Production of Bio-Methane from Woody Biomass using the MILENA Gasification Technology

Abstract

Bio-fuels like bio-methane produced from biomass have the potential to become a CO₂-negative fuel, because part of the carbon from biomass is transformed into CO₂ during the production process. If this pure CO₂ stream is sequestrated, these fuels become truly CO₂ negative. This could be an attractive option for even reducing the level of greenhouse gases in the atmosphere. Several bio-methane demonstration projects are underway based on thermal gasification of woody biomass. Most of the projects are planning to produce bio-methane for transportation purposes. The most visible demonstration project at the moment is the 20 MW GoBiGas project in Gothenburg (Sweden) by Göteborg Energi. ECN (Energy research Centre of the Netherlands) has been working in the development of an alternative gasification process called MILENA that is optimized for the production of bio-methane. The aim is to increase the overall efficiency of the production process. An overall efficiency of 70% from wood to bio-methane is expected. ECN produced the first bio-methane in 2006 using a conventional fluidized bed gasifier. The lab-scale MILENA gasifier was built in 2004. The installation is capable of producing approximately 8 m_n³/h methane-rich medium-calorific gas with high efficiency. The lab-scale gasifier is coupled to a lab-scale gas cleaning installation, named OLGA and a methanation unit. Since then, extensive lab-scale tests were done with different methanation catalysts and different process configurations. The results of these tests were positive and convinced the project partners of the technical feasibility. In the last few years a lot of work has been carried out to prepare a bioSNG demonstration plant in the Netherlands. A consortium with a number of partners (Gasunie, Dahlman) was formed to determine the feasibility of such a plant. On top of this, several subsidy applications were made to make the demonstration economically feasible. At the moment several options for the realization of the demonstration plant are under consideration. It is expected that the final investment decision will be taken in 2016. The size of the demonstration plant will likely be approx. 0.003 bcm of natural gas per year. The produced bio-methane will be injected in the gas grid. The scale foreseen for a commercial single-train bio-methane production facility is between  0.03 and 0.3 bcm/year. In this paper, some results from the 500-hour bio-SNG test performed at ECN are presented and an overview of the activities toward the demo plant producing bio-methane will be given.