(19)
(11)EP 2 992 268 B1

(12)EUROPEAN PATENT SPECIFICATION

(45)Mention of the grant of the patent:
15.01.2020 Bulletin 2020/03

(21)Application number: 13722355.8

(22)Date of filing:  03.05.2013
(51)International Patent Classification (IPC): 
F23G 5/02(2006.01)
C02F 11/00(2006.01)
C02F 11/10(2006.01)
C02F 101/20(2006.01)
C02F 11/06(2006.01)
C02F 9/00(2006.01)
(86)International application number:
PCT/EP2013/059285
(87)International publication number:
WO 2014/177228 (06.11.2014 Gazette  2014/45)

(54)

PROCESS AND PLANT FOR SEPARATING HEAVY METALS FROM PHOSPHORUS-CONTAINING STARTING MATERIAL

VERFAHREN UND ANLAGE ZUR ABTRENNUNG VON SCHWERMETALLEN VON PHOSPHORHALTIGEM AUSGANGSMATERIAL

PROCÉDÉ ET INSTALLATION DE SÉPARATION DE MÉTAUX LOURDS D'UN MATÉRIAU DE DÉPART CONTENANT DU PHOSPHORE


(84)Designated Contracting States:
AL AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HR HU IE IS IT LI LT LU LV MC MK MT NL NO PL PT RO RS SE SI SK SM TR

(43)Date of publication of application:
09.03.2016 Bulletin 2016/10

(73)Proprietor: Outotec (Finland) Oy
02230 Espoo (FI)

(72)Inventors:
  • HERMANN, Ludwig
    A-2214 Auersthal (AT)
  • SCHNEIDER, Günter
    64653 Lorsch (DE)
  • LOHRBERG, Dirk
    63069 Offenbach (DE)

(74)Representative: Keil & Schaafhausen Patent- und Rechtsanwälte PartGmbB 
Friedrichstraße 2-6
60323 Frankfurt am Main
60323 Frankfurt am Main (DE)


(56)References cited: : 
EP-A1- 0 908 673
  
  • ADAM C ET AL: "Thermochemical treatment of sewage sludge ashes for phosphorus recovery", WASTE MANAGEMENT, ELSEVIER, NEW YORK, NY, US, vol. 29, no. 3, 1 March 2009 (2009-03-01), pages 1122-1128, XP025769686, ISSN: 0956-053X, DOI: 10.1016/J.WASMAN.2008.09.011 [retrieved on 2008-11-25]
  • S. PETZET ET AL: "Towards a complete recycling of phosphorus in wastewater treatment - options in Germany", WATER SCIENCE & TECHNOLOGY, vol. 64, no. 1, 1 July 2011 (2011-07-01), page 29, XP055098665, ISSN: 0273-1223, DOI: 10.2166/wst.2011.540
  
Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention).


Description


[0001] The present invention is directed to a process and a plant for separating heavy metals from phosphoric starting material.

[0002] Phosphate is a very important nutrient for the photosynthesis of plants so that more than 90 % of the global production of phosphate is processed to phosphorus fertilizers. The availability of phosphorus, however, is limited. In order to enhance the limited availability of phosphoric material there have been efforts to use sewage sludge ash, which often contains a considerable amount of phosphorus and which usually is disposed of in a landfill, as a source to recover phosphorus. It has been proposed to burn phosphorus containing sewage sludge to obtain a phosphorus containing ash with a phosphorus content of 8 to 20 wt.-%. The main chemical components of the resulting sewage sludge ashes are SiO2, CaO, Al2O3, Fe2O3 and P2O5. The ashes, however, also contain heavy metals, such as lead, cadmium, arsenic, chrome, copper, nickel, zinc or mercury. As the content of these elements exceeds the limits provided by official regulations and as the plant availability of its phosphate compounds is poor, the sewage sludge ash as such cannot be used as fertilizer and has to be processed beforehand.

[0003] Application PCT/EP2012/061986 describes a process for the separation of heavy metals from phosphorus-containing sewage sludge ash, wherein the starting material is heated to a temperature of between 700°C and 1.100°C in a first reactor, combustion gases are withdrawn and the heated starting material is transferred to a second reactor where chlorides of alkaline and earth alkaline metals are added.

[0004] It is also known from the prior art (see Böhm, H., Werner W., "Entwicklung und Erprobung eines Verfahrens zur chemisch-thermischen Verarbeitung P-haltiger Klärschlammasche zu Düngerphosphaten", German Federal Ministry of Research and Technology, Research Report T 81-127, July 1981) to heat a mixture of soda, phosphate-containing sewage sludge ash and sand to a temperature of between 1.100°C and 1.250°C in a rotary kiln. There are numerous technical disadvantages to this process: firstly heavy metals that are present in the starting material will not be removed from the resulting fertilizer; secondly the process is very energy intensive because the air within the rotary kiln, although not used in the process, needs to be heated in order to retain the required reaction temperature.

[0005] The document Adam C. et al, "Thermochemical treatment of sewage sludge ashes for phosphorus recovery", in Waste Management, 2009, pp 1122-1128, discloses a thermochemical treatment of sewage sludge ashes for phosphorus recovery is disclosed wherein chloride salts are added to remove heavy metals.

[0006] It is the object of the present invention to provide for a reliable separation of heavy metals from phosphoric material in an energy efficient way which is also easier to operate and less cost intensive than the processes of the prior art. This problem is solved by the present invention in a process according to claim 1 comprising the following steps:
  1. (i) heating the starting material to a temperature of 600 to 1.200 °C, preferably 700 to 1.100°C, in a first reactor and withdrawing combustion gas;
  2. (ii) using the combustion gas of step (i) to preheat an alkaline source; and
  3. (iii) transferring the heated starting material of step (i) and the preheated alkaline source of step (ii) to a second reactor, adding an elemental carbon source, heating to a temperature of between 700 to 1.100 °C and withdrawing process gas and a product stream.


[0007] The process according to the invention uses an alkaline source to convert the phosphorous contained in the starting material into soluble phosphate compounds. Preferably, the alkaline source is selected from the group consisting of sodium carbonates, sodium hydroxides, potassium carbonates and potassium hydroxides. Most preferably the alkaline source is Na2CO3 (soda ash). Preferably, the alkaline source is added in an amount of 2-80 wt.-%, preferably 10-50 wt.-% of the starting material.

[0008] According to the invention, elemental carbon is used to reduce the heavy metal components of the starting material for subsequent elimination. Preferably, the elemental carbon source is selected from the group consisting of pulverized lignites, dry sewage sludge or dry biomass. Most preferably, the elemental carbon source is pre-dried sewage sludge. Preferably, the elemental carbon source is added in an amount of 1-40 wt.-%, preferably 3-15 wt.-% of the starting material.

[0009] In order to reach the temperatures inside the first reactor of step (i), it is preferred that a mixture of air and fuel are supplied to said first reactor. Generally, any fuel capable of producing the required temperatures inside the first reactor can be used. Preferred fuels according to the invention are natural gas, sewage sludge and phosphorus containing biomass such as farmyard manure or animal by-products.

[0010] It is preferred that the starting material is pre-heated to a temperature of 300 to 800°C, preferably 400 to 600 °C, and more preferably 520-580°C, prior to the heating in the first reactor of step (i). Said pre-heating is preferably done in multiple stages in order to cool down the combustion gas to a suitable temperature for the preheating of the alkaline source. If soda ash is used as alkaline source, its melting point is 851 °C, so that it should not be directly contacted with the hot combustion gas exiting the first reactor.

[0011] According to the invention the alkaline source is pre-heated in a second pre-heating stage preferably to a temperature of 200 to 500°C, preferably 300 to 400°C, prior to the introduction into the second reactor.

[0012] The process according to the invention is advantageous compared to the state of the art in several aspects.

[0013] Since the major amount of flue gas is generated in the first reactor of step (i), the dimensions of the second reactor in step (iii) can be significantly reduced. Furthermore, there is no need to heat gaseous compounds in the second reactor in step (iii) that are not used in the reaction, thereby drastically reducing energy requirements compared to the state of the art processes.

[0014] The pre-heating of the alkaline source in step (ii) of the process according to the invention further reduces the energy necessary to heat the second reactor in step (iii).

[0015] The mixture of the alkaline source and the elemental carbon source in the second reactor in step (iii) enhances the decomposition of the alkaline source and therefore the formation of soluble phosphate compounds.

[0016] It is preferred that the process gas in step (iii) is cooled below the condensation temperature of the heavy metal compounds to allow for their precipitation and removal.

[0017] The remaining, phosphorus rich solids leave the reactor and are conveyed to a finishing section to manufacture straight phosphorus or complex fertilizer.

[0018] The phosphorus rich solids withdrawn from the second reactor in step (iii) may be mixed with a high grade straight phosphorus carrier and/or a nutrition carrier to obtain highly valuable phosphate fertilizer. The solids may be homogenized and granulated to facilitate the further handling.

[0019] According to an embodiment of the present invention the combustion gases from step (i) are fed into a cyclone separator and subsequently into a Venturi section of the first preheating stage.

[0020] Subsequently, the combustion gases are withdrawn from the cyclone separator, enter a Venturi section of a second preheating section and are admixed with an alkaline source according to step (ii).

[0021] The present invention is also directed to a plant for separating heavy metals from phosphoric starting material according to claim 12 which is adapted to perform the process as described above. The plant comprises a first reactor for heating the material having at least one line for withdrawing combustion gas, a first preheating stage for preheating the starting material, a second preheating stage for heating an alkaline source, and a second reactor for heating the heated starting material and the preheated alkaline source as well as an elemental carbon source having at least one line for withdrawing process gas and at least one line for withdrawing a product stream.

[0022] Preferably, the first reactor of step (i) is a fluidized bed reactor, operating with an expanded solids surface that ensures an ideal heat transfer. The second reactor in step (iii) preferably is a rotary kiln.

[0023] According to a preferred embodiment of the invention, the first and/or the second pre-heating stage each comprises a Venturi section and a cyclone separator. The Venturi section assists in mixing the added material with the hot gas while in the cyclone separator the solids are separated from the gas and then transferred to the first and second reactor, respectively.

[0024] The invention will now be described in more detail on the basis of preferred embodiments and the drawings.

[0025] In the drawings:
Fig. 1
is a simplified block diagram of a plant implementing the process of the present invention.


[0026] In the plant shown in Fig. 1, a phosphorous-containing raw or starting material such as sewage sludge or biomass ash or rock phosphate is pneumatically conveyed from non-illustrated storage silos to a first preheating stage 2 comprising a Venturi section 2a and a cyclone separator 2b. Thereby, the starting material is intensively mixed with a hot combustion gas withdrawn from a first reactor 1 and heated to a temperature of 400 to 600°C, preferably about 575°C. In the cyclone separator 2b the solid material is separated from the gas and transferred via line 3 into the first reactor 1, which preferably is a fluidized bed reactor. In the first reactor 1, the preheated starting material is heated by the combustion of fuel, such as natural gas, biomass or sewage sludge supplied through fuel line 4 with air supplied through air line 5. The air may be introduced under elevated pressure via compressor 6. In the first reactor 1 the starting material is heated to a temperature of 700 to 1.100°C, preferably 900 to 1.000°C and in particular about 950°C.

[0027] The thus heated starting material is withdrawn from the first reactor 1 through line 7 and is fed to a second reactor 20, preferably a rotary kiln reactor. The level of the inventory in the first reactor 1 can be controlled by a seal pot 8 such as described in document WO 2008/104250 A, a dip leg seal or the like. The combustion gases are withdrawn from the first reactor 1 through line 9 into a cyclone separator 10 for separating the gas from the solid material. The solid material is withdrawn at the bottom of the cyclone separator 10 and transferred to the second reactor 20 through line 7. The hot combustion gases enter into the Venturi section 2a of the first preheating stage 2 for preheating the starting material.

[0028] From the cyclone separator 2b of the first preheating stage 2 the gas is withdrawn at the top and enters a Venturi section 11a of a second preheating stage 11 where soda ash is added as a preferred alkaline source and mixed with the heating gas. The mixture then is transferred into a cyclone separator 11b for separating the solids from the gas. In the second preheating stage 11 the alkaline source is preheated to 300 to 400°C, preferably about 360°C, and then transferred into the second reactor 20 through line 16. The gas is withdrawn at the top of cyclone separator 11b and transferred into separator 13 via line 12, where the solids are separated from the gas after a suitable, calcium or sodium based, sorbent such as calcium hydrate, calcium carbonate or sodium hydrogen carbonate has been added. Finally, after passing through a filter 14, preferably an electrostatic precipitator and other suitable cleaning device, for recovering additional solids that may be introduced into the second reactor 20 though line 15, the clean gas is removed from the plant.

[0029] The starting material supplied from the first reactor 1 through line 7 and the alkaline source supplied through lines 15, 16 is introduced into the second reactor 20 and heated therein to a temperature of 700 to 1.100, preferably 900 to 1.000°C and in particular about 950°C. In addition to the starting material and the alkaline source an elemental carbon source, in particular pre-dried sewage sludge, biomass, pulverized lignite or coal and/or coke, is fed to the second reactor 20 through line 17. Air may be introduced through line 5. The compounds may be mixed before entering the second reactor 20 or supplied separately and mixed within reactor 20, preferably by rotation. Thereby the alkaline source decomposes into X + Y (where X is the alkaline ion and Y is a carbonate or hydrogen anion) and the elemental carbon source reduces the heavy metals to their elemental form. For soda ash the reaction is as follows:

        Na2CO3 + C → Na2O + 2CO



[0030] The heavy metals evaporate and leave the second reactor 20 with the process gas through line 21. The remaining, phosphorus rich solids leave the second reactor 20 through a gas-tight outlet and product line 22 and are cooled.

[0031] The semi-product withdrawn through product line 22 is free from toxic heavy metals and conveyed to a finishing section (not shown) where it is manufactured to straight phosphorus or complex fertilizers.

[0032] The process gas from the second reactor 20 contains the elemental heavy metals. Said process gas is transmitted via line 21 into separator 23 where it is quenched to about 200-400°C with fresh air or water to condensate the heavy metal compounds to solid particles. These particles are captured in a baghouse filter(not shown) as filter dust. Alternatively, the solids may be separated from the gas by electrostatic precipitation. Until heavy metal recycling will be commercially viable, the filter dust will be deposited as secondary waste. Finally, the purified process gas is fed back into first reactor 1 via line 24.

[0033] At the point of leaving the thermo-chemical process, the semi-product already complies with the requirements of the fertilizer act. The concentration of toxic substances and particularly of cadmium and uranium is one to two orders of magnitude below the respective concentrations in phosphate rock based fertilizers.

[0034] To comply with the phosphate concentration tolerances required by most fertilizer acts in the order of +/- 0.8 percentage points of total P2O5, a measured amount of a high grade straight phosphorus (P) carrier may be added to the semi-product. For this purpose, the semi-product is analyzed online for its concentration of P2O5 and one or several guiding heavy metals. Depending on the desired phosphate concentration in the final product, a measured quantity of triple-superphosphate (TSP) or phosphoric acid is admixed and homogenized. Alternatively and for the production of a phosphate fertilizer for organic farming, phosphate rock is used instead of TSP to adjust the P-concentration.

[0035] As a first option the product is homogenized and granulated in a mixer-granulator and - depending on the final purpose - finished as dust free powder or as final granules. From this stage, the product has become the final product of the plant that either will be sold to the agricultural product distributors or to fertilizer manufacturers.

[0036] As a second option, the plant can be extended to manufacture complex fertilizers by admixture of additional nutrient carriers. This step requires additional silos/storing facilities and the corresponding design of the finishing section of the plant to handle the additional nutrient and fertilizer quantities. In this case, the product and additional nutrient carriers are conveyed and fed to the mixer-granulator in ratios determined by the target fertilizer type. By adding small amounts of water and - depending on the requirements - binders and coating agents, complex fertilizer granules of homogenous composition and a determined corn size distribution are produced that comply with all requirements in terms of threshold values, tolerances and nutrient solubility.

[0037] The raw material, ash, does not contain combustible and halogenic-organic substances. It mainly consists of phosphate, calcium, silicon, iron and aluminum compounds.

[0038] The starting material treatment capacity of the plant may be e.g. 4-10 tons per hour. Raw materials are heated by natural gas burners or by combusting sewage sludge or biomass, and energy is efficiently recycled within the plant. Process emissions are effectively controlled by a sequence of adsorption reactors and baghouse filters. The heavy metals are captured as dry filter dust and safely disposed of in a landfill.

[0039] Application of the product as a phosphate fertilizer is more environment friendly than using either conventional mineral fertilizers or recycled organic fertilizers. In comparison to conventional mineral fertilizers, concentrations of cadmium and uranium are 1-2 orders of magnitude lower. In comparison to organic fertilizers, no risk of transfer of organic pollutants to the food and feed chain exists.

[0040] Additional nutrient carriers are exclusively licensed fertilizers as ammonium sulfate, potassium chloride (MOP), potassium sulfate (SOP) and converter slag. Triple-superphosphate and the finished products will be stored in silos or as bulk material in covered warehouses. Binders and coating agents and - on demand - phosphorus and sulfuric acid are stored in compliance with legal requirements.

List of reference numerals:



[0041] 
1
first reactor
2
first preheating stage
2a
Venturi section
2b
cyclone separator
3
line
4
fuel line
5
air line
6
compressor
7
line
8
dip leg seal
9
line
10
cyclone separator
11
first preheating stage
11a
Venturi section
11b
cyclone separator
12
line
13
separator
14
filter
15
line
16
line
17
line
20
second reactor
21
line
22
product line
23
separator
24
line



Claims

1. A process for separating heavy metals from phosphoric starting material comprising the following steps:

(i) heating the starting material to a temperature of 600 to 1.200°C in a first reactor (1) and withdrawing combustion gas;

(ii) using the combustion gas of step (i) to preheat an alkaline source; and

(iii) transferring the heated starting material of step (i) and the heated alkaline source of step (ii) to a second reactor (20), adding an elemental carbon source, heating to a temperature of 700 to 1.100°C and withdrawing process gas and a product stream.


 
2. The process according to claim 1, characterized in that the starting material is pre-heated in at least a first preheating stage (2) to a temperature of 300 to 800°C prior to step (i).
 
3. The process according to claim 1 or 2, characterized in that the starting material is pre-heated in multiple stages prior to step (i).
 
4. The process according to any of the preceding claims, characterized in that the alkaline source is pre-heated in a second preheating stage (11) to a temperature of 200 to 500°C prior to the introduction into the second reactor (20).
 
5. The process according to any of the preceding claims, characterized in that the alkaline source is selected from the group consisting of sodium carbonates, sodium hydroxides, potassium carbonates and potassium hydroxides or any combination thereof, wherein the alkaline source preferably is soda ash.
 
6. The process according to any of the preceding claims, characterized in that the alkaline source is added in an amount of 2 to 80 wt.-%, preferably 10-50 wt.-%, of the starting material
 
7. The process according to any of the preceding claims, characterized in that the elemental carbon source is selected from the group consisting of pulverized lignites, dry sewage sludge, dry biomass, pulverized lignite, coal and/or coke or any combination thereof, and wherein the elemental carbon source preferably is added in an amount of 1 to 40 wt.-%, more preferably 3 to 15 wt.- %, of the starting material.
 
8. The process according to claim 2, characterized in that the combustion gases from step (i) are fed into a cyclone separator (10) and subsequently into a Venturi section (2a) of the first preheating stage (2).
 
9. The process according to any of the preceding claims, characterized in that the combustion gases from step (i) are withdrawn from a cyclone separator (2b), enter a Venturi section (11a) and are admixed with an alkaline source according to step (ii).
 
10. The process according to any of the preceding claims, characterized in that the process gas in step (iii) is cooled below the condensation temperature of the heavy metal compounds to allow for their precipitation and removal.
 
11. The process according to claim 10, characterized in that the heavy metal-free process gas is recycled into the first reactor (1).
 
12. A plant for separating heavy metals from phosphoric starting material adapted to perform a process as defined in any of the preceding claims, wherein the plant comprises a first reactor (1) adapted to heat the starting material to a temperature of 600 to 1.200°C, a first preheating stage (2) for preheating the starting material, a second preheating stage (11) for heating an alkaline source, and a second reactor (20) adapted to heat the heated starting material and the pre-heated alkaline source as well as an elemental carbon source to a temperature of 700 to 1.100°C and having at least one line (21) for withdrawing process gas and at least one product line (22) for withdrawing a product stream, and the first reactor (1) having at least one line for withdrawing combustion gas for preheating the alkaline source.
 
13. The plant according to claim 12, characterized in that the first preheating stage (2) for preheating the starting material fed to the first reactor (1) comprises multiple stages.
 
14. The plant according to claim 12 or 13, characterized in that the first and/or the second pre-heating stage (2; 11) each comprises a Venturi section (2a; 11a) and a cyclone separator (2b; 11b).
 
15. The plant according to any of claims 12 to 14, characterized in that the first reactor (1) is a fluidized bed reactor and/or the second reactor (20) is a rotary kiln.
 


Ansprüche

1. Ein Verfahren zum Abtrennen von Schwermetallen aus phosphorhaltigem Ausgangsmaterial umfassend die folgenden Schritte:

(i) Aufheizen des Ausgangsmaterials auf eine Temperatur von 600°C bis 1200°C in einem ersten Reaktor (1) und Abziehen von Verbrennungsgas;

(ii) Verwenden des Verbrennungsgases aus Schritt (i) zum Vorwärmen einer alkalischen Quelle; und

(iii) Übertragen des aufgeheizten Ausgangsmaterials aus Schritt (i) und der aufgeheizten alkalischen Quelle aus Schritt (ii) zu einem zweiten Reaktor (20), Hinzufügen einer Quelle elementaren Kohlenstoffs, Aufheizen auf eine Temperatur von 700°C bis 1100°C und Abziehen von Prozessgas und einem Produktstrom.


 
2. Das Verfahren nach Anspruch 1, dadurch gekennzeichnet, dass das Ausgangsmaterial vor dem Schritt (i) in wenigstens einer Vorwärmestufe (2) auf eine Temperatur von 300°C bis 800°C vorgewärmt wird.
 
3. Das Verfahren nach Anspruch 1 oder 2, dadurch gekennzeichnet, dass das Ausgangsmaterial vor dem Schritt (i) in mehreren Stufen vorgewärmt wird.
 
4. Das Verfahren nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass die alkalische Quelle vor dem Einbringen in den zweiten Reaktor (20) in einer zweiten Vorwärmestufe (11) auf eine Temperatur von 200°C bis 500°C vorgewärmt wird.
 
5. Das Verfahren nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass die alkalische Quelle aus der Gruppe ausgewählt wird, die aus Natriumcarbonaten, Natriumhydroxiden, Kaliumcarbonaten und Kaliumhydroxiden oder Kombinationen hiervon besteht, wobei die alkalische Quelle vorzugsweise kalziniertes Soda ist.
 
6. Das Verfahren nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass die alkalische Quelle in einer Menge von 2 bis 80 Gewichtsprozent, vorzugsweise 10 bis 50 Gewichtsprozent des Ausgangsmaterials hinzugefügt wird.
 
7. Das Verfahren nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass die Quelle elementaren Kohlenstoffs aus der Gruppe ausgewählt wird, die aus pulverisierten Ligniten, trockenem Klärschlamm, trockener Biomasse, pulverisierter Braunkohle, Kohle und/oder Koks oder einer Kombination hiervon besteht, und wobei die Quelle elementaren Kohlenstoffs vorzugsweise in einer Menge von 1 bis 40 Gewichtsprozent, stärker bevorzugt 3 bis 15 Gewichtsprozent des Ausgangsmaterials hinzugefügt wird.
 
8. Das Verfahren nach Anspruch 2, dadurch gekennzeichnet, dass die Verbrennungsgase aus Schritt (i) in einen Zyklonabscheider (10) und anschließend in einen Venturi-Abschnitt (2a) der ersten Vorwärmstufe (2) eingebracht werden.
 
9. Das Verfahren nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass die Verbrennungsgase aus Schritt (i) von einem Zyklonabscheider (2b) abgezogen werden, in einen Venturi-Abschnitt (11a) eintreten und gemäß Schritt (ii) mit einer alkalischen Quelle gemischt werden.
 
10. Das Verfahren nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass das Prozessgas in Schritt (iii) unter die Kondensationstemperatur der Schwermetallverbindungen gekühlt wird, um ihre Abscheidung und Entfernung zu ermöglichen.
 
11. Das Verfahren nach Anspruch 10, dadurch gekennzeichnet, dass das schwermetallfreie Prozessgas in den ersten Reaktor (1) zurückgeführt wird.
 
12. Eine Anlage zum Abtrennen von Schwermetall aus phosphorhaltigem Ausgangsmaterial, die dazu ausgestaltet ist, ein Verfahren nach einem der vorhergehenden Ansprüche durchzuführen, wobei die Anlage einen ersten Reaktor (1), der dazu ausgestaltet ist, das Ausgangsmaterial auf eine Temperatur von 600°C bis 1200°C aufzuheizen, eine erste Vorwärmestufe (2) zum Vorwärmen des Ausgangsmaterials, eine zweite Vorwärmestufe (11) zum Aufheizen einer alkalischen Quelle und einen zweiten Reaktor (20), der dazu ausgestaltet ist, das aufgeheizte Ausgangsmaterial und die vorgewärmte alkalische Quelle sowie eine Quelle elementaren Kohlenstoffs auf eine Temperatur von 700°C bis 1100°C aufzuheizen, und der wenigstens eine Leitung (21) zum Abziehen von Prozessgas und wenigstens eine Produktleitung (22) zum Abziehen eines Produktstroms hat, aufweist, und wobei der erste Reaktor (1) wenigstens eine Leitung zum Abziehen von Verbrennungsgas zum Vorwärmen der alkalischen Quelle aufweist.
 
13. Die Anlage nach Anspruch 12, dadurch gekennzeichnet, dass die erste Vorwärmestufe (2) zum Vorwärmen des Ausgangsmaterials, das dem ersten Reaktor (1) zugeführt wird, mehrere Stufen aufweist.
 
14. Die Anlage nach Anspruch 12 oder 13, dadurch gekennzeichnet, dass die erste und/oder die zweite Vorwärmestufe (2; 11) jeweils einen Venturi-Abschnitt (2a; 11a) und einen Zyklonabscheider (2b, 11b) aufweist.
 
15. Die Anlage nach einem der Ansprüche 12 bis 14, dadurch gekennzeichnet, dass der erste Reaktor (1) ein Wirbelschichtreaktor und/oder dass der zweite Reaktor (20) ein Drehrohrofen ist.
 


Revendications

1. Procédé de séparation de métaux lourds à partir d'un matériau de départ phosphorique comprenant les étapes suivantes :

(i) chauffer le matériau de départ à une température de 600 à 1200 °C dans un premier réacteur (1) et retirer le gaz de combustion ;

(ii) utiliser le gaz de combustion de l'étape (i) pour préchauffer une source alcaline ; et

(iii) transférer le matériau de départ chauffé de l'étape (i) et la source alcaline chauffée de l'étape (ii) à un second réacteur (20), en ajoutant une source de carbone élémentaire, chauffer à une température de 700 à 1100 °C et retirer le gaz du procédé et un courant de produit.


 
2. Procédé selon la revendication 1, caractérisé en ce que le matériau de départ est préchauffé en au moins une première étape de préchauffage (2) à une température de 300 à 800 °C avant l'étape (i).
 
3. Procédé selon la revendication 1 ou 2, caractérisé en ce que le matériau de départ est préchauffé en de multiples étapes avant l'étape (i).
 
4. Procédé selon l'une quelconque des revendications précédentes, caractérisé en ce que la source alcaline est préchauffée dans une seconde étape de préchauffage (11) à une température de 200 à 500 °C avant l'introduction dans le second réacteur (20).
 
5. Procédé selon l'une quelconque des revendications précédentes, caractérisé en ce que la source alcaline est choisie dans le groupe constitué par les carbonates de sodium, les hydroxydes de sodium, les carbonates de potassium et les hydroxydes de potassium ou une quelconque de leurs combinaisons, où la source alcaline est de préférence de la cendre de soude.
 
6. Procédé selon l'une quelconque des revendications précédentes, caractérisé en ce que la source alcaline est ajoutée en une quantité de 2 à 80 % en poids, de préférence de 10 à 50% en poids, du matériau de départ.
 
7. Procédé selon l'une quelconque des revendications précédentes, caractérisé en ce que la source de carbone élémentaire est choisie dans le groupe constitué par les lignites pulvérisées, la boue d'épuration sèche, la biomasse sèche, la lignite pulvérisée, le charbon et/ou le coke ou l'une quelconque de leurs combinaisons, et où la source de carbone élémentaire est de préférence ajoutée en une quantité de 1 à 40 % en poids, davantage de préférence de 3 à 15 % en poids du matériau de départ.
 
8. Procédé selon la revendication 2, caractérisé en ce que les gaz de combustion de l'étape (i) sont alimentés dans un séparateur à cyclone (10) et ensuite dans une section de Venturi (2a) de la première étape de préchauffage (2).
 
9. Procédé selon l'une quelconque des revendications précédentes, caractérisé en ce que les gaz de combustion de l'étape (i) sont retirés d'un séparateur à cyclone (2b), entrent dans une section de Venturi (11a) et sont mélangés avec une source alcaline selon l'étape (ii).
 
10. Procédé selon l'une quelconque des revendications précédentes, caractérisé en ce que le gaz du procédé dans l'étape (iii) est refroidi au dessous de la température de condensation des composés de métaux lourds pour permettre leur précipitation et enlèvement.
 
11. Procédé selon la revendication 10, caractérisé en ce que le gaz du procédé sans métal lourd est recyclé dans le premier réacteur (1).
 
12. Installation de séparation de métaux lourds à partir d'un matériau de départ phosphorique adaptée pour effectuer un procédé tel que défini dans l'une quelconque des revendications précédentes, où l'installation comprend un premier réacteur (1) adapté pour chauffer le matériau de départ à une température de 600 à 1200 °C, une première étape de préchauffage (2) pour préchauffer le matériau de départ, une seconde étape de préchauffage (11) pour chauffer une source alcaline, et un second réacteur (20) adapté pour chauffer le matériau de départ chauffé et la source alcaline préchauffée ainsi qu'une source de carbone élémentaire à une température de 700 à 1100 °C et ayant au moins une ligne (21) pour retirer le gaz du procédé et au moins une ligne de produit (22) pour retirer un courant de produit, et le premier réacteur (1) ayant au moins une ligne pour retirer le gaz de combustion pour préchauffer la source alcaline.
 
13. Installation selon la revendication 12, caractérisée en ce que la première étape de préchauffage (2) pour préchauffer le matériau de départ alimenté au premier réacteur (1) comprend de multiples étapes.
 
14. Installation selon la revendication 12 ou 13, caractérisée en ce que la première et/ou la seconde étape de préchauffage (2, 11) comprennent chacune une section de Venturi (2a ; 11a) et un séparateur à cyclone (2b ; 11b).
 
15. Installation selon l'une quelconque des revendications 12 à 14, caractérisée en ce que le premier réacteur (1) est un réacteur à lit fluidisé et le second réacteur (20) est un four rotatif.
 




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Cited references

REFERENCES CITED IN THE DESCRIPTION



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Non-patent literature cited in the description