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Hydroscav: Principles of Operation

WHITE PAPER © 2017 AGC Refining & Filtration LLC

AGC REFINING & FILTRATION

HYDROSCAV: PRINCIPLES OF OPERATION 2

Contents Summary 3

Description of Design 3

Equipment Description 6

The Aero-Jet Mixer 6

Hydrocarbon Gas Removal with the Hydroscav 8

Nitrogen Supply Option 8

Factors Influencing the Cost of a Hydroscav 15

References 16



Summary

The useful life of industrial oil can be extended indefinitely by continuous removal of contaminants such as solid particles, free water, oil/water emulsions, hydrocarbon gases, acids, and dissolved water. The principle operation of the Allen Hydroscav™ Oil Purifier is the creation of a phase change of the water in the oil from liquid to vapor. This is accomplished by the specially designed and patented Allen Aero-Jet Mixer™. The high-dehydration efficiency of the Hydroscav’s air-stripping technology is due to the fact that air at elevated temperatures can absorb more water than ambient air. The contact time between the air and water-contaminated oil further enhances the dehydration efficiency. High relative humidity of the surrounding air does not have a significant effect on purifier performance. A Hydroscav is capable of removing free, dissolved, and emulsified water to well below saturation levels, reducing water concentrations to as low as 20 ppm by weight. (See Figure 1 and the white paper titled Water Activity)

Description of Design

Hydroscavs are designed as either mobile units or permanent installations on oil systems of critical machinery for continuous, on-stream purification. The units are used for small- to medium-sized oil reservoirs. Units are available at a relatively low initial cost and generally require very little operator attention with easy installation and maintenance.

Uncomplicated Design

Hydroscavs usually are small, compact, lightweight, easily maintained, and energy efficient. With a minimum of moving parts, Hydroscavs do not require expensive consumables; they have no complex, failure-prone instrumentation or electrical control equipment. The only replacement parts necessary are inexpensive filter elements. (See Figure 2)



Figure 1: Solubility of Water in Oil at Different Temperatures



Figure 2: Schematic of a Typical Hydroscav Oil Purifier

Energy Efficient and Economical to Operate

The electrical and electronic components are designed to operate with minimum power requirements; a minimum of parts allows reliable and economical operation for long periods of time.

Durable Rugged Construction

The oil-wetted parts of a Hydroscav can be constructed of carbon steel or 316 stainless steel to resist external corrosion and increase durability and reliability while the open-frame design reduces weight and permits easy access for maintenance. Equipment is mounted either on a rugged, reinforced steel base or on a heavy-duty trailer and designed to operate continuously out in the open.



Capable of Removing Dissolved Hydrocarbons

The Hydroscav can quickly and efficiently remove hydrocarbon gases up to C9 (Nonane). Mixtures of longer-chain hydrocarbon components will take somewhat longer depending on the molecular weight of the particular compound. Eventually almost all entrained or dissolved gases are removed.

Equipment Description

An electric, motor-driven duplex-positive displacement gear pump forces contaminated oil through a 5-micron filter (other micron sizes are available) to remove sludge and solid particles such as corrosion products; this protects the internals of the equipment from solids contamination. The pressurized oil passes through an electric, low-watt-density immersion heater which is specifically designed to maximize dehydration efficiency and prevent hot spots and carbonization of the oil. An accurate temperature controller with a sensor downstream of the heater is the secondary protection of the heater in addition to the protection provided by the programmable logic controller (PLC).

The heated oil then enters the Aero-Jet Mixer which generates a vacuum and induces filtered ambient air into the wet oil stream, intimately mixing them together. Heated air captures the moisture in the oil and the mixture flows to a separator vessel. The sudden expansion of the mixture causes the oil to separate and drop to the bottom for discharge, while the air/moisture mixture is discharged to the atmosphere through a vent as well as a mist eliminator.

An optional nitrogen injection system can be provided to aid in the removal of entrained or dissolved hydrocarbon gases such as H2S, HCl, and hydrocarbon gases with carbon chains up to C8, which can be exited to a flare line.

The clean, dehydrated and degassed oil collects in the bottom of the separator vessel and—under level control—is returned to the reservoir, ensuring the vessel cannot be overfilled. Specially designed internals ensure optimum efficiency of separation between oil and vapor.

Process temperatures and pressures are field-adjustable with temperatures generally set from 140° F (60° C) to 170° F (93° C) and pressure set at atmospheric. Separation efficiency can sometimes be improved at the higher process temperatures, depending on the oil. On the positive-return Hydroscav models, an outlet pump draws the dehydrated oil from the knockout vessel and returns it to the reservoir. Because water is removed as a vapor, additives present in the oil are not removed.

Hydroscav units can be designed and manufactured for a variety of oils and can handle a wide range of viscosities. A PLC allows for fully automatic, unattended operation. After shutdown, the PLC also allows the flow to subside gradually in order to cool the heater down and prevent localized “hot spots” that could carbonize the oil on the elements. The pump motor speed is controlled by an optional variable-frequency controller which allows for adjustment of the pumping speed to different oil viscosities.

The Aero-Jet Mixer

The heart of the Hydroscav Oil Purifier is the patented Aero-Jet Mixer. (See Figures 3 and 4) As is shown in the flow diagram (Figure 1), the heated oil is pumped through a filter which primarily protects the precisely calibrated orifice in the Aero-Jet Mixer and keeps it from plugging up.

Hot oil is then injected through the Aero-Jet Mixer nozzle into the primary mixing area where—due to the progressively narrowing orifice—the stream is accelerated to a high velocity. This creates a vacuum ahead of the orifice that draws in ambient air into the oil stream. The profile of the primary mixing area has been designed using computational fluid dynamics; this provides an area of high turbulence and intense mixing. The orifice has a special component built into it which induces a spiral flow pattern that promotes intimate mixing of oil, water, and air. Altogether the device generates a vacuum of up to 26 inches of Hg to draw in ambient air.



Note: If entrained or dissolved hydrocarbon gases are present in the oil, nitrogen can be injected at this point to convey the combustible mixture to the flare system.

The secondary mixing area is similarly designed to allow a gradual decay of turbulence, thereby allowing the heated air to absorb the water that was dissolved in the oil. This oil and moisture-laden stream is then injected tangentially into the separator vessel which is provided with a specially designed system of baffles to facilitate separation. When injected tangentially, the stream forms a vortex which facilitates the separation of clean, dry oil that exits from the bottom of the separator vessel while the moisture (and hydrocarbon) vapor is vented from the top. The vessel is designed to prevent accumulation of sediment and deposits that occur in corners of rectangular vessels.

Caution: Some equipment manufacturers have adopted the same configuration of eductor/mixer with some even using two mixers in series. The obvious fallacy of such a design lies in the fact that—after turbulent mixing in the first stage and initial separation in the second stage of the first mixer—a second phase of turbulent mixing of oil and water will create a tight emulsion that is difficult to separate. Thus in the case of mixing, two consecutive stages are never better than a single stage. The design of the internal flow path inside the Aero-Jet Mixer is an original patented invention of Allen Filters, Inc. The effectiveness of this design has been optimized using computational fluid dynamics modeling and has been proven most effective in over one-thousand Hydroscav models sold in the past few years.

Figure 3: The Allen Spiral Flow Aero-Jet Mixer



Figure 4: The Flow Pattern in the AFI Vortex Flow

Hydrocarbon Gas Removal with the Hydroscav

The Hydroscav is designed to process continuously at the rated flow removing solids and sludge down to 10 microns (other micron sizes are available); free, emulsified, and dissolved water; and Hydrocarbon gases to C9 (Nonane). The water removal rate is more than sufficient to maintain the reservoir moisture below the saturation point of water in oil. (See Figure 1 and the white paper titled Water Activity)

Experiments regarding single-pass removal efficiencies have shown the following:

Table 1: Typical Hydroscav Single-Pass Removal Efficiencies

Hydrogen H 99%

Hydrogen Sulfide H2S 90%

Methane C1 97%

Ethane C2 90%

Propane C3 77%

Butane C4 60%

Pentane C5 35%

Hexane C6 18%

Heptane C7 9%

Octane C8 4%

Nonane C9 1.7%

Longer-chain hydrocarbon gases are also removed but will take more passes through the system.

Nitrogen Supply Option

If it is necessary to discharge the vapor from the separator vessel to a flare line, nitrogen can be used to overcome the back pressure of the flare header. Nitrogen is injected at the rate of 15 to 22 m3/hr (9 to 13 cfm) for hydrocarbon gas removal. Nitrogen will also enhance the removal of hydrocarbon gas because a dry, inert gas can prevent the creation of a combustible vapor mixture. The separator vessel is designed with a vent manifold that allows discharge to the atmosphere or—alternatively—to a flare. The latter



allows safe and secure removal of combustible gas vapors to the flare line.

Figure 5: A Hydroscav Model HS200-EPRX1

Capacities available: 200–2,000 gallons per hour (gph); explosion-proof model with nitrogen injection accessory



Figure 6a: Details of a Hydroscav

1. Low-Watt-Density Oil Heater 2. Temperature Gauge 3. Air Intake Filter 4. Air Intake Filter 5. Air Shut-Off Valve During Nitrogen Operation 6. Separator Vessel 7. Aero-Jet Mixer 8. Tangential Injection Point Into the Separator Vessel 9. Nitrogen Injection Line



Figure 6b: Details of a Hydroscav

1. Air Intake Filter 2. Aero-Jet Mixer 3. Separator Vessel 4. Heater 5. Nitrogen Flow Meter 6. Inlet/Outlet Duplex

Positive Displacement Gear Pump



Figure 7: Model HS200-EPR4, (Nema 4) Non-Explosion-Proof

1. Heater 2. Control Panel 3. Air Intake Filter (5-micron) 4. Aero-Jet Mixer 5. Separator Vessel 6. Oil

Accumulator Tank (optional)



Figure 8a: Details of a Hydroscav

1. Motor 2. Duplex Positive Displacement Pump

Figure 8b: Details of a Hydroscav

1. Re-cleanable Air Intake Filter Elements



Figure 8c: Details of a Hydroscav

1. Control Panel 2. Aero-Jet Mixer 3. In-line Oil Heaters



Figure 8d: Details of a Hydroscav

1. Temperature Gauge 2. Air Intake Filters 3. Aero-Jet Mixer 4. Separator Vessel

Figure 9: Process of Purification in a Hydroscav Oil Purifier

Factors Influencing the Cost of a Hydroscav

The purifier design flow rate depends on:

The rate of contamination coming into the lube oil tank (for instance, water or gas from a leaking shaft seal).

The required turnover time of the tank volume (how fast does the oil need to be purified to stay ahead of the incoming contamination).



The budgeted cost for the purifier.

The purification efficiency depends on:

The design flow rate.

The amount of heat supplied to the oil flow (the number of heaters required to increase the lube oil operating temperature to 170° F).

The number of passes through the purifier.

The budgeted cost for the purifier.

The number of passes depends on:


The volume of the lube oil tank to be purified.

The price of the purifier depends on:


The number of heaters required.

The type of contaminants (water, solids, hydrocarbon gases, etc.).

References

1. Allen, K. “A Hydroscav Reduces Waste Oil and Produces a Fast Pay-back.” Internal publication.

2. Allen, K. “Principles of Operation of the Hydroscav Oil Purifier.” Internal publication (1957).

3. Bloch, H.P. “Cost Justification and Latest Technology for On-Stream Purification of Turbo machinery Lube Oil.” Exxon Corp./AFI joint publication.

4. Bloch, H.P. “On-Stream Purification of Turbo Machinery Lube Oil.” Exxon Corp./AFI joint publication.

5. Simon, R. J. “Hydrocarbon Gas Mass Transport Phenomena in the Hydroscav Oil Purifier.” Internal publication (2000).

6. Simon, R. J. and A. Al-Amoudi. “Technical Evaluation of a Gulfgate LV360 Oil Purifier and an Allen BCCX150 Vacuum Dehydrator.” Internal publication, Saudi Aramco Mobil Refinery (1995).

7. Simon, R. J. and K. Allen. “Computer Model of Spiral Mixing Flow Regime in the Allen Aero-Jet Mixer.” Internal publication (2001).

8. Simon, R. J. and K. Allen. “Hydrodynamic Behavior of a Two-Phase Fluid Mixture in an Ejector.” Internal publication (1989).

9. Simon, R. J. and K. Allen. “Investigations Into the Dehydration Efficiency of an HS200-EPRX1 Hydroscav Oil Purifier.” Internal publication (1999, 2007).

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