The people's perspective on the haze | Li Yanxin: to clarify the ins and outs, symptom-based measures, the source of the haze
2021/11/18 16:20:00 本站

Ultra-low emissions, coal-to-gas, coal-to-electricity for many years, the atmosphere of SO2, NOx has long fallen back to the level of the 1990s, blue skies and white clouds significantly increased the effect of air pollution treatment is remarkable. It should be noted that: autumn and winter as long as the wind does not blow for a few days, the haze will return. To further reduce PM2.5, more than 70 new initiatives have recently been introduced at the national level to control pollution in cities and regions. In retrospect, when the epidemic and the national shutdown during the Chinese New Year last year, there were still many days of heavy haze, and it is clearly not optimistic that the new initiatives will ensure that heavy haze will not return.

In the face of the last two days of domestic haze people can not help but ask: after thousands of scientists for many years of research, numerous high profile papers, the state also spent a lot of silver, ultra-low emissions, corporate shutdown of governance measures are still increasing, why the heavy haze in the autumn and winter seasons for a long time to cure? I would like to share with you my perception of the haze in plain language that can be understood by people.

Ins and Outs of Haze

Haze is a combination of "fog" and "haze". "Fog" is a large number of small droplets floating in the air, this natural phenomenon on the ground called "fog", floating in the air is called "cloud". The "haze" is the general term for particulate matter, the main components of which are sulfates and nitrates with particle sizes less than 2.5 microns. These plume microparticles are very large than the surface area and are difficult to settle when floating in the air for long periods of time.

1. sulfate mainly comes from the wet desulfurization process of coal-fired flue gas, to the coal-fired boiler room will understand at a glance: the so-called "zero discharge of desulfurized sewage" is the form of desulfurization liquid to oversaturated wet smoke all blowing into the sky, water mist white smoke after the tail plume is PM2.5 sulfate.

2.nitrates mainly come from nitrogen oxides in the air of the secondary synthesis, coal and gas flue gas, automobile exhaust emissions of NOx in alkaline mist droplets will become nitrates.

Overview

Fog droplets are condensed water, which is very pure, while "haze", which is smaller than PM2.5, is a pollutant, and if they meet, haze is formed.

The formation of haze is closely related to meteorological conditions. In October this year, it rained twice a day in Beijing, and the particles floating in the air fell to the ground with the rain, thus cleaning the air. Even if there is no rain and no wind, due to the high temperature on the ground, fine particulate matter is pushed up into the high altitude by the vertical rising thermal airflow, indicating that many times the atmosphere has a strong self-cleaning ability. At this time, if there are clouds at high altitude, the clouds will absorb these hydrophilic micro-particles, and the micro-particles gathered in the clouds will not be felt on the ground.

Clouds can be seen as a "lid". The higher the lid, the larger the space below, and the more micro-particles can be accommodated. When there is no wind and fog on the ground in autumn and winter, the "lid" becomes the "quilt", and the space in the quilt is too small for PM2.5 to accumulate and quickly integrate into the fog, thus creating an explosive growth of haze, and people will soon be surrounded by haze.

Second, symptom-based measures

By clarifying the ins and outs of the haze, we can target the prevention and control of the haze. Since the composition of the haze is "fog" and "haze", it is natural to start with the elimination of condensable particles and the reduction of man-made emissions of water vapor.

1.Elimination of sulfate

Sulfate mainly comes from wet desulfurization of water mist white smoke, and only by eliminating wet flue gas with condensable particles can the sulfate in haze be reduced. Flue gas dehydration and mist removal is not difficult to implement, and economic income can be obtained through waste heat utilization. Also the use of dry desulfurization technology for flue gas can avoid the emission of wet flue gas.


2.Nitrate elimination

Nitrate in haze mainly comes from the secondary synthesis of NOx and alkaline substances such as ammonia in the air. Only by reducing NOx emissions from coal, gas and automobiles, as well as reducing ammonia escape from the ammonia spray denitrification process to manage nitrates.

3.Eliminate the artificial emission of water vapor

In the past, people ignored the important role of water vapor in producing haze, ignoring the simple physical phenomenon that 5g of water can saturate the air humidity under the temperature condition of 0. Therefore the wet flue gases from various coal-fired boilers and furnaces, cooling water towers, and various wet flue gases generated during the production of iron and steel building materials are randomly emitting huge amounts of water into the atmosphere, while these wet flue gases are also important carriers of entrained condensable particulate matter. Collecting these artificially emitted wet flue gases can not only reduce the high humidity of the air under static weather conditions, but also greatly reduce the emission of condensable particulate matter.

With 1,670g of water vapor produced for every 1M3 of natural gas burned, the large increase in air humidity caused by burning natural gas under static weather conditions is also an important factor in aggravating dense fog. A variety of artificial emissions of water vapor dehumidification is not difficult, through the recovery of flue gas waste heat and the addition of mist eliminator can receive good results.

Third, eliminating haze from the source of combustion

A large amount of data proves that: haze mainly comes from the end of the flue gas treatment process, if the use of disruptive clean and efficient combustion technology in the combustion stage to achieve desulfurization and denitrification (desulfurization without water, denitrification without ammonia spray), it can eliminate the haze caused by coal combustion flue gas from the source of combustion.

At present, the clean combustion boiler made by clean and efficient combustion technology has long passed the testing and certification of authoritative testing institutions, and the vigorous promotion and application of clean combustion boilers will certainly receive good results of haze control with half the effort and low cost.

Clean combustion boilers using clean and efficient combustion technology, the function of burning coal is equivalent to burning gas, the operation of the chimney than the natural gas-fired boiler is also transparent and smoke-free, and the operating costs are lower than all ultra-low emission coal-fired boilers. As the load regulation ratio of clean-burning boiler is 5:1, it can be used for deep peaking of new energy for scenic power. Clean and efficient combustion technology can also be extended to waste, biomass power generation and building materials kilns, so vigorously promote clean and efficient combustion technology not only has good practical significance for energy saving and emission reduction to combat haze, but also will have extremely far-reaching historical significance for the completion of the double carbon goal.

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Original Chinese article:  https://mp.weixin.qq.com/s/8-zo6Uw9SK5oi0wVWXzcGQ

Translator/ Lucy
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