Zhao Yongchun

Preliminary study of trace element emissions and control during coal combustion

Hazardous trace element emissions have caused serious harm to human health in China. Several typical high-toxic trace element coals were collected from different districts and were used to investigate the emission characteristics of toxic trace elements (As, Se, Cr, Hg) and to explore preliminary control methods. Coal combustion tests were conducted in several bench-scale furnaces including drop tube furnace (DTF), circulating fluidized bed (CFB) combustion furnace, and fixed-bed combustion furnace. Calcium oxide was used to control the emission of arsenic and selenium. The granular activated carbons (AC) and activated-carbon fibers (ACF) were used to remove mercury in the flue gas from coal combustion. The chemical composition and trace element contents of ash and particulate matter (PM) were determined by X-ray fluorescence (XRF) spectrometry and inductively coupled plasma-atomic emission spectrometry (ICP-AES), respectively. The speciation and concentration of mercury were investigated using the Ontario-Hydro method. X-ray diffraction spectrometry (XRD) was used to determine the mineral composition of production during combustion experiments. With the addition of a calcium-based sorbent, arsenic concentration in PM1 sharply decreased from 0.25–0.11 mg/m3. In fixed-bed combustion of coal, the retention rates of selenium volatiles were between 11.6% and 50.7% using lime. In the circulating fluidized-bed combustion of coal, the content of selenium in ash from the chimney was reduced to one-fourth of its original value and that in leaching water from the chimney decreased by two orders of magnitude using lime. Calcium-based sorbent is an effective additive to control the emission of As and Se during coal combustion. The emission of chromium is influenced by the occurrence mode of Cr in coal. Chromium emission in PM2.5 during coal combustion is 55.5 and 34.7 μg/m3 for Shenbei coal and mixed Pingdingshan coal, respectively. The adsorptive capacity of granular activated carbon for Hg0 is significantly enhanced through ZnCl2-impregnation. The activated carbon fibers showed decent efficiency in mercury adsorption, on which surface oxygen complex showed positive effects on mercury adsorption.

Thermodynamic equilibrium study of mineral elements evaporation in O2/CO2 recycle combustion

Abstract The facility for the analysis of chemical thermodynamics method (F*A*C*T) based on the Gibbs energy minimization principle, was used to characterize the evaporation of mineral elements of coal in O 2 /CO 2 recycle combustion. The effects of atmosphere and temperature on the speciation of mineral species were discussed. The results show that Na(K)Cl(g), FeO(g), and SiO(g) are the dominant gaseous species of the mineral elements. The dominant species of mineral elements in flue gases depend on both the combustion conditions (reducing or oxidizing) and the atmosphere. In O 2 /CO 2 mixture combustion, the evaporation rate of mineral elements is much lower than that in air combustion, especially under reducing atmosphere. The total evaporation of mineral elements in O 2 /CO 2 atmosphere and air combustion under reducing conditions is 4.46% and 9.65% respectively, up to the temperature of 2400 K. The calculation values are consistent with the experiment values. The decrease in the mineral element evaporation is helpful to suppress the tendency to form fine particle matter and the tendency of initial ash deposition.

Integrated Control of Submicron Particles and Toxic Trace Elements by ESPs Combined with Chemical Agglomeration

Enrichment of typical toxic trace elements As on PM2.5 was investigated through bench scale experiments. Results showed that the vaporization of arsenic in pyrite was easier than in arsenate form. Along with increasing temperature from 1100°C to 1400°C, arsenic content in PM2.5 increased from 0.09 mg/Nm3 to 0.35 mg/Nm3. Then, a novel Electrostatic precipitators (ESPs) combined with chemical agglomeration technique was developed to control the emission of PM2.5 and toxic trace elements. PM2.5 enriched toxic trace elements are agglomerated by some new chemical agents injected as an aqueous solution upstream of ESPs and come into being conglomerations which can be captured by ESPs easily. Systematic experiments of PM2.5 agglomeration showed that chemical agglomeration was a useful method to promote growing up process of submicron particles, XTG was the most effective agglomerant. Resistivity tests revealed that agglomerants could make fly ash resistivity two orders lower at certain concentration, would improve the performance of ESPs with resistivity related performance problems.

Agglomeration Modelling of Sub-Micron Particle during Coal Combustion Based on the Flocculation Theory

The monte carlo method was used to simulate chemical agglomeration of sub-micron particle which based on the flocculation model of the water processing, the influence of different agglomeration solution volume on sub-micron particle agglomeration was investigated. Simulation results show that the growth of particle mean diameter and the decrease of particle number are fast at the initial stage of agglomeration, and the speed of them increase with agglomeration solution volume increasing. After achieving stability, as a whole, the particle mean diameter is almost in proportion to agglomeration solution volume. At the last stage of agglomeration, particle number follows a similar bimodal distribution, which is varying with different agglomeration solution volumes. When agglomeration solution volume is 2 ml/min, the peak value of diameter is the biggest.