Uphill Condensate Flow 2

[Pulpeng]

I have 3 condensate lines (400KPA) running through some control valves and then immediately going up into the top of the flash tank. (First off I didn't design it).

That being said I have a lot of errosion issues presumably with flashing steam through the valves driving the condensate at high velocity uphill around various elbows etc.

I've thought about a small flash tank venting the steam to the flash tank and pumping the condensate uphill but I thought I'd ask if anyone has a simpler solution? (By pumping I mean either a steam pump or mechanical pump).

 

[rmw]

Move your 3 valves to each end of their respective line right up against and as close to the flash tank you can get it. If they are joined prior to arriving at the tank, separate them and do the above.

Cheaper than installing another flash tank and a pump, and it solves the problem, not the symptom of the problem.

rmw

 

[casflo]

Before to implement the solution that rmw suggests you must check that the valves in the top of the tank have enough capacity to drain the same flow rate as now, because in the actual position the flow at the valve inlet will be subcooled or saturated but in the upper position the flow at the valve inlet could be flashed and this has impact on valve capacity.

 

[Pulpeng]

I cannot move the valves closer so RMW's suggestion will not work although it's not a bad idea.

 

[ione]

Move to a different type of valve which can handle flashing steam minimizing erosion issue. The attached paper describes three options to deal with flashing steam.

 

[casflo]

Try to change the valve downstream pipe by other of stainless steel to resist the erosion.

 

[MJCronin]

Pulp..

Consider the use of Chrome-moly piping (ASTM A335 P11 or P22). It works well for the utility industry in flashing service.

Stainless piping also has a much better life that CS in flashing service (might be too expensive..)

Or......Consider schedule 80 (or higher) carbon steel piping in the downstream leg.

-MJC

 

[Pulpeng]

A pipe material change might be in order. It certainly would be the easiest solution. We already have schedule 80 A106 Gr B.

I have a Chrome Moly spec I could use - I have no stainless spec but I'll ask if one could be made.

 

[rmw]

The condensate is going to flash coming across the valves regardless of whether they are below the tank or at the top of the tank. The valves are flashing now if they are doing the duty Pulpeng describes. The reason for recommending to put them on top was to minimize the impact of the damaging effects of 2 phase flow downstream of the valves.

Since you can't move them, then you are going to have to size your down stream piping (as well as pay attention to materials) for 2 phase flow, and possibly slug flow.

If you size the pipes right, and set the valve control function so that it is not varying too much, you might benefit from the "percolation" effect of the vapor traveling with the fluid. Coffee percolators work on that principal and boiler circulation does too. Make it work for you.

The idea of flashing to atmosphere and pumping will waste the flash steam from your condensate saturation pressure to atmosphere (unless you have a use for and a way to collect atmospheric flash). If you have lots of free fuel (bark, liquor, etc) maybe you can afford it. If you are using purchased fuel to supplement the bark and liquor, then you pay a price for your method. You can do the calculations.

rmw