• Energy Research

Abstract As a renewable source of energy, biomass is expected to play more prominent role in our future metallurgical applications as a sustainable energy and reductant source. In this respect, an understanding of the thermal decomposition of biomass is clearly of great importance because thermal degradation is always the first step in the conversion process. The present study investigates thermal decomposition of wood samples using an advanced computational thermal analysis method. With this method the apparent specific heats of selected biomass samples were estimated during continuous heating at 10 °C/min for the temperatures of up to 600 °C. The rate of change in the heat of reaction with respect to temperature ( Δ H / Δ T ) was determined from the measured data and the consequent heats quantified for each sample. The results indicated that biomass pyrolysis has an overall exothermic effect with an endothermic decomposition of its cellulosic component. The exothermic reaction of wood at higher temperatures was primarily affected by its lignin content and the char formation reactions.

AbstractA comprehensive overview of coal oxidation methods under mild conditions is provided, including oxidation with oxygen, ozone, ruthenium ion catalysis, oxidizing acid, electrolysis, sodium hypochlorite, and hydrogen peroxide. The changes in chemical structure of coal during oxidation, the mechanism of different types of oxidation methods, and the possible applications of oxidation products are summarized. Comparison of these oxidation methods demonstrated that hydrogen peroxide and sodium hypochlorite oxidation of coal under mild conditions are the most suitable methods to study the molecular structure of coal and to obtain high‐value organic chemicals. Applications of different analytical techniques for determination and quantification of products and coal structures are also reviewed.

The paper provides an overview of current studies on the behaviour of coal during devolatilization, especially the experimental studies and modelling efforts on the formation of char structure of bituminous coals in the open literature. Coal is the most abundant fossil fuel in the world. It dominates the energy supply in the future and plays an increasing role particularly in the developing countries. Coal utilization processes such as combustion or gasification generally involve several steps: i.e., the devolatilization of organic materials, homogeneous reactions of volatile matter with the reactant gases and heterogeneous reactions of chars with the reactant gases. The devolatilization process exerts its influence throughout the life of the solid particles from the injection to the burnout, therefore is the most important step which needs to be understood. When volatile matter is generated, the physical structure of a char changes significantly during the devolatilization, some accompanying a particle's swelling. The complexity of a char's structure lies in the facts that the structure of a char itself is highly heterogenous inside an individual particle and between different particles and the chemistry of a char is strongly dependent on the raw coal properties. A char's structure is strongly dependent on the heating conditions such as temperature, heating rate and pressure. Understanding the swelling of coal and the formation of char's pore structure during the devolatilization of pulverized coal is essential to the development of advanced coal utilization technologies. During combustion and gasification of pulverized coal, the behaviour of individual particles differs markedly due to the variation of their maceral composition. Particles with different maceral constituents generate different types of char structure. The structure of a char has a significant impact on its subsequent heterogeneous reactions and ash formation. The review also covers the most recent studies carried out by the authors, including the experimental observations of the thermoplastic behaviour of individual coal particles from the density fractions using a single-particle reactor, the experimental analysis on chars prepared in a drop tube furnace using the density-separated coal samples, the development of a mathematical model for the formation of char's pore structure based on a simplified multi-bubble mechanism and the investigation on the effect of pressure on char formation in a pressurized entrained-flow reactor.

In this research, coal combustion behavior across the regions of blowpipe, tuyere, and raceway of blast furnace are numerically examined. Three different lance configurations, including a single lance, a double air-cooled coaxial lance, and an oxy-coal lance with different oxygen enrichment patterns, are taken into consideration. The coal combustion efficiency by the double lance injection is 5.1% higher than that by single lance injection. From the calculated temperature by the oxy-coal lance, coal ignition is retarded due to the cooling effect of enriched oxygen flowing through the lance annulus, resulting in the moderation of pressure loss within the raceway. Most importantly, the enriched oxygen becomes the combustion enhancer in the downstream of coal plume after ignition is triggered. Consequently, the coal burnout under the oxy-coal lance injection is comparative to that under the double air-cooled lance injection. The performance of blast furnace may be improved with the advantages provided by the oxy-coal lance injection. Compared with the single lance injection, coal trajectories under the oxy-coal lance injection are closer to the tuyere exit due to the higher inertia force of coal particles against hot blast. This should be taken into account for the designs of the oxy-coal lance.

Abstract In this paper, process simulation of a near-zero-carbon-emission power plant using CO 2 as the renewable energy storage medium was carried out. Liquid fuels that can be burned either in boilers or compression ignition engines to generate electricity have been the target products. The CO 2 and H 2 O produced from combustion are recirculated back to the synthesis units, thus forming a closed cycle of “renewable energy (unstable energy supply) + CO 2 + H 2 O → liquid fuels → electricity (stable supply)”. This novel closed loop energy storage process integrated with a 670 MW supercritical power plant was analyzed using the Aspen Plus software package. Methanol was selected as the targeted liquid fuel through three major synthesis routes: CO + H 2 , CO 2 + H 2 and CO 2 + H 2 O, in which CO and H 2 came from the electrolysis of CO 2 and H 2 O. The performances of the three methanol synthesis routes were thermodynamically analyzed. The results show that the optimal methanol synthesis route is the direct conversion of CO 2 and H 2 O through electrocatalysis when CO 2 conversion is above 42%, while when CO 2 conversion is below 42% the best choice turned out to be the CO hydrogenation. The direct conversion of (CO 2 + H 2 O) using electrocatalysis method was adopted as the liquid fuel synthesis route for the near-zero-carbon-emission power plant. The overall CO 2 emission from the near-zero-carbon-emission power plant is 44.13 kg/MWh accounting for just 6.45% of the advanced coal fired power plant.

Abstract In this paper, fundamental mechanisms for iron ore reduction in coal–ore mixtures have been investigated using several advanced experimental techniques. Firstly, the thermal properties of coal–ore mixtures were studied and apparent specific heat of coal–ore mixtures against temperature was obtained at a heating rate of 10 °C/min. Several exothermic and endothermic peaks were observed which were related to the decomposition reactions and reduction. The flue gases from the mixture were analysed using a mass spectrometer. Secondly, the X-ray diffraction (XRD) and the iron phase analytical techniques were applied to identify the iron phase changes with the temperature. It has been found that coal devolatilisation and iron oxides reduction occur simultaneously during the heating of the mixture. H2 and CO gases produced from coal devolatilisation and char gasification were responsible for the reduction of iron oxides at these temperatures. Iron oxides undergo step-wise reduction over the whole process. The results in this work provide a fundamental understanding for the direct reduced ironmaking processes.

Combustion efficiencies of pulverized coal in blowpipes and tuyeres under various operational conditions are numerically predicted to recognize the performance of pulverized coal injection in a blast furnace. A variety of parameters including the injection pattern of the pulverized coal, oxygen content in the hot blast, inlet temperature of the hot blast and mass flow rate of coal carrier gas are taken into consideration. The effect of installing a ceramic sleeve around the tuyere on pulverized coal combustion is also evaluated. The predictions indicate that pulverized coal combustion is highly related to the injection pattern, hot blast temperature, mass flow rate of the carrier gas and installation of the ceramic sleeve, whereas it is insensitive to the oxygen concentration. The present study is conducted based on the practical operational conditions of the blast furnace at the China Steel Corporation. Consequently, the obtained results have provided a useful insight into the operation of pulverized coal injection, and they enable us to further improve the blast furnace performance in the future.

Microwave pyrolysis of an Indonesian lignite is investigated in this study. The effects of experimental parameters, such as microwave receptor/coal ratio, residence time, temperature, microwave pow...

Abstract Dynamic measurements of physical, chemical and thermal changes in the transformation of coal maceral concentrates were made during heating at a rate of 10 °C/min to 1000 °C. The endothermic and exothermic processes were identified by measurements of apparent specific heat while the fluidity was indicated by the estimated thermal conductivity. Measurements of swelling and bed permeability were made, with continuous quantitative elemental analysis of gases and tars as they evolved. Data for two coal concentrates of high and moderate vitrinite indicate that the same reactions and events are occurring for the two samples, but to a greater extent for the high vitrinite sample. The research has noted the significance of evolved tars in the early events, being the lowest temperature event identified, with rapid tar evolution prior to the onset of swelling associated with permeability change. Further tar release and gas evolution is associated with a rapid swelling event, this event being substantially greater for the high vitrinite sample. The data has also quantified contraction at higher temperatures following swelling which is associated with the release of hydrogen containing gases. Evolved tars from the high vitrinite sample showed elevated H/C ratio indicating that vitrinite tars appear to be more aliphatic than those evolved from inertinite. A comparison of measured swelling with estimated volumetric flow rate of the volatiles has indicated that thermo-expansion of coal utilised up to 21% of the volatiles to drive bubble growth. This utilisation rate varied significantly across the plastic temperature range.