Application
Large high speed rotation equipment such as gas turbines,
steam turbines, axial and centrifugal compressors, requires
a large volume of oil for lubrication, cooling, and sealing
of the bearings. The lubricating oil can be either mineral
based or synthetic.
Turbines are widely found throughout the world used in a
variety of mechanical drive applications, including compressors,
electric generators, marine propulsion, pumps and other
loads. These applications are typically found in air separation,
power generating, gas transmission and petrochemical facilities.
The bearing surfaces that the oil comes in contact with
are very hot (350° - 700°F), and are rotating at high speeds.
The high temperature and shearing action generates a large
volume of very fine oil mist (droplets) plus a considerable
amount of vapor (gas). When this oil mist and oil vapor
is vented from the lube oil tank, it causes a visible plume.
This oil plume is subject to increasingly stringent environmental
laws and regulations at all government levels throughout
the United States and the world.
Lube
Oil Systems
The emissions from the vent of a lube oil tank are difficult
to eliminate because the majority of oil mist
droplets fall in the range
of less than 1 micron in diameter. Oil mist control technologies
that have been used in the past include electrostatic precipitators
(ESPs), rotating drums, packed fiber beds and mesh pads.
The manufacturers of these technologies all claim at lest
95% efficiency, some even go as high as 99% efficiency.
While
all of these types of technologies are satisfactory for
removing large droplets of oil, they are not adequate enough
for removing sub-micron particles 0.5 microns and smaller.
Typical
Lube Oil System – The primary parts of a lube oil system
are as follows:
- Lube
Oil Reservoir
- Lube
Oil Filters
- Lube
Oil Pumps
- Lines
from the Reservoir to the Bearings
- Lines
returning from the Bearing to the Reservoir
The
basic operation of a lube oil system is similar for all
designs. Lubricating oil (mineral or synthetic) is pumped
to the bearings to lubricate and cool the metal to metal
surface contacts. The high speed shearing and heat that
occurs at the metal to metal contact causes droplet formation
and vaporization of some of the oil.
Therefore, the return lines to the lube oil reservoir contain
not only hot oil but also mist-laden air and vapor. On the
return trip to the reservoir, most of the vapor cools and
condenses back into oil droplets. Our detailed field and
laboratory research have shown that these droplets are extremely
small – between 0.05 and 0.5 microns. (See table below
of particle size and distribution).
| Particle
Size and Distribution for Typical Turbo Machinery
Lube Oil Vent |
| 10
– 20% |
.56
micron |
| 10
– 15% |
.28
micron |
| 25
– 30% |
.14
micron |
| 40
– 50% |
<.07
micron |
The
large droplets (>1 micron) drop out on the return to
the reservoir. Vapor created by the high temperature at
the bearing recondenses into submicronic droplets.
Once
back in the reservoir, most of the larger droplets fall
out; however the reservoir must be vented or open to atmosphere.
This is accomplished by two means:
- By
injecting pressurized air at the bearings, thus keeping
a slightly positive pressure in the lube oil reservoir
as compared to atmosphere.
- By
connecting the suction side of a blower to the top of
the reservoir, thus creating a slight vacuum in the
reservoir, as compared to atmosphere.
How
Coalescers Work –
At the heart of the Dollinger Oil Must Eliminator is a high
efficiency coalescing element. Coalescers
combine small aerosols through the filter media to form
large droplets. The droplets recombine until their mass
is significant enough to gravity-drain away from the element
to a sump area.
