Case Study: Skid Mounted Hydrofluoric (HF) Acid Neutralization and Fluoride Reduction System.
Industry: Semiconductor Manufacturing.
Installation Date: June 2001.
Objective: To remove fluoride and neutralize hydrofluoric acid and fluoride laden wastewater from semiconductor fab area.
Criteria and Limitations: Influent flow can vary from 5,000 GPD to over 40,000 GPD with HF and BOE concentrations ranging up to 2%. Fluoride influent limit is 10 ppm of total fluoride and effluent pH range is
6.0 < pH < 9.0
Fluorine, an anion, is unique and behaves much differently than the cations, or heavy metals, that industry is experienced in removing. Ion exchange does not work economically because of very low affinity that anion exchange resins have for fluorides (abv. F-). Membrane technology is normally not economical because of low flux and membrane fouling. Fluoride bearing waste streams are normally high in silica, the bane of crossflow membranes.
Fluorides can be precipitated as Calcium Fluoride (CaF2), however, due to the solubility of this salt, and due to the difficulty in separating this salt from solution, this can be very problematic also.
Solution: Our batchTREAT wastewater treatment systems are very versatile, modular, skid mounted and flexible. In this application the BT125 served as the heart of the treatment system which consisted of several totally automated stages as listed below:
- Influent Equalization.
- Duplex batch treatment precipitating the F- ion as calcium fluoride (CaF2).
- Duplex batch flocculation stages.
- Duplex batch clarification stages.
- Simplex final effluent polishing stage.
- Simplex sludge thickener and filter press with room allocated for a duplex configuration.
- SCADA system monitoring and continuous data logging.
- Continuous online total fluoride analyzer for monitoring total fluoride in the effluent stream.
Conclusion: The project, as with many wastewater treatment systems, was constrained by time, space, and money. The use of a standard packaged system at the center of the treatment process allowed us to offer the customer a very capable system with a good delivery time, very competitive price, and minimal installation since the entire treatment system was fabricated in our shop prior to shipping.
The system performance has exceeded all specified and published requirements. In the first 2 years of operation there has not been a single discharge contravention and the total plant fluoride has averaged 2ppm. The system has been fully functional 24/7 for the first 2 years with no downtime, other than routine calibrations (weekly) and routine and scheduled maintenance. The influent fluoride levels are routinely in excess of 1,500 ppm.
Description: The system supplied for this application utilizes our unique process for reduction and removal of fluoride from semi-conductor wastewater streams as non- hazardous calcium fluoride (CaF2). The process we employ is totally automated, requires no operator intervention (other than periodic maintenance and calibrations), is safe and can yield total fluoride levels as low as 2 ppm, depending on configuration.
The system featured in this case review is a duplex system. Two totally independent systems operate in parallel with only minimal common components. One stream can be taken offline for service while the other continues to operate totally independent of the other branch.
This package was totally fabricated in our facility and shipped as several subsystems, including a catwalk for servicing equipment at higher elevations. Installation was minimized by the fact that the entire system was fabricated in our shop prior to shipping.
A Supervisory Control And Data Acquisition (SCADA) system is installed that monitors the entire system. All of the programmable parameters, tuning variables, and setpoints are available through the SCADA system. All process variables and system performance are monitored continuously via the SCADA system. Historical logging will maintain a continuous stream of data that may span several years.
A remote connection is available via an Internet connection that allows us to monitor the system from anywhere in the world. We are able to troubleshoot, modify tuning parameters, or conduct training via this online connection.
We manufacture a complete line of Fluoride Reduction Systems for industrial waste water streams ranging from 100 GPD to over 1,000,000 GPD.
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