间接换热抑制二噁英生成的可行性调研

介绍了废物焚烧过程中二噁英的产生方式及形成机理,理论表明废物焚烧过程中的二噁英主要通过燃后区域的低温异相催化方式生成。通过对国内外采用间接换热抑制焚烧过程中二噁英生成的研究与实践进行调研,证实了间接换热抑制燃后区域二噁英产生的合理性与可行性。综合考虑放射性废物焚烧的实际工况,提出我国放射性废物焚烧过程采用间接换热技术抑制二噁英的生成具备可行性。     

二噁英在垃圾焚烧过程中的产生与控制

介绍了二噁英在焚烧过程中的产生机理及对环境的危害,提出了垃圾焚烧过程中二噁英的有效控制方法。     

农药生产过程中危险废物焚烧产生二噁英的控制

农药生产过程产生大量危险废物,并且危险废物中有机氯含量较高,焚烧是危险废物的主要处置手段之一,焚烧过程易产生二噁英。并且二噁英是一种强致癌物质,对人身体有极大的危害,备受社会及环境保护领域关注。近年来对二噁英的研究越来越多,本文就其结构、产生机制来源、监测方法以及主要控制措施进行分析和研究。     

垃圾焚烧电厂二噁英的产生及控制

垃圾焚烧是世界各国普遍采用的一种垃圾处理方法,但其在焚烧过程中产生二噁英,不加以控制处理会对环境造成严重危害。文章对垃圾焚烧过程中二噁英的产生及控制做系统介绍。     

焚烧烟气中二噁英污染控制技术

介绍了废物焚烧过程中产生的二噁英的机理及污染减排控制技术,重点阐述了国内外烟气净化控制二噁英技术,通过对不同二噁英污染控制技术优缺点的比较,得出:Remedia催化过滤技术是相对最为有效的一种二噁英处理技术,我国应该积极开展该技术的研究。     

城市垃圾焚烧过程中二噁英的产生与防治

本文简要地介绍二噁英的性质,着重分析了城市垃圾焚烧过程中二噁英的来源及其在焚烧产物中的分配和含量,并在此基础上指出了垃圾焚烧产生二噁英的防治途径。     

生活垃圾焚烧影响二噁英排放的相关物质监控

生活垃圾焚烧因其占地小,无害化、减量化和资源化水平高的优势而被越来越多的应用,但焚烧过程中产生的二噁英具有极高的生态风险。由于二噁英的形成机理复杂且测量复杂昂贵,故寻求一种简单的方法来预测甚至在线测量焚化过程中二噁英的排放,具有很好的现实意义。因此,需要探究生活垃圾焚烧处理中影响二噁英产生的强相关物质作为二噁英排放预测指标的可能性,以对后续二噁英控制提供指导。     

板链提升机在垃圾焚烧领域的应用原则

目前,利用水泥窑系统协同处置垃圾的技术有多种,但是大多没有二噁英消除装置。因为在垃圾处理及焚烧过程中会产生二噁英,当温度高于800℃时二噁英分解失去毒性,但是随着烟气温度的降低二噁英会重新再合成。为此,北京四方联公司的垃圾焚烧系统独特地增加了二噁英再合成消除装置。     

垃圾发电中的二噁英污染控制及治理技术

采用焚烧法处理城市生活垃圾,在我国正得到广泛的推广和应用.但是焚烧产生毒性很大的二噁英,二噁英对环境的危害引起人们的关注与重视.本文介绍了二噁英的组成、性质、来源、危害及控制和国内外的先进治理技术.     

一种可以分解二噁英及危险烟气的氢氧混合气体焚烧装置

介绍了一种以碱性水溶液为电解质原料,按氢氧固定比例生成的氢氧混合气焚烧装置。所述的氢氧混合气加入到焚烧装置后,对二噁英及危险废物烟气焚烧具有快速分解效果:空气过量系数α1.05;烟气中CO氧化速度加快;无二次污染;分解二噁英及危险气体,尤其是对含硫高的气体分解效果更佳。     

水对前驱物催化合成二噁英的影响

The effect of water on the formation of polychlorinated dibenzo-p-dioxins（PCDDs）and dibenzofurans（PCDFs）from precursor was investigated by the experiments with a fixed-bed reactor：the reactant mixture with different moisture of 123-TrCB and CuCl₂ for metal-catalyzed formation,that of 123-TrCB and fly ash for surface-catalyzed formation. The experimental results show that the water has the following effects：first,suppressing the formation of PCDD/Fs as less its yield;second,inhibiting chlorination reaction as lower chlorination degree;third,having different effect on PCDDs and PCDFs as lower ratio of PCDFs/PCDDs.The explanations might be the competitive adsorption of water vapor with TrCB on active sites of the fly ash and the catalysis of copper was weakened chloride because of its oxidative conversion to copper oxide.     

硫酸铵和尿素抑制飞灰合成二(口恶)英

二(口恶)英(PCDD/Fs)排放制约了当前焚烧技术在垃圾处置和资源化利用领域的应用和推广。研究了硫酸铵和尿素在不同温度下对垃圾焚烧飞灰合成PCDD/Fs的抑制能力。实验结果表明:高温下(650℃)硫酸铵和尿素对PCDD/Fs合成具有更高的抑制效率,但高温下飞灰合成PCDD/Fs量远低于低温下(350℃)的生成量;PCDD/Fs的降低量均主要来自于PCDFs的减少,并且低温下TeCDF减少量最大,而高温下减少最多的同系物为OCDF。由于实际烟道中,高温处投入的抑制剂会进入低温段继续产生抑制作用,所以仍需要更多的研究正确评价抑制剂的抑制效果和最优使用温度。     

Determination of the vapor pressures of select polychlorinated dibenzo-p-dioxins and dibenzofurans at 75-275 °C

Vapor pressures were determined for several polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) at 75-275 °C, extending the available literature data to more relevant temperature regions and providing the first experimental data for 2,3,7-trichlorodibenzo-p-dioxin (2,3,7-TriCD). A modification of the effusion technique, based upon controlling the diffusion of the target compound and subsequent high resolution gas chromatography/low resolution mass spectrometry (HRGC/LRMS) analysis, was proven comparable to other accepted methods for determining the vapor pressures of semi-volatile organic compounds (SVOCs). Vapor pressures for octachlorodibenzo-p-dioxin (OCDD) and octachlorodibenzofuran (OCDF) were in excellent agreement with those reported in literature. The application of the current method for the vapor pressure determinations of eight polychlorinated dibenzo-p-dioxins/dibenzofurans (PCDDs/PCDFs) in the extended temperature range (up to 275 °C) is reported. The extension of the vapor pressures to such temperatures, unprecedented for the PCDDs/Fs, is important for vapor-particle partitioning modeling in regions relevant to PCDD/F formation and control. Estimates for the melting temperatures and enthalpies of sublimation and vaporization are also reported, the latter for which no experimentally determined values have been found in the literature. The use of the method to deliver reproducible, trace concentrations (ppt-ppb) of targets was applied to the calibration of the jet-REMPI/TOFMS as an online detector for low chlorinated PCDDs/Fs.     

五氯酚在飞灰表面低温反应生成二口恶英特性

在管式炉上研究了不同试验条件飞灰/五氯酚生成二口恶英的分布特性.采用色质联机(HRGC/LRMS)测定了PCP中以及生成产物中的二口恶英含量.结果表明，生成产物中的二口恶英主要以气态形式存在，总的二口恶英中以PCDDs为主，比例高于97％，PCDDs中主要同系物是六至八氯代PCDDs.分析了飞灰含量以及氧含量对二口恶英生成的影响，二口恶英生成量随着飞灰中含碳量的增加而增大，氧含量是控制二口恶英生成的关键因素，氧含量在6.7％时生成的二口恶英总量及毒性当量值最小.对试验中产生的二口恶英进行了质量平衡，为进一步研究垃圾焚烧过程中二口恶英排放以及分布特性打下基础.     

Effect of the reducing agent on the hydrodechlorination of dioxins over 2 wt.% Pd/γ-Al2O3

2-Propanol and molecular H₂ (in methanol (MeOH) and MeOH–water) were examined as reducing agents for the liquid phase hydrodechlorination (HDC) of dioxins over 2 wt.% Pd/γ-Al₂O₃. Different amounts of NaOH were added to the reaction mixtures. The 2-propanol and H₂(g)/MeOH systems presented similar HDC activity. Notwithstanding, Pd sintering and graphitic carbon directly bonded to Pd on catalyst surface was observed on samples used with H₂(g)/MeOH. The addition of water to H₂(g)/MeOH decreased Pd sintering and favored dissolution of sodium compounds. However, dioxin degradation efficiency diminished. By contrast, 2-propanol acting both as reducing agent and solvent provided hydrogen to the HDC reaction, avoided metal sintering and Pd–C formation. Besides, almost complete dioxin degradation under mild reaction conditions was obtained. Kinetic experiments of dioxin HDC with 2-propanol showed a maximum net reaction rate and turnover frequency (TOF) for a given initial concentration of polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs). After that value, both reaction rate and TOF decreased. On the other hand, reaction rates and TOFs of dioxin-like polychlorinated biphenyls (DL-PCBs) linearly increased with concentration.     

二口恶英类化合物多氯代二苯并呋喃色谱保留值与基团修饰指数的相关性

为了研究多氯代二苯并呋喃（PCDFs）的构效关系，采用基团修饰指数作为PCDFs的分子结构描述符，通过线性回归方法建立了色谱保留指数RI、相对保留时间RRT与分子结构描述符之间的定量关系模型，各样本总体模型的相关系数均在0.97以上，估算色谱保留指数RI的平均相对误差为1.09%.利用方程对另外一些二口恶英分子的气相色谱保留指数RI和相对保留时间RRT进行了预测，预测平均值和相同氯原子数的实验平均值较为吻合，预测能力优于文献.     

SO2抑制二英从头合成的实验及其过程模拟

实验研究了不同温度下SO₂对二 英（PCDD/Fs）从头合成的抑制特点,运用HSC Chemistry 6.1软件对主要无机化学反应过程进行模拟,探究了SO₂的抑制机理。结果表明,SO₂对PCDD/Fs总浓度和I-TEQ浓度的抑制效果随温度的升高而增强。PCDD/Fs总浓度和I-TEQ浓度抑制率从200℃不足20%分别提高到300℃时的75.6%和77.3%及400℃时的89.2%和80.5%;SO₂的添加促进了PCDD/Fs尤其是PCDDs同系物分布的低氯代化。在从头合成的高温段和低温段,SO₂分别侧重抑制PCDFs和PCDDs。相平衡计算和Gibbs自由能计算表明,SO₂优先与催化剂CuCl₂反应生成无催化活性的CuSO₄,其次与氯源Cl₂反应,最终实现PCDD/Fs的生成抑制。模拟结果对现有硫基抑制机理进行了验证和补充,对高效、廉价抑制剂的开发及工程使用具有重要意义。     

载气流量及升温速率对污染土壤中多氯联苯热脱附的影响

利用小型管式炉进行了载气流量和升温速率对多氯联苯污染土壤的热脱附过程影响的实验研究。结果表明流量的增大对多氯联苯含量和毒性当量的去除效率影响不大,载气流量小于400 ml·min^-1时,气相中的脱附量明显增大,载气流量大于400 ml·min^-1则脱附量变化较小,而多氯联苯的毒性当量则随着载气流量增大呈线性增加趋势。实验结果还表明污染土壤中多氯联苯变化速率与升温速率呈明显的正线性相关,随着升温速率增加,污染土壤中多氯联苯去除效率总体呈上升趋势,毒性当量去除效率降低。总体结果分析可以看到升温速率越大,总体效果也越好。污染土壤经热脱附处理后气固相的二 英毒性当量则有不同程度提升,尤其气相内检测到了大量多氯二苯并呋喃生成。     

Thermal Behavior of PAHs,Hexachlorobenzene and PCDDs/PCDFs Adsorbed on Lignite Coke From Flue-Gas Cleaning in Municipal Waste Incinerators

Abstract

Lignite coke is increasingly employed as an adsorbent for flue-gas cleaning, for example, in waste incinerators. The aim of the studies described here was to verify the assumed deposition reliability of moving bed adsorbers even in the case of operational malfunction. To this end, the occurrence of glow clusters in coke beds loaded with various pollutants such as polyaromatic hydrocarbons (PAHs), hexachlorobenzene (HCB), polychlorinated dibenzodioxins and dibenzofurans (PCDDs, PCDFs) was simulated and the thermal behavior of adsorbed compounds recorded by quantitative measurement of the coke pollutant and of the desorption gases. Assuming an incident that would lead to the spontaneous ignition of the adsorber, the results of our studies show that due to the desorption or decomposition reactions of PAHs, PCDDs and PCDFs, as well as HCB as a model substance for high-chlorinated compounds, only small fractions of pollutants are released.     

Low temperature decomposition of PCDD/PCDF, chlorobenzenes and PAHs by TiO2-based V2O5–WO3 catalysts

The oxidation of representative congeners of polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), polychlorinated chlorobenzenes (PCBzs), and of polyaromatic hydrocarbons (PAHs) was investigated on two commercial V₂O₅–WO₃/TiO₂-based catalysts, optimized for the combined reduction of nitrogen oxides and decomposition of dioxins.

The non-chlorinated polyaromatic compounds (including non-chlorinated dibenzodioxin and dibenzofuran) are destroyed at temperatures as low as 150°C with an efficiency of more than 95%. PCDD and PCDF were also removed from the gas phase with an efficiency of >98%. However, at 150°C they remained mainly unchanged (up to 75%) adsorbed on the catalyst.

A decrease in the oxidation rate with increasing chlorine substitution was found for the PCDD/PCDF. This could be explained by an increasing “redox potential” with increasing chlorine substitution due to the electron withdrawing effect of the chlorine.

For the more volatile monoaromatic PCBz, however, the effect of lowering the volatility with increasing chlorine substitution (resulting in longer residence time on the catalyst) over-compensates the effect of the increasing “redox potential” with higher degree of chlorination.