Your choices:
1 Biomass (digestible sludge); 2 Process heat; 3 Fuel: gaseous
| What is your resource? | What do you want to deliver? | What is the service the customer wants? |
| 1 Biomass (digestible sludge) | District cooling | Comfortable indoor climate |
| Biomass (fermentable sludge) | District heating | Electricity |
| Biomass (solid) | Electricity | Process cooling (< 0 °C) |
| Geothermal | 3 Fuel: Gaseous | 2 Process heat/steam (50 - 150 °C) |
| Sunshine | Fuel: Liquid | 2 Process heat (150 - 1000 °C) |
| Water | Fuel: Solid | 2 Process heat (> 1000 °C) |
| Wind | Local cooling (ind. house) | Transport |
| Residual oils/fats etc | Local heating (ind. house) |
In case the main idea with the biogas production is to supply process heat and the energy carrier is selected to be a gaseous fuel, there are two major alternatives:
- In case the industrial site is close to the biogas production site, and the use of raw biogas will not have any adverse effects on the product quality, the raw biogas may be piped to the site and used directly.
- The second option is that the gas is upgraded at the production site, including doping it with a bit of heavier hydrocarbons so as to be accepted as a substitute gas from the operator of the fossil gas pipeline network. The gas can then be injected into the fossil gas pipeline grid and can be contractually extracted at any point in the grid. In this case, the process industry will operate on a gas with exactly the same quality as the normal fossil gas – but may contractually operate on biogas. In this case, the gas actually fired in the furnace will only be in contractual balance with the gas fed to the grid – in will not physically be the same gas. Hence, any variations in gas flow or -quality will be evened out over the contractual periods and the industrial process will not be affected at all.
Problems associated with the use of raw biogas for process heating are not so much the temperatures attainable but the combustion properties of the gas and its content of contaminants:
- Using the raw biogas in a process flame furnace will first call for a burner designed for the gas. Such burners are not (yet) readily available on the open market, but any of the major burner manufacturers would be able to design and supply such a burner.
- During start-up, while the furnace is still cold, there will be a need for a pilot burner, fired either with LPG, fossil gas or oil for security reasons.
- Since the raw biogas contains hydrogen chloride, this will also be present in the furnace gas atmosphere. Depending on the product, this may have an adverse effect on the product quality. There will also be other compounds in the furnace atmosphere, the presence of which are directly connected to the biogas composition.
With the second option – gas upgrading and injection to the fossil gas pipeline system – there will also be the extra possibility to sell any surplus gas for transport purposes.