agc wp-hselimparaffincontamlos

How a Hydroscav Can Eliminate

Paraffin Contamination in a Lube Oil

System

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AGC REFINING & FILTRATION

HOW A HYDROSCAV CAN ELIMINATE PARAFFIN CONTAMINATION IN A LUBE OIL SYSTEM 2

Contents How Paraffin Can Contaminate a Lube Oil System 3

Prevention of Wax Crystal Formation 5

Where to Inject a Paraffin Eliminator 7



How Paraffin Can Contaminate a Lube Oil System

Figure 1: How Paraffin Can Contaminate a Lube Oil System

In this particular case a natural gas was used as a buffer gas in a compressor. The buffer gas separates the hydrocarbon gases inside the compressor from escaping to the atmosphere. One of the constituents of the buffer gas is paraffin. Depending on the condition of the shaft seals, a certain amount of buffer gas leaks past the seals. In doing so it comes in contact and contaminates the lube oil with paraffin.

Hydrocarbon molecules principally take four different forms: paraffins, olefins, cycloparaffins, and aromatics. The simplest case is the paraffins-chain-like molecules in which strings of carbon atoms are decorated with hydrogen atoms.

Some paraffin molecules have only a single chain as in figure 2c while others branch out extensively as in figure 1d. Branching allows the carbon atoms in a paraffin molecule to arrange themselves in many different ways.

The 2,2,4-trimethyl-pentane molecule shown in figure 1d is just one of eighteen ways in which 8 carbon atoms and 18 hydrogen atoms can join together to form a molecule. These are called isomers.



Figure 2: Various Paraffin Molecules

While the paraffin molecules in figure 2 appear to be rigid, orderly structures, they actually are free to move to a certain extent around the axis of the bond between them as is shown in figure 3.

Figure 3: The Paraffin Molecule Swivel Action



The paraffin molecules can and do swivel about the bond between them. As a result the paraffin molecules are very flexible.

In addition to the chain-like paraffin molecules, natural gas can also contain ring-like molecules called cycloparaffins. These occur because the chain-like molecules are flexible and can form coils or loops.

The two ends of a typical chain-like paraffin molecule can touch and will bind together to form a ring by removing two hydrogen atoms as is shown in figure 4.

Figure 4: Cycloparaffins

At the usual lube oil process temperature the paraffin crystals are dispersed throughout the oil. If the temperature remains constant throughout the lube oil system and does not drop below a certain temperature, the paraffin crystals remain dispersed.

At a certain temperature the unbranched paraffin molecules are able to join together to form crystalline solids. These solids are called paraffin waxes. Over time these waxes settle out of lubricating oils and coat the internal surfaces of the lube oil system to such an extent that they sometimes plug piping and cause oil flow to stop, cutting of oil flow to the bearings.

At lower temperatures the shorter unbranched paraffin molecules also settle out of the lube oil, forming a semi-solid called petroleum jelly.

Prevention of Wax Crystal Formation

Various paraffin control chemicals have been in use for decades. These include:

Pour point depressants (PPDs)

Paraffin dispersants (PDs)



Paraffin crystal modifiers (PCMs)

Pour Point Depressants (PPDs)

The pour point of a lubricant is the lowest temperature that the fluid will flow under standard conditions. Pour point depressants are polymers that are designed to control wax crystal formation in a lubricant resulting in a lower pour point and better flow properties. PPDs are structures so that part of the molecule is like a paraffin wax crystal, which acts by providing nucleation sites and co-crystallization with the waxes. The selection of a PPD depends on the base oil used, the additive packages, and any viscosity improver.

Paraffin Dispersants (PDs)

These are used to prevent or retard the deposition of paraffin crystals. The dispersants coat the small paraffin crystals as they come out of solution (approach the pour point). In doing so, they prevent the crystals form forming large agglomerates or sticking to pipe surfaces. When used in concentrated batch treatments, these dispersants can dissolve and remove existing paraffin deposits. Continuous injection can be used to prevent paraffin deposition.

Paraffin Crystal Modifiers (PCMs)

After existing paraffin deposits have been removed, crystal modifiers can be used as a preventive treatment. Crystal modifiers are polymeric substances which work by co-crystallizing with the wax crystals. This causes the wax crystals to be less likely to agglomerate and adhere to pipe surfaces.. This in turn reduces paraffin deposition and also lowers the pour point. Paraffin crystal modifiers can be injected continuously or used in batch treatments. They work better and are more economical when injected into the system before paraffin formation begins. Paraffin usually forms when the oil cools in the system piping near the surface and get more cooling in the flow lines.



Where to Inject a Paraffin Eliminator

Figure 5: Schematic of a Hyrdoscav Oil Purifier



Figure 6: Showing the Buffer Gas Line to the Jet Mixer Manifold

The injection point for the paraffin elimination material is just upstream of the Aero-Jet Mixer into the manifold. This insures instantaneous and complete mixing with the oil and the buffer gas, which is injected into the Aero-Jet Mixer itself (see figure 6).

The buffer gas is safely vented to the flare header via the flare manifold on top of the Separator Vessel as shown in figure 7.



Figure 7: Flare Vent Manifold Routes Buffer Gas to the Flare Header

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