Bypass flue heating system and method for increasing SCR inlet smoke temperature

Abstract

The invention belongs to the field of thermal power plant boilers, and discloses a bypass flue heating system and method for increasing the SCR inlet smoke temperature. A bypass flue is arranged, one end of the bypass flue is communicated with an outlet flue of a coal economizer, the other end of the bypass flue is communicated with a tail flue, and a steam heater is arranged in the bypass flue; a steam inlet channel of the steam heater is connected with the high-temperature reheater, a steam heater inlet steam isolating valve and a steam heater inlet steam adjusting valve are sequentially arranged on the steam inlet channel of the steam heater in the steam flowing direction, and a steam outlet channel of the steam heater is connected with a steam turbine middle row. A steam outlet channel of the steam heater is provided with a steam heater outlet steam isolating valve; a flue gas primary baffle and a steam heater flue gas secondary baffle are sequentially arranged on the upstream of the steam heater in the bypass flue in the flue gas flowing direction; an outlet of the tail flue is communicated with a flue gas inlet of the SCR denitration device; and an SCR inlet flue temperature detection device is arranged on the inlet side of the SCR denitration device.

Description

Technical Field

[0001] The invention belongs to the field of thermal power plant boilers, and in particular relates to a bypass flue heating system and method for increasing the SCR inlet flue gas temperature. Background Art

[0002] With the rapid growth of renewable clean energy power generation, the annual utilization time of coal-fired units has been reduced year by year. Therefore, variable load operation and long-term operation in the low-load range of large coal-fired thermal power units have become the norm. However, when the coal-fired units are running at low load, the inlet flue gas temperature of the selective catalytic reduction (SCR) system often does not meet the operating requirements. Therefore, when the unit is running at low load, it is necessary to increase the inlet flue gas temperature of the SCR to ensure the catalyst reaction temperature, achieve stable output, and achieve clean emissions.

[0003] SCR denitrification generally uses medium and high temperature catalysts, and the designed operating temperature range is 320-420℃. When the power plant operating load is less than 50%, the flue gas temperature is usually lower than 320℃. When running at low load, the SCR catalyst cannot fully react, resulting in a decrease in denitrification efficiency and a risk of over-emission. At the same time, the decrease in flue gas temperature will cause SO 2 Transformed into SO 3 , SO 3 There is a risk of condensation and deposition of ammonium sulfate salts. 3 Will be with SO 3 The reaction generates ammonium bisulfate. When the temperature is low, ammonium bisulfate will be deposited on the surface of the catalyst and the air preheater, causing problems such as catalyst blockage and increased air preheater resistance. The tail heating method is a method to increase the temperature of the SCR zone, but because the heater is arranged in the tail flue, the flue gas circulation resistance is increased, which seriously affects the boiler efficiency. Therefore, it is very meaningful to study a method to increase the temperature of the SCR zone with low modification of the boiler body and little effect on the flue gas circulation resistance. Summary of the invention

[0004] In order to solve the problems existing in the prior art, the purpose of the present invention is to provide a bypass flue heating system and method for increasing the SCR inlet smoke temperature. The present invention heats the high-temperature flue gas by bypass, installs a steam heater in the bypass flue, and uses high-temperature reheated steam to heat the low-temperature flue gas to increase the flue gas temperature, thereby avoiding the problem of increased flue gas resistance after installing a heater in the tail flue.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is as follows: A bypass flue heating system for increasing the inlet flue gas temperature of an SCR comprises a boiler system, an SCR degassing device, a bypass flue and a steam turbine, wherein one end of the bypass flue is connected to the outlet flue of the economizer of the boiler system, and the other end of the bypass flue is connected to the tail flue of the boiler system. A steam heater is arranged in the bypass flue, and a steam inlet passage of the steam heater is connected to a high-temperature reheater of the boiler system. A steam heater inlet steam isolation valve and a steam heater inlet steam regulating valve are arranged in sequence on the steam inlet passage of the steam heater along the steam flow direction. The steam outlet passage of the steam heater is connected to the middle row of the steam turbine, and a steam heater outlet steam isolation valve is arranged on the steam outlet passage of the steam heater; a flue gas primary baffle and a steam heater flue gas secondary baffle are arranged in sequence on the upstream of the steam heater along the flue gas flow direction in the bypass flue; the outlet of the tail flue is connected to the flue gas inlet of the SCR degassing device; an SCR inlet flue temperature detection device is arranged on the inlet side of the SCR degassing device.

[0006] Preferably, a steam heater downstream temperature detection device is provided in the bypass flue downstream of the steam heater.

[0007] Preferably, a steam heater outlet steam temperature detection device is provided on the steam outlet channel of the steam heater at the outlet side of the steam heater.

[0008] Preferably, the bypass flue comprises a bypass flue inlet flue and a plurality of bypass flue outlet flues, wherein one end of the bypass flue inlet flue is connected to the outlet flue of the economizer of the boiler system, the other end of the bypass flue inlet flue is connected to one end of all bypass flue outlet flues, and the other end of the bypass flue outlet is connected to the tail flue; For each bypass flue gas outlet duct, a steam heater is provided in the bypass flue gas outlet duct, and a steam heater flue gas secondary baffle is provided upstream of the steam heater.

[0009] Preferably, the primary flue gas baffle is arranged in the air inlet flue of the bypass flue.

[0010] Preferably, the bypass flue air inlet flue is arranged horizontally, and the bypass flue air outlet flue is arranged vertically.

[0011] Preferably, the steam outlet of the high temperature reheater is also connected to the steam inlet of the intermediate pressure cylinder of the steam turbine.

[0012] Preferably, a guide plate No. 1 is provided at the outlet of the bypass flue, and a guide plate No. 2 is provided at the downstream side of the outlet of the bypass flue in the tail flue, and the guide direction of the guide plate No. 1 and the guide direction of the guide plate No. 2 form an acute angle.

[0013] Preferably, a guide plate No. 3 is provided at the corner where the tail flue is connected to the SCR inlet flue of the SCR de-binding device, a guide plate No. 4 is provided at the corner of the SCR inlet flue, and a guide plate No. 5 is provided at the inlet of the SCR de-binding device; The angles of guide plate No. 3 and guide plate No. 4 are toward the center of the boiler, the angle between guide plate No. 3 and the center of the boiler is an acute angle, the angle between guide plate No. 4 and the center of the boiler is an obtuse angle, and guide plate No. 5 is toward the SCR catalyst, with an acute angle.

[0014] The present invention further provides a bypass flue heating method for increasing the flue gas temperature at an SCR inlet, the method adopting the bypass flue heating system for increasing the flue gas temperature at an SCR inlet as described above, the method comprising: When the boiler is in low-load operation, the flue gas temperature at the inlet side of the SCR de-binding device is detected by the SCR inlet flue temperature detection device. When the detection value of the SCR inlet flue temperature detection device is less than the first preset range, the steam heater inlet steam isolation valve and the steam heater outlet steam isolation valve are opened, and the steam heater inlet steam regulating valve is opened to the maximum, so that the temperature of the hot side of the steam heater is increased, and the flue gas in the economizer outlet flue flows into the bypass flue and exchanges heat with the steam heater. The flue gas heated by the steam heater enters the tail flue and mixes with the tail flue in the tail flue, so that the tail flue gas temperature is increased until the detection value of the SCR inlet flue temperature detection device is increased to the first preset range; Afterwards, when the SCR inlet flue gas temperature is lower than the first pre-range, the secondary damper of the steam heater flue gas is opened wide and the steam regulating valve at the steam heater inlet is opened wide to maintain the SCR deducting flue gas temperature within the first pre-range; Wherein, when the detection value of the SCR inlet flue gas temperature detection device is within the first predetermined range, the SCR denitration device can be maintained in a normal operating state; When the boiler is operating at normal load, close the primary flue gas damper, the steam isolating valve at the steam heater inlet, and the regulating valve at the steam heater inlet. After the steam circulation is completed, close the steam isolating valve at the steam heater outlet. After the flue gas circulation is completed, close the secondary flue gas damper of the steam heater.

[0015] The present invention has the following beneficial effects: In the bypass flue heating system for increasing the inlet flue temperature of the SCR of the present invention, a bypass flue is provided, a steam heater is provided in the bypass flue, and the steam inlet channel of the steam heater is connected to the high-temperature reheater of the boiler system, so the flue gas of the tail flue is heated by introducing the high-temperature reheater steam. In the present invention, no heating device is provided in the tail flue of the boiler system to heat the high-temperature flue gas used for the operation of the SCR de-binding device, and the inlet flue gas temperature of the SCR de-binding device can be effectively maintained to meet the requirements. It can be seen that the present invention effectively avoids the problems of providing a heater in the tail flue, affecting the flue gas flow field, and increasing the flue gas resistance in the prior art. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 A schematic diagram of the structure of a bypass flue heating system for increasing the SCR inlet smoke temperature according to the present invention; Figure 2 This is a layout diagram of a bypass flue heater in an embodiment of the present invention; Figure 3 Schematic diagram of the guide plates in the bypass flue and the tail flue in the embodiment of the present invention; Figure 4 It is a schematic diagram of the logical structure (PID) in the bypass flue and the tail flue in an embodiment of the present invention.

[0017] Among them: 1 is high-temperature reheater, 2 is superheater, 3 is low-temperature reheater, 4 is economizer, 5 is No. 1 steam heater, 6 is No. 2 steam heater, 7 is turbine intermediate pressure cylinder, 8 is turbine low pressure cylinder, 9 is high-temperature reheat steam, 10 is low-temperature cooling steam, 11 is flue gas primary baffle, 12 is No. 1 steam heater flue gas secondary baffle, 13 is SCR de-binding device, 22 is No. 2 steam heater flue gas secondary baffle, 51 is bypass flue, 52 is bypass flue inlet flue, 53 is bypass flue outlet flue, 54 is tail flue, 55 is SCR inlet flue, 110 is No. 1 steam heater downstream temperature detection device, 120 is No. 2 steam heater downstream temperature detection device 1 is the steam isolating valve at the inlet of steam heater No. 1, 121 is the steam isolating valve at the inlet of steam heater No. 2, 112 is the steam regulating valve at the inlet of steam heater No. 1, 122 is the steam regulating valve at the inlet of steam heater No. 2, 113 is the steam temperature detecting device at the outlet of steam heater No. 1, 123 is the steam temperature detecting device at the outlet of steam heater No. 2, 114 is the steam isolating valve at the outlet of steam heater No. 1, 124 is the steam isolating valve at the outlet of steam heater No. 2, 130 is the SCR inlet flue temperature detecting device, 210 is the guide plate No. 1, 220 is the guide plate No. 2, 230 is the guide plate No. 3, 240 is the guide plate No. 4, and 250 is the guide plate No. 5. DETAILED DESCRIPTION

[0018] 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.

[0019] In order to achieve a tail flue temperature ≥ 315°C and ensure that the flue gas temperature before entering the SCR inlet reaches a temperature suitable for the catalyst reaction, the present invention provides a bypass flue heating system and method for increasing the SCR inlet flue temperature, which can effectively maintain the tail flue temperature and use reasonable control and adjustment to reduce the impact of the bypass flue on the tail flue and reduce the impact on the subsequent operation of the boiler and turbine.

[0020] See also Figure 1-Figure 4 The bypass flue heating system for improving the inlet flue gas temperature of SCR in this embodiment comprises a boiler system, an SCR deactivation device 13, a bypass flue 51 and a steam turbine. One end of the bypass flue 51 is connected to the outlet flue of the economizer 4 of the boiler system, and the other end of the bypass flue 51 is connected to the tail flue 54 of the boiler system. A steam heater is provided in the bypass flue 51. The steam inlet passage of the steam heater is connected to the high-temperature reheater 1 of the boiler system. A steam heater inlet steam isolation valve and a steam heater inlet steam regulating valve are provided in sequence on the steam inlet passage of the steam heater along the steam flow direction. The steam outlet passage of the steam heater is connected to the middle row of the steam turbine, and a steam heater outlet steam isolation valve is provided on the steam outlet passage of the steam heater. A flue gas primary baffle 11 and a steam heater flue gas secondary baffle are provided in sequence in the bypass flue 51 upstream of the steam heater along the flue gas flow direction. The outlet of the tail flue 54 is connected to the flue gas inlet of the SCR deactivation device 13. An SCR inlet flue temperature detection device 130 is provided on the inlet side of the SCR deactivation device 13.

[0021] The bypass flue heating method for increasing the SCR inlet smoke temperature by using the bypass flue heating system of the above embodiment includes: When the boiler is in low-load operation, the flue gas temperature at the inlet side of the SCR de-binding device 13 is detected by the SCR inlet flue temperature detection device 130. When the detection value of the SCR inlet flue temperature detection device 130 is less than the first preset range, the steam heater inlet steam isolation valve and the steam heater outlet steam isolation valve are opened, and the steam heater inlet steam regulating valve is opened to the maximum, so that the temperature of the hot side of the steam heater is increased, and the flue gas in the economizer 4 outlet flue flows into the bypass flue 51 and exchanges heat with the steam heater. The flue gas heated by the steam heater enters the tail flue 54 and mixes with the tail flue gas in the tail flue 54, so that the tail flue gas temperature is increased until the detection value of the SCR inlet flue temperature detection device 130 is increased to the first preset range; Afterwards, when the SCR inlet flue gas temperature is lower than the first pre-range, the secondary damper of the steam heater flue gas is opened wide and the steam regulating valve at the steam heater inlet is opened wide to maintain the SCR deducting flue gas temperature within the first pre-range; Wherein, when the detection value of the SCR inlet flue gas temperature detection device 130 is within the first pre-range, the SCR denitration device 13 can be maintained in a normal operating state; When the boiler is operating at normal load, close the primary flue gas damper 11, the steam isolation valve at the steam heater inlet, and the regulating valve at the steam heater inlet. After the steam circulation is completed, close the steam isolation valve at the steam heater outlet. After the flue gas circulation is completed, close the secondary flue gas damper of the steam heater.

[0022] See also Figure 1-Figure 4In this embodiment, the bypass flue 51 includes a bypass flue air inlet 51 and a plurality of bypass flue air outlet ducts 53, wherein one end of the bypass flue air inlet 51 is connected to the outlet flue of the economizer 4 of the boiler system, the other end of the bypass flue air inlet 51 is connected to one end of all bypass flue air outlet ducts 53, and the other end of the bypass flue air outlet duct 53 is connected to the tail flue 54. The provision of a plurality of bypass flue air outlet ducts 53 can make the heated flue gas enter the tail flue uniformly, thereby reducing the flow field resistance. For each bypass flue air outlet duct 53, a steam heater is provided in the bypass flue air outlet duct 53, and a steam heater flue gas secondary baffle is provided upstream of the steam heater. The bypass flue heating system for increasing the SCR inlet flue temperature in this embodiment is described by setting two bypass flue outlet flues 53 as an example. This embodiment specifically includes a high-temperature reheater 1, a low-temperature reheater 3, an economizer 4, a No. 1 steam heater 5, a No. 2 steam heater 6, a flue primary baffle 11, a No. 1 steam heater flue gas secondary baffle 12, a No. 2 steam heater flue gas secondary baffle 22, a No. 1 steam heater downstream temperature detection device 110, a No. 2 steam heater downstream temperature detection device 120, an SCR inlet flue temperature detection device 130, and a bypass flue 51. The inlet of the bypass flue inlet flue 52 is located between the economizer 4 outlet flue and the tail flue 54, and the bypass flue inlet flue 52 is the horizontal section of the bypass flue; the bypass flue outlet flue 53 is connected to the tail flue 54, and the bypass flue outlet flue 53 is the vertical section of the bypass flue. The outlet of the tail flue 54 is connected to the SCR inlet flue 55. Among them, the flue gas primary damper 11 is arranged in the bypass flue gas inlet flue 51, and the flue gas primary damper 11 is used to isolate the flue gas, and the No. 1 steam heater flue gas secondary damper 12 corresponding to the inlet side of the No. 1 steam heater 5 is used to adjust the flue gas volume on the inlet side of the No. 1 steam heater 5, and the No. 2 steam heater flue gas secondary damper 22 corresponding to the inlet side of the No. 2 steam heater 6 is used to adjust the flue gas volume on the inlet side of the No. 2 steam heater 6. The No. 1 steam heater 5 and the No. 2 steam heater 6 are respectively arranged in the two bypass flue gas outlet flues 53, and the No. 1 steam heater 5 and the No. 2 steam heater 6 are both arranged vertically. In the SCR inlet flue 55, an SCR inlet flue temperature detection device 130 is arranged to detect the inlet flue gas temperature before the SCR inlet. A steam temperature detection device 113 is correspondingly provided at the steam outlet of steam heater No. 1 5, and a steam temperature detection device 123 is correspondingly provided at the steam outlet of steam heater No. 2 6. The steam temperature detection device 113 is provided at the steam outlet of steam heater No. 1 and the steam temperature detection device 123 is provided at the steam outlet of steam heater No. 2. The steam temperature detection device 113 is provided at the steam outlet of steam heater No. 1 and the steam temperature detection device 123 is provided at the steam outlet of steam heater No. 2, and are used for detecting the outlet steam temperatures of steam heater No. 1 5 and steam heater No. 2 6, respectively.A temperature detection device 110 downstream of steam heater No. 1 is provided at the downstream flue of steam heater No. 1, and a temperature detection device 120 downstream of steam heater No. 2 is provided at the downstream flue of steam heater No. 2. The temperature detection device 110 downstream of steam heater No. 1 and the temperature detection device 120 downstream of steam heater No. 2 are used to detect the flue gas temperature downstream of steam heater No. 1 and steam heater No. 2, respectively. Steam heater No. 1 and steam heater No. 2 are placed in parallel, with the same height and the same flow area. Steam heater No. 1 and steam heater No. 2 have steam inlet channels and steam outlet channels. Their steam inlet channels are connected to the high-temperature reheater, and their steam outlet channels are connected to the middle row of the steam turbine. The inlet steam of steam heater No. 1 and steam heater No. 2 is the high-temperature superheated steam at the outlet of the high-temperature reheater, and the outlet steam after heat exchange in the heater enters the middle row of the steam turbine. The reheated steam at the outlet of the high-temperature reheater 1 is divided into two paths, one path entering the No. 1 steam heater 5 and the other path entering the No. 2 steam heater 6. The arrangement of the No. 1 steam heater 5 and the No. 2 steam heater 6 can heat the tail flue gas more effectively and prevent uneven flow field of the tail flue gas. The No. 1 steam heater inlet steam regulating valve 112 and the No. 2 steam heater inlet steam regulating valve 122 are respectively arranged at the inlets of the No. 1 steam heater and the No. 2 steam heater.

[0023] The bypass flue heating method for increasing the flue gas temperature at the SCR inlet by using the bypass flue heating system of the above embodiment includes: when the boiler is in low load operation, if the detection value of the SCR inlet flue temperature detection device 130 is less than the first preset range, the flue gas primary damper 11, the No. 1 steam heater flue gas secondary damper 12 and the No. 2 steam heater flue gas secondary damper 22 are opened, the No. 1 steam heater inlet steam isolation valve 111, the No. 2 steam heater inlet steam isolation valve 121, the No. 1 steam heater outlet steam isolation valve 114, the No. 2 steam heater outlet steam isolation valve 125 are opened, and the No. 1 steam heater inlet steam isolation valve 116 is opened. The outlet steam isolation valve 124, the No. 1 steam heater inlet steam regulating valve 112, and the No. 2 steam heater inlet steam regulating valve 122 are opened, and the temperature of the flue gas in the bypass flue is increased by the No. 1 steam heater 5 and the No. 2 steam heater 6, so that when the flue gas in the bypass flue is mixed with the flue gas in the tail flue 54, the flue gas temperature of the SCR inlet flue is increased, and the detection value of the SCR inlet flue temperature detection device 130 is increased to the first preset range, and the detection value of the SCR inlet flue temperature detection device 130 is maintained within the first preset range. The range is specifically comprised of: when the detection value of the SCR inlet smoke temperature monitoring device 130 exceeds the first preset range, the secondary damper of the steam heater smoke (i.e., the secondary damper 12 of the No. 1 steam heater smoke and / or the secondary damper 22 of the No. 2 steam heater smoke) is closed to reduce the effect of the bypass flue smoke on the flue gas temperature of the tail flue, and the steam regulating valve of the steam heater inlet (i.e., the steam regulating valve 112 of the No. 1 steam heater inlet and / or the steam regulating valve 122 of the No. 2 steam heater inlet) is closed to reduce the smoke temperature until The detection value of the SCR inlet flue temperature detection device 130 is reduced to the first preset range. When the detection value of the SCR inlet flue temperature detection device 130 is lower than the first preset range, the steam input is increased by increasing the steam regulating valve at the steam heater inlet (i.e., the No. 1 steam heater inlet steam regulating valve 112 and / or the No. 2 steam heater inlet steam regulating valve 122), thereby increasing the heat exchange capacity of the steam heater in the bypass flue, thereby promoting the increase of the flue gas temperature of the tail flue, until the detection value of the SCR inlet flue temperature detection device 130 is increased to the first preset range. When the detection value of the SCR inlet flue temperature detection device 130 is within the first preset range, the SCR de-binding device 13 can be maintained in a normal state. Generally, when the detection value of the SCR inlet flue temperature detection device 130 is between 315°C and 400°C, the SCR de-binding device 13 can be maintained in a normal operating state.

[0024] In this embodiment, two bypass flue gas outlet flues 53 are set, and the corresponding steam heaters include two parts (i.e., steam heater No. 1 5 and steam heater No. 2 6). Steam heater No. 1 5 and steam heater No. 2 6 are arranged on both sides of the bypass flue gas outlet flue, respectively. A flue gas damper should be provided upstream of each steam heater, and each flue gas damper is used to adjust the flue gas flow upstream of the corresponding steam heater downstream; each steam heater corresponds to a steam heater inlet steam regulating valve and a steam heater outlet steam temperature detection device. At the same time, a temperature detection device should be provided downstream of each steam heater at the downstream of the bypass flue gas outlet flue and below the steam heater. In this embodiment, considering that when one steam heater is used, the flexibility of the steam heater adjustment is limited because the tail flue gas temperature is constantly changing, and the steam enters the turbine middle row after passing through the steam heater. The steam temperature entering the turbine middle row is difficult to control and is unstable, which affects the subsequent operation of the boiler. Therefore, in this embodiment, steam heaters (i.e., steam heater No. 1 5 and steam heater No. 2 6) are provided in both bypass flue outlet flues 53. This can increase the flexibility of regulation compared to only one steam heater. Since the flue gas temperature distribution in the bypass flue is also uneven, compared to only one steam heater, adding a steam heater can separately regulate this uneven phenomenon, reducing the impact and influence of the uneven flue gas in the bypass flue on the flue gas in the tail flue. In addition, since there are two steam heaters, they can be regulated separately, and the output is equivalent, which can relatively reduce the failure rate. At the same time, the steam temperature at the outlet of the steam heater can be kept within a reasonable range to avoid a significant impact on the operation of the steam turbine. At the same time, for the two steam heaters, a flue gas damper (i.e., a flue gas primary damper 11) is provided upstream, and the flue gas damper adjustment (i.e., a flue gas secondary damper 12 of the No. 1 steam heater and a flue gas secondary damper 22 of the No. 2 steam heater) is more flexible and can efficiently increase the flue gas temperature.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 adjustment process: periodically obtaining the temperature detection value of the downstream flue temperature detection device of each steam heater, and calculating the temperature average value of the temperature detection values ​​of the downstream temperature detection devices of all steam heaters; for steam heaters whose temperature detection values ​​are greater than the temperature average value (indicating that the output of the steam heater is large), adjusting the secondary flue gas damper of the steam heater upstream of the steam heater to reduce the output of the steam heater, thereby reducing the flue gas temperature downstream of the steam heater until the temperature detection value of the outlet temperature detection device of the steam heater is equal to the temperature average value; for steam heaters whose temperature detection values ​​are less than the temperature average value, adjusting the secondary flue gas damper of the steam heater upstream of the steam heater to increase the output of the steam heater and increase the downstream flue gas temperature until the temperature detection value of the downstream temperature detection device of the steam heater is equal to the temperature average value; when the flue gas damper upstream of the steam heater has been opened to the maximum, the flue gas damper on the steam heater is not adjusted.

[0025] In this embodiment, the steam outlets of the steam heaters are all discharged to the middle row of the steam turbine, but since the steam outlet temperatures of the two steam heaters may be different, this may cause problems in the operation of the steam turbine. Therefore, temperature detection devices are respectively provided at the steam outlets of the steam heaters, and steam regulating valves and steam isolation valves are provided on the steam pipelines of the steam heaters. A steam isolation valve is provided downstream, wherein the steam isolation valve is used to isolate the steam, and the steam regulating valve is used to adjust the steam volume. Since the steam temperature at the outlet of the steam heater is not necessarily balanced, and when only one steam heater is provided, the steam outlet is even more uncontrollable, parallel steam heaters should be provided in several ways for flexible adjustment. 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 adjustment process: periodically obtaining the temperature detection value of the steam outlet temperature detection device of each steam heater, and calculating the temperature average value of the temperature detection values ​​of the steam outlet temperature detection devices of all steam heaters; for steam heaters whose temperature detection value is greater than the temperature average value (indicating that the output of the steam heater is small), fine-tuning the steam regulating valve at the steam inlet of the steam heater, and slowly reducing the steam input until the temperature detection value of the steam outlet temperature detection device is equal to the temperature average value; similarly, for steam heaters whose temperature detection value is less than the temperature average value (indicating that the output of the steam heater is large), fine-tuning the steam regulating valve at the steam inlet of the steam heater, and slowly increasing the steam input until the temperature detection value of the steam outlet temperature detection device is equal to the temperature average value.

[0026] In this embodiment, in order to avoid ash accumulation, the No. 1 steam heater and the No. 2 steam heater are placed vertically to minimize the horizontal section. When the SCR inlet temperature is low, the flue gas bypassed by the tail flue is heated by steam, mixed with the flue gas of the tail flue, and enters the SCR desulfurization device. The inlet steam of the No. 1 steam heater and the No. 2 steam heater are both from the outlet steam of the high-temperature reheater, and the outlet steam is returned to the steam turbine. There are steam heaters and regulating valves at the steam inlets of the No. 1 steam heater and the No. 2 steam heater to control the steam flow and avoid wasting steam.

[0027] In this embodiment, steam heater No. 1 and steam heater No. 2 are placed in parallel in the bypass flue gas outlet flue and arranged vertically. The steam at the inlet of the steam pipeline of steam heater No. 1 and steam heater No. 2 is high-temperature reheated steam at the outlet of the high-temperature reheater, and the outlets enter the middle row of the steam turbine. The inlet steam regulating valve of steam heater No. 1, the inlet steam isolation valve of steam heater No. 1, the inlet steam regulating valve of steam heater No. 2, and the inlet steam isolation valve of steam heater No. 2 are arranged at the inlet of the steam pipeline respectively, and the outlet steam isolation valve of steam heater No. 1 and the outlet steam isolation valve of steam heater No. 2 are arranged at the outlet of the steam pipeline respectively. The flue gas volume in the bypass flue is regulated by the secondary flue gas baffle of steam heater No. 1 and the secondary flue gas baffle of steam heater No. 2, which can quickly adjust the problem of uneven flue gas in the bypass flue, and the arrangement of the two steam heaters can quickly adjust the flue gas temperature in the bypass flue and increase flexibility. The steam amount in the steam heater can be regulated by the steam regulating valve at the inlet of the No. 1 steam heater and the steam regulating valve at the inlet of the No. 2 steam heater, which can improve the problem of uncontrollable outlet temperature of a single steam heater, improve the operating environment of the steam turbine, and facilitate safe operation of the boiler. 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: Open the primary damper of the bypass flue, open the secondary damper of the flue gas of steam heater No. 1 and steam heater No. 2 to the maximum, open the steam isolation valve at the inlet of steam heater No. 1, steam isolation valve at the inlet of steam heater No. 2, steam isolation valve at the outlet of steam heater No. 1, and steam isolation valve at the outlet of steam heater No. 2, open the steam regulating valve at the inlet of steam heater No. 1 and steam regulating valve at the inlet of steam heater No. 2 to the maximum, and put the two steam heaters into maximum output, so as to quickly increase the temperature before the SCR inlet to the preset range in a short time. When the temperature before the SCR inlet enters the preset range, but the unit is still running at low load, the steam heater needs to continue to be put into operation to keep the temperature before the SCR inlet stable, so make the following adjustments.

[0028] The specific adjustment process is as follows: periodically obtain the temperature detection values ​​of the temperature detection devices downstream of steam heater No. 1 and steam heater No. 2, and calculate the average value of the two temperature detection values. For steam heaters whose temperature detection values ​​are greater than the temperature average value (such as steam heater No. 1), adjust the flue gas secondary baffle upstream of the steam heater (such as the flue gas secondary baffle of steam heater No. 1) to reduce the output of the steam heater, thereby reducing the flue gas temperature downstream of the steam heater until the temperature detection value of the outlet temperature detection device of the steam heater is equal to the temperature average value; for steam heaters whose temperature detection values ​​are less than the temperature average value (such as steam heater No. 1), adjust the flue gas damper upstream of the steam heater (such as the flue gas secondary baffle of steam heater No. 1) to increase the output of the steam heater and increase the downstream flue gas temperature until the temperature detection value of the temperature detection device downstream of the steam heater is equal to the temperature average value. When the flue gas damper upstream of the steam heater has been opened to the maximum, the flue gas damper on the steam heater is not adjusted.

[0029] At the same time, since the steam regulating valve in front of the steam heater is in a fully open state at the beginning, the output will be redundant, so it is necessary to adjust the steam input in time to avoid steam waste and affect subsequent operations (such as the situation where the temperature in the SCR area is too high and the exhaust steam temperature entering the turbine after cooling is unstable). Therefore, the temperature detection values ​​of the steam outlet temperature detection devices of steam heater No. 1 and steam heater No. 2 are periodically obtained, and the temperature average value of the temperature detection values ​​of the steam outlet temperature detection devices of the two steam heaters is calculated. For steam heaters whose temperature detection values ​​are greater than the temperature average value (such as steam heater No. 1), the steam regulating valve at the steam inlet of this steam heater (such as the steam regulating valve at the inlet of steam heater No. 1) is fine-tuned to slowly reduce the steam input until the temperature detection value of the steam outlet temperature detection device is equal to the temperature average value; similarly, for steam heaters whose temperature detection values ​​are less than the temperature average value (such as steam heater No. 1), the steam regulating valve at the steam inlet of this steam heater (such as the steam regulating valve at the inlet of steam heater No. 1) is fine-tuned to slowly increase the steam input until the temperature detection value of the steam outlet temperature detection device is equal to the temperature average value. The above adjustment premise is that when the unit is running at low load, the temperature detection value of the SCR inlet flue temperature detection device is within the first preset range and this state is to be maintained.

[0030] As a preferred embodiment of the present invention, on the basis of the above embodiments, this embodiment further provides several guide plates, specifically, a guide plate No. 1 210 is provided at the outlet of the bypass flue 51, a guide plate No. 2 220 is provided at the downstream side of the outlet of the bypass flue 51 in the tail flue 54, a guide plate No. 3 230 is provided at the corner where the tail flue 54 is connected to the SCR inlet flue of the SCR de-binding device 13, a guide plate No. 4 240 is provided at the corner of the SCR inlet flue, and a guide plate No. 5 250 is provided at the inlet of the SCR de-binding device 13. Since the temperature of the flue gas in the bypass flue is relatively high after being heated, there may be an uneven mixing problem when it is mixed with the flue gas in the tail flue, so the guide plate No. 1 210 and the guide plate No. 2 220 are added, and the guide direction of the guide plate No. 1 210 and the guide direction of the guide plate No. 2 220 are at an acute angle, so that the flue gas can be evenly mixed in the tail flue. In addition, in order to ensure the smooth circulation of flue gas, guide plate No. 3 230, guide plate No. 4 240 and guide plate No. 5 250 are added. Guide plate No. 3 230, guide plate No. 4 240 and guide plate No. 5 250 are all arc-shaped guide plates. Guide plate No. 3 230 and guide plate No. 4 240 are angled toward the center of the boiler. The guide angles of guide plate No. 3 230 and guide plate No. 4 240 are obtuse. Guide plate No. 5 250 is directed toward the SCR catalyst, and the guide angle of guide plate No. 5 250 is acute. This arrangement can make the flue gas more evenly mixed during the circulation process, avoiding the problem of uneven flow field in the SCR area.

[0031] According to the above analysis, the bypass flue heating system and method for increasing the SCR inlet flue temperature provided by the present invention, by setting up a bypass flue, introduces high-temperature reheater steam to heat the flue gas in the tail flue, on the one hand, avoids setting a heater in the tail flue, affecting the flue gas flow field and increasing the flue gas resistance, and secondly, by setting a guide plate, the flue gas flow velocity in the bypass flue is slowed down, and the direction is partially offset with the flue gas in the tail flue, so that the high-temperature flue gas and the low-temperature flue gas are evenly mixed, on the other hand, through logical control, the temperature detection data is periodically acquired and adjusted, so that the final SCR zone inlet temperature can be controlled to be higher than the SCR deoxidation catalyst reaction temperature through appropriate valve opening and baffle opening, and through reasonable temperature detection system adjustment, the impact of the additional bypass flue on the flue gas temperature distribution in the tail flue and the influence of the steam after the steam heater on the operation of the turbine are reduced.

[0032] 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 bypass flue heating system for increasing the SCR inlet smoke temperature, characterized in that: The invention comprises a boiler system, an SCR deoxidation device (13), a bypass flue (51) and a steam turbine, wherein one end of the bypass flue (51) is connected to the outlet flue of the economizer (4) of the boiler system, and the other end of the bypass flue (51) is connected to the tail flue (54) of the boiler system. A steam heater is provided in the bypass flue (51), and a steam inlet passage of the steam heater is connected to a high-temperature reheater (1) of the boiler system. A steam heater inlet steam isolation valve and a steam heater inlet steam isolation valve are provided in sequence on the steam inlet passage of the steam heater along the steam flow direction. An inlet steam regulating valve, a steam outlet passage of the steam heater is connected to the middle row of the steam turbine, and a steam heater outlet steam isolation valve is provided on the steam outlet passage of the steam heater; a flue gas primary baffle (11) and a steam heater flue gas secondary baffle are provided in sequence upstream of the steam heater along the flue gas flow direction in the bypass flue (51); the outlet of the tail flue (54) is connected to the flue gas inlet of the SCR de-binding device (13); and an SCR inlet flue temperature detection device (130) is provided on the inlet side of the SCR de-binding device (13).

2. A bypass flue heating system for increasing the SCR inlet smoke temperature according to claim 1, characterized in that: A steam heater downstream temperature detection device is provided in the bypass flue (51) downstream of the steam heater.

3. A bypass flue heating system for increasing the SCR inlet smoke temperature according to claim 1, characterized in that: A steam heater outlet steam temperature detection device is provided on the steam outlet passage of the steam heater at the outlet side of the steam heater.

4. A bypass flue heating system for increasing the SCR inlet smoke temperature according to any one of claims 1 to 3, characterized in that: The bypass flue (51) comprises a bypass flue air inlet duct (51) and a plurality of bypass flue air outlet ducts (53), wherein one end of the bypass flue air inlet duct (51) is connected to the outlet flue of the economizer (4) of the boiler system, the other end of the bypass flue air inlet duct (51) is connected to one end of all the bypass flue air outlet ducts (53), and the other end of the bypass flue air outlet duct (53) is connected to the tail flue (54); For each bypass flue gas outlet flue (53), a steam heater is provided in the bypass flue gas outlet flue (53), and a steam heater flue gas secondary baffle is provided upstream of the steam heater.

5. A bypass flue heating system for increasing the SCR inlet smoke temperature according to claim 4, characterized in that: The flue gas primary damper (11) is arranged in the bypass flue gas inlet flue (51).

6. A bypass flue heating system for increasing the SCR inlet smoke temperature according to claim 4, characterized in that: The bypass flue gas inlet flue (51) is arranged horizontally, and the bypass flue gas outlet flue (53) is arranged vertically.

7. A bypass flue heating system for increasing the SCR inlet smoke temperature according to claim 1, characterized in that: The steam outlet of the high-temperature reheater (1) is also connected to the steam inlet of the intermediate-pressure cylinder (7) of the steam turbine.

8. A bypass flue heating system for increasing the SCR inlet smoke temperature according to claim 1, characterized in that: A No. 1 guide plate (210) is provided at the outlet of the bypass flue (51), and a No. 2 guide plate (220) is provided at the downstream side of the outlet of the bypass flue (51) in the tail flue (54), wherein the guide direction of the No. 1 guide plate (210) and the guide direction of the No. 2 guide plate (220) form an acute angle.

9. A bypass flue heating system for increasing the SCR inlet smoke temperature according to claim 1, characterized in that: A No. 3 guide plate (230) is provided at the corner where the tail flue (54) is connected to the SCR inlet flue of the SCR de-pinning device (13), a No. 4 guide plate (240) is provided at the corner of the SCR inlet flue, and a No. 5 guide plate (250) is provided at the inlet of the SCR de-pinning device (13); The guide plate No. 3 (230) and the guide plate No. 4 (240) are oriented toward the center of the boiler. The angle between the guide plate No. 3 (230) and the center of the boiler is an acute angle, the angle between the guide plate No. 4 (240) and the center of the boiler is an obtuse angle, and the guide plate No. 5 (250) is oriented toward the SCR catalyst at an acute angle.

10. A bypass flue heating method for increasing the SCR inlet smoke temperature, characterized in that: The method is carried out by using a bypass flue heating system for increasing the SCR inlet smoke temperature according to any one of claims 1 to 9, and the method comprises: When the boiler is in low-load operation, the flue gas temperature at the inlet side of the SCR de-binding device (13) is detected by the SCR inlet flue temperature detection device (130). When the detection value of the SCR inlet flue temperature detection device (130) is less than a first preset range, the steam heater inlet steam isolation valve and the steam heater outlet steam isolation valve are opened, and the steam heater inlet steam regulating valve is opened to the maximum, so that the temperature of the hot side of the steam heater is increased, and the flue gas in the economizer (4) outlet flue flows into the bypass flue (51) and exchanges heat with the steam heater. The flue gas heated by the steam heater enters the tail flue (54) and mixes with the tail flue gas in the tail flue (54), so that the tail flue gas temperature is increased until the detection value of the SCR inlet flue temperature detection device (130) is increased to the first preset range; Afterwards, when the SCR inlet flue gas temperature is lower than the first pre-range, the secondary damper of the steam heater flue gas is opened wide and the steam regulating valve at the steam heater inlet is opened wide to maintain the SCR deducting flue gas temperature within the first pre-range; Wherein, when the detection value of the SCR inlet flue gas temperature detection device (130) is within the first predetermined range, the SCR denitration device (13) can be maintained in a normal operating state; When the boiler is operating at normal load, the primary flue gas damper (11), the steam isolation valve at the steam heater inlet, and the regulating valve at the steam heater inlet are closed. After the steam circulation is completed, the steam isolation valve at the steam heater outlet is closed. After the flue gas circulation is completed, the secondary flue gas damper of the steam heater is closed.

Images