Design of a Lab-scale system for the study of dry desulfurization process

Abstract

Sulphur dioxide (SO2) is a major contributor to contamination and environmental degradation. The limit emission values are becoming tighter and nowadays, the Industrial Emissions Directive (EID) of the European Union has been demanding the cement, lime, and magnesium oxide industries to reduce their SO2 emissions by means of sustainable methods. The main industrial activity of Magnesitas Navarras S.A. (MAGNA), Company located in Zubiri (Navarra, Spain), is obtaining magnesium oxide, MgO, from calcination of natural magnesite MgCO3. Emissions of SOX are mainly in the form of sulfur dioxide (SO2), whose emission concentration directly depend on the amount of sulphur contained in the raw material and more importantly in the type of fuel used during the firing process. The reuse of by-products like Low Grade Magnesium Oxide (LG-MgO) during the calcination of magnesite for flue gas desulfurization (FGD) can generate a loop process optimizing the efficiency and revaluating those by-products. FGD is the widest applied measure for SO2 reduction. It allows an industrial plant to reduce its emission by up to 99%. Essentially, is an acid-base reaction in wet or dry conditions. Although wet methods present many advantages such as their high desulfurization efficiency and low economic cost, the conclusions also brought up the fact that the large amounts of liquid effluents produced at the end of the process require a proper management. After research work in wet conditions, MAGNA requested DIOPMA to start a study of Dry FGD. The first benefit of using the dry method is wastes, which are easier to handle than wet flue gas desulfurization. Moreover, requires less energy inputs and lower operation costs. The scope of this project is the lab-scale design to achieve the study of the LG-MgO performance as a desulfurization agent.There are different considerations to take into account for the design of the lab-scale experiment for the dry desulfurization process: gas composition, flow rate, heat flow, corrosion resistance, among others, in order to achieve the company conditions for a reliable study. The process of heat exchange becomes the core of the project since the bottles with the gas composition and the particulate solid have been provided by the company. The design requires heating the gas from room temperature to 200ºC before putting it in contact with the LG-MgO. The calculation to determine the fluid flow conditions has been made in order to use the best correlations to approximate the heat transfer system for the project. The laboratory system designed includes a 1m length furnace and a pipe that goes through to reach the working temperature. Additionally the minimum radius of insulation has been calculated to avoid the heat losses between the exit of the furnace and the the reactor input. Boundary conditions of energy-efficient walls, for furnace and maximum service temperature or durability for pipe have been studied in order to select the best materials for each one using Granta CES EduPack software. As a main conclusions for this work, it has been determined that the flow conditions directly influences the convection heat transfer, suggesting a turbulent flow as a better ally for its optimization. On the other hand, another configuration can be made and allows to use a resistance instead of a furnace. Therefore, and an external insulation should be used in order to ensure that all the heat generated is absorbed by the fluid