A comparative simulation study of power generation plants involving chemical looping combustion systems
Abstract This work presents a simulation study on both energy and economics of power generation plants with inherent CO 2 capture based on chemical looping combustion technologies. Combustion systems considered include a conventional chemical looping system and two extended three-reactor alternatives (exCLC and CLC3) for simultaneous hydrogen production. The power generation cycles include a combined cycle with steam injected gas turbines, a humid air turbine cycle and a simple steam cycle. Two oxygen carriers are considered in our study, iron and nickel. We further analyze the effect of the pressure reaction and the turbine inlet temperature on the plant efficiency. Results show that plant efficiencies as high as 54% are achieved by the chemical looping based systems with competitive costs. That value is well above the efficiency of 46% obtained by a conventional natural gas combined cycle system under the same conditions and simulation assumptions.
Prospects and issues of integration of co-combustion of solid fuels (coal and biomass) in chemical looping technology.
The utilization of fossil fuels leads to the emission of greenhouse gases into the environment. As a consequence, ozone layer depletion, global warming, acid rain, etc. are caused. Thus, alternate ways have to be planned to eradicate the detrimental effects of the usage of fossil fuels. As biomass is a renewable energy source, co-utilization of coal with biomass could significantly reduce carbon emission. In addition, chemical looping combustion (CLC) is a promising technology for the inherent capture of CO2 without any post-treatment of flue gas. Hence, the integration of co-combustion of solid fuel with CLC technology can produce clean energy in the context of carbon negative system. The present study addresses the issues and prospects of the co-CLC process of solid fuels such as coal and biomass. Low-cost oxygen carriers, which are suitable for the solid-CLC process, are elucidated. The effect of solid fuel based inherent constituents such as ash, volatile matter and tar on the performance of the CLC process is discussed. Furthermore, the beneficial and inhibitory effects of the co-combustion of solid fuels are elaborated. The formation and reduction mechanism of NOx and SOx pollutants during the CLC process are investigated. In addition, the effect of gasifying medium (CO2 and steam) during the co-CLC technology is also discussed. The performance of the CLC based thermal power plants is analyzed, and the results show a gain of 5-6% in net thermal efficiency, compared to a power system operating under conventional technology. The effect of the process parameters on gas conversion, char conversion, overall solid fuel conversion, combustion efficiency and CO2 yield is investigated. The investigation shows that the co-combustion based CLC is a potential technology for the implementation of carbon capture and storage (CCS) with a low energy penalty.
Characterization and performance in a multicycle test in a fixed-bed reactor of silica-supported copper oxide as oxygen carrier for chemical-looping combustion of methane
Chemical-looping combustion of carbonaceous compounds is a proposed two-step process for complete CO2 capture and substantial reduction of NOx emissions. In the first stage, the reduction stage, the framework oxygen of a reducible inorganic oxide is used for the combustion of the carbonaceous material. In the second stage, the regeneration stage, the carrier in a reduced state is regenerated with air to recover the properties of the fresh carrier, ready to reinitiate a new cycle. This article provides results for the performance of a copper oxide silica-supported oxygen carrier in a 20-cycle test of chemical-looping of methane in a fixed-bed reactor at 800 °C and atmospheric pressure. The mesoporous nature of silica provided a good dispersion of the active phase imparting a high mechanical strength to the overall carrier. Additionally, silica is stable under highly reducing agents and inert in the two involved processes. The respective CH4, CO2, and CO breakthrough curves in the reduction stage show that ...