What is a tank

What is a tank?

Storage tank is used to store refined chemicals such as acid and alkali, alcohol, gas and liquid. Storage tanks are widely used in North China. According to different materials, they generally include polyethylene storage tanks, polypropylene storage tanks, FRP storage tanks, ceramic storage tanks, rubber storage tanks, stainless steel storage tanks, etc.
In terms of the cost performance of storage tanks, steel lined polyethylene storage tanks are the most superior. They have excellent corrosion resistance, high strength and long service life. They can be manufactured in many varieties, such as built-up, horizontal, transportation and mixing.

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Steel sealed containers used to store liquids or gases are steel storage tanks. Steel storage tank engineering is an essential and important infrastructure in petroleum, chemical industry, grain and oil, food, fire protection, transportation, metallurgy, national defense and other industries. Our economic life is always inseparable from large and small steel storage tanks, Steel storage tanks play an irreplaceable role in the development of national economy. With the continuous development of the storage tank industry, more and more industries and enterprises have applied to the storage tank, and more and more enterprises have entered the storage tank industry. Steel storage tank is a special equipment for storing various liquid (or gas) raw materials and finished products. For many enterprises, normal production cannot be carried out without storage tank, In particular, national strategic material reserves are inseparable from storage tanks of various capacities and types. Most of the oil storage facilities in China are aboveground storage tanks, and most of them are metal structures.

Classification of storage tanks

Due to different storage media, the forms of storage tanks are also diverse.

  • Classified by location: it can be divided into aboveground storage tanks, underground storage tanks, semi underground storage tanks, offshore storage tanks, submarine storage tanks, etc.
  • Classification by oil products: it can be divided into crude oil storage tank, fuel oil storage tank, lubricating oil tank, edible oil tank, fire water tank, etc.
  • Classification by purpose: it can be divided into production oil tank, storage oil tank, etc.
  • Classification by form: it can be divided into vertical storage tank, horizontal storage tank, etc.
  • Classification by structure: it can be divided into fixed roof storage tank, floating roof storage tank, spherical storage tank, etc.
  • Classification by size: large storage tanks above 50m3, mostly vertical storage tanks; Those below 50m3 are small tanks, mostly horizontal tanks.
  • According to the materials of storage tanks: the materials required for storage tank engineering are divided into tank materials and auxiliary facilities materials. Tank body materials can be divided into low strength steel and high strength steel according to tensile yield strength or tensile standard strength. High strength steel is mostly used for storage tanks above 5000m3; Auxiliary facilities (including wind resistant ring beam, lock mouth, winding ladder, guardrail, etc.) are made of ordinary carbon structural steel with low strength, and other accessories and accessories are made of other materials according to different purposes. Domestic steels commonly used for tank manufacturing include 20, 20R, 16Mn, 16MnR, Q235 series, etc.

FRP section

FRP storage tanks have the following characteristics:
(1) It is light and high-strength

With a relative density of 1.5 – 2.0, which is only 1/4 – 1/5 of that of carbon steel, but the tensile strength is close to or even higher than that of carbon steel, and the specific strength can be compared with that of high-grade alloy steel. Therefore, it has excellent results in aviation, rockets, spacecraft, high-pressure vessels and other products that need to reduce self weight. The tensile, flexural and compressive strength of some epoxy FRP can reach more than 400MPa.
(2) Good corrosion resistance
FRP is a good corrosion-resistant material. It has good resistance to atmosphere, water, acid, alkali, salt of general concentration, as well as a variety of oils and solvents. It has been applied to all aspects of chemical anti-corrosion and is replacing carbon steel, stainless steel, wood, non-ferrous metals, etc.
(3) Good electrical performance
It is an excellent insulating material used to make insulators. It can still protect good dielectric at high frequency. With good microwave transmission, it has been widely used in radar radome.
(4) Good thermal performance
FRP has low thermal conductivity, which is 1.25 – 1.67kj/(m.h.K) at room temperature, only 1/100 – 1/1000 of metal. It is an excellent thermal insulation material. Under the condition of instantaneous ultra-high temperature, it is an ideal thermal protection and ablation resistant material, which can protect the spacecraft from the erosion of high-speed airflow above 2000 ℃.
(5) Good designability

  • ① Various structural products can be flexibly designed according to needs to meet the use requirements, which can make the product have good integrity.
  • ② Materials can be fully selected to meet the performance of products, such as corrosion-resistant, instantaneous high temperature resistant, products with special high strength and good dielectric in a certain direction, etc.

(6) Excellent processability

  • ① The forming process can be flexibly selected according to the shape, technical requirements, purpose and quantity of products.
  • ② The process is simple, can be formed at one time, and the economic effect is outstanding. Especially for the products with complex shape and small quantity that are not easy to form, its process advantages are more prominent.

Polyethylene type

Polyethylene is abbreviated as PE in foreign languages. The maximum application temperature is 60 ℃ for low density polyethylene and 70 ℃ for high density polyethylene. The minimum application temperature is – 70 ℃. It has the advantages of no welding joint, no leakage, no toxicity, anti-aging, impact resistance, corrosion resistance, long life, and meets hygienic standard. It makes up for the shortcomings of poor rigid strength, no pressure resistance and temperature difference resistance of all plastic rotational plastic storage tank. The lining surface of the product is flat, smooth and firm. Compared with the traditional steel lined plastic plate storage tank, steel lined rubber storage tank and steel lined FRP storage tank, it has better corrosion resistance, no leakage, no peeling, wear resistance, certain pressure resistance, higher temperature resistance and longer service life. Its price is lower than the traditional storage tank of the same specification. It is an ideal container for storing corrosive liquid. Therefore, it is an extremely excellent corrosion-resistant storage tank. The steel lined plastic vertical storage tank also has the characteristics of convenient installation, small floor area, and can be made into the shape required by users. The super large steel lined plastic tank has better integrity and is more prominent, which can not be achieved by other tank manufacturing processes.
Storable substance

  • (1) Inorganic acid: (dilute sulfuric acid, dilute nitric acid, hydrochloric acid, phosphoric acid, hydrofluoric acid, hydrobromic acid, hypochlorous acid, silicic acid, nitrous acid, sulfite, carbonic acid, fluorosilicic acid, fluoroboric acid, etc.)
  • (2) Organic acids: (formic acid, acetic acid, propionic acid, maleic acid, lauric acid, fatty acid, lactic acid, glycolic acid, peracetic acid, oxalic acid, malonic acid, succinic acid, maleic acid, malic acid, tartaric acid, benzoic acid, phenylacetic acid, etc.)
  • (3) Alkali and hydroxide: (sodium hydroxide, potassium hydroxide, ammonia hydroxide, calcium hydroxide, magnesium hydroxide, barium hydroxide, aluminum hydroxide, iron hydroxide, ammonium sulfate, ammonium nitrate, ammonium carbonate, ammonium nitrate, ammonium phosphate, ammonium persulfate, ammonium chloride, sodium silicate, potassium hypochlorite, aluminum carbonate, aluminum nitrate, aluminum sulfate, potassium acetate, potassium formate, potassium, copper sulfate, copper nitrate, alum, calcium carbonate).
  • (4) Elements, gases, and other inorganic compounds (sulfur, sulfur colloid, phosphorus, mercury, hydrogen peroxide, ammonia, coal, carbon monoxide, carbon dioxide, sulfur dioxide, hydrogen chloride, hydrogen bromide, hydrogen sulfide, phosphine, boron fluoride, calcium oxide, zinc oxide)
  • (5) Alcohols, aldehydes, ketones, ethers, esters, hydrocarbons and petroleum products (methanol, ethanol, n-propanol, isopropanol, dilute propanol, butanol, SEC butanol, tert butanol, n-ethanol, tert ethanol, formaldehyde, acetaldehyde, butyraldehyde, asphalt, etc.)
  • (6) Other elemental compounds, industrial liquids and products, food and vegetable oils, atmosphere, water, soil (soap, detergent, sulfur lime, bleach, ink, latex, starch, gelatin, animal oil, rosin, nicotine, vinegar, yeast, wine, seawater, brine, high-purity water, acidic mineral water, sewage, soil, etc.)
  • (7) Halogen containing organic compounds, amines, phenols and other organic compounds (chloropropanol, chloramine, hexachlorobenzene, freon, dimethylformamide, Resorcinol, hydroquinone, sodium phenol, mylin, nicotine, etc.)

Specifications
Among them, polyethylene all plastic storage tank (storage tank) has vertical (flat bottom, cone bottom) and horizontal; transport tank has automobile transport tank car and carriage transport tank; mixing tank has flat cover, flat cover, cone bottom and reaction tank type; steel lined plastic storage tank (storage tank) (steel plastic composite storage tank (storage tank)) has vertical (flat bottom, cone bottom) Horizontal and other series products. Various storage tanks can also be customized according to needs. Generally, the applicable size of all plastic storage tanks is about 1m3 to 50m3. The specification of steel plastic lined vertical storage tanks, steel plastic composite vertical storage tanks and tortoise shell lined storage tanks is about 1m3 to 150m3.

Stainless steel type

Classification

  • 1. Classification by form: it can be divided into vertical stainless steel tank and horizontal stainless steel tank;
  • 2. Classification by purpose: it can be divided into stainless steel tanks for brewing, food, pharmaceutical, dairy, chemical, petroleum, building materials, electric power and metallurgy;
  • 3. Classification according to hygienic standard: sanitary stainless steel tank and ordinary stainless steel tank;
  • 4. Classification according to pressure requirements: stainless steel pressure vessel, non stainless steel pressure vessel.

Common stainless steel tanks
Structure and performance of stainless steel storage tank, stainless steel pressure tank, stainless steel wine tank, stainless steel milk tank, stainless steel reaction tank, stainless steel vacuum tank, stainless steel fermentation tank.

  • Container heat insulation materials are made of high temperature resistant, aging resistant polyurethane foam or pearl cotton.
  • the interface adopts international general standard quick loading chuck type, the inner tank adopts imported 316L or 304, and the mirror polishing Ra of the inner surface is ≤ 0.28 μ m. External surface matte, mirror, sand blasting or cold rolling primary color matte.
  • Pipe orifice: liquid level gauge (digital display or glass tube type), air breathing port, thermometer (digital display or dial type), CIP cleaning port, mirror, explosion-proof sight lamp, SIP sterilization port, liquid inlet and outlet, manhole, etc.
  • The volume includes 500l-30000l, etc., which can also be designed and manufactured according to the actual needs of customers.

Overview of stainless steel tanks:
1. Food and pharmaceutical stainless steel storage tanks:
Stainless steel batching storage tank, stainless steel concentrated distribution storage tank, stainless steel dilute distribution storage tank, stainless steel extraction storage tank, stainless steel reaction storage tank, stainless steel liquid storage tank, stainless steel mixing tank, stainless steel seed storage tank, stainless steel nitric acid storage tank, stainless steel glacial acetic acid storage tank, stainless steel carbon disulfide drum tank and stainless steel water tower storage tank.
2. Stainless steel tanks for brewing and dairy industry:
Stainless steel wine storage tank, stainless steel Baijiu storage tank, stainless steel wine storage tank, stainless steel milk (milk) pot, stainless steel beverage storage tank.
3. Chemical stainless steel tank:
Stainless steel oil storage tank, stainless steel transportation storage tank, stainless steel cooling storage tank, stainless steel insulation storage tank, stainless steel heat exchange storage tank, stainless steel buffer tank, stainless steel outdoor storage tank and various levels of stainless steel pressure vessels in the chemical industry.
Features of stainless steel storage tank:

  • 1. Stainless steel tanks have strong corrosion resistance and are not corroded by residual chlorine in external air and water. Each spherical tank is subjected to super pressure test and inspection before leaving the factory, and its service life can reach more than 100 years under normal pressure.
  • 2. The stainless steel tank has good sealing performance; the sealed design completely prevents harmful substances in air dust and mosquitoes from invading the tank, so as to ensure that the water quality is not polluted by the outside world and red insects breed.
  • 3. The scientific water flow design makes the sediment at the tank bottom not turn up due to the water flow, ensures the natural stratification of domestic water and fire water, and reduces the turbidity of domestic water from the tank by 48.5%, but the water pressure increases significantly, which is conducive to improving the performance of domestic water and fire water facilities.
  • 4. Stainless steel tanks do not need to be cleaned frequently; the precipitates in the water can be discharged only by opening the blowdown valve at the bottom of the tank regularly. Simple equipment can be used to remove the scale every 3 years, greatly reducing the cleaning cost and completely avoiding human bacterial and viral pollution.

PP type vertical storage tank

Equipment features:

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  • Working pressure: normal pressure;
  • Working temperature: pp-10 ℃~ 120 ℃, pvc-40 ℃~ 60 ℃.

2. PP horizontal storage tank: equipment features:

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  • Working pressure: normal pressure;
  • Working temperature: pp-10 ℃~ 120 ℃, pvc-40 ℃~ 60 ℃.

Standard for storage tanks

Common tank standards:

  • 1. American Petroleum Institute standard API650;
  • 2. British standard BS2654;
  • 3. Japanese standard JISb8501;
  • 4. German standard DIN4119;
  • 5. Petroleum industry standard SYJ1016;
  • 6. Petrochemical industry standard SH3046.

Material of storage tank

The materials required for storage tank engineering are divided into tank body materials and auxiliary facilities materials.

Tank body materials can be divided into low strength steel and high strength steel according to tensile yield strength or tensile standard strength. High strength steel is mostly used for 5000m ³ Above storage tanks; Auxiliary facilities (including wind resistant ring beam, lock opening, winding ladder, guardrail, etc.) are made of ordinary carbon structural steel with low strength, and other accessories and accessories are made of other materials according to different purposes. Domestic steels commonly used in tank manufacturing include 20, 20R, 16Mn, 16MnR and Q235 series.

Structure of storage tank

At present, the dome roof storage tank, floating roof storage tank and horizontal storage tank are the most widely used and the most mature production and installation technology in China.

Structure of dome roof storage tank

Dome roof storage tank is a kind of steel container with spherical crown on the top and cylindrical body. Dome roof storage tank has the advantages of simple manufacture and low cost, so it is most widely used in many industries at home and abroad, and the most commonly used volume is 1000-10000m ³, At present, the maximum volume of domestic dome roof storage tank has reached 150000 M ³.

Tank bottom

The tank bottom is assembled by steel plates. The steel plate in the middle of the tank bottom is the middle plate, and the surrounding steel plate is the edge plate. The edge plate can be strip plate or bow plate. Generally, when the inner diameter of the storage tank is less than 16.5m, the strip edge plate should be used, and when the inner diameter of the storage tank is ≥ 16.5m, the bow edge plate should be used.

Tank wall

The tank wall is assembled and welded by multiple circles of steel plates, which is divided into sleeve type and linear type.
The circumferential weld of sleeve tank wall plate is overlapped, and the longitudinal weld is butt joint. This form is mostly used for dome roof storage tanks, which has the advantage that it is convenient for the assembly of each ring of wall plates, and it is safer to use the inversion method for construction.
The circumferential weld of linear tank wall plate is butt joint. The advantage is that the overall diameter of the tank wall is the same from top to bottom, which is especially suitable for internal floating roof storage tanks, but the assembly has high requirements for installation and is difficult.

Tank top

Multiple sector plates are assembled and welded on the tank top to form a spherical crown. The inner side of the tank top is made of flat steel, and lap welds are adopted between each sector plate. The whole tank top is welded with the angle steel ring (or lock mouth) on the upper part of the tank wall plate.

Structure of floating roof storage tank

Floating roof tank is composed of floating roof floating on the surface of medium and vertical cylindrical tank wall. The floating roof rises and falls with the increase or decrease of medium reserves in the tank. There is an annular sealing device between the outer edge of the floating roof and the tank wall. The medium in the tank is always directly covered by the inner floating roof to reduce medium volatilization.

Tank bottom

The volume of floating roof tank is generally large, and its bottom plate adopts arched edge plate.

Tank wall

The linear tank wall is adopted, and the butt weld should be polished smooth to ensure the flatness of the inner surface. The upper part of the floating roof tank is open. In order to increase the stiffness of the wall plate, the wind resistant ring beam and stiffening ring shall be set at the top of the tank wall according to the wind load of the area.

Floating roof

The floating roof is divided into single disc floating roof, double disc floating roof and float floating roof.
Single disc floating roof
It is an annular floating ship composed of several independent compartments, and the inner side of the annular is the single disc roof. A plurality of annular steel rings are arranged at the bottom of the single panel top plate for reinforcement. The utility model has the advantages of low cost and easy maintenance.
Double disc floating roof
It is composed of upper plate, lower plate and cabin edge plate. It is separated into several independent annular tanks by radial diaphragm and circumferential diaphragm. The utility model has the advantages of large buoyancy and good drainage effect.

Structure of internal floating roof storage tank

The internal floating roof storage tank is formed by adding a floating roof inside the dome roof storage tank. Adding a floating roof in the tank can reduce the volatilization loss of media, and the external dome can prevent rainwater, snow and dust from entering the tank to ensure the cleanness of media in the tank. This kind of storage tank is mainly used to store light oil, such as gasoline, aviation kerosene, etc. The inner floating roof storage tank adopts linear tank wall, the wall plate is butt welded, and the dome roof is made according to the requirements of the dome roof storage tank. At present, there are two kinds of internal floating roof structures in China: one is the same steel floating roof as floating roof storage tank; The other is the assembled aluminum alloy floating roof.

Structure of horizontal storage tank

The volume of horizontal storage tanks is generally less than 100m3, which is usually used in production links or gas stations. The circumferential weld of horizontal storage tank shall be overlapped, and the longitudinal weld shall be butt welded. The ring plates are arranged alternately, and the odd number is taken to make the diameter of the end cover the same. The end cover of horizontal storage tank is divided into flat end cover and dished end cover. The horizontal storage tank with flat end cover can withstand 40kpa internal pressure and the horizontal storage tank with dished end cover can withstand 0.2MPa internal pressure. The underground horizontal storage tank must be provided with a reinforcing ring, which is also made by simmering with angle bar.

Foundation selection of storage tank

1. When the local foundation soil layer can meet the requirements of bearing capacity design value and settlement difference, and the site is not limited, slope protection or outer ring wall foundation should be adopted;
2. When the local foundation soil layer cannot meet the requirements of the design value of bearing capacity, but the settlement does not exceed the allowable value, the ring wall type or outer ring wall type foundation can be adopted;
3. When the local foundation soil layer is soft soil layer, the outer ring wall foundation should be adopted after foundation treatment;
4. When the site is limited, the ring wall foundation can be used.

Foundation construction of storage tank

  • 1. Earth excavation: Foundation Pit compaction;
  • 2. Reinforced concrete and masonry works: (omitted);
  • 3. Earthwork backfilling: mechanical compaction, and the backfilled soil layer is greater than 500mm;
  • 4. Sand cushion: medium and coarse sand shall be selected, the laying thickness shall be 200-250mm, and the flat vibrator shall be used for watering and compaction;
  • 5. Asphalt sand cushion: medium and coarse sand and petroleum asphalt of road 60 A are selected to be heated to make asphalt sand, which is paved in layers and blocks, with a thickness of 80-100mm, and the slope of the top surface of the storage tank foundation from the center to the surrounding is 15-35‰;
  • 6. Slope protection construction: the slope protection construction shall be carried out after the hydrostatic test of the storage tank, and the slope protection width is 800-1000mm. Asphalt mastic shall be used for filling between the revetment and the tank bottom plate.
  • 7. During the design and construction of storage tank foundation, please carefully refer to SH/t3083 technical code for foundation treatment of petrochemical steel storage tank and sh3086 code for design of foundation and foundation of petrochemical steel storage tank.

Fabrication and installation of storage tank

  • 1. The tank construction process is divided into two parts: semi-finished product prefabrication and on-site assembly and installation.
  • 2. Prefabrication of semi-finished products: the tank bottom, tank wall, tank top and other components need to be prefabricated (the specific prefabrication method is omitted).
  • 3. Site assembly and installation method: it is roughly divided into inverted method construction process, formal method construction process and special method construction process.

Tank accessories

1. Oil tank accessories are an important part of the oil tank itself. Its settings can be divided into four types according to their functions:

  • Ensure the completion of oil receiving, dispatching and storage, which is convenient for production, operation and management.
  • Ensure the safe use of oil tanks and prevent and eliminate all kinds of oil tank accidents.
  • Oil tank cleaning and maintenance.
  • It can reduce the evaporation loss of oil products.

2. Winding ladder (or vertical ladder): with rest platform, 650mm wide, counterclockwise rotation. The tank top is equipped with anti-skid steps. The escalator is specially set up for operators to go up to the tank for ruler inspection, temperature measurement, sampling and patrol inspection. It has two types: vertical ladder and rotary ladder. Generally speaking, vertical ladders are used for small oil tanks and rotary ladders are used for large oil tanks. Guardrail: 800-1000mm high.
3. Overpass: used for connection between tanks, with a width of 650mm.
4. Manhole: there are three common specifications: DN500, DN600 and dn750. Manhole is provided for operators to enter and exit the oil tank when cleaning and repairing the oil tank. For general vertical oil tanks, manholes are installed on the lowest ring plate of the tank wall and opposite to the daylighting hole above the tank top. The diameter of manhole is mostly 600mm, and the distance from the hole center to the tank bottom is 750mm. Generally, one manhole shall be set for oil tanks below 3000 m3, one to two manholes shall be set for oil tanks above 5000 m3, and two manholes must be set for oil tanks above 5000 m3.
5. Transparent hole: common specification: DN500. Light transmission hole, also known as daylighting hole, is set for daylighting and ventilation during cleaning or maintenance of oil supply tank. It is usually set on the tank top above the inlet and outlet oil pipes, with a diameter of 500mm, and the outer edge is 800-1000mm away from the tank wall. The number of settings is the same as that of manholes.
6. Cleaning hole or blowdown hole: blowdown hole for light oil and cleaning hole for heavy oil. There are three models: DN50, DN80 and DN100.
7. Oil measuring hole: common specification: DN150. The oil measuring hole is set for ruler, temperature measurement and sampling, and is installed near the tank top platform. Each oil tank is only equipped with an oil measuring hole with a diameter of 150mm and a distance of 1m from the tank wall.
8. Drain pipe and automatic water cutter: the dehydration pipe, also known as drain pipe, is specially set up to remove water impurities in the tank and remove dirty oil residue at the bottom of the tank. The drain pipe is equipped with a valve on the outer side of the tank. In order to prevent the dehydration valve from being loose or damaged, two valves are usually installed. In winter, the dehydration valve shall also be well insulated to prevent freezing or valve cracking.
9. Inlet and outlet joint pipe.
10. Fire fighting foam room: fire foam room, also known as foam generator, is a fire extinguishing device fixed on oil tank. One end of the foam generator is connected to the foam pipeline, and one end is flanged on the top layer of the tank wall. Fire extinguishing foam flows through the air intake entrance of the fire foam chamber, inhaling a large amount of air to form foam, and breaking through the insulating glass into the tank (glass thickness is not greater than 2mm), so as to achieve the purpose of incoming fire.
11. Grounding wire: grounding wire is a device to eliminate static electricity of oil tank.
12. Special accessories for light oil
Light oil (including gasoline, kerosene, diesel oil, etc.) is a kind of oil with low viscosity, light weight and volatile. The oil tanks containing such oil products are equipped with various special accessories for oil tanks that meet their characteristics and meet the needs of production and safety.

  • Oil tank breather valve: oil tank breather valve is an important equipment to ensure the safe use of oil tank and reduce oil loss.
  • Hydraulic safety valve: hydraulic safety valve is another important equipment to improve the safe use performance of oil tank. Its working pressure is 5-10% higher than that of mechanical call valve. Under normal circumstances, it does not move. When the mechanical breather valve fails due to the corrosion or jamming of the valve disc or the overpressure or excessive vacuum in the tank due to the abnormal collection and payment operation of the oil tank, it will play a role in the safe sealing of the oil tank and preventing the damage of the oil tank.
  • Flame arrester: flame arrester, also known as oil tank fire arrester, is the fire safety facility of oil tank. It is installed under mechanical breather valve or hydraulic safety valve, and is internally equipped with many wire mesh or corrugated plates made of copper, aluminum or other high heat capacity metals. In case of external flame or spark entering the fire extinguisher through the breather valve, the metal mesh or corrugated plate can quickly absorb the heat of burning substances to extinguish the flame or spark, so as to prevent the oil tank from catching fire.
  • Spray cooling device: the spray cooling device is an energy-saving device installed to reduce the oil temperature in the tank and reduce the breathing loss of the oil tank.

13. Special accessories for inner floating roof oil tank
Compared with the general dome roof tank, the inner floating roof tank is equipped with unique special accessories due to its different structure and according to its service performance requirements.

  • Vent hole: because the inner floating plate covers the oil surface of the inner floating roof oil tank, the oil-gas space is basically eliminated, so the evaporation loss is very small, so the mechanical breather valve and safety valve are not set on the top of the tank. However, in practice, oil and gas leakage is still inevitable in the annular gap of the floating roof or the joint parts of other accessories. In order to prevent the accumulation of oil and gas from reaching a dangerous level, vent holes are opened on the tank top and tank wall.
  • Electrostatic export device: during the oil inlet and outlet operation of the inner floating roof oil tank, a large amount of static charge is accumulated on the floating plate. Since insulation is often used as sealing material between the floating plate and the tank wall, the static charge accumulated on the floating plate cannot be guided through the tank wall. In order to guide away this part of electrostatic charge, an electrostatic outlet line is installed between the floating plate and the tank top. Generally, there are 2 bare soft copper strands, the upper end is connected with the daylighting hole, and the lower end is pressed on the cover strip of the floating plate.
  • Anti rotation steel rope: in order to prevent the deformation of the oil tank wall and the smooth lifting affected by the rotation of the floating plate, two stainless steel cables are vertically tensioned between the tank top and bottom of the inner floating roof tank, and the two steel cables are symmetrically arranged at both ends of the floating roof diameter. Under the restriction of steel rope, the floating roof can only rise and fall vertically, thus preventing the floating plate from rotating.
  • Automatic vent valve: the automatic vent valve is set in the middle of the floating plate. It is designed to protect the oil tank from breathing normally when entering and leaving the oil tank when the floating plate is in the supporting position, so as to prevent evacuation or pressure holding below the floating plate.
  • Floating plate support: after the internal floating roof oil tank is used for a period of time, the floating roof needs to be repaired and the oil tank needs to be cleaned. At this time, the floating roof needs to be lowered to a certain height from the tank bottom and supported by several supports on the floating plate.
  • Diffusion pipe: the diffusion pipe is connected with the inlet pipe in the oil tank, the pipe diameter is twice that of the inlet pipe, and many small holes with a diameter of 2mm are evenly drilled on both sides. It plays the role of reducing the flow rate and protecting the floating plate strut when the oil tank receives oil.

Discharge during crude oil storage and loading

It mainly includes: large and small breathing loss of storage tank, oil leakage and loading loss.
1. Large breathing loss of storage tank
Big breathing refers to the breathing when the oil tank is fed and distributed. When the oil tank enters the oil, the oil level gradually increases, the gas space gradually decreases, and the pressure in the tank increases. When the pressure exceeds the control pressure of the breather valve, a certain concentration of oil vapor begins to exhale from the breather valve until the oil tank stops receiving oil, and the exhaled oil vapor causes the loss of oil evaporation.
When the oil tank sends oil outward, due to the continuous decrease of the oil level, the gas space gradually decreases and the pressure in the tank decreases. When the pressure is less than the vacuum controlled by the breather valve, the oil tank begins to inhale fresh air. Because the oil and gas in the space above the oil level does not reach saturation, the evaporation of oil is accelerated, so that it reaches saturation again, and the pressure in the tank rises again, Cause some oil vapor to exhale from the breather valve. The main factors affecting large breathing are:

  • Oil properties. The smaller the oil density, the more light fraction and the greater the loss;
  • Oil receiving and transmitting speed. The faster the oil inlet and outlet speed, the greater the loss;
  • Pressure level of oil tank. The better the pressure resistance of the oil tank, the smaller the respiratory loss. When the pressure of the oil tank reaches 5kpa, the consumption reduction rate is 25.1%. If the pressure increases to 26kpa, the small respiratory loss can be basically eliminated and the large respiratory loss can be reduced to a certain extent.
  • It is related to the geographical location, atmospheric temperature, wind direction, wind force and management level of the oil tank.
  • Measures taken: the oil stored in the project is crude oil, which is less volatile than gasoline and diesel. The pipelines of various storage tanks are interconnected. At the same time, internal floating roof tanks are used, so the crude oil is large and the respiratory loss is less.

2. Small breathing loss of storage tank
When there is no oil receiving and distributing operation in the oil tank, with the rise and fall cycle of external air temperature and pressure in one day, the gas space temperature, oil evaporation rate, oil and gas concentration and steam pressure in the tank also change. The loss of oil and gas caused by the process of discharging oil vapor and inhaling air is called small breathing loss. The main influencing factors of small respiratory loss are as follows:

  • Variation of temperature difference between day and night. The greater the temperature difference between day and night, the greater the respiratory loss.
  • Sunshine intensity in the area where the oil tank is located. The greater the sunshine intensity, the greater the respiratory loss.
  • The larger the storage tank, the larger the cross-sectional area and the greater the respiratory loss.
  • Atmospheric pressure. The lower the atmospheric pressure, the greater the respiratory loss.
  • Oil tank filling degree. The oil tank is full, the gas space volume is small, and the breathing loss is small.
  • Measures taken: the oil stored in the project is crude oil, and the pipelines of various storage tanks are interconnected. At the same time, internal floating roof tanks are used. Cooling water will be sprayed regularly in summer to prevent small breathing. Therefore, small breathing loss of crude oil is less.
  • The tank accessories are not tight, resulting in loss.
  • Measures taken: strengthen the maintenance of auxiliary equipment of oil tank, maintain the tightness of oil tank, and improve the operation management of oil tank as the cheapest and very effective measures to reduce loss and prevent pollution. The fire arrester, liquid sealing oil, mechanical breathing valve, fire foam glass chamber and oil measuring hole are thoroughly inspected two times a year, so that tightness meets the requirements. The oil tank shall be filled to the allowable level as much as possible. The lower the filling level, the greater the loss.

Crude oil loading loss
The loss of crude oil loading mainly refers to the loss caused by the process of loading crude oil into the truck tanker. 50% of the crude oil is transported out of the ship by pipeline and 50% by truck. The shipment is balanced and brought back to the gas system, so the loss is very small. The loading is immersion loading.
Measures taken: crane tube loading and submerged loading are adopted.

Source: China Tube Sheet Manufacturer – Yaang Pipe Industry (www.steeljrv.com)

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

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