EP0341580A2 - Process for purifying by distillation mercury-containing materials or mixed materials - Google Patents

Abstract

The invention relates to a process for the distillative purification of mercury-containing substances or mixtures of substances and / or for the production of mercury from the same, which is characterized in that the feed material is injected into the distillation apparatus as a solid / liquid suspension or solution or atomized or sprayed therein is sprayed, preferably by means of a rotary atomizer, and in that work is carried out at a pressure lower than 1 bar, under reduced pressure relative to atmospheric pressure or vacuum, and in that the feed material is moved.

Description

The invention relates to a method for the purification by distillation of mercury-containing substances or mixtures of substances and / or for the production of mercury therefrom.

The method according to the prior art is described below with reference to the processing of Hg-containing activated carbon or the extraction of metallic mercury from ores or concentrates.

Processes for the production of mercury by dry distillation from mercury-containing substances are known from the smelting of ores or minerals containing mercury. It is also known to purify mercury-containing residues, for example from acetaldehyde electrolysis or activated carbon sludges from chloralkali electrolysis, by such dry distillation from mercury. These prior art methods include that the feed is dried as much as possible before being introduced into the distillation apparatus so as not to have to additionally apply the heat of vaporization for the water in the distillation process, which must therefore be removed beforehand by drying. If, for example, the raw material was enriched by flotation in the case of mercury smelting, the aim is to use the material in the still lation or roasting ovens reduce the moisture content to approx. 8 to 10%. According to the prior art, residues containing mercury are also dewatered by mechanical separation processes before the mercury is removed by distillation by thermal treatment of the feed material; for example, mercury-containing sludges from chlor-alkali electrolysis are reduced to approx. 20 to 45% by weight in the moisture content by filter presses.

The known distillers for the production of mercury or the purification of mercury can be classified according to whether and how the feed material is moved during the distillation process.

In one variant, the material is not moved. It rests in one or more layers either directly on the walls of the distillation apparatus or on sheets to which it was previously applied and which are then introduced into the distillation apparatus. These apparatuses are preferably used when fine-grained or powdery material is treated in order to minimize the dust discharge with the vapors and gases which are derived from the distillation apparatus. This process is a batch operation with the Heating of inert masses.

In another variant, the material is moved slightly during the distillation process, but migrates through the distillation apparatus during the process. This principle is preferably used in the smelting of minerals containing mercury, e.g. in shaft furnaces with or without built-in.

A third variant involves moving the material during the distillation process in order to improve mass and heat transfer processes during the distillation process.
For this, rotary kilns are known in the prior art. These work by rotating a rotary tube with its axis set up horizontally or slightly inclined against the horizontal around its axis. This means that the material always comes into contact with new parts of the wall or, in contrast to a dormant layer, is exposed to a different surface of the furnace atmosphere. When arranged horizontally, rotary kiln devices are usually loaded and emptied in batch mode. In the case of a slightly inclined arrangement, the material to be treated migrates in the direction of inclination of the axis through the rotary kiln, the residence time being the set speed is true. It is also known to install internals inside the rotary tubes which are intended to prevent the material from being reduced in size and to support movements of the goods.

The known methods for the distillation treatment of mercury-containing substances can also be differentiated according to whether the distillation
- at atmospheric pressure or slight negative pressure,
- Or is carried out in a vacuum.

Both are known for the devices mentioned above. The known apparatus for treating mercury-containing substances are operated at about atmospheric pressure. A slight negative pressure is set, which has the purpose of preventing leaks from the furnace atmosphere to the outside, to prevent mercury losses to the environment, as well as for reasons of occupational health and safety and to increase the mercury yield.
The low pressure in the distillation apparatus is usually only a few millimeters of water, but not less than 0.9 bar absolute pressure.

It is also known that during the distillation of mercury-containing substances, dust formation from the material causes problems in the subsequent condensation. From the extraction process of mercury smelters is known that the condensation product always comes to a greater or lesser extent from a moist or muddy material permeated with metallic mercury, which is called "Stupp". The formation of stupps in processes according to the prior art is favored by the following factors:
Presence of carbon, fine-grained loading and when the goods move.

In the known methods, the distillation furnaces are heated either directly, for example by flames or flue gases, or indirectly via one of the walls, for example by flames or electrically.
The processes that work at atmospheric pressure or slight negative pressure to reduce the leakage, and essentially all of those in which the material is moved during the distillation process, require high temperatures, above about 400 to 600 ° C. Otherwise the residual mercury content in the treated substances is too high.
At this temperature level, the introduction of the required heat in indirect heat exchange by condensing steam from a heating medium or by releasing the heat of a heat transfer fluid is technically not possible under economic conditions. In distillation ovens, in which the good during the distillation process is not moved, working in a vacuum is known. Under these conditions, indirect heating with equipment such as water vapor or heat transfer oil is known. Such heating is desirable because it gives better heat transfer coefficients than heating with gaseous media. Overall, indirect heating is desirable, because with direct heating the amount of exhaust gas increases and the mercury losses increase due to the partial pressure of mercury. This is the main source of loss in mercury smelters. With direct heating, there is also a greater risk of dust being carried away due to higher flow velocities in the furnace. There is also a fire risk if mercury-containing activated carbon is to be freed from mercury.

Distillation ovens with essentially static goods have the disadvantage of poor heat and mass transfer. Layers can crust over, especially with fine-grained substances such as activated carbon in powder form. There is no adequate transport mechanism through the dormant material layer to create a sufficient partial pressure gradient for mercury. As a result, there are long treatment times in the ovens. The usual reduction of the water content before on according to the state of the art The introduction into the distillation apparatus should also be considered with regard to the formation of dust in the distillation apparatus and the introduction of dust into the condensation stage. By reducing the water content in the feed, the amount of water evaporating in the still is to be reduced. In the case of directly heated stoves, the amount of flue gas can be kept lower. The oven throughput time can be shortened for indirectly heated, especially those with stationary goods.

The heating and evaporation takes place, for example, via electrical heating elements which were arranged in the interior of the furnace.
Heat transfer takes place
- by radiation from the heating elements to the hood,
- from the hood in turn to the hordes by radiation,
- Of these by heat conduction and radiation to the feed.

Large ballast masses of steel must be warmed up and cooled for each batch. This is very energy intensive. In addition, due to the sluggish heat transfer only one oven load in 24 hours.

In order to achieve sufficient de-quenching of the material at the prevailing atmospheric pressure, heating temperatures of up to 550 ° C must be achieved. The residual content in the treated material is in the range of approximately 20 to 50 mg / Hg per kg of material. A further reduction is limited by the lack of mass transfer mechanisms in the atmosphere inside the hood with the resting layer of feed material on the tray trays. The construction does not allow the goods to move. It also prohibits this principle of procedure; because after the water has evaporated (many A-coals come from wet filtration and still carry a moisture content) there is otherwise the previously mentioned risk of exothermic reactions due to deflagration or fire. In addition, too much activated carbon dust is entrained in the downstream injection condensation.

The furnace heating is switched off when the shift of the system operated in viewing mode ends. The ovens are left with the trolleys and the feed material until the start of the shift the next morning for cooling by natural convection. To reload the ovens in the 24 hour rhythm during the shift and to be able to heat up, the emergency vehicles have to be changed at the beginning of the shift. To do this, the flange connection for exhaust gas cleaning must be loosened on the emergency vehicle that has not yet cooled to ambient temperature. The emergency vehicle, which is pulled out of the oven by muscle power, is then left to cool down further. The liquid mercury, which had accumulated in the collecting pipe under the emergency vehicle, is drained by gravity in the open river into a collecting vessel, driven with the forklift to the collecting container of the mercury filling and drained there.

The many open handling of mercury-containing material or mercury, sometimes at elevated temperatures, is problematic for occupational safety. There is a problem with keeping the MAK values for Hg for the staff employed.

After the stack of trays has cooled down on the kiln car, the hood is pulled. The tray trays on the emergency vehicles are transported to the emptying site by forklift trucks. The treated material is transferred to the landfill in transport packaging using a vacuum suction system.

For the second of these tasks it applies that no large amounts of heat are to be transferred and indirect heating with an organic heat transfer medium is provided in the method according to the invention.

With the method and the device according to the present invention, mercury can be obtained from substances containing mercury.
Furthermore, gases or vapors are led to the condensation stage, which contain little dust due to the washing effect of the suspension applied. Without this washing effect, the intended movement of the goods in the apparatus would not be possible, since too much dust would be discharged, especially when treating activated carbon, which is already in powder form, which would be ground, or which would have had the corresponding amounts of dust due to the abrasion of granular coal. Especially when it comes to the treatment of activated carbon, there are all the features that favor the formation of stupp according to the known state of the art:
- carbon content,
- fine grain,
- Movement in the still.

The possibility of working in a vacuum in the method according to the invention enables indirect heating with steam and / or a heat transfer fluid to be implemented,

It has hitherto not been known to operate distillation furnaces for mercury in which the material is moved during the distillation process in a vacuum, in order thereby to be able to carry out indirect heating with water vapor and / or a heat transfer fluid. The resulting high heat transfer numbers are a prerequisite for the larger amount of moisture to be evaporated inside the apparatus.

• 1. Verdampfung der Flüssigkeitsmenge bei nicht zu hohen Temperaturen.
• 2. Reduzierung des Restgehaltes an Quecksilber in dem im wesentlichen von der Flüssigkeit befreiten Material bei höheren Temperaturen.

In the interior of the distillation apparatus, essentially two different process engineering tasks had to be solved in the direction of movement of the feed material, which are important for the process:

• 1. Evaporation of the amount of liquid at not too high temperatures.
• 2. Reduction of the residual mercury content in the essentially freed of material at higher temperatures.

For the first of these tasks, there is a need to transfer large amounts of heat to evaporate the liquid; in the method according to the invention, this is provided on the equipment side by heating by means of condensing steam.

For the second of these tasks it applies that no large amounts of heat are to be transferred and indirect heating with an organic heat transfer medium is provided in the method according to the invention.

With the method and the device according to the present invention, mercury can be obtained from substances containing mercury.
Furthermore, gases or vapors are led to the condensation stage, which contain little dust due to the washing effect of the suspension applied. Without this washing effect, the intended movement of the goods in the apparatus would not be possible, since too much dust would be discharged, in particular when treating activated carbon, which is already in powder form, and would be ground, or would have been given the appropriate proportion of dust by abrasion of granular coal. Especially when it comes to the treatment of activated carbon, there are all the features that favor the formation of stupp according to the known state of the art:
Carbon content,
Fine grain,
Movement in the still.

The possibility of working in a vacuum in the method according to the invention enables indirect heating with steam and / or a heat transfer fluid to be implemented, because the vapor pressure of the mercury then enables a sufficiently low residual mercury content in the treated material at temperatures below 400 ° C. The lower temperatures simplify the choice of material for the distillation apparatus, and the conditions are created for the mechanical implementation of the rotating internals for scraping the material off walls. The disadvantage of the dormant layers of the material to be treated with poor heat and mass transfer ratios is avoided. The batch operation typical of stills with still layers is avoided, in which, when heating up and cooling down, ever larger masses of the furnace construction have to be heated and cooled as ballast. Health hazards to the operating personnel when handling material containing mercury, which is mostly manual loading, are avoided.

Due to the movement of the goods for better heat and mass transfer, compared to quiescent layers, it offers the advantages of a continuous process control instead of a batch process. The disadvantages of rotary tubular furnaces are thus avoided, in which the good movement results in a greater dust discharge, which leads to a corresponding formation of stumps in the condensation devices.

In the process of the present invention, it is advantageously possible to use, in particular, powdery mercury-containing substances or those in which abrasion can easily occur. These can be activated carbons loaded with mercury, for example, which at the same time also contain the carbon that promotes stupp formation. In contrast to a jacket, which rests in a rotating tube, according to the device according to the invention, the attachment of the operating medium spaces for indirect heating is easily possible. While in the rotary tube the lower and side part occupied with material always causes the heat transfer from the rotating jacket to the material to be treated, in the method and apparatus according to the invention, practically the entire jacket surface is effective as a heat exchange surface in a vertical arrangement. Due to the constant peeling of the material layer building up on the jacket by the rotating internals, a smaller layer thickness on the walls is realized than occurs in the rotary kiln, which further improves the heat and mass transfer ratios. This combination of advantages is made possible by a combination of process features that run counter to the previously known processes. So far, in order to keep the amount of liquid to be evaporated in the distillation furnaces apart from the mercury, the feed material has been largely drained or dried before use, at most wetting took place to reduce dust discharge.
In contrast, the opposite is done in the method according to the invention. In a pretreatment stage, a solid-liquid suspension is produced by targeted addition of liquid, with such a high proportion of liquid in the slurry that the suspension can be sprayed in the distillation apparatus. This was not possible with the low moisture levels that had been achieved to date.
In the process according to the invention, the liquid of the sprayed-in suspension exerts a washing action on the vapors and gases passing in countercurrent in the upper part of the distillation apparatus and thus reduces the dust discharge to a tolerable residue.

The methods of the prior art only allow inadequate cleaning of mercury-containing substances or substance mixtures, they are environmentally harmful, harmful to people, time and costly.

In contrast, the present invention is based on the object of providing a method for the distillative cleaning of mercury-containing substances or mixtures of substances which enables extensive cleaning of the feed material, is environmentally friendly and does not burden people, which can be operated continuously and is energy-efficient.

This object is achieved according to the invention in a method of the type mentioned at the outset by injecting the feed material into the distillation apparatus as a solid / liquid suspension or solution, or atomizing or spraying therein, preferably by means of a rotary atomizer.

Special embodiments are characterized in that work is carried out at a pressure lower than 1 bar, under vacuum compared to atmospheric pressure or in a vacuum,
that the feed is moved
that the liquid phase begins to boil at lower temperatures than mercury,
that the feed has a dry matter content ≦ (less than or equal to) 42% by weight, preferably 10 to 30% by weight,
that the feed material has been warmed up to such an extent before it is introduced into the still that the temperature level is not lower than 10 K below the evaporation point of the earliest boiling liquid constituents of the suspension - calculated at the absolute pressure prevailing in the still, preferably at or above it Temperature, but not higher than it would correspond to a spontaneous evaporation of 10% of the liquid when relaxing to the pressure prevailing in the distillation apparatus that a gaseous medium is introduced into the distillation apparatus at the outlet end in order to improve the mass transport for mercury in the part of the distillation apparatus as an entraining gas, in which the suspension liquid has largely evaporated and that the suspension is wet-milled before it is used in the distillation apparatus in order to set an optimal particle size and particle size distribution.

Other special embodiments are characterized in that
that the vaporized substances flow through the distillation apparatus in countercurrent to the direction in which the feed material migrates,
that at least two different temperature levels are selected for the operating rooms, adapted to the various process engineering tasks to be solved in the distillation apparatus,
that it works at a low temperature level at the beginning of the conveying path of the feed material in the apparatus, preferably for evaporating the liquid phase of the suspension in the operating medium space, and
a higher temperature level downstream on the path of the feed material in the distillation apparatus in order to achieve the lowest possible residual mercury content in the feed material, which leaves the distillation apparatus in the operating space so that the feed material is thrown onto indirectly heated walls of the distillation apparatus and before a thick layer is formed , which would hinder the heat and mass transfer, is mechanically scraped off again by the device (thin-film evaporation) in order to be thrown back onto the inner wall of the distillation apparatus downstream of the feed device by other parts of the rotating device,
that a fractional condensation is carried out with
- A first stage in indirect and / or direct heat exchange with one or more colder cooling media (apparatus) and discharge of a first liquid phase from the remaining steam / gas flow in a separator to separate the mercury from the lighter liquid phase.
- and a second stage, designed as direct condensation in the heat and mass transfer with a liquid>,
that the second stage is designed as a washing column, preferably with a packed bed, and the liquid phase is discharged via a separating vessel,
that a substance is added to the washing liquid to selectively increase the absorption of mercury,
that the direct condensation works at a temperature of the feed liquid at the top of the column which is ≦ (less than or equal to) 6 ° C., and that the partial pressure of the mercury in the gases which are not condensed when leaving the column is greatly reduced,
that the direct condensation stage is carried out in two stages with
- a lower stage, in which the circulating liquid is recooled by a cooling medium that has a flow temperature ≧ (greater / equal) 6 ° C, and a second stage, in which the added liquid has a temperature ≦ (less / equal) 6 ° C is given up,
that it is used for the regeneration of activated carbon, that a washing effect is exerted on occurring and discharged gases or vapors,
that the distillation apparatus is designed as a cylindrical container so that the inside length is at least four times as large as the inside diameter, and consists of a fixed jacket (3)
- And a rotating device (4) inside the same
. for moving / promoting the feed material,
. as well as for scraping or scraping the latter off the inner wall of the distillation apparatus, for preventing the feed material from falling freely until the end of the apparatus after scraping with a vertical arrangement of the axis of rotation of the distillation apparatus,
. and bringing the feed material back into contact with the inner wall at another point.

A device for carrying out the method according to the invention is also claimed, which is characterized in that
that the distillation apparatus is designed as a cylindrical container so that the inside length is at least four times as large as the inside knife, and consists of a fixed jacket - and a rotating device inside the same
. for moving / promoting the feed material,. and for scraping or scraping the latter off the inner wall of the distillation apparatus, for preventing the feed material from falling freely until the end of the apparatus after scraping with a vertical arrangement of the axis of rotation of the distillation apparatus,. and bringing the feed material back into contact with the inner wall at another point,
that the walls of the distillation apparatus are largely designed as double jackets or are equipped with pipe coils welded onto the outside,
that the outer wall of the distillation apparatus is equipped with at least two different operating rooms,
that the lower temperature level is generated on the equipment side by condensing water vapor in the equipment room at a pressure of 2 to 25 bar, preferably 10 to 12 bar, and the higher by heating the equipment rooms with a heat transfer medium in the temperature range of 250 to 370 ° C, preferably 300 to 350 ° C,
that the vacuum generating device, preferably a water ring pump, is arranged between the first and second condensation stages.

The state of the art is the "Textbook of Metallurgy", by Tafel, Victor and Wagemann, Karl, Volume 1, S. Herzel Verlag-Buchhandlung, Leipzig 1951.
This textbook describes, among other things, the formation of the Stupp formation, as well as furnace types, including rotary tube furnaces for roasting and mercury distillation from ores.

Regarding the state of the art, Gmelins Handbuch der inorganic Chemie, 8th edition, system no. 34, relating to mercury, published by Verlag Chemie, Weinheim / Bergstrasse, 1960. There, the drying of mercury-containing sludge in a vacuum is described, as well as the extraction of mercury from activated carbon in a dormant layer. It is necessary to bind powdered coal with water glass.

In the process of the present invention, for example, an Hg-containing activated carbon suspension is introduced into this distillation apparatus and the treatment is freed of mercury in the manner described and thus
- regenerates for reuse in adsorption processes
- Or can be sent for further disposal by incineration or landfill without this mercury content.

The designs of the walls of the distillation apparatus have the task of keeping the wall temperatures at nominal operation above the dew point of vapors, which are evaporated from the feed material, and to serve as operating room for vaporous or liquid heating media for the transfer of the heat of vaporization and the sensible heat in indirect Heat exchange through the wall of the still to the feed.

When the vaporized substances flow according to the invention in countercurrent to the wall device of the feed material through the distillation apparatus, a mass and heat exchange takes place in such a way that the finely divided feed material brings about a washing action for those flowing in countercurrent
- mercury vapors,
Vapors of the liquids present in the suspension,
-Gases that were dissolved in the suspension or were specifically introduced at the exit end of the feed from the distillation apparatus.
This results in a reduction of the dust-like impurities which would otherwise be discharged from the distillation apparatus by the vapors or the steam / gas mixture. This is achieved, except for the chosen procedure, through the chosen liquid content of the feed suspension. This prevents dry dust from being present in the area of the feed zone of the suspension, in which vapors or a gas / vapor mixture are drawn off from the distillation apparatus, as a result of which a largely mercury-free and liquid-free dry substance is released at the end of the distillation apparatus the treated feed leaves it.

The division of the apparatus means that impurities from the distillation apparatus preferably precipitate out in the first stage and, as a result, the washing liquid is not loaded with them in the second stage and pure Hg is obtained.

Batches which should not reach the intended residual mercury content, but which are between 0.6 and 50 mg / kg, are sent to the landfill. Faulty batches with residual mercury content> 50 mg / kg are treated again in the plant.

The substances evaporating from the activated carbon - essentially mercury and water - pass through at the upper end of the vertical dryer after they exit
- heat exchanger for heat recovery in hot water,
- condenser with indirect cooling water cooling,
- Water washing in a packed column, the fresh water added in the last stage being cooled by cold water from a refrigerator process. This lowers the partial pressure for Hg very far in the non-condensed exhaust gas,
- vacuum station
- Exhaust gas cleaning with the individual process stages
. Acid wash with sulfuric acid
. Wash with caustic soda
. Water wash
. Warming up by indirect heat exchange with hot water to 20 ° C above the water dew point (so that the subsequent adsorption stage works perfectly)
. Activated carbon adsorber.

In this way, substances evaporated from the activated carbon are removed from the exhaust gas, in particular the residual Hg value thereof is brought below 0.001 mg / cbm of exhaust gas.

The cleaned exhaust gas is released into the atmosphere via an exhaust gas chimney.

The liquids condensed out in the condensation stages - essentially water and mercury with impurities - are separated by decantation. The water is fed to a process water collection container. From it, the amount of water required for the preparation station is used again. The rest are then cleaned and then stored in a container for clean process water to e.g. to be used again as washing water in the process or the barrel washing station. Excess quantities are discharged into the sewage system as waste water after cleaning.

The separated mercury is weighed in a weighing station so that the recovered mercury can be assigned to the processed customer batches. Then it is collected in a buffer container. From there, if it is necessary for the respective application, it is further cleaned and in the filling station in the Commercially available 36.5 kg steel containers filled ready for dispatch.

• 1. Die Austreibung des Hg aus dem Einsatzmaterial erfolgt in einer geschlossenen, dichten Apparatur unter Vakuum. Dadurch kann anstelle einer elektrischen Beheizung bei Normaldruck und 550°C mit flüssigem Wärmeträgermedium von 360°C in der Endstufe beheizt werden. In der Eingangszone, in der vor allem Wasser zu verdampfen ist, kann der gute Wärmeübergang der Wasserdampf­kondensation ausgenutzt werden.
• 2. Bei Undichtigkeiten in der Apparatur kann nur Leckluft nach innen gelangen, es können aber keine Hg-Dämpfe nach außen dringen. Die Sicherheit des Anlagenbe­triebs für Arbeitsschutz- und Emissionsschutzbelange wird dadurch wesentlich erhöht. Beim bisherigen Ver­fahren bestand beim Eindringen von Luft in der letzten Ausheizphase, in der wasserfreie Aktivkohle Temperaturen über 500°C ausgesetzt war, Brandgefahr. Diese ist bei den infolge des Vakuumbetriebs tieferen Prozeßtemperaturen nicht gegeben.
• 2. Die im oberen Teil des Dünnschichtverdampfers abge­zogenen Wasser- und Hg-Dämpfe werden von dem einge­spritzten wässrigen Aufgabegut einer Wäsche unter­zogen. Dadurch wird weniger festes Material in die anschließenden Verfahrensstufen der Kondensation ver­schleppt. Trockener,Aktivkohlestaub, der am leichtesten von einem Gas-/Dampfstrom mitgetragen wird, kommt im oberen Teil des Trockners gar nicht vor. Dies ist ein wesentlicher Vorteil dieses kontinuierlich beschickten Trockners gegenüber dem Chargenprozeß in einem Ofen, wo nach der Phase des Verdampfens von Wasser immer trockene Aktivkohle im Bereich des Gas-/Dampf-Abzugs liegt.
• 3. In dem Trockner dieses Verfahrens findet ein intensiver Stoff- und Wärmeaustausch statt durch
  - feine Zerstäubung der für diesen Zweck aufgeschlämmten Suspension. Das Material liegt nicht in einer ruhenden Schicht auf Hordenblechen.
  - ständige Verwirbelung und Bewegung des aufzuarbei­tenden Materials. Es entstehen keine an der Oberfläche verkrustenden Schichten, die Stoff- und Wärmeübergang der tiefer liegenden Schichten stark behindern, wie dies bei einem chargenweise mit Horden beschickten Ofenprozeß der Fall ist.
  - verdampfendes Wasser als Transportmedium für Hg. Beim Ofenprozeß verbot sich eine weitere Wasserzugabe wegen der teuren elektrischen Heizkosten für die Ver­dampfung desselben.
  - über den Kühler in den unteren Teil des Trockners gezielt eindosiertes Strippgas als Transportmedium bzw. zur Verstärkung des Partialdruckgefälles für Hg im unteren, wasserfreien Bereich. Eine solche Zugabe von Strippgas war beim chargenweise be­triebenen Ofenprozeß nicht möglich, weil zu viel Aktivkohlestaub mitgerissen worden wäre bzw. bei den hohen Temperaturen bei Luftzugabe Brandgefahr aufgetreten wäre.
  Auf diese Weise sind deutlich geringere Rest-Hg-Gehalte zu erzielen als bei dem Chargen-Ofenprozeß und es wird die Erwartung gerechtfertigt, daß das behandelte Gut wie Kohlestaub verbrannt werden kann und nicht als Ab­fall deponiert werden muß.
• 4. Es handelt sich um einen kontinuierlichen Prozeß, in dem
  - nicht bei jeder Charge große Stahlmassen als Ballast mit aufgewärmt und abgekühlt werden müssen und bei dem praktisch keine Möglichkeit zu einer Wärmerück­gewinnung gegeben war.
  - die Transporte des Materials vom Ansatz bis zur Ab­füllung in geschlossenen Ausrüstungen durch maschi­nelle Einrichtungen erledigt werden -und nicht durch Handarbeit des Bedienungspersonals . Damit wird ein wesentlich höheres Maß an Vorsorge hinsichtlich Arbeitssicherheit und Arbeitsschutz für das Be­dienungspersonl als inhärente Eigenschaft dieses Verfahrens realisiert. Die Einhaltung der bio­logischen Arbeitsstoff-Toleranzwerte für Hg beim Bedienungspersonal wird dadurch wesentlich besser möglich, als es unter den Verhältnissen des bis­herigen Verfahrens der Fall sein konnte mit seinen manuellen Hantierungen und den hohen Temperaturen bei praktisch atmosphärischen Verhältnissen im Ofen.

The described method has various innovations and serious advantages over what is known so far:

• 1. The mercury is expelled from the feed material in a closed, sealed apparatus under vacuum. This means that instead of electrical heating at normal pressure and 550 ° C with liquid heat transfer medium of 360 ° C in the final stage can be heated. The good heat transfer of the water vapor condensation can be exploited in the entrance zone, in which water is to be evaporated.
• 2. In the event of leaks in the equipment, only leak air can get in, but no mercury vapors can escape to the outside. This significantly increases the safety of plant operations for occupational safety and emissions protection issues. With the previous method, there was a risk of fire when air penetrated in the last baking phase, in which anhydrous activated carbon was exposed to temperatures above 500 ° C. This is not the case at the lower process temperatures due to vacuum operation.
• 2. The water and mercury vapors drawn off in the upper part of the thin-film evaporator are subjected to washing by the injected aqueous feed. As a result, less solid material is carried over into the subsequent process steps of the condensation. Dry, activated carbon dust, which is most easily carried by a gas / steam flow, does not occur in the upper part of the dryer. This is a major advantage of this continuously charged dryer compared to the batch process in an oven, where after the phase of evaporation of water, dry activated carbon is always in the area of the gas / steam extraction.
• 3. An intensive mass and heat exchange takes place in the dryer of this process
  - Fine atomization of the suspension slurried for this purpose. The material is not in a resting layer on trays.
  - Constant swirling and movement of the material to be processed. There are no incrusting layers on the surface that severely hinder the mass and heat transfer of the deeper layers, as is the case with a batch process of trays loaded with trays.
  - Evaporating water as a transport medium for Hg. In the furnace process, further water addition was prohibited because of the expensive electric heating costs for the evaporation of the same.
  - Stripping gas metered into the lower part of the dryer via the cooler as a transport medium or to reinforce the partial pressure drop for mercury in the lower, water-free area. Such addition of stripping gas was not possible in the batch-operated furnace process because too much activated carbon dust would have been entrained or at the high temperatures with the addition of air there would have been a fire hazard.
  In this way, significantly lower residual mercury contents can be achieved than in the batch furnace process and the expectation is justified that the treated material can be burned like coal dust and does not have to be disposed of as waste.
• 4. It is a continuous process in which
  - Do not have to heat and cool large quantities of steel as ballast with each batch and for which there was practically no possibility of heat recovery.
  - The transport of the material from the batch to the filling in closed equipment is done by machine equipment - and not by manual work of the operating personnel. With that a much higher level of precaution with regard to occupational safety and health protection for the operator as an inherent property of this method. Compliance with the biological working substance tolerance values for Hg is therefore much easier for the operating personnel than it could have been under the conditions of the previous method with its manual handling and the high temperatures at practically atmospheric conditions in the furnace.

FIG. 1 shows a device for carrying out the method according to the invention.

It is a distillation apparatus 1 with a rotary atomizer 2. The jacket 3 of the distillation apparatus contains a rotating device 4 in the distillation apparatus. The distillation apparatus 1 has an operating medium space 5 for water vapor and operating medium spaces 6, 7 for hot oil as the heat transfer medium.

The device has a heat exchanger 8 for water heating. There is also an injection condenser 9, separator / decanter 10, washing column 11 and separator / decanter 12. The system has a vacuum pump 13 as well as an attachment and preheating container 14. A mill 15 for wet grinding, which is connected to a circulation pump 16, is used to prepare the material. Furthermore, there is a membrane pump 17. The distillation apparatus 1 is connected to a cooling device 18, which in turn is connected to discharge containers 19 and 20 from vacuum. In addition, there is a pneumatic conveying device 21 and a dipping tank 22 in a barometric height difference from the separator / decanter 10. The system also has circulation pumps 23 and 25 and coolers 24 and 26.

The name of the process media and equipment can be seen in the following table: A Feed containing mercury B Treated good, unquenched C. Exhaust gas G gas HG mercury HO Hot oil (heat transfer medium) KO condensate KW Cooling water KM Cold medium (refrigerant, cold water) PF Process fluid WA water WD Wasserdamf WF Washing liquid WW Hot water

List of reference numbers

• 1 still
• 2 rotary atomizers
• 3 jacket of the distillation apparatus
• 4 Rotating device in the distillation apparatus
• 5 Equipment room water vapor
• 6 Operating room for hot oil (heat transfer medium)
• 7 Operating room for hot oil (heat transfer medium)
• 8 heat exchanger hot water preparation
• 9 injection condenser
• 10 separators / decanter
• 11 washing column
• 12 separators / decanter
• 13 vacuum pump
• 14 neck and preheating container (2 times including items 15 to 17 for continuous loading of item 1)
• 15 grinder for wet grinding
• 16 circulation pump
• 17 diaphragm pump
• 18 cooling device
• 19 discharge container from vacuum
• 20 discharge containers from vacuum
• 21 Pneumatic conveyor
• 22 Immersion vessel in barometric height difference to item 10
• 23 circulation pump
• 24 coolers
• 25 circulation pump
• 26 cooler

Claims (24)

1. A process for the purification of mercury-containing substances or mixtures of substances by distillation and / or for the production thereof, characterized in that
that the feed material is injected into the distillation apparatus as a solid / liquid suspension or solution or is atomized or sprayed in it, preferably by a rotary atomizer. 2. The method according to claim 1
characterized,
that work is carried out at a pressure lower than 1 bar, at reduced pressure compared to atmospheric pressure or in a vacuum. 3. The method according to claims 1 to 2,
characterized,
that the feed material is moved. 4. Process according to claims 1-3,
characterized,
that the liquid phase begins to boil at lower temperatures than mercury. 5. The method according to claims 1 to 4,
characterized,
that the feed has a dry matter content ≦ (less than or equal to) 42% by weight, preferably 10 to 30% by weight. 6. The method according to claims 1 to 5,
characterized,
that the feed material has been warmed up so far before it is introduced into the distillation apparatus that it the temperature level is not lower than 10 K below the evaporation point of the earliest boiling liquid constituents of the suspension - calculated at the absolute pressure prevailing in the distillation apparatus - preferably at or above this temperature, but not higher than corresponds to a spontaneous evaporation of 10 of the liquid would relax to the pressure in the distillation apparatus. 7. The method according to claims 1 to 6,
characterized,
that a gaseous medium is introduced at the outlet end of the distillation apparatus in order to improve the mass transport for mercury as a trailing gas in the part of the distillation apparatus in which the suspension liquid has largely evaporated. 8. The method according to claims 1 to 7,
characterized,
that a wet grinding of the suspension is carried out before the same is used in the distillation apparatus in order to set an optimal particle size and particle size distribution. 9. The method according to claims 1 to 8,
characterized,
that the vaporized substances flow in countercurrent to the direction of travel of the feed material through the distillation apparatus. 10. The method according to claims 1 to 9,
characterized,
that at least two different temperature levels are selected for the operating rooms, adapted to the various process engineering tasks to be solved in the distillation apparatus. 11. The method according to claims 1 to 10,
characterized,
that it works at a low temperature level at the beginning of the conveying path of the feed material in the apparatus, preferably for the evaporation of the liquid phase of the suspension in the operating medium space (5), and
a higher temperature level downstream on the way of the feed material in the distillation apparatus in order to achieve the lowest possible residual mercury content in the feed material which leaves the distillation apparatus in the operating fluid space (6,7). 12. The method according to claims 1 to 11,
characterized,
that the feed material is thrown onto indirectly heated walls of the distillation apparatus and is mechanically scraped off again by the device (4) (thin-layer evaporation) before the formation of a thick layer, which would hinder the heat and mass transfer, in order to be downstream of the feed material from others Parts of the rotating device to be thrown back onto the inner wall of the distillation apparatus. 13. The method according to claims 1 to 12,
characterized,
that a fractional condensation is carried out with
- A first stage in indirect and / or direct heat exchange with one or more colder cooling media (apparatus (8,9)) and discharge of a first liquid phase from the remaining steam / gas flow in a separator for separating the mercury from the lighter liquid phase.
- And a second stage, designed as direct condensation in the heat and mass transfer with a liquid. 14. The method according to claims 1 to 13,
characterized,
that the second stage is designed as a washing column, preferably with a packed bed and the liquid phase is discharged via a separating vessel (12). 15. The method according to claims 1 to 14,
characterized,
that a substance is added to the washing liquid to selectively increase the absorption of mercury. 16. The method according to claims 1 to 15,
characterized,
that the direct condensation works at a temperature of the feed liquid at the top of the column (11), which is ≦ (less than or equal to) 6 ° C, and that the partial pressure of the mercury in the gases which are not condensed when leaving the column is greatly reduced . 17. The method according to claims 1 to 16,
characterized,
that the direct condensation stage is carried out in two stages with
a lower stage in which the circulating liquid is recooled by a cooling medium which has a flow temperature ≧ (greater than or equal to) 6 ° C,
- and a second stage in which the liquid applied is applied at a temperature ≦ (less than or equal to) 6 ° C. 18. The method according to claims 1 to 17,
characterized,
that it is used to regenerate activated carbon. 19. The method according to claims 1 to 18,
characterized,
that a washing effect is exerted on occurring and discharged gases or vapors. 20. Device for performing the method according to claims 1 to 19,
characterized,
that the distillation apparatus is designed as a cylindrical container so that the inside length is at least four times as large as the inside diameter, and consists of a fixed jacket (3)
- And a rotating device (4) inside the same
. for moving / promoting the feed material,
. as well as for scraping or scraping the latter off the inner wall of the distillation apparatus, for preventing the feed material from falling freely until the end of the apparatus after scraping with a vertical arrangement of the axis of rotation of the distillation apparatus,
. and bringing the feed material back into contact with the inner wall at another point. 21. The device according to claim 1 to 20,
characterized,
that the walls of the distillation apparatus are largely designed as double jackets or are equipped with pipe coils welded on the outside. 22. The device according to claims 1 to 21,
characterized,
that the outer wall of the distillation apparatus is equipped with at least two different operating rooms (5,6,7). 23. The device according to claims 1 to 22,
characterized,
that the lower temperature level is generated on the equipment side by condensing water vapor in the equipment room (5) at a pressure of 2 to 25 bar, preferably 10 to 12 bar, and the higher by heating the equipment rooms (6,7) with a heat transfer medium in the temperature range of 250 to 370 ° C, preferably 300 to 350 ° C. 24. The device according to claims 1 to 23,
characterized,
that the vacuum generating device (13), preferably a water ring pump, is arranged between the first and second condensation stages.

Images