Operation and management of LNG gasification station
Basic requirements for the operation of 1 LNG gasification station
The basic requirements for the operation of the LNG gasification station are:
(1) to prevent the leakage of LNG and gaseous natural gas to form an explosive mixture with the air.
The basic conditions of burning and explosion are eliminated, and the LNG process system and equipment are protected according to the requirements of the standard. (3) to prevent the overpressure and overpressure of LNG equipment.
(4) to prevent the low temperature characteristics of LNG and the harm of the huge temperature difference to the process system and the cold burn of the operator.
Pre cooling of process system of 2LNG gasification station
Before the completion of the LNG gasification station, liquid nitrogen should be used to dry, pre cool, inert and passivate the equipment and process pipes in the low temperature system. Pre cooling by liquid nitrogen tank valve opening degree to control the pipeline or equipment cooling rate is not higher than 1 DEG /min. The temperature of the pipe or equipment is reduced by 20 degrees centigrade, and the pre cooling is stopped, and the air tightness of the system and the displacement of the pipe and equipment are checked. After the pre cooling is finished, the residual liquid nitrogen in the LNG tank will be blown to replace the normal temperature equipment and pipeline after gasification. Then the liquid nitrogen in the tank can be replaced by LNG, and the LNG can be formally filled with gas supply.
Operation management and safety protection of 3 LNG gasification station
1) pressure control of LNG cryogenic storage tank
In normal operation, the operating pressure of the LNG cryogenic tank must be controlled within the allowable range. The normal working pressure range of LNG storage tank in Southern China area is 0.3 ~ 0.7MPa. When the pressure in the tank is lower than the set point, the self pressurizing vaporizer and the self boosting valve can be used to pressurize the storage tank. The lower limit is determined by the self pressurization pressurization valve opening pressure, pressure limit is determined by the automatic closing pressure self pressurization valve, its value is usually higher than the self pressure valve opening pressure is 15% set. For example, when LNG is used as the main source of city gas, if the opening pressure of the booster valve is set to 0.6MPa, the closing pressure of the booster valve is about 0.69 MPa, and the booster value of the tank is 0.09MPa.
The maximum working pressure of the low temperature storage tank is limited by the constant pressure value (front pressure) of the automatic pressure reducing valve set on the low temperature gas pipeline of the storage tank. When the maximum working pressure of the tank reaches the setting value of the pressure relief valve, the pressure relief valve opens the pressure automatically in order to protect the safety of the storage tank. In order to ensure that the booster valve and the pressure reducing valve do not interfere with each other, the closing pressure of the booster valve and the opening pressure of the relief valve can not be overlapped. The pressure difference above 0.05MPa should be guaranteed. Considering the manufacturing accuracy of the two valve, the appropriate pressure difference should be determined in the commissioning of the equipment.
2) overpressure protection for LNG storage tank
LNG due to tank "environmental heat leakage and slow evaporation during storage (on the static evaporation volume fraction is less than or equal to
0.3%), the pressure of the tank is gradually increased, which endanger the safety of the tank. In order to ensure the safe operation of the storage tank, the tank's pressure relief valve, pressure alarm manual release and safety valve take-off three level safety protection measures are adopted to carry out the over pressure protection of the tank.
The protective order: when the tank pressure rises to the set value of decompression valve, pressure regulating valve automatically opens the discharge of gaseous natural gas; when the pressure regulating valve failure, the tank pressure continues to rise, the pressure to achieve the alarm value, pressure alarm, manual discharge pressure relief; when the pressure reducing valve failure and manual release not open when the safety valve pressure relief, to ensure the safe operation of the LNG tank. For a LNG storage tank with a maximum working pressure of 0.80MPa, the design pressure is 0.84MPa, the setting pressure of the pressure regulating valve is 0.76MPa, the alarm pressure of the storage tank is 0.78MPa, the opening pressure of the safety valve is 0.80MPa, and the discharge pressure of the safety valve is 0.88MPa.