Note: Descriptions are shown in the official language in which they were submitted.
This invention relates to an apparatus and a process
suitable for use in absorbing in a liquid medium a gas which
evolves heat on absorption in the liquid medium.
More particularly, but not exclusively, the present
invention relates to an appara-tus adapted to absorb with water
the ammonia in an ammonia-containing gaseous mixture~ In much of
the following description, reference will be made to this par-
ticular case, although it is to be appreciated that the appara-
tus can be used for the absorption in a liquid medium of any
heat-evolving gaseous substance.
It is known from Italian Patent Specifications Nos.
891,098, granted on October 1st, 1971, 907,085, granted on
February 15, 1972 and 953,035, granted on August 10, 1973, that
the absorption of NH3,with water can be carried out with verti
cally disposed film-exchangers. The main feature of such appara-
tuses is that a single surface is used for simultaneously effect-
ing two operations, namely the transEer of materials (i.e. ab-
sorption of ammonia gas in water) and the heat transfer (i~e.
the transfer of the heat evolved on absorption of NH3 in water).
The use of these apparatus can be particularly useful in all
those cases in which the transfer of materials is conditioned
by the removal of heat as particularly occurs in the operation
of absorbing NH3 with water.
Nonetheless the known apparatuses have the defect that
to permit the optimum absorption of the gas, they have to be of
considerable length, the result being an increase of their cost
and their weight.
It has now been found ~hat it is possible to reduce
considerably the length of the film absorption unit by causing
the absorp-tion of the last residual amounts of ammonia to take
place on one or more adiabatic plates, whereby the heat evolved
on absorption ls transferred to the gas.
According to the present invention there is provided
an apparatus suitable for use in the absorption in a liquid me-
dium of gas which evolves heat on absorption, which appara-tus
comprises a casing which encloses a bundle of tubes and two
spaced aparttube~lates to which the tubes are fixed and through
which the tubes extend; at least one conduit for feeding the
absorbing liquid medium at a point above the tube bundle; means
for distributing the liquid medium in the form of a film in the
interior of the tubes; at least one conduit for introducing the
gas to be adsorbed into that region of the casing below the
tube bundle; at least one conduit in a lower end region of the
casing for the withdrawal from the casing of the solution of
gas absorbed in liquid medium; at leastone conduit in an upper
end region of the casing for the withdrawal from the casing of
non-absorbed gas; at least one inlet and at least one outlet
conduit for a coolant to be passed through that zone defined
by the casing.tube-plates and the e~terior of the tubes, these
inlet and outlet conduits communicating with that zone; one or
. more plates arranged in the interior of the casing above the
tube bundle; and means for directing influent liquid medium
onto the one or more plates.
Preferably the means for directing the influent liqui.d
medium onto the one or more plates causes the liquid medium to
be sprayed or sprinkled onto the plates.
According to the present invention there is also pro-
vided a process for absorbing in a liquid medium a gas which
evolves heat on absorptio~comprising~directing absorbing liquid
medium onto the one or more plates provided inside a casing of
the apparatus as above defined, introducing gas to be absorbed
into a lower end region of the casing, passing coolant through
a zone between the tube-~ates, withdrawing a solution of gas
absorbed in liquid medium from a lower end region of the casing,
and withdrawing any non-absorbed gas from an upper end region
,. . ..
. -- 2
of the casing.
For a better understanding of the present invention
and to show how the same may be carried into effect, reference
will now be made, by way of example, to the accompanying drawing,
in which:
Figure 1 is a vertical section through a known appara-
tus; and
Figure 2 is a vertical section through one embodiment
of the apparatus according to the present invention.
Referring firstly to Figure 1, the prior art appara-
tus comprises a casing 1 containing a bundle of tubes (only
one 2 of which is shown) extending through and fixed to tube-
plates 3 and 4. Also provided are a conduit 5 for introducing
ammonia-containing gas into the lower end region of the casing
1, a conduit 6 for introducing water or another absorbing
liquor into the upper end region of the casing, a conduit 7
for withdrawing the resulting ammoniacal solu-tion, a conduit 8
for withdrawing substantially ammonia-free gas, and conduits 9
and 10, respectively the inlet and the outlet for the coolant
liquid.
Referring now to the novel apparatus of Figure 2, the
reference numerals 1 to 10 indicate the same components as in-
dicated above. Also present is a conduit 11 for introducing
water (or another absorbing liquor) into an upper region of
casing 1. Between the conduit 11 and the bundle of tubes 2 are
plates 12, 13, 14, 15 where ammonia can be adiabatically ab-
sorbed by water. Optionally the conduit 6 can be dispensed with,
in which case the water can be fed entirely through conduit 11.
The present invention will now be illustrated by the
following Example carried out in the apparatus of Figure 2. In
Run No. 1 the adiabatic plates~, 13, 14 and 15 were removed,
whereas in Run No. 2 these plates were in position.
EXAMPLE
Run No. 1 Run No. 2
Rate of flow of the influent gas
via pipe 5 1,~20 normal cubic 1,970 normal cubic
metres per hour metres per hour
Influent gas temperature 50C 50C
Influent gas p~essure 200 kg/sq.cm200 kg/sq.cm
absolute.absolute.
Influent gas composition:
N2+3H2 85.85% by volume 86.3% by volume
NH3 14.15% by volume 13.7% byvolume
Effluent gas composition
in pipe ~:
N2+3H2 96.1% by volume 97.8% by volume
NEl3 3.9% by volume 2.2 by volume
Effluent gas tempera~ure 30 C 50 C
Temperature of the cooling
water in the inlet conduit 9 28C 28C
Rate of introduction of the
absorption water 48 kg/hour43 kg/hour
(in pipe 6)(in pipe 11)
Concentration of the ammoniacal
solution in pipe 7 76.~% 80.5%
Rate of absorption of NH3 155 kg/hour 170 kg/hour
Owing to the addition of the adiabatic plates in the
manner described above the following advantages can be obtained:-
an increase in the quantity of the absorbed NH3;
a significant reduction in the content of residual
NH3 in the effluent gas; and
the production of a more concentrated ammoniacal so-
lution.
In order to obtain the same performance in a conven-
tional film absorber not provided with the adiabatic plate unit,
the exchange surface would have to be considerably increased.
Attention is drawn,in addition, to the temperature
increase of the gas emerging from the adiabatic pla-te unit,
4 -
~ 10~5~7
compared ~o that when no adiabatic plate unit i8 employed.As a matter of fact, the temperature rises from 30C to
50C, and it is on account of this temperature rise and.the
associated withdrawn heat that it is possible to improve the
overall performance of the absorption unit.
