Method and system for high-oxygen-concentration combustion in fluidized bed coupled with liquid oxygen energy storage for peak shaving

Abstract

The present invention discloses a method and system for fluidized bed high-oxygen-concentration combustion coupled with liquid oxygen energy storage for peak shaving. The steps of the method are as follows: high-concentration oxygen produced by an air separation device is mixed with air and then enters a fluidized bed boiler to organize combustion together with inferior fuels that are difficult to burn, such as solid waste and coal gangue. The generated flue gas exchanges heat through a radiation heat exchanger and a convection heat exchanger, and part of it enters the furnace again as recycled flue gas, while the other part is discharged into the atmosphere after passing through a purification treatment device. When the external electricity load decreases, the high-concentration liquid oxygen produced by the air separation device is stored in a liquid oxygen storage tank, and the electricity output by the unit to the outside is reduced without significantly reducing the boiler load. When the external electricity load increases, the air separation device stops working, and the oxygen in the oxygen storage tank is used for combustion, reducing the power consumption of the air separation device and increasing the electricity output of the unit to the outside.

Description

Technical Field

[0001] The present invention belongs to the cross - field of energy technology and environmental protection technology, and particularly relates to a method and system for high - oxygen - concentration combustion in a fluidized bed coupled with liquid - oxygen energy storage for peak shaving. Background Art

[0002] China is accelerating the construction of a clean, low - carbon, efficient and diversified energy consumption structure. In the future, with an increasing proportion of intermittent power sources connecting to the power grid, the demand of the power system for regulating power capacity is extremely huge. It is imperative to vigorously develop safe and reliable power sources with low - carbon, high - efficiency and deep - flexible - regulation characteristics, which is also the historical responsibility that thermal power must and should be able to undertake in the future.

[0003] According to different energy storage forms, energy storage technologies can be divided into: mechanical energy storage, chemical energy storage, electromagnetic energy storage and thermal energy storage. At present, most energy storage technologies are still in the research stage or demonstration stage, and only compressed - air energy storage, pumped - storage energy storage and battery energy storage technologies are relatively mature. Among them, compressed - air energy storage and pumped - storage energy storage can achieve large - scale energy storage (100 MW and above), but their energy storage densities are relatively low, requiring large storage spaces, and geographical conditions limit their wide application. Battery energy storage has a high energy storage density and is not restricted by geographical location, but the storage capacity of battery energy storage is low, the production cost is high, and there is no effective solution to the environmental pollution problems caused during the production and scrapping of batteries. To solve the limitations of the above - mentioned energy storage technologies, in recent years, many scholars have proposed various novel energy storage concepts (such as thermochemical energy storage) to achieve high cost - effectiveness, geographical unrestriction and environmental friendliness. Compared with other energy storage technologies, thermochemical energy storage has a very wide range of applications. Thermochemical energy storage can be used for heating and cooling of buildings, and can also be integrated with thermal power plants for power generation. In addition, thermochemical energy storage systems can also be coupled with other energy storage systems (such as compressed - air energy storage systems, liquid - air energy storage systems) to improve the overall efficiency of the system, smooth the significant fluctuations of power plant generating units and reduce greenhouse gas emissions. However, thermochemical energy storage also has problems such as low energy conversion efficiency. Summary of the Invention

[0004] Object of the Invention: The object of the present invention is to provide a method and system for high - oxygen - concentration combustion in a fluidized - bed boiler coupled with liquid - oxygen energy storage for peak shaving, to give play to the advantages of high - oxygen - concentration combustion technology in dealing with difficult - to - burn fuels such as solid waste and coal gangue, and at the same time, combined with liquid - oxygen energy storage technology, to expand the boundary output of the power plant and achieve flexible peak shaving of thermal power units.

[0005] Technical Solution: The method for high - oxygen - concentration combustion in a fluidized bed coupled with liquid - oxygen energy storage for peak shaving according to the present invention is characterized in that it includes the following steps:

[0006] Step 1: The liquid oxygen generated by the air separation ion system enters the liquid oxygen storage tank for storage; the liquid oxygen in the storage tank is pressurized by a booster pump and then enters the liquid oxygen evaporator, oxygen turbine, and oxygen heat exchanger of the thermoelectric generation subsystem in sequence to generate gaseous oxygen that meets the combustion requirements, and a certain amount of electricity is generated through the oxygen turbine;

[0007] Step 2: The gaseous oxygen at the outlet of the oxygen heat exchanger is divided into two paths. One path is mixed with the recycled flue gas in a certain proportion and enters the fluidized bed boiler as primary air, and the other path of gaseous oxygen is mixed with air in a certain proportion and enters the fluidized bed boiler as secondary air; the fuel burns together with the primary air and secondary air in the fluidized bed boiler;

[0008] Step 3: The flue gas generated by fuel combustion flows through the radiant heat exchanger and the convective heat exchanger in sequence and is then divided into two paths. One path directly enters the flue gas purification and treatment subsystem, and the other path is pressurized by a flue gas circulation fan and used as recycled flue gas to be mixed with gaseous oxygen; the high-pressure steam generated by the fluidized bed boiler enters the steam turbine, drives the turbine to do work, and drives the generator to generate electricity;

[0009] Step 4: When the external power demand decreases, the fluidized bed boiler still operates at a high load. The electricity generated, in addition to being transmitted externally, the excess electricity is used to supply the air separation ion system; the generated liquid oxygen is partially used for fuel combustion, and the remaining part is stored in the liquid oxygen storage tank;

[0010] Step 5: When the external power demand increases, the air separation ion system stops operating, and the fluidized bed boiler operates at full load. At this time, the high-concentration oxygen required by the unit comes from the liquid oxygen storage tank. The electricity generated by the fluidized bed boiler is all transmitted externally except for a small part of the plant electricity.

[0011] Further, in Step 1, the air separation ion system adopts a cryogenic air separation device or a molecular sieve type air separation device.

[0012] Further, in Step 2, the fuel of the fluidized bed boiler is solid waste, coal gangue, petroleum coke, or oil shale.

[0013] Further, in Step 2, the oxygen concentration in the primary air is 10% - 20%, and the oxygen concentration in the secondary air is 30% - 50%.

[0014] The present invention also discloses a fluidized bed high-oxygen concentration combustion system coupled with liquid oxygen energy storage for peak shaving, including an air separation ion system, a liquid oxygen storage tank, a thermoelectric generation subsystem, a fluidized bed boiler subsystem, and a flue gas purification and treatment subsystem, wherein:

[0015] The thermoelectric generation subsystem includes a liquid oxygen booster pump, a liquid oxygen evaporator, an oxygen turbine, and an oxygen heat exchanger connected in sequence;

[0016] The fluidized bed boiler subsystem includes a fluidized bed burner, a radiant heat exchanger, a convective heat exchanger, and a flue gas circulation fan connected in sequence;

[0017] The air separation subsystem is connected to a liquid oxygen storage tank, which is then connected to the liquid oxygen booster pump of the thermoelectric generation subsystem; the heat exchanger of the thermoelectric generation subsystem is connected to the fluidized bed burner of the fluidized bed boiler subsystem, and the flue gas circulation fan of the fluidized bed boiler subsystem is connected to the flue gas purification and treatment subsystem.

[0018] Advantages: Compared with the prior art, the present invention has the following remarkable advantages:

[0019] (1) The high-oxygen-concentration combustion technology is beneficial to increasing the combustion temperature and reducing the generation amount of pollutants such as dioxins during the solid waste combustion process;

[0020] (2) The liquid oxygen energy storage technology is adopted to expand the boundary output of the power plant and achieve flexible peak regulation of thermal power units;

[0021] (3) The primary and secondary air combustion staging technology is adopted to reduce the original generation amount of NOx during the combustion process.

[0022] (4) The high-oxygen-concentration combustion technology is used to treat inferior and difficult-to-burn solid fuels such as solid waste and coal gangue, reducing the fuel cost; Description of the Drawings

[0023] Figure 1 It is a schematic diagram of the system structure and process of the present invention;

[0024] In the figure, 1 - air separation device; 2 - liquid oxygen storage tank; 3 - liquid oxygen booster pump; 4 - liquid oxygen evaporator; 5 - oxygen turbine; 6 - oxygen heat exchanger; 7 - fluidized bed burner; 8 - radiant heat exchanger; 9 - convective heat exchanger; 10 - flue gas circulation fan; 11 - flue gas purification and treatment device;

[0025] L1 - liquid oxygen; G1 - gaseous oxygen; G2 - air; G3 - secondary air; G4 - primary air; G5 - flue gas; G6 - recycled flue gas; S1 - fuel. Detailed Embodiments

[0026] The technical solution of the present invention will be further described below with reference to the drawings.

[0027] As Figure 1 shown is a system for fluidized bed high-oxygen-concentration combustion coupled with liquid oxygen energy storage peak regulation, including an air separation subsystem, a liquid oxygen storage tank, a thermoelectric generation subsystem, a fluidized bed boiler subsystem, a flue gas purification and treatment subsystem, etc., wherein:

[0028] The thermoelectric generation subsystem includes a liquid oxygen booster pump, a liquid oxygen evaporator, an oxygen turbine, and an oxygen heat exchanger connected in sequence;

[0029] The fluidized bed boiler subsystem includes a fluidized bed combustor, a radiation heat exchanger, a convection heat exchanger, and a flue gas circulation fan connected in sequence.

[0030] The air separation subsystem is connected to a liquid oxygen storage tank, and the liquid oxygen storage tank is connected to the liquid oxygen booster pump of the thermoelectric generation subsystem; the heat exchanger of the thermoelectric generation subsystem is connected to the fluidized bed combustor of the fluidized bed boiler subsystem, and the flue gas circulation fan of the fluidized bed boiler subsystem is connected to the flue gas purification and treatment subsystem.

[0031] Using the above system, the method of fluidized bed high-oxygen concentration combustion coupled with liquid oxygen energy storage for peak shaving is as follows:

[0032] The air separation subsystem uses a molecular sieve air separation device or a cryogenic air separation device, consumes a certain amount of electricity and produces low-temperature liquid oxygen. The generated liquid oxygen enters the liquid oxygen storage tank for storage. The liquid oxygen in the storage tank is pressurized to 5 MPa by a booster pump, and then enters the liquid oxygen evaporator, oxygen turbine, and oxygen heat exchanger of the thermoelectric generation subsystem in sequence to generate gaseous oxygen that meets the combustion requirements, and a certain amount of electricity is generated through the oxygen turbine. The thermoelectric generation subsystem can select a single-stage, double-stage or multi-stage turbine for power generation.

[0033] The gaseous oxygen at the outlet of the oxygen heat exchanger is divided into two paths. One path is mixed with the recycled flue gas in a certain proportion and enters the fluidized bed boiler as primary air. In the fluidized bed, the primary air is used to maintain a good fluidization state. Usually, the oxygen concentration in the primary air is controlled between 10% and 20%. The other path of gaseous oxygen is mixed with air in a certain proportion and enters the fluidized bed boiler as secondary air, and the oxygen concentration in the secondary air is 30% - 50%. The fuel burns in the fluidized bed boiler together with the primary air and secondary air. The different oxygen concentrations in the primary and secondary air make a relatively strong reducing atmosphere form in the dense phase region of the furnace, reducing the emission of NOx. And a large amount of recycled flue gas passes through the dense phase bed layer again, and the NOx in it will also be reduced to N2 by a large amount of coke or CO in the dense phase region.

[0034] This system can select solid waste as fuel. Usually, there will be problems with unstable fuel combustion during the combustion of solid waste. However, this system uses high-oxygen concentration combustion, and the oxygen concentration in the combustion atmosphere is above 30%, which can greatly improve the combustion performance of the fuel.

[0035] The flue gas generated by fuel combustion flows through the radiation heat exchanger and the convection heat exchanger in sequence, and the flue gas temperature is reduced to 150 - 200 °C. After that, the flue gas is divided into two paths. One path directly enters the flue gas purification and treatment subsystem and is discharged into the atmosphere after passing through environmental protection devices such as desulfurization, denitrification, and dust removal. The other path of flue gas is pressurized by a flue gas circulation fan and used as recycled flue gas to be mixed with gaseous oxygen. The high-pressure steam generated by the fluidized bed boiler enters the steam turbine, drives the turbine to do work and drives the generator to generate electricity.

[0036] When the external power demand decreases, i.e., during the low electricity consumption period, the fluidized bed boiler still operates at a high load. The electricity generated, besides being transmitted externally, the excess electricity is used to supply the air separation subsystem. Part of the generated liquid oxygen is used for fuel combustion, and the remaining part is stored in the liquid oxygen storage tank. In this way, the boiler can maintain a high load while reducing the unit's power transmission load, reducing the consumption of diesel oil for stable combustion, improving the economic efficiency of the power plant, and ensuring the safety of the boiler at the same time.

[0037] When the external power demand increases, i.e., during the high electricity consumption period, the air separation subsystem stops operating, and the fluidized bed boiler operates at full load. At this time, the high-concentration oxygen required by the unit comes from the liquid oxygen storage tank. Except for a small part of the auxiliary power consumption in the plant, all the electricity produced by the fluidized bed boiler is transmitted externally.

Claims

1. A method for high-oxygen-concentration combustion in a fluidized bed coupled with liquid oxygen energy storage for peak shaving, characterized in that: It includes the following steps: Step 1: The liquid oxygen generated by the air separation ion system enters the liquid oxygen storage tank for storage; the liquid oxygen in the storage tank is pressurized by a booster pump and then enters the liquid oxygen evaporator, oxygen turbine and oxygen heat exchanger of the thermoelectric generation system in sequence to generate gaseous oxygen meeting the combustion requirements, and a certain amount of electricity is generated through the oxygen turbine; Step 2: The gaseous oxygen at the outlet of the oxygen heat exchanger is divided into two paths. One path is mixed with the recycled flue gas in a certain proportion and enters the fluidized bed boiler as the primary air, and the other path of gaseous oxygen is mixed with air in a certain proportion and enters the fluidized bed boiler as the secondary air; the fuel burns together with the primary air and secondary air in the fluidized bed boiler; Step 3: The flue gas generated by fuel combustion flows through the radiation heat exchanger and the convection heat exchanger in sequence and is then divided into two paths. One path directly enters the flue gas purification and treatment subsystem, and the other path is pressurized by a flue gas circulation fan and used as recycled flue gas to be mixed with the gaseous oxygen; the high-pressure steam generated by the fluidized bed boiler enters the steam turbine, drives the turbine to do work and drives the generator to generate electricity; Step 4: When the external power demand decreases, the fluidized bed boiler still operates at a high load. The electricity generated, except for being transmitted externally, the excess electricity is used to supply the air separation ion system; the generated liquid oxygen is partially used for fuel combustion, and the remaining part is stored in the liquid oxygen storage tank; Step 5: When the external power demand increases, the air separation ion system stops operating, and the fluidized bed boiler operates at full load. At this time, the high-concentration oxygen required by the unit comes from the liquid oxygen storage tank. The electricity generated by the fluidized bed boiler is all transmitted externally except for a small amount of auxiliary power consumption in the plant.

2. The method for high-oxygen-concentration combustion in a fluidized bed for coupling liquid oxygen energy storage for peak shaving according to claim 1, wherein: In Step 1, the air separation ion system adopts a cryogenic air separation device or a molecular sieve type air separation device.

3. The method for high-oxygen-concentration combustion in a fluidized bed with coupled liquid oxygen energy storage for peak shaving according to claim 1, characterized in that: In Step 2, the fuel of the fluidized bed boiler is solid waste, coal gangue, petroleum coke or oil shale.

4. The method for high-oxygen-concentration combustion in a fluidized bed for coupling liquid oxygen energy storage for peak shaving according to claim 1, characterized in that: In Step 2, the oxygen concentration in the primary air is 10% - 20%, and the oxygen concentration in the secondary air is 30% - 50%.

5. A system for fluidized bed high-oxygen concentration combustion with coupled liquid oxygen energy storage for peak shaving, operating by the method described in claim 1, characterized in that, It includes an air separation ion system, a liquid oxygen storage tank, a thermoelectric generation system, a fluidized bed boiler subsystem and a flue gas purification and treatment subsystem, where: The thermoelectric generation system includes a liquid oxygen booster pump, a liquid oxygen evaporator, an oxygen turbine and an oxygen heat exchanger connected in sequence; The fluidized bed boiler subsystem includes a fluidized bed burner, a radiation heat exchanger, a convection heat exchanger, and a flue gas circulation fan connected in sequence; The air separation ion system is connected to the liquid oxygen storage tank, and the liquid oxygen storage tank is connected to the liquid oxygen booster pump of the thermoelectric generation system; the heat exchanger of the thermoelectric generation system is connected to the fluidized bed burner of the fluidized bed boiler subsystem, and the flue gas circulation fan of the fluidized bed boiler subsystem is connected to the flue gas purification and treatment subsystem.

Images