Mine Water as a Source of Energy—Case Study from Poland

Abstract

The energy sector in Poland is primarily based on fossil fuels, mainly coal. Hard coal mining is one of the most important industries in Poland. Hard coal deposits in Poland are found in three basins, but mining is currently carried out in the Upper Silesian Coal Basin (USCB) and the Lublin Coal Basin (LCB). The Upper Silesian Coal Basin is Poland’s central hard coal basin, with the most significant coal production extending across Poland and the Czech Republic. Approximately 80% of proven hard coal resources in Poland are found in the Upper Silesian Coal Basin (USCB). There is a tremendous amount of water in active and abandoned hard coal mines, which must be drained daily. Relatively high temperatures characterize mine water. This study analyzed the geological and hydrogeological conditions of the Upper Silesian Coal Basin and determined the potential for the use of mine waters for energy purposes. Depending on the location of the mine, the volume of mine water inflow ranges from 1 to 60 m³/min. The temperature of the pumped water is between 13 and 25 °C. In Poland, several such pilot installations have already been created; it is worth taking a closer look at the following examples. Heat recovery from mine drainage water can significantly reduce atmospheric emissions, which is particularly important in mining areas affected by low emissions. Therefore, Poland must raise the issue of using mined water for energy purposes, especially when making decisions related to decommissioning mines and developing post-mining areas.

1. Introduction

Hard coal deposits in Poland belong to the Carboniferous Euro-American province; they occur in three depressions: the Upper Silesian Coal Basin (USCB), the Lublin Coal Basin (LCB) and the Lower Silesian Coal Basin (LSCB). The Upper Silesian Coal Basin is the leading coal basin in Poland; all active mines are currently located here. The total area of the USCB within the Polish borders is estimated to be 5600 km². In the case of the Lublin Coal Basin, about 4730 km² is taken as the prospective area, while documented deposits occupy an area of about 1200 km². The only coal mine in the LCB currently operates three deposits, Bogdanka, Lublin Coal Basin—K-3 area, and Ostrow, which accounts for 14% of the entire basin. Hard coal mining was completed in the Lower Silesian Coal Basin in 2000. The document balance sheet of the resources in the hard coal deposits on 31 December 2023 amounted to 64,596.29 million tons [1].

Coal mines in the Upper Silesian Coal Basin are prospective locations for installing heat pumps. This is due, among other things, to the large volumes of warm mine water pumped to the surface every day. This amounts to approximately 500,000 m³ of mine water per day, with a temperature of more than 13 °C. Mine water inflows range from 1 to 60 m³/min for the individual mines. The temperature of the pumped water is between 13 and 25 °C. Due to the geological structure, it will be necessary to drain active and decommissioned plants for the next few decades. In the case of mines located within the Silesian agglomeration, a significant advantage is the proximity of potential energy consumers—housing estates and residential buildings. The mines themselves may be substantial consumers of thermal energy. The demand for thermal power in active mines is estimated to range from a few to several MW. The transformation of mining areas into renewable energy-related areas can improve the image of regions associated with coal mining and environmental pollution. The use of mine waters for energy purposes enables active land development after the closure of mining plants, contributing to revitalization. This helps create new, sustainable workplaces and supports regional economic growth. Closed mines require regular drainage, which generates high costs. The use of mined water for energy production allows for a partial or total reduction in the maintenance costs of pumping stations, transforming waste into energy resources. In the case of decommissioned mines with dewatering operations, it is approximately 2–6 MW [2]. In many mines, these resources are sufficient to meet their needs and those of neighboring facilities; however, utilization rates still need to be higher. A specialized atlas of geothermal energy resources in the Upper Silesian region has even been produced, showing potential for their use. Despite the relatively large amounts of geothermal energy in these waters, the resource must be used. There is huge potential in using mined waters as bottom sources for heat pumps. Thanks to the existing shafts through which these waters are pumped out, the costs of geothermal installations become lower as the costs of drilling new boreholes and pumping the waters to the surface can be deducted [3]. The most expensive element in building new geothermal installations that use heat pumps is drilling holes; it is not necessary to drill them in the case of using mine water for energy purposes. The pumped water from closed mines has a relatively high temperature (in some cases, it exceeds 13 °C), it is a source of energy and can be used for this type of installation. In Poland, several such pilot installations have already been created, and it is worth taking a closer look at a few examples. According to laws concerning water, the drainage water from mines [4] is treated as sewage and, in the vast majority of cases, discharged into surface water. Each mining plant is obliged to have a water permit to conduct drainage, allowing for a significant reduction in formal and legal procedures when implementing investments related to heat acquisition. Due to the need to dehydrate all active mines and parts of the liquid, potential installation investors will not bear the costs associated with pumping water.

Example of Mine Water Use in Poland

The Central Mine Dewatering Plant (CZOK) in Czeladź was established in 2000 as part of the Mine Restructuring Company (MRC). Its main task is to protect active mines from water hazards by dewatering and decommissioning them. One of these is the Saturn Pumping Plant (formerly the Saturn Coal Mine (CM)) located in Czeladź, where the CZOK headquarters are also located. In 2008, the MRC joined the international REMINING-LOWEX project to assess the possibility of using heat from mine water in EU (European Union) countries. The aim of this project was, among other things, to build a pilot heat recovery installation at the CZOK site in Czeladź. The decommissioned Saturn CM is being dewatered to secure the active mines in the northern part of the USCB. This mine was one of the most failing mines in Poland’s complex coal mining industry. In 2011, the existing dewatering system was modernized and simplified to reduce costs. The volume of water pumped is currently about 15 m³/min (900 m³/h), and the temperature is about 13 °C. The water has a relatively low mineralization, with high concentrations of iron and manganese compounds [5]. The installation consists of the following:

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A mine water treatment plant based on the oxidation of iron and manganese compounds using air from a compressor and filtration based on a mixture of quartz and hydro anthracite deposits.

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Two water-to-water heat pumps—Viessmann Vitocal 300-G with a total power of 117.8 kW. The heat pump cascade requires a supply of approximately 18.6 m³/h of mine water.

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The central heating system uses 55/45 °C water heating with panel radiators.

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The heating system also uses five buffer heat accumulators with a capacity of 1000 dm³ each.

Annual electricity consumption for heating purposes was 410.7 MWh/year before thermomodernisation. Following the start of the operation of the heat pump installation, electricity consumption for heating purposes fell to 132.9 MWh/year. This means a reduction in electricity demand of almost 278 MWh/year [6].

In 2015, an installation was made at Sobieski Mine to recover the heat from mine water obtained in the primary dewatering process, which used heat pumps to prepare domestic hot water. The graphic below (Figure 1) shows the scheme of the heat pump installation in Sobieski Mine.

The installation consists of a pump station building with an intake well, a transfer primary, and a heat pump station in the technical room of the bathhouse. Two circulating pumps and one submersible pump are connected to the underground water intake point [7]. The heat pump station works in a cascade system, with bottom water being pumped to the Sobieski III shaft from 500 m underground. The location was selected due to the high temperature of the heat source, 19.8 °C. At a depth of 1.20 m below the ground surface, a pre-insulated manifold was routed through which the circulating pumps pump water with an estimated flow rate of 68 m³/h. Furthermore, water supplies five sets of high-end dual-compressor heat pumps (blue line) of the Swedish concern NBE AP-BW30-85H, each with a power of 84 kW [3]. Based on the preliminary balance of the installation of heat pumps for domestic hot water production (red line), it was assumed that the heating power requirement for four daily cycles (after 6 h each) is between 9.30 and 15.30 (1 cycle), which is approx. 395 kW/h, and in the remaining, approx. 265 kW/h. Hot water is produced on an ongoing basis through a jacket–tube exchanger and stored in storage tanks with a total capacity of 63 m³. This water is used to wash miners exiting to the surface [8].

Figure 1. Operating diagram of the heat pump installation (based on [8]).

Figure 1. Operating diagram of the heat pump installation (based on [8]).

In 2023, an ultramodern hydrogenerator was launched in the Boze Dary Pumping Station. This is the first such project in Europe and, most likely, the world. It enables electricity produced from mine waters to supply the needs of the mine. The hydrogenerator produces electricity using the natural groundwater supply, which drops from 183 m to 416 m. The construction of a water system ensuring the flow of water through the hydrogenerator will allow for the production of electricity, which will then be consumed for the needs of the pumping station. It is estimated that the average annual electricity production in this case will be less than 1600 MWh [9].

2. Upper Silesian Coal Basin

The Upper Silesian Coal Basin is located in the Silesian Voivodeship and the eastern part in the Małopolskie Voivodeship. The USCB occupies an area of about 7490 km²; in Poland, the basin area is estimated to be about 5760 km² [10]. The total area of the documented deposits is over 3049 km². Currently, 80.05% of the documented resources of proven reserves of Polish hard coals occur in this basin. As of 31 December 2023, 40 deposits have been found in the basin where hard coal mining is carried out (the total number of deposits in the USCB is 144; the rest are undeveloped, or their exploitation has been abandoned) [11]. The map (Figure 2) shows the localization of the USCB.

Most of the basin is located within the range of the Carpathian Foredeep, covered with Neogene molasses, and some of its fragments lie under the influence of the Flemish Carpathians. The northeastern part of the USCB is located within the reach of the platform cover, which is covered with Mesozoic sediments. In this part of the basin, Jurassic and Triassic formations constitute the southern part of the Silesian–Krakow monocline, and the productive carbon formations occurring in this area are part of the younger Paleozoic pedestal of the Varyscian platform [12]. The boundaries of the USCB were determined based on the range of coal-bearing tracks of the upper carbon and through fault lines. In the west, it is limited by folded flysch formations containing less carbon. The northern and east boundaries pass under the Perm and the Triassic series. Below the carboniferous formations are folded Lower-Paleozoic formations, on which Devonian (carbon limestone) and bottom carbon are located. The southern border runs under the impression of the Carpathian flysch; in this area, there are metamorphic rocks of the Precambrian and above the tracks of Cambric and Devonian. The carboniferous floor in this area lies below 2000–3000 m; in some places, it reaches even 5000 m [5]. Formations of productive carbon dominate the geological profile of the basin. In the ceiling are deposits of Cenozoic and Mesozoic, locally also Perm, while there are pieces of older Paleozoic in the ceiling. Four lithostratigraphic series are distinguished in the carbon profile: the parallel series (SP), the Upper Silesian sandstone series (GSP), the Mudstone Series (SM), and the Krakow Sandstone Series (KSP). In these formations are complexes of clay–mudstone–sandstone rocks with decks of hard coal. The GSP and KSP are dominated by sandstones; therefore, a greater presence of aquifers than the others characterizes these formations.

3. Characteristics of Hydrogeological and Geothermal Conditions of the Upper Silesian Coal Basin

In the Upper Silesian collapse, a sedimentary basin with an area of about 7500 km² and a thickness of up to 11 km of sediments formed. The boundaries of the basin are defined by carbonate-bearing formations of the productive Carboniferous. The hydrogeological profile distinguishes between Cenozoic, Mesozoic, and Paleozoic aquifers, which are divided by weak or impermeable isolation horizons (Figure 3) [12].

The USCB lists two hydrogeological subregions, the northeast subregion (I) and the southwest (II), whose geological structure and hydrogeological conditions vary.

The northeastern subregion includes two alpine tectonic structures: the Silesian–Cracow Monocline and the base of the Epivariscan platform. The monocline is characterized by fold and block structures and is built of Triassic, Jurassic, and Quaternary sediments, as well as local Cretaceous. Within this subregion’s range, a part of the monocline is covered by Bytomian, Chrzanów, and partly Gliwice Triassic formations. The Triassic formations lie directly on Carboniferous formations and locally on Permian sediments. In the Triassic formations described above, three fracture–race reservoirs are included in the main groundwater reservoirs: Bytom, Chrzanów, and Gliwice [12].

The northeast subregion is located relatively higher than the southwest region, and the existing hydraulic contacts between the aquifers of the Cenozoic, Mesozoic, and Paleozoic have made it considered to be a regional zone for the supply of carbon aquifers [10]. The southwestern subregion (marked as II on the map) lies within the range of alpine sinkhole structures. It is filled with clayey Tertiary formations overlying Carboniferous formations. Water is found in Quaternary formations. The Pre-Carpathian collapse is an area of high water pressure in Paleozoic aquifers [12]. The areas of the USCB are characterized by groundwater stories, distinguished by the presence of originating aquifers in which water-bearing horizons or complexes occur. Poorly or practically impermeable hydrostratigraphic units separate the aquifers. In the subregions described above, the occurrence and structure of the aquifers vary. The northeastern subregion’s groundwater occurs within the Silesian–Cracow monocline’s boundaries in Mesozoic formations. Lower Devonian and Cambrian aquifers were found to be absent in this area. In the southwestern subregion, the Tertiary marine isolation complex occurs directly on the roof of the Upper Carboniferous, whereas in the Carpathian overthrust region, fissile and clayey Tertiary form the Upper Carboniferous isolation complex in this area. The USCB’s groundwaters occur in quaternary, Tertiary, Cretaceous, Jurassic, Triassic, Permian, Carboniferous, Devonian, and Cambrian aquifers. Quaternary formations are characterized by diverse hydrogeological conditions [12].

The Quaternary aquifer shows a diversity of hydrogeological conditions. The most saturated areas are in the valleys of the Vistula, Przemsza, Brynica, Ruda, Bierawka, and Kłodnica rivers. The thickness of Quaternary aquifers in modern valleys ranges up to 30 m, while it exceeds 100 m in places in fossil valleys. Well yields in the area vary from 4.9 to 200 m³/s. Quaternary aquifers are fed by precipitation, locally by valley drainage, and by the recharge of older aquifers. Water flow occurs in a westerly direction and a northerly and north-easterly direction. Quaternary waters are in direct contact with surface waters, with mineralization ranging from 47 to 1374 mg/L. The waters in the Quaternary aquifer complex are classified as Class II and III. Within the range of Quaternary waters, five main groundwater reservoirs have been identified: Kłodnica, Ruda, Bierawka, Pra-Visła and Wisła [12].

The Tertiary formations are dominated by a clay and sandstone complex, with depths reaching over 1000 m in the southern part of the USCB. The most excellent permeability is observed in the Pliocene sands and gravels, which locally occur in Gliwice and Dzierżno. The Sarmat formations also show high permeability. The water in these formations is characterized by low mineralization values ranging from 160 to 432 mg/L. The waters in the Sarmat formations belong to the types HCO₃-Ca, HCO₃-Ca-Mg, and HCO₃-Na-Ca and are classified as Class I and Class II. The Baden formations are practically waterless and are regarded as a complex of insulating layers. The largest groundwater reservoir is formed by the Dębowiec conglomerate, composed of breccia, conglomerates, and sandstone. This reservoir is non-renewable. The Baden formations are divided into two hydrogeochemical provinces: northern and southern. The southern province contains chloride-type waters, while the north contains sulfate- and chloride-sulfate-type waters. The boundary between the areas described above is marked by chemical sediments (mainly gypsum). In the Carpathian flysch formations, the occurrence of waters mainly of the HCO₃-Ca-Mg and HCO₃-SO₄-Ca-Mg types is observed, and their mineralization ranges from 60 to 404 mg/L [12].

Jurassic aquifers are observed within the boundaries of the Chrzanow Triassic reservoir. Two aquifers of the Upper Jurassic and Middle Jurassic occur here. Waters belonging to the HCO₃-Ca type have only been recognized in the Upper Jurassic complex. Three aquifer complexes belong to the Triassic aquifer: the shell limestone, the rest, and the Middle and Lower Brash Sandstone. Dolomites and limestones represent shell limestone and ret limestone aquifers. These formations conventionally form one Triassic carbonate series aquifer complex. Marly sediments form the isolation layer. The Lower Sandstone and Paster Sandstone aquifer complexes comprise sands and sandstones. This horizon is subject to drainage by ongoing coal mining. The Permian formations are represented by conglomerate sandstones and claystone, which are practically waterless [12].

The Carboniferous formations comprise four water-bearing complexes: the Cracow Sandstone Series (KSP), the Silty Sandstone Series (SM), the Upper Silesian Sandstone Series (GSP), and the Paralic Sandstone Series (SP). The KSP aquifer extends to approximately 1500 km² and has the highest water-bearing capacity. The thicknesses range from a few tens to 1140 m. The GSP complex covers an area of 2800 km², and its thicknesses range from a few tens of meters to 1200 m. Towards the east, the depth decreases until it is wholly wedged out. The SM horizon is bounded on the top by the KSP and on the bottom by the GSP, forming a boundary between them. The thickness of this complex is variable, reaching up to 1800 m in places. The SP aquifer entrains the entire surface of the USCB, and its thickness ranges between 200 and 3780 m. In the productive Carboniferous, it was observed that the occurrence of individual water types is related to their mineralization. Waters with mineralization below 3 mg/L belong to the multi-ionic waters, mainly of the HCO₃-Ca, HCO₃-SO₄-Ca, SO₄-HCO₃-Ca-Mg types. Waters with mineralization above 10 mg/L are of the Cl-Na type, whose composition is dominated by oxygen, nitrogen, and methane. In comparison, brines (mineralization above 35 mg/L) are of the Cl-Na and Cl-Na-Ca types, and their composition is dominated by methane [14].

The following types of brines were distinguished in the Upper Silesian Coal Basin:

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Sedimentary Miocene brines;

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Paleoinfiltration brines occurring in deeper parts of the Carboniferous and older formations in the whole area of the Upper Silesian Coal Basin;

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Holocene, interglacial, and glacial waters (formed in the Quaternary);

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Sulfate brines;

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Sulfate-free brines;

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Waters that are a mixture of the above water types.

Identifying mine water types also makes it possible to predict the presence of the radioactive elements uranium and radium in these waters. The occurrence of large amounts of radium and barium, negligible amounts of uranium in low-sulfate waters, and large amounts of radium in waters containing high sulfate concentrations has been found. In palaeoinfiltration brines, no uranium has been found, with relatively high radium concentrations, while in Quaternary waters, with moderate uranium concentrations, the amounts of radium are virtually zero. Occasionally, barium is also present in mine waters, containing radium isotopes at concentrations as high as 1.5 kg/m³. These deposits may precipitate on the surface in settling tanks or pipelines. The transport of water containing high concentrations of these components in pipelines results in radioactive contamination of the environment and is hazardous to health and life [15]

The table below (

Table 1. Statistical parameters of temperatures in the USCB (based on [14,15,16]).

Level	Number of Measurements	Minimum Temperature [°C]	Maximum Temperature [°C]	Average [°C]	Median [°C]
0 m (sea level)	491	8.6	26.8	15.8	15.7
250 m (below sea level)	479	12.5	30.6	22.2	22.3
500 m (below sea level)	421	18.5	41.1	29.7	29.9
750 m (below sea level)	312	24.8	50.3	38.4	38.8
1000 m (below sea level)	185	32.6	59.3	49.4	49.5
1250 m (below sea level)	71	39.2	70.8	58.6	59.2
1500 m (below sea level)	22	47.9	81.4	68.4	69.8

) summarizes the statistical parameters relating to the temperatures in the USCB.

The number of temperature measurements decreases with depth, which is reflected in the accuracy of recognizing a given level. The mean and median of the analyzed parameters remain almost identical.

The studies carried out in Carboniferous formations made it possible to determine the geothermal gradient for individual lithostratigraphic units. The table (

Table 2. Geothermal parameters of Carboniferous formations (based on [14,15,16]).

Lithostratigraphic Unit	Number of Measurements	Geothermal Gradient Minimum [°C/100 m]	Geothermal Gradient Maximum [°C/100 m]	Geothermal Gradient [°C/100 m]	Median [°C]
Krakow Sandstone Series (KSP)	145	1.04	3.34	1.89	1.87
Siltstone Series (SM)	322	1.94	5.06	3.53	3.52
Upper Silesian Sandstone Series (GSP)	204	2	5.87	3.88	3.94
Paralytic Series (SP)	140	2.01	5.04	3.40	3.43

) summarizes the parameters of Carboniferous formations.

The geothermal gradient for individual lithostratigraphic complexes varies. The lowest gradient was observed in the KSP, while the highest was observed in the GSP. The analyzed formations are predominantly sedimentary covers characterized by high porosity; therefore, heat flow occurs not only via conduction but also convection, mainly in the areas of ascent and descent groundwater movement. Rock mass temperatures vary considerably depending on the area’s location, geological structure, and the presence of lithostratigraphic units. The rock mass temperatures also determine the boundaries of overthrusts and faults. For the individual levels, the temperatures are as follows:

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Level, 250 m: Temperatures range from 12 °C to 28 °C;

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Level, 500 m: Temperatures range from 20 °C to 36 °C (the highest temperatures were observed in the vicinity of Jastrzębie Zdrój and Katowice);

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Level, 750 m: Temperatures range from 28 °C to 42 °C (the highest temperatures were observed in the vicinity of Jastrzębie Zdrój, Katowice and Sosnowiec);

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Level, 1250 m: Temperatures range from 40 °C to 68 °C (the highest temperatures were observed in the vicinity of Jastrzębie Zdrój);

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Level, 1500 m: Temperatures range from 48 °C to 78 °C (the highest temperatures were observed in the vicinity of Jastrzębie Zdrój, Pszczyna and Goczałkowice) [6].

There is an upward trend in temperature towards the southwest of the USCB. Four lithostratigraphic series were identified in the Carboniferous profile: the Cracow Sandstone Series (KSP), the Upper Silesian Sandstone Series (GSP), the Paralic Series (SP), and the Mudstone Series (SM). The geothermal gradient varies between the individual lithostratigraphic series, as follows:

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Krakow Sandstone Series: 1.5–2 °C/100 m.

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Upper Silesian Sandstone Series: 2.75–4.5 °C/100 m; the highest gradient occurs near Goczałkowice.

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Paralic Series: 2.75–4.75 °C/100 m, an increase in the gradient towards the southwest is observed.

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Mudstone Series: 2.5–4.5 °C/100 m, the highest gradient is observed in the southern part [6].

The lowest gradient values were observed for the Krakow sandstone series, with the highest values occurring in the southern and central parts [16].

The problem of dewatering mines undergoing closure mainly concerns mines located in the northern part of the Upper Silesian Coal Basin. About 40 mines are hydrogeologically interconnected in this area, forming a system of interconnected vessels. Discontinuing dewatering and allowing for the uncontrolled accumulation of water can directly threaten active mines. Mine dewatering levels are set based on hydrogeological conditions and hydraulic connections to other mines. The lowest direct connections determine the acceptable level of flooding and dewatering. Water parameters vary depending on the location of the mine and the level of dewatering. In the following section, the parameters of pumped water and the possibility of using it for energy purposes are analyzed using the example of the Witold shaft at the Jan Kanty mine [16,17].

4. Jan Kanty Pumping Station

The Jan Kanty mine in Jaworzno was one of the hard coal mines located in Upper Silesia in Poland; it was founded in the 19th century. Due to the depletion of resources, mining was terminated in 2000, and the mine was closed in 2001–2002. Since then, the mine has been continuously dewatering to protect the Sobieski mine. The dewatering system of the Jan Kanty mine includes the central pumping station located on the surface; the discharged water is pumped through the Witold I and Witold II shafts and then discharged into the Przemsza River. The table below (

Table 3. Quality of water pumped out from Jan Kanty coal mine.

Parameter	Value	Unit
Dissolved substances	520–1280	mg/L
pH	7–8.86	-
Chlorides [Cl−]	130–170	mg/L
Sulfates [SO42−]	290–350	mg/L
Iron [Fe]	3.46	mg/L
Total hardness [CaCO3]	536	mg/L
Inflow	21.1	m3/min
Temperature	11.8	°C

) summarizes the most important parameters of the water pumped out of the mine.

The average water inflow is 21.1 m³/min, and its temperature remains at 11.8 °C. The discharge waters from the Jan Kanty mine are characterized by relatively stable physicochemical parameters, with mineralization below 1300 mg/L. The waters analyzed contained the following: chlorides at levels exceeding 200 mg/L, sulfates at a maximum level of 350 mg/L, and iron at 3.46 mg/L. The waters are characterized by low turbidity and high total hardness due to the presence of carbonates. The potential of hydrogen (pH) ranges from 7 to 8.86, which means that we are dealing with alkaline waters.

The graphic below (Figure 4) shows the profile of the pumping station. The three submersible pumps are located at a depth of approximately 290 m. The level of the top pump is at a depth of 283.5 m bsl, and the bottom pump level is at a depth of 291.16 m bsl. This installation also includes water level sensors (the first is located above the maximum emergency flooding levels, and the second is located above the submersible pumps). Two fans are located on the surface. The main support bridge is located at a depth 7.5 m bsl. The approximate capacity of the emergency reservoir is 103,300 m³.

5. Discussion about Possibilities of Mine-Water Usage for Heating and Cooling Purposes

The extraction of fossil fuels is increasingly harmful to the environment and increases the rate of global warming. The future is the development of renewable energy sources. Therefore, an energy policy has been implemented in Poland. It involves the process of decarbonization, i.e., the complete abandonment of the use of coal in electricity, heating, industry, and households. Decommissioning a mine involves the cessation of dewatering and subsequent self-drowning with water from natural tributaries or the continued pumping of water to protect active mines from water hazards. Continued dewatering is required when underground connections, such as excavations, connect abandoned and active mines. In this case, maintaining the water levels in decommissioned mines is often necessary so that neighboring active mines are not flooded. Restructuring Poland’s complex coal mining industry involves specific technical problems related to protecting active mines from water hazards. For safety reasons, mine dewatering must continue even after they have been closed, and the costs associated with the maintenance of underground and surface infrastructure associated with dewatering must continue to be incurred. Several direct connections exist between neighboring mines, mainly through old mine workings. Once mining operations have ceased, favorable conditions are created in the rock mass for the accumulation of groundwater in mine workings, forming reservoirs with capacities often reaching several million m³. The possibility of water from these reservoirs entering active mining sites with catastrophic consequences is a water hazard for mining crews [17]. An article produced by Cień et al. [18] describes the hydraulic connections between mines in the northern part of the USCB and the potential of using mine water for drinking and industrial purposes. Significant quantities of mine drainage water, some containing brine, chlorides, and sulfates in very high concentrations, harm the water status of surface watercourses and water bodies. The reduction in salt concentrations in mine waters discharged into surface waters is based on the retention principle of saline waters and their controlled discharge. The Olza collector receives saline waters with an average salinity of 42 g/L from eight mines in the southern part of the SCI, providing the capacity to discharge 30,000 m³/d of water in a way that keeps the salt concentration in the Oder below 1 g/L. It includes the treatment of the water to remove suspended solids, barium ions, and radium. It also ensures the maximum use of saline waters for the operational purposes of mines. The remaining water is dosed from mine retention and dosing reservoirs into the Oder River at Olza. The second system used for the controlled discharge of saline water is used to collect saline water and brine from the Piast and Ziemowit mines, using the goaves of the decommissioned Czeczott mine as a retention reservoir with a volume of 0.5 million m³. These mines are responsible for two-thirds of the total salt entering surface watercourses from the mines located in the USCB [19].

The use of mine water for energy purposes has yet to become a top-rated solution in Poland. Rising energy costs and stringent environmental protection requirements have resulted in the search for new sources of electricity and heat generation. Poland can boast of geothermal energy installations in mines, e.g., Sobieski Mine, the Saturn Pumping Station, and Boże Dary. This is mainly related to the discharge of warm mine waters, which are pumped to the surface daily in hard coal mines in the Upper Silesian Coal Basin. The use of this source of energy in our country is not yet prevalent in Western Europe. The energy transformation of Poland and the liquidation of active coal mines in the Upper Silesian coal basin may contribute to the development of this technology in our country. An article produced by Chudy [20] presented the potential of using mine waters as a source of geothermal energy for the Nowa Ruda region. In contrast, in an article produced by Jason et al. [21], an analysis of the potential of mine water utilization for the Bytom region was carried out. Mine water from the disused Szombierki mine is used to heat residential buildings. This system uses heat pump technology, which extracts heat energy from mine waters. This makes it possible to provide heat for many households while reducing CO₂ emissions to the atmosphere.

The use of mine water for energy purposes is an issue that is becoming increasingly important in the search for alternative energy sources. Mine water, underground water found in mine workings, can be used for various energy purposes, such as the production of heat or electricity. The proposal for this solution at the Jan Kanty mine described above is most reasonable. The Jan Kanty mine, located in Jaworzno in the Silesian Voivodeship, is one of many examples of disused mines that could become a renewable energy source. One of the most direct uses of mine water is in heating and cooling systems. The mine water discharged from the Jan Kanty mine is characterized by a temperature of 11.8 °C which makes it suitable as a heat source for heat pumps. The relatively low mineralization (below 1300 mg/L) means that there is no need for additional water treatment; only a system of appropriately selected filters is required to protect the equipment used for heat production. This type of solution will allow for the production of thermal energy, which can then be used to heat residential, commercial, and industrial buildings. The location of this mine is noteworthy; it is close to the Jaworzno Economic Zone. The buildings, halls, and production plants may be potential energy consumers. An additional advantage of this type of investment is the use of existing infrastructure—pumping stations; moreover, according to the Geological and Mining Law of 9 June 2011 [22], the heat extracted from mine waters is not subject to royalties. Using mined water for energy purposes has many benefits, such as reducing greenhouse gas emissions, using renewable resources, and increasing energy security. At the same time, however, it comes with some challenges, such as high initial costs, technical problems, and environmental impacts. Mine water can be a valuable element in the energy mix, provided its use is properly managed and monitored in the context of changing energy needs and the search for alternative energy sources. To maximize its potential, it is worth continuing research and technology development in this area.

Technology relating to heat recovery from mine waters using heat pumps is relatively well known and does not cause harmful emissions at the place of use. Although using waste heat for coal mines has been proposed for many years by other authors, it still needs to become a standardized solution. The use of mine water for energy purposes can significantly improve the economic and environmental efficiency of mining facilities. This article points out the significant potential of using mined water for energy. Geothermal installations based on mine drainage water can successfully serve as sources of heating or cooling. Heat recovery from mine drainage water can significantly reduce atmospheric emissions, which is particularly important in mining areas affected by low emissions. Therefore, Poland must raise the issue of using mined water for energy purposes, especially when making decisions related to decommissioning mines and developing post-mining areas. Using mine waters for energy purposes in Poland is an opportunity for energy transformation in mining regions and contributes to the development of renewable energy sources. These actions require political support, investment, and new legal regulations. According to the provisions of geological and mining laws, the use of mine waters is strictly regulated, and in order for them to be used for energy purposes, changes to existing mining and renewable energy regulations are necessary. The introduction of governmental financial support mechanisms for projects related to the use of mine waters for energy purposes is also a key factor. An essential step in the development of technologies associated with the use of mine waters is investing in research and development.

6. Summary

Coal mining is associated with mine drainage. The mining plants located in Upper Silesia show great potential in terms of obtaining energy from mine water. A significant advantage is that it can be extracted from mine shafts without the need for costly drilling, significantly affecting the installation’s cost-effectiveness. Research published by Michlowicz and Wojciechowski [23] shows that the energy consumption of the pumping unit from the level of 500 m bsl ranges from 2.17 to 2.67 kWh/m³. Data on energy prices for 2021 show that pumping out 1000 m³ of water is about 1000–1200 PLN. Acquiring part of the energy contained in mine waters for heating, for example, mining plant facilities or residential buildings, will reduce drainage expenses by reducing the costs of heating or hot water preparation costs. The costs of such an investment are lower due to the existence of a pumping station system. Mine water reduces the environmental burden and improves environmental and air quality. Looking at the above example, it is easy to see the profitability of such investments, all the more so due to the fact that the geothermal resources available on-site can be used. Particular attention should be paid to using existing mine shafts in which water is discharged (drainage of mine waters is necessary, both in the case of existing and inactive mines). In many mines, these resources are sufficient to meet the needs of their own and even neighboring facilities. Heat pumps are devices that do not emit any pollutants at their place of application; therefore, they are an excellent alternative to commonly used emitting heat sources. Despite the relatively large amount of geothermal energy in these waters, these resources are rarely used. The huge potential lies in using mined waters as a lower source for heat pumps. By using existing mine shafts, the mine water that can be pumped out reduces the costs of geothermal installations due to the fact that the costs of drilling new wells and pumping the water to the surface can be deducted. Mining activities carried out within the Upper Silesian Coal Basin create opportunities for the use of waste energy. The potential for heat recovery from mine water depends on some mining–technical and natural factors. Among the most important are flow rate and temperature. Due to their high mineralization, corrosive nature, and tendency to precipitate sediment, mine waters require intermediate exchangers in the plant or prior treatments. The use of mine water for energy purposes can significantly improve the economic and environmental efficiency of mining plants.