Treatment of tar pond sludge in a circulating fluidized bed combustor

A series of tests to burn mixtures of tar pond sludge and coal was carried out using a mini‐circulating fluidized bed combustor (mini‐CFBC). During the tests, carbon dioxide, oxygen, carbon monoxide, sulfur dioxide, and nitrogen oxides in the flue gas were monitored continuously. Stack gas sampling was carried out for hydrochloric acid, metals, particulate matter, volatile organic compounds (VOCs), total hydrocarbons, semivolatile organic compounds (SVOCs), dioxins and furans (PCDD/Fs), and polychlorinated biphenyls (PCBs). Results showed that hydrochloric acid, mercury, particulate matter, PCDD/F, and metal concentrations were all below both the current limits and the gas‐release limits to be implemented in 2008 in Canada. The new 2008 emissions limits will reduce the maximum allowable concentrations of most pollutants by half. Thus, the maximum concentration for particulate matter will be 5 mg/m³ (from the current maximum concentration of 10 mg/m³);the maximum concentration for hydrochloric acid will be 5 mg/m³ (from 10 mg/m³); and the‐maximum concentration for dioxins and furans will be 0.032 ng/m toxic equivalent (from 0.08 ng/mcurrently). Sulfur capture efficiency was 89–91 percent. The percentage of fuel nitrogen converted to nitrogen oxides was of the order of 4.7 to 6.1, which is significantly lower than that of conventional pulverized coal‐fired boilers and well within the normal range for fluidized bed combustors (FBCs). PCB and polycyclic aromatic hydrocarbon (PAH) emissions levels were comparable or lower than levels reported in the literature for industrial‐scale FBCs. VOC concentrations were low except for benzene, for which the concentration was higher than that reported for pulverized coal‐fired utility boilers. In addition, carbon monoxide concentration was high at 1,200 to 2,200 parts per million. However, these carbon monoxide concentrations are typical of the mini‐CFBC firing coal. The trials showed that for 10 percent by weight tar pond sludge mixed with 90 percent by weight coal, the combustion was both stable and efficient. The tests demonstrated that CFBC technology is an environmentally sound option for eliminating tar pond waste sludge. © 2005 Wiley Periodicals, Inc.     

Germinable Soil Seed Banks and the Restoration Potential of Abandoned Cropland on the Chinese Hilly-Gullied Loess Plateau

Poor vegetation cover is generally considered to be a major factor causing soil erosion on the Loess Plateau in China. It has been argued that tree planting restoration is ineffective, and natural re-vegetation is an alternative ecological solution for restoring abandoned cropland and controlling soil erosion. The aims of this study were to investigate the characteristics of soil seed banks and to assess the natural restoration potential of abandoned cropland in the hilly-gullied Loess Plateau. The soil seed bank was identified by the germination method with the soil samples, which were collected at four sampling times (April, August, and October 2005 and August 2006) from 12 plots abandoned 3–30 years prior to sampling. The seed bank densities of all of the samples in the 0–10 cm soil layer varied from 1,067 ± 225 to 14,967 ± 1,606 seeds m⁻². Fifty-one species (24 annual and 27 perennial species) belonging to 18 families were identified, and 39% of these species belonged to the families Compositae and Gramineae. The pioneer species Artemisia scoparia dominated the seed bank, with an average seed density of 3,722 seeds m⁻², and accounted for 74.4% of the seeds in the bank. The local dominant species (such as Lespedeza davurica, Artemisia gmelinii, Bothriochloa ischaemun and Stipa bungeana) of the later succession stages also existed at densities varying from 17 to 1, 383 seeds m⁻². The combination of soil seed bank characteristics, reproductive traits of the species, the specific landscape conditions indicates that the potential to restoring the abandoned croplands in the hilly-gullied Loess Plateau via natural re-vegetation could be substantial.     

全球面临的环境问题及其特点

本文从环境问题的严重性和全球性出发,阐述了当前世界面临的主要环境问题和当代环境问题的特点,指出了经济与环境协调发展的必要性和艰巨性。结合我国的环境现状,说明随着人类改造自然能力的不断提高和活动匠逐步扩大,环境保护已成为一个刻不容缓的问题摆有人们面前,如何处理好环境保护与经济发展这对矛盾,是中国乃至全人类都必须正视的艰巨课题。     

基于C5.0决策树的船舶交通事故致因分析模型及应用

为减少船舶交通事故的发生,对船舶交通事故的致因展开研究。首先,以事故类型作为输出变量,以船舶交通事故数据为样本,构建基于C5.0算法的船舶交通事故致因路径分析模型;然后,确定事故致因路径分析有效性评价指标;再次,运用“2-4”模型(24Model),对所识别出的不同类型事故致因路径因果关系进一步分析,提出通过切断事故潜在致因路径的船舶交通事故预控措施;最后,将894起船舶交通事故数据样本随机分为80%的训练集和20%的测试集,应用所提出的模型进行分析。结果表明:所提出的模型可以生成不同类型事故的分类规则集,模型分类正确率达到90%以上,且模型具有强的泛化能力。结合分类规则集构建的船舶交通事故致因链为船舶交通事故的防范提供定量化的理论依据。     

丰润热电2#机组超低排放改造效果分析评价

更换除雾器为高效除尘除雾器,实现对丰润热电2#机组除尘、脱硫系统的超低改造;保留原有低氮燃烧器,在SCR反应器上加装预留层催化剂来改造脱硝系统。改造后,烟尘、SO2和NOx排放浓度分别为2.29 mg/Nm3、20.02 mg/Nm3和22.60 mg/Nm3,污染物年总减排量为198.94 t,污染物排放浓度平均波动程度减小了42.51%。结果表明:此次改造卓有成效,排放浓度月均值符合最新标准限值;年减排效果明显;排放浓度波动程度减小,系统间协调性各系统运行稳定性显著提升。     

火灾情况下小学生应急疏散量化分析研究

我国是一个火灾发生频率高的国家,为切实保障在校学生的人身安全,提高学生应急疏散能力,最大限度地减轻火灾造成的人员伤亡,有必要针对不同学生群体举行应急疏散演练训练。针对火灾中影响人员安全疏散的因素和不同年龄层次小学生特点设计实验方案,以时间为量化衡量值,对小学生疏散训练的效果进行量化分析,通过采用现场实验的方法采集数据,并采用SPSS进行统计分析归纳测试结果,归纳出小学生应急疏散训练特点,为将来国内小学校应急疏散训练效果评价指标体系研究提供参考依据,并且为针对小学生群体疏散演练的训练模式奠定一定的实验基础。     

壳聚糖絮凝剂处理废水的研究进展

壳聚糖是一种新型天然高分子絮凝剂，对动植物无毒、无害。壳聚糖可以用于处理印染、味精、食品、含重金属离子废水等。系统地阐述了壳聚糖絮凝剂的结构及在水处理方面的研究应用情况，讨论了其絮凝机理，提出了看法。     

浅谈改革中国土地租、税、费体系

土地租、税、费体系在市场经济备件下具有调节土地资源配置的作用。加入WTO后,我国土地租、税、费体系存在着关系混乱,征收差异大,重流转税轻保有税及耕地保护不力等诸多问题。解决上述问题需完善市场地租体系、深化土地税制改革、规范土地费体系,充分发挥其在资源配置中的杠杆作用。