688
ISDUSTRIAL A S D E;VGILVEERI~\~G CHE-VISTRY
think there were no middlings in the feed. The tailings ran about 2 per cent lead, the initial feed about 8 to 10 per cent. -six-spigot I Fahrenwald sizer was installed. Each of the first five spigots was sent to one table, the sixth spigot was divided between two tables and the overflow, which was -200 mesh, was thickened and split between three slime tables. It was evident a t once that, while before no middlings were apparent on the table, they now had a beautiful stratification. The first stratum was a clean galena product assaying 82 to 84 per cent lead. The second was a streak of middlings varying in size according to the percentage in the feed, and lastly, a streak of clean tailings assaying between 0.4 and 0.5 per cent lead. The middlings were reground to -200 mesh. Reducing the tailings from 2 per cent to 0.5 per cent or less, and a t the same time decreasing the number of tables required, represented a tremendous saving. Scope of Application
Although the remarks in this paper have been confined to the field of grading concentrating table feeds, the scope of the eizer is by no means limited to this use. Stress has been laid on this particular field because it is, to date, the largest single application in which the machine has been commercially demonstrated. However, as operators familiarize themselves with the device it is becoming apparent that the uses for which the Fahrenwald sizer is peculiarly fitted are many and widely diversified. Although its application to purely chemical processes may be few, there is a wide field for it in the treatment of non-metallics, sand, abrasives, and the like, which are closely akin to the chemical industry. Experiments are now under way on a modified type for the preparation of fine sizes of anthracite coal. This application shows considerable promise.
Vol. 19, KO. 6
The Fahrenivald sizer acts as a classifier, a bizer, or a concentrator, depending entirely on the type of feed it is given and the nature of the products. To illustrate: 1-With a pulp consisting of two or more materials of distinctly different specific gravities, the machine will, if given a n unsized feed, produce a series of very closely classified products. That is, each material will be graded to size, but each spigot product will consist of a mixture of the materials associated according to their hindered settling ratios. As previously brought out, such products are ideal as table feed, or where the specific gravities are widely different, the materials may subsequently be separated by screening. 2-With a pulp consisting of particles of uniform specific gravity i t will, if given a n unsized feed, produce a series of very closely sized products analogous and in most cases better than those produced by screens. 3-With a pulp consisting of two or more materials of distinctly different specific gravities the machine will, if given a properly sized feed, concentrate the particles according to their specific gravity. A properly sized feed is one wherein the ratios cf the diameters of the largest and smallest particles are less than the hindered settling ratios of the materials.
It cannot be emphasized too strongly that the Fahrenwald sizer is not just another hydraulic classifier. There is probably no other successful hindered settling classifier now on the market. The few that are in use are mostly home-made and violate the essential rules for successful hydraulic classification. The patented discharge density control device is novel and of tremendous advantage in producing uniform products and eliminating the human factor. The Fahrenwald sizer requires no power, uses very little water, is inexpensive, requires practically no attention, is not affected by fluctuation in quality or quantity of feed, and the products that can be produced are almost unbelievably clean and closely graded.
Filter Presses-Standard
Types
By John H. Clark, Jr. T. SHRIVER 8r COMPAKY, HARRISON, N. J.
HERE are very few branches of cheniical manufacture which do not have the problem of filtration, and of the various types of equipment used to accomplish filtration the filter press is probably the most widely used, most easily operated, and most adaptable to a raried assortment of problems. A large proportion of the men responsible for the selection of equipment realize the advantages of adhering to standard types of filter press. Many engineers, however, consider that their particular problem requires a filter press of a special type. Of these, some can be quickly convinced that standard equipment is satisfactory. Others become antagonistic if any attempt is made to convince them. Such men can always have exactly what they want, but they surely pay for it. Then there are problems which really require special filter presses. We have made square, circular, triangular, and rectangular presses in sizes from 7 inches square up to 4 by 6 feet. There are various standard ways of feeding, discharging the filtrate, closing, etc. We have made four to five hundred types of filter presses, each distinct from all others in some important respect. It would seem that a buyer could satisfy his requirements from an assortment of five hundred; but it is surprising how often this is not true. I n several instances buyers have insisted that we furnish
T
certain working parts of their own special design when i t was perfectly clear that our standard design permitted much quicker operation. I n such cases we draw up new designs, make the patterns, and then as a rule never use the pattern3 again unless the customer re-orders. The prospective buyer may be a new man on the job. He wants to prove to his new employer that he is productive of ideas, so he decides on some change to be made in a certain filter press. If we cannot convince him of the inadvisability of making a change contrary to our standard practice, we make up special patterns and he pays for them. If we cannot first sell a standard type, we will design a press of any size or shape, whether it is elliptical, parabolic, 4 inches square, or 6 feet square. This is no. attempt t o belittle the new ideas that engineers may hare about the particular line of equipment which we manufacture. They give us many good ideas and we welcome them. I n fact, we encourage our customers to do this and ask them if we can make modifications that will simplify their filtration problems. This is rather a plea to buyers that they consider standard types of equipment without prejudice. The advantages and disadvantages of the various standard types are not always fully realized. These will now be briefly summarized.
June, 1927
I S D C S T R I S L A4sD ENG S E E R I S G CHE.IfISTRY
689
design makes it unnecessary to cut holes in the filter cloth and the clothing of the press is a simple operation. It is Shall a filter press be recessed plate or a flush plate and only necessary to cut the cloths to length and fold them over frame type? I n the former the press cake is formed be- each plate. Rubber collars or cloth pockets are used to make tween two recessed plptes. I n other words, the pyramid the lug joint surfaces tight. or drainage surd feed through an eye in the joint surface can be located i:icc. i.. n u t flu41 a t any point of that surface. We, however, use the corners with the j o i i i t only. For this type of feed it is necessary to locate a hole .urface. SO properly in the cloths, but the use of rubber collars is obirsiiies are used viated. The cost is very slightly less than with outside lugs. with this type. I n t h e ilusli O p e n us. Closed Delivery pl;itc : i d frnnie type both Shall the press be open or closed delivery? For an open p 1 .i t e s R 11 d delivery press some means is provided for discharging the i r : i i i i e s a r e filtrate from each plate by a cast-on bibb, a screw or flanged used. ~ i i dt h e cock, either one- or two-way, or a quick-action flap cock. surd r:i i 11a g e~. When the filtrate from any one plate runs cloudy in an open . .3 -v f a c e is Flush delivery press, that particular plate can be quickly located Figure 1-Recessed Plate, Center Feed, Open with the joint and the cock on that plate closed, unless a cast-on bibb has Delivery s u r f a c e . The been used. press cake is formed within the frames. I n a closed delivery press the filtrate from each plate is The advantages of the recessed type over the flush plate led either to an eye in the joint surface or an outside lug, and frame type are: and delivered out through the head of the press. This method is particularly adapted to volatile liquids. Further(1’1 Ten to twenty-five per cent lower cost, the difference being least in the larger sizes. more, it enables the filtrate to be delivered a t a level above (2) I t is shorter and lighter per unit of filtering area and the press without additional pumping equipment, Howholding capacity. ever. if the filtrate from any one plate begins to run cloudy, (3) The feed channel is large and there is no danger of this plate can be located only by opening the press. This stoppage and resulting plate breakage due to unequal pressures. (1) There are half as many joint surfaces t o be kept tight. difficulty can be aroided by using a gage glass and cock on the side of each plate, running the filtrate first through this The advantages of the flush plate and frame type are: and then back to the closed channel, This feature raises the cost considerably. (1) The press cake can be thoroughly washed. This cannot Recessed P l a t e us. F l u s h P l a t e and F r a m e
be accomplished in the recess type. (2) .4 flush plate is lighter than a recessed plate and therefore easier to handlp. ( 3 ) The p r e s s cake can be made u n i f o r m l y solid There IS usually a soft core around the feed channel of a recessed plate (4) F r a m e s of any reasonable t h i c k n e s s can be used. ( 5 ) The f i l t e r cloth is not subiect to severe strain as on a recessed plate. (6) Filter paper or fine-meshed wire Figure 2-Recessed Plate, Center Feed, can be Closed Delivery LI s e d a s a filtering medium. Location of Feed
Should the press be center-fed, fed through an eye in the joint surface, or through a lug outside the joint surface? A center feed is necessarily limited to a recessed type of plate. As previously mentioned, it allows an unrestricted feed with little danger of plugging. The feed can be a t any point in the recessed portion of the plate, but we standardize on the center of the plate and do not find it necessary to locate it otherwise. Holes must be properly located in the cloths, which are made tight a t the centers of the plates, either by clip nuts or sewing. A feed outside the joint surface can be through lugs a t any point. It can be applied t o the plate and frame press only. We standardize on side lugs, about one-third the height of the plate or frame from the top. These lugs then act also as the supports for the plates and frames. This
W a s h i n g v s . Non-Washing
Rhether the filter press shall be a washing or non-washing type is determined by the requirements of the problem. The wash is delivered to the filter press either by eyes or side lugs, and the remarks as to feed apply equally as well here. The washing feature can be added to the recessed plate type, but this type can never compete with the flush plate and frame type in this respect. How Shall t h e Press Be Closed?
Ratchet, gear and pinion, and hydraulic are the three usual methods of closing. As a rule, a ratchet closing device is sufficient up to and including a 30inch press. I t is advisable t o use a gear and p i n i o n closing on the 36inch size a n d l a r g e r . It adds about $40 to the cost, but is well worth it. The use of hydraulic closing will depend on the filtration cycle, and the number of Figure 3-Recessed Plate, Center Feed, Closed Delivery, kisible presses to which it Discharge ;night be applied. A 36-inch press can be closed or opened in 30 seconds with hydraulic closing, whereas a gear and pinion will require 10 to 20 minutes. It can easily be determined whether the additional cost is advisable.
9
I
690
INDUSTRIAL A N D EhTGINEERISG CHEMISTRY
Other Considerations in Determining Type of Press
I n the determination of the best type, there are still a few more points to be considered. Shall the frames be open or of the so-called solid type? The required holding capacity of the press will determine this. If the amount of the solids to be removed is very small, the frames should be cast with a solid web. The holding capacity of the press can thereby be reduced SO that the amount of unfiltered liquid remaining in the press at the end of the filtration cycle is exceedingly small.
Figure 4 Flush Plate a n d Frame, Side Feed, Closed Delivery,
selection of a washing type is of course imperative. The plate and frame type gives the most satisfactory washing. Open delivery is necessary owing to the danger of one or more chambers running cloudy. Clay. This is purely a dewatering proposition, so that the cheapest type is quite satisfactory. A center-feed, cast-iron recessed-plate press with either open delivery with cast-on bibbs, or closed delivery is chosen. The center feed allows the passage of any large lumps. Lacquers, Varnishes, and Enamels. The selection is a plate and frame press with closed delivery through an eye and feed through an eye. The plates are cast with solid webs. Closed delivery is used because of v o 1a t il e c o n s t i t u e n t s . Flush plates are necessary so that paper or fine-mesh wire screens may be u s e d a s t h e filtering medium. Feed and delivery are through eyes to avoid the use of rubber collars which might be affected by solvents. Solid frames are used to give a small holding capacity. Fruit juices are handled either in wood or aluminum presses. The Figure 5 flush plate and frame type is most desirable as thicker press cakes can Washing Type then be formed. Wood presses are used for cider and vinegar, a recessed plate for cider and a flush plate for vinegar. Thicker press cakes can be formed with vinegar when using a filtration aid so that the flush plate is desirable. Dry and pulp colors usually require either a center or side feed cast-iron press. If the user does not believe that washing can be accomplished in a filter press, a center feed type is used; otherwise a side feed washing press. Shellac is handled in a plate and frame press so as to use paper or to form thick cakes by use of a filter aid. Closed delirery is usually preferred. Yeast requires a center feed cast-iron press designed for pressures higher than standard. The dyesti$ industry runs very largely to wood plate
Shall the plates be cored so that they may be steamheated or brine-cooled during the filtration? Determination of this question should not be subject to guess work as cored plates add considerably to the cost. What material may be used for the plates and frames? Special alloys quickly increase the cost of a filter press. Wood plates and frames can be used up to about 70-80" C., depending on the material to be filtered. It should be remembered that the joint surfaces on wood plates and frames are wider. A larger size is therefore required to give the same filtering area as on a metal plate. The cost per square foot of filtering area of a press with wood plates and frames is, however, about the same as that for one with cast-iron plates and frames. No attempt will be made here to discuss the methods of determining the proper size of press and number of chambers. This should be no matter of guess work. It is surprising how many inquiries are received for a filter press to produce so many gallons, no mention a t all being made of the characteristics of the material to be filtered. Apparently crankcase oil can be pumped through a filter press as quickly as distilled water. Most any combinations of the various methods of feed, wash, and delivery can be made in standard types, so that conditions of nearly every problem can be met Figure 6 Flush Plate a n d with standard equipment. Presses Used in Various Industries
Some industries use certain types of filter presses almost exclusively. A few of these will be mentioned and reasons given for the choice of the particular types. Raw Sugar. A side-feed, open-delivery, flush plate and frame, cast-iron washing press is used in nearly every case. A side feed is chosen to avoid wastage of filter cloth due to improper cutting of eyes in the cloth by cheap labor. Inconvenience of cloth shrinkage is also avoided. The
Vol. 19, No. G
Figure 7 Frame, Eye Feed, Closed Delivery, Washing Type
and frame presses of the washing type with open delivery. Waxes require steam-heated plates. In some cases several different types will be found in use for exactly the same purpose. Conclusion
I n closing, we wish again to emphasize the advantage in not assuming that your particular filtration problem is different-somebody else has probably done about the same
June, 1V27
1SIX'STEI.2iI. A S D EJVGI.VEEIUjVG' CN E M I S T R Y
thing io a standard type of filter press. Yiiu ~ i i ndo it, too, md you can save money by doing it. And saving a few
691
dollars will make niore n S a hit thaii tiie doubtful cleverness of special designs.
Industrial Heating by Oil Circulation By Alexander B. McKechnie i'nxxs Cunaaa 0 . .111,61insr.
li RISG the last thirty US there h i v e bccn m i n y rttlernpts to constriict a high-tcni~~clatiircheatilig tern in which a liquid would act as n whicli would, in principle a t least, I the i d - k n o w n hot water hcnter. These att bruuglit about because the industries were ilemnndiiig higher temperatures in their process ~ o r kand tlic only availahle method was either high-pressure steam or direct fire. It will be readily understood that many difficult problems arc encouiitered when steam above 123 pounds is applied tu ordinary heat-consuming vessels oi either the cast integrnl or the welded steel jacket type, and that any direct fire methods are usually accompanied by hazard, ill effects on ilie product, and inefficiency. It was supposed by the builders of tlie earlier systems tliat ail that was necessary to s o h Ihe problem was to place any medium with a high boiling point int,o some kind of a system arranged for heating and circulating. In fact, several attempts were made in which no pump at all w&s used, depending ent.irely on thermal cireulat ion. ' All these systems were very short-lived as they ceased to operate owing either to fouling by carbon which deposited r:ipitily, or to burning out of the heaters themselves. It xiis quite natural for tlie designers to suppose that all t,lieir troubles lay in the circulating fluid, and because they were iisirig the best that the market produced it \\'as probably decided that a practical solutio11 oi their problems was iiiipossible. There is no question that the same difficulties would be nict today by anyone building up a circulating oil system with no experieiice in this connection. In fact, in the develupment of the pnrticulnr system discussed here there iiied to he no end of p ~ i i b h: ~ i d: oii tlie solution oS one ut, ICM of even greater difficultyiirore. I%ycoiisirlently tiltlicking e:u:ii new p n h i t ~ i ias i it caiiil: irp--
thc tmpcrxture being sujhciwitly liigli IU perform the work Init, \vitliiiut &imaging t,hc produc,t. ?'lie tcnipcriiturr: can be controlled within close iimits (:ither maiiiially or by thcrmostatic devices. This is OS vit,nl iiiiportniiec in delicatc reactions where temperature varintioiis i i i tho 1ie:itiiig iiiedium are not permissible. Cliarts from recordiiig thcmiometers show a temperature difference of from about, 3" to 7" F. in the circulating oil vhen it is tliermost,:iticaily coritrolled. The fire Iiasnrd is removed as there is no flame in coritact with t,hc vcssels. The absorber iuriiacc, the only place -,here flmie exists, is isoiated from the manufacturing equipment, arid where conditions make it necessary t.lie entire Iieat,ing plant can /)e installed in a separat,e building. Design of System
In tlie desigii of a system of this kind, !.liere are fire maio ertcli m e of which requires most careful 8tntly. IIESIGN OF HEATEEtilt Ansormmit-The absorber, lilre any other lieat exchanger, must be designed for maxirnnm etIieicricy consist,ent Tvith long life and freedom from trouble. It must be readily accessible for inspection or repsir. The Sunince must be built to withstand the high temperatures met in work OS this kind nnd be thoroughly iiisulated to prevent undue radiation losses, Such points as tile length and size of tubes. the velocity of the circu1:ttiiig oil, and prnximity of the fire to tlie tubes require careful stiidy. S&urh,
v1,IqiNl.
Advantages
lient tnansniis5ioii by llot oil eiiiijudies iirc ilceir:ibIe Sciitures and eliminates the objections US other irieti1oih for oiit:iining high temperatures. Tlic quantity of licat delivered is under control at, all tinics, mil product tcmpcratures t i p to 5.50" I". are reached TT-itliout difiicuity. l h c pressure on the entire system is priicticnlly iiegligible, rmikiiig it particul:irly atlaptable to vcsscls 1vit.h cast integral j x h e t r , ususiiy built to \\-itlistarid pres.iurm nf :ibout~ 100 pow&, and to the jackets OS gl tinlclcd steel tnnks, xhirli are built only for pressures 75 pouriris a ~ i dare used extensively in the maiiufacture of c1iemL:als and food This point is rcndily understood when we c.oiirider tlmt 100 pounds of st,etim represciits only 338" F. Ihtribution OS heat is uniform oi'er the entire siirfacc of tlic ressel and the entire mass is treated instantly and alike,
Standard 400,0@@B. f. U. per Hour hlerrill Process System
/ >
(Iriicnr.a.rrl-c, l ' u m - I t is generally believed thst tlie circu1;rting pimp should Le of the positive displncenient rotary type to insure a knoivii and non-pulsating flow. 'l'lic iiecossity for these Scatures is re:idily understood as the temperature drop in the circulating oil of 11 system of given ciipcity is iiivcrsely proportional to the rate of flow of the circulating oil. A small t,einpcrotire drop is desirable iis it iiieans a inore uniform tempetature over the entire surface of the vessel bciiig heated.
