DE102004025871A1 - Through-flow device for removing metallic mercury from a mercury-containing fluid comprises a surface region made from an amalgam-forming metal over which the fluid flows - Google Patents

Abstract

Through-flow device (10) comprises a surface region (12) made from an amalgam-forming metal selected from gold, silver, tin, copper, zinc, platinum, iridium and/or palladium over which the fluid flows. Partial regions of the surface region can be removed from the surface region after covering with mercury after removing mercury from the fluid stream and returning to the fluid stream (14). An independent claim is also included for a process for removing mercury from fluids containing mercury.

Description

object The invention relates to an apparatus and a method for continuous Mercury removal.

The 17th Federal Immission Control Ordinance (17th BImSchV), as well as the new EU directives (Air Quality Guideline 11/96, IVU and National Emission Limits NEC-RL) require a maximum mercury content in waste incineration plants (MVA) purified flue gas of 30 μg / Nm ³ as the daily average and 50 μg / Nm ³ as half-hour mean. In addition, there is a requirement that the highly volatile mercury, as the only heavy metal, must be continuously measured in the clean gas with a measuring instrument that is suitable for the 17th BImSchV. This compliance with the limit values does not pose a problem during normal operation of an incinerator. The measured values online generally fluctuate around 0-8 μg / Nm ³ . Even tips in the "normal" daily routine remain below the above limits.

• a) Nur kurze Zeit (1-2 min) vorher erfolgter, direkter Eintrag von quecksilberreichem Müll in die Verbrennung, wie z.B. Laborabfälle, Thermometer, Leuchtstoffröhren, Schütze älterer Bauart, alte, noch quecksilberhaltige Batterien und
• b) über längere Zeit akkumuliertes Quecksilber z.B. in Wandablagerungen im Nasswäscher der Rauchgasreinigungsanlage, ggf. auch in staubförmigen Wandablagerungen, das dann bei zufälligen oder gezielten Änderungen des chemischen Umfeldes (Redox-Potential, pH-Wert) plötzlich in größerem Umfang remobilisiert wird.

From time to time, however, higher mercury levels suddenly occur, which may then be several hours longer than the limit values in the peaks. This can lead to multi-day losses and thus to considerable financial damage to the operators of the affected plants. There are basically two reasons for high Hg concentrations in the purified waste gas of a waste incineration plant with trouble-free functioning flue gas cleaning:

• a) Only a short time (1-2 min) previously made, direct entry of mercury-rich waste in the incineration, such as laboratory waste, thermometers, fluorescent tubes, contactors of older design, old, still mercury-containing batteries and
• b) mercury accumulated over a prolonged period, for example in wall deposits in the wet scrubber of the flue gas cleaning plant, possibly also in dusty wall deposits, which is then suddenly remobilised to a greater extent in the case of random or targeted changes in the chemical environment (redox potential, pH value).

Independently of, from which source the acutely released mercury ultimately comes from, there is a demand from the operator for a sustainable Reduction of mercury emissions from the chimney of a waste incineration plant.

An amount of 200 g (equivalent to 14.7 cc ³ ) of released metallic mercury distributed over the period of, for example, 1 h in a typical flue gas volume flow of 62,000 Nm ³ / h after all means over this period averaged Hg value of 3226 μg / Nm ³ in the flue gas. A release in one minute even meant a peak of 194,000 μg / Nm ³ . Advantageously, takes place in the usual flue gas cleaning of waste incineration plants, a mercury reduction by an average of about 95-98%, so that remain of the above raw gas value at the fireplace in the best case still about 65 ug / Nm ³ . However, according to the abovementioned limit values, this means exceeding two half-hourly means according to the 17th BImSchV. Consequently, MVA operators are interested in a precipitation process for mercury from the flue gas, which acts primarily against peak values.

For the mercury removal from flue gases, there are a variety of methods, including the installation of activated carbon fixed bed filters, - air flow method, zeolite fixed bed filters, use of mercury-binding chemicals such as sodium tetrasulfide in the flue gas channel, TMT15 ^® (an organosulfide from Degussa ^® ) or Nalmet ^® (heavy metal remover from Nalco ^® ) For example, in the wet scrubber or adding highly oxidizing substances (peroxides, hypochlorite, H ₂ O ₂ , etc.), adding HCl or better HBr in the hot flue gas stream to form Cl ₂ or Br ₂ via the Deacon reaction. However, all these methods also entail more or less severe disadvantages, be it high investment costs and / or space requirements for additional large aggregates (fixed bed filters) or changes in the sensitive chemical balance in the flue gas cleaning. The result is increased emissions of other pollutants (eg SO ₂ ), corrosion, caking and the like.

Various Methods for the removal of mercury from waste water or exhaust gases are therefore already known. The majority of these processes become either discontinuous or semi-continuously carried out in that apparatuses for discontinuous Removal of mercury can be used in parallel, with a Part of the apparatus Mercury from the fluid stream to be cleaned removed and another part of the equipment is regenerated, and, if a certain saturation the former is given to the apparatus, the fluid flow through the regenerated Equipment is diverted while then those saturated with mercury Apparatus be regenerated. In a variety of procedures Mercury removal from fluid streams becomes particulate filters used, for example, in the form of fixed bed filters. This Process or the washing of exhaust gases with liquids mean often a significant flow resistance in the purification of mercury-containing fluids.

US 5,437,797 A describes a process for the removal of organically or inorganically bound mercury from the effluents of a vaccine production facility with the aid of activated carbon filters and filters containing chelating resins. The described method can neither remove metallic mercury from the wastewater, nor be operated continuously for a long period of time, since the filters used must be replaced at regular intervals.

WHERE 00/78463 A1 describes a composition and a method for Conditioning of exhaust gases. The described method is used above all for removal of monovalent solid organometallic particles from the gas stream. The method is not suitable for removal of metallic mercury and is mainly used for removal of used organic sodium compounds.

The US 5,989,506 A and US 5,354,357 A each describe a semi-continuous process for removing mercury from fluid streams. In both methods, at least two filters are used, with one of the filters removing mercury from the fluid to be cleaned while the other filter is being regenerated. In one of the methods, fixed bed filters are used, while in the other described method, washing is done with liquids. Due to the nature of these filter methods, a significant flow resistance is opposed to the process fluid. This is especially clear that at least in the case of fixed bed a pump is necessary. In the aforementioned processes, the process flow becomes relatively complex in that the process fluid has to be regularly diverted from one filter to the other filter.

WHERE 97/25612 A1 describes a method and a device for monitoring of mercury emissions.

US 5,409,522 A describes an apparatus and method for removing mercury from a gas stream. The process described is discontinuous and results in system downtime, since the collecting surface used for mercury often has to be regenerated as a whole.

In the "FGD and DeNOx newsletter N ° 297 "from January 2003 becomes a discontinuous process for the removal of mercury described from exhaust gases. Mercury is used on gold surfaces as an amalgam deposited. These surfaces then have to be replaced in the form of a cartridge or regenerated in situ become.

US 6,695,894 B2 describes an apparatus and method for continuously removing mercury from an exhaust stream. In the described method, the substrates for the removal of mercury are arranged rigidly in the exhaust gas stream and can not be removed from it individually and can not be moved. The exhaust stream is kept away from the substrates by flow dampers or valves and the substrates are regenerated at their place in the exhaust passage. Alternatively, the use of cartridges of substrates that can be replaced is described. However, for this purpose, the operation of the device for the period of replacement must be set.

It Therefore, the object of the present invention is a device and a method for the continuous removal of metallic mercury from a mercury-containing fluid to provide, wherein the flow resistance for the as possible to clean the fluid should be low and where it is for a continuous operation should not be necessary, that too purifying mercury-containing fluid by more than one mercury absorber or filter to lead.

The above object is achieved in a first embodiment by a flow device 10 for removal of metallic mercury 48 from a mercury-containing fluid 14 comprising one with the fluid 14 flowed surface area 12 , characterized in that the surface area 12 an amalgam-forming metal selected from the group consisting of gold, silver, tin, copper, zinc, platinum, iridium and palladium, their alloys or mixtures with other metals, and subregions of the surface region 12 after mercury has been applied to remove the mercury from the surface area 12 from the fluid stream 14 removable and into the fluid stream 14 are traceable.

The surface area 12 may also consist entirely of the amalgam-forming metal.

This causes a portion of the surface area 12 from the fluid stream 14 removable and into the fluid stream 14 is traceable, is a continuous removal of metallic mercury 48 with a single surface area 12 possible.

This flow device 10 utilizes the well known tendency of mercury to alloy with other metals, forming so-called amalgams. The material, the one with the fluid 14 flowed surface area 12 contains, is preferably a metal, since metals are mechanical loads against mostly less sensitive than, for example, ceramics or plastics, which is why the surface area 12 structure may be constructed of particularly thin structures. Thereby In turn, the weight and flow resistance for the mercury-containing fluid can be reduced. Metals which form stable alloys with the abovementioned amalgam-forming metals are preferably used, since this provides a good support for the amalgam-forming metals and permits long-term stable, non-flaking metallization with the amalgam-forming metals.

The flow-through device preferably comprises 10 a heating device 22 a portion of the surface area 12 to remove the mercury 48 from the surface area 12 , At least part of the surface area 12 can through the heater 22 be heated with a heating medium, so that the mercury 48 is released from the amalgam compound and can be collected.

The surface area 12 contains gold or is advantageously made of gold. To ensure a good amalgam formation, the surface of the amalgam former should be metallic bright and have no oxide or corrosion layer. Because of its corrosion resistance, gold is particularly suitable as an amalgam former. It also has the advantage of forming up to 150 ° C thermally stable amalgams, which are characterized by a very high affinity between gold and mercury. For this reason, the amalgam process has also been widely used in the recent past to obtain gold flakes from ores containing precious metals. Common mercury gauges also exploit this effect by accumulating minute amounts of mercury on a so-called gold trap in order to expel and measure it only after sufficient enrichment. The formation of amalgam is so intense that virtually no metallic mercury is detectable after the gold trap. Ionic mercury, on the other hand, is allowed to pass through unhindered. The ionic mercury content can according to the invention, for example, with a scrubber from the mercury-containing fluid stream 14 be removed. If a small proportion of ionic mercury (Hg ⁺ , Hg ²⁺ ) reaches the device, it can be reduced to metallic mercury (Hg) by spraying minute amounts of a reducing agent. For example, SnCl ₂ and / or NaBH ₄ can be used here as the reducing agent. The surface area of gold and / or gold 12 may be in the form of an extremely thin gold film whose layer thickness varies, for example, in a range of 0.1 - 1 microns, since the mercury diffuses into the gold very slowly. How much mercury can absorb the gold depends strongly on the surface supply. The use of gold selectively removes metallic mercury from the mercury-containing fluid 14 which is difficult or impossible to separate with other methods. The gold can continue to recover after dismantling the plant.

following the invention with reference to preferred embodiments with reference to the attached drawings closer explained.

It demonstrate:

1 : Schematic side view of the flow device 10 .

2 : A schematic top view of the surface area in the flow-through device 10 .

3 : Schematic test arrangement for the removal of mercury from exhaust gases of a waste incineration plant.

1 shows that the flow-through device according to the invention 10 a surface area 12 comprising a mercury-containing fluid 14 is streamed and so around an axis 16 rotatably arranged, that the surface area 12 from the fluid stream 14 removable and into the fluid stream 14 is traceable. At least part of the surface area 12 is in a regeneration area 18 arranged, which is a housing 20 and a heater 22 having. The housing 20 is at its top by a gas inlet 24 with a gas pipe 26 connected by the inert gas 28 in the regeneration area 18 can be initiated. The inert gas 28 This is achieved by a valve or mass flow controller 30 and a heat exchanger 32 passed to temperature (for example 200 to 250 ° C) and mass flow of the inert gas 28 to be able to regulate. The inert gas 28 will be at the top of the case 20 of the regeneration area 18 through a gas outlet 34 through the gas line 36 in a cooling spiral 38 passed, located in a cooler 40 located. This cooling device is equipped with a cooling medium 42 equipped. At the foot of the cooling spiral 38 becomes the inert gas 28 at the junction 44 through the gas line 46 fed back to the mercury-containing fluid. The condensed metallic mercury 48 becomes at the junction 44 through the pipe 50 in a collection container 52 directed. The flow device 10 is here above all other cleaning devices of the exhaust gases in the fireplace 54 built-in. The flow device 10 but can also be placed elsewhere, preferably in purified flue gas. The surface area 12 can be a height 56 in the range of 0.5 to 1.5 m.

The semicircular area to the left of line 16-16 becomes here flue gas flows through, as in 2 is shown.

3 shows the experimental setup 60 , which has been shown that even a simple gold-plated knitted fabric 62 that in the exhaust stream 64 inside a fireplace 66 was installed, sufficient, the mercury content of the exhaust stream 64 to effectively reduce even at peak loads. To do this, the mercury content was measured using a mercury meter 68 before reaching the gilded wire mesh 62 measured and with another mercury meter 70 was the mercury content of the exhaust gas in the gilded wire mesh 62 measured. This was the exhaust gas 64 through a heated tee 72 and a heated sample gas line 74 into the mercury meter 70 guided. The knitted fabric 62 discharged exhaust gas 64 was continued through an insulated hose line 76 a fan 78 fed and by a Float flowmeter 80 and a manual valve for fine adjustment of the volume flow 82 again the exhaust gas flow 64 fed. The principle of mercury removal with gold from the waste gas of a waste incineration plant works very well 4 clearly in which the mercury content in μg / Nm ³ is plotted against time. It was the experimental design as in 3 used. The curve 90 shows the original mercury content of the exhaust gases 64 measured with the mercury meter 68 , The curve 92 shows the mercury content in the exhaust stream 64 inside the wire mesh pack 62 measured by the mercury meter 70 , By using catalysts, a permanent depletion of the mercury content up to the detection limit can be achieved.

In a particularly preferred embodiment, the surface area is located 12 partially in contact with the flow-through fluid 14 and is partly in a regeneration area 18 to remove the mercury 48 from the surface area 12 arranged. By this constellation can work with only one surface area 12 continuously mercury 48 from the fluid stream 14 be removed.

In a further preferred embodiment, the surface area 12 the flow device 10 around an axis 16 rotatable, more preferably the axis of rotation 16 substantially parallel to the flow direction of the fluid 14 is aligned. This allows the surface area 12 be rotated so that always part of the surface area 12 from a mercury-containing fluid 14 is impinged and another part of the surface area 12 in a regeneration area 18 to remove the mercury 48 located. In this regeneration area 18 is preferably a heater 22 with which as an amalgam on the surface area 12 bound mercury 48 can be removed and removed.

Advantageously, the surface area 12 the outer shape of a heat exchanger or a catalytic converter. Due to the honeycomb shape of the catalytic converter or the nature of a heat exchanger ensures that the flowing mercury-containing fluid 14 with the surface area 12 has the greatest possible contact. This expressly nature and shape similar embodiments are included to a heat exchanger or an exhaust gas catalyst. Particularly advantageous is a surface area 12 in the form of a Ljungström generator as standard for air preheating in coal power plants. The surface area in this case may be configured in the external form like a catalyst honeycomb package and integrated on a large turntable which is either very slow (in the range of one full turn per week or per month) continuously about an axis 16 rotates, or if rapid regeneration is required, if necessary, rotated by half a turn at a time. While part of the turntable and thus the surface area 12 from the mercury-containing fluid 14 is impinged, is another part of the turntable and thus the surface area 12 in a regeneration area to remove the mercury 48 from the surface area 12 , As the surface area 12 , which may be configured as a catalyst honeycomb pack, for reasons of residence time and pressure loss at speeds of 3 to 6m / sec. should be flowed through, a widening of the flow channel 54 of the fluid 14 to be required. In order to lower mercury peak emission values to 1/10, in most cases even less than 1/20, of their original value, the surface area should be affected 12 have a particularly streamlined shape. In addition to the outer forms of a heat exchanger or an exhaust gas catalytic converter, this can also be any other network, tube or honeycomb structure or also a wire mesh pack. A structure that seems particularly suitable to cause the lowest possible pressure loss or flow resistance (Δp <10mbar), is a catalyst honeycomb package as it is used in the automotive industry. This can be in the flow direction of the fluid aligned to a package bound tube, 6-corner honeycomb, 4-corner - or 3-corner structures. Since the lanes thus formed are flowed through smoothly, the pressure loss is low and the surface increased as much as is technically possible. Thus, the largest possible specific surface, for example, 2100 m ² / m ³ total package volume at a pressure drop of 4.2 mbar for mercury deposition made available who the.

Particularly preferred is the surface area 12 at least partially against the flow direction of the fluid 14 inclined. As a result, on the one hand, the contact of the flowing mercury-containing fluid 14 with the surface area 12 on the other hand, a rotatably arranged surface area 12 through the flow of the fluid 14 be rotated and thus driven.

• a) Anströmen eines Teilbereichs eines Oberflächenbereichs 12 mit dem quecksilberhaltigen Fluid 14 unter Amalgambildung auf dem Teilbereich, der ein Amalgam-bildendes Metall, ausgewählt aus der Gruppe Gold, Silber, Zinn, Kupfer, Zink, Platin, Iridium und Palladium, deren Legierungen oder Mischungen mit anderen Metallen enthält,
• b) kontinuierliches Entfernen der Teilbereiche 12 aus dem Fluidstrom 14,
• c) Entfernen des Quecksilbers 48 von dem Teilbereich 12,
• d) kontinuierliche Rückführung der quecksilberfreien Teilbereiche 12 in den Fluidstrom 14.

The aforementioned problem of the underlying invention is solved in a further embodiment by a method for removing mercury 48 from mercury-containing fluids 14 characterized by the method steps

• a) Influx of a portion of a surface area 12 with the mercury-containing fluid 14 amalgamation on the portion containing an amalgam-forming metal selected from the group consisting of gold, silver, tin, copper, zinc, platinum, iridium and palladium, their alloys or mixtures with other metals,
• b) continuous removal of the subregions 12 from the fluid stream 14 .
• c) removing the mercury 48 from the subarea 12 .
• d) continuous recycling of the mercury-free subregions 12 in the fluid stream 14 ,

Preferably, the fluid used 14 here a temperature in the range between 80 and 140 ° C and is essentially free of dust, which is on the surface area 12 could accumulate and thus hinder the formation of gold amalgam. A temperature above 150 ° C could cause the mercury bound as amalgam to be released. Also liquid water or other condensates in a gaseous fluid 14 The amalgam formation could be due to precipitation on the surface area 12 hinder. Therefore, it is particularly preferred if an inserted gaseous fluid 14 does not contain any liquid water or other condensates. Preferably, in step b) the subareas of the surface area 12 removed at least at the speed at which the amalgam-forming metal of the surface area 12 can be nearly saturated with mercury. This can be determined by the detection of mercury emission peaks with a mercury meter, which is the mercury content of the fluid 14 after flowing through the flow device 10 measures. mercury 48 can be recovered with the above-mentioned process in at least 99.9% purity. In contrast to other mercury removal processes, the process according to the invention does not involve the consumption of additional substances, for example HCl. Also, the method of the invention does not affect the other methods of cleaning the fluid practically.

Preference is given as a fluid 14 Wastewater or waste gas from power plants, oil or chemical refineries, incinerators, metal processing plants or thermal treatment plants in particular waste gas from waste incineration plants used. Especially with waste gases from waste incineration plants, a high efficiency of the process according to the invention was observed.

It is particularly preferable to use a surface area 12 one made of gold or containing gold. Gold surface areas 12 theoretically as often as the mercury-containing fluid 14 be exposed because gold practically does not consume, provided no mechanical abrasion or overheating occurs. A roughening of the surface over time would even benefit the absorption effect.

In a last preferred embodiment, the method according to the invention is characterized in that the mercury is present on the surface areas 12 removed by heating. The regeneration of a mercury-laden surface area 12 For example, by heating, preferably at a temperature in the range of 200 to 250 ° C, but not above the boiling point of mercury of 357 ° C. The resulting mercury gas can by means of a preheated inert gas stream 28 expelled and / or sucked off. The inert gas 28 may be, for example, nitrogen, argon or carbon dioxide, preferably nitrogen. The mercury-containing inert gas stream can pass through a cold trap 40 be directed, taking the mercury 48 in a temperature range of at least -38.8 ° C (melting point of mercury) and about 80 ° C is condensed out. The mercury-liberated inert gas can then be the fluid 14 be mixed, or recirculated via a blower and fed back into the process. After heating the mercury 48 from the surface area 12 Again, this is essentially mercury-free and can be re-introduced into the mercury-containing gas 14 to remove mercury.

Claims (11)

Flow device ( 10 ) for removing metallic mercury from a mercury-containing fluid, comprising a surface area ( 12 ), characterized in that the surface area ( 12 ) an amalgam-forming metal selected from the group gold, silver, tin, copper, zinc, platinum, iridium and palladium, their alloys or mixtures with other metals, and subregions of the upper area ( 12 after mercury occupancy to remove mercury from the surface area ( 12 ) are removable from the fluid flow and are traceable in the fluid flow. Contraption ( 10 ) according to claim 1 comprising a heating device ( 22 ) of a portion of the surface area ( 12 ) for removing the mercury from the surface area ( 12 ). Contraption ( 10 ) according to claim 1 or 2, characterized in that the surface area ( 12 ) consists of gold. Contraption ( 10 ) according to one of claims 1 to 3, characterized in that the surface area ( 12 ) partially in contact with the flow-through fluid ( 14 ) and partially in a regeneration area ( 18 ) for removing the mercury from the surface area ( 12 ) is arranged. Contraption ( 10 ) according to one of claims 1 to 4, characterized in that the surface area ( 12 ) about an axis ( 16 ) is rotatable, in particular the axis of rotation ( 16 ) substantially parallel to the flow direction of the fluid ( 14 ) is aligned. Contraption ( 10 ) according to one of claims 1 to 5, characterized in that the surface area ( 12 ) has the outer shape of a heat exchanger or a catalytic converter. Contraption ( 10 ) according to one of claims 5 to 6, characterized in that the surface area ( 12 ) at least partially against the flow direction of the fluid ( 14 ) is inclined. Method for removing mercury from mercury-containing fluids ( 14 ) characterized by the method steps a) influx of a portion of a surface area ( 12 ) with the mercury-containing fluid ( 14 ) with amalgam formation on the subregion ( 12 ) containing an amalgam-forming metal selected from the group gold, silver, tin, copper, zinc, platinum, iridium and palladium, their alloys or mixtures with other metals, b) continuous removal of the subregions ( 12 ) from the fluid stream, c) removing the mercury from the subregion ( 12 ), d) continuous recycling of the mercury-free subregions ( 12 ) in the fluid stream ( 14 ). Process according to claim 8, characterized in that as fluid ( 14 ) Wastewater or waste gas from power plants, oil or chemical refineries, incinerators, metalworking companies or thermal treatment plants in particular waste gas from waste incineration plants begins. Process according to claim 8 or 9, characterized in that a surface area ( 12 ), which consists of gold or contains gold. Process according to one of Claims 8 to 10, characterized in that the mercury is applied to the surface areas ( 12 ) removed by heating.