Estimating local CH4 emissions in the Upper Silesian Coal Basin using inverse modelling

<p>Methane (CH<sub>4</sub>) is the second most important anthropogenic greenhouse gas (GHG) with respect to radiative forcing. Since pre-industrial times, the globally averaged CH<sub>4</sub> concentration in the atmosphere has risen by a factor of 2.5. A large fraction of global anthropogenic CH<sub>4</sub> emissions originates from localized point sources, e.g. coal mine ventilation shafts. International treaties foresee GHG emission reductions, entailing independent monitoring and verification support capacities. Considering the spatially widespread distribution of point sources, remote sensing approaches are favourable, in order to enable rapid survey of larger areas. In this respect, active remote sensing by airborne lidar is promising, such as provided by the integrated-path differential-absorption lidar CHARM-F operated by DLR. Installed onboard the German research aircraft HALO, CHARM-F serves as a demonstrator for future satellite missions, e.g. MERLIN. CHARM-F simultaneously measures weighted vertical column mixing ratios of CO<sub>2</sub> and CH<sub>4</sub> below the aircraft. In spring 2018, during the CoMet field campaign, measurements were taken in the Upper Silesian Coal Basin (USCB) in Poland. The USCB is considered to be a European hotspot of CH<sub>4</sub> emissions, covering an area of approximately 50 km × 50 km. Due to the high number of coal mines and density of ventilation shafts in the USCB, individual CH<sub>4</sub> exhaust plumes can overlap. This makes simple approaches to determine the emission rates of single shafts, i.e. the cross-sectional flux method, difficult. Therefore, we use an inverse modelling approach to obtain an estimate of the individual emission rates. Specifically, we employ the Weather Research and Forecast Model (WRF) coupled to the CarbonTracker Data Assimilation Shell (CTDAS), an Ensemble Kalman Filter. CTDAS-WRF propagates an ensemble realization of the a priori CH<sub>4</sub> emissions forward in space and time, samples the simulated CH<sub>4</sub> concentrations along the measurement’s flight path, and scales the a priori emission rates to optimally fit the measured values, while remaining tied to the prior. Hereby, we obtain a regularized a posteriori best emission estimate for the individual ventilation shafts. Here, we report on the results of this inverse modelling approach, including individual and aggregated emission estimates, their uncertainties, and to which extent the data are able to constrain individual emitters independently.</p>

Observational constraints on methane emissions from Polish coal mines using a ground-based remote sensing network

Given its abundant coal mining activities, the Upper Silesian Coal Basin (USCB) in southern Poland is one of the largest sources for anthropogenic methane (CH4) emissions in Europe. Here, we report on CH4 emission estimates for coal mine ventilation facilities in the USCB. Our estimates are driven by pair-wise upwind-downwind observations of the column-average dry-air mole fractions of CH4 (XCH4) by a network of four portable, ground-based, sun-viewing Fourier Transform Spectrometers of the type EM27/SUN operated during the CoMet campaign in May/June 2018. The EM27/SUN were deployed in the four cardinal directions around the USCB in approx. 50 km distance to the center of the basin. We report on six case studies for which we inferred emissions by evaluating the mismatch between the observed downwind enhancements and simulations based on trajectory calculations releasing particles out of the ventilation shafts using the Lagrangian particle dispersion model FLEXPART. The latter was driven by wind fields calculated by WRF (Weather Research and Forecasting model) under assimilation of vertical wind profile measurements of three co-deployed wind lidars. For emission estimation, we use a Phillips-Tikhonov regularization scheme with the L-curve criterion. Diagnosed by the averaging kernels, we find that, depending on the catchment area of the downwind measurements, our ad-hoc network can resolve individual facilities or groups of ventilation facilities but that inspecting the averaging kernels is essential to detected correlated estimates. Generally, our instantaneous emission estimates range between 80 and 133 kt CH4 a−1 for the south-eastern part of the USCB and between 414 and 790 kt CH4 a−1 for various larger parts of the basin, suggesting higher emissions than expected from the annual emissions reported by the E-PRTR (European Pollutant Release and Transfer Register). Uncertainties range between 23 and 36 % dominated by the error contribution from uncertain wind fields.

Assessment of Sinkhole Hazard in the Area of Shallow Mining Workings Using Electrical Resistivity Tomography

This paper presents the results of investigating shallow rock mass layers with the use of electrical resistivity tomography. The aim of the study was to assess the condition of near-surface rock mass layers located above shallow mining workings of a historical mine in view of the possibility of the occurrence of loose zones or possible voids that could pose a sinkhole hazard for the surface. The study was carried out under the conditions of the “Sztygarka” Training Mine and Museum in Dąbrowa Górnicza City (Upper Silesian Coal Basin, Poland), where discontinuous surface deformations occurred in the past in the form of sinkholes. The study and its interpretation indicate the existence of a sinkhole hazard due to the ongoing processes of the transformation of the near-surface rock mass layers above the shallow workings of a historical mine.

Selected Critical Raw Materials in Waste from Coal Gasification in Poland

In an effort to identify new sources of critical raw materials (CRMs) possibility of recovering selected CRMs from Polish coals, chars, and ashes resulting from the combustion of coals and chars was investigated. The samples were collected from pilot fluidized bed gasification systems. The search for CRMs in coal gasification wastes has not been widely reported before. The study used 2 bituminous coal and 1 lignite sample; the concentration of individual critical raw materials (CRMs) was analyzed using the ICP-MS method. The obtained results were compared with Clarke values in coal ash and in the Earth’s crust, and with the adopted cut-off grade. As shown by the analysis, the highest concentrations of CRMs can be found in fly ash, mainly in samples from the eastern part of the Upper Silesian Coal Basin. This applies mostly to Be, Cs, or Sb due to the fact that their concentrations were found to be higher than the Clarke value in the Earth’s crust; the mentioned fly ashes could be used as potential sources of critical elements if appropriate recovery technologies are developed. In addition, the tested materials have elevated Se, Pb, Ni concentrations, but their recovery is currently not economically viable. Compared to the currently adopted cut-off grade levels, there are no critical elements in the analyzed coal gasification waste that could be recovered.

Methane emissions against the background of natural and mining conditions in the Budryk and Pniówek mines in the Upper Silesian Coal Basin (Poland)

The paper presents the variability of hard coal output, methane content and methane emissions into coal workings and into the atmosphere from the two most methane-gassy coal mines in Poland. The Budryk mine is one of the youngest mines in Poland, but it is the most methane-gassy as well. In 2016, the total CH4 emissions exceed 140 million of m3. This large increase in methane emissions to mine workings is primarily related to the increase in the depth of coal extraction (up to 1290 m) and, consequently, the rapid increase in the methane content in coal seams (up to 10–12 m3/Mg coaldaf). On the other hand, in the Pniówek mine, methane emission was the highest at the beginning of the study period (1986–1991). During the following years, emission decreased to the values of less than 140 million of m3, which were still one of the largest amounts of emitted methane in the entire Upper Silesian Coal Basin. The coexistence of natural factors, such as the geological structure and gas distribution, as well as mining-related factors, i.e. the depth of mining, the intensity of coal extraction determines the temporal variability of methane emissions in the studied mines.

Sorption and Micro-Scale Strength Properties of Coals Susceptible to Outburst Caused by Changes in Degree of Coalification

Coals from the south-western part of the Upper Silesian Coal Basin have a strong outburst susceptibility. The objective of this study was to identify the influence of coalification degree on methane sorption and micro scale strength properties of 24 coals from Jastrzębie Zdrój. Coal samples showed a reflectance Ro between 0.98 and 1.25%. Sorption measurements were carried out by gravimetric method. Sorption capacities were determined at mean deposit temperature of 35 °C. Using the unipore model and solution of Fick’s second law, the effective diffusion coefficients of methane in the studied coals were obtained. The Vickers method was used to study the microhardness and the modulus of elasticity. It has been shown that the increase in the coalification degree reduces the sorption capacity of coal and also reduces the rate of methane emission. Coals the most susceptible to outbursts, were the most brittle. With the increase in Ro, the methane seam pressure p increased as well as desorbable methane content DMC, both due to the reduction in the sorption capacity of coal. The increased dp index is a warning sign indicating an increased total methane content of coal seam, an increased seam pressure or an alternation of coal structure.