Measurement of Cane Preparation

Milling Seminar11 May 2005

Peter ReinAudubon Sugar Institute

Measurement of Cane Preparation

• Cane Preparation has a very large effect on extraction and moisture content of bagasse

• It is important to measure preparation

• Methods of measurement include:– Bulk density– Mean particle size– Extent of breakage of cells

Sampling

• The measurement is only as good as the sampling• It is difficult to get a representative sample, unless

a full-width hatch sampler is used• Sampling from the top layer gives a biased sample

(classification of fines)• Cane is non-homogenous and requires that a

number of samples across the conveyor at different depths be taken

• Mixing and sub-sampling is difficult• If the sample is not well-prepared, biased sampling

sometimes omits large chunks

Mean Particle Size• Particle size measurement by screening is

possible• The sample needs to be dried first• The sieving efficiency is low, because of the

large length/diameter ratio of the particles• The results are technique and equipment

dependent• Reliable measurements can be obtained

from a standardized procedure• May be expressed as a mean particle size

or a “fineness figure”

Bulk Density

• Compressing a sample under standard conditions gives the bulk density, which depends on the cane preparation.

• Fine preparation leads to a high bulk density

• Crawford (Australia) compressed a 15 lb sample at 15 psi for 5 minutes

• Pressure chosen so that no juice expression occurs

Correlation between

bulk density and

fineness (Crawford 1970)

Measurement of Cell Breakage• This is the best method, since it characterizes the

preparation in terms of its extractability• Cane and water tumbled together for a standard

length of time, and the sucrose content of the extract measures the extent of cell breakage and the availability of juice

• If the ratio of water to sample is the same in the tumbler and in the cold digester, PI = 100.(tumbler conc.)/(digester extract conc.)

• Cane sample is small (~ 500 g) and needs replicates

Equipment Used

Problems

• Different test conditions lead to different results

• Test conditions in Australia, Hawaii, South Africa and Louisiana are all different

• PI is affected by excessive trash in cane

• Pi is not reliable with coarse preparation; should not be used if PI < ~80

Comparison of Test Conditions

Australia Hawaii South Africa

(ICUMSA)

Louisiana

Test duration (min.)

10 15 30 30

Measure of juice conc.

Pol Pol (Brix) Brix Pol

Conclusions

• It is worthwhile to measure the degree of preparation routinely

• PI is probably the best routine method• It is not a precise measure, but the average over

time gives the best indication of preparation• In making comparisons, be aware which method

is being used• PI (SA) is greater than POC (Austr.) by about 5

units• PI (La) is greater than PI (SA) by about 5 units