Air Pollution Acronyms

Abstract

Computational fluid dynamic (CFD) analysis of the thermal flow in the combustion chamber of a solid waste incinerator provides crucial insight into the incinerator’s performance. However, the interrelation of the gas flow with the burning waste has not been adequately treated in many CFD models. A strategy for a combined simulation of the waste combustion and the gas flow in the furnace is introduced here. When coupled with CFD, a model of the waste combustion in the bed provides the inlet conditions for the gas flow field and receives the radiative heat flux onto the bed from the furnace wall and gaseous species. An unsteady one-dimensional bed model was used for the test simulation, in which the moving bed was treated as a packed bed of homogeneous fuel particles. The simulation results show the physical processes of the waste combustion and its interaction with the gas flow for various operational parameters.     

Combined simulation of combustion and gas flow in a grate-type incinerator

Computational fluid dynamic (CFD) analysis of the thermal flow in the combustion chamber of a solid waste incinerator provides crucial insight into the incinerator's performance. However, the interrelation of the gas flow with the burning waste has not been adequately treated in many CFD models. A strategy for a combined simulation of the waste combustion and the gas flow in the furnace is introduced here. When coupled with CFD, a model of the waste combustion in the bed provides the inlet conditions for the gas flow field and receives the radiative heat flux onto the bed from the furnace wall and gaseous species. An unsteady one-dimensional bed model was used for the test simulation, in which the moving bed was treated as a packed bed of homogeneous fuel particles. The simulation results show the physical processes of the waste combustion and its interaction with the gas flow for various operational parameters.     

3-D Flow Modeling of a Hazardous Waste Incinerator

A three-dimensional flow model of a hazardous waste incinerator kiln and vertical secondary combustion chamber arrangement was constructed to evaluate critical system parameters. The chamber wall configuration, location and arrangement of burners, and the positioning of the outlet duct were examined to determine the critical secondary combustion chamber gas residence time and mixing of the combustion flows. The scale model consisted of the rotary kiln as a primary combustion chamber, the secondary combustion chamber, two burners, and the exhaust ducting. Flue gas velocities in the model inlets and outlet were maintained to provide a Reynolds numbers equal to the full size unit. Patterns of smoke which were injected into the model inlets were viewed to evaluate flow mixing. Slow motion playback of video tape was used to determine the minimum residence time of flow in the high temperature combustion zone. The results of the model study were used to complete the engineering of a waste incineration system.     

Prediction of Flue Gas Composition of an Incinerator Based on a Nonequilibrium-Reaction Approach

A nonequilibrium-reaetion model is developed to predict the flue gas composition of an incinerator for solid waste combustion and gasification. The model may also be effectively utilized to predict the composition of exit gas from the primary chamber of an incinerator where invariably substoichiometrie combustion conditions exist The model assumes that the drying and pyrolysis of waste occurs in sequence followed by combustion of devolatilized gas and residue separately. The model is applied to the combustion of pine wood, and the flue gas compositions are computed as a function of operating parameters such as temperature (1100 to 1500 K), initial moisture content (0 to 40 percent), and percentage excess air (up to 100 percent). The model is extended to include substoichiometric combustion (to simulate the gasification process without steam injection) to compare its predictions with the available experimental data. The general agreement of theory and experiment is good.     

垃圾焚烧炉炉膛温度的影响因素

垃圾焚烧过程的不稳定会导致大量有害物质的生成,为确保垃圾的清洁燃烧需要将炉膛温度控制在850℃以上,为此测试了焚烧炉运行的主要可控参数对炉膛温度的影响。结果表明,垃圾堆放位置在垃圾池深3～8 m处,并经过6 d以上发酵脱水后适合焚烧;炉膛温度随给料量、一次风率和一次风温增加而增大,随过量空气系数增加而降低,其中给料量宜控制在95%～110%之间;当过量空气系数为1.6、一次风率为90%、一次风温为260℃、给料量为100%时炉膛温度达901℃。     

Transient puffs of trace organic emissions from a batch-fed waste propellant incinerator

Emissions data have been obtained from a waste propellant incinerator. The incinerator is a dual fixed hearth, controlled air incinerator equipped with acid gas and particulate scrubbing. "Puffing" has been evident in this waste propellant incinerator by spikes in the CO concentration. Transient puffs of organics may travel down the combustion chambers and lead to stack emissions. The major conclusions from this study are that (1) transient puffs are formed due to the semi-batch feed nature of the combustion process (causing a local oxygen deficiency) and high water content of the desensitized propellant; (2) in batch-fed combustors, puffs can contribute to most of the organic emissions (which are relatively low) measured with US EPA sampling and analytical methods; (3) it is estimated that batch-fed combustion contributes up to 7-18 times more emissions than steady-state combustion will generate; (4) by applying dispersion analyses to determine the amount of oxygen deficiency in the flame zone, the combustion zone concentration of CO during batch-fed operation could be as high as 160,000 ppm, compared to a measured peak stack concentration of 1200 ppm CO; and (5) an organic sample is collected and averaged over at least a 2-h period that smooths out the transient peaks of organics emissions during batch-fed operation. For emissions that are associated with long-term potential health impacts, this is an appropriate sampling method. However, if a compound has a short-term potential health impact, it may be important to measure the time-resolved emissions of the compound.     

Combustion modeling and performance evaluation in a full-scale rotary kiln incinerator.

This work summarizes the results of numerical investigations and in situ measurements for turbulent combustion in a full-scale rotary kiln incinerator (RKI). The three-dimensional (3D) governing equations for mass, momentum, energy, and species, together with the kappa - epsilon turbulence model, are formulated and solved using a finite volume method. Volatile gases from solid waste were simulated by gaseous CH4 distributed nonuniformly along the kiln bed. The combustion process was considered to be a two-step stoichiometric reaction for primary air mixed with CH4 gas in the combustion chamber. The mixing-controlled eddy-dissipation model (EDM) was employed to predict the conversion rates of CH4, O2, CO2, and CO. The results of the prediction show that reverse flows occur near the entrance of the first combustion chamber (FCC) and the turning point at the entrance to the second combustion chamber (SCC). Temperature and species are nonuniform and are vertically stratified. Meanwhile, additional mixing in the SCC enhances postflame oxidation. A combustion efficiency of up to 99.96% can be achieved at approximately 150% excess air and 20-30% secondary air. Reasonable agreement is achieved between numerical predictions and in situ measurements.     

Interactive analysis of waste recycling and energy recovery program in a small-scale incinerator

Conflicting goals affecting solid waste management are explored in this paper to find the best implementation of resource recovery with a small-scale waste-to-energy process. Recycling paper and plastic material often leaves a shortage of thermal energy to support incineration that forces operators to supplement the process with auxiliary fuels. Although there are considerable profits to be made from material recovery, the increase of fuel usage causes conflict given that it is cost prohibitive. A series of trials performed on a small-scale 1.5-t/day incineration plant with a cyclone heat recovery system found that material recycling can impede performance. Experimental results are expressed as empirical regression formulas with regard to combustion temperature, energy transfer, and heat recovery. Process optimization is possible if the waste moisture content remains <30%. To test the robustness of the optimization analysis, a series of sensitivity analyses clarify the extent of material recycling needed with regard to plastic, paper, and metal. The experiments also test whether the moisture in the waste would decrease when recycling paper because of its exceptional capacity to absorb moisture. Results show that recycling paper is strongly recommended when the moisture content is >20%, whereas plastic recycling is not necessary at that moisture condition. Notably, plastic recovery reduces the heat needed to vaporize the water content of the solid waste, thus it is recommended only when the moisture content is <10%. For above-normal incineration temperatures, plastic recycling is encouraged, because it removes excess energy. Metal is confirmed as an overall priority in material recycling regardless of the moisture content of the incoming waste.     

垃圾焚烧过程中水分促燃脱氯效果的研究

分别在转式垃圾焚烧炉和固定床加热炉中,研究了水分对垃圾焚烧及钙基脱氯效果的影响.研究结果表明,垃圾焚烧过程中一定量水分的存在能促进垃圾焚烧效率,提高钙基氯剂的脱氯效率.同时,分析水分促进垃圾焚烧率和脱氯效果提高的原因,这是由于水分能强化焚烧过程的传质传热,能活化脱氯剂,改善脱氯剂的物理和化学性质,这些研究结果将为垃圾焚烧技术在我国的进一步推广提供科学依据.     

垃圾焚烧过程中水分促燃脱氯效果的研究

分别在转式垃圾焚烧炉和固定床加热炉中，研究了水分对垃圾焚烧及钙基脱氯效果的影响。研究结果表明，垃圾焚烧过程中一定量水分的存在能促进垃圾焚烧效率，提高钙基氯剂的脱氯效率。同时，分析水分促进垃圾焚烧率和脱氯效果提高的原因，这是由于水分能强化焚烧过程的传质传热，能活化脱氯剂，改善脱氯剂的物理和化学性质，这些研究结果将为垃圾焚烧技术在我国的进一步推广提供科学依据。     

Particulate PAHs observed in the surrounding of a municipal incinerator

An intensive sampling campaign was undertaken in the surroundings of a municipal waste incinerator located in a French great urban centre in order to evaluate the impact of particles emissions on the ambient air and to estimate the exposure levels to toxic or carcinogenic compounds for a population living in the neighbourhood of this incinerator. To minimise the effect of industrial and road activities, sampling was performed during the 2 days of a weekend and on Monday morning. Different operating modes of the incinerator were investigated: (i) normal incinerator functioning and (ii) maintenance activity of the combustion chamber corresponding to the stop and cooling furnace periods. Particulate polycyclic aromatic hydrocarbons (PAHs) and total particulate carbon concentrations were determined in three sites situated, respectively, close to the incinerator, 2 km downwind and 1 km upwind of the plant. In normal operating mode similar concentrations were observed in the three sites. During the furnace stop an increase of total PAH concentrations was observed in the sampling site close to the incinerator. The concentration was 3 times higher than those measured in the other two sampling sites. But this increase was limited in time and in space since this phenomenon is only observed in the vicinity of the incinerator. The study of PAH profiles indicated that Pyrene and Retene showed the highest enhancement of their relative concentrations. The influence of incinerator functioning parameters on the PAHs concentrations is discussed. The furnace temperature and the mode of exhaust fumes seem to be deciding parameters to explain the increase of PAH level in the incinerator site. However, the incinerator emissions remained a minor part of the atmospheric pollution in the urban area.     

Research and development to improve naval shipboard waste management using a compact closed-loop-controlled waste incinerator

Research has been conducted into the application of forced acoustics for enhancing the performance of a pyrolyzed waste afterburner configured as a dump combustor. Subscale studies showed that acoustic forcing of an air jet entering a dump chamber could trigger the formation of coherent vortices generated by entrainment of ambient gases. Subsequent studies showed that combustible gases could be introduced into the coherent vortices, and with additional modulation this configuration would lead to an enhanced combustion rate with low emissions of pollutants. The acoustically forced burner concept was scaled up to practical levels and tested as an afterburner on a commercial waste incinerator operating in pyrolysis mode. Results show that the afterburner can promote both compactness, due to the rapid combustion rate, and low pollutant emissions resulting from enhanced mixing prior to combustion.     

Emission of organic compounds by combustion of waste plastics involving vinyl chloride polymer

Organic compounds emitted from combustion of waste plastics involving vinyl chloride polymer were investigated in an actual waste incinerator. The amounts of volatile aliphatic hydrocarbons and volatile chlorinated organic compounds decreased when the secondary combustion temperature was controlled over 900°C. On the other hand, the amounts of some aromatic hydrocarbons increased with a rise of the secondary combustion temperature.     

Influence of variation in the operating conditions on PCDD/F distribution in a full-scale MSW incinerator

Optimizing the operating parameters to minimize polychlorodibenzo-p-dioxins and polychlorodibenzofurans (PCDD/F) emission is the common interest of the municipal solid waste (MSW) incineration industry. In this study, we investigated the distribution of tetra- to octa-CDD/F along the flue gas line in a full-scale reciprocating grate incinerator and evaluated the effects of temperature control and O(2) level on PCDD/F formation. Six runs were laid out and all performed under sufficient burning conditions, in which the combustion efficiency of MSW was more than 99.9%. The total concentration of tetra- to octa-CDD/F measured at the boiler outlet showed an increasing tendency with the increase of boiler outlet temperature (T(B)) from 214 degrees C to 264 degrees C. When flue gas ran across the semi-dry scrubber and cyclone precipitator, in which the temperature varied from 264 degrees C to 162 degrees C, the concentrations of the lower chlorinated dioxins and furans were significantly raised, especially for the TCDF. Increasing O(2) supply from 6.0% to 10.5% essentially led to a higher yield of tetra- to octa-PCDD/F, suggested that under sufficient burning conditions the lower O(2) level was favorable for reducing PCDD/F formation and emission. The variation of O(2) level did not give rise to a systematical change of PCDD/F homologue pattern. For all measurements, the isomer distributions of tetra- to hepta-PCDD/F were more or less the same, nearly independent of variations in the operating conditions and sampling positions. Only the significant increase of the sum of 1,3,7,8-TCDF and 1,3,7,9-TCDF was found in the zone after the boiler section.     

Interactive Analysis of Waste Recycling and Energy Recovery Program in a Small-Scale Incinerator

Abstract

Conflicting goals affecting solid waste management are explored in this paper to find the best implementation of resource recovery with a small-scale waste-to-energy process. Recycling paper and plastic material often leaves a shortage of thermal energy to support incineration that forces operators to supplement the process with auxiliary fuels. Although there are considerable profits to be made from material recovery, the increase of fuel usage causes conflict given that it is cost prohibitive. A series of trials performed on a small-scale 1.5-t/day incineration plant with a cyclone heat recovery system found that material recycling can impede performance. Experimental results are expressed as empirical regression formulas with regard to combustion temperature, energy transfer, and heat recovery. Process optimization is possible if the waste moisture content remains <30%. To test the robustness of the optimization analysis, a series of sensitivity analyses clarify the extent of material recycling needed with regard to plastic, paper, and metal. The experiments also test whether the moisture in the waste would decrease when recycling paper because of its exceptional capacity to absorb moisture. Results show that recycling paper is strongly recommended when the moisture content is >20%, whereas plastic recycling is not necessary at that moisture condition. Notably, plastic recovery reduces the heat needed to vaporize the water content of the solid waste, thus it is recommended only when the moisture content is <10%. For above-normal incineration temperatures, plastic recycling is encouraged, because it removes excess energy. Metal is confirmed as an overall priority in material recycling regardless of the moisture content of the incoming waste.     

垃圾炉一次风量对炉床燃烧影响的仿真研究

针对垃圾焚烧炉床层内垃圾燃烧过程复杂性及影响垃圾燃烧效率因素多的问题,运用数值仿真方法对某垃圾焚烧炉床层垃圾燃烧进行了模拟,获得了垃圾质量流失速率、水分蒸发速率、挥发分释放速率、焦炭燃烧速率和烟气的温度;并在50~1 000 Nm3/min范围内改变一次风流量,获得了床层质量流失比值、过剩空气系数和烟气中各组分的质量百分比含量。仿真结果显示,一次风流量取值517.47~6`32.09 Nm3/min时燃烧效率较高;炉排两端区域的一次风流量在50~75 Nm3/min时,可以使垃圾床表面平均温度明显提高,而且还可以提高燃烧效率,同时减少供风总量,节约能源与动力资源。本研究对优化设计垃圾焚烧炉,提高床层内垃圾的燃烧效率有一定参考价值。     

The Development of Open Pit Incinerators for Solid Waste Disposal

A discussion is presented of a newly developed incinerator for the disposal of solid wastes. It is distinguished from conventional types by its open top, and features a system of closely spaced nozzles admitting a screen of high-velocity air over the burning zone. Results, with a variety of solid industrial wastes, show high burning rates, leading to complete combustion and high flame temperature.     

150t/d循环流化床生活垃圾焚烧炉的工艺结构与污染排放

垃圾焚烧处理技术在我国的应用越来越广泛 ,单纯引进国外的垃圾焚烧处理技术已经无法满足我国经济发展的需要。清华大学自主开发研制的 15 0t/d循环流化床生活垃圾焚烧炉已经通过专家鉴定 ,各项焚烧污染物排放指标均达到或优于国家标准 ,总体水平居国内领先水平。本文详细介绍了该焚烧炉的系统及结构 ,并对有关控制污染物排放的技术手段进行了详细分析     

新型转式垃圾焚烧炉焚烧技术研究

研究了新型转式焚烧炉稳定燃烧工艺和有机垃圾在新型转式焚烧炉中焚烧过程HCl和NOx释放和控制特性。结果表明,新型转式焚烧炉采用二次燃烧技术,能有效控制和降低二次污染物的生成。     

垃圾焚烧炉二次配风优化数值模拟

针对城市生活垃圾焚烧发电的排放问题，以重庆市某垃圾焚烧炉为原始模型，在炉膛两侧炉壁的适当位置设置二次配风口，并采用CFD（计算流体动力学）方法对炉膛内气体的二次燃烧过程进行数值模拟。通过观察对比有无二次配风以及二次配风口位置不同时炉膛内气体的温度场、气体在炉膛内的停留时间分布以及炉膛内气体的混合程度和湍动能等，重点分析了二次风在气体燃烧过程中所起的作用，并对2种不同二次配风口位置时抑制二恶英产生的效果进行了评价。通过对垃圾焚烧炉二次风的优化数值模拟，获得了适合本焚烧炉的比较合理的二次配风条件，可为焚烧炉的设计和改进提供一些有价值的参考。