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Strategies for follow-up care and utilisation of closing and flooding in European hard coal mining areasAbstractThe already implemented or near end of mining in the European hard coal mining areas will cause the rise of the water table which had been kept down for mining activities, and will finally re-establish the contact with the groundwater layers near the surface. This flood water causes contaminations of groundwater used for drinking water and therefore calls for immediate action, because of the in part high salinity and concentration of mobilization products from the oxidised rocks. On the other hand the long-term process offers new options for discharge optimisation and utilisation. The FLOMINET project carried out within the frame of the European RFCS programdevelops numericalmodels to forecast the impact of regional minewater rebound on mine, ground and surface water in interconnected underground hard coal mines. The research is also dedicated to the industrial utilisation of the rising mine water for renewable energy in form of electricity and geothermal heat. For this purpose numerical models have been enhanced in terms of density and temperature to become a practical planning tool for these activities. One additional application is the appraisal of gas reservoirs for methane gas extraction, the influence of the flooding process on such extraction, and the forecast of risks originating from mine gases dissolved in water after mine flooding.1. Introduction: implications of closing and flooding in European hard coal mining areasThe development of coal consumption, worldwide exploration of coal deposits, transport conditions and world market prices have caused intensive effects on European hard coal mining areas in the last decades. Closure and flooding affected the mining areas in France, Belgium and England first but also Germany, where currently only 5 mines have remained active. The last of these mines is supposed to be closed by 2018. The flooding process in the Ruhr area becomes evident by the recent water level distribution. Even when taking the northern dip of the coal bearing strata into account, the 3 active mines appear as islands surrounded by abandoned mines with at least partial water accumulation. Furthermore, large mining areas in Spain and even in Poland are equally affected by a closing process induced by the exploitation progress and shifting of mining activities.In spite of site specific geological settings and varying mining technologies there are common processes accompanying the closure of mines established in Carboniferous strata in central Europe: The oxidation of pyrite in coal and host rock during active mining and ventilation forms a pool of soluble iron salts, which can be mobilized during flooding . Subsequent mine water drainage is mostly affected by iron concentrations demanding water treatment before discharge. The flushing of these oxidation products can take decades. The rising of the water table into the overlying strata may cause contact between mine water and the overlying groundwater aquifer, which was not possible under pre-mining conditions. This may affect groundwater quality and, because of subsidence, also the groundwater level requiring intensive long term pumping activities . Mine water flowing through deep mine voids shows high temperatures which in some cases reach more than 30 C and might demand cooling before discharge. However, this also offers the chance for geothermal heat recovery when the mines are situated in a densely populated area and the pumping costs are not charged to the user. In addition, the geothermal potential accessed by the mine voids can be used by closed loop systems. The rocks caved by longwall mining are very sensitive to water and as they are constituted by an assemblage of blocks, the equilibrium found may be affected by the presence of water and a disturbance of the surface either by resettlement or uplift. Additionally, volumetric changes due to swelling of coal and clays upon water saturation contribute to uplift processes.These demands and potentials of the mine closure process show the requirement for the coordination of this process not only taking into account the economics of a short-term decommissioning but also the ecological and, the long-term economic situation. Flooding processes and their various impacts do not take place in a linear way. Fig.1 illustrates the development of water levels in the Lorraine coal basin. Strategies for follow-up care and utilisation of mine closing and flooding require specially adopted model tools in order to provide forecasts of water table developments and environmental impacts on the surface.Fig.12. The modelling tool BoxmodelThe Boxmodel program code forms an application orientated model tool for water flow, mass transport, heat transport and interaction in watergas-systems. In most cases mining fields with intensive mining activities resulting in a homogenously reacting hydraulic system are taken as boxes in the Boxmodel. These boxes are subdivided vertically into model slices and form the balance elements for all calculations . The software allows for defining the structure of modelling cells and for installing many different kinds of connections among mining fields.The Boxmodel already serves as a prognostic tool for mine water issues in some important hard coal mining areas. Meanwhile considerable data are available to verify input parameters and assumptions.DMT has continued the development of the Boxmodel with the objective to improve the practicability and to standardise the methodology at various sites. In addition to the improvement of the already well established mine water flow models some important innovative programme codes have been implemented to model the following processes: coupled gas-water flow, energy production, high turbulent flow (storage), coupling of mine water with near surface ground water models and heat transport .The concept of the Boxmodel allows coupling of the mine model with groundwater aquifer models. Groundwater aquifer layers can be discretised by the Boxmodel in geometry and quality identically to the world wide most accepted groundwater models likeMODFLOW(finite difference method) or FEFLOW (finite element models). There is also the option to couple existing groundwater models.Apart from the water balance the most relevant input data comprise the void volume which includes open drifts,workings (remaining voids after subsidence in the gob) and porosity of the rocks. The chemical composition of the water is required for the investigation of quality effects. The transport-tool of the Boxmodel is considering the transport phenomena convection, molecular diffusion, dispersion, geochemical solution-/precipitation processes, sorption / desorption as well as microbiological processes. The Boxmodel is a multimigrant reactive mass-transport model. Up to now 30 inorganic and 27 organic chemical componentsare considered.Detailed regional Boxmodels have been developed for the mining areas of the Ruhr Area.Saar Area, Lorraine Coal Basin, Asturias, Upper Silesian Coal Basin and the Durham Coal field. A coupled interactive optimisation tool will allows cenario analysis regarding impacts on energy costs, environmental protection limits, payments and fees in regional mining network scales.3. Geothermal heat recovery3.1. geothermal heat recovery from mine waterDue to drainage effects the concentrated mine water outflows have anomalous yield,specific chemical composition and higher temperature in comparison with natural springs. Furthermore, this temperature remains steady throughout the year (Sanner et al., 2003), making mine water suitable for geothermal energy recovery: all three elements of a low-grade geothermal system (heat source, water and permeability) are readily available . Permeability is extensively present due to mine workings (in addition to fracture zones) while water is abundant below the water table.3.2. Technical feasibility of geothermal recovery in Asturias Carboniferous Basin: Geothermal potential assessmentThe shaft of the Barredo Colliery has been selected for detailed geothermal study due to an average water temperature between 20 C to 25 C. This is the lowest discharge point of the regional mining infrastructure formed by Barredo, Figaredo, San Jos and Santa Barbara Collieries. Thus pumping costs have been optimised. Barredo Shaft is placed in the urban centre of the municipality of Mieres, at the right bank of Caudal river. In this town, the University of Oviedo was developing two new buildings, some 200m from the shaft. Barredo Shaft is located at +220 m.a.s.l. The mine has five floors and the total depth of the shaft is 362 m. As Barredo Shaft has a direct connection with Figaredo Colliery all the water from the system could be drained by the former. The average water flow here reaches 4 Mm3/year.For the detailed studies being carried out in order to characterize the mine for geothermal energy production and to assess the evolution of its water quality, a Boxmodel of the whole Asturian Coal Basin has been generated. This allows for consideration of the hydraulic boundary conditions.The chemical characteristics of the water must be established in order to guarantee proper design and operational reliability. Chemical analyses of Asturian mine water proved there were no corrosion problemswith the equipment. The minewaterwasmainly bicarbonate sodium water with pH above 7. However, the main water problem identified was its high hardness, exceeding in some cases 1000 mg/L. This follows that the main expected risk would be carbonate deposits that may harm the energy generation equipment. Results show that there will be some scaling problems related to this. Intermediate heat exchangers are necessary, instead of guiding the mine water directly into the heat pump. To assess the energy potential of Barredo- Figaredo Unit, an average water flow of 4 Mm3 per year has been considered. Although re-injection of the water has not been considered so far there is an option to do so in the future. Therefore, the thermal potential in the cold source can be calculated as the product of the thermal gap, the water flow, the density of the water and the specific heat:where:- T Thermal gap, 5 C (on conventional heat pumps)- V Water flow per year (4 Mm3/year)- Ce Water specific heat (4186.8 J/kg C)- DensityThese data allowed estimation of the thermal potential of the mine water as 2.65 MWth at the cold source. The thermal potential of the hot focus can be calculated as:Where We is the energy consumed by the heat pump compressor (We0.66 MW). The water temperature is around 23 C and it is intended to produce energy at 40 C, thus a standard Coefficient of Performance (COP) can reach 5 The energy supplied to the heat pump at the compressor will be around 0.66 MW, reaching a thermal potential of the hot focus of 3.31 MW of heating-cooling power.4. Gas mobilisation, migration and extractionMine gas consisting of Methane, Oxygen, N2 and CO2 is the natural attendant of coal and coal mining. Closure of hard coal mines has therefore to consider interactions between water and gas in a hydro-geological context of mines during and after flooding. The corresponding processes can be described in two different approaches at two different scales.Interactions between water level rise and gas emissions during flooding can be described with the Boxmodel at a large scale. The concept of the Boxmodel approach considers one gas phase for describing the gas-flow and a multi-component concept for the mass transport model. A minimum of two components is considered: the concentration of methane and the sumof the rest (N2, CO2, H2S). Because of the large scale of the Boxmodel the gas dissolved in water is not considered. The flooding water table forms a sharp boundary to the mine not yet flooded, but still filled with gas. After flooding of coal seams the methane source is blocked.4.1. Gas extraction during mine voids floodingThe source-term of gas generation depends on the real gas content (given by the residual gas content in coal (kg/m3-coal) and the mass of residual coal (t) per mine field) and the permeability from the point of gas sorption to the open drift system. In the so called passive period methane flows from the seam to the drift system without a suction pressure only on basis of the higher sorption pressure in the seam. This process is the reason for uncontrolled methane emissions from closed mines . Active gas pumping results in pressure reduction in the mine voids and enhanced desorption and migration of methane to the pumping station. A typical feature of gas production in active mines is a much higher gas production rate than under post mining conditions, caused primarily by movement of geological formations (subsidence after exploitation of the coal) and secondly by artificial measures to prevent gas flow into the drifts (gas suction from seems over special drill holes).Active gas extraction therefore provides the possibility of postActive gas extraction therefore provides the possibility of post mining hydrocarbon use with additional reduction of uncontrolled gas release into the environment. It is limited, however, by the flooding process causing gas production to cease. On the other hand diffuse gas flux to the surface is enhanced during the flooding and affects urban hard coal mining areas in the post mining stage.The dependency of gas pressure and flow on gas pumping activities and the development of methane concentration in the Lorraine Coal Basin are shown in Figs. 2 and 3 on the basis of measuring data (BRGM) and Boxmodel results. Fig. 2. Calculated and measured gas flow (influenced by flooding) in the Lorraine Coal Basin, Simon shaft.Fig. 3. Calculated and measured development of the methane fraction in the gas phase in the Lorraine Coal Basin, Simon shaft.The following input data have been considered for calibration of the gas model tool for the regional model:- Points of gas pumping (x,y,z)- Pressure development versus time p(t)- Volume of gas pumped- Concentration development of methane at the pumping points- Source term description: residual gas content in coal kg/m3-coal- Mass of residual coal (t) per mine field.The source-termof gas production (mainly the coal seams) is linked to the rising water table. Successive flooding of seams causes cut-off of the specific gas production in this source. As a result the total gas production rate is decreasing with rising water table.The considered differential equation for the transport of the gas phase is:with Porosity Density of gas phase kg/m3u Darcy-velocity of gas phase m/s q Sink/source term of gas phase kg/s/m3pg Pressure of phase kg/(s2m)On the basis of the mass-flow formula of the gas phase the transport of two components (1: methane, 2: anonym gas for dilution (CO2, O2, N2, ) must be described (coupled one phase and two components flow). For this reason the formula of mass flow of the gas phase has to be extended by the concentration to:withc Concentration of a component 1 or 100%4.2. Effect of flooding on gas emission at short time scaleIn situ gasmonitoring performed in old shafts during the flooding of the La Houve Basin confirmed a first massive gas release just after the beginning of thewater level rise. This first period of gas flowis followed by a constant decrease until the end of the flooding. At this stage and during water level increase, gas is expelled by piston effect due to the void volume reduction.However, there is a positive effect on gas emissions coming fromold mines just after flooding. After flooding of the last mine voids gas flow out of wells reached concentration levels (CO2, CH4 and O2) comparable to atmospheric gas concentrations. Therefore, the evolution of void volume during flooding is the main parameter which controls mine gas outflow.5. ConclusionIn spite of obvious demand for further enhancements the model approaches seem promising for integration of post mining demands into recent strategies for mining management and closedown. In contrast to newmining projects the consequences of the mining period for the environment in the long term have not been subject to initial planning, and the recent mining structure is often the result of a long and changeful history. Appropriate model tools are available to assess the complex site data in order to develop the long termconcepts important for the overall cost effectiveness now, when mining is still active and required infrastructural procedures can be implemented.欧洲煤炭开采区域关闭和水浸后后续关注和利用的策略摘要在欧洲煤炭开采区域已经实施或者接近完成的采矿活动将会导致地下水位的上升，并且，将会最终导致重新与接近地面的地下水层建立联系。矿井涌水导致用于饮用的地下水污染，因此要求立刻采取行动，原因是极易氧化的岩石具有高矿化度及大量活化产物的聚集。另一方面长期的过程为排放和利用提供了新的选择。在欧洲RFCS项目框架内的FLOMINEF工程开发了关联的数值模型来预测区域矿井水在关联煤矿地下开采区域对于煤矿、地表以及地下水的影响。研究也致力于对于上升矿井水的工业利用，以电力和地热的形式获取可再生能源。基于这个目的，密度以及温度的数值模型已经被加强建立来打造一种实际可行的工具，附加的应用是瓦斯气体提取研究，涌水过程瓦斯提取的影响以及从自溶解在水浸矿井里水里的气体预测危险性。1、简介：欧洲煤炭开采领域关闭或水浸矿井造成的影响 消费量、全球范围内煤炭矿藏的勘探运输条件以及世界范围内煤炭市价格的上涨导致在过去的十年里对欧洲煤炭开采活动造成巨大影响。矿井封闭以及涌水影响着法国比利时英国以及德国，在那里只有五座矿山仍在生产。这下煤矿将会在2018年相继关闭，通过最近的水位分不可见鲁尔区的矿井水淹过程非常明显，甚至将北部含煤地层的倾角考虑在内，三条生产矿山呈现为被局部积水废弃矿山的岛屿。此外，在西班牙和波兰大的煤矿开采区域被关闭矿井以及采矿活动转移影响着，尽管有特殊的矿床地质特征和不同的采矿技术，在欧洲中部伴随着矿山关闭有着类似的过程：（1）在采矿和通风期间黄铁矿在煤层和围岩中的氧化形成了可溶性铁盐池可以在水浸过程中移动。随后的矿井排水被铁浓度影响，冲流这下氧化物需要十年以上的时间。（2）上升的地下水位引起矿井水和上覆地下水含水层的联系，这是在不开采煤矿的条件下不可能发生的，可能影响地下水质量，因为下陷的地下水位需要密集的长期的抽水活动。流经深矿孔隙的矿井水显示出高温在，在某种程度上可以超过30摄氏度，因此也需要在排放抽取前冷却处理，但是，这同样提供了地热回收的机会。当矿井坐落在人口稠密区以及抽水费用可以不用向用户收取。另外，矿孔隙产生的地热潜力可以被应用于闭环系统。（3）长壁开采塌陷的岩石对水很敏感，由于他们是块体集合组成，平衡可能因为水的存在而干扰。另外，由于煤和粘土体积膨胀变化有助于提升流程。这些要求和矿山关闭过程的潜在问题，表明协调这个过程的要求不仅要考虑到短期的退役经济效益也要考虑生态的经济形势。水淹过程及各种影响不采取线性方式进行。图二说明了洛林煤盆地地下水位的发展状况。对于矿山关闭及涌水后期的后续关注和利用的策略需要专门的模型工具，目的是为了提供矿井水位和地表环境影响准确的预报。2、建模工具BOXMODELBOXMODEL程序代码里包含水流、运输、热运输以及水汽系统的相互利用。在大多数的情况下，伴随着强烈采矿活动的井田在BOXMODEL中被当做一个箱子垂直细分成模型切片以及形成用于所有计算的平衡元素。该软件允许定义建模细胞的结构和架构许多不同采矿领域之间的连接。BOXMODEL模型已经作为一个预测工具在一些重要的煤矿开采领域。同时，大量的数据可用来验证输入参数和假设。DMT促进了BOXMODEL的发展，提高了模型的实用性以及在不同领域的规范方法。除了已经建立的矿井水量流动模型的改善，一些重要的创新程序代码已经被实施模拟一下过程：耦合气水流量、能量产生高湍流、矿井水以及附近的地表水模型的耦合及热传输。BOXMODEL的理念要求矿井模型与地下含水层模型的耦合，地下含水层可以被BOXMODEL在几何形状和质量离散成。世界范围内都可以接受的像BOXMODEL或FEFLOW地下水模型。也有选择去耦合已有的地下水模型。除了水平衡，最大相关的输入数据包括孔隙体积，里面包括开放的飘移运作以及岩石的孔隙密度。水的化学成分需要质量影响的调查。交通的BOXMODEL正在考虑运输对象对流、分子扩散、分散、地球化学解决方案、降水过程、吸附、脱附及微生物过程。BOXMODEL是一个反应性运输集体模型，到现在为止，30个无机27个有机的化学成分被考虑。鲁尔区、节尔区、洛林煤盆地、阿斯图里亚斯、上西里西亚煤盆地和达勒姆盆地已经制定了详细的区域BOXMODEL模型。耦合互动的优化工具将允许分析有关能源成本的影响、环境保护限制以及在区域采矿网络规模的支出和费用。3、地热回收3.1、矿井水里地热回收由于排水效果，集中矿井水流出和天然泉水比较有异常收益率、特殊化学成分和较高的温度。而且，温度全年保持稳定，使得矿井水适合地热回收。低档的地热系统的所有三个要素随时可用。由于采矿活动，渗透率普遍存在而且在地下水位一下水量是丰富的。3.2、阿里斯图里盆地地热恢复技术的可行性：地热潜能评估由于平均水温在20-25，巴雷煤矿轴已经被选定为详细的地热研究，由巴雷非加雷多、圣巴巴拉煤矿形成的，这是该区域的采矿基础设施的最低排放点。因此，抽水成本却得到了优化，巴雷轴位置在mieres直辖市的城市中心，在尾鳍河右岸。在这个城镇，奥维多大学正在开发两个新的建筑，离轴大概200