Using Steam as a Coolant? 2

[BoilRUP]

I am a recent Purdue Grad, and I am currently employed for a company that does consulting for Northwest Indiana steel mills. I have been presented with an interesting study for my current project. A steel mill is has asked my employer to investigate the potential of cooling an oxygen lance using steam. The system currently in place uses spray water to cool the oxygen lance (the oxygen lance blows oxygen into the steel making vessel) and they want to replace the spray water with steam. The reason being is that if the current system was to leak water into the vessel, before the heat was poured, it could cause a catastrophic explosion. It has been my task to see if this is going to be possible using the existing system, which is a ring that sprays water 315 degrees around the lance, and steam that is produced by the cooling hood.

My initial thoughts were that steam would be very poor at removing heat from the lance. I thought that steam would insulate the lance from the ambient air and slow cooling. Thus, reducing the life of the lance and increasing cycle time per heat. Assuming the lance is 1600 F, and steam at 400 F; will the steam be able to remove heat from lance? Perhaps somebody could shine some light on the subject. I am not familiar with steam being used to cool anything, has anyone come across a similar problem in the past?

 

[zdas04]

The reason that steam is rarely used as a coolant is that it is a very poor coolant. With your water cooling, you get the benefit of the latent heat of vaporization. With steam you get very few BTU's per unit temperature change, so it takes a lot of steam to remove the same amount of heat that a very small amount of boiling water would remove.

It can be done, but it is expensive and takes a lot of steam.

David

 

[racookpe1978]

Compare, for example, what the result would be if you used air (at 70 degree ambient, cooling down even more as it expanded passing down the pipe) to steam as a cooling medium passing down the lance at 400 degree.

The delta T (lance to cooling medium) is greater with air, and the transfer coefficient (from the lance to either gas) is similar.

So, why not use air? Would the steam (not containing free O2 but with water vapor) be safer/better for the processed steeel characateristics when it hits the metal?

 

[BoilRUP]

Throughout the course of the day more information was come to light and I have come to realize that my understanding of the problem was incorrect. The spray water currently used does provide cooling but it provides another more important function as well. When the cooling water hits the oxygen lance it forms a steam barrier around the neck of the lance port. This barrier reduces the venturi effect created by the blowing lance. This reduces the amount of air borne contaminants and other undesirable ingredients from fouling up the soup so to speak.

So now the question becomes if steam is run through lance port, in the place of water, will it survive? The lance port is double walled steel plate with baffles for water to flow through. I think this opens up another list of unknowns that I am going to have to get pinned down before I can proceed.

Thank you to everyone who replied to my post. This is my first thread I have posted and I find it a very valuable way to organize your thoughts and think about a problem.

Best Regards to all.

 

[zdas04]

You'll have steam at the nozzle in either case. You just have to figure out how many BTU's are required and determine the required mass flow rate of steam and water to accomplish the heat transfer. In either case with that magnitude of heat source I'd expect that the steam at the nozzle tip to be super heated, with heat transfer characteristics similar to any gas.

David