[학위논문]NiO 산소공여입자를 사용하는 기포유동층 매체 순환식 메탄연소 공정의 모사 및 설계 Design and Simulation of Chemical-Looping Combustion of Methane in a Bubbling Fluidized Bed Process Using NiO as an Oxygen Carrier원문보기
The capability to capture a pure carbon dioxide with high potential and without any extra energy makes the chemical looping combustion (CLC) one of the leading technologies for CO2 capture compared to other capture techniques; the compressed carbon dioxide can be injected into oil and natural gas re...
The capability to capture a pure carbon dioxide with high potential and without any extra energy makes the chemical looping combustion (CLC) one of the leading technologies for CO2 capture compared to other capture techniques; the compressed carbon dioxide can be injected into oil and natural gas reservoirs for the purpose of simultaneously enhancing oil recovery and reducing the CO2 emissions since it is considered as the main greenhouse gas causing global warming. The chemical looping combustion is an unmixed combustion concept [1-4]. It consists of two interconnected fluidized bed reactors, an air reactor (AR) and a fuel reactor (FR), using circulating metal oxide particles to transfer oxygen from AR to FR. Metal oxide oxidizes in AR with air and it is reduced in FR by methane, thus eliminating NOx formation [1,5-7] and producing almost pure carbon dioxide. The purpose of this study was to develop the CLC process for methane using NiO-based as an oxygen carrier to determine the proper operating conditions for complete combustion of methane to carbon dioxide and water in the FR, therefore enhancing the performance of the CLC system. The hydrodynamic characteristics of a gas-solid fluidized bed were carried out at operating pressures from atmosphere to 5.013 bars in a pressurized fluidized bed. The effects of the fluidizing velocity, solid inventory and the operating pressure on the solid-holdup in the dense bed were studied. The experimental results showed that the solid-holdup decreases with increase of fluidizing velocity or the operating pressure, but there was no significant effect of pressure on the minimum fluidization velocity in this operating pressure range. The performance of the CLC system was investigated under various operating conditions such as temperature, bed weight and solid circulation rate, in two interconnected bubbling fluidized beds, a high velocity fluidized bed for the AR and a low velocity fluidized bed for the FR .The proper operating conditions in both AR and FR for complete combustion of methane were discussed, with consideration of the particle attrition and required makeup of fresh oxygen carrier (OC) particles. The simulation results showed that the efficiency of combustion of methane was strongly affected by the distribution of OC between the air reactor (AR) and fuel reactor (FR) at a constant temperature, circulation rate of OC, and total bed mass. The range of OC distribution possible to achieve complete combustion became wider with increasing either the temperature or the circulation rate of OC at a constant total bed mass. In this range, the amount of elutriated OC particles decreased a little as the FR mass increased because of the higher rates of particle elutriation and attrition in AR than in FR. More particularly interesting results were presented in this work, illustrating the effect of each reactor on the behavior of the whole process. Ultimately lead to a better design procedure of the CLC process of pure methane in a continuous bubbling fluidized bed process with NiO-based oxygen carrier, by estimating the minimum requirements of solids inventory in each reactor and the minimum solids circulation rate to maintain a complete conversion of methane to CO2 and H2O over a wide range of operating parameters. It was found that the minimum requirements of solids inventory in each reactor, operating temperature and solid circulation rate were necessary and could not be compensated by any other parameter. Moreover, it was found that for gaining more flexibility, the increase of the temperature is preferred rather than increasing of the total solids inventory, regarding to the economic considerations.
The capability to capture a pure carbon dioxide with high potential and without any extra energy makes the chemical looping combustion (CLC) one of the leading technologies for CO2 capture compared to other capture techniques; the compressed carbon dioxide can be injected into oil and natural gas reservoirs for the purpose of simultaneously enhancing oil recovery and reducing the CO2 emissions since it is considered as the main greenhouse gas causing global warming. The chemical looping combustion is an unmixed combustion concept [1-4]. It consists of two interconnected fluidized bed reactors, an air reactor (AR) and a fuel reactor (FR), using circulating metal oxide particles to transfer oxygen from AR to FR. Metal oxide oxidizes in AR with air and it is reduced in FR by methane, thus eliminating NOx formation [1,5-7] and producing almost pure carbon dioxide. The purpose of this study was to develop the CLC process for methane using NiO-based as an oxygen carrier to determine the proper operating conditions for complete combustion of methane to carbon dioxide and water in the FR, therefore enhancing the performance of the CLC system. The hydrodynamic characteristics of a gas-solid fluidized bed were carried out at operating pressures from atmosphere to 5.013 bars in a pressurized fluidized bed. The effects of the fluidizing velocity, solid inventory and the operating pressure on the solid-holdup in the dense bed were studied. The experimental results showed that the solid-holdup decreases with increase of fluidizing velocity or the operating pressure, but there was no significant effect of pressure on the minimum fluidization velocity in this operating pressure range. The performance of the CLC system was investigated under various operating conditions such as temperature, bed weight and solid circulation rate, in two interconnected bubbling fluidized beds, a high velocity fluidized bed for the AR and a low velocity fluidized bed for the FR .The proper operating conditions in both AR and FR for complete combustion of methane were discussed, with consideration of the particle attrition and required makeup of fresh oxygen carrier (OC) particles. The simulation results showed that the efficiency of combustion of methane was strongly affected by the distribution of OC between the air reactor (AR) and fuel reactor (FR) at a constant temperature, circulation rate of OC, and total bed mass. The range of OC distribution possible to achieve complete combustion became wider with increasing either the temperature or the circulation rate of OC at a constant total bed mass. In this range, the amount of elutriated OC particles decreased a little as the FR mass increased because of the higher rates of particle elutriation and attrition in AR than in FR. More particularly interesting results were presented in this work, illustrating the effect of each reactor on the behavior of the whole process. Ultimately lead to a better design procedure of the CLC process of pure methane in a continuous bubbling fluidized bed process with NiO-based oxygen carrier, by estimating the minimum requirements of solids inventory in each reactor and the minimum solids circulation rate to maintain a complete conversion of methane to CO2 and H2O over a wide range of operating parameters. It was found that the minimum requirements of solids inventory in each reactor, operating temperature and solid circulation rate were necessary and could not be compensated by any other parameter. Moreover, it was found that for gaining more flexibility, the increase of the temperature is preferred rather than increasing of the total solids inventory, regarding to the economic considerations.
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