o. 



L 



12V DC 



BLOWER 



(120SCFM1 



DIST. DUCT. 



MECHANICAL H,0 SILICA GEL 



SEPARATOR 

 (COLD TRAP) 



2 



DRY AIR LESS CO, & O, 



PURGE LINES 



Fig. 9.6 Schematic of the molecular sieve carbon dioxide scrubbing system for a manned 

 submersible. (Mr. P. Dostal, Alvin, Texas) 



tic, hard to store, cost $5.00 a pound 

 and had to be thrown away when 

 expired. We then decided to try a 

 product of Linde Division of Union 

 Carbide called molecular sieves. This 

 substance was originally manufac- 

 tured for use in water vapor removal 

 for industrial gas processes, but using 

 the right size (5 angstrom pores) it can 

 remove CO from an airstream. It does 

 this by absorption, which is not a 

 chemical process; therefore, you can 

 purge the system with a dry gas at 

 about 800 F and use it over find over 

 again. To use it €is a CO^ scrubber, the 

 entering airstream must be free of any 

 water vapor. This is because the water 

 molecule is a much more polar mole- 

 cule than COo, and the sieve has a 

 preference for polar molecules. We 

 are therefore designing a water sepa- 

 rator (cold trap) to be used upstream 

 of the scrubber; this mechanism will 

 condense out the water vapor which 

 tvill be collected ami redistributed 

 downstream of the scrubber. Since the 

 air coming out of the scrubber tvill be 

 100 percent dry, by adjusting the 

 amount of water redistributed we can 

 control our humidity. We will also 



have a smetll container of Silica Gel 

 upstream to assure that the air ivill be 

 dry before entering the scrubber. The 

 ivhole system should be a fairly small 

 and light-weight package. We will 

 leave the system in the submarine, and 

 have our purge lines running to fit- 

 tings in the hull. Our purge system, of 

 course, will be external, and the cost 

 of the purge gas fiV,) will be the only 

 expense of our system.'^ 



The final selection of a carbon dioxide 

 scrubbing system and compounds should be 

 made only after very careful deliberation. 

 Not only should the approach take into con- 

 sideration the more obvious factors of cost, 

 scrubbing efficiency, packaging, handling, 

 etc., which can be gained from the foregoing 

 discussion, but, to the extent possible, the 

 less obvious factors which may be external to 

 the vehicle. According to reference (6), it was 

 known that the effectiveness of Baralyme 

 (the scrubbing compound used in JOHNSON 

 SEA LINK) decreased markedly as tempera- 

 ture decreased. However, the operators an- 

 ticipated that all dives would be in warm 

 waters (65'F or higher), but the data pre- 

 sented in Figure 9.5 show that the seawater 



425 



