Prepared By:

Shafaat KhanChemical Engineering

University of Engineering & Technology Peshawar, Pakistan

Cooling of Natural Gas by Refrigeration Process

Contents

Natural Gas Composition Main Uses Natural Gas Processing Cooling Cooling Methods Refrigeration Parts of MRU

Contents (Cont…..)

Refrigerant Cycle Recommendations

Natural Gas

Natural gas consisting mainly of methane.

Nonrenewable fossil fuel. It is found associated with fossil fuels, in

coal beds.

Composition

Methane 70-90% Ethane 5-15% Propane 5% Butane 5%

Main Uses

Power generation Domestic use Transportation Fuel Fertilizer Aviation Hydrogen

Natural Gas Processing Dehydration Desulphurization Cooling

Dehydration

Removal of water content from natural gas.

Because:

i). Water forms hydrates

ii). Water causes corrosion

Desulphurization

Removal of Sulpher content from natural gas is called Desulphurization.

Because

i). Sulpher pollutes the environment.

Cooling

Lowering the temperature of the raw gas so condensates can be removed.

Control the Hydrocarbon Dew Point.

Cooling Methods

Refrigeration Turbo Expander JT Valve

Refrigeration

Mechanical Refrigeration Unit is used for refrigeration Process

Parts of MRU

Coalescer Filter Unit Gas-Gas Exchanger Gas-Liquid Exchanger Chiller Low Temperature

Separator De-Ethanizer MEG Injection

Coalescer Filter Unit

It consist of two sections

i). Coalescer Element

ii). Double Pocket Vane It removes initially free liquid contents

www.amistco.com

Gas-Gas Exchanger

Gas-Gas Exchanger is used to cool the gas by exchanging heat with the cooled residue gas.

MEG is used in this step It is a mixture of water(20%) and Mono

Ethylene glycol(80%).

Gas-Liquid Exchanger

Condensate Enters form Shell side Raw Gas from Gas-Gas Exchanger enters

the tube side. Raw Gas temperature lowers from 70ºF to

50ºF Condensate temperature rises from -15ºF

to 30ºF

Chiller

Pre cooled gas from gas-gas exchanger enters the chiller.

The function of chiller is to further reduce the temperature of raw gas before it enters LTS.

It is just like a heat exchanger and propane is used as a refrigerant.

Low Temperature Separator High pressure horizontal vessel. It consist of deflector plates. It separates the liquid from gas on the

basis of gravity and retention time.

De-Ethanizer

Hydrocarbon Liquids passes through the liquid gas heat exchanger.

From gas liquid heat exchanger it enters the De-Ethanizer and Showered from top of De-Ethanizer.

Mono ethylene Glycol Injection

MEG is injected along with raw gas before it enters the Gas/Gas exchanger.

It enters the tube side of the gas/gas Heat exchanger.

It prevents Hydrates formation. It is 80% MEG and 20% water.

Refrigerant cycle

It recovers the refrigerant.

Refrigerant Accumulator A horizontal high pressure vessel. For maintaining high pressure,

regulators are installed. It accumulates the refrigerant.

Dessicator

It consist of silica gel, which acts as moisture absorbent.

Acts as filter for removal of impurities.

Overhead Heat Exchanger It is a U type Shell and tube Heat

Exchanger. It cools the refrigerant prior to the

throttling valve.

Refrigerant Shell Side

De Ethanizer Vapor Tube Side

Expansion Valve

Refrigerant passes through it. Sudden expansion occurs. Due to which pressure drops and

temperature lowers.

Economizer

Reduces the load on the compressor. Make the process economical. Consist of the level control valve which

works as an expansion valve. Pressure drops and temperature lowers.

Evaporator

Just like a heat exchanger.

Refrigerant Shell side

Gas Tube side After Heat exchange the refrigerant

enters the compressor

Compressor

Compressor draws the refrigerant vapors from evaporator.

Rises the pressure and temperature. Sends the compressed refrigerant to the

condenser.

Condenser The condenser accepts the high

pressurized refrigerant from the compressor.

Exchanges the heat with the atmosphere.

Here phase change occurs. Refrigerant Liquefies. Liquefied Refrigerant back to the

accumulator.

Recommendations

Refrigerant Selection Magnetic Refrigeration

Factors affecting Refrigerant

Properties Operating condition System components Chemical stability Cost Environmental Friendly

Properties

Temperature Pressure Toxicity Heat Capacity

Operating Conditions

Environmental Effect on the operation Temperature Difference

System Components

Temperature Withstand Corrosiveness

Selected

Ammonia Toxic, High Temp, Environment

R-134 Corrosive R-122 Selected

Magnetic refrigeration Working principle are based on the

magnetocaloric effect. MCE is the lowering of temperature. Temperature as low as 0.3K MCE is the phenomena in which a material

temperature is changed by exposing it to the changing magnetic field.

Paramagnetic salt is used as refrigerant. e.g. cerium magnesium nitrate.

References

www.processgroup.com.au www.britannica.com www.wipo.int www.naturalgas.org www.pfaudler.com www.amistco.com