Evaporator

“ Vacuum Multiple Effect Evaporation.—Advantage is taken of the fact that water boils at a lower temperature in a vacuum than at the ordinary pressure of the atmosphere. There are many forms of apparatus based on this principle, amongst which the most recent is Scott's evaporator. The black liquor from the boilers is pumped through tubes heated externally by high-pressure steam. The liquor is passed into a chamber in which a slight vacuum is maintained, so that immediately on entering, the liquor parts with a good deal of water in the shape of steam. ”

“ High-pressure steam is passed from the engine boilers into the tubes of an evaporator, and converts the salt water surrounding it into steam. The boiler steam then travels into its own condenser or into the feed water heater, while the steam it generated passes into the coils of a second evaporator, converts water there into steam, and itself goes to a condenser. The steam generated in the second evaporator does similar duty in a third evaporator. So that one pound of high-pressure steam is directly reconverted to water, and also indirectly produces between two and three pounds of fresh water. ”

“ Under suitable conditions this evaporator is most economical in its results. It can be erected cheaply, and when all the heat is fully used in every possible direction it can be worked at a low cost compared with the more modern multiple effect evaporators. ”

“ Direct Evaporation.—The liquors may be evaporated to a small bulk ready for incineration by treatment in long shallow pans or furnaces, the heat necessary for the process [Pg 80] being obtained mainly from the combustion of the thick concentrated liquor. The most familiar type of this form of apparatus is the Porion evaporator.
Fig. 23.—Scott's Multiple Effect Evaporator.
The combustion of the concentrated liquor is started by a coal furnace at one end of the apparatus. ”

“ In practice the working of an evaporator is often not a very difficult matter, and large numbers of machines are operated by unskilled labour. Troubles generally arise from inconstant steam pressure, incrustation, leakages of air, which reduce the vacuum, the temperature head, and hinder heat transmission. For the evaporation of gelatine liquors the Yaryan, the Kestner, and the Blair-Campbell film evaporators are the most widely used. The velocity of the liquor through some of these machines is so great that occasionally no vacuum is used. ”

“ The multiple-effect evaporator, originally invented and constructed by Norberto Rilleux in New Orleans in 1840, has undergone Multiple-Effect Evaporators.many changes in design and construction since that year. ”

“ At the top of all is a covered tank, where the temperature of the liquor is raised before it is run into the evaporator. In order to promote the heating of the liquor in this tank, the lower part of the tank is made to communicate by side pipes with tubes passing across the evaporator near the fire, as, for instance, at the bridge and at the further end of the calcining floor. In this way a circulation of liquor is set up which serves to heat the [208] liquor in the tank more effectually. A pipe from the top of the tank leads to the chimney-shaft, conducting any vapours into it. ”

“ The same objection, of course, applies, though perhaps in a less degree, to all systems of evaporation in which the flame is in contact with the liquor to be evaporated.
The Porion evaporator can be erected at very small cost, and costs but little for maintenance. It is capable of producing 3⁄4 ton of recovered soda per ton of coal with liquors {184} of the usual strength. It has proved itself to be perhaps the most economical evaporator existing. ”

“ With this apparatus it has been found that the work furnished by one kilogramme of steam passing through the motive cylinder, from a pressure of 5 atmospheres to one of 1.4, is sufficient to compress 2.5 kilogrammes of steam taken from the juice, led into the compressor at one atmosphere and escaping therefrom at 1.4. In other words, one kilogramme of motive steam is sufficient to convert into heating steam for the first evaporator 2.5 kilogrammes of steam taken from the juice in this same evaporator. ”

“ When spacecraft altitude exceeds 100,000 feet, water in the heat exchanger will boil absorbing heat from the coolant. This absorbed heat is then expelled overboard in the form of steam.
When the coolant reaches a temperature of 46°F the temperature control valve repositions to relieve pressure to the donut shaped bellows holding the poppet open. As this pressure diminishes, a spring behind the poppet will reposition it to the closed position. The evaporator selector valve is positioned to allow all flow to go through the evaporator. ”

“ Each is connected by an iron supply pipe, having a steam gauge or indicator attached, with a large manifold, and that by other pipes with a steam boiler of thirty horse power capacity. Steam being let on at from twenty five to thirty pounds pressure, the stream of sirup is received from the defecator through a strainer, which removes any impurities possibly remaining into the upper evaporator tube ”

“ Of course he has an ample supply of wood fuel that has been provided a year or more in advance under an adjoining shed so that it may be very dry for a quick fire is one of the main factors of rapid evaporation so necessary for good product, and another quite as important is that the evaporator room be built for it, with a space of about 5 feet all around it, and the walls sealed close to make a hot air draft upward. ”

“ When the evaporator is full of fruit, the holes below should be open full size, except at night, when fruit is nearly dried, they should be closed, or partly so, which is done by tacking a small piece of board over hole, which can be pushed to one side and a nail or screw hold it in place. ”

“ VOLUTE DOUBLE DISTILLING APPARATUS.
The steam from the boiler after passing through the volute, B, is conveyed by means of a pipe to the second volute, H, where it is condensed, and the water resulting is conveyed by means of a pump to the hot well or feed tank. The necessary condensing water enters at J and is discharged at K. The method of keeping the supply of salt water in the evaporator at a constant level is very efficient and ingenious. ”

“ The evaporation is effected at a low temperature in three vacuum pans E, and with the unusual result that the concentrated liquor gelatinises after leaving the third vacuum-pan, instead of taking the ordinary form of the concentrated products of other evaporators. It is said that this apparatus gives an excellent product, with great economy of labour and water, and with no drainage of foul liquor from the buildings. Observations extending over three months have proved that it evaporates 22 lb. of water from the liquor per lb. of coal used under the boiler. It is however very costly to erect. ”

“ Back of the arch, and at one corner, stands a large hogshead containing sap, with a faucet at the bottom, and a small tube opening into the rear compartment of the evaporator. This tube has a self-acting valve, which closes when the sap has reached the proper height in the pan, and opens again when it has been lowered by boiling.
When the sap is first turned on it at once runs through the entire passage-way, and covers the bottom of the pan. Thenceforward it enters slowly, and is heated gradually in the rear compartments, while the boiling is confined to the front portion of the pan. ”

“ The suit loop consists of two suit pressure demand regulator valves, four check valves, two throttle valves, two solid traps, a system shutoff and high flow rate valve, two compressors, one carbon dioxide and odor absorber, and a suit heat exchanger.
WATER MANAGEMENT SYSTEM The purpose of the water management system is to store and dispense drinking water, collect and route unwanted water to the evaporator or dump overboard. ”

“ The "covers" or vats are usually sixteen by eighteen feet, and the product of each one per year is estimated at one hundred and fifty bushels; while the product at Syracuse is only about half that quantity. It is also claimed that the slope of the valley at Warsaw is peculiarly adapted to rapid evaporation by the sun. When the finer grades of salt are wanted, the brine is led from the reservoirs to an evaporating-pan, where a gentle heat is applied. Similar treatment in another pan completes the process, and the residuum of salt is raked upon a shelf at the side of the evaporator. ”

“ When all the water has been expelled, the resulting dry mass is ignited and allowed to burn out, when the black ash that remains, which is carbonate of soda, is afterwards dissolved out, and the alkaline liquor causticised with lime in the usual manner. According to Dunbar, 8 cwt. of recovered ash and 41⁄2 cwt. of good lime will produce 900 gallons of caustic ley at 11° Tw. The liquor is then pumped into settling tanks, from which it is delivered to the boilers when required.
Fig. 64.
Evaporating Apparatus.—An ordinary form of evaporator for the recovery of the soda is shown in Fig. 64. ”

“ ReCoefficient of Transmission of Heat, k/, and the Mean Temperature Difference, θ/m—Parallel and Opposite Currents—Apparatus for Heating with Direct Fire—The Injection of Saturated Steam—Superheated Steam—Evaporation by Means of Hot Liquids—The Transference of Heat in General, and Transference by means of Saturated Steam in Particular—The Transference of Heat from Saturated Steam in Pipes (Coils) and Double Bottoms—Evaporation in a Vacuum—The Multiple-effect Evaporator—Multiple-effect Evaporators from which Extra Steam is Taken—The Weight of Water which must be Evaporated from 100 Kilos. ”

“ Place a test-tube or a little thin vial with water in it in the midst of some ether in a shallow vessel under the receiver of an air-pump. On exhausting the air the ether will boil, evaporation taking place rapidly because the pressure of the air is taken off from the ether. Now as the ether passes into vapor it extracts so much free heat from the vial of water that the water is cooled down to the freezing point, and so becomes solid. Water can be frozen even by its own evaporation. ”

“ All liquids do not evaporate at the same temperature as water. Some require a great deal more than 212 degrees; others, like, for instance, dioxide-of-carbon, will evaporate at 110 degrees, or about one half the heat necessary to turn water into steam.
On the other hand, all gases act alike so far as their heat absorption is concerned, so that by using a material with a low evaporative unit, less [195] fuel will be required to get the same expansion, which means the same power. ”

“ The apparatus consists of a number of boiling bodies connected in such a manner as to secure a progressive decrease in atmospheric pressure.
[114]
The thin juice enters the first body where evaporation takes place under a slight pressure. The steam for this evaporation is usually the waste or exhaust from the engines and pumps. The vapors generated by the evaporation of water from the juice in the first body enter the heating tubes of the second body and are used in further concentrating the somewhat concentrated juice from the first body. ”

“ On the small scale, shallow capsules of glass, wedgwood-ware, porcelain, or metal, are commonly employed as evaporating vessels, and these are exposed to heat by placing them over a lamp, or naked fire, or in a water bath, or sand bath, according to the temperature at which it is proper to conduct the process. On the large scale, high-pressure steam is usually employed as the source of heat. The term ‘spontaneous evaporation’ is applied to the dissipation of a fluid by mere exposure in open vessels, at the common temperature of the atmosphere, and without the application of artificial heat. ”

“ Another method of increasing evaporation is to increase the surface of the liquid. A pint of water in a large flat pan will evaporate much more rapidly than the same amount of water in an ordinary tin cup. Still another method of hastening evaporation is to place the liquid under the receiver of an air-pump and pump the vapor off. Strong sulphuric acid, which greedily absorbs water-vapor, will act in the same way. ”

“ EVAPORATION OF LIQUIDS The greatest care must be taken to prevent loss of solutions during processes of evaporation, either from too violent ebullition, from evaporation to dryness and spattering, or from the evolution of gas during the heating. In general, evaporation upon the steam bath is to be preferred to other methods on account of the impossibility of loss by spattering. If the steam baths are well protected from dust, solutions should be left without covers during evaporation ”

“ If heat be added to water at 212 degrees under atmospheric pressure, the water will not become hotter but will be evaporated into steam, the temperature of which will also be 212 degrees. The heat so utilized is called the latent heat of evaporation and is the heat which apparently disappears in causing the substance to pass from a liquid to a gaseous state.
[Pg 85]
Latent heat is not lost, but reappears whenever the substances pass through a reverse cycle, from a gaseous to a liquid, or from a liquid to a solid state. ”

“ On a dry, bracing day, evaporation goes on rapidly, because the air has not nearly got all the quantity of vapor it can hold in solution. On a damp day, however, when the air contains about as much vapor as it can hold at that particular temperature, evaporation is quite feeble, or ceases altogether. This varying capacity of the air for vapor is the reason why laundresses find so much difference between days, in the ease with which they can have their clothes dried. ”