Carbon Dioxide Removal with Mixture of Lithium Hydroxide and Sodasorb in Underwater Life Support Systems

Abstract

The p u r p o s e o f t h i s s t u d y i s t o use t h e m i x t u r e o f l i t h i u m hydrox ide and sodasorb t o remove CO, a t c o l d t e m p e r a t u r e i n u n d e r w a t e r 1 i f e s u p p o r t systems. S p e c i f i c goa ls a r e to : 1) c o n t r o l d u s t i n g tendency and c a u s t i c i t y o f L iOH f o r s a f e d i v i n g and s u b m e r s i b l e ope ra t i ons and 2) d e f i n e a d i s t i n c t s e n s i n g p a r a m e t e r i n t h e c a n i s t e r bed t o m o n i t o r c a n i s t e r performance & s i t u . R e s u l t s show t h a t a 50% m i x t u r e by weight i s e f f e c t i v e t o c o n t r o l c a u s t i c d u s t s f r o m a b s o r b e n t s and y e t i s a l s o e f f e c t i v e f o r c o l d t e m p e r a t u r e CO, absorpt ion. When t h e mixed bed i s no l onger e f f e c t i v e t o remove CO, f r o m t h e gas stream, temperature p r o f i l e s i n t h e mixed absorbent bed near 1 cen t ime te r o f t h e e x i t end o f t h e c a n i s t e r n o r m a l l y p rov ide a d i s t i n c t s lope change (AS) and a c r i t i c a l temperature d i f f e r e n c e (AT) between bed and i n l e t gas t e m p e r a t u r e . B o t h parameters observed f rom t h i s s tudy can be used t o m o n i t o r scrubber p e r f o r mance i n s i t u . An a x i a l f l o w c a n i s t e r ( 4 x 17 cm, l e n g t h x d iameter) packed w i t h 263 grams o f sodasorb a t t h e end o f t h e c a n i s t e r and 493 grams o f each sodasorb and l i t h i u m hydrox ide m i x t u r e would reduce f o u r t i m e s o f t h e d u s t i n g t e n d e n c y and c a u s t i c i t y f r o m p u r e l i t h i u m hydroxide. The d i s t i n c t s lope (AS) and c r i t i c a l t e m p e r a t u r e d i f f e r e n c e (AT) were 8"C/hr and 16OC, r e s p e c t i v e l y . T h i s i n d i c a t e s t h a t when a s e n s o r d e t e c t s t h e AS value o f t h e temperature p r o f i l e i n t h e c a n i s t e r bed g r e a t e r than 8"C/hr and t h e AT l e s s t h a n 16OC, t h e CO, concen t ra t i on i n t h e t e s t e d chamber (203 !I) norma l l y reaches 2% i n t he a i r . t h e a b s o r b e n t bed i s no l o n g e r e f f e c t i v e t o remove CO,. Both AS and AT a r e v a r i e d w i t h c a n i s t e r con f igu ra t i ons . A p r e s c r i b e d c a n i s t e r i s n o r m a l l y needed t o be t e s t e d a t va r ious opera t i ng c o n d i t i o n s t o d e f i n e b o t h A S and AT v a l u e s f o r t h e sensing requirements.