H. Singh
CSIR-Indian Institute of Petroleum DehraDun IndiaRetd professional,
India
Keywords: carbon dioxide capture, membrane vacuum regeneration, pre combustion, post combustion, oxy fuel combustion, hydrogen, ionic liquids & cryogenic
Summary:
There is a clear scientific consensus that emissions of carbon dioxide and other greenhouse gases, are the major cause of global warming. In a country such as India, transportation and electricity generation contribute to 45% of the country’s total greenhouse gas emissions. While the primary goal must be to reduce the world’s reliance on fossil fuels, by switching to renewable energy sources (RES), a secondary goal is to capture emissions from processes fueled by hydrocarbons. It is for this reason the leading edge technological pathways of carbon capture from power and other industrial plants are the subject matter of intensive investigations In terms of the technology used for separation, CO2 scrubbing via liquid solvents (chemical or physical) is a mature process that builds upon several commercial solutions employed in hundreds of plants with no major challenges. A fourth category is that of direct air capture (DAC),which has been demonstrated at commercial scale by companies such as Climeworks and Global Thermostat. Challenges include integrating current and future technologies with renewable sources of electricity, heat and the need for significant cost reductions. Since 2000 the chemical industry has invested in the development of leading edge processes which are less energy intensive, have higher efficiency and environmentally more acceptable. New methods and techniques utilized for pre-combustion, post-combustion and oxy fuel combustion are being developed. Dedicated research programs, mainly in the US and Europe, have set ambitious targets to achieve a carbon capture cost approaching $20/t. Novel solvents with phase change systems, ionic liquids and other non-aqueous solvents aim to achieve lower regeneration energy requirements than conventional amines. Ionic liquids (ILs) are most promising green solvents as they have shown incredible potential for CO2 absorption, have negligible vapor pressure, have adjustable structures and are eco-friendly. Techniques used in other commercial gas separations, such as solid sorbents, membranes, and cryogenic separation may be applied to carbon capture. Electrochemical carbon capture as well as the co-production of hydrogen with carbon capture are the two alternative paths under development. In oxy-fuel combustion, pressurized systems have shown a high tendency for efficiency improvements within the supercritical CO2 cycle at some unique conditions of combustion. Dramatic energy saving can be achieved via chemical looping strategies, as a result of the inherent avoidance of the possibility of a gas separation step. This technology offers significant scale-up options to companies and research institutes. Researchers have also argued the use of hybrid systems, which in turn give synergistic effects/properties which are better compared to those of the individual components that make up the composites. This article summarizes the current state of the art for conventional solvents and the most recent leading-edge investigations (2nd& 3rd generation technologies) as applicable to carbon capture from point sources.