Starafrica Gold Star Sugar’s market share has risen to over 80 percent thanks to a plant upgrade of 2014. However, operational challenges arising from shortages of critical supplies to a point the plant was shut down for a month recently, remain. Business Times senior reporter Taurai Mangudhla (TM) last week toured the Gold Star Sugars plant in Harare where the company’s technical services manager Khopolo Setopoli (KS) explained the refining process and what inputs come with it. Below are excerpts.
TM: What raw materials does the company require to enable sugar production?
KS: Our biggest inputs are raw sugar which comes from Chiredzi, coal from Hwange because our heating source comes from boilers, which use the mineral. and then water of over a million litres per day.
TM: If you use coal for boilers does this mean that you have less requirements for electricity.
KS: We still need electricity and we have suffered greatly due to the ongoing power cuts. When power goes out we are in trouble because sugar solidifies and becomes rock hard so you need jack hammers to separate it. We had to stop the plant from about the 5th of July to the 1st of August because of load shedding.
TM: What about water?
KS: We sunk a lot of boreholes, I think we have nine or ten. Water levels have been receding because of the low rains. We are now waiting for the rains but in the last couple of weeks, council water has been very reliable.
TM: Can you get into detail of the plant and the refining process?
KS: We receive our raw sugar from Hippo Valley in brown form. It comes by road in trucks. We used to also bring it by rail wagons in the past. WAe have got a warehouse that holds the raw sugar which is then fed to the factory via a bely. We have got a weighbridge where we weigh what gets inside. The sugar comes up this belt and it goes into the mingler.
As we talk about sugar processing, what you need to have at the back of your mind is that sugar refining is a colour removal process, in other words you are just cleaning up the sugar; from brown raw sugar until you get to white. In mingling, we take our raw sugar and mingle it with raw syrup at around 80 Degrees Celsius to make the molasses coating softer. This enables it to take out the impurities.
TM: What is the result at this stage?
KS: At that stage alone we remove 50 percent colour. So raw sugar comes typically at about up to 2000 colour units. We started at 2000 you are now at 1000, if you started at 1600 you are now at 800. After this you get sugar this is brown but a lot cleaner, we mingle it also with water and take that to the melter.
TM: What happens at the melter?
KS: We call it the melter, but in principle it actually a dissolution vessel. It’s not like we are heating sugar to melting point, but we are taking that sugar and mixing it with water at temperatures of about 80 degrees Celsius, changing it into liquid form. When it is now liquid form, we pump it via our pumps and comes up to a pretesting point. At the back of your mind, we are just cleaning up the sugar.
Like I was saying we use sieves to remove foreign particles that come with the sugar. These sieves are vibrating so here we trap some of the things like fine sugar cane particles. Once we have taken them out, we are practically over the physical process of colour removal and then we move to the use of chemicals.
TM: What does the chemical process involve?
KS: We have to invoke chemicals to sort of get colour out of this sugar. We pilfer it, take it to clarity tests after heating it on the heat exchangers.
Once it is heated, it leaves the heat exchanger; it comes to a place where now you want it to react. So in that that reaction we add lime we add sulphuric acid then we also add some color precipitant. Once that is done we take it to the flocculating vessel to just add air. Once that reaction has happened here, we then take it to the clarifier where the separation of impurities which were removed chemically from the sugar can be separated from the sugar.
TM: Would it be the final stage?
KS: No, no.
We take the mud from the process and clean it again because it still got some raw sugar in it, when we have done it three times, the mud that remains goes out to be used as manure as it contains good phosphate.
If you look at the sugar at various stages you can see the results. The colour removal at the end of this stage is 40 percent colour removal so if you came from 2000 then you went to 1000 then you remove 60percent you end up with 600 colour units.
It looks good at this stage, but if you were to crsytalise it to sugar, it will not be the white sugar you see there. It would be light brown sugar, it would be better that the other brown sugar.
TM: What happens next?
KS: We take this clarified liquor, we filter it. We filter it through deep bed filters. They are just vessels with different grains of stones and sand.From there we come to the main de-colorisation process.
TM: What happens at this main process?
KS: We are now using iron exchange.
Once you are done here you can achieve colour removal in excess of 50 percent up to even 70 percent depending on other factors.
For instance after you remove the 50 percent of 600 you are now around 300 from the original 2000 colour units.
Then from 300, the first stage resin is different from the second stage resin where you then move to acrylic resin which can be handled at higher colour like the 600 or 700.
Once you are done with acrylic you take it to the second phase which is styrene resin which deals with low colours so it can handle the 300 and do the same as well. That means at 50 to 70 percent you can reduce the 300 to 150 colour units. Once you are at 150, you have got something which we call fine liquor. When you look at it you will definitely say it is real fine.
If you crystalise that fine liquor it’s so clean that the crystal that comes out from there no longer has colour. That’s why it comes out white.
What is important is to not that if you boil sugar at 200 colour unit , the colour of the sugar crystal as a rule of thumb is about 10 percent of the liquid that you boil so it ends up at 20 colour
TM: What then happens once you hit the 20?
KS: Once it crystalises they take the sugar through centrifugal, the syrup goes across the screen the good crystals are harvested, you put them to the next stage. Because there is moisture in there, you take it to the dryers where you dry it at about 65 to 70 degrees Celsius to take away any residual moisture on the sugar. Once the sugar has dried and is cooled you then send it to the silos. We have two silos which can hold up to a maximum of 500t combined.
Once it has been taken to the silos its ready for packaging and then dispatch.
TM: How much sugar do you produce per month?
KS: Per month I would put it between 6000t to about 9000t of sugar because at 300t per day.
