Professional Engineering

You’d expect a British Sugar plant to make sugar – the clue is in its name. But how about producing tomatoes? And animal feed. Oh, and don’t forget compounds for cosmetics.

Perhaps the most surprising aspect of this multi-stranded approach is that all of these products are made at one facility – the company’s Wissington plant in Norfolk. British Sugar has adopted an integrated manufacturing system at the site, so that the output of each process becomes the input of the next. 

The result is true sustainability in action: all raw materials are turned into products, so waste is virtually non-existent. That approach allows Wissington to be globally competitive, securing its long-term future.

None of this is done out of some nebulous sense of responsibility to the environment, says the company. “It’s a commercially driven approach – each investment makes good business sense,” says Mark Carr, group chief executive of parent firm AB Sugar. 

“We don’t grow tomatoes just because it feels good to make effective use of our waste carbon-dioxide streams. We do it because we think we can make a return on the investment. It’s a good example of how sustainability can be used to drive a business forward.”

Wissington is a gigantic site – it can be seen from miles around across the flat Norfolk landscape. The plant’s primary role is to take three million tonnes of beet from 1,200 local growers, turning it into 420,000 tonnes of sugar which is supplied to food and drink manufacturers in the UK and across Europe. But that’s just one part of the story.

As well as enriching the production of millions of tonnes of tomatoes each year by piping CO₂ into an adjacent glasshouse, Wissington produces 120,000 tonnes of a lime-based soil conditioner used in agriculture. The site also makes 140,000 tonnes of high-protein animal feed and 6,000 tonnes of a speciality nutrient that helps support stomach function and protein digestion when added to other animal feed foods. 

These are all products derived from what, in the past, would have been considered waste streams. “These days Wissington is much more than a sugar factory. We see it more as a bio-refinery now,” says Carr.

The production chain starts with the arrival of the sugar beet which, during peak periods, comes in on lorries at a rate of 900 loads a day. The first stage of processing involves cleaning the beet. Soil is separated, dried, screened and blended before being sold as high-quality topsoil to landscapers and builders. In addition, rotary stone catchers remove 5,000 tonnes of stones each year, which are washed and sold as aggregate.

Clean beet is sliced into thin strips called cossettes. These are pumped to three separate diffusers, where they are mixed with hot water to extract the sugar. The juice is used to preheat the cossettes before it passes to heat-recovery systems and on to purification. The remaining fibre is mechanically pressed before being dried in gas-fired rotary dryers. This process produces the familiar plume of steam that rises from the dryer chimney in winter. The dry fibre is compressed into pellets which are sold in bulk as animal feed.  

Factory manager Paul Hitchcock says: “The pulp still contains a certain amount of sugar. When it is mixed with a bit of molasses, it makes for a high-value co-product that is used as animal feed all-year-round.”

The raw juice is progressively heated through complex heat-recovery systems, which minimise the plant’s energy demand. Milk of lime (a suspension of calcium hydroxide) and CO₂ are added to precipitate calcium carbonate or chalk, which removes the impurities in the raw juice. The extracted “thin juice” passes through multiple-effect evaporators, which boil off the water and produce a syrup known as “thick juice”. This is the complex heart of the factory’s energy efficiency. The water that has been removed by evaporation is used for further heating, and then stored to be used again in other processes on site.