Hazardous or toxic waste destruction or containment – Containment – Solidification – vitrification – or cementation
Reexamination Certificate
1999-05-07
2002-04-23
Griffin, Steven P. (Department: 1754)
Hazardous or toxic waste destruction or containment
Containment
Solidification, vitrification, or cementation
C588S253000, C588S253000, C204S157150, C204S157400
Reexamination Certificate
active
06376739
ABSTRACT:
FIELD OF THE INVENTION
The invention is concerned with a process for the treatment of residues containing polluting and/or toxic materials. More specifically, the invention is directed to a process for treating residues containing oxidizable organic materials.
BACKGROUND OF THE INVENTION
Today's industries require practical solutions for the management of liquid and solid waste. For example, they must reduce the level of contamination of effluents before being released. Manuring and landfill of waste has become less popular, and incineration in large treating plants does not allow for the recovery of by-products. Liquid effluents and sludges generated by industries represent important concentrations of organic products as well as other oxidizable products. Each year, thousands of tons of organic materials and residues of various origins representing oxygen-demanding loads, are either treated or disposed of in landfills sites. However, an “on-site” treatment process represents an interesting alternative, especially if the process allows for the recovery of heat in the recycling of water and ashes produced.
The conventional approach, which comprises a drying step by evaporation, followed by an incineration step, is well known, but has limitations in terms of the energy yield. In particular, a lot of heat is lost from the air or the gases produced during the drying step. Also, many conventional incineration processes operate at high temperatures, for example around 1100° C. The sludge to be incinerated must therefore be substantially dry and have a high concentration of combustible materials to obtain a self-heating process. Otherwise, external heating with gas burners will be required.
Oxidation at 1100° C. requires a lot of energy to heat the gases and the water vapor. Therefore, incineration necessitates a heat source such as natural gas or fuel to initiate the reaction and maintenance thereof, as well as a high input of air that must be heated because the heat source already consumes a lot of oxygen. Furthermore, at such treatment temperature, salts and other volatile compounds escape from the incinerator. Also, the ashes, which contain alkali metal oxides, can form eutectics that are damageable to the refractory materials of the process or form melted heaps.
Landfilling of sludges requires large fields and is increasingly regulated because of long-term rigorous controls of liquid effluents. Landfill however has the advantage of being cheap and “apparently” offers a simple and quick solution to the disposal of sludges. However, the waste producer always remain responsible for any damage to the environment resulting from such landfilling.
Manuring also has the advantage of being cheap, and often represent an alternative less expensive than landfill because it is done on the surface. Liquids as well as sludges with high concentration of organic materials can easily be manured. However, the materials must not be toxic, nor bearing pathogenic microorganisms, and must have a relatively neutral pH. Also, the leaching waters should not contaminate rivers, lakes or ground water. And even if the materials to be manured possesses fertilising properties, the available manuring sites should be as close as possible to the production site to avoid high shipping costs because of the presence of high water volume therein. Manuring nearby residential areas is generally unpopular because of the various odours that may emanate from the site.
Airy ponds cause problems in terms of the management of the sludges as well as the space required for the installations. Such process generally uses compressors to supply air under pressure by injection. A lot of electrical energy is used, but no energy is recovered or recycled.
Composting is applicable only to sludges containing biodegradable materials. Such sludges must be dry enough to avoid secondary leaching. If the sludge contains too much water, the liquid or the sludge can be mixed with straw to ensure good absorption of the liquids and good product aeration, but the downside is that the volume of product to be treated, the storage requirement and the length of treatment are significantly increased. Again, the product cannot contain toxic materials that would impair the effect of the composting microorganisms, and to ensure that the material produced can be released into the environment without causing damages thereto.
A few damp oxidations technologies in super critical phase or in liquid/gas phase are available commercially. One of the major drawbacks of the implementation of these technologies is the high investment required. This is caused by the size and complexity of the equipment necessary. The super critical oxidation process could be economically attractive, but is useful only for low effluent flows if the latter are highly toxic.
The present invention has been designed to overcome the above limitations.
The invention relates to a process for treating residues containing oxidizable organic matter. The process of the invention comprises the steps of:
a) introducing the residues in a rotating furnace having a refractory lining and containing a thermo-transfer agent;
b) heating the residues in admixture with the thermo-transfer agent at a temperature of at least 300° C. in the presence of chemically active species and UV radiation generated electrically, while rotating the furnace, so as to dry the residues and cause oxidation of the organic matter and formation of gases, the organic matter oxidation being catalysed by the chemically active species and the UV radiation; and
c) expelling the gases from the furnace.
The process of the present invention allows the drying and destruction by oxidation of the organic matter contained in the residues treated. It is based on the use of an electrically catalysed oxidation reactor, in particular for the treatment of effluents comprising high organic matter concentration, such as those found in the pulp and paper, textiles, paper de-inking, and food industries. Electricity is used to induce catalytic effects and transport phenomenons in combustion reactors.
Preferably, step b) is performed with a plasma torch. It is also possible to use electric arc system or an electrical discharge system comprised between two electrodes made of metals or graphite. These devices allow the heating of the mixture of the residues and the thermo-transfer agent at the desired temperature, and permit a generation of an ultraviolet-type radiation as well as chemically active species, such as free radicals, ions and excited species, which catalyzed the oxidation reactions. This is a rational use of electricity for the generation of phenomenons assisting transport mechanisms in chemical reactions taking place in an oxidation reactor. As a result, incineration process is performed in a smaller reactor in comparison with conventional incineration processes.
The process according to the invention aims at taking advantage of the calorific value of the oxidizable matter contained in the residues to be treated, to help the water evaporation process in the thermal destruction of the polluting materials. For sufficiently concentrated sludges (dryness higher than 10%), and if the calorific power of the oxidisable materials is sufficiently high, it will be possible to reach a self heating operation, and even exothermic, for the oxidation reactor. The expression “dryness” is defined as the mass proportion including the organic matter and the inorganic matter, excluding water, with respect to the total mass of the damp residues for diluted liquid effluents. The concentration of these matters can be increased through conventional standard techniques. These include the use of separation processes with membranes, such as inverted osmosis, ultrafiltration, nanofiltration and/or microfiltration, the latter being tangential flow filtration processes. Also included are the mechanical dehydration processes with or without flocculation/coagulation products, such as centrifuges, screw presses, seave filters, press filters, sedimentation process
Labrecque Raynald
Laflamme Claude B.
Griffin Steven P.
Hydro-Quebec
Katten Muchin & Zavis
Nave Eileen E.
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