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Air-Lift for Ponds posted by Youmanitas

  1. 1. Air-Lift History By Brian Sidney Johnson Page 1 Louisiana State University -Spotte (1970) promoted the use of airlift assembly which was fixed in the be noted that discharge from an airliftpumps over mechanical pumps for a well of water. A mixture of air will not occur until a minimum air in-number of reasons which include: lower and water would be formed put volume is reached for a given airliftinitial cost, lower maintenance, easy in- within the rising main. Since the configuration i.e. riser pipe diameter,stallation, ability to resist clogging, small density of the air-water mixture is submergence depth, and lift heightspace requirements, simplistic design much less than that of pure water, (Awari et al., 2004, Todoroki et al,and construction, ease of flow rate regu- a very long column of air-water 1973).lation, and versatility in many applica- mixture will be required to bal- The airlift phenomena occurs becausetions. The airlift pump concept was dis- ance even a very short column of of a pressure differential created whencovered by a German engineer in the pure water. As such, the air-water air which has a much lower densitymining industry by the name of Carl E. mixture will begin to flow up- than water is injected into a containedLoescher in 1797 where he found it use- wards though the rising main and water column (i.e. a submerged pipe)ful for pumping wells (Castro et al, it will be issued continuously at and a lower combined density of the1975). Much of the early use of the air- the top of the rising main so long air/water mixture reduces to somethinglift pump was seen in the coal mining as the supply of air is maintained. less than that of the pure water sur-industry because of its ability to extract Most of the literature agrees that rounding. Nicklin (1963) suggestedminerals from deep mine shafts. The first for a given configuration, water that the major factors contributing topractical application of this technology discharge increases as air input the performance of airlift pumps are:in the United States was not seen until increases until an optimum air submergence depth, lift height, gas1846 where it was used in Pennsylvaniain the oil field industry (Castro et al,1975). Airlift pumps have been used forsample collection of seawater (Tokar etal., 1981) as well as water circulationand aeration in aquaculture ponds(Parker and Suttle, 1987; Wurts et al,1994). Airlift pumps have also seen agreat deal of use in recirculating aqua-culture systems (RAS) because of theirability to aerate, circulate, and degasifyCO2 from the water column (Loyless,1995; Gudipati, 2005; Castro, 1975;Reinemann et al., 2001). Reinemann etal. (1987) reported that approximatelyone third of the energy for a properlydesigned airlift pumped RAS wasneeded for overall system operation asapposed to that necessary for a tradi-tional RAS supported by a centrifugalpump and aerator configuration. Similarfindings can be seen in studies conductedby Castro and Zielinski, 1980; Castro et Figure 2-2 Sketch of common airlift pump showing the differenceal, 1975; and Reinemann et al, 2001) between static lift, dynamic lift, and submergence (Gudipati, 2005)Airlift Pump OperationAwari et al. (2004) described an airlift flow rate is reached after which flow, and area of riser pipe.pump as a device for raising liquids or discharge is reduced (Awari et Submergence Depth to Lift Heightmixtures of liquids (mostly water) and al., 2004, Castro et al, 1975; Cas- Ratio, S:Lsolids through a vertical pipe partially tro and Zielinski, 1990; Grand- The total lift height (L) was defined assubmerged in the liquid, by means of jean et al Part 1, 1987; Khalil et the combination of the static watercompressed air introduced into the pipe al, 1999; Morrison et al, 1987; height and the dynamic head loss thatnear the lower end by means of an open- Stenning and Martin, 1968; To- the airlift must overcome. The staticing or nozzle. A rising main covered this doroki et al, 1973). It should also water height was measured as the dis-
  2. 2. Air-Lift History By Brian Sidney Johnson Page 2 Louisiana State University -tance at which water was being submergence, 4 cfm for a 75% sub- diameter or cross-sectional areapumped above the surface of the sur- mergence and 7 cfm for a 66% sub- available in the airlift pump for airrounding water column (figure 2-2). mergence was needed in order to bubble and water interaction/The dynamic head loss was defined as pump 15 gallons per minute. movement. A pipe diameter of 6the pressure loss incurred in the water Gas to Liquid Ratio, Qg:Qw inches was the focus for this study.loop preceding the point of discharge The third factor controlling airlift The physical geometric configurationin the airlift pump which was com- pump operation was the air input of an airlift pump and method of airmonly referred to as frictional head (Qg) or flow of air injected. The gas injection (i.e. air diffusers or openloss. In his application, L was usually to liquid ratio (Qg:Qw) referred to the end pipe) could also influence airliftdefined in units of inches of water. amount of gas that was required to pump operation. Discharge perform- generate a given liquid or water flow ance for smaller diameter pumps has (Qw) in an airlift pump. The Qg:Qw also been enhanced through the useThe second major factor controlling ratio also known as the G:L, helped of various distributed air injectionairlift pump operation was the submer- to identify the level of efficiency that methods i.e. air stones, injectorgence depth (S). Usually defined as the a pump was operating under. In the plates, injector jackets (Khalil et al,vertical distance between the tank wa- aquaculture industry, Malone and 1999; Morrison et al, 1987). Loylesster elevation and the depth of air injec- Gudipati (2005) strived to achieve a (1995) was able to show that an in-tion (static submergence), S, in this Qg:Qw ratio between 1:1 and 2:1. For crease in the overall surface area ofapplication is best envisioned as the example, a Qg:Qw ratio of 1.6 for a gas bubbles within the draft tube ofvertical distance between the water given airlift pump would imply that an airlift (or number of bubbles perlevel in a pitot tube located just prior to 1.6 gallons per minute of air was volume of air injected) through thethe point of air injection and the water needed to pump 1.0 gallon per min- use of an air stone could significantlylevel in the tank only when water is ute of water. Loyless (1995) found enhance performance. This phenome-flowing through the pump (dynamic that lift could have a big impact on non was particularly true for oxygensubmergence). The difference between Qg:Qw. Using a 2″ airlift, he supplied transfer into the water column due tostatic and dynamic submergence re- 9 scfm of Qg at 92% submergence the increased amount of air/waterflected the significant headloss that can (33″ submergence, 3″ lift) and 59% interface which resulted from the in-be incurred as water flows from the submergence (21″ submergence, 15″ creased surface area. However, thesetank through the filter and subsequent lift) and was able to pump 27 and 12 techniques have only really been ef-pipes before reaching the airlift. S dic- gallons per minute respectively. This fective in the bubble flow regime.tates the required energy or pressure correlated to a Qg:Qw ratio of 2.5 and Therefore, these configuration modi-needed to drive the airlift operation. 6.7 for the two configurations. He fications were beyond the scope of was able to show that for a given in- this study.These two terms were usually de- jection depth, a small increase in ei- Airlifts by the very nature of theirscribed together in the form of an S:L ther static or dynamic lift can have a design induce oxygen transfer intoratio or percent submergence. The lift significant impact on airlift perform- the water that is being submergence ratio (S:L) was de- ance. Wurts (1994) conducted several Loyless (1995) studied the oxygenscribed using the following equation: tests using 6″ airlift pumps at 100% transfer properties of 2″ riser airliftHeightLiftTotalDeptheSubmer- submergence (pumped water returned pumps for recirculating aquaculturegencL:S= Equation 2-1 to the surface of the pond) for appli- system (RAS) with lift height andFor an airlift pump having a dynamic cations related to pond destratifica- percent submergence as high as 12″lift of 12 inches and a submergence of tion. He found that at injection depths and 75% respectively. He found that48 inches, the S:L ratio would be 4:1 of 127″, 165″, and 203″ optimal the multiple roles supported by theor just 4 and the percent submergence Qg:Qw ratios equated to 0.39, 0.65, airlift pump could adequately supportwould be 80% with a 20% lift. Gudi- and 0.93 for water discharge per- the circulation and oxygen demandspati (2001) looked at the pumping ca- formance of 27, 56, and 56 gallons exerted by properly sized RAS.pacity of 2″ and 3″ diameter airlifts per minute respectively. Bellelo (2006) successfully utilizedwith percent submergence of 67%, Riser Pipe Diameter and Air Injec- the airlift pump to provide for recir-75%, and 80% of which correlated to a tion Method culation and aeration within a SLDM2:1, 3:1, and 4:1 S:L ratio respectively. Airlift pumps have also effectively filter used for tertiary treatment ofUsing a 3″ draft tube, she found that an performed the role of aeration. The domestic wastewater generated by aair inflow rate of 3 cfm for an 80% riser pipe diameter referred to the road-side rest stop. Reinemann and
  3. 3. Air-Lift History By Brian Sidney Johnson Page 3 Louisiana State University -Timmons (1989) found that the maxi-mum pumping efficiencies for a 1.5″airlift pump occurred in the bubbleflow regime but was limited to thephysical constraint that for 1 unit oflift, over 6 units of submergence wererequired (S:L of 6:1). They also pro-claimed that the maximum airlift oxy-gen transfer efficiencies in the bubbleflow regime are equal to or abovethose reported by Colt and Tcho-banoglous (1981) for fine bubble dif-fused aeration systems and approachthose for U-tube aerators.Airlift Pump Flow RegimesAirlifts have also been described totransform into different two-phase Figure 2-3 Two-Phase flow regimes in airlift pumps as air inputflow regimes as air input increases. At increases (Reinemann and Timmons, 1988)low air input rates, if small bubbles areinjected into the draft tube through adiffuser, the bubbles will remain dis- NOTE: This only covers a small por-tributed over the cross section of the tion of this thesis. Copy the linktube with little interaction and sustain a above for the full text.flow regime known as bubble flow(figure 2-3). As the input rate in- The following pages are other articlescreases, the smaller bubbles begin to that I have found.coalesce into larger bubbles or gasslugs which in essence separate thewater column into the slug flow re-gime. The transition between these twoflow regimes is characterized as thebubbly-slug flow regime where smallbubbles are found suspended withinthe liquid slugs between the larger gasslugs (Reinemann and Timmons,1989).Much of the research performed todate correlates these latter two flowregimes with the familiar pulsatingnature of airlift pump operation(Castro and Zielinski, 1980; Cachardand Delhaye, 1998; Richardson et al,1962). Castro and Zielinski (1980) ad-vocated a simple method for “tuning”an airlift for maximum liquid flow rateby adjusting the air flow until the pe-riod of flow oscillations fell between0.5 and 2.0 seconds for each cycle.This maximum liquid flow rate wouldimply that for a given airlift pump con-figuration, the Qg:Qw ratio reached itslowest level.
  4. 4. Air-Lift Pumps As found on Page 4Air-lift pumps are used entirely in well around the foot piece, and up the submergence of the foot piece below thepumping. Unlike the pumps studied earlier, discharge pipe. The air-water dis- water level in the discharge pipe thethe air-lift pump needs no moving or rotat- charge then strikes a separator or greater the volume (column) of water theing mechanism to produce liquid move- deflector that relieves the water of pump can deliver per unit of time. How-ment. Instead, the pump uses compressed air bubbles and entrained air va- ever, the deeper the foot piece is sub-air to move or lift the liquid. por. The discharge then settles in a merged, the greater the compressed airThe air-lift pump operates on the principle collector tank. The airlift pump can pressure must be to lift the column of wa-that water mixed with air has less weight, or deliver considerable quantities of ter. In other words, a higher column ofis more buoyant, than water without air. water in the manner just described. water (in the discharge pipe) above theWhen compressed air is introduced, a mix- The discharge pressure, at which it foot piece exerts a greater weight or pres-ture of water and air is formed in one leg of sure at the foot piece. The greater thethe U-shaped pipe, as shown in figure 6-25. static water pressure at the foot piece,The solid column of water in the other leg the greater the air pressure must be to in-now has greater weight or is exerting a fuse air with the water. Starting air pres-greater static pressure than the column con- sure is always greater than working airtaining air. Thus the air-water column is pressure. When the pump is started, the static (at rest) level of water is drawn down somewhat to a pumping or working level. In effect, the column of water above the foot piece is decreased or lowered, and this, in turn, decreases the air pressure required to infuse the water with air. In wells where the drawdown is rather large, the pump is sometimes equipped with an auxiliary air compressor, connected in series with the main compressor, for start- ing. Once the pump has been started and the pumping level reached, the auxiliary compressor is no longer required, and is secured. Air-lift pumps have a low dis-Figure 6-25. charge pressure and require more depth so the foot piece can submerge deep enough.forced upward until it discharges over the Additionally, the entrained oxygen in air-top of the U-shaped pipe. In practice, of lifted water tends to make it more corro-course, wells are not dug in a U- shape. sive. In spite of these drawbacks, air-lift pumps have several advantages especiallyFigure 6-26 shows a CENTRAL AIR-LIFT their simplicity of construction and lack ofPUMP. Compressed air is led down an air maintenance problems. Particularly usefulpipe to a nozzle or foot piece submerged in emergencies for deep well pumping,well below the water level. Notice that the air-lift pumps can be used to pumpfoot piece is suspended within a discharge crooked wells and wells with sand andpipe which, in turn, is contained within the other impurities. They can also pump hot-well casing. Notice that the discharge pipe Figure 6-26. water wells with ease. In air-lift pumpis open at the bottom, directly beneath the is delivered, however, is relatively operation, compressed air has to be regu-foot piece. When compressed air is dis- low. For this reason air-lift pumps lated correctly. The amount of compressedcharged through the foot piece, a column or cannot be used to discharge directly air shouldmixture of air is formed above the foot into a water distribution system. be the minimum needed to produce a con-piece in the discharge pipe. The solid col- They do not develop sufficient pres- tinuous flow of water. Too little air resultsumn of water in the well casing, resting sure to distribute water horizontally in water being discharged in spurts, or nothigh above the foot piece and discharge above the ground for any apprecia- at all. Too much air causes an increase inpipe inlet, now has greater weight or static ble distance, and the discharge can the volume of discharge but at lower dis-pressure. This effect forces the air-water only be collected at the well for charge pressure. If air is increased stillmixture upward in the discharge pipe where ground storage. The capacity of the further, discharge volume begins to de-it is vented to the atmosphere through an air-lift pump depends largely on the discharge outlet. In effect, the flow of percentage of submergence of thewater has a U-shape down the well casing, foot piece; that is, the greater the
  5. 5. Page 5 Air-Lift Pumps for Koi Ponds By Larry LunsfordAirlifts are simple but efficient devices Some generalizations can be made inside threaded pipe/hose barb adaptersfor moving water. The concept of airlifts about the relationship of these is a convenient way of connecting thehas been around for centuries. This arti- parameters and the design of an air stone. The threaded end of thecle will show you how you can use an air- airlift. adapter makes it easy to remove the airlift pump to operate your Koi pond, in- • Increasing air injection depth stone for cleaning or replacement. Forcluding waterfalls. Under some circum- increases water flow. small diameter lift pipes, I use a tee tostances, using an airlift can help you to • Increasing lift height decreases connect a single air stone. For large di-realize significant savings on your power water flow. ameter lift pipes, I drill and tap severalbill by using a low power air pump instead • Smaller diameter pipes are ca- holes in the pipe and then screw theof a much higher power water pump. pable of higher lift. adapters into the threaded holes. ToMuch has been written about the use of • Small air bubbles produce more provide more pipe thickness for thread-airlift pumps for aquaculture where air- lift than large bubbles. ing, you can put a pipe coupling in thelifts are used for aeration and circulation. The key to producing an efficient place where you want the air stones andKoi ponds differ from aqua cultural ponds airlift is to find the best air flow. drill and tap through the coupling andin that they are smaller (500 to 50,000 Very low air flow will just produce pipe. I like to put some clear pipe justgallons vs. 100s of thousand of gallons) bubbles in the pipe and no water above the air stones so that I can keepand they usually include ornamental fea- will make it to the top. As the air an eye on things. If your airlift does nottures such as streams and waterfalls. Op- volume is increased, water will exit directly into your pond or filter, beerating these features requires lifting the start to flow to the top. Shortly sure to provide some means to allow thewater instead of just moving it. beyond this point, increasing the air to escape before piping the water volume of air will result in the back to the pond. You may be able toBefore delving into the design of airlifts, most efficient flow of water incorporate a foam fractionator into theit is important to understand their limits. (efficiency measured in water system at this point.Airlifts are extremely good for aerating flow per air flow). Continuing toand circulating water. Airlifts can be good increase the air volume will pro- There are many combinations of designfor lifting water if the amount of lift is duce increases in water flow, but parameters that will work. The diagramsmall. Airlifts will not lift water to great at reduced efficiency. To effi- shows details of the design I used. Onheights. Airlifts are not appropriate for ciently increase the flow of water, my pond I used L-70 linear air pumpsoperating tall waterfalls or filters requir- you should add more lift pipes from AES. These pumps are efficient,ing a lot of pressure (such as a pool style operating in parallel instead of quiet, and capable of producing pres-sand filter). putting more air into a single lift sures of over 4PSI. On my old pond, I pipe. (or use a larger diameter was using an air injection depth of 8,General Airlift Principles pipe.)( bdt) six airlift pipes in parallel, four air stones per lift pipe, and my pond re-Airlift pumps are simple devices. An air- Design Details quired around 36" of lift. Recent im-lift is simply a vertical pipe. Water enters provements in normal pump perform-at the bottom of the pipe and air is in- ance combined with the cost of repair There are many ways to constructjected into the pipe, usually near the bot- kits for the air pumps would cause me an airlift. The diagram shows thetom. The rising air bubbles create an up- to either use a normal pump or design design I prefer which is also theward water current. The top of the airlift the pond with shorter water falls if I design I used on my previouspipe can be from even with the top to pond. The best method of inject- were to use airlifts again.several inches above the pond level. You ing air is to use air stones. Airare probably already familiar with airlifts stones provide the smallest bub- For a typical pond, I would suggest theand dont even know it. Did you ever no- bles which result in the best lift following: Lift Pipe - 1.5", Air Injectiontice the aquarium filters that have air and aeration. When using air Depth - 6, Lift Height - 0 to 24". Use thebubbles going up a vertical pipe to draw stones, you should increase the charts to determine an appropriate airwater through the filter - thats an airlift.diameter of the pipe at the injec- flow. Use enough lifts in parallel toThe critical factors in airlift design and tion area to allow water to flow achieve the desired water flow rate. Tothe range of values that are typical for a better since part of the pipe area keep wear on your air pump reasonable,Koi pond are: is blocked by the air stones. When I would not use the maximum air injec- using multiple airlifts that are tion depth that the air pump is capable driven by a common air pump, the of supporting. Running the pump at• air volume up to 10 cfm lower pressure will lengthen the life of• air pressure (air injection depth) 4 to 12 air stones provide enough resis- tance that the air will distribute the valves which are expensive to re-feet evenly without having to use any place.• water volume 1 to 100 gpm• lift height (water pressure) 0 to 36 other valves to control air flow.inches• lift pipe diameter 0.5 to 3 inches I have found that gluing air stones
  6. 6. Page 6 Air-Lift Pumps By Larry LunsfordAirlift Performance Data ing the bottom of the airlift • Plumbing drag 3 inches (each at a significant depth below way)The results of my tests are shown the level of the pond. Thein the charts. The charts show per- air pressure required is the • Total lift required 18 inchesformance of airlifts in a range that air injection depth plus theis typical of those that would be resistance of air lines and • Flow required 2500 gph - 42used in a Koi pond. The chart ti- air stones. Air stones pro- gpmtled Performance shows the duce a pressure drop of aamount of water that flows for few inches. Looking at the performancegiven air flows and lift heights. chart, you can see that an airliftThe chart titled Efficiency shows The remaining design pa- with 1.5" lift pipe, air injectionhow well the airlift works. You will rameters to be set are: air depth of 6, and lift of 18" willprobably want to design your sys- pump selection, lift pipe di- produce the following watertem to work in the most efficient ameter, number of lift pipes flows vs. air flows:range possible. in parallel. Setting these pa- rameters is largely a matter 7 GPM water with 0.5 CFM air, 11Designing Your Airlift of compromise. Some fac- GPM water with 1.0 CFM air, and tors to consider are: 13 GPM water with 1.5 CFM air.I will assume that you will be usinga diaphragm type of air pump Air Pump: Performance (air To achieve the desired flow of 42(other common types include pis- flow and pressure); purchase GPM, you would need one of theton compressor, rotary lobe blower cost; operating cost; avail- following configurations:and regenerative blowers). Dia- ability; indoor/outdoor use;phragm air pumps operate at air operating noise; mainte- 6 lifts at 0.5 CFM each (totalpressures of 1 to 5 psi (26 to 130 nance. Consider the fail-safe air - 3.0 CFM)inches of water). Better results redundancy of multiple 4 lifts at 1.0 CFM (total air -will be had operating the pump at pumps vs. efficiency of sin- 4.0 CFM)the higher pressure end of its op- gle larger pump. 3 lifts at 1.5 CFM (total air -erating range. The reason for this 4.5 CFM)is that the pumps air output vol- Airlift: There are no goodume changes relatively little with formulas to find the best de- Building a set of airlifts using 6changes in the operating pressure sign. The best way to de- pipes will allow you to use aover its rated pressure range, but velop your design is to use smaller air pump. If space isthe airlifts performance changes the performance charts to more of a concern, you can usesignificantly, producing more wa- calculate the air require- fewer lifts, but they will requireter volume with greater air injec- ments for some possible a larger air pump.tion depths. The water flow rate configurations.and lift required will be dictatedby the nature of the pond. The lift Design Examplerequired is the total of: the dropof all streams and waterfalls, the Lets consider using an airliftdrag of all plumbing, and the drop for a pond with the follow-across the filter system. The air ing specs.injection depth will probably bedetermined by the landscape sub- • Total pond volume 5,000ject to the limits of the air pump. galMany pond keepers will not bewilling or able to use the full pres- • Waterfall height 8 inchessure available from the air pumpsince doing so would require hav- • Filter drag 4 inches
  7. 7. Air-Lift Pumps By Larry Lunsford Page 7
  8. 8. Air-Lift Pumps By Larry Lunsford Page 8Misc.Pond product suppliers should beable to provide you with data onthe performance of their products.They should be able to provide in-formation on electrical power con-sumption and on pressure vs. vol-ume for any air pump that is largeenough to be practical for a pondairlift. Most small aquariumair pumps do not have muchdata available about theirperformance, but thesepumps are too small for thistype of application. Ive donea lot of testing of various air-lift configurations. I will beposting more performancedata as time permits.
  9. 9. by Bob & Doug Bransfield Page 9 Lifting Water with Air has its Advantages Reprinted from Koi USAAir lift is far more energy efficient than stead,powered by the force of ducing bells to fit the 4" pipe aroundwater pumps in moving water between the rising air. Air lift systems by the 2" pipe. Rubber bushings can alsothe pond and the water purification divers to gently lift lobsters be used to connect the 4" pipe aroundsystem. Other advantages include: the from the ocean floor up to the the 2" pipe. A 1/2" hole was drilledbenefits of aeration and air stripping, boat without being harmed in into the 4" pipe at the center and ano need for ground fault circuiting, no the process. The simplest air lift 1/2" PVC pipe was glued in place.electrical contact with the pond, they system is a vertical pipe with an This 1/2" pipe was connected to thecan be modified as heating units, fish air stone dropped down into the air line.and eggs can pass through the entire pipe. The air stone however,filtration system without being harmed, creates resistance to the escap- Multiple air lifts can be used from themultiple systems can be operated on ing air and also creates resis- same power source. High efficiencyone power source they are quiet, they tance to the flow of water in the air pumps and air blowers are pre-dont leak oil into the pond, an impeller lumen of the pipe. Some of you ferred. The depth of injection is acan not get stuck and they are simple to may recall a system using air critical issue to maximize the effi-operate. stones which I was using about ciency of the air pump. Other critical 10 years ago. considerations are the size of theDisadvantages of air lift powered Koi pipe, volume of water to be moved,ponds include a loss of efficiency when A more efficient system em- volume of air, and the size and num-used to lift water a significant height, ploys the injection of air into a ber of the injection holes. If the injec-which limits their use with some water- series of holes in the circumfer- tion holes are too small, they can clogfalls. They are large volume, low pres- ence of the pipe. This eliminates in hard water conditions. The watersure systems, and can not be used the resistance to both air and can exit from the pipe below the wa-when the filter has significant resis- water which is created by the air ter level. If an elbow is used at thetance. Large piping is needed with stone. exit, it would preferably be posi-broad, sweeping bends, and open flow tioned so half the exit flow is belowmedia with low resistance is also re- Ill describe an example of a water level and one half is above thequired. They can be adapted to some, system I have used. I powered water level. Lets save money andbut not all, ponds currently powered by an Everflow 500 filter with a make greater use of air lift systems.water pumps. Sweetwater 2 cu. ft/minute air With the greater use of open flow, pump at 57 watts. This unit fil- low pressure filters, its a goodAir lift is the main system used for tered my 9.000 gallon pond method of powering our systems.commercial fish farming and for small from October to March. Theaquariums. The largest and smallest water was crystal clean (32systems are powered by this method. fish). In the colder months, IWhy did we overlook it in the mid- placed the air pump in a Styro-sized systems? One reason is its hard foam box and wrapped extrato find an inexpensive mid-size air lengths of the air hose in thesource. box to heat the air from the heat of the pump. A 3 vertical 2"The principle of air lift is simple. Air is Pvc pipe was used, and itintroduced into a vertical pipe contain- moved about 50 gallons pering water. As the air rises, it imparts minute through the to the water and forces the wa-ter to move vertically up the pipe. In a To construct this system on thesmall plastic aquarium filter, periodic 2" pipe. I drew a circle andbubbles are released with a column of drilled 8 holes 1/8" in diameterwater in between each bubble. In a on this circle. Around this pipe,large system, the bubble and column of I placed a 4" PVC pipe about 8"water approach is not used: it is, in- long. I modified 2-4" to 2" re-
  10. 10. Air Lift Pumps By Douglas J. Reinemann Page 10 Joshua Hansen Mark Raabe Department of Biological Systems Engineering University of Wisconsin-MadisonRecirculation aquaculture is energy inten- catalogs for the aquaculture indus- pumps. If thissive because water must move continu- try do not market airlift pumps. technology is to become a standard forously through the system to remove Furthermore, companies that sell recirculation aquaculture, the utility in-wastes and replace oxygen. The standard package aquaculture systems typi- dustry needs to become proactive bymethod of moving water is the use of a cally use electrical pumps. The providing information to its prospectivecentrifugal pump. An alternative majority of customers. The information will be ex-pumping system is the airlift pump, which recirculation aquaculture systems tremely valuable to the customeruses the buoyancy produced by entrained are not designed to take advantage when planning the design of the recircu-air bubbles to lift water. Studies of the efficiencies of the airlift lation aquaculture Reinemann (1987), Turk et al (1991), pump. Changesand others indicate that use of the airlift in hydraulic grade line through thepump is substantially more energy system are typically too great. Thisefficient for moving water under low-head is done as a cost saving measureconditions than centrifugal pumps. The (when usingeconomic benefits of the airlift centrifugal pumps) to avoid the usepump are further increased when the elec- of multiple pumps. Conversely,trical requirements for aeration, carbon multiple airlift pumps are not adioxide removal, and foam significant costfractionation are considered. The airlift consideration; they are actuallypump does all of these simultaneously, necessary to maintain the hydraulicwhereas separate component systems grade line within the optimal rangeare required when standard pumps are of the airliftused. Energy usage for a combination pump. Furthermore, where airliftspumping and aeration are are employed, the design of theapproximately one-third the cost of a con- airlift typically employed does notventional pumping system (Reinemann et maximize itsal., 1987). performance capabilities. For in-The airlift pump has other important bene- stance, the flow rate is typicallyfits to the aqua culturist. Capital costs are less than optimum because the liftsignificantly less than that for is either too high Operating principals of the air-liftstandard electrical (i.e., centrifugal) or the pipe diameter-to-rise is too pump.pumps. The simplicity in its design—there large. Hydraulic efficiency is also Lift is the distance between the surface ofare no moving parts—means that reduced when obstructions such as the water and the discharge point or themaintenance costs are also low. air stones are vertical distance the water must beDespite the fact that the existing body of placed in the airlift tubes. moved above the surface. (1 to 2)research indicates that the airlift pump is It is anticipated that the growth ofunder most instances the preferred recirculation aquaculture will pro- Total lift is the distance between the airsystem for recirculation aquaculture, the vide a new market to the utility injection point and the water dischargeaquaculture industry is generally biased industry for point, or the total vertical distance thatagainst investment in culture electrical power. For example, the water must be moved. (1 to 3)systems employing the airlift pump. The based upon an energy requirementreasons for this are lack of awareness of its of 8 Mcal per kilogram of fish Submergence is the distance between theinherent advantages, lack of (Reinemann, 1987) water level and the air injection point (2available systems that employ the airlift and a business producing 150,000 to 3).pump, and performance deficiencies in pounds of fish per year, the ex- Submergence ratio is the ratio of theinstances where they are used. The pected annual energy requirement distance between the air injection pointsimplicity in its design—made mostly is approximately and the surface of the water (2 to 3) tofrom PVC pipe—makes it less profitable 475,000 kWh. The most efficient total lift (1 to 3).to market relative to standard use of this electrical power will beelectrical pumps. Most of the major supply achieved through use of airlift
  11. 11. By Douglas J. Reinemann Air Lift Pumps Joshua Hansen Page 11 Mark RaabeMore Accurate Pump Curve with All ParametersF.A. Zenz with AIMS proposed a way to relate mostimportant parameters in the Journal of "Chemical En-gineering Progress" in 1993. The parameters and hisgraph are summarized below. Pumping rate Submergence Ratio Required Air Flow [GPM] Submergence [ft] Lift [ft] [%] [cfm] Source 200 5 1.25 80 Not possible Zenz(1993) 200 8 2 80 28 Zenz(1993) 200 10 2.5 80 23 Zenz(1993) 200 15 3.75 80 17 Zenz(1993) 200 ? ? 80 23 Company A 200 ? ? 80 19 Company B Comparison of Three Pump Curves Required air flow is calculated for the condition of 200 GPM, 6" airlift pump, submergence ratio of 80%, Obviously the graphs by Company A and B are erroneous.
  12. 12. Page 12This pump uses compressed air, delivered to the bottom of a submerged pipein a well, to lift an air/water mixture to the surface. The pump principle is that an air/watermixture, with as little as half the density of water, will rise to a height above the water levelapproximately equal to the immersed depth of the pipe. Depending on the lift required, thissubmersion depth may require a deep well (refer to “Total Length” in table 2 below). The airline can be placed inside the discharge pipe or, as shown in figure 8 below, outside and parallelto it. A ‘foot piece’ breaks the air into small bubbles that conserve air and improves efficiency.A homemade device can be used consisting of 1/16” holes in a copper tube that extends upinto the pipe. (We would likely use an air stone or a diffuser).The main advantage of this pump is its simplicity. The disadvantages are the very low overallefficiency when higher lifts are required. Submergence in Table 2, below, is“ minimum” (the least submergence but requires more compressed airper volume of waterdelivered) or “best” (least amount of compressed air per volume of water delivered but deepestwell—”total depth—required). Compressed Air Inlet Lift (L) Static Water Level Drain Total Pumping Water Level Down Length (L+S) Submergence Submergence Length Percentage = 100* S / L+S (S)
  13. 13. Page 13Tested Flow Rates Water pressure air flow flow in diffuser in PSI in LMP GPM lift Pipe dia submergence7 micron x 3" dia 5 25 1 20 3" 52"50-90 micron x 3" dia 2 22 3 20 3" 52"50-90 micron x 3" dia 2.25 62 4.5 23 3" 52"90-130 micron x 3" dia 1.8 30 5 23 2" 52"70 micron 3/4" muffler 2 28 5 23 2" 52"50-90 micron x 3" dia 2 32 5 23 2" 52"250 micron 3/4" muffler 2 96 5 23 3" 52"90-130 micron x 3" dia 2 46 5.5 23 2" 52"90-130 micron x 3" dia 2.2 94 6 23 3" 52"70 micron 3/4" muffler 2 45 6.6 23 2" 52"50-90 micron x 3" dia 2.4 90 6.6 23 3" 52"250 micron 3/4" muffler 2 48 7.5 23 2" 52"50-90 micron x 3" dia 2.2 50 7.5 23 2" 52"250 micron 3/4" muffler 1.9 62 8.5 23 1.5" 5290-130 micron x 3" dia 2 62 8.5 23 2" 52"35 micron 3/4" muffler 2.4 34 8.5 23 2" 52"250 micron 3/4" muffler 2 62 10 23 2" 52"70 micron 3/4" muffler 2 62 10 23 2" 52"35 micron 3/4" muffler 2.5 50 10 23 2" 52"250 micron 3/4" muffler 2.1 92 11.1 23 1.5 5290-130 micron x 3" dia 2.1 78 12 23 2" 52"70 micron 3/4" muffler 2.2 78 12 23 2" 52"35 micron 3/4" muffler 2.75 64 12 23 2" 52"250 micron 3/4" muffler 2 78 13 23 2" 52"90-130 micron x 3" dia 2.2 92 13 23 2" 52"
  14. 14. Page 14 Alita AL-80 Alitas Published Flow Actual Flow as Tested 120 4 100 3 80Flow L/min Flow CFM 60 2 40 1 20 0 1 2 3 4 5 6 7 8 PSI
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