Blending and Distillation

Mon, 01/29/2007 - 4:31am

How to Monitor Liquid Density

Distillation, fermentation, or liquid blending operations in large tanks frequently call for real-time monitoring, measuring, logging, or controlling of the density of the liquid during the operation. Using traditional hand-held instruments to do this job can be costly and labor-intensive. So says George A. Articolo, Ph.D., with Sundial Analytics LLC, the Marlton, NJ, producer and distributor of process control liquid instrumentation products.

To illustrate his point, Articolo offers an example involving a container of an alcohol-water blend of density 0.810 sgu. Imagine it's necessary to dilute this mix with water of density 1.0 sgu until the blend has an overall density of 0.940 sgu. By what means do you monitor this blending operation to eventually meet the target density? He says using traditional hand-held hydrometers — assuming you're close enough to the tank to use them — would force the sequential adding of water with measurement of the blend after each addition. This would certainly be a time-consuming, costly operation. Furthermore, if the tank is remotely located or very deep at the desired point of measurement, then the problem is even more difficult.

Articolo believes such an operation is more efficient if real-time measuring and monitoring of the liquid density is performed — continuously — as the water is added. What is best, he says, is monitoring the liquid density and controlling the amount of water going into the container until the target density is met. There is an electronic hydrometer made by Sundial Analytics that can handle such a task. The hydrometer uses a rugged, portable, freestanding, submersible probe that allows for continuous, infinite resolution, real-time monitoring and logging of liquid density during fermentation, mixing, and blending operations. In addition, it provides an analog output (4-20 ma or 0-5 Vdc), which can be used as a signal for control functions such as turning valves on or off. The hydrometer is shown here with the submersible probe connected by way of a lead wire (4-100 feet) to the electronic module. The probe is 10 in. long and 2 in. wide. The module provides power to the sensors (120 Vac or battery) and contains a programmable process meter that can be pushbutton-programmed to provide digital panel readout of the density in the preferred engineering units (sgu, percent concentration, Baume, Brix, etc.) The module can accommodate optional microprocessor boards that provide a choice of analog output (4-20 ma or 0-5 Vdc) for process control or an RS232 serial port interface and recording software for real-time continuous monitoring and logging.

More information about this instrument is available at

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