In defence of blue skies

By 2020, the total emissions of SO_X and NO_X will be more than 15% lower than those in 2015. The PM2.5 concentration of the cities of prefecture level or above will be more than 18% lower than that in 2015. The ratio of good air quality days of the cities of prefecture level or above will be 80%. The ratio of the pollution days of severe pollution or above will be more than 25% lower than that in 2015. In addition, many local governments are implementing higher action targets, according to the actual local conditions.

Influence of the action plan on cement industry

The main atmospheric pollutants of the cement industry include NOX, oxysulfide, and dust particles. Current emission limits for NO_X, oxysulfide and dust particles are 400mg/Nm³, 3200 mg/Nm³, and 30 mg/Nm³, respectively. The limits for key areas (economically developed and densely populated areas) are 320 mg/Nm³, 3100 mg/Nm³, and 20 mg/Nm³, respectively.

For realising the target of the three-year action plan, the emission limits of the above three pollutants shall be correspondingly decreased to 340 mg/Nm³, 170 mg/Nm³, and 25.5 mg/Nm³, while in key areas they will be lowered to 272 mg/Nm³, 85 mg/Nm³, and 17 mg/Nm³.

In April, Qiao Longde, President of China Building Material Federation, proposed at an industry conference, that the cement industry will soon reduce emissions standards beyond that require in the Blue Sky Defence plant. These ultra-low emission standards will be 100 mg/Nm³, 50 mg/Nm³, and 10 mg/Nm³ for NO_X, oxysulfide, and dust particles, respectively. This proves the efforts of the Chinese cement industry for controlling air pollution and are higher the emission standards in most countries.

Indeed, some local governments have already implemented the ultra-low emission standards for the emission limits of cement plants. Jiangsu Province requires that cement plants emit lower than 100 mg/Nm³ of NO_X by the end of June 2019. Henan Province also requires that cement plants emit lower than 100 mg/Nm³ of NO_X. Hebei Province requires that local cement plants emit lower than 150 mg/Nm³ NO_X through technical upgrading and transformation before 2020. Thus, Chinese cement plants and the Chinese cement industry are encountering high pressures from environmental protection.

The Chinese cement industry is actively reducing the emission of atmospheric pollutants through diversified measures. As indicated by the current technical development of the cement industry, the cement industry has many practical technical means for controlling oxysulfide and dust. The industry can meet the requirement for ultra-low emissions in future with only a limited increase in production costs that will be brought about by technical upgrade and transformation.

The NO_X challenge

The reduction of NO_X emissions is the main difficulty for controlling the air pollution of the cement industry (the emission of nitrogen oxides is about 10% of the emission of the whole country). The current applicable emission reduction technologies include SNCR, controlling and regulating the temperature field of the calciner and atmosphere field with the fractional combustion of air and fuel, and burner optimisation, etc. A few cement plants have controlled the emission of NO_X to less than 100 mg/Nm³ with the collaborative application of the above technical means, as well as the refined operation and management of production processes. But these methods depend on much experience and operational factors and cannot be copied broadly.

Most enterprises reduce the NO_X by increasing the consumption of ammonia and commonly control the NO_X emissions to be about 200 mg/Nm³; however, this brings the side effects of production cost increase, ammonia slip, and corrosion of equipment and filtering bags, etc.

For the exploration of new technologies, many Chinese research institutions and enterprises are developing high-temperature and low-temperature SCR technologies, which are applicable for the high-dust working conditions of the cement industry and have achieved fruitful progresses.

Besides the use of vanadium and titanium as catalysts, the rare-earth-based catalyst – which is totally toxicity-free and can be applied to the cement industry – has been successfully researched and developed. The rare-earth-based catalyst can be sprayed on the filtering bag surface to remove NO_X.

At the same time, to solve the issue of catalyst poisoning caused by dust and harmful ingredients, a Chinese scientific research institution has combined the ceramic film dedusting with SCR and developed a product that integrates denitrogenation and dedusting. It can remove more than 90% of the NO_X and achieve lower than 50 mg/Nm³ NO_X emissions. It has now been applied on an industrial facility of which the exhaust gas quantity is 300 000m³/hour. In future, it will be applied to and tested in the cement industry.

In addition, organic substances, which can replace ammonia and have low cost, are being investigated.

Conclusion

Indicated by the analysis above, the current emission reduction capability of atmospheric pollutants of the Chinese cement industry can meet the target of 15% reduction of the emission of relevant pollutants, which is required by the action plan. However, high pressure for environmental protection will be brought to bear on the cement industry when encountering the stricter standards of local governments and the ultra-low emission standard for the atmospheric pollutants of the industry (particularly the requirement on the emission reduction of NO_X), which may be implemented in future.

Thus, production costs will be increased and the plants that cannot meet the emissions regulations will be closed. This will, however, benefit the cement industry, which has overcapacity, as well as the construction of beautiful China. Experts predict in the next 20 years, the mission of eliminating an average capacity of 100 million tpy can be successfully completed. In addition, the stricter requirements of environmental protection will accelerate the development of new technologies of emission reduction.

About the authors: Jiang Yongfu, Xu Rong and Cui Yuansheng, Institute of Technical Information for Building Materials Industry of China (TIBMIC).