Low-carbon footprint pure water preparation process

Abstract

The invention discloses a low-carbon footprint pure water preparation process which comprises the following steps: firstly, treating raw water to be treated through a pretreatment device to remove particulate matters, suspended matters and residual chlorine impurities in the water, feeding the pretreated water into an NF device to intercept divalent ions, monovalent ions and macromolecular organic matters of Ca < 2 + >, Mg < 2 + > and Si032-in the water, so as to reduce the difficulty of subsequent treatment; feeding the water treated by the NF device into an RO (reverse osmosis) device, removing dissolved salts, organic matters, microorganisms and viruses in the water, further improving the purity of the water, and feeding the water treated by the RO device into an EDI (electrodeionization) device. A hollow fiber nanofiltration device with a special structure is used for replacing a traditional ultrafiltration device and a first-stage reverse osmosis device, a brand new NF + RO + EDI technology is used for replacing a UF + 2RO + EDI traditional technology, the water quality requirement of electronic-grade ultrapure water is met, meanwhile, the equipment investment cost and the system operation energy consumption are greatly reduced, the system water efficiency is greatly improved, and the concept of low-carbon footprint is met.

Description

Technical Field

[0001] The invention belongs to the technical field of water treatment, and in particular relates to a pure water preparation process with a low carbon footprint. Background Art

[0002] Carbon Footprint is a measurement indicator used to represent the total amount of greenhouse gas (GHG) emissions directly and indirectly generated by an individual, organization, activity or product during its life cycle. This concept reflects the impact of human activities on global climate change. Carbon footprint calculation includes all processes that lead to greenhouse gas emissions and is usually expressed in carbon dioxide equivalent (CO2e). In order to reduce carbon footprint, people take various energy-saving and emission reduction measures, including the use of renewable energy, improving energy efficiency, changing consumption patterns and living habits, and adopting carbon capture and storage technology.

[0003] As one of the fastest growing industries in recent years, the pan-semiconductor industry has its products inseparable from people's daily lives. For the pan-semiconductor industry, the purity of ultrapure water is one of the cornerstones to ensure efficient production. In the production process, the cleaning step accounts for one-third of the total chip production steps, which is the largest proportion of the chip manufacturing process steps. It consumes a large amount of ultrapure water in production and manufacturing, which also makes the carbon footprint of ultrapure water one of the key factors affecting the comprehensive carbon footprint of its products. Therefore, in the specific field of ultrapure water treatment systems, it is urgent to achieve the technical goal of low carbon footprint. The existing ultrapure water treatment systems and production processes generally use UF+2R O+EDI process, this process first pre-treats the raw water to remove impurities such as suspended solids, organic matter and residual chlorine in the water, and then performs ultrafiltration (UF) to further remove colloids, microorganisms and macromolecular organic matter in the water, followed by a primary reverse osmosis (RO) to remove most of the dissolved salts, organic matter, microorganisms and viruses in the water, and then a secondary reverse osmosis to remove the remaining trace dissolved salts to further improve the purity of the water, and then use the electric field of the electrodeionization device (EDI) to remove residual ions in the water to achieve deep desalination, and finally use ultraviolet disinfection (UV) and TOC treatment at the terminal to remove microorganisms and organic carbon in the water, and use a polishing mixed bed to remove trace ions, the final The water is then supplied after the residual particles in the water are further removed by the terminal precision filter. This process achieves a high degree of water purification through the combined use of multiple membrane technologies and resin adsorption. The resistivity of the outlet water can reach above 18MΩ.CM, and the TOC is less than 5PPb or even as low as PPT level, which can meet the water quality requirements of high-end electronic grade ultrapure water. However, this process system that excessively enhances the disposal capacity in pursuit of a single indicator and sacrifices a large amount of energy consumption and resources does not actually conform to the design concept of low carbon footprint. Reverse osmosis and other membrane treatment processes require higher pressure and produce concentrated water, so the energy consumption is large and the water utilization rate is low, especially with each additional level of reverse osmosis, the energy consumption increases and the water utilization rate decreases. It will be more obvious. The water utilization rate of the first-stage reverse osmosis can be maintained at more than 75%, while the water utilization rate of the two-stage reverse osmosis is usually only about 65%, and nearly 35% will be discharged as concentrated water, resulting in a large amount of energy consumption and water resources being wasted. However, if only one-stage RO is used, the effluent water quality is not easy to meet the EDI inlet water requirements. The main reason is that the first-stage RO has insufficient removal rate for water hardness (Ca2+, Mg2+) and total silicon and neutral organic molecules, while the EDI device has a high removal rate for ionic substances and a low removal rate for non-ionic substances such as large molecules and silicon. In addition, Ca2+ and Mg2+ are easily adsorbed on the surface of the resin and electrodialysis membrane, causing scaling of the EDI device, resulting in a decrease in the quality of produced water.

[0004] At present, the nanofiltration membranes on the market are basically roll membranes or flat membranes, which cannot be backwashed, are easy to scale, have a short service life, and are expensive. If such nanofiltration membranes are used, an ultrafiltration system needs to be added in front of the nanofiltration device, resulting in the traditional nanofiltration device being able to replace the first-stage RO at most, but not the ultrafiltration, or using two-stage nanofiltration, with one stage replacing the ultrafiltration and the other stage replacing the first-stage RO;

[0005] Traditional rolled nanofiltration membranes, flat nanofiltration membranes or other non-high-polymerization-density structured nanofiltration membranes are prone to fouling and clogging during long-term operation and have a short service life. It is necessary to add an ultrafiltration system in front of the NF device or use multi-stage nanofiltration to further improve water quality, resulting in high equipment investment costs.

[0006] In response to such problems, a patent has proposed a coupling process of nanofiltration + reverse osmosis. For example, CN104817134A discloses an integrated system and integrated process for full-membrane seawater desalination using ultrafiltration-nanofiltration-reverse osmosis. Although this method uses nanofiltration instead of primary RO to improve water utilization, the system needs to add an ultrafiltration system in front of the nanofiltration to treat the seawater, otherwise the inlet water quality will not meet the nanofiltration membrane inlet requirements, which will cause membrane blockage. In addition, the nanofiltration system needs to adopt a three-stage type, with the first and second stages being reverse osmosis pretreatment and the third stage further treating the nanofiltration concentrated water from the first two stages. Not only is the process lengthy, but it also increases costs and energy consumption. It does not conform to the concept of low carbon footprint. Therefore, a low-carbon footprint pure water preparation process is proposed to develop and optimize a low-carbon footprint pure water system from the perspective of reducing carbon footprint, which can effectively remove impurities in water to meet the requirements of electronic-grade ultrapure water, and can significantly reduce energy consumption and improve water efficiency. Summary of the invention

[0007] The object of the present invention is to provide a pure water preparation process with a low carbon footprint to solve the problems raised in the above background technology.

[0008] To achieve the above object, the present invention provides the following technical solution: a pure water preparation process with a low carbon footprint, comprising the following specific steps:

[0009] Step 1: First, the raw water to be treated is treated by a pretreatment device to remove particulate matter, suspended matter and residual chlorine impurities in the water;

[0010] Step 2: Send the pre-treated water into the NF device to treat the Ca 2+ Mg 2+ 、Si03 2- The interception of divalent ions, monovalent ions and macromolecular organic matter reduces the difficulty of subsequent treatment;

[0011] Step 3: The water treated by the NF device is then sent to the RO device to remove dissolved salts, organic matter, microorganisms and viruses in the water, further improving the purity of the water;

[0012] Step 4: Send the water treated by the RO device to the EDI device, and remove the residual ions in the water through the electric field of the EDI device to achieve deep desalination;

[0013] Step 5: Send the water treated by the EDI device to the UV disinfection device and the TOC treatment device in sequence to remove trace microorganisms and organic carbon in the water;

[0014] Step 6: The water treated in step 5 is passed through a polishing mixed bed to remove trace ions, and then the terminal treatment device further removes residual particles in the water to produce water that meets the standards.

[0015] Furthermore, the NF device includes a nanofiltration membrane group, and the nanofiltration membrane group is a hollow fiber nanofiltration membrane group.

[0016] Furthermore, the hollow fiber nanofiltration membrane includes a nanofiltration membrane that can be backwashed, and the nanofiltration membrane that can be backwashed is a membrane group structure formed by a group of selective layers and support layers with highly polymerized interfaces.

[0017] Furthermore, the hollow nanofiltration membrane is made of one or more of polyvinylidene fluoride, polyethersulfone, polyamide, and cellulose acetate, preferably polyvinylidene fluoride.

[0018] Furthermore, the operating pressure of the hollow fiber nanofiltration membrane is 0.1-1.2Mpa, preferably 0.4Mpa-0.8Mpa.

[0019] Furthermore, the pretreatment device is one or more combinations of a bag filter, a disc filter, a multi-media filter or an activated carbon adsorber.

[0020] Furthermore, the terminal treatment device is one or more combinations of a nitrogen-sealed water tank, TOC-UV, a polishing mixed bed, and a precision filter.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] 1. A hollow fiber nanofiltration device with a special structure is used to replace the traditional ultrafiltration device and the first-stage reverse osmosis device. This HFNF can not only play the role of ultrafiltration, but also can remove divalent Ca 2+ Mg 2+ 、Si03 2- Ion interception enables the treated water to reach the EDI device water inlet index with only one reverse osmosis stage, thus meeting the water quality requirements while saving equipment investment costs.

[0023] 2. The hollow fiber nanofiltration membrane with a membrane group structure formed by the selective layer and the support layer with high interface polymerization has the advantages of high flux and backwashability, solving the long-standing problem of easy fouling and clogging of traditional flat or rolled nanofiltration membranes.

[0024] 3. Based on the small concentration difference between the thick and thin sides of the nanofiltration membrane, it only requires a smaller operating pressure than the reverse osmosis membrane, and the hollow fiber nanofiltration membrane has a large flow channel and a higher water yield than the traditional rolled RO membrane. Therefore, the NF+RO+EDI process of the present invention can also save the concentrated water discharge of the first-stage RO and the energy consumption of the high-pressure pump compared to the traditional UF+2RO+EDI process.

[0025] 4. A hollow fiber nanofiltration device with a special structure is used to replace the traditional ultrafiltration device and the first-stage reverse osmosis device, and the new process of NF+RO+EDI is used to replace the traditional process of UF+2RO+EDI. This not only meets the water quality requirements of electronic-grade ultrapure water, but also greatly reduces the equipment investment cost and system operation energy consumption and greatly improves the system water efficiency, which is in line with the concept of low carbon footprint. DETAILED DESCRIPTION

[0026] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0027] A process for preparing pure water with a low carbon footprint comprises the following specific steps:

[0028] Step 1: First, the raw water to be treated is treated by a pretreatment device to remove particulate matter, suspended matter and residual chlorine impurities in the water;

[0029] Step 2: Send the pretreated water into the NF device to treat the Ca 2+ Mg 2+ 、Si03 2- The interception of divalent ions, monovalent ions and macromolecular organic matter reduces the difficulty of subsequent treatment;

[0030] Step 3: The water treated by the NF device is then sent to the RO device to remove dissolved salts, organic matter, microorganisms and viruses in the water, further improving the purity of the water;

[0031] Step 4: Send the water treated by the RO device to the EDI device, and remove the residual ions in the water through the electric field of the EDI device to achieve deep desalination;

[0032] Step 5: Send the water treated by the EDI device to the UV disinfection device and the TOC treatment device in sequence to remove trace microorganisms and organic carbon in the water;

[0033] Step 6: The water treated in step 5 is passed through a polishing mixed bed to remove trace ions, and then the terminal treatment device further removes residual particles in the water to produce water that meets the standards.

[0034] Wherein, the NF device comprises a nanofiltration membrane group, and the nanofiltration membrane group is a hollow fiber nanofiltration membrane group.

[0035] Wherein, the hollow fiber nanofiltration membrane includes a nanofiltration membrane that can be backwashed, and the nanofiltration membrane that can be backwashed is a membrane group structure formed by a group of selective layers and support layers with highly polymerized interfaces.

[0036] Wherein, the hollow nanofiltration membrane is made of one or more of polyvinylidene fluoride, polyethersulfone, polyamide, and cellulose acetate, preferably polyvinylidene fluoride.

[0037] Wherein, the operating pressure of the hollow fiber nanofiltration membrane is 0.1-1.2Mpa, preferably 0.4Mpa-0.8Mpa.

[0038] Wherein, the pretreatment device is one or more combinations of a bag filter, a disc filter, a multi-media filter or an activated carbon adsorber.

[0039] Wherein, the terminal treatment device is one or more combinations of a nitrogen-sealed water tank, TOC-UV, a polishing mixed bed, and a precision filter.

[0040] The working principle and use process of the present invention are as follows: first, the raw water to be treated is treated by a pretreatment device to remove particles, suspended matter and residual chlorine impurities in the water, and the pretreated water is sent to the NF device to treat the Ca 2+ Mg 2 + 、Si03 2- Divalent ions, monovalent ions, and macromolecular organic matter are intercepted to reduce the difficulty of subsequent treatment. The water treated by the NF device is then sent to the RO device to remove dissolved salts, organic matter, microorganisms, and viruses in the water to further improve the purity of the water. The water treated by the RO device is sent to the EDI device, and the residual ions in the water are removed by the electric field of the EDI device to achieve deep desalination. The water treated by the EDI device is sent to the UV disinfection device and the TOC treatment device in turn to remove trace microorganisms and organic carbon in the water. The water treated in step five is polished in a mixed bed to remove trace ions, and the terminal treatment device further removes residual particles in the water to produce water that meets the standards.

[0041] Among them, the NF device adopts a hollow fiber nanofiltration membrane with a double-sided support structure with a high degree of polymerization at the interface between the selection layer and the support layer, so it can be backwashed, while the traditional rolled nanofiltration membrane, flat nanofiltration membrane or other non-high-polymerization hollow fiber nanofiltration membrane is single-sided supported and cannot support the support structure of backwashing. The hollow fiber nanofiltration membrane in this application is made of polyvinylidene fluoride, and its membrane surface is smooth and dense, which can effectively reduce the oxidation and surface adhesion of the membrane, and solves the problem that the traditional rolled nanofiltration membrane, flat nanofiltration membrane or other non-high-polymerization structure nanofiltration membrane is easy to be fouled and blocked during long-term operation and has a short service life. The special structure of the hollow fiber nanofiltration membrane in this application only needs one stage, which can simultaneously replace the ultrafiltration plus one stage of RO, thereby reducing the equipment investment cost;

[0042] Among them, in the actual overall pure water preparation process, the hollow fiber nanofiltration membrane with a special structure provided by this patent does not need to be ultrafiltered, and only one stage of nanofiltration is needed to replace ultrafiltration and one stage of RO at the same time. From the perspective of low carbon footprint, compared with traditional water treatment processes, this process is a better solution for energy saving and efficiency improvement;

[0043] When the present invention is in use, due to the small concentration difference between the thick and thin sides of the nanofiltration membrane, a smaller operating pressure is required compared with the reverse osmosis membrane, and the hollow fiber nanofiltration membrane has a large flow channel and a higher water yield than the rolled RO membrane. Therefore, the NF+RO+EDI process of the present invention can also save the concentrated water discharge of the first-stage RO and the energy consumption of the high-pressure pump compared to the traditional UF+2RO+EDI process, thereby achieving improved water efficiency and reduced energy consumption.

[0044] Implementation case: Taking a domestic pan-semiconductor enterprise's production pure water treatment system as an example, the raw water of the pure water system comes from the local municipal water supply, and its various indicators meet my country's municipal water standards. The designed water output is 100 tons per hour. This example compares the water quality, comprehensive water efficiency, and comprehensive energy consumption of the new process of NF+RO+EDI of the present invention and the traditional UF+2RO+EDI process, and is expected to more intuitively and clearly describe the invention's advanced nature in energy saving and efficiency improvement and the creativity of low carbon footprint. The specific comparison data are as follows:

[0045]

[0046]

[0047] From the data in the table, it can be seen that under the same influent water quality and water output:

[0048] In terms of effluent quality: the resistivity of the NF+RO+EDI process system of the present invention at the EDI water production end is 15.1MΩ.CM, and the resistivity of the traditional UF+2RO+EDI process system at the EDI water production end is 15.2MΩ.CM. The water production standards both meet the standard that the resistivity of EDI water production for electronic grade ultrapure water is greater than 15.0MΩ.CM. At the terminal water production, the water quality resistivity of the NF+RO+EDI process system of the present invention and the traditional UF+2RO+EDI process system is greater than 18.0MΩ.CM, which meets the industry standard for electronic grade ultrapure water.

[0049] In terms of water efficiency: in the NF+RO+EDI process system of the present invention, the NF water production rate is 92%, the RO water production rate is 80%, and the NF+RO comprehensive water production rate is 73.6%. In the traditional UF+2RO+EDI process system, the UF water production rate is 95%, the primary RO water production rate is 76%, the secondary RO water production rate is 90%, and the NF+2RO comprehensive water production rate is 64.98%. Compared with the traditional UF+2RO+EDI process system, the water efficiency of the NF+RO+EDI process system of the present invention can be improved by 8.62%.

[0050] In terms of energy consumption: in the NF+RO+EDI process system of the present invention, the power of the NF booster pump is 50KW / H, the power of the RO booster pump is 30KW / H, the power of the RO high-pressure pump is 90KW / H, and the comprehensive power of NF+RO is 170KW / H. In the traditional UF+2RO+EDI process system, the power of the UF booster pump is 30KW / H, the RO booster pump is 30KW / H, the power of the first-level RO high-pressure pump is 110KW / H, the power of the second-level RO high-pressure pump is 75KW / H, and the comprehensive power of UF+2RO is 245KW / H. Compared with the traditional UF+2RO+EDI process system, the NF+RO+EDI process system of the present invention can save 75KW / H of electricity consumption, and the energy consumption is reduced by 30.6% year-on-year.

[0051] The present invention innovatively replaces the traditional UF+first-stage RO with NF, which not only saves the investment in ultrafiltration equipment, but also saves the energy consumption of the first-stage RO concentrated water discharge and pump. While meeting the water quality requirements of electronic-grade ultrapure water, it also greatly reduces the equipment investment cost and system operation energy consumption and greatly improves the system water efficiency, achieving both economic and environmental benefits, and is very consistent with the concept of low carbon footprint.

[0052] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A process for preparing pure water with a low carbon footprint, characterized in that: The specific steps include: Step 1: First, the raw water to be treated is treated by a pretreatment device to remove particulate matter, suspended matter and residual chlorine impurities in the water; Step 2: Send the pre-treated water into the NF device to treat the Ca 2+ Mg 2+ 、Si03 2- The interception of divalent ions, monovalent ions and macromolecular organic matter reduces the difficulty of subsequent treatment; Step 3: The water treated by the NF device is then sent to the RO device to remove dissolved salts, organic matter, microorganisms and viruses in the water, further improving the purity of the water; Step 4: Send the water treated by the RO device to the EDI device, and remove the residual ions in the water through the electric field of the EDI device to achieve deep desalination; Step 5: Send the water treated by the EDI device to the UV disinfection device and the TOC treatment device in sequence to remove trace microorganisms and organic carbon in the water; Step 6: The water treated in step 5 is passed through a polishing mixed bed to remove trace ions, and then the terminal treatment device further removes residual particles in the water to produce water that meets the standards.

2. A process for preparing pure water with a low carbon footprint according to claim 1, characterized in that: The NF device comprises a nanofiltration membrane group, and the nanofiltration membrane group is a hollow fiber nanofiltration membrane group.

3. A process for preparing pure water with a low carbon footprint according to claim 1, characterized in that: The hollow fiber nanofiltration membrane comprises a nanofiltration membrane capable of backwashing, wherein the nanofiltration membrane capable of backwashing is a membrane group structure formed by a group of selective layers and supporting layers with highly polymerized interfaces.

4. A process for preparing pure water with a low carbon footprint according to claim 1, characterized in that: The hollow nanofiltration membrane is made of one or more of polyvinylidene fluoride, polyethersulfone, polyamide, and cellulose acetate, preferably polyvinylidene fluoride.

5. A process for preparing pure water with a low carbon footprint according to claim 1, characterized in that: The operating pressure of the hollow fiber nanofiltration membrane is 0.1-1.2Mpa, preferably 0.4Mpa-0.8Mpa.

6. A process for preparing pure water with a low carbon footprint according to claim 1, characterized in that: The pretreatment device is one or more combinations of a bag filter, a disc filter, a multi-media filter or an activated carbon adsorber.

7. A process for preparing pure water with a low carbon footprint according to claim 1, characterized in that: The terminal treatment device is one or more combinations of a nitrogen-sealed water tank, a TOC-UV, a polishing mixed bed, and a precision filter.

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