Simulation of the flue gas cleaning system of an RDF incineration power plant

Because of the stringent pollutant emission standards introduced with the European Union guidelines for waste incineration, it is very important to optimize the flue gas cleaning systems which are able to result in a low environmental impact according to the emission limits. In this paper a thermochemical model has been proposed for the simulation of the flue gas cleaning system of an RDF incineration plant. The model simulates the operation of the flue-gas treatment section and the combustion section by using a simplified approach. The combustion includes the grate incinerator and the post-combustion chamber, while the cleaning section includes the NO(x) reduction process (urea injection) and the scrubbing of SO(2) and HCl (Ca(OH)(2) as sorbent). The modelling has been conducted by means of ASPEN PLUS code. The simulation results have been validated with the operating data. The model proposed by the authors can be a useful tool in both evaluating the efficiency of the gas cleaning system by verifying the environmental pollution of an incinerator power plant in nominal operating conditions and in forecasting the efficiency of the cleaning system in off-design operating conditions.     

Adsorption of SO2 and NO from incineration flue gas onto activated carbon fibers

Activated carbon fibers (ACFs) were used to remove SO(2) and NO from incineration flue gas. Three types of ACFs in their origin state and after pretreatment with HNO(3), NaOH, and KOH were investigated. The removal efficiencies of SO(2) and NO were determined experimentally at defined SO(2) and NO concentrations and at temperatures of 150, 200 and 260 degrees C. Experimental results indicated that the removal efficiencies of SO(2) and NO using the original ACFs were <56% and <27%, respectively. All ACFs modified with HNO(3), NaOH, and KOH solution could increase the removal efficiencies of SO(2) and NO. The mesopore volumes and functional groups of ACFs are important in determining the removal of SO(2) and NO. When the mesopore volumes of the ACFs are insufficient for removing SO(2) and NO, the functional groups on the ACFs are not important in determining the removal of SO(2) and NO. On the contrary, the effects of the functional groups on the removal of SO(2) and NO are more important than the mesopore volumes as the amount of mesopores on the ACFs is sufficient to remove SO(2) and NO. Moreover, the removal efficiencies of SO(2) and NO were greatest at 200 degrees C. When the inlet concentration of SO(2) increased to 600ppm, the removal efficiency of SO(2) increased slightly and the removal efficiency of NO decreased.     

Activated carbon from Ceiba pentandra hulls, an agricultural waste, as an adsorbent in the removal of lead and zinc from aqueous solutions

The ability of low-cost activated carbon prepared from Ceiba pentandra hulls, an agricultural waste material, for the removal of lead and zinc from aqueous solutions has been investigated. In the batch tests experimental parameters were studied, including solution pH, contact time, adsorbent dose and initial metal ions concentration. The adsorbent exhibited good sorption potential at pH 6.0. Maximum removal of lead (99.5%) and of zinc (99.1%) with 10 g/l of sorbent was observed at 50 mg/L sorbate concentration. Removals of about 60-70% occurred in 10 min, and equilibrium was attained at around 50 min for both metals. The functional groups (CO, SO,-OH) present on the carbon surface were responsible for the adsorption of metal ions. The adsorption parameters were analysed using both the Freundlich and Langmuir models. The data are better fitted by the Freundlich isotherm as compared to Langmuir model, and the adsorption capacities for lead and zinc were 25.5 and 24.1 mg/g, respectively. Kinetics of adsorption obeyed a second order rate equation and the rate constant was found to be 2.71 x 10(-2) and 2.08 x 10(-2) g/mg/min for lead and zinc, respectively. The desorption studies were carried out using dilute HCl, and the effect of HCl concentration on desorption was studied. Maximum desorptions of 85% for lead and 78% for zinc were attained with 0.15 M HCl.     

Fundamental study of the behavior of chlorine during the combustion of single RDF

A fundamental study of the combustion characteristics and the de-HCl behavior of a single refuse-derived fuel (RDF) pellet was carried out to explain the de-HCl phenomena of RDF during fluidized bed combustion and to provide data for the development of high efficiency power generation technology using RDF. In this research, combustion and pyrolysis experiments were carried out in an electrical furnace using a series of model and actual RDF samples. The de-HCl capability of Ca(OH)2 in RDF was evaluated by measuring the emission fraction of HCl in the flue gas and the capture fraction of Cl in the residue. It was found that the capture fraction of Cl components in the residue increased from 0 to nearly 70% when the molar ratio of Ca/Cl was changed from 0 to around 13. Apparently, the capture fraction also decreased with increasing oxygen concentration in the feed gas. The devolatilization process of RDF was confirmed to be a very important part of de-HCl process. The effect of temperature profile of the RDF pellet on the de-HCl process, as it varies with the heating rate of RDF and the oxygen concentration in the vicinity of the sample, is discussed.     

Incineration of healthcare wastes: management of atmospheric emissions through waste segregation

The amount of atmospheric pollutants emitted through the incineration of healthcare wastes can be estimated using emission factors. Emission factors have been published without including sufficient information about the types of wastes incinerated. This paper reports the first emission factors estimated for the incineration of wastes segregated into different types according to the Portuguese legislation. One controlled-air incinerator without air pollution control devices was used in the research. The main objectives of the study were: (i) to estimate the emission factors for particulate matter, dioxins, heavy metals and gaseous pollutants, according to the type of waste incinerated; (ii) to evaluate the quality of atmospheric emissions; and (iii) to define a methodology for the management of atmospheric emissions, evaluating the influence of type of waste incinerated and of the segregation method used on the emitted amounts. It was concluded that: (i) when emission factors are not associated with the type of incinerated mixture, the utility of the emission factors is highly doubtful; (ii) without appropriate equipment to control atmospheric pollution, incineration emissions exceed legal limits, neglecting the protection of human health (the legal limit for pollutant concentrations could only be met for NO(x), all other concentrations were higher than the maximum allowed: dioxins, 93-710 times; Hg, 1.3-226 times; CO, 11-24 times; SO(2), 2-5 times; and HCl, 9-200 times); (iii) rigorous segregation methodologies must be used to minimize atmospheric emissions, and incinerate only those wastes that should be incinerated according to the law. A rigorous segregation program can result in a reduction of the amount of waste that should be incinerated by 80%. A reduction in the quantity of waste incinerated results in a reduction on the amounts of pollutants emitted: particulate matter, 98%; dioxins, 99.5%; As, Cd, Cr, Mn and Ni, respectively, 90%, 92%, 84%, 77% and 92%; Hg and Pb, practically eliminated; SO(2) and NO(x), 93%; and CO and HCl, more than 99%.     

Effect of mixing on NO removal in the selective noncatalytic reduction reaction process

The effect of mixing of NH₃ and NO on the selective noncatalytic reduction (SNCR) reaction was investigated using a bench-scale reactor. Three different experimental conditions were compared for the removal of NO in the bulk gas with NH₃, a reducing agent, by means of mixing and contacting. The temperature that gave the highest NO removal efficiency was about 800°C when NH₃ was injected with air or NH₃ was premixed and air was injected. It is suggested that control of mixing of the reducing agent and the injection conditions could be a good way to increase NO removal efficiency as well as to lower the reaction temperature. When NH₃ was injected with air, the NO removal efficiency increased with increasing injected air flow if the initial NO concentration was low, whereas for high NO concentrations, the NO removal efficiency slightly increased up to an injected air flow rate of 100 ml/min. A proposed mixed-flow model can be used as a prediction tool for the NO removal efficiency covering various conditions of the real SNCR process.     

工业烟气氨法-络合法同时脱硫脱硝

在脱硫脱硝喷淋装置上采用氨法-络合法处理工业烟气。考察了吸收液pH、Fe(Ⅱ)EDTA浓度、初始烟气浓度、液气比对烟气同时脱硫脱硝效果的影响。实验结果表明:吸收液的酸碱度通过影响Fe(Ⅱ)与EDTA的络合形式进而影响NO去除率;SO_2去除率主要受吸收液pH和初始SO_2质量浓度的影响;当吸收液pH大于8、吸收液Fe(Ⅱ)EDTA浓度大于0.100 mol/L、初始SO_2质量浓度小于1 500 mg/m3、初始NO质量浓度为1 200 mg/m3时,SO_2去除率均在95%以上,NO去除率为54%;当液气比由1 L/m3增大至4 L/m3时,有效脱硫时间和有效脱硝时间分别增长了7 min和4 min。     

Combustion characteristics of simulated gas fuel in a 30 kg/h scale pyrolysis-melting incinerator

Combustion characteristics of gas fuel in a pyrolysis-melting incinerator having a 30kg/h capacity were investigated. Pyrolyzed gas from waste was simulated by propane that was injected in the combustion chamber, and burnt through multi-staged combustion by distributing the combustion air to primary, secondary, and tertiary air nozzles. Temperatures and the concentrations of gas components in the combustion chamber were measured. Combustion performance was evaluated with respect to the temperature distribution and combustion gas concentrations of O(2), CO and NO(x). Using secondary air and/or tertiary air, the combustion performance was improved, and, in particular, NO(x) concentration decreased significantly following the tertiary air injection.     

NaClO_2/氨水溶液同时脱除SO_2和NO的热力学研究

利用化学热力学基本原理分别对NaClO2/氨水溶液同时脱除SO2、NO的反应过程中摩尔反应吉布斯自由能变、摩尔反应焓变、化学反应平衡常数以及化学反应达到平衡时的SO2和NO的分压力进行了计算,结果表明：利用NaClO2/氨水溶液同时脱除SO2、NO是可行的,且SO2和NO的脱除效率几乎可以达到100%。     

差分吸收光谱法多组分浓度反演试验研究

应用新的差分吸收光谱烟气浓度反演算法对SO2、NO、NO2混合气体浓度反演进行了试验研究。与常规反演算法相比,该算法充分考虑了被测对象在不同波段上的差分吸收结构差异,避免了多组分同时反演时使用同一频率进行数字滤波引入的误差。结果表明,该算法能对多组分气体浓度进行快速、准确的反演,误差小于5%。     

NiO-CuO/ZSM-5催化剂对催化裂化烟气的脱硫脱硝性能

采用浸渍法制备了不同NiO和CuO质量分数的NiO-CuO/ZSM-5催化剂，并以CH4为还原剂研究了NiO-CuO/ZSM-5催化剂对催化裂化烟气的脱硫脱硝活性。XRD分析结果表明，NiO质量分数为4%、CuO质量分数为6%的催化剂4%NiO-6%CuO/ZSM-5中的ZSM-5结构完好，CuO和NiO高度分散在ZSM-5骨架中，表明具有较好的催化活性。4%NiO-6%CuO/ZSM-5的脱硫脱硝起活温度均较低，无氧条件下最高NO转化率和SO2转化率分别为94.7%和95.9%，O2体积分数为1.0%时的NO转化率和SO2转化率分别为97.7%和89.0%。     

活性焦烟气脱汞的试验研究与数值模拟

采用固定床吸附系统，对自制褐煤活性焦的脱汞性能进行了试验研究，研究发现自制活性焦对烟气中Hg0有一定的吸附能力，随着Hg0的入口浓度的增加，活性焦质量的增加，活性焦的吸附量也在增加。40mg时3号活性焦由10ng/min汞入1：2浓度时26．68％的最大吸附效率提高到40ng／min汞入口浓度时的53．12％。10ng/min汞入口浓度时3号活性焦在40mg时的最大吸附效率为26．68％，而在80mg时吸附效率提高到43．2％。烟气中的SO2、NO气体对活性焦吸附汞有一定的促进作用。在试验的基础上建立了固定床吸附系统的数学模型，基于Lan—mguir吸附系数，考虑吸附过程中颗粒内、外的传质控制过程，建立质量平衡方程。通过Matlab模型计算，计算结果与试验结果基本吻合，计算的活性焦脱汞效率要优于试验数值，计算的是理想情况下活性焦对汞的吸附效率，实际情况会有所降低。     

Technical assessment of fuel cell operation on anaerobic digester gas at the Yonkers, NY, wastewater treatment plant

This paper summarizes the results of a 2-year field test to assess the performance of a specially modified commercial phosphoric acid 200-kW fuel cell power plant to recover energy from anaerobic digester gas (ADG) which has been cleansed of contaminants (sulfur and halide compounds) using a patented gas pretreatment unit (GPU). Specific project goals include characterization of the fuel cell power plant emissions and verification of the GPU performance for removing sulfur contaminants. To remove halide contaminants from the ADG, a halide guard, consisting of a vessel with a metal oxide supported on alumina, was incorporated into the fuel cell reactant supply. This first-of-a-kind demonstration was conducted at the Yonkers, NY, wastewater treatment plant, a sewage processing facility owned and operated by Westchester County. Results have demonstrated that the ADG fuel cell power plant can produce electrical output levels close to full power (200 kW) with negligible air emissions of CO, NO(x), and SO(2). The GPU removed virtually 100% of H(2)S and 88% of organic sulfur, bringing the overall sulfur removal efficiency of the GPU to over 99%. The halide guard removed up to 96% of the halides exiting the GPU.     

Mathematical modeling of MSW combustion and SNCR in a full-scale municipal incinerator and effects of grate speed and oxygen-enriched atmospheres on operating conditions

The rising popularity of incineration of municipal solid waste (MSW) calls for detailed mathematical modeling and accurate prediction of pollutant emissions. In this paper, mathematical modeling methods for both solid and gaseous phases were employed to simulate the operation of a 450 t/d MSW-burning incinerator to obtain detailed information on the flow and combustion characteristics in the furnace and to predict the amount of pollutant emissions. The predicted data were compared to on-site measurements of gas temperature, gas composition and SNCR de-NO_X system. The major operating conditions considered in this paper were grate speed and oxygen concentration. A suitable grate speed ensures complete waste combustion. The predictions are as follows: volatile release increases with increasing grate speed, and the maximal value is within the range of 700–800 kg/m² h; slow grate speeds result in incomplete combustion of fixed carbon; the gas temperature at slow grate speeds is higher due to adequate oxygenation for fixed carbon combustion, and the deviation reaches 200 K; NO_X emission decreases, but CO emission and O₂ concentrations increase, and the deviation is 63%, 34% and 35%, respectively. Oxygen-enriched atmospheres promote the destruction of most pollutants due to the high oxygen partial pressure and temperature. The furnace temperature, NO production and CO emission increase as the oxygen concentration increases, and the deviation of furnace exit temperature, NO and CO concentration is 38.26%, 58.43% and 86.67%, respectively. Finally, oxygen concentration is limited to below 35% to prevent excessive CO and NO_X emission without compromising plant performance. The current work greatly helps to understand the operating characteristics of large-scale MSW-burning plants.     

Emissions from a controlled fire in municipal solid waste bales

Environmental and safety aspects of seasonal storage of baled municipal solid waste to be used as fuel for energy production (waste fuel), was investigated and experiments were carried out on burning of bales. The flammability, combustion processes and emissions were studied by simulating, in small-scale, potential effects of a possible fire in full-scale bale storage area. Despite the high water content and the high density of the bales, after setting fire, the bales burned well, even though no risk for self-ignition exists. The following parameters of the combustion product were measured continuously: O2, CO2, CO, SO2, NO, NO2, NOx, THC, smoke gas rate and the temperature of the smoke. Soot particles in the smoke were collected and analysed for Hg, Pb, Cd, As, Ni, Cr, Mn, Cu, Co, Sb and V concentrations. The analysis of the moisture content, concentrations of Hg, Cd, HCl, HF, HBr, NH3, polyaromatic hydrocarbons (PAH), chlorinated and brominated dioxins (PCDD/F and PBrDD/F, respectively) were carried out. It was found that the PCDD/F levels (TEQs) varied according to the system used: 12.53 ng (I-TEF-88)/Nm3; 14.09 ng (I-TEF-99)/Nm3; 13.86 ng (Eadons)/Nm3. The PAH concentration was 3.04 microg/Nm3. The contents of the metals in the smoke (with the exceptions of Pb and Cd with mean values of 1.74 and 0.36 mg/m3, respectively) were below the limit values established by the Swedish Ministry of Environment for emissions from incineration plants [Swedish Ministry of Environment, (2002:1060), F?rordning 2002:1060 om avfallsf?rbr?nning. Available from http://www.notisum.se/rnp/SLS/LAG/20021060.HTM]/EU-directive [(2000/76/EC), Directive 2000/76/EC, of the European Parliament and of the Council of 4 December 2000 on the Incineration of Waste. http://www.Scotland. gov.uk/library5/environment/iecda.pdf]. The HCl concentration was 10 times higher than the limit value (mean value of 99 mg/m3).     

软锰矿浆催化氧化烟气中二氧化硫产酸过程研究

采用软锰矿浆催化氧化烟气中的SO2,使其生成硫酸。考察了软锰矿浆液固比、软锰矿浆初始pH、气体流量、进口SO2浓度、气体中氧浓度和反应温度对硫酸浓度的影响。试验结果表明,软锰矿浆的液固比和气体中的氧浓度对产酸速率的影响最大。软锰矿浆与SO2反应生成硫酸的过程分为线性阶段和幂函数两个阶段,符合Pasiuk提出的反应动力学模型。     

火电厂降低NOx排放的技术研究

NOx是燃煤电厂烟气排放三大有害物（SO2、NOx及悬浮颗粒物TSP）之一。从污染角度考虑的氮氧化物主要是NO和NO2,统称为NOx。介绍了NOx的生成机理,即热力型NOx和燃料型NOx,前者由参与燃烧的空气中所含的N2生成,后者由燃料本身的氮元素生成。分析了低氮燃烧技术、SCR烟气脱硝技术、SNCR烟气脱硝技术及SCR＋SNCR组合式等NOx控制技术。其中,在燃烧过程中降低NOx生成的主要手段是采用分级燃烧,降低燃烧区域的氧浓度和降低火焰温度;在燃烧后可采用烟气处理技术降低烟气中的NOx含量。     

Effects of gaseous NH(3) and SO(2) on the concentration profiles of PCDD/F in flyash under post-combustion zone conditions

The influence of gaseous ammonia and sulphur dioxide on the formation of 2378-substituted PCDD/F on a reference flyash from a municipal waste incinerator has been investigated using a laboratory scale fixed-bed reactor. The reference flyash samples (BCR-490) was reacted under a simulated flue gas stream at temperatures of 225 and 375°C for 96h. The experiments were carried out in two series: first with simulated flue gas alone, and then with injection of NH(3) or SO(2) gas into the flue gas just before the reactor inlet. It was found that the injection of gaseous ammonia into the flue gas could decrease the concentration of both PCDD and PCDF by 34-75% from the solid phase and by 21-40% from the gas phase. Converting the results to I-TEQ values, it could reduce the total I-TEQ values of PCDD and PCDF in the sum of the flyash and exhaust flue gas by 42-75% and 24-57% respectively. The application of SO(2) led to 99% and 93% reductions in the PCDD and PCDF average congener concentrations, respectively in the solid phase. In the gas phase, the total reductions were 89% and 76% for PCDD and PCDF, respectively. Moreover, addition of SO(2) reduced the total I-TEQ value of PCDD and PCDF in the flyash and exhaust flue gas together by 60-86% and 72-82% respectively. Sulphur dioxide was more effective than ammonia in suppressing PCDD/F formation in flyash under the conditions investigated.     

AERMOD在火电大气环评中出现山地极端异常值的分析

利用AERMOD模型预测了我国东部某电厂＂上大压小＂项目污染物排放对评价区域大气环境的影响。结果发现,受厂址东南山体影响,SO2、NO2小时最大落地浓度分别为环境空气质量二级标准的552.00%和1223.33%,NO2日均最大落地浓度为环境空气质量二级标准的117.50%。据统计,SO2小时贡献值超过标准时次为1次;NO2小时贡献值超过标准时次为5次,超标发生的概率均较低。预测超标原因主要与预测模型中烟羽遇到山体后的烟羽分层简化处理与实际烟羽运行状况存在一定差异有关。     

Treatment of exhaust fluorescent lamps to recover yttrium: experimental and process analyses

The paper deals with recovery of yttrium from fluorescent powder coming from dismantling of spent fluorescent tubes. Metals are leached by using different acids (nitric, hydrochloric and sulphuric) and ammonia in different leaching tests. These tests show that ammonia is not suitable to recover yttrium, whereas HNO(3) produces toxic vapours. A full factorial design is carried out with HCl and H(2)SO(4) to evaluate the influence of operating factors. HCl and H(2)SO(4) leaching systems give similar results in terms of yttrium extraction yield, but the last one allows to reduce calcium extraction with subsequent advantage during recovery of yttrium compounds in the downstream. The greatest extraction of yttrium is obtained by 20% w/v S/L ratio, 4N H(2)SO(4) concentration and 90°C. Yttrium and calcium yields are nearly 85% and 5%, respectively. The analysis of variance shows that acid concentration alone and interaction between acid and pulp density have a significant positive effect on yttrium solubilization for both HCl and H(2)SO(4) medium. Two models are empirically developed to estimate yttrium and calcium concentration during leaching. Precipitation tests demonstrate that at least the stoichiometric amount of oxalic acid is necessary to recover yttrium efficiently and a pure yttrium oxalate n-hydrate can be produced (99% grade). The process is economically feasible if other components of the fluorescent lamps (glass, ferrous and non-ferrous scraps) are recovered after the equipment dismantling and valorized, besides the cost that is usually paid to recycling companies for collection, treatment or final disposal of such fluorescent powders.