Protherm Systems has completed the customisation of a hi-tech falling-film evaporator plant and vacuum flash cooler for Nkwaleni Processors as part of a multimillion-rand expansion of its citrus-juice factory in the Nkwalini Valley near Empangeni in Kwazulu-Natal.

The plant is a three-effect, multi-stage falling-film type evapo-rator with thermocompressors, which enables the produc-tion of top-quality juice concentrates for export, and is de-signed for optimum energy utilisation. The juice concentrate is subjected to minimal heat exposure, and is instantly flash-cooled to below 10°C on exiting the plant. The Protherm plant is itself valued in excess of R2,6-million, and was supplied as a completely-assembled module in a steel structure. The module comprises several large calandrias or evaporator heat exchangers, vessels, venturi-type ejectors, pumps and plate preheaters, all in stainless materials. The project, which was only embarked upon in December 2000, was completed on a fast-track basis, so as to enable plant commissioning to be completed in time for the upcoming citrus season. The module was about 3,5 m X 5 m X 20 m long, and weighed about 20 t.

The evaporator uses long tubes that maximise wetting and minimise juice contact time in the high temperature stages of the evaporation process. The key factor in the production of high-quality juice concentrates is minimal heat exposure for the juice, and the long-tube, falling-film evaporator achieves this requirement. The evaporator plant is designed to pro-cess 10 000 litres per hour of citrus juice (orange, grapefruit or lemon), and concentrates the juice from a solids content of about 10% to a syrup-like concentrate at about 65% sol-ids. The 10 000 litres per hour fresh juice is reduced to just over 1 000 litres per hour of concentrate.

Concentrated Juice is cooled
The concentrated juice is then cooled in a heat exchanger to about 30°C, and is then cooled further in a vacuum flash cooler to below 10°C. Water would boil in the high vacuum flash cooler at about 3°C, but orange juice, having a higher boiling point temperature, will boil at about 10°C in the flash cooler. The cooled concentrate is pumped as a very viscous and thick syrup from the plant. The product is eventually packed into drums and is frozen for export.

An essential part of the design of the evaporator is to minimise the use of energy. The evaporator is driven by steam, which is produced in a coal-fired boiler. Evaporation processes are highly energy-intensive, and steam and ulti-mately coal cost is a major factor in the production of con-centrated juices. The evaporator thus utilises three effects, whereby the vapour boiling off one effect or stage is sued to heat the next stage, which operates at a lower temperature.

Energy economy is improved further by using a thermocompressor. The combination of three effects or stages achieves a steam economy ratio of about 4:1, in that 1 kg of steam introduced to the plant will cause the evaporation of about 4 kg of water This is not strictly the case due to heat losses, et cetera, bringing the actual ratio down to about 3,5:1. The plant also incorporates several Thermowave-type heat exchangers that recover heat from outgoing streams in Tan liquor evaporator order to heat the incoming juice stream.

The plant also incorporates an automated cleaning in place (CIP) system that enables clean-out and sanitisation of the plant after each run on a daily basis. The net result is that the Protherm plant will allow Nkwaleni Processors to pro-duce juice concentrates of the highest quality in order to satisfy their exacting local and export customers.

Orange Gold
Protherm Systems director Laurence Fienberg comments that while there is always "a lot of song and dance" about the Alusaf-type projects in KwaZulu-Natal, the citrus-juice industry is an important player in the province's economy. "Citrus concentrate is orange gold as it can command about $6 000 a ton, and therefore projects such as this are signifi-cant in terms of boosting the country's export earnings," says Feinberg. He says that Protherm's success was due to the dedication of all involved, especially stainless tube producer Salmac, which had to produce special tubing in a record time. 'The standard and quality of engineering on this project is a testament to our local capability as a whole," concludes Feinberg.

Protherm Systems is a process engineering and specialist supplier of thermal equipment, including an extensive range of heat exchangers, industrial dryers and evaporators, gas scrubbing and odour control plant.

Laurence Fienberg, Protherm Systems, Tel. (011) 786-0652, prothm@iafrica.com