Derivation of Kinetics and Design Parameters for a Carbonator Reactor in a Greenhouse Calcium Looping Process

Abstract

The carbonation/calcination reaction cycle of a limestone sorbent was studied experimentally by using a thermogravimetric analyzer for unique conditions, such as low temperature (400 to 500 °C) and low CO2 partial pressure (0.05 to 0.1 %), pertinent to a novel greenhouse calcium looping process. The kinetic parameters were obtained and compared with those reported in the literature. Various gas–solid reaction mechanisms were considered to determine the best reaction mechanism for the carbonation reaction. The diffusion function, or G(x)=x2, had the best least‐squares linear fit, which resulted in a first‐order reaction for the carbonation reaction in the greenhouse calcium looping process. Moreover, the activation energy and pre‐exponential factor of the carbonation reaction were established to be 19.7 kJ mol−1 and 295.8 min−1 kPa−1, respectively. The derived kinetic parameters were used in Aspen Plus to optimize the carbonator reactor size. The required size of the reactor decreased with increasing operating temperature of the reactor. Exergy analysis revealed that the overall exergetic efficiency of greenhouse calcium looping could be more than 80 %.

Kinetics and Design Parameter Determination for a Calciner Reactor in Unique Conditions of a Novel Greenhouse Calcium Looping Process

“…Five milligrams of raw Omya limestone sorbent (75–150 μm), provided by a local Australian supplier, was inserted into a platinum crucible of a Q50 TGA. The elemental analysis of this sorbent, carried out in an X-ray fluorescence (XRF) apparatus (Spectro X-lab 2000), can be found in our previous publication . At ramp rate of 20 °C min –1 , the limestone sample was initially heated to 700 °C, in a N 2 environment, and held isothermally for 10 min to ensure that the limestone sorbent was completely converted to CaO.…”

“…The calcination reaction kinetic parameters required for the simulation of the RPlug reactor were derived experimentally and introduced to the reaction tool of Aspen Plus. In addition, the kinetic parameters of the reverse reaction, the carbonation reaction, were also taken into account by using the results of our recent publication regarding determination of the carbonation reaction parameters . The conversion of MgO to MgCO 3 was also taken into account as there was a small amount of MgO in the inventory.…”

“…The exergy of a process consists of three categories: exergy of work transfer, exergy of heat transfer, and exergy related to a steady stream of matter. All of the equations and assumptions applied to calculate the exergy efficiency of each unit in the process and the overall process were the same as our recent publication . Like our previous work, for every stream a heater block was considered to be working at reference conditions of 25 °C and 1 atm, and according to the method suggested by Querol et al, there was no requirement to calculate the mixing exergy term when determining the chemical exergy of a stream of matter.…”

“…Following this trend, a novel renewable process that is based on the calcium looping process was proposed in our previous publications. , This process, known as the greenhouse calcium looping (GCL) process, uses limestone (CaCO 3 ) as a key sorbent in the cyclic carbonation/calcination reactions, providing the required heat as well as CO 2 enrichment to greenhouses. This study was involved in a broad area of chemical looping research, which has been carried out at the University of Newcastle since 2007. , These chemical looping based processes need metal oxide oxygen carriers, while in the GCL process, proposed in our previous study, limestone was used as the key sorbent and worked via the cyclic carbonation/calcination reaction mechanism.…”

“…To simulate the process with an RPlug unit, the stoichiometry and kinetics of the reaction is required. Recently, we published our investigation on deriving kinetic parameters of the carbonation reaction in the unique conditions of the GCL process (low temperature and CO 2 partial pressure ranges), and these kinetic parameters were then utilized in Aspen Plus simulations of the carbonation reaction of the GCL process considering an RPlug reactor.…”