Patent Publication Number: US-2019186478-A1

Title: Reciprocating compressor and manufacturing method

Description:
TECHNICAL FIELD 
     The subject matter disclosed herein generally relates to compressors and more specifically to reciprocating compressors. In particular, embodiments of the present disclosure concern double-acting reciprocating compressors. 
     BACKGROUND 
     Reciprocating compressors are used in several industrial fields for compressing a gas, in particular when relatively small gas flow rates require to be compressed with a high compression ratio. 
     Exemplary embodiments of double-acting reciprocating compressors are disclosed in U.S. Pat. Nos. 7,418,355, 8,807,959 and in U.S. Pat. No. 8,203,350. A reciprocating compressor comprises a compressor cylinder forming a cylinder chamber therein. A piston is arranged in the cylinder chamber and is driven into reciprocating motion by a prime mover, such as an electric motor, a turbine or a reciprocating internal or external combustion engine, such as a Stirling engine. A crankshaft and a connecting rod mechanism converts the rotary motion of a motor shaft into reciprocating motion of the piston. The connecting rod is usually drivingly coupled to the piston through a cross-head and a piston rod. 
     A valve arrangement provides for gas delivery into the cylinder chamber and gas discharge from the cylinder chamber. In double-acting reciprocating compressors the piston divides the cylinder chamber into a first compression chamber and a second compression chamber. At least one suction valve and one delivery valve are fluidly coupled to the first compression chamber, and at least a further suction valve and a further delivery valve are fluidly coupled to the second compression chamber. The reciprocating motion of the piston in the cylinder chamber causes gas to be sucked in one of the compression chambers through the respective suction valve, while gas is compressed in the other compression chamber and discharged through the respective delivery valve, when a delivery pressure is achieved at which the delivery valve is opened. 
     Suction valves and delivery valves are usually automatic valves, which automatically open and close in response to a pressure differential thereacross. 
     The suction valves are fluidly coupled to an inlet plenum, which feeds gas at a lower pressure to the cylinder chamber. The delivery valves are in turn fluidly coupled to a discharge plenum, which collects gas at a higher pressure from the cylinder chamber. 
       FIG. 1  illustrates a double-acting reciprocating compressor  100  of the current art. The compressor  100  comprises a compressor head  101 , a compressor frame  102  and a distance piece  103 , which connects the compressor head  101  to the compressor frame  102 . A crankshaft  104  is arranged in the compressor frame  102 . The crankshaft  104  rotates around a rotation axis  106 . A prime mover, not shown, drives the crankshaft  104  into rotation. A connecting rod  108  transmits the motion from the crankshaft  104  to a crosshead  110 , which moves reciprocatingly in a crosshead guide  112 . A piston rod  114  connects the crosshead  110  to a piston  116 , which is adapted to reciprocatingly slide in a chamber  118  of a compressor cylinder  120 . The piston  116  divides the chamber  118  in a first compression chamber and a second compression chamber. In some embodiments, the first and second compression chambers can be a head-end chamber  118 A, and a crank-end chamber  118 B. A process gas is selectively sucked into each one of said head-end and crank-end chambers  118 A,  118 B at a lower pressure (suction pressure), compressed and discharged at a higher pressure (delivery pressure). Said head-end chamber  118 A and crank-end chamber  118 B are provided each with at least one suction valve and one delivery valve. The suction, compression and discharge process is performed alternatively in the two chambers, i.e. when gas is sucked into one of the head-end chamber  118 A and crank-end chamber  118 B, gas in the other of said head-end chamber  118 A and crank-end chamber  118 B is compressed and discharged. 
     Suction valves  122  of both crank-end chamber  118 B and head-end chamber  118 A are fluidly coupled to an inlet plenum  126 , which is in turn fluidly coupled to a gas source  128 . Delivery valves  124  of both crank-end chamber  118 B and head-end chamber  118 A are fluidly coupled to a discharge plenum  130 , which is in turn fluidly coupled to a gas output  134 . The inlet plenum  126  and the discharge plenum  130  are both formed in a barrel  132 , which in turn forms a cylindrical side wall of the chamber  118 . The gaseous flow through the inlet plenum  126  and the discharge plenum  130  and respective suction valves and delivery valves is complex and involves sharp bends due to the position of the valves in respective valve seats formed in the barrel  132 . Specifically, gas enters the valve seats in a direction orthogonal to the axial direction of the valves, such that the gas flow turns by 90° when flowing from the inlet plenum into the suction valves and when flowing from the delivery valves into the discharge plenum. 
     Cooling ducts  136  are further provided in the barrel  132 . 
     The need to provide inlet plenum, discharge plenum, valve seats and cooling ducts therein, makes the barrel  132  a quite complex and expensive piece of machinery, which must be manufactured by iron or steel casting. Casting of complicated components is time consuming and may frequently lead to scraps. 
     The shape of the inlet plenum and discharge plenum is restricted by the structure of the barrel. Mechanical constraints result in suboptimal fluid-dynamic design of the gas inlet and discharge plenums, which in turn causes fluid-dynamic losses and reduction of the overall efficiency of the compressor. 
     Also, cooling of the compressor head is inefficient and manufacturing of the cooling ducts is rendered complicated by the combined presence of valve seats, plenums and cooling arrangements in the barrel. 
     A need therefore exists, for improvements in the design of reciprocating compressors, in particular double-acting reciprocating compressors, in order to solve or alleviate one or more of the drawbacks of the compressors of the current art. 
     SUMMARY 
     According to one aspect, the present disclosure concerns a manufacturing method for manufacturing a cylinder for a reciprocating compressor. The method comprises a step of manufacturing a compressor barrel comprised of a cylinder chamber, a first suction valve seat, fluidly coupled to the cylinder chamber through a respective first gas suction port; and a first delivery valve seat, fluidly coupled to the cylinder chamber through a respective first gas delivery port. The method further comprises the step of manufacturing a gas inlet plenum and further manufacturing a gas discharge plenum, separately from the compressor barrel. 
     The gas inlet plenum and the gas discharge plenum can be attached around the compressor barrel in fluid communication with the gas suction port and the gas delivery port. The gas inlet plenum and the gas discharge plenum can thus be designed according to optimization criteria, to minimize the gas pressure losses along the gas path, without being subjected to mechanical constraints imposed by the shape of the compressor barrel. 
     According to a further aspect, a manufacturing method for manufacturing a cylinder for a reciprocating compressor is described herein, which comprises the following steps: 
     mounting a first suction valve in a first suction valve seat provided in a compressor barrel and fluidly coupled through a first gas suction port to a cylinder chamber arranged in the compressor barrel; 
     mounting a first delivery valve in a first delivery valve seat provided in the compressor barrel and fluidly coupled to the cylinder chamber through a first gas delivery port; 
     mounting a gas inlet plenum on the compressor barrel and in fluid communication with first suction valve seat; 
     mounting a gas discharge plenum on the compressor barrel and in fluid communication with the first delivery valve. 
     According to a yet further aspect, a reciprocating compressor is disclosed, comprising a compressor barrel with a cylinder chamber therein and a piston, adapted for reciprocatingly sliding in the cylinder chamber. The compressor further comprises a first suction valve fluidly coupled to the cylinder chamber and a first delivery valve fluidly coupled to the cylinder chamber. Furthermore, the compressor comprises a gas inlet plenum fluidly coupled to the first suction valve and a gas discharge plenum fluidly coupled to the first delivery valve. The gas inlet plenum and the gas discharge plenum are mechanically connected to the compressor barrel and external thereto. 
     Features and embodiments are disclosed here below and are further set forth in the appended claims, which form an integral part of the present description. The above brief description sets forth features of the various embodiments of the present invention in order that the detailed description that follows may be better understood and in order that the present contributions to the art may be better appreciated. There are, of course, other features of the invention that will be described hereinafter and which will be set forth in the appended claims. In this respect, before explaining several embodiments of the invention in details, it is understood that the various embodiments of the invention are not limited in their application to the details of the construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting. 
     As such, those skilled in the art will appreciate that the conception, upon which the disclosure is based, may readily be utilized as a basis for designing other structures, methods, and/or systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete appreciation of the disclosed embodiments of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: 
         FIG. 1  illustrates a sectional view of a double-effect reciprocating compressor of the current art; 
         FIG. 2  illustrates a sectional view of a double-effect reciprocating compressor according to an embodiment according to the present disclosure; 
         FIG. 3  illustrates a sectional view taken along the line of  FIG. 2 ; 
         FIG. 4  illustrates a flowchart summarizing manufacturing methods according to the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The following detailed description of the exemplary embodiments refers to the accompanying drawings. The same reference numbers in different drawings identify the same or similar elements. Additionally, the drawings are not necessarily drawn to scale. Also, 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” or “some embodiments” means that the 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 phrase “in one embodiment” or “in an embodiment” or “in some embodiments” in various places throughout the specification is not necessarily referring to the same embodiment(s). Further, the particular features, structures or characteristics may be combined in any suitable manner in one or more embodiments. 
     The exemplary reciprocating compressors disclosed herein alleviate or solve the drawbacks and limitations of the prior art by separating the gas inlet plenum and gas discharge plenum from the compressor barrel. The design of both the gas inlet plenum and the gas discharge plenum can thus be optimized from a fluid-dynamic perspective, since less mechanical constraints are present. The shape of the inlet plenum and discharge plenum do not have to conform to the shape of the barrel, the cooling ducts and valve seats housed therein. The orientation of the inlet plenum and discharge plenum with respect to the position of the suction valves and delivery valves can be optimized. More space is available in the wall of the barrel to accommodate the valve seats and the cooling ducts. Also the shape of the cooling ducts can be ameliorated from the point of view of heat exchange efficiency, as well as from the point of view of machining. 
     The barrel can be more easily manufactured and less expensive production techniques, rather than iron or steel casting, can be used. For instance, the barrel can be manufactured by forging or centrifugal casting, which makes the overall manufacturing process quicker, less expensive and less prone to generate scraps. 
     The inlet plenum and discharge plenum can be produced using manufacturing processes, which allow complex shapes to be achieved, e.g. by additive manufacturing. Optimal design can thus be achieved, which result in reduction of fluid-dynamic losses in the inlet and discharge gas flows. 
     While the compressor structure and the manufacturing processes disclosed herein can be beneficial also for the production of single-acting reciprocating compressors, they are particularly beneficial for the production of double-acting reciprocating compressors, where the shape of the gas inlet plenum and gas discharge plenum is particularly complex due to the higher number of suction valves and delivery valves provided in the compressor head. 
     A double-acting reciprocating compressor comprises a cylinder comprised of a compressor barrel and a cylinder chamber formed in the barrel. The cylinder chamber is divided in a so-called head-end chamber and a so-called crank-end chamber by a piston, arranged for reciprocatingly sliding therein. The head-end chamber is fluidly coupled to a first suction valve through a first gas suction port and to a first delivery valve through a first gas delivery port. The crank-end chamber is fluidly coupled to a second suction valve through a second gas suction port and to a second delivery valve through a second gas delivery port. 
     Thus, the double-acting reciprocating compressor is adapted to suck gas in one of the crank-end chamber and head-end chamber through the respective suction valve, while gas is compressed in the other of the crank-end chamber and head-end chamber and finally delivered through the respective delivery valve. 
     Each crank-end chamber and head-end chamber can be fluidly coupled to more than one suction valve and one delivery valve. For instance, two respective suction valves and two respective delivery valves can be fluidly coupled to each one of said head-end chamber and crank-end chamber, to maximize gas flow and minimize head losses. 
     The larger the number of suction valves and delivery valves, the more beneficial the use of gas inlet plenum and gas discharge plenum manufactured separately from the compressor barrel, as this gives more freedom in shaping the gas ducts in the gas inlet and discharge plenums, and imposes less space and mechanical constraints. 
     All suction valves can be fluidly coupled to a single gas inlet plenum. All delivery valves can be fluidly coupled to a single gas discharge plenum. 
     The suction valves and the delivery valves can be automatic valves, which open and close responsive to a pressure difference thereacross. 
     The piston can be connected to a rotary crankshaft trough a connecting rod. Large reciprocating compressors, especially double-acting reciprocating compressors as disclosed herein are further provided with a piston rod and a crosshead. The piston, the piston rod and the cross-head are controlled according to a reciprocating rectilinear motion imparted to the crosshead by the rotary crankshaft and the connecting rod. 
       FIG. 2  illustrates a schematic sectional view of a cylinder and relevant components of a double-acting reciprocating compressor  1  according to the present disclosure in one embodiment. The section is taken along the axis of the reciprocating compressor cylinder. 
     According to embodiments disclosed herein, the compressor  1  can comprise a compressor head  3 , a compressor frame  5  and a distance piece  7 , which connects the compressor head  3  to the compressor frame  5 . The compressor head  3  contains the compression chamber, as will be described below. 
     A crankshaft  9  is arranged in the compressor frame  5  for rotation around a shaft axis  9 A. A prime mover, not shown, drives the crankshaft  9  into rotation around the axis  9 A. The prime mover can be a reciprocating internal combustion engine, such as a Diesel engine. In other embodiments, the prime mover can be a reciprocating external combustion engine, such as a Stirling engine. The reciprocating compressor  1  can also be driven by a gas turbine engine, by a steam turbine, or by an electric motor, for instance. 
     A connecting rod  11  connects the crankshaft  9  to a crosshead  13 . The crosshead  13  is guided along cross-head guides  15  housed in the frame  5 . The rotation motion of the crankshaft  9  (arrow f 9 ) is thus converted into a reciprocating motion of the crosshead  13  (arrow f 13 ). A piston rod  17  connects the crosshead  13  to a piston  19 , which is adapted to reciprocatingly slide in a chamber  21  of a compressor barrel  18 . The piston  19  divides the chamber  21  in two compression chambers, namely a head-end chamber  21 A, and a crank-end chamber  21 B. 
     One or more respective suction valves are provided to fluidly connect the head-end chamber  21 A and the crank-end chamber  21 B selectively with a gas inlet plenum  20 . One or more respective delivery valves are further provided to fluidly connect the head-end chamber  21 A and the crank-end chamber  21 B selectively with a gas discharge plenum  22 . 
     The gas inlet plenum  20  is fluidly coupled to a low-pressure gas source  31 , and the gas discharge plenum  22  is fluidly coupled to a high-pressure gas source  33 . 
     In the sectional view of  FIG. 2  a single gas suction valve for each chamber  21 A,  21 B and a single gas delivery valve for each chamber  21 A,  21 B are visible. A plurality of such gas suction valves and gas delivery valves can be provided for each one of said head-end chamber  21 A and crank-end chamber  21 B. Specifically in the sectional view of  FIG. 2  a first gas suction valve  23 A is shown for fluidly connecting the head-end chamber  21 A with the gas inlet plenum  22  and a second gas suction valve  23 B is shown for fluidly connecting the crank-end chamber  21 B to the gas inlet plenum  22 . Similarly, a first gas delivery valve  25 A is provided for fluidly connecting the head-end chamber  21 A with the gas discharge plenum  25  and a second gas delivery valve  23 B is shown for fluidly connecting the crank-end chamber  21 B to the gas discharge plenum  22 . 
     In the cross-sectional view of  FIG. 3  a total of four gas valves, namely two gas suction valves and two gas delivery valves, are shown in fluid communication with the head-end side chamber  21 A. A similar arrangement is provided for the crank-end chamber  21 B. 
     In other embodiments, not shown, a different number of valves can be provided for each chamber. 
     The gas suction valves  23 A,  23 B and the gas delivery valves  25 A,  25 B can be automatic valves, i.e. valves which automatically open and close in response to a pressure differential thereacross. 
     As known, the reciprocating motion of the piston  19  according to double arrow f 19  causes gas to be sucked through gas suction valves  23 A,  23 B from the gas inlet plenum  20  in the head-end chamber  21 A and in the crank-end chamber  21 B, selectively. Simultaneously, gas is compressed is selectively compressed in the crank-end chamber  21 B and in the head-end chamber  21 A and discharged through the gas delivery valves  25 B,  25 A in the discharge plenum  22 . 
     The gas suction valves  23 A,  23 B and the gas delivery valves  25 A,  25 B can be housed in respective valve seats schematically shown at  27 A,  27 B for the gas suction valves  23 A,  23 B and at  29 A,  29 B for the gas delivery valves  25 A,  25 B, see also  FIG. 3 . The valve seats  27 A,  27 B are in fluid communication with the respective head-end chamber  21 A and crank-end chamber  21 B through respective gas suction ports  30  ( FIG. 3 ). The valve seats  29 A,  29 B are in fluid communication with the respective head-end chamber  21 A and crank-end chamber  21 B through respective gas delivery ports  32  ( FIG. 3 ). 
     The valve seats  27 A,  27 B and  29 A,  29 B are arranged in the compressor barrel  18 , develop along the thickness thereof and have respective gas inlet apertures  34  and gas outlet apertures  36  on the outer surface of compressor barrel  18 . 
     The gas inlet plenum  20  and the gas discharge plenum  22  are mounted on the outer surface of the compressor barrel  18 . The gas inlet plenum  20  can be provided with a total number of gas ports  20 A equal to the total number of suction valves  23 A,  23 B of the compressor head  3 . The gas discharge plenum  22  can in turn be comprised of a total number of gas ports  22 A equal to the total number of delivery valves  25 B of the compressor head  3 . 
     The arrangement of the gas ports and apertures of the gas discharge plenum  22 , the gas inlet plenum  20  and the valve seats  27 A,  27 B,  29 A,  29 B is such that gas flows in a substantially axial direction from the gas outlet  20 A of the gas inlet plenum  20  towards and through the valve seats  27 A,  27 B and the respective gas suction valves  23 A,  23 B. Moreover, the gas flows in a substantially axial direction through the gas delivery valves  25 A,  25 B, the valve seats  29 A,  29 B towards the gas ports  22 A of the gas discharge plenum  22 . 
     The term “axial direction” as used herein can be understood as a direction substantially parallel to an axial extension of the gas suction valves  23 A,  23 B and gas delivery valves  25 A,  25 B, along which the gas flows through the respective valves. 
     By arranging the gas inlet plenum  20  and the gas discharge plenum  22  outside the barrel  18 , the gas flow is optimized, since no sharp 90° bent is required for the gas upon entering the valve seats. The gas inlet plenum  20  and the gas discharge plenum  22  can be designed with a higher degree of freedom, as they do not require to be housed in the reduced space available within the thickness of the compressor barrel, as in the reciprocating compressors of the current art. The shape of the inner gas passages in the gas inlet plenum  20  and gas discharge plenum  22  can be optimized for reduced pressure losses. 
     In addition, manufacturing of the barrel  18  is made simpler. As a matter of fact, the barrel  18  can have a simple cylindrical shape, and can be obtained by forging or centrifugal casting. The valve seats  27 A,  27 B and  29 A,  29 B can be produced by simple machining through the cylindrical wall of the semi-finished barrel  18 . 
     Additionally, cooling ducts  38  ( FIG. 3 ) can be provided in the semi-finished barrel  18 . In some embodiments, the cooling ducts  38  extend parallel to the barrel axis, i.e. parallel to the direction of the reciprocating motion of the piston  19  in the chamber  21 , as shown in  FIG. 3 . Machining of the cooling ducts  38  is simple and inexpensive, if compared to the manufacturing of complex cooling ducts in the barrels of the current art. 
     In other embodiments, the valve seats  27 A,  27 B,  29 A,  29 B and/or the cooling ducts  38  can be produced during casting. 
     According to some embodiments, the cooling ducts and/or the valve seats are produced by chip-removal machining. 
     The gas inlet plenum, or the gas discharge plenum or both can be manufactured by additive manufacturing. This manufacturing technique allows the production of components having a complex shape at low cost. The shape of the gas flow paths inside the gas inlet plenum and the gas discharge plenum can be designed such as to achieve optimum flow conditions and minimize losses. Additive manufacturing allows production of flow ducts of substantially any shape, no matter how complex they are. The additive manufacturing process can be selected from the group comprising: Selective Laser Sintering (SLS), Powder bed fusion (PBF), Selective Laser Melting (SLM), Direct Metal Laser Sintering (DMLS), Electron Beam Melting (EBM), Multi Jet Fusion (MJF). 
     Both the gas inlet plenum and the gas discharge plenum can be manufactured as a single, monolithic piece of machinery, without the need for connecting to one another two or more elements, e.g. by soldering, welding, screwing or the like. The resulting single-piece monolithic plenum meets higher quality standards. Production of scraps or defective components is prevented or limited. The manufacturing process is faster and requires less manufacturing skill. 
     The gas inlet plenum  20  and the gas discharge plenum  22  can be mounted around the compressor barrel  18  and coupled thereto by any suitable means. For instance, connecting flanges can be provided around each inlet aperture  34  and each outlet aperture  36 . The flanges can be connected to the compressor barrel  18  e.g. by means of screws, such that the gas inlet plenum and the gas discharge plenum can be easily disassembled from the compressor barrel  18 , e.g. in order to repair or replace the suction valves and delivery valves, as required. 
     In less advantageous embodiments, the gas inlet plenum and the gas discharge plenum can be manufactured by assembling to one another pipe sections, which can in turn be made by any manufacturing process suitable for pipe manufacturing. 
     While the disclosed embodiments of the subject matter described herein have been shown in the drawings and fully described above with particularity and detail in connection with several exemplary embodiments, it will be apparent to those of ordinary skill in the art that many modifications, changes, and omissions are possible without materially departing from the novel teachings, the principles and concepts set forth herein, and advantages of the subject matter recited in the appended claims. Hence, the proper scope of the disclosed innovations should be determined only by the broadest interpretation of the appended claims so as to encompass all such modifications, changes, and omissions. In addition, the order or sequence of any process or method steps may be varied or re-sequenced according to alternative embodiments.