AVERAGE OF 4 DAYS COMMERCIAL OPERATION C-SUGAR
POL COLOR CONTINUOUS 91.20 106.5 BATCH 86.19 153.5
MOLASSES PURITY BRIX
35.95 92.28 36.19 92.34 MASSECUITE PURITY BRIX TEMP.
62.82 96.89 131.5° F
THROUGHPUT CU. FT MASS/HR.
142 4 5
CHART NO. 2
This continuous centrifugal is a different method of spinning sugar.
It has many characteristics that are different from batch machines. One of these is its ability to handle poor strikes or strikes with mixed grain. The sugar moves up the basket in a very thin layer. Small crystals do not have the opportunity to block the flow of syrup like they do in a batch machine.
The results of spinning such a strike are shown on CHART NO. 3.
Another different characteristic is the action of wash water. This also is due to the fact that the layer of sugar on the basket is extremely thin.
Wash water can be applied so that a crystal moves under the spray, has its molasses washed off, then moves on before any sugar is melted. Each crystal is treated directly under the water spray. It is not necessary for the water to move through four or five inches of sugar, becoming saturated with melted sugar, in order to treat all of the crystals.
CONTINUOUS SUGAR
p0L 93.8
COLOR 60 MOLASSES PURITY 39.19 BRIX 92.62
BATCH
79.2 230
38.98 93.82
MASSECUITE BRIX 96.14 PURITY 60.0 TEMP. 120 F
CHART NO. 3--Color and purity comparisons between continuous and batch machines on poor strike
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The present thinking is that "C" sugar must not be washed because any washing melts sugar into the discard molasses. This is not true with our continuous machine. A small quantity of wash water can be applied to raise the sugar purity without raising the molasses purity. At Valentine Sugars, Inc., an average of 0.1 gallon per minute was used.
CHART NO. 4 shows the operating variables of the continuous centrifugal as wash water is applied and as the throughput is changed. These trends are applicable to the spinning of any sugar. You will note that as the quantity of wash is increased, the purity of the sugar rises very rapidly to a plateau, while the purity of the syrup rises very slowly. The left hand curve shows the effect of throughput on sugar purity. An understanding of these character- istics will enable the operator to set the machine so as to obtain the optimum values of sugar and syrup purities, while at the same time getting the maximum capacity.
CHART NO. 5 shows a typical horsepower curve for a batch centrifugal superimposed upon the horsepower curve for the continuous. This shows very graphically the power saving of the continuous centrifugal and points out one of the reasons for long trouble-free life, since it is not subjected to the frequent high accelerating and braking loads.
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CHART NO.4
CHART NO. 5--Comparative power curves
TIME
This is a new method of spinning sugar. Its simplicity with resultant lower first cost and operating costs is obvious. It has demonstrated its ability to give equal or better results than batch machines with "C" sugar when used under exactly the same conditions. It can do the same for other sugars.
Without a doubt, additional benefits can be obtained by adjusting boiling practices to take advantage of the improved sugar purities available and arranging massecuite handling facilities to properly prepare the massecuite for the continuous centrifugal.
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EXPERIENCES WITH CONTINUOUS CENTRIFUGALS AT VALENTINE by Hector Elizondo
SCORE OF TEST:
To determine possibilities of new Silver continuous centrifugal size 63 for drying "C" sugars in our factory. To determine actual capacity of this continuous machine under similar conditions in terms of our standard batch machines. To this purpose we obtained simultaneous data on our batch machines and the continuous to compare results.
CONCLUSIONS:
As we can see from the accompanying graphs of results, the quality of sugar and molasses are comparable. A bit higher purity in molasses of the continuous machine, but better color and polarization on sugar. This higher purities we see in the continuous machine may be due to little crystals being able to go through the screen because of its thin layer drying principle. In the batch machines some of these grains are caught in the thick sugar layer.
We tried to run this machine without water or steam, the same way we run our batch "C" sugar machines, but sometimes we found dust in the sugar, which disappeared as soon as we applied a very small amount of water or steam. Of course, they are different machines and we cannot expect exactly the same operation out of both.
The Silver continuous seems to be a more versatile machine, since you can change the quality of your sugars by making very little change in operation.
I believe it would be an ideal machine to dry double purge massecuites in order to obtain a cleaner seed sugar for our footings in making turbinado sugar.
Averages and maximum ranges during tests were as follows:
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Sugar Pol Continuous 84.10 to 95.70 Ave. 91.07
" Batch... ...79.20 to 93.20 Ave. 89.70 Sugar Color Continuous .50.00 to 150.00 Ave. 96.36
" Batch.... ...70.00 to 250.00 Ave. 115.50 Molasses Purity Continuous...31.35 to 42.37 Ave. 37.18 Molasses Purity Batch...32.10 to 41.81 Ave. 36.20 We can see very clearly that the continuous sugar is of better quality than batch sugar. But we can also notice a slight increase in purity in continuous molasses. Of course these results average the total of 61 tests analyzed.
Capacity of Silver continuous can be said to be three times the capacity of one regular batch machine under our test conditions.
Most of our capacity tests were run on low load conditions and average capacity comes to be 121.39 cu. ft./hr., while batch machines were making 37.5 cu. ft./hr.
ADVANTAGES OF THE SILVER CONTINUOUS OVER THE BATCH MACHINES:
1. Does not need manual labor in its operation, and very little supervision. I believe one man can operate even 20 of these machines, to say a figure.
2. The capacity of one Silver continuous is better than three 24" x 40" batch machines.
3. Its cost is approximately the cost of a regular 24" x 40" batch machine.
4. The remarkable simplicity and reliability of its control equipment.
Upkeep and maintenance can be made by a good mechanic.
5. Because of its principle of operation it rotates the sugar crystals in many positions avoiding the outside blind face where molasses may cling to the crystal.
6. The small amount of energy needed to operate this machine. 25 hp.
did the work of three batch machines (40 hp. each).
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7. The results of these tests show a superiority handling "C"
massecuites, and it may be expected to do even better work drying
"A" or "B" massecuites, since "C" massecuites are the hardest to dry due to their gummy nature.
DISADVANTAGES OF THE SILVER CONTINUOUS MACHINE:
1. A higher purity molasses. In our tests it showed 0.98 higher values as an average on 36 different "C" strikes.
2. The need of some water or steam for its satisfactory operation. In our tests it showed about 0.15 g.p.m. necessary to avoid sugar dusting, or the use of some steam (10 psi) in the gage.
3. The relatively high cost of screens. About $120.00 each. One screen is supposed to last one full crop.
4. During clean outs a special connection must be made to discharge washings-out of molasses troughs. The same must be done when washing sugar curb, since these sweet waters cannot be mixed with the dried sugars. Probably will have to be taken to syrup tanks when drying
"A" and "B" sugars. Most probably, a mechanical device could be devised so as to clean mechanically sugar curb without the addition of water.
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RESULTS OF TEST RUNS ( C o n t ' d ) C O N T I N U O U S C E N T R I F U G A L
Wash Steam Batch Centrifugal
RESULTS OF CAPACITY TESTS
Average Capacity for these tests 121.39 Cu. Ft./Hr. or 5.967 Tons/hr.
THE BACH POLY-CELL SUBSIDER by
Wilmer M. Grayson
The Bach Poly-Cell Subsider (Clarifier) was designed by Mr, Niels B.
Bach after many years of experimenting with various types of clarifiers. Mr.
Bach also designed the original Bach Subsider which is known all over the world for its simplicity of construction and operating efficiency.
It is a well-known fact that given an opportunity, fresh sugarcane juice, properly limed and heated, will settle fast and clear. Sometimes, during adverse weather conditions when sugarcane must be harvested from necessity, clarification is very difficult to achieve. Whenever a mud problem exists, there is a loss of capacity, loss of yield and poor quality sugar. The excess- ive trashy condition of the cane along with field mud causes money loss to the processor on every ton of cane he produced or buys. At this time especially, clear juice free of bagacillo would be of inestimable value to any mill. The Poly-Cell Subsider gives almost instant settling on whole juice, juice that will be in process just a short time, juice that is clear and sparkling and with little or no loss of sucrose and purity.
It is also a well-known fact, proved in any laboratory that properly treated juice will settle rapidly for the first five or ten minutes, seen by filling a glass cylinder with hot, properly limed juice. This settling rate is about an inch a minute for the first five minutes. After that the rate of settling is slow even if the juice is kept hot. In the old type of open clarifier, within a few minutes after filling, it was possible to draw off clear juice from the top draw-off cock, but it usually took an hour or more of settling before the last bit of clear juice could be drawn from the last cock. The reason for this is the fact that the specific gravity of the juice and the solids is about
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the same and the flocs at the bottom of the tank are competing with the flocs at the top which are trying to settle, and equilibrium almost occurs. Settling slows down and it is then said that settling takes place by compression. That takes time.
In the continuous clarifier of today much the same thing happens. The hot juice remains in process from two to three hours with consequent losses from inversion and decomposition. The speed of settling depends among other things, on the design of the clarifier, the tray area as well as the gallon capacity. With a given flow rate of juice, the smaller the clarifier the less time the juice remains in the clarifier, the lower the loss of sugar from inversion. The more rapid the settling, the more brilliant the juice, the higher the sucrose and purity. The ideal situation therefore, is one in which settling occurs in a matter of minutes instead of in a matter of hours. WE BELIEVE THE POLY-CELL SUBSIDES. FULFILLS THIS REQUIREMENT.
The principle behind the design of the Bach Poly-Cell Subsider is based
on the fact that fresh sugarcane juice, properly right temperature will settle about an inch a minute if the flocs are separated into
layers. Therefore, if a clarifier could have a multiple of trays instead of the conventional four or five, the mud would not have far to travel on each tray and would settle in a matter of minutes without competition within itself.
Of course that is mechanically and economically impossible with the conventional clarifier because of the necessity for some kind of scraping mechanism to remove the mud from each tray. In the Poly-Cell Clarifier this is not the case as there are no scrapers on any of the trays (only in the mud compartment). Each cones lopes downward at a 60 degree angle. The mud slides off the cones by gravity.
To put it simply, the Poly-Cell Clarifier is just a tank with a 45 degree angle conical bottom having scrapers in the cone to ease the mud to a central
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draw-off sump. In this tank there is fixed a cylindrical baffle which extends downward to just above where the conical bottom begins. Smaller units need not have this baffle. However, if used the baffle must provide sufficient space to permit the placing of a number of Poly-Cell units between it and the outer wall and leave enough space for the settling mud to fall to the mud compartment. Usually the space between the diameter of the cell cluster and the width of the annular space is about four inches.
Each Poly-Cell unit is made up an inch and a half steel pipe of proper length, closed on the bottom end. At two inch intervals along the length of the pipe, quarter inch holes are drilled in a straight line. Just above each of these holes, cones having a base diameter of varying widths, usually 20 inches and having a 60 degree angle slope are welded or clamped to it to make a leak-proof joint. During operation the clear juice flows through each of these holes and leaves the pipe through a header, or each pipe may have a separate outlet to an outside trough. Since the hole is just under the apex of the cone tray no mud. can enter, for to do so it would have to climb up the underside of the cone for about a foot. This would be impossible unless the clarifier filled up with mud a foot or so above the bottom hole.
The sketch you have shows the detail of the cone arrangement, the outlet holes and the pitch of the cones. It also shows the general arrangement of a Poly-Cell Subsider having just three units. This unit was designed for experimental purposes for the College of Tropical Agriculture in Trinidad.
It is not a commercial clarifier. On theblackboard is a drawing of a unit we first proposed for Lula Factory but this will be expanded as will be explained later in this paper. The number of units required in any commercial installation depends on the work capacity desired and generally runs as high as twenty-five or thirty. In other words, you may put in as many cells as you have room for.
The unit on the blackboard will handle about thirty gallons of filtrate a minute, 90
or 1,800 gallons per hour. I am sorry I do not have enough of these drawings to pass around but you may, if you wish examine it more closely after the meeting.
We intended at first, through the splendid cooperation of Charlie Savoie and Pat Cancienne, to put this identical unit in at Lula for operation this fall. However, we realized it would not be large enough to handle all of their filtrate so we decided to build a larger unit with eight cells instead of three. This unit will handle all of the filtrate from 150 to 160 tons of cane per hour. This unit is now under construction and will be ready for grinding this fall. We will keep accurate account of such items as flow- through, Ph, temperature of incoming and outgoing juice, sucrose and purity in and out, mud height and thickness, etc. The results will be published at a later date.
If the Poly-Cell works on filtrate, it will help to solve a lot of mud problems which are now plagueing Louisiana processors. We already know it will work on mill juice it having already given excellent results in Florida.
The juice was heated but not limed as it went into syrup, and yet the overflow from each poly-cell was brilliantly clear and without a trace of bagacillo.
It was doing this without supervision to any extent. In fact when I was there there didn't seem to be anybody watching it. If you are interested, we will be happy for you to come over and have a look at it when Lula gets going.
Thank you.
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A SUGARCANE CARRIER CONTROL SYSTEM by
Sidney J. Levet, III
This system is capable of delivering more tons of cane per unit time at the crusher, by more efficient use of the knives and shredder. This is accomplished by regulating, by use of a feedback circuit, the load on these units. Moving the cane from the yard to the mill is the function of the carrier. While on the carrier, the cane is prepared for milling by the knives and the shredder. It is at these stations that trouble is likely to occur. The load on the turbine and motor changes due to the varying amounts of cane being passed. Overloading is a frequent problem.
The load on these units changes so quickly that the reaction time of the operator is sometimes not fast enough to prevent a choke. Even if a choke is prevented the wear and tear on the units by repeated overloading is excessive. The other extreme is also expensive, the operator, feating a choke, will underload the units thereby passing less cane. With this system, the load and hence the feed is kept relatively constant and chokes are a thing of the past.
The system is in use presently at Frisco Cane Company's San Francisco factory. The carrier is powered by a steam engine. It was decided that the carrier should have three speeds of operation - stop, slow and fast.
The exact rate of carrier movement for the slow and fast speed was determined once the system was in operation. Three speeds were chosen but as many speeds as desired are possible.
The carrier engine's steam supply is controlled by two solenoid valves one 3/4 inch in diameter and the other 1 1/4 inches in diameter. Each valve has a hand valve connected in series for fine speed adjustment. The operation
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of these values is determined by the load on the knives and shredder, and the level of cane above the crusher.
The three points of control are at the knives, the shredder and the crusher. The knives are powered by a steam turbine and the load is determined by a special DC generator. As the load increases, the speed of the knife shaft decreases. The generator develops a voltage in proportion to the speed of the knift shaft. The voltage developed actuates two special voltage relays.
One relay controls the fast speed, the other the slow speed. When both relays are open the carrier is stopped. Since the normal speed of the knife shaft is 600 RPM, at full load, the relay that controls the fast speed is set to close at 600 RPM and to open at 500 RPM which is 120% full load. The relay that controls the slow speed is set to close at 500 RPM and to open at 400 RPM, 150% full load. Below 400 RPM the relays are open and the carrier is stopped. The 100 RPM difference between the drop-out speed and pull-in speed of each relay is such that once the relay is open it gives the turbine time to gather some momentum before closing and the load is applied. In actual operation, this worked to the satisfaction of all concerned. The relays used were built to specifications for this system by Potter and Brumfield. The shredder is powered by a three-phase 440 volt electric motor. The means used to determine the load on this unit was the line current. Two current trans- formers and two current relays are used. The operating points for the relays are 125% and 145%, of full load current and these can be safely handled by the motor. With the motor operating at normal load both relays are closed. As the load increases so does the line current, and when it reaches 125% of full load the current relay connected to the fast speed opens and operation in that speed ceases. If the current increases to 145% of full load, the relay connected to the slow speed opens and stops the carrier. As the load on the motor drops the process is reversed. Just as on the turbine there is a delay between the