In the DME process shown in Figure B.1.1, the reactor feed exchanges heat with the reactor effluent stream in exchanger E-202. From the diagram, it is evident that the temperature of the stream entering the reactor is controlled by regulating the amount of reactor effluent that is bypassed around the heat exchanger. For this system, answer the following questions:

1. Explain how this system works. For example, explain what happens if the temperature of the feed into E-202 (Stream 4) were to increase or decrease.

2. How would this system respond to fouling in the heat exchanger or a loss of activity of catalyst in the reactor?

3. What type of control strategy is used in this example—feedback, feedforward, and so on?

4. Design a control system that would regulate the exit temperature of the reactor (Stream 6) rather than the inlet stream temperature.

Figure B.1.1

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V-201 E-201 E-206 T-202 E-207 V-203 P-203A/B E-208 E-203 T-201 E-204 E-205 V-202 P-202A/B Methanol DME DME DME DME DME DME Reflux Methanol Methanol Methanol Methanol Methanol Wastewater Vessel Preheater Cooler Tower Reboiler Condenser Reflux Pumps Reboiler Tower Condenser Reflux Pumps Cooler Drum Feed Drum P-201A/B Feed Pump Methanol E-202 R-201 Reactor Reactor Cooler V-201 P-201A/B mps E-201 E-202 4 Temperature, °C Pressure, bar R-201 6 CW E-203 T-201 mps E-204 12 22 46 10.3 CW T-202 V-202 P-202A/B E-205 139 7.4 mps E-206 26 121 7.3 CW E-207 V-203 P-203A/B CW E-208 LIC DME Wastewater