Patent Publication Number: US-9890977-B2

Title: Flash tank economizer for two stage centrifugal water chillers

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     Benefit is claimed of U.S. Patent Application Ser. No. 61/886,610, filed Oct. 3, 2013, and entitled “Flash Tank Economizer for Two Stage Centrifugal Water Chillers”, the disclosure of which is incorporated by reference herein in its entirety as if set forth at length. 
    
    
     BACKGROUND 
     The disclosure relates to refrigeration. More particularly, the disclosure relates to economized chiller systems. 
     A typical chiller system comprises a vapor compression refrigeration system having a compressor, a condenser, and an evaporator along a recirculating refrigeration flowpath. An expansion device is between condenser and evaporator. Exemplary condensers and evaporators are refrigerant-water heat exchangers so that refrigerant compressed by the compressor is cooled in the condenser by transferring heat to a first water loop. Refrigerant is further cooled by expansion in the expansion device and absorbs heat in the evaporator from a second water loop. 
     An economizer may be added to the system to reduce the vapor percentage of refrigerant delivered to the evaporator, thereby increasing the latent heat of refrigerant delivered to the evaporator. An exemplary economizer is a flash tank economizer wherein a portion of the refrigerant delivered from the condenser is expanded (flashed) into a vapor portion, leaving a liquid portion. The vaporized refrigerant is returned to an economizer port along the compressor. The expansion further cools the liquid refrigerant prior to its delivery to the primary expansion device and then the evaporator. Two exemplary economized chillers are the models 19EX and 23XRV of Carrier Corporation, Syracuse, N.Y., USA. 
     SUMMARY 
     One aspect of the disclosure involves a system comprising the integrated combination of: a condenser having a condenser water path leg extending from a water inlet to a water outlet; a first expansion device; a flash tank economizer; a second expansion device; an evaporator having an evaporator water path leg extending from a water inlet to a water outlet; and a refrigerant flowpath passing sequentially through the condenser, the first expansion device, the economizer, the second expansion device and the evaporator. The flash tank economizer comprises a horizontally elongate body having a first end and a second end. The economizer has an inlet conduit having an outlet. The economizer has a liquid outlet, a vapor outlet, and a medium between the outlet of the inlet conduit and the liquid outlet. A length of the refrigerant flowpath between the first expansion device and the outlet of the inlet conduit is at least 0.5 m. 
     In one or more embodiments of any of the foregoing embodiments, the outlet of the inlet conduit faces the first end and the liquid outlet is proximate the second end. 
     In one or more embodiments of any of the foregoing embodiments, the medium comprises a pair of perforated plates. 
     In one or more embodiments of any of the foregoing embodiments, the plates are parallel and spaced-apart from each other. 
     In one or more embodiments of any of the foregoing embodiments, the plates spaced-apart from each other by a gap of 10 mm to 25 mm. 
     In one or more embodiments of any of the foregoing embodiments, the plates comprise a first plate and a second plate and holes of the first plate are offset from holes of the second plate. 
     In one or more embodiments of any of the foregoing embodiments, the medium comprises a third plate having holes offset from holes of the first plate. 
     In one or more embodiments of any of the foregoing embodiments, the holes of the third plate are aligned with the holes of the second plate. 
     In one or more embodiments of any of the foregoing embodiments, the holes of the first plate and the holes of the second plate are circular in a square array. 
     In one or more embodiments of any of the foregoing embodiments, the holes of the first plate and holes of the second plate are circular in planform and of the same diameter and the square array has an on-center spacing (X 10 ) being 141% to 300% of the hole diameter (D 10 ). 
     In one or more embodiments of any of the foregoing embodiments, the economizer comprises a vessel having a main cylinder extending from the first end toward the second end and a second cylinder at the second end and forming a sump, the liquid outlet extending from the sump. 
     In one or more embodiments of any of the foregoing embodiments, the economizer lacks a spray bar and a wire mesh-type demister. 
     In one or more embodiments of any of the foregoing embodiments, the system has a compressor. The compressor has: an outlet upstream of the condenser along the refrigerant flowpath; a suction port downstream of the second expansion device along a first branch of the refrigerant flowpath; and an economizer port downstream of the economizer vapor outlet along a second branch of the refrigerant flowpath. 
     In one or more embodiments of any of the foregoing embodiments, the system is a chiller. 
     In one or more embodiments of any of the foregoing embodiments, a method for using the system comprises: running the compressor to draw refrigerant from the suction port and the economizer port, compress said refrigerant, and drive the refrigerant downstream from the outlet along the refrigerant flowpath; rejecting heat from the refrigerant in the condenser to water flowing along the condenser water path leg; after the rejecting, expanding the refrigerant in the first expansion device; passing the expanded refrigerant from the first expansion device to the flash tank economizer; passing a first branch flow of the refrigerant from the flash tank economizer back to the economizer port; passing a second branch flow of the refrigerant to the second expansion device; passing the expanded refrigerant from the second expansion device to the evaporator; absorbing heat by refrigerant passing through the evaporator from water passing along the evaporator water path leg; and returning refrigerant from the evaporator to the suction port. 
     In one or more embodiments of any of the foregoing embodiments, the medium is effective to remove droplets of liquid refrigerant from a vapor flow passing to the vapor outlet and deliver said droplets to a liquid accumulation for forming a liquid flow from the liquid outlet. 
     In one or more embodiments of any of the foregoing embodiments, refrigerant discharged from the inlet conduit outlet is deflected off an interior surface of the body at the first end. 
     Another aspect of the disclosure involves an economizer comprising: an elongate body having a first end and a second end; an inlet conduit having an outlet; a liquid outlet; a vapor outlet; and first and second spaced-apart foraminate plates between the outlet of the inlet conduit and the liquid outlet. 
     The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view of a chiller system. 
         FIG. 2  is a partially schematic central longitudinal vertical sectional view of a first economizer. 
         FIG. 3  is a partially schematic central longitudinal vertical sectional view of a second economizer. 
         FIG. 4  is a bottom perspective view of an integrated condenser/economizer/evaporator unit. 
         FIG. 5  is a partial perspective view of the unit of  FIG. 4  with condenser removed. 
         FIG. 6  is an axial partially vertically cutaway view of the economizer of the unit of  FIG. 4 . 
         FIG. 7  is a transverse sectional view of the economizer of  FIG. 6 , taken along line  6 - 6 . 
         FIG. 8  is a transverse sectional view of the economizer of  FIG. 6 , taken along line  8 - 8  of  FIG. 6 . 
     
    
    
     Like reference numbers and designations in the various drawings indicate like elements. 
     DETAILED DESCRIPTION 
       FIG. 1  shows a chiller system  20  having a vapor compression circuit or system including a compressor  22  having a fluid (refrigerant) primary inlet  24  and a refrigerant primary outlet  26 . The exemplary compressor includes an intermediate port or economizer port  28 , intermediate the ports  24  and  26  along a compression path within the compressor. In the case of reciprocating compressors, the economizer port maybe at an interstage between multiple cylinders. In the case of screw compressors, this may be open to the compression pockets at an intermediate stage of compression. In the case of multi-stage centrifugal compressors, the economizer port may be between stages (e.g., between the first stage impeller and a second stage impeller). 
     The exemplary compressor has an electric motor  30  for driving the working element(s) such as pistons, screws, impeller(s) and the like. The compressor discharge line  32  extends downstream from the discharge port  26  along a refrigerant primary flowpath to a refrigerant inlet port  36  of a heat exchanger  34 . In a normal operating mode, the heat exchanger  34  is a heat rejection heat exchanger also known as a condenser or gas cooler. The heat exchanger  34  has a refrigerant outlet  38  along the refrigerant primary flowpath. 
     The heat exchanger  34  also includes ports for receiving and discharging a heat transfer fluid. Exemplary heat transfer fluid is a liquid, more particularly water, flowing along a loop or flowpath  530 . Depending upon the implementation, the flowpath  530  may be an open flowpath or a closed/recirculating flowpath.  FIG. 1  shows a water inlet port  40  and a water outlet port  42  of the condenser along the flowpath  530  so that water flowing along the flowpath  530  within the heat exchanger  34  is in heat exchange relationship with refrigerant passing along the primary flowpath  520  within the heat exchanger  34 . In the normal operating mode, heat is transferred from the refrigerant to the water (or other fluid) to elevate the temperature of the discharge water relative to inlet water and to reduce the temperature of discharged refrigerant relative to inlet refrigerant. 
     Downstream of the heat exchanger  34  along the primary flowpath  520  is an expansion device  50 . The expansion device  50  serves as an economizer expansion device as described below. An exemplary expansion device  50  is an electronic expansion device which may be controlled by a system controller  200  described below. 
     Downstream of the expansion device  50  along the primary flowpath  520  is an economizer  60 . An exemplary economizer  60  is a flash tank economizer having an inlet port  62  and outlet ports  64  and  66 . The exemplary outlet port  64  is a vapor outlet for returning vaporous refrigerant to the economizer port  28  via an economizer line  68  along an economizer branch  522  of the refrigerant flowpath. The outlet port  66  is a liquid outlet port for discharging liquid refrigerant along flowpath branch  524 , ultimately returning to the compressor inlet port  24 . 
     In typical implementations, the majority of the mass flow of refrigerant along the primary flowpath  520  will be carried by the branch  524 . Accordingly, the branch  524  may, alternatively, be characterized as a continuation of the primary flowpath with the branch  522  being a bypass/diversion/branch thereof. An expansion device  70  is along the flowpath  524  downstream of the outlet  66  and upstream of a refrigerant inlet  74  of a heat exchanger  72 . In the normal operating mode, the heat exchanger  72  is a heat absorption heat exchanger (evaporator or cooler) having an outlet  76  discharging refrigerant to a suction line  78  to return the refrigerant to the compressor inlet  24 . The exemplary heat exchanger  72  is also a refrigerant-water heat exchanger transferring heat from a water flowpath or loop  540  via a water inlet  80  and a water outlet  82  in similar fashion to the heat exchanger  36  and its associated water loop  530 . 
     Expansion of the refrigerant in the device  50  reduces the temperature of the refrigerant. Accordingly, the liquid refrigerant delivered to the expansion device  70  will be colder than the liquid refrigerant discharged from the heat exchanger  34 . This allows the expanded refrigerant delivered to the evaporator to be cooler than if there was merely a single stage expansion of refrigerant from the heat exchanger  34  being delivered to the heat exchanger  72 . 
       FIG. 1  further shows a controller  200 . The controller may receive user inputs from an input device (e.g., switches, keyboard, or the like) and sensors (not shown, e.g., pressure sensors and temperature sensors at various system locations). The controller may be coupled to the sensors and controllable system components (e.g., the expansion device and other valves, the bearings, the compressor motor, vane actuators, and the like) via control lines (e.g., hardwired or wireless communication paths). The controller may include one or more: processors; memory (e.g., for storing program information for execution by the processor to perform the operational methods and for storing data used or generated by the program(s)); and hardware interface devices (e.g., ports) for interfacing with input/output devices and controllable system components. 
       FIG. 2  shows further details of an exemplary economizer  60 . 
     The exemplary economizer  60  comprises an elongate vessel  100  having a sidewall  102  (e.g., circular cylindrical) extending between a first rim at a first end  104  and a second rim at a second end  106 . Respective end walls  108  and  110  are secured to the sidewall proximate the ends  104  and  106 . Exemplary end walls are flat plates or outwardly convex domes. The exemplary overall length of an interior  112  of the vessel is shown as L 1 . An exemplary interior diameter is shown as D 1 . Exemplary D 1  is 0.5 m, more broadly, 0.3 m to 1.0 m or 0.4 m to 0.7 m. Exemplary L 1  is 2 m or 1.6 m to 2.4 m, more broadly, 1 m to 4 m or 1.0 m to 2.5 m. Exemplary L 1  is three to six times D 1 , more particularly, 3.0 to 5.0 times. 
       FIG. 2  also shows an inlet conduit  120  extending into the interior  112  from the inlet  62  and terminating in an inlet conduit opening or outlet  122  (e.g., a single circular outlet) for discharging a flow  124 . Exemplary outlet  122  is in close facing proximity to the wall  108  (inlet end wall). For example, the outlet  122  may be spaced by a distance S 1  away from the adjacent surface of the wall  108 . The exemplary outlet is spaced above a bottom of the vessel by a height H 1 . 
     The exemplary ports  64  and  66  are formed in the sidewall  102  at respective lower and upper extremities thereof and have respective on-center spacings from the associated rim of the sidewall  102  of S 2  and S 3 .  FIG. 2  also shows a vortex breaker  130  spaced apart from the sidewall outlet opening  132  (associated with the outlet port  66 ) by a height of H 2  The vortex breaker helps provide a liquid seal by stopping swirling to prevent vapor entrainment in the liquid outlet flow. The exemplary vortex breaker  130  is shaped as a rectangular plate (i.e., as a chord) spanning the sidewall and has a longitudinal dimension of W 1 . 
       FIG. 2  further shows a liquid refrigerant accumulation  140  within the interior  112  and having an upper surface  142 . 
     It is desirable that refrigerant discharged from the outlet port  64  be pure vapor or close thereto. It is similarly desirable that refrigerant discharged from outlet port  66  be pure liquid or close thereto. Accordingly, it is desirable to configure the economizer to minimize vapor bubbles in the liquid refrigerant adjacent the opening  132  and minimize liquid droplets reaching the outlet  64 . 
     The flow  124  discharged from the inlet conduit outlet  122  will be mixed phase. Advantageously, the liquid and vapor phases in the flow  124  are in thermal equilibrium. This may be achieved by placing the expansion device  50  well upstream of the outlet  122 . Initially, at expansion by the expansion device  50 , the vapor will be cooler than the liquid. By providing a sufficient length of primary flowpath  520  between the expansion device  50  and the outlet  122  there is time for the two phases to equilibrate. The exemplary length between the expansion device  50  and the outlet  122  is at least 0.5 m, more particularly at least 0.8 m or 0.8 m to 2.0 m. 
     The discharged flow  124  will deflect off the interior surface of the wall  108 . Liquid will tend to collect on wall  108  by inertia and flow downward while the vapor is deflected and drawn by pressure difference toward the outlet  64 . Gravity will tend to draw the liquid downward into the accumulation  140 . There will be substantial turbulence in the accumulation near the wall  108  and thus some residual intermixing of vapor in the liquid. 
     In the exemplary implementation a foraminate member  158  in the form of multiple foraminate plates (e.g., a pair of perforated plates  160 ,  162 ) is positioned spanning the interior of the housing slightly downstream of the inlet conduit. In the exemplary embodiment, the first plate  162  is spaced by a distance S 4  from the inlet end rim of the sidewall  102 . Exemplary S 4  is less than half of L 1 , more particularly less than a third of L 1 , and, more particularly about 15% to 25% of L 1 . 
     Exemplary spacing between the plates is shown as S 5 . Exemplary S 5  is small. An exemplary spacing is the thickness of a gap between plates rather than the on-center spacing. The small spacing combined with the offset of holes in the respective plates serves to prevent any residual high speed droplets from passing through the pair and reaching the outlet  64 . Any droplet passing through a hole in the first plate  160  will impact the second plate  162  and will then flow downward into the accumulation  140 . Any droplet hitting the plate  160  will flow down the upstream face of the plate  160  and then into the accumulation. There may be greater splashing/reflection of droplets but the same principle generally applies. 
     Within the accumulation  140 , the interruption provided by the plates helps reduce sloshing and facilitates having a lower concentration of vapor in the liquid to the outlet discharge side of the plates compared to the inlet/upstream side of the plates. The combination of the outlet  122  directing flow against a vessel interior wall and the intervening media or foraminate member  158  may avoid the expense of an economizer having a spray bar in combination with a wire mesh demister. 
       FIG. 3  shows an alternative economizer  360  formed with a dual-cylinder vessel configuration. A main or primary cylinder  370  extends downstream from an upstream end and contains the inlet conduit and perforated plates in similar fashion to the  FIG. 2  embodiment. At the downstream/discharge end, however, there are differences. The second shorter cylinder  380  of similar diameter to the first cylinder is end-to-end with the first cylinder but downwardly shifted relative thereto to provide an increased depth of sump  400 . The liquid outlet  66  thus extends from the second cylinder/sump. The main cylinder thus has a partial downstream wall  390  closed relative to the exterior but open to the interior of the second cylinder. Similarly, the second cylinder has an upstream end wall  392  closed to the exterior but open to the main cylinder. 
       FIGS. 4 and 5  show the integration of an economizer  420  with the heat exchangers  34  and  72 . Having a horizontally elongate economizer provides for a compact integration with horizontally elongate heat exchangers. 
     Although the exemplary economizer  420  has slightly different internal features relative to the more schematically illustrated economizers  60  and  360 , shared features are referenced with shared reference numerals. In the exemplary illustration, the economizer main or primary cylinder  370  is nested in the valley or cusp below and between the cylindrical bodies of the condenser  34  and evaporator  72 . In the exemplary implementation, the condenser is slightly vertically offset relative to the evaporator (e.g., by less than the radius of either). 
       FIGS. 6 and 8  show the outlet  122  centered along the centerline  500  of the primary cylinder  370 . Additionally, the illustrated foraminate member comprises three plates instead of two. For arbitrary purposes of reference, the additional plate  161  is at the inlet end of the plate group. The holes in each plate are out of phase with the holes in the next. In this example, therefore, the holes in the plates  161  and  162  at respective ends of the group of three plates have holes in phase with each other. In an exemplary situation, the holes  170  ( FIG. 7 ) are in a square array. Thus, the holes  170  of a given plate are aligned with the intact inter-hole areas  172  (e.g., centered between a group of four holes) of the next plate. Exemplary hole diameter D 10  is approximately half or slightly less than half of the on-center spacing S 10  of the holes along the two directions of the square array. Because the holes are out of phase in both directions of the square array, the transverse dimensions of the intact areas are greater than the hole diameter even with hole diameter equal to half of S 10 . Accordingly, any liquid passing through one hole will tend to hit the next plate (either on intact surface or sides of a hole) and lose momentum. 
     Exemplary plate thickness is 7 mm, more broadly, 5 mm to 10 mm. Exemplary hole diameter D 10  is 19 mm, more broadly, 10 mm to 30 mm or 15 mm to 25 mm. Exemplary grid spacing S 10  is 38 mm, more broadly, 15 mm to 100 mm or 20 mm to 60 mm or 141%-300% of D 10  or 150% to 250% of D 10 . Exemplary gap thickness S 5  between plates is 13 mm, more broadly, 5 mm to 30 mm or 10 mm to 25 mm or 10 mm to 20 mm. 
       FIG. 6  further shows a deflector plate  180  extending vertically downward within the vessel  370  between the plates and the vapor outlet. The exemplary plate  180  has a lower edge  182 . Exemplary lower edge  182  forms a chord of the cross-section of the vessel  370  and has edges welded to the vessel interior. The exemplary edge  182  is spaced horizontally partially above the horizontal centerplane of the vessel (e.g., by an eighth to a half of the vessel inner diameter). The exemplary plate  180  serves as a further baffle or barrier to collect and/or deflect any yet residual droplets which have passed through the foraminate member. 
       FIG. 6  also shows a float valve assembly  190  for controlling flow from the liquid outlet. This functions as the primary expansion device  70 . 
     Exemplary manufacture techniques and materials may be those conventionally used for economizers and other chiller components (evaporator, condenser, and the like). Similarly, exemplary use steps may be conventional. Exemplary vessel material is metal such as steel (e.g., carbon steel) meeting American Society of Mechanical Engineers (ASME) code. Similar material may be used for the perforated plates, other plates, conduits and the like. Such metal allows ease of manufacture, cutting, forming welding, and the like. 
     The use of “first”, “second”, and the like in the description and following claims is for differentiation within the claim only and does not necessarily indicate relative or absolute importance or temporal order. Similarly, the identification in a claim of one element as “first” (or the like) does not preclude such “first” element from identifying an element that is referred to as “second” (or the like) in another claim or in the description. 
     Where a measure is given in English units followed by a parenthetical containing SI or other units, the parenthetical&#39;s units are a conversion and should not imply a degree of precision not found in the English units. 
     One or more embodiments have been described. Nevertheless, it will be understood that various modifications may be made. For example, when applied to an existing basic system, details of such configuration or its associated use may influence details of particular implementations. Accordingly, other embodiments are within the scope of the following claims.