Engineer Chemical Industry cheat sheet

Steady-state energy balance for open system: Q − W = Σ n_out h_out − Σ n_in h_in + ΔKE + ΔPE; set ΔKE and ΔPE to zero for most process streams.

Ideal gas: PV = nRT with R = 8.314 J/(mol·K) = 8.314 kPa·m³/(kmol·K); at 1 atm and 0 °C molar volume is 22.414 L/mol.

Raoult's law for ideal mixtures: p_i = x_i·P_i^sat; dew point is reached when Σ (y_i·P)/P_i^sat = 1 and bubble point when Σ x_i·P_i^sat = P.

Modified Raoult's law uses γ_i from an activity-coefficient model (Margules, van Laar, NRTL, UNIQUAC); γ_i > 1 indicates positive deviation from ideality.

Gibbs phase rule: F = C − P + 2; for a reacting system use F = C − P + 2 − r where r is the number of independent reactions.

Clausius–Clapeyron: ln(P₂/P₁) = −(ΔH_vap/R)(1/T₂ − 1/T₁); plot ln P vs 1/T to obtain ΔH_vap from the slope.

Second law: ΔS_total = ΔS_system + ΔS_surroundings ≥ 0; isentropic efficiency of a compressor is η = (h₂s − h₁)/(h₂ − h₁).

Exergy (availability) destruction equals T₀·ΔS_gen; minimum work of separation is the reversible work calculated from chemical potentials, not the actual work.

Arrhenius: k = A·exp(−E_a/RT); doubling k for a 10 K rise implies E_a ≈ 53 kJ/mol near 300 K (rule of thumb, not exact).

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

First-order conversion in a CSTR: X = kτ/(1 + kτ); in a PFR: X = 1 − exp(−kτ).

Selectivity = (moles desired product)/(moles undesired product); yield = moles desired product formed per mole of key reactant fed.

Langmuir–Hinshelwood rate: r = k·K_A·p_A/(1 + K_A·p_A + K_B·p_B); high K·p gives zero-order behavior, low K·p gives first-order.

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

Catalyst deactivation: activity a(t) = k(t)/k₀; first-order decay a = exp(−k_d·t), and for a CSTR with decay, X depends on time on stream.

Levenspiel plot (1/−r_A vs X): reactor volume is the area under the curve for PFR and rectangle area for CSTR; CSTR is favored at high X for autocatalytic or inhibited kinetics.

Fenske: N_min = ln[(x_D/(1 − x_D))·((1 − x_B)/x_B)]/ln α; Underwood gives minimum reflux; Gilliland correlates actual stages to N_min and R_min.

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

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

Liquid–liquid extraction: distribution coefficient K = y/x; extraction factor E = K·V_organic/V_aqueous; % recovery = (E − 1)/(E^(n+1) − 1) style expressions for cross-current stages.

Drying: constant-rate period rate is set by external heat/mass transfer; falling-rate period follows diffusion control; critical moisture content marks the transition.

Filtration: constant-pressure cake filtration follows V² vs t linearity (Ruth equation); specific cake resistance rises with compressibility coefficient s.

Heat exchanger: Q = U·A·ΔT_lm·F; LMTD correction factor F < 1 for multipass and crossflow; effectiveness–NTU method used when outlet temperatures are unknown.

Centrifugal pump: NPSH_available = (p_suction − p_vapor)/(ρg) + z − h_f; cavitation occurs when NPSH_available < NPSH_required.

Sequential-modular simulators solve unit models in flowsheet order with recycle loops handled by tearing and successive substitution or Wegstein acceleration.

Degrees of freedom (Gibbs): F = 2 − π + C − r for a single-phase system; a flowsheet is fully specified when all design variables are fixed and the model is not over- or under-specified.

Pinch analysis: minimum utility targets from the composite curve; pinch temperature is where hot and cold composite curves are closest; ΔT_min trades capital against energy cost.

Optimization: set ∂f/∂x_i = 0 subject to constraints; use Lagrange multipliers for equality constraints and KKT conditions for inequality constraints.

Economic pipe diameter scales roughly as D ∝ Q^0.45–0.5; capital cost rises with diameter while pumping cost falls, giving a minimum total cost.

Heat exchanger network design rule: do not transfer heat across the pinch; number of units target is N − 1 + loops for a network with N streams.

Process flow diagram (PFD) shows major equipment and streams; piping and instrumentation diagram (P&ID) adds instruments, control loops, line sizes and valves.

Scale-up: geometric similarity, constant tip speed vs constant power per unit volume for agitators; mixing time scales differently from mass transfer coefficient.

PID controller: u(t) = K_c·e(t) + (K_c/τ_I)∫e dt + K_c·τ_D·de/dt; integral action removes offset, derivative action anticipates error.

First-order process with dead time: G(s) = K·e^(−θs)/(τs + 1); Ziegler–Nichols and Cohen–Coon tuning use K, τ, θ from a step test.

Closed-loop stability: poles of the characteristic equation must lie in the left half-plane; Routh array or Nyquist criterion determines stability for higher-order systems.

Control valve sizing: C_v = Q·√(SG/ΔP); choked flow occurs when ΔP exceeds about 0.5·P₁ for liquids (vapor pressure limits).

Flow measurement: orifice plate has a square-root relationship between flow and differential pressure; Coriolis meter measures mass flow directly via phase shift.

Cascade control uses a fast inner loop (flow) and slower outer loop (temperature); ratio control maintains a fixed ratio of two flows.

Dead time dominates control difficulty: θ/τ ratio > 1 makes feedback control difficult; feedforward or model predictive control is preferred.

Instrumentation: 4–20 mA current loop is standard; 4 mA is live zero for fault detection; HART superimposes digital signal on the analog loop.

HAZOP uses guide words (no, more, less, reverse, as well as, part of, other than) applied to process parameters at nodes to identify deviations.

Layer of protection analysis (LOPA): risk reduction factor = initiating frequency × consequence / tolerable frequency; independent protection layers must be independent and auditable.

Safety integrity level (SIL) is tied to probability of failure on demand: SIL 1 = 10⁻¹–10⁻², SIL 2 = 10⁻²–10⁻³, SIL 3 = 10⁻³–10⁻⁴ (PFD average).

Flammability: LFL and UFL bound the flammable range; adding inert gas narrows the range; flash point is the temperature at which vapor pressure reaches the LFL.

Dust explosions require five conditions: fuel, oxygen, ignition, dispersion and confinement; K_st and P_max characterize dust explosibility.

Relief valve sizing for gas: use the ideal-gas isentropic flow equation with critical pressure ratio (P₂/P₁ ≈ 0.528 for air); for liquids use the API 520 liquid sizing equation.

Bow-tie analysis links threats to a top event through preventive barriers and to consequences through mitigative barriers.

Risk = likelihood × consequence; ALARP principle requires risk to be as low as reasonably practicable, with cost–benefit justification for further reduction.

CO₂ emissions from fuel combustion: mass CO₂ = fuel mass × carbon fraction × (44/12); natural gas ≈ 2.0 kg CO₂ per kg fuel, coal ≈ 2.5–3.0.

Wastewater: BOD₅ measures biodegradable organic load over 5 days at 20 °C; COD measures total oxidizable matter; BOD/COD ratio > 0.4 suggests good biodegradability.

Air dispersion: Gaussian plume model C(x,y) = Q/(2πσ_yσ_z u)·exp(−y²/2σ_y²)·[exp(−(z−H)²/2σ_z²) + exp(−(z+H)²/2σ_z²)].

Stack height and plume rise: effective stack height H = h_stack + Δh; ground-level concentration falls roughly with 1/H².

Scrubber efficiency: η = (C_in − C_out)/C_in; absorption of acid gases (SO₂, HCl) with alkaline solution is the common control method.

Life cycle assessment stages: goal and scope, inventory analysis, impact assessment, interpretation; functional unit is the basis for comparison.

Carbon capture: amine absorption (MEA) captures CO₂ from flue gas; regeneration energy is the main cost driver; capture efficiency often 85–95%.

Sustainability metrics: carbon intensity (kg CO₂e per tonne product), water footprint, and energy intensity are standard reporting measures.

Carbon steel is the default material; stainless steel 304 (18% Cr, 8% Ni) resists oxidation but is susceptible to chloride stress-corrosion cracking; 316 adds 2–3% Mo for chloride resistance.

Galvanic corrosion requires dissimilar metals in contact with an electrolyte; the more active metal (lower in the galvanic series) corrodes; avoid large cathode-to-anode area ratios.

Pitting resistance equivalent number (PREN) = %Cr + 3.3·%Mo + 16·%N; higher PREN means better chloride pitting resistance.

Nelson curves give temperature limits for hydrogen attack in carbon steel; above the curve, hydrogen reacts with carbides to form methane, causing blistering and cracking.

ASME B31.3 gives allowable stress and wall thickness for process piping: t = P·D/(2·S·E + P·Y) + corrosion allowance.

Corrosion allowance is added to minimum wall thickness; remaining life = (t_actual − t_required)/corrosion rate.

Hydrogen embrittlement affects high-strength steels; sulfide stress cracking occurs in wet H₂S service above a partial pressure of about 0.05 psi (NACE MR0175).

Mechanical integrity: API 570 covers piping inspection, API 510 pressure vessels, API 653 storage tanks; inspection intervals are set by corrosion rate and remaining life.

Capital cost estimate classes: order-of-magnitude (±30–50%), study (±30%), preliminary (±20%), definitive (±10%), detailed (±5%).

Six-tenths rule: C₂ = C₁·(Q₂/Q₁)^0.6 for equipment cost scaling; the exponent varies (0.4–0.9) by equipment type.

Payback period = fixed capital investment / annual net cash flow; simple and useful but ignores time value of money.

Net present value: NPV = Σ (cash flow_t)/(1 + i)^t − initial investment; positive NPV means the project earns above the discount rate.

Internal rate of return is the discount rate at which NPV = 0; IRR is compared to the hurdle rate (often 10–15% for chemical projects).

Engineering ethics: paramount obligation is public safety and health; engineers must report hazards, avoid conflicts of interest, and maintain competence.

Project schedule: critical path is the longest path through the network; any delay on the critical path delays the project; float is slack on non-critical paths.

Break-even point in units = fixed costs / (unit price − unit variable cost); contribution margin is the denominator.

OSHA Process Safety Management (PSM) applies to processes with highly hazardous chemicals above threshold quantities, flammable liquids ≥ 10,000 lb, or flammable gases ≥ 10,000 lb.

EPA Risk Management Program (RMP) requires hazard assessment, prevention program and emergency response; three program levels based on quantity and offsite impact.

Clean Air Act Title V operating permits apply to major sources; New Source Review applies to modifications that increase emissions significantly.

RCRA governs hazardous waste from cradle to grave; generator status depends on monthly quantity (large, small, very small).

REACH (EU) requires registration of substances above 1 tonne/year; SDS and labeling follow GHS/CLP classification.

Piping and equipment codes: ASME Boiler and Pressure Vessel Code (Section VIII for pressure vessels), ASME B31.3 for process piping, API 650 for storage tanks.

Management of change (MOC) is required before altering process chemicals, technology, equipment or procedures; pre-startup safety review (PSSR) is required before introducing hazardous chemicals.

Professional registration and codes of conduct require competence only in areas of expertise, continuing education, and truthful reporting of data and test results.

Cathodic protection: sacrificial anode (galvanic) or impressed current; protection potential for steel in soil is about −0.85 V vs Cu/CuSO₄ reference.

Corrosion rate (mpy) = 0.128 × (weight loss in g) × 1000 / (density × area in cm² × time in hours) - verify units against the standard formula used in your reference.

Erosion–corrosion is accelerated by high velocity and turbulence; keep flow velocities below the critical velocity for the material and service.

Stress-corrosion cracking of stainless steel in chlorides is mitigated by reducing stress, lowering temperature, or selecting duplex or higher-Mo alloys.

Coatings and linings provide barrier protection; holiday (coating defect) detection is critical for buried pipelines.

Material selection considers corrosion resistance, mechanical properties, weldability, availability and cost; life cycle cost often favors higher-grade alloys.

Hydrogen-induced cracking is prevented by post-weld heat treatment and low-hardness welds (typically < 22 HRC for sour service).

Water chemistry control (pH, dissolved oxygen, chlorides) is the primary lever for boiler and cooling-water corrosion control.

Total capital investment = fixed capital investment + working capital; working capital is often 10–20% of fixed capital.

Operating cost components: raw materials, utilities, labor, maintenance, overhead, depreciation, and taxes; raw materials usually dominate.

Depreciation methods: straight-line, declining balance, and MACRS; depreciation is a non-cash expense that reduces taxable income.

Cash flow = net income + depreciation − capital expenditure; use after-tax cash flow for project evaluation.

Profitability measures: NPV, IRR, payback, and return on investment (ROI = annual profit / capital investment).

Cost index escalation: C₂ = C₁·(index₂/index₁); use published cost indices (e.g., Chemical Engineering Plant Cost Index) for time adjustment.

Utility costs: steam, cooling water, electricity and fuel are priced per unit; energy integration reduces utility consumption and operating cost.

Sensitivity analysis varies one parameter at a time; Monte Carlo simulation varies many parameters to give a distribution of NPV.

Runaway reaction occurs when heat generation exceeds heat removal; the Semenov criterion compares heat generation and removal curves.

Adiabatic temperature rise ΔT_ad = (−ΔH_r)·C_A0/(ρ·C_p); it sets the maximum temperature if cooling is lost.

Thermal runaway indicators: onset temperature, time to maximum rate (TMR_ad), and self-accelerating decomposition temperature (SADT) for storage.

Calorimetry: DSC, ARC (accelerating rate calorimetry) and reaction calorimetry measure heat release and onset temperatures for scale-up.

Emergency relief sizing for runaway reactions uses the DIERS methodology (two-phase flow, homogeneous vessel venting).

Inherent safety hierarchy: minimize, substitute, moderate, simplify; reducing inventory is the most effective runaway risk reduction.

Cooling failure scenarios: loss of cooling, mischarge, and agitation failure are common initiating events; design for them explicitly.

Process hazard analysis should include reactivity hazards; incompatible chemical storage and mixing must be prevented by design.

Conduction: q = −k·A·dT/dx; Fourier's law; thermal conductivity of metals is much higher than that of gases and organic liquids.

Convection: q = h·A·ΔT; Nusselt number Nu = h·D/k; forced convection in tubes correlates with Re and Pr.

Radiation: q = ε·σ·A·(T₁⁴ − T₂⁴); σ = 5.67 × 10⁻⁸ W/(m²·K⁴); radiation dominates at high temperature.

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.

Heat exchanger types: shell-and-tube (most common), plate-and-frame (compact, high U), air-cooled (no cooling water), double-pipe (small duty).

Boiling regimes: nucleate boiling (high heat transfer), transition boiling (unstable), film boiling (poor heat transfer, risk of burnout).

Condensation: dropwise gives higher h than filmwise; non-condensable gases reduce condenser performance significantly.

Distillation energy: reboiler duty is roughly proportional to reflux ratio; minimum reflux gives infinite stages and minimum energy.

Reynolds number Re = ρ·v·D/μ; laminar flow Re < 2100, transitional 2100–4000, turbulent > 4000 in pipes.

Darcy–Weisbach: ΔP = f·(L/D)·(ρ·v²/2); friction factor f from Moody chart or Colebrook equation; f ≈ 0.316·Re^(−0.25) for smooth turbulent pipes.

Bernoulli equation with friction: P₁/ρg + v₁²/2g + z₁ = P₂/ρg + v₂²/2g + z₂ + h_f.

Pump power: P = ρ·g·Q·H/η; brake horsepower includes pump efficiency; system curve determines operating point.

Pump and system curves intersect at the operating point; throttling moves the operating point along the pump curve and wastes energy.

Fan and compressor laws: flow ∝ speed, head ∝ speed², power ∝ speed³ (affinity laws).

Fluidization: minimum fluidization velocity from Ergun equation balance; bubbling regime above U_mf; entrainment limits gas velocity.

Mixing: impeller power number N_p = P/(ρ·N³·D⁵); turbulent N_p is constant for a given impeller geometry.

PSM elements (OSHA 1910.119): process safety information, process hazard analysis, operating procedures, training, mechanical integrity, MOC, incident investigation, emergency planning, compliance audits.

Process hazard analysis methods: HAZOP, what-if, checklist, FMEA, fault tree analysis, event tree analysis; HAZOP is the most common for continuous processes.

Mechanical integrity programs cover pressure vessels, piping, relief devices, controls, and rotating equipment; inspection and testing frequencies are documented.

Incident investigation should identify root causes, not just immediate causes; use techniques like 5-whys and fault tree analysis.

Emergency planning includes evacuation routes, alarm systems, and coordination with local responders; drills verify effectiveness.

Compliance audits are required at least every three years under OSHA PSM.

Management of change must address technical, organizational and procedural changes; temporary changes also require MOC.

Pre-startup safety review confirms construction meets design, procedures are in place, and hazards are addressed before startup.

Clean Water Act: NPDES permits regulate point-source discharges; effluent limits are set by technology-based and water-quality-based standards.

Clean Air Act: National Ambient Air Quality Standards (NAAQS) for six criteria pollutants; State Implementation Plans (SIPs) enforce attainment.

Hazardous air pollutants (HAPs) are regulated under MACT standards; major sources emit ≥ 10 tons/year of a single HAP or ≥ 25 tons/year total.

Greenhouse gas reporting: facilities emitting ≥ 25,000 metric tons CO₂e per year must report under EPA GHG Reporting Program.

Spill Prevention, Control and Countermeasure (SPCC) plans are required for facilities storing oil above threshold quantities.

Emergency Planning and Community Right-to-Know Act (EPCRA) requires Tier II reporting of hazardous chemicals stored above thresholds.

Solid waste: RCRA subtitle C regulates hazardous waste; subtitle D regulates non-hazardous solid waste.

Environmental permits often require best available control technology (BACT) or lowest achievable emission rate (LAER) depending on attainment status.

CSTR in series approaches PFR behavior as the number of tanks increases; N tanks in series with equal volume gives narrower residence time distribution.

Residence time distribution: E(t) for CSTR is (1/τ)·exp(−t/τ); for PFR it is a delta function at t = τ.

Mixing effects: poor mixing in large reactors causes concentration and temperature gradients; scale-up must maintain mixing time relative to reaction time.

Heat transfer in reactors: jacket, coil, and external heat exchanger; heat transfer area per unit volume falls as reactor size increases (area ∝ D², volume ∝ D³).

Reactor scale-up: constant power per unit volume is common for gas–liquid systems; constant tip speed for shear-sensitive systems.

Multiple steady states in exothermic CSTRs: ignition and extinction points; hysteresis loop; stability determined by slope of heat generation vs heat removal.

Recycle reactors: recycle ratio affects conversion per pass and overall conversion; high recycle approaches CSTR behavior.

Catalyst scale-up: pressure drop, channel size, and maldistribution in large beds; radial mixing and bypassing must be checked.

Minimum reflux ratio for binary distillation from Underwood equations; actual reflux typically 1.2–1.5 times minimum.

Number of theoretical stages from Gilliland correlation or McCabe–Thiele graphical construction; stage efficiency converts theoretical to actual trays.

Packed column design: HETP (height equivalent to a theoretical plate) and HTU/NTU method; random packing vs structured packing trade-off.

Flooding in packed and tray columns sets the maximum vapor/liquid loading; design at 70–80% of flooding velocity.

Absorption: physical absorption depends on solubility and Henry's law; chemical absorption with reaction enhances rate and capacity.

Stripping is the reverse of absorption; steam stripping is common for removing volatile organics from water.

Azeotropic distillation: entrainer breaks the azeotrope; pressure-swing distillation uses pressure-dependent azeotrope composition.

Energy integration in distillation: heat pump, divided wall column, and multiple-effect distillation reduce energy use significantly.

Feedback control loop components: sensor, transmitter, controller, final control element (valve); loop tuning depends on process dynamics.

Controller modes: on/off, proportional, PI, PID; proportional-only leaves offset; integral eliminates offset but can cause windup.

Anti-windup: integral action is limited when the valve saturates; bumpless transfer between manual and automatic modes.

Valve characteristics: linear, equal-percentage, quick-opening; equal-percentage is common for level and pressure control.

Loop tuning methods: Ziegler–Nichols (ultimate gain and period), Cohen–Coon, IMC (internal model control), and relay auto-tuning.

Process control safety: fail-safe valve action (fail-closed or fail-open) is chosen based on the safe state of the process.

Advanced control: feedforward, cascade, ratio, and model predictive control (MPC) handle interacting loops and constraints.

Instrumentation standards: ISA symbols and P&ID conventions; loop numbering and tag naming follow ISA-5.1.

Feasibility study: market analysis, technical feasibility, economic analysis, and risk assessment before detailed design.

Capital cost estimate accuracy improves with project stage: order-of-magnitude (±30–50%), study (±30%), preliminary (±20%), definitive (±10%), detailed (±5%).

Operating cost includes raw materials, utilities, labor, maintenance, and overhead; raw material cost is often 60–80% of total for commodity chemicals.

Profitability: gross profit = revenue − cost of goods sold; net profit after tax; margins depend on feedstock and product prices.

Break-even analysis: fixed costs / (unit price − variable cost per unit); sensitivity to price and volume is critical.

Project financing: debt vs equity; cost of capital; hurdle rate often 10–15% for chemical projects.

Inflation and escalation: use cost indices to adjust historical costs; location factors adjust for regional labor and material costs.

Risk analysis: scenario analysis, sensitivity analysis, and Monte Carlo simulation quantify uncertainty in NPV and IRR.

Engineers must hold paramount the safety, health, and welfare of the public; this overrides employer and client interests.

Competence: practice only within areas of expertise; disclose limitations and seek expert review when needed.

Conflicts of interest: disclose financial or personal interests that could influence judgment; avoid accepting gifts that compromise objectivity.

Truthful reporting: present data accurately, do not fabricate or selectively report results; acknowledge uncertainty.

Whistleblowing: report hazards or violations through internal channels first; external reporting is justified when public safety is at risk.

Confidentiality: protect proprietary information; exceptions for legal requirements and public safety.

Sustainability: consider environmental impact and resource use in design decisions; engineers have a role in reducing emissions and waste.

Professional development: maintain competence through continuing education and stay current with codes and standards.

Rate law: −r_A = k·C_A^n·C_B^m; overall order = n + m; elementary reactions have orders equal to stoichiometric coefficients.

Rate-determining step in a mechanism controls the overall rate; steady-state approximation for reactive intermediates.

Catalysis: homogeneous, heterogeneous, and enzymatic; catalyst lowers activation energy without changing equilibrium.

Enzyme kinetics: Michaelis–Menten rate = V_max·S/(K_m + S); Lineweaver–Burk plot linearizes the data.

Chain reactions: initiation, propagation, termination; radical mechanisms in polymerization and combustion.

Temperature dependence: Arrhenius; activation energy from slope of ln k vs 1/T; catalysis reduces E_a.

Reversible reactions: equilibrium constant K = k_forward/k_reverse; approach to equilibrium limits conversion.

Selectivity and yield in complex reaction networks: series and parallel reactions; selectivity depends on concentration and temperature.

HAZOP guide words applied to nodes: no, more, less, reverse, as well as, part of, other than; deviations from design intent are identified.

Fault tree analysis: top event traced to basic events through AND/OR gates; minimal cut sets identify critical failure combinations.

Event tree analysis: initiating event branches into success/failure paths; quantifies consequence frequencies.

LOPA: independent protection layers reduce risk; each IPL must be independent, specific, dependable, and auditable.

SIL determination: risk reduction factor from LOPA maps to SIL; SIL 1–4 with PFD ranges.

Bow-tie analysis: threats and consequences linked to a top event through preventive and mitigative barriers.

Risk matrix: likelihood × consequence; risk ranking guides prioritization of safeguards.

ALARP: risk reduced as low as reasonably practicable; cost–benefit analysis for further risk reduction.

Air pollution control: cyclones, baghouses, electrostatic precipitators, scrubbers; selection depends on particle size and gas properties.

Particulate removal: cyclone efficiency depends on particle size and gas velocity; baghouse efficiency > 99% for fine particles.

SO₂ control: wet flue gas desulfurization with limestone slurry; efficiency 90–98%.

NOx control: low-NOx burners, selective catalytic reduction (SCR) with ammonia, selective non-catalytic reduction (SNCR).

Wastewater treatment: primary (settling), secondary (biological), tertiary (advanced); activated sludge is the most common secondary process.

BOD and COD: BOD₅ measures biodegradable organics; COD measures total oxidizable matter; BOD/COD ratio indicates biodegradability.

Solid waste: landfill, incineration, recycling, composting; hazardous waste requires special handling and permits.

Green chemistry principles: atom economy, less hazardous synthesis, safer solvents, energy efficiency, renewable feedstocks.

Corrosion types: uniform, galvanic, pitting, crevice, stress-corrosion cracking, erosion–corrosion, hydrogen damage.

Material selection: carbon steel, stainless steels (304, 316, duplex), nickel alloys, titanium, plastics, and composites; selection based on environment and cost.

Galvanic series: metals ordered by potential; the more active metal corrodes when coupled; avoid small anode/large cathode area ratios.

Cathodic protection: sacrificial anodes or impressed current; protection potential for steel in soil about −0.85 V vs Cu/CuSO₄.

Coatings and linings: barrier protection; surface preparation is critical for adhesion and performance.

Corrosion monitoring: coupons, probes, ultrasonic thickness measurement, and inspection per API 570/510.

Stress-corrosion cracking: chloride SCC in stainless steel; mitigate by reducing stress, lowering temperature, or using duplex alloys.

Hydrogen damage: hydrogen embrittlement, blistering, and sulfide stress cracking; NACE MR0175 limits hardness and requires post-weld heat treatment.

Capital cost estimate classes: order-of-magnitude (±30–50%), study (±30%), preliminary (±20%), definitive (±10%), detailed (±5%).

Six-tenths rule: C₂ = C₁·(Q₂/Q₁)^0.6; exponent varies by equipment type (0.4–0.9).

Payback period = fixed capital / annual net cash flow; simple but ignores time value.

NPV = Σ cash flow_t/(1 + i)^t − initial investment; positive NPV means project earns above discount rate.

IRR: discount rate where NPV = 0; compare to hurdle rate (often 10–15%).

Depreciation: straight-line, declining balance, MACRS; non-cash expense that reduces taxable income.

Working capital: 10–20% of fixed capital; recovered at end of project life.

Sensitivity analysis: vary one parameter at a time; Monte Carlo varies many to give NPV distribution.

Flowsheet simulation: sequential-modular vs equation-oriented; recycle loops handled by tearing and convergence acceleration.

Degrees of freedom: F = 2 − π + C − r for a single-phase system; flowsheet fully specified when all design variables fixed.

Pinch analysis: minimum utility targets from composite curves; pinch temperature where hot and cold curves closest; ΔT_min trades capital vs energy.

Heat exchanger network: do not transfer heat across pinch; number of units target N − 1 + loops for N streams.

Optimization: set ∂f/∂x_i = 0 subject to constraints; Lagrange multipliers for equality constraints, KKT for inequality constraints.

Economic pipe diameter: D ∝ Q^0.45–0.5; capital cost rises with diameter while pumping cost falls, giving minimum total cost.

PFD vs P&ID: PFD shows major equipment and streams; P&ID adds instruments, control loops, line sizes, and valves.

Scale-up: geometric similarity; constant tip speed vs constant power per unit volume for agitators; mixing time scales differently from mass transfer.

PID controller: u(t) = K_c·e(t) + (K_c/τ_I)∫e dt + K_c·τ_D·de/dt; integral removes offset, derivative anticipates error.

First-order plus dead time: G(s) = K·e^(−θs)/(τs + 1); Ziegler–Nichols and Cohen–Coon tuning use K, τ, θ from step test.

Closed-loop stability: poles of characteristic equation must lie in left half-plane; Routh array or Nyquist criterion for higher-order systems.

Control valve sizing: C_v = Q·√(SG/ΔP); choked flow when ΔP exceeds about 0.5·P₁ for liquids.

Flow measurement: orifice plate has square-root relationship between flow and differential pressure; Coriolis meter measures mass flow directly.

Cascade control: fast inner loop (flow) and slower outer loop (temperature); ratio control maintains fixed ratio of two flows.

Dead time dominates control difficulty: θ/τ > 1 makes feedback control difficult; feedforward or MPC preferred.

Instrumentation: 4–20 mA current loop standard; 4 mA is live zero for fault detection; HART superimposes digital signal on analog loop.

HAZOP guide words: no, more, less, reverse, as well as, part of, other than; applied to process parameters at nodes.

LOPA: risk reduction factor = initiating frequency × consequence / tolerable frequency; IPLs must be independent and auditable.

SIL: PFD ranges SIL 1 = 10⁻¹–10⁻², SIL 2 = 10⁻²–10⁻³, SIL 3 = 10⁻³–10⁻⁴.

Flammability: LFL and UFL bound flammable range; inert gas narrows range; flash point is temperature where vapor pressure reaches LFL.

Dust explosions: fuel, oxygen, ignition, dispersion, confinement; K_st and P_max characterize explosibility.

Relief valve sizing for gas: ideal-gas isentropic flow with critical pressure ratio (P₂/P₁ ≈ 0.528 for air); liquids use API 520 equation.

Bow-tie analysis: threats to top event through preventive barriers; consequences through mitigative barriers.

Risk = likelihood × consequence; ALARP requires risk as low as reasonably practicable with cost–benefit justification.

CO₂ emissions from fuel combustion: mass CO₂ = fuel mass × carbon fraction × (44/12); natural gas ≈ 2.0 kg CO₂/kg fuel, coal ≈ 2.5–3.0.

Wastewater: BOD₅ measures biodegradable organic load over 5 days at 20 °C; COD measures total oxidizable matter; BOD/COD > 0.4 suggests good biodegradability.

Air dispersion: Gaussian plume model C(x,y) = Q/(2πσ_yσ_z u)·exp(−y²/2σ_y²)·[exp(−(z−H)²/2σ_z²) + exp(−(z+H)²/2σ_z²)].

Stack height and plume rise: effective stack height H = h_stack + Δh; ground-level concentration falls roughly with 1/H².

Scrubber efficiency: η = (C_in − C_out)/C_in; absorption of acid gases with alkaline solution is common control method.

Life cycle assessment stages: goal and scope, inventory analysis, impact assessment, interpretation; functional unit is basis for comparison.

Carbon capture: amine absorption (MEA) captures CO₂ from flue gas; regeneration energy is main cost driver; capture efficiency often 85–95%.

Sustainability metrics: carbon intensity (kg CO₂e per tonne product), water footprint, and energy intensity are standard reporting measures.

Carbon steel default; stainless steel 304 (18% Cr, 8% Ni) resists oxidation but susceptible to chloride SCC; 316 adds 2–3% Mo for chloride resistance.

Galvanic corrosion requires dissimilar metals in contact with electrolyte; more active metal corrodes; avoid large cathode-to-anode area ratios.

PREN = %Cr + 3.3·%Mo + 16·%N; higher PREN means better chloride pitting resistance.

Nelson curves give temperature limits for hydrogen attack in carbon steel; above curve, hydrogen reacts with carbides to form methane.

ASME B31.3: t = P·D/(2·S·E + P·Y) + corrosion allowance for process piping wall thickness.

Corrosion allowance added to minimum wall thickness; remaining life = (t_actual − t_required)/corrosion rate.

Hydrogen embrittlement affects high-strength steels; sulfide stress cracking in wet H₂S above about 0.05 psi partial pressure (NACE MR0175).

Mechanical integrity: API 570 piping inspection, API 510 pressure vessels, API 653 storage tanks; inspection intervals set by corrosion rate and remaining life.