If you have read this blog for any amount of time, you probably know that I do not hold a very favorable view of fuel cells. I think they suck in general and good ones provide marginal benefit over other solutions.
For example, batteries are better than fuel cells in cell phones. They keep promising cell phone fuel cells, but the stuff required to make the fuel cell work makes it too bulky to be inside of a cell phone, no matter what companies are showing in their PR. At best we will see some box-on-cord systems that will still be bigger and more expensive to run, than keeping an external battery charged up.
I recently mentioned fuel cell cars in another post. So far, they are all requiring hydrogen infrastructure to work. And where do we get most of our hydrogen? Natural gas. That means that even if we use hydrogen for these things, we are still creating just as much CO2 (although there might be an efficiency play to be had, but we aren’t talking about a dramatic reduction in greenhouse gases).
I only mention fuel cells for this article, because the company I’m talking about uses fuel cell materials but doesn’t make fuel cells. H2Pump LLC uses fuel cell materials to pump hydrogen with no moving parts. In pumping hydrogen, they also pressurize it and purify it. They are specifically not a fuel cell company.
Before looking into it deeply, lets take a minute to try to understand why that is significant. The most common way to move gas and pressurize it is to use a compressor. We are all probably familiar with air compressors and may even have one in your garage. The issue with hydrogen is that the molecule is so small, that a normal compressor can really pump it. Further, the gas itself can embrittle steel. There are a host of problems with pumping pure hydrogen. But to date, the only way to do it is with a mechanical hydrogen compressor.
There are also hydrogen purification systems available. These are generally done with a PSA (pressure swing adsorption) system. Basically, gas is fed into a tank with these pellets in it. The pellets, when under pressure, adsorb everything except hydrogen which passes through the tank. Then when the pellets are full of the contaminants, the inlet gas is routed to another PSA tank, and the first tank is depressurized, releasing the contaminant into a waste stream and making it ready to start again. There are also low pressure Temperature Swing Adsorption units which do the same thing, but release contaminants upon heating. These systems can be used to purify a variety of other gases, not just hydrogen.
So, in order to pump and purify hydrogen, you would need a hydrogen capable compressor and a PSA system. There are companies that make the system I just described.
Why would you have a system like this? Where is hydrogen recovery useful? Fuel cells consume hydrogen, so there is nothing to recycle. Well it turns out there are a variety of industries that use hydrogen, but do not consume it. Instead it is simply released, either by flaming it at a stack, or just releasing it into the air! Industries that do this are:
Heat treating industry
Float glass production
Fats and oils (hydrogenation)
Any chemical process which generates by-product hydrogen such as biogas production
Its amazing to think that these companies are getting hydrogen, in huge quantities, flowing it into their process and then dumping it out the vent. Can this possibly be true? At worst it seems like they could burn it and use it as heat. However the heating value of H2 is only 2 or 3 times higher than that of natural gas but pure H2 is over an order of magnitude higher than natural gas in cost. So who knows? As mentioned before, companies make systems to recapture this hydrogen, but they are generally sized for the huge quantities of hydrogen and have very short times before failure (multiple failures per year), usually due to the compressor (there is little to go wrong in the PSA part).
OK, we know why we might recycle hydrogen, we know how we might recycle hydrogen, and we know a couple of companies who make equipment to recycle hydrogen. Now we can focus on H2Pump.
H2 pump has a different technology. They use fuel cell materials, but unlike fuel cells which consume hydrogen to generate power, these pumps consume electricity to pump hydrogen.
Hydrogen is fed to one side of the membrane with a catalyst on it (the anode electrode). The hydrogen molecules are split and pass through the membrane as protons. On the other side of the membrane is another electrode, the cathode, where the two proton recombine to produce H2. This action doesn’t happen to any other molecule. So if there is hydrogen and carbon dioxide and carbon monoxide (common ingredients in a process), only the pure hydrogen appears on the cathode, the other things get passed through the anode.
The flow rate of hydrogen coming off the cathode is directly dependant on the current. The more current supplied the higher the flow rate. If a restriction is placed on the outlet, the pressure will rise. The molar flow rate coming off the cathode will remain constant, however the volumetric flow rate will be completely dependant on the pressure differential between the anode and whatever is after the flow restriction. Some of these membrane are very strong because they are fluouropolymers, like Teflon. Therefore large pressures, even in the hundreds of PSI, could be generated.
Costs and value proposition
Hydrogen is expensive. These guestimates don’t take into account the purity required for most of these processes (1 gallon of gas equivalent is about 1kg of H2). (I gotta write a post on the farce that is the difference between projections of hydrogen costs and what pure hydrogen actually costs right now). I’ll get hard data later, but depending on purity and volume, hydrogen costs between 4 dollars/kilogram (high volume, lower purity) and 100 dollars per kg (high purity, low volumes) according the H2Pumps website. They claim to be able to recover 90% of the hydrogen in the waste stream for what is essentially just the cost of the electricity to move the protons from one side to the other.
So how much does it cost to reclaim the hydrogen? Well, get ready for some arithmetic.
On their technology page, they explain how to calculate hydrogen flow based on current (actually they say how to calculate current based on flow), and they say that a typical voltage of a cell may be 50mV. If we do an example, of say, 100 kg/day of H2 (=1.157 grams/sec =1.148 mol/sec) , you would need 220,000 amps. In order to make that reasonable (to have a decent power supply), you would break that up into multiple cells, lets say 220 cells (just to make math easier). Each cell runs at 50mW, so you would consume, 0.050V x 220 x 1000 amps = 11kW.
So for each hour you run the machine you use up 11kWhs of energy. Its easy to find out the cost of energy where you live. For industrial use, the average cost of energy is 7 cents per kWh. So, for each day you pump 100kG of H2, you would pay $18.50, we are talking about 19 cents per kg of hydrogen if it is reclaimed instead of being thrown out the window! And this is for pure, pressurized hydrogen from a system with no moving parts (I can imagine valves being required). I gotta say, these numbers seem a bit too good to be true, but even if their numbers are off by an order of magnitude, it is still cheap hydrogen.
Now I am quite sure I have left out some stuff that they have not included on their page. For example, how much power does the system use to make the stack work? Are there things I have to replace every year? Are there other consumables? Then there is the cost of the system, they say a one or two year payback, but what are they assuming about my gas and electricity use?
So there are tons of questions to ask. However, they do not have many of the problems of fuel cells, namely oxygen screwing up a lot of things up and the fact that there is no flooding on the cathode (because hydrogen evolves there and no water is made). Further they do not have the big issue of PSA systems, namely a failure prone compressor. It seems like this may work.
Maybe all those companies making fuel cell materials may find a market after all.