Lanterna Rally

Author: Amoolya Dattatraya Lalsare

Publisher:

Published: 2016

Total Pages: 67

ISBN-13:

Calcium looping is a sorbent based chemical looping process that uses calcium oxide or similar calcium sorbent precursors for pre-/post-combustion carbon dioxide capture. Extensive study of this process at the Ohio State University has led to the development of two variants of this process: Carbonation-calcination reaction (CCR) process for post-combustion carbon capture in electricity generation and calcium looping process (CLP) for pre-combustion carbon capture in hydrogen production and electricity generation. CCR is a cyclic post-combustion carbon capture process, demonstrated at a 120 KWth scale at OSU. This demonstration achieved more than 90% carbon dioxide removal and over 99% sulfur dioxide (SO2) removal. It has been shown through process simulations that CCR process induces less energy penalty than the conventional amine/oxy-combustion based carbon dioxide capture technologies. This process involves carbonation-calcination-steam hydration of calcium sorbents. Steam hydration is a reactivation step which mitigates the effect of sintering of sorbents during calcination, regenerates the sorbent surface, and retains carbon capture capacity over a large number of cycles. High pressure steam reactivation of calcium sorbents was investigated and the dependence of hydration rate on steam pressure is obtained. Higher steam partial pressure allows for higher temperatures (500-550oC) to get higher hydration conversions. The reaction being highly exothermic (-109 kJ/mol), high temperature gives high quality heat which can be used elsewhere in the process. Reaction kinetics of steam hydration for four different limestone based sorbents was studied using high pressure thermogravimetric analysis. Elevated pressures (1-3.5 atm) and high temperature (500-530oC) were used in this study. Steam hydration of PG Graymont limestone sorbent experimentally showed second order w.r.t steam pressure driving force (PH2O – P*H2O). Rate constants for each operating conditions were calculated and activation energy of the reaction was computed from these calculations. The activation energy obtained from this study is 5.18 KJ/mol. Nitrogen physisorption studies were performed for characterization of the sorbents and their reactivity was compared via the steam hydration studies in the TGA at 500oC and PH2O 1.5 atm. CaO sorbent derived after hydration shows the highest surface area and pore volume, which is more than 6-10 times that of the sorbent derived by calcination of CaCO3. This study is a strong indication that hydration with water/steam regenerates the sorbent morphology, in process reactivating the sorbents with high porosity. It is believed, however, that initial particle size has little or no bearing on the reactivation process or sorbent reactivity in the multi-cyclic studies as hydration causes particle breakage. This study is significant in regard to the post-combustion and pre-combustion carbon capture calcium looping processes developed at OSU as the hydration temperature would be comparable to the carbonator temperature as it is expected to make the processes economically viable. There exists a trade-off however for the steam pressure to be used for hydration. Very high steam pressure would incur high compression costs and affect the energy penalty of the process. This could deter the compensating effect of heat recovered from the hydrator and in turn make the process more energy intensive. This study is limits the pressure to 4-5 times the atmospheric pressure and still obtain higher conversions.