AbstractOne of the major problems experienced in the development of filtration for coal liquefaction has been the rapid clogging of fine metal filter screens. Tests have shown that the screens could be cleanedin situ, and the frequency of such cleaning could be reduced by using precoats. Standard diatomaceous precoats could be used, but these are expensive and their use could reduce the thermal value of the filter cake. Various carbonaceous products derived from coal and petroleum have been suggested as alternatives. 15 different samples of coke have been assessed in laboratory tests. All had a good performance in terms of low cake resistivities, screen bridging, and effected considerable protection for metal screens against clogging. When used in plant tests as a 5 mm precoat, the petroleum coke fines effected a doubling of interval betweenin‐situcleaning (sluicing) and was resistant to particle breakdown during slurry recycle. Coal extract coke and carbonized coal used as filter aids in plant tests also doubled the interval betweenin‐situcleaning, but they behaved similarly to celite in the breakdown tests, being inferior to cyclone fines in this respect. The use of carbonaceous materials as body feed leads to a marked decrease in filter‐cake resistivity and, therefore, to an increased efficiency of filtration
展开▼
