Abstract:
A system for compressing air includes: a variable speed driver having a drive shaft; at least one pre-main air compressor having at least one stage and adapted to receive and compress a flow of ambient or other air and to be driven by the drive shaft of the variable speed driver; at least one main air compressor having at least one stage on a first pinion shaft and adapted to receive and further compress a flow of compressed air transmitted from the at least one pre-main air compressor; at least one booster air compressor having at least one stage on a second pinion shaft and adapted to receive and further compress a flow of further compressed air transmitted from the at least one main air compressor; and another driver adapted to drive at least one of the first pinion shaft and the second pinion shaft through at least one transmission.

Description:
BACKGROUND 
       [0001]    Applicant&#39;s systems and methods relate to compressor arrangements and applications where high air flows from ambient air or other sources are required, such as in large cryogenic air separation units. 
         [0002]    In a cryogenic air separation unit (ASU), feed air is passed through a main air compressor (MAC) to attain a desired pressure. The feed air is then cooled and water vapor and other gaseous impurities, such as carbon dioxide, are removed. Part or all of the feed air stream is then passed to a booster air compressor (BAC) to attain a desired pressure before the compressed air stream(s) is/are passed to the cryogenic part of the ASU for separation. The MAC and BAC usually each comprise more than one compression stage. 
         [0003]    High flow rate process plant compressors typically include centrifugal (i.e., radial) compression stages. A centrifugal compression stage includes an impeller mounted for rotation within a shaped housing and a diffuser. Each compressor section includes an inlet and an outlet for the fluid being compressed. Impellers may be arranged either on multiple shafts or on a single shaft. Where multiple shafts are used, a large diameter bull gear drives meshing pinions (i.e., pinion shafts) upon the ends of which compression impellers are mounted. The multiple impellers within their own respective housings provide several stages of compression, as desired. The bull gear and the meshing pinions are usually contained within a common housing known as a gearbox. Consequently, such compressors are known as integrally geared compressors. The meshing pinions may have different diameters to best match the speed requirements of the compression impellers that they drive. The compressed air between any two stages may be piped to an external intercooler or pass through an intercooler inside the compressor casing, wherein the compressed air is cooled, thereby reducing gas power consumption. 
         [0004]    It is known to compress air for an ASU using multiple compression stages, at least one of which is driven by an expander turbine. For example, European Patent Application Publication No. 0 672 877 A1 discloses a cryogenic air separation unit having three compression stages, at least one of which is driven by two or more expander turbines acting in parallel or series and linked for driving one or more compression stages via a bull gear. 
         [0005]    A typical compression arrangement for use in an ASU is shown in  FIG. 1 . This arrangement has been applied for MAC suction flow rates up to 550,000 m 3 /h. The number of booster stages is limited to four. 
         [0006]    Bull gear  46  of compression arrangement  10  is driven from steam turbine  20  through couplings  30  and  45  and an intermediate gearbox  40 . MAC stages  11  and BAC stages  12  are driven from bull gear  46 . There are three MAC compression stages (MAC 1 , MAC 2 , and MAC 3 ), with MAC 1  and MAC 2  being driven from a first pinion  50  and MAC 3  being driven from a second pinion  60 . There also are four BAC compression stages (BAC 1 , BAC 2 , BAC 3 , and BAC 4 ), with BAC 1  and BAC 2  being driven from a third pinion  70 , and BAC 3  and BAC 4  being driven from a fourth pinion  80 . The numbering of the MAC and BAC stages reflects the order in which fluid to be compressed will pass through the stages (i.e., fluid will pass successively through MAC 1 , MAC 2 , and MAC 3 , for example). 
         [0007]    To improve the overall efficiency of the compression arrangement  10 , intercoolers  90 ,  100 ,  110 ,  120 , and  130  are provided between the MAC compression stages and between the BAC compression stages to remove heat from the compressed fluid. An aftercooler  140  is provided at the outlet of BAC 4  to cool the compressed fluid to the temperature at which it is desired that the fluid enters the ASU (not shown). 
         [0008]    In use, the air to be separated is fed into the first MAC compression stage MAC 1  through air inlet filter  150  (not shown), is compressed typically to about 0.2 MPa (2 bar absolute or “bara”), and leaves MAC 1  through line  160 , then passes through intercooler  90  before entering the second compression stage MAC 2  for further compression. The compressed air, typically at about 0.35 MPa (3.5 bara), then leaves MAC 2  through line  170  and passes through intercooler  100  before entering the third compression stage MAC 3 . The compressed air, typically at about 0.6 MPa (6 bara), is then passed to the ASU purification systems via outlet  180  for cooling and removal of water vapor and other gaseous impurities, such as carbon dioxide. 
         [0009]    After passage through the ASU purification systems, the air is passed to the BAC stages  12 , entering the first BAC compression stage BAC 1  by inlet  190  and exiting, typically at about 1.1 MPa (11 bara), through line  200 . The compressed air is then passed through intercooler  110  for temperature reduction, and enters the second BAC compression stage BAC 2 . The air successively passes through BAC 2  outlet line  210 , typically at about 2 MPA (20 bara), intercooler  120 , the third BAC compression stage BAC 3 , outlet line  220 , typically at about 3.5 MPa (35 bara), intercooler  130 , and the fourth BAC compression stage BAC 4 . The compressed air, typically at about 5.5 MPa (55 bara) is then passed via line  230  through aftercooler  140  to be brought to the desired temperature and enters the ASU for separation. 
         [0010]    There are many other conventional compression arrangements, and variations thereof, used in ASUs. Some examples of such arrangements are illustrated in  FIGS. 2 through 6 . In these arrangements, air is compressed in the MAC stages from ambient pressure to a discharge pressure greater than 5 bara. The required discharge pressure depends on the site elevation, cryogenic cycle, heat exchangers, distillation columns, front end, piping used, etc. 
         [0011]      FIG. 2  illustrates a compression arrangement including an integrally geared centrifugal MAC that has three MAC compression stages (MAC 1 , MAC 2 , and MAC 3 ) ( 101 ,  102 , and  103 ) mounted on two high-speed pinion shafts driven by a driver  21 . A gearbox  40  is used between the driver  21  and the bull gear of an integrally geared centrifugal BAC. This arrangement has one suction inlet that takes air at ambient condition for up to 550,000 m 3 /hr flow rate. Limiting factors on flow capacity may include required space between the two pinions and between a pinion and the bull gear, rotordynamics, mechanical losses, overall dimensions, overall weight, overall cost, etc. All MAC compression stages are on the same power train. Therefore, once a design speed is selected for the driver  21 , there is little room to change the speed, since any speed change will impact all of the MAC compression stages. The MAC stages and the BAC stages may be driven by two different drivers, although it becomes common that both the MAC and the BAC stages are driven by a same driver  21 , as shown in  FIG. 2 . If the MAC and the BAC stages are driven by the same driver  21 , then speeds of all of the MAC and the BAC stages are coupled, meaning that the speed of one stage cannot be changed without effecting the other stages. 
         [0012]      FIG. 3  illustrates a compression arrangement including an integrally geared centrifugal MAC that has three MAC compression stages (MAC 1 A and MAC 1 B, MAC 2 , and MAC 3 ) ( 101 A,  101 B,  102 , and  103 ) mounted on two high-speed pinion shafts driven by a driver  21 . A gearbox  40  is used between the driver  21  and the BAC. This arrangement has two same size suction inlets that take air at ambient condition for up to 800,000 m 3 /hr flow rate in total. Limiting factors on flow capacity may include the required space between two pinions and between a pinion shaft and the bull gear, rotordynamics, mechanical losses, overall dimensions, overall weight, overall cost, etc. In addition, at the suction inlets, a reasonably long (e.g., 4× pipe diameter or more) straight inlet piping run is preferred or required to avoid inducing turbulence and allow a piping sectional change so that the surge taps can function properly. Such requirement imposes extra challenges for the second main suction close to the driver. All MAC compression stages are on the same power train. Therefore, once a design speed is selected for the driver  21 , there is little room to change the speed, since any speed change will impact all of the MAC compression stages. The MAC stages and the BAC stages may be driven by two separate drivers, although it becomes common that both the MAC and the BAC stages are driven by the same driver  21 , as shown in  FIG. 3 . When the MAC and the BAC stages are driven by the same driver  21 , all of the MAC stages and all of the BAC stages are related, meaning any speed change of the driver  21  would impact all of the MAC stages and all of the BAC stages. 
         [0013]      FIG. 4  illustrates a compression arrangement including a single shaft centrifugal MAC that has three or more MAC compression stages (MAC 1 , MAC 2 , MAC 3 , and MAC 4 ) ( 101 ,  102 ,  103  and  104 ) mounted on one shaft. This arrangement has one suction inlet that takes air at ambient condition for up to 650,000 m 3 /hr flow rate. Limiting factors on flow capacity may include impeller sizes that can be manufactured with current tooling, stress limit or tip speed limit, rotordynamics, overall dimensions, overall weight, overall cost, etc. All MAC compression stages are on the same shaft. Therefore, once a design speed is selected for the driver  21 , there is little room to change the speed, since any speed change will impact all of the MAC compression stages. It is common that the MAC stages and the BAC stages are driven by the same driver  21 , as shown in  FIG. 4 . In this case, any speed change on the driver  21  will impact all of the MAC stages as well as all of the BAC stages. 
         [0014]      FIG. 5  illustrates a compression arrangement including a single shaft axial-radial MAC that has six axial MAC compression stages (MAC 1 ) ( 101 ) and one or more centrifugal MAC compression stages (MAC 2  and MAC 3 ) ( 102  and  103 ) mounted on one shaft. This arrangement has one suction inlet that takes air at ambient condition for up to 1,000,000 m 3 /hr flow rate or more. There is no inter-stage cooling in the axial compression section due to rotordynamics and cost constraints, and therefore, the compressor power consumption would be higher than an equivalent isothermal compressor. An isothermal compressor means there is inter-stage cooling after each compression stage. All MAC compression stages are on the same shaft. Therefore, once a design speed is selected for the driver  21 , there is little room to change the speed since any speed change will impact all of the MAC compression stages. When the MAC and the BAC compression stages are driven by the same driver  21 , as shown in  FIG. 5 , any speed change of the driver  21  will impact all of the MAC compression stages as well as all of the BAC compression stages. 
         [0015]      FIG. 6  illustrates another compression arrangement. The first MAC compression stage (MAC 1 )( 101 ) is driven on one end of a driver  21 , while an integrally geared centrifugal compressor contains two remaining MAC compression stages (MAC 2  and MAC 3 )( 102  and  103 ) on one high-speed pinion shaft. The two remaining MAC compression stages are combined with four BAC compression stages (BAC 1 , BAC 2 , BAC 3 , and BAC 4 )( 501 ,  502 ,  503 , and  504 ) on the same machine. Generally, there can be up to four high-speed pinion shafts and up to eight stages in total in a combined MAC/BAC compressor. A gearbox  40  is used between the driver  21  and the combined MAC/BAC (MAC 2 , MAC 3 , BAC 1 , BAC 2 , BAC 3 , and BAC 4 ). This arrangement has one suction inlet that takes air at ambient condition. The maximum flow of this arrangement is to be determined by relevant machinery suppliers. The maximum flow capacity of this arrangement will be limited by centrifugal impeller size that can be manufactured by Original Equipment Manufacturers (OEMs) and the allowable impeller tip speed. All MAC compression stages are on a same power train. Therefore, once a design speed is selected for the driver  21 , there is little room to change the speed, since any speed change will impact all of the MAC compression stages as well as all of the BAC compression stages that are on the same power train. 
         [0016]    Major challenges common to all of the compression arrangements illustrated in  FIGS. 1-6  are:
       1. How to increase flow capacity without sacrificing efficiency;   2. How to handle various operating conditions more effectively to achieve yearly power savings, including reduce venting for turndown; and   3. How to achieve compression train cost reduction through standardization.       
 
       BRIEF SUMMARY 
       [0020]    There are various aspects of Applicant&#39;s apparatus and methods, and many variations of each aspect. 
         [0021]    One aspect is a system for compressing air. The system includes a variable speed driver, at least one pre-main air compressor, at least one main air compressor, at least one booster air compressor, and at least one other driver. The variable speed driver has at least one drive shaft. The at least one pre-main air compressor has at least one stage and is adapted to receive and compress a flow of ambient air or other air and to be driven by the at least one drive shaft of the variable speed driver. The at least one main air compressor has at least one stage on a first pinion shaft and is adapted to receive and further compress at least a portion of a flow of compressed air transmitted from the at least one pre-main air compressor. The at least one booster air compressor has at least one stage on a second pinion shaft and is adapted to receive and further compress at least a portion of a flow of further compressed air transmitted from the at least one main air compressor. The at least one other driver is adapted to drive at least one of the first pinion shaft and the second pinion shaft directly or indirectly through at least one transmission. 
         [0022]    In a first variation of the system, a first drive shaft of the variable speed driver drives a first pre-main air compressor at a variable speed, and a second drive shaft of the variable speed driver drives a second pre-main air compressor at the variable speed. In a variant of this variation, at least one of the first pre-main air compressor and the second pre-main air compressor is a centrifugal air compressor. 
         [0023]    In another variation of the system, a first stage of the at least one main compressor on the first pinion shaft is adapted to receive and further compress the at least a portion of the flow of compressed air transmitted from the at least one pre-main air compressor at a pre-defined discharge pressure, and a second stage of the at least one main air compressor on the first pinion shaft is adapted to receive and further compress at least a portion of a flow of further compressed air transmitted from the first stage of the at least one main air compressor. 
         [0024]    In yet another variation of the system, a first stage of the at least one booster air compressor on the second pinion shaft is adapted to receive and further compress the at least a portion of the flow of further compressed air transmitted from the at least one main air compressor, and a second stage of the at least one booster air compressor on the second pinion shaft is adapted to receive and further compress at least a portion of the flow of further compressed air transmitted from the first stage of the at least one booster air compressor. 
         [0025]    In another variation of any of the systems discussed in the previous four paragraphs, the at least one transmission includes at least one bull gear. 
         [0026]    A second system is similar to the first system or any of the variations discussed above, but also includes at least one supplementary booster air compressor having at least one stage on a third pinion shaft and is adapted to receive and further compress at least a portion of a flow of further compressed air transmitted from the at least one booster air compressor, wherein the at least one other driver or another driver is adapted to drive at least one of another drive shaft, the first pinion shaft, the second pinion shaft, and the third pinion shaft directly or indirectly through the at least one transmission or another transmission. 
         [0027]    In a variation of the second system, a first stage of the at least one supplementary booster air compressor on the third pinion shaft is adapted to receive and further compress at least a portion of the flow of further compressed air transmitted from a second stage of the at least one booster air compressor, and a second stage of the at least one supplementary booster air compressor on the third pinion shaft is adapted to receive and further compress at least a portion of a flow of further compressed air transmitted from the first stage of the at least one supplementary booster air compressor. 
         [0028]    A third system is similar to the first or second system or any of the variations thereof discussed above, but includes at least one cooler, each cooler adapted to cool at least one of at least a portion of the flow of compressed air transmitted from the at least one pre-main air compressor, at least a portion of the flow of further compressed air transmitted from the at least one main air compressor, and at least a portion of a flow of further compressed air transmitted from the at least one booster air compressor. 
         [0029]    A fourth system includes a variable speed driver, a first pre-main centrifugal air compressor, a second pre-main centrifugal air compressor, a manifold, a main air compressor, a booster air compressor, a supplementary booster air compressor, one other driver, and at least one cooler. The variable speed driver has a first drive shaft and a second drive shaft. The first pre-main centrifugal air compressor has at least one stage and is adapted to receive and compress a first flow of ambient air and to be driven at a first variable speed by the first drive shaft of the variable speed driver. The second pre-main centrifugal air compressor has at least one stage and is adapted to receive and compress a second flow of ambient air and to be driven at the first variable speed by the second drive shaft of the variable speed driver. The manifold is adapted to receive and combine at least a portion of a first flow of compressed air from the first pre-main centrifugal air compressor and at least a portion of a second flow of compressed air from the second pre-main centrifugal air compressor. The main air compressor has a first and a second stage. The first stage is on a first pinion shaft and is adapted to receive and further compress at least a portion of a flow of compressed air transmitted from the manifold at a pre-defined discharge pressure. The second stage of the main air compressor is on the first pinion shaft and is adapted to receive and further compress at least a portion of a flow of further compressed air transmitted from the first stage of the main air compressor. The booster air compressor has a first stage and a second stage. The first stage is on a second pinion shaft and is adapted to receive and further compress at least a portion of a flow of further compressed air transmitted from the main air compressor. The second stage of the booster air compressor is on a second pinion shaft and is adapted to receive and further compress at least a portion of a flow of further compressed air transmitted from the first stage of the booster air compressor. The supplementary booster air compressor has a first stage and a second stage. The first stage is on a third pinion shaft and is adapted to receive and further compress at least a portion of a flow of further compressed air transmitted from the second stage of the booster air compressor. 
         [0030]    The second stage of the supplementary booster air compressor is on the third pinion shaft and is adapted to receive and further compress at least a portion of a flow of further compressed air transmitted from the first stage of the supplementary booster air compressor. The one other driver is adapted to drive at least one of another drive shaft, the first pinion shaft, the second pinion shaft, and the third pinion shaft directly or indirectly through at least one of a bull gear and an other transmission. Each cooler is adapted to cool at least one of at least a portion of the first and second flows of compressed air transmitted from the first and second pre-main centrifugal air compressors, at least a portion of each flow of further compressed air transmitted from each stage of the main air compressor, at least a portion of each flow of further compressed air transmitted from each stage of the booster air compressor, and at least a portion of each flow of further compressed air transmitted from each stage of the supplementary booster air compressor. 
         [0031]    Another aspect is a method for compressing air, which includes eight steps. The first step is to transmit a flow of ambient air or other air to at least one pre-main air compressor having at least one stage. The second step is to drive the at least one pre-main air compressor with a variable speed driver having at least one drive shaft. The third step is to compress the flow of ambient air or other air in the at least one pre-main air compressor, thereby producing a flow of compressed air from the at least one pre-main air compressor. The fourth step is to transmit at least a portion of the flow of compressed air from the at least one pre-main air compressor to at least one main air compressor having at least one stage and a first pinion shaft. The fifth step is to compress further the at least a portion of the flow of compressed air in the at least one main air compressor, thereby producing a flow of further compressed air from the at least one main air compressor. The sixth step is to transmit at least a portion of the flow of further compressed air from the at least one main air compressor to at least one booster air compressor having at least one stage on a second pinion shaft. The seventh step is to compress further the at least a portion of the flow of further compressed air in the at least one booster air compressor, thereby producing a flow of further compressed air from the at least one booster air compressor. The eighth step is to drive at least one of the first pinion shaft and the second pinion shaft with at least one other driver directly or indirectly through at least one transmission. 
         [0032]    In a first variation of the method, a first drive shaft of the variable speed driver drives a first pre-main air compressor at a variable speed, and a second drive shaft of the variable speed driver drives a second pre-main air compressor at the variable speed. 
         [0033]    In another variation of the method, a first stage of the at least one main air compressor of the first pinion shaft receives and further compresses the at least a portion of the flow of compressed air transmitted from the at least one pre-main air compressor at a pre-defined discharge pressure, and a second stage of the at least one main air compressor on the first pinion shaft receives and further compresses at least a portion of a flow of further compressed air transmitted from the first stage of the at least one main air compressor. 
         [0034]    In yet another variation of the method, a first stage of the at least one booster air compressor on the second pinion shaft receives and further compresses the at least a portion of the flow of further compressed air transmitted from the at least one main air compressor, and a second stage of the at least one booster air compressor on the second pinion shaft receives and further compresses at least a portion of a flow of further compressed air transmitted from the first stage of the at least one booster air compressor. 
         [0035]    In another variation of any of the methods discussed in the previous four paragraphs, the at least one transmission includes at least one bull gear. 
         [0036]    A second method is similar to the first method or any of the variations discussed above, but includes three additional steps. The first additional step is to transmit at least a portion of the flow of further compressed air from the at least one booster air compressor to at least one supplementary booster air compressor having at least one stage on a third pinion shaft. The second additional step is to drive with the at least one other driver or another driver at least one of another drive shaft, the first pinion shaft, the second pinion shaft, and the third pinion shaft directly or indirectly through the at least one transmission or another transmission. The third additional step is to compress further the at least a portion of the flow of further compressed air from the at least one booster air compressor, thereby producing a flow of further compressed air from the supplementary booster air compressor. 
         [0037]    In a variation of the second method, a first stage of the at least one supplementary booster air compressor on the third pinion shaft receives and further compresses a portion of the flow of further compressed air transmitted from a second stage of the at least one booster air compressor, and a second stage of the at least one supplementary booster air compressor on the third pinion shaft receives and further compresses at least a portion of a flow of further compressed air transmitted from the first stage of the at least one supplementary booster air compressor. 
         [0038]    A third method is similar to the first or second method or any of the variations thereof discussed above, but includes an additional step of cooling with at least one cooler at least one of at least a portion of the flow of compressed air transmitted from the at least one pre-main air compressor, at least a portion of the flow of further compressed air transmitted from the at least one main air compressor, and at least a portion of a flow of further compressed air transmitted from the at least one booster air compressor. 
         [0039]    A fourth method includes 18 steps. The first step is to transmit a first flow of ambient air to a first pre-main centrifugal air compressor having at least one stage. The second step is to drive the first pre-main centrifugal air compressor at a first variable speed with a first drive shaft of a variable speed driver. The third step is to transmit a second flow of ambient air to a second pre-main centrifugal air compressor having at least one stage. The fourth step is to drive a second pre-main centrifugal air compressor at the first variable speed with a second drive shaft of the variable speed driver. The fifth step is to compress the first flow of ambient air in the first pre-main centrifugal air compressor, thereby producing a first flow of compressed air at a pre-defined discharge pressure. The sixth step is to compress the second flow of ambient air in the second pre-main centrifugal air compressor, thereby producing a second flow of compressed air at the pre-defined discharge pressure. The seventh step is to combine in a manifold at least a portion of the first flow of compressed air from the first pre-main centrifugal air compressor and at least a portion of a second flow of compressed air from the second pre-main centrifugal air compressor. The eighth step is to transmit a flow of compressed air from the manifold to a main air compressor having a first stage on a first pinion shaft and a second stage on the first pinion shaft. The ninth step is to compress further in the first stage of the main air compressor at least a portion of the flow of compressed air transmitted from the manifold. The tenth step is to compress further in the second stage of the main air compressor at least a portion of a flow of further compressed air transmitted from the first stage of the main air compressor. The eleventh step is to transmit a flow of further compressed air from the main air compressor to a booster air compressor having a first stage on a second pinion shaft and a second stage on the second pinion shaft. The twelfth step is to compress further in the first stage of the booster air compressor at least a portion of a flow of further compressed air from the main air compressor. The thirteenth step is to compress further in the second stage of the booster air compressor at least a portion of a flow of further compressed air transmitted from the first stage of the booster air compressor. The fourteenth step is to transmit a flow of further compressed air from the booster air compressor to a supplementary booster air compressor having a first stage on a third pinion shaft and a second stage on the third pinion shaft. The fifteenth step is to compress further in the first stage of the supplementary booster air compressor at least a portion of the flow of further compressed air from the booster air compressor. The sixteenth step is to compress further in the second stage of the supplementary booster air compressor at least a portion of a flow of further compressed air transmitted from the first stage of the supplementary booster air compressor, thereby producing a flow of further compressed air from the supplementary booster air compressor. The seventeenth step is to drive at least one of another drive shaft, the first pinion shaft, the second pinion shaft, and the third pinion shaft with at least one other driver directly or indirectly through at least one of a bull gear and an other transmission. The eighteenth step is to cool with at least one cooler at least one of at least a portion of the first and second flows of compressed air transmitted from the first and second pre-main centrifugal air compressors, at least a portion of each flow of further compressed air transmitted from each stage of the main air compressor, at least a portion of each flow of further compressed air transmitted from each stage of the booster air compressor, and at least a portion of each flow of further compressed air transmitted from each stage of the supplementary booster air compressor. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0040]    Applicant&#39;s systems and methods will be described by way of example with reference to the accompanying drawings, in which: 
           [0041]      FIG. 1  is a schematic diagram of a conventional compression arrangement for use in an air separation unit (ASU); 
           [0042]      FIG. 2  is a schematic diagram of another conventional compression arrangement for use in an ASU; 
           [0043]      FIG. 3  is a schematic diagram of another conventional compression arrangement for use in an ASU; 
           [0044]      FIG. 4  is a schematic diagram of another conventional compression arrangement for use in an ASU; 
           [0045]      FIG. 5  is a schematic diagram of another conventional compression arrangement for use in an ASU; 
           [0046]      FIG. 6  is a schematic diagram of another conventional compression arrangement for use in an ASU; and 
           [0047]      FIG. 7  is a schematic diagram illustrating one embodiment of a compression arrangement for Applicant&#39;s systems and methods. 
       
    
    
     DETAILED DESCRIPTION 
       [0048]      FIG. 7  illustrates one exemplary embodiment of a compression arrangement  10  for Applicant&#39;s systems and methods of which there are many variations and many variants of the variations. The compression arrangement  10  includes Pre-MAC stages  2 , MAC stages  4 , and BAC stages  6 . There are two Pre-MAC compressors ( 56  and  76 ), two MAC compression stages (MAC 1  and MAC 2 )( 182  and  222 ), and four BAC compression stages (BAC 1 , BAC 2 , BAC 3 , and BAC 4 ) ( 290 ,  330 ,  370 , and  410 ). 
         [0049]    Referring to the exemplary embodiment illustrated in  FIG. 7 , a variable speed driver ( 162 ) (e.g., a steam turbine or a variable speed motor) drives two single stage centrifugal pre-main air compressors (Pre-MAC)  56 ,  76  through two couplings  92 ,  96 . The first Pre-MAC compressor  56  takes air from ambient (or another source), pulls the air through an inlet air filter  52  and inlet line  54 , and compresses the air to about  2  bara. The compressed air is routed by line  58  to a Pre-MAC after-cooler (Pre-MAC AC)  61  and the cooled air is routed by line  62  to a manifold  86 . The second Pre-MAC compressor  76  takes air from ambient (or another source), pulls the air through a second inlet air filter  72  and inlet line  74 , and compresses the air to about  2  bara. The compressed air is routed by line  78  to the second Pre-MAC after-cooler (Pre-MAC AC)  81  and the cooled air is routed by line  82  to the manifold  86 . 
         [0050]    The compressed and cooled air (at about  2  bara) from the Pre-MAC after coolers  61 ,  81  is fed through line  172  to the first MAC compression stage MAC 1  ( 182 ) where it is further compressed and then fed through line  192  to the interstage cooler  202  (MAC 1  IC) of MAC 1 . The cooled air from the interstage cooler  202  is fed through line  212  to the second MAC compression stage MAC 2  ( 222 ) where it is further compressed, and then is routed through line  232  to the after cooler  240  (MAC 2  AC) of MAC  2 . The cooled air from after cooler  240  is routed by line  250  to air separation unit (ASU) stream  260 . 
         [0051]    Preferably, the discharge pressure of Pre-MAC, or the inlet pressure of MAC, is a pre-defined pressure or constant pressure for any ambient pressure. However, persons skilled in the art will recognize that various other pressures are possible even though they may not provide the best economic benefits. 
         [0052]    ASU stream  260  passes through purification units (not shown) and heat exchangers (not shown) and part of the ASU stream comes back from BAC inlet stream  270 , which is routed through line  280  to the first BAC compression stage BAC 1  ( 290 ), is further compressed, and is routed through line  300  to the interstage cooler  310  (BAC 1  IC) of BAC 1 . 
         [0053]    The cooled air from interstage cooler  310  is routed by line  320  to the second BAC compression stage BAC 2  ( 330 ), is further compressed, and is routed by line  340  to the interstage cooler  350  (BAC 2  IC) of BAC 2 . 
         [0054]    Part or all of the cooled air from interstage cooler  350  is routed by line  360  to the third BAC compression stage BAC 3  ( 370 ), is further compressed, and is routed by line  380  to the interstage cooler  390  (BAC 3  IC) of BAC 3 . 
         [0055]    The cooled air from interstage cooler  390  is routed by line  400  to the fourth BAC compression stage BAC 4  ( 410 ), is further compressed, and is routed by line  420  to the after cooler  430  (BAC 4  AC) of BAC 4 . The cooled air from the after cooler  430  is routed by line  440  and goes to ASU stream  450  for further processing. 
         [0056]    In the compression arrangement  10  of the exemplary embodiment illustrated in  FIG. 7 , MAC 1  ( 182 ) and MAC 2  ( 222 ) are both on a first pinion shaft  8 . BAC 1  ( 290 ) and BAC 2  ( 330 ) are both on a second pinion shaft  14 . BAC 3  ( 370 ) and BAC 4  ( 410 ) are both on a third pinion shaft  16 . The second driver  600  drives combined MAC stages  4  and BAC stages  6  on pinion shafts  8 ,  14 , and  16  through a coupling  42  [maybe also through a gearbox (not shown), if needed] and a drive shaft which may be the shaft of the bull gear  18 . 
         [0057]    If, for example, the BAC stages  6  has additional stages beyond four stages (e.g., five or six stages), the extra stage(s) beyond four may be included in the combined MAC 1  stages  4  and BAC stages  6  with an additional pinion shaft. 
         [0058]    The design speed at which the variable speed driver  162  drives the Pre-MAC compressors  56 ,  76  is optimized based on site elevation and site average ambient temperature to achieve the best efficiency and the lowest power consumption. A variable inlet guide vane (IGV) and/or a variable diffuser may be used in combination with variable speed adjustments to handle other process duty conditions to reduce power consumption more effectively for those process conditions. 
         [0059]    Applicant&#39;s systems and methods address at least in part three challenges common to the conventional compression arrangements illustrated in  FIGS. 1-6  in at least several ways, including:
       Applicant&#39;s systems and methods use two main suctions that take air from ambient or other source, and thereby double the flow capacity that can be handled by the conventional compression arrangements in  FIGS. 1 ,  2 ,  4 , and  6 , which have only one main suction that takes air from ambient;   Applicant&#39;s systems and methods eliminate the space and dimension constraints imposed by the compression arrangement illustrated in  FIG. 3 , since Applicant&#39;s systems and methods use a stand-alone power train that does not have any adjacent stage or compressor scroll to interfere with it. As a result, Applicant&#39;s systems and methods can handle much higher flows (&gt;1,000,000 m 3 /hr); and   Applicant&#39;s systems and methods save power since Pre-MAC is driven by a variable speed drive without any mechanical loss associated with a gearing. And Applicant&#39;s systems and methods provide an isothermal compression which uses less power, as shown by Example 1 in the “EXAMPLES” section below.       
 
         [0063]    For any given site, while the air inlet pressure is constant, the air inlet temperature can vary significantly from winter to summer, leading to considerable variation on volumetric flow and variation on head. Volumetric flow and head increase with the inlet temperature. 
         [0064]    As previously explained above, for all conventional compression arrangements, the MAC stages (and all BAC stages for all large machines) are on the same power train; and therefore, once the design speed is selected, there is little room to change this speed to accommodate seasonal temperature and/or production changes. Thus, the most effective compressor performance control variable, i.e., speed, is not a degree of freedom to use for conventional compression arrangements. To handle the required flow and the head for the summer high temperature condition, MAC will need to be sized for the summer high temperature condition and IGV will be partially closed to handle normal operating conditions. This could reduce the compressor efficiency for other operating conditions and its turndown range (La, the range from the design flow to the minimum allowable flow without compressor surge). During winter or turndown condition, the volumetric flow reduces significantly comparing to the flow for the summer high temperature condition, and therefore, the IGV has to be closed further and the compressed air may have to be vented to the atmosphere to prevent the compressor from surging. Both will lead to power waste. 
         [0065]    In contrast, a compression arrangement using Pre-MAC has its own stand-alone variable speed as a true degree of freedom. For summer high temperature condition, the speed can be increased; and for winter or turndown condition, the speed can be reduced. Variable IGV and a variable diffuser (if needed) can further enhance the range of operation. The compressor efficiency for other operating conditions will be better in comparison with conventional arrangements. Venting can be completely eliminated, resulting in additional power savings. 
         [0066]    Air inlet pressure of MAC may vary considerably with elevation among different sites. Average air inlet temperature may also vary considerably with climate condition among different sites. For example, if a MAC is moved from a site where the inlet pressure is 1.01 bara and the average inlet temperature is 7.2° C. to another site where the inlet pressure is 0.852 bara and the average inlet temperature is 20° C., the inlet volumetric flow would be increased by more than 25%, and first stage head would be increased by more than 34%, for the same air separation products and cryogenic process cycle. 
         [0067]    As previously discussed above, all MAC stages in conventional arrangements are on the same power train. Once the speed is selected, there is little room to change the speed. As a result, the most effective compressor performance control variable, i.e., speed, is not a degree of freedom for a given MAC hardware. For a site with high elevation and/or high average inlet temperature, the design speed needs to be higher for the first stage for a given MAC hardware. However, any speed increase will be applied to all MAC stages as well as BAC stages on the same power train, and therefore, will not work for a given cryogenic process cycle and ASU design. For these reasons, conventional arrangements have to be customized for each site. 
         [0068]    In contrast, a compression arrangement using Pre-MAC has its own stand-alone variable speed as a true degree of freedom. Pre-MAC can use higher design speeds for applications with high elevation and/or high average air inlet temperature and lower speeds for applications with sea level elevation and low average air inlet temperature, all with the same Pre-MAC hardware. Variable IGV and a variable diffuser (if needed) can further enhance Pre-MAC&#39;s capability to handle such variations. Pre-MAC can also cover a wider range of air separation products than conventional compression arrangements. 
         [0069]    Regardless of site elevation and air inlet temperature, Pre-MAC feeds pre-processed “utility” air at almost constant pressure and temperature to MAC, and therefore, MAC can now be standardized. 
       EXAMPLES 
       [0070]    Flow capacity limitations on the compression arrangements in  FIGS. 1 ,  2 ,  4 , and  6  are directly set by the maximum flow capacity that can be handled by one centrifugal stage, since all of those arrangements have only one main inlet that takes air from ambient conditions. 
         [0071]    The compression arrangement in  FIG. 5  has an axial compression section, and it can handle 1,000,000 m 3 /hr or even higher flow rate. However, because there is no inter-stage cooling within the axial compression section, the compressor power consumption is higher than an equivalent isothermal compression. See Example 1 below. 
       EXAMPLE 1   
       [0072]    Air flow=1,000,000 m 3 /hr 
         [0073]    MAC inlet pressure=0.879 bara 
         [0074]    MAC inlet temperature=29° C. 
         [0075]    Relative Humidity=55% 
         [0076]    MAC discharge pressure=5.85 bara 
         [0077]    Assume that an axial-radial compressor, such as that illustrated in  FIG. 5 , is used where a multistage axial section compresses air to 3.4 bara, and then a centrifugal stage compresses air from 3.4 bara to the final discharge pressure of 5.85 bara. In comparison to the axial compression section, a centrifugal stage compresses air from 0.879 bara to 2 bara, cools the discharge air to 40° C., and then compresses air to 3.4 bara using the second centrifugal stage. A comparison of the power consumption between the multistage axial compression section and two centrifugal stages with an interstage cooler follows: 
         [0000]    
       
         
               
               
               
             
               
               
               
             
           
               
                   
               
               
                   
                 Multistage  
                 Two Centrifugal  
               
               
                   
                 Axial 
                 Stages 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Assumed Polytropic  
                 90.5 
                 88 
               
               
                 Efficiency (%) 
                   
                   
               
               
                 Calculated Gas Power (KW) 
                 45,468 
                 42,898 
               
               
                 Gas Power Saving (KW) 
                 — 
                 2,570 
               
               
                   
               
             
          
         
       
     
         [0078]    As demonstrated in Example 1, although an axial-radial compressor arrangement like that illustrated in  FIG. 5  can handle higher flow, it needs higher gas power compared to an isothermal compressor. 
         [0079]    The compression arrangement in  FIG. 3  has two suctions. Its current flow limit is 800,000 m 3 hr and is unlikely to go above 1,000,000 m 3 /hr for the reasons previously discussed above for this arrangement. Also, when flow rate increases, the impeller size and scroll size increase proportionally. In order to maintain required space between adjacent scrolls, a bigger bull gear or addition of an idler is needed, leading to higher mechanical loss, increased weight and dimensions, and higher cost. The piping route of the second main inlet close to the driver will be more challenging when pipe size becomes larger. 
       EXAMPLE 2  
       [0080]    For a MAC machinery compression arrangement of  FIG. 3 , assume the total flow rate Q=800,000 m 3 /hr, i.e., MAC  1 A ( 101 A) and MAC  1 B ( 101 B) each have a flow rate Q 1 =400,000 m 3 /hr. 
         [0081]    MAC inlet pressure=0.879 BarA 
         [0082]    MAC inlet temperature=29° C. 
         [0083]    Relative Humidity=55% 
         [0084]    MAC  1 A and MAC  1 B discharge pressure=2 bara 
         [0085]    For an integrally geared centrifugal compressor with double suctions, as shown in  FIG. 3 , MAC  1 A ( 101 A) and MAC  1 B ( 101 B) are on the same pinion shaft. Since this pinion shaft interacts with the bull gear, a mechanical gearing loss (typically around 2.5% of gas power, or maybe even higher to more than 5%) is incurred. For Applicant&#39;s Pre-MAC compression arrangement, the pre-MAC  56  and the pre-MAC  76  are directly driven by a variable speed driver  162  without any gearing, and therefore, there is no mechanical gearing loss. For MAC  1 B ( 101 B) on the driver side, as shown in  FIG. 3 , a straight piping section of 6.8 m or longer and 1.7 m in diameter may be needed and will cause interference with the driver and block required access for maintenance. For Applicant&#39;s Pre-MAC compression arrangement, both suctions of Pre-MAC  56  and Pre-MAC  76  are facing away from the variable speed driver  162 , and therefore, there is no possibility of interference with the driver. 
         [0000]    
       
         
               
               
               
             
               
               
               
             
           
               
                   
               
               
                   
                 Double Suction Integrally 
                 Pre-MAC  
               
               
                   
                 Geared MAC (FIG. 3) 
                 (FIG. 7) 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Assumed Polytropic Efficiency (%) 
                 88 
                 88 
               
               
                 Required Gas Power (KW) 
                 20,883 
                 20,883 
               
               
                 Gearing Loss (assume 2.5%) 
                 522 
                 NA 
               
               
                 Power Saving (KW) 
                 — 
                 522 
               
               
                 Inlet Piping Diameter D (m) 
                 1.7 
                 1.7 
               
               
                 Required Straight Piping Run  
                 6.8 
                 6.8 
               
               
                 4 × D (m) 
                   
                   
               
               
                 Interference On Driver Side 
                 Yes 
                 No 
               
               
                   
               
             
          
         
       
     
         [0086]    Although illustrated and described herein with reference to one or more specific embodiments, Applicant&#39;s systems and methods are nevertheless not intended to be limited to the details shown. Rather, various modifications may be made in the details within the scope and range of equivalents of the claims and without departing from the spirit of the invention. 
         [0087]    Applicant&#39;s systems and methods include many other aspects and variations thereof which are not illustrated in the drawings or discussed in the Detailed Description section. Those aspects and variations, however, do fall within the scope of the appended claims and equivalents thereof. 
         [0088]    Persons skilled in the art will recognize that the embodiments and variations illustrated in the drawings and discussed in the Detailed Description section do not disclose all of the possible arrangements of Applicant&#39;s systems, and that other arrangements are possible. Accordingly, all such other arrangements are contemplated by Applicant&#39;s systems and methods, and are within the scope of the appended claims and equivalents thereof. 
         [0089]    Persons skilled in the art also will recognize that many other embodiments incorporating Applicant&#39;s inventive concepts are possible, as well as many variations of the embodiments illustrated and described herein.