Performance of the carbonator and calciner during long-term carbonate looping tests in a 1 MWth pilot plant

Carbon capture and utilization/storage is an effective means to reduce CO2 emissions from power and energy intensive industries. Carbonate looping is a 2nd generation post-combustion CO2 capture technology using solid sorbents that form carbonates when reacting with CO2. This technology has economic benefits caused by the low efficiency penalty and the low cost of the sorbent. Autothermal continuous operation of this process at high CO2 capture rates has been successfully proven in several pilot plants up to 1.7 MWth. The 1 MWth pilot plant in Darmstadt has been operated for more than 2000 h with long periods of steady-state conditions, which allows the evaluation of the performance of the reactor system during long-term operation. This paper presents complementary results of these pilot tests focussing on the performance of the carbonator and calciner reactors. A high carbonator efficiency above 80 % is possible in the temperature range of 650-675 °C with a specific solid inventory above 700 kg/m2 combined with either a high sorbent looping ratio of 16 molCa/molCO2 or a high make-up ratio of 0.13 molCa/molCO2. A calcination efficiency of 90 % can be achieved by a calciner space time above 6 min, if the calciner temperature is 30 K above the equilibrium temperature at the prevailing CO2 concentration. Heating of the sorbent entering the calciner consumes almost half of the thermal fuel input.