PRES 2 cheat sheet

Kraft cooking targets: white liquor sulfidity typically 25-35%, effective alkali (EA) charged 15-22% on wood for softwood kraft, liquor-to-wood ratio 3.5:1 to 4.5:1 in batch; H-factor integrates time and temperature to predict kappa number (H = ∫exp(43.2 − 16113/T)dt, T in K).

Kappa number approximates residual lignin; Kappa × 0.15 ≈ % lignin in pulp (Klason). Target kappa: softwood kraft ~28-32, hardwood ~15-18 before oxygen delignification.

Oxygen delignification removes 40-60% of residual lignin with 1.5-3% NaOH and 0.5-1.0 MPa O2 at 85-105 °C; selectivity limited by carbohydrate degradation - viscosity drop signals cellulose damage.

Bleaching sequences: D0-E-D1-D2 or D0-EOP-D1-D2 for ECF; TCF uses ozone/peroxide (Z-P). Hydrogen peroxide needs silicate stabilizer and MgSO4 to prevent Fenton-type radical degradation.

Black liquor recovery: solids 12-18% from washers, concentrated to 65-80% before recovery boiler firing; higher heating value ~13.5-14.5 MJ/kg dry solids at 75% solids.

Green liquor causticizing: Na2CO3 + Ca(OH)2 → 2NaOH + CaCO3; causticizing efficiency typically 80-85%, measured as NaOH/(NaOH+Na2CO3). Lime mud reburned in lime kiln at 800-1100 °C.

Screening and cleaning: knotter rejects > screen rejects > centricleaner rejects; slot size 0.15-0.35 mm for pressure screens; consistency 2-4% for screening, 0.5-1.5% for centrifugal cleaners.

Chip quality rules: chip thickness 3-8 mm optimal, 2 mm fines < 2% and overthick > 5% cause rejects; bark content < 1% for kraft; moisture 45-50% wet basis typical.

Continuous digester zones: impregnation (110-130 °C), heating (to 160-170 °C), cooking (co-current or modified), and counter-current washing zone; chip residence 90-180 min total.

Batch digester design pressure typically 1.0-1.2 MPa (150-175 psi) at 165-175 °C; continuous digesters operate at 1.0-1.7 MPa with design temperatures up to 180 °C.

Modified continuous cooking (MCC) and ITC split white liquor addition to lower kappa and improve viscosity; split typically 60-70% co-current, 30-40% counter-current.

Digester shell design per ASME Section VIII Div 1 or EN 13445; corrosion allowance 3-6 mm on carbon steel with stainless overlay in cooking zone.

Top separator and chip feeding: high-pressure feeder to 1.0-1.7 MPa; steam packing to prevent blowback; liquor-to-wood ratio controlled by trim liquor flow.

Blow line and blow tank design must accommodate pressure drop from digester (1.0 MPa) to atmospheric; blow tank vented to recovery; flashing steam recovered for liquor heating.

Heat exchangers for liquor heating: black liquor fouling factor 0.0005-0.002 m²·K/W; design velocity > 1.5 m/s to reduce scaling; tube material 316L or duplex.

Design for hydrostatic test at 1.3× MAWP; PWHT required for carbon steel wall thickness > 38 mm per ASME VIII Div 1 UCS-56.

Carbon steel acceptable for neutral-to-alkaline black liquor lines below 100 °C; above 100 °C in white liquor and cooking zones, 316L or duplex 2205 is standard.

Chloride stress corrosion cracking: 300-series austenitic stainless steels crack above ~60 °C with > 50 ppm chloride; use duplex or 6-Mo superaustenitic (254 SMO) in bleach plant.

Bleach plant chlorine dioxide service: titanium (Grade 2) or 254 SMO for D-stage washers and piping; titanium immune to wet chlorine but attacked by dry chlorine gas.

Caustic stress corrosion cracking of carbon steel occurs above 50-60 °C in concentrated NaOH; PWHT (stress relief) required for carbon steel white liquor and green liquor equipment.

Sulfate reduction corrosion in recovery boiler lower furnace: carbon steel with chromized or weld-overlay protection; waterwall tubes at 300-400 °C in reducing atmosphere require composite tubes (304L/SA210).

Pitting resistance equivalent number PREN = %Cr + 3.3%Mo + 16%N; PREN > 40 for bleach plant, > 34 for digester, > 25 for neutral sulfite.

Erosion-corrosion in high-velocity white liquor: velocities < 2 m/s for carbon steel, < 4 m/s for 316L; impingement at bends and pump casings is a common failure site.

Graphitic corrosion of cast iron in buried piping; use ductile iron or HDPE for underground; cathodic protection with -850 mV CSE criterion.

ASME BPVC Section VIII Division 1: design by rules, joint efficiency E = 1.0 for full RT, 0.85 for spot, 0.70 for none; allowable stress from Section II Part D.

Thin-wall formula: t = PR/(SE − 0.6P) + corrosion allowance for cylindrical shell under internal pressure; head thickness per UG-32 (2:1 ellipsoidal t = PD/(2SE − 0.2P)).

ASME B31.3 process piping: allowable stress at design temperature from Table A-1; longitudinal joint factor E; weld joint strength reduction factor W for creep range.

ASME B31.1 power piping for steam and boiler external piping; B31.3 for process; B31.5 for refrigeration; choose by service, not by plant location.

MAWP determination per UG-98: maximum allowable working pressure at coincident temperature; hydrostatic test per UG-99 = 1.3 × MAWP × (S_test/S_design).

Nozzle reinforcement per UG-37/UG-45: area replacement method; reinforcement must lie within limits of reinforcement (parallel to shell: 2× shell diameter; normal: 2.5× nozzle thickness).

Impact testing per UG-84 required for carbon steel > 25 mm or MDMT below curve; SA-516 Gr 70 exempt to −29 °C at thickness ≤ 25 mm in normalized condition.

Piping flexibility per B31.3 Chapter II: allowable stress range SA = f(1.25Sc + 0.25Sh); thermal expansion of carbon steel 12 µm/m·K, stainless 16-17 µm/m·K.

RT (radiography) per ASME Section V Article 2: density 2.0-4.0 for X-ray, IQI essential wire based on material thickness; acceptance per VIII Div 1 UW-51 for full RT.

UT per Article 4/5: straight-beam for thickness and laminations, angle-beam for welds; calibration blocks per ASME; acceptance per UW-53.

PT and MT surface methods: PT detects surface-breaking defects in non-porous materials; MT detects surface and near-surface in ferromagnetic materials only; MT per Article 7, PT per Article 6.

Hydrostatic test pressure 1.3× MAWP (UG-99) held long enough for leakage inspection; pneumatic test per UG-100 at 1.1× MAWP with remote monitoring and safety barriers.

Visual examination VT per Article 9; welder qualification per Section IX QW-300 series; WPS/PQR essential variables include process, thickness range, position.

Phased array UT (PAUT) and TOFD for thick-section welds; TOFD excellent for height sizing but poor near-surface resolution; combine with pulse-echo.

Fitness-for-service per API 579-1/ASME FFS-1: Level 1 screening, Level 2 assessment, Level 3 detailed; remaining strength factor RSF = LDC/LUC.

Corrosion monitoring: UT thickness readings, ER probes, and coupons; set inspection intervals based on measured corrosion rate - half-life rule for remaining thickness.

ASME Section VIII Div 1 UG-125 to UG-137 and Section XIII govern relief device sizing; set pressure ≤ MAWP; accumulation limited to 10% above MAWP for single device, 16% for multiple.

Relief valve sizing for vapor: A = W/(CKP√(M/T)) per API 520; for liquid: A = Q/(K√(ΔP/ρ)); use certified Kd (0.975 for gas, 0.65 for liquid typical).

Rupture disk upstream of relief valve requires derating of valve capacity by 0.9 factor and disk burst tolerance (±5% standard); disk alone per API 520 Part I.

Reaction force and discharge piping per API 520 Part II; backpressure limits: conventional valve 10% of set pressure, bellows valve 30-50%.

HAZOP per IEC 61882: guide words (no, more, less, reverse, part of, other than) applied to nodes; risk ranking matrix severity × likelihood.

LOPA per IEC 61511: independent protection layers (IPL) must be independent, auditable, and have PFD < 0.1; SIL 1 (PFD 10⁻¹-10⁻²), SIL 2 (10⁻²-10⁻³), SIL 3 (10⁻³-10⁻⁴).

Relief device inspection interval: typically 1-5 years based on service; test bench set pressure tolerance ±3% for steam, ±5% for process; recalibrate after any chattering or fouling.

Recovery boiler safety: black liquor guns, smelt-water explosion risk - smelt must not contact water; ESP and dissolving tank design per NFPA 85 and 654.

Remaining life estimate: t_remaining = (t_actual − t_min)/corrosion_rate; t_min from ASME VIII formula with corrosion allowance; inspect at half remaining life intervals.

Weld repair per NBIC (National Board Inspection Code) NB-23 for fired and unfired pressure vessels; R-stamp required for repairs to code-stamped vessels.

Post-weld heat treatment after repair of carbon steel > 38 mm or per UCS-56; alternative tempering per UCS-56 for P-No. 1 materials.

Hot tapping and line stopping per API 2201: only on carbon steel with wall thickness ≥ schedule 40; prohibitions on high-alloy and cast iron.

Digester shell inspection: internal visual + UT grid mapping; typical corrosion allowance consumption 0.1-0.3 mm/year in cooking zone; repair by weld overlay or stainless liner.

Fitness-for-service per API 579: remaining strength factor for general metal loss per Part 4; local thin areas per Part 5; crack-like flaws per Part 9 (FAD).

Recovery boiler tube life: fireside corrosion rate 0.1-0.5 mm/year in lower furnace; composite tube waterwalls extend life; monitor with tube thickness surveys each outage.

Risk-based inspection per API 580/581: risk = probability of failure × consequence; inspection effectiveness categories (highly, usually, fairly, poorly effective) drive interval.