UCL Company, a diverse agricultural operation based in Dalton, KwaZulu-Natal, has expertise in wattle bark extract exports, sugar cane production and pine lumber. The company identified a need to upgrade the controls on its boiler number 5 in order to replace the manual nature of the control. Furthermore, a need existed to optimise the process control of the boiler in order to reduce the use of coal and maximise the use of bagasse as a primary fuel source, thereby substantially reducing operating costs.
The existing system controlled the drum level, furnace pressure and master pressure of the boiler. The fuel feed motors and draught air fans were started manually from a control desk situated in the boiler control room. The existing system required a high level of operator interaction, but was not able to provide much information in terms of plant status.
The objectives of the project were to modernise, optimise the efficiency, and to create more transparency on the boiler. UCL approached Afrilek to provide a solution to benefit the production, maintenance and management teams. According to Afrilek’s Grant Douglas, the engineering manager at UCL – Ryno van Zyl – played a crucial role in demonstrating to management the needs and merits of the upgrade.
A race against time
The time factor was a major challenge for the team, with only three months being scheduled for all work, including design, procurement, installation and commissioning. Douglas explains that this process normally takes in excess of four months to complete. “Afrilek and the end user had to work closely together to complete the design in order to ensure that the equipment was delivered and installed before the deadline. We were able to overcome the challenges for two reasons: (1) our extensive experience on similar boiler upgrade projects and (2) by using standard Siemens Advanced Process Library (APL) templates.”
The end user already had Siemens PCS 7 installed onsite for the control of the pans, which included a redundant OS pair, engineering station and process historian. The boiler control system was integrated into the existing PCS 7 infrastructure after a new fibre optic network was installed throughout the plant to allow for future upgrades of other plant areas. The fibre network consisted of Siemens Scalance switches installed throughout the plant in a redundant ring structure.
To allow more availability of the operator stations, one of the OS servers was moved to a different location in the power house. This allowed for the operation of the plant even if there is a loss of communication to the pan floor or power house. A Siemens Scalance XR324 19-inch switch was used at the pan floor and was installed into the existing server cabinet housing the PCS 7 computers. Its modular nature will allow the end user to add more fibre or copper ports for future upgrades.
Siemens Scalance X308-2M switches were used at the balance of the locations (front-end, diffuser, 11 kV substation, power house, boilers and extract factory). The X308-2M is DIN rail mounted and also allows for expansion of ports for future upgrades. The switches are installed in a redundant ring structure and are all connected to UPS power to allow for high levels of availability. With the network infrastructure in place, a new Siemens S7400 CPU was installed in the power house to control both the boilers and the TAs in the power house. In addition, two new OS scada clients were installed, one for the operation and monitoring of Boiler 5, and one for the power house.
A new Siemens ET200M remote I/O station at the boiler integrates all the I/O from new Endress and Hauser instrumentation to the boiler MCC via Profinet. The exiting switchgear cabinets had to be retrofitted to allow for local and remote start of the starters as well as the indication and control of the starters from the PLC.
Afrilek provides UCL with 24-hour support on an ongoing basis. A VPN connection into the control system is used to provide remote support if the team is not onsite. All project objectives were successfully met within the stipulated timeframe.
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