Scientists from Ottawa University developed a compact integrated heat exchanger reactor designed for scrubbing the stack gas received during operation of pressurized chemical loop unit (PCLC). Such system is efficient not only for eliminating residual trace elements before sending CO₂ to burial, but also for converting the reaction heat into useful steam, thus improving the overall energy efficiency of the process.
Stack gases from PCLC-systems contain a lot of CO₂, however, they always contain traces of methane and carbon monoxide. Pipeline standards require almost complete removal of them, and the researchers used non-traditional ways to resolve this task: they combined several steps of catalytic afterburning with interim cooling in one compact appliance. Inside the reactor, where impurities incineration takes place, catalytic plates alternate with ultra-compact printed heat exchangers, which immediately remove the released heat and convert it into steam.
To define the optimal structure of the reactor, detailed computer calculations were performed. At first the thermodynamics of the process were studied: to which extent gas will be heated and how many reaction steps will be needed to achieve the required pureness of the flow. Six short catalytic sections turned out to be the optimal solution. Then the scientists calculated the length of each of them using the kinetic data of CO oxidation – about 6 cm in total. Simultaneously the design of the heat exchangers was specified: the parameters were selected to effectively decrease the gas temperature between the reaction zones and produced the steam with the required characteristics.
The final design represented a compact unit less than 1.7 meters long capable of servicing the flow from a big 100-MW unit. The reactor not only brings the gas composition to the compliance with pipeline standards, but also generates about 1.6 MW of heat in the form of saturated steam under 180 °C – i.e., converts the unavoidable purification stage from energy consuming into energy profitable. The thermal power density reaches 2.3 MW per cubic meter, which is a very high metric for such systems.
The researchers emphasize that the proposed approach is an important step towards chemical and thermal processes integration. The methodology of reactors engineering is scalable and may be used for resolving other industrial tasks, where gas purification needs to be combined with simultaneous heat recovering. The main limitation of the current work is the need to adjust the catalytic materials for specific conditions of PCLC-gases.
Development of specialized catalysts will be the next stage, and after that the technology will move from the engineering concept to practical implementation.
