Measurement problems of orifice plate flowmeters
Thread Content
Excuse me, our EJA orifice flow meter measured 110 tons per hour of rich amine fluid yesterday. Today, the process conditions and reactions remain unchanged; there are still two reference flow rates involved – the ammonia-poor liquid coming out of the unit, and the ammonia-rich liquid returning from other units, with both amounts being around 110 tons. However, the flow rate for this unit is 150 tons per hour. It was checked that the pressure tap pipes were unobstructed, and after replacing the EJA transmitter, the flow rate remained at 150 tons per hour. There are no issues with the configuration, cards, or wiring. What could be causing this?
Is a orifice plate used with a transmitter? Check the zero point and range of the differential pressure transmitter, as well as whether squaring is applied
The gauge was taken out for inspection; the zero point was normal, and the range setting matched that of the DCS. The flow rate was normal yesterday, but it’s different today. The output from the gauge is linear, square root calculation is performed on-site, and the readings inside and outside are consistent – no problems detected. The amount of material processed is about 30 tons more than normal, but no issues were found with the gauge; the cause remains unknown
I think you should first take a look at this traffic trend; it might provide some directions for the search.
I don’t know much about the process. It is unknown what the viscosity and freezing point of the rich amine solution are, but under these conditions, it is recommended to check whether there are any particles attached to the orifice plate, which could cause an increase in differential pressure. Since the transmitter measures the differential pressure, the greater the differential pressure, the higher the corresponding flow rate.
Well, that makes a lot of sense, thank you!
Based on what you’ve described, the transmitter should be fine; the key issue lies in the pressure transfer tubes. If the operating conditions have not changed, it is recommended that you check whether there are any leaks in the pressure transfer tubes on the negative pressure side. Also, does your flow meter have temperature and pressure compensation? Both temperature and pressure have an impact on flow rate
Check the two signals for temperature and pressure compensation; if it’s not a process-related issue, then one of these two signals must be defective.
I wonder how long your orifice plate has been in use?
The pressure tap is unobstructed, and no signs of leakage have been detected. The maximum load at which the process pump operates at its power frequency is 127 M3/h; therefore, a reading of 157 shown by the instrument must be problematic
It’s not steam flow rate, so there’s no need for temperature or pressure compensation. Moreover, the flow rates measured before were always normal; the problem only started appearing in the past few days. I still suspect that there’s an issue with the instrument transmitter or the orifice plate – I can’t think of any other possible cause!