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Tangshan Keyuan Environmental Protection Technology & Equipment Co., Ltd
Purification and Desulfurization of Coal Gas from Lignite

Keywords: Lignite, Pyrolysis Matter Obtaining, Pyrolysis coal gas, Coal gas purification, Coal gas desulfurization,Coal gasifiers, coal gas, producer gas, coal gasification, clean gas, hot gas, crude gas, raw gas, coal gas generator

 1 Gas purification system

     Gas purification is the process of improving quality lignite pyrolysis heat generated crude gas is cooled cooling, dust (oil) purification process, improving quality lignite pyrolysis process system, gas purification system but its one of a number of subsystems , gas purification process to determine, in conjunction with the nature of the gas itself, the need for purification purposes and goals, as far as possible and reasonable process, economical and practical.
     Document [4] on the Dalian University of Technology, "lignite solid heat carrier fast pyrolysis technology" shows a gas purification cooling process shown in Figure 1, 490 ℃ pyrolysis of dust into the hot gas first of all, to remove gas in the carrying The particulate dust; then enters heat exchanger, in which water as a cooling medium gas recovery indirect sensible heat, while the water is vaporized to steam, the gas temperature is reduced to about 150-160 ℃; through the cold heat exchanger First After re-entering the air cooler gas, natural gas and the outside air by indirect heat exchange, so that the gas temperature is reduced to about 110-120 ℃; Then decoking gas into the electrostatic device, in addition to gas in the vast majority of this catch tar; Gas an electrostatic device into the indirect coke cooler, gas temperature drops in this 30-35 ℃, while the majority of the gas and light oil phenolic wastewater is condensed out; gas after the indirect cooler gas pressure machine pressurized gas into the next system.

     The gas purification process system, heat exchanger indirectly heated by high temperature gas cooled medium "water", effective on gas while taking full advantage of the cooling gas sensible heat, thereby effectively improve system efficiency. Figure 2 shows a gas purification system with a gas washing tower replaces the heat exchanger, and also cool the gas sensible heat utilization of the effective combination. After high temperature after hot gas precipitator dust into the scrubber, the use of the system for catching the tar out for spray cooling gas, gas temperature is reduced to about 110-120 ℃; Then decoking gas into the electrostatic device, in addition to gas capture The vast majority of tar; gas decoking control of static electricity into the indirect cooler, gas temperature dropped to 30-35 ℃, and then pressurized by gas pressure machine into the next system.

     Low temperature carbonization tar density is relatively small, due to the nature of raw coal and carbonization method varies, generally 0.95-1.1g/cm3 about tar and coal gas purification process cooling phenol caught out quite close to the density of water, relying on density separation very difficult to separate tar. Figure 2 shows the use of a gas purification process, the hot gas through the gas washing column and the system for capturing the heat of tar, tar is heated to about 100-110 ℃, the phenol tar Tar pool water is evaporated so that water can be effectively tar and phenol separation. But the use of the oil-water separation method, must be equipped with phenol vapor recovery system, which will cause secondary pollution, the process has the advantage of purifying the gas cooling, heat recovery and tar oil-water separator organic combination.

    Where in the cold gas clean for the remote user application process, the gas temperature to 30-35 ℃ can effectively avoid the gas in the transportation process phenol water condensation occurs, resulting in environmental pollution. Some mention the quality of lignite pyrolysis process requires the use of production systems pyrolysis gas as a heat source, the short distance transport of gas, gas condensate occurring during transport of water can be very convenient phenol phenol-water collection system back, will not cause secondary pollution, Figure 3, Figure 4 shows the cooling gas purification process is more suitable for such personal use of lignite coal pyrolysis mention the quality system. As can be seen in Figure 3, Figure 4 is a purification process of the cooling gas in Figure 1, Figure 2, an indirect cooler to remove the formation, the gas temperature of about 100-110 ℃ outbound so. In [5] that similar to Figure 3, Figure 4, the gas purification process, only after the primary cooling gas, without further end of the cold and direct pressurized process of transportation, is the most economical and the most favorable environment for effective solutions.

2 Gas desulfurization system

     Improving quality of lignite pyrolysis process, part of the coal in the form of sulfur as H2S transformed into pyrolysis gas, the Li Wenying, etc. [3] describes several lignite pyrolysis solid heat carrier technology and quality and content of H2S gas byproduct reference Table 2. Method for removing H2S gas in general can be divided into two types: hot gas desulfurization and cold gas desulfurization. In our country is still in hot gas desulfurization pilot study stage, needs to be further improved, and the cold gas desulfurization is a relatively mature technology, its desulfurization method also many cold gas desulfurization desulfurization can be roughly divided into dry and wet FGD two kinds method, dry desulfurization iron oxide law and wider application of activated carbon and alkaline wet desulfurization with arsenic, ADA, ADA and modified tannin extract representative.
     Li Jinhai, introduced in the selection of a good reactivity, high sulfur capacity of desulfurization agent of the premise, dry desulfurization desulfurization efficiency is higher, more appropriate fine desulfurization, the process gas containing H2S low because of H2S gas over high will cause desulfurizer soon lapsed; currently wet FGD gas desulfurization generally dominated, if the sulfur content of gas more strict control, you can step off the wet rough finishing off with a dry desulfurization process. Gas is widely used wet FGD technology has tannin and 888 catalytic desulfurization desulfurization, desulfurization method tannin soda ash as an absorbent to tannin as oxygen carriers to NaVO3 as oxidant; 888 catalytic desulfurization method as soda ash absorbents, catalysts in a catalytic oxidizer 888, the above two desulfurization same desulfurization and regeneration process, the process shown in Figure 5. Wet FGD system desulfurization and regeneration at the same time, gas desulfurization and regeneration of the desulfurization solution is a continuous online process gas desulfurization degree of purification as needed, timely adjustment by adjusting the ratio of the solution to be controlled, purified gas H2S content and stability.

     Wet desulfurization process gas temperature of the gas and water, oil, and the amount of impurities have certain requirements, if the Figure 1 and Figure 2 shows a process for purification of the gas after wet desulfurization, the gas must be added before entering the pressurizer an electrostatic decoking processes to ensure access to wet gas desulfurization system containing as little water and light oil, light oil mixed with water and avoid those that affect the desulfurization liquid solution ratio, reducing the desulfurization efficiency. Figure 3 and Figure 4 the purified process gas not suitable for wet gas desulfurization, the process is suitable for handling and quality and low-sulfur pyrolysis gas produced.

3 Conclusion
     Relative abroad, the lignite processing and utilization technology development in China started late, lignite pyrolysis to mention the quality of industrial production technology to be further developed and improved, and its byproduct pyrolysis gas purification and pyrolytic desulfurization as to mention the quality of lignite an important part of the system, also need to optimize and improve, requires a combination of brown coal pyrolysis process characteristics to mention the quality system, the nature of the pyrolysis gas and gas desulphurization own purpose and objectives and requirements, reasonably determine its byproduct pyrolysis gas purification and desulfurization process route.

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