EP0221028B1

EP0221028B1 - A process for the decontamination of apparatus or other materials contaminated by pcb or other toxic and noxious substances

Info

Publication number: EP0221028B1
Application number: EP86830132A
Authority: EP
Inventors: Mario Coppo; Piera Tacchina
Original assignee: ECOLSIR Srl
Current assignee: ECOLSIR Srl
Priority date: 1985-10-24
Filing date: 1986-05-20
Publication date: 1991-08-07
Also published as: EP0221028A1; IT8522607A0; DE3680744D1; IT1190411B; ATE65925T1

Abstract

A process for the decontamination of apparatus or other materials being contaminated with PCB or other toxic and noxious substances, comprises introducing the contaminated apparatus or material into an autoclave provided with a condenser, charging a liquid solvent to the autoclave to fill it up, applying an ultrasonic charge to the autoclave containing the liquid solvent, removing the dissolved contaminant-containing solvent from the autoclave while producing a vacuum, admitting solvent vapors to the autoclave until they reach the top part of the autoclave where the solvent vapors condense and commence to drop off, stopping the solvent vapor admission and repeating the above steps a few cycles.

Description

This invention relates to a process for decontaminating apparatus, particularly electrical apparatus, contaminated by toxic and noxious substances.
Included among noxious contaminants are arsenic compounds, chlorinated compounds, etc., but especially polychlorobiphenyls and dioxin.
As is known, polychlorobiphenyl (PCB) has physical and chemical properties which make it very suitable for a large range of applications. In general, aromatic chlorinated compounds possess very good chemical and dielectric properties and heat stability. In particular, polychlorobiphenyls are very stable, in general chemically inert, compounds and they do not react under normal conditions, so that only when in presence of reagents and under extreme reactive conditions they give rise to the formation of new compounds.
Accordingly, PCB was used as an electro-insulating fluid for transformers and condensers, as an industrial fluid for use in coolants for machine operations, in hydraulic systems and vacuum pumps. It is also utilizable as a flame retardant, heat transfer agent and plasticizer.
Unfortunately, some of the properties of PCB that contribute to its spreading range of applications are also involved in sanitary and ecologic problems recently abscribed to the use of polychlorobiphenyls. PCB are a class of compounds which, even though present in small amounts, are very toxic towards living cells and they produce systematic toxic effects. Comparatively recent research work has shown PCB as being a possible carcinogen and inducing neoplastic changes in mice.
PCB accumulates in aliments owing to its solubility in fatty tissues and its resistance to chemical degradation. Basically, the problems with PCB are that PCB is soluble in fats, is stored in animal lipids and tends to be concentrated in foods in high quantities. Moreover, resistance of PCB to thermal, chemical and biological degradation has contributed to its accumulation, particularly in industrial environments. The very low biodegradation rates and the high resistance to metabolic changes of PCB are causes for ecologic and pollution problems, so that measures have to be taken for elimination thereof. The system only used for eliminating PCB is incineration but incinerators are very expensive and cause further problems to arise. PCB is usually destroyed by incineration at high temperatures, say in excess of 1100°C with long residence times in the incinerators being required. The ordinary incinerators, as used for eliminating organic matters, normally tend to vaporize PCB rather than converting it to CO₂, water and HCl. Obviously, other toxic and objectionable substances exist which are very hard to eliminate and materials contaminated thereby require likewise special measures for elimination thereof.
Thus, there is a need for other methods of disposal of apparatus, particularly electrical apparatus, when contaminated by PCB and other contaminating substances. For example, most of them are presently buried into pits or caverns.
Accordingly, a different decontamination system for such apparatus has to be found which also should permit reutilization thereof without involving any dangers to the persons who have to manipulate them, or to the environment.
Most recently proposed processes for the decontamination of apparatus contaminated with PCB and other toxic and noxious substances have provided for consecutive washings with liquid solvent at atmospheric pressure to dissolve as high an amount of contaminant as possible in the liquid solvent, the contaminant being then eliminated and the solvent recovered. In the following, the term 'contaminant' is intended to include PCB and all other toxic and noxious substances such as dioxin, arsenic compounds, etc..
However, the above processes have not proven satisfactory in that, as already said, the involved contaminant is a chemical compound hard to dissolve, and this is especially so when apparatus to be decontaminated have parts to which access by solvent is difficult.
Other processes are also known which provide for washing the apparatus with solvent, the washing being effected in a vapor phase and under vacuum. These processes have proven satisfactory in that they succeed in removing contaminant from an apparatus to bring it down to an amount less than that accepted by ecological defense authorities. However, a disadvantage of these processes is the time they require for the decontamination of an apparatus, which time is in any case, under best operating conditions, of the order of not less than 48h.
European Patent No. 98 811 discloses a method of decontamination from PCB which is carried out completely under vacuum with solvent vapours. The curve of the solvent vapour temperature versus time in the autoclave is stepped with steps vertically extending, that is, the solvent vapour temperature in the autoclave and therefore the transformer temperature is increased or decreased by vertical steps. In the autoclave there is never liquid solvent, but only solvent vapours and the transformer is never cooled by liquid solvent.
US Patent No. 4,425,949 discloses a method of removal of undesirable substances, such as water, PCBs and air from the internal components of electrical devices, such as transformers. This method is carried out any time under vacuum and with solvent vapours in the transformer itself. This method does not carry out a decontamination, but a washing under vacuum and with solvent vapours. In fact, the transformer is treated in order to obtain a drying and degassing under vacuum of the components thereof by employing the condensating and heating process (vapour phase process).
An object of this invention is therefore to obviate also this latter disadvantage by providing a process for the decontamination of apparatus contaminated with toxic and noxious substances which requires a very reduced time over that involved in said other processes, while retaining efficiency of these latter.
Another object of this invention is to provide a process for the decontamination of apparatus which enables recovery of the solvent to be achieved in an automatic cycle without requiring any integrating distillation.
More specifically, the process according to this invention for the decontamination of apparatus being contaminated by toxic and noxious substances comprises:

a) introducing the apparatus to be decontaminated into an autoclave provided with a top condenser;
b) hermetically sealing the autoclave;
c) introducing a liquid solvent into the autoclave until it is filled;
d) applying a ultrasonic discharge to the autoclave containing the liquid solvent so as to promote the dissolution of the contaminant therein;
e) draining the liquid solvent containing the contaminant dissolved therein from the autoclave, thereby simultaneously producing a vacuum therein;
f) injecting solvent vapours in the autoclave until they, after having heated the apparatus, reach the top condenser where the solvent vapours begin to condensate;
g) stopping the injection of solvent vapours at the beginning of their condensation at the top condenser;
h) introducing again liquid solvent into the autoclave until it is filled and the solvent vapours are condensated so as to cool the apparatus;
i) repeating the steps d) to h) for a few cycles in order to cause the apparatus to undergo alternate washings with solvent in a liquid phase and in a vapour phase under vacuum.

This method permits an apparatus to be decontaminated. in a matter of a few hours, the apparatus being decontaminated to a residual contaminant content of less than 50 ppm.
The invention will now be described in full details in connection with a preferred embodiment thereof shown by way of a non restrictive example in the accompanying drawing, wherein the single figure diagrammatically shows a plant for carrying out the process of the invention.
Referring now to the drawing, there is illustrated a plant that comprises an autoclave A having a condenser C at its upper part, the condenser C forming a top wall for said autoclave. Provided in this top wall is a check valve V6 permitting the air in the autoclave to pass out thereof. An apparatus to be decontaminated, such for example as an electric transformer generally designated at T, is introduced into the autoclave by the aid of a basket D.
An orifice E is provided in the bottom of the autoclave and communicates the autoclave with an outlet pipe U branching into three pipe legs R1, R2, R8.
The pipe leg R1 is connected via a valve V1 and a circulating pump P1 to a pure liquid solvent tank SL, the pipe leg R2 is connected via a valve V2 and a circulating pump P2 to a tank SR for collecting the solvent having the contaminant dissolved therein, while the pipe leg R8 leads to discharge via a valve V8.
The collecting tank SR is connected through a pipe R3 and associated pump P3, to a distillation column Z which is designed for the distillation of the contaminant-containing solvent and from which pure solvent fractions in the form of vapors are supplied through a pipe R4, a pump P4 and a three-way valve V4, to either the condenser CO via a pipe R5, or the inlet G to autoclave A via a pipe R6. The pure solvent vapors condensed in condenser CO are supplied to the pure solvent tank SL through pipe R7 and pump P5. A valve V5 permits the residues of distillation to be discharged.
Mounted on the outside of autoclave A is an ultrasonic generator US which operates to cause a short ultrasonic discharge to pass through the autoclave walls with the purpose of enhancing solubility of contaminant in the solvent and ability of the solvent to penetrate porous materials.
Operation of the plant is very simple.
Once the transformer T has been introduced in the autoclave A, the autoclave A is closed to tightness and supply of pure liquid solvent from tank SL to the bottom of autoclave A commences to take place through pipe branch R1 and tube U via circulating pump P1 and valve V1, the valves V2 and V8 being closed. Upon the liquid solvent coming into contact with the transformer contaminated by toxic and noxious substances, the solvent commences to dissolve said substance. When the solvent has reached the top wall of autoclave A, valve V1 is closed and a ultrasonic discharge is effected from ultrasonic generator US whereupon valve V2 is opened so that liquid solvent, with the contaminant dissolved therein, is withdrawn by extracting pump P2 to be conveyed to receiving tan, SR. During this extraction of solvent from autoclave, a vacuum is produced therein due to the autoclave being thoroughly closed to tightness. Once the liquid solvent has been drained off the autoclave A, valve V2 is closed and thereafter valve V4 is opened to permit a stream of hot (50° - 80°C) solvent vapors from distiller Z to be admitted to the autoclave via the pipe R6. The solvent vapors flow upwardly and upon reaching the toy of autoclave they commence to condense under effect of condenser C to fall down in the form of droplets. At this time, a signal is issued from a level indicator ML and causes valve V4 to be operated so as to permit solvent vapors to enter the condenser CO whereupon condensed pure liquid solvent formed in this condenser is supplied back to tank SL through pipe R7 and pump P5. The solvent vapors injected into the autoclave act on the treated apparatus in such a manner as to remove contaminant particles from the most hidden interstices of said apparatus. At this time, valve V1 is re-opened to admit again fresh liquid solvent to the autoclave via the circulating pump P1.
The fresh liquid solvent entering the autoclave causes the solvent vapors still contained therein to condense and this condensate is mixed with the liquid solvent which is rising to fill the autoclave A.
The procedure described above is repeated for a two-three cycles until the amount of contaminant on the apparatus or the material is reduced to below 50 ppm. The time for performing this process of decontamination is about 10h, which is far below that required by the prior art decontamination processes.
The most suitable solvents for use in the process of this invention are, in general, the chlorinated compounds of paraffinic or olefinic hydrocarbons which have a high dissolving power towards the above mentioned contaminants, in particular use being made of perchloro-ethylene for the olefinic chlorinated hydrocarbons and of 1,1,1-trichloroethane for the paraffinic chlorinated hydrocarbons.
Recovery of these solvents is quite easy to obtain so that the plant can be expected to be operating on a thoroughly automatic cycle.
To this end, a control station can be provided which is designed to govern all of the decontaminating and other related operations in a predetermined automatic sequence such that a very reduced personnel is required for operation of the plant.
Furthermore, with the process of the invention the apparatus or the material to be decontaminated is always immersed in the solvent.
Of particular importance in this respect is the ultrasonic discharge whereby a pulsating movement is transmitted to the liquid solvent to cause it to penetrate more and more deep the inaccessible recesses or interstices in the apparatus or material to be treated, such that, upon extracting solvent from the autoclave the extracted solvent already contains contaminant to a large amount.
It is to be noted that the expression "other materials" in this context is intended to include, in addition to apparatus, also, for example, a PCB- or dioxin-contaminated soil which will be thoroughly reclaimed by this process.
From the above, it will be appreciated that the process of the invention offers a number of advantages over the prior art processes, the most significant advantages residing in that :

the time of treatment is substantially reduced due to the alternate use of liquid-phase and vapor-phase solvent-extraction steps,
recovery of the solvent is achieved on an automatic cycle-base without requiring any integrating process of distillation, the removed contaminant being collected immediately,
decontamination of apparatus or materials is achieved to a drastic extent due to the action of the ultrasonic discharge which is used as an integrating and basic technique of the inventive process to cause the liquid solvent to penetrate the most inaccessible interstices or recesses of the material to be decontaminated,
a vacuum is produced by merely draining the autoclave.

Claims

Method for the decontamination of apparatus or other materials contaminated by toxic and noxious substances, in particular PCBs and dioxin, comprising:
a) introducing the apparatus to be decontaminated into an autoclave provided with a top condenser;

b) hermetically sealing the autoclave;

c) introducing a liquid solvent into the autoclave until it is filled;

d) applying an ultrasonic discharge to the autoclave containing the liquid solvent so as to promote the dissolution of the contaminant therein;

e) draining the liquid solvent containing the contaminant dissolved therein from the autoclave, thereby simultaneously producing a vacuum therein;

f) injecting solvent vapours in the autoclave until they, after having heated the apparatus, reach the top condenser where the solvent vapours begin to condensate;

g) stopping the injection of solvent vapours at the beginning of their condensation at the top condenser;

h) introducing again liquid solvent into the autoclave until it is filled and the solvent vapours are condensated so as to cool the apparatus;

i) repeating the steps d) to h) for a few cycles in order to cause the apparatus to undergo alternate washings with solvent in a liquid phase and in a vapour phase under vacuum.
Method as claimed in claim 1, characterized in that the solvent vapours are generated outside the autoclave and then injected therein to heat and wash the apparatus.