Furnaces – Process – Incinerating refuse
Patent
1993-10-13
1995-03-14
Favors, Edward G.
Furnaces
Process
Incinerating refuse
110235, 422184, 588201, F23G 500
Patent
active
053968506
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to the destruction of organic waste and in particular toxic organic waste.
The term "organic waste" is herein understood to include but is not limited to toxic materials such as pesticides, herbicides, paints, medical residues, waste oils, contaminated solvents, and black liquor.
U.S. Pat. Nos. 4,574,714 and 4,602,574 by Bach and Nagel disclose a method of destroying organic waste which is based on the use of a bath of molten metal, typically comprising at least 10% iron. The method comprises maintaining the bath at a temperature of at least 1400.degree. C. and injecting organic waste and oxygen-containing gas into the bath from above and/or below the surface of the bath to crack thermally (pyrolyse) and at least partially oxidize the oxidizable portions of the organic waste. The amount of oxygen-containing gas added to the bath is selected so that the stoichiometric ratio of oxygen to the oxidizable portion of the organic waste is at least 1:1 to ensure that there is sufficient oxygen input to oxidize completely the oxidizable portions in and above the surface of the bath.
The complete oxidation of the oxidizable portions of the organic waste is particularly important to ensure that there are no hydrocarbons remaining in the off-gas which are toxic or could form toxic organic materials such as furans and dioxins as the off-gas cools to ambient temperature. A further important consideration in this regard is to ensure that the concentration of oxygen in the off-gas is as low as possible since there is some evidence that oxygen is favourable to the formation of at least dioxins.
A disadvantage of the method disclosed in the U.S. patents is that there is a relatively high risk of the formation of a continuous path in the bath through which the organic waste can flow to escape the bath in a substantially untreated form.
An object of the present invention is to provide a method of destroying organic waste which has a higher assurance against such break-out of organic waste from the bath than is possible with the method disclosed in the U.S. patents.
According to the present invention there is provided a method of destroying organic waste in a bath of molten metal and slag contained in a vessel, the method comprising: in which the organic waste is thermally cracked and the products of the thermal cracking which are not absorbed into the bath are released into the space above the surface of the bath; and form a secondary reaction zone in the space above the surface of the bath in which the oxidizable materials in the products from the primary reaction zone are completely oxidized and the heat released by such oxidation is transferred to the bath.
The above described method of the present invention provides a high level of assurance against unreacted or partially reacted organic waste short circuiting the process and reporting in the exit gas stream from the vessel. This is achieved by providing at least two separate reaction zones through which the organic waste must pass before exiting the vessel.
It is preferred that the method comprises injecting organic waste with a carrier gas into the bath to form the primary reaction zone. It is preferred that the carrier gas be an inert gas.
It is preferred that the method further comprises injecting oxygen-containing gas into the primary reaction zone to at least partially oxidize the products of thermal cracking.
It is particularly preferred that the method comprises injecting the oxygen-containing gas into the primary reaction zone in a stoichiometric ratio of oxygen to the oxidizable portion of at least 1:1.
It is preferred that the method further comprises controlling the temperature in the secondary reaction zone to be at least 200.degree. C. higher than the temperature of the bath.
It is preferred particularly that the method comprises controlling the temperature in the secondary reaction zone to be in the range of 1500.degree. to 2700.degree. C.
It is particularly preferred that the method further comprises injecting carbonaceous mat
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Batterham Robin J.
Conochie David. S.
Matthews Terry A.
Favors Edward G.
Technological Resources Pty. Limited
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