Abstract:
A radial turbocompressor having at least two compressor stages is provided. A motor is co-axially located on a shaft with radial impellers of the compressor stages, and the motor and the compressor stages are arranged in a common, vertically-split housing. The medium to be compressed enters the housing through an intake opening in the housing, flows past and/or through the motor, and then is compressed in the compressor stages. The medium leaves the housing through an discharge opening that is arranged co-axially with the shaft, thereby minimizing axial forces in the turbocompressor.

Description:
[0001]    This application is a National Phase of PCT International Application No. PCT/EP2012/066672, filed Aug. 28, 2012, which claims priority under 35 U.S.C. §119 from German Patent Application No. 10 2011 081 801.4, filed Aug. 30, 2011 and German Patent Application 10 2012 016 844.6, filed Aug. 27, 2012, the entire disclosures of which are herein expressly incorporated by reference. 
     
    
     BACKGROUND AND SUMMARY OF THE INVENTION 
       [0002]    The invention relates to a radial turbocompressor having at least two compressor stages, wherein a motor drives radial impellers of the compressor stages which are arranged on a shaft, wherein the motor and the compressor stages are arranged in a common housing and a medium enters the housing through an intake opening, and wherein one part of the medium is guided through the motor and another part flows past the motor, both parts are then brought back together, are compressed and exit the housing through a discharge opening. 
         [0003]    Both blowers and compressors can be used for the delivery of gases, the fundamental differences being in their construction and field of application. In contrast to compressors, blowers are set up for high flow rates and produce only a small increase in pressure. 
         [0004]    German patent document no. DE 60016886 T2 describes a blower acting as an air pump and used for inflating air mattresses, bicycle tires or sports balls. The air is delivered by impeller wheels which are arranged in a housing made of hard plastic. 
         [0005]    As their name suggests, compressors are set up for compressing gases. During this process, and under appropriate operating conditions, the gas can also enter a supercritical state. The turbocompressor according to the invention is preferably used for the delivery of carbon dioxide. During the compression step, the carbon dioxide passes from a gaseous state to a supercritical state as the critical temperature is only 31.0° C. and carbon dioxide has a relatively low critical pressure of just 73.8 bar. The carbon dioxide is sometimes already in a supercritical state upon entry to the compressor. In order to encompass both gases and supercritical fluids, reference is made in the context of the invention to a medium which is compressed. 
         [0006]    Compressors can operate either according to the displacement principle or the dynamic principle. In the case of the displacement principle, compression is achieved by enclosing a body of gas and then reducing the space in which the gas is contained. Examples of compressors operating according to the displacement principle are reciprocating-piston compressors and rotary piston compressors. 
         [0007]    By contrast, the present invention relates to compressors operating according to the dynamic principle. In the case of the dynamic principle, the gas is strongly accelerated in an impeller and is compressed by deceleration in a downstream diffuser. Compressors operating according to the dynamic principle are called turbocompressors. 
         [0008]    Turbocompressors fall into one of two main types: axial turbocompressors and radial turbocompressors. In axial turbocompressors, the gas flows through the compressor in a direction parallel to the shaft. 
         [0009]    The present invention relates to radial turbocompressors. The gas flows axially into the impeller of the compressor stage and is then accelerated, by centrifugal force, radially outward in the impeller intermediate space which narrows in the manner of a nozzle. The gas leaves the impeller intermediate spaces with great speed at the impeller circumference and flows into the diffuser. In the case of conventional radial turbocompressors, after the last compressor stage, the gas flows away radially outward through a pressure pipe oriented vertically with respect to the rotor axis. 
         [0010]    The compressor stages are driven by a motor. The electric motor comprises a rotor and a stator. In the case of the present invention, the rotor and the radial impellers are arranged on a common shaft. 
         [0011]    The prior art discloses embodiments in which the compressor stages and the motor are in each case surrounded by an individual housing, wherein the motor shaft leaves the motor housing and enters the compressor stage housing. 
         [0012]    By contrast, in the case of the present invention, the motor and the compressor stages are arranged in a common housing. The gas enters the housing through an intake opening. The uncompressed medium first flows past the motor and is then compressed. After passing through the compressor stages, the medium leaves the housing through a discharge opening. 
         [0013]    In the case of conventional radial turbocompressors, the housing is often split horizontally. During assembly, the shaft together with the impellers is placed in the lower half of the housing. The upper half of the housing contains the intake pipe and the pressure pipe, which are formed perpendicularly outward on the upper half of the housing. The two halves are then brought together. The medium is supplied and removed through the pipes which project vertically outward with respect to the axis of rotation of the shaft. 
         [0014]    Turbocompressors often have to be integrated inside a machine building. This often raises problems in terms of space, owing to the arrangement of many other apparatus and machines. In addition, largely vibration-free operation of the turbocompressor has to be guaranteed in order that neither the machine itself nor adjacent apparatus are damaged. To this end, costly mounting of the rotor by means of axial and radial bearings is necessary. Costly bearing constructions are necessary in order to compensate for the axial force of the impellers. 
         [0015]    Against this technical backdrop, the present turbocompressor is constructed in such a manner that it has a compact and stable construction and compensates for the axial force in a simple and cost-effective manner by virtue of the fact that the discharge opening is arranged centrally in the axial direction with respect to the axis of rotation of the shaft. 
         [0016]    In the final compressor stage, the medium first flows through a radial impeller and is then guided into a diffuser. A return duct feeds the medium to the axial discharge opening. 
         [0017]    In contrast to conventional turbocompressors, the medium leaves the housing not through a pressure pipe arranged radially with respect to the shaft but through a discharge opening arranged axially with respect to the axis of rotation of the shaft. The housing is embodied as a compact pressure vessel whose cylindrical casing does not have any disruptive pressure pipes but instead a discharge opening on the end face of the pressure vessel. The connection flanges employed in the case of the present invention are very stable in comparison to pressure pipes which lead away perpendicularly. 
         [0018]    The axial arrangement of the discharge opening, centrally with respect to the shaft, means that the outlet pressure of the medium in the axial direction acts as a reaction force on the outlet-side end of the shaft. This compensates for the axial force. 
         [0019]    Preferably, the intake opening of the turbocompressor is also arranged centrally in the axial direction with respect to the axis of rotation of the shaft. The housing, embodied as a cylindrical pressure vessel, then has no pipes on the casing surface. Both the supply and removal of the medium occur via the end faces of the cylindrical pressure vessel. The end faces are preferably formed as curved bases on the casing part of the pressure vessel. The circular intake opening is introduced into the center of one base. The circular discharge opening is introduced into the center of the opposite base. 
         [0020]    The described compressor very efficiently compresses the medium which is guided through, although a considerable quantity of heat can nonetheless be released in the motor. It is an object of the invention to simply and cost-effectively remove the waste heat generated. 
         [0021]    The impellers of the turbocompressor are preferably driven by an electric motor having a rotor and a stator. In an embodiment of the compressor according to the invention, the medium is split into two partial flows, wherein a first partial flow of the medium is guided past between the stator of the motor and a static component of the turbocompressor and a second partial flow is fed through the motor, in particular between the rotor and stator of the motor. The static component can be the housing itself or a component connected to the housing. The medium which is guided past takes up heat and thus serves to cool the motor. After passing the motor region, the two partial flows are reunited and enter the first compressor stage, in which the medium is compressed. In one variation, the second partial flow can also be guided through the stator of the motor. Corresponding ducts must be provided to this end. 
         [0022]    In an advantageous configuration of the invention, bearings, in particular radial bearings and axial bearings, are arranged between the motor and the impellers. The arrangement at this location prevents excessive heating of the bearings as the medium is not yet in a compressed state. 
         [0023]    For further cooling of the device, it is proposed that the surface be configured so as to favor a transfer of heat between the individual components of the compressor and the medium. To that end, the surface of the components is to be roughened so as to increase the surface area while at the same time markedly preventing the formation of eddies. If this transfer is carried out at a point at which the medium is not yet compressed, the temperature difference between the medium and the components is very large, thus favoring the process. 
         [0024]    The present invention is very advantageously employed for use in a heat pump in which a heat transfer medium is pumped. The heat produced by the motor is supplied to this heat transfer medium, thus increasing an increase in the overall efficiency of such an installation as practically no electrical power is lost. The waste heat from the motor can be directly recovered upon compression of the heat transfer medium. 
         [0025]    In one advantageous configuration, CO2 is used as heat transfer medium. This gas is chemically harmless and is available at low cost almost everywhere. For use in a heat pump, it can be employed in the critical region, where the physical properties can be used to particularly good effect. 
         [0026]    Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0027]      FIG. 1  shows a turbocompressor in accordance with an embodiment of the present invention in axial section, 
           [0028]      FIG. 2  shows the guiding paths of the medium of  FIG. 1  in the turbocompressor, 
           [0029]      FIG. 3  is a perspective representation of the compressor stages of  FIG. 1 , 
           [0030]      FIG. 4  shows the  FIG. 3  compressor stages in axial section, 
           [0031]      FIG. 5  is a perspective cutaway representation of the housing of the turbocompressor of  FIG. 1 , 
           [0032]      FIG. 6   a  is a perspective view of a radial impeller in accordance with an embodiment of the present invention, and 
           [0033]      FIG. 6   b  is a perspective view of the  FIG. 6A  radial impeller, represented without a cover disk. 
       
    
    
     DETAILED DESCRIPTION 
       [0034]      FIG. 1  shows an axial section through an oil-free turbocompressor which, in the exemplary embodiment, is designed for the delivery of carbon dioxide. The guiding paths of the carbon dioxide are represented in  FIG. 2 . In the following, both figures are referred to in parallel, where the components are detailed in  FIG. 1  and  FIG. 2  shows the guiding paths. 
         [0035]    The carbon dioxide enters the housing  2  of the turbocompressor through the intake opening  1 . In the exemplary embodiment, the carbon dioxide has at the intake opening  1  a pressure of 38 bar and a temperature of 8° C. The carbon dioxide flow splits into two partial flows  3 ,  4 . 
         [0036]    The as-yet uncompressed carbon dioxide flows past the motor  5  of the turbocompressor. The motor  5  is embodied as an electric motor. It is a two-pole permanent magnet machine rotating, at the reference point, at 141,000 rpm. The motor  5  is arranged on the low-pressure side of the compressor. It comprises a rotor  6  and a stator  7 . The active part of the rotor  6  consists of a cylindrical, diametrically magnetized solid magnet. The magnet is encased on account of its mechanical properties. 
         [0037]    The stator  7  is made up of individual metal plates. The grooves are insulated from copper windings by an insulating foil. The motor  5  is cooled by the carbon dioxide flowing past. 
         [0038]    A gap exists between the rotor  6  and the stator  7 . The inner partial flow  4  flows through this gap between the rotor  6  and the stator  7 . In order to reduce friction losses, a free-floating axially mounted sleeve  8  can be inserted into the gap. The inner partial flow  4  is guided through between the rotor  6  and the floating sleeve  8  and between the sleeve  8  and the stator  7 , and in so doing removes heat. As the gaps between the sleeve  8  and the rotor  6  and between the sleeve  8  and the stator  7  are very small, a pressure loss arises which must be considered when designing the turbocompressor. 
         [0039]    The outer partial flow  4  is fed past between the stator  7  and a static component  9 . The static component  9  is an inner support structure. The outer partial flow  4  cools the stator  7 . It is fed along the winding heads and the laminated core. In order to set the ratio between the two partial flows  3 ,  4 , a throttle is integrated into the path of the outer partial flow  4 . A split of 97% outer partial flow  4  to 3% inner partial flow  3  has proven particularly advantageous. A 3% proportion of the inner partial flow allows the rotor  6  to be cooled to approx. 50° C. 
         [0040]    The stator  7  is attached to the inner support structure. The inner support structure, for its part, is secured to the main flange  10  of the housing  2 . 
         [0041]    The magnet of the rotor  6  is shrunk into a shaft  11 . In addition, three radial impellers  12  are secured on the shaft  11 . The shaft  11  is mounted with two radial gas bearings  13  and one axial gas bearing  14 . The turbocompressor is entirely oil-free. 
         [0042]    Both partial flows  3 ,  4  are united before entering the first compressor stage. The carbon dioxide is compressed in the three compressor stages to a pressure of 90 bar and exits at the discharge opening  19 . According to the invention, the discharge opening  19  is arranged centrally in the axial direction with respect to the axis of rotation of the shaft  11 . At the outlet, the carbon dioxide is in a supercritical state. 
         [0043]      FIG. 3  shows the three radial impellers  12  arranged one behind another. The radial impellers  12  are arranged in parallel next to one another on the shaft  11 . In this case they are closed radial impellers. The carbon dioxide enters inlet openings  15  of the radial impellers  12  in the axial direction and exits in the radial direction from the outlet openings  16 . The carbon dioxide is compressed from left to right as seen in the depiction and hence always in the same axial direction. 
         [0044]      FIG. 4  shows an axial section through the three compressor stages. After the radial impeller  12 , the carbon dioxide passes into a diffuser  17  and then flows on into a return duct  18 . Kinetic energy is imparted to the carbon dioxide in the radial impellers  12  and is converted to pressure energy in the diffusers  17 . The return ducts  18  feed the carbon dioxide to the next compressor stage. According to the invention, in the final compressor stage, the carbon dioxide flows first through a radial impeller  12 , then through a diffuser  17  and then through a return duct  18  which feeds the carbon dioxide directly to the discharge opening  19  which is arranged centrally in the axial direction with respect to the axis of rotation of the shaft  11 . 
         [0045]      FIG. 5  shows the housing  2  of the turbocompressor. The housing  2  is embodied as a cylindrical pressure vessel. According to the invention, the housing  2  is split vertically. It consists of the main flange  10 , an intake-side part  20  and a discharge-side part  21 . The discharge-side part  21  consists of a flange ring  22 , a tubular piece  23  and a torispherical head  24  which are welded together to form one component. At the center of the torispherical head  24  is a connection piece  25  which projects outward in the axial direction and has a duct as discharge opening  19  for the carbon dioxide. 
         [0046]    The intake-side part  20  of the housing  2  has a torispherical head  26 . The intake opening  1  is introduced into the housing  2  at the center of the torispherical head  26 . The intake opening  1  and the discharge opening  19  lie on an axis A A′ which passes axially through the center of the cylindrical housing  2 . 
         [0047]    The main flange  10  supports all the integrated elements and provides space for leadthroughs such as the electrical supply or temperature probe. The main flange  10  serves as a basic element for the assembly as all integrated elements are secured to the main flange  10 . 
         [0048]      FIGS. 6   a  and  6   b  show the construction of the radial impellers  12 .  FIG. 6   a  shows the assembled state with cover disk  27 . The cover disk  27  is not shown in  FIG. 6   b  in order to show the inside of the radial impeller  12 . The blades  28  of the radial impeller  12  are formed on a support body  29 . The cover disk  27  is manufactured separately and is positioned on the support body  29  having its blades  28 . The cover disk  27  is connected over the entire surface to the upper edges of the blades  28  and therefore rotates, when the turbocompressor is in operation, at the same rotational speed as the support body  29  having its blades  28 . The radial impellers  12  are pushed onto the shaft  11  via the hub  30 . 
         [0049]    The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.