CA1340230C - Process for removing heavy metal compounds from the filtrer dust from trash incinerators, flue gas dust precipitators and gas-cleaning units - Google Patents
Process for removing heavy metal compounds from the filtrer dust from trash incinerators, flue gas dust precipitators and gas-cleaning unitsInfo
- Publication number
- CA1340230C CA1340230C CA 571902 CA571902A CA1340230C CA 1340230 C CA1340230 C CA 1340230C CA 571902 CA571902 CA 571902 CA 571902 A CA571902 A CA 571902A CA 1340230 C CA1340230 C CA 1340230C
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- CA
- Canada
- Prior art keywords
- dust
- heavy metal
- metal compounds
- gas
- filter dust
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D7/00—Sublimation
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/34—Chemical or biological purification of waste gases
- B01D53/46—Removing components of defined structure
- B01D53/64—Heavy metals or compounds thereof, e.g. mercury
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B09—DISPOSAL OF SOLID WASTE; RECLAMATION OF CONTAMINATED SOIL
- B09B—DISPOSAL OF SOLID WASTE
- B09B3/00—Destroying solid waste or transforming solid waste into something useful or harmless
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
- C22B5/00—General methods of reducing to metals
- C22B5/02—Dry methods smelting of sulfides or formation of mattes
- C22B5/16—Dry methods smelting of sulfides or formation of mattes with volatilisation or condensation of the metal being produced
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
- C22B7/00—Working up raw materials other than ores, e.g. scrap, to produce non-ferrous metals and compounds thereof; Methods of a general interest or applied to the winning of more than two metals
- C22B7/02—Working-up flue dust
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
- Y02P10/20—Recycling
Abstract
The invention is concerned with a process for removing heavy metals and/or heavy metal compounds from the filter dust of refuse incinerators, flue gas dust precipitators and gas-cleaning units, in which the filter dust is heated in a reaction vessel at least up to the vaporisation temperature of the heavy metals and/or heavy metal compounds which are to be removed, the vaporised heavy metals and/or heavy metal compounds are then quenched in a cooler and converted to a liquid or solid state, and removed. The process of the invention is characterized in that before the vaporization of the heavy metals and/or heavy metal compounds to be removed, superfine dust particles with a particle size smaller than 5µm are separated in a cold state from the filter dust by mechanical, hydraulic or pneumatic means or by filtration, and the remaining filter dust fraction is fed to the reaction vessel.
Description
13~0230 DESCRIPTION
TITLE OF THE INVENTION Process for removing heavy metal compounds from the filter dust from trash ;ncinerators, flue gas dust precipitators and gas-cleaning units GACKGROUND Of THE INVENTION
Field of the Invention Processing of pulverulent residues laden ~ith pollutants and originating in most cases from combustion processes. Dust precipitation and gas cleaning have g?ined importance in conjunction ~ith regulations for protection of the environment. As a result, more stringent demands have to be met also by the associated further process;ng and storage of the pollutants and their carriers.
The invention relates to the further development, improvement and simplification of the separation of pol-lutants, vhich have to be treated separately, from a com-lex particle mixture arising in combustion processes.
In particular, it relates to a process for removing heavy metal compounds from the filter dust from trash in-cinerators, flue gas dust precipitators and gas-cleaning units by vaporisation, separation and subsequent conden-sation and/or sublimation of the heavy metal compounds.
Discussion of background Filter dust from industrial combustion installa-tions, specifically electrostatic precipitator dust, hasa high content of harmful substances ~hich contaminate the surroundings, pollute the environment and in some cases are toxic. These include certain organic compounds and above all heavy metal compounds, for example of the elements Pb, Zn, Cd, Tl and Cu. Special regulations therefore apply to such mixtures, and the filter dust must be regarded and treated as special waste.
At present, the treatment is carried out in accordance with 3 principles:
- Agglomeration and compaction of the dust to give larger pieces by means of binders such as cement, asphalt and the like. This is followed by final deposition in a dump [cf."Behandlung und Verfest-igung von Ruckstanden aus Kehrichtverbrennungs-anlagen (Treatment and solidification of residues from trash incinerators]" Schriftenreihe Umwelt-schutz [Protection of the Environment Publica-tions] No. 62, Bundesamt fur Umweltschutz [Federal office of the environment], Berne 1987). In this case, a product is formed, the mass of which is greater than that of the loose starting material.
Final deposition is therefore expensive and raises problems because the space available is in most cases restricted.
- Chemical treatment with acids. The heavy metal compounds are leached out with aqueous acids. The heavy metal-free residue is deposited in a dump and the acid solutions containing heavy metals are processed further (cf. H. Vogg "Rauchgas-reinigungsverfahren [Flue gas cleaning processes]", paper read at the VDI seminar 43.32.02 "Abfallbe-handlung und -verwertung durch Mullverbrennung [Waste treatment and utilization by trash incineration]" VDI, Dusseldorf 1986). These leaching processes are not true solutions of the waste problem, but merely shift it to a different plane. The further treatment of the heavy metal-containing solutions and their concentration - 2a - 1~230 involves considerable consumption of energy. New problems (effluent, pollution of the environment) are created.
- Thermomechanical separation by heating of the dust laden with heavy metals in a gas stream, vaporization of the heavy metal compounds and mechanical separation of the solid suspended particles from the gas phase at . .. . .
13~0230 high temperatures (hot-gas cyclone, hot-gas filter, etc.). The heavy metal vapors are then condensed in a cooler (cf. W. Weissweiler et al, "Anreicherung von Thallium-und Bleihalogeniden [Concentrating of thallium and lead halides]", Staub, Reinhaltung der Luft, volume 46, No. 3, pages 120-124, March 1986).
The hot-gas separators (cyclones, electrostatic precipitators, ceramic honeycomb filters, etc.) must operate isothermally at high temperatures (1000~C
and higher), which makes severe demands on their design and their operation. Moreover, separation of the fine dust (less than lum particle diameter), which is disproportionately important as a carrier of the heavy metal compounds in percentage terms, can hardly be accomplished by economical means.
SUMMARY OF THE INVENTION
Accordingly, one object of this invention is to provide a novel process for removing heavy metal compounds from the filter dust from combustion plants of any type, which process, while utilizing the principle of vaporization and subsequent conden-sation, avoids the difficult and extensive mechani-cal separation of pollutant vapor and dust particles at high temperatures (hot-gas filtration, hot-gas separation) and as far as possible suppresses a later reattachment of the condensed pollutants to the fine dust particles. The process should be sim-ple and ensure the most economical individual further processing of the various separated products for final deposition.
In accordance with the present invention, there is thus provided a process for removing heavy metals and/or heavy metal compounds from the filter dust of refuse incinerators, flue gas dust precipit-ators and gas-cleaning units, in which the filter . _ _ . . . . .. . -- . . . . .. . .
- 3a -'~- 1340230 dust is heated in a reaction vessel at least up to the vaporization temperature of the heavy metals and/or heavy metal compounds which are to be removed, the vaporized heavy metals and/or heavy metal compounds are then quenched in a cooler and converted to a liquid or solid state, and removed.
The process of the invention is characterized in that before the vaporization of the heavy metals and/or heavy metal compounds to be removed, superfine dust particles with a particle size smaller than 5~m are separated in a cold state from the filter dust by mechanical, hydraulic or pneumatic means or by filtration, and the remaining filter dust fraction is fed to the reaction vessel.
BRIEF DESCRIPTION OF THE DRAWINGS
A more complete appreciation of the invention and many of the attendant advantages thereof will be 134023~
readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:
Figure 1 shows a flow diagram of a discontinuous process for removing heavy metal compounds by means of a carrier gas;
Figure 2 shows a diagrammatic illustration of equipment for discontinuous removal of heavy metal compounds;
Figure 3 shows a flow diagram of a continuous process for the removal of heavy metal compounds by means of a carrier gas;
Figure 4 shows a flow diagram of a discontinuous process for the removal of heavy metal compounds with application of reduced pressure, and Figure 5 shows a flow diagram of any desired process for the removal of heavy metal compounds by separating the fine dust off beforehand by means of a carrier gas.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, Figure 1 shows the flow diagram of a discontinuous process, operating batchwise, for removing heavy metal compounds from filter dusts by means of a fluidizing carrier gas. 1 is the raw dust supply, indicated by an arrow, to the dust silo 2 which is closed at the bottom by a periodically operable gate valve 3 for solids. 4 is a reaction vessel for high temperatures (about 1000~C, sometimes even higher) which is provided with heat insulation 5 (if appropriate, with additional heating 24, cf. Figure 2) and which contains a sieve tray 6 ~displaceable) in its interior at the lower end. In operation, a fluidized layer 7 (fluidized bed, fluid bed) is generated above ~ 1~230 - 4a -the sieve tray 6 (indicated by arrows). The lower, conical end of the reaction vessel 4 is connected via a gate valve 3 to a tank 8 which is to receive the purified dust. 9 represents the fresh -13~0230 carrier gas (inlet indicated by an arro~). 10 is a fan for conveying the carrier gas 9, and 11 is a corresponding gas isolation valve. 12 represents a heater tup to about 1200~C) for the gas stream partially laden ~ith particles. This heater 1Z is advantageously provided ~ith a contro~ system, since it largely determines the thermo-dynamics in the reaction vessel 4. 13 is a cooler sur-rounded by a cooling jacket 14 and having a greater length as compared ~ith the cross-section. The coolant 15 (in most cases water) enters at one end of the cooling jacket 14 and leaves at the other end (indicated by arro~s). 16 represents the circulating gas ~hich still contains cer-tain fractions of dust particles held in suspension. 17 is the circulation pump (fan) and 18 is the preheater (up to about 800~C) for the circulating gas 16. 19 is a tank ~hich is to receive the heavy metal compounds and ~hich is connected via the discontinuously operable gate valve 3 to the lo~er conical end of the cooler 13.
Figure 2 relates to a diagrammatic representation of equipment for the discontinuous removal of heavy metal compounds from filter dusts by processes according to ~
Figure 1. 3 are the conventional, discontinuously (batch-~ise) operable gate valves for solids and 4 is the reac-tion vessel for high temperatures, ~hich is provided with a heater 24 and heat insulation 5 in the form of approp-riate casings. 6 represents a sieve tray which is here designed as a t~in tray ~ith a laterally disp~aceable lover part (indicated by double arro~). The gas stream can be regulated in this ~ay. After the batch has been completed, the reaction vessel 4 can be partially opened for discharging the purified dust. 7 is the fluidized bed marked by arro~s. 25 is the ra~ dust feed uhich takes place in the upper part of the reaction vessel 4 through a central pipe. 21 is the carrier gas, 22 is its feed line, 23 is the blast box of the reaction vessel 4, 16 is the circulating gas taken from the cooler 13, and 14 is the cooling jacket through ~hich the coolant 15 flo~s.
It must be ensured that the cooler 13 is connected to the reaction vessel 4 by a line ~hich is as short as possible.
.. ~ . .. . .. , . . .. ... ., . ~
in practice, the former immediately adjoins the latter, so that there is no undesired condensation of the vapors of the heavy metal compounds in the connecting line. For the sake of clarity, 4 and 13 are shown separately in the drawing.
Figure 3 shows a flow diagram of a continuous process for removing heavy metal compounds from filter dusts by means of a fluidizing carrier gas. The reference numerals 1, 2, 3, 8 and 19 and their meanings correspond exactly to those of Figure 1. 9 is the fresh carrier gas which is delivered by the fan 10 and is passed via the valve 27 and the heater 12 into the reaction vessel 4 provided with the heat insulation 5.
The valve 27 can be designed as a non-return valve, differential valve or a controlled or regulated valve.
The lower end of the reaction vessel 4 is directly adjoined by the cooler 13 which is surrounded by the cooling jacket 14 and is of very slender design. Water is used in most cases as the coolant 15. 28 represents the additives feed which may be necessary or desirable.
These can have a physical or chemical action. In most cases, they are materials which lower the vaporization temperature, such as metal halides, NH4Cl, etc. or reducing agents such as C, CO, etc.
Figure 4 shows a flow diagram of a discontinuous process for removing heavy metal compounds from filter dusts by the application of reduced pressure ("vacuum").
The reference numerals 1, 2, 3, 8 and 19 correspond exactly to those of Figure 1. The reaction vessel 4, provided with a heater 24 (up to about 1200~C) and a heat insulation 5, has at the lower end a conical part, is designed to be vacuum-tight and can be sealed from the surroundings by vacuum-tight gate valves 3. The reaction vessel 4 is connected via a short duct directly to the vacuum-tight cooler 13 which is provided with a cooling jacket 14 (coolant 15) and which can be - 6a -connected from time to time via the likewise vacuum-tight gate valve 3 to the heavy metal compounds tank 19.
At the upper outlet of the cooler 13, there is a vacuum-tight three-way valve 29, whose normal operating position (as drawn) is such that it opens ~ 13~0230 the ~ay from the cooler 13 via a filter 30 (fine filter) to a vacuum pump 3Z. The filter 30 is connected to a fine dust ~filter dust) tank 31. From time to time, a temor-ary air feed 33 (dashed arrow) for flooding the unit can be effected via the three-~ay valve,29.
Figure S relates to a flow diagram of any desired process for the removal of heavy metal compounds from filter dusts by separating the fine dust off beforehand by means of a carrier gas. 1 is the ra~ dust supply to the dust silo 2 which is connected by a pipe to a m;xer 34. 9 is the carrier gas ~hich is delivered by the fan 10 into the mixer 34. In the latter, intense turbulence and fluidization of the dust particles takes place. The fluidized gas/dust mixture passes into the separator 35 ~here the coarser fraction (in the present case of parti-cle diameter > S ~m) is separated off as dust 36 and pas-sed into a unit 37 (for example according to Figures 1 to 4) for removing heavy metal compounds. The separator ~ 35 can consist of a filter (for example an electro-I Z0 static precipitator) or of a cyclone. Carrier gas ~
_ dust (finer fraction of a particle diameter of < S ~m)'38leave the separator 35 and are delivered to the unit 39 for further processing. This can in principle consist of a trash incinerator, a fine filter or a scrubber.
Embodiment example 1:
See Figures 1 and 2.
In a small pilot unit for batch~ise operation, filter dust from a trash incinerator ~as treated. The re-action vessel 4, consisting of a ceramic material and pro-vided vith a sieve tray 6, had a cylindrical shape. Itsinternal diameter ~as 50 mm and its height (internal, cylindrical part) ~as 200 mm. The cooler 13 consisted of a double-~alled pipe of stainless steel, having an inter-nal diameter of 10 mm and a length of 1000 mm. ~ater flo~ed as the coolant through the cooling jacket 14.
The filter dust contains inter alia, the following metals:
~ , . . ..
Ca: 11.5 wt.%
Cu: 0.09 wt.%
Zn: 3.3 wt.%
Pb: 0.8 wt.%
Cd: 0.05 wt.%
Sn: 0.34 wt.%
Sb: 0.16 wt.%
Ba: 0.34 wt.%
The reaction vessel 4 was charged with 10 g of filter dust and heated to a temperature of 1000~C. At this temperature, the dust was fluidized by means of a stream of nitrogen as the carrier gas 9 and held in suspension in the fluidized bed 7. The major part of the heavy metal compounds vaporized in the reaction vessel 4 and was continuously condensed in the cooler 13. The precipitated metal salts were here only slightly contaminated by superfine parti-cles entrained by the gas stream. After 1 hour, the process was complete and the reaction vessel 4 was cooled. The filter dust was analyzed before and after the thermal separation of the heavy metal com-pounds. This gave the following picture:
Before After separation separation Total quantity 10.0 g 8.0 g Zn content 3.3 wt.% 0.3 wt.%
Pb content 0.8 wt.% 0.4 wt.%
Cd content 0.05 wt.% 0.005 wt.
Moreover, samples of the filter dust before and after thermal separation were leached with CO2-saturated water and the solutions thus obtained were examined for their heavy metal ion content:
Heavy metal Before After separation separation (mg/l of solution) (mg/l of solution) zn2+ 1600 63 1~023~
pb2+ 13 7.8 Cd2+ 37 2.4 Embodiment example 2:
See Figures 1 and 2.
In a pilot unit, filter dust from a trash incinerator was treated similarly as in example 1.
The unit was of similar structure as in example 1, but had greater dimensions.
The reaction vessel 4 was charged with 1000 g of filter dust and held at a temperature of 1000~C for 3 hours. Instead of nitrogen, the acid off-gas of a trash incinerator was used as the carrier gas 9. After the charge had been completed, the reaction vessel was cooled and the residue was examined. The result was as follows:
Before After Analyzed separation separation total quantity 10.0 g 8.2 g Zn content 3.3 wt.% 0.02 wt.%
20 Pb content 0.8 wt.% 0.3 wt.%
Cd content 0.05 wt.% 0.003 wt.%
In addition, samples of the filter dust before and thermal separation were leached with CO2-saturated water, and the solutions thus obtained were examined for their heavy metal ion content:
Heavy metal Before After separation separation (mg/l of solution) (mg/l of solution) zn2+ 1600 1.3 Pb2+ 13 2 Cd2+ 37 < 1 This shows that it was possible, by using a chemically active gas instead of the largely inert nitrogen, to achieve a better yield of heavy metal removal from the filter dust.
Embodiment example 3:
See Figure 3.
- lO- 13~02~0 In a pilot unit for continuous operation, filter dust from a trash incinerator was processed.
The reaction vessel 4 consisted of refractory ceramic material and had a casing-like heat insula-tion 5 consisting likewise of ceramic material andglass wool. The cylindrical interior had a diameter of 100 mm and a height of 500 mm. The cooler 13, provided with a cooling jacket 14 carrying a water flow, was of cylindrical shape and had an internal diameter of 20 mm and a height of 1600 mm.
The filter dust was injected continuously into the reaction vessel 4 and fluidized by carrier gas 9 preheated to 1400~C (heater 12). Analogously to example 2, the carrier gas consisted of acid off-gas from a trash incinerator. In addition, 5 wt.% ofNH4Cl, relative to the quantity of the filter dust, was injected as additive (25) into the reaction vessel 4. The throughput of filter dust was about l g/second, and that of carrier gas was about l dm3/second, relative to the standard state. This gave a flow velocity of about 0.55 m/second in the reaction vessel 4 at a temperature of 1000~C, and a flow velocity of about 12.5 m/second at the inlet and about 5 m/second at the outlet of the cooler 13.
The downstream separator 26 was designed as a cyclone and constructed and adjusted in such a way that the coarser fraction was separated off down to a particle size of 5um with a separation efficiency of at least 95%.
Before and after the separation, the dust was examined as in the preceding examples. The result was:
Before After Analyzed separation separation total quantity 10.0 g 8.4 g Zn content 3.3 wt.% 0.3 wt.%
Pb content 0.8 wt.% 0.1 wt.%
~.~
11 - 1~ 40 230 Cd content 0.05 wt.% 0.0005 wt.%
At the same time, samples of the filter dust were leached according to example 1, and the solutions thus obtained were examined for their heavy metal ion content:
Heavy metal Before After separation separation (mg/l of solution) (mg/l of solution) zn2+ 1600 43 Pb2+ 13 O.g Cd2+ 37 0.2 Embodiment example 4:
See Figure 3.
In a unit for continuous operation, filter dust from a trash incinerator was treated. The re-action vessel 4 consisted of refractory ceramics and had a heat insulation 5 in the form of a casing, likewise consisting of ceramic material and slag wool. The cylindrical interior had a diameter of 200 mm and a height of 800 mm. The cooler 13, consisting of stainless steel, was built up from 3 parallel-connected cylindrical pipes each of 25 mm internal diameter and 1800 mm length.
The carrier gas 9 used was nitrogen at a rate of 4 dm3/second (relative to standard state) which was heated in the heater 12 to a temperature of 1300~C, in order to release an excess of sensible heat to the charge and to cover all heat losses. The filter dust, which was not preheated, was added to the reaction vessel at a rate of about 1 g/second.
At the same time, a rate of about 0.05 g/second of coke powder (85 wt.% C) was injected, which amounted to about 4 wt.% C relative to the filter dust. The separator 26 in the form of an electrostatic pre-cipitator had a separation efficiency of 92% forparticles down to 3um diameter. The fine fraction was recycled via the circulation pump 17 into the - 12 - 13 40 23q circulation. The dust was analyzed before and after the separation:
Before After Analyzed separation separation 5 total quantity 10.0 g 9.1 g Zn content 3.3 wt.% 0.1 wt.%
Pb content 0.8 wt.% 0.005 wt.%
Cd content 0.05 wt.% not detectable The samples of filter dust were leached according to example 1, and the solutions obtained were examined for their heavy metal ion content:
Heavy metal Before After separation separation (mg/l of solution) (mg/l of solution) Zn2+ 1600 8 pb2+ 13 Not detectable Cd2+ 37 Not detectable Embodiment example 5:
See Figure 3.
Filter dust from a trash incinerator was treated in the pilot unit according to example 3.
The filter dust was continuously injected into the reaction vessel 4 and fluidized. The carrier gas 9 used was nitrogen preheated to 1200~C
by means of the heater 12. At the same time, 3% by volume of CO, relative to the volume of nitrogen, were injected as additive 28 into the reaction vessel 4. As a result, a reactive (reducing) mixture was formed. The rate of filter dust per gas volume was about 150 g/m3, and the throughput of filter dust was about 0.15 g/second, and that of carrier gas was about 1 dm3/second. The mean flow velocity in the reaction vessel 4 at a temperature of 1000~C
was about 0.5 m/second, and that in the cooler 13 was about 12 m/second at the inlet and about 5 m/second at the outlet. A cyclone was used as the separator 26.
- 13 - 134023~
The dust was examined before and after the separation, analogously to the preceding examples.
The following values were obtained:
Before After 5 Analysed separation separation total quantity 10.0 g 8.2 g Zn content 3.3 wt.% 0.5 wt.%
Pb content 0.8 wt.% 0.4 wt.%
Cd content 0.05 wt.% 0.005 wt.%
In addition, samples of the filter dust were leached with a CO2-saturated aqueous solution, and the lyes were examined for their heavy metal ion content:
Heavy metal Before After separation separation (mg/l of solution) (mg/l of solution) Zn2+ 1600 122 pb2+ 13 4.2 Cd2+ 37 4.1 Embodiment example 6 In a pilot unit for continuous operation, electrostatic precipitator ash from a trash incinerator was treated. Unlike Figure 3 the filter ash was first fluidized with nitrogen (throughput about 0.14 dm3/second) in a mixer and then passed into an electrically heated reaction furnace. In the latter, the fluidized mixture was brought to a temperature of 1100~C and held at this temperature for a residence time of 3 seconds. On this occasion, the major part of the heavy metal compounds was vaporized and passed into the gas phase. The gas/particle mixture then flowed through a hollow cylindrical cooler of 10 mm internal diameter, on the inner wall of which the heavy metal compounds condensed. The cooled gas stream, laden with particles and largely free of heavy metal compounds, J
was passed into a dust filter, where the dust was separated out.
The analysis gave the following picture:
Before After 5 Analyzed separation separation total quantity 8.0 g 6.5 g Zn content 3.3 wt.% 0.07 wt.%
Pb content 0.8 wt.% 0.02 wt.~
Cd content 0.05 wt.% 0.001 wt.%
Samples of the filter dust were leached with CO2-saturated water. This gave the following heavy metal content of the solution:
Heavy metal Before After separation separation (mg/l of solution) (mg/l of solution) zn2+ 1600 45 pb2+ 13 0 9 Cd2+ 37 0.8 Embodiment example 7:
See Figure 4.
In a small pilot unit for discontinuous batchwise operation, filter dust from a trash incinerator was processed. The reaction vessel 4 consisting of ceramic material had a hollow cylin-drical shape with a conical bottom. It was fittedwith heating 24 and a casing-shaped heat insulation 5. The internal diameter was 40 mm and the height was 240 mm. The cooler 13 consisted of a double-walled pipe of 6 mm internal diameter and 1500 mm length. The cooling jacket 14 was charged with water as the coolant 15.
The charge consisted of 100 g of filter dust, which was heated in the reaction vessel 4 to 1000~C. At the same time, the entire unit was evacu-ated slowly via the three-way valve 29 by means of the vacuum pump 32 at a pressure drop of 10 kPa/minute down to a final pressure of l kPa .. , .. . . ~, . ..
- 15 - 134~230 (about 0.01 bar). This step thus took about 10 minutes. The charge was kept in this state for about 1 hour. During this time, the heavy metal compounds largely vaporized under the reduced pressure and condensed or sublimed in the slim cooler 13, where they were discharged via the vacuum-tight gate valve 3, after the batch has been completed. Air was then admitted to the unit via the three-way valve 29, the dust residue was discharged from the bottom of reac-tion vessel 4 and the latter was charged with thenext batch.
The fine dust entrained by the vapor stream was kept away from the vacuum pump 32 in the filter 30 and discharged from time to time.
The dust was analyzed before and after the separation, the following picture being obtained:
Before After Analyzed separation separation total quantity 10.0 g 8.4 g 20 Zn content 3.3 wt.% 0.4 wt.%
Pb content 0.8 wt.~ 0.4 wt.%
Cd content 0.05 wt.% 0.005 wt.%
Samples of the filter dust were leached with CO2-saturated water. The heavy metal content of the solutions was found to be as follows:
Heavy metal Before After separation separation (mg/l of solution) (mg/l of solution) zn2+ 1600 87 Pb2+ 13 6.4 Cd2+ 87 1.7 Embodiment example 8:
See Figure 5.
Filter dust from a trash incinerator was, before removal of the heavy metal compounds, mechanically treated in such a way that it was - 15a - 1340230 divided into a coarser fraction and a finer frac-tion.
Fresh carrier gas 9 was injected into the mixer 34 by means of a fan 10. The throughput was about 0.55 dm3/second. Filter dust from the dust silo 2 was fed to the mixer, so that a suspension of about 100 g of dust/m3 was formed. The mixture fluidized in this way was conveyed in the cold state through a cyclone 35, where the coarser fraction of more than 5um particle diameter was precipitated.
This fraction represented about 98% of the mass of the total dust. It was fed directly to a unit 37 for removing heavy metal compounds - in the present case according to Figure 3. The dust 38 passing through the cyclone 35 and conveyed by the carrier gas still amounted to only about 2% by weight of the mass of the original dust and was passed into a unit 39 for further processing. This dust was precipitated in a superfine filter and further treated separately.
The invention is not restricted to the embodiment examples. The filter dust is heated in the reaction vessel up to the vaporization tempera-ture of the heavy metal compounds, which are to be removed, at the prevailing partial pressure and the resulting vapor is separated purely thermally from the dust particles, by quenching the mixture and converting the steam by condensation or - 16 - 13~ 2~0 solidification or sublimation into the liquid or solid state. In the process ~ith fluidization by means of a gaseous medium, at least a part of the carrier gas is re-cycled as circulating gas in the cyclic process to the charging point of the filter dust. The carrier gas is advantageous~y preheated in such a ~ay that the entire heat requirement - apart from losses - is covered by its sensible heat. In this ~ay, high heat transfer coeffic-ients for heating of the charge are achieved. The proce-dure can in principle be continuous or discontinuous,in the form of batches. In the latter case, it is also possible to operate batch~ise ~ithout carrier gas under a greatly reduced partial pressure of the heavy metal com-pounds, ~hich are to be vaporized, or in vacuo. In this ~ay, the vaporization temperature can be substantially lo~ered, the vaporization process can be accelerated and the yield of heavy metal compounds in the condensate/sub-limate can be improved. Solid, liquid or gaseous substances can additionally be added in principle to the filter dust in all processes in the reaction vessel, by admixing the additives to the dust itself or to the carrier gas, if~
any, or introducing them directly into the reaction ves-sel. These substances have a physical and/or chemical action on the charge, by accelerating the vaporization of ZS the heavy metal compounds as a result of reducing the va-porization temperature, converting the heavy metals into more volatile substances, and the like. In an advantageous manner, metal halides, ammonium halides or reducing agents, preferably carbon or carbon monoxide, are added. It is of advantage to split the filter dust, before the remova~
of the heavy metal compounds, in the cold state purely mechanically to a coarser fraction and a finer fraction tfor example less than 5 ~m particle size) and separately to treat each fraction further. The separation can be carried out by mechanical, pneumatic or hydraulic means with the aid of cyclones, electrostatic precipitators, dry filters, scrubbers and the like. The coarser fraction is taken to the heavy metal removal unit, and the finer fraction is taken to the unit for concentration, . .~ , ~, ~ - 17 -agglomeration, briquetting and dumping (final deposition) and the like.
Obviously, numerous modifications and variations of the present invention are possible in the light of the S above teachings. It is therefore to be understood that, ~ithin the scope of the appended claims, the invention may be practiced other~ise than as specifically described herein.
TITLE OF THE INVENTION Process for removing heavy metal compounds from the filter dust from trash ;ncinerators, flue gas dust precipitators and gas-cleaning units GACKGROUND Of THE INVENTION
Field of the Invention Processing of pulverulent residues laden ~ith pollutants and originating in most cases from combustion processes. Dust precipitation and gas cleaning have g?ined importance in conjunction ~ith regulations for protection of the environment. As a result, more stringent demands have to be met also by the associated further process;ng and storage of the pollutants and their carriers.
The invention relates to the further development, improvement and simplification of the separation of pol-lutants, vhich have to be treated separately, from a com-lex particle mixture arising in combustion processes.
In particular, it relates to a process for removing heavy metal compounds from the filter dust from trash in-cinerators, flue gas dust precipitators and gas-cleaning units by vaporisation, separation and subsequent conden-sation and/or sublimation of the heavy metal compounds.
Discussion of background Filter dust from industrial combustion installa-tions, specifically electrostatic precipitator dust, hasa high content of harmful substances ~hich contaminate the surroundings, pollute the environment and in some cases are toxic. These include certain organic compounds and above all heavy metal compounds, for example of the elements Pb, Zn, Cd, Tl and Cu. Special regulations therefore apply to such mixtures, and the filter dust must be regarded and treated as special waste.
At present, the treatment is carried out in accordance with 3 principles:
- Agglomeration and compaction of the dust to give larger pieces by means of binders such as cement, asphalt and the like. This is followed by final deposition in a dump [cf."Behandlung und Verfest-igung von Ruckstanden aus Kehrichtverbrennungs-anlagen (Treatment and solidification of residues from trash incinerators]" Schriftenreihe Umwelt-schutz [Protection of the Environment Publica-tions] No. 62, Bundesamt fur Umweltschutz [Federal office of the environment], Berne 1987). In this case, a product is formed, the mass of which is greater than that of the loose starting material.
Final deposition is therefore expensive and raises problems because the space available is in most cases restricted.
- Chemical treatment with acids. The heavy metal compounds are leached out with aqueous acids. The heavy metal-free residue is deposited in a dump and the acid solutions containing heavy metals are processed further (cf. H. Vogg "Rauchgas-reinigungsverfahren [Flue gas cleaning processes]", paper read at the VDI seminar 43.32.02 "Abfallbe-handlung und -verwertung durch Mullverbrennung [Waste treatment and utilization by trash incineration]" VDI, Dusseldorf 1986). These leaching processes are not true solutions of the waste problem, but merely shift it to a different plane. The further treatment of the heavy metal-containing solutions and their concentration - 2a - 1~230 involves considerable consumption of energy. New problems (effluent, pollution of the environment) are created.
- Thermomechanical separation by heating of the dust laden with heavy metals in a gas stream, vaporization of the heavy metal compounds and mechanical separation of the solid suspended particles from the gas phase at . .. . .
13~0230 high temperatures (hot-gas cyclone, hot-gas filter, etc.). The heavy metal vapors are then condensed in a cooler (cf. W. Weissweiler et al, "Anreicherung von Thallium-und Bleihalogeniden [Concentrating of thallium and lead halides]", Staub, Reinhaltung der Luft, volume 46, No. 3, pages 120-124, March 1986).
The hot-gas separators (cyclones, electrostatic precipitators, ceramic honeycomb filters, etc.) must operate isothermally at high temperatures (1000~C
and higher), which makes severe demands on their design and their operation. Moreover, separation of the fine dust (less than lum particle diameter), which is disproportionately important as a carrier of the heavy metal compounds in percentage terms, can hardly be accomplished by economical means.
SUMMARY OF THE INVENTION
Accordingly, one object of this invention is to provide a novel process for removing heavy metal compounds from the filter dust from combustion plants of any type, which process, while utilizing the principle of vaporization and subsequent conden-sation, avoids the difficult and extensive mechani-cal separation of pollutant vapor and dust particles at high temperatures (hot-gas filtration, hot-gas separation) and as far as possible suppresses a later reattachment of the condensed pollutants to the fine dust particles. The process should be sim-ple and ensure the most economical individual further processing of the various separated products for final deposition.
In accordance with the present invention, there is thus provided a process for removing heavy metals and/or heavy metal compounds from the filter dust of refuse incinerators, flue gas dust precipit-ators and gas-cleaning units, in which the filter . _ _ . . . . .. . -- . . . . .. . .
- 3a -'~- 1340230 dust is heated in a reaction vessel at least up to the vaporization temperature of the heavy metals and/or heavy metal compounds which are to be removed, the vaporized heavy metals and/or heavy metal compounds are then quenched in a cooler and converted to a liquid or solid state, and removed.
The process of the invention is characterized in that before the vaporization of the heavy metals and/or heavy metal compounds to be removed, superfine dust particles with a particle size smaller than 5~m are separated in a cold state from the filter dust by mechanical, hydraulic or pneumatic means or by filtration, and the remaining filter dust fraction is fed to the reaction vessel.
BRIEF DESCRIPTION OF THE DRAWINGS
A more complete appreciation of the invention and many of the attendant advantages thereof will be 134023~
readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:
Figure 1 shows a flow diagram of a discontinuous process for removing heavy metal compounds by means of a carrier gas;
Figure 2 shows a diagrammatic illustration of equipment for discontinuous removal of heavy metal compounds;
Figure 3 shows a flow diagram of a continuous process for the removal of heavy metal compounds by means of a carrier gas;
Figure 4 shows a flow diagram of a discontinuous process for the removal of heavy metal compounds with application of reduced pressure, and Figure 5 shows a flow diagram of any desired process for the removal of heavy metal compounds by separating the fine dust off beforehand by means of a carrier gas.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, Figure 1 shows the flow diagram of a discontinuous process, operating batchwise, for removing heavy metal compounds from filter dusts by means of a fluidizing carrier gas. 1 is the raw dust supply, indicated by an arrow, to the dust silo 2 which is closed at the bottom by a periodically operable gate valve 3 for solids. 4 is a reaction vessel for high temperatures (about 1000~C, sometimes even higher) which is provided with heat insulation 5 (if appropriate, with additional heating 24, cf. Figure 2) and which contains a sieve tray 6 ~displaceable) in its interior at the lower end. In operation, a fluidized layer 7 (fluidized bed, fluid bed) is generated above ~ 1~230 - 4a -the sieve tray 6 (indicated by arrows). The lower, conical end of the reaction vessel 4 is connected via a gate valve 3 to a tank 8 which is to receive the purified dust. 9 represents the fresh -13~0230 carrier gas (inlet indicated by an arro~). 10 is a fan for conveying the carrier gas 9, and 11 is a corresponding gas isolation valve. 12 represents a heater tup to about 1200~C) for the gas stream partially laden ~ith particles. This heater 1Z is advantageously provided ~ith a contro~ system, since it largely determines the thermo-dynamics in the reaction vessel 4. 13 is a cooler sur-rounded by a cooling jacket 14 and having a greater length as compared ~ith the cross-section. The coolant 15 (in most cases water) enters at one end of the cooling jacket 14 and leaves at the other end (indicated by arro~s). 16 represents the circulating gas ~hich still contains cer-tain fractions of dust particles held in suspension. 17 is the circulation pump (fan) and 18 is the preheater (up to about 800~C) for the circulating gas 16. 19 is a tank ~hich is to receive the heavy metal compounds and ~hich is connected via the discontinuously operable gate valve 3 to the lo~er conical end of the cooler 13.
Figure 2 relates to a diagrammatic representation of equipment for the discontinuous removal of heavy metal compounds from filter dusts by processes according to ~
Figure 1. 3 are the conventional, discontinuously (batch-~ise) operable gate valves for solids and 4 is the reac-tion vessel for high temperatures, ~hich is provided with a heater 24 and heat insulation 5 in the form of approp-riate casings. 6 represents a sieve tray which is here designed as a t~in tray ~ith a laterally disp~aceable lover part (indicated by double arro~). The gas stream can be regulated in this ~ay. After the batch has been completed, the reaction vessel 4 can be partially opened for discharging the purified dust. 7 is the fluidized bed marked by arro~s. 25 is the ra~ dust feed uhich takes place in the upper part of the reaction vessel 4 through a central pipe. 21 is the carrier gas, 22 is its feed line, 23 is the blast box of the reaction vessel 4, 16 is the circulating gas taken from the cooler 13, and 14 is the cooling jacket through ~hich the coolant 15 flo~s.
It must be ensured that the cooler 13 is connected to the reaction vessel 4 by a line ~hich is as short as possible.
.. ~ . .. . .. , . . .. ... ., . ~
in practice, the former immediately adjoins the latter, so that there is no undesired condensation of the vapors of the heavy metal compounds in the connecting line. For the sake of clarity, 4 and 13 are shown separately in the drawing.
Figure 3 shows a flow diagram of a continuous process for removing heavy metal compounds from filter dusts by means of a fluidizing carrier gas. The reference numerals 1, 2, 3, 8 and 19 and their meanings correspond exactly to those of Figure 1. 9 is the fresh carrier gas which is delivered by the fan 10 and is passed via the valve 27 and the heater 12 into the reaction vessel 4 provided with the heat insulation 5.
The valve 27 can be designed as a non-return valve, differential valve or a controlled or regulated valve.
The lower end of the reaction vessel 4 is directly adjoined by the cooler 13 which is surrounded by the cooling jacket 14 and is of very slender design. Water is used in most cases as the coolant 15. 28 represents the additives feed which may be necessary or desirable.
These can have a physical or chemical action. In most cases, they are materials which lower the vaporization temperature, such as metal halides, NH4Cl, etc. or reducing agents such as C, CO, etc.
Figure 4 shows a flow diagram of a discontinuous process for removing heavy metal compounds from filter dusts by the application of reduced pressure ("vacuum").
The reference numerals 1, 2, 3, 8 and 19 correspond exactly to those of Figure 1. The reaction vessel 4, provided with a heater 24 (up to about 1200~C) and a heat insulation 5, has at the lower end a conical part, is designed to be vacuum-tight and can be sealed from the surroundings by vacuum-tight gate valves 3. The reaction vessel 4 is connected via a short duct directly to the vacuum-tight cooler 13 which is provided with a cooling jacket 14 (coolant 15) and which can be - 6a -connected from time to time via the likewise vacuum-tight gate valve 3 to the heavy metal compounds tank 19.
At the upper outlet of the cooler 13, there is a vacuum-tight three-way valve 29, whose normal operating position (as drawn) is such that it opens ~ 13~0230 the ~ay from the cooler 13 via a filter 30 (fine filter) to a vacuum pump 3Z. The filter 30 is connected to a fine dust ~filter dust) tank 31. From time to time, a temor-ary air feed 33 (dashed arrow) for flooding the unit can be effected via the three-~ay valve,29.
Figure S relates to a flow diagram of any desired process for the removal of heavy metal compounds from filter dusts by separating the fine dust off beforehand by means of a carrier gas. 1 is the ra~ dust supply to the dust silo 2 which is connected by a pipe to a m;xer 34. 9 is the carrier gas ~hich is delivered by the fan 10 into the mixer 34. In the latter, intense turbulence and fluidization of the dust particles takes place. The fluidized gas/dust mixture passes into the separator 35 ~here the coarser fraction (in the present case of parti-cle diameter > S ~m) is separated off as dust 36 and pas-sed into a unit 37 (for example according to Figures 1 to 4) for removing heavy metal compounds. The separator ~ 35 can consist of a filter (for example an electro-I Z0 static precipitator) or of a cyclone. Carrier gas ~
_ dust (finer fraction of a particle diameter of < S ~m)'38leave the separator 35 and are delivered to the unit 39 for further processing. This can in principle consist of a trash incinerator, a fine filter or a scrubber.
Embodiment example 1:
See Figures 1 and 2.
In a small pilot unit for batch~ise operation, filter dust from a trash incinerator ~as treated. The re-action vessel 4, consisting of a ceramic material and pro-vided vith a sieve tray 6, had a cylindrical shape. Itsinternal diameter ~as 50 mm and its height (internal, cylindrical part) ~as 200 mm. The cooler 13 consisted of a double-~alled pipe of stainless steel, having an inter-nal diameter of 10 mm and a length of 1000 mm. ~ater flo~ed as the coolant through the cooling jacket 14.
The filter dust contains inter alia, the following metals:
~ , . . ..
Ca: 11.5 wt.%
Cu: 0.09 wt.%
Zn: 3.3 wt.%
Pb: 0.8 wt.%
Cd: 0.05 wt.%
Sn: 0.34 wt.%
Sb: 0.16 wt.%
Ba: 0.34 wt.%
The reaction vessel 4 was charged with 10 g of filter dust and heated to a temperature of 1000~C. At this temperature, the dust was fluidized by means of a stream of nitrogen as the carrier gas 9 and held in suspension in the fluidized bed 7. The major part of the heavy metal compounds vaporized in the reaction vessel 4 and was continuously condensed in the cooler 13. The precipitated metal salts were here only slightly contaminated by superfine parti-cles entrained by the gas stream. After 1 hour, the process was complete and the reaction vessel 4 was cooled. The filter dust was analyzed before and after the thermal separation of the heavy metal com-pounds. This gave the following picture:
Before After separation separation Total quantity 10.0 g 8.0 g Zn content 3.3 wt.% 0.3 wt.%
Pb content 0.8 wt.% 0.4 wt.%
Cd content 0.05 wt.% 0.005 wt.
Moreover, samples of the filter dust before and after thermal separation were leached with CO2-saturated water and the solutions thus obtained were examined for their heavy metal ion content:
Heavy metal Before After separation separation (mg/l of solution) (mg/l of solution) zn2+ 1600 63 1~023~
pb2+ 13 7.8 Cd2+ 37 2.4 Embodiment example 2:
See Figures 1 and 2.
In a pilot unit, filter dust from a trash incinerator was treated similarly as in example 1.
The unit was of similar structure as in example 1, but had greater dimensions.
The reaction vessel 4 was charged with 1000 g of filter dust and held at a temperature of 1000~C for 3 hours. Instead of nitrogen, the acid off-gas of a trash incinerator was used as the carrier gas 9. After the charge had been completed, the reaction vessel was cooled and the residue was examined. The result was as follows:
Before After Analyzed separation separation total quantity 10.0 g 8.2 g Zn content 3.3 wt.% 0.02 wt.%
20 Pb content 0.8 wt.% 0.3 wt.%
Cd content 0.05 wt.% 0.003 wt.%
In addition, samples of the filter dust before and thermal separation were leached with CO2-saturated water, and the solutions thus obtained were examined for their heavy metal ion content:
Heavy metal Before After separation separation (mg/l of solution) (mg/l of solution) zn2+ 1600 1.3 Pb2+ 13 2 Cd2+ 37 < 1 This shows that it was possible, by using a chemically active gas instead of the largely inert nitrogen, to achieve a better yield of heavy metal removal from the filter dust.
Embodiment example 3:
See Figure 3.
- lO- 13~02~0 In a pilot unit for continuous operation, filter dust from a trash incinerator was processed.
The reaction vessel 4 consisted of refractory ceramic material and had a casing-like heat insula-tion 5 consisting likewise of ceramic material andglass wool. The cylindrical interior had a diameter of 100 mm and a height of 500 mm. The cooler 13, provided with a cooling jacket 14 carrying a water flow, was of cylindrical shape and had an internal diameter of 20 mm and a height of 1600 mm.
The filter dust was injected continuously into the reaction vessel 4 and fluidized by carrier gas 9 preheated to 1400~C (heater 12). Analogously to example 2, the carrier gas consisted of acid off-gas from a trash incinerator. In addition, 5 wt.% ofNH4Cl, relative to the quantity of the filter dust, was injected as additive (25) into the reaction vessel 4. The throughput of filter dust was about l g/second, and that of carrier gas was about l dm3/second, relative to the standard state. This gave a flow velocity of about 0.55 m/second in the reaction vessel 4 at a temperature of 1000~C, and a flow velocity of about 12.5 m/second at the inlet and about 5 m/second at the outlet of the cooler 13.
The downstream separator 26 was designed as a cyclone and constructed and adjusted in such a way that the coarser fraction was separated off down to a particle size of 5um with a separation efficiency of at least 95%.
Before and after the separation, the dust was examined as in the preceding examples. The result was:
Before After Analyzed separation separation total quantity 10.0 g 8.4 g Zn content 3.3 wt.% 0.3 wt.%
Pb content 0.8 wt.% 0.1 wt.%
~.~
11 - 1~ 40 230 Cd content 0.05 wt.% 0.0005 wt.%
At the same time, samples of the filter dust were leached according to example 1, and the solutions thus obtained were examined for their heavy metal ion content:
Heavy metal Before After separation separation (mg/l of solution) (mg/l of solution) zn2+ 1600 43 Pb2+ 13 O.g Cd2+ 37 0.2 Embodiment example 4:
See Figure 3.
In a unit for continuous operation, filter dust from a trash incinerator was treated. The re-action vessel 4 consisted of refractory ceramics and had a heat insulation 5 in the form of a casing, likewise consisting of ceramic material and slag wool. The cylindrical interior had a diameter of 200 mm and a height of 800 mm. The cooler 13, consisting of stainless steel, was built up from 3 parallel-connected cylindrical pipes each of 25 mm internal diameter and 1800 mm length.
The carrier gas 9 used was nitrogen at a rate of 4 dm3/second (relative to standard state) which was heated in the heater 12 to a temperature of 1300~C, in order to release an excess of sensible heat to the charge and to cover all heat losses. The filter dust, which was not preheated, was added to the reaction vessel at a rate of about 1 g/second.
At the same time, a rate of about 0.05 g/second of coke powder (85 wt.% C) was injected, which amounted to about 4 wt.% C relative to the filter dust. The separator 26 in the form of an electrostatic pre-cipitator had a separation efficiency of 92% forparticles down to 3um diameter. The fine fraction was recycled via the circulation pump 17 into the - 12 - 13 40 23q circulation. The dust was analyzed before and after the separation:
Before After Analyzed separation separation 5 total quantity 10.0 g 9.1 g Zn content 3.3 wt.% 0.1 wt.%
Pb content 0.8 wt.% 0.005 wt.%
Cd content 0.05 wt.% not detectable The samples of filter dust were leached according to example 1, and the solutions obtained were examined for their heavy metal ion content:
Heavy metal Before After separation separation (mg/l of solution) (mg/l of solution) Zn2+ 1600 8 pb2+ 13 Not detectable Cd2+ 37 Not detectable Embodiment example 5:
See Figure 3.
Filter dust from a trash incinerator was treated in the pilot unit according to example 3.
The filter dust was continuously injected into the reaction vessel 4 and fluidized. The carrier gas 9 used was nitrogen preheated to 1200~C
by means of the heater 12. At the same time, 3% by volume of CO, relative to the volume of nitrogen, were injected as additive 28 into the reaction vessel 4. As a result, a reactive (reducing) mixture was formed. The rate of filter dust per gas volume was about 150 g/m3, and the throughput of filter dust was about 0.15 g/second, and that of carrier gas was about 1 dm3/second. The mean flow velocity in the reaction vessel 4 at a temperature of 1000~C
was about 0.5 m/second, and that in the cooler 13 was about 12 m/second at the inlet and about 5 m/second at the outlet. A cyclone was used as the separator 26.
- 13 - 134023~
The dust was examined before and after the separation, analogously to the preceding examples.
The following values were obtained:
Before After 5 Analysed separation separation total quantity 10.0 g 8.2 g Zn content 3.3 wt.% 0.5 wt.%
Pb content 0.8 wt.% 0.4 wt.%
Cd content 0.05 wt.% 0.005 wt.%
In addition, samples of the filter dust were leached with a CO2-saturated aqueous solution, and the lyes were examined for their heavy metal ion content:
Heavy metal Before After separation separation (mg/l of solution) (mg/l of solution) Zn2+ 1600 122 pb2+ 13 4.2 Cd2+ 37 4.1 Embodiment example 6 In a pilot unit for continuous operation, electrostatic precipitator ash from a trash incinerator was treated. Unlike Figure 3 the filter ash was first fluidized with nitrogen (throughput about 0.14 dm3/second) in a mixer and then passed into an electrically heated reaction furnace. In the latter, the fluidized mixture was brought to a temperature of 1100~C and held at this temperature for a residence time of 3 seconds. On this occasion, the major part of the heavy metal compounds was vaporized and passed into the gas phase. The gas/particle mixture then flowed through a hollow cylindrical cooler of 10 mm internal diameter, on the inner wall of which the heavy metal compounds condensed. The cooled gas stream, laden with particles and largely free of heavy metal compounds, J
was passed into a dust filter, where the dust was separated out.
The analysis gave the following picture:
Before After 5 Analyzed separation separation total quantity 8.0 g 6.5 g Zn content 3.3 wt.% 0.07 wt.%
Pb content 0.8 wt.% 0.02 wt.~
Cd content 0.05 wt.% 0.001 wt.%
Samples of the filter dust were leached with CO2-saturated water. This gave the following heavy metal content of the solution:
Heavy metal Before After separation separation (mg/l of solution) (mg/l of solution) zn2+ 1600 45 pb2+ 13 0 9 Cd2+ 37 0.8 Embodiment example 7:
See Figure 4.
In a small pilot unit for discontinuous batchwise operation, filter dust from a trash incinerator was processed. The reaction vessel 4 consisting of ceramic material had a hollow cylin-drical shape with a conical bottom. It was fittedwith heating 24 and a casing-shaped heat insulation 5. The internal diameter was 40 mm and the height was 240 mm. The cooler 13 consisted of a double-walled pipe of 6 mm internal diameter and 1500 mm length. The cooling jacket 14 was charged with water as the coolant 15.
The charge consisted of 100 g of filter dust, which was heated in the reaction vessel 4 to 1000~C. At the same time, the entire unit was evacu-ated slowly via the three-way valve 29 by means of the vacuum pump 32 at a pressure drop of 10 kPa/minute down to a final pressure of l kPa .. , .. . . ~, . ..
- 15 - 134~230 (about 0.01 bar). This step thus took about 10 minutes. The charge was kept in this state for about 1 hour. During this time, the heavy metal compounds largely vaporized under the reduced pressure and condensed or sublimed in the slim cooler 13, where they were discharged via the vacuum-tight gate valve 3, after the batch has been completed. Air was then admitted to the unit via the three-way valve 29, the dust residue was discharged from the bottom of reac-tion vessel 4 and the latter was charged with thenext batch.
The fine dust entrained by the vapor stream was kept away from the vacuum pump 32 in the filter 30 and discharged from time to time.
The dust was analyzed before and after the separation, the following picture being obtained:
Before After Analyzed separation separation total quantity 10.0 g 8.4 g 20 Zn content 3.3 wt.% 0.4 wt.%
Pb content 0.8 wt.~ 0.4 wt.%
Cd content 0.05 wt.% 0.005 wt.%
Samples of the filter dust were leached with CO2-saturated water. The heavy metal content of the solutions was found to be as follows:
Heavy metal Before After separation separation (mg/l of solution) (mg/l of solution) zn2+ 1600 87 Pb2+ 13 6.4 Cd2+ 87 1.7 Embodiment example 8:
See Figure 5.
Filter dust from a trash incinerator was, before removal of the heavy metal compounds, mechanically treated in such a way that it was - 15a - 1340230 divided into a coarser fraction and a finer frac-tion.
Fresh carrier gas 9 was injected into the mixer 34 by means of a fan 10. The throughput was about 0.55 dm3/second. Filter dust from the dust silo 2 was fed to the mixer, so that a suspension of about 100 g of dust/m3 was formed. The mixture fluidized in this way was conveyed in the cold state through a cyclone 35, where the coarser fraction of more than 5um particle diameter was precipitated.
This fraction represented about 98% of the mass of the total dust. It was fed directly to a unit 37 for removing heavy metal compounds - in the present case according to Figure 3. The dust 38 passing through the cyclone 35 and conveyed by the carrier gas still amounted to only about 2% by weight of the mass of the original dust and was passed into a unit 39 for further processing. This dust was precipitated in a superfine filter and further treated separately.
The invention is not restricted to the embodiment examples. The filter dust is heated in the reaction vessel up to the vaporization tempera-ture of the heavy metal compounds, which are to be removed, at the prevailing partial pressure and the resulting vapor is separated purely thermally from the dust particles, by quenching the mixture and converting the steam by condensation or - 16 - 13~ 2~0 solidification or sublimation into the liquid or solid state. In the process ~ith fluidization by means of a gaseous medium, at least a part of the carrier gas is re-cycled as circulating gas in the cyclic process to the charging point of the filter dust. The carrier gas is advantageous~y preheated in such a ~ay that the entire heat requirement - apart from losses - is covered by its sensible heat. In this ~ay, high heat transfer coeffic-ients for heating of the charge are achieved. The proce-dure can in principle be continuous or discontinuous,in the form of batches. In the latter case, it is also possible to operate batch~ise ~ithout carrier gas under a greatly reduced partial pressure of the heavy metal com-pounds, ~hich are to be vaporized, or in vacuo. In this ~ay, the vaporization temperature can be substantially lo~ered, the vaporization process can be accelerated and the yield of heavy metal compounds in the condensate/sub-limate can be improved. Solid, liquid or gaseous substances can additionally be added in principle to the filter dust in all processes in the reaction vessel, by admixing the additives to the dust itself or to the carrier gas, if~
any, or introducing them directly into the reaction ves-sel. These substances have a physical and/or chemical action on the charge, by accelerating the vaporization of ZS the heavy metal compounds as a result of reducing the va-porization temperature, converting the heavy metals into more volatile substances, and the like. In an advantageous manner, metal halides, ammonium halides or reducing agents, preferably carbon or carbon monoxide, are added. It is of advantage to split the filter dust, before the remova~
of the heavy metal compounds, in the cold state purely mechanically to a coarser fraction and a finer fraction tfor example less than 5 ~m particle size) and separately to treat each fraction further. The separation can be carried out by mechanical, pneumatic or hydraulic means with the aid of cyclones, electrostatic precipitators, dry filters, scrubbers and the like. The coarser fraction is taken to the heavy metal removal unit, and the finer fraction is taken to the unit for concentration, . .~ , ~, ~ - 17 -agglomeration, briquetting and dumping (final deposition) and the like.
Obviously, numerous modifications and variations of the present invention are possible in the light of the S above teachings. It is therefore to be understood that, ~ithin the scope of the appended claims, the invention may be practiced other~ise than as specifically described herein.
Claims (4)
1. Process for removing heavy metals and/or heavy metal compounds from the filter dust of refuse incinerators, flue gas dust precipitators and gas-cleaning units, in which the filter dust is heated in a reaction vessel at least up to the vaporisation temperature of the heavy metals and/or heavy metal compounds which are to be removed, at least the vaporised heavy metals and/or heavy metal compounds are then quenched in a cooler and converted to the liquid or solid state, and removed, characterised in that before the vaporisation of the heavy metals and/or heavy metal compounds to be removed, superfine dust particles with a particle size smaller than 5µm are separated in a cold state from the filter dust by mechanical, hydraulic or pneumatic means or by filtration, and the remaining filter dust fraction is fed to the reaction vessel.
2. Process according to claim 1, characterized in that a fresh carrier gas is fed in counter-current to the heated filter dust through a sieve tray of the reaction vessel, the carrier gas being heated to a temperature in the range of 1100°C-1400°C
before flowing through the sieve tray, and a part of the carrier gas is mixed as a circulating gas with the fresh carrier gas before heating.
before flowing through the sieve tray, and a part of the carrier gas is mixed as a circulating gas with the fresh carrier gas before heating.
3. Process according to claim 2, characterized in that the fresh carrier gas and the circulating gas are fed to the reaction vessel to generate a fluidized dust bed above the sieve tray.
4. Process according to claim 1, characterized in that the filter dust is transported without the aid of a carrier medium, is extracted from the cooler under vacuum in countercurrent to the heavy metals and/or heavy metal compounds to be condensed and is separated off by filtration.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CH267787 | 1987-07-15 | ||
| CH2677/87-2 | 1987-07-15 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1340230C true CA1340230C (en) | 1998-12-15 |
Family
ID=4239102
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 571902 Expired - Fee Related CA1340230C (en) | 1987-07-15 | 1988-07-13 | Process for removing heavy metal compounds from the filtrer dust from trash incinerators, flue gas dust precipitators and gas-cleaning units |
Country Status (8)
| Country | Link |
|---|---|
| EP (1) | EP0299340B1 (en) |
| JP (1) | JPS6434483A (en) |
| AT (1) | ATE76594T1 (en) |
| CA (1) | CA1340230C (en) |
| DE (1) | DE3871448D1 (en) |
| DK (1) | DK394188A (en) |
| ES (1) | ES2031958T3 (en) |
| SU (1) | SU1739858A3 (en) |
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| CN111498910A (en) * | 2020-05-26 | 2020-08-07 | 宜宾天原海丰和泰有限公司 | Resource utilization method of chlorination waste residue |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| AT394102B (en) * | 1989-01-26 | 1992-02-10 | Sgp Va Energie Umwelt | METHOD FOR COMBINED DISMANTLING OF ORGANIC COMPOUNDS AND REMOVAL OF HG, PB AND CR FROM DUST-BASED RESIDUES THERMAL DISPOSAL PROCESSES |
| DE3925399A1 (en) * | 1989-08-01 | 1991-02-07 | Rheinische Braunkohlenw Ag | METHOD FOR REFURBISHING ACTIVE CARBON LOADED WITH HEAVY METAL |
| JPH03196887A (en) * | 1989-12-26 | 1991-08-28 | Takuma Co Ltd | Ash treating device in refuse incinerator |
| DE4035777A1 (en) * | 1990-11-08 | 1992-05-14 | Noell Gmbh | METHOD FOR THE DISPOSAL OF DUST CONTAINING TOXIC HEAVY METALS, TOXIC ORGANIC MATERIALS AND SIMILAR COMPOUNDS |
| DE4109126A1 (en) * | 1991-03-20 | 1992-09-24 | Aquamot Ag | METHOD FOR TREATING COMBUSTION AND / OR SMOKE GAS CLEANING RESIDUES |
| DE4120277A1 (en) * | 1991-06-19 | 1992-12-24 | Krupp Polysius Ag | METHOD AND DEVICE FOR PURIFYING EXHAUST GASES FROM OVEN PLANTS |
| US5245120A (en) * | 1991-12-27 | 1993-09-14 | Physical Sciences, Inc. | Process for treating metal-contaminated materials |
| DE4342494C1 (en) * | 1993-12-07 | 1995-07-20 | Mannesmann Ag | Method and device for separating heavy metals and compounds containing heavy metals |
| DE102009036950A1 (en) | 2009-08-11 | 2011-03-03 | Polysius Ag | Process and installation for separating mercury from exhaust gases from a cement production process |
| CN109701382B (en) * | 2019-02-28 | 2022-05-17 | 兖矿集团有限公司 | Superfine powder dispersing and spraying system and processing method and application thereof |
| PL3747847T3 (en) * | 2019-06-05 | 2022-03-28 | Steinmüller Engineering GmbH | Mercury separation for the production of a cement clinker |
Family Cites Families (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS4997774A (en) * | 1973-01-25 | 1974-09-17 | ||
| GB1602376A (en) * | 1977-06-09 | 1981-11-11 | Encomech Eng Services Ltd | Material separation |
| DE3018319A1 (en) * | 1979-05-18 | 1980-11-27 | Niro Atomizer As | METHOD FOR REMOVING MERCURY FROM EXHAUST GASES |
| LU81330A1 (en) * | 1979-05-30 | 1980-12-16 | Arbed | PROCESS AND PLANT FOR THE RECOVERY OF IRON, ZINC AND LEAD CONTAINED IN DUST AND SLUDGE FROM BLAST FURNACES, AS WELL AS CONVERTERS AND ELECTRIC STEEL FURNACES |
| JPS595354B2 (en) * | 1981-02-19 | 1984-02-03 | 山口共英工業株式会社 | How to treat electric furnace dust |
| AT380901B (en) * | 1984-09-28 | 1986-07-25 | Voest Alpine Ag | METHOD FOR RECOVERING METALS FROM METAL-OXIDE-CONTAINING HOSPITAL DUST AND SYSTEM FOR CARRYING OUT THE METHOD |
| FR2581656B1 (en) * | 1985-05-10 | 1987-07-03 | Maillet Alain | ELECTROTHERMAL PROCESS FOR SEPARATING AND REFINING METALS FROM RECOVERY PRODUCTS AND INSTALLATION FOR IMPLEMENTING SAME |
| US4673431A (en) * | 1986-01-08 | 1987-06-16 | Bricmont & Associates, Inc. | Furnace dust recovery process |
| EP0274037A1 (en) * | 1986-12-10 | 1988-07-13 | BBC Brown Boveri AG | Process and device for the separation of particles |
| EP0272465B1 (en) * | 1986-12-10 | 1993-02-24 | BBC Brown Boveri AG | Process and device for the separation and/or reaction of particles |
-
1988
- 1988-07-06 AT AT88110747T patent/ATE76594T1/en active
- 1988-07-06 EP EP19880110747 patent/EP0299340B1/en not_active Expired - Lifetime
- 1988-07-06 DE DE8888110747T patent/DE3871448D1/en not_active Expired - Fee Related
- 1988-07-06 ES ES88110747T patent/ES2031958T3/en not_active Expired - Lifetime
- 1988-07-12 JP JP17199188A patent/JPS6434483A/en active Pending
- 1988-07-13 CA CA 571902 patent/CA1340230C/en not_active Expired - Fee Related
- 1988-07-14 DK DK394188A patent/DK394188A/en not_active Application Discontinuation
- 1988-07-14 SU SU884356213A patent/SU1739858A3/en active
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN111498910A (en) * | 2020-05-26 | 2020-08-07 | 宜宾天原海丰和泰有限公司 | Resource utilization method of chlorination waste residue |
| CN111498910B (en) * | 2020-05-26 | 2022-09-16 | 宜宾海丰和锐有限公司 | Resource utilization method of chlorination waste residue |
Also Published As
| Publication number | Publication date |
|---|---|
| ATE76594T1 (en) | 1992-06-15 |
| DK394188A (en) | 1989-01-15 |
| JPS6434483A (en) | 1989-02-03 |
| SU1739858A3 (en) | 1992-06-07 |
| DK394188D0 (en) | 1988-07-14 |
| EP0299340B1 (en) | 1992-05-27 |
| EP0299340A1 (en) | 1989-01-18 |
| ES2031958T3 (en) | 1993-01-01 |
| DE3871448D1 (en) | 1992-07-02 |
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