On the segmented control of the methanol flash tank

By staged control, you mean using two valves (staged valves) in the same control loop, which operate separately depending on different ranges of the process variable. Specifically regarding the level and pressure range control you mentioned: 1. Level range (for example, 50%~100%) – If the level range is set to 50%~100%, it means that when the level is below 50%, the corresponding output signal is 0% ； Only when the liquid level rises above 50% does the control valve begin to open gradually (from 0% to 100%). - In other words, when you set 50% as the target value for the liquid level, the control valve begins to open slightly only when the liquid level remains around 50% ； If the liquid level continues to rise, the valve opening gradually increases, sending more methanol to the tank area in order to prevent the liquid level from rising further. - Both level valves are positive acting, which means that as the controller’s output signal increases, the valve opening also increases. II. Pressure range (e.g., 0–50%) – The control pressure for the flash tank is, for example, set at 0.4 MPa. If the control range corresponds to an output signal of 0%–50%, this means that, for instance, when the pressure is below 0.4 MPa, the control valve will not open (or will be at its minimum opening position) ； When the pressure exceeds 0.4 MPa, the valve gradually opens to release gas and reduce the pressure. It could also be the other way around (depending on the specific logic); for example, 0–50% corresponds to a pressure of 0.2–0.4 MPa, no action is taken when the pressure is below 0.2 MPa, and the valve gradually opens as the pressure increases from 0.2 MPa to 0.4 MPa. In actual engineering projects, it is necessary to determine the actual pressure values corresponding to the set ranges in the PLC or DCS system; typically, the specific correspondence is provided in the engineering drawings or on-site instructions. - Difference between direct and reverse action of valves: For valve A in direct action, an increase in the control signal leads to an increase in the opening degree (an increase in output → the valve opens). Reaction of valve B: Increase in control signal —— decrease in opening degree (increase in output → valve closes). By combining two valves with different directions in this way, a more stable and accurate control of the tank pressure can be achieved. For example, when pressure increases: – A directly-acting valve opens more as it receives an increased signal, thereby reducing the pressure ； - The reaction valve operates in the opposite way: as the control signal increases, its opening degree decreases, thereby preventing additional substances from entering or unnecessary leakage, achieving precise control. In actual production, it is necessary to obtain specific process manuals or engineering documents that detail the range of settings for each pressure and liquid level range; this enables a more intuitive understanding of the valve’s operating behavior. Simple summary for easy memorization: – The range of 50%~100% for the liquid level indicates that the valve starts to open for discharge or transfer only when the level exceeds 50%. - Pressure staging involves dividing pressure control into multiple ranges, with each range corresponding to a specific valve operation range. - Positive effect: Increase in control signal → Increase in valve opening ； The reaction is the opposite. .

Firstly, FC and FO refer to the state of the valve in the event of an accident/failure； And split control is the control under normal regulatory conditions ； When it is below 50%, it goes to the fuel gas pipeline network ； Once it exceeds that level, the valves leading to the Torch official website begin to open simultaneously. That’s how I understand it; I’ll need to take a look at the logic diagram for more details.