Effects Of Different Operating Conditions Research Articles

Characterization of gaseous and particulate pollutants from gasification-based improved cookstoves

Cookstove studies have reported pollutant concentrations (mainly PM2.5, black carbon and CO) without routinely associating it with the design and operating principles of the stoves. Extensive characterization of pollutants from cookstoves and the effect of different operating conditions are required for a better understanding of the mechanisms of pollutant formation. In this study, a forced draft (FD) and a natural draft (ND) gasification-based improved cookstove were tested under controlled conditions. Real-time pollutant concentrations, both particulate (PM2.5, lung-deposited surface area and particle number size distribution) and gaseous (CO, CO2 and NOx), from these stoves using three types of fuel (applewood chips and chunks, cowdung cake and coal) along with different cookstove operating conditions (airflow rates and with or without a cooking pot) were measured and compared. The FD cookstove tended to exhibit higher concentrations of emissions compared to the ND cookstove. Increasing airflow through the FD stove decreased flame length and the residence time of VOCs inside the flame zone, which in turn increased pollutant concentrations. An optimum airflow producing the lowest particulate matter (PM) concentrations was established for the FD cookstove. The CO–CO2 ratio, an indicator of combustion efficiency, demonstrated strong correlations with PM2.5 (r=0.857), particle geometric mean diameter (r=0.900) and the total surface area concentration (r=0.908) indicating that CO–CO2 ratio may be used as a proxy for these PM metrics. Results reported in this study will facilitate further improvements in the design of future cookstoves.

Effective ammonia recovery from swine excreta through dry anaerobic digestion followed by ammonia stripping at high total solids content

This study investigated ammonia recovery from swine excreta through dry anaerobic digestion (AD) and ammonia stripping. The effects of different operation conditions including temperature (25–55 °C), total solids (TS, 20%–35%) and initial pH (7.0–12.0) were assessed on ammonia production in terms of organic nitrogen (organic-N) conversion and process kinetics through 8 days' trials. All experimental data fitted well to the pseudo first-order kinetic models during dry AD and the maximum organic-N mass conversion ratio was estimated to be 65.1% when dry AD was conducted at 55 °C, 20% TS, and initial pH 10.0. Changes in biogas production and its composition signaled the bioactivity of the bacteria involving in ammonia production from swine excreta during dry AD. Finally, greater than 90% of the total ammonia nitrogen (TAN) in swine excreta was efficiently recovered by air stripping at TS about 20%. Restated, the combination of short-term dry AD with ammonia stripping achieved about 60% of total nitrogen recovery efficiency.

Reduction of primary tar vapor from biomass by hot char particles in fixed bed gasification

This study investigated the reduction of primary tar vapor from biomass pyrolysis over a bed of hot char particles, focusing on the effect of different operating conditions and char properties. The char samples were prepared from wood, paddy straw, palm kernel shell, and activated carbon. The primary tar was produced from fir wood by pyrolysis at 500 °C and passed through a reactor filled with char particles with different lengths and temperatures.The tar cracking reactions became active above 700 °C, and the presence of hot char particles promoted more tar reduction compared with thermal cracking alone. The mass yield of the primary tar was reduced from 24.8% by pyrolysis to 13.7% by thermal cracking at 800 °C, and further to 7.7% by hot char particles in a reactor volume of 1.48 cm3/gwood. In terms of carbon yield, these values correspond to 32.1%, 19.9% and 11.8%, respectively. The tar with smaller molecular weights was quickly decomposed to gases, whereas the heavy tar was resistant to cracking, even when the reactor volume was increased to 6.90 cm3/gwood. The tar cracking behaviors were similar for four char types despite differences in microscopic surface areas, pore-size distributions, and inorganic contents. The results suggest that creating a tar-cracking zone using char particles situated between the pyrolysis and gasification zones could be helpful in converting the primary tar vapor in a downdraft fixed-bed gasifier, but the degree of conversion is not high enough to eliminate tar issues completely.

Modeling Transport Phenomena in Ammonia Fuel Cells

Introduction Ammonia has been considered as a potential fuel for alkaline fuel cells. Ammonia can be produced at low cost, and inexpensive catalysts can be used in Ammonia Fuel Cells (AFC) [1, 2]. In AFC, ammonia is oxidized at the anode side and OH-, nitrogen and water are produced (1). OH- anion moves through membrane and reduced into water at the cathode side (2). 1/3 NH3 + OH- ↔ 1/6 N2 + H2O + e-, E0=0.40V ----- Eqn. 1 1/4 O2 + 1/2 H2O + e- ↔ OH-, E0=0.40V ----- Eqn. 2 The theoretical open-circuit voltage (OCV) of the AFC is 1.17 V at standard conditions. The value is less than that of Hydrogen Fuel Cells (HFC), but AFC has a higher energy efficiency, 88.7%, than HFC of 83% [1]. Performance and durability of hydrogen PEM fuel cells has been improved over the last decade by extensive experiments and computations. In particular, continuum modeling has been an important tool for understanding and insight into processes and phenomena, which cannot be captured through experiments [3]. Recently, AFCs have attracted the attention of fuel cell researchers due to its high potential for a clean future energy device. However, AFCs show some problems in related to mass transfer and fuel crossover in the membrane electrode assembly. In this study, transport phenomena in AFCs are analyzed using a computational model. Objective When the AFC is in operation, complex phenomena occur in the Membrane Electrode Assembly (MEA) including mass and heat transfer, electrochemical reactions, and charge (OH- and electron) transport (Fig.1). Therefore, a continuum model was developed to simulate the phenomena in MEA. Figure 1. Illustration of Mass Transport in Membrane Electrode Assembly depicting individual layers and chemical components. cCL and aCL depict the cathode and anode catalyst layers respectively, while cGDL and aGDL depict the cathode and anode gas diffusion layers respectively. Results Using the model, potential and species distribution in MEA, and the extent of electrochemical reaction in catalyst layer were calculated. In addition, the effect of different operating conditions on these phenomena were analyzed. These results, along with the effect of water transfer and ammonia crossover on cell performance will be discussed. Detailed accounts of the governing equations and their numerical solving procedure will also be provided.

Flash sintering of alumina: Effect of different operating conditions on densification

Nearly pure α-alumina samples produced by uniaxial pressing were flash sintered under electrical fields ranging from 500V/cm to 1500V/cm in experiments at constant heating rate. Sintering temperature significantly decreased with the applied E-field even down to ≈900°C at 1500V/cm. The onset temperature for flash sintering can be successfully modelled as a function of the applied voltage. The sintering temperature is also shown to be strongly affected by the electrode materials used during the treatment: using silver or carbon electrodes the sintering temperature is about 300°C lower than when using platinum electrodes. In addition, the bulk density and porosity of the sintered alumina ceramic correlate strongly with the imposed current limit. Power dissipation was analysed before and during flash sintering; the activation energy for conduction was calculated in both cases, indicating that the process is based on ionic diffusion phenomena. Finally, we showed that during flash sintering the activation energy for conduction decreases, suggesting the occurrence of physical or structural modifications induced by current localization at the grain boundaries.

Experimental study of a cascade solar still coupled with a humidification–dehumidification system

In this study, coupling of a cascade solar still with a humidification–dehumidification system was investigated experimentally under the climatological conditions of Zahedan (Latitude: 29.49, Longitude: 60.87), Iran. The inclined solar stills produce distillated and hot water simultaneously. In addition, the effects of different operating conditions and configurations on thermal performance and productivity of the solar system were studied. The effect of feed water and air flow rates on the daily productivity of HD system in different conditions such as feed water temperature has been investigated. The daily productivity of cascade solar still with and without HD system at different flow rates is investigated. Moreover, the end result of assembling the HD system with a cascade solar still was studied. The daily productivity of the system increases from 28% to 141% in the presence of humidification–dehumidification system. It also improves the thermal efficiency from 9% to 20% after using 40–150ml/min of flow rate, respectively. The maximum productivity and efficiency were 5.4kg/m2day and 39% for minimum flow rate.

Experimental study of a hybrid solvent MEA-Methanol for post-combustion CO 2 absorption in an absorber packed with three different packing: Sulzer BX500, Mellapale Y500, Pall rings 16 × 16

Abstract Effects of different operating conditions on the CO 2 capture and mass transfer performance of the absorption of CO 2 into a hybrid solvent MEA-Methanol were studied in a pilot-plant absorber packed with three different packing consist of Sulzer BX500, Mellapale Y500 and Pall rings 16 × 16. The results showed that the structured packing had an obvious advantage in the mass transfer performance. And Sulzer BX500 was better than Mellapale Y500 for it had a more uniform gas–liquid distribution on the packing surface. In addition, CO 2 lean loading, lean solvent temperature, lean solvent flow rate and flue gas flow rate all had great effects on the absorption performance of the MEA-Methanol absorption system.

Harmonic power flow of VSC-HVDC based AC/DC power systems

This paper extends the traditional harmonic power flow (HPF) to include voltage source converter (VSC) based HVDC. First, a new harmonic model of VSCs, called the real harmonic coupling matrix (RHCM), is developed. The real-valued model is simple in form and easy to calculate. The nonlinear relationship between harmonics and VSC control variables is analytically represented. Then, the model is used to integrate VSC-HVDC into the rectangular-form HPF. Newton's method is adopted to simultaneously solve the AC and DC system harmonics and fundamental power flow. The algorithm is validated by time-domain simulation and tested on a 10-bus AC/DC power system. The effect of VSC harmonics on fundamental power flow is investigated, so is the effect of different operating conditions on harmonics. The results demonstrate that the proposed HPF makes a very useful tool in the harmonic analysis of VSC-HVDC based AC/DC power systems.

Experimental Study and Numerical Simulation of the Air Gap Membrane Distillation (AGMD) Process

Abstract Some challenges, including inappropriate distribution of currents on the membrane surface, poor hydrodynamics and existing severe temperature polarization (TP) phenomenon in MD modules, impede industrialization of MD process. Computational fluid dynamics (CFD) method was used for numerical simulation of hydrodynamics in air gap membrane distillation modules. One of two simulated modules in this work is a novel developed one in which heat and mass transfer data was compared with available literature data. Moreover, the effect of using baffles in module was investigated. Comparison between the novel module and conventional module indicates higher trans-membrane mass flux and gained output ratio (GOR) coefficient by 7% and 15%, respectively. Moreover, the effects of different operating conditions including feed temperatures and feed flow rates on permeate flux were investigated.

Optimization of Phenol Removal Using Ti/PbO2 Anode with Response Surface Methodology

AbstractScale-up of a lead dioxide (PbO2) anode system is significant to the practical application of electrochemical oxidation (EO) in biorefractory wastewater treatment. In this study, response surface methodology (RSM) was employed to investigate the effects of different operating conditions on phenol removal by electro-oxidation with a Ti/PbO2 anode. A central composite design (CCD) was used to optimize the electro-oxidation process and to evaluate the individual and interactions effects of current intensity, electrolysis time, and recirculation flow rate on phenol removal. Synthetic wastewater (or distillate water) with phenol concentration of 10 mg/L−1 was used in this study. Optimal conditions for phenol removal were established at 1.12 A current intensity, 40 min electrolysis time, and 188 mL·min−1 recirculation flow rate, in which a removal of 78.97±1.72% was achieved. The decay kinetics of phenol removal was fitted a first-order reaction.

Evaluating effective factors on the activity and loading of immobilized α-amylase onto magnetic nanoparticles using a response surface-desirability approach

The effects of different operational conditions of α-amylase covalent immobilization on magnetic nanoparticles were investigated using a central composite design.

The influences of operating conditions and design configurations on the performance of symmetric electrochemical capacitors.

The influence of different charging current densities, charging times and several structural designs on symmetric electrochemical capacitor (EC) performance, including capacitance, energy density and power density, has been investigated via modelling and simulation. Understanding the effects of different operating conditions and structural design variables on a capacitor's performance will guide in the optimal design and fabrication of high performance ECs. The operating conditions and design configurations examined were charging current density, charging times, electrode and electrolyte effective conductivity, electrode thickness and electrode porosity. The results reveal that ECs with low electrode and electrolyte effective conductivities can only be effectively charged at low current density for long times. ECs with a high concentration of impurity ions or redox species exhibit high self-discharge rates, and fast charging of the ECs greatly reduces the self-discharge rate, compared to slow charging, provided that the effective conductivities of the electrode and electrolyte are high enough. The simulation showed the typical electrode length scale over which the liquid potential drop occurs and electrode utilization can be employed as a design parameter to optimize electrode thickness (effective thickness) for ECs designed to operate under a specific current density range. The expression for electrode utilization (u) and the guidelines that can also be used to determine optimum electrode thickness/effective thickness (100% electrode utilization), optimum charging time and optimum current density in a cell of a given voltage and effective conductivity of electrode and electrolyte, were derived. The energy and power density of ECs were increased when the electrode thickness was reduced in the given charging conditions. The Ragone plots can be used to select optimum electrode dimensions to attain given energy and power density specifications.

Numerical Study on Sediment Erosion of Francis Turbine with Different Operating Conditions and Sediment Inflow Rates

Francis turbines are thought to be good solutions for both small and large-scale hydro power plant so, they have been used widely to produce power from the water sources. The turbines can be subject to erosion when the turbines operate in sediment-laden water. The erosion can reduce the performance, changes in flow pattern and even breakdown of turbine. To prevent this erosion in turbine components, predicting the region of erosion might be very useful for developing coating techniques and optimization of hydraulic design of the turbine components. In this study to predict the sediment erosion of Francis turbine runner with different operating conditions and sediment concentrations, Tabakoff and Grant model was used and erosion rate was calculated. In order to figure out the effect of different operating conditions, simulations were conducted at best efficiency and full load condition. Also, to investigate the effect of sediment inflow rates, inflow rates were varied with the value of 1, 5, 10, 20, 30, 40 and 50kg/s. The predicted erosion patterns were similar for both operating conditions and mainly found on the pressure side of runner blades. Most of the erosion was thought to occur near the outlet side of runner due to high relative velocity for both best efficiency and full load condition. It was also found that erosion rate increased almost linearly on increasing sediment inflow rate regardless of the operating conditions.

Optimization and modelling using the response surface methodology (RSM) for ciprofloxacin removal by electrocoagulation.

In this study, response surface methodology (RSM) was used to investigate the effects of different operating conditions on the removal of ciprofloxacin (CIP) by the electrocoagulation (EC) with pure iron electrodes. Box-Behnken design was used for the optimization of the EC process and to evaluate the effects and interactions of process variables such as applied current density, process time, initial CIP concentration and pH on the removal of CIP by the EC process. The optimum conditions for maximum CIP removal (86.6%) were found as pH = 4; Co = 5 mg.L(1-); Id = 4.325 mA.cm(2-); tprocess = 10 min. The model adequacy and the validity of the optimization step were confirmed with additional experiments which were performed under the proposed optimum conditions. The predicted CIP removal as 86.6% was achieved at each experiment by using the optimum conditions. These results specify that the RSM is a useful tool for optimizing the operational conditions for CIP removal by the EC process.

Visual experimental research on bubble absorption in a vertical tube with R124–DMAC working pair

Visual experimental investigations were carried out on a vertical co-current glass tube absorber to observe the behavior of the R124 (2-chloro-l,l,l,2,-tetrafluoroethane)–DMAC (N′,N′-dimethylacetamide) bubble absorption process and study the effects of different operating conditions on absorption performance. The results show that the refrigerant vapor flow rate, absorption solution flow rate, concentration, temperature and nozzle orifice diameter significantly affect the flow pattern and absorption height. As the vapor flow rate, absorption solution concentration and temperature, and nozzle orifice diameter increases, the absorption height increases. As the absorption solution flow rate increase, the absorption height reduces. Under the conditions of a large refrigerant vapor flow rate, high solution inlet concentration and temperature, three kinds of flow pattern, namely churn, slug and bubbly flow, can be simultaneously observed in the absorption tube.

Exergy analysis of a coal/biomass co-hydrogasification based chemical looping power generation system

Power generation from co-utilization of coal and biomass is very attractive since this technology can not only save the coal resource but make sufficient utilization of biomass. In addition, with this concept, net carbon discharge per unit electric power generation can also be sharply reduced. In this work, a coal/biomass co-hydrogasification based chemical looping power generation system is presented and analyzed with the assistance of Aspen Plus. The effects of different operating conditions including the biomass mass fraction, Rb, the hydrogen recycle ratio, Rhr, the hydrogasification pressure, Phg, the iron to fuel mole ratio, Rif, the reducer temperature, Tre, the oxidizer temperature, Tox, and the fuel utilization factor, Uf of the SOFC (solid oxide fuel cell) on the system operation results including the energy efficiency, ηe, the total energy efficiency, ηte, the exergy efficiency, ηex, the total exergy efficiency, ηtex and the carbon capture rate, ηcc, are analyzed. The energy and exergy balances of the whole system are also calculated and the corresponding Sankey diagram and Grassmann diagram are drawn. Under the benchmark condition, exergy efficiencies of different units in the system are calculated. ηte, ηtex and ηcc of the system are also found to be 43.6%, 41.2% and 99.1%, respectively.

Experimental Investigation on the Absorption Enhancement of CO2 by Various Nanofluids in Hollow Fiber Membrane Contactors

In this work, suspensions of Fe3O4, CNT, SiO2, and Al2O3 nanoparticles in distilled water are produced and tested as new absorbents in a gas–liquid hollow fiber membrane contactor to investigate the effect of nanoparticles on the rate of mass transfer during CO2 absorption. For this purpose, a pilot-scaled hollow fiber membrane contactor was constructed. A gas mixture was passed through the shell-side, and the nanofluid flowed cocurrently through the lumen side of the fibers. The effects of different operating conditions including gas flow rate, liquid flow rate, inlet CO2 concentration, and nanoparticle concentration on the CO2 absorption have been studied. The results showed that among the operating parameters, liquid flow rate and nanoparticle concentration had the greatest effects on the CO2 absorption. Moreover, UV–vis spectroscopy and DLS method were employed to explore the dispersion stability and hydrodynamic diameter of nanoparticles in the base fluid. The results revealed that nanofluid stabilit...

Application of nanofiltration membrane for treatment of chloride rich steel plant effluent

Composite charged nanofiltration membrane of polysulfone and zinc chloride was used to treat the effluent from TATA Steel, India. The effluent contained high amount of total solid and various ions, namely chloride (1000–1200mg/l), fluoride (140mg/l), nitrate (37mg/l) and phosphate (1730mg/l). The effluent was pre-treated by passing over granular activated carbon and total solid was reduced by 38%. The membrane containing 1wt% ZnCl2 was found to be optimized one. Chloride concentration was reduced below 800mg/l via charge–charge interaction by nanofiltration. Similarly fluoride, nitrate and phosphate ions were rejected around 32%, 27% and 70%, respectively. Effect of different operating conditions (transmembrane pressure, cross-flow rate and solution pH) was studied. Rejection of various ions and solid content was reduced with increase in transmembrane pressure and cross flow rate. Based on permeate flux and quality, 1380kPa and 80l/h cross flow rate were selected as optimum operating conditions. Simple in-situ washing of the membrane with tap water could recover permeate flux upto 97%. A resistance in series model was used to quantify the effects of polarization on system performance. This system can be scaled up in spiral wound configuration for final deployment.

An innovative static mixer photoreactor: Proof of concept

An innovative application for the NETmix® reactor is validated in the present work, namely the homogeneous photo-Fenton treatment of natural waters contaminated with organic pollutants using solar light. Three antibiotics presenting high bacterial resistance (ciprofloxacin, sulfamethoxazole and trimethoprim) were selected as model pollutants. The influence of Reynolds number (Re=38–400) on the pollutants degradation was studied in continuous flow, and the flow rate and pH optimized (i.e., 500mLmin−1 and pH of 2.8, respectively). Under recirculation flow, the effect of different operating conditions on the degradation of the mixture of three antibiotics was then studied by changing the hydrogen peroxide (0–2.5mM) and iron (II) sulfate (0–4mgFeL−1) concentrations. Results establish high degradation rates using, 2.5mM H2O2, 2mgL−1Fe2+, pH of 2.8, 262Wm−2 irradiance and Re=300. Complete conversion of the antibiotics was achieved, demonstrating the potential application of the NETmix® technology as an efficient photoreactor configuration.

Model-based analysis of the effect of different operating conditions on fouling mechanisms in a membrane bioreactor

This study proposes a model-based evaluation of the effect of different operating conditions with and without pre-denitrification treatment and applying three different solids retention times on the fouling mechanisms involved in membrane bioreactors (MBRs). A total of 11 fouling models obtained from literature were used to fit the transmembrane pressure variations measured in a pilot-scale MBR treating real wastewater for more than 1year. The results showed that all the models represent reasonable descriptions of the fouling processes in the MBR tested. The model-based analysis confirmed that membrane fouling started by pore blocking (complete blocking model) and by a reduction of the pore diameter (standard blocking) while cake filtration became the dominant fouling mechanism over long-term operation. However, the different fouling mechanisms occurred almost simultaneously making it rather difficult to identify each one. The membrane "history" (i.e. age, lifespan, etc.) seems the most important factor affecting the fouling mechanism more than the applied operating conditions. Nonlinear regression of the most complex models (combined models) evaluated in this study sometimes demonstrated unreliable parameter estimates suggesting that the four basic fouling models (complete, standard, intermediate blocking and cake filtration) contain enough details to represent a reasonable description of the main fouling processes occurring in MBRs.