Article Cite This: Ind. Eng. Chem. Res. XXXX, XXX, XXX-XXX
pubs.acs.org/IECR
Dynamic Flocculation of Ultrafine Particles of Coal-Fired Power Plant Induced by Ionic Polyacrylamides at Bench and Pilot Scales Xiaobang Hou,#,† Yi Zhang,# Yuanfeng Pan,*,§ Huining Xiao,*,#,† Haoren Chen,‡ Yiwei Chen,‡ Shuming Du,‡ and Hua Guo‡ #
Department of Environmental Science & Engineering, North China Electric Power University, Baoding 071003, China Beijing Key Laboratory of Power Generation System Function Materials, Guodian New Energy Technology Research Institute, Beijing 102209, China § School of Chemistry and Chemical Engineering, Guangxi University, Nanning 530004, China † Department of Chemical Engineering, University of New Brunswick, Fredericton, NB E3B 5A3, Canada ‡
S Supporting Information *
ABSTRACT: Ultrafine particles or particulate matter emitted from coal-fired power plants pose serious threats to public health. In this work, unique processes for flocculating ultrafine particles were developed and conducted at both bench and pilot scales. The results from dynamic flocculation processes, monitored through a benchtop photometric dispersion analyzer, indicated that ionic polyacrylamide of high molecular weight (MW) induced effective flocculation at concentrations of 1−3 ppm and neutral pH. Such conditions were adopted in a pilot-scale flocculation tower in accordance with the actual operating parameters of a power plant to verify the flocculation of ultrafine particles induced by counter-flow spraying flocculant solution into simulated flue gas. Results showed that the best conditions in pilot trials were to spray the diluted solution of anionic polymer with ultrahigh MW at 20 mL/min, which increased fine particle size from 2.46 to 25.9 μm (floc size), thus demonstrating the effectiveness of the process. symptoms and chronic diseases.6−11 The time-series study of short-term effects by Kan et al.12 found that a 10 μg/m3 increase in the 2-day moving average concentration of PM2.5 leads to a 0.36% increase of total mortality in Shanghai, China (based on the data collected from March 2004 to December 2005). Long-term exposures of PM2.5 have larger and more persistent cumulative effects than short-term exposures.13 For instance, Pope et al.14 linked the risk factor data for approximately 500 000 adults (from the American Cancer Society cohort study) with ambient air pollution data throughout the United States over a 17 year period from 1982 to 1998 and found that each 10 μg/m3 elevation in fine particulate air pollution is associated with approximately a 4% increase in all-cause mortality. In addition, Dockery et al.15 examined the effect of long-term air pollution exposure on adult mortalities during the 1970s and 1980s based on the Harvard Six Cities Study. The estimated mortality ratio was 1.13 for a 10 μg/m3 increase in PM2.5 concentrations. In recent years, the impact of PM2.5 on human health has been revealed in detail.
1. INTRODUCTION Urban environment pollution has attracted much attention recently.1 One of the significant air pollutants in urban environments is particulate matter (PM); haze is mainly formed by PM2.5 (diameter of 2.5 μm or less), which has negative impacts on climate, such as deterioration of atmospheric visibility, causing haze weather and climate change.2 Apart from reducing radiation from the sun, the suspended fine particles in the atmosphere disorder the energy distribution balance and change the cloud cover and reflectivity;3 whereas the visibility reduction due to haze below national standards has a detrimental impact on transportation, particularly aviation.4 PM2.5 has been studied more frequently because of its greater potential to cause health problems than the coarse particles with aerodynamic diameters larger than 2.5 μm. Although accounting for only a small fraction of total PM, PM2.5 has high specific area, which enables PM2.5 to enrich sulfates, nitrates, acids, heavy metals, and bacteria on their surfaces.5 Furthermore, because the fine particles can remain suspended for longer periods of time than coarse particles, they can penetrate deeply into the lungs after being inhaled into the respiratory system. PM2.5 has more potential to cause health effects than coarse particles, inducing cardiovascular and respiratory diseases, as well as acute © XXXX American Chemical Society
Received: Revised: Accepted: Published: A
June 30, 2017 October 9, 2017 October 12, 2017 October 12, 2017 DOI: 10.1021/acs.iecr.7b02674 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX
Article
Industrial & Engineering Chemistry Research
reported previously, the dynamic flocculation for PM2.5 ultrafine particles from coal-fired power plants has been seldom reported. Moreover, a pilot-scale flocculation system was designed and assembled in an attempt to simulate the dynamic agglomeration conditions similar to the actual parameters in a coal-fired power plant. Several influencing factors, such as flocculant type, solution concentration of flocculants, and the dosages of flocculants, were dynamically monitored in the flocculation experiments. In the pilot-scale experiment, the polymeric flocculant solution was sprayed into flue gas containing ultrafine particles with tailored PM2.5 concentration to promote the flocculation interaction and the growth of ultrafine particle sizes. The resulting large flocs or particles after flocculation could be much easily removed by the existing dust removal equipment. The findings from the dynamic flocculation of ultrafine particles provide an important guide for the implementation of the as-developed flocculation technique to tackle the PM2.5 issues.
It has been found that some diseases associated with the respiratory system are attributed to PM2.5 fine particles, such as type II diabetes,16 brain damage, obesity, and hypertension.17 One study even found that PM2.5 was related to the hospitalization of neurodegenerative diseases, including Alzheimer’s disease, dementia, and Parkinson’s disease.18 It was reported that coal accounted for more than 76.5% of China’s energy production and about 68.0% of its energy consumption in 2010.19 The PM2.5 emission over the period of 2005−2014 was mainly contributed from biomass burning, thermal power, and building dusts. Because of strict policies, the proportion of PM2.5 emissions from biomass burning was decreased from 37.8% to 16.7% annually. Meanwhile, the proportion of PM2.5 originating from thermal power increased steadily and reached 36.9% in 2014, nearly 1.3 times higher than that in 2005.20 According to the data from the National Bureau of Statistics of China in 2016, the generating capacity exceeded 6 trillion kWh, an increase of 5.6% over the previous year in China. Correspondingly, the annual total energy consumption was 436 billion tons of standard coal, an increase of 1.4% over the previous year. Moreover, it is expected that China’s coal-dominated energy structure will be difficult to change in the foreseeable future.21 It is projected that coal will continue to contribute 60−70% to China’s energy consumption to the middle of the 21st century, namely, 2050. Therefore, PM emission control in coal-fired power plants has become a hot topic in many environmental studies in recent years. Postcombustion control can be used to maximize the removal efficiency of fine PM that is suspended in the flue gas. It includes various agglomeration approaches to aggregate the fine PM into larger ones, such as pretreating before particles are removed, and modifications of conventional particle emission control devices (PECDs) to achieve high performance. At present, most of the conventional PECDs of coal-fired power plants are electrostatic precipitator and bag filter, which can remove more than 99% of the large particles in soot particles, but the removal efficiency of ultrafine particles (
