Rockwood Additives, based in Widnes UK, is a subsidiary of Rockwood Specialties. Along with its sister companies Rockwood Clay Additives and Southern Clay Products, it produces and markets an extensive range of natural and synthetic additives that are used to perform critical functions by manufacturers of industrial and consumer products.

Now Rockwood Additives is set to standardise on ABBAP200pH probes supplied by ABB Instrumentation Alliance(*) partner WH Good following successful trials of the instruments at its Widnes plant. The move follows years of maintenance headaches associated with pH probes from other manufacturers.

The Widnes plant manufactures active clay products, including Rockwood’s Fulacolor and Laponite ranges. Fulacolor is used in carbonless paper systems while Laponite is used to alter the flow characteristics of products as diverse as household cleaners, toothpaste and ceramic glazes. The company needs to monitor pH closely at various stages of production, but particularly in its effluent control plant in order to comply with discharge consents under the pollution prevention and control regulations.

First the acidic effluent from Fulacolor production is mixed with the alkaline effluent from Laponite production to achieve partial neutralisation. The resulting slurry remains extremely acidic, with a pH of between 1 and 2.5. This then passes through two balancing tanks, where the addition of magnesium hydroxide continues to raise the pH. The first tank raises the pH to around 4.5 and the second brings it up to around 7. The neutralised slurry is then clarified and the liquid is discharged, while the solids are concentrated in filter presses before being disposed of or recycled.

Rockwood had been experiencing ongoing problems with the existing pH probes in the balancing tanks. “The original probes were failing regularly as a result of poisoning by the liquid in the tanks,” explains control technician Paul Berry. “We were eventually forced to replace them with flowing junction-type probes. These worked ok but they were so fragile that they kept breaking whenever we tried to carry out routine maintenance. We then replaced these with more robust probes from a second manufacturer, but these were still flowing junction-type probes that required frequent topping up and were also very bulky.”

WH Good suggested trying AP200 probes from ABB. “We were initially cautious because of the poisoning problems we had experienced with the other manufacturer's probes,” explains Berry. “But we trialled a couple of units and they've now been working trouble-free for six months.”

AP200 probes are based on a solid polymer system that offers a high resistance to poisoning and pressure cycling. With wetted parts manufactured from Ryton, the probes withstand very aggressive environments at up to 130°C and 6bar. “We’ve used the trial units in various situations with very harsh conditions and they’ve been working well. We’ll be installing more in the next few weeks,” says Berry.

The AP200’s robust autowash system was another advantage for Rockwood, according to Berry. The magnesium hydroxide that the company uses to neutralise the acid in the balancing tanks tends to coat any probes, so regular cleaning is essential. “The old probes included a wash system, but it frequently got clogged and it was so fragile that the ends used to snap off when we tried to unscrew it for cleaning. The ABB units don’t clog up so easily. They also have a bayonet fitting that makes them easier to dismantle and they don’t break if we do need to take them apart,” he says.

ABB’s AP200 pH probes are designed to provide high reliability measurement even in the toughest environments. The rugged assembly is built to bear the rigours of weather and process. Parts in contact with the process comprise chemically-resistant PPS Ryton and stainless steel, or PPS Ryton and Hastelloy C.

Flow-through holders are available in polypropylene, while the PPS Ryton insertion adapter enables installation in alternative material pipelines. Insertion and flow-through systems tolerate temperatures up to 130°C and pressures up to 6 bar . The inner electrode connections are ingress-protected to IP67/NEMA 6P. l

* The ABB Instrumentation Alliance (www.abbiap.com) is a comprehensive instrumentation supply and service network that has been created by ABB to serve customers throughout the UK. It comprises of five partners and backs up ABB’s portfolio of instrumentation products with unrivalled levels of availability, delivery, service and support. Each ABB Instrumentation Alliance partner has been carefully selected to ensure that customers in every part of the country will enjoy the same high levels of service and support.