Methods for self-balancing control of mixing and pumping

A control method for continuously mixing at least two materials, comprising the actions of:

• (a) in a first control stage, 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
• (b) in an additional control stage, 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;
• wherein said difference can be due to a supply constraint of at least one of said individual materials;
• whereby the error between said desired value and said sensed value is reduced when said supply constraint occurs.

A control method for continuously mixing at least two materials, comprising the actions of:

• (a) controlling the respective flow rates of individual materials feeding into a mixing process, with respect to a desired value of the density of the resulting mixture;
• (b) maintaining an estimate of the expected density of the mixed materials;
• and, if the actual density of the mixed materials falls below the desired density, without a corresponding change in any controlled variable, then temporarily reducing the total flow rate through said process;
• whereby density errors due to supply constraints on the dry material are temporarily ameliorated by reduced total flow;
• and
• (c) if actuator response to commanded increases in supply flow of a liquid material component of the slurry is inadequate, then temporarily reducing said total flow rate;
• whereby density errors due to supply constraints on said liquid material are temporarily ameliorated by reduced total flow.

A control method for continuously mixing at least two materials, comprising the actions of:

• (a) controlling the respective flow rates of individual materials feeding into a mixing process, based on a desired density for the resulting mixture;
• (b) generating a master flow rate set point, based on:
• (i) the difference between a sensed value and an estimated value for said density;
• 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;
• and
• (c) controlling the discharge flow rate from said process, based on said master flow rate set point.

A control method for continuously mixing at least two materials, comprising the actions of:

• (a) controlling the relative proportion and total flow rate of two materials entering a continuous mixing process to thereby achieve a desired total flow rate and a desired density of the resulting mixture;
• wherein the materials differ in density;
• (b) estimating the density of said mixture using a density observer;
• (c) comparing said density estimate to a sensed measurement of the density of said mixture;
• wherein a material supply constraint for at least one said material is inferred if said observed density deviates from said sensed density without a corresponding change in control variables;
• and
• (d) temporarily reducing said total flow rate if said observed density is greater than said sensed density.