A method for stripping ammonia nitrogen from biogas slurry

Abstract

The present invention belongs to the technical field of environmentally friendly recovery of ammonia nitrogen resources, and specifically relates to a method for stripping ammonia nitrogen from biogas slurry, including processes such as adjustment, filtration, heating, and stripping. A filtered clear liquid is obtained by filtration through a ceramic membrane; the suspended matter in the filtered clear liquid is less than 50 mg / L and enters a heating tank to create conditions for ammonia stripping. During the stripping process, the incoming water is atomized under the action of the micron pore size and high-speed rotating ceramic membrane disc, and the atomized droplets and the air generated by the deammonification blower are fully and violently collided and mixed, and the free ammonia in the water is transferred from the liquid phase to the gas phase and enters the air to form ammonia gas, which can be absorbed by clean water or acid in a subsequent absorption tank. The method of the present application reduces the problem of inefficient mass transfer faced by traditional biogas slurry ammonia nitrogen stripping, has a good gas-water mixing effect, ensures deammoniation efficiency, saves resources, and avoids secondary pollution.

Description

Technical Field

[0001] The invention belongs to the technical field of environmentally friendly recovery of ammonia nitrogen resources, and in particular relates to a method for stripping ammonia nitrogen from biogas slurry. Background Art

[0002] With the large-scale application of biogas projects, if the biogas slurry produced at the same time cannot be treated and utilized, it is easy to cause resource waste and secondary environmental pollution. Biogas slurry has the characteristics of high solid content and high ammonia nitrogen concentration. The ammonia nitrogen stripping process utilizes the ionization balance of ammonium ions. Through a certain method, the wastewater is fully contacted with the carrier gas, so that the ammonia in the wastewater is desorbed and transferred to the gas phase and carried out with the air flow. It is a physical and chemical denitrification process with relatively low treatment cost, good effect and simple operation. It has been applied to the treatment of high ammonia nitrogen wastewater. However, in actual use, a large amount of foam will appear in the stripping process of high-viscosity biogas slurry, which affects the gas-liquid mass transfer and causes the stripping effect of ammonia nitrogen to deteriorate. In addition, in the use of conventional stripping devices, it is not easy to disperse the water flow into fine droplets after it is input into the stripping device. When the water flow decreases, the stripping effect is poor during the air stripping process. Therefore, it is necessary to transform and improve the existing ammonia stripping technology. Summary of the invention

[0003] The purpose of the present invention is to provide a method for stripping ammonia nitrogen from biogas slurry, so as to overcome the problem in the prior art that the biogas slurry high in ammonia nitrogen is not easy to be dispersed into fine water droplets after rushing into the stripping device, and the problem that the ammonia nitrogen gas is not easy to be stripped during the air delivery of the fan.

[0004] The present invention provides a method for stripping ammonia nitrogen from biogas slurry, wherein the device used comprises a regulating tank, a filtering tank, a heating tank, and a stripping tank connected in series in sequence, and the method comprises the following steps:

[0005] (1) Pumping the biogas slurry into the regulating tank for water volume regulation;

[0006] (2) The biogas slurry is sent to a filter tank, which includes a cylindrical shell and a filtering mechanism arranged in the shell. The shell is provided with a liquid inlet pipe and a return pipe connected to the regulating tank. The filtering mechanism includes: a disc-shaped hollow ceramic membrane and a hollow rotating shaft passing through the central axis and fixedly connected to the central axis. A through hole is opened on the side wall of the hollow rotating shaft, which is connected to the internal flow channel of the disc-shaped hollow ceramic membrane. A clear liquid outlet is provided on the hollow rotating shaft. The filter tank removes suspended matter by solid-liquid separation through the disc-shaped hollow ceramic membrane to obtain filtered clear liquid. The concentrated liquid is returned to the regulating tank. After the solid content of the concentrated liquid reaches 15%, the concentrated liquid is discharged into the subsequent treatment unit, and the filtering pressure is maintained at 0.1MPa to 0.2MPa.

[0007] (3) The filtered clear liquid enters a heating tank for heating and temperature rise and pH adjustment. After heating and temperature rise, the outlet water temperature is controlled between 40° C. and 60° C., and after pH adjustment, the outlet water pH value is controlled between 9 and 12;

[0008] (4) The water from the heating tank enters the stripping tank, which includes a cylindrical atomizing mechanism arranged in a shell. The shell is connected to the air inlet pipe and the air outlet pipe. The atomizing mechanism includes: a disc-shaped hollow ceramic membrane and a hollow rotating shaft passing through the central axis and fixedly connected thereto. A through hole is opened on the side wall of the hollow rotating shaft, and the through hole is connected to the internal flow channel of the disc-shaped hollow ceramic membrane; a feed port is provided on the hollow rotating shaft; air is blown into the tank through the deammonification blower, and after being vigorously stirred and mixed to form a gas-water mixture, it enters the subsequent absorption equipment.

[0009] As a preferred solution, the air-water ratio of the deammoniation blower in step 4 is controlled at 1000-2500:1, and the stripping time is 0.5h-8h.

[0010] As a preferred solution, in order to effectively filter out suspended matter and organic matter, the pore size of the disc-shaped hollow ceramic membrane is 0.05 μm to 1 μm, and the material is selected from one or more of aluminum oxide, zirconium oxide, titanium dioxide and silicon oxide.

[0011] As a preferred solution, the rotation speed of the hollow rotating shaft is controlled at 400-900 rpm / min.

[0012] As a preferred solution, in order to improve the efficiency of filtering out suspended matter and organic matter; or to improve the efficiency of generating fine droplets, the disc-shaped hollow ceramic membrane includes a plurality of groups parallel to each other.

[0013] As a preferred solution, in order to prevent the filtered matter from accumulating on the outer surface of the disc-shaped hollow ceramic membrane and affecting the filtering effect, in addition to increasing the rotation speed to increase the friction between it and the biogas slurry, ridge-like protrusions are provided on the outer surface of the disc-shaped hollow ceramic membrane. The ridge-like protrusions are perpendicular to the tangent direction of the disc-shaped hollow ceramic membrane. After increasing the rotation speed, the protrusions can cut the biogas slurry more quickly and form a certain vacuum degree at the rear thereof, thereby achieving the removal of the filtered matter from the surface of the ceramic membrane.

[0014] Compared with the prior art, the present invention has the following characteristics:

[0015] (1) The present invention effectively solves the problem of a large amount of foam appearing during the stripping process of biogas slurry, which affects the gas-liquid mass transfer, and effectively improves the stripping effect of ammonia nitrogen. The idea is to reduce the suspended matter, organic matter and viscosity index in the biogas slurry through the regulating tank and the filter tank, so that the biogas slurry from different raw materials can be pretreated to improve the subsequent stripping effect.

[0016] (2) The ammonia nitrogen stripping equipment of the present invention uses ceramic membranes with micron pore sizes that are arranged in parallel on the outer circumference of the hollow rotating shaft, and the hollow rotating shaft is fixed to the deammonification tank through a bearing. The hollow rotating shaft rotates under the driving force of the motor, causing the liquid to overflow from the pores of the ceramic membrane to form fine droplets, which are then atomized. The droplets collide and mix with the air vigorously under the action of the fan stripping, and the free ammonia in the water is transferred from the liquid phase to the gas phase, enters the air, and enters the absorption tank. Compared with traditional stripping, the present invention makes it easier to blow away wastewater, increases the blowing surface, and thus blows out ammonia nitrogen more quickly, greatly improving the stripping efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings in the following description are some embodiments of the present invention.

[0018] Figure 1 The present invention is a process flow chart of a method for stripping ammonia nitrogen from biogas slurry in one embodiment of the present invention.

[0019] Figure 2 This is a schematic diagram of equipment for ammonia nitrogen stripping method of biogas slurry in one embodiment of the present invention.

[0020] Figure 3 This is a schematic diagram of the structure of a disc-shaped hollow ceramic membrane used for filtration in one embodiment of the present invention.

[0021] The figure includes: 1-main feed pipe; 2-adjusting tank; 3-filter feed pump; 4-filter feed pipe; 5-filter tank; 6-first hollow rotating shaft; 7-disc-shaped hollow ceramic membrane for filtering; 71-prismatic protrusion; 8-concentrate reflux valve; 9-first motor; 10-concentrate reflux pipe; 11-clear liquid discharge pipe; 12-heating rod; 13-heating tank; 14-alkali solution addition pipe; 15-pressure gauge; 16-blowing Stripping tank feed pump; 17-blow-off tank feed pipe; 18-second motor; 19-blow-off tank; 20-second hollow rotating shaft; 21-disc-shaped hollow ceramic membrane for atomization; 22-air pipe; 23-air pump; 24-water outlet pipe; 25-air outlet pipe; 26-aeration plate; 27-concentrate discharge valve; 28-concentrate discharge pipe; 29-outlet water reflux pump; 30-outlet water reflux valve; 31-outlet valve; 32-demister. DETAILED DESCRIPTION

[0022] The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention. If no specific techniques or conditions are specified in the examples, the techniques or conditions described in the literature in the art or the product instructions are used.

[0023] In the description of the present invention, unless otherwise specified, the terms "upper", "lower", etc. indicating the orientation or state relationship are based on the orientation or state relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0024] In the following examples, the instruments and equipment used without indicating the manufacturer are all conventional products that can be purchased through regular channels. The methods described are conventional methods unless otherwise specified, and the raw materials described can be obtained from public commercial channels unless otherwise specified.

[0025] Example 1

[0026] like Figure 1 , 2 As shown in Figure 3, this embodiment provides a method for stripping ammonia nitrogen from biogas slurry, particularly a method for stripping ammonia from biogas slurry with high solid content and high ammonia nitrogen. The device involved mainly includes a raw material regulating tank 2, a filter tank 5, a heating tank 13, and a stripping tank 19 connected in sequence. The four devices are connected in series, and the raw material regulating tank 2 is fed by a main feed pipe 1.

[0027] The method comprises the following steps: (1) pumping the biogas slurry into a regulating tank to adjust the amount of biogas slurry; (2) pumping the biogas slurry into a filter tank at a certain pressure, wherein a ceramic membrane cross-flow filter unit in the filter tank performs solid-liquid separation to remove suspended matter, and obtains filtered clear liquid, and the concentrated liquid is refluxed to the regulating tank, and after the solid content of the concentrated liquid reaches 15%, the concentrated liquid is discharged into other processing units, such as a plate-frame filter press or a dryer; (3) the filtered clear liquid enters a heating tank for heating and pH adjustment; (4) the water discharged from the heating tank enters a stripping tank, and a deammonification fan blows air into the tank. The mixture is vigorously stirred and mixed in the deammonification fan to form an air-water mixture, which then enters the absorption equipment, and the ammonia absorption liquid is clean water or dilute sulfuric acid.

[0028] The filter feed pump 3 is turned on to pump the biogas slurry in the regulating tank into the filter tank 5 through the filter feed pipe 4. The inlet of the filter feed pipe 4 is located in the middle of the filter pipe 5. The filter tank 5 includes a cylindrical shell and a filter mechanism arranged in the shell. The filter mechanism includes a disc-shaped hollow ceramic membrane for filtering and a first hollow rotating shaft 6 that passes through its central axis and is fixedly connected to it. The filter feed pump 3 and the regulating tank 2 are connected through the concentrated liquid reflux pipe 10 to form a circulation loop. The opening of the concentrated liquid reflux valve 8 is controlled to maintain the pressure of the pressure gauge 15 at 0.1MPa~0.2MPa. The preferred pressure in this embodiment is 0.15MPa. The first motor 9 at the bottom of the filter tank 5 is connected to the first hollow rotating shaft 6, the lower port of the first hollow rotating shaft 6 is closed, and the upper end is provided with a filter clear liquid discharge port; in order to improve efficiency, it is preferred to use 15 disc-shaped hollow ceramic membranes 7 for filtering, which are parallel to each other and are sleeved along their axial direction on the outer periphery of the first hollow rotating shaft 6, and are clamped and fixed by spacers. The upper and lower surfaces of any disc-shaped hollow ceramic membrane 7 for filtering are filter layers. In this application, the material selected is aluminum oxide, with a pore size of 0.5 μm, which plays a role in intercepting suspended matter, and the middle is a hollow cavity; the surface of the first hollow rotating shaft 6 is provided with The through hole is connected with the inner hollow cavity of the disc-shaped hollow ceramic membrane 7 used for filtration to form a sealed channel, so that the clear liquid filtered by the filter layer can flow into the first hollow rotating shaft 6. In order to avoid the accumulation of filtered matter on the surface of the disc-shaped hollow ceramic membrane and maintain its good filtration performance, the rotation speed of the hollow rotating shaft is controlled at 400-900rpm / min, and a prismatic protrusion 71 is provided on the outer surface of the disc-shaped hollow ceramic membrane 7 used for filtration. The prismatic protrusion 71 is perpendicular to the tangent direction of the disc-shaped hollow ceramic membrane used for filtration, and the height of the prismatic protrusion 71 is usually not more than 1cm.

[0029] When the solid content of the concentrate in the regulating tank 2 reaches 15%, the concentrate discharge valve 27 is opened to discharge the concentrate through the discharge pipe 28 to other processing units, such as a plate and frame filter press or a dryer.

[0030] After filtration, the clear liquid enters the heating tank 13 through the clear liquid discharge pipe 11. The tank is heated to 40°C~60°C and the pH is adjusted to 9~12 by the heating rod 12 and the alkali solution addition pipe 14 in the heating tank 13. The preferred temperature in this embodiment is 50°C and the pH value is 10. The clear liquid is pumped into the stripping tank 19 through the stripping tank feed pipe 17 by the stripping tank feed pump 16. The stripping tank 19 includes a cylindrical shell and an atomizing mechanism arranged in the shell. The atomizing mechanism includes: a disc-shaped hollow ceramic membrane 21 for atomization and a second hollow rotating shaft 20 passing through its central axis and fixedly connected thereto. The second motor 18 at the bottom of the stripping tank 19 is connected to the second hollow rotating shaft 20. The lower end of the second hollow rotating shaft 20 is closed and the upper end is connected to the stripping tank feed pipe 17. To improve efficiency, it is preferred to use 15 disc-shaped hollow ceramic membranes 21 for atomization, which are arranged in parallel on the outer periphery of the second hollow rotating shaft 20 (fixed by clamping rings), and the upper and lower surfaces of any disc-shaped hollow ceramic membrane 21 for atomization are dispersion layers (made of aluminum oxide, pore size: 0.5μm), and the second hollow rotating shaft 20 is fixed to the stripping tank 19 through a bearing. In order to improve the efficiency of producing fine droplets, the speed of the hollow rotating shaft is controlled at 400-900rpm / min to generate sufficient centrifugal force. At the same time, combined with the pressure provided by the feed pump 16 of the stripping tank, the liquid overflows from the micropores of the disc-shaped hollow ceramic membrane 21 used for atomization to form fine droplets, thereby atomizing. At the same time, the second hollow rotating shaft 20 rotates under the driving force of the second motor 18. The droplets are fully and violently collided and mixed with the air under the stripping effect of the air pump 23. The free ammonia in the liquid is transferred from the liquid phase to the gas phase and discharged along the outlet pipe 25 at the top of the stripping tank 19, and then enters the subsequent absorption unit after passing through the demister 32. The liquid part after stripping is pumped into the upper part of the stripping tank 19 through the outlet water reflux pump 29 for circulating stripping. The outlet of the outlet water reflux pump 29 is provided with an outlet water reflux valve 30. According to the needs, the concentration of ammonia nitrogen in the stripping outlet water is controlled by adjusting the gas-liquid ratio and the circulation volume of the waste water at the bottom of the stripping tower. After stripping, the remaining liquid is discharged from the system through the outlet pipe 24, on which an outlet valve 31 is provided. The air pump 23 is connected to the inner tank bottom of the stripping tank 19 through the air pipe 22. In order to better disperse the air, an aeration plate 26 is also provided at the air outlet.

[0031] Example 2

[0032] The method used in this embodiment is basically the same as that in embodiment 1. The biogas slurry treated is anaerobic biogas slurry from thermal hydrolysis of sludge. The total COD of the biogas slurry is 22310 mg / L, the solid content is 7.43%, and the NH 3 -N is 2488 mg / L.

[0033] The specific steps include:

[0034] (1) Pumping the anaerobic digestion liquid into the regulating tank 2;

[0035] (2) Start the feed pump 3 to pump the anaerobic biogas slurry into the filter tank 5 (feed rate is 60L / (m 2 h), the biogas slurry is subjected to dynamic cross-flow filtration, and the permeate is obtained in the heating tank 13, the concentrated liquid is refluxed to the regulating tank 2 through the concentrated liquid reflux pipe 10, and the filtration pressure is maintained at 0.1 MPa by the feed pump 3; the speed of the hollow rotating shaft is 900 r / min, the temperature is 15°C to 20°C at room temperature, the temperature in this embodiment is 18°C, and the average membrane flux is 30L / (m 2 h);

[0036] (3) When the solid content in the regulating tank 2 reaches 15%, the filtration and separation of the biogas slurry is completed, and the concentrated liquid discharge valve 27 is opened to discharge the concentrated liquid through the concentrated liquid discharge pipe 28.

[0037] (4) After filtration, the suspended solid concentration of the clear liquid is 23 mg / L. The clear liquid enters the heating tank 13 through the discharge pipe 11. The tank is heated to 60°C and the pH is adjusted to 12 by the heating rod 12 and the alkali solution adding pipe 14. The clear liquid is pumped into the stripping tank 19 through the stripping tank feeding pipe 17 by the stripping tank feeding pump 16.

[0038] The second motor 18 at the bottom of the stripping tank 19 is connected to the second hollow rotating shaft 20, the lower end of the second hollow rotating shaft 20 is closed, and the upper end is connected to the stripping tank feed pipe 17. 15 disc-shaped hollow ceramic membranes 21 are sleeved on the outer periphery of the second hollow rotating shaft 20 in parallel with each other (fixed by spacer clamping), and the upper and lower surfaces of any disc-shaped hollow ceramic membrane 21 are dispersion layers (made of aluminum oxide, pore size: 0.5μm), and the second hollow rotating shaft 20 is fixed to the stripping tank 19 through a bearing. The pressure provided by the stripping tank feed pump 16 causes the liquid to overflow from the micropores of the disc-shaped hollow ceramic membrane 21 to form fine droplets and thus atomize. At the same time, the second hollow rotating shaft 20 rotates under the driving force of the second motor 18. The droplets are fully and violently collided, rubbed and mixed with the air under the stripping action of the air pump 23. The gas-water ratio is controlled at 1000:1, and the stripping time is 5h. The free ammonia in the liquid is transferred from the liquid phase to the gas phase, enters the air, and enters the absorption unit. The remaining liquid is discharged from the system through the outlet pipe 24. The ammonia nitrogen removal rate reaches more than 95%, and the ammonia nitrogen concentration in the outlet water is reduced to less than 50 mg / L, and the deammoniation effect is ideal.

[0039] It should be noted that, with respect to the selection of the above parameter range values, ordinary technicians in this field can make adjustments based on actual conditions, and this application will not go into details.

[0040] The technical solution of the present application is clearly and completely described through the above embodiments. Obviously, the described embodiments are only part of the embodiments of this patent, not all of the embodiments. Common knowledge such as the known specific structures and characteristics in the scheme is not described in detail here. It should be pointed out that for those skilled in the art, without departing from the concept of the present invention, several variations and improvements can be made, such as simply adjusting the parameters within or near the specified parameter range, which should also be regarded as the scope of protection of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection claimed by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims

1. A method for stripping ammonia nitrogen from biogas slurry, characterized by: It comprises a regulating tank, a filtering tank, a heating tank and a stripping tank which are connected in series in sequence, and is characterized in that the biogas slurry ammonia nitrogen stripping method comprises the following steps: (1) Pumping the biogas slurry into the regulating tank for water volume regulation; (2) The adjusted biogas slurry is sent to a filter tank, and the filter tank performs solid-liquid separation through a ceramic membrane to remove suspended matter to obtain a filtered clear liquid, and the concentrated liquid is refluxed to the regulating tank to maintain a filtration pressure of 0.1MPa to 0.2MPa. The filter tank includes a cylindrical first shell and a filtering mechanism arranged in the first shell, and the first shell is provided with a liquid inlet pipe and a reflux pipe connected to the regulating tank, and the filtering mechanism includes: a disc-shaped hollow ceramic membrane for filtering and a first hollow rotating shaft passing through its central axis and fixedly connected thereto, the lower port of the first hollow rotating shaft is closed, and the upper end is provided with a filtered clear liquid discharge port, and the side wall of the first hollow rotating shaft is provided with a first through hole, and the first through hole is connected to the internal flow channel of the disc-shaped hollow ceramic membrane for filtering, and the outer surface of the disc-shaped hollow ceramic membrane for filtering is provided with a prismatic protrusion, and the prismatic protrusion is perpendicular to the tangent direction of the disc-shaped hollow ceramic membrane for filtering, and the height of the prismatic protrusion does not exceed 1cm; (3) The filtered clear liquid enters a heating tank for heating and temperature rise and pH adjustment. After heating and temperature rise, the outlet water temperature is controlled between 40° C. and 60° C., and after pH adjustment, the outlet water pH value is controlled between 9 and 12; (4) The water output from the heating tank enters the stripping tank through the stripping tank feed pipe, and the air is blown into the stripping tank through the deammoniation blower. The stripping tank includes a cylindrical second shell and an atomizing mechanism arranged in the second shell, and the second shell is connected to the air inlet pipe and the air outlet pipe. The atomizing mechanism includes: a disc-shaped hollow ceramic membrane for atomization and a second hollow rotating shaft passing through the central axis thereof and fixedly connected thereto, a second through hole is opened on the side wall of the second hollow rotating shaft, and the second through hole is connected to the internal flow channel of the disc-shaped hollow ceramic membrane for atomization; the lower end of the second hollow rotating shaft is closed, and the upper end is connected to the stripping tank feed pipe.

2. The method for stripping ammonia nitrogen from biogas slurry according to claim 1, characterized in that: In the step (2), after the solid content of the concentrated liquid reaches 15%, the concentrated liquid is discharged into a subsequent processing unit.

3. The method for stripping ammonia nitrogen from biogas slurry according to claim 1, characterized in that: The pore size of the disc-shaped hollow ceramic membrane used for filtration is 0.05 μm to 1 μm, and the material is selected from one or more of aluminum oxide, zirconium oxide, titanium dioxide and silicon oxide.

4. The method for stripping ammonia nitrogen from biogas slurry according to claim 1, characterized in that: The rotation speed of the first hollow rotating shaft and the rotation speed of the second hollow rotating shaft are both controlled within a range of 400 to 900 rpm / min.

5. The method for stripping ammonia nitrogen from biogas slurry according to claim 1, characterized in that: The disc-shaped hollow ceramic membrane for filtering and the disc-shaped hollow ceramic membrane for atomization both include a plurality of groups parallel to each other.

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