JP2011043130A - Centrifugal compressor and refrigeration equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a highly efficient centrifugal compressor for a turbo refrigerating machine and a refrigeration equipment with wide operating range in various flow volume conditions. <P>SOLUTION: The centrifugal compressor of the refrigeration equipment is provided with several stages of impeller 9, a diffuser with vanes 10 and a vaneless diffuser 19 positioned on the outer periphery of each impeller 9, and a return flow path 11 which connects the diffuser with vane 10 and the impeller 9 on the back stage. Several movable downstream guide vanes 13 are positioned in the circumferential direction of the return flow path 11 which leads to the impeller 9 on the last stage, and the diffuser on the last stage is composed of the vaneless diffuser 19 in which a diffuser vane is installed. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a centrifugal compressor and a refrigeration apparatus, and more particularly to a centrifugal compressor and a refrigeration apparatus for a turbo chiller having a diffuser and a guide vane whose flow rate can be controlled during partial load operation.

  A turbo chiller used for air conditioning is a refrigeration system based on a vapor compression refrigeration cycle. It consumes power from a centrifugal compressor and takes heat from an object to be cooled via an evaporator. Heat is discharged from the low temperature to the high temperature by discharging heat to the high temperature part.

  The operation state of the centrifugal chiller is roughly divided into a rated operation which is 100% output operation and a partial load operation which is other output operation. In general, turbo chillers are designed to meet the performance of rated operation, but the operating conditions change sequentially according to the usage environment. Required.

  Accordingly, the present invention relates to expansion of the operating range and efficiency of a turbo chiller in partial load operation. Similarly, Patent Documents 1, 2, and 3 are related to expansion of the operating range and efficiency improvement.

Japanese Patent Laid-Open No. 2001-200787 JP 2002-327700 A JP-A-8-284892

  As shown in FIG. 8, the conventional centrifugal compressor 1 ′ includes an inlet guide vane 16 ′ provided in the first stage suction portion, an impeller 9 ′ provided in a plurality of stages, and a downstream side of each impeller. A vane diffuser 10 'provided, a return passage 11' installed downstream of the vane diffuser 10 'and guiding the flow to a subsequent impeller, and a circular blade row disposed in the return passage 11' A fixed guide vane 17 'is provided.

  In such a configuration, the inlet guide vane 16 'is provided with a mechanism that can move around the rotation shaft, and the centrifugal compressor can be operated by operating the centrifugal chiller by changing the flow angle of the fluid flowing into the impeller. The flow rate can be arbitrarily controlled according to the above.

  However, in the conventional centrifugal compressor for a centrifugal chiller shown in FIG. 8, the inlet guide vane 16 'is not installed in the rear stage, which causes the problem that the rear impeller is stalled during partial load operation and the operating range is narrowed. is there.

  Further, in a conventional centrifugal compressor for a centrifugal chiller, as shown in FIG. 8, a vaned diffuser 10 'is installed on the downstream side of each impeller for the purpose of improving the efficiency during rated operation. The vane diffuser 10 'is a diffuser in which a plurality of diffuser vanes 18' are attached in the circumferential direction.

  Generally, the diffuser vane 18 'is designed so that the impeller outflow angle and the vane inlet angle of the diffuser vane 18' substantially coincide with each other in rated operation. At this time, the compressor can obtain high efficiency. Efficiency decreases due to changes in the car outflow angle.

  Accordingly, an object of the present invention is to provide a centrifugal compressor and a refrigeration apparatus for a centrifugal chiller having a wide operating range and high efficiency under various flow conditions.

  In order to solve the above problems, the present invention employs the following configuration.

  A centrifugal compressor according to the present invention is a centrifugal compressor provided with a plurality of impellers, a plurality of diffusers disposed on the outer periphery of each impeller, and a return flow path connecting the diffuser and the subsequent impeller. A plurality of movable guide vanes are arranged in the circumferential direction in the return flow path connected to the final stage impeller, and the final stage diffuser is configured by a vaneless diffuser in which no diffuser vane is provided.

  Alternatively, the refrigeration apparatus according to the present invention includes a centrifugal compressor including a plurality of impellers, a plurality of diffusers disposed on the outer periphery of each impeller, and a return flow path connecting the diffuser and the subsequent impeller. In the refrigerating apparatus in which a refrigerating cycle is configured by sequentially connecting an evaporator, a condenser, and an intercooler, a movable guide vane is provided in a return flow path connected to the impeller at the final stage of the centrifugal compressor. Are arranged in the circumferential direction, and the last stage diffuser is constituted by a vaneless diffuser in which no diffuser vane is provided.

  According to the present invention, it is possible to provide a centrifugal compressor and a refrigeration apparatus for a centrifugal chiller that have a wide operating range and high efficiency under various flow conditions.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows 1st Example which concerns on this invention, Comprising: It is sectional drawing of the centrifugal compressor in 1st Example. It is the schematic which shows the system configuration | structure of the centrifugal compressor in a 1st Example. It is a refrigerating cycle diagram in the 1st example. It is the figure which showed the arrangement | positioning of the upstream guide vane and downstream guide vane in 1st Example, and the axial support position of a downstream guide vane. It is the graph which showed the relationship between the flow volume and efficiency of a diffuser with a vane and a vaneless diffuser. It is the graph which showed the flow rate of a diffuser with a vane and a vaneless diffuser, and the relationship of a heat insulation head. It is a figure which shows 2nd Example which concerns on this invention, Comprising: It is sectional drawing of the centrifugal compressor in 2nd Example. It is sectional drawing of the conventional centrifugal compressor.

  Hereinafter, embodiments of the present invention will be described.

  A centrifugal compressor according to this embodiment includes a plurality of impellers, a plurality of diffusers disposed on the outer periphery of each impeller, and a return flow path that connects the diffuser and a subsequent impeller. , A plurality of movable guide vanes are arranged in the circumferential direction in the return flow path connected to the final stage impeller, and the final stage diffuser is configured by a vaneless diffuser in which no diffuser vane is provided. .

  Further, the refrigeration apparatus according to the present embodiment includes a plurality of impellers, a plurality of diffusers disposed on the outer periphery of each impeller, and a centrifugal compression unit including a return flow path that connects the diffuser and the subsequent impeller. And a refrigerating apparatus in which a refrigerating cycle is configured by sequentially connecting an evaporator, a condenser, and an intercooler, a movable guide is provided in a return flow path connected to the final impeller of the centrifugal compressor. A plurality of vanes are arranged in the circumferential direction, and the last-stage diffuser is configured by a vaneless diffuser in which no diffuser vane is provided.

  According to the above configuration, the flow rate of the rear-stage impeller can be controlled by the movable guide vane arranged in the return flow path connected to the final-stage impeller, and the efficiency and operating range at the partial load are expanded. In addition, the movable guide vane and the vaneless diffuser provided in the final stage suppress the stall in the partial load operation and expand the operating range. Therefore, a refrigeration apparatus including such a centrifugal compressor can be operated with high efficiency in a stable state even during partial load operation.

  In addition, at least one of the diffusers other than the final stage is configured by a vaned diffuser including a plurality of diffuser vanes in the circumferential direction. Therefore, the vane diffuser can minimize the loss in the return flow path and guide a uniform flow to the downstream side, so that the efficiency of the centrifugal compressor can be increased.

  A fixed guide vane is disposed in the return flow path upstream of the movable guide vane. Therefore, the diffuser with vanes can minimize the loss in the return flow path and can guide a uniform flow to the stationary guide vanes, so that it is possible to improve the efficiency of the centrifugal compressor. Become.

  The ratio of the exit radius of the stage impeller provided with the vane diffuser and the exit radius of the vane diffuser is set to 1.3 to 1.8.

  Hereinafter, Example 1 will be described in detail with reference to the accompanying drawings. Embodiment 1 is a two-stage turbo refrigeration engine based on a vapor compression refrigeration cycle as a basic principle. FIG. 2 schematically shows the configuration of the turbo refrigerator according to the first embodiment, and FIG. 3 schematically shows a refrigeration cycle diagram based on the ph diagram.

This turbo refrigerator includes a two-stage centrifugal compressor as shown in FIG. 2, and operates according to the following principle. As shown in FIG. 3, the refrigerant that is the wet steam at the state point S <b> 9 takes heat from the object to be cooled in the evaporator 5 and reaches the state point S <b> 1. The refrigerant whose state has been changed to superheated steam is adiabatically compressed in the first stage of the centrifugal compressor 1 to increase the internal energy, and the pressure is increased to the state point S2 having a higher degree of superheat. The refrigerant at the state point S2 takes in the flash vapor generated at the time of expansion by the economizer 4 and reaches the state point S3. The state point the compressor second stage In S3 the state point S4, with additional superheat is raised to a pressure P _4.

Thereafter, in the process of passing through the condenser 2, the refrigerant passes the amount of heat transported to the cooling water, is cooled, undergoes a state change to dry saturated steam, wet steam, and saturated liquid, and then goes to the state point S5 that is a supercooled liquid. Reach. The refrigerant that has become the supercooled liquid passes through the liquid receiver 3 with the state point S5 and flows into the economizer 4. The economizer 4 is once depressurized to an intermediate pressure P _eco and separated into flash vapor and high-pressure liquid generated at that time. Of these, only the high-pressure liquid is squeezed and expanded to the evaporation pressure P ₁ , returns to wet steam at the state point S9, and repeats the same cycle again.

  As shown in FIG. 1, the centrifugal compressor 1 employs a two-stage turbo centrifugal compressor, includes an inlet guide vane 16 in the first stage suction portion, and each stage rotates and rotates. There is an impeller 9 provided with blades that are held by the rotating shaft 8 and provided at substantially equal intervals in the circumferential direction, and a plurality of diffuser vanes 18 arranged in the circumferential direction are provided on the outer periphery of the first stage impeller 9a. A vaneless diffuser 10 having a vaneless diffuser 19 having no diffuser vane is installed on the outer periphery of the second stage impeller 9b, and a return flow path 11 and a refrigerant are discharged as a stationary flow path connecting the stages. A scroll 15 is provided.

  The return flow path 11 is provided with a fixed upstream guide vane 12 (corresponding to the fixed guide vane) and a movable downstream guide vane 13 (corresponding to the movable guide vane). Make it. In the centrifugal compressor 1 of the first embodiment, the downstream guide vane 13 is rotatably supported via the downstream guide vane rotating shaft 14 and is rotated by the driving device 7 provided in the vane.

  In the above-described configuration, the refrigerant drawn into the inlet guide vane 16 through the suction port by the rotation of the first stage impeller 9a is increased and increased in pressure by the centrifugal action of the first stage impeller 9a, and passes through the vaned diffuser 10. The kinetic energy is converted into internal energy by being decelerated in the process, and is further decelerated by the upstream guide vane 12 and the downstream guide vane 13 installed in the return flow path 11, and in the rated operation, an axial flow is given. It is guided to the second stage impeller 9b. Further, in the partial load operation, a pre-turn angle corresponding to the operation state is given, and it is guided to the second stage impeller 9b.

  FIG. 4 shows the arrangement of the upstream guide vane 12 and the downstream guide vane 13 and the support position of the downstream guide vane rotating shaft 14 in the first embodiment. During rated operation, a line connecting the rear edge 12a of the upstream guide vane 12 and the front edge 13a of the downstream guide vane 13 (shown by a broken line in FIG. 4) is installed so as to face in the radial direction. Remove and guide to the second stage impeller 9b.

  On the other hand, when the flow rate changes such as in partial load operation, the inflow angle to the second stage impeller 9b becomes too large (or small) with respect to the blade inlet angle, the impeller stalls, and the operating range is narrowed. In order to avoid such a situation, the downstream guide vane 13 (shown by a solid line in FIG. 4) is rotated by the downstream guide vane rotating shaft 14 to give a swirl component to the fluid, and the inflow angle to the impeller and the blade inlet angle Eliminate the gap. The relationship between the upstream guide vane 12 and the downstream guide vane 13 in the first embodiment is as follows.

The front and rear edge radius difference L ₁ of the upstream guide vane 12 is used as the front edge radius r ₂ and the rear edge radius r ₂ , and the front and rear edge radius difference L ₂ of the downstream guide vane 13 is used as the front edge radius r ₃ and the rear edge radius r _4. , Formula (1), Formula (2)
L ₁ = r ₁ −r ₂ (1)
L ₂ = r ₃ −r ₄ (2)
When expressed in the leading and trailing-edge radius difference L ₂ of the upstream guide the front and rear vanes 12 edge radius difference L ₁ and downstream guide vane 13 to the same length. That is, Formula (3)
L ₁ = L ₂ (3)
It is.

As described above, when the flow rate changes such as in partial load operation, it is necessary to give a pre-turn to the second stage impeller 9b. At this time, for example, if L ₁ > L ₂ , the downstream guide vane rotation angle necessary for obtaining the pre-turning angle in an arbitrary operation state increases. As a result, the angle of the downstream guide vane with respect to the flow becomes too large, pressure loss increases in the entire flow rate region, and efficiency decreases.

  On the other hand, when the flow rate decreases, the angle of attack of the refrigerant flowing into the upstream guide vane 12 increases, and the flow stalls at the trailing edge of the blade. Therefore, the pressure loss increases and the efficiency decreases. In the first embodiment, by rotating the downstream guide vane 13, a gap is formed between the trailing edge of the upstream guide vane 12 and the leading edge of the downstream guide vane 13, and high energy on the pressure surface side of the upstream guide vane 12 from this gap. The fluid is guided to the suction side and energy is supplied to the stalled area.

By the action of the flow that has passed through such a gap, the separation of the flow at the trailing edge of the upstream guide vane 12 is eliminated, the pressure loss can be reduced, and the efficiency can be improved. At this time, if the pivot position radius of the downstream guide vane rotating shaft 14 is r _rot , the difference L _rot between the leading edge of the downstream guide vane 13 and the pivot position is expressed by Equation (4),
L _rot = r ₃ −r _rot (4)
The relationship between the front and rear edge radius difference L ₂ of the downstream guide vane 13 is expressed by equation (5).
_{L 2/2 ≧ L rot ≧} L 2 (5)
Configure as. If the shaft support position is too close to the front edge of the downstream guide vane 13, the supply of energy for eliminating the stall becomes insufficient and the efficiency decreases. Therefore, if installing a rotary shaft at a position that satisfies _{L 2/2 ≧ L rot ≧} L 2, it is possible obtain a sufficient effect of the gap.

  In the first embodiment, together with the upstream guide vane 12 and the downstream guide vane 13, the diffuser with vane 10 having a plurality of diffuser vanes 18 disposed in the circumferential direction on the outer periphery of the first stage impeller 9a is provided with 2 By installing a vaneless diffuser 19 having no diffuser vane on the outer periphery of the stage impeller 9b, an optimum configuration can be obtained in order to satisfy both the operating range and the efficiency.

  First, the vane-equipped diffuser 10 installed in the first stage has a function of sufficiently decelerating the refrigerant discharged from the first stage impeller 9 a and leading it to the return flow path 11. Generally, the return flow path 11 has a bend portion 20 for turning the flow of the refrigerant from the outer diameter direction to the inner diameter direction. For example, in the case of a vaneless diffuser without a diffuser vane, sufficient deceleration cannot be obtained. The bend portion 20 causes a wall friction loss and a collision loss, resulting in a decrease in efficiency.

  Further, at this time, the flow becomes uneven in the bend portion 20 and must be rectified by the upstream guide vane 12 installed on the downstream side, and a sufficient distance is required. As a result, the size of the upstream guide vane 12 is increased, and the relationship of formula (3) cannot be maintained in a limited space of the centrifugal compressor for turbo chillers.

  Further, when the vaneless diffuser is extended in the radial direction to obtain sufficient deceleration, the wall friction loss in the diffuser increases and the efficiency decreases. FIG. 5 is a graph showing the relationship between the flow rate V and the efficiency E of the diffuser with vane and the vaneless diffuser described above. This graph shows that in the configuration of the first embodiment, when a vane diffuser is installed in the first stage (shown by A in FIG. 5), the efficiency is higher than when a vaneless diffuser is installed (shown by B in FIG. 5). It shows a marked improvement.

  As described above, the diffuser 10 with vanes is installed and combined with the relationship of the expressions (3) and (5) in the upstream guide vane 12 and the downstream guide vane 13 to increase the efficiency of the centrifugal compressor in all flow ranges. It becomes possible.

  Next, the vaneless diffuser 19 installed in the second stage will be described. As described above, in the first embodiment, during the partial load operation, the downstream guide vane 13 is rotated by the downstream guide vane rotating shaft 14 to give a swirl component to the fluid, thereby eliminating the deviation between the inlet angle to the impeller and the blade inlet angle. And suppress the impeller stall. As a result, since the uniformity of the flow at the impeller exit is ensured, it is not necessary to install a diffuser vane and rectify the flow as in the prior art.

  In general, diffuser vanes are designed so that the impeller outflow angle and diffuser vane blade inlet angle are almost the same in rated operation. At this time, the compressor can achieve high efficiency. It is better not to install a diffuser vane because the outflow angle of the gas changes and does not coincide with the vane inlet angle of the diffuser vane and the flow stalls and reaches the operating limit.

  FIG. 6 is a graph showing the relationship between the flow rate V of the diffuser with vane and the vaneless diffuser and the heat insulation head H. This graph shows the operation range when the vaneless diffuser is installed in the second stage (indicated by C in FIG. 6) than in the case where the vaned diffuser is installed (indicated by D in FIG. 6) in the configuration of the first embodiment. Shows that it improves. That is, in FIG. 6, the operating range is expanded to the low flow rate side.

  As described above, a vaneless diffuser is installed in the second stage, and by combining with the upstream guide vane 12 and the downstream guide vane 13, it is possible to expand the operating range during partial load operation. In the first embodiment, the two-stage centrifugal compressor has been described. However, the present invention is not limited to such a configuration, and can be similarly applied to a multistage centrifugal compressor having three or more stages as shown in the second embodiment. it can.

  The second embodiment relates to a multistage turbo chiller based on a vapor compression refrigeration cycle as a basic principle. FIG. 7 is a configuration diagram of a multistage centrifugal compressor according to the second embodiment.

  As shown in FIG. 7, the centrifugal compressor 1 employs a multi-stage turbo centrifugal compressor, and includes an inlet guide vane 16 in the first stage suction portion, and each stage rotates and rotates with a rotating shaft 8 and a rotating shaft 8. It has an impeller 9 having blades that are held by a shaft 8 and provided at substantially equal intervals in the circumferential direction, and includes a return flow channel 11 as a stationary flow channel that connects the steps, and a scroll 15 that discharges the refrigerant. In at least one of the first stage and the intermediate stage, a vaned diffuser 10 having a plurality of diffuser vanes 18 arranged in the circumferential direction is installed on the outer periphery of the impeller 9, and the outer periphery of the impeller 9 in the final stage A vaneless diffuser 19 having no diffuser vane is installed in the. Further, a fixed upstream guide vane 12 and a movable downstream guide vane 13 are installed in the return flow path 11, and each form a circular blade row.

  In the multistage centrifugal compressor according to the second embodiment, the downstream guide vane 13 is rotatably supported via the downstream guide vane rotating shaft 14 and is rotated by the driving device 7 provided to the vane according to the operating state of the turbo refrigerator. The flow angle of the fluid flowing into the impeller 9 is changed. With this effect, the inlet angle of the impeller 9 and the flow angle of the refrigerant flowing into the impeller 9 do not deviate in any operating state, and the efficiency of the centrifugal compressor 1 can be maintained.

Further, in the diffuser with vane 10 installed on the upstream side of the return flow path 11 including the fixed upstream guide vane 12 and the movable downstream guide vane 13, the exit radius r _A and the vane of the impeller 9 shown in FIG. If the ratio r _B / r _A of the outlet radius r _B of the attached diffuser 10 satisfies the relationship of formula (6),
1.3 <r _B / r _A <1.8 (6)
Sufficient deceleration is obtained in the vaned diffuser 10, and collision loss and wall friction loss at the bend portion 20 are minimized. Therefore, it is possible to improve the efficiency of the centrifugal compressor in all flow ranges.

The relationship of equation (6) relating to the ratio r _B / r _A of the outlet radius r _B of the outlet radius r _A and the vane with the diffuser 10 of the impeller 9, as well as multistage centrifugal compressor of the second embodiment, This also applies to the two-stage centrifugal compressor of Example 1.

  In the centrifugal compressor configured as described above, the guide vane installed in the return flow path connecting the diffuser and the rear impeller is divided into a fixed upstream guide vane and a movable downstream guide vane, and the downstream guide vane is rotated. It has a movable configuration in the center, and a vaned diffuser is installed in one of the first and intermediate stages, and a vaneless diffuser is installed in the final stage. As a result, the flow rate of the rear impeller can be controlled by the effect of the downstream guide vane, and the efficiency and operating range at the partial load are expanded.

  In addition, the effect of the diffuser with vane provided on the upstream side of the return flow path can minimize the loss at the bend portion installed in the return flow path, and can lead a uniform flow to the upstream guide vane. Therefore, it is possible to increase the efficiency of the centrifugal compressor.

  Moreover, the stall of the partial load operation is suppressed and the operating range is expanded by the effects of the downstream guide vane and the vaneless diffuser provided in the final stage. By satisfying the above configuration, a turbo chiller having a wide operating range and high efficiency can be realized even under various flow conditions.

  The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention.

  For example, in the above-described embodiment, the guide vane installed in the return flow path is divided into the fixed upstream guide vane and the movable downstream guide vane, but only the movable downstream guide vane is provided. It may be provided and no fixed guide vane is provided.

  Further, in the multistage centrifugal compressor, the movable guide vanes are not limited to those installed in all the return flow paths, and may be those installed in at least one return flow path.

DESCRIPTION OF SYMBOLS 1 Centrifugal compressor 2 Condenser 3 Liquid receiver 4 Economizer 5 Evaporator 6 Motor 7 Drive device 8 Rotating shaft 9 Impeller 9a First stage impeller 9b Second stage impeller 10 Vane diffuser 11 Return flow path 12 Upstream guide Vane 13 Downstream guide vane 14 Downstream guide vane rotating shaft 15 Scroll 16 Inlet guide vane 17 Fixed guide vane 18 Diffuser vane 19 Vaneless diffuser 20 Bend part

Claims (5)

In a centrifugal compressor having a multi-stage impeller, a plurality of diffusers disposed on the outer periphery of each impeller, and a return flow path connecting the diffuser and a rear-stage impeller,
A plurality of movable guide vanes are arranged in the circumferential direction in the return flow path leading to the final stage impeller,
The final stage diffuser is constituted by a vaneless diffuser without a diffuser vane.   2. The centrifugal compressor according to claim 1, wherein at least one of the diffusers other than the final stage is configured by a vaned diffuser including a plurality of diffuser vanes in a circumferential direction. .   3. The centrifugal compressor according to claim 1, wherein a fixed guide vane is disposed upstream of the movable guide vane in the return flow path.   The centrifugal compressor according to any one of claims 1 to 3, wherein a ratio of an exit radius of an impeller at a stage where the diffuser with vane is provided and an exit radius of the diffuser with vane is 1.3 to 1. A centrifugal compressor characterized by being set to 8. Centrifugal compressor including a multi-stage impeller, a plurality of diffusers arranged on the outer periphery of each impeller, a return flow path connecting the diffuser and the rear impeller, and an evaporator, a condenser, an intermediate In a refrigeration system in which a refrigeration cycle is configured by sequentially connecting coolers,
A plurality of movable guide vanes are arranged in the circumferential direction in the return flow path leading to the final stage impeller of the centrifugal compressor,
The last stage diffuser is constituted by a vaneless diffuser in which a diffuser vane is not provided.

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