Effect of internal cooling/heating coil on adsorption/regeneration of solid desiccant tray for controlling air humidity

Thermal performances of solid desiccant tray having internal cooling/heating coil for air humidity adsorption and desiccant regeneration are investigated. Three units of desiccant tray each of 48 cm × 48 cm cross‐sectional area and 2.5 cm thickness filled with silica gel are tested in a wind tunnel. For adsorption process, an air stream is flowing through the desiccant trays and the air humidity is captured by the silica gel. Approximately 10–40% of air humidity could be adsorbed more in case of the internal cooling. Besides, the outlet air temperature increases only slightly. In regeneration process, a hot air stream is used to repel the moisture in the silica gel. With the internal heating, the regeneration time is shorter compared with that without internal water heating. In addition, a correlation for calculating the adsorption/regeneration performance of the silica gel trays is developed and the results from the model agree well with the experimental data. Copyright © 2008 John Wiley & Sons, Ltd.     

电站失活SCR催化剂再生试验研究

以在电站烟气实际运行中失活的催化剂为原料,通过去离子水水洗、硫酸酸洗、钒钨等活性物质重新负载等方法,开发了一套廉价有效的再生工艺,并通过ICP-OES、SEM、XRD等表征研究了每一步处理方法对催化剂结构和性能的影响。研究表明,经过完整再生工艺处理后失活催化剂脱硝活性在300～400℃温度窗口内提升30%以上,水洗过程能够去除大部分硫、钙等中毒元素,而酸洗经过硫酸化过程后增加催化活性中心的数量和酸性,从而提高催化剂脱硝活性,XRD表明再生后V2O5或WO3仍然以无定形态或高分散的形态分布在载体表面上。     

铁改性活性炭对水中镉的吸附和再生实验研究

制备了铁改性活性炭,通过快速动态小柱实验研究了活性炭改性前后对镉的吸附性能,同时考察了进水pH、进水流量和初始质量浓度等因素对吸附材料穿透特性的影响,最后对铁改性活性炭再生方法进行了研究.结果表明,铁改性活性炭对镉的吸附量是未改性活性炭的3.7倍,负载的铁氧化物大大提高了改性活性炭对镉的吸附能力,同时铁改性活性炭对镉的吸附受溶液pH、进水流量和初始质量浓度的影响.0.05 mol·L-1的EDTA-2Na溶液能有效再生吸附饱和后的改性活性炭,再生后的改性活性炭可重复使用.     

Study on the heat transfer and sorption characteristics of a consolidated composite sorbent for solar-powered thermochemical cooling systems

In this paper, a new consolidated composite sorbent made from barium chloride and expanded graphite is presented for solar-powered thermochemical sorption cooling systems. A larger sorption capacity and volume cooling density can be obtained with chemisorption systems when compared with those based on physicosorption. The heat transfer and sorption characteristics of the composite sorbent were investigated. Experimental results showed that the chemical composite sorbent can effectively utilize solar energy or low-grade waste heat sources with temperature ranging from 75 to 90 °C, and it could incorporate 0.61 kg of ammonia per kg of the reactive salt. The temperature evolution in the reactor was strongly influenced by the physicochemical reaction, whereas the transient heat transfer properties in the reactive composite material were different during the decomposition and the synthesis phases owing to the variation of the ammonia content and solid configuration inside the metallic salt complex. The rate of conversion in the reactor was very sensitive to the working temperatures and pressures, and the COP (coefficient of performance) obtained with the consolidated composite sorbent varied between 0.50 and 0.53 when the evaporation temperature ranged from 0 to 15 °C at a generation temperature of 80 °C.     

Effects of impregnating variables on dynamic sorption characteristics and storage properties of composite sorbent for solar heat storage

A family of composite sorbents was prepared by impregnating silica gel in the solution of the hygroscopic salt CaCl₂ for solar heat storage. The characteristics of water adsorbed on the composite sorbents prepared under different impregnating conditions were measured by a micromeritics gas adsorption analyzer, a Calvet-type microcalorimeter and an open-type gravimetric method. From the results of these dynamic sorption measurements, the effects of impregnating variables on the characteristics of water adsorbed on the composite sorbents were evaluated. The composite sorbents prepared under different impregnating conditions were also tested on an open-type sorption storage system. The composite sorbent prepared by impregnating in the CaCl₂ solution of 30% showed a high and stable storage capacity of 1020 J g⁻¹ at the charging temperature of about 90 °C. This study demonstrates a great potential in controlling the sorption characteristics as well as the storage properties of the composite sorbents by optimizing the impregnating variables to meet the specific demands of solar heat storage.     

Comparison of absorption and regeneration performance for post-combustion CO2 capture by mixed MEA solvents

In this work, the absorption performance, regeneration performance, and cyclic absorption capacity of three kinds of mixed monoethanolamine (MEA) solvents were studied compared to those of using MEA solvents alone in self-made apparatuses, including MEA-piperazine (PZ), MEA-potassium carbonate (K₂CO₃), and MEA-ammonia (NH₃). The mixed solvent of 10 wt% MEA/5 wt% PZ has a similar absorption performance and a higher regeneration temperature compared with the 20 wt% MEA solvent. And the mixed solvent of 10 wt% MEA/5 wt% K₂CO₃ has the lowest initial absorption rate, but it has a better cyclic absorption performance and a longer effective reaction time. The mixed solvent of 10 wt% MEA/5 wt% NH₃ has both a faster absorption rate and a lower regeneration temperature. These results prove that the mixed MEA solvent mixed with K₂CO₃ or NH₃ has good potential to replace the MEA solvent alone with a lower energy consumption.     

Effect of thermal storage on the performance of greenhouse

In this communication, thermal model of a greenhouse has been developed by incorporating the effect of water wall in the north side. Various temperatures, namely plant, water wall and room temperatures as a function of climatic and design parameters have been obtained by solving coupled single-order differential equation using Runge–Kutta method. Numerical methods have been carried out for a typical day of winter for Delhi condition. It has been observed that there is significant effect in the plant, room air and water temperatures due to change in fraction of solar radiation incident on north wall (F_n) and heat capacity of water wall. Experimental validation of the proposed model for a greenhouse with brick north wall has also been carried out. It has been observed that there is a fair agreement between experimental and theoretical values. Copyright © 2002 John Wiley & Sons, Ltd.     

Effect of reaction conditions and surface characteristics of Ru/CeO2 on catalytic performance for ammonia synthesis as a clean fuel

The impact of reaction parameters and surface characteristics on NH₃ synthesis activity of the Ru/CeO₂ catalyst was explored. An exceptionally higher NH₃ synthesis activity was observed at 375 °C and 2.5 MPa gauge pressure. The H₂/N₂ ratio among the reactants strongly affected the catalytic activity. The catalytic activity enhanced at higher temperatures for a higher H₂/N₂ ratio, while the lower H₂/N₂ ratio was suitable for improved NH₃ synthesis at a lower temperature while working at 2.5 MPa gauge pressure. Likewise, NH₃ synthesis activity of Ru/CeO₂ catalyst enhanced abruptly on increasing pressure at relatively higher temperature conditions, using a reactant flow with a higher H₂/N₂ ratio. The NH₃ synthesis activity enhanced with time on stream. This increase in activity was associated with an increase in Ru particles with high dispersion on the surface of the catalyst during NH₃ synthesis, confirmed by FIB-TEM and EDS analysis of the cross-sections of catalyst particles.     

Influence of the management strategy and operating conditions on the performance of an adsorption chiller

The aim of this experimental work was to study the influence of the operation mode (i.e. cycle time and relative duration of ads-/desorption phases, R) as well as of the operating conditions on the performance of an adsorption chiller. The testing campaign demonstrated that the management optimization strongly improves the performance of such kind of machines. The Coefficient of Performance (COP) and the Specific/Volumetric Cooling Power (SCP, VCP) vary, respectively, in a range of ±133% and ±43% when the cycle time (τ_cycle) increases from 5 to 20 min at fixed boundary conditions (T_e = 15 °C, T_c = 35 °C, T_h = 90 °C) while a further increasing in performance (up to 15%) is reached, at fixed cycle time, by protracting the duration of the adsorption phase at the expense of the desorption one. The complete set of results allowed to draw a map of performance suitable for the optimization of the management mode taking into account the specific application. At T_e = 15 °C, T_c = 35 °C, T_h = 90 °C, if high SCP is required (e.g. automotive air conditioning), the optimal choice is τ_cycle = 7 min and R = 2.5 (SCP = 394 W/kg, COP = 0.60, VCP = 223 W/m³) while to assure a good efficiency (e.g. solar cooling) the proper management is τ_cycle = 20 min and R = 1 (SCP = 204 W/kg, COP = 0.69, VCP = 116 W/m³).     

Effect of CaO hydration and carbonation on the hydrogen production from sorption enhanced water gas shift reaction

Sorption enhanced water gas shift reaction (SEWGS) based on calcium looping is an emerging technology for hydrogen production and CO₂ capture. SEWGS involves mainly two reactions, the catalytic WGS reaction and the bulk carbonation of CaO with CO₂, and the solid product is CaCO₃, and the Ca(OH)₂ may be formed from the reaction of CaO with H₂O with the presence of steam in gas phase. The effect of Ca(OH)₂ and CaCO₃ on the catalytic WGS reaction and carbonation reaction was studied in a fluidized bed reactor. It was found that the hydrated sorbent and CaCO₃ did not show any catalytic reactivity toward WGS reaction at 400 °C. When the temperature was increased to 500 °C and 600 °C, the catalytic reactivity of hydrated sorbent was recovered partially, but this will depend on the steam fraction in gas phase, the recovery of fresh CaO surface from dehydration of Ca(OH)₂ may be the reason of catalytic reactivity recovery. CaCO₃ can catalyze the WGS reaction at the high-temperature (>600 °C), this may due to the CaCO₃ decomposition and recarbonation processes in which the CaO is transiently formed. The possible mechanism was discussed.     

Effect of storage tanks on solar-powered absorption chiller cooling system performance

Thermal storage, low power tariff at night, and low nocturnal temperature can be used in synergy to reduce the cooling costs of the solar-powered absorption chiller cooling systems. This study aims to reduce the required cooling capacity of an absorption chiller (ACH) powered by a solar parabolic trough collector (PTC) and a backup fuel boiler by integrating thermal storage tanks. The thermal performance of the system is simulated for a building that is cooled for 14 h/day. The system uses 1000 m² PTC with 1020 kW ACH. Chilled water storage (CHWS) and cooling water storage (CWS) effects on the system performance for different operation hours per day of the ACH under Izmir (Turkey) and Phoenix (USA) weather conditions are analyzed. When the ACH operates 14 h/day as the load for both systems and both locations, the variations of the solar collector efficiency and the cooling load to heat input ratio remain less than 4% after the modifications. From the addition of CHWS to the reference system, a parametric study consisting of changing the ACH operation hours per day shows that the required cooling capacity of the ACH can be reduced to 34%. The capacity factor of the ACH is improved from its reference value of 41% up to 96%.     

Effect of the anisotropic thermal conductivity of GDL on the performance of PEM fuel cells

Gas diffusion layers (GDLs) are one of the main components in proton exchange membrane (PEM) fuel cells. In this paper, the effect of anisotropic thermal conductivity of the GDL is numerically investigated under different operating temperatures. Furthermore, the sensitivity of the PEM fuel cell performance to the thermal conductivity of the GDL is investigated for both in-plane and through-plane directions and the temperature distributions between the different GDL thermal conductivities are compared. The results show that increasing the in-plane and through-plane thermal conductivity of the GDL increases the power density of PEM fuel cells significantly. Moreover, the temperature gradients show a greater sensitivity to the in-plane thermal conductivity of the GDL as opposed to the through-plane thermal conductivity.     

Experimental investigation on performance improvement of electro-osmotic regeneration for solid desiccant

Electro-osmotic regeneration for the solid desiccant has been proved to have many merits such as regeneration without the heat source; energy-saving and simple structure. However; the previous work has revealed that its performance is seriously limited by the severe Joule heating effect and electrode corrosion; which demands further improvement to meet the practical requirement. In this paper; four possible improvement methods are investigated experimentally; including changing the material of anode; changing layout of cathode; applying the interrupted power and optimizing the electrical field strength. Through detailed experiments and analysis; we found that applying the platinum-plated titanium mesh as anode could improve the working lifetime from 6 h to over 120 h and effectively reduce Joule heating effect simultaneously; laying a piece of filter cloth under the cathode could enhance the EO regeneration rate up to 0.0021 g s⁻¹; the application of interrupted power could increase the regeneration rate up to 1.5 times; the optimal on–off-time was found at 30 s:1.3 s with 17 V cm⁻¹ electric field strength and 30 s:0.8 s with 11 V cm⁻¹; and the most suitable value of electric field strength was observed as ranging from 8.5 to 13 V cm⁻¹ in our EO regeneration system.     

Effect of carboxyl graphene nanofluid on automobile radiator performance

Nanofluid is a promising solution for the improvement of the radiator performance. In the current research work, the effect of the nanofluid carboxyl graphene on the performance of a radiator is studied. Carboxyl graphene nanoplatelets are added to 50:50 ethylene glycol–distilled water at three concentrations of 0.02, 0.03, and 0.04 vol%. The liquid flow rate is varied from 3 liters per minute (LPM) to 6 LPM, and the inlet liquid to the radiator has been maintained at constant temperatures of 40 °C and 50 °C. The inlet air Reynolds number is varied between 1200 and 2500. The effects of these on performance parameters such as Nusselt number, effectiveness, and friction factor are investigated. It is observed that addition of carboxyl graphene nanoplatelets increases the Nusselt number and effectiveness of radiator while friction factor is unaltered. The effectiveness of radiator increases by 27.38% and 23.41% for inlet temperatures of 40 °C and 50 °C respectively at 0.02 vol% and 5 LPM flow rate.     

Effect of nonideal conditions on the electrical performance of faraday MHD generators

The effect of nonideal conditions on the current flow in a MHD generator has been investigated by two-dimensional analysis in terms of internal resistance, Hall voltage and uniformity of current distribution. In particular, the effects of (a) temperature profile along the Faraday direction in the plasma, (b) current bunching on cathode surfaces due to phenomena like arc spots, and (c) electrical leakage between adjacent electrodes due to finite resistance of the insulator segments are investigated. the results show that cold boundary layers near metallic electrode surfaces tend to relieve current concentration. the optimum resistivity of wedge-shaped electrodes for obtaining uniform current distribution in the duct has been calculated for various temperature profiles. the results indicate that the internal resistance of a MHD generator strongly depends on the location and size of current bunched spots on cathodes. the fluctuations in the spot size and its location can lead to large fluctuations in power output. the present calculations reveal that the electrical performance of a MHD generator is not adversely affected by current leakage along insulator segments for small insulator conductivities.     

一种基于太阳能供能的CCRs捕捉CO_2方案研究

文章提出一种基于太阳能供能的的CCRs火电厂CO2回收系统,该系统将高温太阳能集热技术和钙基吸收剂循环煅烧/碳酸化法（CCRs）进行耦合。以目前国内外研究的塔式太阳能集热器以及双流化床反应器为基础,提出一种基于太阳能供能的CCRs捕捉火电厂CO2方案,并对其可行性进行初步分析,最后指出了该方案需进一步解决和研究的问题。     

热阻和回热损失对埃里克森循环性能的影响

建立受热阻和回热损失影响的埃里克森循环模型,以输出功率为目标函数,导出循环的基本优化关系式,由此获得循环的特性曲线,并对特殊的工况点作了详细的讨论,从而得到一些新的结论。     

Effect of synthesis conditions on performance of a hydrogen selective nano-composite ceramic membrane

A hydrogen-selective nano-composite ceramic membrane was prepared by depositing a dense layer composed of SiO₂ and Al₂O₃ on top of a graded multilayer substrate using co-current chemical vapor deposition (CVD) method. The multilayer substrate was made by dip-coating a macroporous α-alumina tubular support by a series of boehmite solutions to get a graded structure. Using DLS analysis, it was concluded that decreasing hydrolysis time and increasing acid concentration lead to smaller particle size of boehmite sols. XRD analysis was carried out to investigate the structure of intermediate layer and an optimized calcination temperature of 973 K was obtained. SEM images indicated the formation of a graded membrane with a porous intermediate layer having a thickness of about 2 μm and a dense top selective layer with a thickness of 80–100 nm. Permeation tests showed that H₂ permeance flux decreased from 5 × 10⁻⁵ mol m⁻² s⁻¹ Pa⁻¹ for a fresh substrate to 6.30 × 10⁻⁷ mol m⁻² s⁻¹ Pa⁻¹ after 6 h of deposition, but H₂ selectivity over N₂ increased considerably from 5.6 to 203.     

660 MW超超临界机组活性焦解析热源选取方案研究

活性焦烟气净化技术是一种多污染物一体化脱除技术,活性焦再生是其中的关键步骤之一,采用热力解析能量消耗较大,而在燃煤电站采用较低品位的热源——烟气以及中低压蒸汽,是一种值得探讨的方法。以某660 MW超超临界机组为例,提出从二级省煤器前抽烟气并在低负荷时辅以4号抽汽的蒸汽（方案1）以及从后烟道低温过热器前抽烟气（方案2）两种方案分别作为活性焦解析热源,计算结果表明：100%负荷时两种方案对省煤器出口水温无影响,排烟温度分别下降3.7和2 ℃,供电标准煤耗分别增加3.34和3.64 g/(kW·h);50%负荷时省煤器出口水温分别下降6.2和3.4 ℃,〖JP2〗排烟温度下降2.1和1.6 ℃,供电标准煤耗分别增加10.32和8.13 g/(kW·h)。〖JP〗可根据机组特点,高负荷运行时长占比大的机组可选择方案1、低负荷运行时长占比大的机组可选择方案2作为解析热源。     

Thermal performance investigation of a single medium temperature phase change microcapsule used for wind power absorption and heat storage system

Phase change microcapsules have a wide application in the heat storage system. The medium temperature heat storage systems such as medium temperature solar thermal plants, waste heat recovery systems and wind power absorption systems. In order to analyse the effects of configuration parameters and materials on phase change heat transfer process in a single medium temperature microcapsule, an enthalpy-transforming model was applied to trace the location of the solid-liquid interface and obtain the liquid fraction at different time in the melting process. Based on this model, the effects of particle size, the effects of wall thickness, the effects of wall materials and different medium temperature phase change materials were analyzed. The numerical results show that the larger particle size has a longer melting time, the melting time of 50 μm particle size and 250 μm particle size is 0.036 s and 2.48 s, respectively. In addition, the melting time of microcapsules with different wall thicknesses from the 1μm to 9μm is the same i.e., 0.14 s. Therefore, the wall thickness has little effect on the melting time of microcapsules. Besides, the microcapsule with the erythritol as inner material and the polystyrene as wall material has the longest melting time. Furthermore, the thermal conductivity of the wall materials is the main factor affecting the melting time. Moreover, the product of latent heat and density of phase change material is the main factor of the melting time.