Denitration device stable operation system and method for emergency operation of coal-fired power plants with boilers kept running after power generation units are shut down

Abstract

The present invention discloses a stable operation system for a denitration device during emergency operation of a coal-fired power unit with the boiler in operation while the unit is shut down. The heating steam source of the high-pressure heater group comes from the cold reheat steam main pipe of the coal-fired power generating unit, as well as the main steam and reheated steam that have been depressurized and cooled down. The heating steam source of the deaerator is taken from the cold reheat steam main pipe of the coal-fired power generating unit. A part of the water-side outlet of the high-pressure heater group enters the boiler to complete the steam-water thermodynamic cycle, and the other part is used as desuperheating water to be mixed with the depressurized and cooled main steam and reheated steam and then transported as the heating steam source to the No. 1 high-pressure heater and the No. 3 high-pressure heater. A economizer is arranged in the boiler of the coal-fired power generating unit, and the flue gas at the outlet of the economizer enters the flue gas denitration device. In the operation mode of the unit with the boiler in operation while the unit is shut down, the present invention sets the steam sources of the deaerator, the No. 3 high-pressure heater and the No. 1 high-pressure heater to increase the temperature at the boiler inlet. At the same time, the reheated steam with high superheat degree is used to heat the flue gas temperature at the denitration device inlet. The two work together to ensure the denitration effect of the boiler flue gas and the compliance of pollutant emissions under the emergency operation condition of the unit with the boiler in operation while the unit is shut down.

Description

Technical Field

[0001] The present invention belongs to the technical field of coal-fired power generation, and relates to a stable operation system and method for a denitration device during emergency operation of a coal-fired power plant with the boiler in operation while the turbine is shut down.

Background Art

[0002] The "Code for Design of Large and Medium-sized Thermal Power Plants" (GB50660-2011) stipulates that cogeneration units should be designed to take into account both power generation and heat supply functions. During the period of external heat supply, high heat supply reliability should be ensured. For extraction condensing steam turbines, it is advisable to match one boiler for each turbine. When the largest steam boiler is out of service, if the external steam supply capacity of the remaining boilers cannot meet the requirements of 100% of the production steam demand for continuous production of thermal users, 60% - 75% (the upper limit is taken in severe cold areas) of the heat demand for winter heating, ventilation and domestic use, other standby heat sources should be configured by the heat network. When equipment such as the steam turbine and generator of a heat supply unit fails and needs to be repaired during the heating period, problems such as unqualified heat supply, heat supply interruption, and steam supply interruption will occur, affecting the heating experience of residents and causing production losses to enterprises, with a great social impact.

[0003] The combined high and low pressure bypass heat supply technology can achieve the goal of enabling a coal-fired power generation unit to still supply centralized heat to residents under the conditions of turbine and generator failures: the boiler and its supporting auxiliary equipment operate, the turbine and generator are shut down, the regenerative system is put into operation or shut down according to specific requirements and steam source conditions, the feed water enters the boiler to be heated, and the new steam at the outlet enters the cold reheat steam main pipe after being desuperheated and depressurized by the high pressure bypass, and then enters the in-plant heating steam main pipe after being reheated for the second time in the boiler reheater, which is called the emergency operation condition of boiler in operation while the turbine is shut down.

[0004] In the operation condition of boiler in operation while the turbine is shut down, the generator power of the coal-fired power generation unit drops to zero. Following the principle of conservation of heat, the heat released by the boiler is used for heating the feed water in the thermal system, and the rest is used for external heating and heat supply. Limited by the steam parameters and flow capacity of the main steam, cold reheat steam, hot reheat steam and heating steam pipelines, the boiler load is relatively low under the condition of boiler in operation while the turbine is shut down, about 20% - 40% of the rated load. Except for the extraction steam of the No. 2 high pressure heater whose steam source is taken from the cold reheat main pipe, the steam sources of the other high pressure heaters in the turbine regenerative system are all taken from the turbine flow path. Therefore, except for the No. 2 high pressure heater, the steam sides of the other high pressure heaters are shut down under the condition of boiler in operation while the turbine is shut down, and the feed water temperature at the boiler inlet drops significantly. Due to the increase in the heat transfer temperature difference in the economizer, the outlet flue gas temperature drops significantly. Factors such as low boiler load and low feed water temperature lead to a significant decrease in the flue gas temperature at the inlet of the denitration device, deviating from the catalytic high-efficiency operation temperature range, reducing the catalyst activity, decreasing the denitration efficiency, thereby increasing the ammonia escape rate and causing the problem of non-compliance of nitrogen oxide NOx emissions, resulting in serious environmental protection problems.

[0005] Currently, there is no operating engineering case of boiler in operation while the turbine is shut down, nor is there a publicly reported technical solution for the stable operation of the denitration device.

[0006] Since the efficient operating temperature range of the catalyst is affected by the inherent characteristics of the material itself, the key to ensuring the denitration effect of boiler flue gas under low load and meeting the pollutant emission standards lies in increasing the flue gas temperature. To address the above problems, the present invention proposes a stable operation system for the denitration device during the shutdown of coal-fired power generation units without stopping the boiler operation, mainly starting from two aspects: increasing the feed water temperature and reducing the heat release of the upstream flue gas, so as to increase the flue gas temperature at the inlet of the denitration device.

Summary of the Invention

[0007] The purpose of the present invention is to solve the problems in the prior art such as low flue gas temperature at the inlet of the denitration device, poor denitration effect, and excessive pollutant emissions during the shutdown of coal-fired power generation units without stopping the boiler operation, and to provide a stable operation system and method for the denitration device during the emergency operation of coal-fired power generation units during shutdown without stopping the boiler.

[0008] To achieve the above object, the present invention adopts the following technical solutions:

[0009] A stable operation system for the denitration device during the emergency operation of coal-fired power generation units during shutdown without stopping the boiler, including a coal-fired power generation unit. The exhaust steam of the low-pressure cylinder of the coal-fired power generation unit enters the condenser for condensation, and the condensed water sequentially passes through a condensate pump, a low-pressure heater group, a deaerator, a feed pump group, and the No. 3 high-pressure heater, No. 2 high-pressure heater, and No. 1 high-pressure heater. Under the emergency operation condition of shutdown without stopping the boiler, the heating steam sources of the No. 3 high-pressure heater, No. 2 high-pressure heater, and No. 1 high-pressure heater respectively come from the reheated steam with reduced pressure and temperature of the coal-fired power generation unit, the cold reheat steam main pipe, and the main steam with reduced pressure and temperature. The heating steam source of the deaerator is taken from the cold reheat steam main pipe of the coal-fired power generation unit. A part of the water-side outlet of the No. 1 high-pressure heater enters the boiler to complete the steam-water thermodynamic cycle, and the other part is used as desuperheating water to be mixed with the main steam and reheated steam with reduced pressure as the heating steam source to be transported to the No. 1 high-pressure heater and No. 3 high-pressure heater. A economizer is provided in the boiler of the coal-fired power generation unit, and the flue gas at the outlet of the economizer enters the flue gas denitration device.

[0010] A further improvement of the present invention is as follows:

[0011] The coal-fired power generation unit includes a boiler. When the coal-fired power generation unit operates normally, the new steam of the boiler enters the high-pressure cylinder to do work, the exhaust steam of the high-pressure cylinder enters the reheater of the boiler through the cold reheat steam main pipe for secondary temperature increase, the reheated steam of the boiler enters the intermediate-pressure cylinder to do work, and the exhaust steam of the intermediate-pressure cylinder enters the low-pressure cylinder to do work. The high-pressure heater group includes the No. 1 high-pressure heater, No. 2 high-pressure heater, and No. 3 high-pressure heater connected in sequence. The high-pressure cylinder, intermediate-pressure cylinder, and low-pressure cylinder are coaxially connected and jointly drive the generator to generate electricity.

[0012] The new steam of the boiler is divided into three paths. The first path passes through the high-pressure cylinder steam inlet valve group to the high-pressure cylinder to do work. The second path passes through the first desuperheating and pressure-reducing valve group to the cold reheat steam main pipe. The third path passes through the second desuperheating and pressure-reducing valve group to the No. 1 high-pressure heater.

[0013] The reheated steam of the boiler is divided into three paths. The first path passes through the intermediate-pressure cylinder steam inlet valve group to the intermediate-pressure cylinder to do work. The second path passes through the third desuperheating and pressure-reducing valve group to the No. 3 high-pressure heater. The third path passes through the sixth valve group to the steam side inlet of the flue gas heater. The steam side outlet of the flue gas heater transports the reheated steam after heat exchange to the heat network heater through the seventh valve group.

[0014] The heat source of the heat network heater comes from part of the exhaust steam of the intermediate-pressure cylinder and part of the reheated steam of the boiler. Part of the exhaust steam of the intermediate-pressure cylinder is output through the first valve group to the steam side inlet of the heat network heater. Part of the reheated steam of the boiler is mixed with part of the exhaust steam from the intermediate-pressure cylinder after heat exchange with part of the flue gas of the economizer in the flue gas heater, and then transported to the steam side inlet of the heat network heater to exchange heat with the heating circulating water. The drain water of the heat network heater is transported to the water side inlet of the deaerator.

[0015] The feed water at the outlet of the No. 1 high-pressure heater is divided into two paths. The first path enters the boiler, and the second path enters the first desuperheating and pressure-reducing valve group, the third path enters the second desuperheating and pressure-reducing valve group, and the fourth path enters the third desuperheating and pressure-reducing valve group respectively through the tenth valve group.

[0016] The exhaust steam of the high-pressure cylinder is connected to the cold reheat steam main pipe through the second valve group. The cold reheat steam main pipe transports the exhaust steam of the high-pressure cylinder to the boiler reheater. The first-stage extraction steam of the high-pressure cylinder is connected to the first-stage extraction steam pipeline through the third valve group. The first-stage extraction steam pipeline transports the first-stage extraction steam to the steam side inlet of the No. 1 high-pressure heater. The cold reheat steam main pipe transports part of the steam to the steam side inlet of the No. 2 high-pressure heater through the eighth valve group and to the steam side inlet of the deaerator through the ninth valve group. The ninth valve group performs pressure reduction adjustment.

[0017] The third-stage extraction steam of the intermediate-pressure cylinder is connected to the third-stage extraction steam pipeline through the fourth valve group. The third-stage extraction steam pipeline transports the third-stage extraction steam to the steam side inlet of the No. 3 high-pressure heater. The fourth-stage extraction steam of the intermediate-pressure cylinder is connected to the heating steam source inlet of the deaerator through the fifth valve group.

[0018] The drain water after heat exchange in the No. 1 high-pressure heater is output to the No. 2 high-pressure heater for heat exchange, and then output to the No. 3 high-pressure heater for heat exchange. The drain water after heat exchange is output to the deaerator.

[0019] A heat network circulating water pump group is arranged on the heat network return water main pipe at the inlet of the heat network heater.

[0020] A method for stably operating a denitration device during the emergency operation of a coal-fired power unit with the boiler in operation while the unit is shut down includes the following steps:

[0021] During the heating season for residents, when the coal-fired power generation unit is operating normally

[0022] Open the high-pressure cylinder steam inlet valve group, intermediate-pressure cylinder steam inlet valve group, heating butterfly valve of the intermediate-low pressure connecting pipe, first valve group, second valve group, third valve group, fourth valve group, fifth valve group and eighth valve group, and close the first desuperheating and pressure-reducing valve group, second desuperheating and pressure-reducing valve group, third desuperheating and pressure-reducing valve group, sixth valve group, seventh valve group, ninth valve group and tenth valve group;

[0023] The new steam at the boiler outlet enters the high-pressure cylinder to do work, and the exhaust steam enters the boiler reheater through the cold reheat steam main pipe to achieve secondary temperature increase and avoid overheating of the reheater. Then it enters the intermediate-pressure cylinder to do work. The exhaust steam is divided into two paths. One path goes through the valve group to the heating steam main pipe for the heating network to heat the heating circulating water. The condensate is boosted by the condensate pump group and then flows into the water side inlet of the deaerator. The remaining steam enters the low-pressure cylinder to continue doing work; the exhaust steam of the low-pressure cylinder is condensed in the condenser, and the condensate flows through the condensate pump, low-pressure heater group, deaerator, feed pump group, No. 3 high-pressure heater, No. 2 high-pressure heater and No. 1 high-pressure heater in sequence to increase the temperature and pressure and then enters the boiler to complete the steam-water thermodynamic cycle;

[0024] When one or both of the steam turbine and the generator fail, this unit still needs to supply centralized heating externally. At this time, it is called the emergency heating operation mode of shutting down the machine but not the boiler:

[0025] Close the high-pressure cylinder steam inlet valve group, intermediate-pressure cylinder steam inlet valve group and heating butterfly valve of the intermediate-low pressure connecting pipe, close the first valve group, second valve group, third valve group, fourth valve group and fifth valve group, and open the first desuperheating and pressure-reducing valve group, second desuperheating and pressure-reducing valve group, third desuperheating and pressure-reducing valve group, sixth valve group, seventh valve group, ninth valve group and tenth valve group; Shut down the high-pressure cylinder, intermediate-pressure cylinder, low-pressure cylinder, generator, condenser and condensate pump.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] The present invention realizes a stable operation system for the denitration device in the emergency operation of shutting down the coal-fired power unit but not the boiler. In the operation mode of shutting down the machine but not the boiler, the heating steam sources of the deaerator, No. 3 high-pressure heater and No. 1 high-pressure heater are set to increase the temperature at the boiler inlet. At the same time, the reheated steam with high superheat is used to heat the flue gas temperature at the denitration device inlet to meet the temperature requirements for the safe operation of the denitration system. The two work together to ensure the denitration effect of the boiler flue gas and the compliance of pollutant emissions under the condition of shutting down the machine but not the boiler.

Description of the Drawings

[0028] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as limiting the scope. For those of ordinary skill in the art, without creative efforts, other related drawings can also be obtained based on these drawings.

[0029] Figure 1 System schematic diagram of the present invention;

[0030] Wherein, 1 - boiler, 2 - high-pressure cylinder, 3 - intermediate-pressure cylinder, 4 - low-pressure cylinder, 5 - generator, 6 - condenser, 7 - condensate pump, 8 - deaerator, 9 - feed water pump group, 10 - No. 3 high-pressure heater, 11 - No. 2 high-pressure heater, 12 - No. 1 high-pressure heater, 13 - heat network circulating water pump group, 13 - heat network heater, 15 - drain pump group, 16 - flue gas heater, 17 - denitration device, 18 - high-pressure cylinder steam inlet valve group, 19 - intermediate-pressure cylinder steam inlet valve group, 20 - heat supply butterfly valve for the intermediate and low-pressure connecting pipe, 21 - first valve group, 22 - second valve group, 23 - third valve group, 24 - fourth valve group, 25 - fifth valve group, 26 - first desuperheating and pressure reducing valve group, 27 - second desuperheating and pressure reducing valve group, 28 - third desuperheating and pressure reducing valve group, 29 - sixth valve group, 30 - seventh valve group, 31 - eighth valve group, 32 - ninth valve group, 33 - tenth valve group, 34 - low-pressure heater group.

Detailed implementation manners

[0031] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. Usually, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0032] Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed present invention, but merely represents the selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0033] It should be noted that: Similar reference numerals and letters denote similar items in the following drawings. Therefore, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings.

[0034] In the description of the embodiments of the present invention, it should be noted that if the terms "upper", "lower", "horizontal", "inner", etc. indicate an orientation or positional relationship based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship in which the product of the invention is usually placed when in use, it is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention. In addition, the terms "first", "second", etc. are only used to distinguish the description, and cannot be understood as indicating or implying relative importance.

[0035] In addition, if the term "horizontal" appears, it does not mean that the component must be absolutely horizontal, but can be slightly tilted. For example, "horizontal" only means that its direction is more horizontal than "vertical", which does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0036] In the description of the embodiments of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "set", "install", "connect", and "connect" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal connection of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0037] The present invention is further described in detail below in conjunction with the accompanying drawings:

[0038] See also Figure 1 The present invention proposes a stable operation system for a denitrification device for emergency operation during shutdown without stopping the furnace, including a coal-fired power unit, wherein the exhaust steam of the low-pressure cylinder 4 of the coal-fired power unit enters the condenser 6 for condensation, and the condensed water passes through the condensate pump 7, the low-pressure heater group 34, the deaerator 8, the feed water pump group 9, and the No. 3 high-pressure heater 10, the No. 2 high-pressure heater 11, and the No. 1 high-pressure heater 12 in sequence. Under the emergency operation condition of shutdown without stopping the furnace, the heating steam sources of the No. 3 high-pressure heater 10, the No. 2 high-pressure heater 11, and the No. 1 high-pressure heater 12 are respectively from the reheated steam of the coal-fired power unit with reduced pressure and temperature, the cold re-steam main pipe, and the main steam with reduced pressure and temperature; the heating steam source of the deaerator 8 is taken from the cold re-steam main pipe of the coal-fired power generation unit;

[0039] A part of the water side outlet of the No. 1 high-pressure heater 12 enters the boiler 1 to complete the steam-water thermal cycle, and the other part is mixed with the reduced-pressure main steam and reheated steam as cooling water and transported to the No. 1 high-pressure heater 12 and the No. 3 high-pressure heater 10 as a heating steam source; an economizer is installed in the boiler 1 of the coal-fired power unit, and the flue gas at the economizer outlet enters the flue gas denitrification device 17.

[0040] The coal-fired power generation unit includes a boiler 1. The new steam of the boiler 1 enters the high-pressure cylinder 2 to do work. The exhaust steam of the high-pressure cylinder 2 enters the reheater of the boiler 1 through the cold reheat steam main pipe for secondary temperature increase. The reheated steam of the boiler 1 enters the intermediate-pressure cylinder 3 to do work, and the exhaust steam of the intermediate-pressure cylinder 3 enters the low-pressure cylinder 4 to do work. The high-pressure heater group includes the No. 1 high-pressure heater 12, the No. 2 high-pressure heater 11, and the No. 3 high-pressure heater 10 connected in sequence. The high-pressure cylinder 2, the intermediate-pressure cylinder 3, and the low-pressure cylinder 4 are coaxially connected and jointly drive the generator 5 to generate electricity.

[0041] The feed water at the outlet of the No. 1 high-pressure heater 12 is divided into two paths. The first path enters the boiler 1, and the second path enters the first desuperheating and pressure-reducing valve group 26, the third path enters the second desuperheating and pressure-reducing valve group 27, and the fourth path enters the third desuperheating and pressure-reducing valve group 28 through the tenth valve group respectively. The exhaust steam of the high-pressure cylinder 2 is connected to the cold reheat steam main pipe through the second valve group 22, and the cold reheat steam main pipe transports the exhaust steam of the high-pressure cylinder 2 to the reheater of the boiler 1. The first-stage extraction steam of the high-pressure cylinder 2 is connected to the first-stage extraction steam pipeline through the third valve group 23, and the first-stage extraction steam pipeline transports the first-stage extraction steam to the steam-side inlet of the No. 1 high-pressure heater 12. The cold reheat steam main pipe transports part of the feed water to the steam-side inlet of the No. 2 high-pressure heater 11 through the eighth valve group 31 and to the steam-side inlet of the deaerator 8 through the ninth valve group 32. The third-stage extraction steam of the intermediate-pressure cylinder 3 is connected to the third-stage extraction steam pipeline through the fourth valve group 24, and the third-stage extraction steam pipeline transports the third-stage extraction steam to the steam-side inlet of the No. 3 high-pressure heater 10. The fourth-stage extraction steam of the intermediate-pressure cylinder 3 is connected to the heating steam source inlet of the deaerator 8 through the fifth valve group. The steam drain after heat exchange in the No. 1 high-pressure heater 12 is output to the No. 2 high-pressure heater 11 for heat exchange, the steam drain after heat exchange is output to the No. 3 high-pressure heater 10 for heat exchange, and the drain after heat exchange is output to the deaerator 8.

[0042] The new steam of the boiler 1 is divided into three paths. The first path goes through the high-pressure cylinder steam inlet valve group 18 to the high-pressure cylinder 2 to do work, the second path goes through the first desuperheating and pressure-reducing valve group 26 to the cold reheat steam main pipe, and the third path goes through the second desuperheating and pressure-reducing valve group 27 to the No. 1 high-pressure heater 12. The reheated steam of the boiler 1 is divided into three paths. The first path goes through the intermediate-pressure cylinder steam inlet valve group 19 to the intermediate-pressure cylinder 3 to do work, the second path goes through the third desuperheating and pressure-reducing valve group 28 to the No. 3 high-pressure heater 10, and the third path goes through the sixth valve group 29 to the steam-side inlet of the flue gas heater 16. The steam-side outlet of the flue gas heater 16 transports the reheated steam after heat exchange to the heat network heater 14 through the seventh valve group 30.

[0043] The heat source of the heat network heater 14 comes from the partial extraction steam of the intermediate pressure cylinder 3 and the partial reheated steam of the boiler 1; the partial extraction steam of the intermediate pressure cylinder 3 is output to the steam side inlet of the heat network heater 14 through the first valve group 21; the partial reheated steam of the boiler 1 exchanges heat with the partial flue gas of the economizer in the flue gas heater 16 and then converges with the partial extraction steam from the intermediate pressure cylinder 3, and is transported to the steam side inlet of the heat network heater 14 to exchange heat with the heating circulating water; the condensate of the heat network heater 14 is transported to the water side inlet of the deaerator 8. A heat network circulating water pump group 13 is arranged on the heat network return water main pipe at the inlet of the heat network heater 14.

[0044] Principle of the present invention:

[0045] During the residential heating season, when the coal-fired power unit is operating normally, the new steam at the outlet of the boiler 1 enters the high-pressure cylinder 2 to do work, and the exhaust steam enters the reheater of the boiler 1 through the cold reheat steam main pipe to achieve secondary temperature rise and avoid overheating of the reheater. Then it enters the intermediate pressure cylinder 3 to do work, and the exhaust steam is divided into two paths. One path passes through the valve group 21 to the heating supply steam main pipe and enters the heat network heater 14 to heat the heating circulating water. The condensate is boosted by the condensate pump group 15 and then converges into the water side inlet of the deaerator 8; the remaining steam enters the low-pressure cylinder 4 to continue doing work. The high-pressure cylinder 2, the intermediate pressure cylinder 3, and the low-pressure cylinder 4 are coaxially connected and jointly drive the generator 5 to generate electricity. The exhaust steam of the low-pressure cylinder 4 is condensed in the condenser 6, and the condensate flows through the condensate pump 7, the low-pressure heater group 34, the deaerator 8, the feed water pump group 9, the No. 3 high-pressure heater 10, the No. 2 high-pressure heater 11, and the No. 1 high-pressure heater 12 in sequence to increase the temperature and pressure and then enter the boiler 1 to complete the steam-water thermodynamic cycle. At this time, the high-pressure cylinder steam inlet valve group 18, the intermediate pressure cylinder steam inlet valve group 19, the heat supply butterfly valve 20 of the intermediate and low-pressure connecting pipe, the first valve group 21, the second valve group 22, the third valve group 23, the fourth valve group 24, the fifth valve group 25, and the eighth valve group 31 are opened, and the first desuperheating and pressure-reducing valve group 26, the second desuperheating and pressure-reducing valve group 27, the third desuperheating and pressure-reducing valve group 28, the sixth valve group 29, the seventh valve group 30, the ninth valve group 32, and the tenth valve group 33 are closed.

[0046] When one or both of the steam turbine and the generator fail, this unit still needs to supply centralized heating externally. At this time, it is called the emergency operation mode of shutting down the machine but not the boiler: the high-pressure cylinder steam inlet valve group 18, the intermediate pressure cylinder steam inlet valve group 19, and the heat supply butterfly valve 20 of the intermediate and low-pressure connecting pipe of the steam turbine are closed, the first valve group 21, the second valve group 22, the third valve group 23, the fourth valve group 24, and the fifth valve group 25 are closed, and the first desuperheating and pressure-reducing valve group 26, the second desuperheating and pressure-reducing valve group 27, the third desuperheating and pressure-reducing valve group 28, the sixth valve group 29, the seventh valve group 30, the ninth valve group 32, and the tenth valve group 33 are opened. The high-pressure cylinder 2, the intermediate pressure cylinder 3, the low-pressure cylinder 4, the generator 5, the condenser 6, and the condensate pump 7 are shut down.

[0047] The new steam at the outlet of boiler 1 is divided into two paths: one path is cooled and depressurized by the second desuperheating and pressure-reducing valve group 27 and then reaches the extraction steam pipeline of the first stage of the steam turbine, after the third valve group 23, and is used as the heating steam for the No. 1 high-pressure heater 12. The desuperheating water is taken from the feed water at the outlet of the No. 1 high-pressure heater group 12. The other path is cooled and depressurized by the first desuperheating and pressure-reducing valve group 26 to the cold reheat steam main pipe, after the second valve group 22, enters the reheater of the boiler 1 for secondary temperature increase and avoids overheating of the reheater, and then is divided into two paths: one path is cooled and depressurized by the third desuperheating and pressure-reducing valve group 28 and then reaches the extraction steam pipeline of the third stage of the steam turbine, after the fourth valve group 24, and is used as the heating steam for the No. 3 high-pressure heater 10. The desuperheating water is taken from the feed water at the outlet of the No. 1 high-pressure heater group 12. The other path enters the flue gas heater 16 through the sixth valve group 29 to heat a part of the flue gas at the outlet of the economizer of the boiler 1, and after cooling, enters the heat network heater 14 through the seventh valve group 30 to heat the heating circulating water. The drain water is boosted by the drain pump group 15 and then flows into the water side inlet of the deaerator 8. After passing through the deaerator 8, the feed water pump group 9, the No. 3 high-pressure heater 10, the No. 2 high-pressure heater 11 and the No. 1 high-pressure heater 12 for temperature increase and pressure boost, it enters the boiler 1 to complete the steam-water thermodynamic cycle.

[0048] The heating steam sources for the deaerator 8 and the No. 2 high-pressure heater 11 are taken from the cold reheat steam main pipe. The eighth valve group 31 and the ninth valve group 32 are opened. The heating steam source for the No. 3 high-pressure heater 10 is taken from the depressurized and cooled hot reheat steam. The heating steam source for the No. 1 high-pressure heater 12 is taken from the depressurized and cooled main steam. The second desuperheating and pressure-reducing valve group 27 and the third desuperheating and pressure-reducing valve group 28 are opened. The desuperheating water is taken from the feed water at the outlet of the No. 1 high-pressure heater 12 to ensure that the steam temperature entering the steam pipeline and the heater is within the design range, so as to avoid affecting the safety of the equipment and pipeline due to overheating. The flue gas at the outlet of the economizer of the boiler 1 is divided into two paths: one path enters the flue gas heater 16 to increase the temperature and then merges with the other path and enters the flue gas denitration device 17. The present invention ensures the denitration effect of the boiler flue gas and the compliance of pollutant emissions under the condition of shutdown without stopping the furnace by reasonably setting the steam sources to enable the normal operation of the high-pressure heater group (No. 1 - No. 3) to increase the feed water temperature entering the boiler 1 and using the high superheat degree of the high-temperature steam to heat the inlet flue gas temperature of the denitration device 16.

[0049] The main steam operating pressure of the boiler 1 is between the constant pressure operating condition and the sliding pressure operating condition. At this time, the initial steam pressure on the boiler side is completely provided by the feed water pump group 9. The steam pressure at the outlet of the high-temperature superheater reaches the required inlet pressure of the reheater after passing through the desuperheating and pressure-reducing device, and the outlet hot reheat steam is directly supplied for heating after desuperheating and pressure reduction. The present invention proposes a steam pressure adjustment method for the inlet of the reheater (consistent with the steam source of the second stage extraction), the first stage extraction, the third stage extraction and the inlet of the deaerator.

[0050] The regenerative extraction steam of the coal-fired generating unit adopts a self-balancing regulation method. Under the operating condition of shutting down the turbine while keeping the boiler running, the boiler evaporation is taken as the dependent variable, and the relationship curve between the extraction steam pressures of the first and second stages of the steam turbine and the boiler evaporation under the pure condensing operation condition is used as the basis; for the extraction steam of the third and fourth stages, the inlet steam flow of the intermediate pressure cylinder is taken as the dependent variable, and the relationship curve between the extraction steam pressures of the third and fourth stages of the steam turbine and the boiler evaporation under the pure condensing operation condition is used as the basis to adjust the inlet steam pressure of the deaerator 8 and the high-pressure heater group (No. 1 - No. 3) under the condition of shutting down the turbine while keeping the boiler running. The correlation equations for the extraction steam pressure control of the 1st - 4th stages of the 300MW cogeneration unit when shutting down the turbine while keeping the boiler running are as follows:

[0051] P 1 = 0.005711×Q ms + 0.181253

[0052] P 2 = 0.00346×Q ms + 0.10007

[0053] P 3 = 0.00209×Q rh + 0.00034

[0054] P 4 = 0.8 ± 0.05MPa

[0055] T 1 = 380 ± 10℃

[0056] T 2 = 320 ± 10℃

[0057] T 3 = 445 ± 10℃

[0058] T 4 = f(P 4 , H(P 2 , T 2 ))

[0059] Among them, T 4 is the isenthalpic temperature after the cold reheat steam is decompressed. Q ms , Q rh are the boiler evaporation and the steam flow at the outlet of the boiler reheater respectively, t / h; P 1 ~P 4 are the inlet steam pressures of the No. 1 - No. 3 high-pressure heaters and the deaerator respectively, MPa; T 1 ~T 4 are the inlet steam temperatures of the No. 1 - No. 3 high-pressure heaters and the deaerator respectively, ℃.

[0060] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A stable operation system for the denitration device during the emergency operation of coal-fired power plants with shutdown of the steam turbine but continuous operation of the boiler, characterized in that, it includes a coal-fired power generation unit. The exhaust steam of the low-pressure cylinder (4) of the coal-fired power generation unit enters the condenser (6) for condensation. The condensed water successively passes through the condensate pump (7), the low-pressure heater group (34), the deaerator (8), the feed pump group (9), and the No. 3 high-pressure heater (10), the No. 2 high-pressure heater (11), and the No. 1 high-pressure heater (12); the cold reheat steam main pipe transports the exhaust steam of the high-pressure cylinder (2) to the reheater of the boiler (1); the flue gas at the outlet of the economizer of the boiler (1) is divided into two paths. One path enters the flue gas heater (16) to be heated and then merges with the other path and enters the flue gas denitration device (17); The new steam of the boiler (1) is divided into three paths. The first path passes through the high-pressure cylinder steam inlet valve group (18) to the high-pressure cylinder (2) to do work. The second path passes through the first desuperheating and pressure-reducing valve group (26) to the cold reheat steam main pipe. The third path passes through the second desuperheating and pressure-reducing valve group (27) to the No. 1 high-pressure heater (12); The reheated steam of the boiler (1) is divided into three paths. The first path passes through the intermediate-pressure cylinder steam inlet valve group (19) to the intermediate-pressure cylinder (3) to do work. The second path passes through the third desuperheating and pressure-reducing valve group (28) to the No. 3 high-pressure heater (10). The third path passes through the sixth valve group (29) to the steam side inlet of the flue gas heater (16). The steam side outlet of the flue gas heater (16) transports the reheated steam after heat exchange and merges with a part of the exhaust steam from the intermediate-pressure cylinder (3) through the seventh valve group (30), and then transports it to the heat network heater (14); A part of the exhaust steam of the intermediate-pressure cylinder (3) is output through the first valve group (21) to the steam side inlet of the heat network heater (14); the drain water of the heat network heater (14) is transported to the water side inlet of the deaerator (8); The feed water at the outlet of the No. 1 high-pressure heater (12) is divided into two paths. The first path enters the boiler (1). The second path enters the tenth valve group (33) as desuperheating water. The feed water at the outlet of the tenth valve group (33) respectively enters the first desuperheating and pressure-reducing valve group (26), the second desuperheating and pressure-reducing valve group (27), and the third desuperheating and pressure-reducing valve group (28); Under the emergency operation condition of shutdown of the steam turbine but continuous operation of the boiler, the first desuperheating and pressure-reducing valve group (26), the second desuperheating and pressure-reducing valve group (27), and the third desuperheating and pressure-reducing valve group (28) are opened. A part of the desuperheating water and the depressurized main steam are used as heat sources to be transported to the No. 1 high-pressure heater (12). A part of the desuperheating water is mixed with the depressurized reheated steam and used as a heating steam source to be transported to the No. 3 high-pressure heater (10). Another part of the desuperheating water is mixed with the steam in the cold reheat steam main pipe and used as a heating steam source to be transported to the No. 2 high-pressure heater (11) and the deaerator (8).

2. The stable operation system for the denitration device during the emergency operation of coal-fired power plants with shutdown of the steam turbine but continuous operation of the boiler according to claim 1, characterized in that, The coal-fired power unit includes a boiler (1). When the coal-fired power unit operates normally, the new steam of the boiler (1) enters the high-pressure cylinder (2) to do work. The exhaust steam of the high-pressure cylinder (2) enters the reheater of the boiler (1) through the cold reheat steam main pipe for secondary temperature increase. The reheated steam of the boiler (1) enters the intermediate-pressure cylinder (3) to do work, and the exhaust steam of the intermediate-pressure cylinder (3) enters the low-pressure cylinder (4) to do work; the high-pressure cylinder (2), the intermediate-pressure cylinder (3), and the low-pressure cylinder (4) are coaxially connected and jointly drive the generator (5) to do work and generate electricity.

3. The stable operation system for the denitration device during emergency operation of the coal-fired power unit with shutdown but boiler still running according to claim 1, characterized in that, the exhaust steam of the high-pressure cylinder (2) is connected to the cold reheat steam main pipe through the second valve group (22); the first-stage extraction steam of the high-pressure cylinder (2) is connected to the first-stage extraction steam pipeline through the third valve group (23), and the first-stage extraction steam pipeline transports the first-stage extraction steam to the steam side inlet of the No. 1 high-pressure heater (12); the cold reheat steam main pipe transports part of the steam to the steam side inlet of the No. 2 high-pressure heater (11) through the eighth valve group (31), and transports it to the steam side inlet of the deaerator (8) through the ninth valve group (32), and the ninth valve group (32) performs pressure reduction adjustment.

4. The stable operation system for the denitration device during emergency operation of the coal-fired power unit with shutdown but boiler still running according to claim 3, characterized in that, the third-stage extraction steam of the intermediate-pressure cylinder (3) is connected to the third-stage extraction steam pipeline through the fourth valve group (24), and the third-stage extraction steam pipeline transports the third-stage extraction steam to the steam side inlet of the No. 3 high-pressure heater (10); the fourth-stage extraction steam of the intermediate-pressure cylinder (3) is connected to the heating steam source inlet of the deaerator (8) through the fifth valve group.

5. The stable operation system for the denitration device during emergency operation of the coal-fired power unit with shutdown but boiler still running according to any one of claims 1-4, characterized in that, the condensate water after heat exchange in the No. 1 high-pressure heater (12) is output to the No. 2 high-pressure heater (11) for heat exchange, and after heat exchange, it is output to the No. 3 high-pressure heater (10) for heat exchange, and the condensate water after heat exchange is output to the deaerator (8).

6. The stable operation system for the denitration device during emergency operation of the coal-fired power unit with shutdown but boiler still running according to any one of claims 1-4, characterized in that, a heat network circulating water pump group (13) is arranged on the heat network return water main pipe at the inlet of the heat network heater (14).

7. A method for stable operation of the denitration device during emergency operation of the coal-fired power unit with shutdown but boiler still running using the system according to claim 4, characterized in that, it includes the following steps: During the residential heating season, when the coal-fired power generation unit operates normally: Open the high-pressure cylinder steam inlet valve group (18), the intermediate-pressure cylinder steam inlet valve group (19), the heat supply butterfly valve of the intermediate-low pressure connecting pipe (20), the first valve group (21), the second valve group (22), the third valve group (23), the fourth valve group (24), the fifth valve group (25), and the eighth valve group (31), and close the first desuperheating and pressure reducing valve group (26), the second desuperheating and pressure reducing valve group (27), the third desuperheating and pressure reducing valve group (28), the sixth valve group (29), the seventh valve group (30), the ninth valve group (32), and the tenth valve group (33); The fresh steam at the outlet of the boiler (1) enters the high-pressure cylinder (2) to do work. After the exhaust steam passes through the cold reheat steam header and then enters the reheater of the boiler (1) to achieve secondary temperature increase and avoid overheating of the reheater, it enters the intermediate-pressure cylinder (3) to do work. The exhaust steam is divided into two paths. One path passes through the valve group (21) to the heating and supply steam header and enters the heat network heater (14) to heat the heating circulating water. The drain water is boosted by the drain pump group (15) and then flows into the water side inlet of the deaerator (8). The remaining steam enters the low-pressure cylinder (4) to continue doing work. The exhaust steam from the low-pressure cylinder (4) goes to the condenser (6) for condensation. The condensate flows through the condensate pump (7), the low-pressure heater group (34), the deaerator (8), the feed pump group (9), the No. 3 high-pressure heater (10), the No. 2 high-pressure heater (11), and the No. 1 high-pressure heater (12) in sequence to increase in temperature and pressure and then enters the boiler (1) to complete the steam-water thermodynamic cycle. When one or both of the steam turbine and the generator fail, central heating still needs to be provided externally. This is called the emergency heating operation mode of shutting down the machine but not the boiler: Close the high-pressure cylinder steam inlet valve group (18), the intermediate-pressure cylinder steam inlet valve group (19), and the heating butterfly valve of the medium-low pressure connecting pipe (20). Close the first valve group (21), the second valve group (22), the third valve group (23), the fourth valve group (24), and the fifth valve group (25). Open the first desuperheating and pressure-reducing valve group (26), the second desuperheating and pressure-reducing valve group (27), the third desuperheating and pressure-reducing valve group (28), the sixth valve group (29), the seventh valve group (30), the ninth valve group (32), and the tenth valve group (33). Shut down the high-pressure cylinder (2), the intermediate-pressure cylinder (3), the low-pressure cylinder (4), the generator (5), the condenser (6), and the condensate pump (7).

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