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ABSTRACT: The emission characteristics of polycyclic aromatic hydrocarbons (PAHs) during coal and sewage sludge co-combustion were investigated in a laboratory-scale drop tube furnace. The experimental results demonstrated that coal and sewage sludge co-combustion was beneficial in reducing PAH emissions and PAH toxic equivalent (TEQ) concentrations. Meanwhile, the five-ring PAHs were the main contributor in reducing the concentration of PAHs and TEQ. Moreover, the two- and five-ring PAH concentrations decreased as the mass fraction of sewage sludge in the mixture increased from 0% to 100%. It was also found that PAHs from coal mono-combustion was dominated by the four- and five-ring PAHs. As for the sewage sludge mono-combustion, the three- and four-ring PAHs were the principal components.
Waste management & research : the journal of the International Solid Wastes and Public Cleansing Association, ISWA. 06/2012; 30(9):875-82.
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ABSTRACT: In order to study the distribution and partitioning of heavy and alkali metals in the flue gases of a sewage sludge incinerator, an experiment was carried out in a pilot scale combustor. The results indicated that it was feasible to separate part of metals from flue gases by collecting fly ash at different temperatures. On the basis of their separation temperature, heavy and alkali metals could be divided into three groups: group A included Zn, K and P, which converted from gaseous phase to liquid or solid when temperature was above 600 degrees C. Pb and Cu were the metals of group B, with optimum transformation temperature of 400 degrees C. Na and As belonged to group C, with conversion temperatures of 300 degrees C. Moreover, the effect of temperature gradient on heavy and alkali metal gas-solid transformation was also experimentally investigated. It was observed that the temperature gradient could promote the gas-solid conversion of heavy and alkali metals. However, too high a temperature gradient would suppress the formation of fine particles. The peak of conversion rate for K, Pb and Na occurred at 434 degrees C s(-1), while that of P and Cu was 487 degrees C s(-1).
Waste management & research : the journal of the International Solid Wastes and Public Cleansing Association, ISWA. 10/2009; 28(2):158-64.
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ABSTRACT: A combustion experiment with cedar pellet fuel was carried out in a semi-pilot scale bubbling fluidized bed combustor. The effects of temperature, fluidized velocity, and bed material particle size on the emission of NOx, CO, and CO2 were investigated. The variations in the temperature profile and gas concentration in the vertical and horizontal directions of the combustor were also studied. The results showed that high temperature can improve the combustion efficiency and decrease CO emission. Moreover, increasing the fluidized velocity suppressed CO formation. In addition to temperature and fluidized velocity, the bed material also played an important role during cedar pellet combustion. Coarse bed materials were better than fine materials. In these test runs, the CO emission varied from 20 to 189 ppm, CO2 emission ranged from 5.7% to 19.5%, while NOx emission was quite stable at about 220 ppm.
Bioresource Technology 07/2008; 99(9):3782-6. · 4.98 Impact Factor
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ABSTRACT: In order to separate and reuse heavy and alkali metals from flue gas during sewage sludge incineration, experiments were carried out in a pilot incinerator. The experimental results show that most of the heavy and alkali metals form condensed phase at temperature above 600 degrees C. With the addition of 5% calcium chloride into sewage sludge, the gas/solid transformation temperature of part of the metals (As, Cu, Mg and Na) is evidently decreased due to the formation of chloride, while calcium chloride seems to have no significant influence on Zn and P. Moreover, the mass fractions of some heavy and alkali metals in the collected fly ash are relatively high. For example, the mass fractions for Pb and Cu in the fly ash collected by the filter are 1.19% and 19.7%, respectively, which are well above those in lead and copper ores. In the case of adding 5% calcium chloride, the heavy and alkali metals can be divided into three groups based on their conversion temperature: Group A that includes Na, Zn, K, Mg and P, which are converted into condensed phase above 600 degrees C; Group B that includes Pb and Cu which solidify when the temperature is above 400 degrees C; and Group C that includes As, whose condensation temperature is as low as 300 degrees C.
Waste Management 02/2008; 28(5):833-9. · 2.43 Impact Factor
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ABSTRACT: Biomass is an important primary energy source as well as renewable energy source. As the most promising biomass utilization method, gasification/pyrolysis produces not only useful fuel gases, char and chemicals, but also some byproducts like fly ash, NOx, SO2 and tar. Tar in the product gases will condense at low temperature, and lead to clogged or blockage in fuel lines, filters and engines. Moreover, too much tar in product gases will reduce the utilization efficiency of biomass. Therefore, the reduction or decomposition of tar in biomass derived fuel gases is one of the biggest obstacles in its utilization for power generation. In this paper, we review the literatures pertaining to tar reduction or destruction methods during biomass gasification/pyrolysis. On the basis of their characteristics, the current tar reduction or destruction methods can be broadly divided into five main groups: mechanism methods, self-modification, thermal cracking, catalyst cracking and plasma methods.
Renewable and Sustainable Energy Reviews. 01/2008;
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ABSTRACT: A mathematical model (FPM) is presented to predict the transformation of heavy metals in the downstream of combustor or incinerator. The model accounts for the transformation of heavy metals through the combined effect of condensation, nucleation, coagulation, external force and thermophoresis force. The calculation of heavy metals is embodied in the post-processor appended to Fluent soft. Before the simulation, velocity, temperature, PbCl2 concentration and other initial parameters are obtained by experiment. In addition, the transformation of PbCl2 is also experimentally studied. The comparison of experimental and predicted results indicate that the fine particle model (FPM) is valid for predicting the transformation of heavy metals in the downstream of incinerator or combustor.
Journal of Environmental Science and Health Part A 03/2007; 42(2):217-24. · 1.19 Impact Factor
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ABSTRACT: In previous research, a new nonthermal plasma hybrid reactor was developed for removing SO2 from flue gas. The high efficiency and cost performance were proven through experiments. However, the research on simultaneously removing SO2 and NOx has not yet been reported. The objective of this work is to find a high-efficiency multifunctional catalyst for simultaneous removal of SO2 and NOx from flue gas. In addition, we also studied the effects of temperature and discharge power on the SO2 and NOx oxidation fraction to find the optimum operation condition. The investigated catalysts are NiO/TiO2,V2O5/TiO2, and TiO2. The discharge power varies from 9 to 15 W, and the reaction temperature range is 200−450 °C. The experimental results show that NiO/TiO2 is the best among the three catalysts. Meanwhile, temperature and discharge power have a positive influence on SO2 oxidation in the case of using NiO/TiO2, while the effects on NOx and NO are negative.
11/2006;
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ABSTRACT: The agglomeration of bed material is a serious problem during biomass combustion. In this paper, an alternative bed material (porous alumina) was used to prevent defluidization and to improve efficiency during cedar pellet combustion. During the tests, we observed that porous alumina was more difficult to agglomerate than silica sand, because of its specific properties. The volatile matter from cedar pellets mostly burned in the dense bed when the porous alumina was employed, as porous alumina captured part of the volatile matter released from the fuel pellets. Therefore, the temperature of the alumina bed was higher than that of silica sand under the same experimental conditions (fuel feed rate and air feed rate), and the temperature gradient in the freeboard region using the former was larger than that using the latter. In addition, the temperature distribution in the horizontal direction was notably uniform. When silica sand was used as a bed material, the CO concentration sharply decreased with the height in the freeboard region. In the horizontal direction, the maximum CO concentration was found in the middle of the bed. By contrast, the height of the combustor had a minor influence on the CO concentration when porous alumina was used as the bed material. Our experimental results also showed that NOx emission was not affected by the type of bed material.
10/2006;
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ABSTRACT: In this paper, two approaches are used to investigate the transformation of heavy and alkali metals during sewage sludge incineration: a thermodynamic equilibrium calculation and experiments using a bench-scale combustor. The distribution of heavy and alkali metals at different temperatures (800, 700, 600, 400, and 200 °C) is studied in these experiments. The chemical equilibrium calculation shows that vaporized metallic compounds form a condensed phase at different temperatures. The calculation results show that vaporized lead compounds begin to transfer to the solid phase at 500 °C. The main species of solid lead in the flue gas is PbCl2(s) below 500 °C. Zn and K have the same temperature range (300−500 °C), while the conversion temperature for As is 600 °C and that for Na and Cu is above 800 °C. The experimental results also prove the feasibility of separating heavy and alkali metals according to their gas−solid transformation temperature zones. On the basis of the experimental results, the optimum separation temperature is <400 °C for Pb and K, 600 °C for As, and 800 °C for Cu, Zn, and Na.
02/2006;
