German Lignite Research Articles

Oxy-fuel co-gasification of coal and biomass for negative CO2 emissions

A novel process has been investigated to enable CO2 to be isolated as a concentrated stream from the exhaust of a power station, without the use of separate, downstream capture technology. In this concept, a fluidised bed gasifier is operated with pure O2 and CO2, recycled from the combusted fuel gas stream, combining the advantages of gasification, fluidised bed operation and use of oxygen. With the combination of CO2 capture and biomass as the feedstock, net negative emissions can be achieved. This is the fifth in a series of papers which investigate the underlying science of the concept. It studies the influence of the use of different coals and mixtures containing coal/biomass on the process performance. A continuously fed, laboratory scale spouted bed reactor has been used for this study, and Daw Mill coal (DM), German lignite (GL), Polish coal (PC) and Olive bagasse (OB) were used as fuels. Carbon conversions for DM and PC were around 20–30% and dominated by release by pyrolysis. High conversions (60–80%) were observed for GL and the char showed an appreciable gasification reactivity. Co-processing of OB with GL proved to be a good way to further improve the overall process performance and complete conversion was achieved under some conditions. Processing biomass with lignite, with CO2 capture, is a technically viable way of producing energy from a waste material with a negative process carbon footprint.

Increasing the efficiency of chemical looping combustion of biomass by a dual-stage fuel reactor design to reduce carbon capture costs

This paper analyzes the capabilities of a pilot-scale chemical looping combustion plant firing wood biomass in two stages to efficiently achieve negative carbon dioxide emissions. The utilized in situ gasification-chemical looping combustion (iG-CLC) process isolates the oxygen supply via air from the fuel conversion itself with the help of two separate fluidized bed reactors and an oxygen carrier to supply the necessary oxygen for the combustion. As a result, a relatively pure stream of carbon dioxide and steam is generated. Thus, the process makes capturing carbon emissions more feasible since it eliminates the need for the cost- and energy-intensive separation of the produced gases. A major issue when using biomass in a chemical looping plant is the high amount of the volatiles exiting unconverted. This problem was mitigated by using a two-stage fuel reactor system. Two bubbling fluidized beds were arranged one upon the other. The lower stage, where the fuel is introduced, is used to release the volatiles and partly convert them. The remaining volatiles rise up into the second stage and are further converted to a high degree. A series of experiments were carried out with a 25-kWth pilot plant located at the Hamburg University of Technology. Gas concentrations were continuously measured after both stages of the fuel reactor to see the gradual conversion of the fuel gases. Additionally, carbon slip at the exhaust was measured to show the effectiveness. The experiments with the reactor concept showed promising results since already at a reactor temperature of 850 °C, the total oxygen demand needed to oxidize the combustible component in the exhaust gas was well below 2%. The carbon dioxide (CO2) capture efficiency when using German hardwood slightly decreased to 93–96% compared to 97% for German lignite. In the future, the reactor design must prove that it scales and that the efficiency can be further increased. Nevertheless, firing biomass with a two-stage iG-CLC process might allow a cost-efficient negative carbon dioxide emission while generating heat with relatively high efficiency. Therefore, it might be a sustainable alternative to generate heat in the future.

In-lake Neutralization of East German Lignite Pit Lakes: Technical History and New Approaches from LMBV

The Lausitzer und Mitteldeutsche Bergbau Verwaltungsgesellschaft (LMBV), a state-owned company, is the responsible partner for remediation of East Germany’s lignite mining areas. This includes the obligation to create ecological and economically sustainable pit lakes. LMBV currently opts for in-lake treatment as the more reasonable alternative to classical discharge treatment in terms of environment and economics. LMBV has neutralized more than 20 highly acidic pit lakes and keep them in neutral conditions by regular follow up neutralization. Techniques especially adapted for the needs of East German pit lakes were developed. Of note has been the development and construction of the mobile treatment vessel “Klara”, which combines a high daily neutralization agent input with a high efficiency factor. Some whole lake experiments with in-lake treatment plants for buffering pit lakes with CO2 were also carried out. These techniques are quite costly, but under long term conditions, the buffering can be necessary to prevent re-acidification when the continuous addition of a neutralization agent is not possible, for instance under an ice cover.

Fluidised bed oxy-fuel gasification of coal: Interactions between volatiles and char at varying pressures and fuel feed rates

Fluidised bed gasification is a versatile technology in terms of load flexibility and ability to process various fuels. However, fluidised bed gasification processes are usually air-blown, making integration with CO2 capture difficult and expensive. Operation of a fluidised bed gasifier with O2/recycled CO2 mixtures has been proposed as a route to overcome this drawback. In this work, the effect of pressure and fuel feed rate on the extent of gasification of German lignite in a CO2 rich atmosphere has been examined in a fluidised bed reactor (FBR). A 19% decrease in carbon conversion with increasing pressure from 5 to 20 bara was observed. The higher fuel feeding rates needed to maintain the gasification agent to coal ratio in the FBR at high pressures produces a larger concentration of tars in the reactor, which seems to cause deposition, by intra and inter particle reaction, on the char and reduces its reactivity.

Estimation of Self-Neutralisation Rates in a Lignite Pit Lake

Natural anaerobic biogeochemical processes used for passive treatment of AMD were observed in the extensive shallow water zone of a polymictic pit lake in the former German lignite district of Upper Palatinate. Although continuously fed by acidic metalliferous groundwater, lake-pH increased from 3.5 to circumneutral over a little more than 10 years. The natural attenuation processes were studied and quantified using a regional surface- and groundwater flow model linked with hydrochemical monitoring datasets to establish a simple mass balance. The acidity inflow was estimated at ≈ 5900 kmol over the period 2014–2018, which corresponds to an average inflow of ≈ 1190 kmol/a. This estimate is in very good accordance with an acidity inflow rate for the period 2000–2014 estimated from acidity deposition in the sediment based on sediment core analyses plus the calculated cumulative acidity outflow based on extrapolation of pre-neutralisation acidity levels in the pit lake, together yielding a total acidity of ≈ 15,000 kmol, which corresponds to an inflow rate of ≈ 960 kmol/a. The results strongly indicate that the pit lake self-neutralised due to beneficial environmental and ecological conditions, amplified and potentially initialised by the circumneutral discharge from a chemical mine water treatment plant, and that well-known biogeochemical mechanisms such as natural microbial sulfate reduction were the driving force. The results give rise to perspectives concerning the potential development of pit lakes if ecological considerations are considered.

Simultaneous analysis of light gases and heavy pyrolyzates evolved from lignite and hard coal by pyrolysis–GC/MS–GC/TCD

The pyrolysis of solid fossil fuels and biomass is of great relevance, because it influences the combustion kinetics of these fuels, and the pyrolysis products are potential raw materials for further chemical processing. The aim of this work was to develop a pyrolysis system able to separate the whole variety of pyrolysis products during one pyrolysis experiment without the need to replace GC columns for improved resolution. A conventional pyrolysis system equipped with a coupled gas chromatography (GC)/mass spectrometry (MS) detector was extended by a second GC with a fused-silica capillary column and a thermal conductivity detector (TCD). The coupled pyrolysis–GC/MS–GC/TCD system was used to investigate the evolved pyrolysis products of two lignites and a hard coal enabling the qualitative detection of pyrolyzates (GC/MS) while simultaneously quantifying the light gases (TCD). Benzofuran, catechol, and a preference for even-numbered hydrocarbon pyrolyzates in addition to a higher pristene/heptadecane ratio were found to be characteristic for the two studied German lignites in comparison to the Columbian hard coal as well as a higher release of especially oxygen-containing light gases.

Determination of mercury binding forms in humic substances of lignite

Mercury is known for primarily binding organically in lignite and inorganically in coal. The knowledge about the binding forms does not impact the speciation of mercury in the combustion chamber of a power plant. However, the relation between binding forms and release behavior is crucial for modelling the material flow of mercury in the firing process. Oxidizing agents like halogen salts could be added more effectively. There are different analyzing methods like the float-sink-analysis or the sequential leaching to determine the mercury binding forms. Nevertheless, there is no standard procedure for each analyzing method, which allows a comparison. In this work, mercury binding forms in Central German lignite were investigated. Results from thermal treatment of the lignite show a loss of mercury of 87% up to a temperature of 200 °C. The responsible mercury binding form for that release behavior is discussed by using the results of a leaching process for the extraction of humic substances, mercury analyses and simultaneous thermal analyses with mass spectrometry (TG/DSC-MS). The results show that mercury is bound to humic acids with 0.261 mg/kgdry and in humin with 0.735 mg/kgdry. The high mercury affinity of humic substances is noted as the result of chemical binding with functional groups like the carboxyl group, hydroxyl group and thiol group. Compared to the raw sample, a thermally treated lignite (at 200 °C) does not show any thiol group (m/z=48) in ion intensity measurement. This work proves the organic binding form of mercury with humic substances in lignite.

Economic Resilience of German Lignite Regions in Transition

This paper recalls the development of the German lignite regions Rhineland and Lusatia since 1945 to allow for a better understanding of their situation in 2019. We analyze their economic resilience, defined as adaptive capacity, using Holling’s adaptive cycle model. We find that the Rhineland is currently in the conservation phase, while Lusatia experiences a reorganization phase following the economic shock of the German reunification. Key policy recommendations for the upcoming coal phase-out are to foster innovation within the Rhineland’s infrastructures to avoid overconnection, and to expand digital and transportation infrastructure in Lusatia so that the structurally weak region can enter the exploitation phase. Future policymaking should take into consideration the differences between the two regions in order to enable a just and timely transition during which lasting adaptive capacity can be built.

Production of a fuel gas by fluidised bed coal gasification compatible with CO2 capture

A continuously fed, laboratory scale spouted bed gasifier has been used to study oxy-fuel gasification of German lignite. In this paper, the influence of different gasification agents and bed temperature on the process performance, during tests at atmospheric and elevated pressure are studied. Two gasification agents have been used, CO2 (with different CO2/C ratios) and mixtures of CO2/steam. The results show that despite the relatively slow CO2-char reaction, good gasification performance could be achieved with German lignite by adjusting the operating conditions at atmospheric pressure: complete carbon conversion, high energy conversion and a medium heating value fuel gas (8–10 MJ m−3). The CO2/C ratio was found to have a large effect on the gasification performance. Increasing the ratio increased the carbon conversion, but the CO2 conversion decreased. At 950 °C, maximum carbon conversion was already achieved with pure CO2, therefore using steam at this temperature could not increase the conversion, but did increase the H2/CO ratio in the fuel gas. At 850 °C, replacing 25% of CO2 with steam increased the carbon conversion to the level achieved at 950 °C without steam. Replacing more than 25% of CO2 with steam increased the H2/CO ratio further. Therefore, with the addition of steam, the operating temperature could be reduced from 950 °C to 850 °C while maintaining the gasification performance. The changes of gasification performance with steam addition at pressures up to 10 bara followed the same trends achieved at atmospheric pressure.

Chemical looping combustion of high sodium lignite in the fluidized bed: Combustion performance and sodium transfer

The Zhundong coalfield in Xinjiang, China, is the largest integrated coal basin newly found. The present work concentrates on the application of chemical looping combustion (CLC) with a Zhundong lignite, which is characterized by high sodium content. Some experiments in a laboratory scale fluidized bed facility with an active iron ore oxygen carrier, were performed using the lignite as fuel and CO2 as gasifying agent at a temperature of 900 °C, with the objective of investigating its combustion performance and sodium transfer behavior in CLC. Results indicate that the gasification reactivity of the three coals follows the order of German lignite > Zhundong lignite > American bituminous coal in the current experimental conditions. During reducing stage, the unique product of sodium transfer from coal to the fly ash is albite (NaAlSi3O8) due to the reactions between sodium and other coal ash. The sodium deposition on the oxygen carrier particles was not found. 40 reducing-oxidizing cycles were performed, and sodium accumulation in the bed materials with cycles was found due to some ash staying in the bed. However, the growth of bed particles due to the sodium accumulation was not observed by determining the particle size distributions of bed materials. This indicates that burning the high sodium Zhundong coal in the present conditions have no influence on the particle agglomeration.Finally, a literature survey was made and results indicate that the main sodium in the Xinjiang coal basin of China is water soluble with an average value of 64%. The pure salt of NaCl, as one common water soluble sodium phase in Zhundong coals, was introduced to a bed of iron ore particles at 900 °C with regard to investigate the influence of NaCl on fluidization stability. Based on the measurements of pressure drop, bed temperature and SEM-EDS, it was found that NaCl does not react with the iron ore but in fact only acts as glue between iron ore particles. Further, the sodium transfer routes in CLC of Zhundong coal with iron ore based oxygen carrier are given and some discussions are made with regard to practical operation. The corrosion problems on the heating surface in the air reactor can be significantly reduced compared to a conventional Zhundong coal fueled furnace, since most of sodium will release and be converted in the fuel reactor.

In-situ investigation of single particle gasification in a defined gas flow applying TGA with optical measurements

The newly developed HITECOM reactor provides the possibility of in-situ analysis of single particle reactions. It combines the capabilities of a magnetic suspension thermobalance with state of the art optical analysis. The surface temperature and carbon conversion of single particles are measured under well-defined flow conditions. The generated data enables the detailed validation of CFD single particle models. For this reactor, a special temperature resistant particle holder had to be constructed, which is able to fix various particles in direct flow during gasification. An in-situ Raman spectroscopy setup was established for quantitative gas analysis at pressures between 1 and 20bar and temperatures up to 965°C. Here, a pulsed Nd:YAG laser at 355nm was used as excitation source. The Rayleigh/Raman scattering was measured perpendicular to the flow direction with a spectrograph and ICCD camera. From the recorded spectra the gas concentrations were calculated. Generally, the calculated concentrations of CO, CO2 and N2 match the reference values from the gas chromatograph.In the present study, single coal particles of one Central German lignite and one hard coal were analyzed and monitored during gasification. The particle diameter ranged from 1 to 3mm. Gasification experiments with CO2 were carried out under isothermal conditions at 1bar total pressure and temperatures of 800–1200°C.The experimental data were adjusted with models by data fitting. It was found that the Random Pore Model (RPM) matches the carbon conversion of the hard coal sample and the Shrinking Core Model (SCM) matches the carbon conversion of the lignite sample.Further analysis revealed that inhomogeneous particles affect gasification kinetics. The differences in reactivity between several particles from the hard coal are significantly larger than for the lignite particles, which is in accordance to the results of the respective ultimate and proximate analyses.Additionally, it was discovered that the difference between gas and particle temperature is negligible for low reactive feedstocks within the investigated temperature range (ΔT⩽5K at 1070°C, hard coal), whereas there was a significant difference for reactive particles (ΔT⩽40K at 1070°C, lignite).

Catalytic pyrolysis of central German lignite in a semi-continuous rotary kiln — Performance of pulverized one-way ZSM-5 catalyst and ZSM-5-coated beads

Central German lignites with high numbers of aliphatic and bituminous molecular structures are potential feedstocks for light hydrocarbons as intermediates for the chemical industry. This study pursues a new approach to the direct conversion of lignites by heterogeneous catalysis under pyrolytic conditions and without additional hydrogenation. Promising results were achieved in lab-scale investigations with ZSM-5 catalyst and these results were confirmed at a semi-technical scale rotary kiln. ZSM-5-coated beads were examined as an interesting alternative for reutilization and simple separation from the solid pyrolysis products.Based on parameter studies, the maximum yields of low molecular hydrocarbons occurred at a reaction temperature of 500°C at a catalyst-to-coal ratio of 0.1 to 0.2 (maf). Comparison between the pulverized one-way ZSM-5 catalyst and ZSM-5-coated beads shows similar results concerning the amounts of pyrolysis products, especially gaseous alkenes like propene. At a certain catalyst-to-coal ratio, comparable results of propene liberation can be found also. The main reaction pathways were identified based on the distribution of the catalytic pyrolysis products, especially of low molecular hydrocarbons.

English

Oxygen has been considered the main driver of the weathering processes in mining wastes, omitting the role of microbes. Among many approaches to control oxygen access to the wastes, in situ treatment of the mineral surface has been tried since the late eighties. Various materials including NPR (Natural Phosphate Rock) were added with the expectation of finding an iron-phosphate coating. Irregular and inconsistent results were obtained when the effluents were evaluated according to NPR stoichiometry; however, the lower dosages showed some improvements in the effluents. Since the results did not consistently produce iron phosphate, any positive effects on effluents were considered accidental and the approach abandoned. We suspected microbes at work based on basic ecological considerations. Hence 1991, we began experimenting on tailings and waste rock with additions of NPR, postulating that if chemo-lithotrophic microbes on the mineral surface accelerate oxidation, then heterotrophic (oxygen-consuming) microbes would reduce oxidation. Samples from tailings plots where NPR was tilled into the surface were tested for pore-water quality after eight years. Effluents from waste rock exposed outdoors in drums were monitored for 2.7 years. Repeatedly, the one-time addition of NPR produced effluents with elevated pH and low metal acidity. Later, microscopic investigations of the rocks found an organic layer on the mineral surfaces. Investigations by scientists in 6 different universities confirmed the presence of a biofilm as the cause of the reduced acid generation. In 2013, heterotrophs were identified and quantified as they covered the surface of German lignite, following a bioleach testing protocol starting at pH around 1. These findings conclusively showed that the development of heterotrophic biofilms and improved effluents from sulfidic mine wastes are a consequence of adding waste NPR. We conclude that sufficient evidence has been gathered to prove that the geo- microbial control or in situ control of sulfide oxidation is a viable concept. It needs to be pursued to control or curtail acid mine drainage now and in the future. In this paper, we document the evolving ecological thought process over 23 years of research, which lead step by step toward understanding of the effects of NPR on the reduction of sulfide oxidation.

The temperature-dependent release of volatile inorganic species from Victorian brown coals and German lignites under CO2 and H2O gasification conditions

Abstract To promote the use of abundant low rank coal resources, and to assist with the design, development and optimisation of hot gas cleaning and downstream processes, it is necessary to understand the release mechanisms of volatile inorganic species from low rank coals under high temperature gasification conditions. Although a significant amount of work has been reported under combustion and oxygen lean gasification conditions, these studies do not sufficiently explain the role of the gasification reagents CO 2 and H 2 O in the mechanisms. Therefore, gasification experiments under 20% CO 2 and 20% H 2 O in He were conducted at 1100 °C, 1200 °C and 1400 °C for two Victorian brown coals and four Rhenish lignites. Hot gas analysis was conducted by online molecular beam mass spectrometry to determine the intensity, relative quantity and timing of the release of volatile species of interest. Two overlapping phases were clearly observed from the results – devolatilisation and char gasification. Major species detected were 23 Na + , 34 H 2 S + , 35 Cl + , 36 HCl + , 39 K + / 39 NaO + , 58 NaCl + , 60 COS + / 60 NaCl + , and 64 SO 2 + . The release during devolatilisation was essentially independent of the bulk gas atmosphere and constituted the majority of Na and Cl species. The release of S-species occurred predominantly during gasification under both CO 2 and H 2 O atmospheres by similar but distinct mechanisms, and was directly affected by the absence, presence and concentration of the gasification reagents.

Influence of Temperature on the Release of Inorganic Species from Victorian Brown Coals and German Lignites under CO2 Gasification Conditions

The release of volatile inorganic species containing Na, K, S, and Cl during coal gasification is of interest due to the known associated issues related to corrosion and fouling in coal-to-product processes. Therefore, laboratory-scale experiments using two Victorian brown coals and four German lignites were performed at 1100, 1200, and 1400 °C under an atmosphere of 20% CO2 in He to simulate gasification conditions. The reaction products were analyzed online by the well-established molecular beam mass spectrometry technique, and qualitative and semiquantitative analysis of the results was performed. The primary release occurred during the initial devolatilization phase, with less volatile and secondary products released during the gasification phase. The main inorganic species detected were 34H2S+, 35Cl+, 36HCl+, 39K+/39NaO+, 58NaCl+, 60COS+/60NaCl+, and 64SO2+. The release of sodium and chlorine species was highly dependent on temperature and the inherent Al and Si content of the coals. The release of sulfur-containing species was highly dependent on temperature and the inherent Ca content of the coals. Mechanisms for the initial release and subsequent reaction of intermediate inorganic species are offered herein to explain the observed trends with temperature and coal properties.

Mutagenicity, dioxin-like activity and bioaccumulation of alkylated picene and chrysene derivatives in a German lignite

In a former study, a German lignite extract exhibited toxicity to Danio rerio and Caenorhabditis elegans and was shown to have mutagenic and dioxin-like activity. Besides the comparatively low content of known toxic polycyclic aromatic hydrocarbons (PAH), highly intensive peaks of m/z 274 and m/z 324 were observed during the chromatographic analysis. These compounds are assumed to be alkylated chrysenes and picenes (3,3,7-trimethyl-1,2,3,4-tetrahydrochrysene, 1,2-(1′-isopropylpropano)-7-methylchrysene and an isomer of the latter, 1,2,9-trimethyl-1,2,3,4-tetrahydropicene and 2,2,9-trimethyl-1,2,3,4-tetrahydropicene). These compounds are intermediates in the diagenetic formation of chrysene and picene from triterpenoids. Due to their general high abundance in lignites and the toxicity observed for the lignite extract, the mechanism-specific toxicity and bioavailability of these compounds were investigated in the present study using the approach of effect-directed analysis. After the separation of the compounds from other PAH, their mutagenic activity (Ames Fluctuation test) and dioxin-like activity (EROD activity) were studied. Both, mutation induction factor (up to 2.9±2.7) and dioxin-like activity (Bio-TEQ of 224±75pg/g; represents the amount (pg) 2,3,7,8-tetrachlorodibenzo-p-dioxin per g coal that would provoke the same toxic effect) were rather low. Bioavailability estimated by the bioaccumulation test with Lumbriculus variegatus was also very limited. Based on the obtained results, the environmental risk of the highly abundant alkylated chrysenes and picenes in lignites is concluded to be low.

Two‐Dimensional Correlation Spectroscopy for Interpretation of Demineralization and Aging of German Lignite

AbstractFür die Analyse von Kohle gibt es verschiedene Methoden, die jedoch alle unterschiedliche Ergebnisse liefern und schlecht miteinander vergleichbar sind. Die 2D‐Korrelationsspektroskopie ermöglicht jedoch durch die Anwendung synchroner und asynchroner Berechnungsalgorithmen eine erhöhte Auflösung der Daten sowie einen Vergleich. In dieser Arbeit wurde deutsche Braunkohle zeitabhängig entmineralisiert sowie einem simulierten Alterungsprozess unterzogen und mit Infrarotspektrometrie in abgeschwächter Totalreflexion analysiert. Zur Auswertung beider Messreihen wurde die 2D‐Korrelationsspektroskopie angewendet, um deren Potenzial aufgezeigt.

How to develop native plant communities in heavily altered ecosystems: examples from large‐scale surface mining in Germany

AbstractQuestionsDoes site alteration caused by mining impede spontaneous colonization of native species assemblies to the advantage of neophytic species at the landscape unit and plant community scale? To what extent can mined site conditions support the establishment of rare plant species assemblies that are locally novel but of regional conservation value? What effects have dispersal limitation and stochasticity on spontaneous succession trajectories and how does community structure and composition differ between actively restored sites and ancient grasslands?LocationCentral German Lignite Mining District.MethodsWe used comprehensive databases to compare floristic composition in mined sites and their surroundings. At the community level, we choose a chronosequence approach to analyse spontaneous colonization of target species into mined sites and the development of calcareous grasslands, compared to ancient as well as actively restored grasslands. Statistical analyses involved Mann–Whitney U‐test, GNMDS and binary logistic regression.ResultsThe proportion of neophytes in spontaneously developing mined sites was low and similar to the unmined surroundings at the landscape unit as well as plant community scale. Mined sites harbour an impressive number of native and even rare species. However, plant communities lacking immigration of target grasses typical for calcareous grasslands lead to divergences regarding species and functional composition compared to ancient calcareous grasslands. In contrast, plots with actively introduced target species at the onset of succession show a generally more rapid trajectory towards ancient grasslands. The probability of establishing in mined sites increases with higher abundance of calcareous dry grassland species in the vicinity, indicating the importance of high propagule pressure in a landscape context, whereas long‐distance dispersal traits were significant, but less important.ConclusionsSpontaneous succession supports the development of native plant communities. However, because of propagule limitation, colonization processes may lead to novel species assemblies. While dispersal stochasticity during spontaneous succession results in a higher γ‐diversity, species introduction supports faster trajectories towards desired reference states providing important ecosystem services such as erosion control. The key decision of whether to rely on spontaneous succession or not mainly depends on the surrounding landscape matrix and history, the need for erosion control and/or rapid compensation for lost habitats.

CO2-gasification of a lignite coal in the presence of an iron-based oxygen carrier for chemical-looping combustion

Chemical-looping combustion (CLC) has the inherent property of separating the product CO2 from flue gases. Instead of air, it uses an oxygen carrier, usually in the form of a metal oxide, to provide oxygen for combustion. All techniques so far proposed for chemical looping with solid fuels involve initially the gasification of the solid fuel in order for the gaseous products to react with the oxygen carrier. Here, the rates of gasification of coal were compared when gasification was undertaken in a fluidised bed of either (i) an active Fe-based oxygen carrier used for chemical looping or (ii) inert sand. This enabled an examination of the ability of chemical looping materials to enhance the rate of gasification of solid fuels. Batch gasification and chemical-looping combustion experiments with a German lignite and its char are reported, using an electrically-heated fluidised bed reactor at temperatures from 1073 to 1223K. The fluidising gas was CO2 in nitrogen. The kinetics of the gasification were found to be significantly faster in the presence of the oxygen carrier, especially at temperatures above 1123K. A numerical model was developed to account for external and internal mass transfer and for the effect of the looping agent. The model also included the effects of the evolution of the pore structure at different conversions. The presence of Fe2O3 led to an increase in the rate of gasification because of the rapid oxidation of CO by the oxygen carrier to CO2. This resulted in the removal of CO and maintained a higher mole fraction of CO2 in the mixture of gas around the particle of char, i.e. within the mass transfer boundary layer surrounding the particle. This effect was most prominent at about 20% conversion when (i) the surface area for reaction was at its maximum and (ii) because of the accompanying increase in porosity and pore size, intraparticle resistance to gas mass transfer within the particle of char had fallen, compared with that in the initial particle. Excellent agreement was observed between the rates predicted by the numerical model and those observed experimentally.

Post-Mining Vegetation Database Eastern Germany

In eastern Germany, surface mining of lignite led to the destruction of entire landscapes and the interlinked ecosystems. After the German reunification in 1990, the majority of mining sites across eastern Germany were closed. During the last two decades, post-mining landscapes offered a unique chance to observe primary succession and have been subject to scientific research on spontaneous and assisted site recovery of heavily disturbed sites. Beginning in 1993, several research projects in surface-mined land have collected comprehensive vegetation data. The main objective was to gain knowledge about spatial and temporal processes of vegetation recovery and to derive guidelines for further restoration planning. Up to now, the post-mining vegetation database contains more than 5,000 vegetation releves that have been compiled over the last two decades. The majority of the plots investigated are located in the post-mining landscapes of the Central German lignite mining district. Also, releves were collected in the Lusatian mining region. Some of the plots were regularly revisited. Usually, the metadata of each releve includes information on plot location (GPS coordinates) and abiotic conditions (exposition, pH and other soil attributes). This report describes the available content in the Post-Mining Vegetation Database Eastern Germany (GIVD ID EU-DE-023).