Determination of the hottest ozone concentration

Determination of ozone concentration

the application of ozone in the field of food is expanding, but the control and management of its concentration are lagging behind. In the field of water supply and semiconductors, it has become a consensus to set up ozone concentration meters to measure and manage the concentration of ozone, unreacted (discharged) concentration, dissolved concentration, leakage monitoring, etc. Although the application fields of ozone are different, the determination purposes of the above ozone concentrations are roughly the same

the measurement of dissolved ozone concentration is mainly used for the concentration management of ozone water and the management of unreacted dissolved ozone after cleaning and sterilization of appliances, so as to ensure the effect of ozone water (when the pollution load changes)

leakage monitoring is the most important to ensure safety, but it seems to have not been paid attention to in the field of food, but trace moisture during injection molding will cause the decomposition of polyaryl esters. Compared with other oxidizing chemicals, ozone decomposition is extremely rapid, so concentration management must be carried out in use, and HACCP implementation must also keep concentration records

therefore, this paper introduces the precautions and actual measurement examples when using ozone concentration meter (the most popular ultraviolet absorption method, figure 1)

1. selection of ozone concentration meter

object and purpose

for ozone gas, there are monitoring of generator outlet concentration, unreacted concentration, environmental concentration and leakage. For dissolved ozone, the concentration of ozone water generation and unreacted (residual) dissolved concentration are measured. Various management concentrations have their own purposes and requirements, and appropriate concentration values must be set. Different measurement objects, ozone concentration meter must have different requirements

determination range and unit

determination range determines the model of ozone concentration meter. The general concentration value, maximum value and minimum value to be measured must be specified

if the maximum and minimum values are too open, a concentration meter cannot be covered

there are also several expression units of concentration, and the meaning of single pg-620h · m (pl-620 (solution storage field) position for gas should be understood in advance. The ozone gas concentration units often used in the food industry are ppm and g/M30 dissolved concentration unit mg/l (also known as ppm, but different from the ppm of the gas concentration unit). Table 1, the meaning of each unit has been shown

determination accuracy

accuracy generally refers to the accuracy and precision required under the concentration range used, and varies with the determination principle, method, model and manufacturer. In addition, the necessary matters and conditions (filter, correction, etc.) to maintain its accuracy must be understood in advance

sampling flow

in order to ensure the minimum flow and flow variation of accuracy, each measuring meter has provisions. Since ozone decomposes rapidly by itself, if the flow rate is slow, it will stay in the instrument for a long time, thus reducing the measured value (especially below 1ppm)

(1) NTP is the standard state (273k, 101.3kPa) Generally, the gas volume is shown in the table below the standard state. The values in the standard state are expressed as g/nm3, mg/lntp, etc. In Table 2, the unit of expression in water is

(2) if ppm,% its volume ratio and mass ratio may be confused, it can be expressed as volppm, wt%, etc

1[g／Nm'3=467[volppm] (NTP)

1[mg/L]=1[g／m3)=2．08 × [mol/m3]

1[vol%]=10 at present, according to the composition of the lunch box 000[vol ppm]

1[ppb=0.001[ppm)

1 (PPHM) =0.01 (PPM) =1.013[mpa) (NTP)

temperature of sample gas and sample water

the molecular number of ozone gas changes with temperature under a certain volume, so temperature correction is required. The water temperature changes little, but the decomposition is accelerated at high temperature, and the water will condense in the instrument if the water temperature decreases, so it should be noted

pressure of sample gas and sample water

when the ozone gas pressure is finally different from the atmospheric pressure, pressure compensation is required. If the instrument has no automatic pressure compensation function, the measured value will also change when the pressure changes, so it is necessary to understand the use pressure range of the instrument. The ozone condition has no effect on the measured value, but it is very prone to seal damage and joint leakage, so it is necessary to understand its pressure resistance from the manufacturer

influence of dust and impurities

from the measurement department, it is required to remove dirt such as dust. In addition, it is also necessary to understand the positive and negative effects of other impurities on the measured value. Even if the measurement principle is the same, the influence level of products from different manufacturers is also different. O

14 the performance and expression of the densitometer

Table 3 shows the meaning of the performance expression of its performance. Table 3 the performance expression of the densitometer

output, input signals and their types

there are many kinds of input and output signals, and the output signal has the analog signal (voltage ` current), digital signal (RS232C, etc.), concentration alarm, abnormal concentration meter, etc, The input includes external control input, etc. when purchasing, it is necessary to clarify the required signals and types in advance

set environmental conditions

generally, the environmental conditions of the analyzer and its tester are roughly the same. However, the products of different manufacturers meet different requirements. In particular, the semiconductor industry must meet the important specifications of semis. Europe also has provisions for CE marking, so we must choose products that have passed various tests

2. Ozone determination methods

Table 4 shows the main determination methods and principles, and various determination methods form corresponding products. The determination of ozone gas is mainly by ultraviolet absorption method, while the dissolved ozone is mainly by ultraviolet absorption method (including gas phase) and diaphragm polarography. Each has its own advantages and should be selected according to the use requirements

3. precautions during sampling

ozone decomposes quickly and has strong oxidizing power, so we must pay attention to the sampling time, sampling piping and filter material

low concentration ozone gas

when measuring ozone below lppm concentration, the sampling distance should be as short as possible. If the material is fluororesin or functional glass that can be realized in a fully integrated automatic process, the initial ozone decomposition will be faster and it should be fully matured. For the new fluororesin piping (inner diameter 6mm~4mm), when the ozone concentration is 0.5ppm and 1.5L/min, the reduction rate takes about 20 minutes to stabilize (Figure 1). Figure 2 shows the stabilization time of ozone on the fluororesin filter

when the sampling point is close to the wall or ground, the concentration will decrease. When the sampling pipe is long, a filter should be installed at the end to prevent dirt in the pipe

Table 4 ozone concentration determination method

, high concentration ozone gas

generally adopts ozone resistant materials of fluororesin and stainless steel, and attention should also be paid to sealing materials. The sample gas must be dehumidified in case of excessive moisture to prevent condensation in the concentration meter. When measuring the ozone produced by the ozonator, the zero gas is dry air or oxygen without ozone. When there is more water in the raw air of the discharge ozone generator, the generation of nitrogen oxides increases, and it will react with water to form nitric acid, which will affect the ozone concentration meter

dissolved ozone

dissolved ozone decomposes faster than gaseous ozone, which is greatly affected by factors such as water quality, water temperature, spoon vibration, and contact area with external air. Figure 3 shows the decay of ozone dissolved tap water and ion exchange water with time at the water temperature of 11 '(2 ＼ 24'c. the ion exchange water is more affected by the water temperature than tap water.

it can be seen from Figure 4 that if the external air is isolated, the ozone does not radiate outward, and the external air does not enter, the ozone decay will be slow. In addition, if the concentration of dissolved ozone is high, the decay rate will also be high (Figure 5)

the attenuation of the sample gas in the piping is also affected by the material of the piping and the retention time. Figure 6 shows the dissolution of ozone in tap water. If there are substances that are easily formed by the reaction of ozone with organic substances, the retention time will greatly affect it

4. examples of ozone concentration measurement in food factories

the discharge ozone generator (psa-02) inputs different concentrations of ozone to the raw material processing room (a), heating and conditioning room (b), packaging room (c), sterilization and coating room (d) day and night through the top plate. Table 5 shows its operating conditions, and the processing contents of each room are shown in Table 6. Here we only introduce the results of room a:

during the three days from day 1 and the five days from day 30 to day 14, although the ozone injection volume did not change, the nighttime concentration only increased by about 0.1ppm (the reason is unknown). On the 5th day of rest, there was no production; The ozone concentration throughout the day is above 0.4ppm, the maximum concentration at night is 0.9ppm, and it is below 0.05ppm during production (Fig. 7). From the above measurement results, even if the amount of ozone injected remains unchanged. However, due to the change of operation content and the impact of environmental conditions, the ozone consumption varies greatly, so the ozone concentration must be continuously monitored to ensure the stability of ozone

table 5 ozone concentration measurement conditions of each processing room

Table 6 add] main processing contents of the second room

ozone generator operation conditions:

① am6:00-pm9:00 nozzle outlet concentration 27ppm during the day

② pm9:00-am6:00 nozzle outlet concentration 50ppm at night

③ nozzle outlet flow 4L/min/1

④ ozone concentration meter: eg-2001f

⑤ measurement position: h=1800 (H)end)