Have a question about orifice plate flow meters?
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During the startup of the ammonia synthesis system, a problem was detected with the natural gas flow meter; upon inspection by the instrumentation team, it was found that there was a blockage in the pressure tap tube of the orifice flow meter. The flow rate before treatment was 3050 NM3/H. The flow rate after treatment is 4170 NM3/H. During driving, our load keeps increasing. I would like to ask. Will this error before and after processing increase as our load increases? In other words, if the natural gas flow rate shows 1500 NM3/H before processing, what is the actual flow rate? What is it when 2500 NM3/H is displayed? I’d appreciate some guidance from those who know more. I have high-level craftsmanship skills, but I don’t understand anything about instruments.
Due to their limited accuracy, orifice plate flowmeters are not often used for precise measurement. If your production conditions are demanding, it is recommended to choose other types of flowmeters. The problems mentioned in the text should not occur, as long as your process conditions meet the requirements of the flow meter, the deviation will not be that large. The above opinions are for your reference!
This problem is caused by the pressure tapping tube, so it’s difficult to analyze, as there isn’t necessarily any pattern
Agree with the opinion from the 3rd floor; if there is an opportunity for parking and maintenance, it is recommended to thoroughly disassemble and inspect the orifice plate, or use another type of flow meter, along with adding temperature and pressure compensation.
The errors caused by blockages in the instrument pressure guiding tubes are not regular; they are not errors inherent to the instrument itself, and such errors do not remain constant linearly across the entire range of measurement.
I wonder if the traffic from your company is not used for trade settlements? For trade settlement, it is recommended to use flow meters with higher precision. The progress of orifice plate measurements is not very high. From your description, it seems that the positive-pressure section of the pressure-taking pipeline is a bit blocked. I wonder if the pipes are clogged by polymers? The pressure tap section can be cleared using a pressure testing pump, and the pressure sampling holes of the orifice plate should be thoroughly cleaned whenever there is an opportunity to stop the system. The error caused by a blocked pressure tap cannot be quantitatively calculated. I’m not sure if your measurement system has temperature and pressure compensation; if not, it is necessary to add such compensation.
In situations like the one you described, there is usually no reference performance value. The reason for the pipe blockage – is it due to an increase in load that exacerbates the blockage? Under the same conditions of blockage, the error should not increase; rather, it should decrease. As the load increases, the differential pressure also rises, and the effect of the blockage-related error decreases. However, the exact amount requires calculation using formulas.
It is recommended to install a demister on each side, the high-pressure side and the low-pressure side, before the fluid enters the transmitter, and to carry out regular drainage.
It would be better to fill the pressure tap conduit with an isolation fluid.
I agree with the opinion above; isolation tanks can be added to the high and low pressure sides of the differential pressure transmitter, which helps to prevent clogging. If accurate measurement is required, an eddy current flow meter that comes with built-in temperature and pressure compensation could be considered – its measurement accuracy can reach 0.5 grade, it performs well, and requires little maintenance.
It’s completely blocked; the displayed traffic volume has no relation to the actual traffic volume. If there is a slight amount of traffic flow, the displayed value is more or less accurate, though there is a delay in the display
The orifice plate flow transmitter on the rich oil pipeline of the coke oven feed tube furnace in our company has also been showing abnormal readings recently; the displayed values fluctuate sharply, jumping from positive values to 0 and then to negative values, going back and forth. After cleaning the pressure-taking pipeline and the balance valve, the fluctuation problem improved. It’s likely that the cold weather caused the rich oil to become thick and viscous It should be better if an isolation fluid is used. If the pressure measurement pipeline is blocked and the pressure reading is inaccurate, why would he panic?
I recommend a flow meter to the original poster: its pressure loss is 0.3 times that of an orifice plate. It requires a straight pipe section of 0.5D on each side, and its accuracy is 0.5. It is an energy-saving flow meter. You can search for it online if you need it.
Based on what you’ve described: if the pipeline for instrument measurement is properly handled, and there are no issues with the orifice plate calculations and instrument selection, the error will not increase；