LNG

What is LNG and its properties

a natural gas that has been cooled and condensed to a liquid

colorless, odorless, non-corrosive and non-toxic

Domestic uses

cooking, drying, airconditioning, lighting, water heating

Industrial uses

fuel, generating electricity at power plants, heating buildings and water

Production of LNG

1. pre-treatment

2. refrigeration process

3. storage and transport

4. re-gasification

Pre-treatment (step 1)

1.Liquid removal and treatment

2. Acid gas removal

3. Moisture removal

4. Mercury removal

Liquid removal and treatment

The incoming feed gas (vapor and condensate) enters a Slug Catcher where liquids are separated.

Acid Gas Removal

A recirculating amine system removes carbon dioxide (CO₂) and hydrogen sulfide (H₂S). Why? CO₂ would freeze in the cold exchangers. H₂S is corrosive and must meet sulfur specifications

Moisture Removal (Adsorbtion)

The gas passes through molecular sieve dehydrators (aluminosilicates) to remove water. Why? Water would freeze and block the cryogenic equipment.

Mercury Removal

The gas passes through a sulphur-impregnated activated carbon bed. Why? Mercury would corrode and damage the aluminum cryogenic heat exchanger

LNG refrigeration methods (step 2)

Conoco Phillips optimized cascade process

C3mr technology

Conoco Phillips optimized cascade process

1. Propane refrigeration: Cools gas from ~17°C down to -29.6°C.

2. Ethylene refrigeration: Further cools gas down to -85.8°C (gas begins to partially condense).

3. Methane refrigeration: Cools the gas to -160°C, producing LNG.

C3MR technology

Treated natural gas is precooled by propane to -35 (as well as mixed refrigerant)
Cooled gas enters MCHE and is cooled by mixed gas to -162

Storage and transport (step 3)

storage:

LNG is stored in full-containment tanks. These have a 9% nickel alloy inner shell (for low-temperature resistance) and a prestressed concrete outer shell, with insulation to keep the LNG at -160°C.

Transportation:

LNG is shipped in specialized double-hull ships with membrane or spherical (Moss) tanks, with insulation to reduce cargo boil-off to less than 0.15% per day

Re-gasification (step 4)

LNG is converted back to gas using heat exchangers:

1.Submerged combustion vaporizer: Burns a small amount of LNG to heat the rest.

2. Open rack vaporizer: Uses ambient water (seawater/river water) to warm the LNG.

Environmental impacts

lower co2 emissions

reduces sulphur and particulate matter emissions

methane leakages