A newcomer to design wants to ask the experts here a question regarding steam measurement
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First, I would like to pay my respects to all the seniors here~ There is a problem at present: it involves a DN350 pipeline for steam at 1.0 Mpa, with flow rates of over 50 tons during start-up and shutdown operations, and less than 10 tons under normal conditions. The required accuracy level for measurement is 1.0 grade. The integrated orifice plate flow meter in use has reached its limit; I’m not quite sure why it shows such high values – the actual flow rate is only around 5/6 tons, yet the DCS displays values of around 53 tons or in the 50s. Operators use the value shown on the DCS, divided by 9.5, as a reference figure. Since this flow meter needs to be replaced, I first of all don’t understand what’s going on with the over-range issue, and I have no idea how to proceed. Could some experts please give me some advice?
Is there a problem with the flow meter? Can it be calibrated?
How about checking what the flow meter on site shows first?
Try cleaning the pressure guiding tube of the orifice flow meter, or recalibrate the differential pressure transmitter. By the way, how long is your pressure guide tube? Where are you located, or what is the current temperature in your surroundings?
Steam pipeline with a pressure of 1.0 Mpa and a diameter of DN350; flow rate during startup/shutdown is over 50 tons, while it’s below 10 tons under normal operating conditions. The required accuracy level for measurement is 1.0 grade. Given your measurement requirements, choosing an integrated orifice plate is questionable. It is well known that orifice plate flowmeters have relatively low accuracy among all types of flowmeters; when used to measure steam flow, their accuracy cannot even reach the 1.0 class. Based on a capacity ratio of 50 tons per start-stop cycle, it is clear that orifice plates cannot meet the requirements. An actual flow rate of 5 to 6 tons is essentially at the very lower limit for measurement by orifice plates; it’s doubtful whether such a flow rate can be measured at all, and if it can be measured, the data obtained will not be reliable. For a problem like the one mentioned by the original poster, the most likely cause is an issue with the flow meter measurement system. First, check the positive and negative pressure chambers as well as the pipes, as these are the areas where problems are most likely to occur. This is especially true when the furnace is shut down for a period of time before being restarted, as impurities can accumulate in the pipes, blocking the flow of fluid and preventing the positive and negative pressure chambers from maintaining a stable zero level. For systems that use orifice plates to measure steam flow, it is advisable to perform regular drain cleaning and check the dynamic zero point, addressing any issues promptly.
Go and check the data displayed on the instruments to see whether it is differential pressure or flow rate; calculate it to see if it matches what the system shows. Also, verify that the ranges for differential pressure and flow rate are set correctly
Are the measurement ranges consistent? Does the zero point return to zero?
Thank you all. I later found out that the error in the range was caused by a design flaw from ten years ago