Re: Ok, let's do this.
Posted by Dale on Feb 23, 2002 at 10:16
Re: Superconductivity- Oxygen drips Upwards (Mike Kremer)
Ok, I have time this weekend and am winding down for a major change 4/1 so I may have some time next month. Let's do this. Exactly what part of the impossibility of the hydrogen economy would you like to solve? If you want to discuss the volume problem Iím game as long as you know I reserve the right to eventually concede the a volume solution but maintain it is still physically impossible for all the other reasons (greenhouse warming, no source of low cost hydrogen, global political upset, fuel leakage, etc. etc. etc.).
So letís set the boundary conditions. If we want to replace gasoline with hydrogen in an automobile we will need enough hydrogen to get 2,500,000 BTU when we combine it with oxygen. Thatís 40 pounds of hydrogen or about 8,000 standard cubic feet.
Letís assume some type of metallic lattice structure to grab hydrogen molecules and get the compression we need. Letís assume each atom of metal in the lattice can simultaneously hold 5 hydrogen atoms. Thatís better than hydrocarbon binding. Iím going to give you a break and use a real light metal. Letís dig up a bunch of magnesium. To store 40 pounds of hydrogen with 5 hydrogen atoms per magnesium atom, your magnesium tank is going to weigh 200 pounds. If, on the other hand, the lightest metal you find that will keep that many hydrogen atoms held at the same time is say rubidium, then your tank goes to 700 pounds.
Iím afraid that by the time you find something that will hold enough hydrogen (and then release it without taking more energy to effect the release than is stored in the hydrogen) your car is going to weigh as much as an SUV even when the tank is empty.
But letís assume that you can find some light metal (or any other atom) than can hold enough hydrogen. Letís look at that releasing problem. The reason the problem of compressing hydrogen is a problem is because those protons donít like getting too close together. You have to push real hard (i.e. 50,000 PSI to compress to a transportable volume using just a normal tank). But we are going to invent some magic/impossible tank that can do this compression without the pressure. Just how is that going to work? Yes, you can make a sponge-like material that allows atoms to enter the holes. You can even design it such that the atoms of the sponge attract the atoms of hydrogen so that they want to move into the holes without help/pressure. But not only do you have to get them squeezed in there, you have to get them back out when you want to oxidize them. Ah, thereís the rub. Thatís a potentially very explosive design. You have hydrogen that is held in a lattice by extreme forces (something that simulates 50,000PSI yet you can easily release the hydrogen back to atmospheric pressure. Think about it. What controls the release? You need to release 1 SCF every 3 seconds. How do you keep it from releasing 2 SCF in those 3 seconds? What happens when you rupture the tank? Is the hydrogen going to slowly release or is there going to be an expanding ball of hydrogen shooting up to the sky?
OK, letís just wave our magic wand and create a lattice that attracts the hydrogen into the spaces at atmospheric pressure. That solves the explosion problem. When you rupture the tank the hydrogen just sits in there. UhhÖ Sir, how are you going to get the hydrogen out of the lattice when you want to use it? To keep it from exploding we designed a real tight trap. To get it back out you are going to have to insert enough energy to overcome the 50,000 PSI attraction. Thatís more energy than you are going to get out of the hydrogen when you oxidize it.
Yes, Iím sure we can solve a few of the ďimpossibleĒ problems but we have to solve them all for a hydrogen economy to ever become feasible.
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