Yao Hu1, Zhiyong Li 1,2, Lei Wang1, Hongtao Zhu3, Lan Chen1,2, Xiaobiao Guo1,2, Caixiu An3, Yunjun Jiang3, Aiqin Liu3

Hebei Key Lab of Power Plant Flue Gas Multi-Pollutants Control, Department of Environmental Science and Engineering, North China Electric Power University, Baoding 071003, China
MOE Key Laboratory of Resources and Environmental Systems Optimization, Ministry of Education, Beijing 102206, China
Hebei Research Center for Geoanalysis, Baoding 071000, China


Received: June 13, 2019
Revised: July 4, 2019
Accepted: July 15, 2019

Download Citation: ||https://doi.org/10.4209/aaqr.2019.06.0304  


Cite this article:

Hu, Y., Li, Z., Wang, L., Zhu, H., Chen, L., Guo, X., An, C., Jiang, Y. and Liu, A. (2019). Emission Factors of NOx, SO2, PM and VOCs in Pharmaceuticals, Brick and Food Industries in Shanxi, China. Aerosol Air Qual. Res. 19: 1785-1797. https://doi.org/10.4209/aaqr.2019.06.0304


HIGHLIGHTS

  • Investigated Emission factors (EFs) for pharmaceuticals, brick and food industries.
  • EFs were expressed by three ways.
  • Co-burning of coal/gangue weaken the influence of sulfur content on SO2 emission.
  • Organic solvent utility and some food production promoted VOCs emission.
  • SO2 EFs dominated among EFs of 4 air pollutants.
 

ABSTRACT


The acquisition of accurate emission factors (EFs) of pollutants is an inevitable step to the establishment of emission inventories for development of pollution control policies. The current studies were focused on large-scale industries (LSIs) although tremendous pollutants emitted from the small-scale industries (SSIs) with small coal-fired boilers (SCFBs) ascribe to the deficiency of pollutant removal facilities (RFs). A systematic field sampling and measurements conducted in 51 enterprises involving production of pharmaceuticals, brick and food to obtain the EFs of SO2, NOx, PM, and VOCs (SNPV) associated with coal consumption (EFI), industrial output (EFII), and product yield (EFIII). Among them, PM-RFs were all equipped except for 3 brick factories, no NOx- and VOCs-RFs were installed, and SO2-RFs were installed in part. Obvious fluctuations existed in EFI and EFII values among 51 companies owning to the differences of pollutant removal efficiencies, coal compositions, annual outputs, production processes, and products. Co-burning of coal and coal gangue (raw material) in brick production weakened the correlation between sulfur contents in coal and SO2 EFI values. The using of organic solvents in drug making process promoted the emission of VOCs. SO2 EFs in factories with RFs were much lower than those factories without RFs. SO2 EFs dominated over those of PM and NOx among three kinds of enterprises, especially in brick companies. For EFI (in kg t–1), food industry possessed highest value for SO2, PM, and NOx, while the maximum value for VOCs occurred at pharmaceuticals industry. Due to the low output values of brick companies, their SNPV possessed the highest EFII compared to the other two kinds of factories. NOx EFs experienced lessen fluctuations than other pollutants among all the factories due to the different formation mechanism and no installation of NOx RFs. EFIII showed various fluctuations due to the different product types.


Keywords: Emission factor; NOx; SOx; VOCs; Pharmaceutical industry; Brick industry.


INTRODUCTION


In recent years, serious atmospheric quality deterioration had occurred in cities of Asian, European and North American, especially in rapidly developing China (Fang et al., 2009; Pascal et al., 2013; Li et al., 2017). At present, the common air pollutants in China are SO2, NOx and PM emitted from various factories, which have caused great harm to the environment and human health (Delmelle et al., 2002; Srivastava et al., 2005; Lepeule et al., 2012; Tam et al., 2016; Guttikunda and Jawahar, 2018; Hu et al., 2018; Zhao et al., 2018; Zhai et al., 2019).

PM, especially PM2.5 should be responsible for Chinese 1.1 million excess deaths in 2015 (Zhai et al., 2019). The sulphate and nitrate originated from their precursors of SO2 and NOx were main contributors to PM2.5 (Yao et al., 2014). PM has the potential effects to human health due to their deposition capabilities in the body. Besides, there are many evidences for the impacts of PM on the human respiratory system (Crouse et al., 2012; Lepeule et al., 2012). The increasing SO2 emission will lead to an increase in the mortality risk of 1.01% through the respiratory system (Hussain and Luo., 2018). Acid rain caused by sulfate acid deposition can be detrimental to ecosystems, plants and animals, both aquatic and terrestrial (Cronin et al., 2002; Tam et al., 2016). NOx can promote the formation of photo-chemical smog, visibility reduction, and acid rain, and ozone depletion. As the main compositions of NOx, NO and NO2 seriously injured people by invading the bronchioles and alveoli in the deep part of the respiratory tract (Yang, 2017). VOCs in ambient air are an increasing concern because many of them have been identified to be human carcinogens and precursors of both secondary organic aerosols and O3 (Zhang et al., 2015; Hu et al., 2018).

Along with China's economic development, emissions of PM, NOx, SO2, and VOCs in developed areas have increased rapidly. The acquisition of detailed source emission inventories rely on accurate EFs data, which is premise for development of control policies of these pollutants (Li et al., 2018). Prior researches on emission factors mainly focused on LSIs, such as coal-fired power generation, cement production, coke making, and iron and steel production (Guo et al., 2017; Li et al., 2018; Ni et al., 2018). But the SSIs should be paid more attentions because of tremendous emissions owning to the lack of advanced technology and facilities for pollutants removal (Li et al., 2018).

Coal burning associated with SSIs is main source of air pollutants with its emissions is depend on pollutant removal efficiencies, coal quality, and the amount of coal combustion (Li et al., 2018). The SSIs related to coal burning including pharmaceuticals production, food processing, and brick making should be more concerned.

A large amount of heat was need during the synthetic and fermentation processes, the mostly common steps for pharmaceuticals production. In pharmaceuticals companies, SNP originated mainly from coal combustion, while VOCs was also formed from evaporation of organic solvent used in extraction and solvent recovery processes (Guo et al., 2014).

Food processing industry is the pillar industry of the national economy and the basic industry to guarantee people's livelihood (Ma et al., 2019). The food industries use SCFBs for heating with drastic pollutants released due to the lack of RFs. VOCs with strong odors were also released from food processing, which imposed seriously adverse effects on surrounding environment and human health (Xi et al., 2014; Li et al., 2017a). Previous researches were mainly focused on the smell of the food and cooking fumes, while fewer researches were conducted on the VOCs from SCFBs applied in food processing (Liu et al., 2016; Li et al.,2017b; Xu et al., 2017; Gao et al., 2018).

As a developing country, China has a well-developed construction industry and a strong demand for bricks, which yielded abundant air pollutants during coal combustion for production and pose threat to environment (Toledo et al., 2004; Kan et al., 2012; Huang et al., 2014; Wang et al., 2014; Kadir et al., 2015). There are approximately 80,000 brick factories in China, 90% of which are the traditional type and characterized as utility of low-quality coal and lack of lack of pollutant RFs (General Administration of Quality Supervision, 2013). However, the emission inventories of brick production in China counted on the EFs of other countries to a great extent, regardless of scarce reported data related to NOx and PM released from brick factories in China (Zhao et al., 2013).

In a word, the EFs associated systematically researches related to coal combustion in SSIs should be paid more attentions. To our knowledge, fewer data related to pollutant EFs were available in China for SCFBs used in SSIs such as pharmaceuticals production, food processing, and brick making. The establishment of pollutant inventories for these enterprises relied on the foreign data, while considerable bias occurred due to the significantly regional discrepancies in coal quality and combustion mode, production process, and pollutant RFs (Huang et al., 2014; Wang et al., 2014). Greater uncertainties existed in the establishment of emission inventories due to the absence of detailed EF values (Yue et al., 2018). Localization and particularization of EFs related to these enterprises were urgently needed in China (Horák et al., 2018).  

In this study, a total of 51 related enterprises about brick making, pharmaceuticals manufacturing, food processing were investigated for annual output, product yield, and coal quality. Also the field measurements of SO2, PM, and NOx, and VOCs sampling and subsequently instrumental analysis were conducted. All of these works aimed to achieve following purposes: 1) Acquisition of localized EFs associated with SO2, PM, NOx, and VOCs for these enterprises; 2) Improvement of practicability by the output, product yields, and coal consumptions associated EFs; 3) Refinement of EFs based on specific products.


METHODOLOGY



Investigation of Related Enterprises

In this study, 51 companies in Shanxi Province including 34 for brick making, 8 for pharmaceuticals manufacturing, and 9 for food processing were on-site investigated for their production and coal related information. Meanwhile, SO2, PM, and NOx were real-time monitored using a flue gas sampler, while VOCs were collected and subsequent analyzed by a GC-MS system.

The information about product types and yields, raw materials, output, and coal compositions were detailed described in Tables 1, 2, and 3. The abbreviations used in this study including RE, CC, and MY were removal efficiency, coal consumptions and millionaire yuan (RMB), respectively. It should be noted that all of factories were not equipped with NOx and VOCs RFs, while PM RFs were all installed for all of them except for 3 brick factories. The SO2 RFs were erected for 3 of 8 pharmaceuticals factories, 3 of 9 food plants, and 13 of 34 brick enterprises. PM RE values showed not the correlation with annual output of enterprises, which suggested more advanced PM removal technologies were not always adopted by enterprises with high output. The sulfur contents contained in coal were 0.456 ± 0.118 for pharmaceuticals, 0.792 ± 0.444% for food, and 0.661 ± 0.817% for brick, the highest corresponding value (2.5%) occurred at brick factories of 32, 33, and 34. The main products of pharmaceuticals plants were vaccine, injection, pills, and sterile powder. Coal gangue, coal burning fly ash, and clay were used as raw materials in 31, 1, and 2 of 34 brick factories and the outputs were ranged from 0.150 to 69.41 MY. The main products vinegar, steamed bread slices, bean products, sour milk, and liquor were contained in food factories, which possessed largely variable outputs from 3.00 to 383 MY.


Table 1. Statistics about coal components, output, and yield for pharmaceuticals plants.


Table 2. Statistics about coal compositions, output, and yield for food processing.


Table 3. Statistics about coal compositions, output, and yield of brick factories.


Sampling and Measurement of SO2, NOx, and PM

The pollutants such as gaseous SO2, NOx and CO, and PM originated from all the enterprises were analyzed by a flue gas analyzer (Laoying-3012H, Qingdao LaoYing Environmental Science and Technology, Co., Ltd.) installed at outlet of flue gas after pollutant RFs aimed to investigate the pollutants actually discharged into atmosphere. In addition, the extra information related to temperature and flow velocity (m s1) of flue gas was also provided. A pilot tube was used to the measurement of flue gas velocity and collection of PM. PM mass concentration was calculated as PM mass divided by the volume of sampled flue gas. The gas analyzers were calibrated with zero gas and targeted by standard gases (NOx, SO2 and O2) before the test day to eliminate the possible interferences. The pollutant mass emissions were obtained using pollutant concentrations multiplied by volume of flue gas.

The proximate and ultimate analysis of coal was carried on for access to the information about contents of sulfur, carbon, hydrogen, nitrogen, oxygen, and water. All the analysis processes subordinated to the Chinese standard methods of GB/T 212-2008 and GB/T 476-2001. The same calculation methods of EFs described by Li et al. (2018) were adopted in this study. 


Calculation of Emission Factors Associated with Coal Consumption, Output, and Product

In order to enhance the practical purpose, EFs were provided based on coal consumptions (EFI reported in kg t–1), annual output (EFII reported in kg MY–1), and product (reported in kg t–1). All the EF forms were calculated using Eqs. (1)–(3).

 

where C was mass concentrations of pollutants in flue gas and VFA is the actual flue gas volume originated from combustion of 1 kg coal.

  

VFA was derived from the theoretical air amount required by 1 kg of coal combustion (VAT) calculated by Eq. (4).

 

VAT is the air amount needed for complete burning of 1 kg coal (m3 kg–1), elements C, H, O, N, and S marked by “ar” in the lower right corner indicate the contents of corresponding element in coal on the received basis.

The theoretical flue gas volume generated from burning of 1 kg of coal was calculated using Eq. (5).

  

where VCO2, VSO2, and VNO2 refer to volumes of CO2, SO2, and NO2 derived from burning of coal containing carbon, sulfur, and nitrogen, VN2 is the N2 volume in theoretical air volume (VAT) and calculated as 0.79VAT, and VH2O is the water vapor volume originated from combustion of hydrogen in coal (0.112ω(Har)), vaporization of water in coal (0.00124ω(Mar)), and vapor in air (0.0161VAT).

Finally, the actual flue gas generated from 1 kg of coal burning was calculated by Eq. (7).

 

α is the excess air coefficient and provided by corresponding enterprises. 


VOCs Sampling and Analysis

VOCs sampling and analysis procedure was conducted according to standard method designated by Chinese Ministry of Environmental Protection (HJ 734-2014) for VOCs in flue gas from stationary sources. The whole procedure was simply divided into three steps, adsorption by a stainless pipe for TD-100 system (Markes International, UK), thermal desorption by TD-100, and measurement by a HP6890 GC/5973i MS system. The sampling flow-sheet was shown in Fig. S1. A adsorption pipe placed behind the sampling gun (volume 2 L and at a flow rate of 40 mL min–1) was used to collected VOCs in flue gas. An ice bath impact bottle placed before adsorption pipe to eliminate the water interference. The adsorption pipes pumped into a cryofocus trap (–40°C) to concentrate VOCs and rapidly h desorbed by a TD-100 system , and then transferred to GC-MS system equipped with a DB-1 capillary column (60 m × 0.32 mm × 1.0 mm, Agilent Technologies, USA). The GC oven temperature was set at 35°C, increased to 140°C at 6°C min–1, and then ramped to 220°C at 15°C min–1 and held for 3 min. The calibration standards were prepared by diluting 100 ppbv of PAMS (Photochemical Assessment Monitoring Station, USA) certified gas to 0.5, 1, 5, 15, 50, and 100 ppbv (Yan et al., 2016; Widiana et al., 2017). A sum of 57 VOC species identified and measured in this study was used to represent the total VOCs.

For quality assurance and quality control, all the samples were analyzed within 24 h, and a series of experiments including penetration of adsorption pipe and field blank were conducted every 8 samples. The sampling pipes were heated in highly pure N2 gas (99.999%) at 350°C for 15 min with a flow rate of 40 mL min–1 for activation prior to sampling. 1,4-difluorobenzene and chlorobenzene-d5 were selected as internal standards in samples. A reference standard (1 ppbv) was injected before every testing day to ensure the instrument stability. The method detection limits (MDLs) (reported in µg m–3) for 57 species ranged from 0.1 of C6H14 (CAS: 75–83–2) to 1 of C3H6O (CAS: 67–64–1) with the mean value as 0.45 ± 0.19 (Table 1S). 


RESULT AND DISCUSSION



Emission of Air Pollutants from Pharmaceutical Industries

Although much lower amount of coal linked with heating and concentrating of drug production were consumed compared to coal burning boilers used in LSIs, huge quantities of air pollutants discharged from them due to the lack of pollutant RFs. The information about ash content and sulfur content, and coal consumptions were listed in Table 1. The coal consumptions (reported in t a–1) of 8 pharmaceuticals plants ranged from 150 to 6790 with a mean value as 2339, and showed a weak correlation with their output (R2 = 0.13, p < 0.05), indicated the influence of drug prices. Generally the SO2 RFs occurred in factories with high output values such as P2, P4, and P8, while NOx and VOCs RFs were not equipped among all the 8 factories. As a contrast, all the factories installed PM RFs with the PM RE ranged from 77% to 99%. The emission amounts increased along with the increasing of coal consumptions. Figs. 1 and 2, and Tables S2–S5 listed three types of EFs for each pharmaceuticals factory and mean value of EFs for 8 factories.

The key influencing factors on the SO2 emissions were sulfur content of coal and removal efficiency of SO2 (Li et al., 2018). The drastic fluctuations of EFI and EFII for SO2 occurred among 8 plants and the weak correlation was found between EFI and EFII (R2 = 0.12, p < 0.05), which reflect the greater impact of product prices of different factories. The EFI values ranged from 1.91 to 11.2 kg t–1 (mean: 5.86 ± 2.95), and they were 5.01–231 kg MY–1 (mean: 130 ± 88.3) for EFII (Figs. 1 and 2). The highest SO2 EFI of 11.2 kg t–1 occurred at P1, while the lowest value of 1.91 k g t–1 was attributed to P4. The high Sad (0.70%) of coal and the deficiency of SO2 RFs for P1 were explanations. For SO2 EFII values, the highest and lowest EFII were owned by P3 (231 kg MY–1) and P8 (5.01 kg MY–1), respectively.

The EFs of SO2 for 8 plants could be identified as two categories based on with or without SO2 RFs. Class I including P2, P4, and P8 had a low EFI value (3.01, 1.91 and 2.51 kg t–1) with installed SO2 RFs and high outputs, while high EFI values (6.67 to 11.2 kg t–1) were possessed by Class II (P1, P3, P5, P6, and P7) with low output values (Table 1). The EFI (7.90 kg t–1) and EFII (35.8 kg MY–1) of SO2 for Class II were 3.20 and 5.20 times of corresponding values of Class I. EFI values were well correlated with sulfur contents of coal among 5 plants in Class II (R2 = 0.92), while the weak correlation was found among 8 factories (R2 = 0.52), indicating more strong influence of SO2 RE than sulfur content. The 3 factories within Class I possessed much lower EFII of 35.8 kg MY–1 than mean value of 186 kg MY–1 of 5 plants in Class II. EFII was more affected by product price than coal compositions.

There was little fluctuation for NOx EFI values among the 8 plants compared to corresponding values for SO2, from 1.38 of P4 to 4.18 kg t–1 of P1 with the average value as 2.72 kg t–1. No NOx removal equipment among all the 8 factories should be underlined. The highest NOx EFI occurred at P1 with the coal consumption as 400 t a–1. Drastic emissions of fuel-NOx related to burning of high nitrogen content of coal and thermal NOx associated with high burning temperature in P1 was impetus for the highest NOx EFI (Löffler et al., 2005). EFII values (reported in kg MY–1) of NOx varied from 5.63 of P8 to 93.8 of P3 with the mean value as 56.6 (Fig. 1 and 2). Low NOx EFII values were found for P2 and P8 as 9.96 kg MY–1 and 5.63 kg MY–1, respectively, owning to the high price of products from two factories. The rest 6 factories possessed high NOx EFII values from 27.83 to 93.7 kg MY–1. It should be noted that NOx emission was less influenced by coal quality than SO2 emission due to the different formation mechanisms between NOx and SO2.


Fig. 1. Statistical values of EFI, EFII, and EFIII for 8 pharmaceuticals making factories
Fig. 1. Statistical values of EFI, EFII, and EFIII for 8 pharmaceuticals making factories.


Fig. 2. Mean values of pollutant EFs for 8 pharmaceuticals factories.
Fig. 2. Mean values of pollutant EFs for 8 pharmaceuticals factories.

In regard to PM emissions, the EFI of the 8 factories were in the range of 0.26–7.5 kg t–1, with an average of 3.87 kg t–1 (Fig. 2). Among 8 factories, 4 ones possessed higher PM EFI than 3.87 kg t–1, and the highest PM EFI (7.5 kg t–1) appeared at P1 ascribe to the highest ash contend (20%) (Table 1). The coal with medium ash content based on Ad (ash content on dry basis) was used in these 8 plants, and the highest Aad of 20% in P1 resulted in the highest EFI. P2 owned the lowest PM EFI value resulted from low Aad (6%) of coal. In a word, The PM EFI was mainly subjected to ash content of coal and PM RE of RFs. The PM EFII values exhibited a similar trend with NOx EFII, P2 and P8 owned low values of 1.40 and 4.75 kg MY–1, while they varied from 50 to 191.3 kg MY–1 with a mean as 109 kg MY–1. The product price and coal quality were main influencing factors on PM EFII. So the application of ash removal technologies prior to coal burning was a key factor to reduce the PM emissions.

For the VOCs emissions, P2 and P6 owned much higher EFI values as 22.9 and 15.3 kg t–1 than 0.18–0.40 kg t–1 of remaining 6 factories. A large amount of organic solvents application in two plants and roasting of Chinese medicinal herbs would be contributors to VOCs. In addition, the Vad (volatile contents on air dried basis) values were similar among all the 8 factories and ranged from 28.5% to 31.1%, which further verified the high contributions of organic solvents and related production processes. P1, P2, and P8 exhibited lower EFII levels (0.90, 2.39 and 0.88 kg MY–1) compared to the corresponding values (21.85–41.54 kg MY–1) of the rest 5 factories, which implied the stronger influence of product price and output than nitrogen content and production processes on VOCs EFII values.

 In regard to EFIII values of SNPV for these 8 factories, the average of the 3 factories which equipped SO2 RFs was 86.6 ± 35.5 kg t–1, it was much lower than those 5 factories with the average as 161 ± 92.7 kg t–1. Due to the different drug production processes, higher fluctuation was showed in NOx PM and VOCs values which ranged from 8.35 to 1256 kg t–1, 10.9–1059 kg t–1 and 0.36–951 kg t–1 with the average as 396 ± 211, 328 ± 202 and 313 ± 187kg t–1. In addition, P1 and P5 produced veterinary drugs, P2, P3, and P4 made Chinese patent medicines, while P6, P7, and P8 intended to make western medicines by chemical method.

In addition, three types were also identified based on products as Class I for veterinary drug production (P1 and P5), Class II for production of (P2, P3, and P4), and Class III for making of western medicines by chemical method (P6, P7, and P8). Due to difference of measurement unit of products among different enterprises, it was difficult to conduct a comparing analysis of each other. EFI and EFII values showed not the obvious differences among 8 factories with different target products. 


Emission of Air Pollutants from Food Industries

In this study, coal compositions and pollutant removal efficiencies of SCFBs applied in 9 food factories, and their outputs and products were investigated to obtain the EFs. Although only small amount of coal consumed for heating in 9 food industries, the pollutants produced could not be ignored owning to the pollutant removal equipments behind the times and inferior coal. The coal consumptions (reported in t a–1) of 9 food factories ranged from 120 to 1428 with a mean value as 796, lower than pharmaceutical factories and much lower than brick plants, which showed a weak correlation with the industrial output (R2 = 0.14) due to the influence of product price. 3 of 4 factories with high output values were equipped with SO2 RFs such as P7, P8, and P9, while the rest F4 without SO2 RFs installed regardless of its highest output of 383 MY. The PM RFs installed in all the 9 plants with the PM RE ranged from 67% to 99%, while all the factories were not possessed the NOx and VOCs RFs. Fig. 3, and Table S6–S9 listed three types of EFs for each food factory.


Fig. 3. Values of pollutant EFI, EFII, and EFIII for 9 food processing plants.Fig. 3. Values of pollutant EFI, EFII, and EFIII for 9 food processing plants.

The Pearson's correlation coefficient between sulfur content and SO2 EFI values for 6 factories without SO2 RFs was 0.98, indicated that sulfur content had a great influence on SO2 EFI. The 3 factories owning SO2 RFs possessed much lower SO2 EFI (6.94 ± 2.51kg t–1) than that (10.5 ± 4.05 kg t–1) of the other factories. The highest EFI occurred in F5, as high as 16.0 kg t–1, might be related to the high sulfur content in coal (1%). The average EFI of 9.31 kg t–1 for food processing plants was higher than corresponding value of 5.86 kg t–1, which was attributed to high sulfur content of coal in food plants. Considering SO2 EFII, it showed a different trend compared to EFI, implied the influence of product price beside aforementioned sulfur content and SO2 RE. The average SO2 EFII of the 3 companies with installed SO2 RFs was 326 kg MY–1, far less than that of the companies without SO2 RFs (607 kg MY–1). The highest EFII owner was F6 (2111 kg MY–1) among 9 enterprises, which might be ascribed to its cheap product (vinegar), while the lowest value of occurred at F. Among 3 factories containing SO2 RFs, F9 possessed the highest SO2 EFII of 647 kg MY–1, while P8 owned the lowest value of 5.39 kg MY–1, which were attributed to the differences of coal consumption, product price, sulfur content, and SO2 RE of RFs.

All the 9 enterprises were not equipped with NOx RFs, so the NOx formation processes became the determining factors for NOx emissions. Unlike SO2 forming by combustion of sulfur in coal, NOx mainly originated from oxidation of air N2 at high temperature regardless of that small proportion of NOx formed by burning of fuel-nitrogen (Löffler et al., 2005), so SO2 emissions were more depended on the coal compositions than NOx due to the different formation mechanisms between them. Therefore, NOx EFI values experienced minor fluctuation compared to SO2 EFI, which ranged from 2.58 to 4.72 kg t–1 with the mean value as 3.09 kg t–1. F9 had the maximum NOx EFI (4.72 kg t–1) owning to its high level of nitrogen content in coal, and the minimum value was found in F8 (2.58 kg t–1). Unlike NOx EFI, huge fluctuation existed in NOx EFII values (reported in kg MY–1), varied from 4.44 of F8 to 777 of F6 with the mean as 151 kg MY–1, which was in part resulted from the output difference among 9 enterprises.

The EFI values were mainly determined by two factors such as PM RE values and ash content of coal. The factories with PM REs < 80% owned much higher PM EFI of 7.49 kg t–1 than 2.67 kg t–1 of the other enterprises with PM REs > 85%. The PM EFII values varied significantly from 9.83 to 678 kg MY–1 with an average of 162 ± 194 kg MY1, which was similar to NOx.

It should be mentioned that VOCs EFI of F1 (37.0 kg MY–1) dominated over the remaining 8 factories (0.18–3.08 kg t–1), which was explained by not only the lacks of the VOCs RFs, but also the production process of white spirit. The average plus standard deviation of VOCs EFII was 93.1 ± 184 kg MY–1, which exhibited a significant fluctuation. F1 was the highest among the 9 companies and as high as 624 kg MY–1.

For EFIII values, F1 owned the maximum values of SNPV, the correspondingly lower values occurred at F4 and F8, which reflected the influence of product yield. The EFIII values of 3 companies equipped with SO2 RFs were 4.73, 0.02 and 1.68 kg t–1 respectively with the average was 1.52 ± 2.32 kg t–1, while they ranged from 0.650 to 3.97 kg t–1 with mean value as 2.41 ± 1.35 kg t–1 for the rest factories. Unlike NOx EFII, EFIII values also possessed large fluctuation (0.010–2.00 kg t–1) among 9 enterprises due to the differences of product yields among 9 enterprises. Due to the high emission in F1, the EFIII of VOCs (25.1 kg t–1) was far more than the other factories (0.010–1.16 kg t–1).

Li et al. (2018) discussed the EFs of SO2, NOx, and PM for coal-fired power plants (CFPPs), cement factories, and coking enterprises. Comparing the corresponding values with abovementioned large-scale coal-fired power plants, food factories possessed higher EFI values of SO2, NOx, and PM due to the perfect pollutant RFs in power generation industries. The EFI in food factories (report in kg t–1) were 9.31 ± 4.23 (SO2), 3.10 ± 0.56 (NOx), and 5.01 ± 2.36 (PM), while the cement factories were 4.35 ± 3.01, 7.73 ± 5.98, and 50.7 ± 77.1. SO2 EFI of food factories was lower than cement enterprises due to the SO2 RFs installed in all the cement factories, while higher NOx and PM EFI values occurred at cement industries due to the difference of production processes.


Emission of Air Pollutants from Brick Factories

In this study, 34 small-size brick manufacturing factories using coal gangue, clay, and coal fly ash as raw materials were investigated to analyze the emissions of pollutants and calculate the EFs. Coal consumptions, output values, and product yields differed significantly among different companies. The coal consumptions of these plants ranged from 1.00 × 103 t a–1 to 1.47 × 105 t a–1, the product outputs varied from 1,500 to 150,000 t a–1, and the annual outputs were in the range of 15.0 to 6.94 × 103 MY. In regard to raw materials, 31 of 34 companies applied coal gangue in production process, and 1 and the rest 2 factories used the fly ash used clay in production. Among the 34 factories, only 13 of them equipped with SO2 RFs with the removal rate as 30.0%–88.9%. Owning to the small enterprise size, none of these factories installed the devices to remove the NOx and VOCs. For PM, 31 of them had the DRs with REs ranged from 41.0% to 99.0%.

All the EF values expressed as EFI, EFII, and EFIII for each brick factory were listed in Tables S10–S13. The EFI values about SO2 for 34 brick factories were weak correlated with their sulfur contents in coal, which might be related to the co-burning of coal and coal gangue process and unique smoke venting mode in brick production. Coal gangue containing sulfur contents also resulted in the SO2 formation, which could weaken the correlation between coal containing sulfur contents with SO2 EFI. Co-emission of water vapor from drying process of unfired brick and flue gas from roasting process decreased the temperature of flue gas, further reduce the SO2 REs. Significant difference existed between companies with and without SO2 RFs, the mean value of SO2 EFI for both companies were 3.73 and 9.29 kg t–1, respectively (Fig. 4). SO2 EFI values ranged from 0.65 and 35.0 kg t–1, the highest value occurred in B24 (35.0 kg t–1). The lack of the SO2 RFs and the highest sulfur content of 3.5% could be the reason. EFI values of NOx, PM, and VOCs varied from 0.08 to 2.94 from 0.03 to 6.27 kg t–1; and from 0.02 to 5.33 kg t–1. It should be noted that B7 produced with fly ash emitted the highest PM, which proved the influence of raw materials on pollutant emissions. The significant difference between whether installed the SO2 RFs could explain the rapid EF values.


Fig. 4. EFI values for 34 brick production factories.Fig. 4. EFI values for 34 brick production factories.

Fig. 5 showed the EFII (reported in t MY–1) of these factories, they ranged from 0.68 to 400, 0.42 to 9.41, 0 to 3.24 and 0.06 to 4.52 for SO2, NOx, PM and VOCs, respectively. Fig. 6 showed the EFIII values and for SNPV, the values were ranged from 0.09 to 20.0, 0.05 to 4.82, 0.03 to 1.17 and 0.01 to 2.75 kg t–1, respectively. 13 factories with SO2 RFs showed a lower EFIII values than the other 21 factories without SO2 RFs installed, the mean values were 3.85 ± 4.25 and 7.54 ± 6.53 kg t–1. It should be noticed that the highest EFIII values about SO2, NOx and VOCs all occurred in B25 (20.0, 4.82 and 2.75 kg t–1), the low product yield and the high amount of emission would be the explanations.


Fig. 5. EFII values for 34 brick production factories.Fig. 5. EFII values for 34 brick production factories.

Figs. 4, 5 and 6 also listed the mean values of EFI, EFII, and EFIII of 4 air pollutants. For EFI, the mean values were 7.17 ± 7.49 for SO2, 1.09 ± 0.90 for NOx, 0.56 ± 1.13 for PM and 0.52 ± 0.92 for VOCs. Considering EFII, the mean values were 56.5 ± 94.1 for SO2, 2.74 ± 2.08 for NOx, 0.86 ± 0.82 for PM and 1.15 ± 0.89 for VOCs. In regard to EFIII, the mean values were 137 ± 156 for SO2, 14.8 ± 19.9 for NOx, 4.79 ± 6.72 for PM and 6.79 ± 11.4 for VOCs. In regard to EFIII, the mean values were 5.48 ± 6.25 for SO2, 0.59 ± 0.80 for NOx, 0.19 ± 0.27 for PM and 0.27 ± 0.45 for VOCs.


Fig. 6. EFIII values for 34 brick production factories.Fig. 6. EFIII values for 34 brick production factories.

The obvious fluctuation of EFs occurred among 34 companies owning to the influence of the pollutant removal rates, sulfur contents within coal and coal gangue, ash contents, and conditions of coal combustion.

The EFI values for SO2 and NOx for the CFPPs were much lower than those of brick making factories, the corresponding values in CFPPs and brick factories were 1.03 ± 1.25 vs. 1.04 ± 0.69, and 7.17 ± 7.49 vs.1.09 ± 0.90, respectively (Li et al., 2018). However, the average PM EFI of brick companies was lower than that of CFPPs. The EFI of cement plants were 4.35 ± 3.02, 7.73 ± 5.98, 50.8 ± 77.1 kg t–1, respectively (Li et al., 2018). SO2 EFI values of brick factories were higher than those of cement ones due to the installation of effective SO2 RFs in cement companies, while higher NOx and PM EFI values occurred at cement industries. 


CONCLUSIONS


In this study, 51 companies in Shanxi Province detailed described in methodology part were surveyed for their coal compositions and consumptions, annual outputs, product yields, and pollutant RFs. Also, SO2, PM, and NOx, were on-site measured, and VOCs were sampled and analyzed in laboratory aimed to obtain the pollutant EFs associated with coal consumptions, annual output, and product yield.

Overall the SO2 EFs dominated all the other three pollutants among all the three kinds of companies. The key influencing factors on the SO2 emissions were sulfur content of coal and SO2 RE for food and pharmaceuticals factories, while the sulfur content in coal gangue was also an important factor for brick companies. Increased VOCs emissions could be resulted from the utility of organic solvents in small fractional pharmaceuticals factories and production of white spirit. Unlike SO2 completely originated from burning of sulfur in coal, NOx also could be formed by oxidation of air N2 at high combustion temperature, NOx EFI values experienced minor fluctuations within the same industries compared to the other air pollutants. EFII values for 4 air pollutants for brick factories dominated over the other two kinds of industries due to its low output.

3 of 8 pharmaceuticals factories with SO2 RFs (P2, P4, and P8) possessed SO2 EFI values of 3.00, 1.91 and 2.51 kg t–1, and SO2 EFII values of 16.1, 86.3 and 5.01 kg MY–1. The values of EFI and EFII of SO2 for rest 5 factories were in the range of 6.67 to 11.2 kg t–1, and 74.7 to 231 kg MY–1. The same trends occurred in food and brick factories, the EFI and EFII in food factories were 6.94 ± 2.51 kg t–1, 37.9 ± 24.6 kg MY–1 with SO2 RFs, and 10.5 ± 4.05 kg t–1, 702 ± 715 kg MY–1 without SO2 RFs. In brick factories, the EFI and EFII values were 3.73 ± 3.80 kg t–1, 11.5 ± 12.5 kg MY–1 with SO2 RFs, and 9.29 ± 8.37 kg t–1, 84.4 ± 110 kg MY–1.

The mean value of NOx EFI (in kg t–1) was 2.71 ± 0.78, 3.10 ± 0.56, and 1.09 ± 0.90 for pharmaceuticals, food, and brick companies, and the corresponding NOx EFII values were 56.6 ± 34.3 kg MY–1, 151 ± 223 kg MY–1, and 2.74 ± 2.08 t MY–1.

In terms of coal quality in three types of companies, PM emissions depended on not only the dust RE, but also the ash content in coal. The ash content of coal used in P1 reached 20.0%, and the PM EFI was the highest (7.5 kg t–1) among the 8 pharmaceuticals companies, while their average value was 3.87 ± 2.35 kg t–1. The corresponding PM EFI and EFII were 5.01 ± 2.36 kg t–1 vs. 162 ± 194 kg MY–1 in food factories, and 0.55 ± 1.12 kg t–1 vs. 0.84 ± 0.83 t MY1 in brick factories.

The 2nd and 6th pharmaceuticals factories possessed a prominent VOCs EFI values compared with other plants due to the utility of organic solvents which were 22.9 and 15.3 kg t–1, while the average was 5.03 ± 8.35 kg t–1. The mean value of VOCs EFI in food and brick factories (in kg t–1) were 4.83 ± 10.9 and 0.52 ± 0.92, and EFII were 93.2 ± 184 kg MY–1, 1.15 ± 0.89 t MY–1. The 1st food factory owned the highest EFI value as 37.0 kg t–1 due to the production process of white spirit.

In general, compared with LSIs, SO2 EFs for these SSIs were much higher than those of LSIs such as CFPPs and cement factories, NOx EFs were at the same level with those of LSIs, and PM EFs were much lower than cement factories and similar to CFPPs. 


ACKNOWLEDGEMENTS


This study was supported by the Fundamental Research Funds for the Central Universities (2017MS142) and National Natural Science Foundation of China (21407048).



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