CN1199717C - External pressure pillar type hollow fiber films subassemblies capable of air blast - Google Patents

Abstract

The present invention relates to an outer pressure post type hollow fibre membrane assembly capable of flushed by gas, particularly to structural design of a hollow fibre membrane assembly and a use method thereof. The present invention has the technical characteristics that a special gas flushing component is arranged in the middle of membrane fibre at the bottom of the membrane assembly; by setting the height-diameter ratio of a shell cylindrical body of the membrane assembly, the length-diameter ratio of the membrane fibre and the filling density of the membrane assembly, the movement trace of gas and water and the flow state of two-phase flow are reasonably normalized; simultaneously, the membrane assembly works in a subcritical flux operation area under the selected operation condition. The present invention can effectively control membrane pollution development under the condition of maintaining low aeration quantity, and the high membrane flux is maintained. The running power consumption is reduced, and the long running of the membrane assembly is realized and maintained.

Description

An air flushable external pressure column type hollow fiber membrane module

technical field

The invention relates to a membrane module used in a membrane bioreactor, in particular to a structural design and a use method of a hollow fiber membrane module, and belongs to the technical field of membrane bioreactors and sewage treatment and reuse.

Background technique

Membrane Bioreactor (MBR) is a new type of efficient sewage treatment and reuse technology that organically combines membrane separation technology with traditional biological treatment technology. In membrane-bioreactor applications, larger area membranes are usually required. The smallest unit for installing a membrane is called a membrane module. There are many forms of membrane modules, which can basically be divided into two categories: tubular and flat. Commonly used membrane modules include flat plate membrane, tubular membrane, capillary membrane, hollow fiber membrane module, etc., and their properties are shown in Table 1-1.

Table 1-1 Performance list of membrane modules project Tubular membrane module Plate and basket membrane module Wound Membrane Module capillary membrane module Hollow Fiber Membrane Module outer diameter 6~25mm - - 0.5~2mm 40~500um Liquid flow go inside the tube - - go inside the tube Go inside or outside the tube support tube have - - none none Packing density Low lower medium high very high Membrane area very small medium medium medium Very big Membrane shear rate very high medium medium medium very low membrane flux big big medium big Small cost high medium medium Low very low Pollution Not easy to pollute Not easy to pollute Not easy to pollute Easy to clog Easy to clog cleaning condition easy to clean easy to clean not easy to clean not easy to clean not easy to clean Application range Microfiltration, ultrafiltration, reverse osmosis Microfiltration, ultrafiltration, reverse osmosis, gas separation Reverse osmosis, nanofiltration, gas separation, pervaporation Ultrafiltration, gas separation, membrane distillation, pervaporation Microfiltration, ultrafiltration, reverse osmosis

It can be seen from Table 1-1 that hollow fiber membranes have been widely used in wastewater treatment because of their large packing density and membrane area, low price, and overcoming the shortcomings of capillary membrane modules that are not pressure-resistant.

For a membrane separation process, the choice of membrane components depends on two aspects: one is the nature of the membrane itself, and the other is the particularity of the process. In the membrane bioreactor, because the object of treatment is sludge, membrane fouling is inevitable and serious, and the amount of sewage is relatively large, so the module form that is resistant to pollution and has a large membrane flux should be selected. As the membrane separation process proceeds, the macromolecular substances and dissolved substances in the solution are adsorbed to the membrane surface, and then enter the membrane pores to block the membrane pores and the deposition of particulate matter on the membrane surface is called membrane fouling. For the increase of membrane resistance and the decrease of membrane flux. In general, in membrane bioreactors, there are two main types of substances that cause membrane fouling. One is the macromolecular substances and soluble substances in the solution (such as microbial metabolites SMP), which will be adsorbed to the surface of the membrane to form a gel layer, or then enter the membrane pores to block the membrane pores, which is called irreversible pollution. Another type of material is granular material. As the membrane separation process proceeds, this type of material will deposit on the membrane surface to form a filter cake layer. The membrane fouling developed in this way often accounts for a large proportion of the total membrane fouling resistance. However, this kind of pollution is generally reversible, which is called reversible pollution. How to use effective physical means to control the development of reversible pollution is the key to control membrane fouling in membrane bioreactors.

According to the installation position of the membrane module, the membrane-bioreactor can be divided into two categories: the separated membrane-bioreactor and the integrated (or submerged, built-in) membrane-bioreactor. Traditional external membrane bioreactors generally use column membrane modules, and adopt the hydrodynamic operation mode of single-phase cross-flow filtration, and rely on the positive pressure provided by the circulating pump to form the driving pressure of the membrane. It has two main advantages of large membrane flux and convenient membrane cleaning. However, in order to effectively control membrane fouling, a relatively large membrane surface flow rate is often required, the required flow rate and head are large, and the energy consumption is also large (4 to 6 times that of the built-in membrane bioreactor). Traditional integrated membrane bioreactors generally use curtain-type membrane modules. Using the principle of air lift, a gas-water two-phase flow is formed to circulate in the upflow zone and downflow zone to scour the membrane surface and control membrane fouling. The suction pump adopted adopts the water outlet method of vacuum forming the driving pressure of the membrane. Its main advantage is that the energy consumption is relatively lower than that of the external type, and the land use is less, but its membrane cleaning is inconvenient, the membrane cleaning cost is high, and the membrane flux is relatively small. Moreover, since the air stripping is the suspension in the whole reactor, the fluid section of the gas-water two-phase flow is also relatively large, how to reduce its energy consumption is still an important concern of people. The energy consumption per unit of water treatment of the currently applied integrated membrane bioreactor is about 1.0-2.4kw h/ ^m3 (Gu Pingping, 2000, China Water Supply and Wastewater Vol.16(3), 5-8; Tatsuki Ueda and Kenji Hata 1999, waterreseach, 33, 2888-2892).

Can a new type of membrane module be designed to organically combine the external membrane bioreactor and the built-in membrane bioreactor to take advantage of their strengths and make up for their weaknesses, so that it has low energy consumption, large flux, and membrane Pollution develops slowly and the membrane is easy to clean.

Contents of the invention

The purpose of the present invention is to provide an air flushable external pressure column hollow fiber membrane module, which can effectively control the development of membrane fouling and maintain a high membrane flux while maintaining a low aeration rate. Further reduce its operating energy consumption to achieve and maintain its long-term operation.

The purpose of the present invention is achieved through the following technical solutions.

An air flushable external pressure column type hollow fiber membrane module mainly includes a shell cylinder of the membrane module, a U-shaped hollow fiber membrane thread arranged in the shell cylinder, a feed liquid outlet at the top, a feed liquid inlet and a The fixed area for fixing the bonded membrane filaments and the permeated water outlet are characterized in that a special air flushing part is arranged in the middle of the membrane filaments at the bottom of the hollow fiber membrane module.

The air flushing part described in the present invention can adopt a perforated aeration tube, a microporous aeration tube or a microporous aeration head.

The present invention is also characterized in rationally standardizing the trajectory of gas and water and the flow state of two-phase flow. This is mainly achieved by setting the height-to-diameter ratio of the shell column of the membrane module, the length-to-diameter ratio of the membrane filament, and the packing density of the membrane module. The shell cylinder of the membrane module of the present invention has an aspect ratio of 5 to 20:1; the membrane filament of the membrane module has an aspect ratio of 50 to 300:1; the membrane filament of the membrane module The packing density is 500~1500m ² /m ³ .

The present invention also provides a method for using an air flushable external pressure column type hollow fiber membrane module, that is, to rationally use the "subcritical flux operation method" to make the subcritical flux of the membrane module under selected operating conditions Working in the operating area, the subcritical flux operating area is determined by the flux step-increasing method, which can be carried out according to the following steps:

(1) Under the selected operating conditions, use the method of constant flux to make the membrane work for a time period ΔT of at least 30min, observe the change of the membrane operating pressure within ΔT, if the membrane operating pressure remains constant, adjust the stage of the effluent suction pump number, to increase the membrane flux by one order; re-observe the change of the membrane operating pressure in another ΔT, and so on, until the membrane operating pressure cannot be stabilized within ΔT;

(2) Record the membrane flux at this time as F _N+1 , that is, F _N+1 is the minimum membrane flux that increases the operating pressure of the membrane under this operating condition, and F _N is the operating pressure of the membrane under this operating condition constant maximum membrane flux; the critical flux is between F _N+1 and F _N , the flux region greater than F _N+1 is called the supercritical flux region under this operating condition, and the flux region smaller than F _N The flow area is called the subcritical flux area under this operating condition, so that the membrane module works in the subcritical flux operating area.

Compared with the existing hollow fiber membrane module, the present invention has the following advantages and outstanding effects:

(1) The flux is large, and its working flux can reach 15-30L/m ² h. The membrane flux of the known hollow fiber membrane modules generally used in integrated membrane bioreactors is only 5-10 L/m ² h.

(2) The gas-water ratio can be reduced to 20-25:1, thereby reducing energy consumption. The air-water ratio of the known hollow fiber membrane modules generally used in integrated membrane bioreactors is 40-60:1.

(3) Greatly reduce the cross-flow velocity on the membrane surface to 0.04-0.1m/s, thereby reducing circulation flow and energy consumption. The well-known cross-flow velocity on the membrane surface generally used in split-type membrane bioreactors is 2-4 m/s.

(4) Good anti-pollution performance. Since the aeration is concentrated directly in the membrane module, when the aeration rate is 20-25:1, the aeration intensity can reach 125-200m ³ /m ² h. Therefore, the turbulence of the membrane module fluid can be greatly increased, the deposition of particulate matter on the membrane surface can be controlled, and the anti-pollution performance of the membrane module can be greatly improved.

Description of drawings

Fig. 1 is a schematic structural diagram of an external pressure column hollow fiber membrane module used in a separate membrane bioreactor provided by the present invention.

Fig. 2 is a schematic structural diagram of an external pressure column hollow fiber membrane module used in an integrated membrane bioreactor provided by the present invention.

Fig. 3 shows a process device diagram of an external pressure column hollow fiber membrane module used in a split membrane bioreactor.

Fig. 4 shows a process device diagram of an external pressure column hollow fiber membrane module used in an integrated membrane bioreactor.

Detailed ways

The technical solutions of the present invention will be further described below in conjunction with the accompanying drawings and embodiments.

Fig. 1 is a schematic structural diagram of an external pressure column hollow fiber membrane module used in a separate membrane bioreactor provided by the present invention. Its main components include "U"-shaped hollow fiber membrane filament 1, membrane module shell cylinder 2, air flushing part 3, feed liquid inlet 6 at the bottom, permeate water outlet 5, feed liquid outlet 7 at the top, and pressure measuring tube interface 8 and the fixed area 4 bonded to the membrane silk.

Fig. 2 is a schematic structural diagram of an external pressure column hollow fiber membrane module used in an integrated membrane bioreactor provided by the present invention. Its main components include "U"-shaped hollow fiber membrane 1, membrane module shell cylinder 2, air flushing part 3, feed liquid inlet 6 at the bottom, permeate water outlet 5, feed liquid outlet 7 at the top and membrane filament bonding Fixed area 4.

Fig. 3 shows a process device diagram of an external pressure column hollow fiber membrane module used in a split membrane bioreactor. This device consists of a bioreactor 9, a circulating water inlet pipe 13, a circulating pump 14, an air supply device 10, a water outlet suction pump 11, a top water inlet pipe 12, a pressure gauge 15 and an external pressure column type hollow fiber membrane module. The air flushing part 3 at the bottom of the membrane module is connected with the air supply device 10 . The gas and the effluent of the circulating pump form a gas-water two-phase flow in the membrane module to control membrane fouling. Moreover, the gas-water two-phase flow flows in from the bottom of the reactor 9, on the one hand, the feed liquid in the reactor can be completely mixed, and on the other hand, it can provide oxygen for the microorganisms in the reactor 9. The raw water flowing in from 12 is completely mixed with the feed liquid in the reactor 9, and then injected into the membrane module by the circulating pump 14 through the circulating water inlet pipe 13. The membrane permeated water is discharged by the water outlet suction pump 11 through the permeated water pipe 5 .

Fig. 4 shows a process device diagram of an external pressure column hollow fiber membrane module used in an integrated membrane bioreactor. The device consists of a bioreactor 9, an air supply device 10, an outlet water suction pump 11, a top water inlet pipe 12 and an external pressure column type hollow fiber membrane module. The air flushing part 3 arranged at the bottom of the membrane module is connected with the air supply device 10 . There is an opening at the bottom of the side of the membrane module casing. When the air supply device aerates the membrane module, the column wall of the membrane module casing is used as a guide ring plate to form an upstream zone of gas-water two-phase flow in the membrane module. A descending zone is formed between the column wall and the reactor wall, thereby forming a circulating gas-water two-phase flow.

The height-to-diameter ratio of the shell cylinder of the membrane module in the present invention is (5-20): 1, the flow state of the gas-water unsteady flow is based on the formation of Taylor bubbles, and the gas supply method is to use perforated tubes, microfiltration tubes, and micropores. The aeration head or other porous materials introduce the gas into the middle of the inner membrane filament of the membrane module shell, so that the air bubbles can be freely and evenly distributed on the cross-section of the membrane module cylinder.

Unsteady fluid motion means that in the flow system, the relative physical quantities such as flow velocity, pressure and density of the fluid on each membrane surface not only change with the position, but also change with time. Compared with steady-state turbulent flow, unsteady flow can strengthen the filtering effect in both laminar flow and turbulent flow state. Fluid unsteady flow mode is a practical technology with good strengthening effect, low energy and simple equipment, which is highly efficient for design. , Anti-fouling membrane components have a great role in promoting. The gas-water two-phase flow is an unstable flow. The proper ratio of the height to diameter of the shell cylinder of the membrane module can effectively develop the flow state of the gas-water two-phase flow. , is also sufficient to form a strong unsteady flow.

For hollow fiber membranes, the ratio of the length and diameter of the membrane filaments directly affects the flow state of the permeated water in the membrane filaments and the flux distribution in the axial direction of the membrane filaments. If the aspect ratio of the membrane filament is too large, the membrane flux near the non-water outlet terminal part of the membrane filament will be much smaller than the membrane flux of the water outlet terminal part of the membrane filament, resulting in uneven distribution of membrane flux. If the diameter of the membrane filament is too large, the specific surface area of the membrane filament will be reduced too much. The aspect ratio of the membrane filament required by the present invention is: 50-300:1.

The packing density of the membrane module will affect the flow state of the gas-water two-phase flow. If the packing density is too high, the membrane filaments will not have enough oscillation space, and the turbulence will be weakened, which is not conducive to controlling the deposition of particulate matter. If the packing density is too small, the economic efficiency of the membrane module will decrease. The packing density of the membrane module required by the present invention is: 500-1500m ² /m ³ .

The present invention also requires continuous gas supply when the membrane module is working, but the membrane module adopts intermittent suction to discharge water.

The present invention rationally utilizes the "subcritical flux operation method" to determine the working flux of the membrane module using the method. Critical flux is a concept that is very important to membrane fouling. It means that there is a critical value in constant flux filtration. When the membrane flux is greater than this value, the membrane operating pressure TMP (Transmembrane Pressure) rises rapidly and membrane fouling Rapid development; when the membrane flux is less than this value, membrane fouling does not occur or develops very slowly. The critical flux is related to hydraulic operating conditions, membrane separation operation mode, feed liquid properties and the properties of the membrane itself. The subcritical operation of membrane bioreactor is based on such a concept that under certain operating conditions, the membrane flux is maintained below the critical flux to obtain long-term stable operation of the membrane bioreactor.

Generally, there are two types of substances that pollute the membrane: one is soluble macromolecular substances, such as soluble microbial products (Soluble Microbial Products, referred to as SMP) and extracellular polymers (Extracellular Polymers, referred to as ECP). During the separation, this kind of substance will be adsorbed to the surface of the membrane to form a gel layer (Gel Layer). The pollution is generally irreversible, but the development is relatively slow, which is called irreversible fouling (Irreversible Fouling). Another type of substance is particulate matter. Such as sludge flocs, this kind of material deposits on the surface of the membrane to form a sludge layer (Cake Layer), the pollution is reversible, called reversible fouling (Reversible Fouling), this kind of pollution occupies a large part in dead-end filtration ( 80% or more), and is developing rapidly, it is also the main object of hydrodynamic control of membrane fouling. In membrane bioreactors, the critical flux is also for reversible pollution, and the leading idea of subcritical operation is to make the membrane run During the process, try to avoid the deposition of sludge particles and avoid reversible pollution.

Example 1

Please refer to Figure 3 for the process installation diagram of the external pressure column hollow fiber membrane module used in a separate membrane bioreactor. The height-to-diameter ratio of the shell of the pressure-column hollow fiber membrane module is 11:1, the length-to-diameter ratio of the hollow fiber membrane is 200:1, the packing density of the membrane is 829m ² /m ³ , and the membrane area is 0.5m ² . When the concentration of mixed liquid sludge in the reactor is 3-10g/L, the membrane flux can reach 20L/m ² h, the circulating water volume of the circulating pump is 200L/h, the head is 2.0m, and the total efficiency of the unit is 0.49, then the unit treated water volume is circulated The energy consumption of the water pump is 0.21kw·h/m ³ . The cross-flow velocity on the membrane surface can be controlled at 0.04-0.06m/s, which is much lower than the 3-4m/s cross-flow velocity of the known split-type membrane bioreactor process. The aeration rate is 250L/h, the boost pressure is 20kPa, and the blower efficiency is 0.44, so the energy consumption of the blower per unit of treated water is 0.35kw·h/m ³ . The gas-water ratio is only 25:1, which is much smaller than the gas-water ratio (40-60:1) of the known integrated membrane bioreactor. The flow rate of the suction pump is 10L/h, the head is 10m, and the total efficiency of the unit is 0.49, so the energy consumption of the suction pump per unit of treated water is 0.06kw·h/m ³ . The total energy consumption per unit water treatment is 0.62kw·h/m ³ , which is much smaller than the 3.0-5.5kw·h/m ³ energy consumption per unit water treatment of the known cross-flow split membrane bioreactor.

Due to the use of concentrated aeration, the aeration intensity in the membrane module can reach 160~190m ³ /m ² h, which greatly increases the turbulence of the gas-water two-phase flow and is beneficial to control the deposition of particulate matter on the membrane surface To achieve the purpose of controlling reversible fouling of the membrane, the growth rate of the membrane operating pressure of the system is 0.15kPa/d. So as to realize the long-term and stable operation of the membrane bioreactor.

Example 2

Please refer to Figure 4 for a process device diagram of an external pressure column hollow fiber membrane module used in an integrated membrane bioreactor. The height-to-diameter ratio of the shell of the pressure-column hollow fiber membrane module is 6:1, the length-to-diameter ratio of the hollow fiber membrane is 100:1, the packing density of the membrane is 702m ² /m ³ , and the membrane area is 1.0m ² . When the mixed liquid sludge concentration in the reactor is 3-10g/L, the membrane flux can reach 15L/m ² h, the aeration rate is 390L/h, the boost pressure is 20kPa, and the blast efficiency is 0.44. The energy consumption is 0.49kw·h/m ³ . The gas-water ratio is only 26:1, which is much smaller than the gas-water ratio (40-60:1) of the known integrated membrane bioreactor. The flow rate of the suction pump is 15L/h, the head is 10m, and the total efficiency of the unit is 0.49, so the energy consumption of the suction pump per unit of treated water is 0.06kw·h/m ³ . The total energy consumption per unit water treatment is 0.55kw·h/m ³ , which is much smaller than the energy consumption per unit water treatment of known integrated membrane bioreactors of 1.0-2.4kw·h/m ³ .

However, the aeration intensity in the membrane module can reach 130-150m ³ /m ² h, which greatly increases the turbulence of the gas-water two-phase flow, which is beneficial to control the deposition of particulate matter on the membrane surface and achieve control of membrane reversible fouling. For the purpose, the growth rate of the membrane operating pressure of the system is 0.25kPa/d. So as to realize the long-term and stable operation of the membrane bioreactor.

Claims (2)

1. annoying external pressure pillar hollow fiber film assembly that dashes, mainly comprise membrane module shell cylinder, be arranged on the intravital U shape of shell post hollow-fibre membrane silk, the material liquid outlet at top, be arranged on the liquor inlet and fixed area that is used for fixing the adhesive film silk and permeate water outlet of bottom, it is characterized in that: be provided with special-purpose gas towards parts in the middle of the film silk of the bottom of hollow fiber film assembly, this gas adopts boring aeration pipe, micropore aeration pipe or micro porous aeration head towards parts; The shell cylinder aspect ratio of described hollow fiber film assembly is 5～20: 1; The film silk length-to-diameter ratio of described hollow fiber film assembly is 50～300: 1; The film silk packing density of described hollow fiber film assembly is 500～1500m ²/ m ³

2. the using method of an annoying according to claim 1 external pressure pillar hollow fiber film assembly that dashes, it is characterized in that: this method is to make the subcritical flux operating area work of membrane module under selected operational condition, described subcritical flux operating area adopts flux stepwise incremental method to determine, can carry out as follows:

(1) under the Xuan Ding operational condition, adopt the method for permanent flux to make a time period of film work Δ T be at least 30min, the variation of observation membrane operations pressure in Δ T, constant if membrane operations pressure keeps, regulate the progression of water outlet suction pump, make membrane flux increase a rank amount; Again observe the variation of membrane operations pressure in another Δ T, so continue, till membrane operations pressure occurring and in Δ T, can not stablizing;

(2) note membrane flux at this moment is F _N+1, i.e. F _N+1For under this operational condition, making the membrane flux of the minimum that membrane operations pressure goes up, F _NMembrane flux for the maximum of membrane operations constant pressure under this operational condition; Then critical flux is between F _N+1And F _NBetween, greater than F _N+1Flux regions be called overcritical flux regions under this operational condition, less than F _NFlux regions be called subcritical flux regions under this operational condition, make membrane module in this subcritical flux operating area work.

Images