The modified arrangement introduced is decidedly interesting. The offal is cooked in the steam-jacketed cooker, as much as possible of the oil being skimmed from the mixture at the critical stage of coagulation. The sediment, or mud-like residue, is then transferred to an extractor where the remaining oil is recovered. This converts the residue into a still stiffer substance to be finished off in the ordinary steam-jacketed drier, instead of being completely dried in the extractor as originally designed.
This solution has proved to be exceedingly simple and eminently efficient. Although considerable handling is involved the extracting capacity of the plant has been nearly doubled. The advantages to be recorded are:—
(1) Ability to handle very much larger charges of waste when not reducing the material to a dry meal;
(2) Reduction of the raw material to the extent of the oil removed from the cookers;
(3) Reduction of the time required for the oil extraction by approximately 50 per cent.
Consequently, although the adapted, or modified, process entails the employment of extra labour, a result entirely due in this instance to the disposition of the plant in the works, the firm in question is able to obtain the value of the oil which would otherwise be lost, and which more than offsets the cost of the extra labour involved.
As a result of this development a review of the whole problem associated with the recovery of the by-products from fish-scrap was made. Cooking plant is not so expensive as extraction equipment. The question arose as to whether, or not, it would be possible, by the introduction of suitable automatic handling and other labour-saving devices, to obtain highly satisfactory results and efficiency from a combined plant. If this could be done then it would be comparatively easy and inexpensive to bring many of the existing recovery plants up to date to the advantage of the firms concerned. But the factor of capital outlay demands careful consideration, more especially in all matters pertaining to the utilization of waste products, because costs must be forced down to the irreducible minimum to show the necessary return to render them attractive. The result of close investigation of the issue led to the ultimate conclusion that the cost involved in connection with the cookers, extraction plant, and driers, in all probability, would be heavier than that incidental to the laying down of a straightforward extraction plant, pure and simple, to deal with the raw material and to turn it out as a dry product in one operation. One admitted advantage accrues from subjecting the material to preliminary cooking in steam-jacketed cookers. The oil thus obtained is somewhat better in quality than that derived by recourse to the solvent.
The modified or combined process above described enables one distinct end to be achieved. The objectionable and wasteful, as well as expensive pressing plant can be dispensed with. It also enables the ammonia content of the finished meal to be improved very noticeably, as the following analyses of typical meals produced by the respective processes prove somewhat conclusively.
|
Phosphates. Per cent. | Ammonia. Per cent. | |
|---|---|---|
| Pressing process | 6·5 | 7·5 |
| Combined process | 9·5 | 10·5 |
From the foregoing it will be seen that the enhanced yield of phosphates and ammonia fully justifies the additional expenditure incurred in regard to the plant and labour in connection with the extraction process, quite apart from the main duty of the plant. This is to extract all the oil, multiplying the usual yield many times over. Moreover, the quality of the oil-free meal obviously is superior.