Refrigeration – Cryogenic treatment of gas or gas mixture – Separation of gas mixture
Reexamination Certificate
2000-02-01
2001-08-07
Capossela, Ronald (Department: 3744)
Refrigeration
Cryogenic treatment of gas or gas mixture
Separation of gas mixture
C062S654000, C062S924000
Reexamination Certificate
active
06269659
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to an air distillation process with production of argon by means of an air distillation plant comprising an air distillation apparatus and at least one column for production of impure argon, the plant being intended to deliver argon with a nominal argon extraction yield &rgr;
n
at the outlet of the said impure-argon production column.
BACKGROUND OF THE INVENTION
The invention applies in particular to the production of argon by means of air distillation plants having a double distillation column.
In such a plant with a double air distillation column, medium-pressure nitrogen is generally removed from the top of the medium-pressure column of the double column. This medium-pressure nitrogen is generally used, after expansion in a turbine, as a source of refrigeration, especially to cool the air to be distilled. Thus, a portion of the refrigeration energy supplied to the air to be distilled can be recovered and therefore the operating costs of such a plant can be reduced.
Such a plant is designed to meet nominal argon production requirements with a nominal argon extraction yield &rgr;
n
at the outlet of the impure-argon production column, called the mixture column. In general, it is sought to have a maximum yield &rgr;
n
.
Hitherto, when the argon production requirements decrease, for example during periods of less load on a consuming plant or when storage tanks to be filled are full, the argon extraction yield &rgr; at the outlet of the impure-argon production column is correspondingly reduced in order to meet at the very most these reduced argon-proauction requirements.
SUMMARY OF THE INVENTION
The object of the invention is to provide an air distillation process with production of argon allowing the operating costs to be optimized when the argon-production requirements are less than the nominal requirements.
For this purpose, the subject of the invention is an air distillation process with production of argon by means of an air distillation plant comprising an air distillation apparatus and at least one column for production of impure argon, the plant being designed to deliver argon with a nominal argon extraction yield &rgr;
n
at the outlet of the said impure-argon production column, characterized in that, for reduced argon production requirements corresponding to a necessary argon extraction yield &rgr; at the outlet of the impure-argon production column with &rgr;≦&rgr;
o
≦&rgr;
n
, where &rgr;
o
is a predetermined optimum yield, the argon extraction yield at the outlet of the impure-argon production column is maintained at approximately the value &rgr;
o
.
Depending on the particular embodiments, the process may comprise one or more of the following characteristics, taken in isolation or in any technically possible combination:
the argon extracted in excess with respect to the necessary extraction yield &rgr; is used as a source of refrigeration in the air distillation plant, for example to cool the air to be distilled;
the said excess argon is at least partially withdrawn in gas and/or liquid form at the top of the impure-argon production column and this withdrawn portion is sent into at least one heat exchanger of the plant or into the air distillation apparatus;
the said at least partially withdrawn portion is mixed with a residual fluid withdrawn from one of the columns of the plant before it is sent into the said heat exchanger;
the said at least partially withdrawn portion is mixed with a fluid intended for one of the columns of the plant;
since the plant also comprises a column for production of nearly pure argon by argon removal connected to the said impure-argon production column, at least a portion of the excess argon is withdrawn in gas and/or liquid form at the bottom or at the top of the pure-argon production column and this withdrawn portion is sent into at least one heat exchanger of the plant or into the air distillation apparatus;
since the air distillation apparatus comprises a double column which itself comprises a medium-pressure column, a low-pressure column and a reboiler for bringing the top of the medium-pressure column into heat-exchange relationship with the bottom of the low-pressure column, medium-pressure nitrogen is withdrawn from the top of the medium-pressure column, &rgr;
o
is the yield for which medium-pressure nitrogen can be withdrawn at a maximum flow rate D(&rgr;
o
) and, for a necessary extraction yield &rgr; of less than &rgr;
o
, medium-pressure nitrogen is withdrawn at a flow rate of greater than D(&rgr;);
for a necessary extraction yield &rgr; of less than &rgr;
o
, medium-pressure nitrogen is withdrawn at the maximum flow rate D(&rgr;
o
);
the medium-pressure nitrogen withdrawn as source of refrigeration in the plant is used by sending it, especially after expansion in a turbine, in a heat exchanger of the plant, for example to cool the air to be distilled;
since the air distillation apparatus comprises a double column which itself comprises a medium-pressure column, a low-pressure column and a reboiler for bringing the top of the medium-pressure column into heat-exchange relationship with the bottom of the low-pressure column, medium-pressure nitrogen is withdrawn from the top of the medium-pressure column, &rgr;
o
is the yield for which air can be expanded to the low pressure at a maximum flow rate D′ (&rgr;
o
) with the performance of external work, for the purpose of blowing it into the low-pressure column, and, for a necessary extract-ion yield &rgr; of less than &rgr;
o
, air is expanded to the low pressure, with the performance of external work, at a flow rage greater than D′ (&rgr;
o
), and especially a flow rate equal to D′ (&rgr;
o
)
The subject of the invention is also a plant for the implementation of the process as defined above, characterized in that it comprises an air distillation apparatus, at least one impure-argon production column, a heat exchanger, especially one through which a feed line for air to be distilled passes, and at least one branch line for sending at least one portion of the argon extracted in excess into the said heat exchanger.
Depending on the particular embodiments, the plant may comprise one or more of the following characteristics, taken in isolation or in any technically possible combination:
an inlet of the said branch line is connected to an outlet for liquid or gaseous argon from the top of the impure-argon production column;
the plant comprises a nearly-pure argon production column connected to the impure-argon production column, and an inlet of the said branch line is connected to an outlet for gas or liquid from the bottom or from the top of the nearly-pure argon production column;
the said branch line is connected to an outlet for residual fluid from one of the columns of the plant in order to mix a residual fluid with the argon conveyed in the said branch line;
the said branch line is connected to an inlet for fluid into one of the columns of the plant in order to mix the fluid with the argon conveyed in the said branch line;
the distillation apparatus comprises a double distillation column which itself comprises a medium-pressure column, a low-pressure column and a reboiler for bringing the top of the medium-pressure column into heat-exchange relationship with the bottom of the low-pressure column, the top of the medium-pressure column has a medium-pressure nitrogen outlet and a line connects the said medium-pressure nitrogen outlet to a heat exchanger of the plant, especially one through which a feed line for air to be distilled passes;
the said line is provided with a turbine for expanding the medium-pressure nitrogen withdrawn; and
the plant comprises a turbine for blowing purified air into the low-pressure column.
REFERENCES:
patent: 3447331 (1969-06-01), Smith
patent: 4932212 (1990-06-01), Rohde
patent: 5426946 (1995-06-01), Corduan et al.
patent: 5505051 (1996-04-01), Darredeau et al.
patent: 5682767 (1997-11-01), De Bussy et al.
patent: 0 384 213 (1990-08-01), None
patent: 0 540 900 (1993-05-01),
De Bussy Francois
Saulnier Bernard
Staine Frédéric
Capossela Ronald
L'Air Liquide, Societe Anonyme pour l'Etude et l'
Young & Thompson
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