Gas scrubber vessel sizing - liquid density?

[rtbdr]

Hello,

I am curious what approach you guys take when sizing a vertical vessel for gas scrubbing e.g. a compressor suction scrubber. The Souders-Brown equation that is typically used to determine the vessel diameter requires the liquid density. However, for a suction scrubber service, the vapor is often well-superheated. In this case, what value do you use for the liquid density? Do you take a completely different approach altogether to size the vessel?

One of my colleagues suggested to use something like the density of water or of the compressor lubricating oil. One instance where liquids would likely enter the compressor suction scrubber is if the compressor runs in recycle and some of the lubricating oil is entrained in the vapor. However, I feel as though this approach is not conservative enough. The density value from this approach is quite high, which results in a smaller vessel diameter.

What are your thoughts?

Thanks,

Best Regards.

 

[zdas04]

A mechanical separator cannot, will not separate one gas from another. If the gas is actually superheated, then no separator or scrubber will ever remove a single drop of liquid. The liquid density that goes into vessel sizing equations is assuming multi-phase flow with gas and liquid both contained in the flow stream.

[bold]David Simpson, PE[/bold]
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist

 

[rtbdr]

I don't think you understand the application here. We're not trying to condense any liquids from the gas. We're trying to knock out any liquid particles that may get entrained in the gas so that they don't enter and damage the compressors.

Under normal operation, the inlet gas is superheated and no liquids should be in the stream going to the compressor. As such, we cannot rely on steady-state vapor-liquid equilibrium calculations to predict the density of the liquid entering the scrubber. This scrubber is just a final safeguard to protect the downstream equipment from serious damage.

 

[georgeverghese]

So what liquid do you get for abnormal conditions ?

 

[MortenA]

@rtbdr,

I think your colleagues suggestion sound good, water or lubeoil (if its a compressor type where relevant). If there is an abnormal situation e.g. startup where the gas is not super-heated then you could also use such a value.

At the end of the day - if you for some other reason find the vessel ID to be too small then just specify a "minimum diameter"

Best regards, Morten

 

[georgeverghese]

Does this scrubber recieve feed from an upstream V/L separator ? What liquid would be carried over into its exit gas stream for example ? There is no such thing as a perfect V/L separator.