Changes in the state of mixed refrigerants

It is a gas before compression, a liquid after compression; it is a gas-liquid mixture behind the JT valve, and a gas after the cryogenic tank.

In mixed-refrigerant refrigeration cycles, the fluid downstream of the compressor is typically in a two-phase state, consisting of gas and liquid. Both the gas phase and the liquid phase need to be cooled or subcooled in a cold box before throttling to reduce pressure, which allows for lower temperatures and energy savings.

The compressed mixture is indeed a gas-liquid mixture, but it is separated; the gas and liquid resulting from this separation go into separate cold boxes, and before entering these cold boxes they pass through a throttling device (the JT valve). There is a liquid valve before the JT valve, and a gas-liquid mixture after it.

The mixed refrigerant components, from lightest to heaviest, are nitrogen, methane, ethylene, propane, and isopentane. Starting with entry into the compressor, the mixed refrigerant coming out of the cold box passes through the separator tank at the compressor inlet, where the liquid phase is separated off (under normal operating conditions, there is no liquid; liquid may appear when the temperature outside the cold box is very low, at a few degrees below zero, but liquid must not be present inside the compressor!) ) The gas phase enters the first stage of the compressor for compression; after compression, the temperature is around 100 degrees and the substance is still mostly in gas form. It then passes through a heat exchanger where its temperature is reduced to 35 degrees, causing liquid to precipitate out (propane). Isopentane, along with a small amount of ethylene), then passes through a gas-liquid separator to separate the liquid phase; the gas proceeds to the two-stage compressor, where it is compressed to a temperature of around 100 degrees, at which point it is almost entirely in gaseous form. It is then cooled to 40 degrees degrees through a two-stage heat exchanger, and again passes through a gas-liquid separator to separate the gas and liquid phases, which go into separate cold boxes. The gas and liquid refrigerants exchange heat with the cold boxes, causing them to cool down (the liquid refrigerant becomes supercooled, while all of the gas refrigerant liquefies). After that, it passes through a throttle valve, where the refrigerant undergoes throttling expansion, increasing its volume and doing work; as a result, some of it vaporizes and its temperature drops further. The throttled refrigerant exchanges heat with the natural gas that needs to be liquefied; the refrigerant gradually absorbs the heat from the natural gas and is completely vaporized, before exiting the cold box!

As a supplementary note, we need to top up the coolant daily here. Why is that?

Take cold remedies every day? There must be a leak point; check the safety valve and dry gas seal

The refrigerant consumption is 10 tons per month, mainly through the safety valves and compressor seals, as well as various static sealing points in the system