Modelling of a sulfuric acid production plant

Abstract

The goal of this work is to model a sulfuric acid unit that belongs to Prayon with the Mathcad software. The company would like to revamp this installation in order to improve its performances from an ecological and economic point of view. The thermodynamic model developed in this project must be able to predict the evolution of the process due to a change in the latter.

First, the thesis includes a section related to the state of the art. This one contains the different process used to produce sulfuric acid. This section allows to understand the way the sulfuric acid unit of Prayon operates.

Then, a chapter is dedicated to the description of the thermodynamic properties required to model the unit. The thermodynamic models used are quite simple in order to be implemented in the Mathcad software. However, they are complex enough to correctly predict the operation of the plant.

The studied process includes several pieces of equipment. Those ones have been modelled for specific conditions. A combustion chamber allows to produce a gaseous stream containing about 10% of SO2 while recycling a SO2-rich flow. This SO2 is then converted into SO3 in catalytic beds placed in series and separated by intercoolers. Several kinetic expressions have been studied. The kinetics used in the model are the ones of Collina, Mars and Maessen and Doering. Finally, two absorption towers allow the production of H2SO4 from the gaseous SO3. For that purpose, the SO3 rich gas are put in contact with an acid that contains about 98,5% of H2SO4.

The models of each piece of equipment were then put together to form the final model. This one also includes the heat integration of the process, which allows the production of high pressure steam and electricity.

At last, the results obtained by the model are compared to the design values of the installation. Furthermore, several sensitivity analyses are carried out in order to understand the impact of few key parameters on the operation of one piece of equipment or the whole unit. Those studies show that the results given by the model developed in this report are consistent with the ones provided by the actual installation.