Coal-fired boiler low-load operation emission reduction system

Abstract

The utility model provides a coal-fired boiler low-load operation emission reduction system. The coal-fired boiler low-load operation emission reduction system comprises a boiler, and a primary air pipeline is connected with a primary air inlet of the boiler through an air pre-heater and a coal mill in sequence; the secondary air pipeline is connected with a secondary air inlet of the boiler through the air pre-heater; a flue of the boiler is connected with the air pre-heater through the denitration device and is also connected with the coal mill through the flue gas recirculation flow control device; a secondary air heater is arranged between the air pre-heater and the secondary air inlet, and a heat exchange medium inlet of the secondary air heater is connected with the boiler through a steam recirculation flow control device. According to the system, through cooperative use of the devices, the defects that when a coal-fired boiler operates at a low load, the combustion stability of a hearth is poor, the oxygen content of primary air is high, and the oxygen-coal mass ratio of primary combustion of pulverized coal is large, so that nitric oxide generated by the pulverized coal is high, the denitration load of a catalyst is large, and the denitration efficiency is low are overcome. And flue gas denitration does not reach the standard due to insufficient flue gas temperature at the inlet of the denitration device.

Description

Technical Field

[0001] This application relates to the field of thermal power generation technology, and in particular to an emission reduction system for low-load operation of a coal-fired boiler. Background Technology

[0002] With the increasing proportion of new energy sources in the power industry, the role of traditional coal-fired power units has shifted from "supporting" power sources to "peak-shaving" power sources, and low-load operation will become the norm. During low-load operation, the excess air coefficient is too high, the oxygen-to-coal mass ratio in primary combustion of pulverized coal is too high, and the oxygen content in the initial stage of combustion is too high, leading to higher NOx production from pulverized coal combustion. This results in an excessive workload on the denitrification catalyst, easily causing denitrification failure. Furthermore, during low-load boiler operation, due to the reduced fuel quantity, the furnace volumetric heat load, cross-sectional heat load, and furnace center temperature all decrease significantly, making pulverized coal ignition difficult, resulting in poor flame stability, easy flameout, and significant hidden dangers such as furnace flameout and deflagration. Simultaneously, during low-load operation, the inlet flue gas temperature of the SCR denitrification system does not meet the requirements for safe SCR operation, causing the SCR system to malfunction. Utility Model Content

[0003] This application provides a low-load operation emission reduction system for coal-fired boilers to address the following problems when coal-fired boilers are operating at low loads: high oxygen content in primary air, poor combustion stability in the furnace, high oxygen-to-coal mass ratio in primary combustion of pulverized coal leading to high nitrogen oxides produced by pulverized coal, high catalyst denitrification load, and insufficient flue gas temperature at the inlet of the denitrification device causing substandard flue gas denitrification.

[0004] This application provides a low-load operation emission reduction system for a coal-fired boiler, including a boiler, and a primary air pipeline connected to the primary air inlet of the boiler in sequence through an air preheater and a coal mill;

[0005] The secondary air pipeline is connected to the secondary air inlet of the boiler through the air preheater;

[0006] The boiler's flue is connected to the flue gas treatment device through a denitrification device and an air preheater;

[0007] The boiler's flue is also connected to the coal mill via a flue gas recirculation flow control device;

[0008] The boiler is connected in sequence to the steam turbine unit, condenser, pump, heater unit and economizer through steam pipes;

[0009] The turbine unit is also connected to the heater unit;

[0010] A secondary air heater is installed between the air preheater and the secondary air inlet. The heat exchange medium inlet of the secondary air heater is connected to the boiler through a steam recirculation flow control device, and the heat exchange medium outlet of the secondary air heater is connected to the heater group.

[0011] Optionally, the turbine unit includes a first turbine unit and a second turbine unit connected together;

[0012] The heater group includes a first heater group, a second heater group, and a third heater group connected in sequence;

[0013] The boiler is also connected in sequence to the first steam turbine unit, the second steam turbine unit, the condenser, and the pump.

[0014] The first steam turbine unit is connected to the third heater unit and the second heater unit respectively;

[0015] The second steam turbine unit is connected to the first heater unit;

[0016] The heat exchange medium inlet of the secondary air heater is connected to the boiler through a steam recirculation flow control device, and the heat exchange medium outlet of the secondary air heater is connected to the third heater group.

[0017] The boiler is also connected to a third heater unit;

[0018] The third heater unit is also connected to the economizer.

[0019] Optionally, the flue gas treatment device includes a dust collector, a desulfurization unit, and a chimney connected in series.

[0020] Optionally, the first turbine unit includes a high-pressure cylinder side and an intermediate-pressure cylinder side, and the second turbine unit includes a low-pressure cylinder;

[0021] The boiler is connected to the high-pressure cylinder side and the intermediate-pressure cylinder side respectively, and the intermediate-pressure cylinder side is connected to the low-pressure cylinder.

[0022] Optionally, a steam accumulator is connected in parallel between the boiler and the high-pressure cylinder side.

[0023] Alternatively, the dust collector may be a cyclone dust collector, an electrostatic precipitator, or a bag filter dust collector.

[0024] The system of this application, by setting up a flue gas recirculation flow control device, diverts the high-temperature flue gas in the flue into the primary air pipeline entering the coal mill, mixing it with the primary air to increase the temperature of the primary air and reduce its oxygen content. This has the beneficial effects of improving furnace combustion stability, reducing nitrogen oxide generation, and controlling pollutant production. Furthermore, this system uses boiler steam to heat the secondary air, increasing its temperature and thus improving the combustion stability of the boiler at low loads. It also increases the flue gas temperature at the economizer outlet, ensuring that the inlet flue gas temperature of the denitrification device meets the requirements for low-load operation. Through the combined use of the above devices, the system of this application overcomes the drawbacks of poor furnace combustion stability, high primary air oxygen content, high oxygen-to-coal mass ratio in primary coal combustion leading to high nitrogen oxide production from pulverized coal, high catalyst denitrification load, and insufficient flue gas temperature at the inlet flue gas temperature of the denitrification device causing substandard denitrification when the coal-fired boiler is operating at low loads. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 This is a schematic diagram of a low-load operation emission reduction system for a coal-fired boiler provided in an embodiment of this application;

[0027] Figure 2 A schematic diagram of a low-load operation emission reduction system for a coal-fired boiler provided in another embodiment of this application;

[0028] Figure 3 A schematic diagram of a low-load operation emission reduction system for a coal-fired boiler provided in another embodiment of this application.

[0029] Explanation of reference numerals in the attached figures:

[0030] 1. Boiler; 2. Air preheater; 3. Coal mill; 4. Denitrification unit; 5. Flue gas treatment unit; 6. First turbine unit; 7. Second turbine unit; 8. Steam accumulator; 10. Primary air pipeline; 11. Economizer; 20. Secondary air pipeline; 21. Secondary air heater; 51. Dust collector; 52. Desulfurization unit; 53. Chimney; 71. Condenser; 72. Pump; 100. Flue gas recirculation flow control device; 200. Steam recirculation flow control device; 721. First heater group; 722. Second heater group; 723. Third heater group; 1000. Turbine unit; 2000. Heater group. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application are described clearly and completely below. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are also within the scope of protection of this application.

[0032] like Figure 1 As shown, this application provides a low-load operation emission reduction system for a coal-fired boiler, including a boiler 1, and a primary air pipeline 10 connected to the primary air inlet of the boiler 1 in sequence through an air preheater 2 and a coal mill 3.

[0033] The secondary air duct 20 is connected to the secondary air inlet of the boiler 1 through the air preheater 2;

[0034] The flue of boiler 1 is connected to flue gas treatment device 5 through denitrification device 4 and air preheater 2;

[0035] The flue of boiler 1 is also connected to coal mill 3 through flue gas recirculation flow control device 100;

[0036] Boiler 1 is connected in sequence to turbine unit 1000, condenser 71, pump 72, heater unit 2000 and economizer 11 via steam pipes;

[0037] The turbine unit 1000 is also connected to the heater unit 2000;

[0038] A secondary air heater 21 is installed between the air preheater 2 and the secondary air inlet. The heat exchange medium inlet of the secondary air heater 21 is connected to the boiler 1 through the steam recirculation flow control device 200, and the heat exchange medium outlet of the secondary air heater 21 is connected to the heater group 2000.

[0039] In this application, during operation, the furnace of boiler 1 is ignited and started. The primary air supplied by the primary air pipeline 10 is heated by heat exchange in the air preheater 2. The heated primary air is fed into the furnace along with the pulverized coal through the primary air inlet of the furnace by the coal mill 3. At the same time, the secondary air supplied by the secondary air pipeline 20 is preheated by the air preheater 2 and then introduced into the furnace from the secondary air inlet of boiler 1 to promote the complete combustion of the fuel (pulverized coal in this application) in the furnace.

[0040] The flue gas produced after fuel combustion is discharged through the flue. A portion of the discharged flue gas is drawn in by the flue gas recirculation flow control device 100 (e.g., an induced draft fan) (the extraction point is set before the flue gas enters the economizer), and merged with the primary air entering the coal mill 3. This further heats the primary air while reducing its oxygen content, thus reducing the formation of nitrogen oxides (NOx) and controlling pollutants. As the flue gas continues to be discharged along the flue, it absorbs heat from the economizer and further heats the water or steam in the economizer, thereby lowering the flue gas temperature. The cooled flue gas then passes through the denitrification device 4 (SCR denitrification catalyst, with pyrolytic urea or liquid ammonia as the reducing agent) for selective reduction denitrification, reducing nitrogen oxides in the flue gas to nitrogen, reducing pollution. The denitrified flue gas then enters the air preheater 2 as a heat exchange medium to exchange heat and raise the temperature of the primary and secondary air. The heat-exchanged flue gas is then discharged from the air preheater 2 and treated by the flue gas treatment device 5 before being discharged.

[0041] The heat generated by the combustion of pulverized coal in the furnace heats the steam within the water-cooled walls of the furnace, producing superheated steam. Part of this steam enters the turbine unit 1000 for power generation, while the other part is introduced through steam pipes into the secondary air heater 21 to further heat the secondary air, increasing its inlet temperature and consequently raising the outlet flue gas temperature of the economizer 11. This ensures that the flue gas temperature entering the denitrification unit 4 remains within the range where the denitrification catalyst can exert its catalytic activity. After performing work in the turbine unit 1000, the steam's temperature and pressure decrease, producing exhaust steam. Part of this exhaust steam enters the heater unit 2000 from the turbine unit 1000 to heat the steam condensate. The other part of the exhaust steam enters the condenser 71 to condense into condensate. The condensed condensate is then pressurized and transported by the pump 72, sequentially passing through the heater unit 2000 for heating, while simultaneously absorbing steam. The condensate heated by the aforementioned heater group enters the economizer 11 to exchange heat with the flue gas and increase its temperature. Then, after passing through the steam drum, it enters the water-cooled wall to absorb the heat generated by the combustion of fuel in the furnace.

[0042] The system of this application, by setting up a flue gas recirculation flow control device 100, transfers the high-temperature flue gas in the flue into the primary air pipeline entering the coal mill 3, mixing it with the primary air to increase the temperature of the primary air and reduce its oxygen content. This has the beneficial effects of improving furnace combustion stability, reducing nitrogen oxide generation, and controlling pollutant production. Furthermore, this system uses boiler steam to heat the secondary air, increasing its temperature and thus improving the combustion stability of the boiler at low loads. It also increases the flue gas temperature at the economizer outlet, ensuring that the inlet flue gas temperature of the denitrification device 4 meets the requirements for low-load operation. Through the combined use of the above devices, the system of this application overcomes the drawbacks of poor furnace combustion stability, high primary air oxygen content, high oxygen-to-coal mass ratio in primary coal combustion leading to high nitrogen oxide production from pulverized coal, high catalyst denitrification load, and insufficient flue gas temperature at the inlet of the denitrification device causing substandard flue gas denitrification when the coal-fired boiler is operating at low loads.

[0043] like Figure 2 As shown, optionally, the steam turbine unit 1000 includes a first steam turbine unit 6 and a second steam turbine unit 7 connected together;

[0044] The heater assembly 2000 includes a first heater assembly 721, a second heater assembly 722, and a third heater assembly 723 connected in sequence;

[0045] Boiler 1 is also connected in sequence to the first steam turbine unit 6, the second steam turbine unit 7, the condenser 71 and the pump 72;

[0046] The first steam turbine unit 6 is connected to the third heater unit 723 and the second heater unit 722 respectively;

[0047] The second steam turbine unit 7 is connected to the first heater unit 721;

[0048] The heat exchange medium inlet of the secondary air heater 21 is connected to the boiler 1 through the steam recirculation flow control device 200, and the heat exchange medium outlet of the secondary air heater 21 is connected to the third heater group 723.

[0049] Boiler 1 is also connected to the third heater group 723;

[0050] The third heater group 723 is also connected to the economizer 11.

[0051] In this application, in order to further heat the secondary air and improve the combustion stability of the boiler at low load, and at the same time increase the flue gas temperature at the economizer 11 outlet so that the flue gas temperature at the SCR inlet can meet the requirements for low load operation, a portion of steam is drawn from the steam pipeline connecting the boiler 1 and the first turbine unit 6, and the flow rate is controlled by the steam recirculation flow control device 200 (such as a valve) and then introduced into the secondary air heater 21 to further heat the secondary air after it has been heated by the air preheater 2, so as to meet the requirements for low load operation.

[0052] In this application, the first heater group 721 includes a plurality of first heaters connected in series, the second heater group 722 includes at least one second heater, and the third heater group 723 includes a plurality of third heaters. The first heater group 721 is used for mixing and heat exchange with the low-pressure steam output from the second turbine group 7, the second heater group 722 is used for mixing and heat exchange with the medium-pressure steam output from the first turbine group 6, and the third heater group 723 is used for mixing and heat exchange with the high-pressure steam output from the first turbine group 6. The condensate after condensation of the steam output from the second turbine group 7 passes through the first heater group 721, the second heater group 722, and the third heater group 723 in a step-by-step heat exchange and temperature increase, which can fully transfer mass and heat with the steam, thereby making full use of the heat of the steam.

[0053] Optionally, the first turbine unit 6 includes a high-pressure cylinder side and an intermediate-pressure cylinder side, and the second turbine unit 7 includes a low-pressure cylinder;

[0054] Boiler 1 is connected to the high-pressure cylinder side and the medium-pressure cylinder side respectively, and the medium-pressure cylinder side is connected to the low-pressure cylinder.

[0055] The heat generated by the combustion of pulverized coal in the furnace heats the steam within the water-cooled walls of the furnace, producing superheated steam. A portion of this superheated steam enters the high-pressure cylinder side of the first turbine unit 6, while another portion enters the intermediate-pressure cylinder side, driving the first turbine unit 6 to generate electricity. After performing work in the first turbine unit 6, the steam's temperature and pressure decrease, producing high-pressure exhaust steam. A portion of this high-pressure exhaust steam exits from the middle of the first turbine unit 6 and enters the third heater group 723, heating the steam condensate within the third heater group 723. Another portion of the high-pressure exhaust steam is output from the end of the intermediate-pressure cylinder side of the first turbine unit 6 (where the steam temperature and pressure are relatively lowest) to the second turbine unit 7 and the second heater group 722. The steam entering the second turbine unit 7 drives the low-pressure cylinder of the second turbine unit 7 to perform work and generate electricity. After the steam performs work in the second turbine unit 7, its temperature and pressure further decrease, producing low-pressure exhaust steam. The low-pressure exhaust steam at the end of the low-pressure cylinder (where the steam temperature and pressure are relatively lowest) is passed into the condenser 71 to condense into condensate. The steam in the middle of the second turbine unit 7 (where the temperature is relatively higher) is passed into the first heater group 721 to heat the condensate. The condensed condensate is pressurized and transported by the pump 72, and sequentially passes through the first heater group 721, the second heater group 722, and the third heater group 723 to be heated, while absorbing steam. The condensate heated by the aforementioned heater group enters the economizer 11 to exchange heat with the flue gas and increase its temperature. Then, after passing through the steam drum, it enters the water-cooled wall to absorb the heat generated by the combustion of fuel in the furnace.

[0056] If the condensate fails to reach the required temperature after being heated by the third heater group 723, a portion of the steam from boiler 1 can be drawn out and introduced into the third heater group 723 to raise the temperature of the condensate, ensuring that the water temperature entering economizer 11 is up to standard.

[0057] like Figure 2 As shown, optionally, the flue gas treatment device 5 includes a dust collector 51, a desulfurization device 52 and a chimney 53 connected in series.

[0058] In operation, the flue gas after denitrification by the denitrification device 4 enters the air preheater 2 as a heat exchange medium to exchange heat and raise the temperature of the primary and secondary air. The heat-exchanged flue gas then exits the air preheater 2 and passes through the dust collector 51 to remove particulate matter and other solid particles, reducing the content of solid particles and further reducing the pollutant content in the flue gas. The dust-removed flue gas then enters the desulfurization device 52 (mainly the desulfurization tower), where the absorbent liquid (such as lime slurry or organic amine) absorbs, neutralizes, and removes sulfur oxides from the flue gas. After passing the desulfurization test and meeting the standards, the flue gas can be discharged through the chimney 53.

[0059] like Figure 3As shown, optionally, a steam accumulator 8 is connected in parallel between the boiler 1 and the high-pressure cylinder side.

[0060] In actual production, boiler 1 operates at low load, and its operating load is determined by actual production demand, which is unstable due to market fluctuations. Therefore, the steam produced by boiler 1 fluctuates. Consequently, a steam accumulator 8 is connected in parallel to the steam pipeline on the high-pressure cylinder side of boiler 1 and the first turbine unit 6. When the steam output of boiler 1 exceeds the overall plant steam load, the excess saturated steam is fed into the steam accumulator 8. This process is called the heat charging process, during which the water temperature, water level, and pressure within the accumulator increase. The maximum charging pressure is designed based on the rated pressure of boiler 1. When the charging pressure reaches its maximum value, the volume of the accumulator is also at its maximum, as is the water filling coefficient. When the steam load increases, the steam production of boiler 1 cannot meet the steam demand. In this case, the valve of the steam accumulator is opened to release heat. As the pressure inside the accumulator changes, the saturated water flashes into steam to supplement the steam supply. When the set heat release pressure decreases, the difference between the heat release pressure and the charging pressure increases, resulting in a relatively larger heat storage capacity, and vice versa. Therefore, the heat release pressure needs to be reduced while still meeting the steam demand. When the steam production and steam load of boiler 1 are the same, boiler 1 and the steam accumulator system reach a balanced state, neither charging nor releasing heat. By setting up the steam accumulator 8, boiler production can be stabilized and steam fluctuations reduced.

[0061] Optionally, the dust collector 51 is a cyclone dust collector, an electrostatic precipitator, or a bag filter dust collector.

[0062] In this application, the dust collector 51 is selected from cyclone dust collectors, electrostatic precipitators or bag dust collectors. The above types of dust collectors are easy to maintain, operate and install.

[0063] A low-load operation emission reduction system for a coal-fired boiler operates as follows:

[0064] During operation, the boiler 1 is ignited and started in the furnace. The primary air supplied by the primary air pipeline 10 is heated by heat exchange in the air preheater 2. The heated primary air is fed into the furnace along with the pulverized coal through the primary air inlet of the furnace by the coal mill 3. At the same time, the secondary air supplied by the secondary air pipeline 20 is preheated by the air preheater 2 and then further heated by heat exchange with the high-temperature steam from the boiler in the secondary air heater 21. After the temperature is increased, it is introduced into the furnace from the secondary air inlet of the boiler 1 to promote the complete combustion of the fuel (pulverized coal in this application) in the furnace.

[0065] The flue gas produced after fuel combustion is discharged through the flue. A portion of the flue gas discharged through the flue is drawn in by the flue gas recirculation flow control device 100 (such as an induced draft fan) (the drawing point is set before the flue gas enters the economizer 11), and merged with the primary air entering the coal mill 3. While further heating the primary air, it can also reduce the oxygen content of the primary air, reduce the generation of nitrogen oxides (i.e., NOx), and control pollutants. As the flue gas continues to be discharged along the flue, it absorbs heat from the flue gas through the economizer 11, further heating the water or steam in the economizer 11. Simultaneously, the flue gas temperature decreases. The cooled flue gas continues to be discharged through the denitrification device 4 (SCR denitrification catalyst, reducing agent is pyrolytic urea or liquid ammonia) for selective reduction denitrification, reducing nitrogen oxides in the flue gas to nitrogen gas, thus reducing pollution. The denitrified flue gas then enters the air preheater 2 as a heat exchange medium to exchange heat and raise the temperature of the primary and secondary air. The heat-exchanged flue gas then exits from the air preheater 2 and passes through the dust collector 51 to trap and remove solid particles such as soot, reducing the content of solid particles in the flue gas and further reducing the content of pollutants. The dust-removed flue gas then enters the desulfurization device 52 (mainly the desulfurization tower), where the absorbent liquid (such as lime slurry or organic amine) absorbs, neutralizes, and removes sulfur oxides from the flue gas. After the flue gas undergoes desulfurization and meets the standards, it can be discharged into chimney 53.

[0066] The heat generated by the combustion of pulverized coal in the furnace heats the steam within the water-cooled walls of the furnace, producing superheated steam. A portion of this superheated steam enters the high-pressure cylinder side of the first turbine unit 6, while another portion enters the intermediate-pressure cylinder side, driving the first turbine unit 6 to generate electricity. After performing work in the first turbine unit 6, the steam's temperature and pressure decrease, producing high-pressure exhaust steam. A portion of this high-pressure exhaust steam exits from the middle of the first turbine unit 6 and enters the third heater group 723, heating the steam condensate within the third heater group 723. Another portion of the high-pressure exhaust steam is output from the end of the intermediate-pressure cylinder side of the first turbine unit 6 (where the steam temperature and pressure are relatively lowest) to the second turbine unit 7 and the second heater group 722. The steam entering the second turbine unit 7 drives the low-pressure cylinder of the second turbine unit 7 to perform work and generate electricity. After the steam performs work in the second turbine unit 7, its temperature and pressure further decrease, producing low-pressure exhaust steam. The low-pressure exhaust steam at the end of the low-pressure cylinder (where the steam temperature and pressure are relatively lowest) is passed into the condenser 71 to condense into condensate. The steam in the middle of the second turbine unit 7 (where the temperature is relatively higher) is passed into the first heater group 721 to heat the condensate. The condensed condensate is pressurized and transported by the pump 72, and sequentially passes through the first heater group 721, the second heater group 722, and the third heater group 723 to be heated, while absorbing steam. The condensate heated by the aforementioned heater group enters the economizer 11 to exchange heat with the flue gas and increase its temperature. Then, after passing through the steam drum, it enters the water-cooled wall to absorb the heat generated by the combustion of fuel in the furnace.

[0067] If the condensate fails to reach the required temperature after being heated by the third heater group 723, a portion of the steam from boiler 1 can be drawn out and introduced into the third heater group 723 to raise the temperature of the condensate, ensuring that the water temperature entering economizer 11 is up to standard.

[0068] To further heat the secondary air and improve the combustion stability of the boiler at low load, and to increase the flue gas temperature at the economizer 11 outlet so that the SCR inlet flue gas temperature can meet the requirements for low load operation, a portion of steam is drawn from the steam pipeline connecting boiler 1 and the first turbine unit 6. After the flow rate is controlled by the steam recirculation flow control device 200 (such as a valve), the steam is introduced into the secondary air heater 21 to further heat the secondary air after it has been heated by the air preheater 2, so as to meet the requirements for low load operation.

[0069] In actual production, boiler 1 operates at low load, and its operating load is determined by actual production demand, which is unstable due to market fluctuations. Therefore, the steam produced by boiler 1 fluctuates. Consequently, a steam accumulator 8 is connected in parallel to the steam pipeline on the high-pressure cylinder side of boiler 1 and the first turbine unit 6. When the steam output of boiler 1 exceeds the overall plant steam load, the excess saturated steam is fed into the steam accumulator 8. This process is called the heat charging process, during which the water temperature, water level, and pressure within the accumulator increase. The maximum charging pressure is designed based on the rated pressure of boiler 1. When the charging pressure reaches its maximum value, the volume of the accumulator is also at its maximum, as is the water filling coefficient. When the steam load increases, the steam production of boiler 1 cannot meet the steam demand. In this case, the valve of the steam accumulator is opened to release heat. As the pressure inside the accumulator changes, the saturated water flashes into steam to supplement the steam supply. When the set heat release pressure decreases, the difference between the heat release pressure and the charging pressure increases, resulting in a relatively larger heat storage capacity, and vice versa. Therefore, the heat release pressure needs to be reduced while still meeting the steam demand. When the steam production and steam load of boiler 1 are the same, boiler 1 and the steam accumulator system reach a balanced state, neither charging nor releasing heat. By setting up the steam accumulator 8, boiler production can be stabilized and steam fluctuations reduced.

[0070] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A low-load operation emission reduction system for a coal-fired boiler, characterized in that, Including the boiler (1), the primary air pipeline (10) is connected to the primary air inlet of the boiler (1) in sequence through the air preheater (2) and the coal mill (3); The secondary air pipeline (20) is connected to the secondary air inlet of the boiler (1) through the air preheater (2); The flue of the boiler (1) is connected to the flue gas treatment device (5) through the denitrification device (4) and the air preheater (2); The flue of the boiler (1) is also connected to the coal mill (3) through a flue gas recirculation flow control device (100); The boiler (1) is connected in sequence to the steam turbine unit (1000), condenser (71), pump (72), heater unit (2000) and economizer (11) via steam pipes; The turbine unit (1000) is also connected to the heater unit (2000); A secondary air heater (21) is provided between the air preheater (2) and the secondary air inlet. The heat exchange medium inlet of the secondary air heater (21) is connected to the boiler (1) through a steam recirculation flow control device (200), and the heat exchange medium outlet of the secondary air heater (21) is connected to the heater group (2000).

2. The emission reduction system for low-load operation of a coal-fired boiler according to claim 1, characterized in that, The turbine unit (1000) includes a first turbine unit (6) and a second turbine unit (7) connected together. The heater group (2000) includes a first heater group (721), a second heater group (722) and a third heater group (723) connected in sequence. The first steam turbine unit (6) is connected to the third heater group (723) and the second heater group (722) respectively; The second steam turbine unit (7) is connected to the first heater unit (721); The heat exchange medium outlet of the secondary air heater (21) is connected to the third heater group (723); The third heater group (723) is also connected to the economizer (11).

3. The emission reduction system for low-load operation of a coal-fired boiler according to claim 1, characterized in that, The flue gas treatment device (5) includes a dust collector (51), a desulfurization device (52) and a chimney (53) connected in series.

4. The emission reduction system for low-load operation of a coal-fired boiler according to claim 2, characterized in that, The first turbine unit (6) includes a high-pressure cylinder side and an intermediate-pressure cylinder side, and the second turbine unit (7) includes a low-pressure cylinder; The boiler (1) is connected to the high-pressure cylinder side and the medium-pressure cylinder side respectively, and the medium-pressure cylinder side is connected to the low-pressure cylinder.

5. The emission reduction system for low-load operation of a coal-fired boiler according to claim 4, characterized in that, A steam accumulator (8) is connected in parallel between the boiler (1) and the high-pressure cylinder side.

6. The emission reduction system for low-load operation of a coal-fired boiler according to claim 3, characterized in that, The dust collector (51) is a cyclone dust collector, an electrostatic precipitator, or a bag filter dust collector.

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