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Report on the cost of converting seawater by distillation and condensation into fresh water for domestic supply purposes.
HON. D. P. W.,
I have to report that in accordance with the Hong Kong Government's request, I investigated the question of the cost of converting seawater by distillation and condensa- tion into fresh-water for domestic supply purposes, whilst on leave in England and on my return journey to Hong Kong.
Through the Crown Agents I was put into communication with the firm of Messrs. Caird and Rayner, Manufacturers of Distilling and Condensing Plants, whose works I visited in London and who supplied me with information of the cost of these plants and plans and particulars explaining the method of working them.
I inspected also the Military and Civil Distilling and Condensing Plants in operation at Aden during the short stay of the steamer there on my return journey to Hong Kong.
I have other manufacturers' catalogues giving particulars of the efficiency of the plants they manufacture.
I do not propose to explain the method of working these plants as it is set forth in considerable detail in the correspondence and manufacturers' catalogues which I attach.
The efficiency of a plant is chiefly dependent on the kind and quality of the fuel and that given in the manufacturers' catalogues vary generally from 35 to 44 lbs. of gained distilled water to 1 lb. of fuel burnt.
The efficiency obtained in every day working of a plant is usually lower than that given in catalogues and the efficiencies of the distilling and condensing plants at Aden were certainly not as high, but I was informed that these plants had been in operation for a considerable time.
Messrs. Caird and Rayner stated that they could guarantee an efficiency of 32 lbs. of gained distilled water for 1 lb. of oil fuel and I am inclined to think this is a conservative figure for this fuel.
It will be noticed that owing to the large consumption of fuel to convert seawater into distilled water the cost of running a plant is extremely high when compared with other means of obtaining a supply of fresh water for domestic purposes in this Colony.
Water supply by a distilling and condensing plant is therefore only resorted to when conditions are very exceptional, where fresh water by any other less costly method is unobtainable, or where distilled water is required for a special purpose in some manufac- turing process.
The water distribution has to be very strictly limited in domestic supply owing to the huge plants that would be required to produce a large quantity of fresh water.
The Sextuple Effect Water Distilling Plant is probably the cheapest method up to the present time of producing distilled water in fairly large quantities.
The largest size manufactured is capable of producing 400 tons or 89,600 gallons of distilled water in 24 hours for each set and any number of these sets may be erected ac- cording to the supply required.
The fuel used may be either coal or oil, but where the cost of these is in the pro- portion of about 1 to 1.4 it would be preferable to use the latter on account of its higher calorific value, its mobility, cleaner working, and less cost of labour.
The calorific value of the Kaiping No. 1 Lump Coal supplied by the Kailan Mining Administration to Hong Kong Government is said to be between 12,000 and 12,500 British Thermal Units that of medium Welsh about 14,000 B.T.Us., and for Oil Fuel supplied by the Standard Oil Coy 19,000 B.T.Us. If calculations are based on the