WO2019008741A1

WO2019008741A1 - Ammonia recovery method and recovery device

Info

Publication number: WO2019008741A1
Application number: PCT/JP2017/024951
Authority: WO
Inventors: 桃子加藤; 嘉之渡邉
Original assignee: 日揮株式会社
Priority date: 2017-07-07
Filing date: 2017-07-07
Publication date: 2019-01-10

Abstract

The present invention relates to an efficient ammonia recovery method and recovery device for industrially synthesizing ammonia using nitrogen gas and hydrogen as raw material. The ammonia recovery method is characterized in that nitrogen-containing gas is reacted with hydrogen, ammonia in the produced gas obtained thereby is cooled to a temperature of -10 to -20°C and primarily recovered, and ammonia unrecovered during the primary recovery is cooled to -80 to -130°C and secondarily recovered, so that 98 weight% or more of the ammonia in the produced gas is recovered. The ammonia recovery device comprises an ammonia synthesis reactor, an ammonia recovery device, and a separator for recovered ammonia, and is characterized by being configured from a primary cooler using ammonia as a coolant for cooling to a temperature of -10 to -20°C and a secondary cooler using adiabatic expansion or external cold for cooling to -80 to -130°C.

Description

Method and apparatus for recovering ammonia

TECHNICAL FIELD The present invention relates to an efficient ammonia recovery method and apparatus for industrially synthesizing ammonia from nitrogen gas and hydrogen as raw materials.

Ammonia is catalytically synthesized from hydrogen produced by the reforming reaction of natural gas and nitrogen in the air as raw materials. The synthesis of ammonia is largely governed by equilibrium, and the unreacted gas is recycled and supplied again to the ammonia synthesis reactor. An outline of such an existing ammonia synthesis process is shown in FIG.

In FIG. 3, the reaction gas containing ammonia synthesized in the ammonia synthesis reactor is cooled and separated, ammonia is recovered, and the separated unreacted raw material gas is recycled.

Since the raw material gas contains an inert component, the inert component may be concentrated in the ammonia synthesis loop by recycling. To prevent this, a purge gas line is provided, which is withdrawn from the synthesis loop along with the syngas and a small amount of ammonia. The synthesized ammonia is cooled and separated by cold heat from the ammonia chiller, and is decompressed by the expansion valve from the bottom of the separator provided in the synthesis loop and stored as liquid ammonia at normal pressure.

In the existing ammonia synthesis process, ammonia is used as a refrigerant in the cooling separation unit, and 30 to 40% (dimensionless) of the energy input to the ammonia synthesis unit is used for the cooling liquefaction separation of ammonia.

The ammonia synthesized in the ammonia synthesis reactor and the unreacted source gas are separated by an ammonia separator installed in the synthesis loop. The ammonia concentration of the ammonia separator overhead is determined by vapor-liquid equilibrium at the operating pressure and temperature of the ammonia separator. Although the separation temperature depends on the operating pressure of the ammonia refrigerant circuit, generally -10 ° C to -20 ° C is adopted, the lower the cooling temperature, the larger the energy input to the refrigeration compressor and the cooling efficiency Declines.

Therefore, in the ammonia process currently commercialized, the overhead gas of the ammonia separator generally contains about 2 to 4% by volume of ammonia. The ammonia concentration in the product gas at a general reactor outlet is about 17 to 25% by volume. For this reason, about 10 to 20% by volume of ammonia generated in the ammonia synthesis reactor is circulated without being separated, and not only motive power for circulation is necessary, Since ammonia is present to a certain extent, ammonia synthesis is performed in a high concentration region where the reaction rate is small, so there is a problem that the reactor capacity needs to be increased. Furthermore, when a large amount of recycle gas having a high ammonia concentration is contained, the specific heat of ammonia is larger than that of the synthesis gases hydrogen and nitrogen, and the heat recovery efficiency is degraded.

In addition, the source gas generally contains inert components such as methane and argon that do not contribute to the reaction, and the synthesis gas containing several volume% of ammonia after the separation device is outside the loop in order to prevent accumulation in the synthesis loop. Purge to

The purge gas contains ammonia and hydrogen and nitrogen of the source gas. An ammonia scrubber is installed to recover ammonia, and 97 to 98% by weight of the ammonia contained in the purge gas is recovered. Also, in order to recover hydrogen, a membrane separation device or a cryogenic separation device is installed. Of the hydrogen used as the raw material, about 85% by weight in the case of membrane separation, and 95% by weight or more of hydrogen in the case of a cryogenic separation device are recovered. It is about 50% by weight of hydrogen used.

WO 2011/124268 (patent document 1) proposes a method for separating and recovering synthesis gas from purge gas by cryogenic separation. Further, US 20050013768 A1 (Patent Document 2) proposes a process of removing inert components by cryogenic separation before introducing synthesis gas into a synthesis loop.

Although it is possible to reduce the amount of purge gas by using the processes of Patent Documents 1 and 2, it is also not possible to completely remove the inert component, so the inert component is concentrated to a certain concentration and purged in the synthesis loop And equipment for separation and recovery is required.

WO2011 / 124268 US20050013768A1

Although it is conceivable to lower the synthesis pressure as a means of improving the energy saving of the ammonia production facility, cold heat at a lower temperature is required to maintain the liquefaction separation rate of ammonia at a low pressure.

In addition, in order to carry out efficient synthesis of ammonia, it is an issue to lower the concentration of ammonia and inert components in the loop after cooling separation, and to reduce the loss of ammonia product, hydrogen and nitrogen by purge. .

In order to solve the above problems, as a result of intensive investigations by the present inventor, the present inventors have found that by combining the two-stage cooling recovery process, the above problems can be solved and 98% by weight or more of ammonia in the product gas can be recovered. We came to solve the invention.
[1] Ammonia in the product gas obtained by reacting nitrogen-containing gas with hydrogen is firstly cooled after cooling to a temperature of -10 to -20 ° C,
Unrecovered ammonia from primary recovery is secondarily recovered by cooling to -80 to -130 ° C.
A method of recovering ammonia, comprising recovering 98 wt% or more of ammonia in a product gas.
[2] The ammonia recovery method according to [1], wherein cold energy by adiabatic expansion is used for cooling at the time of secondary recovery.
[3] The ammonia recovery method according to [2], wherein the cooling means by adiabatic expansion is at least one selected from an expander generator, an expander compressor, and a Joule Thomson valve.
[4] After secondary recovery, residual gas components separated from ammonia are further separated into hydrogen and nitrogen as raw material components and inert gas components using adiabatic expansion or cold energy by external cold heat, and raw materials The method for recovering ammonia according to [1] to [3], wherein components are reused.
[5] An ammonia synthesis reactor, an ammonia recovery device, and a recovery ammonia separation device
The ammonia recovery system consists of a primary cooler that cools to a temperature of -10 to -20 ° C with ammonia as the refrigerant, and a secondary cooler that cools to -80 to 130 ° C using adiabatic expansion or external cooling. Ammonia recovery device characterized in that
[6] The ammonia recovery device of [5], wherein the secondary cooler is a cooler with an expansion device selected from an expander generator, an expander compressor, and a Joule Thomson valve.
[7] The ammonia recovery device according to [5] or [6], including a mechanism for sending the unreacted raw material gas separated by the separation device to the ammonia synthesis reactor.
[8] The ammonia recovery device according to any one of [5] to [7], including a recovery mechanism that recovers ammonia used as a refrigerant, and a separation device and ammonia transferred to the gas phase from a storage and transport device of recovered ammonia.
[9] A separation mechanism for separating an inert component and a raw material gas component from unreacted raw material gas separated by the separation device, and a mechanism for sending the separated raw material gas component to an ammonia synthesis reactor, [5] to [8 ] Ammonia recovery device.
[10] The ammonia recovery device according to [5] to [9], further comprising a mechanism for liquefying and pressurizing the unreacted gas.

According to the present invention, it is possible to increase ammonia production by 10 to 15% by weight as compared with the existing equipment as shown in FIG.

In addition, the existing equipment is used and the number of equipment to be added is small. In addition, since there is little interaction between the extension part and the existing part, and the reinforcement work can be performed while continuing the operation to the maximum, it is possible to reduce the opportunity loss accompanying the production stop during the reinforcement period.

Since the synthesis can be performed at a high reaction rate by lowering the ammonia concentration of the inlet gas of the ammonia synthesis reactor, the production can be increased without changing the reactor size. With regard to the heat of reaction associated with the increase in production, in the case of the adiabatic reactor, the reactor inlet temperature can be adjusted, and it is also possible to respond by adding a heat removal device.

Furthermore, it is also possible not to use the ammonia scrubber shown in FIG. 3, and it becomes unnecessary to make up industrial water and to process ammonia-containing water. In addition, dehydration equipment for ammonia scrubber overhead gas and its regeneration equipment become unnecessary. The cryogenic separation can eliminate the loss of the ammonia product, and the loss of hydrogen can be suppressed to 0.1% by weight or less of the hydrogen used as the raw material.

The outline figure of one mode of the recovery method and recovery device of ammonia concerning the present invention is shown. The outline figure of one mode of the recovery method and recovery device of ammonia concerning the present invention is shown. The outline figure of the existing recovery method and recovery device of ammonia is shown.

In the method for producing ammonia according to the present invention, after nitrogen-containing gas is reacted with hydrogen to synthesize ammonia,
The ammonia in the resulting product gas is firstly cooled to a temperature of -10 to -20 ° C and recovered,
The primary recovered ammonia is secondarily recovered by cooling to -80 to -130 ° C,
It is characterized in that 98% by weight or more of ammonia in the product gas is recovered.
Ammonia raw material Ammonia is synthesized by reacting a nitrogen-containing gas with hydrogen as a raw material.

As the nitrogen-containing gas used as a raw material, it is preferable to use nitrogen gas separated from air. As means for obtaining nitrogen gas, there are generally a cryogenic separation type and an adsorption separation type. In the adsorption separation type, pressure swing adsorption method (PSA) that separates and recovers nitrogen by fluctuating (swing) pressure, temperature or pressure and temperature using a plurality of adsorption towers arranged in parallel, temperature swing Either adsorption (TSA) or pressure temperature swing adsorption (PTSA) can be used. As the adsorbent, activated carbon, molecular sieves, zeolite, etc. are packed. The nitrogen gas may contain an inert gas such as argon or methane as an impurity.

As a hydrogen source at the time of ammonia synthesis, hydrogen obtained by steam reforming such as natural gas or hydrogen obtained by electrolysis of water can be used.
Ammonia Synthesis Ammonia synthesis can be carried out by known ammonia production processes.

For example, it is also possible to adopt the Haber-Bosch method using an iron-based catalyst. In the Harbor-Bosch method, a synthesis reaction is performed under high pressure of one hundred and several tens of atmosphere or more, and is also called high-pressure method. Moreover, the method (low pressure method) which manufactures ammonia on low pressure conditions using a ruthenium catalyst is also employable.

In ammonia production using a ruthenium catalyst, a catalyst having a ruthenium catalyst supported on a carrier can be used. As a support for supporting ruthenium, alumina or a rare earth oxide can be used as a support for the catalyst.

In addition, recently, an ammonia synthesis method has been proposed in which hydrogen (ion) supplied via a proton exchange membrane and nitrogen are reacted.

The ammonia synthesis reactor is appropriately selected depending on the production process, but in the present invention, a method of reacting nitrogen-containing gas with hydrogen to synthesize ammonia is employed.

The outline flow of one mode of the recovery method of ammonia concerning the present invention is shown in Drawing 1 with a recovery device.

Specifically, an ammonia synthesis reactor, a recovery device for ammonia, and a separation device for recovered ammonia are provided, and the ammonia recovery device includes a primary cooler and a secondary cooler.

The raw material gas, hydrogen gas and nitrogen-containing gas, are pressurized to a predetermined pressure by the raw gas compressor, mixed with the recovered recycle gas, and then pressurized to the reaction pressure.

The pressurized synthesis gas is preheated and supplied to the ammonia synthesis reactor.

In the reactor, the reaction is carried out and the reaction gas is discharged from the reactor outlet. The reaction gas is cooled by cooling water or chiller water after heat recovery by steam production or the like.
Primary Recovery The ammonia in the resulting product gas is primarily recovered by cooling to a temperature of −10 to −20 ° C.

Cooling at the time of primary recovery (referred to as a primary cooler) is performed by an ammonia chiller using ammonia as a refrigerant. The ammonia used for the chiller is the one recovered from the product or the like. The ammonia liquefied by being cooled is separated into gas and liquid by an ammonia separator.
Secondary Recovery The overhead gas on the gas phase side of the ammonia separator in the primary recovery contains ammonia that could not be recovered in the primary recovery. The unrecovered ammonia is cooled to −80 to −130 ° C. by a cooling means installed in a cold box, and separated again by gas-liquid separation with an ammonia separator to recover liquid ammonia (secondary recovery).

In the case of the existing remodeling, using a cooling means by adiabatic expansion or external cooling for cooling in the secondary recovery (secondary cooler) is easy to cool to the above temperature range, and it is a major effort in enhancing existing facilities This is preferable because it does not require any construction work and there is no need to stop the operation of the entire apparatus.

The cooling means by adiabatic expansion shown in FIG. 1 is preferably adopted because it can be easily brought to a low temperature. It is preferable that it is at least 1 sort (s) chosen from an expander generator, an expander compressor, and Joule Thomson valve | bulb as a cooling means by specific adiabatic expansion. These means can easily obtain low temperatures, and the recovered power can be used as the power of the compressor. In addition, additional energy input can be reduced.

Moreover, you may cool to the temperature of -30 degrees C or less using the external refrigeration installation which used nitrogen, methane, ethane, and ethylene as a refrigerant as an external cooling means used for cooling of secondary recovery, and secondary recovery The means may be a combination of adiabatic expansion and external refrigeration means.

These secondary recovery may be performed in multiple steps.

The two-stage refrigeration recovery liquefies and separates 98% by weight or more of ammonia contained in the reactor outlet gas. The ammonia synthesis reaction is an equilibrium reaction, and if the recovery rate is high, the energy input of the compressor at the time of recycling, refrigeration compressor, etc. can be reduced by improving the conversion rate of one pass, so the reactor and the synthesis loop Size can be reduced.

The secondly recovered ammonia is combined with the firstly recovered ammonia, and the ammonia separated on the liquid side is reduced in pressure by the liquid expander or liquid expansion valve, if necessary, and dissolved in a small amount in the ammonia flash drum After removing the unreacted raw material gas components, it is supplied to an ammonia product drum under normal pressure and sent to an ammonia transportation / storage device.

Preferably, unreacted secondary gas components are recycled after secondary recovery. At this time, it may pass through a pressurizer (compressor), a heat exchanger, and a cooling device so as to obtain a predetermined pressure and temperature.

In addition, an ammonia chiller for recollecting the volatilized ammonia may be provided in the combined container and the ammonia flash drum for the primary recovery and the secondary recovery.

The ammonia used as a refrigerant, and the ammonia transferred to the gas phase from the separation device and the storage and transportation device of the recovered ammonia are recovered again as required, separated and recovered again, or pressurized with the source gas, and both reactors are used. Or may be removed by an ammonia removal treatment such as absorption into water.

Since the unreacted raw material gas component contains an inert component such as argon or methane, the inert component may be concentrated to the unreacted raw material gas component after recovering the ammonia residue by recycling. If the inert component is contained, the partial pressure of the raw material may be lowered during the ammonia synthesis, and the reactivity may be lowered. In order to prevent this, a purge gas line may be provided, and the inert component may be withdrawn from the synthesis loop together with unreacted raw material gas and a small amount of ammonia as a product. Extraction of the purge gas is performed from the separator gas phase side at the time of secondary recovery, the gas phase side of ammonia merged after recovery, the evaporation portion of the flash drum, or the like. As the purge gas contains ammonia, an ammonia scrubber may be used to absorb the ammonia. The ammonia scrubber uses a liquid such as water as an absorbing liquid to collect and separate ammonia in the liquid. Usually, industrial water is used as the absorbing solution, but an acid component such as sulfuric acid may be contained to prevent the desorption of ammonia. Moreover, you may carry out the processing equipment (neutralization etc.) of ammonia containing water as needed. In addition, although the overhead gas of the ammonia scrubber contains nitrogen, hydrogen and an inert component, a dewatering facility for dewatering these and a regenerating facility therefor may be provided.

The overhead gas of the ammonia scrubber can be further separated by membrane separation or cryogenic separation and recycled as a source gas, or the inert component can be used as a fuel.
Separation and Recovery of Raw Material Gas As shown in FIG. 2, the unreacted raw material gas separated from ammonia is further cooled through a two-stage cooling process to obtain inert components and raw material gas components (hydrogen and nitrogen). It may be separated.

Specifically, the overhead gas of the secondary cooling ammonia separator is further brought to a low temperature by adiabatic expansion means or external cooling. Among these, it is preferable to use an expander as the adiabatic expansion means because lower temperatures can be achieved.

The separated overhead gas is further cooled by a multi-pass heat exchanger installed in a cold box and supplied to a hydrogen separation column (or drum) that separates hydrogen and other inert components. The bottom solution of the hydrogen separation column is pumped up to the loop pressure. Part of it is supplied to the top of the hydrogen separation column as reflux, and the hydrogen contained in the bottom of the hydrogen separation column is recovered to the gas phase, and nitrogen, methane, and argon contained in the gas phase are recovered in the liquid phase It is also possible. Hydrogen is recycled as a source gas and adjusted to a predetermined temperature and pressure.

The cold heat is recovered until all the methane, which has been pressurized to the loop pressure, liquid nitrogen containing argon is vaporized by the multi-pass heat exchanger installed in the cold box. A portion of the vaporized gas is withdrawn and further expanded to be partially liquefied by an expander, separated into a methane / high argon concentration liquid and a high nitrogen concentration gas, and separated by a low pressure separator. The low temperature gas (nitrogen) and the liquid (methane, argon) are again sent to the multipass heat exchanger in the cold box to recover the cold.

The gas containing high concentration of methane and argon recovered to the liquid phase side by the low pressure separator may be purged out of the loop.

The other gases are mixed with the ammonia flash drum and the ammonia chiller flash gas, boosted to the source gas pressure by the boosting compressor, and returned to the loop by the source gas compressor and the recycle compressor.

The overhead gas of the hydrogen separation column, which is substantially composed of hydrogen, has its cold heat recovered by a multipass heat exchanger installed in a cold box, and is boosted to a loop pressure by a boosting compressor or the like. It is returned to the loop by the recycle compressor.

According to the method of FIG. 2, by liquefying nitrogen by cooling to a cryogenic temperature, pressure increase by a pump becomes possible, and energy can be largely reduced as compared with pressure increase by a compressor. Since the source gas component and the inert component can be separated from the unreacted source gas, it is not necessary to discharge the purge gas, or the amount thereof is reduced. Therefore, the ammonia scrubber may not be used or may be used less frequently.

Therefore, it is possible to eliminate or reduce the make-up of the industrial water, so that the treatment of the ammonia-containing water becomes unnecessary and the amount of treatment can be reduced. Furthermore, it is possible to eliminate the need for dehydration equipment for the ammonia scrubber overhead gas and its regeneration equipment, or to reduce the size of the equipment. Furthermore, it is possible to make the loss of the ammonia product zero by cryogenic separation, and the loss of hydrogen can also be suppressed to 0.1 wt% or less of the hydrogen used for the raw material.
In the recovery method shown in the embodiment, for example, FIG. 1, the following operating conditions can be adopted.

The source gases, hydrogen gas and nitrogen gas, are pressurized by the source gas compressor to a loop pressure of 50 to 200 barG. Furthermore, after being mixed with the recycle gas sent from the overhead of the ammonia separator, the pressure is raised to the reaction pressure by the recycle compressor.

The pressurized synthesis gas is preheated to 150 ° C. to 250 ° C. by the hot reactor outlet gas and supplied to the reactor. The synthesis reaction is carried out at 300 ° C. to 500 ° C.

The reactor outlet gas at 400 ° C. to 500 ° C. is subjected to heat recovery by steam production or the like, and then cooled to 20 ° C. to 50 ° C. by cooling water or chiller water.

Further, the reactor is cooled to −10 ° C. to −20 ° C. by an ammonia chiller (primary recovery), 80 to 90% by weight of ammonia contained in the reactor outlet gas is liquefied and separated by an ammonia separator.

The separated ammonia is depressurized to 15 to 20 bar G by a liquid expander or liquid expansion valve, and after removing a small amount of synthesis gas components dissolved by an ammonia flash drum, it is supplied to an ammonia product drum under normal pressure.

The overhead gas of the ammonia separator is cooled to -80 ° C to -130 ° C by the multiple pass heat exchanger installed in the cold box (second recovery), and 99.9 weight of ammonia contained in the reactor outlet gas % Or more of ammonia is liquefied and separated in the second ammonia separator. The recovered ammonia is combined with the primary recovery ammonia and supplied to the ammonia flash drum.

The recovery method and recovery system shown in Fig. 1 can increase production by 10 to 15% by weight simply by applying this process to an existing ammonia plant, and can use a low-pressure drum, expander compressor (or expander generator and so on). Only the combination of compressors) or additional refrigeration equipment can be added, and the number of additional equipment can be reduced.

In addition, since there is little interaction between the extension part and the existing part, and the reinforcement work can be performed while continuing the operation to the maximum, it is possible to reduce the opportunity loss accompanying the production stop during the reinforcement period. Furthermore, since the synthesis can be performed at a large reaction rate by lowering the ammonia concentration of the inlet gas of the ammonia synthesis reactor, the production can be increased without changing the reactor size. In the case of the adiabatic reactor, the reaction heat content associated with the increase in production is adjusted by adjusting the reactor inlet temperature or adding a heat removal device.

Claims

The ammonia in the resulting product gas is cooled to a temperature of −10 to −20 ° C. and primarily recovered by reacting nitrogen-containing gas with hydrogen,
Unrecovered ammonia from primary recovery is secondarily recovered by cooling to -80 to -130 ° C.
A method of recovering ammonia, comprising recovering 98 wt% or more of ammonia in a product gas.
2. The method for recovering ammonia according to claim 1, wherein cold energy by adiabatic expansion is used for cooling at the time of secondary recovery.
The method for recovering ammonia according to claim 2, wherein the cooling means by adiabatic expansion is at least one selected from an expander generator, an expander compressor, and a Joule Thomson valve.
After secondary recovery, residual gas components separated from ammonia are further separated into hydrogen and nitrogen source components and inert gas components using adiabatic expansion or cold energy by external cooling, and the source components are re-used. The method for recovering ammonia according to any one of claims 1 to 3, wherein the method is used.
An ammonia synthesis reactor, an ammonia recovery device, and a recovery ammonia separation device
Ammonia recovery unit from a primary cooler that cools to a temperature of -10 to -20 ° C with ammonia as a refrigerant, and a secondary cooler that cools to -80 to -130 ° C using adiabatic expansion or external cooling An ammonia recovery device characterized by comprising.
The ammonia recovery device according to claim 5, wherein the secondary cooler is a cooler with an expansion device selected from an expander generator, an expander compressor, and a Joule Thomson valve.
The ammonia recovery device according to claim 5 or 6, further comprising a mechanism for sending the unreacted raw material gas separated by the separation device to the ammonia synthesis reactor.
8. The method according to any one of claims 5 to 7, further comprising: a recovery mechanism for recovering ammonia used as a refrigerant, and ammonia and non-reacted gas transferred to the gas phase from the separation device and the storage and transport device of recovered ammonia. Ammonia recovery equipment.
9. A separation mechanism for separating an inert component and a raw material gas component from unreacted raw material gas separated by a separation device, and a mechanism for feeding the separated raw material gas component to an ammonia synthesis reactor. The ammonia recovery device according to any one of the above.
The ammonia recovery apparatus according to any one of claims 5 to 9, further comprising a mechanism for liquefying and pressurizing the unreacted gas.