Oxy-fuel combustion in a two-pass oxygen transport reactor for fire tube boiler application

Application of oxy-fuel combustion carbon capture technology to power plants is currently getting special attention as one of the means of curtailing CO2 emission responsible for the current climate change. The key concept of oxy-fuel combustion technology is the use of pure oxygen, obtained via air separation technologies, for combustion instead of air. Currently, the membrane separation technology is gaining high momentum due to its flexibility for different applications. Integrating oxygen transport membrane reactors to fire tube boilers has the prospects of concurrent permeation of oxygen, in-situ combustion as well as steam generation within a confined space, thus, potential for more compact boilers. Despite the in-situ prospects of the Oxygen Transport Membrane (OTM) integration, it comes with the heat transfer design challenges due to fragile nature of the membrane as well as maintaining the required operating temperatures for optimum performance. Hence the geometry as well as the heat transfer characteristics need to be well designed and the system needs to be thoroughly investigated for optimum performance. In this study, numerical modeling of a two-pass oxygen transport membrane reactor for oxygen permeation and oxy-fuel combustion characteristics analyses for fire tube boilers application was conducted. It was found that, for the non-reactive conditions, the effects of gases inlet temperature and mass flow rates on oxygen permeation along the length of the membrane was meager within the scope of this study. The gases inlet conditions dictate the rate of oxygen permeation under reactive conditions. Also, the gases inlet temperature and mass flow rates control the amount of heat transfer to the load. The sweep gas inlet condition was more critical to the stability of the combustion reaction. The current design of the proposed OTM reactor can deliver power output in the range from 1 to 5 MWe when applied to a typical fire-tube boiler.