The final replacement and pressure relief tasks for the liquefied gas tank truck have been completed
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After the liquefied gas tank truck is filled, close the manual valves at both ends of the gas-liquid pipelines connecting the tank truck and the loading station (the valves on the tank truck and those on the loading station). How then is the pressure in this section released? Empty directly? Or?
Under normal circumstances, a dedicated pressure relief line is installed on the pipeline leading to the liquefied gas tank.
Someone upstairs said to use nitrogen pressure to push the liquid into the tank truck. I want to ask: the nitrogen pressure is 0.7 Mpa, while the pressure for liquefied light hydrocarbons is 1.3 Mpa – how can we use pressure in this case? As required, low-pressure flare vent lines are installed at the liquefied gas piers; the liquefied gas stored in such locations can be directly vented to the low-pressure flare line at a pressure of up to 0.05 Mpa ； Safe and reliable ；
Reply to 4#: That’s all. Just to add, it refers to LNG.
In most cases of this kind in China at present, the gas is simply released directly into the atmosphere; the cost of recovery is high. Moreover, the connection pipes between the gas and liquid pipelines and the tank truck are quite short (about 200 mm), and there is a quick-opening valve beside them. After loading is complete, the gas is released directly into the atmosphere by opening that valve. As for purging with nitrogen, I’ve never seen it done; it’s not practical whether it’s done into a tank or a tank truck, as there are issues with pressure and quality that cannot be guaranteed. These are just my personal opinions for reference only
Direct emptying is sufficient; in fact, the valve on the tank truck is quite close to the valve at the loading station, so there is no need for a separate recycling system. Moreover, the dip pipe is equipped with a dedicated vent valve.
The connection pipes between the gas and liquid pipelines and the tank truck are quite short (about 200 mm), and there is a quick-opening valve next to each of them. There are two approaches: 1. Connect it to the gas-phase pipeline. (Including low-pressure gas pipelines) It is generally vented directly to storage tank 2 equipped with an ice maker. Have seen it too
Our company connects the gas and liquid lines to the flare line behind the control valves, and after loading is complete, the fluids are discharged directly into the flare line.
Since the valve on the tank truck is very close to the valve on the loading platform, there are methods for draining air from both the loading and unloading pipes, with most cases being handled using direct drainage.
“There are evacuation methods available for both loading and unloading pipes, and most of them involve direct discharge; what is the concentration of combustible gases that can be achieved? Over 20% LEL? "Connect the gas and liquid lines to the flare line behind the control valve; after loading is complete, discharge directly to the flare line. Should low-temperature liquids be discharged to the flare through a heat exchanger (vaporizer), or via low-temperature stainless steel pipes?