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CHEN3005 / CHEN5041 Process Instrumentation and Control Semester 2, 2020 Project Statement 3: Bioethanol Production from Sugarcane Blackstrap Molasses – Part 1: Bioreactor Modelling and Control Process Description You have been appointed as a team leader who is responsible for developing the control system for a newly constructed bioethanol production plant. Part of the plant which includes a continuous bioreactor and a distillation column is shown in Figure 1. The fresh feed to the bioreactor contains high concentration of sugarcane molasses, with concentration ranging between 150????/??3 − 200????/??3 and the feed volumetric flowrate ranging between 80??3/ℎ?? − 160??3/ℎ??. The bioreactor effluent is sent to a filter bank which separates the Baker’s yeast cells (heavy phase) from the liquid (light phase) which contains ethanol and unreacted sugar. Between 5% − 15% of the heavy phase is purged to prevent the accumulation of the dead cells and other contaminants in the bioreactor; the remaining portion of the heavy phase is recycled back into the bioreactor. Note that, partial aeration is required to improve the cell viability and ethanol productivity. This partial aeration provides micro- aerobic fermentation condition (between 5% to 10% of dissolved oxygen in the broth) to the yeast cells. The operational concerns are summarized as follows: • Concentration of ethanol in the bioreactor effluent should be no less than 40kg/m3 and no larger than 50kg/m3. If the concentration drops below 40kg/m3, then the energy consumption in the distillation column will increase dramatically leading to poor plant profit. On the other hand, if the ethanol concentration exceeds 50kg/m3, then the cell death rate will increase rapidly leading to poor ethanol productivity, which will in turn lead to higher energy consumption in the distillation column. • Dissolved oxygen (DO) in the fermentation broth must be kept below 10%, as a higher DO will reduce the yield of ethanol formation on substrate (i.e., excessive biomass formation), thus reducing the ethanol productivity. On the other hand, if the DO is below 5%, then the death rate will increase dramatically leading to a possibility of fermentation failure. Information given: • Monod kinetic equation for growth rate (???? − ??????????????/ℎ??.??3): ???? = ???????? � ?? ???? + ?? �?? • Substrate consumption rate (???? − ??????????????????/ℎ??.??3): ???? = ???? ????/?? • Ethanol (product) formation rate (???? − ????ℎ????????/ℎ??.??3): ???? = ????/?????? • Nominal feed flowrate is 100m3/hr • Nominal biomass concentration in the bioreactor is specified at 30kg-cell/m3. • Periodic backwashing of the filter is required; backwashing frequency is 6 times per year based on the nominal bioreactor biomass concentration of 30kg-cell/m3. A higher nominal biomass concentration will lead to a higher frequency of filter cleaning and this will lead to higher maintenance cost and longer downtime. • An ethanol sensor has a time constant of 10 minutes and deadtime of 5 minutes. • A sugar sensor has a time constant of 1 minute and deadtime of 2 minutes • All sensors are with 100% accuracy • A control valve has a time constant of 1.2 minutes and deadtime of 0.5 minutes. Table 1. Kinetic data Maximum specific growth rate ???????? 0.093 ℎ??−1 Yield of biomass on substrate ????/?? 0.077 ???? − ?????????????? ???? − ??????????????????⁄ Yield of ethanol on substrate ????/?? 0.437 ???? − ????ℎ???????? ???? − ??????????????????⁄ Half saturation constant ???? 20 ???? − ?????????????????? ??3⁄ Figure 1. Part of bioethanol production plant. Each group is required to perform the following tasks as a team. Task 1: To identify: • Implicit and explicit operating objectives • Number of measurements and controlled variables • Number of potential manipulated inputs • Number of disturbances Based on your explicit operating objective(s) above, draw a Process & Instrumentation Diagram (P&ID) for the Bioreactor ONLY and show all of the control loops, sensors and valves. Also, clearly denote on the diagram, the location of all sensors and valves. Task 2: To discuss on the selections of suitable sensors and control valves for the Bioreactor system (excluding the distillation column). Task 3: To develop dynamic model for the Bioreactor. Clearly show and calculate: • Modelling goal(s) and purposes • Input-output to be modelled • Model assumptions • Mathematical consistency analysis • Degree of Freedom (DOF) analysis • Bioreactor dimension based on your nominal operating conditions The model should capture at least 2 dependent variables and at least 2 independent inputs (i.e., 2 input and 2 output system). Task 4: To develop a Matlab Simulink model for the dynamic model established in Task 3. Need to prepare: • A m-file to translate the dynamic model into executable Matlab program • A m-file for the s-function block application • A Matlab Simulink model that includes: o User-defined s-function block o Input sources o Output viewing panels o Data export ability o And others as desired by the group Upon completing the Matlab Simulink model above, the students are required to choose one of the explicit control objectives (should be the most important one), and for this selected objective, design a P/PI/PID controller. The following activities should be performed and clearly reported: • Conduct one or more step tests using the Matlab Simulink model • Use the data obtained from the step test(s) to develop linear empirical transfer function(s). • Design a P or PI or PID controller (justify why using a certain controller type) using the obtained transfer function. Use at least 3 PID tuning formulas available in the open literature, or/and in Matlab Control System Designer, to design the required P/PI/PID controller. • Duplicate the Matlab Simulink model, and use the duplicated model (save and name the model differently from the original one), to implement your P/PI/PID controller above. Note that, if you have 3 different P/PI/PID controllers (i.e., based on 3 different tuning formulas), you need to have 3 duplicated Matlab Simulink models, each should be named uniquely, as you like. • Compare the performances of the 3 or more different PID controllers; show the simulations results in tables or/and figures; critically, evaluate the simulation results and provide concise conclusions and 2-3 recommendations. For the individual tasks, the following choices are available: Individual Task 1: Design one of the sensors or control valves required in the Bioreactor system. i. Glucose sensor ii. Ethanol sensor iii. Dissolve Oxygen (DO) sensor Note that, you need to provide a detailed design for your sensor and discuss all the ramifications of your design. Individual Task 2: Do a recent literature search around the sensor/valve in the Individual Task 1 • Carry out a critical review of the current advancements and limitations of existing technologies for your sensor/valve. • The report should not be more than five typed pages, with the following headings: o Introduction and Background o Current Work and Advancements o Limitations of Existing Technologies o Conclusions o References.