TOKYO GAS TOP > Corporate Information > Approach/Activity > Technical development > Low-carbon society > Biogas Upgrading System

Biogas Upgrading System

By recovering methane contained in biogas at a high degree of concentration, and upgrading it to the quality of city gas, it becomes possible to expand the fields that can efficiently utilize biogas. Although there are a variety of upgrading methods, the bulk of the upgrading equipment that has been commercialized has only been introduced at large-scale plants. Tokyo Gas is focusing on the membrane separation method and pushing ahead with the development of systems that can also be introduced at small and medium-scale biogas generating plants.
 

Purpose


The biogas generated from biological conversion of biomass is approximately 60% methane and 40% CO2, and contains additional trace impurities. Generally, applications of using biogas have special species. However, the problem is that only a limited number of such applications types are available. In addition, the cost of application comparatively expensive. Accordingly, by introducing a biogas upgrading system which separates the CO2 from biogas, it becomes possible to obtain a calorific value for biogas that is on par with city gas. This in turn enables the utilization of city gas applications, raising expectations of expanding usage of renewable energy. 
 
Method to effectively use biogas
(example: sewage treatment plant) 

Method to effectively use biogas

 

Development of biogas upgrading system with membrane separation method


Methane and CO2 have different degrees of permeability through a membrane. CO2 is more permeable, which means the off gas (permeated gas) will be CO2-rich while the upgrading gas (non-permeated gas) will be methane-rich.

 
Biogas separation via membrane separation method

Biogas separation via membrane separation method


In addition to methane and CO2, biogas contains impurities such as hydrogen sulfide, siloxane and water. These impurities are removed via the pre-treatment filter, and the concentrated gas is then supplied to the membrane. A primary and secondary membrane are arranged in a serial, it becomes possible to increase the methane concentration to 98% in the upgrading gas. In addition, by recycling the off gas from the secondary membrane, the methane recovery rate (the rate of methane contained in the biogas which is recovered as upgrading gas) is increased to over 90%.


 
Biogas upgrading system flow diagram
Biogas upgrading system flow diagram


 

Perspective


Since 2013, Tokyo Gas and Yokohama City have been conducting joint research into “upgrading sewage sludge digestion gas via the membrane separation method”. This research involves subjecting the digestion gas (biogas produced by fermenting sewage sludge through biological conversion) generated from the North Yokohama Sludge Recycling Center to refinement testing with the membrane separation method and finding ways of effectively utilizing it.
We intend to continue leveraging this expertise to research and develop practical applications, enabling the use of upgrading gas as an alternative fuel to city gas in various applications.
 
Biogas upgrading test at the North Yokohama Sewerage Center
Biogas upgrading test at the North Yokohama Sewerage Center
 
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