So how can we help an ailing industry?

It’s a long read but definitely worth it.

While sugar production in the cane sugar industry was largely the same for decades, market developments have now provided an impetus for change. In particular for large production units, adapting to new production conditions proves to be profitable in the long run. There are three major requirements that present day sugar production has to meet:

 

  1. Higher sugar quality: With a wider range of information, competition on the local sugar market is becoming more transparent, making it easier to translate higher sugar quality into higher revenues. Key account customers, in addition, have their own standards and often ask for qualities that match those achieved in the beet sugar industry.
  2. Reduced process steam consumption in sugar production: With the efficient use of bagasse, sugar production is no longer the only potential source of earnings. Excess bagasse is normally burnt in co-generation plants and excess power is fed into the local power grid. A more recent application, currently on a small scale, has been the sale of bagasse for use by third parties. For cost reasons, using additional fossil fuels as a source of energy for sugar production must strictly be avoided.
  3. Maximised sugar output: The cane sugar industry has to face new challenges in the form of low sugar prices and a cutback in local subsidies.

A possible option in this situation is to provide for optimal molasses exhaustion in order to maximise crystalline sugar output. This only makes economic sense if the sugar contained in the molasses cannot be put to other more profitable uses, e.g. in the production of ethanol.

So how is it done?

Through unrivalled process knowledge of the sugar industry.

The primary criterion for sugar house operation is the quality of the product sugar. To some extent, this applies to the production of raw sugar from sugarcane, but certainly to the production of plantation-white sugar and refined sugar.

Maximising sugar output and minimising molasses purity have been defined as additional targets. With steam savings throughout the sugar process as yet another target, cane sugar factories are now focusing also on steam consumption in the sugar house.

Numerous process details from crystallisation, which are commonly applied in beet sugar factories but not yet considered to be state of the art in the cane sugar industry, have in recent years also been implemented in cane sugar factories.

This offers cane sugar factories new ways of reacting to a changed market situation

(Lehnberger 2015).

Below, we describe some of these processes.

Exhaustion of C product with continuous crystallisation in an oscillating vertical cooling crystalliser (OVC)

One of the primary objectives of almost every sugar factory is to ensure that the molasses is exhausted as much as possible. Since any sugar that is additionally centrifuged from the C massecuite can be sold as extra crystalline sugar, all efforts aimed at increasing the ‘C’ product yield can count as additional sugar production.

Based on the mass of dry substance, any additional output of crystalline sugar will reduce the amount of molasses produced.

Cooling of C massecuite to raise the crystal yield is a measure that has been known for some time and is widely used. As a rule of thumb, lowering the temperature by 4 to 5°C will reduce the purity of the mother liquor by one purity point. For the beet sugar industry, these conditions have been analysed in detail

(Wagnerowski et al. 1962; Ekelhof 1997;

McGillivray et al. 2003), leading to the development of continuous cooling crystallisers several decades ago.

With long retention times, which can be up to 36 h (Südzucker 1994) and sometimes more, and uniform temperature difference between massecuite and cooling water, these crystallisers produce a low outlet temperature. The maximum viscosity of massecuite that cooling crystallisers and centrifugals can still handle represents the technical limit to this process.

Although OVC continuous cooling crystallisers are proven performers in the beet sugar industry, the jump to applications in cane sugar factories was hesitant. The main reason for this reservation was the doubt that these crystallisers would yield the same technological results in cane as in beet sugar factories.

The experience gathered from operation of 10 of these crystallisers installed in cane sugar factories show comparable technological results.

One such OVC crystalliser has been in operation in the Puga sugar factory in Mexico for 5 years. It has a capacity of 900 t and a cooling area of 1,000 m², and, at a height of 33.5 m, it is one of the tallest piece of equipment in that factory.

With the OVC, 33 t/h of C massecuite is steadily cooled by about 1°C per hour from about 65°C to 40°C (Anon. 2012). This gradual cooling with constant temperature difference between massecuite and cooling water ensures that supersaturation in the OVC is always kept within a range in which only existing crystals grow but no new nuclei are formed.

A crucial factor is that the temperature is lowered consistently in the entire mass flow of massecuite, which the OVC achieves with a typical 10°C difference between massecuite and cooling water. In the OVC, the cooling surfaces oscillate up and down in the massecuite volume, producing uniform heat transfer conditions everywhere in the system. Because of the elements mounted inside the OVC, the material behaves under plug flow conditions. This prevents local supersaturation peaks.

This prevents the formation of fine crystals, which cannot be separated in continuous centrifugals and would therefore increase the molasses purity.

With the oscillating system of the cooling coils, which has a stroke of 1 m, no agitator is necessary. The hydraulic unit to move the coils by hydraulic pistons imposes a power demand of less than 20 kW in the above mentioned installation.

OVCs installed in cane sugar factories have helped to reduce the molasses purity by an average 4 to 5 percentage points in comparison to horizontal crystallisers. From an original temperature of 55°C down to a temperature of 40°C, the mother liquor purity reduction accounts for three purity percentage points, as in the beet sugar industry. Furthermore, improved separation in the centrifugals due to reduced fine crystal content reduces the purity by another one to two percentage points compared with the original setup.

Controlled crystallisation, along with the prevention of the formation of fine crystals while cooling the C massecuite and a low final massecuite temperature, are the preconditions for achieving the improvements in molasses purity. These have been demonstrated in cane sugar factories in Mexico, India, Senegal and El Salvador.

In our next Newsletter we will continue with:

Continuous boiling of plantation white sugar in a vertical continuous pan (VKT)

Crystal seed preparation for refined and raw sugar by cooling of syrup

Sucrotech has been serving the industry since 1974 and the one issue we detest is slating.

All centrifugals will produce sugar when spun at the correct surface speed but the reason there are different brands in the market is because of different technology. Some use R&D to better their designs, testing new materials and programs, so as to produce a more reliable and safer operation.

Some share the same philosophy that their machines should be built to last whilst others have more short term goals. Each to their own.

As most of our readers are aware, Sucrotech often assists with operational problems on other brands of machines, but slating of that machine’s performance or design is not assisting the client.

We recently had a case at SASTA where a competitor machine supplier was complaining that the BMA machines next to his machine were vibrating so badly during operation that it was having a detrimental effect on their brand new machine’s operation.

So, being the type of service orientated operation we are, we went to find out why our machines were vibrating. As we all know the main cause of vibration 90% of the time is product related. In this case it wasn’t to be as the vibrations analysis report shows.

All the BMA batch machines were running satisfactory.

Slating will catch you out.

General                        engineering@sucrotech.co.za

Ronnie Chetty          - Business Manager Sugar    ronnie@sucrotech.co.za

Sheryl Moodley        - Spares servicing   sherylm@sucrotech.co.za            

Cheryl Callanan        - Accounts   cherylc@sucrotech.co.za 

Clayton Chinneck         - Works Manager     clayton@sucrotech.co.za

Stuart Ritchie            - Engineering    stuart@sucrotech.co.za

Ian Ivison                  - Commercial     ian@sucrotech.co.za

 Web site:                    https://sucrotech.co.za/

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