Your choices so far:
1 Biomass (digestible sludge); 2 Comfortable indoor climate
| What is your resource? | What do you want to deliver? | What is the service the customer wants? |
| 1 Biomass (digestible sludge) | District cooling | 2 Comfortable indoor climate |
| Biomass (fermentable sludge) | District heating | Electricity |
| Biomass (solid) | Electricity | Process cooling (< 0 °C) |
| Geothermal | 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) |
A common situation in agricultural areas is that the individual farm has access to digestible biomass and then the option to use this resource for individual house heating and maybe also for electricity production is an obvious one. Depending on the size of the farm, the total resource and the actual production at the farm, the heat may also be used for drying of cereals or hay, for pasteurization of milk or for any other purposes.
In case heat production is the main aim of the biogas digester, then it must be remembered that the raw biogas is a low-grade fuel with variable properties.
The cheapest way to make use of the raw biogas for heat production, and especially so if the temperatures desired are in the range 60 °C (tap water production and comfort heat) and up to 150 °C (hygienization, pasteurization and alike) is to use the raw biogas to replace fossil fuel firing directly in the steam boiler.
It must then be remembered, though, that burners for raw biogas are not (yet) readily available on the open market. However, any of the major burner manufacturers would be able to design and supply such a burner.
Independent of burner design, there will also be a need for a pilot burner, fired either with LPG, fossil gas or oil for security reasons. Hence, the use of biogas will not make the farm completely independent of fossil fuel.
Since the raw biogas contains hydrogen chloride, this will also be present in the boiler gas atmosphere. There will also be other compounds in the furnace atmosphere, the presence of which are directly connected to the biogas composition. This will call for attention with respect to any corrosion problems in the boiler heat transfer sections.
The steam supply and utilisation system will be completely un-affected by a change of fuel in the boiler.
For large-scale consumers, biogas of sng-quality is available from the gas grid.