Dec-2024

Refining the future: How smarter desalter operations drive efficiencies and sustainability

"If you cannot measure it, you cannot improve it.” This insight from Lord Kelvin highlights a fundamental principle of industrial processes, especially in refining: accurate measurement is the cornerstone of any improvement. H. James Harrington expanded on this idea, stating, “Measurement is the first step that leads to control and, ultimately, to improvement. If you can’t measure something, you can’t understand it. If you can’t understand it, you can’t control it. And if you can’t control it, you can’t improve it.”

David Williams
Berthold Technologies

Article Summary

Together, these perspectives emphasise that without precise measurement, efforts to refine and enhance processes remain fundamentally limited.

As the global energy landscape shifts towards greener alternatives and a hydrogen-based economy, the refining industry faces increasing pressure to improve efficiency and reduce its carbon footprint. Optimising desalter operations is central to these goals. Effective management of this critical process can significantly boost refinery efficiency, lower energy consumption, and advance sustainability efforts (Bain et al., 2019). Among all industrial processes, refineries top the list as the most energy-intensive of them all. In fact, in a typical 150,000 BPD refinery, 663 MW of energy is generally required, out of which approximately 217 MW is consumed by a crude distillation unit, accounting for more than one-third. The main purpose of this energy is heating crude oil to the 350°C to 400°C temperatures required for the separation of crude into its constituent fractions (Figure 1).

This is an enormously energy-intensive process, and inefficiencies, such as fouling in furnace tubes and heat exchangers, can lead to significant energy losses. Fouling reduces heat transfer efficiency, requiring more fuel to maintain essential process temperatures, which in turn raises operational costs and expands the refinery‘s carbon footprint. Addressing these waste sources is essential for refineries aiming to improve energy efficiency and enhance sustainability. The desalter, one of the initial processing units in a refinery, plays a critical role in preparing crude oil for further processing. Its main purpose is to remove salts, minerals, and metals from crude oil before it enters this crude distillation unit. If not effectively removed, these contaminants can cause significant issues downstream, such as corrosion of equipment, fouling of heat exchangers and furnace tubes, and the deactivation of catalysts, all of which lead to increased operational costs, elevated energy consumption, and greater maintenance demands.

Desalters function through gravity separation, whereby fresh wash water is injected into the crude oil to dissolve salts and capture impurities. As the water mixes with the oil, it absorbs these contaminants, and the water droplets then coalesce and separate from the oil phase, adhering to Stokes‘ law of particle settling. For efficient desalter operation, it is essential that the water droplets have adequate residence time to settle out of the oil phase, making precise level control within the desalter vessel a key factor for optimal performance (Boughaba et al., 2020).

Optimise the desalter efficiency
Effective removal of salts, minerals, and metals in the desalter is essential to avoid major operational challenges. Salts, especially chlorides, are highly corrosive and can produce hydrochloric acid at high temperatures, leading to significant damage to refinery equipment. Such corrosion increases maintenance costs, raises the risk of unexpected equipment failures, and creates hazardous operational conditions. Furthermore, contaminants left in the crude can deposit on heat exchanger and furnace tube surfaces, forming insulating layers that hinder heat transfer efficiency and driveup fuel consumption. This not only raises operational costs but also increases greenhouse gas emissions.

Effective optimisation of desalter operations translates directly into substantial cost savings by reducing catalyst poisoning in refinery processes. When contaminant metals, such as iron (Fe), are not adequately removed in the desalter, they accumulate downstream, poisoning catalysts in critical units like hydrocrackers and fluid catalytic crackers (FCCs). This contamination can necessitate costly catalyst replacements, potentially reaching $15-20 million annually for fresh catalyst alone, not accounting for additional operational costs due to reduced catalyst efficiency (Mani, V., 2024).

In addition to level control, several other factors influence desalter efficiency, including crude oil temperature, water injection volume, mix valve settings, grid voltages, and water outlet valve operation. The temperature of the crude oil is particularly important, as it affects both the viscosity of the oil-water mixture and the solubility of water in oil, both of which are critical for effective separation. The volume of water injected into the crude oil prior to the mix valve is also crucial: too little water may fail to dissolve all salts, while excessive water can overwhelm the desalter, reducing efficiency (Cahill, 2019). The mix valve is essential in atomising water droplets within crude oil, ensuring they are sized optimally for effective separation. Proper management of grid voltages is critical to facilitate the coalescence of water droplets, while the water outlet valve must be precisely controlled to maintain the appropriate water level and maximise residence time. All these factors require careful control to ensure the desalter operates efficiently, minimising fouling, corrosion, and energy consumption. (Mani, V. 2024).

The ability to monitor the rag layer in real-time is crucial for optimising desalter performance. The rag layer, which is formed as an emulsion of oil, water, solids, and surfactants, presents a significant challenge to effective oil-water separation. If left unchecked, its growth can reduce the effective separation volume within the desalter, shorten residence time, and ultimately lower operational efficiency. This results in higher levels of contaminants in the desalted crude and increases the risk of fouling and corrosion in downstream equipment. Accurate measurement of the rag layer‘s thickness and position allows operators to take timely corrective actions, such as adjusting chemical treatments, demulsifier injection, or washwater, to prevent emulsion buildup. Without precise monitoring, refineries are forced to rely on estimates, which can lead to inefficiencies, increased maintenance costs, and compromised equipment reliability.

Density profiles in operation
When operating correctly, a desalter should exhibit a clear transition from 100% water at the bottom of the vessel to 100% oil at the top. This transition is reflected in density readings, which smoothly decrease from bottom to top. However, when a desalter loses coalescence, a rag layer, a mixture of water, oil, surfactants, and solids, can form on top of the water, disrupting this transition. The presence of a rag layer reduces the desalter‘s efficiency by diminishing The tables and corresponding graphs below illustrate the differences in density profiles during normal operation versus when a rag layer is present.

Unveiling the invisible: the EmulsionSENS advantage
Berthold‘s EmulsionSENS is not only theoretically advantageous; real-world refinery operations demonstrate its genuine benefits. The ability to accurately assess and control desalter performance results in substantial improvements in operational efficiency and sustainability. By maintaining optimal water levels and precisely managing transition zones, refineries can reduce energy consumption, prevent fouling, and extend the lifespan of critical equipment. As highlighted in the case study from Veolia at a Southeast Asia refinery, traditional measurement technologies, such as capacitance probes, have limitations in accurately detecting both the interface between water and oil and the rag layer when present. Capacitance-based instruments rely on differences in dielectric properties to differentiate between oil and water phases. However, they struggle in the presence of emulsified layers, where the mixture of oil, water, and solids disrupts the dielectric contrast, making it difficult to reliably detect the boundary between the rag layer and the water. Consequently, capacitance probes may provide a steady reading even as the rag layer grows, failing to alert operators to changes in the desalter’s internal conditions.