控制燃油锅炉运行中NOx生成的技术研究

分析燃油锅炉运行中NOx产生的机理,探讨影响其生成的因素,研究抑制其生成和排放的燃烧技术低氧燃烧、掺水燃烧、空气分级燃烧和废气循环燃烧等.结合实验研究结果,重点分析空气分级燃烧和废气循环燃烧对油燃烧中燃料氮转化和氮氧化物生成的影响,并介绍一种新型低氮氧化物排放的燃油技术--预蒸发燃烧技术.     

真空紫外灯动态降解空气中低浓度甲醛的研究

以集中空调中处理室内可挥发性有机物(VOCs)为应用背景,搭建了试验台.实验研究了真空紫外灯(主波长254 nm,185 nm)降解甲醛的影响因素以及产生O3的情况.研究表明,在产生的O3浓度低于室内空气质量标准(0.16mg/m3)的情况下,真空紫外灯也能够高效地降解空气中低浓度甲醛(＜1 mg/m3);甲醛降解率与反应器空气流速及甲醛初始浓度成反比;降解速率与甲醛初始浓度成正比,与反应器空气的流速成反比;绝对湿度对真空紫外灯降解甲醛有一定的影响;反应器空间大小对甲醛降解影响比较显著.应用于集中空调系统净化室内空气中VOCs,取得了很好的效果.     

控制燃油锅炉运行中NOx 生成的技术研究

分析燃油锅炉运行中NOx产生的机理，探讨影响其生成的因素，研究抑制其生成和排放的燃烧技术：低氧燃烧、掺水燃烧、空气分级燃烧和废气循环燃烧等。结合实验研究结果，重点分析空气分级燃烧和废气循环燃烧对油燃烧中燃料氮转化和氮氧化物生成的影响，并介绍一种新型低氮氧化物排放的燃油技术——预蒸发燃烧技术。     

化工制药工艺残渣燃烧过程固氯研究

采用管式固定床反应器对化工制药工艺残渣的燃烧分解进行了实验研究,进一步通过加入氧化钙/碳酸钙来防止燃烧过程残渣中氯的释放.实验结果表明,残渣在燃烧时氯主要以氯化氢形式排出,加入固氯剂后能有效地抑制氯化氢的生成,且固氯效果随着钙化物投加量的增加而明显提高.当氧化钙/残渣比(质量比)达到0.8时,固氯率可达97%以上;当碳酸钙/残渣比(质量比)提高到2.0时,固氯率为76%.与此对应的Ca/Cl摩尔比分别为30和40.继续增加钙投加量,固氯效果基本不变.同时发现添加一定量的木屑在助燃的同时有助于提高固氯效果.     

基于Fluent的整体式催化反应系统降解甲苯的数值模拟

为得到甲苯在整体式催化系统中的燃烧规律,利用Fluent 18.1对整体式催化反应系统中甲苯-空气在铂(Pt)上的燃烧特性进行了数值模拟。通过假设多孔介质内气固间局部能够达到热平衡,建立了三维的多孔介质催化燃烧模型。经验证,该模型能够很好地反映甲苯在整个系统中的燃烧特性。通过对整个反应系统中温度场、浓度场和速度场的工况探究和通过分段控制燃烧反应发现:贫燃条件有利于催化燃烧,富燃条件有利于引发热力燃烧;当量比小于1,入口流速小于2 m·s~(-1)时,有利于催化燃烧,催化转化率在96%以上;当量比较高,入口流速较大时,有利于引发热力燃烧。以上研究结果为该技术的实际应用提供了参考。     

富氧燃烧条件下燃煤NO_x排放的实验研究

以神华(SH)烟煤和晋城(JC)无烟煤为研究对象,利用一维沉降炉(DTF)开展了煤粉在O_2/N_2、O_2/Ar、O_2/CO_2和O_2/RFG 4种气氛下燃烧时的NO_x排放特性实验,研究了温度和氧浓度对NO_x排放特性的影响,探讨了富氧燃烧条件下导致NO_x排放降低的各个因素的贡献率的变化。结果表明:温度上升会导致燃料氮向NO_x的转化率增大;氧浓度的上升同样会导致转化率的增加,SH烟煤由于挥发分含量较大,受氧浓度影响较大;定量分析结果表明,富氧燃烧条件下导致NO_x排放降低的主要因素是循环NO_x的还原,占整体的50%以上;其次是高浓度CO_2气氛对NO_x的还原,约占20%~30%;而热力型和快速型NO_x的缺失对降低NO_x排放的贡献率不及20%。温度的上升对JC无烟煤各因素贡献率有较大影响;氧浓度的增加会导致SH烟煤各因素贡献率有明显变化。     

生活垃圾衍生燃料分段催化气化

利用下吸式分段催化固定床反应器对生活垃圾衍生燃料进行了气化实验。研究了气化温度、当量空气系数、气化介质和催化剂对气化产物的影响。结果表明,生活垃圾衍生燃料以塑料、纸类和厨余组分为主,热值在10 MJ·kg~(-1)以上,适合直接气化。随着气化温度升高,气化气中H_2和CO的含量、产气率、气化气热值、碳转化率和冷煤气效率升高,而焦油和CO_2含量明显降低;随着当量空气系数升高,CO_2含量、产气率和碳转化率升高,而焦油含量和气化气热值降低,在当量空气系数为0.33时冷煤气效率最高;当采用富氧空气作为气化介质时,N_2对于气化气的稀释作用减弱;添加催化剂能有效减少气化气中焦油的含量,提高H_2和CO的含量。采用下吸式分段催化气化,能有效提高气化气品质和冷煤气效率。     

燃煤电厂多环芳烃的生成与控制

多环芳烃 (PAHs)对人体健康的危害极大。本文综述了燃煤电厂煤燃烧过程中多环芳烃的生成机理 (直接释放、热解合成和高温缩合机理 )和影响因素 (煤种、温度、锅炉负荷、过剩空气系数、停留时间、钙硫比和一次风 /二次风比 ) ,在此基础上介绍了煤燃烧过程中多环芳烃的各种控制技术和方法     

空气过剩系数与节能,消烟除尘的关系

根据国务院环委会颁发的城市烟尘控制区管理办法中规定,在建设烟尘控制区,改造治理炉、窑,污染物申报中必须对炉、窑的烟尘排放浓度进行监测。在实际测试工作中发现对空气过剩系数一事未能引起重视。事实上空气过剩系数是与节能、消烟除尘有着密切的关系。在烟尘浓度测试中有一个空气过剩系数,即当煤(或油)在只供给理论空气量的环境中完全燃烧后,空气中含有的氧都与煤(或油)中的可燃元素化合,生成二氧化碳、二氧化硫、氮氧化合物和水蒸汽等。理论上充分燃烧后没有自由氧存在。事实上在锅炉、炉窑的实际运行中不能保证燃料和空气完全混合,因此仅仅供给理论空气量是不可能达到完全燃烧     

超积累植物与煤在混烧过程中重金属的迁移特性

通过在管式炉中进行了煤与超积累植物——伴矿景天的混烧实验,主要研究了不同燃烧温度、不同氮氧比气氛以及煤与伴矿景天的不同混合质量比对混烧过程中重金属(Cd、Zn与Pb)迁移情况的影响,并应用XRD技术分析灰渣中重金属的存在形式。实验分析表明:升高温度能在不同程度上增强Cd、Zn与Pb的挥发,提高其在飞灰中的含量;与单独燃烧伴矿景天相比,煤与伴矿景天混烧更有利于Cd和Zn保留在底渣中,但不利于Pb保留在底渣中;对于不同氮氧比气氛而言,Zn和Cd在底渣中的含量随着气氛中氧气含量的提高而升高,而气氛对Pb的影响是随着氧气含量的增加,Pb在底渣的含量是先增加后减少;当煤在混烧中的比例较高时,Cd更多向飞灰迁移,Pb和Zn则更多地残留于底渣。     

Study on transformation and enrichment behavior of selenium in particulate matter in combustion flame

An ethylene/air inverse diffusion flame (IDF) burner was employed to generate a stable flame, and selenium was introduced into the combustion flame in vapor phase under different air-fuel ratio (A/F) with SO2 additive. At different height above burner (HAB) along the flame edge, selenium of different speciation (gaseous selenium and particulate selenium) was sampled via the U.S. EPA method 29, and the samples were determined by hydride generation atomic fluorescence spectrometry (HG-AFS), in order to study the mechanism of transformation and enrichment behavior of selenium during the combustion process. The results showed that selenium presented in vapor phase, crossing the flame into air, which means gaseous phase is the main form of selenium during combustion process. Both gaseous selenium and particulate selenium increased with elevated temperature from 820K to 1650K, suggesting that higher temperature is beneficial to the release of selenium. Low concentration of sulfur dioxide would increase the concentration of particulate selenium and gaseous selenium, and accelerate the release of selenium.

Implications: The enrichment behavior of selenium and its transformation in combustion flame were studied. The results showed that gaseous selenium is found in higher quantity in compared to particulate selenium during combustion. Higher temperature and air–fuel ratio will cause an increase in the formation of selenium. While the presence of sulfur dioxide in a range of 0–200 ppm will promote the release of selenium, higher sulfur dioxide level in a range of 200–350 ppm will have a reverse effect.     

Effect of Methanol on Exhaust Composition of a Fuel Containing Toluene,n-Heptane,and Isooctane

This study describes the variations in the chemical composition of the exhaust from a single cylinder engine when up to 25% methanol is added to a fuel blend of toluene, isooctane, and n-heptane. Under fuel-rich conditions, and with increasing methanol concentration, it is observed that unburned fuel and benzene emissions increase, exhaust acetylene remains constant, and propylene, isobutylene, methane, ethylbenzene, and styrene concentrations decrease. As oxygen becomes more available, the effects of methanol are reduced, and at an equivalence ratio of 1.25—excess oxygen now is present—methanol no longer affects the concentration of exhaust hydrocarbons. These observations are explained by the reactions of formaldehyde—an incomplete combustion product of methanol— with alkyl radicals derived from the fuel. The photochemical reactivity of the exhaust is unchanged when up to 15% of methanol is present in the fuel at an equivalence ratio of 0.85, but increases at higher methanol contents because of the increase in unburned toluene in the exhaust.     

大尺寸大孔径TiO_2/SiO_2光催化剂的制备及甲醛去除研究

以大孔径SiO2为载体,通过钛酸丁酯溶液的浸渍、原位水解以及高温煅烧制备出大尺寸、大孔径的TiO2/SiO2光催化剂。利用自制空气净化装置对室内甲醛的清除进行研究,分别考察了TiO2的百分含量、紫外光光强、温度、湿度和空气流量等不同条件下TiO2/SiO2光催化剂对除去甲醛效率的影响。结果表明,反应温度从10～50℃依次升高,去除率逐渐下降。在相对湿度为50%,TiO2负载率为55.6%,流量为8 m3/h时,甲醛的最佳除去率达96.5%;经过7周时间的考察,发现TiO2/SiO2光催化剂的催化活性没有明显的下降。     

The influence of air–fuel ratio on engine performance and pollutant emission of an SI engine using ethanol–gasoline-blended fuels

Ethanol–gasoline-blended fuel was tested in a conventional engine under various air–fuel equivalence ratios (λ) for its performance and emissions. The amount of fuel injection was adjusted manually by an open-loop control system using a CONSULT controller. It was found that without changing throttle opening and injection strategy, λ could be extended to a leaner condition as ethanol content increased. The results of engine performance tests showed that torque output would increase slightly at small throttle valve opening when ethanol–gasoline-blended fuel was used. It was also shown that CO and HC emissions were reduced with the increase of ethanol content in the blended fuel, which resulted from oxygen enrichment. At an air–fuel equivalence ratio slightly larger than one, the smallest amounts of CO and HC and the largest amounts of CO₂ resulted. It was noted that under the lean combustion condition, CO₂ emission was controlled by air–fuel equivalence ratio; while under the rich combustion condition, CO₂ emission is offset by CO emission. It was also found that CO₂ emission per unit horse power output for blended fuel was similar or less than that for gasoline fuel. From the experimental data, the optimal ethanol content in the gasoline and air–fuel equivalence ratio in terms of engine performance and air pollution was found.     

Spectroscopic behavior of oxygenated combustion by-products

The oxygenated species, massively produced in the energy production plants based on combustion processes, constitute one of the most numerous categories of hazardous air pollutants. Therefore, development of real time diagnostic tools are needed in order to study their formation during combustion processes and to reveal their presence both in the exhaust and in the atmosphere. In this work, oxygenated compounds were identified inside fuel-rich premixed ethylene/air flames by means of ultraviolet fluorescence spectroscopy with the support of qualitative chemical analysis of the sampled combustion gases.

Strong band progression, typical of aldehydic functionality, were recognized in fluorescence spectra (λ_exc=355 nm) measured in the early oxidation region of premixed flames varying the equivalence ratio from 3.0 up 21.6. Downstream of the oxidation region, spectroscopic signatures of pyrolytic species were found to prevail on those peculiar of oxygenated compound. The position and the extension of the two main flame zones were found to depend on the flame conditions (C/O ratio) due to the effect of the C/O ratio on the temperature history along the flame axis. This correlation was interpreted on the basis of the measured axial temperature profiles.     

Emission of specific pollutants from a compression ignition engine. Influence of fuel hydrotreatment and fuel/air equivalence ratio

A compression ignition engine is used for the study of the fuel (one reference and one hydrotreated) and the fuel/air equivalence ratio influence on the exhaust emissions of specific pollutants. Under the experimental conditions used, seven hydrocarbons, nine aldehydes and three organic acids are detected in the exhaust gas. No alcohols are detected under these conditions, indicating that these compounds are emitted only if they (or probably other oxygenated compounds) are introduced in the fuel. Fuel hydrotreatment decreases most of the exhaust pollutants, the four toxics and also the quantity of the ozone that could be formed from the exhaust gas. It also changes the composition of exhaust gas: it increases the proportion of methane, benzene, formaldehyde, acetaldehyde, acroleine, and propionic acid, while it decreases the proportion of all other pollutants detected. Fuel/air equivalence ratio also decreases most of the exhaust emissions, the emission of the total toxics and the quantity of the ozone that could be formed. It also changes the proportion of each pollutant in exhaust gas: the percentages of methane, benzene, acetone and acetic acid increase, while those of the other pollutants detected decrease. The majority of the specific pollutants detected corresponds to organic acids, followed by hydrocarbons and aldehydes.     

Soot Control During the Combustion of Polystyrene

This paper describes an experimental study on the control of soot formation during the combustion of polystyrene (PS). A stable, twodimensional flame generated by using a Wolfhard-Parker type diffusion flame burner was used to simulate practical combustion situations. The combustion characteristics, effects of operating conditions on soot formation, and the effectiveness of various metallic additives as soot suppressants were investigated. It was found that soot yield could not be significantly reduced by controlling the oxidizer (air) flow rate. Increasing the O₂ mole fraction of the oxidlzer increased soot yield under typical operating conditions. However, soot yield could be greatly reduced by adding small amounts of air into the pyrolysis zone of the flame. The additional air would probably increase the combustion reaction rate while decreasing the soot precursor formation rate, thereby causing the observed effect. It was thus suggested that effective soot control could be accomplished by improving mixing between air and the PS devolatilizatlon products In practical combustion situations. The metallic additives tested in this study were the salts of Na, K, Ca, and Ba. Among these salts, Ca was the least effective in reducing soot, and K and Na were nearly equally effective. Ba was much more effective than all the others, and Its effectiveness was strongly dependent on its addition rate.     

Semi-volatile and particulate emissions from the combustion of alternative diesel fuels

Motor vehicle emissions are a major anthropogenic source of air pollution and contribute to the deterioration of urban air quality. In this paper, we report results of a laboratory investigation of particle formation from four different alternative diesel fuels, namely, compressed natural gas (CNG), dimethyl ether (DME), biodiesel, and diesel, under fuel-rich conditions in the temperature range of 800-1200 degrees C at pressures of approximately 24 atm. A single pulse shock tube was used to simulate compression ignition (CI) combustion conditions. Gaseous fuels (CNG and DME) were exposed premixed in air while liquid fuels (diesel and biodiesel) were injected using a high-pressure liquid injector. The results of surface analysis using a scanning electron microscope showed that the particles formed from combustion of all four of the above-mentioned fuels had a mean diameter less than 0.1 microm. From results of gravimetric analysis and fuel injection size it was found that under the test conditions described above the relative particulate yields from CNG, DME, biodiesel, and diesel were 0.30%. 0.026%, 0.52%, and 0.51%, respectively. Chemical analysis of particles showed that DME combustion particles had the highest soluble organic fraction (SOF) at 71%, followed by biodiesel (66%), CNG (38%) and diesel (20%). This illustrates that in case of both gaseous and liquid fuels, oxygenated fuels have a higher SOF than non-oxygenated fuels.     

Validation of Models for Predicting Formaldehyde Concentrations in Residences due to Pressed-Wood Products

This paper describes a laboratory project to assess the accuracy of emission and indoor air quality models to be used in predicting formaldehyde (HCHO) concentrations in residences due to pressed-wood products made with urea-formaldehyde bonding resins. The products tested were partlcleboard underlayment, hardwood- plywood paneling and medium-density fiberboard (mdf). The products were initially characterized in chambers by measuring their formaldehyde surface emission rates over a range of formaldehyde concentrations, air exchange rates and two combinations of temperature and relative humidity (23° C and 5 0% RH; 26°C and 60% RH). They were then installed in a two-room prototype house in three different combinations (underlayment flooring only; underlayment flooring and paneling; and underlayment flooring, paneling, and mdf). The equilibrium formaldehyde concentrations were monitored as a function of air exchange rate. Particleboard underlayment and mdf, but not paneling, behaved as the emission model predicted over a large concentration range, under both sets of temperature and relative humidity. Good agreement was also obtained between measured formaldehyde concentrations and those predicted by a mass-balance indoor air quality model.