Combustion behaviour of Bowen Basin coals

Tightly constrained experimental thermogravimetry proves to be effective for characterising the effects of rank and maceral variations on Bowen Basin coal combustion behaviour. These coals show an increase in char burnout temperature with rank for both dull, inertinite-rich and bright, vitrinite-rich coals. Most dull coals have higher char burnout and peak combustion temperatures than their bright rank equivalents. The maximum rates of combustion for dull coals are lower than their bright counterparts, with the difference between the two varying with rank.     

Combustion characteristics of coals using a drop-tube furnace

Fourteen coals were selected for char refiring tests using a drop-tube furnace (DTF) in order to compare with previous tests on a 1 MW combustion facility. Each coal was sieved into two size fractions (53-75 and 106-125 μm) and characterised using proximate analysis and conventional petrographic tests as well as a test for % unreactives using image-analysis. The coal fractions were then pyrolysed at 1300 °C for 200 ms in 1 vol% oxygen in nitrogen. The reactivity, morphology and surface area of the chars were evaluated using thermal, optical and adsorption techniques. Each char fraction was then passed through the DTF at 1300 °C using a residence time of 600 ms and a furnace atmosphere of 5 vol% oxygen in nitrogen to evaluate burnout propensity. The characteristics of the coals, the chars and the residues after refiring were compared to determine whether any links exist between burnout, intermediate char products and coal composition. The link between % unreactives and burnout was confirmed for high volatile bituminous coals. Results obtained from two low volatile coals confirmed that their burnout was better than predicted from their properties. For the S. American (Guasare) coal poorer than expected burnout was obtained, as in previous work, but only for the larger size fraction.     

劣质煤的燃烧及燃烧器的设计

阐述了评价煤的燃烧特性指标,通过分析煤粉气流的着火,指出了强化炮粉燃烧的主要措施和燃烧器的设计时应考虑的问题。     

微生物溶煤研究进展

煤的微生物溶解是煤炭加工与综合利用的新领域。笔者从微生物溶煤的研究背景、研究方法、机理研究、溶煤产物应用及存在的问题与发展前景等方面进行了详细探讨。指出加强对煤炭结构、煤炭和微生物的生态关系以及微生物溶煤新方法的研究是今后微生物溶煤领域的主要研究方向。     

Biodegradation of coals

Selected strains of bacteria [from the Brookhaven National Laboratory (BNL) collection], capable of degrading heavy crude oils, were used to treat bituminous and lignite coals. Products resulting from biochemical reactions among several microorganisms and different coals were examined by pyrolysis gas chromatography-mass spectrometry (Py. g.c.-m.s.), and X-ray absorption near edge structure (XANES) spectroscopy. The results indicated considerable variations in the organic sulfur as well as modifications in coal structure. Furthermore, biochemical reactions involved in the microbial interactions with coals appeared to be microbial species dependent.     

Conversion of non-coking coals to coking coals by thermal hydrogenation

Coking properties are observed in four non-coking coals, a lignite, a subbituminous coal, a semianthracite and an oxidized bituminous coal which had been treated by partial thermal hydrogenation. The effects of temperature, reaction time and hydrogen pressure on liquid and solid product yields are examined. Microscopic examination of the hydrogenated solid residues shows that they all contain structures somewhat spherical in shape which are associated with mesophase development. The dilatation, plastic character and free swelling index of the hydrogenated solid products were considerably better than those of the original coals. Dilatation residues produced from hydrogenated solids exhibited anisotropic structures.     

Combustion and De-SOx behavior of high-sulfur coals added with calcium acetate produced from biomass pyroligneous acid

This paper first aims to evaluate the possibility of synthesizing organic calcium through the use of pyroligneous acid and raw limestone. The factors affecting this reaction were investigated including the particle size of limestone, the type of pyroligneous acid and reaction conditions as well. Secondly, two low-rank coals were mixed with the calcium-enriched pyroligneous acid to evaluate the possibility of desulfurization in the combustion furnace. The soluble calcium within pyroligneous acid is in the form of calcium acetate having a low decomposition temperature around 400 °C, far lower than that of raw limestone being about 700 °C. Due to its solubility, calcium within pyroligneous acid was loaded readily on the coals, forming the ultrafine particles in the impregnated coal matrix. During coal combustion, the loaded calcium underwent quick decomposition prior to char combustion and subsequently, the formed ultrafine calcium oxide captured the evolved sulfur oxide. Around 85% desulfurization efficiency was achieved for coal combustion. S/Ca molar ratio around 1.0 was formed for the particles less than 1.0 μm, whereas it decreased gradually with the increasing particle size.     

Raman studies of coals

Raman spectra were used to estimate the sizes of microcrystalline regions in coal. A variety of different Polish coals were investigated by means of the laser Raman technique. To prevent decomposition of the coals in the laser beam, the rotating disc technique was used to obtain the spectra. Some i.r. spectra of the coals under investigation were also considered. The aromatic carbon content was determined by the method of Oelert. The results of both spectroscopic techniques were compared and found to lead to the same order of magnitude of microcrystalline regions. The Tuingstra and Koenig method used for evaluation of microcrystalline regions in coal was found to be applicable if infrared studies indicate a high value of the aromaticity coefficient, i.e. if aromatic bonds are predominant in the coal under investigation.     

Classification of coking coals

None of the established coal classification systems was specifically designed to meet the requirements of the modern blast furnace coke producer. Meanwhile, more stringent blast furnace coke specifications have demanded sophisticated coal blending plants and close control of coal blend quality. A coking coal classification system^* based on reflectance and dilatation is proposed for classifying single coals or coal blends with individual macrocomponents of similar rank and dilatation. Coals are grouped into classes which can be represented by four digit numbers, the first two integers representing the reflectance and the last two integers the dilatation. The basic parameters are already widely used as quality-control tools at coking plants and the procedures for their measurement are currently being standardized in the United Kingdom. It is suggested that the proposed classification system substantially fulfills the requirements of the coke-maker in that it is sensitive to small changes in coal composition and condition and the parameters used can be correlated with coke physical quality. The time appears to be opportune therefore for the implementation of such a classification system for the more efficient control of coal preparation and blending at coking plants.     

Macromolecular structure of coals

Summary The Flory thermodynamic interaction parameter, X, was calculated for a range of solvents interacting with the crosslinked macromolecular structure of coals of a wide range of carbon content.     

Reactivity of heat-treated coals

Lignite and two bituminous coals were pyrolysed at 1023 and 1223 K at different rates and for different heating times, producing different chars. The extent of devolatilization, the evolution of the pore structure and the differences in the ignition characteristics and reactivities of the chars during pyrolysis were examined. The kinetic data on the coals and chars produced by pyrolysis of these coals were obtained under ignition conditions. The apparent reactivity varied by two orders of magnitude among the parent coals and chars at a given temperature, whereas the intrinsic reactivity was found to vary over four orders of magnitude. Low-rank parent coal, high heat-up rates, and moderate pyrolysis time and temperature produced the most reactive chars. The values of hydrogen, volatile matter and ash content or the pore surface area could not provide an explanation for the differences in reactivity.     

Hydrodevolatilisation of precarbonised coals

Devolatilisation under hydrogen pressure of chars prepared by carbonisation of coal in inert gas, between 500°C and 900°C, has been performed. The influence of the precarbonisation temperature, time, pressure and gas atmosphere has been studied. Comparisons are made between the hydrogasification yield with and without precarbonisation. Cokes prepared between 900°C and 1200°C have also been submitted to secondary hydrodevolatilisation. The results show that, except for high temperature cokes, the total gasification yield for precarbonised coal is nearly as high as for the uncarbonised coal. The “hydrogen-extractible” fraction of the coal is not destroyed by preliminary carbonisation even when performed at 900°C for three hours. A correlation has been found between surface area values and hydrogenation rates.     

Abrasion characteristics of coals

The silica content and ash level of the various fractions of an abrasive coal from the Talcher coalfield, Orissa state, India, are reported. Free silica, to which the abrasion of the coal is attributed, appears to be relatively evenly distributed among the size fractions, occurring at levels of 9.02–10.55 wt%.     

Hot-compaction behaviour of coals

Hot-compaction behaviour of semi-anthracite, low-, medium- and high-volatile caking, oxidized medium-volatile, sub-bituminous and lignite coals was studied under a constant load of 3.45 MPa. Generally, total compaction decreased and initial compaction temperatures increased with increasing coal rank. Initial compaction of the caking coals was noted at temperatures below their Ruhr dilatometer softening temperatures. For the high-volatile sample, this softening temperature was low enough, at about 250 °C, to imply possible thermal breakdown of such coals in preheating processes used before coke-making. The visco-elastic behaviour of coals of different rank over a range of temperature was examined. Densification mechanisms are suggested and the rate-controlling steps are discussed. Devolatilization is an important factor in particle-flow and shrinkage/dilatation mechanisms, as inferred from the similarities of the activation energies associated with these mechanisms and the reported values for devolatilization processes. Non-caking coals exhibit visco-elasticity at temperatures where they are expected to be semi-chars, in contrast with the caking coals.     

Moisture-holding capacity of coals

As a result of a comprehensive study of 63 samples of coal concentrates (from Ukraine, Russia and countries outside the former Soviet Union), it was established that the prediction of the moisture-holding capacity of coals can be appropriately performed according to their values of W ^a, R ₀, O _d ^daf , and O _s ^daf . It was found that the oxidation of coal increased its moisture-holding capacity; however, in this case, the absolute change in this parameter was smaller than the error of its determination (0.5%). Therefore, upon the oxidation of almost 30% of the organic matter of coal, the moisture-holding capacity increased by only 0.4%. There is a close correlation between the maximum moisture capacity of coals and the water pore volume, and this correlation was described by a linear equation in the studies.     

Pyrolysis—gas chromatography of Australian coals. 2. Bituminous coals

Pyrolysis—gas chromatography (Py—g.c.) was used to characterize quantitatively a series of high- to low-volatile bituminous Permian Australian coals. The levels of n-alkanes, n-alkenes and triterpenoids released by pyrolysis all decrease as a function of increasing rank and thus, the coal samples can be classified into three distinct groups. Carbon Preference Indices (CPI's) for alkanes and alkene/alkane ratios also decrease as a function of rank. The triterpenoids have exclusively the hopane skeleton. The hopane isomeric distributions exemplify the geological maturity of bituminous coals relative to brown coal (lignite). A significant correlation has been established between the level of n-alkanes and n-alkenes released under Py-g.c. conditions and the predicted oil yield by pyrolysis of these coals. Further development and application of the techniqueshould enable much to be learnt relating to the quality and yield of flash pyrolysis tars as well as the original coal macromolecular structure.     

The nature of coking coals

A review of the properties and the structure of coals occupying the middle position in the coalification scale that show the best coking properties — gas coals, gas-coking coals, ortho, meta and semi-coking coals — with particular regard to their behaviour on heat treatment is presented. Problems of coking coals as components of blends in the production of metallurgical coke, as component and binding agent in the process of obtaining metallurgical formed-cokes, and the utilization of coking coals and their extracts as raw materials in the electrode industry, are discussed. The classification of coking coals and questions still to be solved concerning the origin, properties, structure and rational utilization of coking coals, are commented on.     

Depolymerization of oxidized bituminous coals

Certain high-sulphur-containing, high-volatile bituminous (hvb) coals have been converted into products which are almost completely soluble in chloroform. These products were obtained by a series of reactions involving initial oxidation with 2N nitric acid, depolymerization with boron trifluoride-phenol, and acetylation. Solubility of the depolymerized coal decreased sharply when the nitric acid reaction was eliminated or was replaced with a hydrochloric acid treatment. The extent of oxidation by the nitric acid treatment is discussed. Also included in this investigation are a low-sulphur-containing hvb coal and a low-volatile bituminous coal. After depolymerization, the solubilities of these two coals in chloroform were comparatively low.