Automated controls improve productivity and quality for resins manufacturer

Manufacturing efficiencies, materials savings, right first time improvements and faster scale-up from pilot to mass production for new products – those are just some of the benefits resins manufacturer Scott Bader is seeing at its plant at Wollaston in Northamptonshire, as it implements its plant management systems. Not only are the improvements manifestly paying for the entire cost of the systems within two years, but aspects like support for much faster continuous improvement and best practice skill capture are bound to build on that. Scott Bader is a £100 million turnover employee-owned company that can trace its heritage back to the 1920s. It produces a range of polyester resins for several industries – in particular marine, land transport and plastic pipelines: everything from lorry aerodynamic kits to sports car bodies, boat hulls and, more recently, stone-effect fireplaces and kitchen work tops. The Wollaston plant has eight reactor vessels ranging from 2.5 to 15 tonnes and 18 vessels in all, the largest of which is 23 tonnes, so its specialist batch manufacturing, with vessels arranged in sets for production of specific product groups, like pre-accelerated resins. Most production is two stage, although some are three, typically starting with cooking the charge and heating to distill off water in a reactor, followed by solvent blending and, in some cases, then properties modification with fillers and the like to create characteristics suited to end purpose. Top level issues around that involve ensuring appropriate campaigns and sequencing of batches to maintain good quality production through the vessels and pipework, and that’s managed by planners and chemists with experience spanning many years. Additionally, the firm needs to retain substantial R&D and technical services teams not only to develop innovative new products, but to provide ‘packaged’ services to clients involving appropriate product advice, associated materials and so on. Beyond that though, to remain competitive, the firm has to maintain world class manufacturing productivity and efficiency standards – and achieving that is what this story is about. Two years ago, the company started investing in Rockwell Automation networked automatic batch monitoring and control systems to take it away from its manually operated plant roots. “To increase our output, the aim was to improve the efficiency of our existing capacity rather than adding new plant or working extra shifts,” says James Harris, Scott Bader’s process operations engineering manager. “Automating the plant has turned out to be a cost effective means of increasing productivity by 20%.” While at the time the company was unfamiliar with advanced, plant-wide automated controls, it had some experience with Allen-Bradley PLC5/40 programmable controllers and PanelView human machine interfaces (HMIs). Those had been implemented as an interim measure to improve the charging of expensive and sometimes difficult materials to the reactors, harnessing Emerson MicroMotion mass flowmeters, and also monitoring some valves and temperatures. That system had been successful, so based on their reliability and performance, Scott Bader awarded Rockwell Automation a contract to design and commission new plant automation systems. In terms of the systems themselves, the firm is basing its development on Rockwell Allen-Bradley ProcessLogix controllers, RSBatch batch automation software and a ControlNet digital plant network. Phase One, completed in November 2001 for Reactor 8, which is a relatively new facility for the plant, illustrates the set-up. That system uses a dedicated ProcessLogix PLC-cum-distributed control system module at the plant controls level. It provides the global plant database, with all the essentials for plant management – redundancy, deterministic control, integrated HMI, range of process control algorithms, high speed logic and a scaleable architecture – as well as off the shelf, robust hardware. In this case, it’s installed in an Allen-Bradley 1756 chassis together with the I/O racks in a panel in an interface room separated from the hazardous plant floor by a blast-proof wall. That part of the plant is now managed using three identical PC-based operator stations and a main server linked by an Ethernet LAN. Two PCs are in a new air-conditioned control room, also located behind the blast-proof wall, along with the server. Images from a number of CCTV cameras monitoring the process are part of the system, enabling plant to be viewed at the operator desk in the control room. The third operator station is on the blender floor level floor below the control room. Three operator stations are part of the redundancy set-up: plant control can be switched between machines in the event of a failure. Controls on the plant floor operate at 24V dc, while the control room in a designated safe area is supplied with 230V ac, all with uninterruptible power supplies. Meanwhile, the server runs the RSBatch batch control software for process creation and batch processing. Harris says it’s lived up to its expectations. “The automated controls have increased the reliability and availability of the plant, improved the accuracy of execution of batch recipes, enhanced the quality and consistency of the end product and reduced wastage of high value ingredients.” And putting some meat on those bones he explains that there are many aspects to this. For example, by moving from manual to automated processes, issues like experienced operators retiring are less of a problem – new recruits get a system already geared and programmed to execute best practice automatically and consistently. Then again, since the system is consistent, the running around, changing valves, charging materials and, in particular, monitoring and testing for progress have been massively reduced – which means staff able to get on with preparing the next batch or whatever. “It’s saving us hours of checking and wasted time between shifts,” says Harris. “The system just gets on with the job, alerting operators when they need to get involved with critical stages. Also, because it’s automated and checking temperatures and so on all the time, it runs the batches closer to the wire, completing them more quickly, with better quality and without incurring materials usage or quality penalties. No-one needs to manually adjust the plant to achieve the required batch quality and, because repeatability is much better, we get more batches right first time. In fact, we’re getting 93% right first time production now, compared with 65% before. “So not only do we now consistently use 2% less glycol, which saves us tends of thousands of pounds per year, but we’re getting around six or seven batches through a week, compared with four or five before. That 20% productivity improvement means hundreds of thousands of pounds to us.” And he goes on to say that being more productive has “helped us out of a hole in recent months” since the fact of problems with one reactor hasn’t got in the way of producing batches and meeting customer requirements. Harris reckons that with total savings of more than £250,000 each year, the systems are paying for themselves within two years of installation. And there are other softer benefits. He makes the point that, because the batch management system ensures predictable operation of batch processing, consistency between batches and provides event data during batch runs, it’s making scale-up from pilot plant production of new products much faster. “Because the system breaks down batches into blocks of jobs and functions in sequence, they’re easy to see, so I can look at getting improvements on new product batches with the plant chemists and make changes in minutes ready for the second batch. It means we can be at optimum shortly after the second batch rather than several batches later, so we avoid rework, double handling, further mixing – inefficiency.” Incidentally, it’s also worth noting that resin manufacturing involves hazardous chemicals including highly flammable solvents, so another benefit of automation is improved working conditions for the employees. Instead of controlling the process by manually opening and closing valves on the factory floor, operatives are running and monitoring the plant from the control room. Following successful completion of Phase One, Scott Bader moved on to Phase Two in March last year, automating a new vessel and charging system for DCPD resins production with a similar Rockwell system. Phase Three, automating Reactor Seven, went live at the beginning of this year; Phase Four, involving Reactor Six, is happening now; and Phase Five, for Reactor Two, is scheduled for early in 2004. The rest of the system is due to for completion late in 2004.