稀薄氨气的燃烧特性及动力学研究

文章通过稀薄氨气在固定床反应器中的燃烧,研究了反应温度、停留时间、氨气浓度和氧气浓度对低浓度氨气燃烧特性的影响,并描述了氨气在氧气过量条件下在陶瓷蜂窝蓄热体中燃烧的动力学过程。研究结果表明:提高反应温度、延长停留时间以及增大氧气浓度和氨气浓度均可以提高NH3转化率,氧气浓度过高会促进NO生成;当反应温度为740~770℃、氨气浓度为1%、氧气浓度为15%时,氨气在陶瓷蓄热体中燃烧的活化能为253.56 kJ/mol;与氨气在自由空间内的燃烧相比,氨气在陶瓷蜂窝蓄热体中主要发生表面燃烧反应。     

650MW电厂SCR脱硝系统喷氨装置协调优化

山东某电厂650MW燃煤机组SCR（selective catalytic reduction）脱硝系统氨气逃逸率较大,导致催化剂的堵塞、失活及中毒。通过FLUENT数值模拟建立三维脱硝系统模型,模拟了在反应器顶部不同导流板数量及喷氨速度下SCR系统流场分布,通过对结果的分析比较,得出适当增加导流板组数和合理差异化的调整各喷口喷氨速度能够使第一层催化剂入口的NH₃浓度、NO_X浓度及NH₃/NO_X分布更加均匀化合理化,很好的满足了设计和运行的双重检测,为SCR脱硝系统的协调优化和机组运行的稳定性提供了实际参考价值。     

蜂窝状催化剂脱硝过程数值计算

对蜂窝状催化剂内部的对流、传质、化学反应过程进行分析研究。建立壁面区域的控制方程,由几何对称性及扩散平衡写出边界条件,生成自适应网格,利用有限差分法对控制方程进行离散,求壁面NO浓度分布;建立蜂窝状催化剂通道内部区域的控制方程,由几何对称性及扩散平衡写出边界条件,采用交替方向隐式(ADI)算法对控制方程进行离散;最后通过方程式联立并求解,得到对于给定温度、气流速率、一定的脱硝效率和可接受氨泄漏量的条件下最佳NH3/NO比的计算式。实例计算得出:SCR反应仅发生在靠近催化剂壁面的一薄层内,其余部分均为死区;由催化剂单个孔内NH3和NO沿轴向的浓度分布情况,得到各断面上NH3的浓度下降比NO来得快,主要由于NH3在高温下被氧化而导致的结果;由一定NO进气浓度、温度和气流速率下的最佳NH3/NO比,得出最合适的NH3给气流量与NO不是等摩尔。     

无电晕式高温高压静电除尘器的数值模拟

基于实验研究结果，对无电晕式高温高压静电除尘器的阴极电子发射、粉尘荷电、浓度扩散、烟气流动、尘粒捕集等过程进行了数值模拟，从理论上分析讨论了温度、压力、电压、流速、含尘浓度、比电阻以及粒径等因素对除尘效率的影响，计算结果与实验结果基本吻合。研究发现，与传统的电晕式静电除尘器不同，无电晕式静电除尘器可以在较高含尘浓度和较低电压下正常工作，且特别适用于高温(高压)烟气的除尘。图11参6     

Effects of NH＿3 on N＿2O Formation and Destruction in Fluidized Bed Coal Combustion

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Production of hydrogen from purge gases of ammonia plants in a catalytic hydrogen-permselective membrane reactor

The present study investigates hydrogen production in a hydrogen-permselective membrane reactor from purge gases of an ammonia plant. Hydrogen which initially exists in the purge gases and hydrogen that is produced from decomposition of ammonia on nickel–Alumina catalyst bed simultaneously permeate from reaction side to shell side through a thin layer of palladium–silver membrane. A sweep gas can be used in the shell side for increasing driving force. The amount of hydrogen that can be gained annually and effect of pressure, temperature, thickness of Pd–Ag layer, configuration of flow in the membrane reactor and sweep gas flow ratio have been studied. This study shows that the countercurrent mode is better than co-current mode of operation. The rate of hydrogen permeation increases with increasing of temperature, pressure and sweep gas flow rate. This approach produces and separates large amounts of hydrogen and decreases environmental impacts owing to ammonia emission.     

气体横掠单管强制对流换热的大涡模拟

应用大涡模拟与二价全展开ETC有限元离散格式相结合的方法对气体横掠单管强制对流换热进行了数值模拟,分别计算了气体横掠团管和方管时的温度场,得到了管壁平均换热系数,数值结果与实验关联式符合较好。同时还表明大涡模拟方法善于捕捉温度场以及流场涡系的时间演化过程,非常适合于具有大尺度涡的绕流运动温度场的分析。     

Experimental study on the electrolytic treatment of ammonia and chlorine in the wastewater from the precipitation of rare earth carbonate

The high concentration of ammonium chloride in the wastewater from the precipitation of rare earth carbonate was studied by an electrolytic method in this paper. The decomposition rate of ammonium chloride is obtained by electrolysis experiment, and the main components of wastewater can be transformed into raw and auxiliary materials that can be reused in the rare earth smelting process, so as to achieve the purpose of treating rare earth carbonate precipitation wastewater and provide a new method for the treatment of rare earth carbonate precipitation wastewater. The principle of the electrolysis process is analyzed in this study, and the optimum electrolysis factor is determined by the condition experiment. The changes in membrane materials and electrode materials before and after use are discussed. The experiments of stripping ammonia water and the reaction conditions of the formation experiment of ammonium bicarbonate are studied. The rare earth carbonate precipitation wastewater with the initial ammonium chloride concentration of 50 g/L was electrolyzed. The concentration of ammonia chloride was reduced to 3.5 g/L after electrolysis, and the electrolysis rate exceeded 90%. The purity of the ammonium chloride after electrolysis could exceed 93%. No industrial reagent was introduced in the electrolysis process, and no other pollutants were produced.     

Effects of particulate concentrations on temperature and heat flux distributions in a pulverized-coal fired furnace

A simple methodology for numerical modelling of total heat transfer in an axisymmetric, cylindrical pulverized coal-fired furnace is introduced. The solution for the flow field and energy equations are coupled with the solution of the radiative transfer equation. The SIMPLER code is employed to solve all the equations numerically. The radiation part is modelled using the first-order spherical harmonics approximation. The radiative properties of the gases and particulates such as soot, coal/char and fly-ash are obtained locally to account for the temperature and concentration distribution effects. Using a k - ε model, the turbulence closure is obtained. Parametric studies are performed and are presented graphically to demonstrate the effects of particulate concentrations on the distributions of medium radiative and physical properties, temperature, and the wall total and radiative heat fluxes.     

Three-dimensional numerical study of flow and species transport in an elevated jet in crossflow

The jet fluid coming out of the elevated source behaves as the efflux of exhaust gases from a stack and the crossflow stream representing the natural wind flow. Direct numerical simulations (DNS) in an elevated jet in crossflow have been performed at a Reynolds number of 250 and a Schmidt number of 7.25. The flow field and concentration distribution of pollutants have been explored by solving three-dimensional unsteady Navier–Stokes and species transport equations using second order spatial and temporal discretization. Three different blowing ratios (0.5, 1.0 and 1.5) have been used to quantify the effect of blowing ratio on the flow field and pollutant dispersion. The blowing ratio is found have significant effect on both the flow and dispersion of pollutant. The evolution of various flow structures associated with the elevated jet in crossflow such as wakes, loop vortices is discussed. The instantaneous behavior of jet has been observed to be dependent on the unsteadiness of flow structures that varies with the blowing ratio. The downwash of jet has been observed at the lowest blowing ratio.     

Numerical modelling of isothermal release and distribution of helium and hydrogen gases inside the AIHMS cylindrical enclosure

Hydrogen is a highly flammable gas and accidental release in confined space can pose serious combustion hazards. Numerical studies are required to assess the formation of flammable hydrogen cloud within confined spaces. In the present study, numerical investigations on the release of helium and hydrogen gases as high-velocity jets and their subsequent distribution inside an unventilated cylindrical enclosure (AIHMS facility) has been carried out as a first step towards numerical studies on hydrogen distribution in confined spaces for safety assessments. Experimental data for jet release of helium at volume Richardson number 0.1 and subsequent distribution has been used as benchmark data. Sensitivity studies on the influence of grid sizes, time-steps and turbulence models are performed. The performance of the validated numerical model is evaluated using statistical performance parameters. Similarity relations are used to determine input parameters for hydrogen jet for corresponding experimental data with helium jets. Finally, the mixing and flammability aspects of hydrogen distribution inside the enclosure are studied using four numerical indices that quantify mixing and deflagration potential of a distribution. It is concluded that the helium experiments can be used for validation of numerical models for hydrogen safety studies and any one of the similarity relationships, viz., equal buoyancy, equal volumetric flow, or equal concentration can be used for assessing the behaviour of hydrogen release and distribution within confined spaces.     

烟气脱硝系统NH_3逃逸对引风机运行的影响

NH3逃逸率高是火电厂烟气脱硝(SCR)系统普遍存在的技术难题。逃逸的NH3与烟气中的水蒸气、SO3在一定条件下反应会生成NH4HSO4,随着烟气的流动会吸附在空气预热器储热元件及引风机叶片上,造成空气预热器腐蚀和堵塞,大大增加烟气流动阻力,严重影响引风机正常运行。因此,从安全性和经济性角度,研究分析脱硝系统NH4逃逸对引风机运行的影响,为实现合理可行的运行方式及改造提供依据。     

Analysis of horizontal mantle heat exchangers in solar water heating systems

The characteristics of horizontal mantle heat exchangers are investigated for application in thermosyphon solar water heaters. An experimental model of a horizontal mantle heat exchanger was used to evaluate the flow patterns in the annular passageways and the heat transfer into the inner tank. Flow visualisation was used to investigate the flow structure, and the heat transfer was measured for isothermal inner tank conditions. A numerical model of the flow and heat transfer in the annular passageway was developed and used to evaluate the heat flux distribution over the surface of the inner tank. The numerical results indicate that configurations of mantle heat exchangers used in current solar water heater applications degrade thermal stratification in the inner tank. The effects of inlet flow rate, temperature and connecting port location are quantified.     

Experimental investigation of stabilization and emission characteristics of ammonia/air premixed flames in a swirl combustor

Ammonia is a possible candidate for use as a hydrogen energy carrier as well as a carbon-free fuel. In this study, flame stability and emission characteristics of swirl stabilized ammonia/air premixed flames were experimentally investigated. Results showed that ammonia/air premixed flame could be stabilized for various equivalence ratios and inlet flow velocity conditions in a swirl burner without any additives to enhance the reaction of ammonia even though the laminar burning velocity of ammonia is very slow. The lean and rich blowoff limits were found to be close to the flammability limits of the ammonia flame. In addition, emission characteristics were investigated using an FTIR gas analyzer. The NO concentration decreased and ammonia concentration increased under rich conditions. Moreover, it was found that there is an equivalence ratio in rich condition in which NO and ammonia emission are in the same order.     

3D contaminant transport by GFEM with hexahedral elements

This work aims to apply the GFEM (Galerkin Finite Element Method), with hexahedral elements in concentration transport problems in a three-dimensional domain. Since these problems are highly convective in nature, a study of the GFEM with 8 and 27-node hexahedron is performed. For such, an application with an analytical solution is performed by examining the norms L₂ and L_∞ from the error in the numerical solution; especially considering the variation of the velocity components, and the geometry of the proposal. Finally, the application involved the transport of an ammonia concentration through a tubulation containing holes caused by ruptures, which allows for inward air flow; thus, in this study, the influence of the variation of hole quantities, the maximum drainage velocity, and the geometry employed are analyzed.     

Ammonia decomposition to clean hydrogen using non-thermal atmospheric-pressure plasma

The plasma decomposition of ammonia was studied as a function of applied voltage/power, residence time including length of an inner electrode and flow rate of reactant gases, partial pressure of ammonia, and amount and the metal species of the inner electrodes. The ammonia decomposition rates were in excellent agreement with the hydrogen production rates and no hydrazine production was detected, indicating the clean decomposition of ammonia in the current system. The decomposition rates were dependent on the applied power and the residence time and independent of metal species of the inner electrodes, in contrast to the strong dependence of the ammonia synthesis reaction on the metal species. A hydrogen yield of 100% was achieved with an applied power of approximately 50 W and a residence time of 1.2 s at ambient temperature and atmospheric pressure, with an applied voltage of 5 kV and a frequency of 50 kHz.     

High levels of ammonia nitrogen for biological biogas upgrading

This study aimed to propose a novel method for ex-situ biogas upgrading by adding ammonium chloride to increase the concentration of ammonia nitrogen. The results showed that ammonia nitrogen had a significant effect on biogas upgrading. The maximum content of CH₄ reached 94.1% when the concentration of ammonia nitrogen was 5500 mg/L. At the same time, CH₄ yield of increased by 57.5%. High throughput sequencing results showed that the relative abundance of hydrogenotrophic methanogens reached 73.1%, while that of acetotrophic methanogens was only 1.3%, which greatly increased the content and yield of CH₄. For the bacterial community, Clostridium was the dominant bacteria and the ammonia nitrogen concentration had little effect on it. These results demonstrate that upgrading biogas by increasing the concentration of ammonia nitrogen is feasible.     

基于CFD的天然气管道混气扩散规律研究

随着我国多气源天然气市场发展和整体供气管网的形成,多气源直接接入管网混输已成为必然,不同气质气源直接管道混气的技术问题亟待研究和解决。基于CFD模拟,对不同气源混合输运的气质扩散规律进行研究,为混输管网合理设计和准确设定气质监控点提供依据,以保证燃气管网系统的安全可靠运行。重点对典型混气管路(Y型管)的天然气气质扩散规律进行数值模拟,获得掺混流体剪切层质量传递特征和天然气气质扩散规律。根据混气湍流形态和浓度场分布特征,获得Y型管的三类混气类型。通过对气质扩散浓度的不均匀性理论分析和模拟结果的综合数据分析,建立了预测混气管道达到气质均匀的混合长度无因次准则方程,为工程设计提供理论方法和计算基础。     

石灰石脱硫反应对喷氨脱硝反应影响的实验研究

在循环流化床锅炉炉膛尾部或旋风分离器入口喷入氨气可以降低烟气中的NOx含量。在循环流化床锅炉中,为脱硫而加入的石灰石会影响喷氨脱硝反应。通过实验研究了石灰石热解产物和脱硫产物对喷氨脱硝反应的影响,发现石灰石的热解产物在脱硫前,比表面积较大,CaO对喷氨脱硝反应显示出一定的催化活性,能够促进喷氨脱硝反应;石灰石的脱硫产物,对喷氨脱硝反应影响较小,但在T>1 200 K以上时,能够促进NH3的氧化,降低NH3的逸出,对喷氨脱硝反应有利。     

Independent testing and validation of prototype hydrogen sensors

In this article, the independent testing and validation of a packaged, electrochemical prototype hydrogen sensor at the National Renewable Energy Laboratory (NREL) is reported. Custom electronics were developed to be compatible with the data acquisition system at NREL. The specialized hydrogen sensor-testing laboratory at NREL used a variety of standardized test protocols to assess sensor performance. The system controlled and monitored humidity, pressure, and hydrogen gas concentration and introduced interference gases such as methane, carbon dioxide, carbon monoxide and ammonia.