Production of Synthetic Natural Gas (BioSNG)

Introduction

The production of synthetic natural gas (SNG) from woody and herbaceous biomasses is one interesting option within the numerous options of second generation biofuels for the transportation sector. The advantage of SNG compared to hydrogen is the already existing infrastructure such as pipelines and compressed natural gas (CNG) cars. Compared to BtL fuels, the advantage of SNG is the simplicity of the fuel production process, i.e. fuel synthesis and fuel upgrading. Till now, the major disadvantage of SNG is the uncertainty about the development of CNG cars, i.e. the marked share.

This work is done in cooperation with the scientific partner Paul Scherrer Institute from Switherland, and with the industrial partners Repotec and CTU. The work is funded from the EC-project BioSNG and from national funds from Switzerland and Austria.

The first proof of concept was already done in 2003. Here a slip stream of product gas from the biomass CHP Güssing was taken before the gas engine and converted over the methanation reactor to CH4. As these test were very succesful, a Container based System for Methanation (COSYMA) was builded and used at the biomass CHP Güssing for experiments. Here the additional gas cleaning and the methanation istself were investigated.

Experimental results of COSYMA

The COSYMA has a size of 10kW and is designed to operate from atmospheric level up to 10 bars at temperatures up to 500°C. Here different parameters of the methanation itself and also different gas cleaning devices were tested. After succesful parameter varation a long term test over 1000 hours was done succesfully in 2007. Based on these results the design of the demonstration plant is going on.

Demonstration of the BioSNG concept

To demonstrate the production of BioSNG from wood chips a slip stream plant in the size of 1MW SNG production (=100Nm³/h of SNG) is at the moment under construction. Here the gas is also taken before the gas engine from the biomass CHP, then sulphur and halogens are removed and the gas is then converted to raw SNG. After removal of CO2 and H2 from the raw SNG it can be used in a fuel station for natural gas. As in Güssing there is no natural gas grid, the demonstration plant is constructed in a way, that it can be easily transported also to other locations, where then the feeding in of the BioSNG into the natural gas grid can be demonstrated.

Conclusion and Outlook

The Container based System for Methanation (COSYMA) is a valuable tool for field experiments with producer gas derived from an industrial biomass gasifier. Due to the flexibility of the setup design specifications for the scale up can be generated. Furthermore, the expected chemical efficiency of an industrial size link-up of a gasifier with the methanation can already be predicted.
For the experiments, a CO conversion of > 98% and a conversion of aromatic hydrocarbons of 99% were calculated from the measured data. Assuming a cold gas efficiency of 70 % for the gasifier, the chemical efficiency for the overall process “wood to SNG” is expected to be around 60 %. There is further potential in the optimization of the interaction of gasifier and methanation, as the gasifier right now is optimized to feed the gas engine.