5 replies to this topic

[reckless]

We are having problems in our steam disengaging drum. Basically, it is designed to accommodate 32 MT/hr steam production without carry-over but we are currently seeing this significantly after operating above 28 MT/hr. We are currently looking into the design of the drum for improvements. In parallel, we are thinking about installing another drum thus we would like to know the best orientation of their installation (parallel or series). We would highly appreciate your inputs on this.

[Zauberberg]

And we would appreciate a sketch at least, coupled with design vs. operating data of the system. In addition, if you can write whatever you have done so far, and what are the results of your investigation work - that way we could be of more help.

Best regards,

[ankur2061]

reckless,

A steam disengaging drum is a very specific term for a two-phase vapor liquid separator in the sense that it separates steam from condensate and functions to produce essentially dry steam from the vapor outlet nozzle while removing liquid condensate from the liquid outlet nozzle.

There are some essential things that you need to check for the proper functioning of your existing "steam disengagement drum":

1. Is there a demister pad or mist eliminator in your drum (normally should be there)?

2. During a maintenance turnover you should check if the mist eliminator or demister has got damaged. If it is a wire mesh type check whether the wire mesh has got damaged. Also check if the demister / wire mesh has got displaced from its original intended position due to damage / distortion of the support plate / structure of the demister / wire mesh.

3. Check if the inlet steam conditions (pressure / temperature) have changed. It is important to note that for proper separation and distribution of vapor in any vapor-liquid separator, the inlet nozzle plays a vital role. Extremely high momentum values (rho*v²) where rho is the two-phase fluid density and v is the velocity at the inlet are detrimental to proper vapor-liquid separation and they need to be maintained below a prescribed value or else an inlet device needs to be provided if momentum values cannot be lowered. "Schoepentoeter" or "half-open pipes" as inlet or feed devices allow higher momentum values while ensuring good distribution and separation in the vapor-liquid separator.

If you are planning a second drum I would suggest you go for a parallel drum which could be of the same capacity as the existing one or lower capacity (cost saving) for the simple reason that you may not have to take a shutdown of the system if you have an existing spare connection / tapping on the inlet line to the existing steam disengagement drum. Even if you don't have such a spare connection, you can provide a "hot tap" on the existing line which will save you a shutdown of the system.

A drum in series would have the disadvantage of having to be of the same capacity as the existing one as well as require a shutdown of the system. So I wouldn't consider this to be a sensible configuration.

Hope this helps.

Regards,
Ankur,

[reckless]

Hi Ankur,

Thank you very much for the valuable input.

1. What we have in the drum is a cyclone separator. There aren't any problems found in it during the last ispection.

2. We will surely check this in April 2011. We just want to be ready of what to expect. What are the usual problems encountered with drums similar to ours?

3. The operating parameter and steam conditions did not change. What we are sure of is that the problem when we operated at steam generation of 28 - 30 MT/hr. In the history of the unit, the highest generation that we had was about 27 MT/hr.

Thanks.

[reckless]

Hi Ankur,

Good day. If we were to have two drums in parallel, what is the recommended control scheme for the distribution of flow? THank you!

[ankur2061]

Reckless,

In my experience if you have two identical drums in parallel then the only thing you need to provide symmetrical piping connecting the drums for equal flow distribution. This kind of arrangement does not require any instrumentation for flow distribution. However, this is easier said then done and if this is not possible, you could provide a three-way flow distribution control valve for flow splitting to the two drums receiving a ratio or bias signal from the flowmeter in the common header formed by joining the individual vapor flow lines from each drum.

You could set the ratio or bias signal for equal distribution (50:50) or any other ratio (say 60:40. 70:30) through the flow controller. I have seen this kind of flow splitting arrangement working quite successfully.

Fisher supplies excellent 3-way control valves and you could consult them for this kind of flow splitting application. The link provided should help you:

http://www.documenta...d103305x012.pdf

Hope this helps.

Regards,
Ankur.