非平衡等离子体特征量对NO脱除效率的影响

采用数值模拟的方法开展了非平衡等离子体脱除烟气中NO的研究,考察了非平衡等离子体放电中的2个主要特征量（电子数密度n_e和电子平均能量 ）对NO脱除效率的影响。计算结果表明,NO脱除效率随电子数密度n_e和电子平均能量 的变化而有不同程度的变化,相比较而言,电子数密度量级变化对NO脱除效率的影响更大。在NO初始分子浓度（粒子数密度）为10¹⁶ cm^-3情况下,电子数密度较高（10¹⁷ cm^-3）时,即使电子平均能量 低至4 eV,也可获得高达99%的NO脱除效率。当电子数密度和电子平均能量保持不变时,NO脱除效率随着NO初始分子浓度的增加而降低。     

NO-N2系统不同电离度下非平衡等离子体脱除NO的数值模拟

采用非平衡等离子体脱除NO—N2系统中NO的简化模型,对不同电离度下反应中主要粒子的变化规律及NO脱除效率进行分析和计算。结果表明,电子数密度随时间按指数规律快速衰减;初始电子相对数密度是决定体系非平衡等离子体NO脱除的本质因素,初始电子相对数密度大,体系NO脱除效率高;较高的电离度适合产生高密度的中间产物N和O,N和O数密度随时间呈现快速增长达到峰值又快速衰减为0的变化趋势;反应的最终产物为N,,但也有一定量的O2和少量的NO2。O2产率随电离度的增大而增大,O2最大产率与NO初始数密度同一量级;NO2产率随电离度变化规律较复杂,电离度过高或偏低,O2产率都较低,最大O2产率比NO初始数密度至少低一个数量级。     

O3 /NaClO气液相氧化吸收剂同时脱硫脱硝试验研究

提出以O₃/NaClO为复合吸收剂对火电厂烟气进行同时脱硫脱硝的方法,研究了该方法在不同条件下的脱硫脱硝效率。模拟实际工况,给定SO₂与NO的初始质量浓度分别为600 mg/m³ 和500 mg /m³。模拟试验结果表明：在臭氧投加量为5.35 g/h,NaClO摩尔浓度为15 mmol/L,吸收液初始pH值为5,液气比为50 L/m³,反应温度为50 ℃时,脱硫和脱硝效率分别可达97.04%和95.08%。所研究的方法工艺操作简单,脱除SO₂和NO_x速度快,不存在堵塞、结垢等问题,若能有效降低O₃的生产成本,则具有较好的实用意义和推广应用前景。     

大气压He/O2等离子体活性粒子在水溶液中传质的氧含量效应

大气压低温等离子体作用于生物组织要穿过其表面几十到几百微米厚的水溶液，将会涉及等离子体中活性粒子在水溶液中的传质，而活性粒子的生成与放电气体的氧含量密切相关。该文基于一维流体模型，研究了在放电气体中不同的氧含量下(体积分数为0.1%～5%)大气压He/O₂等离子体中五种主要活性粒子H₂O₂、O₂^-、HO₂、O₃及OH在水溶液中的渗透深度分布，并阐释了相关机理。研究表明，氧含量对活性粒子的生成与消耗反应产生较大影响，进而影响到活性粒子在水溶液中的渗透深度。随着氧含量的增加，H₂O₂、O₂^-和HO₂的渗透深度减小，但仍维持在数百微米以上的可观量值，而O₃和OH的渗透深度增加，并可达20μm以上，这一深度使得两种粒子可以直接作用到某些生物组织，因而对于等离子体的生物医学应用具有重要意义。     

气体成分对介质阻挡放电脱除NO影响试验研究

为实现电厂排放达标,通过研究用柱筒型介质阻挡反应器对烟气成分对NO脱除率的影响,主要分析了烟气温度、氧气,二氧化硫和水蒸气含量对脱除率的影响。结果表明:烟气温度对脱除率影响不大。O2的加入使得脱除率降低,氧量越多,脱除率越低。同时NO2的生成量随着含氧量增加而增大。SO2抑制NO的脱除,SO2体积分数越大,脱除率越低。加入水蒸气后,脱除率有明显下降,且水量越高,脱除率越低。水蒸气也会促进NO2的生成。     

O2/H2O燃烧方式下焦炭N向NO的转化机理

采用实验与密度泛函理论(density function theory,DFT)计算相结合的方法,对oxy-steam燃烧方式下焦炭N向NO的转化机理进行研究;重点探讨O₂/H₂O工况下煤焦中氮元素的演化机制及NO生成与还原反应过程,得到了主导NO释放的关键反应路径。结果表明：O₂/H₂O燃烧过程中,由H₂O分解产生的OH基团改变了焦炭N的演化,进而影响了NO的释放。主要表现为,OH自由基吸附在吡啶N表面形成2-吡啶酮,促使更加稳定的N-6向不稳定的N-5发生迁移,从而导致N-5成为含氮前驱物HCN与NH₃的主要来源。在NO释放过程中,基元步骤HCN/NH₃+OH→NH₂+O₂→NO主导了NO的生成。随着H₂O浓度升高,OH和NH₃产率增大,NH₂、NH和N产率降低;说明高浓度的H₂O在促进N-6→N-5...     

工业烟气SO3吸收脱除性能研究

燃用高硫煤和安装选择性催化还原(selective catalytic reduction,SCR)装置会引起烟气中SO₃浓度增加,带来设备腐蚀与环境污染问题。分别以Ca(OH)₂和Na₂SO₃为吸收剂,通过数值模拟研究吸收剂脱除工业烟气中SO₃的性能,讨论Ca(OH)₂/Na₂SO₃:SO₃、SO₃浓度和降温历程对SO₃脱除的影响。结果表明,在SCR脱硝装置后加入2种吸收剂均能有效脱除SO₃。在烟气降温过程中,加入吸收剂后,SO₃的脱除率和吸收剂总转化率均呈现初期快速增长、后期缓慢增长的趋势。Na₂SO₃对SO₃的脱除性能明显优于Ca(OH)₂。Ca(OH)₂/Na₂SO<...     

考虑微量CO2影响的He+Air等离子体反应动力学研究

He+Air等离子体是常见的大气压冷等离子体类型，具有活性粒子众多、反应体系复杂的典型特征，使得实验研究难以系统开展，因而仿真研究非常重要。尽管如此，目前的仿真模型鲜有考虑空气中的微量CO₂，而笔者课题组与同行均发现，微量气体组分可能会对等离子体的活性粒子带来显著影响。鉴于此，基于前期报道的He+Air等离子体全局模型，新增了CO₂及其7种放电产物与120个相关反应，研究了地表空气中5种典型CO₂浓度下的等离子体反应动力学特性。发现在放电功率密度为10 W/cm³时，CO₂的放电转化率达到37%以上，CO₂的转化明显加强了等离子体的电离过程，削弱了解离和吸附过程。在地表空气常见的CO₂浓度范围内，考虑CO₂可使He+Air等离子体中活性粒子的平均密度改变1.8%～11.2%。该研究量化了微量CO₂对He+Air等离子体中活性粒子的重要影响，揭示了不同地域CO₂浓度差异会...     

纳秒脉冲液相放电耦合微气泡固氮影响因素分析

由气液等离子体放电产生的活化水富含活性氧和活性氮(NO₂^-、NO₃^-、H₂O₂、O₃等)，在环境治理、材料合成和医疗卫生等领域有着广泛的应用前景。该文提出了一种“多微孔-同轴式”的微气泡等离子体放电结构，微孔和微气泡的引入降低了在液相中的击穿场强，并且微气泡增加了气液界面的化学反应和活性物质的溶解。以空气为放电气体，主要探究了正、负极性脉冲参数对活化水固氮特性的影响。此外，还考察了气体流速、温度等因素对活化水中的氮特性的影响，并诊断了电学特性。结果表明，正极性放电下NO₂^-产量和NO₃^-产量分别为7.2 mg、28.8 mg，相比负极性放电分别高出0.43 mg、3 mg，经计算正极性放电能量效率高达15.02 g/(kW·h)。同时研究发现，当气流流速为2 L/min时，固氮性能最佳；水温越高，氮含量会随着液相分解动力学温度的降低而减弱。     

微波放电NO-O2-H2O-He体系脱除NO的数值模拟

采用微波放电NO-O2-H2O-He体系脱除NO的反应模型,对NO脱除及其转化进行分析计算。通过建立并数值求解化学反应动力学方程组,对NO-O2-H2O-He体系微波直接分解脱除NO过程进行反应动力学研究,分析影响NO脱除效率及其向N2和NO2转化的各种因素及规律。计算结果表明,在NO-O2-H2O-He体系中,微波功率,NO、O2和H2O的初始浓度等对NO脱除效率有较大影响,即微波功率的增大有利于NO的脱除及其向N2的转化;NO初始浓度的增加降低了体系的微波脱硝效率;脱硝效率随着模拟烟气相对湿度的增加而增加;微波放电条件下,O2的加入可增加产物中NO2的生成量;微波放电NO-O2-H2O-He体系脱除NO为还原和氧化反应共同作用的结果,NO转化为N2的效率总大于其转化为NO2的效率。     

Gas cleaning with semi-wet type plasma reactor

An experimental study on the removal of NH₃, NO, NO_x in concentration of 10-40 ppm in air has been carried out using plasma chemical reactions in a streamer corona discharge. The results of the performance of dry type and semi-wet type reactors are compared. The effects of different type of applied voltages such as rectangular pulse, 60-Hz sinusoidal, and 18-kHz alternating voltages are investigated. During NO removal, O₃ and NO₂ are produced. NO₂ can, partially, be removed with higher power input into the discharge. Another undesirable pollutant, namely N₂ O, is also produced, especially, in case of dry reactors having long residence time (~2.4 s). N₂O production decreases, essentially, to zero at 0.6-s residence time while using a semi-wet reactor. In general, higher removal efficiency has been obtained with pulse voltage in a semi-wet reactor. NH₃ in air appears to produce ozone and ammonium nitrate in a discharge. The performance of semi-wet reactors an the removal of submicron dust particles has also been investigated and very high removal efficiency (~93% at 0.6-s residence time) has been obtained     

NOx removal process using pulsed discharge plasma

Nonequilibrium plasma can be used to promote chemical reactions that reduce the emission of gaseous pollutants, such as NO_x, produced by coal-burning power plants or by diesel engines. Laboratory experiments were carried out to study the decrease of NO_x in simulated flue gases (initial concentration of NO: 200-800 ppm, O₂ : 10%, N₂-balance gas) by means of a pulsed discharge plasma generated in a cylinder type reactor (outer electrode: 20-mm diameter). A rotating spark gap provided square wave high-voltages up to 25-kV, at a frequency of 250 Hz, to corona electrodes of 0.1-, 3.3-, and 6.4-mm diameter. The tests were performed at various temperatures (ambient to 220°C) and constant residence time (0.6 s). The removal performance depended on the size of the discharge electrode and was better at room temperature. The addition of C₂H₄ significantly enhanced the removal performance, concentration of NO_x decreased from 800 ppm to 300 ppm in the discharge. The by-products of this process were analyzed using infrared spectroscopy. No traces of toxic gases could be detected     

Control of NOx by positive and negative pulsed coronadischarges

The pulse-induced plasma chemical process (PPCP) is a novel means of processing with great potential in various applications including the removal of NO, SO₂, HCl, and Hg vapor and other gaseous pollutants from combustion gases, the composition of gaseous and solid substances, the production of ultrafine particulate materials, the treatment of surfaces, etc. An investigation of the DENOX and DESOX of combustion gas by PPCP was conducted, confirming that DENOX is possible by both positive and negative pulsings and DESOX only by positive pulsing. NO is oxidized by PPCP to NO₂, which is removed again by PPCP. The reaction speed for PPCP with positive pulsing is more than one order of magnitude higher than that with negative pulsing applicable to electrostatic precipitators. The reaction speed is greatly enhanced by raising the peak field intensity, which requires the use of a very sharp pulses. The speed is also enhanced by raising pulse frequency, lowering the gas temperature, and using sharp corona wires. The oxidation of NO and removal of NO₂ can proceed without O ₂ and moisture, but is greatly enhanced by them. The addition of NH₃ also enhances NO₂ removal, possibly by its NO₂-scavenging effect from the gas phase, while it does not enhance NO oxidation. The combination of PPCP with the electron-beam DENOX and DESOX does not produce a nonlinear enhancing effect beyond the independent effect of PPCP alone     

Energy Efficiency of Corona Discharge Reactor Driven by Inductive Energy Storage System Pulsed Power Generator

Characteristics of a pulse corona reactor driven by an inductive energy storage (IES) pulsed power generator are described in this paper with focusing on the influence of streamer-to-glow transition on NO removal efficiency. A pulsed high voltage with a short rise time of under 30 ns is employed to generate streamer discharges homogeneously in whole the discharge region. Fast recovery diodes are used as semiconductor opening switch (SOS) to shorten the rise time. The various resistors are employed as dummy load to clarify a suitable circuit parameter such as the capacitance of a primary energy storage capacitor and/or the inductance of a secondary energy storage inductor. The energy transfer efficiency of the pulsed power generator has a maximum value of 50% at 714 Omega dummy load resistance. A co-axial cylinder type discharge chamber was used as the corona discharge plasma reactor driven by the IES pulsed power generator. The pulsed power generator supplies 30 kV pulse with 300 pps repetition rate. The co-axial cylinder plasma reactor consists of 1 mm diameter tungsten wire and 19 mm i.d. copper tube with 30 cm length. NO removal from the simulated diesel engine exhaust gas (N₂:O₂=9:1, Initial NO concentration=200 ppm) increased with input energy into the reactor. The energy efficiency for NO removal was obtained to be 25 g/kWh at 30 % removal in gas flow rate of 2 L/min. However, the energy efficiency decreased to 5 g/kWh with increasing capacitance of the primary capacitor from several hundreds pF to several nF. This decrease was caused by a streamer-to-glow transition. The efficiency was affected by oxygen concentration in the gas mixture.     

商用SCR催化剂对单质汞（Hg0）的氧化作用研究

为开发对烟气NO_x和汞等多种污染物具有良好联合脱除效用的一体化新型催化剂,研究了目前商用SCR脱硝催化剂对单质汞（Hg⁰）的氧化作用及其影响因素,探求Hg⁰氧化反应机理。实验结果表明：SCR催化剂对烟气中的Hg⁰具有一定的氧化作用,但在催化剂最佳反应温度250~300 ℃时,其对Hg⁰的最大氧化效率仍低于50%。在低浓度NO和5%O₂同时存在的情况下,催化剂对Hg⁰有相对较高的氧化效率;SO₂存在时,Hg⁰的氧化明显被抑制,SO₂对催化剂的毒性基本不可逆转;NH₃与Hg⁰在吸附过程中存在竞争关系,因而NH₃的存在降低了催化剂对Hg⁰的氧化效率;H₂O对Hg⁰的氧化有十分明显的负面影响。     

The influence of reaction conditions on SO2 oxidation ina discharge plasma reactor

In this paper, experimental approaches have been carried out to investigate the removal of sulfur dioxide (SO₂) using pulsed discharge nonthermal plasma in the absence of ammonia (NH₃). The gas-phase reaction was found to be less attractive due to its large energy cost. The increase in temperature decreased the SO₂ removal rate, resulting in large energy cost. SO₂ removal was increased as the concentration of water vapor increased. The presence of SO₂ did not influence the gas-phase removal of NO in an NO-SO ₂-O₂-H₂O-N₂ system. In the case of the wet-type plasma reactor, gas-phase discharge plasma directed to the surface of water film greatly enhanced the liquid-phase oxidation of HSO₃^- to SO₄^2-. Comparing the results with different absorbents indicated that the hydroxyl (OH) radical plays a key role in the plasma induced liquid-phase reactions     

低温等离子体去除空气中NO2技术的研究

用针—板电极实验研究了影响脉冲放电等离子体去除NO2效率的主要因素:正脉冲电压的去除效率远高 于负脉冲;脉冲峰值电压越高效率越高;随着NO2初始质量浓度的增加,去除效率呈现为先增后减的非单调曲线。 还首次研究了磁场对NO2去除效率的影响及其规律,实验表明磁场能有效提高NO2的去除效率。