Process flow of large ethylene cryogenic full capacity tank system

Process overview of large ethylene cryogenic full capacity tank system

The liquid ethylene sent from the ethylene unloading platform is sent to the ethylene full capacity tank for storage through the low-temperature cold insulation pipe. The liquid ethylene is output by the ethylene submerged pump, the flash steam (bog) generated by the ethylene storage tank is recovered by the bog system, and the gas behind the safety valve enters the flare through the safety vent gas (EAG) system.

1. Liquid inlet and purging system

◆ liquid inlet system: the liquid ethylene sent by ethylene liquefaction unit or unloading platform is sent to ethylene storage tank for storage through low-temperature process pipeline, which can be fed through top liquid inlet pipeline or bottom liquid inlet pipeline. Both top liquid inlet pipeline and bottom liquid inlet pipeline shall be equipped with remote-controlled emergency shut-off valve.

◆ purging system: the normal temperature and low pressure nitrogen sent from the process unit area enters the main container through the purging ring pipeline set in the main container, enters the insulation layer at the bottom of the storage tank through the nitrogen purging pipeline of the bottom insulation layer, and enters the pump well of the submersible pump through the purging pipeline of the submersible pump, so as to ensure the air replacement at all corners of the storage tank and the drying of internal thermal insulation materials, In addition, a nitrogen purging exhaust pipeline is set at the top of the secondary vessel, a purging exhaust pipe is set at the bottom insulation layer, and an annular exhaust pipe is set in the interlayer space for the discharge of replacement air during purging.

2 tank drainage and reflux system

Liquid out of storage tank (gasification or loading): the storage tank is equipped with two submerged pumps. The discharge pipes of the submerged pumps are equipped with remote low-temperature shut-off valve and ethylene orifice flowmeter, and the return pipeline after the pump is set. After each pump column discharge pipe is led out, the check valve and root stop valve are installed respectively, and then the discharge pipes are summarized (one orifice flowmeter and one low-temperature shut-off valve are installed on the discharge pipe).

◆ the submersible pump is provided with a backflow pipeline behind the pump, and a low-temperature regulating valve is set on the backflow main line behind the pump, which is used as the starting pipeline of the submersible pump.

3 bog recovery system

◆ when the gas phase pressure in the storage tank rises to 10-13kpa (which can be adjusted according to the process package), the low-temperature automatic regulating valve opens and the gas is discharged into the bog heater or low-pressure flare to balance the pressure in the storage tank; When the gas phase pressure in the tank drops to 10KPA (which can be adjusted according to the process package), the low-temperature regulating valve is closed to maintain the pressure of the tank within the safe range.

4 air supply system

◆ if the gas phase pressure in the storage tank drops to 2KPa, the low-temperature automatic regulating valve on the gas make-up pipeline will be opened. When the storage tank pressure rises to 5kpa, stop gas make-up (fine adjustment can be made according to the liquefaction process package) to keep the storage tank pressure within a safe pressure range.

5 EAG to torch

◆ when the gas phase pressure in the storage tank is higher than 14kpa, the flare control valve is opened, and the gas inside the storage tank is discharged into the low-pressure flare system to ensure the safety of the storage tank.

◆ the pressure and vacuum relief valve is an integral part of the tank. Two sets of safety vent pipelines are set on the top of the storage tank, and two sets of storage tank pressure relief valves are equipped, one for use and one for standby. There is always one set of pressure relief valve in operation. When the gas phase pressure of the storage tank reaches 17kpa, the pressure relief valve will be opened to vent and depressurize.

◆ three sets of vacuum suction valves are set on the top of the storage tank, one for dual use and one for standby. There are always two sets of suction valves in operation. When the gas phase pressure of the storage tank reaches -0.22kpa, the suction valve opens to increase the gas phase pressure in the storage tank.