Your choices:
1 Process cooling (< 0 °C); Electricity; 2 Biomass (solid)
| 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 |
| 2 Biomass (solid) | Electricity | 1 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) |
Electricity should never be produced as a stand-alone product (i.e. in condensing power plants) based on fuel firing. In case there is no CHP production plant available and there is no market for the heat produced, the biomass should be used to replace coal in a condensing power station.
Solid biomass is best used in combined heat-and-power processes in which the fuel is first combusted in a steam boiler, the steam runs through a turbine to produce electricity and the turbine outlet is cooled by district heating water so as to produce district heating.
Using this type of system, total efficiencies well above 90% are common, 95% in case the plant has a thermal power about 100 MW or more and even if the fuel has moisture contents exceeding 40% by weight. If the fuel has higher moisture contents, then a flue-gas condenser should be included in the system to further raise the energy transferred to the district heating system.
The energy input with the fuel will then be approximately split to 5-10% losses, 30-38% electricity and the remaining energy as district heating.
If the demand for district heating is low – i.e. during summer – the district heating water can be used to produce district cooling via an absorption heat pump, tri-generation.
The most highly valued product will usually be the electricity. However, the size off the plant should not be chosen to maximise electricity but to fit the market for heat. The total economy for the plant will be strongly depending on the possibilities to sell all the heat produced – or to use all the heat for district cooling production.
Pulverized fuel combustion is commonly used in large-scale coal fired plants and solid biofuel suitable for milling, such as non-durable pellets and briquettes or torrefied material, are well-suited to be used as a complementary fuel in such plants. Easiest, the biomass is milled together with coal and co-fired in pulverized coal power stations.
In many cases this may be the simplest and cheapest method to introduce biofuel into the national electricity system. Experience from several types of plants and installations have for example been reported and documented by the International Energy Agency (IEA), clearly demonstrating the feasibility of this technology.