Method for separating elemental phosphorus from phosphate-containing starting materials

Abstract

The invention relates to a method for separating elemental phosphorus from phosphate-containing starting materials, in particular from phosphate-containing waste materials such as sewage sludge, comprising at least the following steps: providing at least one phosphate-containing starting material together with free carbon; due to a carbon excess in relation to combustion oxygen, incompletely combusting the free carbon together with the phosphate-containing starting material; collecting a melt (11) of the dephosphorized starting material; withdrawing elemental phosphorus and carbon monoxide, formed during the incomplete combustion, with the gas phase; and separating elemental phosphorus from the gas phase.

Description

[0001] Method for separating elemental phosphorus from phosphate-containing starting materials

[0002] The present invention relates to a method for separating elemental phosphorus from phosphate-containing starting materials, in particular from phosphate-containing waste materials such as sewage sludge, and to a device for carrying out the method according to the invention.

[0003] Prices for phosphate rock have been steadily increasing recently due to the scarcity of suitable raw material sources. Furthermore, the extracted phosphate ores increasingly contain significant levels of uranium, cadmium, selenium, and other harmful substances. Removing such elements is extremely costly, making the use of phosphates from these contaminated ores increasingly uneconomical.

[0004] On the other hand, waste materials sometimes contain relatively high levels of phosphorus compounds. This applies, for example, to sewage sludge, animal meal, bone meal, but also to steel slag, as well as residues from the electronics industry and the like.

[0005] Especially for food production and the pharmaceutical industry, but also for other areas of technology such as electromobility, plant protection products, flame retardants, lubricant production, catalysis and electronic applications, high-purity phosphorus starting materials are needed, which can be produced from elemental phosphorus (P4, white phosphorus).

[0006] However, production is becoming increasingly difficult and is currently no longer carried out, at least in Europe. A major problem in the extraction of elemental phosphorus from the aforementioned feedstocks, particularly from waste materials such as sewage sludge, animal meal, bone meal, and / or steel slag, and / or from materials such as apatite, phosphate ores, and / or phosphorite, lies in the formation of phosphorus sludge. This sludge forms, for example, during the Wöhler process from silicate- and carbon-containing byproducts of iron oxide- and phosphate-containing substances, incorporating various phosphorus species. Phosphorus sludge is highly toxic and poses an immense problem, as its disposal makes the extraction of elemental phosphorus using currently known methods more or less economically unfeasible.Furthermore, in conventional processes for obtaining elemental phosphorus, the formation of phosphines (especially PH3, and in connection with the present invention also generally PH3) is a significant problem. X ) , which are volatile as odorless gases and highly toxic, pose a major problem .

[0007] The present invention is therefore based on the objective of creating a method and a corresponding apparatus that enable the recovery of elemental phosphorus from phosphate-containing waste materials such as sewage sludge and the like, without the formation of phosphorus sludge or phosphines. At the same time, the formation of undesirable iron-phosphorus alloys such as iron phosphides, ferrophores, and Fe3P, as well as CO2 emissions, are to be avoided compared to prior art processes.

[0008] To solve this problem, the aforementioned method according to the invention comprises at least the following steps:

[0009] Providing at least one phosphate-containing feedstock fs together with free carbon f, incomplete combustion of the free carbon fs together with the phosphate-containing feedstock f at an excess of carbon f compared to combustion oxygen f,

[0010] Collecting a melt of the dephosphorus-treated feedstock, removing elemental phosphorus and carbon monoxide formed during incomplete combustion with the gas phase, and separating elemental phosphorus from the gas phase.

[0011] The process according to the invention is thus based on the idea of ​​subjecting the phosphate-containing starting materials, in particular sewage sludge and / or bone meal, together with free carbon, i.e., elemental carbon, to an incomplete combustion process. Within the scope of the present invention, an incomplete combustion process is understood to be an exothermic gasification or carbonization process. Combustion oxygen is supplied to such a process in an amount that does not lead to the complete oxidation of the carbon provided by the phosphate-containing starting material. In other words, the incomplete combustion of the free carbon together with the starting material is carried out at a carbon surplus compared to combustion oxygen.In this way, the carbon is only burned or charred to the point of carbon monoxide, so that virtually no carbon dioxide is emitted in the process according to the invention. The incomplete combustion step results in a melt of the dephosphorus-treated feedstock, which is collected and suitablely further processed, utilized, and / or disposed of. The phosphates contained in the feedstock are reduced during combustion, so that they pass into the gas phase formed during combustion as elemental phosphorus and can be removed with the gas phase. Carbon monoxide is also removed with the gas phase and suitablely further treated. Finally, the elemental phosphorus is separated from the gas phase and utilized. The process according to the invention thus makes it possible to use phosphate-containing feedstocks for the recovery of elemental phosphorus even with relatively low phosphate content.

[0012] To effectively prevent the formation of carbon dioxide in the process according to the invention, a preferred embodiment of the present invention adjusts the proportion of carbon supplied with the phosphate-containing starting material such that the carbon excess compared to the combustion oxygen during the incomplete combustion step is adjusted to a molar ratio of carbon (C) to combustion oxygen (O2) of 2:1 to 8:1, preferably 3:1 to 7:1, more preferably 4:1 to 6:1, and particularly preferably 5:1. Thus, carbon is present in at least the same molar amount as oxygen; however, a significant carbon excess, in particular up to eight times the molar amount of oxygen, is utilized during the partial combustion step, so that carbon is oxidized only to carbon monoxide, but not completely to carbon dioxide.

[0013] Depending on whether the phosphate-containing starting material contains carbon or not, the step of providing the phosphate-containing starting material together with the free carbon according to a preferred embodiment of the present invention is carried out by pyrolysis of dried organic and phosphate-containing starting material, wherein a carbon carrier may optionally be added, and / or by pyrolysis of incinerated phosphate-containing starting material, which is necessarily carried out together with at least one added carbon carrier.In other words, a phosphate-containing organic feedstock, i.e., one containing organic substances and thus carbon, can be provided for the process according to the invention by pyrolysis, whereas a phosphate-containing feedstock that has been incinerated, as is the case with sewage sludge ash, and which therefore no longer contains carbon, requires the addition of a carbon carrier to provide the carbon for the subsequent incomplete combustion in the form of pyrolysis coke. Nevertheless, a carbon carrier can also be added to an organic, phosphate-containing feedstock to adjust or increase the carbon content for incomplete combustion as appropriate, depending on the composition of the phosphate-containing feedstock.

[0014] Wood, preferably waste wood or damaged wood, plastic, preferably recycled plastic, and / or an organic waste fraction can be used as the added carbon carrier, as corresponds to a preferred embodiment of the present invention.

[0015] According to a preferred embodiment of the present invention, the process can be carried out such that the heat generated during incomplete combustion of the gas phase and / or the melt is supplied to the step of providing the phosphate-containing feedstock together with the free carbon, in particular to a pyrolysis of a phosphate-containing feedstock together with a carbon carrier. Naturally, large quantities of heat occur during the incomplete combustion process step, which can be used in an energetically efficient manner for drying, preheating, and preferably also for pyrolyzing the feedstocks.

[0016] Likewise, the pyrolysis gas produced during pyrolysis can be preferentially and particularly advantageously fed into a combustion chamber to generate heat for the pyrolysis process. In this way, a largely closed-loop energy process is created, in which the relatively high heat requirement for drying and, in particular, pyrolysis during the preparation of the feedstocks can be largely met by the subsequent partial combustion. In addition to methane, the gas fractions also contain unsaturated and saturated hydrocarbons, including aliphatics and aromatics, as well as organic acids such as formic acid and acetic acid, and various sulfur and nitrogen compounds such as hydrogen sulfide and ammonia, as well as heterocycles in complex compositions. Such gases must be thermally utilized immediately, which can also be achieved through combustion and thus be used to heat the pyrolysis process.All of this allows for a process that is extremely favorable from an economic and ecological point of view, so that the process according to the invention can be carried out cost-effectively and strict environmental regulations can also be met.

[0017] As mentioned at the outset, the phosphate-containing starting materials can contain not only organic components but also toxins, and in particular heavy metal fractions and alkali compounds. To degrade these harmful accompanying substances as far as possible during the partial combustion process step, the process according to the invention can advantageously be further developed by adding steel mill dust to the starting materials for pyrolysis. Preferably, electric arc furnace dust from the production of specialty steels and stainless steels can be used as steel mill dust, which contains, among other things, catalytically active amounts of zinc, chromium, and nickel. The catalytic effect of this dust leads to the degradation of organics in the gas phase, so that the gas stream generated during the process can be easily dedusted and thus detoxing by conventional filter systems.The catalytic effect of the steelworks dust also extends to the gasification process during the incomplete combustion of the phosphate-containing starting materials, so that the reaction kinetics are favored in the direction of carbon monoxide and elemental phosphorus in accordance with the invention.

[0018] According to a preferred embodiment of the present invention, the pyrolysis oil formed during pyrolysis can be refined into synthetic fuel by hydrogenation. This naturally requires the reaction of the pyrolysis oil with hydrogen. In this context, the process according to the invention can advantageously be further developed such that the carbon monoxide removed with the gas phase is converted to carbon dioxide and hydrogen, preferably by a water-gas shift reaction. In this way, a further beneficial integration of end products and intermediates of the process according to the invention can be achieved, so that, overall, valuable propellants and fuels can be obtained from problematic starting materials, such as sewage sludge, in addition to elemental phosphorus.

[0019] Preferably, the melt of the dephosphorus-treated feedstock is collected as a melt of an iron alloy overlaid with a molten pozzolan. The two phases of this melt can be subjected to different recycling or disposal processes. For example, the molten pozzolan can be further processed into insulating or soundproofing wool. A suitable device for this purpose is described, for example, in publication WO 98 / 45215 A2.

[0020] The puzzolane formed in the process according to the invention can alternatively be processed to obtain a cement component if the puzzolane is rapidly cooled and thus vitrified. In this context, it can be advantageous to add animal meal and / or bone meal to the starting material, for example, sewage sludge, before pyrolysis, as corresponds to a preferred embodiment of the present invention. This increases the calcium content of the mixture and thus the hydraulicity of the resulting cement component. Furthermore, animal meal or bone meal has a particularly high phosphate content as well as a significant organic fraction. In this way, phosphates from animal and bone meal are also made accessible as elemental phosphorus using the process according to the invention.The aforementioned organic substances in turn lead to an increase in the carbon content and thus to an increased yield of pyrolysis gas and pyrolysis oil, which can in turn be used to generate energy for pyrolysis or to produce fuels and propellants.

[0021] According to a preferred embodiment of the present invention, the process is carried out such that the step of incomplete combustion of the free carbon together with the phosphate-containing feedstock takes place, firstly, in a fluidized bed in a riser pipe and, secondly, in a refractory bed connected to the riser pipe via a cyclone separator, wherein elemental phosphorus and carbon monoxide are removed from the cyclone separator and downstream of the refractory bed. In the riser pipe, the pyrolysis coke is exothermically gasified to carbon monoxide using oxygen, i.e., partially or incompletely combusted. The temperature is preferably set such that the temperature at the cyclone separator is at most 850 °C, thereby preventing the gasification material from accumulating on the riser pipe and / or the cyclone separator.To regulate the temperature, a hydrogen-free carbon carrier can be added with stoichiometric oxygen. This allows for the setting of an optimal temperature range with a suitable carbon monoxide partial pressure for the reduction processes. Indirect reduction of the phosphorus and iron oxides already takes place in the riser pipe. This produces metallic iron and gaseous elemental phosphorus (P₂), with the iron occurring in solid and dust form. This hot dust / gas mixture is then immediately introduced into the test bed.

[0022] However, the elemental phosphorus already accumulating in the riser pipe is removed before it enters the refractory bed in order to prevent the formation of iron phosphides in the refractory bed, which would occur at high concentrations of elemental phosphorus.

[0023] The further addition of oxygen causes the temperature in the refractory bed to rise to a maximum of 1500 °C, whereby the residual carbon in the mixture is gasified to carbon monoxide. This melts the dust, and a two-phase smelt can be collected. As described above, the collected smelt consists of an iron alloy overlying a pozzolan smelt. The iron alloy is particularly rich in phosphorus and copper and also collects all siderophilic heavy metals. The atmospheric heavy metal species pass into the gas phase, whereby the relatively high zinc content of the starting material used, especially sewage sludge, leads to residual desulfurization through the formation of zinc sulfide in the refractory bed or in a combustion device such as a burner downstream of the cyclone separator.

[0024] In the process according to the invention, the refractory bed is arranged in a tubular reactor functioning as a co-current shaft furnace, wherein an upper layer of the refractory bed consists of high-alumina refractory particles and a lower layer of the refractory bed preferably consists of coarse-grained coke and / or graphite. At the lower end of the refractory bed, a collection area for the molten metal is formed in the form of a sump, in which the separation of the two molten metal phases into the iron alloy layer and the puzzol layer takes place. The molten metal can be tapped at this point.

[0025] Furthermore, the hot gas from the incomplete combustion is also extracted from the extraction area or sump. According to the invention, this hot gas contains carbon monoxide and elemental phosphorus (P₂) as well as the atmospheric heavy metal compounds of the transition metals. The hot gas, at approximately 1500 °C, is cooled to approximately 600 °C by means of a heat exchanger and separated from the volatile heavy metal species by means of a hot gas filter. The product gas is then cooled further to approximately 150 °C, whereby P₂ is converted to P₄, which can be condensed by water injection. Carbon monoxide and water vapor are removed from the system and can be further converted to synthesis gas. As already mentioned, the hot air obtained in this process, at a temperature of approximately 1400 °C, can be used to heat the pyrolysis process.Furthermore, this excess heat can also be used for pre-drying, for example, mechanically dewatered sewage sludge as a phosphate-containing feedstock.

[0026] In the process according to the invention, the supply of combustion oxygen is preferably carried out in such a way that combustion oxygen is supplied into the riser pipe and / or after the cyclone separator.

[0027] To prevent a backflow of reaction and product gas through the oxygen supply into the riser pipe and / or the cyclone separator, the inventive method can advantageously be further developed such that the pressure drop from the gas outlet of the cyclone separator and / or the pressure drop between the cyclone separator and the refractory bed is controlled. In this way, it can be ensured that, despite the injection of combustion oxygen-containing gas into the riser pipe or into a swirl chamber formed downstream of the cyclone separator, the pressure conditions can be controlled so that a backflow of combustion oxygen-containing gas and / or a backflow of product gas into the riser pipe does not occur.

[0028] According to an alternative process, the invention can advantageously be further developed in such a way that the phosphate-containing starting material is pre-reduced in the fluidized stream in a riser pipe and blown into a burner for incomplete combustion. The burner is connected to the riser pipe via an intermediate cyclone separator, whereby elemental phosphorus and carbon monoxide are drawn off from the burner as hot gas. The burner represents an alternative to the previously described reduction of the phosphates in the refractory bed.

[0029] Naturally, hot gas containing elemental phosphorus and carbon monoxide is also produced in the burner. The process according to the invention can preferably be further developed such that the burner hot gas is directed into the riser pipe for pre-reduction of the phosphate-containing feedstock, in particular anhydrous and preferably hydrogen-free sewage sludge pyrolysate. Unlike the previously described process with a riser pipe and a refractory packing, in which oxygen is introduced into the riser pipe, no oxygen is added to the riser pipe in this process, so that only a pre-reduction of the phosphates takes place. However, the direct contact of the burner hot gas with the feedstock leads to a strong heating of the feedstock, so that the reduction of the phosphates in the burner subsequently occurs very rapidly and completely in a kinetically favorable manner after the addition of oxygen.

[0030] According to a preferred embodiment of the present invention, the phosphate-containing starting material is metered into the riser pipe via a secondary cyclone separator. The phosphate-containing starting material is supplied to the riser pipe via the gas outlet of the cyclone separator located between the riser pipe and the burner. This also results in the phosphate-containing starting materials being preheated and fluidized, so that they already have a large specific surface area in the riser pipe, thus promoting pre-reduction. The starting materials are already anhydrous and hydrogen-free to prevent the formation of phosphines.

[0031] According to a preferred embodiment of the present invention, the process is carried out such that elemental phosphorus and carbon monoxide are extracted from the secondary cyclone separator. In the secondary cyclone separator, elemental phosphorus and carbon monoxide are present in the gas phase after incomplete combustion in the burner and, if applicable, after passing through the riser pipe and the primary cyclone separator, which is arranged between the riser pipe and the burner. By using a primary and a secondary cyclone separator, even larger quantities of hot gas from the burner can be reliably separated from any phosphates that may still be unreduced and therefore still solid. Any unreacted phosphates form an aerosol as solid dust and are separated from the gas phase in the cyclone separator and conveyed into the riser pipe.This ensures that the phosphates are completely converted, even if it requires repeated passes through the riser tube and burner. Atmospheric heavy metal species are also removed from the cycle.

[0032] According to a preferred alternative, the process according to the invention can also be further developed such that the step of incomplete combustion of the free carbon together with the phosphate-containing feedstock takes place in an electrically heated furnace, preferably a low-shaft furnace. In this variant of the process, the at least one phosphate-containing feedstock, provided together with free carbon, is introduced into a furnace such as can be used, for example, in the Wöhler process for the production of pure aluminum. Such a furnace, in particular a low-shaft furnace, has a bed of coke that is heated by electrodes immersed in the bed. Alternatively or additionally, heating by an inductive heating device is also conceivable, which is configured to heat the bed of coke inductively.

[0033] In this preferred alternative to carrying out the step of incomplete combustion of free carbon together with the phosphate-containing feedstock at a carbon surplus compared to combustion oxygen, a significant portion of the reaction energy is supplied electrically, so that a greater proportion of the free carbon is directly available for the reduction of the phosphates in the feedstock. This leads to a significantly higher partial pressure of phosphorus in the process gas (P₂ / CO), which simplifies process gas treatment. The free carbon in the coke bed of the low-shaft kiln has a much higher affinity for the phosphate-containing feedstock, so that the kiln's coke bed, in contrast, can be considered largely inert and is therefore not, or hardly, consumed.

[0034] In a furnace, particularly a low-shaft furnace, chemically bound carbon in the feedstock can be released from its compounds by the input electrical energy, thus allowing the phosphate-containing feedstocks, along with the free carbon, to be introduced into the low-shaft furnace using a largely or completely oxygen-free gas as a carrier gas. For this purpose, carbon monoxide, for example, can also be recycled as exhaust gas from the carbonization process within the low-shaft furnace itself to absorb the feedstock along with the free carbon.

[0035] As already explained above, pyrolysis gas and / or pyrolysis oil can be used to generate energy for pyrolysis or for the production of fuels. However, pyrolysis gas and pyrolysis oil consist mainly of aromatic and polyunsaturated hydrocarbon compounds, which can therefore easily lead to resinification through oxidation processes. Nevertheless, the energy content of these byproducts exceeds the energy required for pyrolysis many times over. Thus, an excess of energy is available from the pyrolysis gas or pyrolysis oil. According to a preferred embodiment of the process according to the invention, this excess can be used to produce elemental carbon and hydrogen if the pyrolysis gas and / or pyrolysis oil formed during pyrolysis is introduced into a heated, preferably inductively and / or conductively heated, metal bath.The metal bath preferably consists essentially of molten tin, zinc, copper, and nickel. The temperature of the metal bath is preferably between approximately 850°C and 1150°C.

[0036] In such a metal bath, the hydrocarbons of the pyrolysis gas or pyrolysis oil are cracked after their introduction, producing hydrogen gas and elemental carbon. The hydrogen can be used conventionally for synthesis purposes or as a fuel, while the elemental carbon produced is released inertly. The inert elemental carbon can be disposed of without problems and, unlike the starting materials, is not subject to any further degradation reactions, so no carbon dioxide can be produced from the released carbon. However, the elemental carbon can also be used in wastewater treatment and for the production of building materials or asphalt. If a carbon deficiency occurs during the incomplete combustion stage, the carbon can also be used to compensate for this deficiency. This also prevents the formation of resin deposits.

[0037] Furthermore, organically bound sulfur in the starting materials reacts with the components of the metal bath to form sulfides, and the organic oxygen compounds are converted to water and carbon monoxide (CO), and partially to methane (CH4) or short-chain hydrocarbons. The organic amino compounds, mainly ammonia, are also cracked to nitrogen and hydrogen. This results in a hot product gas consisting primarily of hydrogen with traces of nitrogen, carbon monoxide, and short-chain hydrocarbons.

[0038] The majority of the elemental carbon formed (possibly with a graphene fraction) is removed from the metal bath primarily via a hot gas cyclone from the product gas, or periodically as a deposit from the surface of the metal bath. The separation of hydrogen, carbon monoxide, methane, short-chain hydrocarbons, and nitrogen from the product gas is carried out according to state-of-the-art technology.

[0039] The regeneration of the sulfidated metal bath is achieved through periodic oxidation, producing a concentrated SO₂ / SO₃ gas that can be used to produce gypsum or sulfuric acid. A portion of the metal bath is also oxidized in this process. However, the metal bath can be reduced again by subsequently introducing pyrolysis gas and gaseous pyrolysis oil. The atmospheric heavy metal load of the starting materials consists primarily of zinc, copper, lead, and mercury compounds, some of which are released into the gas phase during pyrolysis. Zinc and copper precipitate in the molten metal of the metal bath. Lead and mercury pass into the gas phase and are removed from the product gas, which consists mainly of hydrogen, by condensation and via an activated carbon filter. The alkalis (sodium and potassium) and their compounds largely remain in the pyrolysis coke produced.

[0040] In this context, it is further preferred that the molten pozzolan be added to the metal bath. The heat from the molten pozzolan can then be used to heat the metal bath. In the metal bath, the molten pozzolan cools extremely rapidly, resulting in a glassy, ​​amorphous byproduct that is compatible with cement.

[0041] The apparatus according to the invention for carrying out the process according to the invention comprises at least one combustion device, in particular a refractory bed or a burner, connected to a riser pipe via an intermediate cyclone separator. The riser pipe can be fed with a phosphate-containing feedstock in a fluidized stream, and the combustion device has a collection vessel for collecting a melt of the dephosphorus-treated feedstock as well as a vent for elemental phosphorus and carbon monoxide. The significance and advantages of the aforementioned apparatus elements have already been discussed in the description of the process according to the invention. Thus, two apparatus variants are conceivable according to the invention, which, however, have in common a riser pipe, a combustion device, and a primary cyclone separator arranged between them.As a combustion device in which the phosphates are reduced as completely as possible, a fireproof bed or a burner is conceivable within the scope of the present invention, as described above.

[0042] In both device variants, it is preferable that the combustion device is connected to the cyclone separator via an intermediate fluidized bed for the injection of combustion oxygen. Such a fluidized bed, into which combustion oxygen is injected, ensures optimal fluidization of the phosphate-containing feedstocks, thereby optimally increasing the specific surface area of ​​the feedstocks, thus promoting the reaction kinetics and the completeness of the reduction of the phosphates to elemental phosphorus.

[0043] To prevent a backflow of reaction and product gas through the oxygen supply into the vortex chamber, the device according to the invention can be further developed such that a physical or gas-dynamic and preferably controllable blocking device is arranged between the vortex chamber and the cyclone separator and / or at the gas outlet of the cyclone separator.

[0044] Preferably, a secondary cyclone separator, arranged between the riser pipe and the combustion device, is configured as a vent for elemental phosphorus and carbon monoxide. In the case of the device variant with a burner, this can be advantageous for reliably separating large quantities of hot gas from the solids. In this variant of the invention, the hot gas is first guided through the riser pipe into the primary cyclone separator located between the riser pipe and the burner, where the phosphate-containing feedstocks are separated from the hot gas, allowing the phosphate-containing feedstocks to enter the burner via the swirl chamber.

[0045] According to a preferred embodiment of the present invention, the gas outlet of the cyclone separator between the riser pipe and the burner is fed to the secondary cyclone separator. In this way, the phosphate-containing feedstocks can be fed to the gas outlet of the primary cyclone separator between the riser pipe and the burner, where they are already fluidized by the hot gas. The phosphate-containing feedstocks then pass through the secondary cyclone separator and from there into the riser pipe, where they are again fluidized by the hot gas stream from the burner and conveyed into the primary cyclone separator. The hot gas passes through the primary cyclone separator between the riser pipe and the burner and then enters the secondary cyclone separator and subsequently the riser pipe.

[0046] The metal bath for receiving the pyrolysis gas and / or the pyrolysis oil is preferably designed in a bubble column reactor, to which pyrolysis gas and / or pyrolysis oil are supplied via bottom nozzles and / or an immersion lance, wherein the column height of the reactor determines the residence time of pyrolysis gas and / or pyrolysis oil in the metal bath.

[0047] The bubble column reactor essentially consists of a heat-resistant steel tube with an inner lining of carbonaceous refractory material, e.g., graphite. Heating is achieved, for example, via electrical resistance heating, where direct or alternating current is passed through the steel tube, the carbonaceous refractory material, and the molten metal, which act as electrical resistance elements. Alternatively or additionally, induction heating can be used. Applying a medium frequency to the inductor allows for inductive stirring of the metal bath due to the Lorentz force, which accelerates the exchange kinetics of the reduction process and thus minimizes the required residence time and heat losses.

[0048] The invention is explained in more detail below with reference to an exemplary embodiment shown in the drawing. Figure 1 shows a schematic representation of a variant of the method according to the invention, Figure 2 shows a detail of a first apparatus variant for carrying out the method, Figure 3 shows a schematic representation of an apparatus for carrying out a second variant of the method according to the invention, and Figure 4 shows a schematic representation of a bubble column reactor for receiving a metal bath for utilizing excess pyrolysis gas or pyrolysis oil.

[0049] Figure 1 shows a combustion device of a device according to the invention for carrying out the method according to the invention, designated by reference numeral 1. In the combustion device 1, the partial combustion or exothermic gasification of the phosphate-containing starting materials takes place, whereby, according to the variant shown in Figure 1, this also partially takes place in the riser pipe 2. Combustion oxygen can be supplied to the riser pipe 2 at different points.

[0050] Reference numeral 3 denotes a pyrolysis reactor to which sewage sludge or sewage sludge ash, as a phosphate-containing feedstock, is fed at position 4, along with optionally wood or plastic as a carbon carrier. The pyrolysis reactor 3 is fired by a combustion chamber 5, from which pyrolysis gas can be drawn off at position 6 and pyrolysis oil at position 7. The exhaust gas from the pyrolysis reactor 3 is drawn off at position 8. In the example shown in Figure 1, the pyrolysis gas is again fed to the combustion chamber 5. Optionally, it can be fed, together with the pyrolysis oil, to the metal bath shown in Figure 4 to form inert elemental carbon as described above and thus remove it from the atmospheric cycle. After pyrolysis in pyrolysis reactor 3, the pyrolysis coke formed in reactor 3 is hot-milled in a grinding device 9. The ground pyrolysis coke can then be fed into the riser pipe 2.

[0051] After the reduction of the phosphates to elemental phosphorus (P2) and the oxidation of the free carbon to carbon monoxide (CO) have taken place in the riser pipe 2 and in the combustion unit 1, as already mentioned, these gaseous process products can be drawn off from the exhaust device 10. The molten metal 11 collects in the sump 12 at the lower end of the refractory bed 13 and forms a layer 11a of a phosphorus-containing iron alloy, which is overlain by a layer of pozzolan 11b. The pozzolan and the iron alloy can be tapped from the sump 12, and the pozzolan molten metal can also be fed into the bubble column reactor shown in Figure 4 to heat it and to generate a cement-compatible byproduct.

[0052] The approximately 1500 °C hot gaseous process products P2 and carbon monoxide are subsequently cooled to about 600 °C in a heat exchanger 14, filtered in a hot gas filter 15, and cooled to about 150 °C in another heat exchanger 16. They are then cooled in a splash condenser 17 to a P4 molten 18 at a temperature of approximately 50 °C. The phosphorus molten 18 can be tapped at position 19, and carbon monoxide and water are discharged at position 20. Reference numeral 21 indicates a supply for cooling water. Cooling air is supplied to heat exchangers 14 and 16 in counterflow in the direction of arrows 22. This air is subsequently heated to up to 1400 °C and can be supplied as hot air to the combustion chamber 5 of the pyrolysis process.

[0053] In Figure 2, identical parts are designated with the same reference numerals where possible, and it can be seen that the riser pipe 2 is connected via a cyclone separator 23 to a combustion device 1 in the form of a refractory bed 13. Reference numerals 24 denote adjustable shut-off devices by which the pressure drop through the gas outlet 25 of the cyclone separator 23 and through the swirl chamber can be controlled. A heat exchanger is designated with reference numeral 27, and the gas outlet through the gas outlet 25 is achieved by a controlled induced draft fan 28. As already described in connection with Figure 1, the product gas is fed to a splash condenser 17 for the condensation of P2 to P4. Reference numeral 29 designates an axially displaceable suction pipe of the cyclone separator 23, with which the separation performance of the cyclone separator can be adjusted.

[0054] Figure 3 schematically shows a riser pipe 2, which leads to a primary cyclone separator 23 located between the riser pipe 2 and the combustion device 1. The combustion device 1 is designed as a burner 30, to which the phosphorus-containing feedstock is supplied via a lance 31. For this purpose, a rotary valve 32 is also provided, which receives the feedstock from the primary cyclone separator 23.

[0055] The pyrolysis coke is fed to the device according to Figure 3 at position 33 into the gas outlet of the cyclone separator 23, where it is fluidized by the hot gas from the burner 30 and fed to a secondary cyclone separator 34. The dust fraction containing the phosphates is conveyed via line 35 to the riser pipe 2 and, in this pipe, is pumped upwards by the hot product gas from the burner 30 and pre-reduced in the process. The pre-treated phosphate-containing feedstock then enters the cyclone separator 23 and from there the rotary valve 32 and the burner 30 for complete reduction to elemental phosphorus and carbon monoxide. The melt is again collected in a vent 11 and withdrawn in phase separation. Gaseous elemental phosphorus and carbon monoxide are withdrawn through the gas outlet 36 of the secondary cyclone separator 34, for which an induced draft fan 28 is provided.The gas processing and separation of elemental phosphorus (P4) at position 37 and carbon monoxide at position 38 is schematically indicated in Figure 3 by reference numeral 39.

[0056] In Figure 4, the heated, preferably inductively and / or conductively heated, metal bath for the utilization of excess pyrolysis gas is designated by reference numeral 40. The metal bath 40 preferably consists essentially of molten tin, zinc, copper, and nickel. The temperature of the metal bath 40 is preferably between 850°C and 1150°C. The pyrolysis gas, which, according to Figure 1, was drawn off from the pyrolysis reactor 3 at position 6, is blown into the metal bath 40 through a bottom nozzle 41. Optionally, pyrolysis oil, which, according to Figure 1, was drawn off at position 7, can also be introduced into the metal bath 40. The metal bath 40 forms a bubble column reactor in column 42, in which the pyrolysis gas rises in bubbles in column 42, whereby the hydrocarbons of the pyrolysis gas or pyrolysis oil are cracked into hydrogen gas and elemental carbon. The carbon is discharged via a screw conveyor 43 at the top 44 of column 42.

[0057] The gas phase from the metal bath is directed into a hot gas filter 45, where any carbon that may have been transported into the gas phase is separated from hydrogen and carbon monoxide. An additional column, designated by reference numeral 46, is called a degasser, in which further hydrogen or carbon monoxide is released from the metal bath 40.

[0058] The reactor further comprises a secondary column 47 into which the pozzolan molten 11b, formed according to Figure 1, can be finely introduced into the metal bath 40 at a temperature of approximately 1500 °C via a rotary tube 48 with a subsequent vane rotor 49. The pozzolan molten 11b solidifies immediately in the significantly cooler metal bath 40, forming an amorphous granulate that can be used in the cement industry as a hydraulically active cement component. The addition of the pozzolan molten 11b supplies considerable amounts of heat to the metal bath at this point, thus heating the metal bath 40 in addition to the inductive and / or conductive heating agents 50.

[0059] While the metal bath 40 in the secondary column 47 is compact and free of gas bubbles, and thus has a high density, the density of the metal bath 40 in the column 42 is reduced by the pyrolysis gas bubbles, resulting in a flow from the secondary column 37 through the connecting line 51 into the column 42, or main column 42. In this way, the heat from the pozzolan melt ze 11b is transferred from the secondary column 47 into the main column 42. Due to the effect of the rising gas bubbles of the pyrolysis gas in the secondary column 42 and the higher density in the secondary column 47 relative to the secondary column 42, an increase Ü occurs in the levels of the metal bath 40 in the column 42 and the secondary column 47.

Claims

24 Patent claims:

1. A process for separating elemental phosphorus from phosphate-containing feedstocks, in particular from phosphate-containing waste materials such as sewage sludge, comprising at least the following steps: Providing at least one phosphate-containing feedstock together with free carbon, incomplete combustion of the free carbon together with the phosphate-containing feedstock with an excess of carbon relative to combustion oxygen, collecting a melt (11) of the dephosphorus-treated Starting material, Removal of elemental phosphorus and carbon monoxide formed during incomplete combustion with the gas phase, and separation of elemental phosphorus from the gas phase.

2. Method according to claim 1, characterized in that the carbon excess compared to the combustion oxygen during the incomplete combustion step is characterized by a molar ratio of carbon (C) to combustion oxygen (O2) of 2:1 to 8:1, preferably of 3:1 to 7:1, further preferably of 4:1 to 6:1 and particularly preferably of 5:

1.

3. A method according to claim 1 or 2, characterized in that the step of providing the phosphate-containing starting material together with the free carbon is carried out by pyrolysis of dried organic and phosphate-containing starting material, preferably together with at least one added carbon carrier and / or by pyrolysis of incinerated phosphate-containing starting material together with at least one added carbon carrier.

4. Method according to claim 3, characterized in that the added carbon carrier is wood, preferably waste wood or damaged wood, plastic, preferably recycled plastic, and / or an organic waste fraction.

5. Method according to one of claims 1 to 4, characterized in that heat generated during incomplete combustion of the gas phase and / or the melt is supplied to the step of providing the phosphate-containing starting material together with the free carbon, in particular to a pyrolysis of a phosphate-containing starting material together with a carbon carrier.

6. Method according to one of claims 3 to 5, characterized in that pyrolysis gas formed during pyrolysis is supplied to a combustion chamber (5) to generate heat for the pyrolysis.

7. Method according to one of claims 3 to 6, characterized in that steel mill dust is added to the starting materials of the pyrolysis.

8. Method according to one of claims 3 to 6, characterized in that the pyrolysis oil formed during pyrolysis is refined to synthetic fuel by hydrogenation.

9. Method according to any one of claims 1 to 8, characterized in that the carbon monoxide withdrawn with the gas phase is converted to carbon dioxide and hydrogen, preferably by a water-gas shift reaction.

10. Method according to any one of claims 1 to 9, characterized in that the melt (11) of the dephosphorized The starting material is collected as a melt (11a) of an iron alloy overlaid with a pozzolan melt (Hb).

11. Method according to any one of claims 1 to 10, characterized in that the step of incomplete combustion of the free carbon together with the phosphate-containing starting material is carried out to a first part in the entrained flow in a riser tube. (2) and to a second part in a refractory bed (13) which connects to the riser pipe (2) via an intermediate cyclone separator (23), whereby elemental phosphorus and carbon monoxide are removed from the cyclone separator (23) and after the refractory bed (13).

12. Method according to claim 11, characterized in that combustion oxygen is supplied to the riser pipe (2) and / or after the cyclone separator (23).

13. Method according to claim 11 or 12, characterized in that the pressure loss from the gas outlet (25) of the cyclone separator (23) and / or the pressure loss between the cyclone separator (23) and the refractory packing (13) is controlled.

14. Method according to one of claims 1 to 10, characterized in that the phosphate-containing starting material is pre-reduced in the entrained flow in a riser pipe (2) and blown into a burner (30) for incomplete combustion, which is connected to the riser pipe (2) via an intermediate cyclone separator (23), wherein elemental phosphorus and carbon monoxide are drawn off from the burner (30) as burner hot gas.

15. Method according to claim 14, characterized in that the burner hot gas is directed into the riser pipe (2) for pre-reducing the phosphate-containing starting material. 27 16. Method according to claim 11 or 12, characterized in that the phosphate-containing starting material is dosed into the riser pipe (2) via a secondary cyclone separator (34), to which the phosphate-containing starting material is supplied via the gas outlet (25) of the cyclone separator (23) between the riser pipe (2) and the burner (30).

17. Method according to claim 16, characterized in that elemental phosphorus and carbon monoxide are withdrawn from the secondary cyclone separator (34).

18. Method according to one of claims 1 to 10, characterized in that the step of incomplete combustion of the free carbon together with the phosphate-containing starting material takes place in an electrically heated low-shaft furnace.

19. Method according to one of claims 1 to 18, characterized in that pyrolysis gas and / or pyrolysis oil formed during pyrolysis is introduced into a heated, preferably inductively and / or conductively heated, metal bath.

20. Method according to claim 19, characterized in that the pozzolan melt (11b) is added to the metal bath.

21. Device for carrying out the method according to one of claims 1 to 20, comprising at least one combustion device (1) connected to a riser pipe (2) via an intermediate cyclone separator (23), in particular a refractory packing (13), a burner (30) or an electrically heated low-shaft furnace, wherein the riser pipe (2) can be supplied with a phosphate-containing feedstock in a fluidized stream and the combustion device (1) has a collection container for collecting a 28 comprising a melt (11) of the dephosphorus-treated starting material and a venting device (10) for elemental phosphorus and carbon monoxide.

22. Device according to claim 21, characterized in that the combustion device (1) is connected to the cyclone separator (23) via an intermediate swirl chamber for injecting combustion oxygen.

23. Device according to claim 22, characterized in that a physical or gas-dynamic and preferably controllable blocking device (24) is arranged between the vortex chamber and the cyclone separator (23) and / or at the gas outlet (25) of the cyclone separator (23).

24. Device according to one of claims 21 to 23, characterized in that a secondary cyclone separator (34) different from the cyclone separator (23) arranged between the riser pipe (2) and the combustion device (1) is designed as an extraction device for elemental phosphorus and carbon monoxide.

25. Device according to claim 24, characterized in that the gas outlet (25) of the cyclone separator (23) is fed to the secondary cyclone separator (34) between the riser pipe (2) and the combustion device (1).

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