IND UXTRIAL AND ENGINEERING CHEMISTRY
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Vol. 16, No. 11
T h e Petree Process for t h e Clarification of Cane Juices’ By E.E. Hartmann PETREE & DORRENGINEERS, INC.,67 WALL ST., N E W YORK,N. Y.
T
HE manufacture of is Possible to Prepare a mud The Petree process is a new deoelopment in the clarification of raw Cane sugar has which j S retained by the sugar canejuices resulting in the reduction of sugar losses during made great strides fiber of the bagasse. This discovery was incidental to in recent years. Rut progThe compact equipment used in this process replaces the trains of ress has been mostly in the experiments made on Plant clarifiers, mud tanks, and filter presses, thus reducing operating line of milling and heat scale in an Australian faccosts and minimizing the soace requirements. economy-i. e., in the contory on the separate lime struction of power, grinding, and heat treatment under and evaporating equipment. Little progress has been made given special conditions of the relatively pure juice expressed in the treatment of the juice although some interesting work by the first mill and of the more impure juices expressed by in connection with clarification is now being done a t several the subsequent mills. They noticed that the mud resulting cane sugar equipment stations. Van Harreveld,2 the director from this treatment possessed physical characteristics entirely of the Java Experiment Station, which had devoted consid- different from those of ordinary settlings, and it was this oberable time to clarification, said in his program for 1924, servation which suggested to them. the possibility that the “We shall for the present discontinue all other experiments, bagasse might retain the mud if prepared in this manner. Proceeding on this basis, they put all the mud on the bagasse because the Petree process demands our full attention.” What is the Petree process? It is the outcome of the and the results were so startling that, within twelve months of natural desire of cane sugar technicians to get away from the their discovery, twelve other factories operated their process. use of filter presses and to avoid the losses, known and unOPERATION known, sustained a t the filter-press station, which are always The Petree process is practically automatic; it is continua source of great expense and are generally considered a ous throughout and easily controlled. The mill juices are nuisance. Attempts have been made repeatedly to avoid the use of separated into a high purity, high density, primary juice and filter presses by returning the settlings from the clarifiers and a low purity, low density, secondary juice. These juices are mud tanks to the bagasse, using the latter as a filtering treated separately. The primary juice, this term being medium. All these attempts have ended in failure, mainly used to denote the mixture of the limed crusher and first because the bagasse is not able to retain a sufficient quantity mill juice, together with the clarified secondary juice, is of the ordinary mud. The resulting accumulation of mud pumped through the primary juice heaters to the xtrimarv clarifier. From this proved to have a detLEGEND primary clarifier about rimental effect on the @ 95 per cent of the mixed q u a l i t y of the juice. juice (there are records Besides, it was in every of 97 per cent) leaves as instance only a question perfectly clear, sparkling of hours before the sysjuice at a temperature of tem became clogged 209’ to 210” F. The Another f a c t o r t h a t quantity of juice carried would render such a prowith the muds is therecedure u n e c o n o m i c a l , fore very small. The even if m e c h a n i c a l l y second mill juice, which practicable, is the high c o n t a i n s most of the sucrose content of the g u m m y and colloidal mud, which would inbodies expressed by the evitably lead to serious second and subsequent losses of sucrose in the mills, is limed separately baga~se.~ and after being mixed Thomas and Petree, with the rich settlings the former a t the time from the primary clarifier chief inspecting chemist is pumped through the and the latter chief insecondary juice heater to specting engineer of the the secondary clarifier. Colonial Sugar Refining The secondary mud, reCompany, found that it sulting from the settling 1 P r e s e n t e d before the of the mixture of second Division of Sugar Chemistry at mill juice and the prithe 67th Meeting of the Amelimary mud, is mixed with can Chemical Society, Washthe third mill juice, and ington, D. C., April 21 to 26, 1924. this mixture is distrib2 Arch. S u i k e v i n d , 8 0 , uted over the bagasse (1923). as it issues from the 8 Louisiana Planter, 70, first mill. The juice 286 (1923). CLARIFIER FOR CANESUGAR JUICES 411 VENT OlPrS
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INDUSTRIAL A N D ENGINEERING CHEMISTRY
November, 1924
F I G . 1-SECTION
OF CLARIFICATION AND
DOUBLE FILTRATION E Q U I P M E N T OF
from the fourth mill is returned to the bagasse from the second mill, as is customary under the usual compound maceration procedure. The details of the operation may be varied. For instance, it may be found preferable to distribute the macerating mud over the first and second mill, or to put it all on the second mill. Local conditions will influence such details. The changes in equipment necessitated by the Petree process consist in the substituting of two continuous clarifiers of different sizes for all the defecators, mud-settling tanks, and the whole filter-press statiop, presses, pumps, the laundry, and the equipment for the disposal of the mud. A liming machine, which distributes the lime continuously between the first and second mill juices a t the mills, forms part of the Petree process equipment. One unit of two clarifiers is sufficient for capacities up to 2000 tons of cane per day. No additional equipment is required, except that it is necessary to have the juice heaters with an increase of
AN
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AUSTRALIAN SUGARHOUSl3
10 to 15 per cent in heating surface in a sufficient number of units to allow the separate treatment of primary and secondary juices. The primary clarifier furnishes the supply for the evaporator in a continuous stream of perfectly clear juice a t a temperature of from 209" to 210' F. The secondary clarifier stands in direct operating relation with the mills. It turns out the twice limed, twice heated, granular Petree mud held in a juice of much lower sucrose content than that of the residual juice in the bagasse, which is to absorb it. The stability of the Petree mud is such that only a negligible amount is regxpressed from the bagasse with the juice-and here is the key to the practical success of the process. Such mud particles as are reexpressed are trapped within the secondary clarifier circuit and are ultimately sent to the furnaces; their entrance into the juice flow, which leads to the evaporator, is barred. The second mill juice resulting from compound maceration practice carries most of the gummy and colloidal bodies.
FIG.2-SECTIONOF PETREEPROCESS EQUIPMENT OP SAM& CAPACITY AS FIG. I
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INDUSTRIAL A N D ENGINEERING CHEMISTRY
I n ordinary defecation practice, this low density, low purity juice is mixed with the high density, high purity, first mill juice, and it is quite evident that these suspended bodies cannot settle so well in this mixture as they could in a liquid of lower specific gravity. This thin second mill juice is therefore limed, heated, and clarified apart from the primary juice. The mixing of the rich primary mud with this thin juice seems to assist by a dragnet action in carrying down gummy and colloidal bodies and other solids held in extremely fine suspension in this thin juice. That the Petree mud as discharged by the pump of the secondary clarifier has physical characteristics entirely different from that settled out in the primary clarifier is made quite evident by the fact that the settling area of the secondary clarifier need not be more than about half that of the primary, and this in spite of the fact that it has to handle nearly double the quantity of settlings, those precipitated from the thin juice added to those coming from the primary. The mud is withdrawn from the clarifiers continuously by a diaphragm pump. Very little power is required for the operation of these clarifiers, the load varying between 1 and 2 horsepower. ADVANTAGES The advantages of this process over the old way of working are : 1-Low cost and compactness of equipment. 2-Elimination of the filter-press station, always a source of great expense and very often a breeding place for all kinds of molds and ferments and unpleasant smells resulting from their activities. That the sugar loss caused by the operation of filter presses is in excess of that shown by the figure “sucrose in presscake,” will be admitted pretty generally. The item “undetermined losses” covers a multitude of sins, and there does seem to be a’tendency for these losses to be highest when the sucrose in press cake is low-i. e., when the cake is sludged up with water and again pressed. A certain amount of deleterious impurities is unavoidably redissolved by this procedure. There are other drawbacks to the operation of filter presses. Cloths will break. A faucet here and there delivers muddy juice, with the result that some of the very fine mud, which we know impairs boiling-house work, finds its way to the evaporators. 3-A considerable saving in fuel, due in part to the actual addition to the fuel supply, since the solids, which previously formed the filter press cake, are now burned with the bagasse, and in part to the restricted and more efficiently insulated radiating surfaces. Together, these heat savings are equivalent to an increase of from 8 to 10 per cent in the amount of bagasse. 4-0ne man per shift easily replaces ten to fifteen men usually employed on the defecators and mud tanks and a t the filterpress station. 5-The money spent on filter-press cloths and plate and frame renewals can be put to other uses. 6-Greater ease in cleaning evaporators due to the practical absence of organic, solids in suspension. 7-A great improvement in the working of low-grade sugar, only from half to two-thirds the centrifugal equipment being necessary. &Better exhaustion of the molasses due to lower viscosity, and consequently less sugar losses. 9-Better keeping sugars; the practical absence of bagacillo, which cannot be washed out of the sugar in the centrifugals, means a lower moisture content and less danger of fermentation. 10-Absence of clinker in furnaces; and, as a result of all this, 11-An actual increase of 1t o 2 per cent in the sugar recovered.
There are many more points in favor of this process, such as greater comfort for the workmen, greater cleanliness, no useless dilution of juices by washing tanks, etc.l No innovation in manufacturing processes can be brought about without pretty severe scrutiny, and rightly so. Perhaps the most plausible and the most frequently voiced objection to the Petree process is the loss of the press cake as fertilizer. At most sugar mills the press cake is considered in the light of a liability rather than that of an asset; on the other hand, there are those who ascribe almost supernatural pokers of raising cane to this evil-smelling refuse. 4
Louisiana Planter, 73, 307 (1924).
Vol. 16, No. 11
On the basis of a table of analyses shown in Noel1 Deerr’s book, the fertilizer value of the press cake is so low (less than 93 per ton) that the cost of distribution a t most places is far in excess of its value. But even this value is more than offset by the effect the Petree mud has on the bagasse ash. This ash contains in most cases so much clinker that the amount of available potash in it is practically negligible. The lime content of the mud returned to the bagasse raises the fusion point of the ash sufficiently to leave it in a friabIe condition with the bulk of the potash in available form. Thus the bagasse ash, which has in most cases been a liability, becomes an asset and the press cake is replaced by a material of higher fertilizing value, which can be quite easily distributed. Another criticism deals with the fact that the percentage of sucrose in cane under the Petree process is based on the weight of the clarified juice instead of the weight of the raw mixed juice. There was really no reason to assume that there would be any difference between the two methods. The proof that the sucrose in cane figure is not affected by this modification is furnished by the factor sucrose per cent cane to sucrose percent first mill juice, which was found to he the same in every instance where data for comparisons were available whether on weight and analysis of cold or hot juice.
Determination of Phosphoric Acid in Fertilizersiz By 3. E. Breckenridge AMERICAN AGRICULTURAL CHEXICAL Co., CARTBRBT, N . J.
C O O P E R A T I V E work on determination of phosphoric acid in phosphate rock shows very good checks with the volumetric method as compared with the gravimetric method. In phosphate rock, however, there are no sulfates, which seem to be a disturbing factor in the volumetric method when applied to mixed fertilizers and- acid phosphate. Many laboratories recognizing this standardize their alkali against a known solution of acid phosphate and do not use the standard given in the A. 0.A. C. Methods. As a result of work done in the writer’s Iaboratories it has been found that precipitating the sulfates with 5 per cent barium nitrate solution, the method as given can be used, and gives results agreeing closely with the gravimetric method.
METHOD Boil a 2-gram sample for 30 minutes in a 200-cc. flask with 30 cc. of nitric acid plus a few cubic centimeters of hydrochloric acid. Add 50 cc. water and boil. Add while hot 5 per cent barium nitrate solution (50 cc. for acid phosphate and 25 cc. for mixed goods). Allow to cool and proceed with volumetric method. RESULTS Gravimetric 19 31 Maximum Minimum 9 Ii7 16 52 Average Number of determinations, 9.
--VOLUMETRIC-Regular Ba(N0s)z 19 47 19.37 9 78 9.5s 16 90 16 52
Although the addition of ammonium nitrate is supposed to overcome the disturbing feature of the sulfates, in general work erratic results are obtained when the volumetric method as given in Association of Official Agricultural Chemists, Methods, 1920, p. 3, is used on acid phosphates and mixed fertilizers. 1 Presented before the Diwsion of Fertilizer Chemistry at the 68th Meeting of the American Chemlcal Society, Ithaca, N . Y., September 8 t o 13, 1924. A. H. McDowell, 1 Work done by M. H. Plngree, Baltimore, Md.; Charleston, S. C.
