But there is a tremendous gulf between the laboratory and the factory. It was many years ago that the possibility of extracting alcohol from wood first aroused the serious attention of the industrial chemists. They are still wrestling with the problem. Time after time the world is startled by the announcement of a new and inexpensive process for the distillation of alcohol from wood and the prospect of extracting whisky and other popular beverages from sawdust excites intense interest. But, metaphorically speaking, nine days later a strange silence is encountered. The new process has vanished from aught but a memory of much claimed but nothing forthcoming. Fortunes have been sunk and lost in the attempts to solve this momentous problem, and it is probable, from the state of knowledge and the stage of experiment at the moment attained, that many millions more will be expended before commercial success is achieved. One of the greatest obstacles to the realization of the chemist’s dream has been the extremely high temperatures to which resort has to be made, which plays sad havoc with the plant involved, and the charges incident to the renewal of which are so heavy as to render the financial outlook extremely depressing. Even the conditions of war, which scouted all considerations of expense, have not carried us an inch forward. We built one factory to conduct the distillation of wood for the alcohol which was so sorely needed, and planned a second installation. The first factory was promptly abandoned after the signing of the armistice, while the second factory was never completed, owing to the indifferent results achieved with the conduct of the initial plant.
Similar experiences may be narrated in many other fields of attempted waste recovery. Fortunately, however, for every dismal failure recorded a dozen or more overwhelming triumphs can be related. It is this circumstance which induces the experimenter to persevere upon his ventures of discovery. But this is not the only satisfactory feature of success in this field. The spirit of rivalry is so keen that the industrial chemist and the chemical engineer are for ever striving might and main to improve the methods which they have evolved, and in the determination to secure the uttermost ounce of the elusive fat, they proceed to extreme lengths. The eternal quest for improved efficiency is not confined to the extraction of fats; it is equally applicable to the recovery of other products in keen demand and commanding an attractive market price, but I select fat as an example because it is familiar to all.
Moreover, in elaborating his fruitful thoughts the investigator is compelled to bear in mind varying conditions. Accordingly he must adapt his ideas to the prevailing requirements. Obviously it would be inexpedient to concentrate perfecting effort upon one definite system. The plant involved may necessitate a capital outlay possible only to the wealthy firm or city, and utterly beyond the small man anxious to embark upon such an enterprise, or be impracticable to the average town, to which the plant, owing to the limited volume of material to be handled, would never justify the probable expense.
In these circumstances we see plants and methods being adapted to varying demands so that the reclamation of the urgently required fats, oils and greases may be pursued by one and all. In a previous chapter, describing the recovery of these commodities from the swill-tubs of the army, I referred to one system which is wholly mechanical in its operation. In this instance success depends essentially upon the centrifugal turbine extractor or “whizzer,” which it must be admitted has proved exceedingly attractive in application. For this reason the “Iwel” system, as it is called, has met with conspicuous success and wide application, being found in every industry.
But there is another system, or rather wide range of systems, known as the Scott, differing entirely from the one already mentioned. This, too, is of British origin and construction, and compels attention from its applicability to every possible requirement as well as adaptability to every conceivable condition, from the factory handling only a few thousand pounds of miscellaneous fat-carrying refuse a day, to the huge packing plants to be found upon the American continent, both North and South, Australia and New Zealand, where the accumulations of fresh fat are imposing, and where the necessity for prompt big-scale treatment to secure the attractive prices ruling for high-grade fats is so obvious. The operations of the firm under review demand additional attention inasmuch as, through the combined efforts of its chemists and engineers, it has been able to evolve and perfect a process which is distinctly remarkable, seeing that it enables all but 1 per cent. of the fat contained in the crude refuse to be reclaimed, and in such a manner as to render the method completely profitable.
The Scott systems, fundamentally, are three in number. In the one the waste animal products are digested with open steam in conjunction with a vacuum; the second method comprises the dry rendering of edible fats under vacuum; while the third practice is the extraction of the grease by what is known as the solvent system. Each possesses its individual features, making direct appeal to the situation to which it is most eminently adapted, and, to a certain degree, the three respective methods may be said to represent an equal number of progressive strides towards maximum efficiency, with the solvent process constituting the pinnacle of success so far achieved in this province from the simple fact that it reduces the loss of fat to 1 per cent. absolute.
However, it is difficult to lay down any hard-and-fast rule concerning the selection of any of these three processes because, in deciding a question of this character, full consideration must be given to the class of material to be handled. For instance, although the dry rendering system under vacuum is especially applicable for the reclamation of edible fats, it is not to say that the first, or open steam, process is only adapted to the production of non-edible fats. As a matter of fact there are certain classes of offal which are not suited to dry steam rendering. The fat contained in such refuse can be most advantageously extracted only by the open steam process. This particularly applies to the offal produced in the large killing establishments, where such refuse can be dealt with in the fresh condition.
The dry steam rendering process is particularly applicable to the production of fine or high grade edible fats. The finest fat recovered from an animal source is that known as “Oleo” margarine or “Premier Jus.” This is rendered from the very finest crude fat obtainable, and in order to ensure super quality being obtained the conventional treatment is one demanding extreme care so that its inherent qualities may not suffer the slightest injury. The general practice is to mince the raw material very finely and then to treat it in hot water-jacketed pans at a very low temperature, every attention being observed to prevent the temperature rising above a rigidly predetermined point. In these circumstances it will readily be observed that the process is necessarily somewhat costly and occupies appreciable time. But by means of the dry rendering process under vacuum the raw material may be subjected to very high temperatures, and that without the product being impaired in any way. In fact, it is equal in every respect to that obtained by the orthodox process, while, of course, it is far more expeditious and cheaper.
The plant necessary to the vacuum system is simple. It comprises a cylinder or boiler called a digester, into which the offal to be treated is placed. Under the wet steam process and after the vessel has been closed a vacuum is created. Open steam then is admitted into the digester and in such a way as to enable the steam to pass upwards through the mass, thereby thoroughly permeating it. Naturally the hot steam renders the fat fluid, that which is free running readily to the attached tanks.
Rendering is conducted under a pressure varying from 20 lb. to 40 lb. as the case may be, but the lower the pressure the better. The application of the vacuum to the process constitutes the crux of the invention. At first sight the advantages of the principle may not be readily apparent, but they may be simply explained. In the first instance the creation of vacuum conditions effects the removal of the greatest obstruction to the influence of heat, namely air. If this be eliminated cooking can be conducted at a much lower temperature than would otherwise be practicable. Fat, indeed all animal matter, carries a certain proportion of moisture and this must be withdrawn before the actual release of the commodity can be effected. In vacuum water boils at a temperature below one-half of that required at ordinary atmospheric pressure. In other words, instead of the boiling-point of water being 212 degrees Fahrenheit, as is the case with the kettle on the hob, it will boil at less than 106 degrees Fahrenheit. Consequently, if a high vacuum be established within the digester the latent water can be converted into steam to assist in the melting process proper, which then can be conducted unhampered. Temperature, moreover, exercises a decisive influence upon the quality of the product, this being very superior in quality when the recovery is carried out at a low degree.