Assessment and Control of Operational Loss of Sugar During Sugar Cane Processing

Table of Contents

Abstract

1. Introduction
1.1 Sugar production process
1.2 Background of the problem
1.3 Significance of the study
1.4 Methodology

2. Results and Discussion
2.1 Sugar loss in final molasses
2.1.1 How is sugar lost in molasses?
2.1.2 What to be done to minimize sugar loss in molasses
2.2 Sugar loss in bagasse
2.2.1 What to be done to minimize sugar loss in final bagasse
2.3 Sugar loss in filter cake
2.3.1 What to do to further minimize sucrose loss in filter cake
2.4 Sugar loss in undetermined channels:

3. General conclusion

References

Abstract

This paper concentrated on assessing and controlling the operational loss of sugar in various sugar byproducts during cane processing in cane sugar factory. In the study, factors associated with operational loss were discussed and Kagera Sugar Limited (KSL) was taken as a case study. Operational sucrose loss is divided into two major categories namely, determined losses and undetermined losses. Determined losses are those which can be easily quantified through lab analysis, such as loss in molasses, filter cake and bagasse. Unlike determined losses, undetermined losses are difficult to estimate directly but rather by factory material balance. Undetermined loss is further classified into chemical loss, mechanical loss and administrative loss. In both losses, the loss through molasses is by far the largest of total loss encountered during cane processing. Objective of this paper was to develop means of increasing sucrose recovery by monitoring sugar loss. After analyzing data collected from KSL production reports, for crushing seasons 2015/16 and 2016/17 the operational loss was 2.83 and 2.87 pol % cane crushed in respective seasons. This means KSL loses significant amount of sucrose as compared to 2.20 pol% cane crushed for plants installed after 1994 as reported by (Sharma Chetan and Kumar Vikas, 2015). Sugar loss in molasses and bagasse was high than others, it was concluded that, the use of three laws of sucrose loss in molasses coupled with optimization of boiling house operations would result in minimized loss of sucrose in molasses. Also, improving extraction would result in minimum sucrose loss in bagasse.

1. Introduction

1.1 Sugar production process

The raw materials used for sugar production at commercial scale are sugar cane and sugar beet because they produce enough sugar per hectare (Perk, 1973). In Tanzania in which KSL is exclusively an example, sugar is produced from sugar cane. Cane typically consists of 15% dissolved substances in which about 13% is sucrose and 2% are other substance such as other sugars i.e. fructose and glucose (0.9%), inorganic salt/ash (0.6%) and organic salt, organic acids, polysaccharides, gums, protein, amino acid and amides (0.5%). Cane also consists of insoluble matters which are vegetable fibers (13%) and soil (2%), and water (70%) (SMRI, 2012). A conventional cane sugar factory has a one intention, to extract about 87% of cane dissolved substances.

The cane sugar production process consists of cane size reduction, juice extraction (cane milling), juice clarification, filtration, evaporation, crystallization, centrifuging, drying and packing. Steam generation using bagasse as fuel for electricity generation and/or prime movers driving is also an important operation in sugar producing factories. See sugar production flow diagram presented in figure 1:

The purpose of any cane sugar factory is to maximize recovery of sucrose from cane and to produce high amount of sugar of the desired quality at minimum cost of production. However, from processing point of view, not all sucrose contained in sugar cane is recovered from the cane as commercial sugar. Some of it is lost in the course of cane processing in the factory. The major losses in a typical cane factory are due to Molasses, Bagasse and filter cake and undetermined factors. It’s a job of production team to ensure that operational loss is kept as minimum as possible.

Figure 1 sugar production process flow diagram

Total of sugar loss encountered by any factory during particular crushing season is one of the significant factors when assessing technical performance of that sugar factory. Sugar loss by operations of any sugar factory depends on performance in milling station, boiling house efficiency, machinery and skilled manpower. It has been reported that, for sugar plants installed before and after 1994 the operational loss of sugar should be kept below 2.10 pol% cane and 2.20 pol% cane respectively (Sharma Chetan and Kumar Vikas, 2015).

1.2 Background of the problem

Kagera Sugar Limited (KSL) as other conventional sugar factories, suffers the loss of sugar during sugar production. The sugar loss in operation from cane milling station to centrifugation station was examined and found to be 2.83 and 2.87 pol % cane for seasons 2015/16 and 2016/17 respectively (see appendix A). The total sugar loss by operational activities in KSL was assessed and compared to literally reported loss figures for cane sugar industries. The loss for both seasons was higher than 2.20 pol% cane for plants installed after 1994 as reported by (Sharma Chetan and Kumar Vikas, 2015), so there was a need to investigate and give possible solution.

1.3 Significance of the study

The author was confident to say, if the proposed methods to control operational losses are employed, KSL will not only improve technical performance of the plant but also will increase business profit and help the struggle towards meeting the country’s sugar demand.

1.4 Methodology

This study was undertaken under method of quantitative and arm chair thinking type of research. The data was collected from KSL reports of annual production of seasons 2015/16 and 2016/17.

2. Results and Discussion

KSL as any other conventional sugar mill, the total operational loss of sugar is broken into number of specific components. Operational sugar loss experienced during sugar production process in KSL is classified into the following components:

2.1 Sugar loss in final molasses

Sugar loss in molasses is highly dependent on the efficiency of the process and cane quality, the only factor that can be manipulated to minimize the loss by molasses is optimization of a process. For conventional factories, Molasses gives a loss of 1 to 1.3 pol% cane . But for KSL, loss in molasses for seasons ending 2015/16 and 2016/17 were 1.43 and 1.48 pol % cane respectively (see appendix A). As shown in figure 3, loss in molasses made 50.53 and 51.63 % of the total loss in the respective seasons. This means that, more sugar was lost in molasses compared to other operational losses.

2.1.1 How is sugar lost in molasses?

Loss of sugar in molasses is the function of processing techniques of boiling house. As reported by , sucrose is lost through molasses because during separation of mother liquor and sugar crystals some sucrose will remain in the final molasses. The author reports that there is a lower limit of exhaustion below which the amount of sucrose in final molasses cannot be reduced, this is defined by solubility of sucrose in molasses. Also reports that mediocre molasses exhaustion gives molasses of purity of 40 while exceptional exhaustion gives a final molasses of purity of 28. This means there is a limited chance that final molasses purity drops below 28.Final molasses purity is therefore a function of processing technique, cane quality and geographical position of the cane sugar factory.

2.1.2 What to be done to minimize sugar loss in molasses

The research by , reports that to minimize the loss in molasses three laws of molasses loss should be used:

First law: The quantity of non-sucrose in final molasses must be minimized because, at any given purity P, each unit of non-sucrose will take with it P/(100-P) units of sucrose. This means if P is constant, to reduce loss in final molasses, only the quantity of non-sucrose should be minimized. This can be done by improving clarification process.

Second law: The achievable final molasses purity or target purity must be kept as low as possible except where this would contradict the First Law. The only way to reduce the target purity of final molasses can be speculated from the equation of calculating target purity adopted from (Rein, 2007):

Target Purity (South Africa) = 43.1 – 17.5 *(1 – e -0.74 · (F+G)/A)

To reduce the target purity is only by increasing the factor (F+G)/A, as it can be seen on the plot hereunder:

Abbildung in dieser Leseprobe nicht enthalten

Figure 2 The influence of (F+G)/A ratio on Target Purity (adopted from Love DJ et al., 2009) F - fructose% final molasses, G - glucose% final molasses and A -Ash % molasses

This factor can be increased by adding the quantity of F and G and reducing A, but beware not to increase amount of F and G by inversion of sugar (which of course contradicts the first law). The only value to manipulate on this law is A, reduce the quantity of ash by proper clarification. Also Do not destroy the F+G to create other non-sucrose for the first law will also be contradicted.

Third law: The actual final molasses purity must be reduced to as close to the target purity as possible (or even better, below) except where this would also contradict the First or Second Law. This law deals with increasing exhaustion of final molasses purity to as close as target purity without increasing non-sucrose and/or reducing target purity. The author depicts that achieving low final molasses purity is a combination of optimized performances of seed preparation station, massecuite boiling, massecuite reheating, massecuite centrifugation.

All the laws, especially the third law if well implemented will help KSL produce much sugar with less loss in final molasses. And since molasses loss is the greater of all losses, it would also help reduce total seasonal sugar loss.

2.2 Sugar loss in bagasse

The aim of the milling station is to extract more sugar into mixed juice with minimum loss to bagasse. For good extraction sugar (pol)% bagasse from the last mill should be <1% ( 0.3 pol% cane) . It’s this pol% bagasse which will determine how much sugar is lost in bagasse in a particular crush year. For KSL the target loss in bagasse is <3 pol% final bagasse (0.9 pol% cane) which is relatively a higher figure comparing to that reported literally by . For seasons 2015/16 and 2016/17 the loss in bagasse in KSL was 1.16 and 1.18 pol % cane (see appendix A).

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