THE IGNITABILITY (EXPLOSION GROUP CLASSIFICATION) OF VARIOUS PRODUCER GAS COMPOSITIONS

摘要

Biomass gasification represents one of the most promising and effective methods to cover future energy demands. However the construction and the operation of a biomass gasification plant often involves difficulties. On the one hand the feed should have a stable and uniform composition to assure a certain quality of the producer gas. On the other hand there are explosion protection requirements because explosive gas/air mixtures may occur. Design features based on explosion protection requirements may be expensive and are prone to create problems during operation. E.g. the small gaps of a flame arrester may be to blocked partly or completely. Moreover additional maintenance and downtime could appear. The explosion protection measures used are based on the so called Maximum Experimental Safe Gap (MESG). Flammable gases and vapours (producer gases) as well as explosion proof equipment are classified into the explosion groups IIA, IIB, IIC based on MESG values (group I is for mining) . The MESG is determined according to standard IEC 60079-20-1. The MESG of most of the pure flammable gases is well known. Because of the wide range of the producer gas composition the determination of each MESG is not appropriate. Therefore, it is good practice to base the safety requirements of current wood gas plants on the compound having the lowest MESG. Doing so the inert gas amounts are ignored entirely. Thus, some wood gas plants are likely to be designed too conservative resulting in flame arrester equipment that causes additional difficulties during operation. Based on a calculation method [formula 2] by PTB [1] further investigations have been done. This current calculation method has been extended to take into account the inert gases amounts. As a result of comparative studies of calculated MESG and measured MESG it has been verified that the classification of some existing producer gases is definitely too conservative. Furthermore, depending on the oxidant used during the gasification process even wood gas classified as IIA seems to be possiblegasification possible.