Method for performing salt extraction and sand removal on sludge

Abstract

The invention relates to the technical field of environmental protection, in particular to a method for salt extraction and sand removal of sludge. The method comprises the following steps: 1) carrying out pyrohydrolysis treatment on the sludge; step 2), adjusting the water content of the sludge subjected to the thermal hydrolysis treatment to 85 wt%-98 wt%; (3) putting the sludge treated in the step (2) into a pickling tank, then adding inorganic acid or organic acid, adjusting the pH value of the sludge to be less than 2, stirring the sludge for reaction, and then separating to obtain salt-extracted sludge; (4) putting the salt-extracted sludge separated in the step (3) into a neutralizing tank, and adding alkali to adjust the pH value of the sludge to be greater than 6; and (5) pumping the sludge neutralized in the step (4) into a cyclone separator for desanding, and feeding the desanded sludge into a wet oxidation reactor. According to the method, the sludge is subjected to salt extraction and sand removal, and the subcritical wet oxidation reaction efficiency of the sludge in the subsequent wet oxidation reaction is high.

Description

Technical Field

[0001] The invention relates to the technical field of environmental protection, and in particular to a method for extracting salt and removing sand from sludge. Background Art

[0002] With the development of urbanization and industrial and mining enterprises, as well as the continuous improvement of people's living standards, urban residents and enterprises produce a large amount of sewage every day, which will also produce a large amount of sludge. The large-scale production of sludge will bring severe pressure to the environment and sustainable development of cities. Therefore, it is urgent to achieve the reduction, harmlessness, stabilization, resource treatment and utilization of sludge. However, traditional sludge treatment methods, such as sludge landfill and sludge composting, do not treat sludge thoroughly and can easily form new secondary pollution. The field of sludge treatment needs the injection of new processes and technologies.

[0003] Subcritical wet oxidation of sludge has become a research hotspot in recent years. This method can not only significantly reduce the amount and volume of sludge, but also obtain organic matter and struvite. It is low-cost, low-pollution, and can achieve sludge reduction and resource utilization. Sludge wet oxidation refers to the use of wet oxidation to treat sludge. Usually, the sludge is placed in a closed reactor, and air or oxygen is introduced as an oxidant under high temperature and high pressure conditions. The high-molecular organic matter in the sludge is oxidized and decomposed according to the principle of submerged fuel, and the high-molecular organic matter is converted into small-molecular organic matter and inorganic matter, including hydrolysis, cracking and oxidation processes.

[0004] However, in the process of implementing the embodiments of the present invention, the inventors found that the content of inorganic salts and sand particles in the sludge is as high as 50% or even more, and it is difficult to efficiently recycle the sludge when the sludge is subjected to subcritical wet oxidation treatment. Summary of the invention

[0005] In view of the above problems, the present invention provides a method for extracting salt and removing sand from sludge, which overcomes the above problems or at least partially solves the above problems.

[0006] According to one aspect of the present invention, a method for extracting salt and removing sand from sludge is provided, comprising: step 1), subjecting the sludge to thermal hydrolysis treatment; step 2), adjusting the moisture content of the sludge after the thermal hydrolysis treatment to 85wt%-98wt%; step 3), placing the sludge treated in step 2) in a pickling tank, then adding an inorganic acid or an organic acid to adjust the pH value of the sludge to less than 2, stirring the sludge for reaction and separating it to obtain salt-extracted sludge; step 4), placing the salt-extracted sludge separated in step 3) in a neutralization tank, adding alkali to adjust the pH value of the sludge to greater than 6; step 5), pumping the sludge neutralized in step 4) into a cyclone separator to remove sand, and the sludge after sand removal enters a wet oxidation reactor.

[0007] In an alternative embodiment, the step of subjecting the sludge to hydrothermal treatment further includes heating and stirring the sludge and introducing steam.

[0008] In an alternative embodiment, the time for heating and stirring is more than 15 minutes.

[0009] In an alternative embodiment, the heat generated after the sludge passes through the wet oxidation reactor is displaced, and at least part of the heat source for heating the sludge in step 1) is derived from the displaced heat.

[0010] In an alternative embodiment, the pressure value of the steam is 0.4 Mpa to 0.7 Mpa.

[0011] In an alternative embodiment, the temperature for heating the sludge is 85 - 95 degrees, preferably 90 degrees.

[0012] In an alternative embodiment, after the sludge is subjected to hydrothermal treatment, the sludge after hydrothermal treatment is placed in a cell inactivation device to inactivate the cells, remove the organic matter outside the cells, and destroy the aggregation of the sludge flocs.

[0013] In an alternative embodiment, the inorganic acid is at least one of hydrochloric acid, sulfuric acid, or nitric acid.

[0014] In an alternative embodiment, the organic acid is oxalic acid.

[0015] In an alternative embodiment, the salt-extracted sludge enters the subsequent neutralization tank for neutralization only after being washed at least once. Among them, the washing supernatant generated from the Nth washing of the current batch of salt-extracted sludge is used for the (N - 1)th washing of the next batch of salt-extracted sludge, gradually increasing the inorganic salt concentration in the washing liquid.

[0016] In an alternative embodiment, the base is at least one of calcium hydroxide, sodium hydroxide, magnesium hydroxide, and potassium hydroxide.

[0017] The beneficial effects of the present invention are:

[0018] Different from the existing methods for treating sludge, in the embodiment of the present invention, in step 1), the sludge is subjected to hydrothermal treatment; in step 2), the water content of the sludge after the hydrothermal treatment is adjusted to 85wt%-98wt%; in step 3), the sludge after the treatment in step 2) is placed in a pickling tank, and then inorganic acid or organic acid is added to adjust the pH value of the sludge to be less than 2. After stirring and reacting the sludge, separation is carried out to obtain salt-extracted sludge; in step 4), the salt-extracted sludge separated in step 3) is placed in a neutralization tank, and alkali is added to adjust the pH value of the sludge to be greater than 6; in step 5), the sludge neutralized in step 4) is pumped into a hydrocyclone for sand removal, and the sludge after sand removal enters a wet oxidation reactor. Thus, the sludge is subjected to salt extraction and sand removal to remove inorganic salts and sand grains in the sludge, so that the efficiency of the subcritical wet oxidation reaction of the sludge in the subsequent wet oxidation reaction is high. In addition, the inorganic salt solution separated in the above step 3) can be further utilized resourcefully. Finally, the sand grains separated in the above step 4) can be used as building materials.

[0019] Therefore, the present invention provides an environmentally friendly and economical method for treating sludge. Through a series of innovative technological steps such as hydrothermal treatment, water content adjustment, pickling for salt extraction, neutralization, and hydrocyclone separation, the method effectively removes inorganic salts and sand grains in the sludge, significantly improving the efficiency and resource utilization rate of sludge treatment. The present invention not only realizes the reduction, harmlessness, stabilization, and resource utilization of sludge, solves the problems of low efficiency and easy secondary pollution of traditional sludge treatment methods, but also improves the efficiency of the sludge in the subsequent wet oxidation reaction. At the same time, the separated inorganic salt solution and sand grains are respectively utilized resourcefully, making up for the deficiencies of the existing technology and injecting new processes and new technologies into the field of sludge treatment. Description of the Drawings

[0020] One or more embodiments are exemplarily illustrated by the pictures in the corresponding drawings. These exemplary illustrations do not constitute limitations on the embodiments. Elements with the same reference numerals in the drawings are represented as similar elements. Unless otherwise stated, the drawings in the drawings do not constitute a proportional limitation.

[0021] Figure 1 It is a schematic flow chart of a method for salt extraction and sand removal of sludge provided by an embodiment of the present invention;

[0022] Figure 2 It is a process flow block diagram of a method for salt extraction and sand removal of sludge provided by an embodiment of the present invention. Detailed Embodiments

[0023] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0024] It should be noted that when an element is described as being "fixed to" another element, it may be directly on the other element, or one or more elements may be located therebetween. When an element is described as being "connected to" another element, it may be directly connected to the other element, or one or more elements may be located therebetween. The terms "vertical", "horizontal", "left", "right" and similar expressions used in this specification are for illustrative purposes only.

[0025] In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0026] See also Figure 1 , Figure 1 The present invention provides a flow chart of a method for extracting salt and removing sand from sludge, which comprises the following steps:

[0027] Step 1), subjecting the sludge to thermal hydrolysis treatment.

[0028] In some embodiments, the sludge comes from the residual sludge after denitrification treatment of municipal sewage, and the sludge contains organic matter, inorganic salts and sand particles, and the inorganic salts include one or more of zinc, copper, chromium, arsenic, iron, phosphate, cadmium, nickel, lead and aluminum.

[0029] In some embodiments, the step of subjecting the sludge to thermal hydrolysis further comprises heating and stirring the sludge and introducing steam.

[0030] In an embodiment of the present invention, the sludge after salt extraction and sand removal will enter the wet oxidation reactor for subcritical wet oxidation reaction. The heat generated by the sludge after the wet oxidation reactor is replaced, and the heat source for heating the sludge is at least partially derived from the replaced heat. The temperature for heating the sludge is 85-95 degrees, preferably 90 degrees. When the replaced heat does not reach 90 degrees, an external heat source will be used to heat and stir the sludge.

[0031] In some embodiments, the sludge is heated and stirred for 15 minutes.

[0032] It should be noted that the pressure value of the steam is 0.4 Mpa - 0.7 Mpa.

[0033] In some embodiments, the holding time of the above steam is 30 minutes. After the sludge is subjected to hydrothermal treatment, pressure relief will be carried out.

[0034] In some embodiments, the steam is uniformly introduced into the sludge for hydrothermal treatment.

[0035] After the sludge is subjected to hydrothermal treatment, the viscous organic matter in the sludge will undergo hydrolysis under certain temperature and pressure, the microbial cells in the sludge will be separated or broken, and the sand grains between and inside the microbial cells will be released, preparing for subsequent sand removal.

[0036] In some embodiments, after the sludge is subjected to hydrothermal treatment, the sludge after hydrothermal treatment is placed in a cell inactivation device to inactivate the cells, so as to further remove the organic matter outside the cells, further destroy the aggregation of the sludge flocs, and realize the further separation of organic matter, inorganic salts and sand grains in the sludge.

[0037] The above methods for inactivating cells can be electrocatalytic inactivation, using oxidation agents and using chlorine dioxide oxidation, etc.

[0038] Step 2), adjust the water content of the sludge after the hydrothermal treatment to 85wt% - 98wt%.

[0039] When the water content of the raw sludge is lower than 85wt%, water is added to the sludge for conditioning and dilution to a water content of 85wt% - 98wt%. When the water content of the raw sludge is between 85wt% - 98wt%, it can be placed in an acid pickling tank to extract salts.

[0040] Step 3), place the sludge treated in Step 2) in an acid pickling tank, then add inorganic acid or organic acid, adjust the pH value of the sludge to less than 2, stir and react the sludge and then separate to obtain salt-extracted sludge.

[0041] In some embodiments, the inorganic acid is at least one of hydrochloric acid, sulfuric acid or nitric acid.

[0042] In some embodiments, the organic acid is oxalic acid.

[0043] Among them, the inorganic acid or organic acid is added to the sludge while stirring, and the pH value of the sludge is adjusted to less than 2.

[0044] The sludge after hydrothermal treatment is placed in an acid pickling tank. By adding inorganic acid or organic acid and fully stirring and reacting, and then separating, the inorganic salts in the sludge are separated out. The separated inorganic salts are in the liquid phase, and the salt-extracted sludge after separation is in the solid phase. The inorganic salts in the liquid phase can be further processed to achieve resource utilization.

[0045] In some embodiments, the time for stirring and reacting the sludge is 30 minutes.

[0046] In some embodiments, the method for separating the sludge can be concentration, centrifugation or filtration. To improve the effect of salt extraction from the sludge, the separation time of the sludge can be reasonably set according to the actual situation. Generally, the separation time of the sludge is 30 minutes to 90 minutes.

[0047] In some embodiments, the salt-extracted sludge enters the subsequent neutralization tank for neutralization after at least one water wash.

[0048] When the salt-extracted sludge is washed with water multiple times for salt extraction, the above-mentioned salt-extracted sludge is washed once, twice until N times. The inorganic salt content of the sludge after N times of water washing is low. The supernatant after the Nth water wash enters the salt extraction process of the (N - 1)th water wash, and the supernatant generated in the salt extraction process of the (N - 1)th water wash enters the salt extraction process of the (N - 2)th water wash. Thus, the inorganic salt components in the supernatant generated after one water wash are getting higher and higher, and high-salt water is obtained, which can be further resourcefully utilized.

[0049] Step 4), place the salt-extracted sludge separated in step 3) in a neutralization tank, add alkali, and adjust the pH value of the sludge to be greater than 6.

[0050] Among them, the alkali is at least one of calcium hydroxide, sodium hydroxide, magnesium hydroxide and potassium hydroxide.

[0051] Step 5), pump the sludge neutralized in step 4) into a hydrocyclone for sand removal, and the sludge after sand removal enters a wet oxidation reactor.

[0052] In some embodiments, the step of pumping the sludge neutralized in step 4) into a hydrocyclone for sand removal further includes using a pressure pump to pressurize the sludge and then pump it into the hydrocyclone. The sludge pressurized by the pressure pump meets the inlet requirements of the sand cyclone, so that the continuous transfer of the sludge from the neutralization tank to the hydrocyclone can be realized, and the efficiency of sludge salt extraction and sand removal can be improved.

[0053] It should be noted that, in some embodiments, the process of the sludge participating in the subcritical wet oxidation reaction in the wet oxidation reactor is as follows:

[0054] Initiation of the chain:

[0055] RH + O2 → R· + HOO· (where RH is the high-molecular organic matter in the sludge)

[0056] 2RH + O2 → 2R· + H2O2

[0057] H2O2 + M → 2OH· (where M is the catalyst)

[0058] Chain transfer:

[0059] RH + ·OH → R· + H2O

[0060] R· + O2 → ROO·

[0061] ROO· + RH → ROOH + R·

[0062] Chain termination:

[0063] R· + R· → R - R

[0064] ROO· + R· → ROOR

[0065] ROO· + ROO· + H2O → ROOH + ROH + O2 (where ROOH is the organic acid)

[0066] The following further describes the process for desalting and sand removal of sludge applicable to the method for desalting and sand removal of sludge provided in the embodiments of the present invention.

[0067] Please refer to Figure 2 , the process for desalting and sand removal of sludge is provided with a hydrothermal reactor, a conditioning tank, an acid washing tank, a separator, a neutralization tank, a hydrocyclone separator and a wet oxidation reactor. The hydrothermal reactor, the conditioning tank, the acid washing tank, the separator, the neutralization tank, the hydrocyclone separator and the wet oxidation reactor are connected in sequence. It should be noted that there may be other processing devices between the hydrocyclone separator and the wet oxidation reactor, such as a secondary heating device, etc.

[0068] In this process, the sludge is subjected to hydrothermal treatment in the hydrothermal reactor. In some embodiments, the hydrothermal reactor is in the shape of a vertical cylinder, so as to not only achieve a compact layout of the process flow in space. In addition, since steam needs to be introduced into the hydrothermal reactor to perform hydrothermal treatment on the sludge, the cylindrical hydrothermal reactor can be provided with multiple steam inlets, so as to achieve uniform hydrothermal treatment of the sludge.

[0069] In some embodiments, the hydrothermal reactor is a pressure-bearing vessel, the design pressure of the vessel is greater than 1.0 Mpa, and the working pressure of the reactor is not greater than 1.0 Mpa.

[0070] In this process, the sludge after hydrothermal treatment enters the conditioning tank for moisture content adjustment. In the embodiments of the present invention, the sludge needs to be adjusted to a moisture content of 85% to 98% to facilitate further salt extraction.

[0071] Further, the sludge after conditioning and dilution enters the pickling tank, and inorganic acid or organic acid is used to adjust the pH value so that the pH value of the sludge is less than 2, and the sludge is stirred and reacted.

[0072] The sludge passing through the pickling tank enters the separator for solid-liquid separation. The separated liquid phase contains inorganic salts, while the remaining salt-extracted sludge contains organic matter and sand particles.

[0073] The salt-extracted sludge obtained after solid-liquid separation enters the neutralization tank for neutralization, and the pH value of the sludge is adjusted to be greater than 6 by adding alkali.

[0074] The neutralized sludge is pumped into a hydrocyclone separator by a pump for separation of organic matter and sand particles in the sludge. The separated sand particles can be used in construction projects. The sand-removed sludge after sand removal can enter a wet oxidation reactor for subcritical wet oxidation reaction, thereby decomposing macromolecular organic matter into small-molecular organic matter, such as organic acids, to achieve resource utilization.

[0075] In some embodiments, the heat generated in the wet oxidation reactor can be exchanged and enter the hydrothermal reactor to supply heat.

[0076] It should be noted that pumps can be provided between the hydrothermal reactor and the conditioning tank, between the conditioning tank and the pickling tank, between the pickling tank and the separator, between the separator and the neutralization tank, and between the hydrocyclone separator and the wet oxidation reactor, so as to realize the transfer of sludge between various containers.

[0077] In the embodiments of the present invention, through step 1), the sludge is subjected to hydrothermal treatment; step 2), the moisture content of the sludge after the hydrothermal treatment is adjusted to 85% to 98%; step 3), the sludge after being treated in step 2) is placed in the pickling tank, and then inorganic acid or organic acid is added to adjust the pH value of the sludge to be less than 2, and after stirring and reacting the sludge, separation is carried out to obtain salt-extracted sludge; step 4), the salt-extracted sludge separated in step 3) is placed in the neutralization tank, and alkali is added to adjust the pH value of the sludge to be greater than 6; step 5), the sludge neutralized in step 4) is pumped into a hydrocyclone separator for sand removal, and the sludge after sand removal enters the wet oxidation reactor, so that the sludge is subjected to salt extraction and sand removal, removing inorganic salts and sand particles in the sludge, so that the efficiency of the subcritical wet oxidation reaction of the sludge in the subsequent wet oxidation reaction is high. In addition, the inorganic salt solution separated in the above step 3) can be further subjected to resource utilization. Finally, the sand particles separated in the above step 4) can be used as building materials.

[0078] Example

[0079] Please refer to Figure 1 and Figure 2 , a method for desalting and sand removal of sludge provided by an embodiment of the present application, the method specifically includes the following steps:

[0080] Step 1), perform hydrothermal treatment on the sludge, that is, heat the sludge to 90 degrees, stir for 15 minutes and introduce steam (steam pressure value is 0.5 Mpa), place the sludge after hydrothermal treatment in a cell inactivation device to inactivate the cells, remove the organic matter outside the cells, and destroy the aggregation of the sludge flocs. ;

[0081] Step 2), adjust the water content of the sludge after the hydrothermal treatment to 90 wt%;

[0082] Step 3), place the sludge after being treated in Step 2) in a pickling tank, then add hydrochloric acid to adjust the pH value of the sludge to 1.5, stir and react the sludge and then separate to obtain desalted sludge;

[0083] Step 4), wash the desalted sludge separated in Step 3) three times and then place it in a neutralization tank, add sodium hydroxide to adjust the pH value of the sludge to 7;

[0084] Step 5), pump the sludge neutralized in Step 4) into a hydrocyclone for sand removal, and the sludge after sand removal enters a wet oxidation reactor.

[0085] Experimental verification

[0086] It is measured that through the above process method, the removal rate of inorganic salts in the supernatant separated from the pickling tank reaches 59.5%, the separated inorganic salt solution has a high concentration and few impurities, and it is easier to carry out subsequent resource treatment and utilization. At the same time, the sand content separated by the hydrocyclone reaches 49.7%, and the separated sand can be used as building materials, correspondingly improving the utilization rate of waste sand in the sludge.

[0087] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; under the idea of the present invention, the technical features in the above embodiments or different embodiments can also be combined, and the steps can be implemented in any order, and there are many other changes in different aspects of the present invention as described above. For the sake of brevity, they are not provided in detail; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for extracting salt and removing sand from sludge, characterized in that: include: Step 1), subjecting the sludge to thermal hydrolysis treatment; Step 2), adjusting the moisture content of the sludge after the thermal hydrolysis treatment to 85wt%-98wt%; Step 3), placing the sludge treated in step 2) in a pickling tank, then adding an inorganic acid or an organic acid to adjust the pH value of the sludge to less than 2, stirring the sludge for reaction and then separating to obtain salt extraction sludge; Step 4), placing the salt extraction sludge separated in step 3) in a neutralization tank, adding alkali, and adjusting the pH value of the sludge to be greater than 6; Step 5), the sludge neutralized in step 4) is pumped into a cyclone separator to remove sand, and the sludge after the sand is removed enters a wet oxidation reactor.

2. The method according to claim 1, characterized in that The step of thermally hydrolyzing the sludge further includes heating and stirring the sludge and introducing steam.

3. The method according to claim 2, characterized in that The heating and stirring time is 15 minutes or more.

4. The method according to claim 2, characterized in that: The heat generated by the sludge after passing through the wet oxidation reactor is replaced, and the heat source for thermal hydrolysis of the sludge is at least partially derived from the replaced heat.

5. The method according to claim 2, characterized in that: The pressure value of the steam is 0.4Mpa-0.7Mpa.

6. The method according to claim 2, characterized in that The temperature for heating the sludge is 85-95 degrees, preferably 90 degrees.

7. The method according to any one of claims 1 to 6, characterized in that: After the sludge is treated by thermal hydrolysis, it is placed in a cell inactivation device to inactivate the cells, remove the organic matter outside the cells, and destroy the aggregation of the sludge bacterial flocs.

8. The method according to any one of claims 1 to 6, characterized in that: The inorganic acid is at least one of hydrochloric acid, sulfuric acid or nitric acid, and the organic acid is oxalic acid.

9. The method according to any one of claims 1 to 6, characterized in that: The salt-extracting sludge is washed at least once before entering the subsequent neutralization tank for neutralization, wherein the washing supernatant produced by the Nth washing of the current batch of salt-extracting sludge is used for the N-1th washing of the next batch of salt-extracting sludge, gradually increasing the concentration of inorganic salts in the washing liquid.

10. The method according to any one of claims 1 to 6, characterized in that: The alkali is at least one of calcium hydroxide, sodium hydroxide, magnesium hydroxide and potassium hydroxide.

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