By F. C. W I L L I A M S . This method does not seem to be generally
known in Natal, but has been used in Australia and Central America for some time, and latterly in many distilleries in Germany. I have used it for the past nine years.
The treacle is thoroughly mixed with water to form a wash of from 9° to 10° Be. The boiler is then filled to a point well above the water line, and is not allowed to fall below 70oF. Fermentation occurs spontaneously with free evolution of hydro- gen, an indication of which is its appearance in the form of bubbles on the surface of the wash. Naked lights should not be allowed near the boiler man- hole at this stage.
After nine or ten days the plate surface should be watched to see if the scale has started to soften.
In three weeks, more or less, the scale should be quite soft and of a jelly-like consistency. The wash should now be lowered in one of the boilers to a couple of inches below the water line, and if the plate, when wiped, is found to be quite clean, the boiler should be emptied.
As the boiler is now chemically clean, it should immediately be filled with water, and sufficient paraffin (dependent upon the size of the boiler) added so that when the boiler is very slowly emptied, a film of paraffin is left on the boiler plates.
A quantity of disintegrated jelly-like scale will now be present at the bottom of the boiler, which is easily washed out with a hose pipe. In the case of a B. & W. boiler, a tube brush should be put through the tubes. This method has also been successfully used in the cleaning of evaporators.
If any delay occurs in the spontaneous starting of fermentation, it can quickly be developed by the adding of a few gallons of wash taken from an evaporator which has been standing full of wash for a couple of days.
Finally, care should be taken that the boiler is emptied when the plates are clean, as there may be a possibility of pitting setting in, although this has not been my experience. It would be of in- terest if experiments were carried out with plates to find if pitting is possible.
An article called "Removing Scale from Boilers by Molasses Fermentation" appeared in the Inter- national Sugar Journal for February, 1937.
Many German distilleries are said to be loosen- ing their boiler scale by means of molasses fermen- tation. Their practice is to add about 1 lb. of molasses per square foot of heating surface.
^jfiijA^ftalaf
By G. S. M O B E R L Y . The operation of the quota provision of the pre-
sent Agreement necessitates a periodical estimation of the tonnage of cane which will be required to make the sugar quota.
During the 1938 Conference of this Association, Mr. C. L. Waters presented a short paper entitled
" Conversion Ratios''1 in which he suggested that the cane to. sugar ratio for the season might be estimated by averaging the ratios of the 9th, 10th, and 11th weeks and then averaging this figure with the ratio for the week ending nearest to the 1st of August. Some infor- mation from chemists as to how nearly this agreed with actual results during the past two seasons would be of interest.
The Committee of the International Society of Sugar Cane Technologists for Uniformity in Re- porting Factory Data in their report to the Sixth International Conference referred to, though they did not recommend, the general adoption of, a figure known as the Demerara Index2. This has been defined by Follet-Smith & Williams3 as the sum of the sucrose per cent, cane and the tons of cane per ton of sugar. This figure remains fairly constant for any one factory, though it tends to decrease over a series of years as. manufacturing efficiency improves. At present it varies from 21.8 to 22.8 for our factories.
If at any period of the season an estimate can be made of the probable sucrose per cent, cane for the season, it is possible to estimate with reasonable accuracy the tons of cane which will be required per ton of sugar. It is preferable to use the figure tons cane per ton of sugar on the basis of 96° pol.
sugar.
F o r both Natal and Trinidad the correlation co- efficient is r=0.97, and for British Guiana r=0.98.
The attached table for the proceedings shows the way in which the Demerara Index keeps fairly con- stant with large fluctuations of sucrose per cent, cane.
It will be observed that the Demerara Index was not very greatly affected by the unusual conditions prevailing in the locust year of 1934.
A similar table for British Guiana factories is given in the International Sugar Journal for July,
1937 (p. 271).
For any month at any factory the Demerara In- dex to date will be a figure approximating to, but not quite equalling, the Demerara Index for the whole crop. T h e variation of the monthly to-date figure from the crop figure has been recorded for nine factories for five years, and from these forty- five instances, the mean variation and the standard variation from the mean has been calculated. From these figures the following formulae have been pre- pared for the estimation of the Demerara Index for the whole season at various times during the season.
End of July Index = D + 0.06 ± 0.32 End of August Index = I) + 0.05 ± 0.24 End of September Index = D -f 0.03 ± 0.18 End of October .. . . . . Index = D - 0.01 ± 0.12 End of November Index = D — 0.01 ± 0.09 Where D is the Demerara Index to date at the period stated. The final figure after the + sign represents the probable degree of accuracy at 19 to 1 odds.
The tons of cane required to make a ton of sugar for the whole season are estimated by deducting the. predicted sucrose per cent, cane from the esti- mated Demerara Index.
For instance, at the end of October it might be estimated that the sucrose per cent, cane for the whole season will be 13 80; the Demerara Index to date at the same time is 22.66. Then the tons of cane required to make a ton of sugar would be:—
22.66—0.01+0.12—13.80.
i.e.. would be expected to be between 8.73 and 897 This is for 96° pol. sugar, and would have to be corrected for the expected average pol. of sugar produced. If this were 98.5 the conversion ratio would be expected to be between 8.96 and 9.20. If the mean value of 9.08 were taken, the error in a crop of 30,000 tons of sugar would probably not amount to more than 3.600 tons of cane. This sounds a lot, but it is probably at least as close, as could be estimated by any other means two months before the close of the season. In any case, it is very difficult to estimate the probable percent- age of sucrose in the cane for the balance of the season.
T h e estimation of sucrose per cent, cane from precedent conditions of rainfall and sunshine offers a useful scope for investigation.
Expressions of opinion as to how this estimate might be made, as well as further suggestions for estimating the tons cane per ton of sugar are invited.
References.
1. Waters, C. L. (1938), Proc. S.A. Sugar Tec. Assoc.
12, 63.
2. (1938) Proc. Sixth Congress Inter. Soc. Sugar Cane Tech., 854.
3. Follet-Smith, R. R. & Williams, J. E., (1936) Agr.
Jnl. British Guiana, 7, 231.
The P R E S I D E N T thanked Mr. Moberly for bringing forward this brief paper. He thought Mr.
Moberly's method of arriving at the amount of cane at the beginning of the season would be very helpful.
Mr. DODDS drew attention to the Demarara Ratio which was considered some years ago for in- clusion in the Annual Summary. He was glad Mr.
Moberly h a d referred to it again and indicated its useful possibilities.
Mr. B I J O U X asked if the Experiment Station had drawn up any correlations between weather conditions and sucrose content, and mentioned also t h a t there was a formula known as Water's Formula for doing so.
Mr. MOBERLY did not think t h a t t h e Demarara Ratio was of much comparative value between factories. Each factory would know its own, which would be sufficient. Referring to Mr. Bijoux, he said Mr. Beater had an interesting paper a few years ago on weather conditions. With these meteor- logical data a lot of useful investigation could be carried out with regard to estimation of sucrose per cent, cane from weather conditions.
A hearty vote of thanks was accorded to Mr.
Moberly.
Multi-Tray Continuous Settlers Versus Intermittent Settlers in the Clarification of Cane Juices.
By M. V I G E R . The man who makes two blades of grass to grow
where only one grew formerly is admittedly a bene- factor of the human race.
So also should be regarded he who enables, or even assists, one man to do the work of two or more.
The equipment of Sugar Factories, which, in the days of the past, occupied the energies of many men, has now, in these clays of highly-organised effort and economics, been replaced by more modern units where only one man is used.
This has only been made possible through the facilities which modern inventions and improve- ments have placed at our disposal.
In the juice settling department of Sugar Fac- tories Multi-Tray clarifiers have been known and used for almost twenty years. During this period a large number of designs have been proposed:—
the Dorr, Seip and Bach Continuous Subsiders are well known to every one of us. Some appartus are of the counter flow type, others use the parallel flow principle.
Each maker naturally claims some specific advan- tage as to his design.
Last year (1939), a trial Bach was installed at Darnall on account of shortage of settling capacity at that mill. The settler started to operate from the 17th July to the end of the season. T h e Bach is 20 feet in diameter and 19 feet 3 inches high, with five trays, its capacity is of 24,000 gallons, and can cope with 70 tons of juice per hour.
The apparatus is heavily insulated against heat losses, a layer of oil of about 1/4 inch in thickness seals the surface of the juice. The juice from the heaters was split equally between the Bach and the ordinary intermittent settling tanks, so that the time of settling in both types of subsiding tanks, was, as much as possible, the same, and could be compared against one another.
The following tests were carried, averages are shown hereunder:—
BACH
Reducing Temperature Purity Sugar pH. Clarity of Juice
Ratio at OutletoF
88.3 2.174 7.7 37 210oF
I N T E R M I T T E N T SUBSIDERS.
88.3 2.15 7.7 35 185oF.
These figures show that the Purity, Reducing Sugar Ratio, and pH. are the same in both cases, there is a slight advantage in the Clarity of the Juice from the Bach, it is two degrees higher than the intermittent subsiders.
T h e temperature of the juice from the Multi- Tray Settler is 210oF., whereas the juice from the intermittent settling tanks shows a loss of 25"F.
through radiation.
After a week-end stop of twenty-four hours, the temperature of the juice from the Bach is be- tween 185o to 190oF., and 133o to 135°F. from the intermittent settling tanks. It is generally ad- mitted that juices do not deteriorate readily if they are held at a temperature of 180o to 185°F.
When this point was examined, it was found that the degree of deterioration was the same in both types of subsiders, the drop in Purity being about 1.° after a week-end stop. Although, strange to say, the pH. loss was far greater in the intermittent tanks.
The mud from the Bach can be concentrated to a porridge-like consistency with 15% to 20%
of solids, this is not attained with the ordinary type of intermittent settlers.
Unfortunately, if the sludge is allowed to thicken to this extent, it decomposes, Hydrogen Sulphide is evolved, this is a sure sign of deterio- ration. To obviate this decomposition, the mud is only allowed to thicken in the neighbourhood of 7°/o to 10% solids at the most. It is the writer's experience that Sulphitation Muds decompose more readily than simple defecation sludge.
It is advisable to empty out the apparatus every fortnight or every three weeks at the most, and wash it thoroughly with boiling hot water. To obtain good results cleanliness is essential, a spare unit is therefore necessary.
The advantages of this type of subsider as against the intermittent settling tanks are as follows :—
1. T h e space occupied is reduced considerably as compared with the ordinary type of subsi.der.
2. It is very simple to operate, and the process of settling is continuous, resulting in a saving of labour.
3. The juices dealt with by means of this process are more uniform and lend themselves to better clarification.
4. T h e Subsider is a sealed unit, there is no steam evaporation from the juice, thereby keeping the entire station cool and reducing maintenance costs on the steel structure and roof.
5. A considerable saving in steam is effected.
An endeavour to express the savings monetarily is as follows :—
LABOUR SAVING
One unit with wages and r a t i o n s = £ 2 / 1 5 / 0 per month.
Saving on 8 hour shift 15 u n i t s = £ 4 1 / 5 / 0 per month.
Saving per season of eight m o n t h s = £ 3 3 0 . SAVING IN STEAM.
Tons of mixed juice per hour comprising filter press juice and dilution at the filter presses=110.3 tons per hour.
110.3 x 2,000=220,600 lbs. per hour.
Temperature drop in intermittent settling tanks 25°F.
220,600 lbs. x 25=5,515,000 B.T.U.s per hour (specific heat being neglected).
Calorific value of Coal=13,500 B.T.U.s/lb.
Coal per hour lbs.=
Coal effectively used lbs. hour (say 70%)
Mill crushed for season, 5,013 hours.
Coal saved per season=5,013 x 583
=2,922,579 lbs., or 1461.2 tons.
The price of coal delivered at the mill costs 15s. l0d. per ton. Therefore 1461.2 tons coal cost
£1156 15s. 8d.
T O T A L SAVINGS.
Labour £330 0 0 Steam 1156 0 0 Total £1.486 0 0 The above calculated savings only apply to a complete installation of Multi-Tray Clarifiers.
Darnell.
9th March, 1940.
a
The P R E S I D E N T said t h a t a lot of experience had to be gained with continuous settlers, and the latest advances gave much promise. Mr. Viger mentioned three types, but there was another type invented by Mr. Mclntyre of Natal Estates, which would work exactly the same in the sulphitation factories. The President thought continuous settlers should be installed in every factory.
Mr. R I S H W O R T H remarked on the interesting comparison between two types of subsiders. If juices at 210°F instead of 185°F were received by the evaporator, much advantage would thereby be gained, particularly in factories with a small evap- orator capacity. More uniform juices and better classification referred to by Mr. Viger would of course reduce the amount of scale in the evaporator, with consequently more efficient heat transference over the weeks' run.
Mr. BOOTH asked if Mr. Mclntyre's defecator could be demonstrated ? If it was successful it should be given every support.
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