Patent Publication Number: US-11029065-B2

Title: Multi-stage oil batch boiling system

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     Benefit is claimed of U.S. Patent Application No. 62/241,994, filed Oct. 15, 2015, and entitled “Multi-Stage Oil Batch Boiling System”, 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 oil reclaim vaporizers for chiller systems. 
     In refrigeration systems such as chillers, it is known to use a vaporizer to separate refrigerant from a refrigerant/lubricant (oil) mixture. U.S. Pat. No. 6,672,102 of Huenniger et al. discloses a system wherein a vaporizer receives a refrigerant/lubricant mixture flow drained from an evaporator. The flow is mostly oil and it is desired to remove the refrigerant before returning the oil to lubricate the compressor. The flow is placed in heat exchange relation with a hot gas bypass flow passed from the compressor discharge to the evaporator. Vaporized refrigerant is passed to compressor suction and oil is drained to an oil sump to be returned to a compressor oil return port for lubrication (e.g., of bearings and rotors). 
     PCT/US2012/048562 of Molavi discloses an alternative vaporizer configuration. PCT/US2014/054193 of Molavi et al. discloses yet another alternative vaporizer configuration. The disclosures of these applications are incorporated by reference in their entireties herein as if set forth at length. 
     SUMMARY 
     One aspect of the disclosure involves a vapor compression system comprising: a compressor having a suction port and a discharge port; a refrigerant flowpath from the discharge port and returning to the suction port; a first heat exchanger along the refrigerant flowpath; a second heat exchanger along the refrigerant flowpath; and a vaporizer system. The vaporizer system comprises: a first vaporizer and a second vaporizer each comprising: a vessel having an inlet, a vapor outlet, and a liquid outlet; and a gas bypass flowpath in heat transfer relation with an interior of the vessel. 
     In one or more embodiments of any of the foregoing embodiments, the first vaporizer vessel and the second vaporizer vessel are separate vessels. 
     In one or more embodiments of any of the foregoing embodiments, the first vaporizer vessel and the second vaporizer vessel are each a metallic vessel having a cylindrical sidewall and domed end walls. 
     In one or more embodiments of any of the foregoing embodiments, a single tank with a partition forms, in common, the first vaporizer vessel and the second vaporizer vessel. 
     In one or more embodiments of any of the foregoing embodiments, a sump has a single vessel positioned to receive lubricant flow from the first vaporizer and the second vaporizer. 
     In one or more embodiments of any of the foregoing embodiments, the first vaporizer, the second vaporizer, and the sump each have an electric heater. 
     In one or more embodiments of any of the foregoing embodiments, the sump is a first sump, and the system further comprises: a second sump positioned to receive lubricant from the first sump. 
     In one or more embodiments of any of the foregoing embodiments, the first sump has a vent and the second sump does not have a vent. 
     In one or more embodiments of any of the foregoing embodiments, a pump is coupled to an outlet of the second sump along a lubricant supply flowpath to the compressor. 
     In one or more embodiments of any of the foregoing embodiments, one or more valves are positioned to provide: a first operational condition comprising draining lubricant from the first vaporizer while not draining lubricant from the second vaporizer; and a second operational condition comprising draining lubricant from the second vaporizer while not draining lubricant from the first vaporizer 
     In one or more embodiments of any of the foregoing embodiments, the one or more valves comprise: a first three-way valve positioned to control flow to the inlets of the first vaporizer and the inlet of the second vaporizer; and a second three-way valve positioned to control flow from the liquid outlet of the first vaporizer and the liquid outlet of the second vaporizer. 
     In one or more embodiments of any of the foregoing embodiments, a controller is configured to provide: said first operational condition; and said second operational condition. 
     In one or more embodiments of any of the foregoing embodiments, the controller is further configured to provide: control of a pump for returning lubricant to the compressor. 
     In one or more embodiments of any of the foregoing embodiments, a method for using the system comprises: running the compressor to drive a refrigerant flow along the refrigerant flowpath, the refrigerant flow containing a lubricant; and diverting a flow of the refrigerant and lubricant to the vaporizer unit to alternatingly deliver the refrigerant and lubricant to the first vaporizer and the second vaporizer through the respective inlet thereof. 
     In one or more embodiments of any of the foregoing embodiments, the method further comprises: draining lubricant from the first vaporizer while not draining lubricant from the second vaporizer; and draining lubricant from the second vaporizer while not draining lubricant from the first vaporizer. 
     In one or more embodiments of any of the foregoing embodiments, the drainings from the first vaporizer and the second vaporizer are to a sump. 
     In one or more embodiments of any of the foregoing embodiments, the method further comprises pumping the drained lubricant back to the compressor. 
     In one or more embodiments of any of the foregoing embodiments, the draining of lubricant from the first vaporizer occurs while not introducing refrigerant via the inlet of said first vaporizer; and the draining of lubricant from the second vaporizer occurs while not introducing refrigerant through the inlet of the second vaporizer. 
     In one or more embodiments of any of the foregoing embodiments, the draining of lubricant from the first vaporizer occurs while not draining lubricant from the second vaporizer; and the draining of lubricant from the second vaporizer occurs while not draining lubricant from the first vaporizer. 
     In one or more embodiments of any of the foregoing embodiments, the method further comprises passing refrigerant through a conduit to transfer heat to refrigerant and lubricant in the first vaporizer and second vaporizer. 
     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 partially schematic view of a chiller system. 
         FIG. 2  is a partially schematic view of a vaporizer system within the chiller system of  FIG. 1  in a first operational condition. 
         FIG. 3  is a partially schematic view of the vaporizer system in a second operational condition. 
         FIG. 4  is a partially schematic view of a second vaporizer system in a first operational condition. 
         FIG. 5  is a sectional view of a vaporizer unit of the vaporizer system of the second vaporizer system taken along line  5 - 5  of  FIG. 4 . 
         FIG. 6  is a partially schematic view of the second vaporizer system in a second operational condition. 
     
    
    
     Like reference numbers and designations in the various drawings indicate like elements. 
     DETAILED DESCRIPTION 
       FIG. 1  shows a vapor compression system (e.g., shown as a chiller)  20  including a vaporizer system  22 . The system  20  includes a compressor  24  having a suction port  26  and a discharge port  28 . An exemplary compressor  24  is a screw compressor having a hermetic electric motor (not shown) within a case. Alternative compressors are centrifugal compressors, scroll compressors, or reciprocating compressors. A condenser  30  has a gas/vapor inlet port  32  downstream of the discharge port  28  along a refrigerant primary flowpath  33  for a refrigerant primary flow  500 . In operation, the compressor compresses refrigerant to drive a recirculating flow of refrigerant along the refrigerant primary flowpath  33  and branches off of it. The condenser has a liquid outlet  34  downstream along the refrigerant primary flowpath. The exemplary condenser is a liquid-cooled (e.g., water-cooled) condenser having a water inlet  36  and a water outlet  38  for water flow  510  passing along a water flowpath  39  through a tube bundle (not shown) in heat transfer relation with the refrigerant primary flow to absorb heat from the refrigerant to cool and condense the refrigerant. The condenser may be of any appropriate existing or yet-developed type. The exemplary condenser unit includes a float valve  40  which acts as an expansion device. Alternative implementations may include alternative expansion devices. A controller  400  (e.g., microprocessor based) may control operation of various components of the system  20  and may receive input from various sensors and user input devices. 
     Downstream of the condenser along the refrigerant primary flowpath  33  is an evaporator or cooler  50 . The exemplary evaporator has a refrigerant inlet  52  and a refrigerant outlet  54  along the primary flowpath  33 . The exemplary evaporator is used to chill a second heat transfer liquid (e.g., water) flow  520 . Accordingly, the exemplary evaporator  50  has a water inlet  56  and a water outlet  58  along a water flowpath  59 . Refrigerant passing along the refrigerant primary flowpath  33  through the evaporator is in heat exchange relation with the water (e.g., the water flowpath  59  passes through a tube bundle (not shown) over which the refrigerant flows) to absorb heat from the water (to cool the water). As with the condenser, the evaporator may represent any appropriate existing or yet-developed configuration. Additional evaporator ports cooperating with the vaporizer system  22  are discussed below. 
     There are several additional flowpaths through the vaporizer system  22  for passing refrigerant and/or lubricant (e.g., oil). 
     The exemplary vaporizer system  22  includes multiple (e.g., two shown) main vaporizer units  68 A,  68 B and an oil sump or reservoir  70 . Depending upon context, the term “vaporizer” may designate the system  22  or the unit(s)  68 A,  68 B or the vaporizer chamber(s) discussed below. 
     The exemplary conduits or lines along the refrigerant primary flowpath  33  are a discharge line/conduit  42  between the discharge port  28  and the condenser inlet  32 , an intermediate line/conduit  44  between the condenser outlet  34  and the evaporator inlet  52 , and a suction line/conduit  46  between the evaporator outlet  54  and the suction port  26 . 
     The exemplary system  22  has an inlet  72  (a main inlet) for receiving a refrigerant/oil mixture flow  530 . The exemplary inlet  72  receives the mixture from the evaporator. The exemplary refrigerant/oil mixture passes along/through a skim line/conduit  74  along a mixture inlet flowpath  75  from a skim port (or group of ports)  76  on the evaporator. The exemplary inlet  72  is one port of an exemplary three-way valve  80  whose other two ports  82 A,  82 B are in respective communication with the individual main vaporizer units  68 A,  68 B via inlet ports  84  in the vessels  86  (e.g., dome-ended cylindrical tanks) of such main vaporizer units.  FIG. 1  shows lines  88 A,  88 B extending from the valve  80  to the respective ports  84 . The enlarged view of  FIG. 2  shows respective surfaces  580 A,  580 B of liquid (principally refrigerant and oil with the percentage of oil increasing during heating) in the two vaporizer units  68 A,  68 B. Vapor (refrigerant and potentially contaminant) may exist in the headspace thereabove. 
     In addition to the line  74  and flowpath  75  for introducing the mixture of refrigerant and oil to the vaporizer system for separation, there are several return flowpaths. A line  90  and flowpath  92  may carry a lubricating flow  540  (e.g., majority by weight lubricant) back to the compressor (e.g., to a lubricant port  94  on the compressor housing). Depending on the particular compressor configuration, the lubricant flowpath  75  may branch to respective branches feeding compressor bearings and/or the working elements to lubricate their interface with each other or with fixed structure. As is discussed further below, the flowpath  92  may extend from a port  100  on the vaporizer system. The exemplary port  100  is along a second separation stage discussed below in which flow  542  drawn from the sump  70  may be more lubricant-rich than flow  544  delivered to the sump  70  from the main vaporizer units. 
     A refrigerant-rich flow  550  separated from the original mixed flow  530  may also be returned to the main flowpath  33 . In the exemplary embodiment, this is done via a line  110  and flowpath  112  to an additional suction port  114  on the compressor. Alternative connections might be along the suction line  46 . 
     The exemplary line  110  may extend from a port  116  on the vaporizer system. The flowpath  112  may reflect the merger of several branches upstream of the port  116 .  FIG. 2  shows respective lines  120 A and  120 B and associated branches  112 A and  112 B coming from vapor outlets  124  of the respective vaporizer units  68 A,  68 B. These flowpath branches merge with a branch  112 C and line  126  from a vapor outlet  128  (vent) on a vessel  71  of the sump  70 . 
     To withdraw lubricant (e.g., oil) from the vaporizer units  68 A and  68 B, each includes a liquid outlet  130  for passing a flow along an associated line  132 A,  132 B. The lines  132 A and  132 B pass to a valve (e.g., a three-way solenoid valve)  140  having respective associated ports  142 A and  142 B and a third port  144 . The third port  144  is connected via a line  146  to an inlet port  148  of the vessel of the sump  70 . The valve  140  may place the liquid outlets  130  of the two vaporizer units in alternative communication with the inlet port  148  to pass the flow  544  of mostly oil to the sump. 
     To supply heat to the vaporizer units  68 A and  68 B, two exemplary means are shown. The first means involves refrigerant-refrigerant heat exchange with refrigerant passing through a conduit  150  in heat exchange relation with refrigerant in the vessel interior to transfer heat to such refrigerant in the vessel interior to vaporize it. An exemplary conduit  150  is shown as a tubular coil within the vessel. One end of the coil is connected to an inlet  152  on the vessel and the other hand is connected to an outlet  154 . 
     Returning to  FIG. 1 , a flowpath  160  is seen passing a refrigerant flow  560  through the coil from the main flowpath  33  and returning it to the main flowpath  33 . The exemplary gas bypass flowpath  160  (bypassing the condenser  30 ) includes a line  162  extending from a location (e.g., port) along the main flowpath  33 . The exemplary location is along the discharge line. However, other locations may include from the condenser vessel. The flowpath separates into respective branches  160 A and  160 B to feed the respective ports  152  of the two vaporizers  68 A and  68 B. Downstream of the outlets  154 , the flowpath branches merge to return to the main flowpath  33 . An exemplary return is at a port  170  on the cooler from a port  190  ( FIG. 2 ) of the vaporizer system. 
       FIG. 2  further shows continuous flow  560  along both branches  160 A and  160 B. In alternative implementations, one or more valves (not shown) may be provided to control flow. In one example, a valve which may be otherwise similar to the valves  80  and  140  may be at a junction of the branches  160 A and  160 B. The valve may have respective ports for receiving the flow  560  from the branches  160 A and  160 B. The valve may have a port for returning the flow  560  to the port  170 . The valve may be configured to allow alternative communication from either of its two branch port to its trunk port. It may additionally have other modes such as placing all three ports in communication with each other or blocking all communication. In another alternative, a single valve is positioned away from the branches to provide intermittent simultaneous flow. 
       FIG. 2  further shows additional heating means in the form of electric heaters  180 . Each of the two vaporizer units  68 A,  68 B includes such a heater  180 , as does the sump  70 . The exemplary configuration orients the elongate vessels of the vaporizer units vertically with the heater  180  centrally located extending upward from a lower end of the vessel. The exemplary configuration orients the elongate vessel  71  of the sump  70  horizontally with the heater  180  oriented horizontally at a lower portion of the vessel. This serves to heat the liquid accumulation in the bottom of the sump vessel  71  to more fully vaporize/volatilize the refrigerant or contaminant to discharge it through the vapor outlet  128 . 
       FIG. 2  also shows secondary sump  200  and pump  202  along the flowpath  92  upstream of the outlet  100 .  FIG. 2  further shows a pressure regulator  204  along a bypass flowpath  206  and line  208  extending from downstream of the pump  202  back to a port on the sump vessel  71 . If the pressure difference across the pump exceeds a threshold value, the pressure regulator  204  allows a flow from the pump outlet back to the sump  70  to relieve that pressure. This prevents the compressor from being exposed to excessive lubricant pressure. 
     Returning to  FIG. 1 , the exemplary vaporizer system  22  also includes a lubricant filter  240  and a pair of shutoff valves  242  allowing servicing of the pump  202  and filter. 
     Via actuation of valves (e.g.,  80  and  140  in the exemplary embodiment) the system may be shifted between two or more modes. For example, two of these modes may represent the alternating operational stages of a batch process wherein sequential batches of lubricant are alternatingly separated in the respective vaporizers  68 A,  68 B and delivered to the sump  70 . 
     The exemplary  FIG. 2  condition involves the vaporizer  68 B discharging a flow  544  of oil from its port  130  through the valve  140  to the sump  70 . While this is happening, the vaporizer  68 A receives a fresh charge of refrigerant and lubricant via the flow  530  entering the port  84  through the valve  80 . The vaporizer  68 B had already received a charge of refrigerant and oil and, therefore, may largely have completed the process of boiling off refrigerant vapor  550 . The exemplary  FIG. 2  condition shows simultaneous flows  550  of vapor from both vaporizers. In practice, the flow rate will vary based upon the temperature and ratio of mixture in each of the vaporizers. In alternative embodiments, additional valves may be provided to allow only one such flow. 
     In the  FIG. 2  condition, the valve  80  is set so that the flow  530  is passed to the vaporizer  68 A but not the vaporizer  68 B. Similarly, the valve  140  is set so that the flow  544  passes from the vaporizer  68 B with similar drain flow being blocked from the vaporizer  68 A. Thus, in this example, the flow  530  entering the vaporizer will immediately begin to be heated and boil. If the hot gas flow  560  is insufficient (e.g., if lift is lower than a threshold value such as 22.5° F. (12.5° C.)) the electric heater will also be used in the vaporizer where boiling is occurring. 
     In the  FIG. 3  condition, however, the valve states are reversed so that the roles of the two vaporizers  68 A,  68 B are reversed. In the  FIG. 2  condition, refrigerant is being boiled off the mixture in the vaporizer  68 A leading to increased oil concentration in the liquid accumulation at the bottom of the vessel  86  of such vaporizer  68 A. The vaporizer  68 B had already completed sufficient boiling. Once relatively pure oil has been expended from the vaporizer  68 B or once the vaporizer  68 A has completed filling with liquid, the valves may be shifted to the second mode to initiate the  FIG. 3  draining of oil from the vaporizer  68 A and recharging of the vaporizer  68 B. 
     In addition to the operational mode of the system  20  described, there may be additional modes. In addition to the conditions described for an individual one of the vaporizer units  68 A,  68 B, other conditions may be provided. There may also be transitory conditions between modes and other conditions such as startup and shutdown in which parameters change. For example, there may be implementations with three or more vaporizer units in place of the two units shown. If two of the three were in conditions discussed above, the third could be in a different condition (e.g., each unit could cycle through three or more operational conditions in a given operational mode of the overall system  20 ). 
       FIGS. 4-6  show a system vaporizer  300  based upon the configuration of vaporizer shown in PCT/US2014/054193. 
     In the system  300 , the two units  368 A and  368 B are formed as portions of a single larger unit  368  with a single main vessel  386  having a dividing wall or partition  387  to divide the vessel into individual vessels associated with the individual units.  FIG. 5  shows the vessel cross-section as being generally square (e.g., with one square metallic tube stock). The exemplary vessel  386  has flat endplates at respective ends. 
     A further difference relative to the units  68 A,  68 B is that the spiral or coiled conduit  150  is replaced by a bundle of tubes  350  fluidically in parallel with each other between an inlet manifold  351  and an outlet manifold  352 . The exemplary manifolds are formed by plates spanning the cross-section of the vessel sidewall spaced slightly inboard of the respective endplate of the associated unit  368 A,  368 B and the central partition  387 . Otherwise, the illustrated ports, connections, and other components may be similar to those of the vaporizer system  22  as discussed above. 
       FIG. 1  further shows the controller  400 . 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., 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. 
     In one exemplary control implementation, the controller may receive inputs from liquid level sensors (not shown) in the various vessels. The controller  400  may be programmed for changeover between the two vaporizers  68 A and  68 B when the liquid level in the vaporizer that is filling reaches a given threshold. Other control methodologies are possible. 
     The systems  20  and  300  may be made using otherwise conventional or yet-developed materials and techniques. 
     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.