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Multi-Criteria Evaluation of Coal Properties in Terms of Gasification

Multi-Criteria Evaluation of Coal Properties in Terms of Gasification Arch. Min. Sci., Vol. 59 (2014), No 3, p. 677­690 Electronic version (in color) of this paper is available: http://mining.archives.pl DOI 10.2478/amsc-2014-0047 JOLANTA MARCINIAK-KOWALSKA*, TOMASZ NIEDOBA*, AGNIESZKA SUROWIAK*, TADEUSZ TUMIDAJSKI* WIELOKRYTERIALNA OCENA WLACIWOCI WGLA W KONTEKCIE JEGO ZGAZOWANIA This paper presents a comparative analysis of two types of coal taken from the ZG Janina and ZG Wieczorek coalmines. The aim of this study has been to analyze the suitability of the coal in the context of the gasification process. The types of coal vary considerably in terms of their characteristics. Each of them was subjected to treatment in a ten-ringed annular jig. A particle size of 0-18 mm constituted the feed. The separated coal was divided into five layers, each of them containing material from two additional annular jigs. Analysis of their characteristics was carried out for each of the five layers and for both types of coal obtained, taking into account both their physicochemical properties as well as chemical ones. Each of these characteristics was then presented in three-dimensional surface diagrams, where the ordinate (or Y-axis) and abscissa (X-axis) was the particle size and height in which the material ended up in the jig (expressed as a percentage of the total height of the device). On the basis of observations, it was found that the types of coal have different potential for gasification, although both types are within the limits specified on the basis of previous studies. A correlation analysis between particle size and remaining characteristics of coal was carried out for each of the layers, allowing to determine which of the studied characteristics induced changes significant from the point of view of the coal gasification process. The entire research and observation was supported by conclusions and findings, which shall form the basis for further, in-depth analysis of coal. Keywords: coal gasification, suitability for gasification, multivariate data analysis, correlation matrix Proces zgazowania wgla technologi naziemn jest coraz czciej rozwaanym rozwizaniem na calym wiecie. Przyczyn tego stanu jest zarówno kwestia ochrony rodowiska, jak i logistyki zagospodarowania produktów przeróbki wgla. Nie inaczej jest równie w Polsce, gdzie od kilku lat proces zgazowania jest jednym z glównych tematów badawczych w dziedzinie polskiego górnictwa wglowego. Efektem tego jest szereg bada i dowiadcze, jak równie publikacji naukowych. W artykule dokonano analizy porównawczej dwóch typów wgla kamiennego, które pobrane byly w Zakladach Górniczych * AGH UNIVERSITY OF SCIENCE AND TECHNOLOGY, FACULTY OF MINING AND GEOENGINEERING, DEPARTMENT OF ENVIRONMENTAL ENGINEERING AND MINERAL PROCESSING, AL. MICKIEWICZA 30, 30-059 KRAKÓW. E-mail: jmk@agh.edu.pl, tniedoba@agh.edu.pl, asur@agh.edu.pl, tadeusz.tumidajski@agh.edu.pl Janina (typ wgla 31.2) oraz Zakladach Górniczych Wieczorek (typ wgla 32). Wgle te znaczco si róni pod wzgldem charakterystyk. Kady z nich zostal poddany rozdzialowi w osadzarce piercieniowej o 10 piercieniach. Nadaw stanowil wgiel o uziarnieniu 0-18 mm. Rozdzielony wgiel zostal podzielony na 5 warstw, z których kada zawierala material z dwóch kolejnych piercieni osadzarki. Dla kadej z otrzymanych w ten sposób piciu warstw dla obu typów wgli dokonano nastpnie analizy ich charakterystyk, biorc pod uwag zarówno cechy fizykochemiczne, jak i czysto chemiczne. Do tych pierwszych zaliczono takie parametry, jak zawarto wgla pierwiastkowego, zawarto popiolu oraz cieplo spalania, do drugich za zawarto azotu, zawarto chloru, zawarto siarki oraz zawarto wodoru. Szczególowe dane dla dwóch skrajnych warstw przedstawiono w tabelach 1-4. Kad z omawianych cech przedstawiono nastpnie na trójwymiarowych wykresach powierzchniowych, gdzie osiami rzdnych i odcitych byly wielko ziarna oraz wysoko, na której znalazl si material w osadzarce (wyraona w procentach wysokoci urzdzeni. Wykresy te (rys. 1-8) stanowily baz do analizy porównawczej obu wgli pod ktem ich przydatnoci do procesu zgazowania naziemnego. Wyranie wida, e wgle te maj inny potencjal do zgazowania, cho oba typy mieszcz si w granicach wartoci ograniczajcych (tab. 5), okrelonych na podstawie wczeniejszych bada. Nastpnie dokonano jeszcze analizy korelacji pomidzy wielkoci ziarna a pozostalymi charakterystykami badanych wgli dla kadej z warstw. Wyniki zobrazowano w tabeli 6. Przykladowo stwierdzono, e: ­ wraz ze wzrostem wielkoci ziaren w warstwach zmieniaj si ich zwizki z charakterystykami pierwiastkowymi wgli (w kolumnach (warstwach) nastpuje zmiana znaku wspólczynnika korelacji oraz miary jego istotnoci); ­ zasadnicze rónice wystpuj dla siarki ­ dla KWK Wieczorek wspólczynniki te s ujemne, co wiadczy o tym, e siarka w tym wglu jest prawdopodobnie siark organiczn (w warstwach najciszych poziom siarki maleje). Przeciwnie jest w ZG Janina, gdzie dla najciszych warstw zawarto siarki nie zmienia si (co moe by spowodowane znaczcym udzialem zrostów pirytowych). Chlor w ZG Janina koncentruje si zwlaszcza w klasach najdrobniejszych niezalenie od warstwy. Inaczej ukladaj si wspólczynniki dla ZG Janina, ich istotno spada a dla warstw najciszych ilo chloru nieznacznie wzrasta wraz z wielkoci ziaren. Stopie uwglenia w warstwach najlejszych ronie wraz ze wzrostem wielkoci ziaren dla warstw najciszych maleje. Mona powiedzie, e w KWK Wieczorek tylko ostatnia warstwa zawiera niewielkie zrosty wgla. Analiza wspólczynników korelacji dla ciepla spalania i zawartoci popiolu prowadzi do analogicznych wniosków (ze wzgldu na naturalne powizania fizyczne tych wlaciwoci). Wspólczynniki korelacji pomidzy wielkoci ziarna a zawartociami azotu w obu kopalniach ukladaj si podobnie, przy czym zalenoci te s bardziej znaczce dla wgli z ZG Janina; dla obu wgli wspólczynniki s dodatnie dla trzech najlejszych warstw i ujemne dla warstw najciszych (azot wystpuje w wikszych i ciszych kawalkach wgl. Na podstawie dokonanych analiz mona stwierdzi, i oba wgle s dostatecznie dobre aby mona je bylo podda procesowi zgazowania, cho wicej cech sprzyjajcych temu procesowi posiada wgiel z KWK Wieczorek. Dalsze badania w tym aspekcie trwaj i bd przedmiotem kolejnych publikacji. Slowa kluczowe: zgazowanie wgla, podatno na zgazowanie, wielokryterialna analiza danych, macierz korelacji 1. Introduction Coal properties targeted for gasification must fulfill a number of limitations (Agrawal, 2011; Blaschke, 2009; Chmielniak & Tomaszewicz, 2012; Borowiecki et al., 2008; Govind & Shah, 1984; Kosminski et al., 2006; Li et al., 2005; Lee et al., 2007; Park et al., 2011; Seo et al., 2011; Sobolewski et al., 2012; Xu et al., 2012), wherein it is essential to notice that they are connected to one another. Evaluation of the suitability of coal for gasification should therefore be carried out on a multidimensional basis using multidimensional distribution features and statistics (Jamróz, 2009; 2014; b; Jamróz & Niedoba, 2014; Niedoba & Jamróz, 2013; Niedoba, 2013; 2014; Tumidajski, 1997). It is only natural that the analysis of multidimensional features and statistics begins with an analysis of the densitometry composition of grinded coal and is extended further based on the coal characteristics, especially the contents of the components and reactions to the processing stages. Analysis of the distribution of coal in terms of the so-called class-fraction is deemed as preliminary information in respect of coal capabilities in developing the specific surface area and concentrating combustible, volatile and ash components. Determining the remaining properties allows for additional distinction of the relationships of these properties with each other as well as the aforementioned geometrical and physical features. The paper presents an approach method to analyze these issues and this is documented in the coal databases of the ZG Janina and KWK Wieczorek coal mines. The preliminary analysis was based on the results of the initial separation of coal in the annular jig of the laboratory ­ analysis of fractions contained in the next annular column jig obtained in the course of research carried out under the task outlined in 2.1.2 on the subject of coal cleaning tests by mechanical processing, "which was carried out between 2012-13 in the department. The multidimensional approach in obtaining results allows to evaluate the susceptibility of coal to gasification. This problem has already been the subject of other publications in the scope of NCBiR project number 23.23.100.8498/R34 entitled "Development of coal gasification technology for highly efficient production of fuels and energy" as part of a strategic program of research and development entitled "Advanced technologies in obtaining energy" (Strugala et al., 2011; 2012). 2. Established methods The separation of the grinded material in the jig proceeds on the basis of differences in the speed of descent of individual particles (Broek & Surowiak, 2010; Stpiski 1964; Surowiak, 2013; 2014b; Surowiak & Broek, 2014a, . The separation of coal from the ZG Janina and KWK Wieczorek coal mines was carried out using a laboratory annular jig ring. After jigging, the material (from the two adjacent rings) was separated into layers, which were spread, then analyzed for the content of elements in classes and evaluated in terms of heat of combustion (in accordance with Polish standards in force, including PN-80 / G-04512). Separation of the material layer allows for the introduction of a conventional variable, which shall be called H, specifying the position of particles (associated with the speed of descent of particles), which will enable the two-dimensional distribution of particles (D, H) to be defined, whereby D is a random variable representing the particle size, and H ­ a random variable representing the position of the particle as a fraction of the height of the jig column. Such a conventional presentation of the distribution of the random variables (D, H) will allow for the evaluation of particle concentration in the coal and the breakdown of these characteristic values essential for gasification. Based on the literature review it can be concluded that: ­ the most important characteristics of coal (the key parameters) (Sobolewski et al., 2013) directed to the process of surface gasification in a pressure reactor of the circulating fluidized deposits in a CO2 atmosphere are carbon reaction, ash content, sulphur, chlorine, melting point of ash and the viscosity of the resulting slag (Yun et al., 2007). It is worth noting that the higher content of volatile matter arising from the thermal decomposition of coal without air supply is connected with the lower degree of carbonification (Krawczykowski et al., 2013; Surowiak, 2013; 2013b; 2014); ­ the reduced content of nitric oxides and sulphur in syngas reduces emissions as well as the corrosiveness of devices (Bai et al., 2010; Krawczykowski et al., 2013); ­ fuel properties, particle size, reactivity and catalytic substance content affect the kinetics of coal gasification in a deposit fluidized gas generator (Labojko et al., 2012; Nonaka et al., 2013); ­ in order to obtain high-quality process gas (used as an energy component in IGCC ­ Integrated Gasification Combined Cycle systems, or in chemistry as a raw material) it is necessary to take additional action in the area of preliminary coal cleaning and analyze the possibility of separating minerals and undesirable substances (Pomykala & Mazurkiewicz, 2011; Surowiak, 2013). Concentrates of different qualities are obtained depending on the form of the presence of coal contaminants, the degree of clean coal comminution, as well as the gravity separation method (in this case, the differences in sedimentation velocities of particles in an aqueous-jig) ­ as can be seen in Tables 1-10 (Marciniak-Kowalska et al. ­ research reports 2012, 2013). Not only have upgrading curves been used as the main criterion for the effectiveness of the upgrading process (Krawczykowski et al., 2013), but also a comparative analysis of primary upgraded coal. The gravity separation method in elements of coal will be possible and effective if the density of the carbonate substance containing only the so-called internal mineral substance is in the range of 1170 to about 1500 kg/m3 (Blaschke, 2009). 3. Research methodology ­ comparative analysis of coal from ZG "Janina" and KWK "Wieczorek" 3.1. Preparation of test material and primary results In order to investigate fossil fuel upgrading intended for the gasification process of fluidized layers of bituminous coals from ZG Janina (coal type 31.2), and KWK Wieczorek (coal type 32) ­ each of these was subjected to upgrading in a laboratory annular jig (of 10 rings ­ 0-18 mm coal class). After separation process has been completed, the material was divided into five layers (two rings each) and each of them was then scattered onto sieves into 10 particle classes, determining the weight recovery of layers and their classes. Afterwards, the derived product i.e. particle classes, was subjected to a preliminary chemical analysis, after separation of analytical samples and a technical analysis of coal for the purpose of characterizing the properties affecting the gasification processes. Due to the fact that this data formed the characteristic basis of threedimensional graphs of the coal examined (Figs. 1-8), only the results for the extreme layers of both coal types (Tables 1-4), which best characterize the dispersion in the quality of the layers of the separated coal, are presented. In the first 3 layers, coal from ZG Janina contains less than 1% sulphur, which is twice as much as coal from the KWK Wieczorek coalmine. In the case of nitrogen content of coal from ZG Janina, it is about 1% in four successive layers, whereas coal from KWK Wieczorek has an average of more than 1.5%. In the case of chlorine content of coal from ZG Janina, it is 2 times lower than that of ZG Wieczorek. Therefore, it can be seen that coal from the Wieczorek coalmine is more burdensome for the environment in terms of precursors that cause acidification of the atmosphere (acidic oxides). However, in terms of higher efficiency of coal gasification, the coal from KWK Wieczorek is better because it has a higher hydrogen content of above 5%, more than 80% carbon element and more than 32.6 MJ/kg heat of combustion. The results summarized in Tables 1-4 can be interpreted in three-dimensional graphs, i.e. designated variables F(d, h) and surfaces, depending on D and H, and particular characteristics of coal. The overview of results shall begin with the analysis of the physical properties of coal. TABLE 1 Primary analysis of coal in layer I after jigging ­ ZG Janina (Marciniak-Kowalska et al. ­ research report 2012, 2013) Class d [mm] Total sulphur Hydrogen Nitrogen Chlorine Total carbon Heat of Ash content content content content content content combustion Aa [%] a a a a a a St [%] H [%] N [%] Cl [%] C [%] Qs [kJ/kg] TABLE 2 Primary analysis of coal in layer V after jigging ­ ZG Janina [Marciniak-Kowalska et al. ­ research report 2012, 2013] Class d [mm] Total sulphur Hydrogen Nitrogen Chlorine Total carbon Heat of Ash Content content content content content content combustion Aa [%] a a a a a a St [%] H [%] N [%] Cl [%] C [%] Qs [kJ/kg] TABLE 3 Primary analysis of coal in layer I after jigging ­ KWK Wieczorek (Marciniak-Kowalska et al. ­ research report 2012, 2013) Class d [mm] Total sulphur Hydrogen Nitrogen Chlorine Total carbon Heat Ash Content content content content content content combustion A a [%] a a a a a a St [%] H [%] N [%] Cl [%] C [%] Qs [kJ/kg] TABLE 4 Primary analysis of coal in layer V after jigging ­ KWK Wieczorek (Marciniak-Kowalska et al. ­ research report 2012, 2013) Class d [mm] Total sulphur Hydrogen Nitrogen Chlorine Total carbon Heat of Ash content content content content content content combustion Aa [%] a a a a a a St [%] H [%] N [%] Cl [%] C [%] Qs [kJ/kg] 3.2. Analysis of the physicochemical properties of coal In proceeding to examine the distribution of coal constituents important in terms of gasification, it is necessary to pay attention to their acceptable levels. Table 5 presents a set of characteristics examined for the purposes of this article and standards by which they should be analyzed, as well as the permissible levels of characteristics examined. Generally, these parameters are divided into key and significant features (due to gasification in a pressurized gas generator with CFB circulating fluidized bed in a CO2 atmosphere). The key features include items such as the calorific value of over 18000 [kJ/kg], ash content of less than 25%, melting point of above 1373 [K], carbonate reactivity in terms of CO2 above 2; in terms of carbon of below 20, chlorine content of less than 0.1%; the Hardgrove's GrH grinding susceptibility in the range of 45-65; sinterability using the Roga RI method of under 15. Significant features included the content of volatile matter, total moisture, total sulphur content, carbon content, hydrogen content, nitrogen content, oxide content, i.e., SiO2, Al2O3, Fe2O3, CaO, MgO, P2O5, TiO2, Na2O, K2O (Sobolewski et al., 2012; 2013). An important parameter for a given gas generator is the appropriate grinding of coal, i.e. fuel, since the fluidized reactor processes coal with a particle size from 0.5 mm to 3 mm (5 mm) (Sobolewski et al., 2012; 2013). Table 5 shows the values only for the relevant features in the experiment. It is worth noting that the graphs illustrate the full grain composition of upgraded coal, that is with a range of up to 18 mm. Material > 3 mm would be appropriate for gasification following proper fragmentation. TABLE 5 Limitations in respect of hard coal designated for the ground gasification process for the CFB reactor (Sobolewski et al., 2012) Parameter [unit] Standard Fluidized bed reactor Calorific value [kJ/kg] Ash content [%] Chlorine content [%] Hydrogen content [%] Nitrogen content [%] Carbon element content [%] Sulphur content[%] PN-81/G-04513 PN-80/G-451 PN-G-05460 PN-ISO 11711 PN-G-4534 PN-ISO 587 PN-G-04571:1998 PN-G-04571:1998 PN-G-04571:1998 PN-04584:2001 > 18 000 < 25 < 0.1 3.5-5.5 < 2.0 > 60 < 2.0 Fig. 1. F(d, h) Variables for coal: ZG Janina; KWK Wieczorek Fig. 2. Surface ­ coal element content = f (d, h) for coal ZG Janina; KWK Wieczorek Fig. 3. Surface ­ ash content = f(d, h) for coal: ZG Janina; KWK Wieczorek Fig. 4. Surface ­ heat of combustion = f(d, h) for coal: ZG Janina; KWK Wieczorek Density, particle size and the associated content of correlated carbon element, ash and heat of combustion resulting from the last two, have been accepted as physicochemical properties of coal. In analyzing the variants F(d, h) of both types of coal, it should be noted that these have different structure and texture. Coal from KWK Wieczorek contains significantly smaller amounts of fine classes, larger amounts of lighter fraction classes (with a higher carbon content). It is suspected that coal from ZG Janina is easier to break up and creates larger appropriate areas, relevant for gasification. It can be said that this is the result of lower metamorphisation of coal layers from ZG Janina. Analyses of ash and carbon element content (Figs. 2 and 3) show the fundamental differences between the two types of coal: ­ for lighter fractions, regardless of their particle size (besides the finest class), the ash content of coal from KWK Wieczorek is twice as low as that of ZG Janina, whereas the carbon element content of both types of coal is high: higher for coal from KWK Wieczorek (approximately 80%C) and by about 10% lower for coal from ZG Janina; ­ in analyzing the heaviest density fractions, it can be noted that high carbon element content is present in both types of coal and significantly lower in thicker grades, indicating stone enrichment, which in turn is reflected in the analysis of the ash in individual coarser size fractions of both types of coal. ­ the distribution of ash content in coal in the last layer of density (beyond the finest grade) confirms observations that there is a high concentration of ash in the previous layers (even above 60%) of coal from KWK Wieczorek ­ resulting from its ease of upgrading, while for ZG Janina the ash is more evenly distributed in the final three layers (between 30% and 50%). Correlating the heat of combustion of carbon element contents and ash contents causes the graphic image to be practically identical to the image of carbon element content depending on the heat of variables D and H. Heat of combustion values for lighter fractions are lower for ZG Janina than for KWK Wieczorek and in both cases independent from the scope of the particle class. 3.3. Analysis of the chemical distribution of coal properties Based on previous studies (section 3.2) it can be stated that obtaining coal that meets the requirements in terms of carbon element content, ash content and calorific value is not a problem, especially in the case of KWK Wieczorek. A certain problem may be ensuring appropriate carbon element content in ZG Janina. Figs. 5-8 illustrate the comparison of both types of coal in terms of the distribution of their chemical properties. Fig. 5. Surface ­ sulphur content = f(d, h) for coal: ZG Janina; KWK Wieczorek Fig. 6. Surface ­ hydrogen content = f(d, h) for coal: ZG Janina; KWK Wieczorek Fig. 7. Surface: the nitrogen content = f(d, h) for coal: ZG Janina; KWK Wieczorek Fig. 8. Surface: chlorine content = f(d, h) for coal: ZG Janina; KWK Wieczorek In observing the distribution of nitrogen content (Fig. 7) it is clear that both types of coal fully comply with the thresholds, whereby the coal from ZG Janina has a lower N content distributed very evenly in classes and layers. Also, the distribution of hydrogen content in the coal does not cause any problems. Coal from KWK Wieczorek has a significantly larger distribution of the H content. In ZG Janina the heaviest layers should be removed from the gasification process (not only for this reason). In terms of sulphur content distribution, the two types of coal vary significantly. The sulphur content in KWK Wieczorek does not exceed 1%, so there is no reason to take an interest in this issue. As far as ZG Janina is concerned, the heaviest layer, in which sulphur is bound with pyrite, should be removed in order to reduce the sulphur content. As far as the chlorine content is concerned, both types of coal slightly exceed the standards. It seems that removing the heaviest layers should lead to a chlorine balance within the normal limits. 3.4. Analysis of selected coal according to the correlation between the test characteristics Line correlation coefficients have been determined between the particle size and characteristics of coals examined for each individual layer for the purpose of identifying the most important relationships between the parameters of the coal. In this case, with the significance level of = 0.05, the critical value of the correlation coefficient is rkryt = 0.63. The results are presented in Table 6. TABLE 6 Correlation coefficients between particle size and other characteristics of the examined coal from ZG Janina and KWK Wieczorek coalmines for each of the layers Sulphur 1 2 Hydrogen 3 Nitrogen 4 Chlorine 5 Carbon 6 Heat of combustion 7 Ash 8 ZG Janina Particle size layer 1 Particle size layer 2 ­0.33 ­0.65 0.66 0.84 0.67 0.60 ­0.65 ­0.77 0.42 0.81 0.52 0.83 ­0.34 ­0.46 Particle size layer 3 Particle size layer 4 Particle size layer 5 Particle size layer 1 Particle size layer 2 Particle size layer 3 Particle size layer 4 Particle size layer 5 ­0.64 0.05 0.12 0.29 ­0.32 ­0.32 0.65 ­0.36 ­0.59 ­0.85 ­0.58 ­0.69 0.70 ­0.73 ­0.52 0.68 ­0.68 ­0.51 ­0.49 0.80 0.55 KWK Wieczorek ­0.33 ­0.32 ­0.61 ­0.70 ­0.30 ­0.32 0.43 0.60 ­0.03 ­0.69 0.48 0.21 0.57 ­0.49 ­0.68 ­0.45 ­0.13 ­0.28 0.23 0.11 0.41 0.50 0.52 0.24 ­0.7 0.43 0.51 0.59 0.10 ­0.69 ­0.40 ­0.54 ­0.54 ­0.09 0.7 When analyzing the table of correlation coefficients, the following conclusions can be made: ­ with increasing particle size, the layers change in relation to the characteristics of the carbon element content (in columns (layers), the correlation coefficient symbol and the measure of its importance change); ­ fundamental differences exist for sulphur - in coal from KWK Wieczorek these coefficients are negative, which indicates that the sulphur in the coal is probably organic sulphur (sulphur level decrease in the heaviest layers). This is in contrast to the coal from ZG Janina, in which the sulphur content in the heaviest layers does not change (which may be due to a significant presence of pyrites). Chlorine contained in coal from ZG Janina is particularly concentrated in the smallest classes regardless of layer. The coefficients for coal from ZG Janina are arranged differently and their significance decreases. For the heaviest layers the amount of chlorine slightly increases with particle size. The degree of carbonification increases in the lightest layers and decreases in the heaviest layers together with the increase in particle size. It can be said that only the last layer of coal from KWK Wieczorek contains minor carbon adhesions. Analysis of correlation coefficients for heat of combustion and ash content leads to analogical conclusions (due to the natural physical connection of these properties). The correlation coefficients between particle size and nitrogen contents in the coal from the two mines are arranged similarly, whereby these dependencies are more significant for coal from ZG Janina. In both types of coal the coefficients are positive for the three lightest layers and negative for the heaviest layers (nitrogen is present in bigger and heavier lumps of coal). It can be assumed that extended analysis of the correlation coefficients between the characteristics of coal in classes (correlation between the columns of tables 1-4) will allow for a very precise description of the coal types and their suitability for gasification. 4. Summary and Conclusions The proposed method of evaluating the suitability of coal for gasification is illustrative and offers a wide range of opportunities to observe the association of coal characteristics whereby certain values are significant or necessary in fulfilling the conditions in the light of their subsequent surface gasification. The two types of coal can be clearly differentiated on the basis of analysis. In comparing the measured values with those required, it was stated that the coal from KWK Wieczorek is better in terms of suitability for gasification, above all because it is characterized by higher heat of combustion and the values of measured properties are within the expected range. The correlation analysis also showed that it might be worth to consider eliminating the lowest layers of the material in the jig, as they can potentially generate the biggest problems during the gasification process (especially in the case of coal from ZG Janin. The types of coal under consideration differ from each other by age and origin. Coal from ZG Janina is younger than that from KWK Wieczorek, therefore its components are not fully metamorphosed. Hard coal designated for the gasification process in a gas generator as a fluidized layer is a rock, which undergoes various transformations during the carbonization process, as the result of which it is characterized by a variety of mineral, petrographic, chemical and structural compositions. Therefore, there is a variety of mineral and organic carbon components depending on the petrographic type. A number of components (ash, sulphur pyrites, carbon elements, heat of combustion, and calorific value) is closely related to the density distribution of carbonaceous material and can easily be isolated by mechanical processing. In contrast, compounds containing organic sulphur, nitrogen, chlorine, hydrogen, are those associated with coal structure as a result of geochemical, biochemical and salinity changes. Removal of these components is difficult and requires the use of chemical methods, in this case ­ demineralization. As multidimensional analysis individual primary components presented in the article showed, tested coal can easily be cleaned by gravitational methods and the components which correlate with the distribution of density removed. Ash and pyritic sulphur can be passed for heavy fractions (of high density). Carbon elements are concentrated in light fractions and high heat of combustion values can be observed. The Article has been compiled as a result of NCBiR project no. 23.23.100.8498/R34 entitled "Development of coal gasification technology for highly efficient production of fuels and energy" in the scope of tasks 2.1.2 on the subject of research on coal upgrading through mechanical processing. "between 2012-13 as part of a strategic program of research and development entitled "Advanced energy generation technologies." http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Archives of Mining Sciences de Gruyter

Multi-Criteria Evaluation of Coal Properties in Terms of Gasification

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Abstract

Arch. Min. Sci., Vol. 59 (2014), No 3, p. 677­690 Electronic version (in color) of this paper is available: http://mining.archives.pl DOI 10.2478/amsc-2014-0047 JOLANTA MARCINIAK-KOWALSKA*, TOMASZ NIEDOBA*, AGNIESZKA SUROWIAK*, TADEUSZ TUMIDAJSKI* WIELOKRYTERIALNA OCENA WLACIWOCI WGLA W KONTEKCIE JEGO ZGAZOWANIA This paper presents a comparative analysis of two types of coal taken from the ZG Janina and ZG Wieczorek coalmines. The aim of this study has been to analyze the suitability of the coal in the context of the gasification process. The types of coal vary considerably in terms of their characteristics. Each of them was subjected to treatment in a ten-ringed annular jig. A particle size of 0-18 mm constituted the feed. The separated coal was divided into five layers, each of them containing material from two additional annular jigs. Analysis of their characteristics was carried out for each of the five layers and for both types of coal obtained, taking into account both their physicochemical properties as well as chemical ones. Each of these characteristics was then presented in three-dimensional surface diagrams, where the ordinate (or Y-axis) and abscissa (X-axis) was the particle size and height in which the material ended up in the jig (expressed as a percentage of the total height of the device). On the basis of observations, it was found that the types of coal have different potential for gasification, although both types are within the limits specified on the basis of previous studies. A correlation analysis between particle size and remaining characteristics of coal was carried out for each of the layers, allowing to determine which of the studied characteristics induced changes significant from the point of view of the coal gasification process. The entire research and observation was supported by conclusions and findings, which shall form the basis for further, in-depth analysis of coal. Keywords: coal gasification, suitability for gasification, multivariate data analysis, correlation matrix Proces zgazowania wgla technologi naziemn jest coraz czciej rozwaanym rozwizaniem na calym wiecie. Przyczyn tego stanu jest zarówno kwestia ochrony rodowiska, jak i logistyki zagospodarowania produktów przeróbki wgla. Nie inaczej jest równie w Polsce, gdzie od kilku lat proces zgazowania jest jednym z glównych tematów badawczych w dziedzinie polskiego górnictwa wglowego. Efektem tego jest szereg bada i dowiadcze, jak równie publikacji naukowych. W artykule dokonano analizy porównawczej dwóch typów wgla kamiennego, które pobrane byly w Zakladach Górniczych * AGH UNIVERSITY OF SCIENCE AND TECHNOLOGY, FACULTY OF MINING AND GEOENGINEERING, DEPARTMENT OF ENVIRONMENTAL ENGINEERING AND MINERAL PROCESSING, AL. MICKIEWICZA 30, 30-059 KRAKÓW. E-mail: jmk@agh.edu.pl, tniedoba@agh.edu.pl, asur@agh.edu.pl, tadeusz.tumidajski@agh.edu.pl Janina (typ wgla 31.2) oraz Zakladach Górniczych Wieczorek (typ wgla 32). Wgle te znaczco si róni pod wzgldem charakterystyk. Kady z nich zostal poddany rozdzialowi w osadzarce piercieniowej o 10 piercieniach. Nadaw stanowil wgiel o uziarnieniu 0-18 mm. Rozdzielony wgiel zostal podzielony na 5 warstw, z których kada zawierala material z dwóch kolejnych piercieni osadzarki. Dla kadej z otrzymanych w ten sposób piciu warstw dla obu typów wgli dokonano nastpnie analizy ich charakterystyk, biorc pod uwag zarówno cechy fizykochemiczne, jak i czysto chemiczne. Do tych pierwszych zaliczono takie parametry, jak zawarto wgla pierwiastkowego, zawarto popiolu oraz cieplo spalania, do drugich za zawarto azotu, zawarto chloru, zawarto siarki oraz zawarto wodoru. Szczególowe dane dla dwóch skrajnych warstw przedstawiono w tabelach 1-4. Kad z omawianych cech przedstawiono nastpnie na trójwymiarowych wykresach powierzchniowych, gdzie osiami rzdnych i odcitych byly wielko ziarna oraz wysoko, na której znalazl si material w osadzarce (wyraona w procentach wysokoci urzdzeni. Wykresy te (rys. 1-8) stanowily baz do analizy porównawczej obu wgli pod ktem ich przydatnoci do procesu zgazowania naziemnego. Wyranie wida, e wgle te maj inny potencjal do zgazowania, cho oba typy mieszcz si w granicach wartoci ograniczajcych (tab. 5), okrelonych na podstawie wczeniejszych bada. Nastpnie dokonano jeszcze analizy korelacji pomidzy wielkoci ziarna a pozostalymi charakterystykami badanych wgli dla kadej z warstw. Wyniki zobrazowano w tabeli 6. Przykladowo stwierdzono, e: ­ wraz ze wzrostem wielkoci ziaren w warstwach zmieniaj si ich zwizki z charakterystykami pierwiastkowymi wgli (w kolumnach (warstwach) nastpuje zmiana znaku wspólczynnika korelacji oraz miary jego istotnoci); ­ zasadnicze rónice wystpuj dla siarki ­ dla KWK Wieczorek wspólczynniki te s ujemne, co wiadczy o tym, e siarka w tym wglu jest prawdopodobnie siark organiczn (w warstwach najciszych poziom siarki maleje). Przeciwnie jest w ZG Janina, gdzie dla najciszych warstw zawarto siarki nie zmienia si (co moe by spowodowane znaczcym udzialem zrostów pirytowych). Chlor w ZG Janina koncentruje si zwlaszcza w klasach najdrobniejszych niezalenie od warstwy. Inaczej ukladaj si wspólczynniki dla ZG Janina, ich istotno spada a dla warstw najciszych ilo chloru nieznacznie wzrasta wraz z wielkoci ziaren. Stopie uwglenia w warstwach najlejszych ronie wraz ze wzrostem wielkoci ziaren dla warstw najciszych maleje. Mona powiedzie, e w KWK Wieczorek tylko ostatnia warstwa zawiera niewielkie zrosty wgla. Analiza wspólczynników korelacji dla ciepla spalania i zawartoci popiolu prowadzi do analogicznych wniosków (ze wzgldu na naturalne powizania fizyczne tych wlaciwoci). Wspólczynniki korelacji pomidzy wielkoci ziarna a zawartociami azotu w obu kopalniach ukladaj si podobnie, przy czym zalenoci te s bardziej znaczce dla wgli z ZG Janina; dla obu wgli wspólczynniki s dodatnie dla trzech najlejszych warstw i ujemne dla warstw najciszych (azot wystpuje w wikszych i ciszych kawalkach wgl. Na podstawie dokonanych analiz mona stwierdzi, i oba wgle s dostatecznie dobre aby mona je bylo podda procesowi zgazowania, cho wicej cech sprzyjajcych temu procesowi posiada wgiel z KWK Wieczorek. Dalsze badania w tym aspekcie trwaj i bd przedmiotem kolejnych publikacji. Slowa kluczowe: zgazowanie wgla, podatno na zgazowanie, wielokryterialna analiza danych, macierz korelacji 1. Introduction Coal properties targeted for gasification must fulfill a number of limitations (Agrawal, 2011; Blaschke, 2009; Chmielniak & Tomaszewicz, 2012; Borowiecki et al., 2008; Govind & Shah, 1984; Kosminski et al., 2006; Li et al., 2005; Lee et al., 2007; Park et al., 2011; Seo et al., 2011; Sobolewski et al., 2012; Xu et al., 2012), wherein it is essential to notice that they are connected to one another. Evaluation of the suitability of coal for gasification should therefore be carried out on a multidimensional basis using multidimensional distribution features and statistics (Jamróz, 2009; 2014; b; Jamróz & Niedoba, 2014; Niedoba & Jamróz, 2013; Niedoba, 2013; 2014; Tumidajski, 1997). It is only natural that the analysis of multidimensional features and statistics begins with an analysis of the densitometry composition of grinded coal and is extended further based on the coal characteristics, especially the contents of the components and reactions to the processing stages. Analysis of the distribution of coal in terms of the so-called class-fraction is deemed as preliminary information in respect of coal capabilities in developing the specific surface area and concentrating combustible, volatile and ash components. Determining the remaining properties allows for additional distinction of the relationships of these properties with each other as well as the aforementioned geometrical and physical features. The paper presents an approach method to analyze these issues and this is documented in the coal databases of the ZG Janina and KWK Wieczorek coal mines. The preliminary analysis was based on the results of the initial separation of coal in the annular jig of the laboratory ­ analysis of fractions contained in the next annular column jig obtained in the course of research carried out under the task outlined in 2.1.2 on the subject of coal cleaning tests by mechanical processing, "which was carried out between 2012-13 in the department. The multidimensional approach in obtaining results allows to evaluate the susceptibility of coal to gasification. This problem has already been the subject of other publications in the scope of NCBiR project number 23.23.100.8498/R34 entitled "Development of coal gasification technology for highly efficient production of fuels and energy" as part of a strategic program of research and development entitled "Advanced technologies in obtaining energy" (Strugala et al., 2011; 2012). 2. Established methods The separation of the grinded material in the jig proceeds on the basis of differences in the speed of descent of individual particles (Broek & Surowiak, 2010; Stpiski 1964; Surowiak, 2013; 2014b; Surowiak & Broek, 2014a, . The separation of coal from the ZG Janina and KWK Wieczorek coal mines was carried out using a laboratory annular jig ring. After jigging, the material (from the two adjacent rings) was separated into layers, which were spread, then analyzed for the content of elements in classes and evaluated in terms of heat of combustion (in accordance with Polish standards in force, including PN-80 / G-04512). Separation of the material layer allows for the introduction of a conventional variable, which shall be called H, specifying the position of particles (associated with the speed of descent of particles), which will enable the two-dimensional distribution of particles (D, H) to be defined, whereby D is a random variable representing the particle size, and H ­ a random variable representing the position of the particle as a fraction of the height of the jig column. Such a conventional presentation of the distribution of the random variables (D, H) will allow for the evaluation of particle concentration in the coal and the breakdown of these characteristic values essential for gasification. Based on the literature review it can be concluded that: ­ the most important characteristics of coal (the key parameters) (Sobolewski et al., 2013) directed to the process of surface gasification in a pressure reactor of the circulating fluidized deposits in a CO2 atmosphere are carbon reaction, ash content, sulphur, chlorine, melting point of ash and the viscosity of the resulting slag (Yun et al., 2007). It is worth noting that the higher content of volatile matter arising from the thermal decomposition of coal without air supply is connected with the lower degree of carbonification (Krawczykowski et al., 2013; Surowiak, 2013; 2013b; 2014); ­ the reduced content of nitric oxides and sulphur in syngas reduces emissions as well as the corrosiveness of devices (Bai et al., 2010; Krawczykowski et al., 2013); ­ fuel properties, particle size, reactivity and catalytic substance content affect the kinetics of coal gasification in a deposit fluidized gas generator (Labojko et al., 2012; Nonaka et al., 2013); ­ in order to obtain high-quality process gas (used as an energy component in IGCC ­ Integrated Gasification Combined Cycle systems, or in chemistry as a raw material) it is necessary to take additional action in the area of preliminary coal cleaning and analyze the possibility of separating minerals and undesirable substances (Pomykala & Mazurkiewicz, 2011; Surowiak, 2013). Concentrates of different qualities are obtained depending on the form of the presence of coal contaminants, the degree of clean coal comminution, as well as the gravity separation method (in this case, the differences in sedimentation velocities of particles in an aqueous-jig) ­ as can be seen in Tables 1-10 (Marciniak-Kowalska et al. ­ research reports 2012, 2013). Not only have upgrading curves been used as the main criterion for the effectiveness of the upgrading process (Krawczykowski et al., 2013), but also a comparative analysis of primary upgraded coal. The gravity separation method in elements of coal will be possible and effective if the density of the carbonate substance containing only the so-called internal mineral substance is in the range of 1170 to about 1500 kg/m3 (Blaschke, 2009). 3. Research methodology ­ comparative analysis of coal from ZG "Janina" and KWK "Wieczorek" 3.1. Preparation of test material and primary results In order to investigate fossil fuel upgrading intended for the gasification process of fluidized layers of bituminous coals from ZG Janina (coal type 31.2), and KWK Wieczorek (coal type 32) ­ each of these was subjected to upgrading in a laboratory annular jig (of 10 rings ­ 0-18 mm coal class). After separation process has been completed, the material was divided into five layers (two rings each) and each of them was then scattered onto sieves into 10 particle classes, determining the weight recovery of layers and their classes. Afterwards, the derived product i.e. particle classes, was subjected to a preliminary chemical analysis, after separation of analytical samples and a technical analysis of coal for the purpose of characterizing the properties affecting the gasification processes. Due to the fact that this data formed the characteristic basis of threedimensional graphs of the coal examined (Figs. 1-8), only the results for the extreme layers of both coal types (Tables 1-4), which best characterize the dispersion in the quality of the layers of the separated coal, are presented. In the first 3 layers, coal from ZG Janina contains less than 1% sulphur, which is twice as much as coal from the KWK Wieczorek coalmine. In the case of nitrogen content of coal from ZG Janina, it is about 1% in four successive layers, whereas coal from KWK Wieczorek has an average of more than 1.5%. In the case of chlorine content of coal from ZG Janina, it is 2 times lower than that of ZG Wieczorek. Therefore, it can be seen that coal from the Wieczorek coalmine is more burdensome for the environment in terms of precursors that cause acidification of the atmosphere (acidic oxides). However, in terms of higher efficiency of coal gasification, the coal from KWK Wieczorek is better because it has a higher hydrogen content of above 5%, more than 80% carbon element and more than 32.6 MJ/kg heat of combustion. The results summarized in Tables 1-4 can be interpreted in three-dimensional graphs, i.e. designated variables F(d, h) and surfaces, depending on D and H, and particular characteristics of coal. The overview of results shall begin with the analysis of the physical properties of coal. TABLE 1 Primary analysis of coal in layer I after jigging ­ ZG Janina (Marciniak-Kowalska et al. ­ research report 2012, 2013) Class d [mm] Total sulphur Hydrogen Nitrogen Chlorine Total carbon Heat of Ash content content content content content content combustion Aa [%] a a a a a a St [%] H [%] N [%] Cl [%] C [%] Qs [kJ/kg] TABLE 2 Primary analysis of coal in layer V after jigging ­ ZG Janina [Marciniak-Kowalska et al. ­ research report 2012, 2013] Class d [mm] Total sulphur Hydrogen Nitrogen Chlorine Total carbon Heat of Ash Content content content content content content combustion Aa [%] a a a a a a St [%] H [%] N [%] Cl [%] C [%] Qs [kJ/kg] TABLE 3 Primary analysis of coal in layer I after jigging ­ KWK Wieczorek (Marciniak-Kowalska et al. ­ research report 2012, 2013) Class d [mm] Total sulphur Hydrogen Nitrogen Chlorine Total carbon Heat Ash Content content content content content content combustion A a [%] a a a a a a St [%] H [%] N [%] Cl [%] C [%] Qs [kJ/kg] TABLE 4 Primary analysis of coal in layer V after jigging ­ KWK Wieczorek (Marciniak-Kowalska et al. ­ research report 2012, 2013) Class d [mm] Total sulphur Hydrogen Nitrogen Chlorine Total carbon Heat of Ash content content content content content content combustion Aa [%] a a a a a a St [%] H [%] N [%] Cl [%] C [%] Qs [kJ/kg] 3.2. Analysis of the physicochemical properties of coal In proceeding to examine the distribution of coal constituents important in terms of gasification, it is necessary to pay attention to their acceptable levels. Table 5 presents a set of characteristics examined for the purposes of this article and standards by which they should be analyzed, as well as the permissible levels of characteristics examined. Generally, these parameters are divided into key and significant features (due to gasification in a pressurized gas generator with CFB circulating fluidized bed in a CO2 atmosphere). The key features include items such as the calorific value of over 18000 [kJ/kg], ash content of less than 25%, melting point of above 1373 [K], carbonate reactivity in terms of CO2 above 2; in terms of carbon of below 20, chlorine content of less than 0.1%; the Hardgrove's GrH grinding susceptibility in the range of 45-65; sinterability using the Roga RI method of under 15. Significant features included the content of volatile matter, total moisture, total sulphur content, carbon content, hydrogen content, nitrogen content, oxide content, i.e., SiO2, Al2O3, Fe2O3, CaO, MgO, P2O5, TiO2, Na2O, K2O (Sobolewski et al., 2012; 2013). An important parameter for a given gas generator is the appropriate grinding of coal, i.e. fuel, since the fluidized reactor processes coal with a particle size from 0.5 mm to 3 mm (5 mm) (Sobolewski et al., 2012; 2013). Table 5 shows the values only for the relevant features in the experiment. It is worth noting that the graphs illustrate the full grain composition of upgraded coal, that is with a range of up to 18 mm. Material > 3 mm would be appropriate for gasification following proper fragmentation. TABLE 5 Limitations in respect of hard coal designated for the ground gasification process for the CFB reactor (Sobolewski et al., 2012) Parameter [unit] Standard Fluidized bed reactor Calorific value [kJ/kg] Ash content [%] Chlorine content [%] Hydrogen content [%] Nitrogen content [%] Carbon element content [%] Sulphur content[%] PN-81/G-04513 PN-80/G-451 PN-G-05460 PN-ISO 11711 PN-G-4534 PN-ISO 587 PN-G-04571:1998 PN-G-04571:1998 PN-G-04571:1998 PN-04584:2001 > 18 000 < 25 < 0.1 3.5-5.5 < 2.0 > 60 < 2.0 Fig. 1. F(d, h) Variables for coal: ZG Janina; KWK Wieczorek Fig. 2. Surface ­ coal element content = f (d, h) for coal ZG Janina; KWK Wieczorek Fig. 3. Surface ­ ash content = f(d, h) for coal: ZG Janina; KWK Wieczorek Fig. 4. Surface ­ heat of combustion = f(d, h) for coal: ZG Janina; KWK Wieczorek Density, particle size and the associated content of correlated carbon element, ash and heat of combustion resulting from the last two, have been accepted as physicochemical properties of coal. In analyzing the variants F(d, h) of both types of coal, it should be noted that these have different structure and texture. Coal from KWK Wieczorek contains significantly smaller amounts of fine classes, larger amounts of lighter fraction classes (with a higher carbon content). It is suspected that coal from ZG Janina is easier to break up and creates larger appropriate areas, relevant for gasification. It can be said that this is the result of lower metamorphisation of coal layers from ZG Janina. Analyses of ash and carbon element content (Figs. 2 and 3) show the fundamental differences between the two types of coal: ­ for lighter fractions, regardless of their particle size (besides the finest class), the ash content of coal from KWK Wieczorek is twice as low as that of ZG Janina, whereas the carbon element content of both types of coal is high: higher for coal from KWK Wieczorek (approximately 80%C) and by about 10% lower for coal from ZG Janina; ­ in analyzing the heaviest density fractions, it can be noted that high carbon element content is present in both types of coal and significantly lower in thicker grades, indicating stone enrichment, which in turn is reflected in the analysis of the ash in individual coarser size fractions of both types of coal. ­ the distribution of ash content in coal in the last layer of density (beyond the finest grade) confirms observations that there is a high concentration of ash in the previous layers (even above 60%) of coal from KWK Wieczorek ­ resulting from its ease of upgrading, while for ZG Janina the ash is more evenly distributed in the final three layers (between 30% and 50%). Correlating the heat of combustion of carbon element contents and ash contents causes the graphic image to be practically identical to the image of carbon element content depending on the heat of variables D and H. Heat of combustion values for lighter fractions are lower for ZG Janina than for KWK Wieczorek and in both cases independent from the scope of the particle class. 3.3. Analysis of the chemical distribution of coal properties Based on previous studies (section 3.2) it can be stated that obtaining coal that meets the requirements in terms of carbon element content, ash content and calorific value is not a problem, especially in the case of KWK Wieczorek. A certain problem may be ensuring appropriate carbon element content in ZG Janina. Figs. 5-8 illustrate the comparison of both types of coal in terms of the distribution of their chemical properties. Fig. 5. Surface ­ sulphur content = f(d, h) for coal: ZG Janina; KWK Wieczorek Fig. 6. Surface ­ hydrogen content = f(d, h) for coal: ZG Janina; KWK Wieczorek Fig. 7. Surface: the nitrogen content = f(d, h) for coal: ZG Janina; KWK Wieczorek Fig. 8. Surface: chlorine content = f(d, h) for coal: ZG Janina; KWK Wieczorek In observing the distribution of nitrogen content (Fig. 7) it is clear that both types of coal fully comply with the thresholds, whereby the coal from ZG Janina has a lower N content distributed very evenly in classes and layers. Also, the distribution of hydrogen content in the coal does not cause any problems. Coal from KWK Wieczorek has a significantly larger distribution of the H content. In ZG Janina the heaviest layers should be removed from the gasification process (not only for this reason). In terms of sulphur content distribution, the two types of coal vary significantly. The sulphur content in KWK Wieczorek does not exceed 1%, so there is no reason to take an interest in this issue. As far as ZG Janina is concerned, the heaviest layer, in which sulphur is bound with pyrite, should be removed in order to reduce the sulphur content. As far as the chlorine content is concerned, both types of coal slightly exceed the standards. It seems that removing the heaviest layers should lead to a chlorine balance within the normal limits. 3.4. Analysis of selected coal according to the correlation between the test characteristics Line correlation coefficients have been determined between the particle size and characteristics of coals examined for each individual layer for the purpose of identifying the most important relationships between the parameters of the coal. In this case, with the significance level of = 0.05, the critical value of the correlation coefficient is rkryt = 0.63. The results are presented in Table 6. TABLE 6 Correlation coefficients between particle size and other characteristics of the examined coal from ZG Janina and KWK Wieczorek coalmines for each of the layers Sulphur 1 2 Hydrogen 3 Nitrogen 4 Chlorine 5 Carbon 6 Heat of combustion 7 Ash 8 ZG Janina Particle size layer 1 Particle size layer 2 ­0.33 ­0.65 0.66 0.84 0.67 0.60 ­0.65 ­0.77 0.42 0.81 0.52 0.83 ­0.34 ­0.46 Particle size layer 3 Particle size layer 4 Particle size layer 5 Particle size layer 1 Particle size layer 2 Particle size layer 3 Particle size layer 4 Particle size layer 5 ­0.64 0.05 0.12 0.29 ­0.32 ­0.32 0.65 ­0.36 ­0.59 ­0.85 ­0.58 ­0.69 0.70 ­0.73 ­0.52 0.68 ­0.68 ­0.51 ­0.49 0.80 0.55 KWK Wieczorek ­0.33 ­0.32 ­0.61 ­0.70 ­0.30 ­0.32 0.43 0.60 ­0.03 ­0.69 0.48 0.21 0.57 ­0.49 ­0.68 ­0.45 ­0.13 ­0.28 0.23 0.11 0.41 0.50 0.52 0.24 ­0.7 0.43 0.51 0.59 0.10 ­0.69 ­0.40 ­0.54 ­0.54 ­0.09 0.7 When analyzing the table of correlation coefficients, the following conclusions can be made: ­ with increasing particle size, the layers change in relation to the characteristics of the carbon element content (in columns (layers), the correlation coefficient symbol and the measure of its importance change); ­ fundamental differences exist for sulphur - in coal from KWK Wieczorek these coefficients are negative, which indicates that the sulphur in the coal is probably organic sulphur (sulphur level decrease in the heaviest layers). This is in contrast to the coal from ZG Janina, in which the sulphur content in the heaviest layers does not change (which may be due to a significant presence of pyrites). Chlorine contained in coal from ZG Janina is particularly concentrated in the smallest classes regardless of layer. The coefficients for coal from ZG Janina are arranged differently and their significance decreases. For the heaviest layers the amount of chlorine slightly increases with particle size. The degree of carbonification increases in the lightest layers and decreases in the heaviest layers together with the increase in particle size. It can be said that only the last layer of coal from KWK Wieczorek contains minor carbon adhesions. Analysis of correlation coefficients for heat of combustion and ash content leads to analogical conclusions (due to the natural physical connection of these properties). The correlation coefficients between particle size and nitrogen contents in the coal from the two mines are arranged similarly, whereby these dependencies are more significant for coal from ZG Janina. In both types of coal the coefficients are positive for the three lightest layers and negative for the heaviest layers (nitrogen is present in bigger and heavier lumps of coal). It can be assumed that extended analysis of the correlation coefficients between the characteristics of coal in classes (correlation between the columns of tables 1-4) will allow for a very precise description of the coal types and their suitability for gasification. 4. Summary and Conclusions The proposed method of evaluating the suitability of coal for gasification is illustrative and offers a wide range of opportunities to observe the association of coal characteristics whereby certain values are significant or necessary in fulfilling the conditions in the light of their subsequent surface gasification. The two types of coal can be clearly differentiated on the basis of analysis. In comparing the measured values with those required, it was stated that the coal from KWK Wieczorek is better in terms of suitability for gasification, above all because it is characterized by higher heat of combustion and the values of measured properties are within the expected range. The correlation analysis also showed that it might be worth to consider eliminating the lowest layers of the material in the jig, as they can potentially generate the biggest problems during the gasification process (especially in the case of coal from ZG Janin. The types of coal under consideration differ from each other by age and origin. Coal from ZG Janina is younger than that from KWK Wieczorek, therefore its components are not fully metamorphosed. Hard coal designated for the gasification process in a gas generator as a fluidized layer is a rock, which undergoes various transformations during the carbonization process, as the result of which it is characterized by a variety of mineral, petrographic, chemical and structural compositions. Therefore, there is a variety of mineral and organic carbon components depending on the petrographic type. A number of components (ash, sulphur pyrites, carbon elements, heat of combustion, and calorific value) is closely related to the density distribution of carbonaceous material and can easily be isolated by mechanical processing. In contrast, compounds containing organic sulphur, nitrogen, chlorine, hydrogen, are those associated with coal structure as a result of geochemical, biochemical and salinity changes. Removal of these components is difficult and requires the use of chemical methods, in this case ­ demineralization. As multidimensional analysis individual primary components presented in the article showed, tested coal can easily be cleaned by gravitational methods and the components which correlate with the distribution of density removed. Ash and pyritic sulphur can be passed for heavy fractions (of high density). Carbon elements are concentrated in light fractions and high heat of combustion values can be observed. The Article has been compiled as a result of NCBiR project no. 23.23.100.8498/R34 entitled "Development of coal gasification technology for highly efficient production of fuels and energy" in the scope of tasks 2.1.2 on the subject of research on coal upgrading through mechanical processing. "between 2012-13 as part of a strategic program of research and development entitled "Advanced energy generation technologies."

Journal

Archives of Mining Sciencesde Gruyter

Published: Oct 20, 2014

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