The oil drying process is one of the important steps in the oil refining process. It is usually used to remove residual moisture in the oil to improve the quality, stability and shelf life of the oil. The presence of moisture may cause adverse reactions such as oxidation, deterioration and rancidity of the oil, so the drying process is crucial to the refining of edible oil.
Introduction to oil drying process
Principle:
Oil drying is to evaporate and remove moisture from the oil by heating or by reducing the pressure of the oil system (vacuum drying). Heating increases the evaporation rate of moisture in the oil, and vacuum conditions reduce the boiling point of moisture, thereby effectively removing moisture at a lower temperature to avoid excessive heating of the oil and causing quality loss.
Usually, the residual moisture in the oil should be controlled below 0.1% to ensure the stability of the oil quality.
The role of drying:
Remove moisture: If the moisture introduced during the refining process (such as after the water washing step) is not removed in time, it is easy to cause the acid value of the oil to increase, affecting its stability.
Improve oil quality: Drying can effectively reduce the moisture content of the oil, prevent the oil from mildew or oxidation during storage and transportation, and extend the shelf life.
Prevent further reaction: The presence of water will promote some chemical reactions, such as hydrolysis, so that the oil will produce more free fatty acids. The drying process can effectively inhibit these adverse reactions.
Classification of oil drying process
1. Vacuum drying:
Principle: Vacuum drying is to place the oil in a low-pressure environment to evaporate the water at low temperature. Since the vacuum state lowers the boiling point of water, the water can be evaporated at a lower temperature, thereby reducing the thermal damage of the oil.
Scope of application: Vacuum drying is widely used in the production of temperature-sensitive or high-quality oils, such as olive oil, peanut oil, etc. It is suitable for refined oils that require higher quality.
Advantages: Low-temperature drying can maximize the maintenance of the nutrients and color of the oil, and the drying effect is better.
Disadvantages: The equipment investment is high, and the operating cost is relatively large, which is suitable for large-scale production.
2. Heating drying:
Principle: By heating the oil, the water evaporates quickly. Usually, the oil is heated by heat transfer oil or electric heating system, and the temperature range is between 80-150°C, which is adjusted according to the characteristics of different oils.
Scope of application: Suitable for refining of high-temperature resistant oils and fats, such as palm oil, soybean oil, etc., especially widely used in industrial mass production.
Advantages: The process is relatively simple, the equipment cost is low, and the moisture in the oil can be quickly removed.
Disadvantages: Temperature-sensitive oils and fats may suffer quality degradation due to long heating time or high temperature, such as oxidation or color change.
3. Freeze drying (less used in oil drying):
Principle: By freezing the oil and sublimating it under vacuum conditions, the water is directly changed from solid to gaseous, thereby achieving the purpose of removing moisture.
Scope of application: Freeze drying is usually used for high-end products or special-purpose oils and fats, such as cosmetics and pharmaceutical-grade oils and fats.
Advantages: Maintain the natural properties and nutrients of the oil.
Disadvantages: The equipment cost is extremely high, the process is complicated, and it is usually not used for large-scale oil refining.
Detailed introduction of oil drying equipment
1. Vacuum dryer
Working principle: The vacuum dryer reduces the pressure in the drying chamber through the vacuum pump system, so that the oil evaporates water in a low-pressure and low-temperature environment. It is usually equipped with a condenser to capture the evaporated water and prevent it from flowing back into the oil.
Main features:
The evaporation temperature of water in a vacuum environment is low, and oils and fats are not easy to oxidize or react chemically, which is suitable for refining high-end oils and fats.
The drying speed is fast, the efficiency is high, and the energy consumption is relatively low, which is suitable for continuous production.
Advantages: low temperature drying to ensure the high quality of oils and fats; high energy efficiency.
Disadvantages: high equipment cost and relatively complex maintenance.
2. Hot air circulation drying equipment
Working principle: use circulating hot air to heat oils and fats to promote water evaporation. Usually used in large-scale industrial production, the hot air temperature and flow rate can be controlled during the drying process to ensure uniform drying.
Main features:
The drying temperature is adjustable and suitable for drying different types of oils and fats.
The equipment has a simple structure and is suitable for large-scale production.
Advantages: simple structure, convenient operation, and low equipment investment.
Disadvantages: high requirements for temperature control, which may cause partial oxidation or color change of oils and fats.
3. Thermal oil heating drying equipment
Working principle: The thermal oil heating system transfers heat energy to the oils and fats to evaporate the water in the oils and fats. Thermal oil heating systems are usually used in continuous production lines to maintain a stable heating effect.
Main features:
The temperature of the heat transfer oil is controllable and stable, and it can maintain a consistent heating effect for a long time, which is suitable for large-scale continuous drying.
The system is well closed, avoiding heat loss and low energy consumption.
Advantages: High heating efficiency, suitable for large-scale continuous production.
Disadvantages: The heat transfer oil system needs to be maintained regularly, and the equipment investment is high.
4. Multi-layer dryer
Working principle: The multi-layer dryer uses multiple heating layers to distribute the oil in each layer, and the water in the oil evaporates layer by layer through heating and circulating air. This equipment is usually used for large-scale refining and continuous production.
Main features:
Multi-layer design saves space and can ensure a large processing volume.
It can be heated in sections to control the temperature of each layer to ensure the uniformity and effect of drying.
Advantages: Large processing volume, suitable for continuous production; can accurately control the temperature of each layer.
Disadvantages: The equipment structure is complex and the initial investment is large.
5. Drum drying equipment
Working principle: The oil is constantly turned in the rotating drum, and the water evaporates while heating. Drum dryers are usually suitable for processing viscous or high-viscosity oils.
Main features:
The oil is in constant contact with the heating surface in the drum, so that the water evaporates evenly.
It can adapt to the drying of various types of oils, especially for viscous oils.
Advantages: strong adaptability, especially suitable for the drying of viscous oils.
Disadvantages: large floor space and high energy consumption.
Choice of drying process
Oil types: Different types of oils are sensitive to temperature to different degrees. For example, high-end oils such as olive oil should choose vacuum low-temperature drying, while palm oil, soybean oil, etc. can use heating drying.
Production scale: Large-scale continuous production usually uses vacuum drying or multi-layer drying equipment, while small-scale production can choose hot air circulation or drum drying equipment.
Product quality requirements: For the refining of high-end edible oils or oils for medicine and cosmetics, high-quality and low-temperature drying are required; for ordinary industrial oils or bulk edible oils, heating drying is more often used.
By rationally selecting oil drying processes and equipment, the moisture in the oil can be effectively removed, the purity and stability of the oil can be improved, and its safety in storage and transportation can be ensured.