Process Analysis of Carbon Capture Using Chemical Looping Combustion

Abstract

The global warming issue has been validated at various international forums and a strong consensus was developed to reduce concentration of greenhouse gases particularly CO2. In sight of these developments, various Carbon Capture and Storage technologies emerged to significantly reduce CO2 emissions generated by the industrial sector. However, alltraditional carbon capture technologies are constrained by their energy intensive nature which results in reduced plant thermal efficiencies. Chemical looping Combustion (CLC) is a pioneering combustion concept, which offers a potentially attractive option to capture CO2 with a significantly lower energy penalty than other existing carbon-capture technologies. In this regard, this technology could be of vital significance for UAE where carbon capture and storage is being actively pursued and efficient carbon capture schemes shall be highly anticipated. The main idea of CLC is to split the combustion of the fuel into two separate reactions carried out in two separate reactors: an oxidation reactor and a reduction reactor, by introducing suitable metal oxide as an oxygen-carrier (OC) that circulates between the two reactors. Although various segments of the CLC technology are being actively researched but further simulation and empirical investigations need to be performed for macro scale implementation of the technology to understand possible drawbacks of CLC based power plants. This thesis presents a thermodynamic and parametric analysis performed on a macro scale, natural and synthesis gas fired power plant with CO2 capture using multistage,chemical looping combustion (CLC). The parametric analysis presents the effect of air, fuel and OC mass flow rates; operating pressures; extent of exhaust heat recovered and different OCs used on plant temperatures, emissions and efficiencies. To simulate the CLC based power generation plants, the Aspen Plus simulation engine and a linked excel based solver were used to tabulate plant thermodynamic and exergetic efficiencies based on conservative principles of mass and energy. The variations in CLC plant performance using three different OCs (Nickel, Copper and Iron) were also analyzed. The integration of CLC in different cogeneration schemes was also explored and evaluated. In sequence to usage of equilibrium based reactor models, chemical kinetic based reactor models were employed to depict the performance of CLC plants more accurately. The kinetic modeling of CLC reactors demonstrated high reaction rates for reduction reaction using bulk Nickel as oxygen carrier achieving 60-70% conversion in 1.5 minutes. However, the oxidation reaction was slower attaining 50% conversion in 4 minutes. With incorporation of kinetics, high level of CH4, CO and H2 emissions were monitored. The results demonstrate that if the energy penalty due to traditional carbon capture technologies (drop of 8-10 efficiency points) is taken into account, CLC could offer significant advantages in terms of higher plant thermal efficiencies, lower irreversibilities and negligible NOx emissions.

Date of Award	2012
Original language	American English
Supervisor	Tariq Shamim (Supervisor)