城市污泥热解中试系统集成一体化研究及运行效果评估

为了促进城市污泥热解工艺的工程化应用,组建了污泥热解系统、热解产物分离回收利用系统、废气净化排放系统于一体较完整的热解中试装置,在实现污泥有效处置的同时也实现了高值能源回收利用。中试工况优化,较好工况为：热解时间30-40 min,热解终温450-500℃,在此条件下,干化污泥（含水率5%）减量率为50%;热值为33.8 MJ/kg的热解油产率为17.1%左右。通过对中试运行效果的评估,得出热解油和热解气两者能量或污泥炭自身能量可供干化污泥热解本身所需能量,从而为推动污水污泥热解工艺的工程化利用提供了支持。     

Urban CO Concentrations and Vehicle Emissions

The effect of the general growth of CO vehicular emissions in urban areas on the CAMP station measurements in downtown areas, where vehicular traffic is saturated is considered. With the assumption that the street-level CO concentration is derived from the sum of an urban background term and a local street-effect term, the urban background CO concentration is computed with a diffusion model by introducing a simple area source distribution. The local street-effect term is taken to be constant at a saturation emission level corresponding to a saturation traffic density when the emission per vehicle-mile and meteorological conditions are fixed. The present analysis indicates that the local street-effect term, AC, has a major role in determining street-level concentrations for pollutants, such as CO, whose air quality standard is based on maximum concentrations with averaging times of 1 hour and 8 hours. The relevance of this analysis to the abatement requirements of the Clean Air Amendments and to the driving cycle adopted is discussed.     

Short-chain chlorinated paraffins (SCCPs) in surface soil from a background area in China: occurrence, distribution, and congener profiles

Short-chain chlorinated paraffins (SCCPs) are extremely complex technical mixtures of polychlorinated n-alkanes with carbon chain lengths from C₁₀ to C₁₃ and chlorine content between 49 and 70 %. SCCPs are under consideration for inclusion in the Stockholm Convention on persistent organic pollutants. SCCPs have been used extensively in industrial production, but little is known about the pollution level in soil environment in China. In this study, levels and distribution of SCCPs in soil samples from Chongming Island were analyzed. Concentrations of total SCCPs in soil samples ranged from 0.42 to 420 ng?g^?1, with a median of 9.6 ng?g^?1. The ubiquitous occurrence of SCCPs in Chongming Island implied that long-range atmospheric transport and soil–air exchange may be the most important pathways for SCCP contamination in the background area. The localized SCCP contamination could be derived from an unidentified source. Hierarchical cluster analysis indicated that C₁₃- and C₁₁-congeners were predominant in most soils and C₁₀- and C₁₂-congeners dominated in the remaining soils. Cl₇- and Cl₈-congeners were on the average the most dominant chlorine congeners in nearly all soils. Principal component analysis suggested that the separation of even and odd carbon chain congeners occurred during long-range atmospheric transport and aging in soil in the study area.     

An Equilibrium Analysis of Some Chlorinated Hydrocarbons in Stoichiometric to Fuel-rich Post-flame Combustion Environments

The equilibrium composition of product gases from the combustion of chlorinated hydrocarbons (CHC) has been studied for varying ratios of C, H, Cl, and O under stoichiometric to fuel-rich conditions. An interactive, PC-compatible FORTRAN program, STANJAN, was utilized in conjunction with thermochemical data sources to calculate equilibrium compositions of gas mixtures as a function of temperature. The predicted results, when judiciously Interpreted, assist in the understanding of the potential for formation of residual organic substance emissions (ROSEs) in post-flame environments of an incinerator.

Arguments are presented for the potential formation of chlorinated species, which are stable at ambient temperature, if locally fuel-rich mixtures penetrate into the lower temperature zones of an incinerator. ROSEs that have been observed in field tests of incinerators burning chlorinated compounds are predicted to form under the fuel-rich condition. Furthermore, when the equivalence ratio is greater than unity by even a slight amount, the degree of chlorination of product gases increases markedly when the Cl/H ratio also exceeds unity. In that case, time, temperature, turbulence and an overall fuel-lean stoichiometry may not be sufficient to guarantee elimination of measurable levels of chlorinated products. Possible implications of the equilibrium calculations are discussed. Further systematic studies with additional CHCs, nitrogen?, sulfur?, and heavy metal-bearing compounds are recommended as well as continued efforts to carry out kinetic studies.     

Nutrient Limitation in a Compost Biofilter Degrading Hexane

Abstract

A laboratory-scale compost-based biofilter was operated over a six-month period to study the requirements for removal of n-hexane from air. Hexane is a relatively short chain aliphatic hydrocarbon with a high Henry's coefficient and a low water solubility. Acclimation of the biofilter was slow, but removal efficiencies around 80% were achieved after one month of operation. However, performance decreased during the next two months of operation to 50% removal efficiency. Nutrient limitation was proposed as a reason for the decrease in reactor performance. After the addition of a concentrated nitrogen solution, reactor performance increased almost immediately to >99%. Removal efficiency remained above 99% for the following two months of operation at inlet concentrations of 0.7 g/m3 (200 ppmv), at superficial bed velocities approaching 50 m/h, and empty bed residence times of about one minute. Thus, nutrient availability may well limit biofilter performance even in compost- based units. It was shown that nutrients can be added effectively in a soluble form if compost quality is poor and a method is proposed for the evaluation of compost quality.     

Incineration of Paper Sludge in a Prototype Vortexing Fluidized Bed Combustor

ABSTRACT

All experiments were carried out in a prototype vortexing fluidized bed combustor (VFBC). The dimension of the combustion chamber is 0.7 x 1.4 x 2 m, and the freeboard section is 1 m i.d. and 4 m in height. Paper sludge was used as the feeding material. Two types of coal particles were employed as the supplementary fuel. In order to understand the characteristics of the VFBC system for paper sludge incineration, the effect of various operating parameters, such as the primary airflow, excess air ratio, and secondary airflow rates, on temperature distribution, ash elutriation, combustion efficiency, and pollutant emissions were investigated.     

Effect of NOx Control Processes on Mercury Speciation in Utility Flue Gas

Abstract

The speciation of Hg in coal-fired flue gas can be important in determining the ultimate Hg emissions as well as potential control options for the utility. The effects of NO_x control processes, such as selective catalytic reduction (SCR) and selective non-catalytic reduction (SNCR), on Hg speciation are not well understood but may impact emissions of Hg. EPRI has investigated the reactions of Hg in flue gas at conditions expected for some NO_x control processes. This paper describes the methodology used to investigate these reactions in actual flue gas at several power plants. Results have indicated that some commercial SCR catalysts are capable of oxidizing elemental Hg in flue gas obtained from the inlets of SCR or air heater units. Results are affected by various flue gas and operating parameters. The effect of flue gas composition, including the presence of NH₃, has been evaluated. The influence of NH₃ on fly ash Hg reactions also is being investigated.     

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.