Effect of coal particle size distribution,volume fraction and rank on the rheology of coal–water slurries

The aim of this study was to understanding of the effect of coal particle size distributions on rheology of coal–water slurries (CWS). Experiments have been carried out on the coal samples that were different in rank. Besides two different Turkish lignites (Soma and Istanbul–Agacli), a bituminous coal from Siberia (Russia) has been used. In addition to the determination of the chemical and physical properties of the coal samples, their zeta potentials were also measured. The pulps of different solids percentage composed of coal particles with d₅₀ sizes of 19, 35 and 50 μm were used to determine the effect of volume fraction on the viscosity of the slurry.     

Low-temperature—long-time,high-temperature—short-time liquefaction of coal (Hokudai process): 2. Effect of reaction conditions

A vitrinite-rich Australian subbituminous coal (77 wt %) was subjected to two-stage hydrogenation (low-temperature-long-time, high-temperature-short-time) using several different catalysts with or without donor solvent and with the temperature range and time of the first hydrogenation stage varied. The condition used in the first stage did not significantly affect the final results of the hydrogenation and ≈ 30 wt % always remained as an undistillable fraction. The use of donor solvent or higher pressure improved the distillate yield and the use of active catalyst had a significant effect. In the best case (450 °C-60 min and 500 °C-20min, under 12 MPa initial hydrogen pressure, using Co-Mo catalyst) 54 wt % of oil boiling up to 325 °C and 68 wt % of total distillable oil boiling up to 500 °C were obtained.     

The influence of nitric acid oxidation of low rank coal and its impact on coal structure☆

FT-i.r. was used to examine the behaviour of a Spanish lignite during its oxidative treatment with nitric acid with a view to assessing the different forms of sulphur reduction and the changes produced in the coal structure, as a result of the action of the reagent. Inorganic sulphur decreases rapidly and practically disappears, even under mild attack conditions (50 °C, 20% acid concentration). At first, organic sulphur undergoes a rapid decrease but more energetic conditions are required to maintain the reduction. Reduction may even reach 53% under such conditions.Unfortunately, energetic attacks (90 °C) lead to a high-level of coal organic matter solubilization and an increase in oxygen content. Basically, the oxygen appears as carbonyl group within the desulphurized coal.The nitric acid causes effective nitration of the coal, the nitrogen being incorporated especially as aromatic nitrogen. The substitution is easily produced (50 °C) when there are two adjacent aromatic hydrogens per ring. The isolated hydrogens in aryl- or polycyclic aromatic structures, are more resistant to attack under mild conditions but not so at 90 °C. As nitration progresses, more electrophilic molecules appear and aliphatic hydrogen tends to increase after initially decreasing under mild attack and increases more so under more energetic condition. This aliphatic hydrogen compensates for the decrease in aromatic hydrogen.     

Occurrence,leaching behavior,and detoxification of heavy metal Cr in coal gasification slag

Coal gasification slag(CGS) is a type of solid waste produced during coal gasification, in which heavy metals severely restrict its resource utilization. In this work, the mineral occurrence and distribution of typical heavy metal Cr in CGS is investigated. The leaching behavior of Cr under different conditions is studied in detail. Acid leaching–selective oxidation–coprecipitation method is proposed based on the characteristics of Cr in CGS. The detoxification of Cr in CGS is realized, and the ...     

Evidence of coal and tire interactions in coal–tire coprocessing for short residence times

In this paper, the factors controlling the hydrocoprocessing of coal and waste tires in tubing bomb reactors are studied. The fixed experimental conditions were 400°C and 10 MPa of H₂ pressure. Five different coprocessing times (60, 30, 10, 5 and 3 min) and two coal–tire ratios (80% coal–20% tire and 20% coal–80% tire) were the studied variables. Results are compared with those obtained when coal and tire were processed by isolate. At these conditions, it was observed that reaction time has no effect on tire conversion in obtaining the possible maximum value. However, with coal, reaction time is a fundamental variable because total conversion depends on it. In tire, reaction time has no effect on total conversion, but it affects product distribution in obtaining lower oils yields at longer reaction times due to hydrocracking reactions. In hydrocoprocessing of both materials, a synergism in asphaltenes formation is observed at short reaction times. This synergism has been explained by the inter-reactions between coal and tire radicals. Besides, tire addition to coal hydrogenation processes improves the quality of the oils.     

Emission control in the combustion of coal–water and organic coal–water fuels

Promising methods for decreasing anthropogenic emissions due to the combustion of coals of different ranks and coal–water fuel (CWF) and organic coal–water fuel (OCWF) slurries on their basis are considered. The maximum concentrations of the main anthropogenic emissions of sulfur, nitrogen, and carbon oxides (SO _x , NO _x , and CO _x ) formed upon the combustion of solid fuels in a powdered state and as the components of CWF and OCWF slurries were determined. The concentrations of the most hazardous oxides formed upon the combustion of coals of different ranks (brown and black coals) and CWF and OCWF slurries were compared. The experimental results substantiated the use of CWF and OCWF slurries for emission control in coal-burning power engineering. The addition of a combustible liquid component to a CWF slurry (the production of an OCWF slurry) makes it possible to ensure acceptable environmental and energy characteristics.     

Burn-out of pulverised coal and biomass chars☆

The burn-out of carbon in pulverised fired power stations is commercially important. Interest in the burn-out of biomass chars is growing because biomass is increasingly being co-fired with coal to reduce the carbon dioxide emissions. The significance of carbon burn-out is that it is linked with the efficiency of the plant and the suitability of the coal ash for construction purposes. Residual carbon in ash has generally increased in recent years because of the influence of the lower temperatures and slower mixing resulting from the use of low NO_x burners. The amount of unburned carbon is thus a function of the plant design and operating conditions but it is also linked to the ease of combustion of the coal and the char formed. These latter factors are related to the properties of the coal and this paper attempts to quantify the impact of certain coal and char properties on carbon-out. An approach for assessing biomass combustion performance is also discussed.