The K-CLC project: Construction of 3 MWth NG-fueled CLC steam generation system and sythetic oxygen carrier development

Current commercial boilers to produce steam for heat supply or power generation require costly post-combustion CO2 capture plant to reduce carbon emission. In chemical looping combustion (CLC), CO2 capture facility is not necessary because CO2 is internally separated during fuel combustion that is made by pure oxygen supplied from solid particles called oxygen carrier (OC). CLC has been studied for dozens of years to reduce carbon capture cost and energy efficiency drop accompanied by carbon capture. Currently, several MWth pilot studies are ongoing globally. In Korea, Korea CLC project (K-CLC project) aiming at demonstrating steam generation by NG-fueled CLC in a 3 MWth plant was launched in 2021. The plant was built in 6 months after beginning of construction. Hot run tests were performed to confirm that each part of the plant works correctly. Main troubles occurred in the equipment installed for fuel gas supply to the fuel reactor. The plant was operated in 3.1 MWth capacity in CLC mode under the abnormal fuel gas supply and obtained fuel conversion of 95.5%. Repair works are presently undergoing to fix several faults found in the test runs. One of huddles for scale-up of CLC technology is to acquire high quality OC with long-term durability and high oxygen transfer capacity and reactivity. KEPCO developed high quality Ni-based OC and verified its performance in a 0.5 MWth CLC system. The physical properties and reactivity data of the Ni-based OC were used for the design of the 3 MWth CLC plant. A total of 12 tonnes of Ni-based OC was produced using an industrial spray dryer for the operation of the 3 MWth pilot plant. The mass-produced Ni-based OC showed similar oxygen transfer capacity of around 12 wt% and a little bit less strong mechanical strength compared to that of OC prepared in KEPCO laboratory. Along with the mass production of the Ni-based OC, KEPCO improved the reactivity of a previously developed Mn-based OC. In the tests of CLC of methane using a bench-scale bubbling fluidized-bed reactor, fuel conversion efficiency and CO2 selectivity of the new Mn-based OC reached up to 99.4% and 99.2%, respectively, which are considerably enhanced values compared with 93.6% and 91.3% for the previously developed one. The time span of high CO2 selectivity zone of the new Mn-based OC was shorter than Ni-based OC due to its less oxygen transfer capacity, around 6 wt%. However, it is expected that high fuel conversion and CO2 selectivity would be possible with the new Mn-based OC by designing a fuel reactor to have sufficient contact time between OC and gaseous fuels.