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Methods and systems for controlling rate and output of heat exchanger fluidsRelated Patent Categories: Refrigeration, Automatic ControlMethods and systems for controlling rate and output of heat exchanger fluids description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20060112701, Methods and systems for controlling rate and output of heat exchanger fluids. Brief Patent Description - Full Patent Description - Patent Application Claims
BACKGROUND [0001] The present invention relates, in general, to process control, and more particularly to controlling the rate and output of a controlled fluid through a heat exchanger. More specifically, the present invention relates to methods and systems for controlling a plurality of parameters of a heat exchanger system such as the temperature and the mass flow rate of a controlled fluid. [0002] Many chemical processes may require control of a plurality of parameters. For example, control of a heat exchanger may involve control of parameters such as temperature and mass flow rate of one of more fluids in a heat exchanger system. Some heat exchanger systems include two fluids: a heat transfer fluid and a controlled fluid. Typically, the mass flow rates or temperatures of both fluids to a heat exchanger may be independently controlled by actuators. Moreover, changes in the mass flow rates of one of both input fluids of a heat exchanger may lead to large changes in temperature. Consequently, temperature tracking in many heat exchangers may be poor. [0003] A change in the mass flow rate of the controlled fluid in the heat exchanger may propagate through the entire system within a few seconds. Concomitant with the change in mass flow rate, however, is a change in temperature of the controlled fluid. As a result, a temperature gradient may be established within a heat exchanger system, and this gradient may propagate through the system within tens of seconds or minutes following a change in mass flow rate. Thus, many control systems for heat exchangers do not function well in response to a change in a desired temperature or desired mass flow rate of the controlled fluid. Moreover, due to actuator dynamics, many control systems cannot maintain a desired temperature following a large change in the desired mass flow rate of the controlled fluid. SUMMARY [0004] The present invention relates, in general, to process control, and more particularly to controlling the rate and output of the controlled fluid through a heat exchanger. [0005] More specifically, the present invention relates to methods and apparatus for controlling a plurality of parameters of a heat exchanger system such as the temperature and the mass flow rate of a controlled fluid. [0006] In a first aspect of the invention, a method of maintaining a desired first parameter of a controlled fluid in a heat exchanger system, comprises the steps of measuring a second parameter of the controlled fluid; varying an input to a first parameter actuator as a function of the second parameter of the controlled fluid; measuring the first parameter of the controlled fluid; and varying the input to the first parameter actuator to reduce an error of the first parameter of the controlled fluid indicative of the difference between the measured and desired values of first parameter. [0007] Additionally, the method comprises the steps of varying an input to a second parameter actuator as a function of the first parameter of the controlled fluid; measuring the second parameter of the controlled fluid; and varying the input to the second parameter actuator to reduce an error of the second parameter of the controlled fluid indicative of the difference between the measured and desired values of the second parameter. [0008] A second aspect of the invention, a method of maintaining a desired temperature of a controlled fluid in a heat exchanger system, comprises the steps of measuring a parameter of the controlled fluid; varying an input to a temperature actuator as a function of the parameter of the controlled fluid; measuring a temperature of the controlled fluid; and varying the input to the temperature actuator to reduce an error of the temperature of the controlled fluid indicative of the difference between the measured and desired temperature. [0009] Additionally, when the parameter of the controlled fluid is a mass flow rate, the method comprises the steps of varying an input to a parameter actuator as a function of the temperature of the controlled fluid; measuring the parameter of the control fluid; and varying the input to the parameter actuator to reduce an error of the parameter of the controlled fluid indicative of the difference between the measured and desired values of the parameter. [0010] In a third aspect, a method of maintaining desired parameters of a controlled fluid in a heat exchanger system, wherein the controlled fluid has one or more parameters, and the heat transfer fluid has a parameter, the method comprises the steps of measuring a first parameter of the controlled fluid; and varying an input to a first actuator of the parameter of the heat transfer fluid as a function of an error of the first parameter of the controlled fluid indicative of the difference between the measured and desired values of the first parameter of the controlled fluid. [0011] Additionally, the method comprises the steps of measuring the second parameter of the controlled fluid; and varying an input to a second actuator of the second parameter of the controlled fluid as a function of the second parameter of the controlled fluid. [0012] In a fourth aspect, an apparatus for controlling one or more parameters of a first fluid or a second fluid of a heat exchanger system, wherein the heat exchanger includes a first fluid having one or more parameters and a second fluid having one or more parameters, the apparatus comprises a first controller controlling a first parameter of the heat exchanger system; a second controller controlling a second parameter of the heat exchanger system; and a first cross coupling gain coupling an input of the first controller and an output of the second controller. [0013] In a fifth aspect, an apparatus for controlling one or more parameters of a heat exchanger system, the heat exchanger including a heat transfer fluid and a controlled fluid, the apparatus comprises a first controller controlling an input to a first actuator, the first actuator controlling a first parameter of the heat exchanger system; a second controller controlling an input to a second actuator, the second actuator controlling a second parameter of the heat exchanger system; and a first cross coupling gain coupling an input of the first controller and an output of the second controller. [0014] In another aspect, a system for controlling one or more parameters of a heat exchanger, the heat exchanger including a heat transfer fluid and a controlled fluid, the system comprises a heat exchanger; a first actuator controlling a first parameter of the heat exchanger; a second actuator controlling a second parameter of the heat exchanger; a first parameter monitor; a second parameter monitor; and a controller for controlling the heat exchanger. The controller comprises a first controller controlling an input to the first actuator; a second controller controlling an input to a second actuator; and a first cross coupling gain the first controller and the second controller. [0015] The features and advantages of the present invention will be readily apparent to those skilled in the art upon a reading of the description of the exemplary embodiments which follows. BRIEF DESCRIPTION OF THE DRAWINGS [0016] A more complete understanding of the present disclosure and advantages thereof may be acquired by referring to the following description taken in conjunction with the accompanying drawings wherein: [0017] FIG. 1 is a block diagram of a system for controlling the controlled fluid of a heat exchanger according to the present invention; [0018] FIG. 2 is a block diagram of a system for controlling the controlled fluid of a heat exchanger according to the present invention; [0019] FIG. 3 is a schematic diagram of one embodiment of a control circuit according to the present invention; [0020] FIG. 4 is one embodiment of a control circuit according to the present invention; and [0021] FIG. 5 is another embodiment of a control circuit according to the present invention. Continue reading about Methods and systems for controlling rate and output of heat exchanger fluids... 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