Process development and performance assessment of flexible calcium looping biomass gasification for production of renewable gas with adjustable composition

In recent years, the field of biomass gasification as a method of transforming biomass into a more useable gaseous fuel experienced expedited development since it represents a prominent way to achieve sustainability goals and targets set by the Paris accord and, more recently, the European Green Deal. The use of natural gas is projected to reduce with the transition toward exploitation of renewable gas, while a new area of hydrogen applications is also emerging. However, with uncertain production of current processes, and consumption patterns seen on the market, an opportunity for a new flexible process exists. This article investigates a concept process design of sorption-enhanced gasification (SEG) based on calcium looping. Aspen Plus simulation software was used to develop and simulate the process models for flexible production of bio-SNG or bio-H2. The process parameters can be manipulated to either achieve a high-purity bio-H2 (>96 mol%) or high-purity bio-SNG (>95 mol%), as well as any other combination of the two main products. The concept process is based on a low-pressure, low-temperature dual-fluidized bed reactor with steam as a gasifying agent and an additional downstream Sabatier process reactor to achieve high CH4 contents. The simulated process achieves process efficiency of up to 62.2%LHV and 78.0%LHV for H2 and CH4 production, respectively, with production yields reaching 0.112 kg H2/kg BM and 0.23 kg CH4/kg BM. These values were validated and benchmarked against comparable process designs, and the performance of the proposed process was found to be on par or superior. Overall, the proposed process design exhibits clear benefits of calcium looping gasification, with high process efficiency, negligible NOx, SO2, and H2S content, and high flexibility. Therefore, the proposed process addressed and successfully solved some of the key challenges of achieving viability of a gasification plant on a commercial scale.