Bio-SNG (gasification)

Besides the production of bio-SNG from biogas, which was discussed earlier, bio-SNG can be produced by a gasification process, which aims at producing a large amount of methane. This technology is able to use a broad range of biomass feedstocks, in contrast to digestion for the production of biogas. Since SNG is gaseous at ambient conditions, it has to be compressed (CNG) or liquefied (LNG) in order to use it as an automotive fuel. In both cases, larger storage and fuel tanks are needed, because of the lower volumetric energy content of the fuel. The octane number is very high, but the cetane number is very low, which means that SNG has to be used in spark ignition engines, which have to be adapted for use of SNG.

Since for the production of SNG a low-temperature gasification process can be used, the earlier mentioned technological barriers for gasification processes for production of Fischer-Tropsch liquids, biomethanol, bio-DME or biohydrogen, are non-existent or easier to overcome. However, in this case the gas cleaning, especially tar removal, and catalyst development are the most important technological issues. Many solutions for the tar problem have been proposed in the past, but only two of them, tar scrubbing and tar cracking seem viable, but they need further improvement. Another technology to produce SNG is supercritical gasification of biomass, which is currently available on lab scale. In this highly efficient process, the oxygen in water is transferred to the biomass, which disintegrates forming a mixture of carbon dioxide, carbon monoxide and methane (SNG). Molecular hydrogen is produced from the hydrogen atoms present in the water and the biomass. This process is expected to be especially suitable for wet (polluted) biomass.