A modified coal

Abstract

The invention discloses a modified coal. By adding solid particles or powders such as kaolin, bauxite, limestone, quartz ore, titanium dioxide, etc. to the coal, the ash composition and ash content of the modified coal are controlled, and the silicon and aluminum compounds in the ash are converted into silicon dioxide and aluminum trioxide. The mass ratio of silicon dioxide to aluminum trioxide is (1.0-4.0):1, and the sum of the mass of silicon dioxide and aluminum trioxide accounts for more than 40% of the total mass of the ash. The slagging and contamination characteristics of the coal can be improved, the serious slagging and contamination problems of the boiler can be alleviated and avoided, and the adaptability of the boiler to the fuel can be improved. The modified coal of the invention has simple components, the raw materials used are cheap and easy to obtain, and has good market prospects.

Description

Technical Field

[0001] The invention belongs to the technical field of coal-fired boilers, and in particular relates to a modified coal, which improves the slagging and contamination performance of the coal by adding part of a solid mixture to the coal to adjust the ash content and ash composition. Background Art

[0002] In coal-fired power station boilers, high-temperature combustion of pulverized coal is a complex physical-chemical process. The ash in the coal will also undergo complex physical and chemical reactions at high temperatures. Compounds with lower melting points will sublime and melt, and react with other compounds to form new compounds with lower melting points. These substances will condense, agglomerate, and condense in the form of melt or semi-melt on the heating surface, capturing solid ash particles in the coal, forming slag or contamination layers of different shapes and bonding strengths on the heating surface. These slag or contamination layers will directly increase the thermal resistance of the heating surface, reduce the thermal efficiency of the boiler, destroy the balance of heat absorption by the boiler evaporation and superheated heating surface, and reduce the thermal performance of the boiler. In addition, severe slagging and contamination are also major safety hazards. Thermal power plants often experience boiler safety accidents and forced shutdowns of units due to severe slagging and contamination.

[0003] The composition of coal ash directly affects the melting characteristics of ash and is the fundamental factor affecting boiler slagging and fouling. For coal-fired power plant boilers that have been designed, built, and put into operation, once the fuel is greatly adjusted, due to the large changes in the mineral composition of the coal, the boiler heating surface will often suffer from serious slagging and fouling problems, which directly affects the safe, economical, and stable operation of the boiler.

[0004] Through research, we believe that the slagging of the furnace and the fouling of the convection heating surface are complex and multi-factor coupled processes. The mechanisms are different and the degree of harm varies greatly. Only by clarifying the mechanism can we propose effective prevention and control measures. For example: K and Na compounds will become ionic at temperatures above 800°C and evaporate into the high-temperature flue gas. When they are cooled, they will condense on the surface of the ash particles and the surface of the heating surface, becoming "glue" and bonding other ash particles, forming serious slagging and fouling that is difficult to remove, directly endangering the safe, economical, clean and stable operation of the boiler. For example: Fe often exists in the form of pyrite. At high temperatures, due to different atmospheres, the intermediate compounds will be very different. In an aerobic environment, it can be converted into Fe 2 O 3 , Fe 3 O 4 In the absence of oxygen, it can be transformed into unstable FeS and FeO with low melting points, which will greatly reduce the ash melting point and worsen slagging and contamination. Summary of the invention

[0005] The purpose of the present invention is to provide a modified coal which can effectively alleviate the slagging and contamination problems of existing coal and improve the morphology of the slagging and contamination layer so that the slagging and contamination layer can be easily removed.

[0006] To achieve the above-mentioned purpose, the modified coal used in the present invention is composed of the following raw materials in percentage by mass: 80% to 98.5% coal, 1.5% to 20% kaolin, 0% to 15% bauxite, 0% to 8% limestone, 0% to 5% quartz ore, and 0% to 5% titanium dioxide. The silicon and aluminum compounds in the ash of the modified coal are converted into silicon dioxide and aluminum oxide, and the mass ratio of silicon dioxide to aluminum oxide is (1.0 to 4.0):1, and the sum of the mass of silicon dioxide and aluminum oxide accounts for more than 40% of the total mass of the ash.

[0007] The modified coal of the present invention is preferably composed of the following raw materials in percentage by mass: 85% to 98% coal, 2% to 15% kaolin, 0% to 10% bauxite, 0% to 5% limestone, 0% to 4% quartz ore, and 0% to 3% titanium dioxide. The silicon and aluminum compounds in the ash of the modified coal are converted into silicon dioxide and aluminum oxide, and the mass ratio of silicon dioxide to aluminum oxide is (1.3 to 3.2):1, and the sum of the mass of silicon dioxide and aluminum oxide accounts for 50% to 80% of the total mass of the ash.

[0008] The above-mentioned coal is the coal that is easy or relatively easy to form slag and stain on the boiler heating surface during high-temperature combustion.

[0009] The present invention adds a certain amount of solid matter (such as kaolin and bauxite) to coal that is prone to slagging and contamination. On the one hand, by increasing the total mass of ash in the coal, the content of harmful components in the ash is relatively reduced. On the other hand, by changing the composition of the ash, the physical and chemical reaction process and products of the ash during the combustion of the coal are directly affected, and the slagging and contamination of the coal are greatly improved. The added solid matter uses readily available, non-deeply processed raw minerals, which reduces costs. The detection method of the main compound components and content in the added solid matter can be consistent with the detection method of the ash and main components in the coal.

[0010] The test results show that the modified coal of the present invention can effectively alleviate and solve the problems of coal slagging and contamination, and the functions of each component are as follows:

[0011] 1. Provide necessary chemical reaction substances to promote the generation of low-melting-point substances in the furnace and capture more volatile and strong contaminants. Inside the furnace, adjust and supplement the necessary chemical reaction substances, and through the chemical reaction of high-temperature combustion, try to promote the generation of more low-melting-point substances, capture more strong contaminants that are volatile under high temperature conditions, reduce the proportion of these substances in high-temperature flue gas, and reduce their condensation on the subsequent convection heating surface, so as to achieve the goal of strengthening furnace slagging and reducing contamination of convection heating surfaces. The experimental results show that the reasonable control of the total amount of silicon dioxide and aluminum oxide, as well as the control of the ratio of silicon dioxide and aluminum oxide within a certain range can effectively adjust the ash melting point, and form aluminosilicates with volatile strong contaminants (such as alkali metals, alkaline earth metals, etc.), such as sodium aluminosilicate, potassium aluminosilicate, iron aluminosilicate and other substances. Kaolin, bauxite, and quartz can be used as raw materials for adjusting these two indicators.

[0012] 2. Effectively adjust the melting point of coal ash. The experimental results show that, except for the above-mentioned content and proportion of silicon dioxide and aluminum oxide, which have a great influence on the ash melting point, as the limestone content increases, the coal ash melting point will first decrease and then increase, and it is a better ash melting point regulator. Therefore, the amount of limestone added needs to be adjusted according to the distribution of coal ash components. For example, if the calcium content index in the coal ash is low, the content needs to be increased. If the content is high or too high, it can be omitted, or other components can be increased to relatively reduce the calcium content.

[0013] 3. Alleviate and avoid sulfur corrosion on boiler heating surfaces. Adding limestone can effectively reduce the high-temperature corrosion of hydrogen sulfide on furnace heating surfaces in coal-fired boilers, and reduce the low-temperature corrosion of sulfur trioxide on heating surfaces such as air preheaters. The addition of an appropriate amount of limestone can capture and solidify hydrogen sulfide and sulfur trioxide released and converted during high-temperature combustion of sulfur in coal, forming stable, non-corrosive calcium sulfate.

[0014] 4. Increase the number of high melting point solid particles and reduce the bonding strength of slagging and contamination. There are substances that are volatile at high temperatures and can condense on the surface of ash particles at lower temperatures, such as silicates, alkali metal compounds, etc. They have the ability to strongly bond other solid ash particles and play the role of "glue", causing ash particles to condense and coagulate, forming serious slagging and contamination. Titanium dioxide is a solid particle with a very high melting point. It plays the role of "aggregate" in slagging and contamination. Adding titanium dioxide can increase the ratio of "aggregate" to "glue", which can effectively reduce the bonding strength of slagging and contamination, making slagging and contamination loose and fragile, and easy to be effectively removed online. However, due to its high price, the actual amount is minimized while ensuring the basic requirements. In addition, other remaining solid particles with high melting points such as bauxite, kaolin, quartz ore, etc. that are not directly involved in the chemical reaction, as well as other condensed solid ash particles can also play the role of "aggregate". DETAILED DESCRIPTION

[0015] The present invention is further described in detail below in conjunction with the embodiments, but the protection scope of the present invention is not limited to these embodiments.

[0016] Example 1

[0017] 880g of a certain mine's strongly slagging and strongly contaminated bituminous coal, 80g of kaolin, 30g of bauxite, and 10g of titanium dioxide were mixed evenly to obtain modified coal. The test results of the ash content and main components of the modified coal and its components are shown in Table 1.

[0018] Table 1

[0019]

[0020]

[0021] As can be seen from Table 1, the alkali-acid ratio, FA index and contamination index Rf of the modified coal are greatly improved. The study shows that for the strongly contaminated coal ash melting point index is invalid, the actual slagging is significantly reduced, the contamination is significantly reduced, and the slagging and contamination become loose and fragile, and can be easily and effectively removed online.

[0022] Example 2

[0023] 920g of a certain mine's strong slagging bituminous coal, 70g of kaolin, and 10g of quartz ore were mixed evenly to obtain modified coal. The test results of the ash content and main components of the modified coal and its components are shown in Table 2.

[0024] Table 2

[0025]

[0026] It can be seen from Table 2 that the alkali-acid ratio, FA index and contamination index Rf of the modified coal are greatly improved, the contamination characteristics are relatively strong, the ash melting point is not significantly improved, and the actual slagging and contamination are significantly reduced.

[0027] Example 3

[0028] 950g of a certain mine's strong slagging bituminous coal, 45g of kaolin and 5g of titanium dioxide were mixed evenly to obtain modified fuel coal.

[0029] The test results of the ash content and main components of the modified coal and its components are shown in Table 3.

[0030] Table 3

[0031]

[0032] It can be seen from Table 3 that the ash melting point type slagging index RT of the modified coal is significantly improved, the ash melting point is increased, the alkali-acid ratio, FA index and contamination index Rf are improved, and the actual slagging situation is significantly alleviated and controllable.

Claims

1. A modified coal, characterized in that It is composed of the following raw materials in percentage by mass: The modified coal comprises 85% to 98% coal, 2% to 15% kaolin, 0% to 10% bauxite, 0% to 5% limestone, 0% to 4% quartz ore, and 0% to 3% titanium dioxide. The silicon and aluminum compounds in the ash of the modified coal are converted into silicon dioxide and aluminum trioxide, and the mass ratio of silicon dioxide to aluminum trioxide is (1.3 to 3.2):1, and the sum of the mass of silicon dioxide and aluminum trioxide accounts for 50% to 80% of the total mass of the ash. The coal is easy or relatively easy to slag and contaminate during high-temperature combustion.

2. The modified coal according to claim 1, characterized in that The raw materials are composed of the following mass percentages: The modified coal comprises 88%, kaolin 8%, bauxite 3%, and titanium dioxide 1%. The silicon and aluminum compounds in the ash of the modified coal are converted into silicon dioxide and aluminum oxide, and the mass ratio of silicon dioxide to aluminum oxide is 1.85:

1. The sum of the mass of silicon dioxide and aluminum oxide accounts for 62.24% of the total mass of the ash.

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