Hazardous or toxic waste destruction or containment – Containment – Solidification – vitrification – or cementation
Patent
1991-11-22
1996-01-02
Kamen, Noah P.
Hazardous or toxic waste destruction or containment
Containment
Solidification, vitrification, or cementation
423240S, 588206, 110342, F23B 700, C01B 700
Patent
active
054810639
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method of treating various materials such as wastes, biological sludges and even metal oxide concentrates, which materials contain halogenated hydrocarbon compounds, at a high temperature, and of cooling the resultant process gases for minimizing the amount of polyhalogen compounds harmful to the environment, such as dioxins and furans, in the emissions of combustion processes.
The chlorine-containing environmental poisons resulting from the combustion of municipal waste and also from the combustion of biological sludges and from smelting processes have been recognized as constituting a problem. It has been found that polychlorinated aromatic compounds categorized as superpoisons, such as coplanar PCB, polychlorinated dioxins and polychlorinated furans, are produced to a great extent in both municipal waste incinerator plants and industrial combustion plants for biological waste. Dioxins have also been found in flue gases from metal smelteries. These chlorine-containing compounds are superpoisonous for human beings and animals; they bring about genetic damages and obviously cause also cancer. Toxic compounds spread in the environment mostly bound to flue dust.
It has been found that the lower the temperature and the shorter the residence time, the greater amount of superpoisons results. Combustion at 500.degree.-700.degree. C. has been established to be especially favourable for the formation of polychlorinated dioxins and furans. This has led to the conclusion that the combustion should be carried out at a higher temperature and with a longer residence time in order to decompose the superpoisons. On the other hand, it has also been suggested that the wastes could be safely destroyed by incinerating them at relatively low temperatures if the flue gases are post-combusted at such a high temperature that, for example, dioxin and furan toxins decompose.
Recently, it has been found that heavy metals are of great significance in the formation of dioxins in the combustion. Heavy metals catalyze, for example, the production of dioxins. Dioxins are formed by synthetization from chlorine compounds in the presence of coal, water and oxygen at favourable temperatures, for example, in flue gases. It has been established that a great portion of the dioxins of fly ash is formed only after the combustion by means of a so-called "de novo synthesis" in the heat exchangers and the stack because the "de novo synthesis" of the dioxins is to a great extent dependent on the temperature, and the temperature of 250.degree. to 400.degree. C. is especially suitable for this synthesis. Efforts have been made, by an as complete as possible combustion, by a high combustion temperature and a long residence time, to produce fly ash containing as little carbon as possible, whereby the synthesis would be prevented. By separating metals from the wastes, it has also been attempted to decrease the amount of polychlorinated aromats in the flue gases.
U.S. Pat. No. 4,762,074 suggests the combustion of wastes containing pre-stages of toxic dioxins and furans by means of oxygenated air at a high at least 1200.degree. C. temperature for destroying the toxins. By using highly excessive amount of oxygen, it is also attempted to maintain the amount of those nitrogen oxides, which increase at high temperatures, at an acceptable level. Swedish patent specification 453 777 discloses a method of combusting solid waste in a reactor in a bubbling fluidized bed at a temperature below 900.degree. C. In the reactor, above the actual fluidized bed, the temperature of the flue gases is raised at least to 950.degree. C. by adding secondary air and insulating the reactor walls. The temperature of the flue gases is maintained at the level above 950.degree. C. for as long as required for the hydrocarbons and dioxins to become decomposed, by conducting the flue gases through an uncooled gas duct. The gases are cooled prior to the heat exchangers by injecting air or flue gases into the gases.
U.S. Pat. No. 4,794,871 discloses a met
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Hiltunen Matti
Lampenius Harry
Westerlund Kurt
A. Ahlstrom Corporation
Kamen Noah P.
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