Steam Dewatering of Filter Cakes in a Vertical Filter Press

Abstract

Steam dewatering of filter cakes is recognized as a competitive alternative to conventional air drying and thermally assisted mechanical dewatering (TAMD). The main benefit of cake dewatering with high-pressure steam is that mechanical and thermal dewatering can be efficiently performed in a single process step. The target of this study was to determine the potential of a steam-dewatering technique for two industrial mineral suspensions. The first mineral, kaolin, was very difficult to dewater using conventional mechanical dewatering techniques, whereas the second one, ground calcium carbonate (GCC), represented only moderate resistance to filtration. The secondary objective was to compare the filterability of the original kaolin slurry with the same slurry treated with a coagulant (aluminum sulphate, Al₂(SO₄)₃ · 16H₂O). Four different kinds of experiments were performed: tests without any kind of cake dewatering, tests with air drying, tests with steam drying, and tests with both coagulation and steam drying. The obtained results show that steam dewatering is an efficient technique for achieving lower cake-moisture contents. Also, the positive influence of coagulation on the filtration capacity was found to be considerable in the case of kaolin. An approximate energy balance was created for the steam-drying process and the determined energy efficiencies were compared with those obtainable with an ideal thermal drier. The main conclusion from these comparisons is that steam drying can be effectively used instead of traditional thermal drying if the large energy losses can be reduced by proper insulation and heat recovery systems.

Keywords:

• Energy balance
• Filter press
• Ground calcium carbonate (GCC)
• Kaolin
• Steam dewatering

Notes

*In tests 7–18, long and short filtration times were 200 s and 20 s., respectively. In tests 19–27, long and short filtration times were 100 and 20 s, respectively.

^c Aluminium sulfate was used as a coagulant.

*In tests A1–A9, air-drying pressure was contant, 5 bar. ⁺In tests S1–S30, steam drying was stopped when steam was observed at the filtrate outlet.