METHOD AND APPARATUS FOR THERMAL TREATMENT

Abstract: A method for thermal treatment of materials/substances that can be pumped or blown, particularly for the pyrolysis of waste materials, where the matter to be treated is pumped or blown into a heat chamber with a high temperature smelt, particularly a metal smelt. The material is fed into a gas which conducts the electricity in electric arc discharges, as the decomposition products of this thermal treatment are forced to pass through the smelt. The method can be carried out by the means of a sealed receptacle (11) which is equipped with a tubular electrode (15) which supplies the material and which has an open end directed towards or located in the smelt. Organs (25) can be placed near the tubular electrode to create circulation and to spread the decomposition products in the smelt.

Description: Method and apparatus for thermal treatment. The invention concerns a method of thermal treatment of materials/substances that can be pumped or blown, particularly concerning the pyrolysis of waste products where the material/substance is pumped or blown into a heat chamber with a high temperature smelt, preferably a metal smelt, and where the heat chamber receives the thermic energy required from the electrical discharge of electrodes. A range of chemical compounds are extremely stable or have stable decomposition products. Most of these compounds can however be broken down into their separate chemical components by maintaining the initial materials at a high temperature for a long period of time. This can be exemplified by the destruction of various types of wase, from for instance the production of plastics. For this purpose there are known pyrolysis plants with metal baths where the substance which is to be thermically processed resp. destructed is fed into the metal bath and heated by and in it by means of electrodes with an electrical discharge over the metal bath. Methods such as this will not produce high enough temperatures or long enough exposure for the most exacting thermal processes such as the destruction of matter. The objects of the invention: The main object of the invention is to provide a method resp. an apparatus for the thermal treatment of substances which can be pumped or blown, where a predetermined high temperature and sufficient exposure in the heated zone is obtained for a given substance. Another object is finding a method and an apparatus where thermal treatment can be carried out without the addition of an oxidizing agent and which in a simple manner allows the collection of the gases and the other products of pyrolysis connected with the thermal treatment. The principle of the invention: According to the invention this can be obtained by a method outlined in patent claim 1. At the end of the electrodes where the electric arc discharges occur, the temperature is in the region of 5000°-12000°K, and the material to be destructed is forced to pass through this area. Lengthy exposure at a high temperature is ensured by forcing the products of the thermal treatment/pyrolysis in the vicinity of the electrodes to pass through a smelting bath which contributes to a final catalytic decomposition of extremely stable organic compounds. Patent claim 2 describes an apparatus for carrying out the method in accordance with the invention. The subclaims, state the advantages of this apparatus. Thermal treatment with the apparatus according to the invention is possible without the addition of oxidizing agents. This reduces the amount of gas which has to be treated. Any valuable elements in the redisual gas will consequently be more concentrated and in an easier utilized form than was previously found in combustion processes. Following the destruction of the non-halogen- containing organic matter, the products of pyrolysis will consist of carbon (Carbon Black), H , CO as well as smaller quantities of N . Carbon Black will follow the gas out. Following the destruction of halogen-containing waste matter from the production of plastics, the products of pyrolysis will contain carbon (Carbon Black) and smaller quantities of halogenides which can be filtered off from the gas. The gas may usually consist of 60-96% HC1, 1-30% CO, 1-5% H as well as 2-8% N all calculated on the basis of weight. Such a gas mixture is a suitable starting point for the production of technical hydrochloric acid using an existing method. In some cases, the materials which are to be subjected to thermal treatment may contain heavy metals. Thus following destruction the main part of the most common heavy metals will remain in the metal bath. The metal bath must consequently be refined in known manner from time to time to catch the heavy metals in a slag smelt. Some types of organic materials such as dioxines and polychlorinated biphenyls are difficult to destruct entirely by combustion processes alone, as the temperature should be in the region of 1200-1800°C for complete destruction. The method and apparatus according to the invention facilitate the destruction of such materials without the addition of combustibles at the same time as the destruction temperature can be selected independently of the combustible value of the material. This will result in less gas being produced than is the case with any. other method known. Examples: The invention will be described more closely below by reference to the drawings where Fig. 1 illustrates a vertical cross-section in a shematic presentation of central parts of an apparatus for realizing the method according to the invention, Fig. 2A and 2B show a vertical cross-section and a horizontal cross-section, respectively of an alternative embodiment, whilst Fig. 3 shows yet another embodiment from a vertical cross-section. In Fig. 1, a sealed thermically-insulated receptacle or container 11 for a metal smelt 12 is shown. There is an opening in the lid 13 with a pipe connection 14 for the outlet of gas and a central opening for an electrode tube 15 The electrode tube 15 is led down into the metal smelt 12, in the example this is about half-way into it. A rod-shaped electrode 16 is located centrally in the electrode tube 15. The pair of electrodes 15-16 constitute a unit and can be shaped as described in Norwegian Patent No. 141.183. Other heat sources based on electrodes can also be used providing they produce sufficiently high temperatures and where the electrodes can be built into a chamber where the exhaust gases from the combustion unit are forced to rise through a metal bath. In the example the upper part of the electrode tube 15 " is attached to a lower electrode holder 17 to which a coolant, preferably water, and electric current are supplied through a combined coolant and electric conductor 18. The coaxially-located electrode rod 16 is attached to the upper electrode holder 19 which has a combined supply of coolant and electric current 20. The upper electrode holder 19, is electrically insulated from the lower electrode holder 17 and vice versa. The upper electrode holder can be equipped with a device which can continuously displace the central electrode rod in an axial direction in relation to the outer electrode tube. This is not illustrated in Fig. 1. Between the electrode tube 15 and the electrode rod 16 there is an annular space 21. Into the annular space 21 in the division between the upper and lower electrode holders one or more supply conduits are led. The example shows two of these supply conduits, 22 and 23, which supply the material which is to be thermically treated and are supplied from a feed pipe 24. The feed pipe 24 can be linked to a dosage unit which pumps or blows controlled amounts of the substance into the annular space. Following the introduction of this matter, a gas zone will be formed in the lower part of the annular space 21 in the electrode tube 15. This gas zone will extend into the metal bath 12 and will be kept heated by the electrical discharge at the end of the electrodes. Thermal treatment such as the destruction of the material which has been fed in will commence in this area. The gas supplied and the gas generated by the heating will recede from the bottom of the metal bath 12 and flow up the outer side of the electrode tube 15. At a certain distance from the outside of the electrode tube 15, a pipe 25 has been located under the lid 13 with its free end 26 lowered into the metal bath to spread the discharged gas in a larger part of the metal bath 12. Furthermore, this allows longer contact time between the material and the hot metal bath. The free ende 26 creates an annular space 27 around the electrode tube 15. From this annular space there are radial openings 28, for example four out from the pipe 25 in the metal bath. When gas is supplied to the metal bath the mean specific weight of the metal bath will be reduced in the bubble region compared with the metal smelt without bubbles. This difference in density results in setting the metal bath into circulation, leading to increased contact time between the gas and the smelt. The metal spray is reduced by fitting the outlet for the products of pyrolysis through the connection pipe 14 with a stop plate 29 located on a central support 30. The intimate mixture of gas and smelt given by the pipe end 26 can also be achieved by other configurations. One such design is exemplified in Figs. 2A and 2B, which illustrate a sealed thermically insulated receptacle or container 31 for a metal smelt 32. There is a connection pipe 34 in the lid 33 of the receptacle for the extraction of gas, and an opening for the combustion unit 35. The combustion unit 35 and the supply conduits for the material to be thermically treated have been described above in connection with Fig. 1. However, in this configuration the combustion unit is located in a gas-tight chamber 36. The chamber 36 may be a part of the container 31 separated from- the rest of the container with a vertical dividing wall 37 that is lowered into the metal smelt 32. There are gaps 38 in the dividing wall 37 which ensure the circulation of gas and smelt in the receptacle 31. When the chamber 36 is gas-tight, the decomposition products from the combustion unit 35 are forced through the gaps 38 in the dividing wall 37 since the outlet for gas 34 is located outside the chamber 36. The chamber 36 and the combustion unit 35 can be located in different parts of the receptacle. There are a number of other usable configurations for the dividing wall than the one illustrated here. Fig. 3 illustrates a third embodiment with a non-perforated dividing wall. More detailed information about materials and dimensions are indicated, since these are considerations which have to be scientifically determined and adjusted to the various application areas. Alternative solutions: The congigurations shown can be modified in a variety of ways. The electrode combustion unit described can be replaced by another type of electrode system where the pipe 25 is mounted on the electrode tube 15 to spread and increase the duration of the gas in the metal bath, and where the "mammoth pump" principle as it is frequently termed can either be excluded or made more extensive. The intimate micture between the gas and the smelt which is the result of the skirt 26 can also be achieved by using other configurations. One example of such is shown in Fig. 2.

Claims: Patent claims: 1. A method for thermal treatment of materials/substances that can be pumped or blown, particularly the pyrolysis of waste products where the substance to be treated is pumped or blown into a heat chamber with a high temperature smelt, particularly a metal smelt, and where the thermic energy is supplied from electric arc discharges between electrodes, c h a r a c t e r i z e d in that the substance is fed into gas which conducts the electricity in the electric arc discharge, and that the decomposition products of this thermal treatment are forced to pass through the smelt. 2. An apparatus for carrying out the method in accordance with claim 1 with a sealed receptacle or container (11) for high temperature smelts (12) and which is equipped with an inlet pipe for the supply of the materials which are to be thermically treated and electrodes for the supply of thermic energy, c h a r a c t e r i z e d by a tubular electrode (15) which in known manner (15) designed to supply the material, and which has an open end directed towards or located in the smelt, and possibly organs (25) placed near the tubular electrode to create movement, especially in the form of circulation, in the smelt and spread of the decomposition products in the smelt. 3. The apparatus in accordance with claim 2, c h a r a c t e r i z e d in that the tubular electrode (15) is surrounded by a pipe (28) with opening pointed downwards, preferably with side flow outlets (31) beneath the level of the bath. 4. The apparatus in accordance with claim 2 c h a r a c t e r i z e d in that the tubular electode (15) is led into a chamber in the receptacle which is separated from the rest of the smelt by a dividing wall which may be perforated beneath the level of the bath with the outlet for decompostion products from the receptacle located outside this dividing wall.

Inventors: PRYTZ STEINAR, RAANESS OLA S, WAERNES AUD N, PRYTZ, STEINAR, RAANESS, OLA, S., WAERNES, AUD, N.
Applicants: STIFTELSEN IND OG TEK FORSK, STIFTELSEN FOR INDUSTRIELL OG TEKNISK FORSKNING VE
Application year: 1986
Main classification: F23G5
IPC codes: C10B19, C10B49, C10B53