Heating – Processes of heating or heater operation – Including passing – treating or conveying gas into or through...
Utility Patent
1999-12-30
2001-01-02
Ferensic, Denise L. (Department: 3749)
Heating
Processes of heating or heater operation
Including passing, treating or conveying gas into or through...
C432S058000, C404S075000, C106S773000
Utility Patent
active
06168424
ABSTRACT:
FIELD OF THE INVENTION
The invention concerns an installation for the rapid heat treatment of suspended powdered materials, in particular for the flash calcination of mineral materials. (“Powdered” is hereinafter understood to denote a material being in a divided state which is capable of being suspended in a gas flow). It applies in particular to the calcination of clay-bearing materials with a view to preparing a binder for stabilizing soil on a road construction site.
BACKGROUND OF THE INVENTION
Traditional installations for carrying out heat treatment, in particular calcination of mineral materials, operate in a fixed bed and/or a long cycle, for example in the cement-making sector where the calcination of materials takes several hours. In order to improve heat exchanges and to reduce firing times, certain installations have been adapted to work in a fluidized bed but the operating and firing parameters are difficult to control, in particular for certain materials with heterogeneous particles. All these installations are heavy and very bulky installations in which heat treatment is linked to production capacity.
Another method of calcining powdered materials is also known, often designated as “flash calcination” which consists of heat treating suspended materials over very short periods, by passing them through a combustion chamber in an airflow which carries them in the chamber and serves as an oxidant. This method of flash calcination is currently often used in cement works in order to ensure the precalcination of materials, but corresponding industrial installations remain very bulky, in particular as regards their height, on account of the accumulation of the necessary stages inside which the materials descend by gravity from the point at which they are fed at the top until they leave at the bottom (U.S. Pat. Nos. 4,321,238, 4,416,622, 4,668,182). These installations do not lend themselves to a reduction in size and bulk.
The flash calcination process (or more generally the process consisting of subjecting suspended materials to a rapid heat treatment) could have considerable value in many applications, in particular for activating clay-bearing materials (in particular to obtain a metakaolin) with a view to manufacturing a hydraulic binder which can be used in a road application, in a low-cost construction, in “small civil engineering works” etc. (cf. in particular the following publications: “Pozzolanic properties . . . with soak-calcined products”, S. SALVADOR, Cement and Concr. Res. 25 (1995) 102-112”; “Evolution of structural changes during flash calcination of kaolinite”, SLADE and DAVIES—J MATER—Chem.1991—1(3)—361-364; “Flash calcines of kaolinite: effect of process variables on physical characteristics”, SLADE et al., JOURNAL OF MATERIALS SCIENCE 27(1992)2490-2500; “Phototyping flash calciners for the manufacture of synthetic pozzolana from kaolinite clay” SALVADOR S., Flash Reaction Processes, 295-318, T. W. Davies(ed)., 1995 Kluwer Academic Publishers. Printed in the Netherlands, NATO ASI Series, Series E: Applied Science—vol.282). It is however desirable, for these applications, to make use of installations with a moderate capacity and small bulk, more particularly in road construction techniques or in a mobile or semi-mobile installation which would enable clays to be treated on site and which would enable the installation to move as the construction site advances.
SUMMARY OF THE INVENTION
The object of the present invention is to provide an installation for the rapid heat treatment of suspended powdered materials, of which the structure lends itself to changes in scale compared with known installations and equally well enables installations with small overall size to be constructed having small or moderate capacities (1 to 10 tonnes/hour) as well as installations with high capacities benefiting from a smaller overall size than those of known flash calcination installations.
“Rapid heat treatment” is understood to mean a treatment with a duration of the order of a few seconds to a few tens of seconds, this heat treatment being designated as “flash calcination” in the particular case where powdered materials undergo a mineralogical transformation.
One objective of the invention is in particular to enable mobile installations to be constructed which are easily transportable on a road jig.
Another object is to provide installations benefiting from a high degree of operating flexibility, with in particular a low starting and stopping inertia, which lends itself as required to daily operation during the hours of activity on a construction site.
Another objective is to provide installations benefiting from very good thermal yield, even in the case of small size or very small size installations and those with a small capacity (less than 5 tonnes/hour for example).
To this end, the installation according to the invention for heat treating suspended powdered materials comprises:
means for feeding in powdered materials,
a device for preheating the materials, provided with an inlet for hot gases, an outlet for the preheated materials and a gas outlet,
a combustion chamber containing at least one burner and provided with an inlet for introducing reheated air and preheated powdered materials, and an outlet for fumes containing the materials after passage through the chamber,
a separator provided with an inlet receiving the fumes and powdered materials coming from the combustion chamber, a fume outlet connected to the inlet for hot gases of the preheating device, and an outlet for powdered materials,
an assembly for cooling the materials, provided with an inlet for powdered materials coming from the separator, an inlet for fresh air, so-called principal air, an outlet for cooled materials and a reheated principal air outlet,
at least two conduits connected to the reheated principal air outlet of the cooling assembly with a view to dividing the reheated principal air into two flows, one referred to as reheated air and the other as diverted air, the reheated air conduit being provided with an inlet for materials connected to the preheated materials outlet of the preheating device, with a view to introducing the said materials into the said conduit, and being connected to the reheated air inlet of the combustion chamber with a view to injecting the said materials into the said combustion chamber, the installation extending vertically between a lower level Ni and an upper level Ns, wherein the diverted air conduit, the so-called by-pass conduit, includes a section descending from the reheated principal air outlet to the lower level of the installation, is connected to means of supply by a powdered material inlet in the vicinity of the said lower level with a view to receiving the powdered materials, and includes a section rising towards the fume outlet of the separator to form therewith a common conduit connected to the hot gas inlet of the preheating device, with a view to providing pneumatic transport for the said powdered materials from the level Ni and a first reheating of these upstream from the said preheating device.
The installation according to the invention uses the principle of flash calcination by introducing into the combustion chamber powdered materials suspended in part of the combustion air. This air comes from the principal air flow which is reheated in the cooling assembly by recovering heat liberated in this assembly. The diverted air, also reheated, which is conveyed in the by-pass conduit, conveys the powdered materials pneumatically to the preheating device (these materials are therefore able to enter at the lower part of the installation so as to avoid additions to the height) while providing a first reheating of the said materials. These materials thus undergo preheating at the same time by virtue of the heat from the fumes coming from the combustion chamber and the residual heat of the air diverted by the by-pass conduit. An excellent thermal yield is obtained in this way while profiting to the greatest extent from the advantages of flash calcination
Pons Olivier
Raynaud Gilbert
Salvador Sylvain
Valmalette Pierre
Demeter Technologies
Ferensic Denise L.
Wilson Gregory A.
Young & Thompson
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