You designed your PRICO LNG plant, you know what it is supposed to do at the design condition. Do you really know how it performs at off design conditions?
Two rate based process simulation models are developed by Guofu Chen. One is a fast rating method utilizing UA, while the other method embeds Aspen EDR to rigorously model the performance of the plate-fin heat exchangers.
UA Method
Let us first take a look at the fast rating method. The compressor is modeled with multiple IGV curves. This graph is the head curve and the other one is the efficiency curve.
Main heat exchanger has a fixed UA of 23 million Btu/F-hr.
If the natural gas flow is dropped to 100,000 lb/hr, what will be the LNG temperature? Currently it is -247.9 F
Simply type the new flow of 100,000 lb/hr, the LNG becomes colder at a temperature of -262.1 F. As you see the fuel compressor becomes yellow and it is because the LNG is sub-cooled with 0 flashed flow in the tank. However, the liquefaction power increases to 19.63 kW/TPD.
ASPEN EDR Rigorous Method
The second model does rigorous heat transfer calculation of the main plate fin heat exchangers through embed AspenTech Exchanger Design and Rating Program EDR. The main heat exchangers comprise of 4 cores with a widths of 47", a depth of 48" and a length of 300".
Currently the stage 1 IGV is 100%; the vapor fraction goes to the tank is about 4%. what's going to happen if we run the IGV at 105% for stage 1? Now the vapor fraction becomes 1.5%.
Benefits of Rate Based Simulations
Rate based process simulation model is very helpful when the actual site conditions are different from the design condition. If you plan to have a standard product, rate based simulation is the only way to have a true standard. Simply put the flow into the model and you will be able to see if the natural gas is partially liquefied or completely liquefied.
Thanks for watching this video. It is brought to you by Guofu Chen. More interesting topics can be found at showcase.guofuchen.com
