Experiment On Coal Low-tar Gasification And Optimizing Design Of Gasifier

Fixed bed is used widely as a reactor which has mature technology, high heat efficiency and high carbon conversion. But high tar content of the gas is a important factor that constraints rapidly and healthy development of fixed bed gasification. The existence of coal tar in the gas may erode and jam the pipelines; on the other hand, it may waste energy and pollute environment. So high tar content of the gas is the bottle-neck of development on fixed bed gasification.In this paper various methods which can remove tars of the gas are analyzed. It shows that, tar reduction outside gasifier and in the gasifier itself. Although the former method can remove tar effectively, tar only experienced a conversion phase and not really removed, the energy in tar is not reclaimed sufficiently and environmental pollution is inevitable; The latter is not only able to remove tar, but also increase the conversion of raw materials, and it is very helpful with gasification process.This paper introduced low-tar coal gasification experiment by fixed-bed reactor. Effects of operation parameter such as air/steam preheated temperature, gasification temperature, ER, the ratio of steam to carbon and the ratio of the secondary to primary air on coal gasification index such as gas composition, gas heating value, and tar content in the gas were investigated. The results show that:higher air/steam preheated temperature contributes to more tar cracking, increasing gas heating value, but the gasification production drops. The raising of gasification temperature improves gas heating value, carbon conversion, and the gasification production significantly, drops tar content, but higher temperature will degrade gas heating value. There is a optimal operating range to ER and the ratio of steam to carbon on gas heating value, if the introduction of the two parameters are increased, the tar content in the gas drops. The introduction of the secondary air contributes to tar cracking, but excessive secondary air will lead to more tar contents, lower gas heating value. So the choice of secondary air volume is very important.Based on the results and the rules of the gasification experiment, optimizing design is carried on the up-draft fixed bed gasifier. For the purpose of reducing the tar content in gas at maximum, the pyrolysis of the up-draft fixed bed gasifier added a throat where the secondary air is injected can provide suitable conditions for tar cracking in the gasifier. It can offer theory gist for exploitation of the no-tars gasifier in the future.