Glass fiber entrapped sorbent for reformates desulfurization for logistic PEM fuel cell power systems

Glass fiber entrapped ZnO/SiO₂ sorbent (GFES) was developed to remove sulfur species (mainly hydrogen sulfide, H₂S) from reformates for logistic PEM fuel cell power systems. Due to the use of microfibrous media and nanosized ZnO grains on highly porous SiO₂ support, GFES demonstrated excellent desulfurization performance and potential to miniaturize the desulfurization reactors. In the thin bed test, GFES (2.5 mm bed thickness) attained a breakthrough time of 540 min with up to 75% ZnO utilization at 1 ppm breakthrough. At equivalent ZnO loading, GFES yielded a breakthrough time twice as long as the ZnO/SiO₂ sorbent; at equivalent bed volume, GFES provided a three times longer breakthrough time (with 67% reduction in ZnO loading) than packed beds of 1–2 mm commercial extrudates. GFES is highly regenerable compared with the commercial extrudates, and can easily be regenerated in situ in air at 500 °C. During 50 regeneration/desulfurization cycles, GFES maintained its desulfurization performance and structural integrity. A composite bed consisting of a packed bed of large extrudates followed by a polishing layer of GFES demonstrated a great extension in gas life and overall bed utilization. This approach synergistically combines the high volume loading of packed beds with the overall contacting efficiency of small particulates.     

Tributyl phosphate additive enhancing catalytic absorption of NO2 for simultaneous removal of SO2/NOx in wet desulfurization system

Removal of SO₂ and NO emissions from coal-fired power plants have always been the focus in coal's utilization industries for which traditional wet desulfurization system hold the potential to achieve simultaneous removal of SO₂/NO_x. In this work, a novel liquid catalyst (tributyl phosphate, TBP) was investigated for the simultaneous removal of SO₂ and NO_x in a NO pre-oxidation (ozone oxidation) assisted process. The absorption process and reaction mechanism of SO₂ and NO₂ were studied in a small-scale experimental system, and the removal efficiency of pollutant and the key parameters were examined in a pilot-scale system. The results show that the removal efficiency of NO₂ in traditional wet desulfurization system is only 20–40%; however greatly increases to >90% when TBP is added. Moreover, TBP can enhance the NO₂ removal performance in the presence of SO₂ due to the formation of TBP–NO₂–SO₃²⁻ complex. Considering the oily nature of TBP that can be easily separated, such addition strategy hold great potential for industrial SO₂/NO_x simultaneously removal.     

Economics of electric power generation options and sulfur oxide emission control

By the use of spreadsheet techniques, a simple but versatile program has been developed for analyzing the economics of electric power generation for all types of plants. The incentives for various power-generation options are quantified.The impact of SO_x, emission control using flue-gas desulfurization (FGD) on power cost is about $0.013/kWhr for plants with a load factor of 0.7 and represents 20% of the power cost. It is shown that use of an aged plant is more economical than of a new plant equipped with FGD to meet the SO_x emission regulations, even though continued use of old plants defeats measures for environmental improvement. With the current price structures, continued use of an aged, oil-fired, steam-electric plant is economically attractive, and a natural gas combined-cycle electric plant may now be economically viable.     

Effect of Prussian Blue on Organic Sulfur of Coal in Aqueous Medium

Abstract

This study is an attempt to desulfurize organic sulfur from coal samples with ferric hexacyanoferrate (II), Fe₄ [Fe(CN)₆], as the desulfurization agent. Effect of temperature, particle size and concentration of ferrocyanide ion on desulfurization from the coal samples has been investigated. The temperature and stirring time are the most important parameters for the level of desulfurization of organic sulfur. Removal of organic sulfur content increased continuously with increasing temperature from 298 to 368 K. The organic sulfur removal rate sharply increases from 10 min to 30 min stirring time. After 30 min, it reaches a value of plateau. Particle size between ?100 mesh and ?200 mesh slightly affects the amount of organic sulfur removal. Gradual increase in the concentration of ferric hexacyanoferrate (II) raised the magnitude of desulfurization, but at higher concentration, the variation is not significant.     

Desulfurization and tar reforming of biogenous syngas over Ni/olivine in a decoupled dual loop gasifier

For the production of bio-SNG (substitute natural gas) from syngas of biomass steam gasification, trace amounts of sulfur and tar compounds in raw syngas must be removed. In present work, biomass gasification and in-bed raw gas upgrading have been performed in a decoupled dual loop gasifier (DDLG), with aggregation-resistant nickel supported on calcined olivine (Ni/olivine) as the upgrading catalyst for simultaneous desulfurization and tar elimination of biogenous syngas. The effects of catalyst preparation, upgrading temperature and steam content of raw syngas on sulfur removal were investigated and the catalytic tar reforming at different temperatures was evaluated as well. It was found that 850 °C calcined Ni/olivine was efficient for both inorganic-sulfur (H₂S) and organic-sulfur (thiophene) removal at 600–680 °C and the excellent desulfurization performance was maintained with wide range H₂O content (27.0–40.7%). Meanwhile, tar was mostly eliminated and H₂ content increased much in the same temperature range. The favorable results indicate that biomass gasification in DDLG with Ni/olivine as the upgrading bed material could be a promising approach to produce qualified biogenous syngas for bio-SNG production and other syngas-derived applications in electric power, heat or fuels.     

Exergoenvironmental analysis and optimization of a cogeneration plant system using Multimodal Genetic Algorithm (MGA)

In the present work, a combined heat and power plant for cogeneration purposes that produces 50 MW of electricity and 33.3 kg/s of saturated steam at 13 bar is optimized using genetic algorithm. The design parameters of the plant considered are compressor pressure ratio (r_AC), compressor isentropic efficiency (η_comp), gas turbine isentropic efficiency (η_GT), combustion chamber inlet temperature (T₃), and turbine inlet temperature (TIT). In addition, to optimally find the optimum design parameters, an exergoeconomic approach is employed. A new objective function, representing total cost rate of the system product including cost rate of each equipment (sum of the operating cost, related to the fuel consumption) and cost rate of environmental impact (NO_x and CO) is considered. Finally, the optimal values of decision variables are obtained by minimizing the objective function using evolutionary genetic algorithm. Moreover, the influence of changes in the demanded power on various design parameters are parametrically studied for 50, 60, 70 MW of net power output. The results show that for a specific unit cost of fuel, the values of design parameters increase, as the required, with net power output increases. Also, the variations of the optimal decision variables versus unit cost of fuel reveal that by increasing the fuel cost, the pressure ratio, r_AC, compressor isentropic efficiency, η_AC, turbine isentropic efficiency, η_GT, and turbine inlet temperature (TIT) increase.     

Desulfurization behavior of Ca-based absorbents under periodically changing condition between reducing and oxidizing atmosphere

The capture of H₂S or SO₂ with Ca-based absorbents, limestone and dolomite, was investigated under a periodically changing condition between reducing and oxidizing atmospheres, taking account of the coexistence of these atmospheres in a fluidized-bed coal gasifier. The degree of desulfurization in the reducing atmosphere was large compared with that in the oxidizing atmosphere. Apparent difference in desulfurization behavior was scarcely observed between limestone and dolomite. Stabilization of CaS in in situ desulfurization residues derived from both limestone and dolomite to harmless CaSO₄ was also investigated. Absorbents maintaining porous-structure, such as dolomite, will be preferable for desulfurization in the coal gasification/combustion types of hybrid power systems.     

Non-linear analyses of temperature oscillations in a closed-loop pulsating heat pipe

In this paper, the chaotic behavior of wall temperature oscillations in a closed-loop pulsating heat pipe was investigated using non-linear analyses on temperature data. The tested heat pipe, consisting of 5 turns, was made of copper capillary tube and had an internal diameter of 2 mm. Ethanol was selected as the working fluid with filling ratios (FR) of 30%, 50% and 70%. Wall temperature fluctuations were recorded under three different heating power inputs of 37, 60, and 87 W. Various methods, including pseudo-phase-plane trajectories, correlation dimensions (D_E), Lyapunov exponents, and recurrence plots, were used to analyze the non-linear dynamics characteristics of temperature oscillation data. Three types of attractors were identified under different power inputs. All of the calculated positive largest Lyapunov exponents were found to be less than 0.1, demonstrating the weak chaos characteristics of the pulsating heat pipe. The increase of the power input augments the correlation dimensions and contributes to the improvement of the thermal performance of the pulsating heat pipe. For each power input, the correlation dimensions have the trend of D_E,FR=50% > D_E,FR=70% > D_E,FR=30%, and the best thermal performance was obtained at 50% filling ratio. At least four independent variables are required in order to describe the heat transfer characteristics of a PHP. The average time of the temperature oscillation stability loss, i.e., the inverse of the largest Lyapunov exponent, decreases as the power input increases. In the recurrence plots, chaotic states were observed. The Recurrence Quantification Analysis indicates larger values of the order-2 Renyi entropies K₂ at the evaporation section than at the condensation section. Moreover, the trend that K_2,Q=87W > K_2,Q=60W > K_2,Q=37W at each filling ratio both for T_e4 and T_c4 collaborating with the positive, finite largest Lyapunov exponent gives a hint of the maximum entropy self-organization process of the temperature oscillations with the increase of power input.     

基于Aspen Plus的船舶尾气海水脱硫过程模拟分析

利用Aspen Plus中的rate-based模式,对船舶尾气海水脱硫过程进行模拟.首先计算了填料高度以达到设计效率,然后考察填料高度、海水量、海水碱度、海水温度、SO2体积分数及烟气流量对脱硫效率的影响.结果 表明:填料高度、海水量、海水碱度与脱硫效率正相关;海水温度、SO2体积分数、烟气流量与脱硫效率负相关.考虑油耗、负荷率、烟气量等因素的影响,提出了船舶尾气SO2体积分数的计算公式,对脱硫废水中的亚硫酸盐体系进行分析,计算得到了排放水的PH值,并分析了排放水在舷外稀释过程中亚硫酸盐体系组分的变化.     

Preparation of various manganese dioxide composites and their desulfurization performance

The performance of desulfurization materials plays a key role in desulfurization technology. In this study, different types of manganese dioxide (MnO₂) composites were prepared to improve desulfurization performance. These composites were characterized intensively via SEM, XRD, XPS, and BET. Desulfurization performance was measured through thermogravimetry (TG), and the desulfurization mechanism of different types of MnO₂ composite was investigated. Results showed that the desulfurization performances of MnO₂ composites are determined by the combined effects of the materials’ pore structure, specific surface area, active components and Mn valence contents. The desulfurization performances of high specific surface area MnO₂ and porous MnO₂ were enhanced on account of their excellent physical structures. The desulfurization performance of alkali metal additive LiOH doped MnO₂ improved through the addition of active components. The desulfurization performance of bimetallic oxide MnO₂/CeO₂ improved through the synergistic effect of bimetallic oxides. The desulfurization performance of carrier type MnO₂/NaY improved through the dispersion of MnO₂ particles. Among the composites obtained, porous MnO₂ revealed the best desulfurization performance, this composite demonstrated an average SO₂ capture rate of 0.283 g_SO2/g_material·h within the first hour of reaction, and its SO₂ capture capacity was 0.633 g_SO2/g_material.     

Thermodynamic performance assessment of IGCC power plants with various syngas cleanup processes

The present work explores how much IGCC can benefit from warm gas clean-up(WGCU)in comparison with conventional cold gas clean-up(CGCU) and what are the respective contributions of dry particulates removal and warm gas desulfurization (WGD) in a plant-wide point of view. Influences of key parameters of WGD on ther- modynamic performance of IGCC plant including desulfurization temperature, oxygen concentration in the re- generation stream, and H 2 S removal efficiency are discussed. It is obtained that the net efficiency of IGCC with full WGCU experiences an improvement of 1.77 percentage points compared with IGCC with full CGCU. Of which, dry particulates removal without water scrubber contributes about 1 percentage point. The influence of desulfurization temperature on thermodynamic performance of IGCC with WGD is weak especially when it is higher than about 350℃, which indicates that more focus should be put on investment cost, technical feasibility and sorbent stability for the selection of optimal operation temperature. Generally, 2%~3% of oxygen concentra- tion in the regeneration stream might be reasonable in a thermodynamic performance point of view. In addition, the improvement of 0.31 percentage points can be obtained by removal of H 2 S in the syngas from 27 ppm to 3 ppm.     

Convection in a horizontal rectangular duct under constant and variable property formulations

The convective laminar flow through a horizontal rectangular duct, with significant buoyancy effects, has been investigated analytically and numerically, employing the constant property (CP) model and the variable property (VP) model. The duct has a finite heated region on the bottom and three-dimensional transport is studied. The CP model employs the Boussinesq approximations and uses properties evaluated at four different reference temperatures, i.e. the ambient temperature T₀, the average temperature T_f, the integrated average temperature T_int, and the heat source temperature T_h. In the VP model, the density and the transport properties are computed using the state equation of an ideal gas and power law correlations, respectively. Numerical results for temperature ratio ?, where ?=(T_h−T₀)/T₀, ranging from 0.033 to 2.33 are presented. The spanwise variation of the transport quantities is investigated in detail for the different models, and several interesting and important tends are obtained. These results will be of considerable value in model development for a wide variety of thermal systems and processes, where large changes in material properties are encountered.     

8 MeV electron irradiation studies on electrical characteristics of Cu(In,Ga)Se2 solar cells

Cu(In,Ga)Se₂ (CIGS) solar cells are gaining considerable interest due to their high optical absorption coefficient and adjustable band gap, which enables them to achieve high conversion efficiency and also present many promising applications in space power systems. In this paper we report the results of the effect of temperature and 8 MeV electron irradiation on the electrical characteristics of ZnO/CdS/Cu(In,Ga)Se₂/Mo polycrystalline thin-film solar cells under forward and reverse bias studied in the temperature range 270-315 K. The solar cells were subjected to 8 MeV electron irradiation from the Microtron accelerator and were exposed to graded doses of electrons up to 75 kGy. I-V characteristics of the cells under dark and AM 1.5 illumination condition were studied before and after the irradiation. Capacitance measurements were also carried out at various frequencies before and after irradiation. In the measured temperature range, the dark current contribution is due to the generation-recombination of the minority carriers in the depletion region. The ideality factor is found to decrease with increase in temperature. It seems that electron irradiation has not altered the dark current conduction mechanism significantly. The effect of electron irradiation on the solar cell parameters such as fill factor (FF), conversion efficiency (η), saturation current (I_o), short circuit current (I_sc), open circuit voltage (V_oc), and ideality factor (n) was studied. They were found to be stable up to 75 kGy of electron dose as only small changes were observed in the solar cell parameters.     

Wind energy assessment and wind farm simulation in Triunfo – Pernambuco,Brazil

This paper presents a wind energy assessment and a wind farm simulation in the city of Triunfo in the state of Pernambuco in the northeast region of Brazil. The wind data were obtained from the SONDA (Sistema de Organização Nacional de Dados Ambientais) project’s meteor station (wind speed, wind direction and temperature) at both heights of 50 m during a period of time of 30 months. The Triunfo wind characterization and wind power potential assessment study shows an average wind speed (V) of 11.27 m/s (predominant Southeast wind direction), an average wind power density (P/A_T) of 1.672 W/m² and Weibull parameters shape (K) and scale (A) respectively equal to 2.0 and 12.7 m/s. Those values demonstrate an important wind potential in this region for future wind farm prospection. The wind farm (TRI) was simulated by using 850 kW wind turbines given a total of 20 MW installed. The simulated results show(s) an AEP (annual energy produced) of 111.4 GWh, a capacity factor (C_f) of 62% and a total of 5.462 h of operation by year (full load hours). The economical simulated results show(s) a Pay-back of 3 years Internal Rate of Return (IRR) of 47% and Net Present Value (NPV) of 85.506 k€ (both in a period of time of 20 years).     

Capturing CO2 in flue gas from fossil fuel-fired power plants using dry regenerable alkali metal-based sorbent

CO₂ capture and storage (CCS) has received significant attention recently and is recognized as an important option for reducing CO₂ emissions from fossil fuel combustion. A particularly promising option involves the use of dry alkali metal-based sorbents to capture CO₂ from flue gas. Here, alkali metal carbonates are used to capture CO₂ in the presence of H₂O to form either sodium or potassium bicarbonate at temperatures below 100 °C. A moderate temperature swing of 120–200 °C then causes the bicarbonate to decompose and release a mixture of CO₂/H₂O that can be converted into a “sequestration-ready” CO₂ stream by condensing the steam. This process can be readily used for retrofitting existing facilities and easily integrated with new power generation facilities. It is ideally suited for coal-fired power plants incorporating wet flue gas desulfurization, due to the associated cooling and saturation of the flue gas. It is expected to be both cost effective and energy efficient.     

Analysis of thermoelectric cooler performance for high power electronic packages

In this paper, an analysis of thermoelectric cooler (TEC) performance is conducted for high power electronic packages such as processors. Based on the TEC module parameters, two sets of analytical solutions for TECs in system constraints are derived for the junction temperature T_j at a fixed cooling power Q_c, and for Q_c at a fixed T_j, respectively. As against the iterative procedure often reported in literature, the major advantage of the present analytical method lies in the fact that the solutions can be obtained without resorting to the pellet thermoelectric parameters and geometric details. Two cooling scenarios, the processor test and the processor cooling under end-user conditions, are analyzed based on the present analysis models for two commercial TECs with high cooling power capacities nominal. Analytical results show that significant thermal enhancements are achievable based on optimized currents and cooling configurations. The validation of the present analysis is also conducted through experimental measurements and comparison with previous solutions.     

Effect of ceramic supports on microwave processing of porous food samples

A theoretical analysis has been carried out to study efficient microwave heating of porous dielectrics. The heating effects are analyzed for two types of porous material: beef-air (b/a) and beef-oil (b/o) with and without ceramic supports (Al₂O₃ and SiC). Three test cases for porosities (ϕ) 0.3, 0.45 and 0.6 are considered. The maxima in average power corresponding to resonances occur at various sample thicknesses for all porous materials with and without supports and two dominant resonance modes R₁ and R₂ are considered where the average power at R₁ is larger than that at R₂. It is interesting to observe that average power absorption is enhanced for samples (b/a and b/o) in presence of Al₂O₃ support whereas the average power is smaller with SiC support. From the analysis on spatial distribution of electric field, power and temperature, it is seen that runaway heating is observed at the face which is not attached with support for b/a samples, and the intensity of thermal runaway increases with porosity whereas lower thermal runaway is observed for b/o samples at all porosity values. An efficient heating strategy has been investigated for various distributions of microwave incidences. It is observed that one side incidence may correspond to the largest heating rates whereas distributed sources may correspond to smaller thermal runaway for both beef-air (b/a) and beef-oil (b/o) samples.     

A low temperature electrolyte for primary Li/CFx batteries

In this work, a 1:1 by weight blend of acetonitrile (AN) and γ-butyrolactone (BL) was studied as the solvent of low temperature electrolyte for high energy density Li/CF_x batteries. Both visual observation and impedance analysis show that metallic Li is kinetically stable in a 0.5 m LiBF₄ 1:1 AN/BL electrolyte. This property is attributed to the formation of a protective passivation film on the surface of metallic Li, and it has been successfully used to develop the low temperature electrolyte for Li/CF_x cells. It is shown that the cell with such an electrolyte outperforms the control cell with 0.5 m LiBF₄ 1:1 (wt.) propylene carbonate (PC)/1,2-dimethoxyethane (DME) electrolyte in both power capability and low temperature discharge performance. Impedance analyses reveal that the improved discharge performance is attributed to the reduction in both the bulk resistance and cell reaction resistance of the Li/CF_x cell, which is related to the high ionic conductivity of the AN/BL electrolyte. Due to the chemical incompatibility between metallic Li and AN at high temperatures, the storage and operation temperature for the Li/CF_x cells with 0.5 m LiBF₄ 1:1 AN/BL electrolyte is limited to or below ambient temperature (30 °C).     

The reversible hydrogen storage abilities of metal Na (Li,K, Ca,Mg, Sc,Ti, Y) decorated all-boron cage B28

The density functional theory is used to study the hydrogen storage abilities of alkali metal Li (Na, K), alkaline-earth metal Mg (Ca), and transition metal Ti (Ti, Sc, Y) decorated B₂₈, which is the possible smallest all-boron cage and contains one hexagonal hole and two octagonal holes. The most stable structure of B₂₈ explored by the calypso search is as same as that explored by Zhao et al. [Nanoscale 7(2015)15086]. It is calculated that the hollow sites outside of the cavities should be the most stable for all metals except for Ti. The average adsorption energy of H₂ molecules (E_ad) adsorbed by each Na (Ca, K, Mg, Sc, Y and Li) atom outside of the B₂₈ cage are in the range from 0.2 to 0.6 eV, which is suitable for hydrogen storage under near-ambient conditions. However, the largest hydrogen gravimetric density (HGD) for the B₂₈Sc₃-12H₂ structure is smaller than the target of 5.5 wt% by the year 2017 specified by the US Department of Energy (DOE). Therefore, the metal Ti (Sc) decorated all-boron cage B₂₈ should not be good candidates for hydrogen storage. The calculated desorption temperature and the molecular dynamic simulation indicate that the B₂₈M₃-nH₂ (M = Na, Li, Ca, K, Mg, Y) structures are easy to desorb the H₂ molecules at the room temperature (T = 300 k). Furthermore, the B₂₈ cages bridged by the sp²-terminated B₅ chain can hold Na (Li, Ca, K, Mg, Y) atoms to capture hydrogen molecules with moderate E_ad and HGD. These findings suggest a new route to design hydrogen storage materials under the near-ambient conditions.