CN106915878B - method for recovering phosphorus in phosphorus-containing sludge - Google Patents
method for recovering phosphorus in phosphorus-containing sludge Download PDFInfo
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- CN106915878B CN106915878B CN201710186409.0A CN201710186409A CN106915878B CN 106915878 B CN106915878 B CN 106915878B CN 201710186409 A CN201710186409 A CN 201710186409A CN 106915878 B CN106915878 B CN 106915878B
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- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F11/00—Treatment of sludge; Devices therefor
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- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/28—Treatment of water, waste water, or sewage by sorption
- C02F1/281—Treatment of water, waste water, or sewage by sorption using inorganic sorbents
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- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/52—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities
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- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/52—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities
- C02F1/5236—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities using inorganic agents
- C02F1/5245—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities using inorganic agents using basic salts, e.g. of aluminium and iron
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- C02F11/00—Treatment of sludge; Devices therefor
- C02F11/06—Treatment of sludge; Devices therefor by oxidation
- C02F11/08—Wet air oxidation
- C02F11/086—Wet air oxidation in the supercritical state
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Abstract
The embodiment of the invention discloses a method for recovering phosphorus in phosphorus-containing sludge, which comprises the following steps: grinding, screening and slurrying the phosphorus-containing sludge, and then performing thermal refining to obtain sludge with the water content of 85% -95%; introducing the sludge subjected to quenching and tempering and excessive oxygen into a supercritical water oxidation reaction device to perform supercritical water oxidation reaction, and staying for 10-30 seconds to obtain concentrated salt water and supercritical fluid; detecting the content of heavy metal in the concentrated brine, adjusting the concentrated brine to be alkaline under the condition that the content of heavy metal in the concentrated brine is not higher than a preset value, adding a precipitator into the concentrated brine for precipitation treatment, and separating a product to obtain a phosphorus-containing precipitate. Because the supercritical water has strong oxidizing capacity, the phosphorus-containing sludge fully reacts in the supercritical water oxidation reaction device, phosphorus in the phosphorus-containing sludge can be basically and completely released, and the recovery efficiency of the phosphorus in the phosphorus-containing sludge is greatly improved.
Description
Technical Field
The invention relates to the field of sludge treatment, in particular to a method for recovering phosphorus in phosphorus-containing sludge.
background
phosphorus is an important non-metal mineral resource which is difficult to regenerate, and is an essential nutrient element for maintaining life activities. According to the estimation of an authoritative institution, phosphorus resources all over the world can only be used for 60-130 years, and phosphorus is listed as one of 20 mineral resources which can not meet the national economic development requirements of China. On the other hand, the problem of water eutrophication caused by nutrient elements such as phosphorus discharged along with sewage is increasingly serious, and the water is seriously polluted, so that the water becomes an important environmental problem at present.
Because phosphorus element has the characteristic of unidirectional flow, most of phosphorus can be stored in organisms only in the form of necessary elements in the sewage treatment process and is finally discharged in the form of excess sludge, so that the recovery of phosphorus in phosphorus-containing sludge is an important method for relieving water body pollution and phosphorus resource shortage.
At present, in the recovery technology of phosphorus in phosphorus-containing sludge, methods such as acidification and normal-pressure microwave radiation combination, squeezing filtration, soaking, re-aeration, anaerobic heating and the like are commonly adopted to promote phosphorus in the sludge to be released to a supernatant as much as possible, and the phosphorus-rich supernatant after solid-liquid separation is treated by a deposition method to obtain phosphorus-containing precipitates such as struvite, calcium phosphate crystals and the like, so that the recovery of phosphorus is realized. However, when these methods are used for the recovery treatment of phosphorus, the release concentration of phosphorus in the phosphorus-containing sludge is limited, and the recovery efficiency of phosphorus in the phosphorus-containing sludge is low.
Disclosure of Invention
the embodiment of the invention discloses a method for recovering phosphorus from phosphorus-containing sludge, which aims to improve the recovery efficiency of phosphorus from phosphorus-containing sludge. The technical scheme is as follows:
The embodiment of the invention provides a method for recovering phosphorus in phosphorus-containing sludge, which comprises the following steps:
grinding, screening and slurrying the phosphorus-containing sludge, and then performing thermal refining to obtain sludge with the water content of 85% -95%;
introducing the sludge subjected to quenching and tempering and excessive oxygen into a supercritical water oxidation reaction device to perform supercritical water oxidation reaction, and staying for 10-30 seconds to obtain concentrated salt water and supercritical fluid, wherein the peroxide coefficient is 1.5-2;
detecting the content of heavy metals in the strong brine, adjusting the strong brine to be alkaline under the condition that the content of heavy metals in the strong brine is not higher than a preset value, adding a precipitator into the strong brine to perform precipitation treatment, and separating a product to obtain a phosphorus-containing precipitate, preferably, the precipitation treatment further comprises: adding an anion coagulant aid to promote precipitation, wherein the adding amount of the anion coagulant aid is 0.1-0.3% of the mass of the concentrated brine.
optionally, in the case that the content of the heavy metal in the concentrated brine is detected to be higher than the preset value, the method further includes:
Adding hydrochloric acid to adjust the pH value of the concentrated brine to 4-6;
carrying out adsorption treatment on the concentrated brine after the pH value is adjusted, and carrying out analysis treatment on an obtained adsorption product in an alkaline solution to obtain an analysis solution containing phosphate;
adding a precipitator into the phosphate-containing desorption solution for precipitation treatment, and separating a product to obtain a phosphorus-containing precipitate, wherein the precipitation treatment preferably further comprises: adding an anionic coagulant aid to promote precipitation, wherein the adding amount of the anionic coagulant aid is 0.1-0.3% of the mass of the analysis liquid.
optionally, the adsorption treatment includes:
Carrying out vibration adsorption treatment on the strong brine after the pH value is adjusted by adopting modified alumina, wherein the adsorption time is 0.5-3 hours, and preferably, the modified alumina comprises: aluminum sulfate-modified alumina and/or ferric sulfate-modified alumina.
optionally, the alkaline solution is a sodium hydroxide or potassium hydroxide solution with a mass fraction of 1%.
Optionally, the precipitating agent is selected from: one or more of a mixture of magnesium salt and ammonium salt, aluminum salt, ferric salt and saturated solution of calcium hydroxide, wherein the molar ratio of cations to phosphate radicals in the precipitator is (1-1.5) to 1.
Optionally, the anionic coagulant aid comprises: one or more of polyacrylamide, polyacrylic acid, sodium polyacrylate and calcium polyacrylate.
optionally, the supercritical water oxidation reaction apparatus includes: the system comprises a heat exchanger, a high-pressure plunger pump and a supercritical water oxidation reaction kettle, wherein the heat exchanger, the high-pressure plunger pump and the supercritical water oxidation reaction kettle are connected in series;
The supercritical water oxidation reaction process comprises the following steps:
introducing the sludge subjected to the quenching and tempering treatment into the heat exchanger, heating to 320-350 ℃, and pressurizing to 22-30MPa through the high-pressure plunger pump;
And introducing excessive oxygen and the sludge pressurized by the high-pressure plunger pump into the supercritical water oxidation reaction kettle to perform supercritical water oxidation reaction, and staying for 10-30 seconds to obtain concentrated brine and supercritical fluid.
Optionally, be provided with evaporation wall and porous inner tube in the supercritical water oxidation reation kettle, the evaporation wall with fill supercritical water in the cavity between the porous inner tube, supercritical water oxidation reation kettle bottom is provided with the strong brine export, and the top is provided with supercritical fluid export, liquid oxygen entry and mud import.
Optionally, the method further includes:
Passing the supercritical fluid into the heat exchanger;
Cooling and depressurizing the supercritical fluid passing through the heat exchanger, and then carrying out gas-liquid separation to obtain a gaseous product and liquid water;
And (3) recycling the liquid water to the quenching and tempering process or directly discharging, compressing and separating the gaseous product, recovering oxygen in the gaseous product, and returning the obtained oxygen to the supercritical water oxidation reaction device.
Optionally, the pH of the concentrated brine is adjusted to 8.5-9.
According to the scheme provided by the embodiment of the invention, after grinding, screening and slurrying the phosphorus-containing sludge, carrying out thermal refining treatment to obtain the sludge with the water content of 85-95%, then introducing the thermal refined sludge and excessive oxygen into a supercritical water oxidation reaction device to carry out supercritical water oxidation reaction, staying for 10-30 seconds to obtain concentrated salt water and supercritical fluid, detecting the heavy metal content in the concentrated salt water, adjusting the concentrated salt water to be alkaline under the condition that the heavy metal content in the concentrated salt water is not higher than a preset value, adding a precipitator into the concentrated salt water to carry out precipitation treatment, separating the product to obtain phosphorus-containing precipitate, and further recovering phosphorus in the phosphorus-containing sludge. Because the supercritical water has strong oxidizing capacity, the phosphorus-containing sludge fully reacts in the supercritical water oxidation reaction device, phosphorus in the phosphorus-containing sludge can be basically and completely released, and the recovery efficiency of the phosphorus in the phosphorus-containing sludge is greatly improved.
Drawings
in order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
FIG. 1 is a flow chart of a method for recovering phosphorus from phosphorus-containing sludge according to an embodiment of the present invention;
FIG. 2 is a schematic structural diagram of the supercritical water oxidation reaction apparatus in the embodiment shown in FIG. 1.
wherein, the corresponding relationship between each component name and the corresponding reference numeral in fig. 2 is:
Evaporation wall 01, porous inner tube 02, strong brine outlet 03, supercritical fluid outlet 04, liquid oxygen inlet 05, sludge inlet 06.
Detailed Description
the embodiment of the invention provides a method for recovering phosphorus in phosphorus-containing sludge, which specifically comprises the following steps of:
grinding, screening and slurrying the phosphorus-containing sludge, and then performing thermal refining to obtain sludge with the water content of 85% -95%;
introducing the sludge subjected to quenching and tempering and excessive oxygen into a supercritical water oxidation reaction device to perform supercritical water oxidation reaction, and staying for 10-30 seconds to obtain concentrated salt water and supercritical fluid, wherein the peroxide coefficient is 1.5-2;
detecting the content of heavy metal in the concentrated brine, adjusting the concentrated brine to be alkaline under the condition that the content of heavy metal in the concentrated brine is not higher than a preset value, adding a precipitator into the concentrated brine for precipitation treatment, and separating a product to obtain a phosphorus-containing precipitate.
Because the phosphorus-containing sludge is generally uneven in texture and may have the phenomena of caking or solid impurities, the phosphorus-containing sludge can be ground, screened and pulped to remove the solid impurities in the sludge and eliminate the caking phenomenon so as to be beneficial to the release of phosphorus in the subsequent recovery treatment process. Generally, the sieve can be screened to below 20 meshes. When the phosphorus-containing sludge is slurried, the sludge can be stirred in an anoxic environment, the physical slurrying effect and the biological slurrying effect are synergistic by controlling the stirring speed, the viscosity of the sludge is reduced, agents such as demulsifiers and the like which can eliminate emulsified substances can be properly added to destroy the emulsified substances in the phosphorus-containing sludge, the phosphorus-containing sludge is fully slurried, and the specific addition amount of the demulsifiers can be determined by a person skilled in the art according to the actual emulsified state of the phosphorus-containing sludge, and is not particularly limited herein.
Furthermore, in order to ensure that the quality of the phosphorus-containing sludge is uniform and the treatment effect of the subsequent supercritical water oxidation reaction is not affected, after the slurrying treatment, the phosphorus-containing sludge can be subjected to conditioning treatment, clear water and/or wastewater which does not affect the phosphorus recovery effect are/is added into the phosphorus-containing sludge, stirring is carried out, the water content of the phosphorus-containing sludge is adjusted, and then the sludge with uniform quality and the water content of 85% -95% is obtained. In practical application, the inventor finds that the moisture content of the sludge is 85% -95%, the recovery treatment of phosphorus in the sludge is facilitated, and the recovery efficiency is higher.
The grinding, screening, slurrying, and conditioning are all processing methods commonly used in the art, and may be determined by those skilled in the art according to factors such as the impurity content and the water content in the phosphorus-containing sludge, and are not specifically limited and described herein.
after the quenching and tempering treatment, the sludge with the water content of 85-95 percent and excessive oxygen can be introduced into a supercritical water oxidation reaction device for supercritical water oxidation reaction. In the process of carrying out the supercritical water oxidation reaction, the peroxide coefficient is generally 1.5-2, and it is understood that the peroxide coefficient refers to the ratio of the mass of the oxygen actually supplied to the mass of the oxygen theoretically required for complete oxidation of the quenched and tempered sludge. Staying in the supercritical water oxidation reaction device for 10-30 seconds, and finishing the reaction of the sludge after the quenching and tempering treatment to obtain the supercritical fluid and the concentrated brine rich in phosphate. Because the oxidizing power of supercritical water is strong, phosphorus in the phosphorus-containing sludge can be almost completely released through the treatment of the supercritical water oxidation reaction device, strong brine is formed, and sludge reduction can be realized. On the other hand, the products of the supercritical water oxidation reaction are generally carbon dioxide, water, nitrogen and inorganic salts, and no secondary pollution is generated.
In an embodiment of the present invention, the supercritical water oxidation apparatus may include: the device comprises a heat exchanger, a high-pressure plunger pump and a supercritical water oxidation reaction kettle, wherein the heat exchanger, the high-pressure plunger pump and the supercritical water oxidation reaction kettle are connected in series. In the supercritical water oxidation reaction process, the sludge after the quenching and tempering treatment can be introduced into a heat exchanger, heated to 320-350 ℃, pressurized to 22-30MPa by a high-pressure plunger pump, and then the excess oxygen and the sludge pressurized by the high-pressure plunger pump are introduced into a supercritical water oxidation reaction kettle to carry out the supercritical water oxidation reaction and stay for 10-30 seconds, so as to obtain concentrated brine and supercritical fluid. The heat exchanger and the high-pressure plunger pump may both adopt corresponding devices in the prior art, and are not specifically limited herein.
Above-mentioned supercritical water oxidation reation kettle can adopt arbitrary supercritical water oxidation reation kettle among the prior art, does not do specific limitation here. Preferably, as shown in fig. 2, an evaporation wall 01 and a porous inner tube 02 are arranged in the supercritical water oxidation reaction kettle, the evaporation wall 01 may be a shell structure and has a pressure-bearing effect, evaporated water is filled in a cavity between the evaporation wall 01 and the porous inner tube 02, a concentrated brine outlet 03 is arranged at the bottom of the supercritical water oxidation reaction kettle, and a supercritical fluid outlet 04, a liquid oxygen inlet 05 and a sludge inlet 06 are arranged at the top of the supercritical water oxidation reaction kettle. The evaporation water forms annular water curtain in the cavity between 01 and the porous inner tube 02 of evaporation wall, gets into supercritical water oxidation reation kettle through porous inner tube 02 in, forms the water film at porous inner tube 02 internal surface, makes the reactant not with supercritical water oxidation reation kettle inner wall direct contact, effectively avoids the corruption of supercritical water oxidation reaction to supercritical water oxidation reation kettle inner wall, causes the destruction to supercritical water oxidation reation kettle. It should be noted that, the above description of the supercritical water oxidation reactor focuses on the difference between the supercritical water oxidation reactor and the supercritical water oxidation reactor in the prior art, and reference may be made to the supercritical water oxidation reactor in the prior art without detailed description.
In order to avoid resource waste, the supercritical water oxidation reaction device can be self-maintained, and supercritical fluid obtained by supercritical water oxidation reaction can be introduced into the heat exchanger to heat sludge after quenching and tempering. It should be noted that, when the supercritical water oxidation reaction apparatus performs the supercritical water oxidation reaction for the first time, the electric heater can be used to heat the conditioned sludge, and when the supercritical fluid generated by the supercritical water oxidation reaction can meet the requirement of heating the conditioned sludge, the electric heater is no longer needed to heat, thereby realizing the self-maintenance of the supercritical water oxidation reaction apparatus.
Furthermore, the supercritical fluid passing through the heat exchanger can be cooled and depressurized, then gas-liquid separation is carried out to obtain a gaseous product and liquid water, and the liquid water is returned to the tempering process to recycle the liquid water, thereby avoiding resource waste. Of course, the liquid water can also be discharged directly. And for the gaseous product, the gaseous product can be subjected to compression separation treatment, oxygen in the gaseous product is recovered, and the obtained oxygen is returned to the supercritical water oxidation reaction device to provide oxygen for the supercritical water oxidation reaction, so that the treatment cost is reduced. And gases such as nitrogen in the gaseous product which do not contaminate the air can be discharged to the air.
because the strong brine obtained through the treatment of the supercritical water oxidation reaction device possibly contains heavy metals, in order to ensure that the obtained phosphorus-containing precipitate meets the recycling standard, whether the content of the heavy metals in the strong brine is higher than a preset value can be detected. It should be noted that the kind and preset value of the heavy metal can be determined by those skilled in the art according to the recycling purpose, and are not specifically limited herein. For example, if the phosphorus-containing precipitate obtained by the recycling process is used for preparing fertilizer, the heavy metals and the heavy metal content threshold specified in the national standard GB/T23349-: 50mg/kg, 10mg/kg, 200mg/kg, 500mg/kg and 5 mg/kg. The method for detecting the content of the heavy metal in the concentrated brine can adopt any existing heavy metal detection method, and is not particularly limited herein.
Under the condition that the content of heavy metal in the concentrated brine is not higher than a preset value, the concentrated brine can be adjusted to be alkaline, a precipitator is added into the concentrated brine for precipitation treatment, and a product is separated, so that a phosphorus-containing precipitate is obtained. Generally, the pH value of the concentrated brine can be adjusted to 8.5-9, and the precipitation treatment effect is better. Wherein, the precipitant can be one or more of magnesium salt and ammonium salt mixture, aluminum salt, iron salt and calcium hydroxide saturated solution.
specifically, the mixture of magnesium salt and ammonium salt and the concentrated brine can be prepared according to the following formula: p: the Mg is added at a molar ratio of 1:1.05:1.1, so that struvite (Mg (NH4) PO 4.6H 2O) is generated by the mixture of the magnesium salt and the ammonium salt and phosphate in the concentrated brine, and the recovery efficiency is improved. The saturated solution of aluminum salt, iron salt and calcium hydroxide may be added in small excess to ensure that phosphate in concentrated saline produces phosphorus-containing precipitate as much as possible. It will be appreciated that saturated solutions of aluminium, iron and calcium hydroxide react with phosphate in concentrated brine to produce aluminium phosphate, iron phosphate and calcium phosphate precipitates respectively. Wherein, the molar ratio of the cation in the saturated solution of aluminum salt, ferric salt and calcium hydroxide to the phosphate radical in the concentrated saline is (1-1.5) to 1, and the precipitation effect is better.
the above separation treatment is a technique commonly used in the art, and for example, the product may be separated by filtration to obtain a phosphorus-containing precipitate, which is not specifically described and limited herein.
During the precipitation treatment, an anionic coagulant aid may be added to promote precipitation. The anionic coagulant aid may include, among others: one or more of polyacrylamide, polyacrylic acid, sodium polyacrylate and calcium polyacrylate, and the adding amount of the anionic coagulant aid is 0.1-0.3% of the mass of the concentrated brine, so that the precipitation promoting effect is better.
and under the condition that the heavy metal content in the concentrated brine is higher than a preset value, in order to ensure that the heavy metal content in the phosphorus-containing precipitate obtained by recovery does not exceed the recovery standard, the aim of purifying the product can be achieved through adsorption and desorption treatment. Specifically, hydrochloric acid may be added to adjust the pH of the concentrated brine to 4 to 6, the concentrated brine after pH adjustment is subjected to adsorption treatment, the obtained adsorption product is subjected to desorption treatment in an alkaline solution to obtain a phosphate-containing desorption solution, finally, a precipitant is added to the phosphate-containing desorption solution to perform precipitation treatment, and the product is separated to obtain a phosphorus-containing precipitate.
The pH value of the strong brine is adjusted to 4-6, so that adsorption treatment can be favorably carried out, and during adsorption treatment, the strong brine after the pH value is adjusted can be subjected to shock adsorption treatment by adopting modified alumina, and the adsorption time is generally 0.5-3 hours. Preferably, the modified alumina may include: aluminum sulfate-modified alumina and/or ferric sulfate-modified alumina. In the adsorption process, the adsorption rate of the modified alumina to phosphate in the concentrated brine is very high, but the adsorption rate to heavy metals in the concentrated brine is very low except chromium, generally lower than 10%, and further, the adsorption product has very low content of other heavy metals except chromium.
after the adsorption treatment, the adsorbed product may be subjected to an analytic treatment in an alkaline solution to obtain an analytic solution containing phosphate, wherein the alkaline solution may be a sodium hydroxide or potassium hydroxide solution with a mass fraction of 1%. And (3) resolving the adsorption product in an alkaline solution to obtain a resolving solution containing sodium phosphate or potassium phosphate, and realizing regeneration of the modified alumina. Finally, carrying out precipitation treatment on the analysis solution to obtain the phosphorus-containing precipitate. If the adsorption product contains chromium, CrO 42-and HCrO 4-do not react with the precipitator, so that heavy metal chromium is dissolved in the desorption solution and removed, and the phosphorus-containing precipitate does not contain heavy metal chromium.
it should be noted that the precipitant used in the case that the heavy metal content in the concentrated brine is higher than the preset value is the same as the precipitant used in the case that the heavy metal content is not higher than the preset value, and will not be described herein again. Under the condition that the heavy metal content in the concentrated brine is higher than a preset value, the molar ratio of the cations in the precipitator to the phosphate radicals in the desorption solution is generally (1-1.5) to 1. It should be further noted that, in the case that the heavy metal content in the concentrated brine is higher than the preset value, an anion coagulant aid may also be added to promote precipitation, and the specific type of the anion coagulant aid is the same as the type of the anion coagulant aid used in the case that the heavy metal content is not higher than the preset value, and will not be described herein again. Under the condition that the heavy metal content in the concentrated brine is higher than a preset value, the dosage of the anion coagulant aid can be 0.1-0.3% of the mass of the desorption solution generally.
The technical solutions in the embodiments of the present invention will be described below with reference to the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
It should be noted that, in the following embodiments, the heavy metals include arsenic, cadmium, lead, chromium, and mercury, and the preset values are respectively: 50mg/kg, 10mg/kg, 200mg/kg, 500mg/kg and 5 mg/kg.
Example 1:
grinding and screening the phosphorus-containing sludge to below 20 meshes, pulping and then carrying out quenching and tempering treatment to obtain sludge with the water content of 85%;
Introducing the sludge after the quenching and tempering treatment into a heat exchanger, heating to 320 ℃, and pressurizing to 22MPa by a high-pressure plunger pump;
introducing excessive oxygen and sludge pressurized by a high-pressure plunger pump into a supercritical water oxidation reaction kettle to perform supercritical water oxidation reaction, and staying for 10 seconds to obtain strong brine and supercritical fluid, wherein the peroxide coefficient is 1.5;
the detection of the contents of heavy metals of arsenic, cadmium, lead, chromium and mercury in the concentrated brine respectively comprises the following steps: 10mg/kg, 6mg/kg, 100mg/kg, 300mg/kg and 2mg/kg, which are not higher than the preset values, adjusting the pH value of the concentrated brine to 8.5, adding a mixture of a magnesium salt and an ammonium salt into the concentrated brine for precipitation treatment, and separating the product to obtain a phosphorus-containing precipitate. Through detection, the content of heavy metal in the phosphorus-containing precipitate does not exceed the preset value, and the phosphorus recovery rate is 90.5%.
Example 2:
grinding and screening the phosphorus-containing sludge to below 20 meshes, pulping and then carrying out quenching and tempering treatment to obtain sludge with the water content of 90%;
introducing the sludge after the quenching and tempering treatment into a heat exchanger, heating to 330 ℃, and pressurizing to 30MPa by a high-pressure plunger pump;
Introducing excessive oxygen and sludge pressurized by a high-pressure plunger pump into a supercritical water oxidation reaction kettle to perform supercritical water oxidation reaction, and staying for 20 seconds to obtain strong brine and supercritical fluid, wherein the peroxide coefficient is 1.8;
The detection of the contents of heavy metals of arsenic, cadmium, lead, chromium and mercury in the concentrated brine respectively comprises the following steps: 10mg/kg, 5mg/kg, 100mg/kg, 200mg/kg and 3mg/kg, which are not higher than the preset values, adjusting the pH value of the concentrated brine to 8.8, adding an iron salt and an anion coagulant aid into the concentrated brine for precipitation treatment, and separating the product to obtain the phosphorus-containing precipitate. Through detection, the content of heavy metal in the phosphorus-containing precipitate does not exceed the preset value, and the phosphorus recovery rate is 96.1%.
Example 3:
grinding and screening the phosphorus-containing sludge to below 20 meshes, pulping and then carrying out quenching and tempering treatment to obtain sludge with the water content of 95%;
Introducing the sludge after the quenching and tempering treatment into a heat exchanger, heating to 350 ℃, and pressurizing to 27MPa by a high-pressure plunger pump;
Introducing excessive oxygen and sludge pressurized by a high-pressure plunger pump into a supercritical water oxidation reaction kettle to perform supercritical water oxidation reaction, and staying for 25 seconds to obtain strong brine and supercritical fluid, wherein the peroxide coefficient is 2.0;
Introducing the supercritical fluid into a heat exchanger, cooling and depressurizing the supercritical fluid passing through the heat exchanger, and performing gas-liquid separation treatment to obtain a gaseous product and liquid water;
returning liquid water to the quenching and tempering process, compressing and separating gaseous products, and returning obtained oxygen to the supercritical water oxidation reaction kettle;
the detection of the contents of heavy metals of arsenic, cadmium, lead, chromium and mercury in the concentrated brine respectively comprises the following steps: 20mg/kg, 2mg/kg, 50mg/kg, 10mg/kg and 1mg/kg, which are not higher than the preset values, adjusting the pH value of the concentrated brine to 9, adding a saturated solution of calcium hydroxide into the concentrated brine for precipitation treatment, and separating the product to obtain a phosphorus-containing precipitate. Through detection, the content of heavy metal in the phosphorus-containing precipitate does not exceed the preset value, and the phosphorus recovery rate is 92.6%.
example 4:
grinding and screening the phosphorus-containing sludge to below 20 meshes, pulping and then carrying out quenching and tempering treatment to obtain sludge with the water content of 85%;
Introducing the sludge after the quenching and tempering treatment into a heat exchanger, heating to 330 ℃, and pressurizing to 25MPa through a high-pressure plunger pump;
Introducing excessive oxygen and sludge pressurized by a high-pressure plunger pump into a supercritical water oxidation reaction kettle to perform supercritical water oxidation reaction, and staying for 15 seconds to obtain strong brine and supercritical fluid, wherein the peroxide coefficient is 1.5;
The detection of the contents of heavy metals of arsenic, cadmium, lead, chromium and mercury in the concentrated brine respectively comprises the following steps: 65mg/kg, 12mg/kg, 220mg/kg, 550mg/kg and 10mg/kg, the content of heavy metal is higher than the preset value, and hydrochloric acid is added to adjust the pH value of the concentrated brine to 4;
Carrying out oscillation adsorption treatment on the concentrated brine after the pH value is adjusted by adopting aluminum sulfate modified alumina, wherein the adsorption time is 0.5 hour, and analyzing the obtained adsorption product in a sodium hydroxide solution with the mass fraction of 1% to obtain an analysis solution containing phosphate;
Adding aluminum salt into the analysis solution containing phosphate for precipitation treatment, and separating the product to obtain phosphorus-containing precipitate. Through detection, the content of heavy metal in the phosphorus-containing precipitate does not exceed a preset value, and the phosphorus recovery rate is 95.0%.
Example 5:
grinding and screening the phosphorus-containing sludge to below 20 meshes, pulping and then carrying out quenching and tempering treatment to obtain sludge with the water content of 90%;
introducing the sludge after the quenching and tempering treatment into a heat exchanger, heating to 350 ℃, and pressurizing to 28MPa through a high-pressure plunger pump;
Introducing excessive oxygen and sludge pressurized by a high-pressure plunger pump into a supercritical water oxidation reaction kettle to perform supercritical water oxidation reaction, and staying for 20 seconds to obtain strong brine and supercritical fluid, wherein the peroxide coefficient is 2;
the detection of the contents of heavy metals of arsenic, cadmium, lead, chromium and mercury in the concentrated brine respectively comprises the following steps: 55mg/kg, 10mg/kg, 300mg/kg, 400mg/kg and 8mg/kg, the content of heavy metals arsenic, lead and mercury is higher than the preset value, and hydrochloric acid is added to adjust the pH value of the concentrated brine to 5;
carrying out oscillation adsorption treatment on the concentrated brine after the pH value is adjusted by adopting ferric sulfate modified alumina, wherein the adsorption time is 1.5 hours, and analyzing the obtained adsorption product in a potassium hydroxide solution with the mass fraction of 1% to obtain an analysis solution containing phosphate;
Adding a mixture of magnesium salt and ammonium salt and an anion coagulant aid into a phosphate-containing desorption solution for precipitation treatment, and separating a product to obtain a phosphorus-containing precipitate. Through detection, the content of heavy metal in the phosphorus-containing precipitate does not exceed the preset value, and the phosphorus recovery rate is 93.5%.
Example 6:
grinding and screening the phosphorus-containing sludge to below 20 meshes, pulping and then carrying out quenching and tempering treatment to obtain sludge with the water content of 95%;
Introducing the sludge after the quenching and tempering treatment into a heat exchanger, heating to 330 ℃, and pressurizing to 30MPa by a high-pressure plunger pump;
introducing excessive oxygen and sludge pressurized by a high-pressure plunger pump into a supercritical water oxidation reaction kettle to perform supercritical water oxidation reaction, and staying for 25 seconds to obtain strong brine and supercritical fluid, wherein the peroxide coefficient is 1.7;
introducing the supercritical fluid into a heat exchanger, cooling and depressurizing the supercritical fluid passing through the heat exchanger, and performing gas-liquid separation treatment to obtain a gaseous product and liquid water;
Returning liquid water to the quenching and tempering process, compressing and separating gaseous products, and returning obtained oxygen to the supercritical water oxidation reaction kettle;
The detection of the contents of heavy metals of arsenic, cadmium, lead, chromium and mercury in the concentrated brine respectively comprises the following steps: 40mg/kg, 10mg/kg, 250mg/kg, 550mg/kg and 9mg/kg, the content of heavy metals of lead, chromium and mercury is higher than the preset value, and hydrochloric acid is added to adjust the pH value of the concentrated brine to 6;
carrying out oscillation adsorption treatment on the concentrated brine after the pH value is adjusted by adopting aluminum sulfate modified alumina and ferric sulfate modified alumina, wherein the adsorption time is 3 hours, and the obtained adsorption product is subjected to analysis treatment in a sodium hydroxide solution with the mass fraction of 1% to obtain an analysis solution containing phosphate;
Adding iron salt into the analytic solution containing phosphate for precipitation treatment, and separating the product to obtain phosphorus-containing precipitate. Through detection, the content of heavy metal in the phosphorus-containing precipitate does not exceed the preset value, and the phosphorus recovery rate is 96.2%.
comparative example 1
centrifuging the phosphorus-containing sludge for 5 minutes, adding 1% hydrochloric acid by mass into the centrifuged phosphorus-containing sludge to obtain a mixed solution, wherein the volume ratio of the centrifuged phosphorus-containing sludge to the hydrochloric acid is 1: 10;
heating the mixed solution in a water area at 70 ℃ for 1 hour, and then carrying out centrifugal treatment to obtain a supernatant;
adjusting the pH value of the supernatant to 10.5 by adopting sodium hydroxide with the concentration of 5mol/L, adding a mixed medicament, precipitating for 1-2 hours, wherein the molar ratio of Ca2+ to Ca P, NH4+ in the mixed medicament is 1.8: 1: 1.2;
and drying the precipitate at 40 ℃ to obtain a dry phosphorus-containing precipitate. Through detection, the cadmium content in the phosphorus-containing precipitate is 26.2mg/kg, the cadmium content exceeds the preset value, and the phosphorus recovery rate is 70.6%.
comparative example 2
carrying out gravity concentration treatment on the phosphorus-containing sludge to obtain sludge with the concentration of 7000 mg/L;
At room temperature, adding hydrochloric acid with the concentration of 2.5mol/L into sludge with the concentration of 7000mg/L, and adjusting the pH value of the acidified sludge to be 2.0;
placing the acidified sludge into a microwave reactor, wherein the microwave frequency is 2.45GHz, and performing microwave radiation on the acidified sludge under normal pressure, wherein the end point temperature of the sludge subjected to microwave radiation is 95 ℃;
Performing solid-liquid separation on the sludge subjected to microwave radiation in a natural sedimentation mode, and collecting phosphorus-rich supernatant after the solid-liquid separation;
adding a calcium hydroxide solution into the supernatant according to the molar ratio of Ca2+ to P of 1.8:1, adjusting the pH of the supernatant to 10.5, reacting for 30min, and filtering to obtain a phosphorus-containing precipitate. Through detection, the cadmium content in the phosphorus-containing precipitate is 23.4mg/kg, which exceeds the preset value, and the phosphorus recovery rate is 83.6%.
it can be seen from the above examples 1-6 that, by using the method for recovering phosphorus from phosphorus-containing sludge provided by the embodiment of the present invention, the recovery rate of phosphorus in phosphorus-containing sludge is as high as more than 90%, and the content of heavy metals in the recovered phosphorus-containing precipitate is low and does not exceed a preset value. As can be seen from the comparative examples 1 and 2, the recovery rate of phosphorus in the phosphorus-containing sludge is low by adopting the method for recovering phosphorus in the phosphorus-containing sludge in the prior art, and the content of heavy metal in the recovered phosphorus-containing precipitate is easy to exceed the preset value, so that the recovery and utilization of the phosphorus-containing precipitate are influenced.
The method for recovering phosphorus from phosphorus-containing sludge provided by the embodiment of the invention is simple and easy to operate, the supercritical water oxidation reaction device is adopted for treatment, the phosphorus-containing sludge is fully reacted, phosphorus in the phosphorus-containing sludge can be basically and completely released, the recovery efficiency of phosphorus in the phosphorus-containing sludge is greatly improved, and sludge reduction can be realized. On the other hand, under the condition that the heavy metal content in the concentrated brine is higher than the preset value, the aim of purifying the product is fulfilled by adopting adsorption and analysis treatment, so that the heavy metal content in the obtained phosphorus-containing precipitate does not exceed the preset value, and the recycling of the phosphorus-containing precipitate is not influenced.
the method for recovering phosphorus from the phosphorus-containing sludge provided by the invention is described in detail above. The principles and embodiments of the present invention are explained herein using specific examples, which are presented only to assist in understanding the method and its central concept. It should be noted that it would be apparent to those skilled in the art that various changes and modifications can be made in the invention without departing from the principles of the invention, and such changes and modifications are intended to be covered by the appended claims.
Claims (9)
1. a method for recovering phosphorus from phosphorus-containing sludge is characterized by comprising the following steps:
grinding, screening and slurrying the phosphorus-containing sludge, and then performing thermal refining to obtain sludge with the water content of 85% -95%;
introducing the sludge subjected to quenching and tempering and excessive oxygen into a supercritical water oxidation reaction device to perform supercritical water oxidation reaction, and staying for 10-30 seconds to obtain concentrated salt water and supercritical fluid, wherein the peroxide coefficient is 1.5-2;
Detecting the heavy metal content in the strong brine, adjusting the strong brine to be alkaline under the condition that the heavy metal content in the strong brine is not higher than a preset value, adding a precipitator into the strong brine to carry out precipitation treatment, separating a product to obtain a phosphorus-containing precipitate, wherein the precipitation treatment further comprises: adding an anion coagulant aid to promote precipitation, wherein the adding amount of the anion coagulant aid is 0.1-0.3% of the mass of the concentrated brine;
Under the condition that the heavy metal content in the concentrated brine is detected to be higher than the preset value, adding hydrochloric acid to adjust the pH value of the concentrated brine to 4-6; carrying out adsorption treatment on the concentrated brine after the pH value is adjusted, and carrying out analysis treatment on an obtained adsorption product in an alkaline solution to obtain an analysis solution containing phosphate; adding a precipitator into the phosphate-containing analysis solution for precipitation treatment, and separating a product to obtain a phosphorus-containing precipitate, wherein the precipitation treatment further comprises the following steps: adding an anionic coagulant aid to promote precipitation, wherein the adding amount of the anionic coagulant aid is 0.1-0.3% of the mass of the analysis liquid; the adsorption treatment comprises: and carrying out shock adsorption treatment on the concentrated brine after the pH value is adjusted by adopting modified alumina, wherein the adsorption time is 0.5-3 hours.
2. The recovery method of claim 1, wherein the modified alumina comprises: aluminum sulfate-modified alumina and/or ferric sulfate-modified alumina.
3. The recovery method according to claim 1, wherein the alkaline solution is a 1% sodium hydroxide or potassium hydroxide solution by mass fraction.
4. the recovery method of claim 1, wherein the precipitating agent is selected from the group consisting of: one or more of a mixture of magnesium salt and ammonium salt, aluminum salt, ferric salt and saturated solution of calcium hydroxide, wherein the molar ratio of cations to phosphate radicals in the precipitator is (1-1.5) to 1.
5. the recovery method of claim 1 or 2, wherein the anionic coagulant aid comprises: one or more of polyacrylamide, polyacrylic acid, sodium polyacrylate and calcium polyacrylate.
6. the recovery method according to claim 1, wherein the supercritical water oxidation reaction apparatus comprises: the system comprises a heat exchanger, a high-pressure plunger pump and a supercritical water oxidation reaction kettle, wherein the heat exchanger, the high-pressure plunger pump and the supercritical water oxidation reaction kettle are connected in series;
The supercritical water oxidation reaction process comprises the following steps:
introducing the sludge subjected to the quenching and tempering treatment into the heat exchanger, heating to 320-350 ℃, and pressurizing to 22-30MPa through the high-pressure plunger pump;
And introducing excessive oxygen and the sludge pressurized by the high-pressure plunger pump into the supercritical water oxidation reaction kettle to perform supercritical water oxidation reaction, and staying for 10-30 seconds to obtain concentrated brine and supercritical fluid.
7. the recycling method according to claim 6, wherein an evaporation wall and a porous inner pipe are arranged in the supercritical water oxidation reaction kettle, supercritical water is filled in a cavity between the evaporation wall and the porous inner pipe, a concentrated brine outlet is arranged at the bottom of the supercritical water oxidation reaction kettle, and a supercritical fluid outlet, a liquid oxygen inlet and a sludge inlet are arranged at the top of the supercritical water oxidation reaction kettle.
8. the recycling method according to claim 6, further comprising:
passing the supercritical fluid into the heat exchanger;
Cooling and depressurizing the supercritical fluid passing through the heat exchanger, and then carrying out gas-liquid separation to obtain a gaseous product and liquid water;
and (3) recycling the liquid water to the quenching and tempering process or directly discharging, compressing and separating the gaseous product, recovering oxygen in the gaseous product, and returning the obtained oxygen to the supercritical water oxidation reaction device.
9. The recovery process of claim 1, wherein the pH of the concentrated brine is adjusted to 8.5 to 9.
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| CN108395061B (en) * | 2018-05-11 | 2020-05-22 | 西安交通大学 | System and method for recovering phosphorus in phosphorus-containing biomass based on supercritical oxidation technology |
| CN109020145B (en) * | 2018-09-03 | 2024-05-14 | 嘉兴德达资源循环利用有限公司 | Treatment device for phosphorus-containing sludge |
| CN109019865B (en) * | 2018-10-12 | 2021-06-25 | 合肥学院 | Three-dimensional artificial sewage purification floating island |
| CN109867421A (en) * | 2019-04-08 | 2019-06-11 | 陕西科技大学 | A kind of chromium-bearing sludge processing method and system based on supercritical water oxidation |
| US20230348306A1 (en) * | 2020-04-06 | 2023-11-02 | Scfi Limited | Process for the supercritical oxidation of sewage sludge and other waste streams |
| CN111392997B (en) * | 2020-05-19 | 2022-03-01 | 杭州秀澈环保科技有限公司 | Recycling process of organophosphorus sludge |
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