Method for cryogenically separating a mixture of nitrogen and carbon monoxide

Abstract

A method for separating a feed gas, containing nitrogen and carbon monoxide as main components, in a distillation column: the feed gas is cooled in a heat exchanger; at least a portion of the feed gas, or at least a portion of a gas derived from the feed gas, is sent to a reboiler of the distillation column so as to condense the gas while producing a liquid, and optionally a gas; at least a portion of the liquid is sent to the distillation column; a nitrogen gas-rich flow is extracted from the distillation column; a carbon monoxide-rich flow is extracted from the distillation column, heated in the heat exchanger, and compressed so as to provide a carbon monoxide-rich material at production pressure.

Claims

1. A process for separating a feed gas containing, as main components, nitrogen and carbon monoxide and optionally hydrogen in a distillation column wherein: i) the feed gas is cooled in a heat exchanger; ii) at least one portion of the feed gas or at least one portion of a gas derived from the feed gas is sent to a bottom reboiler of the distillation column in order to condense at least partially the feed gas or the at least one portion of the gas derived from the feed gas while producing a liquid and optionally a gas; iii) at least one portion of the liquid and optionally at least one portion of the gas are sent to the distillation column; iv) a stream enriched in gaseous nitrogen is withdrawn from the distillation column; and v) a stream enriched in carbon monoxide is withdrawn from the distillation column and is heated in the heat exchanger, wherein the stream enriched in carbon monoxide is compressed in order to provide a product enriched in carbon monoxide at a production pressure, the feed gas is sent, after cooling, into a first phase separator, the liquid from the first phase separator is expanded, the expanded liquid is sent to a second phase separator and at least one portion of the liquid from the second phase separator is vaporized against a portion of the compressed stream enriched in carbon monoxide in order to derive the gas to be sent to the bottom reboiler.

2. The process as claimed in claim 1, wherein a portion of the carbon monoxide is compressed to a pressure less than or equal to the production pressure, and is then cooled in the heat exchanger and sent to the bottom of the distillation column.

3. The process as claimed in claim 1, wherein at least one portion of the liquid from the second phase separator is vaporized in the heat exchanger.

4. A process for separating a feed gas comprising nitrogen and carbon monoxide, the process comprising the steps of: cooling the feed gas to form a cooled feed gas; separating the cooled feed gas into a first gas and a first liquid using a first phase separator; expanding the first liquid across a first valve to form an expanded liquid; separating the expanded liquid into a second gas and a second liquid using a second phase separator; heating a first portion of the second liquid to form a vaporized second liquid; at least partially condensing the vaporized second liquid in a bottom reboiler of a distillation column to form a condensed vaporized second liquid; introducing the condensed vaporized second liquid to the distillation column; withdrawing a stream enriched in gaseous nitrogen from the distillation column; withdrawing a stream enriched in carbon monoxide from the distillation column; heating the stream enriched in carbon monoxide; and compressing the stream enriched in carbon monoxide to provide a product enriched in carbon monoxide at a production pressure, wherein the heating of the first portion of the second liquid is performed against a portion of the compressed stream enriched in carbon monoxide to form the vaporized second liquid.

5. The process as claimed in claim 4 further comprising the step of introducing a portion of the product enriched in carbon monoxide to the bottom of the distillation column after cooling the portion of the product enriched in carbon monoxide.

6. The process as claimed in claim 4 further comprising the steps of: expanding a second portion of the second liquid to form an expanded second portion; and introducing the expanded second portion to the distillation column.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description, claims, and accompanying drawings. It is to be noted, however, that the drawings illustrate only several embodiments of the invention and are therefore not to be considered limiting of the invention's scope as it can admit to other equally effective embodiments.

(2) FIG. 1 represents a unit in accordance with the prior art.

(3) FIG. 2 represents a unit in accordance with an embodiment of the invention.

(4) FIG. 3 represents a unit in accordance with an embodiment of the invention.

DETAILED DESCRIPTION

(5) The invention will be described in greater detail while referring to the figures which represent a unit substantially according to the prior art for separating a gas having, as main components, nitrogen and carbon monoxide for FIG. 1 and a unit according to the invention for separating a gas having, as main components, nitrogen, hydrogen and carbon monoxide for FIGS. 2 and 3.

(6) According to FIG. 2, a stream of nitrogen, hydrogen and carbon monoxide 101 is cooled in a heat exchanger 103 and then in a heat exchanger 103A. The stream 101 is sent to a first phase separator 151 where it is separated into a hydrogen-rich gas stream 153 and a liquid stream 157. The stream 153 is heated in the heat exchangers 103, 103A and the stream 157 is expanded in a valve 155 and then sent to a second phase separator 161. The gas from the second phase separator is heated in the heat exchangers 103, 103A in order to form the stream 177. The liquid 163 is separated into two. One portion 167 is expanded in a valve 169, sent to a third phase separator 171 and then the streams formed 173, 175 are sent to the distillation column 115. The rest 165 of the liquid from the separator 161 is heated in the heat exchanger 103A in order to form the stream 165 which is used to heat the reboiler 105 fed by the bottoms liquid 117 from the distillation column 115. Having been used to reboil the distillation column 115, the stream 165 is expanded in the valve 107, sent to the fourth separator 109 and then to the distillation column 115 in the same way as for FIG. 1.

(7) A stream of nitrogen is removed as a purge 125 and is heated in the heat exchanger 103. The vaporized carbon monoxide 127 is also heated in the heat exchanger 103 and is compressed in the first stage 129 of a compressor. It is cooled in a cooler 131 by water and then divided into two. The stream 133 is cooled to an intermediate temperature in the heat exchanger 103 and is divided into two in order to form the stream 133. This stream 133 is cooled in the heat exchanger 134 against liquid nitrogen 137. The liquid nitrogen 137 is vaporized and heated in the heat exchanger 103. The stream 133 is expanded and mixed with the stream 21 downstream of the valve 119. The stream 145 which is sent to the bottom of the distillation column 15 after cooling in the heat exchanger 103A.

(8) Liquid carbon monoxide 179 is withdrawn from the condenser 123, expanded in the valve 181, sent to the fifth phase separator 183 in order to produce a liquid portion 185 and a gaseous portion 187. The liquid portion is vaporized in the exchange line 103A and the gas 187 is mixed with the carbon monoxide stream 127 intended for the compressor 129.

(9) According to FIG. 3, a stream of nitrogen, hydrogen and carbon monoxide 101 is cooled in a heat exchanger 103 and then in a heat exchanger 103A. The stream 101 is sent to a first phase separator 151 where it is separated into a hydrogen-rich gas stream 153 and a liquid stream 157. The stream 153 is heated in the heat exchangers 103, 103A and the stream 157 is expanded in a valve 155 and then sent to a second phase separator 161. The gas from the second phase separator is heated in the heat exchangers 103, 103A in order to form the stream 177. The liquid 163 is separated into two. One portion 167 is expanded in a valve 169, sent to a third phase separator 171 and then the streams formed 173, 175 are sent to the distillation column 115. The remainder 165 of the liquid from the separator 161 is heated in the heat exchanger 103A to form the stream 165 which is used to heat the reboiler 105 fed by the bottoms liquid 117 from the distillation column 115. Having been used to reboil the distillation column, the stream 165 is expanded in the valve 107, sent to the fourth separator 109 and then to the distillation column in the same manner as for FIG. 1.

(10) A stream of nitrogen is removed as a purge 125 and is heated in the heat exchanger 103. The vaporized carbon monoxide-enriched stream 127 is also heated in the heat exchanger 103 and is compressed in the first stage 129 of a compressor. It is cooled in a cooler 131 by water and then divided into two. The stream 133 is cooled to an intermediate temperature in the heat exchanger 103 and is divided into two in order to form the stream 193. This stream 193 is expanded in the turbine 191 in order to form the expanded stream 193 which is mixed with the stream 127 in order to be heated in the heat exchanger 103. The stream 145 originating from the stage 129 is sent to the bottom of the distillation column 115 after cooling in the heat exchanger 103A.

(11) Liquid carbon monoxide 179 is withdrawn from the condenser 123, expanded in the valve 181, sent to the fifth phase separator 183 in order to produce a liquid portion 185 and a gaseous portion 187. The liquid portion is vaporized in the exchange line 103A and the gas 187 is mixed with the carbon monoxide stream 127 intended for the compressor 129.

(12) While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations as fall within the spirit and broad scope of the appended claims. The present invention may suitably comprise, consist or consist essentially of the elements disclosed and may be practiced in the absence of an element not disclosed. Furthermore, if there is language referring to order, such as first and second, it should be understood in an exemplary sense and not in a limiting sense. For example, it can be recognized by those skilled in the art that certain steps can be combined into a single step.

(13) The singular forms a, an and the include plural referents, unless the context clearly dictates otherwise.

(14) Optional or optionally means that the subsequently described event or circumstances may or may not occur. The description includes instances where the event or circumstance occurs and instances where it does not occur.

(15) Ranges may be expressed herein as from about one particular value, and/or to about another particular value. When such a range is expressed, it is to be understood that another embodiment is from the one particular value and/or to the other particular value, along with all combinations within said range.