Sludge treatment method and plant

Abstract

(57) This invention relates to a method and an installation for treating waste sludge obtained after distillation of solvents contaminated with printing inks, which will find application in the wastewater treatment industry. The plant comprises a vacuum drying chamber (1) comprising a door (13 tightened by wing nuts (14) and a support frame (2) to which is fixed a heat exchange surface (4) on which trays (3) are fixedly arranged. The vacuum drying chamber (1) is functionally connected to both a heating module and a jacketed condenser (5). The heating module comprises an oil heater (9) which is composed of a tank with heaters mounted therein and an expansion tank (10). The jacketed condenser (5), composed of tubes (6) and an intertube space (7), is connected on one side to a refrigeration module (8) and on the other side to a vacuum module consisting of a vacuum pump (11) and a receiver (12).

Description

[0001] Sludge treatment method and plant

[0002] Technical field

[0003] This invention relates to a method and plant for treating waste sludge obtained after distillation of solvents contaminated with printing inks, which will find application in the wastewater treatment industry and more particularly for distillation of solvents used in the printing industry.

[0004] Background of the invention

[0005] For the printing of text and drawings, the methods most used in practice are flexo and gravure, the different types being carried out with nitrocellulose, polyurethane or polyamide-based inks. Flexo is one of the main printing methods in the field of packaging and printing in the future. Typically, flexo inks are composed of 60- 70% ethyl acetate; 10-15% ethoxypropanol; 15-20% propylene glycol ether; 10- 15% pigments; 10-15% isopropyl alcohol. Different types of inks have different drying mechanisms and environmental impacts due to their different compositions and properties. Very often inks are further diluted with ethanol and ethyl acetate- based solvents. In addition, when changing colours, printing presses are washed with ethanol and ethyl acetate solvents, which generate contaminated solvents with additional impurities due to mixing with the inks. The resulting ink- contaminated solvents are usually distilled to reuse the recycled solvent in the washing of the printing presses. Two types of distillers are used, the ordinary distiller, in which distillation takes place at atmospheric pressure, and the vacuum distiller, in which distillation is more intensive than in the ordinary distiller. Both types of distillation produce a precipitate, the contents of which are again solvent containing ink pigment, and vacuum distillation achieves, in addition to higher solvent extraction, a higher viscosity of the resulting precipitate than ordinary distillation. Both types of distillation produce a precipitate whose content is again solvent containing pigment from the inks, the residual solvent content being not less than 20%. The distillation process is terminated due to the increased viscosity of the final product and the inability to extract the remaining solvent, and the residue is disposed of by incineration as it is a hazardous product which cannot be disposed of in the environment.

[0006] International application WO2014037955A1 dated 05.09. 2012 entitled “Method for extracting reusable material from paint sludge” presents a method for treating and extracting reusable material from paint sludge comprising the operations: extracting the solvent contained in the residue of said paint sludge; treating the mixture of the paint sludge residue with a compatible oil in a mixing chamber to fluidize the mixture at a suitable operating temperature; reusing the semi-solid residue of the resulting mixture as reinforcing fillers.

[0007] The known method does not provide complete solvent extraction such that the residue is a dry material. The residue obtained by this known method is a viscous product with a liquid material content of 12.6%, the recovery percentage being no higher than 90%.

[0008] The US patent US 6729565 B2 dated 04.05. 2004 entitled “Method and device for reusing solvents from waste paint” presents a method for reusing waste paint which includes the operations: drying and dehydrating waste paint sludge between a pair of heated rotating drums of a roll dryer; extracting the solvent from the treated sludge by distillation; removing the dried waste paint from the pairs of heated rotating drums; grinding the dehydrated and dried waste paint by means of a rotating grinding rotor; delivering the dehydrated and dried waste paint to a device with a tank for agitating and pulverizing the dried waste paint. The known device includes a drying device, in this case a roll dryer, provided with a pair of heated rotating drums, wherein a scraper blade in the form of a plate is disposed on each of the rotating drums in a lateral direction of the drums. Said scraper blade has an edge that is in contact with the surface of each of the drums to scratch the dehydrated and dried waste paint on the drums, said scraper blade having a plurality of cutting blades arranged at predetermined intervals along the edge of the scraper blade.

[0009] The presence of moving mechanisms in the known device complicates the construction, which also leads to complication of its operation.

[0010] Technical essence of the invention

[0011] It is an object of the invention to provide a method of treating waste sludge by which to treat highly viscous hazardous wastes in the form of sludge, providing a maximum percentage of solvent recovery from the sludge, wherein the waste to be disposed of is negligible relative to the initial amount of sludge treated.

[0012] It is also an object of the invention to provide a waste sludge treatment plant which is of simple construction, without moving parts and facilitated operation.

[0013] The task is solved by creating a method for treating waste sludge, which includes the operations: drying waste sludge from waste paint. According to the invention, the drying operation takes place in a fixed layer of batched waste sludge and is carried out in trays housed in a vacuum drying chamber, the method further comprising the operations: conductively heating the trays in the vacuum drying chamber by hot oil heated in a separate oil heater; evaporation of the solvent from the waste sludge under vacuum due to the heat input; liquefaction of the solvent vapour separated from the waste sludge in a jacketed condenser cooled by an intermediate refrigerant coming from the refrigeration module; separation of the non-condensable gases from the liquefied solvent in a receiver; and removal of the liquid solvent for reuse.

[0014] The task has been solved by setting up a plant for the treatment of waste sludge, which includes a drying device. According to the invention, the drying device is a vacuum drying chamber comprising a wing-nut tightening door and a supporting frame to which a heat exchange surface is mounted, wherein trays for filling with waste sludge are fixedly arranged on the heat exchange surface. The vacuum drying chamber is functionally connected to both a heating module and a jacketed condenser. The heating module comprises an oil heater which is composed of a tank with heaters mounted in it and an expansion tank. The jacketed condenser, composed of tubes and an intertube space, is connected on one side to a refrigeration module and on the other side to a vacuum drying chamber from which the vapours of the separated solvent are discharged. In the condenser tubes, the refrigerant is circulated and in the intertube space, the vapours released from the vacuum dryer are condensed.

[0015] The vacuum drying chamber and the condenser are connected by a vacuum module consisting of a receiver and a vacuum pump.

[0016] An advantage of the established method and installation for the treatment of waste sludge is the possibility created to treat highly viscous hazardous waste in the form of sludge. In addition, the possibility is provided to extract the solvent contained in the sludge up to 98.5%, resulting in a waste subject to further disposal of no more than 1.5% of the initial amount of material treated. An advantage of the invention is also the ease of operation of the plant created, due to its simplified construction, as a result of the incorporation therein of the vacuum drying chamber created, in which there are no moving parts.

[0017] Description of the attached figures

[0018] This invention is illustrated in the attached Figure 1, which is a schematic in principle of a plant for the treatment of waste printing ink sludge according to the invention.

[0019] Examples of embodiments of the invention

[0020] The plant for treating waste sludge, as illustrated in Figure 1, comprises a drying device which is a vacuum drying chamber 1 comprising a door 13 tightened by wing nuts 14 and a support frame 2 to which a heat exchange surface 4 is mounted, serving for conductive heating of the waste sludge. Trays 3 filled with waste sludge are fixedly arranged on the heat exchange surface 4. The vacuum drying chamber 1 is functionally connected to both a heating module and a jacketed condenser 5. The heating module comprises an oil heater 9 composed of a tank with heaters mounted therein and an expansion tank 10, and the jacketed condenser 5, composed of tubes 6 and an intertube space 7, is connected on one side to a refrigeration module 8 and on the other side to a vacuum module consisting of a receiver 12 and a vacuum pump 11.

[0021] The so created plant is used as follows. The waste sludge is dosed into the trays 3, the height of the sludge must not exceed 20 mm, and the trays 3 are placed in the vacuum di er 1. The door 13 of the vacuum drying chamber 1 is closed and tightened with the wing nuts 14. The heat exchange surface 4 of the drying chamber 1 is fed with a heat transfer medium which has been preheated in the oil heater 9 to a temperature higher than the boiling point of the solvent constituting the sludge component, at an appropriate pressure. By means of the vacuum module, a vacuum is created in the drying chamber 1 at which the solvent begins to evaporate intensively. The resulting vapours condense in the intertube space 7 of the jacketed condenser 5, the liquid being collected in the receiver 12 and the non-condensed gases being drawn into the upper part of the receiver 12 by the vacuum pump 11. Cooling of the vapor in the jacketed condenser 5 is accomplished by a low temperature intermediate refrigerant entering from the refrigeration module 8. After separation of the solvent from the waste sludge, a dry residue with a solvent content of not more than 1,5 % remains in the trays 3, which dry residue is separated from the trays 3 by means of a special tool and fed for incineration.

[0022] Periodically, the liquid solvent is removed from the receiver 12 by means of a pump and fed for use, and the trays 3 of the drying chamber 1 are filled with new quantities of waste sludge.

[0023] The mode parameters under which the operations of the method are carried out are: the solvent content of the spent sludge is 80%; the boiling temperature in the vacuum drying chamber 1 is from 30 to 78°C; the absolute pressure in the vacuum drying chamber 1 is 5600 Pa and the final solvent content of the residue dried in the vacuum drying chamber 1 is 1.5%. The method and the plant make it possible to treat, in addition to waste printing ink residues, residues of other types of organic solvents based on methoxypropanol, butyl acetate, acetone, orthoxylene and toluene.

Claims

PATENT CLAIMS1. A method for treating waste sludge comprising the operations of: drying waste paint sludge, characterized in that the drying operation takes place in a fixed layer of batched waste sludge and is carried out in trays (3) housed in a vacuum drying chamber (1), the method further comprising the operations: conductively heating the trays (3) in the vacuum drying chamber ( 1 ) by hot oil heated in a separate oil heater (9); evaporation of the solvent from the spent sludge under vacuum due to the heat input; liquefaction of the solvent vapour separated from the waste sludge in a jacketed condenser (5) cooled by an intermediate refrigerant flowing from a refrigeration module (8); separation of the non-condensable gases from the liquefied solvent in a receiver (12); and removal of the liquid solvent for reuse.

2. A plant for treating waste sludge comprising a drying device, characterized in that the drying device is a vacuum drying chamber (1) comprising a door (13) tightened by wing nuts (14) and a support frame (2), to which a heat exchange surface (4) is mounted, on which trays (3) for filling with waste sludge are fixedly arranged, wherein the vacuum drying chamber (1) is functionally connected both to a heating module, and a jacketed condenser (5), wherein the heating module comprises an oil heater (9) which is composed of a tank with heaters mounted therein and an expansion tank (10), the jacketed condenser (5), composed of tubes (6) and an intertube space (7), being connected on the one hand to a refrigeration module (8) and on the other hand to a vacuum module consisting of a vacuum pump (11) and a receiver (12).

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