Abstract
Seven different types of gasification-based coal conversion processes for producing mainly electricity and in some cases hydrogen (H2), with and without carbon dioxide (CO2) capture, were compared on a consistent basis through simulation studies. The flowsheet for each process was developed in a chemical process simulation tool “Aspen Plus”. The pressure swing adsorption (PSA), physical absorption (Selexol), and chemical looping combustion (CLC) technologies were separately analyzed for processes with CO2 capture. The performances of the above three capture technologies were compared with respect to energetic and exergetic efficiencies, and the level of CO2 emission. The effect of air separation unit (ASU) and gas turbine (GT) integration on the power output of all the CO2 capture cases is assessed. Sensitivity analysis was carried out for the CLC process (electricity-only case) to examine the effect of temperature and water-cooling of the air reactor on the overall efficiency of the process. The results show that, when only electricity production in considered, the case using CLC technology has an electrical efficiency 1.3% and 2.3% higher than the PSA and Selexol based cases, respectively. The CLC based process achieves an overall CO2 capture efficiency of 99.9% in contrast to 89.9% for PSA and 93.5% for Selexol based processes. The overall efficiency of the CLC case for combined electricity and H2 production is marginally higher (by 0.3%) than Selexol and lower (by 0.6%) than PSA cases. The integration between the ASU and GT units benefits all three technologies in terms of electrical efficiency. Furthermore, our results suggest that it is favorable to operate the air reactor of the CLC process at higher temperatures with excess air supply in order to achieve higher power efficiency.
Highlights
Energy is the backbone of every modern society
Future forecasts for the economic growth in Asia Pacific and industrial development in Africa indicate that the total world energy demand will increase from 462 quadrillion British Thermal Units (BTU) in 2005 to over 695 quadrillion BTU by 2030.3 The exponential rise in emissions of CO2 from fossil fuel utilization to around 30 Gt per year will lead to significant climate change unless the emissions are captured and stored.[4]
The net electrical efficiency and CO2 captured shown in Tables 5 and 6 are the two main investigated parameters, which are discussed to net gas turbine (GT) output steam turbine output gross electric power output (B)
Summary
Energy is the backbone of every modern society. On the other hand, its production is one of the key contributors toward the global climate change. The renewable energy technologies can reduce CO2 emissions but are still costly. Even if they are made cost-competitive in the few years, they will still need time to penetrate the market. Some researchers consider coal as the primary source of energy at least for the 5−6 decades since its supply will last over 150 years compared with 50−60 years for oil and natural gas.[5] there is a large international research effort toward developing technologies to use coal in an environmentally sustainable manner.[6]
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