Gas separation: processes – Solid sorption – Including reduction of pressure
Patent
1992-05-07
1993-08-31
Spitzer, Robert
Gas separation: processes
Solid sorption
Including reduction of pressure
55269, 95107, 96121, 96123, B01D 5304
Patent
active
052404757
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a method for the separation of one or more agents, specially solvents, from gases. The agent or the agents are adsorbed by an adsorbent and thereafter desorbed and separated in a condenser. The invention also includes an apparatus for carrying out the method.
BACKGROUND OF THE INVENTION AND PRIOR ART
Methods of the kind indicated in the introduction have been described in the patent specifications WO 88/01534, GB 218 974 and CA 1 144 873.
Activated carbon is generally used as an adsorbent. In connection with the regeneration of the active carbon the temperature is increased, whereby e.g. volatile solvents are volatilized. The heating can be carried out directly by means of steam injection or indirectly, in which case the heating medium does not get in touch with the adsorbent.
In connection with the volatilization by means of a stripping gas the temperature of the adsorbent does not need to reach the boiling point of the solvent due to the fact that the stripping gas reduces the partial pressure of the solvent. The volatilized solvent is separated in a condenser.
When using steam for direct heating and also using steam as a stripping gas, the condensed solvent is, however, to a high degree diluted in water. This inconvenience does not occur, if heating is carried out indirectly and if a not condensable gas as e.g. air or nitrogen is used. In this case energy consumption is also reduced due to the fact that the heat of vaporization is considerable and that there is no need to take care of more or less poluted waste water. New laws and regulations have given rise to increased demands regarding the purification of exhaust air carrying solvents as well as on the efficiency of equipment for gas purification. From the point of view of environment as well as from an economical point of view it is thus important that apparatuses and devices for purification can be made small, economical and efficient. It has also become evident that the purification of gases can be of interest and at least less expensive if the purification process is used for recovering e.g. expensive solvents.
DISCLOSURE OF THE INVENTION
The invention is based on a bed design with indirect heating using a stripping gas, and the purpose of the invention is to provide a method permitting the use of small, simple and efficient beds.
The problem has been solved using a method in connection with which the regeneration of the adsorbent includes an initial phase, during which the adsorbed agent or the adsorbed agents are separated from a part of the adsorbent and transferred to the remaining parts of the adsorbent, which remaining parts are situated closer to the condenser in the direction of flow, thus increasing the concentration of the agent or the agents in these remaining parts of the adsorbent. The remaining parts of the adsorbent are regenerated in a final phase.
An increased concentration of the agent or the agents, which are separated, is obtained in those parts of the adsorbent which in the direction of flow are situated closest to the condenser. In connection with the separation of the agent or the agents from this part of the adsorbent a much higher concentration is obtained in the stripping gas than would otherwise be the case.
This is due to the fact that the equilibrium functions for the relation between the content of solvent in the adsorbent and the content of solvent in the stripping gas, respectively, in most cases are such that an increased content in the adsorbent leads to a considerably increased content in the stripping gas. It is of considerable importance for the heat exchange in the condenser that the content of condensable components in the gas mixture, which is introduced into the condenser, is as high as possible, due to the fact that the quantity of condensed agents in the condenser increases with an increased content in the stripping gas. At the same time the quantity of not condensed agents which pass through the condenser is reduced. In order to maintain a high eff
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Andersson Jan
Nilsson Lars
Bednarek Michael D.
Spitzer Robert
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