Drives and Controls January 2023

32 n VARIABLE SPEED DRIVES January 2023 www.drivesncontrols.com Drives help to create green power in Greece R enewable energy is helping to reduce the amount of harmful emissions released into the atmosphere and to cut the world’s reliance on fossil fuels. Biogas produced through anaerobic digestion is one such environmentally-friendly energy source helping to generate green electricity. Biogas production in Greece is on the increase and the latest project began operating at Kefalovrysos, Trikala, central Greece, in October. Animal and food waste is broken down into micro-organisms in two oxygen-free stores. Pumps ensure the right quantity of material is fed into them before being mixed to create the gas. The gas passes through two on-site cogeneration systems to produce 3MW of electricity per hour. This is then fed into the mains grid. The €10m project was undertaken by PK Energy, a Greek company that specialises in building electricity production systems powered by renewable energy sources. It has already completed several biogas systems using animal effluent and vegetable waste that produce gas through anaerobic digestion which is, in turn, converted into electricity. For the Kefalovrysos project, PK worked with a local supplier of variable-speed drives, Automation Experts, to develop methods for pumping the animal and vegetable waste into the reactors, as well as the mixing process. Both processes are controlled using VSDs. Automation Experts’technical director, Theodore Amiridis, reports that the 18 VSDs used were an integral part of the project, ensuring that the optimum amount of gas is created through controlled pumping and mixing. “The whole process relies on pumping and mixing processes, each requiring the VSDs to accurately control the amount of waste going in and out, and the speed of the mixing,”he explains.“Material is pumped into tanks one and two where it is mixed to produce the gas. “After some time, pumps are then used to transfer the material from these tanks into a third one where it undergoes centrifugal treatment.” Each of the pump and mixing processes is controlled using Invertek Optidrive E3 three- phase VSDs, with ratings ranging from 4– 37kW and housed in IP20 enclosures. The drives control the mixers and pumps using PID functions to ensure the accurate flow and mix of the material. Amiridis says that the drives were easy to program, install and commission. Each one was connected to a PLC via Ethernet/IP. “The whole process, combined with our expertise, ensured the optimum levels of gas were produced by ensuring the correct motor and pump speed.” n A newly-commissioned biogas-fuelled power generation project in Greece is relying on 18 variable- speed drives supplied by a Welsh drives-maker. The drives’ PID functions have been harnesssed to control the mixing of animal effluent and food waste. The Kefalovrysos biogas project during construction in central Greece The biogas scheme relies on 18 VSDs to control the pumping and mixing processes