Page 65 - Analysis, Synthesis and Design of Chemical Processes, Third Edition

c. It has been decided to add a second (backup) drive for an existing compressor.

d. The locations of several control valves have changed to allow for better operator access.
During a retrofit of an existing process, a vessel used to supply the feed pump to a batch reactor has
been replaced because of excessive corrosion. The vessel is essentially identical to the original one,
except it is now grounded differently to reduce the corrosion. If the function of the vessel (namely to
supply liquid to a pump) has not changed, answer the following questions:

11.
a. Should the new vessel have a new equipment number, or should the old vessel number be used
again? Explain your answer.

b. On which diagram or diagrams (BFD, PFD, or P&D) should the change in the grounding setup be
noted?

Draw a section of a P&ID diagram for a vessel receiving a process liquid through an insulated 4″ sch
40 pipe. The purpose of the vessel is to store approximately 5 minutes of liquid volume and to

provide “capacity” for a feed pump connected to the bottom of the pump using a 6″ sch 40 pipe. The
diagram should include the following features:

a. The vessel is numbered V-1402 and the pump(s) are P-1407 A/B.

b. The discharge side of the pump is made of 4″ sch 40 carbon steel pipe and all pipe is insulated.

c. A control valve is located in the discharge line of the pump, and a double block and bleed
arrangement is used (see Problem 1.13 for more information).

d. Both pumps and vessel have isolation (gate) valves.
12.

e. The pumps should be equipped with drain lines that discharge to a chemical sewer.

f. The vessel is equipped with local pressure and temperature indicators.

g. The vessel has a pressure relief valve set to 50 psig that discharges to a flare system.

h. The tank has a drain valve and a sampling valve, both of which are connected to the tank through
separate 2″ sch 40 CS lines.

i. The tank level is used to control the flow of liquid out of the tank by adjusting the setting of the
control valve on the discharge side of the pump. The instrumentation is similar to that shown for V-
104 in Figure 1.7.

A standard method for instrumenting a control valve is termed the “double block and bleed,” which is
illustrated in Figure P1.13.

Figure P1.13 Double Block and Bleed Arrangement for Problem 13