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Disc tube membrane modules
DT membrane technology is disc tube membrane technology, which is divided into two categories: DTRO (disc tube reverse osmosis) and DTNF (dish tube nanofiltration), which is a patented membrane separation equipment. Its membrane module structure is completely different from the traditional spiral membrane, the dope flow channel: the disc tube membrane module has a patented flow channel design form, using an open flow channel, the material liquid enters the pressure vessel through the inlet, and flows from the channel between the deflector plate and the shell to the other end of the assembly, at the other end of the flange, the material liquid enters the deflector tray through 8 channels, and the treated liquid flows quickly through the filter membrane at the shortest distance, and then 180ºReversing to the other membrane surface, it flows from the notch in the center of the deflector plate to the next deflector plate, thus forming a double "S" shaped route on the membrane surface from the circumference of the deflector disc to the center of the circle, then to the circumference and then to the center of the circle, and finally the concentrate flows out of the flange of the feed end. The distance between the two deflector plates of the DT assembly is 4mm, and there are bumps arranged in a certain way on the surface of the deflector plate. This special hydraulic design makes the treatment liquid flow through the surface of the filter membrane under pressure to form turbulence when it collides with bumps, increases the permeability rate and self-cleaning function, thus effectively avoiding the blockage of the membrane and the concentration polarization, and successfully prolongs the service life of the diaphragm.
Permeable flow channel: The filter membrane is composed of two concentric annular reverse osmosis membranes, and a filamentous scaffold is sandwiched between the membranes, so that the purified water passing through the membrane can quickly flow to the outlet. The outer ring of these three layers of annular material is welded with ultrasonic technology, and the inner ring is open for the water purification outlet. The permeate flows along the filamentous support in the middle of the diaphragm to the permeate channel on the periphery of the central tie rod, and the O-ring on the deflector prevents raw water from entering the permeate channel, and the distance from the permeate to the center is very short and equal to the filter diaphragm in the module.
Schematic diagram of the flow channel of the disc tube membrane column
DT diaphragm and deflector plate
1.1 Two-stage DTRO process
The two-stage DTRO process is based on the process application of the disc tube reverse osmosis membrane, and its core technology lies in the unique structure of the disc tube reverse osmosis membrane, which makes it possible for the reverse osmosis membrane to directly treat high-concentration wastewater, and is a stable and reliable treatment technology, with the characteristics of low investment, high degree of automatic control, easy operation and maintenance, low operating cost and stable and continuous meeting of discharge requirements, as follows:
(1) The process is simple and compact, and the complete sets of equipment are standardized
As shown in the diagram of the two-stage DTRO complete set of equipment, the complete set of equipment integrates a sand filter system for pretreatment, a security filter, a membrane module for reverse osmosis separation, a high-pressure pump, a circulating pump, a cleaning water tank for system cleaning, and an MCC cabinet and PLC cabinet for equipment power supply and control.
In addition, the raw water tanks, pump valves, etc., which are used for raw water acid adjustment and effluent alkali callback, are also standardized complete sets of equipment, which are processed, installed and debugged in the factory, and can be debugged after being hoisted in place at the delivery site, and the operation period is short.
(2) Strong process stability, simple maintenance and low energy consumption
Because there are few factors affecting the rejection rate of the membrane system, the effluent water quality of the system is very stable, and is not affected by the factors such as biodegradability and carbon-nitrogen ratio; the DT membrane module used in the process adopts standardized design, the component is easy to disassemble and maintain, and the DT component can be easily checked and maintained by opening the DT module, and the maintenance is simple, when the number of parts is insufficient, the module allows less diaphragm and diversion plate to be installed without affecting the use of DT membrane module.
DT membrane module effectively avoids the fouling of the membrane, reduces the membrane fouling, and prolongs the life of the reverse osmosis membrane. The special structure and hydraulic design of the DT make the membrane stack easy to clean, and the flux recovery after cleaning is very good, thus prolonging the life of the diaphragm. Practical engineering has shown that in the treatment of ulate, the life of the first-class DT diaphragm can be as long as 3 years, or even longer, and the life of other treatment facilities (such as MBR) can be as long as 5 years, which is unattainable by the general reverse osmosis treatment system.
In this process, no final removal of contaminants is required, only separation, so the operating energy consumption is significantly reduced, and any individual parts inside the DT assembly can be replaced individually. The filter part is assembled by a plurality of filter diaphragms and deflector plates, when the filter diaphragm needs to be replaced, a single replacement can be carried out, and the diaphragm with good filtration performance can still be used, which maximizes the procedure to reduce the cost of changing the membrane.
(3) The effluent quality is good
Reverse osmosis membrane has a very high removal rate of various pollutants, good effluent quality, the current main use of single-stage (series to biochemical effluent) and two-stage DTRO, can fully meet all kinds of reuse or discharge standards.
(4) Flexible operation
As a set of physical separation equipment, the DTRO system is very flexible in operation, can operate continuously or intermittently, and can also adjust the series and parallel connection mode of the system to meet the requirements of water quality and quantity.
(5) The construction period is short, and the commissioning and start-up are rapid
The core components of the two-stage DTRO process are assembled in the factory, with supporting plant and pool construction, which is small in scale and fast in construction. After the equipment arrives at the site, it only takes about two weeks to install and debug the work.
(6) High degree of automation and simple operation
The process system is fully automatic, the whole system is equipped with a perfect monitoring and control system, PLC can automatically adjust according to the sensor parameters, send out alarm signals in a timely manner, and protect the system, the operator only needs to find the error code according to the operation manual to troubleshoot, and there is no excessive requirement for the experience of the operator.
(7) Small footprint
The core equipment of the two-stage DTRO process is an integrated installation, and the ancillary structures and facilities are also small structures with a small footprint.
(8) Recyclable
The core component of the two-stage DTRO process is the DTRO integrated equipment, which is easy to move and install, and the overall service life of the equipment is more than 20 years.
1.2 Process flow and description
1.2.1 Process flow
1.2.2 Process description
1.2.2.1 Pretreatment
Due to the different factory conditions and pre-treatment processes, the composition of high-concentration wastewater is complex, and there are various insoluble salts such as calcium, magnesium, barium, silicon, etc., which are highly concentrated after entering the reverse osmosis system, and when their concentration exceeds the solubility under the conditions, scaling will occur on the surface of the membrane. Adjusting the pH value of the raw water can effectively prevent the scaling of carbonate inorganic salts, so the pH value of the raw water must be adjusted before entering reverse osmosis.
The effluent of the regulating tank is pumped into the raw water tank of the reverse osmosis system, and the pH is adjusted by adding acid in the raw water tank, and the effluent of the raw water tank is pressurized by the raw water pump and then enters the quartz sand filter, and the number of sand filters is determined according to the specific treatment scale, and its filtration accuracy is 50μm. There are pressure gauges at the inlet and outlet ends of the sand filter, and when the pressure difference exceeds 2.5 bar, the backwash procedure must be carried out. The frequency of backwashing of the sand filter depends on the suspended solids content of the influent water, for the general wastewater, the backwashing cycle of the sand filter is about 100 hours, for the raw water with low SS value, if the pressure difference does not exceed 2.5bar after 100 hours of sand filter operation, it must also be backwashed, so as to avoid the over-compaction and compaction of quartz sand, and the backwashing time of the sand filter will be automatically activated at the first time. The sand filter water washing uses raw water for cleaning, and the air washing uses the compressed air generated by the rotary vane compressor.
For the leachate grade system, due to the high content of calcium, magnesium, barium and other easy scaling ions and silicates in the raw water, these salts are easy to appear supersaturated on the concentrate side after the DT membrane module is concentrated at high magnification, so according to the actual water quality situation, a certain amount of scale inhibitor is added in front of the core filter to prevent the occurrence of silica scale and sulfate scaling, and the specific amount added is determined by the analysis of raw water quality, and the scale inhibitor should be diluted with 20 times of water before use. The cartridge filter provides the final protective barrier to the membrane column and has an accuracy of 10 μm. Similarly, the number of cartridge filters is determined by the specific treatment scale as with sand filters.
1.2.2.2 Two-level DTRO system
The membrane system is a two-stage reverse osmosis, the first stage of reverse osmosis needs to enter water from behind the cartridge filter, and the second stage of reverse osmosis treats the first stage of permeable water.
The effluent of the raw water storage tank is supplied by the pump PK00211 to the reverse osmosis equipment, and the sand filter booster pump PK13011 provide pressure to the raw water. There is a total of 1 sand filter, FS13011. There are pressure gauges at the inlet and outlet ends of the sand filter, and when the pressure difference exceeds 2.5 bar, the backwash procedure must be carried out. The frequency of backwashing of the sand filter depends on the suspended solids content of the incoming water. When backwashing, air washing is carried out with an air pump RK13811, and then a pump PK13011 is used for flushing, and the filtration accuracy of the sand filter is 50μm. After passing through the sand filter, the raw water directly enters the core filter, and the equipment is equipped with 2 core filters, which have pressure gauges at the inlet and outlet ends, and the filter element is replaced when the pressure difference exceeds 2.0bar. The cartridge filter filtration has a precision of 10 μm and provides the final protective barrier for the membrane column. In order to prevent the fouling of various insoluble sulfates and silicates in the membrane module due to high concentration, and effectively prolong the service life of the membrane, a certain amount of scale inhibitor needs to be added before the first-class reverse osmosis membrane. The amount of addition is determined by the concentration of insoluble salts in the raw water.
The raw water passing through the cartridge filter is fed directly into the first-stage reverse osmosis high-pressure piston pump.
The DT membrane system has a shock absorber at the back of each piston pump to absorb the pressure pulses generated by the high-pressure pump and provide smooth pressure to the membrane column. The effluent after the high-pressure pump enters the membrane module, and the membrane module adopts the disc tubular reverse osmosis membrane column, which has the advantages of strong anti-pollution and good material exchange effect, and has strong adaptability to leachate, and the life of the first-class DTRO membrane can reach more than 3 years, and the life of the second-level DTRO membrane is as long as 5 years. The first-stage reverse osmosis system is planned to be set up in two groups, which are connected in series, the first group of reverse osmosis concentrated liquid enters the second group after series connection, and the COD concentration and salt content of the concentrated liquid treated by each group increase sequentially. The second stage of reverse osmosis is set up in one group.
The effluent of the shock absorber of the first stage of reverse osmosis enters the first membrane group (FM161), the first group is directly supplied by a high-pressure pump, and the second group of membrane columns is equipped with an online circulating pump to generate sufficient flow and flow rate to overcome membrane pollution;
The water outlet of the membrane column group is divided into two parts. The permeate of the first stage of reverse osmosis is discharged to the inlet end of the second stage of reverse osmosis, and the concentrate is discharged into the concentrate storage tank. The permeate of the second stage of reverse osmosis enters the water purification storage tank for reuse, and the concentrate enters the inlet end of the first stage of reverse osmosis for further treatment. The concentrate end of the two-stage reverse osmosis has a pressure regulating valve (VS1601 and VS2601) to control the pressure within the stack to produce the necessary clean water recovery.
1.2.2.3 Degassing of water and pH adjustment
Because the high-concentration wastewater contains a certain amount of dissolved gas, and the reverse osmosis membrane can remove dissolved ions but can not remove the dissolved gas, it may lead to the pH value of the reverse osmosis membrane produced water will be slightly lower than the discharge requirement, after the degassing tower removes the dissolved acid gas in the permeate solution, the pH value can rise significantly, if the pH value of the clean water after the degassing tower is still lower than the discharge requirement, the system will automatically add a small amount of alkali to adjust the pH value to the discharge requirement. Since the effluent is degassed by the degassing tower, only a small amount of lye needs to be added to meet the discharge requirements.
The pH of the effluent is carried out in the clear water tank, and the pH value sensor is installed in the clear water discharge pipe, and the PLC judges the pH value of the effluent and automatically adjusts the frequency of the metering pump to adjust the amount of alkali added, and finally makes the pH value of the effluent meet the discharge requirements.
1.2.2.4 Flushing and cleaning of equipment
There are two types of cleaning: rinsing and chemical cleaning.
The reverse osmosis system has cleaning agent A, cleaning agent C, scale inhibitor and cleaning buffer tank. The operator needs to add cleaning agents and antiscalants to the tank regularly, set the cleaning execution time, and the system will automatically perform the cleaning when it is needed.
System Flushing:
The flushing of the membrane pack is carried out every time the system is shut down, and when it needs to be shut down under normal start-up operation, the mode of flushing first and then stopping is generally adopted. Automatic shutdown in the event of a system failure, and flushing procedures are also performed. The main purpose of rinsing is to prevent contaminants from the raw water from depositing on the surface of the diaphragm. There are two kinds of flushing, one is rinsing with raw water, the other is purified water rinsing, and the time of both flushing can be set on the operation interface, generally 2-5 minutes.