Boiler water flow fluctuation issue
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In our plant, the process involves the deaeration station, which uses boiler feed pumps to raise the boiler water from 25 Kpa and 103 degrees Celsius to a pressure of 60 kilograms per square meter. This water is then sent to four steam drums through four control valves; the capacities of these drums are A: 160T, B: 40T, C: 15T, and D: 50T. Only drum A’s pressure may fluctuate from time to time to 140T, while the pressures of the other drums remain relatively constant； If the valve does not operate, it will automatically return to normal after about one minute; sometimes it does not return to normal, but adjusting the valve can still keep the pressure at 160T. There is only one control valve in this pipeline. Previously, it was suspected that the actuator was not functioning properly, so three new Fox 520 series actuators were installed, along with a valve position feedback system. The valve body was inspected twice, and no foreign objects were found. It is a single-seat control valve without a valve cage ； The pumps are arranged in a two-in-one-backup configuration; attempts were made to switch pumps, but with no effect. Even when the valve position feedback remained unchanged, the flow rate still fluctuated, and the pressure at the pump outlet increased while the current drawn by the pump decreased. Vibrations at the site were quite severe during these fluctuations. Please help identify the issue – what other factors could cause such fluctuations? The attached diagram shows the fluctuations in flow rate; another diagram depicts the pressure fluctuations. The pressure values are from three transmitters, while the diagram showing valve positions indicates that the movement of the valves is not caused by the flow rate itself, but rather by operator control
Based on your description, I personally think the possibility of inaccurate instrument readings should be ruled out. Since the behavior of the pump when the flow rate fluctuates is entirely consistent with its performance under those operating conditions, it is recommended that your technical team check whether there have been any changes in the operating conditions of the rear boiler – for example, whether there are significant changes in the steam generation rate or load, as well as examining parameters such as the range of boiler pressure fluctuations. Also, can’t your DCS system analyze some interrelated parameters together? That is more intuitive, and the sequence relationship is also clearer.
No, this is a new installation; the boiler’s water pipeline network is not connected to the system – there is simply a separate deaeration station that supplies water to the boiler
It would be best for the poster to plot traffic, pressure, current, and feedback on a trend chart, and add annotations to explain the values on that chart. Mark 2 or more eigenvalues for each curve if necessary
Personal opinion: Control in two steps: First, use a pressure transformer to control the feed water pump in order to achieve constant-pressure water supply. Second, use the water level to control the opening degree of the inlet valve. This way, the disturbance will be smaller.
Based on the situation described by the poster, the possibilities related to instruments and pumps have been ruled out. Apart from the load variations mentioned by Haiyou, it is possible that foreign objects are causing blockages in the water supply as it passes through devices such as the economizer containers; this needs to be checked.
No, I’m referring to fluctuations in the steam pipeline network. Fluctuations caused by the pressure in the steam pipeline network or the quality of the boiler water act on the water supplied to the boiler through a three-impulse mechanism