Condensate Receiver Sizing 1

[RGPaul]

What is the basis for sizing a vented atmospheric condnesate receiver to prevent condensate entrainment/carryover into the vent stack? In my situation, I have a condensate load of 35,000 lb/hr (5,891 lb/hr flash, 29,108 condensate) that is collected in a vented condensate tank and sent either to a hotwell or pumped to a condensate storage tank, depending on the hotwell level and the condensate reciever level. The pump is sized to deliver 100 gpm, well in excess of the incoming condensate. The condensate reciever appears to be undersized (horizontal tank 3' dia x 6'long)and we are draining a "considerable" amount of water from the steam separator that we have installed on the 10" ventline. Any guidance for checking the sizing?

 

[TD2K]

I would suggest an approach similar to a two phase separator. Calculate the allowable vapor velocity in the drum with an appropriate K factor (I would try 0.15 since you likely don't have any sort of de-entrainment device other than the separator on top of the stack).

Basically, you are trying to get the droplets to settle out before the rising steam enters the stack and accelerates to the point that you aren't going to remove any droplets before hitting the stack separator.

 

[quark]

thread794-55572 will be of some help to you.

 

[gladkenn]

If it is possible to pressurized the condensate tank, it may help. A higher pressure of condensate has a greater mass per equivalent volume of the low pressure condensate.


gladkenn

 

[mbeychok]

RGPaul:

I realize that this may be too late for answering your question, but perhaps the following may be useful to others:

The size of a flash drum (or knock-out pot, or vapor-liquid separator) should be dictated by the anticipated flow rate of vapor and liquid from the drum. The following sizing methodology is based on the assumption that those flow rates are known.

Use a vertical pressure vessel with a length-to-diameter ratio of about 3 to 4, and size the vessel to provide about 5 minutes of liquid inventory between the normal liquid level and the bottom of the vessel (with the normal liquid level being at about the vessel's half-full level).

For the maximum vapor velocity (which will set the drum's diameter), use the Souders-Brown equation:

Vmax = (k) [ (dL - dV) / dV ]^0.5

where:
Vmax = maximum vapor velocity, ft/sec
dL = liquid density, lb/ft3
dV = vapor density, lb/ft3
k = 0.35 (when the drum includes a de-entraining mesh pad)

The GPSA Engineering Data Book recommends the following k values for vertical drums with horizontal mesh pads (at the denoted operating pressures):

0 psig: 0.35
300 psig: 0.33
600 psig: 0.30
900 psig: 0.27
1500 psig: 0.21

GPSA Notes:
1. K = 0.35 at 100 psig; subtract 0.01 for every 100 psi above 100 psig
2. Typically use one-half of the above K values for approximate sizing of vertical separators without mist eliminators.
3. For compressor suction scrubbers and expander inlet separators, multiply K by 0.7 – 0.8

The drum should have a vapor outlet at the top, liquid outlet at the bottom, and feed inlet at somewhat above the half-full level. At the vapor outlet, provide a de-entraining mesh section within the drum such that the vapor must pass through that mesh before it can leave the drum. Depending upon how much liquid flow you expect, the liquid outlet line should probably have a level control valve.

As for the mechanical design of the drum (i.e., materials of construction, wall thickness, corrosion allowance, etc.), use the same methodology as for any pressure vessel.



Milton Beychok
(Contact me at www.air-dispersion.com)
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