Electric.ie May/June 2021

46 ELECTRIC.IE • The Magazine & Website for the Irish Electrical Industry • Mitsubishi Electric Ensuring reliable heat and power generation M itsubishi Electric Ireland Automation Partner, Ashdale Engineering, located in Northern Ireland, has designed a highly accurate control system for an anaerobic digestion (AD) plant. The precision process control is achieved using Mitsubishi Electric automation components and is vital to ensuring continued operation of the live AD process, enabling the generation of heat and electricity that the plant operator now plans to sell to the grid. The anaerobic digester at a large farm near Armagh drives a combined heating and power (CHP) plant that heats the farm’s buildings while also producing electricity. Animal slurry, silage and additives are mixed together and the resulting biomass then is heated to produce biogas, used to power the CHP. Based in Belfast, Ashdale Engineering became involved with the project because of its specialist expertise, having worked on AD projects for over 10 years in Northern Ireland together with Mitsubishi Electric. One of the crucial aspects of anaerobic digestion is temperature control, as the microorganisms that break down the biomass require temperature stability. Fluctuations above one degree centigrade per day can kill them, stopping the process and with it, the generation of heat and power. In the event that this occurs, it takes considerable time to remove and replenish the biomass to restart the AD process. In addition to offering stability, the control system also needs to be responsive, easy to use and reliable. Accurate control with Mitsubishi Electric PLC By utilising the advanced programming features of the Mitsubishi Electric MELSEC-Q Series PLC, Ashdale Engineering was able to develop an accurate and reliable control solution. Analogue flow and temperature signals transmitted from the pump house and digesters, which could be up to 30 metres away, are communicated over CC-Link via remote I/O. Interaction with the PLC takes place via a HMI communicating over Ethernet and a variety of Mitsubishi Electric variable speed drives control the system’s pumps. The solution ensures reliable heating and power generation and is now providing the opportunity for profitable export to the grid. “The AD plant has capacity for around 40,000 m³ of biomass fuel and small changes to any of the variables can impact the temperature of the biomass,” says Adrian Whitten, Systems Manager at Ashdale Engineering. ർ Mitsubishi Electric’s automation technology delivers highly accurate control solution for anaerobic digestion plant “Floating point number calculations, made possible by Mitsubishi Electric’s MELSEC-Q Series PLC, were vital to achieve the precise control required to ensure long-term stability of the process. Combined with high resolution analogue inputs, the accuracy of calculations gives greater control, meaning continued assurance for heat and power generation.” High resolution and accuracy are also critical for recipe control. The ratio of ingredients can change dependent on seasonality as well as adjustments for desired outcomes. “Some farmers may overfeed the AD system, or feed a recipe that is too rich,” explains Adrian. “Again, this can kill the microbes and stop the process. Any changes in the feed have to be made very gradually and with precise control. That’s what the MELSEC-Q PLC enables us to do.” Simple AD system management Ashdale also accounted for the AD plant’s wish to expand in the future. The MELSEC-Q Series PLC offers By utilising the advanced programming features of the Mitsubishi Electric MELSEC-Q Series PLC, Ashdale Engineering was able to develop an accurate and reliable control solution.