Compact wastewater concentrator and contaminant scrubber

A compact and portable liquid concentrator and contaminant scrubber includes a gas inlet, a gas exit and a 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 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. A demister or fluid scrubber downstream of the narrowed portion removes entrained liquid droplets from the gas stream and re-circulates the removed liquid to the liquid inlet through a re-circulating circuit. A reagent may be mixed with the liquid to react with contaminants in the liquid.

FIELD OF THE DISCLOSURE

This application relates generally to liquid concentrators, and more specifically to compact, portable, cost-effective wastewater concentrators that can be easily connected to and use sources of waste heat and more specifically to compact, portable, cost-effective wastewater concentrators that simultaneously concentrate wastewater while removing contaminants dissolved within the wastewater stream.

BACKGROUND

Concentration 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. 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.

Generally, conventional processes that affect concentration by evaporation of water and other volatile substances use indirect heat transfer systems. Indirect heat transfer systems generally include a vessel that holds a process fluid and a plate, a bayonet tube, or a coil-type heat exchanger immersed within the process fluid. Mediums such as steam or hot oil are passed through the heat exchangers in order to transfer the heat required for evaporation.

Indirect heat transfer systems that rely on heat exchangers such as 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 (i.e., inverse solubility), 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 (i.e., saturation). Built up layers of solids on heat exchange surfaces act as an insulation barrier that reduces the rate of heat transfer. Additionally, solid deposits may have the potential to corrode certain materials within the heat exchanger. Such deposits, which necessitate frequent cycles of heat exchange surface cleaning to maintain process efficiency and to reduce the potential for corrosion, may be any combination of suspended solids carried into the process with the wastewater feed and solids that precipitate out of the process fluid. To counteract the loss of efficiency and to extend time between cleanings, designers of indirect heat exchange evaporators generally scale up the heat exchange surfaces. In other words, indirect heat exchange surfaces are built larger than needed to reduce cleaning cycles. Additionally, to counteract the potential for corrosion, designers typically select expensive high alloy materials for the heat exchangers. The effect of solid buildup in indirect heat exchangers imposes 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.

Due to the factors listed above, designers of indirect heat exchange evaporators must balance cost, cleaning cycles, corrosion resistance, and efficiency when designing such systems. In order to extend the time between cleaning cycles, indirect heat exchange evaporators are often limited in differential pressure, which limits the maximum concentration of the process fluid. As a result, known indirect heat exchange evaporators are often limited to less than 20% total solids as a maximum concentration in order to reduce the rate of solid buildup on the heat exchange surfaces.

Another drawback to known indirect heat exchange evaporators is the large amount of heat required to evaporate water in the wastewater. At sea level, generally 1 Btu/Lb/° F. is required to heat the wastewater to its boiling point (this heat is generally called “sensible heat”). Thereafter, approximately 1,000 Btu/Lb is required to effect evaporation of the water (this heat is generally known as “latent heat”).

Some indirect heat exchange evaporators have attempted to reduce the amount of thermal energy required to evaporate the water. In particular, a multi-stage indirect evaporative process has been developed that operates under a partial vacuum in an effort to reduce the thermal energy required. Although such designs have been somewhat effective in reducing the amount of thermal energy required, these designs are very expensive and they remain subject to the drawbacks discussed above, in particular, solid deposits and concentration limits.

In addition to evaporation, some traditional wastewater treatment systems include a series of process steps, or “unit operations,” that interact to provide a final treated product that is safe. Examples these types of wastewater treatment systems include conventional sewage treatment systems. Conventional sewage treatment systems include process steps, such as, dewatering, heating, microbiological digestion (aerobic and anaerobic), pH adjustment, precipitation, sludge thickening, sludge drying, and denitrification and filtration of treated effluent. Even with the several process steps, which are aimed at cleaning the sewage and producing a safe product, the end product of conventional sewage treatment systems is generally a sludge of some sort. Some of the resultant sludge may contain heavy metals that precipitated out of solution during the treatment process. These heavy metals may be toxic and the heavy metals are difficult to extract from the sludge.

Another drawback to conventional sewage treatment systems is that the process fluid is very sensitive to variations in pH. Moreover, the process fluid may contain compounds that interfere with the microbiological digestion. In other words, the process fluid may contain compounds that are harmful to the bacteria used in the conventional sewage treatment systems.

Yet another conventional method of treating wastewater is a filtration system. Filtration systems may use a diverse range of filtration methods to purify wastewater. Some examples of filtration methods are reverse osmosis, ultrafiltration, and ion exchange. Each of these filtration systems includes a certain degree of sensitivity to contaminants on membranes within the system. Thus, the membranes must be backwashed or cleaned regularly. Moreover, secondary systems may be needed to remove these contaminants, resulting in a more expensive and complex system.

SUMMARY

A compact liquid concentrating device may be easily connected to a source of waste heat, such as a natural gas flare or a combustion engine exhaust stack, and use this waste heat to perform a direct heat transfer concentration and contaminant removal 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 no 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, such as natural gas well flares. Thus, the concentrator described herein is a cost-effective, reliable and durable device that operates to continuously concentrate abroad 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.

The compact liquid concentrator advantageously operates on direct heat exchange without the need for solid heat exchange surfaces. As a result, the compact liquid concentrator is not subject the drawbacks of solid deposits on heat exchange surfaces. Moreover, the compact liquid concentrator is able to operate continuously at very high levels of wastewater concentration. High turbulence in the concentrator forestalls the formation of large crystals and keeps solids suspended in solution. As a result, the compact liquid concentrator experiences very little solid buildup on surfaces. Precipitated solids may be removed from the concentrator through a side process, such as a settling tank or a vacuum belt filter, while the liquid portion is returned to the concentrator. In this way, the concentrator approaches a zero liquid discharge during continuous operation. The precipitated solids may often be deposited in a landfill for disposal.

In one embodiment of the concentrator a reagent may be added to the wastewater pre or post concentration. The reagent may chemically or mechanically react with hazardous components of the wastewater to produce non-hazardous or insoluble products. Thus, the concentrator may be useful in removing harmful substances from wastewater streams.

DETAILED DESCRIPTION

FIG. 1illustrates one particular embodiment of a compact liquid concentrator110, which is connected to a source of waste heat in the form of a natural gas flare from a natural gas well. Generally speaking, the compact liquid concentrator110operates to concentrate wastewater, such as flowback water from a natural gas well, using exhaust or waste heat created within a natural gas flare that burns natural gas in a manner that meets the standards set by the U.S. Environmental Protection Agency (EPA) and/or local regulatory authority. As is known, most natural gas wells include a flare which is used to burn excess natural gas. Typically, the gas exiting the flare is between 1200 and 1500 degrees Fahrenheit and may reach 1800 degrees Fahrenheit. The compact liquid concentrator100is equally effective in concentrating landfill leachate or other produced waters and may be operated on exhaust gas from a landfill gas flare, a propane flare, or heat from virtually any other source.

As illustrated inFIG. 1, the compact liquid concentrator110generally includes or is connected to a flare assembly115, and includes a heat transfer assembly117, an air pre-treatment assembly119, a concentrator assembly120(shown in more detail inFIG. 2), a fluid scrubber122, and an exhaust section124. Importantly, the flare assembly115includes a flare130, which burns natural gas (or other combustible fuel) therein according to any known principles, and a flare cap assembly132. The flare cap assembly132may include a moveable cap134(e.g., a flare cap, an exhaust gas cap, etc.) which covers the top of the flare130, or other type of stack (e.g., a combustion gas exhaust stack), to seal off the top of the flare130when the flare cap134is 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 flare130to escape to the atmosphere through an open end that forms a primary gas outlet143, when the flare cap134is in an open or partially open position. The flare cap assembly132also includes a cap actuator, such as a motor135(seeFIG. 3) which moves the flare cap134between the fully open and the fully closed positions. The flare cap actuator may utilize a chain drive or any other type of drive mechanism connected to the flare cap134to move the flare cap134around a pivot point. The flare cap assembly132may also include a counter-weight (seeFIG. 3) disposed on the opposite side of the pivot point from the flare cap134to balance or offset a portion of the weight of the flare cap134when moving the flare cap134around the pivot point. The counter-weight enables the actuator to be reduced in size or power while still being capable of moving or rotating the flare cap134between an open position, in which the top of the flare130(or the primary combustion gas outlet143) is open to the atmosphere, and a closed position, in which the flare cap134covers and essentially seals the top of the flare130(or the primary combustion gas outlet143). The flare cap134itself 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 cap134is in the closed position.

If desired, the flare130may include an adapter section138including the primary combustion gas outlet143and a secondary combustion gas outlet141upstream of the primary combustion gas outlet143. When the flare cap130is in the closed position, or in a partially closed position, combustion gas is diverted through the secondary combustion gas outlet141. The adapter section138may include a connector section139that connects the flare130(or exhaust stack) to the heat transfer section117using a 90 degree elbow or turn. Other connector arrangements are possible. For example, the flare130and heat transfer section117may be connected at virtually any angle between 0 degrees and 180 degrees. In this case, the flare cap assembly132is mounted on the top of the adaptor section138proximate the primary combustion gas outlet143.

As illustrated inFIG. 1the heat transfer assembly117includes a transfer pipe140, which connects to an inlet of the air pre-treatment assembly119to the flare130and, more particularly, to the adaptor section138of the flare130. A support member142, in the form of a vertical bar or pole, supports the heat transfer pipe140between the flare130and the air pre-treatment assembly119at a predetermined level or height above the ground. The heat transfer pipe140is connected to the connector section139or the adapter section138at the secondary combustion gas outlet141, the transfer pipe forming a portion of a fluid passageway between the adapter section138and a secondary process, such as a fluid concentrating process. The support member142may be necessary because the heat transfer pipe140will 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 flare130to the air pre-treatment assembly119. Thus, the heat transfer pipe140will typically be a heavy piece of equipment. However, because the flare130, on the one hand, and the air pre-treatment assembly119and the concentrator assembly120, on the other hand, are disposed immediately adjacent to one another, the heat transfer pipe140generally only needs to be of a relatively short length, thereby reducing the cost of the materials used in the concentrator110, as well as reducing the amount of support structure needed to bear the weight of the heavy parts of the concentrator110above the ground. As illustrated inFIG. 1, the heat transfer pipe140and the air pre-treatment assembly119form an upside-down U-shaped structure.

The air pre-treatment assembly119includes a vertical piping section150and an ambient air valve306(seeFIG. 3) disposed at the top of the vertical piping section150. The ambient air valve306(also referred to as a damper or bleed valve) forms a fluid passageway between the heat transfer pipe140(or air pre-treatment assembly119) and the atmosphere. The ambient air valve306operates to allow ambient air to flow through a mesh screen152(typically wire or metal) and into the interior of the air pre-treatment assembly119to mix with the hot gas coming from the flare130. If desired, the air pre-treatment assembly119may include a permanently open section proximate to the ambient air valve306which always allows some amount of bleed air into the air pre-treatment assembly119, which may be desirable to reduce the size of the required ambient air valve306and for safety reasons. A pressure blower (not shown) may be connected to the inlet side of the ambient air valve306, if desired, to force ambient air through the ambient air valve306. If a pressure blower is implemented, the screen152and permanently open section (if implemented) may be relocated to the inlet side of the pressure blower. While the control of the ambient air306will be discussed in greater detail hereinafter, the ambient air valve306generally allows the gas from the flare130to be cooled to a more desirable temperature before entering into the concentrator assembly120. The air pre-treatment assembly119may be supported in part by cross-members154connected to the support member142. The cross-members154stabilize the air pre-treatment assembly119, 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 concentrator110. If desired, the vertical piping section150may be extendable to adapt to or account for flares of differing heights so as to make the liquid concentrator110easily adaptable to many different flares or to flares of different heights and also to improve efficiency when erecting concentrators by correcting for slight vertical and/or horizontal misalignment of components. The vertical piping section150may include a first section150A (shown using dotted lines) that rides inside of a second section150B thereby allowing the vertical piping section150to be adjustable in length (height).

Generally speaking, the air pre-treatment assembly119operates to mix ambient air provided through the ambient air valve306beneath the screen152and the hot gas flowing from the flare130through the heat transfer pipe140to create a desired temperature of gas at the inlet of the concentrator assembly120.

The liquid concentrator assembly120includes a lead-in section156, having a reduced cross-section at the bottom end thereof, which mates the bottom of the piping section150to a quencher159of the concentrator assembly120. The concentrator assembly120also includes a first fluid inlet160, which injects new or untreated liquid to be concentrated, such as flowback water from a natural gas well, into the interior of the quencher159. While not shown inFIG. 1, the inlet160may include a coarse sprayer with a large nozzle for spraying the untreated liquid into the quencher159. Because the liquid being sprayed into the quencher159at 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 quencher159operates 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 inlet160. If desired, a temperature sensor308(seeFIG. 3) may be located at or near the exit of the piping section150or in the quencher159and 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 assembly120.

As shown inFIGS. 1 and 2, the quencher159is connected to liquid injection chamber which is connected to a narrowed portion or a venturi section162which has a narrowed cross section with respect to the quencher159and which has a venturi plate163(shown in dotted line) disposed therein. The venturi plate163creates a narrow passage through the venturi section162, which creates a large pressure drop between the entrance and the exit of the venturi section162. This large pressure drop causes turbulent gas flow and shearing forces within the quencher159and the top or entrance of the venturi section162, and causes a high rate of gas flow out of the venturi section162, both of which lead to thorough mixing of the gas and liquid in the venturi section162. The position of the venturi plate163may be controlled with a manual control rod165(seeFIG. 2) connected to the pivot point of the plate163, or via an automatic positioner that may be driven by an electric motor or pneumatic cylinder.

A re-circulating pipe166extends around opposite sides of the entrance of the venturi section162and operates to inject partially concentrated (i.e., re-circulated) liquid into the venturi section162to be further concentrated and/or to prevent the formation of dry particulate within the concentrator assembly120through multiple fluid entrances located on one or more sides of the flow corridor. While not explicitly shown inFIGS. 1 and 2, a number of pipes, such as three pipes of, for example, ½ inch diameter, may extend from each of the opposites legs of the pipe166partially surrounding the venturi section162, and through the walls and into the interior of the venturi section162. Because the liquid being ejected into the concentrator110at 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 inlet160, 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 diameter pipes to cause the liquid being injected at this point in the system to hit the baffle and disperse into the concentrator assembly120as 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 assembly120.

The combined hot gas and liquid flows in a turbulent manner through the venturi section162. As noted above, the venturi section162, which has a moveable venturi plate163disposed across the width of the concentrator assembly120, causes turbulent flow and complete mixture of the liquid and gas, causing rapid evaporation of the discontinuous liquid phase into the continuous gas phase. Because the mixing action caused by the venturi section162provides a high degree of evaporation, the gas cools substantially in the concentrator assembly120, and exits the venturi section162into a flooded elbow164at high rates of speed. In fact, the temperature of the gas-liquid mixture at this point may be about 160 degrees Fahrenheit. In one embodiment, the total length of the concentrator assembly may be 20 feet or less, particularly between about 4 feet to about 12 feet, and more particularly between about 5 feet and about 10 feet. In one embodiment, the maximum cross sectional area of the venturi section162may be about 25 square feet or less, particularly between about 2 square feet and about 16 square feet, and more particularly between about 3 square feet and about 8 square feet. The above described dimensions produce an efficient and sufficient amount of turbulence in the gas/liquid flow that enhances heat and mass transfer between the gas and the liquid particles because these dimensions result in the formation of a significant amount of interfacial area between the gas and liquid phases. In one embodiment, in which 8.75 gallons per minute of wastewater that contained approximately 26% total solids by weight was introduced into the concentrator110, while 85 gallons per minute of concentrated wastewater was continually recirculated from the sump172(for a total of approximately 93.75 gallons per minute of fluid total), along with approximately 14,000 cubic feet per minute of combustion gas, created approximately 5.26 acres/minute of total interfacial area between the gas and liquid phases (assuming an average liquid particle size of approximately 110 microns in diameter). This amount of interfacial area far exceeds the interfacial area achievable in known indirect heat exchanger evaporation systems.

A weir arrangement (not shown) within the bottom of the flooded elbow164maintains aconstant level of partially or fully concentrated re-circulated liquid disposed therein. Droplets of re-circulated liquid that are entrained in the gas phase as the gas-liquid mixture exits the ventufi section162at high rates of speed are thrown outward onto the surface of the re-circulated liquid held within the bottom of the flooded elbow164by centrifugal force generated when the gas-liquid mixture is forced to turn 90 degrees to flow into the fluid scrubber122. Significant numbers of liquid droplets entrained within the gas phase that impinge on the surface of the re-circulated liquid held in the bottom of the flooded elbow164coalesce and join with the re-circulated liquid thereby increasing the volume of re-circulated liquid in the bottom of the flooded elbow164causing an equal amount of the re-circulated liquid to overflow the weir arrangement and flow by gravity into the sump172at the bottom of the fluid scrubber122. Thus, interaction of the gas-liquid stream with the liquid within the flooded elbow164removes liquid droplets from the gas-liquid stream, and also prevents suspended particles within the gas-liquid stream from hitting the bottom of the flooded elbow164at high velocities, thereby preventing erosion of the metal that forms the portions of side walls located beneath the level of the weir arrangement and the bottom of the flooded elbow164.

After leaving the flooded elbow164, the gas-liquid stream in which evaporated liquid and some liquid and other particles still exist, flows through the fluid scrubber122which is, in this case, across-flow fluid scrubber. The fluid scrubber122includes various screens or filters which serve to remove entrained liquids and other particles from the gas-liquid stream. In one particular example, the cross flow scrubber122may include an initial coarse impingement baffle169at 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 chevrons170are disposed across the fluid path through the fluid scrubber122, and the chevrons170may 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 filters169and170and the overflow weir arrangement within the bottom of the flooded elbow164drain by gravity into the reservoir or sump172located at the bottom of the fluid scrubber122. The sump172, which may hold, for example, approximately 200 gallons of liquid, 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 assembly120to be further treated and/or to prevent the formation of dry particulate within the concentrator assembly120. In one embodiment, the sump172may include a sloped V-shaped bottom171having a V-shaped groove175extending from the back of the fluid scrubber122(furthest away from the flooded elbow164) to the front of the fluid scrubber122(closest to the flooded elbow164), wherein the V-shaped groove175is sloped such that the bottom of the V-shaped groove175is lower at the end of the fluid scrubber122nearest the flooded elbow164than at an end farther away from the flooded elbow164. In other words, the V-shaped bottom171may be sloped with the lowest point of the V-shaped bottom171proximate the exit port173and/or the pump182. Additionally, a washing circuit177(seeFIG. 3) may pump concentrated fluid from the sump172to a sprayer179within the cross flow scrubber122, the sprayer179being aimed to spray liquid at the V-shaped bottom171. Alternatively, the sprayer179may spray un-concentrated liquid or clean water at the V-shaped bottom171. The sprayer179may periodically or constantly spray liquid onto the surface of the V-shaped bottom171to wash solids and prevent solid buildup on the V-shaped bottom171or at the exit port173and/or the pump182. As a result of this V-shaped sloped bottom171and washing circuit177, liquid collecting in the sump172is continuously agitated and renewed, thereby maintaining a relatively constant consistency and maintaining solids in suspension. If desired, the spraying circuit177may be a separate circuit using a separate pump with, for example, an inlet inside of the sump172, or may use a pump182associated with a concentrated liquid re-circulating circuit described below to spray concentrated fluid from the sump172onto the V-shaped bottom171.

As illustrated inFIG. 1, a return line180, as well as the pump182, operates to re-circulate fluid removed from the gas-liquid stream from the sump172back to the concentrator120and thereby complete a fluid or liquid re-circulating circuit. Likewise, a pump184may be provided within an input line186to pump new or untreated liquid, such as flowback water from a natural gas well, to the input160of the concentrator assembly120. Also, one or more sprayers (not shown) may be disposed inside the fluid scrubber122adjacent the chevrons170and may be operated periodically to spray clean water or a portion of the wastewater feed on the chevrons170to keep them clean.

Concentrated liquid also may be removed from the bottom of the fluid scrubber122via the exit port173and may be further processed or disposed of in any suitable manner in a side-arm process or secondary re-circulating circuit181. In particular, the concentrated liquid removed by the exit port173contains 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 the secondary re-circulating circuit181. In one example, the concentrated fluid may include from between about 50% to about 60% total solids. Concentrated liquid removed from the exit port173may be transported through the secondary re-circulating circuit181to one or more solid/liquid separating devices183, such as gravity settling tanks, vibrating screens, rotary vacuum filters, horizontal belt vacuum filters, belt presses, filter presses, and/or hydro-cyclones. The solid/liquid separating device183may provide a zone of low turbulence that favors crystallization of precipitates, which may cause particles of suspended solids to enlarge, settle more rapidly and separate more readily. After the suspended solids and liquid portion of the concentrated wastewater are separated by the solid/liquid separating device183, the liquid portion of the concentrated wastewater with suspended particles substantially removed may be returned to the sump172for further processing in the first or primary re-circulating circuit connected to the concentrator. The solid portion of the concentrated wastewater, which in one embodiment may include approximately 80% total solids or more, may be removed from the system through extraction port215and disposed of by depositing the solid portion in a landfill, for example. Alternatively, the solid portion of the concentrated wastewater may undergo further processing to recover salable materials, such as road salt, or ingredients for drilling mud.

The gas, which flows through and out of the fluid scrubber122with the liquid and suspended solids removed therefrom, exits out of piping or ductwork at the back of the fluid scrubber122(downstream of the chevrons170) and flows through an induced draft fan190of the exhaust assembly124, 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 motor192is connected to and operates the fan190to create negative pressure within the fluid scrubber122so as to ultimately draw gas from the flare130through the transfer pipe140, the air pre-treatment assembly119and the concentrator assembly120. The induced draft fan190needs only to provide a slight negative pressure within the fluid scrubber122to assure proper operation of the concentrator110.

While the speed of the induced draft fan190can be varied by a device such as a variable frequency drive operated to create varying levels of negative pressure within the fluid scrubber122and thus can usually be operated within a range of gas flow capacity to assure complete gas flow from the flare130, if the gas being produced by the flare130is not of sufficient quantity, the operation of the induced draft fan190cannot necessarily be adjusted to assure a proper pressure drop across the fluid scrubber122itself. That is, to operate efficiently and properly, the gas flowing through the fluid scrubber122must be at a sufficient (minimal) flow rate at the input of the fluid scrubber122. Typically this requirement is controlled by keeping at least a preset minimal pressure drop across the fluid scrubber122. However, if the flare130is not producing at least a minimal level of gas, increasing the speed of the induced draft fan190will not be able to create the required pressure drop across the fluid scrubber122.

To compensate for this situation, the cross flow scrubber122is 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 scrubber122to enable the system to acquire the needed pressure drop across the fluid scrubber122. In particular, the gas re-circulating circuit includes a gas return line or return duct196which connects the high pressure side of the exhaust assembly124(e.g., downstream of the induced draft fan190) to the input of the fluid scrubber122(e.g., a gas input of the fluid scrubber122) and a baffle or control mechanism198disposed in the return duct196which operates to open and close the return duct196to thereby fluidly connect the high pressure side of the exhaust assembly124to the input of the fluid scrubber122. During operation, when the gas entering into the fluid scrubber122is not of sufficient quantity to obtain the minimal required pressure drop across the fluid scrubber122, the baffle198(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 assembly124(i.e., gas that has traveled through the induced draft fan190) back to the input of the fluid scrubber122. This operation thereby provides a sufficient quantity of gas at the input of the fluid scrubber122to enable the operation of the induced draft fan190to acquire the minimal required pressure drop across the fluid scrubber122.

Referring back toFIG. 2, it will be seen that the front the flooded elbow164of the concentrator assembly120also includes a quick opening access door200, which allows easy access to the inside of the flooded elbow164. However, similar quick opening access doors could be located on any desired part of the fluid concentrator110, as most of the elements of the concentrator10operate under negative pressure.

The combination of features illustrated inFIGS. 1 and 2makes for a compact fluid concentrator110that uses waste heat in the form of gas resulting from the operation of a natural gas flare, which waste heat would otherwise be vented directly to the atmosphere. Importantly, the concentrator110uses only a minimal amount of expensive high temperature resistant material to provide the piping and structural equipment required to use the high temperature gases exiting from the flare130. For example, the small length of the transfer pipe140, which is made of the most expensive materials, is minimized, thereby reducing the cost and weight of the fluid concentrator110. Moreover, because of the small size of the heat transfer pipe140, only a single support member142is needed thereby further reducing the costs of building the concentrator110. Still further, the fact that the air pre-treatment assembly119is disposed directly on top of the fluid concentrator assembly120, with the gas in these sections flowing downward towards the ground, enables these sections of the concentrator110to be supported directly by the ground or by a skid on which these members are mounted. This configuration keeps the concentrator110disposed very close to the flare130, making it more compact. Likewise, this configuration keeps the high temperature sections of the concentrator110(e.g., the top of the flare130, the heat transfer pipe140and the air pre-treatment assembly119) above the ground and away from accidental human contact, leading to a safer configuration. In fact, due to the rapid cooling that takes place in the venturi section162of the concentrator assembly120, the venturi section162, the flooded elbow164and the fluid scrubber122are typically cool enough to touch without harm (even when the gases exiting the flare130are at 1800 degrees Fahrenheit). Rapid cooling of the gas-liquid mixture allows the use of generally lower cost materials that are easier to fabricate and that are corrosion resistant. Moreover, parts downstream of the flooded elbow164, such as the fluid scrubber122, induced draft fan190, and exhaust section124may be fabricated from materials such as fiberglass.

The fluid concentrator110is also a very fast-acting concentrator. Because the concentrator110is 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 cap134to open and close, depending on whether the concentrator110is being used or operated, allows the flare130to be used to burn gas without interruption when starting and stopping the concentrator110. More particularly, the flare cap134can be quickly opened at any time to allow the flare130to simply burn gas as normal while the concentrator110is shut down. On the other hand, the flare cap134can be quickly closed when the concentrator110is started up, thereby diverting hot gasses created in the flare130to the concentrator110, and allowing the concentrator110to operate without interrupting the operation of the flare130. In either case, the concentrator110can be started and stopped based on the operation of the flare cap134without interrupting the operation of the flare130.

If desired, the flare cap134may be opened to a partial amount during operation of the concentrator110to control the amount of gas that is transferred from the flare130to the concentrator110. 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 section162.

Moreover, due to the compact configuration of the air pre-treatment assembly119, the concentrator assembly120and the fluid scrubber122, parts of the concentrator assembly120, the fluid scrubber122, the draft fan190and at least a lower portion of the exhaust section124can be permanently mounted on (connected to and supported by) a skid or plate. The upper parts of the concentrator assembly120, the air pre-treatment assembly119and the heat transfer pipe140, as well as a top portion of the exhaust stack, may be removed and stored on the skid or plate for transport, or may be transported in a separate truck. Because of the manner in which the lower portions of the concentrator110can be mounted to a skid or plate, the concentrator110is easy to move and install. In particular, during set up of the concentrator110, the skid, with the fluid scrubber122, the flooded elbow164and the draft fan190mounted thereon, may be offloaded at the site at which the concentrator110is to be used by simply offloading the skid onto the ground or other containment area at which the concentrator110is to be assembled. Thereafter, the venturi section162, the quencher159, and the air pre-treatment assembly119may be placed on top of and attached to the flooded elbow164. The piping section150may then be extended in height to match the height of the flare130to which the concentrator110is to be connected. In some cases, this may first require mounting the flare cap assembly132onto a pre-existing flare130. Thereafter, the heat transfer pipe140may be raised to the proper height and attached between the flare130and the air pre-treatment assembly119, while the support member142is disposed in place. For concentrators in the range of 10,000 to 30,000 gallons per day evaporative capacity, it is possible that the entire flare assembly115may be mounted on the same skid or plate as the concentrator120.

Because most of the pumps, fluid lines, sensors and electronic equipment are disposed on or are connected to the fluid concentrator assembly120, the fluid scrubber122or the draft fan assembly190, setup of the concentrator110at a particular site requires only minimal plumbing, mechanical, and electrical work at the site. As a result, the concentrator110is 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 concentrator110are permanently mounted to the skid, the concentrator110can be easily transported 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. 3illustrates a schematic diagram of a control system300that may be used to operate the concentrator110ofFIG. 1. As illustrated inFIG. 3, the control system300includes a controller302, 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 controller302is, of course, connected to various components within the concentrator110. In particular, the controller302is connected to the flare cap drive motor135, which controls the opening and closing operation of the flare cap134. The motor135may be set up to control the flare cap134to move between a fully open and a fully closed position. However, if desired, the controller302may control the drive motor135to open the flare cap134to any of a set of various different controllable positions between the fully opened and the fully closed position. The motor135may be continuously variable if desired, so that the flare cap134may be positioned at any desired point between fully open and fully closed.

Additionally, the controller302is connected to and controls the ambient air inlet valve306disposed in the air pre-treatment assembly119ofFIG. 1upstream of the venturi section162and may be used to control the pumps182and184which 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 concentrator110. The controller302may be operatively connected to a sump level sensor317(e.g., a float sensor, anon-Contact sensor such as a radar or sonic unit, or a differential pressure cell). The controller302may use a signal from the sump level sensor317to control the pumps182and184to maintain the level of concentrated fluid within the sump172at a predetermined or desired level. Also, the controller302may be connected to the induced draft fan190to control the operation of the fan190, which may be a single speed fan, a variable speed fan or a continuously controllable speed fan. In one embodiment, the induced draft fan190is driven by a variable frequency motor, so that the frequency of the motor is changed to control the speed of the fan. Moreover, the controller302is connected to a temperature sensor308disposed at, for example, the inlet of the concentrator assembly120or at the inlet of the venturi section162, and receives a temperature signal generated by the temperature sensor308. The temperature sensor308may alternatively be located downstream of the venturi section162or the temperature sensor308may include a pressure sensor for generating a pressure signal.

During operation and at, for example, the initiation of the concentrator110, when the flare130is actually running and is thus burning natural gas, the controller302may first turn on the induced draft fan190to create a negative pressure within the fluid scrubber122and the concentrator assembly120. The controller302may then or at the same time, send a signal to the motor135to close the flare cap134either partially or completely, to direct waste heat from the flare130into the transfer pipe140and thus to the air pre-treatment assembly119. Based on the temperature signal from the temperature sensor308, the controller302may control the ambient air valve306(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 assembly120. Generally speaking, the ambient air valve306may be biased in a fully open position (i.e., may be normally open) by a biasing element such as a spring, and the controller302may begin to close the valve306to control the amount of ambient air that is diverted into the air pre-treatment assembly119(due to the negative pressure in the air pre-treatment assembly119), so as to cause the mixture of the ambient air and the hot gases from the flare130to reach a desired temperature. Additionally, if desired, the controller302may control the position of the flare cap134(anywhere from fully open to fully closed) and may control the speed of the induced draft fan190, to control the amount of gas that enters the air pre-treatment assembly119from the flare130. As will be understood, the amount of gas flowing through the concentrator110may need to vary depending on ambient air temperature and humidity, the temperature of the flare gas, the amount of gas exiting the flare130, etc. The controller302may therefore control the temperature and the amount of gas flowing through the concentrator assembly120by controlling one or any combination of the ambient air control valve306, the position of the flare cap134and the speed of the induced draft fan190based on, for example, the measurement of the temperature sensor308at the inlet of the concentrator assembly120. This feedback system is desirable because, in many cases, the air coming out of a flare130is between 1200 and 1800 degrees Fahrenheit, which may be too hot, or hotter than required for the concentrator110to operate efficiently and effectively.

In any event, as illustrated inFIG. 3, the controller302may also be connected to a motor310which drives or controls the position of the venturi plate163within the narrowed portion of the concentrator assembly120to control the amount of turbulence caused within the concentrator assembly120. Still further, the controller302may control the operation of the pumps182and184to control the rate at which (and the ratio at which) the pumps182and184provide re-circulating liquid and new waste fluid to be treated to the inputs of the quencher159and the venturi section162. In one embodiment, the controller302may control the ratio of the re-circulating fluid to new fluid to be about 10:1, so that if the pump184is providing 8 gallons per minute of new liquid to the input160, the re-circulating pump182is pumping 80 gallons per minute. Additionally, or alternatively, the controller302may control the flow of new liquid to be processed into the concentrator (via the pump184) by maintaining a constant or predetermined level of concentrated liquid in the sump172using, for example, the level sensor317. Of course, the amount of liquid in the sump172will be dependent on the rate of concentration in the concentrator, the rate at which concentrated liquid is pumped from or otherwise exists the sump172via the secondary re-circulating circuit and the rate at which liquid from the secondary re-circulating circuit is provided back to the sump172, as well as the rate at which the pump182pumps liquid from the sump172for delivery to the concentrator via the primary re-circulating circuit.

If desired, one or both of the ambient air valve306and the flare cap134may be operated in a fail-safe open position, such that the flare cap134and the ambient air valve306open in the case of a failure of the system (e.g., a loss of control signal) or a shutdown of the concentrator110. In one case, the flare cap motor135may be spring loaded or biased with a biasing element, such as a spring, to open the flare cap134or to allow the flare cap134to open upon loss of power to the motor135. Alternatively, the biasing element may be the counter-weight137on the flare cap134may be so positioned that the flare cap134itself swings to the open position under the applied force of the counter-weight137when the motor135loses power or loses a control signal. This operation causes the flare cap134to open quickly, either when power is lost or when the controller302opens the flare cap134, to thereby allow hot gas within the flare130to exit out of the top of the flare130. Of course, other manners of causing the flare cap134to open upon loss of control signal can be used, including the use of a torsion spring on the pivot point136of the flare cap134, a hydraulic or pressurized air system that pressurizes a cylinder to close the flare cap134, loss of which pressure causes the flare cap134to open upon loss of the control signal, etc.

Thus, as will be noted from the above discussion, the combination of the flare cap134and the ambient air valve306work in unison to protect the engineered material incorporated into the concentrator110, as whenever the system is shut down, the flare cap and the air valve306automatically immediately open, thereby isolating hot gas generated in the flare130from the process while quickly admitting ambient air to cool the process.

Moreover, in the same manner, the ambient air valve306may be spring biased or otherwise configured to open upon shut down of the concentrator110or loss of signal to the valve306. This operation causes quick cooling of the air pre-treatment assembly119and the concentrator assembly120when the flare cap134opens. Moreover, because of the quick opening nature of the ambient air valve306and the flare cap134, the controller302can quickly shut down the concentrator110without having to turn off or effect the operation of the flare130.

Furthermore, as illustrated in theFIG. 3, the controller302may be connected to the venturi plate motor310or other actuator which moves or actuates the angle at which the venturi plate163is disposed within the venturi section162. Using the motor310, the controller302may change the angle of the venturi plate163to alter the gas flow through the concentrator assembly120, thereby changing the nature of the turbulent flow of the gas through concentrator assembly120, which may provide for better mixing of the liquid and gas therein and obtain better or more complete evaporation of the liquid. In this case, the controller302may operate the speed of the pumps182and184in conjunction with the operation of the venturi plate163to provide for optimal concentration of the wastewater being treated. Thus, as will be understood, the controller302may coordinate the position of the venturi plate163with the operation of the flare cap134, the position of the ambient air or bleed valve306, and the speed of the induction fan190to maximize wastewater concentration (turbulent mixing) without fully drying the wastewater so as to prevent formation of dry particulates. The controller302may use pressure inputs from the pressure sensors to position the venturi plate163. Of course, the venturi plate163may be manually controlled or automatically controlled.

The controller302may also be connected to a motor312which controls the operation of the damper198in the gas re-circulating circuit of the fluid scrubber122. The controller302may cause the motor312or other type of actuator to move the damper198from a closed position to an open or to a partially open position based on, for example, signals from pressure sensors313,315disposed at the gas exit and the gas entrance of the fluid scrubber122, respectively. The controller302may control the damper198to force gas from the high pressure side of the exhaust section124(downstream of the induced draft fan190) into the fluid scrubber entrance to maintain a predetermined minimum pressure difference between the two pressure sensors313,315. Maintaining this minimum pressure difference assures proper operation of the fluid scrubber122. Of course, the damper198may be manually controlled instead or in addition to being electrically controlled.

As will be understood, the concentrator110described 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.

While the liquid concentrator110has been described above as being connected to a natural gas flare to use the waste heat generated in the natural gas flare, the liquid concentrator110can be easily connected to other sources of waste heat. For example, another embodiment of the concentrator110may be connected to an exhaust stack of a combustion engine plant and to use the waste heat from the engine exhaust to perform liquid concentration. While, in yet another embodiment, the engine within the plant may operate on landfill gas to produce electricity, the concentrator110can 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, propane, natural gas, etc.

Removal of Contaminants from Wastewater and/or Combustion Gas

Embodiments of the concentrators and processes described above can be readily modified to accommodate the removal of contaminants from the wastewater being concentrated and also from the combustion gas employed to concentrate that wastewater. Such modifications are contemplated to be particularly advantageous where the contaminants sought to be removed are among those whose emissions are typically regulated by governmental authorities. Examples of such contaminants include barium and other harmful materials (e.g., calcium, iron, magnesium potassium, sodium, strontium, sulfate, etc.) dissolved in flowback water from natural gas wells. Additionally, fouling substances, such as scaling metals, may be removed from flowback water. Described below are modifications that may be made to the embodiments of the concentrators and processes described above to accommodate removal of barium or other harmful materials or scaling metals, but the description is not intended to be limiting to the removal of only such contaminants.

For example, two methods of removal of contaminants from wastewater include pre-concentration treatment and post-concentration treatment. More particularly, contaminants may be scrubbed by injecting a reagent or stabilizing compound into the wastewater that reacts chemically or mechanically with the contaminant prior to wastewater concentration, or contaminants may be scrubbed by mixing a stabilizing compound into the concentrated wastewater after concentration.

In the pre-concentration treatment method, contaminants may be either sequestered or stabilized. In pre-concentration sequestration, a reagent (e.g., sodium sulfate) is mixed with the wastewater prior to concentration and the reagent chemically reacts with the contaminant to form an insoluble chemical compound (e.g., barium sulfate) that precipitates out of solution. The insoluble chemical compound may settle out of the concentrated wastewater, for example, in the settling tank183(FIG. 1). Once the insoluble chemical compound settles out of the concentrated wastewater in the settling tank, the insoluble chemical compound may be drawn off, along with other solids, for example, through the extraction port215.

In pre-concentration stabilization, a stabilizing compound is mixed with the wastewater prior to concentration and the stabilizing compound reacts chemically or mechanically with the contaminant to render the contaminant non-hazardous or insoluble. For example, the stabilizing compound may encase the contaminant in a crystalline matrix that is insoluble. Thus, the contaminant is also rendered insoluble. Once stabilized, the contaminant and stabilizing compound may be extracted, for example, from the settling tank183, similar to pre-concentration sequestration.

Post-concentration stabilization includes mixing a stabilizing compound with the concentrated wastewater in the settling tank183. The stabilizing compound reacts chemically or mechanically to render the contaminant non-hazardous or insoluble, similar to the pre-concentration stabilization. The stabilized contaminant may be removed, for example, from the settling tank183and through the extraction port215.

Both the pre-concentration and post-concentration removal methods described above may be used to remove high levels of dissolved barium (e.g., barium chloride) from flowback water. Barium is a known hazardous material that is occasionally found dissolved in flowback water from natural gas wells. Flowback water from natural gas wells in the Marcellus Shale Bed (located in the vicinity of the northern Appalachian Mountains) contains high levels of dissolved barium. Additionally, this flowback water contains extremely high levels of total dissolved solids, in the range of 250,000 parts per million (ppm) or 25% by weight, or higher. Such high levels of dissolved solids are extremely difficult to concentrate via conventional methods. However, these high levels of dissolved solids are treatable with the concentrator disclosed herein. Soluble barium compounds, such as those found in some flowback water, are highly poisonous if ingested. As a result, disposal of barium compounds is often regulated by state or federal authorities.

As described above, two examples of methods of barium removal from flowback water using the disclosed concentrator are pre-concentration treatment and post-concentration treatment. In pre-treatment sequestering certain chemical reagents are added to the flowback water before the flowback water is injected into the concentrator causing chemical reactions with the barium ions to form insoluble barium compounds. In pre or post-concentration stabilization barium compounds are mechanically or chemically prevented from reacting chemically with other compounds to produce unwanted barium compounds, such as barium compounds that are soluble.

As discussed above, flowback water from natural gas wells can contain high levels of dissolved barium compounds. One such dissolved barium compound is barium chloride. A method of removing the barium from the flowback water involves chemically reacting the barium chloride with another substance to produce a relatively insoluble barium compound. One way to accomplish this reaction is to introduce a reagent comprising a sulfate ion into the flowback water. A particularly useful reagent is sodium sulfate. Other useful reagents include, but are not limited to, aluminum sulfate, ammonium sulfate, magnesium sulfate, potassium sulfate, and sulfuric acid. The sulfate ion from the reagent reacts with the barium ion to form barium sulfate (BaSO4). Barium sulfate is highly insoluble and precipitates out of solution rapidly. One advantage to the pre-concentration sequestration of barium by precipitating barium sulfate is that barium sulfate may be disposed of relatively inexpensively by depositing the barium sulfate in a landfill.

Barium sulfate will not leach from a landfill back into groundwater due to the high insolubility of barium sulfate, even in the presence of strong acids. In fact, in spite of barium's toxicity to humans, barium sulfate is used in the medical community to diagnose certain digestive tract illnesses because the barium sulfate shows up on x-rays and because the barium sulfate will not dissolve even in the presence of stomach acid. Thus, barium sulfate passes harmlessly though the digestive tract. This high insolubility of barium sulfate leads to solid waste containing barium sulfate passing the Toxicity Characteristic Leaching Procedure (TCLP) administered by the Environmental Protection Agency (EPA). The EPA requires certain wastes to pass the TCLP test before approving such wastes for disposal in landfills. Barium is one waste product required to pass the TCLP test. TCLP is one of the Federal EPA test methods that are used to exclude leachable toxic substances from landfills. The TCLP test is outlined in EPA publication SW-846, entitled “Test Methods for Evaluating Solid Waste, Physical/Chemical Methods,” which is hereby incorporated by reference herein. If a substance passes the TCLP test, that substance is classified as non-hazardous and may be disposed of in a landfill. Another EPA test used to exclude potentially dangerous substances from landfills is the Paint Filter Test.

Referring again toFIGS. 1 and 2, to implement one of the barium removal methods described above, the concentrator section120may include a reagent inlet187that is connected to a supply of reagent in a tank193(e.g., sodium sulfate, sulfuric acid, aluminum sulfate, ammonium sulfate, magnesium sulfate, or potassium sulfate, etc.) by a reagent supply line189. A reagent pump191may pressurize the reagent supply line189with reagent material from the tank193so that the reagent material is ejected into the concentrator section120(e.g., upstream of, or proximate to, the venturi162) to mix with the exhaust gas from the flare130or generator and flowback water injected by the inlet160. The reagent pump191may be operatively connected to the controller302(seeFIG. 3) and the controller302may operate the reagent pump191to meter reagent based on gas and flowback water flow rates to ensure proper ratios and mixing. When mixed with the flowback water in the concentrator section120, the reagent reacts with dissolved barium ions to form barium sulfate, which rapidly precipitates out of solution in solid form. Due to the ability of the concentrator110to handle very high levels of total solids, the precipitated barium sulfate is maintained in suspension and eventually ends up in the settling tank183along with other materials that make up a solid portion of the concentrated flowback water. Solid and liquid portions of the concentrated flowback water separate from one another in the settling tank183. If the solid portions, which may contain up to about 20% liquid, need further separation, some of the solid portion may be drawn off from the settling tank183through line221and directed to a further separation device, such as a rotary belt vacuum filter223. Liquid from the rotary belt vacuum filter223may be returned to the concentrator via line225into the sump172of the demister122. Solids may be removed from the rotary belt vacuum filter223through an exit line227for disposal, for example in a landfill. Alternatively, solids removed from the rotary belt vacuum filter223may be purified and sold, for example to mining companies, as drilling mud.

Alternatively, a pre-concentration sequestration process may involve mixing the reagent with the flowback water upstream of the flowback water inlet160, for example in a sequential mixing and settling tank201(SeeFIG. 4). In this case, reagent material may be supplied to the sequential mixing and settling tank201from a supply of reagent material in a tank203via a reagent supply line195. A reagent supply pump205may supply the reagent material under pressure to the sequential mixing and settling tank201. The reagent supply pump205may be operatively connected to the controller302(seeFIG. 3) and the controller302may operate the reagent supply pump205to meter reagent based on gas and flowback water flow rates to ensure proper ratios and mixing. Barium precipitates out of solution as barium sulfate, as described above, and may be drawn out of the mixing and settling tank201through a line207, prior to introduction into the concentrator. The solid portion, which may include up to about 20% liquid, may be further separated in a solid/liquid separating device, such as a rotary belt vacuum filter231or other separating device. Thereafter, barium sulfate may be drawn off through a line233and may be further processed, purified, and sold, for example to drilling companies for use in drilling mud.

Because the reagent supplied to react with the dissolved barium ions may also react with other dissolved compounds in the flowback water, such as calcium, greater quantities of reagent may be needed than would otherwise be needed to react with the barium alone. For example, in some cases between approximately 150% and 600% more reagent may be mixed with the flowback water than would be required by the amount of barium in the flowback water alone. Preferably between 200% and 500% more reagent may be used, and more preferably approximately 400% more reagent may be used. By providing excess amounts of reagent, almost all dissolved barium will precipitate out of the flowback water. Some other dissolved reactive materials that may be found in flowback water include, calcium, magnesium, and strontium. In some cases, the product of the reagent reaction with these additional metals may result in commercially salable products. As a result, these additional products may also be drawn off through the line233for further processing. Alternatively, these additional products may simply be fed into the concentrator with the flowback water, as the concentrator is capable of handling large amounts of suspended solids, as described above.

Pre or Post Concentration Stabilization

Another way to remove barium from flowback water is to chemically or mechanically stabilize the barium either before or after the flowback water is concentrated. If the barium is not treated before concentration, the dissolved barium ions may react with other chemicals in the flowback water to form compounds that will precipitate out of solution when concentrations of the compounds reach saturation. Some of these barium compounds are water soluble and must be stabilized prior to extraction from the concentrator system. These barium compounds may be stabilized, for example, in the settling tank183. The barium compounds may be mechanically or chemically stabilized. With mechanical stabilization, the barium compounds are incased in glass, or other crystalline structure so that the barium compounds cannot react with other materials, or cannot dissolve in solution. In chemical stabilization, a reagent is provided into the settling tank that reacts with the barium compounds to produce insoluble compounds. In either case, the stabilizing compound may be pumped into the settling tank183from a tank211(seeFIG. 1) via a pipeline213, for example. The stabilized compounds may be drawn out of the settling tank183via the extraction port215. In this case, the stabilized barium compounds are insoluble and will not leach out in the presence of strong acids. As a result, the stabilized barium compounds will pass the TCLP test.

Alternatively, the stabilizing reagent may be added to the wastewater before the wastewater is introduced into the concentrator110through the wastewater inlet160using, for example, the concentrator ofFIG. 4by pumping stabilizing agent from the tank203into the mixing and settling tank201. In this case, the stabilizing agent may prevent certain chemical reactions of the barium that would result in soluble barium compounds. The stabilizing agent could also be introduced into the concentrator110separately from the wastewater using, for example, the concentrator ofFIG. 1by pumping stabilizing agent from the tank197(FIG. 4) into port199, so that the stabilizing agent and the wastewater mix in the concentrating section120of the concentrator110. In these cases, the insoluble solids formed by reaction between the barium and the stabilizing agent ultimately end up in the settling tank183, where the insoluble barium compounds may be further processed as described above.

Example Test Results

The following paragraphs describe actual test results of one embodiment of the disclosed concentrator when used to concentrate samples of flowback water containing dissolved barium. These test results are examples only and are not meant to limit the disclosed concentrator, or operation of the disclosed concentrator, in any way.

In a first test, the disclosed concentrator was used to concentrate flowback water from a natural gas well located in Pennsylvania. The chemical breakdown of the flowback water is listed below in Table 1.

As illustrated in Table 1, the flowback sample included approximately 260,000 mg/l total solids (see line 3 of Table 1). After processing, a heavy slurry was extracted from the gravity settling tank including over 800,000 mg/l total solids. Supernatant liquid from the gravity settling tank was re-circulated into the concentrator as described above. The concentrator experienced no deleterious effects from scaling or blockages. Stack tests on the exhaust stack indicated that gaseous emissions remained within the permitted ranges established by local regulatory authorities. In other words, the disclosed concentrator does not significantly change the chemical makeup of gas emissions from existing exhaust stacks. As a result of this first test, the disclosed concentrator proved its ability to process liquids with extremely high levels of total solids.

Several more tests were conducted on the wastewater sample of Table 1. Two test runs are summarized below in Table 2, Test 2A and Test 2B. In Test 2A, the wastewater was pretreated with approximately 45 g/l of Na2SO4. During Test 2A the pH of the wastewater was varied from about 1 to about 4. In Test 2B, the wastewater was treated with approximately 22.5 g/l of Na2SO4(or about half the amount of Na2SO4of Test 2A) and the pH of the wastewater was varied from about 1 to about 4. The test results for Test 2A and 2B are summarized below in Table 2.

As illustrated in Table 2, the wastewater feed contained approximately 11,000 mg/l of barium (see line 5 of Table 2). Almost all of the barium was precipitated out of solution with the addition of sodium sulfate in Test 2A. More particularly, at a pH of between 1 and 2, only 0.5 mg/l of barium remained in solution, at a pH of between 2 and 3, only 0.36 mg/l of barium remained in solution, and at a pH of between 3 and 4, only 160 mg/l of barium remained in solution (see line 5 of Table 2). Approximately 4 times the theoretical amount of sodium sulfate was mixed with the wastewater because the sulfate reacts also with other chemical compounds in the wastewater. The excess sodium sulfate ensures that virtually all of the barium precipitates out of solution, especially at lower pH levels.

During another test, one embodiment of the concentrator was used to concentrate wastewater from a known difficult-to-treat source of wastewater. The difficult-to-treat wastewater included the chemical makeup illustrated below in Table 3.

The wastewater was treated to zero liquid discharge and solids produced by the treatment process passed both the Paint Filter and TCLP tests. Results of the this test are summarized below in Table 4 in which results of several samples are listed. (e.g., sample IDs 01-09)

In this test, sodium sulfate was again used as the pre-treatment reagent. Concentrated wastewater was sent to a gravity settling tank. Solids were drawn out of the gravity settling tank and were further separated in a vacuum belt filtration system. This process yielded a zero liquid discharge rate from the concentrator. All supernatant liquid was re-circulated through the concentrator as described above. The resultant solids passed both the Paint Filter and TCLP tests. Table 4 summarizes the chemical makeup of the solids before and after concentration. As illustrated above, barium levels were not reduced to zero in this test. However, current regulations allow up to 100 mg/l of detectable barium, thus the resultant solids passed the TCLP test.

With the barium level in pre-treated wastewater liquid feed at 46 mg/l (see line 6 of Table 4), solids that settled out of the feed liquid passed the TCLP with non-detectable amounts of barium. When pre-treated feed was passed through the concentrator and solids were removed from the vacuum belt filter, the liquid phase from which the solids were removed contained 220 mg/l of Barium (see line 6 of Table 4) while the collected solids passed both the Paint Filter Test and the TCLP test with non-detectable levels of barium.

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. For example, the disclosed concentrator may be used to scnib contaminants other than barium from wastewater. In particular, other contaminants may be scrubbed from wastewater by injecting a reagent from the reagent tank either into the wastewater upstream of wastewater injection into the venturi section, or into the venturi section simultaneously with the wastewater. Additionally, other contaminants may be chemically or mechanically stabilized by either injecting a reagent or stabilizing substance into the wastewater upstream of wastewater injection into the venturi section, or injecting a reagent or stabilizing substance into the settling tank.