Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
  • F25B29/00—Combined heating and refrigeration systems, e.g. operating alternately or simultaneously
  • F25B29/003—Combined heating and refrigeration systems, e.g. operating alternately or simultaneously of the compression type system
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01C—AMMONIA; CYANOGEN; COMPOUNDS THEREOF
  • C01C1/00—Ammonia; Compounds thereof
  • C01C1/02—Preparation, purification or separation of ammonia
  • C01C1/04—Preparation of ammonia by synthesis in the gas phase
  • C01C1/0405—Preparation of ammonia by synthesis in the gas phase from N2 and H2 in presence of a catalyst
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01C—AMMONIA; CYANOGEN; COMPOUNDS THEREOF
  • C01C1/00—Ammonia; Compounds thereof
  • C01C1/003—Storage or handling of ammonia
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
  • F25B7/00—Compression machines, plants or systems, with cascade operation, i.e. with two or more circuits, the heat from the condenser of one circuit being absorbed by the evaporator of the next circuit
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J2219/00—Chemical, physical or physico-chemical processes in general; Their relevant apparatus
  • B01J2219/00002—Chemical plants
  • B01J2219/00004—Scale aspects
  • B01J2219/00006—Large-scale industrial plants
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P20/00—Technologies relating to chemical industry
  • Y02P20/10—Process efficiency
  • Y02P20/129—Energy recovery, e.g. by cogeneration, H2recovery or pressure recovery turbines
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P20/00—Technologies relating to chemical industry
  • Y02P20/50—Improvements relating to the production of bulk chemicals
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P20/00—Technologies relating to chemical industry
  • Y02P20/50—Improvements relating to the production of bulk chemicals
  • Y02P20/52—Improvements relating to the production of bulk chemicals using catalysts, e.g. selective catalysts

Definitions

• This disclosure relates to multistage chilling of a process air compressor by integrating refrigerant ammonia stream at different temperature levels from an existing or new ammonia compression system to provide air chilling leading to a significant increase in process air compression capacity and a much higher energy efficiency, with relatively low capital.
• it relates to the downstream splitting and preheating of the resultant higher air production flow rates feeding the secondary reformer in an ammonia plant.
• the process air compressor in most operating ammonia plants is normally the first major bottleneck to increase the ammonia production.
• the process air compressor for typical average size ammonia plant is a multistage centrifugal machine driven by steam turbine using high- pressure superheated steam. It is one of the major consumers of steam in the plant.
• ammonia plant operators have conventionally used a combination of the following measures: a. Modification of existing compressor rotor and other essential internals of the compressor;
• Items (a) and (b) require significant capital and downtime with a long delivery schedule besides modifications and/or additional driver and energy requirement of high pressure steam for the turbine drive.
• the option (a) could typically achieve about 20% additional capacity.
• the potential of capacity increase with option (b) is much more and also requires additional compression power, and increased capital and plot space than option (a). In most cases, these options are frequently not economically justifiable based on the payback criteria.
• Suction chilling of ltem(c) has been practiced for long time and is also an expensive option for process air compressors since it requires an external mechanical refrigeration system with additional compression energy and plot space.
• this option may be somewhat less expensive than the first two options (a and b) but provides only a modest increase in capacity and is rarely justified economically- evident from the fact that only a handful of plants implemented suction chilling in ammonia plants. However, it remains a common feature for gas turbines in power plants.
• Two modes are presented - a direct multistage chilling and an indirect multistage chilling.
• the integration is accomplished by an ammonia plant system upgrade utilizing a direct multistage chilling system in the ammonia plant air compression train to increase process air flow to the secondary ammonia reformer of the ammonia plant including at least: a two stage suction air chiller in the air compression system that chills incoming air by heat exchange with expanded high pressure ammonia from the ammonia compression system of the ammonia plant; additional two stage air chillers between each of the air compressors of the air compression train, each air chiller chilling incoming air by heat exchange with expanded high pressure ammonia from the ammonia compression system of the ammonia plant.
• the upgrade includes at least: a new steam preheater for heating the increased process air flow; wherein the preheated and increased production flow from the air compression train is separated into three streams which are further heated in: the existing dedicated process air preheat coils of the secondary reformer; modified feed preheat convection coils of the secondary reformer; and modified boiler feedwater convection coils; and wherein the combined heated three streams are fed to the secondary reformer.
• the integration can be accomplished by an ammonia plant system upgrade utilizing an indirect multistage chilling system in the ammonia plant air compression train to increase process air flow to the secondary ammonia reformer of the ammonia plant including at least: a two stage suction air chiller in the air compression system that chills incoming air by heat exchange with chilled water from the ammonia compression system; additional two stage air chillers between each of the air compressors of the air compression train, each air chiller chilling incoming air by heat exchange with chilled water from the ammonia compression system; a staged water chiller that chills water for the air compression system by heat exchange with expanded high pressure ammonia from the ammonia compression train.
• an ammonia plant system upgrade utilizing an indirect multistage chilling system in the ammonia plant air compression train to increase process air flow to the secondary ammonia reformer of the ammonia plant including at least: a two stage suction air chiller in the air compression system that chills incoming air by heat exchange with chilled water from the ammonia compression system; additional two stage air chillers
• the upgrade includes at least: a new steam preheater for heating the increased process air flow; wherein the preheated and increased production flow from the air compression train is separated into three streams which are further heated in: the existing dedicated process air preheat coils of the secondary reformer; modified feed preheat convection coils of the secondary reformer; and modified boiler feedwater convection coils; and wherein the combined heated three streams are fed to the secondary reformer.
• Figure 1 is a schematic drawing of a prior art process air compression train in a typical ammonia plant.
• Figure 2 is a schematic drawing of a direct integrated multistage air chilling embodiment of this disclosure.
• Figure 3 is a schematic drawing of a indirect integrated multistage air chilling embodiment of this disclosure using ammonia and chilled water.
• Figure 4 is a schematic drawing of a prior art process air compression train showing its connection to the secondary reformer in the ammonia plant.
• Figure 5 is a schematic drawing of a direct integrated multistage air chilling embodiment of this disclosure with a disclosed modification of the heating arrangement for the secondary reformer.
• Figure 6 is a schematic drawing of a direct integrated multistage air chilling embodiment of this disclosure with a disclosed modification of the heating arrangement for the secondary reformer.
• FIG. 1 a prior art process air compression train in an ammonia plant, is shown overall as numeral 100.
• Four compressor stages 120, 130, 140, and 150 are shown, with intercoolers 132, 135, and 138 used between compressors 120 and 130, compressors 130 and 140, and compressors 140 and 150, respectively.
• Inter-stage coolers 132, 135, and 138 use plant cooling water to partially remove the heat of compression and in the process remove some moisture 107, 109, and 111 as condensate.
• High pressure process air 118 is the output from the process air compression train.
• the first compressor accepts filtered 102 and chilled 104 air from a suction air chiller 155 that both cools the filtered air and removes condensate 103.
• the filtered air is produced from a filter 105 drawing in atmospheric air 101.
• Suction chillers such as 155 are often not present in all prior art process air compression trains.
• Prior art suction air chillers such as 155 typically use chilled water supplied from a water chiller 160 that chills the water using a stand alone refrigeration package 170.
• Various refrigerants can be used in such packages, including the use of ammonia as the refrigerant.
• Figure 2 shows the ammonia plant upgrade using the direct integrated multistage embodiment of the disclosure.
• the numeral 200 represents the process air compression train and the numeral 300 an ammonia compression train.
• an ammonia production plant there is always an ammonia compression train but it is not integrated with the air compression train to provide cooling.
• the overall Figure 2 shows how the two are tied together, which is one of the embodiments of the present invention.
• the air compression train with its four compressor stages 120, 130, 140, and 150 are shown, with intercoolers 132, 135, and 138 used between compressors 120 and 130, compressors 130 and 140, and compressors 140 and 150, respectively.
• Inter-stage coolers 132, 135, and 138 again use plant cooling water to partially remove the heat of compression and in the process remove some moisture as condensate. Thus this aspect of the embodiment is not changed - that is to say - the existing compressors and inter-stage coolers are used.
• High pressure process air 224 exit compressor stage 150 is the output from the process air compression system in Figure 2.
• Added chillers 230, 235, and 240 are now in the process in each case following the intercoolers 132, 135, and 138 used between compressors.
• a new suction air chiller 250 either replaces the previous suction air chiller 155 of figure 1 or is a new addition.
• Air chiller 250 accepts filtered air 102, removes condensate 203, and delivers chilled air 204 to compressor 120.
• Numeral 300 exhibits the ammonia compression train that already exists in ammonia manufacture.
• This closed loop ammonia compression system involves three stages of compression in two casings, compressor casings 320 and 310.
• Compressor casing 310 has a lower pressure (LP) and a higher pressure (HP) section.
• Ammonia from the ammonia synthesis loop 394 enters into the low pressure flash drum 385.
• An ammonia vapor stream 387 is fed from the low pressure flash drum 385 to compressor 320 and compressor 320 compresses the vapor state to about 40 psig, shown as stream 302. At this stage the ammonia temperature is about 175° F.
• the compressed ammonia passes to second stage (high pressure case) ammonia compressor 310 where it is further compressed and inter-cooled by removing some of the ammonia and passing it through water pressurized ammonia cooler 255.
• the cooled ammonia in the vapor phase 306 is further compressed in the 3 rd stage of high pressure casing 310.
• the resulting higher pressure ammonia 308 passes through compressed ammonia cooler 345 to liquid ammonia buffer drum 390, where inert hydrocarbons 392 are removed and compressed ammonia 312 at about 235 psig and 100°F is sent to the air compression train where it is used is to provide the additional chilling needed by the air compression system to boost the production capacity of the existing air compression train.
• Warm ammonia product 393 is drawn off at this point for other uses.
• the ammonia from the ammonia compression train is now used as a coolant in added chillers 230, 235, and 240, and in the new suction air chiller 250. These are all two stage chillers with the second stage being cooler than the first.
• the high pressure ammonia is expanded through valves to provide cooling and the resulting ammonia after passing through the coolers and chiller is collected in headers 280 and 290.
• Header 280 is at about 95 psig and header 290 is about 33 psig.
• the expanded ammonia from header 280 is at a higher pressure than that in header 290 and is returned (via 309) to high pressure flash drum 365 in the ammonia compression train 300 and is then flashed vapor recycled (via 307) back into the last compressor stage of compressor 310.
• the expanded ammonia from header 290 is at a lower pressure and is returned via stream 334 to medium pressure ammonia flash drum 375 from where some of the liquid ammonia is further expanded to provide cooling to various other plant users pressure. Expanded ammonia is fed, after cooling in heat exchanger 380, via stream 387 to the inlet of the LP stage of the ammonia compressor 320.
• ammonia vapors from ammonia flash drum 375 is combined with the compressed ammonia stream 302 exiting compressor 320. Additional cooling at the various pressure stages in the ammonia train is supplied by heat exchangers 335, 370, and 380, which are already existent in ammonia compression train 300.
• This embodiment then represents an effective and affordable integration of an existing air compression train with an existing ammonia compression system to achieve a substantial increase in production with minimal capital investment.
• Figure 3 shows an alternate embodiment that also uses high pressure ammonia from the ammonia compression unit but in a different way.
• This embodiment is termed Indirect Multistage Air Chilling and the key difference is that the air compression train does not see any direct contact with ammonia streams but instead uses chill water obtained from direct heat exchange from the ammonia compression train through a new staged water chiller 520.
• the numeral 400 represents the air compression train and the numeral 500 an ammonia compression train.
• an ammonia production plant there is always an ammonia compression train but it is not integrated with the air compression train to provide and cooling or chilling.
• the overall Figure 3 shows how the two are tied together, which is one of the embodiments of the present invention.
• the air compression train with its four compressor stages 120, 130, 140, and 150 are shown, with intercoolers 132, 135, and 138 used between compressors 120 and 130, compressors 130 and 140, and compressors 140 and 150, respectively.
• Inter-stage coolers 132, 135, and 138 again use plant cooling water to partially remove the heat of compression and in the process remove some moisture as condensate.
• High pressure process air 424 is the output from compressor stage 150 of the process air compression system in Figure 3.
• suction air chiller 450 replaces the previous suction air chiller 250 of figure 2.
• modified air chillers 430, 440, and 460 replace chillers 230, 235 , and 240 of Figure 2.
• Numeral 500 exhibits the ammonia compression train that already exists in ammonia manufacture.
• This closed loop ammonia compression system involves three stages of compression, with LP and HP compressor casings 320 and 310 respectively.
• Ammonia from the ammonia synthesis loop 394 enters into the low pressure flash drum 385.
• An ammonia stream 587 is fed from a low pressure flash drum 385 to first stage ammonia compressor 320 and the LP compressor casing 320 compresses ammonia vapor to about 40 psig, shown as stream 501.
• the ammonia temperature is about 175° F.
• the compressed ammonia passes to the high pressure ammonia compressor 310 where it is further compressed and water cooled by removing some of the ammonia and passing it through pressurized ammonia intercooler 255.
• the resulting higher pressure ammonia 521 after being compressed in the third stage passes through a water cooled condenser 345 to liquid ammonia buffer drum 390, where inert hydrocarbons 510 are removed.
• a portion of the liquid compressed ammonia stream 504 at about 235 psig and 100°F is sent to a new staged water chiller 520 where it is expanded to provide for cooling and used is to chill the return cooling water from headers 480, 490 that provide the additional cooling needed by the air compression system to boost the production capacity of the existing air compression train.
• a key sub-system in the Figure 3 embodiment is the use of the new staged water chiller 520 to provide cooling to a chilled water loop used in the air compression train.
• High pressure ammonia 504 is supplied to staged water chiller 520 where it is expanded to provide cooling in the staged water chiller.
• the two stages result in two chilled water streams 419 and 464 that feed into each side of staged chillers 430, 440, 460, and 450 to provide enhanced cooling to the intermediate stages as well as the suction chiller of air compression.
• Condensate streams 403, 405, 407, and 409 are collected and fed to condensate collection 435.
• the combined condensate stream 401 is used to provide additional cooling/chilling in the suction chiller 450 or could be used in the suction chiller 250 of Figure 2 as well.
• the warm water condensate stream 402 is routed via stream 406 back to warm water header 480 and any excess condensate 404 is disposed of.
• the recycle ammonia from the two stages of staged water chiller 520 consists of two streams expanded to two different pressures and as a result two different temperatures.
• the higher pressure and higher temperature stream 506 returns to high pressure ammonia flash drum 365 from where some of the expanded ammonia is fed, via stream 561 after expanding and cooling in a set of heat exchangers 370, to medium pressure ammonia flash drum 375.
• the remaining ammonia vapor from high pressure ammonia flash drum 365 is fed, via stream 523 to the second stage of the high pressure stage of second stage ammonia compressor 310.
• the second lower pressure and lower temperature recycle ammonia stream 509 feeds medium pressure ammonia flash drum 375.
• the liquid ammonia is further expanded to provide cooling for various plant users through a set of heat exchangers 380, and flashed into low pressure flash drum 385 and is routed via stream 587 to the inlet of first stage ammonia compressor 320.
• the liquid ammonia from flash drum 385 is taken as product ammonia 395 and further routed to storage tanks via pumps as required.
• Ammonia vapors from ammonia flash drum 375 is combined with the compressed ammonia stream 501 exiting compressor 320.
• the compressed process air 118 in Ammonia plants is further preheated through convection coils of the Primary Reformer (a small amount of medium pressure steam 903 is also added to it before preheating).
• the preheated process air mixture 912 is then injected into the Secondary reformer 740 to provide the necessary heat of reforming and also to adjust the required H2/N2 ratio for the Ammonia synthesis reaction.
• the process air is conventionally preheated in the existing dedicated convection coils 710 of the Primary reformer by exchanging heat against the hot flue gases 917.
• the process air flow is split in two or more streams to be further preheated through the existing process air convection coil and through other identified coils in the convection section.
• Compressed process air (224 in Figure 5 or 424 in Figure 6) is first preheated in a new steam air preheater 700- outside the convection section. This is done with pressure steam 901.
• the preheated air flow from (or before the steam exchanger) is then split in two or three parts to be further preheated in the convection section as follows; between 60% to 85% of the total air flow is routed to the existing dedicated process air preheat coils 710. And between 15% to 40% of air is routed to the modified feed preheat convection coil 720 for air preheating service and between 15% to 40% of air is routed to the modified boiler feed water (BFW) preheat convection coil 730 for air preheating service.
• a hydrocarbon feed inlet 909 and exit 910 passes through existing feed preheat convection coils 720.
• Boiler feed water 915 is also heated in the existing boiler feed water convection coils.
• the combined flow preheated air 912 from these three sources is then fed, along with reformed gas 913 from the primary reformer into secondary reformer 740, resulting in 914 reformed gas from the secondary reformer.
• Multistage external preheating of process air including the external preheating coupled with splitting the air flow for further preheating results in the following benefits: a) Splitting the process air flow in two or three parts reduces the pressure drop in the process air path- thereby further reducing compression energy of process air compressor; b) Multistage external preheating of process air coupled with the additional heat transfer surface area utilization in the convection section significantly raises the air preheat temperature- thereby reducing methane slip to the secondary reformer while reducing firing in the Primary reformer and also resulting in higher ammonia production with further energy savings; c) Reduced air flow and heat duty in the existing convection air coils raises the temperature of flue gas leaving it. The higher flue gas temperature entering the next convection coil for steam superheating- raises the temperature of the superheated steam. Higher steam superheat temperature further reduces the steam demand for the steam drivers of various compressors in the ammonia plant.

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• Inorganic Chemistry (AREA)
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• Thermal Sciences (AREA)
• General Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
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• Sorption Type Refrigeration Machines (AREA)
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• 2013
  • 2013-08-14 US US14/241,018 patent/US9772129B2/en not_active Expired - Fee Related
  • 2013-08-14 WO PCT/US2013/054951 patent/WO2014028623A1/en not_active Ceased
• 2015
  • 2015-02-12 IN IN1173DEN2015 patent/IN2015DN01173A/en unknown
• 2017
  • 2017-08-22 US US15/682,974 patent/US10302337B2/en not_active Expired - Fee Related
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• 2019
  • 2019-04-10 US US16/380,127 patent/US11131486B2/en not_active Expired - Fee Related

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