Method for deep dehydration and resource comprehensive utilization of sludge with relatively low water content

Abstract

The invention relates to the technical field of sludge treatment and resource utilization, in particular to a method for deep dehydration and resource comprehensive utilization of sludge with low water content. The method comprises the following steps: firstly, performing freeze thawing pretreatment on sludge to rupture sludge cells and separate out water in the cells; performing deep filter pressing on the frozen and thawed sludge, applying a direct-current electric field to the sludge for electroosmosis in the filter pressing process, and further separating mud and water in the sludge under the action of the direct-current electric field; in the deep filter pressing process of the sludge, the water absorption layer is additionally arranged between the two layers of filter cloth, so that floating water on the upper surface and the lower surface of the sludge layer can be removed, and the dewatering efficiency of the sludge is further improved; and the dehydrated sludge is subjected to drying granulation and pyrolysis gasification to obtain combustible gas, so that comprehensive utilization of the sludge is realized. The method is friendly to the human body and the environment, the sludge dewatering efficiency is high, reduction, harmlessness and recycling of the sludge are achieved, and the method has positive significance in environmental protection and resource reutilization.

Description

Technical Field

[0001] The invention relates to the technical field of sludge disposal and resource utilization, and in particular to a method for deep dehydration and comprehensive resource utilization of sludge with relatively low water content. Background Art

[0002] At present, most sewage treatment plants treat sewage based on the activated sludge method. This method produces a large amount of activated sludge. If it is not disposed of, it will cause serious harm to the environment and human body. At the same time, activated sludge is also a resource that can be comprehensively utilized because it is rich in organic and inorganic matter. In the process of comprehensive utilization of activated sludge, it is necessary to reduce the amount of activated sludge. The existing activated sludge is reduced by dehydrating and drying the activated sludge. Common dehydration equipment includes sludge dehydration centrifuge, belt sludge filter press, plate and frame filter press, etc. The moisture content of the sludge discharged from the equipment is about 65-85%. Although the volume and weight of the sludge with a moisture content of 99% are reduced by more than 90%, the treated sludge is plastic and the moisture content is still high. The energy consumption of direct drying is too high, and the moisture content of direct treatment and disposal exceeds the standard, which brings inconvenience to the further treatment of the sludge.

[0003] The existing combined sludge conditioning and mechanical dehydration can further remove the water contained in the sludge; the commonly used sludge conditioning methods are adding conditioning agents and physical methods such as ultrasound and microwave. Common conditioning agents are harmful to equipment, environment and human body. Among them, PAM decomposes slowly and is easy to accumulate in the environment, polluting the soil and water environment; the chloride ions in PAC will destroy the balance of the aquatic ecosystem, and excessive aluminum is toxic to microorganisms, animals, plants and humans; PFS is too acidic and contains sulfur elements, which has a great negative effect on equipment corrosion and subsequent sludge treatment and exhaust gas treatment; energy fields such as ultrasound and microwave are potential carcinogenic and teratogenic factors to the human body; in addition, it is found in actual production that after the deep filter press is unloaded, there is a layer of floating water on the upper and lower surfaces of each layer of mud cake during the mud cake unloading process, which cannot be discharged and the filter cloth cannot absorb, which will also cause the mud cake to have a high moisture content.

[0004] Therefore, a method for deep dehydration and comprehensive resource utilization of sludge that is friendly to the environment and human body is a problem that needs to be solved. Summary of the invention

[0005] The purpose of the present invention is to provide a method for deep dehydration and comprehensive resource utilization of sludge with low moisture content, so as to solve the problems that in the existing process of treating plastic sludge with low moisture content, the treatment agent and energy field have potential risks to the environment and human body, and in the process of deep filter pressing dehydration, there is floating water on the upper and lower surfaces of the mud cake, which affects the dehydration efficiency.

[0006] To achieve the above object, the present invention adopts the following technical scheme: a method for deep dehydration and comprehensive resource utilization of sludge with low moisture content, characterized in that it comprises the following steps:

[0007] S1. Pretreatment of sludge

[0008] Sludge with a moisture content of 65-85% was placed in a freeze-thaw cylinder for freezing treatment; after freezing treatment, it was thawed;

[0009] The freeze-thaw cylinder comprises a cylinder body, a pressure plug is arranged in the cylinder body, and a heat exchange tube is installed through the pressure plug; the heat exchange tube is used for the circulation of refrigerant and heat medium;

[0010] S2: deep filtration and electroosmosis treatment of the sludge pretreated in S1

[0011] The thawed sludge S1 is spread on the filter cloth of the deep filter press equipment for deep filter pressing; two layers of filter cloth are arranged between the layers of sludge, and a water absorption layer is added between the two layers of filter cloth; the water absorption layer is used to remove floating water on the upper and lower surfaces of the mud cake;

[0012] During the filtration process, direct current is passed between the piston and the cylinder to perform a combined filtration and electroosmosis treatment on the sludge.

[0013] S3, Drying Granulation and Pyrolysis Gasification

[0014] The sludge after S2 treatment is granulated by drying and granulating equipment; after granulation, the sludge enters the pyrolysis and gasification equipment for pyrolysis and generates fuel gas, so as to achieve the reduction, harmlessness and resource utilization of the sludge.

[0015] Furthermore, in the S1, the freeze-thaw temperature is -18 to -2°C, and the freezing time is 4 to 20 hours.

[0016] Furthermore, in the S1, the refrigerant is a low GWP environmentally friendly refrigerant with a temperature of -40 to -4°C, including but not limited to slurry ice; the heat medium includes but is not limited to hot dry air.

[0017] Furthermore, in the S2, the water-absorbing layer includes but is not limited to pure cotton cloth and geotextile.

[0018] Furthermore, in the S2, the bottom of the piston is the anode, the bottom of the cylinder is the cathode, the piston and the cylinder are insulated, and only the vertical current channel is retained; the voltage gradient of the direct current is 2 to 8 V / cm.

[0019] Furthermore, in the S2, the pressure of the deep filtration equipment is 3-6 MPa, a step-by-step pressure increase method is adopted, and the filtration time is 40-120 min.

[0020] Furthermore, in the S2-S3, after the combined treatment of filter pressing and electroosmosis, the water content in the sludge is reduced to below 40%; after drying and granulation, the water content in the sludge is reduced to below 20%.

[0021] Furthermore, in S3, the heat generated by combustion of the fuel gas produced by pyrolysis and gasification can be used for energy exchange of heat medium in freeze-thaw treatment and drying and granulation process.

[0022] Beneficial effects of the present invention:

[0023] 1. The method of the present invention does not use chemical agents, does not apply harmful energy fields, is friendly to the environment and human body, and is convenient for practical production and application;

[0024] 2. The method of the present invention can remove floating water on the upper and lower surfaces of the mud cake during deep filtration, thereby further improving the dehydration rate of the sludge; it helps to improve the efficiency of subsequent treatment, improve the treatment effect and reduce energy consumption, and plays a positive role in the subsequent sludge treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic diagram of the process flow of the method of the present invention;

[0026] Figure 2 Schematic diagram of the freeze-thaw cylinder structure involved in the method of the present invention;

[0027] Figure 3 The present invention is a schematic diagram of the structure and principle of the existing deep filter press equipment involved in the method of the present invention.

[0028] The names corresponding to the marks in the figure are:

[0029] 1. Cylinder body; 11. Insulation layer; 2. Press plug; 21. Heat exchange tube; 3. Cylinder body; 31. Filter cloth layer; 32. Sludge layer; 33. Water absorption layer; 4. Piston. DETAILED DESCRIPTION

[0030] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0031] like Figure 1 As shown, the method of the present invention takes plastic sludge with a moisture content of 65-85%, and then performs freeze-thaw treatment, wherein the sludge is frozen by a refrigeration system, and the frozen sludge is thawed by heat exchange with hot dry air.

[0032] The sludge after freeze-thaw treatment is added to the deep filter press equipment for filter pressing. During the filter pressing process, electricity is passed between the piston 4 and the cylinder 3 to form electro-osmosis, and a water-absorbing layer 33 is added between the filter cloth layers 31, so that the sludge can be further dehydrated to obtain sludge with a moisture content of less than 40%. The obtained sludge is dried, granulated and pyrolyzed and gasified to obtain combustible gas, which can be used in production to realize the resource recovery and comprehensive utilization of the sludge.

[0033] like Figure 2 As shown, different from traditional belt pre-pressing or freezing equipment, the freeze-thaw equipment used in the method of the present invention is a cylindrical freeze-thaw cylinder. During use, there is no need to set up a thin-laying device, and the mud can be directly and quickly fed in. A large amount of mud can be processed at a single time. The freeze-thaw and storage collection are all in the same space, and there is no need to set up a separate collection tank or storage tank. The freeze-thaw cylinder is wrapped with an insulation layer 11 of appropriate thickness, and the space heating and cooling method is abandoned. It can accurately keep cold and heat, and the insulation space is effectively concentrated, which can effectively improve the freezing and melting rates, reduce the heat or cold loss rate, and reduce energy loss.

[0034] The freeze-thaw cylinder includes a cylinder body 1 and a pre-compression plug 2. The plug 2 has the functions of compacting the sludge, increasing the contact area between the cold and hot media and the sludge, and shortening the freezing and thawing time of the sludge. A heat exchange pipe 21 is arranged under the plug 2, and the switching between the cold media and the hot media can be controlled by a control valve.

[0035] In actual production, the freeze-thaw cylinder is 5m in diameter and 2.5m in height, and can accommodate 23-28t of sludge at a time. A group is equipped with 4 freeze-thaw cylinders, and cooperates with a deep filter press with a single sludge pressing capacity of 20-100t (the number of freeze-thaw cylinders used can be adjusted at any time according to the amount of incoming sludge, sludge quality and the status of the deep filter press equipment). It can also be equipped with a large freeze-thaw cylinder with a diameter of 8m and a height of 4m, which can accommodate about 100t of sludge at a time. It can freeze and thaw one day's amount of sludge at one time and wait for the deep filter press to use in batches.

[0036] During the freeze-thaw process, the freeze-thaw temperature is -18 to -2°C, and the freezing time is about 4 to 20 hours (this time is determined by the refrigerant circulation temperature, the higher the temperature, the longer the freezing time); the refrigeration system uses refrigerant (coolant) circulation for indirect cooling, and the refrigerant can use low GWP refrigerants, such as fluidized ice, etc., and the cooling temperature ranges from -40 to -4°C. In order to save costs, the cold storage system of the present invention can increase the capacity of the refrigerant and use the peak-filling method to store cold, thereby reducing production costs.

[0037] After freezing and thawing, the sludge cells are broken and the water in the cells is analyzed out; in the deep filtration stage, a DC electric field is added between the cylinder 3 and the piston 4 to form an electro-osmosis phenomenon. In this process, the sludge solids are ionized and adsorbed on the interface in contact with the polar water phase, so that their surfaces are positively or negatively charged. The charged particles form a double layer structure with the counter ions in the water, so that the sludge particles are negatively charged and the water is positively charged. Under the action of the external electric field, the sludge particles move toward the anode and the water in the sludge moves toward the cathode, so that the mud and water in the sludge are separated.

[0038] like Figure 3 As shown, the deep filter press equipment involved in the present invention is an existing mature equipment, including a cylinder body 3 and a piston 4, a filter cloth layer 31 is reciprocatingly folded in the cylinder body 3, a sludge layer 32 is laid on the filter cloth layer 31, and a water absorption layer 33 is added between the filter cloth layers 31.

[0039] For deep filter pressing equipment, the sludge after freeze-thaw is directly spread on the filter cloth for deep filter pressing. During the filter pressing process, direct current is passed between the piston 4 and the cylinder 3, and the voltage gradient is 2 to 8 V / cm. The bottom of the piston 4 is the anode, and the bottom of the cylinder 3 is the cathode. The area around the piston 4 and the area around the cylinder 3 are insulated, and only the vertical electric channel is retained (the area with electricity is slightly smaller than the area of ​​the mud being spread).

[0040] Turning on the power will increase the temperature of the mud cake and transfer the water from the bottom of the piston 4 to the bottom of the cylinder 3, which is beneficial to the migration and evaporation of water. A water-absorbing layer 33 is added between the filter cloth layers 31. The water-absorbing layer 33 also has a certain toughness and good water absorption, such as pure cotton cloth and geotextile, which can absorb floating water on the surface of the mud cake and reduce the moisture content of the mud cake. The filtration pressure of a deep filter press is 3-6MPa, with step-by-step pressure increase and a total time of 40-120min. Multiple groups of deep filter press equipment can be set to achieve uninterrupted mud inlet, filtration and mud discharge.

[0041] Example 1

[0042] The centrifuged sludge with a moisture content of 82% entered the freeze-thaw cylinder, was frozen at -15℃ for 5 hours, and was filtered by a deep filter press. A pure cotton cloth water-absorbing layer was added between the filter cloth layers. Direct current was passed through the filter press piston and cylinder body with a voltage gradient of 2V / cm. The pressure was increased to 3MPa in 10 stages for a total of 46 minutes. The average moisture content of the mud cake was about 39.6%.

[0043] Example 2

[0044] The centrifuged sludge with a moisture content of 82% entered the freeze-thaw cylinder, was frozen at -15℃ for 5 hours, and was filtered by a deep filter press. A pure cotton cloth water-absorbing layer was added between the filter cloth layers. Direct current was passed through the filter press piston and cylinder body with a voltage gradient of 4V / cm. The sludge was pressed to 3MPa in 10 stages for a total of 46 minutes. The average moisture content of the mud cake was about 39.3%.

[0045] Example 3

[0046] The centrifuged sludge with a moisture content of 82% entered the freeze-thaw cylinder, was frozen at -15℃ for 5 hours, and was filtered by a deep filter press. A pure cotton cloth water-absorbing layer was added between the filter cloth layers. Direct current was passed through the filter press piston and cylinder body with a voltage gradient of 8V / cm. The sludge was pressed to 3MPa in 10 stages for a total of 46 minutes. The average moisture content of the mud cake was about 38.8%.

[0047] Example 4

[0048] The centrifuged sludge with a moisture content of 82% entered the freeze-thaw cylinder, was frozen at -15℃ for 5 hours, and was filtered by a deep filter press. A geotextile water-absorbing layer was added between the filter cloth layers. Direct current was passed through the filter press piston and cylinder with a voltage gradient of 4V / cm. The sludge was pressed to 3MPa in 10 stages for a total of 46 minutes. The average moisture content of the mud cake was about 39.5%.

[0049] Comparative Example 1

[0050] The centrifuged sludge with a moisture content of 82% entered the freeze-thaw cylinder and was frozen at -15℃ for 5h. It was only filtered by the deep filter press. No water absorption layer was added between the filter cloth layers. The filter press piston and cylinder were not energized and no electroosmotic dehydration was performed. It was pressed to 3MPa in 10 stages for a total of 46min. The average moisture content of the mud cake was about 48.2%.

[0051] Comparative Example 2

[0052] The centrifuged sludge with a moisture content of 82% entered the freeze-thaw cylinder and was frozen at -15℃ for 5 hours. It was only filtered by the deep filter press. A pure cotton cloth water-absorbing layer was added between the filter cloth layers. The filter press piston and cylinder were not energized and no electroosmotic dehydration was performed. The 10-stage pressure reached 3MPa for a total of 46 minutes, and the average moisture content of the mud cake was about 47.1%.

[0053] Comparative Example 3

[0054] The centrifuged sludge with a moisture content of 82% entered the freeze-thaw cylinder and was frozen at -15℃ for 5h. It was filtered only by the deep filter press. No water-absorbing layer was added between the filter cloth layers. Direct current was passed through the filter press piston and the cylinder with a voltage gradient of 4V / cm. It was pressed to 3MPa in 10 stages for a total of 46min. The average moisture content of the mud cake was about 40.2%.

[0055] The present invention is not limited to the above-mentioned optimal implementation mode. Anyone can derive other various forms of products under the inspiration of the present invention. However, no matter what changes are made in the shape or structure, all technical solutions that are the same or similar to those of the present application fall within the protection scope of the present invention.

Claims

1. A method for deep dehydration and comprehensive resource utilization of sludge with low moisture content, characterized in that: The following steps are involved: S1. Pretreatment of sludge Take the sludge with a moisture content of 65-85% and place it in a freeze-thaw cylinder for freezing treatment; and then thaw and melt it after freezing treatment; The freeze-thaw cylinder comprises a cylinder body (1), a pressure plug (2) is arranged in the cylinder body (1), and a heat exchange tube (21) is arranged and installed through the pressure plug (2); the heat exchange tube (21) is used for the circulation of refrigerant and heat medium; S2: deep filtration and electroosmosis treatment of the sludge pretreated in S1 The thawed sludge S1 is spread on the filter cloth of the deep filter press equipment for deep filter press; two layers of filter cloth are arranged between the layers of sludge, and a water absorption layer (33) is added between the two layers of filter cloth; the water absorption layer (33) is used to remove floating water on the upper and lower surfaces of the mud cake; During the filtration process, direct current is passed between the piston (4) and the cylinder (3) to perform a combined filtration and electroosmosis treatment on the sludge. S3, Drying Granulation and Pyrolysis Gasification The sludge after S2 treatment is granulated by drying and granulating equipment; after granulation, the sludge enters the pyrolysis and gasification equipment for pyrolysis and generates fuel gas, so as to achieve the reduction, harmlessness and resource utilization of the sludge.

2. The method for deep dehydration and comprehensive resource utilization of sludge with low moisture content according to claim 1, characterized in that: In the above-mentioned S1, the freezing and thawing temperature is -18 to -2°C, and the freezing time is 4 to 20 hours.

3. The method for deep dehydration and comprehensive resource utilization of sludge with low moisture content according to claim 2, characterized in that: In the above-mentioned S1, the refrigerant is a low GWP environmentally friendly refrigerant with a temperature of -40 to -4°C, including but not limited to slurry ice; the heat medium includes but is not limited to hot dry air.

4. The method for deep dehydration and comprehensive resource utilization of sludge with low moisture content according to claim 1, characterized in that: In the above-mentioned S2, the water-absorbing layer (33) includes but is not limited to pure cotton cloth and geotextile.

5. The method for deep dehydration and comprehensive resource utilization of sludge with low moisture content according to claim 1, characterized in that: In the S2, the bottom of the piston (4) is the anode, the bottom of the cylinder (3) is the cathode, the piston (4) and the cylinder (3) are insulated, and only the vertical current channel is retained; the voltage gradient of the direct current is 2 to 8 V / cm.

6. The method for deep dehydration and comprehensive resource utilization of sludge with low moisture content according to claim 1, characterized in that: In the S2, the pressure of the deep filter pressing equipment is 3-6 MPa, and a step-by-step pressure increase method is adopted, and the filter pressing time is 40-120 minutes.

7. The method for deep dehydration and comprehensive resource utilization of sludge with low moisture content according to claim 1, characterized in that: In the above-mentioned S2-S3, after the combined treatment of filter pressing and electroosmosis, the water content in the sludge is reduced to below 40%; After drying and granulation, the water content in the sludge drops below 20%.

8. The method for deep dehydration and comprehensive resource utilization of sludge with low moisture content according to claim 3, characterized in that: In the above-mentioned S3, the heat generated by the combustion of the fuel gas produced by pyrolysis and gasification can be used for energy exchange of heat medium in the freeze-thaw treatment and the drying and granulation process.

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