Coal? …Fold

For all the issues with gas via fracking, at least it’s not coal.  Whine all you want about some “war on coal,” it’s just a lesser fuel, from both a chemical and financial standpoint.  Natural gas has been displacing coal since the Eighties- oooh, that tree-hugging Reagan!- due to Wall Street hassles, not so much today’s environmental movement.  I’ll get to Wall Street, though.

People who do physics, and in particular thermodynamics, become familiar with condensed matter issues, separate from the rest of the field.  Solid-state physics (and to a lesser extent true liquids) have issues versus gases and plasmas.  Namely, their enthalpies of fusion, and of vaporization.  In street terms, it takes energy to melt a solid into a liquid, and still more energy to vaporize that liquid.  Lots of energy.

This matters because only gases burn.  Yup, hard for people on the street to understand, but coal itself does not burn; neither does wood or any other solid.  Liquids, neither (technically).  Condensed matter must be heated to produce volatiles; only then do those volatiles mix with oxygen and burn.  That volatilization energy isn’t free, of course- it had to come from the previously-burnt volatiles.  This is partly why campfires are hard to light.  Coal, wood, and other solids are like land animals, trying to tread water before they can even start paddling forward.  Gaseous fuels, though, are like fish, swimming because… they’re fish, and they swim rings around land animals without a thought.

See where I’m going?  Natural gas burns directly, yielding its heat of combustion without taking back its heat of vaporization, like a liquid would.  Nor its heat of fusion too, like a solid.  For coal, this takeback is a significant fraction of its available energy.  This characteristic was noticed by shipbuilders.  Around the turn of the 20th century, some warships laid out their coal bunkers around vital areas of the ship.  Coal, being difficult to ignite, served as a last-ditch defense against incoming shells and torpedos.  Eventually, however, coal-fired ships gave way to oil-fired ships, because other fuels were simply better.  Yes, this will become relevant later.

Granted, the coal people won’t sit back and sunset; there are modern developments in coal generation.  But arguably all these developments are compensating for its inherent disadvantages.  In other words, treading water just to keep up.

Probably the biggest development in coal is gasification.  Here, coal is pre-vaporized, before the burners, not in them.  But the same issue applies- where did that significant vaporization energy come from?  Often, some or all this energy comes from “waste heat” in the exhaust.  No process is 100% efficient; some heat always escapes without doing work.  (In the field, this is the Second Law of Thermodynamics.)  In this case, heat escapes the generators without making electricity; instead, that heat (normally) goes up the smokestack and escapes.  Gasifiers may instead tap some of this heat to gasify the coal.  Sound impressive?

Not really, because we’re still treading water here compared to natural gas.  The Second Law of Thermodynamics also applies to gas, which also creates “waste heat”… which also is being tapped.  Newer power plants may be “combined cycle” plants, also tapping their waste heat.  After burning the fuel to create electricity, combined cycle plants use hot exhausts to generate more electricity, in a second generator.  Unless of course that heat was already claimed by a gasifier, which then costs money, instead of making money.  Again, coal is just trying to keep up; natural gas was already ahead, and coal gasification doesn’t close the gap.

We can go on and on like this.  You can put a combined cycle generator on the exhaust of a coal gasification plant, to recover a bit more energy.  But at the same time, you could put a second combined cycle on the natural gas plant, and recover more of its energy.  Coal is inherently behind, and still not caught up.  You can also tap the exhaust heat directly, for heating homes and water, or for any factories that need process heat.  This is called “cogeneration,” or CHP (Combined Heat and Power).

Natural gas still wins in cogeneration.  Because gas burns with no heavy soots or ashes, it can be burnt in units much closer to homes and offices without drawing complaints- including my home, and possibly yours.  The potential for cogeneration is thus far higher with gas than coal.  All prototypes I see for home cogenerators have been gas-fired, not coal-fired.

So try all the coal gasification you can- natural gas will be better, always, simply because it’s not coal.  It doesn’t need gasification, and it yields a more usable exhaust.  I haven’t even mentioned the ash filters and exhaust scrubbers required on coal smokestacks yet.  Combined cycle plants won’t catch up coal, either, since natural gas burners are simply more practical, with or without gasification.  Coal will always suffer just from being coal.

Mind you, nothing ever really goes away, and there’s an argument for legacy fuels in token power plants.  The argument is that coal can be stockpiled- literally in a big pile- where gas can’t.  Even oil tanks are cumbersome.  You then have a coal buffer, versus gas (which is hard to store), and electricity, which is even more difficult to store on these huge scales.  But even if nothing ever goes away to zero, the stockpile argument is going further and further towards irrelevancy.  Most directly, gas and electricity storage are advancing, while the problems of coal storage are growing, too.

The natural gas industry isn’t standing still, either, and tanks for compressed natural gas (CNG) are becoming more and more practical.  Small-scale, moderate-pressure gas tanks exist, relatively- they’re still far bigger than my house, and yours too I’ll bet.  The field of materials science is working on practical tank materials for large-scale, high-pressure CNG storage.  If nothing else, multiple fields are working on underground holding caverns.  Caverns are useful for air pressurization (doing grid leveling), and in some cases cheap CNG storage.  Further into the future, grid-scale gas liquefaction is technically possible, just not profitable right now.  It’s chilled into liquid natural gas (LNG), for transoceanic shipment in LNG carriers, and some trucking applications.  As the price falls, limited grid-scale LNG storage will start appearing.  We’re already seeing highway truck stops selling LNG from local-sized tanks.

Meanwhile, coal has an ash problem that, again, doesn’t exist with gas at all.  Coal generates clinkers (solid bits that didn’t burn), and fly ash (airborne dust).  Fly ash is by many definitions toxic waste, and cannot be simply left in a pile.  We’ve tried that; multiple floods have happened when ponds of fly ash slurry have been breached.  That’s right, ponds.  Near coal burning areas will be storage facilities for fly ash, in the form of huge ponds of the stuff.  This situation cannot persist indefinitely; one ultimate solution is for coal residues to be returned to coal mines, but at substantial handling costs.  A cost that gas will completely ignore.

Even if you rely on coal plants for grid buffering, that doesn’t mean relying on 100% coal.  Many “coal” facilities are turning to co-firing: using multiple fuels, not just lump coal.  The same burners, with little or sometimes no modification, can take wood scrap and possibly farm wastes.  Granted, you don’t switch from 100% coal to 100% something else; you go with blends, to minimize adjustments and rework.  Still, the claim that “fuel security == coal trafficking” is not a hard rule, and getting softer all the time.  If nothing else, you can add backup burners (for gas and/or oil) to a coal plant, for a little more money.  In the early 20th century, some ships burnt coal/oil mixtures as a supply hedge and a transitional technology.

And of course, the very need for supply leveling (and thus coal stockpiling) is being challenged head-on by multiple fields.  Caverns, as mentioned above, are already in trials to store energy as pressurized air.  Electricity storage in gigantic batteries is already being done in Japan and Texas.  Literally, town-scale batteries.  Energy storage in electric vehicle packs (“vehicle to grid,” or V2G) is already being demonstrated by a university, the military, and private companies.  This is all in addition to pumped hydroelectric storage, now being done around the world- has been, for decades now.  There are even experiments with running aluminum plants backwards, turning them from massive electricity consumers to massive emergency generators.  Our storage options, besides just piles of coal, will only increase in the future.

And speaking of increasing in the future, coal suffers from an interest problem, and I don’t mean I’m not interested.  Coal plants are huge, and growing huger.  In order to compete, coal generating facilities must become ever larger and more complex, including gasification and combined cycles but also simple economies of scale.  One huge plant beats multiple smaller plants, in terms of power efficiency and operating costs.

But not financing costs.  Huge coal plants become civil engineering projects, not factory widgets.  One huge plant takes years to architect, construct, and finish out, on prepared real estate, before it will ever turn one penny in electrical revenue.  All this time, it’s racking up salaries and parts bills and interest charges, and interest charges on the salaries and parts.  And if unlucky, interest on the interest.

Natural gas turbines, on the other hand, fit on a truck.  They are produced in a factory, on an assembly line.  You order one, and a bit later the truck shows up with your natural gas generator.  More crucially, you need one more, and you get one more, extremely quickly versus coal.  In other words, gas turbines are scalable technology, if not actual widgets.  The financing costs for this are a fraction of what a coal project will rack up.  For use as emergency generators, you may even leave a turbine on the back of its truck.

And that’s why gas installations have been outpacing coal projects, starting in the Eighties.  Ordering one more gas turbine makes the company books balance, where coal would go red, not black.  Another reason: synergy between the power plant and shipping people.  Ships went to gas turbines, again as they’re simply faster and cheaper to purchase and fit out than big steam boilers.  Why is this?  Synergy between the shipping people, and airliner people.  Efficient turbine technology was developed for jets, then borrowed and exploited by heavier ships, and then borrowed and exploited by even heavier land facilities.  This is a combined cycle, but of engineering and business, not exhaust heat.  Again, scalability.

Upshot?  Coal is a legacy not of the 20th century, but the 19th.  Coal was good in steam engine vehicles, which we technically don’t use; even if we did, natural gas still runs steam engines better.  Coal is, at best, treading water, in the jet age.  Oooh, those hippie jets!


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