Upgrading Biogas to Bio-methane Using Absorption

Background and Motivation

Biogas has been traditionally used for generating heat and electricity, and its popularity in Germany has been increasing over the last several years as indicated by the growing number of biogas plants. If biogas is purified such that the methane concentration is above 98 %, biomethane (pipeline quality natural gas) is obtained. The first biomethane plant in Germany was setup in the year 2006. Since then, the number of biomethane plants and consequently the quantity of biomethane produced has been rapidly increasing. It is expected that biomethane will meet around 2 % of the total primary energy requirement in Germany for the year 2020, which is a 100-fold increase from the year 2010. Biomethane shall support Germany in undergoing the challenging energy transition (sustainable energy production through renewable resources).

The absorption process performs the task of removing CO2 and/or H2S from natural gas, syngas and flue gas well, and the process can be used for biogas, too. However, not all solvents from those units are suitable for biogas treatment because of differences in gas composition and conditions under which these gases are available. The major factors influencing the design of the absorption process are availability at atmospheric pressure, presence of oxygen, low ratio of H2S to CO2 and less total H2S content.

Project objectives

• Classify absorption solvents based upon their capability to absorb CO2 or CO2 and H2S at atmospheric pressure, their stability in the presence of oxygen, and the recommended operating temperature and pressure in the absorber and desorber
• Compile data from literature and through experiments on the thermodynamic and transport properties of selected solvents
• Simulate and compare the performance of absorption solvents in the absorption process
• Conduct experiments with absorption solvent in the absorption test-rig to validate the simulation results and optimize the Liquid/Gas Ratio
• Incorporate hazards and calculate risks that may originate from a biomethane plant

Doctoral Candidate: Dipl.-Ing. Onkar Dixit
First (Main-) Supervisor: Prof. Dr.-Ing. Norbert Mollekopf
Second Supervisor: Prof. Möst