Cascade usage
Thread Content
original: * * * * liquid level and * * * * The medium-pressure steam supply flow is controlled by a cascade system. * * * The medium-pressure steam supply flow control is the secondary loop, and the methanol vapor-liquid separation tank liquid level control is the main loop. translation: The liquid level of * * * * * and the flowrate of the MP steam supplied for * * * controlled by the cascade system. The control of the flowrate of the MP steam is subloop, and the control of the liquid level of * * * * is main loop. Question: 1. I don’t know if the usage of cascade is correct 2. The usage of secondary circuit and main circuit
FYI. It seems that the main loop is primary loop or master loop. The secondary loop is secondary loop or slave loop. Cascade control is often used with levels on distillation columns and in reflux drums (condensate receivers). Figure 1 shows bottoms level control with the bottoms level directly controlling the bottoms product rate. Figure 2 shows bottoms level control with the bottoms level resetting a flow controller on the bottoms rate. Connected loops with one loop resetting the set point of a second loop are usually referred to as cascaded loops or cascade control. The outer loop is the primary loop or master loop. The inner loop is the secondary loop or slave loop (Figure 3). http://www.distillationgroup.com/questions/07_Fig01.gif Figure 1 Direct bottoms level control on a fractionator
* * * * liquid level and * * * * The medium-pressure steam supply flow is controlled by a cascade system. * * * The medium-pressure steam supply flow control is the secondary loop, and the methanol vapor-liquid separation tank liquid level control is the main loop. Try1: The level of XXX and the flow of MP steam are controlled in cascade, with the methanol KO drum level control as primary control loop and the MP steam control as secondary control loop. Try 2:The level of XXX is controlled cascade with the flow of MP steam, with the methanol KO drum…..
Agree with the translation of echo's try1. Try2 is modified as follows: The MP steam flow is cascade controlled by the level of * * * . When the loop is in cascade control mode, the main loop is in automatic mode and the auxiliary loop is in cascade mode. For this example, the liquid level control of the methanol vapor-liquid separation tank is LIC, and the medium-pressure steam supply flow control is FIC. During cascade control, FIC is in cascade mode and LIC is in automatic mode.
Flow and liquid level are the most common cascade control. Which of the "liquid level" and "flow" is the main control variable is determined by its importance. In this example, as Ludinggi said, XX liquid level is the main control variable, and the liquid level controls the XX flow. That is, the output value of the XX liquid level is the set value of the XX flow control. If you want to be specific about this, you can also change it to: The flow of MP steam is controlled in cascade by the level of XXX ,with …