In China, low-rank coal reserves represented by lignite and low-metamorphic bituminous coal account for more than 55% of the total coal resources, mainly distributed in the eastern Inner Mongolia, Yunnan, Xinjiang and Ordos basins. With the more metamorphic coal less used, the optimal use of low rank coal is increasingly important. Relative to low-rank direct utilization of existing coal technology or economic problems, low-rank coal after the quality of graded use should be an important direction.
As a technology that is later than coal gasification technology to realize industrialization, the low-grade coal quality upgrading is virtually given the expectation of "coal that is misplaced with coal gasification." In some large-scale coal deep-processing projects, low-rank coal pyrolysis qualifications are listed as the first step in the conversion of raw coal. The quality of raw coal is first divided into three parts: solid, liquid and gas. The solid products enter the gasifier as raw materials for gasification or fuel into the boiler. The liquid tar is hydrogenated to produce clean oil. The gas pyrolysis gas is used for hydrogen extraction for tar processing. The remaining gas and then into the gasification system combined use. However, in fact, the current low-grade coal quality upgrading technology is still difficult to take such a heavy responsibility, the project program is often to do a multi-million-ton or million-ton industrialization experiment, after the success of a comprehensive "convergence" and "convergence" Engineering parameters before and after the change has not been carefully considered, the success of "convergence" there are variables.
Up to now, dozens of technologies have been adopted to treat low rank coal at home and abroad, of which only about ten are pyrolysis technologies in China. Depending on the heating method, the carrier form, bed structure, pyrolysis of low-grade coal pyrolysis technology blossom, each with its own characteristics. Due to the existing technology to varying degrees, there are safety, environmental protection, energy saving, stability, high investment, high operating costs, low-grade pyrolysis and upgrading of new technologies are still emerging, and continuously carry out hundreds of thousands of tons or even millions of tons Of industrial experiments, hoping to gain more engineering experience in constant attempts to make up for the lack of laboratory technology.
However, precisely because there are many technical schools and great differences in process principles, our understanding of the quality improvement of low-rank coal pyrolysis is not clear enough and not deep enough. At present, some major problems in the engineering of some low-rank coal pyrolysis technologies have been realized. First, the adaptability of coal is limited, and some technologies can only use lump coal, and some are difficult to adapt due to the change of coal indexes. Second, the product quality Differences are large, and some mention of quality coal products are still prone to oxidation, fragile and other issues, and some oil with ash, post-processing difficulties; Third, environmental protection, however, the high emission intensity, pollutants exceeded; Fourth, trapped In a variety of factors, safety, stability, long-term operation difficulties, poor economy.
Therefore, I believe that we should go back and do more solid work in basic research. Beginning with the solution of technical problems, the first objective of improving the quality of low-rank coal pyrolysis should strive to achieve safe, stable, long-term and continuous operation under the premise of energy conservation, water conservation, environmental protection and economy. The second objective Should be to broaden the adaptability of coal, such as making good use of low-quality pulverized coal; the third goal is to achieve more coal and large coal-fired power plants or more joint projects to optimize the use of materials and energy, "three wastes" centralized treatment. Faced with the common problems of various low-rank coal technologies and methods, all technical parties should step up exchanges and cooperate with each other to go hand in hand.