不同规模的煤燃烧装置中燃料-N向N2O和NOx的转化（英文）

With focus on investigating the effect of combustor scale on the conversion of fuel-N to NOx and N20, experiments are carried out in three combustors, including single coal particle combustion test rig, laboratory scale circulating fluidized-bed boiler （CFB） and full scale CFB in this work. For single coal particle combustion, the majority of f-uel-N （65%-82%） is released as NOx, while only a little （less than 8%） fuel-N yields N20. But in labora- tory scale CFB, the conversion of fuel-N to N20 is increases, but the conversion of fuel-N to NOx is quite less than that of single coal particle combustion. This is because much char in CFB can promote the NOx reduction by in- creasing N20 formation. In full scale CFB, both of the conversion of fuel-N to NOx and the conversion of fuel-N to N20 are smaller than laboratory scale CFB.     

Study on the emission characteristics of nitrogen oxides with coal combustion in pressurized fluidized bed

Nitrogen oxides are one of the most significant pollution sources during coal combustion. This experimental study was conducted in a 15 kWthlab-scale pressurized fluidized bed(inner diameter = 81–100 mm, H =2100 mm) firing with bituminous coals. The effects of operating parameters, including bed temperature(800 ℃–900 ℃), operating pressure(0.1–0.4 MPa), excess air level(16%–30%) and flow pattern on NOx and N_2 O emissions were systematically studied during the tests. During each test the interaction effects of all the operating parameters were properly controlled. The results show that most operating parameters have an opposite effect on NOxand N_2 O emissions, and the N_2 O emissions mainly depend on the bed temperature. Increasing the operating pressure can significantly suppress the fuel-N conversion to NOxbut enhance its conversion to N_2 O. With the rise of the excess air level and fluidization number, NOxemissions grow distinctly while N_2 O emissions remain almost unchanged. Total nitrogen oxide emissions increase with the bed temperature while decrease with the operating pressure.     

DETERMINATION OF DILUTE SLURRY DENSITIES IN A VERTICAL ANNULUS USING ISOKINETIC SAMPLING

The effects of coal properties on N₂O and NO_x formation from circulating fluidized bed combustion of coal was examined through burning nine typical coals and a coal shale, widely used in China over a wide range of coal ranks, in a bench-scale circulating fluidized bed. It was found that N₂O and NO_x formation had similar dependence on coal rank. Fixed carbon content and nitrogen content were the most important coal properties to influence N₂O and NO_x emissions from circulating fluidized bed combustion of coal. A coal with high fixed carbon content had high conversion ratio of fuel-N into N₂O and NO_x. The conversion ratio of fuel-N into N₂O or NO_x increased with nitrogen content of coal, whereas it decreased with O/N ratio. No significant correlation between conversion ratio of fuel-N into N₂O or NO_x and C/N ratio was identified. To clarify the coal property effect, investigation of a wide range of coal rank, is important.     

Effect of fuel composition on the conversion of volatile solid fuel-N to N2O and NO

Older fuels, which generally have a low fuel-O/fuel-N ratio, produce more N₂O in fluidized bed combustion than younger fuels. Here, a proposal is made regarding the effect of fuel composition on the conversion of fuel-N to N₂O and NO through HCN and NH₃ at temperatures typical of fluidized bed combustion. Because earlier experiments have shown that the fuel oxygen plays an important role in fuel-N chemistry, fuel oxygen was considered together with fuel nitrogen. In model compound studies, phenolic OH-groups in particular were found to increase the conversion of HCN to NH₃. In general, the abundance of phenolic oxygen in fuel follows the fuel oxygen concentration. The importance of reactions between OH radicals and HCN was therefore considered.     

低温燃烧下NH3的氧化特性

NH₃的气相氧化是低温燃烧过程中NO_x（NO和NO₂）与N₂O的重要来源,为了深入认识其反应规律,在管式流动反应器系统中进行了实验研究。重点考察了挥发分中的可燃气（CO、CH₄或H₂）和NO对NH₃氧化及氮氧化物排放的影响规律,并根据化学反应机理对实验结果进行了分析。研究结果表明,低温氧化性气氛下微量的可燃气就能够显著促进NH₃的氧化,并使NO_x和N₂O的生成量大幅度升高。当可燃气体浓度相同时,H₂对NH₃氧化的影响最大,CO的影响最小,CH₄对NH₃氧化的影响略大于CO。随着可燃气体浓度的升高,其对NH₃氧化与氮氧化物生成的影响先逐渐增加,然后趋于稳定。反应初始气体中存在NO时,也会加速NH₃的氧化。     

无烟煤化学链燃烧过程燃料氮转化释放特性

基于赤铁矿石载氧体,在小型单流化床反应器上,开展煤挥发分和焦炭的化学链燃烧研究,探讨挥发分氮和焦氮在化学链燃烧过程中的转化特性。研究表明:燃料氮释放的中间产物HCN和NH₃与铁矿石载氧体具有较高的化学反应亲和性,易于被载氧体氧化生成N₂和NO。淮北无烟煤挥发分氮转化过程中,NO是唯一的氮氧化物,反应器出口中间产物NH₃的释放份额略高于HCN。在煤焦化学链燃烧还原过程中,部分燃料氮释放的中间产物HCN和NH₃被铁矿石氧化导致少量NO的生成,还原过程中无N₂O的释放;较高的还原反应温度加速了NO的生成。减少进入载氧体氧化再生过程的焦炭量可减少空气反应器NO和N₂O的生成。     

含氮模型化合物用于化学链燃烧的氮氧化物释放特性

以谷氨酸、甘氨酸和苯丙氨酸作为生物质的含氮模型化合物,进行化学链燃烧实验,主要考察了反应温度、氨基酸种类、碱金属钾元素等对化学链燃烧还原反应过程中氮氧化物释放特性的影响。结果显示,挥发分氮的释放迅速,温度的升高有利于NO和NO₂的生成,N₂O的生成会出现波动。模型化合物的氮含量越高,可能越不利于氮向氮氧化物的转化。钾元素对苯丙氨酸的化学链燃烧过程中NO的释放抑制作用较强,而对其他氨基酸化学链燃烧过程中氮氧化物释放的影响则不太显著。     

鼓泡流化床煤燃烧中燃料氮转化的研究（Ⅰ）影响因素

本文研究了各种操作因素如床温、过量氧率、煤种、脱硫、燃料粒径等对流化床煤燃烧中燃料氮转化为ＮＯ＿ｘ和Ｎ＿２Ｏ的影响，为找到减少流化床煤燃烧中氮氧化物的排放措施提供依据。     

高含水菌渣流化床燃烧NOx、SO2排放特性

采用流化床反应器，研究了高含水抗生素菌渣直接燃烧的NO_x、SO₂排放特性。结果表明，增加过量空气系数，NO_x排放浓度升高，SO₂排放浓度降低；升高燃烧温度，NO_x及SO₂排放浓度均升高；随着燃料含水率的增加，NO_x及SO₂排放浓度均呈现先降低后升高的趋势。空气分级燃烧能有效降低NO_x排放，二次风率增加，NO_x排放浓度显著降低；当二次风率为3/7时，NO_x排放浓度较传统燃烧降低50%。添加CaCO₃进行炉内脱硫，实验结果显示：随钙硫摩尔比（Ca/S）增加，SO₂排放浓度下降，当Ca/S 3时，SO₂排放浓度降低到25 mg·m^-3以下，脱硫效率超过99%。     

Combined plasma-catalytic processing of nitrous oxide

The gliding arc discharge, combined with a catalytic bed, has been applied for nitrous oxide processing in oxygen containing gases. It has been found that under conditions of the gliding arc, nitrous oxide in mixtures with oxygen or air not only decomposes to oxygen and nitrogen, but is also oxidised to nitric oxide. The overall conversion of nitrous oxide, as well as the degree of N₂O oxidation to NO were studied as a function of its initial concentration, flow rate, and discharge power. The overall N₂O conversion and degree of oxidation to NO decreased with increasing flow rate and initial N₂O concentration, and increased with increasing discharge power. The degree of N₂O oxidation to NO varied within 20–37%. The overall conversion and degree of N₂O oxidation increased when granular dielectric materials (TiO₂, SiO₂ (quartz glass), and γ-Al₂O₃) were introduced into the reaction zone. The energy efficiency and the overall conversion of N₂O were still further increased due to catalytic effects of a number of metal oxides (CuO, NiO, MnO₂, Fe₂O₃, Co₃O₄, ZrO₂) deposited on γ-Al₂O₃. The activity of the oxide catalysts within the active power range of 300–360 W decreased in the order: CuO>Fe₂O₃>NiO>MnO₂>Co₃O₄>ZrO₂. It has been concluded that the combined plasma-catalytic processing may be an efficient way for the reduction of N₂O emissions.     

SULFUR CAPTURE DURING PARTIAL COAL COMBUSTION

A coal-water slurry is an econonical substitute for premium liquid fuels, but the amount of sulfur in coal is usually higher than in petroleum liquids. Lime has been used to capture sulfur in fluidized coal combustion as CaSO₄, but the latter decomposes above 1273 K. We report here on the possible capture of sulfur in the ash as CaS, which has higher thermal stability than CaSO₄. This can be accomplished using a fuel-rich first stage in a coal-water slurry combustor, or under the conditions normally encountered in some coal gasifiers. Thermodynamic calculations and some preliminary experiments suggest that the concept is promising for effective sulfur removal and, by extension, for NO_x, control.     

重型柴油机主要含氮化合物的排放特性

采用傅里叶变换红外光谱(FTIR)技术,研究了加装选择性催化还原SCR装置的重型柴油机主要含氮化合物排放,重点探索了不同工况下主要含氮化合物NO、NO₂和N₂O的排放特性。结果表明:未加装SCR的原机,随负荷的增加,柴油机NO排放持续上升,NO₂排放先升后降,N₂O排放很少。加装SCR后该柴油机NO与NO₂排放均明显下降,标定转速下NO₂排放降幅较大,主要是其NO₂/NO值稍高导致快速SCR反应较多的原因。由于存在SCR副反应,与原机相比,柴油机N₂O排放比原机平均增加2倍以上,最大转矩转速下N₂O排放升幅更高。N₂O排放随负荷的增加而上升,主要是排温升高导致NH₃氧化生成N₂O反应速率增加的原因。加装SCR后,该机排气中的NO/NO_x值要明显低于原机状态,而外特性的NO₂/NO_x值和N₂O/NO_x值高达12.8%和20.7%,均远高于原机的3.0%和0.5%。     

Simultaneous SO2/NOx removal by a powder-particle fluidized bed

Simultaneous dry removal of SO₂ and NO_x from flue gas has been investigated using a powder-particle fluidized bed. In a process of flue gas desulfurization by use of solid sorbents such as FeO (dust from a steel plant) and CuO, the smaller the particle size of sorbents, the higher the expected SO₂ conversion. In a powder-particle fluidized bed (PPFB), fine particles less than 40 μm in diameter fed into the bed are fluidized with coarse particles. But only the fine particles are entrained from the bed, and their residence time in the bed is remarkably long.

The reduction of NO_x with NH₃ in the fluidized bed is catalyzed by coarse particles or both coarse and fine particles. In this study, PPFB was applied to simultaneous dry SO₂/NO_x removal process, and several kinds of sorbents or catalysts were evaluated in a PPFB. Using the selected sorbents and catalysts, kinetic measurements were made in the temperature range of 300 to 600°C. SO₂ removal efficiencies were affected by reaction temperature, sorbent/S ratio, and static bed height. NO_x removal efficiencies in excess of 95% were achieved at NH₃/NO_x mole ratio of 1.0. When FeO was used as sorbent, SO₂ conversion increased with increasing temperature and reached 80% at 600°C.     

Effect of operating conditions on the reduction of nitrous oxide by propane over a Fe-zeolite monolith

Fluidised bed combustion is an important source of nitrous oxide emissions. The influence of different operating parameters, such as catalyst volume, temperature, gas hourly space velocity, and hydrocarbon addition, on the activity, selectivity, and poisoning tolerance of a Fe-ZSM-5 monolith for the nitrous oxide selective catalytic reduction, has been investigated under realistic conditions, at bench scale.

Both in the absence or in the presence of poisons, such as H₂O, NO, and SO₂, the optimisation of operating conditions gives rise to a broadening of the temperature window for N₂O reduction, making it more compatible with real application conditions, with a simultaneous reduction in hydrocarbon fugitive emission, resulting in an environmental friendly process.

Excessively high reaction temperatures seem to be needed to obtain an acceptable level of N₂O decomposition. On the contrary, high N₂O reduction conversions are obtained, even in the presence of poisons and at relatively low temperatures, which is the preferred situation in the processes of pollutants removal from stationary combustion sources.

The optimum value of C₃H₈/N₂O ratio to be used for reducing N₂O over the catalyst system seems to be about the unity, since higher N₂O and C₃H₈ conversions and lower hydrocarbon unwanted emissions are attained, with a low consume of propane as selective reductant.     

Characterization and reactivity of pure TiO2–SO4 SCR catalyst: influence of SO4 content

The kinetics of the reaction of NO, N₂O and CO₂ with activated carbon without catalyst and impregnated with a precursor salt of vanadium (ammonium monovanadate) was investigated. The conversion of NO, N₂O and CO₂ was studied (450–900°C) using a TGA apparatus and a fixed bed reactor. The reactor effluents were analysed using a GC/MS on line. The addition of vanadium increased carbon reactivity and adsorption at lower temperatures. For NO and N₂O conversion the main products obtained were N₂, N₂O, CO and CO₂ but for CO₂ conversion only CO was detected. In situ XRD was a useful tool for interpreting catalyst behaviour and identifying phases present during reaction conditions. The catalytic effect of vanadium can be explained by the occurrence of redox processes in which the catalyst is reduced to lower oxidation states such as V₂O₅/V₆O₁₃.     

温度和气氛对高K高S糠醛渣灰分的烧结特性研究

糠醛渣的能源化利用是糠醛产业清洁生产和碳减排的有效途径。然而,现有的直接燃烧利用常面临着因糠醛渣高K引起的灰分烧结严重、高S导致的SO_x排放量大和高水含量导致的燃烧效率低等难题。基于此,在管式炉中考察了单一气氛(N₂、CO₂、O₂)和混合气氛(N₂+H₂O、CO₂+H₂O、O₂+H₂O)中糠醛渣灰在不同温度下的烧结特性,并对灰分颜色、收缩率、微观形貌、矿物质成分和K/S释放等特性进行系统分析。灰分热收缩行为显示,随温度升高,灰样收缩率增加;在单一气氛中添加水蒸气能促进灰分烧结。SEM分析发现,在灰分烧结前,其微观结构在低温下已出现熔融和结渣。XRD分析表明,灰分烧结与低熔点矿物生成紧密相关。单一气氛中,高温下N₂促进钾长石生成;CO₂抑制钾长石生成;O₂促进钙铝黄长石和透辉石生成。在混合气氛中,水蒸气的出现促进多种低熔点钾铝硅酸盐生成,如钾长石和白榴石等。XRF分析显示,随温度升高,灰样中K的固留率(G_K)和S的固留率(G_S)降低;在考察的单一气氛中,高温时,N₂中G_K最低;G_S受气氛的影响较小。在考察的复合气氛中,高温时,G_K受气氛影响较小;G_S受气氛影响严重,特别地,O₂+H₂O气氛中G_S最高,S逸散最少。为抑制糠醛渣灰分烧结和K/S元素逸散到气相中,糠醛渣在流化床燃烧过程中应控制运行温度(低于900℃)、降低气氛中N₂的含量。     

Nitrogen release during high temperature pyrolysis of coals and catalytic role of calcium in N2 formation

Pyrolysis of 10 coals with carbon contents of less than 80 wt%(daf) has been studied with a fixed bed quartz reactor to examine mainly nitrogen release from char-N without volatile matters. When temperature is raised from 1000 to 1350 °C, N₂ yield increases but char-N decreases for all the coals used. There is a strong reverse correlation between N₂ and char-N, which points out that most of N₂ arises from char-N via solid phase reactions. NH₃ is also formed from char-N at high temperatures of ≥1000 °C. In the pyrolysis of low rank coals, demineralization by HCl washing increases yields of tar-N, HCN and char-N, but decreases NH₃ and N₂. The addition of 3 wt% Ca to the demineralized coals shows almost the reverse effect. The XRD measurements after pyrolysis at 1000–1350 °C reveal that the Ca exists predominantly as CaO with the average crystallite size of 25–65 nm and promotes carbon crystallization. As the extent of crystallized carbon increases, N₂ yield increases remarkably. It is likely that the highly dispersed CaO catalyzes efficiently conversion reactions of char-N to N₂ in the process of carbon crystallization. The reaction mechanism is discussed in term of interactions between CaO particles and char-N.     

NTP转化C3H6/NO/N2气氛中NO及发射光谱分析

利用介质阻挡放电产生低温等离子体转化C₃H₆/NO/N₂气氛中NO,结合发射光谱诊断法研究了碳氢化合物C₃H₆对NO转化的影响。研究结果表明,随着放电功率的升高,NO转化率先升高后逐渐趋于平缓,NO₂浓度持续降低,N₂O浓度呈先升高后降低趋势,NO主要被还原为N₂;相同放电功率下,随着C₃H₆初始浓度升高,NO_x转化率和N₂O浓度升高、NO₂浓度降低;添加C₃H₆会降低N₂第二正带系和NO-γ带的发射光谱强度,产生CN自由基的激发跃迁谱线,影响NO的化学反应机制,同时生成了棕黄色的聚合物。     

V2O5-WO3-MoO3/TiO2催化剂在柴油机NH3-SCR系统中的性能

针对柴油机运行工况特点及柴油机尾气成分特点,以工业纯锐钛型二氧化钛、偏钒酸铵、偏钨酸铵、钼酸铵为主要原料制备了颗粒状V₂O₅-WO₃-MoO₃/TiO₂催化剂,以Lister Petter TR1重型直喷式单缸柴油机为依托搭建试验台,研究了在真实柴油机尾气环境下催化剂的脱硝性能。结果表明,柴油机负载增大,催化剂脱硝活性呈现下降趋势。1800 r·min^-1时,脱硝活性最大值87.1%在负载25%、反应温度380℃、空速20000 h^-1、氨氮比1.0处取得。柴油机负载不同,导致催化剂活性温度窗口(脱硝活性>70%)发生较大变化,与负载25%相比,负载50%活性温度窗口减小约60℃。增大柴油机负载可以提高NH₃/N₂O反应起始温度,但是同时会导致高温区间(>400℃)N₂O生成量增大。     

串行流化床煤气化试验

针对串行流化床煤气化技术特点,以水蒸气为气化剂,在串行流化床试验装置上进行煤气化特性的试验研究,考察了气化反应器温度、蒸汽煤比对煤气组成、热值、冷煤气效率和碳转化率的影响。结果表明,燃烧反应器内燃烧烟气不会串混至气化反应器,该煤气化技术能够稳定连续地从气化反应器获得不含N₂的高品质合成气。随着气化反应器温度的升高、蒸汽煤比的增加,煤气热值和冷煤气效率均会提高,但对碳转化率影响有所不同。在试验阶段获得的最高煤气热值为6.9 MJ•m^-3,冷煤气效率为68％,碳转化率为92％。