Coal-fired unit steam supply system and method and coal-fired unit

Abstract

The invention discloses a coal-fired unit steam supply system which comprises an external supply heater and a branch steam-water line, the branch steam-water line is a line branched and led out from a water supply pipeline of a main steam-water line of a coal-fired unit, and the outlet end of the branch steam-water line is connected with the external supply heater so as to supply a working medium extracted from the water supply pipeline to the external supply heater. The external supply heater is arranged in a boiler flue system of the coal-fired unit and located in a heated area where flue gas passes through, and the outlet end of the external supply heater is connected with an external thermal load so that a working medium can be supplied to the external thermal load after exchanging heat with the flue gas. According to the steam supply system of the coal-fired unit, the steam supply stability can be guaranteed, the flexibility of the unit can be brought into full play, meanwhile, normal operation of the coal-fired unit is not affected, the transformation cost and the purchase cost are low, the thermoelectric decoupling degree is high, and the energy utilization rate is high. The invention further provides a coal-fired unit steam supply method and a coal-fired unit.

Description

Technical Field

[0001] The present invention specifically relates to a steam supply system and method for a coal-fired unit, and a coal-fired unit. Background Art

[0002] In the context of large-scale construction and grid connection of renewable energy power, coal power will face a transformation from the main power source to a security power source. The flexibility of coal power helps to accommodate renewable energy power and ensure the stability of the power system.

[0003] However, the variable load capacity of traditional coal-fired units is limited and cannot provide sufficient regulation capacity for renewable energy, thus restricting the large-scale accommodation of renewable energy. At the same time, due to the decrease in power generation, coal-fired power plants face the problem of reduced revenue. Currently, the revenue can be compensated by extracting steam for heating and steam supply from the steam turbine. However, the traditional steam supply method requires extracting steam from multiple cylinders of the steam turbine. Therefore, the steam turbine must maintain sufficient steam inlet volume to ensure steam supply stability, which restricts the variable load capacity of the unit, further limits the flexibility of the unit, affects its variable load operation and the ability to deeply regulate the peak load of renewable energy power.

[0004] Therefore, thermoelectric decoupling has become the key to solving this problem. Currently, there is a solution for coal-fired units to use intermittent steam extraction in combination with electrothermal conversion equipment and energy storage and heat storage facilities for thermoelectric decoupling. However, there are many energy conversion steps in this process, resulting in low energy utilization rate; and there are energy losses in energy storage and heat storage elements, and the energy storage and heat storage capacity highly depends on the energy storage and heat storage materials themselves; and the entire process is complex and non-continuous. Intermittent steam extraction will affect the stability of the unit, and then affect the stability of the unit and steam supply. At the same time, long-term continuous use of power equipment is required for working medium transfer and energy conversion, with high purchase costs and great impact on the normal operation mode of existing coal-fired units, and high transformation costs.

[0005] That is, generally speaking, the steam extraction and steam supply scheme of existing coal-fired power plants not only restricts the variable load capacity of the unit, but also may affect the stability of steam supply. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a steam supply system for a coal-fired unit aiming at the above deficiencies in the prior art. This steam supply system can not only ensure the stability of steam supply, but also give full play to the flexibility of the unit, and at the same time does not affect the normal operation of the coal-fired unit, with low transformation costs and purchase costs, deep thermoelectric decoupling degree, and high energy utilization rate. The present invention also provides a steam supply method for a coal-fired unit and a coal-fired unit.

[0007] The present invention provides a steam supply system for a coal-fired unit, which includes an external supply heater and a steam and water separation line. The steam and water separation line is a line branched from the feed water pipe of the main steam and water line of the coal-fired unit. The outlet end of the steam and water separation line is connected to the external supply heater to supply the working medium extracted from the feed water pipe to the external supply heater. The external supply heater is arranged inside the boiler flue gas system of the coal-fired unit and located in the heat absorption area where the flue gas passes through. The outlet end is connected to an external thermal load to supply the working medium to the external thermal load after heat exchange with the flue gas.

[0008] Further, a plurality of the external supply heaters are provided, and each external supply heater is arranged in sequence along the flue gas flow direction in the boiler flue gas system. The steam and water separation line is connected to each external supply heater in sequence along the reverse direction of the flue gas flow, so that the working medium can pass through each external supply heater in sequence along the reverse direction of the flue gas flow.

[0009] Further, the plurality of external supply heaters are connected in series, and a section of flow-through pipeline is connected in parallel between both ends of each external supply heater. A valve body is provided at each section of the flow-through pipeline and each external supply heater, so that the flow path of the working medium can pass through each flow-through pipeline through the opening and closing of the valve body to bypass part or all of the external supply heaters.

[0010] Further, the steam supply system of the coal-fired unit further includes a first control unit, which is electrically connected to each valve body and the generator of the coal-fired unit. When the output power of the generator is greater than a first set value, it is used to control the valve body at the set external supply heater to close, and the valve body at the flow-through pipeline corresponding to the set external supply heater to open, so that the flow path of the working medium bypasses at least one external supply heater; when the output power of the generator is less than a second set value, it is used to control the valve bodies at each external supply heater to open and the valve bodies at each flow-through pipeline to close, so that the flow path of the working medium passes through all the external supply heaters. The first set value is greater than the second set value.

[0011] Further, each of the external supply heaters is respectively an external supply primary heater, an external supply secondary heater, an external supply tertiary heater, an external supply quaternary heater, and an external supply quinary heater. The external supply quinary heater is arranged at the boiler furnace in the boiler flue gas system, corresponding to the height position of the water wall. The external supply quaternary heater is arranged at the bottom of the boiler horizontal flue. The external supply tertiary heater is arranged at the junction of the boiler horizontal flue and the tail shaft flue. The external supply secondary heater is arranged at the flue gas inlet of the flue in the boiler flue gas system. The external supply primary heater is arranged at the flue gas outlet of the flue.

[0012] Further, the steam supply system of the coal-fired unit further includes a desuperheating water line. The inlet end of the desuperheating water line is provided with a tap and is connected to the feed water pump on the feed water pipe. The outlet end is divided into a plurality of branches, and each branch is respectively connected to each external supply heater, and is used to extract the working medium at the feed water pump to cool the working medium of the external supply heater.

[0013] Further, the steam supply system of the coal-fired unit further includes a steam compressor and a spray desuperheater. Both the steam compressor and the spray desuperheater are connected between the outlet end of the external supply heater and the external thermal load, and are respectively used to adjust the pressure and temperature of the working medium.

[0014] Further, the water and steam separation line includes a split feed water pump and a first economizer. The split feed water pump is connected to the low-pressure heater on the feed water pipeline and is used to extract the working medium at the low-pressure heater. One side of the first economizer is connected between the split feed water pump and the external supply heater, and the other side is connected to the flue gas line of the coal-fired unit to enable heat exchange between the working medium and the flue gas.

[0015] The present invention also provides a method for supplying steam to a coal-fired unit, using the above-mentioned steam supply system of the coal-fired unit. The method includes the following steps:

[0016] Extract the working medium from the feed water pipeline of the main steam and water line of the coal-fired unit through the water and steam separation line;

[0017] Supply the working medium to the external thermal load after heat exchange between the working medium and the flue gas in the boiler flue gas system through the external supply heater.

[0018] Further, the step of supplying the working medium to the external thermal load after heat exchange between the working medium and the flue gas in the boiler flue gas system through the external supply heater specifically includes: after heat exchange between the working medium and the flue gas in the boiler flue gas system through the external supply heater, supply the working medium to the external thermal load using a steam compressor;

[0019] During the process of supplying the working medium to the external thermal load after heat exchange between the working medium and the flue gas in the boiler flue gas system through the external supply heater, the method further includes the following steps:

[0020] Based on the total coal input of the boiler of the coal-fired unit, the total air input of the boiler, the water supply to the boiler flue gas system from the feed water pipeline, the water supply for extracting the working medium from the feed water pipeline, the output electric power of the generator, the rotational speed of the steam compressor, and the flow rate, temperature and pressure of the working medium supplied to the external thermal load, establish a supply model;

[0021] According to the real-time value of the output electric power of the generator and the supply model, adjust the total coal input of the boiler of the coal-fired unit, the total air input of the boiler, the water supply to the boiler flue gas system from the feed water pipeline, the water supply for extracting the working medium from the feed water pipeline, and the rotational speed of the steam compressor, so that the flow rate, temperature and pressure of the working medium supplied to the external thermal load are all maintained within the set range.

[0022] The present invention also provides a coal-fired unit, which includes a boiler flue gas system, a main steam-water line, a flue gas line, and the above-mentioned steam supply system for the coal-fired unit. The flue gas generated by combustion in the boiler flue gas system is discharged through the flue gas line. The main steam-water line sends the working medium into the boiler flue gas system to exchange heat with the flue gas and then do work for the generator of the coal-fired unit. The steam supply system for the coal-fired unit extracts the working medium from the main steam-water line, exchanges heat with the flue gas, and supplies it to an external thermal load.

[0023] Further, a water wall, a high-temperature superheater, a high-temperature reheater, a low-temperature superheater, a low-temperature reheater, and a second economizer are provided in the boiler of the boiler flue gas system. The main steam-water line includes an output pipeline and a feed water pipeline. A high-pressure cylinder, a medium-pressure cylinder, a low-pressure cylinder, and a condenser are provided on the output pipeline. A condensate pump, a low-pressure heater, a deaerator, a feed water pump, and a high-pressure heater are provided on the feed water pipeline. The water condensed by the condenser enters the feed water pipeline, and successively passes through the condensate pump, the low-pressure heater, the deaerator, the feed water pump, and the high-pressure heater and then enters the boiler, and then successively passes through the second economizer, the water wall, the low-temperature superheater, and the high-temperature superheater to exchange heat with the flue gas in the boiler to obtain steam and then enter the high-pressure cylinder. The steam discharged from the high-pressure cylinder successively passes through the low-temperature reheater and the high-temperature reheater to exchange heat with the flue gas in the boiler again, and then successively passes through the medium-pressure cylinder and the low-pressure cylinder and is discharged into the condenser to be condensed. The high-pressure cylinder, the medium-pressure cylinder, and the low-pressure cylinder are driven by steam and are used to do work for the generator.

[0024] Further, an SCR reactor (Selective Catalytic Reduction), an air preheater, a dust collector, an induced draft fan, and a desulfurization tower are provided on the flue gas line. The flue gas generated by combustion in the boiler of the boiler flue gas system passes through the flue and successively passes through the SCR reactor, the air preheater, the dust collector, the induced draft fan, and the desulfurization tower, and is discharged after being treated by the desulfurization tower.

[0025] The steam supply system of the coal-fired unit of the present invention sets an external supply heater inside the boiler flue gas system, and bifurcates and leads out the feed water pipeline that supplies water to the boiler flue gas system, supplies the working medium to the external supply heater, and realizes that the working medium exchanges heat with the flue gas in the boiler flue gas system and then supplies it to an external thermal load (i.e., a steam demand user).

[0026] Since the working medium of the steam supply system itself is the liquid working medium extracted from the feed water pipeline, it avoids extracting steam for supply in each cylinder of the steam turbine. Therefore, during the steam supply process, stable steam supply no longer depends on the steam turbine having a specific steam inlet volume, thus breaking through this limitation, and it will not affect the variable load capacity and flexibility of the unit itself. It can achieve the flexibility of the unit under a large variable load of the coal-fired unit and realize the compensation during the peak shaving process of the power grid system.

[0027] The formation of steam by the heat exchange of the working medium is achieved by utilizing the waste heat of the flue gas in the boiler flue gas system. There are no any extra energy conversion steps in the middle. Therefore, the energy utilization rate is high, unnecessary energy losses are avoided, and there is no need to rely on the performance of energy storage materials. It can also adjust the steam parameters according to user needs, supply stable industrial steam, and at the same time can obtain higher steam supply benefits, and realize combined heat and power generation to improve the thermal efficiency of the power plant.

[0028] Moreover, the entire steam supply system will not transform the original cylinder block. The steam and water separation line can be used as an overall module. Only the external supply heater needs to be arranged inside the boiler flue gas system, without the need for other external flue gas separation line arrangements and the purchase of steam generation devices. The system transformation cost and purchase cost are low, providing a new low-cost solution for realizing stable steam supply and flexible power generation of coal-fired units. And the whole process is continuously stable and adjustable, easy to operate, with high energy utilization rate and deep thermal electrolysis decoupling degree. Brief Description of the Drawings

[0029] Figure 1 It is a schematic structural diagram of the steam supply system of the coal-fired unit in Embodiment 1 of the present invention;

[0030] Figure 2 It is a schematic layout diagram of the external supply heater of the steam supply system of the coal-fired unit in Embodiment 1 of the present invention inside the boiler;

[0031] Figure 3 It is a schematic layout diagram of the desuperheating water line of the steam supply system of the coal-fired unit in Embodiment 1 of the present invention;

[0032] Figure 4 It is a schematic connection diagram between the external supply heaters of the steam supply system of the coal-fired unit in Embodiment 1 of the present invention.

[0033] In the figure: 1. External supply heater; 11. External supply primary heater; 12. External supply secondary heater; 13. External supply tertiary heater; 14. External supply quaternary heater; 15. External supply quinary heater; 16. Steam compressor; 17. Spray desuperheater; 18. Flow pipeline;

[0034] 19. Valve body; 2. Steam and water separation line; 21. Shunt feed pump; 22. First economizer;

[0035] 3. Boiler flue gas system; 31. Boiler; 311. Furnace; 312. Horizontal flue;

[0036] 313. Tail shaft flue; 32. Flue; 33. Second economizer; 34. Water wall;

[0037] 35. High-temperature superheater; 36. High-temperature reheater; 37. Low-temperature superheater; 38. Low-temperature reheater;

[0038] 4. Main steam and water circuit; 41. Feed water pipe; 411. Feed water pump; 412. Low-pressure heater; 413. Condensate pump; 414. Deaerator; 415. High-pressure heater; 42. Output pipe; 421. High-pressure cylinder; 422. Intermediate-pressure cylinder; 423. Low-pressure cylinder; 424. Generator; 425. Condenser; 5. Desuperheating water circuit; 6. Flue gas circuit; 61. SCR reactor; 611. Catalyst; 62. Air preheater; 63. Dust collector; 64. Induced draft fan; 65. Desulfurization tower. Detailed implementation manners

[0039] The technical solutions in the present invention will be clearly and completely described below with reference to the accompanying drawings in the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present invention without creative efforts shall fall within the scope of the present invention.

[0040] In the description of the present invention, it should be noted that the terms "upper", "lower", etc. indicating the orientation or position relationship are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of description and simplification, rather than indicating or implying 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 of the present invention.

[0041] In the description of the present invention, the terms "first", "second", "third" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0042] In the description of the present invention, it should be noted that unless otherwise clearly defined and limited, the terms "connection", "installation", "fixation", etc. should be understood in a broad sense. For example, it can be a fixed connection or a detachable connection, or an integral connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the internal communication of two elements. For those skilled in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0043] Embodiment 1

[0044] As Figure 1 And Figure 2As shown in the figure, the steam supply system of the coal-fired unit in this embodiment includes an external supply heater 1 and a steam and water separation line 2. The steam and water separation line 2 is a line branched from the feed water pipe 41 of the main steam and water line 4 of the coal-fired unit. The outlet end of the steam and water separation line 2 is connected to the external supply heater 1 to supply the working medium extracted from the feed water pipe 41 to the external supply heater 1. The external supply heater 1 is arranged inside the boiler flue gas system 3 of the coal-fired unit, in the heat absorption area where the flue gas passes through. The outlet end is connected to an external thermal load to supply the working medium to the external thermal load (i.e., the steam demand user) after heat exchange with the flue gas.

[0045] Since the working medium of the steam supply system itself is the liquid working medium extracted from the feed water pipe 41, it avoids extracting steam from each cylinder of the steam turbine. Therefore, during the steam supply process, stable steam supply no longer depends on the steam turbine having a specific steam inlet volume, thus breaking through this limitation and not affecting the unit's own variable load capacity and flexibility. It can achieve the flexibility of the unit under a large range of variable loads of the coal-fired unit and realize the compensation during the peak shaving process of the power grid system.

[0046] The formation of steam by heat exchange of the working medium is achieved by utilizing the waste heat of the flue gas in the boiler flue gas system 3. There is no any redundant energy conversion step in the middle. Therefore, the energy utilization rate is high, avoiding redundant energy loss, and there is no need to rely on the performance of energy storage materials itself. It can also adjust the steam parameters according to user needs, supply stable industrial steam, and at the same time can obtain higher steam supply benefits and realize combined heat and power generation to improve the thermal efficiency of the power plant.

[0047] Moreover, the entire steam supply system does not require modification of the original cylinder block. The steam and water separation line can be used as a whole module. Only the external supply heater needs to be arranged inside the boiler flue gas system 3, without the need for other external flue gas separation line arrangements and steam generator purchases. The system transformation cost and purchase cost are low, providing a new low-cost solution for realizing stable steam supply and flexible power generation of the coal-fired unit. And the whole process is continuously stable and adjustable, easy to operate, with high energy utilization rate and deep degree of heat and power decoupling.

[0048] In this embodiment, there are multiple external supply heaters 1, and each external supply heater 1 is arranged in sequence along the flue gas flow direction in the boiler flue gas system 3. The steam and water separation line 2 is connected to each external supply heater 1 in sequence along the reverse direction of the flue gas flow direction, so that the working medium can pass through each external supply heater 1 in sequence along the reverse direction of the flue gas flow direction. In this layout method, each external supply heater 1 is equivalent to being in multiple regions with different temperatures respectively, and can contact flue gas with different temperatures to realize the utilization of waste heat in each temperature region, with higher heat energy utilization rate. And the steam and water separation line 2 is connected to each external supply heater 1 in sequence along the reverse direction of the flue gas flow direction, so that the working medium gradually passes through each external supply heater 1 from the low-temperature region to the high-temperature region, thereby realizing multi-stage heating of the working medium from low temperature to high temperature and gradually raising the temperature of the working medium.

[0049] In this embodiment, asFigure 4 As shown, multiple external heaters 1 are connected in series, and a section of flow pipeline 18 is connected in parallel between both ends of each external heater 1. There is no work equipment on the flow pipeline 18, allowing the internal medium to flow directly through. A valve body 19 is provided at each section of the flow pipeline 18 and each external heater 1 to control the on-off of the passage of the external heater 1 and the flow pipeline 18 where it is located, so that the flow path of the working medium can pass through each flow pipeline 18 to bypass some or all of the external heaters 1, achieving adjustable temperature of the heated steam and avoiding over-temperature of the steam in the steam and water separation line 2.

[0050] In this embodiment, the steam supply system of the coal-fired unit further includes a first control unit, which is electrically connected to each valve body 19 and the generator 424 of the coal-fired unit. When the output power of the generator 424 is greater than a first set value, it controls the valve body 19 at the set external heater 1 to close, and the valve body 19 at the flow pipeline 18 corresponding to the set external heater 1 to open, so that the flow path of the working medium bypasses at least one external heater 1; when the output power of the generator 424 is less than a second set value, it controls the valve body 19 at each external heater 1 to open, and the valve body 19 at each flow pipeline 18 to close, so that the flow path of the working medium passes through all external heaters 1. The first set value is greater than the second set value.

[0051] Specifically, when the coal-fired unit and the steam supply system are operating normally, the actual output power of the generator 424 is 80% of the maximum output power of the generator 424. When the output power of the generator 424 is above 80% (of the maximum output power), that is, greater than the first set value, the coal feeding amount increases, the total air volume increases, and the flue gas temperature rises; at this time, according to the flue gas temperature situation, the steam and water separation line 2 may not flow through some heaters (external primary heater 11 or external secondary heater 12 or external tertiary heater 13 or external quaternary heater 14 or external quinary heater 15), reducing heat absorption. According to the actual steam temperature situation, the desuperheating water volume extracted from the middle tap of the feed water pump 411 in the desuperheating water line 5 is increased to maintain the temperature of the external supply steam. When necessary, the steam compressor 16 and the tail spray desuperheater 17 can be used for final adjustment of pressure and temperature.

[0052] When the output power of the generator 424 is below 30% (of the maximum output power), the coal feeding amount decreases, the total air volume decreases, and the flue gas temperature drops; at this time, according to the flue gas temperature situation, the steam and water separation line 2 may flow through all heaters (external primary heater 11 or external secondary heater 12 or external tertiary heater 13 or external quaternary heater 14 or external quinary heater 15). If the steam temperature is still insufficient, the steam compressor 16 and the tail spray desuperheater 17 can be used for pressure increase and temperature increase.

[0053] In this embodiment, each externally-supplied heater 1 is respectively an externally-supplied primary heater 11, an externally-supplied secondary heater 12, an externally-supplied tertiary heater 13, an externally-supplied quaternary heater 14, and an externally-supplied quinary heater 15. The externally-supplied quinary heater 15 is arranged at the furnace 311 of the boiler 31 in the boiler flue gas system 3, corresponding to the height position of the water wall 34; the externally-supplied quaternary heater 14 is arranged at the bottom of the horizontal flue 312 of the boiler 31, opposite to the positions of the high-temperature superheater 35 and the high-temperature reheater 36; the externally-supplied tertiary heater 13 is arranged at the junction of the horizontal flue 312 and the tail shaft flue 313 of the boiler 31; the externally-supplied secondary heater 12 is arranged at the flue gas inlet of the flue 32 in the boiler flue gas system 3 (at the outlet of the tail shaft flue 313); the externally-supplied primary heater 11 is arranged at the flue gas outlet of the flue 32 (at the flue gas inlet of the SCR reactor 61). The hot side of each externally-supplied heater 1 is the hot flue gas in the boiler 31 and the flue 32, and the cold side is the working medium supplied by the steam-water separation line 2 (the separated feed water drawn from the low-pressure heater 412 using the shunt feed pump 21).

[0054] In this embodiment, the externally-supplied primary heater 11, the externally-supplied secondary heater 12, the externally-supplied tertiary heater 13, the externally-supplied quaternary heater 14, and the externally-supplied quinary heater 15 are all arranged in the spare space of the boiler flue gas system, and can be arranged simultaneously or separately. The corresponding steam-water separation line 2 will be changed according to the actual arrangement method. The valves 19 provided at the externally-supplied heaters 1 from the primary to the quinary are the primary valve to the quinary valve in sequence, and the valves 19 at the corresponding parallel flow pipelines 18 are the primary parallel valve to the quinary parallel valve in sequence.

[0055] In this embodiment, as Figure 3 shown, the steam supply system of the coal-fired unit further includes a desuperheating water line 5. The inlet end of the desuperheating water line 5 is provided with a tap, connected to the feed pump 411 on the feed water pipe 41, and the outlet end is divided into multiple branches, each branch is respectively connected to each externally-supplied heater 1, used to extract the working medium at the feed pump 411, and the extracted working medium is used as desuperheating water to cool the working medium of the externally-supplied heater 1. By adjusting the desuperheating water volume and the shunt feed water flow of the shunt feed pump 21, the stability of the externally-supplied steam flow can also be maintained.

[0056] Specifically, to prevent the steam in the steam-water separation line 2 from overheating, the outlet end of the desuperheating water line 5 is respectively connected to the cold-side steam-water outlet of the first economizer 22, the cold-side steam-water outlet of the externally-supplied primary heater 11, the cold-side steam-water outlet of the externally-supplied secondary heater 12, the cold-side steam-water outlet of the externally-supplied tertiary heater 13, the cold-side steam-water outlet of the externally-supplied quaternary heater 14, and the cold-side steam-water outlet of the externally-supplied quinary heater 15.

[0057] In this embodiment, the temperature of the desuperheating water is 0°C to 80°C, the pressure is 0.1 MPa to 40 MPa, and the steam-water flow rate at the tapping of the inlet end of the desuperheating water line 5 accounts for 0 to 10% of the steam-water flow rate entering the feed water pump 411.

[0058] In this embodiment, the steam supply system of the coal-fired unit further includes a steam compressor 16 and a spray desuperheater 17. The steam compressor 16 and the spray desuperheater 17 are both connected between the outlet end of the external supply heater 1 and the external thermal load, and are respectively used to adjust the pressure and temperature of the working medium.

[0059] In this embodiment, the steam compressor 16 and the tail spray desuperheater 17 are used to adjust the final supplied steam parameters. The steam pressure at the outlet of the steam compressor 16 is 0.1 MPa to 40 MPa, and the temperature is 100°C to 700°C; the temperature adjustment range of the steam by the tail spray desuperheater 17 is 0°C to 50°C.

[0060] In this embodiment, the steam-water separation line 2 includes a shunt feed water pump 21 and a first economizer 22. The shunt feed water pump 21 is connected to the low-pressure heater 412 on the feed water pipe 41 and is used to extract the working medium at the low-pressure heater 412. One side of the first economizer 22 is connected between the shunt feed water pump 21 and the external supply heater 1, and the other side is connected to the flue gas line 6 of the coal-fired unit, so that the working medium exchanges heat with the flue gas, thereby adding an additional stage of heating to further improve the thermal energy utilization rate.

[0061] In this embodiment, the shunt feed water pump 21 is connected to the cold side of the low-pressure heater 412 and is used to adjust the pressure of the shunt feed water. The feed water outlet pressure of the shunt feed water pump 21 is 0.1 MPa to 40 MPa, and the shunt feed water flow rate accounts for 0 to 90% of the steam-water flow rate on the cold side of the low-pressure heater 412.

[0062] This embodiment can be used in the coal power field. During the process of stable steam supply and variable load power generation in a coal-fired power plant, it enables the steam turbine to avoid extraction steam for steam supply, improves the variable load capacity of the unit, and can achieve the steam supply stability and unit flexibility of the steam supply unit in a coal-fired power plant at low cost. The coal-fired unit adopted has the capabilities of heat supply and steam supply, variable load operation, deep peak shaving, thermal power decoupling, and multi-stage flue gas heat utilization. Specifically, it relates to a non-steam turbine extraction steam supply system under variable load of a coal-fired unit.

[0063] This steam supply system places the thermal power decoupling position outside the steam turbine and does not require modification of the steam turbine. Therefore, the supplied steam and the steam turbine supply do not contact each other, do not affect each other, can be adjusted separately, and the extracted medium is condensed water, which can fully achieve continuous steam supply without any interruption, and the whole process is continuously, stably and adjustable.

[0064] This steam supply system specifically realizes thermal power decoupling by directly arranging an external supply heater 1 and a first economizer 22 (or a low-temperature economizer) in the boiler 31 and its subsequent flue 32 to produce split steam, avoiding the load limitation of steam extraction from the steam turbine, ensuring the variable load capacity of the unit; using a split feed water pump 21 to adjust the feed water flow rate, and using a steam compressor 16 and a desuperheater 17 to adjust the steam temperature and pressure to supply stable steam. The entire solution has little impact on the operation mode of the original coal-fired unit. At the same time, it breaks through the lower limit of the steam extraction load of the unit, does not excessively increase the power devices that need to be continuously used for a long time, utilizes the spare space in the boiler 31 and the flue 32 to arrange the heater, improves the energy utilization efficiency, and realizes thermal power decoupling.

[0065] Embodiment 2

[0066] The method for supplying steam to a coal-fired unit in this embodiment can be realized by using the steam supply system in Embodiment 1. The method includes the following steps:

[0067] Extract the working medium from the feed water pipe 41 of the main steam-water line 4 of the coal-fired unit through the water and steam separation line 2;

[0068] Supply the working medium to an external thermal load after heat exchange between the working medium and the flue gas in the boiler flue system 3 through the external supply heater 1.

[0069] In this embodiment, supplying the working medium to an external thermal load after heat exchange between the working medium and the flue gas in the boiler flue system 3 specifically includes:

[0070] After heat exchange between the working medium and the flue gas in the boiler flue system 3 through the external supply heater 1, use a steam compressor 16 to supply the working medium to an external thermal load;

[0071] In the process of supplying the working medium to an external thermal load after heat exchange between the working medium and the flue gas in the boiler flue system 3 through the external supply heater 1, the method further includes the following (adjustment) steps:

[0072] Based on the total coal input of the boiler of the coal-fired unit, the total air input of the boiler, the feed water volume supplied by the feed water pipe 41 to the boiler flue system 3, the feed water volume of the working medium extracted from the feed water pipe 41, the output electric power of the generator 424, the rotation speed of the steam compressor 16, and the flow rate, temperature, and pressure of the working medium supplied to the external thermal load, establish a supply model;

[0073] According to the real-time value of the output electric power of the generator 424 and the supply model, adjust the total coal input of the boiler of the coal-fired unit, the total air input of the boiler, the feed water volume supplied by the feed water pipe 41 to the boiler flue system 3, the feed water volume of the working medium extracted from the feed water pipe 41, and the rotation speed of the steam compressor 16, so that the flow rate, temperature, and pressure of the working medium supplied to the external thermal load are all maintained within the set range.

[0074] Combined with the system in Embodiment 1, the above adjustment steps of the present method can be further specifically described as follows:

[0075] S1: Based on the online and historical operation data, combined with the flow rate, temperature, and pressure of the supplied steam (i.e., the flow rate, temperature, and pressure of the working medium supplied to the external thermal load), establish a parameter database covering the total coal input of the boiler, the total air volume input of the boiler, the feed water volume at the outlet of the feed water pump 411 (i.e., the feed water volume supplied by the feed water pipe 41 to the boiler flue system 3), the split feed water volume at the outlet of the split feed water pump 21 (i.e., the feed water volume of the working medium extracted from the feed water pipe 41), the output electric power of the generator 424, and the rotation speed of the steam compressor 16;

[0076] S2: Based on the parameter database constructed in step S1, for the action mechanism of adjusting the flow rate, temperature, and pressure of the supplied steam for each parameter, combined with methods such as deep learning, establish a stable steam supply model under variable load regulation of the coal-fired unit.

[0077] The stable steam supply model established in step S2 under variable load regulation of the coal-fired unit is expressed as:

[0078] [S f ,S t ,S p =F(Q c ,Q w ,Q h1 ,Q h2 ,T,K s )

[0079] Wherein, S f 、S t and S p are the flow rate, temperature, and pressure of the supplied steam respectively; Q c is the total coal input of the boiler; Q w is the total air volume input of the boiler; Q h1 and Q h2 are the feed water volume at the outlet of the feed water pump 411 and the split feed water volume at the outlet of the split feed water pump 21 respectively; T is the output electric power of the generator 424; K s is the rotation speed of the steam compressor 16. Based on the real-time output power of the generator 424, reasonably adjust other parameters to keep the steam supply parameters stable.

[0080] Embodiment 3

[0081] The coal-fired unit of this embodiment includes a boiler flue gas system 3, a main steam-water line 4, a flue gas line 6, and the steam supply system of the coal-fired unit in Embodiment 1. The flue gas generated by the combustion of the boiler flue gas system 3 is discharged through the flue gas line 6. The main steam-water line 4 sends the working medium into the boiler flue gas system 3 to exchange heat with the flue gas and then do work for the generator 424 of the coal-fired unit. The steam supply system of the coal-fired unit extracts the working medium from the main steam-water line 4, exchanges heat with the flue gas, and supplies it to an external thermal load. That is, the coal-fired unit of this embodiment includes two lines, namely the flue gas line 6 and the steam-water line. The steam-water line includes two steam-water lines, namely the main steam-water line 4 and the branch steam-water line 2.

[0082] The boiler 31 includes a vertical furnace 311, a horizontal flue 312, and a tail shaft flue 313. The combustion methods that the boiler 31 can adopt include suspension combustion boilers and fluidized bed combustion boilers, etc. The circulation methods that the boiler 31 can adopt include natural circulation boilers, forced circulation boilers, controlled circulation boilers, and once-through boilers, etc.

[0083] In this embodiment, a water wall 34, a high-temperature superheater 35, a high-temperature reheater 36, a low-temperature superheater 37, a low-temperature reheater 38, and a second economizer 33 are provided in the boiler 31 of the boiler flue gas system 3. The water wall 34 is arranged on the surrounding wall surfaces of the furnace 311 in the boiler 31. The high-temperature superheater 35 and the high-temperature reheater 36 are arranged at the top of the horizontal flue 312 in the boiler 31. The low-temperature reheater 38 is arranged on one side of the tail shaft flue 313 of the boiler 31. The low-temperature superheater 37 and the second economizer 33 are arranged from top to bottom on the other side of the tail shaft flue 313.

[0084] The cold sides (steam-water sides) of heat exchangers such as the water wall 34, the high-temperature superheater 35, the high-temperature reheater 36, the low-temperature superheater 37, the low-temperature reheater 38, the second economizer 33, the external supply fifth-stage heater 15, the external supply fourth-stage heater 14, the external supply third-stage heater 13, the external supply second-stage heater 12, the external supply first-stage heater 11, and the first economizer 22 have temperatures of 0.1 °C to 700 °C and pressures of 0.1 MPa to 40 MPa. The temperatures of the hot sides (flue gas sides) are 100 °C to 1700 °C.

[0085] The deaerator 414 can include forms such as vacuum type, thermal type, and chemical type. The hot sides of heat exchangers such as the thermal deaerator 414, the low-pressure heater 412, and the high-pressure heater 415 in this embodiment have temperatures of 0 °C to 600 °C and pressures of 0.1 MPa to 40 MPa. The cold sides have temperatures of 0 °C to 300 °C and pressures of 0.1 MPa to 40 MPa. The steam-water sources of their hot sides can include extraction steam from the high-pressure cylinder, extraction steam from the intermediate-pressure cylinder, extraction steam from the low-pressure cylinder, and auxiliary steam, etc.

[0086] The main steam-water circuit 4 includes an output pipeline 42 and a feedwater pipeline 41. A high-pressure cylinder 421, a medium-pressure cylinder 422, a low-pressure cylinder 423, and a condenser 425 are provided on the output pipeline 42. A condensate pump 413, a low-pressure heater 412, a deaerator 414, a feed pump 411, and a high-pressure heater 415 are provided on the feedwater pipeline 41.

[0087] The main steam-water circuit 4 includes the cold side of the second economizer 33, the cold side of the water wall 34, the cold side of the low-temperature superheater 37, the cold side of the high-temperature superheater 35, the high-pressure cylinder 421, the cold side of the low-temperature reheater 38, the hot side of the high-temperature reheater 36, the medium-pressure cylinder 422, the low-pressure cylinder 423, the hot side of the condenser 425, the condensate pump 413, the cold side of the low-pressure heater 412, the deaerator 414, the feed pump 411, and the cold side of the high-pressure heater 415, which are connected in a closed loop.

[0088] The sub-steam-water circuit 2 includes the cold side of the low-pressure heater 412, a shunt feed pump 21, the cold side of the first economizer 22, the cold side of the external supply first-stage heater 11, the cold side of the external supply second-stage heater 12, the cold side of the external supply third-stage heater 13, the cold side of the external supply fourth-stage heater 14, the cold side of the external supply fifth-stage heater 15, a steam compressor 16, and a spray desuperheater 17, and finally reaches the steam supply demand users.

[0089] The water condensed by the condenser 425 enters the feedwater pipeline 41, and after passing through the condensate pump 413, the low-pressure heater 412, the deaerator 414, the feed pump 411, and the high-pressure heater 415 in sequence, it enters the boiler 31. Then, it passes through the second economizer 33, the water wall 34, the low-temperature superheater 37, and the high-temperature superheater 35 in sequence to exchange heat with the flue gas in the boiler 31 to obtain steam and then enters the high-pressure cylinder 421. The steam discharged from the high-pressure cylinder 421 passes through the low-temperature reheater 38 and the high-temperature reheater 36 in sequence to exchange heat with the flue gas in the boiler 31 again, and then passes through the medium-pressure cylinder 422 and the low-pressure cylinder 423 in sequence and is discharged into the condenser 425 to be condensed. The high-pressure cylinder 421, the medium-pressure cylinder 422, and the low-pressure cylinder 423 are driven by steam and are used to do work for the generator 424.

[0090] In this embodiment, an SCR reactor 61 (selective catalytic reduction method), an air preheater 62, a dust collector 63, an induced draft fan 64, and a desulfurization tower 65 are provided on the flue gas circuit 6. A catalyst 611 is arranged in the SCR reactor 61 to catalytically remove nitrogen oxides, and the temperature range with the highest reaction activity of the catalyst 611 is 100°C to 500°C.

[0091] The flue gas passes through the furnace 311, the horizontal flue 312, and the tail shaft flue 313 in the boiler 31 in sequence. The flue gas generated by combustion in the boiler 31 of the boiler flue gas system 3 passes through the flue 32 and then passes through the SCR reactor 61, the air preheater 62, the dust collector 63, the induced draft fan 64, and the desulfurization tower 65 in sequence, and is discharged after being treated by the desulfurization tower 65.

[0092] The specific flue gas circuit in the boiler 31 is the hot side of the water wall 34, the hot side of the externally supplied fifth-stage heater 15, the hot side of the high-temperature superheater 35, the hot side of the externally supplied fourth-stage heater 14, the hot side of the high-temperature reheater 36, the hot side of the externally supplied third-stage heater 13, the hot side of the low-temperature reheater 38, the hot side of the low-temperature superheater 37, and the hot side of the second economizer 33. The water wall 34, the high-temperature superheater 35, the high-temperature reheater 36, the low-temperature superheater 37, the low-temperature reheater 38, the second economizer 33, the externally supplied fifth-stage heater 15, the externally supplied fourth-stage heater 14, and the externally supplied third-stage heater 13 can be arranged in the boiler 31 horizontally, vertically, or in a combination of both, and can be arranged in multiple stages.

[0093] It can be understood that the above embodiments are merely exemplary embodiments adopted to illustrate the principle of the present invention. However, the present invention is not limited thereto. For those of ordinary skill in the art, various modifications and improvements can be made without departing from the spirit and essence of the present invention, and these modifications and improvements are also regarded as the protection scope of the present invention.

Claims

1. A steam supply system for a coal-fired unit, characterized in that: It comprises an external heater (1) and a steam-water distribution circuit (2). The steam-water separation circuit (2) is a circuit branched from a water supply pipeline (41) of a main steam-water circuit (4) of a coal-fired unit. The outlet end of the steam-water separation circuit (2) is connected to an external heater (1) so as to supply the working fluid extracted from the water supply pipeline (41) to the external heater (1). The external heater (1) is arranged inside the boiler flue system (3) of the coal-fired unit, in the heating area through which the flue gas passes, and its outlet end is connected to an external thermal load to supply the working fluid to the external thermal load after heat exchange with the flue gas.

2. The steam supply system for a coal-fired unit according to claim 1, characterized in that: There are a plurality of external heaters (1), each of which is arranged in sequence along the flue gas flow direction in the boiler flue system (3). The steam-water separation circuit (2) is connected to each external supply heater (1) in sequence in the opposite direction of the flue gas flow, so that the working medium can pass through each external supply heater (1) in sequence in the opposite direction of the flue gas flow.

3. The steam supply system for a coal-fired unit according to claim 2, characterized in that: The plurality of external heaters (1) are connected in series, and a flow pipeline (18) is connected in parallel between the two ends of each external heater (1). A valve body (19) is provided at each section of the flow pipeline (18) and each external supply heater (1), so that the flow path of the working medium can pass through each flow pipeline (18) by opening and closing the valve body (19) to bypass part or all of the external supply heater (1).

4. The steam supply system for a coal-fired unit according to claim 3, characterized in that: It also includes a first control unit, which is electrically connected to each valve body (19) and a generator (424) of the coal-fired unit. It is used to control the valve body (19) at the external heater (1) to be closed when the output power of the generator (424) is greater than a first set value, and to control the valve body (19) at the flow pipeline (18) of the corresponding external heater (1) to be opened, so that the flow path of the working medium bypasses at least one external heater (1); when the output power of the generator (424) is less than a second set value, control the valve bodies (19) at each external heater (1) to be opened, and the valve bodies (19) at each flow pipeline (18) to be closed, so that the flow path of the working medium passes through all the external heaters (1), and the first set value is greater than the second set value.

5. The steam supply system for coal-fired units according to claim 2, characterized in that: Each of the external supply heaters (1) is respectively an external supply first-stage heater (11), an external supply second-stage heater (12), an external supply third-stage heater (13), an external supply fourth-stage heater (14) and an external supply fifth-stage heater (15), The external five-stage heater (15) is arranged at the furnace (311) of the boiler (31) in the boiler flue system (3), corresponding to the height position of the water-cooled wall (34). The external four-stage heater (14) is arranged at the bottom of the horizontal flue (312) of the boiler (31). The external three-stage heater (13) is arranged at the junction of the horizontal flue (312) of the boiler (31) and the tail shaft flue (313). The external secondary heater (12) is arranged at the flue gas inlet of the flue (32) in the boiler flue system (3). The external primary heater (11) is arranged at the smoke outlet of the smoke duct (32).

6. The steam supply system for a coal-fired unit according to claim 2, characterized in that: It also includes a cooling water circuit (5), wherein a tap is provided at the inlet end of the cooling water circuit (5) and connected to a water supply pump (411) on a water supply pipe (41), and the outlet end is divided into a plurality of branches, each branch being respectively connected to each external supply heater (1) and used to extract the working fluid at the water supply pump (411) to cool the working fluid at the external supply heater (1).

7. The steam supply system for a coal-fired unit according to claim 1, characterized in that: It also includes a steam compressor (16) and a water spray desuperheater (17), wherein the steam compressor (16) and the water spray desuperheater (17) are both connected between the outlet end of the external heater (1) and the external thermal load, and are used to adjust the pressure and temperature of the working fluid respectively.

8. The steam supply system for a coal-fired unit according to any one of claims 1 to 7, characterized in that: The steam-water separation circuit (2) comprises a split feed water pump (21) and a first economizer (22). The split-flow water supply pump (21) is connected to the low-pressure heater (412) on the water supply pipeline (41) and is used to extract the working fluid from the low-pressure heater (412). One side of the first economizer (22) is connected between the split-flow feedwater pump (21) and the external heater (1), and the other side is connected to the flue gas line (6) of the coal-fired unit so that the working medium and the flue gas can exchange heat.

9. A method for supplying steam to a coal-fired unit, characterized in that: Using the coal-fired unit steam supply system according to any one of claims 1 to 8, the method comprises the following steps: Extracting working fluid from a water supply pipeline (41) of a main steam-water circuit (4) of a coal-fired unit through a steam-water circuit (2); The working medium is supplied to an external thermal load after heat is exchanged between the working medium and the flue gas in the boiler flue system (3) through an external heater (1).

10. The method for supplying steam to a coal-fired unit according to claim 9, characterized in that: The method of exchanging heat between the working medium and the flue gas in the boiler flue system (3) through the external heater (1) and then supplying the working medium to the external thermal load specifically includes: After the working medium is heat exchanged with the flue gas in the boiler flue system (3) by an external heater (1), the working medium is supplied to an external thermal load by a steam compressor (16); In the process of supplying the working medium to an external thermal load after exchanging heat with the flue gas in the boiler flue system (3) through the external supply heater (1), the method further comprises the following steps: A supply model is established based on the total amount of coal input to the boiler of the coal-fired unit, the total amount of air input to the boiler, the amount of water supplied to the boiler flue system (3) by the water supply pipeline (41), the amount of water for extracting the working medium from the water supply pipeline (41), the output power of the generator (424), the speed of the steam compressor (16), and the flow rate, temperature and pressure of the working medium supplied to the external thermal load; According to the real-time value of the electric power output of the generator (424) and the supply model, the total coal input to the boiler of the coal-fired unit, the total air input to the boiler, the water supply from the water supply pipe (41) to the boiler flue system (3), the water supply for the working fluid extracted from the water supply pipe (41), and the speed of the steam compressor (16) are adjusted to ensure that the flow rate, temperature and pressure of the working fluid supplied to the external thermal load are maintained within a set range.

11. A coal-fired unit, characterized in that: It comprises a boiler flue system (3), a main steam-water line (4), a flue gas line (6) and a coal-fired unit steam supply system according to any one of claims 1 to 8, The flue gas generated by the combustion of the boiler flue system (3) is discharged through the flue gas line (6). The main steam-water line (4) delivers the working fluid into the boiler flue system (3) to exchange heat with the flue gas and then perform work for the generator (424) of the coal-fired unit. The coal-fired unit steam supply system extracts working fluid from the main steam-water line (4) and exchanges heat with flue gas to supply external thermal loads.

12. The coal-fired unit according to claim 11, characterized in that: The boiler (31) of the boiler flue system (3) is provided with a water-cooled wall (34), a high-temperature superheater (35), a high-temperature reheater (36), a low-temperature superheater (37), a low-temperature reheater (38), and a second economizer (33). The main steam-water line (4) comprises an output pipeline (42) and a water supply pipeline (41), wherein the output pipeline (42) is provided with a high-pressure cylinder (421), a medium-pressure cylinder (422), a low-pressure cylinder (423) and a condenser (425). The water supply pipeline (41) is provided with a condensate pump (413), a low-pressure heater (412), a deaerator (414), a water supply pump (411) and a high-pressure heater (415). The water condensed by the condenser (425) enters the water supply pipe (41), and passes through the condensate pump (413), the low-pressure heater (412), the deaerator (414), the water supply pump (411) and the high-pressure heater (415) in sequence before entering the boiler (31). Then, the steam passes through the second economizer (33), the water-cooled wall (34), the low-temperature superheater (37), and the high-temperature superheater (35) in sequence to exchange heat with the flue gas in the boiler (31) to obtain steam, and then enters the high-pressure cylinder (421). The steam discharged from the high-pressure cylinder (421) passes through the low-temperature reheater (38) and the high-temperature reheater (36) in sequence, exchanges heat with the flue gas in the boiler (31) again, passes through the medium-pressure cylinder (422) and the low-pressure cylinder (423) in sequence, and is discharged into the condenser (425) for condensation. The high-pressure cylinder (421), the medium-pressure cylinder (422) and the low-pressure cylinder (423) are driven by steam to perform work for the generator (424).

13. The coal-fired unit according to claim 11, characterized in that: The flue gas line (6) is provided with an SCR reactor (61), an air preheater (62), a dust collector (63), an induced draft fan (64) and a desulfurization tower (65). The flue gas generated by combustion in the boiler (31) of the boiler flue system (3) passes through the flue (32) and then sequentially passes through the SCR reactor (61), the air preheater (62), the dust collector (63), the induced draft fan (64) and the desulfurization tower (65), and is discharged after being treated in the desulfurization tower (65).

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