Integrating carbon capture and blast furnace technologies

Abstract

It is now widely acknowledged that industrial emissions play a large part in the increase of global temperatures. One industry yet to show significant signs of reducing emissions of CO2 is the steel industry despite accounting for approximately 7% of industrial emissions. There is however a wide range of research available on carbon capture and utilisation techniques from several other industries. This gives confidence that such technologies could also be applied to the steel industry. The aim of this project was to suggest methods to reduce CO2 emissions per tonne of steel produced by considering likely changes in steel production methods up to 2050. By assessing eleven combinations of crude steel production methods, the average CO2 emission intensity was derived. This was based on applying best available techniques to existing processes and increasing the proportion of crude steel generated by scrap recycling and directly reduced iron. These options are limited by the availability of raw materials and therefore the effect of a new, undeveloped, technology was also considered. This would allow for a greater reduction in average CO2 intensity of crude steel but is unlikely to be available for widescale adoption before 2050. This leads to the conclusion that existing technologies will need to be augmented to meet binding 2050 CO2 emission reduction targets. The technological compatibility of several available and soon to be available techniques for the treatment of blast furnace gas were considered. This was carried out using a flowsheet approach combining the blast furnace process with gas treatment technologies. These technologies included CO2 removal using chemical absorption, physical absorption and physical adsorption with the effect of water gas shift to maximise CO2 removal also considered. Technologies to utilise this captured CO2 were also analysed such as regeneration of CO2 using plasma catalysis, solid oxide electrolysis and reverse water gas shift. In many cases the resulting gas streams were recycled back to the blast furnace to displace other fuels. Six metrics were used to assess each of the flowsheet cases with an approximate operating cost for utilities also considered. By assessing the options based on these considerations and technological compatibility with the established blast furnace process, the most attractive options to a steelmaker were determined. This leads to the conclusion that chemical absorption for CO2 capture is the most compatible technology although not necessarily the lowest operating cost option. iii The work also presents an analysis of different chemical absorption amines on the capital cost of such a system for treating blast furnace gas. This analysis was carried out by developing models within Aspen HYSYS to estimate operation considering three types of amine solution and a further three mixtures of amines. Factors such as equipment size and regeneration energy were used to determine the effect of the different amines to treat the blast furnace gas. The equipment size was used to prepare an approximate capital cost for eleven different options considering different concentrations of the amines and amine blends. By comparing these costs to a benchmark of 28wt% monoethanolamine, the most promising amine for treating blast furnace gas was identified to be piperazine. This amine reacts quickly with CO2 in the gas stream resulting in smaller equipment size and hence capital cost. However, this case also produced one of the highest levels of solvent loss driven by the high temperature of gas leaving the absorber vessel. This will either increase operating costs or the complexity of the gas cooling section of the absorber column.