Big thanks to Exotic Chem Lab for providing lots of guidance / info on this project. Check out his channel at:
/ @exotic_chem_lab
In this video I'll be building on the work I did in my last 2 videos (DIY vapor compression refrigeration & Ethylene Production) to create a 2-stage or "cascade" vapor compression refrigeration system that uses propylene (aka MAPP gas) in the first stage, and Ethylene (R1150) in the second stage. The goal of the project is to hit -100C.
A major snag i ran into was that I wasn't getting the temperature drop I thought i'd be getting from my Ethylene refrigerant. Running the second stage condenser below -30C and 400 psi, no condensation was occuring, despite the fact that my Ethylene should have begun condensing around ~300 psi. After some investigation, it figured out that the Ethylene refrigerant was highly contaminated (about 30%) with Hydrogen gas from running the catalyst too hot during the production process. This resulting in the partial pressure of Ethylene being reduced to the point that condensation couldn't be achieved at a reasonable total pressure.
Using a converted ice maker, i built a second cascade system where the second stage was essentially static, as opposed to a continuous loop. The purpose of this was to collect my ethylene and get it to the lowest possible temperature and condense it under pressure, then release it and hopefully allow the hydrogen to be purged out by phase separation. This allowed me to analyze the behavior of my gas mixture, and i found that at -38C, the mixture that should have condensed at around ~16 bar actually required ~23 bar to condense. This information is what allowed me to make a rough determination of the Ethylene's purity (around 70%).
Unfortunately, my attempt to purify the Ethylene through phase separation simply resulted in all of it boiling off because my flow rate was so high. However, in the process, I did manage to capture a temperature drop on my thermocouple of as low as -83C, meaning Ethylene did in fact condense in my icemaker unit and then evaporate again, so while I technically achieved cascade refrigeration, there's more work that has to be done before I can get continuous refrigeration down to -100C, which will be the focus of my next video. The two main areas of improvement are:
-Making Ethylene of a significantly higher purity (95% or higher)
-Fine tuning the second stage flow resistance / high side volume / low side volume for optimal flow rate / pressure drop
Once temperatures of -100C can be consistently achieved, it will become possible to produce Liquid Methane (or LNG), such as what's used in modern rocket engines like the SpaceX Raptor. This will be done by using a third compressor to take natural gas from a residential source and condense it at a pressure of 26 bar (370 psig) at -100C. When expanded back to 1 bar, the temperature will drop to -162C.
Music:
Kevin MacLeod - George Street Shuffle
13 май 2023
