Qwestrum Engineering360 · Petroleum & Energy · Natural Gas Engineering
Gas Dehydration
Gas dehydration removes water vapor to prevent hydrate formation, corrosion, and pipeline flow assurance problems.
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.
- Glycol absorber TEG regeneration
- Molecular sieve for low dew point LNG feed
- Hydrate formation temperature prediction
Topic details
Introduction
Ahmed and Craft & Hawkins compare glycol and molecular-sieve systems by dew point target and regeneration energy. Indian exam questions often ask qualitative selection plus one circulation-rate numerical.
Key relations & formulas
Formulas (Indian textbook notation)
Formulas (Indian textbook notation)
Formulas (Indian textbook notation)
Notation and sign conventions
Relation 1 —
Formulas (Indian textbook notation)
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 —
Formulas (Indian textbook notation)
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 —
Formulas (Indian textbook notation)
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
TEG contactors absorb water from wet gas; rich glycol is then regenerated for recycle. For very low dew-point requirements, molecular sieves are preferred. Proper dehydration protects transmission lines and cryogenic units from hydrate plugging and ice formation.
Assumptions and validity limits
State assumptions explicitly before using any relation for gas dehydration — 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 gas dehydration.
4. Use equation 1:
5. Use equation 2:
6. Substitute values, compute, and verify units and sign (direction).
7. State conclusion in one line — e.g. safe/unsafe, stable/unstable, feasible/infeasible.
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 gas dehydration.
4. Use equation 1:
.
5. Use equation 2:
.
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
Gas Dehydration 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 gas dehydration with earlier units — revise prerequisites before attempting mixed problems.
Industry interview panels sometimes ask: "Where did you use gas dehydration?" — answer with a lab, mini-project, or plant visit example if possible.
Common mistakes in exams
Students frequently ignore pressure effect on water content, assume one-pass complete drying in TEG, and confuse dew-point depression with absolute water removal.
Quick revision checklist
Before attempting gas dehydration problems, confirm you can:
1. Glycol absorber TEG regeneration
2. Molecular sieve for low dew point LNG feed
3. Hydrate formation temperature prediction
2. Molecular sieve for low dew point LNG feed
3. Hydrate formation temperature prediction
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.
Water Removal Estimate
Problem
Wet gas contains 45 lb/MMscf water and sales spec is 7 lb/MMscf at 20 MMscfd. Find required water removal per day.
Solution
Removal = (45 - 7) × 20 = 760 lb/day water equivalent.
Conceptual check — Gas Dehydration
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 gas dehydration." 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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