Abstracts Category : Other

Application of calcium looping for heat generation and CO enrichment in greenhouses

by Mohammad Ramezani

Professional Doctorate - Doctor of Philosophy (PhD) Greenhouses typically employ conventional natural gas burners to meet the heat demand especially during cold winter nights and make use of additional carbon dioxide (CO2) to increase the CO2concentration above the atmospheric levels, thereby, accelerating the photosynthesis process and plant growth. As an alternative, this thesis describes a novel Greenhouse Calcium Looping (GCL) process which offers a cost effective solution for satisfying both heat and CO2 demands of modern greenhouses. More specifically, the GCL process can produce significant quantity of heat during night-time through an exothermic carbonation reaction between calcium oxide (CaO) particles and the CO2 emitted by growing plants. The resulting calcium carbonate (CaCO3) particles are then calcined during day-time releasing their CO2 content so that the photosynthesis process can be enhanced. The carbonation-calcination cycle is then repeated again. Interestingly, the greenhouse calcium looping (GCL) process is found to have better efficiencies and nearly zero CO2 emission profile compared to other conventional processes. However, so far, the optimum conditions, i.e. temperature and pressure, for providing the required heat and CO2 to the greenhouses in the GCL process are not clear. This includes also finding out how much CaO inventory is required for fulfilling the requirements of greenhouses? Accordingly, the main objective of this study is to find out the feasibility of the GCL process using Aspen Plus simulator software and establish the optimum conditions of the GCL process using Aspen Plus and experimental data. The conceptual design of greenhouse calcium looping process was carried out in the Aspen Plus v 7.3 simulator. The process simulations carried out in Aspen indicated that the GCL process theoretically contributes to net zero emission of carbon dioxide given that the CO2 released by plants over the night cycle are absorbed again during the day cycle through the photosynthesis. Moreover, in a scenario modelling study compared to the conventional natural gas burner system, the heat duty requirements in the GCL process were found to reduce by as much as 72%. Unique conditions of the GCL process (low temperature and low CO2 partial pressure) led to determination of the intrinsic carbonation reaction kinetic parameters in a temperature range of 400 to 500 oC and CO2 partial pressures of 0.05 to 0.1% (500 to 1000 ppm) which were carried out experimentally via a thermogravimetric analyser (TGA). Various gas-solid reaction mechanisms were considered to determine the best reaction mechanism for the carbonation reaction. Moreover, the activation energy and pre-exponential factor of the carbonation reaction were established. The derived kinetic parameters were used in Aspen Plus to establish the optimum carbonator size considering an RPlug unit. The requiredAdvisors/Committee Members: University of Newcastle. Faculty of Engineering & Built Environment, School of Engineering.