Main Types of Storage Tanks
Storage tanks are classified into multiple categories based on structural design, operating pressure, and storage medium, each with distinct characteristics and application scopes:
1. Classification by Structural Design
- Vertical Cylindrical Tanks
The most widely used type in industrial storage, featuring a vertical cylindrical body with a flat or conical bottom and a fixed or floating roof. Fixed-roof vertical tanks are suitable for storing non-volatile or low-volatility liquids (e.g., crude oil, diesel, water). Floating-roof vertical tanks are designed for volatile liquids (e.g., gasoline, methanol, benzene); the roof floats on the liquid surface, eliminating the vapor space between the roof and liquid, thus reducing evaporation loss and explosion risks. Their volume ranges from a few cubic meters to over 100,000 cubic meters, making them ideal for large-scale storage in refineries and chemical plants.
- Horizontal Cylindrical Tanks
Composed of a horizontal cylindrical body and elliptical heads at both ends, with a compact structure and small floor space. They are mainly used for small-to-medium volume storage, especially in mobile or space-constrained scenarios, such as fuel storage for vehicles, chemical reagent storage in laboratories, and on-site liquid supply for construction sites. Horizontal tanks can be installed underground to save space and ensure safety.
- Spherical Tanks
Characterized by a spherical structure, which has the best pressure-bearing capacity and uniform stress distribution. Spherical tanks are primarily used for storing high-pressure gases or liquefied gases (e.g., liquefied natural gas, liquefied petroleum gas, liquid ammonia). Compared with cylindrical tanks of the same volume, spherical tanks use less material and occupy a smaller area, but their manufacturing and installation processes are more complex and costly.
- Special-shaped Tanks
Customized according to specific process requirements, including rectangular tanks, cone-bottom tanks, and double-layer tanks. Rectangular tanks are widely used in the food and pharmaceutical industries for storing raw materials and finished products; cone-bottom tanks facilitate the complete discharge of viscous or solid-containing liquids; double-layer tanks are designed with an inner tank for storage and an outer tank for leakage protection, suitable for hazardous chemicals and underground storage.
2. Classification by Operating Pressure
- Atmospheric Storage Tanks: Operating pressure close to atmospheric pressure (gauge pressure -0.02 MPa to 0.02 MPa), mainly for storing liquids with low vapor pressure, such as water, crude oil, and lubricating oil.
- Low-pressure Storage Tanks: Operating pressure ranging from 0.02 MPa to 1.6 MPa, suitable for storing volatile liquids and liquefied gases under low pressure, such as propane and butane.
- High-pressure Storage Tanks: Operating pressure above 1.6 MPa, mainly for storing high-pressure liquefied gases and compressed gases, such as liquid nitrogen, liquid oxygen, and hydrogen.
3. Classification by Storage Medium
- Liquid Storage Tanks: The most common type, used for storing various liquids including petroleum products, chemicals, food raw materials, and water.
- Gas Storage Tanks: Divided into compressed gas tanks and liquefied gas tanks, used for storing industrial gases and fuel gases.
- Solid Storage Tanks: Designed for storing granular or powdered solids (e.g., grains, cement, coal), usually equipped with feeding, discharging, and fluidization devices to prevent material caking and blockage.
Storage tanks are essential equipment for material storage and management in various industries, with the following key application scenarios:
1. Petroleum and Petrochemical Industry
The largest application field of storage tanks, involving the storage of crude oil, refined oil products (gasoline, diesel, kerosene), and petrochemical raw materials (ethylene, propylene, benzene, toluene). Refineries and chemical plants typically use large-scale vertical floating-roof tanks for crude oil and gasoline storage, and spherical tanks for liquefied gas storage. These tanks are equipped with safety systems such as flame arresters, breathing valves, and leak detection devices to prevent fire, explosion, and environmental pollution.
2. Food and Beverage Industry
Storage tanks in this industry are made of food-grade materials to ensure product safety and hygiene. They are used for storing raw materials (milk, fruit juice, syrup, edible oil) and finished products (beverages, sauces, canned food). Common types include stainless steel vertical tanks and horizontal tanks, equipped with cleaning-in-place (CIP) systems to meet strict sanitary standards. Cone-bottom tanks are widely used for storing viscous materials such as honey and jam to facilitate complete discharge.
3. Pharmaceutical and Biotechnology Industry
Storage tanks are used for storing pharmaceutical raw materials, intermediates, and finished products, with high requirements for material purity and corrosion resistance. Stainless steel 316L is the preferred material, and some tanks are lined with PTFE to meet the needs of storing strong corrosive or high-purity drugs. Aseptic storage tanks are used for storing sterile drugs, equipped with sterile air systems and online monitoring devices to maintain a sterile environment inside the tank.
4. Energy Industry
With the development of new energy, storage tanks play an important role in the storage of liquefied natural gas (LNG), hydrogen, and battery raw materials. LNG storage tanks are usually large-scale double-layer tanks with an inner tank made of aluminum alloy or stainless steel and an outer tank made of carbon steel, filled with thermal insulation materials to maintain ultra-low temperatures (-162℃). Hydrogen storage tanks are divided into high-pressure gaseous hydrogen tanks and liquid hydrogen tanks, which are key equipment for hydrogen energy utilization.
5. Environmental Protection and Water Treatment Industry
Storage tanks are used for storing water, wastewater, and chemical reagents (coagulants, flocculants, disinfectants) in water treatment plants. Large-scale vertical tanks are used for raw water and purified water storage, while corrosion-resistant tanks (e.g., FRP tanks) are used for storing acidic or alkaline reagents. In addition, storage tanks are used for storing hazardous waste in waste treatment plants to prevent secondary pollution.
Material Characteristics and Selection Principles of Storage Tanks
The material of storage tanks directly determines their corrosion resistance, pressure-bearing capacity, service life, and application scope. Common materials and their characteristics are as follows:
1. Carbon Steel
- Characteristics: High strength, good weldability, and low cost. Carbon steel has poor corrosion resistance and is prone to rust when exposed to moisture and corrosive media.
- Applications: Suitable for storing non-corrosive media such as crude oil, diesel, lubricating oil, and water. Carbon steel tanks can be coated with anti-corrosion paint or lined with other materials to improve their corrosion resistance.
- Limitations: Not suitable for storing acidic, alkaline, or salt-containing media, as these will cause rapid corrosion of the tank body.
2. Stainless Steel
- Characteristics: Excellent corrosion resistance, good hygiene performance, and high-temperature resistance. Common grades include 304, 316, and 316L. 316 and 316L contain molybdenum, which has stronger corrosion resistance to chloride ions than 304.
- Applications: Widely used in food, beverage, pharmaceutical, and chemical industries for storing corrosive media, high-purity liquids, and food-grade materials. 316L stainless steel is the preferred material for sterile storage tanks in the pharmaceutical industry due to its low carbon content and good weldability.
- Limitations: Higher cost than carbon steel, which limits its application in large-scale storage of non-corrosive media.
3. Fiberglass Reinforced Plastic (FRP)
- Characteristics: Light weight, high strength, excellent corrosion resistance, and good insulation performance. FRP tanks can be customized according to the properties of the stored medium.
- Applications: Suitable for storing acidic, alkaline, and salt-containing corrosive media such as sulfuric acid, hydrochloric acid, and sodium hydroxide. They are widely used in chemical plants, wastewater treatment plants, and electroplating factories.
- Limitations: Low temperature resistance and pressure-bearing capacity; not suitable for storing high-temperature or high-pressure media.
4. Plastic
- Characteristics: Light weight, corrosion resistance, low cost, and easy processing. Common types include polyethylene (PE), polypropylene (PP), and polyvinyl chloride (PVC).
- Applications: PE tanks are suitable for storing dilute acids, alkalis, and water; PP tanks have better high-temperature resistance and are used for storing media at temperatures up to 100℃; PVC tanks are mainly used for storing low-temperature corrosive media. Plastic tanks are widely used in laboratories, small-scale chemical plants, and agricultural irrigation.
- Limitations: Low strength and poor pressure-bearing capacity; not suitable for storing high-pressure or high-temperature media.
5. Aluminum Alloy
- Characteristics: Light weight, good corrosion resistance to cryogenic media, and high thermal conductivity.
- Applications: Mainly used for manufacturing LNG storage tanks and other cryogenic liquid storage tanks, as aluminum alloy has good toughness at ultra-low temperatures and will not become brittle.
- Limitations: High cost and poor strength at high temperatures; not suitable for storing high-temperature media.
6. Lined Materials
For media with special corrosion resistance requirements, storage tanks can be lined with PTFE, rubber, or glass to improve their corrosion resistance. Lined tanks combine the high strength of the base material (e.g., carbon steel) with the excellent corrosion resistance of the lining material, achieving a balance between performance and cost.
7. Selection Principles
- Medium Properties: Select materials based on the corrosivity, temperature, and pressure of the stored medium. For corrosive media, choose stainless steel, FRP, or lined tanks; for high-pressure media, choose carbon steel or stainless steel with high strength.
- Industry Requirements: Food and pharmaceutical industries require materials with good hygiene performance, such as 304 or 316L stainless steel; chemical industries prioritize corrosion resistance; energy industries focus on low-temperature or high-pressure resistance.
- Cost-effectiveness: Balance performance and cost. For large-scale storage of non-corrosive media, carbon steel tanks are the most economical choice; for small-scale storage of corrosive media, plastic or FRP tanks are more cost-effective.
Conclusion
As core equipment for material storage in various industries, storage tanks have diverse types, wide application fields, and rich material options. The selection of storage tanks should be based on the properties of the stored medium, process requirements, industry standards, and cost factors to ensure safe, efficient, and economical storage. With the development of material science and intelligent technology, future storage tanks will develop in the direction of high corrosion resistance, high pressure-bearing capacity, intelligence, and environmental protection, such as the application of new corrosion-resistant alloys, the integration of online monitoring systems, and the adoption of energy-saving thermal insulation technologies. These advancements will further improve the safety and efficiency of storage tank systems, providing strong support for the sustainable development of various industries.
