REVIEW QUESTIONS Gas Absorption
1. Acetone Acetone is to be recovered recovered from an acetone-air acetone-air mixture mixture by counter-cu counter-curren rrentt scrubbing scrubbing with water water in a packed packed tower. tower. " The inlet gas mixture has 5 mole% acetone. The gas flow rate is .5 kg!m s #$ & "'( and the li)uid flow rate is .*5 kg!m"s #$ & 1*(. The overall mass transfer coefficient + ya may be taken as .15" kg-mole!#m,.s.mole fraction(. The system may be considered as dilute. a( hat should should be the the height of the tower tower to remove remove '*% '*% of the enteri entering ng acetone acetone b( epeat epeat the calculati calculations ons for the tower tower height height if the the li)uid li)uid rate used is 1." 1." kg!m".s The e)uilibrium data for the mixture are/ mole fraction acetone in li)uid #x A( mole fraction acetone in gas #y A(
.0 .''
.15 .1'
., .,1
.,,, .2
". Acetone Acetone is being being absorbed absorbed by water water in a packed packed tower having having a cross-sec cross-sectiona tionall area of .1* .1* m" operating at "', + and 11.," k3a. The inlet air contains ". mole% acetone and the outlet gas contains .5 mole% acetone. The total inlet gas flow is 1,.5 kg-mole!hr #$ & "'(. The pure water inlet flow is 25., kg-mole water!hr #$ & 1*(. The individual mass transfer coefficients are k xa & .'* kg-mole!#m,.s.mole fraction( and k ya & .,0'5 kg-mole! #m,.s.mole fraction( respectively. 4alculate + ya and the tower height re)uired. mole fraction acetone in li)uid #x A(
. .
partial pressure of acetone in vapor #mm g(
., , ,.
.0 " ".*
.110
.101
*5.2
1,.
,. 6ulfur 6ulfur dioxi dioxide de is to be be recover recovered ed from from an air-67 air-67" mixture by contacting the gas mixture with pure water in a packed tower. The The tower will be operated at , o4 and 1 atm #abs(. The entering gas contains 5% mole 67 " and the exiting gas is to contain no more than .5% mole 67 ". 6ince the concentration of 67 " in water is small8 the system can be considered as dilute system. The total gas flow rate entering the tower is 1 kg-mole!m ".hr. The molecular weights of 67" and "7 are 2 and 1* respectively. 9f the overall mass transfer coefficient for the vapor phase is + ya & kg-mole!#m,.hr. mole fraction(8 determine/ a( The mini minimum mum pure pure wate waterr rate rate #in kg-mo kg-mole le!m !m".hr( needed for this separation8 b( The height height of the tower tower #in m( re)uired re)uired if the the actual water water rate rate entering entering the tower tower is 1." times times the minimum minimum value. The e)uilibrium data for 67 "-water system at ,o4 and 1 atm #abs( are given below/ $ass 67" per 1 mass "7 3artial 3ressure of 67 " in :apor p A #mm g(
0.5
5.
".5
1.5
1.
.0
.5
.,
.1
.5
**.
25".
"1.
1"5.
0'.
5".
,.
1'.0
2.01
.0
2. A tray tray tower is to be used used to remove ammonia ammonia from from an entering entering air stream stream containing containing mole% mole% ammonia ammonia at "', + 5 " and 1.1, x 1 3a. The entering pure water flow rate is 122 kg!m .hr #$ of "7 & 1*( and the total inlet gas flow rate is 11 kg!m ".hr #$ of gas & "' (. The ammonia concentration in the outlet gas is to be not more than .2 mole %.The system can be assumed to be dilute. a( 4alculate 4alculate the number number of theore theoretica ticall trays trays needed. needed. b( 9f the overall overall efficienc efficiency y is "5%8 determine determine the actual actual number number of trays needed needed for the separation. separation. 5.
9t is desired desired to absorb absorb '% of the acetone in in a gas containing containing 1. mole% acetone in air in in a counter-current counter-current tray column. The total inlet gas flow to the column is ,. kg-mole!hr8 and pure water is to be used to absorb the acetone. The process is to operate isothermally at , + and a total pressure of 11.," k3a. The e)uilibrium solubility relationship for acetone in water is y & ".5, x. 4alculate/ a( The minimum minimum pure water flow in kg-mol kg-mole!hr e!hr.. b( The number of theoretical trays re)uired re)uired for the separation if the pure water flow is 1." times times the minimum. minimum. c( 4ompare 4ompare your your answers answers for part #b( #b( using using the +remse +remserr ;)uation ;)uation.. d(
