INDUSTRIAL A N D ENGINEERING CHEMISTRY
298
Vol. 23, No. 3
Packed Heat from a New Type of Electric Steam Generator Howard Bidwell and Linus H. Jones MASSACHUSETTS AGRICULTURAL EXPERIMRNT STATION, AMHERST, MASS.
A recent development in an electric steam generator, offset may be varied to meet which gives all that can be desired as a source of steam esses in the scientific the particular conditions unand heat, is described. A reservoir properly located and i n d u s t r i a l fields der consideration. Figure 1 between high- and low-water levels serves as a source that require large amounts of shows such a boiler with its of energy, so that the pressure from the boiler is imsteam for p e r i o d s of short offset. mediately available when required. The steam genduration. H i g h - p r e s s u r e The reservoir is attached to erator is made independent of the autoclave by closing steam is expensive and its cost the boiler either by pipe convalves in the feed and return pipes, and the working is becoming so excessive that nections or welding, or conefficiency of an autoclave is increased four or five times. this method is almost prohibistructed in the boiler so that The apparatus is under automatic pressure control tive during the non-heating it carries its full charge of with no limitations of allowable pressures imposed m o n t h s . There is also a water between the high- and by license laws. The angular offset of the boiler perlabor cost if t h e law of the low-level water lines. The mits installation under conditions where there is but state demands a licensed opdesign and location of the little space. erator. The n e c e s s i t y of reservoir and its connections This generator is applicable for use with hospital greater economy in the use of have an important bearing on sterilizers, pressure-cookingretorts, or in any industrial coal a t this institution led to the results. It is responsible process where a large quantity of steam is necessary the application of low-presfor rapid circulation and the for a short period of time. sure m e t h o d s for heating. maintenance of a nearly conFor sterilizing: muposes this stant water level. with a minichange brought much discouragement to those accustomed to mum change. As the steam is drawn from the generator, high-pressure steam. The best gas and electric steam genera- water can be supplied to the reservoir without the absorp tors were purchased and substituted wherever possible, but tion of heat, thus generating steam very quickly. they did not meet the requirements of the various departments. A diagram of the essential features of the apparatus is The problem has now been solved by the construction of shown in Figure 2. The re!atively small space needed for an electric steam generator, not only of original design, but a the installation of the boiler is c!early illustrated. The decided departure from the usual method employed in con- sterilizing retort is indicated by A and the boiler with its nection with this type of equipment. This generator has a angular offset by 1. The reservoir, 2, is located between the reservoir in which heat is packed and stored. The result is high- and low-water levels on the water gage, 3. The steam that within 30 seconds from the time of closing the autoclave gage, 4, is conveniently attached to the same connection the required sterilizing pressure is registered. This may fitting with the boiler that carries the low, 5, and high, 6, be obtained at any time by throwing a switch and open- pressure controls. The immersion heating elements, 7, ing two valves. The principle employed in the action of are protected a t the place of insertion by a metal guard, 17. this boiler is that law of physics which governs the varying Safety valves, 8 and 9, are set, respectively, for high pressure boiling points of water under different pressures. Depend- on the boiler and the sterilizing pressure on the retort. Steam ing upon the water capacity of the generator, irrespective of enters the sterilizing chamber from the boiler through the the steam space, any desired volume of steam a t a lower pres- feed pipe, 10, and returns to the boiler by 11. Water may sure can instantly be made available by suddenly relieving be admitted a t 12 by piping to the water system of the building. Drainage is provided in 13. To prevent air pockets the pressure on the generator. in the reservoir, a connection, 14, for equalizing pressures is Description of Generator placed between the top of the reservoir and the boiler. Proper The design is original in that almost the entire water of circulation between the boiler and the reservoir is made posthe generator and reservoir is available for conversion into sible by connections, 16, from the bottom of the reservoir to steam when so required, since but a small percentage is below the bottom of the boiler. The boiler and its attendant reserthe lowest allowable water level for the immersion of the heat- voir are supported by the standard, 15. The apparatus has exceeded expectations in all tests to ing elements. The design also incorporates the safety features of small diameters. Another advantage is that, to which it has been subjected. For the most part this new the writers’ knowledge, there are no limitations of allowable steam generator has been used on the sterilizers in the various pressures imposed by license laws or safety boiler rules and departments of the institution. Such data as are supplied regulations of any state. This feature is particularly im- relating to time and energy consumption of this type of portant in the industrial field, since other types of boilers boiler have been taken from tests on sterilizers. However, the require a licensed operator and come under various restric- apparatus is applicable to many other industrial practices. tions, rulings, and regulations requiring frequent inspections, Manipulation for Sterilizing with accompanying fee in some states, when 15 pounds pressure or more is maintained. A special feature of the design The generator with its reservoir of available heat is inis the angular offset on the boiler, which allows the installa- dependent of the sterilizing retort by a set of valves in the tion of this boiler in connection with equipment for which connections. Because of the small volume of water, it is other types of boilers cannot be adapted. The angle of the possible to maintain a ready supply of steam with slight energy consumption under pressure control. These condi1 Received October 24, 1930. Published as Paper No. 114 from the tions reduce the time of a sterilizing process to a minimum, Department of Botany, Massachusetts Agricultural Experiment Station.
HERE are many proc-
T
L
_
sinci, no time is lost in building up a pressure and no time is tnkcmi to cool anything but the charge after sterilization is coirrpleted. Wlieir the charge to be sterilized liirs boon placed in the retort aiid the door closed, the operator opens the Feed valve sligtitly, allowing the steam to clear the retort of iiir by expelling it through suitable vents. Hteani rnny he used freely for this purpose, as the reservoir holds a sufficient supply for several sterilizations. I n tlie medium-sisod aotoclave the retort mar lie cleared of air and a sterilizing pressure
gonerator, heated by two -I-kilowatt elements, was attraclied to a Bramliall-L)cane 2B autoclave. The large size, heated by Four 5-kilowatt elements, was attached t o a11Arthur I I . Thomas No. 1687 new laboratory model horizontal autoclave. The eIect,ricsteam generators, altliougll designed to he kept hot, may be without heat when they are used but little. However, tliey are so well insulated that pressure may be maintained all the time at relatively little cost. Table I shows the time in minutes and energy coirsumption in kilowatt-hours to obtain various pressures, starting with a cool systom.
stt:mi
'Sable I-Time and Energy C ~ n s ~ m p t i oto n Obfain Pressure on the Efectrlc Boilers SfarfinB with the Boiler at Zeru Pounds Pres~ure and sf Room Temp~ratilire ~___. ..~
Lbr.
Kw-hvs.
5 10 15
1.4s 1.65 1.75
20 25
30 45 50 60 76 90 100
____
..
2:oO 2.15
2:3s 2.45
2.65
Min. 10
M*"
Kw-brs.
a
10
4
13
12
4
I4
5 5
15 16 17 18
31
b
15 6
..
17 18.5
0
21
7
23
19.5
..
25
'Sshle 11-Time and Energy consumption t o Obtain Preeeure on the Electric Boltera Sfartlns a t the End Polnt of 81 Previoua Sterllizing Pressure
1
2
1 1
4
6 9
2
..
..
-2 .obtained within the remarkably short time of 3 niiiiutes. When the thermometer on thesterilizing retortregisters 100°C. ur when the steam flows freely through the vents, the latter may be closed and the proper prcssure obtained. While the autoclave is being cleared of air, the steam generator is adjusted for low-pressure control. Aft,er the pressures on the generator and retort are equalized, the opening of another valve bring8 botli the generator and sterilizer into such a balsnee that ria attention is reoilired until sterilisatiion iu finished. since the supply of heat is under antoinatic control and there is a sufficient supply of water circulatimg in ii closed system. The cooling process is quickened by cutting off the generator from the autoclave. This is accomplished by closing two valves and saves tlie time of cooling iinnecessary equipment and water. While cooling is taking placo, the high-pressure control is turned on and the generator left in readiness for the next charge. With one or two trials the operator can cd readily judge whero t o set the high-pressure control to meet any load condition so that the generator and sterilizer pressures can be nicely equalized. The working efficiencyof an autoclave may be increased as much as five tinios by this procedure.
.
As successive st:crilii.,ationsare made, the electric boiler is cut off from the sterilizing retort at the end of each sterilization. Tlie high-pressure switch is then turned on. While one charge is cooling, the boiler builds up a new store of heat in tho reservoir to meet the demands of the next charge. Table 11 gives the time and energy consumption required to build up a new high pressure, starting at the end point of the sterilizing pressure.
\!
Tlme and Energy Consumption Tests
Two installations ham bceil tested quite coinyletely with the object of securing dnt,a on time and energy consumption. The mediumaiaed electric
11
Side view Front uiew Fl'lgure l-Dlafirammaflc Sketch of ElfctrJc Steam Generacur
INDUSTRIAL A N D ENGINEERlh'G CHEMISTRY
:300
The capacity of each reservoir on the electric boiler is calculated on the basis of storing sufficient steam and heat to expel sll the air from the retort, bring the charge to a sterilizing temperature, and carry it through the period of sterilization without the addition of make-up water. The time necessary to expel the air depends upon the nature and size of the charge, which must be heated to the boiling point of water before condensation stops. After this point is reached, the steam can gradually expel the air through suitable vents. These vents should not be closed until a clear Row of steam is established. The energy consumption necessary to maintain a sterilizing temperature is very low, as is evident by the data in Table 111. Table IlI-Eoer@
8%
PnTlnda
-
nlliira
H. l'hninas N-, 1687: charge, 18 gal. 1 1 0 eighteen l ~ g a l giilrs . ?a,; ics,"eialurr. 21" A.
c.-
An Inexpensive Crystal or Molasses Separator' R. H. King Uarviixsirv os
T H E PBILIPPINBS, E r r e n l u z ~ Srn'rro~ ~ 071.
L ~ o i i a n .P. I
tiur-hrr.
Mi*.
30
and cooling a large volume of water means time lost. Not only is the delay hothersome to the manipulator, but i t may also be a menace to tlie proper chemical constituents of the charge, especially to certain sugars in media, some of which are very high priced. The exposure to heat while a sterilizing pressure is being built up in a gas-heated generator is lengthened by the process of cooling down after sterilization has been completed. The cooling process is proportionally delayed by the amount of heat still in tlie generator, under pressure. after the gas bas been turned off. The most satisfactory method is that which gives a sterilizing temperature immediately and allows one to stop the supply of heat as soon as the charge has been sterilized.
Consumption for Vsrlovs Sferillrlne Time3 nf L A K C S Silil"
15 20 2.5
Vol. 23, No. 3
0.85 1 ~ 5
1.6
3 0 0 0
.. 7 . 0 ...
A set of tests was conducted in which the temperature in tho retort w&s chocked each minute with the pressure. In Table I V it will be noticed how quickly a sterilizing temperatitre was reached. Also it will be noted how little lag there was in tlie thermometer as the rxessure was increased or allowed to drop. The vents were not closed until 100' C . had been attained. 'This temperature is more quickly reached by using 0.5 pound pressure in clearing the retort of air. On this aotoclave it took 12 minutes at 0.5 pound pressure to clear of air and 17 minutes at 0 pounds pressure using tlie same charge of 4 gallons of water at 21" C . Discussion
For sterilizing purposes aiid other processes where steam and heat are required, the use of the electric steam generator as described in this paper is a forward step in economy. It is not now necessary to maintain the yearly expense of providing steam in higli-pressure mains. Ttiis electric highpressure steam boiler will give all that can be desired from a high-pressure main, not only in the service performed, but also in manipulation and constancy of temperature, and with a fraction of the cost in producing lieat. The use of fuel or electric steam generators that build up a sterilizing temperature in a retort decreases the working efficiency of the autoclave and its attendant. Time consumed in heating
ROCESSES involving the Crystallization of a aolid from II.' impure solutions generally require a systematic, comparable method of control in order that the conditions for the maximum crvstallization may bo determined. For
drainage, Tlie separator is assembled in tlie follo~ving manner: The piece of GO-mesh screen is placed in tlie depression of the 4-incb pipe plug with the l/*-ineh lioles and the 200-mesh screen is placed over tlie 60-mesh s c r e e n . T h e 60-mesh screen provides a firm support for the delicnte 200mesh screen as well as d r a i n a g e space. The 4-inch p i p e plug is screwed into one of the unions and tlie union is screwed into the nipple. The other union is then screwed into the nipple and a container is tlrereby obtained. To charge the separat.or, massecuite, or the magma of crystals and mother liquor, is poured in at the top; the top plug with the airinch pipe is then screwed in and the pipe coupling tightened; air, a t any desired constant pressure from an air tank is admitted. It is not essential for control purposes that the separation be quantitative. If the ratio of concentrations of the product desired in the original magma or massecuite to that in the mother liquor or molasses separated after crystallization is known the efficiency can he computed. 1 Received
September 26, 1930.
