Steam Coal Gasifier Plant

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The combustible gases from the gasifier can be used For direct and Indirect heat applications. 

However in order for the gas to be used for any of the above applications it should be cleaned of tar and dust and be cooled.  As previously mentioned cooling and cleaning of the gas is one of the most important processes in the  whole gasification system. The failure or the success of producer gas units depends completely on their ability to provide a clean and cool gas to the engines or for burners. Thus the importance of cleaning and cooling systems cannot be overemphasized.

The temperature of gas coming out is normally between 300-500. This gas has to be cooled in order to raise its energy density. Various types of cooling equipment have been used to achieve this end. Most coolers are gas to air heat exchangers where the cooling is done by free convection of air on the outside surface of heat exchanger. Since the gas also contains moisture and tar, some heat exchangers provide partial scrubbing of gas. Thus, ideally the gas going to an internal combustion engine should be cooled to nearly ambient temperature. Cleaning of the gas is trickier and is very critical.  Normally three types of filters are used in this process.  They are classified as dry, moist and wet. In the dry category are cyclone filters. They are designed according to the rate of gas production and its dust content. The cyclone filters are useful for particle size of 5m and greater. Since 60-65% of the producer  gas contains particles above 60m in size the cyclone filter is an excellent cleaning device. After passing through cyclone filter the gas still contains fine dust particles and tar. It is further cleaned by passing through either a wet scrubber or dry cloth filter. In the wet scrubber the gas is washed by water in counter current mode.  The scrubber also acts like a cooler,  from where the gas goes to cloth filter for final cleaning. Since cloth filter is a fine filter, any condensation of water on it stops the gas flow because of increase in pressure drop across it. Thus in quite a number of gasification systems the hot gases are passed through the cloth filter and then only do they go to the cooler Since the gases are still above dew point, no condensation takes place in filter.