Properties and uses of water-coal slurry
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China has abundant coal but little oil; coal accounts for 92.94% of its fossil fuel reserves. The outline of the 15th Five-Year Plan states that it is necessary to leverage resource advantages and use coal as the primary energy source. It is predicted that by the middle of this century, coal’s share in China’s primary energy consumption structure will still be difficult to drop below 50%. Oil is an important strategic resource, but China’s oil reserves account for only 5.35% of the total fossil fuel reserves. The increase in domestic oil production is far from sufficient to meet the growing demand. In 2003, China imported 90 million tons of crude oil. It is predicted that in 2004, China’s oil imports will reach 120 million tons, surpassing Japan and making China the world’s second-largest oil importer after the United States. China’s growing dependence on foreign oil poses a serious threat to its security. Replacing oil with coal is China’s established energy policy. There are many ways to address the shortage of oil resources in our country; for example, coal liquefaction can be used to produce refined oil directly. However, the technology and equipment needed to build large-scale coal liquefaction plants still have to be imported. The investment is large, and the cost of the resulting fuel is high. According to Xinhua News Agency, an annual oil production capacity of 1 million tons requires an investment of 10 billion yuan, which is equivalent to 10,000 yuan per ton of oil produced. Therefore, it is very necessary to build coal liquefaction demonstration plants, but it is currently difficult to implement them on a large scale. At present, water-coal slurry is only a substitute for fuel oil. However, by deeply processing the alternative fuel oil, it is possible to obtain approximately 45% gasoline and diesel, 6% fuel gas, and 25%–35% heavy fractions. Water-coal slurry remains the feedstock for gasification in coal indirect liquefaction, and the use of water-coal slurry in Texaco furnaces for gas production has been industrialized in China. Furthermore, a fine water-coal slurry that can serve as a substitute for diesel has also achieved laboratory-level results at our university. After industrialization, the scope of using water-coal slurry as a substitute for oil will be further expanded.
Coal water slurry is generally divided into two types. The first is the coal water slurry used for gasification, which is what we usually refer to and is also the most commonly used type. This kind of slurry is required to have a concentration of over 55%, and it is primarily used for gasification processes. It does not have high requirements regarding the particle size of the coal, nor regarding the fluidity and stability of the slurry; generally, stability is defined as the ability to avoid the formation of solid precipitates over a period of one day or more. In factories, this slurry is prepared as needed. Another option is to use water-coal slurry for combustion; this is mainly used in boilers that burn heavy oil. By simply modifying the delivery system and nozzles, it can replace heavy oil. Generally, 2 tons of coal slurry can substitute for 1 ton of heavy oil. However, this type of coal slurry requires high levels of stability and fluidity; the average particle size of the coal powder is generally below 100 microns, giving it excellent fluidity, similar to that of heavy oil. Since it needs to be stored, high stability is also required – generally, no solid precipitation should occur over a period of 2 months, while the amount of soft precipitation should be less than 10%. This is the simplest and most direct method of adding oil to coal; since the coal slurry is well atomized when injected, the combustion efficiency is high, and almost no black smoke is produced. For direct combustion, it is an excellent alternative to heavy oil. The concentration of this coal slurry is also very high; generally, the solid content of the coal slurry is required to be greater than 65%.
The expert on the third floor, thanks for the advice – I really didn’t know that before. 3# Garbled text
Coal-to-oil is merely a strategic reserve; from an energy utilization perspective, it is neither economical nor environmentally friendly.
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