FIG. 296.—COMPRESSION PUMPS OF ICE PLANT.
Probably the earliest practical ice machine to be organized on a commercial basis was the ammonia absorption machine of Ferdinand Carré, which was a continuously working machine. It is disclosed in French patents Nos. 81 and 404, of 1860, and No. 75,702, of 1867; United States patent No. 30,201, October 2, 1860. In this case advantage is taken first of the very volatile character of anhydrous ammonia, in the expansion part of the process, and, secondly, of the great affinity which water has for absorbing such gas. Strange as it may appear, the production of ice in the Carré process begins with the application of heat. It must be understood, however, that this forms no part of the refrigerating process proper, but only a means of driving off or distilling the anhydrous ammonia gas (the refrigerant) from its aqueous solution. Ammonia dissolved in water, known as aqua ammonia, is placed in a boiler or still above a furnace. The pure ammonia gas is thus driven off from the water by heat under pressure, similar to that in a steam boiler, and passes direct to a condenser, where, by cold water flowing through pipes, the pure gas is liquefied under pressure. The liquefied gas is then admitted to the evaporating or refrigerating chamber, where it expands to produce the cold, and is afterward re-absorbed by the water from which it was originally driven off in the still, to be used over again. Machines of this type are known as absorption machines, for the reason that the volatile gas is after expansion re-absorbed by the liquid in which it was dissolved, and is continuously driven off therefrom by the heat of a still. Absorption machines were the outgrowth of Faraday’s observations in 1823. A bent glass tube was prepared containing at one end a quantity of chloride of silver, saturated with ammonia and hermetically sealed. When the mixture was heated, the ammonia was driven over to the other end of the tube, immersed in a cold bath, and the ammonia gas became liquefied. It was found by him then that if the end containing the chloride was plunged in a cold bath and the end containing liquid ammonia was immersed in water, the heat of the water made the ammonia rapidly evaporate, the chloride at the other end of the tube absorbed the ammonia vapors, and the water around the end of the tube containing the liquefied ammonia was converted into ice, by the loss of its heat imparted to the ammonia to volatilize it. It only needed the substitution of water for the chloride of silver, as an absorbing agent for the ammonia, and mechanical means for economically working the process in a continuous way to produce the Carré absorption machine. The most common form of ice machine to-day is, however, what is known as the compression or direct system, in which the absorption principle is dispensed with, the ammonia being compressed by powerful steam pumps, then cooled to liquid form by condensers, and then allowed to expand from its own pressure through pipes immersed in brine in a large floor tank, in which cans containing pure water are immersed, and the water frozen. [Fig. 296][5] shows the compression pumps, and [Fig. 297] the floor tanks, of such a system. Many hundred cans filled with pure water are lowered into the cold brine of the tank, and their upper ends form a complete floor, as seen in [Fig. 297]. When the water in the cans is frozen, the cans are raised out of the floor by a traveling crane and carried to one of the four doors seen at the far end of the room. The ice in the can is then loosened by warm water, and the block dumped through the door into a chute, whence it passes into the storage room below, seen in [Fig. 298]. In the can system the water is frozen from all four sides to the center, and imprisons in the center any air bubbles or impurities that may exist in the water. The plate system freezes the water on the exterior walls of hollow plates, which contain within them the freezing medium. In freezing the water externally on these plates all impurities and air bubbles are repelled and excluded, and the ice rendered clear and transparent.
[5] By courtesy of “Ice and Refrigeration.”
FIG. 297.—FLOOR TANK OF CAN SYSTEM.
