State-of-the-art VKT design for high– and low–grade massecuites!

In recent years, several cane sugar factories have installed vertical continuous vacuum pans (CVPs) with mechanical agitators capable of operating on low-pressure vapours to further reduce exhaust steam consumption. The cane sugar industry has until now mostly used horizontal CVPs, however, vertical CVPs offer additional advantages over horizontal CVPs, such as flexibility for cleaning chamber on the run and a smaller footprint even for pans of very large volume. 

VerdampfungsKristallisationsTurm (VKT) from BMA  

BMA is the forerunner in this technology with their VKT, having commissioned several vertical continuous vacuum pans for A, B and C massecuites in cane sugar factories in Northern and Southern Africa, Asia, Latin America.  

Key features of BMA’s VKT design included:  

1. Welded heating tubes, with tube-to-tube distance <10 mm, providing larger heating surface area 
2. S/V ratio of 12.5 
3. Cylindrical chambers, promoting homogeneous mixing 
4. Optimal calandria deaeration and condensate removal 
5. Mechanical stirrer conformed to calandria, downtake, shape of pan bottom and application 
6. Pan bottom designed for optimum circulation (no dead zone) 

Sophisticated control system: 

1. Defined flow of massecuite from 1st chamber to 4th chamber 
2. Controlled process conditions (calandria pressure, vapour pressure) 
3. DS measurement using “Microwave” regulating feed solution quantity 
4. Using “ratio controller” for addition of seed magma to first chamber 

Flexibility in operation: 

1. Any chamber could be brought off-line for cleaning during operation. 
2. The throughput of the VKT is unchanged – slight changes in operating conditions  

A prime example of the VKT installation in the cane sugar industry is the one operating at the Indian Cane & Power Limited (ICPL) factory in India for A massecuite. Below are some of the operating results: 

• 4-chamber VKT with a diameter of 5.6 m  
• 636 m2 heating surface of each chamber  
• Massecuite throughput: 80 t/h, 87% purity, crystal size (MA) up to 2 mm 
• Seed from batch pans: 35 t/h, crystal size (MA) up to 1.5 mm 
• Limited crystallisation rate by crystal size: 4 – 5 h retention time 
• Pan vapour 160 – 190 mbar abs.  
• Heating steam 400 – 500 mbar abs.: Vapour 4 from evaporation station 
• Temperature difference between heating steam and massecuite: 10 – 14°C