Currently have a transmitter for LP Steam Flow. The transmitter is set 0-47.5" H2O. The control room sees it at 0-75kpph. They are having an issue with the kpph going too high and into bad quality causing issues with 3 element control (LP drum level). I was asked to re-range both inches of water and kpph (0-100kpph). I am not familiar with the conversion and have researched and didn't find anything helpful. Any and all advise greatly appreciated!!

 

You don’t say whether this is a new problem or not. Has the plant been upgraded or changed so the LP Steam is now greater than the original design? Or has this been a problem from the beginning?
First, dig out your flow element calibration sheet. It will tell you the design point of the flow element. (This is usually the maximum flow point.) The design point parameters you need are:

1. Mass Flow(kpph)

2. Steam Line Pressure (psia)

3. Steam Line Temperature (degF)

4. Flow element differential pressure (inches H2O)

Is the design flow 75 kpph with a design differential pressure of 47.5” H2O? If so, then either the flow element was improperly specified, or plant conditions have changed.

If the calibration sheet shows maximum flow at or near 100 kpph and a correspondingly higher differential pressure, then your system is mis-calibrated.

The next issue to deal with is how is the current flow calculation done? Is there a “flow calculation block” in the control that has above 4 parameters as inputs (constants)? (Pressure parameter could be in psig, since most pressure transmitters are gauge pressure rather than absolute pressure.)

Answer the above, and I will make a recommendation on how to proceed.