Coal ash component-based mixed coal slagging tendency prediction method

Abstract

The invention discloses a coal ash component-based mixed coal slagging tendency prediction method, and belongs to the field of coal-fired boilers. The method comprises the following steps: firstly, according to the early-stage operation condition of the boiler, roughly judging which coal types are easy to ash and slag on the heating surface of the boiler and which coal types are not easy to ash and slag on the heating surface of the boiler; then, coal ash of all coal types is obtained through a combustion experiment, component analysis of the coal ash is conducted, the slagging tendency of all the coal types is judged according to the ash component result, and the maximum coal ash sodium equivalent value allowed by the boiler is obtained. According to the method, the slagging tendency of the mixed coal can be predicted according to the components of the coal ash, so that a guidance basis is provided for formulating and optimizing a boiler field coal blending combustion scheme of a coal-fired enterprise, the slagging degree of the boiler when high-alkali coal is independently combusted is relieved by adopting the mixed coal blending combustion scheme, and it is ensured that the boiler can operate safely, economically and stably.

Description

Technical Field

[0001] The invention relates to a coal-fired boiler, and in particular to a method for predicting the slagging tendency of mixed coal based on coal ash components. Background Art

[0002] As we all know, the development of modern society is still very dependent on traditional fossil energy. According to relevant statistics, about 70% of the world's total energy consumption comes from primary energy such as coal, oil, and natural gas. In recent years, my country's total consumption of coal, oil, natural gas, primary electricity and other energy has exceeded 4 billion tons of standard coal; among them, coal accounts for about 60% of the total energy consumption. In the future, as the total global power generation and energy consumption continue to increase, coal will still be the main source of energy and power for developing countries including China.

[0003] Power plant boilers and industrial boilers in my country are generally coal-fired, and the coal used often deviates from the designed coal type. The quality of power coal is poor, with high ash and sulfur content, which is very easy to cause contamination, ash accumulation, slagging, corrosion and wear of the boiler heating surface. High-alkali coal, such as Xinjiang Zhundong coal, is prone to serious ash accumulation and slagging problems in the actual combustion and utilization process. When the boiler directly burns high-alkali coal, alkali metals (Na, K) will form a sticky inner white layer on the surface of the heating surface and fly ash particles, making it easy for fly ash particles to deposit on the heating surface. Under the action of high temperature for a long time, the elements such as Ca, Mg, Fe, Al, S in the ash will produce a melting effect, and chemical reactions such as corrosion and replacement will occur on the heating surface, gradually forming serious slagging, which may cause the boiler to reduce efficiency, flameout, or even stop the boiler due to over-temperature pipe bursting. Major safety accidents, seriously affecting the safe and stable operation of the boiler. Therefore, how to alleviate the ash accumulation and slagging of high-alkali coal is a practical engineering problem that needs to be solved urgently.

[0004] Mixed coal combustion is one of the important ways to solve the problems of tight fuel supply and complex and changeable coal types in coal-fired power plant boilers in my country, and to improve the safety, economy and environmental protection of unit operation. However, most of my country's power plants currently rely mainly on experience to use different types of coal for mixed combustion during operation. In addition, the on-site operators do not have enough understanding of the combustion state in the furnace. When faced with complex and changeable coal types, if the boiler cannot be operated under the optimal combustion state, the slagging of the boiler will become more serious. At present, the method of mixed coal combustion generally selected by power plants based on experience is highly random, and the negative impact of unreasonable ratios of mixed combustion is not responded to in time, which may not only aggravate the ash and slagging of the boiler heating surface, but also increase the operating costs of the power plant. Therefore, it is urgent to find a more complete solution for mixed coal combustion in related fields.

[0005] In summary, adopting a scientific and reasonable coal blending and combustion scheme is of great research significance for ensuring the safe and stable operation of the boiler. Therefore, the present invention provides a method for predicting the slagging tendency of mixed coal based on coal ash composition, which can provide a guiding basis for the formulation and optimization of on-site coal blending and combustion schemes for coal-fired enterprises. Summary of the invention

[0006] Purpose of the invention: The purpose of the present invention is to provide a method for predicting the slagging tendency of mixed coal based on coal ash composition.

[0007] Technical solution: A method for predicting the slagging tendency of mixed coal based on coal ash composition, the method comprising the following steps:

[0008] S1. According to the previous operation of the boiler, first roughly determine which coal types are likely to cause ash and slag on the boiler heating surface, and which coal types are not likely to cause ash and slag on the boiler heating surface;

[0009] S2. Obtain the coal ash of each type of coal through combustion experiments, and analyze the composition of the coal ash. According to the ash composition results, the slagging tendency of each type of coal is judged, and the maximum coal ash sodium equivalent value allowed by the boiler is obtained;

[0010] S3. Blend high-alkali coal that is prone to slagging with other types of coal that are not prone to slagging in different proportions to obtain mixed coal samples, and conduct combustion experiments on the mixed coal samples to obtain coal ash of the mixed coal. After analyzing the coal ash of the mixed coal, the slagging tendency of the mixed coal is judged, thereby providing guidance for determining the blending plan.

[0011] Preferably, in steps S2 and S3, the slagging tendency of each type of coal and the slagging tendency of mixed coal are judged using the following formula:

[0012]

[0013] Wherein, DL is the sodium equivalent, A is the ash content percentage of coal (%), 0.659 is the molar equivalent ratio of Na2O to K2O, ω(Na2O) is the percentage content of Na2O in coal ash (%), and ω(K2O) is the percentage content of K2O in coal ash (%).

[0014] Beneficial effect: The present invention can predict the slagging tendency of mixed coal according to the coal ash composition, thereby providing guidance for the formulation and optimization of on-site coal blending and combustion schemes for coal-fired enterprises' boilers. By adopting a mixed coal blending scheme, the slagging degree when the boiler burns high-alkali coal alone can be alleviated, ensuring that the boiler can operate safely, economically and stably. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a schematic diagram of a pulverized coal combustion system coupled with a settling furnace and a deposition furnace;

[0016] Figure 2 The graph shows the calculation results of slagging tendency of five coal samples burning separately;

[0017] Figure 3 This is the calculation result diagram of the slagging tendency of mixed coal samples at different blending ratios. DETAILED DESCRIPTION

[0018] In order to make the technical solution of the present invention clearer, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0019] A method for predicting the slagging tendency of mixed coal based on coal ash composition, characterized in that the method comprises the following steps:

[0020] (1) Based on the previous operation of the boiler, first roughly determine which types of coal are likely to cause ash and slagging on the boiler heating area, and which types of coal are not likely to cause ash and slagging on the boiler heating area.

[0021] (2) The ash of each type of coal is obtained through combustion experiments, and the composition of the ash is analyzed. The slagging tendency of each type of coal is judged based on the ash composition results using the formula (EQ), and the maximum ash sodium equivalent value (DL) allowed by the boiler is obtained. max ).

[0022] Among them, the formula (EQ) is:

[0023] Wherein, DL is the sodium equivalent, A is the ash content of coal (%), 0.659 is the molar equivalent ratio of Na2O to K2O, ω(Na2O) is the percentage content of Na2O in coal ash (%), and ω(K2O) is the percentage content of K2O in coal ash (%).

[0024] (3) High-alkali coal that is easy to slag and other types of coal that are not easy to slag are mixed in different proportions to obtain mixed coal samples, and combustion experiments are carried out on the mixed coal samples to obtain the coal ash of the mixed coal. After analyzing the coal ash of the mixed coal, the slag tendency of the mixed coal is judged according to the formula (EQ), thereby providing guidance for determining the blending plan.

[0025] Example

[0026] The boiler of the power generation unit of the Energy and Environmental Department of Zhanjiang Iron and Steel is a 350MW coal-gas mixed-fired boiler produced by Dongfang Boiler (Group) Co., Ltd., model DG1165.49 / 17.5-Ⅱ21, with subcritical parameters. The boiler type is a single furnace, Π-type open-air layout, balanced ventilation, one-time intermediate reheating, and four-corner tangential combustion. 5 medium-speed coal mills are positive pressure direct-blowing pulverizing systems, each with 4 pulverized coal burners, and 8 burnout air dampers are arranged on the upper part of the secondary air. The boiler is designed for Shenfu power coal, and the verification coal is Datong mixed coal.

[0027] In step (1), according to the previous operation of the boiler, one high-alkali coal (abbreviated as GJM) and four low-sodium coals (abbreviated as DN1, DN2, DN3, and DN4, respectively) were burned separately. When the high-alkali coal was burned separately, the boiler heating surface was prone to serious fouling and slagging, which could not be solved by combustion adjustment and enhanced soot blowing. When the above four low-sodium coals were burned separately, the boiler operation was generally good without obvious ash accumulation and slagging. Therefore, it is considered to mix and burn low-sodium coal in an appropriate proportion to solve the problem of slagging on the boiler heating surface caused by direct combustion of high-alkali coal.

[0028] Furthermore, in step (2), combustion experiments are conducted on the above five types of coal respectively, and then the components of the five types of coal ash are analyzed. Figure 1 The experimental conditions are as follows: the powder feeding device adopts a vibrating micro-powder feeder, and the powder feeding speed is 0.1 g min -1 The amount of pulverized coal used in each experiment was 18g. The pulverized coal was carried into the furnace by the primary air, mixed with the secondary air and burned in the furnace. The total ash produced after combustion was collected by a glass fiber filter cartridge. The gas supply device consists of a gas cylinder and a gas distributor, including primary air, secondary air and cooling air. The primary air flow rate is 5L·min -1 , secondary air flow rate is 10L·min -1 , cooling air flow rate is 10L·min -1 . The cooling air is used to cool the sampling device to prevent the collected total ash from undergoing secondary reactions. The combustion atmosphere used in the experiment was N2 / O2=21 / 79, which was used to simulate the air combustion atmosphere. The settling furnace and the deposition furnace are coupled and the furnace temperature is controlled by temperature control device 1 and temperature control device 2 respectively. The temperature of the settling furnace is set to 1300°C and the temperature of the deposition furnace is set to 800°C. The sampling device consists of an ash collector, a flow meter and an exhaust pump. The glass fiber filter cartridge for collecting total ash is placed in the ash collector.

[0029] Then, the slagging tendency of each type of coal is judged according to the ash composition results using the formula (EQ), and the maximum coal ash sodium equivalent value (DL max ). Among them, Table 1 shows the results of the ash composition of the five coal samples after the combustion experiment. Although the chemical composition of coal ash does not represent the specific composition of the physical phase, the difference in the percentage content (mass fraction) of its various components can be used to evaluate the slagging tendency of the coal types. It can be found that the ash content of GJM and DN2 is the lowest, about 5%, while the ash content of DN1, DN3 and DN4 exceeds 10%. The alkali metal content (Na2O+K2O) of GJM exceeds 4%, and the alkali metal content (Na2O+K2O) of DN1, DN2, DN3 and DN4 is all below 1%. Other components in coal ash mainly include SiO2, Fe2O3, Al2O3, CaO, SO3, MgO and TiO2. Therefore, based on the results of coal ash composition, the slagging tendency of the five coal samples burned separately was calculated, see Figure 2 According to the coal ash sodium equivalent index, GJM has the highest slagging tendency, which is much higher than the other four low-sodium coals, which is consistent with the actual situation. Since 0.05 is the maximum coal ash sodium equivalent among the four low-sodium coals, the maximum coal ash sodium equivalent value (DL max ) is set to 0.05.

[0030] Table 1 Ash composition of 5 coal samples after combustion experiment (wt%)

[0031] Coal Sample A <![CDATA[Na2O]]> <![CDATA[K2O]]> <![CDATA[SiO2]]> <![CDATA[Fe2O3]]> <![CDATA[Al2O3]]> CaO <![CDATA[SO3]]> MgO <![CDATA[TiO2]]> G J M 4.89 3.96 0.16 41.62 4.20 33.60 11.21 2.35 1.33 0.89 DN1 10.21 - 0.56 45.13 5.65 27.05 13.36 2.79 3.42 0.96 DN2 5.23 - 0.35 44.06 5.09 37.59 7.46 1.81 1.34 1.50 DN3 13.21 - 0.16 43.23 6.86 35.99 7.63 2.31 1.54 1.31 DN4 12.08 - 0.60 33.01 6.05 18.48 33.88 3.94 1.33 1.04

[0032] Note: “-” indicates below the detection limit

[0033] Finally, in step 3, the high-alkali coal (GJM) that is easy to slag and other types of coal that are not easy to slag (DN1, DN2, DN3, DN4) are mixed in different proportions to obtain mixed coal samples, and a combustion experiment is carried out on the mixed coal samples to obtain the coal ash of the mixed coal. After the coal ash of the mixed coal is analyzed, the slag tendency of the mixed coal is judged according to the formula (EQ). Among them, Table 2 shows the coal ash composition results of the mixed coal samples at different blending ratios after the combustion experiment. Based on the coal ash composition results, the slag tendency of the mixed coal samples at different blending ratios was calculated and compared with that when they were burned separately. See details. Figure 3. It can be found that the slagging tendency of high-alkali coal can be effectively reduced by blending with low-sodium coal for combustion. Among them, the sodium equivalent index of high-alkali coal can be reduced by about one-half by blending 25% or more of low-sodium coal. As the blending ratio of low-sodium coal increases, the sodium equivalent of the mixed coal ash decreases accordingly, which correspondingly indicates that the slagging tendency of the mixed coal is further reduced. Among them, when the blending ratio of low-sodium coal reaches 75%, the sodium equivalent of the mixed coal ash for blending DN2 and DN3 is already less than that for burning DN4 alone. According to the sodium equivalent index, the slagging tendency of coal types when burned alone is ranked from large to small as follows: GJM>DN4>DN1>DN3>DN2. Accordingly, when blending is carried out, the order according to the effect of blending is: DN2>DN3>DN1>DN4. Further, for the blending scheme of this boiler, it is recommended that when burning GJM, it should be blended with more than 75% of DN2 or DN3 to make the maximum coal ash sodium equivalent value (DL max ) is less than 0.05, thus ensuring that the boiler can operate safely, economically and stably.

[0034] Table 2 Ash composition (wt%) of mixed coal samples after combustion test at different blending ratios

[0035] Mixing ratio A <![CDATA[Na2O]]> <![CDATA[K2O]]> <![CDATA[SiO2]]> <![CDATA[Fe2O3]]> <![CDATA[Al2O3]]> CaO <![CDATA[SO3]]> MgO <![CDATA[TiO2]]> GJM / 25%DN1 4.98 1.76 0.17 27.95 6.99 17.59 39.88 2.86 0.71 1.13 GJM / 50%DN1 6.12 1.06 0.19 34.29 5.18 25.40 24.80 5.87 1.43 1.07 GJM / 75%DN1 8.13 0.58 0.22 37.28 5.17 29.08 21.68 2.60 1.39 1.17 GJM / 25% DN2 4.93 1.35 0.17 35.59 5.45 17.94 31.51 4.12 1.85 0.91 GJM / 50%DN2 5.00 0.94 0.18 35.81 5.44 19.84 27.97 5.76 1.70 0.88 GJM / 75%DN2 5.07 0.49 0.19 42.06 5.72 19.49 23.39 4.38 2.70 0.87 GJM / 25% DN3 7.16 1.05 0.16 29.97 4.57 22.01 28.73 10.09 1.06 1.06 GJM / 50%DN3 7.94 0.64 0.17 37.19 5.08 26.54 24.33 3.09 1.30 1.01 GJM / 75%DN3 8.35 0.36 0.16 36.21 5.61 28.20 22.01 4.14 1.24 1.24 GJM / 25%DN4 6.56 1.41 0.24 31.08 5.03 22.77 27.80 8.47 0.91 1.26 GJM / 50%DN4 7.67 0.89 0.28 34.56 5.10 25.56 21.87 8.30 1.07 1.37 GJM / 75%DN4 8.13 0.58 0.31 36.75 5.58 27.14 19.07 7.02 1.28 1.48

[0036] The present invention proposes a mixed coal burning scheme of high-alkali coal and low-sodium coal by analyzing the early operation of the 350MW coal-gas mixed-fired boiler of the power generation unit of the Energy and Environmental Department of Zhanjiang Iron and Steel, and predicts the slagging tendency of the mixed coal based on the ash composition, so that the ash sodium equivalent value of the mixed coal is less than the maximum ash sodium equivalent value of 0.05 allowed by the boiler, thereby ensuring that the boiler can operate safely, economically and stably. The present invention also has certain reference significance for the formulation and optimization of on-site coal blending and burning schemes for boilers of other coal-fired enterprises, and has good promotion and application prospects.

[0037] The above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the patent of the present invention. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for predicting the slagging tendency of mixed coal based on coal ash composition, characterized in that: The method comprises the following steps: S1. According to the previous operation of the boiler, first roughly determine which coal types are likely to cause ash and slag on the boiler heating surface, and which coal types are not likely to cause ash and slag on the boiler heating surface; S2. Obtain the coal ash of each type of coal through combustion experiments, and analyze the composition of the coal ash. According to the ash composition results, the slagging tendency of each type of coal is judged, and the maximum coal ash sodium equivalent value allowed by the boiler is obtained; S3. Blend high-alkali coal that is prone to slagging with other types of coal that are not prone to slagging in different proportions to obtain mixed coal samples, and conduct combustion experiments on the mixed coal samples to obtain coal ash of the mixed coal. After analyzing the coal ash of the mixed coal, the slagging tendency of the mixed coal is judged, thereby providing guidance for determining the blending plan.

2. The method for predicting the slagging tendency of mixed coal based on coal ash composition according to claim 1, characterized in that: In steps S2 and S3, the slagging tendency of each type of coal and the slagging tendency of mixed coal are judged using the following formula: Wherein, DL is the sodium equivalent, A is the ash content percentage of coal (%), 0.659 is the molar equivalent ratio of Na2O to K2O, ω(Na2O) is the percentage content of Na2O in coal ash (%), and ω(K2O) is the percentage content of K2O in coal ash (%).

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