About the Crystalactor™ for fluoride recovery in Nanjing
At a large industrial production complex in Nanjing City, the chemical polyisobutene (PIB) is produced. For this production process a Fluoride-containing compound is employed. A large part of this compound is recovered. During the recovery process water is used. After this process the wastewater is polluted with high concentrations of fluoride, which needs to be treated before discharge into the biological wastewater treatment system.
The client has made an inventory of various available treatment technologies and it turned out that the Crystalactor was identified as an attractive technology for the treatment of this F-containing waste stream. Through this technology, not only the Fluoride content can be reduced to the required level, but also the removed Fluoride can be recovered and reused due to high-purity, low-water-content crystals ("pellets") which are formed.
Technical specifications, sustainability and space
As one of the world’s leading chemical companies, the client operates under a complete set of technical specifications, engineering criteria and quality standards. All works (both production facility and utilities, such as this Crystalactor) are to be implemented in compliance with these stringent requirements. At the same time sustainability is a must. Besides treatment and de-contamination of the waste water, the client requires a minimum waste production from treatment processes with a recovery and reuse of fluoride of more than 90%.
The required fluoride recovery unit is projected in between other production facilities, leaving a very small footprint available for the unit so that the system had to be remarkably compact compared with conventional treatment systems.
The delivered solution
Based upon our rich experience in Crystalactor application and the results of pilot tests performed, a design for recovery of fluoride via the calcium fluoride (CaF2) route was offered. Important aspects in the design include:
- a high on-stream availability, since the treatment plant is fully integrated with the production plant without use of installed spares for critical equipment;
- easy continuous operation with a minimum of supervision and operator input;
- minimum total cost of operation and waste generation. The produced CaF2-pellets are sold for reuse by other industries;
- the whole unit is fully integrated with the production plant and is designed and constructed in a very compact way for a minimal footprint.
The Crystalactor as Fluoride Recovery Unit system consists of the following main components:
- Crystalactor (reactor);
- Rapid filter unit (3 Sand filters, 2 on duty, 1 stand by);
- Sand washing and dosing system;
- Chemical dosing;
- Pellets discharge and collection unit.
Fully automated and integrated process
Design of the unit and material selection is fully in line with the tough quality demands set by chemical environment in EX classification area and the aggressive wastewater characteristics. The operation of the unit is fully automated and integrated in the process control system. An excellent effluent quality is obtained showing typical remaining F- levels of 10 - 20 ppm in effluent. As by-product compact and dry CaF2-pellets are obtained, which are transported to an external company for recuperation.