FR3013107A1 - METHOD AND APPARATUS FOR DEAZATING A FLUID RICH IN CARBON MONOXIDE - Google Patents

Abstract

An apparatus for denitrogenating a gaseous mixture containing at least 80% carbon monoxide and nitrogen comprises a heat exchanger (HX) in which the gaseous mixture is cooled to form a cooled gaseous mixture, a turbine for cooling at at least a portion of the cooled gaseous mixture, a distillation column (K) having a head condenser (C), means for sending the expanded flow rate in the turbine to the distillation column, a conduit for supplying a tank liquid (27). ) from the column to the overhead condenser where it at least partially vaporizes to form a gas containing more than 80% carbon monoxide, a pipe for sending the gas (13) to heat up in the heat exchanger to form a product (17,19) or part of a product.

Description

The production units for carbon monoxide and hydrogen can be separated into two parts: - generation of the synthesis gas (mixture containing H2, CO, CH4, CO2, Ar and N2 essentially). Among the various synthetic gas production lines, the most developed use natural gas as raw material such as: reforming furnaces, auto-thermal reactors or partial oxidation reactors. Other industrial processes that are developing more and more use coal as raw material that requires a carrier gas to the reactor. - purification of the synthesis gas. We find: - a washing unit with a liquid solvent to remove most of the acid gases contained in the synthesis gas - an adsorbent bed purification unit.

A cryogenic separation unit called cold box for the production of CO. Most existing H2 and CO cryogenic separation units do not include a means of separating the nitrogen-contaminated CO because the nitrogen contents in the synthesis gas are compatible with the CO purity required by the customer. In other cases, the cryogenic gas synthesis separation units comprise a CO / N2 separation column completely integrated in the initial cold box. The N 2 content in the raw material tends to increase over time because the N 2 content increases in the natural gas supplying the synthesis gas generation or nitrogen is used as the carrier fluid for the coal. Thus, the purity of the CO of existing cryogenic separation units is degraded and leads to losses of production yields of products that consume CO.

In order to increase the productivity of the downstream units that consume CO, it is necessary to define a CO / N2 separation unit which is fed by the impure CO produced by the existing cold box. The new cold box is powered by a CO / N2 mixture produced by the existing unit (taken from the impure product CO line from the output of the existing cycle compressor).

The new cold box comprises a CO / N2 distillation column and a set of heat exchangers for cooling the CO / N2 mixture as well as bringing the condensation and reboiling energies to the CO / N2 column. A pure CO cycle compressor with an impure CO turbine ensures the refrigeration balance. According to one object of the invention, there is provided a method of denitrogenation of a gaseous mixture containing at least 80% of carbon monoxide and nitrogen in which: i) the gaseous mixture is cooled in a heat exchanger, ii) at least a portion of the cooled mixture is expanded in the heat exchanger in a turbine and the flow rate expanded in the turbine is sent to a distillation column having a head condenser; iii) a bottom liquid is sent from the column; to the overhead condenser where it at least partially vaporizes to form a gas containing more than 80% carbon monoxide, the gas is heated in the heat exchanger to form a product or part of a product and iv) condense in the condenser a gas at the top of the column. According to other optional objects: the gas mixture containing more than 80% of carbon monoxide is compressed in a compressor and divided into two parts, one part being the product of the process and the remainder being cooled in the heat exchanger; heat and returned to the bottom of the column. - The first part is at a higher or lower pressure than the second part, the parts being withdrawn at different pressures of the compressor. the product of the process is at a higher or lower pressure than the remainder, the remainder and the product being withdrawn at different compressor pressures. the compressor is driven by the turbine. the mixture comes from an apparatus for separating a mixture of carbon monoxide, nitrogen and hydrogen which produces a fraction containing carbon monoxide with a first purity, at least a part of which constitutes the gaseous mixture . the compressor is a cycle compressor of the apparatus for separating a mixture of carbon monoxide, nitrogen and hydrogen - a first part of the fraction is treated according to steps i) to iv) to form the gas containing more than 80% carbon monoxide, this purity being a second purity higher than the first purity and wherein the gas is mixed at the second purity with the first part at the first purity to form a product. the column operates at a pressure of between 1.5 bar abs and 15 bar abs. According to another object of the invention, there is provided an apparatus for denitrogenating a gaseous mixture containing at least 80% carbon monoxide and nitrogen comprising a heat exchanger in which the gaseous mixture is cooled to form a gas mixture. cooled gas mixture, a turbine for expanding at least a portion of the cooled gas mixture, a distillation column having a head condenser, means for supplying the expanded flow rate in the turbine to the distillation column, a pipe for supplying a cooling liquid. column vessel to the head condenser where it vaporizes at least partially to form a gas containing more than 80% carbon monoxide, a pipe for sending the gas to heat up in the heat exchanger to form a product or a part of a product and means for sending a top gas from the column to condense in the condenser. The apparatus may comprise a compressor for compressing the gas mixture upstream of the heat exchanger and for compressing a product of the process, possibly at different pressures. The apparatus may comprise an apparatus for separating a mixture of carbon monoxide, nitrogen and hydrogen which produces a fraction containing carbon monoxide with a first purity, at least a part of which constitutes the gaseous mixture. The invention will be described in more detail with reference to the figures; FIG. 1 shows a denitrogenation process according to the invention integrated into an existing process and FIG. 2 shows the detail of the denitrogenation process according to the invention. In Figure 1, the cold box CB1 contains an apparatus for separating a mixture of hydrogen, carbon monoxide and nitrogen. The apparatus is kept cold by a CO cycle using a two-stage compressor C1, C2. The carbon monoxide 1 is partially compressed in both stages and returned as flow 5 to the cold box CB1. The cold box CB1 produces a fraction 3 having a first purity equal to at least 80% of carbon monoxide. All the percentages mentioned in this document relating to purities are molar purities.

Before the modification of the apparatus, this fraction was sent through the valve V11, to a pipe 19 of CO supply. With time, the fraction 3 becomes more and more rich in nitrogen and thus the process is modified to send only part 7 of the fraction 3 directly to the pipe 19 without separation or no part. Part 9 or all fraction 3 is filtered by a filter F1 and sent to a second cold box CB2 where it is separated to produce a flow 13 at a second purity containing less nitrogen and more carbon monoxide than fraction 3 After compression in the compressor C3, a part 15 of the flow 13 is sent back to the cold box CB2 and the remainder 17 of the flow is sent to the valve V15 and is used to enrich the flow rate 7 with carbon monoxide to form the flow 19 sent to customers. A nitrogen enriched flow is sent as a purge to a fuel flow.

The cold box CB1 may not contain a denitrogenation column or may contain a denitrogenation column which no longer manages to eliminate enough nitrogen. In FIG. 2, the flow rate 9 filtered in the filter F2 enters the second cold box CB2 and cools in the heat exchanger HX from the ambient temperature to the cold end of the exchanger. The flow 9 is divided into two parts, a part 9A being sent to a valve V17 and then to an expansion turbine T and the other part 9B being expanded in a valve V2. The two parts together as flow 9 are sent into the exchanger HX and the flow 9 is sent in the column K at an intermediate level in gaseous form. Flow 9 is separated in column K to form a nitrogen enriched overhead gas and a carbon monoxide enriched bottom liquid. The liquid 27 is expanded in a valve V3 and sent to the head condenser C of the column K. There the liquid vaporizes at least partially and the formed gas 13 is heated in the exchanger HX and out of the second cold box. the gas 13 can be compressed in the compressor C3 and divided in two. A part 17 is sent by the valve V15 to the flow 19 The remainder 15 is filtered in the filter F2, cooled in the exchanger HX and sent to the bottom of the column K for reboiling. The nitrogen separated in the condenser C exits as flow 25, is heated in the exchanger HX and leaves the cold box CB2 to be used as fuel for example through the line 41. The compressor C3 can be driven by the turbine T .

The flow 13 contains at least 85% carbon monoxide, or even at least 90 or even at least 95% carbon monoxide. Column K operates at a pressure generally between 1.5 bar abs and 15 bar abs.

Claims (10)

REVENDICATIONS1. Process for the denitrogenation of a gaseous mixture containing at least 80% carbon monoxide and nitrogen in which: i) the gaseous mixture (9) is cooled in a heat exchanger (HX), ii) at least one a portion (9A) of the mixture cooled in the heat exchanger in a turbine (T) and the flow rate expanded in the turbine is sent to a distillation column (K) having a top condenser (C) iii) a tank liquid (27) from the column to the overhead condenser where it at least partially vaporizes to form a gas (13) containing more than 80% carbon monoxide, the gas is heated in the heat exchanger to form a product or a part of a product (17,19) and iv) condensing in the condenser a gas overhead column 2. Process according to claim 1, in which the gaseous mixture (3, 9) containing more than 80% of carbon monoxide is compressed in a compressor (C1, C2) and divided into two parts, a first part (7). being the product of the process and a second part (9) being cooled in the heat exchanger (HX) and returned to the bottom of the column (K). 3. The method of claim 2 wherein the first portion (7) is at a higher or lower pressure than the second portion (9), the parts being withdrawn at different pressures of the compressor (C1, C2). 4. The method of claim 2 or 3 wherein the compressor (C1, C2) is driven by the turbine (T). 5. Method according to one of the preceding claims wherein the mixture (9) comes from a separating apparatus (CB1) of a mixture of carbon monoxide, nitrogen and hydrogen which produces a fraction containing monoxide 3013 10 7 7 of carbon (3) with a first purity, at least a portion of which constitutes the gaseous mixture (9). The process according to claim 5 wherein a second portion (9) of the fraction is treated according to steps i) to) iv) to form the gas containing more than 80% carbon monoxide, this purity being a second purity greater than the first purity and wherein the second purity gas is mixed with a first portion at the first purity (7) to form a product (19). 10 7. Method according to one of the preceding claims wherein the column (K) operates at a pressure between 1.5 bar abs and 15 bar abs. 8. Apparatus for denitrogenating a gas mixture containing at least 80% carbon monoxide and nitrogen comprising a heat exchanger (HX) 15 in which the gaseous mixture is cooled to form a cooled gaseous mixture, a turbine for at least a portion of the cooled gaseous mixture, a distillation column (K) having a head condenser (C), means for sending the expanded flow rate in the turbine to the distillation column, a conduit for discharging a liquid (27) from the column to the overhead condenser where it vaporizes at least partially to form a gas containing more than 80% carbon monoxide, a pipe for sending the gas (13) to heat up in the heat exchanger for forming a product (17,19) or a part of a product and means for sending a top gas from the column to condense in the condenser. 25 9. Apparatus according to claim 8 comprising a compressor (C1, C2) for compressing the gas mixture upstream of the heat exchanger and for compressing a product of the process, possibly at different pressures. 30 10. Apparatus according to one of claims 8 or 9 comprising an apparatus for separating (CB1) a mixture of carbon monoxide, nitrogen and hydrogen which produces a fraction (3) containing carbon monoxide with a first purity, at least a portion of which constitutes the gaseous mixture.