Chemical Engineering Principles

What are the seven SI base quantities?

Length, mass, time, temperature, current, amount of substance, luminous intensity.

What are the SI units for length, mass and time?

Metre (m), kilogram (kg), second (s).

What are the SI units for temperature and current?

Kelvin (K) and ampere (A).

What are the SI units for amount and luminous intensity?

Mole (mol) and candela (cd).

What is the SI unit of force?

Newton (N) = kg m/s².

What is the SI unit of pressure?

Pascal (Pa) = N/m².

What is the SI unit of energy?

Joule (J) = N m.

What is the SI unit of power?

Watt (W) = J/s.

What are the basic units of the American engineering system?

Foot, pound, second.

What does nano (n) mean?

10^-9.

What does micro (µ) mean?

10^-6.

What does milli (m) mean?

10^-3.

What does centi (c) mean?

10^-2.

What does deci (d) mean?

10^-1.

What does deka (da) mean?

10^1.

What does hecto (h) mean?

10^2.

What does kilo (k) mean?

10^3.

What does mega (M) mean?

10^6.

What does giga (G) mean?

10^9.

What is absolute error?

Magnitude of uncertainty expressed in the measurement's units. Subtract actual from expected

What is relative error?

Absolute error divided by the true value (or measured value if true unknown).

How should intermediate calculation figures be handled?

Keep one or two extra figures; round the final answer appropriately.

Why is unit consistency essential?

Unit conversion errors can cause serious engineering failures.

What is a chemical process?

A series of steps or units converting raw materials to products.

What is a unit operation?

An individual processing step within a chemical process.

Name five common process functions.

Mixing, transport, reaction, separation and heat transfer.

What are the three modes of process operation?

Batch, continuous and semi-batch.

How does a batch process operate?

Load, close, process, then unload.

How does a continuous process operate?

Inputs and outputs flow continuously during operation.

How does a semi-batch process operate?

One material is charged initially; another enters or leaves during operation.

What is steady state?

Process variables remain constant (or fluctuate around a mean) over time.

What is transient operation?

One or more process variables change with time.

What are the three flow patterns listed in the slides?

Co-current, counter-current and cross-flow.

Why monitor process variables?

Safety, performance assessment and product quality control.

What is temperature?

A measure related to the kinetic energy of atoms and molecules.

How do you convert Celsius to kelvin?

Kelvin = degrees Celsius + 273.15.

How do you convert Celsius to Fahrenheit?

Fahrenheit = 1.8 × degrees Celsius + 32.

How do you convert kelvin to Rankine?

Degrees Rankine = 1.8 × kelvin.

What is pressure?

Force acting perpendicular to a surface divided by area.

What is absolute pressure?

Pressure measured relative to a perfect vacuum.

What is gauge pressure?

Pressure measured relative to local atmospheric pressure.

How are absolute and gauge pressure related?

Absolute pressure = gauge pressure + atmospheric pressure.

What is density?

Mass per unit volume: ρ = m/V.

How is mass flow related to volumetric flow?

Mass flow rate = density × volumetric flow rate.

What is mass flow rate?

Mass transferred per unit time, for example kg/s.

What is volumetric flow rate?

Volume transferred per unit time, for example m³/s.

What is molar flow rate?

Amount of substance transferred per unit time, for example mol/s.

How is molar mass calculated?

Sum of the atomic masses in a chemical formula.

How are mass and amount in moles related?

Moles = mass ÷ molar mass (use consistent units).

How do you calculate component mass fraction?

Mass of component / total mixture mass.

How do you calculate component mole fraction?

Moles of component / total mixture moles.

What must component mass fractions sum to?

1 (or 100%).

What must component mole fractions sum to?

1 (or 100%).

When can gas volume fractions approximate mole fractions?

For gases under conditions where the ideal-gas approximation is reasonable.

What disciplines underpin chemical engineering?

Mathematics, chemistry, physics and biology.

What is chemical process engineering?

Applying science and engineering to transform materials into useful products.

What is process synthesis?

Choosing a suitable route from raw materials to desired products among alternatives.

What is process design?

Choosing operating and equipment variables for a selected process flowsheet.

How do process synthesis and design differ?

Synthesis selects the route; design specifies equipment and operating conditions.

What are commodity chemicals?

Large-volume products mainly sold on composition, purity and price.

What is a process design specification?

A requirement or performance target that a proposed process must meet.

What is the balanced ammonia synthesis reaction?

Nitrogen + 3 hydrogen → 2 ammonia (N₂ + 3H₂ → 2NH₃).

Why condense ammonia after its reactor?

Separate ammonia product from unreacted gases.

Why recycle unreacted nitrogen and hydrogen?

Improve raw-material use and reduce waste.

Why might ammonia synthesis need a purge?

Prevent accumulation of inert gases such as methane.

What is the overall urea synthesis reaction?

2NH₃ + CO₂ → CO(NH₂)₂ + H₂O.

What are typical process-development stages?

Customer needs → specifications → concepts → evaluation → detailed design → construction.

What sustainability questions should a designer ask?

What, why, where and how to manufacture; resource use and waste impacts.

Name four resources a process can consume.

Energy, water, minerals and raw materials.

What is the purpose of process optimisation?

Choose a better design against performance and other constraints.

What is a useful first step when solving engineering problems?

Define clearly what the problem asks.

Why sketch a process before calculating?

Identify streams, equipment, variables and relationships.

Why check degrees of freedom before solving?

Check whether enough independent information is available.

What is a process flowsheet?

A diagram showing process units and connecting material streams.

What is a block flow diagram?

A simple diagram showing process stages as blocks.

What is a process flow diagram?

A detailed diagram showing equipment and process streams.

What is a piping and instrumentation diagram?

A diagram showing equipment, pipes, valves and instruments.

Which is simplest: block, process flow or instrumentation diagram?

Block flow diagram.

Which process diagram shows instruments and valves?

Piping and instrumentation diagram.

What is a process stream?

Material flow connecting process units.

What should a block flow diagram stream label show?

Flow rate, composition, and known temperature and pressure.

What does a splitter do?

Divides one inlet into multiple outlets of the same composition.

What does a mixer do?

Combines multiple inputs into one outlet without reaction.

What does a separator do?

Produces output streams with different compositions.

What does a pump do?

Changes fluid pressure.

What does a heat exchanger do?

Transfers heat between streams without chemical reaction.

What does a reactor do?

Converts chemical species by reaction.

What does a distillation column exploit?

Differences in volatility/boiling behaviour to separate mixtures.

What is a recycle stream?

Material returned to an earlier stage instead of discarded.

What is a purge stream?

Material removed to prevent unwanted component accumulation.

What is a bypass stream?

A stream that skips one or more process units.

What is a stream table?

A table listing characteristics of numbered process streams.

What stream-table data are normally required?

Composition, component and total flow rates, pressure and temperature.

What optional properties can a stream table include?

Density, viscosity, enthalpy and phase.

How should streams be numbered?

Consistently along the process flow path.

In which direction is a process flow diagram usually drawn?

Left to right, on a landscape page.

Are process flow diagrams drawn to scale?

No. They are schematic diagrams.

Why avoid overcrowding a process flow diagram?

To keep it clear and readable.

Which utilities might appear on a process flow diagram?

Major heating and cooling utility streams.

What does a process flow diagram usually omit?

Most detailed controls, measurements and valves.