Vol. 20, No. 11
INDUSTRIAL AND ENGINEERING CHEMISTRY
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10 nun. wide and 150 mm. long, and the average thickness was approximately 1.2 mm. They were stored in distilled water and in wet condition subjected to a tensile strength test. The results are shown in Table I. Table I-Tensile
specimens for these determinations were cut 50 mm. wide, and those for tensile strength tests 5 mm. wide. The top, central, and bottom parts of the separators were examined separately. The results are presented in Table 11. Strength of Wood Separators after Use in Electric Coup& S-EXT TO POSITIVE PLATES &-EXT TO NEGATIVE PLATES Resistance to Resistance to Tensilea penetrationb Tensilea penetrationb Kg. per sq. mm. Kg. Kg. per sg. mm. Kg. TOP 0.538 1.254 0.755 1.517 Center 0.592 1.212 0.866 1.895 Bottom 0.575 1.152 0.851 1.645 Average 0.568 1.206 0.824 1.686 Ratio N : P-tensile, 1.45; resistance to Denetration, 1.40 a Average of 80 determinations. b Average of 35 determinations. Table 11-Mechanical
Strength of Wood Separators after Use in Truck
(Figures represent average of 55 determinations) N E X T TO POSITIVE NEXT TO iYEGATIVE PLATES(P) PLATES(N) Kg. per sq. mm. Kg. per sq. mm. End parts 0.418 0.520 Central parts 0.464 0.614 Average 0.441 0.567 1.29 Ratio N : P
Unused Separators
Comparative tests were carried out with unused separators of the same make which had been stored in slightly acidulated water. The results were: Tensile strength (25 detns.) Resistance to penetration (70 detns.)
T
2 . 0 6 kg. per sq. mm. 5.96 kg.
Conclusion
Figure 1-Apparatus for Testing Separators from Coup;! Battery
Separators from Coupe Battery
Based on the experience gained on testing the first type of separators, the apparatus and conditions were improved for the tests on the coup6 battery. The apparatus shown in Figure 1 was designed for testinff the resistance of the seaaraiors to penetra6ng a hard sharp-edged object. The ;est
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A noticeable difference in mechanical strength has been found in used smooth wood separators which during use had been placed in close contact with the positive and the negative plates, respectively, in two electric traction batteries, the separators next to the negative plates showing about 30 to 45 per cent higher mechanical strength than those next to the positive plates. However, the difference is not so great as might be expected, and the destructive effect of the positive plates upon the wood substance can hardly be considered an objection to placing a flat side of a wood separator next to the positive plates if in particular cases such a design of the cell is preferable,
Automatic Control through Temperature or Pressure’ C. J. Swan2 AMERICAh.
RADIATOR COMPANY, 40 WEST 4CTH S T . , NEW YORK, N. Y.
H E increasing cost of labor, together with the keen competition which characterizes our day, has made profitable larger capital expenditures for labor-saving devices and the employment of fewer but higher paid skilled workmen. A manufacturer can no longer afford to employ labor merely to turn valves and watch the height of liquid in tanks or the degree of pressure, vacuum, or temperature on gages and dials. Twenty-five years ago there was no alternative, and cases have been known where the valve man, grown weary with the monotony of his job, was asleep when the bell rang and disastrous tank overflows resulted. Mercoid Control
T
A considerable number of devices have been brought to commercial perfection within the past few years. Each has its own points of advantage. The method of control to be described here is unique in several respects, an outstanding feature being the design of the electric switch which makes and breaks contacts, depending upon changes in temperature, vacuum, or pressure. This switch consists of a glass tube, A , 1 2
Received August 21, 1928. Assistant manager, Accessories Division.
in which leads of a special material are sealed. The circuit is made or broken by a small quantity of mercury when the tube is tilted. Arcing is instantly dampened or stifled by inert gases which are hermetically sealed within the tube. Operation with safety is thus possible where there are fumes or other conditions usually hazardous. There being no oxidation or corrosion, the contact is instantaneous in operation and the contact points are permanently maintained in a clean and satisfactory condition. The control in which this switch is employed is known as the “Mercoid control.” (Figure 1) The control will carry the full-line current a t 110 or 220 volts with sufficient amperage in most cases to operate electric units up to the capacity of one horsepower. Through the use of an automatic starting switch electric units of any capacity can be operated by merely securing an across-theline starter of proper capacity. KO relay or automatic starting switch is required on loads up to 10 amperes a t 110 volts or 5 amperes a t 220 volts, as the switch will make and break the circuit across the line on loads of those amounts. The power element which operates to tilt the switch described above is a seamless, all-metal bellows, D,provided with
INDUSTRIAL AhiD ENCI NEERING CHEMISTRY
November, 1928
E Fleure I
a spring cap, ti, which may be screwed up or down to change
the operating point. Closeness of control is secured by turning the screw, C, indicated in the drawing. This means for adjusting the operating d ~ e r e n t i a lenables changes to be made quickly even after installation. ,When used thermost.atically, liquids of such boiling points as necessary for the desired temperatures are placed within the bellows. For pressure control, the apparatus is connected to the bellows chamber, direct or by piping at E . From what is said above, it will he obvious that by increasing the compression of the spring against the pressure within the bellows, the degree of temperature or pressure a t which the instrument will operate will be raised. The
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F i ~ u r e2
'l'emperatures as low as 34" C. and as high :is 300" C. cnn be controlled through such a device within *0.5" C. Where control is operated by changes in the pressure, these may be adjusted from complete vacuum up to 1500 pounds, a i d even higher where special conditions are to be met. Control in many instances can he secured as close as 1 ounce between the making and breaking of the circuit or in t.he ease of vacuum as close as 3 mm. of mercury. When regulation is secured by controlling an electric unit, t.he aut.omatic control is connected directly in bhe circuitas, for example, the starting or stopping of a blower, pump, or other motor-driven device. With electric heat,ing the control simply makes and breaks the circuit to the heating element. 'Where regplation is secured hy controlling the flow of steam, water, oil, air, gas, brine, etc., the control opcrabes a motor valve placed in the pipe line. Motor Valve
The motor valve (Figure 2) is of special design, driven by 8 universal motor, A . in turn controlled by the mercury switch above described. yi'hcn contact is made as a result of increase or decrease of pressure or temperature, the main gear shaft of the motor valve makes a half revolution, thus closing the valve. Contact on the opposite side of the switch causes the shaft to make another half revolution, thus openiug the valve. The circuit is broken at the end of each half revolution by means of a switch mounted on the main gear shaft. This motor-driven valve cannot stop in a midway position and is either tightly closed or wide open. The wiring eonFigure 3
differential is a number of degrees or pounds pressure hetween operation at high and operation at t.he low point. Thus a control device may be set to maintain a temperature of 180" C. and the differential adjustment may then be set so that the inst.rument n4l operate within a 2O C. change in temperature-that is, operating in one direction at 181' C. and in the reverse directiop at 179" C. If desired, this differential may be broadened so that a change of 10" C. or more may he necessary before the power element, operated hy the bellows movement, tilts the glass tube through a system of levers and causes the flowing mercury to make or break the circuit as may be desired. The possibility of adjusting the diRerent.ia1 widens the application of this type of control device. In some instances, as for example, in automatic refrigerating units, too close control is a disadvantage, for if set to operate within a range of 2' C. the frequent opening of the refrigerator door would cause eontinual st,nrt,ingand stopping of the power unit.
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nections determine whether the valve is to be open or closed as the temperature or pressure advances. .Applications
It will be obvious that such control, together with motor valves with which they are frequently installed, can be used separately or in combination for many operations in the chemical industry. Automatic control of liquids, gases, or vapors, heated by steam or hot water or cooled by cold water or brine, is easily secured. Where electrically operated gas valves are used, it is possible to secure control of heaters or driers where gas is the fuel. Pressure controls can be used to start and stop motors, ring alarms, operate pumps, blowers, and compressors, and control electrically heated elements. By using head pressure the levers of liquids may be controlled, and as this device operates with but a slight change in pressure, accurate liquid-level control may be secured by static head. Instruments of this type are used a5 bearing thermostats to sound alarms in case the bearing temperature reaches a predetermined point. A few typical installations will indicate the wide possible application of these devices in the chemical industry. Figure 3 shows the use of a temperature control together with a motor valve employed to maintain the even temperature of hot water circulated from a reservoir through the hollow shelves of a vacuum shelf drier. When the temperature ,----+ON
i@d
ALTERNATE REMOTE OF MERCOID ,-AUTO.
STARTlNe SWITCH
Figure 6
varies beyond the limits for which the control has been set, i t operates to open or close the valve in the steam-supply line connected to the water heater. Figure 4 shows a temperature control and motor valve used to regulate the temperature of alcohol vapor in the manufacture of formaldehyde. Here a copper coil is used as the thermostatic element and the valve is operated to regulate the low-pressure steam supply to the heating coil in the alcohol tank. As vapor is wanted a t a constant temperature, the copper coil is placed in the vapor outlet from the tank. In Figure 5 is shown the adaptation of similar equipment for the control of the temperature of dried starch drawn through a drier by a suction fan. Here powdered starch passing over the thermostatic element causes the steam supply to coils in the drier to be opened or closed by the motor valve, according to the temperature of the dried starch. I n Figure 6 we see pressure controls maintaining even gas pressure, which is very important in certain manufacturing operations. There are three motor-driven gas boosters. The first operates continually, but when the demand increases and the pressure falls, the second booster automatically comes into service. A further increase in demand causes a third booster to start. With a decrease in demand the boosters, one after the other, automatically go out of operation. By such devices pressure control can be regulated as close as 1 ounce or less and can be maintained equally close in the same way on vacuum. Figure 7 shows two methods of applying pressure controls to sewage-lift stations. Here there are no floats or rods and no open contacts. The circuit is opened and closed by AUTO STARTING
MERCOID PRESSURE
[PUMP
SUMP
Figure ?a
Figure 7 b
SWITCH.
MOTOR
November. 1928
I N D U S T R I A L A N D ENGINEERING CHEMISTRY
the switch, which causes the pump motor to start or stop when the contents of the sump reach a predetermined level. Other applications not illustrated include the starting and stopping of the motor of a unit heater; to open or close a steam supply to unit heaters; for the control of the temperature of a drying tumbler, where in addition to stopping the motor which operates the tumbler, the blower to the heater may also be stopped and an alarm sounded to notify the attendant that the tumbler should be emptied. Liquids heat)ed by steam or by hot-water coils may be kept a t an even temperature by such devices and installed therefore to control cookers, stills, washers, and the like. High-pressure booster lines to instantaneous heaters using exhaust steam are also subject to such control, and when the temperature requirements exceed that obtainable with the exhaust steam, installations may be made to cause the high
1155
pressure line to be opened or closed as required. Dry kiln rooms, candy-drying rooms, conditioning chambers, the control of air compressors maintaining pressures on air receiving tanks, maintenance of water level in storage tanks and temperature in commercial refrigeration are among other obvious applications. In the construction of these devices delicate adjustments and light mechanisms have been avoided. Rugged instruments with parts exposed to corroding influences made of materials designed to withstand them, have been produced. The simplicity of operation and the fact that, wherever changes of temperature, pressure, or vacuum occur, devices of this sort may be installed, indicate the possible wide”application in the chemical industry. Accuracy of automatic control is so much to be desired as to require no special emphasis.
Fuel Economy in Burning Portland Cement Clinker‘ Fundamental Data Robert I). Pike PIKE & WEST, 4068 HOLDENST., EMERYVILLE, CALIF.
ROGRESS has been made in fuel economy in burning Portland cement clinker in the direction of recovering heat from the stack gases by use of waste-heat boilers; but in late years there has been little advance in reducing the consumption of fuel in the kiln itself. It can be shown that in the dry process clinker can be burned with from 40 to 50 per cent less fuel than is used in present practice, and that a fuel saving of this magnitude in the burning process itself is far preferable to the recovery of heat from the stack gases of an inefficient kiln. It can be further shown that in properly designed apparatus using the dry process a barrel of clinker can be burned with about 600,000 B. t. u. less than in an equally efficient apparatus using the wet process. When such efficient apparatus has been adopted, the dry process will possess this constant advantage over the wet process, and it is believed that this advantage, when combined with modern dry-process grinding and sampling equipment, will establish a definite economic superiority of the dry process. In attacking the problem of obtaining the maximum practical fuel economy in burning clinker, it is first desirable to visualize an “ideal apparatus” and to calculate the fuel economy for such an apparatus, based upon the latest available fundamental data. An investigation of the ideal apparatus will by comparison serve to emphasize the weak elements of present-day apparatus and to point out the direction for improvement. Such an ideal fuel economy has been sometimes called the theoretical fuel economy and several approximate methods have been suggested for its calculation, none of which appear to be rigorously correct, nor are they based upon the most acceptable fundamental data. The present paper is concerned with the fundamentals of clinker-burning and presents what is believed to be a rigorously correct method for calculating the ideal fuel economy. Later publications will be devoted to methods for calculating the design of efficient practical apparatus. Next to labor the fuel for burning clinker is the largest single item of cost in the manufacture of Portland cement. With reference to actual consumption of fuel per barrel of
clinker in American practice, we quote from certain unpublished sources: There are very few kilns over 175 feet in length in America operating on the dry process. One large company has one kiln 10 feet in diameter by 232 feet in length. They also have a number of kilns 12 feet in diameter and approximately the same length, all using the dry process, but unfortunately operating data such as fuel consumption and output are not available. In one dry process plant where the kilns measure 10 X 164 feet the average B. t. u. required per barrel of clinker is 1,460,000. In another plant operating under similar conditions, except that the kilns measure 10 X 175 feet, 1,240,000 B. t. u.’s are consumed per barrel of clinker. In wet process kilns of 10 X 240 feet using limestone and shale, the average B. t. u. per barrel of clinker burned is 1,560,000. On the other hand, in one of the most modern kiln installations using wet process with 33 per cent water in the slurry and the kilns measuring 10 X 9 X 250 feet the average number of B. t. u.’s required is 1,365,000. In the latter kilns the actual burning surface is exactly 235 feet, the last 15 feet being used as a cooler to convey the thoroughly burned clinker t o the discharge end of the kiln.
The actual costs per barrel, with coal and oil fuels a t different prices, are given in Table I. The barrel of cement weighs 376 pounds, including gypsum, and the barrel of clinker, before adding gypsum, is taken as 365 pounds. If $4.00 per ton is taken as an average of the cost of finished coal of 13,000 B. t. u. per pound a t the kiln in American plants and 150,000,000 barrels as the annual production of cement, the annual fuel bill is something in excess of $30,000,000. A flank attack, as it were, has been made on the cost of fuel in cement-burning by use of waste-heat boilers, in itself an admission of the thermal inefficiency of the rotary kiln. No attempt will be made here to analyze this practice in detail. Suffice it to say that waste-heat boilers have been installed in many cement plants and some records on their design and performance may be found in the literat~re.~#3 Note-There are no direct data available on cost of coal a t cement plants, hut Murray, U. S. Geol. Survey, Professional Paper 123 (1921),makes the following statement: “The cost of coal per short ton ranged from $2.79 2
Received May 16.1928.
8
Baylor, Trans. Am. Inst. Chem. Eng., 10,209 (1917). Anon., “Waste Heat Recovery by the Edge Moor System,” 1920.
