E3 Solutions' Rotary Atomizers vs Competitive Pressure Nozzles

E3 Solutions' Rotary Atomizers vs Competitive Pressure Nozzles

E3 Solutions' Rotary Atomizer vs Competitive Pressure Nozzles

 

The enhanced evaporation technology market is still advancing and there are different systems being developed and refined. When examining natural evaporation, there are many factors, such as water temperature, wind, humidity, water vapor pressure, dew point, outside temperature, and many more. There are also many factors to consider when choosing to introduce enhanced evaporation into your process. This blog post will clarify some main differences between E3 Solutions Varimax® mechanical rotary atomization versus pressurized spiral and pressurized hollow nozzles ie, snow cannons.


E3 Solutions' patented rotary atomization unit consists of a small compact 2-hp electric totally enclosed water cooled motor that can operate at speeds between 0 and 15,000 rpm’s using a variable frequency driver (VFD). The rotary atomizer hub Figure 1 is attached to the motor, and the water flows through several tubes around the motor down into the hub nearest the motor shaft. The water dually fractures through the hub, which has 180 small holes and 300 serrations. The water flow uses very little water pressure. The water flow is similar to a garden hose faucet and engineered for a maximum flow rate of 10 GPM.

Varimax Atomizer Hub
                                         Figure 1. Varimax atomizing hub has 300 serrations and 180 water fracturing outlets.
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The water flow rate is fractured through the E3’s patented hub using centrifugal force. This process allows higher TDS waters to flow smoothly through the atomizing hub without causing significant friction or wear. In Figure 2, you will notice a closeup view of the E3 atomizer hub using a 5 GPM flow rate through the hub. The pictures are time lapsed from 0 RPM to show the evolution of fracturing water once the atomizing hub begins to rotate.

Varimax Atomizer Timelapse                                                          Figure 2. Time-lapse E3 atomizer hub at 5 GPM.

As the E3 atomizer gains speed above 500 RPM, you will notice the 5 GPM flow turned into a fine mist and in the shape of a V-pattern being horizontally distributed (Figure 3). The horizontal V-pattern gives the small micron droplets a little boost upwards and outwards from the E3 hub, allowing maximum interaction with the surrounding air. The surrounding air moves the mist horizontally across the water surface dispersing and mixing with the available dry air.

Varimax Atomizer Timelapse2                             Figure 3. Time-lapse E3 atomizer hub at 5 GPM showing continued fracturing and V-shape pattern.

My Movie 2

                                                  Watch the rotary atomizer video in real time.

Once the atomizer reaches higher speeds, the droplets become smaller, creating more surface area of the volume of throughput. See the E3 droplet study. The only way to view the size of these small droplets is through a laser. The laser is positioned 12” away from the atomizer hub, and the full spectrum analysis is performed. After the results are collected, the results reveal the average micron spectra of the droplets created and converted to volumetric percentages and additional surface area. E3’s spectrum analysis revealed the droplet spectrum for most operational settings is 80% of the water volume was 150 microns or less with averages between 50 to 120 microns.

Why is it essential to know droplet spectrums for enhanced evaporation equipment?
There are two main reasons, one is related to performance, and the other is related to overspray conditions. An Ohio State drift study concluded that water droplets <50-microns evaporate entirely within 18 inches from the discharge point in relative humidity levels between 20-80%. See Figure 4. The same study also analyzes the drift distances of different size droplets using changing weather and wind speed inputs.


drift50micron                                                                 Figure 4. Drift distances for 50-micron drop.

 

Rotary atomization allows for the manipulation of droplet sizes by changing the speed of the atomizer that allows control during overspray conditions. Spiral and pressure nozzles only operate in an on-and-off operation to control overspray. Therefore, the only way to change droplet sizes is through nozzle replacement or water pressure changes. Table 1 shows E3’s micron spectrum using different atomizer speeds, while Figure 5 shows competitive pressure nozzle size and average micron mean.

Table 1. Droplet size data for different Varimax® motor speeds at 5 GPM.

Flow rate, GPM

RPM

Mean Dv0.5, µm

STD

ERROR

Mean D31, µm

STD

ERROR

5

2400

264.63

4.68

177.36

+/- 1.45

5

4500

169.05

0.96

106.39

+/- 0.48

5

6000

154.00

1.52

88.48

+/- 1.15

5

10200

98.68

1.13

50.39

+/- 0.31

5

10800

95.65

1.37

47.65

+/- 0.80

5

11500

98.68

1.06

33.03

+/- 2.00

5

12000

83.73

1.60

33.93

+/- 0.57

5

12500

82.31

2.00

35.02

+/- 0.32

 

vmdvspressure

 Figure 5. Mean Droplet Diameter of Spraying Systems CO. 8-15W Hollow Core Pressure Nozzle.

 

One of the top benefits of using E3's rotary atomizers versus pressurized nozzles is E3's flow rate design. E3's uses just enough head pressure to flow the exact amount of water to the atomizing hub from the water body. E3 uses a titanium sump style pump designed for high corrosive and salt environments. This results in no clogging or buildup once the water is centrifugally forced out of the atomizing hub.  Figure 6 shows the E3 Varimax atomizing hub after several months operating in 90,000 TDS produced water.  Figure 7 shows competitive pressurized nozzles clogging in a high TDS application.  

 

IMG-1752

   Figure 6. Varimax Hub operating in 90,000 TDS Produced Water

 

Screen Shot 2020-09-12 at 11.12.16 AM Figure 7. Pressurized nozzles clogging with buildup

 

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The Spraying Systems Co. 8-15W nozzle is used on a snowmaking type cannon at 40 psi. The 8-15W nozzle has a mean water droplet average of 500 to 600 microns. The cannon uses over 270 8-15W pressure nozzles to obtain a 25 L/S flow rate. These nozzles are spaced very tightly around the end of the cannon creating multiple collisions of 500-micron droplets due to each nozzle having a 100° cone spray angle. See the nozzle cone spray video that shows the dispersion angle. Several studies regarding the collision-coalescence of water droplets prove droplets increase in size as they move away from the nozzle. “During this process, smaller droplets collide, form larger droplets, and lose their momentum due to drag. Thus, the droplet diameter starts increasing away from the nozzle. As the droplets become larger and slower, the probability of subsequent droplet-droplet collision increases, resulting in further coalescence.”  See Figure 8 for a closer look at the coalescence location beyond the initial fracturing from a pressure hollow-core nozzle.

                           

figure6
                                                      Figure 8. Hollow Pressure Nozzle Coalescence Zone

In a recent white paper offered at a mining conference, it explains the use of the 500-micron nozzle from Spraying Systems Co. The main reason for the choice of the nozzle is because it provides higher flow rates and is less likely to clog. “Large-bore nozzles were selected to maximize throughput and prevent blockages by entrained solids.” The paper continues stating that a single unit can pump 600 GPM and blow it up to 150’ high into the air. The most intriguing point made in this paper is the 50% evaporation rate based solely on the droplet size reduction and not droplet reduction. In the reference section of the paper, it mentions the droplet size information used was from a dust suppression upgrade project using the same Spraying Systems Co. nozzle. However, in the reference mentioned, it seems to suggest the complete opposite of using the nozzle size and flow rates for evaporation.
Here are the critical highlights from the Project showing that the best use of the same nozzles is for dust suppression:
  • Evaporation, although beneficial in regards to overspray, is not a significant factor for the VMD droplet sizes produced by the proposed nozzles.
  • For the prevention of dust generation for stockpiles, standard hydraulic nozzles that produce drops between 200 and 1,200 μm are generally used.
  • The size of the droplet affects the vertical velocity at which it falls. A larger droplet will fall at a greater speed than a smaller droplet in the same conditions.
  • 500-micron droplets fall in a speed similar to light rain.
  • Water drops that are greater than 300 μm in diameter will experience negligible evaporation from a fall over 1000m in an atmosphere with relative humidity as low as 40% (Pruppacher & Klett, 1980; Gunn & Kinzer, 1951).
  • Since the fall distance from the Spray Tower will be no more than 40 m and the VMD is 500 μm, we are basically off the chart ie the effects of evaporation for the VMD can be disregarded.

Figure 9 shows the light rainfall effects of shooting 500-micron water over a large open-pit mine wall, and the results in the image speak for themselves. The question to consider in using snow cannon pressurized nozzle technology is do you have over 1000m of drop on your project site for a 500-micron drop to evaporate.

Screen Shot 2020-09-12 at 9.49.23 AM                                                    Figure 9. Snow cannon units operating over open pit mine site.

Figure 10 other snowmaking/evaporation cannon style systems use pressurized spiral nozzles to obtain droplet fracturing.

figure8                                                                    Figure 10. TF Series Spiral Nozzle by Bete.

Bete and Spray Systems manufactures a typical spiral nozzle for disposal purposes. Spiral nozzles need pressures between 40 to 400 psi to gain needed flow rates. The snow cannon system places around 30 of these nozzles on a 2” ring and are placed tightly together and angled towards the inner core of the cannon face. Flow rates vary based on the pressure provided by secondary pump systems. The increased pressure from the pump system increases flow rates through the spiral nozzle and increases atomization. Because pressures are higher with spiral nozzles, wear is a considerable challenge to detect. As these nozzles deteriorate and wear, increased flow rates or lower spraying pressures increase droplet size.

Figure 11 shows how difficult it is to monitor wear in a spiral nozzle. In applications with higher TDS, nozzle tip wear would be difficult to detect and, in essence, create challenges in evaporation droplet sizes, not to mention the increased coalescing of drops.


figure9                                                 Figure 11. Tip Wear as shown in Spray Systems Technical Appendix

Figure 12  average droplet sizes produced from spiral nozzles are shown in Spray Systems Technical Reference Appendix with a snapshot shown. Based on typical pressures and flow rates, the average micron calculation for a hollow cone spiral nozzle is between 200 microns at a flow rate of 0.16 GPM up to 1250 microns at 38 GPM. The approximate flow rate for a 30 nozzle system would be approximately 3.6 GPM, which would likely place the droplet sizing between 300-400 microns, making this nozzle friendlier for dust suppression.

Rotary Atomizers vs Pressure Spiral Nozzles-Aug-05-2020-07-30-29-57-PM                                                    Figure 12. Hollow Cone Spiral Nozzle Micron Sizing

Bete nozzles provided micron data from their most popular used evaporation and snowmaking spiral nozzle tips. Bete’s engineer further stated the 3/8” TF12XPN is the smallest clog-resistant nozzle purchased for snow cannons or fan guns.

Figure 13
 for the data provided by Bete. Bete provided additional data for smaller nozzles that are not as clog-resistant and have D32 droplet sizes at 112 and 140 microns. The models offered were the TF6NN and TF8NN.


figure11                                                         Figure 13. Bete Fan Gun Nozzle Data

The snow cannon design used in many evaporation projects uses the concept of saturating the flow of ambient air with lots of water flow. The coalesced water begins its saturation point at the end of the cannon to cool the temperatures below wet-bulb when mixing with outside ambient air. Once the wet-bulb temperatures lower, snowmaking potential rises mostly in high altitudinal locations.

Figure 14 shows the high amounts of saturation at the end of the fan-style evaporator. A two-year consumptive water loss from man-made snow study determined a mean loss of only 6% from evaporation and sublimation during initial loss calculations. When you saturate the outside air to 100% humidity, the remaining water falls back to the surface, similar to rain.

 

figure12

Figure 14. Closeup snow cannon

 

The only in-depth evaporation study found using fan-style cannons was performed in the Southeast United States near Savannah, GA. Due to the significant fallback associated with these styles of evaporation systems, much lower volumes of water were used with the spiral nozzles so that data could be collected. The study concluded if significant fallback was tolerable, then the expectation of evaporation efficiency would be 10-12 GPM from the 70 GPM spray rate. This is a 14% modeled evaporation rate during daylight operation only and was never confirmed directly from the study.

One of the other limiting variables for the fan-style cannon evaporators is when they operate from the land. Overspray concerns from differing wind directions throughout the day cause shutdowns that lower production.

Figure 15, which shows the 180 degrees of operational capacity.

                                                         Rotary Atomizers vs Pressure Spiral Nozzles-Aug-05-2020-07-30-29-40-PM                                                      Figure 15. Land based pressure nozzle cannon shut down zone

Figure 16 land-based cannon configurations have difficulty when winds blow back towards the saturated blast zone, which causes a severe overspray condition back onto the land behind the system.


Figures 17-18,
these show the typical way cannons combat overspray to operate without shutting off. The cannons often get lowered to a position of shooting the saturated stream directly back into the ponded water.


Rotary Atomizers vs Pressure Spiral Nozzles-Aug-05-2020-07-30-28-45-PM                                                              Figure 16. Overspray condition using land-based cannon


Rotary Atomizers vs Pressure Spiral Nozzles-4                                                                          Figure 17. Cannon style overspray position

 

figure16                                                                Figure 18. Cannon overspray setting in high wind region.

Other considerations during overspray operations are the mist digestion of dissolved solids back into the internals of the cannon fan blades and the fouling of the spiral nozzles, as noted in this Salton Sea study with a few notations from the study bulleted below.  Snow cannons offer an optional vibration shutoff to combat the digestion concerns. 

Figures 19-20 show a cannon unit with mist digestion.

  • The nozzles on the units plugged up.
  • Mist fouling of the evaporators was a major problem.
  • The inline filters had to be cleaned numerous times per day to keep the units in operation.
  • Left unattended, enough mist could be digested into the units to force the impeller blades
    out of balance.
  • The device had to be shut down every couple of days and pressure washed both inside
    and outside of the housing. This process was time-consuming and was an endless task in the course of project operations.
  • Mist fouling of the evaporators was a major problem. Any wind from a non-aligned direction resulted in mist surrounding the units. Much of the mist was sucked into the impellers of the turbofans, resulting in deposits like those shown in figure 5.8. Left unattended, enough mist could be ingested into the units to force the impeller blades out of balance. The devices had to be shut down every couple of days and pressure washed, both inside and outside of the housings. This process was repetitive and time consuming for project operation.
  • During the test, the machine could average 54 gpm. throughput at a power consumption of
    93 kwh. Our machine operates at 80 gpm. using less than 75 kwh. The client must understand that this is gallons pumped through the unit, not water evaporated.
  • To reduce, but not eliminate, the risk of mist digestion by the EES units, each
    EES unit needs to be robotically slaved to multiple wind direction, wind speed, and wind shear detection systems. Any fouling by mist digestion by a significant number of EES units would be very expensive and time-consuming to clean up.

figure17Figure 19. Mist digestion side view


figure18Figure 20. Mist digestion inside cannon

 

Figure 21 another type of pressurized nozzle system has recently entered the market. The design places a few pressurized atomization nozzles just above the top of the surface water. This helps the system alleviate some overspray concerns. What the system doesn’t provide is enough evaporative spacing above the water level, where studies have shown higher levels of saturated water vapor interfaces. Based on the Craig & Gordon model from 1965, turbulent, dryer wind is needed to create an uplift into the higher layers from their modeling interfaces.


Screen Shot 2020-09-12 at 10.20.25 AMFigure 21. Pressurized nozzle operating just above the water to vapor exchange interface

 

Efficiencies in electrical consumption during evaporation bear mentioning when comparing the differences between rotary atomization and pressurized nozzles for enhanced evaporation projects. Table 2 depicts the electrical differences between E3’s rotary atomizers and a typical cannon setup. The cannon needs a separate 160kW/h water pump in conjunction with a 75kW motor to spin the cannon blades versus E3’s Varimax 60 unit only using 9.7kW/h.

 

Table 2. Electrical Cost Differences E3 vs Snow cannon
Screen Shot 2020-09-12 at 9.37.40 AM
                                                    

Performance comparisons in Table 3 show typical evaporation rates in high humid locations such as the Southeast United States operating 14 hours daily.


Table 3.
Performance Differences between E3 & Snow cannon

Screen Shot 2020-09-12 at 9.35.23 AM
                                                            
Table 4 depicts the efficiencies of evaporative volume OPEX cost between the two systems and illustrates that higher water volume throughput doesn’t necessarily equal more evaporation. It does mean it will cost you more per 1,000 gallons of the operational expense using a snow cannon versus an E3 Varimax accelerated evaporation system to achieve a similar amount of evaporated volume.

 

 Table 4. Actual Evaporation OPEX Cost
Screen Shot 2020-09-12 at 9.40.11 AM
                                                                                       
There are many sustainable advantages related to using rotary atomization versus pressurized nozzles. The electrical cost and cost per 1,000 gallons evaporated show two of the main differentiators in the side by side comparisons. The cannon style evaporator aims large water droplets high into the air with most of them raining back. The E3 rotary atomization technology creates smaller droplets that quickly evaporate and mix with the available unsaturated dry air.

 

Please feel free to contact one of E3’s evaporation experts to discuss how rotary atomization will effectively respond to any of your accelerated evaporation needs.

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