Condensate issues!

[Christoph]

I have a chill water system consisting of a main tertiary loop
feeding 2 dozen other branch tertiary loops. my problem is
in the chill rolls on the paper line. Control point is the exit
water temp. heated water is let out and replaced by chilled water.
Works fine while running at full speed. When line stops the
3-way valve closes and water is just circulated in the loop.
Which is cold enough to cause condensation, causing web
breaks at start up. Using an AB PLC 5/40 for control.
Any ideas???

 

[Steve Bailey]

Condensation happens when you cool the chill roll to a temperature below the dew point of the am_bient air. Plumbers sometimes feed warm water instead of cold to toilet tanks to prevent them from sweating in hot weather. You may need to do something similar when the line is stopped.

 

[Christoph]

Introduction of warm water would work but is not available

and they probably would not purchase equipment for this.
I do have steam available but would still require more
equipment and spending is a no no..

 

[Steve Bailey]

This sounds like a classic example of trying to tweak the control system to make up for shortcomings in the mechanical design. Be careful. Once you start making changes to the controls to try to fix it, you will have assumed ownership of the problem.

 

[Tharon]

So they want you to stop the water from condensating on a tube filled with cold water, using nothing more than the cold water they fill the tube with (which of course, is the cause of the problem)? Don't you hate money pinching managers?


You could just put a valve at the beginning of the system to stop all water circulation when the machine is stopped. This will make the water existing in the system stay warm (or warm up to ambi_ent as the machien sits. This would cause a longer start up (the water having to rechill everthing) but would stop the condensation from causing problems at start up.

You could also add a climate control to the area this machine is in (or adjust any existing) so that the humidity is at a level that the dew point is lower than the temperature of the chill water.

Either way, you are going to have to spend some money... nothing is free.

 

[Christoph]

I all ready own this thing and Ya I need some cash to make a good

fix, that is not likely to happen. Just thought I would
put this out here and see what great ideas it might spark
hopefully some I could use!!!

 

[rsdoran]

Is the chilled water replenished? i.e. water replaced in case of evaporation etc.? If so then change the valve to bypass the roll when not in motion.

I am at this time assuming flexo type printing press from the information, please correct if wrong.

 

[Christoph]

the chilled water loop is closed it has a make up water

feed at the circ pump. water circs thru 1 of 2 100 ton
chillers. then back out to supply the branch loops.
the chillers use tower water on the condenser side
to exchange the heat. And this application is a high speed
coating laminating line. (sticky paper)

 

[rsdoran]

I have worked with chill rolls but they can be setup differntly, just depends. Usually the chill roll is fixed with a nip roll that moves. If the chill roll is above the laminate and nip roll what you may do is make sure they separate on shutdown then pre-startup make the chill roll run independently to dispel any condenation and/or with some kind of blower drying it.

I am assuming the chill roll is a driver i.e. has a motor,if not or the rolls are fixed position then have to think of something else.

Another thought, if this is happening regularly the line ops should know to dry the chill roll, is it inacessible or hard to get to? Or is material left in the web and this happens over a short period?

 

[Christoph]

It is a driven roll it consists of 2 rolls staggered so that the
web is threaded in a s wrap and it is a tension zone, so it
also has a nip. Ops wipe it off ya! thats gonna happen. And when line
is down the web is left in the machine. The rolls are a little difficult
to get at and are about 3 feet in diameter and 100" wide
approx 130" with shaft included.

 

[RussB]

If the chilled water is not flowing it should reach ******t (room) temp. and stay there. Can you use on/off flow control?

 

[Christoph]

when line goes below 200 fpm It closes a 3-way valve that is
regulating the temp. whatever water is in the loop is now trapped
and constantly circulating. the loop holds several hundred gallons.
it takes hours for it to reach room temp. water temp is probably 50 deg F
when line shuts down.

 

[kamenges]

If you are unwilling to change your physical configuration you are pretty much stuck. I have yet to see a control system that can change a physical law.

This sounds like a water injection cooling system. So when you stop you isolate yourself from the master cooling loop but your secondary loop is still circulating. Some of your options depend on the chill roll construction. If it is an open drum construction there isn't much you can do. The majority of the water is in the drum. If this is a shell over core design then there really isn't much water in the roll and it's temperature should change relatively quickly.

Can you just shut down the pump on your chill roll water loop?

Keith

 

[TConnolly]

We raised our chiller water temperature from 10C (50F) to 12C (53F) That simple step solved most condsensation problems.

 

[Christoph]

The rolls are jacketed. And I am pretty sure I can switch the pumps.
I might have to try that. We have 2 chillers. 1 is set for 48 deg
the other for 51 deg F. This gives a little lead lag.