LNG thermal expansion safety valve
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We have collected some information on the LNG processing processes, and found that on the LNG pipelines, the thermal expansion safety valves are installed with a section that is not insulated. We believe this means that the discharge occurs in gaseous form; could we seek advice from those familiar with the process engineering to confirm this?
I haven’t worked with LNG before, but based on the back pressure released by the safety valve, it’s clear that there is a gas phase behind the valve
Setting a section without insulation is intended to ensure that the medium in the pipeline ahead of the safety valve is in gaseous state
I work in the LNG industry, and as for the lack of insulation around the inlet of thermal expansion safety valves, there are several reasons for this (based on my personal opinion): 1. On pipelines carrying liquid LNG, the diameter of the pipe at the inlet of thermal expansion safety valves is usually 1 inch; the insulation is added mainly to reduce the amount of heat absorbed by the LNG from the surrounding environment, as well as to prevent personnel from getting frostbitten； 2. The reason for the lack of insulation in Section 1 is that the safety valve does not activate, resulting in a dead zone; the medium inside is gaseous and not flowing, and it is at room temperature. Therefore, removing the insulation in Section 1 has no impact on the insulation effect of the main pipeline ； 3. Eliminating this section of insulation can save costs and reduce construction time ； 4. When removing the insulation section, wire mesh should be added to prevent people from getting frostbite ； 5. The conversion to liquid and gas state after a safe takeoff has no direct relation to heat insulation; both the reduction of vaporization and the prevention of frostbite in personnel have been achieved ； These are my personal views; discussions are welcome.
This section without insulation is there to insulate the gasified dead air inside the pipeline; otherwise, the low temperature of LNG would change the spring force.
Liquid phase! It’s an expansion valve; pay close attention – when LNG is heated, its volume increases, and there is an expansion coefficient that can be used for calculations.
As can be seen from the PID diagram, there is a liquid phase in front of the thermal expansion safety valve; when heating causes expansion, the pressure reaches the set point, and behind the valve, it becomes a gas phase