A soot blowing method and system for improving air preheater blockage

Abstract

This invention discloses a soot blowing method to improve air preheater blockage, comprising the following steps: First, determine the soot blowing steam source parameter point A on the steam enthalpy-entropy diagram; reduce the steam temperature by 5-15°C along the isobaric line to point B as a process design margin; draw a pressure-reducing isoenthalpy process line through point B; determine the soot blowing steam temperature required to decompose ammonium bisulfate; find the soot blowing steam temperature point D at the flue gas pressure that can decompose ammonium bisulfate on the steam enthalpy-entropy diagram, and draw a spray line through point D; the intersection point C of the isoenthalpy process line and the spray line is the spray point; determine the corresponding size of the soot blowing nozzle based on the pressure at point C and the required soot blowing radius; after setting the parameters of the soot blower, complete the soot blowing operation. This invention ensures that the air preheater steam used for soot blowing is high-temperature dry steam capable of decomposing ammonium bisulfate, effectively removing ash that is severely caked at the cold end of the air preheater due to sulfuric acid and ammonium bisulfate, thus contributing to the stable operation of the unit.

Description

Technical Field

[0001] This invention relates to thermal power units, and more particularly to soot blowing technology for air preheaters, specifically a soot blowing method and system for improving air preheater blockage. Background Technology

[0002] With increasingly stringent environmental protection requirements, large thermal power units have undergone ultra-clean emission retrofits. However, in actual operation, the presence of ammonia escape in the SCR system can easily lead to ammonium sulfate or ammonium bisulfate blockage in the air preheater, causing increased pressure differential and affecting the stable operation of the unit. In existing technologies, frequent operation of steam soot blowers to clean the air preheater relies on the stagnant kinetic energy of high-speed dry steam to remove dirt. The high-pressure, medium-temperature steam leaving the soot blower nozzle is typically dry steam slightly above 100°C. However, due to the special corrugated plate design of the air preheater's heat storage elements, even with frequent soot blowing at the cost of increased energy consumption and air preheater wear, it is still not effective in cleaning the air preheater when ash caking occurs.

[0003] In addition, existing technologies include cold-end warm air heaters, hot air recirculation, hot air return and splitting, forced circulation hot air, and coupled flue gas heat exchange, among other anti-clogging technologies. However, all of these technologies utilize the characteristic that ammonium bisulfate decomposes above 207°C. By raising the wall temperature of the heat storage element to above 207°C using high-temperature flue gas, the ash is first decomposed, thus loosening the clumps. This is then further aided by sootblowing for removal. While these methods are effective to some extent, they have significant side effects, and the investment costs are often over ten million yuan, with high operating costs. Moreover, they only delay cold-end clogging and corrosion. For denitrification air preheaters, especially those under ultra-low emission requirements, they cannot effectively eliminate clogging. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a soot blowing method and system for improving air preheater blockage. It overcomes the deficiencies of existing technologies, is reasonably designed, and ensures that the air preheater steam soot blowing is high-temperature dry steam that can decompose ammonium bisulfate. This effectively removes ash that is severely caked at the cold end of the air preheater due to sulfuric acid and ammonium bisulfate, which is beneficial to the stable operation of the unit.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A method for improving soot blowing to reduce air preheater blockage includes the following steps:

[0007] Step S1: On the water vapor enthalpy-entropy diagram, first determine the soot blowing steam source parameter point A;

[0008] Step S2: Reduce the steam temperature by 5-15℃ along the isobaric line to point B as a process design margin;

[0009] Step S3: Draw the isenthalpic process curve for pressure reduction through point B;

[0010] Step S4: Determine the temperature of the soot blowing steam required to decompose ammonium bisulfate;

[0011] Step S5: On the water vapor enthalpy-entropy diagram, find the soot blowing steam temperature point D that can decompose ammonium bisulfate under flue gas pressure, and draw the blowing line with a nozzle efficiency of 0.9 through point D.

[0012] Step S6: The point C where the isenthalpic process line and the injection line intersect is the injection point;

[0013] Step S7: Determine the appropriate size of the soot blowing nozzle based on the pressure at the blowing point C and the required soot blowing radius;

[0014] Step S8: Based on the soot blowing steam temperature data obtained in step S4 and the soot blowing nozzle size data obtained in step S7, set the soot blowing temperature and soot blowing nozzle parameters of the soot blower, and then start the soot blower to complete the soot blowing work.

[0015] Preferably, in step S2, the steam temperature adjustment range of 5-15℃, 5℃ is used as the fluctuation margin for the steam source operating conditions, and the remaining 0-10℃ is used as the standard nozzle selection adjustment range.

[0016] The present invention also discloses a soot blowing system applied to the above-mentioned soot blowing method, comprising a plurality of soot blowers, each soot blower being fixedly connected to a gas pipeline, the end of the gas pipeline being connected to the outlet end of a soot blowing gas source, an electric shut-off valve being installed at the end of the gas pipeline near the soot blowing gas source, and a pneumatic regulating valve being fixedly installed at the end of the gas pipeline near the soot blower, the control end of the pneumatic regulating valve being connected to a pressure transmitter, and the detection end of the pressure transmitter being fixedly connected to the gas pipeline.

[0017] Preferably, the signal output terminal of the pressure transmitter is electrically connected to the signal input terminal of the DSC pressure control device, and the signal output terminal of the DSC pressure control device is electrically connected to the signal input terminal of the pneumatic regulating valve.

[0018] This invention provides a soot blowing method and system for improving air preheater clogging. It offers the following advantages: Based on the mechanical cleaning principle of the air preheater soot blower, and utilizing a steam enthalpy-entropy diagram to select a suitable steam source location for different types of units, high-temperature dry steam is used to thermally decompose ammonium bisulfate and ammonium sulfate, which cause ash caking at the cold end of the air preheater, before mechanical cleaning. This loosens the ash, allowing for its mechanical removal and effectively alleviating clogging. Suitable steam source locations can be found in various types of large thermal power units to obtain high-temperature dry steam capable of decomposing ammonium bisulfate and ammonium sulfate for air preheater soot blowing. The soot blowing system is simple and reliable. Compared to other air preheater clogging mitigation technologies, the system is simpler, has lower initial and operating costs, better performance, and significant energy savings. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in this invention or the prior art, the accompanying drawings used in the description of the prior art will be briefly introduced below.

[0020] Figure 1 The steam enthalpy-entropy diagram and steam soot blowing thermodynamic process diagram used in this invention;

[0021] Figure 2 This is a schematic diagram of the soot blowing system of the present invention. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0023] Example 1

[0024] like Figure 1 As shown, this invention discloses a soot blowing method for improving air preheater blockage, comprising the following steps:

[0025] Step S1: On a water vapor enthalpy-entropy diagram, first determine the soot blowing steam source parameter point A;

[0026] Step S2: Reduce the steam temperature by 5-15℃ along the isobaric line to point B as a process design margin;

[0027] Step S3: Draw the isenthalpic process curve for pressure reduction through point B;

[0028] Step S4: Determine the temperature of the soot blowing steam required to decompose ammonium bisulfate;

[0029] Step S5: On the water vapor enthalpy-entropy diagram, find the soot blowing steam temperature point D that can decompose ammonium bisulfate under flue gas pressure, and draw the blowing line with a nozzle efficiency of 0.9 through point D; where 0.9 is used, it is a relatively high nozzle efficiency, which can obtain a more conservative result.

[0030] Step S6: The point C where the isenthalpic process line and the injection line intersect is the injection point;

[0031] Step S7: Determine the appropriate size of the soot blowing nozzle based on the pressure at the blowing point C and the required soot blowing radius;

[0032] Step S8: Based on the soot blowing steam temperature data obtained in step S4 and the soot blowing nozzle size data obtained in step S7, set the soot blowing temperature and soot blowing nozzle parameters of the soot blower, and then start the soot blower to complete the soot blowing work.

[0033] In step S2, within the steam temperature adjustment range of 5-15℃, 5℃ serves as a fluctuation margin for the steam source operating conditions, while the remaining 0-10℃ represents the standard nozzle selection adjustment range. By varying point B in the above process within the 5-15℃ range, the above derivation process is repeated to determine the size of the sootblowing nozzle.

[0034] In this embodiment, the required soot blowing steam temperature (greater than 207°C) is obtained through step S4. Under the action of steam temperature higher than 207°C at the outlet of the soot blower nozzle, the sulfuric acid at the cold end of the air preheater can be completely converted into a gaseous state and no longer caking into ash. Most of the ammonium bisulfate located at the middle and low ends can also be decomposed, thus changing the originally severely caking ash into loose dry ash. In this way, the heat exchange elements of the air preheater can be easily cleaned under the action of steam power, thereby greatly improving the clogging condition of the air preheater.

[0035] Through the above steps, a suitable steam source location can be found in various types of large thermal power units to obtain high-temperature dry steam that can decompose ammonium bisulfate and ammonium sulfate for air preheater soot blowing. This effectively removes ash that is severely caked at the cold end of the air preheater due to sulfuric acid and ammonium bisulfate, which is beneficial to the stable operation of the unit. Moreover, the soot blowing system is simple and reliable. Compared with other air preheater slow-clogging technologies, the system is simple, has low initial and operating costs, good effect, and good energy-saving effect.

[0036] like Figure 1 The diagram shows the enthalpy-entropy diagram of steam and the thermal process of steam soot blowing. The diagram is divided into two distinct regions: a wet steam region and a dry steam region, with the boundary line between 100% dry steam and wet steam in the middle. In the diagram, A represents the steam source, B represents the point where the steam source temperature drops by 5-15°C, C represents the nozzle inlet, D represents the nozzle outlet, BC represents the isoenthalpy process line of pressure reduction, and CD represents the blowing line. The steam soot blowing thermal process corresponding to ABCD is the soot blowing thermal process described in this invention.

[0037] This invention is based on the mechanical cleaning principle of conventional air preheater soot blowers in current thermal power generating units. It utilizes the steam enthalpy-entropy diagram to select a suitable steam source location in different types of units. Before mechanical cleaning of the soot blower, it uses the thermal process characteristics of steam to thermally decompose ammonium bisulfate and ammonium sulfate, which cause ash caking at the cold end of the air preheater, by using high-temperature dry steam. This loosens the ash before mechanically removing it, thus effectively alleviating blockage.

[0038] Example 2

[0039] like Figure 2 As shown, this invention also discloses a soot blowing system applied to the above-mentioned soot blowing method, comprising a plurality of soot blowers 1, each soot blower 1 being fixedly connected to a gas pipeline 2, the end of the gas pipeline 2 being connected to the outlet end of a soot blowing gas source 4, an electrically operated shut-off valve 6 being installed at the end of the gas pipeline 2 near the soot blowing gas source 4, and a pneumatic regulating valve 7 being fixedly installed at the end of the gas pipeline 2 near the soot blower 1, the control end of the pneumatic regulating valve 7 being connected to a pressure transmitter 8, and the detection end of the pressure transmitter 8 being fixedly connected to the gas pipeline 2. The signal output end of the pressure transmitter 8 is electrically connected to the signal input end of a DSC pressure control device 9, and the signal output end of the DSC pressure control device 9 is electrically connected to the signal input end of the pneumatic regulating valve 7.

[0040] In use, the soot blowing steam enters each soot blower 1 directly through the electric shut-off valve 6, the pneumatic regulating valve 7, and the gas pipeline 2. In addition, the pressure transmitter 8 detects the gas pressure in the gas pipeline 2 and transmits the signal to the DSC pressure control device 9. The DSC pressure control device 9 processes and analyzes the signal to control the opening and closing of the pneumatic regulating valve 7, thereby controlling the gas pressure in the gas pipeline 2.

[0041] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for improving soot blowing to reduce blockage in an air preheater, characterized in that, Includes the following steps: Step S1: On the water vapor enthalpy-entropy diagram, first determine the soot blowing steam source parameter point A; Step S2: Reduce the steam temperature by 5-15℃ along the isobaric line to point B as a process design margin; Step S3: Draw the isenthalpic process curve for pressure reduction through point B; Step S4: Determine the temperature of the soot blowing steam required to decompose ammonium bisulfate; Step S5: On the water vapor enthalpy-entropy diagram, find the soot blowing steam temperature point D that can decompose ammonium bisulfate under flue gas pressure, and draw the blowing line with a nozzle efficiency of 0.9 through point D. Step S6: The point C where the isenthalpic process line and the injection line intersect is the injection point; Step S7: Determine the appropriate size of the soot blowing nozzle based on the pressure at the blowing point C and the required soot blowing radius; Step S8: Based on the soot blowing steam temperature data obtained in step S4 and the soot blowing nozzle size data obtained in step S7, set the soot blowing temperature and soot blowing nozzle parameters of the soot blower, and then start the soot blower to complete the soot blowing work. In step S2, the steam temperature adjustment range is 5-15℃, where 5℃ is used as a fluctuation margin for the steam source operating conditions, and the remaining 0-10℃ is used as the standard nozzle selection adjustment range.

2. A soot blowing system employing the soot blowing method of claim 1, characterized in that: It includes several soot blowers (1), each soot blower (1) is fixedly connected to a gas pipeline (2), the end of the gas pipeline (2) is connected to the outlet end of the soot blowing gas source (4), an electric shut-off valve (6) is installed at the end of the gas pipeline (2) near the soot blowing gas source (4), and a pneumatic regulating valve (7) is fixedly installed at the end of the gas pipeline (2) near the soot blower (1), the control end of the pneumatic regulating valve (7) is connected to a pressure transmitter (8), and the detection end of the pressure transmitter (8) is fixedly connected to the gas pipeline (2).

3. The soot blowing system according to claim 2, characterized in that: The signal output terminal of the pressure transmitter (8) is electrically connected to the signal input terminal of the DSC pressure control device (9), and the signal output terminal of the DSC pressure control device (9) is electrically connected to the signal input terminal of the pneumatic regulating valve (7).

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