Improvement potential analysis for integrated fractionating and heat exchange processes in delayed coking units

A novel diagram-based representation approach is developed to analyze the thermodynamic efficiency and identify quickly the promising energy-use improvement for integrated fractionating and heat exchange processes in delayed coking units. For considering temperature dependence of heat capacity and integrating fractionating and heat exchange processes, an advanced energy level composite curve is constructed by using the simulation results and a stepwise procedure. More accurate results of exergy analysis are obtained and the interaction between different components of the integrated system can be properly revealed in an integrated figure. Then the exergy calculation is performed to validate the performance of processes and to define the targets for improvement. The avoidable exergy destruction is also analyzed by applying the concepts of avoidable and unavoidable exergy destructions for the integrated system. In a case study for a Chinese refinery, the results reveal that the heat exchange between gas oil and deethanization gasoline is the most inefficient process with the highest retrofitting potential, and the lowest exergy efficiency of component in the integration system is only 29.4%. The improvement potential and exergy efficiency for the fractionator are 38.1% and 97.3%, respectively. It is obvious that the fractionator is not the most promising component for improvement.     

Exergoeconomic (Thermoeconomic) Analysis and Performance Assessment of a Gas Engine–Driven Heat Pump Drying System Based on Experimental Data

Exergoeconomic analysis has been used as a powerful tool to study and optimize various types of energy-related systems. In this study, we use the specific exergy cost (SPECO) method to calculate exergy-related parameters and display cost flows for all streams and components in a gas engine–driven heat pump drying system based on the experimental data. We analyze and evaluate the performance of the drying system components and the drying process for three different medicinal and aromatic plants from an exergoeconomic point of view. We also investigate the effect of varying dead (reference) state temperatures on exergoeconomic performance parameters for the drying system components and drying process. Although the condenser and drying chamber of the gas engine–driven heat pump dryer were significantly affected by the ambient temperature, the gas engine was slightly influenced by the ambient temperature. At low ambient temperatures, the exergy rates increased and the most effective performance obtained from this dryer was at 0°C. The performance of the drying process also increased at low ambient temperatures. This study demonstrated that exergoeconomic analysis can provide more information than exergy analysis, and the results obtained from the exergoeconomic analysis provided cost-based information, suggesting potential locations for drying system improvement.     

Advanced Exergy Analysis of a Heat Pump Drying System Used in Food Drying

Exergy analysis has been used as a powerful tool to study and optimize various types of energy systems. However, the methodology of splitting the exergy destructions (the so-called advanced exergy analysis) allows for a further understanding of the exergy destruction values to improve the system efficiency. In this study, advanced exergy analysis was applied to a pilot-scale heat pump drying system used in food drying for the first time to evaluate its performance at different drying temperatures. The results showed that inefficiencies within the compressor and condenser were mainly due to the internal operating conditions and the efficiencies in the evaporator and heat recovery system could be improved by structural improvements of the whole system and remaining system components.     

Exergoeconomic Analysis of a Combined Ammonia Based Solid Oxide Fuel Cell System

An exergoeconomic study of an ammonia‐fed solid oxide fuel cell (SOFC) based combined system for transportation applications is presented in this paper. The relations between capital costs and thermodynamic losses for the system components are investigated. The exergoeconomic analysis includes the SOFC stack and system components, including the compressor, microturbine, pressure regulator, and heat exchangers. A parametric study is also conducted to investigate the system performance and costs of the components, depending on the operating temperature, exhaust temperature, and fuel utilization ratio. A parametric study is performed to show how the ratio of the thermodynamic loss rate to capital cost changes with operating parameters. For the devices and the overall system, some practical correlations are introduced to relate the capital cost and total exergy loss. The ratio of exergy consumption to capital cost is found to be strongly dependent on the current density and stack temperature, but less affected by the fuel utilization ratio.     

Exergy analysis of a seawater reverse osmosis plant

Exergy analysis is a powerful tool to determine how inefficiencies of the processes influence system performance. The exergy analysis of a seawater reverse osmosis desalination plant with 21,000 m³/d of nominal capacity located in Tenerife (Canary Islands, Spain) was studied. Once defined, the flow chart of the process, the exergy rate and exergy cost of flows were determined as well as the exergy destruction rate in equipment. The main results indicate that 80% of the exergy destruction is placed on core processes (high pressure pumping and valve regulation, reverse osmosis separation and energy recovery), 29% extra exergy is necessary to obtain the unit of feed exergy from previous stages (seawater pumping and pretreatment) and extra exergy of 1.06 kJ is needed to generate 1 kJ of final product exergy (exergy performance about 50%). In addition, the moderate fluctuations of seawater environmental conditions in the Santa Cruz de Tenerife metropolitan area (and Canary Islands as a whole) establish that environmental parameters present a less important influence on exergy analysis.     

Multi-objective thermoeconomic optimization of coupling MSF desalination with PWR nuclear power plant through evolutionary algorithms

This paper deals with the application of an evolutionary algorithm to multi-objective thermoeconomic optimization of coupling a multi stage flash desalination (MSF) plant with a pressurized water reactor (PWR) nuclear power plant. The thermodynamic simulation of this initial PWR plant has been performed in a Thermoflex simulator. An Excel add-in called Thermoflex Link has been developed to calculate the exergy of each stream from Thermoflex simulation results. Meanwhile, a computer code has been developed for thermoeconomic and improved combined pinch-exergy analysis in Matlab environment. Both the design configuration (feed water heater structure) and the process variables are optimized simultaneously. The optimization algorithm can choose among several design options included in a superstructure of the feed water heater in dual purpose plant. For the assumptions and simplifications made in this study, a 3000 MW (thermal) PWR power plant such as the Bushehr power plant has been considered. A detailed exergy and exergoeconomic analysis of selected final optimal design identifies the magnitude, location and causes of the thermodynamic inefficiencies. Improved combined pinch and exergy analysis has been applied to display the system information graphically for one to visualize the performance of the system in the initial and final case.     

A Comparative Study on Exergetic Performance Assessment for Drying of Broccoli Florets in Three Different Drying Systems

This article deals with the exergy analysis and evaluation of broccoli in three different drying systems. The effects of drying air temperature on the exergy destruction, exergy efficiency, and exergetic improvement potential of the drying process were investigated. The exergy destruction rate for the drying chamber increased with the rise in the drying air temperature at 1.5 m/s, both in the tray and the heat pump dryer. The highest exergy efficiency value was obtained as 90.86% in the fluid bed dryer in comparison to the other two drying systems and the improvement potential rate was the highest in the heat pump dryer during drying of broccoli at the drying air temperature of 45°C and the drying air velocity of 1.0 m/s.     

Thermal analysis of ME—TVC+MEE desalination systems

Thermal analysis of three different configurations of a multi-effect thermal vapor compression desalting system is presented: conventional ME—TVC,ME—TVC with regenerative feed heaters (ME—TVC,FH) and ME—TVC coupled with a conventional MEE system (ME—TVC+MEE). The analysis is based on the First and Second Law of Thermodynamics. A parametric study was carried out to investigate the impact of motive steam pressure, temperature difference per effect, top brine temperature, feed seawater temperature and motive steam flow rate on the system's performance for each configuration. The exergy analysis showed that irreversibilities in the steam ejector and evaporators are the main sources of exergy destruction in the three configurations. When steam is supplied directly from the boiler to all configurations, results showed that the first effect was responsible for about 50% of the total effect exergy destruction. The study also showed that the decrease in exergy destruction is more pronounced than the decrease in the gain ratio at lower values of motive steam pressure. Lowering the temperature difference across the effects, by increasing the surface area, decreases the specific heat consumption. On the other hand, exergy losses are small at low temperature differences and low top brine temperature. The analysis showed that the third configuration (ME—TVC+MEE) has two main features compared to ME—TVC and ME—TVC, FH. First it has a lower compression ratio, which makes the motive steam capable of compressing larger amounts of the entrained vapor; as a result, the amount of motive steam is reduced. Second, the configuration can be used for large-scale production.     

Enhanced exergy cost optimization of operating conditions in FCCU main fractionator

Exergy indicates the maximal energy that can do work effectively. Different from optimization of product quality or calculation of generic energy conservation in most previous studies, the application of exergy analysis and exergy cost optimization in petrochemical industry is of great economic and environmental significance. Based on the main fractionator in Jiujiang Petrochemical Complex No. 2 FCCU, an enhanced exergy cost optimization under different operating conditions by adjusting set points of temperature and valves opening degree for flow control is studied in this paper in order to reduce exergy cost and improve the quality of energy. A steady-state optimization algorithm to enhance exergy availability and an objective function comprehensively considering exergy loss are proposed. On the basis of ensuring the quality of petroleum products, the economic benefits can be improved by optimizing the controllable variables due to the fact that exergy cost is decreased.     

Exergy analysis of a reverse osmosis desalination plant in California

The exergy analysis of a 7250 m³/d reverse osmosis (RO) desalination plant in California was conducted by using actual plant operation data, and an alternative design was investigated to improve its performance. The RO plant is described in detail, and the exergies across the major components of the plant are calculated and illustrated using exergy flow diagrams in an attempt to assess the exergy destruction distribution. The primary locations of exergy destruction were the membrane modules in which the saline water is separated into the brine and the permeate, and the throttling valves where the pressure of liquid is reduced, pressure drops through various process components, and the mixing chamber where the permeate and blend are mixed. The largest exergy destruction occurred in the membrane modules, and this amounted to 74.07% of the total exergy input. The smallest exergy destruction occurred in the mixing chamber. The mixing accounted for 0.67% of the total exergy input and presents a relatively small fraction. The second law of efficiency of the plant was calculated to be 4.3%, which seems to be low. The analysis of the alternative design was based on the exergy analysis. It is shown that the second law of efficiency can be increased to 4.9% by introducing a pressure exchanger with two throttling valves on the brine stream, and this saved 19.8 kW electricity by reducing the pumping power of the incoming saline water.     

Performance assessment and system optimization of a combined cycle power plant (CCPP) based on exergoeconomic and exergoenvironmental analyses

We propose a systematic approach for performance evaluation and improvement of a combined cycle power plant (CCPP). Exergoeconomic and exergoenvironmental analyses are used to assess CCPP performance and suggest improvement potentials in economic and environmental aspects, respectively. Economic and environmental impacts of individual system components are calculated by cost functions and life cycle assessments. Both analyses are based on a CCPP case study located in Turkey, which consists of two gas turbine cycles and a steam turbine cycle with two different pressure heat recovery units. The results of the exergoeconomic analysis indicate that the combustion chamber and condenser have a high performance improvement potential by increasing capital cost. Furthermore, the exergoenvironmental analysis shows that the exergy destruction of the steam turbine and combustion chamber and/or the capacity of heat recovery units must be reduced in order to improve environmental performance. This study demonstrates that combined exergoeconomic and exergoenvironmental analyses are useful for finding improvement potentials for system optimization by simultaneously evaluating economic and environmental impacts.     

Exergetic Analysis of Textile Convective Drying with Stenters by Subsystem Models: Part 1—Exergetic Modeling and Evaluation

This study, which consists of two parts, deals with the exergy analyses and assessments of the direct gas–heated (DGHS) and hot oil–heated (HOHS) stenters. In the first part, a new model for the exergetic analysis of the convective drying of textiles at stenters was presented and the variations of exergetic parameters for each chamber of the stenter were examined. It was emphasized that the exergy efficiency of the last chambers decreased drastically due to the lower evaporation rate of the falling rate period of drying. Additionally, the subsystems of the chambers were analyzed. For this purpose, the detailed control volume models were conducted for the stenters. It was determined that the combustion chamber and mixing unit of the DGHS and the hot oil boiler of the HOHS led to higher exergy destruction rates. Furthermore, total exergy destruction and loss rates of the HOHS were higher compared to those with the DGHS. The exergy efficiency values of each chamber of the DGHS were calculated to be 10.9, 14.9, 15.3, 12.2, 9.8, and 5.3%, respectively.     

Exergoeconomic analysis of a solar assisted tea drying system

Abstract

In this study, an integrated system which consists of a batch type tea dryer and a PV/T unit is developed and analyzed through the exergoeconomic approach. The EXCEM method based on mass, energy, exergy, and cost balances is performed to find out the exergoeconomic performance of the drying system. The parametric studies are used to see the effect of changing properties utilized in the system on performance. The results of the present study show that the capital cost and the capital productivity of the system are $5953 and 1.54, respectively. The energetic and exergetic loss ratios are calculated as 76.45?MJ/$ and 72.63?MJ/$, respectively. The exergy efficiency and exergy destruction for the whole system are found to be 74% and 201.6?GJ, respectively.     

Optimization and Exergy Analysis of Natural Gas Liquid Recovery Processes for the Maximization of Plant Profits

Maximizing the profits of natural gas liquid recovery plants is a challenge. To improve the performance of an existing plant, three process schemes were compared and analyzed with Aspen HYSYS. A high‐pressure absorber (HPA) performed better owing to the added compressor and more reasonable cold energy utilization. The HPA was further optimized by establishing an objective function and identifying and adjusting the main variables on the basis of a new optimization algorithm. The propane recovery of the optimized HPA was 98.8 %, and the plant profitability increased by 3352 million $ a^?1. Exergy analysis of the optimum process indicated that the column and air cooler contributed the most to the total exergy destruction. Suggestions for decreasing the exergy destruction of the process are also given.     

Exergy analysis of a combined RO, NF, andEDR desalination plant

A brackish water desalination plant in California that incorporates RO, NF, and EDR units was analyzedthermodynamically using actual plant operation data. Exergy flow rates were evaluated throughout the plant, and the exergy flow diagrams were prepared. The rates of exergy destruction and their percentage are indicated on the diagram so that the locations of highest exergy destruction can easily be identified. The analysis shows that most exergy destruction occurs in the pump/motor and the separation units. The fraction of exergy destruction in the pump/motor units is 39.7% for the RO unit, 23.6% for the NF unit, and 54.1 % for the EDR unit. Therefore, using high-efficiency pumps and motors equipped with VFD drives can reduce the cost of desalination significantly. The plant was determined to have a Second Law efficiency of 8.0% for the RO unit, 9.7% for the NF unit, and 6.3% for the EDR unit, which are very low. This indicates that there are major opportunities in the plant to improve thermodynamic: performance by reducing exergy destruction and thus the amount of electrical energy supplied, making the operation of the plant more cost effective.     

Exergy and exergoeconomic analyses for integration of aromatics separation with aromatics upgrading

Methanol to aromatics produces multiple products, resulting in a limited selectivity of xylene. Aromatics upgrading is an effective way to produce more valuable xylene product, and different feed ratios generate discrepant product distributions. This work integrates the aromatics separation with toluene disproportionation, transalkylation of toluene and trimethylbenzene, and isomerization of xylene and trimethylbenzene. Exergy and exergoeconomic analyses are conducted to give insights in the splitting ratios of benzene, toluene and heavy aromatics for aromatics upgrading. First, a detailed simulation model is developed in Aspen HYSYS. Then, 300 splitting ratio sets of benzene and toluene for conversion are studied to investigate the process performances. The results indicate that there are different preferences for the splitting ratios of benzene and toluene in terms of exergy and exergoeconomic performances. The process generates lower total exergy destruction when the splitting ratio of toluene varies between 0.07 and 0.18, and that of benzene fluctuates between 0.55 and 0.6. Nevertheless, the process presents lower total product unit cost with the splitting ratio of toluene less than 0.18 and that of benzene fluctuating between 0.44 and 0.89. Besides, it is found that distillation is the biggest contributor to the total exergy destruction, accounting for 94.97%.     

流化床+铁浴熔融还原炼铁过程的分析

本文对流化床＋铁浴熔融还原炼铁流程进行了分析，从能量守恒以及能量贬质观点，综合评价和分析其用能过程，并绘出了全系统完整的流图，通过对薄弱环节分析，考察了流程的热力学完善性，并提出了一些相应的改善措施，为熔融还原炼铁流程的可行性研究及流程选择提供了依据.     

Thermodynamic Analysis‐Based Improvement for the Boil‐off Gas Reliquefaction Process of Liquefied Ethylene Vessels

A new optimization design of the boil‐off gas (BOG) reliquefaction process for liquefied ethylene (LEG) vessels is proposed in order to reduce the reliquefaction process energy cost and improve its cold exergy efficiency. The exergy loss of each component is calculated and the efficiency of the available energy utilization is evaluated on the basis of a detailed thermodynamic analysis. The exergy analysis results indicate that the exergy efficiency of the improved BOG reliquefaction process is about 19.0 % higher than that of the existing process, and the amount of refrigerant used in the improved process is reduced by about 44.9 % per hour. The power consumption could be decreased by 16 %. The circulation volumes of the refrigerant and BOG are both significantly reduced, thus lowering the equipment and operation costs of the BOG reliquefaction process.     

Exergy analysis of desalination by solar-powered membrane distillation units

There has been an increasing interest in using exergy as a potential tool for analysis and performance evaluation of desalination processes where the optimal use of energy is considered an important issue. Unlike energy, exergy is consumed or destroyed due to irreversibilies in any real process and thus provides deeper insight into process analysis. Exergy analysis method was employed to evaluate the exergy efficiency of the “compact” and “large” solardriven MD desalination units. The exergy efficiency of the compact and large units with reference to the exergy collected by the solar collector was about 0.3% and 0.5% but was 0.01% and 0.05%, respectively, when referenced to the exergy of solar irradiance. The exergy efficiency of the flat plate solar collectors in both units varied diurnally and the maxima was 6.5% ad 3% for the compact and large units, respectively. The highest exergy destruction was found to occur within the membrane distillation module.     

城市燃气门站压力能回收热力学分析

长输来气需在门站内经调压过程将高压燃气降到较低的压力方可送入城市燃气输配系统,节流降压过程存在压力能的损失.采用能量系统的(火用)分析法对城市门站调压过程进行热力学分析,结果表明节流.阀节流降压虽能满足工艺要求,但过程的(火用)损较大,(火用)效率低,应考虑可代替节流阀的其它压力能回收设备,如透平膨胀机、涡轮机等,从而...