Method for producing hydraulic binder and device for carrying out said method

Abstract

The present invention relates to a method for producing a hydraulic binder, in which a molten slag containing P2O5 and iron oxide and further containing CaO and SiO2 is subjected to a cooling step after adding an oxidizing agent for the iron oxide, and the molten slag (6) is granulated to form an amorphous slag glass.

Description

[Technical field]

[0001] The present invention relates to a method for producing a hydraulic binder and to an apparatus for carrying out the method according to the invention. [Background technology]

[0002] Sewage sludge, animal meal, bone meal, and similar organic waste materials can be incinerated and slag-formed at temperatures between about 1420°C and 1600°C to produce a homogeneous slag melt that contains significant amounts of phosphate as well as iron species.

[0003] The slag melt, in which redox reactions between phosphates and iron species are possible and further potential reaction partners are yet to be defined, not only raises the question of the possible formation of iron phosphides from phosphates and iron species, but also makes it desirable to have an economically rational use of this slag melt, which occurs in not inconsiderable quantities. Summary of the Invention

[0004] The object of the present invention is therefore, on the one hand, to render such slag melt harmless and, on the other hand, to obtain valuable products therefrom.

[0005] The present invention therefore provides a method for producing a hydraulic binder, the method comprising the steps of: 2 O 5 and iron oxide, and further contains CaO and SiO 2 The method is characterized in that the molten slag containing the above-mentioned is subjected to a cooling step after adding an oxidizing agent for iron oxide, and the molten slag is granulated to form amorphous slag glass. 2 O 5In the present invention, however, it has surprisingly been found that the addition of an oxidizing agent and the resulting formation of spinel or magnetite from the iron oxides results in hydraulic binders which are characterized by particularly high hydraulic properties and which, when mixed with quicklime, ZnO, soda, water glass, Portland clinker or gypsum, constitute a valuable hydraulically effective cement component. The iron contained in these slags is converted into magnetite by an oxidation process during vitrification.

[0006] In the method according to the invention, the P of the slag melt 2 O 5 The content is preferably 2.5% by weight to 30% by weight, more preferably 7.5% by weight to 25% by weight, more preferably 12.5% ​​by weight to 20% by weight, and further preferably 17% by weight to 19% by weight. 2 O 5 The content is 15.84% by weight, and furthermore, CaO is 27.28% by weight, MgO is 3.08% by weight, and K is 1.06% by weight. 2 O is 0.704% by weight, SiO 2 is 25.08 wt%, Al 2 O 3 13.2% by weight, Fe 2 O 3 12.2% by weight, and SO 3 The slag melt used contains 1.32% by weight of .Other components may also be included.

[0007] In order to be able to carry out the cooling step for granulating the slag melt to produce a highly amorphous hydraulic binder as quickly as possible, the method according to a preferred embodiment of the present invention is characterized in that the basicity of the slag melt (wt.% CaO / SiO 2This is further developed in that the basicity (wt.%) is set to a value of 0.85-1.3, in particular to a value of 1.2, by adding a lime or aluminum carrier before the cooling step. By setting the basicity to a value in this range, the viscosity of the slag melt is low and the largest possible surface is formed during the cooling step, which results in rapid cooling. This prevents the formation of slag crystals and in the best case a completely amorphous product is obtained as slag glass.

[0008] In the method according to the invention, P is used to produce the hydraulic binder. 2 O 5 When using a slag melt with a particularly high content of P, the method according to a preferred embodiment of the invention can be carried out by adding elemental aluminum, preferably together with aluminum oxide, to the slag melt before the cooling step and / or by adding at least one carbon carrier, preferably together with lump coke and coke dust, and by absorbing the P formed thereby. 2 The effect of removing P and CO from the gas phase can be improved by adding elemental aluminum. 2 O 5 From gaseous P 2 The aluminothermic reduction to gaseous P 2 is removed from the gas phase and then obtained by condensation. 2 O 3 The content of Fe 2 O 3 to FeO (Fe 3+ →Fe 2+ In this case, the redox equilibrium is P 2 O 5 The addition of elemental aluminum is established when the content of CaO, SiO in the formed slag glass is about 3.5% by weight. In this way, not only is the quality of the hydraulic binder produced by the method according to the invention ensured, but in addition, extremely pure phosphorus species are obtained, which are valuable raw materials. 2 and Al 2 O 3It is preferable to carry out the process until the weight ratio of P is balanced. 2 O 5 In the case of high contents of ZnO, Zn halides, organic Zn compounds (such as Zn formate and / or Zn acetate) and / or inorganic Zn compounds, these can be advantageously used to obtain special cements with high strength and good biocompatibility. In the case of no addition of the aforementioned Zn species, the formed slag glass can optionally also be used as a fertilizer component rich in lime and phosphate.

[0009] P 2 O 5 Since the aluthermic reduction of is obviously an exothermic reaction, it is necessary to moderate this reaction in order to avoid excessive heating of the slag melt and possible distortion phenomena. For this reason, it is preferable to add aluminium oxide as a moderator of the aluminium reduction. In this case, aluminium oxide, as the oxidation product of aluminium used to reduce phosphorus oxide, is a moderator, and aluminium oxide is known to be easily compatible with cements and significantly increases the early strength of such cements, so that the addition of relatively large amounts of aluminium oxide does not cause problems for the quality of the hydraulic binder produced by the method according to the invention.

[0010] When a carbon carrier is added, lump coke with a high proportion of coke dust is usually used to accelerate the reduction rate because the specific surface area of ​​coke dust is very high, which requires a high level of turbulence between the melt and the reducing agent.

[0011] According to a preferred embodiment of the present invention, the slag reduction is carried out by adding calcium carbide, preferably together with coal dust, to the slag melt before the cooling step, thereby forming P 2and CO from the gas phase. The addition of calcium carbide (optionally mixed with coal dust) results in an exothermic reduction that can be mitigated by an endothermic carbon reduction, optionally occurring simultaneously with the coal dust. The corresponding oxide content is reduced according to the following reaction: P 2 O 5 +CaC 2 +2C → CaO+P 2 (gas) + 4CO(gas)

[0012] The CaO formed here reacts directly in the slag melt, increasing the slag basicity (CaO / SiO 2 ) is very favorably increased. The FeO in the slag melt reacts reductively and exothermically with the addition of calcium carbide according to the following equation: 3FeO+CaC 2 → 3Fe(molten) + CaO + CO(gas)

[0013] Again, the basicity of the slag melt increases. CaC 2 The addition of also leads to optimal desulfurization of P-gas, since sulfur compounds are almost completely incorporated into the slag melt.

[0014] The addition of the Al carrier (skimming or dross)-calcium carbide mixture improves the basicity of the slag and the Al content before granulation of the slag melt. 2 O 3 This is particularly advantageous with regard to the final slag product, in particular its cementitious properties, since both the content of calcium carbide and the amount of calcium carbonate can be adjusted in a particularly advantageous manner. The addition of coal dust results in a more gradual reduction, reducing the need for expensive calcium carbide.

[0015] Alternatively or additionally, according to a preferred embodiment of the present invention, the slag melt before the cooling step is heated at an electrode voltage of preferably 16 V to 24 V under P 2 O 5 and the resulting P 2As a rule, about 6.8 kWh of power is required per kg of phosphorus. If an inert anode is used, O is used as the anode gas. 2 When a graphite anode is used, CO is generated as an anode gas.

[0016] Within the scope of the present invention, it is also possible to combine the aforementioned reduction processes, which allow the target residual phosphate and iron oxide contents of the product slag to be optimally controlled and set, resulting in a valuable hydraulic binder after the cooling process.

[0017] As already mentioned several times, it is desirable for the slag melt used as the starting product of the method according to the invention for producing hydraulic binders to be vitrified as completely as possible. For this purpose, the method according to the invention is preferably further developed in such a way that the cooling step consists of dispersing the slag melt in a water bath, the temperature of the water bath for the slag melt being preferably between 80 ° C and the boiling point, preferably between 85 ° C and the boiling point, more preferably between 90 ° C and the boiling point, particularly preferably between 95 ° C and the boiling point. According to this preferred procedure, the starting slag melt is introduced into the water bath and dispersed as finely as possible in the water bath in order to ensure rapid heat transfer from the slag melt to the water bath. The adjustment of the basicity of the slag melt and the associated reduction in viscosity described above is useful here, since a slag melt with a basicity value between 0.85 and 1.3 is dispersed, i.e. divided and crushed, for example by stirring in a water bath, by the shear forces that arise during stirring. For particularly rapid cooling, the water bath is preferably kept at an elevated temperature, preferably above 80° C., and at its boiling point, so that when the slag melt is introduced, the water in the water bath immediately evaporates, and the enthalpy of vaporization of the water is immediately available for cooling the slag melt; as is well known, a particularly large amount of heat is absorbed by water.

[0018] Of course, a large amount of water is evaporated here and a correspondingly large amount of steam is formed. For this reason, the method according to the invention is preferably further developed in this context in such a way that the steam from the water bath arising during the cooling step is collected, condensed and returned to the water bath, the condensation being preferably carried out in the form of adiabatic compression in order to recover the exergetically usable waste heat from the steam. In this case, a closed steam circuit can be formed, so that there is no leakage of steam, which is problematic when carrying out the method according to the invention. According to a preferred embodiment, the condensation is carried out in the form of adiabatic compression in order to recover the waste heat from the steam. Adiabatic compression of steam for waste heat recovery is known in the art as thermal compression, and since the heat of condensation of the steam occurs at a higher temperature level, in contrast to isobaric compression by cooling, a large part of the waste heat of the steam can also be obtained as sensible heat by heat exchange.

[0019] According to a preferred embodiment of the invention, the steam from the water bath arising during the cooling step is collected, condensed and returned to the water bath, the steam is brought to a temperature between 180°C and 220°C by compression, and the heat of the steam is used for drying the mechanically dewatered sewage sludge. The enthalpy of the steam obtained in the boiling water granulation (100°C, normal pressure) can be raised by a steam compressor (optionally in combination with an adiabatic steam compressor) to the aforementioned temperature level, preferably to a temperature level of about 210°C, and can be advantageously used particularly economically for the thermal drying of mechanically dewatered sewage sludge having a dry matter of about 25% to about 60%. By pre-adding CaO to the still wet sewage sludge, the basicity is pre-set and the nitrogen from the sewage sludge can be converted into valuable ammonia (NH 3 ) is excreted.

[0020] In the thermal compression, the steam is compressed by a steam compressor from 100° C. and normal pressure to 400° C. and an overpressure of 13 bar. For this purpose, a steam compression work of 0.164 kWh / kg is performed. After compression, this high-pressure steam has a heat content of 0.905 kWh / kg, which can be recovered, for example in the form of electricity, by condensing the steam at this temperature via heat exchange. With a realistic efficiency of the steam turbine, about 0.271 kWh / kg can be generated in the form of electric current. Thus, after deducting the compression work, about 0.1 kWh / kg of steam can be exported from this process in the form of electric current. In the method according to the invention, about 1100 kg of steam is generated per tonne of slag melt, which results in the export of 110 kWh of electricity per tonne of slag melt. This results in a reduction in the CO2 emissions from the treatment of the slag melt. 2 can be significantly reduced.

[0021] According to a preferred embodiment, the method according to the invention uses as oxidant an oxygen carrier, in particular air, O 2 , CO 2 , water and / or water steam are used.

[0022] In the process according to the invention, in particular in the procedure in which the cooling step is carried out in a water bath, in particular in a water bath kept at a temperature between 80° and the boiling point, a microporous slag glass is obtained granulated in the form of hollow spheres, which property makes it suitable for further processing, preferably by crushing the granulated slag glass to a particle size preferably less than 80 micrometers. 2 O 5 Compared to slag glass that contains little or no P 2 O 5Due to the extremely high porosity, which is increased by the higher content of , the grinding of the granulated slag glass produced by the method according to the invention requires only very little grinding during grinding and does not cause adhesion to the grinding tool. Thus, very small particle sizes, preferably less than 80 micrometers, can be obtained from the granulated slag glass with little effort. These are very easily compatible and highly reactive with cement, which allows the hydraulic properties of the hydraulic binder produced according to the invention to be further increased. This is accompanied by a particularly advantageous early cement strength.

[0023] The crushing of the highly porous slag glass allows the iron components separated in the oxidation step to be more or less completely separated from the rest of the slag and to be obtained as magnetite, which makes it possible to magnetically separate the iron components from the crushed slag glass, according to a preferred embodiment of the present invention.

[0024] This magnetite is a high-quality synthetic iron ore that can be used, for example, in smelting to form pig iron, as a sintering aid in clinker production, as an adsorbent, or as a catalyst in the Haber-Bosch ammonia synthesis and homogeneous water-gas shift reaction. Furthermore, various spinel-forming substances such as chromium are incorporated into the magnetite phase, resulting in a high-purity cement component that is almost free of heavy metals.

[0025] Any sulfur content that may be present in the starting slag melt is sulfated by the oxidation process to an amorphous slag glass and form gypsum, which further increases the cementitious reactivity of the slag glass. The oxidation of the sulfur present in the starting slag melt to sulfates is catalyzed by magnetite, an iron oxide that is formed during oxidation.

[0026] The apparatus according to the invention for carrying out the method comprises a granulation chamber with a vessel for receiving a water bath and a supply device for the slag melt in the form of an immersion tube reaching into the vessel, the supply device having a rotor that can be rotated in the vessel below the immersion tube in order to rotate the water bath and form a vortex. According to the invention, the supply device is characterized in that it has a melt vessel for the slag melt, at the bottom of which it is arranged concentrically with the immersion tube and has an opening that can be closed by a plunger that is axially displaceable relative to the immersion tube.

[0027] In the device according to the invention, P 2 O 5 and iron oxide, further containing CaO and SiO 2 And Al 2 O 3 The slag melt, which contains the above-mentioned molten metal, can enter the immersion tube as a melt cylinder as thin as possible through an annular gap formed between an opening arranged concentrically at the bottom of the melt vessel for the slag melt and an axially displaceable plunger. The slag melt then impinges on the water bath already as a thin layer and, due to the effect of the rotatably drivable rotor, forms a vortex in the vessel below the immersion tube, so that the slag melt impinging on the rotating water bath is immediately divided and dispersed in the water bath. In this way, extremely rapid cooling of the slag melt occurs and complete vitrification into an amorphous slag glass is achieved.

[0028] To add the oxidizing agent, the device according to the invention is preferably further developed in such a way that a supply line for the gaseous oxidizing agent is led axially through the plunger. In this way, the oxidizing agent is already introduced into the thin layer of the slag melt in the immersion tube and enters the water bath together with the slag melt and is also dispersed there, so that an effective oxidation of the starting slag melt takes place, converting iron oxides into magnetite or spinel, optionally converting sulfur oxides into sulfates and forming gypsum.

[0029] Due to its extremely low density, the amorphous slag glass floats in the vortex of the water bath after being discharged from the area of ​​the rotor. To discharge the hydraulic binder formed in the device according to the invention, the device is designed in accordance with a preferred embodiment of the invention in such a way that the granulation chamber has a discharge area for the granulated slag glass downstream of the weir and is preferably equipped with a sieve surface for drawing off steam to a steam outlet arranged in the discharge area. Alternatively, a hydrocyclone or a pusher centrifuge can be provided for separating the water. The rotation speed of the rotor can be adjusted so that the vortex reaches the very top edge of the weir, so that the floating slag glass is transported over the weir into an application area adjacent to the weir, whereby the slag glass can be discharged from the granulation chamber. By using a sieve surface arranged in the discharge area according to the preferred embodiment, the water, in particular the steam, adhering to the slag glass can be removed through the sieve surface. Thus, completely dry slag glass is obtained after the sieve surface, which can be removed, for example, by the action of a rotary valve.

[0030] According to a preferred embodiment of the invention, the steam outlet forms a siphon which interacts with the vessel, in this way steam condensed at the steam outlet below the sieve surface can be returned directly to the water bath.

[0031] The invention will now be explained in more detail with reference to exemplary embodiments illustrated diagrammatically in the drawings. [Brief description of the drawings]

[0032] [Figure 1] FIG. 1 is a cross-sectional side view of an apparatus according to the present invention. [Diagram 2] FIG. 2 is a vertical section perpendicular to the axial direction at the level of the weir, i.e. at the level of the discharge area from the granulation chamber. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0033] In FIG. 1, an inventive device for carrying out the method according to the invention is designated by the reference number 1. The device 1 comprises a granulation chamber 2 forming a vessel 3 for receiving a water bath 4. The granulation chamber 2 is closed at the upper end by a cover 5, so that the steam generated during the granulation of the slag melt does not escape uncontrollably. A supply device for the slag melt 6 is designated by the reference number 7. The supply device 7 essentially consists of an immersion tube 8 extending into the vessel 3, a melt container 9 for the melt 6 and a plunger 11 displaceable in the axial direction 10 and capable of opening and closing an opening 12 arranged at the bottom 9a of the melt container 9. A supply line 27 for the oxidizer is led axially through the plunger 11. When the opening 12 is opened by the plunger 11, a hollow cylindrical film 13 of the slag melt 6 enters the immersion tube 8 and subsequently impinges on the surface of a vortex 15 formed in the water bath 4 by the action of the rotor 14, where it is immediately dispersed and comminuted. In this way, the slag melt is cooled extremely quickly in the water bath 4 to form amorphous slag glass, which floats on the surface of the vortex 15. By appropriately adjusting the rotation speed of the rotor 14, the formed slag glass reaches the height of the weir 16 and is discharged through it. During discharge, the slag glass flows over a dewatering device in the form of a sieve surface 17, where steam can be removed directly from the slag glass, which is removed through the steam outlet 19 by the action of a suction fan 18. The steam condensed at the steam outlet 19 is again supplied to the water bath through a siphon 20 formed by the steam outlet 19 and interacting with the water bath 4. The steam is then supplied to the compressor 21, where adiabatic compression of the steam takes place, condensed water is produced and returned to the water bath 4 via line 22. Thermal compression also generates waste heat of about 460 kWh per ton of initial slag melt. In addition, non-condensable gases can be removed downstream of the compressor 21. Additionally, water may be supplied via line 23 to make up for losses in the water bath.

[0034] In FIG. 2, the same parts are given the same reference numbers, and it can be seen that the granulation chamber 2 has a substantially rotationally symmetrical cross section and is suitable for forming a vortex by the action of the rotor 14. The amorphous slag glass is discharged tangentially from the water bath into a discharge area 24, in which the weir 15, shown in cross section in FIG. 1, is arranged in the area indicated by reference A in FIG. 2. In the area of ​​the bath 3, a guide element 26, adjustable in the direction of the double arrow 25, can be arranged downstream of the discharge into the discharge area 24 in the direction of rotation of the vortex 15, indicated by the circular arrow in FIG. 2, by means of which the slag glass floating on the vortex can be dammed towards the weir 16. For this purpose, the guide element 26 can also be designed in the form of a rake so as not to excessively hinder the formation of the vortex 15. The dewatering device in the form of a sieve surface is again indicated by reference 17. As already mentioned, the dewatering device can also be designed as a hydrocyclone or a pusher centrifuge.

Claims

1. P ２ O ５ and iron oxide, and further contains CaO and SiO ２ 3. A method for producing a hydraulic binder, comprising the steps of: adding an oxidizing agent for iron oxide to a molten slag (6) and subjecting the molten slag (6) to a cooling step; and granulating the molten slag (6) to form an amorphous slag glass.

2. P of slag melt (6) ２ O ５ 2. The method according to claim 1, characterized in that the content is between 2.5% and 30% by weight, preferably between 7.5% and 25% by weight, more preferably between 12.5% ​​and 20% by weight, even more preferably between 17% and 19% by weight.

3. The basicity of the slag melt (6) (CaO wt.% / SiO ２ 3. The method according to claim 1, wherein the % by weight is set to a value between 0.85 and 1.3 by adding a lime or aluminum carrier before the cooling step.

4. The slag melt (6) before the cooling step is elemental aluminum, preferably together with aluminum oxide, and / or with at least one carbon carrier, preferably lump coke and coke dust, Replenish, The P formed by this ２ and removing CO from the gas phase.

5. Calcium carbide is added to the slag melt (6) before the cooling step, preferably together with coal dust, thereby forming P ２ and removing CO from the gas phase.

6. The slag melt (6) before the cooling step is preferably heated at an electrode voltage of 16V to 24V, ２ O ５ and subjecting the resulting P to electrochemical reduction. ２ The method according to any one of claims 1 to 5, characterized in that the is removed as cathode gas.

7. The method according to any one of claims 1 to 6, characterized in that the cooling step consists of dispersing the slag melt (6) in a water bath (4), the temperature of the water bath (4) for the slag melt (6) being preferably between 80 ° C and the boiling point, more preferably between 85 ° C and the boiling point, even more preferably between 90 ° C and the boiling point, particularly preferably between 95 ° C and the boiling point.

8. 8. The method according to claim 7, characterized in that the steam from the water bath (4) arising during the cooling step is collected, condensed and returned to the water bath (4), the condensation being preferably carried out in the form of an adiabatic compression for the recovery of waste heat from the steam.

9. 6. The method according to claim 5, characterized in that the steam from the water bath (4) arising during the cooling step is collected, condensed and returned to the water bath (4), the steam is brought to a temperature between 180°C and 220°C by compression, and the heat of the steam is used for drying the mechanically dewatered sewage sludge.

10. As an oxidizing agent, an oxygen carrier, particularly air, O ２ , CO ２ 10. The method according to claim 1, wherein water and / or water steam is used.

11. A method according to any one of the preceding claims, characterised in that the granulated slag glass is ground, preferably to a particle size of less than 80 microns.

12. 12. The method according to claim 11, characterized in that the iron components are magnetically separated from the ground slag glass.

13. An apparatus for carrying out the method according to any one of claims 1 to 12, comprising: a granulation chamber (2) provided with a vessel (3) for receiving a water bath (4); a supply device (7) for the slag melt (6) in the form of an immersion tube (8) leading into the vessel (3), the supply device (7) having a rotatably drivable rotor (14) in the vessel (3) below the immersion tube (8) for rotating the water bath (4) and forming a vortex (15); Equipped with 1. An apparatus for carrying out the above-mentioned method, characterized in that the feed device (7) has a melt container (9) for the slag melt (6) and at its bottom (9a) has an opening (12) that is arranged concentrically with the immersion tube (8) and that can be closed by a plunger (11) that is displaceable in the axial direction (10) relative to the immersion tube (8).

14. 14. Apparatus according to claim 13, characterized in that the supply line (27) of the gaseous oxidizer is led axially through the plunger (11).

15. 15. Apparatus according to claim 13 or 14, characterized in that the granulation chamber (2) has, downstream of the weir (16), a discharge area (24) for the granulated slag glass, preferably with a sieve surface (17), and in which a hydrocyclone or a pusher centrifuge is arranged in order to draw off steam to a steam outlet (19).

16. 16. Apparatus according to any one of claims 13 to 15, characterized in that the steam outlet (19) forms a siphon (20) in communication with the vessel (3).

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