NH3 H2O Research Articles

Performance improvement of NH3–H2O absorption chiller with a combined generator

The present experimental work investigates the impact of an innovative falling-film and plate combined generator, associating vapor production and purification, on the performance of an NH3–H2O absorption chiller of 5-kW cooling capacity. The impact of the flooding of the lower part of the exchanger on the performance of the machine is investigated: It decreases the COP by 33% and cooling capacity by 38%. Solution sub-cooling at the combined generator inlet improves the purity of the ammonia vapor produced, but degrades the performance of the chiller. A design of experiments is defined to characterize the performance of the combined generator, which is highly impacted by the solution mass flowrate and concentration. Then, two correlation forms are used to predict the performance, and the adapted NTU model yields better results. Finally, for an air-conditioning application, a low solution mass flowrate allows the energy consumption to be reduced by approximately 15% but it requires a higher temperature for the heat source; while the increase in the solution mass flowrate degrades the performance but enables the machine to self-regulate at a low heat source.

Exergy and thermoeconomic analyses of the diffusion absorption refrigeration system with various nanoparticles and their different ratios as work fluid

The fact that diffusion absorption refrigeration (DAR) systems can also work with low power plants has increased the interest in these cooling systems again. The DAR systems are mostly analyzed using energy analysis. Although, energy analysis is not adequate itself, so exergy analysis is required. In this study, the effects of nanofluid use on the DAR system performance are investigated by performing exergy and thermoeconomic analyses. Some nanoparticles like MgOAl2O3, ZnOAl2O3 and TiO2 in various weight ratios are used in the DAR system. In experiments with different nanoparticles, the effect of utilizing hybrid nanoparticles on enhancing system performance is also evaluated. The highest exergy destruction rate occurs in the solution heat exchanger, although the lowest exergy destruction rate happens in the condenser. The highest exergy efficiency with 0.798 is found in the base fluid (25% NH3–H2O). Besides, it is clearly observed that exergy efficiency decreased in the DAR systems using nanofluids. Moreover, the economic analysis of the DAR system is added to the study in order to evaluate the relationship between the exergy destruction rate and initial investment costs. It is found that the DAR system with ZnOAl2O3 (2 wt%) is preferable compared to other DAR systems.

In-situ self-assembly synthesis of low-cost, long-life, shape-controllable spherical Li4Ti5O12 anode material for Li-ion batteries

Li4Ti5O12 (LTO) is the most promising anode material for lithium-ion batteries owing to its excellent cycle stability and safety. However, the electrochemical performance of LTO at high rates is limited by its low conductivity. Generally, LTO preparation requires organic titanium sources, which are expensive. In this study, inexpensive H2TiO3 was used as the titanium source, LiOH‧H2O served as the lithium source, and NH3‧H2O was added to control the pH of the solution. Simple one-step liquid-phase deposition and calcination were performed for obtaining in situ self-assembled LTO submicron spheres with stable morphology and excellent electrochemical performance. According to electrochemical performance tests, the sample calcined with 4 mL of 25% NH3‧H2O at 700 °C (LTO-4–700) exhibited the best performance. Its discharge capacity remained at 176.4 mAh g−1 over 100 cycles at 87.5 mA g−1 and retained at 136.7 mAh g−1 over 500 cycles at 875 mA g−1, and its specific capacity was 105.6 mAh g−1 over 1000 cycles, even at a current of 1750 mA g−1 with a retention rate of 96.7%. Furthermore, LTO-4–700 exhibited excellent rate performance at 3500 mA g−1 compared to other samples. Cyclic voltammetry and electrochemical impedance spectroscopy confirmed that submicron spherical LTO-4–700 had a high Li+ migration rate and low electrochemical impedance.

Combined Generator for an Nh3–H2o Absorption Chiller

Combined Generator for an Nh3–H2o Absorption Chiller

Fundamental reaction kinetics of high-pressure reductive amination of polyalkylene glycol

This study investigates reaction kinetics of high-pressure amination of polyalkylene glycol (PAG) to polyetheramine (PEA). The reductive amination of PAG was carried out depending on the NH3 amount, reaction temperature, reaction pressure, and H2O content in a batch reactor to understand the effect of these factors on activity and selectivity toward the primary amine. Contrary to the fact that the amination step is a zero-order reaction and dehydrogenation of alcohol to ketone is the rate-limiting step in the reductive amination of alcohol, the amount of NH3 significantly affected the reaction rate. The increased amount of NH3 enhanced the activity and selectivity for PEA, in contrast with the results reported in prior studies. A Langmuir-Hinshelwood kinetic model was established to reflect the effect of the NH3 amount, and kinetic parameters such as the rate constant and activation energy were obtained at a high pressure around 150 bar. It was also found that the absence of NH3 caused the reverse reaction of PEA to the secondary amine in the presence of H2. The fundamental kinetic analysis provides a competitive synthesis route for improving the activity and selectivity toward the primary amine.

Feasibility study of a new solar based trigeneration system for fresh water, cooling, and electricity production

The utilization of solar energy to generate electricity, cooling, and freshwater in remote areas in a sustainable way still poses lots of challenges to researchers. The aim of the current study is to design a new solar-operated trigeneration system to produce electricity, cooling, and fresh water using parabolic trough collectors in remote areas. Electric power is generated by using Organic Rankine Cycle, and cooling and fresh water (using freezing desalination technique) are obtained by two-stage NH3–H2O vapor absorption system run by solar energy. Simulation results show that for PTC arrays of 200 m2, an electrical output obtained is 3.3 kW, cooling rate is 20.4 kW, and mass flow rate of freshwater produced is 36 kg/h for an average solar irradiation of 0.7 kW/m2. Furthermore, sensitivity analysis is conducted by varying the parameter like solar irradiation, evaporator temperature, seawater inlet temperature, etc. and their effect on performance characteristics of the overall setup is investigated.

Organic acid-ammonia ion-induced nucleation pathways unveiled by quantum chemical calculation and kinetics modeling: A case study of 3-methyl-1,2,3-butanetricarboxylic acid

Nucleation of organic acids (OAs) and H2SO4 is an important source for new particle formation in the atmosphere. However, it is still unclear whether organic acids can produce nanoparticles independent of H2SO4. In this study, 3-methyl-1,2,3-butanetricarboxylic acid (MBTCA) was adopted as a model of OAs. Pathways of clustering from MBTCA, ammonia and ions (NH4+ and NO3−) to form a 1.9 nm nucleus were investigated by quantum chemical calculation and kinetic modeling. Results show recombination of charged clusters/ions plays an essential role in the nucleation processes. Cluster formation rates increase by a factor of 103 when NH3 increases from 2.6 × 108 molecules·cm−3 (under clean conditions) to 2.6 × 1011 molecules·cm−3 (under polluted conditions), as NH3 can stabilize MBTCA clusters and change ion compositions from H3O+ to NH4+. Although the proposed new mechanism cannot compete with H2SO4–NH3–H2O or H2SO4-OA nucleation currently, it may be important in the future with the decline of SO2 concentration.

Leaching Kinetics of Secondary Zinc Oxide in a NH3–NH4HCO3–H2O System

Secondary zinc oxide (SZO), which comes from the zinc industry, is an important secondary resource of zinc and other valuable metals. In this study, the production feasibility and rationality of a cleaner zinc recovery process using SZO and a hydrometallurgical method were described. Zinc extraction is promoted by the addition of ammonium bicarbonate to a NH3–H2O system, and the maximum recovery of zinc could be close to 80% at the optimum leaching conditions of a stirring rate of 400 rpm, an ammonia/ammonium ratio of 7:3, a total ammonia concentration of 4 mol/L, and a liquid/solid ratio of 7 mL/g for 30 min at 35 °C. The kinetics of leaching were modeled using the shrinking core model of constant-size particles, and the rate-controlling step was determined to be the diffusion through the product layer. The apparent activation energy of the reaction was estimated to be 11.04 KJ·mol−1, while the order of reaction with respect to total ammonia concentration was 1.53 and the liquid/solid ratio was 2.26. The analysis results of the initial residue and the leached residue indicated that lead was transferred from PbCl2 to PbCO3 and that ZnFe2O4 was not leached in the NH3-NH4HCO3-H2O system.

Enhancement of Ce doped La–Mn oxides for the selective catalytic reduction of NOx with NH3 and SO2 and/or H2O resistance

• A–bit doping is more favorable for improving SCR activity than that of B–bit doping. • A–bit doping enhances SO 2 resistance, but B–bit doping improves N 2 selectivity. • A–bit or B–bit doping can form the perovskite structure but the exposed plane changes. • A–bit doping increases Mn 4+ content but B–bit doping decreases Mn 4+ content. Cerium modified La–Mn oxides for NH 3 –SCR at low temperature is prepared by one–step synthesis method and characterized. The results showed that the perovskite La–Mn oxides at A–bit doped by Ce is more favorable for NOx removal than B–bit doping and achieves about 80% conversion of NOx at 120°C and about 100% in the range temperature of 180–220°C as well as good SO 2 and/or H 2 O resistance. However, LaMn 0.8 Ce 0.2 O 3 (B–bit doping) has better N 2 selectivity than La 0.8 Ce 0.2 MnO 3 (A–bit doping) and LaMnO 3 . The generated N 2 O and NO 2 influence the N 2 selectivity in the NH 3 –SCR reaction, but N 2 O is from the NH 3 oxidation while NO 2 is from the NO oxidation. The perovskite La–Mn oxides at A–bit or B–bit doped by Ce are able to maintain the perovskite structure of LaMnO 3.15 but the exposed plane shifts from (104) to (110). However, for both doped samples, some CeOx and Mn 3 O 4 are spilled out from the perovskite structure of La–Mn oxides. A–bit ions doped by Ce can increase Mn 4+ relative content, specific surface area, available oxygen and surface acid amount, while B–bit doping decreases Mn 4+ relative content and adsorbed oxygen and increases Ce 4+ relative content. After SO 2 resistance testing, the formation of (NH 4 ) 2 SO 4 and MnSO 4 on all catalysts is inevitable, but the binding force of the formed metal sulfate is different on catalyst surface, resulting in the difference of its resistance to sulfur.

Integration of solid-oxide fuel cells and absorption refrigeration for efficient combined cooling, heat and power production

Abstract Combined cooling, heating and power (CCHP) systems are characterized by a substantially higher energy-utilization efficiency compared to standalone systems. In this study, an integrated system comprising a solid-oxide fuel cell (SOFC), hot-water storage tank (HWST) and absorption refrigeration (AR) cycle is considered. The SOFC model was developed in Aspen Plus®. It was used to determine the thermodynamic properties of the exhaust gas that was then used to provide heat for the HWST and to drive the AR cycle. Thermodynamic models for the AR cycles were developed in Engineering Equation Solver, considering LiBr–H2O and NH3–H2O as working fluids. The sensitivity analysis of a number of SOFC output parameters has been carried out. The most optimal case was characterized with the coefficient of performance (COP) and CCHP efficiency of 0.806 and 85.2% for the LiBr–H2O system, and 0.649 and 83.6% for the NH3–H2O system, respectively. Under such optimal operating conditions, the SOFC was characterized by the net electrical efficiency of 57.5% and the net power output of 123.66 kW. Data from the optimal solution were used to perform the thermodynamic study and sensitivity analysis to assess the influence of different absorption cycle operating conditions and to identify possible applications for the considered integrated systems.

A New Approach for Cu and Fe/FexB Production from Chalcopyrite by Molten Salt Electrolysis

In the present study, copper (Cu) and iron boride (FexB) were produced for the first time through molten salt electrolysis using chalcopyrite (CuFeS2) in an oxide-based borax electrolyte. Molten salt electrolysis was carried out at 1073 K and a current density of 600 mA/cm2 for 3600 s under galvanostatic conditions. Cu and Fe/FexB were deposited on the graphite crucible surface used as the cathode. The particles obtained as a result of electrolysis were examined by X-ray diffraction (XRD) and determined to contain Cu and Fe/FexB. The location and ratio of Cu and FexB in the particles were investigated by using EDS mapping, energy-dispersive spectroscopy (EDS), and X-ray spectroscopy (XRD); Cu and Fe/FexB were found to be present throughout the particles at different ratios. Cu and Fe/FexB were successfully separated from each other by selective leaching of copper in a 1 M NH3–H2O solution. The time-dependent dissolution behavior of Cu was investigated at pH 8, 298 K, 600 rpm stirring rate for 900–5400 s, and it was observed that the dissolution rate increased over time and all the copper had completely dissolved after 5400 s. After leaching particles were examined by XRD and SEM, it was revealed that Fe/FexB particles did not contain any Cu.

A semicircular trough solar collector for air-conditioning system using a single effect NH3–H2O absorption chiller

This paper reports on the feasibility of a non-tracking semi-circular trough (SCT) solar thermal collector to operate a 17.6 kW single effect NH3–H2O absorption chiller. The SCT solar collector module employs a novel direct metal-to-water contact resulting in an increased heat transfer to the working fluid. This is the first cooling system of its kind that integrates SCT collectors with NH3–H2O absorption chiller and requires a significantly smaller number of collector tubes compared to a non-concentrating collector in order to attain an optimum operating temperature of ≥100 C. In a sequence of experiments, the efficiency of the SCT collector has been measured in both clear and cloudy conditions. It is concluded that this collector is capable of providing thermal power to drive absorption cooling systems in both clear and cloudy conditions. A record −3.3 C was achieved when the chiller reached an operating temperature of 120 C. The average coefficient of performance of the absorption chiller was measured to be 0.42. The SCT collector’s simple design makes it a highly attractive candidate for solar thermal applications including solar heating, cooling and food processing. The collector is currently in the process of commercialization in Thailand.

Thermo-Economic Evaluation of Aqua-Ammonia Solar Absorption Air Conditioning System Integrated with Various Collector Types.

The main objective of this paper is to simulate solar absorption cooling systems that use ammonia mixture as a working fluid to produce cooling. In this study, we have considered different configurations based on the ammonia–water (NH3–H2O) cooling cycle depending on the solar thermal technology: Evacuated tube collectors (ETC) and parabolic trough (PTC) solar collectors. To compare the configurations we have performed the energy, exergy, and economic analysis. The effect of heat source temperature on the critical parameters such as coefficient of performance (COP) and exegetic efficiency has been investigated for each configuration. Furthermore, the required optimum area and associated cost for each collector type have been determined. The methodology is applied in a specific case study for a sports arena with a 700~800 kW total cooling load. Results reveal that (PTC/NH3-H2O)configuration gives lower design aspects and minimum rates of hourly costs (USD 11.3/h) while (ETC/NH3-H2O) configuration (USD 12.16/h). (ETC/NH3-H2O) gives lower thermo-economic product cost (USD 0.14/GJ). The cycle coefficient of performance (COP) (of 0.5).

Acidity of SiO2-Supported Metal Oxides in the Presence of H2O Using the AEIR Method: 2. Adsorption and Coadsorption of NH3 and H2O on TiO2/SiO2 Catalysts.

Two different TiO2/SiO2 compounds containing TiO2 nanodomains dispersed over SiO2 were investigated applying the AEIR method at the adsorption equilibrium of NH3 and H2O from 300 to 723 K, particularly for the measurement of the individual heats of adsorption of the different species on Lewis acidic sites (LAS) and Brønsted acidic sites (BAS) as evaluation of the strength of the sites. It revealed two types of NH3 adsorption sites: the first ones could correspond either to NH3 species H-bonded to free OH groups or to coordinated weak LAS (named L1). The second ones (L2) were attributed to strongest LAS similar to those present at the surface of TiO2 nanocrystallites. They also correspond to the stronger adsorption sites of H2O. Two types of Brønsted acid sites (BAS) were additionally evidenced by the AEIR method and proposed to be specifically located on the Si-O-Ti bridging bonds at the TiO2/SiO2 interface. The heats of adsorption of the different adsorbed species provided by the AEIR method were consistent with literature data on average values of the heats of adsorption of NH3 and H2O from microcalorimetry measurements. The surface acidity of the two compounds in the presence of H2O was determined using NH3-H2O coadsorption. At T ≥ 473 K, the NH3 species on the L2 sites were not significantly displaced from the surface whatever the partial pressure of H2O studied in agreement with the Temkin competitive model using the individual heats of adsorption of the NH3 and H2O species. This model also revealed the presence of a small amount of H2O species adsorbed on L2 sites allowing H2O dissociation or/and hydrolysis of SiOTi or TiOTi bridges, leading to the formation of a much higher amount of BAS. Therefore, this original work combining the AEIR method and the Temkin competitive model provided new insights for understanding water effects on acidic oxide catalysts.

Comparison the start-up time of the key parameters of aqua-ammonia and water–lithium bromide absorption chiller (AC) under different heat exchanger configurations

The time that an absorption chiller needs to reach the designed working condition is called start-up. During this time, energy is consumed through the system while efficient refrigeration is not available. So, it’s too important to consider the influencing parameters on this period of time so that reduction in energy consumption is achieved. Also, dynamic analysis is used to reduce the startup time and increase system performance in addition to strategic control purposes. Optimizing an absorption cycle during transient operations, such as start up or shut down is very important. The aim of this study is to investigate and compare the effect of employing refrigerant and solution heat exchangers (RHX and SHX) on dynamic performance of both NH3–H2O and H2O–LiBr absorption chillers (ACs). Also, the effect of solution heat exchanger’s efficiency on the start-up time of the key parameters of both ACs is investigated. To diminish the effect of approximate relations on the results, thermodynamic properties of NH3–H2O and H2O–LiBr solutions are extracted from the EES software. By making a link between MATLAB and EES software, a set of differential equations is solved in MATLAB software. The fourth order Runge–Kutta method is employed to solve the differential equations system. This process is continued until convergence criteria are satisfied. The results show that removing SHX from the cycle increases the start-up time of both NH3–H2O and H2O–LiBr AC’s COPs by 11.76% and 45.16% respectively. The start-up time of the COP of H2O–LiBr absorption chiller is highly affected in comparison with the NH3–H2O absorption cycle, by removing SHX or increasing the SHX efficiency. Also, utilizing the RHX does not affect the dynamic response of the key parameters of the both absorption chillers.

Investigation on condensable particulate matter emission characteristics in wet ammonia-based desulfurization system

Particulate matter emissions from ammonia-based wet flue gas desulfurization (Ammonia-WFGD) systems are composed of a filterable particulate matter and a condensable particulate matter (CPM) portion. However, the CPM part has been ignored for a long time, which results in an underestimation of the aerosol problems caused by Ammonia-WFGD systems. In our research, the characteristics of the CPM that emits from an Ammonia-WFGD system are investigated experimentally for the first time, with the US Environmental Protection Agency Method 202 employed as the primary measurement. The influences of some essential desulfurizing parameters are evaluated based on the experimental data. The results show that CPM contributes about 68.8% to the total particulate matter emission. CPM consists mainly of ammonium sulfates/sulfites, with the organic part accounting for less than 4%. CPM is mostly in the submicron fraction, about 71.1% of which originates from the NH3–H2O–SO2 reactions. The appropriate adjustments for the parameters of the flue gas and the desulfurizing solution can inhibit CPM formation to different extents. This indicates that the parameter optimizations are promising in solving CPM emission problems in Ammonia-WFGD systems, in which the pH adjustment alone can abate CPM emission by around 49%. The opposite variations of the parameters need attention because they can cause tremendous CPM emission increase.

Self-adapting double and triple-lift absorption cycles for low-grade heat driven cooling

• Five multiple-lift self-adapting NH 3 H 2 O and NH 3 –LiNO 3 cycles are presented. • The self-adapting concept automatically assures optimum cycle operation. • COP ranges are 0.20–0.35 for double-lift cycles and 0.1–0.25 for triple-lift cycles. • Higher efficiency and wider working range are achieved using more than one pump. • NH 3 H 2 O pair is more efficient at low lift, NH 3 –LiNO 3 at high lift. Multiple-lift absorption cycles are an interesting option for cooling and refrigeration driven by waste or renewable heat. Compared with single effect cycles, they allow higher thermal lift or lower thrust, but they often require the use of controlled valves, which can cause stability and control issues. The self-adapting concept, firstly introduced in the two-pump series-flow double-lift cycle, replaces the valve with a phase separator, overcoming this drawback. In this work, five new cycle layouts, incorporating the self-adapting concept, are presented: the one-pump series-flow double-lift cycle and four triple-lift cycles. The cycles are compared in terms of COP and heat duties under various conditions, using NH 3 H 2 O and NH 3 –LiNO 3 as working pairs. It is found that the double-lift cycles have a COP in the range 0.35–0.20, about 0.1 higher than the triple-lift cycles. However, triple-lift cycles accept cooling water temperature up to 8 °C higher. Cycles with multiple pumps have higher efficiency than single-pump cycles, especially at high lift conditions. The use of NH 3 H 2 O as working pair guarantees higher COP at low thermal lift, while NH 3 –LiNO 3 has wider operating range and better performances at high thermal lift.

Investigation of the launch time of NH3-H2O absorption chiller under different working condition

This study deals with the launch time of main characteristic of NH3-H 2O absorption chiller under different working condition. The aim of this work was about to scrutinize a lumped-parameter dynamic simulation of aqua-ammonia absorption chiller in addition to investigating the effect of subcooled liquid at condenser/absorber outlet on absorption chiller’s key parameters launch time. Also, the effect of ambient temperature on absorption chiller’s key parameters’ launch time is studied. In order to determine the thermodynamic properties of the working fluid, the Engineering Equation Solver software is applied. By making a link between Engineering Equation Solver and MATLAB software, the differential equations are solved in the MATLAB software environment by fourth-order Rung–Kutta method. According to the result, increase of the sub-cool liquid temperature at condenser outlet has no effect on absorption chiller’s key parameters’ launch time. Besides, 10 ℃-increase in subcooled liquid temperature at the absorber outlet leads to decreasing the launch time of the coefficient of performance to 19.35%. The result shows that if cooling tower temperature goes from 22 ℃ to 30 ℃, launch time of the coefficient of performance rises by 10.43%, while evaporator heat transfer rate falls by 30%. To validate the dynamic model, the results deduced from numerical simulation are compared with peer steady–state results.

Experimental investigation on NH3–H2O generator-absorber heat exchange (GAX) absorption heat pump

Compared with conventional fuel-direct-burning heating systems, heat-driven absorption heat pump has high efficiency. To further improve the heating performance, generator-absorber heat exchange (GAX) absorption heat pump was developed, but its experimental research was not enough. The parameters tested were usually just COP and heating capacity in the existing literature, the variation of some internal parameters were rarely measured and analyzed. Besides, the latent heat exchange between the generator and the absorber could not continue normally under high thermal lift (TCON-TEVA) and low thermal thrust (TGEN-TABS), instead, more sensible heat is transferred, the temperature overlap decreases or even disappears, and the circulation process of GAX cycle approaches to that of single-effect cycle. This phenomenon is named “cycle degradation”, and is crucial to understand the working principle of GAX for optimal design and control. The cycle degradation was only simulated under low evaporation temperature, but has not been analyzed with experimental data, the influence rules of other external operational parameters on the phenomenon are also not clear. Therefore, a prototype of GAX absorption heat pump is built up, many internal and external parameters are measured and used to investigate the cycle degradation and overall performance under different testing conditions. During the experiment, the COP is in the range of 1.185–1.506, the cycle degradation occurs when the “lifting factor (Eq [18])” is lower than 2.3. Moreover, the performance improves with the increase of driving temperature or low-grade heat source temperature, and deteriorates due to the rise of supply water temperature.

Thermodynamic Modeling of CaSO4–(NH4)2SO4–NH3–H2O Quaternary System with Asymmetric E-NRTL Model

Ammonium sulfate [(NH4)2SO4], an undesired byproduct in the caprolactam process, can be converted into recyclable NH3 by the substitution reaction with lime milk to reduce the ammonia consumption and produce high-quality gypsum. However, the thermodynamic mechanism of this process has not been clarified, which results in the unpredictable crystal phase of calcium sulfate products. In this work, a thermodynamic model for the CaSO4–(NH4)2SO4–NH3–H2O quaternary system with the asymmetric E-NRTL activity coefficient model was developed to understand the thermodynamic behavior. The modeling works involved the data fitting of binary solubility, osmotic coefficient, enthalpy of solution, and heat capacity data as well as ternary solubility data. It was shown that the model could predict the solubility of ammonia and calcium sulfate in aqueous ammonium sulfate solution with temperature ranging from 0 to 160 °C and pressure up to 1.0 MPa. Furthermore, the constructed model for the quaternary system was proved to b...