Patent Publication Number: US-2017356451-A1

Title: Copmpression unit for high and low pressure services

Description:
BACKGROUND 
     Embodiments of the present invention relate to a compression unit for supplying a complete pressure service to a plant, the single compression unit being capable of supplying high and low pressure services. 
     Within a process plant, to supply high pressure gas and low pressure gas several different units are usually provided to process different flow rates at different pressure values. 
     A main drawback of the prior art is the complexity of the overall architecture and configuration of the compression units, this leading to bulky apparatus. 
     In fact, usually separate units are used to provide gas at different pressure values to a process plant, each of such compression units comprising a dedicated driver and associated impellers which increase the overall dimensions of the units. 
     SUMMARY 
     An embodiment of the present invention relates to a single compression unit for supplying a complete compression service consisting of high and low pressure gas to a process plant. 
     The compression unit is configured to supply high and low pressure gas flow with a simple architecture and with a configuration which reduces overall dimensions and weight of the unit, and also has an increased efficiency with respect to the state of the art. 
     In order to better clarify what is to be intended with the terms “high” and “low” pressure reference to the compressor flanges rating, according to ANSI, will be done hereafter. 
     As known in the art, technical limits exist while designing an impeller. One of these limits is represented by the peripheral speed of the impeller. 
     It is known in the art that impellers having a large diameter can process a high flow rate but work with reduced rotational speed and, therefore, a limited compression ratio. In order to give typical values, the term “low” pressure here indicates rating values within a typical range comprised between 150 and 300, while the impeller can process a flow rate which could be comprised in a range between 50.000 and 200.000 m3 per hour. 
     A typical speed value of an impeller processing said flow rates is 5.000 to 1.800 rounds per minute thus indicated for a direct coupled solution. 
     The term “high” pressure here indicates typical rating values comprised between 300 and 2500, with an inlet pressure value between 3 and 50 bar for the first impeller. In order to reach very high compression rates, the impeller processes low flow rates, typically less than 50.000 m3 per hour. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further details and specific embodiments will refer to the attached drawing, in which: 
         FIG. 1  is a schematic representation of one embodiment of the compression unit; 
         FIG. 2  is a schematic representation of the compression unit according to an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     The following description of exemplary embodiments refers to the accompanying drawings. The following detailed description does not limit the invention. Instead, the scope of the invention is defined by the appended claims. 
     Reference throughout the specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with an embodiment is included in at least one embodiment of the subject matter disclosed. Thus, the appearance of the phrases “in one embodiment” or “in an embodiment” in various places throughout the specification is not necessarily referring to the same embodiment. Further, the particular features, structures or characteristics may be combined in any suitable manner in one or more embodiments. 
     Such compression unit  1  comprises a single driver  2  associated with two driver shaft-ends, and in one embodiment projecting apart from said driver  2  along opposite directions, a first driver shaft end  3  and a second driver shaft end  4 . 
     In order to better describe the compression unit according to embodiments of the present invention, it can be considered that the driver  2  divides the compression unit into two sides; on one side, a first unit  10  is operatively connected to the first driver shaft-end  3 , while a second unit  20  is operatively connected to the second driver shaft-end  4 . 
     According to an embodiment of the present invention, said first unit  10  comprises an impeller  11 , and said second unit comprises a bull gear  21  in an integrally geared-compressor arrangement. 
     More particularly, according to an embodiment said impeller  11  of said first unit  10  is an overhung impeller directly connected to the first driver shaft-end  3 , and in one embodiment by means of a flanged connection or a flexible coupling. 
     According to an embodiment of the present invention, an overhung impeller is an impeller having no bearing/s on the opposite side with respect to the driver, thus all bearing/s of the overhang impeller are arranged between the impeller and the driver. 
     In this case, the impeller  11  of the first unit is the “low” pressure source unit: typical values of flow rate processed by the overhung impeller are about 50.000 m3 per hour, with an inlet pressure value of around 1 bar and an outlet pressure value of about 2 or 3 bar. 
     On the other side, the bull gear  21  is in one embodiment connected by means of a flanged connection, or a flexible coupling, to said second driver shaft-end  4 . 
     According to an embodiment shown in  FIG. 1 , said second unit  20  comprises the bull gear  21  which drives at least one driven shaft  22 ,  23  through pinions in a typical integrally geared-compressor arrangement. In order to obtain higher outlet pressure values, the bull gear  21  comprises two or more driven shafts, for example a first driven shaft  22  and a second driven shaft  23 , which are drivingly connected to the bull gear  21  by means of respectively pinions. 
     Said pinions are teethed wheels having a diameter smaller than the diameter of the bull gear. The pinions are engaged directly on the bull gear so that the rotation of the latter produces the rotation of pinions. 
     Each of said driven shafts supports at its opposite ends an overhung impeller  22   a ,  22   b ,  23   a ,  23   b.    
     According to an embodiment of the present invention, the two driven shafts  22 ,  23  are configured to rotate at different rotary speed. 
     Typical flow rate values for the second unit  20  are about 50.000 and 200.000 m3 per hour, with casing rating varying between ANSI 300 and 1500. 
     According to the first embodiment of the compression unit  1  shown in  FIG. 1 , the driver  2  drives the single overhung impeller  11  connected to said first driver shaft  3 . 
     On the other side of the compression unit  1 , the same driver  2  drives the bull gear  21  which comprises in one embodiment two driven shafts  22 ,  23 , the first driven shaft  22  supports at its ends a couple of first overhung impellers  22   a ,  22   b , the second driven shaft  23  supports at its ends a couple of second overhung impellers  23   a ,  23   b.    
     According to the scheme of  FIG. 1 , the first overhung impellers  22   a ,  22   b  and the second overhung impellers  23   a ,  23   b  are fluidly connected so that the gas flow passes through the first overhung impellers  22   a ,  22   b  of the first driven shaft  22  and then through the second overhung impellers of the second driven shaft  23 , thus forming a first multi stage compression unit for compressing a small flow rate up to high pressure values. This configuration is illustrated in  FIG. 1  by means of dashed lines indicated with the reference number  40  which represent the hydraulic connection between the impellers. 
     According to an embodiment of the present invention, the outlet of the overhung impeller  11  of the first unit  10  is fluidly connected to the inlet of the second unit  20 , thus forming a second multi stage compression unit. This configuration is represented in  FIG. 1  by means of dashed line  30  which represent the hydraulic connection between the units. 
     In this configuration, the first unit  10  provides the gas flow rate to the second unit  20  thus obtaining a compression unit apt to elaborate large flow rates with an high overall compression rate. 
     According to an embodiment of the present invention not shown in the drawings, the first unit  10  comprises an overhung impeller  11  which is connected to said first driver shaft  3  by means of a gear arrangement, instead that flanged to said first driver shaft. 
     According to an embodiment of the present invention shown in  FIG. 2 , the first unit  10  comprises a beam compressor. Said beam compressor may be flanged to said first driver shaft  3  or, alternatively, the beam compressor may be connected to said first driver shaft  3  by means of a gear arrangement. 
     Typical beam compressor casing rating varies from ANSI 600 to API 15000. 
     When the first unit  10  comprises a beam compressor, the inlet of the beam compressor may be hydraulically connected to the output of the bull gear  21  of the second unit  20 . According to this arrangement, the first unit  10  receives the flow rate coming from the output of the second unit  20 , thus forming a third multi stage compression unit allowing to reach higher compression rates. The hydraulic connection between the first  10  and the second  20  unit is represented in  FIG. 2  by means of the dashed line  50 . 
     The compression unit according to an embodiment of the present invention therefore solves the drawbacks afflicting the prior art. 
     One of the results achieved with the compression unit according to the present invention is to reduce the footprint of the apparatus, with an extremely versatile configuration. 
     This written description uses examples to disclose the invention, including the preferred embodiments, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.