tailieunhanh - Nuclear Power Deployment Operation and Sustainability Part 15

Tham khảo tài liệu 'nuclear power deployment operation and sustainability part 15', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 480 Nuclear Power - Deployment Operation and Sustainability the technological limit to be overcome. Globally it is possible to reach CH4 conversion higher than 90 with a permeated H2 flux of 300 Nm3 m2 h bar .5. The achievement of this goal shows the industrial feasibility of this option up to now demonstrated only on a laboratory scale even if the last gap to be overcome for the technology commercialization is represented by the optimization of membrane preparation procedure with enhancement of their stability. Fig. 12. Effect of membrane thickness on CH4 conversion with ECN membrane Application to nuclear power In order to sustain the global endothermic steam reforming reaction a part of the methane feedstock must be burned in a fired heater. To reduce this consumption purge gas coming from PSA unit or retentate from the membrane separation unit have to be burned. The calorific value of these streams is a function of composition and consequently of the achieved conversion. A self-balance of heat exits with a fixed external natural gas supply at an appropriate level of feed conversion. Therefore conversion should not exceed the point closing the heat balance around 60 . Furthermore it must be considered that owing to the high process temperature the thermal efficiency of this process is about 65 to 75 . Also a substantial amount of greenhouse gases GHG is emitted as CO2 produced along with hydrogen. Moreover carbon dioxide is also emitted during the burning of a part of methane feedstock in order to sustain the global endothermic balance of the steam reforming reaction. In total a typical steam reforming process emits up to - 12 kg CO2 per 1 kg H2. To prevent the emitted CO2 to be released into the atmosphere it needs to be captured. Presently all commercial CO2 capture plants use processes based on chemical absorption with amine solvents as monoethanolamine MEA or methyldiethanolamine MDEA which is a considerably energy intensive step and thus is .