Tanks serve many purposes in the industry. This page describes three types of tanks, such as the storage tanks shown here.
Storage tanks, such as these chemical storage tanks, are used to store materials.
Two types of storage tanks are used widely in industry: underground and aboveground. These tanks can be used for storage, mixing, or as vessels for chemical processes. On the left is an example of an underground storage tank. On the right is an aboveground tank used for storing hazardous chemicals.
Storage tanks come in an assortment of sizes, shapes, and designs and are usually constructed of carbon, alloy, or stainless steel. Storage tanks can be built either vertically or horizontally. Some of the main categories of storage tanks include:
Underground vs. aboveground
Storage tanks can be built for aboveground or underground use. Underground tanks do not require much insulation, whereas aboveground tanks may need secondary, outer insulation layers. However, underground tanks need to be stronger, requiring more materials, and they may need special, non-corrosive outer coats.
Rectangular vs. cylindrical
Storage tanks can be rectangular or cylindrical. Underground tanks are typically cylindrical.
Double wall vs. single wall
Some tanks may need a stronger, sturdier design and construction than others. Tanks can be made stronger using double-wall construction, in which the tank walls are composed of two layers of different materials.
The picture below to the left shows an example of a horizontal, cylindrical storage tank. The picture to the right shows a storage tank with four layers of fiberglass filament windings. Each layer provides additional support and wall thickness to the tank, allowing it to be used for multiple applications.
Spherical tanks are particularly useful in high-pressure applications. They can also be insulated and refrigerated to allow for higher pressures.
Heating and Cooling System Design in Storage Tanks
In some cases, storage tanks might require heating systems to maintain product viscosity for example, or cooling systems, such as to prevent product degradation. These systems consist of either direct steam injection or indirect heating or cooling. The direct steam injection consists of directly applying hot steam to the product in an effort to raise the overall temperature of the product inside the tank. This method is used only when dilution or an increase in liquid mass is acceptable within the tank. A tank may also be indirectly heated or cooled in many ways, such as with cooling coils, with the goal of applying an external source to the outside of the storage tank to maintain a certain temperature of the product inside of the tank.
Storage tanks play many different roles in the industry. The pictures below show examples of storage tanks commonly used in industry. The tanks on the left are fiberglass above-ground storage tanks that are corrosion-resistant and used in a wide range of industrial applications.
Underground storage tanks are frequently used in the petroleum storage industry. The picture below shows an example of a fiberglass underground storage tank. The tank features enhanced internal corrosion resistance to ethanol-blended gasoline as well as a wider range of fuel compatibility compared to steel storage tanks.
- Lower production costs compared to other tanks.
- Less demanding storage conditions lead to a wide choice of structural materials.
- Underground storage tanks allow more flexibility in placement location.
- Aboveground storage tanks are simpler and cheaper to construct.
- Aboveground storage tanks have a lower monitoring and record-keeping cost.
- High maintenance is needed due to a susceptibility to corrosion.
- Corrosion of tanks can have expensive environmental consequences.
- Excavation needed to install underground storage tanks is expensive.
- Underground storage tanks may contaminate the land as leaks in these systems are hard to find.
- Aboveground storage tanks have a high risk of fire
Settling tanks are specially designed to settle and separate materials.
Settling tanks are used primarily to separate solids from a solid-liquid mixture. These tanks are equipped with conveyor belts that lift settled solids in the sludge mixture from the bottom of the tank and dump it over the side, as shown in the diagram.
Settling tanks are designed to account for minimum slurry turbulence and rapid, constant settling of materials. A conveyor belt is used to remove sludge from a mixture. All settling tanks are also equipped with pumps to recirculate the liquid component of the mixture, and filters to keep solids out of the recirculating pumps.
Modifications can be made to meet process conditions, such as a variance of slurry build-up.
The picture below shows a settling tank with a multiple weir design. This design makes it possible for the tank to more efficiently remove solids. Both the settling and clean storage tanks have continuous conveyor and weir systems to remove settled deposits and discharge them into sludge bins.
For example, settling tanks with only one section is used when shutting down the process to remove the solids is a convenient option due to the slow buildup of materials. These tanks are usually equipped with a sludge removal door.
If sludge buildup is moderate, continuous removal is not required. However, shutting down the process would be inconvenient, and a different type of tank can be used. Such settling tanks are divided into two sections so that one section can be in operation while the solids are removed from the other.
Commercial uses for settling tanks include:
- Primary dewatering of salvageable materials from a solid-liquid mixture
- Quick quenching and efficient handling of hot materials
- As an alternative to more expensive filtration systems
- Applications with slow sludge build-up allow continuous operation of the tank.
- Use limited to mixtures that are not hazardous when exposed to the atmosphere.
Seamless pressure vessels are designed to contain high-pressure compressed gases and fluids.
Pressure vessels are tanks used to store and transport highly pressurized materials. Pressurizing materials to a minimum volume and using pressure vessels is a highly efficient and economical way to store materials.
Most pressure vessels are long and cylindrical and made of seamless, steel pipe for maximum strength.
Pressure vessels are usually stored and transported in vessel assemblies. These assemblies include racks that secure the pressure vessels in rows.
Examples of the use of pressure vessels can be as simple as a helium tank for balloons, or a propane tank for a gas grill. Some industrial examples are shown in this section.
- By using high pressures, greater quantities of gases or fluids can be stored in the same space as in storage tanks.
- Materials used to construct vessels are often brittle and the possibility of brittle fracture increases with wall thickness.
- Regulatory codes limit use by allowing only specific materials to be stored under a specific range of conditions.
Expansion tanks are designed to allow space for fluid to expand in a system.
Expansion tanks allow for the expansion of a fluid. A properly implemented and maintained tank will allow the system equipment in the system to have a longer life span, be safer to operate and be simpler to maintain.
The expansion tank is normally placed in the system at its highest point. This allows for a positive pressure difference to make pumping easier and allows for simple venting. The legs of the tank are designed to allow a circular flow around the tank. Valves are placed at each of the legs to control the flow to the tank and the expansion of the materials inside of the tank. Normally, only a single leg is open to allow for the expansion of the fluid while the second is closed to block flow through the tank. The size of the tank depends on the thermal expansion of the fluid volume, which can be estimated by multiplying the volume of expansion by two.
Expansion tanks are normally used in heat-transfer systems where fluids will expand as they are heated.
- Allows for thermal expansion of the fluid
- Extends equipment life
- Make operations safer
- Allows for easier maintenance
- Oxidation can make the fluid more acidic and corrode the tank
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