The issue of tar production in coal gasification

Reply to 1# allenhero1228: This question is a bit difficult to answer. First, I don’t know what the quality of coal is where you are, and second, I’m not aware of the gasification techniques used! ! ! !

KBR technology – it is said that this technology can burn lignite, bituminous coal, and sub-bituminous coal at temperatures of 900–1000 degrees without producing tar. I’m skeptical about this, so I’m asking everyone here at Haichuan

Reply to 3# allenhero1228: It’s unlikely that this would be suspicious. From what I know, the Luchi furnace produces the highest amount of tar. That’s good too; it can be sold as a by-product, and the price of tar is currently over 3000. There don’t seem to be many others such as Texaco, Shell, GSP, etc.; their components aren’t mentioned in the crude gas description! ! ! I’m not sure if it’s correct, but I hope it helps you

Tar has certain economic value, as a side note. The key point is that the KBR process does not mention any tar treatment procedures; it claims that this technology does not produce tar. If a company adopts this technology only to find that tar is indeed generated, it will have a serious impact on production. It’s similar to what happened with SHELL’s furnaces – they claimed that they could handle any type of coal, and China imported over twenty such units; billions were spent, yet only a few of them were able to operate properly and stably

It’s almost impossible to claim that no tar is produced; the reason why the Ruhchi furnace generates large amounts of tar is the drying/destillation layer located at the upper part of the fixed bed. If the original poster pays attention, KBR’s gasification furnace uses a fluidized bed system. In simple terms, the apparent gas velocity in the reaction zone lies between that of a gas flow bed and a fixed bed. The advantage of this approach is that the temperature distribution is more even compared to a fixed bed, while the operating temperature is lower than that of a gas flow bed. Therefore, it can be said that when operating at temperatures above 980 degrees, basically no tar is produced. However, if the ash fusion point of the coal is low, in furnaces that use solid slag discharge (other than those with shell-type slag handling systems), whether they are KBR-type gasifiers or other types, the operating temperature will be limited. If the temperature is below 950 degrees, a small amount of tar will be produced. As for the exact amount of tar generated, there are no precise figures; my statements are based on industrial trials using lignite in fluidized bed furnaces at 950 degrees.

Thank you for the advice from above. I would like to ask further: is it suitable to use KBR for coal with a ash melting point of over 1600 degrees and an ash content of over 20%? Thank you

This post was last edited by Zizhu Youjing on 2010-6-4 at 22:00. First, it is necessary to understand the conditions under which tar is produced by the types of coal mentioned: During coal gasification, tar is primarily generated during the pyrolysis stage. It is generally believed that the tar production rate is highest at temperatures between 500 and 650 degrees; above this temperature, the tar begins to decompose. At temperatures of 800–850 degrees, the tar production rate drops by half. However, benzene rings, especially those with multiple rings, cannot be decomposed even at 900 degrees. Yet, in the presence of hydrogen in the system, the decomposition temperature can be reduced to 460 degrees. At the same time, a longer residence time is beneficial for tar cracking. The gasification temperature in KBR is generally between 900 and 1100 degrees, and the raw coal is fed into the high-temperature zone (unlike in the Lurgi furnace), thereby avoiding the pyrolysis process. At the same time, the gas rises along with the fluidized material, which increases the residence time of the gas. This results in almost no tar in the crude gas product. Furthermore, studies have shown that adding an appropriate amount of CaO to coal can not only lower the ash melting point but also significantly reduce tar production, which could be tried in BGL gasifiers. The KBR circulating fluidized reactor is particularly suitable for coals with very high ash fusion points; 20% ash content poses no problem

1600 degrees Celsius, haha – that’s not the strength of a fluidized bed.

Huainan coal belongs to the gas-rich and fertilizer-rich coal category; the ash melting point of this coal is above 1350. As for the tar yield, I’m not sure about that yet – I’ll check the previous experimental data and provide more information later~~