Sulphur reduction evaluation of selected high-sulphur Chinese coals

Under a collaborative project between China and UK partners, investigation was carried out on high-sulphur coals from Beisu Coal Mine in Shandong Province and Dizong Coal Mine in Guizhou Province to evaluate the sulphur reduction potential by coal preparation. Extensive evaluation of raw coal samples was carried out for design of optimum sulphur reduction processes. This paper discusses the background to the project and describes the evaluation process. This involved selection and sampling of the coals, determination of their washability characteristics and application of process prediction models to the washability data to assess their sulphur reduction potential. This paper demonstrates the potential of model predictions for the development of optimum desulphurisation processes using latest separation processes and plant design. The study has shown that over 50 wt% of sulphur can be removed from Beisu coal (ash 17.9 wt%, sulphur 4.8 wt%) and over 60 wt% of sulphur from Dizong coal (ash 33.5 wt%, sulphur 5.1 wt%) using latest coal cleaning processes.     

Processing of coal fines in a water-only cyclone

It is reported in the literature that a water-only cyclone (WOC), a centrifugal gravity concentrator, is an alternative to froth flotation to treat coal fines (below 0.5 mm). This unit overcomes the inherent limitations of froth flotation and the dense-medium cyclone techniques as it requires no chemicals or artificial medium. The literature dealing with WOC performance to treat coal fines is also limited and as a result it is not well established how the design variables affect the performance of a WOC while treating coal fines. Therefore, an attempt has been made to develop regression models based on factorial design of experiments to quantify the effects of major design variables of a WOC on the beneficiation characteristics of a typical coal fine sample. Further attempts have been made to provide possible explanations on the observed trends of the data based on simple hydrodynamic analyses.     

冲击式粉碎机的设计与使用

简要介绍了冲击式粉碎机的设计理论 ,列举了国内主要冲击式粉碎机及ACM -AB型粉碎机的开发。     

Reductive and non-reductive methylation of high-sulphur coals studied by atmospheric pressure-temperature programmed reduction technique

Two kinds of high sulphur content coals Mequinenza and Illinois No. 6 have been subjected to reductive and non-reductive alkylation. The reductive alkylation was performed in the potassium/liquid ammonia system, while the non-reductive one was performed according to the procedure proposed by Liotta. In both processes the alkylating reagent was iodomethane. The products were subjected to elemental analysis and studied by IR spectroscopy and Atmospheric Pressure-Temperature Programmed Reduction (AP-TPR) technique. It has been established that much more information can be elicited from AP-TPR results obtained for the samples after modification by reductive or non-reductive alkylation than for non-modified coals. The Mequinenza coal has been found to contain aryl thiols and almost no alkyl thiols, whereas the Illinois No. 6 coal has been shown to contain alkyl thiols while practically no presence of aryl thiols has been detected.     

Transformations of sulphur compounds in high-sulphur coals during reduction in the potassium/liquid ammonia system

The two types of high-sulphur coals Mequinenza and Illinois No. 6, in the initial form and subjected to potassium/liquid ammonia reduction, were analysed by atmospheric pressure-temperature programmed reduction (AP-TPR) method. It has been shown that preliminary demineralisation was beneficial for AP-TPR measurements because of the removal of calcium compounds. The reduction of sulphides and disulphides in the potassium/liquid ammonia system was found to lead to formation of aromatic and aliphatic thiols. The presence of the latter is better manifested in the AP-TPR kinetograms when the measurements are performed in the presence of a special reducing mixture. It has been shown that the coal reduction in the potassium/liquid ammonia system apart from transformations of non-thiophene sulphur groups also leads to breaking up of the C-S bonds in some thiophene systems.     

Particle size reduction of anthracite coals during devolatilization in a thermobalance reactor

The effects of devolatilization temperature (750-900 °C), coal size (2-12 mm) and coal properties (carbon content, Hardgrove index (HGI), pore volume) of anthracite coals on the primary fragmentation and particle size reduction during devolatilization have been determined in a thermobalance reactor. The fragmentation index increases with increasing devolatilization temperature and particle size. The fragmentation index is also influenced by coal properties, such as carbon content, HGI, pore volume, etc. Thus, the reduction ratio of particle size before and after devolatilization increases with increasing devolatilization temperature and particle size.     

Liquefaction and/or solubilization of Spanish coals by newly isolated microorganisms

A screening procedure has been set up for isolating microorganisms capable of liquefying coal. Spanish coals were used in the tests, namely a brown lignite from Galicia, sub-bituminous coal from Teruel and hard coal from Minas Figaredo S.A. (Asturias). Among the isolated strains several microorganisms proved capable of liquefying untreated lignite. When lignites were pretreated a more intense and rapid liquefaction was achieved, chelating agents being among the best pretreatments. None of the isolated microorganisms could satisfactorily liquefy sub-bituminous and hard coals in solid media. On the other hand, some fungi grew specifically on the untreated coals, engulfing them and in many cases a soft slurry was obtained. Several of the isolated microorganisms were able to solubilize all three untreated Spanish coals in liquid media. Coal solubilization was measured spectrophotometrically at 300, 400 and 450 nm.     

Classification mechanism of the chute, a liquid-phase remover of fines in the micrometre range from a batch of porous particles

A simple and effective classification method, the ‘chute’, has been developed for the liquid-phase removal of fines from a batch of porous (catalyst) particles in the micrometre range. The chute is a continuous sedimentation fractionator, working in the gravitational field. Equations based on the sedimentation of particles were derived for the particle size distribution density function at a given position on the chute as a function of the initial size distribution density function. The particle size distribution on the chute appears to be only a function of the physical constants of the fluid, the particles and the dimensions of the chute. To verify the model equations, experiments with the chute were carried out at different suspension flows and chute angles. It was found that the experimental particle size distribution density functions at various positions on the chute were predicted reasonably well. Due to local disturbances near the bottom of the chute, the experimental curves exhibit a less sharp cut-off in the particle size distribution density function than was predicted by the model equations.     

Characterization of gases and solid residues from closed system pyrolysis of peat and coals at two heating rates

Closed system gold-tube pyrolysis experiments were performed on a peat and two coals (TY: R_o = 0.51%; SX: R_o = 0.94%) at temperatures ranging from 337 to 600 °C and a pressure of 50 MPa with heating rates of 2 and/or 20 °C/h. Solid reaction residues were analyzed microscopically. Yields and chemical and isotopic compositions of the generated gases were also determined. All three samples had similar thermal evolution pathways. With increasing heating temperature, vitrinite reflectances (VR_r) of the residues increased linearly from 0.72% to 4.50%. This increase was lesser for the sample with a higher hydrocarbon generation potential and at faster heating rates. Gas compositions are dominated by CO₂ and CH₄ throughout the experimental process. Total gas and CH₄ yields gradually increase with pyrolysis temperature for all samples. The carbon isotopic compositions of CH₄ generated from the peat are lighter than those from the coals. The δ¹³C_CH4 values exhibit a generic evolution pattern which the initial CH₄ is isotopically heavy, then becomes lighter at moderate temperatures, and finally becomes heavier again. Methane produced from the samples at low heating rate has higher transformation ratio than that at high heating rate under the same temperature, so tends to be isotopically heavy after pyrolysis temperature of more than 408 °C.     

Influence of thermoplastic properties on coking pressure generation: Part 1 - A study of single coals of various rank

In this study a number of high coking pressure coals with different fluidities were evaluated alongside a number of low pressure coals also with differing fluidities. This was to confirm findings from an earlier study using a limited selection of coals, and to establish rheological parameters within which a coal may be considered potentially dangerous with regards to coking pressure. The results have confirmed and elaborated on previous findings which show that parallel plate displacement (ΔL) and axial force profiles can be used to distinguish between high and low pressure coals, with peak values indicating cell rupture and subsequent pore network formation. This is thought to correspond with plastic layer compaction in the coke oven.For low pressure coals pore coalescence occurs quite early in the softening process when viscosity/elasticity are decreasing and consequently a large degree of contraction/collapse is observed. For higher pressure coals the process is delayed since pore development and consequently wall thinning progress at a slower rate. If or when a pore network is established, a lower degree of contraction/collapse is observed because the event occurs closer to resolidification, where viscosity and elasticity are increasing. For the higher fluidity, high coking pressure coals, a greater degree of swelling is observed prior to cell rupture, and this is considered to be the primary reason for the high coking pressure observed with these coals. An additional consequence of these events is that high pressure coals are likely to contain a higher proportion of closed cells both at and during resolidification, reducing permeability in both the semi-coke and high temperature plastic layers, respectively.Using a rheological mapping approach to follow viscoelastic changes during carbonisation it has been possible to identify specific regions associated with dangerous coals. These tend to be fusible coals where at the onset of expansion, δ (elasticity) < 54° and η* (complex viscosity) > 5 × 10⁵ Pa s, and where in most cases δ_MAX does not exceed 65°.     

Petrophysical characterization of coals by low-field nuclear magnetic resonance (NMR)

Nuclear magnetic resonance (NMR) has been widely used in petrophysical characterization of sandstones and carbonates, but little attention has been paid in the use of this technique to study petrophysical properties of coals, which is essential for evaluating coalbed methane reservoir. In this study, two sets of NMR experiments were designed to study the pore types, pore structures, porosity and permeability of coals. Results show that NMR transverse relaxation (T₂) distributions strongly relate to the coal pore structure and coal rank. Three T₂ spectrum peaks identified by the relaxation time at 0.5-2.5 ms, 20-50 ms and >100 ms correspond to pores of <0.1 μm, >0.1 μm and cleats, respectively, which is consistent with results from computed tomography scan and mercury intrusion porosimetry. Based on calculated producible and irreducible porosities through a T₂ cutoff time method, we propose a new NMR-based permeability model that better estimates the permeability of coals. In combination with mercury intrusion porosimetry, we also propose a NMR-based pore structure model that efficiently estimates the pore size distribution of coals. The new experiments and modeling prove the applicability of NMR in petrophysical characterization of intact coal samples, which has potential applications for NMR well logging in coalbed methane exploration.     

Cleaning of Indian coals by agglomeration with xylene and hexane

A laboratory scale agglomeration process has been undertaken for cleaning Indian coals using oils namely, xylene and hexane. Maximum organic matter recovery for xylene has been found to be 91.9% whereas with hexane, the value is 54.7% on a dry basis. The highest ash rejection values with xylene (90.7%) and with hexane (89.7%) are almost same. Promising results for rejection of metals (Fe, Mg and Zn) have been observed. It has been found that xylene is more selective than hexane for the agglomeration process. Knowledge gained from this study will be helpful for technological advancement of this kind of work.     

煤粉改性剂对型焦热性能的影响

在配煤中加入40%~50%无烟煤后,炼制的型焦反应性高,反应后强度低。配入煤粉改性剂（ZBS）炼制型焦的试验表明：ZBS对无烟煤有改质作用,型焦热态性能改善。 当ZBS质量分数达到1‰时,焦炭质量改善幅度最大,CRI降低10.65%,CSR提高13.52%。     

Molecular dynamic simulation of coal-solvent interactions in Permian-aged South African coals

Molecular dynamic simulations were used to examine the initial stages of solvent-coal interactions during solvent swelling. Large-scale (> 10,000 atoms) vitrinite-rich Waterberg and inertinite-rich Highveld coal models used in this study were previously constructed. Isothermal-isobaric molecular dynamics simulated the experimental conditions used for the solvent swelling of these coals. Partially solvent swollen structures were constructed by the addition of solvent molecules to the original coal molecules using an amorphous building approach. The various solvated coal models were simulated using pyridine, N-methylpyrrolidone (NMP) and CS₂/NMP solvents. The changes in bonding and nonbonding energies due to solvent swelling were determined by comparing original coal models to corresponding swollen models. Simulation studies showed that coal-coal nonbonding interactions changed due to disruption of the van der Waals interaction energies. The distributions of hydrogen bonds were calculated and provided a method to evaluate solvent-coal hydrogen interactions. It was found that hydroxyl groups associated with the bituminous coal structure are the dominating hydrogen bond donor in solvent interaction. Therefore, the contributions of nonbonding interactions in coal play an important role during coal-solvent swelling. Molecular modeling and simulation is a useful tool to probe these changes in energies and nonbonding interactions in coal with various solvents.     

Correlations in the properties of Albanian coals

Seventeen Albanian brown coals were analyzed in detail and their properties were compared on both a national and regional basis. The measurements made were moisture, proximate and ultimate analyses, sulfur forms, bituminous matter, humic acids and specific energy, plus Gray-King and free-swelling tests. Linear correlations were derived amongst these coal properties on both dry and dry-ash-free basis. The resulting equations would allow the prediction of many coal properties from a limited number of experimental measurements.     

Treatments of low rank coals for improved power generation and reduction in Greenhouse gas emissions

Reduction in ash constituents by water washing, and also at specific pH values, was systematically studied for three low-rank coals. Acid treatment removed inorganic constituents if accompanied by efficient water washing; at elevated temperatures this can also reduce moisture. The ash components are present in the coal matrix and also as numerous aluminosilicates particles containing K, Na, Mg, Fe and Ca; acid treatment reduced the ash constituents to mainly quartz and clay particles. The ash chemistry of treated and untreated coals was studied over the temperature range 800 °C to 1400 °C. The ash from treated coals consisted mostly of α-quartz, and when heated at 800 °C to 1500 °C, was transformed into mainly amorphous silica and cristobalite, and melted at 1300–1500 °C. Ash from untreated coals melted at or below 1100 °C. The impact of low rank coals with lower moisture, and also coals with lower ash and moisture, was assessed for power generation using the GateCycle™ package. The results show: (i) moisture reduction lowers CO₂/MWh by a small amount but often increases fouling, and (ii) reduction in ash and moisture would eliminate ash fouling and significantly reduce the CO₂/MWh compared with current power plant.     

Selection of IGCC candidate coals by pilot-scale gasifier operation

Nine imported coal samples were tested to make the guidelines for IGCC (Integrated Gasification Combined Cycle) candidate coals — the guidelines that are applicable in future commercial IGCC plants in Korea. Entrained-bed slagging gasifier whose maximum capacity is 3 ton/day has been operated under pressure ranges of 10–29 bar. The factors considered were conversion efficiencies, moisture content, sulfur content, ash content, ash melting temperature, slag viscosity, slag characteristics, and coal reactivity. The best coal type for IGCC applications appears to be the one that contains low ash content with low-enough slag viscosity and high reactivity in coal. However, coal that exhibits high fluidity at the gasifier exit resulted in higher probability in plugging by fly-slag, so that the coal of ash fluid temperature lower than 1260 °C would require precaution for utilizing the feedstock in the entrained-bed gasifier. Conventional ash fusion measurement data might disagree with slag viscosity results in estimating the optimal operation temperature, and thus actual viscosity tests on slag would be necessary.     

High pressure hydropyrolysis of coals by using a continuous free-fall reactor

Rapid hydropyrolysis of coal was carried out at temperatures ranging from 923 to 1123 K and H₂ pressures up to 7 MPa by using a continuous free-fall pyrolyzer. The effects of the reaction conditions on product yields were investigated. Carbon mass balance was fairly good. It was revealed that a large amount of methane was produced due to the hydrogenolysis of higher hydrocarbons and the hydrogasification of char. The influence of pyrolysis temperature was significant on both reactions while H₂ pressure mainly affected the latter. A considerable amount of reactive carbon was formed during hydropyrolysis of coal. It was converted to methane at high temperatures and high H₂ pressures, while the hydrogasification of reactive carbon takes place relatively slowly at low temperatures and low H₂ pressures, resulting in a low overall carbon conversion. The coal conversions observed in the present study were much higher than those obtained with using reactors where the contact between coal particles and H₂ is insufficient.     

Identification of organochlorines and organobromines in coals

Four Chinese bituminous coals were extracted with CS₂, n-hexane, benzene, methanol, acetone, tetrahydrofuran (THF) and THF/methanol (1: 3 vol/vol) mixed solvent sequentially. The resulting 28 extracts were analyzed with GC/MS. Six organochlorines (OCs) and two organobromines (OBs) were identified in eight extracts from the coals. Our experiments provide, for the first time, the information on the molecular structure of OCs and OBs in coals.     

Evaluation of elemental sulphur in biodesulphurized low rank coals

A new procedure for elemental sulphur (S_el) determination in coal and its fractions is offered. It includes exhaustive CHCl₃ extraction and subsequent quantitative analysis of the extracts by HPLC using C₁₈ reversed phase column. Its application gives ground to achieve better sulphur balance and to specify the changes in the organic and elemental sulphur as a result of biotreatments. Two Bulgarian high sulphur containing coal samples, i.e. subbituminious (Pirin) and lignite (Maritza East), and one Turkish lignite (Cayirhan-Beypazari) are used. Prior to biotreatments, the samples are demineralized and depyritized. In the biodesulphurization processes, the applied microorganisms are: the white rot fungi “Phanerochaeta Chrysosporium” - ME446 and the thermophilic and acidophilic archae “Sulfolobus Solfataricus” - ATCC 35091.In the preliminary demineralized and depyritized coals, the highest presence of S_el is registered, which is explained by their natural weathering. As a result of the implemented biotreatments, the amount of S_el could be reduced in the range of 16.1-53.8%. The content of S_el is also assessed as part of the total sulphur and organic sulphur. The following range of S_el content is measured: 0.01-0.16 wt.% or 0.3-4.6% of total sulphur and 0.3-5.1% of organic sulphur. In this way, more precise information is obtained concerning the content of organic sulphur presence.