Storage tank

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Cylindrical fuel storage tank with fixed roof and internal floating roof. Capacity approx 2,000,000 litres Fuel tank gnangarra.jpg
Cylindrical fuel storage tank with fixed roof and internal floating roof. Capacity approx 2,000,000 litres

Storage tanks are containers that hold liquids or compressed gases. The term can be used for reservoirs (artificial lakes and ponds), and for manufactured containers. The usage of the word "tank" for reservoirs is uncommon in American English but is moderately common in British English. In other countries, the term tends to refer only to artificial containers. In the U.S., storage tanks operate under no (or very little) pressure, distinguishing them from pressure vessels .

Contents

Tanks can be used to hold materials as diverse as milk, water, waste, petroleum, chemicals, and other hazardous materials, all while meeting industry standards and regulations. [1] Storage tanks are available in many shapes: vertical and horizontal cylindrical; open top and closed top; flat bottom, cone bottom, slope bottom and dish bottom. Large tanks tend to be vertical cylindrical, with flat bottoms, and a fixed frangible or floating roof, or to have rounded corners transition from the vertical side wall to bottom profile, in order to withstand hydraulic hydrostatic pressure. Tanks built below ground level are sometimes used and referred to as underground storage tanks (USTs).

Reservoirs can be covered, in which case they may be called covered or underground storage tanks or reservoirs. Covered water tanks are common in urban areas.

Tanks can be mounted on a lorry or an articulated lorry trailer. The resulting vehicle is called a road tanker (or simply tanker; tank truck in American English). Tank cars are tanks mounted on goods wagons for rail transportation.

Etymology

The word "tank" originally meant "artificial lake" and came from India, perhaps via Portuguese tanque. It may have some connection with:

Features and maintenance

While steel and concrete remain one the most popular choices for tanks, glass-reinforced plastic, thermoplastic and polyethylene tanks are increasing in popularity. They offer lower build costs and greater chemical resistance, especially for storage of specialty chemicals. There are several relevant standards, such as British Standard  4994 (1989), DVS 2205, and ASME RTP-1 which give advice on wall thickness, quality-control procedures, testing procedures, accreditation, fabrication and design criteria of final product.

Some storage tanks need a floating roof in addition to or in lieu of the fixed roof and structure. This floating roof rises and falls with the liquid level inside the tank, thereby decreasing the vapour space above the liquid level. Floating roofs are considered a safety requirement as well as a pollution prevention measure for many industries including petroleum refining.

Capacity table for horizontal cylindrical storage tank Horizontal LPG reservoir table volume level curve.png
Capacity table for horizontal cylindrical storage tank

In order for volume measurements from the tank to be used, it typically has a capacity table created using appropriate standards. [3] Each row of capacity table contains fill level value and corresponding volume value (and other related data).

In the U.S., metal tanks in contact with soil and containing petroleum products must be protected from corrosion to prevent escape of the product into the environment. [4] The most effective and common corrosion control techniques for steel in contact with soil is cathodic protection. Outside the United States and at some locations in the United States, elevated tank support foundations with a sand bitumen mix finish are often used. These type of foundations keep the tank bottom plates free from water, therefore preventing corrosion.

In addition to their design and application, maintenance and inspection of storage tanks play a critical role in ensuring their safety and efficiency. Regular inspection is essential for identifying potential issues such as corrosion, leaks, structural weaknesses, and compliance with environmental regulations. These inspections can vary in frequency and detail depending on the type of tank, the material stored, and the regulatory requirements applicable in the location where the tank is used. For instance, tanks storing hazardous materials may require more frequent and thorough inspections compared to those used for non-hazardous materials. Maintenance protocols, including cleaning, repairs, and preventative measures, are equally important to prolong the lifespan of the tanks and prevent environmental contamination or accidents. Advanced technologies, such as remote sensing, ultrasonic testing, and robotic inspection tools, like remotely-operated drones, are increasingly being employed to enhance the effectiveness and safety of these inspection processes. Understanding and implementing appropriate inspection and maintenance schedules is paramount for operators of storage tanks to ensure operational reliability and adherence to safety standards. [5]

Several environmental regulations apply to the design and operation of storage tanks, often depending on the nature of the fluid contained within. [1] In the U.S., air emissions are typically required to undergo air quality permitting under the federal Clean Air Act. Quantification of potential emissions from tanks for permitting purposes is most often accomplished by applying emission equations published in chapter 7.1 of the Environmental Protection Agency's AP-42 (Compilation of Air Pollutant Emissions Factors from Stationary Sources).

Since most liquids can spill or seep through even the smallest opening, special consideration must be made for their safe and secure handling. This usually involves building a bunding, or containment dike, around the tank, so that any leakage may be safely contained.

Types of tank

Atmospheric

An atmospheric tank is a container for holding a liquid at atmospheric pressure. The major design codes for welded atmospheric tanks are API  650 and API 620. API 653 is used for analysis of in-service storage tanks. In Europe the applicable design code is EN  14015, which uses load cases from Eurocode 3 (EN 1993), part 4-2.

High-pressure

Horizontal, cylindrical shell, elliptical heads carbon steel pressure vessel Modified Hanson steelwatertank.jpg
Horizontal, cylindrical shell, elliptical heads carbon steel pressure vessel

In the case of a liquefied gas such as hydrogen or chlorine, or a compressed gas such as compressed natural gas or MAPP, the storage tank must be made to withstand the sometimes-considerable pressures exerted by the contents. These tanks, being pressure vessels, are sometimes excluded from the class of "tanks". Container tanks for handling liquids during transportation are often designed to handle varying degrees of pressure.

Thermal storage tanks

One form of seasonal thermal energy storage (STES) is the use of large surface water tanks that are insulated and then covered with earth berms to enable storage of seasonal solar-thermal heat that is collected primarily in the summer for all-year heating. [6] A related technology has become widespread in Danish district heating systems. The thermal storage medium is gravel and water in large, shallow, lined pits that are covered with insulation, soil and grass. [7]

Ice and slush tanks are used for short-term storage of cold for use in air conditioning, allowing refrigeration equipment to be run at night when electric power is less expensive, yet provide cooling during hot daytime hours.

Milk tanks

A bulk milk cooling tank is a storage tank located in a dairy farm's milkhouse used for cooling and holding fluid milk at a low temperature until it can be picked up by a milk hauler. Since milk leaves the udder at approximately 35 °C, milk tanks are needed to rapidly cool fresh raw milk to a storage temperature of 4 °C to 6 °C, thereby slowing growth of microorganisms. [8] Bulk milk cooling tanks are usually made of stainless steel and are constructed to sanitary standards. They must be cleaned after each milk collection. The milk cooling tank may be the property of the farmer, or may be rented by the farmer from a dairy plant.

Septic tanks

A septic tank is part of a small-scale sewage treatment system often referred to as a septic system. Septic systems are commonly used to treat wastewater from homes and small businesses in rural and suburban areas. [9] It consists of the tank and a septic drain field. Waste water enters the tank where solids can settle and scum floats. Anaerobic digestion occurs on the settled solids, reducing the volume of solids. The water released by the system is normally absorbed by the drain field without needing any further treatment.

Mobile tanks

While not strictly a "storage" tank, mobile tanks share many of the same features of storage tanks. Also, they must be designed to deal with a heavy sloshing load and the risk of collision or other accident. Some of these include ocean-going oil tankers and LNG carriers; railroad tank cars; and road tankers. Also included are the holding tanks which are the tanks that store toilet waste on RVs, boats and aircraft.

In refineries

View of Fawley Refinery large atmospheric tanks Oil storage tanks at Fawley Refinery (low-altitude aerial) - geograph.org.uk - 413370.jpg
View of Fawley Refinery large atmospheric tanks

Tanks for crude oil and oil-based fuels are chosen according to the flash point of the material. If the material is not a liquefied gas, such as LPG, tanks are atmospheric and generally come in two types:

  1. Fixed roof tanks are used for liquids with very high flash points (e.g., fuel oil, bitumen). Cone roofs, dome roofs and umbrella roofs are usual. These tanks may be insulated and heated with steam coils to prevent the product to become too viscous, thus plugging pipework and becoming potentially unpumpable. Dome roof tanks are meant for tanks having slightly higher-than-atmospheric storage pressure (e.g., slop oil).
  2. Floating roof tanks are broadly divided into external floating roof tanks (usually referred to simply as floating roof tanks, or FR tanks) and internal floating roof types (IFR Tanks). IFR tanks are used for liquids with lower flash points (e.g., jet fuel, petrol, ethanol). They are essentially cone-roof tanks with an internal floating roof travelling vertically up and down along with the liquid level. This floating roof traps the vapour from low flash-point fuels. Floating roofs are supported with legs or cables on which they rest. FR tanks do not have a fixed roof, being open at the top, and have a floating roof only. Medium flash point liquids such as naphtha, kerosene, diesel, and crude oil are stored in these tanks.
Spherical gas tank farm in the petroleum refinery in Karlsruhe MiRO MiRO4.jpg
Spherical gas tank farm in the petroleum refinery in Karlsruhe MiRO

Liquefied gases (such as LPG, butane, propylene, etc.) may be stored in spherical tanks (or Horton spheres).

Typical classification codes used for tanks in a refinery are:

Use for chemicals

BASF chemical plant in Portsmouth, Virginia. The plant is served by the Commonwealth Railway. CWRYBASF.JPG
BASF chemical plant in Portsmouth, Virginia. The plant is served by the Commonwealth Railway.

Chemical tanks are storage containers for chemicals widely used within the chemical industry. They come in a variety of sizes and shapes, and are used for static storage and transport of both raw materials and finished chemical products.

A chemical tank is of necessity designed for a specific chemical. Chemicals have variable corrosion potentials, so the size and features of chemical tanks are diverse. Chemical resistance is usually the first priority in designing chemical tanks. Selected materials have to be as resistant to the chemical stored as design and economics allow. This includes selection of smaller features such as gaskets and plumbing materials. Other parameters to be taken in consideration are heat, cold, vacuum, pressure, exothermic reactivity and the inherent aggressive nature of the chemical (acids, caustic, etc.). Secondary containment is a back-up strategy sometimes used to mitigate potential failure of the primary container. The typical profile of a vessel with secondary containment is a primary vessel with an exterior vessel shell encompassing the primary vessel with at least 100% capacity. Secondary vessels are available in polyethylene, fiberglass and metal materials. Secondary containment tank systems are suggested for all aggressive chemicals.

Tank failures

There have been numerous catastrophic failures of storage tanks, one of the most notorious being that which occurred at Boston on January 14, 1919. A large tank had only been filled eight times when it failed, and the resulting wave of molasses killed 21 people in the vicinity. The Boston molasses disaster was caused by poor design and construction, with a wall too thin to bear repeated loads from the contents. The tank had not been tested before use by filling with water, and was also poorly riveted. The owner of the tank, United States Industrial Alcohol Company, paid out $300,000 (nearly $4 million in 2012 ) in compensation to the victims or their relatives.

There have been many other accidents caused by tanks since then, often caused by faulty welding or by sub-standard steel. New inventions have at least fixed some of the more common issues around the tanks' seal. [10] [11] However, storage tanks also present another problem, surprisingly, when empty. If they have been used to hold oil or oil products such as gasoline, the atmosphere in the tanks may be highly explosive as the space fills with hydrocarbons. If new welding operations are started, then sparks can easily ignite the contents, with disastrous results for the welders. The problem is similar to that of empty bunkers on tanker ships, which are now required to use an inert gas blanket to prevent explosive atmospheres building up from residues.

Images

See also

Related Research Articles

<span class="mw-page-title-main">Liquefied petroleum gas</span> Fuel for heating, cooking and vehicles

Liquefied petroleum gas, also referred to as liquid petroleum gas, is a fuel gas which contains a flammable mixture of hydrocarbon gases, specifically propane, n-butane and isobutane. It can sometimes contain some propylene, butylene, and isobutene.

<span class="mw-page-title-main">Hydrostatic test</span> Non-destructive test of pressure vessels

A hydrostatic test is a way in which pressure vessels such as pipelines, plumbing, gas cylinders, boilers and fuel tanks can be tested for strength and leaks. The test involves filling the vessel or pipe system with a liquid, usually water, which may be dyed to aid in visual leak detection, and pressurization of the vessel to the specified test pressure. Pressure tightness can be tested by shutting off the supply valve and observing whether there is a pressure loss. The location of a leak can be visually identified more easily if the water contains a colorant. Strength is usually tested by measuring permanent deformation of the container.

<span class="mw-page-title-main">Pressure vessel</span> Vessel for pressurised gases or liquids

A pressure vessel is a container designed to hold gases or liquids at a pressure substantially different from the ambient pressure.

<span class="mw-page-title-main">Liquefied natural gas</span> Form of natural gas for easier storage and transport

Liquefied natural gas (LNG) is natural gas (predominantly methane, CH4, with some mixture of ethane, C2H6) that has been cooled down to liquid form for ease and safety of non-pressurized storage or transport. It takes up about 1/600th the volume of natural gas in the gaseous state at standard conditions for temperature and pressure.

<span class="mw-page-title-main">Gas cylinder</span> Cylindrical container for storing pressurised gas

A gas cylinder is a pressure vessel for storage and containment of gases at above atmospheric pressure. High-pressure gas cylinders are also called bottles. Inside the cylinder the stored contents may be in a state of compressed gas, vapor over liquid, supercritical fluid, or dissolved in a substrate material, depending on the physical characteristics of the contents. A typical gas cylinder design is elongated, standing upright on a flattened bottom end, with the valve and fitting at the top for connecting to the receiving apparatus.

<span class="mw-page-title-main">Tank car</span> Train car for holding liquids and gases

A tank car or tanker is a type of railroad car or rolling stock designed to transport liquid and gaseous commodities.

<span class="mw-page-title-main">Industrial gas</span> Gaseous materials produced for use in industry

Industrial gases are the gaseous materials that are manufactured for use in industry. The principal gases provided are nitrogen, oxygen, carbon dioxide, argon, hydrogen, helium and acetylene, although many other gases and mixtures are also available in gas cylinders. The industry producing these gases is also known as industrial gas, which is seen as also encompassing the supply of equipment and technology to produce and use the gases. Their production is a part of the wider chemical Industry.

<span class="mw-page-title-main">Tank truck</span> Motor vehicle designed to carry liquefied loads, dry bulk cargo or gases on roads

A tank truck, gas truck, fuel truck, or tanker truck or tanker is a motor vehicle designed to carry liquids or gases on roads. The largest such vehicles are similar to railroad tank cars, which are also designed to carry liquid loads. Many variants exist due to the wide variety of liquids that can be transported. Tank trucks tend to be large; they may be insulated or non-insulated; pressurized or non-pressurized; and designed for single or multiple loads. Some are semi-trailer trucks. They are difficult to drive and highly susceptible to rollover due to their high center of gravity, and potentially the free surface effect of liquids sloshing in a partially filled tank.

<span class="mw-page-title-main">Oil terminal</span> Industrial facility for the storage of oil, petroleum and petrochemical products

An oil terminal is an industrial facility for the storage of oil, petroleum and petrochemical products, and from which these products are transported to end users or other storage facilities. An oil terminal typically has a variety of above or below ground tankage; facilities for inter-tank transfer; pumping facilities; loading gantries for filling road tankers or barges; ship loading/unloading equipment at marine terminals; and pipeline connections.

<span class="mw-page-title-main">Bunding</span> Retaining wall around pollution source

Bunding, also called a bund wall, is a constructed retaining wall around storage "where potentially polluting substances are handled, processed or stored, for the purposes of containing any unintended escape of material from that area until such time as a remedial action can be taken."

<span class="mw-page-title-main">Water tank</span> Container for storing water

A water tank is a container for storing water, for many applications, drinking water, irrigation, fire suppression, farming, both for plants and livestock, chemical manufacturing, food preparation as well as many other uses. Water tank parameters include the general design of the tank, and choice of construction materials, linings. Various materials are used for making a water tank: plastics, fiberglass, concrete, stone, steel. Earthen pots, such as matki used in South Asia, can also be used for water storage. Water tanks are an efficient way to help developing countries to store clean water.

An oil production plant is a facility which processes production fluids from oil wells in order to separate out key components and prepare them for export. Typical oil well production fluids are a mixture of oil, gas and produced water. An oil production plant is distinct from an oil depot, which does not have processing facilities.

<span class="mw-page-title-main">LNG carrier</span> Tank ship transporting liquefied natural gas

An LNG carrier is a tank ship designed for transporting liquefied natural gas (LNG).

<span class="mw-page-title-main">Fire extinguisher</span> Active fire protection device

A fire extinguisher is a handheld active fire protection device usually filled with a dry or wet chemical used to extinguish or control small fires, often in emergencies. It is not intended for use on an out-of-control fire, such as one which has reached the ceiling, endangers the user, or otherwise requires the equipment, personnel, resources or expertise of a fire brigade. Typically, a fire extinguisher consists of a hand-held cylindrical pressure vessel containing an agent that can be discharged to extinguish a fire. Fire extinguishers manufactured with non-cylindrical pressure vessels also exist but are less common.

<span class="mw-page-title-main">External floating roof tank</span> Storage facility

An external floating roof tank is a storage tank commonly used to store large quantities of petroleum products such as crude oil or condensate. It consists of an open- topped cylindrical steel shell equipped with a roof that floats on the surface of the stored liquid. The roof rises and falls with the liquid level in the tank. As opposed to a fixed roof tank there is no vapor space (ullage) in the floating roof tank. In principle, this eliminates tank breathing loss and greatly reduces the evaporative loss of the stored liquid. There is a rim seal system between the tank shell and roof to reduce rim evaporation.

A liquid nitrogen engine is powered by liquid nitrogen, which is stored in a tank. Traditional nitrogen engine designs work by heating the liquid nitrogen in a heat exchanger, extracting heat from the ambient air and using the resulting pressurized gas to operate a piston or rotary motor. Vehicles propelled by liquid nitrogen have been demonstrated, but are not used commercially. One such vehicle, Liquid Air, was demonstrated in 1902.

<span class="mw-page-title-main">Flexible tank</span> Storage container

Flexible tanks are a kind of storage equipment for liquids such as water or oil. Compared to steel tanks, flexible tanks have many advantages, including lighter weight and being rustproof, foldable, and quicker and easier to set up. With the same capacity, an empty flexible tank may have just 10% of a steel tank's weight. The disadvantages of flexible tanks include lower durability and shorter longevity. Some flexible tanks can be used as transport containers on trucks, ships, or aeroplanes, with some suitable for use in airdrops, helicopter swing, or hauling water.

<span class="mw-page-title-main">Gas carrier</span> Ship designed to transport liquefied chemical gases in bulk

A gas carrier, gas tanker, LPG carrier, or LPG tanker is a ship designed to transport LPG, LNG, CNG, or liquefied chemical gases in bulk.

<span class="mw-page-title-main">Liquefied natural gas terminal</span> Facility for processing shipments of the fossil fuel

A liquefied natural gas terminal is a facility for managing the import and/or export of liquefied natural gas (LNG). It comprises equipment for loading and unloading of LNG cargo to/from ocean-going tankers, for transfer across the site, liquefaction, re-gasification, processing, storage, pumping, compression, and metering of LNG. LNG as a liquid is the most efficient way to transport natural gas over long distances, usually by sea.

<span class="mw-page-title-main">Marine LNG Engine</span>

A marine LNG engine is a dual fuel engine that uses natural gas and bunker fuel to convert chemical energy in to mechanical energy. Due to natural gas' cleaner burning properties, the use of natural gas in merchant ship propulsion plants is becoming an option for companies in order to comply with IMO and MARPOL environmental regulations. The natural gas is stored in liquid state (LNG) and the boil-off gas is routed to and burned in dual fuel engines. Shipping companies have been cautious when choosing a propulsion system for their fleets. The steam turbine system has been the main choice as the prime mover on LNG carriers over the last several decades. The decades-old system on steam propelled LNG carriers uses BOG. LNG carriers are heavily insulated to keep the LNG at around -160 °C – to keep it liquefied. Despite insulation, the LNG containment area is penetrated by heat which allows for naturally generated boil-off gas (BOG).

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