GB1586290A

GB1586290A - Process for the treatment of effluent

Info

Publication number: GB1586290A
Application number: GB41198/77A
Authority: GB
Original assignee: Bayer AG
Current assignee: Bayer AG
Priority date: 1976-10-09
Filing date: 1977-10-04
Publication date: 1981-03-18
Also published as: BE859482A; JPS5347172A; IT1091344B; NL7710993A; CH624367A5; DE2645658A1; FR2367026A1

Abstract

The waste waters are treated by oxidising the organic pollutants at temperatures above 750 DEG C and separating the inorganic substances which are largely free of organic impurities from the flue gases. They are concentrated in one stage (2) or in a plurality of stages (2, 5) in an evaporation plant (2, 5) to give a concentrate having a maximum residual water content of 50% by weight, and said concentrate, before it is fed to a suitable combustion device (26), is processed prior to the last evaporator stage (5) or immediately after discharge from the evaporator (2, 5), without intermediate storage in a dispersion machine (15) and with the addition of a first amount of a liquid fuel, to give a storable, pumpable and atomisable dispersion. The process is suitable for reprocessing waste waters such as result from the production of colorants, colorant intermediate products, for example the so-called letter acids, and also plastics and plastic precursors, for example caprolactam and chloroprene. <IMAGE>

Description

(54) PROCESS FOR THE TREATMENT OF EFFLUENT (71) We, BAYER AKTIENGESELL SCHAFT, a body corporate organised under the laws of Germany, of Leverkusen, Ger many, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The invention relates to a heat process for working up industrial effluents containing large amounts of chemically and biologically undegradable waste organic substances ( > 0.5 g of organically bonded carbon/l), in addition to a high salt content ( > 10g/l), and which cannot be released unpurified into sewers or onto a dump.

As a rule, effluents of this type are subjected to a combustion process; however, in this process, some of the salts are split by pyrolysis, so that the flue gases contain large proportions of acids, acid hydrides and other harmful substances.

This process is very expensive because of its high fuel requirement.

Effluents of this type are frequently concentrated in evaporators, before the actual combustion, for the purpose of lowering the costs.

However, limits are often set on this preevaporation by a) increasing corrosion and erosion problems and the falling heat transfer values at the heating surfaces of the evaporation equipment, b) worsening quality of the distillate, c) difficult intermediate storage (formation of lumps) and transportation of the concentrate between the evaporation installation and the combustion installation and d) difficult metering into the combustion device, which occur with an increasing concentration of organic and inorganic waste substances.

If, for these reasons, the untreated water can only be pre-evaporated up to a low concentration of harmful substances (for example, a proportion of residual water > 70% by weight) and/or if the ratio of the inorganic or non-combustible waste substances to the organic, combustible substances in the untreated effluent is very large (for example about 10:1 parts by weight), relatively large amounts of additional fuel or additional heat are required in order to achieve the temperature, in the combustion zone, necessary for the decomposition of the harmful substances.

It has now been found that effluents of this type can be worked up by heat at a relatively favourable cost and in a relatively trouble-free manner. According to the present invention there is provided a process for working up an effluent containing inorganic and organic substances and water, comprising oxidising the organic substances by combustion at a temperature above 750"C in a combustion device and separating off the inorganic substances, which are substantially free from organic concomitant substances, from the flue gases, wherein the effluent is concentrated in an evaporator or combination comprising an evaporator and a decanter, to form a concentrate with a maximum residual water content of 50 by weight of the concentrate, the concentrate is discharged into a dispersing machine where it is processed together with liquid fuel to form a dispersion which can be stored, pumped and atomised, the required amount as herein defined, of liquid fuel is added and the dispersion of concentrate and fuel is fed to the combustion device.

Preferably, the maximum residual water content is 30 /O by weight.

Furthermore, it has been shown that the dispersions also remain stable in evaporators.

Preferably, the evaporation is carried out in several stages. The inorganic and organic substances includes salts, and it is easier to achieve higher salt concentrations when at least some of the fuel is dispersed in before the last stage of the evaporation.

Suitable dispersing machines are, for example, Kotthoff stirrers, Supraton machines and Ultra-turrax mixers (the words "Supraton" and "Ultra-turrax" are registered Trade Marks).

The amount of fuel to be dispersed in depends on the ratio of inorganic to organic waste substances in the untreated effluent, on the nature of the salts and on the degree of concentration, or residual water content, which can be achieved in the evaporator. The "required amount" of liquid fuel referred to in the present description and claims is an amount conforming to lower and upper limits as follows: The lower limit for the amount of fuel is determined by the condition that, in total, enough organic material undissolved in the residual water is present around the salt crystals so that these can no longer settle on one another to form lumps. The upper limit of the "required amount" of fuel is given by the maximum amount which can be dispersed in the concentrate, which can optionally be increased by adding dispersing agents and/or by dispersing more intensively, that is to say applying greater shearing stresses over a longer period. However, it is to be understood that it is only necessary to disperse enough fuel so that the calorific value of the mixture is sufficient to achieve a combustion temperature of at least 750 C, preferably of 850--1,000"C, in the oxidation zone of the combustion device, so that all the organic constituents are completely burned and the inorganic concomitant substances form a salt melt. If more fuel than the maximum possible in an effluent concentrate-fuel dispersion which still remains stable is required to achieve the combustion temperature, additional fuel making up the deficit of fuel can be admixed to the dis-.

persion shortly before squirting into the oxidation device, for example by injection under high pressure, so that the additional fuel has no time to coalesce. Usually 5 to 100, preferably 15 to 25, parts by weight of fuel are employed per 100 parts by weight of concentrate.

Suitable dispersing agents which can be added to the concentrate are commercially available, preferably water-soluble compounds, such as, for example, mixtures of long-chain alkyl-sulphates, alkylsulphonates or aralkylsulphonates or sulphite waste liquors on the one hand and polyalkylene oxides on the other hand.

Suitable dispersing agents which can be added to the additional fuels, if used, are preferably oil-soluble, such as, for example, polyalkylene oxides.

Fuels which can be used are, in particular, fuel oil, heavy oil or oil-like waste substances.

By intimately mixing the additional fuel, if used, with the effluent concentrate, the gas phase oxidation processs is at the same time simplified, since it is no longer necessary first to atomise the liquid additional fuel and to burn it with air and then squirt the concentrate into the hot, and also viscous, gas separately and to mix it in thoroughly so that the heat from the flue gases is still transferred to the concentrate droplets within the oxidation zone, that is to say before the cooling on the kettle walls.

The specific consumption of additional fuel (where used) per ms of untreated effluent which is required to achieve the decomposition temperature is considerably lowered by the new process since: a) there is less residual water to evaporate and then to superheat to the combustion temperature; b) the amount of flue gas required to heat the concentrate up to the combustion temperature becomes less, since use is only made of the heat given off until the flue gas has cooled to the temperature in the oxidation zone at which the substances concerned are oxidised (for example 750 C), that is to say use is only made of the heat serving for heating up the concentrate to the oxidation temperature; and c) the heat losses, by radiation, from the flame in which the hot additional fuel is burned in air, before the concentrate is squirted into this flame, become smaller.

The reduction of the maximum temperature in the furnace has the further advantage that the salt vapour elimination treatment of the flue gases is thus also lowered -- and the flue gas after-purification installation thus becomes not only smaller but also simpler.

As a particular variant of the process, it is also possible, in the case of the so-called "heating surface-free" evaporation of effluents, in which the heat required for the pre-evaporation is supplied by mixing a hot liquid heat transfer medium (for example an oil) into the boiling effluent, to leave some of the heat transfer oil in the concentrate and, if appropriate, after adding a dispersing agent, to prepare from this the combustible effluent dispersion according to the invention.

The new process is suitable, above all, for working up effluents which are highly charged inorganically and organically, such as are obtained, in particular, in the production of dyestuffs, dyestuff intermediate products (for example the so-called letter acids) as well as plastics and plastic precursors (for example caprolactam and chloroprene).

The process is now described by way of example with reference to the accompanying drawing, which is a schematic view of apparatus for carrying out gas phase oxidation.

The untreated effluent (1), having a composition of 90 parts by weight of water, 9 parts of inorganic salts and 1 part of organic waste substances, is evaporated in a multistage pre-evaporator (2), (5) (only two stages drawn here) to give a concentrate (10), the first evaporation stage (2) being heated in a known manner with fresh steam (3), the sump outflow (4) of the first stage (2) then being further evaporated, under a low pressure, in the following stage by the vapours (6) from the first stage, and the vapours (7) from the last stage (5) being condensed in a condenser (8).

The distillation streams (9), containing (by weight) a total of approximately 86 parts of water per 90 parts of water in the untreated effluent (1), i.e. approximately 95% by weight of the originally fed water, then comprise effluent which has been purified by distillation. The sump outflow (10) from the last evaporator stage (5) is a suspension consisting of a saturated solution (mother liquor) of the salts and soluble organic substances from the untreated effluent (1), the salts which have precipitated and the solid and liquid organic substances which have precipitated. The sump outflow (10) comprises 70% by weight of water, together with certain minor proportions of inorganic constituents and organic constituents. From the sump outflow (10), 15.71% by weight are separated off, in the decanter (11), as a slurry (13) having a composition of just under 30% by weight of water, 63.64% by weight of inorganic substances and 6.35% by weight of organic substances. The overflow (12) of 84.29% by weight, i.e. the remainder of the sump outflow (10), has a composition of 83.38% by weight of water, 11.87% by weight of inorganic substances and 4.75% by weight of organic substances, and is recycled to the last evaporation stage (5). The slurry (13) comprises 9 parts by weight of inorganic constituents, 1 part by weight of organic constituents and 4.24 parts by weight of water, from the 100 parts by weight fed in as untreated effluent (1). The slurry (13) thus has a water content just under 30% by weight. Of the originally fed 90 parts by weight of water, the remaining 85.76 parts by weight of water are removed as the previously mentioned distillation streams (i.e.

distillate) (9), with negligibly small proportions of other substances. Thus, 85.76/90, i.e.

95.28%, by weight of the originally fed water are pre-evaporated off.

The 14.24 parts by weight of the salt slurry (13) are fed into the Supraton (registered Trade Mark) dispersing machine (15), directly downstream from the decanter, to gether with 2.85 parts by weight of fuel oil (14) and also together with 512.7 parts by weight of the dispersion prepared in the dispersing machine (15), which serves as a reflux (16), in order to feed an already sub stantially pre-dispersed mixture to the dispersing equipment. The effluent (1) originat ing from a paint production contains sufficient organic substances acting as dispersing agents so that the addition of a further dispersing agent is not required here.

17.09 parts by weight are discharged (17) from the dispersion cycle and intermediately stored in the tank (18). This dispersion has a composition of 52.66 ;!. by weight of in- organic substances, 16.68% by weight of fuel oil, 5.85% by weight of other organic substances and 24.81% by weight of water and remains stable for several days. No salt lumps form and the oil does not cream.

The dispersion is then fed from the tank (18) to the combustion device in the form of a burner 24 at the top of a kettle (26), for the oxidation of the organic substances in the gas phase. In addition, the deficit 1.14 parts by weight of fuel oil (21) required to achieve the decomposition temperature, of 900 C here, are also admixed to the dispersion (19) to be "burned", by being squirted into the mixing chamber (20) as a high-pressure jet directly before atomising the mixture, which is then combustible, in the atomising nozzle (22). The 18.23 parts by weight, in total, of effluent concentrate/oil dispersion can be finely atomised in the nozzle (22) with 1 part by weight of steam (23) so that they burn, with 330 parts by weight of air (25), prewarmed to 350"C, in the burner (24), with a stable frame so tnat the flue gas temperature at the end of the oxidation stage is 900"C. The inorganic salts vaporise during the burning; between the parts (24) and (28) there is a cooling step in which they are condensed. The majority of the inorganic salts, substantially free from organic impurities, are then drawn off in the liquid form at (27), in a known manner by cooling the flue gas. The flue gas is freed from residual salt (30) in a suitable dustremoving apparatus of known construction (28) and passed to the chimney at (29).

WHAT WE CLAIM IS: 1. A process for working up an effluent containing inorganic and organic substances and water, comprising oxidising the organic substances by combustion at a temperature above 750"C in a combustion device and separating off the inorganic substances, which are substantially free from organic concomitant substances, from the flue gases, wherein the effluent is concentrated in an evaporator, or combination comprising an evaporator and a decanter, to form a concentrate with a maximum residual water content of 50% by weight of the concentrate, the concentrate is discharged into a dispersing machine where it is processed together with liquid fuel t6 form a dispersion which can be stored, pumped and atomised, the required amount, as herein defined, of liquid fuel is added and the dispersion of concentrate and fuel is fed to the combustion device.

2. A process according to claim 1 wherein

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. first evaporation stage (2) being heated in a known manner with fresh steam (3), the sump outflow (4) of the first stage (2) then being further evaporated, under a low pressure, in the following stage by the vapours (6) from the first stage, and the vapours (7) from the last stage (5) being condensed in a condenser (8). The distillation streams (9), containing (by weight) a total of approximately 86 parts of water per 90 parts of water in the untreated effluent (1), i.e. approximately 95% by weight of the originally fed water, then comprise effluent which has been purified by distillation. The sump outflow (10) from the last evaporator stage (5) is a suspension consisting of a saturated solution (mother liquor) of the salts and soluble organic substances from the untreated effluent (1), the salts which have precipitated and the solid and liquid organic substances which have precipitated. The sump outflow (10) comprises 70% by weight of water, together with certain minor proportions of inorganic constituents and organic constituents. From the sump outflow (10), 15.71% by weight are separated off, in the decanter (11), as a slurry (13) having a composition of just under 30% by weight of water, 63.64% by weight of inorganic substances and 6.35% by weight of organic substances. The overflow (12) of 84.29% by weight, i.e. the remainder of the sump outflow (10), has a composition of 83.38% by weight of water, 11.87% by weight of inorganic substances and 4.75% by weight of organic substances, and is recycled to the last evaporation stage (5). The slurry (13) comprises 9 parts by weight of inorganic constituents, 1 part by weight of organic constituents and 4.24 parts by weight of water, from the 100 parts by weight fed in as untreated effluent (1). The slurry (13) thus has a water content just under 30% by weight. Of the originally fed 90 parts by weight of water, the remaining 85.76 parts by weight of water are removed as the previously mentioned distillation streams (i.e. distillate) (9), with negligibly small proportions of other substances. Thus, 85.76/90, i.e. 95.28%, by weight of the originally fed water are pre-evaporated off. The 14.24 parts by weight of the salt slurry (13) are fed into the Supraton (registered Trade Mark) dispersing machine (15), directly downstream from the decanter, to gether with 2.85 parts by weight of fuel oil (14) and also together with 512.7 parts by weight of the dispersion prepared in the dispersing machine (15), which serves as a reflux (16), in order to feed an already sub stantially pre-dispersed mixture to the dispersing equipment. The effluent (1) originat ing from a paint production contains sufficient organic substances acting as dispersing agents so that the addition of a further dispersing agent is not required here. 17.09 parts by weight are discharged (17) from the dispersion cycle and intermediately stored in the tank (18). This dispersion has a composition of 52.66 ;!. by weight of in- organic substances, 16.68% by weight of fuel oil, 5.85% by weight of other organic substances and 24.81% by weight of water and remains stable for several days. No salt lumps form and the oil does not cream. The dispersion is then fed from the tank (18) to the combustion device in the form of a burner 24 at the top of a kettle (26), for the oxidation of the organic substances in the gas phase. In addition, the deficit 1.14 parts by weight of fuel oil (21) required to achieve the decomposition temperature, of 900 C here, are also admixed to the dispersion (19) to be "burned", by being squirted into the mixing chamber (20) as a high-pressure jet directly before atomising the mixture, which is then combustible, in the atomising nozzle (22). The 18.23 parts by weight, in total, of effluent concentrate/oil dispersion can be finely atomised in the nozzle (22) with 1 part by weight of steam (23) so that they burn, with 330 parts by weight of air (25), prewarmed to 350"C, in the burner (24), with a stable frame so tnat the flue gas temperature at the end of the oxidation stage is 900"C. The inorganic salts vaporise during the burning; between the parts (24) and (28) there is a cooling step in which they are condensed. The majority of the inorganic salts, substantially free from organic impurities, are then drawn off in the liquid form at (27), in a known manner by cooling the flue gas. The flue gas is freed from residual salt (30) in a suitable dustremoving apparatus of known construction (28) and passed to the chimney at (29). WHAT WE CLAIM IS:

1. A process for working up an effluent containing inorganic and organic substances and water, comprising oxidising the organic substances by combustion at a temperature above 750"C in a combustion device and separating off the inorganic substances, which are substantially free from organic concomitant substances, from the flue gases, wherein the effluent is concentrated in an evaporator, or combination comprising an evaporator and a decanter, to form a concentrate with a maximum residual water content of 50% by weight of the concentrate, the concentrate is discharged into a dispersing machine where it is processed together with liquid fuel t6 form a dispersion which can be stored, pumped and atomised, the required amount, as herein defined, of liquid fuel is added and the dispersion of concentrate and fuel is fed to the combustion device.

2. A process according to claim 1 wherein

the maximum residual water content is 30% by weight.

3. A process according to claim 1 or 2 wherein 5 to 100 parts by weight of fuel, per 100 parts by weight of concentrate, are employed.

4. A process according to claim 3 wherein 15 to 25 parts by weight of fuel are employed.

5. A process according to any one of claims 1 to 4 wherein the evaporation is carried out in several stages, at least some of the liquid fuel being added before the last stage.

6. A process according to any one of claims 1 to 5 wherein the dispersion is metered in a zone in the presence of atmospheric oxygen, a sufficiently high temperature being maintained that all the organic substances are completely oxidised and the undecomposable inorganic substances form a salt melt, the supply of heat required to achieve the oxidation temperature originating, completely or largely, from the combustion of the liquid fuel dispersed in the concentrate.

7. A process according to any one of claims 1 to 6 wherein the combustion temperature is from 850" to 1,000"C.

8. A process according to any one of claims 1 to 7 wherein a dispersing auxiliary is added to the concentrate during the dispersing process.

9. A process according to any one of claims 1 to 8 wherein additional fuel is added to the dispersion directly before feeding the dispersion into the combustion device.

10. A process according to any one of claims 1 to 9 wherein the untreated effluent is concentrated in a heating surface-free evaporator by means of a heat transfer medium, some of the heat transfer oil required for the evaporation being dispersed in the effluent concentrate with the aid of dispersing equipment.

11. A process according to claim 1 substantially as hereinbefore described with reference to the accompanying drawing.