Numerous applications produce fluids which require cleaning before they can be processed further. For example, raw syngas from coal gasifiers contains a number of solid contaminants which need to be removed to protect downstream process equipment against corrosion, or to protect downstream catalytic processes (such as shift reactions and hydrogen separation) against poisoning.
Existing gas cleaning processes typically involve barrier filters (such as candle filters) for removing solid contaminants from the gas. However, such processes suffer from a number of problems. For example, an ash deposit can build up when using conventional candle filter apparatus when filtering a waste gas (e.g. raw syngas). In order to clean the candle filters, a reverse pressure pulse is periodically provided to the filters, which causes the accumulated ash to fall off. In some situations, it may also be necessary to vibrate the filter to adequately clean it. Such cleaning operations typically require the filtration process to be stopped, and can then cause the candle filters to break. The reverse pressure pulse can also weaken or even break the candle filters, leading to a shortening of their working life.
Furthermore, a significant proportion of the filtration effect of a barrier filter occurs by virtue of the material deposited as a cake on the filter. In known systems, the periodic reverse pulse cleaning dislodges the cake and can thus allow some particles to pass through the filters immediately after cleaning.