Modelling of CO₂ liquefaction process from biogas plant and optimization of CO₂ logistics

Abstract

Biogas generated by anaerobic digestion and landfills is becoming increasingly relevant in the energy industry as a source of renewable energy. Capturing and liquefying CO₂ from biogas may result in negative CO₂ emissions. Depending on how biogas is used, there are various methods for capturing and liquefying CO₂. A biogas plant that uses raw biogas to generate electricity and heat can be upgraded to include CO₂ capture. Liquefaction of CO₂ is an intermediate step in storage or transportation in which CO₂ is recycled and considered a potential resource for a variety of applications.

This thesis investigated the technological and economic feasibility of CO₂ liquefaction from biogas plants through Aspen Plus™ V11 flowsheet simulations. In particular, three different liquefaction processes were designed in accordance with the traditional method of external refrigeration using ammonia. These processes have the capacity to liquefy from 4380 to 43800 tonnes of CO₂ gas per year. A preliminary investment costs is given to production plants, which are derived from the models that have been developed in this work.

According to the results of the simulation models, it is difficult to achieve the properties of CO₂ in liquid solution (> 99.7% CO₂) using a simplified liquefaction system. The total capital investment cost and operating costs for liquefaction plant is different between cases with two capacity. It is possible to consider the models that were developed in this study to be preliminary work for the detailed engineering that is required before the production of bio-CO₂ liquid on an industrial scale may be realized.