Dehydration Glycol is a liquid desiccant system to remove water from natural gas and natural gas liquids (NGL). This is the most common and economical method of disposal of water from these streams. Glycols typically seen in industry include triethylene glycol (TEG), diethylene glycol (DEG), ethylene glycol (MEG), and tetraethylene glycol (TREG). TEG is the most commonly used glycol in the industry.
Video Glycol dehydration
Destination
The purpose of the glycol dehydration unit is to remove water from natural gas and natural gas liquids. When produced from a reservoir, natural gas usually contains a large amount of water and is usually completely saturated or at the point of water dew. This water can cause some problems for downstream processes and equipment. At low temperatures water may freeze in pipes or, as is more common, form hydrates with CO 2 and hydrocarbons (especially methane hydrates). Depending on the composition, this hydrate can form on relatively high equipment and temperature piping. The glycol dehydration unit suppresses the point of gas hydrate formation through the drainage.
Without dehydration, the free water phase (liquid water) can also come out of natural gas because it is cooled or the pressure is lowered through equipment and piping. This free water phase often contains some parts of acid gas (such as H 2 S and CO 2 ) and can cause corrosion.
For the above two reasons, the Gas Processors Association specifies the quality specifications of pipes for gases whose moisture content should not exceed 7 pounds per million standard cubic feet. Glycol dehydration units should normally meet these minimum specifications, although further removal may be necessary if additional hydrate temperature generation is required, such as a cryogenic upstream process or a gas plant.
Maps Glycol dehydration
Description of process
Lean, water-free glycol (purity & gt; 99%) is fed to the top of the absorber (also known as the "glycol contactor") where it is contacted with a stream of wet natural gas. Glycols remove water from natural gas by physical absorption and carried out the bottom of the column. Once out of the absorber, the flow of glycols is often referred to as the "rich glycol". The dry natural gas leaves the top of the absorption column and fed to the pipe system or to the gas installation. Glycol dampers may be packed columns or columns.
After leaving the absorber, the rich glycol is fed to the flash vessel where the hydrocarbon vapor is released and each liquid hydrocarbon is taken from the glycol. This step is necessary because the absorber is usually operated at high pressure and pressure must be reduced before regeneration step. Due to the rich glycol composition, a vapor phase having a high hydrocarbon content will form when the pressure is lowered.
After leaving the flash vessel, the rich glycol is heated in a cross exchanger and fed to a stripper (also known as a regenerator). Stripper glycol consists of columns, top condenser, and reboiler. Glycol is thermally regenerated to remove excess water and regain high glycol purity.
Hot and slim glycols are cooled by cross exchanges with rich glycols that enter the stripper. It is then fed to a lean pump where the pressure is raised to a glycol absorber. The lean solvent is cooled again with a trim cooler before being fed back to the absorber. This trim cooler may be a cross exchanger with a dry gas leaving an absorber or air-cooled exchanger.
Improved Scaling Method
Most of the glycol units are quite uniform except for the regeneration stage. Several methods are used to increase glycol stripping to higher purity (higher purity is required for the dryer gas of the absorber). Because reboiler temperatures are limited to 400F or less to prevent thermal degradation of glycols, almost all of the system centers are enhanced at lowering the water partial pressure in the system to increase stripping.
The improved general methods include the use of stripping gases, the use of a vacuum system (lowering all stripper pressure), the DRIZO process, similar to the use of stripping gases but using recoverable hydrocarbon solvents, and the Coldfinger process in which the vapor in the reboiler is partially condensed and pulled out in separate from the bulk liquid.
References
External links
- The Processor Supplier Gas Supplier website
- Dehydration using Glycol on SPE Petrowiki
- Comments from the Environmental Protection Agency on best practices of natural gas dehydration
- Practically oriented oil field description of Glycol Dehydration includes Glycol operation and maintenance issues
Source of the article : Wikipedia
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