Operation Windows of the Oxygen Blast Furnace with Top Gas Recycling

摘要

Due to global concern about climate change, efforts in the steel industry to decrease emissions must be introduced, as this industrial sector gives rise to 5-7% of the anthropogenic CO_2 emissions. There are several possibilities to achieve this goal: Making the processes more energy efficient, changing to renewable energy sources, by introducing process modifications or completely new processes, etc. In this paper the concept of oxygen blast furnace, where pure oxygen is used as blast combined with recycling of CO_2-stripped top gas, is studied numerically. In the analysis, special attention is paid to the amount of recycled top gas and how the gas should be divided between injection to the lower (hearth) and upper (shaft) tuyeres. The results shed light on the feasible operation window, under the given process constraints, for the oxygen blast furnace and also how different combinations of hearth and shaft gas injections are reflected in coke rate, oxygen rate and top gas composition, as well as in the emissions. The issue whether the recycled top gas must be heated in regenerative heat exchanges is also addressed by considering the alternative where the recycled gas to the lower tuyeres is injected cold, while the shaft gas is elevated to the reserve zone temperature by partial combustion. The findings of the study are expected to be useful for assessing the feasibility of operating the blast furnace under high top gas recycling rates.