An improved liquefied natural gas fueled combined cycle power plant

Description: TECHNICAL FIELD [Detailed description of the invention]

Field of invention The present invention is combined with a combined cycle plant to cool the heat exchange fluid used for cooling and densifying the supply air to the gas turbine and to condense the exhaust steam from the steam turbine. Regarding the usage and equipment of the liquefied natural gas (LNG). The regasified LNG is used as fuel for gas turbines and, if desired, for supply to other power plants and for natural gas distribution systems.

[Background and gist of the invention]

It has been conventionally known in the art to expand a waste heat boiler to a gas turbine plant and combine the gas turbine plant with a steam turbine. Gas turbines and steam turbines each drive their own generator, or only one generator driven by a common shaft. These combination plants, referred to as co-cycle plants, are generally characterized by very high conversion efficiencies, at the level of about 50-52%. These high efficiencies are obtained in collaboration with the gas turbine and at least one steam turbine circuit. Gas turbine exhaust gas passes through a waste heat boiler, and the residual thermal energy of these exhaust gases is used to generate the steam required to supply the steam turbine. LNG is used in communal cycle plants as a combustion energy source. LNG is generally shipped by sea as a cryogenic liquid in a special container. Terminals that accept this cryogenic liquid, which generally has a temperature of about -160 ° C at about atmospheric pressure, need to be regasified and supplied to the delivery system at an external temperature and generally at an appropriate high pressure up to 80 atm. When the liquid is heated and regasified, it is pumped to the required pressure so that the resulting natural gas does not need to be compressed. Many proposals have been made and several devices have been made to take advantage of the large cold potential of LNG, but in most receiving terminals the cold potential is wasted and LNG is supplied in a way that avoids ice formation. It is simply heated by a large stream of seawater that needs to be. For example, Mandrin et al. Disclose in US Pat. No. 3,978,663 how to improve the efficiency of gas turbines by cooling the supply air with a liquid coolant. The air entering the turbine supply is filtered and cooled by a cooling exchanger. A coolant such as Freon carries heat from the air and the heat exchanger evaporates the LNG. In order to prevent ice blockage in the heat exchanger, methanol is introduced into the air by a mixing device such as an anti-freezing device and separated by a collecting means. Waste heat is utilized to evaporate the water separated from the mixture of methanol and water. Subsequent US Pat. No. 4036028 of Mandrin discloses the use of liquids of various actions associated with open gas turbine equipment. The ultra-low temperature of LNG is used to remove heat from the supply air by the heat exchanger and Freon transfer fluid. A non-freezing fluid such as methanol is injected to prevent freezing in the heat exchanger. This reference discloses a steam turbine arranged in-line with a compressor. In addition, US Pat. No. 4,995,234 discloses a power generator by Kooy et al. This patent discloses the use of gas turbine exhaust systems for heating materials used to drive gas turbines, to cool the supply air for turbines, to heat LNG by contacting and flowing condensed carbon dioxide. doing. Similarly, NOZAWA et al. Disclose ultra-low temperature natural gas-refrigerant power generators in US Pat. Nos. 4330998, 4429536, and 4422298. In general, these patents teach the supply of compressed and heated Freon. The compressed and heated Freon is then used to drive the high pressure turbine. Freon is reheated and passes through a low pressure turbine before being cooled in a heat exchanger against the flow of nitrogen and / or LNG. Woolley's US Pat. No. 3605405 and Keller et al.'S US Pat. No. 4953479 disclose a joint gas and steam power plant. The patent of Keller et al. Discloses a metacol integrated co-cycle power plant using a gas turbine and a steam turbine device, and the exhaust from the gas turbine device is used to generate steam that drives the steam turbine. The steam used is then condensed and reheated by the exhaust system. None of the above or other power generators utilizing LNG address the issue of maximizing the efficiency and capacity of gas-powered turbines. More specifically, none of the above documents address the issue of maximizing the efficiency and capacity of gas-powered turbines in warm weather, such as peak power consumption at peak temperatures. Typically, the efficiency and capacity of gas turbines decrease with increasing air temperature. Therefore, it is an object of the present invention to provide a co-gene system for generating electricity and gas phase hydrocarbons from ultra-low temperature liquefied materials such as LNG. Another object of the present invention is to provide a cogene system that uses an ultra-low temperature liquefied material such as LNG to densify the supply air to maximize the efficiency and capacity of the gas turbine in warm weather. That is. The present invention covers a wide range of devices and methods that improve the capacity of a co-cycle plant by up to 9% and the efficiency of the plant by about 2%, especially when the external temperature exceeds 60 ° F. The LNG fuel supply system will be used in combination with the joint cycle plant. Co-cycle plants include gas turbine plants, waste heat boilers, and steam turbine plants. The first heat exchange fluid is cooled in the LNG fuel supply system and then used in the gas turbine process to cool and densify the air supplied to the gas turbine. The first heat exchange fluid is also used in the steam turbine process to condense the exhaust steam from the steam turbine. Finally, the first heat exchange fluid is recycled to the LNG fuel supply system where it is cooled. The first heat exchange fluid flows through a closed loop while cooling and densifying the supply air while condensing the steam discharged from the steam turbine and recooled by the LNG fuel supply system. The LNG fuel supply system includes an LNG supplier, a regasifier, and a cooler. In the LNG fuel supply system, there is a second heat exchange fluid flowing through a closed loop. The second heat exchange fluid exchanges heat with both the regasifier, which converts LNG into natural gas, and the cooler, which cools the first heat exchange fluid. Natural gas is partially used as fuel for combustors in gas turbine plants. The second heat exchange fluid is cooled in the gasifier by the expanding LNG and cools the first heat exchange fluid in the cooler. LNG is regasified without the need for expensive seawater regasifiers and / or fuel for heat sources. In a preferred embodiment of the present invention, the water of the first heat exchange fluid flows through the water cooler (heat exchanger) of the LNG fuel supply system. The water / glycol mixture of the second heat exchange fluid cools the first heat exchange fluid, which then flows to the heat exchanger of the gas turbine plant. A gas turbine plant fueled by regasified LNG drives a generator. This gas turbine plant has a supply air duct, a heat exchanger, a water separator, an air compressor, a combustor, a gas turbine, and an exhaust unit. The heat exchanger is located in the air supply duct. The first heat exchange fluid passes through the heat exchanger and provides a cooled refrigerant for densifying and cooling the air supply flow to the air compressor. The waste heat boiler is located downstream of the exhaust section of the gas turbine and circulates with the exhaust section. Gas turbine exhaust transforms the flow of water through the boiler into high-pressure steam. The steam turbine plant includes a steam turbine and a drain steam condenser. High pressure steam from the boiler is used to drive the steam turbine. Exhaust steam from the turbine flows into the condenser. The first heat exchange fluid flows through the condenser and condenses the exhaust steam. The first heat exchange fluid then returns to the cooler of the LNG fuel supply system and flows through it. A brief description of the drawing The figure is a process flow diagram of a system that concretely expresses the present invention. Description of preferred embodiments With respect to the drawings, the systems that specifically represent the invention are a liquefied natural gas (LNG) fuel supply system 8, a joint cycle power plant 10 including a gas turbine plant, a steam turbine plant 40, and abolition located between the two plants. Includes thermal boiler 36. A pump that circulates the heat exchange fluid is not shown. The LNG fuel supply system 8 includes a supply tank 12, a pump 14, a regasifier 16, and a cooler (heat exchanger) 18. The closed loop 20 provides the flow of a mixed fluid of water / glycol between the regasifier 16 and the cooler 18. Natural gas from the regasifier 16 flows to the gas turbine plant 10 and other power plants and / or natural gas distribution systems. The gas turbine plant includes an air supply duct 22, a heat exchanger 24 located therein, and a water-particle filter 26 downstream thereof and upstream of an air compressor 28. Water from the cooler 18 of the LNG fuel supply system 8 flows through the heat exchanger 24. The supply air flows across the heat exchanger to be cooled and densified. The cooled and densified air flows into the air compressor 28. The combustor 30 receives the supply air from the air compressor 28, mixes it with the natural gas from the regasifier 16, and sends the hot combustion gas to the gas turbine 32. The combustion gas drives the gas turbine 32 and the associated generator 34. Preferably, the air compressor 28, the gas turbine 32, and the generator 34 are mounted on the same drive shaft. The exhaust gas from the gas turbine 32 is exhausted to the waste heat boiler 36, where the water flowing in the pipe 38 is converted into high-pressure steam. The steam turbine plant 40 includes a steam turbine 42 and an associated generator 44, both the steam turbine 42 and the generator 44, preferably mounted on the same drive shaft. Alternatively, one large generator may be mounted on the common shaft of the gas turbine and the steam turbine. There is a condenser 46 downstream of the turbine 42, through which the first heat exchange fluid flows. If the LNG supply system is offline or the required cooling action is relatively inadequate, an auxiliary condenser 48 is provided. The condenser 46 condenses the output (exhaust steam) from the steam turbine 42, and the output is recirculated back to the waste heat boiler 36. The first heat exchange fluid flows and returns to the cooler 18. In a preferred embodiment, the first and second fluid flows are in closed loops, respectively. Water is used between the LNG fuel supply system and the joint cycle plant as the first heat exchange fluid in the joint cycle plant. Water is kept above the freezing temperature at all times and is treated to prevent corrosion if necessary. If the LNG regasifier is not in operation, the co-cycle plant can be operated independently of the LNG regasifier by providing sufficient external cooling water to cover the overall condensing load. If the co-cycle plant is not in operation, the LNG regasifier can be operated independently of the co-cycle plant by providing an external preheater to heat the circulating water. A second heat exchange fluid, such as water / glycol, is used to avoid the possibility of freezing of pure water in the LNG fuel supply system. Water heated above 95 ° F in a co-cycle plant is used to heat the second fluid to a temperature sufficient to regasify LNG, for example 70 ° F. This water is then cooled by the second fluid to, for example, 35 ° F and returned to the communal cycle plant for precooling the turbine combustion air. The regasifier 16 and cooler 18 (heat exchanger) in the LNG regasification system are countercurrent and use a minimum approach temperature of 25 ° F. The wall temperature at the cold end is somewhat below 32 ° F, and a thin layer of ice will reduce the thermal conductivity enough to raise the outside of the ice to 32 ° F. The temperature of the cooler 18 would be as follows. Water (on) 95 ° F (from condenser 46) Water / glycol (out) 70 ° F (95-25) Water (out) 35 ° F (to heat exchanger 24) Water / glycol (with) 10 ° F (35-25) The temperature of the LNG regasifier 16 would be as follows. Water / glycol (with) 70 ° F (from water cooler 18) Natural gas (out) 45 ° F (70-25) Water / glycol (out) 10 ° F (to water cooler 18) The temperature of the water coming out of the cooler 18 is controlled by adjusting a control valve (not shown) for the outlet flow of water and reducing the amount of water as the available coolant decreases, i.e. the LNG flow rate decreases. The water inlet temperature is controlled by the joint cycle plant. The LNG fuel supply system can provide a large amount of cooling for co-cycle plant cooling and internal cooling. Conversely, a co-cycle plant can provide a large amount of heat to the LNG fuel supply system without degrading the performance of the co-cycle plant at all. The water that circulates between the joint cycle plant and the LNG fuel supply system makes this possible. The second fluid makes it possible to use water at the low temperatures mentioned above. The hot water from the communal cycle plant goes to a large tank 50 that acts as a "flywheel" from which the hot water is pumped to the cooler 18. The hot water can also be used anywhere else that requires "low" heat, eg 95 ° F or less. Preheaters (not shown) can be used when not available from a communal cycle plant or to maintain sufficient hot water to provide the required heat. The water cooled by the cooler 18 is mainly used to precool the combustion air for the turbine 32. Also, this cooled water is, for example, 35 It can also be used for cooling purposes in a variety of plants, including anywhere that requires "low" cooling above F. Excessive cooling is returned with a steam condenser. The above description has been limited to a particular aspect of the invention. However, it will be clear that changes and changes can be made to the present invention, including some or all of the effects of the present invention. Accordingly, any changes or changes that are contained within the scope of the present invention and true technical ideas are the subject of the claims of the present application.