Ammonia-water System Research Articles

Assessing Ammonia Treatment Options

This is the second of three articles to help water system operators understand ammonia and how to monitor and control its effects at the plant and in the distribution system. The first article (Opflow, April 2012) provided an overview of ammonia's chemistry, origins, and water system effects. This article focuses on treatment options for removing ammonia from source water prior to distribution and how to monitor and control ammonia. Next month's article will provide case studies explaining how utilities have dealt with ammonia.

Graphical expression of thermodynamic characteristics of absorption process in ammonia-water system

The adiabatic sorption is very interesting phenomenon that occurs when vapor of refrigerant is in contact with unsaturated liquid absorbent-refrigerant mixture and exchange of heat is forbid between the system and an environment. This contribution introduces new auxiliary lines that enable correct position determination of the adiabatic sorption process in the p-T-x diagram of ammoniawater system. The presented auxiliary lines were obtained from common functions for fast calculation of water-ammonia system properties. Absorption cycles designers often utilize p-t-x diagrams of working mixtures for first suggestion of new absorption cycles. The p-t-x diagrams enable fast correct determination of saturate states of liquid (and gaseous) mixtures of refrigerants and absorbents. The working mixture isn’t only at saturated state during a real working cycle. If we know pressure and temperature of an unsaturated mixture, exact position determination is possible in the p-t-x diagrams too.

Generating of Fresh Water using Vapour Absorption Refrigeration System from the Humidity in the Air

In vapour absorption Refrigeration system, it generates fresh drinking water and also extracts water from humid ambient air by using Cooling Condensation process offers the possibility of using heat to provide cooling. In this method refrigerant circulates through a condenser and an evaporator coil which cools the air surrounding it, lowering the air's dew point and causing water to condense. A controlled-speed fan pushes filtered air over the coil. The resulting water is then passed into a holding tank with purification and filtration system to keep the water pure. For this purpose heat from a conventional boiler can be used or waste heat and solar energy. When the latter systems are used absorption systems minimize also the adverse effects of burning fossil fuels and thus protect the environment. Absorption systems fall into two major categories, depending on the working fluids. These are the ammonia-water systems, in which ammonia is the refrigerant and lithium bromide-water systems in which water vapor is the refrigerant. The future trends of research in this area would be on other refrigerant pairs which will be more effective.

アンモニア-水系を用いた垂誼管流下液膜式吸収器・再生器の熱・物質移動解析:-水 - 臭化リチウム系との比較-

アンモニア-水系を用いた垂誼管流下液膜式吸収器・再生器の熱・物質移動解析:-水 - 臭化リチウム系との比較-

Experimental investigation on an ammonia–water–lithium bromide absorption refrigeration system without solution pump

Experimental researches were carried out on a novel ammonia–water–lithium bromide ternary solution absorption refrigeration and air-conditioning system without solution pump and distillation equipments. The experiments were conducted by using three kinds of NH 3–H 2O binary solution and 17 kinds of ternary solution with difference in mass fraction of NH 3 and LiBr. The experimental results showed that the vapor pressure of the generator in the system would be lower than that of the generator in an ammonia–water absorption system. In above two situations the same ammonia mass fraction and the same solution temperature were kept. The amplitude of vapor pressure decrease of the system generator would be larger with the increase of the mass fraction of LiBr. The maximum amplitude of decrease would be of 50%. With the increase of the mass fraction of LiBr, the coefficient of performance (COP) of the system would be increased initially, and then decreased later when the mass fraction of LiBr exceeded a certain value. This value was about 23% for the solution with ammonia mass fraction of 50% and 55%, and about 30% for the solution with ammonia mass fraction of 60%. Compared with the ammonia–water system, the COP of the ternary solution system with the same mass fraction of ammonia would increase up to 30%. With the ammonia mass fraction of 60% and LiBr mass fraction of 30% applied, the COP of the ternary solution system was increased up to 0.401. It was 51.89% higher than that when binary ammonia–water solution with ammonia mass fraction of 50% was applied. In above two operating situations, the temperature of hot water, cooling water and chilled water in the system would be kept almost constant, respectively.

Experimental and Analytical Investigation of Ammonia Absorption into Ammonia-Water Solution: Estimated Interface Concentration

Ammonia absorption process of ammonia vapor into ammonia water solution has been investigated experimentally, by inserting superheated ammonia vapor into a test cell containing a stagnant pool of ammonia water solution of several ammonia mass fractions, Ci. Before commencing the experiment, the pressure in the test cell corresponds to the equilibrium vapor of the ammonia-water system at room temperature. When the valve is opened, mechanical equilibrium is established quickly and the ammonia vapor diffuses into ammonia solution [1]. The difference between the initial pressure in the vapor cylinder and the initial pressure in the test cell ΔPi is found to have a major influence not only on the absorption rate but also on the estimated interface concentration. The interface concentration Cint of the cases ΔPi = 50 and 100 kPa exhibits a similar tendency, Cint decreases rapidly compared to other initial pressures ΔPi = 150 and 200 kPa. On the other hand, the interface concentration Cint of the cases ΔPi = 250 and 300 kPa are increasing within about 50 sec, then are hardly changing with time. They behave almost in a similar way as of Cint = 0.27 kg/kg. A correlation which gives the total absorbed mass of ammonia as a function of the initial concentration, the initial pressure difference and time is derived. In addition, the absorbed mass at no pressure difference could be estimated from the absorbed mass at initial pressure difference.

A numerical investigation of a diffusion-absorption refrigeration cycle based on R124-DMAC mixture for solar cooling

Abstract Research on new working fluid for uses in absorption systems has been continued. The feasibility of a solar driven DAR using the mixture R124/DMAC as working fluid is investigated by numerical simulation. The cycle is simulated for two cooling medium temperatures, 27 °C and 35 °C, and four driving heat temperatures in the range [90 °C–180 °C]. The performance characteristics of this system is analyzed parametrically by computer simulation for a design cooling capacity of 1 kW. The results show that the system performance and the lowest (minimum) evaporation temperature reached are largely dependent upon the absorber efficiency and the driving temperature. It is shown that for solar applications this fluid mixture has a higher COP and may constitute an alternative to the conventional ammonia–water system.

Recent Patents in Absorption Cooling Systems

Absorption cooling offers the possibility of using heat to provide cooling. For this purpose heat from a conventional boiler can be used or waste heat and solar energy. When the latter systems are used absorption systems minimize also the adverse effects of burning fossil fuels and thus protect the environment. Absorption systems fall into two major categories, depending on the working fluids. These are the ammonia-water systems, in which ammonia is the refrigerant and lithium bromide-water systems in which water vapor is the refrigerant. This paper initially introduces the two systems and then outlines recent patents in this area. The future trends of research in this area would be on other refrigerant pairs which will be more effective.

Electrical conductivity of the ammonia-water system

The electrical conductivity (EC) of the ammonia-water system was studied in the concentration range 0.1–10 mol/L ammonia and the temperature range 15–60°C. The maximal EC of aqueous ammonia at a given temperature is proposed as the parameter for generalizing experimental results. The normalized EC was calculated as the ratio of the EC of aqueous ammonia of a given concentration to the maximal EC at a given temperature. Over the ranges of the concentrations and temperatures studied, all normalized ECs fall on one curve. The EC activation energy was analyzed as a function of ammonia concentration and temperature.

Effect of pressure on mass absorption in an ammonia–water absorption system

Absorption phenomenon of ammonia vapor into ammonia water solution has been investigated experimentally, by inserting superheated ammonia vapor into a test cell containing a stagnant pool of ammonia water solution. Before commencing the experiment, the pressure in the test cell corresponds to the equilibrium vapor of the ammonia–water system at room temperature. When the valve is opened, mechanical equilibrium is established quickly and the pressure in the test cell becomes equal to that of the ammonia vapor cylinder. The difference between the initial pressure in the vapor cylinder and the initial pressure in the test cell is found to have a major influence on the absorption rate. The main objective of this study is to investigate the effect of this initial pressure difference on the absorption rate of ammonia vapor. A correlation which gives the total absorbed mass of ammonia as a function of the initial concentration, the initial pressure difference and time is derived. In addition the absorbed mass at no pressure difference could be estimated from the absorbed mass at initial pressure difference.

Development of a Novel Combined Absorption Cycle for Power Generation and Refrigeration

Cogeneration can improve energy utilization efficiency significantly. In this paper, a new ammonia-water system is proposed for the cogeneration of refrigeration and power. The plant operates in a parallel combined cycle mode with an ammonia-water Rankine cycle and an ammonia refrigeration cycle, interconnected by absorption, separation, and heat transfer processes. The performance was evaluated by both energy and exergy efficiencies, with the latter providing good guidance for system improvement. The influences of the key parameters, which include the basic working solution concentration, the cooling water temperature, and the Rankine cycle turbine inlet parameters on the cycle performance, have been investigated. It is found that the cycle has a good thermal performance, with energy and exergy efficiencies of 27.7% and 55.7%, respectively, for the base-case studied (having a maximum cycle temperature of 450°C). Comparison with the conventional separate generation of power and refrigeration having the same outputs shows that the energy consumption of the cogeneration cycle is markedly lower. A brief review of desirable properties of fluid pairs for such cogeneration cycles was made, and detailed studies for finding new fluid pairs and the impact of their properties on cogeneration system performance are absent and are very recommended.

The ammonia–water system at high pressures: Implications for the methane of Titan

The Cassini/Huygens mission will provide an accurate description of Titan's surface features. One important outcome of these data is that it will help for understanding the processes of methane exchange between Titan's interior and its atmosphere. Such a correlation between surface features and internal processes involving methane will be highly simplified if the nature of methane reservoirs is understood. In this paper, the behavior of methane within Titan is investigated using both data on methane clathrate stability and data on the ammonia–water system. A mathematical description of the different liquidus of the ammonia–water system is proposed. It is shown that the low pressure and water rich domain of the system is very well constrained. On the contrary, both high pressure ices and ammonia hydrates domains are still very badly understood because of the lack of experimental data. Nonetheless, several important characteristics of both ices and hydrates stability are described. These data are used for proposing a new model which computes the thermodynamical characteristics of the liquid layer within Titan. This provides new constraints on the temperature and composition fields within the liquid layer of Titan which indicates that the dissociation of methane clathrates in the deep interior is almost impossible. In the last part, the methane clathrate behavior within the different layer of Titan's interior is investigated. Due to the density contrasts between methane clathrates and ices, it will be shown that methane is certainly trapped within large clathrate reservoirs below the upper conductive lid of Titan. Further ascent and dissociation of clathrate into gaseous methane + ice must then be associated with tectonic and/or volcanic processes which allow rapid ascent without cooling of clathrates. Indeed, the dissociation is only possible at very shallow depth only if hot material from the ice layer can reach the surface rapidly.

Absorption characteristics of ammonia-water system in the cylindrical tube absorber

Experimental analysis was performed in a cylindrical tube absorber which is considered to be suitable for the bubble mode. Characteristics such as concentration, temperature, and pressure were measured and they reflected the condition of absorber well. The variation of characteristics was conspicuous near the inlet region of the ammonia gas. The ammonia gas and the solution flowed cocurrently and countercurrently and the results were compared.

Comparative Investigations of Non-adiabatic Absorption in Film Flow and Bubble Flow

Comparative non-adiabatic absorption experiments were carried out using the ammonia–water system under different two-phase flow regimes. Because of the small thickness of the film, the falling film as a separated two-phase flow shows an effective dynamic and transport behavior. The hydrodynamics and heat transfer modeling is sufficiently exact and the measurement of the interface temperature allows the discussion of the axial local partial resistance of the heat transfer in the falling film.

Thermally controlled bubble collapse in binary solutions

This paper theoretically analyzes thermally controlled bubble collapse in binary solutions. Using a finite difference approach with an adaptive grid, three aspects of bubble collapse are investigated: counter-diffusion, initial bubble diameter, and absorber cooling rate. Results illustrate how counter-diffusion of the absorbent, acting to preserve the bubble life span, is offset by convective mass transfer arising from bubble interface motion. Predicted bubble mass transfer rates for an ammonia water system increase with the square of the bubble radius (diameters: 1.8–5.6 mm) and with increased absorber cooling rates. Model predictions compare well with simple semi-empirical correlations for bubble heat and mass transfer coefficients.

Potential applications of artificial neural networks to thermodynamics: vapor–liquid equilibrium predictions

The associative property of artificial neural networks (ANNs) and their inherent ability to “learn” and “recognize” highly non-linear and complex relationships finds them ideally suited to a wide range of applications in chemical engineering. Dynamic Modeling and Control of Chemical Process Systems and Fault Diagnosis are the two significant applications of ANNs that have been explored so far with success. This paper deals with the potential applications of ANNs in thermodynamics — particularly, the prediction/estimation of vapor–liquid equilibrium (VLE) data. The prediction of VLE data by conventional thermodynamic methods is tedious and requires determination of “constants” which is arbitrary in many ways. Also, the use of conventional thermodynamics for predicting VLE data for highly polar substances introduces a large number of inaccuracies. The possibility of applying ANNs for VLE data prediction/estimation has been explored using the back propagation algorithm. The methane–ethane and ammonia–water systems have been studied and the VLE predictions have been found to be accurate to within ±1%. Preliminary results confirm exciting possibilities of ANNs for applications to thermodynamics of mixtures. Advantages and limitations of this application are also discussed. An heuristic approach to reduce the trial and error process for selecting the “optimum” net architecture is discussed.

Enthalpy of dilution in aqueous systems of single solutes ammonia, sodium sulfate and ammonium sulfate: Experimental results and modeling

The enthalpy of dilution in the sodium sulfate-water, ammonium sulfate-water and ammonia-water systems was measured at temperatures from 313 to 373 K with a Calvet-type batch calorimeter using specially designed mixing cells. The mixing cells allow to pressurize the solutions. The formation of a gas phase during the experiments is thus avoided. Experimental results for the enthalpy of dilution are reported and compared to literature data and correlations.

The Ammonia–Water System and the Chemical Differentiation of Icy Satellites

We report the discovery of the first high-pressure polymorphs of ammonia hydrates: ammonia monohydrate II and ammonia dihydrate II. The subsolidus transitions and melting curves of these substances are shown by their volume–temperature functions; uncalibrated calorimetry corroborates these phase changes. From 20 to 300 MPa ammonia dihydrate and ice melt at a eutectic to form water-rich liquids; at lower and higher pressures, ammonia dihydrate melts incongruently to ammonia-rich liquids. The new data are consistent with independently known thermodynamic parameters of the ammonia–water system. These results fill in an important region of pressure–temperature space not previously studied; a body of previous data reported by other investigators covers a complementary region (higher pressures), but in the light of the new data those earlier results now appear to have been misinterpreted. We show that a suitable reinterpretation of the previous data supports the identification of at least one high-pressure polymorph of each compound. The behavior of the system H2O–NH3in many ways follows that of MgO–SiO2, and the roles of ammonia–water in icy satellite evolution may parallel those of magnesium silicates in Earth's structure, volcanism, and deep mantle tectonism. Pressure-related effects, including a pressure influence on the ammonia content of cryomagmas, might be significant in determining some potentially observable aspects of cryovolcanic morphologies, surface compositions, and interior structures of icy satellites.

Comparative simulation and investigation of ammonia-water: absorption cycles for heat pump applications

Several recent programs in absorption research have focused on technology for domestic heating and cooling utilizing natural gas. In residential and small commercial size applications, ammonia-water cycles offer the possibility of a gas-fired heat pump for both winter heating and summer cooling, at better year-round COPS than currently available by various alternatives. Several cycles have been considered for this purpose, ranging from the simplest single effect to the GAX (Generator-Absorber heat eXchange) with its different variations. Detailed calculations of ammonia-water systems are rather difficult, particularly in complex cycles such as the GAX. This may be the reason that relatively few simulation studies have been published to date that give more than design point performance. The objective of the present study has been a comprehensive investigation of various ammonia-water cycles, with operating conditions and different design parameters varied over a wide range to compare their performance. To this end, a modular simulation program (ABSIM) was employed, which makes it possible to simulate absorption cycles in varying configurations. The cycles investigated increase in complexity from the basic single-effect cycle, through the same cycle with an added precooler, through an added solution-cooled absorber and solution-heated generator, to the GAX and branched GAX cycles with different types of branching. Each cycle was formed on the basis of the previous one by adding one or two components at each stage, resulting in increasing complexity rewarded by improved performance. This kind of investigation enabled determination at each stage of the influence of the added components on the cycle. The results of the investigation show cooling CON ranging from about 0.5 for the simplest single-effect cycle to about 1.0 for the GAX cycle.

Simple functions for fast calculations of selected thermodynamic properties of the ammonia-water system

A set of five equations describing vapour-liquid equilibrium properties of the ammonia-water system is presented. They are intended for use in the design of absorption processes. Using variable dependences of technical relevance the equations make it possible to avoid iterative evaluations. The equations were constructed by fitting critically assessed experimental data using simple functional forms. They cover the region within which absorption cycles commonly used operate most often. The enthalpy of the gas phase has been calculated in the ideal mixture approximation. The results are presented in the form of an enthalpy-concentration diagram.