Method of PCB Disposal and Apparatus Therefor

This invention relates to a method of disposing polychlorinated biphenyl (PCB) waste liquids by combustion of the PCBs with fuel such as diesel oil in a self-contained system.

Safe and efficient disposal of PCB-containing waste and PCB liquids is an ongoing problem, as the widely used PCBs are toxic and difficult to dispose of in a safe and efficient way. Furthermore, it is hazardous to transport such substances from the place where they are used to a site where disposal facilities are available.

Most of the known PCB waste disposal systems destroy PCBs by incineration. Incineration of PCBs, however, requires high temperatures and, therefore, large amounts of fuel. Consequently, the energy consumption of the furnace used for incineration results in very considerable operating costs, particularly, when the heat energy produced by the incinerator cannot be utilized efficiently as is often the case.

A method for treatment of harmful waste vapors derived from chemcial processes is described in U.S. Pat. No. 4,108,113 to Timm. The waste vapors are mixed with air, fed into the combustion chamber of a diesel engine and compressed. Towards the end of the compression stroke fuel is injected into the combustion chamber and the vapor-air-fuel mixture is ignited. On the exhaust stroke the oxidized vapor mixture is discharged into the atmosphere. In order to treat waste liquids such as PCB liquid according to this method, these liquids would have to be vaporized first.

The present invention is designed to avoid these and other disadvantages of the known methods of disposal used for PCB compounds and the like.

It is an object of the present invention to provide a safe and economical method of controlled disposal of PCB liquid and the like by mixing the liquids with fuel, combusting the mixture and scrubbing the exhaust.

It is another object of this invention to provide a self-contained system for disposal of PCBs and the like.

It is a further object of the invention to recover hydrochloric acid from the exhaust gases of the combustion of PCBs and the like.

Further objects and advantages of the invention will become apparent from the following description and claims and from the accompanying drawings.

In one aspect of the invention there is provided an apparatus for disposal of polychlorinated biphenyl (PCB) liquids and the like. The apparatus comprises a substantially air-tight self-contained assembly which includes an internal combustion engine, preferably a diesel engine, for burning of a mixture of PCB liquids and fuel such as diesel oil, and means for processing exhaust gases from the engine. Preferably, the apparatus further includes various fluid pumps. In a preferred embodiment, the power of the engine activates the fluid pumps and generates electricity used in the assembly. The whole self-contained apparatus may, preferably, be mounted on a trailer or automotive unit.

The processing means preferably include at least one gas scrubber, preferably supplied with water, and/or at least one tower with packing material suitable for adsorption of contaminants. The packing material of the tower may be carbon and the like. In a preferred embodiment, the processing means includes at least one gas scrubber supplied with water and at least one gas scrubber supplied with fuel such as diesel oil and the like. The water-supplied gas scrubber may be followed by at least one packed tower which has an inlet for receiving gases from the water-supplied gas scrubber and an outlet for releasing treated gases. The fuel-supplied gas scrubber may be followed by at least one bed with packing material adapted for passage of gases, whereby the bed has an inlet for receiving gases from said fuel-supplied gas scrubber and an outlet for releasing treated gases. In a more preferred embodiment the processing means include at least one gas scrubber supplied with water, a receiving tank which is adapted to be connected to a water-supplied gas scrubber and which has an outlet for gases, and at least one packed tower with an inlet for receiving gases from the receiving tank and an outlet for releasing treated gases. In a most preferred embodiment the processing means further includes at least one gas scrubber supplied with fuel such as diesel oil and the like and adapted to receive exhaust gases from one of the packed towers, and at least one bed with packing material and with an inlet for receiving gases from the fuel-supplied gas scrubber and an outlet for releasing treated gases into the atmosphere. The gas scrubbers may, preferably, be Venturi scrubbers.

In a second aspect of the invention there is provided a method of disposing of PCB liquids and the like which comprises

(a) blending PCB liquids and the like with a sufficient amount of fuel such as diesel oil to provide a combustible mixture;

(b) feeding the mixture into a combustion chamber of an internal combustion engine; (c) burning the mixture in said engine and

(d) subjecting exhaust gases to at least one processing step so as to remove sufficient contaminants for safe release of the gases into the atmosphere.

In a preferred embodiment the diesel oil is blended with the PCB liquids in a ratio of up to 1:1 by volume. Preferably, the efficiency for destruction of PCB liquids is at least 99%, and the efficiency for destruction and removal of PCB liquids is at least 99.5%, more preferably at least 99.9% or 99.99% and most preferably at least 99.998%.

The processing comprises, preferably, the step of treating the exhaust gases in at least one gas scrubber so as to remove contaminants and/or passing the exhaust gases through at least one tower with packing material such as carbon and the like so as to adsorb contaminants. More preferably, the processing comprises the steps of treating the exhaust gases with water in at least one gas scrubber to remove water-soluble contaminants such as acids and the like and contacting the exhaust gases with fuel such as diesel oil in at least one gas scrubber so as to remove contaminants such as organic substances. Treatment of the exhaust gases with water may be followed by the step of passing the gases through at least one packed tower. Contacting the exhaust gases with fuel may be followed by the step of passing the gases through at least one bed of packing material so as to separate the gases from fuel droplets. In a more preferred embodiment the processing comprises the steps of treating the exhaust gases with water in a gas scrubber and a receiving tank so as to remove water-soluble contaminants such as acids and the like from the exhaust gases and separating the gases from water droplets by passing the gases through a packed tower. In a most preferred embodiment the processing further comprises the steps of contacting the water-treated exhaust gases with fuel such as diesel oil in a gas scrubber so as to remove contaminants such as organic substances from the exhaust gases and separating the gases from fuel droplets by passing the gases through a bed of packing material. The gas scrubbers used are, preferably, Venturi scrubbers.

In the drawing which illustrates by way of example, a particular embodiment of the present invention:

The FIGURE is a diagrammatic view of an embodiment of the invention.

Referring now to the drawing, the PCB waste liquids are pumped from storage tanks, drums, transformers, etc. via intake line 1 into vacuum tank 2 which is part of a self-contained unit. Diesel oil is stored in diesel supply tank 4. A blending pump 5 equipped with flow rate controls pumps PCBs and diesel oil in the desired quantities into blend supply tank 3. The resulting diesel oil-PCB mixture is stable even at a ratio of 1:1 by weight. In low temperature conditions care has to be taken that the temperature of the pre-blended fuel does not drop below about -40.degree. C. Alternatively, the blended fuel can be preheated to reach a temperature of at least -40.degree. C. The blended fuel from tank 3 is then introduced into the combustion chamber of the diesel engine 11 via line 10. The air intake of the engine is supplied via line 12. In adverse weather conditions it is preferable to dry the air prior to introducing it into the engine, so as to prevent accumulation of moisture in the combustion chamber.

Following combustion the exhaust gases leave the engine 11 via line 15. A secondary air supply can be connected to line 15 at 16. To ensure that no PCB vapors can escape into the atmosphere vacuum pump 7 pumps any PCB vapors which may accumulate in tank 2 into the exhaust line at 8. The exhaust gases then pass into a Venturi scrubber 20, where they are contacted with water at 21 to convert the hydrogen chloride contained in the exhaust to hydrochloric acid. The acid accumulates in receiving tank 23. Exhaust gases from tank 23 are passed through line 30 into tower 31 which is filled with packing material suitable for the passage of gases. In the tower acid mist is separated from the exhaust gases. If necessary, the acid eliminating step can be repeated until practically all water soluble exhaust gases have been removed from the gas stream.

To further process the exhaust gases, the gas stream from tower 31 is passed through a Venturi scrubber 35 in which it is contacted at 36 with diesel oil coming from diesel supply tank 4 via line 6. The fuel combines with unburned organic compounds in the exhaust. The resulting contaminated fuel is then separated from the gas stream in packed tower or bed 40. The contaminated fuel collecting in the bottom of the tower 40 is returned to blend supply tank 3 via line 41. The purified exhaust gases from tower 40 are monitored in an exhaust analyzer 45 such as a gas chromatograph. Once the exhaust is found to be safe, it is released into the atmosphere at 42. If required, the extraction with diesel fuel can be repeated.

The acid which collects in receiving tank 23 and in tower 31 is passed via lines 24 and 32, respectively, through a filter unit 25 such as a duplex filter unit made up of a fine mesh screen for the removal of particulate materials and an activated carbon filter to remove organic compounds contained in the acid. The strength of the hydrochloric acid generated in this process can be adjusted by recycling the acid from tank 23 and tower 31 into the Venturi scrubber 20 at 21 prior to filtration and recovery of the acid at 26.

In a self-contained unit of the type shown in the FIGURE the diesel engine 11 supplies the power for all the pumps such as the vacuum pump which transfers the PCB liquids into tank 2 and the PCB vapors into the exhaust at 8; the air supply pump; the blending pump 5 which pumps PCB liquids and the diesel oil into tank 3 and controls the ratio of PCBs to diesel oil; the fuel supply pump; the pump supplying Venturi scrubber 20 with water; the pump for pumping the acid from tank 23 and tower 31 through filter unit 25 and/or for recycling the acid; the pump supplying Venturi scrubber 35 with diesel oil from tank 4; the pump for returning contaminated fuel from tower 40 to tank 3; etc. Furthermore, the power of the diesel engine is used for generating electricity necessary for lights and instrumentation such as for monitoring vacuum, flow rates, pressures, pH-values, emission, etc.

A unit of the kind shown in the FIGURE can be adapted to be mounted on a trailer or an automotive unit such as a flatbed truck. Such a mobile unit can easily be operated at the customer's premises thus avoiding the risks involved in the transportation of PCBs from the locations where the PCBs are accumulated to the place where they can be disposed.

It is also possible to add secondary processes to the basic unit for processing PCBs. Examples of such secondary processes are the flushing out of transformers on site and decontamination and subsequent crushing of drums.

From the foregoing description further modifications and embodiments will be apparent to those skilled in the art, and the embodiments disclosed are intended only to illustrate theinvention without limiting the scope therof.

The following examples further illustrate the present invention.

A 4-cylinder, 240 cubic inch Ford diesel engine was connected to a hydraulic pump feeding fuel to the engine and to an emission control system which consisted of a water scrubber tank, a packed tower and mist eliminator, and a carbon adsorber tower. The engine was run on diesel fuel which was blended with 10%(v/v) of a mixture of 70% PCBs and 30% trichlorobenzene. The engine was operated at 2000 rpm. The engine exhaust gases were sampled before the water scrubber and after the carbon adsorber tower. All collected samples were analyzed for PCBs by pulling exhaust gas through two impingers filled with ice water. A Fluorisil (Trademark) adsorbent trap was placed between an empty third impinger and a fourth impinger containing silica gel to collect residual PCBs passing through the first two impingers. The scrubber water was analyzed for PCBs and inorganic chloride.

PCBs were analyzed in a gas liquid chromatograph with electron capture detector (GLC/EC) or in a Finnigan 4023 (Trademark) GC/MS and high resolution capillary gas chromatograph. The results are shown in Tables I and II, respectively.

PCB emission rates are shown in Table III.

Chloride concentrations were determined using a standard Volhard titration. The results are shown in Table IV.

The volume of fuel burned was 10.8 liters/hr. The PCB feed rate to the engine was 1284 g/hr, the PCB emission rate at the scrubber inlet, which corresponded to the engine emission rate, was 7.76 g/hr (see Table III). The engine efficiency for PCB destruction was, therefore, 99.4%. The PCB emission rate after carbon adsorber was 0.0025 g/hr (see Table III). The efficiency of the entire exhaust control system was, therefore, 99.97%.

The amount of PCB collected in the scrubber was 3.6 g/hr and, thus, the scrubber removal efficiency was about 47%. The amount of PCB passing to the adsorber was 4.1 g/hr and the adsorber efficiency rate for PCB removal was, therefore, 99.94%.

An assessment of the chloride concentration in the scrubber water, compared with that predicted for a complete breakdown of PCBs to CO.sub.2 and HCl, indicated that approximately 50% of the PCBs and trichlorobenzene in the fuel were oxidized to HCl. This indicated that a portion of the chlorinated material degraded to lower molecular weight organic chlorides.

Extensive GC/MS analysis showed that besides PCB minor amounts of mono-, di- and trichlorobenzenes were present in the exhaust, but no dioxins or dibenzofurans were detected.