Yinhe Liu

Experimental study on interaction and kinetic characteristics during combustion of blended coals

The combustion behaviors and kinetic parameters of three parent coals (A1, A2, and A3) and their blends (A1/A2 and A2/A3) have been evaluated under oxidizing atmosphere (O2 and N2 mixtures), using a non-isothermal thermo-gravimetric analyzer. The aim of this study is to investigate the interaction between the blended components during the process of co-combustion, and the effects of blending ratio and oxygen concentration (10, 15, and 21%) on combustion performance of blended coals. When high reactivity and low reactivity coals are co-combusted, double peaks are observed in the DTG curves, and significant interaction occurs in the temperature range between the two peaks (Tp1 and Tp2). The activation energies obtained by Coats–Redfern method indicate that the activation energies of blended coals are lower than that of parent coals. The combustibility index S is used to evaluate the combustion performance of blended coals, and the results show the non-additive effects of the combustion characteristics of blended coals. The increased oxygen concentration results in a significant improvement of combustion performance of blended coals. In addition, as the blending ratio of high reactivity coal is increased, the oxygen can greatly enhance the combustion stability of blended coals.

Ignition and Kinetics Analysis of Coal Combustion in Low Oxygen Concentration

Abstract The combustion of coals in low oxygen concentration, which exists widely in industry combustion, was investigated by the use of thermogravimetry. Experimental results show that thermogravity/differential thermogravity/differential scanning calorimetry curves of four studied coals shift to a higher temperature zone in lower oxygen concentration. The ignition temperature is almost constant for each coal and increases with the increased coal rank. The burnout temperature and peak temperature increase with the decreased oxygen concentration. The kinetic parameters were calculated using the Coats-Redfern method for coal combustion in low oxygen concentration. The apparent activation energy increases linearly with oxygen concentration, and high rank coal has a high apparent activation energy. An intensive compensation effect exists between the apparent activation energy E and pre-exponential factor A, and the corresponding compensation coefficients are obtained.

Effects of minerals on the release of nitrogen species from anthracite

Abstract Experiments have been carried out to investigate the effects of minerals on nitrogen species emission including NO and its precursors from a high rank coal during temperature-programmed combustion by TG/EGA method at 10°C/min. Sodium was found to be an excellent catalyst for the reduction of NO and HCN evolution due to its higher catalysis of sodium on the char-NO reaction. However, iron can induce an increase of NO release. Calcium and titanium additives can be classified as inactive constituents because of their weak catalysis on HCN and NO emission. All the metallic additives can promote NH3 emission except sodium. Parent coal has higher fractions of nitrogen release as NO and NH3 and lower fraction of nitrogen release as HCN than demineralized coal, which can be attributed to the catalysis of indigenous minerals in parent coal.

Diffusional effects on differences of coal char reactivity between air and oxy-fuel combustion in thermogravimetric experiments

Oxy-fuel combustion can realize large-scale CO2 capture and low NOx emission from coal-fired power plants, while the evaluation of coal reactivity differences between air and oxy-fuel conditions is of importance for retrofitting existing conventional boilers to oxy-fuel ones. Here, two sets of specially designed experiments were contrastively conducted to assess the diffusional limitation effects on differences of coal char reactivity between air (O2/N2) and oxy-fuel (O2/CO2) combustion in non-isothermal thermogravimetric (TG) experiments, which were seldom investigated previously. Experimental results show that the TG/DTG curves of char combustion present distinct differences before and after reducing diffusional limitation. The differences of char combustion measured in non-isothermal TG experiments between O2/CO2 and O2/N2 conditions are shrinking with the reduction of diffusion resistance. Compared with conventional air combustion, change of combustion atmosphere in oxy-fuel condition mainly exhibits influence on diffusion process, while it has no observable effect on char-O2 chemical reaction in TG experiments. Obviously different results between air and oxy-fuel combustion can be obtained when the diffusional limitation in TG tests is significant, while the change of combustion atmosphere has negligible influence on char reactivity under minimized inhibition of heat and mass transfer. Knowledge of the respective influence of intrinsic reaction and diffusion resistance on the measured TG experiments is of considerable significance for the exploration of reactivity and kinetics differences between air and oxy-fuel combustion.

Effect of Volatile-Char Interaction on Nitrogen Oxide Emission during Combustion of Blended Coal

AbstractUtilization of blended coal has been a great issue due to the increasing off-specification coals received in power plants, while the reduction of nitrogen oxide is also attracting extensive...

Experimental Study on Enhanced Falling Film Absorption Process Using H2O/LiBr Nanofluids

Absorption air conditioning system could be driven by low grade energy, such as solar energy and industrial exhaust heat, for the purposes of energy conservation and emission reduction. Its development is limited by its huge volume and high initial investment. The nanofluids, which possess the superior thermophysical properties, exhibit a great potential in enhancing heat and mass transfer performance. In this paper, nanofluids of H2O/LiBr with Fe3O4 nanoparticles were introduced into absorption air conditioning system. The effects of some parameters, such as the flow rate of H2O/LiBr nanofluids, nanoparticle size and mass fraction, on the falling film absorption were investigated. The H2O/LiBr nanofluids with Fe3O4 nanoparticle mass fractions of 0.01 wt%, 0.05 wt% and 0.1 wt%, and nanoparticle size of 20 nm, 50 nm and 100 nm were tested by experiment. The results imply that the water vapour absorption rate could be improved by adding nanoparticles to H2O/LiBr solution. The smaller the nanoparticle size, the greater enhancement of the heat and mass transfer performance. The absorption enhancement ratio increases sharply at first by increasing the nanoparticle mass fraction within a range of relatively low mass fraction, and then exhibits a slow growing even reducing trends with increasing the mass fraction further. For Fe3O4 nanoparticle mass fraction of 0.05wt% and nanoparticle size of 20nm, the maximum mass transfer enhancement ratio is achieved about 2.28 at the flow rate of 100 L·h−1.Copyright

Study on Fuel-N Conversion During Rapid Pyrolysis of Anthracite in CO 2 at High Temperature

Here, a study was conducted on fuel-N conversion during anthracite rapid pyrolysis in CO2 at high temperature using a drop-tube furnace (DTF). NO and HCN were the main products in CO2 atmosphere and NO occupied a larger proportion. Due to char–CO2 gasification, more oxygen-derived groups were introduced onto the char surfaces. High temperature enhanced gasification reaction, leading to a more developed pore structure and a larger specific surface area of char, which greatly increased the reaction sites of (–CN) with oxidizing free radicals. More active nitrogen sites were exposed in CO2 atmosphere, promoting char-N release. HCN yield in CO2 atmosphere was lower than that in N2 atmosphere due to the oxidation of (–CN) by (–O). Gasification reaction promoted the fuel-N release, resulting in HCN maximum yield at a lower temperature. N2 production increased while char-N yield decreased as temperature was increased from 1173 to 1773 K for anthracite.