Patent Grant
7488141
None.
Not applicable.
Not applicable.
The present disclosure is directed to automated control methods for transferring dry bulk materials. More particularly, but not by way of limitation, the present disclosure is directed to automated control methods for fluidizing dry bulk materials and efficiently transferring measured quantities of the dry bulk materials between tanks in a cement blending plant.
Transferring dry bulk materials efficiently from one location to another in measured quantities is challenging. For efficiency purposes, it is desirable to transfer dry bulk materials rapidly, which may be promoted by fluidizing the materials using air (e.g. aerating) or another type of gas such as nitrogen, for example, prior to and during transfer. However, proper fluidization requires consideration of several factors. For example, recently fluidized materials do not benefit from adding more air or gas, and hence plant resources and time are wasted when such materials are unnecessarily fluidized. In addition, over-fluidization can degrade materials, for example, by introducing too much moisture. Further, the rapid transfer of materials can also create plugs in transfer lines between tanks, thereby reducing material transfer rates. Accordingly, proper fluidization to promote rapid material transfer requires customization based on the material type, how recently the material was fluidized, the characteristics of the transfer line, and other factors.
Transferring measured quantities of dry bulk materials is also challenging due to the difficulty in determining how much material is present within a transfer line at any point in time. In particular, dry bulk material may not be uniformly distributed within a fluidized stream, and therefore, it is difficult to predict exactly how much dry bulk material is contained within the transfer line. Therefore, to obtain a measured weight of dry bulk material within a scale tank, the inefficient process of “dribbling” is employed. Specifically, after most of the dry bulk material has been measured into the scale tank, incremental amounts of the material are moved from the storage tank into the transfer line and then purged into the scale tank. This process is repeated until the desired weight of material is achieved.
Thus, in practice, because several factors must be balanced to transfer dry bulk materials in measured quantities, a conventional cement plant is often manually operated by experienced personnel who transfer dry bulk materials based on intuition and judgment. However, optimum efficiency is still not achieved. Therefore, a need exists for automated control methods for efficiently transferring dry bulk materials in measured quantities.
Disclosed herein is a method for blending dry material in a plant, comprising automatically controlling fluidization of the dry material, transfer of the dry material, or both. In an embodiment, the automatically controlling comprises optimizing an amount of time that the dry material is fluidized prior to transfer. In an embodiment, the automatically controlling comprises optimizing the transfer rate of the dry material. In an embodiment, optimizing the transfer rate of the dry material comprises modulating a quantity of gas injected into the dry material during transfer. In an embodiment, the modulating comprises continually adjusting the quantity of gas injected. In an embodiment, when a maximum transfer rate of the dry material is obtained, the modulating ceases until the maximum transfer rate falls below a setpoint material transfer rate. In an embodiment, when the maximum transfer rate of the dry material is obtained, the modulating comprises finely adjusting the quantity of the gas injected. In an embodiment, the automatically controlling comprises detecting a developing plug of the dry material during transfer. In an embodiment, the detecting a developing plug comprises measuring an increase in a vacuum pressure and a decrease in a transfer rate of the dry material. In an embodiment, the automatically controlling comprises eliminating the developing plug. In an embodiment, the automatically controlling comprises eliminating the developing plug via modulating a quantity of gas injected into the dry material during transfer. In an embodiment, the automatically controlling comprises estimating the weight of the dry material in a transfer line. In an embodiment, the estimating comprises averaging a plurality of measured weights of the dry material in the transfer line over time. In an embodiment, the estimating comprises averaging a measured weight of the dry material in the transfer line with an expected weight of the dry material in the transfer line. In an embodiment, the automatically controlling comprises minimizing dribbling during transfer of the dry material. In an embodiment, the minimizing dribbling comprises limiting dribbling to transfer of a final portion of the dry material.
These and other features and advantages will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings and claims.
For a more complete understanding of the present disclosure and the advantages thereof, reference is now made to the following brief description, taken in connection with the accompanying drawings and detailed description, wherein like reference numerals represent like parts.
a is a flow chart of one embodiment of a method for modulating the pneumatic valve of
b is a flow chart of another embodiment of a method for modulating the pneumatic valve of
c is a flow chart of yet another embodiment of a method for modulating the pneumatic valve of
a and 9b are complementary portions of a flow chart of one embodiment of a method for reducing the overall time associated with blending a composition of dry bulk materials.
It should be understood at the outset that although embodiments of an automated control system for transferring dry bulk materials in a cement plant are described and illustrated below, the control system may be implemented in alternative environments and using any number of techniques, whether or not currently known or in existence. One of ordinary skill in the art will readily understand that the present disclosure is not limited to the drawings and techniques, nor to the design and implementation, illustrated and described herein.
The various tanks 12, 14, 16, 18, 20, 22, 24; the pneumatic source 26; and the vacuum/suction source 60 are interconnected in fluid communication via transfer lines. In particular, as shown in
Referring again to
The base material tank 12 and the additive tanks 14 may be collectively referred to in some contexts herein as “bulk tanks,” and the dry materials contained by the bulk tanks may be collectively referred to as “bulk materials.” The base tank 12 may contain cement, for example, or another base material. The additive tanks 14 may contain sand, silica flour, bentonite, or salt, for example, or other additive materials. Typically, each additive tank 14 contains a single unblended additive material. The sacked additive hopper 16 is operable to receive smaller quantities of additives, such as 50 lb or 100 lb bags, for example. The number and size of bulk tanks 12, 14 and sacked additive hoppers 16 may be selected based upon the number and types of components to be blended.
The scale tank 18 is associated with a scale that measures the contents of the scale tank 18 as material is transferred from the bulk tanks or the sacked additive hopper 16. In an embodiment, the scale tank 18 employs an electronic scale. The scale tank 18 may also be employed to measure the weight of waste materials, such as, for example, leftover unused portions of a blend of bulk materials, before transferring the waste materials to the waste tank 24. In an embodiment each of the bulk tanks, for example the base material tank 12 and the additive material tanks 14, may employ an electronic scale which is used to measure the discharge of bulk material from the bulk tank.
To perform a material transfer via the system of
In more detail, pneumatic power, such as pressurized air or another gas, for example, may be supplied by the pneumatic source 26 to the bulk tanks for purposes of fluidizing the bulk materials in the base material tank 12 and the additive tanks 14 and/or providing positive pressure in such tanks prior to transferring the materials and during transfer of the materials to the scale tank 18. The pneumatic source 26 may also supply pneumatic power to the transfer lines for providing at least supplementary motive force to start the flow and/or aid in transferring the bulk materials and optionally one or more sacked additive materials to the scale tank 18. The pneumatic source 26 may also supply pneumatic power for purging the transfer lines when material flow from the base material tank 12, the additive tanks 14, and the sacked additive hopper 16 is stopped to clear the transfer line of the material.
In addition to the pneumatic power provided by the pneumatic source 26, vacuum or suction may be supplied by vacuum source 60 to create a pressure differential that induces a gas flow, such as an air flow, from the base material tank 12, the additive tanks 14, and/or the sacked additive hopper 16 to the scale tank 18, thus providing at least supplementary motive force to promote transfer of the bulk materials and the sacked additive materials. In an embodiment, the vacuum is applied at the destination tank, e.g., the scale tank 18, the blend tank 20, the storage/transport tank 22, the waste tank 24, or combinations thereof. The terms “vacuum” and “suction” refer to a pressure that is lower than an appropriate reference pressure, such as ambient atmospheric pressure. In an embodiment, one of the bulk tanks is non-pressurized and maintained at ambient atmospheric pressure. In an embodiment, the vacuum source 60 may be supplied by an air compressor, for example by connecting a vacuum line to the inlet of the air compressor.
In operation, bulk materials, and optionally sacked additive materials, are transferred to the scale tank 18 one at a time so that the incremental weight of each different material may be determined. Introduction of sacked additive materials may also be measured into the transfer line by weight using a separate small capacity scale, for example. In some embodiments, it may be desirable to achieve an accuracy of about plus or minus ten pounds when weighing materials for a blend.
In one example, a blend may weigh 50,000 pounds and may comprise, for example, 40,000 pounds of cement and 10,000 pounds of sand. A ⅓ portion of the total weight of cement may be transferred from the base material tank 12 to the scale tank 18, then a ½ portion of the total weight of sand may be transferred from an additive tank 14 to the scale tank 18, followed by the transfer of another ⅓ portion of the total weight of cement to the scale tank 18, then another ½ portion of the sand may be transferred to the scale tank 18, and finally the remaining ⅓ portion of the cement may be transferred to the scale tank 18. The weight of each of these portions may be calculated by the difference in the weight of the scale tank 18 before transferring the portion of the material and after transferring the portion of the material. Other blends may be produced, and these blends may be portioned into more layers and may comprise more than two bulk materials.
Layering the several materials according to the transfer operation described above promotes blending of the materials. To achieve an acceptably homogenous blend of base materials and additive materials, the materials may be repeatedly transferred from the scale tank 18 to the blend tank 20, and then from the blend tank 20 to the scale tank 18 several times. In an embodiment, the material is transferred at least four times to achieve an acceptably homogenous blend. In an embodiment, the system 10 may include additional blend tanks 20, and the succession of transfers to promote blending may take place between two or more blend tanks 20 rather than between the blend tank 20 and the scale tank 18. In an embodiment, transfers between two or more blend tanks 20 may occur at the same time that an independent blend is being transferred to the scale tank 18. In this case, multiple pneumatic sources 26 and multiple vacuum/suction sources 60 may be employed: one pneumatic source 26 and one vacuum/suction source 60 to promote transfer of the blend into the scale tank 18, and one pneumatic source 26 and one vacuum/suction source 60 to promote transfers between the two or more blend tanks 20.
Material transfer is controlled through the several transfer lines described above by opening and closing a plurality of valves in the network of transfer lines. Turning now to
The fill valve 102 may be opened to permit transfer of material into the tank 100 from a material source such as a truck or a railcar and may be closed to prevent transfer of material into the tank 100. The discharge valve 104 may be opened or closed to start or stop discharge of the material stored by the tank 100. The vent valve 106 may be opened to allow air to evacuate the tank 100 as material is introduced into the tank 100 through the fill valve 102, or to allow air to fill the tank 100 as material is discharged from the tank 100 through the discharge valve 104. The aeration valve 108 may be opened to permit air or another gas to be introduced into the tank 100 from the pneumatic source 26, for example, to fluidize or “fluff-up” the dry material stored in the tank 100 prior to and/or during material transfer. This process may be referred to as aerating the tank 100. The pneumatic valve 110, which may be referred to as a pneumatic control valve because it controls the delivery of pneumatic power from the pneumatic source 26, for example, may be opened to provide at least a portion of motive force to promote transfer of the material discharged from the tank 100 along the transfer line 112. The pneumatic valve 110 may also be opened to purge material from the transfer line 112 after discharge of material from the tank 100 is stopped.
Referring again to
To produce this particular cement blend, the cement may be transferred from the base material tank 12 to the scale tank 18 in approximately three 11,666.7 lbs portions, the bentonite may be transferred from the first additive tank 14a to the scale tank 18 in approximately two 5,000 lbs portions, and the salt may be transferred from the second additive tank 14b to the scale tank 18 in approximately two 2,500 lbs portions. To provide a layered composition in the scale tank 18, the first ⅓ portion of the cement is transferred first, the first ½ portion of the bentonite is transferred second, and the first ½ portion of the salt is transferred third. Then, the second ⅓ portion of the cement is transferred, followed by the remaining ½ portion of the bentonite, followed by the remaining ½ portion of the salt, and finally the remaining ⅓ portion of the cement. The layered composition may then be transferred between the scale tank 18 and the blend tank 20 a number of times, such as four transfers, for example, to produce a homogeneous blend. At this point, the cement composition has been blended according to the desired recipe, and the blended composition is ready to be transferred to the storage/transport tank 22 in a ready-to-use form. In one embodiment, for example, the storage/transport tank 22 may be a tank truck to transport the dry cement blend to a well bore location, where it will be mixed with water to produce cement slurry. The cement slurry may be pumped into the well bore to fill the annulus between a casing string and the well bore wall to cement the casing string in place.
When transferring materials to the scale tank 18, some bulk materials are more easily discharged from the bulk storage tanks, namely, the base material tank 12 and the additive tanks 14, if a given tank 12, 14 is first aerated to fluidize or fluff-up the material. In particular, the pneumatic source 26 is operated to blow a gas, such as air or nitrogen, into the tank 12, 14 and through the bulk material for a particular aeration time prior to discharging the material from the tank 12, 14 and transferring the material to the scale tank 18. The fluidization process is used to separate the particles of the material and make it flow more readily.
Referring to
It is preferable to aerate for only the minimum amount of time required to fluidize the bulk materials because excessive aeration slows the transfer and blending process, consumes resources unnecessarily, and may also degrade the bulk materials by introducing moisture, for example. Some bulk materials should not be aerated at all, such as salt, while other bulk materials require varying aeration times depending upon the material type, the length of time since it was last aerated, and other factors. Therefore, in one embodiment, the automated control system comprises a method for determining the proper aeration time for each bulk material for a desired product blend.
However, at block 300, if the material may be aerated, the method proceeds to block 304 where the length of time since the material was last aerated in that tank is determined. The method then proceeds to block 306 where the aeration time(t) is determined based on the length of time since the material was last aerated, the type of material, and properties of the system 10.
The properties of the system 10 which may be considered in determining aeration time for the bulk material include parameters associated with the tank 100, the transfer line 112, the gas supplied, and the bulk material. The parameters associated with the tank 100 may include the construction material; the diameter; the height; the discharge configuration such as the bottom cone angle, use of vibration, etc.; and the aeration inlet configuration of the tank 100. The parameters associated with the transfer line 112 may include the length of the transfer line 112, the diameter of the transfer line 112, and the construction material of the transfer line 112. The parameters associated with the gas supplied may include the type of gas, the gas flow rate, the maximum gas flow rate, the maximum gas pressure, the gas temperature, and the gas humidity. The parameters associated with the bulk material may include the angle of internal friction, the angle of repose, the angle of rupture, the angle of slide, the mean particle diameter, the particle size distribution, the particle density, the aerated density, the packed density, the in situ bulk density, the temperature, the surface moisture, and the time since last replenished.
Each time that a bulk material is scheduled to be discharged, such as, for example when a composition blend recipe has been entered into a blend control program, the software program determines the aeration time and controls the valves and pneumatic source 26 of the system 10 to cause the desired aeration to be provided to the bulk material in the tank. The software program monitors and records the amount of time since the material was replenished, as well as the amount of time since the bulk material in each bulk tank was last aerated. In addition, appropriate transducers associated with the bulk tanks provide the software program with data on a real-time, or near real-time basis, regarding the conditions of the bulk materials, such as, for example, the temperature and surface moisture of the material.
A variety of computer calculations may be employed to determine the aeration time for each subject material. In an embodiment, a look-up table for each material defining desirable aeration times at specific operating points may be employed wherein the software program linearly interpolates between the specified operating points to determine the aeration time.
In an embodiment, a software program implementing the flow chart of
In an embodiment, a series of IF-ELSIF statements may be executed to determine whether the parameters fall within a range of values to select a specific aeration time. The following pseudocode is an example of how IF-ELSIF statements may be employed to determine aeration times.
In this pseudocode the “lastCementAerationTime” and “lastBentoniteAerationTime” variables are expressed in hour time units while the “aerationTime” variable is expressed in minute time units. The intended effect of the switch block of pseudocode is to select a block of instructions for execution based on whether the value of the material variable is SALT, BENTONITE, or CEMENT. This pseudocode is only exemplary and may not provide good programming form or error handling. The genericization of the pseudocode to permit restructuring, for example to add additional setpoints for a specific material, is within the capabilities of one of ordinary skill in the art.
As an alternative to using discrete setpoints and corresponding aeration times via initialization, user input, or a look-up table, the aeration time may be mathematically calculated from the length of time since last aeration, for example via curve fitting (e.g., linear) or other mathematical equations, which may further incorporate one or more of the previously listed properties of the system 10 that may be considered in determining aeration time.
Once the aeration time is determined, then the method proceeds to block 308 where the material is aerated for the aeration time determined in block 306.
Once transfer of the bulk material is complete, the first discharge valve 104a is closed, and the first pneumatic valve 110a is at least partially opened or maintained open to purge the transfer line 112. Then, the first pneumatic valve 110a is closed, the pneumatic source 26 is deactivated, the vacuum source 60 is deactivated, and the first fill valve 102b is closed.
During material transfer, it is desirable to regulate pneumatic power to achieve a maximum material transfer rate of the bulk material from the representative tank 100 to the scale tank 18. At the same time, it is undesirable to use excessive pneumatic power because this unnecessarily consumes resources and may degrade the bulk materials, such as by exposing the bulk materials to moisture. Therefore, in one embodiment, the automated control system comprises a method to regulate the pneumatic power applied to the transfer line 112 via the pneumatic valve 110a so as to achieve the optimum material transfer rate of the bulk material.
The start transient is a time delay to allow for the material to flow into the transfer line 112 and is defined as the time between when the discharge valve 104a is opened and when modulation of the pneumatic valve 110a is begun. The duration of the start transient may be set as a specific length of time after the discharge valve 104a is opened. The length of time may vary depending upon the material and may be configurable from a user interface provided by the software program. Alternately, the duration of the start transient may be determined by detecting that the material flow has reached the scale tank 18, such as by measuring a weight change in the scale tank 18. In block 326, the method determines whether the start transient is complete or not. If the start transient is not complete, the method loops back to block 326. However, if the start transient is complete, the method proceeds to block 328 for modulation of the pneumatic control valve 110a to maintain a maximum transfer rate.
As the material moves into the transfer line 112, the position of the pneumatic valve 110a is adjusted to determine the optimum amount of gas to inject into the transfer line 112 to maximize the material transfer rate. To locate the position of the first pneumatic valve 110a associated with the optimum gas delivery, the first pneumatic valve 110a is first fully opened or fully closed, depending upon the material. In block 328, a determination is made regarding whether the modulation starts with the first pneumatic valve 110a being fully open for the material being transferred, and if so, the method proceeds to block 332 where the first pneumatic valve 110a is fully opened. Otherwise, the method proceeds to block 330 where the first pneumatic valve 110a is fully closed. The method then proceeds to block 334 where the position of the first pneumatic valve 110a is modulated to deliver more or less gas and thereby maximize the material transfer rate of the material. When the material transfer is complete, the method exits.
Turning now to
Next, the method proceeds to block 356 where an appropriate time delay is employed to allow the effect of the preceding position change of the first pneumatic valve 110a to produce a related change in the material transfer rate. The appropriate time delay may vary with the material transfer rate, the material type, the length and diameter of the transfer line 112, the increment of change of the position of the first pneumatic valve 110a, the resolution of the weight transducer 114, and other factors. One skilled in the art will readily determine the appropriate time delay. For example, assuming a material transfer rate of about 5,000 lbs/minute and a weight of bulk material in the transfer line (also referred to as “line weight”) of about 350 lbs, a single increment of change in the position of the first pneumatic valve 110a may produce a measurable change in the material transfer rate in about 5 seconds, which would suggest a time delay of greater than about 5 seconds, such as 6 seconds, for example. For other material transfer rates and other line weights, a different time delay may be required. In an embodiment, the time delay may be set to be slightly longer than the greatest lag between a change in position of the pneumatic valve 110a and a measurable change in the material transfer rate through any of the transfer lines 112 in the system 10.
The method then proceeds to block 358 where the material transfer rate of the bulk material through the transfer line 112 is measured. In block 360, a determination is made regarding whether the material transfer rate determined in block 358 decreased as compared to the material transfer rate determined in block 350, and if not, the method proceeds directly to block 364. Otherwise, if the material transfer rate determined in block 358 did decrease as compared to the material transfer rate determined in block 350, the method proceeds to block 362 where the direction of change in position of the pneumatic valve 110a is reversed. In particular, if the direction of change in the position of the pneumatic valve 110a was set to OPEN in block 352, the direction of change is set to CLOSE in block 362. However, if the direction of change in position of the pneumatic valve 110a was set to CLOSE in block 352, the direction of change is set to OPEN in block 362. The method then proceeds to block 364 to determine if the transfer of the bulk material is complete. If not, the method returns to block 354. Otherwise, when the material transfer is complete, the method exits.
By repeatedly performing the actions associated with blocks 354, 356, 358, 360, 362, and 364 the method continually repositions the first pneumatic valve 110a to maximize the material transfer rate of the bulk material by injecting more or less gas into the transfer line 112.
Turning now to
The method begins at step 370 where the material transfer rate of the bulk material through the transfer line 112 is measured and the direction of change of the pneumatic valve 110a is initialized as described with respect to
In block 372, if the material transfer rate measured in block 371 decreased as compared to the transfer rate measured in block 370, the method proceeds to block 374 where the pneumatic valve 110a is moved one position increment backwards. This is to return the valve 110a to the position in which the maximum material transfer rate was measured. In block 374 the prior measured material transfer rate is stored as the maximum material flow rate. Also, in block 374, an appropriate time delay is employed as described with respect to
The method proceeds to block 376 where a determination is made regarding whether the material transfer rate measured in block 375 is less than a setpoint material transfer rate, and if so, the method proceeds to block 377. The setpoint material transfer rate is related to and less than the maximum material transfer rate. In an embodiment, the setpoint material transfer rate may be proportional to the maximum material transfer rate, for example the setpoint material transfer rate may be 80 percent of the maximum material transfer rate. In another embodiment, the setpoint material transfer rate may be determined by a different calculation. In block 377, the direction of change of the pneumatic valve 110a is reversed, and the method proceeds to block 373 to determine if the material transfer is complete. If not, the method returns to block 371 and modulation of the pneumatic valve 110a resumes.
However, in block 376 if the material transfer rate is equal to or greater than the setpoint material transfer rate, the method proceeds to block 378 where the method employs a time delay appropriate for quickly responding to a declining material transfer rate. In an embodiment, the time delay of block 378 may be completely eliminated, and the method may continually measure the material transfer rate and compare it to the setpoint material transfer rate. The method proceeds to block 379 to determine if the material transfer is complete, and if so, the method exits. Otherwise, the method proceeds to block 375. By looping through blocks 375, 376, 378, and 379 the method stops repositioning the pneumatic valve 110a and monitors the material transfer rate to ensure that it remains substantially at or near the maximum material transfer rate. In block 379, when the material transfer is complete the method exits.
Turning now to
The method begins at block 384 where the material transfer rate of the bulk material through the transfer line 112 is measured and the direction of change of the pneumatic valve 110a is initialized as described with respect to
In block 387, the direction of change of the pneumatic valve 110a is reversed, the valve reposition increment is set to a small increment, and the next to the last measured material transfer rate is stored as the maximum material transfer rate. The method proceeds to block 388 where the pneumatic valve 110a is moved incrementally towards the open or closed position, depending upon the direction of change of the pneumatic valve 110a, and by an amount determined by the valve position increment. The method also employs an appropriate time delay, and the material transfer rate is measured as described above with respect to
The method proceeds to block 389 where a determination is made regarding whether the material transfer rate is equal to or greater than a setpoint material transfer rate, and if so, the method proceeds to block 390. In an embodiment, the setpoint material transfer rate may be proportional to the maximum material transfer rate, for example the setpoint material transfer rate may be 80 percent of the maximum material transfer rate. In another embodiment, the setpoint material transfer rate may be determined by a different calculation. In block 390, a determination is made regarding whether the transfer rate measured in block 388 decreased as compared to the transfer rate measured in block 385, and if so, the method proceeds to block 391 where the direction of change of the pneumatic valve 110a is reversed, and the method proceeds to block 392. Otherwise, in block 390, if the material transfer rate did not decrease, the method proceeds directly to block 392. In block 392, a determination is made regarding whether the material transfer is complete, and if so, the method exits. Otherwise, the method returns to block 388. By looping through blocks 388, 389, 390, 391, and 392 the method modulates the pneumatic valve 110a continuously using small increments. The small increments permit finer tuning of the position of the pneumatic valve 110a.
In block 389, if the material transfer rate is less than the setpoint material transfer rate, the method proceeds to block 393 where the valve reposition increment is set to the large increment and the direction of change of the pneumatic valve 110a is reversed. The method then proceeds to block 394 where a determination is made regarding whether the material transfer is complete, and if so, the process exits. Otherwise, the process returns to block 385. By looping through blocks 385, 386, 387, 388, 389, 393, and 394 the method modulates the position of the pneumatic valve 110a using large increments, and when a maximum material transfer rate is achieved, the process returns to the fine tuning modulation of blocks 390, 391, 392, 388, and 389.
During transfer of bulk material, the transfer line 112 may become blocked or plugged by the bulk material. Generally, this condition is identifiable based on a concurrent increase in the vacuum pressure of the scale tank 18 and a decrease in the material transfer rate of the bulk material. Therefore, in one embodiment, the automated control system comprises a method to detect the onset of a plug in the transfer line 112 and to take corrective action.
In particular,
Some dry bulk materials exhibit substantial variability in their transfer rates during normal transfer, as for example a material that clumps together to move as slugs through the transfer line 112. For such material transfers, it may be useful to employ a sliding window average of the material transfer rate rather than an instantaneous material transfer rate when calculating the transfer rate metric. A sliding window average is an average calculated over the last several data points, for example, the average of the present material transfer rate and the previous four material transfer rates. The appropriate first coefficient and second coefficient in block 395 and the appropriate plug detection limit in block 396 will be readily determined by one skilled in the art.
In block 396, if the sum of the vacuum metric and the transfer rate metric exceeds a plug detection limit, the method proceeds to block 397. The plug detection limit may be exceeded if the vacuum pressure increases and/or the material transfer rate decreases, for example, thereby indicating that a plug may be developing in the transfer line 112. At block 397, the first pneumatic valve 110a is fully opened. This causes the gas flow, such as pneumatic air flow, to increase in the transfer line 112, thereby blowing out the plug of bulk material and restoring normal bulk material flow. The method proceeds to block 398 where the method waits an appropriate period of time to allow the vacuum pressure in the scale tank 18 to decrease. One skilled in the art will readily determine the appropriate period of time to wait in block 398. The method then proceeds to block 399 where, if the vacuum pressure has decreased below the Vacuum Limit, the method exits, but if the vacuum pressure has not decreased below the Vacuum Limit, the method returns to block 398 and waits again.
In an embodiment, after the method of
When producing a blended composition of dry bulk materials, each portion is typically measured out carefully into the scale tank 18, such as the first ⅓ portion of cement weighing 11,666.7 lbs described in the example above. During a transfer operation for a single material, some of the bulk material remains in the transfer line 112 after the discharge valve 104 is closed. This residual bulk material in the transfer line 112 must be transferred to the scale tank 18, since generally the bulk materials cannot be left in the transfer line 112. To ensure that the weight of a single portion of material does not exceed the desired weight, the transfer of bulk material into the scale tank 18 is stopped before the target weight is achieved. Then, the pneumatic valve 110a is opened to flow gas into the transfer line 112 to purge the material into the scale tank 18, and the incremental weight of the portion of bulk material is examined to determine if the desired portion weight has been achieved. If not, the first discharge valve 104a is opened briefly, such as for one second, for example. Then the bulk material in the transfer line 112 is purged again, and the incremental weight of the portion of bulk material is examined. This process is repeated until the weight of the portion of bulk material in the scale tank 18 is correct. This process may be termed “dribbling” or “tip toeing” up to the target weight of the portion of bulk material.
The dribbling process, however, is time consuming. Therefore, in one embodiment, the automated control system comprises a method for estimating the weight of dry bulk material in the transfer line 112 to determine when to close the first discharge valve 104a and purge the transfer line 112 to obtain the desired portion weight in the scale tank 18. For example, if the cement remaining in the transfer line 112 on average weighs 350 lbs, then to achieve the target portion weight of 11,666.7 lbs, the first discharge valve 104a may be closed when the incremental weight of the portion in the scale tank 18 reaches 11,316.7 lbs. Then, when the transfer line 112 is purged to move the 350 lbs of remaining cement to the scale tank 18, the weight of the cement portion increases to the target weight of 11,666.7 lbs.
The weight of bulk material in the transfer line 112, however, varies with the type material, length and diameter of the line, quantity of the transfer gas used, and other factors. Therefore, in one embodiment, the automated control system comprises a method for estimating the weight of the bulk material remaining in the transfer line 112 after the first discharge valve 104a is closed. Using this method, nearly the exact desired weight of the portion of bulk material may be transferred without dribbling. Alternately, the target weight may be set for just slightly less than the desired portion weight, then the method may be employed to transfer the target weight, and minimal dribbling may be employed to achieve the desired weight of the portion of bulk material.
In block 400 an expected line weight for the subject bulk material is provided an initial value. This initial value may be coded into the software program or may be read from a file when bringing up the software program in new plants or when introducing new bulk materials into an existing bulk plant. The line weight of a material may depend upon the density of the material, the length and diameter of the transfer line between the subject bulk tank and the scale tank 18, the transfer characteristics of the subject bulk material, and other factors. The initial value of the expected line weight may be determined by a blend plant designer or a blend plant installation technician who is skilled in the art and may estimate an appropriate initial value for the expected line weight by means other than that described above. In general, the initial expected line weight should be greater than a maximum anticipated line weight, since underestimating the expected line weight may lead to transferring too much of the subject bulk material on the first several transfer operations. One way of determining the initial value of the expected line weight is to multiply a known density of the subject bulk material by a known volume of the transfer line 112 multiplied by 1.5, which provides some margin of error. As the method repeats over and over again, the software program compares the expected line weight to the actual line weight and adjusts the expected line weight accordingly. In this way, the estimated weight of the bulk material in the transfer line 112 converges on the actual weight of the bulk material in the transfer line 112.
The method proceeds to block 402 where a line weight of the subject material is measured. In particular, the first discharge valve 104a is opened and a material is transferred to the scale tank 18. Then the first discharge valve 104a is closed, and a first weight of the scale tank 18 is determined. Then the pneumatic valve 110a is opened, and after an appropriate time period that allows the bulk material in the transfer line 112 to be transferred into the scale tank 18 (i.e. material purge time), a second weight of the scale tank 18 is determined. The material purge time may depend upon the subject bulk material, the length and diameter of the transfer line 112, and other factors. The software program may read the material purge time from a configuration file to facilitate adjusting the material purge time based on experience gained in the field when bringing a new bulk plant into service or when introducing a new bulk material into the bulk plant operation. The material purge time may be determined in the field by observing the time period from the closing of the discharge valve 104a to weight stabilization of the scale tank 18. This procedure may be repeated several times to confirm any variation of range in the material purge time. The material purge time may also be determined by selecting the maximum observed purge time and multiplying the maximum observed purge time by 1.5 to provide a margin of error. Alternately, the material purge time may be determined by a blend plant designer or a blend plant installation technician who is skilled in the art.
In block 402, the line weight is determined as the difference between the first and the second weights of the scale tank 18. The method proceeds to block 404 where an updated expected line weight is calculated as the average of the measured line weight and the prior expected line weight. To accomplish this averaging, a count of averaging events and the sum of line weights may be retained in the memory of the software program.
In an alternative embodiment, the updated expected line weight step of block 404 may be the average of a plurality of the last several measured line weights, for example the last five line weights. This may be termed a sliding window average.
As previously mentioned, the process of dribbling the bulk material to achieve a desired portion weight is time consuming. Therefore, in one embodiment, the automated control system comprises a method of blending a composition of bulk materials to reduce the number of times the dribbling process is employed.
In particular,
The method proceeds to block 426 where a determination is made regarding whether this portion is the last portion of this material to be transferred. If so, the method proceeds to block A. Processing associated with block A is depicted in
The method of
The method of
In block 438, the next material to be transferred is selected. In the example outlined above, after the first portion of cement is transferred, one of the additive materials, such as bentonite, is transferred, and then the remaining additive material, salt, is transferred. For each material, the method loops through blocks 426, 430, 432, 434, 436, and 438 until the last portion or layer of each bulk material is to be transferred.
Returning again to block 426 of
The method proceeds to block 452 where the portion of the selected material is transferred to achieve the reduced target weight determined in block 450. During the transfer, the selected bulk material may be transferred using the method for regulating pneumatic power during bulk material transfer as described above with respect to
The method of
The method of
The above described methods for controlling dry bulk materials storage and blend plant operations are inter-related and may be employed in a single software program or a plurality of software programs commonly managed by a supervisory computer system. Various optimizations of the several automated control methods may thereby be obtained by cooperation among the methods which otherwise may not be readily achievable.
Several examples of the methods disclosed herein are described below.
In this example, dry materials in a blend plant are transferred using automated control methods. The automated control methods provide for fluidizing the dry materials, and optionally injecting a gas into the dry materials prior to transfer and/or during transfer. During transfer of a dry material, the automated control method may detect and remove a developing plug of the dry material by injecting the gas into the dry material. The automated control method may further transfer measured quantities of one or more different dry materials, and may estimate the weight of each dry material in a transfer line.
In this example, an automated control method fluidizes dry material in a blend plant system by injecting gas into the dry material. The automated control method may also comprise determining the duration of gas injection into the dry materials prior to transfer by determining the type of dry material, determining the amount of time since the gas was last injected into the dry material, optionally determining one or more properties of the blend plant system, and determining the duration of gas injection into the dry material prior to transfer based on the type of dry material, the amount of time since the gas was last injected into the dry material, and optionally the one or more properties of the blend plant system. The one or more properties of the blend plant system may comprise properties associated with a tank that stores the dry material, a transfer line for transferring the dry material, the gas injected, the dry material, or combinations thereof. The properties associated with the tank may comprise the construction material, the diameter, the height, the discharge configuration, the gas inlet, or combinations thereof. The properties associated with the transfer line may comprise the length, the diameter, the construction material, and combinations thereof. The properties associated with the gas injected may comprise the type of gas, the flow rate, the maximum flow rate, the maximum pressure, the temperature, the humidity, and combinations thereof. The properties associated with the dry material may comprise the angle of internal friction, the angle of repose, the angle of rupture, the angle of slide, the mean particle diameter, the particle size distribution, the particle density, the fluidized density, the packed density, the in situ bulk density, the temperature, the surface moisture, the time since last replenished, and combinations thereof. The duration of gas injection prior to transfer may be determined: (1) using a look-up table; (2) from user input; or (3) using computer code, as for example using a mathematical equation. The automated control method further comprises injecting the gas into the dry material for the determined duration prior to transfer.
In this example, an automated control method fluidizes a dry material in a blend plant system by injecting gas into the dry material during transfer. The automated control method may also comprise modulating the quantity of gas injection into the dry material during transfer to obtain a maximum transfer rate of the dry material.
In this special case of example 3, the modulation comprises continually adjusting the quantity of gas injection. The modulation may comprise: (1) initially maximizing or minimizing the gas injection based upon the type of dry material, (2) setting a direction of change of the gas injection to decrease the gas injection is initially maximized or to increase if the gas injection is initially minimized, (3) measuring a first transfer rate of the dry material through a transfer line, (4) increasing the gas injection or decreasing the gas injection according to the direction of change, (5) employing a time delay sufficient to detect a change in the first transfer rate, (6) measuring a second transfer rate of the dry material, and (7) comparing the second transfer rate to the first transfer rate until the second transfer rate is less than the first transfer rate or the transfer is complete. When the second transfer rate is less than the first transfer rate, the method may further comprise reversing the direction of change of the gas injection and repeating steps (1) through (7) above, not necessarily in the order presented, until the second transfer rate is again less than the first transfer rate, or the transfer is complete.
In this special case of example 3, the modulation may cease when a maximum transfer rate is achieved and not resume until the transfer rate falls below a setpoint material transfer rate. The modulation may comprise: (1) initially maximizing or minimizing the gas injection based upon the type of dry material, (2) setting a direction of change of the gas injection to decrease if the gas injection is initially maximized or to increase if the gas injection is initially minimized, (3) measuring a first transfer rate of the dry material through a transfer line, (4) increasing the gas injection or decreasing the gas injection according to the direction of change, (5) employing a time delay sufficient to detect a change in the first transfer rate, (6) measuring a second transfer rate of the dry material, and (7) comparing the second transfer rate to the first transfer rate until the second transfer rate is less than the first transfer rate or the transfer is complete. When the second transfer rate is less than the first transfer rate, the method may further comprise reversing the direction of change of the gas injection, increasing or decreasing the gas injection by one increment based on the direction of change, storing the first transfer rate as the maximum transfer rate, and modulation may then end. The method may thereafter include employing a time delay, monitoring an actual transfer rate of the dry material as compared to the setpoint material transfer rate until the actual transfer rate falls below the setpoint material transfer rate or the transfer is complete. If the actual transfer rate falls below the setpoint material transfer rate modulation resumes, the method further comprises reversing the direction of change of the gas injection, increasing or decreasing the gas injection based on the direction of change, and repeating steps (1) through (7) above, not necessarily in the order presented, until the second transfer rate is less than the first transfer rate or until the transfer is complete.
In this special case of example 3, when the maximum transfer rate of the dry material is obtained, modulating may comprise adjusting the quantity of the gas injection in small increments. The modulation may comprise: (1) initially maximizing or minimizing the gas injection based upon the type of dry material, (2) setting a direction of change of the gas injection to decrease if the gas injection is initially maximized or to increase if the gas injection is initially minimized, (3) setting an increment of change of the gas injection to large and wherein increasing the gas injection or decreasing the gas injection is performed according to the increment of change, (4) measuring a first transfer rate of the dry material through a transfer line, (5) increasing the gas injection or decreasing the gas injection according to the direction of change, (6) employing a time delay sufficient to detect a change in the first transfer rate, (7) measuring a second transfer rate of the dry material, and (8) comparing the second transfer rate to the first transfer rate until the second transfer rate is less than the first transfer rate or the transfer is complete. When the second transfer rate is less than the first transfer rate, the method may further comprise reversing the direction of change of the gas injection, resetting the increment of change of the gas injection to small, storing the first transfer rate as the maximum transfer rate, increasing or decreasing the gas injection according to the direction of change and the increment of change, employing a time delay, and monitoring an actual transfer rate of the dry material as compared to a setpoint material transfer rate. If the actual transfer rate of the dry material falls below the setpoint material transfer rate, the method may further comprise resetting the increment of change of the gas injection to large, reversing the direction of change of the gas injection, and repeating steps (1) through (8) above, not necessarily in the order presented, until the transfer is complete.
In this example, an automated control method comprises detecting and removing a developing plug of a dry material during transfer. The automated control method comprises establishing a vacuum limit for a vacuum pressure in a tank receiving the dry material during transfer, establishing a transfer rate limit for a transfer rate of the dry material, monitoring the vacuum pressure and the transfer rate of the dry material, calculating a vacuum metric based on the vacuum limit and the actual vacuum pressure, calculating a transfer rate metric based on the transfer rate limit and the actual transfer rate of the dry material, detecting the development of a plug when the sum of the vacuum metric and the transfer rate metric exceed a plug detection limit, and injecting a gas into the dry material sufficient to remove the developing plug. The actual transfer rate may be an instantaneous transfer rate or a sliding window average calculated using several instantaneous rates over time. The method may further comprise determining that the developing plug has been removed by confirming that the vacuum pressure falls below the vacuum limit.
In this example, an automated control method estimates the weight of the dry material in a transfer line in a bulk plant system. The automated control method comprises providing an initial expected line weight of dry material in a transfer line, transferring a portion of the dry material through the transfer line into a tank, measuring a first weight of the dry material within the tank, purging the remaining portion of the dry material out of the transfer line and into the tank, measuring a second weight of the dry material within the tank, calculating an actual line weight of the dry material in the transfer line based on the difference between the first weight and the second weight, and calculating an updated expected line weight of dry material in the transfer line. The updated expected line weight is based on the average of the initial expected line weight and the actual line weight or on the average of a plurality of several actual line weights.
In this example, an automated control method transfers measured quantities of at least two different dry materials in a bulk plant system. The automated control method comprises determining an overall desired weight for each dry material based upon a blend recipe, determining a number of portions (N) for each dry material based upon how the dry materials will be layered into a receiving tank, determining a target portion weight for each dry material based on the number of portions (N) and the overall desired weight, transferring N−1 portions of each dry material to the receiving tank comprising (a) transferring a portion of each dry material based on the target portion weight, (b) weighing the portions of each dry material in the receiving tank, (c) calculating the remaining weight of each dry material based on the difference between the overall desired weight and the weights of the portions of each dry material already transferred to the receiving tank, (d) recalculating the target portion weight for the remaining N−1 portions of each dry material based on the remaining weight, and (e) repeating steps (a) through (d). The method further comprises determining a reduced target portion weight for the last portion of each dry material based on the difference between the target portion weight and a fixed delta weight, transferring the last portion of each dry material based on the reduced target portion weight, weighing each last portion of each dry material in the receiving tank, calculating the final remaining weight of each dry material based on the difference between the overall desired weight and the weights of the portions of each dry material already transferred to the receiving tank, and dribbling the final remaining weight of each dry material into the receiving tank.
In this example, an automated control method for transferring dry materials in a blend plant comprises monitoring at least one parameter of a first dry material, optionally fluidizing the first dry material based on the at least one parameter, determining a first portion target weight of the first dry material based on a total target weight of the first dry material, modulating a delivery of pneumatic power to transfer the first dry material at a maximum transfer rate, increasing the pneumatic power to remove a plug of the first dry material while transferring the first dry material, estimating the weight of the first dry material in a transfer line while transferring the first dry material, using the estimated weight of the first dry material in the transfer line and a measured weight of the first dry material transferred into a second tank to stop the dispensing of the first dry material from a first tank, and determining a target weight of a second portion of the first dry material based on the difference between the total target weight of the first dry material and the measured weight of the first portion of the first dry material transferred into the second tank.
The method may further comprise transferring a first portion of a second dry material from a third tank into the second tank, transferring the second portion of the first dry material from the first tank to the second tank based on the target weight of the second portion of the first dry material, determining a target weight of a third portion of the first dry material based on the difference between the total weight of the first dry material and the measured weight of the first and second portions of the first dry material transferred to the second tank, transferring a second portion of the second dry material from the third tank to the second tank, and transferring the third portion of the first dry material from the first tank to the second tank based on the target weight of the third portion of the first dry material.
In this example, an automated control method for controlling the pneumatic system of a blend plant comprises setting an initial position of a pneumatic control valve based on a dry material, transferring the dry material using pneumatic power from a first tank over a transfer line to a second tank, measuring the transfer rate of the dry material, and repeatedly moving the pneumatic control valve a portion of the range of travel of the pneumatic control valve until the transfer rate of the dry material decreases. The method may further comprise delaying an interval of time between the repeatedly moving the pneumatic control valve, wherein the interval of time is determined based on the maximum transfer rate of the dry material and the capacity of the transfer line. The method may further comprise optionally fluidizing the dry material prior to transferring the dry material based on the dry material. The method may further comprise monitoring at least one parameter of the dry material and optionally fluidizing the dry material based at least in part on the at least one parameter. The method may further comprise detecting a plug developing in the transfer line and opening the pneumatic control valve when the plug is detected.
In this example, an automated control method for blending dry materials in a bulk plant comprises defining a target weight of a plurality of dry materials to be blended, determining a target first portion weight of a first dry material based on a target weight of the first dry material, conveying a first portion of the first dry material from a first tank to a second tank, determining a target first portion weight of a second dry material based on a target weight of the second dry material, conveying a first portion of the second dry material from a third tank to the second tank, determining a target second portion weight of the first dry material based on the target weight of the first dry material and an actual weight of the first portion of the first dry material transferred to the second tank, conveying a second portion of the first dry material from the first tank to the second tank, determining a target second portion weight of the second dry material based on the target weight of the second bulk material and an actual weight of the first portion of the second dry material transferred to the second tank, conveying a second portion of the second dry material from the third tank to the second tank, determining a target third portion weight of the first dry material based on the target weight of the first dry material and an actual weight of the first and second portions of the first dry material transferred to the second tank, and conveying a third portion of the first dry material from the first tank to the second tank. The method may further comprise determining an estimated line weight of the first dry material in a transfer line between the first tank and the second tank and employing the estimated line weight to measure out the first, second, and third portions of the dry material.
In this example, a system for controlling the transfer of dry materials in a blend plant comprises at least one storage tank equipped with a discharge valve, wherein each storage tank contains a dry material, at least one scale tank, at least one transfer line coupled between the at least one storage tank and the at least one scale tank, a gas injection system operably coupled to each storage tank and each transfer line, a vacuum system operably coupled to each scale tank, and an automated control system for controlling each discharge valve and the gas injection system to maximize a transfer rate of the dry materials from the at least one storage tank to the at least one scale tank. The automated control system may control the gas injection system to regulate the amount of gas injected into the at least one storage tank prior to transfer of the dry materials to the at least one scale tank. The gas injection system may further comprise a pneumatic valve controlled by the automated control system to regulate the amount of gas injected into the at least one transfer line during transfer of the dry materials to the at least one scale tank to maximize a transfer rate of the dry materials. The automated control system may estimate the weight of the dry material within the at least one transfer line during transfer of a dry material from the at least one storage tank to the at least one scale tank. The automated control system may determine when to close the discharge valve based on the estimated weight of dry material within the at least one transfer line and the weight of dry material within the scale tank.
While several embodiments have been provided in the present disclosure, it should be understood that the disclosed systems and methods may be embodied in many other specific forms without departing from the spirit or scope of the present disclosure. The present examples are to be considered as illustrative and not restrictive, and the intention is not to be limited to the details given herein. The methods may be modified within the scope of the appended claims along with their full scope of equivalents. For example, the various elements or components may be combined or integrated in another system or certain features may be omitted, or not implemented.
Also, techniques, systems, subsystems and methods described and illustrated in the various embodiments as discrete or separate may be combined or integrated with other systems, modules, techniques, or methods without departing from the scope of the present disclosure. Other items shown as directly coupled or communicating with each other may be coupled through some interface or device, such that the items may no longer be considered directly coupled to each other, but may still be indirectly coupled and in communication with one another. Other examples of changes, substitutions, and alterations are ascertainable by one skilled in the art and could be made without departing from the spirit and scope disclosed herein.
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