| It’s well accepted that the series of negative impact caused by greenhouse effect is constantly threatening the survival and development. Carbon dioxide (CO2) is responsible for over60%of the enhanced greenhouse effect. Hence, the CO2emitted by coal-fired plant, must be controlled. CO2emission control technology is developing rapidly, such as post-combustion CO2capture, oxy-fuel combustion and pre-combustion CO2separation. Chemical absorption removal of CO2is considered as the more mature and promising choice. However, the traditional thermal regeneration process using MEA, has high energy consumption, there are also corrosion, degradation and other problems. Based on the analysis above, aqueous ammonia (AA) and Membrane Vacuum Regeneration (MVR) is tested in this paper.Ammonia has a good CO2absorption properties and the removal effect. With the ammonia concentration increased, CO2removal rate can be as high as98%or more, and the mass transfer rate will also rise. Liquid flow, gas flow, temperature and CO2volume fraction and other factors can also affect the absorption of CO2effect:CO2removal and mass transfer rate increased with the increase of the liquid flow rate, or temperature. The CO2removal rate increased with the increase of gas flow rate and CO2volume fraction, but CO2mass transfer rate will be reduced.Compared with the traditional thermal regeneration process using AA, MVR has better regeneration effect. AA Rich Solution by MVR can achieve CO2regeneration rate over60%with lower temperature (60℃). CO2regeneration performance is affected by liquid flow rate, temperature and pressure. The CO2regeneration ratio of rich AA solution decreases greatly with the increase of liquid flow rate at all the regeneration temperature, and higher liquid flow rate will lead to the higher mass transfer rate of CO2regeneration. Regeneration effect is better when temperature is higher, or the pressure is lower, but the energy consumption and the lifetime of membrane and other factors must be considered. Energy consumption of MVR contain heat consumption and power consumption, and the heat consumption account for more than70%. Heat consumption increases as the increase of liquid flow rate and pressure, but decreases as the increase of the temperature; electricity consumption of vacuum pump account for more than80%in the total electricity consumption. Compared with the traditional ammonia heat regeneration for coal-fired power plant CO2removal, the energy consumption of MVR using AA is only56.1%of its energy consumption. Ammonia has the strong erosion on membrane material, PP has better corrosion resistance than PVDF. The erosion effect is more serious with the increase of Ammonia concentration, temperature and the rich solution loading.Aqueous ammonia is easy to volatilize. The volatility increases with the increase of temperature, concentration of AA, rich solution loading and flow rate of N2. Adding little ammount of additives (1wt%) AMP can reduce ammonia volatilization by9%. At the same time,the absorption capacity is not affected. Influenced by the absorption process and price of membrane, nowadays MVR don’t have obvious advantages. Investment of membrane accounted more than40%of the total costs, when membrane price can be decreased to less than RMB33.5/m2in the future, MVR case will have the lower cost than the traditional thermal regeneration.At the same time total cost of the MVR decreased with the increases of membrane lifetime, but significant additional costs will need to prevent the membrane wetting and plugging problems. In addition, optimization the regeneration condition to reduce membrane contact area, or reduce the absorption tower investment also can effectively reduce the total investment. |
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