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Art. XV.—On Experiments made to determine the Value of Different Coals for Steam Purposes.
[Read before the Wellington Philosophical Society, 14th October, 1871.]
The value of different New Zealand coals for steam purposes will be best illustrated by comparing the work performed with coal from longer established and more deeply worked mines. Mr. John Kebbell, of Wellington, having kindly furnished me with the result of several trials made at his mill, together with his notes on the subject, I now lay the same before the Society as a continuation of the paper read a short time back on the New Zealand coal for gas purposes.
Mr. Kebbell's trials were made by burning half a ton of coal, and ascertaining the time the engine was kept at work with the consumption of this weight of coal; care was taken in each case that the height of water in the boiler, the pressure of steam, the work being performed by the engine, and all other circumstances, should in each case present exactly the same conditions when the trials were commenced and completed.
The result of three experiments in 1869 was as follows:—
| h. | m. | ||
| No. 1.—English steam coal | worked engine | 3 | 35 |
| No. 2.—Newcastle, N.S.W., | " " | 3 | 50 |
| No. 3.—Bay of Islands (Kawa Kawa) coal | " | 4 | 20 |
No. 1, English coal, would generate steam very rapidly if required.
No. 2, New South Wales coal, made 114 pounds waste from the half ton.
No. 3, Bay of Islands; this coal made twenty-eight pounds pure clinker. The clinker is as injurious to the fire bars as the South Wales coal of England; it adheres very strongly, and can only be removed by allowing the bars to cool down. If it were not for this fault it would be a good steam coal. With narrow spaces between bars, say five-eighths of an inch or less, it might give a better result; the ashes should be returned quickly to the furnace or they waste away.
Experiments made with the same weight of coal, during the present year, gave the following results; the improvement will be due to alterations in the engine and boiler:—
| h. | m. | ||
| No. 1.—English steam coal | worked engine | 4 | 25 |
| No. 2.—Collingwood coal, No. 1 trial | " " | 4 | 55 |
| No. 3.—Collingwood coal, No. 2 " | " " | 5 | 0 |
| No. 4.—Grey coal | " " | 5 | 5 |
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No 1 gave about the same quantity and description of coal as the New South Wales coal.
Nos. 2 and 3. This coal cokes sufficiently to prevent it running through the bars. If the fires are fed regularly they require no stoking, and the least attention of any coal ever used by Mr. Kebbell. The clinker is similar in quantity and quality to the New South Wales coal.
No. 4, Grey coal, is a good coking material, and cakes very much in furnaces with a moderate draught, requiring a good deal of attention. The quantity of clinker and waste was so small as not to be worth mentioning.
In these trials all the New Zealand coals give a better result than either English or New South Wales coal, in work performed with an equal weight.
New Zealand coal, as a rule, appears to be of a less specific gravity than imported coal; this, however, may in time be altered as the mines become more deeply worked, and this renders them at the present time less valuable for steamers, and furnaces with a strong draught.
From inquiries made of the engineers of steamers, who have made use of the Grey and other kinds of coal, it appears to be the fact that the Grey coal is not so economical as the New South Wales for the use of steamers, for the reason that it is more bulky, and with the strong draught of the steamer's furnace burns away more quickly. The engineer of the steamer ‘Luna’ states, in his opinion, first-class New South Wales coal would be worth, for steamers, three shillings per ton more than the Grey, that is to say, if the price of the New South Wales is twenty-six shillings per ton, the Grey coal would only be worth twenty-three; but at the same time he prefers the Grey coal to much of the New South Wales coal that is sold in New Zealand.
For household purposes, all who have tried the Grey and Collingwood coal prefer them to any coal imported into the colony, as being cleaner and burning more freely and pleasantly.
All the experiments made, and information that I have been able to obtain, tend to show that New Zealand possesses superior coal for steam purposes, when worked with stationary engines, at a moderate draught, and for household and gas purposes, to that of New South Wales; but that for steamers' boilers, working at a strong draught, the heavier coals of England and New South Wales have the advantage. It is to be hoped that the further development of the mines will ultimately remove the last-named disadvantage.