the product gas through the generation of high pressure steam water enters the shell into the low temperature section or economizer and is heated and passes to a collector or steam drum heated water from a steam drum passes to the evaporator section of the fire tube heat exchanger the water is then partially vaporized and passes back to the steam drum for subsequent use in the process the high gas velocity mentioned above provides sufficient wall turbulence to realize increased heat transfer coefficients these higher heat transfer coefficients insure lower capital cost exchange and lower maintenance costs than the conventional water wall syngas cooler used with some entrained bed gasifiers the bulk of the flyash contained in the quenched raw gas leaves the fire tube heat exchanger and is removed from the gas using commercially demonstrated filter devices such as bag filters cyclones or ceramic candles filters suitable filter devices include those described in u s pat nos 4 248 604 4 247 302 4 810 264 4 482 363 and 4 121 912 the preferred method of removing the flyslag in the present invention is by ceramic candles or ceramic filters flyslag is recycled to the gasifier to convert any carbon on the flyslag to desirable gaseous products in the gasifier recycle of the flyslag to the gasifier further promotes conversion of its mineral content to slag and increases the overall production of slag the process of the present invention will now be described by referring to the figure pulverized coal is fed via.