Aiming at the current domestic scientific research laboratory's high standard demand for pure water quality, combined with actual engineering design, it introduces the matters that should be paid attention to in the laboratory design process, including the water quality requirements and preparation methods of pure water, the amount and storage of pure water in the laboratory , laboratory pure water pipeline distribution design and pipe material selection, and water quality monitoring during operation. At the same time, in the design process, the relationship between the above-mentioned parts should be comprehensively considered in combination with different types of projects and specific solutions should be drawn. The owner's requirements and relevant standards have accumulated experience for the design of pure water systems for such projects.
Before the design of the Laboratory Water Purification System, as a designer, the user's requirements must first be considered. The importance of water consumption and water quality to the design of the system goes without saying.
1 laboratory pure water quality
The pure water quality required by different laboratories may also vary. Many international organizations (ASTM, NCCLS, CAP, USP) also have their own pure water quality standards and guidelines promulgated, which will help designers determine appropriate water quality.
Among them, the three standards recognized by most users are shown in Table 1 (third-grade water refers to general pure water, second-grade water is analytical grade, and first-grade water is for more sensitive research experiments. First class water.
Combined with some previous project designs of the author, such as the Beijing R&D Center (hereinafter referred to as "NN") of a large multinational biopharmaceutical company and the Shanghai R&D Center (hereinafter referred to as "COV") laboratory of a well-known pharmaceutical company, the experimental cleaning water, disinfection and sterilization Generally, the water used for devices and other equipment is secondary water, which is supplied through a centralized pipeline system, and at some points of use where high purity is required, a terminal ultrafiltration device is separately added to prepare high-purity water. The "NN" project that the author participated in is located in the Environmental Protection Park, Haidian District, Beijing. The experimental building area is divided into three parts: CB, MC and PC. The functions and users are different, but they all need to meet the certification requirements of GLP/GMP , the local raw water quality (influent water quality) used in the design is shown in Table 2.
The effluent water quality is required to meet the secondary standard of , and partially meet the first standard. The total pure water consumption of the three parts of the laboratory CB, MC and PC of this project is 1500L/d.
The pure water preparation process is as follows:
Tap water→quartz sand filter→activated carbon filter→water softener →5μm pre-filter→reverse osmosis column→EDI device ( electrodeionization ) →storage tank→ultraviolet lamp→(purification column→ultrapure water)
Among them, this project uses 2 sets of Elix100 modular , each of which has a water production capacity of 100L/h, uses tap water as the influent, and passes through pretreatment (including softening treatment device), reverse osmosis (RO ) and the continuous current deionization module (EDI) to produce water quality standards not lower than the above-mentioned secondary pure water. The quality of the produced water can reach : the resistivity is 5~15MΩ·cm@25℃ (with temperature compensation), the total organic carbon (TOC) is less than 30μg/L, and the microorganism is less than 10CFU/mL.
2 Consumption and storage of laboratory pure water
The amount of pure water used in the laboratory may vary from a few liters to thousands of liters per day. At the beginning of the design, it should be considered first: determine the daily water consumption of each user and each instrument, the water quality of the required pure water, and the water consumption law, and calculate the total daily water consumption and peak water consumption of the entire laboratory.
The pure water storage system should be able to balance the relationship between the pure water preparation system and the total daily water consumption and peak water consumption of the laboratory. Each laboratory has its own water consumption rules, so the pure water storage system should not only meet the daily water consumption of customers, but also meet the peak water demand of the laboratory.
The storage system can act as a buffer between the daily peak water consumption, so that the pure water preparation system has enough time to produce the pure water required by the laboratory every day. At the same time, the pure water storage tank needs to be able to ensure the water quality of pure water from pollution. The material of the tank and many design details will affect the quality of the pure water stored in the tank.
The "NN" project has been calculated to use a cylindrical Water Tank with a capacity of 1000L to adjust the peak flow of users. In addition, there are some other points that need to be paid attention to in the design: firstly, the no-dead-angle design of the conical bottom can completely empty the water in the Water Tank; the Water Tank is made of imported original ultra-pure PE material, which can reduce the dissolved matter, although the investment will be slightly higher, However, secondary pollution can be reduced as much as possible; in addition, the Water Tank is equipped with a 0.22μm air filter to reduce external pollution to the water quality in the Water Tank, and a sanitary anti-overflow device is provided.
3 laboratory pure water pipeline distribution
The main purpose of the pure water distribution system is to deliver the pure water to each water point through the distribution pump and the pure water distribution pipeline. Generally, a series circulation pipeline is used, so that the pure water in the pipeline can circulate at an appropriate flow rate and suppress The growth of microorganisms and avoid heating. At the same time, in order to ensure the flow rate and pressure of pure water in the pipeline, the pressure loss caused by the pipeline system and equipment in the pipeline should be calculated according to the water condition and frequency of the point of use, so as to select the appropriate distribution circulation pump. The flow chart of the pure water pipeline is shown in Figure 1.
How to distribute the pure water pipeline is also a very important part of the design, which is directly reflected in whether it can meet the requirements of users. For example, the "NN" central laboratory building designed by the author has a total of 4 floors, and there are many different water departments and different use requirements. The traditional design method usually adopts a set of large centralized circulation pipeline system to connect all the water points in series in the whole building, but this design will bring the following problems:
①Because the pipeline is too long, the water quality of some terminal outlets will usually decrease;
②In the event of pipeline or other problems and maintenance, each water sector will be limited to the supply of pure water;
③The increase of the water head loss in the pipeline leads to the increase of the water pump head, which causes the water outlet pressure of the water point close to the distribution pump to be too high;
④ It is not conducive to the flexibility management of pipelines;
⑤Because of the separate water quality, it is unreasonable for some users who originally do not require high purity (such as utensil cleaning).
Therefore, when designing pipelines, fully consider the specific conditions of the user (including consumption, water quality and distribution), and flexibly design the pipeline distribution system. The preparation system should be as close as possible to the point of use, such as layered supply or departmental supply. The length of the pure water circulation pipeline should not exceed 250m as far as possible to avoid the above-mentioned unfavorable situations. Of course, it should also be considered in combination with the cost and cannot be stereotyped.
The pure water preparation, storage and pressurized circulation equipment of the "NN" project are placed in the equipment room on the third floor to supply the pure water use points on each floor. Reduce the length of each circulation pipeline, and consider the flow velocity of pure water in the distribution pipeline at 1 to 1.5m/s when designing the pipe diameter (the diameter of the first and second layers of loops is DN32, and the diameter of the third and fourth layers of pipes DN25) to reduce the risk of microorganisms growing on the inner surface of the pipeline. Each set of Circulating Chillers adopts the way of dual pumps working in turn to distribute pure water.
In order to ensure the water quality of pure water in the pipeline, appropriate pipeline materials and pipeline connection methods should also be selected. Generally, stainless steel and plastic pipes are used (PP type can be used for the second grade and below, and PVDF can be used for the first grade). There are advantages and disadvantages and are related to the cost, and the situation of each project is also different, so it is generally determined through a comprehensive comparison of technology and economy. For example, the pure water centralized pipeline system of the "NN" and "COV" project laboratories has secondary water, and its equipment and materials use polypropylene pipes, while for high-purity water or water for injection in medicine, it is necessary to use 316L stainless steel or PVDF pipes.
The pure water distribution system should also include additional equipment to further purify the pure water and monitor the water quality in the pipeline while maintaining the pure water quality. The "NN" project is equipped with an FDA-approved 0.22μm circulation pipeline filter at the water outlet and return water end to avoid cross-contamination of the storage system and the pipeline system. Microbiological and total organic carbon levels of water.
4 laboratory pure water control
The pure water control system is very important for the operation, maintenance and operation of the whole system. In order to ensure the normal operation of the pure water preparation system and the quality of produced water, not only the quality of produced water and pipeline water must be monitored, but also the quality of influent water (tap water quality) should be monitored.
The "NN" project is equipped with a conductivity Tester and a total organic carbon Tester in the pipeline design to monitor the water quality in the pipeline in real time, and a microbial detection valve is installed on the water distribution pipeline to take water samples regularly and monitor microorganisms regularly content.
The project achieved good results in the later stage of trial operation. Due to the use of Millipore's 2 Elix100 modular pure water manufacturing equipment (with RO+EDI inside), the resistivity of the effluent water reached above 10MΩ·cm through sampling and testing at different points. , and other items also meet the secondary pure water standard, which can fully meet the water requirements of the laboratories of this project.
