Akeem K. Olaleye

Technical and Economic Analysis of Chemical Looping Combustion with Humid Air Turbine Power Cycle

Chemical looping combustion (CLC) is an innovative concept that offers potentially attractive option to capture CO2 with appreciably lower thermal efficiency penalties when compared to the tradition approaches. This paper presents process simulation, technical and economic analysis of the CLC integrated with humid air turbine (HAT) cycle for natural gas-fired power plant with CO2 capture. Aspen Plus® process simulator and Aspen Process Economic Analyzer® were employed for technical and economic analysis of the CLC-HAT and conventional HAT cycle.The analysis shows the CLC- HAT cycle has a thermal efficiency of 57 % at oxidizing temperature of 1,200 oC and reducer inlet temperature of 530 oC. The economic evaluation performed shows that a 50 MWth CLC-HAT plant with a projected lifetime of 30 y has a payback period of 6 y compared to 7 y for conventional HAT cycle. This indicates that CLC-HAT cycle is commercially viable with respect to CO2 capture cost.

Conventional and Advanced Exergy Analysis of Post-combustion CO 2 Capture in the Context of Supercritical Coal-Fired Power Plant

Post-combustion CO2 capture (PCC) is one of the strategic technologies identified to reduce emissions of greenhouse gases (GHG) in an existing power plant. CO2 capture incurs serious energy penalty due to the energy use for solvent regeneration in the capture process and subsequent increase in cost of electricity. Reducing the energy/exergy use in the process can lead to a reduction in energy penalties. Beyond demonstrating this lower level of actual energy/exergy consumption, it is important to increase the efficiency of the CO2 capture system. This study includes steady-state simulation and conventional and advanced exergy analyses of PCC with solvents for emission reduction. It focuses on (1) steady-state simulation of the closed-loop PCC system, (2) conventional and advanced exergy analyses of the CO2 capture process, and (3) strategies to reduce exergy destruction and losses in the capture process. A detailed exergy destruction analysis is performed in this study, both for the absorber and the desorber columns of the system. These analyses allow for a better understanding of the exergy destruction due to a component’s own inefficiency and/or the remaining components’ inefficiencies. The analyses show improvement in reducing exergetic losses in the system without incurring additional penalties. The results show that the energy/exergy destruction in the monoethanol-based (MEA-based) CO2 capture system (and hence the energy penalty) and the efficiency can be improved by recovering the avoidable exergy destructions in the system.

Dynamic Modelling and Analysis of Supercritical Coal-Fired Power Plant Integrated with Post-combustion CO2 Capture

Despite the advances in power plant and CO2 capture modelling, only a few studies have presented a dynamic process model and analysis of the post-combustion CO2 capture integrated with a dynamic model of supercritical power plant. This study presents a dynamic model of a supercritical coal-fired power plant (SCPP) integrated with a dynamic model of MEA-based post-combustion CO2 capture plant (PCC). This study focuses on the impact of integrating PCC unit on the load following the mode of operation of the SCPP. The dynamic model of the PCC was validated against a pilot plant data and was scaled-up to capture the flue gas flow from 600 MWe SCPP. The SCPP model was validated with actual plant operational data for steady-state conditions at full load and at transient load ramp. The dynamic response of the integrated SCPP–PCC model due to changes in load demand is presented. The response of the following variables to changes in load level investigated includes the following scenarios: (i) the flue gas flow rates, (ii) the pulverized coal flow, (iii) the net efficiency of the SCPP, and (iv) and the CO2 capture level. The simulation shows that the CO2 capture level is very sensitive to the solvent–flue gas (L/G) ratio. In addition, steam reduction/stripper stop was analysed as a strategy for operating the SCPP integrated with PCC unit under the UK grid requirement as regards primary frequency response. The result shows that the stripper stop mechanism produces about 4.67 % MCR (~28 MWe) increase in the SCPP at full-load condition. This is however, not sufficient for the 10 % MCR required for the primary response (usually within 10–30 s).

Dynamic Modelling, Validation and Analysis of Coal-fired Supercritical Once-through Boiler-Turbine-Generator Systems Under Stringent UK Grid Requirement

This study presents a dynamic model and analysis of supercritical coal-fired power plant (SCPP). The model includes the main component of the once-through boiler-turbine-electric generator system of a SCPP. The first principle model was developed under the assumptions that the temperature, pressure and flowrate changes in the axial direction in the once-through boiler and assumed well mixed radially. The model parameters were estimated from design and operational data from a reference 600 MWe SCPP. The model was validated with plant operational data for steady state conditions at full load, and at transient load ramp. The model shows relative error of less than 3 % in predicting the reference plant measurements. The model was further used to simulate the flexibility of the SCPP for rapid load changes and variations in system frequency under stringent UK grid system. The UK grid code stipulates that depending on the operating load as a percentage of the registered capacity (MCR), up to 10 % of registered capacity has to be supplied within 10–30 s of a 0.5 Hz frequency drop occurring over a 10-s period. The simulation results show that using turbine throttling approach (about 4 % MCR), extraction stop (about 5 % MCR) or condensate stop (about 2 % MCR) individually was not sufficient to meet the grid requirement. On the other hand, the study shows that a combination of turbine throttling, extraction stop and/or condensate stop can achieve a 10 % increase in generating capacity (MCR) of a SCPP within 10 s to 30 s of primary frequency change as required by the UK grid.