Why Crude Oil Must Be Desalted and Dehydrated Before Entering a Refinery?

Introduction

Crude oil extracted from oil fields is not a pure hydrocarbon product. During production, transportation, and storage, crude oil usually contains different amounts of formation water, dissolved salts, sediments, and other impurities.

Although the content of these impurities is relatively low, they can create serious problems during refinery operations. Water and salt in crude oil may cause corrosion, equipment fouling, pipeline blockage, reduced heat transfer efficiency, and deterioration of product quality.

Therefore, crude oil desalting and dehydration are essential pretreatment processes before crude oil enters refinery units. These processes help protect refinery equipment, improve operational efficiency, and ensure stable production.

At the same time, accurate crude oil sampling before and after treatment provides reliable data support for quality evaluation and process control.

1. What Are Water and Salt in Crude Oil?

Crude oil naturally contains a certain amount of water from underground reservoirs.

This water exists in two main forms:

· Free water

· Emulsified water

Free water can usually be separated by gravity, while emulsified water remains dispersed in crude oil as very small droplets.

Along with water, crude oil also contains dissolved inorganic salts, mainly:

· Sodium chloride (NaCl)

· Calcium chloride (CaCl₂)

· Magnesium chloride (MgCl₂)

These salts are usually dissolved in water droplets suspended inside crude oil.

Although the concentration of salt may appear small, it can create significant operational problems during refining.

2. Why Must Crude Oil Be Desalted and Dehydrated Before Refining?

2.1 Preventing Corrosion of Refinery Equipment

One of the most serious problems caused by untreated crude oil is corrosion.

During the heating process in refineries, calcium chloride and magnesium chloride may undergo hydrolysis reactions and generate hydrochloric acid (HCl).

HCl is highly corrosive and can damage:

· crude oil pipelines

· heat exchangers

· distillation towers

· furnace tubes

In addition, when processing high-sulfur crude oil, hydrogen sulfide (H₂S) may also increase corrosion risks.

The combination of HCl and H₂S can accelerate metal corrosion and shorten equipment service life.

By removing salt and water before refining, refineries can significantly reduce corrosion risks and improve equipment reliability.

2.2 Improving Heat Transfer Efficiency

Heat exchangers are critical equipment in crude oil processing.

However, salts and impurities carried by crude oil may deposit on heat exchanger surfaces and furnace tubes.

These deposits can:

· reduce heat transfer efficiency

· increase fuel consumption

· increase operating costs

· reduce processing capacity

Over time, serious scaling may restrict fluid flow and even cause equipment failure.

Effective desalting helps maintain cleaner heat transfer surfaces and improves refinery energy efficiency.

2.3 Avoiding Pipeline and Equipment Blockage

Water and impurities in crude oil can create deposits during transportation and processing.

Common problems include:

· pipeline restriction

· increased pressure loss

· unstable crude oil flow

For long-distance crude oil pipelines and storage facilities, maintaining stable transportation conditions is extremely important.

Proper dehydration reduces water-related problems and improves transportation reliability.

2.4 Maintaining Stable Distillation Operation

The distillation unit is one of the most important processes in a refinery.

Excess water entering the distillation tower can create additional vapor volume during heating.

This may result in:

· increased tower pressure drop

· unstable operation

· reduced separation efficiency

· possible tower flooding

Controlling water content before refining helps maintain stable distillation performance and improves production efficiency.

2.5 Protecting Catalyst Performance and Product Quality

Salt compounds contained in crude oil may introduce metal ions into refinery processes.

These contaminants can:

· reduce catalyst activity

· affect secondary processing efficiency

· decrease product quality

For refineries using catalytic cracking or hydroprocessing technologies, controlling salt content is especially important.

Proper desalting helps protect catalysts and maintain consistent product quality.

3. How Does Crude Oil Desalting and Dehydration Work?

Crude oil desalting is a process designed to remove dissolved salts and water before refining.

The typical desalting process includes several steps:

Step 1: Mixing Crude Oil With Washing Water

Fresh water is added to crude oil.

The purpose is to dissolve and transfer salt compounds from crude oil into the water phase.

Step 2: Applying an Electric Field

The mixture enters the desalting vessel.

A high-voltage electric field is applied to break the stability of small water droplets.

Small droplets combine into larger droplets through electrical coalescence.

Step 3: Separating Salt Water From Crude Oil

After water droplets become larger, they settle at the bottom of the desalting vessel.

The separated water carries dissolved salts and impurities away.

The treated crude oil continues to the refinery processing units.

4. Typical Quality Requirements Before Refinery Processing

Before entering refinery units, crude oil usually needs to meet specific quality requirements.

Typical requirements include:

Water Content:

0.1%–0.2%

Salt Content:

Less than 5 mg/L

For refineries processing heavy oil or using advanced conversion processes, even stricter salt control may be required.

Maintaining these parameters helps ensure safe and efficient refinery operation.

5. Why Accurate Crude Oil Sampling Is Important Before and After Desalting?

Accurate sampling plays an important role in crude oil quality management.

Before desalting, refineries need reliable information about:

· water content

· salt concentration

· crude oil properties

After desalting, sampling helps verify whether the treatment process has achieved the expected results.

However, traditional manual sampling methods may have limitations:

· samples may not represent actual pipeline conditions

· human operation errors may occur

· safety risks may increase in hazardous areas

Automatic crude oil sampling systems provide a safer and more accurate solution.

6. How Automatic Crude Oil Sampling Supports Oil Quality Control

Modern oil transportation and refining systems increasingly rely on automatic sampling technology.

Compared with manual sampling, automatic crude oil samplers provide:

Representative Sampling

Samples are collected according to actual pipeline conditions, ensuring better accuracy.

Flow-Proportional Sampling

The sampling frequency can be adjusted according to crude oil flow changes, providing more reliable analysis results.

Improved Safety

Operators can reduce direct exposure to high-pressure and hazardous environments.

Data Traceability

Automatic systems improve sample management and quality tracking.

For oil terminals, pipelines, and refinery facilities, automatic crude oil sampling is becoming an important part of modern quality management systems.

7. Supporting Reliable Oil Operations With ZNYB Automatic Crude Oil Sampling System

ZNYB automatic crude oil sampling systems are designed for demanding oil and gas environments.

The system provides:

· automatic representative sampling

· stable operation under harsh conditions

· compatibility with pipeline transportation systems

· improved sampling safety

· reliable quality data support

From oil fields and pipelines to refinery facilities, accurate sampling helps companies make better decisions based on reliable crude oil information.