IE43364B1 - Apparatus for use in absorbing a gas in a liquid - Google Patents

Abstract

The apparatus comprises, in addition to the bundle of vertical cooled tubes (2), one or more plates (12, 15) located inside the shell above the bundle of tubes (2), said plates being sprayed with absorbent liquid. The apparatus enables the degree of absorption to be increased, the amount of residual non-absorbed gas to be reduced and a more concentrated absorption solution to be produced. It is particularly applicable to the absorption of gaseous ammonia in water.

Description

This invention relates to an apparatus 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 apparatus 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 particular case, although it is to be appreciated that the apparatus can be used for the absorption in a liquid medium of any heat-evolving gaseous substa It is known from Italian Patent Specifications Nos. 891 098, 907 085 an 953 035 that the absorption of NHg with water can be carried out with vertically disposed film-exchangers. The main feature of such apparatuses is that a single surface is used for simultaneously effecting two operations, namely the transfer of materials (i.e. absorption of ammonia gas in water) and the heat transfer (i.e the transfer of the heat evolved on absorption of NHg in water). The use of. the apparatuses can be particularly useful in all those cases in which the transfer c materials is conditioned by the removal of heat as particularly occurs in the operation of absorbing NHg 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. - 2 4 3 3 6 4 It has now been found that it is possible to reduce considerably the length of the film absorption unit by causing the absorption of the last residual amounts of ammonia to take place on one or more adiabatic plates, whereby the heat evolved on absorption is transferred to the gas.

According to one aspect of the present invention there is provided an apparatus suitable for use in the absorption in a liquid medium of a gas which evolves heat on absorption, which apparatus comprises a casing which encloses a bundle of tubes and two spaced apart tube-plates 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 least one conduit in an upper end region of the casing from 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 exterior 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 liquid medium onto the one or more plates causes the liquid medium to be sprayed or sprinkled onto the plates.

Another aspect of the present invention provides a process for absorbing in a liquid medium a gas which evolves heat on absorption, wherein the process is effected in an apparatus according to the first mentioned aspect, the process comprising directing absorbing liquid medium onto the one or more plates, introducing gas to be absorbed into the lower end region of the casing, passing coolant through said zone between the tube-plates, withdrawing the solution of gas absorbed - 3 4 3 3 6 4 in liquid medium from the lower end region of the casing, and withdrawing any non-absorbed gas from the upper end region 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 apparatus; 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 apparatus comprises a casing 1 containing a bundle of tubes (only one of which is shown at 2) extnndin 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 solution, 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 numera 1 to 10 indicate the same components as indicated 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 absorbed 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 12, 13, 14 and 15 were removed, whereas in Run No. 2 these plates were in position. - 4 4 3 3 6 4 EXAMPLE Run No. 1 Run No. 2.

Rate of flow of the influent gas, via pipe 5 1,920 normal cubic metres per hour 1,970 normal cubi metres per hour Influent gas temperature 50°C 50°C Influent gas pressure 200 kg/sq.cm. absolute. 200 kg/sq.cm. absolute. Influent gas composition: N2+3H2 85.85% by volume 86.3% by volume nh3 14.15% by volume 13.7% by volume Effluent gas composition in pipe 8: N2+3H2 96.1% by volume 97.8% by volume nh3 3.9% by volume 2.2% by volume Effluent gas temperature 30°C 50°C Temperature of the cooling water in the inlet conduit 9 28°C 28°C Rate of introduction of the absorption water 48 kg/hour (in pipe 6) 43 kg/hour (in pipe 11) Concentration of the ammoniacal solution in pipe 7 76.4% 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 solution.

In order to obtain the same performance in a conventional film absorber not provided with the adiabatic plate unit, the exchange surface would have to be considerably increased. - 5 4 3 3 6 4 Attention is drawn, in addition, to the temperature increase of the g; emerging from the adiabatic plate unit, compared to that when no adiabatic plat< unit is employed. As a matter of fact, the temperature rises from 30°C to 50°( 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.

Claims (6)

1. An apparatus suitable for use in the absorption in a liquid medium of a gas which evolves heat on absorption, which apparatus comprises a casing whici encloses a bundle of tubes and two spaced-apart tube-plates to which the tubes 10 are fixed and through which the tubes extend; at least one conduit for feeding absorbing liquid medium at a point above the tube bundle; means for distributir 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 absorbed into that region of the casin below the tube bundle; at least one conduit in a lower end region of the casing 15 for the withdrawal from the casing of the solution of gas absorbed in liquid med at least one conduit in an upper end region of the casing for the withdrawal fro the casing of non-absorbed gas; at least one inlet and at least one outlet cond for a coolant to be passed through that zone defined by the casing, tube-plates the exterior of the tubes, these inlet and outlet conduits communicating with th ’0 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 pia

2. An apparatus substantially as hereinbefore described with reference to and/or as illustrated in, Figure 2 of the accompanying drawing.

3. A process for absorbing in a liquid medium a gas which evolves heat on !5 absorption, wherein the process is effected in an apparatus according to Claim 1 the process comprising directing absorbing liquid medium onto the one or more pi, introducing gas to be absorbed into the lower end region of the casing, passing coolant through said zone between the tube-plates, withdrawing the solution of g, absorbed in liquid medium from the lower end region of the casing, and withdrawii 10 any non-absorbed gas from the upper end region of the casing. - 6

4. A process according to Claim 3, wherein the gas to be absorbed is ammonia, and the liquid medium is water.

5. A process according to Claim 3, substantially as described in Run No. 2 in the foregoing Example. 5

6. A solution of a gas absorbed in a liquid medium, whenever produced by a process according to Claim 3, 4 or 5.