Since the launch of ultra-low emissions in the cement industry, the problem of ammonia escape has been criticized by some industry insiders. Although a few provinces and cities have provided specific regulations on ammonia escape in the cement industry, for example, Shijiazhuang in Hebei Province requires the installation of online monitoring equipment for ammonia escape in the power and cement industries from June 1, 2019, and networking with ecological environment departments. The implementation plan for the ultra-low emission transformation of the cement industry in Henan Province recently issued shows that by the end of 2020, cement enterprises in the province will complete organized and unorganized ultra-low emission transformation. The ammonia escape concentration using ammonia denitrification and ammonia desulfurization will not exceed 8 milligrams per cubic meter, and the consumption of ammonia water per ton of clinker will not exceed 4 kilograms. However, overall, the issue of ammonia escape has not yet received attention from the entire industry.

At the same time, the progress of ultra-low emission transformation in the cement industry is still accelerating. Recently, the website of the Ministry of Ecology and Environment released opinions on actively serving and implementing the "six guarantees" task under the premise of normalized epidemic prevention and control, and resolutely winning the battle against pollution prevention and control. The opinion is clearly proposed, and it is also the first time that the requirement for ultra-low emissions of cement has been clearly stated in the documents of the ecological environment department. That is, regions with large production capacity in the building materials industry should study and carry out ultra-low emission transformation in industries such as cement and ceramics according to local conditions.

It can be foreseen that ultra-low emissions, as a necessary process in the high-quality development of the industry, are unstoppable. How to balance the dual requirements of emission reduction and ammonia escape reduction for the most challenging nitrogen oxides in ultra-low emission transformation? What situation will ammonia escape face in the future?

Current situation of ammonia escape in the cement industry

Ammonia, NH3, colorless gas, foul odor, highly soluble in water, is an important raw material for manufacturing fertilizers and explosives. The mass concentration of ammonium salts generated by the reaction of ammonia and acid is one of the methods used by scientists to measure the impact of ammonia on air and PM2.5.

Research has found that regional ammonia emissions in China are rising rapidly and have a significant impact, possibly from offshore aquaculture, animal husbandry, agriculture, automobiles (excessive ternary catalysis), industrial denitrification (excessive use of reducing agents such as ammonia or urea), etc. China has been the world's largest emitter of ammonia for nearly 20 years.

Returning to the cement industry, among the three major pollutants "dust, sulfur dioxide, and nitrogen oxides", the difficulty of controlling ultra-low emissions of nitrogen oxides is the greatest. Among the mainstream denitrification technologies in the industry, SNCR (Non Selective Catalytic Reduction) is widely used in the cement industry due to its relatively low cost. However, unlike SCR (Selective Catalytic Reduction) technology, which has a denitrification efficiency of over 90%, SNCR (Non Selective Catalytic Reduction) usually has a denitrification efficiency between 40% and 60%, and ammonia escape is inevitable.

With the popularity of "ultra-low emissions" in the industry in recent years, especially after the introduction of differentiated staggered production, some provinces and cities have stipulated that achieving ultra-low emissions does not require staggered production or reduce the number of days of staggered production. As a result, the enthusiasm for air pollutant emissions control in cement enterprises is high, and efforts are continuously increasing. But some cement companies, in order to meet the ultra-low emission control requirements of their existing denitrification devices, use excessive spraying of ammonia water, resulting in a large amount of ammonia escaping. This seems to reduce the nitrogen oxide emissions of cement plants, but the actual environmental problems may be more serious.

One is that excessive spraying of ammonia water can lead to a significant increase in ammonia escape, causing serious environmental problems. Data shows that ammonia is actually an important factor causing haze. The increase in ammonia escape not only fails to alleviate environmental pollution problems, but may also worsen the already fragile atmospheric environment quality, leading to more serious haze problems. Data shows that 1g of ammonia can generate 80/17g of ammonium nitrate or 132/34g of ammonium sulfate. Escaping 1mg of ammonia will generate 4.7mg of ammonium nitrate or 3.9mg of ammonium sulfate, and the resulting PM2.5 will also increase by 4.7 or 3.9 times.

Secondly, the preparation of ammonia water itself is a high energy consumption and pollution process. As a reducing agent for nitrogen oxides, ammonia water should be used to improve the reaction efficiency as much as possible, allowing as much ammonia water to participate in the reaction process, thereby reducing the consumption of ammonia water. Excessive spraying of ammonia can lead to a significant increase in ammonia consumption, causing greater pollution to the source of ammonia preparation.

Since ammonia escape poses such a serious threat, why hasn't it alerted cement companies?

On the one hand, there is a lack of standards. The structural differences of the cement kiln firing system itself, as well as factors such as working conditions, differences in raw materials and fuels, difficulties in treatment, and even the level of operators, all affect the different levels of ammonia escape. Currently, only a few provinces and cities have issued specific standards for detecting ammonia escape in the cement industry.

On the other hand, according to industry insiders, the ammonia escape volume of many cement enterprises currently ranges from 8mg/m3 to 10mg/m3. Compared to the large emissions of dust and nitrogen oxides, ammonia escape seems to be a bit "minor", which may also be one of the reasons why cement enterprises ignore it.

Reducing ammonia escape is urgent.

The denitrification of cement production lines is a complex system engineering, which is first affected by the composition of various raw materials. The equipment configuration and technical equipment level of each production line are also different, and the production operation technical parameters and control indicators vary greatly. In order to meet the requirements of nitrogen oxide emission standards, it is necessary to conduct in-depth and detailed analysis of the firing process and conduct thorough research on the composition characteristics of various raw materials, Starting from solving the generation of nitrogen oxides, establish an efficient and low consumption denitrification system.

In my opinion, with the advancement and development of technology, nitrogen oxide emission standards will also become increasingly strict. While nitrogen oxide ultra-low emissions are being achieved, attention should be paid to ammonia escape and emission transfer issues.

In the context of the continuous deepening of a series of environmental protection measures such as the national "blue sky defense war" and environmental inspections, and the trend of ultra-low emissions becoming a major industry trend, cement enterprises should also plan ahead and be prepared for the problem of ammonia escape.

Firstly, cement companies should strengthen their attention to the issue of ammonia escape and choose reasonable and effective ways to reduce nitrogen oxide emissions, rather than blindly spraying a large amount of ammonia water to achieve the effect of "robbing Peter to pay Paul".

Secondly, associations and industry leading enterprises should play a guiding role. They should not only encourage research institutions to increase scientific research investment and achieve breakthroughs in cement production technology in the future, and try to control the generation of nitrogen oxides from the source. They should also vigorously promote more provinces and cities to introduce ammonia escape detection standards that are in line with reality, and include the standards in one of the environmental assessment items. Through real-time monitoring and analysis of "ammonia escape", the problem of ammonia pollution can be reduced.

Finally, through the overall efforts of the cement industry, ammonia pollution will be elevated to the level of national air pollution control, promoting China's air pollution to a new level. This is not only an important measure to improve the industry's appearance, but also a necessary way to control "haze" and create a blue sky and white clouds for future generations.