PROCESS ANALYZER: Standardized Solution Savings

Many plants have a process analyzer installed and working that can monitor liquid processes like sugar dosing, soft-drink blending, and paper dyeing. But the process control manager and the QA manager may not even realize that the measurement tool is there. Therefore, they never see the on-line, real-time data it makes available.

Basics

Process analytical systems come in many styles, from speed-of-sound or refractive-index measurement systems, to chromatographs. They consist of different technologies, including selective-ion electrodes to viscosity-monitoring paddles. But many of these complex, expensive systems may be unnecessary. Since industrial fl uids are simple solutions or mixtures, they mainly have simple variations of concentration.

In fact, concentration monitoring can readily be related to a measurement of liquid density (or SG as it is sometimes referred to). Density is a very specific, well-known, well-defi ned anduseful property. It can be checked in the lab, and it is a highlytransferable figure that translates well between facilities. Since liquid products contain well-defined ingredients, the relationship between density and concentration can also be easily established. While temperature can be a disruptive factor, even this variable can be measured, predicted, and manipulated.

This temperature/density/concentration relationship can be illustrated as a three-dimensional surface. A section across this surface at a constant temperature gives a line, or curve, relating the density of a liquid to the concentration of the components. Modern microprocessor-based units can accept and integrate this three-dimensional data and graphs as look-up tables; and an input of density and temperature signals can produce a concentration output. As a result, many process solutions can be monitored: Acetic acid (vinegar), sugar, brine, alcohol, potassium hydroxide, caustic soda, alcohol, hydrogen peroxide, and calcium carbonate. Existing abilities So where is this simple, unrecognized, on-line density measurement system that can provide free process analysis? It can be found in the 400,000 Micro Motion Coriolis mass flowmeters that have been delivered from Emerson Process Management to thousands of process plants worldwide.

This by comparing the vibration of two flow tubes. The flowing mass of fluid also causes a twist in the tubes, and the resonant vibration frequency of the tube is also measured. (This has a direct relationship with the density of the fluid in the tube.) Most Micro Motion flowmeters have a second output available which can transmit this density measurement to the main control system, and act as a process analyzer. On those transmitters where the second output is not available, it is possible to upgrade the meter electronics to achieve a density output. Intelligent electronics allow the density output to be scaled into any units required, and configured to give concentration, or other process analytical measures like ºBrix (a measure of soluble solids in juice) or ºBaume (indicates potential alcohol that may be achieved) to suit the industry requirements. Where meters are used to monitor delivery lines from the output of a fi nal mixing tank, the tank contents are monitored by using a feedback loop from the discharge line. This passes the mixture through the flowmeter, via a two-way valve back to the storage tank. Only when the liquid achieves the right concentration is the two-way valve triggered to start the delivery. If the concentration falls below specification, the delivery can be halted and recycled, until the required concentration is achieved. CSD blending Liquid sugar is highly viscous, and represents a major cost element in most CSDs (carbonated soft drinks). Accurate measurement is important, but difficult for conventional flowmeters that are sensitive to viscosity changes. Density measurement is needed to monitor the sugar concentration, and plants often need this data expressed as a percentage, or ºBrix, ºBaume, or ºPlato (indicates final gravity) depending on their traditional practice. The meter’s algorithms can relate the density measurement obtained on-line to these traditional units. Micro Motion multi-variable flowmeters have been supplied to all the major cola-processing plants throughout the world. Orange juice concentrate is normally supplied at 65 ºBrix, and the units are used to monitor deliveries and control dilution in packaging plants. Sugar dosage in baby food Nutricia, is a Dutch producer of baby food, which uses various suppliers of dextrin-maltose sugar solution as a feedstock. It is important to deliver the correct sugar level into the mixing batches. These meters were installed to replace the previous positive-displacement flowmeters, and the relation between the density measurement and the delivered sugar-level (ºBrix) was investigated for use as an analytical tool. For the dextrin-maltose sugar, the standard sugar-solution algorithm available in the Micro Motion software was not suitable, so in cooperation with engineers from Nutricia, Micro Motion produced a new algorithm to relate the density of dextrin-maltose sugar solutions to ºBrix values. With on-line measurement of flow and sugar content (ºBrix), the operator can now set the desired total-sugar content to be loaded into the batch cooking vessels, and it is delivered under the control of the meter outputs. As a result the baby-food production facility has achieved an improved end-product of consistent quality. More Information www.emersonprocess.com NK.Chaudhany@AP.EmersonProcess.com