Electric steam superheater

[Loumolito]

I am designing a 150 psi natural gas fired steam boiler with an electric superheater raising the delivery temp to 600F.

The horizontal electric superheater has a 3/4" npt drain at the bottom of the vessel.

Any suggestions on how to handle the drain? Bucket trap to vented receiver then waste to drain? Condensate should only form on cold start-up. Superheater sales rep said to put a manual valve with hose connection (disagree completely).

 

[vpl]

I agree with having an isolation valve. Beyond that, I think it's going to depend on a number of factors such as (a) how far does the drain line have to run and (b) what temperatures you realistically (and worst case) expect to be seen at the drain.

You might ask the sales rep what their product manual says -- and ask to see a copy if you haven't already bought the superheater.

You might also ask to speak to a superheater designer (some companies still have them; quality is unknown) and ask him/her your question.

Another place to look would be an industrial boiler standard -- which might be available from your local authority.

I did a quick glance through the US Code of Federal Regulations and all I saw were requirements that superheaters had to have a drain connection without any specification of what the drain line had to be. That was a very cursory look and is not intended to be a definite "there are no requirements."

Patricia Lougheed

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[Loumolito]

I contacted a few superheater manufacturers and none were very reassuring. I requested sales literature or piping diagrams but nothing is available on the drain piping.

 

[SeanB]

Are you located in a cold environment? Is there a chance of liquid freezing? Is a steam trap feasible?

 

[Loumolito]

Superheater is indoors in a boiler room - no freezing. I think a bucket trap with a vented receiver is needed.

 

[MintJulep]

I think I'd be more inclined to use a thermodynamic trap.

 

[willard3]

+1 on the thermodynamic trap. Not many nasties in the condensate.

 

[MintJulep]

I was think more along the lines that a thermodynamic trap will close even when there is no condensate preset.

A bucket trap will piss steam and never close if there is no condensate for the bucket to float on.

 

[Loumolito]

Here's what I found from Armstrong:

Thermodynamic Disc
The disc type of trap is a time cycle device. As soon as the pressure above the disc is dissipated, the trap will open. It cycles whether or not there is condensate behind it. Since very little condensate will be present even at the trap in superheat applications, any small amount will blow through quickly. The disc does not drop in time to prevent some steam passage. Essentially, the trap is opening and closing with little or no
condensate passage. This causes a quicker cycle rate on low or absent load. The result is a very rapid cycle rate with steam passage at high temperatures and pressures causing excessive wear with the result of steam waste and extremely short life.

Inverted Bucket
The loss of prime in an inverted bucket trap will result in the valve opening and blowing of live steam. There are several ways in which this can happen; likewise, there are means for preventing this occurrence. Sudden pressure changes can cause backflow out of the trap or flashing of the prime. The means for
preventing this is to specify an inlet tube with a check valve at the inlet to the trap.

"To summarize, a properly sized and tight shut-off Inverted Bucket steam trap is the best choice for superheat applications."