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Petróleo, Gas y Petroquímica
Homogeneizado de Crudos
Custody Transfer Mixer

[Descripción General|Especificaciones Detalladas|Desaladoras de Crudo]

Descripción General

The Custody Transfer mixer for petroleum products has become the standard in the industry. The "CT" employs an integrated, patented design to provide the ultimate in mixing. Installed upstream of the sampling point in a petroleum product transfer line, this unique synergistic mixer assures that the bottom sediment and water is thoroughly dispersed throughout the product stream for accurate sampling.

Over 8,000 CT Mixers installed to date. Ranging from 1" to 48" diameter.


In 1984 Komax Systems was approached by the chief engineer of the Chevron Pipeline Company with a problem. Chevron knew it was losing millions of dollars each month due to the failure of its crude oil sampling techniques to properly account for the water content of oil being loaded or unloaded from tankers and during oil transfer between companies. Chevron wanted to know, “Could Komax develop a static mixer design to properly mix crude oil and the bottom water for more accurate sampling?”

Per API recommendations most pipeline companies installed a vertical loop in the transfer pipe with a sampling probe on the down side of the loop. The loop was supposed to mix the oil and water so that readings from the sampling probe would accurately reflect the true water content and allow a proper correction to be made to the final invoice for the crude transferred. Chevron and other pipeline companies found they were paying for a lot of water because the vertical loop was not a good mixer. Without good mixing the sampling probe cannot grab accurate samples.

Komax started a research program monitored by Chevron who supplied barrels of clear mineral oil to Komax for test work. Komax built a scale model in two inch diameter glass piping of a typical CT loop and pipe run. Dyed water was metered and injected into the mineral oil flow to simulate bottom water. This allowed us to study what really happens to BS&W as it reaches and passes through a “mixing” loop and other static mixer designs prior to the sampling point.

Experiments were conducted using mineral oil covering a range of viscosity’s to represent variations in crude oil properties and at pipeline velocities ranging from 1.0 to 10 feet per second. Static mixers from several companies were tested. A variety of the Komax static mixer designs were tested modified and retested; Wires 0.030” in diameter were welded to the downstream end of the static mixer. This allowed photographic study of the exit flow to determine water droplet diameter and low and high velocities. Pressure drop was measured for each design.

These lab experiments occupied a period of eight months. During this test period over sixty petroleum engineers from most of the major companies visited Komax to view this operating model. They could see how the pipe loop and different static mixers mixed.

From our testing we developed the design of the low pressure drop CT mixer. There are two very key points in the Komax design. The first mixing element is off set at a 30 degree angle. This allows the bottom static mixer element ear to act as a dam forcing water or BS&W off the bottom of the pipeline up into the mixing zone. The back mixing inside the Komax static mixer produces very small and evenly spaced water droplets across the pipe diameter. On the discharge end of the CT mixer we incorporated an anti-spin fin to cancel the rotation around the axis of the flow. This prevents the 10% denser water from centrifuging out and coalescing on the pipe wall before a sample is grabbed. This centrifuging from the spin in the first up flow elbow is causing one of the mixing problems in the vertical pipe loop. Photos of mixing are on the back page of our Custody Transfer Bulletin 104.

Over the years the success of the Komax CT static mixer alerted other manufacturers to enter this market. They did this with little or no testing. Purchases of static mixers for CT applications were made on purely price basis. This is understandable for externally all static mixers look the same, a flanged pipe section with a sample port down stream. However, this led to very costly accounting errors for several major oil companies. Also to Komax chagrin the statement “I tried a “static mixer” and it didn’t perform that well”.



Off loading a crude oil tanker of 250,000 bbls.
Off loading pipe lines: Two 14 inch diameter lines.
Custody Transfer Mixers one 14 inch in each line.
Flow rate per mixer: 225,000 gph. (5357 bbls/hr)
Pipeline velocity: 9.75 ft/sec. (3 m/s) Tanker off loading time: 23.3 hours ( two lines)

The Komax CT mixer finds just 0.5% additional BS&W over other inline mixing devices.

250,000 bbls X $ 40.00 per barrel = $ 10,000,000.
$10,000,000 X 0.5% = $ 50,000. Cost of the 0.5% BS&W.
Payback time for two 14" CT mixer = 6 hours at 0.5%
Off loading four ships a month = $2,400,000 a year. (double at 1%)

Over fifteen years ago Komax Systems developed the CT Static mixer design at the request of the chief engineer of Chevron Pipeline Company. Standard off the shelf static mixers were not producing repeatable and accurate samples. Vertical pipe loops, as recommended by the API for mixing, were producing even greater errors.

Pipeline engineers from Shell, Chevron, Exxon and other pipeline companies have reported back to Komax Systems that they find typically 1% and higher of additional BS&W over other mixers or loops installed before the sampling probe. To prove mixing the pipeline engineers would inject a known quantity of additional water during a crude oil transfer to see if the sampling was accurate and repeatable. The results of these infield tests is why Komax Systems has sold over 8000 CT mixers world wide from ¾ of an inch to 48 inches in diameter. Even on small diameter pipelines operating twenty four hours a day, the cost savings per year is in six figures.

When buying or selling crude oil your company cannot afford not to install a Komax CT mixer before sampling. As we all know $40 per barrel has come and gone.


Especificaciones Detalladas

Komax Custody Transfer or CT mixer are installed upstream of the sampling point in a crude oil transfer line. They assure that the bottom sediment and water – B, S & W – is thoroughly dispersed throughout the crude oil stream. An even water droplet size and distribution occurs over a wide flow range. This means that the automatic sampler takes a truly representative sample.

Komax CT mixers are installed in petroleum product transfer lines such as ship and tank truck terminals or refinery transfers in combination with a LACT unit. CT mixers are supplied with weld neck flanges or ends prepared for welding. For ease of installation Komax CT mixers are supplied complete with two inch flanged port for the automatic sampler connection. Dimensions and design graphs for all CT mixers are listed below.

Special features provide effective mixing.

The Komax CT mixer was specially designed to solve conventional custody transfer mixing problems. The CT mixer may be installed in a horizontal or vertical pipeline. In a horizontal line, the first mixing element is set 30 degrees off the centerline so the bottom mixing element ear acts as a ramp, forcing the bottom water up into the crude (see Figures 1 and 2). The internal vortices or back-mixing created by the Komax mixing elements also rotate the blend backwards from wall to eliminates any wall streaming and produces a very uniform distribution and droplet size of the water in the crude.

A very important feature of the Komax CT mixer is the addition of a special, last mixing element that cancels all of the axial rotation of the flow downstream of the mixer. Violent rotation of the stream would cause the centrifuging problem (barber poling) of the water to re-occur. The automatic sampler is located two to four pipe diameters downstream of the mixer. The resulting samples provide highly reliable net crude oil measurements.

CT Mixer without side sampler port

Ejemplo real



Desalado de Crudo
Static mixer improves desalting efficiency

An in-line static mixer has increased salt removal from crude oil at a large West Coast refinery, says the mixer supplier, Komax Systems Inc.

The mixer was installed at a 150,000 bid crude distillation unit’s desalter.

Crude at this refinery is a mixture of local production and imports from Indonesia and Alaska.

In the past, the refiner used a typical globe-type mix valve to mix fresh water with crude at the desalters. The crude is heated to 300 degrees F., mixed with 5% fresh water, and then fed to desalters.

Chemical and electrostatic treatment is used in the desalters to remove salt and water from the crude.

Pressure drop in the mix valve was typically set at 10 psi. However, when the processing of heavy (14 degree API) naphthenic crudes was attempted, the oil/water mixture formed a stable emulsion in the desalter. This prevented economic processing of this low cost, domestic crude. Several problem areas were identified which could contribute to stabilizing emulsions. One was the high shear-rate mixing found in the mix valve.

The crude oil and water are then simultaneously mixed though two-by-two division, cross-current mixing, and back-mixing, which improves turbulence and increases mixing efficiency without requiring high fluid shear velocities.

The modified desalter system has operated well on 14" and 22" API naphthenic crudes, with less that 5% oil in the effluent water.

As an unexpected bonus, salt removal also increased as a result of using the static mixer (Table 1). Depending on the type of crude oil, the refiner has been able to remove between 5% and 10% more salt than by the mix valve method. With less salt carried over out of desalter, less corrosive HCI will be generated in the crude unit furnaces. This will require less ammonia to neutralize the atmospheric column overhead stream.

At the same time, the mixer has helped reduce emulsions formed by too much pressure drop created by the mix valve. With less oil carry under, less fuel is consumed from having to reheat recycled oil up to 300 degree F before it re-enters the crude unit.

In addition, the new mixer has a better turndown ratio than the mix valve. The Komax unit has performed satisfactorily at rates as low as 35% of its design capacity.

Previous types of static mixers were unable to operate effectively at these levels.

Also, pressure drop due to the mixing device was decreased for 10 psi to 1.5 psi. Depending on the particular situation this could have energy conservation or through put incentives.

The refiner calculates that the mixer will pay for itself in its first year of operation with combined savings of $4,000/year in lower power consumption and chemical costs and $1,000/year in lower fuel costs.

Average desalter performance *
in, † Salt
out, † %
Mix Valve
90,000 b/d 22º API Crude 42 4.4 89%
14º API Crude § ----- ----- -----

Static Mixer
90,000 b/d 22º API Crude 41 1.6 96%
45,000 b/d 14º Crude 43 º 97%

* Desalters, mix valve, and static mixer all designed for full design crude unit feed rate of 150 MBPD.
† Pounds NaCl per 1000 bbl crude.
§ Crude Unit did not run 14º crude before desalter modifications, which included the static mixer, because stable emulsions were formed.

The in-line static mixer is contained within the flanged section of the pipe shown.


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