发电厂烟气开采天然气水合物过程能效模拟

利用发电厂烟道气(以下简称烟气,主要成分为CO_2与N_2)开采天然气水合物(以下简称水合物)是一种安全、环保的方法,但目前对于该开采方法的能耗及能效情况仍缺乏深入的研究。为此,建立了一种烟气开采水合物的流程:烟气通过增压注入到水合物储层,储层中的水合物一部分发生热分解,另一部分与烟气置换得到CH_4-CO_2-N_2混合气,再经膜组件分离除去N_2得到提浓后的CH_4-CO_2混合气,最后将CH_4-CO_2混合气输送至原发电厂发电。进而采用Aspen Plus软件对这一过程进行了模拟,分析了不同注入压力下烟气置换过程的采注比、置换采出CH_4的比例以及整个过程的能耗与能效。结果表明:(1)烟气开采水合物过程的主要能耗在增压注入阶段,注入压力的增加会导致增压阶段与膜分离阶段的能耗相应增加,但在一定程度上也可提高压力能回收率;(2)注入压力在5~16 MPa条件下,烟气置换过程的采注比为0.03~0.26,置换采出CH_4的比例为19.9%~56.2%,烟气开采水合物全过程的单位能耗为2.15~1.05(k W·h)/kgCH_4,能源投入回报值(EROI)介于7.2~14.7。结论认为:在5~10 MPa范围内增加注入压力可有效地提高烟气开采水合物过程的能效。

Energy efficiency simulation of the process of gas hydrate exploitation from flue gas in an electric power plant

It is a safe and environmentally-friendly method to exploit natural gas hydrates ("hydrate") by using flue gas (mainly includingCO2 and N2) from electric power plants. So far, however, its energy consumption and energy efficiency has not been investigated thoroughly. In this paper, the process to exploit hydrates from flue gas was established. Firstly, flue gas is injected into hydrate reservoirsafter it is pressurized. The hydrates in reservoirs partially experience thermal decomposition while the rest is replaced with flue gas, so CH4–CO2–N2 mixture is formed. Secondly, the concentrated CH4-CO2 mixture is got after N2 is separated and removed by using membrane component. And thirdly, the CH4–CO2 mixture is delivered to the original electric power plant. This process was simulated by using the software Aspen Plus to analyze the production/injection ratio in the process of flue gas replacement under different injection pressures, the methane replacement ratio, and the energy consumption and energy efficiency in the whole process. It is indicated that the energy in the process of hydrate exploitation by using flue gas is mainly consumed at the pressurized injection stage, and the injection pressure increase correspondingly results in the increase of energy consumption at pressurization and membrane separation stages, and to some extent improves the recovery ratio of pressure energy. Besides, when the injection pressure is 5–16 MPa, the production/injection ratio in the process of flue gas replacement is 0.03–0.26, the methane replacement ratio is 19.9–56.2%, the unit energy consumption in the whole process is 2.15–1.05 (kW·h)/kgCH4, and the energy return on investment (EROI) is 7.2–14.7. It is concluded that the energy efficiency of hydrate exploitation by using flue gas can be effectively improved by increasing the injection pressure in the range of 5–10 MPa.