9 replies to this topic

[mbeychok]

Rees:

1 litre per year of oil seems like an insignificant amount to me unless it is causing a problem in the gravity filter for which you are using the air. Does it, in fact, cause any problems?

Each blower discharging 430 m3/hr through a 150mm pipe means that the air velocity in each pipe is about 6.75 m/s. You might try using a knockout drum (i.e., a wide spot in the line) in which the velocity would be slowed down so as to remove the oil from the air.

A knockout drum is a vertical vessel into which a liquid and vapor mixture is fed and wherein the liquid is separated by gravity, falls to the bottom of the vessel, and is withdrawn. The vapor travels upward at a design velocity which minimizes the entrainment of any liquid droplets in the vapor as it exits the top of the vessel.

Use a vertical pressure vessel with a length-to-diameter ratio of about 3 to 4 and size the vessel diameter by the Souders-Brown equation to determine the allowable vapor velocity:

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

where:
V = maximum allowable vapor velocity, m/sec
dL = liquid density, kg/m3
dV = vapor density, kg/m3
k = 0.107 m/s (when the drum includes a de-entraining mesh pad)

Then the cross-sectional area of the drum, in m2 = (vapor flow rate, in m3/s) / (vapor velocity, in m/s)

I am assuming that you meant 0.3 barg (i.e., 1.3 bara) as your air pressure and I am assuming a temperature of 25 °C. At those conditions, the air density (dV) is 1.51 kg/m3. I am also asuming the oil has a density (dL) of about 900 kg/m3 and so:

V = 0.107 [(900 - 1.51)/1.51]^0.5 =0.107 (24.4) = 2.61 m/s
Drum cross-sectional area = (430/3600) / 2.61 = 0.0458 m2
Drum diameter = [(4)(0.0458/3.1416)]^0.5 =0. 242 m = 242 mm
Drum length = 3.5 (0.242) = 0.847 m = 847 mm
Air to enter at midway up the drum and each drum is to have a mesh pad at the top.

Depending on the size of the droplets in your oil mist, the drum may or may not remove all of the oil. On the other hand, the drum size above is quite small and three such drums (one for each blower discharge line) would be quite inexpensive. It might be worth a try.

[mbeychok]

Rees:

I would estimate that the mesh pad should be about 200 mm below the air outlet at the top of the drum. I would also advise you to contact a mesh pad vendor (to ask your other questions) such as Microwire at:

www.microwireproducts.com <== click here and then click on "mist eliminators".

Good luck,

[Rees_101]

mbeychok:

Thanks for the reply, I will make some enquiries.

Do you have the name of any references or text books which incorporate the Souders-brown equation so I can have a read of the theory involved in the process?

Thank you in advance.

Rees

[mbeychok]

Rees:

The Souders-Brown equation has been in use for over 60 years. If you can find this in a good university library, read Souders, M., and G. G. Brown, Industrial Engineering Chemistry; #26; volume 98; (1934).

[joerd]

Porous Media Corporation have very fine mesh filters that allow removal of hydrocarbon mist as fine as <1 micron (i.e. like tobacco smoke). This is something you can't achieve with a regular separator.