Ice buildup on intake screen

[sloughshark]

During the construction of ice roads on lakes and rivers north of the 55th parallel water is pumped to the surface to thicken the and strengthen the road. Water intakes are repeatedly plunged into water and then lifted back into sub zero air temperatures and transported. Time of transport ranges but averages 30 minutes in -20 (celcius) temperatures. Due to environmental regulations a screen must now be placed on the intake.

My concern is how much and how quickly ice will form on screen material?

If anyone can help with the thickness of the water film that would give me a place to start.

Thanks in advance.

 

[dicksewerrat]

Use a removable screen. Then you put on a new screen when the suction hose is taken out of the water. The wet screen can be placed in a warm spot, inside the trck near the heater, to dry as you are moving to next site and while pumping.

 

[jheidt2543]

Doesn't the ice melt once the screen is put back in the water?

 

[sloughshark]

Thanks guys,

The removable screen might be a possible alternative, however we then run the risk of the operator running the rig without the screen, as was done in the past, and setting us up for fines and additional legal actions.

In most cases the ice will hopefully thaw when the intake is returned to the water, but when dealing with rivers the heat transfer rates provided by the flowing water can not only resist thawing but may induce ice build-up.

This problem is definitely testing this bioengineers knowledge of second year university.

 

[ishvaaag]

If your problem is that ice forms at the screen when transporting the contraption from some point to the next, the solution must be in making a source of heat compatible with the mouth also portable. At -20ºC and with a film of water at the screen the period for the formation of ice must be very short, since you have basically what is an very big surface with very little material to cool, both screen and water.

 

[RDK]

You can buy propane infrared heaters that will produce 15,000 BTUH and operate from a standard 20 lb BBQ tank.

These cost around $CDN150-$200 and a bottle is another $CDN 50 or so. A $16 refill will last several hours.

Why not just get one of these and thaw the screens before re- immersing them? You might want to use a tarp if it is windy.





Rick Kitson MBA P.Eng

Construction Project Management
From conception to completion

http://www.kitsonengineering.com

 

[tgreif]

You are most likely going to experience what's referred to as "frazil ice". This is ice crystals that form on water plant or power plant cooling water intake screens at freezing temperatures and below. It's a common phenomenon. You can read about the cause in the following link.

http://www.crrel.usace.army.mil/techpub/CRREL_Reports/reports/CRTD91_01.pdf

 

[sloughshark]

Ah yes, frazil ice.

Well thanks for the insight, the link was very informative although there doesn’t appear to be a very thorough understanding of frazil ice nor remedies for it. I guess we’ll have to go with some sort to resistance heating in the screen.

 

[aviat]

Even if your system does freeze up, if you pour some warm water on it it will thaw out with no problems. Some other means to consider are:

Mading up a small tank, posible out of a 45/55 gal. drum, with a means of securing the end of the hose in it, and then putting hose in tank along with some water. The movement of the truck would prevent the water from freezing for more than 1/2 hour. If you are not moving you could use the air system from truck piped into tank to provide movement to the water. Of course system would have to be dumped if truck is to be shut down overnight.

Another way is if you could find a way to put end of hose back into your tank, below water line, then it would be no freezing as long as there is water in that part of tank.

Other than that a barbecue sized propane tank and a tiger torch would be good for heating. However below -40 the propane tank would have to be kept warm as it won't work otherwise.

I don't envy the people doing this job. You end up covered in ice. Been there! Done that!

 

[Focht3]

Following on [blue]Aviat[/blue]'s suggestion:

Why not construct a short extension to the truck's exhaust system so that the exhaust flows through a small barrel of water on the back of the truck? The scavenged exhaust heat should keep the water pretty warm; then you can put the screened end of the hose into this tank when it freezes up.

And you won't have to worry about the propane if the temperature drops below 40 below.

This approach will work best if your pump uses a PTO from the truck's engine, and not a second engine.



Please see FAQ731-376 by [blue]VPL[/blue] for tips on how to make the best use of Eng-Tips Fora.