By Allen Houtz1 and Doug Cooper A ratio control strategy can play a fundamental role in the safe and profitable operation of fired heaters, boilers, furnaces and similar fuel burning processes. This is because the air-to-fuel ratio in the combustion zone of these processes directly impacts fuel combustion efficiency and environmental emissions.
By Allen Houtz1 and Doug Cooper The ratio control architecture is used to maintain the flow rate of one stream in a process at a defined or specified proportion relative to that of another. A common application for ratio control is to combine or blend two feed streams to produce a mixed flow with a […]
By Doug Cooper and Allen Houtz1 As discussed in previous articles, the purpose of the feed forward controller of the feed forward with feedback trim architecture is to reduce the impact of one specific disturbance, D, on our primary process variable, PV. An additional sensor must be located upstream in our process so we have […]
By Doug Cooper and Allen Houtz1 Both “feed forward with feedback trim” and cascade control can provide improved disturbance rejection performance. They have different architectures, however, andchoosing between the two depends on our specific control objective and the ability to obtain certain process measurements.
By Doug Cooper and Allen Houtz1 The most popular architectures for improved disturbance rejection performance arecascade control and the “feed forward with feedback trim” architecture introduced below. Like cascade, feed forward requires that additional instrumentation be purchased, installed and maintained. Both architectures also require additional engineering time for strategy design, implementation and tuning.
Our control objective for the jacketed stirred reactor is to maintain reactor exit stream temperature at set point in spite of disturbances caused by a changing cooling liquid temperature entering the vessel jacket. In previous articles, we have established thedesign level of operation for the reactor and explored the performance of a single loopPI controller and a PID with CO Filter controller in meeting our control objective.
Our control objective for the jacketed stirred reactor process is to minimize the impact on reactor operation when the temperature of the liquid entering the cooling jacket changes. We have previously explored the modes of operation and dynamic CO-to-PV behavior of the reactor. We also have established the performance of a single loop PI controller […]
When improved disturbance rejection performance is our goal, one benefit of a cascade control (nested loops) architecture over a feed forward strategy is that implementing a cascade builds upon our existing skills. The cascade block diagram is presented in the graphic below (click for a large view) and discussed in detail in this article. As […]
Two popular control strategies for improved disturbance rejection performance are cascade control and feed forward with feedback trim. Improved performance comes at a price. Both strategies require that additional instrumentation be purchased, installed and maintained. Both also require additional engineering time for strategy design, tuning and implementation.
By Bob Rice1 and Doug Cooper The control objective for the pumped tank process is to maintain liquid level at set point by adjusting the discharge flow rate out of the bottom of the tank. This process displays the distinctive integrating (or non-self regulating) behavior, and as such, presents an interesting control challenge. The process […]