CHEMICAL NEWS, Oct. 19, 1917

THE

CHEMICAL

VOL. CXVI., No. 3021.

THE

NEWS

MANUFACTURE OF NITRATE OF AMMONIA BY ELECTRIC POWER AT COKE-OVEN PLANTS. By E. KILBURN SCOTT, A.M.I.C.E.. M.I.E.E. (Concluded from p. 172).

Estimate of Cost.

WE will assume the electro-chemical plant is of such size as to utilise 1000 kw., the round figure above mentioned, which the power-house will supply continuously. The factory will be equipped with the three-phase furnaces and boilers, switchgear and instruments, fans for air supply and circulation of gases; apparatus for cooling and oxidation of gases, also the acid and alkali absorption towers or chambers, complete with acid elevators and distributors; reservoirs and mixing tanks; evaporators, crystallising and drying apparatus, &c. A convenient method of arriving quickly at an over-all price commonly used for electro-chemical plants, is to take a price per kilowatt. £8 is a fair price, so the total is £8000.

The price of electrical energy is assumed at d. per unit, which is fair, because electro-chemical factories in this country have been supplied with electric energy at under that figure for many years.

The number of working hours in a year-namely, 8000 -is convenient because it leaves a balance of 760 hours for overhaul time, &c., and thus less spare plant is required. It also allows for intermittent running off the peak in winter, if found necessary.

Depreciation on the electro-chemical plant may be taken at 10 per cent, this being sufficient to pay for a new plant in about seven years. It should be noted that a large proportion of the capital cost is required for absorption plant which is largely of brickwork, and for which the depreciation might be taken at 2 per cent.

The yield of acid is reckoned at 13 tons of 33 per cent nitric acid per kilowatt year-that is to say, 1500 tons from a plant utilising 1000 kw. This is based on a yield of 66 grms. of concentrated acid, or 200 grms. of 33 per cent acid per kilowatt-hour, thus

200 grms. X 1000 kw. x 8000 hrs. X 2.2
100 X 2240

= 1500 tons.

As a matter of fact greater yields are obtainable, but the above figure is sufficient for the purpose and to show the sequence of the calculations.

Working Expenses.-Assuming the electro-chemical plant to cost £8000, and to utilise 1000 kw. for 8000 hours per annum at d. per unit, the expenses are

This, for an output of 1500 tons, gives £43 per ton of 33 per cent nitric acid, the equivalent rate for pure acid being £13 10s.

For a plant to utilise ten times the amount of energy, or 10,000 kw., the cost should be much less, even taking the above figures for the yield.

The amount of ammonium nitrate that can be made by

* A paper read before the Coke Oven Managers' Association (Midland Section), July 28, 1917. From the Colliery Guardian, August 3, 917.

187

Inserting 1500 tons of acid instead of the figure 189, we get 125 tons of pure ammonia plus 1500 tons of 33 per cent nitric acid gives 635 tons of pure ammonium nitrate. As to the value of ammonia from the coke-oven gas, the author takes the figure mentioned at the beginning of this paper-namely, £30 a ton, or 31d. a lb. It is surprising how opinions differ on this simple matter. Many accepted electrical calculations, which really do involve detailed consideration, and yet quibble as to the value of ammonia. As a rule they go wrong by taking the ruling price of sulphate of ammonia and deducting the price of ammonia from that. It is perfectly obvious that this is incorrect, because no one would make ammonia from such a finished manufactured product.

Cost per Ton.-The cost per ton may now be set out as follows:

1500 tons of 33 per cent nitric acid at £4)
125 tons of pure ammonia
.. at £30

£6750 3750

In addition to ammonium nitrate, there is also the sodium nitrate-nitrite. This may be assumed at 1-10th of a ton per kw. year, and it is readily saleable. It should be worth £1500 a year.

Price. Before the war, nitrate of ammonia made by the electric process in Norway, was sold in large quantities at £28 to £32 a ton. Properly speaking, there is no quotation now, because all the make is taken by the Government for explosives. Its minimum price may, how ever, be fairly taken at double the above figure.

What will happen after the war we cannot tell, but one thing is certain-namely, that the price per unit of contained nitrogen will be higher for nitrate of ammonia than any other nitrogen compound. This has always been so, because the combined nitrogen is 35 per cent. Usual percentages of combined nitrogen are given in the following table :

Usual p.c. of nitrogen. 151

18 13

18

coal .. Made by electric power (35

As a means of transporting combined nitrogen from one part of the world to another, nitrate of ammonia is better than any other medium, so it is likely to always hold the field in the export market.

Uses of Nitrate of Ammonia.

Nitrate of ammonia is the principal ingredient of most safety mining explosives, the word "safety" being a relative term expressing the fact that they are safer than dynamite, &c. On the Continent, before the war, nitrate of ammonia explosives were considered so safe that they were carried on railways at ordinary rates. This, no doubt, had much to do with nitrate of ammonia explosives being adopted more quickly than with us, for our railway authorities have always insisted in charging at the high

rates.

The British and certain other governments have passed regulations insisting on only safety or permitted explosives

eing used in mines. The more this idea extends the more nitrate of ammonia will be required.

Other uses of the nitrate are: in burster charges for shells; as an explosive for tree planting; and as a fertiliser.

Importance of Home Manufacture. Before the war practically all the nitrate of ammonia used in this country for making safety explosives for mining, &c. was imported from Norway, which, considering the necessity for nitrate of ammonia, is another instance of the absurdity of allowing foreigners to control businesses important to the nation. Norway had no coal from which to ohtain ammonia, and so the ammonia had to be sent from England. Ammonia liquor was collected from gasworks and cokeoven plants, and concentrated to bring the ammonia up to 25 per cent. The solution was then railed to Hull, shipped in steel tanks to Skien in Norway, and carried a considerable distance up country to the air nitrate factory. As the proportion of water was 75 per cent, the freight, calculated on the real ammonia in the solution, was naturally high. The cost of carrying steel tanks to and fro, and the heavy depreciation of them, was also a great expense. Finally, the nitrate of ammonia when made was brought from Norway to this country, a great deal of it going to Nobel's works in Ayrshire.

Since the war ammonia liquor has continued to be sent to Norway, and nitrate of ammonia brought back, but since the submarine menace this business has practically stopped. Ammonia is now being made in Norway by acting on calcium cyanide with superheated steam in autoclaves, but the Norwegians prefer our by-product ammonia as being cheaper.

Before the war Germany was the largest purchaser of Chili nitrate, taking twice as much as the next consumer, the United States, and over six times as much as this country. Now Germany does not require any Chilian product, because immense plants to make nitrates from the air have been established. As a matter of fact, this air nitrate development ranks as the most remarkable scientific achievement of the war.

It will easily be seen that by making nitrates from air the Germans are at a great economic advantage, for our complete dependence on Chili nitrate means we have to pay large sums for the nitrate and for transport, insurance, &c. Also there is part of the immense national charge for protecting the sea routes by which we get it here. Large sums are also required for the pyrites, sulphur, and for the plants to manufacture sulphuric acid with which to treat the nitrate.

DISCUSSION.

The PRESIDENT, in inviting discussion, said Mr. Kilburn Scott had opened their eyes to something they did not know of. His paper had been most interesting and of very high educational value.

Mr. B. W. HAIG said that Mr. Kilburn Scott had made a very good case indeed of what he had set out to show. There were doubtless many coke-oven installations in Yorkshire quite large enough to run successfully such an installation as had been described. The paper covered a very wide field, and there were certainly many points upon which they would like to hear a good deal more before they put themselves in a position of recommending their firms to embark upon so large a project. Mr. Kilburn Scott's remarks as to the comparative costs of power derived from steam and gas engines in themselves would have made a valuable paper, and he (Mr. Haig) wished he had come prepared with figures to suggest some questions on this matter. It was somewhat surprising to hear that colliery proprietors could value their power as nothing, in view of the fact that certain coke-oven people were selling their gas at very good prices; and whilst he was not prepared with figures on which to challenge those advanced by Mr. Kilburn Scott, the production of power at d. per

unit certainly struck him as a very low estimate indeed. It would have to be a very large unit in which the process could be profitably adopted. There would have to be highly skilled officials in the electrical department, in view of the danger of using such high voltages as suggested. Most coke-oven plants would not at present have such men on their staff, and the amount put down for salaries and upkeep seemed to him to be on the small side. The technical descriptions given had certainly been most interesting, and it would be interesting to know if there was any such plant in existence in England which could be inspected. With regard to the purity of the product, some of them already made or were going to make concentrated ammonia liquor, and one of their troubles was to get rid of the sulphur compounds, and he was wondering whether they would have a very detrimental effect on the resulting ammonium nitrate. He presumed the sulphur would be precipitated and lower the quality of the ammonium nitrate, and possibly make it dangerous for use. In conclusion Mr. Haig formally moved a vote of thanks to the

author.

Mr. G. A. HEBDEN said some eight or nine years ago he had a somewhat similar experience as that of which the author had spoken in connection with calcium nitrate which his firm used to import from Norway and make into bicarbonate of ammonia, mixing the calcium nitrate and making pure ammonium nitrate with it, and he was surprised that the alkali people had not taken up such a simple process. He believed the calcium nitrate could be converted into ammonium nitrate quite easily, and the waste CO2 utilised with ammonia to make ammonium bicarbonate. It would have been done in England but for the fact that the Norwegian people paid more for the ammonia, and it was still being sent out of this country. They were shipping ammonia of 900 specific gravity, 28.3 per cent.

The PRESIDENT asked if the electrodes in the arc flame furnaces described should be of any particular metal. Had the choice of any special material-aluminium, copper, &c., or any special alloy-any bearing upon the process? With regard to plants in course of erection he had head from a friend that there was a plant of similar description working in South Russia. He would also like to know if there was any possibility of synthetic ammonia being produced by such a process.

Mr. KILBURN SCOTT, in replying to the discussion, agreed that a number of coke-oven proprietors were doing very well by the sale of the gas, but he thought it very likely that a number of the beehive type of ovens - of which there were, he believed, 16,000 in this countrywould be done away with. In future coke would be made on a very much larger scale than at present, and the Government would surely compel the use of coal in this way and stop its being wastefully used, as at present, in boilers by direct burning. When new plants were put down and beehive ovens abolished there would be a tremendous amount of power, in the form of gas, available, and it was to utilise some of that gas that he had suggested the process described. Where coke ovens were near a town then doubtless it would pay them better to sell some of the gas for illuminating purposes, &c.; but a great many installations would be remote from such centres, and in such cases the better plan would be for coke oven proprietors to establish their own power-house, make their own acid, and produce nitrate. He believed that the only electric furnace at present producing nitric acid direct from air in this country was his own. A factory was to be built in Manchester, but it would be some time before it was completed. It was because the nitric-acid process had been hanging fire so long that he had taken the opportunity of putting his views before such a society as theirs, and he was very glad there was such a society to receive the suggestion so sympathetically. With regard to the sulphur compound, the ammonia that went over to Norway had the sulphur carefully removed. Ammonium nitrate for making burster charges must be very pure, but