JP5551063B2 - Method and apparatus for separating a mixture of hydrogen, methane and carbon monoxide by cryogenic distillation - Google Patents

Description

The present invention relates to a method and apparatus for separating a mixture of hydrogen, methane and carbon monoxide by low temperature distillation. In particular, it relates to a process for producing a mixture of H ₂ / CO having a low CH ₄ content that combines CH ₄ products in the liquid state as much as possible.

  The unit for producing carbon monoxide and hydrogen can be divided into two parts.

Generation of synthesis gas (essentially H _2, CO, mixtures containing CH _4, Ar and N _2). Among the various industrial routes used to produce syngas, steam reforming is the most important. The design of this unit, including the furnace, is based on the required CO and hydrogen products. However, coal gasification units represent some benefit in terms of operating costs and appear to experience increasing development, especially in countries such as China. The design of such a unit, comprising a reactor for gasifying coal with oxygen, is based on the required products of CO and hydrogen.

Syngas purification. this is:
A liquid solvent scrubbing unit to remove most of the acid gas contained in the synthesis gas;
A purification unit for refining the absorbent floor,
It features a cryogenic separation unit known as a cold box that produces a mixture of CO and / or hydrogen and / or carbon monoxide and a mixture of hydrogen known as oxygas with a defined H ₂ / CO ratio.

Generally, synthesis gas following compounds: containing _{H 2, CO, CH 4,} N 2, ( between 15 and 60 bar) pressure containing Ar mixture.

  Two known major groups of processes for cryogenic separation of mixtures containing hydrogen, carbon monoxide and methane, these are methane washing and partial condensation.

One benefit of methane scrubbing is to make hydrogen production under pressure with good purity and a CO content that may range from 0.5 mol% to a slight ppm. However, with this type of process using methane washing, the residual CH ₄ content cannot generally be obtained below 1 mol%.

In some desirable examples for producing hydrogen or H ₂ / CO mixtures containing less than 1 mol% CH ₄ (especially for the production of MeOH), the only method that can be taken is that the synthesis gas is H ₂ / CO It is a process that is subjected to partial condensation that is cooled to a temperature of the order of −186 ° C. so as to reach a thermodynamic equilibrium in which the CH ₄ content in the gas mixture is lowered below 1 mol%.

  Reaching this temperature level is expensive with the energy requirements of the circulating compressor.

  The idea based on the invention presented here could clearly reduce the separation energy (and the energy to be supplied to the circulating compressor).

  USA-A-4488890 and US-A-6098424 present a process with a liquid carbon monoxide scrubber tower in which the process produces substantially all of the cooling energy through a carbon monoxide cycle.

In the context of the production of a mixture of hydrogen and a mixture of CO with a low CH ₄ content (generally below 1 mol%), the idea is to bring the synthesis gas to −167 ° C. (and therefore 20 ° C. warmer than the partial condensation skim). By cooling to an approximate temperature, the gas phase is processed in a CO scrubber tower where liquid CO is injected into the top of the tower.

One subject of the present invention is a process for separating a mixture of hydrogen, carbon monoxide and methane by cryogenic distillation, wherein said mixture is cooled in an exchange line and at least partly sent to a liquid CO scrubber column. The gas is poured out at the top of the scrubber tower, and the lower liquor from the scrubber tower is sent to the CO / CH ₄ separation tower after purification as much as possible, and the CO-rich liquid is fed at the top of the CO / CH ₄ separation tower. Withdrawn, at least partially pressurized, and at least partially sent to the top of the scrubber tower, and a methane-rich liquid is withdrawn as a final product at the bottom of the CO / CH ₄ separation tower, at least of the separation energy. Some are provided by a closed cycle using nitrogen, methane, oxygen, argon, helium or hydrogen as the circulating fluid.

Other selection aspects:
Gas poured at the top of the scrubbing column is a mixture of CO containing mixture and 1 less than mole% CH ₄ in H _2;
Said closed cycle is used to condense the CO / CH ₄ separator head liquid;
Said closed cycle is used to re-boil the CO / CH ₄ separation column and / or the lower liquor of the stripping column;
The closed cycle provides at least a portion of the energy used to liquefy this CH ₄ ;
The two liquids in the closed cycle are vaporized at at least two different pressures in the exchange line;
At least a portion of the carbon monoxide rich liquid withdrawn from the CO / CH ₄ separation column is pressurized using a pump and at least a portion of the pumped liquid is sent to the scriber column;
At least two temperatures in the following list differ by at most 5 ° C:
The inlet temperature at which the mixture enters the scrubber tower The temperature of the CO-rich liquid from the CO / CH ₄ tower The temperature of the supercooled liquid methane.

Another aspect of the present invention provides an apparatus for separating hydrogen, carbon monoxide and methane by cryogenic distillation, said apparatus comprising a liquid CO scrubber tower, a CO / CH ₄ separation tower, an exchange line for cooling the mixture, cooling Means for sending at least a portion of the mixture to the scrubber tower, means for pouring gas at the top of the scrubber tower, and lower liquor from the scrubber tower to the CO / CH ₄ separation tower after purification as much as possible. Means for sending, means for withdrawing CO rich liquid from the CO / CH ₄ separation column, means for pressurizing at least a portion of the drawn liquid, sending at least a portion of the pressurized liquid to the top of the scrubber tower It means for withdrawing at unit and lower CO / CH ₄ separation column a liquid rich in methane as a final product for circulation in order to provide at least a portion of the separation energy It comprises nitrogen as the body, methane, oxygen, argon, a closed cycle using helium or hydrogen.

According to another optional aspect, said device is means for withdrawing CH ₄ from the liquid as a final product;
A closed cycle that provides at least a portion of the energy used to liquefy this CH ₄ ;
A stripping tower for purifying the lower liquor of the scrubber tower upstream of the CO / CH ₄ separation tower;
A pump connected to the upper part of the CO / CH ₄ separation tower and the upper part of the scrubber tower;

not listed. not listed.

  The invention will be described in detail with reference to the drawings showing an apparatus according to the invention.

In FIG. 1, the synthesis gas 1 obtained at high pressure (generally between 15 and 60 bar) is cooled in the main heat exchanger 3 and partially condensed in the exchange line to a temperature of −167 ° C. It is done. The gas phase is sent to the lower part of the scrubber tower 5 where it is washed with liquid CO 51 injected into the upper part of the tower 5. The CH ₄ content in the steam 7 purified at the top of the scrubber column 5 can be reduced to less than 1 mol%, so that it can be treated after reheating, for example, in the exchange line of the MeOH unit.

The liquid phase 11 at the bottom of the liquid CO scrubber column 5 is very rich in CH ₄ and also contains CO and dissolved hydrogen. This liquid 11 is sent to the upper part of the stripping column 13 with the lower reboiler to separate and reduce the content of the lower liquor of the flash column 17 and thereby reduce the content of CO and CH ₄ in the column 33. Reduce the amount of hydrogen that cannot be condensed during the separation.

  The gas 21 from the stripping tower is heated in the exchange line 3 and behaves as fuel.

The lower liquor from the stripping tower 13 is supercooled by the heat exchanger 19 and then sent in two parts to the CO / CH ₄ separation tower. Part 27 is expanded by a valve 31 and sent to the top of the tower 33. The remainder 23 is expanded by a valve 29 and then heated by the heating 25 and then sent to the lower part of the tower 33. CO is produced in liquid form 47 at the top and is sent to a pump 49 that raises its pressure to the pressure level of the CO scrubber tower 5. It is therefore an internal liquid CO loop through at least one cryogenic pump and a valve 53 between the top of the CO / CH ₄ separation tower 33 and the top of the CO scrubber tower 5.

Perhaps a part of the liquid CO 55 can be sent through the valve 57 to the top gas of the scrubber column 5 to form a mixed stream 9. This can adjust the CO / H ₂ ratio of the gas.

CH ₄ 39 is produced in liquid form at the bottom of the CO / CH ₄ column 33. The CO / CH ₄ tower has a lower reboiler 37 and an upper condenser 35.

One option with this skim is to produce and supplement an H ₂ / CO mixture 7 with low CH ₄ content, pure methane with a slight trace of CO, thereby bringing it to market in the form of LNG45. it can.

This liquid CH ₄ 39 exiting the bottom of the CO / CH ₄ tower is subcooled in the exchange line 41 before being sent for storage as limited to the production of vaporized liquid called “boil off”. The valve 43 can be used for the short circuit line 41.

The top gas 59 from the CO / CH ₄ tower 33 is compressed by the compressor 61 to form a stream 63, condensed in the exchange line, and in place of or in addition to the pumping stream from the pump 49. Sent to the top of the.

The separation energy is supplied by an external closed cycle. This cycle can also supply energy to liquefy this CH ₄ 39.

The gas used for the cycle can be selected from the list N ₂ , CH ₄ , O ₂ , Ar, He, H ₂ or the like. The gas 65 is used to reboil the CO / CH ₄ tower, and then forms a liquid 67 that is divided in two. Part 71 passes through valve 73 and is sent to upper condenser 35. The flow vaporized in the condenser is sent to the compressors 85, 87, and 89 as flows 81 and 83 in order. The stream 91 compressed by the compressor 89 is divided into two parts 93 and 95 which are compressed in parallel by the two compressors 97 and 99. The compressed streams 95, 101 are combined to form a stream 103 that is divided into two. The part 105 is partially cooled in the exchange line 3 before being divided in two. Fraction 109 is expanded to an intermediate temperature by turbine 111 and its expanded stream 113 is returned to stream 81 at an intermediate temperature level in exchange line 3. The other fraction is sent to the turbine 115 at a temperature level below the temperature of 109 cooled in the exchange line 3 and is combined with the stream 81 upstream of the exchange line 3. Stream 107 is completely cooled in exchange line 3 and sent as stream 65 to reboil the CO / CH ₄ column.

  Vaporizing the streams 77 and 81 at two different pressures in the exchanger 3 can make the most of heat exchange.

In FIG. 2, the synthesis gas 1 obtained at high pressure (generally between 15 and 60 bar) contains 15 mol% of methane. It is divided in two, part 1A is cooled by the main exchanger 3 and the remaining 1B bypasses the main exchanger before being mixed with the stream 1A backwards, and the reboiler 37 of the CO / CH ₄ column 33 and Sent to the annular stream 3. The annular stream 4 cooled in the lower reboiler is returned at the intermediate temperature of the main exchanger 3 and is partially condensed in the exchange line to a temperature of −167 ° C. It is sent to the bottom of the scrubber tower 5 where it is washed with liquid CO 51 injected into the top of the tower 5. The CH ₄ content in the steam 7 purified at the top of the scrubber column 5 can be reduced to less than 1 mol%, so that it can be processed after heating, for example, in the exchange line of the MeOH unit.

The liquid phase 11 at the bottom of the liquid CO scrubber column 5 is very rich in CH ₄ and also contains CO and dissolved hydrogen. This liquid 11 is sent to the upper part of the stripping tower 13 with the lower reboiler to separate and reduce the content of the lower liquor of the flash tower 17, thereby reducing the CO and CH ₄ in the tower 33. Reducing the amount of hydrogen that cannot be condensed during the separation of

  The gas 21 from the stripping tower is heated in the exchange line 3 and behaves as fuel.

The lower liquor from the stripping column 13 is supercooled by the exchanger 19 and then sent in two parts to the CO / CH ₄ separation column. Part 27 is expanded by a valve 31 and sent to the top of the tower 33. The remainder 23 is expanded by a valve 29 and then heated by the heating 25 and then sent to the lower part of the tower 33. CO is produced in liquid form 47 at the top and is sent to a pump 49 that raises its pressure to the pressure level of the CO scrubber tower 5. It is therefore an internal liquid CO loop through at least one cryogenic pump and a valve 53 between the top of the CO / CH ₄ separation tower 33 and the top of the CO scrubber tower 5.

Perhaps a portion of the liquid CO 55 can be sent through the valve 55 to the top gas of the scrubber column 5 to form a mixed stream 9. This can adjust the CO / H ₂ ratio of the gas.

CH ₄ 39 is produced in liquid form at the bottom of the CO / CH ₄ column 33. The CO / CH ₄ tower has a lower reboiler 37 and an upper condenser 35.

One option with this scheme is to produce pure methane containing small traces of H ₂ / CO mixture 7, CO low CH ₄ content so can be marketed in the form of LNG45, cormorants complement That is .

This liquid CH ₄ 39 exiting the bottom of the CO / CH ₄ tower is subcooled in the exchange line 41 before being sent for storage as limited to the production of vaporized liquid called “boil off”. The valve 43 can be used for the short circuit line 41.

The top gas 59 from the CO / CH ₄ tower 33 is compressed by the compressor 61 to form a stream 63, condensed in the exchange line, and in place of or in addition to the pumping stream from the pump 49. Sent to the top of the.

The separation energy is supplied by an external closed cycle. This cycle can also supply energy to liquefy this CH ₄ 39.

The gas used for the circulation can be selected from the list N ₂ , CH ₄ , O ₂ , Ar, He, H ₂ .

The reboiling of the stripper column 13 is performed by the flow of the circulating gas 169. The cooling stream 171 is expanded by a valve 173 and sent to the upper condenser 35 of the CO / CH ₄ tower 33 as a stream 177. Stream 175 is split to form streams 177 and 179. Stream 177 is cooled by condenser 35. Stream 179 is sent to exchanger 3 via valve 181 where it is warmed again. Stream 180 rewarmed with reboiler 35 is mixed with streams 167 and 194 to stream 183. This stream 183 becomes slightly hot once and is combined with stream 179. Stream 185 combined at 10 bar is sent to series cycle compressors 85, 87 and then a portion is sent to compressor 89. A portion 169 of the stream compressed at 89 is sent at 39 bar for reboiling of column 13 and the remainder 191 is compressed at 50 bar by compressor 197 to form stream 201. Stream 201 is split into two to form stream 203, which passes through valve 205 to turbine 211 and becomes expanded stream 167. The stream 202 passes straight through the exchanger 3 and is divided into three. Stream 190 is also sent to turbine 211, stream 174 is mixed with stream 171, and stream 186 is warmed again in the exchanger before it combines with stream 192 from compressor 87 to form combined stream 189. . Stream 189 is sent to compressor 199, partially cooled by exchanger 3, and expanded by turbine 215 to form expanded stream 194.

  The compressor 197 is connected to the turbine 211 and the compressor 199 is connected to the turbine 215.

  Vaporizing streams 179 and 186 at two different pressures in exchanger 3 can maximize heat exchange.

  Throughout this document, the term “top of the tower” includes a range of positions from the top of the tower to a position with a maximum of 10 theoretical plates below this position in the strict sense.

Claims (13)

A process for separating a mixture of hydrogen, carbon monoxide and methane by cryogenic distillation, said mixture being cooled in an exchange line (3) and at least partly sent to a liquid CO scrubber tower (5), where gas (7 ) Is removed at the top of the scrubber tower, the lower liquid (11) exiting the scrubber tower is then purified and sent to the CO / CH ₄ separation tower (33), and the CO rich liquid (47) is CO / CH ₄ Pulled at the top of the separation tower, at least partially pressurized with a pump, and at least a portion of the pressurized liquid is not warmed in the exchange line and sent to the top of the scrubber tower without cooling. is, liquid rich in methane is withdrawn at the bottom of the as a final product CO / CH ₄ separation column (33), at least part of the separation energy nitrogen as the circulating fluid, methane, oxygen Closed cycle (65, 67, 79, 81, 91, 93, 95, 101, 103, 105, 107, 113, 117, 167, 169, 171, 175, 177, 179, 183 using argon, helium or hydrogen 185, 189, 190, 194, 201, 203). The method of claim 1, wherein the gas (7) is a mixture of CO containing CH ₄ mixtures and less than 1 mole% H ₂ withdrawn at the top of the scrubbing column (5). The closed cycle (65, 67, 79, 81, 91, 93, 95, 101, 103, 105, 107, 113, 117, 167, 169, 171, 175, 177, 179, 183, 185, 189, 190, 194,201,203) of claim 1 or 2 the method described is used to condense the top gas of the CO / CH ₄ column. The closed cycle (65, 67, 79, 81, 91, 93, 95, 101, 103, 105, 107, 113, 117, 167, 169, 171, 175, 177, 179, 183, 185, 189, 190, 194,201,203) of claim 1, 2 or 3 the method described is used to reboil the lower liquid of the CO / CH ₄ column and / or stripping column. The closed cycle (65, 67, 79, 81, 91, 93, 95, 101, 103, 105, 107, 113, 117, 167, 169, 171, 175, 177, 179, 183, 185, 189, 190, 194,201,203) the method of any one of claims 1 to 4 to provide at least a portion of the energy used to liquefy the CH _4. The closed cycle (65, 67, 79, 81, 91, 93, 95, 101, 103, 105, 107, 113, 117, 167, 169, 171, 175, 177, 179, 183, 185, 189, 190, during 194,201,203), the branch point and merging point is provided, wherein at least two liquids are branched at the branch point of the closed cycle (77,81,179,186) are merged since the branch that between, any one method according to claims 1-5 that will be vaporized at different pressures in the exchange line. At least two temperatures in the following list differ by at most 5 ° C:
- withdrawn at the bottom of the CO / CH ₄ separation column (33) - wherein the mixture inlet temperature enters the scrubbing column (7) - the temperature of the liquid (47, 51) rich CO from the CO / CH ₄ column 7. The process as claimed in claim 1, wherein the temperature of liquid methane (45) formed by cooling the methane-rich liquid .   The method according to claim 1, wherein the circulating fluid is methane.   The method according to claim 1, wherein the circulating fluid is nitrogen. An apparatus for separating hydrogen, carbon monoxide and methane by low-temperature distillation, including a liquid CO scrubber tower (5), a CO / CH ₄ separation tower (33), an exchange line (3) for cooling the mixture, and a cooling mixture Means for sending at least a portion of the scrubber tower to the scrubber tower, means for removing gas at the top of the scrubber tower, means for purifying the lower liquid exiting the scrubber tower and sending it to the CO / CH ₄ separation tower Means for withdrawing CO rich liquid from the CO / CH ₄ separation column, means for pressurizing at least part of the withdrawn liquid (49), for sending at least part of the pressurized liquid to the top of the scrubber tower It means for withdrawing a liquid rich in the means and methane at the bottom of the CO / CH ₄ separation column as a final product, the circulating fluid in order to provide at least a portion of the separation energy Closed cycle using nitrogen, methane, oxygen, argon, helium or hydrogen (65, 67, 79, 81, 91, 93, 95, 101, 103, 105, 107, 113, 117, 167, 169, 171, 175, 177, 179, 183, 185, 189, 190, 194, 201, 203)
The means for withdrawing the CO-rich liquid is connected to the means for pressurizing at least part of the liquid without going through the exchange line, and the means for pressurizing at least part of the liquid The means is a device connected to the scrubber tower without going through the exchange line. The apparatus of claim 10, further comprising a CO / CH ₄ pump connected on the upper and scrubbing column tower. The closed cycle (65, 67, 79, 81, 91, 93, 95, 101, 103, 105, 107, 113, 117, 167, 169, 171, 175, 177, 179, 183, 185, 189, 190, 194,201,203) is at least partially subjected claim 10 or 11 apparatus according energy used to liquefy the CH _4. The apparatus of any one of claims stripping column (13) from claim 10 with a 12 for cleaning the lower liquid upstream scrubbing column (5) of the CO / CH ₄ separation column (33).

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