摘要:

ABSTRACTThe use of refuse derived fuel (RDF) as additional fuel in multifuel fluidized bed boilers (FBC) is a promising way for rational waste management. Several combustion experiments using RDF as additional fuel have been carried out in the research program of combustion and gasification technologies in Finland under the title Liekki 2.The size of fluidized bed combustors used in these experiments ranged from 15 kWthup to 117 MWth. The chlorine content of fuel rose up to 0.35% as a measured dry base (db). The emissions of the toxic PCDD/F compounds were found to follow fuel-Cl content trendwise, as expected. However, quantitatively the relative emission levels varied with the factor of 103at the same Cl- content in fuel. Using statistical analysis correlations between PCDD/F emissions and combustion conditions (Tg, CO etc.) as well as fuel and ash properties were found.Most of the earlier measurements in commercial plants have been conducted usually after an electrostatic precipitator (ESP), which has made it difficult to relate emission results to corresponding combustion conditions. According to the laboratory scale fluidized bed reactor (15 kWth) using normal (primary and secondary) and staged (primary + secondary + tertiary) combustion air feeding, it was found that in the staged condition (higher vertical temperature profile) the total amount of PCDD/F compounds (gas and particles) decreased, but the amount of PCDD/F in solid phase increased.Although the required European emission level of PCDD/F (0.1 ng/m3nI-TEQ, in 11% O2) can be achieved, the detailed formation and destruction mechanisms of PCDD/F in combustion conditions are not known well enough for quantitative determination of the emissions.

ISSN:0882-5696    

DOI:10.1089/hwm.1996.13.1

年代:1996

数据来源: MAL

摘要:

ABSTRACTThe rapid high temperature (580-680°C) formation of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) in the heterogeneous bed region of a spouted bed combustor occurred within fraction of seconds (0.1-0.2 seconds) using two different precursors; 1,2-dichlorobenzene and 2,4-dichlorophenol. Levels of PCDD/Fs produced from 2,4-dichlorophenol oxidation were two orders of magnitude higher than those produced from 1,2-dichlorobenzene, indicating that the high temperature PCDD/Fs formation rate is much faster from chlorophenol precursors. In agreement with typical incinerator observations, the PCDDs to PCDFs ratios were less than one under all conditions. Modeling calculations were performed using gas phase mechanisms for the formation of PCDDs with chlorophenols as precursors, under the conditions existing in the high temperature bed region. A semi-empirical surface-mediated model is suggested for estimating the formation of PCDDs from chlorophenols

ISSN:0882-5696    

DOI:10.1089/hwm.1996.13.11

年代:1996

数据来源: MAL

摘要:

ABSTRACTMajor thermal decomposition products from polyvinylidene chloride (PVDC) under two pyrolysis conditions (0% O2, and 10% O2) and several different heating rates were determined. Kinetic parameters for the evolution of the major degradation products for polyvinyl chloride (PVC) and PVDC were also determined. Results showed that decomposition products formed were independent of heating rate and degradation atmosphere. Major degradation products from PVDC are HCl, dichlorinated- and trichlorinated-benzenes. Activation energies and pre-Arrhenius terms were determined for HCl and benzene for PVC and HCl, dichloro- and trichloro-benzene for PVDC.

ISSN:0882-5696    

DOI:10.1089/hwm.1996.13.23

年代:1996

数据来源: MAL

摘要:

ABSTRACTThe major concern regarding organic emissions from hazardous waste incineration systems is the formation of products of incomplete combustion (PICs). Previous studies have shed light on the mechanisms of formation and emission of PICs, showing that the formation of these by-products is highly dependent upon the local ratio of fuel and oxidant, and that their amount and composition are sensitive to both turbulent mixing and chemical kinetic constraints. PIC emissions are closely related to the fluctuations in mixture ratio that result from the turbulent mixing process. Experimental and modeling studies are carried out in order to develop a fault diagnostic system for commercial hazardous waste combustors. The experimental facility has been designed to investigate the effects of both mixing and chemical kinetics on product formation. It consists of a Toroidal Jet-Stirred Combustor (TJSC) followed by a Plug Flow Reactor (PFR). An injector positioned at the PFR entrance allows one to inject a selected species directly into the PFR. A mixture of hydrocarbons and chlorocarbons is used as a hazardous waste surrogate. Benzene is injected into the PFR in order to investigate the combined effects of turbulent mixing and chemical kinetic inhibition on PIC emissions. The development of the fault diagnostics is approached by establishing a relationship between the PIC speciation measured in the exhaust and the kinetic and/or mixing failure mode that has led to the emissions. Finally, a numerical simulation of the turbulent reacting flow is attempted by incorporating a highly simplified reaction mechanism in a commercial CFD code. Results for injection of benzene into the PFR are compared to experimental data.

ISSN:0882-5696    

DOI:10.1089/hwm.1996.13.39

年代:1996

数据来源: MAL

摘要:

ABSTRACTWe have examined the suitability of laser spark spectroscopy as a real-time,in situcontinuous monitor for toxic metals. A crucial issue forin situmonitors is the effects of ambient conditions on accuracy. Detailed measurements of the plasma parameters show that the laser-produced spark is remarkably insensitive to ambient conditions such as variations in the background gas, the presence of particles, humidity, and laser power. This is a very positive result for the field use of laser spark spectroscopy to measure toxic metals.

ISSN:0882-5696    

DOI:10.1089/hwm.1996.13.51

年代:1996

数据来源: MAL

摘要:

ABSTRACTThe volatilization characteristics of lead and cadmium were investigated by a series of experiments and theoretical analysis. The experimental part of the research included heating small amounts (approximately 3 gms) of pure metal samples to volatilization temperatures in a laboratory scale furnace and capturing the vapors by condensation and absorption. Temperatures as high as 900°C were attained during experiments. Experiments were conducted with a carrier gas flow rate between 2 lpm and 6 lpm, corresponding to mean velocities of 1.7 to 5 cm/sec. The study showed that temperature, speciation, gas flow velocity over the waste matrix, and the amount of oxygen in the gas flow were the crucial factors affecting the metal volatilization in an incinerator-like environment.Equilibrium calculations were performed to predict the lead vaporization using the chemical equilibrium code, CET89 (1). The theoretical analysis also included modeling the metal vaporization using a transport phenomena approach. The theoretical analyses were compared with experimental results.Based on the experimental analysis it was found that the volatility of cadmium depended strongly on its oxidizing environment; it volatilized more quickly when it was heated in an inert environment than in an oxidizing environment. Further, the volatility of cadmium increased when the rate of flow of the carrier gas was increased. The amounts of lead volatilized with either air or nitrogen carrier gas were below the analytical detection limits of 20 mg/l in the sample solution even with minimum dilution of the collected sample. This corresponds to a maximum of 4 mg lead vaporization during the 15 minute experimental duration

ISSN:0882-5696    

DOI:10.1089/hwm.1996.13.63

年代:1996

数据来源: MAL

摘要:

ABSTRACTConsiderable interest exists in the use of mineral-based sorbents for capturing and retaining hazardous constituent trace metals in the incineration process. The suitability of six minerals, silica, diatomaceous earth, kaolin, bauxite, alumina and attapulgite clay, as potential sorbents for the capture and immobilization of trace metals was evaluated. The behavior of five trace metals, arsenic, cadmium, chromium, lead and nickel was tested. The first five minerals constitute a spectrum of alumino-silicate compounds ranging from pure SiO2(silica) to pure Al2O3(alumina). The sixth mineral, attapulgite clay, is primarily a magnesium hydroxide-silicate compound with alumina as an impurity. It has frequently been used in trace metal related test programs at the Incineration Research Facility (IRF) as a carrier of metals and organics in blended synthetic waste streams.The objective of this test program was to evaluate the candidate sorbents with respect to:- the degree to which they facilitate retention of the trace metals in the sorbent- the degree to which they retain trace metals in the sorbent when subjected to TCLP extractionBench-scale tests were conducted in the IRF's thermal treatability unit (TTU). The test matrix was defined by varying:- mineral (sorbent) type- treatment temperature; treatment temperatures of 540°, 700°, and 870°C were tested- chlorine concentration in the feed; 0 and 4 percent by weight chlorine in the feed were testedGiven the preliminary nature of the tests the results must be viewed qualitatively. Nevertheless, overall trends indicate that under specific conditions, varying for each mineral, all of the mineral sorbents showed promise in limiting metal vaporization, and or TCLP leachability. Combining the dual criteria of limiting metal vaporization and reducing leachability, kaolin and attapulgite clay appear to have the greatest promise as potential sorben

ISSN:0882-5696    

DOI:10.1089/hwm.1996.13.73

年代:1996

数据来源: MAL

摘要:

ABSTRACTIn this work the attention was focused on the adsorption of mercuric chloride on activated carbon and on Na2S impregnated activated carbon. The study was performed in an apparatus at laboratory scale in which simulated flue gas at a given temperature and HgCl2concentration flowed through a fixed bed of adsorbent material. The experiments showed that the impregnation process definitely enhances the adsorption capacity of the carbon, and that the higher the temperature the lower the adsorption capacity, with an effect almost independent of the presence of Na2S. A possible interpretation of the experimental results is that impregnation with Na2S facilitates HgCl2capture by activated carbon, possibly by increasing the concentration of sites available for adsorption. However the heat of adsorption, which was found to be about 25 kJ/mol both for raw and impregnated activated carbon, indicates that the process taking place can be defined as a physical adsorption. The gas-solid equilibrium data were used to evaluate the Langmuir's parameters for the three different materials under investigation. The differential equations modeling the adsorption phenomenon were integrated, leading to the evaluation of a kinetic parameter describing the experimentally determined breakthrough curves.

ISSN:0882-5696    

DOI:10.1089/hwm.1996.13.95

年代:1996

数据来源: MAL

摘要:

ABSTRACTIn flue gases from coal-combustion systems, mercury in either the elemental state or its chloride form (HgCl2) can be predominant among all the possible mercury species present; this predominance largely depends on the chlorine-to-mercury ratio in the coal feeds. Conventional fluegas cleanup technologies are moderately effective in controlling HgCl2but are very poor at controlling elemental mercury. Experiments were conducted on the removal of elemental mercury vapor by means of a number of different types of sorbents, using a fixed-bed adsorption system. Of the four commercial activated carbons evaluated, the sulfur-treated carbon sample gives the best removal performance, with good mercury-sorption capacities. Promising removal results also have been obtained with low-cost minerals after chemical treatments. These inorganic sorbents could potentially be developed into a cost-effective alternative to activated carbons for mercury removal.

ISSN:0882-5696    

DOI:10.1089/hwm.1996.13.107

年代:1996

数据来源: MAL

摘要:

ABSTRACTOne approach to controlling the aerosol size distribution for a variety of applications is the use of acoustic/sonic aerosol agglomeration. Intense acoustic fields have been shown to induce large (as compared to passive processes) relative particle velocities which enhance particle collision frequencies.In this paper, the evolution of aerosol distributions in an intense acoustic field is examined. The particle size distribution is measured as a function of aerosol loading and acoustic field specification. Polystyrene foam fuel samples are burned in a static chamber with final soot mass loading of approximately 1.0 g/m3. An array of piezo-electric acoustic transducers operated at approximately 20 kHz forms one wall of the chamber.Both laser extinction and inertial impactor measurements were used to determine the effectiveness of the acoustic field in shifting the size distribution of the soot agglomerates.

ISSN:0882-5696    

DOI:10.1089/hwm.1996.13.121

年代:1996

数据来源: MAL