Specialized metallurgical processes – compositions for use therei – Processes – Producing or treating free metal
Patent
1992-04-08
1994-11-15
Rosenberg, Peter D.
Specialized metallurgical processes, compositions for use therei
Processes
Producing or treating free metal
75746, 75764, B01J 600, C04B 210
Patent
active
053644468
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to the heating and treatment of solid particulate materials utilising a stream of hot gas, for example, the off-gas from a molten bath reactor.
Carbonate materials such as limestone may be treated according to this invention and subsequently added to an iron-ore derived slag in the molten bath reactor, so as to make a Portland-type cement. Alternatively, the lo treated carbonate materials may be subsequently added to, for example, a direct iron-making molten bath reactor, a ferroalloy molten bath reactor, or a non-ferrous molten bath reactor.
BACKGROUND OF THE INVENTION
The process for the production of a Portland-type cement from blast furnace slag in a molten bath reactor requires additions of calcium carbonate or calcium oxide to the slag.
An object of this invention is to minimise the requirement for additional energy for calcination by utilizing the energy of the hot off-gases that leave the molten bath reactor.
Calcination of, for example, limestone, is performed in a variety of furnaces: vertical shaft kilns, rotary kilns, rotary hearth kilns, twin and multiple shaft regenerative kilns, fluidised beds and entrained flow reactors.
Vertical shaft kilns produce a lower quality of lime compared with other types of kilns, and can only accept feed of no less than about 50 mm in size. Smaller sized feed results in a packed bed of insufficient porosity. Nevertheless, the vertical shaft kiln is a very energy efficient kiln.
Rotary kilns are generally able to accept almost any sized feed, down to about 1 mm in size. However, to obtain good energy efficiency it is necessary to incorporate preheaters in combination with the kilns. This combination suffers from twin disadvantages of having high capital and maintenance costs.
Twin and multiple shaft regenerative kilns offer good energy efficiency, since the waste gas from the calcining kiln is used to preheat other kilns. This sequence is continued around the kilns--successively preheating then calcining in each kiln. However, this type of kiln is not suitable for treating fine sized materials.
Fluidised bed calciners are generally able to treat finer sized materials than shaft furnaces. However, control of particle size distribution is important, and large quantities of hot pressurised gas are needed for the fluidisation.
Unfortunately, non of these processes can be adapted so that the hot off-gases from a molten bath reactor, which usually contain sticky and/or molten material, can be used as the energy source of calcination.
In U.S. Pat. No. 3,022,989 (Union Commerce Bank) a process for manufacturing hydraulic cements is disclosed. In this process there is a fluidised bed of particles, in which gases are combusted. A certain amount of stickiness of particles results, but the degree of stickiness is controlled so as to be insufficient to cause large particles to become attached to one another, and agglomeration of the fluidised mass is thereby prevented.
Unfortunately this process requires a fuel to be combusted to provide the high temperatures. It is unlikely that hot off-gases from a molten bath reactor, which contain sticky grains and/or molten droplets could be used to provide the high temperatures. The process operates at a high solids loading, and as a consequence requires that there be a large pressure drop as gases flow through the bed. Furthermore, by virtue of the well-mixed nature of fluidised beds it is not possible to have very large differences between the temperatures of the hottest and coldest particles in the bed.
In patent application No. P251515 IVa/12g in the Federal Republic of Germany by Polysius GmbH, an apparatus is disclosed for the combustion, calcination and sintering of a pulverized or granulated product in suspension, and to the operating procedure for such an apparatus. The apparatus seems to be a modified cyclone with a flattened or `pancake` cross-section.
The drawings in the Polysius specification are confusing and seem to contradict the specification, since the paths of the trea
REFERENCES:
patent: Re30060 (1979-07-01), Kreiger
patent: 3753683 (1973-08-01), Vlnaty
English Translation of German Patent No. 25.515 IVa/12 g, CRA Services Ltd., by Eng. Otto Heinemann, Filed Aug. 12, 1960, "Device for the Combustion, calcination and Sintering of Pulverized or Granulated Product in Suspension, and Procedure for the Operation of this Device".
Batterham Robin J.
Grant Roderick M.
Happ James V.
Thiele Glenn A.
CRA Services Ltd.
Rosenberg Peter D.
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