Manual control of water draw-off can result in HC product in the discharge. The loss of this HC product means less product available for sale and increases the cost of wastewater treatment. Additionally, environmental regulation trends (e.g., USA Benzene/NESHAP and SOCMI/HON) may impose large economic penalties for designing water draw conveyance and treatment systems that allow HC product in the water draw-off discharge.
Two types of water draw-off control approaches use the AGAR ID-200 Series Interface Detector. Each water draw discharge control strategy has its own advantages and disadvantages.
The control strategies are:
- Using In-Tank Interface/Concentration Detectors
- Using Insertion Hydrocarbon/Water Monitors in the Effluent Water Draw-Off Line
AGAR applications specialists can assist in identifying the optimum strategy for controlling water discharge.
I. IN-TANK INTERFACE DETECTOR
In-Tank measurement of the hydrocarbon/water interface gives the best results for eliminating the discharge of hydrocarbons. Usually, AGAR ID-201 probes are inserted into the tank through AGAR's patented seal housing, as shown in the photo above. Special installation may require the use of the AGAR ID-202 for extended length.
The two probe system can operate under two strategies. A main control/safety strategy - System #1 shown in Figure 1 and a high-low control strategy - System #2 shown in Figure 2.
When the AGAR ID-201 probe detects HC free water, the water discharge valve is opened. As water is drained off the bottom of the tank, the hydrocarbon/water interface begins to drop. When the AGAR ID-201 probe detects the hydrocarbon/water interface, the signal is sent to close the discharge valve. Output options to control the valve can be 4-20 mA, relay and/or pneumatic. Local indicating lights are also available. If the hydrocarbon floats, the ID-201 will prevent it from being discharged with the waste water.
Figure 1 shows an upper probe used for control, with the lower probe used for low-level alarm and positive shutdown of the water discharge valve.