Carbon Capture and Storage
November 2018 has been the 5th warmest Nov. since 1880 with a global land and ocean temperature at 0.75°C higher than the average temperature of 20th century (National centres for environmental information, 2018). Green house gases (GHG) are significantly responsible for rise in global temperatures, one of which is CO2.
Over the next 40 years the global population is expected to reach 9 billion. This triggers the increase in the energy demand by 50% (Zero emission platform, 2010). Today the world’s 80% of energy needs are contented by coal, gas, and oil. It will take decades until the renewable energy sources become the main source of energy. Presently, burning of fossil fuels and gases emits enormous amount of CO2 in the atmosphere which ultimately leads to global warming and irreversible effects of climate change. There is an immediate demand to cut CO2 emission by 50% in next 20 years in order to reduce the effect of global warming (Zero emission platform, 2010). Energy efficiency, Renewable energy and Carbon Capture and Storage are the solutions to this issue. This essay shall discuss on Carbon Capture and storage (CCS) (Zero emission platform, 2010).
CO2 Capture Technologies
CCS includes number of technologies, including processes for CO2 capture, separation, transport, storage and monitoring. Selections for the CO2 capture technologies are affected by the type of combustion processes. The three main processes namely, post – combustion, pre-combustion and oxyfuel combustion (D.Y.C. Leungetal, 2014).
Post- combustion
Preferred for retrofitting existing power plants, post-combustion recovers CO2 from the flue gases at the rate of 800 t/day. The level of CO2 in combustion flue gases is quite low (around 7-14%), in order to transport and store it the concentration of around 95.5% is required which leads to increased energy penalty and associated costs for the capture unit. The U.S. National energy technology Laboratory estimated that this would increase the cost of electricity production by 70% (D.Y.C. Leungetal, 2014).
Pre- combustion
In this process, the fuel is preheated before combustion by gasification process which forms syngas consisting CO and H2. The syngas undergoes water gas shift reaction with steam forming more H2 while CO gas is converted to CO2. The high CO2 concentration in H2/CO2 fuel gas mixture facilitates the CO2 separation. This method is applied in integrated Gasification Combined Cycle (IGCC) power plans using coal as fuel, but this will incur an efficiency loss of 7-8% (D.Y.C. Leungetal, 2014).
Oxyfuel combustion
In this process, oxygen is used in combustion instead of air. This reduces the amount of nitrogen in exhaust gas which affects the separation process. The composition of flue gas contains CO2, water particles, and SO2. SO2 is removed by conventional electrostatic process and flue gas precipitator and flue gas desulphurization methods. The remaining gases contain high concentration of CO2, can be compressed, transported and stored (D.Y.C. Leungetal, 2014).
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