Steam and Condensate Header 2

[Nik456]

My Steam requirement varies from 1500 lb/hr to 13500 lb/hr. Based on 13500 lb/hr flow I am considing 6" steam header and 4" condensate header.

For 6" line and 1500 lb/hr flow I am getting velocity of 7 ft/sec which is lower side for the steam line sizing criteria.

I was just wondring if I can use 6" Steam header and 4" condensate header for low flow case which is 1500 lb/hr so that I dont need to install separate line to cover this case.

 

[pennpiper]

Have you taken the time to create a simple P&ID flow diagram of this proposed dual service scheme?

How are you going to facilitate the crossover at the supply end of both Steam levels. And then, how are you going to accommodate all the complex piping change-overs from Condensate at the outlet of a user in one case to the low pressure Steam Supply to the inlet of a user?

You really need to create that P&ID.

 

[Nik456]

Pennpiper,

I have already prepared the P&ID but I am not sure if 6" Steam and 4" condensate header can be used for small flow of 1500 lb/hr. As it is for a batch process, flow variation is big (1500 lb/hr to 13500 lb/hr). There will be cases where plant will require only 1500 lb/hr of steam.

 

[rmw]

Unless you can stand a high pressure drop at the higher flow rate, you are going to have to size for the maximum flow and then take what you get at the minimum flow. Happens all the time.

You might split the difference and run your velocity at the higher flow to the high side of the acceptable range so as to try to help keep the velocity up at minimum flow.

rmw

 

[sshep]

There is no problem with low flow on the steam, your velocity guidence is only to help find an economical line size- too big is just a waste of money. The reliability problem with undersized lines is much more significant due to poor line trapping and erosion from high velocity entrained water drops.

The condensate lines are more of a problem to size because this is mixed phase. Again, erosion is the big problem, so make sure all line size changes (at trap outlet, mixing points, etc) are immediate. In translation from P&ID to isometric, designers might take a shortcut. Example: you want a 4" return, but your trap outlet is 2". The designer decides he can fit the piping in easier if he puts a 2" elbow in after the trap and then a 2"x4" swage. It meets the P&ID depiction, but the elbow will fail from erosion.

To size the condensate outlet line, you need to know the condensing pressure at your maximum steam flow, and then do the flash calculation. The flash steam sets the line size. It is surprising how often the flash steam is underestimated, and there have been many disasterous cases where a liquid only assumption has been used by the ignorant. It cannot be commented on if your 4" line is adequate without this flash calculation.

These are the main pitfalls that I think apply to your inquiry.

best wishes,
sshep

 

[katmar]

Excellent advice from sshep

Katmar Software
Engineering & Risk Analysis Software

http://katmarsoftware.com

 

[MJCronin]

Please explain...

How can you size a steam line without knowing the pressure ?

(I can guess that you are around 5 psig ???)

The velocity criteria, as described by Crane 410 (and others) is simple. But different criteria apply for different steam types (saturated or superheated)