Chemical Engineering 3P04 Process Control Tutorial # 11 Learning goals Level Control – Getting stuff through the plant Multiloop control – Controlling several variables at the same time

Level Control – Getting stuff through the plant The textbook introduces “feed push” and “product pull” level control designs. In this example, you will design a system that holds F2 very close to a constant value and controls all levels. You will achieve the design goals with feedback control only. F0 LC F1 F2 F3 Feed

Level Control – Getting stuff through the plant The textbook introduces “feed push” and “product pull” level control designs. In this example, you will design a system that holds F2 very close to a constant value and controls all levels. You will achieve the design goals with feedback control only. F0 LC F1 FC2 F3 Feed

18.2 A process with two distillation towers is shown in Figure 18.2. a. Identify all liquid inventory in the process. Discuss advantages and disadvantages for each of the inventories. Critique the type of level control, i.e., which variable is adjusted to control the level, for each inventory. If not acceptable, sketch changes and explain. For every inventory, provide a recommended liquid volume and explain your recommendation.

Extension to Tutorial Question 18.2 Locate all vapor inventories in the process. What type of process variable is measured and controlled to maintain the total vapor inventory constant? For each vapor inventory identified in part (a), critique the type of control, i.e., which variable is manipulated by each controller. If not acceptable, sketch changes and explain. Are these controllers feedback or feedforward?

Level Control – Getting stuff through the plant Let’s do interactive Learning Module exercises 18.2 18.6 18.13 18.14

Multiloop control – Controlling several variables at the same time Vapor T6 P1 product T5 T1 T2 Feed F1 T4 T3 L1 F2 F3 Liquid A1 Process Steam product fluid L. Key

Multiloop control – Controlling several variables at the same time CONTROLLABILITY A system is controllable if its CVs can be maintained at their set points, in the steady-state, in spite of disturbances entering the system. Model for 2x2 system What is required?

Multiloop control – Controlling several variables at the same time CONTROLLABILITY A system is controllable if its CVs can be maintained at their set points, in the steady-state, in spite of disturbances entering the system. Model for 2x2 system A system is controllable when the matrix of process gains can be inverted, i.e., when the determinant of K  0.

Multiloop control – Controlling several variables at the same time Let’s do interactive Learning Module exercises 20.14 20.15 20.16 20.17

Multiloop control – Controlling several variables at the same time Please critique the design for the flash drum. Vapor product PAH TC-6 PC-1 T5 T1 Feed Methane Ethane (LK) Propane Butane Pentane T2 LAL LAH FC-1 T3 LC-1 F2 F3 Liquid product AC-1 Process fluid Steam L. Key (ethane)

Multiloop control – Controlling several variables at the same time The effects of v1 and v2 on steady-state gains are identical, within a constant multiplier. Therefore, the five CVs cannot be independently affected by the five valves. Can we control the CVs with the valves shown, i.e., is the system controllable? Det [KP] = 10-7  0

Multiloop control – Controlling several variables at the same time Boxes are cause-effect relationships (or transfer functions) Not a CV! T2 v1 A1 Let’s select: F1 production rate T6 feed vaporization A1 product quality P safety L liquid to pump P1 T6 v2 sL1 Both v1 and v2 affect all CVs of interest through T6. This is a contraction that reduces the controllability.

Multiloop control – Controlling several variables at the same time This is a good design for the flash drum. cascade Vapor product PAH Split range TC-6 PC-1 T5 T1 Feed Methane Ethane (LK) Propane Butane Pentane T2 LAL LAH FC-1 T3 LC-1 F2 F3 Liquid product AC-1 Process fluid Steam L. Key

Multiloop control – Controlling several variables at the same time Please critique the design for the chemical reactor.

Multiloop control – Controlling several variables at the same time Do not control the same variable with two feedback controllers (at the same set point values).