Liquid purification or separation – Processes – Including controlling process in response to a sensed condition
Reexamination Certificate
1999-12-01
2001-08-28
Drodge, Joseph W. (Department: 1723)
Liquid purification or separation
Processes
Including controlling process in response to a sensed condition
C210S096100, C210S192000, C210S188000, C210S746000, C210S760000, C422S098000, C422S186010, C436S155000, C340S632000
Reexamination Certificate
active
06280633
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to gas concentration sensors and more particularly to a sensor for measuring the concentration of a gas such as ozone in a gas stream. The invention also relates to water purification systems and more particularly to a method and apparatus for sensing the concentration of a reactable gas (such as ozone) in an off-gas during a water purification process.
BACKGROUND OF THE INVENTION
In many areas, a reactable gas is used as a processing agent to treat a liquid. Examples of this include water treatment to remove waste or to create potable water and chemical oxidation (i.e. bleaching) processes.
In such processes, it is important to ensure that treatment of the liquid with the reactable gas continues for a sufficient period that the desired treatment result is achieved. In water treatment applications, commonly used reactable gases include ozone and hydrogen peroxide. Ozone is used in many water treatment applications to remove impurities. It is important to ensure that ozonation of the water continues until the level of impurities has fallen to an acceptable level. One method of doing this is to fix the volume of water and then ozonate the water for a period that is known to be sufficient to reduce the impurity level, regardless of the initial concentration of impurities in the water. However, this method may waste ozone (if the initial level of impurities was relatively low) as well as requiring a fixed, and possibly lengthy, time for each ozonation process. It is preferable to use a system that monitors the impurity level and stops the ozonation process when the acceptable impurity level is achieved.
Accordingly, various different sensors have been developed to measure the level of ozone in water. Some of these sensors operate by passing ultraviolet light through a fluid stream and measuring the ultraviolet light received on a detector. Another type of gas detector is disclosed in U.S. Pat. No. 5,167,927 to Karlson. Karlson discloses a monitor which measures the heat energy released when a gas, e.g. ozone, is catalytically converted into a different compound, e.g. oxygen. A third type of sensor is disclosed in U.S. Pat. No. 5,427,693 to Mausgrover et al. Mausgrover incorporates a meter to measure the oxidation-reduction potential (ORP) of the water being cleaned. The ORP is then equated to an ozone concentration in the water. A fourth type of ozone sensor is disclosed in U.S. Pat. No. 5,683,576 to Olsen. In the system described by Olsen, an ozone containing gas is passed through contaminated water until the concentration of ozone in solution in the water reaches a pre-determined level. Ozonation then continues for a pre-determined period. The objective of this system is to ensure that a specified volume of water will be treated with a specified concentration of ozone for a specified period of time.
Although these systems may provide a reliable measure of the concentration of ozone in water, none of them provides an accurate measure of the degree to which impurities have been removed from the water. Continuing ozonation after the desired ozone concentration is reached for a pre-determined period ensures only that a minimum amount of ozone passes through the water over the entire treatment period. Olsen assumes that once the concentration of ozone reaches the predetermined level, it does not subsequently fall. Further, Olsen assumes that simply allowing a selected concentration of ozone to remain in the water for a selected time ensures that the water is suitable for use. However, this will not necessarily be true, especially in the case of highly contaminated water. For example, lake or well water will normally require more treatment than treated water from a municipal supply.
SUMMARY OF THE INVENTION
Accordingly, there is a need for a method and apparatus to accurately measure, on an ongoing basis, the degree to which impure water has been treated by ozonation. This may be done by measuring the amount of ozone that passes through water in a water purification chamber without being consumed. As the amount of unconsumed ozone exiting the chamber rises, the level of impurities is known to have fallen. When the amount of unconsumed ozone exiting the chamber becomes substantially constant, the water may be reliably considered to be substantially free of impurities that are susceptible to removal by the ozone.
In accordance with a first aspect of the present invention, there is provided a sensor for detecting the concentration of ozone in an incoming gas stream, said sensor comprising a sensing element positioned in the flow path of the incoming gas stream, said sensing element being electrically sensitive to the presence of ozone such that an electrical potential corresponding to said concentration is induced across said sensing element; and an electrical circuit coupled to said sensing element for allowing said electrical potential to be measured.
In accordance with a second aspect of the present invention, there is provided an apparatus for removing impurities from water, said apparatus comprising: a contact chamber for containing said water, said contact chamber having a head space for containing an off-gas and said contact chamber having an off-gas outlet for allowing said off-gas to exit said contact chamber in an off-gas stream; a closure for providing a substantially gas tight seal between the interior and exterior of said contact chamber; a reactable gas source for providing a reactable gas; a reactable gas control for controllably introducing said reactable gas into said contact chamber; a reactable gas sensor for providing a reactable gas concentration signal corresponding to the concentration of reactable gas in said off-gas stream at a signal node, said reactable gas sensor having an off-gas inlet and said off-gas inlet being in fluid communication with said off-gas outlet; and a controller, said controller being coupled to said signal node for receiving said reactable concentration signal and to said reactable gas control for controlling the introduction of said reactable gas into said contact chamber in response to said reactable gas concentration signal.
In accordance with a third aspect of the present invention, there is provided a method of removing impurities from an impure liquid, said method comprising the steps of: providing a quantity of said impure liquid in a contact chamber; providing a controller for controlling the flow of a treatment gas containing a reactable gas into said chamber; initiating the flow of said treatment gas into said contact chamber, wherein said reactable gas flows through said liquid and wherein at least some of said reactable gas reacts with impurities in said liquid consuming at least some of said reactable gas, the remainder of said treatment gas collecting in said chamber as an off-gas; withdrawing some of said off-gas; monitoring the concentration of said reactable gas in said off-gas; and terminating the flow of said treatment gas in response to the rate of change of said concentration of said reactable gas in said off-gas falling below a selected level.
In accordance with a fourth aspect of the invention, there is provided a method of removing impurities from an impure liquid, said method comprising the steps of: providing a quantity of said impure liquid in a contact chamber; providing a supply of a reactable gas; providing a controller for controlling the flow of said reactable gas into said contact chamber; providing a sensor for measuring the concentration of said reactable gas in an off-gas stream exiting said chamber and providing an electrical signal corresponding to said concentration; initiating the flow of said reactable gas into said chamber wherein said reactable gas flows through said liquid, and wherein at least some of said reactable gas reacts with impurities in said liquid consuming at least some of said reactable gas, the remainder of said reactable gas exiting said chamber in said off-gas stream; monitoring said signal until the rate of change of said signal falls
Bohrsen Terry B.
Conrad Wayne Ernest
Duff Richard M.
Bereskin & Parr
Drodge Joseph W.
Fantom Technologies Inc.
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