An efficient supercritical carbon dioxide boiler with a dual working fluid

Abstract

The present invention discloses an efficient supercritical carbon dioxide boiler with a dual working fluid, which includes a furnace, a horizontal flue and a vertical tail flue; the flue gas outlet of the furnace is connected to the horizontal flue and the vertical tail flue, an air-cooled wall is arranged in the furnace, a platen CO2 superheater, a high-temperature CO2 superheater and a high-temperature CO2 reheater are sequentially arranged in the horizontal flue along the flue gas flow direction, a low-temperature CO2 reheater, a low-temperature CO2 superheater, a superheater, a water-cooled wall and an economizer are sequentially arranged in the vertical tail flue from top to bottom. Among them, the working fluid flowing in the air-cooled wall, the low-temperature CO2 superheater, the platen CO2 superheater, the high-temperature CO2 superheater, the low-temperature CO2 reheater and the high-temperature CO2 reheater is carbon dioxide, the working fluid flowing in the economizer and the water-cooled wall is water, and the working fluid flowing in the superheater is steam. This boiler can overcome the problems that the supercritical CO2 working fluid has a high temperature and it is difficult to absorb the heat of the low-temperature flue gas at the tail.

Description

Technical Field

[0001] The present invention belongs to the technical field of boilers in thermal power plants, and relates to a high-efficiency supercritical carbon dioxide boiler with a dual working fluid. Background Art

[0002] The power generation process of modern coal-fired power plants is based on the steam Rankine cycle. The Rankine cycle is the simplest steam power cycle, which consists of four main devices: a water pump, a boiler, a steam turbine, and a condenser. Water is compressed and pressurized in the water pump; then it enters the boiler and is heated and vaporized until it becomes superheated steam, and then enters the steam turbine to expand and do work (driving a generator to generate electricity). The low-pressure steam after doing work enters the condenser and is cooled and condensed into water. Then it returns to the water pump, thus completing a work cycle.

[0003] The supercritical carbon dioxide (S-CO2) power generation system is a Brayton cycle system with supercritical CO2 as the working fluid. Its cycle process is as follows: First, S-CO2 is pressurized by a compressor; then, the S-CO2 working fluid is isobarically heated by an external heat source heater; secondly, the working fluid enters the turbine to drive the turbine to do work, and the turbine drives the motor to generate electricity; finally, the S-CO2 working fluid enters the cooler and returns to the initial state. Then it enters the compressor to form a closed cycle.

[0004] Carbon dioxide has a very unique physical property: when the temperature reaches 30.98 °C and the pressure reaches 7.38 MPa (i.e., the critical point of CO2), its physical state is between liquid and gas, the density is close to that of a liquid, the viscosity is close to that of a gas, and the diffusion coefficient is about 100 times that of a liquid. This state is called the "supercritical" state. Carbon dioxide in the supercritical state has a density greater than that of a gas and a viscosity smaller than that of a liquid, and has the characteristics of strong fluidity, high heat transfer efficiency, and small compressibility. Compared with the critical value of water at 373.95 °C / 22.04 MPa, a lower energy consumption can make CO2 reach the critical state. Using it as a circulating working fluid can effectively improve the power generation efficiency of the unit. Therefore, the supercritical carbon dioxide cycle power generation technology has a bright development prospect.

[0005] Then, in the design and simulation calculations, it is found that the supercritical carbon dioxide boiler has the following problems:

[0006] In the existing supercritical CO2 power generation cycle system, high / low temperature regenerators are designed. Before the CO2 enters the boiler, it is preheated by them and the temperature reaches as high as 500°C. Compared with the feed water temperature of an average of 300°C in a steam boiler, the inlet working fluid temperature of the carbon dioxide boiler is nearly 200°C higher. After the CO2 at a relatively high temperature enters the boiler, it can only absorb the heat of the flue gas with a temperature higher than its own. For the flue gas with a temperature lower than 500°C, it will lose the heating effect on the high-temperature CO2. The low-temperature flue gas in the tail flue cannot be absorbed, and the contained heat can only be discharged into the atmosphere. This will inevitably bring huge flue gas losses and seriously reduce the thermal efficiency of the boiler.

[0007] How to overcome the difficulties of high temperature of the supercritical CO2 working fluid and heat absorption of the low-temperature flue gas at the tail is an issue that has to be considered when designing a supercritical carbon dioxide boiler with practical prospects. Summary of the Invention

[0008] The purpose of the present invention is to overcome the above-mentioned disadvantages of the existing technology and provide a high-efficiency supercritical carbon dioxide boiler with a dual working fluid, which can overcome the problems of high temperature of the supercritical CO2 working fluid and difficulty in heat absorption of the low-temperature flue gas at the tail.

[0009] To achieve the above purpose, the high-efficiency supercritical carbon dioxide boiler with a dual working fluid described in the present invention includes a furnace, a horizontal flue and a vertical tail flue;

[0010] The flue gas outlet of the furnace is connected to the horizontal flue and the vertical tail flue. An air-cooled wall is arranged in the furnace. In the horizontal flue, a platen CO2 superheater, a high-temperature CO2 superheater and a high-temperature CO2 reheater are arranged in sequence along the flue gas flow direction. In the vertical tail flue, a low-temperature CO2 reheater, a low-temperature CO2 superheater, a superheater, a water-cooled wall and an economizer are arranged in sequence from top to bottom. Among them, the working fluid flowing in the air-cooled wall, the low-temperature CO2 superheater, the platen CO2 superheater, the high-temperature CO2 superheater, the low-temperature CO2 reheater and the high-temperature CO2 reheater is carbon dioxide, the working fluid flowing in the economizer and the water-cooled wall is water, and the working fluid flowing in the superheater is steam.

[0011] The outlet of the external compressor is connected to the inlet of the external compressor through the air-cooled wall, the low-temperature CO2 superheater, the platen CO2 superheater, the high-temperature CO2 superheater, the external high-pressure turbine, the low-temperature CO2 reheater, the high-temperature CO2 reheater and the external low-pressure turbine in sequence.

[0012] The outlet of the external feed water pump is connected to the inlet of the external steam drum through the economizer and the water-cooled wall. The steam outlet of the external steam drum is connected to the inlet of the external back pressure turbine through the superheater.

[0013] It also includes an air-cooled wall inlet header. Among them, the outlet of the external compressor is connected to the air-cooled wall through the air-cooled wall inlet header.

[0014] It also includes an air-cooled wall outlet header, and the air-cooled wall is connected to the low-temperature CO2 superheater through the air-cooled wall outlet header.

[0015] It also includes an economizer inlet header. Among them, the outlet of the external feed water pump is connected to the economizer through the economizer inlet header.

[0016] The outlet of the external steam drum is connected with a boiler drain pipe.

[0017] The outlet of the vertical flue at the tail is connected with a chimney.

[0018] The exhaust port of the external back pressure turbine is communicated with an industrial steam supply pipe.

[0019] The water wall adopts a spiral structure.

[0020] The present invention has the following beneficial effects:

[0021] When the high-efficiency supercritical carbon dioxide boiler with dual working fluids of the present invention is in specific operation, two working fluids, namely water vapor and carbon dioxide, are adopted. That is, the working fluid flowing in the air-cooled wall, low-temperature CO2 superheater, platen CO2 superheater, high-temperature CO2 superheater, low-temperature CO2 reheater and high-temperature CO2 reheater is carbon dioxide; the working fluid flowing in the economizer and water wall is water, and the working fluid flowing in the superheater is water vapor. That is, CO2 is used to absorb the heat of medium and high temperature flue gas, and water vapor is used to absorb the heat of low-temperature flue gas in the tail flue, completely solving the problems of high inlet working fluid temperature of the supercritical carbon dioxide boiler and difficult absorption of the heat of low-temperature flue gas at the tail, significantly improving the efficiency of the S-CO2 boiler, and ultimately effectively improving the power generation efficiency of the unit. Description of the Drawings

[0022] Figure 1 It is the schematic diagram of the present invention.

[0023] Among them, 1 is the air-cooled wall inlet header, 2 is the air-cooled wall, 3 is the air-cooled wall outlet header, 4 is the low-temperature CO2 superheater, 5 is the platen CO2 superheater, 6 is the high-temperature CO2 superheater, 7 is the high-pressure turbine, 8 is the low-temperature CO2 reheater, 9 is the high-temperature CO2 reheater, 10 is the low-pressure turbine, 11 is the economizer inlet header, 12 is the economizer, 13 is the water wall, 14 is the steam drum, 15 is the superheater, and 16 is the back pressure turbine. Detailed Embodiment

[0024] The following further describes the present invention in detail with reference to the drawings:

[0025] Reference Figure 1, the high-efficiency supercritical carbon dioxide boiler with dual working fluids according to the present invention includes a furnace, a horizontal flue, and a vertical tail flue; the flue gas outlet of the furnace is connected to the horizontal flue and the vertical tail flue, and a gas-cooled wall 2 is arranged in the furnace. In the horizontal flue, a platen CO2 superheater 5, a high-temperature CO2 superheater 6, and a high-temperature CO2 reheater 9 are sequentially arranged along the flue gas flow direction. In the vertical tail flue, a low-temperature CO2 reheater 8, a low-temperature CO2 superheater 4, a superheater 15, a water-cooled wall 13, and an economizer 12 are sequentially arranged from top to bottom. Among them, the working fluid flowing in the gas-cooled wall 2, the low-temperature CO2 superheater 4, the platen CO2 superheater 5, the high-temperature CO2 superheater 6, the low-temperature CO2 reheater 8, and the high-temperature CO2 reheater 9 is carbon dioxide, the working fluid flowing in the economizer 12 and the water-cooled wall 13 is water, and the working fluid flowing in the superheater 15 is steam.

[0026] The outlet of the external compressor is sequentially connected to the gas-cooled wall 2, the low-temperature CO2 superheater 4, the platen CO2 superheater 5, the high-temperature CO2 superheater 6, the external high-pressure turbine 7, the low-temperature CO2 reheater 8, the high-temperature CO2 reheater 9, and the external low-pressure turbine 10 and then connected to the inlet of the external compressor.

[0027] The outlet of the external feed water pump is connected to the inlet of the external steam drum 14 through the economizer 12 and the water-cooled wall 13, and the steam outlet of the external steam drum 14 is connected to the inlet of the external back pressure turbine 16 through the superheater 15.

[0028] The present invention further includes a gas-cooled wall inlet header 1. Among them, the outlet of the external compressor is connected to the gas-cooled wall 2 through the gas-cooled wall inlet header 1.

[0029] The present invention further includes a gas-cooled wall outlet header 3, and the gas-cooled wall 2 is connected to the low-temperature CO2 superheater 4 through the gas-cooled wall outlet header 3.

[0030] The present invention further includes an economizer inlet header 11. Among them, the outlet of the external feed water pump is connected to the economizer 12 through the economizer inlet header 11.

[0031] The outlet of the external steam drum 14 is connected with a boiler drain pipe; the outlet of the vertical tail flue is connected with a chimney; the exhaust port of the external back pressure turbine 16 is connected with an industrial steam supply pipe; the water-cooled wall 13 adopts a spiral structure.

[0032] The specific working process of the present invention is as follows:

[0033] Two sets of heating surfaces of the present invention share one furnace and flue. The fuel burns and releases heat in the furnace. The CO2 gas output by the compressor enters the gas-cooled wall 2 through the gas-cooled wall inlet header 1, absorbs the heat of the high-temperature (>1000℃) flue gas in the central area of the furnace flame in a radiation manner, and then successively absorbs heat through the low-temperature CO2 superheater 4, the platen CO2 superheater 5 and the high-temperature CO2 superheater 6, and finally reaches the rated parameters and is then sent into the high-pressure turbine 7 for expansion work to drive the impeller to rotate and drive the generator to generate electricity. The exhaust gas discharged from the high-pressure turbine 7 successively absorbs heat through the low-temperature CO2 reheater 8 and the high-temperature CO2 reheater 9, and then is sent into the low-pressure turbine 10 for expansion work to drive the impeller to rotate and then drive the generator to generate electricity. The exhaust gas discharged from the low-pressure turbine 10 enters the compressor to prepare for the next cycle.

[0034] The flue gas discharged from the furnace successively exchanges heat and cools down through the platen CO2 superheater 5, the high-temperature CO2 superheater 6, the high-temperature CO2 reheater 9, the low-temperature CO2 reheater 8 and the low-temperature CO2 superheater 4 to below 600℃ and then enters the tail vertical flue. Then, in the tail vertical flue, it exchanges heat and cools down through the superheater 15, the water-cooled wall 13 and the economizer 12 to about 350℃ and then is discharged.

[0035] The boiler feed water output by the feed water pump enters the economizer 12 through the economizer inlet header 11 for heat exchange and preheating, and then enters the water-cooled wall 13 to absorb heat. Among them, considering the stability of the hydrodynamic conditions, the water-cooled wall 13 adopts a spiral structure. The hot water output by the water-cooled wall 13 enters the steam drum 14 for steam-water separation. Among them, the separated wet steam enters the superheater 15 to be continuously heated into superheated steam, and then is sent into the back pressure turbine 16 for work. The exhaust steam discharged from the back pressure turbine 16 is input into the industrial steam supply system to provide high-temperature steam for production for heat users. The water separated by the steam drum 14 is output as boiler drain water.

Claims

1. An efficient supercritical carbon dioxide boiler with a dual working fluid, characterized in that, It includes a furnace, a horizontal flue, and a vertical tail flue; The flue gas outlet of the furnace is connected to the horizontal flue and the vertical tail flue. An air-cooled wall (2) is arranged in the furnace. A platen CO2 superheater (5), a high-temperature CO2 superheater (6), and a high-temperature CO2 reheater (9) are arranged in sequence along the flue gas flow direction in the horizontal flue. A low-temperature CO2 reheater (8), a low-temperature CO2 superheater (4), a superheater (15), a water-cooled wall (13), and an economizer (12) are arranged in sequence from top to bottom in the vertical tail flue. Among them, the working medium flowing in the air-cooled wall (2), the low-temperature CO2 superheater (4), the platen CO2 superheater (5), the high-temperature CO2 superheater (6), the low-temperature CO2 reheater (8), and the high-temperature CO2 reheater (9) is carbon dioxide. The working medium flowing in the economizer (12) and the water-cooled wall (13) is water. The working medium flowing in the superheater (15) is steam; The outlet of the external compressor is connected to the inlet of the external compressor in sequence through the air-cooled wall (2), the low-temperature CO2 superheater (4), the platen CO2 superheater (5), the high-temperature CO2 superheater (6), the external high-pressure turbine (7), the low-temperature CO2 reheater (8), the high-temperature CO2 reheater (9), and the external low-pressure turbine (10); The outlet of the external feed water pump is connected to the inlet of the external steam drum (14) through the economizer (12) and the water-cooled wall (13). The steam outlet of the external steam drum (14) is connected to the inlet of the external back pressure turbine (16) through the superheater (15).

2. The high-efficiency supercritical carbon dioxide boiler with a dual working fluid according to claim 1, characterized in that, It also includes an air-cooled wall inlet header (1). Among them, the outlet of the external compressor is connected to the air-cooled wall (2) through the air-cooled wall inlet header (1).

3. The high-efficiency supercritical carbon dioxide boiler with a dual working fluid according to claim 1, characterized in that, It also includes an air-cooled wall outlet header (3). The air-cooled wall (2) is connected to the low-temperature CO2 superheater (4) through the air-cooled wall outlet header (3).

4. The high-efficiency supercritical carbon dioxide boiler with a dual working fluid according to claim 1, characterized in that, It also includes an economizer inlet header (11). Among them, the outlet of the external feed water pump is connected to the economizer (12) through the economizer inlet header (11).

5. The high-efficiency supercritical carbon dioxide boiler with a dual working fluid according to claim 1, characterized in that, The outlet of the external steam drum (14) is connected with a boiler drain pipe.

6. The high-efficiency supercritical carbon dioxide boiler with a dual working fluid according to claim 1, characterized in that, The outlet of the vertical tail flue is connected with a chimney.

7. The high-efficiency supercritical carbon dioxide boiler with a dual working fluid according to claim 1, characterized in that, The exhaust port of the external back pressure turbine (16) is connected with an industrial steam supply pipe.

8. The high-efficiency supercritical carbon dioxide boiler with a dual working fluid according to claim 1, characterized in that, The water-cooled wall (13) adopts a spiral structure.

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