Abstract
This paper reports further experimental demonstration of the Gas Switching Combustion (GSC) concept with a focus on the concept sensitivity to the fuel type. 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.
In this paper, the GSC concept is further tested with syngas and methane as reducing gases. First testing of the reactor with carbon monoxide showed large heat losses, but operation could still be maintained. Experiments with syngas (62% CO and 38% H2) and methane were however carried out with external heat supply to compensate for part of heat losses and show the heat removal stage which is an important component of the GSC concept. Three target temperatures have been tested for both fuel gases.
Syngas showed complete conversion with no carbon deposition, leading thereby to high CO2 purity (95%) and capture efficiency (95%). Slightly low CO2 purity has been achieved (around 80%) when methane was used which was mainly caused by unconverted methane and existence of carbon monoxide in the gas stream. High CO2 capture efficiency (95%) has however been achieved due to the absence of carbon deposition.
In the light of its excellent performance, syngas is suitable to fuel the GSC reactor. A syngas fuelled GSC reactor cluster would be deployed in a baseload integrated gasification combined cycle (IGCC) plant where its relative simplicity regarding design, scaling and pressurization could lead to a cost effective solution relative to alternative technologies.
Methane could also be potentially used as fuel for the GSC concept if the issue of the slow reactivity at the start of the reduction stage is solved. This could be achieved through the use of oxygen carriers with low catalytic activity with respect to the steam methane reforming reaction. Successful operation with methane could be important in a future electricity market where moderate penetrations of intermittent wind/solar power require flexible power production with integrated CO2 capture.
In this paper, the GSC concept is further tested with syngas and methane as reducing gases. First testing of the reactor with carbon monoxide showed large heat losses, but operation could still be maintained. Experiments with syngas (62% CO and 38% H2) and methane were however carried out with external heat supply to compensate for part of heat losses and show the heat removal stage which is an important component of the GSC concept. Three target temperatures have been tested for both fuel gases.
Syngas showed complete conversion with no carbon deposition, leading thereby to high CO2 purity (95%) and capture efficiency (95%). Slightly low CO2 purity has been achieved (around 80%) when methane was used which was mainly caused by unconverted methane and existence of carbon monoxide in the gas stream. High CO2 capture efficiency (95%) has however been achieved due to the absence of carbon deposition.
In the light of its excellent performance, syngas is suitable to fuel the GSC reactor. A syngas fuelled GSC reactor cluster would be deployed in a baseload integrated gasification combined cycle (IGCC) plant where its relative simplicity regarding design, scaling and pressurization could lead to a cost effective solution relative to alternative technologies.
Methane could also be potentially used as fuel for the GSC concept if the issue of the slow reactivity at the start of the reduction stage is solved. This could be achieved through the use of oxygen carriers with low catalytic activity with respect to the steam methane reforming reaction. Successful operation with methane could be important in a future electricity market where moderate penetrations of intermittent wind/solar power require flexible power production with integrated CO2 capture.