Question

Question 3 [12 Marks] Use the distillation column process in Question 2 The process requires controlling the bottom composition strictly since the stream is going to the waste water treatment plant. The process needs to control the distillate stream concentration but with less strictness. Sketch your design considering the following a. Propose the type of instrument and controllers that will you use and where would you place them? Use the symbols in developing P&/D Sketch the instrumentations and the control system for this process.[7961 b. As a safety countermeasure, design a pressure interlock (trip) system to prevent overpressure or vacuum of the system. [5%) 7 Condenser 7 7Distilate Reflux Re Boiler -7 Bottam

Answer 1

Since the question refers to details from a previous problem, which are not all mentioned here, we are going to take some assumptions if we are to solve this problem. Also, since there is no feed stream is shown into the distillation column, we assume this is batch distillation.

(a) The bottoms are going to the wastewater treatment, we assume that the monitoring required is of COD or TDS. Hence we can employ a system of online COD analyzer (AI-01) and online conductivity meter (AI-02), and install an actuated valve (XV-01) in downstream to the sensors in the bottoms stream. These sensing instruments can then be interlocked with XV-01 and reboiler to close XV-01 and shut down reboiler if parameters in AI-01 and AI-02 exceed the limit.

(b) Since there is no external vacuum applied in the given diagram, we assume only the case of overpressurization. For that, we can install a pressure transmitter in the condensate stream just above the distillation column, and interlock it to the reboiler to trip the reboiler when pressure increases above the limit.

PT-01 (1-5 Condenser Reflux Drum Reflux Distillate (1-1-(-2) xV-01 Reboiler AI-01 Al-02/ Bottoms I-3i-1-4

Following is the interlock list for the proposed system:

1. I-1 - When HH activated in AI-01, c lose XV-01
2. I-2 - When HH activated in AI-02, close XV-01
3. I-3 - When HH activated in AI-01, trip reboiler
4. I-4 - When HH activated in AI-02, trip reboiler
5. I-5 - When HH activated in PT-01, trip reboiler