Investigation of the possibility of carbon dioxide reduction by Waelz processing of oxidized zinc-containing material

Abstract

The results of model studies on the possibility of reducing energy costs and carbon dioxide emissions during the Waelz processing of oxidized zinc-containing material in waelz kilns are presented. The studies were carried out using a specialized software product METSIM widely known in the world practice of metallurgical process and production modeling that allows analyzing the effect of changes in technological modes on the final results of the process. Model calculations showed that the greatest decrease in specific energy consumption and CO 2 emissions is observed when using blast air heated to 200 °C with an increase in its flow rate from 1000 to 7000 n.m 3 /h and concomitant decrease in atmospheric air suction. The estimated reduction in the specific costs of carbon and CO 2 emissions amounted to 30,2—35,5 %, and the total specific cost of energy carriers — 28—32 %. At the same time, blast air heating to 200 °C in the heat exchanger of the recovery boiler does not require additional energy inputs, in contrast to the use of oxygen blast with the cost of electricity for producing oxygen. Intensification of the waelz process using additional oxygen blasting (or air blast enrichment with oxygen) and heated blast air supply with concomitant decrease in air suction into the furnace from the atmosphere leads not only to a decrease in the specific consumption of the carbon energy carrier, but also to an increase in the degree of carbon utilization. The maximum estimated increase in the degree of carbon utilization was 6,2 rel.% — from 60,3 % on cold air blast without oxygen to 66,5 % on an air-oxygen blast (7000 n.m 3 /h of air and 185 n.m 3 /h of oxygen) heated up to 200 °C without atmospheric air. Maintaining optimal oxidation-reduction and thermal modes of the process requires correct regulation of the kiln draft mode taking into account atmospheric air suction in the unloading head of the kiln. Uncoordinated changes in the specific consumptions of charge, carbon, blast air and rarefaction in the dust chamber lead to a concomitant decrease in the extraction of zinc to sublimates and increase in its losses with clinker.