Chemistry of inorganic compounds – Modifying or removing component of normally gaseous mixture – Carbon dioxide or hydrogen sulfide component
Patent
1987-06-02
1989-07-11
Doll, John
Chemistry of inorganic compounds
Modifying or removing component of normally gaseous mixture
Carbon dioxide or hydrogen sulfide component
55 70, 55 89, 55228, B01D 5314, B01D 5334
Patent
active
048470570
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to the technique of treating gases with ammonia. It more particularly applies to the recovery of CO.sub.2 from smoke which is relatively poor in CO.sub.2, such as combustion smoke which contains about 8 to 20% or cement works smoke or lime furnace smoke which contains 20 to 50% of CO.sub.2. It may also apply to other types of treatments of gases available at high temperature, for example the purifying of acid gases, in particular smoke containing SO.sub.x, NO.sub.x or HCl impurities before they are discharged to the atmosphere or are subsequently treated with PSA (Pressure Swing Adsorption).
In industrial countries, the production of CO.sub.2 has developed most often from industrial or natural sources "rich" in CO.sub.2 (97%) and containing very small amounts of impurities, which results in a relatively cheap CO.sub.2.
The reduction in the number of chemical sources in these countries, in particular the number of ammonia factories, makes it necessary to envisage the production of CO.sub.2 from sources "poor" in CO.sub.2, such as the aforementioned smokes.
In this field of the recovery of CO.sub.2, as in the other aforementioned applications, ammonia is an absorption agent of interest owing to its properties and moderate cost, but it presents a difficult problem as concerns the rejection of gas from the installation. Indeed, the rejected gas contains a relatively large content of ammonia and it must be recovered for reasons of economy and avoidance of pollution of the environment.
An object of the invention is to provide a process and an installation for solving this problem in a particularly economical manner.
The invention therefore provides a process for treating with ammonia a gas available at high temperature, characterised in that it comprises eliminating the ammonia from a gaseous effluent of the treatment by scrubbing with a liquid formed essentially by water, and regenerating the scrubbing liquid by stripping countercurrent with respect to the gas to be treated, then recycling at least the essential part of the regenerated scrubbing liquid by putting it into thermal exchange relation with the scrubbing liquid to be regenerated.
Thus it is the gas to be treated itself by the energy it contains which ensures the regeneration of the scrubbing water and, simultaneously, cools and facilitates its own treatment with the ammonia.
If the treatment with ammonia presents at least one kinetically slow reaction, as is the case in the absorption of the CO.sub.2, in accordance with a first manner of carrying out the invention, downstream of said distillation, the gas to be treated is made to circulate in an absorption apparatus fed with an ammonia solution, then the ammonia is eliminated from the gaseous effluent of this apparatus by said scrubbing.
In this case, advantageously, the liquid effluent leaving the absorption apparatus is desorbed by reduction of pressure.
On the other hand, if the considered reaction is sufficiently rapid, as is the case in the purification of acid smoke, according to another manner of carrying out the invention, downstream of said distillation, the gas is subjected directly to said scrubbing, so that said treatment with ammonia is constituted by said regeneration of the scrubbing liquid. The smoke may then be subjected, if necessary, to a treatment which presents at least one kinetically slow reaction, such as a decarbonation.
The invention also provides an installation for carrying out the aforementioned process. This installation comprises a scrubbing tower fed at its base with the gaseous effluent of the ammonia treatment apparatus and at its top with a liquid essentially constituted by water, a distillation apparatus whose top is connected through a first conduit to the base of the scrubbing tower and which is fed at its base with the gas to be treated, and a recycling conduit, in thermal exchange relation with said first conduit, which connects the base of the distillation apparatus to the top of the scrubbing tower.
BRIEF DESCRIPTION OF THE DRA
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Brugerolle Jean-Renaud
Combe Michel
Paganessi Joseph
Doll John
L'Air Liquide Societe Anonyme pour l'Etude et, l'Exploitation de
Liquid Air Corporation
Russel Jeffrey Edwin
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