Chemistry of hydrocarbon compounds – Purification – separation – or recovery
Patent
1994-02-18
1995-07-04
McFarland, Anthony
Chemistry of hydrocarbon compounds
Purification, separation, or recovery
62 24, 62 32, 62 34, C07C 700, F25J 302
Patent
active
054302234
DESCRIPTION:
BRIEF SUMMARY
SUMMARY OF THE INVENTION
The invention relates to a process for separating higher hydrocarbons from a gas mixture containing the latter and lower-boiling components by rectification, in which process the gas mixture is partially condensed and fed to a separation column, at whose bottom a fraction rich in higher hydrocarbons and at whose top a fraction rich in lower-boiling components are drawn off; in this case the top fraction is partially condensed, and the condensate is fed to the top of the separation column as reflux.
Such a process is known from EP-B-0 318 504. In the known process, the cold required to condense the feed gas and top fraction is made available, on the one hand, by one or more refrigeration circuits and, on the other, by active pressure reduction of the feed gas or residual gas. The refrigeration circuits work at constant evaporation temperature and, with heat exchange with a condensing feed gas or top gas mixture, cause relatively large temperature differences and thus energy losses. The turbines used to generate the extreme cold are not suitable for all processes. In particular, in the case of temperature fluctuations, for example, they exhibit high wear because of unsteady process conditions. The previously known process, therefore, does not work completely satisfactorily in economic terms and operates reliably only if certain boundary conditions are observed.
The object of the invention is to provide a process of the initially mentioned type which works more economically, can be used more flexibly with respect to boundary conditions and, in particular, is also suited for relatively widely fluctuating parameters of the gas mixture to be separated.
This object is achieved by having the condensation of the gas mixture and the condensation the top fraction be produced by indirect heat exchange with a refrigerant, which consists of several components and is conveyed in an external circuit.
Structuring the process in this way makes it possible to variable match the refrigerant temperature to the requirements imposed by the composition of the feed gas and products. Compared to a refrigerant cascade, for example, this makes both low equipment costs and low energy losses possible. Also, extreme cold can be generated at reasonable expense, so that the process of the invention does not require a pressure-reduction turbine. The drawbacks associated with turbines with respect to flexibility are thus avoided.
The energy advantages of the process of the invention are surprisingly great. Not only compensate for extra costs caused by the multicomponent-refrigerant circuit, but overall produce a clear increase in the economic efficiency of the process. In addition, the possible applications of the process are extraordinarily flexible.
The separation column used in the process is generally only operated as an enrichment column, i.e., the partially condensed gas mixture is fed to the lower area of the column.
To improve the rectifying action of the separation column even further, it is advantageous to remove an intermediate fraction from the separation column at an intermediate point. The intermediate friction is at least partially condensed in indirect heat exchange with the refrigerant and is returned to the separation column.
This heat exchange occurs at a temperature that lies between the temperature level of the condensation of the feed gas mixture and that of the condensation of the top fraction. The corresponding heat exchangers are preferably connected in series on the refrigerant side, so that optimum use of the sliding evaporation temperature curve of the multicomponent refrigerant is produced. As a result, the process can be operated especially advantageously with respect to energy. Of course, it is also possible and in many cases also advantageous to remove several such intermediate fractions in an analogous way and to feed them to an indirect heat exchange with the refrigerant.
In the process of the invention, it is further advantageous to separate compressed refrigerant inside the exter
REFERENCES:
patent: 4455158 (1984-06-01), Vines et al.
patent: 4501600 (1985-02-01), Pahade
patent: 4608068 (1986-08-01), Bauer et al.
patent: 4714487 (1987-12-01), Rowles
Forg et al., "Natural-Gas Liquefaction," Linde Reports on Science and Technology, 15/1970, pp. 27-40.
Linde Aktiengesellschaft
McFarland Anthony
Phan Nhat D.
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