Energy intensity in applying low-temperature chemical looping in steam reforming

Abstract

An energy analysis of methanol production via low-temperature chemical looping steam reforming was performed based on the process design; the potential benefits in reducing fuel consumption and excess heat generation were analysed. The feasibility of performing chemical looping reforming at temperatures lower than the conventional 900 °C is linked with the on-going development of a suitable oxygen carrier through the supercritical method. Pinch analyses were performed on designs that operate at three different reforming temperatures, namely 900, 500, and 300 °C, with either a high or a low heat transfer assumption within the reforming furnace. The results show that notable benefits are expected if the heat transfer from the combustion gases to the reformer tube contents improves along with lowering the reforming temperature. This ‘optimistic scenario’ resulted in an ≈ 41% decrease in excess heat generation and an ≈ 55% decrease in fuel consumption, as the reforming temperature decreased from 900° to 300°C. However, in the ‘pessimistic scenario’, where heat transfer does not improve despite the reforming temperature lowering, fuel consumption and excess heat generation remained almost constant when the reforming temperature was lowered from 900° to 300°C. In reality, heat transfer within the reforming furnace could behave somewhere between the low and high heat-transfer assumptions. The benefits of lowering the reforming temperature thus depend on several process and equipment design factors, including the temperature driving force, heat transfer area, and pinch approach temperature. An ill-designed reforming furnace, represented by the low heat-transfer scenarios, could result in no significant improvements despite the lowering of the reforming temperature; whereas well-designed equipment, represented by the high heat-transfer scenarios, could bring a significant improvement in energy consumption and waste heat generation.