When the gas obtained is burned in the biogas plant, electricity and heat are generated. The energy efficiency, depending on the power generation technology used, is up to 43%. Thanks to the increasing use of combined heat and power (CHP) systems, such as CHP units the possibility of using biogas thermally has also developed significantly and is technologically very efficient. Extensive use of the two energetic products of electricity and heat is one of the decisive factors for the business success of a biogas plant. This fact is not always easy, especially when planning the use of heat.
To give you some inspiration, I have put together a list of the usage ideas I know.
List of usage concepts for heat from biogas plants
1. Use of heat from biogas plants for greenhouses
The combination of the two is quite common Biogas technology with plant cultivation (eg vegetables) in greenhouses. The heat generated can be introduced into the greenhouse and helps, especially in winter, to maintain a desired temperature and to use the otherwise wasted heat. Individual temperature control is of course possible.
2. Heat to produce Luxury products
For example, a plant operator in Affinghausen, Lower Saxony, has implemented a business idea in which the heat produced is used on site to operate a modern shrimp breeding facility. The “Affinghauser Meeresfarm” for high-quality shrimp will offer the first fine bites in spring. A similar creative idea can certainly also be realized elsewhere. Such pioneering projects naturally require courage and passion in addition to special expertise in another area, but they are definitely a lot of fun.
3. Use of heat for agriculture
In addition to heating the vehicle fleet hall, which is usually regarded as a less favorable alternative for heating, many synergies can be generated in an agricultural operation. So it was with the Danish project "Pig City" (link) relied on the combination of pig breeding, tomato cultivation and biogas production.
Heating stables is also a comparatively uncomplicated and sensible way of integrating the precious heat into the production cycle.
4. Process heat for the operation of the biogas plant
The production of biogas is based on the fermentation work of many microorganisms that require a certain ambient temperature for their metabolism. Depending on the operating temperature you have chosen as the system operator (usually around 40-45 ° C, but research projects also experiment with 70 ° C), more or less heat is required. Being able to determine the fermenter temperature yourself without having to buy external heat can make the biogas plant more profitable and environmentally friendly.
5. Biogas plant provides heating and room heat
The direct use as heating is the most obvious Form of heat use. Especially in winter, private households or public buildings can benefit greatly from this heat source and step in as a complete buyer. For biogas plants in the vicinity of settlements, a school building, hospital, swimming pool or sauna can be supplied inexpensively and environmentally friendly with heat using a local heating network. For systems that are very decentralized or for which not enough heat consumers can be found, investing in a district heating network can be considered in order to increase the heat distribution area.
6. Cooling by heat pumps
With the help of chillers, the existing heat can even be used to reduce the temperature at a specific location and to provide cooling. Production processes that rely on low temperatures (supermarkets, warehouses) can benefit from the heat conversion. The special thing is that this type of use is also interesting in summer and can be used for air conditioning in buildings!
7. Biogas plants supply process heat for drying processes
Drying is necessary in agriculture (grain drying) or many other industries. This process can be realized or supported by the evaporation of water with the help of high room temperatures. This also gives rise to the possibility of combining two forms of bioenergy. For the pellet production, the raw wood (or sawdust) must first be dried in order to achieve the lowest possible water content and thus higher calorific value. The heat from the biogas plant can be used for this.
8. Generation of pressure with the help of heat
An idea that came to me recently would also be to use thermal energy to press the pellets. The hot gas can be used directly to build up a high pressure or indirectly by generating water vapor. In this case, the biogas plant could supply the process heat for a hammer or screw press.
9. Warmth for washing
Washing processes require certain chemicals and a certain water temperature. The heat generated by biogas combustion can be used for various industries for the water temperature during washing.
10. Heat delivery for paper and pulp production
There are nowhere near as many paper production plants as there are biogas plants, but the combination of both technologies or processes promises a particularly large number of synergies. Both an energetic and a material exchange can take place.
11. Feeding into heat storage and heating networks
In the event of a strongly fluctuating heat requirement at one location, the heat produced can also be fed into a heat store in order to be called up at peak loads. This would enable heat to be used with a time delay.
12. Use of heat for electricity conversion
Theoretically, the residual heat can also be used to heat water again, to drive a turbine with the steam obtained and thus to generate electricity in another circuit. If there is no other possibility of use, this type of subsequent electricity generation is certainly a possibility of using the waste heat in a subsequent electricity generation cycle. How high the efficiency is, especially for small systems, has to be calculated on a case-by-case basis.
For very high pressures and temperatures, such as those used in heavy industry, the heat generated during biogas combustion is of course not sufficient. For use in smaller companies or in light industry, however, there may be very good uses. The question of business efficiency for the heat consumer also depends on the respective heat price (i.e. ultimately the heating oil and natural gas). As an operator of a biogas plant for heat use receives further funding under the EEG (currently 3 cents / kWh), it is definitely worthwhile to find an acceptance partner.
Developments on the biomethane market (biogas feed) will also make it easier to find heat consumers, since heat is no longer used in the immediate vicinity or has to be transported at a loss via district heating networks. Especially in big cities like Berlin Combined heat and power has great potential (link).
If you have other ideas yourself or have even realized them, please write a comment. The further development and success of biogas technology depend, in my opinion, on good heat utilization concepts in the medium term.