Abstract:
An improved design of a vapor compression distiller which makes use of a rapid, highly turbulent flow through the heat-of-evaporation recovery, or primary, heat exchanger. The distiller may also include the use of turbulators to increase turbulence and mixing within the primary heat exchanger. The increased level of turbulence and mixing dramatically reduces fouling inside the primary heat exchanger and increases the heat transfer efficiency. The improvements in the distiller are maximized by recirculating the liquid to be evaporated at a high multiple of the flow rate of the liquid feed to the distiller. The distiller may also include a feed circulation loop with a secondary heat exchanger to increase the efficiency of heat-of-evaporation recovery in the evaporation/condensation cycle. Applications of the vapor compression distiller include purification of waste liquids, concentration of dilute liquid mixtures, and separation of liquid/liquid, liquid/gas, and liquid/solid mixtures.

Description:
This application is a continuation-in-part of U.S. patent application Ser. No. 09/013,343, filed Jan. 26, 1998, abandoned, on behalf of the same inventor and claims benefit of Prov. No&#39;s 60/036,284 filed Jan. 27, 1997 and 60/074,099 filed Feb. 9, 1998. 
    
    
     FIELD OF INVENTION 
     This invention relates to distillation equipment and processing, specifically an improved design for a vapor compression distillation apparatus and method. 
     BACKGROUND 
     Vapor compression distillation has the potential to provide significant savings in capital and operating costs over single or multiple effect evaporators not using this technology. Vapor compression distillation is typically limited in application by economics and operational problems. 
     Vapor compression distillers of various designs have been proposed for many years. Most of these designs have seen little or no commercial use due to both functional problems and for economic reasons. The commercial feasibility for these previous designs is strongly affected by many factors. The exact disadvantages of earlier designs are varied and include poor heat transfer, fouling tendencies, poor or inflexible application of makeup heat for thermal losses, poor equipment reliability, higher operating costs, inflexibility in liquid flows, higher maintenance costs, higher initial capital costs, difficulty in system startup, and lack of flexibility in processing capacity. 
     SUMMARY OF THE INVENTION 
     Briefly described, the invention is vapor compression distillation apparatus and process. A liquid is circulated through an evaporation loop comprising an evaporation vessel in fluid communication with a first side of a primary heat exchanger. The liquid is boiled to produce a vapor. The vapor is passed through a vapor compressor to a second side of the primary heat exchanger so as to condense at least a portion of said vapor. Additional amounts of the liquid are introduced at a feed rate so as to maintain approximately the same volume of liquid in the evaporation loop. The liquid is recirculated at a recirculation rate of 25 to 200 times the feed rate. 
     The invention is also a two-loop vapor compression distiller. The major components of the invention are a primary heat exchanger having a first side thereof which facilitates heat flow to a second side thereof, an evaporation vessel for boiling a liquid and collecting the vapor of the liquid in the upper portion of the evaporation vessel, a vapor compressor communicating with the upper portion of the evaporation vessel and with an inlet to the first side of the primary heat exchanger, and a recirculation pump. There is also an evaporation loop providing fluid communication from the evaporation vessel through the recirculation pump and through the second side of the primary heat exchanger and back to the evaporation vessel, a means for boiling the liquid within the evaporation loop, a transfer line for supplying the liquid to the evaporation loop at a feed rate, a secondary heat exchanger having a first side thereof which facilitates heat flow to a second side thereof, a condensate line for providing fluid communication between an outlet of the first side of the primary heat exchanger and an inlet of the first side of the secondary heat exchanger, a feed pump, a feed loop providing fluid communication from the feed pump through the second side of the secondary heat exchanger to the transfer line and back to the feed pump, and a feed line for supplying the liquid at the feed rate to the feed loop. 
     Accordingly, several objects and advantages of the invention are to provide a vapor compression distiller which addresses the disadvantages of prior vapor compression distillers. These include improved heat transfer by rapid turbulent flow of liquid through the inside of the heat exchanger provided by one or more high volume recirculation pumps, and optionally the use of turbulence enhancing devices (turbulators) inside the heat exchanger which increases the liquid turbulence at the inside walls and dramatically reduces or stops fouling, increased flexibility of addition of makeup heat by providing for the addition of steam to compensate for thermal losses in either the recirculating liquid, the heat exchanger, or the vessel, as well as use of a heat exchanger between the condensate liquid and the feed liquid to recover heat from the hot condensate. Variable system feed rates are addressed by use of a system idle function which allows the system to maintain operating temperatures and rapidly and automatically continue operation when the system feed again resumes. This simple, reliable design allows for easier system operation and reduced maintenance, as well as reduced time required for cleaning of the heat exchanger in high fouling environments. 
     Still further objects and advantages will become apparent from a consideration of the ensuing description and accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram showing the major components of a preferred embodiment of the invention. 
     FIGS. 2A-2H are a composite showing a full-size process and instrumentation drawing of a preferred embodiment of the invention. 
     FIG. 3 is a elevation-view diagram showing the location of the turbulence-enhancing devices inside the tubes of a shell-and-tube primary heat exchanger. 
     FIG. 3 a  is a plan-view diagram showing one of the tubes depicted in FIG. 3 with its turbulence-enhancing device inside. 
     FIG. 3 b  is a partial elevation-view diagram showing a preferred method of hanging the turbulence-enhancing devices inside two of the tubes depicted in FIG.  3 . 
     FIG. 4 a  is a cross section view of the evaporation vessel, taken along line  4 — 4  of FIG.  1 . 
     FIG. 4 b  is a diagrammatic elevation view of the lower portion of the evaporation vessel, showing the cyclonic flow of the liquid to be evaporated. 
     FIG. 5 is an elevation view of the interior components of the upper portion of the evaporation vessel. 
     FIG. 6 a  is an elevation-view diagram showing a chain as a turbulence-enhancing device. 
     FIG. 6 b  is an elevation-view diagram showing a static mixer as a turbulence-enhancing device. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Structure. FIG. 1 shows the major components of the structure of the invention. The distiller comprises two main liquid circulation loops, the feed loop and the evaporation loop. The feed loop circulates a feed liquid to be evaporated. The evaporation loop includes an evaporation vessel  12  in the form of a cylindrical tank. The top of the evaporation vessel  12  is connected by a vapor compression inlet line  34  to a blower or compressor  10 . The blower bypass line  50  bypasses the blower or compressor  10  when valve  51  is open. The compressor  10  provides a method for compressing the vapor that forms when a liquid in the evaporation vessel  12  boils. A vapor compression outlet line  34  exits the blower or compressor  10  to connect with a hot inlet  17  of a primary heat exchanger  18 . Optionally, a degasser  70  may be inserted in the vapor compression outlet line  36  to remove non-compressible gases that may be present in the vapor. A condensate line  30  exits the primary heat exchanger  18  to connect with a hot inlet  13  of a secondary heat exchanger  14 . A condensate outlet line  31  exits the secondary heat exchanger  14  to provide distillate from the distiller. Optionally, the condensate line  30  may be connected directly to the condensate outlet line  31 , eliminating the secondary heat exchanger  14 . 
     A feed inlet line  28  allows liquid feed to enter the vapor compression distiller either directly into the feed loop  74  or into a feed holding tank  76 . The feed loop  74  is pumped by feed pump  56  and passes through the cold side of the secondary heat exchanger  14  and back around to the feed holding tank  76 . A portion of the feed liquid can be bled off through a valve  62  into the evaporation loop  16  via a transfer line  72 . A level control (not shown) operating off a level sensing device  66  in a level well  52  allows a feed rate to be set sufficient to maintain approximately the same volume of liquid in the evaporation vessel. Optionally, the return portion of the feed loop downstream of the valve  62  can be eliminated by setting valve  62  to pass all of the liquid feed to the evaporation loop  16  and controlling the feed pump rate. 
     The evaporation loop  16  allows the liquid feed to circulate and be heated to boiling by the heat of make-up steam and the heat recovered by condensing the vapor in the primary heat exchanger  18 . The evaporation loop  16  exits the evaporation vessel  12  and passes through a high-speed recirculation pump  40 . A portion of the liquid circulating in the evaporation loop  16  may be bled off through a valve  37  into a concentrate outlet  38 . The evaporation loop  16  passes through a self-cleaning strainer  39  and into the cold inlet  19  of the primary heat exchanger  18 . The evaporation loop  16  exits the primary heat exchanger  18  and passes through a mixing loop  26  and returns into the evaporation vessel  12 . The evaporation loop  16  is connected in a tangential manner to the periphery of the evaporation vessel  12  so that a swirling, vortex action is induced by the entry of the circulating liquid into the evaporation vessel  12 . 
     Makeup steam from a boiler (not shown) or external source is provided to initiate operation of the evaporator and to provide for heat losses due to incomplete recovery of the heat of evaporation in the primary heat exchanger  18 . A makeup steam line  32  feeds into the evaporation loop  16  or into the vessel through a sparger (not shown). 
     The evaporation vessel  12  contains a vapor disengagement section  44  above the level of the liquid being evaporated. Optionally, full spray nozzles  49  spray liquid feed or other suitable liquid (such as process water) into the vapor disengagement section to assist the disengagement of the vapor from mist and other liquid droplets. Mist eliminators  46 ,  48  with clean-in-place nozzles  47  are placed above the full spray nozzles  49 . The vapor compressor inlet line  34  is between the blower or compressor  10  and the top of the evaporation vessel  12 . The evaporation vessel has a closed top  65  and a closed bottom  64 , each of which may be generally of any shape. In applications where the feed contains precipitates or solids (such as wastewater), the closed bottom  64  may have a conical shape to facilitate sliding of the solids to the concentrate outlet line  38 . If the bottom is conical, a preferred shape is a cone having an interior cross-section angle of 60 degrees. 
     The composite drawing shown in FIGS. 2A-2H is a process and instrumentation drawing of a major embodiment of this system. The alphanumeric tags in this drawing are provided by Table 1. 
     The primary heat exchanger  18  can be of the shell-and-tube type. In this case, the use of turbulators is preferred. Turbulators are devices to turbulate (i.e., increase turbulence) and rapidly mix the liquid or the liquid/gaseous mixture, thereby transporting heat throughout the mixture and reducing fouling inside the tubes. FIG. 3 depicts an elevation view showing a shell-and-tube primary heat exchanger with turbulators inside the tubes. FIGS. 3 a ,  3   b ,  6   a  and  6   b  show turbulators  53 ,  54 , and  55  inside the tubes  42 . The tube side of the heat exchanger is shown above and below the tubes  42  as well as inside the tubes  42 . The shell side of the primary heat exchanger  18  is shown outside the tubes  42 . The turbulence-enhancing devices  53 ,  54 , and  55  can take a number of forms. 
     Examples include static mixers  53  (more fully described in U.S. Pat. No. 4,670,103, incorporated herein by reference), chains  55 , or metal strips with twists  54  or protuberances designed to produce turbulence at the recirculation rate of the 
     
       
         
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
             
             
               
                 101 
                 PUMP 2″ INLET X 1″ OUTLET FLANGED SS 
               
               
                 102 
                 BASKET STRAINER 1″ FLANGED CPVC 
               
               
                 103 
                 BASKET STRAINER 1″ FLANGED CPVC 
               
               
                 104 
                 SECONDARY HEAT EXCHANGER 2″ FLANGED SS 
               
               
                 105 
                 BLOWER 6″ FLANGED CAST IRON 
               
               
                 106 
                 PRIMARY HEAT EXCHANGER 6″ FLANGED SS 
               
               
                 108 
                 STEAM TRAP 2″ FLANGED CAST IRON 
               
               
                 109 
                 (2) CLEAN IN PLACE SPRAY NOZZLES SS 
               
               
                 110 
                 (1) FULL COVERAGE SPRAY NOZZLE SS 
               
               
                 111 
                 PLATE-PAK 12″ THK IN 3 SECTIONS SS 
               
               
                 112 
                 MIST ELIMINATOR 6″ THK IN 3 SECTIONS SS 
               
               
                 113 
                 SIGHT GLASS 4″ FLANGED SS 
               
               
                 114 
                 VORTEX BREAKER FITS INSIDE 6″ PIPE SS 
               
               
                 115 
                 PUMP 6″ INLET × 4″ OUTLET FLANGED SS 
               
               
                 117 
                 INVERTED CONE STRAINER 8″ FLANGED SS 
               
               
                 119 
                 AIR COMPRESSOR CS 
               
               
                 120 
                 BOILER CS 
               
               
                 121 
                 MOTOR STARTER AND VFD PANEL CS 
               
               
                 122 
                 CONTROL PANEL CS 
               
               
                 CKV101 
                 SWING CHECK VALVE 1″ SW SS 
               
               
                 CKV102 
                 SWING CHECK VALVE 1″ SW SS 
               
               
                 FIT101 
                 FLOW INDICATOR 1″ FNPT BRONZE 
               
               
                 FIT102 
                 FLOW INDICATOR 1″ FNPT BRONZE 
               
               
                 FS101 
                 FLOAT SWITCH ½″ MNPT SS 
               
               
                 FV102 
                 BALL VALVE 3 WAY W/PNEUMATIC ACTUATOR 1″ 
               
               
                   
                 SW SS 
               
               
                 FV103 
                 BALL VALVE W/PNEUMATIC ACTUATOR 2″ SW SS 
               
               
                 FV104 
                 BALL VALVE W/PNEUMATIC ACTUATOR 1″ SW SS 
               
               
                 FV105 
                 BALL VALVE W/PNEUMATIC ACTUATOR &amp; POSR 2″ 
               
               
                   
                 SW SS 
               
               
                 HV103 
                 MANUAL BALL VALVE 1″ SW SS 
               
               
                 HV104 
                 MANUAL BALL VALVE 1″ SW SS 
               
               
                 HV105 
                 MANUAL BALL VALVE 1″ SW SS 
               
               
                 HV106 
                 MANUAL BALL VALVE 1″ SW SS 
               
               
                 HV107 
                 MANUAL BALL VALVE 1″ SW SS 
               
               
                 HV108 
                 MANUAL BALL VALVE 1″ FNPT SS 
               
               
                 HV109 
                 MANUAL BALL VALVE 1″ SW SS 
               
               
                 HV110 
                 MANUAL BALL VALVE 1″ FNPT SS 
               
               
                 HV111 
                 MANUAL BALL VALVE 1″ SW SS 
               
               
                 HV112 
                 MANUAL BALL VALVE 2″ SW SS 
               
               
                 HV113 
                 MANUAL BALL VALVE 1″ FNPT SS 
               
               
                 HV114 
                 MANUAL BALL VALVE ¾″ FNPT SS 
               
               
                 HV118 
                 MANUAL BALL VALVE 1″ FNPT SS 
               
               
                 HV119 
                 MANUAL BALL VALVE ½″ FNPT SS 
               
               
                 HV120 
                 MANUAL BALL VALVE ½″ FNPT SS 
               
               
                 HV121 
                 MANUAL BALL VALVE 1″ SW SS 
               
               
                 HV122 
                 MANUAL BALL VALVE ½″ SW SS 
               
               
                 HV123 
                 MANUAL BALL VALVE ½″ SW SS 
               
               
                 HV124 
                 MANUAL BALL VALVE ½″ SW SS 
               
               
                 HV125 
                 MANUAL BALL VALVE ¾″ FNPT SS 
               
               
                 HV126 
                 MANUAL BALL VALVE 1″ FNPT SS 
               
               
                 HV127 
                 MANUAL BALL VALVE ¾″ FNPT SS 
               
               
                 HV128 
                 MANUAL BALL VALVE 1″ SW SS 
               
               
                 HV129 
                 MANUAL BALL VALVE ½″ FNPT SS 
               
               
                 HV130 
                 MANUAL BALL VALVE 1″ SW SS 
               
               
                 HV131 
                 MANUAL BALL VALVE ½″ FNPT SS 
               
               
                 HV132 
                 MANUAL BALL VALVE 1″ SW SS 
               
               
                 HV133 
                 MANUAL BALL VALVE 1″ SW SS 
               
               
                 HV136 
                 MANUAL BALL VALVE ½″ FNPT SS 
               
               
                 HV137 
                 MANUAL BALL VALVE 2″ SW SS 
               
               
                 HV138 
                 MANUAL BALL VALVE 1″ FNPT SS 
               
               
                 HV139 
                 MANUAL BALL VALVE 6″ FLANGED SS 
               
               
                 HV140 
                 MANUAL BALL VALVE ½″ FNPT SS 
               
               
                 HV141 
                 MANUAL GLOBE VALVE 4″ FLANGED SS 
               
               
                 HV142 
                 MANUAL BALL VALVE 4″ FLANGED SS 
               
               
                 HV144 
                 MANUAL BALL VALVE 4″ FLANGED SS 
               
               
                 HV145 
                 MANUAL BALL VALVE 4″ FLANGED SS 
               
               
                 HV147 
                 MANUAL BALL VALVE 1″ FNPT SS 
               
               
                 HV148 
                 MANUAL BALL VALVE 1″ FNPT SS 
               
               
                 HV150 
                 MANUAL GATE VALVE 1″ SW SS 
               
               
                 HV151 
                 MANUAL BALL VALVE ½″ FNPT SS 
               
               
                 HV153 
                 MANUAL BALL VALVE ½″ FNPT SS 
               
               
                 HV154 
                 MANUAL BALL VALVE ½″ FNPT SS 
               
               
                 HV155 
                 MANUAL BALL VALVE ½″ FNPT SS 
               
               
                 HV156 
                 MANUAL BALL VALVE ½″ FNPT SS 
               
               
                 HV157 
                 MANUAL BALL VALVE ½″ FNPT SS 
               
               
                 HV158 
                 MANUAL BALL VALVE ¾″ FNPT SS 
               
               
                 HV159 
                 MANUAL BALL VALVE ¾″ FNPT SS 
               
               
                 HV160 
                 MANUAL BALL VALVE ¾″ FNPT SS 
               
               
                 HV161 
                 MANUAL BALL VALVE ¾″ FNPT SS 
               
               
                 HV162 
                 MANUAL BALL VALVE ¾″ FNPT SS 
               
               
                 LS101 
                 LEVEL SWITCH 1″ FLANGED SS 
               
               
                 MCV101 
                 AIR VENT ¾″ FNPT CS 
               
               
                 MCV102 
                 AIR VENT ¾″ FNPT CS 
               
               
                 MCV103 
                 AIR VENT ¾″ FNPT CS 
               
               
                 PI101 
                 PRESS. GAUGE W/DIAPHRAGM ?-? PSIG ½″ MNPT SS 
               
               
                 PI102 
                 PRESS. GAUGE W/DIAPHRAGM ?-? PSIG ½″ MNPT SS 
               
               
                 PI103 
                 PRESS. GAUGE W/DIAPHRAGM ?-? PSIG ½″ MNPT SS 
               
               
                 PI104 
                 PRESS. GAUGE W/DIAPHRAGM ?-? PSIG ½″ MNPT SS 
               
               
                 PI105 
                 PRESS. GAUGE W/DIAPHRAGM ?-? PSIG ½″ MNPT SS 
               
               
                 PI111 
                 PRESS. GAUGE W/DIAPHRAGM ?-? PSIG ½″ MNPT SS 
               
               
                 PI112 
                 PRESS. GAUGE W/DIAPHRAGM ?-? PSIG ½″ MNPT SS 
               
               
                 PI113 
                 PRESS. GAUGE W/DIAPHRAGM ?-? PSIG ½″ MNPT SS 
               
               
                 PR101 
                 PRESS. REGULATOR ¼″ FNPT PVC 
               
               
                 PS101 
                 PRESS. SWITCH ½″ MNPT SS 
               
               
                 PS102 
                 PRESS. SWITCH ½″ MNPT SS 
               
               
                 PS103 
                 PRESS. SWITCH ½″ MNPT SS 
               
               
                 PS104 
                 PRESS. SWITCH ½″ MNPT SS 
               
               
                 PS105 
                 PRESS. SWITCH ½″ MNPT SS 
               
               
                 PS106 
                 PRESS. SWITCH ½″ MNPT SS 
               
               
                 PSV101 
                 VACUUM BREAKER 1″ MNPT SS 
               
               
                 PSV102 
                 SAFETY VALVE 3″ FLANGED CS 
               
               
                 SV101 
                 SOLENOID VALVE ½″ FNPT BRASS 
               
               
                 TC101 
                 THERMOCOUPLE W/WELL ¾″ MNPT SS 
               
               
                 TC102 
                 THERMOCOUPLE W/WELL ¾″ MNPT SS 
               
               
                 TI101 
                 TEMPERATURE GAUGE ?-? DEG. F. ½″ MNPT SS 
               
               
                 TI102 
                 TEMPERATURE GAUGE ?-? DEG. F. ½″ MNPT SS 
               
               
                 TI103 
                 TEMPERATURE GAUGE ?-? DEG. F. ½″ MNPT SS 
               
               
                 TI104 
                 TEMPERATURE GAUGE ?-? DEG. F. ½″ MNPT SS 
               
               
                 TI105 
                 TEMPERATURE GAUGE ?-? DEG. F. ½″ MNPT SS 
               
               
                 TI108 
                 TEMPERATURE GAUGE ?-? DEG. F. ½″ MNPT SS 
               
               
                 TSH101 
                 THERMOSWITCH SET AT ? DEG. F. ½″ MNPT SS 
               
               
                 THS102 
                 THERMOSWITCH SET AT ? DEG. F. ½″ MNPT SS 
               
               
                 XJ101 
                 EXPANSION JOINT 6″ FLANGED SS 
               
               
                 XJ102 
                 EXPANSION JOINT 6″ FLANGED SS 
               
               
                   
               
             
          
         
       
     
     liquid. The turbulators  53 ,  54 , and  55  may be mounted inside the tubes  42  in a fixed manner or may be suspended from the top of the tube sheet or otherwise loosely mounted so they will vibrate or rattle in the turbulent liquid flow. Mounting the turbulators  53 ,  54 , and  55  so that they rattle against the interior sides of the tubes  42  is preferable to inhibit scale formation on the interior sides of the tubes  42 . In addition, such mounting helps to break up the laminar flow of the liquid which would otherwise form along the inside surfaces of the tubes, allowing for turbulent flow close to the tube sides. In this manner, the turbulent flow enhances the heat transfer from the exterior of the tube on the shell side of the heat exchanger  18  through to the liquid in the tubes on the tube side of the heat exchanger  18 . 
     FIG. 3 a  shows, in plan view, one of the turbulators  54 . It is a twisted sheet-metal helix just smaller than the inside diameter of a tube  42 . In a preferred design, the tubes are 0.75 inch cylindrical tubes 80 inches long, extending 0.5 inch below the bottom of the tube sheet. The helixes are 18-gauge stainless steel, twisted 360 degrees approximately every 18 inches. As shown in FIG. 3 b , the turbulators  54  may be mounted loosely by drilling a hole  60  in the top of each turbulator  54 , threading a rod  58  (stainless steel) through all turbulators  54  in tubes  42  that form a straight line in the evaporator, and resting the rod  58  on the upper tube sheet. Such a mounting allows the turbulators  54  to rattle against the side walls of the tubes  42  and facilitates removal of the devices for cleaning. 
     It is preferable that the turbulators do not take up a significant portion of the volume of the tubes  42  (preferably less than 10% by volume), thereby minimizing both the volume displacement and the frictional loss of the circulating liquid. 
     The primary heat exchanger can also be a spiral type or a plate type, of the form and structure well known in the art. 
     FIG. 4 a  is a cross section view of the evaporation vessel, taken along line  4 — 4  of FIG.  1 . This view shows the connection of the evaporation loop  16  to the periphery of the evaporation vessel  12  in a tangential manner so that a swirling, vortex action is induced by the entry of the circulating liquid into the evaporation vessel  12 . The vortex action and cyclonic flow is shown in FIG. 4 b . A vortex breaker  80  is located at the bottom of the evaporation vessel  12  at the transition to the evaporation loop  16 . 
     Similarly, the degasser  70  operates by vortex action. To accomplish this, the vapor compression outlet line  36  is connected to the periphery of the degasser  70  in a tangential manner so that a swirling, vortex action is induced by the entry of the circulating liquid into the degasser  70 . Non-condensable gasses build up pressure and a pop-off valve (not shown) located at the bottom of the degasser releases the gasses heavier than the vapor as the pressures builds above a pre-selected set point. 
     FIG. 5 is an elevation view of the interior components of the upper portion of the evaporation vessel. This view shows the vapor disengagement section  44  above the level of the liquid being evaporated. If used, full spray nozzles  49  spray liquid or other suitable liquid into the vapor disengagement section to assist the disengagement of the vapor from mist and other liquid droplets. A plate pack mist eliminator  46  with steam scrubbing nozzle  47  and demister pads  48  with steam scrubbing nozzle  47  are placed above the full spray nozzles  49 . 
     Operation. Vapor that is liberated from the boiling pool in the evaporation vessel  12  is evacuated through a corrugated plate style mist eliminator  46  followed by a demister pad style mist eliminator  48 . Spray nozzles  49  are installed below the corrugated plate mist eliminator to be optionally used for introduction of chemical defoamer or for simple impingement liquid scrubbing of the liberated vapor. The nozzles are flow rated at 5% of the designed evaporation rate. 
     Vapor evacuation is imposed upon the vessel by a positive displacement rotary lobe vapor blower. Saturated vapor at approximately 0-2 psig is evacuated from the evaporation vessel and recycled through the blower to apply its latent heat to the incoming feed liquid within the primary heat exchanger  18 . In the process, the blower  10  imparts an approximate 5 psig differential pressure rise to the vapor prior to reintroduction of the vapor into the hot side of the primary heat exchanger. The blower is supplied with an automatically operated by-pass line  50  to regulate the pressure in the evaporation vessel  12 . If the pressure on gauge  45  falls below 1.5 psig, valve  51  is fully opened. As the pressure rises, a signal from the gauge  45  controls a modulated closing of valve  45  from fully open at 1.5 psig to fully closed at 2.0 psig. 
     As the vapor gives up its latent heat to the incoming feed liquid in the primary heat exchanger  18 , it cools to slightly below the boiling point. Still pressurized by the recycled vapor, the distillate exits the primary heat exchanger through a vapor trap  78  and is transferred to a secondary heat exchanger to partially preheat the incoming feed liquid. Final distillate exist the system at approximately 120-140 degrees Fahrenheit. 
     The heat recovered and recycled is approximately 95% of the heat required for atmospheric evaporation, therefore; make-up heat and heat required for initial start-up can be supplied in the form of steam. This make-up steam is supplied through a modulating valve, controlled with a temperature controller and indirectly introduced into the recirculation loop or into the evaporation vessel  12  through a sparger. 
     The feed rate of the feed liquid is regulated to match the evaporation rate via a level sensor  66  housed in a stand pipe  52  external to the operating evaporation vessel. The level sensor  66  is used to measure the liquid level of the boiling pool and to control the feed pump  56 . As the pool evaporates, the liquid level drops. Once the level reaches a low level point, the two-way valve  62  is activated to provide additional feed liquid to the evaporation loop  16  and the level of the pool rises until a high level point deactivates the two-way valve  62 . This procedure continuously cycles within an approximate level differential of two (2) inches in the standpipe  52 . 
     As 80-98% of the feed liquid is typically evaporated and recovered as distillate, contaminants are continuously recirculated and concentrated within the evaporation vessel. Concentrate is evacuated from the evaporation loop  16  through a slip stream controlled by a valve  37  activated by a timer. The timer is adjustable for regulating the duration and repetition of the valve sequence. The maximum amount of concentrate removed in a single purging cycle is determined by the liquid level of the boiling pool. When the low liquid level switch is reached, it closes the concentrate valve and resets the timer. The timer will then begin a new count down until it initiates another concentrate removal cycle. 
     The operational parameters of the distiller are chosen so as to maintain a liquid, rather than a gaseous, flow throughout the primary heat exchanger  18 . This is done by maintaining the recirculating flow rate at a value 25 to 200 times the feed rate of the liquid to be evaporated. The feed pump  56  has a variable speed drive which can vary the heat recovery of the secondary heat exchanger. In one embodiment, the variable speed drive is rated from 0 to 7 gal/min and is operated at 4 gal/min, or approximately 6000 gallons per day. The recirculation pump  40  is a 5 hp unit, operated at 20 psig to produce 200 gal/min. The recirculation pump rate is preferably controlled manually by reading a pressure gauge on the output side of the recirculation pump  40  and by adjusting a flow control valve to achieve the proper operational pressure. Transfer of heat from the compressed vapor may result in local boiling of the liquid inside the evaporation loop  16  above the primary heat exchanger  18 . The recirculation rate is fast enough to entrain the vapor bubbles in the liquid in the primary heat exchanger  18  and to maintain a turbulent-flow, single liquid phase throughout the primary heat exchanger  18 , thereby increasing the heat transfer to the recirculating liquid. 
     At start up, the evaporation vessel is filled with raw feed liquid until the feed liquid applies an appropriate head pressure for the recirculation pump  40 . In one embodiment, this is approximately 35-45 inches above the center line of the recirculation pump  40 . The recirculation pump  40  is started and steam is introduced live into the system. The temperature of the liquid in the evaporation vessel is raised until there is positive pressure (up to 3 psig, preferably between 1 and 2 psig) on gauge  45  in the vapor disengagement section  44 . At this point a high temperature cut-off point and a lower temperature turn-on point can be set for temperature readings on a temperature sensor in the boiling pool in the evaporation vessel  12 . The temperature settings can thereafter be used to manually or automatically control the introduction of make-up steam to operate the evaporator. With a positive pressure in the vapor disengagement section  44 , the blower or compressor  10  is turned on. This causes a slight drop in pressure, which thereafter rapidly rises as heat is applied to the hot side of the primary heat exchanger  18 . Operating the evaporator at a positive pressure in the vapor disengagement section  44  minimizes physical carry-over of the feed liquid which otherwise would deleteriously affect the quality of the distillate. 
     The advantages of the invention include improved heat transfer by rapid turbulent flow of liquid through the inside of the primary heat exchanger provided by one or more high volume recirculation pumps. Turbulators placed inside the primary heat exchanger (when it is a shell-and-tube type) can also be used to increase the liquid turbulence at the inside walls of the heat exchanger. This also dramatically reduces or stops fouling inside the heat exchanger. 
     Increased flexibility of addition of steam for either startup or as makeup heat is provided by allowing for the addition of makeup steam to compensate for distiller thermal losses. This makeup steam can be added either to the recirculating liquid or directly to the evaporation vessel  12 . Direct injection of the steam to the liquid is the most efficient method to transfer the heat but this results in some dilution of the material being evaporated by the condensed steam. If this is not desired, the steam for startup or makeup heat can be fed into the hot inlet  17  of the primary heat exchanger  18 . 
     Additional energy can be conserved by use of a heat exchanger between the hot condensate liquid and the cool incoming feed liquid. Also, if significant amounts of concentrated feed are to be discharged a heat recovery heat exchanger can be used to recover heat from the hot concentrate also. 
     Accordingly, it can be seen that according to the invention, an improved application of vapor compression evaporation utilizing highly turbulent liquid flow with increased heat transfer on the cold side of the primary heat exchanger surface and the significantly reduced fouling of this surface by highly turbulent flow from both the rapid recirculation of the liquid though the cold side of the primary heat exchanger and by use of the turbulators (shell-and-tube type of primary heat exchanger). 
     As used herein, the term “steam” means the gaseous phase of the liquid being evaporated, whether the liquid is water or not. Although the description above contains many specifics, these should not be construed as limiting the scope of the invention but as merely providing illustrations of some of the presently preferred embodiments of this invention. Various other embodiments and ramifications are possible within the scope of the invention. For example, this vapor compression distiller can be used to process a wide variety of materials under significantly different conditions while maintaining a highly turbulent liquid flow through the primary heat exchanger which has significantly reduced fouling characteristics. Furthermore, the flexibility in addition of the makeup heat in the form of steam allows for either the more efficient method of heat transfer by direct steam injection into the material being evaporated or by indirect means by feeding this makeup steam into the hot side of the primary heat exchanger. This would have the further benefit in not diluting the material to be evaporated during system startup.