Cogeneration of heat and power

The cogeneration of heat and power (CHP) is becoming more and more popular on industrial as well as domestic/ commercial scale. There are several reasons for this:

  • The electricity supply deregulation, which resulted in an increase of the electricity cost, especially in the case of commercial consumers.
  • The development of statutory and technical frameworks, allowing feed-in possibility for the surplus electric energy from cogeneration. The relevant legal provisions (Law 3468/06, Law 3851/10 etc.) ensure this possibility, whether power is produced from biomass / biogas or from conventional fuels.
  • The availability of combustible gases (mainly natural gas) in urban and industrial areas at competitive, compared to liquid fuels, prices.
  • Certain electric power and thermal energy consumers have the possibility to produce fuels through chemical and biological processes (thermal cracking, gasification, anaerobic digestion etc.).
  • As result of the above, the development and commercial availability of cogeneration systems, even of low power rating (down to 3 kW).

In the case of the wastewater treatment plants (of biogas production capacity from 2 to 200 m3/h) the Sustainable Engineering Ltd endeavours, the required power by cogeneration units ranges between 5 and 500 kWe which that are covered by the commercially available units.

The structure of the combined wastewater treatment – cogeneration systems allows the maximum exploitation of the thermal energy, with the bioreactor itself being the first consumer of the thermal energy . The relatively high temperatures achievable by using part of the thermal energy of the CHP, make the operation of the bioreactor possible at the mesophilic area, with impressive results in its efficiency and stability.

After this first retrieval of thermal energy, especially during summer, there is still appreciable surplus of thermal energy at medium temperature that can be fed in other uses, either in the main production line of the industry or for building conditioning. In this way, large quantities of conventional fuels (fuel oil, automotive diesel oil, LPG, natural gas etc.) can be saved.

Indicatively, such usages may be:

  • Production of process steam.
  • Thermal energy for other stages of the wastewater treatment.
  • Hygienization of the digestate that will be used as fertilizer.
  • Heating of production areas or other industrial buildings.
  • Drying of the digestate for production of fertilizers in solid form.
  • District heating.

The maximization of benefit is achieved by means of a good management of the various forms of available energy. For this purpose, suitable automation systems are employed, determining the optimum feeding conditions, external parameters and consumption possibilities.