Injection of flue dust and pulverized coal into blast furnaces

German ironmakers produce about 300000 t/a of flue dust. This dust contains 10-30 % carbon and 25-40 % iron. The possibility of recycling this materia l in a blast furnace by injection with pulverised coal has been investigate d. The influence of the mixture on the process in the raceway and the blast furnace operational parameters has to be considered. Laboratory tests led to the result that the reduction degree of ferrous by- products depends on the content of volatile matter in the coal. The combust ion degree of coals with low volatile matter increases by 10-20 % for flue dust contents of 10-30 % in the mixture. An effective control of the therma l state of the hearth can also be achieved. Industrial tests with a pulverised coal/flue dust mixture injection confirm ed the technical feasibility of flue dust recycling. No negative effect on the blast furnace operation, crushing and injection equipment observed. Cok e consumption decreased, pig iron quality remained constant. The accumulati on of alkalis and zinc in the furnace can be neutralised by applying techni cal measures.