Patent Publication Number: US-11376520-B2

Title: Compact wastewater concentrator using waste heat

Description:
RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 16/828,643, filed on Mar. 24, 2020, which is a continuation of U.S. patent application Ser. No. 16/247,286, filed on Jan. 14, 2019, which is a continuation of U.S. patent application Ser. No. 15/616,274, filed Jun. 7, 2017, which is a continuation of U.S. patent application Ser. No. 14/059,795, filed Oct. 22, 2013, which is a continuation of U.S. patent application Ser. No. 12/705,462, filed Feb. 12, 2010, which is a continuation in part of U.S. patent application Ser. No. 12/530,484, filed on Sep. 9, 2009, which is a U.S. national phase application of International (PCT) Patent Application No. PCT/US08/005672 filed Mar. 12, 2008 and which claims priority benefit of U.S. Provisional Patent Application No. 60/906,743, filed on Mar. 13, 2007. This application also claims priority benefit of U.S. Provisional Patent Application No. 61/152,248, filed Feb. 12, 2009, and U.S. Provisional Patent Application No. 61/229,650, filed Jul. 29, 2009. The entire disclosures of each of application Ser. Nos. 16/247,286; 15/616,274; 14/059,795; 12/705,462; 12/530,484; 60/906,743; 61/152,248; and 61/229,650 are hereby expressly incorporated by reference herein. 
    
    
     FIELD OF THE DISCLOSURE 
     This application relates generally to liquid concentrators, and more specifically to compact, portable, inexpensive wastewater concentrators that can be easily connected to and use sources of waste heat. 
     BACKGROUND 
     Concentration of volatile substances can be an effective form of treatment or pretreatment for a broad variety of wastewater streams and may be carried out within various types of commercial processing systems. At high levels of concentration, many wastewater streams may be reduced to residual material in the form of slurries containing high levels of dissolved and suspended solids. Such concentrated residual may be readily solidified by conventional techniques for disposal within landfills or, as applicable, delivered to downstream processes for further treatment prior to final disposal. Concentrating wastewater can greatly reduce freight costs and required storage capacity and may be beneficial in downstream processes where materials are recovered from the wastewater. 
     Characteristics of industrial wastewater streams are very broad as a result of the large number of industrial processes that produce them. In addition to wastewater produced by design under controlled conditions within industry, uncontrolled events arising from accidents and natural disasters frequently generate wastewater. Techniques for managing wastewater include: direct discharge to sewage treatment plants; pretreatment followed by discharge to sewage treatment plants; on-site or off-site processes to reclaim valuable constituents; and on-site or off-site treatment to simply prepare the wastewater for ultimate disposal. Where the wastewater source is an uncontrolled event, effective containment and recovery techniques must be included with any of these options. 
     An important measure of the effectiveness of a wastewater concentration process is the volume of residual produced in proportion to the volume of wastewater entering the process. In particular, low ratios of residual volume to feed volume (high levels of concentration) are the most desirable. Where the wastewater contains dissolved and/or suspended non-volatile matter, the volume reduction that may be achieved in a particular concentration process that relies on evaporation of volatiles is, to a great extent, limited by the method chosen to transfer heat to the process fluid. 
     Conventional processes that affect concentration by evaporation of water and other volatile substances may be classified as direct or indirect heat transfer systems depending upon the method employed to transfer heat to the liquid undergoing concentration (the process fluid). Indirect heat transfer devices generally include jacketed vessels that contain the process fluid, or plate, bayonet tube or coil type heat exchangers that are immersed within the process fluid. Mediums such as steam or hot oil are passed through the jackets or heat exchangers in order to transfer the heat required for evaporation. Direct heat transfer devices implement processes where the heating medium is brought into direct contact with the process fluid, which occurs in, for example, submerged combustion gas systems. 
     Indirect heat transfer systems that rely on heat exchangers such as jackets, plates, bayonet tubes or coils are generally limited by the buildup of deposits of solids on the surfaces of the heat exchangers that come into direct contact with the process fluid. Also, the design of such systems is complicated by the need for a separate process to transfer heat energy to the heating medium such as a steam boiler or devices used to heat other heat transfer fluids such as hot oil heaters. This design leads to dependence on two indirect heat transfer systems to support the concentration process. Feed streams that produce deposits on heat exchangers while undergoing processing are called fouling fluids. Where feed streams contain certain compounds such as carbonates for which solubility decreases with increasing temperature, deposits, generally known as boiler scale, will form even at relatively low concentrations due to the elevated temperatures at the surfaces of the heat exchangers. Further, when compounds that have high solubility at elevated temperatures such as sodium chloride are present in the wastewater feed, they will also form deposits by precipitating out of the solution as the process fluid reaches high concentrations. Such deposits, which necessitate frequent cycles of heat exchange surface cleaning to maintain process efficiency, may be any combination of suspended solids carried into the process with the wastewater feed and solids that precipitate out of the process fluid. The deleterious effects of deposition of solids on heat exchange surfaces limits the length of time that indirect heat transfer processes may be operated before these processes must be shut down for periodic cleaning. These deleterious effects thereby impose practical limits on the range of wastewater that might be effectively managed, especially when the range of wastewater includes fouling fluids. Therefore, processes that rely on indirect heat transfer mechanisms are generally unsuitable for concentrating wide varieties of wastewater streams and achieving low ratios of residual to feed volume. 
     U.S. Pat. No. 5,342,482, which is hereby incorporated by reference, discloses a particular type of direct heat transfer concentrator in the form of a submerged gas process wherein combustion gas is generated and delivered though an inlet pipe to a dispersal unit submerged within the process fluid. The dispersal unit includes a number of spaced-apart gas delivery pipes extending radially outwardly from the inlet pipe, each of the gas delivery pipes having small holes spaced apart at various locations on the surface of the gas delivery pipe to disperse the combustion gas as small bubbles as uniformly as practical across the cross-sectional area of the liquid held within a processing vessel. According to current understanding within the prior art, this design provides desirable intimate contact between the liquid and the hot gas over a large interfacial surface area. In this process, the intent is that both heat and mass transfer occur at the dynamic and continuously renewable interfacial surface area formed by the dispersion of a gas phase in a process fluid, and not at solid heat exchange surfaces on which deposition of solid particles can occur. Thus, this submerged gas concentrator process provides a significant advantage over conventional indirect heat transfer processes. However, the small holes in the gas delivery pipes that are used to distribute hot gases into the process fluid within the device of U.S. Pat. No. 5,342,482 are subject to blockages by deposits of solids formed from fouling fluids. Thus, the inlet pipe that delivers hot gases to the process fluid is subject to the buildup of deposits of solids. 
     Further, as the result of the need to disperse large volumes of gas throughout a continuous process liquid phase, the containment vessel within U.S. Pat. No. 5,342,482 generally requires significant cross-sectional area. The inner surfaces of such containment vessels and any appurtenances installed within them are collectively referred to as the “wetted surfaces” of the process. These wetted surfaces must withstand varying concentrations of hot process fluids while the system is in operation. For systems designed to treat a broad range of wastewater streams, the materials of construction for the wetted surfaces present critical design decisions in relation to both corrosion and temperature resistance which must be balanced against the cost of equipment and the costs of maintenance/replacement over time. Generally speaking, durability and low maintenance/replacement costs for wetted surfaces are enhanced by selecting either high grades of metal alloys or certain engineered plastics such as those used in manufacturing fiberglass vessels. However, conventional concentration processes that employ either indirect or direct heating systems also require means for hot mediums such as steam, heat transfer oil or gases to transfer heat to the fluid within the vessel. While various different high alloys offer answers in regard to corrosion and temperature resistance, the costs of the vessels and the appurtenances fabricated from them are generally quite high. Further, while engineered plastics may be used either directly to form the containment vessel or as coatings on the wetted surfaces, temperature resistance is generally a limiting factor for many engineered plastics. For example, the high surface temperatures of the inlet pipe for hot gas within vessels used in U.S. Pat. No. 5,342,482 imposes such limits. Thus, the vessels and other equipment used for these processes are typically very expensive to manufacture and maintain. 
     Moreover, in all of these systems, a source of heat is required to perform the concentration or evaporative processes. Numerous systems have been developed to use heat generated by various sources, such as heat generated in an engine, in a combustion chamber, in a gas compression process, etc., as a source of heat for wastewater processing. One example of such a system is disclosed in U.S. Pat. No. 7,214,290 in which heat is generated by combusting landfill gas within a submerged combustion gas evaporator, which is used to process leachate at a landfill site. U.S. Pat. No. 7,416,172 discloses a submerged gas evaporator in which waste heat may be provided to an input of the gas evaporator to be used in concentrating or evaporating liquids. While waste heat is generally considered to be a cheap source of energy, to be used effectively in a wastewater processing operation, the waste heat must in many cases be transported a significant distance from the source of the waste heat to a location at which the evaporative or concentration process is to be performed. For example, in many cases, a landfill operation will have electricity generators which use one or more internal combustion engines operating with landfill gas as a combustion fuel. The exhaust of these generators or engines, which is typically piped through a muffler and an exhaust stack to the atmosphere at the top of a building containing the electrical generators, is a source of waste heat. However, to collect and use this waste heat, significant amounts of expensive piping and ductwork must be coupled to the exhaust stack to transfer the waste heat to location of the processing system, which will usually be at ground level away from the building containing the generators. Importantly, the piping, ducting materials, and control devices (e.g., throttling and shutoff valves) that can withstand the high temperatures (e.g., 1800 degrees Fahrenheit) of the exhaust gases within the exhaust stack are very expensive and must be insulated to retain the heat within the exhaust gases during transport. Acceptable insulating materials used for such purposes are generally prone to failure due to a variety of characteristics that add complexity to the design such as brittleness, tendencies to erode over time, and sensitivity to thermal cycling. Insulation also increases the weight of the piping, ducting, and control devices, which adds costs to structural support requirements. 
     SUMMARY 
     A compact liquid concentrating device disclosed herein may be easily connected to a source of waste heat, such as a landfill gas flare or a combustion engine exhaust stack, and use this waste heat to perform a direct heat transfer concentration process without the need of large and expensive containment vessels and without a lot of expensive high temperature resistant materials. The compact liquid concentrator includes a gas inlet, a gas exit and a mixing or flow corridor connecting the gas inlet and the gas exit, wherein the flow corridor includes a narrowed portion that accelerates the gas through the flow corridor. A liquid inlet located between the gas inlet and the narrowed portion of the flow corridor, injects liquid into the gas stream at a point prior to the narrowed portion so that the gas-liquid mixture is thoroughly mixed within the flow corridor, causing a portion of the liquid to be evaporated or concentrated. A demister or fluid scrubber downstream of the narrowed portion, and connected to the gas exit, removes entrained liquid droplets from the gas stream and re-circulates the removed liquid to the liquid inlet through a re-circulating circuit. Fresh liquid to be concentrated is also introduced into the re-circulating circuit at a rate sufficient to offset the combined total of liquid evaporated in the flow corridor and any concentrated liquid that is withdrawn from the process. 
     The compact liquid concentrator described herein includes a number of attributes that operate to cost-effectively concentrate wastewater streams having broad ranges of characteristics. The concentrator is resistant to corrosive effects over a broad range of feed characteristics, has reasonable manufacturing and operating costs, is able to operate continuously at high levels of concentration, and efficiently utilizes heat energy directly from a wide variety of sources. Moreover, the concentrator is compact enough to be portable, and so may be easily transported to locations where wastewater is generated through uncontrolled events and can be installed in close proximity to waste heat sources. Thus, the concentrator disclosed herein is a cost-effective, reliable and durable device that operates to continuously concentrate a broad range of different types of wastewater streams, and that eliminates the use of conventional solid-surface heat exchangers found in conventional indirect heat transfer systems which lead to clogging and deposit buildups. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a general schematic diagram of a compact liquid concentrator; 
         FIG. 2  depicts an embodiment of the liquid concentrator of  FIG. 1  mounted on a pallet or skid for easy transportation on a truck; 
         FIG. 3  is a perspective view of a compact liquid concentrator which implements the concentration process of  FIG. 1 , connected to a source of waste heat produced by a landfill flare; 
         FIG. 4  is a perspective view of a heat transfer portion of the compact liquid concentrator of  FIG. 3 ; 
         FIG. 5  is a front perspective view of an evaporator/concentrator portion of the compact liquid concentrator of  FIG. 3 ; 
         FIG. 6  is a perspective view of easy opening access doors on a portion of the compact liquid concentrator of  FIG. 3 ; 
         FIG. 7  is a perspective view of one of the easy opening access doors of  FIG. 6  in the open position; 
         FIG. 8  is a perspective view of an easy opening latch mechanism used on the access doors of  FIGS. 6 and 7 ; 
         FIG. 9  is a schematic diagram of a control system which may be used in the compact liquid concentrator of  FIG. 3  to control the operation of the various component parts of the compact liquid concentrator; 
         FIG. 10  is a diagram of the compact liquid concentrator of  FIG. 3  attached to a combustion engine stack as a source of waste heat; 
         FIG. 11  is a general schematic diagram of a second embodiment of a compact liquid concentrator; 
         FIG. 12  is a top view of the compact liquid concentrator of  FIG. 11 ; 
         FIG. 13  is a schematic diagram of a third embodiment of a compact liquid concentrator, the third embodiment being a distributed liquid concentrator; 
         FIG. 14  is a side elevational cross-section of the liquid concentrating portion of the distributed liquid concentrator of  FIG. 13 ; 
         FIG. 15  is a top plan view of the liquid concentrating section of  FIG. 14 ; and 
         FIG. 16  is a close up side view of a quencher and venturi section of the distributed liquid concentrator of  FIG. 13 . 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  depicts a generalized schematic diagram of a liquid concentrator  10  that includes a gas inlet  20 , a gas exit  22  and a flow corridor  24  connecting the gas inlet  20  to the gas exit  22 . The flow corridor  24  includes a narrowed portion  26  that accelerates the flow of gas through the flow corridor  24  creating turbulent flow within the flow corridor  24  at or near this location. The narrowed portion  26  in this embodiment may formed by a venturi device. A liquid inlet  30  injects a liquid to be concentrated (via evaporation) into a liquid concentration chamber in the flow corridor  24  at a point upstream of the narrowed portion  26 , and the injected liquid joins with the gas flow in the flow corridor  24 . The liquid inlet  30  may include one or more replaceable nozzles  31  for spraying the liquid into the flow corridor  24 . The inlet  30 , whether or not equipped with a nozzle  31 , may introduce the liquid in any direction from perpendicular to parallel to the gas flow as the gas moves through the flow corridor  24 . A baffle  33  may also be located near the liquid inlet  30  such that liquid introduced from the liquid inlet  30  impinges on the baffle and disperses into the flow corridor in small droplets. 
     As the gas and liquid flow through the narrowed portion  26 , the venturi principle creates an accelerated and turbulent flow that thoroughly mixes the gas and liquid in the flow corridor  24  at and after the location of the inlet  30 . As a result of the turbulent mixing, a portion of the liquid rapidly vaporizes and becomes part of the gas stream. As the gas-liquid mixture moves through the narrowed portion  26 , the direction and/or velocity of the gas/liquid mixture may be changed by an adjustable flow restriction, such as a venturi plate  32 , which is generally used to create a large pressure difference in the flow corridor  24  upstream and downstream of the venturi plate  32 . The venturi plate  32  may be adjustable to control the size and/or shape of the narrowed portion  26  and may be manufactured from a corrosion resistant material including a high alloy metal such as those manufactured under the trade names of Hastelloy, Inconel® and Monel®. 
     After leaving the narrowed portion  26 , the gas-liquid mixture passes through a demister  34  (also referred to as a fluid scrubber) coupled to the gas exit  22 . The demister  34  removes entrained liquid droplets from the gas stream. The demister  34  includes a gas-flow passage. The removed liquid collects in a liquid collector or sump  36  in the gas-flow passage, the sump  36  may also include a reservoir for holding the removed liquid. A pump  40  fluidly coupled to the sump  40  and/or reservoir moves the liquid through a re-circulating circuit  42  back to the liquid inlet  30  and/or flow corridor  24 . In this manner, the liquid may be reduced through evaporation to a desired concentration. Fresh or new liquid to be concentrated is input to the re-circulating circuit  42  through a liquid inlet  44 . This new liquid may instead be injected directly into the flow corridor  24  upstream of the venturi plate  32 . The rate of fresh liquid input into the re-circulating circuit  42  may be equal to the rate of evaporation of the liquid as the gas-liquid mixture flows through the flow corridor  24  plus the rate of liquid extracted through a concentrated fluid extraction port  46  located in or near the reservoir in the sump  40 . The ratio of re-circulated liquid to fresh liquid may generally be in the range of approximately 1:1 to approximately 100:1, and is usually in the range of approximately 5:1 to approximately 25:1. For example, if the re-circulating circuit  42  circulates fluid at approximately 10 gal/min, fresh or new liquid may be introduced at a rate of approximately 1 gal/min (i.e., a 10:1 ratio). A portion of the liquid may be drawn off through the extraction port  46  when the liquid in the re-circulating circuit  42  reaches a desired concentration. 
     After passing through the demister  34  the gas stream passes through an induction fan  50  that draws the gas through the flow corridor  24  and demister gas-flow corridor under negative pressure. Of course, the concentrator  10  could operate under positive pressure produced by a blower (not shown) prior to the liquid inlet  30 . Finally, the gas is vented to the atmosphere or directed for further processing through the gas exit  22 . 
     The concentrator  10  may include a pre-treatment system  52  for treating the liquid to be concentrated, which may be a wastewater feed. For example, an air stripper may be used as a pre-treatment system  52  to remove substances that may produce foul odors or be regulated as air pollutants. In this case, the air stripper may be any conventional type of air stripper or may be a further concentrator of the type described herein, which may be used in series as the air stripper. The pre-treatment system  52  may, if desired, heat the liquid to be concentrated using any desired heating technique. Additionally, the gas and/or wastewater feed circulating through the concentrator  10  may be pre-heated in a pre-heater  54 . Pre-heating may be used to enhance the rate of evaporation and thus the rate of concentration of the liquid. The gas and/or wastewater feed may be pre-heated through combustion of renewable fuels such as wood chips, bio-gas, methane, or any other type of renewable fuel or any combination of renewable fuels, fossil fuels and waste heat. Furthermore, the gas and/or wastewater may be pre-heated through the use of waste heat generated in a landfill flare or stack. Also, waste heat from an engine, such as an internal combustion engine, may be used to pre-heat the gas and/or wastewater feed. Additionally, the gas streams ejected from the gas exit  22  of the concentrator  10  may be transferred into a flare or other post treatment device  56  which treats the gas before releasing the gas to the atmosphere. 
     The liquid concentrator  10  described herein may be used to concentrate a wide variety of wastewater streams, such as waste water from industry, runoff water from natural disasters (floods, hurricanes), refinery caustic, leachate such as landfill leachate, etc. The liquid concentrator  10  is practical, energy efficient, reliable, and cost-effective. In order to increase the utility of this liquid concentrator, the liquid concentrator  10  is readily adaptable to being mounted on a trailer or a moveable skid to effectively deal with wastewater streams that arise as the result of accidents or natural disasters or to routinely treat wastewater that is generated at spatially separated or remote sites. The liquid concentrator  10  described herein has all of these desirable characteristics and provides significant advantages over conventional wastewater concentrators, especially when the goal is to manage a broad variety of wastewater streams. 
     Moreover, the concentrator  10  may be largely fabricated from highly corrosion resistant, yet low cost materials such as fiberglass and/or other engineered plastics. This is due, in part, to the fact that the disclosed concentrator is designed to operate under minimal differential pressure. For example, a differential pressure generally in the range of only 10 to 30 inches water column is required. Also, because the gas-liquid contact zones of the concentration processes generate high turbulence within narrowed (compact) passages at or directly after the venturi section of the flow path, the overall design is very compact as compared to conventional concentrators where the gas liquid contact occurs in large process vessels. As a result, the amount of high alloy metals required for the concentrator  10  is quite minimal. Also, because these high alloy parts are small and can be readily replaced in a short period of time with minimal labor, fabrication costs may be cut to an even higher degree by designing some or all of these parts to be wear items manufactured from lesser quality alloys that are to be replaced at periodic intervals. If desired, these lesser quality alloys (e.g., carbon steel) may be coated with corrosion and/or erosion resistant liners, such as engineered plastics including elastomeric polymers, to extend the useful life of such components. Likewise, the pump  40  may be provided with corrosion and/or erosion resistant liners to extend the life of the pump  40 , thus further reducing maintenance and replacement costs. 
     As will be understood, the liquid concentrator  10  provides direct contact of the liquid to be concentrated and the hot gas, effecting highly turbulent heat exchange and mass transfer between hot gas and the liquid, e.g., wastewater, undergoing concentration. Moreover, the concentrator  10  employs highly compact gas-liquid contact zones, making it minimal in size as compared to known concentrators. The direct contact heat exchange feature promotes high energy efficiency and eliminates the need for solid surface heat exchangers as used in conventional, indirect heat transfer concentrators. Further, the compact gas-liquid contact zone eliminates the bulky process vessels used in both conventional indirect and direct heat exchange concentrators. These features allow the concentrator  10  to be manufactured using comparatively low cost fabrication techniques and with reduced weight as compared to conventional concentrators. Both of these factors favor portability and cost-effectiveness. Thus, the liquid concentrator  10  is more compact and lighter in weight than conventional concentrators, which make it ideal for use as a portable unit. Additionally, the liquid concentrator  10  is less prone to fouling and blockages due to the direct contact heat exchange operation and the lack of solid heat exchanger surfaces. The liquid concentrator  10  can also process liquids with significant amounts of suspended solids because of the direct contact heat exchange. As a result, high levels of concentration of the process fluids may be achieved without need for frequent cleaning of the concentrator  10 . 
     More specifically, in liquid concentrators that employ indirect heat transfer, the heat exchangers are prone to fouling and are subject to accelerated effects of corrosion at the normal operating temperatures of the hot heat transfer medium that is circulated within them (steam or other hot fluid). Each of these factors places significant limits on the durability and/or costs of building conventional indirectly heated concentrators, and on how long they may be operated before it is necessary to shutdown and clean or repair the heat exchangers. By eliminating the bulky process vessels, the weight of the liquid concentrators and both the initial costs and the replacement costs for high alloy components are greatly reduced. Moreover, due to the temperature difference between the gas and liquid, the relatively small volume of liquid contained within the system, and the reduced relative humidity of the gas prior to mixing with the liquid, the concentrator  10  operates at close to the adiabatic saturation temperature for the particular gas/liquid mixture, which is typically in the range of about 150 degrees Fahrenheit to about 215 degrees Fahrenheit (i.e., this concentrator is a “low momentum” concentrator). 
     Moreover, the concentrator  10  is designed to operate under negative pressure, a feature that greatly enhances the ability to use a very broad range of fuel or waste heat sources as an energy source to affect evaporation. In fact, due to the draft nature of these systems, pressurized or non-pressurized burners may be used to heat and supply the gas used in the concentrator  10 . Further, the simplicity and reliability of the concentrator  10  is enhanced by the minimal number of moving parts and wear parts that are required. In general, only two pumps and a single induced draft fan are required for the concentrator when it is configured to operate on waste heat such as stack gases from engines (e.g., generators or vehicle engines), industrial process stacks, gas compressor systems, and flares, such as landfill gas flares. These features provide significant advantages that reflect favorably on the versatility and the costs of buying, operating and maintaining the concentrator  10 . 
       FIG. 2  illustrates a side view of the liquid concentrator  10  mounted on a movable frame  60 , such as a pallet, a trailer or a skid. The movable frame is sized and shaped for easy loading on, or connection to, a transportation vehicle  62 , such as a tractor-trailer truck. Likewise, such a mounted concentrator may easily be loaded onto a train, a ship or an airplane (not shown) for rapid transportation to remote sites. The liquid concentrator  10  may operate as a totally self-contained unit by having its own burner and fuel supply, or the liquid concentrator  10  may operate using an on-site burner and/or an on-site fuel or waste heat source. Fuels for the concentrator  10  may include renewable fuel sources, such as waste products (paper, wood chips, etc.), and landfill gas. Moreover, the concentrator  10  may operate on any combination of traditional fossil fuels such as coal or petroleum, renewable fuels and/or waste heat. 
     A typical trailer-mounted concentrator  10  may be capable of treating as much as one-hundred thousand gallons or more per day of wastewater, while larger, stationary units, such as those installed at landfills, sewage treatment plants, or natural gas or oil fields, may be capable of treating multiples of one-hundred thousand gallons of wastewater per day. 
       FIG. 3  illustrates one particular embodiment of a compact liquid concentrator  110  which operates using the principles described above with respect to  FIG. 1  and which is connected to a source of waste heat in the form of a landfill flare. Generally speaking, the compact liquid concentrator  110  of  FIG. 3  operates to concentrate wastewater, such as landfill leachate, using exhaust or waste heat created within a landfill flare which burns landfill gas in a manner that meets the standards set by the U.S. Environmental Protection Agency (EPA). As is known, most landfills include a flare which is used to burn landfill gas to eliminate methane and other gases prior to release to the atmosphere. Typically, the gas exiting the flare is between 1000 and 1500 degrees Fahrenheit and may reach 1800 degrees Fahrenheit. 
     As illustrated in  FIG. 3 , the compact liquid concentrator  110  generally includes or is connected to a flare assembly  115 , and includes a heat transfer assembly  117  (shown in more detail in  FIG. 4 ), an air pre-treatment assembly  119 , a concentrator assembly  120  (shown in more detail in  FIG. 5 ), a fluid scrubber  122 , and an exhaust section  124 . Importantly, the flare assembly  115  includes a flare  130 , which burns landfill gas therein according to any known principles, and a flare cap assembly  132 . The flare cap assembly  132  includes a moveable cap  134  (e.g., a flare cap, an exhaust gas cap, etc.) which covers the top of the flare  130 , or other type of stack (e.g., a combustion gas exhaust stack), to seal off the top of the flare  130  when the flare cap  134  is in the closed position, or to divert a portion of the flare gas in a partially closed position, and which allows gas produced within the flare  130  to escape to the atmosphere through an open end that forms a primary gas outlet  143 , when the flare cap  134  is in an open or partially open position. The flare cap assembly  132  also includes a cap actuator  135 , such as a motor (e.g., an electric motor, a hydraulic motor, a pneumatic motor, etc., shown in  FIG. 4 ) which moves the flare cap  134  between the fully open and the fully closed positions. As shown in  FIG. 4 , the flare cap actuator  135  may, for example, rotate or move the flare cap  134  around a pivot point  136  to open and close the flare cap  134 . The flare cap actuator  135  may utilize a chain drive or any other type of drive mechanism connected to the flare cap  134  to move the flare cap  134  around the pivot point  136 . The flare cap assembly  132  may also include a counter-weight  137  disposed on the opposite side of the pivot point  136  from the flare cap  134  to balance or offset a portion of the weight of the flare cap  134  when moving the flare cap  134  around the pivot point  136 . The counter-weight  137  enables the actuator  135  to be reduced in size or power while still being capable of moving or rotating the flare cap  134  between an open position, in which the top of the flare  130  (or the primary combustion gas outlet  143 ) is open to the atmosphere, and a closed position, in which the flare cap  134  covers and essentially seals the top of the flare  130  (or the primary combustion gas outlet  143 ). The flare cap  134  itself may be made of high temperature resistant material, such as stainless steel or carbon steel, and may be lined or insulated with refractory material including aluminum oxide and/or zirconium oxide on the bottom portion thereof which comes into direct contact with the hot flare gases when the flare cap  134  is in the closed position. 
     If desired, the flare  130  may include an adapter section  138  including the primary combustion gas outlet  143  and a secondary combustion gas outlet  141  upstream of the primary combustion gas outlet  143 . When the flare cap  130  is in the closed position, combustion gas is diverted through the secondary combustion gas outlet  141 . The adapter section  138  may include a connector section  139  that connects the flare  130  (or exhaust stack) to the heat transfer section  117  using a 90 degree elbow or turn. Other connector arrangements are possible. For example, the flare  130  and heat transfer section  117  may be connected at virtually any angle between 0 degrees and 180 degrees. In this case, the flare cap assembly  132  is mounted on the top of the adaptor section  138  proximate the primary combustion gas outlet  143 . 
     As illustrated in  FIGS. 3 and 4 , the heat transfer assembly  117  includes a transfer pipe  140 , which connects to an inlet of the air pre-treatment assembly  119  to the flare  130  and, more particularly, to the adaptor section  138  of the flare  130 . A support member  142 , in the form of a vertical bar or pole, supports the heat transfer pipe  140  between the flare  130  and the air pre-treatment assembly  119  at a predetermined level or height above the ground. The heat transfer pipe  140  is connected to the connector section  139  or the adapter section  138  at the secondary combustion gas outlet  141 , the transfer pipe forming a portion of a fluid passageway between the adapter section  138  and a secondary process, such as a fluid concentrating process. The support member  142  is typically necessary because the heat transfer pipe  140  will generally be made of metal, such as carbon or stainless steel, and may be refractory lined with materials such as aluminum oxide and/or zirconium oxide, to withstand the temperature of the gas being transferred from the flare  130  to the air pre-treatment assembly  119 . Thus, the heat transfer pipe  140  will typically be a heavy piece of equipment. However, because the flare  130 , on the one hand, and the air pre-treatment assembly  119  and the concentrator assembly  120 , on the other hand, are disposed immediately adjacent to one another, the heat transfer pipe  140  generally only needs to be of a relatively short length, thereby reducing the cost of the materials used in the concentrator  110 , as well as reducing the amount of support structure needed to bear the weight of the heavy parts of the concentrator  110  above the ground. As illustrated in  FIG. 3 , the heat transfer pipe  140  and the air pre-treatment assembly  1119  form an upside-down U-shaped structure. 
     The air pre-treatment assembly  119  includes a vertical piping section  150  and an ambient air valve (not shown explicitly in  FIGS. 3 and 4 ) disposed at the top of the vertical piping section  150 . The ambient air valve (also referred to as a bleed valve) forms a fluid passageway between the heat transfer pipe  140  (or air pre-treatment assembly  119 ) and the atmosphere. The ambient air valve operates to allow ambient air to flow through a mesh bird screen  152  (typically wire or metal) and into the interior of the air pre-treatment assembly  119  to mix with the hot gas coming from the flare  130 . If desired, the air pre-treatment assembly  119  may include a permanently open section proximate to the bleed valve which always allows some amount of bleed air into the air pre-treatment assembly  119 , which may be desirable to reduce the size of the required bleed valve and for safety reasons. While the control of the ambient air or bleed valve will be discussed in greater detail hereinafter, this valve generally allows the gas from the flare  130  to be cooled to a more useable temperature before entering into the concentrator assembly  120 . The air pre-treatment assembly  119  may be supported in part by cross-members  154  connected to the support member  142 . The cross-members  154  stabilize the air pre-treatment assembly  119 , which is also typically made of heavy carbon or stainless steel or other metal, and which may be refractory-lined to improve energy efficiency and to withstand the high temperature of the gases within this section of the concentrator  110 . If desired, the vertical piping section  150  may be extendable to adapt to or account for flares of differing heights so as to make the liquid concentrator  110  easily adaptable to many different flares or to flares of different heights. This concept is illustrated in more detail in  FIG. 3 . As shown in  FIG. 3 , the vertical piping section  150  may include a first section  150 A (shown using dotted lines) that rides inside of a second section  150 B thereby allowing the vertical piping section  150  to be adjustable in length (height). 
     Generally speaking, the air pre-treatment assembly  119  operates to mix ambient air provided through the ambient air valve beneath the screen  152  and the hot gas flowing from the flare  130  through the heat transfer pipe  140  to create a desired temperature of gas at the inlet of the concentrator assembly  120 . 
     The liquid concentrator assembly  120  includes a lead-in section  156  having a reduced cross-section at the top end thereof which mates the bottom of the piping section  150  to a quencher  159  of the concentrator assembly  120 . The concentrator assembly  120  also includes a first fluid inlet  160 , which injects new or untreated liquid to be concentrated, such as landfill leachate, into the interior of the quencher  159 . While not shown in  FIG. 3 , the inlet  160  may include a coarse sprayer with a large nozzle for spraying the untreated liquid into the quencher  159 . Because the liquid being sprayed into the quencher  159  at this point in the system is not yet concentrated, and thus has large amount of water therein, and because the sprayer is a coarse sprayer, the sprayer nozzle is not subject to fouling or being clogged by the small particles within the liquid. As will be understood, the quencher  159  operates to quickly reduce the temperature of the gas stream (e.g., from about 900 degrees Fahrenheit to less than 200 degrees Fahrenheit) while performing a high degree of evaporation on the liquid injected at the inlet  160 . If desired, but not specifically shown in  FIG. 3 , a temperature sensor may be located at or near the exit of the piping section  150  or in the quencher  159  and may be used to control the position of the ambient air valve to thereby control the temperature of the gas present at the inlet of the concentrator assembly  120 . 
     As shown in  FIGS. 3 and 5 , the quencher  159  is connected to liquid injection chamber which is connected to narrowed portion or venturi section  162  which has a narrowed cross section with respect to the quencher  159  and which has a venturi plate  163  (shown in dotted line) disposed therein. The venturi plate  163  creates a narrow passage through the venturi section  162 , which creates a large pressure drop between the entrance and the exit of the venturi section  162 . This large pressure drop causes turbulent gas flow within the quencher  159  and the top or entrance of the venturi section  162 , and causes a high rate of gas flow out of the venturi section  162 , both of which lead to thorough mixing of the gas and liquid in the venturi section  162 . The position of the venturi plate  163  may be controlled with a manual control rod  165  (shown in  FIG. 5 ) connected to the pivot point of the plate  163 , or via an electric control mechanism, such as motor (not shown in  FIG. 5 ). 
     A re-circulating pipe  166  extends around opposite sides of the entrance of the venturi section  162  and operates to inject partially concentrated (i.e., re-circulated) liquid into the venturi section  162  to be further concentrated and/or to prevent the formation of dry particulate within the concentrator assembly  120  through multiple fluid entrances located on one or more sides of the flow corridor. While not explicitly shown in  FIGS. 3 and 5 , a number of pipes, such as three pipes of, for example, ½ inch diameter, may extend from each of the opposites legs of the pipe  166  partially surrounding the venturi section  162 , and through the walls and into the interior of the venturi section  162 . Because the liquid being ejected into the concentrator  110  at this point is re-circulated liquid, and is thus either partially concentrated or being maintained at a particular equilibrium concentration and more prone to plug a spray nozzle than the less concentrated liquid injected at the inlet  160 , this liquid may be directly injected without a sprayer so as to prevent clogging. However, if desired, a baffle in the form of a flat plate may be disposed in front of each of the openings of the ½ pipes to cause the liquid being injected at this point in the system to hit the baffle and disperse into the concentrator assembly  120  as smaller droplets. In any event, the configuration of this re-circulating system distributes or disperses the re-circulating liquid better within the gas stream flowing through the concentrator assembly  120 . 
     The combined hot gas and liquid flows in a turbulent manner through the venturi section  162 . As noted above, the venturi section  162 , which has a moveable venturi plate  163  disposed across the width of the concentrator assembly  120 , causes turbulent flow and complete mixture of the liquid and gas, causing rapid evaporation of the liquid within the gas. Because the mixing action caused by the venturi section  162  provides a high degree of evaporation, the gas cools substantially in the concentrator assembly  120 , and exits the venturi section  162  into a flooded elbow  164  at high rates of speed. In fact, the temperature of the gas-liquid mixture at this point may be about 160 degrees Fahrenheit. 
     As is typical, the bottom of the flooded elbow  164  has liquid disposed therein, and the gas-liquid mixture exiting the venturi section  162  at high rates of speed impinges on the liquid in the bottom of the flooded elbow  164  as the gas-liquid mixture is forced to turn 90 degrees to flow into the fluid scrubber  122 . The interaction of the gas-liquid stream with the liquid within the flooded elbow  164  removes liquid droplets from the gas-liquid stream, and prevents suspended particles within the gas-liquid stream from hitting the bottom of flooded elbow  164  at high rates of speeds, thereby preventing erosion of the metal wall of the flooded elbow  164 . 
     After leaving the flooded elbow  164 , the gas-liquid stream in which evaporated liquid and some liquid and other particles still exist, flows through the fluid scrubber  122  which is, in this case, a cross-flow fluid scrubber. The fluid scrubber  122  includes various screens or filters which aid in removal of entrained liquids from the gas-liquid stream and removes other particles that might be present with the gas-liquid stream. In one particular example, the cross flow scrubber  122  may include an initial coarse impingement baffle  169  at the input thereof, which is designed to remove liquid droplets in the range of 50 to 100 microns in size or higher. Thereafter, two removable filters in the form of chevrons  170  are disposed across the fluid path through the fluid scrubber  122 , and the chevrons  170  may be progressively sized or configured to remove liquid droplets of smaller and smaller sizes, such as 20-30 microns and less than 10 microns. Of course, more or fewer filters or chevrons could be used. 
     As is typical in cross flow scrubbers, liquid captured by the filters  169  and  170  gravity drains into a reservoir or sump  172  located at the bottom of the fluid scrubber  122 . The sump  172 , which may hold, for example 200 gallons of liquid or more, thereby collects concentrated fluid containing dissolved and suspended solids removed from the gas-liquid stream and operates as a reservoir for a source of re-circulating concentrated liquid back to the concentrator assembly  120  to be further treated and/or to prevent the formation of dry particulate within the concentrator assembly  120  in the manner described above with respect to  FIG. 1 . In one embodiment, the sump  172  may include a sloped V-shaped bottom (not shown in the drawings) having a V-shaped groove extending from the back of the fluid scrubber  122  (furthest away from the flooded elbow  164 ) to the front of the fluid scrubber  122  (closest to the flooded elbow  164 ), wherein the V-shaped groove is sloped such that the bottom of the V-shaped groove is lower at the end of the fluid scrubber  122  nearest the flooded elbow  164  than at an end farther away from the flooded elbow  164 . In other words, the V-shaped bottom may be sloped with the lowest point of the V-shaped bottom proximate the exit port  173  and/or the pump  182 . Additionally, a washing circuit (not shown in the drawings) may pump concentrated fluid from the sump  172  to a sprayer (not shown) within the cross flow scrubber  122 , the sprayer being aimed to spray liquid at the V-shaped bottom. Alternatively, the sprayer may spray unconcentrated liquid or clean water at the V-shaped bottom. The sprayer may periodically or constantly spray liquid onto the surface of the V-shaped bottom to wash solids and prevent solids buildup on the V-shaped bottom or at the exit port  173  and/or the pump  182 . As a result of this V-shaped sloped bottom and pump, liquid collecting in the sump  172  is continuously agitated and renewed, thereby maintaining a relatively constant consistency and maintaining solids in suspension. If desired, the spraying circuit may be a separate circuit using a separate pump with, for example, an inlet inside of the sump  173 , or may use a pump  182  associated with a concentrated liquid re-circulating circuit described below to spray concentrated fluid from the sump onto the V-shaped bottom of the sump  172 . 
     As illustrated in  FIG. 3 , a return line  180 , as well as a pump  182 , operate to re-circulate fluid removed from the gas-liquid stream from the sump  172  back to the concentrator  120  and thereby complete a fluid or liquid re-circulating circuit. Likewise, a pump  184  may be provided within an input line  186  to pump new or untreated liquid, such as landfill leachate, to the input  160  of the concentrator assembly  120 . Also, one or more sprayers  185  may be disposed inside the fluid scrubber  122  adjacent the chevrons  170  and may be operated periodically to spray clean water or a portion of the wastewater feed on the chevrons  170  to keep them clean. 
     Concentrated liquid also be removed from the bottom of the fluid scrubber  122  via the exit port  173  and may be further processed or disposed of in any suitable manner in a secondary re-circulating circuit. In particular, the concentrated liquid removed by the exit port  173  contains a certain amount of suspended solids, which preferably may be separated from the liquid portion of the concentrated liquid and removed from the system using a secondary re-circulating circuit. For example, concentrated liquid removed from the exit port  173  may be transported through a secondary concentrated wastewater circuit (not shown) to a solid/liquid separating device, such as a settling tank, a vibrating screen, a rotary vacuum filter, or a filter press. After the suspended solids and liquid portion of the concentrated wastewater are separated by the solid/liquid separating device, the liquid portion of the concentrated wastewater may be returned to the sump  172  for further processing in the first or primary re-circulating circuit connected to the concentrator. 
     The gas, which flows through and out of the fluid scrubber  122  with the liquid and suspended solids removed therefrom, exits out of piping or ductwork at the back of the fluid scrubber  122  (downstream of the chevrons  170 ) and flows through an induced draft fan  190  of the exhaust assembly  124 , from where it is exhausted to the atmosphere in the form of the cooled hot inlet gas mixed with the evaporated water vapor. Of course, an induced draft fan motor  192  is connected to and operates the fan  190  to create negative pressure within the fluid scrubber  122  so as to ultimately draw gas from the flare  130  through the transfer pipe  140 , the air pre-treatment assembly  119  and the concentrator assembly  120 . As described above with respect to  FIG. 1 , the induced draft fan  190  needs only to provide a slight negative pressure within the fluid scrubber  122  to assure proper operation of the concentrator  110 . 
     While the speed of the induced draft fan  190  can be varied by a device such as a variable frequency drive operated to create varying levels of negative pressure within the fluid scrubber  122  and thus can usually be operated within a range of gas flow capacity to assure complete gas flow from the flare  130 , if the gas being produced by the flare  130  is not of sufficient quantity, the operation of the induced draft fan  190  cannot necessarily be adjusted to assure a proper pressure drop across the fluid scrubber  122  itself. That is, to operate efficiently and properly, the gas flowing through the fluid scrubber  122  must be at a sufficient (minimal) flow rate at the input of the fluid scrubber  122 . Typically this requirement is controlled by keeping at least a preset minimal pressure drop across the fluid scrubber  122 . However, if the flare  130  is not producing at least a minimal level of gas, increasing the speed of the induced draft fan  190  will not be able to create the required pressure drop across the fluid scrubber  122 . 
     To compensate for this situation, the cross flow scrubber  122  is designed to include a gas re-circulating circuit which can be used to assure that enough gas is present at the input of the fluid scrubber  122  to enable the system to acquire the needed pressure drop across the fluid scrubber  122 . In particular, the gas re-circulating circuit includes a gas return line or return duct  196  which connects the high pressure side of the exhaust assembly  124  (e.g., downstream of the induced draft fan  190 ) to the input of the fluid scrubber  122  (e.g., a gas input of the fluid scrubber  122 ) and a baffle or control mechanism  198  disposed in the return duct  196  which operates to open and close the return duct  196  to thereby fluidly connect the high pressure side of the exhaust assembly  124  to the input of the fluid scrubber  122 . During operation, when the gas entering into the fluid scrubber  122  is not of sufficient quantity to obtain the minimal required pressure drop across the fluid scrubber  122 , the baffle  198  (which may be, for example, a gas valve, a damper such as a louvered damper, etc.) is opened to direct gas from the high pressure side of the exhaust assembly  124  (i.e., gas that has traveled through the induced draft fan  190 ) back to the input of the fluid scrubber  122 . This operation thereby provides a sufficient quantity of gas at the input of the fluid scrubber  122  to enable the operation of the induced draft fan  190  to acquire the minimal required pressure drop across the fluid scrubber  122 . 
       FIG. 6  illustrates the particular advantageous feature of the compact liquid concentrator  110  of  FIG. 3  in the form of a set of easy opening access doors  200  which may be used to access the inside of the concentrator  110  for cleaning and viewing purposes. While  FIG. 6  illustrates easy opening access doors  200  on one side of the fluid scrubber  122 , a similar set of doors may be provided on the other side of the fluid scrubber  122 , and a similar door is provided on the front of the flooded elbow  164 , as shown in  FIG. 5 . As illustrated in  FIG. 6 , each of the easy access doors  200  on the fluid scrubber  122  includes a door plate  202 , which may be a flat piece of metal, connected to the fluid scrubber  122  via two hinges  204 , with the door plate  202  being pivotable on the hinges  204  to open and close. A plurality of quick-release handles  206  are disposed around the periphery of the door plate  202  and operate to hold the door plate  202  in the closed position and so to hold the door  200  shut when the fluid scrubber  122  is operating. In the embodiment shown in  FIG. 6 , eight quick-release handles  206  are disposed around each of the door plates  202 , although any other desired number of such quick-release handles  206  could be used instead. 
       FIG. 7  illustrates one of the doors  200  disposed in the open position. As will be seen, a door seat  208  is mounted away from the wall of the fluid scrubber  122  with extension members  209  disposed between the door seat  208  and the outer wall of the fluid scrubber  122 . A gasket  210 , which may be made of rubber or other compressible material, is disposed around the circumference of the opening on the door seat  208 . A similar gasket may additionally or alternatively be disposed around the outer circumference of inner side of the door plate  202 , which provides for better sealing when the door  200  is in the closed position. 
     Each quick-release handle  206 , one of which is shown in more detail in  FIG. 8 , includes a handle  212  and a latch  214  (in this case a U-shaped piece of metal) mounted on a pivot bar  216  disposed through the handle  212 . The handle  212  is mounted on a further pivot point member  218  which is mounted on the outer wall of the door plate  202  via an attachment bracket  219 . The operation of the handle  212  up and around the further pivot member  218  (from the position shown in  FIG. 8 ) moves the latch  214  towards the outer wall of the fluid scrubber  112  (when the door plate  202  is in the closed position) so that the latch  214  may be disposed on the side of a hook  220  away from the door plate  202 , the hook  220  being mounted on the extension member  209 . Rotation of the handle  210  back in the opposite direction pulls the latch  214  up tight against the hook  220 , pulling the further pivot member  218  and therefore the door plate  202  against the door seat  208 . Operation of all of the quick-release handles  206  secures the door plate  202  against door seat  208  and the gasket  210  provides for a fluidly secure connection. Thus, closing all eight of the quick-release handles  206  on a particular door  200 , as illustrated in  FIG. 6 , provides a secure and tight-fitting mechanism for holding the door  200  closed. 
     The use of the easy opening doors  200  replaces the use of a plate with holes, wherein numerous bolts extending from the outer wall of the concentrator are fitted through the holes on the plate and wherein it is necessary to tighten nuts on the bolts to draw the plate against the wall of the concentrator. While such a nut and bolt type of securing mechanism, which is typically used in fluid concentrators to allow access to the interior of the concentrator, is very secure, operation of this configuration takes a long time and a lot of effort when opening or closing an access panel. The use of the quick opening doors  200  with the quick-release handles  206  of  FIG. 6  may be used in this instance because the interior of the fluid scrubber  122  is under negative pressure, in which the pressure inside the fluid scrubber  122  is less than the ambient air pressure, and so does not need the security of a cumbersome bolt and nut type of access panel. Of course, as will be understood, the configuration of the doors  200  allows the doors  200  to be easily opened and closed, with only minimal manual effort, and no tools, thereby allowing for fast and easy access to the structure inside of the fluid scrubber  122 , such as the impingement baffle  169  or the removable filters  170 , or other parts of the concentrator  110  on which an access door  200  is disposed. 
     Referring back to  FIG. 5 , it will be seen that the front the flooded elbow  164  of the concentrator assembly  120  also includes an easy-opening access door  200 , which allows easy access to the inside of the flooded elbow  164 . However, similar easy opening access doors could be located on any desired part of the fluid concentrator  110 , as most of the elements of the concentrator  10  operate under negative pressure. 
     The combination of features illustrated in  FIGS. 3-8  makes for a compact fluid concentrator  110  that uses waste heat in the form of gas resulting from the operation of a landfill flare burning landfill gas, which waste heat would otherwise be vented directly to the atmosphere. Importantly, the concentrator  110  uses only a minimal amount of high temperature resistant (and thus expensive material) to provide the piping and structural equipment required to use the high temperature gases exiting from the flare  130 . In particular, the small length of the transfer pipe  140 , which is made of the most expensive materials, is minimized, thereby reducing the cost and weight of the fluid concentrator  110 . Moreover, because of the small size of the heat transfer pipe  140 , only a minimal amount of scaffolding, in the form of the support member  142 , is needed thereby further reducing the costs of building the concentrator  110 . Still further, the fact that the air pre-treatment assembly  119  is disposed directly on top of the fluid concentrator assembly  120 , with the gas in these sections flowing downward towards the ground, enables these sections of the concentrator  110  to be supported directly by the ground or by a skid on which these members are mounted. Still further, this configuration keeps the concentrator  110  disposed very close to the flare  130 , making it more compact. Likewise, this configuration keeps the high temperature sections of the concentrator  110  (e.g., the top of the flare  130 , the heat transfer pipe  140  and the air pre-treatment assembly  119 ) above the ground and away from inadvertent human contact, leading to a safer configuration. In fact, due to the rapid cooling that takes place in the venturi section  162  of the concentrator assembly  120 , the venturi section  162 , the flooded elbow  164  and the fluid scrubber  122  are typically cool enough to touch without harm (even when the gases exiting the flare  130  are at 1800 degrees Fahrenheit). This fact also enables these components to be made of less expensive or lighter weight materials, such as carbon steel or fiberglass. In fact, in one embodiment, the fluid scrubber  122  is made of fiberglass, making it less expensive than higher alloys while maintaining exceptional corrosion resistance. 
     The fluid concentrator  110  is also a very fast-acting concentrator. Because the concentrator  110  is a direct contact type of concentrator, it is not subject to deposit buildup, clogging and fouling to the same extent as most other concentrators. Still further, the ability to control the flare cap  134  to open and close, depending on whether the concentrator  110  is being used or operated, allows the flare  130  to be used to burn landfill gas without interruption when starting and stopping the concentrator  110 . More particularly, the flare cap  134  can be quickly opened at any time to allow the flare  130  to simply burn landfill gas as normal while the concentrator  110  is shut down. On the other hand, the flare cap  134  can be quickly closed when the concentrator  110  is started up, thereby diverting hot gasses created in the flare  130  to the concentrator  110 , and allowing the concentrator  110  to operate without interrupting the operation of the flare  130 . In either case, the concentrator  110  can be started and stopped based on the operation of the flare cap  134  without interrupting the operation of the flare  130 . 
     If desired, the flare cap  134  may be opened to a partial amount during operation of the concentrator  110  to control the amount of gas that is transferred from the flare  130  to the concentrator  110 . This operation, in conjunction with the operation of the ambient air valve, may be useful in controlling the temperature of the gas at the entrance of the venturi section  162 . 
     Moreover, due to the compact configuration of the air pre-treatment assembly  119 , the concentrator assembly  120  and the fluid scrubber  122 , parts of the concentrator assembly  120 , the fluid scrubber  122 , the draft fan  190  and at least a lower portion of the exhaust section  124  can be permanently mounted on (connected to and supported by) a skid or plate  230 , as illustrated in  FIG. 3 . The upper parts of the concentrator assembly  120 , the air pre-treatment assembly  119  and the heat transfer pipe  140 , as well as a top portion of the exhaust stack, may be removed and stored on the skid or plate  230  for transport, or may be transported in a separate truck. Because of the manner in which the lower portions of the concentrator  110  can be mounted to a skid or plate, the concentrator  110  is easy to move and install. In particular, during set up of the concentrator  110 , the skid  230 , with the fluid scrubber  122 , the flooded elbow  164  and the draft fan  190  mounted thereon, may be offloaded at the site at which the concentrator  110  is to be used by simply offloading the skid  230  onto the ground or other containment area at which the concentrator  110  is to be assembled. Thereafter, the venturi section  162 , the quencher  159 , and the air pre-treatment assembly  119  may be placed on top of and attached to the flooded elbow  164 . The piping section  150  may then be extended in height to match the height of the flare  130  to which the concentrator  110  is to be connected. In some cases, this may first require mounting the flare cap assembly  132  onto a pre-existing flare  130 . Thereafter, the heat transfer pipe  140  may be raised to the proper height and attached between the flare  130  and the air pre-treatment assembly  119 , while the support member  142  is disposed in place. 
     Because most of the pumps, fluid lines, sensors and electronic equipment are disposed on or are connected to the fluid concentrator assembly  120 , the fluid scrubber  122  or the draft fan assembly  190 , set up of the concentrator  110  at a particular site does not require a lot of fluid piping and electrical work at the site. As a result, the concentrator  110  is relatively easy to install and to set up at (and to disassemble and remove from) a particular site. Moreover, because a majority of the components of the concentrator  110  are permanently mounted to the skid  230 , the concentrator  110  can be easily transported around on a truck or other delivery vehicle and can be easily dropped off and installed at particular location, such as next to a landfill flare. 
       FIG. 9  illustrates a schematic diagram of a control system  300  that may be used to operate the concentrator  110  of  FIG. 3 . As illustrated in  FIG. 9 , the control system  300  includes a controller  302 , which may be a form of digital signal processor type of controller, a programmable logic controller (PLC) which may run, for example, ladder logic based control, or any other type of controller. The controller  302  is, of course, connected to various components within the concentrator  110 . In particular, the controller  302  is connected to the flare cap drive motor  135 , which controls the opening and closing operation of the flare cap  134 . The motor  135  may be set up to control the flare cap  134  to move between a fully open and a fully closed position. However, if desired, the controller  302  may control the drive motor  135  to open the flare cap  134  to any of a set of various different controllable positions between the fully opened and the fully closed position. The motor  135  may be continuously variable if desired, so that the flare cap  134  may be positioned at any desired point between fully open and fully closed. 
     Additionally, the controller  302  is connected to and controls the ambient air inlet valve  306  disposed in the air pre-treatment assembly  119  of  FIG. 3  upstream of the venturi section  162  and may be used to control the pumps  182  and  184  which control the amount of and the ratio of the injection of new liquid to be treated and the re-circulating liquid being treated within the concentrator  110 . The controller  302  may be operatively connected to a sump level sensor  317  (e.g., a float sensor, a non-contact sensor such as a radar unit, or a differential pressure cell). The controller  302  may use a signal from the sump level sensor  317  to control the pumps  182  and  184  to maintain the level of concentrated fluid within the sump  172  at a predetermined or desired level. Also, the controller  302  may be connected to the induced draft fan  190  to control the operation of the fan  190 , which may be a single speed fan, a variable speed fan or a continuously controllable speed fan. In one embodiment, the induced draft fan  190  is driven by a variable frequency motor, so that the frequency of the motor is changed to control the speed of the fan. Moreover, the controller  302  is connected to a temperature sensor  308  disposed at, for example, the inlet of the concentrator assembly  120  or at the inlet of the venturi section  162 , and receives a temperature signal generated by the temperature sensor  308 . The temperature sensor  308  may alternatively be located downstream of the venturi section  162  or the temperature sensor  308  may include a pressure sensor for generating a pressure signal. 
     During operation and at, for example, the initiation of the concentrator  110 , when the flare  130  is actually running and is thus burning landfill gas, the controller  302  may first turn on the induced draft fan  190  to create a negative pressure within the fluid scrubber  122  and the concentrator assembly  120 . The controller  302  may then or at the same time, send a signal to the motor  135  to close the flare cap  134  either partially or completely, to direct waste heat from the flare  130  into the transfer pipe  140  and thus to the air pre-treatment assembly  119 . Based on the temperature signal from the temperature sensor  308 , the controller  302  may control the ambient air valve  306  (typically by closing this valve partially or completely) and/or the flare cap actuator to control the temperature of the gas at the inlet of the concentrator assembly  120 . Generally speaking, the ambient air valve  306  may be biased in a fully open position (i.e., may be normally open) by a biasing element such as a spring, and the controller  302  may begin to close the valve  306  to control the amount of ambient air that is diverted into the air pre-treatment assembly  119  (due to the negative pressure in the air pre-treatment assembly  119 ), so as to cause the mixture of the ambient air and the hot gases from the flare  130  to reach a desired temperature. Additionally, if desired, the controller  302  may control the position of the flare cap  134  (anywhere from fully open to fully closed) and may control the speed of the induced draft fan  190 , to control the amount of gas that enters the air pre-treatment assembly  119  from the flare  130 . As will be understood, the amount of gas flowing through the concentrator  110  may need to vary depending on ambient air temperature and humidity, the temperature of the flare gas, the amount of gas exiting the flare  130 , etc. The controller  302  may therefore control the temperature and the amount of gas flowing through the concentrator assembly  120  by controlling one or any combination of the ambient air control valve  306 , the position of the flare cap  134  and the speed of the induced draft fan  190  based on, for example, the measurement of the temperature sensor  308  at the inlet of the concentrator assembly  120 . This feedback system is desirable because, in many cases, the air coming out of a flare  130  is between 1200 and 1800 degrees Fahrenheit, which may be too hot, or hotter than required for the concentrator  110  to operate efficiently and effectively. 
     In any event, as illustrated in  FIG. 9 , the controller  302  may also be connected to a motor  310  which drives or controls the position of the venturi plate  163  within the narrowed portion of the concentrator assembly  120  to control the amount of turbulence caused within the concentrator assembly  120 . Still further, the controller  302  may control the operation of the pumps  182  and  184  to control the rate at which (and the ratio at which) the pumps  182  and  184  provide re-circulating liquid and new waste fluid to be treated to the inputs of the quencher  159  and the venturi section  162 . In one embodiment, the controller  302  may control the ratio of the re-circulating fluid to new fluid to be about 10:1, so that if the pump  184  is providing  8  gallons per minute of new liquid to the input  160 , the re-circulating pump  182  is pumping  80  gallons per minute. Additionally, or alternatively, the controller  302  may control the flow of new liquid to be processed into the concentrator (via the pump  184 ) by maintaining a constant or predetermined level of concentrated liquid in the sump  172  using, for example, the level sensor  317 . Of course, the amount of liquid in the sump  172  will be dependent on the rate of concentration in the concentrator, the rate at which concentrated liquid is pumped from or otherwise exists the sump  172  via the secondary re-circulating circuit and the rate at which liquid from the secondary re-circulating circuit is provided back to the sump  172 , as well as the rate at which the pump  182  pumps liquid from the sump  172  for delivery to the concentrator via the primary re-circulating circuit. 
     If desired, one or both of the ambient air valve  306  and the flare cap  134  may be operated in a fail-safe open position, such that the flare cap  134  and the ambient air valve  306  open in the case of a failure of the system (e.g., a loss of control signal) or a shutdown of the concentrator  110 . In one case, the flare cap motor  135  may be spring loaded or biased with a biasing element, such as a spring, to open the flare cap  134  or to allow the flare cap  134  to open upon loss of power to the motor  135 . Alternatively, the biasing element may be the counter-weight  137  on the flare cap  134  may be so positioned that the flare cap  134  itself swings to the open position under the applied force of the counter-weight  137  when the motor  135  loses power or loses a control signal. This operation causes the flare cap  134  to open quickly, either when power is lost or when the controller  302  opens the flare cap  134 , to thereby allow hot gas within the flare  130  to exit out of the top of the flare  130 . Of course, other manners of causing the flare cap  134  to open upon loss of control signal can be used, including the use of a torsion spring on the pivot point  136  of the flare cap  134 , a hydraulic or pressurized air system that pressurizes a cylinder to close the flare cap  134 , loss of which pressure causes the flare cap  134  to open upon loss of the control signal, etc. 
     Thus, as will be noted from the above discussion, the combination of the flare cap  134  and the ambient air valve  306  work in unison to protect the engineered material incorporated into the concentrator  110 , as whenever the system is shut down, the flare cap and the air valve  306  automatically immediately open, thereby isolating hot gas generated in the flare  130  from the process while quickly admitting ambient air to cool the process. 
     Moreover, in the same manner, the ambient air valve  306  may be spring biased or otherwise configured to open upon shut down of the concentrator  110  or loss of signal to the valve  306 . This operation causes quick cooling of the air pre-treatment assembly  119  and the concentrator assembly  120  when the flare cap  134  opens. Moreover, because of the quick opening nature of the ambient air valve  306  and the flare cap  134 , the controller  302  can quickly shut down the concentrator  110  without having to turn off or effect the operation of the flare  130 . 
     Furthermore, as illustrated in the  FIG. 9 , the controller  302  may be connected to the venturi plate motor  310  or other actuator which moves or actuates the angle at which the venturi plate  163  is disposed within the venturi section  162 . Using the motor  310 , the controller  302  may change the angle of the venturi plate  163  to alter the gas flow through the concentrator assembly  120 , thereby changing the nature of the turbulent flow of the gas through concentrator assembly  120 , which may provide for better mixing of the and liquid and gas therein and obtain better or more complete evaporation of the liquid. In this case, the controller  302  may operate the speed of the pumps  182  and  184  in conjunction with the operation of the venturi plate  163  to provide for optimal concentration of the wastewater being treated. Thus, as will be understood, the controller  302  may coordinate the position of the venturi plate  163  with the operation of the flare cap  134 , the position of the ambient air or bleed valve  306 , and the speed of the induction fan  190  to maximize wastewater concentration (turbulent mixing) without fully drying the wastewater so as to prevent formation of dry particulates. The controller  302  may use pressure inputs from the pressure sensors to position the venturi plate  163 . Of course, the venturi plate  163  may be manually controlled or automatically controlled. 
     The controller  302  may also be connected to a motor  312  which controls the operation of the damper  198  in the gas re-circulating circuit of the fluid scrubber  122 . The controller  302  may cause the motor  312  or other type of actuator to move the damper  198  from a closed position to an open or to a partially open position based on, for example, signals from pressure sensors  313 ,  315  disposed at the gas entrance and the gas exit of the fluid scrubber  122 . The controller  302  may control the damper  198  to force gas from the high pressure side of the exhaust section  124  (downstream of the induced draft fan  190 ) into the fluid scrubber entrance to maintain a predetermined minimum pressure difference between the two pressure sensors  313 .  315 . Maintaining this minimum pressure difference assures proper operation of the fluid scrubber  122 . Of course, the damper  198  may be manually controlled instead or in addition to being electrically controlled. 
     Thus, as will be understood from the above discussion, the controller  302  may implement one or more on/off control loops used to start up or shut down the concentrator  110  without affecting the operation of the flare  130 . For example, the controller  302  may implement a flare cap control loop which opens or closes the flare cap  134 , a bleed valve control loop which opens or begins to close the ambient air valve  306 , and an induced draft fan control loop which starts or stops the induced draft fan  190  based on whether the concentrator  110  is being started or stopped. Moreover, during operation, the controller  302  may implement one or more on-line control loops which may control various elements of the concentrator  110  individually or in conjunction with one another to provide for better or optimal concentration. When implementing these on-line control loops, the controller  302  may control the speed of induced draft fan  190 , the position or angle of the venturi plate  163 , the position of the flare cap  134  and or the position of the ambient air valve  306  to control the fluid flow through the concentrator  110 , and/or the temperature of the air at the inlet of the concentrator assembly  120  based on signals from the temperature and pressure sensors. Moreover, the controller  302  may maintain the performance of the concentration process at steady-state conditions by controlling the pumps  184  and  182  which pump new and re-circulating fluid to be concentrated into the concentrator assembly  120 . Still further, the controller  302  may implement a pressure control loop to control the position of the damper  198  to assure proper operation of the fluid scrubber  122 . Of course, while the controller  302  is illustrated in  FIG. 9  as a single controller device that implements these various control loops, the controller  302  could be implemented as multiple different control devices by, for example, using multiple different PLCs. 
     As will be understood, the concentrator  110  described herein directly utilizes hot waste gases in processes after the gases have been thoroughly treated to meet emission standards, and so seamlessly separates the operational requirements of the process that generates the waste heat from the process which utilizes the waste heat in a simple, reliable and effective manner. 
     In addition to being an important component of the concentrator  110  during operation of the concentrator  110 , the automated or manually actuated flare cap  134  described herein can be used in a standalone situation to provide weather protection to a flare or to a flare and a concentrator combination when the flare stands idle. With the flare cap  134  closed, the interior of the metal shell of the flare  130  along with the refractory, burners and other critical components of the flare assembly  115  and the heat transfer assembly  117  are protected from corrosion and general deterioration related to exposure to the elements. In this case, the controller  302  may operate the flare cap motor  135  to keep the flare cap  134  fully open or partially closed during idling of the flare  130 . Moreover, beyond using a flare cap  134  that closes automatically when the flare  130  shuts down or that opens automatically when the flare  130  is ignited, a small burner, such as the normal pilot light, may be installed inside of the flare  130  and may be run when the flare  130  is shut down but while the flare cap  134  held closed. This small burner adds further protection against deterioration of flare components caused by dampness, as it will keep the interior of the flare  130  dry. An example of a stand alone flare that may use the flare cap  134  described herein in a stand-alone situation is a stand-by flare installed at a landfill to ensure gas control when a landfill gas fueled power plant is off-line. 
     While the liquid concentrator  110  has been described above as being connected to a landfill flare to use the waste heat generated in the landfill flare, the liquid concentrator  110  can be easily connected to other sources of waste heat. For example,  FIG. 10  illustrates the concentrator  110  modified so as to be connected to an exhaust stack of a combustion engine plant  400  and to use the waste heat from the engine exhaust to perform liquid concentration. While, in one embodiment, the engine within the plant  400  may operate on landfill gas to produce electricity, the concentrator  110  can be connected to run with exhaust from other types of engines, including other types of combustion engines, such as those that operate on gasoline, diesel fuel, etc. 
     Referring to  FIG. 10 , exhaust generated in an engine (not shown) within the plant  400  is provided to a muffler  402  on the exterior of the plant  400  and, from there, enters into a combustion gas exhaust stack  404  having a combustion gas exhaust stack cap  406  disposed on the top thereof. The cap  406  is essentially counter-weighted to close over the exhaust stack  404  when no exhaust is exiting the stack  404 , but is easily pushed up by the pressure of the exhaust when exhaust is leaving the stack  404 . In this case, a Y-connector is provided within the exhaust stack  404  and operates to connect the stack  404  to a transfer pipe  408  which transfers exhaust gas (a source of waste heat) from the engine to an expander section  410 . The expander section  410  mates with the quencher  159  of the concentrator  110  and provides the exhaust gas from the engine directly to the concentrator assembly  120  of the concentrator  110 . It is typically not necessary to include an air bleed valve upstream of the concentrator section  120  when using engine exhaust as a source of waste heat because exhaust gas typically leaves an engine at less than 900 degrees Fahrenheit, and so does not need to be cooled significantly before entering the quencher  159 . The remaining parts of the concentrator  110  remain the same as described above with respect to  FIGS. 3-8 . As a result, it can be seen that the liquid concentrator  110  can be easily adapted to use various different sources of waste heat without a lot of modification. 
     Generally, when controlling the liquid concentrator  110  of  FIG. 10 , the controller will turn on the induced draft fan  190  while the engine in the plant  400  is running. The controller will increase the speed of the induced draft fan  190  from a minimal speed until the point that most or all of the exhaust within the stack  404  enters the transfer pipe  408  instead of going out of the top of the exhaust stack  404 . It is easy to detect this point of operation, which is reached when, as the speed of the induced draft fan  190  is increased, the cap  406  first sits back down on the top of the stack  404 . It may be important to prevent increasing the speed of the induced draft fan  190  above this operational point, so as to not create any more of a negative pressure within the concentrator  110  than is necessary, and thereby assuring that the operation of the concentrator  110  does not change the back pressure and, in particular, create undesirable levels of suction experienced by the engine within the plant  400 . Changing the back pressure or applying suction within the exhaust stack  404  may adversely effect the combustion operation of the engine, which is undesirable. In one embodiment, a controller (not shown in  FIG. 10 ), such as a PLC, may use a pressure transducer mounted in the stack  404  close to the location of the cap  406  to continuously monitor the pressure at this location. The controller can then send a signal to the variable frequency drive on the induced draft fan  190  to control the speed of the induced draft fan  190  to maintain the pressure at a desirable set point, so as to assure that undesirable back pressure or suction is not being applied on the engine. 
       FIGS. 11 and 12  illustrate a side cross-sectional view, and a top cross-sectional view, of another embodiment of a liquid concentrator  500 . The concentrator  500  is shown in a generally vertical orientation. However, the concentrator  500  shown in  FIG. 11  may be arranged in a generally horizontal orientation or a generally vertical orientation depending on the particular constraints of a particular application. For example, a truck mounted version of the concentrator may be arranged in a generally horizontal orientation to allow the truck-mounted concentrator to pass under bridges and overpasses during transport from one site to another. The liquid concentrator  500  has a gas inlet  520  and a gas exit  522 . A flow corridor  524  connects the gas inlet  520  to the gas exit  522 . The flow corridor  524  has a narrowed portion  526  that accelerates the gas through the flow corridor  524 . A liquid inlet  530  injects a liquid into the gas stream prior to the narrowed portion  526 . In contrast to the embodiment of  FIG. 1 , the narrowed portion  526  of the embodiment of  FIG. 11  directs the gas-liquid mixture into a cyclonic chamber  551 . The cyclonic chamber  551  enhances the mixing of the gas and liquid while also performing the function of the demister in  FIG. 1 . The gas-liquid mixture enters the cyclonic chamber  551  tangentially (see  FIG. 12 ) and then moves in a cyclonic manner through the cyclonic chamber  551  towards a liquid outlet area  554 . The cyclonic circulation is facilitated by a hollow cylinder  556  disposed in the cyclonic chamber  551  that conducts the gas to the gas outlet  522 . The hollow cylinder  556  presents a physical barrier and maintains the cyclonic circulation throughout the cyclonic chamber  551  including the liquid outlet area  554 . 
     As the gas-liquid mixture passes through the narrowed portion  526  of the flow corridor  524  and circulates in the cyclonic chamber  551 , a portion of the liquid evaporates and is absorbed by the gas. Furthermore, centrifugal force accelerates movement of entrained liquid droplets in the gas towards the side wall  552  of the cyclonic chamber  551  where the entrained liquid droplets coalesce into a film on the side wall  552 . Simultaneously, centripetal forces created by an induction fan  550  collect the demisted gas flow at the inlet  560  of the cylinder  556  and direct the flow to the gas outlet  522 . Thus, the cyclonic chamber  551  functions both as a mixing chamber and a demisting chamber. As the liquid film flows towards the liquid outlet area  554  of the chamber due to the combined effects of the force of gravity and the cyclonic motion within cyclonic chamber  551  toward the liquid outlet area  554 , the continuous circulation of the gas in the cyclonic chamber  551  further evaporates a portion of the liquid film. As the liquid film reaches the liquid outlet area  554  of the cyclonic chamber  551 , the liquid is directed through a re-circulating circuit  542 . Thus, the liquid is re-circulated through the concentrator  500  until a desired level of concentration is reached. A portion of the concentrated slurry may be drawn off through an extraction port  546  when the slurry reaches the desired concentration (this is called blowdown). Fresh liquid is added to the circuit  542  through a fresh liquid inlet  544  at a rate equal to the rate of evaporation plus the rate of slurry drawn off through the extraction port  546 . 
     As the gas circulates in the cyclonic chamber  551 , the gas is cleansed of entrained liquid droplets and drawn towards the liquid discharge area  554  of the cyclonic chamber  551  by the induction fan  550  and towards an inlet  560  of the hollow cylinder  556 . The cleansed gas then travels through the hollow cylinder  556  and finally vents through the gas exit  522  to the atmosphere or further treatment (e.g., oxidization in a flare). 
       FIG. 13  illustrates a schematic view of a distributed liquid concentrator  600  configured in a manner that enables the concentrator  600  to be used with many types of sources of waste heat, even sources of waste heat that are located in places that are hard to access, such as on the sides of buildings, in the middle of various other equipment, away from roads or other access points, etc. While the liquid concentrator  600  will be described herein as being used to process or concentrate leachate, such as leachate collected from a landfill, the liquid concentrator  600  could be used to concentrate other types of liquids as well or instead including many other types of wastewaters. 
     Generally speaking, the liquid concentrator  600  includes a gas inlet  620 , a gas outlet or a gas exit  622 , a flow corridor  624  connecting the gas inlet  620  to the gas exit  622  and a liquid re-circulating system  625 . A concentrator section has a flow corridor  624  that includes a quencher section  659  including the gas inlet  620  and a fluid inlet  630 , a venturi section  626  disposed downstream of the quencher section  659 , and a blower or draft fan  650  connected downstream of the venturi section  626 . The fan  650  and a flooded elbow  654  couple a gas outlet of the concentrator section (e.g., an outlet of the venturi section  626 ) to a piping section  652 . The flooded elbow  654 , in this case, forms a 90 degree turn in the flow corridor  624 . However, the flooded elbow  654  could form a turn that is less than or more than 90 degrees if desired. The piping section  652  is connected to a demister, in this case illustrated in the form of a crossflow scrubber  634 , which is, in turn, connected to a stack  622 A having the gas exit  622 . 
     The re-circulating system  625  includes a sump  636  coupled to a liquid outlet of the crossflow scrubber  634 , and a re-circulating or recycle pump  640  coupled between the sump  636  and a piping section  642  which delivers re-circulated fluid to the fluid inlet  630 . A process fluid feed  644  also delivers leachate or other liquid to be processed (e.g., concentrated) to the fluid inlet  630  to be delivered to the quencher section  659 . The re-circulating system  625  also includes a liquid takeoff  646  connected to the piping section  642 , which delivers some of the recycled fluid (or concentrated fluid) to a storage, settling and recycle tank  649 . The heavier or more concentrated portions of the liquid in the settling tank  649  settle to the bottom of the tank  649  as sludge, and are removed and transported for disposal in concentrated form. Less concentrated portions of the liquid in the tank  649  are delivered back to the sump  636  for reprocessing and further concentration, as well as to assure that an adequate supply of liquid is available at the liquid inlet  630  at all times so to ensure that dry particulate is not formed. Dry particulate can form at reduced ratios of process fluid to hot gas volumes. 
     In operation, the quencher section  659  mixes fluid delivered from the liquid inlet  630  with gas containing waste heat collected from, for example, an engine muffler and stack  629  associated with an internal combustion engine (not shown). The liquid from the fluid inlet  630  may be, for example, leachate to be processed or concentrated. As illustrated in  FIG. 13 , the quencher section  659  is connected vertically above the venturi portion  626  which has a narrowed portion that operates to accelerate the flow of gas and liquid through a section of the fluid flow corridor  624  immediately downstream of the venturi portion  626  and upstream of the fan  650 . Of course, the fan  650  operates to create a low pressure region immediately downstream of the venturi portion  626 , drawing gas from the stack  629  through the venturi portion  626  and the flooded elbow  654  and causing mixing of the gas and liquid. 
     As noted above, the quencher section  659  receives hot exhaust gas from the engine exhaust stack  629  and may be connected directly to any desired portion of the exhaust stack  629 . In this illustrated embodiment, the engine exhaust stack  629  is mounted on an outside of a building  631  that houses one or more electric power generators that generate electric power using landfill gas as a combustion fuel. In this case, the quencher section  659  may be connected directly to a condensate take off (e.g., a weep leg) associated with the stack  629  (i.e., a lower portion of the exhaust stack  629 ). Here, the quencher section  659  may be mounted immediately below or adjacent to the stack  629  requiring only a few inches or at most a few feet of expensive, high temperature piping material to connect the two together. If desired, however, the quencher section  659  may be coupled any other portion of the exhaust stack  629 , including, for example, to the top or to a middle portion of the stack  629  via appropriate elbows or takeoffs. 
     As noted above, the liquid inlet  630  injects a liquid to be evaporated (e.g., landfill leachate) into the flow corridor  624  through the quencher section  659 . If desired, the liquid inlet  630  may include a replaceable nozzle for spraying the liquid into the quencher section  659 . The liquid inlet  630 , whether or not equipped with a nozzle, may introduce the liquid in any direction, from perpendicular to parallel to the gas flow as the gas moves through the flow corridor  624 . Moreover, as the gas (and the waste heat stored therein) and liquid flow through the venturi portion  626 , the venturi principle creates an accelerated and turbulent flow that thoroughly mixes the gas and liquid in the flow corridor  624  immediately downstream of the venturi section  626 . As a result of the turbulent mixing, a portion of the liquid rapidly vaporizes and becomes part of the gas stream. This vaporization consumes a large amount of the heat energy within the waste heat as latent heat that exits the concentrator system  600  as water vapor within the exhaust gas. 
     After leaving the narrowed portion of the venturi section  626 , the gas/liquid mixture passes through the flooded elbow  654  where the flow corridor  624  turns 90 degrees to change from a vertical flow to a horizontal flow. The gas/liquid mixture flows past the fan  650  and enters a high pressure region at the downstream side of the fan  650 , this high pressure region existing in the piping section  652 . The use of a flooded elbow  654  at this point in the system is desirable for at least two reasons. First, the liquid at the bottom portion of the flooded elbow  654  reduces erosion at the turning point in the flow corridor  624 , which erosion would normally occur due to suspended particles within the gas/liquid mixture flowing at high rates of speed through a 90 degree turn and impinging at steep angles directly on the bottom surfaces of a conventional elbow were the flooded elbow  654  not employed. The liquid in the bottom of the flooded elbow  654  absorbs the energy in these particles and therefore prevents erosion on the bottom surface of the flooded elbow  654 . Still further, liquid droplets which still exist in the gas/liquid mixture as this mixture arrives at the flooded elbow  654  are more easily collected and removed from the flow stream if they impinge upon a liquid. That is, the liquid at the bottom of the flooded elbow  654  operates to collect liquid droplets impinging thereon because the liquid droplets within the flow stream are more easily retained when these suspended liquid droplets come into contact with a liquid. Thus, the flooded elbow  654 , which may have a liquid takeoff (not shown) connected to, for example, the re-circulating circuit  625 , operates to remove some of the process fluid droplets and condensation from the gas/liquid mixture exiting the venturi section  626 . 
     Importantly, the gas/liquid mixture while passing through the venturi section  626  quickly approaches the adiabatic saturation point, which is at a temperature that is much lower than that of the gas exiting the stack  629 . For example, while the gas exiting the stack  629  may be between about 900 and about 1800 degrees Fahrenheit, the gas/liquid mixture in all sections of the concentrator system  600  downstream of the venturi section  626  will generally be in the range of 150 degrees to 190 degrees Fahrenheit, although it can range higher or lower than these values based on the operating parameters of the system. As a result, sections of the concentrator system  600  downstream of the venturi section  626  do not need to be made of high temperature resistant materials and do not need to be insulated at all or to the degree that would be necessary for transporting higher temperature gases if insulation were to be applied for the purpose of more fully utilizing the waste heat content of the inlet hot gas. Still further the sections of the concentrator system  600  downstream of the venturi section  626  disposed in areas, such as along the ground that people will come into contact with, without significant danger, or with only minimal exterior protection. In particular, the sections of the concentrator system downstream of the venturi section  626  may be made of fiberglass and may need minimal or no insulation. Importantly, the gas/liquid stream may flow within the sections of the concentrator system downstream of the venturi section  626  over a relatively long distance while maintaining the gas/liquid mixture therein at close to the adiabatic saturation point, thereby allowing the piping section  652  to easily transport the flow stream away from the building  631  to a more easily accessible location, at which the other equipment associated with the concentrator  600  can be conveniently disposed. In particular, the piping section  652  may span 20 feet, 40 feet, or even longer while maintaining the flow therein at close to the adiabatic saturation point. Of course, these lengths may be longer or shorter based on ambient temperature, the type of piping and insulation used, etc. Moreover, because the piping section  652  is disposed on the high pressure side of the fan  650 , it is easier to remove condensation from this stream. In the example embodiment of  FIG. 13 , the piping section  652  is illustrated as flowing past or beneath an air cooler associated with the engines within the building  631 . However, the air cooler of  FIG. 13  is merely one example of the types of obstructions that may be located close to the building  631  which make it problematic to place all of the components of the concentrator  600  in close proximity to the source of the waste heat (in this case, the stack  629 ). Other obstructions could include other equipment, vegetation such as trees, other buildings, inaccessible terrain without roads or easy access points, etc. 
     In any event, the piping section  652  delivers the gas/liquid stream at close to the adiabatic saturation point to the demister  634 , which may be, for example, a crossflow scrubber. The demister  634  operates to remove entrained liquid droplets from the gas/liquid stream. The removed liquid collects in the sump  636  which directs the liquid to the pump  640 . The pump  640  moves the liquid through the return line  642  of the re-circulating circuit  625  back to the liquid inlet  630 . In this manner, the captured liquid may be further reduced through evaporation to a desired concentration and/or re-circulated to prevent the formation of dry particulate. Fresh liquid to be concentrated is input through the fresh liquid inlet  644 . The rate of fresh liquid input into the re-circulating circuit  625  should be equal to the rate of evaporation of the liquid as the gas-liquid mixture flows through the flow corridor  624  plus the rate of liquid or sludge extracted from the settling tank  649  (assuming the material within the settling tank  649  remains at a constant level). In particular, a portion of the liquid may be drawn off through an extraction port  646  when the liquid in the re-circulating circuit  625  reaches a desired concentration. The portion of liquid drawn off through the extraction port  646  may be sent to the storage and settling tank  649  where the concentrated liquid is allowed to settle and separate into its component parts (e.g., a liquid portion and a semi-solid portion). The semi-solid portion may be drawn from the tank  649  and disposed of or further treated. 
     As noted above, the fan  650  draws the gas through a portion of the flow corridor  624  under negative pressure and pushes gas through another portion of the flow corridor  624  under positive pressure. The quencher section  659 , venturi section  626 , and fan  650  may be attached to the building  631  with any type of connecting device and, as illustrated in  FIG. 13 , are disposed in close proximity to the source of waste heat. However the demister  634  and the gas outlet  622 , as well as the settling tank  649 , may be located some distance away from the quencher section  659 , venturi section  626 , and fan  650 , at for example, an easy to access location. In one embodiment, the demister  634  and the gas outlet  622  and even the settling tank  649  may be mounted on a mobile platform such as a pallet or a trailer bed. 
       FIGS. 14-16  illustrate another embodiment of a liquid concentrator  700  which may be mounted on a pallet or trailer bed. In one embodiment, some of the components of the concentrator  700  may remain on the bed and be used to perform concentration activities, while others of these components may be removed and installed near a source of waste heat in the manner illustrated in, for example, the embodiment of  FIG. 13 . The liquid concentrator  700  has a gas inlet  720  and a gas exit  722 . A flow corridor  724  connects the gas inlet  720  to the gas exit  722 . The flow corridor  724  has a narrowed or venturi portion  726  that accelerates the gas through the flow corridor  724 . Gas is drawn into a quencher section  759  by an induction fan (not shown). A liquid inlet  730  injects a liquid into the gas stream in the quencher section  759 . Gas is directed from the venturi section  726  into the demister (or crossflow scrubber)  734  by an elbow section  733 . After exiting the demister  734 , the gas is directed to the gas exit  722  through a stack  723 . Of course, as described above, some of these components may be removed from the bed and installed in close proximity to a source of waste heat while others of these components (such as the demister  734 , the stack  723  and the gas exit  722 ) may remain on the bed. 
     As the gas-liquid mixture passes through the venturi portion  726  of the flow corridor  724 , a portion of the liquid evaporates and is absorbed by the gas, thus consuming a large portion of heat energy within the waste heat as latent heat that exits the concentrator system  700  as water vapor within the exhaust gas. 
     In the embodiment shown in  FIGS. 14-16 , portions of the liquid concentrator  700  may be disassembled and mounted on a pallet or trailer skid for transportation. For example, the quenching section  759  and the venturi section  726  may be removed from the elbow section  733 , as illustrated by the dashed line in  FIG. 14 . Likewise, the stack  723  may be removed from the induction fan  750  as illustrated by the dashed line in  FIG. 14 . The elbow section  733 , demister  734 , and induction fan  750  may be secured on a pallet or trailer skid  799  as a unit. The stack  723  may be secured separately to the pallet or trailer skid  799 . The quenching section  759  and venturi section  726  may also be secured to the pallet or trailer skid  799 , or alternately transported separately. The compartmentalized construction of the liquid concentrator  700  simplifies transportation of the liquid concentrator  700 . 
     While certain representative embodiments and details have been shown for purposes of illustrating the invention, it will be apparent to those skilled in the art that various changes in the methods and apparatus disclosed herein may be made without departing from the scope of the invention.