In New Generation of Instruments Deliver Reliable Process Feedback, we talked of the utility of instrumentation in controlling production processes. There is one more notable area in which instruments are having a large and positive impact on the plant: in the sanitation processes used in between production runs. An example is the shift toward membrane technology to purify process water.
Reverse osmosis and nanofiltration remove virtually all the total dissolved solids in municipal water. That opens the door for conductivity sensors in monitoring CIP water.
Conductivity sensors are among the most economical devices in the field, according to Derek Deubel, vice president at Techniblend Inc., Waukesha, Wis. But if there are too many different elements in the water, their reliability is compromised. When membranes purify the incoming water, "any chemical or ingredient in the water is more identifiable, and that makes conductivity sensors a better option," he says.
Mettler Toledo effectively applied conductivity testing to CIP water at Anheuser-Busch's Columbus, Ohio, brewery. Caustics in the rinse water needed to be under 40 ppb of dissolved solids per liter before discharge. Technicians determined that would translate to 300 micro Siemens of electric conductance. Sensors were installed at the front and end of each CIP loop to monitor caustic levels.
"We knocked (the standard) down to 50 micro Siemens before sending it to drain, just to be safe," recalls Brian Vaillancourt, aftermarket services & key accounts manager in the process analytics division of Mettler Toledo (http://us.mt.com). Sensors also eliminated overdosing in the sanitation cycle. Ten control loops were needed, but the system helped shorten rinse time to 17 minutes from 45. The result was a three-month ROI.
Recovering and reusing chemicals can add to the payback with CIP, adds Rick Cash, marketing technology manager with Thermo Fisher Scientific Inc., Minneapolis. Still, the greatest value from field devices comes from improved product quality, and that can be difficult to express in financial terms.
On the other hand, "we've gotten past the 'does this take accurate measurements?' discussions to 'how does this pay for itself in our plant?' conversations," he says. As more automation is added and production becomes more continuous and less batch oriented, the utility of plant floor instrumentation will increase.
