Types of storage tanks

tanks are used in general chemical industries classified as: atmospheric storage tanks, pressure storage tanks and refrigerated storage tanks

1. 1 Prepared by: Purvin Prajapati TYPES OF STORAGE TANKS

2. 2 Outline Storage tanks Types of storage tanks Atmospheric storage tanks Pressure storage tanks Refrigerated storage tanks

3. 3 Storage tanks General Storage of liquid materials is commonly accomplished in industrial plants by use of cylindrical, spherical or rectangular tanks. Storage tanks are also used as an intermediate stage in process, particularly in batch process These tanks may be constructed of wood, concrete, or metal, with metal being the most common material of construction. Now a days metallic storage tanks are replaced by fiber reinforced plastic(FRP) and high density polyethylene(HDPE).

4. 4 Storage tanks The design of storage vessels involves consideration of details such as size and number of openings, shape of heads, necessary temperature and pressure controls and corrosive action of the content. The design of storage vessels involves consideration of details such as size and number of openings, shape of heads, necessary temperature and pressure controls and corrosive action of the content. Storage tanks having cylindrical shell, flat bottom, conical or dome shaped roof are designed, fabricated and erected as per the standards.

5. 5 Types of storage tanks

6. 6 Atmospheric storage tanks These tanks are used for holding a liquid at atmospheric pressure. The major design code for welded atmospheric tanks are API 650 (for floating roof storage tanks) and API 620 (for fixed roof storage tanks). Atmospheric storage tanks further classified as follows: Open roof tanks Fixed roof tanks Floating roof tanks

7. 7 Open roof tanks This tank has no roof and may store or nonhazardous liquid such as water other aqueous solution can be stored. Figure 1. Open roof tanks

8. 8 Fixed roof tanks These tanks are most common types of tanks which are used in industries. These are used for liquid with very high flash point, ( e.g fuel oil, water, bitumen etc.) Cone roofs, dome roof and umbrella roofs are usual. These are provided with breathers or vents to permit the variation in vapour pressure of liquid with temperature and permit the change in volume of liquid with temperature. These are insulated to prevent the clogging of certain materials, wherein the heat is provided by steam coil within the tanks.

9. 9 Fixed roof tanks Dome roof tanks are used for tanks having slightly higher storage pressure than that of atmospheric. Fixed roof tanks designed to withstand small pressure and vacuum. They are classified further as Class ‘A’ tanks: they can withstand internal pressure of 200 mm water column gauge and vacuum of 65 mm water column. Class ‘B’ tanks: they can withstand maximum internal pressure of 550 mm water column gauge and vacuum of 65 mm water column. These tanks diameter is never greater than 20 meter.

10. 10 Figure 2. Fixed roof tanks

11. 11 Floating roof tanks Floating roof tanks are broadly divided into two types: Internal floating roof tanks (IFR) External floating roof tanks (FR) Internal floating roof tanks (IFR): These tanks are used for liquids with low flash points (e.g. gasoline, ethanol). These tanks are nothing but cone roof tanks with a floating roof inside which travels upward and down along with the liquid level

12. 12 Floating roof tanks Floating roofs are supported with legs or cables on which they rest. Floating roofs are considered a safety requirement as well as a pollution prevention measure for many industries including petroleum refining This type of scenario affords protection for the floating roof from outdoor elements such as rain, frost and snow. In addition, covered floating roof tanks minimize, and in some cases eliminate, the potentially harmful gaseous zone that accumulates over stored liquid and space between the floating roof and fixed roof is always well-ventilated.

13. 13 Figure 3. Internal floating roof tanks

14. 14 Floating roof tanks ii. External floating roof tanks (FR): External floating roofs do not have a fixed roof and has floating roof only. This tank is a storage tank commonly used to store large quantities of petroleum products which have medium flash point such as naphtha, kerosene, diesel, crude oil. It comprises an open-topped cylindrical steel shell equipped with a roof floats on the surface of the storage liquid. Expansion and contraction due to temperature changes.

15. 15 Floating roof tanks This type of roof Expansion and contraction due to temperature changes. This type of tank roof minimise contact area or mass transfer area between liquid and air. Hence rate of diffusion of liquid vapour in to ai reduce. There is a rim seal system between the tank shell and roof to reduce rim evaporation. Advantages of FR tanks over IFR tanks: FR tanks are economical and usually installed for environmental reasons to limit product loss and reduce the emission. A smaller risk of internal expansion.

16. 16 Floating roof tanks Disadvantages of FR tanks over IFR tanks: Rain water and snow can accumulate on the roof , eventually the roof may sink. There are two main types of external floating roofs and each one is employed based on varying circumstances and the specific results desired. Pontoon roof or single deck roof Double deck roof

17. 17 Figure 4. External floating roof tanks

18. 18 Pressure storage tanks Applies to vessels designed to withstand pressures sufficient to keep liquid stored from vaporizing. Used for high vapor pressure liquid such as butane, propane etc. Spheres - Generally used to store high vapor pressure liquid. Advantage is that it can contain the greatest amount of liquid for a given amount of steel. A sphere can also withstand greater pressures with a given plate thickness than cylindrical vessels.

19. 19 Figure 5. Pressure storage tanks

20. 20 Refrigerated storage tanks These tanks refer to low temperature/cryogenic storage. This type is used for gases that liquefy under pressure at atmospheric temperature. In cryogenic storage the gas is at, or near to, atmospheric pressure and remains liquid because of low temperature. Cryogenic refers to temperature below -150 ⁰ C.

21. 21 Figure 6. Refrigerated storage tank

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