RepHEN project

Apart from people working in a refinery, very few people have heard about fouling, which is the accumulation of dirt on heat exchangers. At first glance, it seems like a complex, technical issue, something very far from people’s reality. However this is a top-tier “energy thief,” which complicates the sector’s efforts to reduce its CO₂ emissions and has a direct impact on the world economy.

An unknown problem

At refineries, crude oil is preheated in heat exchangers before entering the furnaces. However the constant flow of different types of fluids causes progressive accumulation in this equipment, which bit by bit experiences a reduction in its capacity to heat crude oil. The result is that, when the crude oil goes through the furnaces, more energy must be used to achieve the required temperature and continue the distillation process.

This accumulation of dirt and heat exchangers is a common phenomenon in refineries throughout the world, which requires these facilities to use, according to various sources, between 2% and 3% more energy, which equals 0.25% of industrialized countries’ GDP.

The problem is so significant that the United Kingdom carried out a three-year program with an estimated investment of €15 million to find formulas that reduced the impact of fouling. At the same time, universities and research centers work throughout the world to determine why it is produced and how it can be measured and prevented.

RepHEN: An innovative solution

Repsol has also been looking for solutions to this global problem for years. In 2010, it developed an internal tool known as rePHEN, Repsol Heat Exchanger Network. This model simulates exchanger networks to analyze their maintenance condition, compare their performance in their current condition and “clean” condition, and calculate the extra energy expense associated with the accumulation of dirt that is needed to heat the crude oil.

Information generated helps specialists design a more appropriate cleaning strategy for the exchangers as they are able to determine what exchanger is the dirtiest at each moment in time and what type of cleaning can have the most impact on the network without taking time for a general shutdown.

And that is not this tool’s only benefit. Periodic analysis of the exchangers condition is helping Repsol technicians to adopt new measures to prevent them from becoming dirty, such as redesigning equipment, installing bypasses to take them out of service, and cleaning them while operating, as well as adding new additives to the crude oil before putting it into the network.

Heat exchangers

In order to properly understand the problem of dirt accumulation, we must be familiar with the role that heat exchangers have at a refinery.

When crude oil reaches a refinery, the first step consists in heeding it in furnaces normally powered with natural gas. In this way the required temperature is reached to then separate the products in distillation columns. To avoid excessive energy use in the furnaces, the crude oil is preheated in what are known as heat exchangers, taking advantage of the heat available from other currents.

How does this heat exchange system work? In this equipment, the crude oil's cold current comes into contact (without mixing) with the hot current of the products that just came out of the distillation column. In this way a double benefit is achieved: the crude oil’s temperature increases before entering the furnace and products cool to be sent to storage tanks and other units. As a result, the furnace uses less fuel, which also reduces CO₂ emissions to the atmosphere.

The problem is that, as the months go by, the exchangers become progressively dirtier. Deposits of organic and non-organic material act as an insulating layer that hinders heat exchange and increases the resistance to the flow of liquid. The result is that the crude oil is preheated less, meaning that this temperature deficit must be made up for in the furnace by burning more fuel.