Integrated gasification combined cycle (IGCC) plants are a promising technology option for power generation with carbon dioxide (CO2) capture in view of their efficiency and environmental advantages over conventional coal utilization technologies. This paper presents a three-phase, top-down, optimization-based approach for designing an IGCC plant with precombustion CO2 capture in a process simulator environment. In the first design phase, important global design decisions are made on the basis of plant-wide optimization studies with the aim of increasing IGCC thermal efficiency and thereby making better use of coal resources and reducing CO2 emissions. For the design of an IGCC plant with 90% CO2 capture, the optimal combination of the extent of carbon monoxide (CO) conversion in the water−gas shift (WGS) reactors and the extent of CO2 capture in the SELEXOL process, using dimethylether of polyethylene glycol as the solvent, is determined in the first phase. In the second design phase, the impact of local design decisions is explored considering the optimum values of the decision variables from the first phase as additional constraints. Two decisions are made focusing on the SELEXOL and Claus unit. In the third design phase, the operating conditions are optimized considering the optimum values of the decision variables from the first and second phases as additional constraints. The operational flexibility of the plant must be taken into account before taking final design decisions. Two studies on the operational flexibility of the WGS reactors and one study focusing on the operational flexibility of the sour water stripper (SWS) are presented. At the end of the first iteration, after executing all the phases once, the net plant efficiency (HHV basis) increases to 34.1% compared to 32.5% in a previously published study (DOE/NETL-2007/1281; National Energy Technology Laboratory, 2007). The study shows that the three-phase, top-down design approach presented is very useful and effective in a process simulator environment for improving efficiency and flexibility of IGCC power plants with CO2 capture. In addition, the study identifies a number of key design variables that has strong impact on the efficiency of an IGCC plant with CO2 capture.

The net greenhouse gases (GHG) emissions of conversional Fischer Tropsch (FT) synthetic fuels derived from coal are about double of those from petroleum fuels. Adding moderate amounts of biomass to coal can substantially reduce the carbon footprint of the indirect fuel production plant. The indirect coalbiomass to liquids (CBTL) technology with CO 2 capture and storage (CCS) is more environmental friendly than the conventional coal to liquids (CTL) processes. This paper focuses on the selection of CCS technologies and obtaining their optimal operating conditions for a CBTL plant. A detailed process model is developed in Aspen Plus V7.3.2 for this purpose. In this plant, syngas is produced in the biomass/coal-fed co-gasifier. Then, a sour water gas shift (WGS) reactor converts a portion of the CO in the syngas to CO 2 to obtain the desired H 2 /CO ratio in the syngas feed to the FT unit. Substantial amount of CO 2 is captured before the FT reactor by using a dual-stage, selective physical solvent-based process. In the FT unit, the Fe-based catalyst is used in the low temperature FT (LTFT) slurry reactor to convert syngas to hydrocarbons. For selection of the post-FT CO 2 capture technology, three candidate technologies-Selexol, MEA and MDEA/PZ, are evaluated. The results show that the MDEA/PZ technology with intercooling has the lowest overall penalty. Impacts of two key design variables, H 2 /CO ratio at the inlet of the FT unit and biomass/coal ratio of the feedstock, on the product yield and utility consumptions are investigated.

In this paper, state-of-the-art dynamic models for solid oxide fuel cells (SOFCs) in the open literature are reviewed. The review also includes the transient modeling of SOFC systems with reformers. In the transients of a SOFC, three characteristic time constants are observed. One of the challenges in transient modeling is to capture these characteristic times. The first characteristic time is on the order of milliseconds and is mostly neglected, because it is too small, from the viewpoint of practical applications. The second time constant is on the order of seconds and arises mainly because of the mass-transport dynamics. The third characteristic time is on the order of minutes or hours and is dependent on the energy transport characteristics of the system. These characteristic times are extremely system-specific and, therefore, must be identified on a caseto-case basis. In this paper, the existing literature on dynamic studies are reviewed, focusing mainly on the fidelity of the model that is required to capture these time constants. The dynamic modeling of SOFC is still not as rich as the steady-state modeling. Therefore, steady-state models are also reviewed, whenever required. The utility of the dynamic models in design, control, and operation is discussed. A dynamic model from the literature is chosen for this purpose.