RPG 연료전지용 고농도 수소생산을 위한 부채꼴형 NTP 개질 시스템

Abstract

Environmental pollutions is becoming increasingly more serious due to the rising use of fossil fuels. With the consequent strengthening focus on developing alternative and clean energy sources, research attention is increasing on the efficient use syngas or hydrogen as an environment-friendly, alternative source of energy. Fuel reforming methods for syngas production are steam reforming, CO2 reforming and POx reforming in the view of reaction aspect, and others. However, above methods are technological limitations and economical factors to be use alone for reforming. Plasma reforming is considered to be a method with the potential to overcome such limitations. Because plasma is high in energy and can transmit energy to other materials easily, it has suitable characteristics to react easily with low-reactant mixtures. Therefore, it is more effective to combine between plasma reforming and above other existing technologies. Plasma is classified as thermal or non-thermal according to the electricity density and temperature. High temperature plasma, which is equilibrium thermodynamically, has the characteristic of high ionization by higher energy. This has the merit of good reaction control and conversion rate, but has the demerit of high power consumption. Low temperature plasma, which is non-equilibrium, has the characteristic of low ionization and is therefore applied widely in various fields, because it is obtained easily by discharging gas in the low or even atmospheric pressure state. Although the non-thermal plasma reforming process is still in its development stage, many results proving the economic feasibility of the process have been reported, demonstrating the possible commercialization of the process. The gliding arc technology is not complex and presents a high flexibility allowing to work in a high range of flow rates and to treat a large amount of chemical species. The main advantage of this device is that we can easily vary the power in the discharge, by acting on the device of the electrode, and on the voltage level. This study has developed the numerical model for optimization design of Gliding arc plasma reformer, and applied for the investigation of flow field and electric characteristics in reformer. Parametric screening studies were conducted, in which there are the variations of electrode length, preheating temperature of reactant gas, flowrate of reactant gas. Therefore designed the Glidarc plasma reformer by predictive results. Glidarc plasma reactor, applying the non-thermal plasma, was designed in this study maintained a very stable discharge state without spark generation within the high temperature reactor while reforming the propane. To improve hydrogen yield and propane conversion rates, parametric screening studies were conducted, in which there are the variations of vapor flow ratio(H2O/TFR), carbon dioxide component ratio(CO2/TFR), input power and retention time. When the variations of vapor flow ratio, carbon dioxide flow ratio, input power and retention time were 0.61, 0.14, 1.37 kW and 4.6 sec, respectively, the conversion rate of the propane reached its most optimal condition, or 91.6%. Under the condition mentioned above, the dry basic concentrations of the synthesis gas(syngas) were H2 46.3%, CO 20.0%, CH4 8.6%, C2H2 5.5%, C3H6 1.52%, C2H4 1.03% and C3H4 0.41%. The conversion rates of carbon dioxide and vapor were 20.0% and 95.5%, respectively, and H2/CO ratio is 2.3. Besides reforming characteristics and economy for syngas production were studied by using Glidarc-assisted plasma with a catalytic reactor. Parametric screening studies were carried out for variations of the following variables: vapor flow ratio, CO2 flow ratio, reactant gas flow rate and input electric power. When these variables were 0.55, 0.14, 14 ℓ/min and 1.37 kW, respectively, the production of hydrogen-rich gas was maximized with an optimal propane conversion rate of 62.6 %. Under these optimal conditions, the following syngas concentrations were determined: H2, 44.4%; CO, 18.2%; CH4, 11.2%; C2H2, 2.7%; C3H6, 1.9%; C2H4, 0.6%; and C3H4, 0.4%. The carbon dioxide conversion rate was 29.2%, energy conversion rate was 25.3% and H2/CO ratio was 2.4. Also electric energy cost produced syngas(H2+CO) was 1.97 kWh/Nm3. Such a electric energy cost was therefore assimilated to the LHV of syngas(H2+CO). The generation of high-purity hydrogen from hydrocarbon fuels is essential for efficient operation of fuel cell. In general, most feasible strategies to generate hydrogen from hydrocarbon fuels consist of a reforming step to generate a mixture of H2, CO, CO2 and H2O(steam) followed by water gas shift(WGS) and preferential oxidation reaction(PrOx) steps. The WGS reaction that shifts CO to CO2 and simultaneously produces another mole of H2 was carried out in a two-stage catalytic conversion process involving a high temperature shift (HTS) and a low temperature shift(LTS). In the WGS operation, gas emerges from the reformer is taken through a high temperature shift catalyst to reduce the CO concentration to about 3～4% followed to about 5000ppm via a low temperature shift catalyst. The WGS reactor was designed and tested in this study to produce hydrogen-rich gas with CO to less than 5000ppm. When the O2/C ratio was 0.3 in the PrOx reactor, steam flow ratio was 2.8 in the HTS, and temperature were 475, 314, 260, 235 ℃ in the HTS, LTS, PrOx, the conversion of CO was optimized conditions of shift reactor using simulated reformate gas. Therefore, purification gas were H2 38%, CO < 10 ppm, N2 36%, CO2 21% and CH4 4%.