I am working on the RFG flow meter 51FT7133.

Originally the D/P flow transmitter was set to the manufacturer default of 210kpa.

Based upon the provided flow calculation (attached) we changed the flow meter calibration to 75Kpa (no square root extraction implemented in the transmitter).

The Mark VI Analog input for this instrument was originally set to 0-101 PSI, we have changed the analog input to 0-10.8778 PSIG corresponding to the calculation sheet. The temperature signal was 0-212F, we changed this to 32-212F to correspond with the field instrument range of 0-100c.

This D/P signal then feeds into a “mass flow” block within Mark VI with inputs from the static pressure and temperature transmitters and a constant.

When we simulated process values as per the supplied calculation sheet (D/P = 75Kpa, Pressure 20 BAR, Temperature 60c) the mass flow output on the Mark VI graphic (and our DCS) showed a flow of about 3600 KG/HR rather than the expected 8132 KG/HR.

Can this please be quantified, are we doing something wrong?

Because we are using the DCS flow for the control on a Fuel Gas heater system the figures are not only important for the operation of the GT.

A prompt reply would be appreciated.

 

Was this working before?

Attachments cannot be attached to posts.

If it was working before, then something is amiss with the configuration changes being made.

If it wasn't working before, something is still amiss with the configuration.

Certainly this can be quantified; it's all mathematics. You should be able to use the Block Help function, or dig into the macro if it's a macro, to see how the Mark VI is calculating the flow.

 

You don't say whether the Mark VI is the GT control or whether it is a BOP (DCS) control panel. If GT, then all calculations will be done in English units. If BOP, they may be in SI units.

Regardless, you need to use a consistent set of units for the mass flow block. There is an input to it that defines which units are to be used (use the block help in toolbox). You may have something wrong there - 3600 Kg/Hr is close to 8132 Lbm/Hr. Besides the differential pressure, line temperature and line pressure signals, the block needs as constants the design pressure, temperature, differential pressure and flow in the same consistent set of units as the signals.

You also did not say what the calibrated range of the line pressure transmitter was - if there is no pressure transmitter then you have to use design pressure, but accuracy will suffer if the line pressure varies.

You need to get the design point values from the flow orifice manufacturer's calibration data.