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Integration of Design & Control CHEN 4470 – Process Design Practice Dr. Mario Richard Eden Department of Chemical Engineering Auburn University Lecture.

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Presentation on theme: "Integration of Design & Control CHEN 4470 – Process Design Practice Dr. Mario Richard Eden Department of Chemical Engineering Auburn University Lecture."— Presentation transcript:

1 Integration of Design & Control CHEN 4470 – Process Design Practice Dr. Mario Richard Eden Department of Chemical Engineering Auburn University Lecture No. 16 – Integration of Design and Control II March 7, 2013 Contains Material Developed by Dr. Daniel R. Lewin, Technion, Israel

2 Plantwide Control Design Luyben et al. (1999) suggest a method for the conceptual design of plant-wide control systems, which consists of the following steps: Step 1: Establish the control objectives. Step 2: Determine the control degrees of freedom. Simply stated – the number of control valves – with additions if necessary. Step 3: Establish the energy management system. Regulation of exothermic or endothermic reactors, and placement of controllers to attenuate temperature disturbances. Step 4: Set the production rate. Step 5: Control the product quality and handle safety, environmental, and operational constraints.

3 Plantwide Control Design Step 6: Fix a flow rate in every recycle loop and control vapor and liquid inventories (vessel pressures and levels). Step 7: Check component balances. Establish control to prevent the accumulation of individual chemical species in the process. Step 8: Control the individual process units. Use remaining DOFs to improve local control, but only after resolving more important plant-wide issues. Step 9: Optimize economics and improve dynamic controllability. Add nice-to-have options with any remaining DOFs.

4 Example 2: Acyclic Process  Maintain a constant production rate  Achieve constant composition in the liquid effluent from flash drum  Keep the conversion of the plant at its highest permissible value. Steps 1 & 2: Establish the control objectives and DOFs: Select V-7 for On-demand product flow Select V-1 for fixed feed

5 Example 2: Acyclic Process  Need to control reactor temperature: Use V-2  Need to control reactor feed temperature: Use V-3 Step 3: Establish energy management system:

6 Example 2: Acyclic Process  For on-demand product: Use V-7 Step 4: Set the production rate:

7 Example 2: Acyclic Process  To regulate V-100 pressure: Use V-5  To regulate V-100 temperature: Use V-6 Step 5: Control product quality, and meet safety, environmental, and operational constraints:

8 Example 2: Acyclic Process  Need to control vapor inventory in V-100: Use V-5 (already installed)  Need to control liquid inventory in V-100: Use V-4  Need to control liquid inventory in R-100: Use V-1 Step 6: Fix recycle flow rates and vapor and liquid inventories :

9 Example 2: Acyclic Process  Install composition controller, cascaded with TC of reactor Step 7: Check component balances Step 8: Control the individual process units Step 9: Optimization N/A: Neither A or B can build up N/A: All control valves in use

10 Example 2: Acyclic Process  The liquid levels in R-100 and V-100 are now controlled in the direction of the process flow, where before they were controlled in the reverse direction. Differences: Only step 6 is different Select V-1 for fixed feed

11 Example 2: Acyclic Process

12 Example 3: Cyclic Process This control structure for fixed feed has an inherent problem. Can you see what it is?

13 Example 3: Cyclic Process F0F0 B D B F 0 + B

14 Example 3: Cyclic Process Molar balance on CSTR: Rearranging: Substitute: Balance on A for perfect separation:

15 Example 3: Cyclic Process BF0F0 e.g., suppose kn T = 200: A more general result uses the dimensionless, Damköhler number: Da = kn T /F 0 giving: “Snowball” effect for Da  1 “Snowball” effect

16 Example 3: Cyclic Process  Maintain the production rate at a specified level  Keep the conversion of the plant at its highest permissible value. Steps 1 & 2: Establish the control objectives and DOFs:

17 Example 3: Cyclic Process  Need to control reactor temperature: Use V-2 Step 3: Establish energy management system:

18 Example 3: Cyclic Process  For on-demand product: Use V-1 Step 4: Set the production rate:

19 Example 3: Cyclic Process  To regulate V-100 pressure: Use V-4  To regulate V-100 temperature: Use V-5 Step 5: Control product quality, and meet safety, environmental, and operational constraints:

20 Example 3: Cyclic Process  Need to control recycle flow rate: Use V-6  Need to control vapor inventory in V-100: Use V-4 (already installed)  Need to control liquid inventory in V-100: Use V-3  Need to control liquid inventory in R-100: Cascade to FC on V-1 Step 6: Fix recycle flow rates and vapor and liquid inventories :

21 Example 3: Cyclic Process  Install composition controller, cascaded with TC of reactor Step 7, 8 and 9: Improvements

22 Summary Part I: Previous Lecture  Provided motivation for handling flowsheet controllability and resiliency as an integral part of the design process  Outlined qualitative approach for unit by unit control structure selection Part II – This Lecture  Outlined a qualitative approach for plantwide control structure selection

23 Next Lecture – March 19 –Equipment sizing and pinch analysis Q&A Session with Consultant – March 21 –Bob Kline will participate via videoconference –Questions can be sent to Bob and/or me ahead of time Other Business


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