Unveil the Mystery of Air Products APCI C3MR LNG Liquefaciton Process in HYSYS

You are an LNG professional. You understand Air Product C3MR is the most popular LNG liquefaction process. But do you really know all the ins and outs of the C3MR process? All the mystery of the APCI C3MR LNG process will be unveiled in this video.

The process is developed based on the published process diagram by Air Products.

As you know, C3 means propane and MR means mixed refrigerant. As you see, natural gas is first precooled by the propane refrigeration loop and then liquefied by the mixed refrigerant loop.

Just like the Cascade LNG process, Propane is compressed in a three-stage compressor and the pressure is letting down stage by stage to match natural gas cooling curve as close as possible. In addition, two flash economizer drums are used to improve the performance of  the propane loop. 

After compressed in a three-stage compressor, the mixed refrigerant is also cooled down to about -27 F by the propane refrigeration loop. Then it goes to a two phase separator, where the gas is cooled in the mixed refrigerant chiller 1 and then finally subcooled in the mixed refrigerant chiller 2. The subcooled liquid of stream 207 is then flashed to a lower pressure of about 70 psia, where it has the lowest temperature of about -254.4 F in the system. The coldest gas is used to liquefy the natural gas and the high pressure mixed refrigerant stream of 206. As mentioned earlier, the liquid outlet of the two phase separator is further subcooled in the mixed refrigerant chiller 1 and then drops the pressure and combines with the stream of 209. Together the mixed stream of 214 is used to chill the natural gas stream of 4, mixed refrigerant vapor of 205 and mixed refrigerant liquid of 211. The heated gas of 215 at a temperature of about -31 F is then sent to the mixed refrigerant compressor, thus it forms a completely closed mixed refrigerant loop.

Let us take a look at the composite heat release curve. The Y-Axis is the heat flow and the X-Axis is the temperature and they match very closely, especially at the cold end. The other view is the delta temperature Vs. the temperature. As you can see, there are almost 6 points that have a pinch of about 4 F.

As some readers recall, Guofu also developed a HYSYS simulation with Cascade LNG process. In that simulation, the same 5 million metric ton per year natural gas is liquefied with a power consumption of about 191,600 kW. While with the APCI C3MR process, as you see, the power consumption is about 179,900 kW. With this said, the C3MR process can save the liquefaction power by about 6%, comparing against the Cascade process.

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For those who can't see the embedded video in this blog, please watch this video on youtube.com at https://youtu.be/3sFCwP0zWuU