Hydraulic and earth engineering – Soil remediation – With treatment
Reexamination Certificate
2002-05-10
2004-07-27
Swann, J. J. (Department: 3677)
Hydraulic and earth engineering
Soil remediation
With treatment
C405S128800, C110S346000, C110S342000, C110S344000
Reexamination Certificate
active
06767163
ABSTRACT:
BACKGROUND OF THE INVENTION
a) Field of the Invention
The present invention relates to a plasma process and appropriate equipment well adapted for the removal of hydrocarbons contained in the sludge formed at the bottom of petroleum storage tanks, which contains crude oil and a significant amount of inorganic solid material and water. The process is applicable for the treatment of contaminated soil and sludges, eliminating toxic or hazardous organic compounds, such as petroleum oils, pesticides, herbicides and various hydrocarbons resulting from spills or inappropriate disposal/handling of these materials.
b) Brief Description of the Prior Art
Soils contaminated with petroleum or other types of oils are normally the result of accidental spills or during maintenance of pipelines, and are commonly found in, or close to, petrochemical and refinery plants. It is common to find soil contaminated with more than 25% in weight of petroleum or oil. Such petroleum or oils present serious threat to the environment, endangering vegetal and animal species, including human beings. In the same category can be included soils, sludges and similar materials contaminated with other organic compounds, such as pesticides and herbicides, in which case contamination could vary from tens of ppm (parts per million) to a significant percentage. In all contamination cases mentioned above there are considerable risks to the environment so that toxic or hazardous organic compounds must be removed from the soil or sludge and properly treated.
Another source of hydrocarbons is the sludge formed in petroleum storage tanks; which contains significant amounts of inorganic solid material, as well as water, and must be properly treated before it can be returned to a natural environment. For simplicity, the different types of organic compounds mentioned above, soil contaminants and those present in different types of sludges will be referred to in this document as hydrocarbons.
There are several treatments processes for the above mentioned contaminated materials. The most commonly used include incineration and the use of centrifuges. However, as will be shown, both methods have serious limitations that the present invention offers a superior and feasible alternative.
Incineration is a common practice in engineering (see for instance Chemical Engineering Handbook, ed. R. H. Perry e C. H. Chilton, McGraw-Hill Book Company, 5
th
Edition, 1973, pg. 9-35 a 9-36). In particular, for the treatment of hydrocarbon contaminated materials. The contaminated material is fed into a rotary furnace having an adequate refractory lining. Gas or oil burners are used to maintain the furnace temperature within a range of 500 to 1,000° C.; air must be present in the furnace, and at this temperature the oxygen from the air causes a partial or complete combustion of the hydrocarbons. The presence of water contained in the contaminated material volatilises and leaves the furnace with the combustion gases. The residue of the process is a material that, in principle, should be free of organic toxic or hazardous compounds, but the problems associated with incineration processes are: a) large volume of effluent gases requiring treatment, (the effluent gases are the sum of: the entrained air for the process, the gases resulting from the combustion of the organic toxic compounds, the gases from the burners and water vapour); b) poor energy efficiency, since a most of the heat from the oil/gas burners leaves the furnace with the exhaust gases; typical energy efficiencies are less than 20% for the overall process; c) no recovery of the initial organic materials is possible, since the hydrocarbons are burnt, which represents a significant loss.
The use of centrifuges to separate liquid from solids is a common engineering practice (see for instance Chemical Engineering Handbook, ed. R. H. Perry e C. H. Chilton, McGraw-Hill Book Company, 5
th
Edition, 1973, pg. 19-87 a 19-98). Centrifuges are used to treat hydrocarbon contaminated soil or sludges (see for instance U.S. Pat. No. 6,149,345-A, P E Atkins, “Remediation of hydrocarbon-contaminated soil or groundwater by apparatus having a centrifugal separator, a vacuum source, a vent, a fractionator (FS) and a fill sensor, where the separated liquid is fed to the FS via a low-shear pump”). In this application the contaminated material, containing variable amounts of hydrocarbons and water, is fed into a rotating vessel, called a centrifuge, in which centrifugal forces separate liquid hydrocarbons and any water from contaminating soil or solids contained in the sludges. The result of the process should, ideally, leave soil or sludge free of hydrocarbons and water, and the recovery of such organic liquids. The problem associated with centrifuges is the impossibility of complete removal of hydrocarbons; the soil or sludge after the treatment still contains typically more than 5% (by weight) of organic contaminants.
The use of thermal plasmas is a recognised method for the disposal of hospital wastes, industrial residues and reclaiming aluminium from foundry waste (dross) and such like. In this connection, reference can be made to the article of R. N. Szente (ASP Conference Proc., n.345, pg. 487, 1995). Thermal plasmas are obtained using an electric arc to heat a common gas to temperatures of the order of 20,000° C. The equipment that generates the thermal plasma is the plasma torch, that can have different geometries, such as tubular metallic electrodes or alternatively graphite electrodes in either case an electric arc is maintained between the electrodes to heat the gases. At these temperatures gases are partially ionised, and are called plasmas, which have different properties from those of the outlet gases and can be employed when high temperatures are needed in a process or when ionised types are necessary for certain chemical reactions or physical modifications of materials. The usual method of generating thermal plasmas is from a direct current power supply, as opposed to the alternating current employed in metallurgical arc furnaces. A given residue will require a specific type of plasma system and reactor. Plasma processes for residues usually need a process temperature of about 1,500° C., in order to melt the inorganic compounds contained in the residues and also to oxidize the organic compounds, generating carbon monoxide or carbon dioxide and water vapour.
With particular reference to the subject invention the following work regarding thermal plasma treatment of aluminium dross should be mentioned: G. Dube, J. P. Huni, W. Stevens, S. Lavoie, “Recovery of Non-Ferrous Metals from Dross Using the Plasma Dross Process”, U.S. Pat. No. 4,960,460, Oct. 2, 1990, since this process has some similarities in its operating conditions and heat transfer mechanisms to that of the present invention. For treating aluminium dross, the material is fed into a rotating reactor, the door of which is then closed. Inside the reactor, a plasma torch or, alternatively, graphite electrodes with a direct current electric arc striking between them, is used to keep a controlled atmosphere and at the same time, to provide the necessary energy for the process. The plasma torch or graphite electrodes are normally located in the central region of the reactor. The process consists basically in melting out aluminium from the dross at approximately 700° C. in a non-oxidising atmosphere in order to avoid the oxidation of the recovered metal. No water should exist with the aluminium dross since it could cause oxidization or even cause an explosion, owing to a reduction of water to hydrogen in the molten aluminium. The process is conducted in a batch form. Once the aluminium contained in the dross has melted the reactor is opened and the liquid metal is poured into molds. Other compounds, principally aluminium oxide, are removed from the reactor and another charge is loaded. The process is well adapted for treating aluminium dross, but has not been used for other types of residues since it is essentially a batch process, has no p
Bachman & LaPointe P.C.
Mitchell Katherine
Swann J. J.
TSL-Engenharia, Manutencao E. Preservacao Ambiental Ltda.
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