EP0098811B1

EP0098811B1 - Method of decontaminating electro-mechanic apparatus from polychlorobiphenyl

Info

Publication number: EP0098811B1
Application number: EP83830130A
Authority: EP
Inventors: Aurelio Colombini; Mario Coppo; Vittorio Colombini; Enrico Colombo
Original assignee: Srl SIREA
Current assignee: Srl SIREA
Priority date: 1982-07-02
Filing date: 1983-06-23
Publication date: 1986-10-15
Anticipated expiration: 2003-06-23
Also published as: ATE22808T1; IT8222207A0; EP0098811B2; DE3366842D1; IT1157287B; EP0098811A1

Abstract

The method of decontaminating electro-mechanical apparatus from polychlorobyphenyl comprises the steps of: - maintaining the apparatus to be decontaminated submerged in a sealed chamber in vapours of a suitable solvent; and - constantly changing the pressure and temperature of this solvent so as to permit at any time a condensation of the solvent vapours on the surfaces under treatment. The solvent vapours can be produced inside the sealed chamber and, by providing a top condenser, a reflux washing can be obtained, or the vapours can be produced outside the sealed chamber and then injected therein at the required pressure and temperature.

Description

The present invention generally relates to a method of decontaminating from polychlorobiphenyl electro-mechanic apparatus.
As known, for antifire purposes, fluids on the basis of polychlorobiphenyl (PCB) as insulating fluids in electrical apparatus or as hydraulic liquids in mechanical apparatus have been often used in the past. These fluids, generally a mixture of 40% of hexachlorobenzene and 60% of polychlorobiphenyl, exhibit antifire properties which assure a reliable operation of electrical or mechanical apparatus even in environments in which the fire conditions could be promoted.
For example, there are in Italy only tens of thousands of transformators, circuit breakers and other electric apparatus still filled with this fluid and an undefined number of hydraulic apparatus almost certainly still contaminated by PCB.
The suspected cancerous action or at any rate the harmfulness of PCB has caused the use of these fluids in the above mentioned apparatus to be suspended, which fluids are gradually substituted by other less dangerous fluids.
The aggressiveness of fluids on the basis of PCB towards the components of these apparatus is so greatthat their decontamination becomes an extremely difficult operation and the great harmfulness thereby exhibited causes it to be more convenient to bury all the apparatus into suitably prepared pits than to try a decontamination thereof.
Of course, for economical reasons, this has given rise to the problem of the recovery of these apparatus by trying to decontaminate them as much as possible by reducing the PCB contents at least within limits which are permissible and tolerable from the ecological standpoint.
Recently, attempts have been made to wash the contaminated apparatus with suitable solvents in a liquid phase,.however this method has proved to be difficult, time consuming, expensive and it has not successfully.
In fact, the PCB absorbed by materials such as paper and wood which are normally present in most apparatus and the PCB adsorbed by the inner portion of the magnetic lamination pack or the electric windings cannot be totally removed, at least in a short time, because of its aggressiveness and therefore a portion thereof remains attached to these apparatus so that, with the passing of time, it can be dissolved in the new liquid used in substitution thereof, thereby forming a contaminating element for the latter.
US―A―4.008.729 discloses an apparatus for cleaning articles in volatile solvent wherein the article to be cleaned is placed in a container connected to a solvent collector with siphon and provided with a condenser. The solvent in the container is heated to boiling temperature to generate solvent vapours to bathe the article in solvent vapours and condensate which forms on the condenser and drips into the container to wash impurities from the article.
In this apparatus the article to be cleaned is immersed in the liquid solvent up to the level of the siphon tube extending in the container and therefore the solvent vapours are not in contact with all the article, but only with the portion thereof emerging from the siphon level. Furthermore this treatment is carried out at atmospheric pressure.
It is therefore the main object of the present invention to obviate the above mentioned disadvantages of the known method by providing a new method permitting the above mentioned apparatus to be decontaminated as much as possible, however within ecological acceptable limits so that the apparatus can be reused.
It is another object of the present invention to provide a method of decontaminating from PCB electrical and mechanical apparatus, which can be carried out without the intervention of operators in contact with the PCB.
It is still another object of the present invention to provide a method of the abovementioned kind, which assures in the most absolute way any possibility of environment contaminations.
It is a further object of the present invention to provide a method of the abovementioned kind, which provides a quick decontaminating action so as to be inexpensive, and which can be carried out as simply as possible without requiring sophisticated and expensive equipment.
These and other objects of the present invention, which will be more apparent from the following description, are attained according to the invention by a method of decontaminating an electrical or mechanical apparatus contaminated with polychlorobiphenyl using a solvent for polychlorobiphenyl which is chemically inert thereto, which method is characterized by:

maintaining the apparatus to be decontaminated submerged in a sealed chamber in vapours of the solvent; and
controlling the pressure and temperature of the solvent vapours so as to permit at all times a condensation of the solvent vapours on the surfaces under treatment.

According to a feature of the present invention, the solvent vapours are generated in a sealed chamber.
According to another feature of the present invention the solvent vapours are generated by heating means and condensed at the top of the sealed chamer so as to perform a reflux washing of the apparatus.
According to a further feature of the invention, the solvent vapours are generated outside the sealed chamber and then injected therein to wash the apparatus.
The solvent is non-toxic and also compatible with the apparatus materials and has a distillation temperature lower than that of PCB.
Advantageously, the distillation temperature of the solvent is lower than the maximum temperature tolerable by the apparatus to be decontaminated and higher than the room temperature for handling and conservation facility thereof.
Preferably, dearomated heptane or trichioro- ethane is employed as solvent.
According to still another feature of the invention the temperature of the solvent vapours is increased stepwise as a function of the average temperature of the apparatus to be decontaminated.
The invention will be now described in more detail in connection with a preferred embodiment thereof, given by way of example only and therefore not intended in a limiting sense, which is shown in the accompanying drawing, wherein:

Fig. 1 is a diagrammatic sectioned view of a box containing the electric apparatus to be decontaminated, for example a transformer, and provided with the necessary means for carrying out the method of the invention;
Fig. 2 diagrammatically shows the solvent action during the washing step in liquid phase;
Fig. 3 diagrammatically shows the solvent action during the washing step in a vapour phase;
Fig. 4 is a plot of the diagram of the solvent condensation temperature vs. time, during the washing process;
Figs. 5 and 6 show a diagram of the PCB contents in the apparatus under treatment vs. the removal time thereof for the liquid phase washing and the vapour phase washing respectively, showing the more than good results obtained by means of the method of the invention.

As can be seen from Fig. 1, the apparatus under treatment is put in a box B which is heated on the bottom and on the four lateral walls by means of jackets E through which a suitable heating fluid passes, which is fed through an inlet G, through a valve I and is discharged through an outlet H. On the top of the box B a condenser L is arranged through which water flows, the temperature of which is controlled by a thermostat M controlling a water discharge valve N.
Inside the box B the temperature is controlled by a thermostat F controlling the valve I and the pressure is controlled by a vacuostat 0 controlling a solvent discharge valve P, everything so as to keep constantly the apparatus A submerged in the solvent vapours under vacuum and to cause the solvent vapours to be always condensed on the walls thereof and to flow downwardly thereon thereby developing their flooding action according to the plot of Fig. 4, where T1 designates the vapour condensation temperature and T2 designates the average temperature of the apparatus A under treatment. Preferably the solvent used in this case is dearomated eptane which exhibits all of the above mentioned features for performing the washing operation.
As can be seen from Fig. 4, the temperature T1 is stepwise controlled as a function of the temperature T2 taken over by the apparatus A, i.e. as the temperature T2 of the apparatus A approaches to vapour condensation temperature T1, the latter is increased of a step ΔT, and this operation is repeated until the washing is ended. The box B is further provided with a solvent inlet S. a thermometer V for measuring the solvent vapour temperature and an inert gas source R connected to the box through a valve Z, a non- return safety valve Q calibrated so as to assure that the pressure inside the box B does not exceed the safety values and a drainage tube D for the gravity discharge of the polychlorobiphenyl.
Once the washing operation is ended it is sufficient to evacuate the box B through the valve P and to condensate the solvent vapours, by recovering all the solvent through the outlet C while the removed PCB is readily discharged through the drainage tube D.
The inert gas source R during the solvent discharge operation is connected to the box B in order to avoid the air to enter therein, which could give rise to possible combustion of the hot solvent.
Although the described embodiment shows a washing method with solvent reflux, the same method could be carried out without the top condenser, or it could be otherwise carried out by providing outside the box B a solvent vapour source and then injecting the solvent vapours into the box B following the requirements for performing the washing operation.
Figs. 2 and 3 diagrammatically show the action of the solvent on the PCB during a liquid phase washing operation and during a vapour phase washing operation, respectively. As can be seen from Fig. 2, the area A is static and therefore there is a poor solvent substitution which, when it is saturated, stops its penetration, whereas in Fig. 3 there is a continuous solvent substitution with resulting higher penetrability into the components of the apparatus to be decontaminated.
By means of the method according to the invention an automatic washing without the intervention of operators in contact with the PCB occurs. During the full washing cycle all the necessary equipment does not come into contact with PCB and, once the washing operation is ended, it is fully cleaned and decontaminated, with the exception of the lower PCB collecting zone. Furthermore, any possibility of environmental contamination is avoided since the system does not provide circuits for the PCB containing solvent (pumps, pipes, connectors etc.), which could give rise to contamination problems. The washing efficiency is very good since the solvent retains always its dissolving capacity without ever reaching the saturation and moreover the solvent can completely penetrate within interstices also of capillary nature.
The decontamination operation is extremely quick. It has been experimentally proved on a tipic series of electric transformators that the PCB embedded in the paper or wood or enclosed in too near walls forming the magnetic core or the windings thereof, is very difficult to remove (see plot of Fig. 5, wherein the curve shows the PCB decontamination efficiency with liquid phase solvent, where after about three hours of treatment the decontamination rate is about 40% of PCB) whereas, according to this method, the PCB is almost fully removed in the same time (see Fig. 6 wherein the curve shows that in the same time as in Fig. 5 the PCB has been removed in a very high percentage).
From tests effectively carried out it has been proved that the amount of PCB remained on a transformator containing 200 Kg of insulating liquid is less than 100 gr.
Another advantage of this invention is the very low amount of solvent required for the decontamination and easy recovery thereof since it is sufficient an amount less than 1% of the amount required for carrying out the liquid phase washing, which results in a lower cost of solvent recovery, asthis can be recovered by taking advantage of the heat supplied by the heaters by simply evacuating the box once the washing is ended and the PCB has been separated therefrom.
The so decontaminated apparatus can then be recovered and reused by substituting forthe PCB a usual oil or a silicone oil or a liquid usually employed to this end.
From the foregoing it will be readily apparent that the method according to this invention permits a decontamination from PCB with very high yields to be obtained, what could not be obtained till now.

Claims

1. Method of decontaminating an electrical or mechanical apparatus contaminated with polychlorobiphenyl using a solvent for polychlorobiphenyl which is chemically inert thereto, characterised by:

maintaining the apparatus to be decontaminated submerged in a sealed chamber in vapours of the solvent; and

controlling the pressure and temperature of the solvent vapours so as to permit at all times a condensation of the solvent vapours on the surfaces under treatment.

2. Method as claimed in claim 1, characterized in that the solvent vapours are generated in the sealed chamber by associated heating means.

3. Method as claimed in claim 2, characterized in that the solvent vapours are generated by heating means and condensed at the top of the sealed chamber so as to perform a reflux washing of the apparatus.

4. Method as claimed in claim 1, characterized in that the solvent vapours are generated outside the sealed chamber and then injected therein to wash the apparatus.

5. Method as claimed in any one of claims 1-4, characterized in that the solvent is non-toxic and is also compatible with the apparatus materials and has a distillation temperature lower than that of PCB.

6. Method as claimed in any one of claims 1-4, characterized in that the distillation temperature of the solvent is lower than the maximum tem- peratue tolerable by the apparatus to be decontaminated and higher than the room temperature for handling and conservation facility thereof.

7. Method as claimed in any one of the preceding claims, characterized in that dearomated heptane or trichloroethane is employed as solvent.

8. Method as claimed in any one of the preceding claims, characterized in that the temperature of the solvent vapours is increased stepwise as a function of the average temperature of the apparatus to be decontaminated.