PRESS RELEASE
January 23, 1996
MVR fans break into pulp industry

Fans are set to supersede compressors in Mechanical Vapour Recompression (MVR) evaporators used in the pulp industry. This follows the successful installation of the first such fan driven evaporator, for magnesium sulphite liquor, at Sappi Saiccor's Umkomaas pulp mill, near Durban, South Africa.

MVR evaporation technology uses a mechanical device, such as a compressor or fan, for recompressing the vapour within the evaporator. Regulation of the vapour is via an inlet guide vane.
The fan manufacturer, ABB Fläkt Oy, says the new fan installation is up to 50% less expensive than
a comparable compressor arrangement with further savings being derived from much reduced
maintenance costs.
Such is the scale of these benefits that Sappi Saiccor opted for the fan evaporator, even though all
other initial proposals were offering a compressor MVR. And they were not to be disappointed. Tests
arranged with an independent third party, show that the guaranteed values were achieved, including:
evaporation at 50 tonne per hour; 55% dry solids; and 1060kW of electrical consumption for both
fans.
"Until now, fan technology could not deliver the large temperature differences of, say 12-15 degrees,
which compressors can," explains Göran Tallberg, Export Manager at ABB Fläkt Oy. "As a result,
fans could not compete against compressors."
It was because of South Africa's low electricity costs - which compensates for the amount of power needed to drive the fans - coupled to the fact that Umkomaas mill uses sulphite liquor, which made the MVR evaporator technique an attractive possibility.
The complete turnkey evaporation plant, built by Finland's A. Ahlstrom Corporation, is part of a new
pulp mill upgrade which will increase the mill's capacity from 1,200 to 1,600 tonnes of pulp per day.


Caption:
The first fans to be used in a MVR evaporator within the pulp industry have been supplied by ABB Fläkt Oy for Sappi Saiccor's Umkomaas mill in South Africa


For more information contact:
Göran Tallberg, Export Manager
ABB Flakt Oy Industrial Fans
PO Box 25
FIN-00381, HELSINKI
Finland
Tel: +358 0 564 3461
Fax: +358 0 564 3480











TECHNICAL INFORMATION

Simple construction

ABB Fläkt's high pressure fans have been developed over many years using the most advanced materials available. Today, the fans use an exceedingly robust duplex stainless steel. Furthermore, the company employs the latest computer mathematical modelling techniques for stress calculations, aimed at providing fan blades and casings with optimum strength characteristics.
The result of these developments is that today's one stage fans can achieve a temperature difference up to 7 degrees C compared to the 4 degrees C of machines in the early 1980s. Thus, their use in MVR evaporators has become more achievable.
But the significant reason for the success of fans is their simplicity of construction compared to the complexity of compressor designs. The fan has an extremely simple plate construction, unlike that of the compressor whose housing and impeller is made from cast metal and then machined to a high precision.
The fan's simple construction makes it is easier to maintain and keeps manufacturing costs down. Even though two turbo fans are used in series at the Umkomaas mill to obtain the same temperature difference as with one compressor, installation costs are vastly reduced.
Furthermore, compressors are built to standard sizes, whereas fans are custom designed: "Fans fit exactly as designed. They bring a high degree of flexibility to an installation and optimise the electrical consumption per fan evaporator," says Tallberg.

MVR v Multi-stage effect

The cost effectiveness of using a compressor or fan MVR technique in the first place, as opposed to
traditional multi-stage effect evaporators, requires low electricity cost compared to steam cost, in the
country concerned.
Secondly, using the MVR evaporator technique successfully, requires that the evaporated liquid has a low Boiling Point Elevation (BPE), such as that of sulphite liquor.
Multi-stage effect evaporators are still considered the norm for sulphate liquor which is usually evaporated to a higher dry solids content and therefore has a high Boiling Point Elevation. Such processes are evaporating up to 1,000 tonnes per hour which is a significant leap from the 150 tonnes per hour possible with MVR.
However, there are moves to use MVR technology as a pre-evaporator for sulphate liquor based industries. This is particularly beneficial when expanding a sulphate plant as it reduces the downtime of the plant during the expansion phase.
"In these evaporators, the fan technology has established its position as a good alternative to compressors," says Tallberg. "The results from using the fan at Umkomaas prove that for new sites, and providing the operating costs are favourable, then fan driven MVR evaporators have a very prosperous future."









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