Nitrogen filling for liquefied gas tank trucks

First, the allowable working pressure of your tank truck must be determined. It is necessary to check whether the safety valve on the vehicle is activated, whether there is a pressure protection valve in place, and whether the pressure gauge shows accurate readings. All these aspects have to meet specific usage requirements, and it is essential to verify that every component complies with the required standards. Oh, and whether there is any blockage in the pumps, delivery pipes, and valves.

If the safety valve does not open, could there be a flow-limiting protection mechanism on the gas-phase valve of the tank truck?

We filled it with nitrogen, and the process went smoothly; the nitrogen pressure was 0.6 MPA, and filling stopped at 0.4 MPA

It seems that the nitrogen we pumped in has been sucked out

The design pressure for liquefied petroleum gas tankers is generally 1.7 Mpa or 1.77 Mpa. This value is determined based on the saturated vapor pressure of propane in liquefied petroleum gas at 50°C; therefore, the possibility that a pressure of 0.7 Mpa from nitrogen could cause the safety valve to activate is ruled out. Secondly, conventional flow-limiting protection systems are installed in the liquid-phase pipelines to prevent the liquid flow rate from becoming too high ； Third: If the material is drawn out too quickly, vortices may form, drawing the gas phase in the tank into the pump and resulting in unstable pressure. Fourth: Check whether the universal arm and pipes are equipped with flame arresters, check valves, or other accessories that could cause blockages in the pipes; a failed pull-valve can also lead to poor gas flow. The LPG unloading methods I have come across generally involve using gas compressors to increase pressure, which is then used to push the gas into spherical tanks; I have no experience with this type of unloading method. The above information is for reference only. If possible, it would be helpful to take some pictures for everyone’s reference in the discussion, as it’s difficult to visualize the issues without any visual aid.

There is a flame arrester on the gas pipeline. Generally, the tank capacity of liquefied petroleum gas trucks is around 60 cubic meters, and the weight of the liquefied gas is about 24 tons. What is the maximum flow rate per hour that can be used for unloading via pump, so as to prevent vortices from forming in the tank and entering the gas phase? Is there any experience to follow here?

It now seems that the reason for no pressure increase with nitrogen is as follows: 1. The gas-phase flame arrester reduces the pressure of nitrogen, resulting in insufficient nitrogen pressure. 2. The pump draws in too much material, creating vortices inside the chamber; the inhalation of vapor leads to evacuation.

I was away for five days recently and missed the updates on the posts; I’m sorry :handshake The maximum volumetric flow rate for unloading liquefied petroleum gas is generally required to be no more than 3 m/s – meeting this requirement is sufficient. The mass flow rate can be estimated roughly by considering the cross-sectional area and density； Additionally, with regard to your company’s unloading method, I’m not sure whether there are any buffering devices at the pump inlet. If not, a low liquid level in the tank may cause air to be drawn into the pipeline, which could also lead to vacuum conditions ； Ordinary flame arresters have no orientation, and there are generally no excessive impurities in the vapor pipelines for liquefied petroleum gas; it is completely impossible to fill them with 0.7 Mpa of nitrogen. As long as the flame arrester is not completely blocked, this situation is highly unlikely to occur. I’m not sure if the original poster has resolved their issue; feel free to share and discuss: handshake

I was away for five days recently and missed the updates on the posts; I’m sorry :handshake The maximum volumetric flow rate for unloading liquefied petroleum gas is generally required to be no more than 3 m/s – meeting this requirement is sufficient. The mass flow rate can be estimated roughly by considering the cross-sectional area and density； Additionally, with regard to your company’s unloading method, I’m not sure whether there are any buffering devices at the pump inlet. If not, a low liquid level in the tank may cause air to be drawn into the pipeline, which could also lead to vacuum conditions ； Ordinary flame arresters have no orientation, and there are generally no excessive impurities in the vapor pipelines for liquefied petroleum gas; it is completely impossible to fill them with 0.7 Mpa of nitrogen. As long as the flame arrester is not completely blocked, this situation is highly unlikely to occur. I’m not sure if the original poster has resolved their issue; feel free to share and discuss: handshake