In recent years, ozone technology has been widely used in industries such as medicine, sanitation, food, food storage, sewage treatment and drinking water sterilization, and has achieved remarkable results. After high-concentration ozone disinfection, the attenuation of ozone in the room has become one of the concerns of the HVAC community. In this paper, an ozone-sterilized pharmaceutical clean room was actually tested. The mass balance model and the first-order decay model were used to theoretically obtain the attenuation concentration curve of ozone, and then the actual measured attenuation concentration of ozone. The curves are compared, and then the difference between the theoretical calculated value and the actual measured value and the causes of these differences are analyzed, and the relevant factors affecting the ozone decay concentration are obtained. By analyzing the ozone concentration data obtained by the detection, the decay time of the ozone concentration after the disinfection is lower than the preset time value, that is, the design time of the ozone decay of the clean room conforms to the principle of labor protection and personnel safety.
Keywords: ozone disinfection first-order attenuation model mass balance model ozone attenuation
1 Introduction
In recent years, ozone technology has been widely used in medicine, health, food, breeding, aquaculture, food storage and preservation, chemical production, atmospheric purification, sewage treatment and drinking water sterilization and disinfection, and has achieved remarkable results. Ozone can destroy the cell wall of microorganisms due to its strong oxidizing ability, thereby cutting off its nucleic acid and causing its vitality. It also has many advantages such as rapid disinfection of ozone, no secondary pollution (decay to oxygen), good sterilization effect, etc. In hospital clean rooms and factories with clean requirements such as food and pharmaceuticals, it is quite common to use high concentrations of ozone for anti-virus. However, on the other hand, ozone is also an indoor pollution gas, which has different degrees of damage to human soft tissues and respiratory organs. According to medical research, ozone is one of the important causes of various respiratory diseases such as emphysema, chronic rhinitis and bronchitis. Therefore, at the same time as ozone disinfection is advocated, after the high-concentration ozone disinfection, whether the concentration of ozone can be lowered to the allowable value specified by the national standard within the recommended time is worthy of discussion. For this reason, we have tested and analyzed the ozone concentration after ozone disinfection at a pharmaceutical plant.
2 Establishment of predictive models
Theoretically, using the mass balance equation and the first-order decay model, the model for ozone generation and attenuation is shown in equation (1). Equation (1) is usually used to predict indoor ozone generation from attenuation to decay. Ozone concentration at any time throughout the process:
Formula (2) is solved by formula (1), that is, the concentration value of indoor ozone concentration changes with time:
among them:
C: indoor ozone concentration in clean room, mg/m3;
C0: background concentration of ozone in the clean room, mg/m3;
S: source of ozone, mg/h;
V: the volume of the clean room being tested, m3;
T: time, h;
Kd: attenuation coefficient of ozone during the test, 1/h;
Because ozone is a strong oxidant and has strong oxidizing properties, it reacts with many substances. Therefore, Kd includes many factors, including the natural attenuation coefficient of ozone, the reaction coefficient of ozone and clean indoor walls, and the transport of ozone. In the process, the reaction coefficient of ozone and air conditioning system components (filter, air return, return air duct, unit surface); usually, the value of Kd is further obtained by the data when the ozone generator is turned on and the concentration is increased. of.
For the concentration of ozone in the process of ozone decay, that is, to turn off the ozone generator, S=0, then the formula (2) is simplified as: (3)
among them:
C0: initial concentration of indoor ozone after the ozone generator is turned off, mg/m3;
3 test methods and test procedures
3.1 Air conditioning system
The air conditioning system is mainly responsible for the 10,000-level clean area in the area of ​​syringe filling and preparation. The air supply volume of the whole system is 19786m3/h (new air volume is 33%), the return air volume is 12722m3/h, the exhaust air volume is 4620 m3/h, and the total volume of the disinfected clean area is 563 m3; the clean room is tested. The air supply volume is 2811m3/h, the return air volume is 969 m3/h, the air exchange frequency is 54.9 1/h, and the volume is 51.5 m3.
First, turn on the ozone generator to increase the ozone concentration in the cleaned room. When the ozone concentration is stable, turn off the ozone generator, open the ventilation system, and the ozone begins to be diluted and attenuated. The attenuation of ozone in the clean room.
3.2 Ozone production
The high concentration of ozone used in the ozone-sterilized biological clean room of this test was generated by an ozone generator. There are usually three specific locations for installation of the ozone generator: it is installed in the air supply duct of the air conditioning system; it is installed in the air return duct of the air conditioning system; it is installed in the air conditioning unit. The ozone generator of the pharmaceutical company's disinfection system is installed in the air conditioning unit, as shown in Figure 1. The selected ozone generator is a built-in ozone generator (model KCF-G60) produced by Kanger, with an amount of 60±6g/h. Since the attenuation of ozone itself is closely related to the temperature and humidity in the room, before the ozone generator is turned on, the humidification and heating section of the air conditioning system should be turned off accordingly. In order to make the internal circulation of ozone in the air conditioning system, fresh air and exhaust air should be turned off. After 1 to 2 hours of starting, the ozone generator should be turned off; the ventilation system should be turned on to ensure that the ozone concentration can be lowered to the standard allowable value within the specified time.
3.3 Sample point location
The specific location of the indoor ozone concentration sampling point is shown in Figure 2. The location is located in a clean room with strict requirements in the air conditioning system. The size of the clean room is 2.2 × 9.0 × 2.6m3, and there are 4 air supply ports. One return air vent, one air vent, two doors that open inward (closed during testing); the height of the sampling point is 1.5m.
3.4 Detection and recording of ozone concentration.
The ozone concentration was measured using a ZX-01 ultraviolet absorption ozone analyzer. The ozone analyzer has a range of 0~10ppm, a minimum detectable amount of 0.004ppm, and an accuracy of two. The front display shows that the number is four or five digits, the RS232 interface, the sampling gas flow rate is 500ml/min, and the instrument working temperature range is 15~35. °C, the standard temperature is 25 ± 1 ° C; the relative humidity range is 0 ~ 95%. The ozone concentration is recorded by a data line connected to a computer, recorded by the corresponding program every 6 seconds, and automatically recorded and saved by the computer.
For the safety of the tester, the tester and the instrument are placed outside the air conditioning system, and a sampling tube is connected to the clean room to be tested, and the sampling tube is connected to the air inlet of the instrument for testing and recording the clean room. Ozone concentration at the moment.
4 test results discussion and analysis
When the indoor ozone content reaches a stable value, when the ozone generator is turned off, the ozone concentration of the room to be tested at this time is 1.537 to 1.545 ppm (3.07 mg/m3), that is, the initial concentration at the time of attenuation. The ventilation system was turned on and the ozone concentration of the fresh air introduced was 0.014 ppm (0.028 mg/m3). By regressing the data when the concentration rises, the value of the attenuation coefficient Kd of ozone in the air conditioning system is 0.126 1/h, and the first-order model and formula (3) can be used to predict the concentration of indoor ozone decay with time. After the ozone disinfection in the clean room, the relationship between the predicted value and the measured value of the ozone entering the decay period is as shown in Figure 3:
The ozone concentration allowed in the room specified in the national standard (GB/T18883-2002) is 0.16 mg/m3 (0.08 ppm). It can be seen from Fig. 3 that the predicted value of the first-order attenuation model requires about 25 minutes of attenuation, and the room can reach the allowable value; and the actual test result is that the indoor ozone concentration drops after 13.5 minutes of opening the ventilation system. It is 0.075ppm. The manufacturer recommends that you enter the room after 30 minutes. It can be seen from Figure 3 that the ozone concentration can be reduced to the specified allowable value within the predetermined time, which can meet the labor protection requirements for personnel.
The measured concentration curve is basically the same as the predicted concentration curve through the model, demonstrating that the first-order attenuation model can be used to study the concentration of gas used for indoor attenuation. The difference between the measured curve and the predicted curve shows that the attenuation of ozone in the room is a very complicated process. For example, the attenuation of ozone has a great relationship with the concentration of ozone in the room, and the organic components in the room that react with ozone are also Affecting the attenuation coefficient Kd, the value of Kd is obtained by mathematical regression and also has a certain error.
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