Presentation: Efforts to Advance Ultrasonic Cleaning for Online Oil in Water Instruments



Presentation by Russell Hempsey, Inov8 Systems

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1: Introduction

This presentation is a summary of significant progress that Inov8 has made with R&D efforts to advance ultrasonic cleaning for online oil in water instruments. The primary goal in this has been to enable ultrasonic cleaning to be effective in the most extreme environments, including when heavy scale build is prevalent, also in high pressure (up to 35 bar) environments.

Furthermore Inov8 Systems wanted to mitigate the damage to optical windows that is caused when ultrasonic cleaning is set to maximum settings. The end goal is to eliminate the trade-off that exists between effective cleaning of the analyser and lifespan of the measurement window.

Inov8 Systems currently have a staff of 14 people, and almost all have 5-20 years experience in produced water, specifically with online oil in water analysis. The company goal has been to progress online oil in water technology to the highest possible level, and so eliminate some of the drawbacks that are commonly experienced with this type of measurement.

After an initial 2 ½ year R&D phase that started in 2016, the products and company was commercially launched in late 2018.

2: Oil in Water Analysis

Here you can see images of our main produced water technology. On the left is the inline probe that is placed directly in the process using the flange connection, and is an in-situ measurement. The unit on the right is the sidestream type unit that requires a bypass system that directs a portion of process fluid through the measurement chamber that extends from the base of the enclosure. Part of our design remit was to make these units as compact as possible, and for size reference the probe unit is less than 1m in length and the bypass unit is the size of an ipad.

3: Laser Induced Fluorescence

The measurement technology is Laser induced fluorescence. This is a well known and industry accepted measurement method for online oil in water analysers, and can be a very robust method, but like most optical measurements it heavily relies on the optical window remaining clean at all times. The optical window can be clearly seen on the probe unit on the right where the laser light is shining through.

4: Cleaning with Laser Induced Fluorescence

This graph of ppm versus time shows how cleaning is critical to the success of laser induced fluorescence, and illustrates what happens when the optical window is allowed to get dirty. You can clearly see how on the left hand side the ppm is fluctuating normally and responding to changes in oil in water content. As time progresses, and the window gets dirty the fluorescence response starts to dampen and will eventually read zero as no more light can pass through the window. This period of fouling can occur in a matter of minutes in extreme circumstances, or in the best case scenario within a few days. Either way unless the window is perfectly clean the measurements cannot be relied upon to be accurate.

5: Rapidwave Ultrasonic Cleaning

Ultrasonic cleaning is known to cause damage (specifically etching) to the measurement window of online oil in water devices, and results in having to change the window on average every 18 months. However, this interval varies depending on the duration and frequency of ultrasonic cleaning which is also related to the difficulty of each application, and is almost always a trade-off between cleaning efficacy and window life. To break this down into easy to understand numbers we can look at the pulses per hour required to clean in certain applications as shown in the table.

The pulses per hour required to clean in certain applications can clearly not be achieved within conventional ultrasonic cleaning, for example achieving 9,000 pulses per hour with standard ultrasonics that only pulse once per second is not possible.
Our research also showed that ultrasonic cleaning is only effective for CLEANING in the first few milliseconds of an ultrasonic pulse, thereafter the ultrasonics are only damaging the window and so is wasted and detrimental energy.

Therefore we understood that to optimise ultrasonic cleaning we had to combine the ability to provide up to 10,000 pulses per hour that were of short enough duration to only deliver cleaning action and not cause damage (or etching) to the window. This led us to develop Rapidwave ultrasonic cleaning that delivers very rapid/short pulses as shown in the video. WARNING this video contains sound so be careful to turn the volume down if using a headset.

6: The Impact of Rapidwave Ultrasonic Cleaning

To understand the impact of Rapidwave ultrasonic cleaning we can review some different scenarios and see how it compares to conventional ultrasonics.

A normal setting for conventional ultrasonics would be to activate for 20 seconds every 15 minutes, which delivers 80 pulses per hour and would be sufficient to clean in applications with less than 10ppm crude oil in water. This would give a predicted (and field proven) lifespan of 18 months before the window becomes etched and has to be changed. The highest setting that would be feasible would be to activate for 20 seconds every minute, which delivers 1200 pulses per hour and is sufficient to clean in crude oil concentration greater than 500ppm. This provides a lifespan of just over 1 month before requiring a service to change the window and is still not sufficient to clean any type of scale build-up.

The Rapidwave normal settings of 20 seconds every 15 minutes delivers 800 pulses per hour and is sufficient to clean in high oil content applications that are greater than 500ppm. This provides a modelled lifespan of 566 months before etching will occur. This figure is not field tested, and it this point should only be considered a modelled figure, however the cleaning efficacy is field proven.

The Rapidwave high settings of 5 seconds every 20 seconds delivers >9000 pulses per hour, and is effective for cleaning in even high scale applications, and provides a lifespan of 30 months. These numbers are actual field data and to date a number of analysers have been in operation for 30 months under such conditions and so far the optical window has remained clean with no damage or etching .  This information satisfies our remit to understand and improve the efficacy of ultrasonic cleaning and extend the life of the measurement window.

7: Enhanced Cleaning through Ultrasonics

The video about to be played shows the optical window in a probe that has been coated with crude oil to replicate a high oil in water scenario. The ultrasonics are then activated to demonstrate the effective cleaning provided by the enhanced cleaning.
NOTE: This slide contains another video with sound, so please reduced sound on your headphones accordingly.

8: Optimising the Use of Ultrasonic Cleaning

The next stage of our R&D with ultrasonic cleaning has been to optimise the use of ultrasonic cleaning in high pressure applications.
Ultrasonic cleaning works by producing micro-bubbles in water (AKA cavitation) that subsequently implode and provide the intense turbulence that leads to effective cleaning. At low pressures of less than 5 bar this can be achieved quite easily, however the action of pressurised water exceeding 10 bar severely limits the ability for cavitation to occur above this threshold.
Our R&D efforts in this field have focused on achieving the required ultrasonic power in the correct location that can deliver cavitation in water pressure at 35 bar.

9: Transducer Simulation

So many parameters affect the resonance of a transducer. Material, length, width, shape etc, Manually calculating a simple rod transducer is straight forward, however, designing a transducer to operate efficiently at the selected frequency, reducing displacement energy to facilitate a hold point (flange) and the amplifying the energy to maximise displacement energy at the desired location is close to impossible.

Historically, what’s been achieved through trial and error suffers from poor efficiency, stability and repeatability. The software recently developed to effectively design and simulate the desired transducer, has not only saved month and years of build and test time, but has also provided a transducer that is ultra-efficient and effective.

Historically, 300-500 Watts of energy has been used in this type of cleaning technique in low pressure applications, mainly to overcome in-efficiencies in the design. Using the software to produce an ultra-efficient transducer reduces cavitation energy requirement to as low as 10Watts, but more importantly for high pressure, allows increased energy efficiency to translate into cavitation at very high pressures. Typically the current Inov8 Systems high pressure transducer operates at 125Watts, still a fraction required in earlier design techniques.

You can see below a screen capture of the transducer simulation and a picture of the actual transducer being tested for resonance efficiency and Q.

10: Function Testing of the Transducer Assembly

The software has allowed us to develop and manufacture a transducer that is highly efficient, uses less power and can produce cavitation at high pressure (35 bar).

As much as we would like to trust the software completely there is still a degree of trial and error involved in transferring what is modelled into an actual working transducer, and then most important of all incorporating that into an analyser probe that will clean effectively at high pressure.

Again just there is noise involved in the following videos.
The video on the left shows our function testing of the transducer assembly. This is the first stage in testing that allows our R&D team to verify that the transducer is following commands from the controller and is pulsing at the correct power output, and ultimately producing cavitation.

The image in the middle is our test set-up with the high pressure transducer fitted to the complete probe assembly and placed into a pipe that can be pressure up to whatever pressure is desired, in order to test the cleaning at various pressures.
The final video on the right shows the end result of the R&D phase. The full probe assembly is installed in a test pipe, the measurement window has been coated with crude oil and the ultrasonics are activated and the crude oil is immediately dispersed and ejected from the window.

Conclusion: Rapidwave Ultrasonics with novel transducer assembly can be used to clean in high pressure applications.

11: Conclusion

The analyser has passed FAT, delivered to customer and installation/commissioning is pending. Results will be fed back in due course…. Watch this space.