September 26 2006 NATURAL GAS DEHYDRATION GAS DEHYDRATION WHAT IS GAS DEHYDRATION The removal of particulate water and water vapor from a produced gas stream Why Dehydrate • • • •

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September 26 2006 NATURAL GAS DEHYDRATION GAS DEHYDRATION WHAT IS GAS DEHYDRATION The removal of particulate water and water vapor from a produced gas stream Why Dehydrate • • • • Powered By Docstoc
					September 26, 2006

NATURAL GAS DEHYDRATION

GAS DEHYDRATION

WHAT IS GAS DEHYDRATION?
The removal of particulate water and water vapor from a produced gas stream.

Why Dehydrate

• • • •

Water in pipelines causes corrosion Water reduces pipeline efficiency Water reduces accuracy in measurement Water can form hydrates and cause plugging

Types of Dehydration
• • • • •

Calcium Chloride Branded desiccants Molecular Sieve Membrane Units Glycol
– Diethylene – Triethylene

Glycol

Glycol is a hygroscopic liquid.

Which simply means GLYCOL has the ability to absorb water.

Diethylene Glycol
• Diethylene Glycol
– Lower Cost – 328° Thermal Decomposition – 474° Boiling Point – 92% - 94% Regeneration – Higher Operating Cost – Higher Capital Cost

Triethylene Glycol
• Triethylene Glycol
– Higher Cost – 404° Thermal Decomposition – 550° Boiling Point – 928% - 99.5% Regeneration – Lower Operating Cost – Lower Capital Cost

Parameters of a Dehy

• Fixed
• Minimum and Maximum gas capacity at a given pressure and temperature • Gas composition • Minimum and Maximum heat input into the regenerator • Fire Tube surface area • Vapor capacity of the still column • Liquid and gas capacity of the inlet scrubber

Parameters of a Dehy

• Variable
• • • • Gas flow into the absorber Water content of the dehydrated gas Glycol circulation rate Glycol concentration

Dehydrator Sizing
• • • • • • Gas Flow Rate Gas Temperature Gas Pressure Pipeline Specifications Utilities Available Pad Size and Location

Dehydrator Sizing
Water Content of Natural Gas Temperature Differences

Dehydrator Sizing
Water Content of Natural Gas Pressure Differences

Dehydrator Sizing
Water Removal

Natural Gas Dehydrator

Contactor Tower

Glycol Cooler

Reboiler

Dry Gas Outlet

Inlet Scrubber

Surge Tank High Pressure Filter Excess Separated Gas Outlet Condensate Outlet

Wet Gas Inlet

Three Phase Gas, Glycol & Condensate Separator Condensate Outlet

Wet Glycol from Absorber (High Pressure) Wet Glycol to Reboiler (Low Pressure) Dry Glycol from Reboiler (Low Pressure) Dry Glycol to Absorber (High Pressure)

Inlet Scrubber

• First stage of liquid removal for the dehydration process • Eliminates free liquids from gas stream • Requires liquid level controller and high pressure dump valve • Used with pre-contactor • Mist Eliminator

Absorber with Integral Scrubber

• Lower capital cost than separate scrubber. • Requires liquid level controller and high pressure dump valve • Reduces footprint of dehydrator • Can not be used with pre-contactor • Mist eliminator

Natural Gas Dehydrator
Dry Gas Out Dry glycol
Absorber (Contactor)

Reboiler

Wet Gas In

Wet glycol Pump

Dry glycol
Wet glycol
Heat exchanger surge tank

Absorber or Contact Tower

• Vessel where glycol and natural gas make contact • Concurrent flow
– Gas flows up – Glycol flows down

• Packed type
– Structured Packing – Pall Ring Packing

• Tray type
– Bubble Cap – Nutter Valve

Absorber with Scrubber
• Gas temp 60°-135° F • Pressure 100 – 2600 psi • Inlet glycol should be 10° F higher than inlet gas
– Lower temp than gas will cause foaming – Higher temp might increase glycol loss

• 5 psig maximum pressure drop between inlet and outlet • Liquid seal must be established
– Glycol circulation established on tray type tower – Gas flow should be gradually increased

Absorber with Scrubber
• pH of Glycol should be 7.0 – 7.5 • Absorber must have an adequate glycol/gas heat exchanger • Gas flow must be kept in turn down range or “channeling” may occur • Mist pad or mist extractor should be used • Glycol loss should be .1 gal per MMSCF • Tower should be level and secure

Surge or Storage Tank

• Holding tank for the dry or lean glycol before it goes to the glycol pump • Level must be maintained for pump head pressure • Can be separate vessel or integral to the reboiler.
– Individual surge tanks may have glycol/glycol heat exchanger internally – Integral surge tanks have panel or tube type glycol/glycol exchangers

Reboiler
• Vessel where water is “cooked” out of the glycol • Temp range 375°- 400° for TEG • Fire tube heat flux
– 6000-8000 BTU/Hr. per Sq./Ft

• Fire tube must be free of deposits
– salt – tar or coke

• Stripping Gas
– sparger style – spillover style – Stahl column

• Temperature Control deadband should be as small as possible • Pressure should be at a minimum

Still Column
• Still Column (where wet or “rich” glycol is injected for water removal) • Packed with ceramic saddles • 225°F Ideal Temperature • Temperatures below 218°F will cause reboiler to flood • Temperatures above 250°F will cause excess glycol loss out vent.

Glycol Pump
• Pump piping should be correctly sized • A High pressure filter MUST be used and maintained • Charcoal filters used for high condensate wells • Inlet strainer MUST be installed and maintained • Pump should be secured on a level surface

3 Phase Glycol/Gas/Condensate
Separator

• Separates any liquids that might get carried over with the glycol such as condensate or compressor oils • Used to reclaim some of the gas that would ordinarily lost through the still column • Flash separator pressure should be kept as low as possible to prevent pump stalling


				
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