Sammendrag
In this paper, the gas switching combustion (GSC) concept is further investigated with a sensitivity analysis for the fuel and oxygen carrier types. The GSC concept offers an alternative to the conventional chemical looping combustion (CLC) process for power production with integrated CO2 capture. In this concept, oxidation and reduction of the oxygen carrier take place in the same reactor by alternating air and fuel gas feeds into the reactor. This completely avoids any need for oxygen carrier circulation and thereby avoids many technical and scale-up challenges related to the looping concept. First demonstration of the concept with carbon monoxide (CO) as reducing gas and Ni-based oxygen carrier showed that the reactor could operate autothermally to continuously convert cold feed gases into hot product gases.
This work consists of two parts: Firstly, the GSC concept is further experimentally tested with syngas and methane as reducing gases on the same Ni-based oxygen carrier as used in the first demonstration. This experimental study is then followed by a more detailed thermodynamic analysis where the bed temperature variation sensitivity to the oxygen carrier and fuel is investigated.
As for the experimental study, syngas showed complete conversion with no carbon deposition, leading thereby to high CO2 purity (95%) and capture efficiency (95%). Lower CO2 purity was achieved (∼80%) when methane was used which was mainly caused by unconverted fuel and the existence of unconverted carbon monoxide as side product. Increasing the operating temperature slightly enhanced methane conversion to 84% which is still below expectations. High CO2 capture efficiency (95%) has however been achieved due to the absence of carbon deposition.
Thermodynamically, the influence of four different oxygen carrier materials on the temperature variation across the GSC cycle has been determined. Minimization of the temperature variation across the cycle is important in order to maximize the electric efficiency of the process and prevent turbine wear. The temperature variation across the four oxygen carriers and two fuel types investigated varied by a factor of 5 and specific recommendations were given to keep this variation to a minimum.
This work consists of two parts: Firstly, the GSC concept is further experimentally tested with syngas and methane as reducing gases on the same Ni-based oxygen carrier as used in the first demonstration. This experimental study is then followed by a more detailed thermodynamic analysis where the bed temperature variation sensitivity to the oxygen carrier and fuel is investigated.
As for the experimental study, syngas showed complete conversion with no carbon deposition, leading thereby to high CO2 purity (95%) and capture efficiency (95%). Lower CO2 purity was achieved (∼80%) when methane was used which was mainly caused by unconverted fuel and the existence of unconverted carbon monoxide as side product. Increasing the operating temperature slightly enhanced methane conversion to 84% which is still below expectations. High CO2 capture efficiency (95%) has however been achieved due to the absence of carbon deposition.
Thermodynamically, the influence of four different oxygen carrier materials on the temperature variation across the GSC cycle has been determined. Minimization of the temperature variation across the cycle is important in order to maximize the electric efficiency of the process and prevent turbine wear. The temperature variation across the four oxygen carriers and two fuel types investigated varied by a factor of 5 and specific recommendations were given to keep this variation to a minimum.