Question: Is there a market demand for pre-drying of raw coal in the coal chemical industry?

This post was last edited by willmar on 2017-10-19 at 22:40. The fluidized bed dryer we have developed for high-temperature flue gas (with an inlet flue gas temperature of 1100 degrees) offers many advantages in projects aimed at the pre-drying of low-grade coal: 1) High output per unit machine (>5 million tons per year); 2) Low investment costs; 3) Low energy consumption. Due to its high inlet temperature, it can even be used in pyrolysis units. 　 Details　　　www.coaldryingtech.com

There is no term for sub-bituminous coal; it is called weakly bituminous coal, which is the term used in the United States. We **do not have such a classification.** It is classified into lignite, bituminous coal, anthracite, semi-anthracite... coking coal... lean coal, thin coal, anthracite, etc. Among them, bituminous coal, anthracite, and semi-anthracite are collectively referred to as low-metamorphic bituminous coals.

Whether raw coal needs to be dried before being fed into the pyrolysis and gasification processes depends on the moisture content of the coal feed, as well as on the pyrolysis and gasification processes themselves, including the requirements placed on the coal by the feeding equipment. If the raw coal is used as a feedstock for producing semi-coke, lump coal, and other products through pyrolysis, and tar is an important target product, then the moisture content of the raw coal should not be high; otherwise, during the cooling process of the pyrolysis gases, water will be released along with the tar, ending up in the tar and affecting its quality. If raw coal is used as the feedstock for gasification, and dry coal powder or coal slurry gasification is employed, the raw coal must be ground into fine powder with a particle size of less than 100 microns. The raw coal needs to be dried before grinding; otherwise, it cannot be reduced to such a fine powder. If fluidized-bed coal gasification technology is used, from the perspective of improving the thermal efficiency of the entire system, the moisture content in the raw coal should not be too high; otherwise, most of the water in the coal remains unbroken down during the gasification process and exists in the gas exiting the furnace as water vapor, which then precipitates out in the gas cooling stage. The water in coal enters the gasifier, where, under the action of radiation and convection heat transfer, it causes the coal to heat up rapidly, resulting in its rapid separation and evaporation into high-temperature water vapor at a temperature close to that of the gasifier. This process absorbs a large amount of heat (latent heat + sensible heat), and this heat cannot be effectively recovered during the subsequent cooling process. The water in coal absorbs heat at high temperatures of around 900–1000°C when it enters the furnace, while it releases heat at lower temperatures during the cooling process of the gas; thus, the quality of the energy recovered is much lower than that of the energy absorbed at high temperatures.

I would like to ask yangshaoj2005: For low-rank coal, drying and preheating it in a high-temperature fluidized bed before gasification, followed by pyrolysis to produce semi-coke, gas, and coal tar, should result in relatively high overall benefits. What is the feasibility of this process? Drying: The raw coal is first crushed to below 50 mm, and then fed into a fluidized bed dryer. There, it is heated and dried by hot flue gas at 1000–1250°C coming from a hot air furnace, until its moisture content reaches 0%, while it is also preheated to 200–250°C (with no volatiles in the coal or only a small amount of them evaporating). Pyrolysis: The coarse coal discharged from the fluidized bed dryer is fed into a moving bed pyrolyzer/cooler where it is further preheated to 400–550°C to enable the volatiles in the coal to be released and semicoke to be formed; thereafter, the resulting semicoke is cooled to around 100°C. Cooled semi-coke: (1) used as a feedstock for gasification (the pyrolysis temperature can be low) ； (2) Used as a civil fuel or injection coal (a high pyrolysis temperature is required to ensure that the volatiles are reduced to around 10%, so that the resulting semi-coke does not catch fire on its own). The coal powder carried in the exhaust gas from the fluidized bed dryer can, after separation, be used as: (1) a raw material for gasification ； (2), or it can be fed into a moving-bed pyrolyzer/cooler for further preheating to 400–550°C in order to cause the volatiles in the coal to evaporate and form semi-coke. The semi-coke produced from coal powder is used as a raw material for gasification. If low-rank coal has a high content of coal tar, more coal tar can be produced ； If low-grade coal has relatively low ash and sulfur content, semi-coke can be used as a blowing coal ； If low-grade coal has high ash and sulfur content, semi-coke can be used as a domestic fuel ；