Control.com - Nerds in Control

In our installations, we have two moisture analysers. One is used to measure moisture in instrument air and the other is used to measure moisture in natural gas. The unit of measurements of both analysers are in PPMv (Parts Per Million by Volume).

We convert these measurements in LB of H2O/MMSCF (Pounds of water/Million Standard Cubic Foot).
We want to know the equations or procedure that can allow us to convert the PPMv measurement unit into H2O/MMSCF in both natural gas & instrument air.

I will appreciate any help.

Hi,
I'm interested to know why you should want to convert a ratio into archaic units. If you are doing further calculations downstream, I would have assumed that a simple ratio would be more useful.

Marc

I don't see the value of measuring the moisture content of instrument air in ppm. A more useful unit is dewpoint which must be measured at full system pressure (as the dewpoint temp rises with pressure). I know that if the dewpoint is greater than or equal to ambient temperature, the moisture will condense and cause big trouble for pneumatic devices.

Our dessicant dryers use dewpoint analyzers to trigger regeneration. This is a more efficient method then timed regeneration, and saves wear and tear on the compressors. OuR DCS monitors the dewpoint temps and alarm if it gets much above -40 degrees.

I understand the historical value of using LBS-H2O/MMSCF. Unfortunately there are no officially approved equations that work. ASTM has some equations but they do not work well for low dewpoints.

The IGT published tables, back in the mid 1950's, derived from empirical measurements, but they have not provided equations.

You can download a moisture conversion calculator from www.phymetrix.com that will perform both kind of conversions; if you need the formulas you can look up the ASTM equations or contact phymetrix.

Hope this helps you.