The Difference Between Gravimetric and Volumetric feed

A recent question came up for Dr. Vent Goode from a customer regarding Gravimetric/Volumetric.

Dr. Vent Goode,

I would appreciate your help on answering these questions.

What is the difference between Gravimetric and Volumetric feed?
What are the Pro’s and Con’s of each and what is the reason to go with one or the other?

Dr. Vent Goode’s response

Volumetric is a system that feeds material in cubic feet per hour, while gravimetric feeds in pounds per hour. They would both be accurate if material density was constant, but it’s not.

Dry, powdered material density can vary greatly. If it’s aerated (mixed with air) it is light and can flow like water. If it’s packed, it is heavier. An extreme case would be the same material pressed together, forming a heavy, solid rock.

On DSI systems, a certain amount of material (lbs) is required to reduce a certain contaminant. If we feed volumetrically, we would get variations depending on the current density, which can vary depending on different factors, such as how much time the material has been sitting in the silo.

The gravimetric system actually weighs the material being fed, so it adjusts for density variation. Bottom line, gravimetric is much more accurate and therefore more expensive.

We highly recommend the gravimetric when accurate material injection is important. Significant savings can be obtained with volumetric feeding, but injection accuracy in lb/hr will vary as much as the material density.

Visit these pages for more  information on Pneumatic Systems or Direct Sorbent Injection Systems.


Dr. Vent Goode

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