Common Questions Asked About the Milhous Company EMF
1. What is the best location for an Electromagnetic Filter to reduce corrosion product oxide concentration in the Feedwater?
In systems having pumped forward drains, the best location is usually in the high pressure feedwater heater drains. Data indicate that in most plants over 50% of feedwater iron oxide contamination is contributed by the heater drains. Filtering this higher concentration, lower mass and lower pressure stream is more cost effective than filtering the lower concentration, higher mass flow, higher pressure feedwater stream.
2. What is the expected form of the corrosion products in the high pressure heater drains during power operation?
Experience indicates that these are predominantly magnetite in nuclear plants. The mixture is usually 80%-20% Fe304 and Fe203.
3 What features in the EMF are provided to assure against inadvertent release of accumulated corrosion product oxides in the event of a power failure?
Quick reaction fail-safe valves are provided on the inlet and outlet to isolate the EMF system. A by-pass valve automatically opens simultaneously to maintain process flow. Residual magnetism in the sphere matrix does not permit immediate, total release of the collected corrosion products.
4. What are some advantages for the EMF as compared to Powdered Resin precoat filters or deep bed demineratizers?
- There is, of course, no chance of adding a contaminant from the EMF such as resin bead fragments or ionic leakage from the ion exchange resins.
- It requires no consumables except power. Power requirements are low.
- It has simple waste disposal requirements.
- It can be applied at high temperatures.
5. What are the advantages of carbon steel over stainless steel as a shell material?
It has a greater magnetic permeability which allows a more efficient magnetic coupling between the coil and the matrix. It is the same material that is typically used in the construction of FW piping systems. It is not as susceptible to stress corrosion cracking as the stainless steels. It can be readily fabricated and is more economical. Although carbon steel is less corrosion resistant, this can be controlled by proper operating chemistry, storage chemistry and storage and shipping procedures.
6. What are some other advantages of the Milhous Company EMF?
It uses water cooling for the coil windings and it occupies a smaller unit volume (space) than high gradient magnetic filters. Of special importance to operators of nuclear plants is the fact that the sphere matrix is permanent. The costly and possibly hazardous task of matrix replacement is therefore eliminated. The EMF requires approximately one third the power of other magnetic filter designs while delivering comparable removal efficiency this power savings can be significant over the operating life of the unit.
7. Does Milhous Company provide services for start-up and operation?
Yes. Milhous provides quick and reliable service as a part of any product supplied.
8. Will the Milhous Company EMF remove other corrosion products and/or paramagnetic corrosion products?
The corrosion product of steel that is paramagnetic is Fe203. This material is weakly magnetic and is removed by magnetic attraction as well as agglomeration and/or removal with magnetically susceptible corrosion products. Other paramagnetic corrosion products such as copper, cobalt and zinc oxide have also been removed. It is believed that these metals are substituted in spinel structures for iron and thus are removed.
9. What is the pressure drop and does the pressure drop increase during operation?
Ordinarily the initial pressure drop is about 10-15 psi and it increases only about 10% at maximum loading. This may vary with application. For instance, the viscosity and density of water is lower at higher temperatures, and this will affect the pressure drop. :
10. What is the retention capacity for particulate?
Our design rule is about 10 Ibs. of oxide per 1000 Ibs. of spheres. We have, however, observed as high as 17 Ibs./lOOO Ibs. in the laboratory. A thirty inch filter with a 2000 gpm flow capacity will retain about 18.5 Ibs. of particulate.
11. What is the frequency between flushes?
It is dependent on the initial concentration and the removal efficiency. However, for an inlet concentration of 100 ppb as Fe and a removal efficiency of 90%, the interval between flushes is about 9 days at design conditions.
12. What is the required backwash time?
It is about 2 minutes. Actual flushing time is 1 minute. The remainder of the time is for degaussing the matrix and the closing and opening of valves.
13. What is the volume of the backwash?
It is about 2-3 filter vessel volumes.
14. What is the backwash fluid?
Process fluid is normally used as the backflush fluid. However, auxiliary backflush water can be used if available.
15. What impact will an EMF system failure have on process availability?
None. It is a fail safe design that will automatically bypass and isolate the EMF upon detection of a fault. It can be bypassed and isolated manually also.
16. Is the EMF effective in removing sub-micron particles?
Milhous Company has investigated particle size distribution of corrosion products in power plant condensate. The data shows that the average particle size is 4.5 micron with less than 5 below 1 micron and less than 1 below .45 microns. The EMF has been tested to verify that it is equally effective in removing sub-micron particles as it is with the larger sizes typical of field corrosion products.
