DE2548282A1 - METHOD FOR WET OXIDATION OF ORGANIC SUBSTANCES - Google Patents

Description

"Process for the wet oxidation of organic substances"

The wet oxidation of organic substances, dissolved or suspended in an aqueous medium or another liquid and devices suitable therefor are known (e.g. DT-OS 22 47 841 and 24 47 546). The wet oxidation is a safe, effective and economical method of destroying organic waste products without the need to use an expensive evaporation or drying stage, as is the case with burning or the like is required. For example, waste water can be disposed of by incineration; to do this, however, must the water content of the sludge, which is normally more than 90%, can be removed. In this procedure So large amounts of energy are required for water removal and a lot of space and large amounts of capital for Plant, laboratory and operation are required.

Wet oxidation is also suitable for the destruction of toxic or dangerous organic products, such as many plastics, explosives and similar flammable

organic substances without the risk of air pollution or the explosion, since the oxidative combustion in wet oxidation occurs in the aqueous phase can be regulated easily.

The proportion of flammable organic substances in suspension or in solution in an aqueous medium is in the generally defined with the help of the theoretical for the reaction of the organic material to its destruction required amount of oxygen (COD). The biological water purification is used in a similar way biological oxygen demand BOD. In a wastewater treatment process, the percentage reduction is of OSB or BOD compared to the initial value. A 100% reduction in the GSB corresponds to a full one Destruction of combustible organic substances through chemical oxidation.

Wet oxidation is an exothermic chemical oxidation that burns at different rates runs, depending to some extent on the concentration of combustible organic substances in the aqueous medium, the availability of oxygen in the liquid System and the size of the organic molecules. The rate of reaction further depends more on temperature and pressure at which the wet oxidation takes place. As for molecular size, seem organic Macromolecules react more easily than low molecular weight substances. Major difficulties observed one in oxidation reactions of lower forms of oxidation reaction products, such as acetic acid and the like. As a result, the percentage reduction in COD is much faster initially when the macromolecules, which are present in large proportions in the liquid system are oxidized and into low molecular weight fractions

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be split up. These accumulate in the oxidation reaction due to their greater resistance to Oxidation under the equivalent process conditions, so the rate of wet oxidation decreases with it increasing concentration of smaller organic molecules in solution or suspension. This change in speed is particularly pronounced with an approximate reduction in COD of 60 to 70%.

For the rate and the extent of the oxidation the temperature and consequently also the pressure is a factor essential J factor. So far one could a complete destruction of the organic matter by wet oxidation only at very high temperatures on the order of

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about 288 to 315 0 and correspondingly high pressures, such as 105 to 140 atm. Due to these conditions, the applicability of this method is significantly restricted in practice due to the high investment costs for the jerk- and corrosion-resistant materials of the system.

According to a known process (US Pat. No. 2,665,249, 2,824,058, 2,903,425, 2,932,613, 3,272,739 and 3,442,798; "Zimpro" method) the wastewater is in an eeaction tower, whereby the organic content makes up about 3 to 6% by weight, with oxygen - normally in the form of air - for Brought Eeaktion, the oxygen content is below the theoretical GSB.

For uassoxidation pressures of 105 to 140 atmospheres are required and temperatures between 260 and 315 ° C are sufficient. Because of the aggressiveness of the substances under these reaction conditions and the pressure and temperature stress the investment costs and operating costs also due to ■ low operating time of the system relatively high, so that a Such a procedure is not an economical solution to the

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can represent water problems.

According to the above older registrations, a noticeable one succeeds Lowering the temperature and pressure conditions with a simultaneous reduction in the reaction time, without this is at the expense of the extent or the rate of combustion of the organic matter, so that one in this way, purified water with low COD can be obtained in an efficient and economical manner.

The invention now relates to the further development of this known method and the reactor suitable for it, in which the contact time of the organic substances with the oxygen in the wet oxidation can be increased under more acceptable conditions at increased concentration can without this leading to an increase in the required reaction space. The drain from the reactor is subsequently worked up to obtain the valuable constituents, so that the process according to the invention particularly suitable for solving the wastewater problems of municipal waste disposal companies and on ships as well for fuel destruction or treatment of waste from the photo industry for the extraction of silver, terephthalic acid and other components from it.

The invention is further illustrated by the figures.

Fig. 1 shows a side view in elevation and partly in section of one for the wet oxidation according to the invention organic waste suitable plant, as it has already been the subject of upper older Registrations is;

F-ig. 2 shows the modifications of the device according to FIG.

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- 5 for carrying out the method according to the invention;

3 shows schematically another possibility for working up the vapor phase;

Fig. 4 shows a schematic partial view of a reactor equipped with overflows for implementation of the method according to the invention;

Figure 5 is a flow sheet for practicing the invention Procedure and

Fig. 6 shows the material balance with continuous wet oxidation an AufsehlußSmamms after method according to the invention.

The plant of Fig. 1 comprises a horizontal cylindrical reactor 10, the reactor chamber 12 by vertical Walls 14, 16, 18 is divided into adjacent chambers 20, 22, 24, which are also cylindrical. the The dimensions of the reactor depend on the desired output, the chambers can be in size or volume vary, preferably the first chambers are larger than the others.

Each chamber is provided with a stirrer, preferably in the form of two disks 28, 30 spaced from one another are rotatable on the shaft 32 in the center of each chamber about a vertical axis in the bearings 34, which are sealed from the reactor. These protruding parts can be disks 36 for driving the stirrer shafts via transmissions or serve with electric motors. The stirrers 28, 30 are provided with radially extending vanes 37 which extend downwardly from the agitator disks. It is expedient, the lower impeller in a third of the

Chamber height and the upper stirring disk in the second third the chamber height to be provided. You can of course also work with only one or more than two stirring disks, with the lowest stirrer is as close as possible to the chamber floor and the uppermost stirrer relatively close to the chamber ceiling should be located. The stirrers are preferably in a space corresponding to a quarter from the top to below Liquid level provided in the chamber.

Air, oxygen or another gas containing oxygen is introduced into the chambers in which the oxidation reaction takes place. The oxygen is supplied via one or more nozzles 38 directly into the largest zone Movement that is below the stirrer. In the embodiment shown, the extend Nozzles 38 from the bottom of the chamber immediately below the Wings of the lowest stirrer upwards, so that the oxygen-containing gas immediately passes through the stirrers induced eddies divided into very fine vesicles which are immediately distributed throughout the liquid by turbulent flow. The nozzles 38 can with aligned with the center of the stirrer or offset from the center. However, you will find them in the realm of the Arrange stirrer so that the air can penetrate into the cone thus created. The oxygen-containing gas will fed to the nozzles via a manifold 40, wherein the pressure should be equal to or preferably higher than that Pressure in the reactor.

The first chamber 20 is provided with a feed 42 at the end of a tube 44, with the aid of which the liquid to be processed is fed in. Preferably this is preheated. The first chamber also has a number of electrical heating elements or heat exchanger coils 48, through which heating fluid flows via a storage vessel 50.

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But you can also use it for the exothermic reaction dissipate developed heat, so that there is a possibility of temperature control in the reaction chamber. The last Chamber or separation zone has a vent 52 from the vapor space for discharging the gaseous phase and a discharge line 54- from the liquid space for discharge the liquid phase.

The chambers are connected to one another by a pipe 56 which extends from the outlet 58 in the upper part of the chamber to a vertical downwardly directed tube 60 of the following chamber. The inlet 58 of the a chamber is located in the upper part and thus divides the chamber into a liquid space that extends into the height of the exit is sufficient, and above it the steam room.

According to the invention, the separation zone 61 is in communication with the last reaction zone 26 via one or more Passages at the interface between the liquid and gaseous phase of the preceding reaction chamber,

as with a tube corresponding to 56, optionally with a downwardly directed tube 60 $, however, preferred an overflow 62, which extends to the liquid-gas interface, over which the liquid flows from the preceding chamber into the separation zone 61 via the free space 64.

The liquid and gaseous material entering the separation zone should preferably not be moved by introduction of oxygen-containing gas or by mechanical means such as stirrers. This makes one practical complete phase separation into the lower liquid phase and the upper gas phase is achieved. To be even better To achieve separation of the phases in the separation zone, it is desirable to close the separation zone with the aid of a baffle plate 66 to subdivide, which extends horizontally across

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the separation zone extends from overflow 62 to just below the end of the separation zone. This divides the separation zone into the liquid zone and the gas zone. In operation, the liquid overflows overflow 62 and the baffle and passes through opening 72 into the liquid zone. In the absence of movement and the presence of the flow over the guide plate, a stationary state is achieved for one Perfect separation between liquid and gaseous phase, the latter only having minimal proportions of solids or takes liquid with him.

The gas phase exits the reactor from gas zone 68 via port and line 74 and is essentially free of liquids and solids. At 54- the liquid phase via line 76 from.

To carry out the method according to the invention can a horizontal cylindrical reactor 100 can also be used according to FIG. 4, the overflows 102, 10J, 104, 105, 106 is subdivided into chambers 107, 108, 109, 110, 111, 112. By choosing the amount of A liquid space and a gas space are formed overflows. The gas space of the chambers stands in with each other Link. The height of the liquid space decreases slightly from chamber to chamber. This will make it safe a flow direction from left to right - as indicated in Fig. - is observed,

According to the invention, the sixth chamber 112 is operated as a separation zone, which with the gas spaces of the chamber 107 to 111 and communicates with the liquid spaces.

Chamber 112 is only equipped with a stirrer operating at such a speed that the solids remain in suspension, but the entrainment of

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Mist or droplets through which the gas phase is prevented.

The "forming water vapor" escapes from the steam space 114- quickly to the vapor discharge 115 from the separation zone. The liquid phase is discharged at 116, this Discharge takes place with the aid of a dip tube that extends to the bottom of the chamber 112. This ensures that sand and heavy precipitations are discharged from the separation chamber. The discharge speed of the liquid Phase is controlled by a liquid level indicator 117, which is one of the works with the help of radioactive material or the level height via conductivity or capacitance measurements notices in the reactor.

The liquid phase and the gas phase are now conducted separately in the heat exchanger in order to achieve the in preheat material fed into the first chamber 107.

The arrangement of the heat exchangers for the two phases as well as the use of aftercoolers for recovery Excess thermal energy in the usual form, such as hot water or low-pressure steam, can be seen from FIG. 5.

An essential aspect of the process according to the invention lies in the removal of the steam from the Steam zone at the temperature and pressure conditions, from what overall there are a number of advantages to wet oxidation. The amount of steam produced during combustion of organic substances is generated in the context of wet oxidation, depends to some extent on the proportion of organic substances and the exothermic reaction developed heat. This introduces further variables that are automatically compensated in the reactor, to mitigate or minimize conditions that are otherwise considered dangerous and restrictions

with regard to the structural design of the system.

The removal of the gases from the vapor phase without condensation allows the discharge of part of the essentially ^e

Amount of water introduced into the reactor so that the residence time of the liquid phase is substantial is extended. This is associated with an increase in the performance of the system and allows further combustion organic material while at the same time further reducing the GSB in the draining liquid.

The vapor phase consists essentially of oxygen, Nitrogen from the air and water vapor from the exothermic reaction and various impurities such as fats and paraffin wax ^ those from a steam distillation

and
come from other low-boiling substances such as ammonia and low-boiling organic acids, aldehydes or ketones such as acetic acid, which are volatile under the prevailing working conditions in the reactor.

These are removed from the reactor with the gas phase. Many of these ingredients can be used in simpler and more convenient ways Way to be worked up on valuable products, so that you get a practically pure exhaust gas, which does not lead to environmental pollution. The condensate of the vapor phase is completely free of heavy metals.

The gas phase can be worked up in various ways. Get according to one embodiment the gases and vapors for heat exchange, with other gases or liquids for heat recovery

before venting into the atmosphere. For example, the process to be processed can be

preheat water for wet oxidation using the gases and vapors emerging from the reactor; instead of this or in addition to this, the hot gases can also be fed into a condenser 80 and come with them In contact with water or another coolant, which can then be used as a heat transfer medium or to generate electricity.

In the embodiment shown in FIG. 2 arrive the hot gases for condensation, which shows, for example, that about 160 liters of fat and paraffin wax in the wet oxidation of 10 tons of sludge are produced. Such waxes and other condensates are "withdrawn" from the heat exchanger 80 at 82.

Such entrained waxes and other condensable material can also be separated off by relaxation of the gases via the expansion valve 84 into the expansion chamber 86, from which via 88 with the help a drum filter 90 the condensed liquids and solids can be recovered. The pure exhaust gas is discharged at 92 or into the heat exchanger of the Fig. 5 returned.

Instead of or in addition to this, the gases and vapors in a rectifying column, such as in a Bell column, contact tower, scrubber or condenser 80 are cooled or the solids in another way and condensable liquids are precipitated while the exhaust gas is vented in pure form via 94 can.

If you work with an expansion stage to adjust temperature and To reduce the pressure of the gases, this can be done, for example, with the help of

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a gas turbine 96 take place to thereby restore energy to win.

The condensate can be recovered and separated into the various components in the usual way.

The exhaust gases after condensation can then also be treated to remove valuable gaseous components, such as low-boiling organic acids, especially acetic acid, and nitrogen compounds such as ammonia ^ as well as Aldehydes, such as formaldehyde, to be obtained. this happens expediently with the aid of a solvent or water or by reaction with an appropriate one Substance in an absorber or a reactor 95

The increase in the residence time of the liquid phase after the gas phase has been removed from the reactor without condensation depends to a certain extent on the gas formation from the liquid during the combustion of the organic substances in the water oxidation. It is assumed that in the combustion reaction of the dissolved or dispersed organic substances in an aqueous medium, about 10 to 40 % of this is converted into water vapor, from which it follows that the volume of the liquid phase decreases with increasing reactor power and with increasing residence time. time of solids in the liquid phase.

The withdrawal of the gas phase from the reactor leads to a further improvement in economy and performance the wet oxidation to remove organic waste products by reducing the volume of the liquid phase it is noticeably reduced with a corresponding increase in the concentration of heavy metal residues and others Solids; consequently, a smaller proportion of liquid must be used for the removal of the heavy metals and for recovery

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- 13 other substances are processed.

The following example explains the method according to the invention in the wet oxidation of sewage sludge from Philadelphia, Pennsylvania, with a COD of 70,850 mg / l.

example

A reactor with a separation chamber 112 as shown in FIG. 1 was used. It was lined with carbon or one Corrosion-resistant acidic ceramic material, the stirrers, air intakes, partitions and baffles were made from Titanium, specification 316 stainless steel, or the like. The procedural conditions became so set so that a scheme according to FIG. 6 resulted.

The pressure was maintained so that the reaction temperature was about 240 ° C. Air was introduced into all chambers except the separation chamber at a rate of about 62.26 to 76.40 l / min (2.2-2.7 cb.ft / min) based on oxygen.

As regards the material balance, so / were 35) 7 '"of the liquid as vapor is withdrawn from the separation zone and about 64.3% as a liquid. The reduction of the liquid in the zone of the liquid phase corresponds to about 35j7 7o of the supplied liquid, leading to leads to a corresponding extension of the residence time of the liquid phase in the liquid zone.

The gas phase condensate contained a slightly broken emulsion of fat in water. The nuclear magnetic resonance spectrum as well as saponification tests showed that the "fat" from straight-chain aliphatic or paraffinic compounds with a boiling range between 190 and 25O ° G.

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The sewage sludge normally provides 15> 9 to 22.7 kg of "fat" per t of dried sludge or approximately 160 liters of "oil" from 10 t of sludge. This material can either be burned directly i ^ ground or is processed into valuable products.

The remaining organic substances of the condensate of the gas phase according to gas chromatographic analysis generally consist of 45 to 55 % acetic acid and 15 to 20 % by weight propionic acid. Traces of butyric acid, acetaldehyde,
Acetone, formic acid, methanol and ethanol are present.

In the withdrawn liquid phase are in
the remaining organic matter is 40 to 70% acetic acid, depending on the type of sludge used. Propionic acid is present in an amount of about 5 to 15% by weight, in addition to smaller proportions of formic acid and acetone as well
Traces of acetaldehyde.

PATENT CLAIMS

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Claims (1)

PATENT CLAIMS (1) Process for the oxidation of organic substances in solution or dispersion in an aqueous medium at elevated temperature and pressure by introducing oxygen-containing gas with the formation of a gaseous and liquid phase in the reaction zone, characterized in that the liquid phase is continuously removed from a separation zone after the reaction zone Phase and the gas phase removed separately. (2) Method according to claim 1, characterized in that the separately discharged Processed phases to gain their heat content and / or the valuable components. (3) Process according to claim 1 or 2, characterized in that the two phases left as calm as possible in the separation zone. (4) The reactor for carrying out the wet oxidation according to claim 1 to J, wherein the horizontal cylindrical Reactor core on one side the liquid to be processed is supplied, in a multitude of interconnected bunkers which reaction is divided by partitions with Feeds for the oxygen-containing gas, LßvLßva η - Separation zone at the » by a
3s reactor with a discharge 'for draws exit side £ the gas phase and for the liquid phase, a guide plate extending horizontally essentially over the entire separation zone at the level of the interface between the liquid and gaseous phase of the preceding reaction chamber is located. 609820/0733