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Qwestrum Engineering360 · Petroleum & Energy · Natural Gas Engineering

LNG Process Fundamentals

LNG process cools pretreated natural gas to cryogenic liquid for efficient storage and marine transport.
Exam tip: keep SI units consistent end-to-end, write the governing relation symbolically before substituting, and sanity-check magnitude and sign.

Key formulas & points

Skim these first — then read the full notes below.

  • Pretreatment remove CO₂ H₂S H₂O before liquefaction
  • Storage tank double containment
  • Regasification terminal send-out

Topic details

Introduction

Ahmed and Craft & Hawkins describe LNG as an integrated chain: pretreatment, liquefaction, storage, shipping, and regasification. B.Tech answers should always mention strict pretreatment before cold section.

Key relations & formulas

Formulas (Indian textbook notation)

  • mixedrefrigerantcascadeorSMRliquefactionmixed refrigerant cascade or SMR liquefaction

Formulas (Indian textbook notation)

  • boil−offgasBOGreliquefactionorfuelboil-off gas BOG reliquefaction or fuel

Formulas (Indian textbook notation)

  • LNGdensity 450kgm3at−162§K0§CLNG density ~450 \frac{kg}{m^{3}} at -162^{§K0§}C

Notation and sign conventions

Relation 1 —
mixedrefrigerantcascadeorSMRliquefactionmixed refrigerant cascade or SMR liquefaction

Formulas (Indian textbook notation)

  • mixedrefrigerantcascadeorSMRliquefactionmixed refrigerant cascade or SMR liquefaction
Write this relation with symbols exactly as in Ikoku Natural Gas Production — Standard reference before substituting numbers. Examiners award partial marks for a correct setup even when arithmetic slips.
Relation 2 —
boil−offgasBOGreliquefactionorfuelboil-off gas BOG reliquefaction or fuel

Formulas (Indian textbook notation)

  • boil−offgasBOGreliquefactionorfuelboil-off gas BOG reliquefaction or fuel
Write this relation with symbols exactly as in Ikoku Natural Gas Production — Standard reference before substituting numbers. Examiners award partial marks for a correct setup even when arithmetic slips.
Relation 3 —
LNGdensity 450kgm3at−162§K0§CLNG density ~450 \frac{kg}{m^{3}} at -162^{§K0§}C

Formulas (Indian textbook notation)

  • LNGdensity 450kgm3at−162§K0§CLNG density ~450 \frac{kg}{m^{3}} at -162^{§K0§}C
Write this relation with symbols exactly as in Ikoku Natural Gas Production — Standard reference before substituting numbers. Examiners award partial marks for a correct setup even when arithmetic slips.

Concept in depth

Cryogenic liquefaction reduces gas volume drastically, enabling long-distance transport where pipelines are uneconomic. Pretreatment removes contaminants that would freeze at low temperature. Boil-off gas handling, tank insulation, and regasification heat integration are key for energy efficiency and safety.

Assumptions and validity limits

State assumptions explicitly before using any relation for lng process fundamentals — steady state, uniform properties, linear elastic material, ideal gas, incompressible flow, etc., as applicable.
Wrong assumptions invalidate the entire solution even when the formula is correct. In Natural Gas Engineering viva and GATE descriptive questions, listing valid assumptions often earns separate marks.

Step-by-step problem approach

1. Read the question and list given data with SI units (common in Natural Gas Engineering papers).
2. Draw a neat labelled diagram where applicable — examiners in Indian universities award diagram marks even when arithmetic slips.
3. Identify which relation from this topic applies to lng process fundamentals.
4. Use equation 1:
mixedrefrigerantcascadeorSMRliquefactionmixed refrigerant cascade or SMR liquefaction
.
5. Use equation 2:
boil−offgasBOGreliquefactionorfuelboil-off gas BOG reliquefaction or fuel
.
6. Substitute values, compute, and verify units and sign (direction).
7. State conclusion in one line — e.g. safe/unsafe, stable/unstable, feasible/infeasible.

Applications & exam relevance

LNG Process Fundamentals appears in CGD and LNG projects. In Indian petroleum curricula this topic is tested because it connects theory to processing and transmission of gas.
GATE and semester exams often combine lng process fundamentals with earlier units — revise prerequisites before attempting mixed problems.
Industry interview panels sometimes ask: "Where did you use lng process fundamentals?" — answer with a lab, mini-project, or plant visit example if possible.

Common mistakes in exams

Students often skip CO2/H2O pretreatment significance, confuse LNG density with gas density at standard conditions, and ignore BOG management in terminal design.

Quick revision checklist

Before attempting lng process fundamentals problems, confirm you can:
1. Pretreatment remove CO₂ H₂S H₂O before liquefaction
2. Storage tank double containment
3. Regasification terminal send-out
Revise the solved examples in Ikoku Natural Gas Production — Standard reference and one previous-year GATE or university paper for this unit.

Worked examples

Try the problem first — open the solution when you are ready to check.

Mass of Stored LNG

Problem

An LNG tank stores 12,000 m3 and LNG density is 450 kg/m3. Estimate stored mass.

Solution

Mass = volume × density = 12000 × 450 = 5,400,000 kg.

Conceptual check — LNG Process Fundamentals

Problem

In a Natural Gas Engineering semester or GATE paper you are asked: "State the main assumption, the governing relation, and one practical consequence of lng process fundamentals." What should a complete answer include?

📖 Standard books (India)

  • Ikoku Natural Gas Production — Standard reference

    Read: Syllabus unit

    Referenced in Indian B.Tech syllabus

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