Engineer Chemical Industry flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Raoult's law

For an ideal mixture, the partial pressure of each component equals its mole fraction in the liquid multiplied by its pure-component vapor pressure at the same temperature.

Gibbs phase rule

Degrees of freedom F = C − P + 2 for a non-reacting system, where C is the number of components and P the number of phases present at equilibrium.

Arrhenius equation

Rate constant k = A·exp(−E_a/RT); a plot of ln k versus 1/T gives a straight line with slope −E_a/R and intercept ln A.

CSTR design equation

Reactor volume V = F_A0·X/(−r_A), where F_A0 is the molar feed rate of the limiting reactant and X is the fractional conversion at the reactor outlet.

Thiele modulus

Dimensionless group φ = L·√(k/D_eff) comparing reaction rate to pore diffusion rate; large φ means strong diffusion limitation and effectiveness factor approaching 1/φ.

Fenske equation

Estimates minimum theoretical stages at total reflux: N_min = ln[(x_D/(1−x_D))·((1−x_B)/x_B)]/ln α, using relative volatility α.

LMTD method

Heat exchanger duty Q = U·A·F·ΔT_lm, where ΔT_lm is the log-mean temperature difference and F corrects for multipass or crossflow arrangements.

NPSH available

Net positive suction head available equals (p_suction − p_vapor)/(ρg) plus static head minus suction friction loss; cavitation occurs when it falls below NPSH required.

Pinch analysis

Method using hot and cold composite curves to find minimum utility targets and the pinch temperature; heat should not be transferred across the pinch.

Degrees of freedom flowsheet

A flowsheet is fully specified when the number of independent design variables fixed equals the model degrees of freedom; over-specification causes simulation failure.

PID controller equation

u(t) = K_c·e(t) + (K_c/τ_I)∫e dt + K_c·τ_D·de/dt; proportional, integral and derivative terms act on the error between setpoint and measurement.

Dead time

Transport delay between a change at the input and its effect at the output; a large dead-time-to-time-constant ratio makes feedback control difficult.

HAZOP guide words

Standard words (no, more, less, reverse, as well as, part of, other than) applied to process parameters at nodes to systematically identify deviations from design intent.

Safety integrity level

SIL 1 corresponds to average probability of failure on demand 10⁻¹ to 10⁻²; SIL 2 to 10⁻² to 10⁻³; SIL 3 to 10⁻³ to 10⁻⁴.

ALARP principle

Risk should be reduced as low as reasonably practicable; further reduction is required unless its cost is grossly disproportionate to the benefit achieved.

BOD and COD

BOD₅ measures biodegradable organic matter consumed by microbes over five days at 20 °C; COD measures total oxidizable matter chemically; BOD/COD above 0.4 indicates good biodegradability.

Gaussian plume model

Dispersion equation predicting downwind concentration from source strength, wind speed, effective stack height and horizontal and vertical dispersion coefficients.

PREN

Pitting resistance equivalent number = %Cr + 3.3·%Mo + 16·%N; higher values indicate greater resistance to chloride pitting corrosion in stainless steels.

Galvanic corrosion

Corrosion caused by coupling dissimilar metals in an electrolyte; the more active metal (anode) corrodes, and small anode-to-large cathode area ratios accelerate attack.

Six-tenths rule

Equipment cost scaling: C₂ = C₁·(Q₂/Q₁)^0.6, where Q is capacity; the exponent typically ranges from 0.4 to 0.9 depending on equipment type.

Net present value

NPV = Σ cash flow_t/(1+i)^t − initial investment; a positive NPV means the project earns more than the discount rate and adds value.

OSHA PSM threshold

Process Safety Management applies to processes with highly hazardous chemicals above threshold quantities, flammable liquids at or above 10,000 lb, or flammable gases at or above 10,000 lb.

Management of change

Formal review required before altering process chemicals, technology, equipment or procedures; temporary changes also require MOC, and a pre-startup safety review follows.

Cathodic protection potential

For steel buried in soil, a protection potential of about −0.85 V relative to a copper/copper sulfate reference electrode indicates adequate cathodic protection.

Remaining corrosion life

Remaining life equals (actual measured thickness minus required minimum thickness) divided by the corrosion rate; used to set inspection intervals.

Adiabatic temperature rise

ΔT_ad = (−ΔH_r)·C_A0/(ρ·C_p); it is the temperature rise if all reacting material converts with no heat removal, a key runaway severity measure.

Inherent safety hierarchy

Order of preference: minimize, substitute, moderate, simplify; reducing inventory is the most effective way to reduce runaway and release consequences.

Overall heat transfer coefficient

1/U = 1/h_i + R_f,i + t/k + R_f,o + 1/h_o; fouling resistance reduces U over time and must be included in design margins.

Reynolds number

Re = ρ·v·D/μ; pipe flow is laminar below about 2100, transitional between 2100 and 4000, and turbulent above 4000.

Affinity laws

For a centrifugal pump or fan at constant impeller diameter: flow proportional to speed, head proportional to speed squared, power proportional to speed cubed.

Semenov criterion

Thermal runaway criterion comparing heat generation and heat removal curves; intersection points define stable and unstable steady states and the ignition temperature.

Michaelis–Menten kinetics

Enzyme rate = V_max·S/(K_m + S); K_m is the substrate concentration at half maximum rate, and a Lineweaver–Burk plot linearizes the data.