Combined cycle unit fast start system and method

Abstract

The present application relates to power generation technology field, disclose a combined cycle unit quick start system and method, the system includes gas turbine, steam turbine, waste heat boiler and heater, waste heat boiler is connected with gas turbine, waste heat boiler includes the heat exchanger and direct flow reheater which are arranged in waste heat boiler and are connected with steam turbine, and the circulation loop is formed between direct flow reheater and steam turbine, heater is connected with heat exchanger and feed water pump, the present application is first injected hot water into heater before starting gas turbine, water is heated into steam, and the steam is input into heat exchanger, after starting gas turbine, the flue gas in gas turbine is input into waste heat boiler and exchanges heat with heat exchanger, then the steam is heated into supersaturated steam, which is used to drive steam turbine to generate electricity, enough supersaturated steam can be generated in a short time, the start of combined cycle unit is accelerated, the power generation efficiency is improved, and the direct flow reheater can absorb part of the temperature in the flue gas, which protects other stage heat exchangers.

Description

Technical Field

[0001] This invention relates to the field of power generation technology, and more specifically to a rapid start-up system and method for combined cycle power units. Background Technology

[0002] A combined cycle power plant (CCPP) primarily works by first pressurizing natural gas or other combustible gases using a gas compressor, then mixing them with air supplied to the combustion chamber for combustion. This produces high-temperature, high-pressure gas, which expands and performs work in a gas turbine. This gas turbine drives the compressor and external load to rotate at high speed. The exhaust gas from the gas turbine is then directed to a waste heat boiler to generate high-temperature, high-pressure steam, which drives a steam turbine and, together with the gas turbine, powers a generator to produce electricity.

[0003] In existing technologies, when a gas turbine starts up, as the flue gas temperature rises, in order to prevent damage such as pipe cracking and welding failure caused by excessive temperature difference between the inside and outside of the thick-walled pressure heat exchanger in the waste heat boiler due to rapid temperature rise, the gas turbine needs to operate at a low load. Only after the waste heat boiler slowly heats up and generates steam suitable for driving the turbine can the gas turbine operate normally in sync with the steam cycle. This results in a long start-up time for combined cycle units, which can easily lead to low power generation efficiency. Summary of the Invention

[0004] In view of this, the present invention provides a system and method for rapid start-up of combined cycle power units to solve the problem of long start-up time of combined cycle power units, which leads to low power generation efficiency.

[0005] In a first aspect, the present invention provides a rapid start-up system for a combined cycle power unit, comprising:

[0006] Gas turbines are suitable for connection to generators;

[0007] Steam turbines are suitable for connection to generators;

[0008] A waste heat boiler is connected to the gas turbine, and the waste heat boiler includes a heat exchanger and a once-through reheater.

[0009] The heat exchanger is installed inside the waste heat boiler and is connected to the steam turbine.

[0010] The DC reheater is installed inside the waste heat boiler, and the DC reheater is connected to the steam turbine, forming a circulation loop between the DC reheater and the steam turbine;

[0011] A heater is connected to the heat exchanger and the water pump.

[0012] By installing a heater, cold water is injected into the heater before starting the gas turbine. The water is heated into steam using renewable energy or surplus electricity from the grid, and the steam is then fed into a heat exchanger. After the gas turbine starts, the flue gas from the gas turbine is fed into a waste heat boiler to exchange heat with the heat exchanger. The steam is then heated into supersaturated steam to drive the turbine for power generation. This process can generate a sufficient amount of supersaturated steam in a short time, accelerating the start-up of the combined cycle unit and thus improving power generation efficiency. Furthermore, a once-through reheater is installed in the waste heat boiler. The once-through reheater can absorb some of the temperature from the flue gas, preventing the temperature of the heat exchanger's outer wall from becoming too high before the internal water temperature rises, which could cause damage due to excessive temperature difference between the inside and outside of the heat exchanger. This process protects the heat exchanger.

[0013] In one alternative embodiment, the steam turbine includes:

[0014] A high-pressure cylinder is connected to the heat exchanger and the DC reheater, forming a circulation loop between the heat exchanger, the high-pressure cylinder, and the DC reheater. The high-pressure cylinder is adapted to drive the generator to generate electricity.

[0015] An intermediate-pressure cylinder is connected to the heat exchanger and the direct-current reheater, forming a circulation loop between the heat exchanger, the intermediate-pressure cylinder, and the direct-current reheater. The intermediate-pressure cylinder is suitable for driving the generator to generate electricity. During the gas turbine's load ramp-up process, the pressure of the high-temperature, high-pressure steam in the heater reaches the main steam level. The low-temperature, low-pressure steam in the heat exchanger is mixed into the heater to cool and depressurize it, and then used as the input steam for the heat exchanger. This ensures that the steam in the heat exchanger does not stagnate and cause thermal overload, and stably delivers main steam with compliant parameters to the turbine.

[0016] In one alternative implementation, it further includes:

[0017] A medium-pressure feedwater pump is connected to the DC reheater;

[0018] A high-pressure water pump is connected to the heater.

[0019] In one alternative implementation, it further includes:

[0020] A separator is connected to the once-through reheater and the intermediate-pressure cylinder. By installing the separator, the steam and water in the steam output from the once-through reheater can be separated. The steam enters the intermediate-pressure cylinder to drive the turbine to generate electricity, while the water flows back to the once-through reheater for heat exchange.

[0021] In one optional embodiment, the steam turbine further includes:

[0022] A low-pressure cylinder is connected to the intermediate-pressure cylinder and the heat exchanger, and the low-pressure cylinder is adapted to drive the generator to generate electricity.

[0023] In one alternative implementation, it further includes:

[0024] A condenser is installed between the low-pressure cylinder and the heat exchanger. By installing a condenser, the steam output from the low-pressure cylinder can be condensed into water, which can then be recycled back into the heat exchanger, allowing the working fluid water to be reused.

[0025] In one alternative implementation, it further includes:

[0026] The first steam pipe is connected to the heat exchanger and the high-pressure cylinder;

[0027] The second steam pipe is connected to the separator, the intermediate pressure cylinder, and the first steam pipe.

[0028] Before the steam turbine starts working, the steam output from the separator and heat exchanger can be preheated by inputting it into the first steam pipe and the second steam pipe to prevent the pipe from being damaged due to excessive temperature difference.

[0029] In one optional embodiment, the heat exchanger includes a superheater, an evaporator, an economizer, and a steam drum.

[0030] The superheater includes a first superheater, a second superheater, a third superheater, a fourth superheater, and a fifth superheater;

[0031] The evaporator includes a first evaporator, a second evaporator, and a third evaporator;

[0032] The economizer includes a first economizer, a second economizer, a third economizer, a fourth economizer, and a fifth economizer;

[0033] The steam drum includes a first steam drum, a second steam drum, and a third steam drum; wherein...

[0034] The first superheater is connected to the heater and the first steam pipe;

[0035] The second superheater is connected to the third superheater and the first evaporator, and the once-through reheater is disposed between the first superheater, the second superheater and the third superheater;

[0036] The first steam drum is connected to the third superheater, the first evaporator and the first economizer, the first economizer is connected to the second economizer, the second economizer is connected to the third economizer, and the third economizer is connected to the high-pressure feedwater pump.

[0037] The fourth superheater is connected to the heater and the second steam drum, the second steam drum is connected to the second evaporator and the fourth economizer, and the fourth economizer is connected to the high-pressure feedwater pump.

[0038] The fifth superheater is connected to the heater and the third steam drum, the third steam drum is connected to the fifth economizer and the third evaporator, and the third evaporator is connected to the medium-pressure feedwater pump and the high-pressure feedwater pump.

[0039] In one alternative embodiment, the second evaporator is connected to the first steam pipe and the second steam pipe, and the first superheater is connected to the first steam pipe and the second steam pipe.

[0040] Secondly, the present invention also provides a method for rapid start-up of a combined cycle unit, comprising:

[0041] The aforementioned combined cycle unit fast start system includes the following fast start methods:

[0042] Water is supplied to the heater, and the heater is started to heat the water into steam, which is then input into the heat exchanger to preheat the heat exchanger.

[0043] Water is fed into the heat exchanger, the gas turbine is started, the gas turbine inputs flue gas into the waste heat boiler, the flue gas exchanges heat with the heat exchanger, and the heat exchanger rapidly heats up to heat the water in the heat exchanger into steam;

[0044] The DC reheater exchanges heat with the flue gas, heating the water in the DC reheater into steam;

[0045] Once the steam temperature reaches the preset value, the heater is turned off, and the steam is input into the steam turbine to drive the generator to generate electricity.

[0046] The steam in the turbine is returned to the once-through reheater for heat exchange. Attached Figure Description

[0047] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0048] Figure 1 This is a schematic diagram of a combined cycle unit rapid start-up system according to an embodiment of the present invention;

[0049] Figure 2 This is a flowchart of a rapid start-up method for a combined cycle unit according to an embodiment of the present invention.

[0050] Explanation of reference numerals in the attached figures:

[0051] 1. Gas turbine;

[0052] 2. Generator;

[0053] 3. Steam turbine; 301. High-pressure cylinder; 302. Intermediate-pressure cylinder; 303. Low-pressure cylinder;

[0054] 4. Waste heat boiler; 401. Heat exchanger; 402. Once-through reheater; 4021. First-stage once-through reheater; 4022. Second-stage once-through reheater; 403. Superheater; 4031. First superheater; 4032. Second superheater; 4033. Third superheater; 4034. Fourth superheater; 4035. Fifth superheater; 404. Evaporator; 4041. First evaporator; 4042. Second evaporator; 4043. Third evaporator; 405. Economizer; 4051. First economizer; 4052. Second economizer; 4053. Third economizer; 4054. Fourth economizer; 4055. Fifth economizer; 406. Steam drum; 4061. First steam drum; 4062. Second steam drum; 4063. Third steam drum;

[0055] 5. Heater;

[0056] 601. Medium-pressure water supply pump; 602. High-pressure water supply pump;

[0057] 7. Separator;

[0058] 8. Condenser;

[0059] 9. First steam pipe;

[0060] 10. Second steam pipe;

[0061] 11. Reheat steam pipeline. Detailed Implementation

[0062] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0063] In related technologies, the heat exchangers 401 in the waste heat boiler 4 of the combined cycle unit have a large number of heat exchange surfaces and a large temperature difference between the heat exchangers 401. If the gas turbine 1 heats up rapidly under high load during startup, the flue gas temperature will rise rapidly. The thick-walled pressure-bearing components in the heat exchangers 401 will rapidly exchange heat with the high-temperature flue gas due to the metal outer wall, while the working fluid water in the heat exchangers 401 conducts heat more slowly. The excessive temperature difference will cause thermal overload of the pressure-bearing components in the heat exchangers 401, resulting in damage such as cracking of the manifold and welding failure. In order to ensure that the heat exchangers 401 are not damaged, the gas turbine 1 usually needs to be operated at a low load, so that the waste heat boiler 4 heats up slowly in a gradient. When the waste heat boiler 4 heats up gradually and can generate enough steam to drive the turbine 3, the gas turbine 1 is switched to normal load operation. Therefore, the hot and cold start-ups of the entire combined cycle unit can take up to 45 minutes and 2 hours respectively, which is slow and affects the power generation efficiency.

[0064] The following is combined with Figure 1 The following describes embodiments of the present invention.

[0065] According to an embodiment of the present invention, in one aspect, a combined cycle unit rapid start-up system is provided, comprising: a gas turbine 1, a steam turbine 3, a waste heat boiler 4, and a heater 5. The gas turbine 1 and the steam turbine 3 are adapted to be connected to a generator 2. The waste heat boiler 4 is connected to the gas turbine 1. The waste heat boiler 4 includes a heat exchanger 401 and a once-through reheater 402. The heat exchanger 401 is disposed within the waste heat boiler 4 and is connected to the steam turbine 3. The once-through reheater 402 is disposed within the waste heat boiler 4 and is connected to the steam turbine 3, and a circulation loop is formed between the once-through reheater 402 and the steam turbine 3. The heater 5 is connected to the heat exchanger 401 and a feedwater pump.

[0066] In this embodiment, heater 5 can be a start-up boiler, which uses renewable energy power or surplus power from the power grid as energy to heat the water in the start-up boiler into steam. In some other embodiments not shown, a start-up boiler using fossil fuels or biofuels as energy can also be used.

[0067] In this embodiment, the DC reheater 402 can be preheated synchronously with the start-up of the gas turbine 1. The DC reheater 402 is provided with multiple tube bundles arranged in parallel. The two ends of each tube are welded to the upper and lower manifolds respectively. The tube bundles have a vertical structure and are made of high-pressure resistant material. They are stacked to form the heat exchange surface of the DC reheater 402.

[0068] In this embodiment, the DC reheater 402 includes a first-stage DC reheater 4021 and a second-stage DC reheater 4022 arranged in parallel. In other embodiments not shown, the DC reheater 402 may also adopt other numbers of multi-stage parallel structures.

[0069] In this embodiment, the DC reheater 402 is located inside the waste heat boiler 4 on the side close to the gas turbine 1. The DC reheater 402 rapidly heats the working fluid from water directly into steam in the tube bundle under overpressure. As the flue gas temperature of the gas turbine 1 increases, the DC reheater 402 absorbs a large amount of heat, so the temperature of the flue gas decreases accordingly after flowing through the DC reheater 402. This reduces the thermal inertia inside the waste heat boiler 4, avoids damage to the heat exchanger 401 caused by high temperature difference and destructive thermal stress, and protects the downstream heat exchanger 401 of the DC reheater 402. This effectively prevents the downstream heat exchanger 401 of the DC reheater 402 from thermal overload and damage during the cold start-up of the gas turbine 1.

[0070] Under the protection of the DC reheater 402, since there is no need to limit power and temperature, the gas turbine 1 can accelerate and reach full load, rapidly raising the exhaust temperature of the gas turbine 1 to over 600 degrees Celsius within 30 minutes, thereby improving both power generation efficiency and power.

[0071] In this embodiment, the gas turbine 1 and the steam turbine 3 can be coaxially connected to the generator 2, or they can be connected to the generator 2 separately through their output shafts.

[0072] By installing heater 5, cold water is injected into heater 5 before starting gas turbine 1. The water is heated into steam using renewable energy power or surplus power from the grid, and the steam is input into heat exchanger 401. After gas turbine 1 starts, the flue gas in gas turbine 1 is input into waste heat boiler 4 to exchange heat with heat exchanger 401, and then the steam is heated into supersaturated steam to drive steam turbine 3 to generate electricity. Sufficient supersaturated steam can be generated in a short time, which speeds up the start-up of the combined cycle unit and improves the power generation efficiency. In addition, a once-through reheater 402 is installed in waste heat boiler 4. The once-through reheater 402 can absorb part of the temperature in the flue gas, which prevents the temperature of the outer wall of heat exchanger 401 from being too high before the water temperature inside heat exchanger 401 rises, thus avoiding damage caused by excessive temperature difference between the inside and outside of heat exchanger 401. This protects heat exchanger 401.

[0073] Specifically, during the start-up process of the gas turbine 1, the hot steam introduced by the heater 5 adds a portion of the external heat source to the waste heat boiler 4, and the feedwater is directly heated through the direct current reheater 402, which is equivalent to adding a portion of the working fluid that can effectively absorb the heat of the flue gas to the high flue gas temperature section of the waste heat boiler 4.

[0074] In this embodiment, the intermittency of renewable energy increases the demand for flexible power generation from conventional fuels as a backup power source. Combined cycle power plants are particularly suitable for compensating for grid fluctuations because gas turbine 1 can reach 100% nominal load in just 20 minutes or reach a low load state of 50% load rate in 7 minutes, which can quickly supply power to the grid that needs compensation.

[0075] In one embodiment, the steam turbine 3 includes a high-pressure cylinder 301 and an intermediate-pressure cylinder 302. The high-pressure cylinder 301 is connected to a heat exchanger 401 and a direct current reheater 402, forming a circulation loop between the heat exchanger 401, the high-pressure cylinder 301, and the direct current reheater 402. The high-pressure cylinder 301 is adapted to drive the generator 2 to generate electricity. The intermediate-pressure cylinder 302 is connected to the heat exchanger 401 and the direct current reheater 402, forming a circulation loop between the heat exchanger 401, the intermediate-pressure cylinder 302, and the direct current reheater 402, and the intermediate-pressure cylinder 302 is adapted to drive the generator 2 to generate electricity.

[0076] During the load ramp-up process of gas turbine 1, the pressure of high-temperature and high-pressure steam in heater 5 reaches the level of main steam. The low-temperature and low-pressure steam in heat exchanger 401 is mixed into heater 5 to cool and depressurize it, and then it can be used as the input steam of heat exchanger 401. This ensures that the steam in heat exchanger 401 will not stagnate and cause thermal overload, and stably delivers main steam with qualified parameters to turbine 3.

[0077] When the gas turbine 1 reaches its rated load, the high-pressure superheated steam in the heat exchanger 401, whose temperature has not yet reached the standard, is mixed into the working fluid input to the once-through reheater 402. This causes the once-through reheater 402 to operate under overpressure to a certain extent, and delivers reheated steam with parameters that meet the start-up standard to the steam turbine 3. The once-through reheater 402 causes the reheated steam formed by water evaporation to gradually rise from the saturation temperature to supersaturation, and allows the intermediate-pressure cylinder 302 of the steam turbine 3 to start up at a temperature of 250°C.

[0078] In one embodiment, the system further includes a medium-pressure feedwater pump 601 connected to the DC reheater 402 and a high-pressure feedwater pump 602 connected to the heater 5. The medium-pressure feedwater pump 601 and the high-pressure feedwater pump 602 can supply water to the DC reheater 402 and the heater 5.

[0079] In this embodiment, subcooled water can be provided in the medium-pressure feedwater pump 601 and the high-pressure feedwater pump 602. The desired flow rate of water or steam into the direct current reheater 402 can be forcibly applied by the feedwater pump to specifically adjust the desired cooling effect on the flue gas. The heat exchanger 401, protected by the direct current reheater 402, has the ability to withstand high-temperature flue gas and heat up rapidly. Therefore, the heat exchanger 401 in the waste heat boiler 4 has the ability to withstand the heat of the flue gas from the gas turbine 1. The waste heat boiler 4 can start up quickly and synchronously with the gas turbine 1, and then produce steam with rated parameters to drive the turbine 3. The turbine 3 can also reach full load operation in a shorter time, thereby improving the unit's power generation flexibility and effectively compensating for and accommodating intermittent renewable energy power such as solar and wind power.

[0080] In one embodiment, a separator 7 is also included, which is connected to the DC reheater 402 and the intermediate-pressure cylinder 302. By setting the separator 7, the steam and water in the steam output from the DC reheater 402 can be separated. The steam enters the intermediate-pressure cylinder 302 to drive the steam turbine 3 to generate electricity, while the water flows back to the DC reheater 402 for heat exchange.

[0081] In this embodiment, the separator 7 is a steam-water separator, which is a separation device with a rotating inertia separation container. This centrifugal separator is also called a rotary separator. The steam rotates through the separator 7 at its own flow rate. The centrifugal force acting on the water droplets causes the water droplets to flow out radially outward along the separator 7, thereby separating them from the steam. The steam flow is then drawn inward from the separator 7 and flows to the intermediate pressure cylinder 302.

[0082] Specifically, when the waste heat boiler 4 and the gas turbine 1 both enter the rated load working state, the circuit breaker separator 7 and the once-through reheater 402 return to the normal heating state, and the steam at the outlet of the once-through reheater 402 is input into the intermediate pressure cylinder 302 of the steam turbine through the reheat steam pipeline 11.

[0083] In one embodiment, the turbine 3 further includes a low-pressure cylinder 303 connected to the intermediate-pressure cylinder 302 and the heat exchanger 401, the low-pressure cylinder 303 being adapted to drive the generator 2 to generate electricity.

[0084] In this embodiment, the high-pressure cylinder 301, the medium-pressure cylinder 302, and the low-pressure cylinder 303 can be coaxially connected to the generator 2, or they can be connected to the generator 2 separately.

[0085] In one embodiment, a condenser 8 is also included, which is disposed between the low-pressure cylinder 303 and the heat exchanger 401. By providing the condenser 8, the low-temperature steam output from the low-pressure cylinder 303 can be condensed into water and recycled back into the heat exchanger 401, so that the working fluid water can be recycled.

[0086] In one embodiment, the system further includes a first steam pipe 9 and a second steam pipe 10. The first steam pipe 9 is connected to the heat exchanger 401 and the high-pressure cylinder 301, and the second steam pipe 10 is connected to the separator 7, the intermediate-pressure cylinder 302, and the first steam pipe 9.

[0087] In this embodiment, the first steam pipe 9 is the main steam pipe, and the second steam pipe 10 is the reheat steam pipe. In actual production, the first steam pipe 9 and the second steam pipe 10 are set according to the actual power plant conditions. If the distance between the waste heat boiler 4 and the steam turbine 3 is far, the length of the first steam pipe 9 and the second steam pipe 10 will be relatively long.

[0088] When the gas turbine 1 is cold-started, the temperature of the first steam pipe 9 and the second steam pipe 10 is low. Before the steam turbine 3 is working, the steam output from the separator 7 and the heat exchanger 401 can be input into the first steam pipe 9 and the second steam pipe 10 to preheat the pipes and prevent the pipes from being damaged due to excessive temperature difference.

[0089] In one embodiment, heat exchanger 401 includes a superheater 403, an evaporator 404, an economizer 405, and a steam drum 406. Superheater 403 includes a first superheater 4031, a second superheater 4032, a third superheater 4033, a fourth superheater 4034, and a fifth superheater 4035. Evaporator 404 includes a first evaporator 4041, a second evaporator 4042, and a third evaporator 4043. Economizer 405 includes a first economizer 4046. 51. A second economizer 4052, a third economizer 4053, a fourth economizer 4054, and a fifth economizer 4055; a steam drum 406 including a first steam drum 4061, a second steam drum 4062, and a third steam drum 4063; wherein, a first superheater 4031 is connected to a heater 5 and a first steam pipe 9, a second superheater 4032 is connected to a third superheater 4033 and a first evaporator 4041, and a once-through reheater 402 is disposed in the first superheater. Between the first superheater 4031, the second superheater 4032, and the third superheater 4033, the first steam drum 4061 is connected to the third superheater 4033, the first evaporator 4041, and the first economizer 4051; the first economizer 4051 is connected to the second economizer 4052; the second economizer 4052 is connected to the third economizer 4053; the third economizer 4053 is connected to the high-pressure feedwater pump 602; and the fourth superheater 4034 is connected to the heater 5 and the second... The first steam drum 4062 is connected to the second steam drum 4062, which is connected to the second evaporator 4042 and the fourth economizer 4054. The fourth economizer 4054 is connected to the high-pressure feedwater pump 602. The fifth superheater 4035 is connected to the heater 5 and the third steam drum 4063. The third steam drum 4063 is connected to the fifth economizer 4055 and the third evaporator 4043. The third evaporator 4043 is connected to the medium-pressure feedwater pump 601 and the high-pressure feedwater pump 602.

[0090] In this embodiment, the first superheater 4031 is the third-stage high-pressure superheater, the second superheater 4032 is the second-stage high-pressure superheater, and the third superheater 4033 is the first and high-pressure superheater. The second superheater 4032 is located between the first DC superheater 403 and the second DC superheater 403, which can protect the first superheater 4031 and the second-stage superheater 403 downstream of the DC reheater 402 from damage due to thermal overload during cold start-up. The fourth superheater 4034 is the medium-pressure superheater 403, and the fifth superheater 4035 is the low-pressure superheater 403.

[0091] The first evaporator 4041 is a high-pressure evaporator 404, the second evaporator 4042 is a medium-pressure evaporator 404, and the third evaporator 4043 is a low-pressure evaporator 404.

[0092] The first economizer 4051 is the third-stage high-pressure economizer 405, the second economizer 4052 is the second-stage high-pressure economizer 405, the third economizer 4053 is the first-stage high-pressure economizer 405, the fourth economizer 4054 is the medium-pressure economizer 405, and the fifth economizer 4055 is the low-pressure economizer 405.

[0093] Specifically, in this embodiment, the DC reheater 402 has a larger heat exchange area with multiple tube bundles, so the static pressure loss of the flue gas in the waste heat boiler 4 will increase slightly. However, the DC reheater 402 only has two heat exchange surfaces, which is negligible compared to the fifteen heat exchange surfaces in the overall waste heat boiler 4.

[0094] In this embodiment, before the unit starts up, the heater 5 preheats the first superheater 4031 located at the flue gas inlet of the waste heat boiler 4. During the load ramp-up process of the gas turbine 1, the pressure of the high-temperature and high-pressure steam in the heater 5 reaches the preset level of the main steam. After mixing with the low-pressure and medium-pressure superheated steam in the fourth superheater 4034 and the fifth superheater 4035, the steam is cooled and depressurized, and used as the input steam for the first superheater 4031. This ensures that the steam in the first superheater 4031 will not stagnate and cause thermal overload, and can stably deliver main steam with qualified parameters to the turbine 3.

[0095] The hot water from the high-pressure feedwater pump 602 passes through the first economizer 4051, the second economizer 4052, the third economizer 4053, the steam drum 406, the first superheater 4031, and the second superheater 4032. It then bypasses the outlet of the second superheater 4032 and enters the second-stage once-through reheater 4022, becoming part of the reheat steam. This replenishes the reheat steam flow while ensuring that the second-stage once-through reheater 4022 will not stagnate and cause thermal overload.

[0096] As the exhaust gas temperature of the gas turbine 1 gradually increases, the heating steam of the first superheater 4031 gradually heats up to supersaturation, allowing the high-pressure cylinder 301 of the steam turbine 3 to start running at a temperature of 370°C.

[0097] In one embodiment, the second evaporator 4042 is connected to the first steam pipe 9 and the second steam pipe 10, and the first superheater 4031 is connected to the first steam pipe 9 and the second steam pipe 10.

[0098] According to an embodiment of the present invention, another aspect provides a method for rapid startup of a combined cycle unit, including the combined cycle unit rapid startup system of this embodiment.

[0099] In one embodiment, such as Figure 2 As shown, the rapid start-up method for combined cycle units includes:

[0100] Water is supplied to heater 5, and heater 5 is started to heat the water into steam and input into heat exchanger 401 to preheat heat exchanger 401.

[0101] Water is fed into heat exchanger 401, gas turbine 1 is started, and gas turbine 1 inputs flue gas into waste heat boiler 4. The flue gas exchanges heat with heat exchanger 401, and heat exchanger 401 heats up rapidly to heat the water in heat exchanger 401 into steam.

[0102] Specifically, before the gas turbine 1 is started, water is supplied to the heater 5 by a high-pressure water pump. The heater 5 is started by combining renewable energy power or surplus power from the grid to generate high-temperature and high-pressure steam. The steam is input into the first superheater 4031 for gradual preheating. The generated steam can be used to preheat the first steam pipe 9 and the second steam pipe 10. After the gas turbine 1 is started, water is supplied to the once-through reheater 402 by a medium-pressure water pump. The water in the tube bundle of the once-through reheater 402 is rapidly heated.

[0103] The DC reheater 402 exchanges heat with the flue gas, heating the water in the DC reheater 402 into steam.

[0104] Specifically, the first evaporator 4041 begins to generate superheated steam, and the low-temperature steam generated by the second superheater 4032 enters the second-stage once-through reheater 4022. By controlling the flow rate of subcooled water pumped into the once-through reheater 402 by the intermediate-pressure feedwater pump 601, saturated hot water is discharged from the lower part of the tube bundle of the second-stage once-through reheater 4022, thereby controlling the temperature of the once-through reheater 402 to not exceed the limit. At this time, the reheated steam reaches the standard for starting the turbine 3, the separator 7 begins to separate the reheated steam, and the intermediate-pressure cylinder 302 of the turbine 3 starts to operate.

[0105] Once the steam temperature reaches the preset value, heater 5 is turned off, and steam is input into turbine 3 to drive generator 2 to generate electricity;

[0106] Specifically, when the second evaporator 4042 and the third evaporator 4043 begin to generate superheated steam, the steam enters the first superheater 4031, providing sufficient steam flow to the first superheater 4031. At this time, the heater 5 is turned off, and the main steam reaches the standard for starting the turbine 3, and the main steam begins to output to start the high-pressure cylinder 301 of the turbine 3.

[0107] The steam in turbine 3 is returned to the once-through reheater 402 for heat exchange.

[0108] Specifically, when the gas turbine 1 reaches its rated full load, the circuit breaker 7 and the waste heat boiler 4 are fully started.

[0109] In another embodiment of the present invention, a third-stage reheater can be additionally arranged after the third-stage high-pressure superheater, so that a start-up boiler is not required, and the steam input to the third-stage high-pressure superheater comes directly from the second-stage high-pressure superheater.

[0110] Although embodiments of the invention have been described in conjunction with the accompanying drawings, those skilled in the art can make various modifications and variations without departing from the spirit and scope of the invention, and such modifications and variations all fall within the scope defined by the appended claims.

Claims

1. A rapid start-up system for a combined cycle power unit, characterized in that, include: A gas turbine (1) is suitable for connection with a generator (2); A steam turbine (3) is adapted to be connected to a generator (2), the steam turbine (3) including a high-pressure cylinder (301), an intermediate-pressure cylinder (302) and a low-pressure cylinder (303). A waste heat boiler (4) is connected to the gas turbine (1). The waste heat boiler (4) includes a heat exchanger (401) and a once-through reheater (402). The heat exchanger (401) is located inside the waste heat boiler (4) and is connected to the steam turbine (3). The once-through reheater (402) is located inside the waste heat boiler (4) near the gas turbine (1) and is connected to the steam turbine (3). A circulation loop is formed between the once-through reheater (402) and the steam turbine (3). The high-pressure cylinder (301) is connected to the heat exchanger (401) and the DC reheater (402), and a circulation loop is formed between the heat exchanger (401), the high-pressure cylinder (301), and the DC reheater (402). The high-pressure cylinder (301) and the intermediate-pressure cylinder (302) are adapted to drive the generator (2) to generate electricity. The intermediate-pressure cylinder (302) is connected to the heat exchanger (401) and the DC reheater (402), and a circulation loop is formed between the heat exchanger (401), the intermediate-pressure cylinder (302), and the DC reheater (402). The heater (5) is connected to the heat exchanger (401). The heater (5) uses renewable energy power or surplus power from the grid to heat water into steam. Before starting the gas turbine (1), the heater (5) injects cold water to heat the water into steam and inputs it into the heat exchanger (401) to preheat the heat exchanger (401). During the load ramp-up process of the gas turbine (1), the steam in the heat exchanger (401) is mixed into the heater (5). After the gas turbine (1) reaches the rated load, the steam in the heat exchanger (401) is mixed into the once-through reheater (402). A medium-pressure feedwater pump (601) is connected to the DC reheater (402); A high-pressure water pump (602) is connected to the heater (5); The separator (7) is connected to the DC reheater (402) and the intermediate pressure cylinder (302).

2. The combined cycle unit rapid start-up system according to claim 1, characterized in that, The steam turbine (3) also includes: The low-pressure cylinder (303) is connected to the medium-pressure cylinder (302) and the heat exchanger (401), and the low-pressure cylinder (303) is adapted to drive the generator (2) to generate electricity.

3. The combined cycle unit rapid start-up system according to claim 2, characterized in that, Also includes: A condenser (8) is disposed between the low-pressure cylinder (303) and the heat exchanger (401).

4. The combined cycle unit rapid start-up system according to claim 3, characterized in that, Also includes: The first steam pipe (9) is connected to the heat exchanger (401) and the high-pressure cylinder (301); The second steam pipe (10) is connected to the separator (7), the intermediate pressure cylinder (302) and the first steam pipe (9).

5. The combined cycle unit rapid start-up system according to claim 4, characterized in that, The heat exchanger (401) includes a superheater (403), an evaporator (404), an economizer (405), and a steam drum (406). The superheater (403) includes a first superheater (4031), a second superheater (4032), a third superheater (4033), a fourth superheater (4034), and a fifth superheater (4035); The evaporator (404) includes a first evaporator (4041), a second evaporator (4042), and a third evaporator (4043). The economizer (405) includes a first economizer (4051), a second economizer (4052), a third economizer (4053), a fourth economizer (4054), and a fifth economizer (4055). The steam drum (406) includes a first steam drum (4061), a second steam drum (4062), and a third steam drum (4063); wherein, The first superheater (4031) is connected to the heater (5) and the first steam pipe (9); The second superheater (4032) is connected to the third superheater (4033) and the first evaporator (4041), and the once-through reheater (402) is disposed between the first superheater (4031), the second superheater (4032) and the third superheater (4033); The first steam drum (4061) is connected to the third superheater (4033), the first evaporator (4041) and the first economizer (4051), the first economizer (4051) is connected to the second economizer (4052), the second economizer (4052) is connected to the third economizer (4053), and the third economizer (4053) is connected to the high-pressure feedwater pump (602). The fourth superheater (4034) is connected to the heater (5) and the second steam drum (4062), the second steam drum (4062) is connected to the second evaporator (4042) and the fourth economizer (4054), and the fourth economizer (4054) is connected to the high-pressure feedwater pump (602); The fifth superheater (4035) is connected to the heater (5) and the third steam drum (4063), the third steam drum (4063) is connected to the fifth economizer (4055) and the third evaporator (4043), and the third evaporator (4043) is connected to the medium-pressure feedwater pump (601) and the high-pressure feedwater pump (602).

6. The combined cycle unit rapid start-up system according to claim 5, characterized in that, The second evaporator (4042) is connected to the first steam pipe (9) and the second steam pipe (10), and the first superheater (4031) is connected to the first steam pipe (9) and the second steam pipe (10).

7. A method for rapid start-up of a combined cycle power unit, characterized in that, The combined cycle unit fast start system includes any one of claims 1 to 6, and the fast start method includes: Water is supplied to the heater (5), the heater (5) is started to heat the water into steam and input into the heat exchanger (401) to preheat the heat exchanger (401); Water is fed into the heat exchanger (401), the gas turbine (1) is started, the gas turbine (1) inputs flue gas into the waste heat boiler (4), the flue gas exchanges heat with the heat exchanger (401), the heat exchanger (401) heats up rapidly to heat the water in the heat exchanger (401) into steam; The DC reheater (402) exchanges heat with the flue gas, heating the water in the DC reheater (402) into steam; When the steam temperature reaches the preset value, the heater (5) is turned off, and the steam is input into the steam turbine (3) to drive the generator (2) to operate and generate electricity; The steam in the turbine (3) is returned to the direct current reheater (402) for heat exchange.

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