Chemistry of inorganic compounds – Miscellaneous process
Reexamination Certificate
2000-03-28
2002-11-05
Silverman, Stanley S. (Department: 1754)
Chemistry of inorganic compounds
Miscellaneous process
C423S047000, C423S089000, C423S110000, C423S153000, C423S154000, C423SDIG001, C422S145000, C422S147000
Reexamination Certificate
active
06475462
ABSTRACT:
The present invention relates to a process for treating particulate matter, in which particles of the material to be treated interact with a non-static second set of particles. The present invention also relates to a reactor apparatus for performing the said process.
A number of techniques have been developed for processing of refractory ores or chemically bonded substrates and these fall into two main categories: hydrometallurgical techniques, such as pressure oxidation and biological leaching; and pyrometallurgical techniques, such as roasting, pyrolysis and calcination.
Several metals occur naturally as the sulphide, for example galena (PbS), copper pyrites and chalcopyrite (Cu
2
S with FeS), pentlandite (NiS with Cu
2
S and FeS), and zinc blende and sphalerite (ZnS). The metal is extracted from the ore by a reducing or electrowinning process, but it is common to first convert the sulphide into an oxide in a preliminary roasting process. In such a process, the sulphide ore is powdered and then roasted to the oxide by heating in air at a temperature below the melting point of either the sulphide or oxide. Roasting reactions are often exothermic and the heat released provides much or all of that needed to keep up the temperature during the roast. During roasting, the particles of powder may become stuck together, i.e. sintered, so forming agglomerates. If sintering develops too quickly, then oxygen may fail to reach all of the particles and some sulphide will remain and in extremis a fluidisation process will fail as particles grow excessively. A process of flash roasting in a dilute spouting bed reactor is known in the art (Australian
Engineering and Mining Journal—June
1993 pp 23). In a flash roaster, hot gases enter a vertical reactor assembly through a narrow throat or venturi which provides a region of high gas velocity. Feed solids are then introduced into the gas stream directly above the venturi, which due to the high gas velocity in the throat prevents weeping of the solids. For large particles the reactor behaves as a back-mixed reactor, whilst fine particles are elutriated directly, and hence the behaviour is more plug flow, that is there is essentially little or no mixing or diffusion of the particles along the flow path.
There are a number of disadvantages associated with systems based on the dilute spouting bed technique. Thermal profiles can be generated across the reactor and between the gas phase spout and the surrounding dense bed leading to poor temperature control resulting in unprocessed material and/or agglomeration or possible sealing over the outer surfaces of the reactant particles reducing access to the particle interior. It is also often difficult to control the temperature in the event of an exotherm. Furthermore, as a result of the bi-modal characteristics of the technique, there is a wide distribution of particle residence times. The residence time is furthermore strongly dependent on the material to be treated. This system is also unable to cater for very finely divided feed stocks, or feed stocks with large exotherms.
Further the use of fluidised beds is common whereby the mineral concentrate is introduced, often as a wet filter cake, directly into the fluidised bed with similar disadvantages.
Other hydrometallurgical processes include the pyrolysis of organic metal salts such as cobalt oxalate, which may also contain bonded water of crystallisation, to produce the metal.
In our European Patent No. 0 0068 853 is described and claimed a process whereby particulate material to be treated is embedded and centrifugally retained within a compact, but turbulent, toroidal bed of further particles within the bed and which circulate about the axis of the processing chamber. Specifically, the resident (“host”) particles within the bed are circulated above a plurality of outwardly, radiating, inclined vanes arranged around the base of the processing chamber. Said vanes are preferably arranged in overlapping relationship and the particles are caused to circulate around the bed by the action of a processing fluid, for example gas injected into the processing chamber from beneath and through the vanes.
It has now been found in accordance with the present invention that by selection of a differential terminal velocity between the particles of material within the bed, the rate of circulation of the treated material through the bed may be varied according to the nature of the material to be treated and the desired reaction to be achieved. Surprisingly, complete reaction may be achieved in a matter of milliseconds as compared with the prior art processes which required residence times of a second to several minutes. By “terminal velocity” is meant the rate at which a particle, under conditions within the processing chamber, will fall towards the vanes forming the base of the chamber.
Accordingly, in a first aspect the present invention provides a process for treating a particulate material, in which particles of the material to be treated interact with non-static particles of a second material, the process comprising the steps of:
(i) providing a processing chamber having an inlet and an outlet spaced downstream therefrom, the base of said chamber comprising a plurality of outwardly is radiating inclined vanes,
(ii) providing a bed of host particles in the chamber and generating a flow of fluid through the vanes at the base of the processing chamber such that the bed of host particles circulates about an axis of the chamber in a compact turbulent band,
(iii) injecting particles of the material to be treated through an inlet into the chamber to contact with the circulating bed of the host particles,
wherein the relative terminal velocity of the particles to be treated and of the host particles is such that there is little or substantially no migration of the host particles to the outlet, and wherein substantially all of the particles of the material to be treated migrate downstream through the circulating host particles to the outlet.
The flow of fluid may be generated either before or after the host bed of particles is introduced into the chamber. Alternatively, the flow of fluid may be generated as the host bed of particles is introduced into the chamber.
The terminal velocity of the particles will depend upon several parameters, in particular upon density and particle size. In general the average terminal velocity of a host bed particle will be greater than the average terminal velocity of a particle of the material to be treated, prior to the latter being introduced in the chamber. However, the process of the present invention may also be used in circumstances where the terminal velocity of the particles of the material to be treated decreases during processing. In addition, the relative particle size of the material to be treated may be smaller than that of the host particles either initially or resulting from processing through the processing chamber.
Advantageously, the circulating bed of host particles define tortuous paths along which the particles of the material to be treated travel before exiting the processing chamber through the outlet. In an embodiment of the process of the invention the host particles may be withdrawn from the processing chamber from time to time and be replenished with fresh material. Similarly where the host particles are themselves reactive, for example by absorption of released gases from the particles being treated, such host particles may be replenished from time to time.
The particles of the material to be treated preferably enter the chamber below and/or adjacent to the circulating host bed particles in order to contact therewith.
The particles of the material to be treated may be injected into the chamber by conventional means, for example by the use of a compressed fluid, such as compressed air, oxygen, chlorine, ozone, hydrogen, carbon monoxide, sulphur dioxide, hydrogen sulphide, methane, inert gases such as nitrogen, CFC and other noble/-mono-atomic gases.
Heating means are advantageously provided for heating the f
Dodson Christopher Edward
Wellwood Grant Ashley
Bacon & Thomas
Mortimer Technology Holdings Limited
Vanoy Timothy C
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