Tech Talk - Fuel Cell Turbo Compressors - Fuel Cell Technology Explained - Hyfindr Brandstätter

Tech Talk - Fuel Cell Turbo Compressors -  Fuel Cell Technology Explained - Hyfindr Brandstätter

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Hello. My name is Steven. Welcome to Hyfindr Tech  Talks. Today, we are going to be talking about turbo compressors and with that is the person here, who has a Ph.D. from arguably Switzerland's most renowned technical institution. He currently works  at severity that's the ETH actually what I meant. He currently works at Celeroton, where he is head of the R&D for fuel cell applications. Welcome Markus, Markus Brandstätter. Hello, Steven. Thank you for having me. It's great to be on your show.

Thank you, Markus. Yeah, you are connected to us  by video link and you are in a special place. Can you tell us a little bit where you are please?  Yes. I'm currently in one of our main working session rooms. Right next to the entire research  and development department of our company, where all the concepts or the new concepts that we  developed are being brainstormed or are being presented. Okay, wonderful. So, that is just next to  all the R&D guys, I know you head off the team but the good news is in case we run into any serious  technical question here you could quickly probably hop over to your colleagues there, right? Exactly,  then I can grab my specialists and take them in it. Okay, so perfect let's go right into  the topic. Markus, what is a turbo compressor?

Actually, I for that matter brought a slide  with me or an image that I could show you to give you a little bit of an overview in  the house that you could talk compressor looks like and how it functions. Okay, yes. We see it. So, you can see. Alright, great. So, on the left hand side you can see a simplified schematic overview of how such a turbo compressor is built. So, fundamentally it consists  of three or in a simple form it consists of three parts, which is the impeller. So, the wheel that works on the fluid. The diffuser which is followed by our impeller  and after the diffuser, we have a so-called Volute or spiral casing, which connects the  compressor to the fuel cell stack for instance. So the impeller is number 2 in that image. Impeller, you can see it right here. Yes.

The diffuser is number 4 and the spiral casing is essentially number 6. Understood. So, maybe and now we can briefly go through  step by step, what happens like from from a fluid perspective. On the right is inlet which is indicate the number 1. Going essentially directly flow is directed  towards the eye of the impeller one is talking about the eye which is the center of  the impeller. High rotational speed impeller is rotating we have a so-called  flow passage which is generated by the blades of such an impeller, were we have basically an increase in or a change in angular momentum of  the flow and the change of total pressure. So, across the flow passage which  is created by the spiral case, which is the outer contour and input around 60% of  the total pressure increase is taking place. Okay, so as that spins that increases the pleasure going out.

Correct. So, it's essentially first of all it changed the angular momentum and it increases the total compression. What is  interesting to note after for instance the edge of these of this impeller we still have  flow velocities of around 200 meter/second, which means we need to still decelerate  this flow and to further increase the static pressure that is required for  certain applications. This is done by the so-called diffuser, where we increase the volume  thereby increasing the static pressure. After the diffuser, we have as I said spiral casing or the  volute where we further reduce radial velocity and collect the flow towards the end application,  which could for instance be a fuel cell stack.

Maybe on the right hand side you  can see one of our more recent design and that we have already presented at numerous fairs, where we can see actually how it looks in real life, which is a cut through one of our CAD design. So, maybe I can also show you how typically  that like what the variation of such impeller designs, which is from my perspective  very interesting just to see that you can see there's a huge variety. Mixed flow designs,  where we have also radial and axial components or the classical design, which one would see in  fuel cell stack applications. So, what is the difference between you know one that narrows up and the one that's completely widening, what's the main difference? So, the main difference  is directly it's a very technical question. Actually, the difference is directly to the flow  coefficient. It's essentially a throughput, that's

such a compressor needs to be able to designed for. For instance, once we go towards axial flow designs, which is  a classic for gas turbine designs for instance that high mass flows requirements. Whereas, when we  go through really radial designs which is a purely radial design pretty even we have very low mass flows. Alright. Okay. So, the mass flor essentially makes a difference. Okay. Well, you have already mentioned  some applications, where do we typically find

turbo compressors in the hydrogen economy. Yes. I mean there are three main applications actually and also actually for  that the purpose I also brought you another image that I could show you, which is a very  simplified schematic of a proton exchange membrane fuel cell (PEMFC). So, a piping diagrams essentially  where we can see the air inlet. And here we have our air compressor where this is one of the main  application areas for these turbo compressors compressing the air generating for the cathode  side to produce the air or eventually that oxygen that is required by these fuel cell stacks. Yeah. So, we see that it pushes, the

air into the humidifier and then into the system  and it needs also cooling as I see from that diagram. So, I know you're an expert. So, can you take  us a little bit more deeply into the actual unit? So, we saw the first picture but please show  us a little bit more about the components of it, please. Yes. So, let me briefly one more  point to clarify so I mean turbo compressors can be used on the cathode side but in addition also  on the anode side. For instance for a hydrogen recirculation with dedicated designs or for electrolyzer hydrogen recirculation. So, you also could use the turbo  compressor for recirculating the hydrogen.

Absolutely. Yes. Dedicated designs though but my business unit is really focusing on  the air paths on the cathode side but generally speaking turbo compressors can also be used for hydrogen recirculation. Understood. So, back to the original question of yours up into the more detailed view of how the turbo compressor system looks like and what  I brought here is actually a cut through of one of our compressor systems. So, first I'm going to zoom out a bit. In the beginning, I only talked about  the aerodynamics which is only a portion Obviously, it's an important part but it's  only a portion of what the compressor system is consisting of. So, on the left  hand side we can see the compressor

and on the right hand side we can see the  converter. So, maybe let's go from left to right. So, I already explained to you the impeller the aerodynamics and the impeller is usually connected to a rotor which rotates at a high  rotational speed. The rotor itself is suspended by so-called gas bearings which makes this  entire thing special. Why does it make it special, because it's generating compressed  air which is oil-free and particle-free. And virtually no wear. That's the second bit. Then obviously the torque needs to be generated to compress this air right and the torque  is generated by an electric motor. In this

particular case, we can see it's mounted  around or in between the two radial bearings which is our winding and in the middle we  have our magnet or a permanent magnet arrangement. Yes. So, we are talking usually about permanent magnet synchronous machines that we use here, which are especially  designed for high rotational speeds, which where we have to take into account a couple  of intricate things in the design process.

Yeah. So, actually you mentioned high rotational  speed so I'm just you know trying to imagine being at the impeller, so that gets up to a  very high RPM stage and you also mentioned some really fast speeds there. I mean don't you reach the sound barrier there? And things like that don't you get into other  kind of physical problems because of that? So, maybe to give you a couple of values here, which might be interesting for the viewer as well. So, we range between rotational  speeds of so for the larger compressors around 120 kRPMs or 120,000 RPM up to  300,000 RPM for the smaller systems. Usually

which means when we convert that into  into velocities we're talking about 300 to 400 meter per second (m/s). Wow. So, generally  speaking of sound barrier is something we try to avoid because supersonic operation always  results in shocks. So, compressibility effects shocks always are associated with irreversible  processes and ultimately also in a reduction in efficiency. Okay. So, that's we are trying not to  operate in the supersonic. And I see there was cooling I saw from diagram. So, what is actually  being called is the electric motor that that's what's being cooled? So, obviously within  that system, we have a couple of of sources for losses and one is for  instance the gas bearings, they generate losses but mainly it is the electric motor as you  indicated and well we either can cool it with water or with a cooling medium or  it is air cooled. Okay. I'm very curious

about the gas bearings, Markus. Maybe you can tell  us a little bit more about that because I know you also have a bit of a specialty around that. Firstly, how does it work and also I mean if it's a compressor it's actually has one chamber where there's air. Isn't that the interaction with the  actual medium that is being pumped? So, we have the same medium  in there obviously. Yeah. So I have to briefly have to check, whether I have a slide that I could show you. Yes, here we go. So let's dive into that the  details of gas bearings. I mean gas bearings are

very interesting. Generally, speaking one can  differentiate between hydrostatic and hydrodynamic bearings for mobility applications which is the most current case for instance for road applications or aerospace applications. Hydrodynamic bearings is the usually that the one uses the reason being simplify design  few external parts and so on. How does it work? One has essentially a shaft and then we  have one has a bushing and through rotation one generates a pressure through the rotation  within the small gaps between the journal and the bushing, which generates a cushion where  the journal floats on top. That's essentially

how it works fundamentally. So, by spinning the  fluid around or in in the gap of these two you create a cushion that is strong enough for that  to carry it. Correct, exactly. I mean I can maybe briefly show you. I mean there are different  types of gas bearings one could for instance use the simplest one. One can think of is a  plane bearing where essentially just as the

cylinder and a bushing which is a  a pipe so to speak and just by rotation and the Couette flow generates a cushion, where the rotor starts floating. Strongly and narrow regime where one can operate  these plain bearings. And for instance the technology that we mostly use is  Herringbone grooved bearings, where we can engrave structures to increase the regime  where these systems can operate. Okay and

when you have this kind of like I said if you have a pressure chamber on one side where it's spinning essentially. Do  you see any effect of the air? In this case, you're moving air but do you see any effect of that  in the bearing when the pressure rises in the spinning. No, there is no direct interaction. Okay, yeah and so essentially  this floats then and just using the opportunity here, what happens  when like you know the compressor shakes or gets shocks and so on? You know because I mean  obviously, if it's a physical bearing let me just call it that you know a ball bearing or so  everyone knows okay there is something but here now we are floating on the cushion. How does that work? Yeah, one is when actually when I talk to other engineers, it's always  surprising to them that these gas bearing type of bearing. I mean I can briefly show you  another image. They actually have stiffnesses, which are comparable to ball bearings which is  for some people very surprising. Which means how does it work. So, by rotation we have this  gas film where the journal is floating and once

we have a vibration shock. So, it's essential  displacement. On one side we decrease the gap of this gas film which increases the  stiffness of this gas film. Thereby, exerting a force on the journal in the opposite direction  which means there is always a force acting into the centering of the journal when we have an  external force acting and it's such as vibration or shock. Here, on the right hand side you can  see actually one of our compressors being tested on a vibrational bench, where we for instance  tested systems up to 20G under real conditions. So, this is clear that it's the shock  perspective. Okay. That's very interesting that is that kind of you know resistance. What about  load bearing? Sorry, if I ask but like you know

so what if it's a very heavy shaft or something. These air bearings fine for that as well. I mean you have to be obviously for it. Yes. The size increases and there needs to be obviously the attention to  how you design such a bearing but in terms of forces, you can definitely design also for larger  shafts. I mean for instance here we tested up to

20G acceleration which means the forces of  this rotor under acceleration is quite large. Okay, last question for the air bearings. what speed does it have to have to actually start working? You know because I was just  going through my head like it could be using another application but it doesn't need to have  a certain speed right before it starts. Yes, I can

briefly elaborate on that as well and actually that's a very common question, which is why I also brought an image that I could show. Oh wow. Typically speaking when we look at curves when we actually accelerate and increase the  speed of such gas bearing type bearings. We have a mixed regime, where essentially the rotor is  still not yet floating and we have a sort of liftoff speed, which is at a very low rotational  speed compared to maximum and after that essentially the rotor floats and has virtually no  contact anymore. Okay wow. Well, no contact that sounds like easy maintenance and these kind  of things, which brings me to another question Markus. I know that the compressors are often  like when we say one of the cost drivers in the whole especially fuel cell systems. Can you  elaborate a little bit on that like why or what is it that's so expensive on a turbo compressor like this? Just for fun. Maybe I can

give you a little bit of an insight into how  much value is also given by such a compressor. Let me briefly show you one of the images here. So, for an entire fuel cell system component share value for the air compressor is  up to 20% when we talk about the entire fuel cell system which also and furthermore not only the  value that is created by the compressor but also the power consumption is also 10% to  20% of the entire system which also is a strong argument why these compressor systems  are worth to further develop and improve. Which is why when they are a substantial part of the  fuel cell system which is what I'm trying to say. Okay so that means you guys are working on getting  them even better hopefully by bringing down the cost as well. Can you give us a bit of an outlook on  what you're working on? Yes, I mean there are a couple of things in the market and in  the development of what is happening these days, one thing is obviously that the market  is moving to larger and larger stack size for instance that's one of the development paths in  the industry and in the market. The second bit

is for instance a continuous integration of for  instance electronics into compressors for a decreasing or downsizing of everything to save space and I think that the last important bit is industrialization. So, further being able to produce  in a process stable and cost efficient manner products for the hydrogen market. Wow, that sounds like a lot of work still for you to do and the guys around you. I know that in the  area of industrialization Celeroton has actually I've personally seen you move from generation  to generation you know integrating more stuff into one unit and making it even easier to  fit in. So, good on you and also good on you for sharing your time and your knowledge during  the session. We've unfortunately already reached the end of the time that we have Markus, but I  guess this was very insightful. So, thank you and

not only thank you to you but thank you to  the viewers for watching. I hope that you enjoyed this video. If you did, please drop us a line or  subscribe to the channel here. I can tell you that when you go on, you can find many  components just like this one that we've talked about. So, you can get into contact with people  like Markus or his colleagues at Celeroton. It

would be a pleasure to have you there. Please enjoy  working on stuff that makes the hydrogen economy and everything else work. We look forward to  seeing you in another video. Thank you again Markus. Thank you for having me. And thank you for watching. Have a wonderful day. Thank you. Bye. Bye-bye.

2023-07-11 16:41

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