Furnaces – Process – Treating fuel constituent or combustion product
Reexamination Certificate
1999-09-08
2001-09-25
Bennett, Henry (Department: 3749)
Furnaces
Process
Treating fuel constituent or combustion product
C110S215000, C110S216000, C110S245000, C110S342000, C075S671000
Reexamination Certificate
active
06293209
ABSTRACT:
TECHNICAL FIELD
This invention relates to a process for treating a raw material containing aluminium or a similar metal melting at a low temperature and organic matter, including metal separation.
BACKGROUND OF THE INVENTION
Raw materials to be treated in accordance with the invention consist primarily of packaging waste containing metallic aluminium, which in addition to aluminium foil comprise polymer material and possibly also fibre residues. The treatment aims to utilise the calorific power of the organic matter and/or to recover the valuable aluminium or other similar metal.
The utilisation of such waste material containing aluminium for energy production has been very difficult or even impossible to control by means of combustion or gasification techniques known so far. The problems have been due to the ash component, which melts at a low temperature considering the conversion techniques applied, and thus tends to form detrimental deposits on the walls of the reaction space, and also to cause sintering of the fluidised bed and other process failures. At the same time, in the cases where aluminium recovery has been the aim, the recovery has been deficient.
SUMMARY OF THE INVENTION
The purpose of this invention is to provide a solution for treating packaging waste containing metal aluminium or a similar raw material containing both readily melting metal and organic matter, which overcomes the problems mentioned above and which, depending on the situation, enables both the organic matter and the metal to be utilised and recovered. The method in accordance with the invention is characterised by the fact that the raw material containing metal and organic matter is introduced in a bubbling fluidised bed, where the organic matter is gasified at a temperature higher than the melting point of the metal present, that the gas removed from the fluidised bed and the accompanying metal are cooled to a temperature below the melting point of metal by admixing a cooling medium into the gas flow, and that solid metal particles are subsequently separated from the gas.
It has been confirmed in accordance with the invention that gasification performed at a controlled temperature in the fluidised bed and subsequent cooling of the gas removed from the fluidised bed allow the metal to be converted to solid particles entrained by the gas flow without the metal and/or ashes adhering to the suspended particles in the fluidised bed, to the walls of the reaction space and to the gas exhaust ducts. Assumingly, the molten metal particles formed in the fluidised bed are immediately covered with a protective oxide layer, which reduces the adhesion of the particles substantially. Moreover, an adequate shape of the reaction space can prevent the particles from hitting the walls, to which they might adhere. The bubbling fluidised bed required in the invention, in contrast to the particles circulating in a circulating reactor, is produced by controlling the fluidisation rate so that the fluidised bed has a specific, essentially constant height in the reaction space. These circumstances result in stable process conditions, which are crucial for the process to succeed.
With the process of the invention, the organic matter contained in packaging waste or other similar raw material can thus be gasified and utilised for energy production without interference of the metal present, at the same time as the metal can be recovered for possible recycling. Energy production may be the chief purpose of the process, the recovered metal being then a by-product whose potential value may increase the profitability of the process. However, the main purpose of the process may equally well be to recover the valuable metal by removing organic matter to be gasified, and in that case the gas, which may perhaps be exploited, will constitute a by-product of the process.
Raw materials to be utilised in accordance with the invention are primarily the polymer material and packaging waste containing aluminium mentioned above, such as plastic/aluminium wrappings and a reject fraction containing aluminium, polymer material and fibre residues produced in the recycling of liquid containers. Such a fraction, which contains approx. 5 to 15% of metallic aluminium and in which fibres account for approx. 1%, is the remainder of recycled liquid containers from which the fibrous layer has been torn off for defibration. The waste material mentioned here can be introduced in a fluidised bed in the form of chip-like or stripe-like pieces having a diametre of approx. 0.5 to 5 cm. The material of the particles suspended in the fluidised bed may vary depending on the quality of the raw material to be treated and the process goals. If the metallic aluminium is to be recovered in as pure a form as possible, the particles used are preferably a nearly ungrindable material, such as sand or aluminium oxide. By contrast, in the treatment of an easily tar-forming raw material, not aiming at the recovery of pure metal, the suspended particles may also consist of a grindable material, such as limestone or dolomite. Should molten material adhere to the suspended particles in the course of time, the particles may be replaced while maintaining the particle size within the fixed limits. The appropriate particle diametre of sand for instance is in the range from 0.3 to 1 mm.
In accordance with the invention, the gasification temperature prevailing in the fluidised bed is preferably approx. in the range from 670 to 900° C., which exceeds the melting point of aluminium and is sufficient for the gasification of polymers used in packaging materials. If the material includes fibres, the gasification temperature is preferably at least approx. 850° C. The temperature of the fluidised bed is controlled by means of the feed ratio of the raw material to be treated to the fluidised gas, which appropriately is air or a mixture of air and water vapour, i.e. with the air coefficient, so as to reach a temperature above the melting point of metal and at the same time a temperature equal to or higher than the melting point of the ashes produced. Depending on the material, the temperature of the fluidised bed can be maintained under control at a temperature which is up to 150 to 200° C. higher than the theoretical melting point of inorganic ash material. The fluidisation rate, which is preferably more than four times as high as the minimum fluidisation rate (V
mf
), and the height of the fluidisation bed depending on this are used to adjust the retention time in the reaction space such that the organic matter reacts effectively with oxygen, water vapour and any reactive gases present. The fluidisation rate is typically in the range from 0.5 to 3.0 m/s. The reaction products of the organic matter and the gasification gases are mainly gaseous and there is a low proportion of heavier, condensable hydrocarbons possibly present.
In a fluidised bed whose temperature exceeds the melting point of the metal contained in the raw material, the metal may melt or even vaporise at least partly. However, detrimental agglomeration or sintering of molten metal is avoided by means of the gasification conditions, such as the temperature, the retention time, the shape of the reaction space and oxygenation of the surface of any molten particles, as mentioned above. The gasification reaction preferably takes place in a vertical reaction vessel with straight and plane walls, where the risk of the gas and the entrained particles hitting solid obstacles is reduced to a minimum.
The cooling medium is preferably introduced in the gas flow above the fluidised bed in the same vertical reaction vessel. The feeding causes the temperature of the gas and the entrained particles to drop below the melting point of metal, preferably to a temperature below 600° C. Water injected into an ascending gas flow is an effective cooling medium, however, cold nitrogen gas or mixtures of nitrogen and water may also be used.
After cooling, solid metal particles are separated from the gas flow, most effectively by means of a cyclon
Kurkela Esa
Nieminen Matti
Bennett Henry
Rinehart K. B.
Valtion teknillinen tutkimuskeskus
Ware Fressola Van der Sluys & Adolphson LLP
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