Chun-Teh Li

PAH emission from the incineration of waste oily sludge and PE plastic mixtures

A batch-type, controlled-air incinerator was used for the treatment of oily sludge and polyethylene (PE) plastic mixtures. The concentration and composition of 21 individual PAHs (polycyclic aromatic hydrocarbons) in the raw wastes, flue gas (gas and particle phases) and ash were determined. Stack flue-gas samples were collected by a PAH stack-sampling system. Twenty one individual PAHs were analyzed primarily by a gas chromatograph and a gas chromatography/mass spectrometer. Due to incomplete combustion, PAH content in the feeding wastes have a strong influence on PAH emission in both stack flue gas and ash residue. With the oily sludge in the feeding waste mixtures, the input mass of lower molecular weight PAHs — Nap, AcPy, Acp, Flu, PA, Ant and FL — was contributed mainly by liquid diesel, while the input mass of higher molecular weight PAHs — Pyr, CYC, CHR, BbF, BkF, BeP, BaP, PER, IND, DBA, BbC, BghiP and COR — was primarily contributed by the oily sludge. For the distribution of individual PAH mean output mass, lower molecular weight PAHs — Nap, AcPy, Acp and Flu — have > 87% of their mass discharged by the stack flue gas. However, the higher molecular weight PAHs — Ant, FL, CHR, BbF, BeP, BaP, PER, IND, DBA, BbC, BghiP and COR — have significant mass fractions (>18%) discharged by the ash residue. The total-PAH output/input mass ratios were between 0.00103 and 0.00360 and averaged 0.00203. This result indicated that the depletion of PAH mass in the combustion process was very significant. The PAH content in the fuel during the combustion process is the control factor of PAH emission. The co-combustion of oily sludge with plastic is a potential method of reducing the PAH emission and of saving the consumption of auxiliary fuel.

PAH emission from the incineration of three plastic wastes.

A batch-type, controlled-air incinerator was used for the treatment of polyvinyl chloride (PVC), high-density polyethylene (HDPE), and polypropylene (PP) plastic wastes. The concentration and composition of 21 individual polycyclic aromatic hydrocarbons (PAHs) in the raw wastes, flue gas (gas and particle phases), and ash were determined. Stack flue-gas samples were collected by a PAH stack-sampling system. Twenty-one individual PAHs were analyzed primarily by a gas chromatograph/mass spectrometer (GC/MS). The CO concentration correlated well with the total PAH (R2 > .89), and thus can be used as a surrogate indicator for PAH emission. Excess amounts of air supply in the incineration of plastic wastes could decrease not only the concentration of the PAHs in the bottom ash but also the emission factor (EF) of the total PAH in the stack flue gas. Of the three plastic wastes, HDPE was found to have the highest mean EF of the total PAHs (462.3 mg/kg waste) from the stack flue gas. Incinerating PVC would result in a higher EF of PAHs (195.4 mg/kg waste) in the bottom ash. When PVC plastic wastes were incinerated, higher-ringed PAHs constituted a larger percentage in the bottom ash as compared to those from PP and HDPE plastics. By judging the output and input (O/I) ratio of the PAHs from the incineration trials of plastic wastes, the PAHs involved in incineration of three plastic wastes were almost entirely destroyed; and a low residual amount between 0.00018 and 0.00032 remained in the emission.

PAH emission from the industrial boilers

Polycyclic aromatic hydrocarbons (PAHs) emitted from 25 industrial boilers were investigated. The fuels used for these 25 boilers included 21 heavy oil, two diesel, a co-combustion of heavy oil and natural gas (HO+NG) and a co-combustion of coke oven gas and blast furnace gas (COG+BFG) boilers. PAH samples from the stack flue gas (gas and particle phases) of these 25 boilers were collected by using a PAH stack sampling system. Twenty one individual PAHs were analyzed primarily by a gas chromatography/mass spectrometer (GC/MS). Total-PAH concentration in the flue gas of 83 measured data for these 25 boiler stacks ranged between 29.0 and 4250 microg/m(3) and averaged 488 microg/m(3). The average of PAH-homologue mass (F%) counted for the total-PAH mass was 54.7%, 9.47% and 15.3% for the 2-ring, 3-ring and 4-ring PAHs, respectively. The PAHs in the stack flue gas were dominant in the lower molecular weight PAHs. The emission factors (EFs) of total-PAHs were 13,300, 2920, 2880 and 208 microg/kg-fuel for the heavy oil, diesel, HO+NG and COG+BFG fueled-boiler, respectively. Nap was the most predominant PAH occurring in the stack flue gas. In addition, the EF of 21 individual PAHs in heavy-oil boiler were almost the highest among the four various fueled-boilers except for those of FL and BkF in the diesel boiler. Furthermore, the EF of total-PAHs or BaP for heavy oil were both one order of magnitude higher than that for the diesel-fueled boiler.

Decomposition of carbon dioxide in the RF plasma environment

Application of radio-frequency (RF) plasma as an alternative technology for the decomposition of carbon dioxide with methane gas is demonstrated. The results of this study revealed that in CO2/CH4/Ar plasma, the best decomposition fraction of carbon dioxide was 60·0%, which occurs around 316°C in the condition designed for 5% feeding concentration of CO2, 5% feeding concentration of CH4, 20 torr operation pressure, 100 sccm total gas flow rate and 90 watts input power wattage. The CH, CH2 and CH3 radicals obtained from the destruction of CH4 could result effectively in high decomposition of CO2 in the plasma reactor. The optimal mathematical models based on the experimental data obtained were also developed and tested by means of sensitivity analysis, which shows that the input power wattage (W) was the most sensitive parameter for the CO2 decomposition.

CH2Cl2 decomposition by using a radio-frequency plasma system

In this study, a radio-frequency plasma system was used to decompose a dichloromethane (CH 2 Cl 2 ) containing gas. Analyses of the reactants and final products were conducted by using Fourier Transform Infrared Spectroscopy. Then, the effects of plasma operation-parameters, including the gas flow rate, the feeding CH 2 Cl 2 concentration, the equivalence ratio Φ (=stoichiometric O 2 needed/actual O 2 used) and the input power wattage, for CH 2 Cl 2 decomposition and for the fraction of total carbon input converted into CO 2 and CO were investigated. Mole fraction profiles for each experimental condition were determined for the reactants (CH 2 Cl 2 and O 2 ) and for CO, CO 2 , H 2 O, HCl, CHCl 3 , CCl 4 , COCl 2 , C 2 HCl 3 and C 2 Cl 4 . In addition, the possible reaction pathways were built up and discussed.

PAH emission from waste ion-exchange resin incineration

A batch-type, controlled-air incinerator was used for the treatment of three kinds of waste ion-exchange resin. The concentration and composition of 21 individual PAHs (polycyclic aromatic hydrocarbons) in raw material, flue gas (gas and particle phases) and ash were determined. Stack flue-gas samples were collected by a PAH stack-sampling system. Twenty one individual PAHs were analyzed primarily by gas chromatography (GC) and a gas chromatography/mass spectrometer (GC/MS). The total-PAH concentration in flue gas and its composition in ash averaged 1782 μg/m3 and 6.00 μg/g, respectively. Phase distribution of the total-PAHs in the flue gas was mainly in the gas phase (92%) with a mean-concentration of 1640 μg/m3, while the total-PAH concentration in the particle phase (averaged 42 μg/m3) only represented a small fraction (9%) of the total-PAH mass collected. The PAH concentration in the stack flue-gas averaged ∼ 990 orders of magnitude higher that that in the ambient air. Phase distribution of the total-PAHs in the flue gas was very similar to that in the ambient air, being primarily in the gas phase. For the individual PAHs, lower molecular weight PAHs were dominant in the gas phase, while higher molecular weight PAHs were associated with the particulate. Of the PAHs from three input sources (diesel, ambient air and waste ion-exchange resins) entering the incinerator, diesel was found to contain the highest total-PAH mass fraction (averaging 99.5%). For PAH output-mass distribution from the incineration, lower molecular weight PAHs were primarily emitted by the stack gas phase, while higher molecular weight PAHs were discharged at a significant fraction by flue-gas particulate and ash. The blank-incineration results of diesel combustion showed that most of the PAHs in the diesel had been destroyed during the combustion process and that there was, therefore, a significant fraction of PAH emission due to the thermal-synthesis process during the waste ion-exchange resin combustion.

Reaction mechanism of 1,2-dichloroethane/O2/Ar in the cold plasma environment

Dichloroethane (EDC) is known to be hazardous to the environment and public health. In this study, application of radio frequency (rf) plasma as an alternative technology for the decomposition of EDC was demonstrated. The species detected in the effluent gas stream included CO2, CO, HCl, CCl4 ,C 2HCl3 ,C 2H3Cl, C2Cl4, CHCl3 ,C 2HCl5, COCl2 ,C 2H2 ,C 2H4 ,C 2H6, and HCOOH. The decomposition fraction of EDC (ηC2H4Cl2 ,( Cin − Cout)/Cin × 100 (%)) was dependent on input power. When input power was 80 W, stable products such as CO, CO2, and HCl were dominant and other product species were inhibited. Equivalence ratio (ϕ = (C2H4Cl2/O2)actual × (O2/C2H4Cl2)stoichiometric) was the other important operational parameter in a plasma system. When the chlorocarbon/oxygen flow was fuel rich, more soot formation was found in the plasma reactor. When it was fuel lean, CO2 and CO dominated over other product species. Within the mixture of EDC and dichloromethane (DCM), the competition of DCM with EDC could affect the decomposition fraction of EDC.