Power to X integration in biogas plants: Comparison of three different pathways

Abstract

The rising levels of greenhouse gas emissions, especially of carbon dioxide, imposes a significant threat to the world, requiring new decarbonisation technologies. This thesis explores integrating a Power to X system with an existing biogas plant utilizing waste from salmon fishery. Three pathways for upgrading biogas to methanol or methane were investigated: (P1) direct carbon dioxide to methanol conversion; (P2) conversion of biogas into methanol via reforming; and (P3) catalytic methanation. Evaluation of the technical feasibility and comparison of the pathways was done using modelling in Aspen Plus®. Catalytic methanation (P3) required the largest alkaline electrolyser. P2 (methanol via reforming) had the smallest, as hydrogen is partly supplied by reforming, but this pathway also resulted in the highest plant complexity due to the added reformer. System efficiencies (LHV basis) for P1 and P2 were low (24.0% and 24.5%, respectively), primarily due to high heat duties from recycling streams. This could be further improved using heat integration. In contrast, catalytic methanation (P3) achieved a higher efficiency of around 46.1%, which is comparable to literature values. The electric efficiency, assuming perfect heat integration, showed P2 (methanol synthesis via reforming) performing best, reaching 57.0% due to its small electrolyser. P1 (CO2 to methanol) showed the lowest electric efficiency at 37.4%, while P3 (catalytic methanation) achieved a moderate value of 46.7%. The results demonstrate clear trade offs between efficiency, electrolyser size, and process complexity. Furthermore, the pathway selection depends on economic considerations and the desired application of the renewable fuel.

Popular Abstract

This thesis assesses the use of Power to X (P2X) technologies for biogas conversion into renewable fuels.
Our planet faces an urgent challenge: rapidly rising greenhouse gas emissions. To combat this, innovative technologies have to be developed. One such technology is Power to X (P2X), which transforms renewable energy into renewable fuels. This research explores how P2X can utilize biogas – a renewable gas produced from organic waste such as waste from salmon fisheries – to produce renewable methanol or methane.
Three pathways for integrating P2X into biogas plants were investigated: Pathway 1 (P1): Methanol synthesis from CO2: In this pathway carbon dioxide from the biogas is directly converted into methanol. Pathway 2 (P2): Methanol synthesis via Reforming: In this pathway carbon dioxide and methane from the biogas are converted into methanol through a process called reforming. Pathway 3 (P3): Methane synthesis from CO2: In this pathway the carbon dioxide from the biogas is converted into methane. Aspen Plus® was used to assess the technical feasibility and performance of the three pathways. The modelling revealed differences between the pathways: Pathway 3 (Methane synthesis from CO2) demanded the largest alkaline electrolyser, which is needed for generating hydrogen from water using electricity. Pathway 2 (methanol via reforming) required the smallest electrolyser because the reforming process itself contributes to hydrogen production. However, Pathway 2 also introduced the highest plant complexity due to the additional reforming plant. Both Pathway 1 and Pathway 2 demonstrated relatively low system efficiencies of 24.0% and 24.5%, respectively. The primary reason for this was the amount of heat required for recycling unreacted gases within the system. In contrast, Pathway 3 (Methane synthesis from CO2) exhibited a more favourable efficiency due to a low heat demand.
The research demonstrates the potential of combining Power to X technologies with existing biogas plants. By utilizing waste from industries like salmon fisheries and converting it into valuable products such as methanol or methane, greenhouse gas emissions can be significantly reduced. While further research is needed, particularly in optimizing heat management and distribution within the system to increase efficiency, the findings offer valuable insights into designing and integrating P2X with biogas facilities.

• author: Höss, Christian
• supervisor: Fatehi Hesameddin; Shi You; Nicolas Jean Bernard Campion
• organization: Department of Energy Sciences
• course: MVKM05 20251
• year: 2025
• type: H2 - Master's Degree (Two Years)
• subject: Technology and Engineering
• keywords: Power to X, Alkaline electrolysis, Renewable methane, Renewable methanol, Biogas upgrading, Steam methane reforming, Aspen Plus
• report number: ISRN LUTMDN/TMPH-25/5629-SE
• ISSN: 0282-1990
• language: English
• id: 9193674
• date added to LUP: 2025-06-09 10:09:51
• date last changed: 2025-06-09 10:09:51