A method for phosphorus recovery from the sole incineration of municipal sludge

Abstract

The present application relates to a method for phosphorus recovery from the incineration of municipal sludge alone, belonging to the technical field of sludge treatment. The method for phosphorus recovery from the incineration of municipal sludge alone provided by the present application comprises the following steps: 1) The dried municipal sludge is incinerated alone to obtain sludge ash, and the sludge ash is made into sludge particles; 2) Magnesium chloride and / or calcium chloride are added to the obtained sludge particles, and heat treatment is carried out under a high temperature condition of not less than 1000 °C to obtain a phosphorus recovery product; quicklime and wollastonite microcrystals are added during the separate incineration in step 1). During the incineration of the sludge in this method, quicklime and wollastonite microcrystals are added, and silicon dioxide in the ash reacts with quicklime to form wollastonite, avoiding the reaction of silicon dioxide with zinc oxide to form zinc silicate, so that zinc is removed by evaporation through the formation of zinc chloride during the high temperature heat treatment, effectively reducing the zinc element in the phosphorus recovery product, so that the phosphorus recovery product can be directly used as a plant phosphate fertilizer.

Description

Technical Field

[0001] The present application relates to a method for recovering phosphorus from municipal sludge by single incineration, belonging to the technical field of sludge treatment. Background Art

[0002] With the rapid development of the economy and the improvement of the urbanization level, the generation and treatment volume of sewage are increasing day by day. As a by-product of sewage treatment, sludge concentrates 30% - 50% of the pollutants in the sewage, having the dual attributes of pollution and resources. The safe treatment and disposal and resource utilization of sludge have always been an international research hotspot in the field of sewage treatment, and a large amount of phosphorus resources are contained in municipal sewage and sludge. In the prior art, wet chemical methods, thermochemical methods and other processes have been developed to recover phosphorus from sewage sludge, sludge liquor and sewage sludge ash.

[0003] Sludge drying and incineration can not only generate heat for power generation, reduce the sludge volume, but also enable 90% of the phosphorus in the influent to remain in the incineration ash, which is the best site for phosphorus recovery. However, the incineration ash contains more heavy metals and is not suitable for direct return to agricultural use or as a raw material for fertilizer production. Therefore, the key to ash phosphorus recovery lies in removing heavy metals and utilizing them, as well as recovering relatively pure phosphates. Ash phosphorus recovery technologies include biological methods, wet chemical methods and thermochemical methods. The biological method relies on the life activities of microorganisms to complete the extraction and purification of phosphorus, including bioleaching and biological phosphorus accumulation. Wet chemical phosphorus recovery is achieved by adding acid or alkali to change the acid-base environment of the ash, increasing the solubility of phosphorus, transferring phosphorus from the solid phase to the liquid phase, and then purifying phosphorus by chemical extraction and other methods. The thermochemical method heats the sludge ash in a high-temperature environment to separate heavy metals and their compounds in the form of steam, thereby realizing the gas-solid separation of ash and heavy metals; then the volatile metals are recovered during the gas washing process. Because the thermochemical method can simultaneously achieve phosphorus extraction and phosphorus purification, it is a relatively simple and economical method for ash phosphorus recovery.

[0004] The prior art thermochemical methods include Thermmphos, Ash Dec, Mephrec, etc. Among them, the Ash Dec process utilizes the characteristics of low melting point, high volatility and easy solubility in water of metal chlorides. The sludge ash can be mixed with environmentally compatible chlorides, and chemical reactions are carried out at high temperature, so that heavy metals such as chromium, copper, lead, zinc and tin form highly volatile metal chlorides with chlorine, and then are separated and removed from the ash; most of the phosphorus-containing compounds in the remaining ash are plant-available phosphorus phases or are supplied as raw materials for phosphate fertilizer production.

[0005] In the Ash Dec process, due to the presence of silica in the ash, after zinc oxide reacts with silica to form zinc silicate salts, the zinc element cannot be volatilized and removed in the form of zinc chloride. Therefore, it is necessary to provide a phosphorus recovery technology to solve the problem that zinc cannot be removed well during the process of recovering phosphorus from sludge combustion ash in the Ash Dec process. Summary of the Invention

[0006] To solve the above problems, a phosphorus recovery method for the separate incineration of municipal sludge is provided. In this method, quicklime and wollastonite microcrystals are added during sludge incineration. The silica in the ash reacts with the quicklime to form wollastonite, avoiding the reaction of silica with zinc oxide to form zinc silicate. Since zinc silicate is difficult to remove, excessive residual zinc metal elements will remain in the phosphorus recovery product. By adding quicklime, the formation of zinc silicate is avoided, so that during high-temperature heat treatment, the zinc metal element can form zinc chloride and be evaporated and removed. Finally, the zinc element in the phosphorus recovery product can be effectively reduced, making the phosphorus recovery product directly usable as a plant phosphate fertilizer.

[0007] According to one aspect of the present application, a phosphorus recovery method for the separate incineration of municipal sludge is provided. The method includes the following steps:

[0008] 1) The dried municipal sludge is separately incinerated to obtain sludge ash, and the sludge ash is made into sludge particles;

[0009] 2) Magnesium chloride and / or calcium chloride are added to the obtained sludge particles, and heat treatment is carried out under high-temperature conditions not lower than 1000 °C to obtain a phosphorus recovery product;

[0010] Quicklime and wollastonite microcrystals are added during the separate incineration in step 1).

[0011] By directly incinerating after adding quicklime and wollastonite microcrystals to the municipal sludge, the quicklime can react with the silica in the municipal sludge to form wollastonite, thereby fixing the silica in the form of wollastonite, avoiding the reaction of silica with zinc oxide to form zinc silicate, which is difficult to remove by the Ash Dec process. Subsequently, through the Ash Dec process, the zinc metal can be evaporated and removed in the form of zinc chloride. The added wollastonite microcrystals can become the carrier of the attached wollastonite component. The presence of wollastonite microcrystals can promote the reaction of calcium oxide with silica to form the wollastonite component, thereby effectively fixing the silica component in the municipal sludge and facilitating the subsequent removal of the zinc metal element.

[0012] Optionally, sodium carbonate or sodium hydroxide is also added during the separate incineration in step 1). The experimenters found that by adding sodium carbonate or sodium hydroxide components for the direct incineration of municipal sludge, the formation of wollastonite components from calcium oxide and silicon dioxide can be promoted.

[0013] Optionally, the conditions for the separate incineration include:

[0014] In the first incineration stage, the temperature is 900 - 1100 °C and the duration is 15 - 25 h. In the second incineration stage, the temperature is 1300 - 1500 °C and the duration is 5 - 10 h. In the third incineration stage, the temperature is 800 - 900 °C and the duration is 2 - 5 h. In the fourth incineration stage, the temperature is 1000 - 1200 °C and the duration is 15 - 25 h.

[0015] Optionally, in the conditions for the separate incineration, the cooling rate from the second incineration stage to the third incineration stage is not less than 80 °C / h.

[0016] Optionally, in the conditions for the separate incineration, the cooling rate from the second incineration stage to the third incineration stage is 100 - 200 °C / h.

[0017] The experimenters found that specific cooling conditions can significantly promote the formation of wollastonite components from calcium oxide and silicon dioxide. There is a third incineration stage in the direct incineration process. The temperature condition in this stage is suitable for the newly formed wollastonite components to combine with the outer layer of the added wollastonite microcrystals. If the temperature in the third incineration stage is too low, the thermal movement ability of the newly formed wollastonite components is weak and it is difficult to effectively adsorb on the outer layer of the wollastonite microcrystals. If the temperature in the third incineration stage is too high, the thermal movement ability of the newly formed wollastonite components is too strong and it is not easy to adsorb and combine with the outer layer of the wollastonite microcrystals. Moreover, the experimenters found that only when the cooling rate entering the third incineration stage meets not less than 80 °C / h can it be ensured that the newly formed wollastonite components are effectively adsorbed on the outer layer of the wollastonite microcrystals.

[0018] Optionally, the weight of the added wollastonite microcrystals is not less than 0.5% of the weight of the added quicklime.

[0019] Optionally, the weight ratio of the added wollastonite microcrystals to the added quicklime is 1 - 2%.

[0020] Optionally, the weight ratio of the added sodium carbonate or sodium hydroxide to the added quicklime is 10 - 30%.

[0021] According to another aspect of the present application, there is provided the application of the phosphorus recovery method for the separate incineration of any of the above-mentioned municipal sludge in sludge treatment.

[0022] Optionally, the sludge treatment method is to directly incinerate the sludge and then recover phosphorus from the ash obtained by incineration using the Ash Dec process.

[0023] The beneficial effects of this application include but are not limited to:

[0024] 1. In the method for recovering phosphorus from municipal sludge by separate incineration according to this application, when treating sludge particles using the Ash Dec process, there is a reaction between silicon dioxide and zinc oxide, resulting in the ineffective removal of zinc metal ions. In the solution of this application, adding calcium oxide and wollastonite microcrystals can effectively fix silicon dioxide, so that the zinc metal in zinc oxide is removed by evaporation in the form of zinc chloride during subsequent high-temperature treatment.

[0025] 2. In the method for recovering phosphorus from municipal sludge by separate incineration according to this application, by adding wollastonite microcrystals, the presence of wollastonite microcrystals during direct incineration can promote the reaction between calcium oxide and silicon dioxide, and promote the reaction between calcium oxide and silicon dioxide to form wollastonite components. Since the generated wollastonite tends to adhere and combine outside the added wollastonite microcrystals, it can significantly improve the reaction between calcium oxide and silicon dioxide.

[0026] 3. In the method for recovering phosphorus from municipal sludge by separate incineration according to this application, by further adding sodium carbonate or sodium hydroxide, the reaction between calcium oxide and silicon dioxide can be significantly promoted, so that silicon dioxide is fixed in the form of wollastonite, and thus it will not react with zinc oxide to form zinc silicate and affect the removal of zinc elements.

[0027] 4. In the method for recovering phosphorus from municipal sludge by separate incineration according to this application, when directly incinerating the sludge, a third incineration stage is added during the incineration process, and the temperature is rapidly reduced to the third incineration stage at a cooling rate of not less than 80 °C / h. After 2 - 5 hours, the temperature is raised again to enter the fourth incineration stage. The cooling link in the third incineration stage can make the wollastonite component formed by calcium oxide and silicon dioxide better adhere and combine outside the added wollastonite microcrystals. Through subsequent high-temperature reaction in the fourth incineration stage, the reaction between silicon dioxide and calcium oxide can be significantly improved, thereby reducing the formation of difficult-to-remove zinc silicate between zinc oxide and silicon dioxide. Detailed Embodiments

[0028] The following describes this application in detail with reference to the embodiments. However, this application is not limited to these embodiments. Unless otherwise specified, the raw materials and catalysts in the embodiments of this application are purchased through commercial channels.

[0029] Example 1

[0030] Directly incinerate the pretreated and dried municipal sludge to prepare ash. The preparation conditions for direct incineration include: in the first incineration stage, the temperature is 1000°C and the duration is 20 h; in the second incineration stage, the temperature is 1400°C and the duration is 8 h; in the third incineration stage, the temperature is 850°C and the duration is 3 h; in the fourth incineration stage, the temperature is 1100°C and the duration is 20 h. The cooling rate from the second incineration stage to the third incineration stage is controlled at 130 - 150°C / h. Before directly incinerating the municipal sludge, a treatment agent is added to the municipal sludge. Specifically, calcium oxide and wollastonite microcrystals are added to the ash, and the weight of the wollastonite microcrystals is 1% of the weight of the quicklime added.

[0031] Prepare the ash obtained by directly incinerating the municipal sludge into sludge particles, add calcium chloride to the sludge particles for high-temperature heat treatment, the heat treatment temperature is not lower than 1000°C, the treatment duration is not less than 10 min, and the phosphorus recovery product is obtained after heat treatment.

[0032] Example 2

[0033] Directly incinerate the pretreated and dried municipal sludge to prepare ash. The preparation conditions for direct incineration include: in the first incineration stage, the temperature is 900°C and the duration is 25 h; in the second incineration stage, the temperature is 1300°C and the duration is 10 h; in the third incineration stage, the temperature is 800°C and the duration is 5 h; in the fourth incineration stage, the temperature is 1000°C and the duration is 25 h. The cooling rate from the second incineration stage to the third incineration stage is controlled at 100 - 130°C / h. Before directly incinerating the municipal sludge, a treatment agent is added to the municipal sludge. Specifically, calcium oxide and wollastonite microcrystals are added to the ash, and the weight of the wollastonite microcrystals is 1.5% of the weight of the quicklime added.

[0034] Prepare the ash obtained by directly incinerating the municipal sludge into sludge particles, add magnesium chloride to the sludge particles for high-temperature heat treatment, the heat treatment temperature is not lower than 1000°C, the treatment duration is not less than 10 min, and the phosphorus recovery product is obtained after heat treatment.

[0035] Example 3

[0036] Directly incinerate the pretreated and dried municipal sludge to prepare ash. The preparation conditions for direct incineration include: in the first incineration stage, the temperature is 1100 °C and the duration is 15 h; in the second incineration stage, the temperature is 1500 °C and the duration is 5 h; in the third incineration stage, the temperature is 900 °C and the duration is 2 h; in the fourth incineration stage, the temperature is 1200 °C and the duration is 15 h. Among them, the cooling rate from the second incineration stage to the third incineration stage is controlled at 150-200 °C / h. Before directly incinerating the municipal sludge, a treatment agent is added to the municipal sludge. Specifically, calcium oxide and wollastonite microcrystals are added to the ash, and the weight of the wollastonite microcrystals is 2% of the weight of the quicklime added.

[0037] Prepare the ash obtained by directly incinerating the municipal sludge into sludge particles, add magnesium chloride and calcium chloride to the sludge particles for high-temperature heat treatment. The heat treatment temperature is not lower than 1000 °C and the treatment duration is not less than 10 min. After heat treatment, the phosphorus recovery product is obtained.

[0038] Example 4

[0039] The conditions of this example are basically the same as those of Example 1, except that sodium carbonate is also added during separate incineration, and the weight ratio of the added sodium carbonate to the added quicklime is 30%.

[0040] Example 5

[0041] The conditions of this example are basically the same as those of Example 1, except that sodium hydroxide is also added during separate incineration, and the weight ratio of the added sodium hydroxide to the added quicklime is 10%.

[0042] Example 6

[0043] The conditions of this example are basically the same as those of Example 1, except that the preparation conditions for direct incineration include: in the first incineration stage, the temperature is 1000 °C and the duration is 20 h; in the second incineration stage, the temperature is 1400 °C and the duration is 8 h; in the third incineration stage, the temperature is 1100 °C and the duration is 25 h.

[0044] Example 7

[0045] The conditions of this example are basically the same as those of Example 1, except that the cooling rate from the second incineration stage to the third incineration stage is controlled at 50 °C / h.

[0046] Example 8

[0047] The conditions of this example are basically the same as those of Example 1, except that the weight of the added wollastonite microcrystals is not less than 0.1% of the weight of the added quicklime.

[0048] Comparative Example 1

[0049] The conditions of this embodiment are basically the same as those of Embodiment 1, except that calcium oxide is only added to the ash.

[0050] Comparative Example 2

[0051] The conditions of this embodiment are basically the same as those of Embodiment 1, except that calcium oxide and wollastonite microcrystals are not added to the ash, and the municipal sludge is directly incinerated.

[0052] Test Example 1

[0053] The zinc metal in the phosphorus recovery products obtained after treating the ash obtained by directly incinerating the municipal sludge in Embodiments 1 to 8 and finally treating it by the AshDec process to remove heavy metal ions was detected, and the results are shown in Table 1 below.

[0054] Table 1 Residual zinc content in the phosphorus recovery product, weight percentage

[0055] Test sample Zinc content (mg / kg) Example 1 8.2 Example 2 11.0 Example 3 9.4 Example 4 5.9 Example 5 4.9 Example 6 24.0 Example 7 19.2 Example 8 22.6 Comparative Example 1 83.5 Comparative Example 2 230.8

[0056] According to the results in Table 1, it can be seen that the method for recovering phosphorus by directly incinerating municipal sludge provided by the solution of the present application can effectively reduce the content of heavy metal zinc in the phosphorus recovery product, making the phosphorus recovery product convenient for application. The phosphorus recovery product provided by the solution of the present application can remove most heavy metal elements, such as copper, lead, nickel, and chromium, after being treated by the Ash Dec process, and the residual zinc element can be further removed by adopting this solution. The prepared phosphorus recovery product can be directly applied to plant fertilizers.

[0057] It should be noted that in the solution of the present application, municipal sludge is used. The municipal sludge can be subjected to sedimentation treatment and biological treatment. At the same time, in order to directly incinerate the municipal sludge, the municipal sludge is treated by conventional means such as drying. In the solution of the present application, the Ash Dec process is used to treat the sludge particles prepared from the ash obtained by direct incineration and recover phosphorus. The Ash Dec process is a process well-known to those skilled in the art. In addition, for other conditions of direct incineration, such as the equipment used, an incinerator can be used, which is a conventional choice in the art. Those skilled in the art can select according to the existing technology or simple screening as needed.

[0058] As described above, only the embodiments of the present application are mentioned. The protection scope of the present application is not limited by these specific embodiments, but is determined by the claims of the present application. For those skilled in the art, various changes and modifications can be made to the present application. Any modification, equivalent replacement, improvement, etc. made within the technical idea and principle of the present application shall be included within the protection scope of the present application.

Claims

1. A method for recovering phosphorus by separately incinerating municipal sludge to prepare plant phosphate fertilizer, characterized in that, The method comprises the following steps: 1) Separately incinerating the dried municipal sludge to obtain sludge ash, and making the sludge ash into sludge particles; 2) Adding magnesium chloride and / or calcium chloride to the obtained sludge particles, and performing heat treatment under a high temperature condition of not less than 1000 °C to obtain a phosphorus recovery product; 3) Treating the obtained phosphorus recovery product by the Ash Dec process to remove heavy metal ions, and the obtained product can be directly used as plant phosphate fertilizer; When performing the separate incineration in step 1), quicklime and wollastonite microcrystals are added, and the weight ratio of the added wollastonite microcrystals to the added quicklime is 1-2%; the conditions of the separate incineration include: in the first incineration stage, the temperature is 900-1100 °C, and the duration is 15-25 h; in the second incineration stage, the temperature is 1300-1500 °C, and the duration is 5-10 h; in the third incineration stage, the temperature is 800-900 °C, and the duration is 2-5 h; in the fourth incineration stage, the temperature is 1000-1200 °C, and the duration is 15-25 h; in the conditions of the separate incineration, the cooling rate from the second incineration stage to the third incineration stage is 100-200 °C / h; When performing the separate incineration in step 1), sodium carbonate or sodium hydroxide is also added, and the weight ratio of the added sodium carbonate or sodium hydroxide to the added quicklime is 10-30%.