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ChemProCal • Separation & Distillation • LNG Feed Gas Readiness & Pre-Treatment Contaminant Screener
SEPARATION & DISTILLATION

LNG Feed Gas Readiness & Pre-Treatment Contaminant Screener

Screen feed gas against baseload LNG cold box specifications (<0.1 ppmv H2O, <50 ppmv CO2, <0.01 ug/Nm3 Hg, <1 ppmv benzene). Assess BAHX mercury liquid metal embrittlement and CO2 dry ice freezeout risks.



LNG Plant Feed Stream Conditions

MMSCFD
barg
°C

Raw Gas Contaminant Assay (Feed Concentrations)

ppmv
Spec: < 0.1 ppmv
ppmv (1.5%)
Spec: < 50 ppmv
ppmv
Spec: < 4.0 ppmv
mg/Nm³
Spec: < 30 mg/Nm³
μg/Nm³
Spec: < 0.01 μg/Nm³ (LME Hazard)
ppmv
Spec: < 1.0 ppmv (Freezeout)
ppmv
Spec: < 100 ppmv
mol%
Spec: < 0.10 mol%
mol%
Spec: < 1.0 mol% (Rollover)
ppmv
Spec: < 10 ppmv

📐 Engineering Formula & Specification Sheet

LNG Feed Gas Readiness & Pre-Treatment Contaminant Screener: Sizing Methodology & Engineering Basis

Screen raw natural gas against baseload LNG cold box limits. Evaluates Brazed Aluminum Heat Exchanger (BAHX) mercury LME rupture and CO2 / benzene freezeout.

👨‍🔬 Reviewed by: Process Design Engineer (B.Tech Chemical Engineering, 5+ Yrs Exp)
🗓️ Standards: ASME / API / GPSA / ISA
⏱️ Format: Quick Reference Spec Sheet

1. Cryogenic Solid-Liquid-Vapor Equilibrium in LNG Plants

Unlike pipeline gas specifications that tolerate up to 2.0 mol% \(\text{CO}_2\) and 4.0 lb/MMSCF \(\text{H}_2\text{O}\), LNG cold boxes operate under extreme cryogenic conditions where component solubilities drop exponentially:

  • Carbon Dioxide (\(\text{CO}_2 < 50\text{ ppmv}\)): Solid \(\text{CO}_2\) (dry ice) precipitates directly from liquid methane below \(-125\text{ }^\circ\text{C}\) if \(\text{CO}_2\) exceeds 50–100 ppmv.
  • Water (\(\text{H}_2\text{O} < 0.1\text{ ppmv}\)): Moisture dew point must be lowered to \(-100\text{ }^\circ\text{C}\) using Type 3A molecular sieves to prevent crystal frosting.
  • Benzene (\(< 1.0\text{ ppmv}\)): Pure benzene solidifies at \(+5.5\text{ }^\circ\text{C}\). Even dissolved in liquefied gas, concentrations above 1 ppmv precipitate at \(-100\text{ }^\circ\text{C}\).

2. Mercury Liquid Metal Embrittlement (LME) of Aluminum BAHX

Brazed Aluminum Heat Exchangers (BAHX) and cold boxes utilize aluminum-manganese alloys (AA 3003) for high cryogenic thermal conductivity. Elemental mercury (\(\text{Hg}\)) amalgamates with aluminum grain boundaries, causing rapid transgranular stress-corrosion cracking and catastrophic pressure boundary rupture. Baseload LNG specifications mandate strictly:

\[ [\text{Hg}] < 0.01 \, \mu\text{g/Nm}^3 \quad (< 1 \, \text{pptv}) \]

📚 ChemProCal Knowledge Base

Need Complete Mathematical Derivations & Industrial Case Studies?

Explore our in-depth engineering textbook guide: LNG Baseload Cryogenic Feed Gas Pre-Treatment: Trace Contaminant Limits, Freeze-Out Thermodynamics & BAHX Asset Protection Guide. Features step-by-step manual hand calculations, thermodynamic proofs, and commercial simulator benchmarks.

Read Full Theory Guide →
Peer Review & Engineering Accuracy

This specification sheet and its mathematical formulations adhere to internationally recognized process codes (ASME, API, GPSA, TEMA, and ISA). Sizing parameters and default design allowances are cross-referenced with empirical industry design practices.

About This Tool

The LNG Feed Gas Readiness & Pre-Treatment Contaminant Screener evaluates raw or treated natural gas compositions against rigorous baseload LNG liquefaction specifications. It predicts solid deposition freeze-out temperatures for \(\text{CO}_2\) dry ice and benzene, screens for catastrophic Mercury Liquid Metal Embrittlement (LME) of Brazed Aluminum Heat Exchangers (BAHX), and specifies necessary midstream pre-treatment unit operations.

Cryogenic liquefaction chills natural gas down to \(-161\text{ }^\circ\text{C}\) to condense it into liquid natural gas at atmospheric pressure. Contaminants that are entirely harmless in conventional pipeline transmission solidify and cause catastrophic failures inside the Main Cryogenic Heat Exchanger (MCHE): \(\text{CO}_2\) forms dry ice that blocks micro-channels, heavy aromatics freeze into sticky waxes, and trace mercury amalgamates with aluminum plates causing structural failure. This tool provides an actionable compliance scorecard before gas enters the liquefaction trains.

2. LNG Storage Tank Stratification & Rollover Risk

If natural gas contains over 1.0 mol% nitrogen (\(\text{N}_2\)), the liquefied product forms density stratification layers inside full-containment cryogenic LNG storage tanks. As nitrogen preferentially boils off, the bottom layer warms while remaining denser. Eventually, rapid convective overturning (tank rollover) occurs, causing massive sudden vapor release that overpowers tank relief vents and triggers hazardous emergency flaring.

Frequently Asked Questions

Why is Type 3A molecular sieve required instead of Type 4A for LNG dehydration?
Type 3A zeolite has an effective pore opening of 3 Angstroms, which admits water molecules (2.8 Å) while strictly excluding methane (3.8 Å) and other hydrocarbons. Type 4A sieves co-adsorb hydrocarbons, leading to heavy coking, pore fouling, and shortened desiccant service life during high-temperature thermal regeneration.
Why can trace mercury not be tolerated even at 0.1 μg/Nm3?
Liquid mercury forms an amalgam with aluminum that destroys the protective aluminum oxide passivation layer. In the presence of ambient moisture during warm-up or shutdown, a continuous catalytic galvanic oxidation reaction proceeds until the heat exchanger wall completely disintegrates.
Tool Units

Input / Output Units

Configure global unit system preset or individual parameter dimensions.