Your choices so far:
1 Process heat (150 - 1000 °C); 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 |
| Biomass (solid) | Electricity | Process cooling (< 0 °C) |
| Geothermal | 2 Fuel: Gaseous | Process heat/steam (50 - 150 °C) |
| Sunshine | Fuel: Liquid | 1 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) |
To obtain the highest efficiency in the full chain from energy source to useful energy with the end user, the number of intermediate steps and conversions should be kept as low as possible.
Direct fuel firing is one of the shortest possible process chains and should be used if at all possible.
Gaseous fuels can be produced from biomass in two ways, by the biochemical process known as anaerobic digestion or by the thermochemical process known as gasification.
In both cases, the aim of the process is to change the state of the solid (in case of digestion is the solid often found in a water suspension) biomass into a gas while at the same time retaining as much as possible of the solar energy originally bound in solid biomass by the photosynthesis.
- The biochemical process makes use of bacteria and fungi first to split up the original carbohydrates, fats and proteins in the organic material by a number of steps releasing carbon dioxide and finally to form methane. Methane gas is the prime energy-carrying component in the biogas formed and typically amounts to some 50-70% by volume of the dry gas.
- Using the thermochemical route, the primary components in solid biomass, cellulose, hemicellulose, lignin, fats and proteins, are broken into smaller molecules by the use of heat. The heat is supplied by combusting part of the fuel and to run, the process requires temperatures in the range 700 – 1000 °C. The prime energy-carrying gas components in gasifier gas (or product gas) are carbon monoxide, hydrogen and methane, typically for air-blown gasifiers containing 10-15% carbon monoxide and similar amounts of hydrogen, methane about 5% on a dry gas basis.
Depending on availability, contracting biogas of sng-quality (substitute natural gas) from the gas grid is the easiest thing in the world.
Unlike biogas, gasifier gas is not commercially available but will have to be produced locally. This will add expense and complexity to the process and will be viable only in few situations.