Core Principles and Methods

liquid carbonic acid in breweries, lime burning plants, etc. Is it inferior in efficiency to a compression ammonia machine ? There is practically little difference ii properly designed. Why should liquid carbonic acid be tested ? Because it may contain air, water, oil or grease, carbon disulphide, hydrocarbons, etc. Is carbonic acid used from fermenting processes ? The collection of carbonic acid on a commerciz! scale from fermentation of beer, spirits, vinegar and molasses has been a proved success for many years. Is it reasonable in cost ? The cost is only a few cents per pound, and the quantity required for a complete charge is very small, being only about a dollar per ton of refrigerating capacity. How may breweries obtain carbonic acid in their own works ? The collection of carbonic acid in a brewery may begin about twenty-four hours after the wort has been pitched, but in a distillery the attenuation is often so rapid that pumping may be commenced from four to six hours after the mash is run into the tuns ; in either case the process can be continued till the yeast head is first skimmed off, or till the fermented wort or mash is run out of the tun. 378 AUDELS ANSWERS. How should the apparatus for collection be arranged ? The type of apparatus through which the gas is drawn from the tuns may be varied to suit each particular situation ; but as the gas immediately above the yeast head is the least mixed with air, it is necessary that the collector should be capable of being raised or lowered to suit the varying level of the infusion. How is the carbonic acid purified ? Purification is usually effected by passing the gas through a series of three sets of horizontal purifying vessels. In the first purifiers the gas is washed through water, which is slowly but continually changed. The next series of purifiers contain sulphuric acid, through which the gas percolates, and by which all volatile ethers are removed from the carbonic acid. Finally, the gas is again washed in a very weak solution of permanganate of potash. How is it put in cylinders ? In cases where it is intended to sell the collected carbonic acid it is usually necessary that it should be purified, and it must always be liquefied and bottled in suitable steel flasks. If, on the other hand, the gas is to be used in the brewery for carbonating purposes, separation of the gas from the other products of fermentation is unnecessary, and the gas may be conveniently stored in receivers at a pressure of about 200 pounds per square inch. How much carbonic acid is shipped in a cylinder ? About twenty pounds. How is it stored in cylinders ? The compression of the gas is effected by a set of pumps form- ing a stage compressor, the first pump also drawing the gas by suction from the fermenting tuns. After leaving each pump the gas is cooled to abstract the heat generated during compression. VACUUM SYSTEM. What do we mean by Vacuum machines ? A class of apparatus where water is usually the refrigerating medium, How is the vacuum produced ? By an air pump which works exactly like a compressor. ‘Who was the first one to produce a machine on the vacuum principle ? Dr. Cullen, who made the discovery in 1755 that the evapora- tion of water could be facilitated by the removal of the atmospheric pressure. Describe the operation of the vacuum machine ? In this type of machine water is the liquid generally used, its evaporation at a low temperature being effected by vacuum pumps, and sulphuric acid which readily absorbs the watery vapor and makes the vacuum effective. What is a special expense of this machine ? The cost of fuel for re-concentrating the sulphuric acid. Who was the first one to see the benefit of sulphuric acid in absorb- ing the moisture of the air in this process ? Nairne noticed it in 1777, but the first machine that was commercially successful was Edmond Carre’s, which was used to cool carafes in Parisian restaurants. Y 379 380 AUDELS ANSWERS. How does the compressor compare in size with an ammonia compressor ? It would have to be 200 times as large to be of the same capacity. How do the manufacturers of vacuum machines avoid such large compressors ? By using some absorbent of the watery vapor, especially concentrated sulphuric acid. What is the summing up of the vacuum process ? The refrigeration is effected by evaporation, the air gaining access either under natural conditions or by artificial draught ; or the evaporation is hastened by reducing the atmospheric pressure. COMPRESSED AIR SYSTEM. Who invented the first air machine ? Franz Windhausen, of Berlin. ‘When was the first machine brought out ? In 1889. What is the characteristic feature of the compressed air system ? That the air is not condensed to a liquid. Explain the operation of the Cold Air machine ? In the compression cylinder the air is compressed to a pressure of ten to fifteen atmospheres, and its temperature saised from 75 degrees to 500 or 000 degrees. This heat is conducted off by the compressed air being held in a coil surrounded by water, or in long pipes passing through the atmosphere as when used for rock drilling machinery. The heat may be reduced by con- duction to 75 degrees, but the pressure is still, say, fifteen atmospheres. If this should be allowed to escape into the atmosphere a temperature of zero to 10 degrees Fahr., would be produced, part of the low temperature being due to the energy required to force itself into the air again against an atmospheric pressure of 14.7 pounds per square inch. ‘Why has the compressed air system been favored on shipboard ? It was an early development of the business, and in the days, too, when no supply of carbonic acid or ammonia could be had in ports over the world, as is the case nowadays. 381 AUDELS ANSWERS. 382 “68¢ PUY OE saBed uo suo OF pus AT eOHEMIUBBE—P DOYS SB ‘IUMIV SoNeIUjIy MY Wes way Te jo GoNvraia apisyno COMPRESSED AIR SYSTEM. 383 What are the essential parts of a compressed air plant ? A prime motor, a compressor, a cooling coil of pipe with a water supply, an expander consisting of a cylinder, piston and valves, arranged like those of a steam engine, with cut off so that the cooled compressed air may be admitted during a portion of the stroke, and act expansively during the remainder, thereby compelling it to take up heat from the surrounding atmosphere. On the return stroke this cooled air is expelled into the coils of the refrigerator, and then returned to the compressor. What is, therefore, absolutely necessary to make use of the vefrigerating power of the air ? The expansion cylinder must be well insulated to prevent the expanding air from taking up heat from the air surrounding the cylinder. The temperature thus drops, and the air will be able to take up the heat from the refrigerating coils. What are the main objections to air machines, afloat ? The large space required, the high cost, comparatively, of operation, and the amount of moisture in the air which interfered not only with the working of the machinery but also in the form of ice or snow is deposited over goods, otherwise the harmlessness of the refrigerant is greatly in its favor. Describe the working of a Windhausen machine ? In the Windhausen machine, which was for a time largely used in marine service, the air, after being compressed in a cylinder has the heat of compression carried off by cooling water. It then expands in a cylinder, its temperature being reduced corresponding to the amount of work done ; it then escapes into the room to be cooled, cooling and ventilating the room at the same time. What is the temperature in the conveying pipes ? About 60 degrees below zero. 384 AUDELS ANSWERS. Perspective view of the Marine Type of the Allen Dense Air Machine as shown in outline on pages 386 and 389. COMPRESSED AIR SYSTEM. 385 How is the moisture a disadvantage in the air machine ? It freezes to ice, or if in a state of vapor forms snow, and not only do the ice and snow clog the valves, but the vapor in changing to a liquid state gives its latent heat of vaporization to the air. How does the Allen Dense Air Machine overcome the objections to an air machine ? The air is kept in the machine at 60 pounds gauge pressure and used over and over. What are the conditions of operation ? The machine is constructed to stand 60 pounds pressure in the conveying and refrigerating pipes and 210 in the compressor. Great care must be taken that the trap, valves or pipes are rot clogged by frozen oil or snow, and the best quality of mine al lubricating oil must be used from which the paraffine has becn extracted. What special advantages does a machine of this type possess ? The refrigerant is everywhere available and a yacht or vessel could go anywhere without possibility of running out of a supply, which might happen if ammonia or carbon dioxide was used. The refrigerant costs nothing. Slight leaks can do no harm. Copper can be used in coils, which is an advantage in salt water. The machine can be put in the engine room where its operation is under the eye of the chief engineer. Less space and power is required because the air is used over and over. In case of accident the escape of the air would not be danger- ous like ammonia, and probably would do little if any harm. 386 AUDELS ANSWERS. shes | yy Diagrammatic plan view of an Allen Dense Air Refrigerating plant, showingall the essential features of the machine. The reference letters are explained on pages 387 and 388. COMPRESSED AIR SYSTEM. 387 What are the important parts of the Allen Dense-Air Machine ? A. The steam cylinder which furnishes the power to its crankshaft, to which the air compressor and the expander are linked. The letters refer to the oppcsite diagram. B. The air compressor cylinder which compresses the air to about three times the entering pressure. As this causes the air to heat, the cylinder is surrounded by a water jacket to make lubrication practicable. The compressing cylinder is constructed with slide valves, instead of the usual conical lift valves, in order to move more quickly and noiselessly. C. Accopper coil in a bath of water ; the compressed hot.air in passing through it cools to the temperature of the water. The return air-cooler which still further reduces the tempera- ture of the air. D. The expansion cylinder, to which the cooled compressed air is admitted until it fills one-third of the volume of the cylinder. The air supply is then cut off, and as the piston makes its full stroke to the end of the cylinder the air expands until the tension is about normal, and the expansion cools the air about as much as the compression heated it. It is constructed like a usual steam-engine cylinder, with slide-valve and cut-off valve. It must cut off the pressure at such a point that the expanded air at the end of the stroke of the piston is very nearly of the same pressure as the air contained in the system of pipes. If it were of much higher pressure it would, at exhausting, warm up again, by exerting its remaining power in producing velocities and fric- tions inside of the apparatus. The air, therefore, leaves this cylinder at a very low tempera- ture and is discharged into a well-insulated pipe which conveys it to the point of use ; there the pipe is exposed and the cooling is effected, the air returning to be used over. The expander helps the steam cylinder and the air compressor takes the power. E. A trap placed just after the expander which intercepts any oil and snow; the trap is provided with a heating pipe and 388 AUDELS ANSWERS. the contents of the trap should be drawn off every few hours. The machine is so arranged that at the same time any frozen deposits in the expander cylinder can be thawed and blown into the trap. F. Is the water-pump which circulates water around the copper coil C, and through a water-jacket which surrounds the working cylinder of the air-compressor B, in order to prevent the heat from injuring the packings. G. Is a small air-compressing pump which takes air from the atmosphere and pushes it into the machine and pipe system. This charges the system with the requisite air-pressure when the machine starts to work, and maintains the pressure against leakages occurring at the stuffing boxes and joints. This air, of course, contains the usual atmospheric moisture, and to expel this, the outlet pipe from this pump passes the air through the trap H. H. A small trap where the air is cooled by being forced into very close contact with the cold head of the reservoir for coil C. This cooling under pressure and contact with moist surfaces deposits out of the air about 80 or 85 per cent. of the contained moisture, which is then drained off by pet-cocks, leaving pure air for the refrigerating work. This is of great importance, as the large amounts of latent heat in the water vapor and latent cold in frozen water would produce very serious losses in the result of the machine if the air contained water, which would be subject to the heating and freezing processes which occur in the machine. Surplus air is blown off by a small safety valve. What special care does the Allen machine require ? Very little besides looking after the traps for oil and snow. They should be cleaned or blown out as may be required. A good water supply is necessary as is the case with all makes of refrig- erating machinery. 389 COMPRESSED AIR SYSTEM. “SUSUR SoNERSUPSY NY Vu WITY 9m) Jo DONeAL2 apis