DE1942950A1 - Recovery of the components from pickling waste water - Google Patents

Description

August 21, 1969 P / Dü

Prenco Manufacturing Company, 2605 West Fourteen Mile Road,

Royal Oak, Michigan / USA

"Recovery of constituents from pickling waste water ^N

This invention relates to the art of working up perrosulfate and dilute free sulfuric acid containing pickling waste water and is concerned with an economical process for the recovery of sulfuric acid from this waste material for reuse as pickling liquid, iron oxide being used at the same time commercial product (e.g. for the parbene industry) wins.

In the steel and related industries, large amounts of pickling wastewater are continuously generated. The recovery this material is a difficult problem. It cannot be discharged into rivers or lakes because it is very acidic is and has components that the animal and

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detrimentally affect vegetative life. Extensive research has been carried out to arrive at a feasible To get process for the recovery of this industrial waste, but has not achieved any noticeable success to date. In which A futile attempt to address this problem has been given to some steel companies by their water control authorities Permission to drill deep deposition holes and to empty the pickling plant wastewater into them. Naturally, this is only one temporary remedy, but not a solution to the problem as the acidic liquid will migrate to other places must where it is again a pollution problem.

The problem of recycling this waste material is in In fact it has only been partially resolved by processes in which ferrous sulfate (as such) is separated from the acidic Liquid was separated and then the latter either by evaporation of parts of its water content or addition was reconstituted by strong sulfuric acid. However, the previously known methods have because of their procedural costs and the loss of -SO, the by-product of ferrous sulphate not found popular in the industry,

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The present process for the recovery of the constituents from sulfuric acid pickling wastewater relates to a Concentrating the liquid, preheating the concentrate, atomizing the preheated concentrate in Air, after which the finely distributed air mixture is a thermal. Subjected to decomposition at a temperature that is high enough 1st to obtain the content of sulfuric acid and iron salts from the pickling plant wastewater, and that one then the solid constituents are separated off and the recovered sulfur is processed into fresh BelzflUssigkeit.

Therefore, an object of the present invention is to provide a process for utilizing spent sulfuric acid To find pickling wastewater. Another object of the invention relates to a method by which the components of the pickling liquid are divided into two (2) separate categories be divided:

(a) harmless elements released into the atmosphere; and

(b) economically valuable chemical constituents that can be used for commercial purposes.

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Another object of the invention is an economical process for the recovery of sulfuric acid from such waste material. Still other goals are directed to the recovery of the iron content of such Waste material in an economically acceptable manner.

These and other inventive features can be recognized when carrying out the method, which in principle and in the Connection with the accompanying drawing is described in which the single figure is a schematic representation or a "flow sheet" of the process of the present invention Invention is.

The following disclosure deals with pickling wastewater "which consists essentially of water" free sulfuric acid and perrosulfate (in solution) without or usually with relatively small amounts of buffering agents or impurities or both. The analytically determined composition of 80% HgO, 11 % HgSO ^ and 9 % Fe serve as an example of such a waste material. The description of the method according to the invention is based on a continuous process in which 3785 liters of this waste material per hour (1000 gal./hour) are given up.

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In the first stage of the process, a substantial part is involved the water content of the pickling water is removed from the latter by evaporation. The type and size of the one used The evaporator preferably corresponds to a device that can evaporate about 3028 1 of water per hour (8OO gal./hour), this at a generally constant temperature, which is essentially not higher than 121 ° C, in order to evaporate to prevent sulfuric acid as such.

The thermal energy required for this process stage is preferably supplied - at least for the most part, if not completely - from hot gases which originate in a later stage (ie from stage ⁿ 4 ^H ) of the overall process. A multi-stage evaporator is preferably used in this process. The evaporation also starts from the acid-forming stage "3", since the exit gas to the atmosphere is saturated with water vapor.

The vaporous effluent, i.e. steam, from the evaporator is added to a condenser (in step "2" of the process) Water condenses, whereby an indirect heat exchange takes place with the air, which becomes under pressure as combustion air a thermal decomposition is carried out, the level "3 * of the overall procedure. As a result, dfe

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The temperature of the combustion air can be increased considerably, e.g. to more or less than 2O4 ° C. For a reason which will be mentioned, this preheating of the combustion air is a very desirable fact. The condensation water (almost 3028.1 per hour (800 gal./hour) can be used as a liquefying agent for the iron hydrate crystals from the evaporator after the 50 % concentrated acid has been removed or it can be used as treatment water for the production of pickling water from fresh acid.

In step £ 3 "of the process of the invention, the hot concentrated liquid obtained from the evaporation of steps" 1 ^M and ^W 6 "and containing 99 + # of the salts and only a small proportion of the free acid of the starting material becomes one Heat decomposition transferred (e.g. pumped), in which the concentrated liquid is subjected to heating in an oxidizing atmosphere at such an elevated temperature - e.g. at a temperature of about 1649 ° C - so that (a) all of the remaining water is converted into steam and (b) the free sulfuric acid is broken down into sulfur dioxide and water vapor; and (c) the iron sulfate is broken down into finely divided (e.g. pigmentary) iron oxide _{- especially ferric oxide, Fe 2} O, - and sulfur dioxide, SOp. This stage of the complete process is as follows carried out.

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The hot concentrated liquid is mixed with a suitable carbonaceous or hydrocarbonaceous one Mixed fuel, for example a BrenntSl, and the mixture is heated in an enclosed space to a temperature at which at least one component the mixture would freely evaporate if the mixture were not limited to the liquid state. The forming critically heated mixture is drawn through a suction device, in which it is atomized to form a combustible or burning, finely distributed air stream in an air duct guided «in the lower end of an extended room, which is partially delimited by fire-proof walls. The flammable bin. Burning finely distributed air flow is generated by surrounded by a circular air jacket extending upwardly from the lower end of the enclosure and which fireproof hands protects the latter.

A preferred form of the device has an upright refractory encased tubular retort, a suction device or nozzle at the bottom of the retort for atomizing the concentrated fuel but still liquid pickling water in this retort in the Primary air as well as devices for supplying secondary "

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runs to the end of the retort's OUse. An important feature of this thermal decomposition device is the internal diameter dimension of the refractory-clad tubular retort or furnace chamber in terms of their height at a ratio of approximately 1: 5. The suction device is preferably connected to the device, which the flow of the concentrated liquid pickling water to the evaporation temperature of at least one of its vaporizable constituents is preheated and immediately prior to the delivery of the stream to the aspirator lies. This preheating device can take, and even preferably, takes the form of a helically wound tube which is arranged approximately in a zone is, in which this suction device will flow out the finely distributed air flow.

The suction device can and preferably has a tubular chamber which is closed at its lower end by means of a closure part and at its opposite end is partially contracted by a conically inwardly extending headpiece, as well as via an inlet for atomizing (primary) air under pressure from a suitable source into the tubular chamber which adjoins the lower end of the latter via a

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longer exhaust pipe extending upwardly through the closure member and coaxially through the chamber to the conical upper part, with the discharge tube at its upper End ends in a conical mouthpiece widening near the outside and the widening mouthpiece of the discharge tube cooperates with the inwardly extending head of the tubular chamber to form a circular one Sole seat for releasing the atomizing air; furthermore about closure parts at the lower end of the exhaust pipe, as well via devices that adjoin the lower end of the discharge pipe to a stream of liquid material to the To supply the discharge pipe via a spherical part above the outwardly widening mouthpiece of the discharge pipe, the spherical part being inclined towards the mouthpiece by means of a rod or a wire, at one end thereof the spherical part is rotatably attached and has an adjustable suspension at the lower end of the rod or the Wire to some predetermined "normal" pressure of the To maintain liquid in its flow through the discharge tube, and which is designed to act as an automatic Pressure relief valve is used in the event that there is an abnormally high pressure in the pumped to the suction device Fluid developed,

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As mentioned above, the concentrated loading liquid that is fed to the thermal decomposition device should contain a sufficient amount of a fuel or fuels that the waste material is accurately decomposed due to the thermal decomposition. Since the concentrated Beizereiabwasser lack of flammable components, it 1st naturally required; Involvement of just more or less combustible material of the liquid. Whatever its type, the amount of fuel added - to the waste material - must be sufficient to achieve the necessary degrees of heat so that a thorough thermal breakdown of the waste liquid occurs. The fuel-rich material added may be a mineral oil (petroleum) fraction or a fuel gas or coal dust.

The above-mentioned "elongated space that is partially through ) fireproof walls is limited ", will or can means a vertical heatable retort consisting of: a metal (e.g. steel ») jacket in cylindrical shape, an intermediate jacket or container with suitable thermal insulation against high temperature and a Internal refractory lining of the free-standing, one-piece construction. The atomizing device described above (including the aforementioned waste

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Suction device) closes the lower end of the retort. At its upper end, the retort is preferably by means of a uniform, conical closure made of sheet metal, which is suspended and balanced, in order to take up a predetermined pressure of the combustion gases, namely in order to achieve a desired retention of the oasis (from the upper Mouth of the retort) in the event that an overpressure develops - e.g. an explosion - with subsequent immediate refilling of its normal position above the mouth of the retort,

In addition to its upper end, the retort is preferably provided with a device for heat exchange in order to that leave the retort to cool significantly if necessary. This device for heat exchange can be designed as a conduit sdn (liquid heat exchange medium), which is simple or several times around the retort, these turns being connected to lines in order to lead the heat exchange medium to and from the turns of the aforementioned evaporator.

The oasis emerging from the thermal decomposition will become in step "4" of the process to a dry separator (e.g. a conventional centrifugal separator) (level "5")

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brings, in which the solid particles (mostly exclusively Iron oxide particles) «which are suspended in the gas flow, separated from the gas and for subsequent deposition (e.g. sales) can be collected.

The hot gases, which have been freed from the suspended solid constituents and contain sulfur dioxide, water vapor and constituents of the exhaust gases (removed from the combustion of the fuel added to the liquid as described above), are passed (stage "6") into an absorption and diffusion tower, which has the characteristics of "auto-oxidation" to form perisulphate, ferrous sulphate and sulfuric acid. The purified remaining gas is vented to the atmosphere. The basic features of the "autoxidation ¹¹ are on page J06 of the book" was published The Manufacture of Sulfuric Acid _"t Werner Duecker and James R. West editors Reinhold Publishing Corp., New York 1959th

The apparatus for performing step "4" of the process can be similar to that described in US Pat

is disclosed and claimed.

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The invention will now be described in more detail and by reference described on the drawing.

According to the drawing, the pickling plant wastewater enters the system through the valve-shaped inlet pipe 11, it then enters a multi-stage evaporator 12 and via the pipe 11a into the absorber 55. The evaporator 12 has an indirect heat exchange device IJ through which a heat exchange medium from the inlet pipe 14 is supplied the outlet pipe 15 flows, it also has an outlet for the concentrated pickling crystal water through the exhaust pipe 20, the pump 21 and the feed pipe 22 to the suction part (not shown in detail) of a retort 25 for thermal decomposition. The evaporator 12 is supplied through the inlet pipe 61, which receives 0 % concentrated mother liquor from "Stage 6", as well as through the inlet pipe 11, which receives the pickling waste water from the process. In addition, a device is provided for removing the concentrated 50% acid from the evaporator via the outlet pipe 62, the remaining precipitate consisting essentially of perrisulphate, perrosulphate monohydrate (referred to herein as iron hydrate) being washed out through the outlet line by means of water, which from the inlet pipe

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is supplied from the water tank 37. Fuel oil will is fed to the system through the valved conduit connected to a conventional source (not shown) of fuel oil and the exhaust pipe 20 for mixing the Fuel in contact with the concentrate before the tube 20 is inserted into the suction portion of the retort 25.

Combustion air (primary air) becomes the intake device and the inner circumference of the retort wall (protective air jacket, later becoming secondary air) through the air duct 30 supplied by a fan designated 31. In the line 30 is an indirect gas-to-gas heat exchange · » Device 32 installed, into which the steam from the evaporator 12 is guided by means of the steam line 35. Of the Steam is condensed in the device 32 and the resulting condensate is passed through the distillation tube 36 in passed a suitable container 37 for distilled water.

In the suction part of the retort 25, the liquid mixture of concentrated pickling waste water and fuel oil that this Part is fed through the feed pipe 22, preheated and then with primary air (from the air line 30) atomized and instantly burned. A protective jacket made of air

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let placed around the inner circumference of the retort wall «the the latter from being destroyed by the flames with high Temperature protects and results in combustion products, the air jacket becoming increasingly secondary combustion air around the combustion of all combustibles To complete the components of the finely distributed air flow that goes up through the retort.

To a very considerable warmth ante 11 In the perfect to deduct burnt oases in the exit from the upper part of the retort 25 "are placed around the latter turns 40" the Retort surrounded several times. The turns are connected to the heat exchanger 13 (in evaporator 12) through tubes 14 and 15 tied together. The system 13 »15« 40, 14 is combined with a suitable « Usual heat exchange medium filled. The latter means is Trläthylenglyool o.a.

The only partially cooled combustion gases obtained pass from the retort 25 through the line 45 into and through a centrifugal dry separator 46 "in which the finely divided particles (namely iron oxide particles)" are in the gases emerging from the retort «at 47 are collected «while those of the solid constituents

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19A2950

liberated gases are drawn off from the separator through the line 49 and the blower 50 and pass through the line 51 to an absorption-diffusion tower 55. The gases (SO ₂ + Og) carried through the line 51 enter the absorption-diffusion tower as fine bubbles. According to the principle of <"autoxidation ¹¹ , the acid content of the diluted, used pickling water increases and the ferrous sulfate is oxidized to iron. The following equations represent the reactions:

2PeS04 + SO ₂ + O ₂ - Pe _g (SO ₄ ), 2H ₂ O + 2SO ₂ + O ₂ «2H ₂ SO ^

If the acid concentration approaches 30%, the precipitated iron salts are withdrawn into the storage tank 63, from where they are used as the feed for stage? 3 ^M. The mother liquor or part of it is drawn off through the pipe 6l and is used as a feed to the evaporator 12 in the "l" stage.

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Claims (4)

Claims • 1. Process for the recovery of the constituents from sulfuric acid pickling waste water, the ferrous sulphate and contain free sulfuric acid, characterized in that a substantial part of the water content of the pickling water is removed by evaporation to form a concentrate, the concentrate in an enclosed space is heated to a temperature which is at least the vaporization temperature of a vaporizable component of the concentrate corresponds to that which was previously heated Concentrate is atomized in air and a stream of the liquid thus atomized undergoes a process of thermal decomposition is subjected by placing this in an oxidizing atmosphere to a temperature of the order of 1649 ° C is heated at which the sulfuric acid content of the concentrate breaks down into sulfur dioxide and water vapor and the ferrous sulfate content of the concentrate in gaseous sulfur dioxide, solid iron oxide, and Water vapor is decomposed, and that the solid iron oxide particles from that which emerged during the thermal decomposition Stream are separated, and that then the sulfur dioxide is separated from the stream, and that finally this deposited sulfur dioxide is mixed with water for the purpose of the formation and recovery of sulfuric acid. - 2 0098U / 1777 2. The method according to claim 1, in which the various cycles are carried out continuously on the basis of the steps described. 3 · Process according to claim 1 or 2, in which a carbon-containing fuel is mixed with the concentrate in order to achieve the thermal units through the combustion of this mixture which are necessary to increase the temperature of the concentrate to the temperature of the thermal decomposition. 4. The method according to claim 1 to 3, in which a substantial portion is supplied to the heat in the stream exiting from the process of thermal decomposition, the stage of evaporation. 0098U / 1777