METHOD AND ARRANGEMENT FOR DESTRUCTION OF HAZARDOUS WASTE

Abstract: This invention relates to a method for destruction of hazardous waste in solid form, for instance strip lights, mercury lamps and other types of light sources containing the substance mercury, which is dangerous to the environment. According to the invention the method is characterized by the combination of the following steps: the method is designed in that way that the destruction process is automated and completely closed; the strip light/mercury lamps (3) are fed into an apparatus (5) for dividing the material into pieces, which apparatus crashes the strip lights/mercury lamps, whereafter the material, crushed into pieces, is fed out of the apparatus for dividing the material into pieces to an oven (12); in the oven (12), where the temperature is 1350 - 1400 DEG C the glass is melted down to a mass, which spontaneously flows out of the same, whereas the mercury is gased off from the glass mass and is sucked into a chamber (17), which is connected with the oven (12); to the chamber (17) which has a temperature that is suitable for the purpose, is dosed a well-balanced amount of selenium, which is evaporated and is mixed with the mercury gas, whereafter the mixed gas is sucked into a cooling device and is precipitated in the form of a not dangerous mercury selenide in solid form.

Description: Method and arrangement for destruction of hazardous waste This invention relates to a method of destruction of hazardous waste in solid form, for instance strip lights, mercury lamps and other types of light sources containing mercury, which substance is dangerous for the environment. Some methods to destruct strip lights and similar hazardous waste are previously known on the market, but these methods have only resulted in that a less part of the used strip lights have been able to be destructed in a suitable way. According to a known method (Swedish "Teknisk tidskrift", 1994:14) the strip lights are melted down in an oven under high temperature. In this connection selenium is added directly to the oven together with the strip lights. There are several disadvantages connected with this known technique. Firstly, the working environment is very bad, since the shutters of the oven have to be opened manually and the strip lights have to be thrown into the oven manually. Furthermore, it is necessary to pull out the melted glass with a rake. Secondly, the addition of selenium directly into the oven means that the melted glass will contain mercury selenide, which accordingly is in a vitrified form. This means that the rest product "glass" cannot be taken care of but has to be left to a dumping place. Thirdly, an apparatus made in accordance to the known method gets a low capacity. This invention intends to eliminate the problems with known technique and provide a new method and a new arrangement for destruction of hazardous waste, which arrangement, due to its construction, gets a very big capacity and makes possible a very effective destruction of the hazardous waste, which usually comprises strip lights and mercury lamps. The new invention gives many advantages compared with known technique: Firstly, the poisonous mercury is neutralised in a secure way by means of selenium, which is added to a reaction chamber outside the oven, whereas glass is re-cycled which is completely free from mercury selenide. Furthermore, the new invention makes also possible a re-cycling of metals from the destructed light sources. Secondly, the invention is arranged in that way that the glass spontaneously leave the oven in melted form, which melted glass easily can be taken care of, whereas the mercury selenide are caught for crystallisation by means of a cooling device. Thirdly, the destruction process according to the invention is automated and completely closed, wherefore the working environment becomes extremely good. The characterizing steps and features of the method and arrangement appear in more detail by the following claims. A preferred embodiment of the invention shall be described in more detail with reference to the accompanying drawing, which shows the different steps of the destruction process. The step 1 of the process comprises feeding hazardous waste into an apparatus for dividing material into pieces, the hazardous waste being assumed to consist of used strip lights. In this case the strip lights are collected to special tubes 1, which are known by the applicant's own international patent application PCT/SE96/00285. As appears from the drawing the tube 1 is intended to be placed in a first, essentially horizontal position in a frame 2, which together with the tube 1 constitutes an infeeding device for the strip lights. The tube 1 is intended in a mechanical way to move upwards in the frame 2 and to take an inclined position of about 45° angular distance from the former one, in which the strip lights 3 by their own weight via an air lock 4 fall down into an apparatus 5 for dividing the material into pieces, which apparatus comprises two longitudinal and circularcylinder-like means 6, which are contra-rotating, and which at their peripheries are provided with projections 7 for effective division into pieces. This division into pieces comprises step 2 of the destruction process and results in a pulverization of the material. In the bottom of the apparatus 5 for dividing the strip lights into pieces is arranged a longitudinal, circularcylinder-like feeding out screw 8, which is intended to feed out the light strips, crashed into pieces, via a duct 9 at the bottom portion of the apparatus 5 for dividing the strip lights into pieces, which duct 9 has a connection with an opening 10 of the backwall 11 of an oven 12, where there prevails a temperature of 1350-1400°C, and where the melting down phase, step 3, takes place. When crashing the strip lights/mercury lamps into pieces in the apparatus 5 for dividing the material into pieces an amount of mercury in gas form is set free. It is important that also this gas comes into the oven and for this reason an underpressure is applied in the oven which underpressure sucks the mercury gas, formed in the apparatus 5 for dividing the strip lights into pieces, out of this one and into the oven. The high temperature of the oven 12 has the consequence that the gas of the strip lights melts to a mass laying itself on the bottom portion 13 of the oven, whereas the mercury and potentially other heavy metals are gased off from the glass mass. The bottom portion 13 of the oven 12 inclines downwords about 10 degrees from the backwall 11 and forwards. At the front portion 14 of the oven there is at the bottom an open- ing 15 where the melted gas flows out, whereafter the glass is suitably cooled down and can be taken care of in solid form. On the inclined roof 16 of the oven 12 is at its front part a chamber 17 connected, an opening 18 being arranged between the oven 12 and the chamber 17. This chamber is under vacuum, the heavy metals being in gas form in the oven 12 being sucked into the chamber 17. In this connection the opening 18 has such a size (-0 50 mm) that the gas flow from the oven to the chamber can amount to approximately 5m /h. To the chamber 17 is dosed a well-balanced amount of selenium via a tubular means 19, and this selenium is evaporated at about 680° and is mixed with the heavy metal gases to a chemical compound, which accordingly constitutes the step 4 of the process. The reaction chamber 17 is in connection with a cooling device 20 via a duct 21, and this cooling device is also under vacuum, and therefore the mixed gas is sucked into the cooling device and is precipitated in the form a solid end product, namely mercury selenide which in principal is insoluble. The cooling of the mixed gas, which can be denoted as step 5 of the process, can be made in several phases, and therefore the cooling device 20 comprises a plurality of units 20a-d. The new apparatus system functions in the following way, while pointing out that all process steps can be mechanized and be carried out automatically: The tube 1, patent applied for and filled with used strip lights, is placed in the frame 2, whereafter it is taken to the inlet position, where the strip lights fall down to the apparatus 5 for dividing the strip lights into pieces and is crashed there to pieces. The glass, crashed into pieces, and heavy metals in solid form are fed into an oven 20 by a feeding screw 8 and potential mercury gas, set free, is sucked into the oven 12 by the underpressure prevailing there. Due to the high temperature in the oven, the glass melts to a mass which spontaneously flows out of the oven at its front end, whereas the heavy metals are gased off from the mass and are sucked into a reaction chamber, which is connected with the oven 12, since there prevail an underpressure in this chamber, which is lower than the pressure of the oven. Into the reaction chamber selenium is added which due to the high temperature (~ 680°) is evaporated and is mixed with the heavy metal gas to a chemical compound. From the chamber 17 the mixed gas is sucked to a cooling device and is precipitated there in the form of mercury selenide, while being assumed that the heavy metal mainly comprises mercury. The new apparatus system is very effective and manages approximately 250 kg strip lights per hour. The invention is not limited to the mentioned embodiment but can be modified within the scoop of the following claims.

Claims: Claims 1. A method for destruction of hazardous waste in solid form, for instance strip lights, mercury lamps and other types of light sources containing the substance mercury, which is dangerous to the environment, c h a r a c t e r i z e d by the combination of the following steps: - The method is designed in that way that the destruction process is automated and completely closed; - The strip lights/mercury lamps (3) are fed into an apparatus (5) for dividing the material into pieces, which apparatus crashes the strip lights/mercury lamps, whereafter the material, crushed into pieces, is fed out of the apparatus for dividing the material into pieces to an oven (12); - In the oven (12), where the temperature is 1350 - 1400°C the glass is melted down to a mass, which spontaneously flows out of the same, whereas the mercury is gased off from the glass mass and is sucked into a chamber (17), which is connected with the oven (12); - To the chamber (17) which has a temperature that is suitable for the purpose, is dosed a well-balanced amount of selenium, which is evaporated and is mixed with the mer- cury gas, whereafter the mixed gas is sucked into a cooling device and is precipitated in the form of a not dangerous mercury selenide in solid form. 2. A method according to claim 1, c h a r a c t e r i z e d in that the oven (12) as well as the chamber (17) are set under underpressure, which makes possible partly that mercury gas, set free, when dividing the strip lights into pieces is sucked into the oven (12), partly that the mercury gas, formed in the oven (12), is sucked into the reaction chamber (17). 3. An arrangement for destruction of hazardous waste in solid form, for instance strip lights, mercury lamps and other types of light sources containing the substance mercury, which is dangerous to the environment, c h a r a c t e r i z e d by the combination of the following devices: - The arrangement is made in that way that the destruction process is automated and completely closed; - An infeeding device (1, 2) is arranged for feeding in strip lights/mercury lamps (3) into an apparatus for dividing the material into pieces, where the strip lights/mercury lamps (3) are crushed into pieces; - An oven (12) which is connected with the apparatus (5) for dividing the material into pieces, and into which the crushed strip lights/mercury lamps (3) are intended to be fed, is heatable to the melting point of the glass and has such a design that the melted glass can spontaneously flow out of the same; - A reaction chamber (17) into which selenium is intended to be fed, is openly connected with the oven (12) so that mercury gas formed in the same can stream into the chamber (17) and be mixed with selenium evaporated in the same; - A cooling device which is connected with the reaction chamber (17) so that the mixed gas formed in the same can stream into the cooling device and be cooled there for forming mercury selenide in solid form. 4. An arrangement according to claim 3, the infeeding device comprising a tube (1) for used strip lights/mercury lamps (3), c h a r a c t e r i z e d in that the tube (1) is intended to be placed in a first essentially horizontal position in a frame (2) and is further intended in a mechanical way to move upwards in the frame (2) and to take an inclined position at an angular distance from the first position, in which the strip lights/mercury lamps (3) by their own weight fall down, and that the apparatus (5) for dividing the material into pieces comprises two contra-rotating, longitudinal and circu- larcylinder-like means (6), which on their periferies are provided with projections (7) for effective dividing the material into pieces. 5. An arrangement according to claim 4, c h a r a c t e r i z e d in that the apparatus (5) for dividing the material into pieces further comprises a longitudinal feeding out screw (8), which is parallel with the contra-rotating means (6), for feeding out the crushed strip lights/mercury lamps to the mentioned oven (12). 6. An arrangement according to any one of the claims 3-5, c h a r a c t e r i z e d in that the reaction chamber (17) is positioned on the roof (16) of the oven (12). 7. An arrangement according to any one of the claims 3-6, characterized in that the cooling device (20) comprises a plurality of units (20a-d), whereby the cooling can be made in several phases. 8. An arrangement according to any one of the claims 3-7, characterized in that the oven (12), reaction chamber (17) and the cooling device (20) are set under underpressure.

Inventors: JONSSON TONY, JONSSON, TONY
Applicants: BJAESTA AATERVINNING AB, JONSSON TONY, JONSSON, TONY
Application year: 1998
Main classification: B09B3
IPC codes: C03B3, C03B5, C22B7, C22B43, H01J9