PRODUCTION OF HYDROGEN AND UTILIZATION IN FUEL CELL

Abstract

Hydrogen is an energy carrier with a very high energy density (>119 MJ/kg) while the heating value on volume basis (~8 MJ/L, which is rather low). Pure hydrogen is barely available; thus, it requires extraction from its compounds. Steam reforming and water electrolysis are commercially viable technologies for hydrogen production from water, alcohols, methane, and other hydrocarbons; however, both processes are energy intensive. Current study aims at understanding the methane and ethanol-water mixture pathway to generate hydrogen molecules. The various intermediate species (like CHX, CH2O, CH3CHO) are generated before decomposing methane/ethanol into hydrogen radicals, which later combine to form hydrogen molecules. About 97-98% of production is through steam reforming natural gas. The plasma reforming process was used to produce hydrogen, and the performance of various parameters on the hydrogen production rate was analyzed using three different ultrasonic transducers. Results showed the higher frequency (2.4 MHz) transducer had about 8-10% higher rate of hydrogen production against 1.7 MHz and 0.3 MHz transducers. The input voltage showed a 14-25% increase in hydrogen production rate from 4 kV to 7.5 kV, and beyond 7.5 kV, it declined. Similarly, the higher methanol concentration of 35% and feed flow rate of 3.5 LPM showed the highest hydrogen production rate. A H2 purification unit was also installed that generated H2 at about 99% purity level. The study uses methanol as the feedstock for hydrogen production via a low-temperature methanol-reforming process. A simulation model was developed, where an equilibrium reactor is used for the reforming process. Effects of parameters like temperature, pressure, and Methanol-to-Water (M-to-W) molar ratio were examined. H2 mole fraction and selectivity rise from 0.54 to 0.64 and from 60.91% to 67.28% when the reaction temperature increases from 100℃ to 400℃. At the same time, the methanol conversion rate reached 95% at 400℃. Reactor pressure showed inverse effects where higher pressure reduced both hydrogen mole fraction and selectivity, and a similar reduction was noticed in the methanol conversion rate. M-to- v W molar ratio played a crucial role in the reaction pathway, and the M-to-W ratio is between 0.5 and 1.5 at 400℃ and 1 atm. reactor pressure showed the highest H2 mole fraction (>0.57) and a maximum methanol conversion rate (>90%). Therefore, the present simulating model effectively determined the impacts of various parameters. Developed simulation model of a methanol-water, and the effects of reaction temperature (RT), reactor pressure (RP), and methanol-to-water (M-to-W) ratio are investigated. In contrast, the optimal conditions for hydrogen selectivity (HS) and feed conversion percentage (FCP) were determined using response surface methodology. Results showed a significant effects on the M-to-W molar ratio ranging between 0.9 and 1.35, whereas higher RT showed a good affinity for higher HS and FCP. The regression analysis showed R 2 values of 0.9877 and 0.9803 for HS and FCP, which is close to unity. Hence, both experimental (and simulated) and predicted values showed better correspondence with each other. In contrast, the optimal HS and FCP of 84.81% and 95.71% were observed at 328℃ RT, 2.6 atm. RP and 1.34 M-to-W molar ratio. A fuel cell generates electricity using hydrogen and oxygen. In the present work, a 1 kW proton exchange membrane fuel cell was evaluated for its performance at variable operating parameters. The operating parameters are important in examining the outputs from the fuel cell. Hydrogen flow rate (HFR) and gas pressure were two operating parameters considered for the cell performance. The hydrogen was generated from a hydrogen production and purification unit, whereas the oxygen was captured from the air. About 61% reduction in the HFR from 13 LPM to 5 LPM resulted in only 29% reduction in output current. In contrast, the addition and subtraction of 10% gas pressure from the rated value resulted in an 8% and 14% decline in output power. Similarly, the fuel cell stack efficiency declined by 10% and 15% with a 10% addition and reduction in the rated gas pressure. Therefore, the present simulation and optimization provide results that may help to enhance the hydrogen production percentage. Also, the lower HFR reduced the cell output but the H2 requirement was also reduced significantly, which showed the percentage decline in output was lower than the H2 percentage saved.