Cold wall horizontal ammonia converter

Systems and methods for producing ammonia. Nitrogen and hydrogen can be supplied to a reaction zone disposed inside an inner shell. The inner shell can be disposed inside an outer shell such that a space is formed therebetween. The reaction zone can include at least one catalyst bed in indirect heat exchange with the space. The nitrogen and hydrogen can be reacted in the reaction zone in the presence of at least one catalyst to form an effluent comprising ammonia. The effluent can be recovered from the inner shell and cooled to provide a cooled effluent stream. A cooling fluid can be provided to the outer shell such that the cooling fluid flows through at least a portion of the space and is in fluid communication with the exterior of the inner shell. At least a portion of the cooled effluent can provide at least a portion of the cooling fluid. The cooling fluid can then be recovered from the outer shell as an ammonia product.

BACKGROUND

The present embodiments generally relate to methods for exothermal synthesis. More particularly, embodiments of the present invention relate to methods for synthesis of ammonia and other chemicals using one or more catalyst beds.

2. Description of the Related Art

Conventional exothermic chemical synthesis reactors feature an exothermal reaction chamber having catalyst beds contained in a catalyst containment basket or a “basket” that is disposed inside an outer pressure shell. The catalyst beds are contained in the basket so that the outer pressure shell is not directly exposed to the high temperatures inherent in the exothermic synthesis reaction. The outer pressure shell is typically cooled by flowing a reactor feed gas through an annular space formed between the outside of the basket and the inside of the outer pressure shell. The heat transferred to the feed gas from the exothermic reaction occurring in the basket preheats the feed gas to the required reaction temperature prior to the feed gas being passed to the catalyst beds. The preheated feed gas then passes to the catalyst beds directly or via an internal heat exchanger, where at least a portion of the flow is converted into a by-product such as ammonia or other known chemical compounds.

The heats and pressures generated by the exothermic synthesis in the annular space between the basket and the outer pressure shell are significant. The design of the basket must take into account the physical realities of the reaction within the catalyst beds by increasing the wall thicknesses of the basket and selecting other metallurgical parameters necessary for the baskets to survive the heat generated during the exothermal process. The design of the outer pressure shell must also take these physical realities into account since the outer shell is exposed to significant heat and pressure during, among other things, the pre-heating of the feed gas prior to introduction into the basket. The metallurgic requirements can drive significant costs into the design and construction of an exothermal reaction chamber. There is a need, therefore, to provide a new system and method that can reduce the metallurgic requirements of exothermal reaction chambers, including those reaction chambers used in the production of ammonia or other known chemicals.

DETAILED DESCRIPTION

Systems and methods for the synthesis of one or more chemicals, including ammonia, are provided. In at least one specific embodiment, nitrogen and hydrogen can be supplied to a reaction zone disposed inside an inner shell. The inner shell can be disposed inside an outer shell such that a space is formed therebetween. The reaction zone can include at least one catalyst bed in indirect heat exchange with the space. The nitrogen and hydrogen can be reacted in the reaction zone in the presence of at least one catalyst to form an effluent comprising ammonia. The effluent can be recovered from the inner shell and cooled to provide a cooled effluent stream. A cooling fluid can be provided to the outer shell such that the cooling fluid flows through at least a portion of the space and is in fluid communication with the exterior of the inner shell. At least a portion of the cooled effluent can provide at least a portion of the cooling fluid. The cooling fluid can then be recovered from the outer shell as an ammonia product.

In at least one other specific embodiment, a synthesis reactor is provided. The reactor can include an inner shell disposed inside an outer shell. A first space can be formed inside the inner shell. The first space can be referred to as a reaction zone. A second space can be formed between the inner shell and the outer shell. In one or more embodiments, at least a portion of the second space can be an annular space. The inner shell and the outer shell can be any shape or size. The synthesis reactor can include one or more catalyst beds disposed in the first space. In one or more embodiments, one or more catalysts can be disposed in the one or more catalyst beds. The catalyst in the catalyst beds can be modified to synthesize one or more chemicals, for example ammonia.

In operation, the synthesis reactor can be the primary and/or secondary synthesis unit in a plant or facility. In one or more embodiments, a feed stream can be introduced into the reaction zone and an exothermal reaction between the catalyst and the feed stream can take place. In one or more embodiments, a cooling fluid can be directed through the second space to cool the inner shell and the outer shell. In one or more embodiments, the outer shell can be cooled such that the outer shell temperature can be maintained at a lower temperature than the inner shell temperature. The synthesis reactor can be referred to as a cold wall synthesis reactor.

FIG. 1depicts a schematic of an illustrative cold wall synthesis reactor for producing ammonia and/or other chemicals, according to one or more embodiments. In one or more embodiments, the reactor10can include an inner shell20disposed inside an outer shell12. A reaction zone24can be formed inside the inner shell20. A space14can be formed between the inner shell20and the outer shell12. One or more catalyst beds25can be disposed inside the inner shell20. The reactor10can include one or more tubes15, one or more inner shell inlets30, and one or more inner shell outlets35. The one or more tubes15, the one or more inner shell inlets30, and the one or more inner shell outlets35can be in fluid communication with the reaction zone24. The outer shell12can include one or more outer shell inlets40and one or more outer shell outlets45. The one or more outer shell inlets40and the one or more outer shell outlets45can be in fluid communication with the space14. In one or more embodiments, the inner shell20and the tubes15can form a first plenum inside the outer shell12. The outer shell12can form a second plenum surrounding the inner shell20. In one or more embodiments, the outer shell12, the one or more outer shell inlets40, and the one or more outer shell outlets45can form a second plenum surrounding the inner shell20.

In one or more embodiments, the inner shell20can have any shape cross-section including a circular cross-section. In one or more embodiments, the inner shell20can include fins (not shown) disposed on the inside and/or the outside of the inner shell20. The fins can enhance heat transfer from the reaction zone24and/or the inner shell20to the space14.

In one or more embodiments, the inner shell20and the one or more catalyst beds25can be supported inside the outer shell12by the one or more tubes15. The inner shell20can be supported by a secondary structure attached to the inner shell20and the outer shell12(not shown). The inner shell20can be supported inside the outer shell12by any known structural support concept. In one or more embodiments, the inner shell20can be removably disposed inside the outer shell12. The catalyst beds25can be supported inside the inner shell20by any known structural support concept. In one or more embodiments, one or more baffles (not shown) can separate two or more catalyst beds25.

In one or more embodiments, the one or more catalyst beds25can contain a catalyst capable of reacting with hydrogen and nitrogen to create ammonia. The catalyst contained in the one or more catalyst beds25can be one or more platinum-group metals, carbon based catalysts, magnetites, and/or combinations thereof.

In one or more embodiments, the outer shell12can have any shape cross-section including a circular cross-section. In one or more embodiments, the outer shell12can include fins (not shown) disposed on the inside and/or the outside of the outer shell12. The fins can enhance heat transfer from the outer shell12to the space14.

Although not shown, one or more inner shells20can be disposed inside the outer shell12. The one or more inner shells20can be in fluid communication with each other and can be configured in series and/or in parallel to each other. In one or more embodiments, the one or more inner shells20can have one or more catalyst beds25disposed in each inner shell20to define one or more reaction zones24.

In one or more embodiments, the totality of the components in the inner shell20can be constructed using materials including stainless steel, incoloy, inconel, titanium, other high alloy metals and/or combinations thereof. In one or more embodiments, the outer shell12can be constructed using materials including carbon steel, other low alloy metals, and/or combinations thereof. Low alloy metals can be less expensive than high metal alloys. For example, it can be less expensive to purchase low alloy metals as compared to high alloy metals. It can also be less expensive to fabricate components using low alloy metals as compared to using high alloy metals. In one or more embodiments, the outer shell12can be produced at a lower cost than the inner shell20. In one or more embodiments, a high alloy metal is defined as a metal containing 8% by weight or more nickel and/or chromium. In one or more embodiments, a high alloy metal is defined as a metal containing 6% by weight or more nickel and/or chromium. In one or more embodiments, a low alloy metal is defined as a metal containing less than 6% by weight nickel and/or chromium.

It should be understood that although the synthesis reactor10inFIG. 1is shown generally in a horizontal configuration having the catalyst beds25in series, this is no limitation on the orientation and/or catalyst bed configurations in the one or more embodiments described herein. For example, the synthesis reactor10can be installed in a generally vertical configuration. In the vertical configuration, the one or more catalyst beds25can be disposed one above another in the reaction zone24. Fluid can flow through the reaction zone24from the top of the vertically oriented synthesis reactor10to the bottom of the vertically oriented synthesis reactor10.

In one or more embodiments, during synthesis reactor10operation, a feed stream32can contain nitrogen and hydrogen and can be supplied to the inner shell inlet30. The feed stream32can be directed through the reaction zone24. The feed stream32can flow from the top to the bottom of each catalyst bed25. The feed stream32can flow over the one or more catalyst beds25either directly or via a heat exchanger (not shown) disposed inside the inner shell20. The resultant reaction between the catalyst in the catalyst beds25and the feed stream32can produce an effluent37that can have an increased ammonia content relative to the feed stream32. The effluent37can be recovered from the inner shell outlet35for further processing. The direction of flow of the feed stream32, as described above, is not limiting and in one or more embodiments, the feed stream32can flow from the bottom to the top of each catalyst bed25.

A cooling medium, such as a cooling fluid22, can be used to remove the heat generated by the reaction between the feed stream32and the catalyst in the catalyst beds25. In one or more embodiments, the cooling fluid22can be supplied to the outer shell inlet40. The space14can direct the cooling fluid22over at least a portion of the inner shell20and can be in indirect heat exchange relationship with the reaction zone24. The cooling fluid22can remove at least a portion of the reaction heat generated by the reaction between the feed stream32and the catalyst in the one or more catalyst beds25. The cooling fluid can then be directed to and can be recovered from the outer shell outlet45for further uses as discussed below or as are known in the art. It should be understood that although only one inlet30,40and one outlet35,45are shown for both the inner shell20and the outer shell12, there are no limits on the number of the inlets30,40and the outlets35,45.

In one or more embodiments, the cooling fluid22can flow through the space14in a counter-current direction to the feed stream32. In one or more embodiments, the cooling fluid22can flow through the space14in a co-current direction to the feed stream32.

In one or more embodiments, the cooling fluid22can be any fluid. In one or more embodiments, the cooling fluid22can transfer heat from the inner shell20and from the outer shell12. In one or more embodiments, the outer shell12can be cooled such that the outer shell12temperature can be maintained at a lower temperature than the inner shell20temperature and the synthesis reactor10can be referred to as a cold wall synthesis reactor10. In one or more embodiments, the average temperature of the reaction zone24can be maintained at a temperature between from about 600° F. to about 950° F. and the average temperature of the outer shell12can be maintained at a temperature between from about 100° F. to about 600° F.

The average temperature of the reaction zone24and the outer shell12can be maintained by introducing the cooling fluid22that can have a temperature between from about 95° F. to about 600° F. In one or more embodiments, the average temperature of the reaction zone24and the outer shell12can be maintained by introducing the cooling fluid22having a temperature between from about 95° F. to about 400° F. and having a mass flow rate of between about 10 percent and about 100 percent of the mass flow rate of the feed stream.

In one or more embodiments, the one or more cold wall synthesis reactors10can be operated in a plant or facility. The one or more cold wall synthesis reactors10can be configured in the plant in parallel and/or in series relative to one another. The one or more cold wall synthesis reactors10can be the primary and/or secondary synthesis units in a plant.

FIG. 2depicts a schematic of an illustrative system for producing ammonia using a cold wall synthesis reactor according to one or more embodiments. In one or more embodiments, the ammonia plant100can include a cold wall synthesis reactor10. The cold wall synthesis reactor10can be a primary ammonia reactor for the ammonia plant100as part of a primary synthesis loop. The primary synthesis loop can include, one or more cold wall synthesis reactors10, one or more reformers50; one or more conditioning units51; one or more chillers or condensation/purification units52; one or more ammonia recovery units55; and one or more hydrogen recovery units65. The cold wall synthesis reactor10can include an outer shell12, an inner shell20, a space14formed between the inner shell20and the outer shell12, and a reaction zone24formed within the inner shell20.

In operation, the reformer50can supply a syngas or feed stream32to the cold wall synthesis reactor10at a suitable pressure and temperature for ammonia synthesis. In one or more embodiments, the feed stream32can be thermally conditioned and/or compressed in the conditioning unit51prior to being supplied to the cold wall synthesis reactor10. In one or more embodiments, the feed stream32can include nitrogen and hydrogen with a purity of from about 90 to 100 volume percent. The feed stream32can include nitrogen and hydrogen with a purity of from about 97.5 to 99.5 volume percent. In one or more embodiments, the feed stream32can include from about 50 to about 75 volume percent hydrogen and from about 25 to about 40 volume percent nitrogen.

The feed stream32can be reacted in the reaction zone24and the resulting effluent37can be directed to the one or more chillers52for cooling and/or thermal conditioning for ammonia condensing. After at least some cooling, at least a portion of the cooled effluent37can be directed to the space14as at least a portion of a cooling fluid22for cooling or transferring heat from the cold wall synthesis reactor10. After the cooling fluid22exits the cold wall synthesis reactor10, the cooling fluid22can be directed to one or more of the chillers52for ammonia condensing and purification, and can yield a purified ammonia93, in a manner known in the art.

In one or more embodiments, a slipstream84of partially purified ammonia can be diverted to the ammonia recovery unit55for use as a makeup fluid to ammonia distillation. A flashed refrigerant slipstream54comprising low pressure ammonia plus non-condensable gases and other vapor from the refrigeration in chillers52can be diverted to the ammonia recovery unit55to separate water vapor and non-condensable gases. The ammonia recovery unit55can return an upgraded, low pressure ammonia vapor82to the chillers52. The ammonia recovery unit55can produce a low-pressure waste gas62, typically at a low mass flow rate of about 0.1 to 0.5 percent of the mass flow rate of the feed stream32.

A high-pressure purge gas56can be taken from the ammonia recovery unit55to remove inert gases such as argon, carbon dioxide, and methane that can accumulate in the primary synthesis loop. At least a portion58of the purge gas56can be sent to the hydrogen recovery unit65. Hydrogen can be recovered as low-pressure hydrogen68and a high-pressure hydrogen73can be recycled with the feed gas32to reformer50and the cold wall ammonia synthesis unit10. A waste gas64comprising primarily nitrogen, plus argon, carbon dioxide, and methane in minor proportions can flow together with a waste gas62to a66. Another portion of the purge gas56can be supplied as a feed60to a secondary synthesis loop or unit, not shown. The secondary synthesis unit can be one or more secondary synthesis units known in the art and/or one or more cold wall synthesis reactors10.

In one or more embodiments, during initial ammonia plant100start-up, at least a portion of the feed stream32can be directed to the space14and can act as an initial cooling fluid32charge in the space14. In one or more embodiments, at least a portion of the feed stream32can be directed to one or more chillers52prior to being supplied to the space14as an initial charge in the space14.

The cooling fluid22can remove heat from the cold wall synthesis reactor10such that the outer shell12average temperature can be maintained at between about 100° F. to about 600° F. In one or more embodiments, the average temperature of the cooling fluid22can be maintained at between about 200° F. and 500° F. The average temperature of the cooling fluid22can be maintained at between about 400° F. and 500° F. In one or more embodiments, the mass flow rate of the cooling fluid22can be maintained at between about 10% to about 100% of the feed stream32. In one or more embodiments, the mass flow rate of the cooling fluid22can be maintained at between about 90% to about 100% of the feed stream32. In one or more embodiments, the cooling fluid22can be directed to the cold wall synthesis reactor10at a point in the primary synthesis loop where the cooling fluid22can be maintained at between about 200° F. and 500° F.

In one or more embodiments, the cooling fluid22can remove heat from the cold wall synthesis reactor10such that the reaction zone24average temperature can be maintained at between about 600° F. to about 950° F. The cooling fluid22can remove heat from the cold wall synthesis reactor10such that the reaction zone24average temperature can be maintained at between about 570° F. to about 1200° F.

FIG. 3depicts a schematic of an illustrative system for producing ammonia using one or more primary synthesis reactors and one or more secondary synthesis reactors according to one or more embodiments. In one or more embodiments, the ammonia plant200can incorporate the cold wall synthesis reactor10as a secondary reactor integrated with a primary ammonia synthesis loop110. In one or more embodiments, one or more cold wall synthesis reactors10can be incorporated as secondary reactors, in situ, into an original ammonia plant primary ammonia loop110. The primary ammonia loop110can include a reformer50, a primary ammonia synthesis unit121, an ammonia condensation and purification or chiller unit52, an ammonia recovery unit55, and a hydrogen recovery unit65, all of which are known in the art.

In operation, a feed stream32of nitrogen and hydrogen can have a purity of from about 95 to 100 volume percent. In one or more embodiments, the feed stream32can have a purity of from about 97.5 to about 99.5 volume percent. The reformer50can supply the feed stream32at a suitable pressure for ammonia synthesis. The feed stream32can be directed to the primary ammonia synthesis unit121, and an ammonia-rich product gas111can flow to the chiller unit52for refrigeration and condensation. An ammonia-lean feed113can be recirculated to the reformer50and a slip84of an ammonia-lean feed vapor can be diverted to the ammonia recovery unit55to separate water vapor and non-condensable gases. Condensate formed in equilibrium with the recirculated feed113can be used as a makeup refrigerant in the chiller unit52. The makeup refrigerant and the ammonia-rich product gas111can cyclically condense and flash through a plurality of stages, not shown, within the chiller unit52, and can yield a purified ammonia93, in a manner known in the art.

A slipstream117of partially purified ammonia refrigerant can be diverted to the ammonia recovery unit55for use as a makeup liquid to ammonia distillation. A flashed refrigerant slipstream54including low pressure ammonia plus noncondensable gases and other vapor from the refrigeration can be diverted to the ammonia recovery unit55to separate water vapor and noncondensable gases. The ammonia recovery unit55can return an upgraded, low pressure ammonia vapor82to the refrigeration subsystem. The ammonia recovery unit55can produce a low-pressure wastegas62.

A high-pressure purge gas56can be taken from the ammonia recovery unit55to remove inert gases such as argon, carbon dioxide, and methane that can accumulate in the primary ammonia synthesis loop110. A portion58of the purge gas56can be sent to the hydrogen recovery unit65. Hydrogen recovered as low-pressure hydrogen68and high-pressure hydrogen73can be recycled to the reformer50and to the primary ammonia synthesis unit121. A waste gas64comprising primarily nitrogen, plus argon, carbon dioxide, and methane in minor proportions can flow together with the waste gas62to a stream66.

Another portion of the purge gas56can be supplied as a secondary ammonia product or a feed60to a secondary ammonia synthesis loop including a cold wall synthesis reactor10having the inner shell20, the outer shell12, the reaction zone24, and the space14. In one or more embodiments, the cold wall synthesis reactor10can be in fluid communication with the chiller unit52for cooling an effluent37. In one or more embodiments, after the feed60passes through the reaction zone24, the cold wall synthesis reactor10can produce an ammonia-rich effluent37that can be directed to the chiller unit52for some cooling. After some cooling, the cooled effluent or cooling fluid22can be directed back through the cold wall synthesis reactor10, for cooling, and fed to an ammonia recovery unit145. In one or more embodiments, the cooling fluid22exiting the cold wall synthesis reactor10can be directed to the ammonia recovery unit55. The ammonia recovery unit145can import a partially purified ammonia refrigerant123from the chiller52as a makeup liquid for ammonia distillation, and can return a high-concentration ammonia vapor136to a stream82. Ammonia-lean stream148can include nitrogen and hydrogen and other gases at relatively high pressure, and if desired can be recycled to the reformer50and the primary synthesis unit121. In operation, the secondary synthesis can improve plant productivity by about5to50percent, for example10to25percent, of the feed60.

The cooling fluid22can remove heat from the cold wall synthesis reactor10such that the outer shell12average temperature can be maintained at between about 100° F. to about 600° F. In one or more embodiments, the average temperature of the cooling fluid22can be maintained at between about 200° F. and 500° F. In one or more embodiments, the mass flow rate of the cooling fluid22can be maintained at between about 50% to about 90% of the feed stream32while the temperature of the cooling fluid steam22can be maintained at between about 100° F. to about 600° F. The cooling fluid22can remove heat from the cold wall synthesis reactor10such that the reaction zone24average temperature can be maintained at between about 570° F. to about 1200° F. The cooling fluid22can remove heat from the cold wall synthesis reactor10such that the reaction zone24average temperature can be maintained at between about 600° F. to about 950° F.