The Thermal History of Select Coal-Waste Dumps in the Upper Silesian Coal Basin, Poland

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CHAPTER 15

The Thermal History of Select Coal-Waste Dumps in the Upper Silesian Coal Basin, Poland

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CHAPTER CONTENTS 15.1  Coal-Waste Dumps  Self-heating 15.2 Characteristics of Waste Dumps in Poland  Introduction   Rymer Cones   The Chwałowice Coal Dump, Starzykowiec  The Marcel Coal Mine Dump 15.3 Monitoring Self-heating Processes 15.4 Results of Waste Dump Monitoring   Rymer Cones

Old part of the Marcel Coal Mine Dump being dismantled. The fire began in 2007. Redevelopment of the dump involved cooling it by digging out burning waste and relocating and cooling it. The horizontal field of view is 150 m. Photo by Adam Tabor, 2008.

  The Chwałowice Coal Dump, Starzykowiec  The Marcel Coal Mine Dump 15.5 Self-heating and Fire Prevention  Discussion  Summary   Important Terms  References

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Coal and Peat Fires: A Global Perspective Edited by Glenn B. Stracher, Anupma Prakash and Ellina V. Sokol Copyright © 2015 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/B978-0-444-59509-6.00015-6

15.1  Coal-Waste Dumps Magdalena Misz-Kennan Adam Tabor

Photo by Adam Tabor, 2007.

A partly burned dump at the Marcel Coal Mine. The vertical field of view is 80 m.

 Self-heating Coal mining is one of the most important industries in the Upper Silesian Coal Basin (USCB) in southern Poland. At present, 95.62 Mt of coal being exploited generate about 40 Mt of waste (Jabłońska, 2004). The waste is derived from premining the coal and from coal cleaning processes (washing mine tailings) (Skarżyńska, 1995). In Poland, exploitation of 1 t of coal generates 0.3–0.6 t of waste. This waste is located in several tens of dumps, mostly sited near mines. In parts of these dumps, self-heating processes are taking place that sometimes evolve into a coal fire. The disposal of the waste gives rise to many environmental hazards, e.g. the possibility of endogenic fires, the emission of gases and dust, the disturbance of water supplies around the dumps, the leaching of soluble salts from the waste, the presence of dust, the level of noise generated by transporting machines and other equipment in the dump, and even the possibility of radiological hazards (Szafer et al., 1994; Tabor, 1995). Coal waste is composed of claystones (40–98%), mudstones (2–40%), coal shales (2–40%), and sandstones (<33%). Conglomeratic and carbonaceous rocks are rarely present. Organic matter present in the form of laminae, lenses, and interlayers and as dispersed organic matter constitutes 3–30 wt.%, usually 8–10 wt.%. In terms of mineral content, the mine stones are made up of clay minerals (50–70%), quartz (20–30%), as well as other minerals (10–20%) represented by pyrite, chlorite, siderite, and ankerite. Gypsum and jarosite can also be present (Skarżyńska, 1995). The processes of self-heating and combustion of coal in coal beds and coal piles are widely discussed in the literature. Relatively little has been published on these processes in coal waste. Thus, the following discussion on oxidation, self-heating, and combustion is biased toward experiences connected with coal. Self-ignition can occur only if three conditions are fulfilled at the same time—the presence of components (organic matter, pyrite) that react with air, easy access for air into the interior of the dump, and the possibility of heat accumulation in the dump (Urbański, 1983; Szafer et al., 1994; Brooks et al., 1988; Tabor, 1999, 2002; Barosz, 2003; Barosz, unpublished data; Pone et al., 2007). The process of self-heating of organic matter is a progressive twostage process. An initial incubation period during which the temperature rises very slowly is followed by a selfheating process during which the temperature rises very rapidly (Sawicki, 2004; Cygankiewicz, 1996) and can reach 1200–1300 °C (Sawicki, 2004). It is the low-temperature oxidation of coal that is the primary source of heat (Krishnaswamy et al., 1996a; Lu et al., 2004; Singh et al., 2007). During the low-temperature oxidation, a number of reactions take place, namely, the chemisorption of oxygen in coal pores and the formation of unstable intermediates, the decomposition of these intermediates into gaseous products and stable oxygenated complexes, and the degradation of the stable complexes and generation of new active sites for coal oxidation followed by the decomposition of the solid complexes (Wang et al., 2002a). The products of oxidation are composed of both solid and gaseous phases (Berkowitz, 1985; Itay et al., 1989; van Krevelen, 1993; Wang et al., 2002a). The primary gaseous products are CO, CO2, and water vapor (Cygankiewicz, 1996; Garcia et al., 1999; Wang et al., 2002b). The products of the solid phases contain phenolic groups and –OH, –COOH, and –C]O in aromatic and aliphatic structures

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(Garcia et al., 1999; Wang et al., 2002a,b; Singh et al., 2007); their contents increase substantially during oxidation (Wang et al., 2002a). Decomposition of hydroxyl groups (–OH) leads to the formation of carbonyl groups (–C]O) and carboxylic acids (–COOH), (Clemens et al., 1991; Marinov, 1977). During oxidation, humic acids are also formed (Berkowitz, 1985; van Krevelen, 1993; Chang and Berner, 1998). Investigations of self-heating of coals indicate that carbon monoxide and paraffin gasses are the main indicators of self-heating at low temperatures. Carbon monoxide is released from coal at temperatures in the range 49.8–54.9 °C in quantities that progressively increase with rising temperature (Lu et al., 2004). It is a very effective early indicator of self-heating as it is released before ethylene and the unsaturated hydrocarbons (Lu et al., 2004; Singh et al., 2007). A temperature of 64 °C combined with the gradual increase of CO and C2H4 are an indication that self-heating is occurring (Lu et al., 2004). Low oxygen contents indicate likewise as does the CO/O2 ratio (Graham’s ratio) which increases with increasing coal oxidation toward values of <0.40; in cases of very intense self-heating, values can reach 0.50–10.0. During coal oxidation under laboratory conditions, the CO/O2 ratio increases from 0.2 at 50 °C to 1.6 at 150 °C (Singh et al., 2007). Oxygen contents decreasing to 12.4% reflect the end of flaming conditions (Banerjee et al., 1965). Some investigations of low-temperature coal oxidation indicate that CO2 is the prime combustion product but that a measurable CO content is observed when the oxygen content is <15% (Singh et al., 2007). According to Wang et al. (2002a,b), the main gaseous product of coal oxidation in the temperature range 60–90 °C is CO2 and that below 60 °C the release of CO is very limited. Dehydroxylation reactions of oxygenated compounds result in the release of substantial amounts of water (Berkowitz, 1985; Clemens et al., 1991; Wang et al., 2002b; Sokol, 2005). The temperature range 60–80 °C is considered to be critical (Sawicki, 2004; Sokol, 2005). Where the temperature of coal does not reach the critical value or if conditions exist that enhance dissipation of heat from the dump, the selfheating process will be interrupted and cooling will take place. Above the critical temperature, a rapid increase in temperature up to the stage of coal ignition is usual (Sawicki, 2004). The centers of self-ignition are usually located at depths of 0.2–4.0 m from the dump surface. As burning progresses, the fire migrates inside the dump and, where burning is complete, incandescent empty places (“wolf’s pits”) that can easily subside can form (Urbański, 1983). A number of factors influence the self-heating processes in coal-waste dumps. These can be classified into internal and external factors (Urbański, 1983). Internal Factors These include the structure of the primary material, the nature of the coaly components, and the presence of substances inhibiting oxidation. It is believed that halogens are substances that halt dump fires (Urbański, 1983; Sensogut and Cinar, 2000). Organic matter in coal waste can vary markedly in petrographic composition. Its dominant component, vitrinite, is considered the maceral most prone to oxidation (Taylor et al., 1998). Research by Benfell et al. (1997) has shown that the addition of resinite to coal can increase the combustion temperature by several degrees. Rank is another influencing factor; with increasing rank, the probability of self-heating decreases (Rosiek and Urbański, 1990; Beamish et al., 2001). However, Beamish et al. (2001) have shown that coals of the low rank (lignites) have a lesser tendency to self-heat than subbituminous coals. Overall, the temperature of coal ignition increases with coal rank from about 150 °C for brown coals to about 200 °C for bituminous coals and to about 300 °C for anthracites (Sawicki, 2004). External Factors External factors pertain to the reaction of oxygen from air at low temperatures. They include any factor that influences the filtration ability of dumps and their heat balance (Urbański, 1983; Szafer et al., 1994). The height and shape of a coal-waste dump have, by determining its filtration properties, a marked influence on whether fires occur or not (Urbański, 1983). High and steep dumps, especially those in the shape of cones, are most prone to self-heating. The reasons relate to particle segregation and the enhanced influence of winds (Urbański, 1983; Szafer et al., 1994); those with steep slopes allow more air to be introduced into the stockpile (Krishnaswamy et al., 1996b). Convection caused by wind is considered the dominant process of air transport in stockpiles. It is believed that dumps are safe in two extreme cases, i.e. where there is no air circulation and where circulation is very strong. At present, the dominant view is that stockpile safety is better served by compaction of the deposited material rather

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than by leaving it loose (Krishnaswamy et al., 1996b). On the windward slopes, the temperature of material is usually much higher than elsewhere in the stockpile. In addition, air pressure in the dump in winter can exceed that in summer by a factor of 2. Thus, the normal course, porous- and coarse-grained waste is more likely to self-heat during winter and autumn; fine-grained waste, during spring and summer (Urbański, 1983; Szafer et al., 1994). During coal-waste deposition, particle segregation commonly occurs. Fine-grained material, usually containing more coaly components, tends to collect in the upper parts of stockpiles—and coarser material at their base. Such segregation creates favorable conditions for the introduction of air into a dump and for self-heating and ignition (Urbański, 1983; Szafer et al., 1994). Hot spots commonly occur on the junctions between layers of differing particle size (Krishnaswamy et al., 1996b). The occurrence and localization of endogenic hot spots is influenced by porosity and rain. Heavy rain especially, by causing damage to stockpile slopes, promotes the introduction of air (Urbański, 1983). The presence of moisture accelerates pyrite decomposition, and organic material is activated to absorb more oxygen. On the one side, the presence of moisture up to a certain level enhances the self-heating process, whereas on the other, any excess slows the self-heating process (Rosiek and Urbański, 1990). Coal porosity increasing with decreasing moisture content leads to a higher rate of oxidation and self-heating (Pone et al., 2007). To date, there are relatively few published data on temperature variations in waste dumps and on variations in CO, CO2, and O2. This chapter presents data about the changes over time in temperature and gas content at a depth of 0.81 m in select coal-waste dumps in the USCB, based on many years of monitoring with regard to various factors that influence thermal processes.

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15.2  Characteristics of Waste Dumps in Poland

Photo by Adam Tabor, 2007.

Redevelopment of the Starzykowiec Coal-Waste dump.

 Introduction Three stockpiles out of many in the USCB, with a history of self-heating, were selected for this chapter. These are a dump at the closed Rymer Coal Mine (the Rymer Cones dump), a dump at the Chwałowice Coal Mine (Starzykowiec), and the dump at the Marcel Coal Mine.

  Rymer Cones The Rymer Cones dump was formed at the beginning of the twentieth century. It is composed of three cones (Figure 15.2.1) formed using outdated techniques. These cones are essentially burned out. During the period 1994–1999, the cones were redeveloped and enclosed with more recent coal waste (Figures 15.2.2 and 15.2.3) as described by Tabor (2002), Barosz (2003), and Barosz (unpublished data). A new dump covering an area of 13.03 ha and rising to a height of +300 m above sea level has a capacity of 2.4 million cubic meter. The old cone No. 1 was left untouched (Barosz, 2003; Barosz, unpublished data). Around the turn of the present century, the surfaces of the cones were sealed with openwork concrete panels and fly ash with the aim of blocking the entry of air into the dump (Figure 15.2.4). Despite all these efforts, after some time the process of self-heating was so intense that it proved necessary to remove the panels and fly ash. At present, only the top and the eastern slope of the dump are sealed. The present aspect of the stockpile is shown in Figure 15.2.5.

Figure 15.2.1.  Rymer Cones in 1996. Photo by Adam Tabor, 1996.

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Figure 15.2.2.  Cone No. 3 at Rymer Cones during redevelopment in 1996. The vertical field of view is 50 m. Photo by Adam Tabor, 1996.

Figure 15.2.3.  Redevelopment in 1996 of cones at Rymer Cones. During redevelopment of the cones, the old heated cones that contained partially burnt material were surrounded by coal waste from coal mining at the now former Rymer Coal Mine. The moat was created to prevent the surrounding coal waste from heating. The moat was later filled, also in 1996, with fly ash. Photo by Adam Tabor, 1996.

Figure 15.2.4.  Remnants of sealing the cones at Rymer Cones with concrete panels and fly ash, as in 2008. The vertical field of view is 50 m. Photo by Adam Tabor, 2008.

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Figure 15.2.5.  The Rymer Cones dump today. Photo by Adam Tabor, 2002.

Figure 15.2.6.  The Starzykowiec dump. The vertical field of view is 15 m. Photo by Magdalena Misz-Kennan, 2008.

  The Chwałowice Coal Dump, Starzykowiec When exactly the Starzykowiec waste dump (Figures 15.2.6 and 15.2.7) was initially formed is not known, although it was probably when the Chwałowice Coal Mine (formerly Donnersmarck) opened in 1903. In later years, the coal-mud collectors (Nos 5, 6, and 7) were constructed on top. At the beginning of the 1970s, the deposition of coal mud here ceased and their exploitation started. Initially, mud was removed from collectors Nos 6 and 7, and then dismantling of the scarp continued till the late 1980s. The burnt out waste was used for rebuilding the railway station in Niedobczyce. In the early 1990s, all work ceased due to the danger of scarp collapse. Complete burning of the waste rocks had occurred over about 30 years before their exploitation originally started. No signs of further thermal activity were seen during their exploitation. In recent years up to 2005, the exploitation of mud collector No. 5 was still going on. Afterward, reclamation using waste from the existing coal mine was started. Since 2004, the west scarp has been surrounded by waste from the current production and a new scarp has been formed in which thermal events started anew in 2006 (information from the mine staff in 2008; Tabor, unpublished data).

  The Marcel Coal Mine Dump The waste dump at the Marcel Coal Mine is an overleveled dump (Figures 15.2.8–15.2.11).

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Figure 15.2.7.  The Starzykowiec dump. The vertical field of view is 10 m. Photo by Magdalena Misz-Kennan, 2008.

Figure 15.2.8.  Old part of the Marcel Coal Mine dump. The horizontal field of view is 15 m. Photo by Magdalena Misz-Kennan, 2007.

Figure 15.2.9.  Old part of the Marcel Coal Mine dump. The vertical field of view is 20 m. Photo by Magdalena Misz-Kennan, 2008.

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Figure 15.2.10.  New part of the Marcel Coal Mine dump, showing the deposition of waste rock. The thickness of the individual layers of coal waste is about 1 m. Photo by Adam Tabor, 2000.

Figure 15.2.11.  New part of the Marcel Coal Mine dump, showing the compaction of coal waste with a vibrating roller. Photo by Adam Tabor, 2000. It is an amalgamation of three dumps that had existed in the area at various times; it is now composed of cones that date from the beginning of the nineteenth century. The first of these covered an area of 19 ha, rose to a maximum height of +353 m above the sea level, and had an estimated capacity of 12 million cubic meter. Dumping here finished in 1986. Self-heating processes of varying intensity characterized the entire dump. A second dump created in 1982 on the western side of the dump covered an area of 33.2 ha, rose to a height of +272 m above the sea level, and had a capacity of 3.7 million cubic meter. The third dump, which enclosed the two discussed above, occupies an area of 56.13 ha and has a capacity of 24.9 million cubic meter. The accepted ordinate is +320 m above the sea level (Barosz, 2003; Barosz, unpublished data).

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15.3 Monitoring Self-heating Processes

Measuring temperature in the ­Starzykowiec Dump.

Photo by Magdalena Misz-Kennan, 2008.

The essential elements involved in the monitoring of coal-waste dumps and their heating are visual field observations; temperature measurements both on the surface and within the dump; measurements of CO, CO2 and O2 contents; and examination of the degree of compaction and sealing of the dump material. In tandem, the degree of air pollution around the dump and the chemistry of any water that came in contact with the waste are examined, as is the level and range of noise connected with works in the dump and the working conditions (Barosz, 2003; Barosz, unpublished data; Tabor, 2002). Visual field observations may permit early detection of some anomalies and abnormalities. Particular attention is paid to vaporization of the dump surface; overdried spots; atrophy of plants; abnormally high plant contents, which can reflect elevated temperatures within the dump; emission of smoke commonly smelling of hydrocarbons; brown stains on the dump surface; sulfur mineralization; and the accelerated melting of snow over sites of self-heating (Barosz, 2003; Barosz, unpublished data; Tabor, 2002). Self-heating and spontaneous combustion is obviously associated with rising temperatures both on the dump surface and inside. Slow at the beginning, the rate of temperature increase accelerates with the passage of time. The self-heating process is also associated with changes in the chemical composition of the atmosphere around the dump, namely, a decrease in oxygen content, the presence of CO, and increasing CO2 (Urbański, 1983; Szafer et al., 1994; Tabor, 2002; Barosz, 2003; Barosz, unpublished data). The aim of temperature measurements of the surface of the dump (Ts) is the determination of any clear anomalies in relation to the temperature of surrounding air (Ta). The surface temperature strongly depends on weather conditions. In the summer, for instance, it can depend on the degree of insolation. As weather conditions must be taken into account, any such measurement is a supplementary result only. In recent years, A. Tabor started to make two surface measurements— one at a depth of about 5 cm where the influence of atmospheric factors is limited and a second on the surface itself. Thus, in Tables 15.4.2–15.4.4, some measurements are single and others double. This method gives a much better estimate of the real surface temperature. The much more important measurement of temperature inside the dump (Ti) is carried out at a depth of 0.8–1.0 m using a probe and thermometer (Tabor, 2002; Barosz, 2003; Barosz, unpublished data). Table 15.3.1 Classification of the thermal state of a coal-waste dump.* Thermal State

Interior Temperature (°C) at a Depth of 0.8–1.0 m

CO Content (vol.%)

No self-heating Self-heating Fire of low intensity Intense fire

<35 36–100 101–200 >200

<0.001 0.001 to <0.01 0.01 to <0.1 >0.1

*After Urbański (1983).

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Gas contents are measured with the metal pipe perforated at the bottom and attached to a rubber tube. The pipe is placed inside the hole made for the temperature measurement. The measurement is carried out using a suction pump to extract 100 ml of gas and feed it into an automated measuring device that gives immediate values for both temperature and gas contents. Nonautomated measurements using glass indicating tubes are more troublesome and time consuming but reasonably accurate (Barosz, 2003; Barosz, unpublished data; Tabor, unpublished data). The classification of the thermal events in waste dumps is based mainly on the measured values of CO contents and temperatures inside the dump. Carbon dioxide and oxygen values are supplementary, although they can underpin conclusions drawn concerning degrees of compaction and intensities of combustion. On the basis of data obtained over longer periods, e.g. an entire year, the dynamics of the thermal processes and their evolution (developing or diminishing) may be determined (Barosz, 2003; Barosz, unpublished data). The classification of the thermal state of a waste dump is given in Table 15.3.1.

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15.4  Results of Waste Dump Monitoring

Photo by Adam Tabor, 2007.

Hot slope under the coal-mud collector at the Marcel Coal Mine dump. The vertical field of view is 80 m.

  Rymer Cones The Rymer Cones dump is still thermally active. Monitoring of that dump has been carried out since 2000 by A. Tabor. Temperatures at 0.8–1.0 m depth range from c. 40 to >600 °C. Measured temperatures on the west slope are generally higher (60–140 °C) and are characterized by greater variation (Table 15.4.1; Figures 15.4.1 and 15.4.2) than are the temperatures (50–80 °C) recorded on the eastern (Figure 15.4.3) and southern slopes (Figure 15.4.4). Temperatures on the south slope sometimes reach higher values (c. 200 °C), even up to about 500 °C. Under the cover of fly ash (Locality R22a), the inside temperature exceeds 80 °C. The highest inside temperatures (>600 °C) were measured on the west slope. Temperatures at the base of the last cone (point R22) range from c. 40 to 70 °C (Figure 15.4.5). Such a distribution of temperatures strongly reflects dominating winds from the west. Commonly, elevated inside temperatures are measured in the summer (Figures 15.4.1–15.4.5). In a number of places, the release of smoke resulting from intense thermal activity within the dump may be observed. This smoke is the cause of the strong smell of hydrocarbons that is experienced everywhere in the vicinity of the dump. These gases are released on the slopes of the dump (Figure 15.4.6) and in places covered by fly ash pulp (Figure 15.4.7). The small number of complaints from residents of nearby houses reflects the dominating winds from the west. The high temperatures measured in winter coincide with places where snow is melted (Figures 15.4.8 and 15.4.9) and, where the measured temperatures are very high (several hundred degrees Celsius), with places where plants are burned (Figure 15.4.10). A large part of the dump is covered by healthy grasses, even in winter (Figures 15.4.11 and 15.4.12), due to the heat and higher moisture levels resulting from dehydroxylation of oxygenated organic compounds. High dump temperatures are also reflected by localized expulsions of hydrocarbons at the dump surface; these places are recognized by the relatively intense color of the waste around them (Figures 15.4.13–15.4.15). Carbon monoxide measurements show that CO contents on the west slope are quite varied and in the range 0–1.2%. In some places in the dump, e.g. points R1 and R2, the CO content increases with increasing internal temperature; correlation coefficients are 0.67 and 0.79, respectively (Figures 15.4.16 and 15.4.17). However, this not observed at many points. On the west slope of the dump, relatively large variations in CO2 (traces: c. 18%) and oxygen contents (0–21%) are also a feature. At point R10, where measured interior temperatures span a relatively small range of 65–89 °C, the CO content is 0.002–0.2%, CO2 content lies in the range 17.5 to over 18%, and oxygen is absent. On the east slope of the dump, the CO content is low (0.001–0.03%) but the CO2 content is high (8 to over 18%). Oxygen, if present, does not exceed 7%. Such values show smaller variations than do values measured on the west slope. Measured temperatures on the east slope are also lower than on the west slope, due, probably, to the westerly winds forcing air into the dump.

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Table 15.4.1 Examples of monitoring results for the Rymer Cones dump.* Gas Contents (vol.%)

Locality No.

Monitoring Date

Ta (°C)

Ts (°C)

Ti (°C)

CO

CO2

O2

R12 R12 R12 R12 R12 R12 R12 R12 R12 R12 R12 R12 R12 R12 R12 R12 R12 R12 R19 R19 R19 R19 R19 R19 R19 R19 R19 R19 R19 R19 R19 R19 R19 R19 R19 R19 R19 R19 R19 R22 R22 R22 R22 R22 R22 R22 R22 R22 R22 R22 R22

02.2006 03.2006 04.2006 05.2006 08.2006 09.2006 11.2006 02.2007 03.2007 04.2007 06.2007 07.2007 08.2007 09.2007 10.2007 11.2007 12.2007 01.2008 02.2006 03.2006 04.2006 05.2006 06.2006 07.2006 08.2006 09.2006 11.2006 12.2006 02.2007 03.2007 05.2007 06.2007 07.2007 09.2007 10.2007 11.2007 01.2008 02.2008 03.2008 02.2006 04.2006 06.2006 07.2006 08.2006 09.2006 11.2006 02.2007 04.2007 06.2007 07.2007 09.2007

37 43 28 24 46 50 44 46 18 47 45 37 60 38 42 47 38 23 1 22 22 38 24 44 30 22 23 22 24 20 22 28 26 22 38 26 26 19 20 15 19 23 30 19 19 8 16 20 25 17 24

−3 0.5 8 16 19 20 5 −0.5 0 12 21 15 25 18 14 5 −3 1.5 −1.5 2 12 19 15 32 22 24.5 7 5 1 0 20 21 15 20 17 5 5.5 5 3 −1.5 8 15 28 19 20 5 1 12 21 15 18

206 75.5 91.1 51.3 86.4 89.5 93.6 102.6 228 89.1 338 345 143.5 188.9 94.6 76.6 148.7 92.4 52.2 58.2 61.5 62.8 60.3 70.2 60.2 60.9 64.1 62.9 62.2 63.1 69.2 71.2 70.1 70.6 80.1 63.7 73.3 67.2 58.8 48.3 53.4 43.8 56.2 56.5 44.3 34.8 44.3 63.2 60.1 55.4 65.6

0.02 0.30 0.10 0.02 0.40 0.10 1.00 0.20 0.05 0.02 1.00 0.70 0.50 0.50 0.20 0.20 0.20 0.02 0.02 0.02 0.03 0.03 0.02 0.02 0.01 0.01 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.001 0.02 0.01 0.002 0.02 0.02 0.001 0.002 0.02 0.02 0.02 0.005

2 19 19 14 19 19 19 19 19 19 19 19 19 19 19 19 19 2 19 19 19 17 17 19 19 19 19 19 19 19 19 19 19 19 19 19 15 19 19 10 19 19 19 19 16 16 14 19 19 19 19

17 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 9 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 6 0 0 0 0 0 2 3 0 0 0 0 Continued

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Table 15.4.1—cont’d Examples of monitoring results for the Rymer Cones dump.* Gas Contents (vol.%)

Locality No.

Monitoring Date

Ta (°C)

Ts (°C)

Ti (°C)

CO

CO2

O2

R22 R22 R22 R31 R31 R31 R31 R31 R31 R31 R31 R31 R31 R31 R31 R31 R31 R31 R31 R31 R31 R31 R31 R31 R37 R37 R37 R37 R37 R37 R37 R37 R37 R37 R37 R37

02.2008 03.2008 04.2008 03.2006 04.2006 06.2006 07.2006 08.2006 09.2006 11.2006 12.2006 03.2007 04.2007 05.2007 06.2007 07.2007 08.2007 09.2007 10.2007 11.2007 12.2007 01.2008 02.2008 03.2008 03.2006 04.2006 05.2006 08.2006 09.2006 05.2007 07.2007 08.2007 10.2007 11.2007 12.2007 04.2008

6 8 14 24 51 260 131 69 101 35 52 47 47 55 57 52 85 47 83 71 54 66 35 45 24 25 42 26 22 38 35 49 30 34 72 23

3 2 8 0.5 8 13.5 28 19 20 5 5 0 12 20 21 15 27 18 14 5 −3 1.5 3 2 2 9 19 22 24.5 20 15 25 18 5 −3 3

35.7 36.4 41.2 66.4 90.2 600 520 600 523 214 255 344 385 285 415 262 280 225 315 292 365 351 311 325 58.2 88.5 62 41.1 39.2 148.9 85.6 95.3 72.4 70.2 90.6 51.2

0.02 0.02 0.001 0.02 0.10 – – – – 4.00 2.00 0.50 1.00 0.20 0.50 0.50 0.50 0.50 1.00 – 0.80 1.00 – 0.10 0.02 0.02 0.02 0.02 0.01 0.10 0.20 0.10 0.02 0.02 1.00 0.20

19 19 19 19 19 – – – – 19 19 19 19 19 19 19 19 19 19 – 19 18 – 19 4 17 7 12 13 19 19 18 19 19 19 19

0 0 0 0 0 – – – – 0 0 0 0 0 0 0 0 0 0 – 0 0 – 0 3 0 0 0 0 0 0 0 0 0 0 0

*Ta, air temperature; Ts, surface temperature; Ti, internal temperature.

Figure 15.4.1.  Variations in air temperature (Ta), surface temperature (Ts), and internal temperature (Ti) at locality R31 on the Rymer Cones dump. Figure by Magdalena Misz-Kennan, 2010.

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Figure 15.4.2.  Variations in air temperature (Ta), surface temperature (Ts), and internal temperature (Ti) at locality R12 on the Rymer Cones dump. Figure by Magdalena Misz-Kennan, 2010.

Figure 15.4.3.  Variations in air temperature (Ta), surface temperature (Ts), and internal temperature (Ti) at locality R19 on the Rymer Cones dump. Figure by Magdalena Misz-Kennan, 2010.

Figure 15.4.4.  Variations in air temperature (Ta), surface temperature (Ts), and internal temperature (Ti) at locality R37 on the Rymer Cones dump. Figure by Magdalena Misz-Kennan, 2010.

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Figure 15.4.5.  Variations in air temperature (Ta), surface temperature (Ts), and internal temperature (Ti) at locality R22 on the Rymer Cones dump. Figure by Magdalena Misz-Kennan, 2010.

Figure 15.4.6.  Smoke with hydrocarbons on the Rymer Cones dump. The height of the trees at the left is about 5 m. Photo by Adam Tabor, 2003.

Figure 15.4.7.  Smoke venting through a fly ash cover on the Rymer Cones dump. Photo by Magdalena Misz-Kennan, 2008.

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Figure 15.4.8.  Northwest slope on the Rymer Cones dump, where snow melted over a hot spot. Photo by Adam Tabor, 2006.

Figure 15.4.9.  The west slope of the Rymer Cones dump, where snow melted over a hot spot. The height of the trees at the left is about 5 m. Photo by Adam Tabor, 2006.

Figure 15.4.10.  Burnt vegetation on the Rymer Cones dump. Photo by Adam Tabor, 2008.

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Figure 15.4.11.  Vegetation on the Rymer Cones dump. The height of the plants is about 1 m. Photo by Magdalena Misz-Kennan, 2008.

Figure 15.4.12.  Vegetation on the Rymer Cones dump. Photo by Magdalena Misz-Kennan, 2007.

Figure 15.4.13.  Vented hydrocarbons (black area) on the Rymer Cones dump. The horizontal field of view is 3 m. Photo by Magdalena Misz-Kennan, 2007.

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Figure 15.4.14.  Vented hydrocarbons (black area) on the Rymer Cones dump. The horizontal field of view is 4 m. Photo by Magdalen Misz-Kennan, 2008.

Figure 15.4.15.  Vented hydrocarbons (black areas) on the Rymer Cones dump. The height of the trees on the sides of the cone to the left of the ground antenna is about 5 m. Photo by Adam Tabor, 2006.

Figure 15.4.16.  Relationship between CO content and interior temperature at locality R1 on the Rymer Cones dump. Figure by Magdalena Misz-Kennan, 2010.

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Figure 15.4.17.  Relationship between CO content and interior temperature at locality R2 on the Rymer Cones dump. Figure by Magdalena Misz-Kennan, 2010.

  The Chwałowice Coal Dump, Starzykowiec The Starzykowiec Dump is characterized by relatively low interior temperatures that usually do not exceed 50 °C (Table 15.4.2). In a few places only, they exceed 100 °C and even reach a few hundred degrees Celsius. Where there is no evidence of self-heating process, measured temperatures vary with the season; surface and interior temperatures are high in summer and low in winter (Figures 15.4.18 and 15.4.19). In some cases, e.g. as at point S1, the patterns of surface and interior and surrounding temperatures almost parallel each other; higher interior temperatures reflect higher air temperatures (r = 0.58; Figure 15.4.20). In some places, e.g. in the vicinity of point S3, intense self-heating occurs, measured temperatures exceed 600 °C and fires are sometimes observed (Figures 15.4.21 and 15.4.22). Due to the tendency for high temperatures there, this site has been redeveloped a number of times. Gas releases and strong hydrocarbon smells also identify local high-temperature sites in this dump (Figure 15.4.23), as does the melting of snow (Figure 15.4.24). Such phenomena are observed usually in the spring or autumn and after heavy rain. Although the hot spots are localized, they migrate with time from place to place in the dump. In the Starzykowiec Dump, carbon monoxide is typically absent. When present, contents are usually <0.1%, in very rare cases <2.5%. The CO2 and O2 show greater diversification. Where CO is absent (sites S1, S2, S2a, S3), CO2 contents are also relatively low (0–0.5%) and oxygen contents high (16–21%) and, conversely, higher carbon monoxide contents are associated with low (0.0–7%) oxygen contents.

  The Marcel Coal Mine Dump In the new part of the reclaimed dump at the Marcel Coal Mine, no self-heating is taking place. It is apparently subject only to weathering processes. This new part was completely reclaimed and is now covered with plants (Figure 15.4.25). In older parts of the dump, interior temperatures usually do not exceed 120 °C, being typically in the range 20–90 °C (Table 15.4.3). The patterns of surface and air temperatures are parallel. Generally, interior temperatures are higher in summer and lower in winter (Figures 15.4.26–15.4.28). Locally, in the old part of the dump, interior temperatures ranged from >100 to 400 °C in the period November 1997–February 2000 and surface temperatures were much higher than the air temperatures (Table 15.4.4) due to the self-heating processes taking place inside the dump. In the area being reclaimed, interior temperatures were lower than surface temperatures in both summer and spring. Elevated temperatures are more often measured in spring and autumn (Barosz, 2003; Barosz, unpublished data). When carbon monoxide is absent, CO2 contents are low and oxygen contents high. Typically, higher CO contents are associated with higher CO2 contents. It can be assumed that oxygen was used for formation of CO and CO2.

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Table 15.4.2 Examples of monitoring results for the Starzykowiec dump.* Gas Contents (vol.%)

Locality No.

Monitoring Date

Ta (°C)

Ts (°C)

Ti (°C)

CO

CO2

O2

S1 S1 S1 S1 S1 S1 S1 S1 S1 S1 S1 S1 S1 S1 S1 S1 S1 S1 S1 S1 S1 S1 S1 S1 S1 S1 S1 S1 S1 S1 S1 S1 S1 S1 S1 S1 S1 S1 S2 S2 S2 S2 S2 S2 S2 S2 S2 S2 S2 S2 S2

03.2004 04.2004 05.2004 06.2004 07.2004 08.2004 09.2004 10.2004 11.2004 12.2004 02.2005 03.2005 04.2005 05.2005 06.2005 07.2005 08.2005 09.2005 10.2005 11.2005 12.2005 03.2006 04.2006 05.2006 06.2006 07.2006 08.2006 09.2006 10.2006 11.2006 12.2006 01.2007 02.2007 03.2007 04.2007 05.2007 07.2007 10.2007 03.2004 04.2004 05.2004 06.2004 07.2004 08.2004 09.2004 10.2004 11.2004 12.2004 02.2005 03.2005 04.2005

22 15 20 38 12 19 14 14 9 −1 1 3 15 15 11 27 14 15 13 2 3 12 2 18/26 20/21 30/33 23/22 17/17 11/11 6/6 9/10 1 9/9 4/5 11/9 19/23 27 7 20 18 24 38 12 28 28 14 8 −1 7 6 18

20 10 20 27 14 26 20.5 15 8 −1 1 2 14 11 10 24 14 14 16 2 1.5 0 3 19 13 27 21 15 12 6 8 −1 8 10 3.5 19 20 8 20 10 20 27 14 26 20.5 15 8 −1 1 2 14

9.5 12.2 12.8 20.0 19.0 23.1 22.2 18.2 18.4 13.8 0.08 13.8 13.5 14.2 17.8 20.9 22.3 20.3 19.4 18.1 16.9 14.6 6.4 13.2 17.3 24.1 26.8 22.9 19.9 17.4 14.2 4.4 16.1 7.8 16.3 16.8 23.6 15.2 9.0 15.6 19.3 19.3 18.3 24.3 23.4 16.8 18.4 13.5 11.8 10.9 12.5

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

Trace Trace Trace 0 1 Trace 0.5 Trace Trace 0 0 Trace Trace 0.5 0.5 Trace 0 Trace 0.5 Trace Trace Trace Trace <0.5 Trace Trace Trace 0.5 0.5 0.5 Trace Trace Trace Trace <0.5 0.5 Trace 0 0 1 Trace Trace Trace 1 Trace Trace Trace Trace Trace Trace Trace

18.0 0 17.5 17.0 16.5 16.5 15.5 16.0 17.0 19.5 18.5 20.5 17.5 18.0 19.0 16.0 18.0 18.0 18.0 16.5 17.5 18.0 17.0 17.5 17.0 20.5 20.0 20.0 20.0 20.5 21.0 20.0 21.0 21.0 20.0 21.0 20.0 21.0 18.0 18.0 17.5 16.0 16.0 16.0 16.0 16.0 17.0 18.0 17.0 19.5 17.0 Continued

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Table 15.4.2—cont’d Examples of monitoring results for the Starzykowiec dump.* Gas Contents (vol.%)

Locality No.

Monitoring Date

Ta (°C)

Ts (°C)

Ti (°C)

CO

CO2

O2

S2 S2 S2 S2 S2 S2 S2 S2 S2 S2 S2 S2 S2 S2 S2 S2 S2 S2 S2 S2 S2 S2 S2

05.2005 06.2005 07.2005 08.2005 09.2005 10.2005 11.2005 03.2006 05.2006 06.2006 07.2006 08.2006 09.2006 10.2006 11.2006 12.2006 01.2007 02.2007 03.2007 04.2007 05.2007 07.2007 10.2007

15 11 28 14 15 13 4 9 18/22 16/20 30/32 23/22 17/17 12/12 7/6 9/9 1 9 4 10/9 22/27 24 8

11 10 24 14 14 16 2 0 19 13 27 21 15 12 6 8 −1 8 10 3.5 19 20 8

12.2 16.8 19.9 21.4 20.9 18.2 16.3 12.9 14.9 16.8 24.9 28.6 22.5 20.3 16.3 15.7 5.1 15.4 8.1 14.1 17.9 27.7 16.8

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

0.5 Trace Trace Trace 0.5 0.5 Trace Trace Trace Trace 0.5 Trace 0.5 1 Trace Trace 0.5 Trace 0 Trace – Trace 1.5

17.0 18.5 17.0 17.0 17.5 17.5 17.0 18.0 17.0 17.0 19.5 20.0 21.0 20.0 21.0 20.0 21.0 21.0 21.0 21.0 – 21.0 19.0

*Ta, air temperature; Ts, surface temperature; Ti, internal temperature.

Figure 15.4.18.  Variations in air temperature (Ta), surface temperature (Ts), and internal temperature (Ti) at locality S1 on the Starzykowiec dump. Figure by Magdalena Misz-Kennan, 2010.

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Figure 15.4.19.  Variations in air temperature (Ta), surface temperature (Ts), and internal temperature (Ti) at locality S2 on the Starzykowiec dump. Figure by Magdalena Misz-Kennan, 2010.

Figure 15.4.20.  Relationship between the internal temperature (Ti) and air temperature (Ta) at locality S1 on the Starzykowiec dump. Figure by Magdalena Misz-Kennan, 2010.

Figure 15.4.21.  Fire excavated to show combustion at the Starzykowiec dump. The horizontal field of view is 3 m. Photo by Adam Tabor, 2008.

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Figure 15.4.22.  Fire excavated to show combustion at the Starzykowiec dump. The horizontal field of view is 3 m. Photo by Adam Tabor, 2008.

Figure 15.4.23.  Vented gases at the Starzykowiec dump. The height of the poles is about 1 m. Photo by Adam Tabor, 2007.

Figure 15.4.24.  Melted snow at the Starzykowiec dump. The vertical field of view is 2 m. Photo by Magdalena Misz-Kennan, 2007.

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Figure 15.4.25.  Revegetated part of the Marcel Coal Mine dump. The height of the trees in the background is about 5 m. Photo by Adam Tabor, 2008. Table 15.4.3 Examples of monitoring results for the Marcel Coal Mine dump.* Gas Contents (vol.%)

Locality No.

Monitoring Date

Ta (°C)

Ts (°C)

M6 M6 M6 M6 M6 M6 M6 M6 M6 M6 M6 M6 M6 M6 M6 M6 M6 M6 M6 M6 M6 M6 M6 M15 M15 M15 M15 M15 M15 M15 M15 M15

07.2003 07.2004 10.2004 02.2005 03.2005 08.2005 09.2005 10.2005 11.2005 12.2005 01.2006 02.2006 03.2006 04.2006 05.2006 06.2006 07.2006 08.2006 11.2006 01.2007 06.2007 09.2007 10.2007 10.2003 01.2004 05.2004 07.2004 10.2004 02.2005 03.2005 04.2005 05.2005

41 31 17 8 2 19 18 13 5 3 2 14 20 28 25 14 37 31 19 16 19 33 29 9 6 25 33 26 12 7 35 25

40 25 15 2 7 20 24 13 1 0 −5 −3 3 22 23 12 29 27 6 4 19 11 13 7 −6 15 25 15 2 7 12 9

Ti (°C) 42.8 43.4 46.8 70.5 70.5 74.2 81.2 71.2 70.6 61.4 55.7 75.9 75.6 74.1 76.5 71.5 101.2 82.3 40.2 91.5 64.5 108.2 97.8 79.5 46.8 56.8 69.3 57.2 76.4 67.1 70.5 82.5

CO

CO2

O2

0 0 0 – 0 0 – 0 0 0 0 0 0 0 0 0.002 0.1 0 – 0.4 0 – 0.5 0 0 0 0 0 0 0 – –

0.5 0.001 0.001 – – 1.5 – 0.001 1.5 1.5 1.5 3.5 1.5 1.5 0.5 2.5 12 2 – 10 3 – – 4 2 0.001 0.001 1 – 1.5 – –

8 16 16 – – – – 17 15 13 12 10 0 9 13 10 0 10 – 0 19 – – 6 14 17 17 15 – 19 – – Continued

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Table 15.4.3—cont’d Examples of monitoring results for the Marcel Coal Mine dump.* Gas Contents (vol.%)

Locality No.

Monitoring Date

Ta (°C)

Ts (°C)

Ti (°C)

CO

CO2

O2

M15 M15 M15 M15 M15 M15 M15 M15 M15 M15 M15 M15 M15 M15 M15 M15 M15 M15 M16 M16 M16 M16 M16 M16 M16 M16 M16 M16 M16 M16 M16 M16 M16 M16 M16 M16 M16 M16 M16 M16

08.2005 09.2005 10.2005 11.2005 12.2005 01.2006 02.2006 03.2006 04.2006 05.2006 06.2006 07.2006 08.2006 09.2006 11.2006 01.2007 03.2007 06.2007 10.2003 01.2004 05.2004 07.2004 10.2004 08.2005 10.2005 11.2005 12.2005 01.2006 02.2006 04.2006 05.2006 06.2006 07.2006 09.2006 11.2006 01.2007 03.2007 06.2007 09.2007 10.2007

25 32 23 10 5 3 2 10 27 30 17 34 33 32 11 7 14 24 8 4 22 32 28 22 16 6 5 4 8 30 30 21 31 30 13 9 19 21 15 14

20 24 13 1 0 −5 −3 3 22 23 12 29 27 19 6 4 8 19 7 −6 15 25 15 20 13 1 0 −5 −3 22 23 12 29 19 6 4 8 19 12 13

69.2 66.7 66.2 60.5 54.1 59.1 55.6 50.4 55.7 56.8 56.4 75.5 63.2 64.8 55.5 44.8 52.1 64.5 45.5 23.2 79.3 58.8 60.1 73.2 77.2 74.6 62.3 50.1 70.4 85.3 89.5 86.2 83 88.4 70.5 70.5 81.5 76.6 80.1 77.3

0 – 0 0 0 0 0 0.01 0 0 0 0.001 0 0.001 0 0 0.001 0 0 0 0 0 0 0 – 0 0 0 0 0.002 0.01 0.001 0.001 0.04 0.001 0 0.002 0 0 0

1 – 3 1.5 0.5 2.5 1 1.5 0.001 0.001 0.001 0.5 0.001 0.5 0.5 1 1 0.4 2.5 0 0.001 0.001 0.001 0.5 – 0.5 1 0.5 3.5 10 5 4 6.7 0.5 3.5 6 13 0.5 14 4

18 – 14.5 19

*Ta, air temperature; Ts, surface temperature; Ti, internal temperature.

10 12 12 12 11 10 17 11 13 18 20 19 20 11 0 15.5 16.5 17 – – – – – 11 0 7 8 – 13 16 18 4 20 0 –

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Figure 15.4.26.  Variations in air temperature (Ta), surface temperature (Ts), and internal temperature (Ti) at locality M6 on the Marcel Coal Mine dump. Figure by Magdalena Misz-Kennan, 2010.

Figure 15.4.27.  Variations in air temperature (Ta), surface temperature (Ts), and internal temperature (Ti) at locality M15 on the Marcel Coal Mine dump. Figure by Magdalena Misz-Kennan, 2010.

Figure 15.4.28.  Variations in air temperature (Ta), surface temperature (Ts), and internal temperature (Ti) at locality M16 on the Marcel Coal Mine dump. Figure by Magdalena Misz-Kennan, 2010.

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Table 15.4.4 Examples of monitoring results for the cone part of the Marcel Coal Mine dump.* Gas Contents (vol.%)

Locality No.

Monitoring Date

Ta (°C)

Ts (°C)

Ti (°C)

CO

CO2

O2

S1 S1 S1 S1 S1 S1 S1 S1 S1 S1 S1 S2 S2 S2 S2 S2 S2 S2 S2 S2 S2 S2 S2 S3 S3 S3 S3 S3 S3 S3 S3 S3 S3 S3 S3 S5 S5 S5 S5 S5 S5 S5 S5 S5 S5 S5 S5

11.1997 12.1997 03.1998 04.1998 08.1998 11.1998 12.1998 01.1999 03.1999 05.1999 02.2000 10.1997 11.1997 12.1997 03.1998 04.1998 08.1998 11.1998 12.1998 01.1999 03.1999 05.1999 02.2000 10.1997 11.1997 12.1997 03.1998 04.1998 08.1998 11.1998 12.1998 01.1999 03.1999 05.1999 02.2000 10.1997 11.1997 12.1997 03.1998 04.1998 08.1998 11.1998 12.1998 01.1999 03.1999 05.1999 02.2000

30 32 47 54 18 20 23 38 37 40 43 54 46 28 65 41 18 69 6 8 20 29 10 36 8 25 40 54 19 11 15 7 27 45 16 252 230 220 260 219 22 255 258 247 247 154 115

2 2 16 36 20 0 −2 −6 7 20 1 3 2 2 16 36 20 0 −2 −6 7 20 1 4 2 2 17 36 20 0 −2 −6 7 20 1 5 3 2 17 31 20 0 −2 −6 7 20 1

52 0 54 61 55 53 52 49 51 52 49 120 111 96 95 100 64 282 85 81 82 68 70 265 230 192 215 226 127 211 245 225 213 259 231 390 310 340 320 262 182 330 306 327 298 298 287

0 0 0 0 0 0 0 0 0 0 0 >0.5 >0.5 >0.5 0.5 0.5 0.093 >0.5 0.01 0.02 0.02 0.02 0.5

3 1.7 1 1.6 1.78 1 1 2 0.5 0.5 0.3 4.5 2 2 2.5 3.5 2.72 16 1 0.5 1 2 3 >18 15 >18 17 >18 1.07 >18 18 18 16

16.5 18 20 16 18.94 21 19.5 17.5 0 0 10.5 0 0 4 16 13 17.88 4 19 19 9 12 17.5 0 0 0 0 0 17.6 0 0 0 0

14 18 5 0.5 0.5 0.5 0.58 2 1 0.5 2 1 0.5

0 0 0 10 8 15.5 20 18.5 18 20 18 18 13

≫ 0.5

>0.5

≫ 0.5 ≫ 0.5

>0.5 7.5 >0.5 >7 >0.5 0.5

≫ 0.5

0.002 0 0.002 0.01 0.004 0.002 0.001 0.01 0.002 0.02 0.002 0.01

*Barosz, (2003); Barosz, unpublished data. Ta, air temperature; Ts, surface temperature; Ti, internal temperature.

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15.5  Self-heating and Fire Prevention

Photo by Magdalena Misz-Kennan, 2008.

Remnants of a fly ash cover on the Rymer Cones dump. The horizontal field of view is 50 m.

 Discussion Fires in coal-waste dumps occur in an uncontrolled way. From an ecological point of view, the best situation would be that self-heating does not occur at all. To this end, waste tips are built such that the angle of slope is small; the deposited material is compacted with, e.g. a vibrating roll as shown in Figure 15.2.11; and additional sealing material, e.g. clays, flotation tailings, and/or fly ash pulp, are added to the waste. At present, three methods of coal-waste dumping are used. The first method involves the waste rock from the mine being transported to the dump by wagon trains, unloaded at dumping fronts, and finally moved from the edge of the waste scarp by bulldozer. In the second system, the waste rock is transported by train to the border of the dump where, using a strap loader or excavator, the material is loaded on to band conveyors that carry the waste to dumping belt conveyors and, finally, a scarp is formed. The third system, in making use of dumping lorries to take mining waste to the dump edges, removes the need for secondary waste relocation (Tabor, 1995). This last method is used at the Marcel Mine. It is a problem dealing with coal-waste dumps that have existed for many years, e.g. Starzykowiec or Rymer Cones. An attempt, in the late 1990s and the early 2000s, by Chwałowice Coal Mine to seal the Rymer Cones with fly ash (Figure 15.2.4) was unsuccessful. The aim had been to limit the access of air into the dump. However, after a short time, internal self-heating temperatures became so great that gases started to escape through cracks in the fly ash pulp. It is for this reason that, in later years, the fly ash sealing was largely removed. It seems impossible to avoid heat accumulation inside already existing dumps, and attempts at sealing them also fail. Thus, it seems that the only feasible solution is to enable full access of air to the hot parts of the dump by making excavations. The introduced air will cause the temperature of the waste rock to rise and burning to occur with attendant emission of fire gases. After several days, the material will burn out and the temperature will drop as conditions favoring heat accumulation cease to exist. After a short interval, inert material can be introduced into the burnt out places (Barosz and Tabor, unpublished data). This method is successfully applied in the dumps at Starzykowiec (Figures 15.5.1 and 15.5.2) and Rymer Cones.

 Summary Coal-waste dumping involves important technological and ecological problems. Despite the use of various methods, e.g. waste-rock compaction, mixing or interlayering with inert material, self-heating and self-ignition still takes place. These processes are influenced by a number of factors such as air inflow, waste grain size, and/or the presence of moisture. The results of many years of measurement of surface, interior, and surrounding air temperatures of the dumps show that one or the other factor commonly plays a dominant role in the self-heating processes encountered in any particular dump.

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Figure 15.5.1.  Excavation at the Starzykowiec Dump to extinguish a fire that began in February of 2008. Photo by Adam Tabor, 2008.

Figure 15.5.2.  Excavation of waste rock at the Starzykowiec Dump to extinguish a fire that began in February 2008. The height of the poles is about 1 m. Photo by Adam Tabor, 2008.

In the Rymer Cones, the most pronounced self-heating associated with the highest interior temperatures occurs on the west slope of the dump, i.e. the slope most affected by the dominant westerly winds. In this case, seasonal changes in temperature constitute a secondary factor. In the coal-waste dumps at Chwałowice and at the Marcel Coal Mines, rises in interior temperatures is mainly linked to the annual seasons. In the summer, interior and surface temperatures are usually higher than in the winter. However, increased rainfall in spring and autumn can frequently trigger intense fires. This is believed, perhaps counterintuitively, to reflect greater oxygen inputs delivered by the rains. In these instances, measured interior temperatures at 0.8–1.0 m depth can exceed 600 °C. Decommissioning of dump fires is an additional and challenging problem. In these hot spots, temperatures commonly exceed 1000 °C. In cases where the elimination of combustible material is not possible and, likewise, any effective limiting of air access, it seems that the excavation of fire-prone coal waste, so as to enable enhanced air access, is the only real solution. By the intensification and acceleration of the waste-rock combustion, the possibility of further heat accumulation in a given place is much reduced. Otherwise, these hot places can sustain high temperatures for many years of the continuous emission of potentially harmful pollutants.

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  Important Terms air temperatures carbon dioxide carbon monoxide coal fire coal waste coal-waste dumps combustion

interior temperatures temperature measurements organic matter oxidation self-heating self-ignition surface temperature

 References Barosz, S., 2003. Monitoring of the dismantling and reclamation of the coal waste dumps (in Polish): VII Conference “Long Term Proecological Undertakings in the Rybnik Coal Area”. Rybnik, pp. 149–156. Barosz, S., unpublished data. Technical, economical and environmental conditions of management of coal waste dumps using the mines from the Rybnik Coal District as examples (in Polish): Ph.D., Academy of Mining and Metallurgy in Cracow, 221 p. Barosz, S., Tabor, A., unpublished data. Limiting the spread of fires, and their extinction, in coal waste dumps (in Polish). Patent No. P-364316, 3 p. Banerjee, S.C., Nandy, D.K., Chakravorty, R.N., 1965. Studies in the mode of disappearance of CO over coal in sealed off area in mines. Indian Journal of Technology 3, 165–166. Beamish, B.B., Barakat, M.A., St George, J.D., 2001. Spontaneous-combustion propensity of New Zealand coals under adiabatic conditions. International Journal of Coal Geology 45, 217–224. Benfell, K.E., Beamish, B.B., Rodgers, K.A., 1997. Effect of resinite on the combustion of New Zealand subbituminous coal. Thermochimica Acta 296, 119–122. Berkowitz, N., 1985. The Chemistry of Coal. Elsevier, Amsterdam-Oxford-New York-Tokyo, 513 p. Brooks, K., Svanas, N., Glasser, D., 1988. Evaluating the risk of spontaneous combustion in coal stockpiles. Fuel 67, 651–656. Chang, S., Berner, R.A., 1998. Humic substance formation via oxidative weathering of coal. Environmental Science and Technology 32, 2883–2886. Clemens, A.H., Matheson, T.W., Rogers, D.E., 1991. Low temperature oxidation studies of dried New Zealand coals. Fuel 70, 215–221. Cygankiewicz, J., 1996. Estimation of the Development of Self-ignition Centers on the Basis of the Precise Analysis of Coal Mine Air Samples (in Polish). Scientific Papers of Central Mining Institute, Katowice, No. 14, pp. 505–530. Garcia, P., Hall, P.J., Mondragon, F., 1999. The use of differential scanning calorimetry to identify coal susceptible to spontaneous combustion. Thermochimica Acta 336, 41–46. Itay, M., Hill, C., Glasser, D., 1989. A study of the low temperature oxidation of coal. Fuel Processing Technology 21, 81–97. Jabłońska, M., 2004. Thousands of tons of waste (in Polish). Biuletyn Górniczy 11–12, 113–114. Krishnaswamy, S., Bhat, S., Gunn, R.D., Agarwal, P.K., 1996a. Low-temperature oxidation of coal. 1. A singleparticle reaction – diffusion model. Fuel 75, 333–343. Krishnaswamy, S., Agarwal, P.K., Gunn, R.D., 1996b. Low-temperature oxidation of coal. 3. Modelling spontaneous combustion in coal stockpiles. Fuel 75, 353–362. Lu, P., Liao, G.X., Sun, J.H., Li, P.D., 2004. Experimental research on index gas of the coal spontaneous at lowtemperature stage. Journal of Loss Prevention in the Process Industries 17, 243–247. Marinov, V.N., 1977. Self-ignition and mechanisms of interaction of coal with oxygen at low temperatures. 2. Changes in weight and thermal effects on gradual heating of coal in air in the range 20–300 °C. Fuel 56, 158–164. Pone, J.D.N., Hein, K.A.A., Stracher, G.B., Annegarn, H.J., Finkelman, R.B., Blake, D.R., McCormack, J.K., Schroeder, P., 2007. The spontaneous combustion of coal and its by-products in the Witbank and Sasolburg coalfields of South Africa. International Journal of Coal Geology 72, 124–140.

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