Boosting Blending Accuracy

Optimizing operations using coriolis technology

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One major benefit of continuous blending with automatic control is enhanced operator safety. The elimination of mix tanks reduces operator risk from material exposure, and eliminates both inert blanketing of related vessels and entry permits. In addition, continuous blending allows a smaller amount of noxious materials at any one location.

Coriolis and continuous blending

One processor of home products successfully installed several lines of continuous blending modules. One stringent requirement of this processor is that the finished products must be perfect, with no variations in product quality. To help accomplish this, the processor decided to use only coriolis meters.

Typically, continuous blending units such as the one used by the home products processors are designed and shipped as pre-assembled and tested modules that measure about 12-feet (ft.) wide, 50-ft. long and 8-ft. high. Each module contains a coriolis meter and a metering valve for each ingredient, as well as many transmitters for pressure and temperature, static mixing, a control panel for the programmable logic controller (PLC) and other instrumentation. Spool pieces can be removed to make process changes or to add process analytical equipment.

Many continuous processes are in some respects batch processes in the sense that the modules could run for years without change. The home products processor actually has more process flexibility than that. Processing durations or operating rates can be adjusted to suit a just-in-time market; additional inputs can be used for new ingredients or clean-in-place (CIP) fluids. The individual input line metering system can be used for detergent conservation and high-purity water.

Coriolis meters offer more than mass flow rate signals. They include volumetric flow, fluid temperature and density, and calculated density-type variables such as Brix, American Petroleum Institute (API) and others. In addition, a 4-20 mA direct current signal from a pressure transmitter can be fed into the flow transmitter and re-transmitted digitally, saving wiring. Fig. 2 shows a cutaway view of a coriolis flowmeter.

Figure 2. Cutaway of a Coriolis Flowmeter

Coriolis meters offer volumetric flow, fluid temperature and density, and calculated density-type variables. Drawing courtesy of Micro Motion

 

Conclusion

Continuous blending offers a time- and space-saving alternative to batch blending. When coriolis meters are used in an automatic-control continuous blending application, whether the application is an upgrade of an existing process or installation of a new process, chemical plants can:

Improve product quality.

Enhance on-stream time.

Optimize floor space.

Reduce staffing costs.

Improve safety.

Improve process information from control system.

Boost product delivery reliably.

Minimize waste disposal. CP

Donovan is an applications engineer for FABCON, a division of PC & E in St. Louis. PC & E is part of Emerson Process Management. He can be reached at jerry.donovan@pceinc.com.

 

Some coriolis meters might have "unadvertised" capability ," in the home product processor's case, a relative-viscosity calculated variable. Although not in standard units of poise, saybolt seconds universal (SSU) or stokes, the variable is relatively accurate and repeatable. It is an important quality variable. Any of these signals, as well as mass flow and density, can be transmitted. Hart, Modbus, Profibus PA and Foundation fieldbus are all available, depending on model selection.

 

The use of coriolis meters can improve blending operations, however, providing a highly accurate automated approach. In batch blending operations, the only measurement technique that can approach the accuracy of coriolis meters is weigh cells. However, for these cells to achieve a reasonable accuracy, a weighed tank must be supplied for each ingredient, and concentrations of feed solutions must be accounted for, typically by density measurement.

 

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