Thermodynamic optimization of steady-flow industrial chemical processes

Leslie Glasser,James Alistair Fox,Diane Hildebrandt,David Glasser

doi:10.1007/s40090-018-0164-1

Leslie Glasser, James Alistair Fox + Show 2 more

Open Access

https://doi.org/10.1007/s40090-018-0164-1

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Abstract

Industrial steady-flow chemical processes are generally organised as a sequence of individually optimised operations. However, this may not achieve overall optimization since material (as recycle), heat and work transfers overall may not be well balanced. We introduce the idea of a preliminary overall thermodynamic balance to produce a reversible process, with the objective of minimising, for both economic and environmental reasons, the quality and quantity of energy used. This balance may later require adjustment to account for the realities of available materials and equipment. For this purpose, we introduce (i) a Carnot temperature, TCarnot, by which a Carnot machine (an engine which can operate as either a heat pump or a turbine) can supply the required heat at the correct temperature for a process to operate reversibly, that is with least energy, and (ii) the GH Diagram on which Carnot temperature-based processes are plotted in ∆G–∆H space. We demonstrate the utility of this analysis by simple application to the Haber–Bosch process for ammonia synthesis and by a sequence of operations for the synthesis of methanol. We also briefly introduce the state function exergy, which uses the natural environment as the reference base for energy in place of pure elements under standard conditions.

Highlights

There is increasing need to minimise the use of energy, high-quality energy, in industrial production, arising from both economic and environmental concerns
Entropy Generation Minimisation (EGM) is thermodynamically equivalent to the GH method (GHM) which we present in this paper
Glasser [7] introduced the van’t Hoff Reaction Box as a descriptive model of an overall chemical process, whereby reactants are introduced into the box, each under their individual prescribed conditions, and products are removed, each under their individual prescribed conditions, resulting in thermodynamic changes overall, while no enquiry is made as to the processes occurring or equipment used within the confines of the box

Summary

Introduction

There is increasing need to minimise the use of energy, high-quality (that is, high temperature) energy, in industrial production, arising from both economic and environmental concerns. Glasser [7] introduced the van’t Hoff Reaction Box as a descriptive model of an overall chemical process, whereby reactants are introduced into the box, each under their individual prescribed conditions, and products are removed, each under their individual prescribed conditions, resulting in thermodynamic changes overall, while no enquiry is made as to the processes occurring or equipment used within the confines of the box This equipment may consist of pumps to generate pressure and produce isentropic flow, heat baths to control temperature, material recycling to increase output, distillation columns or condensers to separate materials, and so forth. This may be accomplished by using other sources of work such as pressure–volume or electrical energy but, in this paper, we will focus on heat

Inducing reversibility in a chemical process with heat

GH diagram

The ammonia process as an example

Conclusions