Mercury in Polish Coking Bituminous Coals - ACS Publications

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Mercury in Polish Coking Bituminous Coals Piotr Burmistrz, Krzysztof Kogut, Marta Marczak, Tadeusz Dziok, and Jerzy Górecki Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.7b03512 • Publication Date (Web): 11 Jan 2018 Downloaded from http://pubs.acs.org on January 11, 2018

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Mercury in Polish coking bituminous coals Piotr Burmistrz a, Krzysztof Kogut a*, Marta Marczak a, Tadeusz Dziok a, Jerzy Górecki a a

AGH University of Science and Technology, Faculty of Energy & Fuels, Mickiewicz Avenue 30, 30-059

Krakow, Poland

ABSTRACT: Poland emits 10.58 Mg of mercury to the atmosphere annually. More than 90% of this emission is generated by combustion and thermochemical usage of coal, including coking. In Poland, the coking industry consumes more than 12 million Mg of bituminous coals each year. Contrary to lignites and subbituminous coals used in power plants, there is not much reliable data on mercury content in Polish bituminous coals. The purpose of this paper was to determine mercury content in bituminous coals delivered to Polish coke plants and to analyze possible removal of mercury during coal cleaning processes. 82 samples from 9 mines were analyzed. The average mercury content varied from 28.4 to 182.6 µg kg–1 with mean value of 75.9 µg kg–1. The analysis of mercury content in three coals treated by (i) flotation, (ii) dense-media washing, and (iii) jig washer cleaning, revealed that mercury content in relation to net calorific value can be reduced by 27% (flotation) to 71% (dense-media washing). In addition, distribution of mercury, ash, and sulfur between products and rejects in the process of coal cleaning was determined. For this purpose samples of raw coals, clean coals, middling products and rejects derived from six coal preparation plants were examined (67 samples). The publication presents the mercury balance results for bituminous coal coking. The mercury is transferred to coal tar (75%, mean mercury content 2007 µg kg–1), coke (6%, 7.5 µg kg–1), sulfur (2%, 2998 µg kg–1) and purified coke oven gas (3%,7.5 µg m-3). Balance data shows that almost 14% of mercury is emitted to the atmosphere during the process of filling the coke oven chambers with coal.

1. INTRODUCTION Mercury is a highly toxic heavy metal, one of three for which the human body has no physiological demand. Due to its toxicity, easy dispersion from emission source and long average

ACS Paragon Plus Environment

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atmospheric residence time1, mercury and its compounds have been classified by the US Environmental Protection Agency (US EPA) as Hazardous Air Pollutants (HAPs).2 Worldwide studies commissioned by the United Nations Environment Programme (UNEP) confirmed harmfulness of mercury that justifies actions on an international scale.3 Global anthropogenic mercury emission to the atmosphere is estimated at approximately 2000 Mg per year.4,5 Combustion and processing of coal accounts for the second largest share (25%) in total mercury emission. In 2014 EU countries emitted 58.38 Mg of mercury, 83% of which was due to industrial coal usage.6 Poland is responsible for one of the highest mercury emissions in Europe. According to the National Centre for Emissions Management (KOBiZE), mercury emission in Poland in 2014 amounted to 10.58 Mg. This was mainly due to coal combustion in power and heat plants (49.6%), industrial combustion processes (35.1%), non-industrial combustion (9.3%), and production processes (5.6%).7 Thus, more than 90% of mercury emitted to the atmosphere in Poland was due to coal-related processes. Mercury content in coals is relatively low, between several tens and hundreds of µg·kg–1.8–12 However, due to the immense scale of coal consumption, mercury in coal constitutes a major threat to the environment. Mercury present in coals is bound to both mineral and organic matter. The share of mercury bound to mineral matter (so-called inorganic Hg) is 54–63%.13 Numerous studies confirm that from 10 to 60% of mercury in coal can be removed during coal cleaning processes.14,15 Mercury is mainly bound to sulfide minerals like pyrite.10,16,17 37–46% of mercury is bound to organic matter, mainly as thiol groups.13,18,19 The physical form of mercury in coal varies depending on the coal source.20 Thermoscaning technique enables assessment of the mercury removal potential in the coal cleaning process.21 Average mercury content in Polish subbituminous coals varies from 25 to 300 µg·kg–1, whereas in Polish lignites from 100 to 450 µg·kg–1.8–10 There is no reliable data on mercury content in Polish bituminous coals. These coals are used for production of metallurgical coke in high temperature pyrolysis, which consists of many sub-processes, including pyrolysis of a coal mixture in a coking chamber and cooling and cleaning of volatile products of coal pyrolysis. These are responsible for the


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generation of products and by-products that contain mercury: coke, purified coke oven gas, coal tar, BTX (benzene, toluene and three xylene isomers), and sulfur. Some mercury is emitted to the atmosphere during the filling of coke oven chambers. Contrary to lignites and subbituminous coals used for energy production, bituminous coal is often cleaned. The coal cleaning process may lead to a reduction of mercury content in coal.14,15 The purpose of this paper was to determine mercury content in bituminous coals delivered to Polish coke plants and to analyze possible mercury removal during coal cleaning processes. 82 samples from 9 coal mines were analyzed. In addition, this paper describes the results of mercury content analysis after treatment of coal using several processes, including: (i) flotation, (ii) densemedia washing, (iii) jig washer cleaning. Mercury balance in the coking process for Polish bituminous coals was also calculated. 2. EXPERIMENTAL SECTION 2.1.

Bituminous coal sampling Samples of Polish bituminous coals used for coke production were acquired from shipments

delivered to three Polish coke plants. A total of 82 samples from 9 coal mines were collected over a two year period (2014–15). Automated samplers acquired samples from conveyor belts in motion in accordance with ISO standard.22 Each sample represented a coal batch of 1400–2400 Mg. Sampling, sample handling and analytical sample preparation schemes are shown in Figure 1. Laboratory analyses are described in section 2.2. 2.2. Analysis of bituminous coal samples Air-dried samples were prepared according to ISO standard.23 The scope of analysis included: proximate and ultimate analysis in accordance with ISO standard,24,25 combustion in bomb calorimeter with Eschka mixture, chlorine content by potentiometric titration and mercury content with absorptive atomic spectrometry with cold vapor (CV-AAS) generation in automated mercury analyzer MA-3000 (Nippon Instruments Corporation). The swelling properties of coal samples were determined when heated under standard conditions in a dilatometer.26


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Values of these parameters were determined in the analytical basis (air-dried) and afterwards recalculated to bases: dry (d), dry ash free (daf), and as received (ar) according to recalculating equations from ISO standard.27

2.3. Analysis of mercury removal during the coal cleaning process The scheme of industrial scale coal cleaning is shown in Figure 2. In Poland, two major coking coal cleaning systems are used: trisectional (Figure 2a), and bisectional (Figure 2b). In the trisectional system, raw coal is divided into three fractions depending on grain size. Each fraction is processed as follows:28 (i) cleaning by dense medium washer for grain class > 20 mm, (ii) cleaning by jig washer for grain class 20–0.5 mm, and (iii) cleaning by flotation for grain class < 0.5 mm. In the bisectional system, raw coal is divided into two grain fractions that are processed as follows: (i) cleaning by coarse jig washer for grain class 70–0.5 mm and (ii) cleaning by flotation for grain class < 0.5 mm. Samples were collected from six coal processing plants (CPP). Four used the trisectional system (CPP1, CPP3, CPP5, CPP6) and two used the bisectional system (CPP2, CPP4). Samples of raw coal, coal sub-fractions for each individual process and (i) middling products, (ii) by-products and (iii) concentrates were collected. The analytical sample was prepared from each sample and analyzed as described in section 2.2. 2.4.

Mercury balance during the coking process Mercury balance during the coking process was analyzed in one of the Polish coke plants. The

source was the coal mixture containing seven bituminous coals analyzed in section 2.1. The scheme of the analyzed system is shown in Figure 3. The coke oven chambers were filled with the coal mixture. The pyrolysis process was conducted in a battery with a production capacity of 560 000 Mg of coke per year. The coke was quenched in a dry quenching installation and the coke oven gas was processed as follows: (i) cooling in the collector and pre-coolers, (ii) ammonia absorption in the scrubber, (iii) catalytic decomposition of ammonia, (iv) production of sulfur from hydrogen sulfide using Claus installation, (v) absorption of benzo-hydrocarbons by scrub oil.


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Thus, the following products are achieved from the coal mixture during the coking and purification of raw coking gas processes: (i) coke, (ii) coal tar, (iii) BTX, (iv) sulfur and (vi) purified coking gas. At least 5 samples were collected from each stream of both resources and products of the coking process over a one month period. Analysis was performed for each sample, including, among others, the determination of mercury and moisture content (see section 2.2). Data on flow of each stream during the balance period was acquired from service control reports in the coke plant. Mercury content was determined in accordance with an original, self-developed methodology. Purified coking gas was isokinetically aspired from the pipe and directed into three parallel lines located in the thermostatic container. The temperature of the container was similar to the gas temperature. Each line contained six mercury traps, 3 of which were composed of sorbent (containing 75% SiO2, 10% Al2O3, 7% Fe2O3). The other 3 traps were composed of activated carbon. The gas flow was approximately 12 dm3 h–1, with incubation time around 45 m. Mercury content for each of 18 mercury traps was determined using the MA-3000 analyzer (Nippon Instruments Corporation) in accordance with the methodology described in section 2.2. 2.5.

Statistical analysis The following statistics were calculated for each parameter of studied coal, resources and coal

cleaning products and for resources and products of the coking process: arithmetic mean, standard deviation (SD), variability coefficient (CV), expanded uncertainty at 95% confidence level. The measure of reliability for a single examination of an analytical sample is the uncertainty of the result considered as the uncertainty that includes: sampling, preparation of the general sample, preparation of the analytic and laboratory samples and the analysis itself. The detailed procedure was described previously.29

3. RESULTS AND DISCUSSION 3.1. Mercury analysis in coal, resources and products of coal cleaning and coking processes Validation study results have shown that the CV-AAS method using the MA-3000 mercury analyzer is accurate for bituminous coals, resources and products of coal cleaning process in the range


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of 25–300 ppb in an air-dried basis. The limit of detection was 0.002 ng and the limit of quantification was 0.006 ng. This method is highly linear (r = 0.9999) and the uncertainty at 95% confidence level ranges from 3 to 10%, depending on the range. The CV-AAS method shows acceptable repeatability and reproducibility across the whole range of the method. Analysis of mercury content in coke oven gas has shown that the first sorbent section (the activated carbon) has adsorbed almost all of the mercury (99.1% of total mercury adsorbed on all traps on average). The difference between the individual lines probably emerges from differences in flow resistance that result from different packing of the traps. Total mercury mass adsorbed in the traps for a single coking gas sample ranged from 60 to 70 ng. Uncertainty at 95% confidence level for mercury content in gas was ±0.2 µg m–3. 3.2.

Mercury content in coal Table 1 SI contains the complete results for 82 analyzed bituminous coal samples from 9 Polish

mines. Mercury content ranged from 28.4 to 182.6 µg kg–1 (see Figure 4), with a mean value of 75.9 µg kg–1 and the variation coefficient was 50.5%. In 77% of analyzed samples mercury content was below 100 µg kg–1. Higher values were measured for 20 samples from 3 mines. The mercury content was not correlated with the degree of metamorphism of analyzed coals, as witnessed by a low correlation coefficient value of r = 0.193 between mercury and volatile matter (see Figure 5a). A significantly higher correlation with mercury content was determined for ash. Figure 5b shows the correlation between mercury and ash contents (r = 0.465). A high correlation was determined for mercury and total sulfur content (r = 0.731) (see Figure 5c). This is in agreement with previous reports 10,12,30,31

, where the dominant form of the mercury in Polish coals is bound to sulfides, particularly

pyrite.10 Table 1 shows the parameters of cleaned coals from 9 Polish mines. Coals from 6 mines contain less than 100 µg Hg kg–1, with an average content of 47.7 µg kg–1. The purpose of coal cleaning is to remove mineral matter, which is required by coking technology. In case of these coals, the mercury was removed along with mineral matter. Mean mercury content in coals from the other 3 mines was around 110 µg kg–1. These coals are cleaned to achieve an ash content of 6.4 to 8.6%, but this does not


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reduce the mercury content significantly. Mercury in these coals is bound to organic and/or so-called internal mineral matter and it is not removed from coal during the cleaning process.10, 32 The range of mercury content variation fit between CV = 7.8% (mine No. 9) and CV = 35.1% (mine No. 4). The mean value of the variation coefficient for mercury content in bituminous coal shipments from 9 mines was 24.2%. Figure 6 shows mercury content in coal shipments from coal mine No. 4 (Figure 6a) and No. 9 (Figure 6b). Coal from mine No. 4 was characterized by one of the highest (next to mine No. 7) variations in mercury content in the analyzed coal shipments, varying from 69.5 to 167.4 µg kg–1, whereas coal from mine No. 9 had the most stable mercury content, ranging from 28.4 to 33.2 µg kg–1. Coking coal mixtures are composed to optimize their coking properties (contraction a and dilatation b) and volatile matter content, not mercury content. Considering that the analyzed coals constitute more than 90% of coals used by Polish coke plants, it can be stated that Polish coking coal mixtures contain 80–100 µg of mercury per kg. With annual coking coal consumption in Poland of 12 million Mg, coking-related mercury emission amounts to 960–1200 kg per year. 3.3.

Bituminous coal cleaning In a typical Polish bituminous coal cleaning installation, the coal load is divided into two

(70–0.5 mm, < 0.5 mm) or three grain size fractions (> 20 mm, 20–0.5 mm, < 0.5 mm). In general, the lower the grain size, the higher the mercury content (see Table 2 SI). The average mercury content values for different grain size fractions were as follows: 91 µg kg–1 (> 20 mm), 116 µg kg–1 (70–0.5 mm), 102 µg kg–1 (20–0.5 mm) and 133 µg kg–1 (< 0.5 mm). A negative correlation was observed for ash. The highest ash content was measured for the > 20 mm fraction (mean 58.4%) and the lowest for the < 0.5 mm fraction (25.2%). Fractions of 70–0.5 and 20–0.5 mm contained 41.2% and 30.5% of ash, respectively. Similar to mercury, the highest sulfur content was observed for the < 0.5 mm fraction (mean 0.52%). The lowest sulfur content was observed in the > 20 mm fraction (mean 0.30%). These results suggest a possible link between mercury and sulfur in Polish bituminous coals.


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During the dense media washing process, ash removal was 90.4% on average, whereas enrichment by jig washer, fine coal jig washer and flotation were 84.5, 80.3, and 69.0%, respectively. This resulted in an increase of the calorific value of cleaned coals (see Table 2 SI). Mercury was removed to a lesser extent than ash. In some cases mercury content increased during the coal cleaning process. Average mercury removal during dense media cleaning was 50.6%, only 12.6% by jig washers, and 18.5% in the flotation process. This can be explained by the presence of mercury in both organic and internal mineral matter. It was noted that sulfur content decreased in only 2 samples. In the remaining 14 samples, sulfur content increased during the cleaning process. A relatively low mercury removal during coal cleaning processes and much more efficient removal of mineral matter resulted in an evident reduction of mercury content to calorific value ratio Hg qp.net–1 (see Table 2 SI and Figure 7). This reduction was observed for flotation (31.3%), fine coal jig washer (49.0%), jig washer (40.1%) and dense media cleaning processes (74.3%). The parameter value for clean coal ranged from 1.182 to 7.182 g Hg TJ–1 (mean 2.818 g TJ–1). This parameter for Polish subbituminous coals, which are practically not cleaned, is 4.591 g TJ–1 on average, sometimes exceeding 20 g TJ–1.9 Middling products are generated during the cleaning process. These are widely used for energy production. The analysis has shown high mercury content, ranging from 119 to 313 µg kg–1 with a mean value of 206 µg kg–1. The Hg qp.net–1 parameter ranged from 4.533 to 24.000 g TJ–1 (mean 11.874 g TJ–1), which is significantly higher than values for subbituminous coals.9 The sequence of individual processes during cleaning of bituminous coal determined mercury content value in the concentrate directed to the coke plant. The comparison between raw coals and final concentrates is shown in Table 3 SI. Characteristics of the concentrates were calculated based on mean shares of individual cleaning processes. Mercury content in raw coals varied from 60 to 117 µg kg–1, and in concentrates from 39 to 127 µg kg–1, as calculated for the air-dried basis. In half of analyzed cases mercury content was lower than in raw coals and higher in the other half (CPP1, CPP2, CPP4) – Figure 7a. It must be noted, however, that the Hg qp.net–1 parameter was lower for concentrates (1.166–3.921 g TJ–1) than for the raw coals in all cases (2.256–8.294 g TJ–1) – Figure 7b.


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Figure 8 shows mercury distribution between concentrates, intermediates, and waste products. From 9 to 62% of mercury was directed to the concentrate. The highest volume of mercury was transferred to the concentrate in jig washers (11–33%), followed by dense media cleaning (2–18%), and the flotation process (2–13%). For each of the analyzed processing installations, the coal cleaning process allowed significant transfer of mercury from coal to waste products (from 23 to 69% of mercury overall; 23–50% for bisectional cleaning, 38–69% for trisectional cleaning). The share of mercury in middling products varied between 0.1 and 42%. In case of CPP2 and CPP4, the high share of mercury in middling products can be explained by high mercury content and deliberate production of middling products for energy production. In addition, in CPP2 the small grain fraction for energy production was acquired during the initial separation. 3.4.

Mercury mass balance during coking of bituminous coal The mass balance for the coking process conducted over a period of one month was as follows:

coking of 1 Mg of dry input yields: (i) 762 kg of dry coke, (ii) 185 kg of purified coking gas (370 m3·Mg–1 of coal with an average gas density of 0.5 kg m–3), (iii) 34 kg of coal tar, (iv) 9 kg of BTX (v) 1 kg of sulfur. The missing 8 kg Mg–1 of dry coal (0.8%) is due to unmeasured ash emission during the filling of the coking chamber and uncertainty of measurements. Average mercury content in coked coal was 91.5 µg kg–1, with a variation coefficient of CV = 10.9% (see Table 2). Sulfur from the Claus installation had the highest mercury content in all coking products. Average mercury content in sulfur was 2997.6 µg kg–1, varying from 2140 to 4380 µg kg–1. A slightly lower mercury content was measured for coal tar (2007.6 µg kg–1 on average, CV = 22.8%). Mercury content in coke was low, ranging from 4.1 to 10.5 µg kg–1. Mercury content in BTX was slightly higher (18.9 µg kg–1), with a variation coefficient of CV = 65.0%. Mercury content in purified coke oven gas was stable, ranging from 6.2 to 8.8 µg m–3 (mean value of 7.5 µg m–3). Results of all analyzed samples are shown in Table 4 SI. In a period of one month, the amount of mercury introduced to coke oven chambers with coal exceeded 6.5 kg (see Figure 9). During coal pyrolysis conducted at approximately 1273 K, practically


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all of the mercury is transferred to raw coking gas, which is subsequently cooled and purified. Coke contains less than 6% of the mercury introduced to the coking chamber with coal, which accounts for a stream of 378.6 g of mercury. During coke oven gas purification, more than 5.6 kg of mercury per month is removed from coke oven chambers. This mercury is distributed between coal tar (4877.4 g Hg, 74.8%), sulfur (158.0 g Hg, 2.4%) and BTX (12.8 g Hg, 0.2%). Purified coking gas contains 2.9% of the mercury (192.2 g of mercury per month). If it would be considered that half of this gas is used to fire coking batteries, the mercury emission indicator would be 1.35 mg Hg Mg–1 of coked coal. According to the balance data, approximately 907 g of mercury per month is emitted to the atmosphere during the filling of coke oven chambers with coal. This is almost 14% of mercury introduced into the process with coal. The mercury fugitive emission indicator based on this data is around 13 mg Hg·Mg–1 of coked coal. This value is higher than the one presented in previous report.33. With an annual coal consumption by the Polish coking industry of 12 million tons, this accounts for 150 kg of mercury per year emitted to the atmosphere. However, this indicator must be treated with caution due to the indirect way of its calculation.

4.

Conclusions Based on the analysis of 82 Polish bituminous coal samples acquired from 9 coal mines, 67

samples acquired during the cleaning process and mercury balance analysis for coking process of bituminous coals, the following statements can be made: 1) The average mercury content in Polish bituminous coals used for coking is 75.9 µg kg–1, with a variation range from 28.4 to 182.6 µg kg–1; 2) Mercury content in coals is highly correlated with sulfur content and to a lesser extent with ash content. No correlation was observed between mercury content and the degree of metamorphism of coal; 3) Coal cleaning processes of bituminous coals removed from 23 to 69% of the mercury. This mercury was transferred to middling products (0.1–42%), and concentrates (9–62%);


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4) During the coking process, approximately 75% of mercury in coal is transferred to coal tar, and less than 6% remains in coke; 5) During coking, approximately 13 mg of mercury per 1 Mg of coal is emitted to the atmosphere during the filling of the coking chamber. The indicator of mercury emission to the atmosphere for combustion of coking gas in heating system is 1.35 mg Hg Mg–1 of coal.

SUPPORTING INFORMATION

The Supporting Information contains tables with detailed results of analyses presented in this work. AUTHOR INFORMATION Corresponding Author *E-mail for Krzysztof Kogut: [email protected] Telephone: +48 12 617 39 01 Notes The authors declare no competing financial interest.

ACKNOWLEDGMENTS

This work was supported by The National Centre for Research and Development in Poland (Project 'Development of mercury content database for national coal, technological guidelines for its further reduction along with the definition of benchmarks for national mercury emission markers' PBS2/A2/14/2013 – Project AGH-University of Science and Technology No 19.19.210.86600). (1)

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Konieczyński, J.; Zajusz-Zubek, E.; Jabłońska M. The Release of Trace Elements in the Process of Coal Coking. The Scientific World Journal 2012, Article ID 294927, 1–8.


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Table captions: Table 1. Characteristics of Polish bituminous coals Table 2. Mercury content in resources and products of the coking process

Figure captions: Figure 1. Coal sampling scheme 8 Figure 2. Scheme for bituminous coal cleaning using trisectional (a) and bisectional (b) systems Figure 3. Balance of the coking process scheme Figure 4. Mercury content in analyzed bituminous coal samples Figure 5. Correlation between mercury content and: a) volatile matter (r = 0.192), b) ash content (r = 0.465), c) sulfur content (r = 0.731) Figure 6. Variation of mercury content in coal shipments from two coal mines with the highest and the lowest variation coefficient Figure 7. Mercury content in raw coals and concentrates of the bituminous coal cleaning process: a) absolute, b) in relation to calorific value Figure 8. Mercury distribution between coal cleaning products Figure 9. Mercury balance in the coking process (mo. – month)


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Table 1. Characteristics of cleaned Polish bituminous coals Mean ± SD n Mine No. 1 Mine No. 2 Mine No. 3 Mine No. 4 Mine No. 5 Mine No. 6 Mine No. 7 Mine No. 8 Mine No. 9

5 7 12 11 11 9 12 12 3

Aad, wt. % 5.1 ± 0.1 7.1 ± 0.6 6.5 ± 1.0 8.6 ± 1.3 7.1 ± 1.2 7.1 ± 1.0 6.4 ± 1.2 8.5 ± 2.2 6.2 ± 0.4

Sad, wt. % 0.46 ± 0.05 0.40 ± 0.03 0.42 ± 0.06 0.60 ± 0.10 0.50 ± 0.07 0.49 ± 0.07 0.68 ± 0.10 0.57 ± 0.05 0.41 ± 0.02

Vad, wt. % 20.06 ± 0.05 21.31 ± 0.68 19.13 ± 0.98 20.94 ± 0.87 19.29 ± 0.55 25.78 ± 0.77 28.07 ± 1.03 22.63 ± 1.07 30.13 ± 1.36

Cad, wt. % 84.1 ± 1.9 82.7 ± 0.7 84.4 ± 1.5 81.4 ± 1.2 83.7 ± 1.7 80.8 ± 1.8 80.2 ± 1.3 80.6 ± 2.1 79.8 ± 1.4


Had, wt. % 4.63 ± 0.17 4.60 ± 0.24 4.45 ± 0.21 4.55 ± 0.22 4.44 ± 0.23 4.83 ± 0.24 4.94 ± 0.25 4.68 ± 0.31 4.89 ± 0.14

Hgad, ppb 48.6 ± 13.6 39.7 ± 7.1 46.9 ± 13.1 109.4 ± 38.3 63.0 ± 14.5 57.2 ± 10.3 109.8 ± 38.3 109.9 ± 27.6 31.0 ± 2.4

a, % 25 ± 2 27 ± 2 27 ± 5 26 ± 4 26 ± 4 26 ± 3 22 ± 5 25 ± 4 17 ± 9

b, % 44 ± 3 47 ± 5 19 ± 10 76 ± 33 18 ± 18 57 ± 55 20 ± 18 102 ± 43 5 ± 15

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Table 2. Mercury content in resources and products of the coking process Resource / product Dry raw coal Dry coke Coal tar Sulfur BTX Coke oven gas

Stream, Mg month–1 71 296.0 54 351.0 2 429.4 52.7 675.0 13 210.4

n 6 6 8 8 6 5

Mercury content, µg kg–1, 1)µg m–3 Estimation Mean SD error 10.9 9.9 91.5 2.9 2.7 7.0 398.4 457.1 2 007.6 199.8 229.3 2 997.6 13.5 12.3 18.9 1) 1) 1.01) 0.8 7.5


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Figure 1. Coal sampling scheme 8


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Figure 2. Scheme for bituminous coal cleaning using trisectional (a) and bisectional (b) systems

a)

b)


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Figure 3. Balance of the coking process scheme


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Figure 4. Mercury content in analyzed bituminous coal samples


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Figure 5. Correlation between mercury content and: a) volatile matter (r = 0.192), b) ash content (r = 0.465), c) sulfur content (r = 0.731)

a)

b)

c)


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Figure 6. Variation of mercury content in coal shipments from two coal mines with the highest and the lowest variation coefficient


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Figure 7. Mercury content in raw coals and concentrates of the bituminous coal cleaning process: a) absolute, b) in relation to calorific value

a)

b)


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Figure 8. Mercury distribution between coal cleaning products


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Figure 9. Mercury balance in the coking process (mo. – month)


Mercury in Polish Coking Bituminous Coals - ACS Publications

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