Absorption Video Lecture | Mass Transfer - Chemical Engineering

this is a quick video over graphically
determining the number of operating
stages for an absorber and the same
concept applies to a stripper let's just
start with Ana's over so I'll draw up an
observer absorber let's make that just a
little bit bigger and we will have our
fluid coming in and that will be X
naught our vapor coming out and that
will be Y 1 and of course our vapor
coming in with containment it this is y
n plus 1 and this is X N and with this
information or this graph we have the
operating line this is the operating
line it is always a line and we also
have the equilibrium curve of curve and
it is set we cannot change it we can't
ever change our operating line and for
instance if we assume that we have X
naught that is clean so there is so this
is like hive impurities in the liquid
and this has no this is like pure clean
liquid right here down here so if we
assume that we always had clean liquid
and we wanted this to be y 1 then we
could change how much the flow rates are
and we get sorry that's about drawing
but we could change the flow rate we
could have it up something high like
this or something like something like
this but it's really important to note
is that this operating line should never
cross the equilibrium line and that will
become hopefully clear in the next few
minutes when actually start showing you
how the stages are made so we know what
y 1 is I mean and we know what X naught
is we assumed X naught was clean so it
will be right here now Y 1 is an
equilibrium is an equilibrium with X X 1
so this is x1 so if we had stage one why
one must be an equilibrium with X 1 X 1
so that is one stage but X 1 is mixing
with Y to just mixing with y 2 so we go
straight up and this represents X 1 Y 2
or their mixing point you can kind of
think of it so this is y 2 so that's the
mixing point but what what is y 2 an
equilibrium with so we have to go
straight across to the equilibrium line
from our operating line and it is an
equilibrium with X 3 so then we have
another stage this is stage 2 and it's
an equilibrium with X 3 and X 3 is
mixing with y whoops that's why - not 3
- oops
because x2 is leaving stage stage 2 so
these two must be in equilibrium with
each other and this is of course y3
because it's coming from stage 3 so we
go up and this is y 3 so go all the way
across so what must y 3 being
equilibrium with well Y 3 must be in
equilibrium with the liquid which is at
which this would be X 3 so then X 3 oops
not doing that right x3 must be is
leaving so it must be in equilibrium
with y 3 and that is mixing with if we
said that our our containment like this
was our should down this is beginning
but we knew our containment our our
vapor had at a containment of this
amount or so this would be n plus 1 this
was our containment it so our
containment was mixing with the outlet
so then if this is X 3 then our
containment or our vapor and the
containment must be Y 4 so we only need
three stages this is actually y 4
because X 3 is mixing with y 4 so this
is y 4 so really this is X 3 and again
just Y 4 and again X 3 is mixing with Y
4 so mixing point mixing point mixing
point so it's really important that you
have to start up here at Y at Y 4 or
really could just start right here maybe
your graphing you got something like
this
if you know it's a straight line down
then you know that this is the
equilibrium point and really the
important thing is knowing that this
represents the state straight across
represents the number of stages it's
also important to know that that the the
number of stages this point has to hit
perfectly are this this line that we go
up and down and across each time like
this must hit perfectly like that so
that's pretty much all there is to an
absorption tower when you're trying to
figure it out graphically there's
actually a little bit more and I'll go
into it about this operating line how
you can change this operating line