Flash Evaporation System Research Articles

Simulation and Experimental Study of Circulatory Flash Evaporation System for High-Salt Wastewater Treatment

Treatment methods for high-salt wastewater mainly consist of physical methods, chemical methods and biological methods. However, there are some problems, such as slow treatment speed, high investment costs and low treatment efficiency. To address NaCl solutions, in this study, a circulatory flash system was designed based on gas–liquid equilibrium, mass conservation equation and energy conservation equation. A circulatory flash evaporation simulation and a static flash evaporation experiment were conducted on NaCl solutions under various operating conditions to investigate the effects of heating temperature, flash pressure and initial NaCl concentration on the circulatory flash evaporation system. The significance of each factor’s influence on the evaporation fraction and energy consumption was examined through static flash experiments. The simulation results demonstrated that increasing the heating temperature, decreasing the flash pressure and having a higher initial NaCl concentration could enhance the treatment capacity of high-salt wastewater. The flow rate of vapor outlets increased with higher heating temperature but decreased as the flash pressure rose. The experimental results demonstrated that flash evaporation pressure was the primary factor influencing both the evaporation fraction and the energy consumption per unit mass of vapor produced. It was observed that with an increase in heating temperature, the flash pressure decreased and there was a corresponding decrease in energy consumption per unit mass of vapor produced. The optimal experimental conditions were achieved at a heating temperature of 99 °C, a flash pressure of 15 kPa, and an initial NaCl concentration of 20%.

Case study for enhancing concentration of waste dilute sulfuric acid by microwave flash evaporation: modelling, heat transfer, energy consumption and process optimization

The ameliorative microwave flash evaporation system (MFE) was utilized to concentrate and distillate waste sulfuric acid, the system may overcome the problems of equipment corrosion, product pollution, high energy consumption, long process flow, and low heat transfer rate during recovery process of waste sulfuric acid. The dilute sulfuric acid with mass fraction of 75 wt% was used as experimental medium, 5 experimental cases was generated to verify the effects of MFE with the conditions of different volume, microwave power and depressurization rate. Experimental results demonstrated that the sulfuric acid could be concentrated to mass fraction of 85–95%, and the heating efficiency was among 30% to 80%, heat transfer volume coefficient was among 100 J/K·L-1 to 500 J/K·L-1 with the combination of vacuum and microwave heating during flash evaporation process. Thermal process analysis indicated that the interaction among experimental factors affected concentration and distillation process. At last, we gave the modeling and process optimization method for concentrating sulfuric acid through MFE process based on analyzing those experimental cases.

Preparation of polyphosphoric acid and recovery of valuable fluorine resources though a microwave intensification flash evaporation process

Traditional evaporators for the concentration of wet process phosphoric acid (WPA) suffer from concentration, corrosion, and low fluorine yield (less than 40 wt.%). Based on the excellent heating and permittivity properties of phosphoric acid in microwave fields, a microwave intensification flash evaporation (MFE) system is proposed to concentrate highly corrosive WPA for preparing polyphosphoric acid (PPA) and efficiently recovering valuable fluoride resources. A polytetrafluoroethylene tank in a microwave resonant cavity coupled with a vacuum pump is used to facilitate boiling and evaporation. This study reports the evolution of the PPA preparation process by flash evaporation, defluorination, and the boiling phenomenon. In addition, the influencing mechanism of pressure and temperature on PPA preparation and fluorine recovery are investigated. The experimental results indicate the successful preparation of PPA with a P2O5 content higher than 75 wt.% and the cost is considerably much lower than the traditional method. Meanwhile, the recovery yield of fluorine exceeds 90 wt.%, alleviating the depletion of strategic natural resources and potential risk of environmental pollution. This study provides a basis for the efficient preparation of PPA and recovery of fluorine resource from WPA. It is also potentially significant to industries such as metallurgy and sewage treatment.

Experimental Results for a Novel Flash Evaporation and Phase Separation System for Desalination of Sea Water

Abstract A novel system combining dynamic flash evaporation and vapor separation for desalination has been investigated in this work. The feed water passes through injection tubes which are connected to injector passages installed tangentially onto a separator tube. Flashing in the injection tubes is initiated from pressure drop due to friction and acceleration resulting in a two-phase mixture. Centrifugal force from tangential injection separates the two-phase mixture. In this compact system, vapor production and phase separation occur on the order of several milliseconds. Tap water and seawater were used as inlet feed water for the system. Thermal conversion efficiency to analyze the vapor production efficacy and phase separation efficiency to evaluate the purity of the condensate were investigated to evaluate the system. Thermal conversion and phase separation efficiencies up to 98% were obtained with the single stage system. Further improvement in purity of condensate was achieved with a two-stage system. In the two-stage system, the vapor captured along with some entrained droplets from the first stage was directed to a second set of injector passages connected in series to the first stage retrieval tube. With a two-stage system and seawater with salt concentration by mass of 2.5%, collected condensate with salt concentrations lower than 0.02% by mass was achieved, which is comparable to that of potable water. Thus, the novel dynamic flash evaporation and vapor separation system have been demonstrated to be very effective in producing potable water.

Flash evaporation of low volatility solid precursors by a scanning infrared laser

The steady and stoichiometric delivery of metal-organic precursor mixtures is essential for the production of complex, functional nanomaterials in the gas phase. Chemical vapor synthesis (CVS) is a corresponding process which enables the production of complex oxide nanoparticles such as perovskites. While there exist a vast number of compositions that form perovskite structures, many technically relevant materials consist of transition metals and lanthanides. Their corresponding metal organic precursors often deviate significantly in their thermal behavior, resulting in a challenging delivery of precursors to the reactor. One suitable method for precursor delivery is flash evaporation by an infrared laser, where a mixture of solid precursors is instantly sublimed. Using flash evaporation, the stoichiometry of the generated vapor corresponds to the composition of precursors in the solid mixture. In this study, we present an alternative flash evaporation system based on a marking laser which rapidly scans a focused infrared beam across a precursor powder bed. By focusing the beam, higher energy densities are reached, compared to existing systems while a large area powder bed is repeatedly scanned and sublimed. Fourier-transform infrared spectroscopy (FTIR) measurements confirm the decomposition-free sublimation of precursor mixtures. Furthermore, we confirm the successful precursor delivery by the synthesis of LaFeO3 nanoparticles with an average crystallite size of 5.3 nm. The structure of the ensemble of nanoparticles is examined using X-ray diffraction (XRD) and Rietveld refinement, transmission electron microscopy (TEM), selected area diffraction (SAED), and extended X-ray absorption fine structure (EXAFS) at the Fe-K edge analyzed by reverse Monte Carlo (RMC) analysis.

The enhancement effect and competition behavior of a flash evaporation system with a continuous DC glow discharge plasma

The transient plasma kinetic has been proved to be able to significantly improve the refrigerant efficiency of vacuum flash evaporation. Here we explore the flash evaporation cooling enhancement effect induced by a continuous glow discharge plasma, generally exists in vacuum, but the heat deposition is more severe than a transient plasma source. Several controlled groups with different discharge currents, which determine the thermal deposition rates, are subjected to an oscilloscope, CCD, and optical emission spectroscopy (OES) for diagnosis of plasma and Infrared Radiation (IR) thermography, vacuum gauge, and electronic balance for thermal and evaporative properties to reveal the influence of plasma characteristics on flash evaporation cooling. The characterization results of plasma show that the translational temperature increases with current while the rotational temperature and electron density are almost independent of current. Compared to plasma-free, the plasma generally leads to a significant increase in the maximum temperature drop (ΔTmax), but the effect increases with current from 0.95 to 3.07 mA and decreases at 3.87 mA. The behavior is attributed to the competition between the positive effect of evaporative cooling enhancement resulted from particle kinetic and the negative effect of joule heat itself. This has also led to that the system presents a best cooling enhancement efficiency defined by the increased ΔTmax per unit watt due to plasma, (ΔTmax(I)−ΔTmax(Plasma−free))/P, at the current of 2.01 mA for our cases. In conclusion, the continuous DC glow discharge plasma has been demonstrated to be useful to enhance flash evaporation cooling.

Energy transfer and efficiency analysis of microwave flash evaporation with tap water as medium

A microwave flash evaporation system is designed and applied to research the intensification effect of microwave on flash evaporation, in present work, a mathematic model of the energy transfer and efficiency of microwave flash evaporation (MFE) process is presented, and series of experiments used water as medium are conducted. Production rate, thermal efficiency of phase transition, thermal proportion of steam, electro-thermal conversion efficiency, and indicator parameters such as, gain output ratio (GOR), specific thermal energy consumption (STEC), and total volumetric heat transfer coefficient are calculated to evaluate energy transfer of MFE process. As a result, the production rate, thermal conversion efficiency and thermal proportion of steam increase with microwave power but decrease with flow rate, and the maximum value of electro-thermal conversion efficiency achieved 76.66%. GOR value and total volumetric heat transfer coefficient of MFE increase with microwave power but decrease with flow rate, the specific thermal energy consumption increases with flow rate but decrease with microwave power. In addition, the economy of MFE process is also discussed. This work may provide the theoretical support for the feasibility of the utilization of microwave heating in flash evaporation.

The impact of inlet flash evaporation conditions on erosion damage characteristics of coal gasification black water angle valve and prevention strategies

In view of the three-stage flash evaporation system of the coal gasification plant, a combination of theoretical analysis and numerical simulation was used to establish the erosion damage evaluation model in the black water angle valve. The influence of the inlet flash evaporation ratio on the inlet velocity, the outlet flash evaporation ratio and the outlet velocity of the low-pressure black water angle valve are systematically studied, the mechanism of erosion damage to the carbon steel valve body by the solid medium in black water was analyzed according to the micro-cutting theory. The results show that the inlet velocity w 1, the outlet flash evaporation ratio x 2, the outlet velocity w 2 of angle valve have linear correlation with the inlet flash evaporation ratio x 1.The upstream volume erosion ratio of the angle valve at the inlet flash ratio x 1 = 3 wt.% is 114 times as much as that at zero inlet flash ratio. Meanwhile, the downstream volume erosion ratio of the angle valve at x 1 = 3 wt.% is only 2.7 times as much as that at zero inlet flash ratio. The prevention strategies to reduce the erosion damage to black water angle valve are proposed by inhibiting the inlet flash evaporation ratio and reducing the inlet flow rate etc. This study is expected to provide guidance for the erosion resistance design and operation of the black water angle valve.

Flash evaporation intensified by microwave energy and performance analysis

A novel microwave flash evaporation (MFE) system is presented in this paper for the first time, which is expected to solve the inherent problems of conventional flash evaporation (CFE) system, such as high energy consumption, scaling, and long stages etc. In order to demonstrate the performance of such a novel system, some single factor experiments have been carried out by using water as experimental material, and the influence of parameters such as microwave power, initial temperature, and liquid flow rate have been studied. The results show that the evaporation quantity increases with the increase of microwave power, flow rate, and initial temperature. Under experimental conditions, the better operation condition is achieved at flow-rate of 40 L/h, initial liquid temperature of 50 °C, and microwave power of 1.35 kW, the evaporation quantity in the case of MFE is as high as 1.35 L in 20 min, but it is only 0.74 L in 20 min for CFE. The enhanced performance of MFE system is shown by comparing with the CFE system under the same conditions. Moreover, the energy efficiency is calculated and represented by a dimensionless parameter Gain Output Ratio (GOR), and the maximum energy efficiency for MSF system is about 79.38% at the better operation condition.

Evaporation rates and temperature distributions in fine droplet flash evaporation sprays

This study reports an experimental investigation of a flash evaporation system based on low-temperature thermal desalination (LTTD) technology. Low temperature liquid in the range of 60–80 °C becomes superheated by injecting it through a nozzle into a depressurized chamber. Previous studies have not attempted to establish a correlation model between the temperature distributions and the evaporation rate. Moreover, this study presents for the first time the temperature distribution in fine droplets (small nozzle, 0.8 mm) sprays upward flash evaporation sprays over a range of conditions. The effect of the operating parameters on the temperature distribution and evaporation rate of flashing spray is also investigated and comparisons are made between the results of the present experiments and flash evaporation jets.The dimensionless temperature introduced (ϴemp) follows an exponential decaying curve and is found to also match temperature distributions in a range of other works covering different nozzles (sprays or jets), in both upward and downward flash evaporation. It is also found that flow rate has a different effect on the evaporation rate depending on whether spray or jet flash evaporation is taking place. Increasing the flow rate in sprays leads to higher flash evaporation, but lowers the evaporation rate in jets.

Experimental and mathematical investigations of spray angle and droplet sizes of a flash evaporation desalination system

This research experimentally studied the effect of operational parameters on spray characteristics of flash evaporation system which is the key component of the discharge thermal energy combined desalination (DTECD) system. For this purpose, initially the effect of superheat degree, inlet pressure, and inlet temperature on the spray angle of three different types of full cone spray nozzles was investigated using a high speed camera. Moreover, a force balanced mathematical model was developed to calculate droplet sizes and the results were compared with experimentally measured values using shadowgraph technique. The results show that the spray angle was largely affected by the superheat degree regardless of nozzle type. In addition, an empirical equation was suggested to correlate inlet pressure, saturation pressure, and spray angle. Further, a model was proposed to estimate the variation of droplet sizes along the spray centreline and concluded that the spray capacity significantly influenced the droplets' lifetime.

Experimental study on heat transfer characteristics of circulatory flash evaporation

Flash evaporation with velocity in horizontal direction, called the circulatory flash evaporation, is the main mechanism in many industry processes such as multi-stage flash (MSF) desalination. The previous studies are mainly concerned about the characteristics of static flash evaporation or the flow pattern of the fluid in the single stage of the MSF. Little work has been performed on the heat transfer characteristics of circulatory flash evaporation. In the present paper a circulatory flash evaporation system was built. The experiments were carried out with flow rates of 400, 600, 800, 1000, 1200Lh−1, initial water film heights ranging from 100 to 265mm and at pressures of 7.4, 12.3, 19.9, 31.2kPa, respectively. Results indicated that non-equilibrium fraction (NEF) augmented to a peak value at first and decreased monotonously when superheat increased. The heat transfer coefficient dropped with the increase in the superheat. The influence of flow rate, pressure in the flash chamber and initial water film height on the variation of NEF and heat transfer coefficient was also investigated. The NEF decreased with increasing flow rate and pressure in the flash chamber but increased as the initial water film height rising. However, the volumetric heat transfer coefficient showed an opposite law.

Simple flash evaporator for making thin films of compounds

A simple and compact arrangement for flash evaporation is described. It uses a cell phone vibrator for powder dispensing that can be incorporated into a vacuum deposition chamber without any major alterations. The performance of the flash evaporation system is checked by making thin films of the optical memory chalcogenide glass Ge2Sb2Te5 (GST). Energy dispersive x-ray analysis shows that the flash evaporation preserves the stoichiometry in thin films.

Laser Annealing of Flash-Evaporated CuInSe<SUB>2</SUB> Thin Films

In this paper, the impact of laser annealing on the structural, electrical, and optical properties of CuInSe2 (CIS) thin films has been investigated. The films were deposited using a modified flash evaporation system onto glass substrates. Structural analysis using x-ray diffraction (XRD) showed that the films have a strong preferred growth direction in the 〈112〉 plane. After laser annealing with a diffused beam of 20 ns width, the structure was relaxed and an increase in the intensity of 〈112〉 diffraction line was observed. A gas-microphone-type, high-resolution, near-infared (IR) photoacoustic spectrometer was used for the analysis of nonradiative defect states in as-grown and laser-annealed CIS thin film samples at room temperature. The absorption coefficient has been derived from photoacoustic spectra to establish activation energies for several defect-related energy levels. The calculated intrinsic defect ionization energies were also compared with the existing data available in the literature. The changes in the optical properties of the films have been explained in terms of the variations in the structural characteristics within the material.

Ar Ion Beam Irradiation Effects on Magnetostrictive Characteristics of Tb-Fe Thin Film

TbFe 2 films prepared by a flash evaporation system onto Si(100) or polyimide substrate have been irradiated with different Ar ion doses at zero, 1.3 × 10 1 7 and 2.7 × 10 1 7 cm - 2 and at 10kV. Magnetostrictive properties, i.e., saturated magnetostriction and magnetostrictive susceptibility, of TbFe 2 film with disordered structure were improved by Ar ion beam irradiation. This result was probably caused increasing of in-plane compressive stress corresponding to change of volume magnetostriction.

Optimal MSF plant design

The aim of this paper is to present a rigorous model for Multi-Stage Flash Evaporation System (MSF). The MSF system is represented as a No Linear Programming (NLP) model. The model incorporates a high number of non-linear restrictions; so the achievement of the global optimum is difficult. Here, the study of an algorithm for the system optimisation is presented.

Transient characteristics and performance of a novel desalination system based on heat storage and spray flashing

A hybrid latent heat storage and spray flash evaporation system has been devised in an attempt to develop an energy saving desalination system that stores intermittent thermal energy such as waste heat, solar heat or heat from the surplus steam of a power station at night and utilizes the stored energy not only for the generation of process steam from seawater for industries and domestic air conditioning but also for the production of fresh water from the generated steam for industrial and domestic uses on demand. Experimental results of the transient discharge characteristics of the heat storage column packed with the phase change material and the transient spray flash evaporation characteristics are reported. It is also shown that by using the numerical results of the discharge characteristics and the empirical equation of the efficiency of spray flash evaporation, the amount of generated steam and produced water can be predicted with sufficient accuracy. The utilization of more than 95% of the amount of stored energy for the generation of process steam and the production of fresh water, substantiated experimentally, confirms the high efficiency of the hybrid system.

98/03326 Transient characteristics and performance of hybrid latent heat storage and spray flash evaporation system: Miyatake, O. et al. J. Chem. Eng. Jpn., 1997, 30, (6), 1076–1082

98/03326 Transient characteristics and performance of hybrid latent heat storage and spray flash evaporation system: Miyatake, O. et al. J. Chem. Eng. Jpn., 1997, 30, (6), 1076–1082

Transient characteristics and performance of hybrid latent heat storage and spray flash evaporation system.

A hybrid system of latent heat storage and spray flash evaporation is devised in an attempt to develop an energy saving system, which stores intermittent thermal energy such as solar heat, waste heat or heat from the surplus steam of a power station at night and utilizes the stored energy for the generation of steam for industries, power stations and domestic air conditioning. Experimental results of the transient discharge characteristics of the heat storage column packed with the phase change material and the transient flash evaporation characteristics are reported. It is also shown that by using the numerical results of the discharge characteristics and the empirical equation of the efficiency of flash evaporation, the amount of generated steam can be predicted with sufficient accuracy. The utilization of more than 97% of the amount of stored energy for the generation of steam, substantiated experimentally, confirms the high efficiency of the present system.

Crystallization Process and Chemical Disorder in Flash Evaporated Amorphous Gallium Antimonide Films

ABSTRACTIn this work we describe a flash evaporation system specially built to produce Amorphous films of III-V compounds and characterize GaSb films using optical, electrical and X-Ray diffraction Measurements. Changes in the composition of the GaSb samples were obtained by the use of different crucible temperatures. In such samples, consequently, the optical absorption edge and the DC electrical conductivity were Modified. The departure from stoichiometry in GaSb films is analyzed on the basis of these results which can be used as an evidence of the chemical disorder. This kind of disorder is represented by either wrong bonds or sites with different coordination.Thermal annealing with a sequence of increasing temperatures first induced detectable variations in the optical absorption edge and in the vibrational properties of the Amorphous GaSb. These variations are compatible with the GaSb local ordering and were observed by Raman scattering and infrared absorption spectra. The annealing at higher temperatures allowed the crystallization of the material confirmed by X-Ray diffraction. From these experimental results a crystallization mechanism based on the segregation of Sb excess coming from the crystallized regions toward the Amorphous tissue is proposed.