Case Story Netherlands

DEN EELDER FARM

Small farm scale mono-digestion of dairy slurry

March 2017

Mission and Vision

The Den Eelder farm’s website proudly boasts that ‘our cows poo electricity and heat!’ Thanks to a closed circuit monodigestion system, the farm actually runs on green energy produced from its own manure. However, owner Ernst van der Schans warns not to expect farm biogas to make you wealthy. In the early 1980s, Mr van der Schans started farming near Well-Ammerzoden, in the province of Gelderland, in the Netherlands. In 1990, he branched out to dairy processing, a rather energy-intensive process. He now has a relatively large dairy farm, with around 500 cows. The concept of producing biogas from cattle manure was of great interest to him. This was not just about using this renewable energy on the Den Eelder farm, but also to reduce methane emissions.

The Biogas System

The decision to use mono- or co-digestion In the beginning, he was not sure if he should use monodigestion (where only manure is converted to biogas) or co-digestion, in which other feedstocks are also fed into the digester. In 2012, Ernst van der Schans finally decided to invest in a Microferm mono-digestion system, with a 66 kWe cogeneration unit. “There were several reasons for this”, says Mr van der Schans. “We didn’t have to add a cost item to our books for the supply of co-products. We did not have to produce any additional manure for the digester, and we just wanted a simple, small-scale installation. So we started small, with 7,000 tons of manure every year.” Ernst van der Schans is happy that he opted for mono-digestion. “It suits our farm. We like using a closed-cycle system. In addition, we prefer not to have any external products or animals on our site. We also wanted a simple logistical process.”

The digester system

The first-phase mono-digestion installation processed 7,000 tons of fresh manure per year. This yielded 250,000 cubic metres of biogas. The combined heat and power (CHP) generator produced 500,000 kWh of electricity and 1 million kWh of heat every year. The heat is used to raise the temperature of the manure before it goes into the digester and to heat the digesters. The electricity is used on the farm. The Den Eelder farm recently expanded its capacity by adding an extra digester. The additional digester can hold up to 1,500cubic metres of manure and store a thousand cubic metres of gas. A biogas heater (700 kW) is used to heat water to 110°C. This addition increased the overall capacity to 15,000tons of fresh manure per year.

The installation (photo 1) now yields 1.5 million kWh of heat per year for the Den Eelder farm’s own dairy produce operation. “We now produce more than enough to meet our farm’s energy demand, except at peak times. The remaining energy that we require will come from the solar panels that we are installing on the roofs of the animal enclosures, which means that we will have zero energy importation.” According to Mr van der Schans, the installation is quite basic. “But I like basic. The digester stirs the manure and heats it to 40°C. This yields 30 to 40 cubic metres of biogas, with a 60% methane content, per ton of manure.”