Energy from waste for cereal manufacturer

A large Australian cereal manufacturer has now been equipped with Rockwell Automation automation and control technologies for its anaerobic digestion plant, which generates energy from organic waste. The technology for the automation and control was supplied by Auto Control Systems (ACS), a Rockwell Automation Silver System Integrator.

The plant will generate methane gas from oat husks (a waste product from the cereal production process) and will use this fuel in a combined heat and power generator unit to offset in full its existing and future energy requirements with surplus energy exported to the grid.

The anaerobic digestion process starts in the storage tank where waste oat husks are stored prior to being processed. The husks are then injected into the reactor tanks where they are heated, stirred and then cooled. The four main stages of the process are hydrolysis, acidogenesis, acetogenesis and methanogenesis. Each stage digests the matter into smaller parts, ultimately resulting in a mixture of methane, biogas, water and digestate. The raw biogas is then used to generate heat and electricity for the plant with surplus energy being exported to the grid.

The anaerobic digestion process is continuous and therefore needs to be closely monitored for pH and temperature by the control system. ACS was responsible for the hazardous area accreditation and has full remote access to the plant.

Andrew Taylor, engineering manager at ACS, detailed the importance of having a scalable solution for the plant. “A scalable solution delivers the flexibility to scale up or down depending on their needs. The automation and control solution we developed delivered that flexibility in a scalable, containerised package. After it was built and pre-tested here in Perth, it was transported to the customer site ready for installation,” he explained.

The Allen‑Bradley CENTERLINE 2500 IEC Low Voltage motor control centre (MCC) from Rockwell Automation was at the heart of the solution. With Ethernet connectivity, the MCC streamlined the pre-testing process and ArcShield technology increased protection against internal electrical arcing faults, providing an extra level of safety.

Control of the plant’s processes was provided by the Allen‑Bradley CompactLogix PLC and the PowerFlex 525 and 753 AC drives deliver the reliability to meet the application requirements of the plant. FactoryTalk View SE delivers an accurate real-time view of the process with alarming via SMS and it also allowed ACS to utilise the PlantPAx libraries to reduce their engineering overheads.

The anaerobic digestion plant has been successfully commissioned and gas is currently being produced. When fully operational, the manufacturing plant will be generating 1.5 MW of electricity and heat which will be used to offset in full the plant’s existing energy requirements.

Image credit: ©stock.adobe.com/au/LianeM