What Is an Underground Storage Tank?

The storage tank is used to store acid, alkali, alcohol, gas, liquid and other refined chemicals. Storage tanks are widely used in North China. According to different materials, there are generally polyethylene storage tanks, polypropylene storage tanks, glass steel storage tanks, ceramic storage tanks, rubber storage tanks, and stainless steel storage tanks.

The steel sealed container used to store liquid or gas is the steel storage tank. The steel storage tank project is an essential and important infrastructure for the petroleum, chemical, grain and oil, food, fire protection, transportation, metallurgy, national defense and other industries. In our economic life, steel storage tanks of various sizes are always inseparable. The important role played by steel storage tanks in the development of the national economy is irreplaceable. With the continuous development of the current storage tank industry, more and more industries and enterprises have used storage tanks, and more and more enterprises have entered the storage tank industry. Steel storage tanks store various liquid (or gas) raw materials and The special equipment for finished products cannot be produced normally without storage tanks for many enterprises, especially the national strategic material reserves cannot be separated from storage tanks of various capacities and types. China's oil storage facilities are mostly ground storage tanks, and most of them are metal structures.

The storage tank is a storage container for transporting medium in long-distance oil and gas pipelines. The oil storage tank at the first station of the oil pipeline is used to collect and store oil and to ensure the stability of the pipeline's oil delivery volume. The oil storage tank at the last station is used to receive and store incoming oil and provide it to the oil consumers. The gas storage tank at the end gate station of the gas pipeline is mainly used for peak regulation of urban gas, and is gradually being replaced by underground gas storage and pipeline gas storage ^[1]

1 Hazard analysis of large crude oil storage tank engineering

1.1 Crude oil risk analysis

Crude oil is a Class A and B flammable liquid with flammability. The explosion limit range is narrow, but the value is low, which has a certain degree of explosion danger. At the same time, the flammability of crude oil should be paid special attention during fire fighting.

1.2 Cause analysis of fire and explosion accidents

The characteristics of crude oil determine the risk of fire and explosion is the most important and important risk factor for large crude oil storage tanks. The three necessary conditions for a fire accident are: ignition source, combustibles and air.

The problem of ignition source is mainly solved through strengthening management, and the problem of combustible leakage must be prevented and controlled during the design of the storage tank.

Leaked crude oil is exposed to the air and constitutes a flammable material. Crude oil leaks occur more frequently during storage and transportation, mainly including tank running and dehydration running, equipment, pipelines, and valve damage due to oil running and oil and gas volatilization due to poor sealing. In addition, there are cracks in the bottom of the tank and welding, and floating disk sink The possibility of a major oversized leak.

Corrosion is one of the important factors for leakage. There have been many oil spills at home and abroad due to corrosion of the bottom of the oil tank. The results of the preliminary investigation of the internal corrosion of crude oil storage tanks show that [1], the bottom of the tank is severely corroded, most of which are ulcer-like pit corrosion, which mainly occurs in the heat-affected zone, depression and deformation of the welding, followed by the tank top corrosion. For uneven and comprehensive corrosion accompanied by pitting corrosion, the tank wall is relatively lightly corroded. For uniform pitting, it mainly occurs at the oil-water interface and the oil-air interface. Relatively speaking, the external corrosion at the bottom of the tank is more serious, which mainly occurs on the side where the edge plate contacts the ring beam foundation.

The floating pan sinking accident is one of the serious vicious equipment accidents that are very taboo when producing floating roof tanks. The occurrence of this type of accident reflects on the one hand serious defects in design, construction, management, etc., on the other hand, it will cause a large amount of crude oil leakage, which will seriously affect production, pollute the environment and pose a fire hazard.

2 Major safety issues and countermeasures in the design of large crude oil storage tanks

2.1 Tank foundation and foundation

The foundation survey and tank foundation design of storage tank engineering are the most fundamental guarantees to ensure the safe operation of large storage tanks. According to the petrochemical industry standard [2], engineering geological survey must be carried out during the site selection process, and the general ground, soft ground, mountainous ground, and special ground must be investigated separately, and corresponding ground treatment methods must be proposed. The seismic effects of the site and the foundation should be evaluated to avoid construction on soft and hard foundations or within the influence of active geological fault zones.

Common tank foundation forms are ring wall (beam) type, outer ring wall (beam) type and slope protection type. Selection should be based on geological conditions. The tank foundation must have sufficient overall stability, uniformity and sufficient plane bending stiffness. The rigidity of the foundation structure directly below the tank wall should be strengthened. The foundation bed supporting the bottom plate should be flexible to absorb welding deformation, and a waterproof barrier should be provided. The distance between the oil layer and the oil spill signal pipe, the groundwater level and the top surface of the foundation shall not be less than the height that the capillary water can reach (generally 2m) [3].

The traditional storage tank heating method is as follows: a tube-type or coil-type heater is installed in the tank, so that the viscous liquid in the tank is exchanged with a heat medium (usually saturated steam is used as the heat medium) to achieve viscous The temperature rise of the liquid reduces the viscosity of the liquid and improves its fluidity to facilitate the pump's delivery.

The traditional tank heating method has been used for many years, and it will inevitably show its disadvantages:

1. Low heat exchange efficiency and large steam consumption. The heating of viscous liquids by traditional tank heaters is a static natural convection heat exchange with extremely low heat release coefficient. Due to the low heat exchange efficiency and the high temperature of the condensate, it is often removed with a large amount of steam. At the same time, because the temperature of the viscous liquid on the surface of the heating tube is too high, and it stays for a long time on the high-temperature surface of the heat exchange tube, it is extremely easy to produce decomposition products, which are aggregated on the surface of the heat exchange tube, which is easy to coke, which seriously hinders the transfer of heat and affects Thermal efficiency.
2. The heating process is uneconomical. When only a small amount of viscous liquid needs to be poured out, the entire viscous liquid in the entire tank must be heated. The amount of heating is several times the amount used at this time, making a large amount of steam useless.
3. The temperature of the viscous liquid in each part of the tank is uneven. The temperature of the viscous liquid near the heater is higher, the temperature of the viscous liquid far from the heater is lower, and the temperature of the viscous liquid is lowered, which seriously affects the fluidity of the oil.
4. Affect the quality of viscous liquid. The viscous liquid in the tank is repeatedly heated, and a large amount of fine decomposition products are generated during the heating process, which has a certain impact on the quality of the viscous liquid and increases the cost of post-processing.

In view of the disadvantages of the traditional tank heating method, a new type of local rapid heater technology has been developed.

New local fast heater

Tank FRP type

FRP storage tank has the following characteristics:

(1) Lightweight and high strength, the relative density is between 1.5 ~ 2.0, only 1/4 ~ 1/5 of carbon steel, but the tensile strength is close to, or even exceeds that of carbon steel, and the specific strength can be compared with that of high-grade alloy steel ratio. Therefore, it has excellent results in aviation, rockets, spacecraft, high-pressure vessels, and other products that need to reduce their weight. The tensile, flexural, and compressive strength of some epoxy FRPs can reach more than 400Mpa. The density, strength and specific strength of some materials are shown in Table 1-1.

(2) Good corrosion resistance

FRP is a good corrosion-resistant material, and has good resistance to the atmosphere, water and general concentrations of acids, alkalis, salts, and a variety of oils and solvents. It has been applied to all aspects of chemical anticorrosion and is replacing carbon steel, stainless steel, wood, non-ferrous metals, etc.

(3) Good electrical performance

Is an excellent insulating material used to make insulators. It can still protect good dielectric properties at high frequencies. Microwave transmission is good and has been widely used in radomes.

(4) Good thermal performance

FRP has low thermal conductivity, 1.25 ~ 1.67kJ / (m · h · K) at room temperature, only 1/100 ~ 1/1000 of metal, which is an excellent thermal insulation material. It is an ideal thermal protection and ablative material under transient ultra-high temperature conditions, which can protect the spacecraft from high-speed airflow above 2000 .

(5) Good designability

Various structural products can be flexibly designed according to needs to meet the requirements of use, which can make the product have a good integrity.

Materials can be fully selected to meet the performance of the product. For example, it can be designed to be resistant to corrosion, instantaneous high temperature, particularly high strength in a certain direction of the product, good dielectric properties, etc.

(6) Excellent processability

The molding process can be flexibly selected according to the shape, technical requirements, use and quantity of the product.

The process is simple and can be molded at one time, and the economic effect is outstanding. Especially for the products with a small number of complex shapes and difficult to form, it also highlights its technological superiority.

Tank polyethylene type

The foreign language of polyethylene is referred to as PE. The highest application temperature is 60 for low density polyethylene and 70 for high density polyethylene. The minimum application temperature is -70 ° C. It has the advantages of no welding seams, no leakage, no toxicity, aging resistance, impact resistance, corrosion resistance, long life, and compliance with health standards. It makes up for the shortcomings of poor rigidity, pressure resistance and temperature difference of all-plastic rotomolded storage tanks. The lining surface of the product is flat, smooth and strong. Compared with traditional steel-lined plastic plate storage tanks, steel-lined rubber storage tanks, and steel-lined FRP storage tanks, the product has better corrosion resistance, no leakage, no peeling, and wear resistance Damage, can withstand a certain pressure, can withstand higher temperatures, longer life and other advantages, its price is lower than the traditional storage tank of the same specifications, is an ideal container for storing corrosive liquids. Therefore, it is an extremely corrosion-resistant storage tank. The steel-lined plastic vertical storage tank also has the characteristics of convenient installation, small footprint, and can be made into the shape required by the user. Extra large steel-lined plastic storage tanks have better integrity and are more outstanding, which cannot be achieved by other storage tank manufacturing processes.

Storeable substance

(1) Inorganic acids: (Sulfuric acid, nitric acid, hydrochloric acid, phosphoric acid, hydrofluoric acid, hydrobromic acid, hypochlorous acid, silicic acid, nitrous acid, sulfurous acid, carbonic acid, fluosilicic acid, fluoboric acid, etc. Wait)

(2) Organic acids: (formic acid, acetic acid, propionic acid, butenoic acid, lauric acid, fatty acids, lactic acid, glycolic acid, peracetic acid, oxalic acid, malonic acid, succinic acid, maleic acid, malic acid, tartaric acid, Phthalic 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. ..and many more)

(4) Elements, gases, and other inorganic compounds (sulfur, sulfur colloid, phosphorus, mercury, hydrogen peroxide, ammonia, coal yuan, carbon monoxide, carbon dioxide, sulfur dioxide, hydrogen chloride, hydrogen bromide, hydrogen sulfide, phosphine, fluorine Boron, 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 ... and so on)

(6) Other element 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, salt water, high-purity water, acidic mineral water, sewage, soil ... and so on)

(7) Halogen-containing organic compounds, amines, phenols, and other organic compounds (chloropropanol, chloramine, hexachlorobenzene, freon, dimethylformamide, resorcinol, hydroquinone, sodium phenoxide, morphine , Nicotine ... and so on)

specification

Among them, polyethylene all-plastic storage tanks (storage tanks) have vertical (flat bottom, cone bottom), horizontal; transport tanks have automobile transport tankers, carriage transport tanks; mixing tanks have flat cover flat bottom, flat cover cone bottom, reaction tank type , Steel-lined plastic storage tanks (storage tanks) (steel-plastic composite storage tanks (storage tanks)) have vertical (flat bottom, cone bottom), horizontal and other queue products. Various types of storage tanks can also be customized according to needs. General plastic storage tanks are suitable for sizes from 1 cubic to 50 cubic meters. Steel-lined plastic vertical storage tanks Steel-plastic composite vertical storage tanks Turtle-lined storage tanks range from 1 to 150 cubic meters.

Tank stainless steel type

Stainless steel tank English translation: Stainless steel tank

classification

1. Classification by form: It can be divided into vertical stainless steel tanks and horizontal stainless steel tanks.

2. Classification by use: It can be divided into stainless steel tanks for brewing, stainless steel tanks for food, stainless steel tanks for pharmaceuticals, stainless steel tanks for dairy industry, stainless steel tanks for chemical industry, stainless steel tanks for petroleum, stainless steel tanks for building materials, stainless steel tanks for power, and metallurgy. Similar stainless steel tank.

3. Classified according to health standards: sanitary stainless steel tanks, ordinary stainless steel tanks.

4. Classified by pressure requirements: stainless steel pressure vessels, non-stainless steel pressure vessels.

Common stainless steel storage tank

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

The container insulation material is made of high temperature resistant and anti-aging polyurethane foam or pearl cotton.

The interface adopts the international standard fast-release chuck type, and the inner container is made of imported 316L or 304. The inner surface is mirror polished Ra0.28m, and the outer surface is matt, mirror, sandblasted or cold-rolled primary color.

Nozzle: liquid level gauge (digital display or glass tube type), air breathing port, thermometer (digital display or dial type), CIP cleaning port, sight glass, explosion-proof vision lamp, SIP sterilization port, liquid inlet and outlet, and Manholes, etc.

The volume contains 500L-30000L, etc., and can also be designed and manufactured according to the actual needs of customers.

Overview of stainless steel storage tanks:

1. Food and pharmaceutical stainless steel storage tank:

Stainless steel ingredient storage tank, stainless steel thick storage tank, stainless steel thin 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 barrel tank, stainless steel water tank storage tank.

2. Stainless steel tanks for brewing and dairy industry:

Stainless steel wine storage tank, stainless steel white wine storage tank, stainless steel wine storage tank, stainless steel milk (milk) tank, stainless steel beverage storage tank

3. Chemical stainless steel tank:

Stainless steel oil storage tanks, stainless steel transport storage tanks, stainless steel cooling storage tanks, stainless steel thermal insulation storage tanks, stainless steel heat exchange storage tanks, stainless steel buffer tanks, stainless steel outdoor storage tanks, and stainless steel pressure vessels of all levels in the chemical industry.

Features of stainless steel storage tank:

1. Stainless steel tank has strong corrosion resistance, it is not corroded by the external air and residual chlorine in water. Each spherical tank has undergone super strong pressure testing 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 a good seal; the sealed design completely prevents harmful substances and mosquitoes in the airborne dust from invading the tank, ensuring that the water quality is not polluted by the outside world and breeding red insects.

3. The scientific design of the water flow prevents the sediment at the bottom of the tank from being lifted by the water flow, ensuring that the domestic water and fire fighting water are naturally layered, and the turbidity of the domestic water coming out of the tank is reduced by 48.5%; but the water pressure is significantly increased. . Conducive to improving the performance of domestic water and fire water facilities.

4. Stainless steel tanks do not need to be cleaned frequently; the sediment in the water can only be discharged by periodically opening the drain valve at the bottom of the tank. Every three years, simple equipment can be used to remove scale, which greatly reduces cleaning costs and completely avoids human bacterial and virus contamination ^[3] .