Exploration of new approaches for the development of the technological process for low-temperature dry distillation of high-volatility coal

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This post was last edited by newsdom on 2019-2-12 at 20:45. Low-temperature carbonization of coal is one of the important processes in coal chemical industry, as well as one of the modern advanced technologies for coal processing. The dry distillation of coal refers to the process in which coal is heated and decomposed in an air-free environment, resulting in products such as coke (or semi-coke), coal tar, crude benzene, and gas. Based on the final heating temperature, it can be divided into three types: dry distillation at 900–1100°C is considered high-temperature dry distillation, or coking; dry distillation at 700–900°C is medium-temperature dry distillation; and dry distillation at 500–600°C is low-temperature dry distillation. Compared to high-temperature dry distillation, low-temperature dry distillation yields coal tar with higher yields, better quality, and superior added value. Although the gas production rate is lower, the high methane content allows for further processing into gas composed mainly of methane, resulting in lower processing costs and excellent investment returns. Low-temperature carbonization allows for the production of semi-coke (commonly known as \"lancang\"), which has low volatile content and is thus easy to transport and store safely, as well as high-quality carbonized gas and low-temperature coal tar. Low-temperature coal tar can be used to produce a variety of high-value chemicals through precise distillation, as well as diesel of blended grade through catalytic hydrogenation. Lantern coal is classified by particle size; the lump form can be used as a raw material for blast furnace iron production, while the powdered form can be used as an adsorbent or filler. It can be said that the large-scale low-temperature dry distillation processing of high-volatility coal brings significant economic, social, and environmental benefits. Currently, the mature industrial technologies for low-temperature coal carbonization mainly include the porous coke oven method, the direct carbonization method which also features partial gas self-circulation, and the rotary kiln method. The porous coke oven method is less commonly used; its main disadvantages include low heat transfer efficiency during heating and dry distillation, as well as long dry distillation times. The advantage is that the quality of low-temperature coal tar and carbonized coal gas is relatively high. Production methods such as direct carbonization and rotary kiln methods have high efficiency, but the quality of coal tar and coal gas is relatively poor. The low-temperature fractions of coal tar are present in low amounts, and the content of inert components in coal gas (such as N2 and CO2) is also relatively high. Below, I will briefly outline the research and development approach I suggest – a dry distillation tower that possesses all the advantages of the mature technologies already in use in industry, while avoiding all their shortcomings, thus offering very promising prospects and incentives for industrialization. I believe that the relevant technologies and materials required are all mature and reliable: coal with a particle size of less than 20 mm is fed in from the top of the tower, moves downward, passes successively through the heating coils in the middle and upper sections as well as the cooling coil at the bottom, and then exits from the bottom to proceed to the subsequent screening process. The coil is filled with high-temperature flue gas, and alloy steel materials that are wear-resistant and designed to enhance heat transfer can be considered for use. To reduce the amount of dust entrained in the gas released from the furnace, an efficient separator can be designed as a composite unit, which can also prevent blockages in the subsequent heat exchange equipment. Those who are truly interested are welcome to have in-depth discussions. Let’s consider this as a starting point for further discussion for now. Thank you