Combustion of solid recovered fuels within the calcium looping process - Experimental demonstration at 1 MWth scale

The calcium looping (CaL) process is an efficient post-combustion CO2 capture technology based on the reversible carbonation-calcination reaction of natural lime. This work presents the results obtained during long-term operation at the 1 MWth CaL pilot plant at Technische Universitat Darmstadt. During more than 230 h of representative CaL operation, the calciner was heated by oxy-fuel combustion of waste derived fuels. During the experimental investigation, two types of solid recovered fuels (SRF) were utilized. Both types of SRF were fed to the process in the form of raw fluff, similar to typical industrial applications. The flue gas to be decarbonized in the carbonator, was supplied by an on-site combustion chamber. The CO2 concentration was kept between 9.5 and 10.5 vol% as typical value for waste-to-energy (WtE) plants fueled by municipal solid waste (MSW). Over a wide range of operation conditions, CO2 absorption rates of 80% and total CO2 capture rates over 90% were achieved. Within this work, exemplary long-term data plots of relevant CaL process parameters are shown for each type of SRF. A chlorine balance for a representative operation period is established based on the relevant effluent streams from the CaL system. Thereby, it was found that the calciner fly ash represents the major chlorine effluent. Furthermore, the retention rate of chlorine was above 82% throughout all test points, respectively. When taking into account the organic waste fractions typically contained in SRF and MSW, this work successfully demonstrates the feasibility of net negative CO2 emissions by means of the CaL process at semi industrial scale.