Biogas an all-rounder

Clever Use of Heat

Biogas can do more than simply produce electricity. When biogas is burned in a CHP plant, heat is always generated as a by-product of electricity production. Technology for recovering and utilising this waste heat enables it to be used economically and efficiently in a variety of ways.

In the Weserbergland region, for example, thanks to biogas, bathers are able to swim outside in warm water even on cold winter days. The heat required for the outdoor pool at the Ith-Sole-Therme thermal baths in Salzhemmendorf is produced by a biogas plant located 1,200 metres away, in the neighbouring village of Lauenstein. The waste heat from two CHP plants is transported to the baths via heating pipes. A cooperative of operators consisting of 13 farmers and 14 private individuals is responsible for biogas production.

Twenty percent lower energy costs

Both sides benefit from this solution: according to the operators, the biogas plant would not have been built had the baths not wanted to purchase the heat. At the same time, the managing director of the Ith-Sole-Therme baths, Stefan Schlichte, was worried about surging energy costs. He has never regretted switching to biogas: it allows him to save around 20 percent in energy costs.

As private baths, the Ith-Sole-Therme receive no public funding. Biogas thus now contributes to keeping entrance prices stable, to the benefit of the many families with children who enjoy using the baths.

The biogas replaces the equivalent of 500,000 litres of fuel oil per year. Electricity generated in the biogas plant is also used by the baths, meaning that their energy supply is 100 percent renewable. The 300,000 people who visit the baths each year can gain information on the supply of energy from biogas in the entrance hall. There, models and a film illustrate how the bathing water is heated with the help of biogas.

Warm plants

The greenhouses of Hortitherm Hinrichsfehn, in the East Frisian town of Wiesmoor, also enjoy a great deal of warmth. Here it is not people, but more than six million flowering plants for homes, gardens and balconies that revel in a constant temperature of between 18 and 22 degrees Celsius. As in the previous example, rising energy costs once again prompted the idea of building a biogas plant. And here, too, the biogas plant is located at some distance from the point of use. The biogas is transported 800 metres to the two pilot-injection motors of the CHP plant. In Wiesmoor, these are located in insulated concrete garages between the greenhouses, where a large, 230 cubic metre buffer storage tank stores the heat.

Waste heat provides additional income

The fermentation substrate, consisting of maize and grass, is bought by farmers. Harvesting is performed by a contractor, who is also responsible for ensilage of the substrate, feeding the plant and spreading the fermentation residue. The fermentation residue is separated into solid and liquid phases, the latter of which is spread by farmers onto the fields which supplied the substrate. The solid phase is mixed with growing substrate at a ratio of 1:4 and used for potted plants. Mixing and turning the material twice produces a material which smells like fresh garden soil.

Waste heat may also be used to supply commercial operations. Food processing plants in particular require large amounts of heat all year round. For this reason, the management of D & S Fleisch in Essen, south of Oldenburg, decided to connect to two nearby biogas plants via a district heating pipe. The slaughterhouse, one of the most modern facilities in Europe, processes more than three million pigs per year, the majority of which come from pig fattening farms in the region. Processing the pigs requires large amounts of energy. Until recently, this was provided by natural gas in addition to electricity. In order to reduce the consumption of natural gas, the waste heat of the two agricultural biogas plants has been used since October 2009.

The water arrives at the slaughterhouse heating centre at a temperature of around 83 degrees Celsius. It is then fed into the facility’s energy supply system via a heat exchanger. The hot water is used for the slaughtering process and for cleaning. Even though the biogas plants are located at a distance of 1,000 and 1,600 metres respectively, the heat loss in the pipes is a mere two percent. Each year, the biogas plants provide an output of twelve million kilowatt hours, replacing an equal amount of natural gas.

This cooperation saves the slaughterhouse more energy than originally expected. The constantly high heating demand makes it an ideal recipient of district heat, and the operators of the biogas plant can sell the entirety of the heat produced during electricity production. Energy cooperation thus allows both the company and the biogas plant operator to make an important contribution to environmental protection.