Performance of CLOU process in the combustion of different types of coal with CO2 capture

Abstract

Chemical-looping with oxygen uncoupling (CLOU) process is a chemical-looping combustion (CLC) technology that allows the combustion of solid fuels using oxygen carriers with inherent CO2 separation. The oxygen necessary for the fuel combustion is supplied by a solid oxygen carrier, which contains a metal oxide. The oxygen carrier circulates between two interconnected fluidized reactors: the fuel and the air reactor. In the CLOU process, the oxygen carrier releases gaseous oxygen in the fuel reactor which burns coal as in common combustion with air, so the CO2 generated is undiluted with N2. The reduced oxygen carrier is oxidized by air to the initial metal oxide in the air reactor, then being ready to start a new cycle. The aim of this work is to study the performance of the CLOU process using coals of different rank. Experiments were carried out in a continuously operated 1.5kWth unit. Particles prepared by spray drying containing 60wt% CuO were used as oxygen carrier. Four coals of different rank (anthracite, low volatile bituminous, medium volatile bituminous and lignite) were used as fuel. Besides, the temperature in the fuel reactor was varied between 900 and 950°C. In all the experiments there was complete combustion of the coal to CO2 and H2O, without any unburnt product. The carbon capture efficiency greatly depends on the coal rank and fuel reactor temperature. High carbon capture efficiencies were obtained for lignite and medium volatile bituminous coals. The maximum capture efficiency was 99.3% at 950°C with lignite. The analysis of the experimental results was used to evaluate the effect of the coal rank in a CLOU system when a carbon separation system is included. At 925°C, the solid inventory needed to reach 95% of CO2 capture efficiency with a carbon separation system of 90% of efficiency is 45kg/MWth using lignite, 85kg/MWth using MV bituminous, 140kg/MWth using LV bituminous and 490kg/MWth using anthracite. It must be pointed out the low solid inventories needed in the CLOU process for the different coal rank analyzed in this work.