METHANE MITIGATION IN NATURAL GAS INDUSTRIAL ENGINES: HYDROGEN FUEL BLENDING AND THE INTEGRATION OF CERAMIC ELECTROCHEMICAL REACTORS

Abstract

Methane emissions are one of the primary emissions causing global warming. Natural gas-fed industrial engines are one of the key drivers in excessive methane emissions due to partial load operations and combustion inefficiencies that can be controlled with modern methane mitigation strategies. In this thesis engine-based and post-combustion methane mitigation strategies are analyzed including spark ignition timing, hydrogen blending, and post-combustion protonic ceramic electrochemical cells (PCERs). The spark ignition timing is used to control the ignition time of the fuel and the electrochemical cells are considered for the conversion of exhaust methane into hydrogen. Hydrogen blending into natural gas is studied at 0%, 10%, and 20% hydrogen mole fraction and an engine load of 60%. The hydrogen mole fraction is calculated using an Aspen HYSYS model of the engine. The addition of hydrogen into the natural gas stream has resulted in a methane emission reduction of 16.2% and 35.2%. Modification of the ignition spark timing is conducted for the angles of 9°BTDC, 11°BTDC, 11.5°BTDC, and 12°BTDC, with the baseline angle being 11°BTDC. A significant methane emission reduction of 56.4% and 60.9% is observed at 11.5°BTDC, and 12°BTDC respectively due to an increase in combustion efficiency. The hydrogen blending and spark ignition are combined to obtain a methane reduction of up to 73% by improving thermal efficiency, promoting flame propagation, and reducing the methane content in the feed fuel. To remove all of the exhausted methane and convert CO to CO2 while obtaining a high-value chemical, an electrochemical cell is proposed as a post-combustion catalyst. The PCER model utilized a tubular, direct pass construction without an internal support tube. The model was constructed in engineering equation solver (EES) using a mole and electrochemical balance using a Ni/CeO2 anode, Ni BCZY electrolyte, and Ni/BCZY cathode. The PCER model was able to obtain complete methane conversion when operating at 2,000-5,000 A/m2 and a temperature between 673-780K when being fueled with realistic engine emissions. The technology developed here shows promising solutions for reducing and mitigating methane emissions from industrial engines and combustion devices.