Dehydration
All natural gas contains water vapour. Said water must be removed to a content of 7 lb/MMSCF for most gas transmission systems and to as low as partial ppm water with dew points lower than –150 °F for cryogenic processing feed pre-treatment. Gas dehydration prevents hydrate formation, potential plugging, and corrosion in the gas gathering, transmission system, or processing plant. KOCKEN Sistemas de Energia Inc. Natural Gas Dehydrators are selected and constructed in accordance with GPSA Section 20, API 12GDU (when applicable) and all other applicable Industry Codes and Standards.
There are several process options that can be utilized to accomplish dehydration. KOCKEN offers a vast array of these processes consisting of the five basic below:
- Compression to a higher pressure with
subsequent cooling and phase separation.
The higher the pressure, the lower the saturated water vapour content in lb/MMSCF at a given temperature - Cooling below initial dew-point
- Absorption with liquid desiccants
- Adsorption with solid desiccants
- Absorption with a deliquescing solid
KOCKEN considers any and all combinations of the available technology processes considering a combination of factors including:
- Water content specification
- Initial water content
- Process character
- Operational nature
- Economic factors
Compression and cooling with separation is typically integral production system / gas gathering and processing arrangement. For natural gas, additional drying is usually applied. However, in some cases this simple approach may be sufficient for field use in gas lift systems.
Cooling below initial dew-point. The lower the temperature, the lower the saturated water vapour content of the gas. This method usually employs a source of hydrate prevention and is applied as Low Temperature Separation. Ethylene glycol is usually used for hydrate prevention and simultaneous dehydration of the gas. This approach is often combined with direct glycol injection on the front end of refrigeration plants or lean oil absorption plants.
Absorption of water with a liquid desiccant. This is generally contacting of TEG and Natural Gas in an absorber column at process temperature and is the most widely applied process. Natural gases can be dehydrated down to 7 lb/MMSCF with standard regeneration systems using TEG or DEG. With stripping gas addition, water contents can be achieved down to 1 lb/MMSCFD. With KOCKEN’s advanced stripping process, glycol and BTEX compounds are used to conduct azeotropic stripping thereby reducing water in lean glycol to very low levels while achieving gas water contents to as low as 0.025 lb/MMSCF.
Adsorption of the water with a solid desiccant. Molecular sieves have found wide acceptance in the gas processing industry for cryogenic plant feed conditioning applications and some sour gas applications with special acid resistant binder formulations.
Deliquescent systems can be attractive for smaller volumes, such as an isolated production system or a fuel gas. Deliquescent desiccants are primarily made from various blends of alkali earth metal halide salts, e.g. calcium chloride and are naturally hygroscopic.