Ammonia-water Solution Research Articles

Energy, exergy, economic, and exergoenvironmental (4E) analyses of new configuration ammonia–water solution cycle driven by biomass to produce power and cooling

ABSTRACT The new integration of a cogeneration system consists of an ammonia–water solution cycle powered by biomass energy resources is applied to produce power and cooling load. In this system, the biomass is converted into syngas in a gasifier, then this syngas in a boiler generates heat to run an ammonia–water solution cycle to achieve these purposes. A 4E analysis including energy, exergy, exergoenvironmental and economic of this cogeneration is examined for the best performance of this system. Moreover, the effect of changing biomass resources including oats strand, rapeseed, wheat straw, and alfalfa in this investigation are examined. The net electrical power of 1364 kW with a 1917 kW cooling load can be produced by this new cogeneration system. Furthermore, the energy and exergy efficiency of this system is computed as 23.3% and 10.1%, respectively. The maximum percent of the exergy destruction rate belongs to the boilers, separator, and vapor generator. The net present value and payback period of the proposed system are equal to 15.1 million $ and 4.9 years, respectively.

Thermodynamic analysis of an ammonia-water solution cross-type absorption-resorption heat pump system

• The cross-type design is first proposed for the absorption-resorption heat pump. • The gas-emission range and mass transfer potential of the system are enhanced. • The performance and working temperature range of the system are increased. • The system is appropriate for applications with larger pressure differences. Absorption-resorption heat pump (ARHP) can realize the efficient utilization of low-grade heat under lower operating pressure than traditional absorption heat pump (AHP), but the application is limited by the low coefficient of performance (COP). In this paper, an ammonia-water solution cross-type absorption-resorption heat pump is proposed to improve the performance, and the rectifier can be eliminated because the ammonia component can be balanced with the adjustment of mass flow rate at the resorber inlet. A thermodynamic model is established to investigate the influences of different parameters on the coefficient of performance. The results reveal that: When the high/low pressure pair is 1.5/0.44 MPa and the temperatures of absorber, resorber and desorber are 40 °C, 40 °C and 5 °C, the COP of the proposed system can reach 1.564, which is 8.1% higher than traditional ARHP. When the temperatures of generator, absorber, resorber and desorber are 115 °C, 35 °C, 40 °C and 5 °C, the COP is improved up to 6.4% compared with the balanced-type ARHP. Besides, the proposed system has wider working temperature ranges than the traditional system and the temperature ranges of absorber and desorber are increased by 1 °C and 2 °C, respectively. The advantages of the proposed system also include the lower optimal low-pressure values. Therefore, the ammonia-water solution cross-type absorption-resorption heat pump is appropriate for working in larger pressure differences and makes waste heat recovery more economical and efficient.

Numerical Investigation of a modified Kalina cycle system for high-temperature application and genetic algorithm based optimization of the multi-phase expander's inlet condition

As an alternative to the conventional steam Rankine Cycle, Kalina Cycle has witnessed a growing interest over the past years for high-temperature applications (A working fluid temperature of 500°C at the turbine inlet). However, the possibility of implementing an additional multi-phase expander on the weak ammonia-water solution loop of the Kalina cycle was hardly analyzed in the available literatures. In this research, two novel Kalina cycles (Kalina cycle-12A and Kalina cycle-12B) have been presented by integrating a multi-phase expander in addition to the turbine installed downstream of the Kalina evaporator. For Kalina cycle -12A, this additional multi-phase expander is positioned downstream of the Kalina separator and on the weak ammonia-water solution loop for Kalina Cycle-12B. A detailed mathematical model based on the thermodynamic laws has been developed to solve and optimize the Kalina Cycles. The influence of critical decision parameters, specifically the ammonia concentration on working fluid and evaporation pressure, were investigated. The optimization was performed based on the objective to maximize the net power output from the multi-phase expander under steady-state operating conditions. When the performance of the proposed Kalina cycles was compared with the conventional Kalina Cycle-12, both of them demonstrated superior performance, i.e., net power output and peak thermal efficiency increased by a maximum value of 3.23% for the proposed Kalina Cycle-12A cycle and 3.94% for the proposed Kalina Cycle-12B cycle. In terms of second law efficiency, Kalina Cycle-12A is 3.68 percent more efficient than Kalina Cycle-12, while Kalina Cycle-12B is 4.04 percent more efficient. Furthermore, 2nd law analysis also reveals, maximum destruction of exergy occurs at the condensers of the cycles.

Complex Brines and Their Implications for Habitability.

There is evidence that life on Earth originated in cold saline waters around scorching hydrothermal vents, and that similar conditions might exist or have existed on Mars, Europa, Ganymede, Enceladus, and other worlds. Could potentially habitable complex brines with extremely low freezing temperatures exist in the shallow subsurface of these frigid worlds? Earth, Mars, and carbonaceous chondrites have similar bulk elemental abundances, but while the Earth is depleted in the most volatile elements, the Icy Worlds of the outer solar system are expected to be rich in them. The cooling of ionic solutions containing substances that likely exist in the Icy Worlds could form complex brines with the lowest eutectic temperature possible for the compounds available in them. Indeed, here, we show observational and theoretical evidence that even elements present in trace amounts in nature are concentrated by freeze–thaw cycles, and therefore contribute significantly to the formation of brine reservoirs that remain liquid throughout the year in some of the coldest places on Earth. This is interesting because the eutectic temperature of water–ammonia solutions can be as low as ~160 K, and significant fractions of the mass of the Icy Worlds are estimated to be water substance and ammonia. Thus, briny solutions with eutectic temperature of at least ~160 K could have formed where, historically, temperature have oscillated above and below ~160 K. We conclude that complex brines must exist in the shallow subsurface of Mars and the Icy Worlds, and that liquid saline water should be present where ice has existed, the temperature is above ~160 K, and evaporation and sublimation have been inhibited.

A novel enhanced ammonia-water power/cooling cogeneration system with dual level cooling temperature: Thermodynamic and economic assessments

The present study proposed and investigated a novel parallel combined cooling and power (CCP) system using the ammonia–water solution as a working fluid. The major advantage of this system is employing two evaporators to produce cooling in dual level cooling temperatures and capacities. To produce high-temperature refrigeration output, an ejector refrigeration loop is introduced. Moreover, the power generation subsystem is employed between absorber and rectifier to recover of ammonia content in the vapor exiting the turbine for refrigeration. To prediction of ejector performance, a new model is proposed based on the shock circle model. To find the effect of key parameters on the system performance, the system is analyzed thermo-economically. The parametric study results show that high-temperature cooling load has the biggest effect on both thermodynamic and economic performance. Moreover, a parametric optimization is conducted and the optimized system is compared with several ammonia-water CCP systems in the literature. The comparison results show a significant enhancement in thermodynamic performance. In this case, the optimal energy efficiency of 68.8 %, exergy efficiency of 37 % and cooling-to-power ratio of 8.77 are estimated. From economic analysis, the optimal net present value and simple payback period are obtained by 49.2 M$ and 4.8 years, respectively.

Analysis of test results of a household absorption refrigerating appliance on an electric and gas source of thermal energy

One of the biggest challenges for refrigeration systems is their conversion to environmentally friendly refrigerants. This attracts the attention of developers of household refrigeration equipment to absorption refrigeration devices (ARD), which include an absorption refrigeration unit (ARU). ARD working fluid consists of natural components - ammonia water solution with the addition of an inert gas (hydrogen). Therefore, the use of ARU can be considered as one of the options for transferring to environmentally friendly refrigerants. In recent years, in connection with the rapidly developing gasification of the population of Europe, an alternative has arisen - the operation of household ARD on natural gas. Natural gas can become an alternative to electrical energy in stationary operating conditions of household refrigeration appliances. Thus, the object of the study was a single-chamber household refrigerator with a low-temperature compartment "Kiev-410" (Ukraine). In this paper, the study is aimed at comparing the thermal modes of operation and the costs of operating a household ARD on electric energy and natural gas. To solve this, it was necessary to determine the temperatures at the characteristic points of the refrigeration apparatus and in the chamber, as well as the energy consumption of the absorption-type apparatus in accordance with regulatory documents, at various values of the thermal load on the thermosyphon and various ambient temperatures. The studies were carried out at elevated outdoor temperatures: 28–33 ° С. The range of thermal loads on the ARU thermosyphon electric heater was 50–130 W. The range of numerical values of natural gas consumption in the burner was (2.8–8.8) • 10-6 m3/s. In the process of conducting experimental studies of household ARD, results were obtained showing the economic prospects of working in stationary conditions on natural gas. At the same time, ARD of increased useful volume (200 dm3 and above) has the greatest prospects. The daily operating costs in them are 0.078...0.084 USD, which is 23...27 % lower than the case of using electricity. When the ARU thermosyphon is built into the heating and hot water supply system, it becomes possible to use the temperature potential of the waste products of combustion and completely eliminate operating costs.

Improving energy efficiency of the systems for obtaining water from atmospheric air

This paper outlines the prospect of obtaining water from atmospheric air by cooling it to the dew point temperature using refrigeration machines in order to partially reduce water scarcity in the arid regions of our planet. To minimize energy costs in the systems for obtaining water from atmospheric air, it is proposed to utilize solar energy with absorption refrigeration units (ARUs) acting as a source of artificial cold. The characteristic thermodynamic processes have been analyzed in a modernized ARU, capable of working at a lower thermal energy source's temperature than its analogs. The possibility has been studied to reduce the temperature of the heat source by including a solution vaporizer in the ARU scheme. The analysis involved an authentic method based on the balance of specific streams of ARU working body components and actual boundary conditions at characteristic points of the cycle. A limit was shown for the level of a minimum boiling temperature in the ARU generator (from 90 °C) when the systems for obtaining water from atmospheric air are operated under current climatic conditions. The simulation of heat-and-mass exchange processes during contact interaction between a steam-gas mixture and ammonia water solution was carried out. Based on variant calculations, it has been shown that the proposed ARU structure with an adiabatic solution vaporizer could work as part of systems to obtain water from atmospheric air at a hot spring temperature above 100 °C and constructively enough fits into the element base of standard models. It has been proposed to use two types of solar thermal energy sources to operate ARU. In a tropical climate, with vacuum solar collectors or solar energy hubs; in a temperate climate zone, with solar collectors with water as a heat carrier

Non-equilibrium modeling of CO2 reactive-absorption process using sodium hydroxide–ammonia–water solution in a packed bed column

In this study, CO2 reactive-absorption process is modeled into the NaOH-NH3-H2O solution in an absorption column. A non-equilibrium or rate-based model is used to simulate the process performance, and the predicted results are compared with the experimental data. In this model, the steady and nonlinear film models are utilized for high and low solubility components, respectively. The average relative deviation (ARD%) is decreased from 9.73 to 4.36 by increasing the number of column stages from 20 to 60 in the simulation. On the other hand, the predicted values by the film and enhancement factor models are compared, and it was concluded that the film model was more accurate than the other. The effects of axial position through the column and initial NaOH concentration on the liquid flow rate, mole fraction of components, and temperature of the gas and liquid phases are also investigated. As a main result, the temperature of the liquid phase and the CO2 concentration in the liquid phase decrease by increasing the axial position through the column.

A Novel Technique for Improving the Performance of Ammonia Absorption Refrigeration Cycle

The world is now living in an energy crisis. Refrigeration and air-conditioning systems have become the basics of daily life in various fields and accordingly, it cannot be dispensed. Refrigeration machines and air-conditioning systems are the most energy-consuming systems, independent on the application whether it is domestic, commercial, industrial or medical. Therefore, using cooling systems which are powered by thermal energy, e.g., solar energy, can save a lot of electrical energy. Absorption refrigeration system is an example of a refrigeration system powered by heat energy. However, the system problem here is that it has low coefficient of performance (COP). The objective of this research is to improve the COP of the ammonia absorption cycle. This is done in the absorber unit by improving the absorption of the refrigerant ammonia into the ammonia–water solution. The absorption efficiency is improved by using (1) a stirrer pump to improve mixing, (2) sprayers to increase the contact area between ammonia and ammonia–water solution and (3) continuous cooling of the solution during the absorption process via an external heat exchanger. The COP of the ammonia absorption cycle has increased from 0.48 to 0.715, i.e., by 49%. This is due to the improvement of the absorption of the ammonia into the ammonia–water solution.

Synthesis and Application of Manganese Oxide Catalysts in Oxidation and Hydrogenation Processes

The analysis is made of the results of performed investigations: elaboration and study of physical-chemical properties of the catalysts on the basis of manganese oxides and on their use in various fields of chemical industry. Physical-chemical and technological foundations of the formation of oxide-manganese catalyst-absorbent of new-type are validated. It has been shown that for processes of purification of combustible gases from H2S and organic sulphur compounds he most favorable thermodynamic and kinetical conditions are created at manganese catalyst the composition of which near to Mn3O4. This type of the catalyst, together with MnO2 and, partially with Mn2O3, hold a firm own place in the catalytic processes. The direction, associated with the use of modified alumooxide carrier for elaboration of oxide-manganese and metallic catalysts (Pt, Pd) became as the new and prospective in the technology of carriers and catalysts, used in the processes of oxidation and hydrogenation. Technological modes, realized in given method, provide to activate solid-phase reaction of the formation of calcium aluminates at lower temperatures, as well as to stabilize surface-structural characteristics and to enhance thermal stability and mechanical strength of modified carrier. In the technology of the catalysts of aluminium oxide, by the use, of the carrier, preliminary modified by calcium oxide, the Mn-Pd catalyst was elaborated available for oxidation of CO and hydrocarbons of spent gases of the motor transport. The addition of palladium to the oxide-manganese catalyst leads to the formation of new centers on the surface which are active in the reaction of CO oxidation. The processes of the formation of manganese catalysts in reaction medium were studied. The method for preparing of the Mn-Pd catalyst includes processing the samples with an ammonia water solution. Treatment of the catalyst with ammonia water causes the formation of a palladium ammonia complex, which decomposes witha formation of palladium black. It can be concluded that the treatment with ammonia water leads to the completion of the formation of the active surface of the catalyst and to the temperature decrease of complete oxidation of CO. The experience of industrial operation of catalysts on the basis of modified alumocalcium carriers has shown that by duration of efficient operation of reburning of discharged gases of the engines of internal combustion they may compete with well-known industrial marks of the catalysts.

Evaluation of the Global S-Entropy Production in Membrane Transport of Aqueous Solutions of Hydrochloric Acid and Ammonia.

The results of experimental studies of volume osmotic fluxes () and fluxes of dissolved substances () in a system containing a synthetic Nephrophan® membrane (Orwo VEB Filmfabrik, Wolfen, Germany) set in a horizontal plane are presented. The membrane separated water and aqueous HCl or ammonia solutions or aqueous ammonia and HCl solutions. It was found that for the homogeneity conditions of the solutions and depend only on the concentration and composition of the solutions. For concentration polarization conditions (where concentration boundary layers are created on both sides), and depend on both the concentration and composition of the solutions and the configuration of the membrane system. The obtained results of the and flux studies were used to assess the global production of entropy for the conditions of homogeneity of solutions (), while and —to assess the global production of entropy for concentration polarization conditions ). In addition, the diffusion-convective effects and the convection effect in the global source of entropy were calculated. The concentration polarization coefficient was related to modified concentration Rayleigh number, e.g., the parameter controlling the transition from non-convective (diffusive) to convective state. This number acts as a switch between two states of the concentration field: convective (with a higher entropy source value) and non-convective (with a lower entropy source value). The operation of this switch indicates the regulatory role of earthly gravity in relation to membrane transport.

Thermo-environ study of a concentrated photovoltaic thermal system integrated with Kalina cycle for multigeneration and hydrogen production

Unlike steam and gas cycles, the Kalina cycle system can utilize low-grade heat to produce electricity with water-ammonia solution and other mixed working fluids with similar thermal properties. Concentrated photovoltaic thermal systems have proven to be a technology that can be used to maximize solar energy conversion and utilization. In this study, the integration of Kalina cycle with a concentrated photovoltaic thermal system for multigeneration and hydrogen production is investigated. The purpose of this research is to develop a system that can generate more electricity from a solar photovoltaic thermal/Kalina system hybridization while multigeneration and producing hydrogen. With this aim, two different system configurations are modeled and presented in this study to compare the performance of a concentrated photovoltaic thermal integrated multigeneration system with and without a Kalina system. The modeled systems will generate hot water, hydrogen, hot air, electricity, and cooling effect with photovoltaic cells, a Kalina cycle, a hot water tank, a proton exchange membrane electrolyzer, a single effect absorption system, and a hot air tank. The environmental benefit of two multigeneration systems modeled in terms of carbon emission reduction and fossil fuel savings is also studied. The energy and exergy efficiencies of the heliostat used in concentrating solar radiation onto the photovoltaic thermal system are 90% and 89.5% respectively, while the hydrogen production from the two multigeneration system configurations is 10.6 L/s. The concentrated photovoltaic thermal system has a 74% energy efficiency and 45.75% exergy efficiency, while the hot air production chamber has an 85% and 62.3% energy and exergy efficiencies, respectively. Results from this study showed that the overall energy efficiency of the multigeneration system increases from 68.73% to 70.08% with the integration of the Kalina system. Also, an additional 417 kW of electricity is produced with the integration of the Kalina system and this justifies the importance of the configuration. The production of hot air at the condensing stage of the photovoltaic thermal/Kalina hybrid system is integral to the overall performance of the system.

An experimental investigation of the performance, emission and combustion stability of compression ignition engine powered by diesel and ammonia solution (NH4OH)

This study presents experimental examinations of a stationary single-cylinder compression ignition dual fuel engine for the combustion of diesel fuel with water ammonia solution. The effect of 25% water ammonia solution on the combustion, performance, emissions and stability of the dual fuel compression ignition engine was investigated, taking into account its different operating conditions. The experiments were carried out for three modes of engine operation with three loads (35%, 60% and 100%) and a change in the water ammonia solution energy fraction at 60% load, within the range from 0% to 17%. Co-combustion of diesel fuel with water ammonia solution in the test engine contributed to an increase in the ignition delay period and combustion duration, and to an increase in the heat release rate. Compared to the combustion of diesel fuel alone, combustion involving ammonia causes deterioration in the stability of the test engine operation, yet not exceeding the permissible stability indices for reciprocating combustion engines. Addition of water ammonia solution led to reduced nitrogen oxide emissions and increasing carbon monoxide and hydrocarbon emissions and did not result in significant changes in carbon dioxide emissions.

RESEARCH OF TECHNOLOGY FOR EXTRACTION OF RARE AND NOBLE METALS FROM RESET CUES AND SLUDGE FIELD SOLUTIONS

Currently, in world practice, standard molybdenum concentrates undergo oxidative firing to obtain technical molybdenum oxide, which is the starting material for the production of ferromolybdenum. For the production of high-purity products, technical oxide is subjected to chemical purification by dissolving it in a solution of ammonia water. Molybdenum salts are precipitated from ammonia solutions, and Fe, Si, Cu, Al impurities are introduced with waste solutions from the technological cycle.

Evidence for Ammonia-bearing Species on the Uranian Satellite Ariel Supports Recent Geologic Activity

Abstract We investigated whether ammonia-rich constituents are present on the surface of the Uranian moon Ariel by analyzing 32 near-infrared reflectance spectra collected over a wide range of sub-observer longitudes and latitudes. We measured the band areas and depths of a 2.2 μm feature in these spectra, which has been attributed to ammonia-bearing species on other icy bodies. Ten spectra display prominent 2.2 μm features with band areas and depths >2σ. We determined the longitudinal distribution of the 2.2 μm band, finding no statistically meaningful differences between Ariel’s leading and trailing hemispheres, indicating that this band is distributed across Ariel’s surface. We compared the band centers and shapes of the five Ariel spectra displaying the strongest 2.2 μm bands to laboratory spectra of various ammonia-bearing and ammonium-bearing species, finding that the spectral signatures of the Ariel spectra are best matched by ammonia-hydrates and flash frozen ammonia-water solutions. Our analysis also revealed that four Ariel spectra display 2.24 μm bands (>2σ band areas and depths), with band centers and shapes that are best matched by ammonia ice. Because ammonia should be efficiently removed over short timescales by ultraviolet photons, cosmic rays, and charged particles trapped in Uranus’ magnetosphere, the possible presence of this constituent supports geologic activity in the recent past, such as emplacement of ammonia-rich cryolavas and exposure of ammonia-rich deposits by tectonism, impact events, and mass wasting.

Conceptual design and analysis of a novel process for BOG re-liquefaction combined with absorption refrigeration cycle

Little attention has been paid to the boil-off gas (BOG) re-liquefaction using the absorption refrigeration cycle (ARC), so a novel process for BOG re-liquefaction combined with the ARC is designed and compared with the traditional parallel nitrogen expansion process. The working fluid of the ARC is ammonia-water solution, and the heat of the reboiler comes from the hot steam heated by the solar energy. Several performance parameters such as specific energy consumption (SEC), exergy efficiency (EXE), coefficient of performance (COP), cold and hot composite curves of the heat exchangers and exergy losses are compared and analyzed. The optimization results show that the process with the ARC performs better. The SEC of the process with the ARC is 0.7878 kWh/kgLNG, which is 11.0% lower than that of the traditional parallel nitrogen expansion process. Meanwhile, the EXE and COP of the process with the ARC are 0.3657 and 0.2636, which are 12.6% and 11.8% higher than that of the traditional parallel nitrogen expansion process. Therefore, this study demonstrates that the process combined the ARC with the traditional processes can improve the system performance. Finally, the cost analysis is given for the two processes.

Monodisperse core–shell silica particles as a high-performance liquid chromatography packing material: Facile in situ silica sol-gel synthesis

In recent years, core–shell silica particles (CSSPs) have been increasingly used for highly efficient separation at fast flow rates and relatively low back pressures in high-performance liquid chromatography (HPLC). However, material synthesis techniques for producing CSSPs economically in batch processes remain elusive. In this report, a practical and straightforward method for the preparation of CSSPs is presented. By refluxing freshly prepared nonporous silica particles in ammonia–water solution in the presence of poly(diallyldimethylammonium chloride) at 70–100 °C, CSSPs with shell thicknesses of up to 300 nm and pore sizes from 8 to 25 nm were easily prepared. The effects of the synthetic conditions on the shell thickness, surface area, and pore size were investigated in detail, and the method reproducibility was evaluated in scale-up experiments. A mechanism of CSSP formation is also proposed. The CSSPs were characterized via scanning electron microscopy, transmission electron microscopy, laser particle size (dynamic light scattering) analysis, and nitrogen adsorption and desorption experiments. The synthesized 3.4-μm CSSPs were functionalized with dimethyloctadecylchlorosilane and used as an HPLC packing material, exhibiting excellent separation performance for both small molecules and large biomolecules. In summary, we report the simplest method developed thus far for the preparation of monodisperse core–shell silica particles suitable for HPLC column packing.

ANALYSIS OF THE POSSIBILITY OF USING SECONDARY ENERGY RESOURCES IN FOOD INDUSTRY ENTERPRISES USING SPECIAL REFRIGERATION EQUIPMENT

Abstract. Aim. Due to the current priority given to energy conservation issues, a promising research avenue in the field of refrigeration consists in the developing of energy-saving systems based on heat-recovery absorption refrigerators. The aim of the work is to study the possibility of using a water-ammonia absorption refrigeration machine to increase the efficiency of food production facilities.Method. Based on an analysis of the initial enterprise data, the possible operating modes of the refrigeration machine were determined considering the various types of heating and cooling sources proposed in the task specification. The identification of the characteristics of single-stage and twostage absorption schemes confirmed the possibility of increasing the enterprise's efficiency through the use of secondary energy resources. Results. The choice of initial data for the design of a singlestage absorption water-ammonia refrigeration machine (AVXM) was justified on the basis of a preliminary analysis carried out to calculate the size of the degassing interval. The calculation was carried out using a ξ – i diagram for the ammonia water solution. Conclusion. Two prior conditions for the design of a high-performance absorption water-ammonia refrigeration machine were determined on the basis of an analysis of four conditions set by the customer. For operating conditions with a low degassing interval value, a scheme for an absorption water-ammonia refrigeration machine employing two-stage absorption is proposed.

Thermodynamic analysis and multi-objective optimization of a novel power generation system driven by geothermal energy

A novel combined system integrated with a Kalina and a transcritical CO2 (T-CO2) cycle is proposed and investigated for making effective use of geothermal resources. Geothermal energy is first utilized by Kalina sub-cycle and then deeply recovered by T-CO2 sub-cycle. A steady-state mathematical model is developed to further study the novel combined system. The result shows that under the given conditions, the system net power output is up to 2808 kW, which is higher than both the single Kalina cycle and single T-CO2 cycle. The exergy analysis shows that the evaporator II is the component with the largest exergy destruction. The parametric analysis shows that increasing the basic ammonia-water solution concentration and turbine I inlet temperature, or decreasing the turbine I inlet pressure and condensation pressure of condenser I have significant effects on system performance. Furthermore, a multi-objective optimization considering both thermodynamic and economic aspects is carried out to obtain the Pareto frontier solutions, and the decision-making analysis shows that the two-stage recycling system could greatly improve the geothermal water utilization degree compared to the conventional system. The findings could provide a useful reference for system design and operation to make better use of geothermal energy.

Effects of Calcium Oxide and Magnesium Oxide Stabilizing Agents on the Critical Transformation Size of Tetragonal Zirconia

The preparation of tetragonal zirconia nanopowders by sol–gel method using zirconium oxychloride as raw material, ammonia water and sodium hydroxide solution as precipitant, and calcium oxide or magnesium oxide powders as stabilizing agents is described. After suction filtration, drying, and calcination, tetragonal zirconia nanopowders with different particle size and tetragonal phase content were obtained. The particle size and phase composition of the powders are characterized by using a laser particle size analyzer and an X-ray diffractometer, and the tetragonal phase content and grain size are calculated from the crystal plane formula and Scherrer formula. The analysis of the relationship between the tetragonal phase content and the particle size of the zirconia nanopowders stabilized by calcium oxide and magnesium oxide at room temperature reveals the inhibitory effect of the stabilizing agents on the growth of zirconia grains. The stabilized zirconia nanopowder is finer than unstabilized zirconia nanopowder, and the particle distribution is more uniform in the former. The stabilizing effect of calcium oxide is superior to that of magnesium oxide; the critical transformation size of the zirconia grains stabilized by calcium oxide is the largest, and that of unstabilized zirconia is the smallest. The critical transformation size of calcium oxide-stabilized, magnesium oxide-stabilized, and unstabilized zirconia nanopowders is 18–22.6 nm, 24–28 nm, and 26–33.6 nm, respectively. Under the same calcination condition, the calcium oxide-stabilized zirconia nanopowder retains the highest tetragonal phase content at room temperature.