pa1778data.pdf

A U.S. STEEL DUQUESNE WORKS
W HAER No. PA-115
(Page 246)
level of each fractionating column at tray forty-five where it
provided the refrigeration for the cycle. The remainder of the
air from the side bleed gel traps was fed to the lower column of
its respective fractionating tower (below tray 1) where it was
rectified or distilled in order to obtain high purity liquid
nitrogen for reflux to the upper column.
The air vapor from the cold end gel traps entered the bottom
of the lower column, which was composed of sixty-three trays, and
rose through twenty-three trays where it was rectified into
nitrogen vapor. The nitrogen vapor then passed through the lines
connecting the lower column with the high pressure side of the
main condenser. It flowed into the condenser where it was
liquefied by the refrigeration supplied by boiling liquid oxygen
on the other side of the condenser. A portion of this nitrogen
liquid was then fed to the lower column at tray twenty-three
while the remainder flowed through the shelf nitrogen subcooler
where it was cooled and subsequently fed to tray sixty-three.
Liquid is also taken from the kettle of the lower column and fed
into the upper column at tray fifty-one.
^P The upper column contains sixty-three trays similar to those
in the lower column. Liquid flows down across the trays to the
oxygen side of the condenser where it was vaporized. This vapor,
rising from the condenser to the upper column, flowed up through
the sieve type trays bubbling through the liquid that was flowing
down, causing a nearly complete separation of the air into 99.5
percent pure oxygen at the bottom and approximately 99 percent
pure nitrogen vapor at the top of the upper column as waste
nitrogen.
Waste nitrogen left the upper column in two streams. One
stream flowed through the three-core section of the waste
nitrogen heat exchanger where it was used to cool the liquid
shelf nitrogen from the main condenser and liquefy some air which
was fed to the lower column at tray three. The second stream of
waste nitrogen left the upper column above tray sixty-three and
flowed through the two-core section of the waste nitrogen heat
exchanger where it was also used to cool the shelf liquid that
was being fed to the upper column and to cool the side bleed air
which was then fed to the lower column below tray one. After
leaving the heat exchangers, the waste nitrogen flowed to the
nitrogen regenerators and reversing heat exchangers where it gave
up its refrigeration to the incoming air.
Product gaseous oxygen was taken from the upper column just
under tray one and passed through the oxygen superheater where it
A was used to liquefy a portion of the cold end air. After leaving
^^ the superheater, the oxygen was fed to the reversing heat