Process Liquid

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Electromagnetic filtration is a simple, cost-effective way to remove suspended, magnetically susceptible material from process streams. Electromagnetic filters (EMFs) were originally intended to remove magnetite (Fe3O4), which is present in most boiler condensate and in nuclear power systems. They have also proved effective in removing weakly magnetic species, such as hematite (Fe2O3) and copper, and other materials such as cobalt, nickel, and chromium, which form spinel crystals or ferrites with the magnetite.

Efficient Filtration

Milhous Company’s electromagnetic filters are extremely efficient. They can easily remove over 95 percent of the magnetite present in a stream, and depending on the conditions in a particular application, can remove over 90 percent of total iron and well over 50 percent of the copper found in typical boiler condensates./p>

Milhous Electromagnetic Filter

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The Milhous Electromagnetic Filter, which is shipped as a skid mounted, self-contained unit, has 6 major components:

1. A pressure vessel containing the matrix through which the liquid to be filtered out must flow.
2. The matrix, which is a bed of magnetizable steel balls.
3. A magnetic coil that provides the magnetic field in the matrix.
4. Iron assemblies to focus the magnetic field in the matrix.
5. Auxiliary equipment necessary for filter operation and flushing, including valves, a power supply, and a power/control system.
6.  A system to cool the magnetic coil.

EMF Performance 

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Since EMFs are magnetic devices, the percentage of magnetite or strongly magnetic species present in the influent will greatly affect the filter’s operating efficiency. With this in mind, it is understandable that a reducing environment in the influent stream and relatively high temperatures make ideal conditions for the use of an EMF. Flow rate is another variable that can impact filter performance, especially when there is a high percentage of weakly magnetic material present. This is because the magnetic force that attracts and holds contaminant in the filter must exceed the dynamic forces of the flowing liquid, which tend to wash the particles out of the matrix. Obviously, the greater the velocity of the liquid, the greater the dynamic force that must be overcome.

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Paramagnetic particles, such as FeO[OH] or Fe2O3, are not strongly held in the filter. When dealing with weakly magnetic species the flow rate can be reduced to achieve optimum performance. Removing weakly magnetic or non-magnetic species with an EMF sounds paradoxical, but it is quite understandable. It is known that some of the weakly magnetic ferrous materials will agglomerate with the strongly magnetic particles and can be removed along with them. Copper, chromium, and nickel, on the other hand, appear to combine chemically with the magnetite forming ferrites or spinel crystals that are strongly magnetic, and thus are easily removed. The elemental copper present in some streams is also effectively removed, apparently by plating or coating itself on to magnetite crystals.

Experience has shown that a sphere matrix filter in a stream where over 50 percent of the iron present is magnetite will easily remove over 60 percent of the copper present in the stream, but there must be sufficient magnetite present to act as a carrier. A stream with no strongly magnetic species present will not be effectively filtered by any electromagnetic device.

Cost Effective Solution

The cost effectiveness of an EMF installation will depend on the application. In a paper mill, the cost of the EMF plus the cost of electrical power and incidental maintenance costs must be weighed against the costs of dumping condensate during startup periods when the level of contamination is too high to permit treatment by conventional condensate polishing systems. To this must be added the costs of correcting iron fouling of resin beds and the costs of chemical cleaning and other magnetite related boiler maintenance – which will be greatly reduced with the use of the EMF. In a nuclear plant, the costs of using an EMF in steam generator blowdown service will be offset by the savings in not using cartridge filtration. Costs associated with cartridge filtration include radwaste disposal costs and the costs of resin bed maintenance that are necessitated by the relatively inefficient cartridge prefilters normally used in these applications. In every situation we have analyzed to date, the payback period for an EMF is under two years.

Since electric power is the only consumable associated with operation of the EMF, a great deal of effort has been expended to design and build equipment that will demand a minimum of power. The result is an EMF that typically uses a third of the power required by other designs. When power requirements over the operating life of the filter (40 years) are considered, the Milhous Company equipment has an overwhelming cost advantage over competing designs. It is not unusual for cost/benefit analyses to show that the difference in operating costs between the Milhous Company filter and a competing filamentary matrix filter over a 10-year period can completely pay the acquisition costs of the filter.

EMF – A Clear Choice

EMFs, unlike ion exchange columns, can handle high temperatures, and unlike cartridge filters, can handle very large flows for a very reasonable cost. Electromagnetic filters generate no waste in addition to the material they remove. An electromagnetic filter will have no effect on water chemistry other than removing suspended, magnetically susceptible solids. Since modern EMFs operate automatically, and the systems are so simple, maintenance requirements are minimal.

Operating Simplicity

The operation of an electromagnetic filter is simplicity itself. The magnet coil is energized by the power supply, creating a magnetic field in the filter matrix. The magnetic field in the matrix is intense (>5 kilogauss), and creates localized areas of higher intensity (high magnetic gradients) within the matrix where the spheres touch each other. Magnetically susceptible material suspended in the process liquid is attracted to and is given up to the matrix. When the matrix is loaded, the filter is bypassed and flushed. The flushing operation, which is controlled by the programmable electronic controller in the power control unit, takes less than two minutes. The frequency of backflushing will depend on the concentration of magnetically susceptible contaminants, but in most cases is not required more than once a week.

The matrix of the EMF is composed of small type-430 stainless steel balls. The efficiency of the filter is unaffected by micron size of the material to be filtered from 20 microns down to 0.08 microns, and, when used in a system where the suspended material is predominantly magnetite, is independent of the flow rate through the filter up to the maximum design flow rate. The EMF is flushed by degaussing the matrix, and reversing the flow of process fluid so that it flows upward through the matrix, causing the bed of spheres to tumble against each other for about 15 seconds. This mild tumbling action is instrumental in removing the accumulated crud from the spheres and results in a completely clean matrix. This unique and complete matrix backflushing capability is one of the reasons that Milhous Company is able to offer a two-year performance warranty on the EMFs.

 

Operation Modes
Bypass Mode Filter in stand-by, unit powered, ready to be placed into operation.
Filtration Mode Filter in stand-by, unit powered, ready to be placed into operation. Sphere bed magnetized. High field gradients in the interstices between the spheres attract the magnetic particles which collect on the spheres.
Degauss Mode Sphere bed is demagnetized. Magnet coil is de-energized and current is reversed and reduced in successive steps to remove residual magnetism.
Flush Mode Sphere bed is fluidized. Tumbling action scrubs and dislodges collected particles which are flushed out through the drain line.