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In this study, the high-pressure carbonation kinetics of calcium oxide (CaO) derived from three calcium-based sorbents, namely, limestone (CaCO3), calcium hydroxide [Ca(OH)2], and precipitated calcium carbonate (PCC), used in the calcium looping process (CLP) system were studied using a magnetic suspension balance (MSB) analyzer. Different total pressures (1000–15000 torr) and concentrations of CO2(10–30%) were tested to determine their effects on the carbonation reaction rate at a specific operating temperature of the CLP system, namely, 700 °C. The carbonation reaction rate was found to increase with increasing concentration of CO2(10–30%) at a constant total pressure of 5000 torr and to exhibit first-order kinetics. However, the total pressure has an effect on the carbonation reaction rate only at lower total pressures. With a 20% CO2stream, the reaction rate was observed to increase until the total pressure reached 4000 torr, beyond which a further increase in total pressure had a negative effect on the rate of the carbonation reaction of CaO derived from all three precursors. Further, the carbonation reaction had a different reaction order with respect to the partial pressure of CO2. It was found that the reaction was first-order at lower total pressures but changed to zeroth-order when the total pressure exceeded 4000 torr. The different reaction order under elevated pressures can be explained by the Langmuir mechanism. In addition, the reaction rate of carbonation conducted at high total pressure was greater than that at atmospheric pressure, under cyclic testing. The results also showed that there was no significant difference in the behavior of the carbonation reaction of CaO at elevated pressures, regardless of the different precursors used to generate the CaO. [ABSTRACT FROM AUTHOR]

A pilot-scale study of the Ohio State Carbonation Ash Reactivation (OSCAR) process was performed to demonstrate the reactivity of two novel calcium-based sorbents toward sulfur and trace heavy metal (arsenic, selenium, and mercury) capture in the furnace sorbent injection (FSI) mode on a 0.365 m3/s slipstream of a bituminous coal-fired stoker boiler. The sorbents were synthesized by bubbling CO2to precipitate calcium carbonate (a) from the unreacted calcium present in the lime spray dryer ash and (b) from calcium hydroxide slurry that contained a negatively charged dispersant. The heterogeneous reaction between these sorbents and SO2gas occurred under entrained flow conditions by injecting fine sorbent powders into the flue gas slipstream. The reacted sorbents were captured either in a hot cyclone (∼650 °C) or in the relatively cooler downstream baghouse (∼230 °C). The baghouse samples indicated ∼90% toward sulfation and captured arsenic, selenium and mercury to 800 ppmw, 175 ppmw and 3.6 ppmw, respectively. [ABSTRACT FROM AUTHOR]

The influence of several process parameters on the calcination of a naturally occurring limestone and a precipitated mesoporous calcium carbonate (CaCO3) sorbent structure to calcium oxide (CaO) is detailed in this study. CaCO3calcination is an integral part of a multicyclic carbonation-calcination reaction (CCR) process that separates carbon dioxide (CO2) from high-temperature gas mixtures into a pure CO2stream. Maintenance of high sorbent reactivity over repeated CCR cycles reduces the capital and operating cost of the CCR process. A lower calcination temperature, required to maintain high sorbent reactivity, reduces the calcination rate of CaCO3. This study investigates various process conditions such as subatmospheric calcination, sorbent dispersion in a rotary calciner, use of a high thermal conductivity sweep gas, etc. in enhancing the calcination rate at lower calcination temperatures. The high-temperature gas-solid carbonation studies of the resulting CaO sorbent prove the necessity to maintain a high porosity structure during limestone calcination. [ABSTRACT FROM AUTHOR]