Decarbonization Through Oxy-Combustion and H2 as A Fuel

Many countries have committed, as per Paris Agreement earlier and reindorsed during COP26, for zero CO2 emission within next thirty to forty years, i.e., by 2050–2060. All efforts made so far within cement industry to reduce CO2 emissions from AFR (alternative fuel and raw materials) would lower CO2 emissions by about 30%. The use of calcined clay (by turning natural clay soils into synthetic pozzolanic materials) may lead to another 40% reductions in CO2 emissions by replacing up to 40% clinker in the cement mix. However, further efforts with new technologies are required to meet the future expectations of the cement plants which may need to run on non-fossil fuels with CCUS (Carbon Capture Usage/Storage) capabilities. R&D exercises have already been started to prepare existing and/or future cement plants with net zero ‘Carbon’ emissions. The main technical challenges relate to the effective use of several thermal inputs from a matrix of energy resources, including H2, plasma, microwave, biomass and oxygen/ CO2 enrichment through recycling of combustion products. The oxygen enrichment, which substitutes the entire air ‘nitrogen’ in the combustion/cooling air, and the minimization of air-in-leakage - so that a CO2 enrichment in excess of 95% is assured. This requires minor modifications to almost all the components of a cement plant, including the clinker cooler, kiln and kiln burner, calciner and cyclones, is necessitated. The most critical issue is the inhibition of the calcination rate consequent of the enriched calciner CO2. Some results are presented from such R&D efforts, prior to full-scale demonstration, to test the use of non-fossil fuel-based cement production, which can be integrated into a CCUS system as these systems are also being developed at present. The by-product of hydrogen generation (i.e., via electrolysis) will be oxygen that will be essential in replacing N2 from the oxidant via oxy-combustion, which has shown to enhance combustion and increase clinker production at a number of cement plants. The plant safety and operational issues for adapting these approaches are of paramount importance and needs to be considered carefully.