Spanish Anthracites Research Articles

Development of 2nd Generation Oxyfuel CFB Technology – Small Scale Combustion Experiments and Model Development Under High Oxygen Concentrations

The 1st generation oxyfuel CFB (Circulating Fluidised Bed) technology has been demonstrated up to 30MWth scale and the commercial concept for 300 MWe air/oxy flexible CFB power plant is available. Currently, the development of 2nd generation oxyfuel CFB technology is ongoing aiming to reduce significantly – around 50% – the overall efficiency penalty of CO2 capture in power plants compared to 1st generation concepts. The 2nd generation oxyfuel CFB plants are designed only to oxyfuel operation with CCS. The experimental results of the test campaigns with 0.1 MWth pilot scale CFB unit and laboratory scale BFB (Bubbling Fluidised Bed) unit under high oxygen concentrations of feed gas are presented. The pilot scale tests were carried out with Spanish anthracite and petroleum coke mixture and with Polish bituminous coal. Two Spanish limestone types were used for in- furnace sulphur capture. Test matrix of pilot scale CFB unit contained 11 test balances with varying feed gas O2 concentrations (between 21…42 vol-%) and O2 staging to primary and secondary gas feeds (primary gas O2 share 50…80 vol-%) at different bed temperature levels (820…920 °C). Combustion performance and emission formation was studied at air combustion and varying oxyfuel combustion conditions. The fuel impulse tests with laboratory scale BFB included 16 tests with Spanish anthracite and Polish bituminous coal in varying feed gas O2 concentrations (5…50 vol-%) with two fuel size fractions (0.5-2.0 mm and 4.0-8.0 mm) at constant bed temperature level (850 °C). The main objective was study how high O2 concentration effects on char reactivity and formation of nitrogen oxide emissions. A one dimensional model for laboratory scale BFB was used to further develop existing sub-models’ descriptions and parameters in the one dimensional model (1D-model) for pilot scale CFB in order to improve modelling capabilities in oxygen combustion conditions. Firstly the sub-models’ equations for different phenomenon – e.g. pyrolysis, char combustion and reactions of nitrogen species – were implemented and validated with bench scale experimental data. Secondly, the sub-model parameters found in bench scale modelling for char reactivity and NOx formation were implemented to the 1D-model of pilot scale CFB combustor. According to the results of the validation modelling against pilot scale experimental results, the combustion was successfully scaled up as the modelled temperature profiles and flue gas oxygen contents were well in line with measurements. Anyhow, further validation of the combustion model is needed by modelling of dynamic responses of pilot scale experiments. The pilot scale 1D-model was not able to predict NOx formation with the sub-model adapted from the bench scale model. Further model development and experimental work are needed with different particle size fractions at different operating conditions. The improved modelling capabilities under high oxygen concentrations can be utilized in the development and designing of 2nd generation oxyfuel CFB power plant concepts. Generally, the CFB technology appears to be ideally suited to oxyfuel combustion. The flexibility of the fluid-bed process offers an outstanding benefit for CFB in retaining uniform furnace temperature profiles, metal temperatures and local heat production rates in air-firing as well as in oxygen-firing and under varying load conditions. These benefits make also possible to apply higher oxygen concentrations which is a key element in the 2nd generation high efficiency oxyfuel CFB concepts.

On the electrochemical performance of anthracite-based graphite materials as anodes in lithium-ion batteries

The electrochemical performance as potential negative electrode in lithium-ion batteries of graphite materials that were prepared from two Spanish anthracites of different characteristics by heat treatment in the temperature interval 2400–2800 °C are investigated by galvanostatic cycling. The interlayer spacing, d 002, and crystallite sizes along the c axis, L c , and the a axis, L a , calculated from X-ray diffractometry (XRD) as well as the relative intensity of the Raman D-band, I D / I t , are used to assess the degree of structural order of the graphite materials. The galvanostatic cycling are carried out in the 2.1–0.003 V potential range at a constant current and C/10 rate during 50 cycles versus Li/Li +. Larger reversible lithium storage capacities are obtained from those anthracite-based graphite materials with higher structural order and crystal orientation. Reasonably good linear correlations were attained between the electrode reversible charge and the materials XRD and Raman crystal parameters. The graphite materials prepared show excellent cyclability as well as low irreversible charge; the reversible capacity being up to ∼250 mA h g −1. From this study, the utilization of anthracite-based graphite materials as negative electrode in lithium-ion batteries appears feasible. Nevertheless, additional work should be done to improve the structural order of the graphite materials prepared and therefore, the reversible capacity.

Structural Characterization of Graphite Materials Prepared from Anthracites of Different Characteristics: A Comparative Analysis

Graphite materials were prepared from two Spanish anthracites, AF and ATO, by heating at different temperatures within the range 2000−2800 °C. XRD and Raman spectroscopy were employed to characterize the degrees of crystallinity and crystal orientation of the materials. In addition to studying the evolution of typical crystal parameters such as interlayer spacing, d002, and crystallite sizes, La and Lc, with temperature, this work aimed to evaluate the influence of elemental composition, texture (as measured by optical microscopy), and mineral matter of the raw anthracites on their ability to graphitize. Two temperature segments were discerned during the development of crystallinity. The first segment exhibited major improvements in crystal parameters, which afterward reached a plateau value. Raman parameters indicated that further improvement in crystal orientation could be obtained after heating at the highest temperature (2800 °C). The limiting temperature at which the materials showed their highest de...

Preparation of activated carbons from Spanish anthracite. I. Activation by KOH

Preparation of activated carbons from Spanish anthracite. I. Activation by KOH

Ash deposition of a Spanish anthracite: effects of included and excluded mineral matter

This study has been undertaken to provide an insight into the effects of mineral matter distributions in coal on the nature of boiler slags formed during the combustion of a high ash Spanish anthracite. Three density fractions were prepared, and the light and heavy fractions were combined to give a sample containing mainly excluded mineral matter. The mineral matter in the medium density fraction was predominantly included. Slag deposits were prepared in the laboratory from the whole coal, the light+heavy and medium density fractions. The coal with excluded mineral matter was found to produce a slag similar in nature and chemistry to the whole coal ash deposit. The coal with included mineral matter produced a vitreous, iron-rich deposit. The deposits were compared with slags, obtained from a Spanish power station boiler, burning a blend containing the same anthracite.

Preparation of activated carbons from Spanish anthracite: II. Activation by NaOH

This paper complements the previous one (activation with KOH) analysing the development of porosity of a Spanish anthracite by chemical activation with NaOH. The preparation method has been optimised through the analysis of diverse experimental variables. Among them, activating agent/coal ratio, drying process, method of mixing of the activating agent and coal, nitrogen flow during pyrolysis and mineral matter content of the coal, have been studied. The results obtained confirm the importance of the activating agent to coal ratio and the flow of gas during carbonisation on the development of porosity. In addition, it shows that chemical activation with NaOH can be successfully used to develop activated carbons with high surface area and micropore volumes (i.e., up to 2700 m 2/g and 1 cm 3/g). Comparing chemical activation using an impregnation method and physical mixing we conclude that physical mixing of NaOH and coal, which is a very easy preparation method, renders the best results. Therefore physical mixing has been also applied in this work to KOH with rather interesting results. Although impregnation produces a higher development of porosity for KOH, activated carbons with high micropore volumes can be synthesised through a much simpler method. Physical mixing produces larger pore volumes by KOH activation than by NaOH activation.

Preparation of activated carbons from Spanish anthracite: I. Activation by KOH

In a previous work, the use of a Spanish anthracite for the preparation of activated carbons by chemical activation was analyzed. The results indicated that this raw material is promising for that purpose. In the present paper, that previous work is extended and the effect of different preparation variables on the final porous texture is discussed, such as KOH/anthracite ratio, heating rate, carbonization temperature and carbonization time. Among those different variables studied, the KOH/anthracite ratio seems to be the most important one. In addition, this study introduces an investigation of the nitrogen flow rate, showing that this variable has a very important effect on porosity development. The study confirms that the raw material used is appropriate for the preparation of activated carbons in a single stage pyrolysis process. The proper choice of the preparation conditions allows us to produce microporous activated carbons with a micropore volume up to 1.45 cm 3/g and a BET surface area of 3290 m 2/g. This work is extended in Part II with a detailed study using NaOH as activating agent and a different preparation method (physical mixing).

98/02695 Role of fine-coal classification efficiency on coal preparation plant performance: Firth, D. A. et al. Miner. Metall. Process., 1997, 14, (1), 1–6.

The aim of this work was to study the feasibility of using vegetable oils for coal agglomeration. Three Spanish anthracites were agglomerated with refined sunflower and soybean oils. The response of coals to agglomeration with these oils was evaluated by measuring the percentages of organic matter recovery and ash and pyritic sulfur rejections. The influence of oil type and concentration on agglomeration results was investigated. In addition, results were compared with those previously obtained in the agglomeration of these coals with n-heptane. It can be concluded that refined sunflower and soybean oils are suitable for use as agglomerants for these high-rank coals, especially to clean those coals with a high content of mineral matter.

On the role of oil wetting in the cleaning of high rank coals by agglomeration

The wettability of three Spanish anthracites with a large mineral matter content was studied by measuring the oil/water/coal contact angle with heptane and with crude and refined vegetable oils. The captive drop method was used for this purpose. The contact angle was found to depend on the coal, oil, and an interaction between coal and oil. Particle agglomeration tests were conducted to determine the maximum recovery of organic matter for each combination of coal and oil. The maximum recovery was observed to correlate well with the three-phase contact angle when heptane was employed as an agglomerant for the different anthracites. When vegetable oils were employed as agglomerants, the maximum recovery was also observed to correlate well with the contact angle in half the cases. For the other half the recovery exceeded what would have been predicted by the contact angle. Therefore, for these cases the oil wettability of the coal seemed greater under dynamic conditions than under static conditions.

Activated Carbons from Spanish Coals. 3. Preoxidation Effect on Anthracite Activation

A Spanish anthracite, with 5.6 wt % ash content, has been submitted to a two-stage activation process to explore its use as an activated carbon precursor. Several oxidation treatments, with two oxidizing agents (air and nitric acid), have been carried out to study the degree of coal oxidation and its influence on both the char porosity and the char activation. Two activating agents, CO2 and steam, have been used to prepare different burn-off samples to analyze the preoxidation effect on the porosity of the resulting activated carbons. The extent of the oxidation degree, followed by TPD experiment in He, increases with the severity of the oxidation treatment in the following order: air 4 h < air 8 h < 4 M HNO3 ≪ 15 M HNO3. All the oxidation treatments carried out in this study introduce important changes in the reactivity of the resulting chars and on the porous development. The more intense the preoxidation treatment is, and hence the amount of oxygen added to the anthracite, the higher is the porosity of the resulting chars. Activated carbons prepared from preoxidized chars, using CO2 or steam, present much larger porous development than the activated carbons coming from the original coal. The results show that the anthracite needs, prior to the pyrolysis process, an oxidation treatment to be used as an activated carbon precursor, as happens with caking coals. High surface area activated carbons (about 1300 m2/g at a 50% burn-off) can be obtained using nitric acid which has proved to be the most effective preoxidation agent. Comparison of both series of activated carbons, prepared in CO2 and steam, shows that steam develops the porosity of the resulting activated carbons more than CO2.

Cleaning of Spanish high-rank coals by agglomeration with vegetable oils

The aim of this work was to study the feasibility of using vegetable oils for coal agglomeration. Three Spanish anthracites were agglomerated with refined sunflower and soybean oils. The response of coals to agglomeration with these oils was evaluated by measuring the percentages of organic matter recovery and ash and pyritic sulfur rejections. The influence of oil type and concentration on agglomeration results was investigated. In addition, results were compared with those previously obtained in the agglomeration of these coals with n-heptane. It can be concluded that refined sunflower and soybean oils are suitable for use as agglomerants for these high-rank coals, especially to clean those coals with a high content of mineral matter.

Effects of oil concentration and particle size on the cleaning of Spanish high-rank coals by agglomeration with n-heptane

The response of three high-ash Spanish anthracites to agglomeration with n-heptane was evaluated by measuring the organic matter recovery, ash rejection and pyritic sulfur rejection. The influence of oil concentration and coal particle size on the agglomeration results was investigated. The combustible recoveries of these coals increased to a maximum as the n-heptane concentration is raised, and then decreased. Ash rejection fell as the coal recovery increased. The effect of oil concentration on pyritic sulfur rejection was comparable with that on ash rejection. Regarding ash, pyritic sulfur was removed from one coal with noticeable selectivity. Ash rejection and organic matter recovery were improved by grinding one coal to <45 μm. Coal particle size had a more pronounced effect than n-heptane concentration on selectivity of oil agglomeration for cleaning this coal.

The removal of trace elements from Spanish high rank coals by a selective agglomeration process

The effectiveness and selectivity, over a wide oil concentration range, of the n-heptane agglomeration for the removal of trace and major elements from the fines of three Spanish anthracites, were studied. X-ray fluorescence spectrometry was used for the analysis of inorganic elements. Contents of trace and major elements in AT, AG and AV high rank coals were reduced in the range 10–55% depending on coal and oil concentration. Al, Ca, Fe, K, Mg and Si major and Ba, Mn, Rb and Zr trace elements were eliminated from the three coals with similar or slightly higher effectiveness than that corresponding to the agglomeration process. The effectiveness of the removal of Na, P and Ti major and Cu, Cr, Ni, Pb, Sr, V, Y and Zn trace elements was similar or less than that of the cleaning process. For a given element and oil concentration, the effectiveness of its removal from coal by agglomeration is influenced by coal type, the morphology of the minerals where the element is present and the composition, the size as well as the distribution of these minerals in coal. The selectivity of element removal from coal by agglomeration is both coal and oil concentration dependent. Pyritic sulfur was removed from AT coal with a remarkable degree of selectivity.

The removal of trace elements from Spanish high-rank coals by a selective oil agglomeration process

Abstract The effectiveness and selectivity, over a wide oil concentration range, of the n -heptane agglomeration for the removal of trace and major elements from the fines of three Spanish anthracites, were studied. X-ray fluorescence spectrometry was used for the analysis of inorganic elements. Contents of trace and major elements in AT, AG and AV high rank coals were reduced in the range 10–55% depending on coal and oil concentration. Al, Ca, Fe, K, Mg and Si major and Ba, Mn, Rb and Zr trace elements were eliminated from the three coals with similar or slightly higher effectiveness than that corresponding to the agglomeration process. The effectiveness of the removal of Na, P and Ti major and Cu, Cr, Ni, Pb, Sr, V, Y and Zn trace elements was similar or less than that of the cleaning process. For a given element and oil concentration, the effectiveness of its removal from coal by agglomeration is influenced by coal type, the morphology of the minerals where the element is present and the composition, the size as well as the distribution of these minerals in coal. The selectivity of element removal from coal by agglomeration is both coal and oil concentration dependent. Pyritic sulfur was removed from AT coal with a remarkable degree of selectivity.