5 replies to this topic

[fahrudin]

All,

any body could give guidance, how to calculate steam rain out from the silencer? how much portion of rain out and the distance of release.

there are access route for operator nearby silencer, and we worry rain out case if steam released from silencer and getting touch to body.

 

thanks for sharing your experience.

[thorium90]

I assume steam rain refers to the droplets of water from the steam vent that has a silencer? Normally its pretty high up and directed away from where people will walk. The droplets are not harmful and are not hot, just slightly warm by the time they reach the ground. Most people wont feel anything as they will likely be wearing clothes and other PPE when they walk by. Even if it did drop on them, its too small to feel.

 

Most of the steam will remain as steam and rise up, even during larger venting it definitely wont be pouring hot boiling water to the people below.

The amount of droplets formed is about proportional to the pressure of the vessel it vents from. The higher the pressure the lesser the droplets.(Although there are quite a number of other factors like piping and equipment in between).

 

As to the calculation, is it really necessary? The amount of droplets formed is minuscule as compared to the amount of vented steam and depends on quite a number of factors and assumptions, to the point that any calculation would likely have large amounts of error. If you are really worried, you can place a bib just below the vent and drain the condensate to the ground by a tubing.

Edited by thorium90, 20 February 2013 - 10:04 AM.

[fahrudin]

Thorium, i also feel like your opinion, 

but when i try to find by the some tool (to find flash fraction). I've got around 90% is liquid phase.

this the data (LP Steam)

P= 4.7 barg

T=150

 

final pressure is 1.02 bara (as the ambient condition)

when I try to solve by software, the result liquid phase is 90%.

I am not sure with this calculation result, it quite big enough.

[thorium90]

I think I get what you mean. You simply put the pressure in through the software, put a control valve, put in the outlet pressure and you get a vapor fraction of 0.1.

 

I take it you put vapor fraction for the inlet stream as 0? Saturated liquid? Do take note that you are relieving the saturated steam and not the saturated liquid....

 

I also assume your vent is connected to a blowdown drum? You can check the P&ID or you can trace the lines on site. The drum acts like a knockout drum.

Edited by thorium90, 20 February 2013 - 10:02 AM.

[fahrudin]

Thorium, this vent silencer is not connect to the blowdown drum.

but this directly vent to the atmospheric, at quite high position. there are control valve (PV) on upstream of each silencer.

operating philosophy of the control valve is only open when the steam line is reach the set point to maintain each steam line not more than certain limit (4.7 for the LP steam and 43 for the HP steam) as the control to maintain stable operation (if silencer are not adequate there are still any PSV as the final protection).

[thorium90]

Well, no worries, the blowdown drum will remove most large droplets but vent directly to atmosphere is still acceptable, it still wont be spraying hot water on the people below. Just some occasional small drops.

Edited by thorium90, 21 February 2013 - 01:10 AM.