Double Absorption Heat Transformer Research Articles

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.

Thermodynamic appraisal of utilizing compressor in double effect absorption heat transformer

In the current appraisal, three various designs of employing compressors in double-effect heat transformers are presented and evaluated from exergy and energy standpoints and collated with the simple configuration of mentioned designs. Water-LiBr is utilized as an operating fluid in noticed systems. As a function of the unit temperatures, the gross temperature lift, pressure ratio (R),and the efficiency of the economizer, a numerical model is also introducedto prognosticatethe irreversibility, exergy coefficient of performance (ECOP),coefficient of performance (COP), and the exergy destruction in each and every one of the key components (EF). The findings show that the generator has the highest exergy destruction, accounting for around 46.06% of the total exergy destruction. Additionally, a decrease in the temperature of the absorber increases the ECOP and COP. The outcomes indicate that systems utilizing water-LiBr as operating fluid have a higher outlet temperature of the absorber as well as higher condenser temperature and lower coefficient of performance (COP). the results showed that, Regarding the simple DEAHT curve, the COP slowly diminishes at low absorber-evaporator temperatures and rapidly at absorber temperatures more than 144.5 °C. Also, Utilizing the compressor in the basic design of the DEAHT unit results in improving the absorber temperature.

Energy grade splitting of hot water via a double effect absorption heat transformer

Energy level mismatch between waste heat and energy users poses huge barrier for local waste heat recovery. To tackle this challenge, an energy grade splitting strategy of hot water via absorption heat transformer is proposed. In this strategy, the hot water is separated into two branches. An absorption heat transformer extracts waste heat from the colder branch, and delivers heat output to increase the temperature of hotter branch. This process could deliver high temperature output and decrease the temperature of waste heat simultaneously, which meets the local waste heat recovery demand. Both experimental and modeling researches are carried out to investigate this strategy. Firstly, double effect LiBr-water absorption heat transformer is adopted for performance enhancement, and experimental investigation was carried out. Testing results showed that 391.4 kW heat output and COP of 0.618 were achieved, under colder branch temperature of 149.7 → 128.1 °C and hotter branch temperature of 151.0 → 128.1 °C. Secondly, modeling framework was built and used to evaluate the energy grade splitting performance under different conditions. Results showed that the proposed energy grade splitting strategy is effective under waste heat source temperatures of 130.0–160.0 °C, temperature lift of 5.0–20.0 °C, mass split ratio of 0.10–1.60 and temperature split ratio of 2.00–20.00. Such an effective and flexible strategy could further be promoted to other scenarios with different heat conversion technologies, and contribute to the wide application of local waste heat recovery.

Novel post combustion CO2 capture in the coal-fired power plant employing a transcritical CO2 power generation and low temperature steam upgraded by an absorption heat transformer

This paper deals with a double effect heat transformer-aided carbon dioxide capture unit with transcritical carbon dioxide power generation for a coal-fired steam power plant. In the proposed system a double absorption heat transformer is used to upgrade low energy level steam into high-level and drive carbon dioxide capture unit. Also, a transcritical carbon dioxide power generation that is utilized captured carbon dioxide to generate power and compensate a portion of the required electrical energy of the carbon dioxide capture unit. This system avoids extracting high-grade temperature steam extracted from high-pressure stage of steam turbine and hence overall thermal efficiency of power plant increases compared to the reference systems. Comprehensive thermodynamic and economic evaluations are conducted to reveal the feasibility of the presented system. The results show that the evaporator temperature has the highest effect on net power output. An increase of 10 K in the evaporator temperature from 80 °C to 90 °C, leads to a reduction of 4.9% in generated power. However, a 50% increase in carbon dioxide capture rate from 40% to 90%, leads to a rise of 23.4% in the exergy destruction rate. Moreover, the payback period is approximately 4 years and 6 months.

A solar-assisted double absorption heat transformer: Off-design performance and optimum control strategy

Using solar-assisted absorption heat transformers to provide high-temperature process heat over 100 °C has raised increasing concern in recent years for its energy saving and environmentally friendly characteristics. In this study, a solar-assisted double absorption heat transformer is proposed and analyzed theoretically. The optimum off-design performance is investigated to develop high-efficient control strategies under various climatic conditions (solar radiation intensity I and ambient temperature tamb). In order to maximize the heating capacity and overall system thermal efficiency (Q̇h and ηsys), the conjugate directions method is applied for searching the optimum operation parameters including the strong solution mass flow rate and bypass ratio (ṁsol and BP). The results show that the ηsys can reach 20.3% with the heating temperature at 130 °C under typical climatic conditions (I = 600 W·m−2 and tamb = 25 °C). Under off-design conditions, the ṁsol and BP exist optimum values, at which the Q̇h reaches the maximum value. Specifically, under typical operation conditions, the maximum Q̇h can be obtained as the ṁsol = 90 kg·h−1 and BP = 0.8. Under higher I and tamb conditions, the control strategies of increasing the collector temperature and ṁsol are very practical to enhance the system performance.

Investigation of crystallization risk in different types of absorption LiBr/H2O heat transformers

Absorption heat transformers are utilized to upgrade the energy of low-temperature heat sources. When the working fluid in such systems is LiBr/H2O solution, there is a possibility of crystallization phenomenon at their generator outlet. This phenomenon has to be avoided because otherwise it stops the system operation. In the present work, the possibility of crystallization, under different operating conditions such as different temperatures in the condenser, evaporator, absorber and absorbing evaporator temperatures as well as different effectiveness of applied heat exchangers, is investigated. Using engineering equation solver software, the investigation is carried out for three types of heat transformers including single-stage, double-effect and triple-effect for identical values of input heat. The results show that at higher absorber temperatures especially in the double and triple-effect absorption heat transformers, crystallization may occur at the outlet of expansion valves in addition to the generator outlet. Moreover, lower values of the condenser temperature and heat exchangers effectiveness increase the possibility of crystallization risk in all the three types investigated.

Thermoeconomic evaluation and optimization of LiBr-H2O double absorption heat transformer driven by flat plate collector

In this paper, a solar double absorption heat transformer (SDAHT) operating with the LiBr-H2O solution is proposed to provide high temperature energy. The flat plate collector (FPC) is used to supply the demanded heat input in the present configuration, which will greatly broaden the application scope of the FPCs. The thermoeconomic concept is applied to the evaluation and optimization of the SDAHT, aimed at minimizing its annual capital cost per kilowatt heat capacity (CPK) and payback period (PP). A dedicated computer model in the software Engineering Equation Solver was developed to conduct the study by means of a parametric analysis. The results show that there exists an optimum absorber/evaporator temperature at which CPK and PP can obtain the minimum values. With solar radiation intensity at 600 W/m2, generation (evaporation) temperature at 75 °C, condensation temperature at 38 °C, absorption temperature at 135 °C and economizer efficiency set to 0.8, the optimum absorber/evaporator temperature and corresponding CPK and PP are 104.0 °C, 928.1 euros/kW and 4.0 years, respectively. The cost of the FPCs takes the major part of CPK. Moreover, the effects of the operating parameters such as the generation (evaporation), condensation, absorption temperatures and design parameters including the first and second economizer efficiencies on the optimum absorber/evaporator temperature and corresponding CPK and PP have been analyzed in detail. Besides, some suggestions derived from the results are also given to assist the engineers in estimation of the economic performance.

Experimental assessment of double-absorption heat transformer operating with H2O/LiBr

This paper reports on the experimental results of a double-absorption heat transformer operating with a H2O/LiBr mixture. The generator and evaporator are pool boiling type heat exchangers, while the remaining components are coils inside shells. Plots of gross temperature lifts, economizer efficiency, and internal and external performance coefficients are reported as functions of diverse operating parameters of the heat transformer. The results indicate that the system can achieve gross temperature lifts (GTLs) of between 48 °C and 74 °C, with internal performance coefficients varying from 0.12 to 0.37. The GTLs achieved are up to 30 °C higher than those reported in the literature, using a single-stage heat transformer operating with the same working mixture. Furthermore, the system exhibits effective stability and repeatability.

Post combustion CO2 capture in power plant using low temperature steam upgraded by double absorption heat transformer

In CO2 capture retrofit unit of existing coal-fired power plants, energy level mismatch between extraction steam from turbines and CO2 regeneration process always results in large exergy destruction and low thermal efficiency. Thus, a new CO2 capture system driven by double absorption heat transformer is proposed. Through the absorption heat transformer, low-temperature steam is upgraded into a higher energy level to match the temperature of CO2 regeneration. Also, flue gas heat is partly recovered to preheat the circulating water from CO2 capture process to further decrease system energy penalty. Aspen Plus 11.0 is used to simulate the system and parameters of key processes are validated by experimental values. It is shown that with 90% CO2 capture, the thermal efficiency of the power plant with proposed CO2 capture system is enhanced by 1.25 percentage points compared with traditional method. And the efficiency enhancement of the proposed system has a trend of increase first and then decrease with CO2 capture rate growth. For a 350MW coal-fired power plant, the optimum CO2 capture rate is 53.65% and the corresponding efficiency enhancement is 2.06 percentage points. Exergy analysis shows that the exergy destruction in CO2 separation and steam condensation process can decrease by 49.5% in the proposed system, and thereby the exergy efficiency is 1.85 percentage points higher than the conventional method. Furthermore, the cost of CO2 avoided and cost of electricity of the proposed system will be reduced by 10.7 $/t-CO2 and 1.9 $/MWh, respectively.

Comparison of single and double stage absorption and resorption heat transformers operating with the ammonia-lithium nitrate mixture

This paper presents the modeling and thermodynamic analysis of different heat transformers configurations using the alternative mixture NH3-LiNO3. The analyzed configurations are: (i) Absorption Heat Transformer (AHT), (ii) Double Absorption Heat Transformer (DAHT), (iii) Resorption Heat Transformer (RHT) and (iv) Double Resorption Heat Transformer (DRHT). Coefficients of performance and exergetic efficiencies are reported for each one of the systems as function of the main system temperatures. The results showed that the coefficients of performance and exergetic efficiencies are higher for the conventional cycles without the resorption circuit (AHT and DAHT), however, their operating pressures are considerable higher than those reached with the systems with the resorption circuit.

Performance Study of a Double Absorption Heat Transformer

Abstract To upgrade the temperature of low or moderately heat source to a more useful temperature level, a novel H 2 O /LiBr double absorption heat transformer (DAHT) is proposed, which utilizes the strong solution from the generator to absorb the refrigerant vapor in the absorber/evaporator. A thermodynamic model of the system is developed to simulate the performance. Based on the first law of thermodynamics, the thermodynamic circuit process performance of the DAHT is analyzed. The calculation of the thermodynamic process of the DAHT is conducted by using an engineering equation solver (EES) program. The coefficient of performance (COP) and COP•ΔT(ΔT is gross temperature lift), serving as important design parameters to illustrate the system thermodynamic performance, are presented. The effects of absorber/evaporator temperature, evaporator temperature, absorber temperature, and condensation temperature on the COP and COP•ΔT are investigated. When the absorber temperature is 130 °C, the evaporator and generator temperature is 80 °C, the absorber/evaporator temperature is 105 °C, and the condensation temperature is 30 °C, the maximum COP of the DAHT can reach as high as 0.332.

Upgrading Low-temperature Steam to Match CO2 Capture in Coal-fired Power Plant Integrated with Double Absorption Heat Transformer

The energy level mismatch between extraction steam from turbines and heat for CO2 regeneration always results in huge exergy destruction and low thermal efficiency in post combustion power plants with CO2 capture. To solve the problem, a new CO2 capture system driven by a double absorption heat transformer is proposed in this paper. Through the absorption heat transformer, low-temperature steam can be upgraded into high level heat to match the temperature of solvent regeneration. Also, flue gas heat is recovered to preheat the circulating water to further decrease system power penalty. Aspen Plus11.0 is used to simulate the system, and the results of the key process are validated by experimental values. It is shown that with 90% CO2 capture, the thermal efficiency of the proposed system is enhanced by 1.25 percentage points. And the efficiency enhancement of proposed system has a trend of increase first and then decrease with the CO2 capture rate growth. For a 350MW coal-fired power plant, the optimum CO2 capture rate is 53.65% and the corresponding efficiency enhancement is 2.06 percentage points. Exergy analysis shows that due to better match between the upgraded steam and CO2 stripping temperature, the exergy destruction in CO2 separation process of proposed system could decrease by 40.3%, and thereby the exergy efficiency of proposed system is 33.76%, which is 1.85 percentage points higher than the conventional method.

Effects of the generator and evaporator temperature differences on a double absorption heat transformer—Different control strategies on utilizing heat sources

The combination of the absorption heat transformer with renewable energy systems, like solar thermal systems, is raising more and more concern. In those combined systems the strategies on utilizing heat sources can affect system thermodynamic performance significantly. Therefore, this study presents a detailed analysis on the effect of the heat source temperature and different heat source flow patterns on the performance of a double absorption heat transformer (DAHT). A detailed comparative study is carried out to clarify the impact of the generator and evaporator temperature differences (GETD) on the coefficient of performance (COP), exergy efficient (ECOP), exergy destruction rates in the individual components and heat transfer areas needed for each component. The results show that the generator, condenser and absorber-evaporator are responsible for most of the exergy destruction rate in the DAHT system; the parallel-flow configuration (the generator temperature is equal to the evaporator temperature) performs better under the high gross temperature lift conditions; in the case of the counter-flow configuration (the generator temperature is relatively higher), better performance can be obtained in both the COP and ECOP under the proper heat source temperature (85 and 95°C); the fair-flow configuration (higher temperature in the evaporator) is not recommended in this paper due to no advantages found in either thermodynamic performance or system size.

Performance analysis on modified cycle of double absorption heat transformer with solution and coolant heat regeneration

A modified cycle of double absorption heat transformer with heat regeneration of both solution and coolant is proposed by adding a heat exchanger at the inlet of coolant and outlet of dilute solution of the absorber-evaporator. The performances of three cycle schemes of double absorption heat transformers without regeneration, with solution heat regeneration and with both solution and coolant heat regeneration for absorber-evaporator are calculated and compared. The results show that the double absorption heat transformer with both solution and coolant heat regeneration has a wider operating range of absorption-evaporation temperature and higher coefficient of performance (COP) and exergy efficiency. When the temperatures of absorption, generation, condensation and absorption-evaporation are respectively 120–150°C, 70°C, 25°C and 80–115°C, the average values of COP or exergy efficiency of the new cycle is 8–9% and 2.5–3.5% respectively higher than the ones without heat regeneration and with solution heat regeneration only. The variation trends of COP and exergy efficiency of three cycles versus the temperatures of absorption-evaporation, condensation, generation and absorption are also presented. The impacts of absorption-evaporation temperature on COP and exergy efficiency under different temperature combinations of generation, absorption and condensation are presented for optimal design of the new double absorption heat transformers.

Comparative assessment of different categories of absorption heat transformers in water desalination process

During the last decade, there has been a significant amount of research conducted on absorption heat pumps (AHPs). Second type AHPs, namely absorption heat transformers (AHTs) are useful devices, capable of raising the temperature of waste heat to more useful temperature levels. The excluded heat from AHTs can provide the required energy for desalination. In the present work, performances of three main categories of AHT systems comprising single, double and triple absorption heat transformers (SAHT, DAHT, and TAHT) while they are coupled to water purification system are investigated and compared. A simulation model has been developed in EES (Engineering Equation Solver) to evaluate the effects of several key thermodynamic parameters on the performance of the cycle and amount of desalinated water. The results show that the highest gross temperature lift can be achieved with TAHT while it has the lowest COP among the other types of AHTs. Additionally, a performance optimization performed by using EES shows that SAHT, DAHT, and TAHT can provide fresh water for 853, 796 and 697 residential units respectively if they operate nonstop.

Optimum performance of a double absorption heat transformer

Double absorption heat transformer (DAHT) is a promising device in reducing the use of fossil fuels since it can utilize renewable sources or waste heat to provide high temperature energy. The absorber-evaporator is an important component in the DAHT system, and there exists an optimum absorber-evaporator temperature (OAET) at which the maximum coefficient of performance (COP) and exergy efficiency (ECOP) can be obtained simultaneously. In this paper, an optimization study is carried out by means of a parametric analysis, using a mathematical model developed in the software Engineering Equation Solver. The effects of the operating parameters such as the absorber, condenser, evaporator and generator temperatures and design parameters including the first and second economizer efficiencies on the OAET and corresponding maximum COP and ECOP have been analyzed in detail. Besides, some suggestions derived from the results are also given.

Applications of innovative configurations of double absorption heat transformers in water purification technology

In this study, first law of thermodynamics has been employed to analyze the performances of two different configurations of double absorption heat transformers (DAHTs) in water purification system. The upgraded heat in the absorber of the absorption heat transformers provides the heat for desalination process. The first investigated configuration is the most efficient DAHT according to the literature, and the second one is a novel configuration proposed by the authors. The aim of this research was to investigate the effects of different parameters on the studied configurations of DAHTs and the desalination system and to compare their performances in detail. Additionally by considering the quantity of the produced water, both the configurations were optimized. The results revealed that the proposed configuration is capable of producing freshwater for 806 residual units.

Performance analysis of absorption heat transformer cycles using ionic liquids based on imidazolium cation as absorbents with 2,2,2-trifluoroethanol as refrigerant

A detailed thermodynamic performance analysis of a single-stage absorption heat transformer and double absorption heat transformer cycles using new working pairs composed of ionic liquids (1-ethyl-3-methylimidazolium tetrafluoroborate ([emim][BF4]) and 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4])) as absorbent and 2,2,2-trifluoroethanol (TFE) as refrigerant has been studied. Several performance indicators were used to evaluate and compare the performance of the cycles using the TFE+[emim][BF4] and TFE+[bmim][BF4] working pairs with the conventional H2O+LiBr and organic TFE+TEGDME working pairs. The obtained results show that the ionic liquid based working pairs are suitable candidates to replace the conventional H2O+LiBr working pairs in order to avoid the disadvantages associated with it mainly crystallization and corrosion and also they perform better (higher gross temperature lift) than TFE+TEGDME working pair at several operating conditions considered in this work.

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.

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.