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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]

Examines the kinetics and mechanism behind the capture of gas-phase arsenic oxide by lime. Interaction between arsenic oxide and lime; Influence of temperature on the capture of gas-phase arsenic oxide by lime; Role of surface area of the sorbent particle in gas-solid chemical reactions.

Redox reactions between fine solid fuels, such as pulverized coal powder, and coarse oxygen carrier particles can be carried out in a fixed/moving bed reactor chemical looping system. The migration pattern of the solid fuel powder and its contact time with coarse particles can significantly affect the reaction rate and the product yield. A number of challenges exist in transporting/mixing of fuel powder and in removing noncombustible waste (e.g., coal ash) from the reactor vessel in the chemical looping operation. Thus, it is important to understand the hydrodynamic behaviors of fine particles in such situations. This study describes an experimental approach that examines migration characteristics of fine particles (Geldart A/B), in both spatial and temporal aspects, in a packed bed of coarse particles (Geldart D). The experimental variables include the particle size distribution of the fine powder, the fine to coarse mass ratio, and flow conditions. At a given upward aeration flow within the range that is higher than the terminal velocity of the fine particles but lower than the minimum fluidization velocity of coarse particles (Ut < Us < Umf,c), the fine particles may travel both upward and downward depending on the gas flow rate and the physical properties of particles and gas. The spatial transport pattern in terms of the upward and static transport partition (wt %) of Geldart A particles can be characterized as an exponential function of a group of dimensionless numbers (e.g., Stk*, Rep* and Us/Ut). The time-dependent upward transport rate of fine particles is measured to determine the temporal migration characteristics. Cluster response time (τc) is introduced to describe how fast a cluster of fine particles in a packed bed respond to the ambient flow. This parameter is normalized by the response time of fine particle (τp) and further correlated with the pseudo-particle Reynolds number (Rep*) via an inverse power function with two coefficients. [ABSTRACT FROM AUTHOR]