The fluid bed dryer was developed to increase energy efficiency of CFB Calciners by utilizing available waste heat to remove free moisture from hydrate prior to feed into the calcination process.
By now the dryer can be used for many more applications where free moisture needs to be removed from solids, which are easily fluidizable. The dryer utilizes our vast experience to install high heat transfer rates into small volumes and makes it therefore highly efficient with very compact dimensions.
Why hydrate drying?
- Reduced specific fuel consumption in calcination
- Flexibility in heat recovery
- Increased premium for dry hydrate
- Increased transport and storage flexibility
- Robust design and easy operation
How does the hydrate dryer work?
The principal use of a hydrate dryer is to reduce the surface moisture of the gibbsite (hydrate feed) after the filtration plant or the stockpile. The surface moisture typically range between 6 and 10 wt-% depending on filtration efficiency and particle size distribution. The dryer operates as a counter-current flow shell-in-tube heat exchanger. When integrated in the calcination scheme, the heat transfer medium is circulated in a closed circuit loop from the fluid bed cooler to the hydrate dryer to provide the heat for drying the wet gibbsite through heating coils.
A separate feed bin is used to feed the moist gibbsite to the hydrate dryer. Fluidising air is introduced through a nozzle grate. The product (dry gibbsite, residual moisture <0.05 wt-%) is discharged from the hydrate dryer via a sealpot and can be transported either to a separate storage bin or fed directly to the first venturi preheating stage of the calcination plant. The bed level in the dryer is controlled by the discharge sealpot using a differential pressure measurement.
The flexible design allows for integration of the hydrate dryer in the alumina calcination unit or as standalone equipment for the production of dry hydrate. Using the hydrate dryer in the calciner reduces the overall specific energy consumption. Dry gibbsite is a marketable product, and reducing the moisture content of hydrate increases the market premium. The transport capacity, per ship/truck load (on a dry basis), is also increased as the surface moisture is removed. Dry hydrate can also be pneumatically conveyed which improves the flexibility with regards to handling and storage.
Due to the versatile design of the hydrate dryer water, steam or oil can be used as a heating medium. The hydrate dryer can also be offered as a stand-alone solution (i.e. not integrated in a calcination plant) utilising condensate or other available heat sources for the drying process.