Patent Application
20180200643
This application relates generally to liquid concentrators, and more specifically to compact, portable, inexpensive wastewater concentrators that can be easily connected to and use sources of low temperature energy, such as low pressure steam from a power plant or jacket water from internal combustion engines.
Concentration of volatile substances can be an effective form of treatment or pretreatment for a broad variety of wastewater streams and may be carried out within various types of commercial processing systems. At high levels of concentration, many wastewater streams may be reduced to residual material in the form of slurries containing high levels of dissolved and suspended solids. Such concentrated residual may be readily solidified by conventional techniques for disposal within landfills or, as applicable, delivered to downstream processes for further treatment prior to final disposal. Concentrating wastewater can greatly reduce freight costs and required storage capacity and may be beneficial in downstream processes where materials are recovered from the wastewater.
An important measure of the effectiveness of a wastewater concentration process is the volume of residual produced in proportion to the volume of wastewater entering the process. In particular, low ratios of residual volume to feed volume (high levels of concentration) are the most desirable. Where the wastewater contains dissolved and/or suspended non-volatile matter, the volume reduction that may be achieved in a particular concentration process that relies on evaporation of volatiles is, to a great extent, limited by the method chosen to transfer heat to the process fluid.
Conventional processes that affect concentration by evaporation of water and other volatile substances may be classified as direct or indirect heat transfer systems depending upon the method employed to transfer heat to the liquid undergoing concentration (the process fluid). Indirect heat transfer devices generally include jacketed vessels that contain the process fluid, or plate, bayonet tube, coil type, shell, and tube type heat exchangers that are immersed within the process fluid. Mediums such as steam or hot oil are passed through the jackets or heat exchangers in order to transfer the heat required for evaporation. Direct heat transfer devices implement processes where the heating medium is brought into direct contact with the process fluid, which occurs in, for example, submerged combustion gas systems.
Generally speaking, a source of heat is required to perform concentration within evaporative processes. Numerous systems have been developed to use heat generated by various sources, such as heat generated in an engine, in a combustion chamber, in a gas compression process, etc., as a source of heat for wastewater processing. One example of such a system is disclosed in U.S. Pat. No. 7,214,290 in which heat is generated by combusting landfill gas within a submerged combustion gas evaporator, which is used to process leachate at a landfill site. U.S. Pat. No. 7,416,172 discloses a submerged gas evaporator in which waste heat may be provided to an input of the gas evaporator to be used in concentrating or evaporating liquids. While waste heat is generally considered to be a cheap source of thermal energy, to be used effectively in a wastewater processing operation, the waste heat must in many cases be transported a significant distance from the source of the waste heat to a location at which the evaporative or concentration process is to be performed. For example, in many cases, a landfill operation will have electricity generators which use one or more internal combustion engines operating with landfill gas as a combustion fuel. The exhaust of these generators or engines, which is typically piped through a muffler and an exhaust stack to the atmosphere at the top of a building containing the electrical generators, is a source of waste heat. However, to collect and use this waste heat, significant amounts of expensive piping and ductwork must be coupled to the exhaust stack to transfer the waste heat to location of the processing system, which will usually be at ground level away from the building containing the generators.
Some evaporative concentration devices use high temperature gases, such as exhaust from a landfill flare or exhaust from an engine, to heat and evaporate water from the wastewater stream. In some cases, supplies of high temperature gases may be limited or non-existent. In these cases, evaporative concentration of wastewater streams may be difficult.
A compact liquid concentrator that uses low temperature, high enthalpy (latent heat) gas streams form a thermal energy source, such as low pressure steam from power plants, includes a gas inlet, a gas outlet, a mixing corridor disposed between the gas inlet and the gas outlet, the mixing corridor forming a tortuous path that induces high turbulence within the flowing gas stream traveling from the gas inlet to the gas outlet, and a liquid inlet through which liquid to be concentrated is injected into the mixing corridor, the liquid inlet disposed in the mixing corridor between the gas inlet and the outlet of the mixing corridor. A demister is disposed downstream of the concentrator section, the demister acting as a liquid collector to remove entrained liquid droplets from gas flowing in the demister gas flow passage. A reservoir collects the liquid removed from the gas flowing in the demister. The collected liquid is circulated through an indirect heat exchanger, for example a heat exchanger that condenses low temperature steam from a power plant, that releases small quantities of sensible heat, and relatively large quantities of latent heat to the collected liquid. The low temperature gas heats the collected liquid sufficiently to accelerate evaporation of the collected liquid as it is recycled through the mixing corridor for further concentration. As a result, the compact liquid concentrator does not need a high temperature gas input and may use ambient air to circulate through the mixing corridor.
In another embodiment, the compact liquid concentrator using low temperature gas may be used as a first stage evaporator in a two-stage evaporation system. Two concentrators may be fluidly attached in series, the first concentrator may use low temperature gas to perform a first stage evaporation and the second concentrator may use high temperature gas to perform a second stage evaporation. By evaporating in two stages, the two-stage evaporation system reduces its need for high temperature gas. As a result, the second concentrator may be reduced in size relative to a single stage high temperature gas concentrator that would be needed to perform the same level of evaporation.
As the gas and liquid flow through the tortuous path 26, the venturi principle creates an accelerated and turbulent flow that thoroughly mixes the gas and liquid in the flow corridor 24 at and after the location of the inlet 30. As a result of the turbulent mixing, a portion of the liquid rapidly vaporizes and becomes part of the gas stream. As the gas-liquid mixture moves through the tortuous path 26, the direction and/or velocity of the gas/liquid mixture may be changed by an adjustable flow restriction, such as a venturi plate 32, which is generally used to create a large pressure difference in the flow corridor 24 upstream and downstream of the venturi plate 32. The venturi plate 32 may be adjustable to control the size and/or shape of the tortuous path 26 and may be manufactured from a corrosion resistant material including a high alloy metal such as those manufactured under the trade names of Hastelloy®, Inconel® and Monel®.
After leaving the tortuous path 26, the gas-liquid mixture passes through a demister 34 (also referred to as a fluid scrubber) coupled to the gas exit 22. The demister 34 removes entrained liquid droplets from the gas stream. The demister 34 includes a gas-flow passage. The removed liquid collects in a liquid collector or sump 36 in the gas-flow passage, the sump 36 may also include a reservoir for holding the removed liquid. A pump 40 fluidly coupled to the sump 40 and/or reservoir moves the liquid through a re-circulating circuit 42 back to the liquid inlet 30 and/or flow corridor 24. In this manner, the liquid may be reduced through evaporation to a desired concentration. Fresh or new liquid to be concentrated is input to the re-circulating circuit 42 through a liquid inlet 44. This new liquid may instead be injected directly into the flow corridor 24 upstream of the venturi plate 32. The rate of fresh liquid input into the re-circulating circuit 42 may be equal to the rate of evaporation of the liquid as the gas-liquid mixture flows through the flow corridor 24 plus the rate of liquid extracted through a concentrated fluid extraction port 46 located in or near the reservoir in the sump 40. The ratio of re-circulated liquid to fresh liquid may generally be in the range of approximately 1:1 to approximately 100:1, and is usually in the range of approximately 5:1 to approximately 25:1. For example, if the re-circulating circuit 42 circulates fluid at approximately 10 gal/min, fresh or new liquid may be introduced at a rate of approximately 1 gal/min (i.e., a 10:1 ratio). A portion of the liquid may be drawn off through the extraction port 46 when the liquid in the re-circulating circuit 42 reaches a desired concentration.
After passing through the demister 34 the gas stream passes through an induction fan 50 that draws the gas through the flow corridor 24 and demister gas-flow corridor under negative pressure. Alternatively, the concentrator 10 could operate under positive pressure produced by a blower (not shown) prior to the liquid inlet 30. Finally, the gas is vented to the atmosphere or directed for further processing through the gas exit 22.
The concentrator 10 may include an optional liquid pre-treatment system 52 for treating the liquid to be concentrated, which may be a wastewater feed, such as a flue gas desulfurization wastewater feed from a power plant. For example, an air stripper may be used as a pre-treatment system 52 to remove substances that may produce foul odors or be regulated as air pollutants. In this case, the air stripper may be any conventional type of air stripper or may be a further concentrator of the type described herein, which may be used in series as the air stripper. The pre-treatment system 52 may, if desired, heat the liquid to be concentrated using any desired heating technique. For example, the pre-treatment system 52 may include a heat exchanger, such as a plate and frame heat exchanger or a shell and tube heat exchanger, that is powered by a low temperature gas or liquid stream, such as low pressure steam from a power plant or a recirculating heat transfer fluid device. The heat exchanger will be discussed further with respect to
The liquid concentrator 10 described herein may be used to concentrate a wide variety of wastewater streams, such as waste water from industry (e.g., flue gas desulfurization water in a power plant or produced water from gas or oil wells). The liquid concentrator 10 is practical, energy efficient, reliable, and cost-effective. In order to increase the utility of this liquid concentrator, the liquid concentrator 10 is readily adaptable to being mounted on a trailer or a moveable skid to effectively deal with wastewater streams in remote or difficult to reach areas. The liquid concentrator 10 described herein has all of these desirable characteristics and provides significant advantages over conventional wastewater concentrators, especially when the goal is to manage a broad variety of wastewater streams.
Moreover, the concentrator 10 may be largely fabricated from highly corrosion resistant, yet low cost materials such as fiberglass and/or other engineered plastics. This is due, in part, to the fact that the disclosed concentrator is designed to operate under minimal differential pressure and relatively mild temperatures. For example, a differential pressure generally in the range of only 10 to 30 inches water column and operating temperatures below 300° F. are all that are required. Also, because the gas-liquid contact zones of the concentration processes generate high turbulence causing rapid evaporation and resultant rapid cooling of the liquid being evaporated within a compact mixing corridor, the overall design is very compact as compared to conventional concentrators where the gas liquid contact occurs in large process vessels with significantly larger high temperature zones. As a result, the amount of high alloy metals required to withstand corrosive forces at elevated temperatures for the concentrator 10 is quite minimal. Also, because these high alloy parts are small and can be readily replaced in a short period of time with minimal labor, fabrication costs may be cut to an even higher degree by designing some or all of these parts to be fabricated either entirely from low-cost engineered materials, such as fiberglass and CPVC, or from lesser quality metals and alloys coated with corrosion and/or erosion resistant liners, such as engineered plastics including elastomeric polymers, to extend the useful life of such components. Likewise, the pump 40 may be provided with corrosion and/or erosion resistant liners to extend the life of the pump 40, thus further reducing maintenance and replacement costs.
The liquid concentrator 10 provides direct contact of the liquid to be concentrated and the gas, effecting highly turbulent and rapid heat exchange and mass transfer between gas and the liquid, e.g., wastewater, undergoing concentration. Moreover, the concentrator 10 employs highly compact gas-liquid contact zones, making it minimal in size as compared to known concentrators. The direct contact heat exchange feature promotes high energy efficiency and eliminates the need for solid surface heat exchangers as used in conventional, indirect heat transfer concentrators. Further, the compact gas-liquid contact zone eliminates the bulky process vessels used in both conventional indirect and direct heat exchange concentrators. These features allow the concentrator 10 to be manufactured using comparatively low cost fabrication techniques and with reduced weight as compared to conventional concentrators. Both of these factors favor portability and cost-effectiveness. Thus, the liquid concentrator 10 is more compact and lighter in weight than conventional concentrators, which make it ideal for use as a portable unit. Additionally, the liquid concentrator 10 is less prone to fouling and blockages due to the direct contact heat exchange operation and the lack of solid heat exchanger surfaces. The liquid concentrator 10 can also process liquids with significant amounts of suspended solids because of the direct contact heat exchange. As a result, high levels of concentration of the process fluids may be achieved without need for frequent cleaning of the concentrator 10.
More specifically, in liquid concentrators that employ indirect heat transfer, the heat exchangers are prone to fouling and are subject to accelerated effects of corrosion at the normal operating temperatures of the hot heat transfer medium that is circulated within them (steam or other hot fluid). Each of these factors places significant limits on the durability and/or costs of building conventional indirectly heated concentrators, and on how long they may be operated before it is necessary to shut down 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 130 degrees Fahrenheit to about 195 degrees Fahrenheit. Further, as an adiabatic evaporation process with no heat being driven into the process through heat exchange surfaces or walls of the process equipment, the gas flowing through the system rapidly approaches saturation, which eliminates a driving force for further evaporation and the potential for concentrated liquid undergoing processing to dry upon, and create buildup on, solid surfaces within the concentrator. This factor reduces the required cleaning frequency while greatly simplifying procedures for periodic cleaning of the concentrator equipment.
Moreover, the concentrator 10 is designed to operate under negative pressure, a feature that greatly enhances the ability to use a very broad range of fuel or waste heat sources as an energy source to affect evaporation. In fact, due to the draft nature of these systems, pressurized or non-pressurized burners may be used to heat and supply the gas used in the concentrator 10. Further, the simplicity and reliability of the concentrator 10 is enhanced by the minimal number of moving parts and wear parts that are required. In general, only two pumps and a single induced draft fan are required for the concentrator when it is configured to operate on waste heat such as stack gases from engines (e.g., generators or vehicle engines), industrial process stacks, gas compressor systems, and flares, such as landfill gas flares. These features provide significant advantages that reflect favorably on the versatility and the costs of buying, operating and maintaining the concentrator 10.
As illustrated in
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 downstream 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 (not shown explicitly 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 bottom 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 flue gas desulfurization water, 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 moveable venturi plate 163 disposed across the width of the concentrator assembly 120, causes turbulent flow and complete mixture of the liquid and gas, causing rapid evaporation of the dispersed liquid droplet phase into the continuous gas phase. Because the mixing action caused by the venturi section 162 provides a high rate of evaporation through continuous creation of dynamic renewable surface area, the gas cools substantially and rapidly in the concentrator assembly 120, and exits the venturi section 162 into a flooded elbow 164 at high velocity. In fact, the temperature of the gas-liquid mixture at this point approaches the adiabatic saturation temperature for the particular gas and volatile liquid mixture, which may be about 160 degrees Fahrenheit in some examples.
The bottom of the flooded elbow 164 has a pool of liquid disposed therein, and the gas-liquid mixture exiting the venturi section 162 at high rates of speed impinges on the pool of liquid, which is maintained at a fixed level by means of an overflow weir that forms a portion of the wall of the flooded elbow 164. The gas-liquid mixture is forced to turn 90 degrees to flow into the fluid scrubber 122 in this example. The interaction of the gas-liquid stream with the liquid within the flooded elbow 164 removes liquid droplets through impingement of the droplets upon the surface of the pool of liquid within the flooded elbow 164 and subsequent coalescence into the liquid. Further, the pool of liquid within the flooded elbow 164 prevents suspended particles within the gas-liquid stream from hitting the bottom of flooded elbow 164 at high rates of speeds, thereby preventing erosion of the metal wall of the flooded elbow 164.
After leaving the flooded elbow 164, the gas-liquid stream in which evaporated liquid and some liquid and other particles still exist, flows through the fluid scrubber 122 which is, in this case, a cross-flow fluid scrubber. The fluid scrubber 122 includes various screens or filters which aid in removal of entrained liquids from the gas-liquid stream and removes other particles that might be present with the gas-liquid stream. In one particular example, the cross flow scrubber 122 may include an initial coarse impingement baffle 169 at the input thereof, which is designed to remove liquid droplets in the range of 50 to 100 microns in size or higher. Thereafter, two removable filters in the form of chevrons 170 are disposed across the fluid path through the fluid scrubber 122, and the chevrons 170 may be progressively sized or configured to remove liquid droplets of smaller and smaller sizes, such as 20-30 microns and less than 10 microns. Of course, more or fewer filters or chevrons could be used.
Liquid captured by the filters 169 and 170 gravity drains into a reservoir or sump 172 located at the bottom of the fluid scrubber 122. The sump 172, which may hold, for example 200 gallons of liquid or more, thereby collects concentrated fluid containing dissolved and suspended solids removed from the gas-liquid stream and operates as a reservoir for a source of re-circulating concentrated liquid back to the concentrator assembly 120 to be further treated and/or to prevent the formation of dry particulate within the concentrator assembly 120 in the manner described above with respect to
As illustrated in
Concentrated liquid also be removed from the bottom of the fluid scrubber 122 via the exit port 173 and may be further processed or disposed of in any suitable manner in a secondary re-circulating circuit. In particular, the concentrated liquid removed by the exit port 173 contains a certain amount of suspended solids, which preferably may be separated from the liquid portion of the concentrated liquid and removed from the system using a secondary re-circulating circuit. For example, concentrated liquid removed from the exit port 173 may be transported through a secondary concentrated wastewater circuit (not shown) to a solid/liquid separating device, such as a settling tank, a vibrating screen, a rotary vacuum filter, or a filter press. After the suspended solids and liquid portion of the concentrated wastewater are separated by the solid/liquid separating device, the liquid portion of the concentrated wastewater may be returned to the sump 172 for further processing in the first or primary re-circulating circuit connected to the concentrator.
The gas, which flows through and out of the fluid scrubber 122 with the liquid and suspended solids removed therefrom, exits out of piping or ductwork at the back of the fluid scrubber 122 (downstream of the chevrons 170) and flows through an induced draft fan 190 of the exhaust assembly 124, from where it is exhausted to the atmosphere in the form of the cooled inlet gas mixed with the evaporated water vapor. Of course, an induced draft fan motor 192 is connected to and operates the fan 190 to create negative pressure within the fluid scrubber 122 so as to ultimately draw gas from the flare 130 through the transfer pipe 140, the air pre-treatment assembly 119 and the concentrator assembly 120. As described above with respect to
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 may designed to include an optional 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 may include 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 combination of features illustrated in
The fluid concentrator 110 is also a very fast-acting concentrator. Because the concentrator 110 is a direct contact type of concentrator, it is not subject to deposit buildup, clogging and fouling to the same extent as most other concentrators. Still further, the ability to control the flare cap 134 to open and close, depending on whether the concentrator 110 is being used or operated, allows the flare 130 to be used to burn gas without interruption when starting and stopping the concentrator 110. More particularly, the flare cap 134 can be quickly opened at any time to allow the flare 130 to simply burn gas as normal while the concentrator 110 is shut down. On the other hand, the flare cap 134 can be quickly closed when the concentrator 110 is started up, thereby diverting hot gasses created in the flare 130 to the concentrator 110, and allowing the concentrator 110 to operate without interrupting the operation of the flare 130. In either case, the concentrator 110 can be started and stopped based on the operation of the flare cap 134 without interrupting the operation of the flare 130.
If desired, the flare cap 134 may be opened to a partial amount during operation of the concentrator 110 to control the amount of gas that is transferred from the flare 130 to the concentrator 110. This operation, in conjunction with the operation of the ambient air valve, may be useful in controlling the temperature of the gas at the entrance of the venturi section 162.
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
If desired, one or both of the ambient air valve 306 and the flare cap 134 may be operated in a fail-safe open position, such that the flare cap 134 and the ambient air valve 306 open in the case of a failure of the system (e.g., a loss of control signal) or a shutdown of the concentrator 110. In one case, the flare cap motor 135 may be spring loaded or biased with a biasing element, such as a spring, to open the flare cap 134 or to allow the flare cap 134 to open upon loss of power to the motor 135. Alternatively, the biasing element may be the counter-weight on the flare cap 134 may be so positioned that the flare cap 134 itself swings to the open position under the applied force of the counter-weight 137 when the motor 135 loses power or loses a control signal. This operation causes the flare cap 134 to open quickly, either when power is lost or when the controller 302 opens the flare cap 134, to thereby allow hot gas within the flare 130 to exit out of the top of the flare 130. Of course, other manners of causing the flare cap 134 to open upon loss of control signal can be used, including the use of a torsion spring on the pivot point 136 of the flare cap 134, a hydraulic or pressurized air system that pressurizes a cylinder to close the flare cap 134, loss of which pressure causes the flare cap 134 to open upon loss of the control signal, etc.
Thus, as will be noted from the above discussion, the combination of the flare cap 134 and the ambient air valve 306 work in unison to protect the engineered material incorporated into the concentrator 110, as whenever the system is shut down, the flare cap and the air valve 306 automatically immediately open, thereby isolating hot gas generated in the flare 130 from the process while quickly admitting ambient air to cool the process.
Moreover, in the same manner, the ambient air valve 306 may be spring biased or otherwise configured to open upon shut down of the concentrator 110 or loss of signal to the valve 306. This operation causes quick cooling of the air pre-treatment assembly 119 and the concentrator assembly 120 when the flare cap 134 opens. Moreover, because of the quick opening nature of the ambient air valve 306 and the flare cap 134, the controller 302 can quickly shut down the concentrator 110 without having to turn off or effect the operation of the flare 130.
Furthermore, as illustrated in the
The controller 302 may also be connected to a motor 312 which controls the operation of the damper 198 in the gas re-circulating circuit of the fluid scrubber 122. The controller 302 may cause the motor 312 or other type of actuator to move the damper 198 from a closed position to an open or to a partially open position based on, for example, signals from pressure sensors 313, 315 disposed at the gas entrance and the gas exit of the fluid scrubber 122. The controller 302 may control the damper 198 to force gas from the high pressure side of the exhaust section 124 (downstream of the induced draft fan 190) into the fluid scrubber entrance to maintain a predetermined minimum pressure difference between the two pressure sensors 313. 315. Maintaining this minimum pressure difference assures proper operation of the fluid scrubber 122. Of course, the damper 198 may be manually controlled instead or in addition to being electrically controlled.
Thus, as will be understood from the above discussion, the controller 302 may implement one or more on/off control loops used to start up or shut down the concentrator 110 without affecting the operation of the flare 130. For example, the controller 302 may implement a flare cap control loop which opens or closes the flare cap 134, a bleed valve control loop which opens or begins to close the ambient air valve 306, and an induced draft fan control loop which starts or stops the induced draft fan 190 based on whether the concentrator 110 is being started or stopped. Moreover, during operation, the controller 302 may implement one or more on-line control loops which may control various elements of the concentrator 110 individually or in conjunction with one another to provide for better or optimal concentration. When implementing these on-line control loops, the controller 302 may control the speed of induced draft fan 190, the position or angle of the venturi plate 163, the position of the flare cap 134 and or the position of the ambient air valve 306 to control the fluid flow through the concentrator 110, and/or the temperature of the air at the inlet of the concentrator assembly 120 based on signals from the temperature and pressure sensors. Moreover, the controller 302 may maintain the performance of the concentration process at steady-state conditions by controlling the pumps 184 and 182 which pump new and re-circulating fluid to be concentrated into the concentrator assembly 120. Still further, the controller 302 may implement a pressure control loop to control the position of the damper 198 to assure proper operation of the fluid scrubber 122. Of course, while the controller 302 is illustrated in
The concentrator 110 of
While the liquid concentrator 110 has been described above as being connected to a flare to use the hot gases generated in the flare, the liquid concentrator 110 can be connected to other sources of hot gas, or to ambient air.
In some instances, the supply of heated gas (such as from a flare or exhaust gas from a power plant) may be limited. In these cases, it may be beneficial to perform a first stage evaporation without heated gas to reduce the overall amount of water in the wastewater, which reduces the need for high temperature (high energy) gas in the second stage concentrator. In other instances, the low temperature gas concentrator may be used as a stand-alone evaporation device.
Some cases where high temperature gas may be limited include when concentrating flue gas desulfurization water from power plants, when concentrating evaporation pond water, or when concentrating landfill leachate. However, in this case, there may be lower temperature gas available to aid in the concentration process. For example, many power plants have a large quantity of low temperature steam (which is the residual gas from an electric turbine) that is normally condensed. While this low temperature steam is not very energy rich in sensible heat it is energy rich in latent heat and the energy in the steam can be used to concentrate the flue gas desulfurization water in a first stage of a two-stage concentration process, or in a stand-alone one stage concentration process. In some embodiments, the concentrator described above, with respect to
Turning now to
The first stage concentrator 1110 may be very similar to the concentrators 10, 110 described above, but with modifications to utilize low energy gas, such as low pressure steam from a power plant. In other embodiments, the first stage concentrator 1110 may take the form of a submerged gas evaporator having a downcomer and a weir, which may be referred to as a continuous liquid phase—discontinuous gas phase concentrator.
Generally speaking, the first stage concentrator 1110 has a first stage evaporation section 1120 having a wastewater input 1160, an ambient air input 1161, and an exhaust 1124 to vent exhaust gas to the atmosphere. Partially concentrated wastewater (in the form of partially concentrated flue gas desulfurization water in the example of
Because the heat from the low temperature steam is transferred to the wastewater through the heat exchanger 1190, and evaporation is accomplished in a separate vessel, fouling and scaling in the heat exchanger 1190 is substantially reduced. Additionally, the low temperature steam 1196 may have a very low pressure or even a negative pressure (e.g., less than 0 psig). In the case of power plant wastewaters, calcium sulfate begins to precipitate at very dilute concentrations. The initial precipitation of calcium sulfate may be kept suspended by the circulation of the wastewater in the first stage concentrator 1110. The suspended calcium sulfate can act as a “seed” location for further calcium sulfate precipitation in the first stage concentrator 1110, which reduces the amount of calcium sulfate that agglomerate on other surfaces in the system. Additionally, chemical dispersants may be added to the partially concentrated wastewater to further reduce agglomeration of calcium sulfate on concentrator surfaces.
Some of the partially concentrated wastewater is drawn off from the first stage evaporation section 1120 thorough a partially concentrated wastewater exit and sent to a holding tank (not shown, but located between the first stage evaporation section 1120 and a second stage evaporation section 1220), which would further direct the partially concentrated wastewater to a liquid inlet 1260 of the second stage evaporation section 1220 of the second stage concentrator 1210. Hot gas is supplied to the second stage evaporation section 1220 and evaporation occurs as described above with respect to
Turning now to
The source of low temperature steam 1196 may include a source of ultra low temperature steam from a power plant. For example, the source of low temperature steam 1196 may include steam having a pressure from about −13 psig to about 40 psi. Steam in this range of pressures has a relatively low temperature. Steam in this range of pressures generally has not been used in concentration processes because the sensible energy in such low temperature steam was thought to be too low to be economically useful. The inventors of the instant application have discovered that this low temperature (energy lean) steam is useful in the concentrator described herein to heat the partially concentrated wastewater. After heating in the heat exchanger 1190, the heated partially concentrated wastewater is returned to the sump 172, where it raises the overall temperature of the partially concentrated wastewater in the sump 172 by, for example, between 120 degrees and 180 degrees. By drawing the partially concentrated wastewater from the sump 172, through the heat exchanger 1190, and back to the sump 172, high flow rates may be maintained through the heat exchanger 1190 and moderate increases in temperature may be realized in the sump without fouling the heat exchanger and/or while maximizing efficiency of heat transfer from the low temperature steam to the partially concentrated wastewater. In an alternate embodiment, a separate recirculating loop may recirculate concentrated wastewater in a separate circuit, through the heat exchanger 1190. Such a separate recirculating loop allows the heat exchanger 1190 to be reduced in size and allows the concentrated wastewater to remain in a turbulent state, which produces better heat exchange while reducing fouling risk.
The moderately heated partially concentrated wastewater in the sump 172 will have enough energy latent in the liquid to enhance evaporation in the first stage evaporation section 1120 without using heated gas. As a result, ambient air may be used for the gas steam in the first stage evaporation section 1120.
Typically, the percentage of water in the wastewater steam may be reduced by 20% to 90% during in the first stage concentrator 1110. As a result, the second stage concentrator 1210 may be reduced in size by between 25% and 50% below what would be needed to affect a comparable evaporation in a single stage hot gas concentrator. The net result is a decrease in high temperature energy that is required for the two-stage concentration system 1000 over a single stage concentration system. In other embodiments, the second stage concentrator may be eliminated if the latent heat in the low temperature steam is sufficient to produce adequate evaporation for an intended use.
While the first stage concentrator 1110 has been described above as part of a two-stage concentration system 1000, the first stage concentrator 1110 may also be used as a stand-alone concentrator when moderate levels of concentration are needed and/or when only moderate levels of volume reduction of the wastewater are required. For example, moderate levels of volume reduction may include 20%-90% of volume reduction.
While the first stage concentrator 1110 has been illustrated as a discontinuous liquid phase—continuous gas phase concentrator, in other embodiments, a continuous liquid phase—discontinuous gas phase concentrator, such as a concentrator having a downcomer and a weir in a liquid containing vessel, may be used.
Turning now to
The first stage concentrator may remove some level of a slipstream water from a main water intake to a power plant and process it through in a combination water heater / clean water recovery unit (first stage concentrator 2110). The first stage concentrator may be driven by low temperature steam from condensing turbines combined with vapor exhaust from the second stage concentrator 2210. The vapor exhaust from the second stage concentrator provides non-condensable gas that prevents the first stage concentrator 2110 from experiencing cavitation. Further, because the vapor exhaust from the second stage concentrator 2210 approaches the adiabatic saturation temperature, the non-condensable portion of this vapor exhaust is saturated and, therefore, not capable of producing an evaporative cooling effect within the first stage evaporator 2110.
This arrangement produces a compact, extremely simple, durable and reliable unit that performs both functions without need for conventional heat exchangers other than that for heat transfer from the hot water produced in the first stage concentrator 2110 to the second stage concentrator 2110 concentrator hot water feed. Advantages include inexpensive highly corrosion resistant construction with self-cleaning action based on turbulence.
By selecting a ratio of plant water intake slipstream volume to combined concentrator exhaust gas and condensing steam mass significant quantities of clean hot water feed for the stage concentrator 2210 may be produced while recovering a significant portion of thermal energy used to evaporate purge water the concentrator and while condensing, capturing and reusing low temperature turbine steam as hot water that is directly returned to the power plant water distribution system after supplying heat for the second stage concentrator 2210. As a result, the water may be reused for boiler water makeup etc. within the power plant.
Additionally, this process reduces river water intake volume via recycle, which is an environmentally sound feature.
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.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US16/42360 | 7/14/2016 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 62192323 | Jul 2015 | US |
