Do I need to trap superheated steam drip pot instead of just draining if before opening valve?

[MinnesotaSlinger]

I have in the design for my project a 4" line of superheated steam (450-500 F, 80-100 psig) connecting to the top of a 10" header. The line goes up about two feet and elbows horizontally to a manual gate valve. Just beyond the gate valve, I would put in a drip leg with a 1" drain line with isolation valve and cap at the base to allow manually draining condensate from the line before opening the 4" gate valve. The 4" line then goes upward with a 1" to 4' slope toward the point of use. (Remember, this is superheated steam rather than saturated steam.) During normal operation, the gate valve will be open, so the 4" line will be hot and pressurized. However, when the gate valve is open but there's no steam demand through the line, I would imagine condensate developing and flowing back toward the header, given that heat loses through the insulation would eventually cause condensation of the stagnant steam. I would expect that this condensate would evaporate as it approaches the connection to the 10" header, but I'm not exactly sure where. And if it doesn't evaporate until it hits the header, it will fall back into it and, I would assume, instantly vaporize as it hits the superheated steam stream. What concerns me though is that condensate would pool in the drip pot. When steam flow in the 4" line reinitiates, flow over the condensate pooled in the drip pot will likely be entrained in the steam. That condensate would, I expect, be close to the saturation temperature of the steam, given that it isn't more than a few feet of 4" piping from the 10" header through the valve to the drip pot. So, I'm thinking that the water that's entrained in the flow as it passes over the drip pot will evaporate quickly. However, I'm nevertheless wondering if I need to put a trap off of the drain line just to collect condensate that collects in the drip pot when the gate valve is open but flow in the 4" steam line is stagnant. During steady state system operation when flow is moving through the 4" line, the pipe will be hot and the steam superheated, so no condensate would be developed. I'm just wondering though about going from no flow to design system flow in that line.

In my case, do I need a trap for the drip pot? Thanks.

 

[MinnesotaSlinger]

Here's a sketch:

http://files.engineering.com/getfil...54a-177608d98987&file=4in_line_w_drip_pot.pdf

 

[MJCronin]

Minnesota...

First, it appears to me that your condensate flow is running in the wrong direction. This is causing your problems with a steam pot and trap.

It is permissible (although considered a poor practice) to have steam flow and condensate flow in opposite directions)

Second, all steam systems must start up. They therefore require steam traps.

Third, you have a modest degree of superheat and therefore can use a standard trap selection from one of the major suppliers ( Spirax Sarco, Armstrong etc) Steam traps and drain systems with SIGNIFICANT superheat (eg. Main Steam Systems in powerplants) require robust traps and a flash tank.

Suggest that you talk with the fine folks at Spirax Sarco.....

Come back and tell us of your final design....

regards

MJCronin
Sr. Process Engineer
Venture Engineering & Construction

http://www.VentureEngr.com

 

[MinnesotaSlinger]

Thanks. Actually, almost all of the steam piping in the plant slopes up. It's all superheated piping throughout the plant. Most all of my prior experience is with saturated steam with steam and condensate flowing in the same direction, that is, downhill with traps at any low point. However, this is superheated steam, and the design of the plant is to have starting load condensate flow back toward drip pots, with condensate development ceasing once pipes are hotter than saturation.

Other lines similar to the one I'm creating do not have their own traps but flow back into the header, which has a large trapped drip pot. My line, however, is different because it has a shutoff valve just off the header and a drain pot just beyond that. If condensate overflows my line's drip pot with the shutoff valve open but no flow through the line, it would just flow back into the header like the other lines off the header.

All the same, I am getting a thermostatic trap to remove condensate from the drip pot.