The role of compressors in LNG

The main function of the compressor is to compress the refrigerant to high pressure, and then the refrigerant passes through the JT valve throttling effect to obtain low temperature； When the refrigerant is compressed by the compressor, its temperature will definitely rise. Cooling the refrigerant through the heat exchanger is equivalent to pre-cooling the refrigerant.

Mainly used for cooling. :D :D

The principle of throttling expansion is that the pressure within a certain temperature and pressure area decreases and the temperature also decreases. The premise is high pressure, so compression is required. Circulating water is used for cooling because if there is no cooling, the temperature after throttling will be higher than before compression (throttling is isenthalpy, etc., and compression is closer to isentropy). Only throttling after cooling can achieve the cooling effect.

After natural gas is compressed to high pressure, the purpose of high-pressure throttling refrigeration cannot be achieved without cooling to reach saturation. Only liquids and gases that reach saturation have the greatest throttling cooling capacity.

The generation of cold energy during the liquefaction process of natural gas can be seen relatively clearly using the T-S diagram. Unfortunately, I cannot post the diagram. I think that in the entire refrigeration process, the compressor is the power source, which can also be said to be the refrigeration source, while the JT valve's throttling and expansion only embodies the cooling capacity and does not produce cold itself.

Haha, if you don’t understand, it might be easier to see how the air conditioner works.

In refrigeration, compression corresponds to throttling or expansion.

I have been engaged in the operation of liquefied natural gas installations. Generally, the role of the compressor is to provide the source of cooling capacity. The energy provided by the refrigerant to provide cooling capacity is provided by the compressor, and the refrigerant is only equivalent to a carrier. You can imagine the conservation of energy. If something takes away the cooling capacity, there must be equipment to provide the cooling capacity. The principle is the same as that of a refrigerator, except that the refrigerant and cooling temperature have changed. Another method is to use an expander. The function of the expander is basically the same as that of the JT valve, except that one can undergo phase change, while the other cannot. (I heard that there are liquid expanders abroad, but I have never come into contact with them.) If you have any other questions, I am willing to help.

The following gas compression situations, especially seagoing ships carrying liquefied gas cargo. 1. Liquefied petroleum gas, such as propane, butane 2. Liquefied natural gas, such as methane, ethane 3. Hydrocarbon petroleum gas, such as: Ethylene, propylene and butylene 4. Petrochemical gases such as: In this environment, petrochemical gases such as ammonia, vinyl chloride and butadiene are miscible with mineral oil, which will dilute the lubricating oil, causing a large decrease in the viscosity of the lubricating oil, resulting in poor lubrication effect.

The principle of cooling capacity generated by an expander or JT valve is the process of adiabatic expansion (isentropic expansion) of fluid (gas or liquid) under higher pressure to a lower pressure through a throttle nozzle (or throttle valve). When a higher-pressure fluid is throttled and expanded into a lower-pressure fluid, the fluid loses more energy in external work. Therefore, in order to obtain more cooling capacity, the pressure needs to be increased. At the same time, the temperature must be ensured not too high before throttling, and it needs to be water-cooled.