Method for controlling ash deposition and slag bonding on heating surface of coal-fired boiler

Abstract

The invention discloses a method for controlling ash deposition and slagging on a heating surface of a coal-fired boiler, relates to the technical field of coal-fired boilers, and aims to solve the technical problems that effective power supply is affected by slagging and ash deposition of a current coal-fired boiler and production accidents are easily caused. Then the coal material is pretreated, and other coal materials are doped into the coal material according to the slagging tendency of the coal material; the tangential diameter of the hearth is controlled, meanwhile, the structural design that the front wall and the rear wall are arranged oppositely is adopted in the hearth, the probability that wind impacts the furnace wall in the tangential diameter of the combustor is reasonably controlled, then the development trend of slag bonding is reduced, mixing is more sufficient, combustion is facilitated, and the combustion efficiency is improved. And meanwhile, the temperature in the boiler, the excess air coefficient in the boiler and the negative pressure strength in the hearth are accurately controlled in an assisted mode, the probability of slagging is further reduced, and therefore accumulated ash and slagging attached to the interior of the boiler are reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of coal-fired boilers, and more particularly to a method for controlling ash and slagging on a heating surface of a coal-fired boiler. Background Art

[0002] Coal occupies a dominant position in the energy consumption structure. It is particularly important to ensure the safe and stable operation of coal-fired power generation units. During the operation of power plant units, ash and slagging on the boiler heating surface is one of the main factors affecting the safe and stable operation of the boiler. Since the combustion products contain a large amount of ash particles, sulfur and nitrogen oxides and other substances, these substances will be deposited on the boiler heating surface in various forms, causing slagging on the boiler heating surface. The ash and slagging of the boiler will not only reduce the economy of the boiler operation, but also increase the safety hazards of the boiler operation. In severe cases, it may cause equipment damage and safety accidents.

[0003] In this case, for thermal power plants, the slagging and ash accumulation of coal-fired boilers will affect the effective supply of electricity, and slagging and ash accumulation can easily cause production accidents. In view of this, we propose a method for controlling ash and slagging on the heating surface of coal-fired boilers. Summary of the invention

[0004] The purpose of the present invention is to overcome the shortcomings of the prior art, meet actual needs, and provide a method for controlling dust and slagging on the heating surface of a coal-fired boiler to solve the technical problem that slagging and dust accumulation in the current coal-fired boiler affects the effective supply of electricity and easily causes production accidents.

[0005] In order to solve the above technical problems, the present invention provides the following technical solutions: a method for controlling ash and slagging on the heating surface of a coal-fired boiler, comprising the following steps:

[0006] S1: Control the quality of coal: obtain various indicators of coal, pre-treat the coal, mix other coal into it according to its slagging tendency, add deslagging agent into the coal, and control the fineness of coal powder;

[0007] S2: Carry out furnace reconstruction: control the tangential diameter of the furnace to an appropriate size and adjust the position of the internal structure of the furnace;

[0008] S3: Control the combustion process: During the coal burning process, control the furnace temperature, excess air coefficient, and negative pressure intensity in the furnace;

[0009] S4: Keep the heating surface clean: Apply a dust-proof coating on the heating surface and blow dust on the heating surface regularly using dust-blowing equipment.

[0010] Preferably, in the step S1 of obtaining various coal indicators, the ash softening temperature and comprehensive discrimination index value of the coal are mainly obtained;

[0011] In the step S1 of pre-treating the coal, the coal is first screened to remove large particles of impurities and gangue in the coal, and then the content of fine impurities in the coal is reduced by coal washing;

[0012] In step S1, other coals are mixed into the coal according to its slagging tendency, and coals that are not easy to slagging are added to the coal with a more serious slagging tendency, and the mixed use reduces the slagging of the coal ash;

[0013] In the step S1, in the step of adding a slag remover into the coal, one of bauxite, silicon carbide or alumina is added into the coal for mixing;

[0014] In the step S1, the fineness of the coal powder is controlled at the same time. When the boiler burns anthracite, the fineness of the coal powder is controlled at 7%-10% during the pulverization process.

[0015] Preferably, when adding coal that is not prone to slagging into coal that has a relatively serious slagging tendency, the coal that has a relatively serious slagging tendency is selected from Jincheng coal in Shanxi, and the coal that is not prone to slagging is selected from Xindeng coal in Henan.

[0016] Preferably, the tangential diameter of the furnace is controlled to be in a suitable size in step S2. For a tangential burner, the tangential diameter is controlled to be between 430 mm and 800 mm.

[0017] In the step S2, when adjusting the position of the internal structure of the furnace, the front and rear walls are arranged in opposition to each other so that the mixed airflows on both sides disturb each other.

[0018] Preferably, in the step S3 of controlling the temperature in the furnace, for most thermal coals, the temperature is controlled at 1200-1500° C.;

[0019] In step S3, the excess air coefficient in the furnace is controlled to be between 1.1 and 1.3;

[0020] The step S3 controls the negative pressure intensity in the furnace to control the negative pressure intensity in the furnace to -50Pa to -100Pa.

[0021] Preferably, in the step S4 of coating the heating surface with an anti-dust coating, the anti-dust coating is made of a ceramic coating;

[0022] In the step S4, soot blowing is performed regularly on the heating surface by using soot blowing equipment, and sonic soot blowing is performed regularly at intervals of 1-7 days.

[0023] Preferably, the ceramic coating comprises a ceramic phase, a metal binder, a lubricant, and a surface modifier.

[0024] Preferably, the ceramic phase is made of silicon carbide material, the metal binder is made of nickel, the lubricant is made of polytetrafluoroethylene lubricant, and the surface modifier is made of silane coupling agent and yellow tungsten oxide.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1. The present invention controls the size of the furnace tangential diameter while adopting a structural design of front and rear wall hedge arrangement in the furnace, so as to reasonably control the probability of wind in the burner tangential diameter impacting the furnace wall, thereby reducing the development trend of slagging and making the mixing more complete, which is conducive to combustion. At the same time, the present invention is assisted by precise control of the furnace temperature, the furnace excess air coefficient, and the negative pressure strength in the furnace, so as to further reduce the probability of slagging, thereby reducing the ash accumulation and slagging attached to the boiler.

[0027] 2. The present invention also applies a special ceramic coating on the heating surface in the boiler. The special ceramic coating uses silicon carbide and nickel as a base, uses polytetrafluoroethylene lubricant to increase surface lubricity, and uses silane coupling agent and yellow tungsten oxide for surface modification, so that dust and slag are not easy to adhere to the heating surface. Even if they are attached to the heating surface, the dust and slag can be easily blown off by ultrasonic soot blowing, and the cleaning is completed quickly. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a schematic structural diagram of the heating surface of a coal-fired power station boiler of the present invention. DETAILED DESCRIPTION

[0029] Embodiment 1, as Figure 1 As shown, the present invention relates to a method for controlling ash and slagging on the heating surface of a coal-fired boiler, comprising the following steps:

[0030] S1: Control the quality of coal: obtain various indicators of coal, pre-treat the coal, mix other coal into it according to its slagging tendency, add deslagging agent into the coal, and control the fineness of coal powder;

[0031] Research has found that for coal-fired boilers, most of the slagging and ash accumulation problems are caused by coal quality problems, such as high impurity content and high moisture content, which can cause slagging and ash accumulation problems. Therefore, controlling the quality of coal should be given priority consideration. Specifically, it can be done from the following aspects:

[0032] (1) Among the various indicators of coal, the ash softening temperature and comprehensive discrimination index value of coal are mainly obtained; the characteristics of coal itself determine its scaling and slagging characteristics to a large extent. The key indicators of ash slagging tendency include ash softening temperature, silicon-aluminum ratio SiO2 / Al2O3, alkali-acid ratio, silicon ratio, sulfur slagging index value, comprehensive discrimination index value, etc. The ash softening temperature and comprehensive discrimination index value can directly reflect the slagging tendency of coal, and measures should be taken to control it in actual use.

[0033] (2) In the pretreatment of coal, the coal is first screened to remove large impurities and gangue in the coal, and then the content of fine impurities in the coal is reduced by coal washing; through pretreatment methods such as coal washing, the content of impurities such as ash and sulfur in the coal is reduced to improve the quality of the fuel. At the same time, the coal can also be screened to remove large impurities and gangue, so that the fuel is more evenly burned during the combustion process and the ash accumulation caused by uneven combustion of the fuel is reduced.

[0034] (3) According to the slagging tendency of coal, other coals are mixed into it. Coals that are not easy to slag are added to coals with a more serious slagging tendency, and the mixture is used to reduce the slagging of coal ash; when adding coals that are not easy to slag to coals with a more serious slagging tendency, the coals with a more serious slagging tendency are selected from Shanxi Jincheng coal, and the coals that are not easy to slag are selected from Henan Xindeng coal; for coals with a relatively large slagging tendency, the slagging of coal ash can be reduced or inhibited through coal blending and combustion. As confirmed by a large number of tests and operational practices, adding coals that are not easy to slag to coals with a more serious slagging tendency can greatly reduce the slagging of coal ash. For example, when Shanxi Jincheng coal is used alone, the boiler slagging is more serious, and coking and coking will be carried out frequently. When using Shanxi Jincheng coal, after adding Henan Xindeng coal, the scaling and slagging conditions are greatly improved.

[0035] (4) Adding a slag remover to the coal, mixing one of bauxite, silicon carbide or alumina into the coal; the working principle of the slag remover is to increase the ash melting point of coal combustion, promote the crystallization of the ash melt, and change it into crystals that are not easy to slag at high temperatures. In other words, a small amount of cheap powdered and granular materials, such as bauxite, silicon carbide and alumina, are injected into the furnace. This method can greatly reduce slagging, reduce the degree of slagging and significantly reduce the slagging speed.

[0036] (5) At the same time, the fineness of the coal powder should be controlled. When burning anthracite in the boiler, the fineness of the coal powder should be controlled at 7% during the pulverization process; the fineness of the coal powder should be controlled moderately in the actual selection of coal. If the coal powder is too fine, the ignition will be too early, which will easily lead to excessive heat load in the burner area, causing coking near the burner and burning the nozzle; if the coal powder is too coarse, the ignition delay time and the flame center will move upward, thereby increasing the flue gas temperature at the furnace outlet. Therefore, during the pulverization process, the fineness of the coal powder should be maintained within an effective range. For boilers burning anthracite, the fineness of the coal powder should be controlled within the range of 7%-10%.

[0037] S2: Carry out furnace reconstruction: control the tangential diameter of the furnace to an appropriate size and adjust the position of the internal structure of the furnace;

[0038] The structure of the furnace of an existing coal-fired boiler is the main factor affecting ash and slagging. Specifically, it can be controlled from the following aspects:

[0039] (1) Control the tangential diameter of the furnace to an appropriate size. For the four-corner tangential burner, the tangential diameter is controlled within 500 mm. For the common four-corner tangential burner, research has found that when the tangential diameter of the furnace is relatively large, the slagging development trend will expand with the expansion of the tangential diameter, and a large amount of molten and semi-molten particles will directly impact the water-cooled wall and adhere to the water-cooled wall, causing slagging. For example, when the tangential diameter is greater than 800 mm, the radial velocity tends to the wall in some areas; when the tangential diameter is less than 430 mm, the radial velocity is all toward the center of the furnace. Both situations will cause slagging. For this reason, reasonable control of the burner tangential diameter will reduce the probability of wind impacting the furnace wall, thereby reducing the development trend of slagging.

[0040] (2) When adjusting the position of the internal structure of the furnace, the front and rear walls are arranged in opposition to each other, so that the mixed airflows on both sides disturb each other. For example, when implementing furnace reconstruction, the front and rear walls are arranged in opposition to each other, so that the mixed airflows on both sides disturb each other, making the mixing more complete and conducive to combustion.

[0041] S3: Control the combustion process: During the coal burning process, control the furnace temperature, excess air coefficient, and negative pressure intensity in the furnace;

[0042] Controlling the combustion process can also effectively control the slagging process. Specifically, it can be controlled from the following aspects:

[0043] (1) Control the temperature in the furnace. For most thermal coals, the temperature is controlled at 1300℃. The temperature level in the furnace has a multi-faceted effect on slagging. The high temperature in the furnace will vaporize the alkaline oxides in the coal and condense the alkaline earth metal compounds on the heating surface, forming dense and strongly bonded ash. When the flue gas temperature and the tube wall temperature are high, the adhesion between the ash surface layer and the alkali metal compounds will increase, thereby accelerating the ash accumulation process. When the temperature is high, the coal ash melts or semi-melts and directly adheres to the heating surface, causing serious slagging. Therefore, the temperature in the furnace must be strictly controlled to prevent the temperature from being too high.

[0044] (2) Control the excess air coefficient in the furnace and keep the excess air coefficient at 1.2; as the excess air coefficient increases, the tendency of ash and slagging on the heating surface decreases. That is, when the excess air coefficient increases, the flue gas temperature at the furnace outlet decreases, which can reduce the ash accumulation and slagging of the superheater. At the same time, as the excess air coefficient increases, the furnace wall temperature decreases, the sediment in the furnace decreases, and the tendency of slagging on the heating surface in the furnace decreases. If the excess air coefficient is too low, it is very easy to cause insufficient oxygen supply, which will increase the probability of slagging. Therefore, it is very important to maintain a moderate excess air coefficient.

[0045] (3) Control the negative pressure strength in the furnace and keep it at -80Pa. Maintaining an appropriate negative pressure in the furnace can not only ensure the stability of the combustion process, but also prevent smoke leakage, and control the flow rate and direction of the smoke. Generally, the negative pressure in the furnace should be controlled between -50Pa and -100Pa, so that the smoke can stay in the furnace for a sufficient time, allowing the ash to settle fully, reducing the amount of ash carried out with the smoke, and thus reducing the risk of ash accumulation.

[0046] S4: Keep the heating surface clean: Apply a dust-proof coating on the heating surface and blow dust on the heating surface regularly using dust-blowing equipment;

[0047] The ash and slagging of the heating surface is an accumulation and superposition process. When a small amount of slagging appears on the heating surface, the surface roughness increases, the temperature rises, and the slagging speed accelerates. Regular soot blowing and keeping the heating surface clean are effective measures to prevent shutdowns caused by slagging. Specifically, it can be controlled from the following aspects:

[0048] (1) In the case of coating the heating surface with an anti-ash deposition coating, the anti-ash deposition coating is made of a ceramic coating; coating the heating surface with an anti-ash deposition coating or performing special surface treatment, such as using a nano coating, a ceramic coating, etc., can change the surface characteristics of the heating surface, making it difficult for ash to adhere, or even if it adheres, it is easy to fall off, thereby effectively reducing the formation of ash deposition.

[0049] (2) The soot blowing equipment is used to blow the heating surface regularly, and the soot blowing is carried out regularly every 3 days. There are many methods of boiler soot blowing. Steam soot blowing uses the kinetic energy of steam and the ash dissolving ability of steam to remove the dust on the surface of the heating surface; soot cleaning uses compressed air as the energy source of the sound wave. The high-strength titanium metal diaphragm oscillates self-excitedly under the action of the compressed air source and resonates in the resonant cavity, converting the potential energy of the compressed air into low-frequency sound energy, and transmitting the sound energy to the corresponding dust accumulation point through the air medium, so that the sound wave has the effect of "acoustic fatigue" on the ash and slag. Due to the repeated action of the sonic oscillation, the extrusion cyclic load applied to the ash and slag reaches a certain number of cyclic stresses. The structure of the ash and slag is destroyed due to fatigue, and then the ash and slag is blown out of the surface of the attachment due to gravity or fluid medium, achieving the effect of cleaning.

[0050] Example 2, based on Example 1, other solutions remain unchanged, and the ceramic coating is replaced with a special ceramic coating including a ceramic phase, a metal binder, a lubricant, and a surface modifier;

[0051] The ceramic phase is made of silicon carbide material, the metal binder is made of nickel, the lubricant is made of polytetrafluoroethylene lubricant, and the surface modifier is made of silane coupling agent and yellow tungsten oxide;

[0052] The crystal structure of silicon carbide (SiC) is hexagonal α-SiC: In hexagonal silicon carbide crystals, the arrangement of atoms presents a hexagonal columnar structure. The atomic arrangement between layers is slightly different, resulting in a certain anisotropy in its crystal structure. Its basic structural unit is also composed of SiC tetrahedrons, but the arrangement and connection of the tetrahedrons are different from those of the cubic system. It has good stability and oxidation resistance at high temperatures and is often used in structural materials and refractory materials in high temperature environments. For example, in the lining of high-temperature boilers, hexagonal silicon carbide ceramics can perform well.

[0053] Nickel has good high-temperature strength and oxidation resistance, and can remain stable in high-temperature environments. It has good bonding ability with silicon carbide ceramics, and can firmly bond ceramic particles together to form a uniform and dense coating. For example, in the lining coating of some high-temperature boilers, silicon carbide ceramic coatings using nickel-based binders can effectively resist the scouring and erosion of high-temperature airflow and extend the service life of the boiler.

[0054] PTFE lubricant has extremely low surface energy, and is one of the lowest surface energies among known solid materials. It has excellent chemical stability, is resistant to corrosion by chemicals such as acids, alkalis, and salts, can maintain stable performance over a wide temperature range, and has good self-lubricity and non-stickiness. PTFE lubricant can form a smooth, non-sticky film on the surface of the equipment, and it is difficult for fly ash particles to adhere to its surface. Even if a small amount of fly ash contacts the PTFE film, due to its non-stickiness, the fly ash can easily fall off under the action of external forces during the operation of the equipment, thereby preventing the fly ash from sticking.

[0055] The molecular structure of silane coupling agent contains organic functional groups and hydrolyzable groups. When it comes into contact with the surface of an object and reacts, it will form a layer of organic silicon film with low surface energy on the surface. The existence of this film increases the contact angle between dust particles and the surface of the object, thereby reducing the adhesion of dust particles on the surface. Taking the heating surface of a boiler as an example, after being treated with silane coupling agent, the surface energy of the heating surface is significantly reduced, and it becomes difficult for dust particles to adhere to its surface, thereby greatly reducing the formation of dust accumulation. Even in an environment with a certain dust concentration, dust is more likely to fall off the surface under the action of airflow or equipment vibration, effectively keeping the surface of the equipment clean.

[0056] Yellow tungsten oxide has a yellow powder appearance and has good application prospects in the field of photocatalysis. It can absorb visible light and ultraviolet light and convert them into active oxygen species, thereby realizing photocatalytic reactions. It has high photoelectric conversion efficiency, good chemical stability and thermal stability, and can maintain catalytic activity under high temperature and acid-base environments. It is suitable for some high-temperature and light-irradiated environments, and has a good effect on preventing dust from adhering and accumulating on the surface of the equipment.

[0057] The embodiments of the present invention disclose preferred embodiments, but are not limited thereto. A person skilled in the art can easily understand the spirit of the present invention based on the above embodiments and make different extensions and changes. However, as long as they do not deviate from the spirit of the present invention, they are all within the protection scope of the present invention.

Claims

1. A method for controlling ash and slagging on the heating surface of a coal-fired boiler, characterized in that: The following steps are involved: S1: Control the quality of coal: obtain various indicators of coal, pre-treat the coal, mix other coal into it according to its slagging tendency, add deslagging agent into the coal, and control the fineness of coal powder; S2: Carry out furnace reconstruction: control the tangential diameter of the furnace to an appropriate size and adjust the position of the internal structure of the furnace; S3: Control the combustion process: During the coal burning process, control the furnace temperature, excess air coefficient, and negative pressure intensity in the furnace; S4: Keep the heating surface clean: Apply a dust-proof coating on the heating surface and blow dust on the heating surface regularly using dust-blowing equipment.

2. The method for controlling ash and slagging on the heating surface of a coal-fired boiler according to claim 1, characterized in that: In the step S1, the coal indexes are mainly obtained, namely, the ash softening temperature and the comprehensive discrimination index value of the coal; In the step S1 of pre-treating the coal, the coal is first screened to remove large particles of impurities and gangue in the coal, and then the content of fine impurities in the coal is reduced by coal washing; In step S1, other coals are mixed into the coal according to its slagging tendency, and coals that are not easy to slagging are added to the coal with a more serious slagging tendency, and the mixed use reduces the slagging of the coal ash; In the step S1, in the step of adding a slag remover into the coal, one of bauxite, silicon carbide or alumina is added into the coal for mixing; In the step S1, the fineness of the coal powder is controlled at the same time. When the boiler burns anthracite, the fineness of the coal powder is controlled at 7%-10% during the pulverization process.

3. The method for controlling ash and slagging on the heating surface of a coal-fired boiler according to claim 2, characterized in that: When adding coal that is not prone to slagging into coal with a more serious slagging tendency, the coal with a more serious slagging tendency is Shanxi Jincheng coal, and the coal that is not prone to slagging is Henan Xindeng coal.

4. The method for controlling ash and slagging on the heating surface of a coal-fired boiler according to claim 1, characterized in that: In step S2, the tangential diameter of the furnace is controlled to be in an appropriate size. For a square tangential burner, the tangential diameter is controlled between 430 mm and 800 mm. In the step S2, when adjusting the position of the internal structure of the furnace, the front and rear walls are arranged in opposition to each other so that the mixed airflows on both sides disturb each other.

5. The method for controlling ash and slagging on the heating surface of a coal-fired boiler according to claim 1, characterized in that: In the step S3 of controlling the temperature in the furnace, for most thermal coals, the temperature is controlled at 1200-1500° C.; In step S3, the excess air coefficient in the furnace is controlled to be between 1.1 and 1.3; The step S3 controls the negative pressure intensity in the furnace to control the negative pressure intensity in the furnace to -50Pa to -100Pa.

6. The method for controlling ash and slagging on the heating surface of a coal-fired boiler according to claim 1, characterized in that: In the step S4 of coating the heated surface with an anti-dust coating, the anti-dust coating is made of a ceramic coating; In the step S4, soot blowing is performed regularly on the heating surface by using soot blowing equipment, and sonic soot blowing is performed regularly at intervals of 1-7 days.

7. The method for controlling ash and slagging on the heating surface of a coal-fired boiler according to claim 6, characterized in that: The ceramic coating comprises a ceramic phase, a metal binder, a lubricant and a surface modifier.

8. The method for controlling ash and slagging on the heating surface of a coal-fired boiler according to claim 7, characterized in that: The ceramic phase is made of silicon carbide material, the metal binder is made of nickel, the lubricant is made of polytetrafluoroethylene lubricant, and the surface modifier is made of silane coupling agent and yellow tungsten oxide.

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