2 replies to this topic

[Art Montemayor]

Mobile:

Please refer to the attached Excel workbook for a sketch of your system. If your Propane evaporator was operating normally before the last turn-around and it now is not, and your demand for make-up liquid propane through the kettle's expansion valve has decreased while the outlet temperature of the natural gas has increased, then your kettle coil is fouled - either on the natural gas side or on the shell side. Hopefully, it is found to be on the tube side - which should be accessible for cleaning.

I don't believe that your H.P. liquid propane make-up liquid is at "11 barg and 38 DegC" as you state. You may have made an error and mean 12 barg. Is this correct?

Your explanation of how the make-up propane is introduced into the evaporator doesn't equate to how I believe it is operated. Perhaps I am wrong, but I believe the evaporator liquid level is controlled as I have shown it in the sketch I supply. Sometimes, in very small and cheap refrigeration systems, an internal level float valve is used to control the refrigerant level automatically. This is a very cheap and inflexible way to do the job and I would not recommend it for an important and critical service as is an LNG plant. What I show is how an LNG plant normally is designed to function in prechilling the feed natural gas. Correct me if I am wrong.

I hope this helps you resolve your fouled evaporator situation. Please give us feed back information on how this problem develops and how it is resolved. We appreciate any feed back information on our recommendations. Good Luck.
 Natural_Gas_Prechiller.zip   276.09KB   131 downloads

[eilpar]

Mobile,

You say that you noted the deterioartion only after the shutdown and can I assume that the performance was satisfactory before that?. How rapid was the performance deteroration? Did it work well for some time and then gradually deteriorated or is performance bad right after shutdown?.
Any fouling will take some time to buildup so please check the period. I generally have the opinion that both the natural gas and the propane are reasonably clean fluids, so I do not know if there are any reasons to foul up and that too after shutdown. Are there changes in the properties or sources of these fluids?
As Art pointed out if there is problem with LC some tubes might have beed exposed to the vapor and hence there is loss of capacity.

I do not know how much I am helpful, but I wanted to share my thoughts.

Regards

PAR