Bypass flue gas channel system

Abstract

The embodiment of the invention provides a bypass flue gas channel system. The bypass flue gas channel system comprises a first air pre-heater, a second air pre-heater, a primary air fan and a secondary air fan. A hot flue gas inlet of the first air pre-heater is communicated with a high-temperature flue gas outlet of the boiler through a hot flue gas pipeline; a primary cold air inlet of the first air pre-heater is communicated with a cold air outlet of the primary fan through a cold air pipeline, and a secondary cold air inlet of the first air pre-heater is communicated with a cold air outlet of the secondary fan through a cold air pipeline; a secondary hot air outlet of the first air pre-heater is communicated with a hearth of the boiler through a pipeline; a hot flue gas inlet of the second air pre-heater is communicated with a high-temperature flue gas outlet of the boiler through a bypass flue gas pipeline; a secondary cold air inlet of the second air pre-heater is communicated with a cold air outlet of the secondary fan through a cold air pipeline; and a secondary hot air outlet of the second air pre-heater is communicated with a pipeline of a secondary hot air outlet of the first air pre-heater through a pipeline.

Description

Technical Field

[0001] The embodiments of the present disclosure belong to the technical field of boiler energy conservation and emission reduction, and specifically relate to a bypass flue gas channel system. Background Art

[0002] In the prior art, the main reasons for the increase in the exhaust gas temperature at the air preheater outlet include: first, the calorific value of the coal entering the furnace decreases, the flue gas volume increases due to the increase in moisture, and the exhaust gas enthalpy increases; second, the heat exchange elements of the air preheater are damaged and contaminated, resulting in a decrease in the heat transfer coefficient.

[0003] By increasing the capacity of the air preheater and remodeling it, its heat exchange capacity can be improved, and the excess heat of the flue gas can be given to the air side, and the heat can directly enter the furnace, which has the most direct effect of saving coal. It has been calculated that for every 1°C reduction in the exhaust gas temperature, the thermal efficiency of the boiler will increase by 0.05%, and the coal consumption for power generation will be saved by 0.15g / kw·h. The energy saving benefit is equivalent to 2~3 times that of the scheme of heating the feed water or condensate water with the waste heat of the flue gas. The air preheater can be increased in height and diameter to increase the heat exchange area. According to the actual situation of the power plant units, the heat exchange area needs to be increased by 20%~40%. This requirement can no longer be directly modified on the existing air preheater. Considering the aging of the air preheater components, the decrease in the heat exchange coefficient is also one of the reasons for the increase in the exhaust gas temperature. It is necessary to adopt a comprehensive replacement modification plan, but it is expensive.

[0004] Therefore, how to solve the above problems has become a technical problem that needs to be solved urgently by those skilled in the art. Summary of the invention

[0005] The embodiments of the present disclosure aim to solve at least one of the technical problems existing in the prior art and provide a bypass flue gas channel system.

[0006] One aspect of an embodiment of the present disclosure provides a bypass flue gas channel system, the system comprising a first air preheater, a second air preheater, a primary fan and a secondary fan; The hot flue gas inlet of the first air preheater is connected to the high-temperature flue gas outlet of the boiler through a hot flue gas pipeline; the primary cold air inlet of the first air preheater is connected to the cold air outlet of the primary fan through a cold air pipeline, and the secondary cold air inlet of the first air preheater is connected to the cold air outlet of the secondary fan through a cold air pipeline; the secondary hot air outlet of the first air preheater is connected to the furnace of the boiler through a pipeline; The hot flue gas inlet of the second air preheater is connected to the high-temperature flue gas outlet of the boiler through a bypass flue gas duct; the secondary cold air inlet of the second air preheater is connected to the cold air outlet of the secondary fan through a cold air duct; the secondary hot air outlet of the second air preheater is connected to the secondary hot air outlet of the first air preheater through a duct.

[0007] Furthermore, a hot air duct is provided between the duct of the secondary hot air outlet of the second air preheater and the air inlet of the secondary air fan.

[0008] Optionally, the first air preheater includes a rotary heat exchanger.

[0009] Optionally, the second air preheater includes a plate heat exchanger.

[0010] Furthermore, it also includes: a first flow regulating device, which is arranged in the bypass flue gas duct and is used to regulate the hot flue gas flow in the bypass flue gas duct.

[0011] Furthermore, it also includes: a first stop valve, which is arranged in the bypass flue gas duct, and the first stop valve is located downstream of the first flow regulating device.

[0012] Furthermore, it also includes: a second flow regulating device, which is arranged in the hot air duct, and the second flow regulating device is used to regulate the hot secondary air flow in the hot air duct.

[0013] Furthermore, it also includes: a second stop valve, which is arranged on the hot air duct, and the second stop valve is located downstream of the second flow regulating device.

[0014] Furthermore, it also includes: a third flow regulating device, which is arranged on the cold air duct of the secondary cold air inlet of the second air preheater.

[0015] Furthermore, it also includes: a third stop valve, which is arranged on the cold air duct of the secondary cold air inlet of the second air preheater, and the third stop valve is located upstream of the third flow regulating device.

[0016] The beneficial effects of the embodiments of the present disclosure include: In the present disclosure, part of the high-temperature flue gas is led into the bypass flue gas duct before the first air preheater, and the high-temperature flue gas enters the second air preheater through the bypass flue gas duct. The second air preheater uses the high-temperature flue gas to heat part of the cold secondary air introduced by the secondary fan, and the hot secondary air formed by heat exchange is mixed with the hot secondary air of the first air preheater to increase the terminal temperature of the hot secondary air. And by adding the bypass flue gas duct and setting the second air preheater, the heat exchange capacity and efficiency of the high-temperature flue gas can be significantly improved, and the exhaust temperature can be effectively reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 The figure is a schematic structural diagram of a bypass flue gas channel system according to an embodiment of the present disclosure.

[0018] In the figure, 1, the first air preheater; 2, the second air preheater; 3, the primary fan; 4, the secondary fan; 5, the hot smoke duct; 6, the bypass smoke duct; 7, the hot air duct; 8, the first flow regulating device; 9, the first stop valve; 10, the second flow regulating device; 11, the second stop valve; 12, the third flow regulating device; 13, the third stop valve. DETAILED DESCRIPTION

[0019] In order to enable those skilled in the art to better understand the technical solution of the present disclosure, the present disclosure is further described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0020] The following is a further detailed description of the implementation methods of the present application in conjunction with the accompanying drawings and examples. The detailed descriptions and drawings of the following examples are used to illustrate the principles of the present application, but cannot be used to limit the scope of the present application, that is, the present application is not limited to the described embodiments. In the description of the present application, it should be noted that, unless otherwise specified, the meaning of "multiple" is more than two; the orientation or position relationship indicated by the terms "upper", "lower", "left", "right", "inside", "outside", etc. is only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present application. In addition, the terms "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance. "Vertical" is not vertical in the strict sense, but within the error tolerance range. "Parallel" is not parallel in the strict sense, but within the error tolerance range.

[0021] In the description of this application, it should also be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be directly connected or indirectly connected through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to the specific circumstances.

[0022] like Figure 1 As shown, a bypass flue gas channel system includes a first air preheater 1, a second air preheater 2, a primary fan 3 and a secondary fan 4.

[0023] The hot flue gas inlet of the first air preheater 1 is connected to the high-temperature flue gas outlet of the boiler through the hot flue gas duct 5, the primary cold air inlet of the first air preheater 1 is connected to the cold air outlet of the primary fan 3 through the cold air duct, the secondary cold air inlet of the first air preheater 1 is connected to the cold air outlet of the secondary fan 4 through the cold air duct, and the secondary hot air outlet of the first air preheater 1 is connected to the furnace of the boiler through a pipeline.

[0024] The hot flue gas inlet of the second air preheater 2 is connected to the high-temperature flue gas outlet of the boiler through the bypass flue gas duct 6, the secondary cold air inlet of the second air preheater 2 is connected to the cold air outlet of the secondary fan 4 through the cold air duct, and the secondary hot air outlet of the second air preheater 2 is connected to the secondary hot air outlet of the first air preheater 1 through a duct.

[0025] It can be understood that the first air preheater 1 and the second air preheater 2 are both air preheaters.

[0026] Before the first air preheater (first air preheater 1), part of the high-temperature flue gas is drawn out and enters the second air preheater (second air preheater 2). The second air preheater heats part of the cold secondary air introduced from the outlet of the secondary blower and outputs hot secondary air. The hot secondary air is then mixed with the hot secondary air heated from the first air preheater and sent into the furnace together to participate in combustion. The flue gas after heat exchange in the second air preheater is mixed with the flue gas after heat exchange in the first air preheater and enters the downstream channel together.

[0027] In the present disclosure, part of the high-temperature flue gas is led out before the first air preheater into the bypass flue gas duct 6, and the high-temperature flue gas enters the second air preheater through the bypass flue gas duct 6. The second air preheater uses the high-temperature flue gas to heat part of the cold secondary air introduced by the secondary fan 4, and the hot secondary air formed by heat exchange is mixed with the hot secondary air of the first air preheater to increase the terminal temperature of the hot secondary air. And by adding the bypass flue gas duct 6 and setting the second air preheater, the heat exchange capacity and efficiency of the high-temperature flue gas can be significantly improved, and the exhaust temperature can be effectively reduced.

[0028] In some embodiments, a hot air duct 7 is further provided between the duct of the secondary hot air outlet of the second air preheater 2 and the air inlet of the secondary air fan 4 .

[0029] In the present disclosure, introducing hot secondary air into the air inlet of the secondary fan 4 can increase the secondary air inlet temperature of the air inlet of the secondary fan 4, enhance the adaptability of the first air preheater and the second air preheater to different types of coal, and improve the tolerance range of the air preheater to the ammonia escape rate.

[0030] In some embodiments, the first air preheater 1 includes a rotary heat exchanger.

[0031] In some embodiments, the second air preheater 2 includes a plate heat exchanger.

[0032] In some embodiments, the system further includes a first flow regulating device 8 , which is disposed in the bypass flue gas duct 6 and is used to regulate the hot flue gas flow in the bypass flue gas duct 6 .

[0033] In the present disclosure, the first flow regulating device 8 can flexibly adjust the hot flue gas flow in the bypass flue gas duct 6, so that the system can be adjusted according to actual needs and adapt to different working conditions. Through flow regulation, the operating parameters of the system can be optimized and the overall efficiency and performance can be improved.

[0034] The flow regulating device can also ensure the stability of the airflow in the bypass flue gas duct 6, reduce the impact of airflow fluctuations on the system, and improve the stability and reliability of the system. By adjusting the flow, the system can be prevented from being overloaded and the equipment can be protected from damage.

[0035] In some embodiments, the system further includes a first stop valve 9 , which is disposed in the bypass flue gas duct 6 , and the first stop valve 9 is located downstream of the first flow regulating device 8 .

[0036] In the present disclosure, the first stop valve 9 can ensure that the hot flue gas in the bypass flue gas duct 6 can only flow in one direction, prevent the flue gas from flowing back, and avoid equipment damage or system failure caused by reverse flow. By preventing backflow, downstream equipment (such as fans, heat exchangers, etc.) can be protected from the impact and damage of reverse airflow.

[0037] In some embodiments, the system further includes a second flow regulating device 10 , which is disposed in the hot air duct 7 , and is used to regulate the hot secondary air flow in the hot air duct 7 .

[0038] In the present disclosure, the second flow regulating device 10 can flexibly adjust the hot secondary air flow in the hot air duct 7, so that the system can be adjusted according to actual needs and adapt to different working conditions. Through flow regulation, the operating parameters of the system can be optimized and the overall efficiency and performance can be improved.

[0039] In some embodiments, the system further includes a second stop valve 11 , which is disposed in the hot air duct 7 , and the second stop valve 11 is located downstream of the second flow regulating device 10 .

[0040] In the present disclosure, the second stop valve 11 can ensure that the hot secondary air in the hot air duct 7 can only flow in one direction, prevent the hot secondary air from flowing back, and avoid equipment damage or system failure caused by reverse flow.

[0041] In some embodiments, the system further includes a third flow regulating device 12 , which is disposed in a cold air duct at the secondary cold air inlet of the second air preheater 2 .

[0042] In the present disclosure, the third flow regulating device 12 can flexibly adjust the cold secondary air flow in the cold air duct, so that the system can be adjusted according to actual needs and adapt to different working conditions. Through flow regulation, the operating parameters of the system can be optimized to improve overall efficiency and performance.

[0043] In some embodiments, the system further includes a third stop valve 13 , which is disposed in a cold air duct at the secondary cold air inlet of the second air preheater 2 , and the third stop valve 13 is located upstream of the third flow regulating device 12 .

[0044] In the present disclosure, the third stop valve 13 can ensure that the cold secondary air in the cold air duct can only flow in one direction, prevent the cold secondary air from flowing back, and avoid equipment damage or system failure caused by reverse flow.

[0045] In the prior art, the rotary air preheater cannot perform this work alone because the design ratio and wind temperature of the primary and secondary air meet the needs of ignition and burnout of coal powder in the furnace.

[0046] In some embodiments, under the premise of meeting the safety and explosion-proof requirements of the coal mill, by adjusting the ratio of the primary and secondary air compartments in the first air preheater, changing the heat exchange area of ​​the primary and secondary air, increasing the heat exchange capacity of the primary air, and moderately increasing the temperature of the hot primary air at the coal mill inlet, the heat exchange capacity of the flue gas is further increased.

[0047] The implementation steps of the present invention are described in detail below in conjunction with the accompanying drawings. A bypass flue gas channel system, the main contents and steps are as follows: S1: Comparative analysis of the first air preheater parameters.

[0048] Table 1 Comparison of actual operating parameters of air preheater

[0049] The power plant's designed coal calorific value is above 22,500 kJ / kg. Due to the need to reduce fuel costs, the operating coal type is significantly different from the designed coal type, and the average coal calorific value is around 18,000 kJ / kg. Under rated load, the coal consumption is increased from 355 t / h to 435 t / h, and the exhaust gas temperature at the air preheater outlet is significantly higher than the design value and also higher than the level of similar units.

[0050] Refer to the hot end difference of the air preheater of the same type of units in the table, and control the air preheater inlet flue gas temperature and the hot primary / secondary air temperature difference at 20℃ and 30℃. In view of the actual situation of the current operation of the air preheater, set the target as follows: increase the primary and secondary air temperatures by 10℃~15℃ respectively, and reduce the exhaust gas temperature by 7℃~10℃.

[0051] S2: Setting of boundary conditions for the second air preheater.

[0052] Table 2 Comparison of air preheater sizes

[0053] From the data in the table, it can be seen that in order to achieve the heat exchange effect of the same type of unit, the single-side preheater needs to increase the area by at least 21500m2 , the total weight of the heat exchange element increases by more than 60t. Since the heat exchange coefficient and element compactness of the heat exchange element of the second air preheater are lower than those of the rotary preheater, the required heat exchange area and total weight need to be determined according to the form of the heat exchange element.

[0054] S3: Determine the type of the second air preheater.

[0055] In order to solve the problem of high air leakage rate of rotary air preheaters, some power station boilers have transformed rotary air preheaters into tubular air preheaters using certain enhanced heat exchange technologies, or adopted a two-stage arrangement of heat pipe air preheaters. A two-stage arrangement scheme with more threaded pipes and heat pipes is used. Due to the limited enhanced heat exchange capacity of threaded pipes, it is difficult to solve the shortcomings of tubular air preheaters, such as large size and difficult arrangement.

[0056] Due to the high heat transfer coefficient, compact structure and easy disassembly and cleaning, the plate air preheater has the advantages of corrosion resistance, no dust accumulation and long service life compared to the tube air preheater in actual application, and is safe and stable during operation. Using the same Reynolds number design, the heat transfer coefficient of the plate air preheater is about 2 times higher than that of the tube air preheater, and the volume is half that of the tube air preheater. The flue gas side resistance of the plate air preheater is 2 / 5~3 / 5 smaller than that of the tube air preheater with the same flow channel length, and the air side resistance is equivalent to that of the tube air preheater with the same flow channel length. Therefore, the second air preheater of this scheme adopts a plate air preheater.

[0057] Component compactness is a key indicator of heat exchanger structural density. The higher the compactness, the smaller the heat exchanger volume and the less restricted by site layout. The compactness of heat exchanger components of air preheaters using DU3 or FNC wave types can reach 460m 2 / m 3 The structure of the plate air preheater is a multi-piece folded corrugated plate that is overlapped and interlocked. The medium flow rate, the corrugation angle, height, pitch and plate spacing of the corrugated plate determine the heat transfer coefficient and flow resistance. Through the numerical simulation of the flow and heat transfer process in the corrugated plate air preheater, a design scheme that is conducive to compact structure is proposed. Through calculation, when the heat transfer coefficient of the element is the same as that of the rotary air preheater, the compactness of the element can reach 289m 2 / m 3 .

[0058] When the plate type solution is adopted for the second air preheater on one side, the heat exchange area is about 21500m 2 , volume is about 75m 3 , which is converted into a structural dimension of 5m (length) × 5m (width) × 3m (height), making it easier to arrange the renovation site.

[0059] S3: Evaluation of the effect of the second air preheater.

[0060] According to the analysis of heat transfer principle, the range of reducing exhaust gas temperature by preheater is not infinite. The smaller the heat transfer end difference, the more heating surfaces need to be arranged. 2 、30000m 2 and 40000m 2 A comparative calculation was carried out and the results are shown in Table 3.

[0061] Table 3 Comparison of air preheater structure and performance data before and after transformation

[0062] After comprehensive consideration and combined with the on-site layout design, it is recommended to choose a design between Option 1 and Option 2. The exhaust temperature can be reduced by 8℃~9℃, the coal consumption can be reduced by 1.21g / kWh, and the payback period is about 5 years.

[0063] The present invention proposes a bypass flue gas channel system, in which the heat exchange performance and resistance characteristics of the air preheater are more excellent, the adaptability of the air preheater to different types of coal can be enhanced, and the tolerance range of the air preheater to the ammonia escape rate can be improved. At the same time, the reliability of the air preheater can be greatly improved, maintenance work can be reduced, and the service life of the equipment can be extended.

[0064] It is to be understood that the above embodiments are merely exemplary embodiments used to illustrate the principles of the present disclosure, but the present disclosure is not limited thereto. For those of ordinary skill in the art, various modifications and improvements can be made without departing from the spirit and substance of the present disclosure, and these modifications and improvements are also considered to be within the scope of protection of the present disclosure.

Claims

1. A bypass flue gas channel system, characterized in that: The system includes a first air preheater, a second air preheater, a primary fan and a secondary fan; The hot flue gas inlet of the first air preheater is connected to the high-temperature flue gas outlet of the boiler through a hot flue gas pipeline; the primary cold air inlet of the first air preheater is connected to the cold air outlet of the primary fan through a cold air pipeline, and the secondary cold air inlet of the first air preheater is connected to the cold air outlet of the secondary fan through a cold air pipeline; the secondary hot air outlet of the first air preheater is connected to the furnace of the boiler through a pipeline; The hot flue gas inlet of the second air preheater is connected to the high-temperature flue gas outlet of the boiler through a bypass flue gas duct; the secondary cold air inlet of the second air preheater is connected to the cold air outlet of the secondary fan through a cold air duct; the secondary hot air outlet of the second air preheater is connected to the secondary hot air outlet of the first air preheater through a duct.

2. A bypass flue gas channel system according to claim 1, characterized in that: A hot air duct is also provided between the duct of the secondary hot air outlet of the second air preheater and the air inlet of the secondary air fan.

3. A bypass flue gas channel system according to claim 1, characterized in that: The first air preheater includes a rotary heat exchanger.

4. A bypass flue gas channel system according to claim 1, characterized in that: The second air preheater includes a plate heat exchanger.

5. A bypass flue gas channel system according to claim 1, characterized in that: Also includes: The first flow regulating device is arranged in the bypass flue gas duct and is used to regulate the hot flue gas flow in the bypass flue gas duct.

6. A bypass flue gas channel system according to claim 5, characterized in that: Also includes: The first stop valve is arranged in the bypass flue gas duct, and the first stop valve is located downstream of the first flow regulating device.

7. A bypass flue gas channel system according to claim 2, characterized in that: Also includes: The second flow regulating device is arranged in the hot air duct, and the second flow regulating device is used to regulate the hot secondary air flow in the hot air duct.

8. A bypass flue gas channel system according to claim 7, characterized in that: Also includes: The second stop valve is arranged in the hot air duct, and the second stop valve is located downstream of the second flow regulating device.

9. A bypass flue gas channel system according to claim 2, characterized in that: Also includes: The third flow regulating device is arranged on the cold air duct at the secondary cold air inlet of the second air preheater.

10. A bypass flue gas channel system according to claim 9, characterized in that: Also includes: The third stop valve is arranged on the cold air duct at the secondary cold air inlet of the second air preheater, and the third stop valve is located upstream of the third flow regulating device.

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