Ammonia-water Absorption Refrigeration Cycle Research Articles

Thermodynamical Analysis of the Distillation Column for Targeting Minimum Energy in Ammonia–Water Absorption Refrigeration Cycle

In this study, a comprehensive method to optimize distillation columns in ammonia–water absorption refrigeration, power, and cogeneration cycles is introduced. The novelty of this work lies in a comprehensive analysis of the distillation column's thermal performance and the introduction of a new design framework that maximizes heat integration. Key findings include the critical role of the solution heat exchanger, especially at lower generation and evaporation temperatures. Using a saturated liquid or two‐phase feed can achieve up to 80% efficiency at a feed composition of 0.3. Moreover, in the results, the substantial potential for improving the coefficient of performance (COP) through strategic design is highlighted. Notably, minimizing the pinch point temperature difference to 0 °C can boost the COP by 6%, while optimal feed placement can increase it by 9%. Incorporating feed preconditioning and side exchangers can lead to a 22% COP enhancement, indicating the significance of heat integration to the distillation column. In this study, a graphic guideline for selecting cycles that can achieve a minimum of 10% COP improvement without introducing unnecessary complexity is delivered and it suggests that distillation columns can be simplified by using a combination of separators, heaters, and coolers in certain cases.

Theoretical and experimental study of the ammonia water absorption refrigeration cycle with side reboiling and side condensing

In the conventional ammonia-water absorption refrigeration cycle, the rectification heat is usually dissipated to the surrounding environment, and the temperature of the weak solution flows at the bottom of the distillation column is normally high. This paper presents an improved cycle implemented with side reboiling by utilizing the heat content of the weak solution, and side condensing by recovering the rectification heat based on the single-effect cycle. The effect of feed thermal conditions and split ratio on the thermal performance of the improved cycle has been explored. The effectiveness of the improved cycle with respect to the single-effect cycle under different operating conditions has been examined. A more conservative effectiveness is selected in this work. The theoretical study demonstrates that the thermal performance of the improved cycle can be as high as 15% more than that of the single-effect cycle, and the improved cycle is more efficient when the heating source temperature or temperature lift is higher. A prototype is developed and tested for experimental verification. The experimental effectiveness ranges from 1.9% to 4.4% based on the test results. The relationship between system performance and temperature lift shows a close tendency with the theoretical results.

Energy and exergy analysis of a subfreezing evaporator environment ammonia-water absorption refrigeration cycle: Machine learning and parametric optimization

The coefficient of performance (COP) and exergy efficiency of a single and double-effect ammonia-water absorption refrigeration system powered by compound parabolic concentrating collectors were analyzed under various operating situations. A novel method was proposed using support vector machine regression and particle swarm optimization to identify optimal operating parameters. The optimal pressure-temperature conditions, including evaporator pressure (Pe), generator pressure (Pg), and absorber temperature (Ta) that maximize the COP and exergy efficiency while minimizing generator temperature (Tg) and evaporator temperature (Te), were investigated. The generator temperature was the main independent variable, ranging from 370 to 470 K. The findings demonstrated that the gain in COP and exergy efficiency caused by raising the generator temperature to more than 430 K is not cost-effective. The COP increased when the evaporator temperature increased along the investigated range of generator temperatures but yielded lower exergy efficiency in all cases. The exergy destruction rate in condenser, pump, recooler, reheater, and expansion valves is insignificant compared to other components. The generator has the highest exergy destruction rate regardless of operating conditions, making it the most crucial component of the absorption system. The optimization process findings showed that, at Pe = 2.8 bar, Pg = 14.5 bar, and Ta = 303.15 K, the maximum COP and exergy efficiency were 0.8483 and 0.3605, respectively, concerning the minimization of Tg and Te, which were 408 and 267 K, respectively. The model produced an acceptable performance with a high prediction accuracy (coefficient of determination > 0.99 and mean square error < 0.0064).

Thermodynamic Analysis of a New Combined Cooling and Power System Coupled by the Kalina Cycle and Ammonia–Water Absorption Refrigeration Cycle

In order to improve the utilization efficiency of low-temperature heat sources, a new combined cooling and power system using ammonia–water is proposed. The system combines Kalina cycle with absorption refrigeration cycle, in which the waste heat of the Kalina cycle serves as the heat source of the absorption refrigeration cycle. The steady-state mathematical model of system is established in detail first, and then the simulation results of design condition are obtained, which show that the thermal efficiency and exergy efficiency can reach 24.62% and 11.52%, respectively. Based on the system design condition, an exergy destruction analysis is conducted and shows that four heat exchangers and the turbine contribute most of the total exergy destruction. Finally, the effects of five key parameters on the system performance are examined, which reveal that within certain ranges, there is an optimal turbine inlet pressure that makes the exergy efficiency maximal. Increasing the ammonia–water temperature at the vapor generator outlet and the ammonia-weak solution temperature at the bottom outlet of the rectification column will reduce the thermal efficiency but raise the exergy efficiency. With the increase of rectification column pressure, both the thermal efficiency and exergy efficiency drop, while the evaporation pressure has an opposite effect on the system performance.

A new combined cooling and power system based on ammonia-water absorption refrigeration cycle: Thermodynamic comparison and analysis

In this paper, a new combined cooling and power (CCP) system, based on ammonia-water absorption refrigeration cycle, is proposed to utilize low-temperature heat sources effectively. The system is characterized by that an ejector is introduced to lower the turbine back pressure by the evaporated ammonia vapor used for cooling, and is appropriate for the working scenarios needing much cooling capacity but bits of electricity. The system mathematical models are set up in detail, based on which the data of the system design working condition are obtained by numerical simulation. The results show that the net power output of the proposed system is 13% more than that of a similar system without ejector and moreover the system thermal efficiency could approach 45%. By performance comparison with a cascade-type CCP system, the proposed system shows the advantages of simple structure and good economy. Finally a thermodynamic parameter analysis is carried out to investigate the effects of five parameters on the system performance. The results show that there is an optimal rectification column pressure leading to the maximal net power output. The increases of rectification column pressure, turbine back pressure and evaporation temperature have negative effects on cooling capacity and thermal efficiency of the system, while the increase of absorber pressure has positive effects on the two indicators. Especially for the increase of ammonia-weak solution temperature of rectification column bottom, all the system performance experiences a process of increasing sharply, increasing slowly and decreasing slightly.

Feasibility study on ammonia water absorption refrigeration cycle without distillation column

The water content in the refrigerant may undermine the cooling effect in ammonia water absorption refrigeration systems. Distillation column is normally implemented. The use of distillation columns, however, may increase system complexity, especially in practical operation. In fact, the distillation column can be eliminated under particular operating conditions. This paper presented an ammonia water absorption refrigeration cycle without distillation column, which is replaced by two separators and one heater. The resulting vapor is nearly pure with an ammonia mass fraction of 0.998. Heat exchanger network analysis is carried out for searching all the potential heating-saving possibilities. The thermal performance was improved by the combination of solution recirculation and absorption heat recovery, and the results indicated that the thermal performance has been increased by 42.6% than that of the basic cycle at certain working condition. The proposed cycle has limited ranges of working conditions operated under small temperature lifts,and the payback period is 4.28years.

Comparative analyses of a novel solar tower assisted multi-generation system with re-compression CO2 power cycle, thermoelectric generator, and hydrogen production unit

In the present paper, a new energy generation system is suggested for multiple outputs, including a hydrogen generation unit. The plant is powered by a solar tower and involves six different subsystems; supercritical carbon dioxide (sCO2) re-compression Brayton cycle, ammonia-water absorption refrigeration cycle, hydrogen generation, steam generation, drying process, and thermoelectric generator. The thermodynamic assessment of the multi-generation system is carried out for three different cities from Turkey, Iran, and Qatar. The energy and exergy efficiencies are calculated for base conditions to compare the different locations. The operating output parameters for the suggested system and simple re-compression Brayton system are compared. A parametric analysis is also done for investigating the influences of different system variables on plant performance. According to the results, Doha city is found to be more effective due to its geographical conditions. Moreover, based on the comparative study, the proposed cycles produce more power than the basic re-compression cycle with 64.59 kW, 47.33 kW, and 52.25 kW for Doha, Isparta, and Tehran, respectively. Additionally, the analyses revealed that in the term of energy efficiency, the suggested system has 32.29%, 32.28%, and 32.29% better performance than the simple cycle, and in terms of exergy efficiency, it has 4%, 4.8%, and 5% better performance than the simple cycle in Doha, Isparta, and Tehran, respectively.

Performance of a Hybrid TEG/Single Stage Ammonia-Water Absorption Refrigeration Cycle with a Combined Effect of Rectifier and Condensate Precooler

In this article, a single stage ammonia-water absorption refrigeration cycle integrated with thermoelectric power generators driven by evacuated tube solar collectors is presented and investigated. The working fluid is ammonia-water solution, and the hybrid system was modeled, and analyzed using EES software. The system coefficient of performance (COP) was found to increase with increasing the generator temperature. From the results obtained, when the cycle operated with 0.99 ammonia mass fraction, it was found that the best location of the thermoelectric generators is at the rectifier between the generator and the condenser where the value of COP exceeds 0.82 at temperature difference across the TEG of 60℃. The other locations, between condenser-evaporator and evaporator-absorber, show similar performance.

Exergy analysis of a hybrid thermoelectric generator/two-stage double-lift aqua-ammonia absorption cooling system

Nowadays, absorption refrigeration cycles using renewable energy or waste heat are very attractive. A hybrid thermoelectric generator/two-stage double-lift ammonia-water absorption refrigeration cycle powered by an evacuated tube solar collector was examined. A detailed thermal analysis was carried out by means of the engineering equation solver. The typical location to install a thermoelectric generator was found to be after the evaporator and desorber 2. The coefficient of performance improves from 0.2 to 0.5 when the temperature difference after desorber 2 is raised from 5°C to 19°C. Installing TEGs after desorber 1 and condenser improves cycle performance by 0.153 and 0.168, respectively.

Heat and mass transfer in falling films technology applied to the generator and the rectifier of an ammonia-water absorption refrigeration cycle

Powering ammonia-water absorption refrigeration cycles with solar energy demands an operating temperature above 170 ∘C for the proper generator operation when conventional flooded generator technologies are used. However, the falling film technology operates at a lower temperature due its superior heat and mass transfer performance. Therefore, an experimental investigation focused on the energy balance along with a heat and mass transfer analysis between liquid and vapor ammonia-water mixtures in the generator and the rectifier have been developed. Four experimental sets of runs were carried out for oil temperatures at 111 and 136 ∘C, strong solution mass fraction between 0.37 and 0.47, two rectification temperatures at 34 and 63 ∘C, and a strong solution mass flow rate of 0.016-0.027 kgs−1. Heat transfer rates for both components were computed by overall energy balances over the components. Moreover, the latent heat and sensible heat rate were calculated. The results indicated that the heat transfer process in the rectifier was lower for the minimum generation temperature. The maximum heat transfer coefficients for the liquid and vapor phase were respectively 5476 and 26Wm−2∘C−1. Analogously, the maximum mass transfer coefficients between the liquid film and vapor phase were 1.27·10−4 and 3.25·10−2ms−1.

An integrated structure of bio-methane/bio-methanol cogeneration composed of biogas upgrading process and alkaline electrolysis unit coupled with parabolic trough solar collectors system

Bio-methanol and bio-methane are flexible fuels that are easily stored and considered as a sustainable alternative energy source due to high octane numbers. In particular, herein biogas is used as a potential fuel for producing bio-methanol and bio-methane. Biogas is mainly composed of methane (CH4) and carbon dioxide (CO2). In this paper, a novel integrated system consists of a biogas upgrading process to pure bio-methane production, a bio-methanol synthesis unit, an alkaline electrolysis unit to produce hydrogen, an organic Rankine cycle (ORC) for power generation, an ammonia/water absorption refrigeration cycle (ARC) for cooling production, and a parabolic trough solar collectors (PTSCs) system is introduced and thermodynamically assessed. Co-generation of bio-methanol and bio-methane results in CO2 emissions reduction. ASPEN HYSYS, TRNSYS, and MATLAB software were used for the simulation of this integrated system. For the simulation of PTSCs, the geographical location of Bandar Abbas with a longitude 56.26° and latitude 27.17° was used. The proposed structure produces 128.4 kgmole/h bio-methanol with a purity of 99.99% and 193.4 kgmole/h bio-methane with a purity of 99.65% as the main products, and also, 2783 kW cooling and 241,930 kgmole/h domestic hot water as by-products. The PTSCs system provides 314.5 MW thermal energy for the ORC. The required hydrogen for bio-methanol synthesis is provided by an alkaline electrolysis unit, which generates 200 and 400 kgmole/h O2 and H2, respectively. The energy, exergy, and parametric analyses were conducted to assess the thermodynamic performance of the proposed system. The overall energy and exergy efficiencies of the integrated system are 92.47% and 45.92%, respectively. The results of the exergy evaluation revealed that the lowest exergy efficiency and the largest exergy destruction rate is related to the PTSCs system with values of 60.03% and 88867.08 kW, respectively. Moreover, at the design condition, the energy and exergy efficiencies of the PTSCs system are 30.69% and 60.03%, respectively.

Performance assessment and optimization of a novel geothermal combined cooling and power system integrating an organic flash cycle with an ammonia-water absorption refrigeration cycle

The organic flash cycle is an efficient low-grade energy conversion technology. However, a large space is left for the organic flash cycle to improve the useful energy output due to the throttling processes. To utilize the thermal energy before the low-pressure throttling process in the organic flash cycle driven by the geothermal energy, an ammonia-water absorption refrigeration cycle is adopted to generate cooling by using this part of heat, thereby forming a novel geothermal combined cooling and power (Geo-CCP) system. Eight different organic flash cycle working fluids are investigated, including n-Nonane, n-Octane, n-Heptane, Cyclopentane, i-Pentane, n-Pentane, R365mfc, and R245fa. Detailed thermodynamic modeling, thermoeconomic analysis, parametric analysis, system optimization, and exergy analysis are carried out for the proposed system. The results show that the total product unit cost and exergy efficiency of the proposed systems are 6.52–11.03% lower and 4.10–5.31%pt (percentage point) higher than those of the geothermal separate cooling and power systems. Among the eight considered organic fluids, the n-Nonane brings the lowest total product unit cost and highest exergy efficiency to the Geo-CCP system (11.20 $·GJ−1 and 37.58%). Exergy analysis indicates that the flasher and condenser-I have the first and second highest exergy destructions.

Multi-objective optimization for a small biomass cooling and power cogeneration system using binary mixtures

This paper aims to find the optimal design for a small-scale cogeneration system using the Organic Rankine cycle (ORC) integrated with an ammonia-water absorption refrigeration cycle. The thermodynamic model included two ORC configurations (with and without an internal heat exchanger) and used eight Siloxanes and their possible mixtures as working fluids. Additionally, the effects of six design parameters were investigated, these being evaporation pressure, superheating, pinch point temperature, condensation pressure, internal heat exchanger effectiveness, and mass fraction in binary mixtures. A multi-objective genetic optimization algorithm (NSGA-II) was employed in order to evaluate the Pareto optimal solutions, maximizing electrical and cooling power and minimizing the overall global conductance, variables that have the greatest influence on the technical and economic performance of the cycle. Pareto optimal solutions present trade-offs between three objective functions, where optimum solutions are found within power generation ranges with overall energy efficiency between 18 and 30%. MM, MM/MD4M, MDM/MD4M and MDM/D5, stand out as the best options for working fluids, with net power output between 700 and 1170 kW, cooling capacity between 80 and 1050 kW, and the product of overall heat transfer coefficient and overall global conductance in the range of 120–620 kW/K.

Waste heat cascade utilisation of solid oxide fuel cell for marine applications

To cope effectively with the world’s energy shortage and environmental pollution, a fuel cell combined with waste heat recovery technology has gradually become the best option for large ship power generation equipment. In this investigation, a combined system comprising a solid-oxide-fuel-cell-gas-turbine subsystem, supercritical carbon dioxide cycle, organic Rankine cycle, ammonia-water absorption refrigeration cycle, and high-pressure reverse osmosis desalination plant is introduced and analysed. Not only the power output of the system is calculated, but also the contribution of cold energy is considered by calculating its equivalent power. The results illustrate that the equivalent net output and thermal efficiency of the system are 278.82 kW and 67.03%, respectively. Compared with the solid oxide fuel cell, the power output increases by 86.35 kW and the fuel efficiency increases by 20.7%. Additionally, the system can provide 5.95 kW of cold energy and 0.94 m3/h of fresh water for the crew under the condition of maximum power output. To summarize, the proposed novel system design can realize the combined production of cold energy, electric energy, and fresh water, and it exhibits the characteristics of high efficiency and cleanliness.

Developing an integrated structure for simultaneous generation of power and liquid CO2 using parabolic solar collectors, solid oxide fuel cell, and post-combustion CO2 separation unit

With decreasing underground resources and increasing carbon dioxide levels, human beings are forced to use renewable energies and new methods for power generation and CO2 elimination. In this paper, an integrated structure is developed for generating power and liquefying CO2 using parabolic solar collectors, solid oxide fuel cell, CO2 power generation cycle, separation unit, and CO2 liquefaction. This integrated structure generates 346.5 kW power, 82.2 kW heat and 158.7 kg/h liquid CO2. The hot flow outlet of the solid oxide fuel cell is used to supply the CO2 power generation cycle and enter the post-combustion CO2 separation unit. The parabolic solar collectors with climatic conditions in Tehran, Iran, are used to supply the heat of integrated structure and the ammonia-water absorption refrigeration cycle is employed to supply cooling for CO2 liquefaction. This integrated structure has a total thermal energy efficiency of 40.81% and SOFC electrical efficiency of 61.71%. Economic analysis is illustrated that the period of return and the prime cost of product are 6.26 years and 0.0855 US$/kWh, respectively. To simulate the developed integrated structure, the TRNSYS, HYSYS, and MATLAB software are used. Then, using the sensitivity analysis, the effects of fuel utilization coefficient, inlet flow temperature on gas turbine and fuel cell temperature on the performance of the integrated structure are investigated.

Performance improvement of biomass-fueled closed cycle gas turbine via compressor inlet cooling using absorption refrigeration; thermoeconomic analysis and multi-objective optimization

Compressor inlet air cooling is a practical and applied methodology to enhance the conventional open cycle gas turbine power plants. This methodology in this paper, is proposed to be applied on an innovative biomass-fueled Closed Cycle Gas Turbine (CCGT), in which the exhaust gas waste heat is utilized to run an ammonia-water absorption refrigeration cycle for compressor inlet cooling. Thermoeconomic analysis is presented to investigate the two systems (with and without inlet cooling) and multi-objective optimization is conducted to compare their performances at optimal operating conditions. Levelized Cost of Electricity (LCOE) and exergy efficiency are selected as the two rational objectives. The results indicated that, for all the practical range of operating conditions, compressor inlet cooling significantly improves the system performance in terms of both thermodynamics and economics, despite the additional costs imposed on the overall system by adding the absorption refrigeration cycle. It is found that, under the optimal operating conditions, incorporation of compressor inlet cooling results in an improvement of net power and exergy efficiency by 30.1%, meanwhile the LCOE would be reduced by 22.5% when inlet cooling is employed.

Performance investigation of a new geothermal combined cooling, heating and power system

In this paper, a new geothermal combined cooling, heating and power system that integrates flash power cycle and ammonia-water absorption refrigeration cycle, is proposed to supply electricity, refrigerant water and domestic hot water simultaneously to users. In the system, the refrigeration cycle serves as the bottom cycle of the power cycle by further utilizing the exhausted geothermal water from the flasher of the power cycle, meanwhile all waste heat of the power and refrigeration cycles is recovered for supplying heat, thus effectively improving the energy conversion efficiency of whole system. This paper establishes detailed mathematical models of the proposed system and conducts a valid model validation. Then a preliminary design condition of the system is given and the results show that the exergy efficiency of system could reach 43.69% under the condition of 170 ℃ geothermal water. An exergy loss analysis is carried out based on the design condition, demonstrating that the maximal exergy destruction exists in the condenser of flash cycle, accounting for 48.53% of the total exergy destruction of the system; the components used for separating or mixing fluids including rectification column, absorber and flasher, occupying 17.68%, 9.02% and 9.30% respectively, are prone to generate exergy destructions. Finally a thermodynamic parameter analysis, in order to assess the effects of seven key parameters on the system performance, is performed. The results show that there are an optimal flash pressure (about 300 kPa) and an optimal generator temperature (about 120 ℃) respectively that could make the exergy efficiency of system maximal. Within some scopes, lower turbine back pressure and rectification column pressure, higher ammonia concentration of ammonia-strong solution, bring about higher exergy efficiency of system. Additionally the evaporation pressure and the reflux ratio of rectifier just make little difference on the exergy efficiency of system.

Proposal and assessment of a combined cooling and power system based on the regenerative supercritical carbon dioxide Brayton cycle integrated with an absorption refrigeration cycle for engine waste heat recovery

This paper proposes a novel combined cooling and power (CCP) system based on a regenerative supercritical carbon dioxide Brayton cycle (sCO2 cycle) and an ammonia-water absorption refrigeration cycle (ARC) for engine waste heat recovery. In the proposed system, the supercritical carbon dioxide Brayton cycle absorbs the waste heat of the internal combustion engine to generate power, and the absorption refrigeration cycle utilizes the low-grade energy in the supercritical carbon dioxide turbine exhaust to provide cooling. Firstly, energy and exergy analysis is performed on the combined cooling and power system. Then, detailed parametric analysis is carried out to study the effects of key parameters, such as the compressor outlet pressure, turbine inlet temperature, generator hot-end temperature difference, and evaporator temperature on the exergy efficiency and total product unit cost. Finally, the non-dominated sorting genetic algorithm II is adopted for multi-objective optimization to obtain the maximum exergy efficiency and the minimum total product unit cost. Multi-objective optimization results reveal that better thermodynamic and economic performances can be obtained by lowering the evaporator temperature. Compared with the single regenerative supercritical carbon dioxide system, the proposed system can increase the exergy efficiency by 2.29–2.54%pt (percentage point), and the thermal efficiency by 8.16–18.93%pt, but might increase the total product unit cost. Under different evaporator temperatures (−10–10 °C), the proposed system can generate 248.19–253.90 kW of net power output, accounting for 8.48–8.67% of the rated power output of the engine, and produce 70.57–168.86 kW of cooling capacity by consuming 0.445–0.532 kW of pump work. In addition, exergy destruction analyses indicate that the components in the bottoming ARC generally have less exergy destructions.

Computer Simulation of an Ammonia-Water Absorption Cycle for Refrigeration: Using a Distillation Tower to Replace the Generator

By using a distillation tower as the regenerator, the coefficient of performance (COP) of the ammonia-water absorption refrigeration cycle is calculated in this work. Two types of distillation towers, namely an equilibrium-stage tower with a total condenser and a packed-bed tower with a partial condenser, are used in the cycle. From the simulation results, it is found that both types of distillation towers can successfully increase the COP of the cycle due to increased ammonia concentration in the vapor phase of the ammonia-water refrigerant. It was also found that the tower equipped with a partial condenser provides higher COP than that of the tower equipped with a total condenser. The value of COP can be further increased when the generator is replaced by the packed-bed tower in this water-ammonia absorption cycle. The effects of the mass flow rate ratio of NH3/H2O, stage number, reflux ratio and energy duty of the tower on the COP of the cycle are also studied in the present paper.

Exergy analysis and optimization of a combined cooling and power system driven by geothermal energy for ice-making and hydrogen production

This paper investigates a combined cooling and power system driven by geothermal energy for ice-making and hydrogen production. The proposed system combines geothermal flash cycle, Kalina cycle, ammonia-water absorption refrigeration cycle and electrolyser. The geothermal energy can be efficiently converted to storable hydrogen and ice. Based on mathematical model, some key parameters are analyzed to figure out their effect on the exergetic performance. An exergy destruction analysis for all components has been performed to find out the distribution of exergy inefficiency. The system exergetic efficiency is optimized by Jaya algorithm and Genetic algorithm and the optimization results are compared. According to the parametric analysis, the exergy efficiency decreases as the back pressure of steam turbine and the back pressure of ammonia-water turbine increase. The exergy efficiency could increase first and then decline, as flash pressure, ammonia-water turbine inlet pressure and ammonia mass fraction of basic solution increase. The optimization results show that the exergy efficiency reaches 23.59%, 25.06% and 26.25% when the geothermal water temperature is 150 °C, 160 °C and 170 °C. Jaya algorithm has highly precise optimization results.