CFD simulation of MSW combustion and SNCR in a commercial incinerator

A CFD scheme was presented for modeling municipal solid waste (MSW) combustion in a moving-grate incinerator, including the in-bed burning of solid wastes, the out-of-bed burnout of gaseous volatiles, and the selective non-catalytic reduction (SNCR) process between urea (CO(NH₂)₂) and NO_x. The in-bed calculations provided 2-D profiles of the gas–solid temperatures and the gas species concentrations along the bed length, which were then used as inlet conditions for the out-of-bed computations. The over-bed simulations provided the profiles of incident radiation heat flux on the top of bed. A 3-dimensional benchmark simulation was conducted with a 750 t/day commercial incinerator using the present coupling scheme incorporating with a reduced SNCR reduction mechanism. Numerical tests were performed to investigate the effects of operating parameters such as injection position, injection speed and the normalized stoichiometric ratio (NSR) on the SNCR performance. The simulation results showed that the distributions of gas velocity, temperature and NO_x concentration were highly non-uniform, which made the injection position one of the most sensitive operating parameters influencing the SNCR performance of moving grate incinerators. The simulation results also showed that multi-layer injections were needed to meet the EU2000 standard, and a NSR 1.5 was suggested as a compromise of a satisfactory NO_x reduction and reasonable NH₃ slip rates. This work provided useful guides to the design and operation of SNCR process in moving-grate incinerators.     

汽油在西北黄土上吸附特性的研究

通过动力学和热力学吸附实验,研究了汽油在西北地区黄土上的吸附行为,同时研究了提取的天然腐植酸对汽油在黄土上吸附行为的影响.结果表明,汽油在黄土上的吸附在6h内达到平衡.无论是否加入腐植酸,汽油在黄土上的吸附动力学过程均符合Elovich方程,其热力学吸附符合Freundlich方程.腐植酸的存在使汽油在黄土上的吸附能力减小.反应温度从25℃升高到45 C,汽油在土壤上的饱和吸附量从6.300mg·g-1减小到1.365 mg·g-1,表明汽油在黄土上的吸附属于放热反应.溶液pH和土壤粒径的增大,均不利于汽油在黄土上的吸附,溶液pH和土壤粒径越大,其在黄土上的吸附量越小.另外,在室温下对吸附了汽油的土壤样品和纯汽油挥发行为的研究表明,吸附了汽油的土壤样品的汽油挥发比纯汽油慢,其挥发率与时间成对数关系.     

非饱和土壤渗透系数空间不确定性对溶质运移的影响

包气带渗透系数的不确定性是影响非饱和带溶质运移的主要因素。应用贝叶斯方法对非饱和土壤渗透系数进行前处理,使用Monte-Carlo方法模拟其空间不确定性,并通过HYDRUS-1D模型对溶质运移进行数值模拟,研究包气带渗透系数的空间不确定性对溶质运移的影响。结果表明,由于包气带渗透性的不确定性使得溶质浓度分布呈现明显的不确定性,包气带内不同点的浓度值相差很大。与忽略包气带土性参数空间不确定性的模拟结果相对比,考虑包气带渗透系数不确定性的模拟结果与实际情况更加接近,更具合理性和科学性。同时,根据模拟结果,对实际工作中进行地下水数值模拟时溶质初始浓度输入值的确定提出相应建议。     

Fe2+和零价铁活化过一硫酸盐降解酸性橙7

采用环境友好的Fe~(2+)和零价铁(ZVI)作活化剂,活化过一硫酸盐(PMS)来降解水中酸性橙7(AO7).结果表明,在Fe~(2+)-PMS体系中,AO7的降解效果不佳,但通过添加适量的络合剂,AO7的去除率会大幅提高.ZVI在PMS存在下被腐蚀,并能够缓慢、持续不断地释放Fe~(2+).ZVI-PMS体系可以在比较宽泛的pH范围(3～9)有效、快速地降解AO7,并且在酸性条件下降解速率较快.淬灭实验结果显示,硫酸根自由基(SO_4~(·-))对AO7的降解起主要作用.除了Cl~-和高浓度(50 mmol·L~(-1))的NO_3~-能够促进AO7的降解外,其他水中共存的阴离子对AO7在ZVI-PMS体系中的降解具有抑制作用,而腐殖酸(HA)则无明显影响.AO7在超纯水中的去除率高于其他实际水体,但反应90 min后,污水厂出水过滤水和胶体浓缩液中的AO7去除率也可高达98.6%和87.6%,说明ZVI-PMS可能可以有效地去除含有较高DOC含量的污水中的AO7.利用GC-MS检测到辐照后溶液中有3种中间产物,推测主要是通过AO7偶氮键断键后的中间产物进一步氧化形成.此外,TOC在一定程度上降低,说明部分AO7被矿化.     

Chemical and colloidal analyses of natural seep water collected from the exploratory studies facility inside Yucca Mountain,Nevada, USA

Yucca Mountain is being considered as a geological repository for the USA’s spent nuclear fuel and high-level nuclear waste. Numerous groundwater seeps appeared during March 2005 within the exploratory studies facility (ESF), a tunnel excavated in the mountain. Because of the relevance to radionuclide transport and unsaturated zone-modeling studies, we analyzed the seep samples for major anions and cations, rare earth elements, and colloids. Major ion species and elemental concentrations in seep samples reflect interaction of the water with the volcanic rock and secondary calcites. Elemental fractograms from flow-injection field-flow fractionation ICP–MS scans detected Br, Ca, Cl, Cu, Fe, I, Mg, Si, Sr, W, and U at void fractions, suggesting they may be present in the form of dissolved anions. Colloids approximately 10 nm in hydrodynamic diameter, possibly calcite, were also present in the seepage samples. Geochemical calculations indicate, however, these may be an artifact (not present in the groundwater) which arose because of loss of CO₂ during sample collection and storage.     

杭州市郊区表层土壤中的多环芳烃

采集了杭州市郊区表层土壤中多环芳烃样品,用内标法和色谱-质谱技术对多环芳烃化合物进行定量分析.美国环保总署推荐优先控制的16种多环芳烃均被检出,多环芳烃单体的质量浓度在1.49～87.43 ng·g-1之间;其中萘、芴、苊等低分子量芳烃的质量浓度相对较低; 、茚并[1,2,3-cd]芘、苯并[ghi]苝等高分子量芳烃的质量浓度相对较高,苯并[ghi]苝的质量浓度最高.16种多环芳烃的质量总浓度超过荷兰政府规定无污染土壤PAHs值的10～40倍;与国内外其他地区相比较,多环芳烃污染处于中等水平.多环芳烃Ant/(Phe+Ant)、BaA/(Chr+BaA)、Flua/(Pyr+Flua)等参数表明,多环芳烃主要来源于燃烧源,且以机动车尾气为主;BeP/(BeP+BaP)比值偏高,可能与土壤中的多环芳烃主要来源于大气沉降有关.     

粉煤灰中微量元素浸出特性试验研究

通过采用不同pH值的浸出剂对淮南上窑贮灰场中粉煤灰进行了室内浸泡试验研究,得出粉煤灰中微量元素的浸出规律.结果表明:微量元素Cu,Mn,Cd,Ni,Zn随着pH值的增大析出浓度减少,而Cr随着pH值的增大溶出浓度增大,B的溶出与pH值的关系不明显;粉煤灰中微量元素溶出率很低,不会对环境造成污染.     

炼厂常柴碱渣处理与利用

介绍了一种处理与利用炼厂常柴碱渣的方法,该方法实用、简单、速度快、成本低,经应用解决了碱渣的污染问题,并回收了可利用成分.     

SBR实现选择性硝化过程及动力学研究

采用序批式生物反应器(SBR)处理模拟氨氮废水,考察了SBR体系中硝化过程中氮组分和溶解氧变化规律,并对硝化动力学进行了研究.结果表明,在低溶解氧下,体系出现亚硝态氮积累;在序批式反应体系中的硝化反应呈现三阶段,即零级反应段、混合反应段和一级反应段,其硝化特性符合Monod动力学方程;根据SBR实现选择性硝化过程控制方法,实现了SBR选择性亚硝化启动,该体系氨氮出水1 mg·L~(-1),氨氮负荷达0.45 kg·kg~(-1)·d~(-1)(以每kg MLSS中的NH_4~+-N量(kg)计),亚硝态氮累积率达95%左右.     

Non-agricultural Population, Employment and Land： An Econometric Study in an Integrated Framework

Abstract： his paper explored the relationships among nonagricultural population, employment and land in an integrated framework, taking account of rural-urban land conversion into Carlino-Mills＇s model on the regional growth. Two-stage-leastsquares and ordinary-least-squares were employed. Recent data for district （grade） cities in China （from 1999 to 2005） were used. Our results showed that： first, urban population influenced non-agricultural employment, and vice versa, but the evidence that non-agricultural employment influenced urban population was stronger than the evidence that urban population influenced non-agricultural employment; second, urban population and non-agricultural employment both influenced ruralurban land conversion, but the evidence that urban population influenced rural urban land conversion was more stronger than the evidence that non-agricultural employment did. We also found that： first, the employment from the secondary industry influenced urban population in a positive way, and vice versa, but the employment from the tertiary industry influenced urban population in a negative way, and vice versa; second, the employment from the secondary industry influenced rural-urban land conversion in a positive way, but the employment from the tertiary industry influenced rural-urban land conversion in a negative way. We can conclude that the key of urbanization is to speed up the process of non-agricultural employment, especially the employment from the tertiary industry, which might promote non-agricultural population, employment and land harmoniously.