Abstract
The use of biogas plants has increased sharply in recent years. A typical biogas plant of 500 kWel produces approx. 10,000 t of digestate per year, with a moisture content of more than 90%. For the purpose of reducing the transport mass and increasing the nutrient concentration, the digestate has to be dried. Using renewable energy is a way to treat biogas digestate without any additional fossil energy requirement for drying. In this study a solar greenhouse dryer was modified to use additional waste-heat from the combined heat and power unit (variant S-CHP), as well as the exhaust gas from a micro turbine (variant S-CHP-MT). The hybrid waste-heat/solar dryer achieved a moisture content for the digestate of 10.9%, and 10.5%, after 13 d of drying for variant S-CHP-MT and S-CHP-MT, respectively. Due to the higher energy input by additional use of the micro turbine, the specific energy consumption is higher for the variant S-CHP-MT. In general, the results showed that the combination of solar energy and waste-heat from electricity generation of a biogas plant is a suitable way to reduce the moisture content of the digestate to a safe level for further handling and storage.
Highlights
Primary biogas energy production worldwide amounted to 16.9 GW in the year 2017, compared to 6.7 GW energy produced in the year 2008
In Europe, 11.9 GW were produced in the year 2017, whereas Germany holds the biggest share, with 4.5 GW produced biogas energy, having 9331 biogas plants operating by the end of the year 2017
Difference wasresults causedshowed by the that additional heat from the drying with an MCThe of 75.6%, and the a specific energy microconsumption turbine, which increased inputwater for the drying process
Summary
Primary biogas energy production worldwide amounted to 16.9 GW in the year 2017, compared to 6.7 GW energy produced in the year 2008. In Europe, 11.9 GW were produced in the year 2017, whereas Germany holds the biggest share, with 4.5 GW produced biogas energy, having 9331 biogas plants operating by the end of the year 2017. An additional installation of approximately 160 new biogas plants was prognosticated for 2018 [1,2]. A typical wet fermentation biogas plant with an installed electrical power of 500 kW produces approx. 10,000 t of digestate per year with a moisture content of 90–95% [3]. Möller and Müller calculated the total amount of digestate in Germany for the year 2011, at approx. Möller and Müller calculated the total amount of digestate in Germany for the year 2011, at approx. 65.5 million cubic metres [4]
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