We present a novel low-temperature chemical looping combustion scheme for simultaneous natural gas conversion into a sequestration-ready CO_2 stream and NO, purification. The scheme employs nickel oxide (NiO) supported on ZrO_2 as the oxygen carrier. In the process, CH_4 reduces the oxidized carrier to Ni/ZrO_2 in a co-current moving bed reactor, which is then oxidized back to NiO/ZrO_2 by the NO,-laden flue gas in a fluidized bed reactor, completing the oxygen carrier loop. Thermodynamic studies demonstrate that the presence of CO_2 does not significantly affect NO_x, purification performance at different flue gas flow rates. The operating temperatures of the reactors are selected based on NO,- temperarure programmed oxidation (TPO) and CH_4-temperature programmed reduction (TPR) experiments. Results show that the process can optimally operate at temperatures close to the combustion plants' flue gas temperature of 400-500 ℃, reducing the need for hot utilities. The study conducts comprehensive isothermal and autothermal analyses of the process to evaluate the effects of temperature and carrier flow rate on CH_4 conversion, CO_2 selectivity, carbon deposition, and NO_x conversion. For the autothermal analysis, the CH_4 reactor operates adiabatically, while the NO, reactor operates isothermally. Comparative studies with the conventional NO, selective catalytic reduction (SCR) process indicate an exergy efficiency and effective thermal efficiency (ETE) improvement of 9 and 18 percentage points, respectively. The findings suggest that this low-temperature chemical looping process is a promising solution for flue gas NO_x treatment, utilizing cheaper natural gas as the reductant and eliminating environmental concerns, such as ammonia or urea slippage. Overall, this study contributes to the development of more efficient and sustainable methods for reducing NO, emissions.
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