Research on NO generation characteristics of ammonia-premixed flame.

Ammonia is a promising fuel with high energy density, accessible storage, and no CO2 production by combustion, but its combustion produces the pollutant NO. In this study, a Bunsen burner experimental bench was selected to investigate the concentration of NO generated by ammonia combustion at different initial oxygen concentrations. Further, the reaction pathways of NO were analyzed in depth, and sensitivity analysis was performed. The results show that the Konnov mechanism has an excellent predictive effect on NO generated by ammonia combustion. In the ammonia-premixed laminar flame at atmospheric pressure, the NO concentration peaked at an equivalence ratio of 0.9. The high initial oxygen concentration enhanced the combustion of ammonia-premixed flame and increased the conversion of NH3 to NO. NO was not only a product but a contribution to the combustion of NH3. As the equivalence ratio increases, NH2 consumes a large amount of NO and reduces NO production. The high initial oxygen concentration enhanced NO production, and the effect was more pronounced at low equivalents. The study results provide theoretical guidance for the utilization of ammonia combustion and pollutant reduction and help to drive the process of ammonia combustion toward practicality.

Study on Permeability Characteristics of Porous Transparent Gels Based on Synthetic Materials.

Advanced knowledge of the permeability characteristics of transparent gels play a key role in providing a rational basis for the study of porous polymer permeability and the research on the migration behavior of superpolymer solutions. Thus, a new type of transparent gel was prepared to simulate porous media, with aim to observe and analyze the permeability characteristics of transparent gel under the conditions of our experimental design by combining a transparent soil test and simple particle image velocimetry. The experimental results showed that the permeability of the transparent gel was similar to that through actual soil. The permeability coefficients of the transparent gel under different pressure gradients varied greatly early in the experimental cycle, while changing only slightly afterward, showing an overall trend of decreasing first and then stabilizing. With the increase of the mass ratio, the permeability coefficient of the sample decreased, the distribution of the low-velocity zone of the intercepted section became wider and tended to move upward. Differences in spatial position also caused different patterns of velocity and direction. The findings presented in this paper contribute to providing a new direction for the study of porous polymer permeability and the porous migration of superpolymer solutions.

Roles of Ion-Exchangeable Sodium in the Conversion Process of Tar to Soot during Rapid Pyrolysis of Two Brown Coals in a Drop-Tube Reactor.

In this work, two series of brown coals (including acid-washed coal and ion-exchangeable Na-loaded coal) were pyrolyzed in a drop-tube reactor. The experimental results revealed that soot and tar yields of Na-loaded coals were significantly lower than that of acid-washed coals. Gasified Na can reduce the formation of big soot agglomerates. During coal primary pyrolysis, ion-exchangeable Na can reduce the amount and aromaticity of primary tar. Na released with volatiles can catalyze the cracking of aliphatic and aromatic compounds, inhibit the polymerization between aromatic rings, and promote the combination of soot/tar with oxygen-containing substances, resulting in the decrease of graphite crystallite size and the increase of amorphous carbon content. Na can also reduce the organization degree of soot by forming intercalation compounds.

Purification characteristics of fine particulate matter treated by a self-flushing wet electrostatic precipitator equipped with a flexible electrode.

A self-flushing wet electrostatic precipitator was developed to investigate the removal performance for fine particles. Flexible material (polypropylene, 840A) and carbon steel in the form of a spiked band were adopted as the collection plate and discharge electrode, respectively. The particle concentration, morphology, and trace-element content were measured by electric low-pressure impactor, scanning electron microscope, and energy-dispersive x-ray spectroscopy, respectively, before and after the electrostatic precipitator. With increasing gas velocity, the collection efficiency of fine particles (up to 0.8 µm in diameter) increased, while it decreased for particles with diameters larger than 0.8 µm. Increasing the dust inlet concentration increased the collection efficiency up to a point, from which it then declined gradually with further increases in the inlet concentration. The particulate matter after the wet electrostatic precipitator showed different degrees of agglomeration. The collection efficiency of trace elements within PM10 was less than that of the PM10 itself. Notably, the water consumption in the current setup was significantly lower than for other treatment processes of comparable collection efficiencies. IMPLICATIONS: Wet electrostatic precipitators, as fine filtration equipment, were generally applicable to coal-fired plants to reduce PM2.5 emissions in China. However, high energy consumption and unstable operation, such as water usage and spray washing directly in the electric field, seriously restricted the further development. The utilization of self-flushing wet electrostatic precipitator can solve these problems to some extent.

[Hazard evaluation modeling of particulate matters emitted by coal-fired boilers and case analysis].

In order to evaluate the hazard of PM2.5 emitted by various boilers, in this paper, segmentation of particulate matters with sizes of below 2. 5 microm was performed based on their formation mechanisms and hazard level to human beings and environment. Meanwhile, taking into account the mass concentration, number concentration, enrichment factor of Hg, and content of Hg element in different coal ashes, a comprehensive model aimed at evaluating hazard of PM2.5 emitted by coal-fired boilers was established in this paper. Finally, through utilizing filed experimental data of previous literatures, a case analysis of the evaluation model was conducted, and the concept of hazard reduction coefficient was proposed, which can be used to evaluate the performance of dust removers.