System and method suitable for increasing temperature of SCR (Selective Catalytic Reduction) area of boiler under low load

Abstract

The invention belongs to the field of coal-fired boilers, and discloses a system and method suitable for increasing the temperature of an SCR area of a boiler under the low load, the system comprises the boiler, an economizer and an SCR denitration device, and the economizer is arranged in a tail flue of the boiler; an inlet of the economizer is provided with an economizer inlet water regulating valve and is connected with a steam heater; an inlet of the steam heater is provided with a steam heater isolating valve, the steam heater is correspondingly provided with a steam heater bypass, the two ends of the steam heater bypass are located on the upstream of the steam heater isolating valve and the downstream of an outlet of the steam heater respectively, and the steam heater bypass is provided with a steam heater bypass isolating valve. A flue gas inlet of the SCR denitration device is connected with the tail flue, and an SCR inlet flue temperature detection device is arranged in the tail flue. Under the condition that an original unit is slightly changed, the SCR inlet temperature can be increased, it is ensured that SCR is normally put into operation, and emission control over pollution gas under the low load of the coal-fired unit is effectively achieved.

Description

Technical Field

[0001] The present invention belongs to the field of coal-fired boilers, and in particular relates to a system and method for increasing the temperature of a boiler SCR zone under low load. Background Art

[0002] As the key force of traditional energy power generation, coal-fired units still account for a very large proportion of installed capacity. How to control the emission of coal-fired units is the focus of current attention. Most coal-fired units currently use the selective catalytic reduction (SCR) flue gas denitrification system, which uses a specific catalyst to react chemically with the NOx contained in the flue gas, thereby achieving effective removal of NOx.

[0003] With the continuous development of new energy power generation, coal-fired units have taken on more peak-shaving tasks. When the units are in peak-shaving state and operate in low-load mode, the temperature of the economizer outlet flue will drop significantly. The catalyst of the SCR denitrification device has a reaction activation temperature in the specific range of 310℃ to 400℃. Under low-load operation, the SCR inlet flue temperature often cannot reach 310℃. In addition, the drop in flue temperature will also promote the SO in the flue gas. 2 Transformed into SO 3 Once this happens, SO 3 There will be a risk of condensation and deposition of ammonium sulfate salts. In addition, under low temperature conditions, it is very likely to cause the catalyst to become blocked, and at the same time, it will cause a series of serious problems such as a significant increase in the resistance of the air preheater.

[0004] At this time, it is necessary to find a way to increase the SCR inlet flue gas temperature, ensure the catalyst reaction temperature, and ensure the SCR commissioning rate, so as to avoid over-emission accidents. Therefore, how to effectively solve the commissioning problem of SCR denitrification device under low-load operation has become an important issue in the current coal-fired flue gas denitrification field. Summary of the invention

[0005] In order to effectively increase the SCR temperature when the boiler is running at low load, the present invention provides a system and method suitable for increasing the temperature of the SCR zone of the boiler under low load. The present invention can increase the SCR inlet temperature with relatively small changes to the original unit, ensure the normal operation of the SCR, and effectively realize the emission control of pollutant gases under low load of the coal-fired unit.

[0006] To achieve the above purpose, the technical solution adopted by the present invention is as follows: A system suitable for increasing the temperature of the SCR zone of a boiler under low load, comprising a boiler, an economizer and an SCR denitration device, wherein the economizer is arranged in the tail flue of the boiler; The inlet of the economizer is provided with an economizer inlet water flow regulating valve, and the inlet of the economizer is connected to a steam heater; A steam heater isolation valve is provided at the inlet of the steam heater, and a steam heater bypass is provided correspondingly to the steam heater. The two ends of the steam heater bypass are respectively located upstream of the steam heater isolation valve and downstream of the steam heater outlet. A steam heater bypass isolation valve is provided on the steam heater bypass; The flue gas inlet of the SCR denitrification device is connected to the tail flue, and an SCR inlet flue temperature detection device is provided in the tail flue.

[0007] Preferably, the economizer includes a plurality of economizer blocks, which are sequentially distributed from the front wall to the rear wall of the tail flue, and a flue gas damper is provided upstream of each economizer block in the tail flue, and each flue gas damper is used to adjust the flue gas flow upstream of the corresponding economizer block downstream thereof; Each economizer block is provided with an economizer inlet water flow regulating valve and an economizer outlet temperature detecting device, and the inlet of each economizer block is connected to the steam heater.

[0008] Preferably, the economizer includes four economizer blocks, and the four economizer blocks are respectively recorded as the first economizer, the second economizer, the third economizer and the fourth economizer in the direction from the front wall to the rear wall of the tail flue, and the flue gas dampers upstream of the first economizer, the second economizer, the third economizer and the fourth economizer are respectively recorded as the first flue gas damper, the second flue gas damper, the third flue gas damper and the fourth flue gas damper.

[0009] Preferably, the inlet and outlet of the first economizer and the second economizer are both extended to one side of the front wall of the tail flue, and the inlet of the first economizer and the second economizer are both connected to the first steam heater, and water is added through the first steam heater; The inlet and outlet of the third economizer and the fourth economizer are both extended to one side of the rear wall of the tail flue, and the inlet of the third economizer and the fourth economizer are both connected to the second steam heater, and water is added through the second steam heater.

[0010] Preferably, a first economizer inlet communication valve is connected between the inlets of the first economizer and the second economizer, and the connection point between the first economizer inlet communication valve and the inlets of the first economizer and the second economizer is located downstream of the economizer inlet water flow regulating valve at the inlets of the first economizer and the second economizer; A second economizer inlet connecting valve is connected between the inlets of the third economizer and the fourth economizer, and the connection point between the second economizer inlet connecting valve and the inlets of the third economizer and the fourth economizer is located downstream of the economizer inlet water flow regulating valve at the inlets of the third economizer and the fourth economizer; The outlets of the first economizer, the second economizer, the third economizer and the fourth economizer are respectively provided with a first economizer outlet water flow regulating valve, a second economizer outlet water flow regulating valve, a third economizer outlet water flow regulating valve and a fourth economizer outlet water flow regulating valve.

[0011] The present invention further provides a method for increasing the temperature of a boiler SCR zone under low load, the method is performed using the system for increasing the temperature of a boiler SCR zone under low load as described above, and the method comprises: When the boiler is in the process of low-load operation, if the detection value of the SCR inlet flue temperature detection device is less than the first preset range, the steam heater isolation valve is opened and the steam heater bypass isolation valve is closed, and the water temperature at the economizer inlet is increased by the steam heater to reduce the heat absorbed by the flue gas of the economizer, thereby increasing the detection value of the SCR inlet flue temperature detection device to the first preset range. After the detection value of the SCR inlet flue temperature detection device reaches the first preset range for the first time, if the detection value of the SCR inlet flue temperature detection device is not within the first preset range, the water amount in the economizer is fine-tuned by the economizer inlet water amount regulating valve to maintain the detection value of the SCR inlet flue temperature detection device within the first preset range. When the detection value of the SCR inlet flue temperature detection device is within the first predetermined range, the SCR denitration device can be maintained in a normal operating state.

[0012] Preferably, if the detection value of the SCR inlet flue temperature detection device is not within the first preset range, the water amount in the economizer is fine-tuned by the economizer inlet water amount regulating valve to maintain the detection value of the SCR inlet flue temperature detection device within the first preset range, specifically including: When the detection value of the SCR inlet flue temperature detection device exceeds the first preset range, the water amount in the economizer is increased through the economizer inlet water flow regulating valve to increase the heat of the flue gas absorbed by the economizer, thereby reducing the flue gas temperature until the detection value of the SCR inlet flue temperature detection device is reduced to the first preset range; when the detection value of the SCR inlet flue temperature detection device is lower than the first preset range, the water amount in the economizer is reduced through the economizer inlet water flow regulating valve to reduce the heat of the flue gas absorbed by the economizer, thereby increasing the flue gas temperature until the detection value of the SCR inlet flue temperature detection device is increased to the first preset range.

[0013] Preferably, the economizer includes a plurality of economizer blocks, which are sequentially distributed from the front wall to the rear wall of the tail flue. A flue gas damper is provided upstream of each economizer block in the tail flue, and each flue gas damper is used to adjust the flue gas flow upstream of the corresponding economizer block downstream thereof; each economizer block is provided with an economizer inlet water flow regulating valve and an economizer outlet temperature detection device, and the inlet of each economizer block is connected to the steam heater; When the boiler is in low-load operation, the method includes the following periodic adjustment process: The temperature detection value of the economizer outlet temperature detection device of each economizer block is periodically obtained, and the temperature average value of the temperature detection values ​​of all economizer outlet temperature detection devices is calculated; for the economizer block whose temperature detection value is greater than the temperature average value, the flue gas damper upstream of the economizer block is adjusted to reduce the flue gas throughput of the economizer, thereby reducing the heat absorbed by the economizer block from the flue gas, until the temperature detection value of the economizer outlet temperature detection device of the economizer block is equal to the temperature average value; for the economizer block whose temperature detection value is less than the temperature average value, the flue gas damper upstream of the economizer block is adjusted to increase the flue gas throughput of the economizer, thereby increasing the heat absorbed by the economizer block from the flue gas, until the temperature detection value of the economizer outlet temperature detection device of the economizer block is equal to the temperature average value; when the opening of the flue gas damper upstream of the economizer block has reached the maximum, the flue gas damper upstream of the economizer block is not adjusted.

[0014] Preferably, the economizer includes four economizer blocks, and the four economizer blocks are respectively recorded as the first economizer, the second economizer, the third economizer and the fourth economizer in the direction from the front wall to the rear wall of the tail flue, and the flue gas dampers upstream of the first economizer, the second economizer, the third economizer and the fourth economizer are respectively recorded as the first flue gas damper, the second flue gas damper, the third flue gas damper and the fourth flue gas damper; the inlet and outlet of the first economizer and the second economizer are extended to the side of the front wall of the tail flue, and the inlet of the first economizer and the second economizer are connected to the first steam heater, and water is added through the first steam heater; the inlet and outlet of the third economizer and the fourth economizer are extended to the side of the rear wall of the tail flue, and the inlet of the third economizer and the fourth economizer are connected to the second steam heater, and water is added through the second steam heater; When the boiler is in low-load operation, the method includes the following steps: When water is added to the first economizer and the second economizer through the first steam heater, the water volume of the first economizer and the water volume of the second economizer are respectively adjusted through the economizer inlet water volume regulating valves corresponding to the first economizer and the second economizer; When water is added to the third economizer and the fourth economizer through the second steam heater, the water volume of the third economizer and the water volume of the fourth economizer are respectively adjusted through the economizer inlet water control valves corresponding to the third economizer and the fourth economizer.

[0015] Preferably, a first economizer inlet connecting valve is connected between the inlets of the first economizer and the second economizer, and the connection point between the first economizer inlet connecting valve and the inlets of the first economizer and the second economizer is located downstream of the economizer inlet water regulating valve at the inlets of the first economizer and the second economizer; a second economizer inlet connecting valve is connected between the inlets of the third economizer and the fourth economizer, and the connection point between the second economizer inlet connecting valve and the inlets of the third economizer and the fourth economizer is located downstream of the economizer inlet water regulating valve at the inlets of the third economizer and the fourth economizer; the outlets of the first economizer, the second economizer, the third economizer and the fourth economizer are respectively provided with the first economizer outlet water regulating valve, the second economizer outlet water regulating valve, the third economizer outlet water regulating valve and the fourth economizer outlet water regulating valve; When the boiler is in normal load operation, the method includes: Close all steam heater isolation valves, open all steam heater bypass isolation valves, and adjust the economizer inlet water flow regulating valve to the maximum opening; When water is added to the first economizer and the second economizer, water in the steam heater bypass corresponding to the first steam heater flows into the first economizer and the second economizer respectively through the first economizer inlet connecting valve, and the following periodic adjustment process is performed: the temperature detection values ​​of the economizer outlet temperature detection devices of the first economizer and the second economizer are periodically obtained, and the temperature average value of the temperature detection values ​​of all economizer outlet temperature detection devices is calculated; for the economizer blocks whose temperature detection values ​​are greater than the temperature average value, the flue gas damper upstream of the economizer block is adjusted to reduce the flue gas flow through the economizer, and at the same time, the opening of the economizer outlet water flow regulating valve at the outlet of the economizer block is increased, thereby reducing the heat absorbed by the economizer block from the flue gas and making the economizer The high-temperature water heated in the block flows out faster until the temperature detection value of the economizer outlet temperature detection device of the economizer block is equal to the temperature average value; for the economizer block whose temperature detection value is less than the temperature average value, the flue gas damper upstream of the economizer block is adjusted to increase the flue gas flow rate of the economizer, and at the same time, the opening of the economizer outlet water flow regulating valve at the economizer block outlet is reduced, thereby increasing the heat absorbed by the economizer block from the flue gas, and accelerating the increase of the water temperature at the economizer block outlet, until the temperature detection value of the economizer outlet temperature detection device of the economizer block is equal to the temperature average value, and when the opening of the flue gas damper upstream of the economizer block has reached the maximum, the flue gas damper upstream of the economizer block is not adjusted; When water is added to the third economizer and the fourth economizer, water in the steam heater bypass corresponding to the second steam heater flows into the third economizer and the fourth economizer respectively through the second economizer inlet connecting valve, and the following periodic adjustment process is performed: the temperature detection values ​​of the economizer outlet temperature detection devices of the third economizer and the fourth economizer are periodically obtained, and the temperature average value of the temperature detection values ​​of all economizer outlet temperature detection devices is calculated; for the economizer blocks whose temperature detection values ​​are greater than the temperature average value, the flue gas damper upstream of the economizer block is adjusted to reduce the flue gas passing through the economizer, and at the same time, the opening of the economizer outlet water flow regulating valve at the outlet of the economizer block is increased, thereby reducing the heat absorbed by the economizer block from the flue gas and making the economizer The high-temperature water heated in the block flows out faster until the temperature detection value of the economizer outlet temperature detection device of the economizer block is equal to the temperature average value; for the economizer block whose temperature detection value is lower than the temperature average value, the flue gas damper upstream of the economizer block is adjusted to increase the flue gas throughput of the economizer, and at the same time, the opening of the economizer outlet water flow regulating valve at the economizer block outlet is reduced, thereby increasing the heat absorbed by the economizer block from the flue gas, and accelerating the increase of the water temperature at the economizer block outlet, until the temperature detection value of the economizer outlet temperature detection device of the economizer block is equal to the temperature average value, and when the opening of the flue gas damper upstream of the economizer block has reached the maximum, the flue gas damper upstream of the economizer block is not adjusted.

[0016] The above technical solution of the present application has the following beneficial technical effects: The present invention is applicable to a system for increasing the temperature of the SCR zone of a boiler under low load. On the basis of an existing unit, a steam heater is added. When the boiler is in a low-load operation process, if the flue gas temperature at the inlet of the SCR denitrification device is lower than a first preset range that can maintain it in a normal operating state, the steam heater can be used to heat the water at the inlet of the economizer to increase the inlet water temperature of the economizer, thereby reducing the heat absorbed by the economizer from the flue gas, thereby increasing the inlet flue gas temperature of the SCR denitrification device, until the inlet flue gas temperature of the SCR denitrification device reaches the first preset range. At the same time, when the inlet flue gas temperature of the SCR denitrification device reaches the first preset range, if the SCR When the flue gas temperature at the inlet of the denitrification device fluctuates, so that the flue gas temperature at the inlet of the SCR denitrification device is not within the first preset range, the water volume of the economizer can be fine-tuned through the economizer inlet water volume regulating valve, thereby changing the heat obtained by the economizer from the flue gas, and then fine-tuning the flue gas temperature at the inlet of the SCR denitrification device, and finally making the flue gas temperature at the inlet of the SCR denitrification device reach the first preset range; and when the boiler is in normal load operation, the steam heater isolation valve can be cut off and the steam heater bypass isolation valve can be opened at the same time, so that the steam heater is cut out, and the water volume at the economizer inlet is no longer adjusted by the steam heater. It can be seen from the above scheme that the present invention can increase the SCR inlet temperature with relatively small changes to the original unit, ensure the normal operation of the SCR, and effectively realize the emission control of pollutant gases under low load of coal-fired units. At the same time, the present invention is suitable for the control of wide load denitrification. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a structural schematic diagram of a system suitable for increasing the temperature of the SCR zone of a boiler under low load in an embodiment of the present invention; Figure 2 It is a structural diagram of the arrangement of the economizer and the flue gas damper in an embodiment of the present invention; Figure 3 It is a longitudinal cross-sectional schematic diagram of the tail flue and SCR denitration device of the system suitable for increasing the temperature of the SCR zone of the boiler under low load in an embodiment of the present invention.

[0018] Among them: 1 is a superheater, 2 is a reheater, 3 is a first economizer, 4 is a second economizer, 5 is a third economizer, 6 is a fourth economizer, 7 is a first flue gas damper, 8 is a second flue gas damper, 9 is a third flue gas damper, 10 is a fourth flue gas damper, 12 is a second steam heater, 13 is a first steam heater, 14 is a second header, 15 is a first header, 16 is an SCR denitrification device, 17 is an air preheater, 18 is a rotating shaft, 19 is a water flow regulating valve for the inlet of the first economizer, 20 is a water flow regulating valve for the inlet of the second economizer, 21 is a water flow regulating valve for the inlet of the third economizer, 22 is a water flow regulating valve for the inlet of the fourth economizer, 23 is the first economizer outlet temperature detection device, 24 is the second economizer outlet temperature detection device, 25 is the third economizer outlet temperature detection device, 26 is the fourth economizer outlet temperature detection device, 27 is the first steam heater isolation valve, 28 is the second steam heater isolation valve, 29 is the first economizer inlet connecting valve, 30 is the second economizer inlet connecting valve, 31 is the SCR inlet flue temperature detection device, 32 is the first steam heater end temperature detection device, 33 is the second steam heater end temperature detection device, 34 is the first steam heater bypass isolation valve, and 35 is the second steam heater bypass isolation valve. DETAILED DESCRIPTION

[0019] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiment of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiment of the present invention. Obviously, the described embodiment is only an embodiment of a part of the present invention, not all embodiments, and is not intended to limit the scope of the present invention. In addition, in the following description, the description of well-known structures and technologies is omitted to avoid unnecessary confusion of the concepts disclosed in the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work should fall within the scope of protection of the present invention.

[0020] See also Figure 1 This embodiment is applicable to a system for increasing the temperature of a boiler SCR zone under low load, and includes a boiler, an economizer and an SCR denitrification device 16, wherein the economizer is arranged in the tail flue of the boiler; an economizer inlet water regulating valve is provided at the inlet of the economizer, and the inlet of the economizer is connected to a steam heater; a steam heater isolation valve is provided at the inlet of the steam heater, and a steam heater bypass is correspondingly provided at the steam heater, and two ends of the steam heater bypass are respectively located upstream of the steam heater isolation valve and downstream of the steam heater outlet, and a steam heater bypass isolation valve is provided on the steam heater bypass; the flue gas inlet of the SCR denitrification device 16 is connected to the tail flue, and an SCR inlet flue temperature detection device 31 is provided in the tail flue.

[0021] The working method of the system for increasing the temperature of the boiler SCR zone under low load in the above embodiment of the present invention includes the following process: When the boiler is in low load operation, if the detection value of the SCR inlet flue temperature detection device 31 is less than the first preset range, the steam heater isolation valve is opened and the steam heater bypass isolation valve is closed, and the water temperature at the economizer inlet is increased by the steam heater to reduce the heat absorbed by the flue gas by the economizer, thereby increasing the detection value of the SCR inlet flue temperature detection device 31 to the first preset range. When the detection value of the SCR inlet flue temperature detection device 31 reaches the first preset range for the first time, if the detection value of the SCR inlet flue temperature detection device 31 is not within the first preset range, the water amount in the economizer is fine-tuned by the economizer inlet water amount regulating valve to make the SCR inlet flue temperature detection device 31 within the first preset range. The detection value of the detection device 31 is maintained within the first preset range, specifically including: when the detection value of the SCR inlet flue temperature detection device 31 exceeds the first preset range, the water amount in the economizer is increased through the economizer inlet water amount regulating valve to increase the heat of the flue gas absorbed by the economizer, so that the flue gas temperature is reduced until the detection value of the SCR inlet flue temperature detection device 31 is reduced to the first preset range; when the detection value of the SCR inlet flue temperature detection device 31 is lower than the first preset range, the water amount in the economizer is reduced through the economizer inlet water amount regulating valve to reduce the heat of the flue gas absorbed by the economizer, so that the flue gas temperature is increased until the detection value of the SCR inlet flue temperature detection device 31 is increased to the first preset range. Among them, when the detection value of the SCR inlet flue temperature detection device 31 is within the first preset range, the SCR denitrification device 16 can be maintained in a normal operating state. Generally, when the detection value of the SCR inlet flue temperature detection device 31 is 315°C, the SCR denitrification device 16 can be maintained in a normal operating state.

[0022] As a preferred embodiment of the present invention and as a further improvement of the above embodiment, in this embodiment, the economizer includes a plurality of economizer blocks, and the plurality of economizer blocks are sequentially distributed in the direction from the front wall to the rear wall of the tail flue, and a flue gas baffle is provided upstream of each economizer block in the tail flue, and each flue gas baffle is used to adjust the flue gas flow upstream of the corresponding economizer block downstream; each economizer block is provided with an economizer inlet water regulating valve and an economizer outlet temperature detection device, and the inlet of each economizer block is connected to the steam heater. In this embodiment, considering that when an integral economizer is used, the amount of water inside it is large, so the thermal inertia is large. Therefore, when it is used to adjust the flue gas temperature, the system reacts slowly, resulting in a relatively long adjustment process. Therefore, in this embodiment, the existing economizer is divided into a number of independent economizer blocks (actually economizers with relatively small volumes). In this way, for a single economizer block, the thermal inertia is small. Therefore, when the flue gas temperature is adjusted by the economizer block, the adjustment speed is relatively fast. At the same time, since the flue gas temperature distribution in the tail flue is uneven, this embodiment can adjust separately according to the flue gas temperature distribution in the area where each economizer block is located. In this way, by controlling the heat absorption of each economizer block separately, each economizer block can work at a relatively high heat exchange efficiency. At the same time, the water temperature at the outlet of each economizer block can be as close as possible, so that the hot water users of the economizer can directly use the hot water provided by all economizer blocks. At the same time, for each economizer block, combined with the action of the flue gas damper, the overall smoke temperature can be increased more quickly and efficiently. Specifically, when the boiler is in the process of low-load operation, the working method of the system for increasing the temperature of the boiler SCR zone under low load in this embodiment includes the following periodic adjustment process: periodically obtaining the temperature detection value of the economizer outlet temperature detection device of each economizer block, and calculating the temperature average value of the temperature detection values ​​of all economizer outlet temperature detection devices, and for the economizer blocks whose temperature detection values ​​are greater than the temperature average value (indicating that the economizer block absorbs relatively more heat from the flue gas), adjusting the flue gas baffle upstream of the economizer block to reduce the flue gas flow through the economizer, thereby reducing the heat absorbed by the economizer block from the flue gas. , until the temperature detection value of the economizer outlet temperature detection device of the economizer block is equal to the temperature average value; for the economizer block whose temperature detection value is less than the temperature average value (indicating that the economizer block absorbs relatively less heat from the flue gas), adjust the flue gas damper upstream of the economizer block to increase the flue gas throughput of the economizer, thereby increasing the heat absorbed by the economizer block from the flue gas, until the temperature detection value of the economizer outlet temperature detection device of the economizer block is equal to the temperature average value, and when the opening of the flue gas damper upstream of the economizer block has reached the maximum, the flue gas damper upstream of the economizer block is not adjusted.

[0023] As a preferred embodiment of the present invention, as a specific situation of the above embodiment, see Figure 1-Figure 3 In this embodiment, the economizer includes four economizer blocks, and the four economizer blocks are respectively recorded as the first economizer 3, the second economizer 4, the third economizer 5 and the fourth economizer 6 along the direction from the front wall to the rear wall of the tail flue, and the flue gas dampers upstream of the first economizer 3, the second economizer 4, the third economizer 5 and the fourth economizer 6 are respectively recorded as the first flue gas damper 7, the second flue gas damper 8, the third flue gas damper 9 and the fourth flue gas damper 10.

[0024] As a preferred embodiment of the present invention, on the basis of the above embodiments, in this embodiment, the inlet and outlet of the first economizer 3 and the second economizer 4 are extended to the front wall side of the tail flue, the inlet of the first economizer 3 and the second economizer 4 are connected to the first steam heater 13, and water is added through the first steam heater 13; the inlet and outlet of the third economizer 5 and the fourth economizer 6 are extended to the rear wall side of the tail flue, the inlet of the third economizer 5 and the fourth economizer 6 are connected to the second steam heater 12, and water is added through the second steam heater 12. When the boiler is in the process of low-load operation, the working method of the system for increasing the temperature of the boiler SCR zone under low load in this embodiment includes the following process: when water is added to the first economizer 3 and the second economizer 4 through the first steam heater 13, the water volume of the first economizer 3 and the water volume of the second economizer 4 are respectively adjusted through the economizer inlet water volume regulating valves corresponding to the first economizer 3 and the second economizer 4 (i.e., the first economizer inlet water volume regulating valve 19 and the second economizer inlet water volume regulating valve 20); when water is added to the third economizer 5 and the fourth economizer 6 through the second steam heater 12, the water volume of the third economizer 5 and the water volume of the fourth economizer 6 are respectively adjusted through the economizer inlet water volume regulating valves corresponding to the third economizer 5 and the fourth economizer 6 (i.e., the third economizer inlet water volume regulating valve 21 and the fourth economizer inlet water volume regulating valve 22). In this embodiment, by providing the above two steam heaters (ie, the first steam heater 13 and the second steam heater 12), it is possible to quickly adjust the water temperature in the economizer block, thereby facilitating a rapid increase in the flue gas temperature.

[0025] As a preferred embodiment of the present invention, on the basis of the above scheme, in this embodiment, a first economizer inlet connecting valve 29 is connected between the inlets of the first economizer 3 and the second economizer 4, and the connection point between the first economizer inlet connecting valve 29 and the inlets of the first economizer 3 and the second economizer 4 is located downstream of the economizer inlet water regulating valve at the inlets of the first economizer 3 and the second economizer 4; a second economizer inlet connecting valve 30 is connected between the inlets of the third economizer 5 and the fourth economizer 6, and the connection point between the second economizer inlet connecting valve 30 and the inlets of the third economizer 5 and the fourth economizer 6 is located downstream of the economizer inlet water regulating valve at the inlets of the third economizer 5 and the fourth economizer 6; the outlets of the first economizer 3, the second economizer 4, the third economizer 5 and the fourth economizer 6 are respectively provided with a first economizer outlet water regulating valve, a second economizer outlet water regulating valve, a third economizer outlet water regulating valve and a fourth economizer outlet water regulating valve. When the boiler is in normal load operation, the working method of the system for increasing the temperature of the boiler SCR zone under low load in this embodiment includes the following process: Close all steam heater isolation valves (i.e., the first steam heater isolation valve 27 and the second steam heater isolation valve 28), open all steam heater bypass isolation valves (i.e., the first steam heater bypass isolation valve 34 and the second steam heater bypass isolation valve), and adjust the opening of all economizer inlet water regulating valves (i.e., the first economizer inlet water regulating valve 19, the second economizer inlet water regulating valve 20, the third economizer inlet water regulating valve 21 and the fourth economizer inlet water regulating valve 22) to the maximum; When water is added to the first economizer 3 and the second economizer 4, water in the steam heater bypass corresponding to the first steam heater 13 flows into the first economizer 3 and the second economizer 4 respectively through the first economizer inlet connecting valve 29, and the following periodic adjustment process is performed: the temperature detection values ​​of the economizer outlet temperature detection devices of the first economizer 3 and the second economizer 4 are periodically obtained, and the temperature average value of the temperature detection values ​​of all economizer outlet temperature detection devices is calculated, and for the economizer block (such as the second economizer 4) whose temperature detection value is greater than the temperature average value, the flue gas damper (such as the second flue gas damper) upstream of the economizer block (such as the second economizer 4) is adjusted. plate 8) to reduce the flue gas flow rate of the economizer block (such as the second economizer 4), and at the same time increase the opening of the economizer outlet water flow regulating valve at the outlet of the economizer block (such as the second economizer 4), thereby reducing the heat absorbed by the economizer block (such as the second economizer 4) from the flue gas, and accelerating the outflow of the heated high-temperature water in the economizer block, until the temperature detection value of the economizer outlet temperature detection device (such as the second economizer outlet temperature detection device) of the economizer block (such as the second economizer 4) is equal to the temperature average value. At the same time, since the flue gas flow rate of the economizer block (such as the second economizer 4) is reduced, the economizer Part of the flue gas blocked by the flue gas damper (such as the second flue gas damper 8) upstream of the economizer block (such as the second economizer 4) will flow to the adjacent economizer block (such as the first economizer 3), thereby increasing the flue gas flow rate of the adjacent economizer block (such as the first economizer 3), which can accelerate the rapid increase of the water temperature of the adjacent economizer block (such as the first economizer 3); for the economizer block (such as the first economizer 3) whose temperature detection value is less than the temperature average value, adjust the flue gas damper (such as the first flue gas damper 7) upstream of the economizer block (such as the first economizer 3) to increase the flue gas flow rate of the economizer (such as the first economizer 3), and at the same time reduce the temperature of the economizer block The opening of the economizer outlet water flow regulating valve at the outlet of the economizer block (such as the first economizer 3) is adjusted, thereby increasing the heat absorbed by the economizer block (such as the first economizer 3) from the flue gas, and accelerating the increase of the water temperature at the outlet of the economizer block (such as the first economizer 3) until the temperature detection value of the economizer outlet temperature detection device of the economizer block is equal to the temperature average value, and when the opening of the flue gas damper (such as the first flue gas damper 7) upstream of the economizer block (such as the first economizer 3) has reached the maximum, the flue gas damper upstream of the economizer block is not adjusted; the above method can make the outlet water temperatures of the first economizer 3 and the second economizer 4 tend to be the same; Similarly, when water is added to the third economizer 5 and the fourth economizer 6, water in the steam heater bypass corresponding to the second steam heater 12 flows into the third economizer 5 and the fourth economizer 6 respectively through the second economizer inlet connecting valve 30, and the following periodic adjustment process is performed: the temperature detection values ​​of the economizer outlet temperature detection devices of the third economizer 5 and the fourth economizer 6 are periodically obtained, and the temperature average value of the temperature detection values ​​of all economizer outlet temperature detection devices is calculated, and for the economizer block (such as the third economizer 5) whose temperature detection value is greater than the temperature average value, the flue gas damper (such as the third flue gas damper 9) upstream of the economizer block (such as the third economizer 5) is adjusted. , so as to reduce the flue gas flow rate of the economizer (such as the third economizer 5), and at the same time increase the opening of the economizer outlet water flow regulating valve at the outlet of the economizer block (such as the third economizer 5), thereby reducing the heat absorbed by the economizer block (such as the third economizer 5) from the flue gas, and accelerating the outflow of the high-temperature water heated in the economizer block (such as the third economizer 5) until the temperature detection value of the economizer outlet temperature detection device of the economizer block (such as the third economizer 5) is equal to the temperature average value. At the same time, since the flue gas flow rate of the economizer block (such as the third economizer 5) is reduced, the flue gas damper upstream of the economizer block (such as the third economizer 5) Part of the flue gas blocked by the third flue gas baffle (such as the fourth economizer 6) will flow to the adjacent economizer block (such as the fourth economizer 6), thereby increasing the flue gas flow rate of the adjacent economizer block (such as the fourth economizer 6), which can accelerate the rapid increase of the water temperature of the adjacent economizer block (such as the third economizer 5); for the economizer block (such as the fourth economizer 6) whose temperature detection value is lower than the temperature average value, adjust the flue gas baffle (such as the fourth flue gas baffle 10) upstream of the economizer block (such as the fourth economizer 6) to increase the flue gas flow rate of the economizer (such as the fourth economizer 6), and at the same time reduce the economizer outlet water flow regulating valve at the outlet of the economizer block (such as the fourth economizer 6). opening, thereby increasing the heat absorbed by the economizer block (such as the fourth economizer 6) from the flue gas, and accelerating the increase in the water temperature at the outlet of the economizer block (such as the fourth economizer 6), until the temperature detection value of the economizer outlet temperature detection device of the economizer block (such as the fourth economizer 6) is equal to the said temperature average value, and when the opening of the flue gas damper (such as the fourth flue gas damper 10) upstream of the economizer block (such as the fourth economizer 6) has reached the maximum, the flue gas damper (such as the fourth flue gas damper 10) upstream of the economizer block (such as the fourth economizer 6) is not adjusted; the above method can make the outlet water temperatures of the third economizer 5 and the fourth economizer 6 tend to be the same.

[0026] Similarly, in the above scheme, if the first economizer 3, the second economizer 4, the third economizer 5 and the fourth economizer 6 periodically obtain the temperature detection values ​​of the economizer outlet temperature detection devices of all economizer blocks, and calculate the temperature average value of the temperature detection values ​​of all economizer outlet temperature detection devices, for the economizer blocks whose temperature detection values ​​are greater than the temperature average value, this can quickly make the water temperatures at the outlets of the first economizer 3, the second economizer 4, the third economizer 5 and the fourth economizer 6 tend to be the same. The specific process is the same as above and will not be repeated in this embodiment.

[0027] In the above scheme of the present invention, a superheater 1 and a reheater 2 are further provided in the flue of the coal-fired boiler, the reheater 2 is arranged upstream of the economizer, and the superheater 1 is arranged upstream of the reheater 2. In the present invention, the flue gas enters the tail flue through the superheater 1, the reheater 2 and the economizer in sequence, enters the SCR ammonia injection grid of the SCR denitration device 16 from the tail flue, and finally enters the SCR denitration reactor to reach the air preheater after denitration treatment.

[0028] In the above scheme of the present invention, the flue gas damper in front of the economizer can use a fan-shaped structure. Since the economizer will not be fully closed under low load conditions, the flow area of ​​the second economizer 4 and the third economizer 5 is 1.5 times the flow area of ​​the first economizer 3 and the fourth economizer 6. The flow areas of the second economizer 4 and the third economizer 5 are the same, and the flow areas of the first economizer 3 and the fourth economizer 6 are the same.

[0029] According to the above analysis, the system for increasing the temperature of the boiler SCR zone under low load provided by the present invention is suitable for deep peak regulation of thermal power plant boilers, and effectively increases the SCR inlet flue gas temperature. By arranging the economizer in parallel blocks, adding a steam heater in front of the economizer and behind the header, and regulating the economizer inlet water temperature, the heat exchange can be effectively reduced when the boiler is running at low load, solving the problem of slow flue gas temperature adjustment and insufficient adjustment capacity caused by traditional economizer grading.

[0030] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A system suitable for increasing the temperature of the SCR zone of a boiler under low load, characterized in that: It comprises a boiler, an economizer and an SCR denitrification device (16), wherein the economizer is arranged in the tail flue of the boiler; The inlet of the economizer is provided with an economizer inlet water flow regulating valve, and the inlet of the economizer is connected to a steam heater; A steam heater isolation valve is provided at the inlet of the steam heater, and a steam heater bypass is provided correspondingly to the steam heater. The two ends of the steam heater bypass are respectively located upstream of the steam heater isolation valve and downstream of the steam heater outlet. A steam heater bypass isolation valve is provided on the steam heater bypass; The flue gas inlet of the SCR denitration device (16) is connected to the tail flue, and the tail flue is provided with an SCR inlet flue temperature detection device (31).

2. A system for increasing the temperature of the boiler SCR zone under low load according to claim 1, characterized in that: The economizer includes a plurality of economizer blocks, which are sequentially distributed from the front wall to the rear wall of the tail flue. A flue gas damper is provided upstream of each economizer block in the tail flue, and each flue gas damper is used to adjust the flue gas flow upstream of the corresponding economizer block downstream thereof; Each economizer block is provided with an economizer inlet water flow regulating valve and an economizer outlet temperature detecting device, and the inlet of each economizer block is connected to the steam heater.

3. A system for increasing the temperature of the boiler SCR zone under low load according to claim 2, characterized in that: The economizer comprises four economizer blocks, which are respectively denoted as a first economizer (3), a second economizer (4), a third economizer (5) and a fourth economizer (6) along the direction from the front wall to the rear wall of the tail flue, and the flue gas dampers upstream of the first economizer (3), the second economizer (4), the third economizer (5) and the fourth economizer (6) are respectively denoted as a first flue gas damper (7), a second flue gas damper (8), a third flue gas damper (9) and a fourth flue gas damper (10).

4. A system for increasing the temperature of the boiler SCR zone under low load according to claim 3, characterized in that: The inlet and outlet of the first economizer (3) and the second economizer (4) are both extended to one side of the front wall of the tail flue, and the inlet of the first economizer (3) and the second economizer (4) are both connected to the first steam heater (13), and water is added through the first steam heater (13); The inlet and outlet of the third economizer (5) and the fourth economizer (6) both extend to one side of the rear wall of the tail flue, and the inlet of the third economizer (5) and the fourth economizer (6) are both connected to the second steam heater (12), and water is added through the second steam heater (12).

5. A system for increasing the temperature of the SCR zone of a boiler under low load according to claim 4, characterized in that: A first economizer inlet connecting valve (29) is connected between the inlets of the first economizer (3) and the second economizer (4), and a connection point between the first economizer inlet connecting valve (29) and the inlets of the first economizer (3) and the second economizer (4) is located downstream of economizer inlet water flow regulating valves at the inlets of the first economizer (3) and the second economizer (4); A second economizer inlet communication valve (30) is connected between the inlets of the third economizer (5) and the fourth economizer (6); the connection points between the second economizer inlet communication valve (30) and the inlets of the third economizer (5) and the fourth economizer (6) are located downstream of economizer inlet water flow regulating valves at the inlets of the third economizer (5) and the fourth economizer (6); The outlets of the first economizer (3), the second economizer (4), the third economizer (5) and the fourth economizer (6) are respectively provided with a first economizer outlet water flow regulating valve, a second economizer outlet water flow regulating valve, a third economizer outlet water flow regulating valve and a fourth economizer outlet water flow regulating valve.

6. A method for increasing the temperature of the SCR zone of a boiler under low load, characterized in that: The method is carried out using the system for increasing the temperature of the SCR zone of the boiler under low load as described in any one of claims 1 to 5, and the method comprises: When the boiler is in a low-load operation process, if the detection value of the SCR inlet flue temperature detection device (31) is less than a first preset range, the steam heater isolation valve is opened and the steam heater bypass isolation valve is closed, and the water temperature at the economizer inlet is increased by the steam heater to reduce the heat absorbed by the flue gas by the economizer, thereby increasing the detection value of the SCR inlet flue temperature detection device (31) to the first preset range; when the detection value of the SCR inlet flue temperature detection device (31) reaches the first preset range for the first time, if the detection value of the SCR inlet flue temperature detection device (31) is not within the first preset range, the water amount in the economizer is fine-tuned by the economizer inlet water amount regulating valve to maintain the detection value of the SCR inlet flue temperature detection device (31) within the first preset range; When the detection value of the SCR inlet flue gas temperature detection device (31) is within the first predetermined range, the SCR denitration device (16) can be maintained in a normal operating state.

7. A method for increasing the temperature of the SCR zone of a boiler under low load according to claim 6, characterized in that: If the detection value of the SCR inlet flue temperature detection device (31) is not within the first preset range, the water volume in the economizer is fine-tuned by the economizer inlet water volume regulating valve so that the detection value of the SCR inlet flue temperature detection device (31) is maintained within the first preset range, specifically including: When the detection value of the SCR inlet flue temperature detection device (31) exceeds a first preset range, the water volume in the economizer is increased by the economizer inlet water volume regulating valve to increase the heat of the flue gas absorbed by the economizer, thereby reducing the flue gas temperature until the detection value of the SCR inlet flue temperature detection device (31) is reduced to the first preset range; when the detection value of the SCR inlet flue temperature detection device (31) is lower than the first preset range, the water volume in the economizer is decreased by the economizer inlet water volume regulating valve to reduce the heat of the flue gas absorbed by the economizer, thereby increasing the flue gas temperature until the detection value of the SCR inlet flue temperature detection device (31) is increased to the first preset range.

8. A method for increasing the temperature of the SCR zone of a boiler under low load according to claim 6, characterized in that: The economizer includes a plurality of economizer blocks, which are sequentially distributed from the front wall to the rear wall of the tail flue. A flue gas damper is provided upstream of each economizer block in the tail flue, and each flue gas damper is used to adjust the flue gas flow upstream of the corresponding economizer block downstream thereof; each economizer block is provided with an economizer inlet water flow regulating valve and an economizer outlet temperature detection device, and the inlet of each economizer block is connected to the steam heater; When the boiler is in low-load operation, the method includes the following periodic adjustment process: The temperature detection value of the economizer outlet temperature detection device of each economizer block is periodically obtained, and the temperature average value of the temperature detection values ​​of all economizer outlet temperature detection devices is calculated; for the economizer block whose temperature detection value is greater than the temperature average value, the flue gas damper upstream of the economizer block is adjusted to reduce the flue gas throughput of the economizer, thereby reducing the heat absorbed by the economizer block from the flue gas, until the temperature detection value of the economizer outlet temperature detection device of the economizer block is equal to the temperature average value; for the economizer block whose temperature detection value is less than the temperature average value, the flue gas damper upstream of the economizer block is adjusted to increase the flue gas throughput of the economizer, thereby increasing the heat absorbed by the economizer block from the flue gas, until the temperature detection value of the economizer outlet temperature detection device of the economizer block is equal to the temperature average value; when the opening of the flue gas damper upstream of the economizer block has reached the maximum, the flue gas damper upstream of the economizer block is not adjusted.

9. A method for increasing the temperature of the SCR zone of a boiler under low load according to claim 8, characterized in that: The economizer includes four economizer blocks, which are respectively denoted as a first economizer (3), a second economizer (4), a third economizer (5) and a fourth economizer (6) along the direction from the front wall to the rear wall of the tail flue, and the flue gas dampers upstream of the first economizer (3), the second economizer (4), the third economizer (5) and the fourth economizer (6) are respectively denoted as a first flue gas damper (7), a second flue gas damper (8), a third flue gas damper (9) and a fourth flue gas damper (10); the first economizer (3) and The inlet and outlet of the second economizer (4) are both extended to the front wall side of the tail flue, the inlets of the first economizer (3) and the second economizer (4) are both connected to the first steam heater (13), and water is added through the first steam heater (13); the inlet and outlet of the third economizer (5) and the fourth economizer (6) are both extended to the rear wall side of the tail flue, the inlets of the third economizer (5) and the fourth economizer (6) are both connected to the second steam heater (12), and water is added through the second steam heater (12); When the boiler is in low-load operation, the method includes the following steps: When water is added to the first economizer (3) and the second economizer (4) through the first steam heater (13), the water volume of the first economizer (3) and the water volume of the second economizer (4) are respectively adjusted through the economizer inlet water volume regulating valves corresponding to the first economizer (3) and the second economizer (4); When water is added to the third economizer (5) and the fourth economizer (6) through the second steam heater (12), the water volume of the third economizer (5) and the water volume of the fourth economizer (6) are respectively adjusted through the economizer inlet water volume regulating valves corresponding to the third economizer (5) and the fourth economizer (6).

10. A method for increasing the temperature of the SCR zone of a boiler under low load according to claim 9, characterized in that: A first economizer inlet connecting valve (29) is connected between the inlets of the first economizer (3) and the second economizer (4), and the connection point between the first economizer inlet connecting valve (29) and the inlets of the first economizer (3) and the second economizer (4) is located downstream of the economizer inlet water flow regulating valve at the inlets of the first economizer (3) and the second economizer (4); a second economizer inlet connecting valve (30) is connected between the inlets of the third economizer (5) and the fourth economizer (6), and the second economizer inlet connecting valve (31) is connected to the inlet of the first economizer (3) and the second economizer (4). The connection points between the through valve (30) and the inlets of the third economizer (5) and the fourth economizer (6) are located downstream of the economizer inlet water flow regulating valves at the inlets of the third economizer (5) and the fourth economizer (6); the outlets of the first economizer (3), the second economizer (4), the third economizer (5) and the fourth economizer (6) are respectively provided with the first economizer outlet water flow regulating valve, the second economizer outlet water flow regulating valve, the third economizer outlet water flow regulating valve and the fourth economizer outlet water flow regulating valve; When the boiler is in normal load operation, the method includes: Close all steam heater isolation valves, open all steam heater bypass isolation valves, and adjust the economizer inlet water flow regulating valve to the maximum opening; When water is added to the first economizer (3) and the second economizer (4), water in the steam heater bypass corresponding to the first steam heater (13) flows into the first economizer (3) and the second economizer (4) respectively through the first economizer inlet connecting valve (29), and the following periodic adjustment process is performed: the temperature detection values ​​of the economizer outlet temperature detection devices of the first economizer (3) and the second economizer (4) are periodically obtained, and the temperature average value of the temperature detection values ​​of all economizer outlet temperature detection devices is calculated. For economizer blocks whose temperature detection values ​​are greater than the temperature average value, the flue gas damper upstream of the economizer block is adjusted to reduce the flue gas flow rate of the economizer, and at the same time, the opening of the economizer outlet water flow regulating valve at the outlet of the economizer block is increased, thereby reducing the amount of flue gas from the economizer block. The heat absorbed by the economizer block and the high-temperature water heated in the economizer block are accelerated to flow out until the temperature detection value of the economizer outlet temperature detection device of the economizer block is equal to the temperature average value; for the economizer block whose temperature detection value is less than the temperature average value, the flue gas damper upstream of the economizer block is adjusted to increase the flue gas flow rate of the economizer, and at the same time, the opening of the economizer outlet water flow regulating valve at the economizer block outlet is reduced, thereby increasing the heat absorbed by the economizer block from the flue gas and accelerating the increase of the water temperature at the economizer block outlet until the temperature detection value of the economizer outlet temperature detection device of the economizer block is equal to the temperature average value. When the opening of the flue gas damper upstream of the economizer block has reached the maximum, the flue gas damper upstream of the economizer block is not adjusted; When water is added to the third economizer (5) and the fourth economizer (6), water in the steam heater bypass corresponding to the second steam heater (12) flows into the third economizer (5) and the fourth economizer (6) respectively through the second economizer inlet connecting valve (30), and the following periodic adjustment process is performed: the temperature detection values ​​of the economizer outlet temperature detection devices of the third economizer (5) and the fourth economizer (6) are periodically obtained, and the temperature average value of the temperature detection values ​​of all economizer outlet temperature detection devices is calculated. For economizer blocks with temperature detection values ​​greater than the temperature average value, the flue gas damper upstream of the economizer block is adjusted to reduce the flue gas flow rate of the economizer, and at the same time, the opening of the economizer outlet water flow regulating valve at the outlet of the economizer block is increased, thereby reducing the amount of flue gas from the economizer block. The heat absorbed by the economizer block and the high-temperature water heated in the economizer block are accelerated to flow out until the temperature detection value of the economizer outlet temperature detection device of the economizer block is equal to the temperature average value; for the economizer block whose temperature detection value is less than the temperature average value, the flue gas damper upstream of the economizer block is adjusted to increase the flue gas throughput of the economizer, and at the same time, the opening of the economizer outlet water flow regulating valve at the economizer block outlet is reduced, thereby increasing the heat absorbed by the economizer block from the flue gas and accelerating the increase in the water temperature at the economizer block outlet until the temperature detection value of the economizer outlet temperature detection device of the economizer block is equal to the temperature average value. When the opening of the flue gas damper upstream of the economizer block has reached the maximum, the flue gas damper upstream of the economizer block is not adjusted.

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