Liquid purification or separation – Processes – Including controlling process in response to a sensed condition
Reexamination Certificate
1999-07-22
2001-06-26
Drodge, Joseph W. (Department: 1723)
Liquid purification or separation
Processes
Including controlling process in response to a sensed condition
C210S776000, C210S086000, C210S104000, C210S123000, C210S143000, C210S242300, C210S923000
Reexamination Certificate
active
06251286
ABSTRACT:
This invention relates to a method and apparatus for cleaning the surface of liquid in a reliable and automated manner.
Many industrial, military and municipal facilities have separation tanks, sumps, lift stations and the like which must have oil or other floating material removed from the surface of the water in these facilities. In general, these tanks and sumps are not hospitable to human observation and consequently, they are not easily cleaned by standard methods. This invention provides a means for accurate reporting of the skimmer related conditions in such tanks and sumps, the control of debris, and the removal of oil accumulations.
Skimmers described in the prior art either deliver an oil and water output which must be separated by an expensive process or require the movement of physical means into the liquid layer to adsorb the oil, a process which is difficult to maintain and often provides unreliable performance. This invention attracts and collects floating oil and debris, stores the debris, and pumps the collected oil to surface collection tanks without underlying water.
SUMMARY OF THE PRESENT INVENTION
It is an important objective of this present invention to combine the attraction characteristics of a weir skimmer and the selectivity of a mechanical skimmer with automatic controls and status signals which provide automatic pure oil recovery in environments where human intervention is not appropriate. One important example of the invention's use is in a basin or sump that collects water (such as rain or wash water) and oil (such as automotive oils or fuels) from a parking lot or a roadway.
In one embodiment of the present invention the skimmer comprises a relatively large sump with flotation tanks, with a lower liquid removal means, an upper liquid removal means, a floating articulated weir for liquid input, a debris screen to keep out larger floating debris and a debris basket to accumulate smaller debris, and related instrumentation and level sensors, with associated logic controls to direct skimmer operations and to report skimmer status.
The logic control will recognize a “start cycle” signal such as a manual switch closure, the passage or arrival of a time event, or the recognition of an event such as a water level in a sump rising. Upon receipt of this signal, the logic unit will turn on the lower liquid removal means (water pump) which will start a skim over the floating weir which controls liquid input into the skimmer body and creates a cascade action that attracts floating material into the skimmer.
The nature of the floating weir is to create a void space behind the weir which has a tendency to cause the body of the skimmer to rise out of the water. As the skimmer rises, the floats are elevated and displacement is lost; ultimately, an equilibrium is established between the rise of the skimmer and the loss of displacement. This change in elevation in relation to the external water level is measured by instrumentation (float switch or ultrasonic level indicator for instance) and logged into the logic controls, thus allowing an accurate reporting of the skim status of the skimmer. If the external water level fails to reach the prescribed level, the logic unit can take corrective steps. In this preferred embodiment, the logic unit will shut down any pumps which are on and allow the system to remain dormant for a period of time; it will then resume the pumping. This procedure may be repeated several times before the skimmer pumps are shut down and an error condition is reported. The assumption behind this type of action is that any correctable problem is due to debris somehow lodging into the moving parts of the skimmer and cessation and resumption of skimming can often clear these problems. It has been observed that particularly viscous oils can prevent liquid from entering the skimmer, but cessation and resumption can overcome this problem.
During the skimming operation, surface liquid is drawn into the skimmer; the external debris screen bars larger debris such as beverage cans from entering the skimmer. A secondary debris basket collects the smaller debris which enters. This secondary debris basket is removable for easy cleaning. Oil accumulates in the upper area of the skimmer sump and is monitored by a specific gravity sensitive switch or other appropriate measurement device to determine when the accumulation of lighter specific gravity liquid (generally oil) is sufficient to activate a pump which has an intake orifice generally in the mid-depth of the accumulation of the light liquid, and which removes the lighter specific gravity liquid. The pump operation is terminated when the specific gravity switch is turned off by the detection of the removal of the lighter specific gravity fluid (or removal to a certain degree).
A low liquid level switch (or other appropriate level sensor) monitors the fluid level inside the skimmer sump. Should this switch indicate that the level of liquid in the skimmer sump is too low, the situation is reported to the control module. Upon receipt of this signal, the control unit may take corrective action. In one embodiment of this invention, the control will shut off any of the pumps which are on. The control will keep the skimmer pumps dormant for a period of time and then resume the pumping; if the signal is cleared, operation can continue as normal. If not, the skimmer will be shut down and an error condition will be indicated. The dormant cycle can be repeated several times before the error condition is indicated and the skimmer is shut down. Generally such a low-liquid condition would be caused by insufficient liquid entering the skimmer, over the weir. This could be from a blockage, or possibly from a problem with the weir itself, where it fails to admit outside liquid.
Because the present invention allows for the accurate presentation of the status of the skimmer and the liquid inside it, the logic controls can direct the operation of the skimmer to suit the needs of the situation. In one embodiment, the logic controls monitor a fluid level switch which measures the level of the liquid in an oil recovery tank which accepts the oil output of the skimmer. The logic controls can therefore suspend oil recovery and signal a “recovery tank full” condition. The logic controls may also determine if oil recovery has occurred over a period of time (example, eight hours of skimming) and if no such oil recovery has occurred, the skimmer can be shut down until the next “start cycle” event occurs.
It is thus an object of the invention to provide automatic operation in separation of two different-density liquids, preferably petroleum derivative and water, with reliable operation, in a situation where human observation and operation are inconvenient or difficult.
These and other objects, advantages and features of the invention will be apparent from the following description of a preferred embodiment, considered along with the accompanying drawings.
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patent: 6027641 (2000-02-01), Spradbury et al.
Cecil Terry K.
Douglas Engineering div.U.S. Hydrex Inc.
Drodge Joseph W.
Freiburger Thomas M.
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