Effect Of Evaporation Temperature Research Articles

Separation of arsenic from tin anode slime by vacuum distillation

Tin anode slime (TAS) is a high-value waste produced by electrolytic refining of crude tin. In order to reduce the discharge of harmful waste and realize rational recycling, a process of removing arsenic from TAS by vacuum distillation was proposed, and theoretical and experimental studies were carried out. The saturated vapor pressure of each element in TAS and the activation energy of arsenic evaporation during vacuum distillation was calculated. The evaporation temperature and holding time of vacuum distillation for arsenic removal were investigated. The effects of evaporation temperature and holding time on arsenic removal were discussed. The results showed that the residual arsenic content is 0.32–0.19%, and the removal rate of arsenic is 84.87–91.90% at 1153 K and the range of holding time is 30–120min. When the temperature is 1353 K and the holding time from 30 to 120 min, the residual arsenic content is 0.029–0.025% and the removal rate is 99.43–99.59%. The activation energy for the evaporation of arsenic from TAS in vacuum distillation is EAs = 52.76 kJ/mol. The removal of arsenic improves the recycling value of TAS, and provides ideas for treating harmful substances from industrial wastes and recovering valuable metals.

Thermodynamic Analysis of Comprehensive Performance of Carbon Dioxide(R744) and Its Mixture With Ethane(R170) Used in Refrigeration and Heating System at Low Evaporation Temperature

Abstract In this paper, the system performance of R744 and R744/R170 mixed refrigerants used in a single-stage compression transcritical cycle at low evaporation temperature was studied by simulation method, and the effect of evaporation temperature, outlet temperature of gas cooler, R170 ratio on coefficient of performance (COP), discharge temperature, optimal pressure, and compression ratio were analyzed. The results show that Popt increases and decreases with the increase of outlet temperature and evaporation temperature of gas cooler and increases first and then decreases with the increase of R170 proportion. In the heating system, the maximum and minimum Popt of R744/R170 (25/75) were 1.35 MPa, 3.6 MPa, and 2.6 MPa and 1.23 MPa, 2.93 MPa, and 1.87 MPa lower than that of R170 (0%, 22.4%, and 50%); compared to pure R744, the system pressure of the mixed R744/R170 is lower. The COPe and COPh increase with the increase of evaporation temperature and decrease with the increase of outlet temperature of the gas cooler. With the increase of R170 proportion, they first decrease and then increase; the maximum COPe and COPh of R744 were 22.4%, 29.6%, and 21.2% and 10.3%, 13.8%, and 10.8% higher than those of R170 at 22.4%, 50% and 75%, respectively.

Energy and exergy analysis of an ejector-compression refrigeration cycle with double IHX

This paper shows an energy and exergy analysis of an ejector-compression refrigeration cycle, in which two heat exchangers are included to the system: 1) between the condenser and liquid separator (IHX-1) and 2) between the condenser and the evaporator (IHX-2), which is an alternative configuration proposed and this configuration is defined as ERC+IHX-1+IHX-2. The effect of evaporation temperature and the heat exchanger effectiveness on the energy and exergy efficiencies and the irreversibilities of each component of the cycle have been analyzed for refrigeration and air conditioning applications. The results show that for the alternative configuration and an effectiveness of IHX-1=80%, it results slightly with a higher COP than when the configurations work with an effectiveness of IHX-2=80%. However, the exergy efficiency increases when the evaporation temperature decreases. The components that show the highest contribution to the irreversibilities in the ERC+IHX-1+IHX-2 configuration are: the condenser, the compressor and the evaporator; whereas that the lowest contribution is due to the expansion valve and IHX-1. In addition, the alternative configuration proposed presents a higher exergetic efficiency and lower irreversibilities than the configurations ERC+IHX-1 y ERC+IHX-2 reported in the literature.

Evaluating Eco-Friendly Refrigerant Alternatives for Cascade Refrigeration Systems: A Thermoeconomic Analysis

A simple vapor-compression refrigeration system becomes ineffective and inefficient as it consumes a huge energy supply when operating between large temperature differences. Moreover, the recent Kigali amendment has raised a concern about phasing out some hydrofluorocarbon refrigerants due to their impact on the environment. In this paper, a numerical investigation is carried out to compare the performance of a cascade refrigeration system with two environmentally friendly refrigerant combinations, namely, R170–R404A and R41–R404A. Refrigerant R170, from the hydrocarbon category, and refrigerant R41, from the hydrofluorocarbon category, are separately chosen for the low-temperature circuit due to their similar thermophysical properties. On the other hand, refrigerant R404A is selected for the high-temperature circuit. An attempt is made to replace refrigerant R41 with refrigerant R170 as a possible alternative. The condenser temperature is kept constant at 40 °C, and the evaporator temperature is varied from −60 °C to −30 °C. The mathematical model developed for the cascade refrigeration system is solved using Engineering Equation Solver (EES). The effect of evaporator temperature on different performance parameters such as the COP, exergetic efficiency, and total plant cost rate is evaluated. The predicted results show that the thermoeconomic performance of the R170–R404A-based system is marginally lower compared to that of the R41–R404A-based system. The system using refrigerant pair R170–R404A has achieved only a 2.4% lower exergetic efficiency compared to the system using R41–R404A, with an increase in the annual plant cost rate of only USD 200. As the global warming potential (GWP) of R170 is less than that of R41, and R170 belongs to the hydrocarbon category, the use of the R170–R404A combination in a cascade refrigeration system can be recommended as an alternative to R41–R404A.

An energy efficient integration of vapour compression refrigeration with LNG-regasification for freeze desalination applications

In freeze desalination systems, there are challenges associated with freezing-thawing separation, thermal instability, and low performance of vapour compression systems. In the current work, an integrated system for freshwater production is introduced using a reverse-vapour compression refrigeration (rVCR) in combination with liquefied natural gas cold energy. In the combined system, the rVCR subsystem performs simultaneous freezing–thawing heat exchange, while LNG regasification subsystem ensures thermal stability of the cycle using cold thermal energy. The computational analysis of the proposed integrated cycle is carried out using environment friendly R1234ze(E). The effect of evaporator temperature on the proposed cycle performance is evaluated. The results show that 15%–20% of the refrigerant mass fraction is condensed at the LNG regasification step. The energy performance of the integrated system is increased by 10% to 16%, compared to conventional two stage systems. Refrigerant R1234ze(E) is found to be a good eco-friendly alternative to current ones. Thermodynamic analysis shows that the modified rVCR-LNG system is an energy-efficient solution for freeze desalination applications.

The effect of wastewater components and operation conditions on selenium release during desulfurization wastewater evaporation: A lab-scale study

Rotary atomization evaporation technology is one of the effective technologies to achieve zero discharge of desulfurization wastewater. However, the migration and transformation mechanism of selenium during desulfurization wastewater evaporation is still unknown, hindering this technology's further application. Therefore, the effects of evaporation temperature, pH, Cl−, S2O2–8, SO2–4and Ca2+ on selenium release during evaporation were investigated in this work. The results showed that elevated temperature promoted the release of selenium, especially in the solid-phase pyrolysis stage. pH affected the release of selenium through influencing its initial species, and the release rate of Se(IV) increased with decreasing pH. The ionic compositions of the solution were also found to be a critical factor in the stability of selenium species during evaporation. Cl− would promote the release of Se(IV), while SO2–4 inhibited the release of selenium species, and Ca2+ had little effect on the final release rate of selenium species release. In addition, it was found that the presence of S2O2–8 would significantly enhance the conversion of Se(IV) to Se(VI) during the evaporation process. The results obtained in this work provided guidelines and suggestions for controlling the selenium release from desulfurization wastewater in power plants.

The optimum discharge pressure of CO2-based refrigeration cycles operating under subcritical and transcritical conditions

In the present study a simple, single stage CO2-based vapour compression refrigeration system cycle, consisting of a compressor, condenser/gas cooler, expansion valve and an evaporator is studied to find the effect of various design and operating parameters on the separation of optimal pressure line from saturation and pseudocritical pressure lines. The results show that the optimum discharge pressure line deviates markedly from the pseudocritical pressure line for the transcritical cycle. In the subcritical cycle, away from the critical point, the optimum discharge pressure is the same as the saturation pressure corresponding to the condenser exit temperature. However, near the critical point, the optimum discharge pressure is different from the saturation pressure. With the help of this study, an optimum discharge pressure equation is developed which is found to be valid for subcritical as well as transcritical CO2 cycles. Highlights The Operation of CO2-based refrigeration cycle across a critical point is analysed. Optimum discharge pressure for sub-and transcritical conditions is obtained. The effects of evaporator temperature and compressor efficiency are studied. A correlation for optimum discharge pressure valid for sub- and transcritical cycles is suggested.

Numerical simulation of heat pump drying system for paper exhaust hood

Abstract In view of the present situation that the exhaust waste heat of the hot air hood in the paper drying section is too much and the environment is not friendly, a closed heat pump drying system model applied to the exhaust air hood is proposed and established. Effects of evaporation temperature and condensation temperature on supply air temperature, supply air moisture content, system performance coefficient (COP) and dehumidification energy consumption ratio (SMER) were studied. Results show that with the increase of condensation temperature, the supply air temperature is unchanged, and the moisture content of the supply air increase, while the COP and SMER of the system show a downward trend. The moisture content of supply air decrease with the increase of evaporation temperature, while the supply air temperature, COP and SMER all show an upward trend. Therefore, in order to improve the drying characteristics and improve the performance of the heat pump system, the condensation temperature can be reduced and the evaporation temperature can be increased.

Fate and distribution of mercury during the desulfurization wastewater evaporation process

The wastewater evaporation technology was a promising method for desulfurization wastewater zero-liquid discharge. However, there is a risk of mercury release during wastewater evaporation, which may cause severe environmental issues. This work investigated the fate and distribution of mercury in the wastewater evaporation process. In the typical working conditions, 93.6% of Hg in the wastewater was released, and the rest part would retain in the final evaporation product. The gaseous Hg release process could be divided into three stages. The gaseous Hg0 was the primary Hg released source in the initial evaporation process. Subsequently, due to the hydrolysis of chloride, the chlorine oxidizing atmosphere was generated, which induced the homogeneous oxidation of Hg0. At the end of evaporation, the pyrolysis of HgS and HgO would release a small amount of Hg. Besides, the effect of evaporation temperature, Cl- and SO32- content on Hg release was investigated. The higher evaporation temperature was adverse to Hg stability. The proportion of gaseous Hg0 and Hg2+ was highly sensitive to the SO32- and Cl- content. In addition, obtained from the risk assessment, the Hg release from the wastewater evaporation would not affect either total Hg content in main flue gas or solid-phase comprehensive utilization.

Optimization Study on Regenerative Organic Rankine Cycle (ORC) with Heat Source of Low-Grade Steam

Aiming at improving the performance of Organic Rankine Cycle (ORC) system with low-grade steam as heat source, this work studied and optimized the main operating parameters of the ORC system. The effects of evaporation temperature, superheat degree, condensation temperature and regenerator pinch temperature difference on the system performance were obtained. The optimization for the operating parameters is based on the indicators of specific net power output, waste heat pollution, cycle exergy efficiency, and total UA value (the product of overall heat transfer coefficient and heat transfer area of heat exchanger). The results show that the increase of the evaporation temperature and the superheat degree, and the decrease of the condensation temperature and regenerator pinch temperature difference can improve general system performance but lead to weaker economic performance. The optimal evaporation temperature, superheat degree, condensation temperature and regenerator pinch temperature difference are determined as 139°C, 4°C, 36°C and 8°C, respectively, reaching net power output of 114.73 kW, exergy efficiency of 37.10%. Besides, it is indicated that the regenerative ORC system can reach 13.6% additional net power output compared to the ORC system without the regenerator.

Thermodynamic and techno-economic performance comparison of two-stage series organic Rankine cycle and organic Rankine flash cycle for geothermal power generation from hot dry rock

• The performance of two geothermal energy cascade utilization systems is optimized. • The thermodynamic and techno-economic performance of the systems are compared. • The influence of heat source temperature on the operating condition is studied. • The exergy destruction of each component in the systems is compared and analyzed. To improve the utilization rate of geothermal resource using organic Rankine cycle (ORC), an organic Rankine flash cycle (ORFC) combined with insufficient evaporation and flash process is proposed to reduce the irreversibility of the power generation cycle. The thermodynamic performance and techno-economic performance of ORFC and two-stage series organic Rankine cycle (TSORC) are optimized, respectively. The effects of evaporation temperature, flash temperature and outlet dryness on the performance of two systems are discussed. The results show that with the increase of heat source temperature, the optimal operating condition value of the system increases, which leads to improving the thermodynamic and techno-economic performance significantly. R601a and R601 are the most suitable working fluids for TSORC and ORFC, respectively. The heat exchanger is the main component that causes the exergy destruction of the system, and its improvement potential is the highest in all components. The thermodynamic performance and techno-economic performances of ORFC are better than those of TSORC. The irreversible loss of the system can be reduced by the insufficient evaporation combined with flash separator.

Mathematical Modelling of Infra-Red Evaporation Characteristics of Wheat Straw Black Liquor

Infrared (IR) evaporation characteristics of Weak Soda Black Liquor (WSBL) were determined at five different temperatures of 80, 90, 100, 110 and 120oC. The effect of constant temperature on evaporation rate and moisture content (on a dry basis) of 1.5 gm approx. WSBL tests were contemplated and required a careful time frame of IR dissipation to vanish the dampness content at a different consistent temperature. The dissipation rate expanded with expanding infrared temperature. Therefore, different numerical models, such as Page and Logarithmic, Henderson, Pabis and Lewis, were utilised to fit the experimental data properly. A Gaussian model equation was developed for evaporation rate and moisture fraction of black liquor. The probable empirical parameters, along with the relating of reduced chi-square (X2), Residual Sum of Square (RSS), and coefficients of determination (adjusted R2) from non-linear regression analysis of all the numerical model equations, were examined. In addition, the effect of evaporation temperature on the water removal rate, the effective diffusion coefficient and activation energy were also estimated. The effective diffusion coefficient ranges from 2.67 × 10–10 m2/s to 10.4 × 10–10 m2/s, and the activation energy was 39.19 kJ/mol. The statistical indicators (chi-square and determination coefficient) showed that the Decay model equation and Gaussian equation are the most suitable models for describing the evaporation process of WSBL.

Preparation of COF-TpPa1 membranes by chemical vapor deposition method for separation of dyes

Covalent organic frameworks (COFs) exhibit potentials in adsorption, separation, heterogeneous catalysis, and energy storage due to low density, high thermal stability and inherent porosity. In this work, p-phenylenediamine (PDA) and 2,4,6-trihydroxy-benzene-1,3,5-tricarbaldehyde (TFP) were simultaneously evaporated onto modified poly(1,1-difluoroethylene) (PVDF) membrane in a chemical vapor deposition reactor to prepare COF-TpPa1 membranes for the separation of dyes. The effects of evaporation temperature, evaporation time, amount of Fe powder and pores size of PVDF membranes were studied, and the long-term operation was evaluated. The membranes showed an excellent water permeance (up to 400 L m−2 h−1 MPa−1) with high rejection (>90%) for different dyes (Mw 450–800), and low rejection (<8.2%) for salts. The COF-TpPa1 membrane also displayed considerable long-term operation stability. This facile approach can be extended to the preparation of a broad range of COFs membranes.

Molecular distillation applied to the purification of biodiesel from ethanol and soybean oil

In the biodiesel production and purification process, the washing step, where impurities such as free glycerol, mono, di and triglycerides are eliminated, is maybe the most questioned step for two reasons: i) for the generation of about 0.5 to 10 L of residual water each biodiesel liter, ii) for the complexity and the cost of productive process. The washing water is eliminated from biodiesel using separation methods that imply high operative and the maintenance costs (ultracentrifuges). Furthermore, this washing water is highly emulsified with high organic load and must be treated before being thrown away. For these reasons the reduction in the water consumption in the biodiesel purification is a priority. This paper presents the use of molecular distillation in the biodiesel purification process as an alternative to the washing conventional process. The employ of molecular distillation would avoid the water consume, a resource of highly value. This operation was employed as a purification technique to decrease the free glycerol and mono, di and triglycerides contained in biodiesel which is obtained by alkaline transesterification of soybean oil with ethanol, with sodium hydroxide as catalyzer. The effect of evaporation temperature and stirring rate on the mass and concentrations in the residue and distillated streams was studied. With two molecular distillation steps it was possible to obtain biodiesel with concentrations of free glycerol and glycerides that respect the limit set by the ASTM D 6751-08 and DIN EN 14,214 international norms.

Energy and Exergy Analysis of a Subcritical Cascade Refrigeration System With Internal Heat Exchangers Using Environmentally Friendly Refrigerants

AbstractThis study focuses on a thermodynamic performance analysis of a subcritical cascade refrigeration system (CRS) with internal heat exchangers (IHXs) using R41/R601, R41/R602A, and R41/cyclopentane as refrigerant pairs. The effect of evaporator temperature (Tev), condenser temperature (Tcond), and temperature difference in the cascade heat exchanger (ΔTCHX) on examined performance parameters are investigated. Each performance parameter is scrutinized by an optimum low-temperature circuit (LTC) condenser temperature. The operating parameters have some implications on the overall thermodynamic performance of the system. A change of 10 °C in the Tev and Tcond affects the performance of the system by approximately +26% and −8%, respectively. Moreover, a variation of 1 °C in the ΔTCHX reduces the performance of the system by about 2%. The effect of IHXs on the system has some interesting results. The coefficient of performance (COP) and exergy efficiency values of the system using R41/cyclopentane tend to constantly decrease by nearly 4.05%. Although not as much as R41/cyclopentane, there is also a slight drop in the performance of other refrigerant pairs. The discharge temperature in LTC and high-temperature circuit (HTC) compressors exceeds 120 °C for low-temperature refrigeration requirements, which is highly undesirable. Furthermore, the top priority components for the system improvement are HTC condenser, HTC compressor, and CHX. The refrigerant pairs with the thermodynamic performance from best to worst are R41/R601, R41/cyclopentane, and R41/R602A, respectively. Finally, the COP and exergy efficiency values of the modeled system are 10.40% higher and 3.06% lower, respectively, compared with current models in the literature.

Design and evaluation of a parallel-connected double-effect mechanical vapor recompression evaporation crystallization system

This paper proposes a parallel-connected double-effect mechanical vapor recompression (MVR) evaporation crystallization system, which combines the falling film evaporator with the forced circulation evaporator. With the purpose of treating high salinity wastewater, the circulation process of the system was designed and mathematical models were established according to the mass and energy balance as well as thermodynamic properties in the heat transfer process. Model calculation was conducted using 5% sodium sulfate solution, based on which the effects of evaporation temperature, feed concentration, and temperature difference between saturated boiling solution and condensate on the system performance were analyzed by a parametric study. The results showed that the optimal values of evaporation temperature and saturation temperature difference could be determined based on a trade-off between power consumption and heat transfer area. After that, the performance of the proposed system was compared with that of a traditional multi-effect evaporation crystallization system, and it was revealed that the coefficient of performance (COP) and exergy efficiency of the proposed system were 21.4 and 49.1%, respectively, 82.2% and 51.5% higher than those of the traditional system under the same working condition. Meanwhile, the exergy destruction of the proposed system was 24.7% lower than that of the traditional system, indicating that the new system performs better regarding energy saving and thermodynamic perfection.

Mathematical Simulation of Fourth Generation Refrigerant R1243zf in Single Stage and Double Stage Vapour Compression Refrigeration System

In this paper a new fourth generation, environment friendly refrigerant R1243zf has been used in performance analysis between single stage and double stage vapour compression refrigeration system working between the same minimum and maximum pressure limits. The analysis has been done by mathematical simulation in Engineering Equation Solve (EES 10.439D, 2019). Results show that in low temperature cooling applications, a single stage vapour compression system does not perform well and a cascade system is the best optimum solution. In the given pressure limit, with the use of double stage vapour compression system, the increase in COP is 14% and decrease in compression work is 11.49%. The effects of evaporator temperature and condenser temperature have been seen on COP for both the systems and results show that with decrease in evaporator temperature, COP is decreasing, where as with decrease in condenser temperature COP is increasing.

Techno-economic performance of two-stage series evaporation organic Rankine cycle with dual-level heat sources

With the increasing of fossil energy crisis and environmental pollution, the development and utilization of renewable energy has become a hot spot in recent years. Based on two-stage serial organic Rankine cycle system of single heat source, the two-stage series organic Rankine cycle system of double heat source is proposed in this paper to realize cascade utilization of heat sources with different temperatures. The composite heat source grade is correlated with the two-stage series evaporation temperature to improve the power generation power and economic benefit of the system. Taking R245fa as an example, the mass flow rate of heat source is 10 kg/s, and the effects of evaporation temperature and heat source temperature on the net output power, thermal efficiency, exergy efficiency, electricity production cost and investment payback period of organic Rankine cycle, two-stage serial organic Rankine cycle system of single heat source and two-stage series organic Rankine cycle system of double heat source are optimized and analyzed. It is found that the electricity production cost and investment payback period of two-stage series organic Rankine cycle system of double heat source are always the smallest, followed by two-stage serial organic Rankine cycle system of single heat source, and the largest is the electricity production cost and investment payback period of organic Rankine cycle system. At the same time, it is found that two-stage series organic Rankine cycle system of double heat source is more suitable for low-temperature heat source.

Thermal performance evaluation of subcritical organic Rankine cycle for waste heat recovery from sinter annular cooler

The sinter cooling flue gas expelled from the end of an annular cooler was taken as the heat source of an organic Rankine cycle (ORC) system, and R123, R245fa, R600, R601 and R601a were selected as the working fluids of the ORC system. The effects of evaporation temperature and superheat degree of working fluid, as well as the pinch point temperature difference in the evaporator on the system thermal performance, were analyzed in detail. The results show that the system net output power and exergy efficiency for different working fluids first increase and then decrease with an increase in the evaporation temperature and decrease with an increase in the superheat degree and pinch point temperature difference. The change in pinch point temperature difference has no effect on the system thermal efficiency. For a given operational condition, the system thermal efficiency and exergy efficiency of R123 are the maximum, while the system total irreversible loss of R245fa is the maximum. When the evaporation temperature is greater than 110 °C, the system net output power of R600 is the maximum. The ORC system could obtain the maximum net output power and exergy efficiency through the adjustment of evaporation temperature of working fluid.

Simulation analysis of performance optimization of gas-driven ammonia-water absorption heat pump

The generator-absorber heat exchange ammonia-water absorption heat pump has a relatively high efficiency and the COP is improved by recovering internal heat. In order to resolve the problem that generator-absorber heat exchange effect becomes less obvious or even fails under the working condition of large temperature lift, a novel system is proposed to recover the rectification heat and absorption heat by solution split method. Compared with the method of using total strong solution to recover absorption heat after extracting rectification heat, the method of solution split avoids the problem of high temperature of inlet strong solution of the solution cooled absorber, and improves the internal heat recovery capacity of the system. When using solution split method to recover the rectification heat and absorption heat, the solution split ratio K has an important influence on the system performance. This paper will theoretically study the selection range of the solution split ratio K and the effect of evaporation temperature, cooling water temperature and generation temperature on the optimum split ratio K. Compared to the system that uses the total strong solution to recover the rectification heat and absorption heat, the performance of the novel system is significantly improved, and the novel system performance coefficient can be increased by up to 15.7%.