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.

Separation of H_2O/CO_2 Mixtures with Layered Adsorption Method for Greenhouse Gas Control

Multiple-layered vacuum swing adsorption technique was used and investigated in order to effectively keep the feed gas that flows into zeolite 13X zone being dry and keep the CAPEX down（not adding pre-treatment equipment）. Activated carbon fiber（ACF） and alumina CDX were laid at the lower parts of the column as pre-layers to selectively adsorb moisture. Zeolite 13X was laid on the top of those two adsorbents as the main layer to capture CO2. Systematic cyclic experiments show that water vapor was successfully contained within the ACF and CDX layers at cyclic steady states. It was also found that ultimate vacuum pressure played a decisive factor for stabilizing the water front, and achieving good CO2 purity and recovery. The findings also reveal the pathway for large-scale CO2 capture process.

Integrated adsorption and absorption process for post-combustion CO_(2) capture

This study explored the feasibility of integrating an adsorption and solvent scrubbing process for postcombustion CO_(2) capture from a coal-fired power plant.This integrated process has two stages:the first is a vacuum swing adsorption(VSA)process using activated carbon as the adsorbent,and the second stage is a solvent scrubber/stripper system using monoethanolamine (30 wt-%) as the solvent.The results showed that the adsorption process could enrich CO_(2) in the flue gas from 12 to 50 mol-% with a CO_(2) recovery of >90%,and the concentrated CO_(2) stream fed to the solvent scrubber had a significantly lower volumetric flowrate.The increased CO_(2) concentration and reduced feed flow to the absorption section resulted in significant reduction in the diameter of the solvent absorber,bringing the size of the absorber from uneconomically large to readily achievable domain.In addition,the VSA process could also remove most of the oxygen initially existed in the feed gas,alleviating the downstream corrosion and degradation problems in the absorption section.The findings in this work will reduce the technical risks associated with the state-of-the art solvent absorption technology for CO_(2) capture and thus accelerate the deployment of such technologies to reduce carbon emissions.

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.