A method for reducing the wall temperature of a low-temperature superheater of a boiler

Abstract

The application relates to the field of boiler design, and discloses a method suitable for reducing the wall temperature of a low-temperature superheater of a boiler, wherein the boiler comprises five coal mills A, B, C, D and E, burners arranged in a four-corner tangential circle mode, and four overfire air dampers respectively arranged at four corners of the upper portion of a furnace and divided into six layers, the overfire air is divided into four layers SA, SB, SC and SD, and the method comprises the following steps: S1, adjusting the running combination of the coal mills and the opening degree of the overfire air dampers according to the load condition of the boiler; S2, improving the residual rotation condition of the flue gas at the outlet of the boiler, so that the tail flue gas temperature is uniformly distributed; and S3, eliminating the unevenness of the flue gas temperature, reducing the overall flue gas temperature, and reducing the wall temperature of the low-temperature superheater. According to the method, the running combination of the coal mills and the opening degree of the overfire air dampers are adjusted according to the load, the residual rotation condition of the flue gas at the outlet of the boiler is improved, the tail flue gas temperature is uniformly distributed, the unevenness of the flue gas temperature is eliminated, the overall flue gas temperature is reduced, and the wall temperature of the low-temperature superheater is reduced.

Description

Technical Field

[0001] This invention relates to the field of boiler design technology, specifically to a method for reducing the wall temperature of a low-temperature superheater in a boiler. Background Technology

[0002] The Harbin Boiler HG1018-18.6-YM23 boiler features tangential combustion at the four corners, with a low-temperature superheater located in the middle section of the tail vertical flue, above the economizer. During normal operation, the steam temperature of the low-temperature superheater is relatively low, approximately 400-485℃, therefore it is constructed from metals with low temperature resistance. The maximum permissible tube temperature for this boiler is 580℃.

[0003] Traditionally, the following methods can be used to reduce the wall temperature of low-temperature superheaters:

[0004] 1. Soot blowing (at the front heating surface) is used to reduce the flue gas temperature. However, frequent soot blowing may cause the wall of the heating surface tubes to thin, increasing the risk of the heating surface bursting.

[0005] 2. Lowering the steam temperature at the front heating surface reduces the corresponding tube wall temperature, thereby lowering the flue gas temperature and achieving the goal of reducing the low-temperature superheater wall temperature. However, lowering the steam temperature significantly reduces the boiler's economic efficiency.

[0006] 3. Reducing the total air volume of the boiler weakens heat exchange in the low-temperature superheater, resulting in a lower wall temperature. However, this method may increase incomplete combustion and have some impact on safety.

[0007] 4. Combustion using low-moisture and easily combustible coal is not easy to implement in power plant boilers due to economic considerations and the limited availability of coal that meets design parameters.

[0008] Therefore, it is essential to propose a suitable method for reducing the wall temperature of the low-temperature superheater for the Harbin Boiler HG1018-18.6-YM23 boiler. Summary of the Invention

[0009] To address the shortcomings of existing technologies, this invention provides a method for reducing the wall temperature of a low-temperature superheater in a boiler. By comprehensively considering factors such as boiler load, adjustment of the coal mill and burnout damper, and optimization of flue gas flow, the method reduces the wall temperature of the low-temperature superheater, thereby improving the boiler's thermal efficiency and safety.

[0010] To achieve the above objectives, the present invention provides the following technical solution: a method for reducing the wall temperature of a low-temperature superheater in a boiler, wherein the boiler comprises five coal mills (A, B, C, D, and E), burners arranged tangentially at the four corners, and burnout dampers divided into six layers installed at the four corners of the upper part of the furnace, wherein the burnout dampers are divided into four layers: SA, SB, SC, and SD. The method comprises the following steps:

[0011] S1. Adjust the coal mill operating combination and the burnout damper opening according to the boiler load;

[0012] S2. Improve the residual swirl of flue gas at the boiler outlet to ensure a uniform temperature distribution of the flue gas at the tail end.

[0013] S3. Eliminate uneven flue gas temperature and reduce the overall flue gas temperature to lower the wall temperature of the low-temperature superheater.

[0014] When the three grinding units ABC are running, set the burnout damper opening of SA and SB layers to 90 degrees, and set the burnout damper opening of SC and SD layers to 20 degrees.

[0015] Preferably, when four grinding units ABCD or BCDE are running, the burnout damper opening of the SA layer is set to 38, the burnout damper opening of the SB layer is set to 25, and the burnout damper opening of the SC and SD layers is set to 40.

[0016] Preferably, when all five mill units (A, B, C, D, and E) are running, the units are in the high-load section and operate in a conventional manner.

[0017] Preferably, the method further includes: judging the risk of overheating of the low-temperature superheater wall based on the moisture content of the coal, and adjusting the coal mill operation combination and the burnout damper opening.

[0018] Preferably, the risk of overheating is determined based on real-time monitoring data of coal moisture content, and the risk of overheating of the low-temperature superheater wall is quantitatively assessed through a risk assessment model or algorithm.

[0019] Preferably, the model or algorithm calculates the risk index or estimates the degree of wall temperature rise by taking into account factors such as coal type characteristics, boiler operating parameters, and superheater design parameters.

[0020] Preferably, the method further includes: by real-time monitoring and controlling the deviation between the boiler inlet pressure and the given pressure, activating the short sootblower to avoid excessive deviation in the inlet pressure, so as to control the rise in the low-temperature superheater wall temperature.

[0021] This invention provides a method for reducing the wall temperature of a low-temperature superheater in a boiler. It has the following beneficial effects:

[0022] 1. This invention adjusts the coal mill operating combination and the burnout damper opening according to the load to improve the residual swirl of the flue gas at the boiler outlet, thereby making the tail flue gas temperature more uniform, eliminating uneven flue gas temperature, reducing the overall flue gas temperature, and thus achieving the purpose of reducing the wall temperature of the low-temperature superheater.

[0023] 2. This invention reduces the wall temperature of the low-temperature superheater and improves the thermal efficiency and safety of the boiler by comprehensively considering factors such as boiler load, adjustment of coal mill and burnout damper, and optimization of flue gas flow. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the tangential combustion at the four corners of the boiler according to the present invention;

[0025] Figure 2 This is a general diagram of the secondary wind distribution at each layer of the present invention. Detailed Implementation

[0026] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] The Harbin Boiler HG1018-18.6-YM23 boiler is currently equipped with a five-layer coal mill. The inlet air ducts are located at the four corners of the boiler, arranged in five layers, from bottom to top as layers A, B, C, D, and E, with tangential combustion at the four corners. Each layer of the mill has corresponding secondary air inlets, and the top layer consists of six layers of burnout air dampers. The function of the burnout air is:

[0028] 1. Change the height of the flame center: The flame center in the furnace depends on the effect of adjusting the burnout air damper on the secondary air of each layer. If the burnout air damper is opened wider, the secondary air volume of the burners in the lower layers will inevitably decrease, resulting in insufficient air for the middle and lower burners. The pulverized coal will not be completely burned in the middle and lower layers, the flame center will move upward, and the flue gas temperature will increase.

[0029] 2. Reduce coking: Excessive burnout air opening causes oxygen deficiency combustion in the middle and lower burners, which easily produces reducing gas CO, increasing the possibility of high-temperature corrosion and coking on the boiler heating surfaces.

[0030] 3. Reduce nitrogen oxides: If the burnout air opening is too small, the carbon content of fly ash will increase, and the NOx content in flue gas will increase.

[0031] 4. To provide oxygen during the fuel burnout stage.

[0032] Please see the appendix Figure 1-2 This invention provides a method for reducing the wall temperature of a low-temperature superheater in a boiler. The boiler includes five coal mills (A, B, C, D, and E), burners arranged tangentially at the four corners, and six layers of burnout dampers installed at the four corners of the upper part of the furnace. The burnout dampers are divided into four layers: SA, SB, SC, and SD. The method includes the following steps:

[0033] S1. Adjust the coal mill operating combination and the burnout damper opening according to the boiler load;

[0034] The purpose of the above steps is to adjust the operating combination of the coal mill and the opening of the burnout damper according to the load of the boiler. Through reasonable adjustments, the appropriate supply of pulverized coal can be achieved during boiler operation, ensuring the stability of the combustion process in the furnace and maximizing fuel combustion efficiency.

[0035] S2. Improve the residual swirl of flue gas at the boiler outlet to ensure a uniform temperature distribution of the flue gas at the tail end.

[0036] The above aims to improve the flow state of the flue gas at the boiler outlet, reduce vortices and uneven distribution in the flue gas, thereby making the temperature distribution of the tail flue gas more uniform. By taking control measures, turbulence and temperature gradient in the flue gas can be reduced, and heat transfer efficiency can be improved.

[0037] S3. Eliminate uneven flue gas temperature and reduce the overall flue gas temperature to reduce the low-temperature superheater wall temperature.

[0038] The above objective is to reduce the overall flue gas temperature by eliminating the non-uniformity of flue gas temperature, thereby reducing the wall temperature of the low-temperature superheater. Uneven flue gas temperature may cause a part of the superheater to be subjected to excessive heat load, resulting in excessively high superheater wall temperature. By adjusting the boiler operation and control strategy and optimizing the flow and distribution of gas, a more uniform flue gas temperature distribution can be achieved, thereby reducing the wall temperature of the low-temperature superheater.

[0039] In this embodiment, the operation combination of the coal mill and the opening of the burnout damper are adjusted according to the load to improve the residual swirl of the flue gas at the boiler outlet, thereby making the flue gas temperature at the tail end more uniform and eliminating uneven flue gas temperature, thus reducing the overall flue gas temperature and achieving the goal of reducing the low-temperature superheater wall temperature. By comprehensively considering factors such as the boiler load, the adjustment of the coal mill and burnout damper, and the optimization of flue gas flow, the low-temperature superheater wall temperature is reduced, thereby improving the boiler's thermal efficiency and safety.

[0040] A boiler at a certain plant, when burning coal of a type not designed for use and with a high moisture content, has consistently suffered from excessively high wall temperatures in its low-temperature superheater. To address this, operators typically adjust the temperature by either continuously blowing even-numbered steam or lowering the main reheat steam temperature when the wall temperature is rapidly exceeding the design limit.

[0041] During even-numbered days, continuous blowing may occur three or more times a day. Alternatively, the main reheat steam temperature may be lowered to below 525℃ to reduce the wall temperature. Over time, this can affect boiler efficiency or cause excessive blowing during even-numbered days, leading to thinning of the corresponding tube walls and increasing the risk of tube rupture.

[0042] Based on experiments, a method was proposed to reduce the low-temperature superheater wall temperature by adjusting the SOFA air, thereby reducing the number of soot blowing cycles during even-numbered long blow cycles, and improving the main reheat steam temperature and boiler efficiency.

[0043] The burnout wind is divided into four layers: SA, SB, SC, and SD.

[0044] 1: When the three grinding units ABC are running, set the burnout air opening of SA and SB layers to 90 and the burnout air opening of SC and SD layers to 20.

[0045] 2: When four grinding units (ABCD or BCDE) are running, the air pressure in the SA layer can be set to 38, the air pressure in the SB layer to 25, and the air pressure in the SC and SD layers to 40.

[0046] 3: When the five grinding units (A, B, C, D, and E) are running, the units are in the high-load section. Generally, the temperature of the low-temperature superheater wall will not exceed the limit. Adjustments can be made according to the table provided by the professionals.

[0047] The above methods were all tested and compared with the adjustment settings given by existing oxygen meter readings. This adjustment method can reduce the sub-wall temperature by 6°C or more, reduce ammonia consumption by about 4 kg / h per side under the same conditions, and maintain the main reheat steam temperature above 546°C. Furthermore, under the same conditions per shift, it can eliminate the need for or only require blowing one double-number sootblower. This significantly reduces the risk of excessive sootblowing leading to tube wall thinning or even tube rupture, and it eliminates the need to lower the main reheat steam temperature, thus reducing ammonia consumption and greatly improving boiler efficiency.

[0048] In one embodiment, the method further includes: judging the risk of overheating of the low-temperature superheater wall based on the moisture content of the coal type, and adjusting the coal mill operation combination and the burnout damper opening.

[0049] Furthermore, the risk of overheating is assessed based on real-time monitoring data of coal moisture content. A risk assessment model or algorithm is used to quantitatively evaluate the risk of overheating of the low-temperature superheater wall.

[0050] Among them, the model or algorithm calculates the risk index or estimates the degree of wall temperature rise by taking into account factors such as coal type characteristics, boiler operating parameters, and superheater design parameters.

[0051] In this embodiment, the further steps described above are explained as follows:

[0052] Assessing the Risk of Low-Temperature Superheater Wall Temperature Overheating Based on Coal Moisture Content: This step aims to determine the likelihood of low-temperature superheater wall temperature overheating based on the moisture content of the coal. Coal moisture content is a parameter that affects combustion and boiler operation; high-moisture coal combustion characteristics may lead to higher combustion temperatures and a greater risk of increased low-temperature superheater wall temperature.

[0053] Adjusting the pulverizer operating configuration and burnout damper opening: Based on the assessed risk of overheating, adjust the pulverizer operating configuration and burnout damper opening accordingly. By adjusting the pulverizer operating configuration and burnout damper opening, the pulverized coal supply and combustion process can be controlled to ensure that the low-temperature superheater wall temperature remains within a reasonable range even with high-moisture coal.

[0054] Real-time monitoring data and risk assessment models or algorithms: Utilizing real-time monitoring data, such as coal moisture content and boiler operating parameters, combined with risk assessment models or algorithms, to quantitatively assess the risk of overheating of the low-temperature superheater wall. These models or algorithms may consider factors such as coal characteristics, boiler operating parameters, and superheater design parameters, thereby calculating a risk index or estimating the degree of increase in the low-temperature superheater wall temperature.

[0055] By combining real-time monitoring data with risk assessment models or algorithms, dynamic risk assessment based on the moisture content of coal can be achieved, allowing for appropriate adjustments to reduce the risk of overheating in low-temperature superheaters. This more effectively protects the low-temperature superheater and improves the reliability and safety of the boiler.

[0056] In one embodiment, the method further includes: by real-time monitoring and controlling the deviation between the boiler inlet pressure and the given pressure, activating the short sootblower to avoid excessive deviation in the inlet pressure, so as to control the rise in the low-temperature superheater wall temperature.

[0057] In this embodiment, the above steps are explained as follows:

[0058] Real-time monitoring and control of the deviation between the boiler inlet pressure and the set pressure: The purpose of this step is to control the rise in the low-temperature superheater wall temperature by monitoring the deviation between the boiler inlet pressure and the set pressure in real time. The inlet pressure refers to the pressure at the inlet of the boiler combustion zone, and the set pressure is the target value. By monitoring the inlet pressure in real time and comparing it with the set pressure, the deviation value can be obtained and used for feedback control of the control system.

[0059] To prevent excessive pressure deviation before the boiler, short sootblowers are used to prevent this: Based on the deviation between the pre-boiler pressure and the given pressure, appropriate control strategies are implemented, including the operation of short sootblowers. A short sootblower is a device used to clean slag buildup on the flame side of the boiler superheater. When the pre-boiler pressure deviation is too large, operating the short sootblower can clean the slag buildup on the superheater surface, reduce pipe blockage, lower the pre-boiler pressure, and control the rise in the low-temperature superheater wall temperature.

[0060] By monitoring the deviation between the boiler inlet pressure and the given pressure in real time, and adjusting the pressure by activating the short soot blower, the boiler's operating status can be controlled and regulated in a timely manner to avoid excessive rise in the low-temperature superheater wall temperature. This protects the low-temperature superheater from overheating and damage, and ensures the safe and stable operation of the boiler.

[0061] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for reducing the wall temperature of a low-temperature superheater in a Harbin Boiler HG1018-18.6-YM23 boiler, wherein the boiler comprises five coal mills (A, B, C, D, and E), burners arranged tangentially at the four corners, and burnout dampers divided into six layers installed at the four corners of the upper part of the furnace, wherein the burnout dampers are divided into four layers: SA, SB, SC, and SD, characterized in that... The method includes the following steps: S1. Adjust the coal mill operating combination and the burnout damper opening according to the boiler load; S2. Improve the residual swirl of flue gas at the boiler outlet to ensure a uniform temperature distribution of the flue gas at the tail end. S3. Eliminate uneven flue gas temperature and reduce the overall flue gas temperature to reduce the low-temperature superheater wall temperature. The specific adjustment steps are as follows: When the three grinding units ABC are running, set the burnout damper opening of SA and SB layers to 90 and the burnout damper opening of SC and SD layers to 20. When four grinding units ABCD or BCDE are running, set the burnout damper opening of SA layer to 38, set the burnout damper opening of SB layer to 25, and set the burnout damper opening of SC and SD layers to 40. The method further includes: Based on real-time monitoring data of coal moisture content, a risk assessment model or algorithm is used to quantitatively assess the risk of overheating of the low-temperature superheater wall, and adjust the coal mill operation combination and burnout damper opening according to the assessment results; wherein, the model or algorithm calculates the risk index or estimates the degree of wall temperature rise by taking into account factors such as coal characteristics, boiler operating parameters, and superheater design parameters. Furthermore, by monitoring and controlling the deviation between the boiler inlet pressure and the given pressure in real time, the short soot blower is put into operation to avoid excessive deviation in the inlet pressure, thereby controlling the rise in the wall temperature of the low-temperature superheater.

2. The method for reducing the low-temperature superheater wall temperature of Harbin Boiler HG1018-18.6-YM23 boiler according to claim 1, characterized in that, When the five mill units (A, B, C, D, and E) are running, the units are in the high-load section and operate in the conventional manner.

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