Simulation of two-step redox recycling of non-stoichiometric ceria with thermochemical dissociation of CO2/H2O in moving bed reactors - Part II: Techno-economic analysis and integration with 100 MW oxyfuel power plant with carbon capture

This paper presents the model of a solar thermochemical looping CO2/H2O dissociation (CL) unit with commercial ceria as the redox oxygen carrier. The CL unit is integrated in an oxy-fuelled combined cycle power plant as an add-on unit to a 100 MW oxy-fuelled natural gas power plant with carbon capture. The efficiency benefit obtained was investigated. A moving bed counter-current reactor model, developed in ASPEN Plus®, consisting of a series of rigorous continuous stirred reactors (RCSTRs) was used for the simulation of both reduction and oxidation reactors of the CL unit. A kinetic subroutine was developed in FORTRAN and linked with each RCSTR for both reduction and oxidation reactions. It is found that the efficiency of the CL unit varies widely with reduction reactor temperature and operating pressure. Considering three different compositions of the feed gas to the oxidation reactor, the CL unit efficiency is obtained as: 35.41% with CO2 only; 30.84% with H2O only; and 35.26% for a mixture of 86% CO2 and 14% H2O. The lower efficiency for H2O-only operation is due to the heat requirement for water vaporization and the higher compression work required for compressing H2 than CO. The maximum solar to electrical efficiency for the whole add-on unit is found to be 25.44% with a reduction reactor operating at a temperature of 1600°C and 10-7 bar vacuum pressure. With 0.5 m3 reduction reactor volume and 5 m3 oxidation reactor volume, the maximum net electricity produced by the CL add-on unit is 12.85 MWe. Economic analysis revealed that the major contributors to total plant cost are the hydrogen compressor and solar field and tower, which are the 19% and 39% of the total equipment cost, giving a specific overnight capital cost of 12136 $/kW with an LCOE of 1321 $/MWh with a capacity factor of 21%. The LCOE drops to 628 $/MWh with a carbon tax of 40 $/tonne of CO2 and increased capacity factor of 26%.