Choose gasification technology

Due to the short coalification time of lignite, its high ash content and high volatile matter content, as well as the low concentration of water-coal slurry, it is recommended to use the powder gasification process. The current powder coal gasification technology is quite mature; options such as the space furnace and Ningmei furnace can be considered – they are all domestically developed and relatively inexpensive.

This post was last edited by defeil on 11-28-2016 at 14:12. Gasification furnaces are quite sensitive to the quality of coal; even coals that belong to the same lignite category can differ significantly in their properties. Generally, high ash content, high moisture levels, and high volatile matter are common characteristics of lignite. The high moisture content leads to low concentrations in lignite-based water-coal slurry systems, while the high volatile matter results in low mechanical strength, making such coal unsuitable for fixed-bed gasification. After excluding these technologies, only fluidized-bed gasification using pulverized coal, certain fixed-bed gasification techniques, and transport-bed methods remain. There are various types of fluidized-bed gasification technologies, each with its own advantages; among those more suitable for lignite gasification are the Dongfang furnace and the Aerospace furnace. As for transport-bed technologies, KBR is a notable example – it has just completed the acceptance testing for its pilot-scale system, and once put into industrial use, each furnace will be able to process up to 5,000 tons per day. Fixed-bed gasification technology is represented by BGL; industrial-scale lignite gasification using this technology has already been implemented at Jinxing Chemical in Hulunbuir. Of course, the choice of specific gasification technology still depends on the particular characteristics of the lignite in question, requiring further analysis

The selection should be based on the actual properties of the coal, such as moisture, ash fusion point, volatile matter, ash content, fixed carbon, and so on. Overall treatment needs to be considered; if the moisture content is too high (I’ve seen cases where it was 50% on a total basis), is the dry pulverized coal process appropriate?

BGL is not a fluidized bed. Hehe

It can be dried; the coal used in Datang Duolun has a high moisture content.

Are the drying costs high, and does it require a large amount of space?

Lignite varies from place to place. In my opinion, fluidized-bed gasification furnaces have quite high requirements regarding coal quality; lignite is not suitable for use in such furnaces. A fluidized-bed system would be a better choice. The transport bed KBR gasifier mentioned earlier is now quite mature; it is widely used in oil refineries, features a high and simple fluidization cycle, which facilitates its use on a large scale.

In principle, the fluidized bed certainly yields the best results. Lignite has poor strength, suffers from severe pulverization, and has an uneven particle size distribution; when a fixed-bed system is used, either high resistance occurs leading to the overturning of the bed layer, or there is uneven oxygen distribution. The two BGL units of Jinxin Chemical have surrendered. A new Shell unit has been installed and is now in operation; BGL actually serves as a cost subsidy mechanism – two units are used to supply half of the original gas volume. Dry powder processing requires significant investment; coal drying is energy-intensive, occupies a lot of space, and poses certain fire hazards. Torrone is still not operating at full capacity yet. The slurry-forming property of water-coal slurry is poor; the performance of water-coal slurry in Hulunbuir is acceptable, but the concentration of the coal slurry is low, resulting in high oxygen and coal consumption. The fluidized bed does not need to be completely dry; a moisture content of less than 8% is sufficient. The requirement regarding particle size distribution is low – particles smaller than 8 mm are acceptable, and the presence of a small amount of fine powder is also no problem. The fluidized bed is simple to manufacture and requires low investment, and it can adapt well to the inherent properties of lignite. However, in global gasification technology, fluidized bed technology is the least developed; there are no large-scale commercial plants with a capacity of over 10 kilograms. Issues such as carbon conversion efficiency, slag discharge problems, and ash in the syngas are quite severe. The low reaction temperature results in long reaction times and larger-sized equipment. Therefore, it can be said that for lignite, the truly suitable technologies are not yet fully developed. If low-cost lignite resources are available, I believe that a fluidized bed is the safest choice. After all, as long as the price of raw coal remains low and operations stay stable, there’s no problem in making a profit. It’s just a matter of making more or less money. Fixed-bed and fluidized-bed systems are likely to not be so lucky. If the entrepreneur is the principal, is it that simple to just give a child someone to help them find the best teaching methods so they can get into Tsinghua University? Is it easier to find a student with good qualifications and use the successful teaching methods already in use to help them get admitted to Tsinghua University? Bosses think every day about gasifying the cheap lignite at hand – but can such coal really compete in the entire coal chemical processing chain?

From the perspectives of environmental protection and operating costs, it is recommended to choose a fluidized bed.