Basics of the Core Sampling System - SIA

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Basics of the Core Sampling System - 1991

Core samplers are now operational at all Jamaican Sugar factories. Installed on the recommendation of the 1988 Mill’s Commission of Enquiry into the Sugar Industry, growers would, by now have been receiving returns from factories with a new set of terms such as FRI, JRCS, etc. If, as expected, the Prices Commission rules on the pricing formula to be adopted, then, by the end of this crop payment should be based on this new system of determining the value of cane delivered. The following provides a ready explanation of terms as well as simple, handy reference to the basics of this system

  1. The core and analysis system enables cane suppliers to be paid for sugar in the cane delivered to the factory gate, in contrast to the prevailing system of payment for sugar output.
  2. Sampling and analysis are done to determine the quantity of sugar in various batches of cane.
  3. Cane quality, not juice quality, is determined; therefore, cane is sampled, not juiced.
  4. Every load of cane (1) is composed of fibre (F) and absolute juice (1-F) which contains the pol (sucrose) or sugar. Once the load is weighed, effort begins to assess the quantity of sugar in the load.
  5. Sugar delivered to the factory gate is equivalent to: (Pol (sucrose) % Absolute juice)÷ 100 x the weight of absolute juice (1-F).
  6. Until the entire load of cane is milled, the quantity of fibre and the quantity of absolute juice cannot be accurately determined. Therefore, core sampling (or any other sampling method) is a tool for estimating the fibre, the absolute juice and the sugar content.
  7. In the same way that the ratio of fibre to absolute juice varies in different parts of a single cane stalk, so will variations be found in each load of cane as well as from one load to the other from the same field. Suppliers should, therefore, not be dismayed to receive widely differing results from individual fields.
  8. The variation between sampling results from a given field will be a great deal less if the field is of uniform stalk and free of extraneous matter.
  9. Fibre consists of the insoluble material including soil, roots, suckers, tops, leaves, trash, and other extraneous matter. The actual constituents affect the recoverable sugar. Estimates of the fibre % cane delivered are provided by weights of the press cake from the core sub-samples.
  10. The juice pressed from the core sub-sample (press juice) is assumed to have the same composition as the absolute juice.
  11. A sediment test is done to measure the suspended solids in the press juice. This is then added to the quantity of fibre obtained from the press cake assessment. The higher the dirt in cane loads, the higher the sediment content, the higher the fibre, the lower the recoverable sugar, and the lower the payment received for cane.
  12. Since the press juice is an approximation of the absolute juice, it is necessary to determine the extent to which the results from analysis of the press juice reflect the actual composition of the absolute juice. It is assumed that the relationship between the two will be constant at a value less than 1 at a given fibre. The constant is referred to as the C Factor, the value of which has been the subject of research by SIRI. This research will be continued over a five year period.
  13. The work by SIRI to date has led to the C Factor being expressed as C = 1.02 - 0.44 Fibre
The C Factor will vary with changes in fibre
At fibre content of 14%, C = 0.9584
At fibre content of 18%, C = 0.9408

 14. The lower the C Factor, the lower the recoverable sugar.
 15. In order to obtain the pol available in the cane delivered, i.e. the pol in cane (Pc), the determination of pol % press juice (P) obtained by analysis of the press juice is multiplied by the C Factor (to relate it to absolute         
     juice) and by the absolute juice % cane as follows:
Pol % cane (Pc) = P (1.02 - 0.44F) (1-F)
16. The pol % cane is subject to unrecoverable loss in the milling train, known as pol loss in fibre or bagasse. Cane with 12.5% fibre is assumed to lose 5% of the recoverable pol in the bagasse, so the reduced pol extraction        (EP) is 95% at that fibre level. It is therefore necessary to estimate the recoverable pol loss at varying fibre levels.

The recovered pol after milling is therefore estimated by 1 - 0.4F.
  1. The pol % cane (Pc) is further subject to unrecoverable losses in the boiling house. Hence, adjustments need to be made to the formula to take account of the recoverable pol only, as follows:
a.sdf recovery after pol loss in the filter cake - estimated at 99.4%;
b. recovery after undetermined pol loss - 98.7%;
c. recovery after pol loss in final molasses - estimated at 1.4 - 40/Q. - where Q is the purity of the press juice;
(Based on Winter & Carp’s estimates that each part of soluble impurities is associated with 0.4 parts of pol).
Note: This formula is based on a final molasses purity of 28.57. But, as Jamaican factories are averaging 33.23, an adjustment may be made
 18. Commercial sugar requires to be converted to 96° polarization sugar and the factor applied from Copp’s tables is 1.0474.
 19. If the assumed fixed numerical terms relating to the recoverable portions of the pol in cane are condensed, a factor of 1.03 is derived as follows:
     Recoverable pol after clarification (0.994) x Recoverable pol after undetermined (0.987) x Copp’s factor (1.0474) = 1.0275 abbreviated to 1.03
 20. Jamaican Recoverable Cane Sugar (JRCS) is then expressed as follows:
JRCS = pol in cane x recovery after milling x recovery after pol loss in final molasses x 1.03
= P(1.02 - 0.44F) (1 - F) (1 - 0.4F) (1.4 - 40/Q) 1.03
= 1.03 P (1.02 - 1.73F) (1.4 - 40/Q)
 21. If the tonnage of 96° sugar produced by a factory is exactly equal to the JRCS, then the factory would be said to have recovered 100% of the Theoretically Recoverable Cane Sugar (TRCS). In other words, it would have        an efficiency of Factory Recovery Index (FRI) of 100. In practice, this figure is normally between 80 and 94, and accounts for cane yard losses and general factory inefficiency. A standard FRI will be determined for the        industry for all factories. Suppliers will then be paid at the standard FRI, regardless of the actual FRI recorded at an individual factory.
 22. All suppliers are already familiar with the application of a Relative Factor (RF) to each individual supplier’s tonnage so that there are no penalties nor advantage s attached to deliveries concentrated in specific segments
     of the cropping period. The RF is determined by dividing a supplier’s JRCS by the average JRCS for all supplier’s to that factory. The new cane payment system retains the RF, which is used to adjust the final price paid
     to suppliers.
 23. Allocation of the sugar revenue between factories and cane suppliers is based on the concept that the Factory Fraction (FF) should be 38% where the factory operates at the standard FRI, in processing cane with the
     standard JRCS. In the case of factories performing below the standard FRI, suppliers delivering cane of standard JRCS will receive a share of the proceeds greater than 62%.

     Conversely, where suppliers deliver cane with less than standard JRCS to a factory which operates at better than standard FRI, the factory will receive a share greater than 38%.

 24. The final component of the cane price formula is the By-product Price (BYP). This is derived by expressing the by-products income on a per cane basis.
 25. The price/tonne cane will be determined as follows:

NB: This formula has since been modified as shown below

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