Advanced Controls Help in Delivering Safe, Sustainable Energy Supply
Rockwell Automation scores a hat-trick with Greenfinch biogas production trio.
| Summary Research and development at Greenfinch proved the viability of anaerobic digestion and biogas technology to provide a safe, sustainable and environmentally friendly source of energy. The result was a contract to supply 'green' energy to a blue-chip retailer from Greenfinch's plant in Ludlow. The development of the plant required a modern control solution to control and collect data from the process. Solution A control solution was built around Rockwell Automation's Allen-Bradley ControlLogix, SCADA, HMI, and intelligent Allen-Bradley E1 motor starters, contactors and pushbuttons. Rockwell Automation helped with best design and practice to implement the SCADA system for data collection. The company also provided technical knowledge for integrating DeviceNet as a network solution with remote I/O and Ethernet programming to the SCADA and HMI interface. Result The Rockwell Automation solution delivered a number of benefits, including reduced build time, reduced wiring and reduced panel size, as well as improved collection of data from the plant for greater information to run the process. As a result, Greenfinch has now decided to use Rockwell Automation equipment again on new plants being built in Ireland and Gloucestershire UK. |
Background
Greenfinch’s South Shropshire Biowaste Digester takes kitchen and garden waste from households throughout the South Shropshire District. Part of the biocycle project, run in partnership with South Shropshire district council, the anaerobic digester, otherwise known as a biogas plant, processes 5,000 tonnes per year of source-separated kitchen and garden waste from landfill. Following its successful implementation, which culminated in a contract to supply ‘green’ energy to a blue-chip retailer, Greenfinch has specified the same Rockwell Automation Allen-Bradley ControlLogix controllers, SCADA, HMI and Intelligent Motor Starters for future plants in Ireland and Gloucestershire UK.
The smell of rotting food waste is unpleasant at best and an environmental hazard at worst. We all know that solutions need to be found for the benign recycling of perishable household waste, as well as restaurant and food processing waste. The simple reason is that perishable waste - when not properly recycled – causes environmental damage, contains pathogenic organisms and contaminates dry recyclable waste.
Research and development at Greenfinch, one of the UK’s anaerobic digestion and biogas specialists, has proved that the process of anaerobic digestion and biogas technology provides a safe, sustainable and environmentally favourable solution.
The company’s pioneering work has been driven by both existing and pending legislation. For example, in its current draft, the EU Biowaste Directive encourages the recycling of food waste to agricultural land to improve the organic quality of soil and its macro- and micro-nutrients. If this directive is implemented, local authorities will be forced to adopt separate collection schemes for food waste.
It is the policy of the EU and its member states that urgent means are applied to significantly reduce the emission of greenhouse gases. The controlled anaerobic digestion of food waste contributes in two ways:
1. It prevents the emission of methane and carbon dioxide to atmosphere from uncontrolled decomposition.
2. By producing renewable energy the carbon dioxide emissions replace those which would otherwise have been emitted from burning fossil fuels.
Greenfinch has recently secured a five-year contract to supply a leading retailer with energy generated from anaerobic digestion, and will be paid for 1.3GWh of energy being generated for the National Grid – the equivalent of the energy needs of two stores.
This is part of a project called Biocycle, run in partnership with South Shropshire district council, taking in around 5,000 tonnes of household food waste each year. The retailer had been interested in using anaerobic digesters for some time as a means of providing renewable energy for its stores and reducing landfill, and chose the plant in Ludlow UK because it is a pioneer.
“This was a new application that required a modern control solution to control and collect data from the process” Russell Mulliner, Operations Director, Greenfinch |
A biogas plant uses a similar biological (fermentation) process to that taking place in a landfill site, the key differences being that the former is contained and controlled, and takes only one month compared with many years in a landfill. The controlled anaerobic digestion process takes place in a vessel sealed from the outside air, and at the Greenfinch plant takes place at 37oc or mesophilic range.
Biogas, a renewable energy source, which consists of 60% methane (CH4) and 40% carbon dioxide (CO2) with traces of hydrogen sulphide (H2S), is produced continuously, and is converted to another energy form almost at once since storage is expensive. A spark ignition gas engine, combining heat and power (CHP) unit is the ideal system for harnessing the energy of the biogas, producing both electricity and heat, a proportion of which is re-used in the process.
A series of analogue 4-20mA signals from instruments measuring the key process parameter on the plant (temperature, gas level, gas flow rate, tank levels), are fed back to a Rockwell Automation Allen-Bradley ControlLogix programmable automation controller (PAC), which controls the anaerobic digestion process and is also used as a control input to the CHP plant.
Many existing sludge digesters give unnecessary problems, which arise due to inadequacies in the process control system. Greenfinch has a reputation for being able to analyse the control requirements from the plant operator's point of view, and then to redesign the process control specification to make plant operation simpler and safer. This task falls to Russell Mulliner, Operations Director at Greenfinch.
“We chose ladder diagram (LD) to program the Rockwell Automation Allen-Bradley ControlLogix controller in preference to the other IEC 1131 programming languages, because it helps our engineers follow the system’s logic more easily,” Mulliner explains.
Ladder diagram is Rockwell Automation’s most popular programmable controller architecture and was in widespread use in industry before the IEC 61131-3 specification was published - listing LD as one of five international standards for logic and automation controller programming languages. For people who understand relay controls, LD continues to have an advantage in terms of usability.
“This was a new application that required a modern control solution to control and collect data from the process. As well as logic programming in ladder diagram, we also had to hardwire the various sensors and controllers used for inputs and outputs to the plant,” Mulliner adds.
“We built the control panel ourselves, while Rockwell Automation helped with best design and practice to implement a decentralised network solution incorporating a supervisory control and data acquisition (SCADA) system for data collection. The company provided the technical knowledge of how to integrate DeviceNet as a network solution with remote I/O and Ethernet programming to the SCADA and HMI interface.”
The Rockwell Automation products and services deployed in the application include ControlLogix, SCADA, HMI and intelligent Allen-Bradley E1 Motor Starters, contactors and push buttons. The unique challenges encountered in the project entailed programming the links between ControlLogix and the E1 Intelligent Motor Starters using 193-EDN DeviceNet communications module for E1 Plus overload relays units over DeviceNet, Ethernet and SCADA.
“The benefits we have experienced as a result of the Rockwell Automation solutions include reduced build time, reduced wiring and reduced panel size, as well as improved collection of data from the plant for greater information to run the process. We have new plants being built in Ireland and Gloucestershire UK and have decided to use Rockwell Automation equipment again for those.”
With Rockwell Automation as a collaborator, Greenfinch is future-proofing the technology of biogas production, having developed successful solutions for the safe and environmentally benign recycling of organic waste into useful soil nutrients and renewable energy.
For more information, please e-mail us at: info_at@ra.rockwell.com with ref: Greenfinch
Signals measuring the key process parameters (temperature, gas level, gas flow rate and tank levels) are fed back to a Rockwell Automation ControlLogix programmable automation controller, which controls the anaerobic digestion process and is also used as a control input to the CHP plant | Greenfinch chose ladder diagram to program the ControlLogix controller in preference to other IEC 1131 programming languages, as it helped its engineers follow the system's logic more easily. For people who understand relay controls, ladder diagram continues to have an advantage in terms of usability | Greenfinch engineers built the control panel themselves, while Rockwell Automation helped with best design practice to implement a decentralised network solution incorporating a SCADA system for data collection | Greenfinch is future-proofing the technology of biogas production, having developed successful solutions for the safe and environmentally benign recycling of organic waste into useful soil nutrients and renewable energy | Greenfinch was able to analyse the plant from the operator's point of view, and then design the process control specification to make plant operation safer and simpler |
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