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Will ozone denitrification aggravate ozone pollution?

2017-10-9 16:21:00

Since the first half of this year, the news about "ozone pollution" has been breaking out all over the country, and the "ozone" before this unfamiliar pollutants began to receive widespread attention. According to the information issued by the China Environmental Monitoring Center, in 2017, the national ozone exceeded the standard rate increased significantly, the peak concentration of obvious uplift.

More surprisingly, the air quality data released by the Ministry of environmental protection in the first half of 2017 showed that ozone concentrations rose in 338 cities in May. Among the 6 major pollutants, the maximum daily 8 hour average concentration index of ozone increased the most.

Unlike haze, ozone is invisible to us, but ozone pollution should never be underestimated. Seriously, its harmfulness is comparable to that of PM2.5.

Is ozone not a "little angel" protecting the earth?

In our impression, the ozone layer is to protect the earth, ozone can also be sterilized, how to become a "little devil"?

In fact, ozone is called "wind in the sky and Buddha in the earth". When ozone is located 15 to 25 kilometers in the stratosphere, it is the umbrella of the earth, the earth's biological barrier against UV intrusion; and near the ground, nitrogen oxides (mainly from motor vehicles, power plants, coal-fired boiler and cement kiln etc.) and volatile organic compounds (mainly from motor vehicle emissions, petrochemical industry and the organic solvent will send) compounds such as high temperature, solar radiation and catalytic ozone formation, a pollutant, ozone concentration will reach the peak at around 3 p.m..

Does ozone pollution cause serious harm to human body?

According to the air quality standards, 1 hours on average when ozone concentration is more than 0.2mg/m, or fand 8 hours moving average more than 0.16mg/m fand means the beginning of time, caused by pollution, also known as photochemical smog. While the general monitoring value exceeds 0.16mg/m fand, human body can obviously feel discomfort.

Ozone can react with almost any biological tissue, and is very destructive to the respiratory tract. According to the Canadian Center for occupation health and safety (CCOHS) introduction, "ozone leads to cough, sore throat, heavy lead to asthma, causing upper respiratory diseases, may also lead to a decrease in lung function, pulmonary emphysema and pulmonary tissue damage, and the damage is often irreversible."

Ozone also stimulates the eye, reducing visual sensitivity and visual acuity. When the ozone concentration in the 0.2mg/m fand above, can damage the central nervous system, headache, chest pain, decline in thinking ability. In addition, ozone will hinder the blood oxygen function caused by hypoxia; the impairment of thyroid function and bone calcification.

The origin of "ozone denitration" technology

The main component of ozone in the atmosphere is of photochemical smog, it is not directly discharged, but turned into, such as motor vehicles, emissions of nitrogen oxides from power plants, coal-fired boilers and furnaces such as cement, as long as the sun radiation and suitable weather conditions can generate ozone. For the emission control of nitrogen oxides, all industries have corresponding emission standards, and the demand for NOx concentration is not more than 50mg/Nm3 in the fire power industry.

The mainstream of the thermal power plant flue gas denitration technology is SCR and SNCR (more than 80% denitration market), the principle is the reducing agent to the flue gas ammonia or urea containing NH-3 free radical, high temperature (cooperative or catalyst under) redox reaction with NOx in flue gas, the reduction of NOx into nitrogen and water. However, these two technologies have strict requirements for temperature, the conventional SCR requires temperature between 300-430 degrees, and SNCR requires temperature between 700-1000 degrees. The temperature window became the limitation of the technology.

For medium and small boilers and industrial boilers, the exhaust gas temperature can not reach the high temperature required by SCR reaction, so the low-temperature flue gas denitration technology has become a must of the market. Ozone denitrification, as a low-temperature flue gas denitration technology, has been applied in industrial boilers and various furnaces in recent years. The principle is generally prepared by ozone ozone generator, the NO in the flue gas into high valence by spraying device into a flue, NO (95%) is difficult to dissolve in water, and the high valence of NO2 and N2O5 are soluble in water to produce HNO2 and HNO3, the dissolution ability is improved, easily by alkali liquid spraying etc. the separated from the flue gas and its method.

The ozone denitrification process is suitable for flue gas with temperature of 90-250 degrees, which makes up the temperature area that SCR denitration can not solve. On the basis of the same denitration efficiency, the investment is lower than the SCR technology, and there is no catalyst replacement cost, the resistance increase is small, for the transformation project will not affect the induced draft fan output. In general, there is another technical choice for the project that the temperature range is not satisfied, the space is limited and the draught fan is insufficient.

Will ozone denitrification aggravate ozone pollution?

As mentioned above, ozone is harmful gas and has serious harm to human body. So, does ozone denitration not control a pollutant, but also bring another kind of pollution? This is not the case.

The chemical property of ozone is very unstable, and it will decompose slowly at room temperature. The ozone content is below 1%. The decomposition half-life of air at normal temperature and normal pressure is about 20~30 minutes. With the increase of temperature, the decomposition rate is accelerated. When the temperature is more than 100 degrees, the decomposition is very violent. When the temperature reaches 270 degrees centigrade, the oxygen can be converted into oxygen immediately. Ozone decomposes faster in water than in air. In an aqueous solution containing impurities, ozone rapidly returns to the oxygen that forms it. As the ozone Denitration Process before wet desulfurization, the reaction temperature is usually above 100 degrees, and the desulfurization tower will be washed again by slurry, the ozone that does not react adequately with NO will be decomposed into the subsequent process