Supersonic Man

June 21, 2018

hydrogen economy? how about methane instead?

Filed under: Hobbyism and Nerdry,science!,technology,the future! — Supersonic Man @ 4:52 pm

Ever since the seventies, there’s been an idea floating around that someday, in order to replace fossil fuels, we’d start using hydrogen as our main chemical fuel.  We’d have hydrogen tanks instead of gasoline tanks, and hydrogen pipelines instead of natural gas pipes.  The hydrogen would be produced from water with either renewable or nuclear energy sources, and then whenever we needed a chemical fuel, we’d use hydrogen.  And wherever we needed a portable source of electric power, we’d use hydrogen fuel cells.  Our cars might be fuel cell powered, for instance.

Since then, fuel cell cars have advanced pretty well, and building a fleet of electric cars which get their power from hydrogen fuel cells looks fairly doable.  There are even some demo filling stations which allow you to fill up a fuel cell car with hydrogen, if you have one of the test vehicles.

So that part is doable, though nobody’s sure if there’ll be any need for it.  Cars might do just as well by simply using batteries, and plugging in to charge, as many people do today.  Making a new network for delivering hydrogen to cars might be an unnecessary expense.

But what about all the other things we use fossil fuel for, besides transportation?  What about heating our houses, and fueling our stoves and ovens?  Could we, for instance, substitute hydrogen for natural gas?

I think the answer is that we could, but maybe we shouldn’t, because there’s a better idea.  An approach which lets us keep using the natural gas infrastructure that we already have.  Switching to hydrogen would entail replacing most of it, because a pipe or a valve that safely contains natural gas can easily fail at containing hydrogen.  Since it is the lightest of all gases, one of its properties is that it can find its way through leaks which, to any ordinary gas, aren’t leaks at all.  Every piece of every pipe, and every valve in every appliance, would have to be either carefully tested, or replaced.  Also, the pipes would either have to be expanded for a larger volume, or operated at higher pressure.

We can avoid all that with one simple step: taking the hydrogen we produce and converting it into methane.  Natural gas is 95% methane, and if we make it artificially, it could be used as a direct replacement for gas.  And the way we’d do that is with a process called the Sabatier reaction.  In this process, hydrogen is combined with carbon dioxide by means of a metallic catalyst.  The oxygen is stripped off of the carbon atoms and hydrogen takes its place.  The result is methane, plus leftover oxygen.

The best part is where we get the carbon dioxide: out of the atmosphere.  At first, we could take it directly from the smokestacks of industries which still burn fossil fuel.  (Steelmaking, for instance, might have a hard time using anything but coal.)  Later, as the scale increases, we could just separate it out of regular air.  This makes your home’s existing stove and furnace and water heater carbon neutral.  And even your car, because existing piston engines can be modified to run on methane, which might help ease the transition to the time when we all go electric.

With some further chemical processes we could probably convert the methane into longer chain hydrocarbons, producing oils and so on — substitutes for things like butane or kerosene or diesel or gear oil or candle wax… or even gasoline for classic car enthusiasts.

Between battery cars and methane conversion, maybe there wouldn’t be all that big a market for straight pure hydrogen.  It would definitely have some uses, but I don’t think all that big a part of our energy supply would be used in hydrogen form.  We might, however, use hydrogen to store solar energy from midday for use at night.  Such hydrogen might be produced directly by vats of algae, then fed to stationary fuel cells as the sun sets.

If a big methane convertor works, we should of course encourage its use.  We’ll have tax credits for making carbon-neutral methane, and penalties for fossil fuels.  The rival approach of getting gas by fracking might even be banned outright, because of its harmful side effects.  This assumes, of course, that at some point we overcome the reactionary political forces who want to prop up the oil and coal industries, and would let all the profitable advances in renewables be done overseas.

One cool thing is that methane making machines are being developed right now, as part of the space program.  Not NASA’s space program, but SpaceX’s private program.  They’re building it for future Martian explorers and colonists, so they’ll be able to make their own rocket fuel for flights back to Earth.  Who knows, maybe at some point they’ll use the machine to fuel rockets here as well, so they can say they have carbon neutral satellite launchers.  Both of the major reusable rocket companies, plus several small up-and-comers, say methane is the fuel they want to use.  There’s no denying that a lot of older rockets are terrible polluters… compared to some of the chemicals that get used in the rocket business, even kerosene looks very green.

Of course, some other rockets will keep on using hydrogen, which when practical is still the cleanest option.  But liquid methane is the second cleanest, and it has nine times the density of liquid hydrogen and therefore requires a far smaller tank to hold it, and less insulation as well, which may save more weight than is lost by using a heavier fuel.

Perhaps the most ideal would be some kind of blend of the two… but then again, one of the big advantages of hydrogen is its very high specific impulse, which is achieved in part by burning a very fuel-rich mixture so that a substantial portion of the exhaust is unburned hydrogen gas.  Densifying the fuel by dissolving some methane into it might save weight by making it require a far smaller tank, but it would lose some of that very high exhaust velocity.

June 3, 2018

Trends in rocketry

Filed under: Hobbyism and Nerdry,technology — Supersonic Man @ 11:07 am

I’ve been taking an interest in the space industry and orbital rockets — a field which is evolving very rapidly nowadays.  So far this year we’ve seen the debut orbital flights of the Electron, the Falcon Heavy and Falcon 9 Block 5, and seen a new record set for the smallest rocket to put up a working satellite.  In the remaining months, we’re expecting the maiden flights of the LauncherOne, the Kuaizhou 11, the Vector R, and the Starliner and Dragon 2 crew capsules.  We just might see one of those capsules take live astronauts to the Space Station by the end of the year.  And the next couple of years will have plenty of action too, with several lunar landers being sent up by different countries, and more new vehicles making their debut: the SLS, the Vulcan, the New Glenn, the Dream Chaser, and more.

With so much short-term activity, it may be hard to spot the longer term trends, but I think I can lay out a few here: (more…)

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