Patent Application
20140016433
The invention relates to a method and apparatus for mixing and/or blending fluids and more specifically to a method and apparatus for generating very fine micro-sized bubbles in a fluid flow.
It is known to use air or gas bubbles to separate particles in a fluid. This method has been used for example in separation of petroleum derivatives, and in separation of sludge from effluent. When separating particles from a fluid flow it has been found that the smaller the bubble, and the more numerous the bubbles, the longer the bubbles are suspended in a fluid, and that these smaller and more numerous bubbles improve flotation of the particles. As the bubbles rise, the particles are attached. The particles are skimmed off once they have risen to the top of the fluid. In the prior art, methods of using flotation to separate particles from a fluid are referred to variously as dissolved air flotation, dissolved gas flotation, and induced air or gas flotation.
It has been found that in some instances the same device used to form micro bubbles may also be used to combine or blend fluids and additionally such blended fluids may result in altered densities to further aid in separation of emulsified fluids. It should be noted that for the purposes of the method and apparatus of the present invention, the term “fluid” or “fluids” may include a gas or a liquid and where a gas may include particles that flow with the gas, and a liquid may include more than one type of liquid. As well, the liquid may include particles. Further, when blending, in some instances the “fluid” may be a dry powder that flows as a liquid. Only the apparatus scale or valve types may be required to change in the event of the mixing or blending of “fluids”.
Accordingly, it is an object of the present invention to provide a method and apparatus that can produce extremely tiny bubbles, advantageously 5 microns or less in diameter; wherein referred to as micro-bubbles.
Another object of the present invention is to provide a method and apparatus that according to alternative embodiments may blend different fluids by using a method of dynamic shearing of one fluid into a second fluid.
Another object of the present invention is to provide for micro-bubble generation for dissolved air or dissolved gas flotation, includes retro-fits of less efficient systems, and to create silky-smooth high viscosity aerated or blended liquids, and/or for solvent extraction for example for treating hydrostatic fracturing flow-back water and oil/water separation, and/or for emulsion breaking for example for treating fracturing flow-back water and oil/water separation for tight emulsions, and/or for aiding in reducing dissolved biochemical oxygen demand (BOD) or chemical oxygen demand (COD), and/or for assisting in the dissolution of ozone in water.
The method and apparatus described herein for generating micro-bubbles and for mixing and/or blending fluids is capable of functioning within many different applications. In general the process includes providing a pressurized container, wherein the container has an inlet and an outlet. A “stinger” tube is mounted in the inlet. The stinger tube is a slender cylindrical tube having a fixed internal diameter for a fixed flow rate. The tubes are referred to as stinger tubes as they are cantilevered from the inlet into the container. The stinger tubes are inter-changeable so that the length of the tube in the container may be adjusted, for example when the system is tuned upon set-up to optimize the generation of micro-bubbles, as discussed in more detail below. The tuning or optimizing of the system is to achieve the required pressure drop and the formation of micro-bubbles of 5 micron or less for a particular flow rate. Pressure from the container outlet is generally controlled by a valve. The valve leads to a second container. The second container may be open to atmospheric pressure.
The distal end of the tube, distal from the container inlet, is referred to as the nozzle. The nozzle may be for example blunt, squared-off, or chamfered.
As mentioned above, micro bubbles, are useful for particle flotation, for example in dissolved gas flotation or dissolved air flotation systems. An optimized pressure drop across the inlet and tube generates micro-bubbles in the flow leaving the tube nozzle, and causes the fluids to dynamically commingle. In some applications the fluids are air and water wherein the water contains particles for separation and air is introduced upstream of the container inlet, for example, upstream of the device used to pressurize the flow entering the tube. That pressure is the inlet pressure. A pressure drop of 60-90% of the container inlet pressure may be adjusted to produce micro-bubbles so as to enhance the separation process by producing a smooth texture, high-viscosity aerated or otherwise blended liquid. Conventionally, using slender, modified hydrocyclones, a micro-bubble size of five microns has been established where the bubble rise rate in potable water at substantially standard temperature and pressure (STP) is 4 inches per minute. The smaller the micro-bubble size, the slower the rise rate. Consequently, as used herein, a micro-bubble size of five microns or less is considered established when the bubble rise rate is substantially three inches per minute or less. A measured bubble rise rate of substantially three inches per minute or less at STP is thus taken as determinative of a micro-bubble size of 5 microns or less. The outlet pressure is controlled by a downstream valve. The downstream valve leads to another container, which may in one embodiment be open to atmospheric pressure and may include a mechanical skimmer to separate off the floating particles, usually as a scum or sludge.
The first container may include a bleeder valve, for example positioned on the top of the container for relief of excess air or gas pressure build-up in the container. Pressure relief may be done manually or automatically with the use of a conventional auto-bleed valve.
It should be noted that in some instances three or more fluids, which may or may not be soluble, may be commingled, blended, mixed and/or dissolved in whole or in part into each other. This may be done for the following purposes: separation of suspended solids by flotation; or blending two or more fluids into a homogeneous mixture; or aerating a fluid or multiple fluids to increase the total volume; or to change the density; or to provide for an efficient method of pressurized oxidation and/or disinfection of a pathogen laden material by use of a gas such as ozone; or for the treatment of flow-back water including oil/water separation in hydrostatic fracturing of geological structures in the oil and gas industry.
In another embodiment described herein, the outlet flow from the first container flows into the inlet of a second container. A secondary process in the second container duplicates the first process in the first container. The second container duplicates the stinger tube structure of the first container and includes a second outlet where the fluids exit the second container, where-after the flow may be returned to atmospheric pressure.
An optional diffuser plate may be mounted adjacent the distal end of each stinger tube to aid in diffusing of certain types of fluids for mixing and/or blending as desired.
In summary, the method according to one aspect of the present invention for generating micro bubbles of substantially five microns or less in a fluid flow may be characterized as including:
In the accompanying drawings, in which like reference characters designate the same or similar parts throughout the several views:
a is a section view along line 6a-6a in
In apparatus 10, as shown by way of example in
The suction side 18a of multi-phase pump 18 is held at a fixed pressure below atmospheric pressure so that no compressor or additional pump is required in order to introduce secondary flow into conduit 16 from conduit 20. The use of a multi-phase pump in the flow path is advantageous because such pumps operate without cavitation and at relatively good efficiency. Two types of multi-phase pumps may be used. One is a two stage progressing cavity pump which will pump a liquid and an adequate amount of gas without cavitating, but does little to contribute to aiding in generation of micro-bubbles. The other is a regenerative turbine pump which does not cavitate and aids in the generation of micro-bubbles when up to 15% volume of gas at standard temperature and pressure (“STP”) is added via conduit 20 at the suction side conduit 16 along with the fluid. The fluid is usually, but not always, water. The use of a regenerative turbine pump has its drawbacks however. Because of the tight tolerances in a regenerative turbine pump, it cannot pump fluid having entrained particles without the risk of it seizing. It does however assist with generation of micro-bubbles by creating bubbles down to about 30-40 microns thereby leaving less work for the downstream micro-bubble generation system described herein, which produces micro-bubbles of 5 microns or less.
As shown in the embodiment of
The hollow cavity within insert 30 provides primary mixing chamber 30c, wherein the diameter of the mixing chamber is greater than the diameter of tube 32. The combined flow flows from the inlet orifice 30a of insert 30, mixes in mixing chamber 30c and flows into the upstream end of tube 32. In the illustrated embodiment of
Insert 30 is rigidly mounted into aperture 34b in bulkhead 34e so as to support tube 32 cantilevered into and centrally along cavity 34a, which is advantageously elongate. Tube 32 may be for example ¼ inch, ⅜ inch or ½ inch stainless steel tubing which may be approximately 20 inches long, subject to the length adjustment discussed below. The combined length of vessel 34 and head 42 may be in the order of 24 to 30 inches, and the diameter of vessel 34 may be in the order of 3 inches. Outlet 34c may include nozzle 48 having a clamp 48a and corresponding ferule. Flow exiting cavity 34a flows through nozzle 48 into conduit 38. Tube 32 may be releasably mounted to insert 30 by conventional means known in the art, for example by the threaded coupling 50 illustrated. The illustrated female NPT ports 52 and 54 may be used for mounting, respectively, pressure gauge 28 to head 42 and pressure gauge 36 to vessel 34.
The stream of gas or gases and/or fluid or fluids moving via conduit 20 into conduit 16 may be naturally aspirated into the primary stream in conduit 16, for example between pressure control valve 14 and multi-phase pump 18, at a controlled flow rate. If a gas is being aspirated via conduit 20 into the primary stream in conduit 16, the flow rate ordinarily should not exceed 20 percent by volume of the primary stream. The discharge pressure (pressure P2) of multi-phase pump 18 is advantageously maintained at a pressure ranging from 50 pounds per square inch-gauge (PSIG) to 150 PSTG. This pressure is controlled by the pump settings and valve 40.
In an alternative embodiment, further gas or gases and/or further fluid or fluids may be injected into the primary stream in conduit 26 via conduit 56, and flowing through flow indicator 58, instead of, or in conjunction with the aspirated stream from conduit 20 into conduit 16 at the suction side 18a of multi-phase pump 18.
Within mixing chamber 30c a slight pressure drop creates turbulence for the primary mixing process. Additional pressure drop is realized in tube 32 and in the mixing zone within cavity 34a where turbulence is created between downstream end 32b of tube 32 and the downstream end 34f of container 34. The pressure in the container cavity 34a will advantageously be from 60-90 percent of pressure P2. Consequently pressure P3 may be in the range of 30 to 135 PSIG, wherein the lowest pressure of 30 PSIG is determined as 60 percent of 50 PSIG and the highest pressure of 135 PSIG is determined as 90 percent of 150 PSIG. This pressure differential between pressure P2 and pressure P3 provides the energy for the mixing and blending. The pressure differential between pressure P2 and pressure P3 will determine the degree of mixing and/or bubble size in flow downstream of outlet 34c as adjusted according to the method described herein.
As seen in
As seen in
As seen in
In embodiments of the invention the inlet pressure (pressure P2) downstream of the multi-phase pump 18 may be in the range of 80-150 PSIG. For example, the inlet pressure P2 of the combined flow in direction A in the configuration of
As discussed above, in the embodiment of
In the alternative embodiment of
Thus although the primary mixing in mixing chamber 30c and the secondary mixing in cavity 34a is important, it is the formation of micro-bubbles of substantially 5 micron diameter or less which is most important for the combined flow to be separated—for example so as to break emulsions or for example to separate the following: solid particle impurities from fluid, oil from fluid such as water, or hydro-carbons from water such as in a hydrostatic fracturing process as described below.
The combined flow is separated downstream in for example a separation chamber wherein the micro bubbles form a very smooth textured foam or blend which slowly rises, at substantially three inches or less in a minute indicating optimized micro-bubbles, to form a sludge or scum which may then be skimmed off. A micro-bubble size of substantially 5 microns or less operates far more effectively in such applications than the use of conventional bubbles such as those of 30 microns in size or so.
During initial set-up, or during maintenance, the system described above is adjusted or tuned to optimize the generation of the 5 micron micro-bubbles. For a given flow rate, a larger internal diameter for tube 32 will result in larger bubble size because of lower differential pressure across the vessel 34. If during operation, larger bubbles are desired, shortening the tube length achieves the same results and saves times as well. If the flow rate is decreased but the same inlet pressure is maintained, differential pressure is reduced and larger bubble size will result. These operational decisions and priorities are adjusted and optimized for the conditions present.
Micro bubbles of five microns or less have been found to occur under a favourable pressure differential measured across insert 30 and tube 32 (for example, P3-P2), in the range of a 20-50 PSIG, and preferably a 30-40 PSIG, pressure drop. Pressure P2 may be regulated by regulating valve 14 and/or and may be adjusted by multi-phase pump 18. Pressure P3 is regulated using valve 40 and/or by adjusting the length and/or diameter of tube 32. That is the pressure drop P3-P2, for example, shortening (by cutting or replacing) or lengthening the length of tube 32 and/or by adjusting the size of the internal diameter of tube 32. Thus, tube 32 may be cut-down to reduce its length, or swapped for another tube of different length and/or diameter, for example ¼, ⅜ or ½ inch. The longer the tube and/or the narrower the tube, the greater the pressure drop P3-P2. Thus in the illustrated example of
If, upon checking, the size of the micro-bubbles being generated is greater than 5 microns, for example if the bubbles rise to quickly, or are individually visible to the un-aided eye, then an installer or person maintaining the system may check the system operation and components according to the following hierarchy:
Thus as will now be understood by those skilled in the art, each apparatus 10 utilizes pressure differential P3-P2 and turbulence to generate two or more high velocity zones, and two or more mixing zones for intimate mixing, blending and/or dissolution of usually two or more dissimilar feeds. To recap, and with reference to
(a) aerated water or two or more different liquids enter apparatus 10 at a pressure usually ranging from 80 PSIG to 150 PSIG. If air or gas is used with water, the ratio of gas to air is typically from 10 to 15% by volume at STP.
(b) the combined flow accelerates as it passes through the inlet 46 and inlet 30a, which are both perpendicular to the direction B of flow through the length of the insert 30, resulting in high turbulence and thorough mixing.
(c) as the internal diameter of insert 30 reduces in flow direction B more intimate mixing occurs before the combined flow enters the tubular section (tube 32) downstream of the insert cavity 30c.
(d) additional mixing takes place in tube 32 and in cavity 34a, in particular in cavity 34a adjacent end 34f, so that the overall pressure drop between P2 and P3 is generally between 20 and 50 PSIG.
(e) the outlet 34c is directed to a pressure control valve 40 where-after the downstream pressure (downstream of valve 40) is usually reduced to near atmospheric pressure. At this point micro-bubbles of typically 5 microns or less are formed.
It was observed that during operation of the micro-bubble generating apparatus (MBG) 10 that turbidity increased indicating the presence of nano-bubbles. In particular it was observed that nano-bubbles formed and remained in suspension in clean tap water for 10 or more minutes. The following experiment was conducted:
A 1000 liter tote was filled with clean tap water and the turbidity was checked. The turbidity was 0.45 Nephelometric Turbidity Units (NTU). The apparatus 10 was run at 8-10 gallons per minute (GPM), circulating in the tote for 10 minutes. The water cleared in 10 minutes and the turbidity was checked again and found to be up to 1.40 NTU. After 1-1½ hours, apparatus 10 was run again for an additional 10 minutes which brought the turbidity from about 1.30 NTU to about 1.50 NTU. As seen in the chart of
In many industries it is beneficial to introduce not only micro-bubbles (i.e. in the order of 10−6 m), but also to introduce nano-bubbles (i.e. in the order of 10−9 m), where extended contact of gases in water or other fluids is desirable. For example, in bioreactors extended contact with oxygen or carbon dioxide is desirable. In algae farming extended contact with carbon dioxide is desirable. In agriculture extended oxygen contact for plants is desirable. In aquaculture maintaining a high dissolved oxygen content in water (for fish and aquatic life) is desirable. In disinfection extended contact with ozone (for more efficient mass transfer) is desirable. In preservatives to kill or deactivate microorganisms residing on the surface of fruits and vegetables maintaining a high dissolved ozone concentration as an example is desirable. In drinking water and other drinking fluids, providing a higher dissolved oxygen content is desirable.
The apparatus 10 may, as mentioned above, be used to treat hydrostatic fracturing flow-back water produced during the hydrostatic fracturing process wherein geological structures are fractured to release hydrocarbons. The flow-back water contains considerable silt, sand, hydrocarbons and other material entrained in the flow-back water. Depending on the geological formation being fractured and the type of hydrocarbon production to be increased, the entrained material will differ.
In most cases sand, silt and hydrocarbons with varying densities will be part of the flow-back. Sand being the most dense will fairly easily drop out of the flow-back in settling tanks if there is adequate retention time. Emulsified hydrocarbons and oil wetted suspended solids can be difficult to separate. Heat and chemicals are often used. However, chemicals and heat energy requirements make this option expensive.
Once the heavier solids have dropped out, the apparatus 10 may be used to separate suspended solids and emulsified hydrocarbons from water. In this case air is not used for creating micro-bubbles. Instead a hydrocarbon gas such as CH4 (methane), C2H6 (ethane), C3H8 (propane) or C4H10 (butane) can be used. These gases will contact and be dissolved in the usually heavier emulsified hydrocarbon that needs to be separated from the water. The emulsified hydrocarbon density will be lowered allowing it to become “free oil” that can be readily skimmed from the surface of the water. Oil wetted solids will be contacted by the micro-bubbles of gas and be lifted to the surface as well.
Light hydrocarbon liquids such as C5H12 (pentane) which is similar to conventional gasoline, can be used in the same manner. In this case the light hydrocarbon liquid will thoroughly contact the heavier emulsified hydrocarbon and oil wetted solids. The lower density overall will allow the solids and hydrocarbons to float to the water surface for skimming. In either case the apparatus 10 may be used equally as well and provide the desired results more efficiently and more economically.
The foregoing descriptions of specific embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the invention and its practical application, to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated.
It is intended that the scope of the invention be defined by the Claims appended hereto and their equivalents.
This application is a continuation-in-part from application Ser. No. 12/386,935, filed Apr. 23, 2009, entitled Method and Apparatus for Mixing and/or Blending Fluids.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 12386935 | Apr 2009 | US |
| Child | 13917477 | US |
