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Several important aspects are described in this paper. The occurrences of trace elements (TEs) in coal are introduced. Four main groups of trace element content level, say, >50, 10–50, 1–10 and <1 ppm, can be drawn. Trace elements partitioning in emission streams; enrichment in submicron particles; vaporization and emission in flue gas; and the mobility and leaching behavior of trace elements in coal and combustion waste are summarized. The mechanisms of trace element transformation during combustion are illustrated as following: the vaporized metals at high temperature near the combustion flame will subsequently nucleate or condense at a lower temperature downstream. These metals form a suspended aerosol along with particles. The conversion of vaporized components into various solid and/or liquid forms is the key factor influencing the final trace elements'' transformation/partitioning behavior. Finally, current trace element emission control technologies are briefly introduced. To control trace elements in particle phase, electrostatic precipitators and fabric filters are mainly used. To control trace elements in vapor phase, spray dryer absorbers, wet scrubbers, condensing wet scrubbers, wet scrubbers and solid sorbent injection should mainly be used. Research needs are identified and potentially promising research topics on trace elements emission are proposed as following: (1) trace element speciation and enrichment in coal and coal ash. (2) Trace elements partitioning in combustion process. (3) Mechanisms of transformation and control technologies for easily vaporized TEs during combustion. [Copyright &y& Elsevier]

In this study, manganese oxides supported on titania was prepared by sol-gel method and employed as SCR catalyst for simultaneous NO and mercury removal from coal combustion flue gas. The simultaneous NO and Hg 0 conversion rate on MnO x /TiO 2 was evaluated in different atmospheres, and the interaction between denitration and demercuration was investigated. The results indicated that MnO x /TiO 2 had good activity in simultaneously removing NO and Hg 0 in SCR atmosphere (NH 3 + NO + O 2 + N 2 ). However, both NO conversion and Hg 0 removal efficiency were inhibited in simulated coal combustion flue gas compared to that in SCR atmosphere because of the presence of SO 2 leading to the generation of sulfite and sulfate on the catalyst. H 2 O in simulated coal combustion flue gas had negative effect on the catalytic performance as well. NO conversion in oxy-fuel combustion flue gas was lower than that in air combustion flue gas, while Hg 0 removal efficiency in oxy-fuel combustion flue gas was higher than that in air combustion flue gas. Hg 0 displayed no obvious influence on NO conversion and N 2 selectivity over SCR process. And SCR atmosphere showed almost no inhibition to Hg 0 removal when the temperature was below 300 °C. At the optimal temperature for NO conversion (250 °C), the inhibition of SCR atmosphere on Hg 0 removal became stronger as the space velocity (GHSV) increased, but the inhibitive effect could be ignored when GHSV slowed down to 50,000 h − 1 or less. [ABSTRACT FROM AUTHOR]

This paper presents an experimental study of coal MILD-Oxy combustion at 0.3mw pilot-scaled facility in Huazhong University of Science and Technology (HUST), which contains an entirely flue gas recycle system. By increasing the jet velocity to 100 m/s, the MILD combustion was achieved without high temperature preheating. Meanwhile the experiment was operated under Oxy-fuel atmosphere that was established by the flue gas recirculation. A swirl Oxy-fuel combustion was also tested as a comparison. The CO 2 concentration in flue gas could sustain a high level during the combustion. The major conclusions include: The coal MILD-Oxy combustion can be achieve by high-velocity jet in some extent. But the full dilution and homogenization of heat and reactants can't be achieved under non-premixed combustion because of the separation of fuel and oxygen, which means the ideal MILD-Oxy combustion can't be achieved but only be approached. The reaction zone was enlarged to the vast area of furnace, in which the combustion temperature and reaction rate decreased. The carbon burnout rate decreased due to the reduction of residence time and reaction rate. The NOx emission decreased nearly 40% because of the lower flame temperature. [ABSTRACT FROM AUTHOR]

This paper numerically investigates the effects of H 2 O addition on pulverized coal oxy-MILD (moderate or intense low oxygen dilution) combustion based on our previous study, in which only O 2 /CO 2 was treated as oxidizer. While in the present study, the initial H 2 O mole fraction in oxidizer is varied at a constant oxygen level (30% by volume) to represent four typical oxy-fuel operations, i.e. ideal dry recycle (0% H 2 O + 70% CO 2 ), practical dry recycle (5% H 2 O + 65% CO 2 ), wet recycle (15% H 2 O + 55% CO 2 ) and oxy-steam (70% H 2 O + 0% CO 2 ). It is revealed that, with the addition of H 2 O, the internal recirculation rate (K V ) as well as the coal ignition is improved, however, due to the difference in physical effects between CO 2 and H 2 O, the temperature peak is likewise promoted. CO 2 is preferred than H 2 O to moderate the flame temperature and realize uniform temperature distribution under MILD combustion. Higher H 2 and lower CO formations are obtained by adding H 2 O because of the competing char gasification reactions between CO 2 and H 2 O under in-furnace low oxygen condition of MILD combustion. H 2 O addition tends to suppress the volatiles-N conversion while accelerate the char-N conversion in the upper furnace, respectively, and reduce the final NO emission by enhanced H 2 formation. Moreover, H 2 O addition is beneficial to increasing heat transfer in both radiative and convective forms. [ABSTRACT FROM AUTHOR]

The effects of the particle size on combustion characteristics of pulverized coals under O 2 /N 2 and O 2 /CO 2 atmospheres were compared using thermo-gravimetric analysis method. The results show the effect is greater in O 2 /CO 2 atmosphere. It presents obvious fluctuation, which becomes greater as the volatile matter content of coal increases. The effects of O 2 concentrations were also compared. The results show a noticeable discrepancy between O 2 /N 2 and O 2 /CO 2 atmospheres at a low O 2 concentration and indiscernible at a high O 2 concentration. Meanwhile, the fluctuation effect is different under the different O 2 concentrations, which can be related to the reaction rate. In conclusion, under the O 2 /CO 2 atmosphere, the effect of the particle size on pulverized coal combustion is completely different from that under O 2 /N 2 condition. [ABSTRACT FROM AUTHOR]

Abstract: Chemical looping combustion (CLC) of coal has received great attention for its verified advantage in the inherent separation of CO2 without great cost penalty. It would be meaningful to adopt anthracite as fuel for CLC application in China due to its abundant reserve in China and also a great challenge for its low reactivity. A typical Chinese anthracite as Yang Quan (YQ) coal was selected in this research as a model fuel and its reaction with both synthesized CuO/Al2O3 and Fe2O3/Al2O3 oxygen carriers (OCs) was performed in a thermogravimetric analyzer (TGA) to investigate the reaction peculiarities involved. Fourier transform infrared spectroscopy (FTIR) was used to in-situ detect the emitted gasses from TGA. Field scanning electron microscopy/energy-dispersive X-ray spectrometry (FSEM-EDX) was used to study the morphology and elemental compositions present in the solid residues collected from the reaction of YQ with these two OCs, and the related phase was identified by X-ray diffraction (XRD). In order to further explore the reaction mechanisms involved, a more realistic reaction system with 426 species was designed for thermodynamic simulation. Through all these measures, two reaction stages were observed for the reaction of YQ with Fe2O3/Al2O3 or CuO/Al2O3 at 300–600°C and 600–850°C after dehydration, respectively. The maximum weight loss rate for YQ with CuO/Al2O3 at the second stage was pronounced enough to reach up to 2.8wt.%/min, greatly higher than that of YQ with Fe2O3/Al2O3. The mixture conversion index for YQ with CuO/Al2O3 was far bigger than that of YQ with Fe2O3/Al2O3, which further indicated that CuO/Al2O3 was more suitable to YQ in CLC. At these two stages throughout 400 to 1100°C, CuO and CuAl2O4 contained in CuO/Al2O3 OC were mainly reduced to Cu and Cu2O or CuAlO2 and Al2O3 by transfer of the lattice oxygen [O] involved to YQ in a sequential mode; however, above 800°C, Cu2O and CuAlO2 were also produced through direct decomposition of CuO or CuAl2O4 by emission of gaseous oxygen O2, which was beneficial to the direct combustion of coal. During reaction of YQ with CuO/Al2O3 OC, active CuO was found to tend to react with various sulfur species produced from YQ pyrolysis and formed to Cu2S, but the Al2SiO5 was formed through the interaction of Al2O3 with SiO2 in the YQ, which resulted in the loss of the inert support involved in the CuO/Al2O3 OC and further degraded its reactivity to YQ due to the lower resistance to sintering. [Copyright &y& Elsevier]

Abstract: A study on pyrolysis of palm oil wastes in a countercurrent fixed bed was carried out, aiming to characterize the hydrogen rich gas products in view of enhanced energy recycling. The effects of temperature, residence time and catalyst adding on the yields and distribution of hydrogen rich gas products were investigated. The main gas species generated, as identified by Micro-GC, were H2, CO, CO2, CH4 and trace amounts of C2H4 and C2H6. With temperature increasing from 500 °C to 900 °C, the total gas yield was enhanced greatly and reached the maximum value (∼70 wt.%, on the raw biomass sample basis) at 900 °C with big portions of H2 (33.49 vol.%) and CO (41.33 vol.%). Residence time showed a significant influence on the upgrading of H2 and CO2 yields. The optimum residence time (9 s) was found to get a higher H2 yield (10.40 g/kg (daf)). The effect of adding chemicals (Ni, γ-Al2O3, Fe2O3 and La/Al2O3, etc.) on gas product yield was investigated and adding Ni showed the greatest catalytic effect with the maximum H2 yield achieved at 29.78 g/kg (daf). [Copyright &y& Elsevier]