Thermoeconomic assessment of the processes. DLV 3.4. TOP-REF project
Creators: name: Círez, F.
Publisher: name: Zenodo
Year: 2020
Subjects: exergy, thermoeconomic assessment

description: This report presents a public summary of the work performed under the Task 3.4 “Thermoeconomic assessment of the processes”.<br> One of the main issues for the industrial sectors is the valuation of market products, by-products and residues. The priority course of actions in almost every company uses to be orientated to cost reduction. Consequently, there is a correspondence with the increment of energy and matter efficiency. In several manufacturing lines, there exist thermal and/or electrical transformation processes that can be easily evaluated under the thermodynamic point of view. However, even knowing the real cost of the raw material, electricity and fuels, in most of the cases the companies are not able to evaluate neither the real cost of the inner processes and the intermediate products, nor the effect or the efficiency of these processes on the global productive process. These intermediate effects can be evaluated by means of the thermoeconomic analysis. Thermoeconomic analysis combines economic and thermodynamic analysis by applying the concept of cost, originally an economic property, to exergy. In this manner, by using the Second Law of Thermodynamics, it is possible to connect the Physics and Economics, in order to calculate the thermodynamic cost of every process, matter and energy flow in a system, and to identify the cost formation within the process. The use of this tool is not a one-time process. One of the best advantages of thermoeconomic assessment is that it can be a cyclic process. Starting with the recompilation and accounting of energy and matter flows, the thermoeconomic analysis can provide a “current status” picture of any manufacturing process that can be used as reference condition. By means of thermoeconomic diagnosis, it is possible to find the effect of operating with different conditions regarding that reference. Any difference between the reference and the operational working conditions will present an effect on the fuel consumption (understanding fuel as the inputs of resources to the system), the exergy efficiency, the irreversibility of the processes and the thermoeconomic exergy cost of every process, matter and/or energy flow of the system under study. In addition, it is possible to identify the “weak” processes of the system in terms of energy efficiency. In this manner, it is possible to improve and even optimize the operational conditions in order to maximize or minimize exergy cost. In the present report, an explanation of the thermoeconomic analysis and diagnosis methodology and its basic concepts (exergy, unit exergy cost and cost formation process) will be provided in the first part. In addition, the application of this methodology to the TOP-REF industrial sectors have allow obtaining thumb rules to increase the efficiency of the industries of these sectors.<br> In the case ethylene production linked to steam grids, one of the main irreversibilities is due to the use of high quality (high temperature) steam in the heat exchangers to heat and evaporate low-temperature substances. It would be necessary to try to approach the thermal pinch in the heat exchangers and in the preheating trains. In the case of the petrochemical sector where cogeneration is used to produce electricity and steam that is sent to a steam grid, two main outputs were obtained: the cogeneration system is practically independent with the working load of the fractionation units and the use of the let-down valves has a great effect on the unit exergy cost of the steam. The specific use of turbo-compressors due to steam requirements is another interesting issue that should be evaluated in order to avoid letdown valves. In the sector of fertilizers two main issues were detected. The first one is the use of fuels that can provide a combustion temperature near to 2000 °C in order to heat environmental air for drying that is required at 200 °C. This operational conditions lead to a relevant irreversibility. The second and the most important irreversibility is due to the high recirculation ratio present in this kind of facilities. This ratio provokes the same matter to be wetted, heated and dried repeatedly, decreasing the system efficiency.<br> Due to the research presented above, this methodology provides information to support a better decision making process to valorize wastes and residues (SPIRE Key Action 1.2 and 4.1) as well as industrial symbiosis initiatives (SPIRE key action 2.5) and the identification of the quality of the by-product resources (SPIRE key actions 1.3 and 1.1).