Method for reducing slagging risk of pulverized coal fired boiler by using coal gangue solid waste

Abstract

The invention provides a method for reducing the slagging risk of a pulverized coal fired boiler through coal gangue solid waste. The method comprises the steps that coal gangue with a preset mixing proportion is added into raw coal, and mixed coal is obtained; carrying out crushing treatment on the blended coal so as to reach preset pulverized coal fineness; and feeding the crushed blended coal into a hearth for combustion. By utilizing the high melting point of the solid waste coal gangue and high-content silicon-aluminum minerals in the solid waste coal gangue, the melting characteristic of the coal as fired can be improved, the ash components can be regulated and controlled, the slagging risk of the pulverized coal fired boiler can be effectively reduced, and the operation safety of the boiler is improved. The slag-bonding risk of the pulverized coal boiler is reduced through the solid waste coal gangue, the coal gangue is low in cost, power plant equipment does not need to be additionally arranged, operation is easy, practicability and high efficiency are achieved, and the economical efficiency of a power plant can be guaranteed; meanwhile, the slag bonding risk of the pulverized coal fired boiler is reduced, the coal gangue solid waste is harmlessly treated, the coal gangue solid waste can be effectively utilized, environmental pollution is avoided, and good social benefits are achieved.

Description

Technical Field

[0001] The present application belongs to the field of thermal power generation technology, and specifically, relates to a method for reducing the slagging risk of pulverized coal boilers by utilizing coal gangue solid waste. Background Art

[0002] At present, the coal supply situation of domestic coal-fired power units is complicated, with various raw coal types, and most of them are mixed coal, most of which deviate from the designed coal types of the units, resulting in slagging problems in the operation of pulverized coal boilers. Among them, the slagging problem caused by high-alkali coal is the most typical. Alkali metals (Na, K) and alkaline earth metals account for a large proportion of the ash content of high-alkali coal. Therefore, burning high-alkali coal will cause serious slagging, which is easy to cause safety problems and economic losses. Power plants often add additives rich in silicon-aluminum minerals to alleviate slagging. Kaolin is a commonly used additive, but kaolin is expensive, which affects the economic efficiency of power plants. Summary of the invention

[0003] The technical problem solved by the present application is: how to provide a low-cost method for reducing the risk of slagging in pulverized coal boilers.

[0004] The present application provides a method for reducing the slagging risk of a pulverized coal boiler by using coal gangue solid waste, the method comprising:

[0005] Adding coal gangue of a preset blending ratio to raw coal to obtain blended coal;

[0006] Crushing the blended coal to achieve the preset coal powder fineness;

[0007] The crushed blended coal is sent into the furnace for combustion.

[0008] Optionally, the method of adding coal gangue of a preset blending ratio to raw coal to obtain blended coal includes:

[0009] Determine the preset blending ratio based on the ash composition, softening temperature and grindability index of the blended coal to be configured;

[0010] The mass of the coal gangue to be added is determined according to the preset blending ratio and the mass of the raw coal, and the coal gangue to be added is mixed with the raw coal to obtain blended coal.

[0011] Optionally, the method of jointly determining the preset blending ratio according to the ash composition, softening temperature, and grindability index of the blended coal to be configured includes:

[0012] The initial addition ratio of coal gangue is determined according to the quality of raw coal, the ash composition of raw coal and coal gangue, and the comprehensive slagging index of blended coal;

[0013] The blended coal samples are prepared according to the initial addition ratio, and the softening temperature and grindability index of the blended coal samples are measured;

[0014] The comprehensive evaluation index of the initial addition ratio is calculated based on the comprehensive slagging index, softening temperature and grindability index of the blended coal;

[0015] If the comprehensive evaluation index meets the preset requirements, the initial addition ratio will be used as the preset blending ratio; if the comprehensive evaluation index does not meet the preset requirements, the comprehensive slagging index will be adjusted and the above steps will be repeated until the comprehensive evaluation index meets the preset requirements.

[0016] Optionally, the method for determining the initial addition ratio of coal gangue according to the quality of raw coal, the ash composition of raw coal and coal gangue, and the comprehensive slagging index of blended coal includes:

[0017] A comprehensive slagging index is set according to a threshold value of the comprehensive slagging index of the blended coal, the preset value being less than or equal to the threshold value;

[0018] The mass of the gangue is calculated according to the comprehensive slagging index, the mass of the raw coal, and the ash composition of the raw coal and the gangue;

[0019] The initial addition ratio is calculated based on the mass of the gangue and the mass of the raw coal.

[0020] Optionally, the method for calculating the comprehensive evaluation index of the preliminary addition ratio according to the comprehensive slagging index, softening temperature and grindability index of the blended coal includes:

[0021] Determine the slagging index evaluation index according to the comprehensive slagging index of the blended coal, determine the softening temperature evaluation index according to the softening temperature, and determine the grindability evaluation index according to the grindability index;

[0022] The slagging index evaluation index, softening temperature evaluation index and grindability evaluation index are weighted averaged to obtain a comprehensive evaluation index.

[0023] Optionally, the method of crushing the blended coal to achieve a preset coal powder fineness includes:

[0024] The coal blending machine is used to crush the blended coal according to the preset coal powder fineness.

[0025] Optionally, the method further comprises:

[0026] Monitor the accident cooling water flow in the DCS system of coal-fired power units;

[0027] When the emergency cooling water flow rate is greater than the preset value, the heating surface in the furnace is purged.

[0028] The present application provides a method for reducing the slagging risk of pulverized coal boilers by using coal gangue solid waste, which has the following technical effects:

[0029] (1) The high melting point of solid waste coal gangue and the high content of silicon and aluminum minerals in it can improve the melting characteristics of the coal entering the furnace and regulate the ash composition, which can effectively reduce the slagging risk of pulverized coal boilers and improve the safety of boiler operation.

[0030] (2) Solid waste coal gangue is used to reduce the slagging risk of pulverized coal boilers. Coal gangue is low-cost, does not require new power plant equipment, is simple to operate, practical and efficient, and can ensure the economy of the power plant. At the same time, it can reduce the slagging risk of pulverized coal boilers and harmlessly treat coal gangue solid waste, which can effectively utilize coal gangue solid waste and avoid environmental pollution, and has good social benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 The present invention is a flow chart of a method for reducing the slagging risk of a pulverized coal boiler by using coal gangue solid waste according to one or more embodiments. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical solution and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0033] Before describing in detail each embodiment of the present application, the technical concept of the present application is briefly described first: At present, due to the presence of alkali metals and alkaline earth metals in coal powder, slagging is prone to occur during combustion, which affects the safety of power plants. Although adding kaolin can reduce the risk of slagging, the cost is high. To this end, the present application provides a method for reducing the slagging risk of coal powder boilers by using coal gangue solid waste. Coal gangue is added to raw coal to obtain blended coal. The blended coal is crushed and sent into the furnace for combustion. The high melting point of coal gangue solid waste and the high content of silicon and aluminum minerals therein can be used to improve the melting characteristics of raw coal and regulate the ash composition, which can effectively reduce the slagging risk of coal powder boilers and improve the safety of boiler operation. At the same time, the cost of coal gangue is low. The specific principle of the method of reducing the slagging risk of coal powder boilers by using coal gangue solid waste in the present application is described in combination with more embodiments.

[0034] Specifically, Figure 1 As shown, the method for reducing the slagging risk of a pulverized coal boiler by using coal gangue solid waste in this embodiment 1 includes the following steps:

[0035] Step S10: adding coal gangue of a preset blending ratio to raw coal to obtain blended coal.

[0036] Step S20: crushing the blended coal to achieve a preset coal powder fineness.

[0037] Step S30: sending the crushed blended coal into the furnace for combustion.

[0038] In one or more embodiments, the method of adding gangue of a preset blending ratio to raw coal to obtain blended coal in step S10 includes two parts: first, determining the preset blending ratio based on the ash content, softening temperature, and grindability index of the blended coal to be configured; second, determining the mass of the gangue to be added based on the preset blending ratio and the mass of the raw coal, and mixing the gangue to be added with the raw coal to obtain the blended coal. The preset blending ratio can be determined by experimental determination.

[0039] When the experimental determination method is adopted, the method for determining the preset blending ratio according to the ash composition, softening temperature and grindability index of the blended coal to be configured includes the following steps:

[0040] Step S101, determine the initial addition ratio of coal gangue according to the mass of raw coal, the ash content of raw coal and coal gangue, and the comprehensive slagging index of blended coal. Specifically, first, a comprehensive slagging index is set according to the threshold of the comprehensive slagging index of blended coal, and the preset value is less than or equal to the threshold; the mass of coal gangue is calculated according to the comprehensive slagging index, the mass of raw coal, and the ash content of raw coal and coal gangue; and the initial addition ratio is calculated according to the mass of coal gangue and the mass of raw coal.

[0041] For example, the comprehensive slagging index R f The lower the value, the lower the possibility of slagging. The threshold value of the comprehensive slagging index is R 1 , control the comprehensive slagging index R of blended coal f ≤R 1 The specific calculation process is as follows:

[0042]

[0043] In the formula, m coal is the mass of raw coal, a known quantity; m gob is the mass of added coal gangue; ∑ω coal,Alk is the mass percentage of each alkaline component in the raw coal ash; ∑ω gob,Alk is the mass percentage of each alkaline component in the lime of coal gangue; ∑ω coal,Aci is the mass percentage of each acidic component in the raw coal ash; ∑ω gob,Aci is the mass percentage of each acidic component in the gangue ash; and are respectively Na in the coal and gangue. 2 O mass content percentage. Alkaline component: Na 2 O.K 2 O, Fe 2 O 3 , CaO, MgO; acidic component: SiO 2 、Al 2 O3 、TiO 2 The raw coal mass m coal The ash composition of the coal and gangue fed into the furnace is known. By adjusting the mass of gangue added m gob The comprehensive slagging index R can be controlled f , and then the initial addition ratio η of coal gangue can be obtained.

[0044] Step S102: Prepare a blended coal sample according to the initial addition ratio, and measure the softening temperature and grindability index of the blended coal sample. For example, given a certain mass of raw coal, a corresponding mass of coal gangue is prepared according to the initial addition ratio η, and the blended coal sample is obtained by mixing, and then the softening temperature and grindability index are measured by experimental determination.

[0045] The softening temperature is determined by referring to the GB / T 219-2008 coal ash fusibility determination method. Take an air-dried coal sample with a particle size of less than 0.2 mm, completely ash it according to GB / T212, and then grind it to less than 0.1 mm with an agate mortar. Make the coal ash into a triangular cone of a certain size, heat it at a certain heating rate in a weak reducing atmosphere, observe the morphological changes of the ash cone during the heating process, and observe and record its four characteristic melting temperatures: deformation temperature, softening temperature, hemispherical temperature and flow temperature.

[0046] The determination of grindability index refers to GB / T2565-2014 coal grindability index determination method: Hardgrove method, using Hardgrove grindability index tester. Coal samples of a certain particle size range and mass are ground by Hardgrove grindability tester and sieved under specified conditions. The mass of the coal sample on the sieve is weighed, and the mass of the coal sample on the sieve is subtracted from the mass of the coal sample before grinding to obtain the mass of the coal sample under the sieve. The Hardgrove grindability index of coal can be obtained from the calibration chart drawn by the Hardgrove grindability index standard material of coal or calculated from the univariate linear regression equation.

[0047] Among them, the softening temperature ST of the blended coal is measured, and its threshold value is R 2 , by adjusting the initial addition ratio η to control the softening temperature ST ≥ R 2 , R 2 Generally, it is selected as the softening temperature of the designed coal or 1300℃. Generally, the ash melting point of coal that is easy to slag is generally low, while the ash melting point of coal gangue solid waste is very high. After blending, its ash melting point can be increased and its melting characteristics can be improved. The grindability index is generally graded by the Hardgrove grindability index. The larger the grindability index HGI is, the easier it is to grind the blended coal. The threshold value of the grindability index HGI is R 3 , and control the grindability index HGI ≥ R 3 For medium speed grinding, HGI ≥ 60 is generally required.

[0048] Step S103: Calculate the comprehensive evaluation index of the initial addition ratio according to the comprehensive slagging index, softening temperature and grindability index of the blended coal. Specifically, as the initial addition ratio η increases, the comprehensive slagging index R f The softening temperature ST decreases, the grindability index HGI decreases. Ideally, when the comprehensive slagging index, softening temperature and grindability index all meet their respective threshold conditions, the corresponding initial addition ratio η is the most optimized and can be directly used as the final preset blending ratio. However, in actual situations, it is usually difficult to meet the above three threshold conditions at the same time. Therefore, different weights are designed for each data to comprehensively evaluate the initial addition ratio η. When the initial addition ratio η reaches the predetermined conditions, it can be used as the preset blending ratio.

[0049] Exemplarily, the method for calculating the comprehensive evaluation index of the preliminary addition ratio according to the comprehensive slagging index, softening temperature and grindability index of the blended coal includes: determining the slagging index evaluation index according to the comprehensive slagging index of the blended coal, determining the softening temperature evaluation index according to the softening temperature, and determining the grindability evaluation index according to the grindability index; performing weighted average on the slagging index evaluation index, the softening temperature evaluation index and the grindability evaluation index to obtain the comprehensive evaluation index. That is, the comprehensive evaluation index P is generated by the weight evaluation method, and the calculation formula is as follows:

[0050] P=0.5P Rf +0.3P HGI +0.2P ST (3)

[0051] Where P Rf is the slagging index evaluation index, when R f When ≤0.2, When 0.2<R f ≤2, When R f >2, P Rf = 0. HGI It is the grindability evaluation index. When HGI≥60, P HGI =1, when 40≤HGI<60, HGI-2, when HGI<40, P HGI =0;P ST It is the softening temperature evaluation index. When ST≥1300℃, P ST =1, when 1200℃≤ST<1300, When ST<1200℃, P ST = 0. If P ≥ 0.6, the blending ratio is designed reasonably.

[0052] Step S104: If the comprehensive evaluation index meets the preset requirements, the initial addition ratio is used as the preset blending ratio; if the comprehensive evaluation index does not meet the preset requirements, the above steps are repeated after adjusting the comprehensive slagging index until the comprehensive evaluation index meets the preset requirements. According to the previous step, when the comprehensive evaluation index is greater than the set value, it means that the initial addition ratio can be used as the preset blending ratio, and the blended coal configured according to the preset blending ratio can effectively reduce the slagging risk.

[0053] In one or more embodiments, the method of crushing the blended coal to achieve a preset coal powder fineness includes: crushing the blended coal according to the preset coal powder fineness using a coal mill. For example, the coal powder fineness of a pulverized coal boiler is generally represented by R90, that is, the proportion of coal powder passing through a sieve with an aperture of 90 microns. The threshold value of the coal powder fineness R90 is R 4 After the blended coal is prepared, the dry ash-free volatile matter is detected and classified. Generally speaking, the control strategy of coal powder fineness R90 is as follows: anthracite: coal powder fineness R90 is controlled at about 6%; bituminous coal: coal powder fineness R90 is between 15% and 20%; lignite: coal powder fineness R90 is between 25% and 40%.

[0054] Specifically, after the preset blending ratio determined in step S10, coal gangue is added to the coal feeding device according to the preset blending ratio, and transported to the coal feeder through the coal conveyor belt. The coal feeder transports the blended coal to the pulverizer according to the set coal feeding amount. The pulverizer crushes the blended coal according to the coal powder fineness determined in 2., and sends it into the furnace for combustion through the primary air powder pipe and the burner. The grindability index of the blended coal after adjustment can meet the output requirements of the pulverizer; the blended coal with a high melting point after adjustment can improve the melting characteristics of the coal entering the furnace, increase the ash melting point, reduce the melting of ash particles, and avoid the appearance of hard slag that is difficult to clean; the high content of silicon-aluminum minerals in the coal gangue changes the ash composition of the coal entering the furnace, plays a certain role in fixing or reducing the release in the thermal conversion of alkali metals and alkaline earth metals, inhibits the deposition of ash on the heating surface, and reduces the risk of slagging in the boiler.

[0055] In one or more embodiments, the method further comprises:

[0056] Step S40: monitor the accident cooling water flow rate in the DCS system of the coal-fired power unit. When the accident cooling water flow rate is greater than a predetermined value, purge the heating surface in the furnace. For example, the predetermined value of the accident cooling water flow rate Att is R 5 , if the accident cooling water flow Att increases beyond the threshold R 5 , it means that the heat exchange effect in the furnace has decreased and the risk of slagging is high. The heating surface in the furnace should be purged immediately to avoid serious slagging.

[0057] The following is a specific example to illustrate the specific process of this method:

[0058] First, determine the preset blending ratio. The ash composition and softening temperature data of raw coal and coal gangue are shown in Table 1. The raw coal is a high-alkali metal and high-alkaline earth metal coal with a softening temperature of 1100℃, which is a typical slagging coal; the main component of coal gangue is silicon-aluminum minerals with a softening temperature of 1500℃.

[0059] Table 1 Ash composition and softening temperature

[0060]

[0061] In this embodiment, the threshold R 1 Set to 0.8, threshold R 2 Set to 1300℃, threshold R 3 Set to 60, threshold R 4 Set to 18%, threshold R 5 Set to 10t / h. Raw coal feed rate m coal =450t / h, comprehensive slagging index R f ≤0.8, calculated according to formula (2), m gob ≥69.71t / h, rounded to 70t / h, the calculated blending ratio η=13.46%. The measured ash melting point of the blended coal is 1420℃, and the grindability index is 50. The comprehensive evaluation index P is calculated, P=0.68, and the blending scheme is reasonable. The dry ash-free volatile matter of the blended coal is detected to be 37.5%, which is bituminous coal, and the coal powder fineness R90 is controlled at 18%. According to the determined blending ratio, coal gangue is added to the coal feeding device according to the proportion, and transported to the coal feeder through the coal conveyor belt. The coal feeder transports the blended coal to the pulverizer according to the set coal feeding amount of 70t / h. The pulverizer determines the coal powder fineness R90=18%, crushes the blended coal, and sends it into the furnace through the primary air powder pipe and burner for combustion. Monitor the accident cooling water flow Att in the DCS system of the coal-fired power unit. If the threshold R 5 If the coal gangue mixing ratio η is 13.46%, the slagging risk of the pulverized coal boiler is greatly reduced, the long-term stable operation of the unit is achieved, and the effective treatment of coal gangue solid waste is achieved.

[0062] The specific implementation methods of the present application are described in detail above. Although some embodiments have been shown and described, those skilled in the art should understand that these embodiments can be modified and improved without departing from the principles and spirit of the present application whose scope is defined by the claims and their equivalents. These modifications and improvements should also be within the scope of protection of the present application.

Claims

1. A method for reducing the slagging risk of pulverized coal boilers by using coal gangue solid waste, characterized in that: The method comprises: Adding coal gangue of a preset blending ratio to raw coal to obtain blended coal; Crushing the blended coal to achieve the preset coal powder fineness; The crushed blended coal is sent into the furnace for combustion.

2. The method for reducing the slagging risk of pulverized coal boilers by using coal gangue solid waste according to claim 1, characterized in that: The method of adding coal gangue of a preset blending ratio to raw coal to obtain blended coal comprises: Determine the preset blending ratio based on the ash composition, softening temperature and grindability index of the blended coal to be configured; The mass of the coal gangue to be added is determined according to the preset blending ratio and the mass of the raw coal, and the coal gangue to be added is mixed with the raw coal to obtain blended coal.

3. The method for reducing the slagging risk of pulverized coal boilers by using coal gangue solid waste according to claim 2, characterized in that: The method for determining the preset blending ratio based on the ash composition, softening temperature and grindability index of the blended coal to be configured includes: The initial addition ratio of coal gangue is determined according to the quality of raw coal, the ash composition of raw coal and coal gangue, and the comprehensive slagging index of blended coal; The blended coal samples are prepared according to the initial addition ratio, and the softening temperature and grindability index of the blended coal samples are measured; The comprehensive evaluation index of the initial addition ratio is calculated based on the comprehensive slagging index, softening temperature and grindability index of the blended coal; If the comprehensive evaluation index meets the preset requirements, the initial addition ratio will be used as the preset blending ratio; if the comprehensive evaluation index does not meet the preset requirements, the comprehensive slagging index will be adjusted and the above steps will be repeated until the comprehensive evaluation index meets the preset requirements.

4. The method for reducing the slagging risk of pulverized coal boilers by using coal gangue solid waste according to claim 3 is characterized in that: The method for determining the initial addition ratio of coal gangue according to the quality of raw coal, the ash composition of raw coal and coal gangue, and the comprehensive slagging index of blended coal includes: A comprehensive slagging index is set according to a threshold value of the comprehensive slagging index of the blended coal, the preset value being less than or equal to the threshold value; The mass of the gangue is calculated according to the comprehensive slagging index, the mass of the raw coal, and the ash composition of the raw coal and the gangue; The initial addition ratio is calculated based on the mass of the gangue and the mass of the raw coal.

5. The method for reducing the slagging risk of pulverized coal boilers by using coal gangue solid waste according to claim 3, characterized in that: The method for calculating the comprehensive evaluation index of the preliminary addition ratio according to the comprehensive slagging index, softening temperature and grindability index of the blended coal includes: Determine the slagging index evaluation index according to the comprehensive slagging index of the blended coal, determine the softening temperature evaluation index according to the softening temperature, and determine the grindability evaluation index according to the grindability index; The slagging index evaluation index, softening temperature evaluation index and grindability evaluation index are weighted averaged to obtain a comprehensive evaluation index.

6. The method for reducing the slagging risk of pulverized coal boilers by using coal gangue solid waste according to claim 1, characterized in that: Methods for crushing blended coal to achieve a preset coal powder fineness include: The coal blending machine is used to crush the blended coal according to the preset coal powder fineness.

7. The method for reducing the slagging risk of pulverized coal boilers by using coal gangue solid waste according to claim 1, characterized in that: The method further comprises: Monitor the accident cooling water flow in the DCS system of coal-fired power units; When the emergency cooling water flow rate is greater than the preset value, the heating surface in the furnace is purged.

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