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JACA (Japan Air Cleaning Association)

The Abstracts of the paper carried by the Journal of JACA

vol.58-6 (2021/3/31)

Suppression methods of ammonia gas emission by the evaluation of the properties of concrete constituent materials

In exhibition and collection facilities of cultural properties, as well as in clean rooms for the prevention of molecular contamination, it is necessary to manage the concentration of chemical substances. Particularly, ammonia is generated in large quantities from the concrete used in construction work, so its countermeasure is an important task. Ammonia is derived from the chemical reaction of nitrogen components which are included in the concrete constituent materials, e.g., cement, sand, gravel and admixtures. In this paper, by using the event that ammonia is generated by mixing an alkaline aqueous solution to the concrete constituent material, the amount of ammonia emitted from the material is evaluated, and the mix proportion for ammonia-less concrete is designed. As for the results, there were large differences in ammonia emission among the concrete constituent materials. Furthermore, it was observed that some kinds of high-performance AE (air entraining) water reducing agents generate extreme amounts of ammonia gas and its difference is 50,000 times greater for certain products. Therefore, it was confirmed that the selection of a suitable concrete constituent material is very important.

Characteristics of submicron oil mist generated from metal processing equipment

Cutting oil is used in the metal processing factories to cool and lubricate the cutting tools. These cutting oils evaporate due to the frictional heat between the tool and the product and condense in the air to generate oil mist. Oil mist has an adverse effect on equipment and the human body, and it is necessary to understand the characteristics such as the particle size distribution of the generated oil mist in order to take countermeasures. Therefore, in a metal processing factory, we have measured the concentration of oil mist generated from the metal processing equipment in the exhaust duct of the processing equipment. As a result, nanoparticles (6 to 100 nm), which are the most harmful to the human body, have accounted for the majority, the number concentration of nanoparticles have been 107 particles/cm3, and the number concentration of fine particles (300 to 17,000 nm) have been about 105 particles /cm3. In addition, the amount of diffusion leakage from the door of the processing equipment has been estimated by the numerical model is less than the actual working environment concentration. In order to reduce the concentration of the working environment, it is necessary to take measures against particles that are accompanied when the product is taken out and particles that cannot be collected by the collecting device.

The installed filter leakage evaluation criterion between aerosol photometer and LSAPC

Aerosol photometers and LSAPCs (Light Scattering Airborne Particle Counters) have different measurement principles, so different leak detection thresholds have been used when using these instruments for filter leak tests. In this study, the leakage rate evaluated by the photometer method and the LSAPC method were theoretically analyzed and were compared in order to unify the leak detection thresholds for these two methods. In addition, conditions assuming upstream particle size distributions with various MMD (Mass Median Diameter), CMD (Count Median Diameter) and GSD (Geometric Standard Deviation), and evaluation by LSAPC with various counting efficiencies were also examined. As the result, it was found that the leak detection threshold of 0.01% for the photometer method was applicable for the LSAPC method when the evaluated air filter had the performance of H14 or higher in EN 1822 (European filter standard). It was also found that the leak detection threshold of 0.1% should be applied when the evaluated air filter had the performance of H13.

Prediction analysis of gas removal ratio for wet scrubbing system in transient state

Wet scrubbing system has been used for gaseous contaminant removal, and understanding the transient behavior of contaminant in the gas-liquid phase has been important for equipment design of wet scrubbing system. Although, prediction analysis of wet scrubbing system in transient state has not been studied enough. In this study, transient behavior of wet scrubbing system has been investigated. Theoretical removal ratio figure of gaseous contaminant has been derived by using mass balance of liquid-phase, Henry’s law and reaction kinetics. For considering the validity of theoretical figure, experiment of gaseous contaminant removal by using impinger has been conducted. Comparing between experimental result and theoretical figure, validity of theoretical figure has been confirmed. Theoretical removal ration figure of gaseous contaminant could be used for design of wet scrubbing system for gaseous contaminant.

Development and performance evaluation of a new type air intake/ exhaust apparatus to reduce disturbance caused by outdoor wind

To maintain the room pressure stability is an important factor to prevent contamination in bio-pharmaceutical facilities. In strong winds, the dynamic pressure of the outside air fluctuates greatly, affecting the air intake/ exhaust of the heating ventilating air conditioning (HVAC) system.
As a result, the duct pressure may be disturbed and the room pressure may become unstable. In order to solve this problem, we have developed a cylindrical air intake/ exhaust apparatus with a double structure of an inner cylinder and an outer cylinder made of punched metal.
This paper describes the experimental and verification results of installing this apparatus in the actual facility.

Operating control of clean air-conditioning system based on particle concentration

A new fan filter unit (FFU) control system has been developed for the clean room (CR). This system uses a particle sensor and a motion sensor to control the FFU, and properly maintain the cleanliness of the air in the CR. Using a prototype of the control system, the FFU operational state and the changes in the particle concentration accompanying the operating state were investigated in an experimental CR. As a result, the FFU was operated properly according to the particle concentration measured by the sensor, and the indoor air cleanliness in the cleanroom was adequately maintained. In addition, the experiments confirmed that a control logic based on the Seidel’s formula for transition between two control modes was effective as a prevention measure for hunting of FFU control.

Sterilization effect by ultraviolet rays at the wavelength 254nm and 222nm

Ultraviolet (UV) rays, a type of electromagnetic wave, is used for sterilization in the food and medical fields. The sterilization mechanism of UV rays depends on the wavelength. The 254nm stops DNA and RNA replication, and the 222nm breaks peptide bonds in proteins. We evaluated the amount of UV radiation required to sterilize Escherichia. coli, Staphylococcus aureus, and Aspergillus brasiliensis using excimer lamp at 222nm and compared it to 254nm. We also evaluated the difference between UV-LEDs (265nm, 285nm, and 300nm) for the sterilization of E. coli and S. aureus. As a result, the UV dose required for 3 log disinfection at 222nm was 1.2 times that of 254nm for E. coli, the same for S. aureus, and about 1/3 for Aspergillus brasiliensis. The UV-LED (285nm) had the highest efficiency among the 3 types.