Webinar: Full PEM Electrolyser Operation including Balance of Plant
Good afternoon to everyone. My name is Hunor, and I am the founder at Hydrogen Training Solutions. Welcome to this webinar on PEM electrolyzer operation, including the balance of plant. This is going to be a relatively short webinar, and I’ll try to get through as many things as possible in such a short period of time.
So, my name is Hunor, and I’m the founder at Hydrogen Training Solutions. What Hydrogen Training Solutions does is help hydrogen organizations upskill their teams and individuals for business growth. The reason this company exists is because a few years ago, when I first got into the electrolysis business in the green energy sector, I personally struggled with finding the right information on how these things work, how the electrolyzers work, to ensure we could push projects through.
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I really struggled with finding reliable information on the electrolysis system. So, I thought to myself that I’m going to learn as much as I possibly can about these systems and help other people when they have questions about these types of things. Because of that, I started Hydrogen Training Solutions. I’m really keen on helping people with their journey and helping organizations build the best electrolyzer systems out there.
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For that, I run PEM electrolyzer operation training courses. This is a two-day training course, and I also run a hydrogen safety training course. What I’m going to do today is give you a bit of an introduction to PEM electrolyzer operation. Here’s the thing: I’m going to try to do this in about 30 minutes, so I’ve got to really hurry up. To get into any depth or detail would take about two days to go through, which is what my training course is for.
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On a personal note, I just became a father last week. So, if you hear a little bit of crying in the background or anything like that, it’s because the baby is just next door. I won’t be able to hear it because my headphones are noise-canceling.
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Can we have everyone in the comment section put where you’re listening from? I think we’ve got quite a lot of people. We’ve had over a hundred signed up for this webinar. Can you just comment in the comment section what country you’re from? Alright, we’ve got UK, Brazil… I think people are still joining. We’ve got UK, Germany, India, Turkey, Brazil again, Austria, Scotland, Uzbekistan, France. Wow, loads of places. Brilliant.
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Without any further ado, I’m just going to go ahead and start. I’m going to try to get through as much as we possibly can in this half hour. It’s a lot to cover. We’ll be answering the question, “What is a PEM electrolyzer?” First of all, it’s pretty obvious, right? We’re going to talk about an overview of things, the balance of plant systems for the entire electrolyzer system, and then we’ll have a brief look at the subsystems. We’ll look at the electrolyzer stack, water purification system, hydrogen dryer, and cooling systems. Hopefully, we can get through all of that, but if not, I might have to skip some things. I understand people’s lunch time is not going to be more than about half an hour.
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First of all, what is an electrolyzer? Well, an electrolyzer is a device that takes water and electrical power and uses the electrical power to split the water into its constituents, which are hydrogen and oxygen. In an electrolyzer scenario, the hydrogen is kept, while the oxygen is normally vented into the atmosphere.
There are a couple of really popular electrolyzer system types. One is alkaline, and the other is PEM, also solid oxide. They are really pushing solid oxide, but today we’ll be talking about PEM. PEM stands for proton exchange membrane. The difference between these two is that an alkaline electrolyzer uses potassium hydroxide as the electrolyte, whereas a PEM electrolyzer uses the PEM membrane, the polymer electrolyte membrane, or proton exchange membrane, as the electrolyte.
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The advantages of PEM are that you’re not using any harsh chemicals. In an alkaline electrolyzer, the solution is about 25% potassium hydroxide and the rest is water. So, you have to use these harsh chemicals, whereas with PEM, it’s basically just pure water going into the stack. You can run them at relatively high current density, which means you can have a much smaller system. You’ll also have very high voltage efficiency. It’s capable of holding pressure, so you can generate hydrogen at pressure without the need for a compressor. The industry standard tends to be about 30 bars for PEM electrolysis, up from about 20 bars, with 35 bars being the industry benchmark, and you don’t need a compressor for that.
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Then, there’s the turndown ratio, which is a huge advantage. What that means is you can turn it on and off very quickly. In fact, you can turn a PEM electrolyzer on and off in less than a couple of seconds—some systems even less than one second. You can also go from, say, 50% gas generation to 100% gas generation very quickly. The hydrogen coming out of a PEM electrolyzer is going to be highly pure because of the purification systems in the electrolyzer, which we’ll talk about in just a second.
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This is a Plug Power electrolyzer, a modular system you’d refer to as a plug-and-play electrolyzer because all of the balance of plant is included in this system. What you see on the right-hand side over here is a transformer, a rectifier, and the stack inside the container. You’ve got the airblast cooler, which is essentially just a radiator. It cools down the water that goes into the stack so we don’t overheat it. Then, we have a process refrigerant chiller, which is essentially for gas cooling and, in some systems, also for rectifier cooling.
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This here is an ITM Power electrolyzer, the same sort of thing. You’ve got the stack, the hydrogen dryer, and the water purification system inside the container. You’ve got the airblast cooler on this side, cooling down the water that goes through the stack to make sure it doesn’t overheat. This is because some inefficiencies during electrolysis release quite a lot of heat, so you’ve got to get rid of that heat. That’s what these air blast coolers are for. On the other side, you’ve got a refrigerant process chiller for the rectifier in some cases, but definitely for gas cooling. We’ll go into why we need that in a second.
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What’s missing from this picture is the power supply unit, which includes the transformer and rectifier. Here, we’ve got another example, pretty similar. I’m not going to go through this one in detail because we need to move on, but this is the PSU, with the coolers and all the other balance of plant inside the container.
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The question is, what’s inside the container? Well, I’ve got a diagram for you here. This is a very basic version of what’s inside. You’ve got water coming in, normally tap water, which is relatively clean, basically drinking water. But it’s not good for PEM electrolysis, and we’ll go through why in a moment. Basically, you’ve got a water purification system. Most electrolyzers want this system to get the water conductivity down to less than 0.2 microsiemens per centimeter. Tap water where I am in the UK varies, but it’s around 500-600 microsiemens per centimeter, which is really not good for electrolysis. You need to get it down to 0.2 microsiemens per centimeter, which means extremely clean, deionized water.
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From there, the water is pumped into the oxygen-water separation vessel. A water circulation pump then pumps the water into the PEM stack. During electrolysis, water and oxygen come out of the stack on the anode side. The oxygen and water go back into the oxygen-water separator. The water goes to the bottom, and the oxygen is vented through a vent line. Then, you have the hydrogen coming out of the stack. Because of how PEM electrolysis works, you’ll have quite a lot of liquid water coming out with the hydrogen. The water and hydrogen go into a vessel called the hydrogen-water separation vessel. The hydrogen bubbles up to the top, while the water stays at the bottom. The hydrogen exits from the top and goes to the next stage.
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The water in this vessel is still pure, good-quality water, and these electrolyzers reuse it to avoid wasting water. In advanced electrolyzers, there are systems to ensure hydrogen doesn’t go back into the oxygen-water separator for safety reasons. We don’t have time to go into that now, as we only have half an hour.
The hydrogen then goes into the deoxidizer, which removes any oxygen in the hydrogen using a catalyst. This process creates a slightly higher water content in the hydrogen, so these vessels are often slightly heated to prevent condensation, which could damage the expensive catalyst. From there, the gas goes into a temperature swing dryer. The gas passes through a desiccant vessel, where moisture is chemically adsorbed. When one vessel is saturated, it’s regenerated by heating and cooling, while the other vessel continues drying. The hydrogen coming out is extremely pure, down to parts per million or even parts per billion, depending on the application.
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In the PEM electrolyzer cell, water goes in, and water and oxygen come out. The cell has a proton exchange membrane in the middle. When electrical power is applied above the threshold voltage (around 1.48 volts, but more like 1.5-1.7 in reality), the water molecule’s hydrogen proton and electron split. The positively charged proton passes through the membrane to the cathode side, while the electron travels through electrical connections. They recombine to form a hydrogen molecule.
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The water purification system includes a water softening unit, a particulate filter, reverse osmosis membranes to remove organic compounds, and a mixed bed deionizing resin to fully demineralize the water. The hydrogen dryer uses a temperature swing desiccant to remove water, achieving gas purity down to parts per million or billion, as needed.
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The cooling system, typically placed after the pump and before the stack, uses a heat exchanger to transfer heat from the water to an antifreeze coolant, which is cooled by an airblast cooler (a giant radiator). There’s also a refrigeration cooler for gas cooling to promote condensation before the hydrogen-water separation vessel or before the desiccant towers.
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The power supply unit includes a step-down transformer (e.g., from 400 volts or 11kV to a suitable voltage) and a rectifier to convert AC to DC power, as electrolysis requires DC current. The electrolyzer setup includes a control room with a human-machine interface and pneumatic systems to ensure safety in hazardous zones.
I hope this gives you more insight into how a PEM electrolyzer works. In half an hour, this high-level overview is all we can do. A full training course takes two days to cover these systems in detail. I hope you’ve enjoyed this session.
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Now, we’ll answer a few questions. My colleague Max will read them out.
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Max: There are three questions from Mr. SMRI. The first one is: Manufacturers include kilowatt hours per kilogram stack efficiencies. Isn’t kilowatt hours per kilogram directly related to the electrolyzer operation? Voltage nominal operating voltage varies between manufacturers, but the maximum capacity of all of them is around 2.1. When calculated from catalogue values, don’t you think that nominal kWh per kilogram values are misleading in a sense?
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Hunor: It depends on how you define that. Yes, about two-thirds of the cost of running a PEM electrolyzer is directly related to electricity costs. It can be misleading, depending on how you define it. Hope that answers the question.
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Max: The second question is: At large systems, around 50 to 100 megawatts, do you use cooling towers instead of radiators for stack cooling, or do you use a chiller system for stack cooling and hydrogen purification?
Hunor: Most systems use large airblast coolers for cooling the water that goes into the stack, not refrigerant chillers, as those are extremely expensive. For large systems, like 100 megawatts, it’s just larger or multiple airblast coolers. Refrigerant chillers might be used in very hot places, like the Australian Outback, where temperatures exceed 45°C, but you want to keep electricity costs low.
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Max: The last question from Mr. SMRI is: Have you ever coupled a solar power plant with the PEM system directly with a DC-to-DC converter?
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Hunor: Yes, I’ve seen that on a smaller scale, about a 200-kilowatt electrolyzer, a few years ago.
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Max: Another question from Mr. Ram Babu: Supplying water to both anode and cathode, how does it affect performance?
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Hunor: Most large-scale electrolyzers only cool the anode side. If you also cool the cathode side, you’d need to remove that water too. The oxygen evolution reaction on the anode side is less efficient, generating more heat, while the hydrogen evolution reaction on the cathode side is more efficient, producing less heat, so cooling the cathode isn’t usually necessary unless you’re at very high current densities.
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Max: I have one question myself. The PEM process is reversible, so you can combine oxygen and hydrogen to generate electricity, as in hydrogen fuel cell cars. Can you use a similar concept?
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Hunor: A PEM fuel cell is built slightly differently, with different catalysts and a thinner membrane, but an electrolyzer is designed solely to generate hydrogen.
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Thank you very much for joining in. We’ve overrun a little, but it was a complicated subject. Please put a reaction or comment on what you liked. I hope you’ve enjoyed it and have a lovely rest of your day. Take care. Bye.