Exergetic and Economic Evaluation of a Transcritical Heat-Driven Compression Refrigeration System with CO2 as the Working Fluid under Hot Climatic Conditions

The purpose of this research is to evaluate a transcritical heat-driven compression refrigeration machine with CO2 as the working fluid from thermodynamic and economic viewpoints. Particular attention was paid to air-conditioning applications under hot climatic conditions. The system was simulated by Aspen HYSYS® (AspenTech, Bedford, MA, USA) and optimized by automation based on a genetic algorithm for achieving the highest exergetic efficiency. In the case of producing only refrigeration, the scenario with the ambient temperature of 35 °C and the evaporation temperature of 5 °C showed the best performance with 4.7% exergetic efficiency, while the exergetic efficiency can be improved to 22% by operating the system at the ambient temperature of 45 °C and the evaporation temperature of 5 °C if the available heating capacity within the gas cooler is utilized (cogeneration operation conditions). Besides, an economic analysis based on the total revenue requirement method was given in detail

Advanced exergoeconomic analysis of a power plant with CO2 capture

Conventional exergy-based analyses reveal options for improving energy conversion systems, but they suffer from some limitations that are addressed by advanced exergy-based analyses. Advanced exergy-based methods are capable of (1) identifying interdependencies among plant components (endogenous / exogenous values), and (2) revealing the potential for improvement (avoidable / unavoidable values). Thus, data obtained from these methods pinpoint strengths and weaknesses of energy conversion systems and are of great importance when complex plants with a large number of interconnected components are considered. This paper presents one of the first applications of an advanced exergoeconomic analysis to a complex power plant. The plant includes a mixed conducting membrane for oxy-fuel combustion and CO2 capture. The results show that for the most influential components of the plant, the largest part of investment cost and of the costs of exergy destruction is unavoidable. Additionally, in most cases the interactions among the components are of lower importance and, for the majority of the components, the endogenous parts of the costs (related to the internal operation of each component) are significantly larger than the corresponding exogenous parts (related to component interactions). Nevertheless, relatively strong interactions have been found among the components that constitute the mixed conducting membrane reactor of the plant.EC/FP7/332028/EU/Green Energy for Islands/GENERGI

Comparative Evaluation of Cryogenic Air Separation Units from the Exergetic and Economic Points of View

The industrial use of cryogenic air separation units started more than 120 years ago. Cryogenic air separation processes produce pure nitrogen, oxygen, and argon, as well as other noble gases. In cryogenic air separation units, the produced amounts of nitrogen and oxygen vary between 200 and 40,000 Nm 3 / h and 1000 and 150,000 Nm 3 / h , respectively. Different configurations of this process lead to various amounts of gaseous and liquid products. In addition, the purity of the products is affected by the schematic. Oxygen in gaseous or liquid form is typically used in the metallurgical (e.g., steel) industry, in chemical applications (as oxidizer), in power plants (for oxy-fuel combustion processes), as well as in the medical and aerospace sectors. Nitrogen in gaseous or liquid form is used as inert or flushing gas in the chemical industry and as a coolant for different applications. In this chapter, different schematics of air separation units are analyzed. An exergetic analysis is applied in order to identify the thermodynamic inefficiencies and the processes that cause them. Finally, the systems are evaluated from the economic point of view

Advanced exergoeconomic analysis of a power plant with CO2 capture

Conventional exergy-based analyses reveal options for improving energy conversion systems, but they suffer from some limitations that are addressed by advanced exergy-based analyses. Advanced exergy-based methods are capable of (1) identifying interdependencies among plant components (endogenous / exogenous values), and (2) revealing the potential for improvement (avoidable / unavoidable values). Thus, data obtained from these methods pinpoint strengths and weaknesses of energy conversion systems and are of great importance when complex plants with a large number of interconnected components are considered. This paper presents one of the first applications of an advanced exergoeconomic analysis to a complex power plant. The plant includes a mixed conducting membrane for oxy-fuel combustion and CO2 capture. The results show that for the most influential components of the plant, the largest part of investment cost and of the costs of exergy destruction is unavoidable. Additionally, in most cases the interactions among the components are of lower importance and, for the majority of the components, the endogenous parts of the costs (related to the internal operation of each component) are significantly larger than the corresponding exogenous parts (related to component interactions). Nevertheless, relatively strong interactions have been found among the components that constitute the mixed conducting membrane reactor of the plant.EC/FP7/332028/EU/Green Energy for Islands/GENERGI

Concepts for Regasification of LNG in Industrial Parks

The exponentially growing markets of liquefied natural gas (LNG) require efficient processes for LNG regasification within import terminals. Usually, the regasification of LNG is accomplished by direct or indirect heating. However, integrating LNG regasification into different processes within industrial parks (mainly processes involving low temperatures) is an efficient approach because of the utilization of the low-temperature energy. In some LNG import terminals, integration technologies are already being used. Previous publications showed an increase in the thermodynamic efficiency for systems combining air separation (as an example) and LNG regasification. In addition, the variation in the efficiency as well as the capital investment depends on the schematic and operation conditions. This fact creates great potential for improving the systems. In this chapter, different schematics are evaluated using exergy-based methods in order to improve the effectiveness of complex industrial processes that can involve LNG regasification

Exergetic and Economic Evaluation of CO2 Liquefaction Processes

The transport of CO2, as a part of the carbon capture and storage chain, has received increased attention in the last decade. This paper aims to evaluate the most promising CO2 liquefaction processes that can be used for port-to-port and port–offshore CO2 ship transportation. The energetic, exergetic, and economic analyses are applied. The liquefaction pressure has been set to 15 bar (liquefaction temperature −30 °C), which corresponds to the design of the existing CO2 carriers. The three-stage vapor-compression process has been selected among closed systems (with propane-R290, ammonia-R717, and R134a as the working fluid) and the precooled Linde–Hampson process—as the open system (with R717). The three-stage vapor-compression process R290 shows the lowest energy consumption, and the CO2 liquefaction cost 21.3 USD/tCO2. Although the power consumption of precooled Linde–Hampson process is 3.1% higher than the vapor-compression process with R209, the lowest total capital expenditures are notable. The CO2 liquefaction cost of precooled Linde–Hampson process is 21.13 USD/tCO2. The exergetic efficiency of the three-stage vapor-compression process with R290 is 66.6%, while the precooled Linde–Hampson process is 64.8%

Superstructure-Based Optimization of Vapor Compression-Absorption Cascade Refrigeration Systems

A system that combines a vapor compression refrigeration system (VCRS) with a vapor absorption refrigeration system (VARS) merges the advantages of both processes, resulting in a more cost-effective system. In such a cascade system, the electrical power for VCRS and the heat energy for VARS can be significantly reduced, resulting in a coefficient of performance (COP) value higher than the value of each system operating in standalone mode. A previously developed optimization model of a series flow double-effect H2O-LiBr VARS is extended to a superstructure-based optimization model to embed several possible configurations. This model is coupled to an R134a VCRS model. The problem consists in finding the optimal configuration of the cascade system and the sizes and operating conditions of all system components that minimize the total heat transfer area of the system, while satisfying given design specifications (evaporator temperature and refrigeration capacity of −17.0 °C and 50.0 kW, respectively), and using steam at 130 °C, by applying mathematical programming methods. The obtained configuration is different from those reported for combinations of double-effect H2O-LiBr VAR and VCR systems. The obtained optimal configuration is compared to the available data. The obtained total heat transfer area is around 7.3% smaller than that of the reference case