Comparative assessment of gasification based coal power plants with various CO2 capture technologies producing electricity and hydrogen

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

Re-thinking the transformation of organics: the role of the UK Government in shaping British organic food and farming

The focus of international scholarship on the contemporary transformation of organic food and farming has been a rather narrow preoccupation with the ‘conventionalisation thesis’ that describes a process whereby the structure and ideology of the expanding organic sector is seen increasingly to resemble that of the conventional food and farming sector that it has traditionally opposed. This study seeks to contribute to this literature by examining the role of the UK government in shaping the British organic sector since 1980, when it first began to engage seriously with organic farming. It draws on the analysis of a wide range of government and organic movement publications for the period 1980–2006, as well as a programme of semi-structured interviews with key organic policy actors during this time frame. By analysing the way in which the UK government has discursively constructed three separate story-lines about organics, this study argues that the effects of government action on British organic food and farming are best described as a process of containment. Further, it posits the need to move on from the rather reductionist focus offered by the conventionalisation thesis to more nuanced approaches to the transformation of contemporary food and farming that account for different geographical contexts, and the particular roles of different actors actively constructing what ‘organics’ is