INTRODUCTION

• Flow rate capacity

• Ability to operate without service or maintenance

• Reliability

• Operator training and attention required

• Oil separation efficiency

• Suspended Solids separation efficiency

  Eff% = 100 x ( Cin - Cout/ Cin)

Cin = feed inlet concentration (mg/l)

Cout = discharge outlet concentration (mg/l)

Usually it is specific client requirements that determine which of these, and other measures, are most important. A primary criterion is oily water separation ability. This is often the main criterion in determining final discharge water quality. Under a given standard set of conditions the effectiveness of the treatment equipment is judged in terms of efficiency of oil removal, under specified conditions.  Separation efficiency can be expressed as follows:    

Oil separation efficiency can be objectively accessed by examining the separator oil droplet size Vs separation efficiency curves.  For higher quality separators these curves should be readily available from manufactures.  Manufactures should also be able to confirm performance to these curves by independent tests.

The purpose of oily water separators is to obtain clean water. However claims of a separator being able to achieve, say less than 10 mg/l discharge are meaningless and deceptive without recourse to oil droplet size performance curves.

The more efficient a separator is at removing smaller oil droplets the more powerful it is.  Typical Spinifex performance curves show it is able to remove more than 90% of 20-micron oil droplets.  Many plate pack manufactures recommend that these separators not be used if oil droplets are less than 60 micron.  Some manufacturers claim high performance but make this claim under very favourable conditions such as very light easy to separate oil. Some manufacturers are not able to produce qualified supporting technical information to match performance claims.

Because Performance curves are critical to determining separator performance more information is available on our Performance Curve page. 

Performance Curve comparisons

The picture above shows typical performance curves for four separators (Click on image to see a larger picture) :

• Spinifex SP2000 separator (one pass and with recycle)    

• Typical High Quality Plate Pack (7 mm)

• Typical Budget Plate Pack (12 mm)

• Typical simple gravity settling tank

More powerful separators have a number of advantages including:

• Obtain better quality discharge water

• Meet or exceed Local and National Trade Waste discharge standards

• Meet or exceed future discharge standards

• Deal with accidental spills

• Tolerate higher strength non-“quick-break “detergents and cleaners

WHAT EFFECTS SEPARATOR PERFORMANCE?

The Spinifex Separator is a mechanical separator; like all mechanical separators the separation performance can be effected by:

• Design of Separator

• Fluid Properties

• Method of Operation

DESIGN OF THE SEPARATOR

Spinifex engineers were the designers of the world’s first commercially successful oil removal hydrocyclones.  One of the keys to our successful designs is the use of optimum geometric ratios, such as separator length, diameter, orifice sizes and taper angles to achieve maximum separation. By comparison with conventional solids removal hydrocyclones, our designs are very long and generate high centrifugal separation forces.

FLUID PROPERTIES

The nature of the oily water mixture to treat can have a large influence on the separation efficiency of all mechanical separators like the Spinifex Separator.

Temperature

The viscosity of the water falls as the temperature rises. This allows oil droplets to move more easily through the water phase, thereby producing better separation.  Therefore increased temperature results in improved separation performance.

Note that for some separators, like Air floatation devices (DAF, CAF IGF), higher temperatures can reduce separation efficiency and hotter fluids may need to be cooled.

Droplet Size

Oily water separation efficiency is highest with large oil droplets.  Very small droplets are more difficult to separate. The nature of the process or application determines the size of the oil droplets and the client or system designer can do little to promote larger oil droplets. In some cases however good process design can maximise droplet size being feed to the oily water separator. Spinifex have many years experience in this field and can make recommendations to reduce the chances of producing small oil droplets.

Because oil droplet size is such an important factor in separator performance more important information is available on our Oil Droplet Page.

Density Difference

The efficiency of separating oil from oil/water mixtures is dependant on the difference in density between the containment and the water.  The separation efficiency increases as the difference in density increases.

Typical oil densities range from 950 to 750 kg/m3. Typical water densities range from 1050 to 995 kg/m3.

Inlet Concentration

For a constant droplet size distribution, increasing inlet oil concentration will not change the separation efficiency.  However, in practice it is found that the droplet size increases with inlet oil concentration and hence the efficiency also increases. 

METHOD OF OPERATION

Like most separators the method of operation of the Separator can affect separation efficiency.

 Flow rate

The strength of the centrifugal forces induced in the Spinifex Separator is a function of flow rate.  At low flows, forces are insufficient to establish the required vortex and little separation can take place.  Once the vortex is established, the efficiency rises rapidly.

Whilst most separators (plate packs, DAF) decrease in efficiency as flow increases, for the Spinifex Separator separation efficiency increases gradually as a function of flow rate.  The upper flow limit generally set by the pressure available between inlet and oil reject streams (Dp_in-rej).

Reject Ratio

The ‘reject ratio’ is defined as the ratio of the oily reject stream leaving the Spinifex Separator to the inlet of feed flow rate of fluid to the separator.

This is an important parameter in the operation of the Spinifex Separator.  Typical reject ratios are from 1 to 20% subject to design requirements.

A minimum reject ratio exists below which the efficiency of the Spinifex Separator can be impaired.  This depends on the size of the reject orifice. A high reject ratio does not affect the performance of the Spinifex Separator.  However, it leads to excess water in the separated oil and can result in unnecessary recirculation of water.  Hence, the optimum reject ratio is just above the minimum reject ratio.  The reject ratio is usually set by the Spinifex Design Engineer and should not require any further adjustment.

Underflow Recycle

A proven method of increasing the power of separation of the Spinifex Separator is to recycle part of the treated underflow back to the inlet for further treatment.  This is a feature unique to the Spinifex Separators. In this way those oil droplets that missed the separation in one pass have a second chance at being recovered.

This can be illustrated by an example:

For one pass (no recycle):                                        85% of 20-micron droplets will be removed.

With two passes (or 50% underflow recycle):             98% of 20-micron droplets will be removed.

Spinifex M19 Low Flow Standard Separator undergoing performance testing.

Separator Configuration 

Typical configurations are:

• Batch Treatment Mode

• Continuos Operation

• Other (Demand activation etc)