BioSNG

Natural Gas is available from various undergroud sources. The gas was produced ages ago and mainly consists of methane (CH₄). Natural gas nowadays corresponds to roughly 25% of the world’s primary energy consumption, and its share is still rising. The popularity can be attributed to its clean combustion, the high conversion efficiency, and the ease of distribution.

During the 70-ties, high natural gas prices and oil crises initiated the development of processes that could produce an “artificial” natural gas from coal. The gas was called Substitute Natural Gas (SNG), sometimes also called Synthetic Natural Gas or Green Gas. It has led to several plans to realize large-scale plants in the US, where coal is relatively abundantly available. One plant actually has been constructed in North-Dakota and still produces approx. 100 PJ of CoalSNG annually. Nowadays, several coal-to-SNG plants are constructed in Asia, mainly China.

SNG produced from biomass (BioSNG) has the additional feature that it basically is CO₂-neutral. The existing natural gas infrastructure offers an excellent stepping stone for implementation of BioSNG (see more benefits). ECN started R&D activities on BioSNG production around the year 2000. The general process is shown in the scheme below. The last step of gas upgrading involves the removal of water and CO₂ to meet the natural gas specifications. It also might include compression.

The R&D at ECN on biomass-to-SNG (BioSNG) concepts is based on the choice to maximally take advantage of existing technology for the production of CoalSNG. This means that ECN-developments focus at upstream technologies, where the differences between biomass and coal have the largest impact on the technology. This strategy means that the ECN R&D is focused on biomass gasification and gas cleaning (see developments). Important criteria for technology choices are formed by efficiency and ability to scale up. Efficiency is an important criterion, because overall biomass-to-SNG production costs are dominated by feedstock costs. Biomass-to-SNG efficiencies of 70-75% are envisaged. Easy scale-up should enable taking maximum advantage of economy-of-scale effects. It is envisaged that SNG will be produced preferably in large-scale installations. If situated at coastal locations, biomass import is possible. But also the concept of producing BioSNG overseas with subsequent transport of BioSNG through pipelines or as LNG is considered.

The current status of the development of BioSNG technologies at ECN is that a lab-scale system from biomass to raw SNG is available consisting of a 5 kg/h MILENA indirect gasifier, OLGA tar removal, various dry cleaning reactors for the removal of other contaminants such as sulphur and chlorine, catalytic conversion of olefins, and catalytic methanation reactors. This lab-scale test facility is used to support the selection of conditions and materials. Furthermore, a 160 kg/h MILENA gasifier has been realized in May 2008. It is connected to gas cooler and OLGA tar removal. Since 2009, ECN cooperates with a large waste and energy company nearby that has the intention to operate and own several large-scale bioSNG plants. The first step will be a 10MW demo. This Milena and OLGA based plant will be realized in phases with increasing complexity starting from boiler application (2013) to the final goal of SNG production.

Image of the process
To make Green Gas out of biomass the process consists of a few different steps starting with MILENA gasification and OLGA tar removal. This process is visualised in a short movie.