The difference between dust particle counter and aerosol generator in high efficiency leak detection
This paper mainly introduces the methods and principles of high-efficiency filter leak detection, which are divided into sodium flame method, counting scanning method, oil mist method, particle counter method and instruments focusing on high-efficiency filter PAO leak detection method and detecting PAO aerosol concentration. It also introduces the service life of the high-efficiency filter and the comprehensive assessment test of the clean room.
The pharmaceutical factory, clean room high efficiency filter leak detection system is composed of aerosol generator (PAO, DOP generator, TDA-6D/4B produced by Suzhou Huayu Purification Equipment Co., Ltd.), aerosol photometer (leak detector ADT- 2I is made by ATI Corporation of the United States.
One. Standards and specifications
1. GB50591-2010 (clean room construction and acceptance specifications) (Appendix D high efficiency air filter on-site scanning leak detection method)
2. ISO 14644-3:2005 (Clean rooms and related controlled environments - Part 3: Test methods
two. For high-efficiency filter leak detection, the following clearly
1. The test aerosol was a polydisperse PAO aerosol with a mass median diameter of (0.3---0.7) microns and a geometric standard deviation of 1.7.
2. The test instrument is divided into two types: aerosol photometer and particle counter. The aerosol photometer measures the mass concentration in micrograms/L. The particle counter tests the particle concentration in units of grains/L. Both methods can be used. Meet the leak detection requirements. For the on-site leak detection of high-efficiency filters in pharmaceutical companies, the photometer is easy to use, the test results are easy to judge, sensitive to leak detection and widely used, and it is the development trend of high-efficiency leak detection in the future.
3. When using a photometer, the upstream concentration needs to reach (20---80) micrograms/L, and can not fluctuate too much, allowing fluctuations within 15% of the average value.
4. The downstream scanning leak detection should use the isokinetic sampling head to ensure the measurement accuracy. The scanning rate is related to the sampling head size. The judgment of the leakage position should be based on whether the leakage rate of the sampling head is more than 0.01%.
3. Leak detection method for high efficiency filter
1.1. Sodium flame method
1.1.1 Principle
The principle of the sodium flame method is to spray and dry an aqueous solution of sodium chloride to form a sodium chloride aerosol having a mass median diameter of about 0.4 μm as test dust. The dusty air is sampled before and after the high-efficiency filter material is measured, and is introduced into a sodium flame photometer to measure the photocurrent value related to the dust concentration, thereby calculating the transmittance of the filter material.
1.1.2 sodium flame test principle
The test dust source is a monodisperse phase sodium chloride salt mist, and the "quantity" is the brightness of the hydrogen flame when the salt spray is contained. The main instrument is a flame photometer. The brine splashes under the agitation of compressed air and is dried to form a tiny salt spray and enter the air duct. Sampling separately before and after the filter, the salt mist sample makes the color of the hydrogen flame blue and the brightness increases. The salt spray concentration of the air is judged by the brightness of the flame, and the filter efficiency of the filter to the salt spray is determined. The average diameter of salt spray particles specified by national standards is 0.4 μm, but the existing measured results in China are 0.5 μm. The measurement of the median diameter of the actual experimental salt spray particles in Europe was 0.65 μm. With the popularity of other detection methods, the sodium flame method is no longer used in Europe. The relevant domestic departments are revising the original national standards, whether to abolish or continue to use the sodium flame method, and the opinions have not yet been implemented.
1.2. Counting scanning method
1.2.1 "Code for Construction and Acceptance of Cleanrooms" (JGJ71-90) stipulates that the air filter to be tested must have been tested for air volume and designed to run between 80% and 120% of the wind speed. The particle concentration for the controlled particle size must be ≥ 3.5 × 104 pc / L for the concentration of particles ≥ 0.5 μm, and the particle concentration for the controlled particle size ≥ 0.1 μm must be ≥ 3.5 × 106 - 3.5 × 107pc / L. Use the particle counter scanning method with minimum sampling amount >1L/min to scan the high-efficiency filter installation joint and main section. The detection point should be 20-30mm away from the surface to be tested, and the probe should move at 5-20mm/s. , scan the entire section of the filter to be inspected, the sealing head and the mounting frame.
1.2.2 In the "Code for Construction and Acceptance of Cleanrooms", it is stipulated that the penetration rate converted from the leakage side of the high-efficiency filter is measured as qualified. The qualification criteria are as follows. For high efficiency filters
k'=1-η
k=c2/c1
k' indicates the rated transmittance of the high efficiency filter
η represents the rated efficiency of the high efficiency filter;
k represents the actual leak rate of the high efficiency filter;
C1 represents the dust concentration on the windward side;
C2 indicates the dust concentration on the downwind side of the high efficiency filter.
The specification stipulates that the actual leakage rate of the high-efficiency filter shall not exceed 2 times the rated transmittance, ie k≤2k'.
1.2.3 Actual problems
The high-efficiency filter is generally carried out after the system air volume and the air volume of each tuyere are adjusted and balanced. According to the specification, the air volume of each tuyere and the designed air volume deviation are less than 15%, which satisfies the condition that the air inlet is close to the design wind speed. Therefore, when the air volume is balanced After the good, it is necessary to carry out the detection of high-efficiency filter leakage in time.
In engineering, the minimum particle size channel of a particle counter generally used for a purification system greater than 100 is 0.3 μm. Therefore, the controlled particle size of the high-efficiency filter on the windward side is ≥0.5μm, the concentration must be ≥3.5×104pc/L, and the concentration of general atmospheric dust is 5.3×104-2.5×105pc/L. It is the upper limit of the reading range of the particle counter.
In many purification systems, the fresh air entering the recirculating air conditioning unit is treated by the filter at a concentration far less than the atmospheric dust concentration, and the concentration after mixing with the return air is lower. Therefore, the introduction of the atmosphere in the installed purified air conditioning system is a problem that deserves careful consideration. In order to ensure the particle concentration requirement upstream of the air filter to be inspected without destroying the balance of the system air volume, it is an ideal means to introduce a uniform concentration of artificial aerosol upstream. How much aerosol concentration is introduced, which is related to the efficiency of the installed high efficiency filter and the resolution of the particle counter. The minimum number of particle counters is ones and the minimum is zero. Test instruments generally have a dead zone. If the required downstream concentration is less than 10, the data is valid. It is difficult to guarantee according to the statistical principle.
At present, most of the domestic DOP tests on the filtration efficiency of 0.3μm particles as a classification of high-efficiency filters. Therefore, when using the counting scan method for leak detection, the measured particle size should be ≥0.3μm, which is better for the upstream concentration. The efficiency of the high efficiency filter is 99.97%, and the downstream concentration is guaranteed to be within three effective figures. The concentration of particles having a particle size of ≥0.3 μm in the upstream air is required to be at least about 6×10 4 pc/L. If a high-efficiency filter with an efficiency of 99.99% is used, the particle concentration of ≥0.3μm upstream is about 2×105pc/L, and the particle concentration of ≥0.5μm upstream is far less than 3.5×104pc/L. Therefore, the use of the atmosphere as a dust source can no longer meet the test requirements.
1.2.4 Large flow particle counter. CLJ-5350 is more suitable for detecting the installation leakage of high efficiency filter. The larger the air sampling amount, the more representative the test result and the higher the accuracy. The sampling required by the specification The amount is 1l/min, and the sample size we use is 0.1cfm (2.83l/min) to meet the requirements of the test instrument, but this will affect the efficiency of the leak detection. Taking the 610×610 high-efficiency filter as an example, when using the moving sampling head to sample the lower side of the high-efficiency filter, the sampling speed is 20mm/s, and the rectangular 100×11.33 sampler needs at least 244 seconds; the sampling speed of the circular sampler is slower. Leak detection scans take longer. The calculation method of ISO14644-3 "metrologyandtestmethods" to calculate the scanning rate and the acceptable observation counting method is more difficult for general engineering and technical personnel. Therefore, in the future, when the country formulates this specification, it will use different levels of high efficiency filters. It is recommended to use the appropriate sampling rate and acceptable observation count to facilitate the actual operation of engineering testers.
1.DOP particle scanning positive pressure leak detection method
The inspector must pay attention to the operability of the parameters such as sampling time and upstream particle concentration required in the specification in practical applications. In the detection of high-efficiency filters in a purification plant of a pharmaceutical factory, combined with Japan JIS-b-9927, the US Fedstd-209d standard, the laskinDOP particle generator is used to generate a large number of stable and suitable particles to cause upstream ≥0.3μm. The particle concentration is greater than or equal to 1 x 105 pc/L. The DOP particles are uniformly sprayed into the system through compressed air (cold generation) upstream of the filter. Since the concentration is generally greater than 1×105pc/L, which exceeds the measurement range of the measuring instrument, the particle concentration diluter is connected in series before the detection instrument to make the measured The concentration is within the measuring range of the test instrument. For the high-efficiency filter leak detection with a factory efficiency of 99.97%, the measured transmittance should be less than 0.06%, that is, the measured particle concentration is less than 0.06% C1 (C1 is the upstream concentration). The particle generator is 3.3×106pc/2.83l when the particle concentration is ≥0.3μm upstream of the filter. For different air volume systems, it is converted to the downstream limit concentration. For example, a design air volume is 15000m3/h. 1960pc/2.83l. After the aerosol concentration of the particle generator is stabilized, the installed high-efficiency filter is subjected to a leak test using a particle counter. The particle counter must scan the outer frame and the inner surface of the high-efficiency filter twice. The aerosol concentration in the air duct must be sampled twice. The sampling and scanning cycles must be equal. Be consistent.
Taking the 610×610 high-efficiency filter as an example, it is recommended to use a sampling period of one minute and a rate of 50 mm/s. Before the leak detection, a 500 mm high enclosure is placed around the high-efficiency filter to prevent eddy currents from forming outside the high-efficiency filter frame and affecting the results of the scanning test. The main reason for the leakage of the filter is that the sealing effect of the outer frame sealing ring is not good, or the filter material is not sufficiently flat and tight. In practical applications, the installation leakage mainly comes from the outer frame, and the quality of the outer frame sealing strip has a great relationship with the leakage. Therefore, when the leak is detected on the project, the enclosure will be placed around the high-efficiency filter. When the outlet area of ​​the lower part of the tuyere is reduced, a certain positive pressure is formed in the enclosure. If the high-efficiency filter is installed, the particles will pass through the enclosure. leakage. At this time, the CLJ-series dust particle counter can scan at 25mm under the high-efficiency filter for 1 minute at a speed of about 50mm/s to judge whether the filter leaks. This is the "positive pressure leak detection method". For a large number of high efficiency For the purification shop of the filter tuyere, the test effect of the high-efficiency positive pressure leak detection method is equivalent to the traditional inner and outer frame scanning method, but the efficiency is doubled. Taking a clean air conditioning system with 60 610×610mm high-efficiency filter air outlets as an example, it takes at least two hours to scan using the traditional method, and the positive pressure leak detection method can save more than half the time in one hour. .
Oil mist method
Test principle:
The dust source is oil mist, the “quantity†is the turbidity of the oil mist-containing air, and the instrument is a turbidity meter. The filter efficiency of the oil mist particles is determined by the difference in turbidity of the gas sample. In Germany, paraffin oil is used, and the oil mist has a particle size of 0.3-0.5 μm. The average diameter of oil mist specified by the Chinese standard is 0.28-0.34μm. There is no specific regulation on the type of oil. Although the Chinese standard stipulates that the oil mist method can be used, domestic manufacturers are more willing to use another sodium flame method of the same standard specification. Some manufacturers still use the oil mist method when measuring filter materials.
1.4 particle counter method
Test principle:
When the dusty airflow passes through the strong light illumination area at a small flow rate, when the dust particles in the air to be tested pass sequentially, each dust particle will generate a light scattering to form an optical pulse signal according to the magnitude of the optical pulse signal amplitude. The size of the surface of the particle is proportional to the relationship between the number of particles and the brightness measured by the photomultiplier tube to determine the filtration efficiency.
1.PAO method (see 4 for details)
4. Introduction to the PAO leak detection method for high efficiency filters
1.1. Purpose and principle
The leak detection of the high-efficiency filter after the on-site installation is to check whether the high-efficiency filter and the matching static pressure box are leaking or leaking within the scope of the specification. If the high-efficiency filter device is qualified for leak detection, it can ensure the safe and reliable operation of the clean room. At this time, the indoor cleanliness is still not up to standard, and the cause should be found from other aspects of the clean room.
On the upper side of the detected high-efficiency filter, the PAO aerosol is used as a dust source, and the leeward side is sampled and detected by a photometer. The scattered light generated by the dusty gas through the photometric time is converted into electric quantity by photoelectric effect and linear amplification, and the micro-ampere meter is used. Quick display, the collected air sample passes through the diffusion chamber of the photometer, and the difference in light intensity is caused by particle diffusion. After measuring the light intensity, the photometer can measure the relative concentration of the aerosol.
1.2. Method of smoking
1. Hot smoke:
The PAO aerosol is heated to 380-390 ° C in the instrument and blown out under the pressure of compressed air.
TDA-5C aerosol generator (5B has been discontinued)
Particles occur: DOP, PAO, polydispersion
Occurrence concentration: 10ug/L: flow rate 65000cfm (about 1839.5m3/min)
100ug/L: flow rate 6500cfm (about 183.95m3/min)
Method of occurrence: heating occurs
Compressed gas: inert gas such as nitrogen, argon or carbon dioxide (50psi)
Flow rate: 1500-65000cfm (42-1839.5m3/min)
1.2.2. Cold smoke:
PAO aerosols occur in condensate oscillations.
TDA-4Blite type aerosol generator
Particles occur: DOP, PAO, polydispersion
Occurrence concentration: 10ug/L: flow rate 4050cfm (about 115m3/min)
100ug/L: flow rate 405cfm (about 11.5m3/min)
Occurrence method: cold occurs, 1-3 nozzles, no power required
Compressed gas: compressed gas 3-9cfm (85-255L/min) 20psi
Flow rate: 50-5000cfm (1.4-141m3/min)
TDA-6C aerosol generator (now 6D)
Particles occur: DOP, PAO, polydispersion
Occurrence concentration: 10ug/L: flow rate 2000cfm (about 56m3/min)
100ug/L: Flow rate 200cfm (about 5.6m3/min)
Occurrence method: cold occurs, 2-6 nozzles
Compressed gas: built-in air compressor
Flow rate: 50-2000cfm (1.4-56.6m3/min)
1.3. Comparison of two methods of smoking
1.3.1. The particle size of the hot smoke is 0.3μm, and the particle size of the cold smoke is 0.55-0.65μm.
1.3.2 The concentration of hot fumes is large and stable. It is suitable for high-efficiency filter leak detection under the air conditioning unit. The cold fumes are small and stable, suitable for the performance test of a single high-efficiency filter, FFU leak detection and efficient manufacturer. Performance testing is more practical.
1. Detection of PAO aerosol concentration instrument
TDA-2H Aerosol Photometer (now replaced with TDA-2I)
Display range: 0.0001%-100%
Test range: 0.0001%-125ug/L
Test accuracy: 0.05% of full scale
Flow rate: 1cfm (28.3L/min)
Output: RS-232C
TDA-2GA aerosol photometer
Display range: 0.0001%-100%
Test range: 0.0001%-100ug/L
Test accuracy: 1.0% of full scale
Flow rate: 1cfm (28.3L/min)
Output: analog output 0~1VDC
1.5PAO aerosol
US DOP leak detector with PAO oil
PAO-4 aerosol stock solution is a kind of stock solution for challenging aerosols in high-efficiency filter leak test. CAS (American Chemical Substance Product Registration Number) is 68649-12-7, and the chemical composition is 1-Decene. , tetramermixedwith1-decene, Chinese corresponding name hydrogenated 1-decene tetramer and 1-decene trimer; also known as polyalpha olefin is poly-alfa-olefins. The concentration of the stock solution is 100%.
1. Analysis of the PAO leak detection operation of the high efficiency filter after installation
Five. The life of the high efficiency filter
For a clean room in operation, the value of the end-height filter is not high, and the total may not be as much as the user's two-hour production value, but the risk and overhead of replacing the filter will be high. When the filter is replaced, the production should be stopped. The loss of production can only be calculated by the owner himself. This loss is definitely higher than the cost of spare parts for the filter.
Replacing the filter is a very careful operation. Everything in the clean room can't stand the toss, and the damage to an inconspicuous device can be more than the cost of all the filters. After the filter is replaced, it should be tested by a professional. Sometimes the air conditioning system should be commissioned, and then after a period of trial operation. Inspection, commissioning, trial operation, three costs added together, may be related to the filter price. Equally comparable. Smart owners always want to extend the life of high-efficiency filters as much as possible, not to save money on filters. They want to avoid a lot of troubles caused by replacing filters.
The design life of the high-efficiency filter at the end of the clean room of the modern chip factory is “one lifetimeâ€, that is, the heart of the high-efficiency filter will never be operated after being put into operation. The technology of that kind of factory is changing with each passing day. After a new project is put into production, it will fall behind in 5-7 years. The process must be updated, the plant needs to be rebuilt, and the high-efficiency filter is also scrapped. At that time, the “lifetime†of the high-efficiency filter is 7 years. For insurance, the designer sets the filter design life to 10-20 years. When the ash is excessively high on the high-efficiency filter, the resistance increases, and when the normal air supply is affected, the high-efficiency filter is scrapped. Increasing the filter area of ​​a high-efficiency filter or increasing the number of filters can extend the life of the filter. However, the operation space of those practices is not large, you can not increase the filter area indefinitely. To extend the service life of the high-efficiency filter, the most fundamental method is to block the dust in the pre-filter. The replacement of the pre-filter generally does not need to be stopped. Commissioning, so experienced owners will pay attention and money on the pre-filter.
For 10,000 and 100000 cleanrooms, the F8 filter (95% colorimetric method) is available for pre-filtration, so that the end-height filter has a service life of up to 5 years. In foreign projects and new domestic projects, the F8 filter is the most common pre-filter for non-uniform flow clean rooms. For cleanrooms of the 100th, 10th or higher level of the chip factory, the common efficiency level of the pre-filter is H10 (MPPS 85%), and many new projects simply use HEPA (efficiency of 0.39 particles for ≥99.97%). The designer claims to ensure that the end-use high-efficiency filter uses "lifetime", but the method is just that. In the past clean room air conditioning system design in the country, the common configuration of the filter is: initial effect → medium efficiency → high efficiency. At that time, the end-of-the-line filter had a service life of only 1-3 years, and the worst was a few months.
In some cases, the requirement for high-efficiency filter life is not due to resistance considerations but to other factors. If there is hydrofluoric acid in the plant, and the workshop air conditioner is not a fresh air system, the glass fiber filter paper in the high efficiency filter will be corroded by the return air. For safety, the high efficiency filter must be replaced regularly. Some wealthy pharmaceutical factories need to replace high-efficiency filters after the rainy season every year in order to prevent any possible mold contamination on the filter. Some biological laboratories and laboratories dealing with dangerous goods require a new high-efficiency filter for reliability before proceeding with a new important issue.
Six. Company Profile
Suzhou Hengyu Testing Technology Co., Ltd., a subsidiary of Suzhou Huayu Purification Equipment Co., Ltd., is a company specializing in the comprehensive performance testing of clean rooms (areas) and the verification of sterilizer performance. The company's current testing projects are: 1. number of suspended particles; 2. floating bacteria; 3. sedimentation bacteria; 4. temperature 5. relative humidity; 6. air exchange times; 7. air volume and wind speed; 8. static pressure difference 9. Illuminance; 10. Noise level; 11. High efficiency filter PAO leak detection; 12. Self-cleaning time; 13. Pollution leakage.
1. Temperature distribution and control
No-load heat distribution test;
Loading heat distribution test;
Thermal penetration test.
1. Sterilization temperature and time
2. Sterilization effect (biological challenge test).
The company has a professional testing team, the technical person in charge / quality in charge is a senior engineer, working in the pharmaceutical industry for nearly 20 years. The inspector has more than five years of work experience in the industry. He has conducted comprehensive performance testing and dozens of sterilizer performance tests in hundreds of clean rooms (districts), and has been repeatedly inspected by the provincial and municipal drug inspection departments. Technical supervision and management department training, has a wealth of theoretical knowledge and practical experience. When the inspection process finds problems in the inspection process, it can analyze the root cause in time, and provide customers with reference improvement suggestions.
The company is equipped with advanced equipment that is compatible with the inspection project. More than 70% of instruments such as aerosol generators, photometers, thermometers and hygrometers, and air volume covers are imported from the United States (ATI), Germany (Germany), the United States (PMS), and the United States (TSI). All of the company's testing equipment is verified and/or calibrated by statutory departments and agencies, providing an objective guarantee for the accuracy of the test data.
The company's management system is established and documented in accordance with the "Laboratory Qualification Assessment Guidelines 2006". The system documents of the quality manual, procedure documents and operation instructions are guaranteed to have rules for the company's work, quality records and technical records. It guarantees the authenticity and traceability of the work. The smooth operation of the system provides a fundamental guarantee for the correct and efficient work of the company.
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