Specialized metallurgical processes – compositions for use therei – Processes – Electrothermic processes
Patent
1994-09-20
1996-02-13
Rosenberg, Peter D.
Specialized metallurgical processes, compositions for use therei
Processes
Electrothermic processes
75 1015, C21B 304
Patent
active
054908698
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a process and device for treating pollutant materials, which are fusible and conductors of electricity in the molten state. This process and this device are specially dedicated to municipal solid waste incineration fly ash which are extracted after fumes treatment.
Ever stricter environment protection regulations are now leading to improvements in techniques for treating fumes released by the burning of fossil fuels and the incineration of industrial, urban and hospital waste.
Household waste incinerators are subject to regulations, especially regarding the quality of fumes released into the atmosphere.
Untreated household incinerator fumes contain a significant amount of dust, metals, hydrochloric acid, etc., raising the need for fume purification systems.
Conventional fume purification systems are dedusters, in particular, bag filters and electrostatic or cyclone separators. These systems are designed to strip the hot fumes of solid particles carried by the fumes or formed by condensation of volatile chemical elements or compounds on dust particles.
In addition, the new standards relating to the quality of fumes have lead to the installation of equipment designed to remove hydrochloric acid from fumes. This equipment employs a base (generally lime) that causes the hydrochloric acid to precipitate in the form of calcium chloride, which is then recovered in the dust or wash water. A number of dechlorination techniques are available including the wet, semi-wet, dry and condensation processes. These techniques produce powders of different qualities. The residue collected in the condensation process is dry and contains hardly any chloride. The residue from the wet process also contains very little chloride (about 2%) but has a high moisture content (up to 60%). In the wet process, the chlorides are dissolved in the wash water which is then discharged into a river or sea, according to regulations. The residues from the semi-wet and dry processes have a high chloride content (about 25%) together with a reagent excess.
The residue collected by dedusters may also contain a significant amount of chloride (approximately 10%). These residues also have a significant heavy metal content.
The elimination of these residues generated by the gases scrubbing of Municipal Solid Waste incineration (REMSW) is now regulated owing to their toxic nature. This is because certain elements, especially metals and chlorides, are likely to be leached when dumped and thus pollute the ground water table. Leaching tests conducted on these residues reveal that the amounts of chloride ions, lead and cadmium in the leacher are far above the maximum acceptable thresholds for urban waste dumping in France and the amounts of chloride ions, lead and cadmium in these residues even exceed the levels set in European Community directives governing hazardous waste.
It is therefore vitally important to envisage treatment processes to make these residues non-reachable, a number of which have already been developed.
One of these is the DEGLOR process developed by the ABB company which is designed to treat filter dust collected by conventional fume purification systems. In this process, the dust is heated to over 1300.degree. C. in an electric melting furnace. Toxic dioxins are destroyed at these high temperatures, this dust also forms a liquid slag and gives off heavy metal vapors. The fumes containing these metals are sucked out and vigorously cooled causing the metal compounds to condense; the dust recovered downstream of the cooling stage contains a high proportion of these metals which can be commercially upgraded. The decontaminated dust is vitrified to obtain a non-leachable material that can be stored in normal depots or used in the building and public works industry.
This process, however, presents many drawbacks. First, the refractory lining required is generally expensive and requires periodical replacement. The lining may become impregnated with toxic products and itself pollute. The lifetime of the furnace heating
REFERENCES:
patent: 4762554 (1988-08-01), Lazcano-Navarro
VGB-Konferenz "Ruckstande aus der Mullverbrennung", VGB Kraftwerkstechnik 70(5) May 3-4, 1990, pp. 428-430.
D'Obrenan Jean V.
Deriaud Thierry
Madigou Nicole
Constructions Electriques Celes
Frommer William S.
Promethee
Rosenberg Peter D.
Soretel
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