Calcium looping processes for carbon capture

In the calcium looping process, a regenerable calcium-based sorbent is used to chemically absorb CO2, sulfur, and halide impurities from synthesis gas or hydrocarbon feedstock during the production of hydrogen(H 2) and electricity or only electricity. The removal of CO2 drives the water-gas shift reaction and hydrocarbon reforming reaction forward via Le Chatelier's principle enabling the production of high-purity H 2. The process operates at high temperature (e.g., 600-700 °C), eliminating the need for a water gas shift catalyst and allowing the exothermic heat of the CO2 absorption reaction to be recovered for use in generating steam. This significantly reduces the energy penalty associated with CO2 capture. The spent sorbent consisting mostly of calcium carbonate (CaCO3) is heated in a calciner to regenerate calcium oxide (CaO) for reuse in the process and to release a concentrated CO 2 stream that can be dried and sequestered. Overall CO2 emissions from the process are essentially zero. The regenerated sorbent is reactivated in a hydrator, to eliminate sintering and improve the recyclability of the sorbent, before being reintroduced into the H2 production reactor.;Among various reaction and process factors that are of importance to the CLP, the reactivity and recyclability of the calcium based sorbent are vital. The nature of calcium sorbent sintering that has been observed during multicyclic operation could pose a severe limitation to the commercialization of the process. In realistic calcination conditions, the sorbent loses one third to half of its original reactivity in a single cycle due to calcination at 950 ºC and 1000 ºC respectively. Several methods of improving the recyclability of CaO sorbents have been investigated including sorbent pretreatment, modification by addition of supports and reactivation. Hydration of the sorbent as a reactivation method after every calcination cycle was found to be very effective in improving sorbent performance. The Wt% capture of the sorbent was found to be constant at 50% during multicyclic CO 2 capture with sorbent hydration in every cycle in both bench scale and subpilot scale tests.;The CLP for production of H2 from syngas was investigated and very high purity H2 was produced with less than 1ppm of hydrogen sulfide (H2S) at high temperatures and pressures. For near stoichiometric steam addition, high carbon monoxide (CO) conversion and H2 purity can be obtained at high pressures and an optimal temperature of 600 °C. At atmospheric pressure, the presence of a water gas shift catalyst with CaO sorbent improves the purity of H2. At high pressures, typical of commercial deployment, the absence of the catalyst and the reduction of excess steam addition do not have any effect on CO conversion and high H2 purity is obtained.;For a hydrocarbon feed, the steam reforming of the hydrocarbon is integrated with the water gas shift and carbonation reaction in a single reactor. In addition to improving the conversion of the hydrocarbon to H2, the CLP also provides an efficient mode of internal heat integration where the endothermic energy for the reforming reaction is obtained from the exothermic energy released by the combined water gas shift and carbonation reaction. Single cycle tests have shown that the conversion of methane (CH4) is improved to a large extent by the addition of CaO sorbent at 650 ºC. High purity H2 is obtained at low steam to carbon(S:C) ratios of 3:1 for various pressures ranging from 1 to 11 atms. The effect of calcination conditions on the extent of CH4 reforming was determined. The reactivity of the sorbent was found to decrease over multiple cycles due to calcination in both pure nitrogen and in a mixture of steam and CO2. Hydration was found to be effective in reducing the sintering of the sorbent. (Abstract shortened by UMI.)...