Exergetic Analysis of a Cryogenic Air Separation Unit.

Sorin Bucsa,Mugur C Balan,Catalina Dobre,Gabriel Nastase,Alexandru Serban,Claudia Ionita,Alexandru Dobrovicescu

doi:10.3390/e24020272

Abstract

This case study analyzes a cryogenic air separation unit (ASU) with a production of of gaseous oxygen with a concentration greater than 98.5%, operating in Romania on a steel plant platform. The goal of the paper is to provide an extensive model of exergetic analysis that could be used in an optimization procedure when decisional parameters are changed or structural design modifications are implemented. For each key part of the Air Separation Unit, an exergetic product and fuel were defined and, based on their definition, the coefficient of performance of each functional zone was calculated. The information about the magnitude of the exergetic losses offers solutions for their future recovery. The analysis of the exergy destructions suggests when it is worth making a larger investment. The exergetic analysis of the compression area of the ASU points out an exergy destruction and loss of 37% from the total plant’s electrical energy input. The exergy loss with the heat transferred to the cooling system of compressors can be recovered; for the exergy destruction portion, the challenge between investment and operating costs should be considered. The exergy destruction of the air separation columns found the High Pressure Column (HPC) to be more destructive than the Low Pressure Column. The share of the exergy destruction in the total plant’s electrical energy input is 8.3% for the HPC. The local COP of the HPC, calculated depending on the total exergy of the local product and fuel, is 62.66%. The calculus of the air separation column is performed with the ChemSep simulator.

Highlights

On a large scale, the cost of separating oxygen and other air gases, such as nitrogen, argon, krypton, and neon, is far cheaper and the purity of the products is far higher when using the cryogenic distillation route.A growing application for oxygen today is for dealing with polluted rivers which have been deoxygenated.Nitrogen is the other main component of the air
This paper presents a model of a detalied exergetic analysis of some key parts of a cryogenic air separation unit, a model that could be integrated into a functional or design optimization procedure
The exergetic method is productive in low temperature operating systems where any irreversibility due to the low temperature level leads to a large generation of entropy and, a large exergy consumption

Summary

Introduction

The cost of separating oxygen and other air gases, such as nitrogen, argon, krypton, and neon, is far cheaper and the purity of the products is far higher when using the cryogenic distillation route.A growing application for oxygen today is for dealing with polluted rivers which have been deoxygenated.Nitrogen is the other main component of the air. The cost of separating oxygen and other air gases, such as nitrogen, argon, krypton, and neon, is far cheaper and the purity of the products is far higher when using the cryogenic distillation route. The overall demand for nitrogen gas exceeds that for oxygen. The semiconductor industry uses large quantities; its demand for higher and still higher purity nitrogen arises from the increasing miniaturization and complexity of the integrated circuit chips being manufactured. These ultra-high levels of purity can be achieved by cryogenic distillation of air

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