Innovative Climate Change Emissions Reduction: The Cargo Ship Flettner Rotor Centrifugal Vortex Exhaust Scrubber
Abstract:Our global cargo ship fleet is responsible for 4% of global climate change emissions as well as particulate pollutants that leads to roughly 7.6 million childhood asthma cases and 150,000 premature deaths annually. Heavy fuel oil or “bunker” is a residual product of petroleum refining for gasoline and diesel and thus unlikely to go away. Marine heavy fuel oil engines are a mature, low cost, and reliable technology. Scrubber technology is well established but costly, adds complexity, and may even have unintended side effects such as reduced cargo capacity, increased maintenance, and water pollution. A novel centrifugal vortex scrubber integrated into a Flettner rotor creates a hybrid wind and fossil fuel powered vessel that cleans exhaust while generating propulsive power that more than compensates for the engine power loss through the scrubber, and the initial capital investment. 3D CAD modeling, computational fluid dynamics analysis, and prototyping were used for design iterations and testing. Flettner rotor performance was tested in a water test tank and wind tunnel and was not affected by the presence of the scrubber. The exhaust scrubber was simplified to replace high maintenance moving parts with a cyclonic separation design that fits well in the Flettner rotor geometry. The scrubber removed 42% of particulate matter. Under even mild wind conditions, the Kutta–Joukowski force generated by the Flettner rotor, more than overcomes the engine efficiency loss due to pressure drop across the scrubber. This Flettner Vortex Scrubber shows promise as an economically attractive design to limit emissions from heavy fuel oil engines in marine applications, as well as provide an auxiliary propulsion source to reduce heavy fuel oil consumption, both climate change causes. If conservative estimates of Flettner rotor auxiliary power performance scale to the global cargo shipping fleet, it could mean a climate change impact equivalent to taking five million cars off the road. Combining Flettner rotors with an exhaust scrubber will make the investment more attractive for ship owners and operators and can increase the rate of adoption of this important climate change, and public health risk mitigation technology.
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Additional Project Information
Innovative Climate Change Emissions Reduction: The Cargo Ship Flettner Rotor Centrifugal Vortex Exhaust Scrubber
This is an exciting time for cargo ship naval architecture as technologies as new as AI and as old as wind power converge to reduce our transportation climate change footprint.
Despite electrification of vehicles, optimistic attempts to “leave it in the ground,” and a fossil fuel shift to plastic, petroleum fuels will be part of our lives for decades, and with it the heavy fuel oil byproducts of gasoline, diesel, and jet fuel. This dirty residual fuel is difficult to further refine and thus finds a use powering our cargo ship fleet, which are coming under increasing scrutiny as they contribute 4% to global climate change contributions. (2020 IEC rule)
Our desire to use raw materials from around the globe or take advantage of relative efficiencies in production shows no sign of slowing, therefore our global cargo fleet consisting of over 100,000 vessels will persist.
Engineering solutions abound, however many are costly, add complexity, and may even have unintended side effects such as reduced cargo capacity, increased maintenance, and water pollution.
A novel centrifugal vortex scrubber integrated into a Flettner rotor creates a hybrid wind and fossil fuel powered vessel that cleans exhaust while generating propulsive power, that more than compensates for the engine power loss through the scrubber, and the initial capital investment.
- Can a centrifugal vortex exhaust scrubber be fitted inside a typical Flettner rotor?
- How will the scrubber affect Flettner rotor performance?
- How will this Flettner Vortex Scrubber affect vessel performance?
- Can an exhaust scrubber be simplified to eliminate high maintenance moving parts and water droplet system?
- What is the pressure drop across the scrubber, indicating loss of engine power?
1) Study bulk cargo ship and engine design. Research Flettner rotors and exhaust scrubbers.
2) Design scrubber in Flettner rotor using 3D modeling to ensure proper fit of overlapping rotating assemblies.
3) Select aspects of design for further design iterations via analysis in Computational Fluid Dynamics: ANSYS will be used.
4) Prototype a scale model Flettner rotor with integral exhaust scrubber. Select 1:39 scale to adapt repurposed and readily available commercial materials wherever possible.
5) Design a statistical sampling plan to evaluate scrubber designs by measuring the efficiency of particulate matter removal.
6) Design and construct a test stand to measure efficiency of the scrubber by drawing simulated cargo ship heavy fuel oil exhaust across filter media.
7) Construct a water test tank to test propulsion force without friction: ballasted columns will be used to trim the tower on the platform so that it floats with stability.
8) Design and construct a wind tunnel test stand to assess the continued performance of the Flettner rotor by measuring propulsion force generated relative to rotor speed, wind speed, and wind angle: A force sensor will be used to measure the propulsion force. A tachometer will be used to measure rpm and an anemometer will be used to measure wind speed.
9) Further iterate and improve design
Risk and Safety:
Personal protective equipment will be used: latex gloves, safety glasses, masks, hearing protection, carving gloves, utility gloves to protect from sharp edges.
Safety disconnects and Ground Fault Current Interrupts will be installed.
Results will be analyzed using spreadsheet software.
Results will be analyzed for statistical significance.
Questions and Answers
1. What was the major objective of your project and what was your plan to achieve it?
My major objective was to find a way to reduce climate change causing cargo ship exhaust by integrating a novel centrifugal vortex scrubber into a Flettner rotor to clean cargo ship exhaust. The Flettner Rotor generates propulsive power that more than compensates for the engine power loss through the scrubber, and the initial capital investment.
To achieve this goal, I set out to first design the proposed assembly using 3D modeling, then optimize it with CFD. Once the design was iterated based on the 3D model and CFD analysis, I built a prototype of the scrubber inside a Flettner Rotor, and developed test stands to study the performance of the prototype.
a. Was that goal the result of any specific situation, experience, or problem you encountered?
Being at sea, having been a lifelong sailor, I have observed many cargo ships enter harbors and clearly see the amount of particulate matter coming from them and can only imagine the climate change emissions that are not visible.
I can understand why people who live near harbors see cargo ship emissions as even more of a critical issue particularly with regards to health.
Ships began using oil as an energy source around 1900, however use of exhaust scrubbers on ships was very limited until recently, due to light regulation. In 1973, the regulation of pollution in international waters was first discussed at the first marine pollution convention, or MARPOL. Sulfur emissions restrictions did not go into effect until 2012 with a 3.5% sulfur cap. In 2020 this cap was reduced to 0.5%, prompting ships to either consume less residual fuels, or install scrubbers. Because of this, it seems like scrubber technology is designed around land-based applications like power generating stations that have been more regulated, and not marine applications. Heavy fuel oil is a residual product of petroleum refining for gasoline and diesel. Marine fuel oil engines are a mature, low cost, and reliable technology. I feel that marine exhaust scrubbers and cargo ship wind power are very important technologies to advance. Large ships contribute to 4% of global climate change emissions. According to the Yale School of the Environment, we are just learning that the combustion products of heavy fuel oil are especially noxious pollutants which can travel hundreds of miles leading to roughly 7.6 million childhood asthma cases and 150,000 premature deaths annually.
b. Were you trying to solve a problem, answer a question, or test a hypothesis?
I believed I was trying to do all three!
I was trying to solve the problem of climate change by reducing emissions.
I was trying to answer questions regarding applying scientific principles to design a new solution.
I was testing my hypothesis that a novel centrifugal vortex scrubber integrated into a Flettner rotor cleans exhaust while generating propulsive power that more than compensates for the engine power loss through the scrubber, and the initial capital investment.
2. What were the major tasks you had to perform in order to complete your project?
- In order to complete my project, I needed to improve my 3D modeling and CFD skills. When my school curriculum was not sufficient, I used online resources, webinars, and a free ANSYS university class.
- I used 3D modeling to design an exhaust scrubber into a Flettner Rotor geometry. In addition to documenting my design, 3D modeling was a great design tool to use to ensure proper fit of rotating cylinders.
- I used computational fluid dynamics to optimize the exhaust scrubber geometry. This required:
- Adapting my 3D model for computational fluid dynamics by defeaturing and creating a domain boundary.
- Developing a mesh for finite element analysis.
- Selecting an appropriate complexity of analysis model. I selected the k–omega two equation turbulence model as an appropriate balance of resolution and complexity. This model is used to approximate Reynolds-averaged Navier–Stokes equations for viscous fluid flow.
- Validating the CFD model.
- Running various input conditions and monitoring the pressure drop across the scrubber as well as the maximum velocity
- Running as an injection in a discrete phase model to track the behavior of exhaust particulate matter.
- Improving and iterating exhaust scrubber geometry to maximize centrifugal force, maximize particulate matter retained, and minimize pressure drop.
- I constructed a prototype exhaust scrubber to fit inside a scale model Flettner rotor.
- I developed and constructed a drive mechanism for the Flettner rotor, and a test stand to measure the efficiency of the exhaust scrubber.
- I developed and constructed a wind tunnel, water test tank and floating Flettner rotor base to confirm the propulsion force generated by the Flettner rotor at various RPM.
a. For teams, describe what each member worked on.
This was not a team project.
3. What is new or novel about your project?
My work is novel in that it combines two shipboard environmental technologies in a way that makes both more economically attractive for ship owners to deploy on their fleets.
The exhaust scrubber is of low density compared to tanks or other shipboard mechanical systems, which makes it ideal to locate above the center of mass without significantly increasing the metacentric height and affecting ship stability or seakeeping. My scrubber design is improved and optimized for shipboard deployment by replacing high maintenance moving parts with cyclonic separation geometry.
a. Is there some aspect of your project's objective, or how you achieved it that you haven't done before?
I had never designed, built or tested an exhaust scrubber before.
I had never designed, built or tested a Flettner rotor before.
I had never created a computational fluid dynamics model that was this complex before.
I had never used ANSYS software before.
b. Is your project's objective, or the way you implemented it, different from anything you have seen?
I have not seen a proposal to utilize the volume inside Flettner rotors. It seems that scrubber technology designed around land-based applications like power generating stations is being “cut-and-pasted” into new and retrofit marine applications due to increased pollution regulation in international waters.
My Flettner Vortex Scrubber recaptures unused shipboard volume and augments auxiliary wind propulsion in an innovative way.
c. If you believe your work to be unique in some way, what research have you done to confirm that it is?
I researched shipboard systems with a focus on pollution reduction and have not seen any that combine engine exhaust scrubbers and Flettner Rotors.
4. What was the most challenging part of completing your project?
A large challenge early on in my planning was that I needed to find a way to accurately measure the propulsion force of the Flettner rotor and minimize interference from friction. This led to my water test tank to minimize friction during the wind tunnel test. The floating test platform was not a ship model and did not have mass or volume proportional to an actual cargo ship that would hold the Flettner Vortex Scrubber prototype upright. Therefore the floating test platform had to be carefully trimmed with foam floats, and removable two liter bottles that could serve as partially filled ballasted columns similar to the design of a semi-submersible oil rig.
a. What problems did you encounter, and how did you overcome them?
In order to make some of the complex modeling geometries in Onshape that were not covered in my school curriculum, I found online tutorials.
Exhaust from the test stand interfered with the flow of the engine-simulating-lantern. I developed a baffle to diffuse the flow.
Finding a way to design a drive for the prototype Flettner rotor that had the right speed and torque output was challenging. I tested and overstressed some repurposed motors designed for high speed low torque air handling applications before settling on repurposing a cordless drill. I tried to use a pulley drive but the lateral load on the turntable caused increased friction on the bearing and inconsistent motion. I ended up redesigning the drive to use a polyurethane wheel that exerted a vertical force on the turntable instead of a horizontal force. This also made it easy to disengage the drive mechanism and let the Flettner rotor spin freely.
An overall challenge was identifying repurposed and commercial materials that met all the dimensional requirements for fitting scrubber components inside of a Flettner rotor cylinder geometry in a way that would not make the entire prototype unmanageably large and therefore more difficult to build test stands for. Sizing the prototype appropriately so that it was small enough to build test stands for, but easy enough to adapt materials to was a fun puzzle.
b. What did you learn from overcoming these problems?
From overcoming these problems, I learned that complex test equipment and expensive testing facilities are not always required for accuracy and precision. Accuracy and precision can be achieved through creative application of physics principles and careful mathematical calculations.
5. If you were going to do this project again, are there any things you would you do differently the next time?
One improvement I would make is putting wheels under the wind tunnel so that it could be easily moved to change tack angle relative to the water test tank and floating Flettner Vortex Scrubber prototype.
6. Did working on this project give you any ideas for other projects?
Absolutely! I am fascinated by all of the engineering solutions that can be developed to make cargo shipping cleaner. There are so many concepts currently being explored, from capturing waste engine heat and generating electricity, to optimizing float plans for optimal weather, currents, and sea state.
I am especially interested in how recent advances in materials and machine learning technology can be used to apply wind power to today’s cargo ships.
Using a filter media to capture nanometer-scale particles also got me thinking about testing the masks we use to protect ourselves and others from COVID-19.
7. How did COVID-19 affect the completion of your project?
I was invited to present some of my research to two professors at Rutgers University and one has invited me to work in their nano lab, specifically to use their equipment to better understand spray technology. This was postponed to this Spring, however, I am very excited to be heading there soon.