Process and apparatus for wet oxidation of wastes

Abstract

A new wet oxidation process of wastes, specifically of mixtures of at least two, liquid (wastewaters) and dense (sludges), pumpable wastes is described. An apparatus useful for a wet oxidation process of this type is also described.

Claims

1. A wet oxidation process for decontaminating a suspension of multi-stream wastes comprising: a) preparing a suspension of at least two wastes by: i) feeding a sludge suspension having a total dry matter (TDM) comprised between 1% and 18%, produced from organic solid sludges having a TDM comprised between 15 and 40% and wastewaters having a chemical oxygen demand (COD) comprised between 10,000 and 120,000 mg/l, fed into at least one mixing tank comprising at least one agitator; ii) mixing said sludges and wastewaters at a rate sufficient to produce a suspension having a TDM comprised between 5 and 18%, and a COD comprised between 10,000 and 150,000 mg/l; and iii) feeding said suspension into at least one storage tank, and mixing said suspension at a rate sufficient to keep it stable; b) preheating the mixed suspension of at least two wastes by injecting at least one direct steam into the suspension; c) feeding a stream of the preheated suspension of at least two wastes into a reactor at a temperature of at least 70° C., and at a pressure comprised between 8 bar and 100 bar, wherein said suspension is fed into the reactor by at least one first mixing ejector; d) feeding a gas phase stream comprising oxygen and high-pressure steam into said reactor at a pressure comprised between 8 bar and 100 bar and at a temperature comprised between 150° C. and 315° C., wherein said gas phase is fed into the reactor by at least one second mixing ejector; e) placing in contact said suspension stream and said gas phase stream into said reactor, so as to flow said streams in countercurrent; f) extracting the decontaminated suspension, after oxidation, from a lower bottom of the reactor; and g) extracting exhaust gases from an upper bottom of the reactor.

2. The process according to claim 1, wherein said reactor operates at a pressure comprised between 8 bar and 100 bar, and at a temperature comprised between 150° C. and 300° C.

3. The process according to claim 1, wherein said at least one first mixing ejector is in communication with the reactor by an inlet positioned on the upper bottom of the reactor.

4. The process according to claim 1, wherein said at least one second mixing ejector is in communication with the reactor by an inlet positioned on the lower bottom of the reactor.

5. The process according to claim 1, wherein said suspension of at least two wastes, and said gas phase are fed into the reactor by lateral inlets.

6. The process according to claim 1, wherein the suspension is preheated to a temperature of at least 70° C.

7. The process according to claim 1, wherein the suspension is preheated by at least two direct steams.

8. The process according to claim 1, further comprising, upstream of step c), a step c.sub.0) of feeding water, compressed air and high-pressure steam into the reactor, at a pressure comprised between 30 and 80 bar, until the reaction temperature and pressure are reached.

9. The process according to claim 1, wherein the suspension is preheated to a temperature between 90° C. and 110° C.

10. An apparatus for carrying out a wet oxidation process according to claim 1, comprising: at least one mixing tank and at least one storage tank for producing said suspension of at least two wastes wherein: the at least one mixing tank comprising at least one first agitator for mixing sludges having a TDM comprised between 1 and 18%, produced from organic solid sludges having a TDM comprised between 15 and 40%, and wastewaters having a COD comprised between 10,000 and 120,000 mg/l, at a rate sufficient to produce a suspension having a TDM comprised between 5 and 18%, and a COD comprised between 10,000 and 150,000 mg/l; and the at least one storage tank comprising at least one second agitator for mixing said suspension at a rate sufficient to keep it stable; at least one oxidation reactor comprising an upper bottom and a lower bottom; a direct steam injector for preheating the mixed suspension of at least two wastes; at least one first mixing ejector comprising an inlet for feeding said preheated suspension of at least two wastes into said at least one oxidation reactor, at a temperature of at least 70° C., and at a pressure comprised between 8 bar and 100 bar; at least one second mixing ejector comprising an inlet for injecting a gas phase comprising oxygen and high-pressure water steam inside said reactor, at a pressure comprised between 8 bar and 100 bar, and at a temperature comprised between 150° C. and 315° C.; a pipeline for removing the decontaminated suspension from the lower bottom of the reactor; and a pipeline for removing the exhaust gases from the upper bottom of the reactor.

11. The apparatus according to claim 10, wherein said at least one first mixing ejector for feeding said suspension of at least two wastes is positioned at the upper bottom of said reactor.

12. The apparatus according to claim 10, wherein said at least one second mixing ejector for injecting oxygen and high-pressure steam is positioned at the lower bottom of said reactor.

13. The apparatus according to claim 10, wherein said inlet for said suspension is positioned on the upper bottom of the reactor.

14. The apparatus according to claim 10, wherein said inlet for said gas phase is positioned on the lower bottom of the reactor.

15. The apparatus according to claim 10, wherein said inlets for the suspension and for the gas phase are positioned laterally in the reactor.

16. The apparatus according to claim 10, wherein the direct steam injector is configured to preheat the suspension of at least two wastes to a temperature of at least 70° C.

17. The apparatus according to claim 10, wherein the direct steam injector is configured to preheat the suspension of at least two wastes to a temperature between 90° C. and 110° C. laimed specific total dry matter (TDM) and chemical oxygen demand (COD) ranges claimed.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further features and advantages of the invention will be better illustrated by the following description of some preferred embodiments thereof, made below, by way of illustrative and non-limiting examples, with reference to the accompanying drawings. In such drawings:

(2) FIG. 1 is a schematic view of an apparatus for wet oxidation according to the process of the present invention;

(3) FIG. 2 is a schematic view of an apparatus for wet oxidation according to the process of the present invention;

(4) FIG. 3 is a schematic view of the start-up phase of the process according to the present invention;

(5) FIG. 4 is a schematic view of an apparatus for producing the pumpable suspension to be decontaminated by the process of the present invention.

DETAILED DESCRIPTION OF CURRENTLY PREFERRED EMBODIMENTS

(6) In the following description, to illustrate the figures identical reference numbers are used to denote same meanings.

(7) Different features in the individual embodiments may be combined together, as desired, according to the foregoing description, if one has to benefit from the specific advantages resulting from a specific combination.

(8) With reference to FIG. 1, the process according to the invention is carried out with the aid of an apparatus 1 made up of at least one oxidation reactor 2 comprising an upper bottom 2a and a lower bottom 2b.

(9) The upper 2a and lower 2b bottoms of the reactor 2 can be flat, convex, elliptical or spherical, welded or flanged.

(10) In the wet oxidation reactor 2, a pumpable suspension 3 of at least two wastes, having a total dry matter (TDM) comprised between 5 and 18%, preferably between 7 and 15%, and a COD comprised between 10,000 and 150,000 mg/l, preferably between 30,000 and 150,000 mg/l, is fed at a temperature of at least 70° C., and at a pressure comprised between 8 bar and 100 bar, preferably between 30 bar and 65 bar, by means of an inlet 3a being provided with at least one first mixing ejector 3b, positioned in correspondence to the upper bottom of the reactor 2a.

(11) At the same time, a gas phase 4 comprising oxygen 4′ and high-pressure water steam 4″ is injected into the reactor, at a pressure comprised between 8 bar and 100 bar, preferably between 30 bar and 65 bar, and at a temperature comprised between 150° C. and 315° C., preferably between 200° C. and 260° C., by means of an inlet 4a being provided with at least one second mixing ejector 4b, positioned in correspondence to the lower bottom of the reactor 2b.

(12) Inlets from the bottoms 3a, 4a, are preferred with reactors made of special alloy coated materials.

(13) Preferably, high-pressure steam 4″ is produced by a high-pressure steam generator (for example, an evaporator) (not shown in FIG. 1).

(14) Preferably, gas oxygen supply 4′ can be obtained by means of a suitable compressor (alternative piston, or membrane, or centrifugal compressor). Alternatively, liquid oxygen supply 4′ can be obtained by means of a cryogenic pump (not shown in FIG. 1).

(15) FIG. 1 shows pipeline 5, suitable for removal of exhaust gases 6 from the upper bottom of the reactor 2a, and pipeline 7, suitable for removal of the decontaminated suspension 8 from the lower bottom of the reactor 2b.

(16) In a preferred embodiment, outlet 7 for the decontaminated suspension 8 may be coaxial with inlet 4a for the gas phase 4 (not shown in FIG. 1).

(17) Such a reactor 2, to carry out the wet oxidation process according to the invention, has already many advantages in itself. However, further advantages may be obtained if such a reactor is used in combination with a coating, such as the one described in the European Patent Application No. 1611947 in the name of the Applicant, whose content is herein fully incorporated by reference.

(18) Such coating is characterized in that it comprises at least two different metal alloys, wherein a first alloy is selected from the group comprising titanium and alloys thereof (for example titanium-palladium, titanium-aluminum-vanadium, titanium niobium alloys, and mixtures thereof), and a second alloy is selected from the group consisting of nickel alloys (for example, nickel-chromium, nickel-chromium-molybdenum, nickel-chromium-iron alloy).

(19) In a preferred embodiment, the coating consists essentially of non-superimposed surfaces of suitable thickness, wherein a first surface is preferably made up of titanium or alloys thereof, and a second surface is preferably made up of nickel alloys.

(20) Advantageously, the coating thickness may not be uniform in all regions and, in any case, it is at least 0.75 mm, preferably comprised between 0.75 and 12.7 mm, more preferably equal to 5 mm.

(21) In a particularly preferred embodiment, the lower part of the reactor is coated by titanium or alloys thereof, and the upper part of the reactor is coated by nickel alloys. Advantageously, titanium is particularly resistant to corrosion.

(22) The nickel alloy, instead, is particularly stable in gas and vapor environments with high oxygen concentration.

(23) According to a preferred embodiment, the two lower and upper regions of the reactor are made separately, and are then joined together by any method known in the art and used for this purpose, such as coupling and/or closure by means of flanges.

(24) According to a preferred embodiment, the titanium-coated area is advantageously comprised between 5% and 95% of the internal reactor volume, and the nickel-coated area is advantageously comprised between 5% and 95% of the i internal reactor volume. Preferred ratios of the two coated areas are 10/90 and 20/80, wherein the largest portion may equally be titanium or nickel.

(25) Alternatively, the wet oxidation reactor according to the invention may be entirely made of special alloys based on nickel and/or titanium.

(26) With reference to FIG. 2, 10 globally refers to an apparatus according to an alternative embodiment of the invention consisting of at least one oxidation reactor 20 comprising an upper bottom 20a and a lower bottom 20b, wherein the inlet 30a for the suspension 3 and the inlet 40a for the gas phase 4, comprising oxygen 4′ and high-pressure water steam 4″, are positioned laterally in the reactor 20.

(27) The same reference numbers have the same meanings as reported in FIG. 1.

(28) Side entrances 30a, 40a are preferred with reactors entirely made of special alloys.

(29) With reference to FIG. 3, the start-up phase of the process according to the present invention is carried out by feeding water 3′, compressed air 4″′, and high-pressure steam 42 into reactor 2 (or into reactor 20 not shown in FIG. 3), at a pressure comprised between 30 bar and 80 bar, until the reaction temperature and pressure are reached.

(30) Preferably, clean water 3′ supply is carried out by means of the plant feeding pump (centrifugal, or alternative piston and/or membrane pump) (not shown in FIG. 3) through the normal supply pipeline 30.

(31) Alternatively, the supply is carried out by means of specially provided equipment and pipeline (not shown in FIG. 3). At the same time, compressed air 4″ is fed by means of a suitable high-pressure compressor (for example, a rotatable or alternative compressor), and high-pressure steam 4″ by means of a high-pressure steam generator (for example, a direct flame boiler, an evaporator heated by a diathermic oil, or an electrically heated evaporator) (not shown in FIG. 3) through the oxygen pipeline 40, until the reaction temperature and pressure are reached.

(32) Once the reaction conditions are reached, the suspension of at least two wastes 3, at steady flow rate, and the oxygen 4′, at increasing flow rate, are fed until the planned amount is reached. In the reactor, clean water 3′ is then gradually replaced by wastes 3 which react with oxygen 4′ to give the oxidized suspension (decontaminated) 8, which is extracted from the lower bottom of reactor 2b (or from the lower bottom of reactor 20b not shown in FIG. 3), and exhaust gases 6, which are extracted from the upper bottom of reactor 2a (or from the upper bottom of reactor 20a not shown in FIG. 3).

(33) With reference to FIG. 4, the apparatus 100 for producing a pumpable suspension 3 of at least two wastes, having a total dry matter (TDM) comprised between 5 and 18%, preferably between 7 and 15%, and a COD comprised between 10,000 and 150,000 mg/l, preferably between 30,000 and 150,000 mg/l, includes at least one mixing tank 110 comprising at least one first agitator 111 (for example, a pulper), wherein sludges 112 having a TDM comprised between 1 and 18%, produced from organic solid sludges 113 having a TDM comprised between 15 and 40%, and wastewaters 114 having a COD comprised between 10,000 and 120,000 mg/l, preferably between 30,000 and 120,000 mg/l, are fed.

(34) In said at least one mixing tank 110, mixing is carried out at a rate sufficient to produce a pumpable suspension 115 having a TDM comprised between 5 and 18%, preferably between 7 and 15%, and a COD comprised between 10.000 and 150.000 mg/l, preferably between 30.000 and 150.000 mg/l. Preferably, at a rate comprised between 200 and 400 rpm.

(35) The pumpable suspension 115 is then discharged from the mixing tank 110, and fed into at least one storage tank 116 comprising at least one second agitator 117.

(36) After mixing said pumpable suspension 115 at a rate sufficient to keep it stable, the pumping suspension 3 is discharged from the storage tank 116, and fed into a reactor 2, 20.