The main causes and treatment of haze

Recently, the air quality index of several cities such as Beijing Tianjin Hebei has exploded, causing heavy smog and poor visibility. Yesterday, Beijing issued its first orange haze warning of the year. Starting from November 27th, the severe air pollution process in Beijing has been ongoing for 4 days, with some monitoring stations approaching a PM2.5 meter burst. The Beijing environmental protection department stated that this round of pollution is the most severe pollution process since the beginning of this year.

Recently, haze has become one of the hot topics. Both the public, relevant industries, and the government have expressed helplessness and even complained about this. But complaining is useless, it is urgent to understand the main reasons for the formation of haze and then discuss how to manage it.

Haze is divided into "primary particles" and "secondary particles". The particles directly emitted from the exhaust gas during the combustion of fossil fuels such as diesel are "Primary Particles", accounting for about 24% of the total haze. The contribution of "secondary particles" to haze is significant, accounting for about 50% of its total amount. Secondary particles "are particles formed by the aerosol reaction of gaseous pollutants (such as NOx, SOx) and volatile organic compounds (VOC) in the exhaust gas of fossil fuel combustion with ammonia and VOC in the air under a certain water mist state. Therefore, to remove haze, it is necessary to reduce the emissions of pollutants such as NOx, SOx, and VOC.

China consumed approximately 470 million tons of oil in 2010 and 570 million tons of crude oil in 2014, while the coal consumption in 2014 was approximately 3.6-3.8 billion tons. The energy structure dominated by coal cannot be changed in the short term, so controlling coal-fired pollution has become the primary issue at present. Large power plants are required to install desulfurization, denitrification, and dust removal equipment according to regulations, with a removal rate of over 90%. Concentrated coal combustion can control the pollutants in the exhaust gas to be similar or even lower than natural gas combustion. The world average coal concentration utilization rate is around 60%, with Europe, America, Japan and other countries reaching over 90%, but China's coal concentration utilization rate is less than 50%. Nearly 700000 small and medium-sized boilers in China have burned hundreds of millions of tons of coal in bulk. Although there are discrepancies in accurate figures and statistical data, it is estimated that about 600 million tons of coal have been burned in bulk; The cost of installing desulfurization and denitrification devices behind each small and medium-sized boiler is too high, and no country or individual will do so. The pollution caused by burning one ton of coal in bulk is about 10-20 times that of large boilers after ultra clean emission reduction; Therefore, the emission of 600 million tons of coal from scattered combustion is equivalent to the pollution generated by approximately 6-12 billion tons of concentrated combustion. Due to the large population base of China, the problem of haze pollution cannot be explained by the calculation method that China's per capita energy consumption and emissions are much lower than those of Europe and America. However, the environmental capacity is determined by the emissions per square kilometer (or energy density), and is not related to per capita emissions (10 or 10000 people may live on 1 square kilometer); The air is flowing, so it is not meaningful to focus solely on local urban data regarding haze issues. From a macro perspective, the total area of Europe is similar to that of China, but the majority of China's population is concentrated in an area of approximately 2 million square kilometers in the east, while the population of Europe is distributed on approximately 4 million square kilometers of land. Compared to China's 3.6 billion tons of coal consumption, the total amount of coal-fired power in Europe is only about 580 million tons, and the vast majority is used in large power plants with pollutant emission control. China not only consumes much more coal than Europe, but also many coal is burned in bulk, so China's emissions per square kilometer are much greater than Europe's. This explains why both sides have a large number of cars, while China has smog, which is rare in Europe.

The author believes that the combustion of loose coal is the primary culprit of haze. People naturally have to ask, why not change the combustion of bulk coal to natural gas? This direction is correct, but China's total natural gas output is not enough. Recently, China's natural gas prices have decreased, and many people believe that China has an excess of natural gas. This is a misunderstanding. China's natural gas is not too much but too expensive (more than twice the price in the United States). From the perspective of environmental protection and haze control, very limited natural gas should be first applied to transform small and medium-sized boilers, rather than converting large power plants from coal to gas. But even if all of China's natural gas is used for the renovation of small and medium-sized boilers, our natural gas is not enough. We cannot install desulfurization, denitrification, and dust removal devices after every small and medium-sized coal-fired boiler. Therefore, in the foreseeable future, a practical and feasible approach is the author's call for graded coal refining technology in recent years, to develop the "coal making" industry, and to clean the coal before supplying it to small and medium-sized boilers for combustion; In the "Coal Refining At the same time, it also produces high-value and cleaner oil and gas fuels. At the same time, it is necessary to strictly regulate the quality of coal burning in small and medium-sized boilers and establish other regulations to control the pollution caused by small and medium-sized boilers. As long as large power plants are willing to spend money, they can reduce their emissions other than CO2 to the same or even lower level as natural gas. This is not surprising. In recent years, the country has done a lot of work in pollution control of large power plants, which is worthy of recognition Some companies have invested heavily in ultra clean coal-fired power plants that are cleaner than natural gas power plants. In fact, these ultra clean emission technologies for desulfurization, denitrification, and dust removal are all readily available, and the key lies in whether it is worth the cost to pursue the goal of removing from 95% to 99% or even higher. The current problem is that on the one hand, the 100% emission of small and medium-sized boilers is neglected due to the inability of small and medium-sized enterprises and individuals to switch from coal to gas; However, large power plants that had already installed over 90% desulfurization have invested heavily in pursuing ultra clean power plants with lower natural gas emissions. On the one hand, major enterprises are upgrading large power plants with installed pollution control at high prices in pursuit of ultra-clean emissions (lower than those from natural gas power plants), On the one hand, no one has invested in solving the "coal refining" technology that can solve the real culprit of haze - the emission control of scattered coal burning in small and medium-sized boilers; to the extent that the country has spent a lot of money on the renovation and upgrading of large power plants, but the effectiveness of haze control is not obvious, because the real culprit of haze is scattered coal burning, rather than large power plants that have installed desulfurization, denitrification, and dust removal.