Refrigeration – Cryogenic treatment of gas or gas mixture – Separation of gas mixture
Patent
1998-06-05
1999-11-09
Capossela, Ronald
Refrigeration
Cryogenic treatment of gas or gas mixture
Separation of gas mixture
62637, F25J 100
Patent
active
059791799
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
In the (petro)chemical industry as well as during the transport of ecologically unsound substances and at petrol pumps and the like, undesirable vapours or gases may be released. The release of ecologically unsound substances is bound by increasingly stringent environmental regulations. In most cases the admissible concentration of such substances is expressed in p.p.m. (parts per million) or gramme per m.sup.3, whereby the admissible concentration has constantly been reduced over the years.
Furthermore solvents and hydrocarbon represent a relatively high value, which can be retained upon recovery and reuse.
The first known method for recovering solvents and/or hydrocarbons utilize filters, which are mostly provided with active carbon--see for example U.S. Pat. No. 4,583,985, U.S. Pat. No. 3,199,679 and U.S. Pat. No. 2,656,696, whereby certain ecologically unsound substances are adsorbed by the filter material.
Filtering and adsorption units of this type require constant maintenance and attention from operating staff and need to be cleaned at regular intervals. Furthermore such units are liable to wear and must be replaced after some time. Regeneration of the adsorption units usually entails the additional necessity of purifying a water flow. Finally it is by no means certain that the present and future stringent environmental regulations can be met by using filtering units of this type.
Furthermore processes are known wherein use is made of solvents, such as liquid carbon dioxide or chlorofluorocarbons (CFC's), the use of the latter being forbidden at the moment.
Examples of this can be found in U.S. Pat. Nos. 3,664,806 and 3,807,948.
Furthermore a purification system is known for for example benzene, which has a solidification point of 6.degree. C., whereby a gas flow containing benzene is passed through a room cooled to a temperature of -80.degree. C. in order for the benzene to deposit on the walls of a cooling element in the form of a solid substance and/or a liquid, and, after the temperature has been raised and the gas flow has been diverted to a second cooled room--or after a temporary interruption of the gas flow--the benzene can be discharged in liquid form. With this existing unit a pre-cooling unit is commonly used for removing water or water vapour from the gas flow. A process for the removal of condensible compounds from a gas flow is disclosed, for example, in DE-A-4001710.
SUMMARY OF THE INVENTION
The present invention provides a method for removing from a gas or vapour flow at least part of an ecologically unsound substance present therein, such as benzene, perchloroethylene or other hydrocarbons and/or solvents, wherein said gas or vapour flow is passed through a cooling room having a temperature which is equal to or lower than the condensation temperature of the ecologically unsound substance, wherein a medium having a solidification temperature which is equal to or higher than the temperature of the cooling room is introduced into the gas or vapour flow prior to the entry of said flow into the cooling room, and wherein the temperature in the cooling room is raised after a predetermined period and the gas or vapour flow is interrupted or diverted so that the gas or vapour flow does not enter the cooling room, in order to liquefy and discharge the solidified medium and the ecologically unsound substance contained therein. The ecologically unsound substance, in particular benzene, deposits in the form of solid matter and/or a liquid (condensation) on walls of preferably spiral cooling elements in the cooling room. The benzene is thereby intercepted ("encapsulated") by the medium, which is depositing on the cooling elements in the form of solid matter. Said encapsulation furthermore makes it impossible for the benzene to evaporate and thus find its way into the gas or vapour flow as yet. By raising the cooling room temperature the solidified medium and the benzene encapsulated therein are liquefied and subsequently discharged, after which further processing o
REFERENCES:
patent: 4169133 (1979-09-01), Staege
patent: 4424680 (1984-01-01), Rothchilo
patent: 4599462 (1986-07-01), Michl
patent: 4755201 (1988-07-01), Eschey et al.
patent: 5540057 (1996-07-01), Cheng
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