Process Measurement & Control Solutions
NOTE 1: DEWATERING OF STORAGE TANKS, AUTOMATIC DRAW WATER CONTROL, & MANUAL TANK GAUGING
APPLICATION NOTE 1
All Agar Corporation Instruments are covered by one or more of the following U.S. Patents: 4,503,383; 4,774,680; 5,099,697; 5,101,163; 5,101,367;
5,263,363; 5,503,004; 5,551,305; 5,589,642; 5,741,977, RE 36,597. Other patents pending in the USA and other countries.
INTRODUCTION
Storage tanks containing hydrocarbon feedstocks, intermediates and finished products will, over time, accumulate a water layer in the bottom of the tank (exceptions are water-soluble hydrocarbons such as alcohols and ethers). Standard industry practice is to periodically drain the water from storage tanks so that the water does not adverly impact specifications of the hydrocarbon. Water removal also reduces corrosion problems on the floor of the tank and the risk of “Boil-Overs” in ca of fire.
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 increas the cost of wastewater treatment. Addit
ionally, environmental regulation trends (e.g., USA Benzene/NESHAP and SOCMI/HON) may impo 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 u the AGAR ID-200 Series Interface Detector. Each water draw discharge control strategy has its own advantages and disadvantages.
The control strategies are:
结项报告■ Using In-Tank Interface/Concentration Detectors ■ Using Inrtion 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
川断的功效与作用In-Tank measurement of the hydrocarbon/water interface gives the best results for eliminating the discharge of hydrocarbons. Usually, AGAR ID-201 probes are inrted into the tank through AGAR’s patented al housing, as shown in the photo above. Special installation may require
the u of the AGAR ID-202 for extended length.
Agar ID System 1 & 2 Tank Installation
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.
System #1
When the AGAR ID-201 probe detects HC free water, the water discharge valve is opened. As water is drained off the
Figure 2
谋划部署System #2
Figure 2 shows the high-low control logic in which the valve would clo only after both probes have
detected hydrocarbon. Figures 1 and 2 also show how to overcome tank bottom sludge build-up problems by placing the active part of the AGAR ID-201 probe over the sump in the bottom of the tank. It is nearly impossible for sludge to build-up and cover the probes in this configuration.
Figure 1
II. IN-LINE HYDROCARBON/WATER MONITORS
The advantage of this approach is the avoidance of tank penetration, elimination of bottom diment build-up, and the elimination of the free water in the tank.
成语abccHowever, there are significant disadvantages that should be considered in design and policy decisions:
1. Some hydrocarbon must be discharged with the waste water in order for the monitor
to detect it in the external pipe.
2. The drain pipe must be altered to avoid the trapping of hydrocarbons.
3. Manual initiation of water-draw cycle is required.
Figure 3 shows how the conventional Vortex Breaker bent pipe traps hydrocarbon at the end of the water draw-off cycle.
带夏字的成语Figure 3
Assume a ca where the hydrocarbon and the water have completely “pha parated” to form a clear-cut interface inside the tank. Becau hydrocarbon is still prent from previous water-draw, the water draw cycle will have to be initiated manually. Water will have to displace the HC before the probe can be activated. Once this has occurred, water will continue to drain until the oil/water monitor again detects hydrocarbons. At this point, the oil/water monitor will nd a control signal that is ud to clo the water draw-off valve. However, due to the bent pipe design, this hydrocarbon is again trapped in the draw-off line. As water gradually builds up in the tank, the hydrocarbon trapped in the line acts as a al (being lighter than water). To re-activate the dump valve for a new water-draw cycle, the oil/water monitor signal must be overridden to flush the hydrocarbon out of the line before water is again detected. Some HC is discharged to the waste water treatment system during every dump cycle.
tank to flush all hydrocarbon out of the water draw-off
月亮河歌词
line. Thus, the pipe must be designed in such a way as
to eliminate the trapping of hydrocarbon. A small upward
inclination is desirable, with a vortex breaker at the intake.
外观好看的手机The latter avoids vortexing and the suction of hydrocarbon
with water when the dump valve is fully open. Figure
4 shows hydrocarbon being discharged with the water
becau of the vortex action.
Figure 4
Figure 5 shows the correct installation with a slotted discharge pipe. Note, the cross-ction of the slot must be at least ten times larger than the cross-ction of the pipe. Similarly, the pipe can be perforated with many holes, who total cross-ction area exceeds the pipe’s area by a factor of ten.
If the hydrocarbon is highly viscous, special care must be taken to compensate for hydrocarbon fouling that will stick to pipe walls and the AGAR oil/water monitor. The amount of hydrocarbons discharged will depend on the oil’s viscosity and the flushing action of the effluent water. Calibration adjustments to the oil/water monitor will negate the effects of fouling.
Figure 5
关于元宵节的儿歌NOTE: Also available in a 2-wire, 24VDC loop-powered system
