Ferric Coagulant Batch Reaction and Adjustment Procedure

Purpose. Describes how a batch of ferric sulfate or ferric chloride coagulant is charged, reacted, monitored, sampled, adjusted and transferred so that the reaction stays within its limits and the product meets specification.

1.Scope

This procedure applies to the two batch reactors in the reactor building and their charge, cooling, scrubber and transfer systems. It must be used by the panel operator, the outside operator and the laboratory technician. It must be read with the batch sheet for the product grade and the safe operating limits sheet for the reactors.

2.Pre-charge checks

Before charging, the panel operator must confirm the reactor is empty, clean and at ambient temperature, that the agitator, cooling water, scrubber circulation and vent are in service, that the relief devices are in service and that the high temperature and high pressure trips have been tested within their interval. The outside operator must confirm the charge line-up against the batch sheet.

3.Charging and reaction

Raw materials must be charged in the order and at the rates on the batch sheet and the quantities must be recorded from the weigh cells. The acid addition rate must be controlled so that the reactor temperature stays below the limit on the safe operating limits sheet. The panel operator must trend temperature, pressure and scrubber pH throughout and the outside operator must check the reactor and scrubber in the field every 30 minutes.

• Charge iron source and water first and start agitation
• Start cooling water before acid addition
• Add acid at the batch sheet rate and hold if temperature approaches the limit
• Confirm scrubber pH remains within its band during off-gassing
• Hold at reaction temperature for the time on the batch sheet

4.Sampling and adjustment

At the end of the hold the outside operator must take the batch sample through the sample point using the sample procedure and deliver it to the laboratory. The laboratory must test iron content, free acid, specific gravity and insolubles and must advise the panel operator of the adjustment required. Adjustments must be made only with the materials and quantities calculated by the laboratory and recorded on the batch sheet, and the batch must be resampled after adjustment.

5.Transfer to storage

The batch must not be transferred until the laboratory records a pass in the shift log and the panel operator confirms the destination tank ullage and line-up. Transfer must follow the bulk fluid transfer procedure. The batch number, quantity and tank must be recorded on the batch sheet and in the transfer and inventory register.

6.Abnormal conditions

If temperature or pressure approaches the limit and cannot be controlled by stopping acid addition and maximising cooling, the panel operator must follow the abnormal situation procedure. A batch that reaches the trip setting must be recorded as a process safety event even if the trip did not activate.