More and more effort is being put into the utilization of organic waste streams in anaerobic digesters, producing useful products such as fertilizers and biogas. DMT has been developing biogas treatment plants for over 25 years, closely following market developments. It is becoming increasingly attractive to upgrade biogas to natural gas quality and inject it into the natural gas grid or use it as transport fuel. In this way, biomethane can be utilized with the highest energy efficiency.
There are several biogas upgrading technologies, ranging from the most commonly used water scrubbing to highly sophisticated cryogenic techniques. Each process has its advantages and disadvantages, depending on the biogas origin, composition and plant location. However, with the latest developments in membrane separation, DMT has developed the Carborex® MS system. This system is based on an ingenious, multi-stage, highly selective membrane system and offers the best economics for almost all situations, especially for plants up to 800 Nm3/h. Besides the economics, it offers several unique technical advantages.
The DMT Carborex® MS is a compact modular unit built into containers. The biogas upgrading is performed with highly selective gas membranes. The upgraded gas has a methane concentration of 97-99% CH4 which greatly reduces the propane consumption and related costs. The bio-methane can be injected into the local gas grid, or further compressed to 220 bar and used as vehicle fuel. This system has the highest energy recovery available (>98%) with only 0.18-0.22 kWh/Nm3 energy consumption and2 is recovered as >99.5% pure. It is the only upgrading technology that also removes significant amounts of oxygen (up to 70%).
In this article the theoretical background of membrane systems is explained along with operation data of the Carborex® MS plant at Poundbury (largest commercial plant in the UK).