이산화탄소 저감을 위한 플라즈마트론 장치 개발

Abstract

The rapid exhaustion of fossil fuel reserves and the adverse effects of climate change caused by increasing global energy demands have attracted great attention and pose serious threats to humankind. Carbon dioxide is known to be a major green house gas that causes global climate changes, and is a main object of treatment because it accounts for about 80 percent of all green house gas emissions. This danger to our world is why research towards new and innovative ways of controlling CO2 emissions from these large sources is necessary. As of now, research is focused on two primary methods of CO2 reduction from condensed CO2 emission sources(like fossil fuel power plants) : Carbon Capture and Sequestration(CCS) and Carbon Capture and Utilization(CCU). CCS is the process of collecting CO2 using absorbers or chemicals, extracting the gas from those absorbers and finally pumping the gas into reservoirs. CCU on the other hand, is the process of reacting CO2 to form value added chemicals, which can then be recycled or stored chemically. This work focuses on the efficacy of plasmas for CCU, specifically gliding arc plasma and polymeric membrane for the dissociation of CO2 into its constituent parts in the hopes of converting it into value added chemicals. Polysulfone hollow fiber membrane was used to recover CO2 which is one of greenhouse gases from flue gas stream being emitted after the combustion of fossil fuels. The prerequisite requirement is to design the membrane process producing high-purity CO2 from flue gas. For separation of CO2, a membrane module and flue gas containing 10% CO2 was used. The effects of operating conditions such as pressure, temperature, feed gas composition and multi-stage membrane on separation performance were examined at various stage cuts. Higher operating pressure and temperature increased CO2 concentration and recovery ratio in permeate. Recovery and separation efficiency increased if a higher content of CO2 injection gas composition. Three-stage membrane system was producing a 95% CO2 with 90% recovery from flue gas. Three stage systems, one stage than the separation efficiency was improved. This study has developed the numerical model for optimization design of gliding arc plasma reactor, and applied for the investigation of flow field and electric characteristics in reactor. Parametric screening studies were conducted, in which there are the variations of electrode shape, electrode length, and flow rate of reactant gas. Therefore designed the gliding arc plasma reactor by predictive results. The gliding arc plasma reactor, applying the non-thermal plasma, was designed in this study maintained a very stable discharge state without spark generation within the reactor while decomposing carbon dioxide. To investigate the carbon dioxide decomposition characteristics, parametric screening studies were conducted, in which there are the variations of the pure CO2 flow rate, the addition of methane and/or steam reforming additives, the electrode geometry, and the electrode length. The maximum CO2 decomposition rate was 6.1% when pure CO2 was supplied, 24.5% when CH4 was injected as a reforming additive, and 27.6% when CH4 and steam were injected together, which showed the highest CO2 decomposition. CO2 decomposition rate was the highest in the electrode length 120 mm and the electrode geometry Arc 1. To increase the decomposition rate of CO2 using the single-phase direct-current gliding arc plasma reactor, it is necessary to develop other plasma devices. The 3-phase gliding arc plasma that was used in this study is known to have higher energy decomposition efficiency(EDE) and a lower manufacturing cost, with its 3-phase power supply, than the single-phase direct-current gliding arc plasma. The 3-phase AC gliding arc plasmatron was designed to decompose carbon dioxide and product hydrogen-rich gas. The changes in the amount of CO2 feed rate, CH4/CO2 ratio, gas injection velocity of the center nozzle, the total gas flow rate, input power, orifice baffle configuration, and the parameter according to catalysts or not were studied. The maximum CO2 decomposition rate was 7.9 % when pure CO2 was supplied. When the CH4/CO2 ratio was 1.29, CO2 decomposition rate and CH4 conversion rate were 37.0%, 47.0% respectively, the concentrations of syngas were H2 17.0% and CO 24.5%. At the nozzle injection speed of 82.9 m/s, the CO2 decomposition rate and CH4 conversion rate were 39.0%, 49.0%, and 0.0038 L/min‧W. The decomposition rate of carbon dioxide decreased from 37.0% to 33.6%, when the total gas flow rate increased. CO2 decomposition and CH4 conversion were influenced significantly by input power. Decomposition of carbon dioxide and conversion of methane rate on the NiO/Al2O3 catalytic process were 48.6 %, 56.5% respectively. For the orifice, Type 1, with a small internal area, showed the greatest efficiency because it could gather the unreacted gases to the center of the discharge area. The CO2 recycling system should be effectively used to reduce CO2 emissions of the fossil fuel combustion systems under the condition that there are no problems with the capacity of the plasmatron and the economically supplement of electric power energy. For the case of the thermal power, the plasmatron contributes to solving the greenhouse gas problem.