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.
Experience indicates that these are predominantly magnetite in nuclear plants. The mixture is usually 80%-20% Fe304 and Fe203.
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.
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.
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.
Yes. Milhous provides quick and reliable service as a part of any product supplied.
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.
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. :
Our design rule is about 10 lbs of oxide per 1000 lbs of spheres. We have, however, observed as high as 17 lbs./1000 Lbs. in the laboratory. A thirty inch filter with a 2000 gpm flow capacity will retain about 18.5 lbs of particulate.
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.
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.
It is about 2-3 filter vessel volumes.
Process fluid is normally used as the backflush fluid. However, auxiliary backflush water can be used if available.
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.
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 0.45 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.