Comparison of the adsorption performance of compound adsorbent in a refrigeration cycle with and without mass recovery

Adsorption and desorption were performed on a compound adsorbent composed of CaCl₂ and activated carbon in cycles both with and without mass recovery and the performances obtained were compared with those of equilibrium adsorption. Experimental results of the cycles without mass recovery carried out on an adsorption refrigeration unit yielded performances that were slightly less than those of equilibrium adsorption. The adsorption performances of the cycle with mass recovery were measured to be much better than those of the cycle without mass recovery. At of evaporating temperature, the cycle adsorption capacity was as high as 0.78 kg/kg for the cycle with mass recovery while it was only 0.55 kg/kg for the cycle without mass recovery. The average adsorption/desorption rate of the cycle with mass recovery, which was 0.031 (kg/kg)/min, has been improved by 47.6% compared with that of the cycle without mass recovery. Research on the cycle adsorption capacity at different evaporating temperatures showed that the improvement of cycle adsorption capacity, with mass recovery, was higher under the condition of lower evaporating temperature. At evaporating temperature, the mass recovery operation had improved the adsorption capacity by 78% compared with the cycle without mass recovery. In addition, refrigeration performances for the cycles with and without mass recovery at an evaporating temperature of were studied. Compared with the results of the cycle without mass recovery, SCP (specific cooling power) and COP (coefficient of refrigeration performance) have been improved by 48.6% and 54.5%, respectively, when mass recovery is performed.     

Energetic and exergetic analysis of a triple-effect distiller driven by solar energy

This paper relates to the energetic and exergetic analysis of single-, double- and triple-effect distiller driven by solar energy. Energetic analysis makes it possible to define an applicable zone of operation according to the following criteria: water rejection limit to 50%, maximum salinity limit to 5.5%, and minimum energy consumption. This analysis also makes it possible to quantify energies: energy necessary for the vapour condensation and the power consumption per unit mass of pure water. Exergetic analysis makes it possible to show that the most significant exergy losses are condenser losses and water alimentation losses and that the condenser losses decrease with the number of effects. The exergetic efficiencies have also been found. They are located between 19 and 26% for a triple-effect system, between 17 and 20% for a double-effect system, and less than 4% for the single-effect system. Consequently, it seems interesting to implement a double- or triple-effect system.     

Thermoeconomic optimization of a LiBr absorption refrigeration system

Optimization of thermal systems is generally based on thermodynamic analysis. Thermoeconomic optimization technique combines thermodynamic analysis with economic constraints to obtain an optimum configuration of a thermal system. In this study, the thermoeconomic optimization technique is applied to a LiBr absorption refrigeration system. Various components of the system such as condenser, evaporator, generator, and absorber heat exchangers are optimized. Additionally, optimum heat exchanger areas with corresponding optimum operating temperatures are determined. A cost function is specified for the optimum conditions. Finally, an example for the optimum design of a 20 kW LiBr system is given.     

热化学复合吸附储热循环的理论及实验

对一种基于固-气可逆化学反应的热化学复合吸附储热循环的储热特性以及能量品位提升性能进行了理论分析,并以MnCl₂/SrCl₂/NH₃作为工质对进行了实验研究。理论分析表明,热化学复合吸附储热循环不仅可以降低外界驱动热源的温度并保证输出热能温度稳定,而且能大幅度地提升输出热能的温度品位。在MnCl₂和SrCl₂都参与放热的实验工况下,获得的储热效率为93.31%。MnCl₂复合吸附剂的总储热密度按单位质量反应盐MnCl₂和单位质量的固化吸附剂计量分别为4393.36和3734.36 kJ·kg^-1;SrCl₂复合吸附剂的总储热密度按单位质量反应盐SrCl₂和单位质量的固化吸附剂计量分别为1947.28和1655.19 kJ·kg^-1。结果表明,热化学储热是一种相当有潜力的储热方式,可为低品位热能的高效回收利用提供强有力的技术支持。     

一种回热回质循环吸附式制冷系统的仿真

吸附式制冷常采用回热回质循环来提升系统性能。研究了一种采用串联回热和类回质方式的回热回质循环吸附式制冷系统,并对其进行仿真。系统的主要部件（含作为储液器的蒸发器）采用3层换热法建立数学模型。仿真结果表明,随着制冷时间的延长,系统性能系数（COP）单调增大,单位质量制冷量（SCP）单调减小。随着回热时间的延长,COP和SCP是先增大后减小,最佳的回热时间为10 s。随着回质时间的延长,COP和SCP波动性下降,回质过程未提高系统性能。COP和SCP随着热水、冷冻水温度的升高以及冷却水温度的下降而增大。热水温度对SCP以及冷冻水、冷却水温度对COP和SCP的影响,呈现线性变化,而热水温度对COP的影响呈现二次变化。     

Exergy analysis of C2 recovery plants refrigeration cycles

This paper provides an exergy analysis of the multistage refrigeration cycle used for Ethane and heavier hydrocarbons (C₂⁺) recovery plant. The behavior of an industrial refrigeration cycle with propane refrigerant has been investigated by the exergy method. The equations of exergy destruction and exergetic efficiency for the main cycle components such as evaporators, condensers, compressors, and expansion valves are developed. The relations for the total exergy destruction in the cycle and the cycle exergetic efficiency are obtained. An ethane recovery unit with its refrigeration cycle has been simulated to prepare the exergy analysis. Using a typical actual work input value; the exergetic efficiency of the refrigeration cycle is determined to be 43.45% indicating a great potential for improvements. The simulation results reveal that the exergetic efficiencies of the heat exchanger and expansion sections get the lowest rank among the other compartments of refrigeration cycle. Refrigeration calculations have been carried out through the analysis of temperature-entropy (T-S) and pressure-enthalpy (P-H) diagrams where coefficient of performance (COP) was obtained as 1.87. The novelty of this article includes the effect and sensitivity analysis of pressure drop and temperature on the exergy efficiency and coefficient of performance of the cycle.     

回质回热吸附式制冷循环的热力学分析与方案优选

吸附式制冷是一种能利用低品位热能的节能环保的制冷方式。在空调工况下,硅胶-水回质回热系统应用最多。为了解在特定工况下选择何种循环能提升系统性能,应用热力学第一与第二定律评价指标分析了基本循环、回质循环、回质回热循环的COP、(火用)效率、循环熵产。分析表明,回质循环存在推荐最高热源温度和最优热源温度,回质回热循环存在推荐最低热源温度和最优热源温度。例如对于典型夏季空调工况热源温度90℃、蒸发温度10℃、冷凝温度40℃,回质循环的推荐最高热源温度为93℃,高于实际热源温度90℃,选用回质循环更合适而非回质回热循环。最后,对制冷机组的分析表明给出的方法和推荐工作温度区间能针对实际系统给出方案优选和系统控制的指导性建议。     

Site-wide low-grade heat recovery with a new cogeneration targeting method

One of the key performance indicators for designing site utility systems is cogeneration potential for the site. A new method has been developed to estimate cogeneration potential of site utility systems by a combination of bottom-up and top-down procedures, which allows systematic optimization of steam levels in the design of site utility configurations. A case study is used to illustrate the usefulness of the new cogeneration targeting method and benefits of optimizing steam levels for reducing the overall energy consumptions for the site. Techno-economic analysis has been carried out to improve heat recovery of low-grade waste heat in process industries, by addressing a wide range of low-grade heat recovery technologies, including heat pumping, organic Rankine cycles, energy recovery from exhaust gases, absorption refrigeration and boiler feed water heating. Simulation models have been built for the evaluation of site-wide impact associated with the introduction of each design option in industrial energy systems in the context of process integration. Integration of heat upgrading technologies within the total site has been demonstrated with a case study for the retrofit scenario.     

Optimal design of cryogenic distillation columns with side heat pumps for the propylene/propane separation

Propylene is one of the most important products in the petrochemical industry, which is used as raw material for a wide variety of products. The propylene/propane separation is a very energy-intensive process because their boiling points are quite similar. In addition, at atmospheric conditions, their boiling points are −47.6 °C and −42.1 °C, respectively. To separate this mixture conventional columns which operate at high pressure and cryogenic distillation columns which operate at low pressure have been used, however, this approaches are still energy-intensive. This work presents energy-efficient and intensified distillation columns which are adiabatic such as the vapor recompression column (VRC) or diabatic such as columns with heat-integrated stages. A design and optimization procedure, which minimizes the energy consumption in the propylene/propane separation is presented. Conceptual design, superstructure representation, rigorous simulations and mathematical programming techniques are effectively combined to assess all the candidate distillation structures, refrigeration cycles, and heat integration possibilities simultaneously. Results showed that VRC and diabatic distillation columns with heat-integrated stages can reduce the energy consumption between 58 and 75% when compared with conventional distillation at high pressure. Furthermore, the proposed synthesis procedure derived simplified optimal distillation structures with few heat-integrated stages and still attained important energy savings.     

Solvent sorption in a polymer-solvent system - Importance of swelling and heat effects

Sorption experiments are often conducted in gravimetric sorption columns where several deviations from ideal conditions could potentially occur. For example, heat effects due to solvent sorption, errors introduced due to concentration dependent diffusion coefficients and swelling are unavoidable. In this study, we develop a model to study the importance of the combination of these effects in obtaining diffusion coefficients from sorption experiments. The model is used to explore a wide range of operating conditions and physical parameters.     

Energy analysis of a lignite predrying power generation system with an efficient waste heat recovery system

Lignite has been extensively used for electricity generation in many regions worldwide. However, its high water content has obviously negative effect on plant thermal efficiency. Performance of lignite-fired power plant can be improved by predrying the lignite before combustion. In addition, recovery of waste heat from the dryer and the power generation system will enhance the plant thermal efficiency further. In the present study, a new lignite predrying power generation system integrated with an efficient waste heat recovery system was proposed. Both dryer exhaust waste heat and steam turbine exhaust latent heat were recovered to heat boiler feed water. Energy analysis indicates that system performance is improved significantly. The plant thermal efficiency increases linearly with drying degree and then increases at a lower rate. The generation of unused dryer exhaust changes the variation tendency of system performance with drying degree.     

Performance improvement of a combined double‐way thermochemical sorption refrigeration cycle with reheating process

A reheating process is proposed aimed at improving the system performance of a combined double‐way thermochemical sorption thermodynamic cycle based on adsorption and resorption refrigeration. The reheating process causes an increase in the driving equilibrium temperature difference, which promotes the reaction rate and thus improves the global conversion of sorbent. Experimental results showed that the proposed reheating process is an effective technique for improving the performance of the combined double‐way cycle. The improvement in the COP ranged between 12 and 48% in the different cycle conditions, when compared with the combined double‐way cycle without reheating. The low pseudo‐evaporation temperature and high heat sink temperature can further improve the system performance. The COP obtained with the combined double‐way cycle without reheating was 0.57, when the heat sink, evaporation, and pseudo‐evaporation temperatures were 25, 10, and 10°C, respectively. However, at the same cycle conditions, the COP increased to 0.64 when the proposed reheating process was introduced in the combined double‐way sorption cycle. © 2009 American Institute of Chemical Engineers AIChE J, 2010     

A numerical study on heat transfer enhancement and design of a heat exchanger with porous media in continuous hydrothermal flow synthesis system

The aim of this study is to use a new configuration of porous media in a heat exchanger in continuous hydrothermal flow synthesis (CHFS) system to enhance the heat transfer and minimize the required length of the heat exchanger.For this purpose,numerous numerical simulations are performed to investigate performance of the system with porons media.First,the numerical simulation for the heat exchanger in CHFS system is validated by experimental data.Then,porous media is added to the system and six different thicknesses for the porous media are examined to obtain the optimum thickness,based on the minimum required length of the heat exchanger.Finally,by changing the flow rate and inlet temperature of the product as well as the cooling water flow rate,the minimum required length of the heat exchanger with porous media for various inlet conditions is assessed.The investigations indicate that using porous media with the proper thickness in the heat exchanger increases the cooling rate of the product by almost 40％and reduces the required length of the heat exchanger by approximately 35％.The results also illustrate that the most proper thickness of the porous media is approximately equal to 90％ of the product tube's thickness.Results of this study lead to design a porous heat exchanger in CHFS system for various inlet conditions.     

Flow and heat transfer characteristics of finned tube with internal and external fins in air cooler for waste heat recovery of gas-fired boiler system

In this present study, attempts were made to investigate the flow and heat transfer characteristics of finned tube with internal fins and external fins by experiment and numerical simulation. The test finned tube was installed in a single smooth tube and formed a shell-and-tube heat exchanger. The experiments were conducted in heat transfer test system with hot air in the tube side and cold air in the shell side. Overall heat transfer coefficients were calculated and heat transfer coefficients in the tube side were determined. Three-dimension computation was performed to predict the flow and heat transfer performance in the finned tube. The effects of external fin height and pitch of the finned tube on shell-side flow and heat transfer were studied by numerical simulation. The numerical results agree well with the measurements. The maximum differences between the present numerical results and the experimental data are approximately 6.9% for heat transfer coefficient and 4.7% for friction factor, respectively. The velocity and temperature fields are obtained to discern the mechanisms of heat transfer enhancement. Numerical results indicate that the steady and spatially periodic growth and disruption of vortices occur in external fin to fin region.     

Numerical optimization of heat recovery steam cycles: Mathematical model, two-stage algorithm and applications

Most of the advanced integrated energy systems need a heat recovery steam cycle (HRSC), either fired or unfired, that recovers the waste heat from gas turbines and process units in order to generate electric power and supply mechanical power to compressors, heat to endothermic processes, and steam to external users. The key feature of such HRSCs is the integration between the heat recovery steam generator (HRSG) and the external heat exchangers. This paper presents a rigorous mathematical programming model, a linear approximation, and a two-stage algorithm for optimizing the design of integrated HRSGs and HRSCs, simultaneously considering the HRSG together with the heat recovery steam network and the intensive steam cycle variables. A detailed application of the methodology is described for an integrated gasification combined cycle plant with CO₂ capture and results for other interesting plants are reported. A significant efficiency gain is obtained with respect to usual practice designs.     

A catalytic diesel particulate filter with a heat recovery function

Based on a folded sheet design, we made and tested a miniature diesel particulate filter (DPF) that can transfer the heat generated by catalytic oxidation in the DPF to its upstream, thus promoting substantial temperature rise at the position where pieces of SiC felt working as PM filters are situated. When 0.6% of H₂, corresponding to 50 K in adiabatic temperature rise, was added to a 43 L/min of exhaust gas, the observed maximum temperature rise at the filter material exceeded 350 K, from which the heat recovery rate was estimated to be more than 86%. The PM filtration rates were 80–90%.     

乙烯精馏塔热泵系统技术分析

分析影响乙烯塔热泵系统综合功能的主要因素，对比评价目前国内已投产乙烯装置中不同的乙烯塔热泵技术优劣。     

芳烃装置低温热回收工艺分析与系统集成

通过对芳烃装置邻二甲苯塔、抽余塔和异构化脱庚烷塔的塔顶物流低温热分析和统计,利用大系统理念,挖掘自备电厂生水和脱盐水加热、生活区采暖和工艺制冷等低温热阱。在此基础上,分析和平衡热源、热阱资源的温位和负荷,结合工程实施上的可行性,提出冬季、夏季组合的运行方案,以循环热水为载体,进行系统集成,实现芳烃装置低温热回收,年节能8.52万t标准煤。     

A practical approach for modelling and control of biomass pyrolysis pilot plant with heat recovery from combustion of pyrolysis products

A pilot plant of biomass pyrolysis using pyrolysis products as fuel has been tested and shown to improve energy balance of the process and to be environmentally friendly by avoiding rejection of pyrolysis pollutants fumes into the atmosphere. The high number of parameters involved in a pyrolysis process makes it difficult to specify an optimum procedure for charcoal yield and pyrolysis cycle durability. So the knowledge of the essential parameters which govern the kinetics mechanisms of the biomass thermal decomposition and the combustion of pyrolysis gases is very useful to understand the operating cycle of the plant. In the present study a thermochemical model is developed in order to simulate and control the operating cycle of the system. The effect of the inlet molar air flow rate on the temporal evolution of biomass mass loss rate and temperatures in the different active zones of the pilot plant as well as the determination of the critical inlet molar air flow rate for which accidental runaway of combustion reactions occurs are presented. To avoid this accidental phenomenon a Proportional-Integral-Derived (PID) anticipated regulation is used in order to control temperatures evolution in the different zones of the device and avoid the runaway of combustion reactions.