Seeking advice on automatic control of the drum in methanol synthesis system

Is there no legend? It should be cascade control, right? Is Y a regulator? Seeking expert advice to learn some!*

1. What does the summation symbol “Σ” in Figure 1 represent? Which two variables are added together? Where should it be sent after the addition? This is a typical three-parameter control system: the opening degree of the feedwater valve is adjusted through PID calculations based on the drum liquid level, feedwater flow rate, and steam flow rate, thereby achieving automatic control of the drum liquid level. Generally speaking, three-impulse control is used for drum control, with the three impulses being the drum liquid level, feedwater flow rate, and steam flow rate. The drum liquid level serves as the main control parameter, the feedwater flow rate acts as a secondary control parameter, while the steam flow rate functions as a feedforward element. Structurally, three impulse regulation is actually a cascade control system with a feedforward signal. The level controller LIC and the feedwater flow controller FIC form a cascade control system. The drum level is the primary variable, while the feedwater flow rate is the secondary variable. The introduction of secondary variables enhances the system’s ability to overcome fluctuations in feedwater pressure (flow rate). The steam flow signal is introduced as a feedforward signal. For the methods of marking symbols, refer to HGT20505; for the diagrams of complex control circuits involving three impulses, refer to INST.304 in HGT20638 (other references may also be used). 2. What do the circles FY, as well as the squares FY and LY, on the valve mean? What is the principle behind the control of the water inlet flow rate and the steam outlet flow rate by this valve? I’m not sure what the lines around these symbols indicate. Thank you. For the methods of marking FY/LY, refer to the explanations in notes 23d, 25, and 26 under 4.1.1 in HGT20505. 23(d) “Auxiliary equipment (Y)” refers to devices or functions driven by “Control (C)”, “Transmission (T)”, and “Switching” signals, and are used for connecting, disconnecting, transmitting, calculating, and/or converting pneumatic, electrical, mechanical, hydraulic, or current signals; 25 “Output functions” – “Auxiliary equipment (Y)” includes, but is not limited to, solenoid valves, relays, calculators (functions), and converters (functions). 26 When the output function “Auxiliary Equipment (Y)” is used for functions such as signal calculation and conversion, its specific function should be indicated outside the instrument graphic symbol on the attached sheet, along with a textual description in the written document.

Thank you for the reply! I’ve also taken a look at the specifications, but I still don’t quite understand what is meant by this addition in relation to this diagram. Is it about adding together the three variables: two flow rates and one liquid level? Which two variables should be added together? FY and LY should be converted here, right?

This post was last edited by sun_fm on 2023-10-19 08:25. Is it about adding together the three variables of flow rate, volume flow, and liquid level? No, which two variables should still be added together? For water and steam (one inlet and one outlet, which can be considered positive and negative), when the inflow and outflow are balanced, the liquid level remains essentially unchanged. The three-element control for the boiler drum refers to the three elements being the feedwater signal, steam flow rate signal, and drum level signal. Compared to single-impulse and double-impulse methods, (the disadvantage of the single-impulse method is that false level readings become more severe; it is suitable for loads below 20t. Dual impulse can correct the misoperations caused by false liquid levels compared to single impulse, enabling the control valve to act more promptly, thereby reducing fluctuations in water level and improving control quality. However, there are still two weaknesses: the operating characteristics of the control valve are not necessarily linear, and it is difficult to achieve static compensation ； Interferences in the water supply system still cannot be effectively overcome. ) The three impulse control system is a composite control system consisting of feedforward and cascade control. The role of local feedback in the water supply is to eliminate the effects of pressure fluctuations in the water supply pipeline; ultimately, all three impulses are used by an adder to control the opening degree of the water supply valve. FY and LY should be converted here, right? It can be called calculation or it can be called transformation……

The control valve 61FV2201 of the BW3 pipeline is operated by the flow variable 61FY2001; this flow control signal is provided by 61FIC2201. Additionally, a manual operator 61HS2001 is used here (which can be understood as a means to force the valve to open or close)； What remains is the source of the signal for 61IFC2201 (the value specified by RSP); at this point, as the outlet steam and liquid level decrease, it is necessary to increase the flow rate of BW3, that is, the sum of ΣNS1 flow rates and the changes in liquid level. Take a look at the automatic control PFD specifically