30, 60, 100 cubic meter LNG storage tanks

30, 60, and 100 cubic meter LNG tanks are frequently used in our production. It's believed that this new type of LNG tank will also be quickly embraced by a wide range of users. Compared to standard tanks, LNG tanks offer enhanced safety. LNG tanks can be categorized by size: small LNG tanks range from 5 to 30 cubic meters and are commonly used in residential gas vaporization stations and LNG refueling stations for vehicles; medium-sized LNG tanks range from 30 to 150 cubic meters and are often used in satellite liquefaction units, making them an excellent alternative to general tanks.

The storage system of the LNG tank consists of low-temperature storage tanks, affiliated pipelines, and control instruments, yet it also falls under the category of low-temperature storage tanks.

2. All LNG storage tank pipelines are made of Austenitic stainless steel tubes. Austenitic stainless steel tubes offer excellent low-temperature properties.

3. LNG storage tanks can be further categorized into vertical (lng) tanks. These tanks employ vacuum powder insulation technology and are constructed with austenitic S30408 stainless steel for the inner tank and piping, while the outer shell is made of high-quality carbon steel Q345R pressure vessel steel plate. These lng storage tanks are not only durable but also extremely safe to use, and have gained widespread recognition.

30, 60, 100 cubic meter LNG storage tanks, LNG gasification stations, and vehicle refueling station process and equipment selection

Key Equipment for LNG Gasification Station

LNG Storage Tank

Tanks are the main equipment of LNG liquefaction stations, accounting for a significant portion of the construction cost. The design of tanks should be given high priority.

1.1 Material Selection for LNG Tanks

During normal operation, the working temperature of the LNG tank is -162.3°C, and it must be pre-cooled to -196°C before the first use.

Liquid nitrogen pre-cools the tank, making the design temperature of the tank -196°C. The inner tank must withstand both the working pressure of the medium and the low temperature of LNG, requiring the inner tank material to have excellent comprehensive mechanical properties at low temperatures, particularly good low-temperature toughness. Therefore, the inner tank material is selected as 0Crl8Ni9, which is equivalent to ASME (American Society of Mechanical Engineers) standard 304.

As a normal temperature and external pressure vessel, the outer shell is made of low alloy steel Q345R, low carbon steel Q245R, and Q235B.

1.2 Takeover Design

Tapped openings on the inner tank of the storage tank include: inlet liquid port, outlet liquid port, liquid discharge port, vapor port, level measurement port, upper level gauge port, lower level gauge port, and 8 process manholes. The material of the tapped openings on the inner tank is all 0Cr18Ni9.

For easy regular measurement of vacuum levels and evacuation, a vacuum evacuation port is provided on the bottom sealed cap of the outer罐. After evacuation, this port is sealed. To prevent vacuum failure and the leakage of the inner罐 medium into the outer罐, a pressure relief device is installed on the sealed cap of the outer罐.

2. Truck Unloading Booster Vaporizer

Due to the absence of pressure boosting equipment on the LNG tanker trucks, a tanker unloading booster gasifier with a gasification capacity of  m3/h is installed at the station to increase the tanker pressure to 0.6 MPa. The temperature of the LNG entering the gasifier is -162.3°C, and the temperature of the gaseous natural gas exiting the gasifier is -145°C.

3. Storage Tank Pressure VapORIZer

After filling a 100m³ LNG tank with 90m³ of LNG, calculate the pressure increase in the 10m³ gas phase space from 0.4 MPa (卸车状态) to 0.6 MPa (工作状态) within 30 minutes. According to the calculation, one 200m³/h capacity atmospheric temperature vaporizer is selected for each tank to boost pressure. The temperature of LNG entering the booster vaporizer is -162.3°C, and the temperature of the gaseous natural gas exiting the booster vaporizer is -145°C.

Designs often feature one LNG tank paired with one booster gasifier. Multiple tanks can also share a single or a set of gasifiers for boosting, which can simplify the process, reduce equipment, and lower costs through valve switching.

4. Air-bleed Vaporizer

The air-temperature type gasifier is the main gasification facility for LNG gasification stations to supply gas to the city. The gasification capacity of the gasifier is determined based on the peak-hour gas consumption, with a certain margin left, typically 1.3 to 1.5 times the peak-hour gas consumption. They are usually configured in groups of 2 to 4, with 2 to 3 groups designed for use in alternating shifts.

5. Water Bath Vaporizer

When the ambient temperature is low and the gaseous natural gas temperature at the outlet of the air-temperature gasifier is below 5°C, a water-bath type natural gas heater is connected in series after the air-temperature gasifier to heat the gaseous natural gas after gasification [5, 6]. The heating capacity of the heater is determined as 1.3 to 1.5 times the peak hour gas consumption.

6. BOG Heater (Boil Off Gas)

Essentially an air-temperature vaporizer

Due to the largest BOG volume occurring after unloading from the regasification trailers, the design capacity of the BOG air-temperature heater is calculated accordingly, with the time for unloading the gaseous natural gas from the trailers set at 30 minutes. Taking a 40m³ trailer with a pressure drop from 0.6MPa to 0.3MPa as an example, the required capacity of the BOG air-temperature gasifier is calculated to be 240m³/h. Generally, the BOG air-temperature heater is selected based on the number of trailers that can be unloaded simultaneously at the gasification station. Typically, the heating capacity of the BOG heater ranges from 500 to 1000m³/h. During winter, the BOG is used as fuel for the hot water boiler in a water bath natural gas heater, while the rest of the year it is sent into the urban transmission and distribution network.

7. BOG Buffer Tank

For peak-shaving type LNG liquefaction stations, to recover excess gas from off-peak period unloading tankers and BOG (Boil Off Gas) from storage tanks, or for natural gas blending stations to achieve uniform blending, a BOG buffer tank is often added at the outlet of the BOG heater. The capacity of the tank is set according to the recovered excess gas volume from the tankers.

8. Safety Relief Gas (EAG) Heater

The EAG air-temperature heating equipment capacity is calculated based on the maximum safe venting volume of a 100m3 tank. Calculation shows that the safe venting volume of a 100m3 tank is 500m3/h, and a single air-temperature heater with a gasification rate of 500m3/h is selected for the design. The incoming gas temperature to the heater is -145℃, and the outgoing gas temperature is -15℃.

9. Pressure Regulating, Metering, and Odorization Equipment

Select pressure-reducing devices based on the scale of the LNG gasification station. Typically, two pressure-reducing lines are set up, with self-contained regulators featuring controllers and overpressure cut-off selected for the pressure regulators.

The measurement is conducted using a turbine flow meter. The odorant is tetrahydrothiophene, and it is added by a diaphragm metering pump powered by the flow signal, injecting the odorant into the gas pipeline.

10. Filter

Filter structural features

The station uses a mesh core filter for particle and water filtration in the outgoing natural gas. The filter cores are replaceable, and the removed cores (made of stainless steel mesh) can be cleaned and reused. The filter is equipped with a pressure gauge indicating the pressure difference between the filter's inlet and outlet gases, which indicates the degree of core clogging. The general precision of the filter cores is 50um, and the water collection chamber's volume is more than 12% of the filter's volume.