Coal-water slurry is a new coal-based fluid clean and environmentally friendly fuel that not only retains the combustion characteristics of coal, but also has the characteristics of liquid combustion similar to heavy oil. It is a practical clean coal technology in China. It is made of 65-70% coal, 29-34% water, and less than 1% chemical additives after a certain processing process. It has the appearance of oil, good fluidity, stable storage (usually 3 to 6 months without precipitation), convenient transportation (train or tank car, pipeline, ship), high combustion efficiency, low emission of pollutants (SO2, Nox), about 2t coal-water slurry can replace 1t of fuel oil, and can be used in industrial boilers, power station boilers, industrial furnaces, etc. instead of oil, coal, and gas.
The preparation technology of coal-water slurry mainly includes pulp selection, gradation technology, preparation process, pulping equipment and additives.
1. Pulping coal selection According to the coal quality index of the coal and laboratory slurrying test, the degree of difficulty in coal slurry formation can be determined. The raw coal requirements for preparation of coal water slurry are: good slurryability and good combustion performance. Studies have shown that China has a wealth of pulping raw coal.
2. Grading technology grading technology is one of the key technologies for preparing coal water slurry. The preparation of high concentration coal-water slurry requires that the size of the coal particles in the coal-water slurry be filled with each other to achieve high packing density. This requires that the distribution of coal particles in the coal water slurry is intensive.
3. Pulp Production Process Coal slurry pulping processes generally include crushing, grinding, mixing and shearing, as well as the filtration of extragranular and debris in the final product.
Grinding is the key step in the preparation of coal-water slurry. Unlike grinding in other industries, not only is the product required to achieve a certain degree of fineness, but more importantly, the product should have a good particle size distribution. Grinding can be dry or wet. However, there are many shortcomings in dry-grinding pulping. It is difficult for pulp mills to meet the requirement that the moisture content in the dry mill is not higher than 5%, the grinding power consumption is approximately 30% higher than that in the wet method, and the fresh surface is easily removed by dry grinding. Oxidation increases the difficulty of pulping, and safety and environmental conditions are not as good as wet grinding. At present, pulping is mainly based on wet grinding ore grinding process. Wet grinding has two methods: high-concentration grinding and medium-concentration grinding. The fineness and particle size distribution of the grinding product are closely related to the particle size distribution of the feedstock, the physical properties of the coal, the type and structure of the mill, and the operating conditions of the mill.
4. Pulping equipment Pulping equipment mainly includes ball mill, slurry pump, mixer and so on. China has developed a variety of types of special coal water slurry mill (ball mill, vibration mill), which can basically meet the requirements of preparation of coal water slurry. China's largest coal water slurry mill processing capacity of 150,000 tons / year. With the expansion of the pulping scale, it is necessary to further develop large-scale, high-efficiency ball mills to reduce the pulping costs.
The establishment of a pulp mill in conjunction with a coal preparation plant is a valuable experience that China has created in the development of the coal-water slurry industry and has not yet been adopted in other countries. When using a coal preparation plant to build a pulp mill, the fine coal product from the coal preparation plant can be used as much as possible, and coal, coal storage, special railway lines, and water and electricity supply facilities can be shared with the coal preparation plant. Infrastructure investment.
5. Coal Water Slurry Additives There are many types of additives for coal water slurry, and indispensable are viscosity-reducing dispersants and stabilizers. Among them, the dispersant is the most important, and it directly affects the quality and preparation cost of the coal water slurry.
1) Dispersing agent: The surface of coal has a strong hydrophobicity and cannot be combined with water into a slurry. At higher concentrations, only a wet muddy mass will form. A small amount of dispersant is added into the pulp to change the surface properties of the coal particles so that the surface of the coal particles is tightly surrounded by additive molecules and a hydration film, so that the coal particles disperse the water evenly, and the flowability of the coal water slurry is increased. About 1% of coal. As the nature of coal varies greatly from place to place, the formula of additives used varies. In general, a dispersant is a surfactant.
2) Stabilizer: After all, coal water slurry is a solid and liquid two-phase coarse dispersion system. Coal particles can easily coalesce with each other spontaneously. Precipitation is unavoidable under the influence of gravity or other external forces. To prevent hard deposits, a small amount of stabilizer must be added. Stabilizers have two functions. On the one hand, they make the coal-water slurry have the rheological properties of shear thinning, that is, when the coal-water slurry is stored at rest, it has a high viscosity, and the viscosity can be rapidly lowered after the slurry begins to flow. On the one hand, the precipitate has a soft structure, preventing irreparable hard precipitation.
China has developed additives such as humic acids, lignin, naphthalene and polymers, which can replace imports. At present, the cost of ton slurry additives is between 20 and 40 yuan, and there is still room for decline.
The preparation technology of coal-water slurry mainly includes pulp selection, gradation technology, preparation process, pulping equipment and additives.
1. Pulping coal selection According to the coal quality index of the coal and laboratory slurrying test, the degree of difficulty in coal slurry formation can be determined. The raw coal requirements for preparation of coal water slurry are: good slurryability and good combustion performance. Studies have shown that China has a wealth of pulping raw coal.
2. Grading technology grading technology is one of the key technologies for preparing coal water slurry. The preparation of high concentration coal-water slurry requires that the size of the coal particles in the coal-water slurry be filled with each other to achieve high packing density. This requires that the distribution of coal particles in the coal water slurry is intensive.
3. Pulp Production Process Coal slurry pulping processes generally include crushing, grinding, mixing and shearing, as well as the filtration of extragranular and debris in the final product.
Grinding is the key step in the preparation of coal-water slurry. Unlike grinding in other industries, not only is the product required to achieve a certain degree of fineness, but more importantly, the product should have a good particle size distribution. Grinding can be dry or wet. However, there are many shortcomings in dry-grinding pulping. It is difficult for pulp mills to meet the requirement that the moisture content in the dry mill is not higher than 5%, the grinding power consumption is approximately 30% higher than that in the wet method, and the fresh surface is easily removed by dry grinding. Oxidation increases the difficulty of pulping, and safety and environmental conditions are not as good as wet grinding. At present, pulping is mainly based on wet grinding ore grinding process. Wet grinding has two methods: high-concentration grinding and medium-concentration grinding. The fineness and particle size distribution of the grinding product are closely related to the particle size distribution of the feedstock, the physical properties of the coal, the type and structure of the mill, and the operating conditions of the mill.
4. Pulping equipment Pulping equipment mainly includes ball mill, slurry pump, mixer and so on. China has developed a variety of types of special coal water slurry mill (ball mill, vibration mill), which can basically meet the requirements of preparation of coal water slurry. China's largest coal water slurry mill processing capacity of 150,000 tons / year. With the expansion of the pulping scale, it is necessary to further develop large-scale, high-efficiency ball mills to reduce the pulping costs.
The establishment of a pulp mill in conjunction with a coal preparation plant is a valuable experience that China has created in the development of the coal-water slurry industry and has not yet been adopted in other countries. When using a coal preparation plant to build a pulp mill, the fine coal product from the coal preparation plant can be used as much as possible, and coal, coal storage, special railway lines, and water and electricity supply facilities can be shared with the coal preparation plant. Infrastructure investment.
5. Coal Water Slurry Additives There are many types of additives for coal water slurry, and indispensable are viscosity-reducing dispersants and stabilizers. Among them, the dispersant is the most important, and it directly affects the quality and preparation cost of the coal water slurry.
1) Dispersing agent: The surface of coal has a strong hydrophobicity and cannot be combined with water into a slurry. At higher concentrations, only a wet muddy mass will form. A small amount of dispersant is added into the pulp to change the surface properties of the coal particles so that the surface of the coal particles is tightly surrounded by additive molecules and a hydration film, so that the coal particles disperse the water evenly, and the flowability of the coal water slurry is increased. About 1% of coal. As the nature of coal varies greatly from place to place, the formula of additives used varies. In general, a dispersant is a surfactant.
2) Stabilizer: After all, coal water slurry is a solid and liquid two-phase coarse dispersion system. Coal particles can easily coalesce with each other spontaneously. Precipitation is unavoidable under the influence of gravity or other external forces. To prevent hard deposits, a small amount of stabilizer must be added. Stabilizers have two functions. On the one hand, they make the coal-water slurry have the rheological properties of shear thinning, that is, when the coal-water slurry is stored at rest, it has a high viscosity, and the viscosity can be rapidly lowered after the slurry begins to flow. On the one hand, the precipitate has a soft structure, preventing irreparable hard precipitation.
China has developed additives such as humic acids, lignin, naphthalene and polymers, which can replace imports. At present, the cost of ton slurry additives is between 20 and 40 yuan, and there is still room for decline.
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