Polymath A (mostly) technical weblog for Archivale.com

August 6, 2010

The Helium Question

Filed under: Aeronautics,Engineering,Lighter than Air,Materials — piolenc @ 11:21 pm

[This piece first appeared in the Fall/Winter 2006 issue of Aerostation magazine]

LTA: 2006 and the Helium Question

The year 2006 was much the same as any other recent year, at least as far as lighter-than-air flight is concerned. Hopes were raised, then dashed. Projects were mooted, then cancelled. Brave talk was uttered, then swallowed.

If Ought Six is remembered for anything, perhaps it will be that the first visible cracks appeared in the ever-rickety edifice of helium supply. For the first time that I can recall, some users of helium were told that they could not have any at any price, due to the fact that one of the world’s few helium extraction plants was undergoing refurbishment. Presumably extraction has since resumed—there are no panic-stricken “Brother, can you spare some gas?” posts on the LTA-related lists—but this little hiccup is a harbinger of things to come.

Those of you who have followed my rants over the years may want to skip the rest of this piece, but some points deserve to be reviewed. As commodities go, helium is extremely unusual—perhaps unique. It is a by-product of the extraction of another commodity—natural gas—whose unit value is much lower, but whose aggregate value is orders of magnitude greater. This means that the usual assumptions about supply and demand do not apply.

To make it clear why this is so, imagine a commodity—say, a precious metal—that exists in a concentration of a fraction of a percent in a matrix that has no market value. If the market value of the metal justifies it, somebody will extract the tiny metal moiety from the huge mass of matrix, refine and market the metal and dispose of the now completely valueless matrix. The key fact is that, in this hypothetical but typical case, the extraction is driven solely by the market for the metal. If the market value of the metal drops below the cost of bringing it to market, extraction ceases and the metal remains in the ground, in its matrix, waiting for changing conditions to again make it profitable to exploit it.
Contrast this with what will happen if there is a significant increase in demand for helium. Helium, as we know, exists as a tiny fraction of natural gas; some deposits contain more helium than others, and gas from some of those favored deposits passes through a helium-extraction plant on its way to market. The helium in natural gas that is produced without extracting the helium is gone forever, wasted.

Now suppose that there is an increase in demand for helium. Once stored helium stock is exhausted, the only way to meet the greater helium demand is to increase the production of natural gas. This may be done, up to the point that storage capacity for natural gas awaiting delivery to consumers is completely used up. At that point, helium production is capped at a rate proportional to the current demand for natural gas, irrespective of demand for helium. Nobody is going to flare off natural gas to accommodate helium users!

Now the operation of a free market, when production of a commodity is fixed and demand for it increasing, is to raise prices until demand drops to match the supply. This gives a bidding advantage to users who are well-funded and use relatively small quantities of helium. LTA doesn’t match that description, and never will. But there’s worse.

Another effect of a free market is that rising prices of a commodity encourage capital to move into production of that commodity, leading to increased capacity, which in turn tends to put the brakes on price increases. Can we expect this to happen with helium? One can imagine that, with helium prices skyrocketing, producers of natural gas from fields less favored by Nature than those now being exploited might install helium extraction plants at their fields, thus intercepting streams of helium now going up the stack. And then again, maybe not. Helium extraction is capital-intensive—essentially, it requires that all gases except helium be liquefied, leaving only helium in gaseous form. Depending on the projected exhaustion of the field, the helium concentration in the gas and their estimate of the persistence of increased demand, the field’s exploiters may or may not feel that they can expect an adequate return on their investment in new helium plant. Even assuming that the answer is always affirmative, there is a definite physical limit to this capacity increase, which is imposed by the rate of production of natural gas. What is more, each increment of production will be smaller than the last and cost more per unit of capacity, as poorer fields are added to the helium production stream.

The best scenario that we can expect, then, in the event of a true rebirth of helium-based LTA, is a steady rise in price, possibly restrained (but not cancelled) by capacity increases. It is a safe bet, however, that any major increase in helium demand will run up against a hard capacity limit, whether imposed by the reluctance of field exploiters to install expensive helium extraction or by the finite and tiny concentration of helium present in the natural gas stream.
When such an absolute limit is reached, modern governments show a deep reluctance to let market forces operate. Instead, rationing and price controls are imposed and favored users are given priority for supply. In the USA, at least, there is no doubt of LTA’s position in the hierarchy of government favor: near bottom, perhaps just one step above party balloons, perhaps even one step below (what would a political campaign be without balloons, eh?).

In the long run, the Earth’s supply of helium will be exhausted when we run out of natural gas, regardless of the level of demand for helium. Helium is the end product of a long chain of radioactive decay, and for practical purposes “they ain’t makin’ any more of it.”

Of course, I’ve been oversimplifying, by assuming that a revival of large-scale helium LTA would occur in the first place. In fact, no prudent investor would invest in commercial helium-lift LTA without considering the prospects for gas supply, and with the certainty of price increases and the uncertainty of future supply at any price, he will put his money elsewhere.

The plain fact is that helium is already too expensive. Its 6% gross lift penalty compared to hydrogen comes directly out of useful lift, imposing a net penalty around 20% depending on payload ratio. Its cost constrains airship operations by limiting operating altitude or fullness (hence lift) to avoid valving gas and by forcing operators to operate at very low purity to delay “shooting” gas as long as possible. Both constraints further reduce the economic viability of an already marginal transport medium.

If large-scale LTA is to survive, there will have to be a transition to hydrogen as the lifting gas. The only question that is open is: when? If LTA is ever to be used for transport of goods or people, that revival will have to be based on hydrogen lift. And it must be soon.

The time to prepare the transition is now, while there are people still living who have handled hydrogen in an LTA context, and who can instruct others. Hydrogen is more dangerous than helium, but there is no alternative. There are obstacles to be overcome in using it, and the sooner we start overcoming them the sooner we will have viable commercial LTA. The principal obstacles are:

• Lack of trained personnel.  Solution: train some.

• Lack of insurance cover.  Solution: insurance companies will ensure anything for which they have reliable actuarial statistics. Only experience can produce those statistics. Until they are available, operators will have to self-insure. It has been done before, and it can be done again.

• Government regulations and statutes.  Solution: a stroke of a pen.

Hindenburg Syndrome.  Solution: education and exposure.

Priced out of the market, or forced out. Those are the only possible fates of LTA if we persist in considering only helium as a lifting gas. It is, in the current jargon, unsustainable.

FMP

March 29, 2010

The Fallacy of “Energy Deficits”

Filed under: Materials — piolenc @ 9:03 am

Biofuels can pay even if they deliver less energy than went into making them

Some time ago, there was a big dustup, on-line and off, about a study of alcohol production from corn that argued that less energy was derived from  the alcohol than was used in making it. This elicited a storm of protest and contestation from alcohol advocates, who believed that, if true, this fact would condemn their favorite renewable motor fuel to oblivion. My reaction was slightly atypical:

I said “who cares?” and turned the page.

It does seem obvious that, if you get less energy out than you put in, the process must not be viable, but a little thought will demonstrate that this is not necessarily so. To set the stage for clearer thinking, let’s use a concrete example.

Suppose that you have a hunting lodge off in the mountains, too far from civilization and its amenities to bring in electricity from the grid. You like your comforts, though, so over the years you’ve built up a sizable array of photovoltaic panels, producing several hundred watts of output in full sun. Unfortunately, most of your electricity consumption takes place at night, so you’ve also had to build up a battery of Edison or Ironclad cells to store energy during the day for use at night. But wait. When you put three kilowatt-hours of energy into the battery, you only get two or so back. You have an energy deficit; your installation is not viable! Fortunately, you’ve never heard of energy deficits, so you go on happily enjoying the light of your compact fluorescents and the sound of your radio and CD player well into the night. You can even talk to the missus using your cell phone and that booster antenna in the treetops, and get your email using that satellite dish on the roof and your laptop computer.

Some will object that the foregoing example is irrelevant, but in fact it is completely on point. Fuel is not an energy source—it is an energy carrier, just like the battery bank in your hypothetical hunting lodge. Like the battery, it allows energy from an intermittent and diffuse source—the Sun—to be concentrated and  stored for later use. In both cases, if the process—battery storage or biofuel production—were not implemented, the result would be that energy would go to waste. In the hunting lodge example, the wasted energy would be the incident solar energy at midday, when you were out hunting and the lodge was only using a few watts of standby power. In the farm alcohol example, the wasted energy is that stored in the waste biomass, usually cornstalks, used to fire the mash heater and the still.

It’s clear, then, that mere quantity of energy does not tell the whole story;  the nature of the input also matters. If, instead of solar panels, you had used a diesel-fired generator to charge your battery bank, the result could be different; you might save diesel fuel by using the generator to power your loads directly, instead of first storing the energy in a battery bank. Likewise, if Farmer Brown used diesel fuel or heating oil to fire his mash tank and still, it might matter very much if the alcohol that he produced had less heating value than the high-grade fuel that he consumed.

I say “might” instead of “would,” because the relative market value of the input and output also matter. Suppose for instance that Farmer Brown was selling into a market dominated by fuel-cell-based cogeneration. It’s relatively easy to make a fuel cell that will consume lower alcohols, but feeding one on a mixture of higher hydrocarbons like fuel oil usually requires a fuel reformer—an expensive piece of equipment that takes a big bite out of efficiency. In that event, Farmer Brown might very well be able to get more for the clean alcohol that he produces than he paid for the fuel oil that he used, even if the heating value of the fuel oil was greater.

December 22, 2009

Early "Seabasing" Concepts – Still Relevant

Filed under: Aeronautics,Engineering,Floating Structures,Materials,Structures — piolenc @ 6:25 pm

Recently, thanks to the efforts of a friend in the States, a report collection that was formerly available only on 35mm microfilm has been scanned into PDF files. While entering the 400 or so reports into my catalog I came across a 1934 critique, by Charles P. Burgess of the US Navy’s Bureau of Aeronautics, of a proposal by Edward R. Armstrong for a chain of floating airstrips called “seadromes.” These were to consist of an overhead deck and a submerged ballast tank, connected by a double row of vertical cylinders. If that sounds familiar, it should – it’s more or less the standard configuration for modern Very Large Floating Structures (VLFS), including the US Navy’s proposed SeaBase platforms. That was a bit of a surprise to me, because none of the articles on VLFS or sea basing that I’ve seen has acknowledged Armstrong’s much earlier work, which began during WW1 and continued until his death in 1955.

But it gets more interesting, because Burgess’ critique and alternative are just as applicable to the modern proposals as they were to Armstrong’s. Noting that a small waterplane area is the ultimate reason for the stability under wave action of Armstrong’s seadromes, Burgess proposed a more shiplike unitary hull with an anvil-shaped cross section – swollen at the bottom to accomodate ballast, spreading at the top into a wide flight deck – giving a small and very fine waterplane area and much lower resistance to forward movement than the multiple prisms of Armstrong’s concept. In the process, he created a configuration now known by the acronym SWASH – Small Waterplane Area Single Hull – about thirty years before its time. Burgess seems to have been more conscious than Armstrong of the difficulties of deep-ocean anchorage; his concept emphasizes powered station-keeping, which is facilitated by the hydrodynamically favorable hull. Burgess also anticipates modern seabasing proposals, emphasizing the value of a shiplike configuration in getting out of harm’s way if the area starts to “heat up.” I’ve uploaded Burgess’ report to the Files area of the Nation-Builders group on Yahoogroups (file name is BA157.pdf).

A good article on Armstrong and his platform proposals:
http://www.americanheritage.com/articles/magazine/it/2001/1/2001_1_32_print.shtml

The back-issue archive at Popular Science magazine’s http://www.popsci.com also has many articles and news items about Armstrong’s work.

The main difference between Armstrong’s proposal (and Burgess’ counterproposal) and what is mooted now is the current emphasis on modularity. Both Armstrong and Burgess proposed unitary platforms, while nowadays the ability to assemble large units from small, identical components is highly prized – one VLFS concept even involves dynamic assembly and disassembly in situ to suit changing conditions! Armstrong’s configuration is implicitly modular – it consists largely of identical units repeating at equal intervals – which explains its prevalence in modern proposals. Burgess the naval architect, on the other hand, gives his SWASH a beautiful continuously-curved waterline in plan, so his hull could only be built as a single unit. It turns out, though, that minor changes would make Burgess’ configuration “modularizable,” and at the same time cheapen its construction considerably, without compromising its main advantages.

The main change is redesigning the load waterline to consist of a long parallel section, tapered abruptly and symmetrically at both ends. This allows the hull to consist of a variable number of identical “center” units capped with identical “end” units at bow and stern. The end units would have identical propulsion units built in, each capable of giving the whole shebang steerage way and not much more. You end up with the SWASH equivalent of a double-ended ferry, but with only enough installed power for station-keeping. Substituting waterjets with orientable nozzles for conventional screw propellers would allow even very large assemblies to be maneuvered without tugboats. The center units, containing no machinery, could be manufactured in very summary facilities much less well-equipped than standard shipyards. It might be advantageous to make the end units in regular shipbuilders’ yards.

Taking the whole idea one step further, the individual units could be built with double hulls, providing enough reserve flotation to allow them to float, albeit with little reserve buoyancy and with decks awash, even when fully flooded. This would allow them to be assembled into complete vessels or platforms on the water. End units would even be navigable under their own power when unmated and fully flooded – the machinery spaces, located in the ballast tank area, would be sealed and connected with the deck by a narrow trunk like the conning tower of an old-style submarine. This in turn would allow end units and center units to be assembled in separate areas, the end units, mated in pairs, being driven under their own power to where their center units awaited them. The mating operation itself could be carried out in open water, with the end units connecting, independently, with center units one by one until they had enough between them; then the two half-vessels would maneuver to join up.

When newly assembled, the new platform would look like a monitor without the gun-turret, deck flush with the water, but with the hull complete it would gradually be pumped dry inside, ready for fitting-out. It might even be possible to equip the propulsion units to serve as high volume, low pressure pumps, at least in the initial stages of pumping-out.

Materials and manufacturing technology are pretty much ad lib. – steel or aluminum, riveted or welded are feasible, but my favorite is of course ferrocement, which if properly executed can be longer-lived than any other material. Joining method for mating the sections is also up in the air. If the sections are made of steel and they were intended to remain assembled, welding would be the obvious method of choice; bolts are the obvious reversible method, but they are very expensive and would have to be fitted, in our hypothetical open-water assembly method, by divers working underwater and in very poor visibility. One technique that appeals to me is adapted from a system developed for assembling buildings from prefabricated panels in earthquake-prone areas, namely lacing the structure together with steel cables. For permanent assembly, the cables can be grouted into their channels; otherwise they can be secured with cable thimbles at their ends. Post-tensioning would then be possible, which would relieve bending loads on very long assemblies.

Armstrong’s patents:
Canada:
253,140
628,310

US:
1,378,394
1,511,153
1,892,125
2,248,051
2,399,611
2,963,868

France:
532,360
572,543

Burgess’ critique: US Navy Bureau of Aeronautics, Lighter than Air Section, Design Memorandum No. 157, February 1934, “A Proposal for a Single Hulled Seadrome,” by C. P. Burgess. Available from the Files section of the Nation-Builders group on Yahoogroups (see link above).

December 3, 2009

Alternative to Portland Cement

Filed under: Materials — piolenc @ 12:18 pm

I have a sinking feeling, because I haven’t been able to find, in my files or elsewhere, a simple, straightforward explanation of how limes, pozzolans and Portland cement relate to each other, their uses and manufacture. So here’s Marc’s Masterly Summary of Several Millennial Industries, to go with my CD of cement, pozzolan and lime information, currently in preparation.

Limestone is calcium carbonate – usually with a bunch of helpful or detrimental impurities thrown in. Heating it (“burning”) drives off carbon dioxide, leaving calcium oxide or quicklime – a very reactive substance. Traditional lime mortar is made by “slaking” the quicklime with water, giving calcium hydroxide (slaked or hydrated lime) and a lot of heat. This is mixed with sand to make the mortar. This mortar is very plastic and remains workable for a long time, because it doesn’t set by hydration like Portland cement and hydraulic lime mortars do. Instead, it slowly reabsorbs carbon dioxide, re-forming limestone over a period that can extend to centuries. This kind of mortar is not waterproof until it is fully carbonated, so it has to be used in areas protected from standing and flowing water. It does however “heal” small cracks, and it is great for gravity rubble masonry because it allows small shifts in the stones’ positions to reduce local stresses. It also breathes, which protects wooden beam-ends embedded in masonry walls by preventing moisture from accumulating against the wood and promoting rot.

Early on, masons noted that certain limestones produced mortars with very different characteristics, which depended on the presence of different kinds and quantities of impurities. The most valued of the limestones were those which produced hydraulic mortars – that is, mortars capable of setting underwater and forming waterproof structures once set. The Romans discovered that non-hydraulic limes could be made hydraulic by adding pozzuolana – the volcanic ash called lehar here in the Philippines. This  ash was a source of chemically reactive silica, which was naturally present in the hydraulic limes. Roman concrete, of which many splendid examples have survived to the present, is made with lime-pozzolan cement, sand and gravel. Substitute Portland cement for the lime-pozzolan cement and you have modern concrete.

In the mid-19th century somebody had the idea of forming a chemically balanced cement by starting with hydraulic limestone and adding more silica to it by grinding it up, mixing it with a suitable silica source (usually some kind of clay), then sintering the two together at high temperatures to form a clinker, which was then ground back into powder. Portland cement’s superior strength and rapid set gave it instant success, and wherever it became available lime all but disappeared from the building trades. This is unfortunate because there are applications where lime is still a far better choice. One has already been mentioned: wall plasters that breathe. Another is grouts (mortars designed for high pressures) that expand slightly when setting. These were used extensively during subway construction when it was necessary to underpin existing buildings to keep them from collapsing into the dig.

Recently, lime-pozzolan cements have come back into consideration because of the much lower energy required to make them and the abundance of suitable silica sources. One of the most abundant in the industrial countries is fly ash, but in the Tropics especially the favored one is rice hull ash. Rice hulls have a very high silica content, and by suitable burning the carbon content is consumed, leaving a very fine, porous white ash with very high reactivity – exactly what is needed. The burning is best done under controlled conditions, because if a certain temperature is exceeded (I’ve forgotten it, but it’s given in UNIDO1984) the resulting ash is crystalline, and less reactive than the amorphous ash formed at lower temperatures. On the other hand, lower temperature makes it harder to burn off all the carbon so the ash tends to be greyish or even black. A lot of work is being done to find simple ways to get the right process parameters, because rice hulls have to be burned near where they are produced – preferably at the rice mill – because they are too bulky to transport economically. So the plant that burns them needs to be simple and cheap enough to be co-located with a rice mill, either permanently or by hauling it to the mill on a trailer.

In India, rice hull ash/lime cements are called ashmoh, and have been extensively researched. See Gupta1978. I can’t help wondering, after re-reading Gupta, whether it would be possible to make ashmoh in one step by using rice hulls as the fuel for burning lime, then grinding the resulting mixture, which should be flaky rather than solid like PC clinker, and therefore cheaper to process. I wonder whether it has been tried.

There is yet another use for pozzolans, namely as extenders and improvers of Portland cement. In setting, Portland cement releases hydroxides which will react with excess silica if it is present in reactive form, making a denser, more waterproof concrete or mortar. Coarse pozzolan can be a liability, as the alkali-silica reaction occurs over a long period after cure and can actually cause deterioration. Fine silica, on the other hand, reacts during cure and gives better strength and density. This sensitivity to the physical form of the silica accounts for the wide range of PC-pozzolan mix properties. Rice hull ash, correctly produced, is ideal: very fine and amorphous. There is an obvious opportunity here to produce very high-grade cement-pozzolan mix at net cost that is much lower than the pure PC. The blending plant, like the rice hull burning plant, would have to be either mobile or co-located with a rice mill.

Further reading:

(UNIDO 1984) Rice Husk Ash Cements: their development and applications. United Nations Industrial Development Organization, 1984

(Gupta1978) Gupta, Hemendra Kumar: Optimization of Manufacturing Parameters for Ashmoh Cement. Thesis, Indian Institute of Technology, Kanpur, 1978

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