A radial flow electrofilter having a vertical cylindrical fluid distributor means adapted to serve as a grounded electrode, a vertical central tubular collector also adapted to serve as an electrode and at least one, preferably a plural odd number, of permeable cylindrical electrodes concentrically positioned between the distributor and the collector. The filter medium preferably consists of non-deformable particles, the filter being provided with backflushing means. In operation, finely divided solids, contained in a liquid of low conductivity, may be efficiently removed by passing the liquid radially through the filter, while subjected to a unidirectional current electric field, from the periphery of the filter toward its center.

FIELD OF THE INVENTION 
This invention relates to electrofiltration apparatus and to a process for 
electrofiltration employing such apparatus. 
BACKGROUND OF THE INVENTION 
It is known to remove solids from hydrocarbon and other organic liquids by 
the use of electrofilters. The electrofilter is a device having a filter 
bed of a porous medium in which an electric field is maintained by one or 
more energized electrodes. The electric field is of high intensity so that 
the solids are removed from the liquid stream by becoming tenaciously 
attached to the surfaces of the porous medium. Such porous medium may be, 
for example, a polyurethane foam or may be composed of hard granular 
particles. 
Among the electrofilters of this general type, mention may be made of those 
shown in U.S. Pat. Nos. 3,799,856 to Franse, 3,891,528 to Griswold, 
3,928,158 to Fritsche, 4,059,498 to Crissman et al and 4,040,926 to 
Oberton. 
It is an object of this invention to provide improved electrofiltration 
apparatus. 
It is a further object of this invention to provide an efficient 
electrofiltration process. 
Other objects of the invention will become apparent from the following 
description. 
SUMMARY OF THE INVENTION 
In accordance with this invention, there is provided an improved 
electrofilter for use in the removal of finely divided solids from liquids 
of low electrical conductivity. The electrofilter comprises a vertical 
cylindrical metallic vessel; a metallic cylindrical fluid distributor 
within the vessel, concentric with and spaced a small distance apart from 
the vessel wall, thereby providing an annular space between the 
distributor and the vessel wall, the distributor being adapted to serve as 
an electrode at ground potential; a fluid inlet in the side of the vessel 
fluidly communicating with the annular space; a metallic permeable central 
tubular outlet collector extending vertically through at least a portion 
of the porous bed and adapted to serve as an electrode; a fluid outlet 
fluidly connected to the outlet collector and extending outside of the 
vessel; at least one permeable cylindrical electrode extending vertically 
through at least a portion of the bed and concentrically positioned 
between the distributor and the outlet collector; and conductor means for 
supplying potential to at least alternately spaced electrodes to provide 
electric fields between adjacent electrodes. 
In the main embodiment contemplated, the electrofilter of this invention 
includes also backflushing means, which may include a backflush inlet, a 
backflush fluid distributor in the bottom portion of the vessel fluidly 
communicating with the backflush inlet and a backflush fluid outlet in the 
upper portion of the vessel. A plural odd number of permeable cylindrical 
electrodes are preferably employed, in which case means are provided for 
electrically grounding the outlet collector and the alternately spaced 
electrodes between the outlet collector and the cylindrical fluid 
distributor. 
Non-deformable particles such as glass or porcelain beads or particles of a 
silicon dioxide containing mineral, such as those disclosed in the above 
referred to Oberton patent, are preferred as the dielectric filtering 
medium in this embodiment, although non-conductive deformable material 
having voids, such as open-pore polyurethane foam or nylon mesh wrapped in 
layers or nylon cord wrapped to create voids, may also be employed. 
A further aspect of the invention relates to a process for the 
electrofiltration of a liquid of low electrical conductivity containing 
finely divided solids, comprising passing the liquid in a radial direction 
through a cylindrical porous bed of a dielectric filtering medium, the bed 
being disposed interiorly of a cylindrical distributor maintained at 
ground potential and exteriorly of a central tubular collector, and being 
traversed for a major portion of its length by at least one permeable 
cylindrical electrode concentrically positioned between the distributor 
and the collector, which also serves as an electrode. A unidirectional 
current electric field is maintained between adjacent electrodes, between 
the distributor and the electrode adjacent thereto and between the 
collector and the electrode adjacent thereto. The electric field is 
discontinued when the bed becomes loaded with finely divided solids to the 
extent that filtering effectiveness becomes impaired and the solids are 
removed from the bed by backflushing it with a backflush liquid. 
The preferred direction of flow of the liquid being filtered is from the 
outer periphery of the bed toward its center. The bed preferably consists 
of non-deformable particles such as glass or porcelain beads or particles 
of a silicon dioxide containing material. 
The unidirectional current electric field utilized is preferably a 
continuous direct current field, preferably provided by a voltage gradient 
between 1 and 60 KV per inch, with the electrodes spaced from 1 to 5 
inches apart. It is preferred to employ an odd number of electrodes, with 
the central collector and the alternate electrodes between the collector 
and the distributor being at ground potential and the remaining electrodes 
energized. Most preferably, a plural odd number of electrodes between the 
collector and distributor are employed. The use of multiple electrodes 
allows close spaced treating gaps in larger vessels. Larger vessels are 
less expensive for large streams than a multiple of smaller units. 
The radial flow of the liquid being treated from the outer perimeter of the 
filter medium to its center, as described above, has the advantage of 
having the dirty oil at the outer perimeter where the radial flow is the 
slowest, as opposed to the center, where the flow rate is the greatest. As 
the rate increases with flow to the center collector, cleaner oil is being 
further cleaned. Radial flow in the reverse direction, i.e., from the 
center outward, has the disadvantage that the dirtiest oil is treated at 
the highest rate of flow. 
It will be seen, however, that regardless of the direction of the flow, the 
apparatus involved may in some cases be the same. In such cases (e.g., the 
embodiment shown in FIGS. 1 and 2, described below), although the 
apparatus is described in the specification and claims employing 
terminology which assumes flow from the outside to the center, the 
apparatus would still be the same and within the intended scope of the 
claims if the flow were in the other direction. Similarly, although the 
terminology in this specification assumes operation of the apparatus in a 
vertical position, the apparatus can be employed in other than a vertical 
position since its operation is not gravity dependent.

FIGS. 1 and 2 show an electrofilter of this invention. This filter includes 
a generally cylindrical metallic electrofilter vessel 1 having a fluid 
feed inlet 2 in the sidewall and provided with a metallic cover 3 having a 
centrally positioned vertical neck portion 4. Inside the vessel 1, 
concentric with and spaced a small distance apart from the vessel walls, 
is a metallic cylindrical distributor liner 5, having meter orifices 6, 
which may be covered by screens or slotted covers 7. Distributor liner 5 
is fastened at its top and bottom to the wall of vessel 1. Interiorly of 
the distributor liner 5 is a porous bed of a dielectric filtering medium 
8, suitably glass or porcelain beads, although other types of 
non-deformable dielectric particles may be employed, including silicon 
dioxide containing minerals such as those disclosed in Oberton U.S. Pat. 
No. 4,040,926. The screens or slotted covers 7 serve to keep these 
particles from plugging the orifices 6. Less preferred as filtering media 
are open-pore polyurethane foam and other non-conductive deformable 
materials having voids, such as nylon wrapped in layers or nylon cord 
wrapped to create voids. A metallic tubular collector 9, having meter 
orifices 10, is centrally positioned within vessel 1 and extends most of 
the height of the vessel. A tubular extension 11 of the collector 9, 
lacking the orifices, extends through the vessel cover 3 and serves as the 
product outlet. As shown in the drawing, a plurality of concentric 
electrodes 12 and 13, concentric with the collector 9, extend vertically 
through the porous bed 8 for most of its height. The electrodes 12 and 13 
are permeable, being formed of expanded metal or other open material, such 
as sheet metal punched with holes or slotted metal. As shown in FIG. 1, 
there are an odd number of electrodes, of which electrodes 12 are at 
ground potential, and electrodes 13, alternating with electrodes 12, are 
energized. In addition to electrodes 12, the distributor liner 5 and the 
collector 9 also constitute ground potential electrodes. As shown, 
electrodes 12 are attached mechanically and electrially to the bottom of 
vessel 1. The distributor liner 5 is similarly attached to upper and lower 
parts of the vessel sidewall and outlet collector 9 is in electrical 
communication with vessel 1 by way of the neck portion 4 of cover 3. An 
annular space 14 exists between outlet collector 8 and the sidewall of 
neck portion 4. Energized electrodes 13 are connected together in parallel 
by a conductor 15 and supported as a unit from entrance bushing 16 and 
insulator support 17. The attachment at entrance bushing 16 also serves as 
the source of electrical potential to the electrodes 13, the entrance 
bushing serving as the conduit for high voltage D.C. power supplied by the 
wire or electrical conduit 18 from a source not shown. 
Although the drawing shows two energized electrodes 13 spaced between 
grounded members 5, 12 and 9, as few as one energized electrode spaced 
between two grounded members is sufficient. Where the outermost and 
innermost electrodes are grounded as shown (e.g., distributor liner 5 and 
outlet collector 9), an odd number of electrodes is thus present. 
It is also possible, although not preferred, to make the outlet collector 9 
function as an energized electrode, in which case there will be an even 
number of electrodes. It is further possible, although also not preferred, 
to employ two separately energized electrode systems. In every case, 
however, the vessel has to be at ground potential for safety. 
A fluid inlet header 19 for backflushing purposes extends through the 
bottom of vessel 1 and communicates fluidly with fluid distributor outlets 
20. These outlets are preferably slotted to prevent the particles of the 
filter medium from plugging them. Suitable for this purpose are Johnson 
Well Screens.RTM.. Annular space 14 serves as an outlet annulus for the 
backflush fluid, being provided with an outlet conduit 21. A pump out 
drain 22 is provided in the bottom portion of vessel 1. 
In operation, a raw liquid feed containing finely divided solid particles 
is introduced into vessel 1 through feed inlet 2 and passes through the 
orifices 6 of the distributor 5 and then in a generally radial direction 
through the filter medium 8 and the permeable electrodes 12 and 13 to the 
outlet collector 9. During its passage through the medium 8, the feed is 
subjected to the action of an electric field between adjacent electrodes, 
the result of which is that the finely divided particles separate from the 
feed and are retained in the medium. 
The product of this operation passes through the orifices 10 of the 
collector 9 and upwardly through the collector and its tubular extension 
11, which serves as the product outlet conduit. 
When the filter medium 8 becomes loaded with the separated solids to the 
extent that the efficiency of the filter is impaired, the filter bed is 
backflushed with a suitable flushing fluid such as a raw feed stream or 
other stream which can be recycled back into processing or otherwise 
disposed of while containing the contaminant. This fluid is introduced 
through backflush inlet header 19 and distributor outlets 20 and passes 
upwardly through the filter medium 8 into the annular space 14, from which 
it exits by means of backflush outlet conduit 21. 
The spaceing between the electrodes and the voltage employed are 
interrelated. In general, these are set so that a voltage gradient in the 
range of 1 KV to 60 KV per inch is achieved, the latter figure being about 
the limit for commercial power supplies. It is possible to design and use 
equipment with higher potentials, but after 75 KV, these are costly. The 
potential gradient chosen will depend on the nature of the solids in the 
feed. The electrodes are ordinarily spaced from 1" to 5" apart, as 
required to achieve the desired potential gradient, taking into 
consideration the power supply capability. 
It will be evident that the forgoing description is illustrative of, rather 
than limitative upon, the invention as defined by the appended claims and 
that various changes and modifications can be made in the apparatus and 
methods exemplified without departing from the spirit of the invention.