Dechlorination of auto shredder residues

Dechlorination of ASR (auto shredder residual) wastes has been studied in the present work. ASR was predechlorinated with Ca(OH)(2) extraction as well as dechlorinated with Ca(OH)(2) during incineration or pyrolysis. Experimentally, pre-dechlorination of ASR via extraction of Cl with a Ca(OH)(2) solution (pH 12.5) may reduce Cl contain in the ASR by 15%. Extraction of Cl at elevated temperatures (such as 373 K), interestingly, led to a further reduction of Cl in the ASR to 33.5%. A small amount of HCl and light hydrocarbons (C(1)-C(5)) were yielded during pyrolysis of the ASR in the presence of Ca(OH)(2) at 773 K. On the contrary, 75-85% of Cl may be mineralized (CaCl(2)) with Ca(OH)(2) (or CaO) during incineration at 1100 K.     

Polycyclic aromatic hydrocarbon (PAH) emissions from a coal-fired pilot FBC system

Due to the extensive amount of data suggesting the hazards of these compounds, 16 polycyclic aromatic hydrocarbons (PAHs) are on the Environmental Protection Agency (EPA) Priority Pollutant List. Emissions of these PAHs in the flue gas from the combustion of four coals were measured during four 1000h combustion runs using the 0.1MW heat-input (MWth) bench-scale fluidized bed combustor (FBC). An on-line sampling system was designed for the 16 PAHs, which consisted of a glass wool filter, condenser, glass fiber filter, Teflon filter, and a Tenax trap. The filters and Tenax were extracted by methylene chloride and hexane, respectively, followed by GC/MS analysis using the selective ion monitoring (SIM) mode. In this project, the effects of operating parameters, limestone addition, chlorine content in the coal, and Ca/S molar ratio on the emissions of PAHs were studied. The results indicated that the emissions of PAHs in an FBC system are primarily dependent on the combustion temperature and excess air ratio. The injection of secondary air with high velocity in the freeboard effectively reduces PAH emissions. The addition of extra limestone can promote the formation of PAHs in the FBC system. Chlorine in the coal can possibly lead to large benzene ring PAH formation during combustion. The total PAH emission increases with an increase in the sulfur content of coal. Incomplete combustion results in PAHs with four or more benzene rings. High efficiency combustion results in PAHs with two or three benzene rings.     

Emission characteristics of coal combustion in different O2/N2, O2/CO2 and O2/RFG atmosphere

This study investigates the emission characteristics of CO(2), SO(2) and NOx in the flue gas of coal combustion by varying the compositions and concentrations of feed gas (O(2)/CO(2)/N(2)) and the ratios of recycled flue gas. The differences between O(2)/recycled flue gas (O(2)/RFG) combustion and general air combustion are also discussed. Experimental results indicate that the maximum concentration of CO(2) in O(2)/CO(2) combustion system is 95% as the feed gas is 30% O(2)/70% CO(2). The average concentration of CO(2) in the flue gas of O(2)/CO(2) coal combustion system is higher than 90% and much higher than that of O(2)/N(2) coal combustion system. This high concentration of CO(2) is beneficial for the separation of CO(2) from the flue gas by adsorption or absorption technologies. The maximum concentration of CO(2) in O(2)/N(2) combustion system is only 34% at the feed gas 50% O(2)/50% N(2), the concentration of CO(2) is increased with the concentration of O(2) in feed gas. By O(2)/CO(2) combustion technology, higher concentration of SO(2) is produced as the feed gas is 30% O(2)/70% CO(2) or 40% O(2)/60% CO(2), while higher concentration of NOx is produced as the feed gas is 20% O(2)/80% CO(2) or 50% O(2)/50% CO(2). The mass flow rates of CO(2), SO(2) and NOx in the flue gas are all increased with the ratio of recycled flue gas except for the feed gas 20% O(2)/80% CO(2). The enhanced mass flow rates of air pollutants in such O(2)/RFG combustion system are also beneficial for improving the control efficiencies of air pollution control devices. By O(2)/N(2) combustion technology, higher concentrations of SO(2) and NOx are produced as the feed gas is 21% O(2)/79% N(2). The results also indicate that the formation of NOx in general air combustion system is higher than that in O(2)/RFG or O(2)/CO(2) combustion system.     

Physical and chemical modification of distillery sludge for Pb(II) biosorption

The waste distillery sludge from sugar-cane industry was pretreated physically (boiled, heated and autoclaved) as well as chemically (HCl, H(2)SO(4), H(3)PO(4), NaOH, Ca(OH)(2), Al(OH)(3), C(6)H(6), HCHO, CH(3)OH and C1(2)H(25)OSO(3)Na (sodium dodecyl sulphate (SDS)) for assessing the comparative sorption capacity of untreated and modified distillery sludge for Pb(II) biosorption from aqueous solutions. Experiments were conducted in shake flasks on a batch basis to access the effect of different experimental parameters such as pH, biosorbent dosage, biosorbent size, initial Pb(II) concentration and contact time. The uptake capacity 'q' (mg/g) of untreated and pretreated distillery sludge was in following order: NaOH (51.29+/-1.21)>HCl (49.82+/-1.22)>HCHO (49.56+/-1.14)>H(2)SO(4) (47.71+/-1.20)>HgCl(2) (45.32+/-1.06)>Ca(OH)(2) (44.01+/-1.18)>MeOH (43.73+/-1.23)>C(6)H(6) (42.72+/-1.19)>H(3)PO(4) (42.01+/-1.17)>SDS (40.87+/-1.27)>autoclaved (40.23+/-1.24)>Boiled (39.95+/-1.19)>heated (38.87+/-1.32)>Al (OH)(3) (38.30+/-1.14)>untreated (37.76+/-1.21). In further parameter studies, the optimized biosorbent size was 0.250 mm at pH 5 and best dose was 0.05 g of biosorbent. The applicability of the Langmuir and Freundlich models for sorption process was tested and best fitted model was Langmuir with the coefficient of determination (R(2)) value, 0.97, the process followed second order kinetic mechanism.     

燃煤电厂烟气中Hg的生成、治理、测试及排放特征研究

燃煤电厂是大气Hg排放的主要来源之一，基于文献调研，分析了燃煤电厂烟气中Hg的来源及生成、燃烧后现有设备协同脱Hg技术和吸附剂喷射脱Hg技术、主要离线测试方法、超低排放实施前后燃煤电厂烟气Hg排放特征等，指出燃煤电厂实施更严格的烟气Hg排放控制是非常有必要的，且改性活性炭、改性飞灰喷射脱Hg技术将是未来应对更严格Hg排放限值的主流技术。研究结果可为燃煤电厂烟气Hg排放控制提供参考。     

The effect of hydrogen peroxide solution on SO2 removal in the semidry flue gas desulfurization process

The present study attempts to use hydrogen peroxide solution to humidify Ca(OH)₂ particles to enhance the absorption of SO₂ to achieve higher removal efficiency and to solve the valuable reuse of the reaction product in the semidry flue gas desulfurization (FGD) process. Experiments were carried out to examine the effect of various operating parameters including hydrogen peroxide solution concentration, Ca/S molar ratio and approach to adiabatic saturation temperature on SO₂ removal efficiency in a laboratory scale spray reactor. The product samples were analyzed to obtain semi-quantitative measures of mineralogical composition by X-ray diffraction (XRD) with reference intensity ratio (RIR) method and the morphology of the samples was examined by scanning electron microscope (SEM). Compared with spraying water to humidify Ca(OH)₂, SO₂ removal efficiency was improved significantly by spraying hydrogen peroxide solution of 1–3 wt.% to humidify Ca(OH)₂ because hydrogen peroxide solution enhanced the dissolution and absorption rate of SO₂. Moreover, XRD and SEM analyses show that the desulfurization products contain less amount of unreacted Ca(OH)₂ and more amount of stable calcium sulfate with increasing hydrogen peroxide solution concentration. Thus, the process mechanism of the enhanced absorption of SO₂ by spraying hydrogen peroxide solution to humidify Ca(OH)₂ was elucidated on the basis of the experimental results.     

Wet flue gas desulphurization using a new O-element design

Scrubbing by liquid sprayingis one of the most effective processes used for removal of fine particles and soluble gas pollutants (such as SO₂, HCl, HF) from the flue gas. The primary function of venturi scrubber, which represents the first stage of the wet flue gas cleaning processes, such as in waste incineration plants, is to capture fine particles as well as remove HCl, HF or SO₂ as a result of the decrease in the flue gas temperature before entering the absorption column. In this paper, a newly developed four-branch O-element is proposed as a replacement for venturi scrubber. By means of this device, sulphur dioxide (SO₂) removal efficiency and pressure loss and temperature drop were experimentally calculated. The dependence of these variables on liquid–gas ratio was monitored. The simulated flue gas was prepared by the combustion of the carbon disulphide solution in toluene (1:1 vol.) in the presence of the flame in the reactor. Such prepared flue gas with temperature around 150 °C was processed in the laboratory-designed O-element scrubber. Water was used as an absorbent liquid. The maximal efficiency of SO₂ removal achieved by this process was up to 70 %, which is far better in comparison with the commonly used venturi scrubbers. The pressure drop of our proposed newly designed wet scrubber is similar to that of the commonly used venturi scrubbers; nevertheless, the influence of the amount of the liquid on pressure drop is not so significant. In parallel, a mathematical model describing the mass transfer, enthalpy balance and pH change of the absorbing solution was also developed. Enthalpy balance was calculated by numerical iteration to determine the unknown outlet liquid temperature. Mass transfer calculation was used for the determination of complete Henry constant from all the subsequent SO₂ absorption reactions.     

Effect of improving flue gas cleaning on characteristics and immobilisation of APC residues from MSW incineration

The flue gas cleaning system of a MSW incinerator with a capacity of 350 kt/year was changed to improve the HCl elimination efficiency. Instead of the semi-wet operating spray reactor and subsequent baghouse, a two-step wet flue gas cleaning was added behind the baghouse. Elemental composition, X-ray powder diffraction patterns and TGA measurements showed that the resulting APC residue was totally different from the former residue. As a consequence, leaching characteristics of both residues also differed and another treatment was required prior to disposal. For the former residue, mainly leaching of Pb (>100 mg/l), necessitated treatment prior to landfilling. The lower alkalinity of the new residue resulted in a leachate pH of 9.7 and a Pb concentration of 0.8 mg/l. The leachate pH of the former residue was 12.4. The leaching of Pb and Zn increased above 100 mg/l when immobilising the new residue with cement. Better results were obtained when immobilising with micro silica. The high CaCl2 x 2H2O content of the new residue brought along clogging of the bag filter system. Adding 1.4% of CaO (or 1.9% of Ca(OH)2) to the residue already improved these inconveniences but again significantly changed the leaching behaviour of the residue.     

Aspen Plus-based simulation of a cement calciner and optimization analysis of air pollutants emission

The cement industry is a typical high energy consumption and heavy pollution industry, in which amounts of CO₂, NO, NO₂, and SO₂ discharge from the pre-calciner kiln system and cause severe greenhouse and acid rain effects. Meanwhile, reasonable division of the combustion environment in the calciner is the main method to control the formation of pollutant gases. In this article, a calciner process model in Aspen Plus is proposed based on the combustion mechanism analysis of the Dual Combustion and Denitration calciner (DD-calciner) and verified by industrial data. Then, for a concrete DD-calciner, the article studies the effects of the flow rate of coal and tertiary air on flue gas compositions and effects of the staging combustion technology on the NO _x , SO₂, and CO concentrations in the flue gas. Through comparing the model results with the relevant environmental standards, the optimization analysis for staging combustion parameters of the calciner is done, and the result shows that when the proportion of tertiary air entering the pyrolysis and combustion zone is controlled within the range of 57–65.52% (0.89 < α < 1.004), all the gas pollutants emit within accepted standards simultaneously. The calciner process model outlined in this article describes the key processes of the physical and chemical reactions in the calciner. It can be used to study the key operation and design parameters which influence the flue gas constituents, so as to provide data support for determining the pollutant emission reduction plan of the cement industries with a view to reduce air pollutant emission.     

Reaction characteristics of Ca(OH)2, HCl and SO2 at low temperature in a spray dryer integrated with a fabric filter

The objective of this research was to evaluate the reaction characteristics of CaOH2, HCl and SO2 in the flue gas emitted by a laboratory incinerator. The amount of sulfur retained in the residues (including the spray dryer ash and baghouse ash) was also evaluated in this study. The experimental parameters included HCl concentration (500-2000 ppm), SO2 concentration (500-2000 ppm), relative humidity (40-80% RH), and the addition of CaCl2 (30 wt.%).The results indicated that an HCl concentration of 500-2000 ppm did not affect HCl removal efficiency in the spray dryer at 150 degrees C and 45+/-5% RH. On the other hand, increase in SO2 concentration from 500 to 2000 ppm enhanced SO2 removal at 150 degrees C and 75+/-5% RH. Moreover, increase in removal efficiency of SO2 was more obvious when the relative humidity was greater than 80%. When the flue gas contained both HCl and SO2 simultaneously, the removal efficiency of SO2 could increase from 56.7 to 90.33% at HCl concentration of 236 ppm. However, when the concentration of HCl exceeded 535 ppm, the removal efficiency of SO2 decreased with increasing concentration of HCl. The removal efficiency of SO2 could be increase to 97.7% with the addition of CaCl2.     

Numerical study of air staging in a coke oven heating system

The air staging to combustion approach introduced to a coke oven heating system as a primary method of nitrogen oxide (NO) formation reduction is considered in this paper. To numerically investigate the thermal and prompt NO formation, a heating flue model representing the most popular Polish coke oven battery was used. The model was developed and experimentally validated as a transient coupled model for the representative heating flue and the two coke ovens. Numerical simulations were performed to estimate the amount of NO passing into the atmosphere during the operation of such a heating system with and without the secondary air inlets. Various strategies for the secondary air distribution along the flue gas flow as well as the secondary air velocity were studied. The results of the numerical investigation demonstrated the substantial positive effect of the considered air staging on NO formation reduction.     

The influence of heavy metals on the formation of organics and HCl during incinerating of PVC-containing waste

The heavy metal, organic pollutants and HCl emissions from incineration pose a grave threat to human health. However, submicro metal particles and organics in gas phase are removed with difficulty by conventional air pollution control apparatus, and could be released into the atmosphere along with the flue gas. This research studied the formation of organics and HCl (hydrogen chloride) during incineration when the feedstock contained different amounts of PVC and heavy metals. The experiments were performed in a bubbling fluidized bed incinerator with two cyclones and scrubbers. Experimental results indicated that the greatest amount of organic compounds produced were aromatic compounds. The amount of organic compounds and HCl increased when the feedstock contained PVC (polyvinyl chloride), and decreased when the feedstock contained heavy metals.     

气相色谱-质谱法测定蔬菜中八氯二丙醚（S-421）的残留量

建立了蔬菜中八氯二丙醚（S-421）农药残留的气相色谱-质谱分析方法。样品采用乙腈提取,氯化钠盐析分层,取部分提取液使用氮气吹干,以正己烷溶解,加浓硫酸进行净化,最后用气相色谱-质谱法进行定量定性分析。在三个添加水平的八氯二丙醚（S-421）平均回收率（n=5）为86％～102％,相对标准偏差为3．2％～6．4％。该方法的检出限为0．005mg／kg。     

The influence of flue gas recirculation on oxy-oil combustion in an existing furnace

Oxy-fuel combustion has received increasing attention as one of the major solutions for CO₂ capture. This study aimed to obtain a better understanding on the oxy-oil firing process and to gain experience handling flue gas recirculation. A 300 kW_th multi-fuel combustion test furnace at National Cheng-Kung University in Tainan, Taiwan was chosen as the experimental facility. This experimental study had successfully converted a conventional air-fired furnace to operate on oxy-fuel firing with various operating conditions. Oxygen-enriched combustion and oxy-fuel combustion tests were conducted. The effects of oxygen enrichment, flue gas recirculation, fuel type, and thermal loading on the operational characteristics of the furnace such as temperature distribution, pressure variation, and emission characteristics were examined and discussed. Several concerns about a conventional air-fired furnace adapted for oxy-fuel combustion were scrutinized, including optimization of flue gas recirculation for better combustion efficiency, higher SO₂ concentration in the flue gas under oxy-fuel operation, and air leakage coming from negative pressure operation. These findings provided valuable data to improve the performance of oxy-fuel combustion and to allow better conceptual designs in future development.     

ANN–GA approach for predictive modeling and optimization of NOx emission in a tangentially fired boiler

An artificial neural network (ANN) and genetic algorithm (GA) approach to predict NOx emission of a 210 MW capacity pulverized coal-fired boiler and combustion parameter optimization to reduce NOx emission in flue gas, is proposed. The effects of oxygen concentration in flue gas, coal properties, coal flow, boiler load, air distribution scheme, flue gas outlet temperature, and nozzle tilt were studied. The data collected from parametric field experiments was used to build a feed-forward back-propagation neural net. The coal combustion parameters were used as inputs and NOx emission as outputs of the model. The ANN model was developed for full load conditions and its predicted values were verified with the actual values. The algebraic equation containing weights and biases of the trained net was used as fitness function in GA. The genetic search was used to find the optimum level of input operating conditions corresponding to low NOx emission. The results proved that the proposed approach could be used for generating feasible operating conditions.     

Continuous monitoring of alkali metals in gas flows using direct-current plasma excited atomic spectroscopy

A measuring instrument employing direct current (dc) plasma excited atomic line spectroscopy was developed for continuous measurement of alkali in combustion flue gases. Alkali compounds are dissociated by mixing sampled flue gas with a nitrogen plasma jet generated with a non-transferred dc plasma torch. The instrument can be used in two operating modes. The molar fraction is determined either by measuring the transmittance of the gas jet or by monitoring the emission. A tungsten halogen lamp and scanning monochromator are used for the measurement of the optical signals. Measurement of sodium and potassium has been demonstrated. The detection limits of the instrument are 50-70 ppb in the absorption mode. The detection limits are 2-3 ppb at 0.1 MPa pressure and 0.1-0.2 ppb at 1.0 MPa in the emission mode. The instrument is designed to withstand corrosive, particle laden, and pressurized flue gases at temperatures up to 1373 K.     

Catalytic effects of carbon sorbents for mercury capture

Activated carbon sorbents have the potential to be an effective means of mercury control in combustion systems. Reactions of activated carbons in flow systems with mercury and gas stream components were investigated to determine the types of chemical interactions that occur on the sorbent surface. The effects of carbon type, particle size, temperature, and reactive gases were studied. Sorption kinetics and capacities for lignite- and bituminous-based carbons were compared with those for catalytic carbons at temperatures of 107 degrees C, 150 degrees C, and 163 degrees C. In the air and baseline gas studies, the catalytic carbons exhibited far better sorption than the lignite- and bituminous-derived carbons. With the catalytic carbons, the greater sorption kinetics and capacity in an air stream or baseline gas composition compared with nitrogen provides a clear demonstration that O(2) is required in the gas stream for higher reactivities and capacities. Thus, a catalytic chemisorption mechanism predominates for the sorption of mercury at these conditions. The reaction kinetics are inversely proportional to the temperature, indicating that a preliminary physisorption step with mercury associating with a surface site is rate-determining. In synthetic flue gas streams containing HCl (50 ppm), the sorption kinetics of the catalytic carbon are slightly inferior to those of lignite-based carbon. Thus, the reaction is dominated by a different interaction, where HCl reacts with mercury on the carbon surface and the oxidation sites on the catalytic carbon apparently have no advantage. Granular and fine-particle carbons gave similar results in flue gas streams.     

Oxidation Reaction between Periodate and Polyhydroxyl Compounds and Its Application to Chemiluminescence

The oxidation reaction between periodate and polyhydroxyl compounds was studied. A strong chemiluminescent (CL) emission was observed when the reaction took place in a strong alkaline solution without any special CL reagent. However, in acidic or neutral solution, it was hard to record the CL with our instrument. It was interesting to find that in the presence of carbonate the CL signal was enhanced significantly. When O(2) gas and N(2) gas were blown into the reagent solutions, both background and CL signals of the sample were enhanced by O(2) and decreased by N(2). The spectral distribution of the CL emission showed two main bands (λ = 436-446 and 471-478 nm). Based on the studies of the spectra of CL, fluorescence and UV-visible, a possible CL mechanism was proposed. In strongly alkaline solution, periodate reacts with the dissolved oxygen to produce superoxide radical ions. A microamount of singlet oxygen ((1)O(2)*) could be produced from the superoxide radicals. A part of the superoxide radicals acts on carbonates and/or bicarbonates leading to the generation of carbonate radicals. Recombination of carbonate radicals may generate excited triplet dimers of two CO(2) molecules ((CO(2))(2)*). Mixing of periodate with carbonate generated were very few (1)O(2)* and (CO(2))(2)*. These two emitters contribute to the CL background. The addition of polyhydroxyl compounds or H(2)O(2) caused enhancement of the CL signal. It may be due to the production of (1)O(2)* during the oxidized decomposition of the analytes in periodate solution. This reaction system has been established as a flow injection analysis for H(2)O(2), pyrogallol, and α-thioglycerol and their detection limits were 5 × 10(-)(9), 5 × 10(-)(9), and 1 × 10(-)(8) M, respectively. Considering the effective reaction ions, IO(4)(-), CO(3)(2)(-), and OH(-) could be immobilized on a strongly basic anion-exchange resin. A highly sensitive flow CL sensor for H(2)O(2), pyrogallol, and α-thioglycerol was also prepared.     

An in vivo study on the reaction of hydroxyapatite-sol injected into blood

In order to identify the possibility of hydroxyapatite-sol being used as a drug carrier and absorbent, an in vivo experimental study was performed. Pure hydroxyapatite microcrystals were synthesized by reaction of high purity Ca(OH)₂ and H₃PO₄ solutions while using an ultrasonic homogenizer. Hydroxyapatite-sol was prepared by dispersing hydroxyapatite microcrystals into physiological salt solution. The hydroxyapatite-sol in different concentrations was injected into veins of both 25 Wistar rats and 5 Beagle dogs. The medium lethal dose was determined as 160 mg/kg. By observing the change of O₂ and CO₂ gas partial pressure, it was considered that the main cause of death by hydroxyapatite-sol injection was due to the blockage of capillaries. When one-sixth amount of the medium lethal dose was injected into the veins of the dogs, the value of phosphorous increased but calcium and magnesium kept stable. LDH, CPK, GOP and GDT values dramatically increased in 30 min after injection, however, one day after injection, the values returned to normal. Repeated experiments by similar methods were continued on same animals for 2 years in two-week intervals, the results in every experiment were almost same, no chronic damage or permanent side effects were discovered in the two years experiment. According to the results above, it was suggested that the hydroxyapatite-sol could be applied as a drug carrier into blood by using a small amount less than one-sixth of the medium lethal dose.     

Chromium behavior during cement-production processes: a clinkerization, hydration, and leaching study

The behavior of chromium during the production of cement clinker, during the hydration of cement and during the leaching of cement mortars was investigated. The microstructures of clinker and mortar properties were investigated using free lime, XRD, SEM/EDS, and TG/DTA techniques. Chromium was found to be incorporated in the clinker phase. The formation of new chromium compounds such as Ca(6)Al(4)Cr(2)O(15), Ca(5)Cr(3)O(12), Ca(5)Cr(2)SiO(12), and CaCr(2)O(7), with chromium oxidation states of +3, +4.6, +5, and +6, respectively, was detected. After the hydration process, additional chromium compounds were identified in the mortar matrix, including Ca(5)(CrO(4))(3)OH, CaCrO(4)·2H(2)O, and Al(2)(OH)(4)CrO(4), with chromium oxidation states of +4.6, +6, and +6, respectively. Additionally, some species of chromium, such as Cr(3+) from Ca(6)Al(4)Cr(2)O(15) and Cr(6+) from CaCr(2)O(7), CaCrO(4)·2H(2)O, and Al(2)(OH)(4)CrO(4), were leached during leaching tests, whereas other species remained in the mortar. The concentrations of chromium that leached from the mortar following U.S. EPA Method 1311 and EA NEN 7375:2004 leaching tests were higher than limits set by the U.S. EPA and the Environment Agency of England and Wales related to hazardous waste disposal in landfills. Thus, waste containing chromium should not be allowed to mix with raw materials in the cement manufacturing process.