1. Field of the Disclosure
This application relates generally to separation and concentration systems for water soluble salts, and more specifically to such systems that comprise direct contact liquid concentrators that selectively separate and concentrate water soluble salts from a liquid stream containing two or more water soluble salts.
2. Background of the Disclosure
Some types of wastewater contain water soluble salts in differing concentrations. For example, some types of wastewater from natural gas wells (typically called produced water or flowback water) can include varying levels of certain salts, such as sodium chloride and potassium nitrate, for example, although virtually any type of water soluble salt may be found in wastewater. Previously, the volumes of such wastewaters have been reduced through evaporation in evaporation ponds, or through concentration in wastewater concentrators. For example, wastewater concentrators, such as those disclosed in U.S. patent application Ser. No. 12/705,462, filed Feb. 12, 2010, U.S. patent application Ser. No. 12/846,257, filed Jul. 29, 2010, U.S. patent application Ser. No. 12/846,337, filed Jul. 29, 2010, and U.S. patent application Ser. No. 12/938,879, filed Nov. 3, 2010, the entirety of each of which is hereby incorporated by reference herein, have been used to remove a portion of liquid water found in the wastewaters to reduce transportation and disposal costs. However, while such concentration reduces overall volume and results in higher concentrations of the water soluble salts, the ratios of the dissolved salts remains the same. For example, if the ratio of sodium chloride to potassium nitrate was 1:2 before concentration, the ratio will also be 1:2 after concentration.
In certain cases, one or more of the dissolved salts may be valuable while other dissolved salts are not valuable. Currently there is no way to separate the valuable salts from the non-valuable salts, or otherwise change the concentration ratios between the two salts.
As illustrated in
In the selective separation and concentration system described below with respect to
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
The air pre-treatment assembly 119 includes a vertical piping section 150 and an ambient air valve disposed at the top of the vertical piping section 150. The ambient air valve (also referred to as a damper or 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. A pressure blower (not shown) may be connected to the inlet side of the ambient air valve, if desired, to force ambient air through the ambient air valve. If a pressure blower is implemented, the bird screen 152 and permanently open section (if implemented) may be relocated to the inlet side of the pressure blower. 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 desirable 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 and also to improve efficiency when erecting concentrators by correcting for slight vertical and/or horizontal misalignment of components. This concept is illustrated in more detail in
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
As shown in
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
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 movable 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 discontinuous liquid phase into the continuous gas phase. 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.
A weir arrangement (not shown) within the bottom of the flooded elbow 164 maintains a constant 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 venturi section 162 at high rates of speed are thrown outward onto the surface of the re-circulated liquid held within the bottom of the flooded elbow 164 by centrifugal force generated when the gas-liquid mixture is forced to turn 90 degrees to flow into the fluid scrubber 122. 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 elbow 164 coalesce and join with the re-circulated liquid thereby increasing the volume of re-circulated liquid in the bottom of the flooded elbow 164 causing an equal amount of the re-circulated liquid to overflow the weir arrangement and flow by gravity into the sump 172 at the bottom of the fluid scrubber 122. Thus, interaction of the gas-liquid stream with the liquid within the flooded elbow 164 removes liquid droplets from the gas-liquid stream, and also prevents suspended particles within the gas-liquid stream from hitting the bottom of the flooded elbow 164 at 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 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 serve to remove entrained liquids and other particles from 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.
Liquid captured by the filters 169 and 170 and the overflow weir arrangement within the bottom of the flooded elbow 164 drain by gravity into a reservoir or sump 172 located at the bottom of the fluid scrubber 122. The sump 172 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 one embodiment, the sump 172 may include a sloped V-shaped bottom 171 having a V-shaped groove 175 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 175 is sloped such that the bottom of the V-shaped groove 175 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 171 may be sloped with the lowest point of the V-shaped bottom 171 proximate the exit port 173 and/or the pump 182. Additionally, a washing circuit 177 (
As illustrated in
Concentrated liquid also may 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 181. 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 the secondary re-circulating circuit 181. For example, concentrated liquid removed from the exit port 173 may be transported through the secondary re-circulating circuit 181 to one or more solid/liquid separating devices 183, such as settling tanks, vibrating screens, rotary vacuum filters, horizontal belt vacuum filters, belt presses, filter presses, and/or hydro-cyclones. After the suspended solids and liquid portion of the concentrated wastewater are separated by the solid/liquid separating device 183, the liquid portion of the concentrated wastewater with suspended particles substantially removed 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. 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.
The liquid concentrator 110 is a very fast-acting concentrator. Because the concentrator 110 is a direct contact type of concentrator (e.g., a discontinuous liquid phase is injected into a continuous gas phase without intermediate heat exchanger surfaces), it is not subject to deposit buildup, clogging and fouling to the same extent as most other concentrators.
Additionally, the controller 302 is connected to and controls the ambient air inlet valve 306 disposed in the air pre-treatment assembly 119 of
During operation and at, for example, the initiation of the concentrator 110, when the flare 130 is actually running and is thus burning 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
Furthermore, as illustrated in the
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.
The liquid concentrator 110 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 110 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 110 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 110 is more compact and lighter in weight than conventional concentrators. Additionally, the liquid concentrator 110 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 110 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 110.
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).
The above described liquid concentrators may be useful in separating and concentrating water soluble salts in wastewater. In particular, the described liquid concentrators may be useful in separating salts of sodium, calcium, magnesium, potassium, sulfate and chloride, and more specifically, sodium chloride, calcium chloride, strontium chloride, barium chloride, magnesium chloride, sodium sulfate, magnesium sulfate, and calcium sulfate.
A first embodiment of a selective separation and concentration system 1000 is illustrated in
As the feed liquid warms during the concentration process in the concentrator, the relative solubilities of the two salts change. The feed liquid is continuously circulated through the concentrator 1110, the first settling tank 1118, and the second settling tank 1122, until the partially concentrated feed liquid reaches a saturation point of the first dissolved salt. At this point, the first dissolved salt will begin to precipitate out of solution due to saturation of the solution. The precipitated first salt will settle out of the solution predominantly in the first settling tank 1118 (although a small portion of the second salt may also precipitate in the first settling tank 1118). The partially concentrated feed liquid delivered to the second settling tank 1112, thereafter will contain a different ratio of first to second salts when compared to the unconcentrated feed liquid (because some of the first salt has been removed from the solution through precipitation in the first settling tank). A slurry enriched in the ratio of the first salt vs. the second salt may be drawn off of the first settling tank 1112 through a first extraction port 1130 and a first extraction line 1132. Similarly, a brine solution enriched in the ratio of the second salt vs. the first salt may be drawn off of the second settling tank 1122 through a second extraction portion 1140 and a second extraction line 1142.
The relative ratios of the first salt to the second salt may be selected by adjusting the operating temperature of the concentrator 1110. For example, if the temperature is increased, more of the second salt may remain dissolved in the solution while the first salt precipitates out of the solution. As a result, higher concentrations of the first salt may remain relative to the second salt. Conversely, if the temperature is decreased, less of the second salt remains dissolved in the solution and a lower concentration of the first salt may remain relative to the second salt.
The relative ratios of the first salt to the second salt may also be selected by adjusting the rate of withdrawal of sludge of fluid through the first extraction port 1130 and the second extraction port 1140. Decreasing a withdrawal rate of slurry from the first extraction port 1130 will reduce the amount of the first salt that is drawn off, which will generally raise the ratio of the first salt to the second salt. Similarly, decreasing a withdrawal rate of brine solution from the second extraction port 1140 will raise the ratio of the second salt to the first salt. Decreasing a withdrawal rate from both the first extraction port 1130 and the second extraction port 1140, will generally tend to raise the concentration of the first salt in the first extraction line 1132 and the concentration of the second salt in the second extraction line 1142. All of these variables may be controlled by an operator to produce 1) a desired ratio of first salt to second salt in the first extraction line 1132, 2) a desired ratio of first salt to second salt in the second extraction line 1142, and 3) a desired ratio of first salt to second salt in the return line 1126. As a result, the two water soluble salts can be separated (at least partially) from one another and relative concentrations of the two salts may be precisely controlled.
In an alternate embodiment, one or both of the first settling tank 1118 and the second settling tank 1122 may include a temperature controlling means, such as a heating or cooling blanket, or a heating or cooling element, to further facilitate precipitation of the desired salt.
In yet other embodiments, three or more settling tanks may be included to separate or concentrate three or more dissolved salts.
A second embodiment of a selective separation and concentration system 2000 is illustrated in
In addition to the elements of the embodiment of
Generally, a process for separating or concentrating water soluble salts in a wastewater stream includes 1) delivering to a concentrator unconcentrated feed liquid including a first water soluble salt dissolved in the feed liquid and a second water soluble salt dissolved in the feed liquid, 2) evaporating a liquid portion of the wastewater in the concentrator, thereby producing a concentrated wastewater stream, 3) continuing to concentrate the concentrated wastewater stream until the concentrated wastewater stream approaches or reaches a saturation level of the first water soluble salt, 4) delivering the concentrated wastewater to a first settling tank, where the first water soluble salt begins to precipitate out of solution in solid form, 5) drawing a sludge from the first settling tank, the sludge having an elevated ratio of the first water soluble salt to the second water soluble salt when compared to the unconcentrated feed liquid, 6) drawing a first liquid solution from the first settling tank and sending the liquid solution to a second settling tank, 7) drawing a second liquid solution from the second settling tank, the second liquid solution having an elevated ratio of the second water soluble salt to the first water soluble salt when compared to the unconcentrated liquid, and 8) drawing a third liquid solution from the second settling tank and delivering the third liquid solution to the concentrator for further concentration.
In one example, the unconcentrated solution includes a holding tank containing 1,000,000 kg of water at approximately 24° C. Equal weights (370,000 kg) of KNO3 and NaCl were dissolved in the water, thereby producing a ratio of KNO3 to NaCl of 1:1. Using the system described above, the water may be concentrated until the concentration of NaCl reaches the saturation point. NaCl will begin to precipitate out of solution in the first settling tank 1118. Sludge drawn off through the first extraction port 1130 will include a ratio of KNO3 to NaCl that is less than 1:1 because most of the KNO3 will remain in solution while some of the NaCl will precipitate out into the sludge. Solution drawn off from the second extraction port 1140 will include a ratio of KNO3 to NaCl that is greater than 1:1 because most of the KNO3 will remain in solution while some of the NaCl will precipitate out into the sludge in the first settling tank. If the withdrawal rate of the sludge through the first extraction port 1130 is decreased, the ratio of KNO3 to NaCl would fall as the sludge would contain more NaCl. Conversely, if the withdrawal rate of the solution through the second extraction port 1140 is decreased, the ratio of KNO3 to NaCl would rise.
On the other hand, increasing the withdrawal rate of the sludge through the first extraction port 1130 would tend to raise the ratio of KNO3 to NaCl. Conversely, increasing the withdrawal rate of the solution through the second extraction port 1140 would tend to lower the ratio of KNO3 to NaCl.
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.
This application claims the benefit of Provisional U.S. Patent Application No. 61/928,688, filed Jan. 17, 2014, the entirety of which is incorporated herein by reference.
Number | Date | Country | |
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61928688 | Jan 2014 | US |