe Mb is provided with a high-pressure feed pump 31, and the downstream side of the return pipe Mb is connected to the exhaust heat recovery boiler 21 after branching to the branch pipes Mb1 and Mb2. The return pipe Mc is provided with a low-pressure condensate pump 32, and the downstream side of the return pipe Mc is connected to the capacitor Cb. Further, a condensate pump 33 for lower pressure than the condensate pump 32 is provided in the return line Md, and the downstream side of the return line Md is connected to the capacitor Cb.

A plurality of heaters Ha1 to Ha3, heaters Hb1 to Hb3, heaters Hc1 and Hc2, and heaters Hd1 and Hd2 are provided in each of the outgoing pipes La, Lb, Lc, and Ld. CO ₂ (here, temperature: 21 ° C., pressure: 60 MPaA) transported by the return pipe Ma is reintroduced into the capacitor Cb.

CO ₂ (here, temperature: −0.9 ° C., pressure: 3.4 MPaA) transported through the return pipe Mb circulates to the exhaust heat recovery boiler 21. The relatively low temperature CO ₂ transported by the branch pipe Mb1 connected to the return pipe Mb is sequentially introduced into the heater Hc1 and the heater Ha1, and exchanges heat with the relatively high temperature CO ₂ transported by the forward pipe Lc · La. Then, it is returned to the exhaust heat recovery boiler 21. In addition, the relatively low-temperature CO ₂ transported by the branch pipe Mb2 is sequentially introduced into the heater Hd1 and the heater Hb1, and after being heat-exchanged with the relatively high-temperature CO ₂ transported by the outward piping Lc · La. Circulate to the exhaust heat recovery boiler 21. The flow rate of CO ₂ to the branch pipes Mb1 and Mb2 can be appropriately adjusted by the valves V5 and V7.

The CO ₂ injection pipe 35 further branched from the downstream side of the branch pipe Mb1 is connected to an intermediate portion of the heat transfer pipe 22 of the exhaust heat recovery boiler 21. By appropriately controlling the amount of CO ₂ injected from the CO ₂ injection pipe 35 using the valve V7, the temperature of CO ₂ in each part (upstream part, intermediate part, downstream part) in the exhaust heat recovery boiler 21 The profile can be optimized. In other words, the specific heat of CO _{2 in} the supercritical state decreases as the temperature increases, but by injecting CO _{2 in} the middle part, it is possible to achieve a temperature decrease of the exhaust gas and a temperature increase of CO ₂ with a substantially constant temperature difference. Highly efficient heat exchange can be performed.

Relatively low-temperature CO ₂ (in this case, temperature: −26.5 ° C., pressure: 1.6 MPaA) transported by the return pipe Mc is sequentially introduced into the heater Hb3 and the heater Ha3, and is transported by the outbound pipe Lb / La. After being exchanged with relatively high-temperature CO ₂ , it is reintroduced into the capacitor Cb.

CO ₂ (here, temperature: −49.4 ° C., pressure: 0.7 MPaA) transported through the return pipe Md is reintroduced into the capacitor Cb. The return pipe Md is branched into branch pipes Md1 and Md2 on the downstream side. The relatively low-temperature CO ₂ transported by the branch pipe Md1 is sequentially introduced into the heater Hc2 and the heater Ha2, and after being heat-exchanged with the relatively high-temperature CO ₂ transported by the outward piping Lc · La, the capacitor Cb Will be introduced again. In addition, the relatively low-temperature CO ₂ transported by the branch pipe Md2 is introduced into the heater Hd2 and the heater Hb2 in order, and is subjected to heat exchange with the relatively high-temperature CO ₂ transported by the forward piping Ld and Lb. It is introduced again into the capacitor Cb.

In the power generation system, capacitors Ca, Cb, Cc, and Cd that condense the exhaust CO ₂ of the CO ₂ turbine 3 are provided in the LNG line 8, vaporize LNG using the exhaust CO ₂ as a heat source, and exhaust CO ₂ after heat exchange. ₂ is circulated to the exhaust heat recovery boiler 21, so that it does not require cooling water such as seawater used in a condenser of a conventional steam turbine, and CO ₂ has a specific volume compared to steam. Therefore, a small and highly efficient power generation system can be realized. Furthermore, since CO ₂ is chemically inert to air and water, there is also an advantage that environmental troubles due to leakage can be avoided even if the piping system and peripheral equipment are damaged.

In the above power generation system, a plurality of capacitors Ca, Cb, Cc, and Cd are provided according to the pressure level of LNG in the LNG line 8, and the capacitors Ca, Cb, Cc, and Cd are heated to each other from the CO ₂ turbine. since different CO ₂ is configured to be supplied, by optimizing the temperature of the heat exchange in the capacitors Ca · Cb · Cc · Cd, it is possible to take advantage of LNG cold more effectively, the CO ₂ The efficiency of the Rankine cycle used as the working fluid can be improved. Further, there is an advantage that pumps for LNG having different boosting capacities can be used efficiently. In particular, heaters Ha1 to Ha3 for heating the relatively low temperature exhaust CO ₂ after heat exchange by the relatively high temperature exhaust CO ₂ supplied from the CO ₂ turbine 3 to the capacitors Ca, Cb, Cc, and Cd. Since the heaters Hb1 to Hb3, the heaters Hc1 and Hc2, and the heaters Hd1 and Hd2 are provided, the efficiency of the Rankine cycle is further improved by the regeneration cycle.

Although the present invention has been described in detail based on specific embodiments, the above embodiments are merely examples, and the present invention is not limited to these embodiments. For example, in the power generation system according to the present invention, the quantity and arrangement of the condenser, the heater, and the pump can be variously changed according to the scale of the system and the use environment, and the pressure of the CO ₂ flow path It is also possible to further use a regulator for adjusting.

DESCRIPTION OF SYMBOLS 1 Power generation system 2 Gas turbine 3 CO ₂ turbine 4 1st generator 5 2nd generator 6 LNG tank 8 LNG line (flow path of liquefied gas)
11 Compressor 12 Combustor 13 Turbine 21 Waste heat recovery boiler (exhaust heat recovery device)
22 Heat transfer pipe 35 CO ₂ injection pipe (injection flow path)
C Capacitor H Heater L Outward piping (CO ₂ outbound channel)
M Return line (CO ₂ return path)
V valve

Claims (4)

A gas turbine using liquefied gas as fuel,
A first generator driven by the gas turbine;
An exhaust heat recovery device that recovers exhaust heat by heating CO ₂ with the exhaust gas of the gas turbine;
A CO ₂ turbine that obtains power from CO ₂ heated in the exhaust heat recovery device;
A second generator driven by the CO ₂ turbine;
A condenser for condensing CO ₂ exhausted from the CO ₂ turbine,
The condenser uses the exhausted CO ₂ as a heat source for vaporization of the liquefied gas, and the exhaust heat recovery device heats the CO ₂ after being used in the condenser. Combined power generation system. A plurality of capacitors are provided in the flow path of the liquefied gas according to the pressure level of the liquefied gas, and the plurality of capacitors are supplied with CO ₂ having different temperatures from the CO ₂ turbine, respectively. The combined power generation system according to claim 1, wherein the combined power generation system is characterized. By the CO ₂ passing through the forward passage of CO ₂ leading to the condenser from the CO ₂ turbine, heat for heating the CO ₂ passing through the return flow path of the CO ₂ leading from said capacitors to said exhaust heat recovery device The combined power generation system according to claim 2, further comprising a generator. The exhaust heat recovery device has a first flow path through which the exhaust CO ₂ adjacent to each other through a heat transfer wall and a second flow path through which the exhaust gas passes,
The exhaust CO ₂ receives heat from the exhaust gas while passing from the inflow portion to the discharge portion of the first flow path,
The first flow path, characterized in that the injection channel for injecting the at least part of the exhaust CO ₂ in an intermediate portion between the discharge portion and the inlet portion is provided, according claim 1 Item 4. The combined power generation system according to any one of Items 3 to 4.

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