Control of the programmable gas chlorine auto valve is provided by the PCS and the Manufacturer-supplied integral auto valve controls. The gas chlorine dosing is based on filter discharge flow rate and an operator input chlorine dose rate. Chlorine residual monitoring following the contact basin is manually tracked to ensure dose rate is adequate. The chlorine feed rate is varied by the gas chlorine auto valve using an analog signal input from the PCS.
The PCS will send an OPEN signal to the vacuum circulation line solenoid and frequency signals to the gas chlorine auto valve.
Local Control:
The gas chlorine auto valve and vacuum circulation line solenoid may each be operated in HAND mode. In HAND mode, auto valve is independent of PCS control.
- When HAND mode is selected, the auto valve will operate according to manual settings available on the LCD display and control panel face.
PLC Control:
During normal operation, AUTO is selected at the integral valve LOS and the chlorinator will control the chlorinator valve by sending two analog 4-20mA signals for valve position: Filters Effluent Flow Rate (FIT-300-1-1) and Finished Water Residual Chlorine (AIT-400-2). Initial valve position is based on filtered water flow rate and chlorine residual measurements. Operator attention is required if actual loads and characteristics diverge from average by more than attributable to flow or chlorine demand variations. The anticipated low end and high chemical doses for the gas chlorine system are as follows:
Gas Chlorine: 20-75 lbs/day (1,000-2,100 gpm, 1.7-3.0 ppm)
The mA signal corresponding to the starting point dose can be determined as follows:
mA start = 4 + (Low End Dose Rate ÷ Full Valve Capacity) × 16
Where:
mA start = milli Amp signal corresponding to the starting point dose/stroke
frequency
Low End Dose Rate= As defined above
Full Pump Capacity = As specified by Manufacturer (100 lbs/day)
Gas chlorine discharge is adjusted from the starting point by the PCS based on variations in filtered flow. When measured flow changes, the auto valve position is proportionally changed based on the following:
mA adj. = mA start + (Measured Flow – 1,000 gpm) ÷ 1,000 gpm × mA start
Where:
mA adj. = milli Amp signal corresponding to the gas chlorine requirement adjusted
based on filtered water flow
Measured Flow = filtered water flow as measured by the WTP common filter outlet pipe magnetic
flow meter
Fail Signals
Fail signals on the gas chlorine system may be generated by a range of conditions including, but not limited to, low vacuum indication, analog signals outside of programmed allowable values, valve overload, and high gas alarm in the room. The fail conditions are programmable in the integral pump panels.
If OFF is selected on the integral Auto Valve LOS, the RTU will generate a FAIL alarm if the gas chlorine system is not operating when called.
PLC / HMI Configuration:
- Status Display:
- Chlorine ratio offset.
- Cylinder WEIGHT indication (each).
- Auto Valve HOA indication.
- Chlorine Contact Basin Residual.
- Operator Entries:
- Chlorine ratio offset.
- Low end dose rate.
- Full valve capacity.
- Alarms:
- GENERAL FAULT for Auto Valve.
- Cylinder HIGH-HIGH Weight ALARM (each).
- Cylinder HIGH Weight ALARM (each).
- Cylinder LOW Weight ALARM (each).
- Cylinder LOW-LOW Weight ALARM (each).
- Chlorine Feed Rate HIGH-HIGH ALARM.
- Chlorine Feed Rate HIGH ALARM.
- Chlorine Feed Rate LOW ALARM.
- Chlorine Feed Rate LOW-LOW ALARM.
- LOW VACUUM switch.
- HIGH GAS alarm for room.
- Chlorine Leak Detector FAULT.
- Chlorine Leak Detector power FAULT.
- Filter Effluent chlorine HIGH ALARM.
- Filter Effluent chlorine LOW ALARM.
- Plant Effluent chlorine HIGH ALARM.
- Plant Effluent chlorine LOW ALARM.
- Potable Water chlorine HIGH ALARM.
- Potable Water chlorine LOW ALARM.
- Historical Trending:
- Finished water chlorine residual.