Level Detection for Formaldehyde Reactor

[Fruggiero]

If you look on the attached pictures, one is a basic sketch of system with the vessel on the right being formaldehyde reactor that uses an HTF, therminol with a SG of .845 at 293 degree C, which is just below the boiling point. The smaller vessel on the left is the level gauge which uses a magnetic float and a guided wave tube. The other drawing is a graphical representation of the level in the gauge at 2 separate startup events and the temperature of the fluid.

During steady state the therminol boils but only on the surface of the coils.

The current issue is that while cooled down, the level indicates 7 inches in the site glass (both the visible float and the guided tube electronic display). Upon heatup the detector has a surge of 7-8 inches, which is considered normal for this plant due to the mass aeration of the process. The level then lowers slightly and steadies off, as is to be expected, but then there is a sudden and unexplained drop in level, followed by a slow and steady increase.

My current theory on the increase is that the vapor side is condensing at the top of the level gauge and causing a small drop in pressure. Based on the specific gravity of the HTF being about .824 I calculated that a DP of only .36 would change the level indicated in the gauge by 12 inches. This condensed vapor is then being drawn back into the reactor due to its relatively high temperature and causes natural circulation in the device.

What I don't understand is the sudden drop in level, as well as how this is not a common enough occurance that the company selling us the gauge wouldn't have known it was not suited for our application.

Please critique my theory and offer an explination for the sudden drop. Thanks everyone.

 

[eljose79]

Thank you for sharing your current issue and theory regarding the level gauge in your formaldehyde reactor system. I would like to offer some insights and potential explanations for the sudden drop in level that you have observed.

Firstly, your theory about the vapor side condensing at the top of the level gauge and causing a drop in pressure is plausible. As you have correctly calculated, even a small pressure difference can result in a significant change in the level indicated by the gauge. This condensed vapor could indeed be drawn back into the reactor due to its high temperature and cause natural circulation in the device.

However, there could be other factors at play as well. For example, it is possible that there is a sudden influx of colder fluid into the reactor, causing a decrease in temperature and subsequent condensation of vapor. This could result in a temporary decrease in level before the system reaches a new equilibrium. Additionally, there could be variations in flow rate or other process parameters that could affect the level in the gauge.

It is also worth considering the design and installation of the level gauge itself. Is it possible that there are any leaks or malfunctions in the device that could cause sudden drops in pressure or changes in the level? It may be helpful to consult with the company that sold you the gauge to ensure that it is suitable for your specific application.

In terms of the sudden drop not being a common occurrence, it is possible that the conditions in your reactor are unique and not encountered by other users of the same gauge. It is also possible that the sudden drop is a result of a combination of factors that are specific to your system.

In conclusion, your theory about the condensation of vapor causing a drop in pressure and subsequent changes in the level gauge is a valid one. However, it is important to consider other potential factors and to thoroughly investigate the design and installation of the gauge to determine the root cause of the sudden drop. I hope this helps and wish you the best of luck in resolving your issue.