Figure 4 illustrates a part of a PI&D of fresh methanol (V-3831) and recycled methanol (V-9101) tanks. Both streams combine before entering a vaporizer, H-2101. The process function of the equipment in this P&ID is controlled as follows.
• Stream temperature before entering H-2101 must be at 90°C and output (after mix with air) must be 200°C.
• The flowrate ratio of Fresh methanol and Recycle methanol flowrate is 9:1
a) Evaluate the P&ID and search at least 10 bad designs in the P&ID. For each item, recommend the correction by drawing it directly into the P&ID. [10%]
b) Estimate the pump P-9105-1/2 required discharge pressure (in atm) to flow methanol from V-9101 to H-2101. Assume the following. [5%]
i. Location of H-2101 is 20 meters above the pump level and has internal air pressure of 0.2 atm.
ii. Pressure drops across piping:
• Heat exchanger = 0.3 atm
• Control valve = 0.1 atm
• Sensor (element) = 0.1 atm
• strainer = 0.1 atm
• Spray in H-2101 = 0.1 atm
iii. No pressure-drop for FG/PG, manual valves, combined flow, elbow, length.
c) Air is mixed with methanol in H-2101. Due to risk of methanol (LEL) explosion and damage of catalyst, the methanol and oxygen concentration must be controlled severely as indicated in the figure below. If you are going to operate methanol and oxygen vol% as in Figure 5, recommend the safety interlock system (instruments, sensors, concentration alarm settings for interlock) for the process.
OXYGEN VOL %
20
18
16
14
12
10
8
6
4
2
Figure 5
RISK FOR EXPLOSION
RISK OF DAMAGING CATALYST
Optimum Operating Area
METHANOL VOL %
1 2 3 4 5 6 7 8 9 10