THE USE OF A NON-THERMAL GLIDING ARC PLASMA REFORMER TO GENERATE HYDROGEN-RICH SYNGAS FOR IMPROVING COMBUSTOR PERFORMANCE

摘要

Non-thermal plasma-assisted partial oxidation of methane is considered with the intent to produce hydrogen-rich syngas with the least amount of electrical power. The syngas produced can be used to fuel quiet SOFC-based auxiliary generators, added to combustors to extend lean operation or further reformed to increase hydrogen yield (via the water-gas shift reaction, WGS) for low-temperature fuel cells and other applications needing hydrogen. Unlike catalytic fuel reformers that suffer from adverse issues involving catalyst deactivation (e.g., sintering, poisoning), plasma reforming is non-catalytic and offers: (1) rapid "on-demand" hydrogen-rich syngas production (quick startup), (2) fuel flexibility, and (3) the ability to produce a varying amount of syngas in response a time-dependent load (e.g., engine acceleration/ deceleration). In this work, experimental results using a non-thermal 'warm' gliding arc plasma discharge are reported. Our focus to date has been on rich methane-air. In terms of performance, near-equilibrium concentrations of hydrogen and carbon monoxide were achieved using rich methane-air premixtures having equivalence ratios between 2.5 to 4.0. Also, attention has been on the electrical energy needed to operate the plasma reformer, expressed in terms of a specific energy density (SED), defined here as the ratio of the electrical energy applied per unit mass of hydrogen or syngas (H_2+CO) produced. For a representative methane-air premixture (at equivalence ratio = 4.0, total flowrate = 35 SLPM, with no preheat), SED values determined from experimental measurements were 12.7 kWh/kg H_2 (45.8 MJ/ kg H_2) and 1.4 kWh/kg H_2+CO (5.1 MJ/kg H_2+CO) respectively. For hydrogen production, this SED is 38% of the lower heat value (LHV) of hydrogen (which is 33 kWh/kg H_2), meaning that roughly 1/3 of the chemical energy associated with the combustion of 1 kg of hydrogen is needed in the form of electricity to generate the 1 kg of hydrogen in the first place from methane. Efforts are currently underway to determine ways to lower the SED through improved thermal management (heat recuperation). With preheating of the methane-air reactants to 550°C (prior to the inlet to the plasma reformer), SED values as low as 5.2 kWh/kg H_2 (18.7 MJ/kg H_2) and 0.51 kWh/kg H_2+CO (1.8 MJ/kg H_2+CO) have been achieved (for a total flowrate of 72.4 SLPM, O/C=1.3 (Φ=3.1), 610W). These are the lowest values achieved to date. For hydrogen production, this SED value is only 16% of the LHV for H_2 (rather than 38% of the LHV without preheating) while for syngas production with preheating, the SED value of 0.51 kWh/kg H_2+CO is also lower (by almost a factor of 3) than the 1.4 kWh/kg H_2+CO SED value achieved without preheating.