A numerical simulation of hazardous waste destruction in a three-dimensional dump incinerator

A predictive model of carbon tetrachloride (CC1₄) incineration in a dump incinerator is described. An empirical model that incorporates the chemical kinetic aspects of CCl₄ destruction is developed to describe the flame inhibition characteristics of CC1₄, which is halogen compounds. Quantitative agreement is found between the predictions of the model and the measured values. Cavity hydrodynamics and flame structure studies are made in a dump incinerator proposed in this study. For the effective destruction of hazardous waste, the waste must injected in the recirculation region of high temperature with the condition of not disturbing the combustion cavity. The core flame has a significant impact on the structure of the recirculation region, in some cases completely changing the nature of the flow within the cavity. The dump incinerator has good characteristics for the destruction of hazardous waste. These characteristics should lead to a very compact device, one which is potentially transportable or usable in a dedicated manner by a small generator.     

Effects of fuel devolatilisation on the combustion of wood chips and incineration of simulated municipal solid wastes in a packed bed

Detailed mathematical simulations as well as experiments have been carried out for the combustion of wood chips and the incineration of simulated municipal solid wastes in a bench-top stationary bed and the effects of devolatilisation rate and moisture level in the fuel were assessed in terms of ignition time, burning rate, reaction zone thickness, peak flame temperature, combustion stoichiometry and unburned gas emissions at the bed top. It is found that devolatilisation kinetic rate has a noticeable effects on the ignition time, peak flame temperature, CO and H₂ emissions at the bed top and the proportion of char burned in the final stage (char burning only) of the combustion. However, it has only a minor effect on the other parameters. Reaction zone thickness ranges from 20 to 55 mm depending on the moisture level in fuel and an increase in the moisture level causes a shift of the combustion stoichiometry to more fuel-lean conditions.     

超临界水热燃烧技术研究及应用进展

超临界水热燃烧技术作为一种新型的高效清洁燃烧技术,为实现有机废物处理、稠油资源高效开发、煤基固体燃料清洁转化利用、新型钻井技术开发及劣质燃料品质提升等提供了一条崭新的途径,具有广阔的发展前景。本文概述了超临界水热燃烧的提出、发展历程及其技术优势,评述了不同燃料的水热火焰特性、水热燃烧反应器形式以及水热燃烧技术工程应用方面的研究现状。指出对于特定燃料,水热燃烧反应器具有较低的燃料熄火温度是提高反应器内水热火焰稳定性的关键。水热燃烧反应器开发过程中水热火焰区的结构布置需综合考虑蓄热需求与反应器壁面安全。水热火焰特性与超临界水中传热传质的耦合机制、水热燃烧过程数值模拟、光-超临水-氧气复杂环境下的材料腐蚀特性、水热火焰辅助降解有机废物、生产多元热流体辅助稠油开采、煤基固体燃料的水热燃烧是超临界水热燃烧领域未来研究热点。     

乙醇浓度和应变率对扩散火焰特性的数值分析

研究液体燃料乙醇对冲燃烧的火焰特性是理解扩散火焰形成和指导乙醇对冲燃烧器设计的关键。采用对冲扩散火焰模型,结合光学薄辐射模型,模拟空气与氮气稀释下乙醇形成的扩散火焰,探讨了乙醇浓度和应变率对扩散火焰的火焰结构、温度分布和温度峰值处的温度敏感性的影响规律。结果表明：随着乙醇浓度的增加,CO和H₂反应区域向燃料侧移动,火焰区域变宽,火焰温度峰值逐渐升高,升高趋势渐缓,中间产物和CO对温度敏感性的影响减弱;随着应变率的增加,自由基和CO增多,中间产物减少,组分的分布区域和火焰区域变窄,火焰温度峰值逐渐降低,中间产物和CO对温度敏感性的影响逐渐增强。     

Emission of Polycyclic Aromatic Hydrocarbons (PAH) from Solid Waste Incinerator Equipped with an After-Combustion Chamber

Abstract

Polycyclic aromatic hydrocarbons (PAH) are typical indicators of incomplete combustion during solid waste incineration. The PAH emissions caused by waste incineration vary according to waste composition and operating parameters such as furnace temperature, after-combustion conditions, excess air, carbon monoxide levels.

In this work, the content of PAH in the fly ashes (sampled upstream the flue gas treatment system) and bottom ashes produced by the combustion of a refuse derived fuel (RDF) in a rotary kiln incinerator equipped with an after-combustion chamber is determined. The emission levels of PAH are correlated with different operating conditions of the incinerator to evaluate the destruction efficiency of the after-combustion chamber for these compounds.     

Correlations between pyrolysis combustion flow calorimetry and conventional flammability tests with halogen‐free flame retardant polyolefin compounds

Seven halogen‐free flame retardant (FR) compounds were evaluated using pyrolysis combustion flow calorimetry (PCFC) and cone calorimetry. Performance of wires coated with the compounds was evaluated using industry standard flame tests. The results suggest that time to peak heat release rate (PHRR) and total heat released (THR) in cone calorimetry (and THR and temperature at PHRR in PCFC) be given more attention in FR compound evaluation. Results were analyzed using flame spread theory. As predicted, the lateral flame spread velocity was independent of PHRR and heat release capacity. However, no angular dependence of flame spread velocity was observed. Thus, the thermal theory of ignition and flame spread, which assumes that ignition at the flame front occurs at a particular flame and ignition temperature, provides little insight into the performance of the compounds. However, results are consistent with a heat release rate greater than about 66kW/m² during flame propagation for sustained ignition of insulated wires containing mineral fillers, in agreement with a critical heat release rate criterion for burning. Mineral fillers can reduce heat release rate below the threshold value by lowering the flaming combustion efficiency and fuel content. A rapid screening procedure using PCFC is suggested by logistic regression of the binary (burn/no‐burn) results. Copyright © 2008 John Wiley & Sons, Ltd.     

磷酸三苯酯和甲基八溴醚在阻燃聚苯乙烯中的协同行为研究

为获得基于甲基八溴醚（MOBE）的高效阻燃聚苯乙烯（PS）复合体系,采用极限氧指数仪、锥形量热仪、热重分析仪（TG）和差示扫描量热仪（DSC）等对纯PS及其复合材料的阻燃性能及机理和热稳定性等进行了测试和表征,探索了MOBE与磷酸三苯酯（TPP）复配阻燃PS的行为规律。结果表明,TPP和MOBE复合体系比二者各自单独作为阻燃剂使用时赋予了PS材料更高的极限氧指数（LOI）,PS/3 %（质量分数,下同）TPP/4 %MOBE的LOI可达27.7 %, 明显高于PS/4 %MOBE（26.1 %）;3 %TPP/4 %MOBE能够在4 %MOBE的基础上进一步抑制PS复合材料的燃烧强度,降低有效燃烧热,降低热释放速率峰值（PHRR）与总热释放量（THR）;TPP和MOBE能够在PS复合材料热降解时将阻燃元素集中释放,同时发挥气相淬灭效应;此外,TPP的加入能够提高PS复合材料的熔体流动速率,降低其玻璃化转变温度,从而使PS热分解产生的熔滴更快地带走热量,最终使TPP与MOBE发挥更好的阻燃效果。     

氯代烃燃烧特性研究综述

氯代烃燃烧特性是用焚烧法处理化工有机废液的重要基础,氯代烃高温分解的化学反应机理和动力学参数则是深刻了解和模拟其燃烧过程的前提。通过总结国内外相关研究工作,介绍了含氯有机废液的主要处理方法,重点分析了氯代烃燃烧过程中氯对液滴燃烧的抑制作用和不完全燃烧产物的排放特性与控制技术,讨论了2种主要的研究氯代烃燃烧反应机理的方法,对测定相关基元反应动力学参数的研究工作的现状也作了介绍,分析指出了一些有待进一步研究的问题。     

高温燃烧过程中Cr的氧化机理及控制方法

Cr作为一种有害元素广泛地存在于化石燃料、生活垃圾和工业固体废物中。其中,化石燃料、相当大部分的生活垃圾以及一部分的工业固体废物都通过燃烧过程来回收能量或者进行减容和无害化处理。因此,通过燃烧过程人类向自然界中排放了大量的Cr。最重要的是,热处置过程中的高温氧化环境容易使低迁移性和毒性的Cr（Ⅲ）氧化为高迁移性和毒性的Cr（Ⅵ）。所以,热处置过程中Cr的反应、行为以及产物中Cr的存在形态得到了越来越多的研究。本文综述了燃料中Cr的存在形态、燃烧过程中Cr的氧化机理、燃烧过程中Cr氧化的控制方法以及燃烧产物中Cr的固化方法四方面内容,为减少燃烧过程中的Cr对环境的危害提供理论基础。     

Heterophase combustion of silane near the first ignition limit

Heterophase combustion of silane near the first ignition limit was studied. It was found that the reaction of chain initiation on quartz in the zone of hydrogen and silane combustion manifested itself as positive feedback, which was enhanced during exposure of the reactor walls to the products of the low-pressure flame. It was shown that, in a silane-oxygen flame at a temperature of 350–500°C the quartz surface was activated as a catalyst of heterogeneous chain initiation much more strongly than it was in a hydrogen flame. It was shown that the previously found increase in the concentration of atomic hydrogen during oxidation of silane in oxygen below the first limit was related to the formation of new lattice structures saturated with crystal lattice defects, whose number on the wall increases continuously during condensation of the final reaction products, together with adsorption silicon-containing radicals.     

染料残渣焚烧过程中微量元素的形态转化及其迁移分配的预测

The release of heavy metals from the combustion of hazardous wastes is an environmental issue of increasing concern. The species transformation characteristics of toxic heavy metals and their distribution are considered to be a complex problem of mechanism. The behavior of hazardous dyestuff residue is investigated in a tubular furnace under the general condition of hazardous waste pyrolysis and gasfication. Data interpretation has been aided by parallel theoretical study based on a thermodynamic equilibrium model based on the principle of Gibbs free energy minimization. The results show that Ni, Zn, Mn, and Cr are more enriched in dyestuff residue incineration than other heavy metals （Hg, As, and Se） subjected to volatilization. The thermodynamic model calculation is used for explaining the experiment data at 800℃ and analyzing species transformation of heavy metals. These results of species transformation are used to predict the distribution and emission characteristics of trace elements. Although most trace element predictions are validated by the measurements, cautions are in order due to the complexity of incineration systems.     

Investigations on MCM-41 as a fume catalytic incinerator: a heptane case study

This study shows that mesoporous MCM-41 compounds, that have hexagonal-close-packed channels, are good candidates as micro-reactors for fume catalytic incineration reactions. MCM-41 is synthesized and used as a catalyst to incinerate normal heptane (nC7) at different temperatures and equivalence ratios (ϕ). Destruction and removal efficiency (DRE, 99.99%) of heptane is achieved at 500 °C and ϕ=0.85 using MCM-41 as a catalyst compared to 73.45% under the same conditions without the catalyst. Even 99.9% DRE of heptane is achieved at 450 °C. The number and quantity of some analyzed products of incomplete combustion (PIC) are dramatically decreased when using MCM-41 material. No coke formation occurs.Under fuel-rich conditions, virtually complete consumption of oxygen molecules occurred at 450 °C when using MCM-41 compared to 75% in thermal incineration at the same conditions.While MCM-41 improves DRE at high temperature, e.g. 450 °C, it worsens it dramatically at lower ones, e.g. 300 °C. This inhibition of destruction effect depends also on the equivalence ratio of the mixture. It seems that diffusion properties and the chromatographic effect of MCM-41 channels become important at low temperatures.The enhanced DRE of heptane, upon using MCM-41, at relatively low temperatures, 450 °C, suggests that MCM-41 channels act as nano-vessels for free radical incineration reactions rather than a meter-scale incineration chamber as in the case in thermal incineration processes.     

Conversion of fuels containing nitrogen to oxides of nitrogen in hydrogen and methane flames

Nitrogen-containing compounds such as hydrogen cyanide, acetonitrile, acrylonitrile, pyridine, benzonitrile, ammonia and methylamine, which are typical of the products likely to be encountered during the decomposition of nitrogen-containing polymers in fires, have been introduced into hydrogen and methane flames burning in oxygen-argon atmospheres. There is a complete conversion of fuel nitrogen in all cases to oxides of nitrogen and molecular nitrogen. The relative conversion to oxides of nitrogen (as NO_x/N₂) increases as the injection rate of nitrogen-containing fuels is decreased. The relative yields of oxides of nitrogen tend to be similar with methane and hydrogen premixed flames and markedly greater than observed with hydrogen diffusion flame. In all cases the yield of oxides of nitrogen-containing products such as hydrogen cyanide can also present a toxic risk during the burning of nitrogen-containing polymers, particularly when high temperature are involved. The combustion of these products in flame zones cannot be assumed to alleviate the additional toxic risk because of their conversion to oxides of nitrogen.     

Impact of co-firing coal and biomass on flame characteristics and stability

This paper presents the use of vision-based measurement techniques for the on-line monitoring and characterisation of coal-biomass co-firing flames on an industrial-scale combustion test facility. The characteristic parameters of the flame, including ignition points, brightness, temperature and oscillation frequency, are measured using a vision-based flame monitoring system in an on-line continuous mode. A common type of pulverised coal was fired with five different types of biomass for different proportions ranging from 0% to 20% by weight. Various combustion conditions were created during the test runs, including variations in excess air and the method of biomass injection. The relationships between the flame characteristics and the primary combustion process data are analysed. The results suggest that, due to the varying physical and chemical properties of the biomass fuels, the biomass additions impact on the characteristics of the flame, particularly the flame ignition points and brightness. However, in all cases studied, the flame stability has been found to be little affected by the amount of biomass added provided that the addition is no more than 20%.     

One‐sided flame spread phenomena of a thermally thin composite cotton/fiberglass fabric

As an experimental necessity, past flame spread studies have relied on fast burning cellulosic papers. For the longer duration tests planned for the International Space Station a 50% fiberglass, 50% cotton composite fabric is better suited for the novel fuel feeding system in the compact hardware design of a current microgravity combustion experiment. The fabric's combustion characteristics in normal gravity include unexpected cases where a flame can be sustained on one side of the fuel. One‐sided flames are smaller in size than their two‐sided counterparts, and propagate at half the speed. Surface temperature distributions were measured using infrared imaging and indicated a high temperature region caused by the non‐flammable fiberglass. Breaching the fiberglass matrix made it possible for the flame to transfer to the other side of the fuel, suggesting that the fiberglass matrix acts as a flame arrester. Copyright © 2004 John Wiley & Sons, Ltd.     

复配阻燃剂对硬质聚氨酯泡沫塑料阻燃性能的影响

研究了甲基膦酸二甲酯(DMMP)、尿素(UC)、磷酸三乙酯(TEP)单独添加及复配使用对硬质聚氨酯泡沫塑料(RPUF)阻燃性能的影响。结果表明,UC与DMMP及TEP复配是气相和凝聚相双相协同阻燃机理的复合阻燃剂;UC与DMMP,UC与TEP复配阻燃RPUF,可达到垂直燃烧分级V0级;UC／DMMP复配使用,UC和DMMP含量分别为15%和25%时,其阻燃RPUF的氧指数最高,为27.3%,阻燃性能优于UC／TEP复配阻燃RPUF;复配阻燃RPUF的压缩强度比单独填充UC体系高,呈现协同作用。     

Effect of Cl/S molar ratio on theoretical partitioning of heavy metals under waste combustion conditions

A simulation calculation was carried out to predict the behavior of heavy metals during waste incineration according to the variation of chlorine content by using a thermodynamic equilibrium model. To predict the behavior of heavy metals in incineration of wastes, chlorine content in wastes was changed up to 3.00 on a Cl/S molar ratio basis. Then the partitioning characteristics of heavy metals with Cl/Metal molar ratio were investigated as solid, liquid, and gas phases of metals. For analysis of emission characteristics, incineration temperature, chlorine content and air-fuel ratio (λ_r) were chosen as major operating parameters. It was found that the distribution characteristics of heavy metals were not significantly affected by air-fuel ratio, but evaporation rate of heavy metals increased with operating temperature. Most of the heavy metals remained in solid phase of metal oxides, such as CdO, CrO₃, CrO₂, CuO and ZnO, except for lead which existed as PbSO₄ in the given operating conditions (i.e., T_b=800 °C, λ_r=1.3, and Cl/S=0). It was found that most of the heavy metals in solid phase changed to gaseous Cl compounds, which have a high volatility with regard to increasing the Cl/S molar ratio under the same conditions. However, Cr compounds were almost not affected as chlorine level increased. This paper is dedicated to Professor Dong Sup Doh on the occasion of his retirement from Korea University.     

Characteristics of diesel fuel combustion in a burner with injection of a superheated steam jet

Basic characteristics of combustion of the diesel fuel in a novel autonomous burner with injection of superheated steam into the combustion region are studied. The temperature distribution in the flame is obtained. Calorimetric measurements of heat release and gas analysis of combustion products are performed. The environmental effects of fuel combustion are compared for regimes with injection of a steam jet and an air jet. It is demonstrated that the combustion regime with steam gasification ensures high combustion intensity and combustion efficiency; moreover, the combustion process becomes more environmentally friendly.     

生物质蜂窝煤燃烧过程SO2排放及灰渣特性研究

以生物质和高硫煤为原料 ,制成了蜂窝状民用生物质复合蜂窝煤 .在一个固定床燃烧实验台上对这种复合蜂窝煤的燃烧特性进行了研究 ,对燃烧过程的 SO2 浓度进行了在线检测 .结果表明 ,生物质的加入能明显减少高硫煤燃烧过程中的 SO2 排放 ,且随着生物质的加入 ,SO2 的排放浓度减小 .并对不含生物质的蜂窝煤和生物质含量为 2 0 %的复合蜂窝煤的燃烧灰渣进行了XRD,SEM分析和比较 ,结果表明 ,生物质复合蜂窝煤灰渣中的 Ca SO4含量比一般蜂窝煤的要高 ,说明生物质能改善蜂窝煤的固硫性能 ,SEM的分析结果表明 ,生物质复合蜂窝煤的灰渣比传统蜂窝煤灰渣具有更发达的微观孔隙结构 ,这种优良的孔隙结构有利于固硫反应的进行 ,进一步讨论了生物质蜂窝煤具有高固硫性能的机制