WO2015198210A1

WO2015198210A1 - System and method for recovering mercury from mercury contaminated materials

Info

Publication number: WO2015198210A1
Application number: PCT/IB2015/054685
Authority: WO
Inventors: Leonard Benjamin Bianchina; Ian Nigel Tunnicliffe
Original assignee: Oss Management Services (Pty) Limited
Priority date: 2014-06-25
Filing date: 2015-06-23
Publication date: 2015-12-30

Abstract

The invention provides a vacuum pyrolysis system and method for removing and distilling mercury from mercury contaminated materials, such as in fluorescent lamps and tubes, LEDs, tilt switches, thermometers, sphygmomanometers, arc rectifiers, mercury containing batteries and dental amalgams, to recycling or re-use. The system comprises and electrically conductive reactor vessel (10) which is operated under pyrolysis conditions and is heated by radio frequency induction; a transmitter (26) which is magnetically coupled to the reactor vessel (10); at least one exhaust for permitting egress of mercury vapour and steam from the reactor vessel (10); a vapour extraction system for removing mercury vapours from within the reactor vessel (10); a condenser for condensing removed mercury vapours into liquid mercury; and a power supply for supplying low frequency power to the reactor vessel (10).

Description

SYSTEM AND METHOD FOR RECOVERING MERCURY FROM

MERCURY CONTAMINATED MATERIALS

INTRODUCTION

The invention provides a system and method for recovering mercury embodied in fluorescent lamps and tubes, LED's, tilt switches, thermometers, sphygmomanometers, arc rectifiers, mercury containing batteries, and dental amalgams, for recycling or re-use in a variety of industries, inter alia, in the production of new lamps or other components.

BACKGROUND TO THE INVENTION

A fluorescent lamp or fluorescent tube is a low pressure mercury-vapor gas-discharge lamp that uses fluorescence to produce visible light. An electric current in the gas excites mercury vapor which produces short-wave ultraviolet light that causes a phosphor coating on the inside of the lamp to fluoresce, producing visible light.

Luminous efficacy of a fluorescent light bulb can exceed 100 lumens per watt, which is several times the efficacy of an incandescent bulb with comparable light output. Consequently, many compact fluorescent lamps are now available in the same popular sizes as incandescent lamps and are increasingly being used as energy-saving alternatives in homes, offices and commercial spaces.

Fluorescent tubes contain in general 94% glass, 4% ferrous and non-ferrous metals, and 2% phosphor powder. It is within this phosphor powder that the most hazardous element is contained, namely mercury. Because they contain mercury, many fluorescent lamps are classified as hazardous waste. For this reason, the United States Environmental Protection Agency recommends that fluorescent lamps be segregated from general waste for recycling or safe disposal.

In terms of the South African National Environmental Management: Waste Act 59 of 2008, fluorescent tubes are classified as hazardous waste in South Africa and should preferably be recycled or, if absolutely necessary, taken to specific landfill sites which can cater for mercury-bearing wastes. The actual number of sites in South Africa that can cater for such waste is very limited and, given high transportation and disposal costs, recycling of fluorescent tubes and lamps is the most economical and environmentally friendly option.

Mercury

When it comes to recycling, fluorescent lamps must be recycled as per section 4.10.5 of the National Waste Management Strategy, The New Mercury Convention, also known as the Minamata Convention on Mercury. The name came about after a serious industrial disaster after the dumping of mercury compounds into Minamata Bay, Japan. It is estimated that over 3,000 people suffered various deformities, severe mercury poisoning symptoms or death from what became known as Minamata disease. In October 2013, 140 countries agreed to sign the Minamata Convention on Mercury by the United Nations Environment Program (UNEP) to prevent emissions.

Mercury is a chemical element with the symbol Hg and atomic number 80. It is commonly known as quicksilver and was formerly named hydrargyrum. A heavy, silvery d-block element, mercury is the only metal that is liquid at standard conditions for temperature and pressure (the only other element that is liquid under these conditions is bromine, although metals such as caesium, gallium and rubidium melt just above room temperature). With a freezing point of -38.83 °C and boiling point of 356.73 °C, mercury has one of the narrowest ranges of its liquid state of any metal. Preindustrial deposition rates of mercury from the atmosphere may be about 4 ng/(1 L of ice deposit). Although that can be considered a natural level of exposure, regional or global sources have significant effects. Volcanic eruptions can increase the atmospheric source by 4-6 times. Natural sources, such as volcanoes, are responsible for approximately half of atmospheric mercury emissions.

The human-generated half can be divided into the following estimated percentages:

• 65% from stationary combustion, of which coal-fired power plants are the largest aggregate source (40% of U.S. mercury emissions in 1999). This includes power plants fueled with gas where the mercury has not been removed. Emissions from coal combustion are between one and two orders of magnitude higher than emissions from oil combustion, depending on the country.

• 1 1 % from gold production. The three largest point sources for mercury emissions in the U.S. are the three largest gold mines. Hydro-geochemical release of mercury from gold-mine tailings has been accounted as a significant source of atmospheric mercury in eastern Canada.

• 6.8% from non-ferrous metal production, typically smelters.

• 6.4% from cement production.

• 3.0% from waste disposal, including municipal and hazardous waste, crematoria, and sewage sludge incineration.

• 3.0% from caustic soda production.

• 1 .4% from pig iron and steel production.

• 1 .1 % from mercury production, mainly for batteries.

• 2.0% from other sources. Fluorescent Lamp Construction

A fluorescent lamp tube is filled with a gas containing low pressure mercury vapor and argon, xenon, neon or krypton. The pressure inside the lamp is around 0.3% of atmospheric pressure. The inner surface of the lamp is coated with a fluorescent (and often slightly phosphorescent) coating made of varying blends of metallic and rare-earth phosphor salts. The lamp's electrodes are typically made of coiled tungsten and usually referred to as cathodes because of their prime function of emitting electrons. For this, they are coated with a mixture of barium, strontium and calcium oxides chosen to have a low thermionic emission temperature.

Fluorescent lamp tubes are typically straight and range in length from about 100 millimeters for miniature lamps, to 2.43 meters for high-output lamps. Some lamps have the tube bent into a circle, used for table lamps or other places where a more compact light source is desired. Larger U-shaped lamps are used to provide the same amount of light in a more compact area, and are used for special architectural purposes. Compact fluorescent lamps have several small-diameter tubes joined in a bundle of two, four or six, or a small diameter tube coiled into a spiral, to provide a high amount of light output in little volume.

Light-emitting phosphors are applied as a paint-like coating to the inside of the tube. The organic solvents are allowed to evaporate, after which the tube is heated to nearly the melting point of glass to drive off remaining organic compounds and fuse the coating to the lamp tube. Careful control of the grain size of the suspended phosphors is necessary: large grains (i.e. 35 micrometers or larger) lead to weak grainy coatings, whereas too many small particles (i.e. 1 or 2 micrometers or smaller) leads to poor light maintenance and efficiency. Most phosphors perform best with a particle size of around 10 micrometers. The coating must be thick enough to capture all the ultraviolet light produced by the mercury arc, but not so thick that the phosphor coating absorbs too much visible light. The first phosphors were synthetic versions of naturally occurring fluorescent minerals, with small amounts of metals added as activators. Later other compounds were discovered, allowing different colors of lamps to be made.

Apart from the environmental aspect to recycling fluorescent tubes and lamps, it is also very important to the health and safety of employees. Should an employee, for example, attempt to dispose of a fluorescent tube in a skip, he would not only be condemning the whole skip as hazardous waste, with costly consequences relating to its safe disposal, but he would also be exposed to the potential dangers of broken glass and inhalation of small amounts of toxic materials that are released as dust and vapour.

LED's

A light-emitting diode (LED) is a two-lead semiconductor light source which emits light when activated. LEDs are often coated with phosphors of different colors to form white light and the resultant LEDs are called phosphor-based or phosphor-converted white LEDs. Some phosphor-based white LEDs encapsulate InGaN blue LEDs inside phosphor-coated epoxy. Alternatively, the LED might be paired with a remote phosphor, a preformed polycarbonate piece coated with the phosphor material. While LEDs have the advantage over fluorescent lamps that they do not contain the same high percentages of mercury, they do contain other hazardous metals such as lead and arsenic. A study published in 201 1 states (concerning toxicity of LEDs when treated as waste): "According to federal standards, LEDs are not hazardous except for low-intensity red LEDs, which leached Pb [lead] at levels exceeding regulatory limits (186 mg/L; regulatory limit: 5). However, according to California regulations, excessive levels of copper (up to 3892 mg/kg; limit: 2500), lead (up to 8103 mg/kg; limit: 1000), nickel (up to 4797 mg/kg; limit: 2000), or silver (up to 721 mg/kg; limit: 500) render all except low-intensity yellow LEDs hazardous." SUMMARY OF THE INVENTION

According to a first aspect of the invention there is provided a sealed, batch-driven vacuum pyrolysis system for use in removing and distilling mercury from mercury contaminated materials and purifying the mercury into various re-usable grades, while simultaneously minimising any residue for final disposal to landfill or incineration, the system comprising - an insulated, ferro- or ferri-magnetic, electrically conductive reactor vessel which is characterised therein that it is operated under pyrolysis conditions and is heated by radio frequency induction of eddy currents into the reactor vessel, the reactor vessel comprising - an elongate cylindrical reactor wall configured to accommodate at least a number of fluorescent tubes, lamps, LEDs or other mercury contaminated materials therein;

an end wall for sealing one end of the cylindrical reactor wall; and a removable lid dimensioned to seal an opposite end of the cylindrical reactor wall; the cylindrical reactor wall, end wall and removable lid being covered with heat- insulating material and together defining a reactor volume for holding a mercury contaminated material load;

a transmitter in the form of an external induction coil, which is magnetically coupled to the cylindrical reactor wall about its circumference and which acts as the transmitter, in the process rendering the reactor vessel a receiver;

at least one exhaust for permitting egress of mercury vapour and steam from the reactor vessel;

a vapour extraction system for removing mercury vapours from within the reactor vessel;

a condenser arranged in flow communication with the reactor vessel and vapour extraction system for condensing removed mercury vapours into liquid mercury; and a power supply for supplying low frequency power to create the eddy currents within the reactor vessel so as to heat a mercury contaminated material load inside the reactor volume by means of radio frequency induction;

the arrangement being such that a radio-frequency alternating current is passed between the first heating element and the reactor vessel, in the absence of oxygen, for volatilising the mercury within the contaminated material load by means of radio frequency induction heating to separate the mercury from the mercury contaminated materials.

According to a second aspect of the invention there is provided the use of a sealed, batch- driven vacuum pyrolysis system for removing and distilling mercury from mercury contaminated materials and purifying the mercury into various re-usable grades, while simultaneously minimising any residue for final disposal to landfill or incineration, wherein the system comprises - an insulated, magnetic, electrically conductive reactor vessel which is characterised therein that it is operated under pyrolysis conditions and is heated by radio frequency induction of eddy currents into the reactor vessel, the reactor vessel comprising - an elongate cylindrical reactor wall configured to accommodate at least a number of fluorescent tubes, lamps, LEDs or other mercury contaminated materials therein;

a transmitter in the form of an external induction coil, which is magnetically coupled to the cylindrical reactor wall about its circumference and which acts as the transmitter, in the process rendering the reactor vessel a receiver; at least one exhaust for permitting egress of mercury vapour and steam from the reactor vessel;

a condenser arranged in flow communication with the reactor vessel and vapour extraction system for condensing removed mercury vapours into liquid mercury; and

a power supply for supplying low frequency power to create the eddy currents within the reactor vessel so as to heat a mercury contaminated material load inside the reactor volume by means of radio frequency induction; the arrangement being such that a radio- frequency alternating current is passed between the first heating element and the reactor vessel, in the absence of oxygen, for volatilising the mercury within the contaminated material load by means of radio frequency induction heating to separate the mercury from the mercury contaminated materials.

According to a third aspect of the invention there is provided a vacuum pyrolysis method for removing and distilling mercury from mercury contaminated materials and purifying the mercury into various re-usable grades, while simultaneously minimising any residue for final disposal to landfill or incineration, the method being characterised therein that heat is supplied by radio frequency induction of eddy currents, the method comprising the steps of - providing a sealed, batch-driven vacuum pyrolysis system as hereinbefore described; loading the reactor vessel with a mercury contaminated material load;

sealing the reactor vessel with the removable lid;

inducing eddy currents into the reactor vessel, in the absence of oxygen, from the external induction coil to heat the mercury contaminated material load so as to vaporize at least the mercury out of the contaminated material load;

condensing the mercury in the condenser to liquid mercury; and

collecting the condensate mercury for recycling. According to a fourth aspect of the invention there is provided a vacuum pyrolysis method for removing and distilling mercury from mercury contaminated LEDs materials and purifying the mercury into various re-usable grades, while simultaneously minimising residual phosphor, lead and LED encapsulating polymers for final disposal to landfill or incineration, the method being characterised therein that heat is supplied by radio frequency induction of eddy currents, the method comprising the steps of - providing a sealed, batch-driven vacuum pyrolysis system as hereinbefore described; loading the reactor vessel with a material load of LEDs;

sealing the reactor vessel with the removable lid;

inducing eddy currents into the reactor vessel from the external induction coil to heat the LED material load so as to vaporize at least the mercury out of the contaminated material load, while at the same time converting the residual phosphor to a phosphorous oxide, the lead to liquid lead, and the LED encapsulating polymers to synthetic gas and char solids; condensing the mercury in the condenser to liquid mercury and the synthetic gas from the LED encapsulating polymers to recoverable pyrolysis oil; and

collecting the condensate mercury and pyrolysis oil for recycling.

According to a fifth aspect of the invention there is provided the use of radio frequency induction heating in a vacuum pyrolysis system for removing and distilling mercury from mercury contaminated materials.

For purposes of this invention the reference to "mercury contaminated materials" shall be interpreted to include, although not necessarily be limited to, one or a combination of used, in-tact fluorescent tubes and lamps, LEDs, tilt switches, thermometers, sphygmomanometers, arc rectifiers, mercury containing batteries, and/or dental amalgams; and "mercury contaminated material load" shall be interpreted to include one, or a combination of, the mercury contaminated materials. In one embodiment of the invention the reactor vessel may be substantially horizontally orientated and suitably dimensioned for receiving a container, platform, basket or the like therein for holding the mercury contaminated materials. The container may be an elongate partitioned cardboard box including a series of elongate parallel pockets suitably dimensioned for each receiving a fluorescent tube therein. For this purpose, the reactor vessel may include guiding means for guiding the container, platform, basket or the like into the reactor vessel and for positioning the container, platform, basket or the like within the reactor vessel when in use.

The reactor vessel may be supported by one or a number of support means for horizontally supporting the vessel above ground level. In one embodiment of the invention, the reactor vessel may include one or a number of support cradles dimensioned to cradle the reactor vessel at least partially about its circumference.

The reactor vessel may include at least one crushing mechanism for breaking or crushing the mercury contaminated materials once they are received within the reactor, for facilitating release of the volatilizing mercury from the mercury contaminated materials once the reactor vessel is heated up. In one embodiment of the invention, the crushing mechanism may include a crushing arm, extending radially inwardly from the cylindrical reactor wall and suitably dimensioned to at least break the mercury contaminated materials in or on the container, platform, basket or the like while they are housed within the reactor vessel.

In an alternative embodiment of the invention the reactor vessel may be substantially vertically orientated and suitably dimensioned for receiving a series of drums within the reactor wall for holding the mercury contaminated materials. Each drum may be a removable elongate cylinder having one open end and an opposite closed end and suitable for receiving a mercury contaminated material load. It is envisaged that the drums will be pre-filled with a contaminated material load, such as pre-crushed fluorescent tubes or LEDs, before being inserted into the reactor vessel.

The method may provide the optional step of breaking or crushing the mercury contaminated materials before inducing eddy currents into the reactor vessel. The mercury contaminated materials may be broken or crushed either before it is introduced into the reactor vessel as a contaminated material load, or after it has been introduced into the reactor.

The method may provide mercury at purity levels of approximately 3N (99.98%).

The method may provide the further step of purging the reactor vessel with an inert gas, such as nitrogen, to facilitate extraction of the mercury vapour to the condenser. Alternatively, the method may provide the step of purging the reactor vessel with a carrier gas which is adapted to create either an oxidizing or a reducing atmosphere within the reactor vessel so as to convert phosphor in a contaminated material load, such as an LEDs load, into a different phosphor composition. The carrier gas may for example be, but is not limited to, air, oxygen or nitrous oxide for an oxidising atmosphere; or carbon monoxide for a reducing atmosphere.

The external induction coil may be connected to an external surface of the cylindrical reactor wall, such that the heat-insulating material is trapped between the cylindrical reactor wall and the external induction coil. The external induction coil may extend substantially the length of the reactor vessel so as to cover at least most of the cylindrical reactor wall between the end wall and the removable lid.

The external induction coil may be connected to a power supply for inducing eddy currents into the reactor vessel from the external induction coil around the reactor vessel so as to heat the mercury contaminated material load inside the reactor volume by means of radio frequency induction. It will be appreciated that in cases where the mercury contaminated materials are manufactured from ferro- or ferri-magnetic material, such materials may act as a receiver and may themselves become magnetically coupled with the external induction coil around the reactor vessel.

The power supply may include an AC to DC converter for converting three-phase AC mains supply voltage from a supply frequency of 50 Hz to DC power. The converter may supply a variable DC voltage, a fixed DC voltage or a variable DC current.

The power supply further may include an inverter for converting the DC power to single phase AC output. In particular, the DC current may be fed to the inverter which converts the DC supply to a single phase AC output at a frequency of between 4KHz and 100KHz. The inverter may include a semi-conductor relay which is configured as an H-bridge. The H- bridge may include four legs, each associated with a switch. The output circuit may be connected across the center of the H-bridge. When the relevant two switches are closed, current may flow through the load in one direction. When the same switches are opened and the opposing two switches closed, current may be allowed to flow in the opposite direction. By precisely timing the opening and closing of the switches, it is possible to sustain oscillations in the load circuit. This is fed to the external induction coil whereupon mutual inductance between the external induction coil and the reactor creates a magnetic coupling. This induction causes eddy currents to be induced into the reactor vessel from the external induction coil around the reactor vessel.

The system also may include a vacuum, not only so as to increase relative volatility of the mercury in the mercury contaminated material load, thus creating a higher yield in recovered elemental mercury, but also to reduce the temperature requirements under which the system would otherwise function. Operating the system under vacuum conditions reduces running costs, increases distillation of mercury fractions, and reduces cycle times. The method further may include the step of operating the sealed, batch-driven pyrolysis system under vacuum conditions.

Operating temperatures within the reactor vessel may vary from 360°C up to about 700°C. Upon heating, mercury in the material load is distilled and/or volatilized and residual oxygen is displaced from the reactor vessel, allowing heat treatment of the mercury contaminated material load to take place in the absence of oxygen. For applications pertaining to fluorescent lamps and tubes, tilt switches, thermometers, sphygmomanometers, arc rectifiers, mercury containing batteries, and dental amalgams an operating temperature of 360°C up to about 400°C would suffice. However, when the system is used for LEDs, operating temperatures need to be higher in order to decompose the LED encapsulating polymers and will typically be in the order of 600°C to 700°C.

The moisture content of a mercury contaminated material load may vary between 2% and 50%.

Recovered mercury products may be returned to a supply chain for re-use, for example recovered mercury may further be refined and re-used in fluorescent tubes and other electronic devices; and metals, both ferrous and non-ferrous, precious metals and glass may be extracted from the remaining residue.

SPECIFIC EMBODIMENT OF THE INVENTION

Without limiting the scope thereof, the invention will now further be described by way of example only and with reference to the following drawings in which - is a perspective view from one angle of rotation of one embodiment of a reactor vessel used in accordance with the invention;

is a perspective view from a different angle of rotation of a slightly different embodiment of the reactor vessel used in accordance with the invention, illustrating the manner in which a container containing a load of fluorescent tubes is receivable within the reactor vessel;

is a schematic illustration of a sealed, batch-driven vacuum pyrolysis system for use in removing and distilling mercury from mercury contaminated materials according to the invention, including the reactor vessel and transmitter, vapour extraction system and condenser;

is a perspective view from above of a second embodiment of a reactor vessel used in accordance with the invention, with the removable lid in an open position;

is a perspective view from above of the reactor vessel of Figure 4, with the removable lid in a partially closed position; and

is a side elevation of the reactor vessel of Figure 4, with the removable lid in a closed position.

An insulated, ferro- or ferri-magnetic, electrically conductive reactor vessel used in the present invention is generally designated by reference numeral [10]. The reactor vessel [10] is characterised therein that it is operated under pyrolysis conditions and is heated by radio frequency induction of eddy currents into the reactor vessel [10].

The reactor vessel [10] includes an elongate cylindrical reactor wall [12] configured to accommodate at least a number of fluorescent tubes or lamps or other mercury contaminated materials therein; an end wall [14] for sealing one end of the cylindrical reactor wall [12]; and a removable lid [16] dimensioned to seal an opposite end of the cylindrical reactor wall [12]. The cylindrical reactor wall [12], end wall [14] and removable lid [16] are covered with heat-insulating material and together define a reactor volume for holding a mercury contaminated material load. The lid [16] is either hingedly connected to the cylindrical reactor wall [12] through hinges [17], as illustrated in Figures 1 to 3; or is completely removable from the reactor wall [12], as illustrated in Figures 4 to 6.

In the embodiment of the invention which is illustrated in Figures 1 to 3, the reactor vessel [10] is horizontally orientated and dimensioned for receiving a container [18], for holding the mercury contaminated materials. In this embodiment the container [18] is an elongate partitioned cardboard box [18] including a series of elongate parallel pockets [18.1 ] suitably dimensioned for each receiving a fluorescent tube therein.

The partitioned cardboard box [18] is typically 2.5m long and is constructed from containerboard, also referred to as CCM or corrugated case material, which is a type of paperboard specially manufactured for the production of corrugated board. The term encompasses both linerboard and corrugating medium (or fluting), the two types of paper that make up corrugated board. Since containerboard is made mainly out of natural unbleached wood fibers, it is generally brown, although its shade may vary depending on the type of wood, pulping process, recycling rate and impurities content. Unbleached containerboard is preferred to reduce the amount of volatile chlorinated compounds that could be released upon pyrolysis.

The reactor vessel [10] includes guiding means [20] for guiding the partitioned cardboard box [18] into the reactor vessel [10].

The reactor vessel [10] is supported by two support means [22] for horizontally supporting the reactor vessel [10] above ground level. In the illustrated embodiment of the invention, the reactor vessel [10] includes two support cradles [22] dimensioned to cradle the reactor vessel [10] at least partially about its circumference. In the embodiment of the invention which is illustrated in Figures 4 to 6, the reactor vessel [10] is substantially vertically orientated and suitably dimensioned for receiving a series of drums [36] within the reactor vessel [10] for holding the mercury contaminated materials. Each drum [36] is an elongate cylinder having one open end and an opposite closed end and suitable for receiving a pre-crushed mercury contaminated material load. In particular, each drum may typically be in the order of 210 litres and dimensioned to accommodate a material load of approximately 1300 crushed fluorescent tubes. The reactor vessel [10] is dimensioned to receive seven drums [36] within the reactor vessel [10].

The reactor vessel [10] includes at least one exhaust [28] for permitting egress of mercury vapour and steam from the reactor vessel [10].

The reactor vessel [10] includes at least one crushing mechanism [24] for breaking or crushing the mercury contaminated materials once they are received within the reactor, thereby facilitating release of the volatilizing mercury from the mercury contaminated materials once the reactor vessel [10] is heated up. In the illustrated embodiment of the invention, the crushing mechanism [24] is a crushing arm, extending radially inwardly from the cylindrical reactor wall [12] and suitably dimensioned to at least break the mercury contaminated materials in the container [18], platform, basket or the like while they are housed within the reactor vessel [10].

A transmitter [26] in the form of an external induction coil is magnetically coupled to the cylindrical reactor wall [12] about its circumference and acts as the transmitter, in the process rendering the reactor vessel [10] a receiver.

The reactor vessel [10] is used in a sealed, batch-driven vacuum pyrolysis system for use in removing and distilling mercury from mercury contaminated materials and purifying the mercury into various re-usable grades, while simultaneously minimising any residue for final disposal to landfill or incineration.

In addition to the reactor vessel [10] and transmitter [26], the system further comprises a vapour extraction system [30] for removing mercury vapours from within the reactor vessel [10]; a condenser [32] arranged in flow communication with the reactor vessel [10] and vapour extraction system [30] for condensing removed mercury vapours into liquid mercury; and a power supply for supplying low frequency power to create the eddy currents within the reactor vessel [10] so as to heat a mercury contaminated material load inside the reactor volume by means of radio frequency induction. In particular, the arrangement is such that a radio-frequency alternating current is passed between the external induction coil [26] and the reactor vessel [10], in the absence of oxygen, for volatilising the mercury within the contaminated material load by means of radio frequency induction heating to separate the mercury from the mercury contaminated materials.

In use, the reactor vessel [10] is loaded with a mercury contaminated material load. More specifically, a container [18], platform, basket or the like is loaded with the mercury contaminated material load and pushed into the reactor vessel [10]. The lid [16] is moved to a closed position to seal the reactor vessel [10]. Eddy currents are induced into the reactor vessel [10], in the absence of oxygen, from the external induction coil [26] to heat the mercury contaminated material load so as to vaporize at least the mercury out of the contaminated material load. Mercury vapors are condensed in the condenser to liquid mercury, after which condensate mercury is collected for recycling.

It will be appreciated that inorganic compounds, such as glass and metal components of fluorescent tubes, do not decompose and will be unaffected by the temperatures involved in the pyrolysis process of the invention (i.e. about 360°C to 400°C). However, the cardboard box [18] will decompose to a carbon residue at somewhere between 250°C and 350°C. This carbon residue itself is inert. Therefore, the mercury can be distilled off and condensed back to a liquid state along with any other fractionated condensable. The glass and metal components and carbon residue is mechanically separated and sent for recycling.

The other compounds of LEDs are also converted for recycling or disposal through this system and method. In particular, the lead component, which is minimal, melts and is collected at the bottom of the reactor vessel [10]. Phosphor reacts with the carrier gas and is converted to a phosphor oxide of the rear earth material used in the LEDs. The phosphor oxide remains in situ and is collected as a dust from the drums [36] or at the bottom of the reactor vessel [10]. The LED encapsulating polymers are converted to synthetic gas and char solids. The synthetic gas, which is typically made up of alkane group materials such as methane, is extracted from the reactor vessel [10] and distilled to recoverable pyrolysis oil, which typically comprises a diesel range of organic groups, C7 to C14. The char solids, such as carbon, are collected with the phosphor oxides from the bottom of the reactor vessel [10] for final disposal.

The method may include the optional step of breaking or crushing the mercury contaminated materials before inducing eddy currents into the reactor vessel [10]. This can be done before the mercury contaminated materials is introduced into the reactor vessel [10] as a contaminated material load, or after it has been introduced into the reactor vessel [10]. In the latter case, the mercury contaminated materials may be broken or crushed through vertical up and down displacement of the crushing arm [24].

The method also may include the optional step of purging the reactor vessel [10] with an inert gas, such as nitrogen, to facilitate extraction of the mercury vapour to the condenser. The inert gas is introduced through one or a combination of inlets [34]. Radio frequency ("RF") has a rate of oscillation in the range of about 30 KHz to 300 GHz, which corresponds to the frequency of electrical signals normally used to produce and detect radio waves. Radio-frequency induction is the use of a radio frequency magnetic field - the transfer of energy by means of electromagnetic induction in the near field.

This invention exploits a so-called near field of electromagnetic radiation. A near field, far field and transition zone are regions in the field of electromagnetic radiation that emanates from a radiating antenna or transmitter, which in this invention is the external induction coil [26] around the reactor vessel [10]. Certain behavioral characteristics of electromagnetic fields dominate at one distance from the transmitter, while a completely different behavior can dominate at another location. Defined boundary regions categorize these behavioral characteristics. The regional boundaries are always measured as a function of a ratio of the distance from the radiating source (i.e. external induction coil [26]) to the wavelength of the radiation.

This invention provides intentionally magnetically coupling the transmitter with the reactor vessel [10]. In this embodiment, conductors are referred to as "mutual-inductively coupled" or "magnetically coupled" when they are configured such that a change in current flow through one wire (the external induction coil [26]) induces a voltage across the ends of the other wire (the reactor vessel [10]) through electromagnetic induction. The amount of inductive coupling between two conductors is measured by their mutual inductance.

The coupling between two wires can be increased by winding them into coils and placing them close together on a common axis, so the magnetic field of one coil (external induction coil [26]) passes through the other coil (reactor vessel [10]). The two coils may be physically contained in a single unit, as in the primary (external induction coil [26]) and secondary sides (reactor vessel [10]) of a transformer, or may be separated. Eddy currents (also called Foucault currents) are currents induced in conductors, opposing the change in flux that generated them. It is caused when a conductor is exposed to a changing magnetic field due to relative motion of the field source and conductor, or due to variations of the field with time. This can cause a circulating flow of electrons, or a current, within the body of the conductor. These circulating eddies of current create induced magnetic fields that oppose the change of the original magnetic field due to Lenz's law, causing repulsive or drag forces between the conductor and the magnet. The stronger the applied magnetic field, or the greater the electrical conductivity of the conductor, or the faster the field that the conductor is exposed to changes, then the greater the currents that are developed and the greater the opposing field. Eddy currents, like all electric currents, generate heat as well as electromagnetic forces. In the present invention this heat is harnessed for heating the reactor vessel [10].

Whilst the magnetic coupling is greatest between the external induction coil [26] and the reactor vessel [10], eddies are also induced into any ferromagnetic material that may be inside the vessel, such as the ferrous component of a used in-tact fluorescent tube, which aids thermal conduction through the solid [16] mercury contaminated material load that is being treated.

It will be appreciated that alternative embodiments on the invention may be possible without deporting from the spirit or scope of the invention as defined in the claims.

Claims

1 . A sealed, batch-driven vacuum pyrolysis system for use in removing and distilling mercury from mercury contaminated materials and purifying the mercury into various re-usable grades, while simultaneously minimising any residue for final disposal to landfill or incineration, the system comprising - an insulated, ferro- or ferri-magnetic, electrically conductive reactor vessel which is characterised therein that it is operated under pyrolysis conditions and is heated by radio frequency induction of eddy currents into the reactor vessel, the reactor vessel comprising - an elongate cylindrical reactor wall configured to accommodate at least a number of fluorescent tubes or lamps, LEDs or other mercury contaminated materials therein;

an end wall for sealing one end of the cylindrical reactor wall; and a removable lid dimensioned to seal an opposite end of the cylindrical reactor wall; the cylindrical reactor wall, end wall and removable lid being covered with heat-insulating material and together defining a reactor volume for holding a mercury contaminated material load;

2. The vacuum pyrolysis system according to claim 1 wherein the reactor vessel is substantially horizontally orientated and suitably dimensioned for receiving a container, platform, basket or similar receptacle therein for holding the mercury contaminated materials.

3. The vacuum pyrolysis system according to claim 2 wherein the reactor vessel includes guiding means for guiding the container, platform, basket or similar receptacle into the reactor vessel and for positioning the container, platform, basket or similar receptacle within the reactor vessel when in use.

4. The vacuum pyrolysis system according to anyone of claims 2 or 3 wherein the container, platform, basket or similar receptacle is an elongate partitioned cardboard box including a series of elongate parallel pockets suitably dimensioned for each receiving a fluorescent tube therein.

5. The vacuum pyrolysis system according to claim 1 wherein the reactor vessel is supported by one or a number of support means for horizontally supporting the vessel above ground level; particularly the reactor vessel includes one or a number of support cradles dimensioned to cradle the reactor vessel at least partially about its circumference.

6. The vacuum pyrolysis system according to claim 2 wherein the reactor vessel includes at least one crushing mechanism for breaking or crushing the mercury contaminated materials once they are received within the reactor, for facilitating release of the volatilizing mercury from the mercury contaminated materials once the reactor vessel is heated up; the crushing mechanism including a crushing arm, extending radially inwardly from the cylindrical reactor wall and suitably dimensioned to at least break the mercury contaminated materials in or on the container, platform, basket or similar receptacle while they are housed within the reactor vessel.

7. The vacuum pyrolysis system according to claim 1 wherein the reactor vessel is substantially vertically orientated and suitably dimensioned for receiving a series of drums within the reactor wall for holding the mercury contaminated materials, with each drum being a removable elongate cylinder having one open end and an opposite closed end and suitable for receiving a mercury contaminated material load therein.

8. The vacuum pyrolysis system according to claim 1 wherein the transmitter is connected to an external surface of the cylindrical reactor wall and extends substantially the length of the reactor vessel so as to cover at least most of the cylindrical reactor wall between the end wall and the removable lid, the arrangement being such that the heat-insulating material is trapped between the cylindrical reactor wall and the transmitter.

9. The vacuum pyrolysis system according to claim 1 wherein the transmitter is connected to the power supply for inducing eddy currents into the reactor vessel from the transmitter around the reactor vessel so as to heat the mercury contaminated material load inside the reactor volume by means of radio frequency induction, the arrangement being such that where the mercury contaminated materials are manufactured from ferro- or ferri-magnetic material, such materials act as a receiver and themselves become magnetically coupled with the external induction coil around the reactor vessel.

10. The vacuum pyrolysis system according to claim 1 wherein the power supply includes an AC to DC converter for converting three-phase AC mains supply voltage from a supply frequency of 50 Hz to DC power, the converter being able to supply a variable DC voltage, a fixed DC voltage or a variable DC current.

1 1 . The vacuum pyrolysis system according to claim 10 wherein the power supply further includes an inverter for converting the DC power to single phase AC output, particularly at a frequency of between 4KHz and 10OKHz.

12. The vacuum pyrolysis system according to claim 1 wherein the system includes a vacuum.

13. The vacuum pyrolysis system according to claim 1 wherein the reactor vessel is operated at a temperature of about 360°C to about 700°C.

14. The vacuum pyrolysis system according to claim 13 wherein the reactor vessel is operated at a temperature of about 360°C to about 400°C for use in recovery mercury from fluorescent lamps and tubes, tilt switches, thermometers, sphygmomanometers, arc rectifiers, mercury containing batteries, and dental amalgams.

15. The vacuum pyrolysis system according to claim 13 wherein the reactor vessel is operated at a temperature of about 400°C to about 700°C for use in recovery mercury and other components from LED's.

16. The vacuum pyrolysis system according to claim 1 wherein the moisture content of a mercury contaminated material load varies between 2% and 50%.

17. The use of a sealed, batch-driven vacuum pyrolysis system for removing and distilling mercury from mercury contaminated materials and purifying the mercury into various re-usable grades, while simultaneously minimising any residue for final disposal to landfill or incineration, wherein the system comprises - an insulated, magnetic, electrically conductive reactor vessel which is characterised therein that it is operated under pyrolysis conditions and is heated by radio frequency induction of eddy currents into the reactor vessel, the reactor vessel comprising - an elongate cylindrical reactor wall configured to accommodate at least a number of fluorescent tubes or lamps or other mercury contaminated materials therein;

at least one exhaust for permitting egress of mercury vapour and steam from the reactor vessel; a vapour extraction system for removing mercury vapours from within the reactor vessel;

a power supply for supplying low frequency power to create the eddy currents within the reactor vessel so as to heat a mercury contaminated material load inside the reactor volume by means of radio frequency induction;

18. A vacuum pyrolysis method for removing and distilling mercury from mercury contaminated materials and purifying the mercury into various re-usable grades, while simultaneously minimising any residue for final disposal to landfill or incineration, the method being characterised therein that heat is supplied by radio frequency induction of eddy currents, the method comprising the steps of - providing a sealed, batch-driven vacuum pyrolysis system according to anyone of claims 1 to 16;

loading the reactor vessel with a mercury contaminated material load;

sealing the reactor vessel with the removable lid;

condensing the mercury in the condenser to liquid mercury; and collecting the condensate mercury for recycling.

19. The pyrolysis method according to claim 18 which includes the optional additional step of breaking or crushing the mercury contaminated materials either before it is introduced into the reactor vessel as a contaminated material load, or after it has been introduced into the reactor, but either way before inducing eddy currents into the reactor vessel.

20. The pyrolysis method according to claim 18 which includes the step of purging the reactor vessel with an inert gas, such as nitrogen, to facilitate extraction of the mercury vapour to the condenser.

21 . The pyrolysis method according to claim 18 which includes the step of operating the sealed, batch-driven pyrolysis system under vacuum conditions.

22. The pyrolysis method according to claim 18 wherein the reactor vessel is operated at a temperature of about 360°C to about 400°C.

23. The use of radio frequency induction heating in a vacuum pyrolysis system for removing and distilling mercury from mercury contaminated materials.

24. A vacuum pyrolysis method for removing and distilling mercury from mercury contaminated LED's and purifying the mercury into various re-usable grades, while simultaneously minimising residual phosphor, lead and LED encapsulating polymers for final disposal to landfill or incineration, the method being characterised therein that heat is supplied by radio frequency induction of eddy currents, the method comprising the steps of - providing a sealed, batch-driven vacuum pyrolysis system according to anyone of claims 1 to 16 ; loading the reactor vessel with a material load of LEDs;

sealing the reactor vessel with the removable lid;

inducing eddy currents into the reactor vessel from the external induction coil to heat the LED material load so as to vaporize at least the mercury out of the contaminated material load, while at the same time converting the residual phosphor to a phosphorous oxide, the lead to liquid lead, and the LED encapsulating polymers to synthetic gas and char solids;

condensing the mercury in the condenser to liquid mercury and the synthetic gas from the LED encapsulating polymers to recoverable pyrolysis oil; and

collecting the condensate mercury and pyrolysis oil for recycling.

25. The pyrolysis method according to claim 24 which includes the step of purging the reactor vessel with a carrier gas which is adapted to create either an oxidizing or a reducing atmosphere within the reactor vessel so as to convert phosphor in the LED contaminated material load into a different phosphor composition.

26. The pyrolysis method according to claim 24 wherein the reactor vessel is operated at a temperature of about 400°C to about 700°C.

27. A sealed, batch-driven vacuum pyrolysis system for use in removing and distilling mercury from mercury contaminated materials and purifying the mercury into various re-usable grades, substantially as herein illustrated and exemplified with reference to the accompanying drawings.