Your choices so far:
1 Biomass (solid); 2 Fuel: gaseous
| What is your resource? | What do you want to deliver? | What is the service the customer wants? |
| Biomass (digestible sludge) | District cooling | Comfortable indoor climate |
| Biomass (fermentable sludge) | District heating | Electricity |
| 1 Biomass (solid) | Electricity | Process cooling (< 0 °C) |
| Geothermal | 2 Fuel: Gaseous | Process heat/steam (50 - 150 °C) |
| Sunshine | Fuel: Liquid | Process heat (150 - 1000 °C) |
| Water | Fuel: Solid | Process heat (> 1000 °C) |
| Wind | Local cooling (ind. house) | Transport |
| Residual oils/fats etc | Local heating (ind. house) |
Gaseous fuels can be of many different qualities ranging from very low heating value, dilute, gases and all the way up to purified and clean methane. Fossil gas ("natural gas") is composed mainly from methane with a bit (some 5%) of heavier hydrocarbons mixed into it.
Renewable gaseous fuels can be produced mainly in two ways; either it can be produced by anaerobic digestion of a wet, organic, raw material or it can be produced via a thermal gasification of solid biomass.
Thermal gasification is a special case of thermochemical conversion making use of elevated temperature, and in some cases elevated pressure, to convert the solid material into a new state. For most processes, the heat needed to arrive at the process temperature is generated through a partial combustion of the feedstock. Depending on the actual temperature and on the process layout, more specifically: the heat recovery system, this partial oxidation will introduce energy losses from the feedstock to the product. Also, the temperature of the product fuel will be that of the process. Unless this sensible heat is recovered and used in the process it will represent another loss.
Thermochemical processes include low-temperature pyrolysis, high-temperature pyrolysis, thermal liquefaction and thermal gasification. Thermal liquefaction is generally not considered a favourable route since the oil produced tends to have inferior quality. Thermal gasification is one of the most complicated conversion processes but it is also one of those that open up the most possibilities for subsequent processing.
Gasifier gas ("product gas" or "gasifier gas", in special cases "syngas", not to be mistaken for biogas) quality can be set within wide limits, from the simplest gasifiers that produce wet, nitrogen- and tar laden gas mainly suitable for direct combustion to highly advanced gasification processes producing synthesis gas well aimed for subsequent chemical upgrading to a number of products. To improve the fuel flexibility in an energy plant a simple gasifier directly connected to a gas-fired steam boiler may be sufficient while a synthesis-gas quality process connected to a Fischer-Tropsch reactor may be the basis in – for example – a bio-DME production plant. The final product needs not be limited to fuel but this process concept can be the heart of a so-called bio refinery with almost any number and variety of products.
If connected to a combined-cycle power production process the total efficiency as calculated from latent energy in the biomass feed to electricity delivered to the grid may be improved. To be viable, this application will require a large-scale CHP plant.