We know what problem we have to deal with when reboiler(s) is placed on independent steel structure. WNC load case may present a real challenge when spring supports must be used.
In my particular case operating movement is 1 (one) inch upwards and upon activation of springs prior to startup, when reboiler is empty, upward thrust force acting on the upper channel side nozzle is absolutely not acceptable. Operations do not approve priming of the vessel before startup and moving supporting lugs down to a skirt elevation is not possible.
My question is about "dual duty spring supports". One of a major vendors in this business claims that an assembly with two different duties spring coils, one of them placed onside of the other one, equipped with an extra hardware can do the job. I cannot visualize how it can work and am highly sceptical about it.
Has anybody ever had a chance to deal with such a problem?
Any ideas would be welcome.
Thank you

I realized that had not been clear enough about type of service. It is hot service, so tower (column) expands thermally one inch up.

It is still difficult to visualize the problem with the available information in my opinion. A sketch would be beneficial for the discussion.

Jerry, I hope what you are speaking is a generalized issue with reboilers as it is supported on springs which may cause issue with nozzle loads and stresses during start-up/normal/shut-down cases.

What I used to do is to calibrate springs for average of empty and operating (filled) condition & then play with the installed loads marginally to qualify the nozzle loads in all conditions.
Do remember that you don't excessively pull or push the spring. Also, PTFE load flange will help to reduce horizontal loads on nozzles and structures.

Dual-type springs is not known to me.

There are sway braces with some stiffnesses uptil some load & other stiffness for higher that load. But that would probably not serve the purpose for your case.

Hope it helps.

Spring with a lock limiting the upward diplacement may be an option. This way during start-up, i.e. the reboiler empty case the springs will not overload the nozzle.