Integrated vacuum pressure swing adsorption and Rectisol process for CO_(2) capture from underground coal gasification syngas

An integrated vacuum pressure swing adsorption(VPSA) and Rectisol process is proposed for CO_(2) capture from underground coal gasification(UCG) syngas. A ten-bed VPSA process with silica gel adsorbent is firstly designed to pre-separate and capture 74.57% CO_(2) with a CO_(2) purity of 98.35% from UCG syngas(CH_(4)/CO/CO_(2)/H_(2)/N_(2)= 30.77%/6.15%/44.10%/18.46%/0.52%, mole fraction, from Shaar Lake Mine Field,Xinjiang Province, China) with a feed pressure of 3.5 MPa. Subsequently, the Rectisol process is constructed to furtherly remove and capture the residual CO_(2)remained in light product gas from the VPSA process using cryogenic methanol(233.15 K, 100%(mass)) as absorbent. A final purified gas with CO_(2) concentration lower than 3% and a regenerated CO_(2) product with CO_(2) purity higher than 95% were achieved by using the Rectisol process. Comparisons indicate that the energy consumption is deceased from 2.143 MJ·kg^(-1) of the single Rectisol process to 1.008 MJ·kg^(-1) of the integrated VPSA & Rectisol process, which demonstrated that the deployed VPSA was an energy conservation process for CO_(2) capture from UCG syngas. Additionally, the high-value gas(e.g., CH_(4)) loss can be decreased and the effects of key operating parameters on the process performances were detailed.

Effects of micropore structure of activated carbons on the CH_(4)/N_(2) adsorption separation and the enrichment of coal-bed methane

In the process of enriching CH4 from coal-bed methane,the separation of CH_(4)/N_(2)is very difficult to accomplish by an adsorption process due to the similar physico-chemical properties of the two molecules.A series of coconut-shell-based granular activated carbons(GACs)with different pore structures were prepared,which were characterized by different methods.The influence of the pore structure on the separation properties was investigated in detail.The results show that one of the carbons prepared(GAC-3)has high CH4 equilibrium adsorption capacity(3.28 mol·kg–1)at 298 K and equilibrium separation coefficient(3.95).The CH_(4)/N_(2)separation on the GACs is controlled by adsorption equilibrium as compared with the dynamic effect.Taking the specific surface area,for example,the common characterization index of the pore structure is not enough to judge the separation performance of the GACs.However,the microstructure of carbon materials plays a decisive role for CH_(4)/N_(2)separation.According to the pore-structure analysis,the effective pore size for the CH_(4)/N_(2)separation is from 0.4 to 0.9 nm,with the optimum effect occurring in the range of 0.6–0.7 nm,followed by the range of 0.7~0.9 nm.Also,a four-bed vacuum pressure swing adsorption process was adopted to evaluate the performance of GACs for the separation of CH4 from nitrogen.