In the last blog I talked about how oxygen was created for the sailors who live inside of submarines. The O2 was created either using specialized electrolysis machines or by burning self-oxidizing candles. Once the oxygen was created, the sailors on board the ship used and converted the oxygen into carbon dioxide. This means that the concentration of CO2 would steadily increase, which is deadly to humans. The solution to this problem may seem easy, just make more oxygen, right? Well it is actually a little bit more complicated than that. If the only process was oxygen creation, the ship would become too pressurized. Since the oxygen is not being made from materials inside the ship, the carbon dioxide has to exit the ship in order to maintain equilibrium! This problem led sailors to find a solution to the carbon dioxide problem. That is what I will cover in this blog.

Just like the creation of oxygen in the submarines, there are two methods of carbon dioxide removal onboard submarines. The first method is a process that doesn’t require electricity, but is chemically intensive. Submarines use machines called “scrubbers” to remove the toxic gasses from the air. A scrubber is essentially an apparatus which passes air through chemical filters. In the case of a submarine, the typical chemicals used are either soda lime or lithium hydroxide. Soda lime consists of sodium hydroxide (NaOH) and calcium hydroxide [Ca(OH)2]. The soda chemically reacts to the CO2 in the submarine’s atmosphere trapping it in the soda. Since the CO2 has been removed from the air, it stays in the soda solution until the soda has been saturated and the chemical process won’t occur any longer. The saturated soda is then discarded and replaced with fresh soda. The other non-electric method is the implementation of lithium hydroxide (LiOH) canisters. When the canisters are opened to the atmosphere, the lithium hydroxide very quickly removes the carbon dioxide from the air around it. While the previous method of scrubbing doesn’t use electricity to remove the CO2 directly, it does use electricity to power fans. LiOH canisters, on the other hand, are only used in power outages since the LiOH absorbs the CO2 so well without the need for electricity. The main problem is that the chemical solution is saturated very quickly.

The next method of CO2 removal is through an energy intensive, but renewable, scrubbing process using the chemical monoethanolamine or MEA for short. To start, the CO2 filled air is transferred to a large tank where the MEA is sprayed over it. The MEA chemically reacts to the CO2 trapping it inside of the MEA solution. Since the CO2 is then inside of the amine solution, the rest of the clean air is distributed around the submarine to be mixed with oxygen. The rich amine, or the MEA saturated with CO2, is then transferred to a boiler where the solution is heated and the CO2 is released in its gaseous form. The liquid amine is then returned to the initial tank where it is sprayed over the CO2. We are then left with a tank that is filled solely with CO2. To remove it from the submarine, it is pressurized until it reaches the pressure of the water outside the submarine. At that point, it is released into the water, and it is no longer a problem.

Now that we know how submarines make oxygen and remove carbon dioxide from their atmospheres, we can understand how sailors survive under the water for so long. Submarines are just one example of how humans can do such amazing things if we are faced with problems that force us to innovate. Engineering is so cool!