Process automation meets strict safety measures for storage vessels
System integrator designs a unique solution with Siemens process technology
PPG Industries knows better than most the challenges of storing solvents. Founded in 1883 in Pittsburgh, the company operates globally in nearly 70 countries, and is a world leader in industrial coatings and specialty products. The company has a plant in Stowmarket, Suffolk, UK, that specializes in paints used for automobile refinishing.
Amazingly, even though there is a modern factory in the middle of this rural English town, and even though there is a public footpath running alongside the Rivers Gipping and Rat which meet in the middle of the property, the factory’s solvent storage tanks don’t look at all out of place so close to a green space.
The fact that the two differing environments can coexist so successfully is proof that PPG is a company dedicated to protecting the ecosystem from the potentially explosive solvents that it works with. Their recent efforts to further improve the safety and efficiency of their storage systems led them to Siemens process instruments through system integrator Lark Technology and distributor Process Instrument Sales.
Over the years, the paint manufacturer has used a number of techniques to gauge the level of material within its various storage vessels at the Stowmarket plant. Most recently, for example, the level in each of the 33 tanks containing various solvents was being measured using a bubbler system. Unfortunately, not only was this system prone to errors, it was also labor intensive to use, maintain, and test.
Still, it was a system that had been operating adequately for the company through the years. This all changed, however, when the UK’s Health and Safety Executive (The HSE), enacted strict legislation in response to the Buncefield disaster, an oil storage facility in Hertfordshire, England that was destroyed in a series of explosions in December 2005. The accident was caused by an overflow while remotely filling a storage tank when multiple systems failed, including the main level gauge and the final point level device.
How strict are the new HSE safety measures? Well, the HSE has legislated that such storage vessels containing potentially flammable materials should each have a continuous level measurement device, a high level switch, and an operator visually monitoring the contents of the tank as it is being filled.
To meet these demanding safety standards, Lark Technology, a system integrator, provided a Totally Integrated Automation control system with Siemens technology and Process Instrument Sales.
Lark Technology, accompanied by Process Instrument Sales, designed a new system for PPG Industries from the bottom up. Both a Sitrans LR250 radar transmitter and a Sitrans LVL200 point level device was installed on each of the paint manufacturer’s 33 storage tanks, and then tied into a custom-built Lark control system using Profibus and intrinsically Safe Profibus. In this configuration, each radar transmitter provides continuous level readings, while the point level switch provides ultimate high-level system protection from overfill.
“We provided a turnkey project that was delivered on time and on budget. What started out with the criteria of an overfill protection scheme is now supporting the site’s procurement department to manage stock levels and to maximize efficiency with available solvent storage space,” recalled James Rawlings from Lark Technology. “It was a text-book installation, using the latest Siemens technology, which we are proud to use as a case study.”
The first piece of this technology is a Sitrans non-contacting radar transmitter that is easy to install and quick to configure. With its small antenna, the device can be installed practically anywhere on a vessel, and its high frequency makes for an impressive signal-to-noise ratio, a feature that is even further improved by Siemens’ patented “Process Intelligence” echo processing software.
Next is a vibrating level switch for use in all liquid and slurry applications such as overflow, high, low, and SIL-2 applications. The device is cost effective, easy to install and acts as an important security device in the unlikely event that the primary level detector fails.
The radar transmitters are connected to the plant’s control system through Profibus, an industrial communication protocol that provides fully integrated, two-way networking between a control system and each of its field devices.
During installation of the new system, extensive validation was carried out to satisfy the HSE, another of the elements Lark Technology offered as part of the turnkey package.
As an added bonus, the radar transmitter is also able to provide trending: all the tanks are monitored when one is being filled so that the operators know immediately if there’s a routing error or leak somewhere.
One of the life cycle requirements of the system, as defined by the HSE, was that all point level devices have to be tested on a regular basis, a stipulation that was time consuming as well as problematic. The 500 millimeter probes are located inside the vessel, and the chances of damaging them increase each time they are removed. A way of testing them in situ was needed, so Lark Technology engineered a unique custom solution.
Lark’s testing device is a long, hollow rod with a small pot at its end that is supported directly beneath the tip of the probe. For testing, the cup is filled remotely with the same solvent that is in the vessel through the hollow rod using an industrial syringe. The rod and pot arrangement is lifted so that it covers the sensing end of the probe. In this way, the system can confirm that the probe operates with the actual product in the tank. Afterwards, the pot is lowered back down, the same syringe is used to remove the test liquid and the handle is locked in place until the next test.
With the new Siemens equipment in place and connected to the control system, PPG is reaping the benefits of a totally integrated and automated system with excellent data control. The new level monitoring equipment is reliable and efficient, giving the company the confidence that they are meeting all of the stipulated HSE standards. This is because they know what’s going on in all of the tanks even when they’re just working with one. The company is also the proud owner of a new custom solution for testing point level probes in situ, in a manner that doesn’t risk damaging them.
What’s more, there are the business opportunities to consider. “There have been some good relationships built as a result of this,” says Jon Tayler of Process Instrument Sales. In fact, PPG is so satisfied with the results and the dedication of all the companies involved that it is now committed to installing more Siemens devices on the next phase of the Stowmarket project.
So, the next time you’re in Stowmarket, make sure to enjoy a walk through the idyllic English countryside on one of their many footpaths. And, if you choose the Gipping Valley River Path—the one that passes under the shadow of PPG’s solvent storage tanks, there’s a Siemens product not too far away maintaining confidence and reliability in safety.