Incineration Conditions Research Articles

Formation of PCDDs and PCDFs during the combustion of polyvinylidene chloride and other polymers in the presence of HCl

PVDC and three non-chlorinated polymers (PP, PET, and PA) were incinerated at 700–850 °C in a laboratory-scale quartz tubular furnace in the presence of HCl (ca. 500 ppm ≅ 0.8 mg/l), and the gas-phase formation of PCDD/Fs, their putative precursors and their homologue profiles were investigated. The addition of HCl had little or no apparent effect on the level of PCDD/Fs formation during PVDC combustion, and their homologue profiles were quite different from those of the three non-chlorinated polymers. With PVDC, O 8CDD and particularly O 8CDF were by far most prevalent, apparently as a result of the selective formation of the precursors. With each of the three non-chlorinated polymers, combustion at 800 °C or higher in the presence of HCl resulted in PCDD/Fs formation at levels equaling or exceeding those observed with PVDC. In trials made with one of them (PP) under the same conditions but using a large polymer sample (100 mg vs 20 mg in all other trials), the level of PCDD/Fs formation was far higher than with the smaller polymer samples, and thus demonstrated the importance of appropriate combustion conditions for polymer incineration.

Co-firing of paper sludge with high-calorific industrial wastes in a pilot-scale nozzle-grate incinerator

Experiments on the co-firing of high-calorific industrial wastes with paper sludge were performed in a pilot-scale industrial waste incinerator with a nozzle-type grate system. The incineration capacity was approximately 160 kg/h. The temporal variations in the temperatures and exhaust gas emissions were monitored and used as parameters for determining the desirable incineration conditions. The high CO emissions that were mainly due to the rapid vaporization of combustibles from high-calorific industrial wastes could be alleviated through the co-firing of sludge with the high-calorific industrial wastes. Because of the high nitrogen content in the sludge, the increase in the co-firing rate caused higher NO emissions in the flue gas. If the total calorific value of the feed was lower than 750,000 kcal/h, for 25–30% of sludge co-firing, the temperature of gases exiting the secondary combustion chamber might be lower than that required by regulations.

Thermal Treatment for Incinerator Ash: Evaporation and Leaching Rates of Metals

The disposal of different residues containing high concentrations of heavy metals causes environmental problems. To under- stand the effects of various properties of the residues on the evaporation and leaching rates of heavy metals ~Cd, Pb, Zn, Cr, and Cu! by thermal treatment, three types of residues ~including bottom ash, spray dryer ash, and baghouse ash! generated from various incineration conditions including spray dryer additives (SiO2 , CaCl2 , and NaHCO3), and feedstock additives @polyvinyl chloride ~PVC!, and NaCl# were investigated in the present study. The results indicated that the evaporation rate of Cd and Pb in the spray dryer ash and in the baghouse ash was higher than that in the bottom ash. The leaching rate of heavy metals in the spray dryer ash was less than 20% before the thermal treatment when Ca~OH)2 was used in the spray dryer. The addition of PVC could increase the evaporation rate of Zn in the spray dryer ash, whereas the addition of NaCl could decrease the leaching rate of Zn and Cu in the baghouse ash after the thermal treatment.

The Competitive Adsorption of Heavy Metals under Various Incineration Conditions.

The main objective of this study is to investigate the competitive adsorption behavior of multiple components on sorbents (silica sand with limestone) at different operating conditions (temperature, additives of chloride, operating time). Moreover, the Toxicity Characteristic Leaching Process (TCLP) analyzed the leaching rates of metals from the spent sorbents.The results show that the adsorption capacities of Pb and Cd are better among those four metals on the sorbents. At 850°C, the adsorption of Pb and Cd can reach the adsorption saturation points. However, the adsorption amounts on the sorbents will increase as the operating temperature increases. X-ray powder diffract meter (XRD) analysis revealed the adsorption components on the sorbents had metal fusion formations. The TCLP tests show that the leaching rate of metals are significantly lower at 600°C, however, as the operating temperature increases (700°C and 850°C), the sorbents became more stable. At the same temperature, increasing the operating time on the incinerator shows a decreasing leaching rate on the sorbent. Adding PVC or NaCl will decrease the adsorption amounts of Pb and Cd, but increase the leaching rates of all metals on the sorbent. Competitive effects were analyzed by comparing single-component adsorption and multiple-component adsorption cases. The result shows that a multiple-component case has a better adsorption capacity than that of a single-component case.

The simulation of condensation removal of a heavy metal from exhaust gases onto sorbent particles

A numerical model BAEROSOL for solving the general dynamic equation (GDE) of aerosols is presented. The goal was to model the capture of volatilized metals by sorbents under incinerator-like conditions. The model is based on algorithms presented by Jacobson and Turco [Aerosol Science and Technology 22 (1995) 73]. A hybrid size bin was used to model growth and formation of particles from the continuum phase and the coagulation of existing particles. Condensation and evaporation growth were calculated in a moving size bin approach, where coagulation and nucleation was modeled in the fixed size bin model of the hybrid grid. To account for the thermodynamic equilibrium in the gas phase, a thermodynamic equilibrium code CET89 was implemented. The particle size distribution (PSD) calculated with the model was then compared to analytical solutions provided for growth, coagulation and both combined. Finally, experimental findings by Rodriguez and Hall [Waste Management 21 (2001) 589–607] were compared to the PSD predicted by the developed model and the applicability of the model under incineration conditions is discussed.

Fireside Corrosion of Superheater Materials in Chlorine Containing Flue Gas

Corrosion resistance of three types of candidate materials for superheater sections under simulated waste incineration conditions was evaluated. A 9Cr1Mo steel, an AISI 310SS, and the Ni-based alloy Sanicro 28 were tested on a laboratory and on a pilot scale with different flue gas compositions (up to 2500 mg/Nm3 of HCl and 1500 mg/Nm3 of fly ash). Laboratory tests were carried out in a furnace up to 200 h. Metal and gas temperature were kept constant at 500 °C. Pilot scale tests were carried out by using a 0.3 × 0.3 m cross-sectional combustor, with flue gas velocity of 5 m/s. Air-cooled probes, designed to operate at a metal temperature of 500 °C and facing gas temperatures as high as 600 °C, were used for 200 h as maximum test time. Qualitative correspondence was found between results obtained by the two sets of experimental tests, but quantitative values were not comparable. Metallographic evaluations, metal loss measurements, and weight loss analysis evidenced as the most suitable alloy Sanicro28. Maximum metal loss observed was 240, 182, and 107 µm, respectively, for 9Cr1Mo, AISI310SS, and Sanicro 28 under the most aggressive conditions. Intergranular corrosion attack was evidenced for AISI310SS, limiting the choice of materials to 9Cr1Mo and Sanicro 28, depending upon the lifetime expected at the design stage.

Chemical kinetic modeling of de novo synthesis of PCDD/F in municipal waste incinerators

A kinetic model is developed for de novo synthesis of PCDD/F from carbon in incinerator fly ash. The main mechanistic steps considered in the model are carbon gasification, PCDD/F formation, desorption and degradation. Rate equations are derived which can relate PCDD/F formation with process variables including carbon concentration of fly ash, partial pressure of oxygen, reaction temperature and time. The kinetic model has been verified using laboratory de novo synthesis data reported in the literature. When the model is applied to industrial incinerator conditions, PCDD/F formation levels of 0.1–0.5 μg/ N m 3 in the gas phase and 0.1–1.2 μg/g in the solid phase are calculated, and both are in good agreement with incinerator measurements.

Pollutants in incineration flue gas

Previous studies have shown that pollutants from incineration include heavy metals, organic compounds, particulate and acid gas. However, most studies on a single pollutant, it is rare for a study to concentrate on all possible pollutants and the relations between these pollutants under various incineration conditions. The objective of this work was to experimentally study the effect of different operating conditions on the pollutants emitted during incineration and the relations between these pollutants. The operating conditions of the experiments included the temperature of the combustion chamber and the species of organics. The findings indicated that the concentration of hydrogen chloride (HCl) in the presence of polyvinyl chloride (PVC) was higher than that of sodium chloride (NaCl). Regardless of what Cl-containing feedstock was added, the concentration of chromium (Cr) was constant. When organic chloride was added, Cr was the main metallic element which influenced the formation of polycyclic aromatic hydrocarbons (PAHs). On the other hand, when inorganic chloride (NaCl) was added, lead (Pb) was the major element.

Chemical kinetic modelling of PCDD formation from chlorophenol catalysed by incinerator fly ash

A kinetic model is developed for PCDD formation from chlorophenol catalysed by incinerator fly ash. The key step in the model is a Langmuir–Hinshelwood type elementary step for the coupling of two adsorbed chlorophenol species to PCDD. Kinetic expression is derived which can relate PCDD formation rates with process variables including temperature, precursor concentration, fly ash loading and number of active sites in fly ash. Calculated PCDD formation rates based on this kinetic model are in good agreement with laboratory measurements reported in the literature. When the model is applied to industrial incinerator conditions, at maximum a PCDD yield of 10 −3 μg/N m 3 is calculated.

Adsorption on Carbon and Zeolite of Pollutants from Flue Gas during Incineration

The volatile organic compound, polycyclic aromatic hydrocarbon, dioxin, and metallic components released from incineration threaten human health. These pollutants, appearing in a molecular state, cannot be effectively removed by baghouse and electrostatic precipitators through capture and filtration mechanisms. Previous studies indicate that activated carbon is conventionally used to remove organic compounds from gas at low temperatures (less than 30°C). However, the adsorption characteristics of organic compounds from a gas phase at high temperatures (over 120°C) are seldom mentioned. Moreover, the complex compositions of flue gas cause the adsorption characteristics of organic compounds and heavy metals on adsorbent tubes to be more complicated. This research examines the adsorption characteristics of organic compounds and heavy metals at various incineration conditions. The evaluated parameters include: (1) the operating temperatures; (2) the characteristics of adsorbents (activated carbon and zeolite); and (3) waste compositions and the presence of heavy metals. The results indicate that activated carbon has a high adsorption capacity compared with zeolite.

Influence of Operating Conditions on the Formation of Heavy Metal Compounds During Incineration

ABSTRACT The formation of Cr, Pb, and Cd species under various operating conditions in a pilot-scale fluidized-bed incinerator was investigated. Examined were the effects of (1) an organic chloride (PVC) additive, (2) an inorganic chloride (NaCl) additive, and (3) NaNO3 and PVC additives, under various operating temperatures. Two-stage modeling was performed to match the actual incineration conditions of the current study. Thermodynamic equilibrium analysis indicated that Cr2O3, PbCl2, and CdCl2 were the dominant species of Cr, Pb, and Cd when an organic chloride (PVC) was present, whereas PbO and CdO were the dominant species under the other operating conditions. The XRD analysis identified Cr2O3, PbCl2, and CdCl2»H2O as the dominant species of Cr, Pb, and Cd when an organic chloride (PVC) was present, whereas Cr2O3, PbO, Pb2O3, CdO, and CdCO3 were identified under the other operating conditions. The sodium contained in the feedstock was shown to react with chlorine to form sodium chloride both in modeling results and by X-ray diffraction (XRD) analysis. The temperature of the operating conditions had little effect on the formation of heavy metal species.

使用施設における可燃性固体RI試料の焼却減容

We want to establish a system of volume reduction by the incineration of the combustible radioactive solid wastes from radioisotope usage at the utilization facility. We have been performing experiments using an experimental incineration system to examine the distribution of radionuclides during incineration and to collect basic data. To reproduce the realistic conditions of incineration of low-level radioactive wastes in an experimental system, we adopted new incineration methods in this study. Low level radioactive samples (LLRS) were set up in a mesh container of stainless steel and incinerated at high temperature (over 800•Ž) generated by two sets of high calorie gas burners. Low energy ƒA-emitters 35S, 45Ca, 33P, and a high energy ƒA-emitter 32P were used for the experiment. Their translocation percentages in exhaust air and dust were estimated using the Imaging Plate. Distribution of radionuclides during the incineration was similar to that estimated by conventional methods by our study or to that reported in incineration of liquid scintillation cocktail waste. We concluded that the use of the Imaging Plates is a simple and reliable method for estimation of the distribution of low energy ƒA-emitters in incineration gas and ash.

The adsorption of heavy metals by different sorbents under various incineration conditions

The emission of heavy metals can be controlled by adding solid sorbents into the combustion chamber during incineration processes. The objective of this work was to experimentally study the adsorption efficiency of different sorbents for heavy metals under various incineration conditions. Each sorbent has its optimum operating temperature. Kaolinite and aluminum oxide have the best adsorption efficiency at 800°C, and bauxite is at 700°C. The adsorption efficiencies of the three sorbents for the four heavy metals all follow the sequence of Pb > Cu > Cr >Cd. The presence of inorganic chloride (NaCl) and sulfate (Na 2SO 4) increases the adsorption efficiency of the sorbents, but organic chloride PVC decreases the adsorption efficiency.

The Major Species of Heavy Metal Aerosol Resulting from Water Cooling Systems and Spray Dryer Systems during Incineration Processes

ABSTRACT Trace toxic metals in municipal solid waste may escape from the incineration process in flue gas, in dry collected ash, in wet scrubbed ash, or as a suspended aerosol. Therefore, understanding the behavior of heavy metals in the flue gas and the best controls in the air pollution control equipment are important and necessary. The control conditions of water cooling and spray dryer systems during incineration processes significantly influence the formation of heavy metal compounds. The formation of chromium (Cr), lead (Pb), and cadmium (Cd) species under various control conditions (water cooling tower and spray dryer reactor) was investigated in this study. The object of the experiment is to understand the effects of water cooling and spray dryer systems individually on the formation of heavy metal species. The operating parameters that are evaluated include different control systems, control temperatures, and chlorine content. A thermodynamic equilibrium model was also used to evaluate experimental data. In order to match real incineration conditions, a two-stage simulation was performed in this experiment. The results showed that the relationship of speciation between the simulation prediction and X-ray diffraction (XRD) analysis is consistent for Cr compounds; both indicated that Cr2O3 is the major species. The relationship is almost the same for Cd compounds, but not for Pb compounds.

Two-stage simulation of the major heavy-metal species under various incineration conditions

A thermodynamic equilibrium model was used to determine the major species of chromium, lead, cadmium, copper, and zinc formed under various incineration conditions. The effects of temperature and oxygen, chlorine, sulfur, and hydrogen content on the speciation were established by the minimum Gibbs free energy method. Sixty-seven compounds of five metallic species were determined in this study. The simulation conditions included: 1) single metal with oxygen, chlorine, and sulfur system; 2) different chlorine and hydrogen content; and 3) comparisons of a single combustion chamber and a two-stage combustion chamber. The simulation results indicated that the oxides were the dominant forms in a single metal-oxygen system, while the metallic chlorides were the major species in a metal-chlorine-oxygen system. When sulfur was present, in the case of all metals other than Pb, the metallic sulfates were the major species at temperatures below 1000 K, and metallic oxides were the dominant species above 1000 K. Increasing the temperatures caused a decrease of lead chloride, but increased the formation of other metallic chlorides. The concentrations of metallic chlorides decreased significantly as the hydrogen moles were 2∼3 orders higher than those of chlorine. The level of difference between one-stage and two-stage simulations depends on the species formed in the one-stage simulation.

The simulation of hexavalent chromium formation under various incineration conditions

The formation of hexavalent chromium Cr(VI) during waste incineration processes is of interested because its carcinogenic characteristic. The objective of this study is to simulate the formation of Cr(VI) species under various operating temperatures and input waste compositions during incineration by a thermodynamic model. The results show that the major hexavalent chromium species are CrO 2Cl 2(g) and CrO 3(g). Chlorine and oxygen can increase the formation of Cr(VI) species; while hydrogen, sulfur, sodium, and calcium can inhibit. The input waste composition has greater effect on the formation of hexavalent chromium species than operating temperature

Emissions of organic compounds from biofuel combustion and influence of different control parameters using a laboratory scale incinerator

This study aimed at spanning the range of different wood combustion conditions by varying primarily load and airfeed in a controlled fashion, thereby investigating different combustion situations in this system. This was done using an experimental design. The aim was to see how these parameters effected organic emissions of PCDD/F, PCBz and PAH and to what extent their formation could be explained by means of the control parameters and other measured data. These data include inorganic combustion gases such as CO 2 and NO and temperatures in the reactor. The results show that under the incineration conditions examined the organic emissions did vary but not in a way explainable by the parameters used here. Two samples were taken in parallel at different locations, before and after the convector region. The formation of PCDD/F and PCBz in the convector could be noted, suggesting similar mechanisms of secondary de novo formation for the two compound classes. This formation is significant, in some experiments up to 1000 % higher than at the furnace exit. Also when using a fuel with bark mixed into it the increase was ten fold.

Mass and Elemental Size Distribution of Chromium, Lead and Cadmium under Various Incineration Conditions.

The main objective of the present study was to investigate the effect of the operating temperature (both sand bed and freeboard) and various chlorine additives (organic or inorganic) on the mass and elemental size distributions of heavy metal Cr, Pb and Cd during fluidized bed incinerasion. The results showed that higher freeboard temperature and additives of PVC, NaCl, and CaCl2 appeared to shift the particles to a finer distribution. The addition of NaCl is more effective in reducing particle size as compared to increase the freeboard temperature or the addition of PVC owing to its mechanism of reduction in particle size. The metal concentration of size segregated coarse particles (5–125 μm) are irregular. But in fine particles (0.1–15.72 μm), the concentration of Pb, Cd is higher in the finer particles.

Thermal Formation of Polychlorinated Dibenzo-p-dioxins and -furans: Investigations on Relevant Pathways

ABSTRACT The recent status of the relevant formation of polychlorinated dibenzo-p-dioxins and -furans (PCDD/F) in technical incineration processes is discussed. Within this discussion, the competition experiments for the alternative pathways, de novo, and precursor reactions are critically evaluated. The results suggest that the precursor mechanism is dominant under conditions of municipal waste incineration (MWI). Results of field observations support this primary hypothesis. Chloroaliphatic compounds such as dichloroacetylene are responsible for the formation of higher or perchlorinated aliphatic and aromatic compounds and precursors in thermal PCDD/F formation. The meaning and implications of indicator compounds for PCDD/F are also evaluated. Observed correlation among interrelated classes of chloroaromatic compounds can be explained by stationary reaction equilibrium in the postcombustion zone of incinerators in the presence of fly ash surfaces (i.e., by heterogeneous catalysis). Recent findings on th...

Equilibrium analysis of the affect of temperature, moisture and sodium content on heavy metal emissions from municipal solid waste incinerators

An equilibrium analysis was performed to determine the impact of the variations in the moisture and sodium contents in the solid waste feed on heavy metal speciation in municipal solid waste (MSW) incinerators. This analysis was based on the speciation of heavy metals among chlorides, oxides and other species under various incinerator conditions. The Gibbs free energy of the reaction mixture was minimized by the method of chemical potentials combined with atom population constraints using a thermodynamic equilibrium computer code. Fifty eight species were considered, including compounds of six trace metals, aluminum, cadmium, chromium, mercury, sodium, and lead. Changes in the moisture and sodium contents in the feed waste were found to significantly impact the speciation of heavy metals among chloride and oxide species. Estimates have been carried out on the impact of these speciation changes on the bottom ash, fly ash and flue gas emissions of heavy metals. The results indicate that, at the typical municipal incineration temperature of 950°C, a decrease in the waste moisture content from 37% to 5% results in a modest increase in the percentage of the lead in the fly ash from about 54% to 68% of the total. Similarly, a decrease in the waste sodium content from 6560 ppm (upper limit for MSW content) to 4500 ppm (MSW average) results in a more significant increase in the percentage of lead in the fly ash from 36% to 60% at the average waste moisture content. Several other heavy metals have also been studied, but the impacts are much smaller. A qualitative discussion and resulting implications of environmental impact due to the shifts in lead speciation are discussed.