Biogas Upgrading to green gas or vehicle fuel
With a Carborex®MS your biogas will be upgraded to pure methane. The biomethane can be supplied to the national gas grid, or be compressed to Natural Gas to be used as vehicle fuel. DMT’s Carborex®MS in Poundbury, UK, was the first commercial biogas upgrading system in the UK, and the first in Europe in 2012. DMT is now the largest producer of biogas upgrading facilities in the world with membrane technology. In 2016 we have installed our biggest plant in the USA.
This is a great contribution to the creation of circular economies and energy independence. Out of waste streams, clean gas can be provided to houses as well as fuel for transport and mobility. Biomethane is fossil-free and considered the energy of the future.
Carborex®MS – Biogas Upgrading
The repurpose of organic waste plays a key part in the effort to diminish our dependence on fossil fuels and to solve a growing environmental problem. With our challenge to create a clear and prosperous future, DMT Clear Gas Solutions has proven its expertise in biogas upgrading and compressing or liquefying biomethane.
Producing natural gas in a sustainable way can be done by upgrading biogas. Biogas is a gas produced by the fermentation of biological waste products. The two main components of this resulting gas are methane (CH4) and carbon dioxide (CO2). Upgrading means that the methane is separated from the carbon dioxide, resulting in a very pure methane gas flow. Unlike biodiesel and bioethanol, this biomethane has better properties than its fossil counterpart natural gas.
The biogas upgrading process can be performed with the Carborex®MS, which separates methane from carbon dioxide by using innovative membrane technology. This process has the advantages of being a dry process (no chemicals involved), having low energy consumption and it is easy to operate. The whole system is built on a skid or in a container, which results in a small footprint and an easily transportable system. The Carborex®MS is, therefore, a cleantech solution with low operational costs (OPEX).
The membranes inside the Carborex®MS are built up of hundreds of hollow fibres, which look like spaghetti. The hollow fibres are non-porous and made of polymers. The separation of methane and carbon dioxide occurs because of the difference in diffusivity rates of the two. The molecular structure of carbon dioxide allows this molecule to pass through the polymer material faster than molecules of methane. Biogas enters the membrane inside the hollow fibres. The separation results in a carbon dioxide rich stream at the permeate side of the membrane and a methane-rich stream at the retentate side of the membrane.
Pre-Treatment and Compression
As mentioned before, biogas consists mainly of methane and carbon dioxide. However, there are still some other components that must be removed before entering the membranes. In many cases, biogas contains H2S, mercaptans and terpenes, which all must be removed. The gas also contains water, which, preferably, is removed before entering the membranes. As a solution, the Carborex MS contains a pre-treatment section where these components are removed. The next step to pure biomethane is to compress the gas by up to 16 bar by a compressor. The pressure optimizes the separation of methane and carbon dioxide by increasing the permeability of the membrane.
Multistage vs. Single Stage
One membrane contains hundreds of hollow fibers, the Carborex®MS contains many membranes. Depending on the inlet flow, the amount of membranes inside the Carborex®MS can vary. Even though a membrane separates carbon dioxide from methane, the selectivity of one membrane is not 100%. This means that at the end of one membrane, the methane flow still contains a notable amount of carbon dioxide. Another set of membranes are placed after the first set of membranes to achieve high purity at the end of the process. We call one set of membranes a stage. The multi-stage process can achieve methane concentrations of greater than 98%. On the permeate side of the membrane, thanks to intelligent recycle loops, the methane concentration in the carbon dioxide stream can be reduced to less than 0.5%.
The Carborex®MS is a modular, easily transportable system with a small footprint. The whole system is started up with one simple touch of the start button. The system is robust, stable and requires very little maintenance. Because it is a dry process, no after-treatment of waste streams is required.
The upgraded biomethane from the Carborex®MS can be used for several purposes. Since biomethane is a replacement for natural gas, it can be injected into the natural gas grid. If no gas grid is available, the gas can be used as transportation fuel. In this case, the gas is compressed to 250 bar as Bio-CNG or liquefied (-324 degrees Fahrenheit) as Bio-LNG.
Liquefied Natural Gas (LNG)
Liquefied Natural Gas, from the liquefaction of high-quality biomethane, is the only biofuel better for the environment than its fossil counterpart. Research shows that Bio-LNG is the most cost-effective fuel available today for reduction of carbon dioxide emissions and, therefore, an ideal investment for reaching climate goals. By combining clean combustion, easy transportation, flexibility and higher security (both in terms of reserve capacity and stability of price), Bio-LNG is gaining worldwide status as the fuel of the future.
Carborex®LNG in Four Steps
Common problems associated with the liquefaction of biogas include the presence of contaminants and the freezing of components such as carbon dioxide and water. After screening established and promising new technologies, DMT has overcome these problems by developing a process comprised of four steps. First, the biogas is pre-treated to remove toxic and harmful contaminants. Pre-treatment also removes water, leaving no water at the end of the process that can be frozen during liquefaction. Second, the biogas is upgraded and polished by membranes in the Carborex®MS to remove carbon dioxide. Finally, the gas is liquefied in a Carborex®LNG and ready to be distributed to fuel stations.
Up to 30 Tons Per Day
While the technology by DMT guarantees a H2O-free, CO2-poor gas stream at high pressure, the liquefaction cycle can harness these same advantages into increasing its own efficiency and eliminating quality related operational risks. The result is a low-cost flexible process, available and scalable up to 30 tons per day which offers a varying degree of integration of the upgrading and liquefaction steps.