Liquid purification or separation – Processes – Including controlling process in response to a sensed condition
Reexamination Certificate
2000-04-25
2002-02-12
Drodge, Joseph W. (Department: 1723)
Liquid purification or separation
Processes
Including controlling process in response to a sensed condition
C210S087000, C210S096100, C210S198100, C210S754000, C436S052000, C436S055000
Reexamination Certificate
active
06346198
ABSTRACT:
FIELD OF THE INVENTION
The following invention relates to fluid control systems which are configured to control the introduction of a treatment fluid into a fluid stream to cause a selected characteristic of the fluid stream to match a desired level. More particularly, this invention relates to treatment fluid injection control systems which divert a pilot stream from the fluid stream, treat the pilot stream with the treatment fluid, analyze the pilot stream downstream from the point of introduction of the treatment fluid and use the results of this analysis to control a main treatment fluid inlet into the fluid stream.
BACKGROUND OF THE INVENTION
Many fluid handling systems require monitoring of selected characteristics of the fluid stream to control the introduction of treatment fluids into the fluid stream. For instance, in waste water treatment facilities a main stream of waste water typically is treated with a chlorine containing compound, such as sodium hypochlorite, to neutralize bacteria in the waste water stream. It is undesirable to undertreat the waste water stream because active bacteria will thus remain in the waste water stream. It is also undesirable to overtreat the waste water with chlorine because a residual chlorine level in the waste water stream will be detrimentally high. Additionally, the chlorine or other treatment fluid is wasted and additional chemical is typically needed to neutralize the excess chlorine.
Many advanced waste water treatment systems include a residual chlorine analyzer downstream from the chlorinator which monitors the levels of chlorine residual remaining in the waste water stream. Controllers are known which utilize the results of this downstream analyzer to provide a feedback signal to the chlorinator. In essence, if an amount of residual chlorine is too high at the downstream analyzer, the chlorinator receives a feedback signal which decreases the rate of introduction of chlorine. If the analyzer detects that no chlorine or too little chlorine remains, indicative that not all of the bacteria has been neutralized, the feedback signal will cause the chlorinator to increase the rate with which it introduces chlorine.
While such residual chlorine analyzers and feedback control systems are generally effective, they suffer from numerous drawbacks. For instance, when the analyzer detects a less than optimal amount of chlorine residual, additional treatment must still occur to the waste water stream to properly treat the waste water. The delay associated with the distance between the analyzer and the chlorinator and the amount of time it takes for the chlorine analyzer to detect any change in chlorine residual causes problems in the control. Such feedback systems have a tendency to enter into an oscillatory state between over and under chlorination which only relatively slowly resolves itself, especially when the chemical requirement within the waste water stream is fluctuating. Waste water treatment facilities can incur fines for releasing waste water which is either undertreated or overtreated with chlorine containing compounds. Waste water treatment facilities additionally suffer financially from the unnecessary use of excess chlorine and chlorine neutralizing chemicals, such as sulphur dioxide when the chlorination system is not operating optimally.
Other fluid control systems exhibit a need corresponding to that identified above. Specifically, systems which require treatment of a main stream with a treatment fluid to cause a selected characteristic of the main fluid stream to match a desired level/set point, often cannot be effectively controlled by having an analyzer downstream from the treatment fluid injection site which feeds back a signal to the treatment fluid injection site. Accordingly, a need exists for a system for fluid stream treatment which can accurately predict the amount of treatment fluid required for a main fluid stream in advance and feed this information forward to the treatment fluid injection site to minimize the amount of treatment fluid necessary to effectively treat the fluid stream in a precise fashion.
SUMMARY OF THE INVENTION
The system of this invention precisely controls the amount of treatment fluid to be introduced into a main fluid stream to cause a selected characteristic of the main fluid stream to match a desired set point for the selected characteristic in the main fluid stream. A pilot stream is diverted out of the main fluid stream at a location upstream from the main treatment fluid injection site in the main fluid stream. This pilot stream has a pilot treatment fluid injector which injects a known amount of the treatment fluid into the pilot stream. The treatment fluid acts on the pilot stream and then an analyzer samples the pilot stream downstream from the pilot treatment fluid injector.
The analyzer measures the level of the selected characteristic present in the pilot fluid stream. The result of this analysis is communicated to a controller which controls both the pilot treatment fluid injector and the main treatment fluid injector within the main fluid stream. If the pilot stream analyzer detects that a level of the selected characteristic is below a set point for the selected characteristic, the pilot treatment fluid injector is adjusted to increase the amount of treatment fluid injected into the pilot stream. If the analyzer detects an excess amount of the selected characteristic above the set point, the controller causes an amount of the treatment fluid injected into the pilot stream to be decreased.
When the analyzer detects a level of the selected characteristic matching the set point for the selected characteristic, or within the range desired by the operator, the controller maintains the rate of injection of the treatment fluid into the pilot stream. The controller additionally adjusts a rate of treatment fluid injection at the main fluid stream treatment fluid injector to correspond to the pilot treatment fluid injector rate. Specifically, the arithmatic product of the rate of injection of the treatment fluid from the pilot treatment fluid injector into the pilot stream and the ratio of the flow rate of the pilot stream to the ratio of the main fluid stream is used to set the flow rate for the treatment fluid into the main fluid stream.
If the characteristics of the main fluid stream are changing, the pilot stream will reflect these changes and the pilot treatment fluid injector, pilot stream analyzer and controller will appropriately adjust to properly neutralize the pilot stream. Once adjusted, a level for the main treatment fluid injector in the main treatment fluid stream is used to adjust the main treatment fluid injector so that the main fluid stream is properly neutralized in a way that reflects changes in the characteristics of the fluid within the main fluid stream.
A verification analyzer can optionally be provided downstream from the main treatment fluid injector to verify that the selected characteristic within the main fluid stream is at the set point. Data associated with settings for the fluid treatment injectors and the pilot stream and the main stream and levels of selected characteristics within the pilot stream and the main stream, as well as flow rates for the pilot stream and the main stream can all be outputted relative to time for analysis by the operator to verify that the system is operating properly.
When the main fluid stream is a waste water stream and bacteria within the waste water stream is to be neutralized, the treatment fluid is typically a chlorine containing compound, such as sodium hypochlorite, and the selected characteristic is the level of residual chlorine existing within the waste water after treatment with the chlorine containing compound.
OBJECTS OF THE INVENTION
Accordingly, a primary object of the present invention is to provide a system for adjusting a rate of introduction of treatment fluid into a main fluid stream which precisely causes a selected characteristic of the main fluid stream to match a set point for the selected charact
Armstrong Stephen J.
Watson Les
Drodge Joseph W.
Heisler & Associates
Industrial Control Systems
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