The majority of the Granular Activated Carbon systems used in the sugar industry are either fixed bed or pulse bed systems.
1. Fixed bed systems
In the fixed bed vessel, the liquor enters the top of the vessel and passes through the activated carbon until the carbon is spent or the outlet specification on color is exceeded. Then, the entire volume of carbon is removed ofrom the vessel and replaced with either virgin or reactivated carbon.
The fixed bed system will have fluctuation in the outlet quality. Initially, the carbon depth is sufficient to contain the mass transfer zone. However, as the carbon becomes spent the remaining carbon is not sufficient to remove the color and some of the color begins exiting the vessel, breakthrough occurs.
2. Pulse bed systems
The pulse bed system provides more control over the outlet quality. It is operated in a true counter current fashion. The liquor enters the bottom of the column, the highly colored liquor enters the most spent carbon. As the liquor rises through the column it is purified; exiting the column at the top where the freshest carbon resides. Because the adsorption process is equilibrium based, this operation best utilizes the carbon capacity. Carbon which has been in equilibrium with a lower color concentration (in the top portion of the column) can come to a new equilibrium with a liquor (in the lower portion of the column) having a higher concentration than the original. This enables carbon to better accommodate fluctuations in the inlet color while maintaining a consistent outlet color concentration.
3.Application: Fructose, Sucrose, MSG, Sorbitol, Citric acid, advanced wastewater treatment
Comparison for fixed bed and pulse bed
| Advantages | Disadvantages |
Fixed beds | Lowest building profile Little operator attention required Self filtering system Easy to inspect vessel interiors Requires lower inlet pressure to pass through the system Can handle large flow Can be designed for backwashing. | Requires greater plot area Higher capital investment than a pulse bed system for the equivalent amount of carbon on stream If a single adsorber is used effluent quality will vary as a function of the on stream time of the column The treatment objective is reached at the same time as the column is disconnected from the system. |
Pulse beds | Requires less plot area Can be controlled to have the quality of the treated product close to the specification value Has the lowest carbon dosage in applications having a long mass transfer zone No peak consumption of water during the recovery of product If gas is present, or can be generated in the carbon bed, an upflow design is the better alternative. | Cannot treat liquids containing significant quantities of suspended solids Inspection and/or repairs can only be done by taking an adsorber off line and emptying the entire carbon content Effluent contains carbon fines after each pulsing operation and should be filtered. |
4. The basic process for AC adsorption and decolorization
Our engineers own abundant design experiences on fixed bed and pulse bed in SHANGDING, we can offer proper adsorption system for clients.
Pulse bed
Can be controlled to have the quality of the treated product close to the specification value
The treated liquid upflow through AC bed from bottom to top
Drains the most saturated AC partially
Minimizes AC usage
Highest efficiency of adsorption
Requires less plot area and investment
Fixed bed
Requires lower inlet pressure to pass through the system
Can handle large flow
Can be designed for backwashing
Lowest building profile
Little operator attention required
Easy to inspect vessel interiors
