Primary Air Pollutant Emissions and Future Prediction of Iron and Steel Industry in China

China is the largest iron and steel producing and consuming country in the world, which leads to enormous quantities of emitted air pollutants. Direct emissions of air pollutants from the iron and steel industry in China were estimated by developing a process and technology-based methodology using information of the proportion of pig iron, crude steel, and rolled steel produced from different processes and technology. Emissions of sulfur dioxide (SO2), nitrogen oxides (NOx), particulate matter (PM), volatile organic compound (VOCs), and dioxin (PCDD/Fs) were estimated for the year 2012, and future emissions of major pollutants (SO2, NOx, TSP) were projected up to 2030 based on technology developing trends and emission control policies. According to the estimation, 2222 kt of SO2, 937 kt of NOx, 1886 kt of TSP, 555 kt of PM2.5, 254 kt of VOCs, 618 g I-TEQ of PCDD/Fs was produced in China in 2012. Sintering produced 72.4% of SO2, 49.4% of NOx, 22.5% of TSP, 24.0% of PM2.5, 69.6% of VOCs and 98.0% of PCDD/Fs, which is the main emission source. Through faithful implementation of closing down outdated production and emission control policies, approximately 77%, 49%, 67% and 64% of SO2, NOx, TSP and PCDD/Fs emissions, respectively, could be further reduced in 2012. Emissions in 2020 and 2030 of iron and steel sectors were predicted applying scenario analysis. The removal potential for SO2 and TSP is larger than NOx by improvement of removal facilities, and southwest, northwest, and north China has the largest SO2, NOx, TSP and PCDD/Fs removal potential respectively.


INTRODUCTION
China is the largest iron and steel producing and consuming country in the world.Crude steel production in China was 717 million metric tons in 2012 (NBS, 2013), which accounted for 46% of the world's production (WSA, 2013).The iron and steel industry is the highest in energy consumption, pollution, and consumption of resources-based industries, which leads to enormous quantities of air pollutants emitted, including SO 2 , NO x , PM, VOC, and PCDD/Fs, resulting in significant regional and global environmental problems.In China, the iron and steel industry has been identified as an important source of pollution.For instance, SO 2 and TSP emissions from smelting and pressing of ferrous metals account for 12.6% and 17.6% of all industrial sources (CEYEC, 2012).What's more, iron and other metal production contributed 49% of total national atmospheric PCDD/Fs emissions (Lv et al., 2008).
Since China's iron and steel industry is an important emission source of several types of air pollutants, the systematic and reliable estimation of its emissions is essential for atmospheric modeling and air pollution policy-making.Much research on emission inventories involving the iron and steel industry in China has been done.Some emission inventories of primary air pollutants for China treat the iron and steel industry as a part of the industrial sector, roughly estimating its emissions based on coal and oil consumption (Streets et al., 2003;Ohara et al., 2007).Some emission inventories estimate the emissions of the regional iron and steel industry (Zheng et al., 2009;Tang et al., 2012); some take processes into account, such as the Huabei region emission inventory (Zhao et al., 2012) and national key iron and steel plants emission inventory (Lei et al., 2008).Moreover, there have been many studies measuring or investigating the emissions of iron and steel equipment, including SO 2 , NO x , PM, VOCs, PCDD/Fs (Gong et al., 2008;Lei et al., 2008;Tsai et al., 2008;Lu et al., 2009;Ma et al., 2009;Zou et al., 2012;Yang et al., 2013).In this work, we developed an emission inventory of major air pollutants from China's iron and steel industry based on detailed activity level (provincial production, iron and steel plants location, production technology, production equipment, emission control facilities and so on) for 2012, and we tentatively predict future emissions in 2030 through scenario analysis, considering different levels of iron and steel production and control measures; existing and possible future regulations were taken into account as well.

Methodology
The study regions covered mainland China including 22 provinces, five autonomous regions and four municipalities (exclusive of Hong Kong, Macau, and Taiwan because of the limited data).Geographical locations of registered iron and steel enterprises in China are shown in Fig. 1.
The emission inventory developed here includes four gaseous air pollutants (SO 2 , NO x , VOCs, and PCDD/Fs) and PM in two different size ranges: PM 2.5 (particulates with a diameter less than 2.5 µm), and TSP (Total Suspended Particulate).The processes of iron and steel production considered in this study include emissions from sintering, pelletizing, iron-making, steel-making, steel rolling and unorganized emissions, while coking is not included because it is a fuel preparing process rather than a producing process; the producing processes and emission links are shown in Fig. 2.
Emissions from the iron and steel industry of each province in China were calculated based on province-level iron and steel industrial production and emission factors (EFs), and then aggregated to the regional level.Emissions of SO 2 , NO x , PM, VOC, and PCDD/Fs from iron and steel industries at the provincial level were calculated using Eqs.(1)-( 5) respectively: , , , , , , where subscripts i, k, m, n and y stands for province, production process, production technology, emission control technology and particulate size; A is the production; EF is the emission factor without control; ef is the real emission factor; C is the application rate of emission control technology; η is the removal efficiency of emission control technology; and f is the particulate fraction by size.

Activity Level
National iron and steel industry production in 2012 was 809.9 Mt of sinter ore, 135.6 Mt of pellets (CMISI, 2012), and 663.5 Mt of pig iron, 723.9 Mt of crude steel, 955.8 Mt of rolled steel, maintaining 15% growth rate since the year of 2000 (NBS, 2012), as shown in Fig. 3. Fig. 4 shows an imbalance of production among provinces and regions,   Hebei had the largest iron and steel production (NBS, 2012).There are no statistical data for provincial sinter ore and pellets production, therefore, they were estimated from the provincial pig iron production.The pelleting production technology (3% of shaft furnace, 35% of grate-kiln, and 62% of belt roaster pelleting) rate was estimated from the 2009 rate data (MPI, 2009).Steel-making production (converter and electric furnace steel) for each province in 2012 was estimated from the historical provincial capacity of converter and electric furnace steel.A breakdown of national rolled steel production in 2012 is available (ASKCI, 2012).The national scale distribution of production devices in 2012 refers to China Steel industry Yearbook 2012.

Sintering and Pelleting
Belt sintering technology was the only technology applied in the sintering process, and pellets producing was divided into three technologies: shaft furnace, grate-kiln, and belt roaster pelleting.Almost all of China's long process iron and steel enterprises produce sinter ore for their own ironmaking, and there was no significant difference in the amount of sinter ore consumed per pig iron production; the amount of sinter ore and pig iron production was positively correlated (Lei, 2008).Pellets are also required iron-making raw materials; generally, 20% to 30% ratio is considered reasonable (Du et al., 2011).
During the "Eleventh Five-Year" period, China's sintering capacity above 90 m 2 rose from 67.9% to 85.2%.With the development of the large-scale blast furnace, the quality of shaft furnace pellets gradually cannot meet the needs of blast furnace iron-making, under this situation, so gratekiln pellet production technology has developed rapidly, and its capacity increased to 61.7% in 2009 (MPI, 2012).

Iron-Making
Iron-making technologies can be divided into blast furnace technology, direct reduction iron (DRI) technology, smelting reduction iron-making (COREX), and so on.Blast furnace iron production produced in China increased from 23% to nearly 60% of the worldwide from 2000 to 2010, while the DRI production was less than 1% (Qi et al., 2013).

Steel-Making
The BOF (basic oxygen furnace) steelmaking and EAF (electric arc furnace) steelmaking methods are the two main steelmaking processes.The proportion of EAF steel production fluctuated around 10% due to lack of resources and a shortage of electricity scrap, and there is a large gap compared with the proportion of the world's 30% EAF steel.China's EAF steel production was 64.5 million tons in 2012, accounting for 8.9% of total crude steel production.The EAF steel production of each province was estimated according to total output and provincial EAF steel capacity, for lack of statistical data.

Steel Rolling
Hot rolling and cold rolling are both steel-rolling technologies.In recent years, China's steel enterprises have made remarkable progress in the modernization of rolling equipment.China's rolled steel production was up to 955.78 million tons, with every type shown in Fig. 5 (ISA, 2013).

Emission Factors (EFs) SO 2
About 50% of SO 2 comes from the oxidation of sulfur in coal and coke (Hu et al., 2008) in the sintering and pelleting process, therefore, we correct provincial SO 2 emissions combined with sulfur content of coal and iron ore for each province (Zhao et al., 2008;MPI, 2012), as shown in Fig. 6.In a sintering machine and pellet furnace, exhaust gas contained with SO 2 is emitted, while in the blast furnace, most of the sulfur is absorbed in the slut by reaction.Since sintering and pelleting are the main SO 2 emission processes, sulfur removal equipment is mainly adopted in these processes, while sintering and pelleting gas desulfurization was started in 2012, and the national average efficiency was 38.6% (MEP, 2013).Sulfur removal equipment put into operation was 389 of sintering and 44 of pelleting, respectively, in 2012 (MEP, 2013).
By 2012, the proportion of WFGD of the sintering process reached 73.1%, and limestone-gypsum FGD was the most popular technology applied, which occupied nearly half of all FGD, as shown in Fig. 7 (MEP, 2013).

NO x
For sintering and pelleting processes, generation of NO x is mainly formed by reaction of nitrogen from the solid fuel or raw material and oxygen from the air at high temperature; and for the exhaust gas from the heating furnace of ironmaking and steel rolling processes, it is highly dependent on temperature and oxygen availability.Until 2012, few NO x removal equipment was put into operation in iron and steel industries because of the high emission limit; we therefore dismiss NO x emission control.

PM
The EFs of PM are dependent on both the characteristics of uncontrolled emissions from the overall production processes and the effectiveness of PM emission control devices, and the uncontrolled emissions are dependent on the type and scale of production devices.Dedusting Engineering Technical Specification of Iron and Steel Industry (MEP, 2008) was released in 2008, which explicitly specifies system and installation of dedusting devices in almost every PM emission node.In this study, we assume dedusting facilities were adopted in the mentioned processes of every iron and steel industries.

VOCs
The EFs of VOCs of the iron and steel industry were mainly gained from domestic research (Lei, 2008;Tsai, 2008).In general, the sintering process, the heating furnace, and the BF are the major VOCs sources.

PCDD/Fs
For iron and steel industries, PCDD/Fs is formed in   sintering and electric steelmaking processes.The EFs were given in quite a few studies measuring PCDD/Fs concentration in sintering and electric furnace gas in China (Gong, 2007;Lu, 2009;Zou, 2012).
All the selected emission factors are shown in Table 1.

Regional Emissions in 2012
Emissions inventories of SO 2 , NO x , TSP, PM 2.5 , VOCs, and PCDD/Fs of the iron and steel industry in 2012 were calculated based on the provincial activity data and emission factors.Fig. 8 show contributions of each iron and steel production processes.SO 2 emission from the iron and steel industry was estimated to be 2,222 kt.As listed in Table 2, five provinces emitting over 100 kt each were Hebei, Shandong, Jiangsu, Liaoning, Shanxi, emitting a total 1,237 kt (56% of nationwide emissions of iron and steel industries).Sintering and pelleting were the main processes emitting SO 2 , contributing 84% to the total emissions.Large SO 2 emissions are attributed to three factors: high sulfur content of solid fuel and iron ore; undistributed desulfurization facilities of sintering machine (50% of national sintering machine area applying desulphurization) and low desulfurization efficiency.
NO x emission from the iron and steel industry was estimated to be 937 kt.(56% of nationwide emissions of iron and steel industries).Sintering and pelleting were still the main processes emitting NO x , contributing 57% of the total emission.DeNO x facilities were few, which largely depended on high emission standard limits.
The primary TSP emission was 1,886 kt from the iron and steel industry, approximately 15% of the total eissions.Three provinces emitting over 150 kt each were Hebei, Shandong, Shanxi, emitting a total of 703 kt (37% of nationwide emissions of iron and steel industries).Although clear dedusting specification was published in 2008 and PM removal facilities were popularized in 2012, TSP emission was high because the dedusting effect of plenty of iron and steel plants was still to be improved, and there were still some gaps compared with international, advanced steel plants.Annual PM 2.5 emissions were 555 kt from iron and steel industry, approximately 29% of the total particles.
VOCs emissions were 254 kt from the iron and steel industry.Hebei, Jiangsu, and Shandong emitted 43% of VOCs from the iron and steel industry.PCDD/Fs emissions were 618 g I-TEQ (the scheme of TEF values agreed by NATO (1988), known as the International Scheme).
Iron and steel enterprises from east and north China emitted more than 60% of mentioned atmospheric pollutants nationwide.

Spatial Distribution of Emissions
The comparison each region of air pollutants emissions showed that north and east China were the main sources, accounting for 61.0% of SO 2 , 62.8% of NO x , 58.4% of PM 2.5 , 59.5% of TSP, 63.0% of VOCs, and 61.0% of PCDD/Fs.

FUTURE EMISSIONS AND MITIGATION POTENTIAL
Accurate emission projections are necessary since emissions from China's national iron and steel industry were a main source of air pollutants.In this study, both iron and steel production and emission control strategies of the iron and steel industry in 2020-2050 were evaluated through scenario analysis for future emission projection.

Production Forecast
Owing to total amount control and implementation of emission control policy, the emissions of iron and steel production should be further restrained in the future.In this study, base (B), normal (N), and strict (S) emission control scenarios were assumed in 2012-2030.We selected the production data of crude steel from Medium and long-term research and development strategy on energy in China (CAE, 2011) in 2020 and 2030, and extrapolate production of pig iron and rolled steel equal proportion to the year of 2012, as shown in Table 3.
The share of EAF is still low in China (about 10% in 2012) because of the limitation of scrap and electricity.However, EAF has many advantages, such as low investment and low emission, which means it has development potential in the future.As the steel demand decreases, the scarp of China will show a rapid growth, which would result in rapid growth of the share of EAF (Hu et al., 2009).We assume in 2020 the share of EAF will increase to 20%, and then increase to 30% in 2030, which is also close to the average OECD level.The share change of EAF and BOF is listed in Table 3.

Emission Control Policy
The key features of technology and scale of the iron and steel industry are projected based on the existing policies on industry structure (NDRC, 2011;MIIT, 2010).
After 2010, the iron and steel industry has become an important emission control source.According to Iron and Steel Industry in the Twelfth Five Year Plan, sintering and pelleting equipment must be equipped with FGD before 2016.In this study, base, normal, and strict scenarios were designed to describe different emission control policies or emission limits.The base scenario is a pessimistic one in which the production status and emission control for all the species would remain at the same proportion.The normal scenario emphasizes the implementation of closing and substitution of small plants capacity, and the improvement   4.

Emissions Projection
Current emission standards have promoted the use of various emission control technologies in each process; however, the level of emission control in China's iron and steel industry is still lower than that of advanced countries.There is potential to substantially reduce the emission of air pollutants from the iron and steel industry in China if advanced control technologies are used.
SO 2 emission is now the major focus of air pollution control from the iron and steel industry in China.According to Twelfth Five Year Plan of Iron and Steel Industry, desulfur facilities should be equipped by all sintering machines before 2015, and all sintering machines are required to meet an emission standard of 200 mg/m 3 flue gas, as of 2015 (SEPA, 2012), which equates to a SO 2 EF for the whole PM removal device is also effective for PCDD/Fs removal because of high share of particle-phase PCDD/Fs, while solutions must be sought to avoid the emission of not only the particle-phase but also the gas-phase PCDD/Fs.In our normal and strict scenarios, during 2012-2030, PCDD/Fs should decrease by 42%-64%.In 2030, PMTSP emission should decrease by 99.8 g I-TEQ and 92.3 g I-TEQ under the strict control scenario compared with the base control scenario in east China and north China.
The emission of SO 2 , NO x , TSP and PCDD/Fs under different scenarios in 2030 are shown in Fig. 9.
To sum up, the potential for SO 2 TSP mitigation was larger than NO x because of the improvement of removal facilities, and the potential for PCDD/Fs emission reduction was considerable compared with world advanced level.It implies that the implementation of control policies in north China and east China would have a significant influence on emissions, while the closing and substitution of small plants capacity would produce little effect.

CONCLUSIONS
The iron and steel industry plays an important role in emissions of many air pollutants in China.We estimated the emissions of primary air pollutants from the iron and steel industry based on information on the development of production technologies and equipment scale, pollutants removal situation, and rising emission standards in China's iron and steel industry.The emissions inventory indicated that sintering was the main emission source which produced 72.4% of SO 2 , 49.4% of NO x , 22.5% of TSP, 24.0% of PM 2.5 , 69.6% of VOCs, and 98.0% of PCDD/Fs of the entire iron and steel industry in China in 2012.Our analysis shows that SO 2 and TSP emissions of the iron and steel industry could be effectively controlled with the measures of the wide application of FGD and high-efficiency PM control facilities; and the implementation of control policies in north China and east China would have a significant influence on emissions.There were few DeNO x facilities due to the high emission limit; NO X control policies being followed through in the future will reduce NO x emissions greatly in the iron and steel industry.Due to the scenario analysis, southwest, northwest, and north China has the largest SO 2 , NO x , TSP and PCDD/Fs removal potential, respectively.
On the other hand, the direct cause of air pollution in the steel industry is mainly dependent on coal and coke energy, and while the DRI industry is able to reduce reliance on coke, it is an energy-saving, low-emission iron-making technology and has good development prospects in China.

Fig. 1 .
Fig. 1.Geographical locations of the 10 839 iron and steel enterprises in China.

Fig. 2 .
Fig. 2. Processes and emission links of iron and steel industry.

Fig. 3 .
Fig. 3. Iron and steel production in China from 1990 to 2012.

Fig. 4 .
Fig. 4. Iron and steel production by region (N: North China, NE: Northeast, E: East China, C&S: Center and South China, SW: Southwest China, and NW: Northwest China).

Fig. 8 .
Fig. 8. Regional emission inventory of (a) different processes and (b) contributions of different processes.

Table 2 .
Emission estimate by region in 2012.

Table 3 .
Iron and steel production change from 2012 to 2030.

Table 4 .
The average removal efficiency and emission concentration in 2020 and 2030.

Table 5 .
The iron and steel sector emissions during 2012-2030 under different scenarios.