Grantville Gazette 38 gg-38
Page 25
This procedure was practical in the early-twentieth century, thanks to the Hall-Heroult electrolytic process for making aluminum.
The Mauricheau Beaupre "activated aluminum" variant involves adding water to a mixture of fine aluminum filings, mercuric chloride, and mercuric cyanide. One kilogram solid mixture, so reacted, yields 1.3 cubic meters in about two hours. The apparatus required is minimal. (Ellis 525). The aluminum must not contain copper (Teel 70).
Hydrolith Process. This was another field expedient, exploiting the reaction
CaH2 (42 grams) +2H2O (36 g) -› Ca(OH)2 (56 g) +2H2 (4 g).
So only 55 pounds of calcium hydride is needed to obtain 1,000 cubic feet hydrogen. The calcium hydride would be made at base, from a calcium salt (oxide, chloride) and hydrogen in presence of a reducing agent (sodium, magnesium).
The French used this system in the early-twentieth century; the calcium hydride was carried on latticed trays, immersed in water; the hydrogen rose up. This gas was contaminated with water vapor, which was removed by passing it over dry calcium hydride. (Taylor 128). You also need to remove ammonia, and heat evolution can be a problem. A typical six generator wagon produces 15,000 cubic feet/hour. (Greenwood 229).
A related, speculative process uses lithium hydride:
LiH2 (9 grams) +4H2O (72g) -› 4 LiOH (75g)+ 3H2 (6g).
Note the enormous yield of hydrogen relative to the amount of lithium hydride. This would be great for the field. The ratio is good enough so it's feasible (from a weight, not necessarily a safety standpoint) to bring the lithium hydride on board for use at a destination to make more hydrogen. It has even been suggested that the reaction could be used to produce hydrogen while in flight, reacting the hydride with water ballast (warning: this can be a violent reaction!), and then dropping the lithium hydroxide. (Teel 67). But the cost of lithium hydride, which is made by reacting lithium metal with hydrogen; is prohibitive (even 1992 price was $72/kg-Kirk-Othmer).
Silicol Process. The basic reaction was
2NaOH+Si+H2O-›NaSiO2+2H2.
It was first proposed in 1909, and became a popular military field expedient, especially on ships. Not only were the ingredients quite safe to transport, the produced hydrogen was of "very high purity." (Taylor 143).
Initially, commercially pure silicon was used, but this was replaced by the cheaper ferrosilicon, which was used for deoxidizing steel and introducing silicon into alloys. Ferrosilicon may be made by reducing sand (silica) with coke in the presence of iron. The ferrosilicon typically contains small amounts of phosphine, arsine, and hydrogen sulfide. (Greenwood 227), as well as air. (Teel 45). The silicon content has to be over 80% for reasonable effectiveness, and particle size affects the production rate. (Teel 50). The caustic soda must be neither too dilute nor too strong. (Teel 52).
In addition, there is an explosion hazard. The ferrosilicon dissolves only slowly in cold solution, and thus can accumulate. But the reaction produces heat, and as the solution gets hotter, the accumulated ferrosilicon is attacked, leading to rapid evolution of hydrogen. (Teel 57).
A transportable plant can produce 60-120 cubic meters/hour, whereas stationary plants of up to 300 capacity have been constructed. (Ellis 523) [The typical portable plant was mounted on a three ton truck and produced 2,500 cubic feet/hour; the largest portable apparatus produced 14,000 cubic feet/hour. The reaction has also been used for stationary production at up to 50,000 cubic feet/hour. (Greenwood 226).
For the 1929 British R100 airship, "249 tons of caustic soda and 183 tons of ferro-silicon produced 8,610,705 cu.ft of hydrogen (20.3 tons) and 929 tons of sludge [sodium silicate]." (Wilcox). The R100 had a gas capacity of about 5,000,000 cubic feet, so the gas produced was substantially in excess of the capacity. Wilcox's information about production rate is somewhat contradictory. He says that the plant could produce 60,000 cubic feet/hour, but that the highest daily production was 500,000 cubic feet. Also, that it took ten days to fill fourteen of the R100's fifteen gas bags.
An alternative reaction that can use the same apparatus exploits the reaction of aluminum with sodium hydroxide, and was used by the Russians in the Russo-Japanese War. (Taylor 145-6). It can produce 10 cubic meters/hour. (Ellis 523).
Hydrogenite process. This starts with a compressed block of a mixture ("hydrogenite") of silicon, caustic soda, and soda lime, kept in an air-tight container. To use, the container is placed in a water jacket, a match or a red hot wire is applied to a small hole in the lid. The silicon is oxidized to silica, a heat-releasing action. This heat makes possible the reaction
Si+Ca(OH)2+2NaOH-›Na2SiO3+CaO+2H2.
The heat turns the water to steam and eventually this is permitted to enter the generator, increasing yield by a reaction of the silicol type.
While it requires that 50% more material be provided than for the silicol process, much less water is needed, which would be advantage for desert use. (Taylor 168). A production rate of 150 cubic meters/hour is possible(Ellis 521ff). The portable wagon-based apparatus of the French army, featuring six generators grouped around a central washer, produced 5000 cubic feet/hour. (Greenwood 228).
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Another "dry" method (by Majert and Richter) involves heating a mixture of zinc dust and slaked lime to redness, but the Prussian army deemed it too slow (it took 2-3 hours to fill a balloon). (AGLJ).
Large-Scale Production
Some processes are best suited to production of hydrogen on a large scale and at a low cost. Unless the airship hangar happens to be near the manufacturing plant, the gas will have to be compressed and shipped in containers (which must be returned empty), which increases the cost.
Steam-Carbon. First, water gas (a mixture of carbon monoxide and hydrogen) is produced by reacting red-hot coke or coal with steam at 800 or 1000oC (2002McGHEST):
H2O (18 grams) + C (12 grams) -› H2 (2 grams) + CO (28 grams).
Just making steam, by itself, consumes fuel. According to EB11/Railways, the faster you burn coal, the lower the efficiency. With Indiana block coal (13000 BTU/lb):
Those are for a 1900 locomotive boiler. and a stationary plant might have a higher efficiency. Additional coal would need to be burnt to superheat the steam to the required temperature. The increase in coal consumption to achieve 100oC superheat is 5.5%, for 150, 8.3%, and for 200, 11%. (Stovel 1475). (Superheated steam is more efficient than ordinary steam, however, in terms of the heat content of the steam relative to that of the coal burnt to produce it. (Babcock 137ff).
With the Baldwin experimental locomotive 60,000 (1926), designed for high efficiency, evaporation declined from 10 to 6.5 pounds water per pound of dry coal, as firing rate increased from 30 to 150 lb/ft2 grate/hr. and superheat increased from 180oF to 257oF. (Pennsylvania RR, Fig. 19).
If you burn carbon in air, the hydrogen will be contaminated with nitrogen from the air. This can be avoided by burning pure oxygen into carbon monoxide, but then you must provide the oxygen somehow.
The process can be operated on a mostly continuous basis; occasionally clinker must be removed. (Teel 81). Water gas has impurities, such as hydrogen sulfide and ash (84).
Water gas in turn can undergo this shift reaction, discovered by Felice Fontana in 1780:
CO (28 grams) + H2O (18 grams) -› CO2 (44 grams) + H2 (2 grams)
Since exposure to CO (carbon monoxide) is dangerous, naturally there was interest in conducting the steam-carbon reaction in such a manner as to minimize its formation, i.e., to obtain the mixture of carbon dioxide and hydrogen:
2H2O + C -› CO2 + 2H2.
Gillard found that this could be accomplished by use of an excess of steam. The carbon dioxide can be removed on a batch basis (see below), but unfortunately it proved "very difficult to carry this out in practice on a large scale. . . ." (Sander).
BAMAG worked at a low temperature (at which the reaction equilibrium is favorable), but with catalysts (typically nickel) to speed up the reaction. This results in what is reportedly the cheapest meth
od of producing hydrogen (1 shilling/9 pence per 1000 cubic feet), but unfortunately the product contained 4% nitrogen, a serious disadvantage for aeronautical use. (Greenwood 162). 2002McGHEST suggests a reaction at 350oC over an iron oxide catalyst.
Griesheim-Elektron instead disturbed the water gas equilibrium by "absorbing" the carbon dioxide with lime or other alkali. Cost of production (1912) was 2s/2s.5p-2s/9p per 1000 cubic feet for a moderate size plant. While the process can be carried out at a lower temperature than the steam-iron process below, reducing maintenance costs, "the handling of the large amounts of lime presents some difficulty." (Greenwood 167ff).
Of course, we can eschew the shift reaction, and remove the carbon monoxide with an "absorbing agent" or by liquefaction. EB11/Carbon notes that it is "rapidly absorbed by an ammoniacal or acid (hydrochloric acid) solution of cuprous chloride," but the resulting hydrogen is only 80% pure. (Sander) Later, Frank and Caro thought of employing heated calcium carbide. This conveniently "absorbed" not only carbon monoxide, but also carbon dioxide and nitrogen, and in the process produces graphite and calcium cyanamide. (Sander; Elis 597).
Liquefaction (Linde-Frank-Caro method) at -200oC works well, but small-scale plant costs are high (Ellis 460) and concerns have been expressed about the dangers of working with compressed carbon monoxide (595). In 1912, a plant producing 3500 cubic feet hydrogen/hour cost about 13,000 pounds, and had a cost of hydrogen production of 3 to 4 shillings per 1000 cubic feet. (Greenwood 174).
A little more explanation of liquefaction may come in handy. A gas can only be liquefied if cooled below its critical temperature; at that temperature, it must be compressed to the critical pressure; at lower temperatures, lesser pressures are needed for condensation.
(Teel 114ff).
It can be seen that cooling water gas to -200oC (usually by surrounding it with liquid nitrogen boiling under reduced pressure) permits separation at normal pressure. Or one may use a more moderate cooling and greater-than-atmospheric pressure. The liquefied carbon monoxide is used to pre-chill the incoming water gas, and then is burnt as a fuel. (Teel 119).
Steam-iron (dry) process. Lavoisier was the first to show (1783) that hydrogen could be produced in an acid-free reaction, by reacting iron with steam. And Argand recognized that the yield would be higher than with the acid process. (Clow 159).
There are really two different steam-iron processes, the single step non-regenerative one for field use, in which iron is consumed, and the two-step cyclic one, in which iron oxide is reduced with water gas to iron, and then the iron is reoxidized to iron oxide with steam, for large plants. The former has the simplified equation
Fe ( 56 grams) + H2O (18) -› H2 (2) + FeO (72)
Steam-iron generators were used by the world's first air force, the 1794 Compagnie d'Aerostiers, as this process was safer, cheaper, and most important, because the sulfuric acid was needed for gunpowder manufacture. (Boyne 378; Langins 536).
In autumn 1793 Coutelle placed iron scrap into a three foot long, one foot diameter cast iron reactor pipe, which in turn was placed inside a furnace. Water was introduced into the pipe, and turned to steam (Langins 537). There's gas flow rate data for six experiments: 0.32-1.114 (0.544 average) m3/hr. Water flow rates were in the 22-58 g/min range. (539). In one experiment, in the course of four days and three nights, 23.83 cubic meters hydrogen was produced. (538). That corresponds to about 40% yield.
The scale of these experiments was almost 150 times that of in the 1780s, and a scale-up problem was encountered: carbon dioxide. The wrought iron musket barrel used in the laboratory experiments was essentially free of carbon, but Coutelle's cast iron pipes were up to 4.5% carbon. The carbon dioxide would reduce the buoyancy of the gas; the density of the produced gas ranged from one-half to one-sixth that of air; pure hydrogen would be about one-fourteenth. The problem was addressed by bubbling the gas through lime water, but even then the gas was on the heavy side (possible explanations include failure to change the limewater frequently enough; use of too high a gas flow rate; or failure to first remove dissolved air. (549).
In March 1794, the technology was taken to a new level; each of seven reactor pipes, eight feet long, one foot in diameter, and one inch thick, were stuffed with 540 pounds iron. (This was essentially the system taken into the "field," see Hoffmann 24). Note that each pipe, so loaded, weighed a ton. At this new scale, a problem that had been minor before became more significant: if the reactor pipes were heated too vigorously; they cracked or melted (cast iron melts at 1050 oC). (543). Sometimes the heating was uneven, with some pipes softening and others not heated enough (546). It didn't help that the pyrometers in use were poorly calibrated, and the pipes were poor in quality; locally produced pipes were even permeable to water! (547). There were also problems with the cement used to seal the reactor pipe to the exterior tubing; it cracked and thus gas was lost. (546, 550).
These French steam-iron generators are best viewed as "relocatable" rather than truly portable field equipment. After the 1793 experiments, it was envisioned that a balloon could be filled five or six days after the arrival of the generator equipment at the launch site. (Langins 542). In actual practice, the furnace, with a twenty-foot tall chimney, took twelve days to build (16,000 bricks were needed, and local bricks weren't necessarily refractory enough). (546). In contrast, the American Civil War generators were up and running within a matter of minutes.
With these main generators, it reportedly took 50 hours to fill a 30 foot diameter (4500 cubic feet) balloon (Delacombe 31) and such production was considered slower than the acid-iron method. (Boyne 378).
However, the French did also have a smaller scale furnace that had a single pipe and could be assembled in an hour. It used as much fuel as the large furnace, but could produce 800 cubic feet in 48 hours using 180 pounds of iron. It was used to "top off" an inflated balloon that had leaked while transported from the main facility to the launch site. (Langins 552).
The French military ballooning company was abolished in 1799, and the steam-iron process didn't return to public notice until 1861. Then, John Wise proposed that the Union adopt a horse-drawn generator wagon with two eighteen-inch cylindrical retorts made from boiler plate, a boiler, and a firebox, the latter generating heat for both steam generation and for heating the solid reactants (a combination of charcoal and iron turnings, so this was really a blend of the steam-carbon and steam-iron methods) in the retorts. (I visualize this as a bit like a locomotive, but with retorts replacing the piston cylinders.) A tender was to carry water, iron turnings, and firewood, again much like a locomotive. He asserted that a 20,000 cubic foot balloon could be inflated in four hours.
Contemporary calculations showed that for a single inflation, the wagon would need to carry 7500 pounds of iron turnings, and twenty-two cubic feet of water (1364 pounds by my calculation). The machinists declared that the generator would weigh more than five tons, and of course the tender would be additional. The estimated cost of the generator was $7,000. The government declined to fund the project. (Haydon 77).
The British experimented with the steam-iron method in 1879. Captain Templer reportedly generated hydrogen at a rate of 1,000 cubic feet/hour (BLE 109). The apparatus weighed 3.5 tons, was carried in three general service wagons, and could generate enough gas for two balloons in twenty-four hours. "But the apparatus did not prove satisfactory." (Baden-Powell 742). Possibly, the British expectations were too high; Templer said that he wanted a production rate of 5,000 cubic feet/hour. By 1885 the British had switched to shipment of compressed hydrogen to the field. (Moedebeck 226).
Insofar as field use in the 1632 universe is concerned, we clearly aren't going to want to go with an installation like that used in the French Revolution. The question is whether a viable system could use a firebox and boiler similar in size and design to that of a nineteenth-century steam locomotive, and then route the steam through reactor tubes to oxidize the iron. (Coutelle in fact considered use of steam engine cylinders as
reactor tubes-the steam engine existed in 1794, even though the steam locomotive didn't.) Such a system could at least be transported by rail.
From the equation quoted earlier, it takes nine pounds of water to make one pound of hydrogen, and 5.23 pounds hydrogen occupies 1000 cubic feet (20oC). A pound of coal should evaporate five to ten pounds water (although more coal would be needed to heat the iron and to superheat the steam to the most effective reaction temperature). But it seems to me that the steam-iron process on the locomotive scale should work (although not necessarily better than the acid-iron process).
One thousand cubic feet hydrogen provides about seventy-two pounds of lift. And to produce it, you need one hundred ten pounds of iron. So carrying iron on board an airship for hydrogen production at destination is a losing proposition.
The purity achievable with the early-twentieth century embodiment of the steam-iron process is 98.5-99% (Taylor 172) . The forward reactions are:
2H2O + 2Fe -› 2FeO + 2H2
3H2O + 2Fe -› Fe2O3 + 3H2
4H2O (72 grams) + 3Fe (168) -› Fe3O4 (232) + 4H2 (8)
The reaction products of the simple process do have possible utility; FeO as a black pigment, Fe2O3 as a red pigment and as jeweler's rouge, Fe3O4 as a black pigment and a catalyst in the water gas shift and other reactions. And, of course, all can be smelted to regenerate iron. Which, of course, is one stage of the regenerative process.
Getting the regenerative steam-iron process working properly isn't trivial. The iron-producing reduction with water gas is endothermic and the hydrogen-producing oxidation is exothermic.
It may be possible in a large plant to use waste heat from retorts that are in the steaming step stage to warm retorts that are in the water gas stage. However, that heat isn't enough, by itself. (Taylor 55). Both the carbon monoxide and the hydrogen of water gas are reducing agents, but there are fuel economies in working at lower temperatures, which favor carbon monoxide activity. The catch is that this results in higher levels of carbon and carbon monoxide in the next step. (Greenwood 178)