Carbon supported platinum catalysts for catalytic wet air oxidation of refractory carboxylic acids

Carbon supported platinum (1% wt) catalysts were prepared by the incipient wetness impregnation method and by organometallic chemical vapor deposition. Catalyst characterization was carried out by means of adsorption and thermogravimetric techniques, and by electron microscopy. The catalyst with higher metal dispersion was produced by incipient wetness impregnation. The catalysts were tested in the catalytic wet air oxidation (200°C and 6.9 bar of oxygen partial pressure) of aqueous solutions containing low molecular weight (C₂ to C₄) carboxylic acids. Significant conversions (greater than 60% over 2 h) and 100% selectivity towards water and non-carboxylic acid products were observed for both systems. The initial reaction rate was used to compare the performance of the two catalytic materials and direct correspondence to the metal dispersion was found. No metal leaching was observed during reaction and no significant deactivation occurred in three successive catalytic oxidation runs. A kinetic model based on the Langmuir–Hinshelwood formulation was applied and the results were analyzed in terms of a heterogeneously catalyzed free radical mechanism.     

Preparation and characterization of inexpensive heterogeneous catalysts for air pollution control: Two case studies

Relatively inexpensive heterogeneous catalysts for two reactions of great importance in air pollution control, NO reduction and VOC combustion, were prepared and characterized. Apart from their common practical goal and the frequent need for simultaneous removal of air pollutants, these reactions share a similar redox mechanism, in which the formulation of more effective catalysts requires an enhancement of oxygen transfer.

For NO reduction, supported catalysts were prepared by adding a metal (Cu, Co, K) using ion exchange (IE) and incipient wetness impregnation (IWI) to chars obtained from pyrolysis of a subbituminous coal. The effects of pyrolysis temperature, between 550 and 1000 °C, on selected catalyst characteristics (e.g., BET surface area, XRD spectrum, support reactivity in O₂) are reported. For IE catalysts, the surface area increased in the presence of the metals while the opposite occurred for IWI catalysts. For the Co-IE catalysts, the highest surface area was obtained at 700 °C. The XRD results showed that, except for Cu (which exhibited sharp Cu⁰ peaks), the catalysts may be highly dispersed (or amorphous) on the carbon surface. For the C–O₂ reaction the order of (re)activity was K  Co > Cu for IE catalysts and K > Cu > Co for IWI catalysts. For NO reduction the orders were K > Co > Cu (IE catalysts) and Cu > Co > K (IWI catalysts). In all cases the catalytic (re)activity for NO reduction was lower than that exhibited for the C–O₂ reaction. The K-IE and Cu-IWI catalysts appeared to be the most promising ones, although further improvements in catalytic activity will be desirable. Some surprising results regarding CO and CO₂ selectivity are also reported, especially for Co catalysts.

In VOC combustion, the effect of the nature of ion B (Fe and Ni) on the partial substitution of ion A (Ca for La) in ABO₃ perovskites (e.g., LaFeO₃ and LaNiO₃) and on their catalytic activity was studied. The perovskite-type oxides were characterized by means of surface area measurements, XRD, temperature-programmed desorption (TPD) and temperature-programmed reduction (TPR). The effect of partial substitution of La³⁺ by Ca²⁺ was more significant for the La_1−xCa_xFeO₃ perovskites. In this case, the electronic perturbation is compensated by an oxidation state increase of part of Fe³⁺ to Fe⁴⁺. The TPD results revealed that, at higher substitution levels, oxygen vacancies are also formed to preserve electroneutrality. For the La_1−xCa_xNiO₃ perovskites, the characterization results showed no evidence of large differences in electronic properties as calcium substitution increases. The La_1−xCa_xNiO₃ perovskites exhibited lower activity than the simple LaNiO₃ perovskite, whereas for the La_1−xCa_xFeO₃ substituted perovskites the most active catalyst (exhibiting the lowest ignition temperature) was obtained at the highest substitution level, La_0.6Ca_0.4FeO₃.

The performance of both groups of catalysts is briefly discussed in terms of redox processes, in which the interplay between oxygen transfer and electron transfer requires further elucidation for the improvement of catalytic activity.     

汽轮机内湿蒸汽测量的控制系统研究

火电厂汽轮机内湿蒸汽的存在对汽轮机经济、安全、可靠的运行造成严重的影响。以汽轮机内蒸汽湿度的准确测量为目的,设计了以微处理器MSP430为系统的控制和处理核心的控制系统,经实验表明,自动频率跟踪系统的跟踪频率达到kHz数量级,能够适应现行的湿度测量方案;等精度频率测量系统在标准频率为10 MHz时,分辨率可达到10-7,也满足了系统设计要求。最后给出了频率偏移和蒸汽湿度的关系图,证明控制系统设计的重要性。     

Interface science for optimizing the size of oxidic nanoparticles in supported catalysts

In the present work we attempt to optimize the size of the supported “molybdenum oxide”/titania and “cobalt oxide”/γ-alumina nanoparticles formed after calcination by “selecting”, respectively, the proper mode of deposition and the local structure of the deposited species achieved upon the impregnation step of catalyst preparation. Concerning the first system, it was found that the disubstituted Mo inner sphere surface complexes, which are bound on the support surface stronger than the monosubstituded ones, resist more effectively to the sintering taking place during calcination where the above complexes are transformed progressively into MoO₃ supported nanoparticles. This leads to a catalyst with very small MoO₃ nanoparticles and thus with very high activity for the selective reduction of NO by NH₃. Concerning the “cobalt oxide”/γ-alumina catalysts, it was found that a relatively large (small) size of the supported nanocrystallites is imposed by the bulk deposition (formation of inner sphere surface complexes). A quite small size of the supported “cobalt oxide” nanocrystallites, not strongly interacted with the support surface, is imposed by the interface precipitation. This is the optimum supported phase for the complete oxidation of benzene.     

单缸低参数汽轮机末级排汽湿度的热力分析

采用VB语言,通过动态链接库的调用,编制了低参数单缸汽轮机热力计算程序.应用此程序,在不同设计参数下,针对无抽汽除湿、级间抽汽除湿和除湿级除湿3种方案,研究了机组末级湿度的变化.结果表明,进汽压力、进汽温度和排汽压力三者对末级湿度的影响不同,进汽温度对末级湿度的影响最大,进汽压力次之,排气压力最小.在本研究所提参数条件下,满负荷运行很难保证末级出口湿度要求,需采用有效的内部除湿措施.研究也表明,在不同位置抽汽除湿和除湿级除湿对机组末级湿度影响较大,在相同的设计参数下,在机组的第四级后抽汽除湿对机组末级湿度的影响最大.在相同的除湿效率下,除湿级位置每向后移动一级,使末级湿度降低约1%,随除湿级位置后移,除湿效率对末级湿度的影响增大.     

新型加热法测量流动湿蒸汽湿度的试验技术

提出了流动湿蒸汽湿度的新型加热法测量思想,并以此为依据进行湿度测量装置的设计研制,建立湿蒸汽实验台,并用所研制的测量装置对收缩喷管试验段出口处汽流的湿度进行测量,测量结果表明：新型加热法的思想是可行的,所研制的装置具有相当高的测量精度,可以作为实际透平中汽流湿度在线测量装置的原型。     

核电汽轮机高压缸回热抽汽及排汽湿度测量方法研究

核电汽轮机高压缸的通流部分大部分处于湿蒸汽区。高压缸的回热抽汽及排汽的湿度和焓值尚无准确的确定方法,从而不能准确计算汽轮机的相对内效率等热力经济型指标。此外湿度的存在还会对机组的经济性及安全性带来影响。同时大型压水堆核电机组的调峰将成为其未来的发展趋势。分析了现有测量湿度方法存在的问题,提出了一种全新的理论计算方法并且给出了具体的计算过程,计算结果证实了此方法的有效性。     

Development of Steam Separator Performance Analysis Code and Its Validation, (II) Carryover Experiments

Abstract

The purpose of the study is to collect data in order to make models that are applicable to calculate carryover droplets that are generated in and flow out of a steam separator. Various effective tests relevant to separation mechanisms in the separator have been conducted with a full-scale steam separator under atmospheric pressure. Separation behaviors for the top of the riser of the separator and for corrugated-separator were clarified and correlated by the experiment. Distinct patterns about the separation at the corrugated-separator, the separation of discharged droplets by gravity, and the separation of droplets by a screen dryer that is used to dry up the steam were also measured with the facility using a full-scale separator in a vessel simulating the flow area of ATR under the high-pressure and high-temperature condition for various water levels. Each separation data were correlated under the condition of maximum steam and liquid flow rates of 7 and 30.5 kg/s, respectively. Liquid droplets containing a small amount of LiOH at several positions were sampled together with steam by iso-kinetic probes, and the amount of carryover was analyzed in PPT range by the chemical analysis of condensed steam. As a result, basic data for separation mechanisms were obtained, and maximum capacity of the separator was estimated.     

激光散射理论在汽轮机蒸汽湿度及水滴直径测量中的应用

蒸汽湿度的存在不但降低汽轮机组的运行效率,而且会引起严重的叶片水蚀,给汽轮机组的经济性和安全性带来很大的危害.根据激光散射理论和Mie散射理论,利用半导体激光器发射出三个不同波长的光能够在线测出汽轮机末级蒸汽湿度及水滴颗粒大小和分布,为监控和减少湿蒸汽对汽轮机的危害提供最直接的数据.图5表1参11