ELECTRICAL FIXATION OF AERIAL NITROGEN.

New Zealand Journal of Agriculture, Volume XVIII, Issue 4, 21 April 1919, Page 200

ELECTRICAL FIXATION OF AERIAL NITROGEN.

By

J. ORCHISTON, M.I.E.E., Wellington.

Wellington.

In a summary of a report by Dr. T. H. Norton on the proposed manufacture of nitrogen from the air in the United States, given by the Electrical Review, the authority named is quoted as stating, “ All the fixation processes at present in industrial use are likely to remain so, and to extend in application according to local circumstances. Further progress will be made, but the general problem of fixing nitrogen from that inexhaustible reservoir the atmosphere is already solved, and the. supremacy of synthetic manufacture over natural supplies of nitrate is already asserted. .. .. The. pre-war cost of producing 100-per-cent. nitric acid from Chile saltpetre was about £22 iOS. The cost of production by the electric arc depends chiefly upon the cost of energy. The new Rankin arc process is reported to give 33 per cent, higher yield than the Norwegian furnaces for equal energy-expenditure. If this claim be justified the furnace has great possibilities, especially in the western .parts of the United States of America, where energy costs as little as £1 is. per horse-power year. The cost of the Ostwald process for oxidizing ammonia is given as £2 ros. per ton of 100-per-cent. nitric acid (including 17s. 6d. for liberating ammonia from cyanamide and concentrating 52-per-cent. nitric acid). The cost of production of 100-per-cent. nitric acid made by various methods may therefore be summarized as follows : —

Electrical Energy per Horse-power per Ton Year - (British).

£ s. £ s. From Chile saltpetre (at 1914 rates) . . . . . . . . 22 10 Birkeland-Ey de arc process .. .. .. ..25 133 ~ ~ .. . . •• . . ..in 10 11 Rankin arc process .. ;. .. .. . . 1 11 ' 915 By oxidizing ammonia (from cyanamide) (a.) Ammonia at per ton . . . . ..25 14 17 (&.) . „ ' „ ’ . . . . ... 111 13 8 (c.) Ammonia at £23 6s. per ton . . . . ..in 10 14

The Electrical Review adds, “ Overpopulation of the world:a contingency which has troubled many people, however unnecessary—practically impossible now that unlimited quantities of atmospheric nitrogen can be fixed to ’meet the needs of intensive agriculture. An abundant supply of synthetic nitrogen compounds, made within our own frontiers, means an assured supply of explosives and security against starvation in war-time. Heavier crops may be obtained with less labour where nitrogenous fertilizers are used liberally. .Finally, a national nitrate industry provides profitable investment for capital and labour, benefits industry and agriculture by its products, and

improves the balance of trade by substituting home production for importation.”

As regards New Zealand, it is estimated that as power can be produced at the Bowen Falls, Milford Sound, at less than 15s. per horse-power year, the corresponding cost to produce a ton of 100-per-cent. nitric acid by the Birkeland-Eyde process would be £7 16s. 2d., by the Rankin method £5 10s., and by the Kilburn Scott furnace somewhat less. It would, however, be well to add 20 per cent, for extra labour charges over that paid in the United States.

To produce calcium nitrate all that is required is to pass a dilute nitric acid (35 per cent, to 40 per cent.) through vats containing limestone or marble until the liquid becomes a saturated solution of calcium nitrate, after which it is crystallized by evaporating the surplus water by means of heat given on from the arc furnace during the process of burning the air. . •

Many people think that because nitrate of soda is found in a natural state in Chile" it is hopeless to attempt to compete with the natural product. They overlook the fact that the nitrate deposit, locally known as caliche, occurs as a layer from 1 in. to 6 in. thick under a bed of conglomerate consisting of sand, feldspar, and pebbles, usually from 20 in. to 30 in. thick. The caliche is never , pure nitrate of soda. It z contains mixtures of nitrate of potash, common salt, iodide and bromide of sodium, alkaline sulphates, sulphate of lime mixed with sand, &c., and only averages 25 per cent, nitrate. Picked pieces contain more.

To extract the crude salt a hole 20 in. in diameter is dug in the ground. When the saltpetre bed is reached a chamber 35 in. to 40 in. in diameter by 12 in. deep is made, and 3 cwt.' to 4 cwt. of powder inserted. - By this means a radius sometimes reaching 40 ft. is laid bare. The crude salt is hand-picked to eliminate stones and fragments of little value. It is then conveyed by means of baskets or trucks, which camels transport or draw, to the works for treatment. To dissolve the crude caliche three kinds of apparatus are used, involving the use of coal for heating and raising steam. When the solution is concentrated enough it is run into cases or boxes, where it clarifies, and is then decanted on Top of the depot into iron or wooden crystallizers. The resultant crystals average about 95 per cent, of nitrate of soda, and are then ready for packing and conveyance by rail to the coast. '

It will thus be seen that the actual labour involved in turning this natural product into a marketable commodity is much in excess of that involved in the electric process, in addition to the cost of coal and explosives. Labour troubles on the nitraterfields have been very pronounced of late years, and still more accentuated after the war began, resulting in a considerable increase in the cost of production. Added to this the Chile Government levies an export duty amounting to £2 5s. per ton. Prior to the war Chile nitrate of soda was delivered in Europe for about £10 per ton. At present it is quoted in New Zealand at about £25 per ton, but is practically unobtainable. There is every indication that it will never return to the pre-war figure ; hence the greater need for developing our water-powers - where, conveniently located for transport facilities.

The following is the atomic composition of a ton of the electrically manufactured fertilizer, calcium nitrate, the second analysis being

another version of the case :—

lb. Nitrogen .. .. 291-58 Calcium .. . . , 437-08 Hydrogen . . .. 58-68 Silicon .. . . 2-60 Oxygen .. .. 1,450-06 Total . . . . 2,240-00

lb. Nitrogen peroxide .. r 124-70 Lime (CaO) ... . . 581-00 Water .. - . . 528-64 Silica . . . . 5-66 Total .. .. 2,240-00

It will be observed that the only raw material not produced by the hydro-electric power is the lime and silica. As unburnt limestone or marble is used, the total amount contained in a ton of nitrates involves an expenditure of only a few shillings.

In addition to the burning of the air in the electric furnace, the bulk of the work of manufacture is performed by electric power, and the whole process is largely automatic —a very important consideration where labour is costly.

Electrically manufactured ammonium nitrate, a combination of ammonia and nitric acid, contains no less than 35 per cent, of nitrogen, and may therefore be classified as a concentrated fertilizer of the greatest value in the smallest bulk.

One great advantage claimed for the electrically manufactured fertilizers is that they can be depended upon to be uniform in quality and always up to standard. Other fertilizers may or may not be up to standard. . It is well known that the proportion of phosphoric acid contained in commercial basic slag varies considerably. For example, eleven samples tested by J. Fritsch, the French agricultural chemist, averaged 18-28 per cent, of -phosphoric acid, being equivalent to 129-39 lb. of phosphorus per ton. The samples fluctuated from 12-41 per cent, to 40-32 per cent, acid, or 87-83 lb. to 285-37 lb. of phosphorus to the ton, the balance being principally lime and silica. Stassfurt kainit usually contains 12-4 per cent, of potash, or 277-7 lb., equivalent to 230 lb. of potassium per ton.

In conclusion, it may be safely stated that owing to their isolation and the intervening mountains and lakes the water-powers of the western Sounds of Otago are practically of no commercial value for transmission to areas where any appreciable population is located. These powers, however, are eminently adapted for electro-chemical works on the spot, such as manufacture of the following products : Nitrogen, calcium carbide, ferro-silicon, ferro-manganese, ferro-titanium, ferro-nickc 1 , ferro-molybdenum, ordinary steel, tool-steels, tungsten, zinc, calcining coal for carbon electrodes, graphite, carborundum, bauxite, aluminum, magnesium.

The electric furnace can utilize power which once over the falls is gone for ever, reclaim materials which in fuel-fired furnaces are irretrievably lost, and produce from them products necessary to the advancing demands of the arts of peace as well as to the national defence.