초록 ▼

Systems for controlling the in-feed and discharge rates of materials flowing into and out of a mixing process where one priority is to achieve a target mixture flow rate from the mixing process and another priority can be to achieve a target value for a mixture property. Actuators can be operated t

Systems for controlling the in-feed and discharge rates of materials flowing into and out of a mixing process where one priority is to achieve a target mixture flow rate from the mixing process and another priority can be to achieve a target value for a mixture property. Actuators can be operated to control material in-feed rates, the mixture composition, and discharge rate, and can maintain a hold-up of the mixture in the mixing process. A total flow rate controller provides a control signal to a controller acting on the discharge rate and a controller acting on the in-feed rates. The mixture discharge flow rate can be automatically reduced from its desired target when the commanded rate of at least one of the materials exceeds its available supply rate as inferred from an inability to maintain the targeted value for the mixture property.

대표청구항 ▼

What is claimed is: 1. A control system for continuously mixing at least two materials, comprising: a mixing process; wherein said process receives at least two input flow streams and has one output flow stream for the resulting mixture; and a process control system acting on said mixing process wh

What is claimed is: 1. A control system for continuously mixing at least two materials, comprising: a mixing process; wherein said process receives at least two input flow streams and has one output flow stream for the resulting mixture; and a process control system acting on said mixing process wherein said control system is configured to: (i) as a first priority, provide a desired density for said mixture; and (ii) as a lower priority, provide a desired flow rate for said mixture. 2. The system of claim 1 wherein said mixing process prepares a wet cement slurry at a hydrocarbon well site; wherein said wet cement is pumped down-hole to cement a well casing to a well bore. 3. The system of claim 1, wherein said materials are selected from the group consisting of water, sea water, re-used process water, carrier fluid, dry cement material, sand, fluid rheology modifying materials, cement property modifying materials, cement accelerators, fracturing fluids, proppant fluids, acidizing fluids, flushing fluids, drilling mud components, gases, and proppants, or various combinations thereof. 4. A control system for continuously mixing at least two materials, comprising: (a) a first control element and a second control element, each operable to control the flow rate of an individual material feeding into a mixing process; (b) a third control element, operable to control the discharge flow rate from said mixing process; and (c) a control system connected to said control elements, comprising: (i) a first control stage for controlling the respective flow rates of individual materials feeding into a mixing process, with respect to a desired value of a property of the resulting mixture; and (ii) a second control stage for controlling the discharge flow rate from said mixing process in dependence on the difference between a sensed value and an estimated value for said property; whereby said difference can be due to a supply constraint of at least one of said individual materials; wherein the error between said desired value and said sensed value is reduced when said supply constraint occurs. 5. The system of claim 4, wherein said control stage (ii) also controls said discharge rate based on a desired discharge flow rate from said mixing process. 6. The system of claim 4, wherein said estimated value for said property is a density value generated by either a density observer or a volumetric observer. 7. The system of claim 4, wherein the total flow rate of materials into said mixing process is controlled based on the hold-up of materials in said mixing process. 8. The system of claim 7, wherein a height observer is used to estimate said hold-up of said mixing process. 9. The system of claim 4, wherein said property of said mixture is selected from the group consisting of density, material volume ratio, and weight or volume fraction of a material in the mixture, or various combinations thereof. 10. The system of claim 4, wherein said controlling actions (i) and (ii) uses actuators to operate said control elements; wherein said actuators are selected from the group consisting of variable speed motors, variable speed drives, pneumatic actuators, electrical actuators, hydraulic actuators, rotary actuators, servo motor actuators, or various combinations thereof. 11. The system of claim 4 wherein the first and second control elements are flow control valves and the third control element is a pump. 12. The system of claim 11 wherein said flow control valves are selected from the group consisting of a rotary-actuated control valve, a vertically-actuated control valve, an actuated metering valve, an actuated gate valve, an actuated ball valve, an actuated globe valve, an actuated diaphragm valve, a variable rate dump valve, a rotary valve, a rotary vane valve, a rotary pocket valve, a variable rate slide gate valve, or various combinations thereof. 13. The system of claim 11 wherein said pump is selected from the group of pumps consisting of a centrifugal pump, a positive displacement pump, a progressive cavity pump, a piston pump, a gear pump, a diaphragm pump, a stuffing pump, and a gas compressor. 14. A control system for continuously mixing at least two materials, comprising: (a) a first actuator and a second actuator, each operable to control the flow rate of an individual material feeding into a mixing process; (b) a third actuator, operable to control the discharge flow rate from said mixing process; and (c) a control system connected to said actuators; and configured to provide: (i) control of the respective flow rates of individual materials feeding into said mixing process, with respect to a desired value of the density of the resulting slurry; (ii) an estimate of the expected density of the mixed materials; wherein if the actual density of the mixed materials falls below the desired density, without corresponding change in any controlled variable, then said control system temporarily reduces the total flow rate through said process; whereby errors due to supply constraints on the dry material are temporarily ameliorated by reduced total flow; and (iii) a temporary reduction of said total flow rate if actuator response to commanded increases in supply flow of a liquid material component of the slurry is inadequate; whereby errors due to supply constraints on said liquid material are temporarily ameliorated by reduced total flow. 15. The system of claim 14, wherein the control of said total flow rate is also based on a desired total flow rate through said mixing process. 16. The system of claim 14, wherein said estimated value for said density is generated by a density observer or a volumetric observer. 17. The system of claim 14, wherein the total flow rate of materials into said mixing process is controlled based on the hold-up of materials in said mixing process. 18. The system of claim 17, wherein a height observer is used to estimate said hold-up of said mixing process. 19. A control system for continuously mixing at least two materials, comprising: (a) actuators and/or control elements for controlling the respective flow rates of individual materials feeding into a mixing process, based on a desired density for the resulting mixture; (b) an actuator and/or a control element for controlling the discharge flow rate from said process, based on a master flow rate set point; and (c) a control system connected to said actuators and/or control elements for generating a master flow rate set point, based on: (i) the difference between a sensed value and an estimated value for said property; wherein said difference can be due to a supply constraint of at least one of said individual materials; and (ii) a desired discharge flow rate for said process. 20. The system of claim 19, wherein said estimated value for said density is generated by a density observer or a volumetric observer. 21. The system of claim 19, wherein the total flow rate of materials into said mixing process is controlled based on the hold-up of materials in said mixing process. 22. The system of claim 21, wherein a height observer is used to estimate said hold-up of said mixing process. 23. The system of claim 19, wherein the master flow rate set point is generated based on: (iii) the proportional drive signal for a liquid material flow control valve. 24. The system of claim 19, wherein the rate of change of said master flow rate set-point is limited to a value no greater than the lesser of: (i) the maximum possible rate of change of the total in-feed flow rate of said materials; and (ii) the maximum possible rate of change of said discharge flow rate. 25. A control system for continuously mixing at least two materials, comprising: means for controlling the flow rates of materials into a mixing process; wherein said means provide control based on a desired density for the mixture resulting from said process; means for controlling the flow rate of the mixture discharging from said process; wherein said means provide control based on a master flow rate set point; means for detecting a material supply constraint for said materials flowing into said process; and means for generating said master flow rate set point; wherein said means generate said set point based on the occurrence of a said material supply constraint. 26. A control system for continuously mixing water and cement, comprising: a cement mixing system, comprising: actuators which control the respective flow rates of water and cement into said mixing system with respect to a desired mixed cement density; and at least one pump for delivering the resulting wet mixed cement into a hydrocarbon well to thereby cement the casing to the well bore; wherein the flow rate generated by said pump is based on a desired pumping rate; and a control system which controls said actuators and said pump; wherein as a first priority, said control system operates to provide said desired density for said mixture.