642 / 2019-01-21 16:01:27

Reduction Characteristic of CaSO4-CuO combined oxygen carrier

Chemical Looping Combustion; Reduction reaction; CO2 capture; CaSO4 oxygen carrier; CuO oxygen carrier, SO2 release.

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CaSO4 oxygen carrier is considered to be a potential oxygen carrier (OC) for Chemical Looping Combustion because of its high oxygen capacity and low price. But its reactivity is lower than the metal oxide oxygen carriers, and it deactivates due to sulfur loss as well as sintering at high reaction temperatures above 920 oC. To improve the performance of of CaSO4-based oxygen carrier, small amounts of CuO particles were mixed mechanistically with CaSO4 particles to use as combined oxygen carrier in this work. XRD, SEM-EDS, BET and gas analyses were performed to investigate the variations of solid phase change, elements composition in solid residual and sulfur release with reaction time. The reactions of CaSO4 oxygen carrier with CO, CuO oxygen carrier with CO and CaSO4-CuO combined oxygen carrier were investigated. The effects of reaction factors such as reaction temperature, the oxygen-carrying ratio of CuO to CaSO4 and mass of oxygen carrier, on the reductions have been investigated in this study. The addition of CuO increases the reactivity of the CaSO4-based oxygen carrier while also suppressing the release of the gas sulfur. The solid products after reduction reaction mainly contain CaS, CaO, CuO, Cu2O and CaSO4, and no copper sulfide is detected. The results show that for the individual reduction of CaSO4 by CO, with the increase of CaSO4 mass (500 - 1200 mg), CO2 yield also increases until 1000 mg stops and SO2 released rises remarkably; An increase in the reaction temperature aggravated the SO2 emission. The carbon dioxide generation efficiency also increases with an increase in temperature, but decreases when the temperature exceeds 950 oC due to sintering of the oxygen carrier particles; With respect to the reaction of CuO with CO, CO2 yield does not change significantly with increasing temperature, due to the sintering of the CuO oxygen carrier in a high temperature reaction environment; For the combined oxygen carrier, the use of CuO additives not only improves the CO conversion rate, but also inhibits the release of gas sulfide. As the oxygen carrying fraction of CuO increases, SO2 released is reduced and the SO2 release time is delayed. When the oxygen-carrying ratio of CuO to CaSO4 is from 15% to 20%, CO2 yield increases greatly. As the reduction reaction temperature increases, the reduction reaction performance of the combined oxygen carrier is enhanced within the reaction temperature range of 750~900 oC.