Balancing biogas, heat and power with an Organic Rankine Cycle
Founded in 2013, Sweden-based Organic Rankine Cycle (ORC) technology developer Againity AB has recently seen unprecedented interest for its technology in Sweden. 2019 order values thus far have already exceeded the total accumulated value of orders for the company until the end of 2018. Bioenergy International met up with founder David Frykerås and co-owner Elin Ledskog at Slottshagen wastewater treatment plant (WWTP) in Norrköping to find out more.
The choice of venue was no coincidence. With Againity hailing from Norrköping and the WWTP being the location of the first commercial delivery for the company, it was an auspicious site. The first-of-its-kind delivery in Sweden, it is also the company’s only delivery to a wastewater treatment plant (WWTP) – thus far one should add.
First though, a little background. The name David Frykerås may sound familiar especially for those with an interest in “farm-scale” biodiesel production technologies. Together with his father, he was behind a previous company called Ageratec AB that made skid-mounted “plug`n´play” biodiesel production units that were exported around the world.
A key patented feature of these modular units was that no water was required in the process making them a viable choice in arid regions. The company was acquired by global technology major Alfa Laval in 2010 and integrated into the company’s vegetable oil technology division.
A mechanical engineer by training, Frykerås has also spent part of his professional career at the Siemens Industrial Turbomachinery plant in neighbouring Finspång. It is here the Germany-headed global technology major produces steam and gas turbines for power plants for global markets.
Thus Frykerås is no stranger to designing efficient yet modular and robust equipment for global markets. Also an engineer by training, Elin Ledskog conducted her bachelor thesis at Againity before subsequently becoming a co-owner in the business.
The heart of the ORC, the patent-pending turbine, is developed in-house and utilizes low-grade heat down to 90 degrees Celsius.
Thanks to the unique design of our turbine and the low number of moving parts in the system, a high-quality product can be offered. This minimizes the need for service and maintenance and significantly shortens the payback time, explained David Frykerås.
When commissioned in 1958, Norrköping’s Slottshagen WWTP was the largest and most modern WWTP in the country. Operated by the municipality-owned water and waste management company Nodra AB, it has since been upgraded and expanded to comprise of mechanical, biological and chemical wastewater treatment.
Today, sixty-one years on, Slottshagen is one of the ten largest in Sweden with some of the original sedimentation and aeration lagoons still in operation.
The company is also something of a circular economy pioneer when it comes to utilizing the biogas and the residual sludge digestate. The latter is composted on-site before use as soil improvement medium for city parks and other lands not used for food production.
ORC to reduce flaring
Produced as a part of the anaerobic digestion (AD) treatment process at Slottshagen, the biogas is upgraded to biomethane and then piped directly to a nearby service and refueling depot for city buses.
However, despite an increase in the biogas powered bus fleet over the fifteen or so years the WWTP has supplied biomethane, biogas production is still higher than demand. Especially during the summer months when the holiday schedule with fewer routes and frequency comes into effect meaning fewer kilometres.
As a result, the excess gas was flared at the WWTP, which on an annual basis meant 900 to 1 200 MWh of gas or around 10 percent of the biogas production. To address this Nodra launched a project tender to make the best and most cost-effective use of the excess gas.
The challenge is that there is only a few hours worth of gas storage on either end of the pipeline before flaring kicks-in. Yet at the same time, the WWTP has both a heat and power demand that cost, explained David Frykerås.
Click here to continue reading this article which was first published in Bioenergy International no. 2-2019. Note that as a magazine subscriber you get access to the e-magazine and articles like this before the print edition reaches your desk!