Solar absorption heat transformer applications to absorption refrigerating machines

This paper concerns the study of a two-stage vapour absorption system (heat transformer and refrigerating machine) employing the refrigerant absorbent combinations of LiBr-H₂O and NH₃-H₂O successively. The system consists of coupling the previous absorption cycles so that the first-stage absorber produces heating water to circulate in the generator of the second stage. The performances of a solar installation (two stage system plus solar collector) had been tested in Rabat (Morocco). It is found that the system can be operated at lower hot source temperatures and, thus, it can be supplied either from flat plate collectors or from thermal effluents.     

Performance analysis on a new multi-effect distillation combined with an open absorption heat transformer driven by waste heat

In this paper, a new water distillation system, which consists of either a single- or multi-effect distiller combined with an open absorption heat transformer (OAHT), has been proposed.The new integrated system can be used for distilling waste water with high amounts of SiO₂ from heavy oil production, and the resultant distilled water can be supplied to steam boilers to produce high quality steam which in turn is injected into oil reservoirs to assist with heavy oil recovery. The thermodynamic cycle performances for these new integrated distillation systems were simulated based on the thermodynamic properties of the aqueous solution of LiBr as well as the mass and energy balance of the system. The results indicate that combined with OAHT, the waste heat at 70 °C can be elevated to 125 °C and thereby produce steam at 120 °C in the absorber, which is able to drive a four-effect distiller to produce distilled water. For a single-effect and four-effect distiller, the coefficients of performance (COP) are approximately 1.02 while the performance ratios are 2.19 and 5.72, respectively. Therefore, the four-effect distillation system combined with an OAHT is more thermally effective and is an ideal option to process the waste water in oilfields.     

Techno-economic analysis of a novel hybrid heat pump system to recover waste heat and condensate from the low-temperature boiler exhaust gas

This paper is based on the proposal of a new waste heat recovery (WHR) system, which can be utilized to heat the boiler return water, boiler supply air, and building heating air. The system is the combination of an indirect contact condensing unit (IDCCU), a mechanical compression heat pump, and two air preheaters. The system is modeled on the basis of mass and energy balance and then thermodynamically analyzed. Improved performance results were obtained in the form of an increase in the boiler's energy efficiency of about 10.47%, with 4.87% increase in exergy efficiency. The coefficient of performance (COP) of the heat pump was increased from 1.23 to 1.45 by the addition of an air heater in the conventional heat pump. The exergy destruction in each component is calculated. Sensitivity analysis was performed to check the influence of different operating parameters on the performance of the WHR system and boiler. It can be observed from the results that for a specific refrigerant temperature and a calculated amount of mass, flow rate can maximize the condensation efficiency of IDCCU by decreasing the flue gas temperature, while the use of the air heater can further reduce the flue gas temperature, and a stream of hot air can be utilized for space heating. A comparison is made with the other system on a performance basis. The results shows a clear difference in efficiencies and profit earned.     

Performance improvement of absorption heat transformer

In this study, a mathematical model of absorption heat transformer (AHT) operating with the aqua/ammonia was developed to simulate the performance of these systems coupled to a solar pond in order to increase the temperature of the useful heat produced by solar ponds and used a special ejector located at the absorber inlet. By the use of the ejector, the obtained absorber pressure becomes higher than the evaporator pressure and thus the system works with triple-pressure-level. The ejector has two functions: (i) aids pressure recovery from the evaporator and (ii) upgrades the mixing process and the pre-absorption by the weak solution of the ammonia coming from the evaporator. The other advantage of the system with ejector is increased absorber temperature. Therefore, pressure recovery and pre-absorption in the ejector improves the efficiency of the AHT. Under the same circumstances, when compared to an AHT with and without an ejector, the system's COP and exergetic coefficient of performance (ECOP) were improved by 14% and 30%, respectively and the circulation ratio (f) was reduced by 57% at the maximum efficiency condition. Due to the reduced circulation ratio, the system dimensions can be reduced; consequently, this decreases overall cost. The maximum upgrading of the solar pond's temperature by the AHT was obtained at 57.5 °C and gross temperature lift at 97.5 °C with coefficients of performance of about 0.5. The maximum temperature of the useful heat produced by the AHT was 150 °C. In addition, exergy losses for each component in the system were calculated at different working temperatures and the results of both systems with and without an ejector were compared. Exergy analysis emphasised that both the losses and irreversibilities have an impact on the system performance and exergy analysis can be used to identify the less efficient components of the system. Exergy analyses also showed that the exergy loss of the absorber of AHT with ejector was higher than those of other components.     

太阳能双吸收式热变换器系统的热力性能研究

建立了一种太阳能双吸收式热变换器的数学模型,研究了设计工况以及不同环境因素影响下的系统热力性能,分析了太阳辐射强度、环境温度、集热温度、吸收/蒸发温度和温升对系统热效率和制热功率的影响。研究结果表明:系统存在最佳的吸收/蒸发温度;辐射强度增加时系统性能明显提高,辐射强度从0.3 k W/m2变化到1.0k W/m2时,系统热效率提高了10.9%,制热功率增加了10.6倍;随环境温度或集热温度的升高,系统性能呈现了先升后降的趋势,在环境温度为26℃或集热温度为82℃时,系统性能分别达到最佳;最佳集热温度随着辐射强度的增大和环境温度的升高呈升高趋势。     

蒸汽型LiBr吸收式热泵在直接空冷机组余热回收技术中的应用

冷端损失是现代火力发电厂的主要损失,约占发电机组能量输入的40%,是发电机组效率低的主要原因。蒸汽型Li Br吸收式热泵可以回收该低品位热源,使电厂能源利用率提高。针对这一技术,介绍了蒸汽型Li Br吸收式热泵的原理及其在某2×330 MW直接空冷机组中的应用,分析了其节能效果,认为该技术经济及环境效益良好,具有广泛的推广价值。     

Upgrading waste heat from a cement plant for thermochemical hydrogen production

A calcium oxide/steam chemical heat pump (CHP) is presented in the study as a means to upgrade waste heat from industrial processes for thermochemical hydrogen production. The CHP is used to upgrade waste heat for the decomposition of copper oxychloride (CuO.CuCl₂) in a copper–chlorine (Cu–Cl) thermochemical cycle. A formulation is presented for high temperature steam electrolysis and thermochemical splitting of water using waste heat of a cement plant. Numerical models are presented for verifying the availability of energy for potential waste heat upgrading in cement plants. The optimal hydration and decomposition temperatures for the calcium oxide/steam reversible reaction of 485 K and 565 K respectively are obtained for the combined heat pump and thermochemical cycle. The coefficient of performance and overall efficiency of 4.6 and 47.8% respectively are presented and discussed for the CHP and hydrogen production from the cement plant.     

热管技术在变压器中的应用

热管在变压器中的应用还处于探索阶段，文中系统地论述了热管技术在变压器中应用的可行性，总结了国内外的研究现状，提出了油浸式变压器用热管散热的新方案，并对其进行了试验，得出重力热管不论从技术特性还是热力性能均能很好地满足变压器的要求，这些工作对以后热管式变压器的设计应用具有较好的参考价值和指导意义。     

Thermodynamic performance of a new type of double absorption heat transformer

The thermodynamic performance of a new type of double absorption heat transformer (DAHT) has been studied based on the thermodynamic properties of the aqueous solution of lithium bromide and the mass and energy balance for each component of the system in this paper. The solution cycle in this new type of DAHT is different from the ones reported in literatures, in which the temperature of the absorbing evaporator is not an independent variable and the degrees of freedom of the system is less than that of the DAHT with other solution cycles by one. The results show that compared with other types of DAHT this new type of DAHT has higher coefficient of performance especially when absorber temperature gets higher. The maximum coefficient of performance and the maximum gross temperature are about 0.32 and (60–100) °C respectively.     

Technologies to recover exhaust heat from internal combustion engines

The focus of this study is to review the latest developments and technologies on waste heat recovery of exhaust gas from internal combustion engines (ICE). These include thermoelectric generators (TEG), organic Rankine cycle (ORC), six-stroke cycle IC engine and new developments on turbocharger technology. Furthermore, the study looked into the potential energy savings and performances of those technologies. The current worldwide trend of increasing energy demand in transportation sector are one of the many segments that is responsible for the growing share of fossil fuel usage and indirectly contribute to the release of harmful greenhouse gas (GHG) emissions. It is hoped that with the latest findings on exhaust heat recovery to increase the efficiency of ICEs, world energy demand on the depleting fossil fuel reserves would be reduced and hence the impact of global warming due to the GHG emissions would fade away.     

Parametric analysis of a hybrid power system using organic Rankine cycle to recover waste heat from proton exchange membrane fuel cell

Using fuel cell systems for distributed generation (DG) applications represents a meaningful candidate to conventional plants due to their high power density and the heat recovery potential during the electrochemical reaction. A hybrid power system consisting of a proton exchange membrane (PEM) fuel cell stack and an organic Rankine cycle (ORC) is proposed to utilize the waste heat generated from PEM fuel cell. The system performance is evaluated by the steady-state mathematical models and thermodynamic laws. Meanwhile, a parametric analysis is also carried out to investigate the effects of some key parameters on the system performance, including the fuel flow rate, PEM fuel cell operating pressure, turbine inlet pressure and turbine backpressure. Results show that the electrical efficiency of the hybrid system combined by PEM fuel cell stack and ORC can be improved by about 5% compared to that of the single PEM fuel cell stack without ORC, and it is also indicated that the high fuel flow rate can reduce the PEM fuel cell electrical efficiency and overall electrical efficiency. Moreover, with an increased fuel cell operating pressure, both PEM fuel cell electrical efficiency and overall electrical efficiency firstly increase, and then decrease. Turbine inlet pressure and backpressure also have effects on the performance of the hybrid power system.     

Behavior of a two-stage absorption heat transformer combining latent and sensible heat exchange modes

A two-stage absorption heat transformer (TAHT) and its improved version, the cycle incorpaorating latent heat and sensible heat modes, are investigated by emplying energy-utilization diagrams (EUDs). Utilizing the exhaust gas of a gas turbine as the heat source and employing the water/lithium bromide as the working fluid, it has been concluded that this is an effective way of decreasing the exergy loss by combining latent and sensible heat exchange modes. Furthermore, the temperature of the useful heat is increased. This analysis can provide a basis for synthesis and development of absorption heat transformer systems.     

第二类吸收式热泵的研究及应用

介绍了第二类吸收式热泵的工作原理,阐述了第二类吸收式热泵在工质对、吸收器、表面添加剂和缓蚀剂四个方向的研究现状,例举了第二类吸收式热泵在冶金、酒精以及橡胶工业中的应用.指出以节能为目的的第二类吸收式热泵在工业中具有广阔的应用前景.     

回收工业废热的吸收式热变换器技术

介绍了提升工业废热温位的吸收式热变换器的工作原理 ,工质的热力循环过程。应用热力学第二定律和工质的热力学性能数据 ,分别对工质的理论循环过程与实际循环过程的性能系数进行了理论分析和计算 ,研究了操作参数对性能系数和温升的影响规律     

Single stage and double absorption heat transformers used to recover energy in a distillation column of butane and pentane

This paper presents the theoretical analysis of the use of single stage and double absorption heat transformers operating with the water–lithium bromide mixture coupled to a butane and pentane distillation column in a Mexican refinery. A mathematical model of the heat transformers was developed in FORTRAN and integrated as a user model to the Aspen Plus simulation code. Both components coupled to the column were modelled on steady-state conditions. The results show that it is theoretically possible to reduce the energy consumed in the reboiler between 26 and 43% by the use of single stage heat transformer at specific conditions, and between 28 and 33% with double absorption heat transformers for a wide range of operating conditions. Copyright © 2003 John Wiley & Sons, Ltd.     

火电厂低温余热利用技术应用分析

综述火电厂低温余热利用技术的特点及应用现状,并对各种技术进行了对比分析,其中集中式吸收式热泵供热技术在当前应用最广泛,是最具发展前景的技术。苇湖梁电厂低温余热利用项目是集中式吸收式热泵125MW水冷机组技术在国内的首次工程应用,项目具有显著的节能效果,可实现年节约标煤41688t,节水65.88万t。     

内可逆四温位吸收式热变换器的热经济性能优化分析

基于一类内可逆四温位吸收式热变换器模型,应用以每单位成本的泵热率作为热经济学目标函数.在牛顿传热定律下,导出了热变换器的热经济学目标函数和泵热系数间的基本优化关系,由此可计算出最大热经济目标和对应的热变换器的性能参数.讨论了循环参数对热变换器热经济性目标的影响.所得结果对实际四温位吸收式热变换器的优化设计具有一定指导意义.     

Experimental performance of ternary solutions in an absorption heat transformer

In this work, results from experiments with ternary solutions in an absorption heat transformer are presented. The experiments were performed under controlled conditions using water/lithium chloride/zinc chloride and water/calcium chloride/zinc chloride solutions as working pairs. The results showed that the gross temperature lift is increased with regard to the results obtained using binary solutions because the concentration of the solutions was enhanced. The water/lithium chloride/zinc chloride solution showed a generally better performance than the water/calcium chloride/zinc chloride mixture. The highest gross temperature lift for the former solution was 37·5°C for an absorber temperature of 96°C. This result compared favourably to that previously obtained for water/lithium bromide in the University of Salford. © 1998 John Wiley & Sons, Ltd.     

高温热管在小氮肥余热回收中的应用

将高温热管蒸汽发生器应用于小氮肥造气工艺，以取代原普通余热锅炉回收煤气工段的高温余热，解决了合成氨生产工艺中煤气降温的难题，取得了很好的经济效益和社会效益。     

烟气冷却器在电厂烟气余热回收中的应用

为了解烟气冷却器对电厂烟气余热的节能作用,深入探讨了烟气冷却器的应用途径及其性能提升的影响因素,着重分析了烟气冷却器在电厂中的布置方式对节能效果的影响,通过比较烟气冷却器布置前后电厂各发电设备的效率及节能指标,达到电厂节能减排,烟气余热利用,提高系统经济性的目的。