Prediction of risers’ tubes temperature in water tube boilers

A dynamic model is developed which enables the prediction of risers’ tubes temperature of water tube boilers under various operating conditions. The model is composed of fluid dynamics model representing the fluid flow in the drum-downcomer-riser loop and a dynamic thermal model of the riser’s temperature. The model gives a detailed account of the two-phase heat transfer process which takes place between the risers’ inner walls and the water–steam mixture flow inside the tubes. The model is used to simulate various operational scenarios of water tube boilers. Results of the simulation provide insight into the dynamic interactions of the boiler’s main variables including the drum pressure, water volume, steam quality and risers’ temperature. Such a model is useful in checking operational scenarios before their actual plant implementation, can be a basis for developing boiler start up procedures and online temperature predictions to prevent eminent tube overheating.     

Toluene steam reforming as tar model molecule produced during biomass gasification with an iron/olivine catalyst

Tar produced during biomass steam reforming is a complex mixture of single to multiple ring aromatic compounds and it is necessary to eliminate them in order to prevent any condensation-polymerisation problem. Tar steam reforming leads to additional hydrogen that improves gas production. Previous works have shown that olivine was active in tar removal during biomass gasification and the iron distribution into the mineral different phases has a real influence on its efficiency. A Fe/olivine catalytic system has been designed to study tar steam reforming. This work presents the Fe/olivine catalyst characterizations (XRD, Mössbauer, TPR) and compares the Fe/olivine and olivine reactivity in toluene steam reforming, a tar model molecule. At 850 °C, an important conversion (95%) was observed for Fe/olivine during 7 h. The strong interaction between iron and olivine, and the equilibrium between Fe⁰/Fe^II/Fe^III seem to be responsible of the catalyst activity and stability in toluene steam reforming.     

Experimental study on the condensation of supersonic steam jet submerged in quiescent subcooled water: Steam plume shape and heat transfer

The condensation of supersonic steam jet submerged in the quiescent subcooled water was investigated experimentally. The results indicated that the shape of steam plume was controlled by the steam exit pressure and water temperature. Six different shapes of steam plume were observed under the present test conditions. Their distribution as a function of the steam exit pressures and water temperatures was given. As the steam mass velocity and water temperature increase, the measured maximum expansion ratio and dimensionless penetration length of steam plume were in the ranges of 1.08–1.95 and 3.05–13.15, respectively. The average heat transfer coefficient of supersonic steam jet condensation was found to be in the range of 0.63–3.44 MW/m²K. An analytical model of steam plume was found and the correlations to predict the maximum expansion ratio, dimensionless penetration length and average heat transfer coefficient were also investigated.     

性能优异的Rh改性的Pd/Al2O3密偶催化剂

采用等体积浸渍法制备了Pd/Al2O3和Rh-Pd/Al2O3密偶催化剂,运用H2程序升温还原、CO化学吸附和X射线光电子能谱等手段对催化剂进行了表征,并考察了催化剂对丙烷总包反应和单反应的转化活性.总包反应结果表明, Rh的添加使起燃温度和完全转化温度分别降低了23和18oC.单反应结果证明,添加Rh能提高各单反应丙烷的转化活性,尤其是有NO参与的反应.表征结果证明,掺杂Rh不仅可以抑制活性组分PdOx的烧结,提高PdOx的分散度,而且可以改变其电子状态.     

蒸氨法制备铜硅催化剂的二甲醚水蒸气重整制氢性能

采用蒸氨法制备出不同Cu负载量的xCu/SiO_2-AE催化剂,并将其用于二甲醚水蒸气重整制氢反应。当Cu负载量为30%(w)时,30Cu/SiO_2-AE催化剂表现出最佳的催化性能。结果显示,该方法制备的催化剂表面具有高度分散的CuO和层状硅酸铜物相,经还原后分别形成Cu~0和Cu~+物种。与常规浸渍法制备的30Cu/SiO_2-IM催化剂相比,蒸氨法制备的30Cu/SiO_2-AE催化剂具有优异的催化稳定性和活性,这与其独特的层状结构和表面Cu~0与Cu~+之间的协同作用相关。     

Experimental studies of a steam jet refrigeration cycle: Effect of the primary nozzle geometries to system performance

This paper describes an experimental investigation of a steam jet refrigeration. A 1 kW cooling capacity experimental refrigerator was constructed and tested. The system was tested with various operating temperatures and various primary nozzles. The boiler saturation temperature ranked from 110 to 150 °C. The evaporator temperature was fixed at 7.5 °C. Eight primary nozzles with difference geometries were used. Six nozzles have throat diameters ranked from 1.4 to 2.6 mm with exit Mach number of 4.0. Two remained nozzles have equal throat diameter of 1.4 mm but difference exit Mach number, 3.0 and 5.5. The experimental results show that the geometry of the primary nozzle has strong effects to the ejector performance and therefore the system COP.     

A novel single particle study of steam gasification kinetics of a coal-derived char at high temperatures and pressures

A novel single particle experiment was developed to allow for detailed char gasification measurements in pure steam at temperatures from 1000 °C to 1400  °C and pressures from 1  bar to 15  bar. A coal-derived activated carbon was thoroughly characterized with respect to its composition, physical structure, and reactivity revealing properties consistent with chars reported in the literature. The single particle approach allowed for the boundary and initial conditions to be well known and for the mass of the particle to be accurately measured before and after testing to provide high-quality conversion data. The resulting conversion data were analyzed using the random pore model and the shrinking core model, of which the random pore model provided the best fit. Apparent activation energies were calculated using the random pore model which provided values ranging from 57.1 kJ/mol to 129 kJ/mol which are nominally half of the magnitude of the values reported in the literature under kinetically controlled conditions, thus demonstrating that regime II conditions were present. Additionally, the activation energies decreased with increasing temperature further demonstrating the presence of regime II conditions. The calculated reaction order ranged from 0 to 0.5 and decreased with increasing pressure agreeing well with literature values and trends.     

Ultrasound-assisted dynamic extraction of valuable compounds from aromatic plants and flowers as compared with steam distillation and superheated liquid extraction

A method for the extraction of valuable compounds from plants and flowers (viz. laurel, rosemary, thyme, oregano and tuberose) is proposed. The dynamic approach allows go-and-backward circulation of the extractant (ethanol) through the solid sample subjected to the action of an ultrasound probe (thus reducing sample amount and avoiding overpressure). A multivariate optimisation study and application of the optimum values of the variables to kinetics studies show that 10 min is sufficient to obtain extraction efficiencies that greatly surpass those provided by steam distillation for essential oils or superheated liquid extraction for these oils and other valuable compounds, with lower costs and higher quality of the extract. The extraction time of the proposed method is 176–165 min shorter than steam distillation and 31–20 min shorter than superheated liquid extraction, depending on the target compound.