HKIE Professional Assessment - Chemical Discipline cheat sheet

Ideal-gas law PV = nRT; compressibility factor Z = PV/(nRT), with Z→1 at low pressure and high temperature and Z<1 where attractive forces dominate.

Carnot efficiency for heat engines: η = 1 − T_C/T_H (absolute temperatures); for refrigeration, COP_Carnot = T_C/(T_H − T_C).

Clausius–Clapeyron: ln(P2/P1) = −(ΔH_vap/R)(1/T2 − 1/T1); use for vapour pressure interpolation over modest ranges.

Raoult's law P_i = x_i·P_i^sat for ideal mixtures; departure is quantified by activity coefficient γ_i, with azeotrope where γ1P1^sat = γ2P2^sat.

Gibbs phase rule F = C − P + 2; for a two-phase binary at fixed T and P, F = 0 - composition is fixed (e.g. azeotrope, VLE tie-line).

First law for steady open system: Q − W = Σṁ_out·h_out − Σṁ_in·h_in (neglect KE/PE); isentropic compressor work ≈ ṁ·∫v dP.

Exergy (availability) of a stream: b = (h − h0) − T0(s − s0); exergy destruction = T0·S_gen, which locates true inefficiency in a network.

Throttling (Joule–Thomson) is isenthalpic; ideal gases show no temperature change, real gases cool below the inversion temperature - basis for refrigeration let-down.

Arrhenius: k = A·exp(−E_a/RT); a plot of ln k vs 1/T gives slope −E_a/R. Apparent E_a in a porous catalyst is roughly half the intrinsic value under strong pore-diffusion limitation.

Batch design equation: t = N_A0·∫dX/(−r_A·V); CSTR: V = F_A0·X/(−r_A); PFR: V = F_A0·∫dX/(−r_A).

Levenspiel plot (1/−r_A vs X): CSTR area is a rectangle, PFR area is under the curve; for positive-order kinetics PFR volume < CSTR volume for the same conversion.

Selectivity and yield: S = (moles desired)/(moles undesired formed); Y = S·X. Series reactions A→B→C peak at B when dC_B/dt = 0, i.e. t_opt = ln(k2/k1)/(k2 − k1).

Thiele modulus φ = L·√(k/D_eff); effectiveness factor η = tanh φ/φ for a first-order slab. η→1/φ for φ > 3 (strong diffusion limitation).

Weisz–Prater criterion: C_WP = (−r_A,obs·L²)/(D_eff·C_As); C_WP << 1 confirms kinetic control, so intrinsic kinetics may be extracted.

Catalyst deactivation: activity a(t) = k(t)/k0; for first-order decay a = exp(−k_d·t); coke fouling is often reversible by controlled regeneration burn-off.

Equilibrium conversion for exothermic reversible reactions falls as T rises; use interstage cooling or cold-shot to follow the maximum-rate trajectory.

Reynolds number Re = ρvD/μ; pipe flow is laminar below Re ≈ 2100 and fully turbulent above ≈ 4000, with a transitional band between.

Darcy–Weisbach: ΔP = f·(L/D)·(ρv²/2); for laminar flow f = 64/Re. Colebrook–White gives f for turbulent flow; Moody chart is its graphical form.

Continuity: ṁ = ρAv = constant for steady incompressible flow; velocity scales as 1/D² for a fixed mass flow.

Fourier's law q = −k·A·dT/dx; cylindrical steady conduction resistance R = ln(r2/r1)/(2πkL). Overall U from 1/U = 1/h_i + R_f,i + wall + 1/h_o.

Dittus–Boelter: Nu = 0.023·Re^0.8·Pr^n (n = 0.4 heating, 0.3 cooling); valid for Re > 10^4, 0.7 < Pr < 160, L/D > 10.

Mass transfer analogy: Sh = 0.023·Re^0.8·Sc^0.33; Sherwood Sh = k_c·L/D_AB, Schmidt Sc = μ/(ρD_AB).

Fick's first law J_A = −D_AB·dC_A/dx; in a porous solid, effective diffusivity D_eff = D·ε/τ (porosity ε, tortuosity τ).

Packed-bed pressure drop (Ergun): ΔP/L = 150·μ·u(1−ε)²/(ε³d_p²) + 1.75·ρ·u²(1−ε)/(ε³d_p).

Fenske: N_min = ln[(x_D/(1−x_D))·((1−x_B)/x_B)]/ln α; Underwood gives minimum reflux; Gilliland correlation links N, N_min, R, R_min.

Distillation operating lines: rectifying y = (R/(R+1))x + x_D/(R+1); q-line slope = q/(q−1), where q is the feed thermal condition.

Kremser equation for absorption/stripping: N = ln[(1−1/A)(y_in − m·x_in)/(y_out − m·x_in) + 1/A]/ln A, with absorption factor A = L/(mV).

McCabe–Thiele assumptions: constant molar overflow, equal latent heats, negligible heat of mixing, adiabatic column.

Filtration: constant-pressure cake filtration gives V² vs t linear with slope 2A²ΔP/(μ·α·c); Ruth equation.

Drying: constant-rate period controlled by external heat/mass transfer; falling-rate period controlled by internal diffusion. Use drying curve to size.

Membrane: flux J = A·(ΔP − Δπ) for reverse osmosis; rejection R = 1 − C_p/C_f. Concentration polarisation raises Δπ at the membrane surface.

Centrifuge/cyclone cut size d_50 scales with √(μ·D/(Δρ·v)); the smaller d_50, the sharper the separation.

Pinch analysis: minimum utility targets from composite curves; ΔT_min sets the utility pinch. Heat recovery = Q_H,min + Q_C,min avoided.

Pinch rules: no heat transfer across the pinch; do not use utility above the pinch for cooling or below for heating; do not place a heat exchanger across it.

Scale-up similarity: geometric, kinematic, dynamic, thermal, chemical. Full similarity is rarely achievable - choose the controlling mechanism (e.g. keep tip speed constant for shear-sensitive systems).

Mixing scale-up: constant power per unit volume (P/V) vs constant tip speed vs constant Reynolds number give different results; match the rate-limiting mechanism.

Simulation convergence: recycle loops need a tear stream and acceleration (Wegstein, Broyden); flash drums use Rachford–Rice. Always check mass and energy balance closure.

Thermodynamic model selection: ideal (Raoult) for light gases; PR/SRK for hydrocarbons; NRTL/UNIQUAC for polar non-ideal; electrolyte models (eNRTL) for aqueous ionic systems.

Equipment sizing checks: line velocity (liquid 1–3 m/s, gas 10–30 m/s), pump NPSH margin ≥ 0.5–1 m, vessel L/D and vapour disengagement.

HAZOP of a design should be completed before detailed engineering freeze; design changes after this point require management of change (MOC).

HAZOP guide words: No/Not, More, Less, As well as, Part of, Reverse, Other than; applied to nodes with design intent and parameters (flow, pressure, temperature, level, composition).

Risk = likelihood × consequence; ALARP requires risk to be reduced until further reduction is grossly disproportionate to benefit. Tolerable risk is not zero risk.

LOPA: initiating event frequency × independent protection layer (IPL) PFDs gives mitigated frequency; each IPL must be independent, specific, auditable, and have PFD ≤ 0.1.

SIL assignment per IEC 61511: SIL 1 PFD 10^-1 to 10^-2, SIL 2 10^-2 to 10^-3, SIL 3 10^-3 to 10^-4, SIL 4 10^-4 to 10^-5 (low demand).

Flammability: LFL/UFL, flash point, autoignition temperature. For gases, use Le Chatelier's mixing rule for LFL of mixtures.

Dust explosion pentagon: fuel, oxygen, dispersion, confinement, ignition. K_st (bar·m/s) and P_max from 20-L sphere tests size venting per NFPA 68.

BLEVE: boiling liquid expanding vapour explosion; requires pressurised liquid, loss of containment, and sudden depressurisation. Jet fire follows a pressurised gas release.

Dow Fire & Explosion Index and Mond Index rank fire/explosion hazard; LOPA and QRA give quantified risk. Bow-tie links threats, top event, consequences, and barriers.

Hong Kong statute: Factories and Industrial Undertakings Ordinance (Cap. 59) and subsidiary regulations (e.g. Dangerous Substances, Safety Management); Labour Department enforces.

Environmental legislation in Hong Kong: Air Pollution Control Ordinance (Cap. 311), Water Pollution Control Ordinance (Cap. 358), Waste Disposal Ordinance (Cap. 354). EPD issues licences.

Chemical Weapons Convention and OPCW schedules; hazardous chemicals may also fall under the Fire Safety (Dangerous Goods) Ordinance.

Occupational exposure limits: use HK Labour Department OELs; compare 8-hour TWA and 15-minute STEL against measured exposures.

Occupational hygiene hierarchy of controls: elimination, substitution, engineering controls (LEV), administrative, PPE - PPE is last resort.

Environmental impact assessment: EIA Ordinance (Cap. 499) requires an Environmental Permit for designated projects; EIA report must be approved by EPD.

Waste management: chemical waste producer registration; disposal through licensed collectors; waste reduction framework (avoid, reduce, reuse, recycle, recover, dispose).

Carbon reporting: HKEX ESG reporting guide and HK's Climate Action Plan; ISO 14064 for GHG quantification and verification.

PID: u(t) = K_c·e(t) + (K_c/τ_I)·∫e dt + K_c·τ_D·de/dt. Proportional band PB = 100/K_c (%).

Closed-loop tuning: Ziegler–Nichols ultimate gain method uses K_u and P_u; K_c = 0.6·K_u, τ_I = P_u/2, τ_D = P_u/8 for PID.

First-order plus dead time (FOPDT): K_p·e^(−θs)/(τs+1). Controllability degrades as θ/τ increases; θ/τ > 1 needs feedforward or model-based control.

Control valve: equal-percentage characteristic for wide range; inherent vs installed characteristic differ due to line pressure drop. Fail-safe action (FC/FO/FL) is set by hazard analysis.

Cascade control: inner (fast) loop on the disturbance, outer (slow) loop on the primary variable. Inner loop must be at least 3–5× faster.

Safety instrumented function (SIF) loop: sensor + logic solver + final element. Final element often dominates PFD; partial stroke testing reduces it.

Digitalisation: ISA-95 levels 0–4; OPC UA for interoperability; IEC 62443 for OT cybersecurity zones and conduits.

Alarm management per ISA-18.2: alarm flood limit ~10 alarms per 10 min per operator; rationalise to avoid nuisance alarms.

Carbon steel is suitable for dry, neutral service; it corrodes in wet CO2, acids, and seawater. Stainless 304 for mild oxidising; 316 for chloride-containing; duplex for high chloride + stress.

Galvanic series: couple metals with small potential difference; avoid large cathode-to-anode area ratio (accelerates attack on the anode).

Pitting resistance equivalent number PREN = %Cr + 3.3·%Mo + 16·%N; PREN > 40 for seawater service (super duplex, 6Mo).

Chloride stress corrosion cracking of austenitic stainless steel: risk above ~60 °C in chlorides; mitigate with duplex, lower stress, or coatings.

Hydrogen-induced cracking and sulfide stress cracking (NACE MR0175/ISO 15156) - hardness limits (HRC 22) and material selection for wet H2S.

API 570 piping inspection and API 510 pressure vessel inspection; RBI per API 580/581 prioritises inspection on risk. Remaining life = (t_actual − t_min)/corrosion rate.

Mechanical integrity elements: relief valves, rupture discs, instrumented protective functions, rotating equipment, piping, vessels. Test intervals defined by code and risk.

Corrosion rate < 0.1 mm/y low, 0.1–0.5 moderate, > 0.5 mm/y high; design corrosion allowance typically 1.5–3 mm for carbon steel.

Scope 1 (direct), Scope 2 (purchased energy), Scope 3 (value chain); report per GHG Protocol and ISO 14064-1.

Carbon intensity: kg CO2e per tonne product or per MWh. Use emission factors from recognised sources (e.g. HK/China grid factors).

Decarbonisation hierarchy: energy efficiency → fuel switching → electrification → hydrogen/biomass → CCS → offsets (last).

Heat pump COP typically 3–6; above ~150 °C steam, mechanical vapour recompression or electric boilers may be more practical.

CCS: amine absorption (MEA, 30 wt%) for post-combustion; capture energy penalty ~2.5–4 GJ/t CO2. Storage requires suitable geological formation and monitoring.

Circular economy: design for disassembly, material passports, take-back schemes. Mass balance and LCA (ISO 14040/44) quantify benefits.

Hydrogen: green (electrolysis), blue (SMR + CCS), grey (SMR). LHV ≈ 120 MJ/kg; storage is energy-intensive (compression 350–700 bar, or liquefaction at −253 °C).

EU CBAM and similar carbon border mechanisms affect export-oriented chemical producers; embedded emissions must be verified.

Project phases: feasibility → concept/pre-FEED → FEED → detailed design → procurement/construction → commissioning → handover. FEL gates reduce rework.

Cost estimate classes per AACE: Class 5 (±50%) through Class 1 (±10%). Accuracy improves with definition maturity.

Capital cost estimate: Lang factor (equipment cost × factor, typically 3–5 for fluids, 4–6 for solids); Hand method for individual equipment.

Economic metrics: NPV = Σ CF_t/(1+r)^t; IRR = discount rate at which NPV = 0; payback period ignores time value. Choose projects with positive NPV and IRR > hurdle.

Contract types: lump-sum (EPC), reimbursable, unit rate, cost-plus. Lump-sum transfers cost risk to contractor; reimbursable retains owner risk but gives flexibility.

FIDIC and HK standard forms of contract; retention (typically 5–10%), performance bond (10%), liquidated damages.

Earned value: CPI = EV/AC, SPI = EV/PV; CPI < 1 means over budget. Use for progress and forecast at completion.

Commissioning: mechanical completion → punch list → system energisation → performance test → acceptance. Punch list closure is contractual.

HKIE Code of Conduct: act with integrity and honesty; avoid conflicts of interest; disclose any potential conflict to employer/client; do not accept undisclosed benefits.

Competence: work only within your competence; seek specialist advice when needed; keep CPD current (HKIE requires CPD for registered engineers).

Public safety first - if a design or operation poses a risk to the public, escalate to management and, if unresolved, to the appropriate authority.

Confidentiality: do not disclose client information without consent, except where required by law or where public safety demands.

Statutory duties: Engineers Registration Ordinance (Cap. 409) - only registered professional engineers may use the title RPE. Building/works approvals under Buildings Ordinance.

Bribery: Prevention of Bribery Ordinance (Cap. 201) - any advantage offered to a public servant or agent is an offence; keep a gifts register.

Whistleblowing: report suspected illegal or unsafe conduct through internal channels first; document everything; retaliation protection exists under employment law.

Professional liability: maintain professional indemnity insurance; understand limitation of liability clauses; keep records of design decisions and peer reviews.