DE3032799A1 - Gas mixt. contg. hydrogen and nitrogen for ammonia synthesis - where hydrogen is purified in adsorbers which are desorbed by nitrogen, and some nitrogen is left in adsorbers - Google Patents

Abstract

A first gas mixt. contg. hydrogen and adsorbable impurities is fed through at least one adsorption bed to remove the impurities and obtain a gas rich in H2, which is fed through a second bed at a lower pressure. Nitrogen gas is then fed in the reverse direction through the first bed to remove the impurities by desorption. Some N2 is intentionally left in the first bed, and is compressed together with more gas. After further adsorption of the impurities, a prod. gas mixt. of H2 and N2 is obtd. The pref. plant uses a row of adsorber beds and alternating gas pressures; and the N2 required is pref. obtd. by the cryogenic treatment of air. The O2 obtd. from the air is pref. used in mfg. gas. Increased yield of H2, and lower energy consumption is provided.

Description

Method and device for producing

Ammonia synthesis gas mixtures The invention relates to a method and a device for forming a gas mixture containing hydrogen and nitrogen for ammonia synthesis, in which a hydrogen and adsorbable impurities containing feed gas mixture decomposed by an adiabatic pressure swing adsorption will.

In the formation of gas mixtures containing hydrogen and nitrogen for the ammonia synthesis, the one that is a component of the synthesis gas mixture can be used Hydrogen can be generated in various ways, for example by steam reforming from natural gas or naphtha, through partial oxidation of hydrocarbons or through Coal gasification. Regardless of the type of hydrogen production used in the individual case, the resulting hydrogen-containing stream typically contains a number of impurities, such as carbon dioxide, carbon monoxide, methane, and water. The hydrogen-rich gas mixture the As a result, the hydrogen production stage is usually further treatment stages subjected, for example, to a carbon monoxide shift conversion for elimination the carbon monoxide content of the mixture, a carbon dioxide removal by selective Adsorption of carbon dioxide from the gas mixture by means of an appropriate liquid solvent in a washing column, and a final cleaning of the Gas mixture through selective adsorption to remove residual impurities and for the delivery of a hydrogen gas of high purity. After that, the hydrogen gas can high purity with compressed nitrogen from an external source mixed to form the ammonia synthesis gas mixture, the hydrogen and nitrogen in the desired proportions, for example a stoichiometric one 3: 1 molar ratio of hydrogen to nitrogen.

In the last cleaning stage of the process explained above, in which residual impurities from the hydrogen-containing gas stream through Selective adsorption can be eliminated conveniently with adiabatic pressure swing adsorption processes as known from US Pat. No. 3,430,418 or US Pat. No. 3,986,849 are. In one of these processes (US Pat. No. 3,430,418), four adsorber beds are used niit7t; it can produce a hydrogen product gas with a purity of 99.9999, the has no detectable amounts of the above impurities, at yields in the order of 75 to 80% can be recovered. The other known one Process (US-PS 3,986,849) at least seven adsorber beds are used, at least two of which each receive feed gas during the process cycle.

The work cycle includes at least three pressure equalization phases. It can produce a hydrogen product gas with a purity of 99.9999% with a hydrogen yield on the order of 85 to 90% can be obtained.

Although with the help of the above-mentioned adiabdic pressure swing adsorption processes a hydrogen product of.

extremely high purity is achieved, a considerable amount goes of the hydrogen in the feed gas mixture supplied to the pressure change process is contained in the exhaust gas, i.e. the countercurrent pressure reducing gas and purge gas, lost, which is discharged from the process. Another disadvantage of the known Pressure swing adsorption processes exist in such ammonia synthesis gas applications in that relatively large amounts of adsorbent in the adsorber beds of the adsorption system required are.

Within the overall process of ammonia synthesis gas production under Use of the process steps discussed above to generate a hydrogen gas stream high purity as the starting component of the synthesis gas mixture the nitrogen gas comes to the delivery with the hydrogen gas of high purity of the final synthesis gas mixture is brought together, typically by one external source, for example a cryogenic or pressure swing adsorption air separation plant, Evaporation systems for liquid nitrogen and nitrogen gas pipelines, with relative low pressures on the order of, for example, 69 to 690 kPa.

Because the necessary pressure of the synthesis gas mixture is usually over 2760 kPa, a considerable amount of compression energy must be used, in order to compress the low-pressure nitrogen to the high pressure values required for the Formation of the product gas mixture are necessary.

The invention is therefore based on the object of an improved method and an improved apparatus for forming a hydrogen and nitrogen containing one To create gas mixture for ammonia synthesis. The method and the device according to the invention should be characterized by a higher percentage hydrogen yield excel in the final cleaning pressure swing adsorption stage than they are known from Processes is achieved. The pressure swing adsorption phase should have less adsorbent than known adsorption devices. The effort of external compression for compressing Low pressure nitrogen gas to the final product pressure should be significantly reduced compared to known processes.

The invention relates to a method and a device for Formation of a gas mixture containing hydrogen and nitrogen for ammonia synthesis, in which a feed gas mixture containing hydrogen and adsorbable impurities by selective adsorption of the impurities in at least one adsorber bed is dismantled according to the work cycle mentioned below.

According to the conventional work cycle of selective adsorption a feed gas mixture is cycled to the inlet end of the bed with a first highest overpressure supplied, while non-adsorbed, hydrogen-rich gas is discharged from the exit end of the bed. Initial void volume gas (i.e. gas trapped in the spaces between the adsorber beds) is released at the outlet end released of the bed; the gas released in this way becomes the outlet end of a others previously cleaned of the impurities and initially on lower ones Bed under pressure until there is a pressure equalization between the two Beds set to a higher intermediate pressure. Additional gas is supplied by the bed to reduce the pressure on one lowest pressure released, and purge gas is fed to the exit end of the bed to remove contaminants desorb and rinse through the inlet end of the bed. The rinsed The bed is repressed to the first highest overpressure, whereupon the work cycle is repeated.

The method according to the invention is characterized in that (a) the adsorber bed during the flushing phase with nitrogen gas coming from an external source it is purged in such a way that nitrogen gas remains in the bed after the purge phase is complete, in the subsequent re-pressing phase of the flushed bed to the first highest Overpressure compressed and then in the non-adsorbed hydrogen-rich Gas is discharged, the discharged gas being the hydrogen and nitrogen-containing Forms gas mixture, and / or (b) the adsorber bed during the repressurization phase is re-pressurized with nitrogen gas coming from an external source in such a way that that the introduced nitrogen gas is compressed to the first highest overpressure and then discharged in the non-adsorbed hydrogen-rich gas, wherein the discharged gas forms the gas mixture containing hydrogen and nitrogen.

According to a preferred embodiment of the invention worked with at least six adsorber beds during the selective adsorption cycle is carried out similarly to the procedure known from US Pat. No. 3,986,849, as explained in more detail below.

According to the invention, therefore, nitrogen is introduced into the through selective adsorption produced, nichtadsorbierfe, hydrogen-rich gas introduced by a Nitrogen gas coming from an external source as a flushing agent and / or as a repressurizing agent is used. This makes it possible to meet the requirements of the system for external compression energy compared to known systems significantly heabhaben, in which the entire nitrogen gas coming from an external source is externally compressed, i.e. outside the adsorber beds is compressed before this gas with the hydrogen-rich Product gas of the adsorber beds is mixed to the product synthesis gas mixture form. In that, according to the present invention, from an external Source-derived nitrogen gas is used to purge and / or purge the adsorber beds to push back at least partially, an internal compression takes place this Gas within the bed so that the gas after the bed has been purged and fully repressed is, along with the non-adsorbed hydrogen-rich gas with the high product pressure is carried out. This increases the need for external compression energy for the nitrogen purge gas and / or nitrogen repressurization gas coming from the external source substantially reduced or even made to zero.

As a result, the one used in the present proceedings is Coming from an external source nitrogen gas expediently to a gas that with low pressure is delivered, that is, a pressure lower than the first highest overpressure of the process and for example in the order of magnitude of 69 to 690 kPa if the nitrogen gas, for example, from an air separation plant, a pipeline or evaporation plant for liquid nitrogen.

In order for a beneficial balance between the economy The operation and efficiency of the process is preferred the ratio between the pressure of the discharged hydrogen-rich gas and the pressure of the nitrogen gas coming from an external source between 3 and 30th

If the hydrogen- and nitrogen-containing gas mixture has a molar ratio of hydrogen to nitrogen of greater than 3 and it is necessary or desirable to use an ammonia synthesis reactor a synthesis gas mixture with a 3: 1 stoichimetric molar ratio of hydrogen to feed nitrogen is expedient from an external source incoming nitrogen gas externally to the pressure of the non-adsorbed, hydrogen and compressed nitrogen-containing gas that is discharged from the adsorption process is, and mixed with the latter to form a product synthesis gas mixture which has a hydrogen to nitrogen molar ratio of about 3.

If the method according to the invention is carried out in such a way, that nitrogen gas coming from an external source is divided into two parts, of which the first part is used as purging gas for the purging phase, during the second part compressed externally and then with the discharged hydrogen-rich Gas of the selective adsorption process with the formation of a synthesis gas mixture is mixed, which has a molar ratio of hydrogen to nitrogen of about 3, is the molar ratio between that introduced into the adsorber bed during the flushing phase all of the first part of the nitrogen gas and all of the second part of the low-pressure nitrogen gas, which is discharged from the bed mixed with the hydrogen-rich gas, preferably over 0.6, in terms of a highly efficient and economical operation the utilization of the nitrogen gas coming from an external source and the with it the associated need for external compression.

Under a nitrogen gas coming from an external source In the present case, nitrogen gas is understood from a source other than that of the selective Adsorption system supplied feed gas mixture comes. With the external source for For example, nitrogen gas can be a cryogenic or pressure swing adsorption air separation plant, a nitrogen gas pipeline or a cryogenic liquid evaporation facility Act nitrogen.

The invention is illustrated below with reference to preferred exemplary embodiments explained in more detail. In the accompanying drawings: FIG. 1 shows a simplified one Flow diagram of a for carrying out the cleaning of hydrogen-containing gas in A system suitable for the process according to the invention with ten adsorber beds, 2 shows a time program for the various phases of a selective adsorption cycle, which according to the method according to the invention in the 10-bed facility according to Fig. 1 expires, 3 shows a simplified flow diagram of an implementation the process according to the invention suitable adsorption system with four adsorber beds, 4 shows a time program for the various phases of a modified embodiment of the adsorption process according to the invention, which is, for example, when applying of the device according to FIG. 3, and FIG. 5 shows a time program of a further embodiment of the selective adsorption process according to the invention, which deals with the plant according to Fig. 1 can be carried out.

The system of Fig. 1 has ten adsorber beds 1 to 10, the Via inlet valves 11 to 20 and product valves 21 to 30 in parallel between one Feed gas line F and a product gas line E are connected. The selective one Adsorption system according to FIG. 1 is constructed so that an adiabatic pressure swing adsorption carried out essentially in accordance with the process known from US Pat. No. 3,986,849 but using nitrogen gas from an external source to flush the various adsorber beds in the pressure swing adsorption zone. In the known method according to U.S. Patent 3,986,849 are at least seven adsorber beds are used, with each adsorber bed being used during the adsorption cycle experiences a pressure reduction in at least three pressure equalization stages and where to Take up at least two adsorber beds of gas mixture at every point in time during the cycle. The application of such a procedure modified by the use of an external source of nitrogen gas for purging and / or repressurization the adsorber beds is preferred here because it is possible in this way, to achieve high levels of product gas purity and because such a process management is particularly suitable for feed gas mixtures in which hydrogen is the main component represents poorly adsorbed impurities such as methane and carbon monoxide, contains, as is the case in the production of ammonia synthesis gas mixtures is.

In the system according to Fig. 1, the line 4EQ is for the fourth (lowest) Provide pressure compensation stage with valves 70 to 79. The exhaust pipe W are exhaust valves 41 to 50 assigned. The line M for the first (highest) pressure equalization repressurization stage is equipped with valves 51 to 60 for the first and third equalization stages. Gas flow control valves 81 and 82 are located in the lines that make up the pressure equalization / repressurization line Connect M and the product gas line E. When the valve 81 is closed and the Valve 82 is open the first pressure equalization phase with even-numbered Beds carried out while at the same time the third pressure equalization phase between two odd-numbered beds expires. Conversely, when valve 81 is open and the valve 82 is closed, the first pressure equalization takes place between odd numbered beds, while the third pressure equalization phase runs concurrently between beds with even numbers.

A common manifold for the second (middle) pressure equalization stage is not scheduled. Instead, there are individual lines that form the exit ends connect the adsorber beds with each other. So there is a line with a Valve 61 between beds 2 and 7. A line with a valve 62 connects the beds 4 and 9. The beds 1 and 6 are via a line with a valve 63 tied together. A line in which a valve 64 is seated connects beds 3 and 4 8. The beds 5 and 10 are in communication with a valve 65 via a line.

To make the assignment between beds 1 to 10 and valves 11 to 60 and 70 to 79 easy to make, the valves are assigned reference numerals, the final number of which corresponds to the reference number of the adsorber bed, which by means of the relevant valves is controlled directly.

For example, the operation is controlled directly of Bed 3 via valves 13, 23, 33, 43, 53 and 73. There is only one exception with regard to the assignment of the valves that make the bed 10 work immediately influence. These are valves 20, 30, 40, 50, 60 and 70.

Fig. 2 shows a preferred cycle program for the system according to Fig. 1 for carrying out a selective adsorption according to a first embodiment. The order of the phases of the work cycle and their names in the program are the following: adsorption (A), first pressure equalization-pressure reduction phase (E1D), second pressure equalization pressure reduction phase (E2D), third pressure equalization pressure reduction phase (E3D), fourth pressure equalization pressure reduction phase (E4D), countercurrent pressure reduction phase (BD), countercurrent purging phase with externally supplied low-pressure nitrogen purging gas (P), fourth pressure equalization reprint phase (E4R), third pressure equalization reprint phase (E3R), second pressure equalization repressure phase (E2R), first pressure equalization repressure phase (EIR) and finally repressing the feed gas pressure by introducing Product gas at the product outlet end (FR).

It should be noted that at every point in time within the work cycle three adsorber beds take up feed gas mixture and non-adsorbed product gas with the operational pressure hand over. For example, in the seventh Time unit a processing of the feed gas mixture in each of the adsorbers 2, 3 and 4.

In operation of the system according to FIG. 1, each of the adsorber beds passes through 1 to 10 the following sequence of work steps: Adsorption, with which feed gas mixture is fed to the inlet end of the bed with a first highest overpressure, while from the exit end of the bed, non-adsorbed, hydrogen-rich gas (Including residual nitrogen gas in the bed at the end of the previous carried out purging phase with nitrogen gas coming from an external source remains) is carried out; Release of initial void volume gas at the exit end of the bed and introducing the thus released initial gas into the outlet end one previously freed from the adsorbable impurities by rinsing and first another adsorber bed at a lower pressure until the pressure is equalized has set to a higher intermediate pressure between the two beds, whereby in the case of this system, the release of initial gap volume gos and the Pressure equalization can be carried out in four separate phases, namely a first Pressure equalization of the adsorber bed that has completed its adsorption phase, with another previously flushed and at least four higher numbered bed, the themselves is initially at intermediate pressure, so that the two beds eventually one reach the first equilibrium pressure, a second pressure equalization of the initial one adsorber bed lying on the first equilibrium pressure with another, previously flushed, at least five-higher numbered bed, which is initially on lower intermediate pressure is, so that the two beds eventually a second Assume equilibrium pressure, a third pressure equalization of the initially on the second equilibrium pressure lying adsorber bed with another previously flushed and at least sixth higher numbered bed, initially on an even lower Intermediate pressure is so that the two beds finally have a third equilibrium pressure reach, and a fourth equalization of the pressure initially on the third Equilibrium pressure located adsorber bed with another previously flushed and at least the seventh higher numbered bed, initially at a lowest pressure so that the two beds finally assume a fourth equilibrium pressure; Release of additional gas from the bed to reduce the pressure to lower levels Pressure (countercurrent blowdown); Introducing low pressure nitrogen purge gas from an external source into the exit end of the bed for contaminant desorption and flushing through the entry end of the bed; and pressing the purged Bed at first highest overpressure in four consecutive Pressure equalization repressurization phases and a final product repressurization phase, whereupon the work cycle is repeated.

Compared to the known method of producing ammonia synthesis gas using the selective adsorption process of US Pat. No. 3,986,849 it is the present process to achieve a significantly higher hydrogen yield, while the cost of compressing external nitrogen is reduced and can be operated with a reduced amount of adsorbent. It is Surprisingly, that the presently explained purging of the adsorber beds with one external source of incoming nitrogen gas the hydrogen yield in which the adsorption system leaving product gas increased compared to the known processes in which a Internal purging takes place by adding a gas depleted in impurities to the purging Bed is fed from another bed. Due to general requirements on the contrary, one would expect the hydrogen yield to be that with a flushing can be achieved with the aid of nitrogen gas from an external source can, compared to known methods, is significantly lower. This is upon it attributed to that in an adsorber bed that completed the adsorption phase has a significant amount of unadsorbed Hydrogen in the adsorber bed interstices is included. This hydrogen-containing gap volume gos can expediently be used for other adsorber beds of the plant in the course to repress one or more pressure equalization phases. However, after the the last pressure equalization is completed, there is still a considerable amount left of hydrogen in the adsorber bed. In known systems, this is in the adsorber bed used hydrogen-containing gas to flush another bed. in the In contrast, in this embodiment of the adsorption process according to the Invention of the hydrogen in the adsorber bed after the last pressure equalization phase remains during the subsequent countercurrent pressure reduction (blow-off) and rinsing phases removed from bed and not recovered. At the end of the rinsing phase with von nitrogen gas coming from an external source is therefore located essentially no hydrogen in the adsorbent bed. As a result one would assume that in this embodiment of the process according to the invention, the hydrogen yield is much lower than in the known process. However, it was surprising found that the values of hydrogen yield that are obtained in this embodiment of the method according to the invention are actually higher than those the known method in which an internal flush is carried out, i.

purging with gas coming from another adsorber bed.

According to a preferred embodiment for which the clock program shows an example according to Fig. 2, at least nine adsorber beds are provided, the overlapping, identical work cycles are operated in such a way, that during the initial part of the bed's adsorption phase the two immediately previous, lower numbered beds also go through the adsorption phase. These are immediately in the middle of the bed's adsorption phase previous, lower numbered and the immediately following, higher numbered Bed in the adsorption phase. During the last part of the adsorption phase of the The bed also goes through the two immediately following, higher-numbered beds their adsorption phase. For example, in the case of the clock sequence according to FIG the adsorption phase of the bed 1 six time units, the units 1 and 2 the initial period and units 5 and 6 the final period of the adsorption phase represent. During the initial period, the adsorption phase also takes place in the beds 9 and 10 (the two beds immediately preceding bed 1). During the middle part pass through the immediately preceding bed 10 and that immediately following bed 2 the adsorption phase. During the end period are also the Beds 2 and 3 (the two immediately following beds with higher numbers) for adsorption switched.

According to a further preferred embodiment for which the Clock program according to FIG. 2 also represents an example, the release takes place of initial void volume gas and the associated pressure equalization in at least three separate phases. First, a pressure equalization of an adsorber bed, that has completed its adsorption phase, with the fourth higher numbered adsorber bed carried out, which is initially at a second equilibrium pressure, until finally both beds are at a first equilibrium pressure. The same adsorber bed in which a pressure reduction to the first equilibrium pressure has taken place, now becomes a second pressure equalization with the fifth higher numbered one Brought adsorber bed, which is initially at the third equilibrium pressure, until the two beds finally assume the second equilibrium pressure. That same adsorber bed, the pressure of which is lowered to the second equilibrium pressure is then with the process pressure initially at the lowest, sixth higher numbered adsorber bed brought to a third pressure equalization until a pressure equalization between these two beds to the third equilibrium pressure has set. That on the third equilibrium pressure relaxed The adsorber bed is then further reduced in pressure either by blowing it off in countercurrent or by a further pressure equalization / pressure reduction stage and countercurrent blow-off, until the lowest process pressure is reached at the end of the countercurrent blow-off phase. After the completion of the countercurrent blowdown phase, in which the bed finally through Releasing gas at the entry end of the bed is relaxed, the bed is too purged from an external source of low pressure nitrogen gas. In connection on it the bed is in successive pressure-equalizing re-cover trousers and a final repress phase, which is the highest among the first Excess pressure product gas is introduced into the bed, pressurized again, before the work cycle is repeated.

If one uses FIG. 2 to look at the relationships between the bed, in which initial void volume gas is released and clears to the other beds, which are brought to pressure equalization (by pressing again), so is closed recognize that the first phase is the release of initial void volume gas through bed 1 (E1D) expires during unit time 7 and with bed 5, the is called the fourth higher numbered adsorption bed, during its highest pressure equalization and repressurization phase (E1R) takes place. The second phase (E2D) of the initial gap volume gas release through bed 1 falls within time unit 8; she will be with the bed 6, the fifth higher numbered adsorber bed, during its second pressure equalization repressurization phase (E2R) carried out. The third phase (E3D) of the initial void volume gas release runs through the bed 1 during the time unit 9 in connection with the bed 7, the sixth higher numbered adsorber bed, during its pressure equalization repressurization phase (E3R). The fourth phase (E4D) of the release of initial void volume gas through bed 1 falls into time unit 10; it takes place with bed 8, the seventh higher numbered adsorber bed, during its lowest pressure equalization reprint phase (E4R). The final countercurrent pressure reduction (BD) takes place during the unit of time 11 instead. This is followed by flushing (P) of bed 1 from an external one Source of incoming low pressure nitrogen gas during time units 12-15.

If, in the relationship defined above, the one calculated in this way higher bed number the actual number of adsorber beds in one exceeds the specified system, the existing number of beds must differ from the calculated Number are subtracted in order to obtain the respective "higher numbered adsorber bed" For example, consider the third pressure equalization phase of the bed 6, which takes place during the time unit 19 with the sixth higher numbered adsorber bed. Since the Embodiment according to FIGS. 1 and 2 ten adsorber beds are present, the bed intended for phase E3R is bed 12-10; H. the bed 2.

Fig. 3 shows a further embodiment of an implementation of the present process suitable adsorption system, which is similar to that from US-PS 3,430,418 known plant is constructed. There are four adsorber beds 1, 2, 3 and 4 are present, the flow in parallel between a feed gas line 410 and a product gas line 411 are connected. Via automatic valves 11, 12, 13 and 14 become the feed gas mixture to bed 1, bed 2, bed 3 and bed 4, respectively fed. The automatic valves 21, 22, 23 and 24 direct product gas therefrom Beds in product gas line 411.

The adsorbed impurities that are in the counterflow pressure reducing and rinsing phases are eliminated, leave the system via an exhaust pipe 412; with the inlet ends of the adsorber beds via the valves 41, 42, 43 and 44 is connected. For pressure equalization via a line 423 and for the final Re-pressurization with non-adsorbed product gas via lines 427 and 428 the valves 51, 52, 53 and 54 are used. The flow rate of the gas for the The final repressurization phase is carried out by means of an in line 427 Valve 60 'regulated.

In the purging phase, nitrogen purging gas coming from an external source is used fed via line 421 and valves 31, 32, 33 and 34, while outgoing Purge gas from the adsorber beds via valves 41, 42, 43 and 44 to the exhaust line 412 is carried out. Gas coming from the blow-off (pressure reducing) phase escapes Via valves 61, 62, 63 and 64 into line 413.

The blow-off gas coming from line 413 can be compressed again and be returned; it can also be partially or fully in the outgoing Purge gas flow are introduced.

After the flushing phase of the adsorber bed running at the lowest pressure 2 has ended, the valve 31 closes; the pressure equalizing valves 51 and 53 become opened.

Either at the same time as or after the pressure equalization has been achieved becomes part of the product gas coming from the adsorber bed 3 in the product gas line 411 via line 427, valve 60 ', line 423 and valve 51 to The outlet end of the adsorber 1 is diverted.

This product gas flow continues until the adsorber bed 1 to about the product pressure is reapplied. The inlet valve 11 and the product valve 21 are closed during re-opening. That lets you push again themselves instead also carry out the feed gas mixture as repressurization gas is used, for example, during the last part of the repressing phase, to bring the adsorber bed to the first, highest overpressure.

FIG. 4 shows a clock program for the device according to FIG. 3. How As can be seen from the cycle program, each of the four adsorber beds runs through the system 3 successively the phases of adsorption, a pressure equalization with a another bed, a countercurrent pressure reduction, a flush with an external one Source of incoming low pressure nitrogen gas, repressurization through pressure equalization with a depressurized bed of the system and a final one Repressurization with product gas, whereupon the work cycle is repeated. The 4-bed facility 3 and 4 is particularly suitable for systems by means of which in comparison to the polybed systems of FIGS. 1 and 2, smaller volumes of ammonia synthesis gas should be produced.

Fig. 5 shows a clock program for a selective adsorption accordingly a further embodiment of the present method. The clock program according to FIG. 5 can be used in a 10-bed system according to FIG. The work cycle according to FIG. 5 differs from that of Fig. 2 in that that immediately following the adsorption phase and before the pressure equalization-pressure reduction phases a co-current purging phase is provided. During this cocurrent purging phase an externally supplied flushing fluid is fed to the bed at the inlet end, while product gas continues to be withdrawn from the exit end of the bed. For this purpose becomes the cocurrent purging medium with the first highest overpressure of the feed gas delivered so that that discharged from the adsorber bed during the cocurrent purging phase Gas has the same pressure as the product gas that during the preceding adsorption phase gets out of bed. The task of the cocurrent purging phase is that of the adsorber bed to displace remaining hydrogen void volume gas into the product gas line.

The for the cocurrent purging phase of the procedure according to FIG. 5 externally supplied flushing fluid used can be nitrogen gas or another Gas, for example methane or natural gas. Which special flushing fluid for the Choosing a concurrent flush phase depends on several factors, below Among other things, the required amount of purging gas, the quality of the pressure swing adsorption system resulting exhaust gas and the quality of the feed gas mixture that the pressure swing adsorption system is forwarded. The quality of the pressure swing adsorption system Exhaust gas is important when the exhaust gas, that is, in countercurrent Desorbate gas blown off and flushed out, used as fuel within the system shall be. The adsorbable components of the pressure swing adsorption system A gas mixture decomposed for ammonia synthesis can use carbon monoxide and methane include, so that the exhaust gas of the pressure swing adsorption system has a moderate calorific value and can conveniently be used as fuel gas.

When the calorific value of the exhaust gas from the adsorption system becomes substantial Factor, it may be appropriate to use a fluid such as natural gas as the cocurrent purging medium to use. In this context, the quality of the Adsorpti-onsanloge incoming feed gas mixture important, namely if the feed gas mixture is large Contains amounts of carbon dioxide, the use of the exhaust gas as fuel gas is impaired or made impossible if nitrogen were used as the cocurrent purging medium.

This is due to the fact that the cocurrent purge gas ended up the co-current pressure reduction pressure equalization phases a large part of the adsorber bed interstices occupies, so that cocurrent purge gas along with the desorbate impurities in is withdrawn from the exhaust gas. Therefore, when the suitability of the exhaust gas as a fuel gas is of importance a flushing fluid such as natural gas is preferably used.

In the working cycle of FIG. 5, the adsorption phase is between and the subsequent pressure equalization phases pushed the concurrent purging phase. Each As a result, adsorber bed goes through the following phases in sequence: adsorption, Direct current purging, three successive pressure equalization / pressure reduction phases, Countercurrent blowdown to the lowest process pressure, flushing with from an external one Source of incoming low-pressure nitrogen gas, three successive pressure equalization-repressurization phases and final repressurization using unadsorbed, hydrogen-rich Product gas. In this working cycle, as in the working cycle according to Fig. 2 feed gas mixture simultaneously three during each point in time of the work cycle Beds fed to the adsorption system.

It was found that when in certain embodiments the bed is expanded by gas from the adsorber bed at a point between the inlet and the discharge end of the bed lying position is discharged, the following Advantages are achieved: (a) The outlet end part of the adsorber bed is countercurrent relaxes, which contributes to a low concentration of purity at the exit end of the bed maintain; (b) the inlet end region of the adsorber bed is in cocurrent relaxes, which helps keep a maximum amount of hydrogen from the inlet end to displace the adsorber bed; (c) a significant part of the in to the Gap volume gas of the carbon monoxide present in the adsorber bed can be combined recover with hydrogen in the sidestream depressurization gas. Because the one significant proportion of carbon monoxide-containing secondary flow pressure reducing gas to can be fed back to the carbon monoxide shift converter of the system, where if more hydrogen can be formed from the returned carbon monoxide, it is in this way possible the hydrogen yield compared to a process to improve, in which the pressure reduction of the entire adsorber bed to the lowest Pressure is done by countercurrent blow-off. It also reduces the amounts of carbon dioxide and methane in the sidestream depressurization gas versus the counterflow depressurization gas of the adsorber bed considerably reduced. The bypass pressure reduction of the adsorber bed The lowest pressure is therefore preferable to the load on the compressor for returned gas and the carbon monoxide shift converter versus one Lower the process in which gas blown off in countercurrent is compressed and used as recycle gas is passed back to the shift converter.

Example I This example is based on a method of generating an ammonia synthesis gas mixture of hydrogen and nitrogen according to the State of the art, whereby the Feed gas mixture a pressure swing adsorption learns to separate carbon monoxide, carbon dioxide and methane and to form the Ammonia synthesis gas mixture to win a hydrogen-rich gas. The selective one Adsorption takes place by means of a 10-bed adsorption system from FIG. 1 of the US-PS 3 986 849 known type. The system is according to the clock program of Fig. 2 of US Pat. No. 3,986,849, the adsorber bed after the adsorption phase three successive pressure equalization / pressure reduction phases immediately before one Purge gas supply phase passes through, during the hydrogen-containing gas of released at the exit end of the bed and used to flush another adsorber bed is used at the lowest process pressure. Following the purge gas supply phase the adsorber bed is depressurized in countercurrent to the lowest process pressure and in turn with hydrogen-containing gas from another bed of the adsorption unit purged, which goes through the purge gas supply phase.

After purging the adsorber bed in three consecutive Pressure equalization re-pressurization phases, followed by a final Repressing with product gas follows. The whole thing is done by an external Source coming low pressure nitrogen gas to the synthesis gas pressure value of 3400 kPa compressed before it is mixed with the hydrogen-rich gas, dos as product gas the pressure swing adsorption system accrues. The operating conditions and the performance characteristics are summarized in Table I below.

TABLE I Operating conditions and performance characteristics of a process using a 10-bed pressure swing adsorption system in accordance with US Pat. No. 3,986,849 Parameter feed gas mixture 1 2 Flow rate of the feed gas mixture of the pressure swing adsorption system, kg mol / h 5910 4520 flow rate of the missing pressure swing adsorption, hydrogen-rich product gas, kg mol / h 3690 4520 Composition of the hydrogen-rich Pressure swing adsorption system product gas: hydrogen (mol%) 99.9 99.9 nitrogen (Mol%) 0.1 0.1 flow rate of the added to form the synthesis gas mixture Nitrogen gas, kg mol / h 1230 1230 TABLE 1 (continued) Parameters Feed gas mixture 1 2 Flow rate of the synthesis gas mixture, kg mol / h 4920 4920 Adsorbent volume per bed, arbitrary units 100 65 Number of adsorber beds the pressure swing adsorption system 10 10 hydrogen yield from the pressure swing adsorption system fed feed gas mixture, expressed as a percentage of the discharged Hydrogen content of the feed gas mixture contained in the product gas stream,% 87.9 88.7 Expenditure of compression energy for that added to form the synthesis gas mixture Nitrogen gas, arbitrary units 100 100 Those tabulated above In the examples below, data serve as the basis for a comparison of various Embodiments of the present method using the known procedure.

Example II This example is based on a method of manufacture an ammonia synthesis gas mixture of hydrogen and nitrogen according to Embodiment of Figures 1 and 2. Compared to Example I is in the selective Adsorption no internal purge gas supply phase provided. Instead, will in the form of a first portion of low pressure nitrogen gas from an external source a cryogenic air separation unit is used as the purge gas, while a second Part of the low pressure nitrogen gas supplied from the external source external compressed and then with the discharged, hydrogen-rich product gas of the selective Adsorption system is mixed to produce the end product in the form of the synthesis gas mixture to build. Because of the omission of the purge gas supply phase, in this case work with a further, fourth pressure equalization phase, while the the same number of adsorber beds as in Example I is provided. Alternatively the omission of the internal purge gas supply phase allows the total number the adsorber of the adsorption plant diminish if with the same number of Pressure equalization phases as in Comparative Example I is carried out. The second alternative the reduction of the total number of adsorbers while maintaining the number of pressure equalization phases the known procedure will be discussed in a later example discussed in more detail.

The operating conditions and performance characteristics of the ammonia synthesis gas manufacturing process using a 10-bed pressure swing adsorption system according to FIGS. 1 and 2 are compiled in Table II below.

TABLE II Operating conditions and performance characteristics of the ammonium synthesis gas production process using the 10 bed pressure swing adsorption system of FIGS. 1 and 2 parameters Feed gas mixture 1 2 Flow rate of the feed gas mixture of the pressure swing adsorption system, kg mol / h 5630 4380 flow rate of the pressure swing adsorption system, hydrogen-rich product gas, kg mol / h 4165 4110 Composition of the hydrogen-rich Pressure swing adsorption system product gas: hydrogen (mol%) 88.6 89.8 nitrogen (Mol%) 11.4 10.2 TABLE II (continued) Parameters of the feed gas mixture 1 2 Flow rate of the externally compressed to form the synthesis gas mixture added nitrogen gas, kg mol / h 755 810 flow rate of the synthesis gas mixture, kg mol / h 4920 4920 volume of adsorbent per bed, arbitrary units 75 41 Number of adsorber beds in the pressure swing adsorption system 10> 10 hydrogen yield from the feed gas mixture fed to the pressure swing adsorption system as a percentage of the hydrogen content contained in the discharged product gas stream of the feed gas mixture,% 92.2 91.6 Compression energy expenditure for the Formation of the synthesis gas mixture, added nitrogen gas (external compression), arbitrary units 60 65 Comparing the table data for this example with those of Table I of Example I shows that the present process leads to a significantly higher hydrogen yield. at the feed gas mixture of column 1 is a hydrogen yield with the present process of 92.2% compared to a yield of only 87.9% of the known method of Example I scored.

Another comparison of the values in column 1 of Tables I and II shows that in Example II the adsorbent volume required per bed is only 75% of that of the known method according to Example I.

Furthermore, in this embodiment of the present Process the external compression energy that must be expended to the Formation of the synthesis gas mixture to compress added nitrogen gas, opposite the energy consumption of the known method for the feed gas mixture of the column 1 reduced by 40% and for the feed gas mixture in column 2 by 35%.

Example III This example uses a 10 bed adsorption rig used, with the pressure swing adsorption system as part of the ammonia synthesis gas production is operated according to FIG. In this embodiment is immediately after the adsorption phase provided a cocurrent purging phase, which is the same Pressure like that Adsorption phase expires in the adsorber bed existing hydrogen void volume gas in the product gas line of the pressure swing adsorption system to drift. As stated above, various co-current flushing media, for example Nitrogen or natural gas, with the choice of several considerations depends, for example, on the amount of flushing gas required and the quality of the feed gas mixture and the exhaust gas of the pressure swing adsorption system with a view to delivery an exhaust gas that has a sufficiently high calorific value to be within the system to be used as fuel gas. The operating conditions and the performance parameters for a 10-bed adsorption system which operates with the operating cycle according to FIG. 5 and when using natural gas at a pressure of 3450 kPa as the co-current purge fluid are listed in column 1 of Table IV below, where the feed gas mixture has the same composition as in the examples in the column 1 of Tables I and II. In column 2 of Table III are the corresponding Values for a 10-bed adsorption system operated according to FIG. 5 compiled, in which nitrogen gas coming from an external source is used as the flushing medium which is compressed to a co-current purge pressure of 3450 kPa. The feed gas mixture has the same composition as in the examples in column 2 of the tables I and II.

TABLE III Operating conditions and performance characteristics of a process for the production of ammonia synthesis gas using a 10-bed pressure swing adsorption system with the clock sequence according to FIG. 5 parameters feed gas mixture 1 2 flow rate of the Feed gas mixture of the pressure swing adsorption system, kg mol / h 5580 4280 flow rate of the hydrogen-rich product gas loading the pressure swing adsorption system, kg Mol / h 4160 4210 Composition of the hydrogen-rich product gas of the pressure swing adsorption system: Hydrogen (mole%) 88.7 88.1 nitrogen (mole%) 11.3 10.3 cocurrent pulse fluid natural gas to 3450 kPa with compressed 3450-kPa from an external source nitrogen gas Flow rate of the cocurrent purging gas, kg mol / h 350 350 TABEL III (continued) Parameter feed gas mixture 1 2 Flow rate of the for formation nitrogen gas added to the synthesis gas mixture, kg mol / h 760 710 flow rate of the synthesis gas mixture, kg mol / h 4920 4920 adsorbent volume per bed, arbitrary Units 73 40 Number of adsorber beds in the pressure swing adsorption system 10 10 Hydrogen yield from the feed gas mixture fed to the pressure swing adsorption system, expressed as a percentage of that contained in the discharged product gas stream Hydrogen content of the feed gas mixture,% 93.1 93.8 Compression energy consumption for the nitrogen gas added to form the synthesis gas mixture (external compression), arbitrary units 61 90 If the values in column 1 of the Table III based on a high pressure co-current purging with natural gas and subsequent Counter-current purging with nitrogen gas from an external source, compared with the corresponding values in column 1 of Table II of Example II where the only flushing phase at low pressure using one external source of nitrogen gas is carried out, it is found that the yield in the first case it is 0.9% higher than in the latter case, while all others Parameters are essentially the same. This is in the first case of the present For example, the quality (the calorific value) of the exhaust gas leaving the adsorption system significantly improved because natural gas is used as the flushing medium. When the values in column 2 of table III with the corresponding values in column 2 of the table II are compared, it can be seen that the hydrogen yield in the previous example to 93.8% compared to the yield of 91.6% for the embodiment accordingly Table II, column 2, is increased where no high pressure co-current purging is provided is.

The energy expenditure for the external compression of nitrogen gas is compared to the embodiment according to Table II, column 2, increased by 39%, which is due to the fact that in the embodiment of the present example nitrogen gas coming from an external source externally to the elevated pressure compressed by 3450 kPa must be used for direct current purging the adsorber beds is required. In contrast to this embodiment of the present Method, the known method according to Table I, column 2, has a hydrogen yield of only 88.7% with a compression energy expenditure for the nitrogen gas to be added which is 11 to 64% higher than that of the embodiment of the present example lies. It follows that the high pressure cocurrent purging phase of this example is too a substantial improvement in the yield over known processes with moderate to considerable savings in terms of the compression of the feed gas mixture leads, which is introduced into the pressure swing adsorption system.

Claims (21)

Claims 1. A method for forming a hydrogen and nitrogen-containing Gas mixture for ammonia synthesis, in which a hydrogen and adsorbable Feed gas mixture containing impurities through selective adsorption of the impurities is broken down in at least one adsorber bed in that the feed gas mixture is cycled fed to the inlet end of the bed with a first highest overpressure, non-adsorbed, hydrogen-rich gas discharged from the exit end of the bed, initial Void volume gas released at the exit end of the bed and the so released Gas at the outlet end of another previously cleaned of the impurities and is initially fed to the bed at a lower pressure until it is a pressure equalization between the two beds is set at a higher intermediate pressure also has additional gas from the bed to reduce the pressure to a lowest level Pressure is released and purge gas is supplied to the exit end of the bed to remove impurities to desorb and through the entry end of the bed to rinse, as well as that the flushed bed is reprinted at the first highest overpressure and then the working cycle is repeated, characterized in that (a) the Adsorber bed during the flushing phase with nitrogen gas coming from an external source it is purged in such a way that nitrogen gas remains in the bed after the purge phase is complete, in the subsequent reprint phase of the flushed bed to the first highest Overpressure compressed and then in the non-adsorbed hydrogen-rich Gas is discharged, the discharged gas being the hydrogen and nitrogen-containing Forms gas mixture, and / or (b) the adsorber bed during the repressurization phase is repressed with nitrogen gas coming from an external source in such a way that that the introduced nitrogen gas is compressed to the first highest overpressure and then discharged in the non-adsorbed hydrogen-rich gas, wherein the discharged gas forms the gas mixture containing hydrogen and nitrogen. 2. The method according to claim 1, characterized in that the rinsed Bed during the repressurization phase with the feed gas mixture or with discharged, non-adsorbed, hydrogen-rich gas will. 3. The method according to claim 1 or 2, characterized in that the hydrogen and nitrogen-containing gas mixture has a molar ratio of hydrogen has to nitrogen of about 3. 4. The method according to any one of the preceding claims, characterized in that that the coiled bed comes from an external source during the repressurization phase incoming nitrogen gas is partially re-injected to an intermediate pressure, which is between 0.10 and 0.30 times the first highest overpressure. 5. The method according to any one of the preceding claims, characterized in, that nitrogen gas coming from an external source is divided into two parts and a first part is used as purging gas for the purging phase, while a second Partly compressed externally and then with the discharged hydrogen-rich gas is mixed to form a synthesis gas mixture having a molar ratio of Has hydrogen to nitrogen of about 3. 6. The method according to any one of the preceding claims using of at least four adsorber beds, characterized in that to push the flushed bed back up to the first highest overpressure that flushed bed with another other bed that is currently in its adsorption phase has completed, is brought to the pressure equalization, at which the two beds finally accept a higher intermediate pressure, and then a final reprint takes place at the first highest overpressure with the feed gas mixture. 7. The method according to any one of the preceding claims, characterized in that that for the purpose of forming the feed gas mixture hydrocarbon and oxygen gas Partial oxidation of the hydrocarbon and formation of a hydrogen, carbon monoxide and partial oxidation product gas mixture containing carbon dioxide are reacted, at least a major portion of the carbon monoxide in the partial oxidation product gas mixture with water for the purpose of supplying hydrogen and carbon dioxide and forming a further reaction product gas mixture is catalytically converted, the hydrogen, Contains carbon dioxide and residual carbon monoxide, as well as that at least one larger one Part of the carbon dioxide contained in the further reaction product gas mixture through selective adsorption is separated with formation of the feed gas mixture, the hydrogen and adsorbable contaminants including residual carbon monoxide and contains carbon dioxide. 8. The method according to claim 7, characterized in that air in the Low-temperature separation process with the formation of oxygen gas for the catalytic Partial oxidation reaction phase and nitrogen gas is decomposed, with the nitrogen gas forms at least in part the nitrogen gas coming from an external source. 9. The method according to claim 5, characterized in that the molar ratio between the total of the first introduced into the adsorber bed during the flushing phase Part of the nitrogen gas and all of the second part of the low pressure nitrogen gas, that mixed with the hydrogen-rich gas from the bed during the adsorption phase is carried out is above 0.6. 10. The method according to any one of the preceding claims, characterized in, that the feed gas mixture is formed by steam reforming of hydrocarbons will. 11. The method according to any one of the preceding claims, characterized in, that at a first highest overpressure, from an external source incoming nitrogen gas to the inlet end of the adsorber bed after completion of the adsorption phase forwarded and thus non-adsorbed, hydrogen-rich gap volume gas displaced as well as from the exit end of the bed as a further part of the discharged hydrogen-rich gas is withdrawn. 12. The method according to any one of the preceding claims, characterized in, that with the release of additional gas for the purpose of reducing the pressure of the adsorber bed to the lowest pressure gas at one between the inlet and outlet ends of the bed and the pressure reducing gas discharged from the bed is returned and processed for the purpose of recovering its hydrogen content, this hydrogen being part of the hydrogen present in the feed gas mixture provides. 13. Device for performing the method according to one of the preceding Claims with at least one adsorber bed, the inlet end of which contains the hydrogen Feed gas mixture can be fed and purified hydrogen gas from its outlet end can be discharged, a device for discharging void volume gas via the outlet and / or the inlet end of the bed for the purpose of reducing the pressure of this bed, one Device for flushing the bed at reduced pressure for the purpose of removing from the feed gas mixture adsorbed impurities, and one Device for pushing the bed back up to the increased pressure, marked by a device (P, 31-40, 421) for acting on the bed (1-10) with from nitrogen gas coming from an external source for the purpose of purging and / or at least partial repressurization of the bed so that the product gas obtained as a gas mixture of purified hydrogen suitable for ammonia gas synthesis and nitrogen is produced. 14. The apparatus according to claim 13, characterized in that the Device (P, 31-40, 421) to act on the bed (1-10) with from an external Source coming nitrogen gas is controllable so that this gas for purging the Serves the bed. 15. Apparatus according to claim 13 or 14, characterized in that that the device (P, 31-40, 421) for acting on the bed (1-10) with from an external source coming nitrogen gas is controllable such that this gas serves to push the bed back open. 16. Device according to one of claims 13 to 15, characterized by a plurality of adsorber beds (1-10), each cyclically in sequence an adsorption phase at increased pressure, a desorption phase, one Rinse phase under reduced pressure and a repressurization phase under increased pressure run through and of which at least one is constantly exposed to the feed gas mixture is. 17. Device according to one of claims 13 to 16, characterized by at least four adsorber beds. 18. Device according to one of claims 13 to 1, characterized by at least six adsorber beds. 19. Device according to one of claims 13 to 18, characterized by a control device for introducing from an external source Nitrogen in the inlet end of the bed (1-10) after the adsorption phase has ended for the purpose of displacing non-adsorbed hydrogen-rich void volume gos and Discharge of this gas from the exit end of the bed. 20. Device according to one of claims 13 to 19, characterized by a device for discharging gas from the adsorber bed at an intermediate the entry and exit end of the bed and through a Device for returning this gas for the purpose of recovering its hydrogen content and providing some of the hydrogen of the feed gas mixture. 21. The device according to claim 19, characterized by at least four and preferably at least six adsorber beds and a control device, by means of which at least one bed is constantly exposed to the feed gas mixture is.