Abstract:
A system and method are disclosed for purifying a waste fluid stream. The system includes a recirculation pump having an inlet for a recirculation stream and an outlet to expel a pressurized stream. The system includes a compressor having an inlet for an evaporation stream and an outlet for a pressurized evaporation stream. A primary heat exchanger has inlets for the pressurized stream and the pressurized evaporation stream, an internal surface area for heat transfer from the evaporation stream to the pressurized stream, and outlets for a cooled product stream and a heated pressurized stream. The heated pressurized stream is formed by heating the pressurized stream and the cooled product stream is formed by cooling the evaporation stream. The system includes an evaporation unit having an inlet for the heated pressurized stream and outlets for an evaporation stream and the recycled liquid bottoms stream.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Patent Application No. 60/968,284 entitled “APPARATUS, SYSTEM, AND METHOD FOR PURIFYING AN AQUEOUS STREAM” and filed on Aug. 27, 2007, for Larry D. Sanderson, et. al which is incorporated herein by reference. The application incorporates by reference U.S. Provisional Application Ser. No. 60/968,285 filed Aug. 27, 2007. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    This invention relates to waste stream purification, and more particularly relates to purification of waste streams containing contaminants typically found in oilfield and industrial applications. 
         [0004]    2. Description of the Related Art 
         [0005]    Water is often used for various tasks in the oil and gas production and other industrial operations. For example, water may be injected into an oil well to repressurize a reservoir, and water may be pumped from a well in the process of extracting oil or gas. As another example, water may used to deliver proppants to underground fractures. Due to environmental concerns, contaminated water cannot simply dumped on the ground or pumped back into wells. The requirement to treat contaminated water sources presents an additional operation and expense for oil and gas well owners and operators. 
         [0006]    Treating waste water typically involves one or more unit operations, such as distillation or filtration. Distillation is an energy-intensive process that frequently requires large distillation columns. Filtration may require frequent filter changes to keep the system operating at the desired contaminant removal levels. The oil or gas producer must have personnel on hand to operate the waste water treatment unit operations, and must have the required energy and materials available to process the produced waste water. All of these constraints cost money and increase the cost of oil and gas production. 
       SUMMARY OF THE INVENTION 
       [0007]    From the foregoing discussion, it should be apparent that a need exists for a system and method for purifying an aqueous stream. Beneficially, such a system and method would provide oil and gas producers a more efficient way to process waste water. Such a system and method would provide a source of clean water for use in further well operations, for human and agricultural needs, or for reinjection into the ground. Further, such a system and method could be used to process waste water in settings other than the petroleum industry. The system and method could be used when circumstances call for a self-contained, energy-efficient purification system. 
         [0008]    In one embodiment, the invention is a system to purify a waste fluid stream. The system includes a recirculation pump having an inlet for a recirculation stream and an outlet to expel a pressurized stream. The recirculation stream includes a waste fluid stream and a recycled liquid bottoms stream. The system also includes a compressor having an inlet for an evaporation stream and an outlet for a pressurized evaporation stream. The system further includes a primary heat exchanger. The primary heat exchanger has inlets for the pressurized stream and the pressurized evaporation stream, an internal surface area for heat transfer from the evaporation stream to the pressurized stream, and outlets for a cooled product stream and a heated pressurized stream. The heated pressurized stream is formed by heating the pressurized stream and the cooled product stream is formed by cooling the evaporation stream. The system further includes an evaporation unit having an inlet for the heated pressurized stream and outlets for an evaporation stream and the recycled liquid bottoms stream. The evaporation stream is formed when volatile compounds in the heated pressurized stream evaporate in the evaporation unit. The liquid bottoms stream is formed from a portion of the heated pressurized stream that does not evaporate. 
         [0009]    In certain embodiments, the system further includes a stripping unit that receives the evaporation stream from the primary heat exchanger. The stripping unit typically includes a stripping vessel, a stripper recycle pump, a reboiler, a condensing unit, and at least one valve. The stripping vessel includes inlets for the cooled product stream, a recycled bottoms stream, and a stripper reflux stream and outlets for a stripper vapor outlet stream and a stripper bottoms stream. The stripper recycle pump includes an inlet for the stripper bottoms stream and an outlet for the recycled bottoms stream. The reboiler includes inlets for the recycled bottoms stream and a heat transfer fluid. The reboiler has an internal surface area for heat transfer from the heat transfer fluid to the recycled bottoms stream. 
         [0010]    The condensing unit has an inlet for the stripper vapor outlet stream and outlets for a volatile fractions stream, a non-condensable stream, and the stripper reflux stream. The stripper reflux stream returns to the stripping vessel. The at least one valve has an inlet for the recycled bottoms stream and at least two outlets, wherein one outlet comprises a final product stream port. 
         [0011]    In a further embodiment, the condensing unit includes a primary condenser. The primary condenser has inlets for the stripper vapor outlet stream and a first coolant stream, has an internal surface area for heat transfer from the stripper vapor outlet stream to the coolant stream, and has outlets for a cooled stripper vapor stream and a spent coolant stream. The condensing unit also includes a collection vessel that has inlets for the cooled stripper vapor stream and a liquid return stream and outlets for a collection vapor stream and a condensed stream. 
         [0012]    The system may further include a secondary condenser. The secondary condenser may have inlets for the collection vapor stream and a second coolant stream, an internal surface area for heat transfer from the collection vapor stream to the second coolant stream, and outlets for a non-condensable stream, the liquid return stream, and a spent coolant stream. The liquid return stream may include a fraction of the collection vapor stream that condenses in the secondary condenser. The non-condensable stream may include a fraction of the collection vapor stream that does not condense in the secondary condenser. The system may include a splitter valve having an inlet for the condensed stream and outlets for the stripper reflux stream and the volatile fractions stream. 
         [0013]    The system may have a ratio of the flow rate of the stripper reflux stream to the sum of the flow rates of the volatile fraction stream and the non-condensable stream between 1 and 200. The system may have a ratio of the flow rate of the stripper reflux stream to the sum of the flow rates of the volatile fraction stream and the non-condensable stream between 10 and 50. The system may have a ratio of the flow rate of the stripper reflux stream to the sum of the flow rates of the volatile fraction stream and the non-condensable stream of approximately 20. 
         [0014]    The system may also include a steam control unit that provides backpressure to keep the cooled product stream in a liquid phase. The steam control unit typically includes a steam trap having an inlet for the cooled product stream from the primary heat exchanger and an outlet for a condensed distillate stream, a storage vessel having an inlet for the condensed distillate stream and outlets for a vapor vent stream and a liquid stream, a pump having an inlet for the liquid stream and an outlet to the stripping unit, and a vent having an inlet for the vapor vent stream and an outlet to the stripping unit. 
         [0015]    In certain embodiments, the steam control unit provides condensed steam to the stripping vessel and the vapor vent stream from the storage vessel is introduced to the stripping vessel below a distribution tray. The steam control unit may provide backpressure to keep the cooled product stream in a liquid phase. The steam control unit may include a separator having an inlet for the cooled product stream from the primary heat exchanger and a outlets for a liquid stream and a vapor vent stream, a pump having an inlet for the liquid stream and an outlet to the stripping unit, and a vent having an inlet for the vapor vent stream and an outlet to the stripping unit. The steam control unit may provide the liquid stream to the stripping vessel and the vapor vent stream may be introduced to the stripping vessel below a distribution tray. 
         [0016]    The system may further include an oxidizer unit. The oxidizer unit may include inlets for a product stream and an oxidizer, an outlet for an oxidized stream, and an ultrasonic vibration source. In another embodiment, the oxidizer unit may include an inlet for a product stream, an outlet for an oxidized stream, and an ultraviolet radiation source. 
         [0017]    The system may include a secondary recovery heat exchanger having inlets for the waste fluid stream and a final product stream, having an internal surface area for heat transfer from the final product stream to the waste fluid stream, and having outlets for a cooled final product stream and a heated waste fluid stream. 
         [0018]    The system may include an additives unit. The additives unit may include a pump having an inlet for additives and an outlet to the recirculation stream. 
         [0019]    The primary heat exchanger is typically configured with an inlet and an outlet for a heat transfer fluid and with an internal surface area for heat transfer from the heat transfer fluid to the pressurized stream. The primary heat exchanger may transfer heat from the evaporation stream to the recirculation stream such that the cooled product stream is a liquid. A secondary recovery heat exchanger may have inlets for the waste fluid stream and a purge stream, an internal surface area for heat transfer from the purge stream to the waste fluid stream, and outlets for a cooled purge stream and a heated waste fluid stream. 
         [0020]    The system may include an air-handling device. The air-handling device may have an inlet for the evaporation stream and an outlet to the primary heat exchanger. The air-handling device may be a blower. 
         [0021]    The system may also include a separator that removes solid material and hydrocarbons immiscible in water from the waste fluid stream before the waste fluid stream joins the recirculation stream. The system may include a feed pump to deliver the waste fluid stream to the separator. 
         [0022]    The system may include a final processing unit configured to remove remaining contaminants from the final product stream. The final processing unit may include a carbon adsorber. 
         [0023]    The system typically includes a controller that receives one or more signals from sensors and sends one or more signals to actuators. The sensors may measure parameters selected from the group consisting of pressure, temperature, level, flow, density, and chemical composition. The actuators may be selected from the group consisting of electronic, hydraulic, and pneumatic manipulation of controlled physical components of the apparatus. The controlled physical components of the apparatus may be selected from the group consisting of valves, pumps, and blowers. The controller may include an operator interface. 
         [0024]    The waste fluid stream may be contaminated oilfield process water. The ratio of the flow rate of the recirculation stream to the flow rate of the waste fluid stream may be between 50 and 500. In other embodiments, the ratio of the flow rate of the recirculation stream to the flow rate of the waste fluid stream is between 150 and 250. In a further embodiment, the ratio of the flow rate of the recirculation stream to the flow rate of the waste fluid stream is approximately 200. 
         [0025]    In one embodiment, the invention is a system to purify a waste fluid stream. The system includes a recirculation pump, a compressor, a primary heat exchanger, an evaporation unit, a stripping vessel, a stripper recycle pump, a reboiler, a condensing unit, and a secondary recovery heat exchanger. The recirculation pump has an inlet for a recirculation stream and an outlet to expel a pressurized stream. The recirculation stream may include a waste fluid stream and a recycled liquid bottoms stream. The compressor may have an inlet for an evaporation stream and an outlet for a pressurized evaporation stream. The primary heat exchanger may have inlets for the pressurized stream, the pressurized evaporation stream, and a heat transfer fluid. The heat exchanger may transfer heat from the heat transfer fluid and from the evaporation stream to the pressurized stream. 
         [0026]    The evaporation unit may have an inlet for the pressurized stream and outlets for an evaporation stream and the recycled liquid bottoms stream. The stripping vessel may have inlets for the evaporation stream, a recycled bottoms stream, and a stripper reflux stream and outlets for a stripper vapor outlet stream and a stripper bottoms stream. The stripper recycle pump may have an inlet for the stripper bottoms stream and an outlet for the recycled bottoms stream. The reboiler may have inlets for the recycled bottoms stream and a heat transfer fluid. The reboiler typically has an internal surface area for heat transfer from the heat transfer fluid to the recycled bottoms stream. The condensing unit may have an inlet for the stripper vapor outlet stream and outlets for a volatile fractions stream, a non-condensable stream, and the stripper reflux stream. The stripper reflux stream typically returns to the stripping vessel. The secondary recovery heat exchanger has inlets for the waste fluid stream and the final product stream. The heat exchanger typically transfers heat from the final product stream to the waste fluid stream. 
         [0027]    In certain embodiments, the invention is a method to purify a waste fluid stream. The method may include joining a waste fluid stream with a pressurized stream, recirculating the pressurized stream through a primary heat exchanger and an evaporation unit, transferring heat from an evaporation stream to the pressurized stream, evaporating volatile compounds from the pressurized stream in the evaporation unit, and returning a portion of the heated pressurized stream that does not evaporate to the pressurized stream. The volatile compounds form the evaporation stream. 
         [0028]    The method may further include introducing the evaporation stream into a stripping vessel, pumping the stripper bottoms stream from the stripping vessel through a reboiler and back to the stripping vessel, extracting a portion of the stripper bottoms stream as a product stream, heating the stripper bottoms stream in the reboiler, condensing a portion of the vapor outlet stream to form a stripper reflux stream and returning the stripper reflux stream to the stripping vessel. The evaporation stream typically separates into a vapor outlet stream and a liquid bottoms stream. 
         [0029]    The method may include mixing a chemical oxidizer with the product stream. The method may include vibrating a mixture of the chemical oxidizer and the product stream with ultrasonic vibration. In some embodiments, the method includes irradiating the product stream with ultraviolet radiation. The method may include removing contaminants from the product stream by passing the product stream through a filter. 
         [0030]    The method typically includes transferring heat from the product stream to the waste fluid stream. The method may include adding chemical additives to the pressurized stream. The method typically includes transferring heat from a heat transfer fluid to the pressurized stream. The method may include separating solid material and hydrocarbons immiscible in water from the waste fluid stream before the waste fluid stream joins the pressurized stream. 
         [0031]    The method may further include receiving one or more signals from sensors and controlling one or more actuators. The sensors may measure parameters selected from the group consisting of pressure, temperature, level, flow, density, and chemical composition. The actuators may be selected from the group consisting of electronic, hydraulic, and pneumatic manipulation of controlled physical components of the apparatus. The controlled physical components of the apparatus may be selected from the group consisting of valves, pumps, and blowers. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0032]    In order that the advantages of the invention will be readily understood, a more particular description of the invention briefly described above will be rendered by reference to specific embodiments that are illustrated in the appended drawings. Understanding that these drawings depict only typical embodiments of the invention and are not therefore to be considered to be limiting of its scope, the invention will be described and explained with additional specificity and detail through the use of the accompanying drawings, in which: 
           [0033]      FIG. 1  is a schematic block diagram illustrating one embodiment of an system for purifying a waste stream in accordance with the present invention; 
           [0034]      FIG. 2  is a schematic block diagram illustrating one embodiment of a condensing system in accordance with to the present invention; 
           [0035]      FIG. 3A  is a schematic block diagram illustrating one embodiment of a steam control unit in accordance with the present invention; 
           [0036]      FIG. 3B  is a schematic block diagram illustrating an alternate embodiment of a steam control unit in accordance with the present invention; and 
           [0037]      FIG. 4  is a schematic flow chart diagram illustrating an embodiment of a method for purifying a waste stream in accordance with the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0038]    It will be readily understood that the components of the present invention, as generally described and illustrated in the figures herein, may be arranged and designed in a wide variety of different configurations. Thus, the following more detailed description of the embodiments of the apparatus, system, and method of the present invention, as presented in  FIGS. 1 through 4 , is not intended to limit the scope of the invention, as claimed, but is merely representative of selected embodiments of the invention. 
         [0039]    Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. 
         [0040]    Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided, such as examples of materials, fasteners, sizes, lengths, widths, shapes, etc., to provide a thorough understanding of embodiments of the invention. One skilled in the relevant art will recognize, however, that the invention can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the invention. 
         [0041]    Many of the functional units described in this specification have been labeled as modules, in order to more particularly emphasize their implementation independence. For example, a module may be implemented as a hardware circuit comprising custom VLSI circuits or gate arrays, off-the-shelf semiconductors such as logic chips, transistors, or other discrete components. A module may also be implemented in programmable hardware devices such as field programmable gate arrays, programmable array logic, programmable logic devices or the like. 
         [0042]    Modules may also be implemented in software for execution by various types of processors. An identified module of executable code may, for instance, comprise one or more physical or logical blocks of computer instructions which may, for instance, be organized as an object, procedure, or function. Nevertheless, the executables of an identified module need not be physically located together, but may comprise disparate instructions stored in different locations which, when joined logically together, comprise the module and achieve the stated purpose for the module. 
         [0043]    Indeed, a module of executable code may be a single instruction, or many instructions, and may even be distributed over several different code segments, among different programs, and across several memory devices. Similarly, operational data may be identified and illustrated herein within modules, and may be embodied in any suitable form and organized within any suitable type of data structure. The operational data may be collected as a single data set, or may be distributed over different locations including over different storage devices, and may exist, at least partially, merely as electronic signals on a system or network. 
         [0044]    Reference throughout this specification to “one embodiment,” “an embodiment,” or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment,” “in an embodiment,” and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment. 
         [0045]    Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided, such as examples of materials, fasteners, sizes, lengths, widths, shapes, etc., to provide a thorough understanding of embodiments of the invention. One skilled in the relevant art will recognize, however, that the invention can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the invention. 
         [0046]      FIG. 1  is a schematic block diagram illustrating one embodiment of a system  100  for purifying a waste fluid stream in accordance with the present invention. The system  100  may include a feed tank  102  holding the waste fluid (e.g. waste water from an oilfield process) to be treated, although any other supply of waste fluid may be used. The waste fluid enters as a waste fluid stream  104  and is supplied by a feed pump  106  to a water-oil separator  108 . The waste fluid stream  104  may be from any oilfield process, industrial process, landfill leachate, and/or naturally occurring water source. 
         [0047]    The separator  108  may be a coalescing separator or any other separation mechanism to separate bulk oil from water, for example including a settling tank. The separator  108  may further perform liquid-solid separation, for example separating large solids such as proppant used to stimulate a well, or sands from a loosely consolidated formation. The separator  108  may include a wedge-wire self-cleaning pre-screen, a rotary screen filter, or other separation mechanism known in the art to perform the liquid-solid separation. The separated solids may leave the separator  108  as a solids waste stream  110 A. Bulk oil (which may be any hydrocarbon or other low-density liquid immiscible in water) leaves the separator  108  as a liquid waste stream  110 B and bulk water leaves the separator  108  as a feed stream  112 . After the separator  108 , the feed stream  112  comprises water with impurities, which may include methanol, other alcohols, hydrocarbon products and/or formation fluids from a well, various chemicals and fluids used to treat the well, and/or any other soluble or miscible fluids. 
         [0048]    The system  100  may include a controller  114  that controls various temperatures, pressures, flow rates, fluid levels, and/or other system operating attributes that will become clear in various embodiments described herein. The controller  114  may be in communication with various sensors and actuators (not shown) depending upon the controls in a specific embodiment. The sensors may include pressures, temperatures, fluid levels, flow rates, densities, and/or other parameters of any stream or vessel. The actuators may include electronic, hydraulic, and/or pneumatic manipulation of any valves, pumps, blowers, and/or other physical components of the system  100 . The controller  114  may be electronic (e.g. a computer with an electronic interface), mechanical (e.g. springs or the like to respond to various system parameters in prescribed ways), and/or may include a manual aspect (e.g. a sight gauge and a hand valve wherein an operator controls a tank level). 
         [0049]    The feed stream  112  may be directed to a secondary recovery heat exchanger  123 , which may be a shell-and-tube heat exchanger or other type of exchanger known in the art. The secondary recovery heat exchanger  123  transfers heat from one or more exiting streams that may have residual heat from the separation process of the system  100  to the feed stream  112  to create a pre-heated feed stream  122 . The pre-heated feed stream  122  enters a separation unit  126  that removes impurities from the pre-heated feed stream  122 . In one embodiment, the separation unit  126  is a mechanical vapor recompression unit. In the separation unit  126 , the pre-heated feed stream  122  may be mixed with a concentrated bottoms stream  130 , and fed through a recirculation pump  128 . The recirculation pump  128  outlet may be split into a pre-recovery concentrated purge stream  124  and a recirculation stream  132 . The pre-recovery concentrated purge stream  124  passes through the secondary recovery heat exchanger  123  and transfers residual heat to the feed stream  112  before exiting as a concentrated purge stream  120 . 
         [0050]    In one embodiment, the secondary recovery heat exchanger  123  heats the feed stream  112  after the separator  108  removes the solids waste stream  110 A from the waste fluid stream  104 , but before the separator  108  removes the liquid waste stream  110 B from the waste fluid stream  104 . The heating of the waste fluid stream  104  after solids  110 A removal allows the secondary recovery heat exchanger  123  to avoid unnecessarily heating waste solids  110 A, while providing some heat to assist in quickly separating the liquid waste stream  110 B. In one embodiment, the separator  108  includes multiple stages and components to perform solid waste removal in one or more stages, and to perform liquid waste removal in one or more stages. The secondary recovery heat exchanger  123  is shown downstream of the separator  108 , but may be upstream of the separator  108  and/or distributed between stages of the separator  108 . 
         [0051]    The separation unit  126  includes an evaporation unit  141  that provides the concentrated bottoms stream  130  to the recirculation pump  128 . The evaporation unit  141  accepts a heated recirculation stream  134  that may be heated in a primary heat exchanger  136  by a steam inlet stream  138  tapped from a system steam inlet  137 . For the purposes of a clear description, the heat inlet stream  137  is referred to as a system steam inlet  137 , but the heat inlet stream  137  and related streams (e.g.  138 ,  140 ,  158 ) may comprise any heat inlet medium including heated glycol, heated oil, and/or other heat transfer media configured to deliver thermal energy from a heat source (not shown) to the heat exchangers  136 ,  158 . The steam inlet stream  138  may leave the primary heat exchanger  136  as a cooled steam outlet  140 . The recirculation stream  132  may further accept heat from a distillate stream  143  out of the evaporation unit  141  that is taken from the evaporation unit  141  by a blower  142  and passed through the primary heat exchanger  136 . 
         [0052]    The primary heat exchanger  136  may be a shell-and-tube heat exchanger with the recirculation stream  132  passing on the tube-side. Preferably, the recirculation stream  132  passes through the primary heat exchanger  136  in highly turbulent flow, increasing the heat transfer rate and reducing the amount of fouling in the primary heat exchanger  136 . Alternatively, the primary heat exchanger  136  may be a plate and frame heat exchanger or another heat exchanging device known in the art. 
         [0053]    In one embodiment, the primary heat exchanger  136  is configured to transfer the heat of vaporization from a charged distillate stream  146  to the recirculation stream  132 , and also heat from a steam inlet stream  138  to the recirculation stream  132 . The heat transfer may be staged such as first transferring the heat of vaporization from the charged distillate stream  146 , then transferring the heat from the steam inlet stream  138 . In one embodiment, the charged distillate stream  146  exits the primary heat exchanger  136  as a condensed distillate stream  148  at a temperature just below the boiling point of the condensed distillate stream  148 . The primary heat exchanger  136  may be designed to deliver the condensed distillate stream  148  at a specified temperature and/or at a specified pressure, and one of skill in the art recognizes the selection of the specified temperature and/or specified pressure affects the final pressure and/or temperature of the condensed distillate stream  148 . 
         [0054]    In the prior art, mechanical vapor recompression recirculation system have recirculation ratios from below about 25 to about 200. The recirculation ratio is defined as the mass flow of recirculation stream  132  divided by the mass flow of the distillate stream  143 . In the present invention, recirculation ratios in the range from below 25 to about 200 are useful when combined with other features of the present invention. Waste fluid streams  104  with low thermal conductivity, specific heat and/or a high tendency to foul in the primary heat exchanger  136  indicate higher recycle ratios. The economics of pumping losses and potential sub-cooling of the charged distillate  146  in the heat exchanger  136  indicate lower recycle ratios. The use of the steam-stripping system  147  and other novel aspects of the present invention allow recycle ratios of 200-300 or greater where the upper economic limit was about 200 times in the prior art, although other aspects of the present invention also differ from the prior art. The heated recirculation stream  134  may pass into the evaporation unit, possibly through an orifice  144  near the evaporation unit  141  entrance such that the heated recirculation stream  134  flashes into the evaporation unit  141 . The orifice  144  is designed to enhance the flash effect of the heated recirculation stream  134 . The orifice  144  may be further configured to maintain backpressure on the primary heat exchanger  136  such that vapor bubbles do not form in the primary heat exchanger  136 , helping to prevent cavitation, wear, and fouling of the heat exchanger. In one embodiment, the orifice  144  may be a valve controlled by the controller  114 , and/or set manually, to provide a designed and/or controlled back pressure on the heated recirculation stream  134 . 
         [0055]    The heat transfer of the primary heat exchanger  136  is further enhanced by high flow rates of the recirculation stream  132 . Using plate-frame heat exchanger elements, and using a shell and tube heat exchanger, recirculation rates above 200× (i.e. mass flow of recirculation stream  132  is 200 times the mass flow of the distillate stream  143 ) economically improve the heat transfer in the primary heat exchanger  136 . In other words, the additional pumping losses incurred by increasing the flow rate are lower than the additional capital costs required to purchase a larger primary heat exchanger. Increasing recirculation rates generally improve the system  100  up to about 300×, although in primary heat exchangers  136  that must be constructed with exotic materials (e.g. titanium alloys, porcelain enamels, etc.), for example due to highly corrosive impurities, the recirculation rates may be economically set even higher to save capital costs. Also, recirculation rates may be economically higher when the size of the system  100  is at a premium—for example a system  100  installed on an offshore drilling platform or a system  100  designed to fit on a standard commercial vehicle. 
         [0056]    The evaporation unit  141  accepts the flashed heated recirculation stream  134 , and has a liquid bottoms to supply the concentrated bottoms stream  130 , and a distillate stream  143 . The distillate stream  143  will be largely water, and will further include any components of the feed stream  112  that have a volatility near or greater than water. A blower  142  may draw the vapors off of the evaporation unit  141 , and send the charged distillate stream  146  through the primary heat exchanger  136 . The charged distillate stream  146  leaves the primary heat exchanger  136  as a condensed distillate stream  148 . 
         [0057]    The system  100  may include a steam-stripping system  147  that strips volatile and non-condensable impurities from the condensed distillate stream  148 , and creates a stripped product stream  150 A that is ready for final processing. The steam-stripping system  147  includes a stripping vessel  152  that accepts the condensed distillate stream  148 , and has a stripper bottoms stream  154 . A stripper recycle pump  156  recycles the bottoms stream  154  through a reboiler  160 , which may be a heat exchanger using a stripper steam inlet  158  taken from the system steam inlet  137  (and/or other heated medium as described above) to heat the bottoms stream  154 . In one embodiment, direct steam injection or other heating methods are utilized to heat the bottoms stream  154 . 
         [0058]    The reboiler  160  heats the bottoms stream  154  to a temperature above the boiling point for target impurities in the condensed distillate stream  148 , but below the boiling point for water. In one embodiment, the reboiler  160  heats the condensed distillate stream  148  to a temperature just below the boiling point for water. The selection of the temperature for the heated bottoms  162  is an economic decision based on the required water purity of the purified product stream  150 D, the cost of steam or available heat source, the target impurities, and similar parameters that vary for specific embodiments of the steam-stripping system  147 . It is within the skill of one in the art to determine an economic heated bottoms  162  temperature based on the disclosures herein. The heated bottoms stream  162  is reinjected into the stripping vessel  152 , driving volatiles and organic fractions out the top in a stripper vapor outlet  164 . The spent steam exits the system  100  as a cooled steam outlet  140 . 
         [0059]    The steam inlet stream  138  may be a small temperature offset (e.g. +/−10° F. offset) above the temperature of the heated recirculation stream  134 , while the steam return stream  140  may be at about the temperature of the heated recirculation stream  134 . For example, the steam inlet stream  138  may be 250° F. while the recirculation stream  132  may be 235° F. The temperature offset allows the primary heat exchanger to remain in an efficient heat transfer regime. 
         [0060]    The stripper vapor outlet  164  passes to a condensing system  166 , which divides the stripper vapor outlet  164  into a volatile fraction stream  168 , a non-condensable stream  170 , and a stripper reflux stream  172 . A reflux ratio is defined as the mass flow rate of the stripper reflux stream  172  divided by the sum of the mass flow rates of the volatile fraction stream  168  and the non-condensable stream  170 . The reflux ratio may vary with the amount of separation required (e.g. the organic fraction of impurities), the size of the stripping vessel  152 , the temperatures of the various streams  148 ,  154 ,  162 ,  164 , and the boiling points of the various components in the condensed distillate stream  148 . Typically, a reflux ratio between about 0.5 and 20.0 will suffice to achieve an acceptably purified stripped product stream  150 A. In other embodiments, various cost considerations may drive a higher or lower reflux ratio. For example where recovery of a valuable volatile fraction from the condensed distillate stream  148  is a primary goal, a reflux ratio higher than 20.0 may be economically desirable. In another example, where a volatile fraction has a much higher vapor pressure than water, a lower reflux ratio may suffice. 
         [0061]    The stripped product stream  150 A may enter an oxidizer unit  174  to remove final traces of alcohols, soluble oils, phenols, and/or any other contaminants. The oxidizer unit  174  may oxidize the stripped product stream  150 A via chemical (e.g. peroxide, bleach, ozone, etc.) and/or ultraviolet means, and the oxidizer unit  174  may include a sonic and/or ultrasonic vibration source to enhance the oxidization. The oxidized product stream  150 B may be passed through the secondary recovery heat exchanger  123  to return remaining heat from the steam-stripping system  147  to the feed stream  112 . In one embodiment, the oxidized product stream  150 B may utilize a separate heat exchanger (not shown) from the heat exchanger  123  utilized by the pre-recovery concentrated purge stream  124 . The post-secondary heat recovery stream  150 C may be passed through a final processing unit  176 , for example a carbon adsorber, before discharge as a purified product stream  150 D. The stripped product stream  150 A may pass through an oxidizer unit  174 , the secondary recovery heat exchanger  123 , and/or the final processing unit  176  in any order, and some or all of these components may be present in a given embodiment of the present invention. 
         [0062]    The flows, temperatures, pressures, and other parameters of the various streams in the system  100  vary according to the application and may be controlled by the controller  114 . In one example, the waste fluid stream  104  flows between 2 and 70 gallons per minute (gpm), and is limited primarily by the capacity of the evaporation unit(s)  141 . The purified product stream  150 D flow rate depends upon the required final purity of the stream and the concentration of impurities in the waste fluid stream  104 , but will typically be a flow rate about 90% of the waste fluid stream  104 . The concentrated purge stream  120  will be the remainder of the waste fluid stream  104 , less the volatile fraction stream  168  and the non-condensable stream  170 . The controller  114  may control the concentrated purge stream  120  to a temperature selected for safe handling (e.g. 140° F.), and/or for other concerns downstream such as the cooling capacity of a waste handling system (not shown). 
         [0063]    The pre-recovery concentrated purge stream  124  may be controlled to 230-240° F., and this temperature may be selected according to the specifications of the primary heat exchanger  136  and/or the secondary recovery heat exchanger  123 . The recirculation pump  128  may operate at about 2-15 psig on the suction side (pre-heated feed stream  122 ) and 25-55 psig on the discharge side (recirculation stream  132 ). 
         [0064]    The controller  114  may control the amount of the pre-recovery concentrated purge stream  124  to keep the desired concentration in the concentrated purge stream  120 . For example, the waste fluid stream  104  may include 1,000 ppm impurities, and the controller  114  may control the pre-recovery concentrated purge stream  124  to 50,000 ppm impurities. In the example, ignoring the volatile fraction stream  168  and the non-condensable stream  170 , at steady state with a waste fluid stream  104  of 100 gpm, the concentrated purge stream  120  would be about 2 gpm, while the purified product stream  150 D would be about 98 gpm. The controller  114  may utilize varying concentrations, temperatures, and/or flow targets during transient operations such as system  100  startup, concentration variations in the waste fluid stream  104 , and the like. 
         [0065]    In one embodiment, the concentration of the concentrated bottoms stream  130 , which controls the concentration of the concentrated purge stream  120 , may be limited by the solubility of the impurities in water. For example, the upper limit of certain salt concentrations may be 200,000 to 400,000 ppm or greater according to the solubility limit of the particular salt. The type of impurity and the concentration of the pre-recovery concentrated purge stream  124  depend upon the application of the system  100 . The final concentration of the pre-recovery concentrated purge stream  124  may be limited by the pumpability of the pre-recovery concentrated purge stream  124 , and therefore any concentration up to saturation and even a little beyond (e.g. if solids are present but in a pumpable suspension) may be utilized depending upon the application. 
         [0066]    In one embodiment, the concentration of the concentrated bottoms stream  130  may be selected according to the utilization of the concentrated purge stream  120  as an intended product. For example, the concentrated purge stream  120  may be utilized as a 4% KCl solution, and the controller  114  may control the concentration of the concentrated bottoms stream  130  such that the concentrated purge stream  120  exits the system  100  as a 4% KCl solution. 
         [0067]    The blower  142  moves the vapor from the evaporation unit  141  through the primary heat exchanger  136 . In one example, the blower  142  operates at about 5-15 psig on the suction side (i.e. the distillate stream  143 ) and about 7-25 psig on the discharge side (i.e. the charged distillate stream  146 ). The distillate stream  143  may be de-superheated (i.e. cooled to the dew point but still steam) by a heat exchanger (not shown) just before the blower  142 , or at any other logical location within the system  100  including after the blower  142 . The de-superheating may be performed by cooling water (not shown), by heat exchange with the feed stream  112 , the pre-recovery concentrated purge stream  124 , and/or another stream in the system  100 . The charged distillate stream  146  enters the primary heat exchanger  136  at approximately the temperature of the dew point of the charged distillate stream  146 . The condensed distillate stream  148  exits the primary heat exchanger  136  at a temperature offset above the recirculation stream  132  temperature—for example about 2-3° F. above the recirculation stream  132  temperature and/or just at or below the boiling point of the condensed distillate stream  148 . In one embodiment, the blower  142  is a disc flow turbine (i.e. a “Tesla turbine”) run as a pump, with work flowing from the shaft to the distillate stream  143 . 
         [0068]    In one embodiment, the system  100  includes a steam control unit  180 . The steam control unit  180  provides backpressure to keep the condensed distillate stream  148  in a liquid phase and to provide condensed steam to the stripping vessel  152 . The steam control unit  180  may comprise a steam trap (refer to the description referencing  FIG. 3A ) or other steam control device (for example, refer to the description referencing  FIG. 3B ). The steam control unit  180  may further comprise a pump that delivers the condensed distillate stream  148  to the stripping vessel  152 . 
         [0069]    In one embodiment, the controller  114  is configured to operate the system  100  at a pressure slightly higher than atmospheric pressure. For example, the blower  142  may run at 5 psig on the suction side and 10 psig at the discharge side nominally, and the controller  114  may increase the pressure to 10 psig and 20 psig respectively under some conditions. Other pressures in the system  100  may likewise be increased, for example the pressures in the evaporation unit  141  and the stripping vessel  152 . In one embodiment, the capacity of the system  100  in terms of the waste fluid stream  104  mass that can be accepted increases by about 5% for each one psi increase of the system  100  pressure. Therefore, the controller  114  can configure the system  100  capacity to a requirement of an application and/or for other reasons. For example, applications may include multiple purification systems  100 , and one or more of the systems  100  may be shut down for maintenance. In the example, the controller  114  may increase the operating pressure for on-line systems  100  during the maintenance shutdown. Other uses of a configurable waste fluid stream  104  capacity are understood by one of skill in the art and contemplated within the scope of the present invention. 
         [0070]    In one embodiment, the system  100  further includes an additives unit  182  that allows additives to be mixed into the recirculation stream  132 . The location of the additives unit  182  in  FIG. 1  is for example only, and the additives unit  182  may be placed anywhere in the recirculation from the concentrated bottoms stream  130  to the heated recirculation stream  134 . The system  100  may further include an additives pump  184  that delivers additives to the additives unit  182 . Additives may include anti-foaming agents, anti-corrosion agents, and/or another type of additive that may be beneficial for a given embodiment of the system  100 . 
         [0071]      FIG. 2  is a schematic block diagram illustrating one embodiment of a condensing system  166  in accordance with the present invention. The condensing system  166  includes a pair of condensers  202 ,  204  accepting cooling water  206  from a water supply, and discharging spent water  207  out of the condensing system  166 . A primary condenser  202  cools the stripper vapor outlet  164 , sending the condensed fluid to a collection vessel  208 . A collection vapor stream  210  goes to a secondary condenser  204  where the vapors leave as a non-condensable stream  170 , and the liquid  212  is returned to the collection vessel  208 . The liquid from the collection vessel  208  exits as a condensed stream  214 , where a pump  216  may deliver it out of the condensing system  166 . 
         [0072]    One or more valves  218 ,  220  may control the liquid output from the condensing system  166 , sending some liquid out as the volatile fraction stream  168 , and returning a portion of the liquid to the stripping vessel  152  as the stripper reflux stream  172 . Methanol and light oils that may not be separated from water in the separation unit  126  may typically be included in the volatile fraction stream  168 . Other volatile compounds may be present in the volatile fraction stream  168  depending upon the impurities in the feed stream  112 . 
         [0073]      FIG. 3A  is a schematic block diagram illustrating one embodiment of a steam control unit  180  in accordance with the present invention. The steam control unit  180  includes a steam trap  302  that maintains pressure on the condensed distillate stream  148  and passes condensate to a storage vessel  304 . The storage vessel may have a vent  306  that releases excess pressure from the storage vessel  304 , for example to the steam stripper  152  below a distribution tray  316 . A pump  308  may deliver liquid in the storage vessel  304  through a level control valve  310  to provide the condensed distillate stream  148  to the stripping vessel  152 . The stripping vessel  152  may include a distribution tray  316 , an upper packed bed portion  312 , and a lower packed bed portion  314 . The stripping vessel  152  may alternatively comprise contact trays (not shown) and/or other mechanisms known in the art to provide surface area for a rising vapor to contact a falling liquid in the stripping vessel  152 . The order of the pump  308  and level control valve  310  may vary depending upon the specific embodiment of the invention. The vapor from the storage vessel  304  may be delivered to the stripping vessel  152  as shown in  FIG. 3A , or may alternatively be vented and/or delivered to another portion of the system  100 . 
         [0074]      FIG. 3B  is a schematic block diagram illustrating an alternate embodiment of a steam control unit  180  in accordance with the present invention. The steam control unit  180  includes a separator  318  that separates a vapor fraction from a liquid fraction of the condensed distillate stream  148 . The vapor fraction passes through a pressure control valve  320  into the stripping vessel  152 . The liquid fraction is delivered by a pump  308  through a level control valve  310  and supplied to the stripping vessel  152 . In the example illustrated in  FIG. 3B , the vapor portion may insert below a distribution tray  316  and the liquid portion may insert above the distribution tray  316  to enable better distribution of the liquid and vapor in the stripping vessel  152 . The stripping vessel  152  may include a distribution tray  316 , an upper packed bed portion  312 , and a lower packed bed portion  314 . The stripping vessel  152  may alternatively comprise contact trays (not shown) and/or other mechanisms known in the art to provide surface area for a rising vapor to contact a falling liquid in the stripping vessel  152 . The order of the pump  308  and level control valve  310  may vary depending upon the specific embodiment of the invention. The vapor from the separator  318  may be delivered to the stripping vessel  152  as shown in  FIG. 3B , or may alternatively be vented and/or delivered to another portion of the system  100 . 
         [0075]    The schematic flow chart diagrams that follow are generally set forth as logical flow chart diagrams. As such, the depicted order and labeled steps are indicative of one embodiment of the presented method. Other steps and methods may be conceived that are equivalent in function, logic, or effect to one or more steps, or portions thereof, of the illustrated method. Additionally, the format and symbols employed are provided to explain the logical steps of the method and are understood not to limit the scope of the method. Although various arrow types and line types may be employed in the flow chart diagrams, they are understood not to limit the scope of the corresponding method. Indeed, some arrows or other connectors may be used to indicate only the logical flow of the method. For instance, an arrow may indicate a waiting or monitoring period of unspecified duration between enumerated steps of the depicted method. Additionally, the order in which a particular method occurs may or may not strictly adhere to the order of the corresponding steps shown. 
         [0076]      FIG. 4  is a schematic flow chart diagram illustrating an embodiment of a method  400  for purifying a waste stream in accordance with the present invention. The method includes a secondary recovery heat exchanger  123  receiving  402  a feed stream  112 , and exchanging  404  heat from a pre-recovery concentrated purge stream  124  to the feed stream  112 . The method  400  further includes a separation unit  126  performing  406  a first stage separation in a mechanical vapor recompression unit, dividing the feed stream  112  into the pre-recovery concentrated purge stream  124  and a condensed distillate stream  148 . The method  400  further includes a primary heat exchanger  136  exchanging  408  heat from the distillate stream  143  to a recirculation stream  132  to generate a heated recirculation stream  134  and the condensed distillate stream  148 . The method  400  further includes performing  410  a second stage separation in a steam-stripping system  147 , dividing the condensed distillate stream  148  into a stripped product stream  150 A, a volatile fraction stream  168 , and a non-condensable stream  170   a.    
         [0077]    The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.