Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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1VAPOR SOLVENT DECONTA;~INATION
2 OF
3PCB TRAI~S~OR I~lER CO~ PO~ENTS
4 Field of Invention
The invention relates in general to electrical apparatus, such as trsns-
6 formers, and more particularly to the remo~al of residual polychlorinated
7 biphenyls from transformer components.
8 Background of the Invention
9 Since 1929, polychlorinated biphenyls (PCB) have been produced industri-
10 ally. The outstanding properties of PCBs include thermal stability, resistsnce
11 to oxidation, acid, bases and other chemical agents and excellent di-electric
12 properties. Because of these properties, PCB fluids were used extensively
13 for electrical transform~ers and capacitors.
14 The toxicity of PCBs has been known for several decades. PCBs cause
yellow atrophy of the liver, fatty degeneration of the liver and dermatitis.
16 In addition, PCB is a suspected carcinogen. In 1966, the presence of PCB in
17 environmental samples was discovered. Concern in the late 1960s and early
18 1970s about potential en~ironmental hazards, coupled with its long-term sta-
19 bility, resulted in the 1976 ban on PCB manufacture and use
(15 U.S.C.A. 2605(e)(2)(A)).
21 The largest remaining source of PCBs is liquid cooled electric transform-
22 ers. Under current Environmental Protection Agency (EPA) regulations, there
23 are two alternstives for possessors of PCB containing transformers, retrofill
24 or replacement. Retrofill of ~existing equipment is usually the least costly
25 and easiest for oil and Askarel- filled transformers.
26 There are numérous methods a-.railable for retro~illing PCB containing
27 transformers, for example, U.S. patent Nos. 4,685,972, 4,124,834, 4,425,949
28 and 4,483,717. These methods deal with removing the PCB liquid, nushing
7 ~ 1
the transformer and refilling with a non-PCB liquid. All of these methods
2 sre specifically aimed at decontaminating useful equipment. More particu-
3 larly, the novelty of those methods is frequently a more efficient or thorough4 process or a process th~t allows the transformer to remain in service during
5 the decontamination. The present invention does not pertain to this category
6 of transformers.
7Retrofilling may not be suitable for all PCB containing transformers.
8Transformers in poor condition, or which have failed, or which are no longer
9useful require replacement and disposal of the removed carcasses.
10Disposal of replaced transformers has long presented the owner with a
11dilemma. Current EPA regulations allow for disposal of PCB transformers in
12Toxic Substances Control Act approved landfills, but only after draining and
13an 18 hour rinse. Although landfill is authorized, this disposal method is not14without substantial potential for long term liability. The transformer carcass15can still contain up to 2% of its nameplate volume (20 to 100 lbs) soaked
16within its internals and the original owner remains responsible, jointly and
17severally, under the Comprehensive Environmental Response Compensation and
18Liability Act (CERCLA or "Superfund").
19The present invention is directed at decontaminating the components of
20PCB containing transformers. Once the transformers are decontaminated, the
21components can be disposed of as non-toxic, non-hazardous waste.
22Summary of the Invention
23The invention consists of a process to recover reclaimable material from
24PCB containing transformers and to reduce the volume of materials which are
25subject to EPA regulations to a minimum.
26The transformer is drained and given an initial cleaning. The transformer
27internal parts are renloved and cleaned a second time as is the empty trans-
28former casing. Recoverable materials such as aluminum and copper are
29cleaned to less than 1011g / lOOcm2 PCB. This allows these metals to be
30 reclaimed rather than buried. Almost all of the remaining non-metallic
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materials are combustible solids or liquids, both of which can be destroyed by
2 incineration.
3 First, 8 PCB contsining transformer is drained of any residual liquid.
4 The drai ned transformer is placed into the primary cleaning tank where sol-
vent is used as a vapor/spray degreaser to remove PCBs from the trans-
6 former.
7 After completing this initial cleaning process, the transformer core and8 wire coils are separated from the transformer casing. The casing is returned
9 to the primary cleaning tank for further cleaning by vapor/spray degreasing.
The insulation on the wire coils is mechanically removed. The trans-
11 former core is dissembled. The transformer core metal components, the bare12 wire coils snd any miscellaneous metal parts are placed into the secondary13 clesning station for further cleaning.
14 The secondary cleaning station is a vapor/degreaser consisting of threeseparated sections. The loose parts are placed into a basket and then into
16 the third section of the secondary cleaning station. The baskets are tumbled
17 while in the secondary cleaning station. The decontamination process consists
18 of solvent degressingr enhanced by the mechanical action of the tumblers.
19 The parts are sequentially processed from section three to section two andthen to section one of the secondary cleaning station. The solvent cascades
21 from section one to section two and then section three. As the parts
22 progress through the three sections of the secondary cleaning station, the23 parts are processed by progressively cleaner solvent which improves the PCB
24 removal rate.
The contaminated solvent is processed in an isothermal separator to sepa-
26 rate the PCB from the solvent. The cleaned solvent is returned to the
27 cleaning station for further use. The still bottoms with high concentrations
28 of PCBs are stored for future shipment and incineration.
29 The transformer casing and dissembled parts are processed until the PCB levels are less than 10ug / 100cm2.
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The cleaned metal is recycled since it is no longer hazardous waste.
2 Any combustible solids such as paper, gaskets, insulation and wood, are col-
3 lected along with any PCB liquids drained from the transformer and the PCB
4 contaminated still bottoms. These combus~ible~ solids and PCB liquids are de-
S stroyed at an EPA approved incinerator.
6 Upon completion of the transformer cleaning process, there are no mate-
7 rials remaining that reguire disposal as hazardous waste by being buried at 8
8 la nd fill .
9 Brief Description of the Drawings
Fig. 1 is a diagram of a process for the decontamination of PCB con-
11 taining transformers.
12 Fig. 2 is a perspective view of the tumbling basket.
13 Detailed Description of the Invention
14 The PCB containing transformer is initially drained of any residual liq-uids. Typically, 1 gallon or less of liquid is drained. The drained liquid is
16 transferred to a holding tank lO for eventual disposal by incineration.
17 The transformer bottom valves and cover are removed. If additional
18 drainage is required, a small hole is drilled in the bottom of the transformer.
19 The transformer 31 is then placed into the primary cleaning tank 1.
The exterior of the transformer and all accessible interior surfaces are
21 washed with liquid solvent using e spray wand 3. The solvent is taken from
22 the bottom of the primary cleaning tank, below a false bottom 7. After this23 initial wash, the vapor hose 8 is plsced inside the transiormer, the primary
24 cleaning tank cover 4 is closed and heated liquid solvent provided by an
isothermal separator 9 is circulated through the transformer for 30 to 90
26 minutes.
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Clean solvent vspor is then circulated through the primary cleaning tank
2 1. The primary cleaning tank operates as a vapor/degreaser for 4 to 8
3 hours; An isothermal separator 9 provides clean solvent to the vapor hose 8
4 through heater 6. The isothermal separator takes a suction from the bottom
5 of the primary cleaning tank whenever the separator requires additional sol-
6 vent. The still bottoms containing high concentrations of PCBs are stored 10
7 until shipped for eventual destruction. Additional clean solvent is provided
8 to the isothermal separator 9 as needed from a makeup tank 17.
9 The transformer casing 31 is drained and after drying, the transformer is
removed from the tank. Typically, this first cleaning reduces PCB levels
11 from the range of 600,000 ppm to around 10,000 ppm.
12 The transformer is dissembled and all external parts, bushings, nuts, bolts,
13 name plates, etc are removed. Internal parts are also removed. Combustible
14 materials such as gaskets, loose insulation, paper and wood are removed and stored for eventual dispoSal as PCB containing solids.
16 The internals of a transformer consist primarily of the transformer core.
17 The transformer core is dissembled to separate the wire coils from the metal
18 laminations. The laminations, nuts, bolts and other miscellaneous metal parts
19 are ready for second stage cleaning in the secondary cleaning station 2.
The wire coils are coated with insulating material which is removed by
21 mechanical abrasion such as wire brushing. The insulation is collected and
22 held for eventual disposal as PCB containing solids. The stripped wire coils
23 are ready for second stage cleaning in the secondary cleaning station 2.
24 The miscellaneous metal parts, such as nuts and bolts, along with the
metal laminations and stripped wire coils are placed into a tumbling basket
26 11. The tumbling basket is then loaded into the secondary cleaning station
27 2. The secondary cleaning station is a vapor/degreaser cleaning tank divided
28 into three sections 12, 13, 14.
29 The parts to be cleaned are placed into section three 14 of the
30 secondary cleaning station 2. The parts are cleaned by both the
2~7 ~1
vspor/degreasing sction of the solvent snd the mechanicsl sction Or tumbling
2 when the basket 11 is rotated. The bsskets are rotated horizontally st two
3 rpm while in the secondsry cleaning station. After a cleaning cycle of 30
4 minutes, the tumblin~ bssket is transferred to section two 13 for a 15 minute
S clesning snd then to section one 12 for a final 15 minute clesning cycle.
6 Clean heated liquid solvent is supplied to section one 12 of the secondary
7 clesning station by an isothermal separator 15. The solvent overflows from
8 this section into section two 13 and then into section one 14. This results
9 in the parts being clesned by progressively cleaner solvent, resulting in more10 efficient decontamination. Makeup to the isothermal separator 15 is taken
11 from section three 14 of the secondary cleaning station 2, which contains the12 most contaminated solvent. The still bottoms with high concentrations of
13 PCBs are stored 10 for future shipment and incineration.
14 The tumbling baskets 11 are partially immersed in liquid solvent. Cooling
coils 16 are provided in the vapor zone of the secondary cleaning station 2
16 to condense sny solvent Yapor. The condensed solvent drips into the region
17 of the secondsry cleaning ststion that is below the cooling coils.
18 The tumblers 11 are six-sided hexagon shaped bsskets sided with a wire
19 mesh screen 21. A drive motor snd gesr sssembly 24 are mounted on an ex-
ternal frame 27. A drive chain 25 snd drive sprocket 26 in conjunction with
21 the drive motor rotste the tumbling bssket 11 horizontally st 2 rpm while in
22 the secondsry clesning station. One section 23 of the tumbling basket is
23 hinged in order to provide access for inserting snd removing psrts. Internsl
24 members 22 sre provided to enhsnce the tumbling action snd prevent the
psrts from bunching together.
26 The empty transformer shell is returned to the primary cleaning tank 1
27 for a second cleaning. The transformer shell is washed using a second sprsy28 wand 18 spplying clean liquid solvent supplied by the isothermal separator 9.
29 The inside snd outside of the trsnsformer shell is washed three times for 10
to 15 minutes each time. The solvent vspor hose 8 is then plsced into the
31 trsnsformer shell and clesn solvent vspor from the isothermal separstor 9 is
32 circulated into the primary cleaning tsnk 1. This vspor/degressing cycle is33 continued for 4 to 8 hours.
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After the trsnsformer shell and parts complete the decontamination pro-
2 cess, the surfaces are tested for PCB contamination. If the PCB level3 exceeds 101~g / 100cm, the parts are returned to the primary cleaning tank
4 1 or the secondary cleaning station 2 for additional decontamination.
The process of decontaminating the transformers uses trichloroethylene as
6 the solvent. Trichloroethylene was chosen for its low boiling point, 189~ F,
7 v~hich mal~es it relstively essy to recycle the trichloroethylene using an
8 isothermal separator. Typically, the trichloroethylene can be maintained be-
9 low 10ppm PCB.
Actual decontamination results are shown in the table below.
11 Asl;arel~ transformers 10C oil transformers
12 Transformer Size 5 - 2000 KVA 45 - 1000 KVA
13 Initial PCB Concentrations, ppm
14 400,000 - 900,000 580 - 13,000
EPA Permitted PCB Residual (~g / 100cm )
16 less than 10.0 Iess than 10.0
17 PCB Residual Range (~Ig / 100cm )
18 Transformer Shell 0.1 - 4.5 less than 1.0
19 Laminations 0.1 - 2.5 less than 1.0
~Yindings 0.1 - 2.1 less than 1.0
21 Average PCB Residual (~Ig / lOOcm2)
22 Transformer Shell 2.2 less thsn 0.1
23 Laminations 0.9 Iess than 0.1
24 7~7indings 1.1 Iess than 0.1
For each 125 cubic foot transformer processed, approximately 438 Ibs of
26 copper and aluminum, 1275 Ibs of steel casing and 1332 Ibs of steel lamins-27 tions are reclaimed rather than being buried. The majority of the remaining
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PCB contaminated solid wsste (approximately 142 Ibs~ is combustible material
2 that cat~ be destroyed in an approved incinerator rather than being buried.
3 Approximately 3 gallons of PCB containing liquids are removed or generated
4 during the decontamination pro~ess. These PCBs can also be destroyed
5 rather than being buried.
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