Guangqian Luo

Emission characteristics of nitrogen- and sulfur-containing odorous compounds during different sewage sludge chemical conditioning processes

Chemical conditioners are often used to enhance sewage sludge dewaterability through altering sludge properties and flocs structure, both affect odorous compounds emissions not only during sludge conditioning but also in subsequent sludge disposal. This study was to investigate emission characteristics of ammonia (NH(3)), sulfur dioxide (SO(2)), hydrogen sulfide (H(2)S) and carbonyl sulfide (COS) generated from sewage sludge conditioned by three representative conditioners, i.e., organic polymers, iron salts and skeleton builders, F-S (Fentons reagent and skeleton builders) composite conditioner. The results demonstrate that polyacrylamide (PAM) has an insignificant effect on emission characteristics of nitrogen- and sulfur-containing odorous compounds, because the properties, sulfur and nitrogen speciations are similar in PAM-conditioned sludge and raw sludge (RS). Significant increases of SO(2) and H(2)S emissions in the H(2)SO(4) conditioning process were observed due to the accelerated decomposition of sulfur-containing amino acids in acidic environment. Fenton peroxidation facilitates the formation of COS. CaO can reduce sulfur-containing gases emission via generation of calcium sulfate. However, under strong alkaline conditions, free ammonia or protonated amine in sludge can be easily converted to volatile ammonia, resulting in a significant release of NH(3).

Comparison of CaO’s effect on the fate of heavy metals during thermal treatment of two typical types of MSWI fly ashes in China

Both grate and fluidized bed incinerators are widely used for MSW incineration in China. CaO addition for removing hazardous emissions from MSWI flue gas changes the characteristics of fly ash and affects the thermal behavior of heavy metals when the ash is reheated. In the present work, two types of MSWI fly ashes, sampled from both grate and fluidized bed incinerators respectively, were thermal treated at 1023-1323 K and the fate of heavy metals was observed. The results show that both of the fly ashes were rich in Ca and Ca-compounds were the main alkaline matter which strongly affected the leaching behavior of heavy metals. Ca was mostly in the forms of Ca(OH)2 and CaCO3 in the fly ash from grate incinerator in which nascent fly ash particles were covered by Ca-compounds. In contrast, the content of Ca was lower in the fly ash from fluidized bed incinerator and Ca was mostly in the form of CaSO4. Chemical reactions among Ca-compounds caused particle agglomeration in thermal treated fly ash from grate incinerator, restraining the heavy metals volatilization. In thermal treated fly ash from fluidized bed incinerator, Ca was converted into aluminosilicates especially at 1323 K which enhanced heavy metals immobilization, decreasing their volatile fractions as well as leaching concentrations. Particle agglomeration hardly affected the leaching behavior of heavy metals. However, it suppressed the leachable-CaCrO4 formation and lowered Cr leaching concentration.

CO2 co-gasification of lower sulphur petroleum coke and sugar cane bagasse via TG–FTIR analysis technique

This study investigates the non-isothermal mechanism and kinetic behaviour of gasification of a lower sulphur petroleum coke, sugar cane bagasse and blends under carbon dioxide atmosphere conditions using the thermogravimetric analyser (TGA). The gas products were measured online with coupled Fourier transform infrared spectroscopy (FTIR). The achieved results explored that the sugar cane bagasse and blend gasification happened in two steps: at (<500 °C) the volatiles are released, and at (>700 °C) char gasification occurred, whereas the lower sulphur petroleum coke presented only one char gasification stage at (>800 °C). Significant interactions were observed in the whole process. Some solid-state mechanisms were studied by the Coats-Redfern method in order to observe the mechanisms responsible for the gasification of samples. The results show that the chemical first order reaction is the best responsible mechanism for whole process. The main released gases are CO2, CO, CH4, HCOOH, C6H5OH and CH3COOH.

The fate of sulfur during rapid pyrolysis of scrap tires

The fate of sulfur during rapid pyrolysis of scrap tires at temperatures from 673 to 1073K was investigated. Sulfur was predominant in the forms of thiophenic and inorganic sulfides in raw scrap tires. In the pyrolysis process, sulfur in organic forms was unstable and decomposed, leading to the sulfur release into tar and gases. At 673 and 773K, a considerable amount of sulfur was distributed in tar. Temperature increasing from 773 to 973K promoted tar decomposition and facilitated sulfur release into gases. At 1073K, the interactions between volatiles and char stimulated the formation of high-molecular-weight sulfur-containing compounds. After pyrolysis, almost half of the total content of sulfur in raw scrap tires still remained in the char and was mostly in the form of sulfides. Moreover, at temperatures higher than 873K, part of sulfur in the char was immobilized in the sulfates. In the pyrolysis gases, H2S was the main sulfur-containing gas. Increasing temperature stimulated the decomposition of organic polymers in scrap tires and more H2S was formed. Besides H2S, other sulfur-containing gases such as CH3SH, COS and SO2 were produced during the rapid pyrolysis of scrap tires.

Degradative solvent extraction of demineralized and ion-exchanged low-rank coals

Abstract Dehydration and upgrading are essential pretreatment methods for efficient utilization of low-rank coal. In previous works the authors employed degradative solvent extraction method to dehydrate and upgrade low-rank coals and fractionate them into several fractions. For further study of this method, two low-rank coals (MM and LY) were pretreated by acid washing for demineralization or acid washing and Na/Co ion-exchange. The pretreated and raw coals were then extracted by 1-methylnaphthalene (1-MN) at 350°C and fractionated into upgraded coal (UC), high molecular weight extract (deposit), low molecular weight extract (soluble), as well as a little H 2 O and gas products. The results show that both acid washing and ion-exchange enhance the yields and carbon contents of the two extracts. Ion-exchange obviously promotes the removal of oxygen-containing functional group during extraction. The yield of high molecular weight extract of demineralized MM increases from 3.5% to 9.5%, and the carbon content and oxygen content of low molecular weight extract of Na ion-exchanged LY are as high as 85.3% and less than 6.4%, respectively. Ion-exchange has a distinct influence on physical and chemical properties of the extracts. The influence of Na ion-exchange is especially remarkable. Thus, demineralization and ion-exchange have evident promotion for the degradative solvent extraction of low-rank coal.

Influence of different distributions of Ca-mineral in coal on trimodal particulate matter formation during combustion

Abstract Calcium acetate was added into a bituminous coal through physically blending and impregnation to obtain the ble-Ca coal rich in excluded Ca-mineral and imp-Ca coal rich in included Ca-mineral, respectively. The raw coal, ble-Ca coal and imp-Ca coal were burned in a drop tube furnace at 1300°C. The generated particulate matters (PMs) were collected and analyzed to study the influence of different distributions of Ca-mineral in coal on trimodal PM formation during combustion. The results showed that for the three coals, PMs with the ultrafine mode, central mode and coarse mode were all in the size range of 2.0 μm, respectively. The included and excluded Ca-minerals can both promote the formation of ultrafine mode PM, and the excluded one had more significant effect. The included Ca-mineral can restrain, while the excluded one can promote the formation of central mode PM. The included Ca-mineral can promote the formation of coarse mode PM, while the excluded one did not have obvious effect.

Kinetic analyses and synergistic effects of CO2 co-gasification of low sulphur petroleum coke and biomass wastes

This study presents thermogravimetric analyses (TGA) of CO2 co-gasification of petroleum coke with low sulphur (PC) and various types of biomass wastes including agricultural (rice husk (RH), rice stalk (RS) and cotton straw (CS)) and by-product wastes (saw dust (SD) and sugar cane bagasse (SCB)). Their reactivities, synergistic effect and kinetics were studied and compared in detail. The homogeneous model (HM) and shrinking core models (SCM) were applied to estimate the kinetic parameters. The results indicated that obvious synergistic effect was observed during the co-gasification of the blends. The PC gasification reactivity was significantly improved by the addition of biomass wastes. The model of R2 was found to be most suitable for the co-gasification. The activation energy of PC was decrease from 293.72 kJ/mol to117.04 kJ/mol by the addition of SD. The co-gasification of PC and biomass waste is a promising way for the efficient utilization of PC and biomass wastes.

Central Mode Particulate Matter Control by Enhanced Liquid Formation Under the Condition of Blended Coal Combustion

The detailed process of central mode particulate matter (PM) control under the condition of blended coal combustion was studied. Blended coal combustion and mineral heating experiments were carried out in a drop tube furnace at 1373 and 1573 K. The two parent coals were, respectively, rich in Ca/Fe minerals and aluminosilicates. Calcite and kaolin, as the typical minerals in the two coals, were selected and used in the following mineral heating experiment. PMs and bulk ashes were, respectively, isokinetically collected by a low-pressure impactor (LPI) and fiber filters through a water-cooled N2-quenched sampling probe. The elemental compositions of PM collected on each stage of the LPI were analyzed, and the central mode PM was identified by the mass fraction size distributions of refractory and volatile elements. The bulk ashes collected in mineral heating experiment were further detected by X-ray diffraction (XRD). Through analyzing the PMs and bulk ashes generated in mineral heating experiment at different temperatures, the probable reason for central mode PM restraint with increasing temperature was found. Ca aluminosilicates generated by the interactions between calcite and kaolin lead to liquid formation at high temperature. The existing liquidus compositions decrease fine particle concentration through two possible ways: restraining the fragmentation of mineral particles and promoting the scavenging of existing fine particles. The decrease of fine particles at the same time decreases the inorganic vapor heterogeneous condensed on these particles, and hence, the central mode PM formation is restrained at high temperature. During blended coal combustion, an enhanced liquid formation caused by mineral interactions could control central mode PM formation through decreasing the concentration of fine particles.