Abstract:
Oil and other contaminants entrained in a water flowstream may be measured to determine the concentration thereof by passing a sample of the flowstream through a vessel defining a chamber in which a light beam is projected to a photo sensitive element. Changes in light intensity caused by changes in concentration of oil or other contaminants are compared with the light intensity measured with a clarified or oil-free sample of liquid. A measuring system utilizes a centrifugal pump having a restricted fluid outlet to provide for thoroughly dispersal of the oil in the liquid flowstream. An alternate source of liquid may include a source of clear water or a source of clarified water which has been held in a holding tank to allow oil to separate from the water sample. The system is adapted for measuring the concentration and absorportion coefficient of oil entrained in a water flowstream such as refinery waste water streams, produced water streams from oil field flooding operations and the like.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention pertains to an apparatus and method for measuring the presence of or change in content of a liquid such as oil entrained in another liquid such as water by comparing clear or clarified water with water having oil entrained therein utilizing a light attenuation measuring system. 
     2. Background 
     Many process systems produce water in which certain types of oil are present in varying amounts. Waste water treatment systems and oilfield production water treatment systems, in particular, need or require means for measuring the amount of oil entrained in the water flowstream on a substantially continuous basis. The time required for periodic sampling and remote analysis of a water flowstream which may contain varying amounts of oil is often excessive with respect to providing suitable monitoring and adjustment of related operations. Accordingly, there has been a strongly felt need for an apparatus or system which can monitor, on a substantially continuous basis, at least relative amounts of oil entrained in a water flowstream and, in particular, a water flowstream which may contain other contaminants wherein the oil contamination must be identified in spite of the presence of other contaminants. It is to this end that the present invention has been developed. 
     SUMMARY OF THE INVENTION 
     The present invention provides an improved apparatus or system for monitoring the presence of a liquid such as oil, including crude oil or the like, entrained in another liquid such as a water flowstream. In accordance with one important aspect of the invention an apparatus is provided which operates on a light attenuation principle for measuring the relative amounts of oil present in a water flowstream. By measuring the variation in light transmission through a continuous stream of water, in which oil has been thoroughly dispersed, utilizing a photosensitive electrical circuit a relatively accurate and sensitive system can be provided for monitoring changes in the oil content of a water flowstream, for example. 
     In accordance with another important aspect of the present invention, an apparatus is provided for monitoring the amount of oil entrained in a water flowstream wherein the water flowstream may have other contaminants which affect the clarity of the water and wherein a comparison may be made between clarified, substantially oil-free water and water containing varying amounts of oil as detected by sampling the flowstream. The present invention also provides a system for monitoring oil entrained in water wherein oil may be added to clarified or clear water to calibrate the system from time to time. 
     Further in accordance with the present invention, a system or apparatus is provided for monitoring oil entrained in water wherein the dispersement of the oil within the water flow steam is enhanced to improve the accuracy of the measuring process and a measuring chamber is provided with an improved arrangement of means for introducing the water flowstream into the chamber in a way in which errors in the operation of the light attenuation measuring system are substantially eliminated. 
     Still further in accordance with the present invention, there are provided improved methods for measuring the oil concentration in a water flowstream and the light absorption coefficient of the specific type of oil being measured. Still further, the mean particle radius of the oil droplets or particles in the water flowstream may also be determined from the measurements taken by the monitoring system. 
    
    
     Those skilled in the art will recognize the above described features and advantages of the present invention as well as other superior aspects thereof upon reading the detailed description which follows in conjunction with the drawing. 
     BRIEF DESCRIPTION OF THE DRAWING 
     The drawing FIGURE is a schematic diagram of a system for monitoring one liquid in another, such as oil entrained in water, in accordance with the present invention. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     In the description which follows like parts are marked throughout the specification and drawing with the same reference numerals, respectively. The drawing FIGURE is in schematic form with conventional elements being shown for the most part by standard graphic symbols for such elements. 
     Referring to the drawing FIGURE, the system for monitoring the relative amount of oil entrained in water is generally designated by the numeral 10 and is adapted to continuously or intermittently sample liquid being conducted through a pipeline 12 for example. The system 10 includes a centrifugal pump 14 which is adapted to have its inlet conduit 16 connected to the pipeline 12 for withdrawing a sample of water therefrom or, alternatively, to a source of clarified or clear water by way of a valve 18. The valve 18 may be motor operated with a timer control so that at periodic intervals the pump 14 draws water from a clarified water tank 20 or from a source wherein the water has been clarified to the point of being clear by way of a positive displacement pump 22. A selector valve 24 is interposed in a conduit 26 for selectively placing the pump 14 in communication with the clarified water tank 20 or the pump 22. 
     In certain applications of the system 10, the water or other liquid being monitored for the quantity of oil or similar contaminant entrained therein may have other contaminants which are not to be considered for monitoring. In a system for monitoring the amount of oil entrained in water a sample of liquid is withdrawn from the pipeline 12 through a conduit 30 and allowed to settle in the tank 20 so that oil will rise to the tank collection dome 21 and somewhat clarified water may be withdrawn from the tank 20 through the conduit 26 which opens into the tank 20 at a bottom inlet conduit portion 27. In this way, as will be explained in further detail herein, clarified water may be measured by the apparatus 10 as a baseline measurement to compare the clarified water with that in which various amounts of oil may be entrained. 
     The pump 14 includes an outlet or discharge conduit portion 15 in which a throttling orifice 17 is interposed to increase the pressure and velocity of the liquid being discharged from the pump to a discharge conduit 32. The discharge conduit 32 is connected to two branch conduits 34 and 36 which open into a chamber 38 formed by a cylindrical sampling enclosure 40. The enclosure 40 is adapted to have light transmitting members or windows 42 and 44 disposed at opposite ends of the chamber 38. The enclosure 40 also has a fluid discharge conduit 46 which opens from the chamber 38 to the pipeline 12. The conduits 34 and 36 are each provided with a jet nozzle 48 disposed to eject a fluid stream on the interior surfaces 43 and 45 of the windows 42 and 44, respectively. A photoresistor 50 is adapted to be disposed directly adjacent to or on the window 44 and is in circuit with a fixed resistance 51, an electrical source 52 and a voltmeter and recorder 54. The voltmeter and recorder 54 is suitably connected to a central processing unit 56 for a purpose to be described in further detail herein. A light source 58 is disposed adjacent to the window 42 for directing a beam of light through the window 42, the chamber 38 and the window 44 to impact on the photoresistor 50. 
     The apparatus or system 10 is further provided with means for adding a predetermined quantity of oil or similar contaminant to the water or liquid flowstream entering the pump 14. A container 62 is arranged to have a discharge conduit 64 connected thereto and in circuit with a control valve 66 and a liquid droplet counter 68. A discharge conduit 70, leading from the droplet counter 68, is suitably connected to the pump inlet conduit 16 for adding a predetermined and measured quantity of oil or other liquid contaminant to the pump inlet flowstream. The vessel 62 is also in communication with the pump discharge conduit 32 by way of a branch conduit 72 which opens into the bottom portion of the interior chamber 74 of the vessel and which forms a source of pressure for forcing liquid in the chamber 74 through the conduit 64 and the droplet counter 68. The pressure differential across the pump 14 is sufficient to provide for circulation of oil stored in the chamber 74 to be metered into the conduit 16 so that controlled calibration of the photo sensitive element 50 may be carried out. 
     The operation of the system 10 may be conducted on a continuous or intermittent basis. Liquid may be continuously withdrawn from the pipeline 12 and conducted through the conduit 16 to the pump 14. The restricted flow through the pump 14 provided, in part, by the orifice 17 assures that the oil entrained in the water or added to the water is thoroughly dispersed due to the shearing action caused by the pump impeller. The oil-water mixture discharged from the pump 14 through the conduit 32 is ejected by the nozzles 48 directly on the light transmitting windows 42 and 44 to keep these windows clear by preventing the accumulation of any debris or oil film. Liquid is conducted back to the pipeline 12 through the conduit 46. Continuous readings of the voltage resulting from the change in resistance of the photoresistor 50 may be monitored by the voltmeter and recorder 54 and the concentration of oil in the water may be computed by the central processing unit 56 by solving one or more of the equations given hereinbelow. 
     When it is desired to calibrate the apparatus 10, the source of liquid to the pump inlet 16 may be switched to the pump 22, if clear water is to be used as the calibration basis, or, in the event that other contaminants are present in the water, the presence of which is not desired to be monitored, a quantity of water may be stored in the vessel 20 to allow the oil to separate so that so-called clarified water is retained in residence in the vessel interior chamber 23. Water may be withdrawn from the chamber 23 by way of the conduit 26, the valve 24 and the valve 18 to the pump inlet 16 during periods when the so-called baseline or reference liquid clarity is being determined. By making the vessel 20 of sufficient size that the contents are allowed to settle and the liquid become clarified substantially all of the oil may rise to the oil storage dome 21. This oil may be conducted to the vessel 62, for example, for use in further calibrating the system 10 by injecting predetermined quantities of oil into the pump inlet 16. 
     Light transmission through the chamber 38 obeys Beer&#39;s Law: 
     
         I/I.sub.o =e.sup.-ACX                                      (1) 
    
     Where A is the specific cross section of light absorbing or scattering particles in the liquid in centimeters squared per gram; C is the weight concentration of particles in the liquid in grams per centimeters cubed; and X is the path length of the light beam in centimeters. I/I o  is the ratio of light intensity with the sample fluid being tested in the chamber 38 to the light intensity with clear or clarified water in the chamber 38. I/I o  is the same as R o  /R, since the resistance of the photoresistor 50 is inversely proportional to light intensity. In a circuit where the photoresistor 50 is connected in series to the source 52 of fixed voltage E and fixed resistance 51, the ratio R o  /R can be calculated from the voltage signal S measured with the sample fluid and the voltage signal S o  measured with clear or clarified liquid as follows: 
     
         R.sub.o /R=S.sub.o (E-S)/S(E-S.sub.o)                      (2) 
    
     If the oil weight concentration C is known, the specific cross section, or also known as absorption coefficient, A applicable to the specific type of oil used may be found as follows: 
     
         A=-1n(R.sub.o /R)/CX                                       (3) 
    
     If the absorbing particles are black then the specific cross sectional area A can be used to find the mean particle radius r: 
     
         r=3/4Ad                                                    (4) 
    
     where d is particle density. 
     For operation of the system 10 to determine the specific cross section or absorption coefficient A of a particular type of oil or oil mixture, the oil may be added to the flowstream entering the chamber 38 by way of the droplet counter 68 and the pump 14. Knowing the flow rate of liquid from a source of clarified liquid or clear liquid as hereinbefore described, oil may be added at a particular rate so that its concentration in the flowstream is known and the resistance for the clarified or clear liquid R o  and the resistance R for the known concentration C of oil determined from equation (2). The path length of light, X, passing through the chamber 38 may be measured and thus the above recited equation (3) solved to determine the absorption coefficient A. Since the action of the pump 14 to shear the oil droplets may have some effect on the absorption coefficient A, the pump should be operated at a constant speed during determination of this parameter. 
     In the system 10 it is desired to measure the oil concentration by comparing the voltage measured by the voltmeter and recorder 54 with the voltage measured based on a clear or clarified liquid sample which is free of oil. Accordingly, the concentration of oil C may be derived from the equation: ##EQU1## 
     Where S and S o  are the voltage signals measured for the liquid sample and the baseline or reference liquid sample such as clear or clarified water, respectively. This equation can be solved by the central processing unit 56 to give more or less continuous readings of the concentration of oil or a similar contaminant in a water or similar liquid being measured by the system 10. 
     In a preferred mode of operation of the system 10 the pump 14 may be adapted to draw a sample directly from the pipeline 12 on a continuous basis. Periodically, perhaps five minutes per hour, the valve 18 may be moved to draw a clear or clarified liquid sample from either the source 22 or the vessel 20, respectively. If clarified water is withdrawn from the chamber 23, the system will measure the concentration of suspended oil which is separated from the water by a period of clarification permitted by storage of water in the chamber 23. Oil present as a true solution and other contaminants would not be measured. Separated oil collected in the chamber 23 could be conveyed to the vessel 62 and periodically oil could be reintroduced into the pump inlet through the droplet counter 68 to provide an accurate measure of the oil light absorption coefficient. The automatic baseline determination plus calibration using separated oil should provide an accurate measurement of the concentration of the suspended oil phase in water being conducted through the pipeline 12. 
     Although a preferred embodiment of the invention has been described in detail, those skilled in the art will recognize that various substitutions and modifications may be made to the embodiment described without departing from the scope and spirit of the invention as recited in the appended claims.