Process Design practice questions

Answer: C) Piping and instrumentation diagram (P&ID)

The P&ID is the drawing that documents instrument tags, control loops, piping, and valve details. Block flow diagrams and PFDs give simpler process overviews, and a plot plan shows physical layout.

• AIncorrect. A PFD shows the main equipment, main streams, and operating conditions such as flows, temperatures, and pressures. It shows only key control points and leaves out the full set of instrument tags, loops, and valve details.
• BIncorrect. A block flow diagram is the simplest view. It shows major process units as blocks connected by flow lines, with no instrumentation or valve details.
• CCorrect. A P&ID shows the detailed piping, valves, instruments with their tags, and control loops that connect the equipment. That is the information piping designers, engineering staff, and process hazard reviews rely on.
• DIncorrect. A plot plan shows where equipment sits on the site, along with spacing and layout. It doesn't show instrumentation or control loops.

Answer: A) The quantity, such as annual profit, that is maximized or minimized

The objective function is the performance measure, such as cost or profit, that is maximized or minimized. The decision variables are adjusted within the feasible region set by the constraints.

• ACorrect. The objective function is the measure of performance (for example cost, profit or yield) that is maximized or minimized, subject to the constraints.
• BIncorrect. This describes a constraint. Constraints limit the search space but are not the quantity being optimized.
• CIncorrect. This is the feasible region. The optimum is the point in the feasible region that gives the best value of the objective function.
• DIncorrect. These are the decision (design) variables. The objective function is calculated from them, but they are not the objective itself.

Answer: B) Don't transfer heat across the pinch

• AIncorrect. Heaters belong above it.
• BCorrect. Doing so raises both hot and cold utility use.
• CIncorrect. Coolers belong below it.
• DIncorrect. ΔT_min sets the pinch.

Answer: A) Increases with both pressure and diameter

• ACorrect. t ≈ PD/(2σ).
• BIncorrect. Higher pressure needs a thicker wall.
• CIncorrect. It depends on pressure and diameter.
• DIncorrect. Larger diameter needs a thicker wall.

Answer: A) Limit fire and explosion consequences

• ACorrect. It reduces escalation between units.
• BIncorrect. Spacing usually adds piping.
• CIncorrect. It's for safety.
• DIncorrect. It's for safety.

Answer: C) Each stream's flow, composition, temperature and pressure

A PFD stream table documents the heat and material balance: flow, composition, temperature and pressure for each numbered stream.

• AIncorrect. That is the equipment summary or equipment list. The stream table describes the process streams, not the equipment.
• BIncorrect. Instrument tags and alarm settings belong on the P&ID and in the instrument index, not in the PFD stream table.
• CCorrect. The stream table records the material and energy balance for each numbered stream: flow rate, composition, temperature and pressure (often phase and enthalpy as well).
• DIncorrect. Pipe size, schedule and insulation details go in the line list and on the P&ID, not in the PFD stream table.

Answer: A) Evaluate each credible cause, such as blocked outlet, external fire and cooling failure, and size for the controlling case

Relief devices are sized for the controlling (worst credible) overpressure scenario. You find it by evaluating every credible cause, such as blocked outlet, external fire and utility or cooling failure.

• ACorrect. The relief design basis lists every credible source of overpressure, estimates the relief load for each, and sizes the device for the worst (controlling) scenario. This is what PSM process safety information is expected to document.
• BIncorrect. Upset cases such as fire exposure or loss of reflux cooling can produce vapor rates far above the normal feed rate. A fixed margin on normal flow doesn't capture them.
• CIncorrect. The relief device is the last layer of protection. It has to handle the largest credible load, not just the most likely one, and alarms don't remove a scenario from the design basis.
• DIncorrect. A valve sized for the average would be too small for the controlling scenario, letting pressure exceed the allowed accumulation. The worst credible case governs.

Answer: D) Supply vapor to the bottom of the column

• AIncorrect. That's a vent system.
• BIncorrect. That's the condenser.
• CIncorrect. That's a tank.
• DCorrect. It boils part of the bottoms liquid.

Answer: C) 0.6 m (24 in)

• AIncorrect. That's far too large.
• BIncorrect. That's too close.
• CCorrect. It allows access and vapor–liquid disengagement.
• DIncorrect. That's too close.

Answer: B) About 10 °C

About 10 °C is the usual ΔTmin starting point for balancing heat recovery against area. Refrigeration uses smaller approaches (about 5 °C), and some services use about 20 °C or more.

• AIncorrect. Approaches this small are used only in special cases such as some cryogenic exchangers. For general process service, the required area and cost rise sharply as ΔTmin approaches zero.
• BCorrect. About 10 °C is the usual starting point for balancing energy recovery against exchanger area. It changes with service: about 5 °C for refrigeration, and about 20 °C or more for some services.
• CIncorrect. This approach is too large for general process service. It gives up a lot of heat recovery, which raises hot and cold utility use.
• DIncorrect. This approach wastes far too much driving force and recovers little heat, so utility costs would dominate.