Abstract:
An automatic control method for the filling of multiple tanks is provided. A controllable valve is coupled to a liquid supply source so that liquid dispensed therefrom must pass through the valve when the tanks are being filled. A variety of conditions/states are monitored and averaged. The averaged conditions/states are evaluated to determine if a valve movement is warranted. If so, the valve is moved by a specified increment. Following each occurrence of a valve movement, a predetermined wait or delay time is implemented before further control processing takes place. The steps of monitoring/averaging, valve movement, and waiting after a valve movement, are repeated until one of a number of events occurs. The occurrence of one of these events initiates a finalize filling process that fully closes the valve in accordance with a series of discrete movements thereof carried out over a specified time period.

Description:
ORIGIN OF THE INVENTION 
     The invention described herein was made in the performance of official duties by employees of the Department of the Navy and may be manufactured, used, licensed by or for the Government for any governmental purpose without payment of any royalties thereon. 
    
    
     FIELD OF THE INVENTION 
     The invention relates generally to the filling of multiple tanks with a liquid, and more particularly to an automatic control method that governs the filling of multiple tanks with a liquid. 
     BACKGROUND OF THE INVENTION 
     Filling or re-filling a ship&#39;s fuel tanks is a process that can take place in port or at sea. In either case, the process of pumping a supply of fuel into the ship&#39;s fuel tanks requires personnel to monitor a variety of flow rate, pressure and tank level sensors. The sensor outputs must then be evaluated and fuel flow rates must be adjusted in order to quickly and safely fill the fuel tanks without any unwanted pressure build-up and/or fuel overflow that results when fuel is pumped even after the fuel tanks have been filled to capacity. It is sometimes more difficult at sea to quickly and safely fill fuel tanks because sea state conditions can have an intermittent impact on tank levels. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide a method of automatically controlling the filling of multiple tanks with a liquid. 
     Another object of the present invention is to provide a method of automatically controlling the filling of a ship&#39;s fuel tanks. 
     Other objects and advantages of the present invention will become more obvious hereinafter in the specification and drawings. 
     In accordance with the present invention, a method is provided to automatically control the filling of a plurality of tanks with a liquid from a supply source. The tanks are equipped with an overflow sensing capability that detects an overflow condition indicative of the tanks being filled to capacity. A controllable valve is coupled to the supply source so that liquid dispensed therefrom must pass through the valve when the tanks are being filled. The valve has an increment associated therewith that defines how much the valve can be opened and closed when liquid is being dispensed therethrough. To start the filling process, the valve is opened to an initial position that defines a flow rate therethrough that falls within a prescribed range of acceptable flow rates. The liquid is then dispensed from the supply source through the controllable valve in its initial position. Each of (i) a flow rate of the liquid being dispensed, (ii) a level of the liquid in each of the tanks, and (iii) a state of the overflow sensor(s), is monitored and averaged over an amount of time. As a result, a corresponding (i) average flow rate, (ii) average level, and (iii) average state are defined. The valve is moved by its associated increment when the average flow rate is outside the range of acceptable flow rates. Specifically, the valve is closed by an amount equal to the increment when the average flow rate is greater than the range, and the valve is opened by an amount equal to the increment when the average flow rate is less than the range. Following each occurrence of a valve movement, a predetermined wait or delay time is implemented before further control processing takes place. The steps of monitoring/averaging, valve movement, and waiting after a valve movement, are repeated until one of a number of events occurs. A finalize filling process is initiated when one of these events occurs. These events include: (i) the average level being equal to a predetermined percentage of the capacity of the tanks, and (ii) the average state indicating the prescribed overflow condition. The finalize filling process fully closes the valve in accordance with a series of discrete movements thereof carried out over a specified time period. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects, features and advantages of the present invention will become apparent upon reference to the following description of the preferred embodiments and to the drawings, wherein corresponding reference characters indicate corresponding parts throughout the several views of the drawings and wherein: 
     FIG. 1 is a schematic view of a seawater-compensated fuel tank system that is to be automatically filled with fuel in accordance with the present invention; 
     FIG. 2 is a schematic view of a non-compensated fuel tank system that is to be automatically filled with fuel in accordance with the present invention; and 
     FIGS. 3A-3C are a flow diagram of the present invention&#39;s method for automatically controlling the filling of multiple tanks such as serially-connected tanks in a seawater-compensated fuel tank system. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings, and more particularly to FIGS. 1 and 2, two types of multiple-tank storage systems are illustrated. By way of example, both storage systems will be described herein as they relate to fuel storage systems used onboard a ship. However, it is to be understood that the method of the present invention can be used with either of the multiple-tank storage systems shown regardless of the liquid being supplied thereto. 
     FIG. 1 illustrates a seawater-compensated fuel storage system in which a plurality of tanks  10 ,  12  and  14  are coupled together in a serial fashion such that the tanks are filled successively. More or fewer tanks can be controlled by the method of the present invention. In the illustrated example, tanks  10 ,  12  and  14  are successively coupled to one another via conduits  16 A and  16 B. Coupled to the first tank (i.e., tank  10 ) via conduit  18  is a fuel supply  20 . Coupled to the last tank (i.e., tank  14 ) via conduit  22  is an expansion overflow reservoir or tank  24  which vents or empties via an orifice  24 A to a surrounding seawater environment. 
     It is well known in the art that each of tanks  10 ,  12  and  14  is filled with seawater prior to being filled with fuel from fuel supply  20 . As tank  10  fills with fuel from the top thereof, the seawater contained in tank  10  is forced out the bottom of the tank and through conduit  16 A (e.g., a sluice pipe) and into the top of tank  12 . In turn, seawater in tank  12  is forced out through conduit  16 B and into tank  14 . This, in turn, forces seawater in tank  14  out through conduit  22  and into overflow tank  24 . Accordingly, once tank  10  is filled with fuel as opposed to seawater, the continuous supply of fuel causes the subsequent and successive filling of tanks  12  and  14 . The pumping of fuel into tank  10  continues until fuel in tank  14  reaches a pre-designated level. One of the goals of the fueling process is to avoid overfilling the system with fuel such that fuel passes through orifice  24 A into the surrounding seawater environment. 
     In order for the above-described process to be carried out quickly, fuel is pumped using high flow rates. However, the use of high flow rates in combination with the closed (i.e., non-vented) nature of a seawater-compensation system means that pressure build-up in the tanks must be closely monitored to avoid a catastrophic event. 
     FIG. 2 illustrates a non-compensated fuel storage system in which a plurality of tanks (e.g., tanks  50 ,  52  and  54 ) are filled with fuel distributed thereto by a supply manifold  56  that receives fuel from a fuel supply  58 . An overflow reservoir in the form of a riser pipe  60  is coupled to supply manifold  56 . Riser pipe  60  fills with fuel and subsequently overflows (into an expansion overflow tank  62 ) once tanks  50 ,  52  and  54  are filled, or if the flow rate of fuel into manifold  56  exceeds the combined flow rate capacities of tanks  50 ,  52  and  54 . Each of tanks  50 ,  52  and  54  is vented to the atmosphere as indicated by arrows  50 A,  52 A and  54 A, respectively. Accordingly, the non-compensated system is not subject to the potential pressure problem associated with the above-described seawater-compensated system. However, the high flow rates used to fill tanks  50 ,  52  and  54  can quickly cause an overflow condition at riser pipe  60 . 
     The above-described problems associated with the filling of multiple-tank systems are addressed and eliminated by the method of the present invention. Automatic control provided by the present invention will be explained with reference to FIGS. 3A-3C which provides a flow diagram of the method as it relates to, for example, a seawater-compensated system such as that illustrated in FIG.  1 . To implement the method, an adjustable or controllable valve  100  is placed in-line with conduit  18  that directs fuel from fuel supply  20  to (first) tank  10 . Controllable valve  100  is any valve device that can be controlled in terms of how much it is opened/closed. A variety of such valve devices are well known in the art and the choice thereof is not a limitation of the present invention. 
     Each of tanks  10 ,  12 ,  14  and  24  has a tank level indicator (“TLI”)  102  mounted therein to detect the level of fuel in each tank. One of tanks  10 ,  12  and  14  (e.g., tank  10  in FIG. 1) has a pressure sensor (“PS”)  104  mounted therein to detect pressure in the tank. Because of the closed nature of a seawater-compensated tank group system, the pressure detected in any one tank is indicative of pressure anywhere in the seawater-compensated system. An overflow system (“OS”)  106  is mounted in overflow tank  24  to detect an overflow condition, i.e., tanks  10 ,  12  and  14  are filled to capacity with fuel. For the seawater-compensated system, fuel will begin to flow into overflow tank  24  when tanks  10 ,  12  and  14  are filled. Accordingly, overflow sensor  106  can be realized by any sensing device (e.g., a float switch) that detects the presence of fuel in overflow tank  24 . 
     The flow rate of fuel going through the seawater-compensated system can be measured anywhere therein. For example, a flow meter (“FM”)  108  can be coupled to orifice  24 A so that flow therefrom passes by or through flow meter  108 . A flow meter coupled to orifice  24 A will measure seawater bieng discharged overboard as a means of measuring the fuel that enters the tank group. This approach is successful because the quantity of seawater discharged equals the quantitiy of fuel supplied to the tank group. Note that this placement of flow meter  108  may prove to be the most convenient since orifice  24 A will normally be located at or near the ship&#39;s hull. The outputs of tank level indicators  102 , pressure sensor  104 , overflow sensor  106  and flow meter  108  are provided to a processor  110 . 
     Processor  110  controls implementation of the method illustrated in FIGS. 3A-3C. At step  200 , a variety of parameters are defined for use in implementing the automatic control process. These parameters can be predetermined (i.e., pre-programmed in processor  110 ) or can be user-supplied/changed without departing from the scope of the present invention. Briefly, the parameters include: 
     (a) valve movement and settling delay times which are used to delay further processing after each valve movement, 
     (b) a valve open/close increment that defines how much controllable valve  100  can be adjusted at any one time during the filling of the tanks, 
     (c) constraints on an averaging process used by the method, 
     (d) a range or window of flow rate values that are acceptable for the filling of tanks  10 ,  12  and  14 , 
     (e) the volume that each of tanks  10 ,  12  and  14  can hold, and 
     (f) the constraints governing the closing of controllable valve  100  when the tanks are almost filled. 
     Initial readings of tank level indicators  102 , overflow sensor  106  and flow meter  108  are taken at step  202 , followed by the opening of controllable valve  100  (step  204 ) to its initial position which should define a flow rate therethrough falling within the flow rate window defined in step  200 . Step  206  starts the filling process as fuel from supply  20  is pumped through controllable valve  100 . The position of controllable valve  100  as well as the outputs of tank level indicators  102 , pressure sensor  104 , overflow sensor  106  and flow meter  108  are monitored (step  208 ) and are provided to processor  110 . Processor  110  accumulates (i.e., averages) this data at step  210  for a period of time defined by the averaging constraints provided thereto. By averaging the data, the effects of data “peaks” and “valleys” associated with changing sea state, signal dropout, etc., are minimized. The time period for averaging as well as the data sampling rate over this time period are application specific and are not limitations of the present invention. 
     The average flow rate from the set of averaged data is first evaluated at step  212 . If the average flow rate is within the defined flow rate window, controllable valve  100  is not adjusted and processing continues with step  214 . However, if the average flow rate is outside (i.e., above or below) the defined flow rate window, a valve open/close sequence is performed at step  216 . Specifically, at step  216 A, processor  110  issues an instruction to controllable valve  100  to open (if the average flow rate is less than the defined window) or close (if the average flow rate is greater than the defined window) an amount equal to the previously-defined valve open/close increment. Following the issuance of this control instruction, further processing is delayed by the combination of the valve movement delay time (step  216 B) and the settling delay time (step  216 C). The valve movement delay time is the amount of time required for controllable valve  100  to move an amount equal to the previously-defined valve open/close increment. This delay time is specific for the particular controllable valve  100 . The settling delay time represents the amount of time needed for the various monitored parameters to settle out after a movement of controllable valve  100 . Settling delay time is predicated on a variety of factors such as the number of tanks being filled and the location of flow meter  108  relative to controllable valve  100  (i.e., the farther apart they are, the greater the settling delay time). Accordingly, the settling delay time may be an adaptive parameter. 
     At the completion of step  216  (or if the average flow rate is within the acceptable flow rate window), step  214  evaluates the fill status of tanks  10 ,  12  and  14  by evaluating the fill status of the last tank, i.e., tank  14 . Specifically, the averaged outputs of tank level indicator  102  in tank  14  is checked to see if it indicates that the tank is almost fully filled with fuel, i.e., whether the average fuel level in the tank has achieved a certain percentage (e.g., 85%, 90%, etc.) of full capacity. If this percentage has not been achieved, processing continues to step  218  (FIG.  3 C). However, if the percentage has been achieved, a close process  220  is implemented. In general, close process  220  involves a stepwise or incremental closing of controllable valve  100  based on the amount that controllable valve  100  is opened at the start of close process  220 . More specifically, the initially-defined close process constraints are used at step  220 A to generate the closing increment and then close valve  100  by an amount equal to this increment. The closing increment could be determined based on a set number of closing increments, incremental flow volume reductions, or a combination thereof. Following the movement of controllable valve  100  in accordance with the closing increment, processing is delayed by the combination of valve movement delay time (step  220 B) and settling delay time (step  220 C). The position of controllable valve  100  is then evaluated at step  220 D. If control valve  100  is not fully closed, steps  220 A- 220 C are repeated. If controllable valve  100  is fully closed, automatic control of the filling process is complete. 
     As mentioned above, processing continues from step  214  to step  218  if the average level in the tank  14  has not reached its prescribed “near capacity percentage”. Since this means that the filling of tanks is continuing, step  218  evaluates the reading from pressure sensor  104 . If the pressure reading is below a given pressure threshold, processing continues with step  222 . However, if the pressure reading is above the pressure threshold, the present invention reduces the flow through controllable valve  100  by implementing the previously-described (step  216 ) valve open/close sequence at step  224 . 
     Step  222  involves evaluating the average of the readings provided by overflow sensor  106 . The type of readings provided by overflow sensor  106  are not a limitation of the present invention. For example, overflow sensor  106  could be a float switch activated when fuel (which is lighter than water) is present in overflow tank  24 . However, it is to be understood that overflow sensor  106  could be any type of sensing device used to detect when there is the presence and/or a specified amount of fuel in overflow tank  24 . If the average readings from overflow sensor  106  indicate the presence of fuel in overflow tank  24 , the present invention initiates the previously-described (step  220 ) close process at step  226 , the completion of which ends the filling process. However, if the average readings from the overflow sensor  106  are acceptable, processing continues with step  228  where the average tank levels and position of controllable valve  100  are evaluated. If tank  14  is full and controllable valve  100  is closed, the filling process is ended. If this condition is not met, processing returns to step  210  where data is again averaged and then evaluated as described above. 
     The same process steps can be applied to the filling of a non-compensated fuel tank system such as that shown in FIG.  2 . Accordingly, this system is shown with: 
     (i) controllable valve  100  in line between fuel supply  58  and manifold  56 , 
     (ii) tank level indicators  102  in each of tanks  50 ,  52  and  54 , and in expansion overflow tank  62 , 
     (iii) overflow sensor  106  coupled to riser pipe  60  for detecting the presence/amount of fuel therein, and 
     (iv) flow meter  108  in line between controllable valve  100  and supply manifold  56 . 
     Note that since this is a vented system, traditional pressure sensing is not required thereby eliminating the need for steps  218  and  224 . However, a pressure sensor (not shown) can be included at the bottom of riser pipe  60  to measure the static head of any fuel contained in riser pipe  60 . Knowledge of pressure at this point in riser pipe  60  can be of value since their is a linear correlation between the static head pressure and fluid level in the riser pipe. Thus, pressure sensing at this point in riser pipe  60  provides a redundant system with respect to sensing any overflow in manifold  56 . 
     The advantages of the present invention are numerous. Efficient and safe filling of multiple tanks from a supply is controlled automatically by the present invention. In terms of filling a ship&#39;s tanks with fuel, the present invention eliminates problems associated with operator error and operator delay. 
     Although the invention has been described relative to a specific embodiment thereof, there are numerous variations and modifications that will be readily apparent to those skilled in the art in light of the above teachings. It is therefore to be understood that, within the scope of the appended claims, the invention may be practiced other than as specifically described.