Statistical Analysis and Linear Modeling of the Heat Exchangers Fouling in Phosphoric Acid Concentration Units

Introduction

In almost all industrial activities, the supply of heat is an essential step in the production chains. It is performed by equipment such as heat exchangers, boilers and furnaces. To achieve this, two modes of heat transfer are possible: either by direct route, where two fluids exchange heat between them without any separation; or by indirect route where the hot fluid gives up its heat through a material, which separates it from the cold fluid. For these purposes, heat exchangers are widely used in industry in different configurations and sizes to best suit their various applications.

In this work, we are particularly interested in the enrichment of studies on the phenomenon of dross deposition on the heat exchange walls of heat exchangers, a phenomenon commonly known as “fouling”. It refers to the accumulation of any unwanted deposit, i.e., crystalline, biological, particulate or chemical reaction product, on the surface of the heat exchanger representing additional thermal resistance, which leads to reducing heat transfer efficiency (Yamamoto et al., 2009).

Taborek (1995) traced the origin of the first industrial concern about fouling in the American electrical industry to 1880. The first mention of fouling in the literature is in the article presented by Orrok (1910). Fouling has been described both as: “The main unresolved problem in heat transfer” and “An almost universal problem in the design and operation of heat exchanger equipment”. It could well be a result of the composition, temperature, pressure, contaminant concentration and rate of circulation of the fluid being treated (Eriksson et al., 2013, Nelson et al., 2006, Yamamoto et al., 2009). As an indication, in industrialized countries, according to Crittenden and Yang (2011), the additional costs due to fouling are of the order of 0.25% of their Gross Domestic Products (GDP) (Dunn, 2019).

According to Garret-Price et al., the conditions, which can influence the fouling factors in the heat exchanger (fouling resistance, thermal efficiency, etc.), can be subdivided into operating parameters, fouling fluid properties and design parameters of the heat exchanger (Hong, 2007).

In this context, the present work aimed to present the energy balances used to control the fouling behavior of the heat exchangers studied. The statistical study of the experimental database thus constituted was used to study the variability of the system, to detect outliers and to model the thermal efficiency of heat exchangers by the Projection to Latent Structures (PLS) regression method.