Firing a sub-bituminous coal in pulverized coal boilers configured for bituminous coals

It is important to adapt utility boilers to sub-bituminous coals to take advantage of their environmental benefits while limiting operation risks. We discuss the performance impact that Adaro, an Indonesian sub-bituminous coal with high moisture content, has on opposite-wall and tangentially-fired utility boilers which were designed for bituminous coals. Numerical simulations were made with GLACIER, a computational-fluid-dynamic code, to depict combustion behavior. The predictions were verified with full-scale test results. For analysis of the operational parameters for firing Adaro coal in both boilers, we used EXPERT system, an on-line supervision system developed by Israel Electric Corporation. It was concluded that firing Adaro coal, compared to a typical bituminous coal, lowers NO_x and SO₂ emissions, lowers LOI content and improves fouling behavior but can cause load limitation which impacts flexible operation.     

Fe/CaO催化剂对脱灰徐州烟煤热解特性的影响

煤热解是一种重要的煤炭分质利用技术,但热解过程中产生的副产物焦油危害极大,催化改质是高效清洁利用煤焦油的方法之一。本文采用溶胶凝胶法制备Fe/CaO催化剂,在管式炉反应器上对脱灰徐州烟煤进行了催化热解实验,对研究催化裂解煤焦油具有重要的意义。结果表明：Fe/CaO催化剂可以明显促进热解气的产生,热解气中CO₂、CO和CH₄的产量均不断增加。Fe/CaO催化剂促进了液体产物的催化裂解,导致液体产率明显下降。Fe/CaO催化剂促进焦油中的稠环芳烃向脂肪烃和轻质芳烃转化,此外,Fe/CaO催化剂还对萘类化合物的产生有促进作用。Fe/CaO催化剂催化后焦油中两环化合物的含量增多,三环及以上的化合物含量减少,焦油分子量呈减少的趋势。     

Effect of temperature on the electrochemical oxidation of ash free coal and carbon in a direct carbon fuel cell

The present study proposes the application of ash-free coal (AFC) as a primary fuel in a direct carbon fuel cell (DCFC) based on a molten carbonate fuel cell (MCFC). AFC was produced by solvent extraction using microwave irradiation. The influence of AFC-to-carbonate ratio (3: 3, 3: 1, 3: 0 and 1: 3 g/g) on the DCFC performance at different temperatures (650, 750 and 850 oC) was systematically investigated with a coin-type cell. The performance of AFC was also compared with carbon and conventional hydrogen fuels. AFC without carbonate (AFC-to-carbonate ratio=3: 0 g/g) gave a comparable performance to other compositions, indicating that the gasification of AFC readily occurred without a carbonate catalyst at 850 oC. The ease of gasification of AFC led to a much higher performance than for carbon fuel, even at 650 oC, where carbon cannot be gasified with a carbonate catalyst.     

Composition and variation of pulverized fuel ash obtained from the combustion of sub-bituminous coals, New Zealand

Twenty daily samples of pulverized fuel ash (PFA), obtained from the combustion of sub-bituminous Waikato coals, have been analysed. The contents of MgO, SO₃, B₂O₃ and total and uncombined CaO in the New Zealand material were high when compared with most PFA produced in Europe and the USA. The PFA was separated into three major components, namely a magnetic fraction, and nonmagnetic acid-insoluble and acid-soluble fractions. These three fractions were related to three major mineral suites found in the coal: respectively hydrated iron carbonates and oxides, quartz and aluminosilicates, and calcium minerals. The variable composition of the PFA arises from differences in the proportions of these three mineral suites in the original coal. The composition was also found to vary with particle size. It is suggested that this was due to differences in the particle sizes of minerals in the coal, and to increased thermal decomposition of minerals in the smaller particles of PFA. A low-density fraction was separated and found to be similar in composition to cenospheres found in British and American PFA. The decomposition and fusion of a mineral common to many coals may be the source of these cenospheres.     

Fusion temperatures of PFA from New Zealand sub-bituminous coals

The ash fusion temperatures of 20 analysed samples of pulverized fuel ash obtained from the Meremere coal-burning power station have been determined. It is shown that the fusion temperatures can be related to the acid-soluble calcium and iron oxide contents, and that it is possible to predict the softening and hemisphere temperatures of ash cubes with a precision of ca. 10 to 20 °C in either oxidizing or reducing atmospheres. Removal of the magnetic iron fraction from the PFA reduced both the softening and hemisphere temperatures by ca. 10 to 15 °C in an oxidizing atmosphere, and in a reducing atmosphere it increased the softening temperature by ca. 10 °C and the hemisphere temperature by ca. 30 °C.     

黏结性烟煤制备球形活性炭的研究

在煤基球形活性炭的制备过程中,生球预氧化条件很大程度上决定了球形炭的球形度和物化特性。以山西柳林华晋焦煤集团焦煤为原料,研究了活性炭制备过程中预氧化、炭化、活化等工艺参数对活性炭质量的影响。结果表明:预处理温度为200℃,预处理时间3 h,炭化终温700℃,炭化升温速率4℃/min,活化温度800℃,活化时间7 h时,制得的活性炭球形度完整,物化性能优良,活性炭的碘值为770.18 mg/g,亚甲基蓝值为64.24 mg/g。随着预处理时间的增加,活性炭的强度和产率都增大。试验结果对煤基球形活性炭的生产具有一定的指导意义。     

A carbon in molten carbonate anode model for a direct carbon fuel cell

The electrochemical oxidation of carbon at the anode of a direct carbon fuel cell (DCFC) includes charge transfer steps and chemical steps. A microstructural model of carbon particle is built, in which perfect graphene stacks are taken as the basic building blocks of carbon. A modified mechanism taking account of the irreversibility of the process and supposing that the electrochemical oxidation of carbon takes place only at the edges of the graphene sheets is proposed. A Tafel type overall rate equation is deduced along with expressions of exchange current density (j₀) and activation polarization (η_act). The performance of carbon black and graphite as the fuel of DCFC is examined. It has been found that j₀ is in the range of 0.10-6.12 mA cm⁻² at 923-1123 K and η_act is in the range of 0.024-0.28 V at 923-1123 K with current density in 10-120 mA cm⁻². Analysis of the j₀, η_act values and the product composition reveals that the charge transfer steps as well as the oxygen ion absorption steps are both important for the reaction rate. The activity of the carbon material with respect to atom location is introduced to the open circuit potential difference (OCP) calculation with Nernst equation.     

Reactions of a bituminous coal with metal chlorides in carbon tetrachloride

The interaction of a bituminous coal (87.2% C) with several metal chlorides in carbon tetrachloride was studied using the conditions under which graphite forms intercalation compounds. Adducts with SbCl₅, AlCl₃, FeCl₃ and MoCl₅ were isolated by filtration and washing with carbon tetrachloride. Atomic ratios versus coal carbon are as follows: C_10.0SbCl_7.4; C_6.2AlCl_4.1; C_6.3FeCl_3.3; and C_11.3MoCl_3.8. X-ray diffraction patterns of the adducts show no 002-band, the latter being partially recovered after extraction with diluted hydrochloric acid. The g-value of the e.s.r. signal of the coal vitrain shows a characteristic increase because of adduct formation with SbCl₅ and AlCl₃ and is reversible by hydrolysis extraction. The results obtained indicate that the bonding with SbCl₅ and AlCl₃ is mainly due to formation of chloro-complexes and with FeCl₃ and MoCl₅ — to formation of organo-metal complexes.     

Oxidation of bituminous coal. 1. Expansion pressure

Experiments show that the oxidation of bituminous coal from the Zasyad’ko mine at 60°C in laboratory conditions increases its expansion pressure from 5.2 to 30.0 kPa in ~28.3 days. Oxidation occurs in stages, as already demonstrated for Ukrainian and imported coal of different metamorphic stages on oxidation in the laboratory and in industrial trials at other temperatures. The rate constant in the initial stage of oxidation is 0.4095 × 10^–4 min^–1 at 60°C and 3.8479 × 10^–4 min^–1 at 140°C. That indicates sharp increase in oxidation rate between 60 and 140°C. In oxidation, the actual coal density, the atomic ratio H/C, and the number of hydrocarbon rings per carbon atom decline, while the molar volume per g-atom of carbon increases. Saturation of the bituminous coal with oxygen on oxidation increases the viscosity of the plastic mass that forms and increases the volume of gas and vapor products. Ultimately, that results in increase in the expansion pressure as the coal is oxidized.     

Biodesulphurization of Hungarian lignite and sub-bituminous coal

The annual SO₂ emission is approx. 0.6 million tons in Hungary because of the high amount of sulphur in the power plant coals. Since Hungary has signed the European Environmental Agreement, the high sulphur emission has to be gradually reduced. To overcome the acid rain problem, the biodesulphurization of Hungarian power plant coals has also been started in Hungary. The R&D programe of biodesulphurization has been launched in 1990. According to our findings the biodesulphurization process is a suitable tool for reducing the pyritic sulphur content in lignite and sub-bituminous coal.     

Characterization of unburned carbon from ash after bituminous coal and lignite combustion in CFBs

This paper deals with the characterisation of carbon (UC) from bottom ash (BA) and fly ash (FA) samples from two fluidised-bed power stations burning bituminous coal and lignite. The laboratory results for the carbon determinations and its mass balances are evaluated. Chemical and mineral analyses and textural characteristics (specific surface area and pore-size distribution) are presented. Depletion/enrichment of selected elements (S, Cl, V, Cr, Ni, Cu, Zn, As, Se, Sb, Hg, and Pb) in carbon from the bottom ash are compared with both ash compostions. The strong positive relationships between the concentrations of some trace element contents (Hg, Se, As, Cu, Ni, V and Cl) in fly ash with the content of carbon and the specific surface area of FA are presented and expressed by regression equations with very high correlation coefficients. Laser ablation-ICP-MS has been used to obtain an insight into element distributions within carbon grains from the bottom ash.     

Flash pyrolysis of coals. Devolatilization of bituminous coals in a small fluidized-bed reactor

The devolatilization behaviour of ten bituminous coals was investigated under rapid heating conditions using a small-scale fluidized-bed pyrolyser. The pyrolyser operated continuously, coal particles being injected at a rate of 1–3 g h^?1 directly into a heated bed of sand fluidized by nitrogen. Yields of tar, C₁–C₃ hydrocarbon gases, and total volatile-matter and an agglomeration index are reported for all coals. Maximum tar yields were obtained at about 600 °C and were always substantially higher than those from the Gray-King assay. Total volatile-matter yields were also substantially higher than the proximate analysis values. The maximum tar yields appear to be directly proportional to the coal atomic $\text{H}\text{C}$ ratio. The elemental analysis of the tar is strongly dependent on pyrolysis temperature. The tar atomic $\text{H}\text{C}$ ratio is proportional to that of the parent coal. The effect on the devolatilization behaviour of two coals produced by changes in the pyrolyser atmosphere and the nature of the fluidized-bed material were also investigated. Substituting an atmosphere of hydrogen, helium, carbon dioxide or steam for nitrogen, has no effect on tar yield and, with one exception, little effect on the hydrocarbon gas yields. In the presence of hydrogen the yield of methane was increased at temperatures above 600 °C. Tar yields were significantly reduced on substituting petroleum coke for sand as the fluid-bed material. A fluidized bed of active char virtually eliminated the tar yield.     

Reaction of coals under plasma conditions: direct production of acetylene from coal

When an argon plasma jet is used for direct conversion of coal into acetylene, the feasibility and efficiency of conversion depend on such factors as coal feed rate, size range of coal particles, volatile matter in the coal, and the plasma operating conditions. Percentage efficiency increased with VM. An attempt has been made to optimize these factors and it is shown that with Assam coal having 46.6% VM (dmf), 20% conversion of the carbon in coal into acetylene can be achieved. The high mineral-matter content of Indian coals was found to have no specific adverse effect on the efficiency though it would increase the energy required per unit of acetylene produced. The nature of the soot formed as revealed by X-ray studies is discussed.     

Optimization of the utilization of a sub-bituminous coal in conventional and form-coking

An attempt has been made to determine the extent to which a sub-bituminous coal can be utilized in the production of coke of metallurgical quality. It was established that coke of acceptable quality can be made from blends of up to 15% low-temperature sub-bituminous char and a high-volatile, high-fluidity coal. With partial agglomeration of the blend, the char constituent can be increased to about 30%. Formcoke of metallurgical quality can be made entirely from the coal by binderless briquetting of fluidized-bed char. It was shown that the strength and abrasion resistance of the formcoke is greatly influenced by the char preparation conditions and the post-briquetting heat treatment.     

Identification and significance of accessory minerals from a bituminous coal

A scanning electron microscope (SEM) has been used to study the in situ accessory minerals in polished blocks and pellets of petrographically analysed samples of the Waynesburg coal (hvb). Individual grains from the low-temperature ash (LTA) of the same coal were also studied. The visual resolution of the SEM permitted the detection of submicron mineral grains, which could then be analysed by the attached energy-dispersive system. Emphasis was placed on the highly reflective grains in the carbominerite bands. Among the most abundant accessory minerals observed were rutile, zircon, and rare-earth-bearing minerals. Small (1–5 μm) particles of what may be authigenic iron-rich chromite and a nickel silicate form rims on quartz grains. The SEM also permits the observation of grain morphology and mineral intergrowths. These data are useful in determining authigenicity and diagenic alteration. Substances in density splits of LTA include authigenic, detrital, extraterrestrial magnetite, tourmaline, and evaporite (?) minerals, and a fluorine-bearing amphibole. This analytical approach allows the determination of specific sites for many of the trace elements in coals. In the Waynesburg coal, most of the chromium is in the iron-chromium rims, the fluorine is in the amphibole, and the rare-earth elements are in rare-earth-bearing minerals. The ability to relate trace-element data to specific minerals will aid in predicting the behaviour of elements in coal during combustion, liquefaction, gasification, weathering, and leaching processes. This ability also permits insight into the degree of mobility of these elements in coal and provides clues to sedimentological and diagenetic conditions.     

烟煤与生物质混烧基础实验分析

在给料方式为下部进料的美国Harman热风炉内进行了烟煤煤棒和生物质棒的燃烧实验,通过燃烧效果和污染物排放情况的特性对比,考察了两种燃料的优缺点;将不同比例的烟煤和生物质的混合样品在Netzsch热重分析仪中进行燃烧动力学分析;结果表明,生物质燃料的烟尘排放指标高于烟煤煤棒,二者的优缺点可以互补,烟煤中掺烧生物质可以提高燃烧效率,混合燃烧降低了反应活化能,着火温度和燃尽温度均前移;生物质燃料和烟煤按照合理配比混烧,可提高两种燃料的清洁高效利用水平。