Microwave Plasma Conversion of Volatile Organic Compounds

Abstract

A microwave-induced, steam/Ar/O₂ , plasma “torch” was operated at atmospheric pressure to determine the feasibility of destroying volatile organic compounds (VOCs) of concern. The plasma process can be coupled with adsorbent technology by providing steam as the fluid carrier for desorbing the VOCs from an adsorbent. Hence, N₂ can be excluded by using a relatively inexpensive carrier gas, and thermal formation of oxides of nitrogen (NO_x ) is avoided in the plasma.

The objectives of the study were to evaluate the technical feasibility of destroying VOCs from gas streams by using a commercially available microwave plasma torch and to examine whether significant byproducts were produced. Trichloroethene (TCE) and toluene (TOL) were added as representative VOCs of interest to a flow that contained Ar as a carrier gas in addition to O₂ and steam.The O₂ was necessary to ensure that undesirable byproducts were not formed in the process. Microwave power applied at 500–600 W was found to be sufficient to achieve the destruction of the test compounds, down to the detection limits of the gas chromatograph that was used in the analysis. Samples of the postmicrowave gases were collected on sorbent tubes for the analysis of dioxins and other byproducts. No hazardous byproducts were detected when sufficient O₂ was added to the flow. The destruction efficiency at a fixed microwave power improved with the addition of steam to the flow that passed through the torch.     

Systematic Evaluation and Uncertainty Analysis of the Refuse-Derived Fuel Process in Taiwan

ABSTRACT

In the last few years, Taiwan has set a bold agenda in solid waste recycling and incineration programs. Not only were the recycling activities and incineration projects promoted by government agencies, but the related laws and regulations were continuously promulgated by the Legislative Yen. The solid waste presorting process that is to be considered prior to the existing incineration facilities has received wide attention. This paper illustrates a thorough evaluation for the first refuse-derived fuel pilot process from both quantitative and qualitative aspects. The process is to be installed and integrated with a large-scale municipal incinerator. This pilot process, developed by an engineering firm in Tainan County, consists of standard unit operations of shredding, magnetic separation, trommel screening, and air classification. A series of sampling and analyses were initialized in order to characterize its potentials in the solid waste management system. The probabilistic modeling for various types o f waste pro perties derived in this analysis may provide a basic understanding of system reliability.     

Correlation between Calcium Carbonate Content and Emission Characteristics of Incense

Abstract

In Taiwan and China, calcium carbonate is commonly added as a filler during incense production to lower the cost. This study has found an unexpected benefit for this practice: it reduces particulate emission. Nine types of the popular incense on the local market were chosen for this study. The calcium content in raw material incense was analyzed by inductively coupled plasma atomic emission spectrometry, followed by X-ray diffraction (XRD) spectroscopy. The correlation between the calcium content and emission characteristics of incense was investigated. The calcium content varied from 1.8 to 60 mg/g (incense burned) among those nine different types of incense. Very little calcium (<1%) was found in natural wood or plants, which is mainly the raw material of incense. Instead, most calcium was artificially added in the form of CaCO₃ during manufacturing. The combustion characteristics, including burning rate, emission factors of particulate, ash, and solid-phase polycyclic aromatic hydrocarbons (SPAHs), varied significantly among the nine types of incense. Incense containing 2% calcium would emit 30% less S-PAHs, compared with those with little (<0.2%) calcium. More importantly, increasing the calcium content from 0.5 to 5% by adding CaCO₃ reduced the particulate emission from incense by ～50%.     

Characteristics of Road Dust from Different Sampling Sites in Northern Taiwan

Abstract

Road dust contributes a large percentage of the atmosphere’s suspended particles in Taiwan. Three road dust samples were collected from downtown, electrical park, and freeway tunnel areas. A mechanical sieve separated the road dust in the initial stage. Particles >100 μm were 75%, 70%, and 60% (wt/wt), respectively, of the samples. Those particles <37 μm were resuspended in another mixing chamber and then collected by a Moudi particle sampler. The largest mass fraction of resuspended road dust was in the range of 1–10 μm. Ultrafine particles (<1 μm) composed 33.7, 17, and 7.4% of the particle samples (downtown, electrical park, and freeway tunnel, respectively). The road dust compositions were analyzed by inductively coupled plasma (ICP)-atomic emissions spectroscopy and ICP-mass spectrometry. The highest concentration fraction contained more aluminum (Al), iron (Fe), calcium (Ca), and potassium than other elements in the road dust particle samples. Additionally, the sulfur (S) content in the road dust from the electrical park and freeway tunnel areas was 2.1 and 3.4 times the downtown area sample, respectively. The sulfur originated from the vehicle and boiler oil combustion and industrial manufacturing processes. Furthermore, zinc (Zn) concentration in the tunnel dust was 2.6 times that of the downtown and electrical park samples, which can be attributed to vehicle tire wear and tear. Resuspended road dusts (<10 μm) from the downtown and freeway tunnel areas were principally 2.5–10 μm Al, barium (Ba), Ca, copper (Cu), Fe, magnesium (Mg), sodium (Na), antimony (Sb), and Zn, whereas arsenic (As), chromium (Cr), and nickel (Ni) were predominant in the ultrafine particle samples (<1 μm). Al, Ba, and Ca are the typical soil elements in coarse particles; and As, and Cr and Ni are the typical fingerprint of oil combustion and vehicle engine abrasion in ultrafine particles. There was a special characteristic of resuspension road dust at electrical park, that is, many elements, including As, Ba, Ca, cadmium, Cr, Cu, Fe, manganese (Mn), Ni, lead (Pb), S, vanadium (V), and Zn, were major in ultrafine particles. These elements should be attributed to the special manufacturing processes of electric products.     

Measurement of Ultrafine Particle Size Distributions from Coal-, Oil-, and Gas-Fired Stationary Combustion Sources

Abstract

Currently, we have limited knowledge of the physical and chemical properties of emitted primary combustion aerosols and the changes in those properties caused by nucleation, condensation growth of volatile species, and particle coagulations under dilution and cooling in the ambient air. A dilution chamber was deployed to sample exhaust from a pilot-scale furnace burning various fuels at a nominal heat input rate of 160 kW/h^?1 and 3% excess oxygen. The formation mechanisms of particles smaller than 420 nm in electrical mobility diameter were experimentally investigated by measurement with a Scanning Mobility Particle Sizer (SMPS) as a function of aging times, dilution air ratios, combustion exhaust temperatures, and fuel types. Particle formation in the dilution process is a complex mixture of nucleation, coagulation, and condensational growth, depending on the concentrations of available condensable species and solid or liquid particles (such as soot, ash) in combustion exhausts. The measured particle size distributions in number concentrations measured show peaks of particle number concentrations for medium sulfur bituminous coal, No. 6 fuel oil, and natural gas at 40-50 nm, 70-100 nm, and 15-25 nm, respectively. For No. 6 fuel oil and coal, the particle number concentration is constant in the range of a dilution air ratio of 50, but the number decreases as the dilution air ratio decreases to 10. However, for natural gas, the particle number concentration is higher at a dilution air ratio of 10 and decreases at dilution air ratios of 20-50. At a dilution air ratio of 10, severe particle coagulation occurs in a relatively short time. Samples taken at different combustion exhaust temperatures for these fuel types show higher particle number concentrations at 645 K than at 450 K. As the aging time of particles increases, the particles increase in size and the number concentrations decrease. The largest gradient of particle number distribution occurs within the first 10 sec after dilution but shows only minor differences between 10 and 80 sec. The lifetimes of the ultrafine particles are relatively short, with a scale on the order of a few seconds. Results from this study suggest that an aging time of 10 sec and a dilution air ratio of 20 are sufficient to obtain representative primary particle emission samples from stationary combustion sources.     

An economic evaluation and assessment of environmental impact of the municipal solid waste management system for Taichung City in Taiwan

Municipal solid waste management (MSWM) is an important environmental challenge and subject in urban planning. For sustainable MSWM strategies, the critical management factors to be considered include not only economic efficiency of MSW treatment but also life-cycle assessment of the environmental impact. This paper employed linear programming technique to establish optimal MSWM strategies considering economic efficiency and the air pollutant emissions during the life cycle of a MSWM system, and investigated the correlations between the economical optimization and pollutant emissions. A case study based on real-world MSW operating parameters in Taichung City is also presented. The results showed that the costs, benefits, streams of MSW, and throughputs of incinerators and landfills will be affected if pollution emission reductions are implemented in the MSWM strategies. In addition, the quantity of particulate matter is the best pollutant indicator for the MSWM system performance of emission reduction. In particular, this model will assist the decision maker in drawing up a friendly MSWM strategy for Taichung City in Taiwan.

Implications: Recently, life-cycle assessments of municipal solid waste management (MSWM) strategies have been given more considerations. However, what seems to be lacking is the consideration of economic factors and environmental impacts simultaneously. This work analyzed real-world data to establish optimal MSWM strategies considering economic efficiency and the air pollutant emissions during the life cycle of the MSWM system. The results indicated that the consideration of environmental impacts will affect the costs, benefits, streams of MSW, and throughputs of incinerators and landfills. This work is relevant to public discussion and may establish useful guidelines for the MSWM policies.     

河湖疏浚淤泥的表征、絮凝和脱水

以无锡锡山湿地公园河道淤泥及太湖贡湖湾疏浚底泥为研究对象,对比分析了两种淤泥的矿物组成、粒径分布及泥微粒表面基团、ζ电位等理化特性。以聚丙烯酰胺类聚合物(polyacrylamide,PAM)为絮凝剂,对比分析了其在2种底泥絮凝分离、真空抽滤脱水过程中的作用特征,并对相关影响因素进行了探讨。结果表明,两种淤泥样具有相近的主体矿物组分、有机基团及ζ电位值,但有机质含量稍高的淤泥样中大颗粒所占比例相对较高。相比阳离子型PAM,阴离子型PAM在较少用量下即可获得较大絮团,但上清液浊度较高。絮凝泥在抽滤过程受絮团尺寸影响较大,PAM不同类型基团间的差异对其影响较小,但对趋于平衡后的泥饼含水率略有影响。     

基于密相半干法脱硫工艺的生石灰消化及改性

以某公司生产的生石灰作为脱硫剂,密相半干法脱硫工艺在某炼铁厂烧结烟气脱硫工程的应用为例,对生石灰的消化反应和调质改性进行实验,考察其满足脱硫要求的最佳消化条件和烧结机头灰作为改性剂的比重。实验表明,当水灰比在1.5～1.7、生石灰粒径在200μm以下、消化温度在55℃左右、搅拌轴转速在15～25 r/min的范围内,可以保证生石灰有最佳的转化率,烧结机头灰占比重的5%时为最佳改性剂量;同时对实验的工程运行成本和脱硫效果进行分析,使用自制改性脱硫剂即可以节约运行成本和水电资源,又能提高脱硫效果,为脱硫设备的长期稳定运行提供了可靠依据。