Specialized metallurgical processes – compositions for use therei – Processes – Electrothermic processes
Patent
1990-08-30
1991-12-24
Rosenberg, Peter D.
Specialized metallurgical processes, compositions for use therei
Processes
Electrothermic processes
75 1034, 75 105, C22B 400
Patent
active
050749064
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a process for recovering energy in metallurgical processes comprising preheating of scrap, or other processes in association with metallurgical industry where combustible gases, such as hydrocarbons, are generated. The method is especially advantageous when hot gases, e.g. from an electric arc furnace, are conducted through a basket for direct heating of scrap, such as iron, which is polluted with lacquer or oil, these pollutants being entrained in the form of droplets or vapour with the emitted gases.
The present invention also relates to an installation for carrying out the method.
STATE OF THE ART
In many metallurgical processes, there are emissions of hot gases which are often heavily polluted with dust. These hot exhaust gases represent a major part of the energy losses in such processes. Many methods have therefore been suggested in order to reduce the losses of energy, e.g. by transmitting energy from the exhaust gases to the raw material supplied in the process. In certain case, the heat in the exhaust gases may also be used for preheating combustion air or other process gases by means of different types of heat exchangers.
It has long been customary to use regenerative heat exchangers for transmitting energy from an emitted polluted gas to gas being supplied. Recuperative heat exchangers, in which heat is transmitted through a partition, become much more expensive and require/far more maintenance. Also, they often provide lower energy saving.
The regenerative heat exchangers may be either fixed or movable. In the former case, the direction of gas flow is periodically changed so that one and the same heat exchanger will be alternately traversed by incoming and outflowing gas. In the latter case, the heat exchanger material is shifted between the ducts for incoming and outflowing gas, e.g. by a rotary movement.
Regenerative heat exchange thus effected is useful also in other processes involving e.g. thermal oxidation (combustion). One example of this is given in U.S. Pat. No. 3,895,918. Of principle interest also are, inter alia, U.S. Pat. No. 2,121,733 and 3,870,474.
Cooling of process gases leaving e.g. an electro-steel furnace, with the scrap iron which is part of the next charge in the furnace is disclosed e.g. in U.S. Pat. No. 4,666,402.
The heating of scrap with hot gases generally involves the emission of considerable amounts of pollutants. The scrap often contains metal parts which are covered with oil, lacquered or otherwise contaminated with substances which evaporate when heated. The gases leaving the scrap preheating process may thus be a considerable strain on the environment.
Many methods are known for cleaning gases. The technique which generally is best suited for the destruction of e.g. hydrocarbons is thermal combustion, which means heating the polluted gas to such a high temperature that residues of oil and lacquer are combusted and substantially leave only harmless remainders, carbon dioxide and water. One example of this given in EP-A-82304463.1, Publ. No 74214.
To recover energy and, thus, reduce the cost for the destruction of combustible pollutants, it is customary practice to perform heat exchange between the gas supplied to the combustion chamber and the gas leaving the combustion chamber. Examples of this are given in earlier cited U.S. Pat. No. 3,895,918, U.S. Pat. No. 2,121,733 and U.S. Pat. No. 3,870,474.
BRIEF ACCOUNT OF THE PRESENT INVENTION
Technical problem
Heat exchangers, both recuperative and regenerative ones, contain relatively narrow ducts through which e.g. a gas flows. If the gas is polluted, pollutants deposit in these ducts which are successively blocked. In recuperative heat exchangers, this very soon means impaired performance of the heat exchangers. While not being equally sensitive, regenerative heat exchangers, too, suffer from impaired heat transfer capacity and increased flow resistance with increasing soiling.
Above-mentioned U.S. Pat. No. 2,121,733 and U.S. Pat. No. 3,870,474 thus disclose
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patent: 3632094 (1972-01-01), Longenecker
patent: 4375958 (1983-03-01), Date et al.
patent: 4478574 (1984-10-01), Okuno et al.
patent: 4619693 (1986-10-01), Takai et al.
Granstrom Staffan
Holmlund Sten
ABB Flakt AB
Rosenberg Peter D.
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