Biomass can be converted into a gas very similar to natural gas. This gas is called SNG or Substitute Natural Gas (bioSNG). It can be used as natural gas in any of its applications such as the production of power, heat and syngas, for example chemicals. Furthermore, SNG from lignocellulosic biomass can also be used as advanced biofuel. The availability of an existing natural gas infrastructure in countries like The Netherlands and the variety of potential applications are attractive arguments for the production of BioSNG.

The production of SNG from biomass starts with thermal gasification at temperatures of at least 800°C, where the biomass is converted into a combustible gas. Subsequent gas cleaning and upgrading results in two separate products, methane (CH4) and carbon dioxide (CO2). The methane is upgraded to the specification of the natural gas grid. The pure CO2 by-product can be wasted, but can also be sequestered in, e. g., underground geological formations to turn the whole biomass value chain into a net CO2-extraction process beyond CO2- neutral. The general process from biomass to SNG is shown in Fig. 21.4.

At the moment, there is no commercial plant producing bioSNG. Developments, however, have been started at the Paul Scherrer Institute (PSI) in Switzerland and the Energy Research Centre of The Netherlands (ECN) in The Netherlands, both have recognised that the gasifier’s choice is crucial for the overall efficiency of the process (Meijden et al., 2009; Rauch, 2009). Both have chosen the concept of indirect gasification to obtain an essentially N2-free gas with relatively high methane content. Additionally, indirect gasifiers do not need pure oxygen and therefore can do without an expensive and energy-consuming air separation unit. There are also some important differences which are summarised in Table 21.1. Included in the table is the process applied by DakotaGas in the US to produce SNG from lignite, in operation since 1984 (Stern, 2006).

As with almost all bioenergy processes, costs are mainly determined by the biomass costs, in particular at larger scales (Zwart et al., 2009a, 2009b; Zwart et al., 2006b). Therefore, SNG production costs are calculated for biomass prices of 0 and 2 €/GJth (e. g. locally available biomass) as well as of 4 and 6 €/GJth (e. g. biomass delivered at the gate of larger power plants). In Fig. 21.5, also reference is made to typical (commodity) prices for natural gas (grid as well as compressed), biogas, and biodiesel (the reference for the current European transportation fuel market), as valid on the Dutch market in 2007. With the natural gas commodity price as reference, it can be calculated that at sufficiently large scale, the cost of avoided CO2-emission can be below 60 €/ton CO2, even at a reasonable biomass price of 4 €/GJ.