(402g) Thermodynamic Analysis of an Integrated Ca-Cu Chemical Loop for Abatement of Ventilation Air Methane

Yongxing Zhang1,*, Xiaoling Chen2, Behdad Moghtaderi3

1National Engineering Laboratory for Pipeline Safety/MOE Key Laboratory of Petroleum

Engineering，

2Beijing Key Laboratory of Process Fluid Filtration and Separation, College of Mechanical and Transportation Engineering, China University of Petroleum-Beijing, China

3Priority Research Centre for Frontier Energy Technologies & Utilisation, Chemical Engineering,

School of Engineering, Faculty of Engineering & Built Environment, The University of

Newcastle, Australia

*Corresponding author: yongxing.zhang@uon.edu.au

Abstract

Methane is a major greenhouse gas (Global Warming Potential is 25 times that of CO2)  and fugitive methane (CH4)  from coal mines is the major source of anthropogenic CH4.  Approximately 64% of methane emissions in coal mine operations are in the form of ventilation air methane (<5 vol% methane in air). An integrated Ca-Cu chemical loop is proposed to utilize ventilation air methane with inherent CO2 capture as demonstrated in Figure 1. Similar with a common chemical looping concept, it mainly consists of two reactors, an oxidation reactor (OR) and a reduction reactor (RR), between which the metal/metal oxides are circulated. In the oxidation reactor, copper is oxidised to its oxide form (mainly CuO), which is then acted as the catalyst for the catalytic combustion of ventilation air methane. Meanwhile, the product of CO2 is adsorbed by the adsorbent of CaO and calcium carbonate (CaCO3) as formed. The mixture of CuO and CaCO3 is then transferred to a reduction reactor, in which CuO is reduced to Cu by high purity methane. Meanwhile, the endothermic calcination reaction of CaCO3  occurs and the thermal heat is provided by the exothermic reaction of CuO reduction. CO2 and steam are the main products from RR and the product gas from OR primarily consists of N2, steam and excess oxygen. As noted, CO2 and N2 do not mix in the proposed process. Most importantly, both OR and RR are in autothermic operation and as such no extra

energy is consumed for the strong endothermic calcination process, causing a large amount of efficiency reduction otherwise.

A detailed thermodynamic analysis of the process was carried out to evaluate its technical viability and overall performance. The overall of the proposed process was found to be superior to the Calcium loop for abatement of ventilation air methane. Taking into account the CO2  capture efficiency and overall efficiency together, the most suitable operation parameters for the process were determined. Specifically, the temperature for OR and RR were set to be 625oC and 850oC respectively. It was also found that the process was able to work with various concentrations of ventilation air methane, but it should be noted that the CO2 capture efficiency was less than 50% for the methane concentration lower than 1 vol%. For ventilation air methane with methane concentration in the range of 3 to 4 vol%, both high CO2 capture efficiency

and overall efficiency could be obtained.