Absorption Heat Transformer System Research Articles

Comparative analysis of thermodynamic performance of high-temperature absorption heat transformers using various ionic liquids as working pairs

The study investigated six sets of ionic liquid (IL) working pairs based on high-temperature vapor-liquid equilibrium data. These sets were modeled using the NRTL activity coefficient model and integrated into a single-stage absorption heat transformer (AHT) for system cycle simulation analysis. A comparison was made with traditional H2O + LiBr working pairs commonly used in AHTs. The study aimed to assess the feasibility of using IL working pairs in high-temperature AHTs to achieve higher output temperatures when dealing with heat sources exceeding 120 °C. Compared to the traditional H2O + LiBr working pair, which has strong COP and ECOP but a limited temperature range, IL pairs offer advantages under various conditions. For instance, H2O + [HMIM][Cl] and H2O + [BMIM][Br] can operate at higher condensation temperatures, providing broader temperature ranges. H2O + [HMIM][Cl] has a wider operational temperature range, suitable for unstable waste heat sources. It also has the highest optimal ECOP value of 0.64 at 197 °C absorption temperature, and shows good cyclic performance, achieving temperature rises of about 78 °C. ILs can maintain stable COPs and circulation ratios over a wide range of absorption temperatures, thus achieving higher temperature rises or meeting the need for higher absorption temperatures. Notably, although the H2O + IL combination exhibits slightly higher exergy loss than the traditional H2O + LiBr pair when comparing exergy losses in the AHT system among different working pairs, its low corrosiveness, lack of crystallization, and wide operating temperature range make these drawbacks insignificant.

Advanced exergy analysis of a double absorption heat transformer recovering industrial waste heat for pure water production

Conventional and advanced exergy analyses are applied for a double absorption heat transformer system utilizing low-grade industrial waste heat for water purification. The conventional method provides information about the location and magnitude of inefficiencies and does not consider any interaction among components regarding the irreversibility occurring in them. The advanced exergy technique however, exposes the real origins of irreversibilities and latent potential for enhancement of each system component, along with reflecting mutual interaction between components. The simulation of the cycle is carried out with engineering equation solver software. The results show that the overall improvement potential of the cycle is only 16%. Also, the mutual interdependency between components is found to be weak as 97% of the total exergy destruction appeared as endogenous. Furthermore, considering endogenous avoidable exergy destruction, the improvement strategy of components obtained by advanced exergy method is disparate from conventional one. Results of the advanced exergy suggest this order: condenser, absorber, evaporator, absorber/evaporator assembly, generator assembly, economizer 1, and economizer 2. Additionally, a parametric investigation is performed to assess the sensitivity of splitting exergy destruction to the variation of heat source temperature for highlighting improvement opportunities. The results indicate that the condenser yields the highest amount of avoidable endogenous exergy destruction in the entire studied temperature range.

Numerical and experimental investigation of the dynamic performance of absorption heat transformers under different solution conditions

Abstract An experimental investigation and dynamic simulation of vertical falling-film LiBr/H2O absorption heat transformer systems have been reported in this paper. The established 20 kW experimental equipment was used to test the dynamic performance and verified the mathematical model. The experimental results show that there is a time delay between the input heat and output useful heat, and the time delay of the experimental results is 115 s. The simulated results show that the response time increases with increasing total solution mass and increases with decreasing solution mass flow rate. The temperature flow oscillations decrease with increasing total solution mass and decrease when the solution mass flow rate decreases. The response time of the absorption heat transformer is almost linearly related to the characteristic time of solution storage, which provides guidance for the operation and prediction. By adjusting the total solution mass and solution mass flow rate, theoretically the response time can be reduced to approximately 150 s. The temperature change range of the absorber outlet water can be controlled within 0.5 K by reducing the solution mass flow rate. The total solution mass and mass flow rate should be reduced, which can reduce temperature flow oscillations and shorten the time delay. The response time can be predicted by combining the experimental data and the linear relationship of the response time for any absorption heat transformer.

Integration of LiBr/H2O Absorption Heat Pump and Absorption Heat Transformer in Total Site Heat Integration

Energy efficiency is one of the main solutions to reduce CO2 emissions in the energy sector and improve primary energy intensity. Energy savings are at the centre of the numerous advantages of energy efficiency and connect to many other economic, social and environmental advantages. Total Site Heat Integration (TSHI) was introduced to maximise the heat recovery from various processes through a centralized utility system. Heat pump using absorption cycle has been identified as one of the waste heat recovery techniques. The challenges of heat pumps applications include limited temperature applications and long payback periods. However, these problems can be tackled by proper design and suitable types of heat pumps considerations. This paper integrates two different kinds of absorption cycle heat pump which are absorption heat pump (AHP) and absorption heat transformer (AHT) into the context of TSHI. This integration is able to reduce the industrial waste heat and generate quality steam. The heat generation of AHP and AHT are estimated based on the enthalpy of working fluid pair of water-lithium bromide. A case study is done to compare and verify the proposed methodology. Economic analysis is performed to compare the different integration approaches of AHP and AHT. Results showed that the integration of hybrid AHP and AHT contribute to the highest annual saving (21,351 USD/y) of utility cost compared to 12,356 USD/y for AHP system and 9,119 USD/y for AHT system.

Energy, exergy, economy analysis and multi-objective optimization of a novel cascade absorption heat transformer driven by low-level waste heat

To solve the increasingly serious global energy problem, an innovative cascade absorption heat transformer system using industrial low-level waste heat is presented in this paper. Based on an accurate model and simulations, the cascade system is studied in terms of an energy, exergy, and economy analysis. To achieve a trade-off between the thermodynamic and economic performance, a multi-objective optimization method is used to optimize the system. The thermodynamic performance (total exergy destruction) of the multi-objective optimized design is 3.64% higher than its ideal minimum value, while the economic performance (total annual cost) is 2.74% higher than its ideal minimum value. This indicates that the multi-objective optimization scheme can provide better comprehensive performance than single optimization schemes for the cascade absorption heat transformer system. In addition, the results show that the exergy destruction rate is 74.30%. The exergy destruction of the NH3/H2O system accounts for 55.62% of the total input exergy; thus, improvements of this system should be prioritized.

Analysis of single stage steam generating absorption heat transformer

Absorption heat transformer (AHT) has played a role in producing available heat from the low temperature of waste heat sources. This study proposes two operating modes regarding the way to supply heat source to the AHT system, and aims to investigate the operating characteristics of the steam generating AHT system concerning heating source temperature. First, this study describes the thermodynamic cycle of the single stage AHT operating with water-lithium bromide pair, and two operating modes are illuminated: a forward flow mode for heat source input to the evaporator and then to the generator, and a reverse flow mode for heat source input to the generator and then to the evaporator. Second, the first law of theoretical simulation characterizes the effects of the different operating modes on the heat transfer rates of each AHT component, the coefficient of performance (COP), and the steam generation rate. The experimental studies validate the theoretical simulation models; consequently, the results obtained herein lay a foundation of further investigation for the thermodynamic characteristics of the steam generating AHT system to maximize the operating performance.

A distributed energy system with advanced utilization of internal combustion engine waste heat

New trigeneration system consists of an internal combustion engine, a power and cooling cogeneration system and an absorption heat transformer system. The exhaust gas is recovered by the power and cooling cogeneration subsystem producing the cooling and power. The jacket water is recovered by the absorption heat transformer subsystem producing lowpressure steam. The exergy performance and the energy saving performance which is evaluated by the primary energy saving ratio of the new distributed energy system are analyzed. The effects of the ratio of the output power and cooling of the power and cooling cogeneration subsystem and the generator outlet temperature of the absorption heat transformer subsystem to the primary energy saving ratio are considered. The contributions of the subsystems to the primary energy saving ratio are quantified. The maximum primary energy saving ratio of the new distributed energy system is 15.8%, which is 3.9 percentage points higher than that of the conventional distributed energy system due to the cascade utilization of the waste heat from the internal combustion engine.

Exergy Analysis of Various Absorption Heat Transformer Systems Using Classical and Modified Gouy–Stodola Equation

In the present study, performance evaluation of three different configurations of absorption heat transformer (AHT) is carried out by supplying the waste heat of same mass and same temperature; and exergy analysis is done using both the classical and modified Gouy–Stodola equation. For this a mathematical model is developed for all the three arrangements in Engineering Equation Solver. Water–lithium bromide is used as a working pair. The results of exergy destruction with classical and modified Gouy–Stodola equation are compared for different systems. Further various operating parameters are varied to predict the performance of the systems on the basis of second law analysis. The result showed that the amount of hot fluid produced in absorber is more for system 3 as compared to other configurations. The irreversibility calculated by the modified approach comes out to be 25.78%, 23.60%, and 23.45% more than the exergy destruction obtained by the classical approach in the three cases, respectively. Thus, there is a need to employ the modified approach of Gouy–Stodola equation for calculating the real irreversibility which helps in predicting the scope of improvement and the performance of the system more accurately.

Simulation and optimization of novel configurations of triple absorption heat transformers integrated to a water desalination system

A thermodynamic analysis of six different configurations of triple absorption heat transformer systems (TAHTs) utilizing H2O/LiBr as the working pair which is integrated into water desalination systems is conducted in this study. The energy source of the desalination system is provided by the high temperature heat of the absorbers of TAHTs by utilizing the waste heat from a textile factory. A computer program is developed in the EES (Engineering Equation Solver) to study the performance of the system such as; COP, ECOP, distilled water, and absorber utilized heat, and also to optimize them in six different configurations. It is shown that modified configurations of TAHTs can increase the COP and fresh water productivity rather than that of conventional systems. The results indicated that the optimized amount of distilled water produced by the last configuration which is 0.1307kg/s can supply 1131 residential units.

Heat Recovery of a Diammonium Phosphates Drying Unit

Solid product drying is a widely used unit operation in the chemical industry. It is highly energy intensive, requiring hot, dry air streams at high temperatures to dry a wide range of products. Exhaust air from a dryer is usually vented to the atmosphere with little or no heat recovery. In the present work, a study was performed to analyze the performance of an absorption heat transformer (AHT) applied to the evaluation of thermal rejections of drying unit of diammonium phosphates (DAP). First, a basic AHT system is described and the operating sequence is explained. Next, an application of the AHT system to an industrial company is analyzed. A numerical simulation of the system using Aspen Plus software was performed to determine the effect of different parameters on the AHT system performance and the results are presented in graphical form.

Heat Transfer and Thermodynamic Performance of LiBr/H2O Absorption Heat Transformer with Vapor Absorption Inside Vertical Spiral Tubes

In this paper, an absorption heat transformer (AHT) with falling film of aqueous LiBr solution inside vertical spiral tubes is installed and tested. The variations of coefficient of performance (COP), thermal efficiency (Eth ), and the heat transfer coefficient of the absorber at different falling film flow rates, hot water flow rates, and operating temperatures are investigated experimentally. The results demonstrated that the coefficient of performance and thermal efficiency of the system decrease with the increase in the flow rate of LiBr solution, and the influence of flow rate of hot water on COP and Eth is insignificant. The available COP in the experiments is higher than 0.4. The heat and mass transfer coefficients of the absorber increase with the increase of the flow rate of LiBr solution, up to 400W/m2/K and 0.013 kg/m2/s (temperature of waste heat is 90°C). The heat transfer coefficient of the absorber increases with the increase of the temperature of waste heat, and decreases with the increase of the cooling water temperature. Meanwhile, the computer code ABSIM (Absorption Simulation) is used to simulate the AHT systems, and the simulated results are compared with the experimental data.

Alternative absorption heat transformer configurations integrated with water desalination system

Alternative configurations of absorption heat transformer (AHT) systems using LiBr/H2O as the working fluid and integrated with a water purification system are analyzed and optimized thermodynamically. The waste heat from a textile factory is utilized to run the AHT systems and the generated high temperature heat is employed for the purpose of desalination. A computer program is developed in EES (Engineering Equation Solver) to investigate the effects of different parameters on four different configurations of AHT and the desalination system. It is shown that applying different modifications can increase the coefficient of performance (COP) of the AHT and consequently the productivity of the desalination system. The maximum rate of distilled pure water reaches 0.2435kg/s when waste heat from the condenser is utilized by the evaporator. Finally, the risk of crystallization of LiBr is lowered in the modified configurations.

ANN and ANFIS Models for COP Prediction of a Water Purification Process Integrated to a Heat Transformer with Energy Recycling

The aim of this study is to demonstrate the comparison of an artificial neural network (ANN) and an adaptive neuro fuzzy inference system (ANFIS) for the prediction of the coefficient of performance (COP) for a water purification process integrated in an absorption heat transformer system with energy recycling. ANN and ANFIS models take into account the input and output temperatures for each one of the four components (absorber, generator, evaporator, and condenser), as well as two presures and LiBr+H2O concentrations. Experimental results are performed to verify the results from the ANN and ANFIS approaches. For the network, a feedforward with one hidden layer, a Levenberg-Marquardt learning algorithm, a hyperbolic tangent sigmoid transfer function and a linear transfer function were used. The best fitting training data set was obtained with three neurons in the hidden layer. On the validaton data set, simulations and experimental data test were in good agreement (R2>0.9980). However, the ANFIS model was developed using the same input variables. The statistical values are given in as tables. However, comparaison between two models shows that ANN provides better results than the ANFIS results. Finally this paper shows the appropriateness of ANN and ANFIS for the quantitative modeling with reasonable accuracy.

Effect of Low Pressure Generator temperature on the performance of double effect vapour absorption heat transformer

In this paper, the energy and exergy analysis of double–effect lithium bromide/water absorption heat transformer system is presented. All exergy destructed that exist in this system are calculated. In addition to the coefficient of performance and the exergy efficiency of the system, the quantum of exergy destructed of each component of the system is also estimated. The effect of Low Pressure Generator (LPG) temperature on the performance of the double–effect vapour absorption heat transformer is analysed. This study gives an indication of which component of the double–effect absorption heat transformer system should be developed.

A novel cogeneration system: A proton exchange membrane fuel cell coupled to a heat transformer

This study focuses on the potential of a novel cogeneration system which consists of a 5kW proton exchange membrane fuel cell (PEMFC) and an absorption heat transformer (AHT). The dissipation heat resulting from the operation of the PEMFC would be used to feed the absorption heat transformer, which is integrated to a water purification system. Therefore, the products of the proposed cogeneration system are heat, electricity and distilled water. The study includes a simulation for the PEMFC as well as experimental results obtained with an experimental AHT facility. Based on the simulation results, experimental tests were performed in order to estimate the performance parameters of the overall system. This is possible due to the matching in power and temperatures between the outlet conditions of the simulated fuel cell and the inlet requirements of the AHT. Experimental coefficients of performance are reported for the AHT as well as the overall cogeneration efficiency for the integrated system. The results show that experimental values of coefficient of performance of the AHT and the overall cogeneration efficiency, can reach up to 0.256 and 0.571, respectively. This represents an increment in 12.4% of efficiency, compared to the fuel cell efficiency working individually. This study shows that the combined use of AHT systems with a PEMFC is possible and it is a very feasible project to be developed in the Centro de Investigación en Energía (Centre of Energy Research), México.

Absorption heat transformers and an industrial application

Abstract Absorption Heat Transformer (AHT) systems are devices with the unique capability of raising the temperature of low or moderately warm waste heat sources to more useful levels. The study includes an investigation to analyze the AHT systems using water-lithium bromide solutions with water as the refrigerant. First, a basic AHT system was described, the operating sequence was explained and thermodynamic system analysis was presented. Next, an application of the AHT system to an industrial company was analyzed. A computer code was prepared to determine the effect of different parameters on the AHT system performance and the results were presented in graphical form. Additionally, it was shown that how the basic AHT system could be modified to increase the COP and the heat transfer at the absorber, in other words, the hot process water produced. The system performance data were presented in a tabular form for different system modifications from the base system for comparison. It was proven that, by applying different modifications, the COP could be increased by 14.1%, the heat transfer at the absorber by 158.5% and the hot process water produced by 3.59% compared to the basic AHT system.

Thermal seawater desalination: Possibilities of using single effect and double effect absorption heat transformer systems

Water and energy are two inseparable items that govern our lives and promote civilisation. The provision of fresh water is becoming an increasingly important issue in many areas in the world. Absorption heat transformer systems are attractive to use solar energy, geothermal energy and waste heat from industrial process as heat source and delivering thermal energy to higher temperature than the temperature of the fluid by which they are fed. In this paper a comparative study between single effect and double effect absorption heat transformer systems used for seawater desalination is carried out. The mathematical formulation will be based on mass, energy and exergy equations and conditions of thermodynamic equilibrium, considering lithium bromide–water as working mixture. Simulation results were used to study and to compare the influence of the absorber temperature and the intermediate heat source temperature (evaporator and generator temperatures) on the energy efficiency, exergy efficiency, and fresh water production of the two systems. The numerical results obtained will serve like a tool to predict the possibilities and limits of application of absorption heat transformers coupled to seawater desalination system.

Single stage and double absorption heat transformers in an industrial application

An industrial application of the single stage and double absorption heat transformer (AHT) systems using water–lithium bromide solutions with water as the refrigerant was analyzed. First, a basic single stage AHT system was described, the operating sequence was explained and thermodynamic system analysis was presented. Next, an application of the single stage AHT system to an industrial company was analyzed. A computer code was prepared to determine the effect of different parameters on the AHT system performance and the results were presented in graphical form. Additionally, the series and parallel double absorption AHT systems were introduced, the operating sequences were explained and thermodynamic system analysis was included. All results were presented in tabular form for comparison. It is concluded that about 50% of the waste heat can be utilized and the hot process water and vapor could be produced by applying single stage and double AHT systems, respectively. The parallel double AHT system could generate more vapor than the series double AHT system. Copyright © 2009 John Wiley & Sons, Ltd.

Application of absorption heat transformer to recover waste heat from a synthetic rubber plant

This paper reports the test results of the first industrial-scale absorption heat transformer (AHT) equipment in China, to recover the waste heat released from mixture of steam and organic vapor at 98 °C in coacervation section, synthetic rubber plant of Yanshan Petrochemical Corporation, Beijing, China. The recovered heat is used to heat hot water from 95 to 110 °C, feeding back to the coagulator as the supplementary heating source. The AHT system is operating with H 2O/LiBr solution with heat flow of 5000 kW. The coefficient of performance (COP), the thermal efficiency and the temperature lift of the AHT system are presented. The heat transfer characteristics of the AHT components, i.e. absorber, generator, evaporator, condenser and the liquid–liquid solution heat exchanger, are also illustrated by comparison of experimental data and the model calculated results. The results show that the mean COP is 0.47, the gross temperature lift of 25 °C can be realized and the payback period is ≈2 years.

Performance analysis of an irreversible cascaded heat-transformer

By employing an irreversible thermodynamic approach the optimum performance of an cascaded absorption heat-transformer system is investigated. To get closer to real machines, the effects of thermal resistances and internal irreversibilities on the performance of the cascaded cycle is considered. An improved equation for the coefficient of performance (COP) of the system under consideration was obtained. The analyses show that the cascaded cycle has a significant increase in the systems gross temperature lift (GTL) over the single stage heat-transformer.