No abstract

No abstract

The pressure swing adsorption models used in ref 1 were incorrect, because they involved the use of a co-current rinse step with pure steam above its dew pressure, yielding unphysical results. These models have been corrected to include an extra depressurization step to first lower the total pressure of the column below the dew point of the steam. The new cycle consists of six steps: pressurization, adsorption, cocurrent depressurization, co-current rinse, countercurrent depressurization, and countercurrent desorption. Furthermore, we have replaced our original linear driving force (LDF) rate expression [rate = k LDF (q* − q)] with one based on the difference between the bulk gas concentration and concentration in equilibrium with the sorbent bed [rate = k LDF (C − C*)], following the method of Seader and Henley. 2 The former rate expression is widely used, 3,4 but we feel the method of Seader and Henley more accurately reflects the limiting behavior of the adsorption rate.The corrected model slightly changes Figures 19−27, but the optimal |ΔH ads | remains unchanged at 65 kJ/mol. With the corrected model, the maximum efficiency achieved in adiabatic operation is 31.9% (down from the originally reported 32.7%), and the maximum efficiency achieved in isothermal operation was unchanged at 33.2%. We have included these corrected models in the Supporting Information for this correction. The results of the membrane calculations were unaffected.

Integrated gasification combined cycle (IGCC) with CO2 capture and sequestration (CCS) offers a promising approach for cleanly using abundant coal reserves of the world to generate electricity. The present state-of-the-art synthesis gas (syngas) cleanup technologies in IGCC involve cooling the syngas from the gasifier to room temperature or lower for removing sulfur, carbon dioxide, and other pollutants, leading to a large efficiency loss. Here we assess the suitability of various alternative syngas cleanup technologies for IGCC with CCS through computational simulations. We model multicomponent gas separation for CO2 capture in IGCC using polymeric membranes and H2 separation from the syngas using both Pd-alloy based composite metallic membranes and polymeric membranes. In addition, we develop a pressure swing adsorption model to estimate the energy efficiency of regenerable sorbent beds for CO2 capture. We use our models with Aspen Plus simulations to identify promising design and operating conditions for membrane and adsorption processes in an IGCC plant. On the basis of our analysis, the benefits of warm gas cleanup are not as great as previously reported in the literature, and only CO2 separations performed using H2-permeable Pd-alloy membranes and CO2 adsorbents produce overall higher heating value (HHV) efficiencies higher than that of Selexol. In addition, many of the technologies surveyed require a narrow operating range of process parameters in order to be viable alternatives. We identify desired material properties of membranes and thermodynamic properties of sorbents that are needed to make these technologies successful, providing direction for ongoing experimental efforts to develop these materials.

Integrated gasification combined cycle (IGCC) with CO2 capture and sequestration (CCS) is a promising technology to efficiently mitigate the emission of CO2. Warm CO2 removal has been predicted to make the CO2 capture process more efficient. Here, we investigate the efficiency penalties associated with CO2 removal via a pressure swing adsorption (PSA) process using metal hydroxide sorbents at elevated temperature. We use numerical models constructed in MATLAB and integrate these with Aspen Plus process simulations. We apply these models to both general metal hydroxides of variable enthalpy of adsorption and real metal hydroxides identified using density functional theory (DFT) calculations. We show that having an enthalpy of adsorption between 15 and 20 kJ/mol results in a PSA process that gives an overall IGCC–CCS efficiency that is competitive with the conventional IGCC–CCS process using (cold) Selexol. An enthalpy of adsorption of 20 kJ/mol is predicted to be the most favorable because it yielded a promising combination of HHV efficiency and higher working capacity. In addition, we identify Fe(OH)2, Co(OH)2, Ni(OH)2, and Zn(OH)2 as potentially favorable real materials, with IGCC–CCS efficiencies predicted to be within 1% HHV of that of Selexol.