Balance of NH3 and behavior of polychlorinated dioxins and furans in the course of the selective non-catalytic reduction of nitric oxide at the TAMARA waste incineration plant

Investigations were performed on the selective non-catalytic reduction (SNCR) of nitric oxide (NO) at TAMARA, the pilot-scale waste incineration plant of the Karlsruhe Research Center. Aqueous ammonia (NH₃) was injected into the combustion chamber as reductant. The influence of NH₃ on various inorganic and organic compounds in the flue gas was investigated. The concentrations of NO were reduced by up to about 90% by NH₃ injection. The concentrations of most of the other inorganic and organic compounds, including in particular PCDD and PCDF, did not change significantly.     

燃煤电站SNCR脱硝系统喷射还原剂介质对锅炉效率的影响

以燃煤电厂1台600MW机组配套SNCR脱硝系统为例,分别介绍了采用尿素、液氨为SNCR脱硝还原剂时,各还原剂的喷入量对锅炉效率和燃煤成本的影响。结果发现,以设计煤种Qnet,ar=11766.7kJ/kg计,当浓度5%的尿素溶液喷入时,有1.67%的燃煤发热量被水蒸发所吸收,导致排烟损失增加0.6659%。假设其他损失不变,不计固体尿素的升温、分解热反应等的影响,尿素溶液的喷入对锅炉热效率的影响在0.6659%左右,燃煤成本约增加900多万元/a;在喷入氨空混合气情况下,约0.2%的燃煤发热量被混合气所吸收,导致排烟损失增加0.02%。假设其他损失都不变,不计分解热反应等的影响,混合气的喷入对锅炉的热效率的影响亦即在0.02%左右,燃煤成本约增加30万元/a。从节能的角度看,液氨为还原剂应作为优选。     

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.     

半干法高活性脱硝剂的制备及其脱硝性能

针对工业上100℃以下的中低温NO废气处理成本高、脱除困难等问题,以氢氧化钙为吸收剂、过碳酸钠为氧化剂,制备用于烟气半干法同时脱硫脱硝的高活性脱硝剂,并研究了NO去除率的影响因素。当气体总流量为1.2 L/min、O_2体积分数为10%、SO_2质量浓度1 428 mg/m~3、N_2为载气时,适宜的工艺条件为:氧化剂与吸收剂质量比5∶8、高活性脱硝剂中液固比80%、反应温度60℃、入口NO质量浓度670 mg/m~3。在此条件下,NO去除率达到55%以上,SO_2去除率达到100%。     

Absorption behavior of chlorine and sulfur by Ca(OH)<Subscript>2</Subscript> under simulated conditions with a fluidized bed combustor

This study was carried out to investigate the absorption reaction of chlorine and sulfur with Ca(OH)₂ under simulated conditions related to the co-combustion of refuse-derived fuel and sewage sludge in the fluidized bed combustor, such as high temperature, moisture and a mixing of samples. The combustion experiments were carried out in an electrical furnace with PVC and sulfur powders as the waste samples. High-purity slaked lime powder was used to capture the chlorine and sulfur. The experimental results showed that the removal efficiencies of both chlorine and sulfur were over 90% when the mole ratios of Ca on Cl and S were over 2.5. Furthermore, simultaneous absorption was helpful in improving the removal efficiency of chlorine and sulfur. The presence of chlorine markedly increased the removal efficiency of sulfur. The removal efficiency of chlorine was the highest at 700°C in both independent and simultaneous absorption. The removal efficiency of sulfur increased as the temperature increased, but the removal efficiency of chlorine sharply decreased from 95 to 83% when the moisture content in gases increased from 0 to 20 vol%. These results were confirmed by the combustion test of granular CaCl₂.     

Energy from Waste – Clean,efficient, renewable: Transitions in combustion efficiency and NOx control

Traditionally EfW (Energy from Waste) plants apply a reciprocating grate to combust waste fuel. An integrated steam generator recovers the heat of combustion and converts it to steam for use in a steam turbine/generator set. This is followed by an array of flue gas cleaning technologies to meet regulatory limitations.Modern combustion applies a two-step method using primary air to fuel the combustion process on the grate. This generates a complex mixture of pyrolysis gases, combustion gases and unused combustion air. The post-combustion step in the first pass of the boiler above the grate is intended to “clean up” this mixture by oxidizing unburned gases with secondary air.This paper describes modifications to the combustion process to minimize exhaust gas volumes and the generation of noxious gases and thus improving the overall thermal efficiency of the EfW plant. The resulting process can be coupled with an innovative SNCR (Selective Non-Catalytic Reduction) technology to form a clean and efficient solid waste combustion system.Measurements immediately above the grate show that gas compositions along the grate vary from 10% CO, 5% H₂ and 0% O₂ to essentially unused “pure” air, in good agreement with results from a mathematical model. Introducing these diverse gas compositions to the post combustion process will overwhelm its ability to process all these gas fractions in an optimal manner. Inserting an intermediate step aimed at homogenizing the mixture above the grate has shown to significantly improve the quality of combustion, allowing for optimized process parameters. These measures also resulted in reduced formation of NO_x (nitrogenous oxides) due to a lower oxygen level at which the combustion process was run (2.6 vol% O_2, wet instead of 6.0 vol% O_2, wet).This reduction establishes optimal conditions for the DyNOR? (Dynamic NO_x Reduction) NO_x reduction process. This innovative SNCR technology is adapted to situations typically encountered in solid fuel combustion. DyNOR? measures temperature in small furnace segments and delivers the reducing reagent to the exact location where it is most effective. The DyNOR? distributor reacts precisely and dynamically to rapid changes in combustion conditions, resulting in very low NO_x emissions from the stack.     

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。     

Determination of nitrous oxide, methane, and ammonia emissions from a swine waste composting process

The amounts of harmful gas emissions from the process of composting swine waste were determined using an experimental composting apparatus. Forced aeration (19.2–96.1 l/m³/min) was carried out continuously, and exhaust gases were collected and analyzed periodically. With weekly turning and the addition of a bulking agent in order to decrease the moisture content and increase air permeability, the temperature of most of the contents rose to 70°C and composting was complete within 3–5 weeks. NH₃, CH₄, and N₂O emissions were high in the early stage of composting. About 10%–25% of the nitrogen in the raw material was lost as NH₃ gas during composting. The emission rate of NH₃ mainly depended on the aeration rate, so that as the aeration rate rose, the level of NH₃ emissions increased. The CH₄ and N₂O emissions could be kept lower with adequate treatment at more than 40 l/m³/min aeration. N₂O may be mainly the result of the denitrification of NO _x -N in the additional matured compost used as a composting accelerator. Received: September 11, 1998 / Accepted: November 8, 1999     

Life cycle assessment of selective non-catalytic reduction (SNCR) of nitrous oxides in a full-scale municipal solid waste incinerator

Selective non-catalytic reduction (SNCR) of nitrous oxides in a full-scale municipal solid waste incinerator was investigated using LCA. The relationship between NO_x-cleaning and ammonia dosage was measured at the plant. Un-reacted ammonia - the ammonia slip - leaving the flue-gas cleaning system adsorbed to fly-ash or in the effluent of the acidic scrubber was quantified from the stoichiometric reaction of NO_x and ammonia assuming no other reaction products was formed. Of the ammonia slip, 37% was associated with the fly-ash and 63% was in the effluent of the acidic scrubber. Based on NO_x-cleaning efficiency, the fate of the ammonia slip as well as the environmental impact from ammonia production, the potential acidification and nutrient enrichment from NO_x-cleaning was calculated as a function of ammonia dosage. Since the exact fate of the ammonia slip could not be measured directly, a number of scenarios were set up ranging from “best case” with no ammonia from the slip ending up in the environment to “worst case” where all the ammonia slip eventually ended up in the environment and contributed to environmental pollution. In the “best case” scenario the highest ammonia dosage was most beneficial demonstrating that the environmental load associated with ammonia production is of minor importance. In contrast, in a “worst case” scenario” NO_x-cleaning using SNCR is not recommendable at all, since the impacts from the ammonia slip exceed the saved impacts from the NO_x removal. Increased dosage of ammonia for removal of NO_x is recommendable as long as less than 10-20% of the ammonia slip to the effluent of the acidic scrubber ends up in the environment and less than 40% of the slip to the fly-ash ends up in the environment. The study suggests that the actual fate of the ammonia slip is crucial, but since the release of the ammonia may take place during transport and at the facilities that treat the wastewater and treat the fly-ash this factor depends strongly on local conditions and may be hard to determine. Thus, LCA-modeling proved useful in assessing the balance between ammonia dosage and NO_x-removal in flue-gas cleaning from waste incineration.     

选择性非催化还原法烟气脱硝工业试验

以氨水作为还原剂,在日产5kt的新型干法水泥生产线分解炉上进行选择性非催化还原脱硝工艺的工业性试验研究。在氨水质量分数为13.0%、喷入点温度为894℃、n（NH₃）∶n（NO_x）为1.2、雾化压力为0.35MPa的条件下,NO_x去除率最高,为72.8%,剩余NO_x质量浓度为196mg/m³,剩余NH₃质量浓度小于0.9mg/m³,远低于《水泥工业大气污染物排放标准》征求意见稿中限定的NO_x和NH₃质量浓度。     

The influence of atmospheric n deposition on nitrous oxide and nitric oxide fluxes and soil ammonium and nitrate concentrations

The deposition of atmospheric N to soils provides sources of available N to the nitrifying and denitrifying microbial community and subsequently influences the rate of NO and N₂O emissions from soil. We have investigated the influence of three different sources of enhanced N deposition on NO and N₂O emissions 1) elevated NH₃ deposition to woodlands downwind of poultry and pig farms, 2) increased wet cloud and occult N deposition to upland forest and moorland and 3) enhanced N deposition to trees as NO^? ₃ and NH⁺ ₄ aerosol. Flux measurements of NO and N₂O were made using static chambers in the field or intact and repacked soil cores in the laboratory and determination of N₂O by gas chromatography and of NO by chemiluminescence analysis. Rates of N deposition to our study sites were derived from modelled estimates of N deposition, NH₃ concentrations measured by passive diffusion and inference from measurements of the ²¹⁰Pb inventory of soils under tree canopies compared with open grassland. NO and N₂O emissions and KCl-extractable soil NH⁺ ₄ and NO^? ₃ concentrations all increased with increasing N deposition rate. The extent of increase did not appear to be influenced by the chemical form of the N deposited. Systems dominated by dry-deposited NH₃ downwind of intensive livestock farms or wet-deposited NH⁺ ₄and NO^? ₃ in the upland regions of Britain resulted in approximately the same linear response. Emissions of NO and N₂O from these soils increased with both N deposition and KCl extractable NH⁺ ₄, but the relationship between NH⁺ ₄ and N deposition (ln NH⁺ ₄ = 0.62 ln N_deposition+0.21, r ² = 0.33, n = 43) was more robust than the relationship between N deposition and soil NO and N₂O fluxes.     

Nitrogen evolution during the co-combustion of hydrothermally treated municipal solid waste and coal in a bubbling fluidized bed

Nitrogen evolution was studied during the co-combustion of hydrothermally treated municipal solid wastes (HT MSW) and coal in a bubbling fluidized bed (BFB). HT MSW blending ratios as 10%, 20% and 30% (wt.%) were selected and tested at 700, 800, 900 °C. Emissions of NO and N₂O from blends were measured and compared with the results of mono-combustion trials. Moreover, concentrations of precursors like NH₃ and HCN were also quantified. The results are summarized as follows: NO emissions were predominant in all the cases, which rose with increasing temperature. The blending of HT MSW contributed to the NO reduction. N₂O emissions decreased with temperature rising and the blending of HT MSW also presented positive effects. At 30% HT MSW addition, both NO and N₂O emissions showed the lowest values (391.85 ppm and 55.33 ppm, respectively at 900 °C). For the precursors, more HCN was detected than NH₃ and both played important roles on the gas side nitrogen evolution.     

Effect of aeration modes on the characteristics of composting emissions and the NH3 removal efficiency by using biotrickling filter

A pilot biotrickling filter (BTF) packed with ZX02 fibrous balls as packing material was tested for the treatment of ammonia (NH₃) released from a composting plant of dairy manure. In order to investigate the effects of three compost aeration modes (mode Co-I, Co-II and In-II) on the NH₃ removal efficiency, a field experiment was continuously carried out for more than eight months. The results demonstrated that under the intermittent aeration mode (In-II), the NH₃ removal efficiency reached 99.2 ± 0.1% when the inlet NH₃ concentration was 7.5-32.3 mg m⁻³ (9.8-42.5 ppmv). The maximum and critical elimination capacity of the biotrickling filter was 22.6 and 4.9 g NH₃ m⁻³ h⁻¹, respectively. The effluent concentration of NH₃ was lower than 1.0 mg m⁻³, which meets the first class discharge standards of GB14554-93. When the concentration of free ammonia in the trickling liquid was varied from 0.1 to 0.4 mg L⁻¹, the nitrification yield was between 47.9% and 103.8%. In addition, the optimum liquid tricking velocity (LTV) of the biotrickling filter was 0.5 m³ m⁻² h⁻¹ for low inlet concentrations and 2.2 m³ m⁻² h⁻¹ for high inlet concentrations. Therefore, the use of the biotrickling filter for the compost under the third aeration mode (In-II) yielded an effective optimum NH₃ removal and reduced the nitrogen loss in the compost.     

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.     

High efficiency chlorine removal from polyvinyl chloride (PVC) pyrolysis with a gas–liquid fluidized bed reactor

In this research a gas–liquid fluidized bed reactor was developed for removing chlorine (Cl) from polyvinyl chloride (PVC) to favor its pyrolysis treatment. In order to efficiently remove Cl within a limited time before extensive generation of hydrocarbon products, the gas–liquid fluidized bed reactor was running at 280–320 °C, where hot N₂ was used as fluidizing gas to fluidize the molten polymer, letting the molten polymer contact well with N₂ to release Cl in form of HCl. Experimental results showed that dechlorination efficiency is mainly temperature dependent and 300 °C is a proper reaction temperature for efficient dechlorination within a limited time duration and for prevention of extensive pyrolysis; under this temperature 99.5% of Cl removal efficiency can be obtained within reaction time around 1 min after melting is completed as the flow rate of N₂ gas was set around 0.47–0.85 Nm³ kg^?1 for the molten PVC. Larger N₂ flow rate and additives in PVC would enhance HCl release but did not change the final dechlorination efficiency; and excessive N₂ flow rate should be avoided for prevention of polymer entrainment. HCl is emitted from PVC granules or scraps at the mean time they started to melt and the melting stage should be taken into consideration when design the gas–liquid fluidized bed reactor for dechlorination.     

Effective Removing of Remazol Black B by the Polyacrylamide Cryogels Modified with Polyethyleneimine

In this study, modified polyacrylamide (PAAm) cryogels with high dye holding capacity were synthesized with an easily and cheaply process and adsorption of Remazol Black B (RBB) with the synthesized materials was investigated. Firstly, PAAm cryogels were synthesized with free radical cryo-copolymerization method and they were modified with Hofmann reaction to form amine groups in the structure of the cyrogels. Then, to increase the removal efficiency of cryogels, polyethylenimine (PEI) molecules were crosslinked onto the cryogels via NH₂ groups present in the PAAm gels modified by the Hofmann reaction. The original and modified cryogels were characterized with fourier transformed infrared spectroscopy, ¹³C nuclear magnetic resonance spectroscopy, scanning electron microscopy and thermogravimetric analysis. The point of zero charge (pH_pzc) of the modified cryogels was found to be 7.13 and RBB removing capabilities of PEI-modified PAAm cryogels were investigated at pH between 2 and 7. In addition, the adsorption treatments were performed at different process time, incubation temperature, initial dye concentration and adsorbent amount to find maximum removal capacity of the adsorbent. The modified cryogels adsorbed maximum amount of RBB at pH 2 and the sorption process reached equilibrium in 6 h. It was observed that the adsorption efficiency did not change much with the increase in temperature. The maximum RBB removal capacity of the modified cyrogels was determined to be 201 mg/g when the initial RBB concentration was 200 mg/L, treatment time was 6 h at pH 2. Moreover, the adsorption of RBB dye with the modified cryogels takes place with a second order kinetic and RBB dye adsorption data showed compliance with the Langmuir isotherm. The findings of the study expose that the obtained PEI-modified PAAm cryogels are a hopeful material for RBB removal in aqueous environment.

     

Variability of nitrous oxide and carbon dioxide emissions continuously measured in solid waste incinerators

Nitrous oxide and carbon dioxide were continuously measured and variability of emission factors (EFs) was evaluated in five municipal waste incinerators (MWIs) and four industrial waste incinerators (IWIs) from 24 to 86 days between 2008 and 2011. N₂O EFs were calculated by Monte Carlo simulation and mean N₂O EFs were 7.1, 107, 127, 219 g N₂O/ton waste combusted in MWIs with selective catalytic reduction (SCR) for NOx control, MWIs with selective non-catalytic reduction (SNCR), IWIs with SNCR, and a MWI using fluidized bed with SNCR, respectively. Climate-relevant CO₂ EFs ranged from 0.45 to 0.72 ton CO₂/ton waste combusted in MWIs. Maximum values of upper limit for 95% confidence intervals (CIs) of N₂O EFs estimated in each MWIs with SCR, MWIs with SNCR, IWIs with SNCR were 185, 94, 101% of mean N₂O EFs, respectively. Meanwhile, maximum values of upper limit for 95% CIs of CO₂ EFs were much lower as between 18 and 36% in those facilities. 84% CIs of mean N₂O EFs in MWIs with SNCR and IWIs with SNCR were overlapped indicating those values are not significantly different.     

Preparation and characterization of mesoporous γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> recovered from aluminum cans waste and its use in the dehydration of methanol to dimethyl ether

The present study includes synthesis of two γ-Al₂O₃ samples from waste aluminum cans using a simple precipitation method. Precipitation was carried out using two different precipitating agents (i.e. NaOH and NH₄OH). The two prepared alumina samples were characterized by means of X-ray diffraction (XRD) and N₂ adsorption–desorption techniques. Surface acidity of γ-Al₂O₃ samples was measured by adsorption of two different probe molecules (i.e. pyridine and dimethyl pyridine) followed by desorption measurements using thermogravimetry (TG) and differential scanning calorimetry (DSC) techniques. Catalytic activity of the two prepared alumina samples towards the dehydration of methanol (to dimethyl ether) was studied in a fixed bed reactor at 300 °C. For comparison reasons, commercial γ-Al₂O₃ sample was, also, tested for the same catalytic reaction under the same conditions. Results showed that the alumina sample prepared using NaOH as a precipitating agent exhibited a better catalytic activity and stability compared with that prepared using NH₄OH and showed a similar activity as the commercial γ-Al₂O₃ sample.     

Development of a high-efficiency rotary dryer for sewage sludge

A rotary drum dryer having an internal rotating body was designed and tested in this study. It was shown that the developed dryer is effective for drying sewage sludge. The best operating conditions in the dryer were low energy input and almost 10% moisture content. The conditions are 255°C for the rotary drum temperature, 17 min for the sludge residence time, and 55 kg/m³ h for the dryer load. Under these conditions, the drying efficiency was 84.8%. The average diameter of dried sludge was less than 8 mm, and the weight reduction rate was 80%. Parametric screening studies achieved the following results. The drying efficiency increased with the increase of the internal temperature and the sludge residence time in the rotary drum, while the drying efficiency decreased when increasing the dryer load. In addition, it was shown that NH₃ and CO₂ were the primary components released from the sewage sludge drying process. The amounts of both of these components increased when the rotary drum temperature was increased.     

亚临界湿式氧化法脱除含油污泥中的重金属

采用亚临界湿式氧化法及金属络合剂协同亚临界湿式氧化法去除含油污泥中的重金属,考察了去除效果,优化了反应条件,并探讨了脱除重金属的含量上限。实验结果表明:在1 L反应釜内加入200 g含油污泥,在反应温度200℃、反应时间60 min、液固比(去离子水与含油污泥的质量比)0.30的优化条件下,Cu和Zn的去除率分别可达67.3%和22.0%;加入金属络合剂后,各重金属的去除率均有明显提高;在金属络合剂加入量为0.05mol/L的优化条件下,应用金属络合剂协同亚临界湿式氧化法可将2.5倍于CJ/T 309—2009《城镇污水处理厂污泥处置农用泥质》B级标准的重金属含量降至标准范围内。