WO1982003112A1 - Method for destruction of problematic wastes - Google Patents

Abstract

In order to destruct problematic wastes such as discarded paints, paint sludge, greasy wastes, distillation residues etc., possibly containing oil sludge, organic compounds etc., the wastes, after tearing and/or comminuting, if required, are dispersed in water to saturation, preferably to a water content of 20 to 40%, whereby a pumpable dispersion is obtained which may be used as a fuel.

Description

Method for destruction of problematic wastes.

Technical Field.

The present invention relates to a method for destruction of problematic wastes from the paint and lacquer industry, the plastics materials industry, the metal industry, the wood pulp industry, the shipping industry, petrochemical plants etc., i.e. wastes of the type discarded paints, paint sludge, greasy wastes, distillation residues etc., possibly containing oil sludge, organic compounds, etc.

The reason why such wastes are called "problematic wastes" is that great problems have till now been involved in handling of such wastes for disposal and/or destruction. One reason therefor is that the wastes are largely solid, viscous or sticky materials which are non-pumpable, the viscosity being above 100.000 cP and the solid matter content being close to 100%, usually about 80%.

Background Art.

Such materials have previously been incinerated in rotary furnaces of the same type as the cement kilns used for calcining cement. The material is fed to the upper end of the inclined rotary furnace, and at the same time oil is burned in order to increase the temperature and thereby enhance the combustion of the wastes. Such rotary furnace plants are extremely large and expensive. They operate with a large surplus of air and the efficiency is relatively low.

The object of the invention is to provide a method for destruction of such problematic wastes, which method may be carried out in substantially smaller and cheaper plants, and which can produce heat with greater efficiency.

Disclosure of Invention.

It has now turned out that such wastes may be dispersed with water, whereby the wastes become pumpable and may be used as fuel in burners similar to oil burners. The water will primarily have a lubricating effect and thereby prevent clogging of pumps and pipes.

It is known to add small amounts of water to heavy oil in order to obtain a better combustion of the oil. However, the amounts of water are far" smaller than those according to the present invention and, furthermore, heavy oil is an already pumpable matter. Thus, the fact that a small addition of water to heavy oil improves the combustion of the oil, does not make it near at hand to disperse essentially solid problematic wastes of the type referred to above in water in order to produce a pumpable dispersion.

More specifically, the invention consists in that the waste by mechanical mixing and, if required, by tearing and/or comminuting are dispersed in water to saturation, preferably to a water content of 20 to 40%, whereby a pumpable dispersion is obtained, which may be used as a fuel.

From GB patent specification 1 337 116 it is known to burn pumpable mixtures containing at least 50% oil and possibly other hydrocarbons. The mixture is pumped to the burner by means of a pump which homogenizes the various liquids and any comminuted solid matter of which the mixture consists. The basis of the method disclosed in the patent specification is accordingly pumpable matter and not viscous, stiff problematic wastes of the type with which the present invention is concerned.

The problematic wastes may for instance be received in large barrels which are emptied into a trough having a paddle screw for coarsely breaking lumps and viscous mass with addition of water through nozzles for lubrication and reduction of the rate of evaporation of solvents, whereupon the coarsely broken mass is treated in a high speed mixer with addition of further water for comminuting lumps and preparing a homogeneous solution and dispersion in the water. In this way it is possible to obtain a mixture having a solid matter content of about 50% and a viscosity of below 1500 cP. When the mixture has become homogeneous, the pumpable dispersion obtained in the high speed mixture is drawn, by vacμum into a combined pressure/vacuum tank, and a new charge is fed to the high speed mixer for comminuting and dispersing. The pumpable dispersion in the pressure/vacuum tank is forced through a self-cleaning filter to a storage tank in which continuous agitation is preferably effected. Even without continuous agitation the ingredients in the mixture will separate only to a small degree, and the dispersion may therefore at any time be re-established by a comparably small mixing effort.

Below the invention will be further described, reference being had to the drawings, which illustrate an apparatus in which the method may be performed, and to photographs illustrating the type of the wastes.

Brief Description of the Dxawings.

Fig. 1 is a side view, partly in section, through parts of an apparatus for carrying out the method according to the invention.

Figs. 2 and 3 illustrate examples of problematic wastes which may be destructed according to the invention.

Figs. 4, 5 and 6 illustrate the emptying of barrels with problematic wastes into a trough having a paddle screw.

Figs. 7 and 8 illustrate the homogeneous mixture obtained in the high speed mixer.

Modes for Carrying Out the Invention.

In fig. 1 there is shown a trough 1 having a double paddle screw 2 driven by a motor 3.

Wastes to be treated are emptied into the trough 1. Examples of the type of wastes to be treated appear from figs. 2 to 6. As illustrated the wastes may be supplied in barrels which after opening are lifted onto a support adjacent to the trough. The support may be somewhat tilted in order to make the contents settle slowly from the barrels. Such settling will usually take place if recourse is had to time, since even viscous wastes are usually emptied in about one hour's time. If the wastes are extremely hard, hand tools may be used to accelerate the emptying operation as indicated in fig. 4.

Fig. 2 illustrates sticky binders and pigments obtained as a distillation residue from paints, and fig. 3 illustrates wastes containing gelled two-component binders.

Fig. 5 illustrates that very solid wastes may be involved, even after a gelled top slab or "cake" has been removed.

In fig. 6 there may be seen a grating on the top of the trough. It may be necessary to remove this grating if the wastes are especially hard.

In the trough 1 lumps and viscous mass are coarsely broken in water added through nozzles. In this connection the water serves for lubrication, and at the same time it reduces the rate of evaporation of any organic solvents.

At the end of the trough 1 there is provided a sluice gate 4 which may be raised in order to allow greater or smaller portions of the contents of the trough to flow into a high speed mixer 5 consisting of a container equipped with an agitating device 6 mounted on a vertical shaft 7. In the mixer further water may be added, and the agitating device will comminute solid lumps and dissolve and disperse them in the water. In this manner a mixture as illustrated in fig. 7 may be obtained, said mixture having a solid matter content of about 50% and a viscosity of below 1500 cP. Fig. 8 illustrates the viscosity of the dispersed mixture obtained. Such a mixture or dispersion is pumpable and is pumped into a combined pressure/vacuum tank 8. The pumpable dispersion in the pressure/vacuum tank is forced through a self-cleaning filter (not shown) and further to a storage tank. In the filter, metal chips and stones which may cause difficulties in burner nozzles, are separated. Only insignificant amounts of the mixture in the order of a few ppm are retained by the filter.

From the storage tank the dispersion may be pumped direct to special atomizing nozzles in a combustion chamber in order to utilize the heat energy in the wastes. Alternatively, the dispersion may be transported in tank lorries to combustion plants in for instance manufacturing companies which may use the heat energy produced. This energy will of course be somewhat reduced because of the addition of water, but this reduction is more than balanced by the fact that a consistency of the wastes has been obtained which allows pumping and combustion in waste burners.

Industrial Applicability.

Operation in a pilot plant has shown that solid, viscous and sticky materials such as discarded paints, paint sludge, distillation residues etc. may be comminuted and made pumpable. It has further proved that clogging of pumps and tubes does not occur, presumably because the relatively high water content provides a lubrication by mechanical surface contact. The control of the combustion is simple due to the fact that the wastes are transformed into a pumpable form, which may be atomized in fuel nozzles. Further, the same advantage is obtained as when water is emulgated into heavy oil, viz. that the emulgated water drops will be exposed during the combustion to a violent expansion which "blasts" the waste particles and thereby provides a further comminution or atomization of the wastes.

It has also proved that the flue gases are relatively easy to clean, which is probably due to the fact that the atomizing obtained produces an agglomeration of non-combustable particles after the combustion zone, so that the size of the solid particles in the flue gases is increased. If the flue gases should be acid, they may easily be neutralized by the addition of for instance caustic soda, NaOH, to the mixture.

Because of the atomization obtained by means of the addition of water, the surplus of air may be reduced to approximately stoichiometric ratios. More. specifically the air surplus may be about 15%, meaning that the ratio between the actual and stoichiometric amounts of air is about 1.15 as opposed to about 2 in a fluidized bed combustion and 3-4 in a combustion in a rotary furnace. The small surplus of air in connection with the high water content will reduce possible formation of free chlorine. Any chlorine molecules will agglomerate with the flue particles and may be caught in bag filters.

The original wastes may contain solvents of class A and B. These solvents are usually present as a relatively small part of the mixture, but still warrant a classification as A or B liquid. In this connection the additional water will inhibit the evaporation of solvents because of the vapour partial pressure of the water and increase the flashing point of solvents which are miscible with water.

The risk of reaction between the various compounds in the mixture has proved to be small. This may be due to the fact that water is a good heat conductor and that water reduces the contact between the compounds.

The operation in the pilot plant has also proved that very little corrosion occurs in tubes and other equipment. The addition of water provides no problems, presumably because of the oil and fat emulsions produced.

Claims

C l a i m s :

1. A method for destruction of solid or viscous problematic wastes such as discarded paints, paint sludge, greasy wastes, distillation residues etc., possibly containing oil sludge, organic compounds etc., c h a r a c t e r i z e d i n that the wastes by mechanical mixing and, if required, by tearing and/or comminuting are dispersed in water to saturation, preferably to a water content of 20 to 40%, whereby a pumpable dispersion is obtained which may be used as a fuel.

2. A method according to claim 1, c h a r a c t e r i z e d i n that the wastes are treated in a trough having a paddle screw for coarsely breaking lumps and viscous mass with addition of water through nozzles for lubrication and reduction of the rate of evaporation of solvents, whereupon the coarsely broken mass is treated in a high speed mixer with addition of further water for comminuting lumps and preparing a homogeneous dispersion in the water.

3. A method according to claim 2, c h a r a c t e r i z e d i n that the pumpable dispersion of paint in the high speed mixer is passed through a filter to a storage tank in which continuous agitation is preferably effected.