Oil and Gas separation in Natural Gas technology

أول موضوع فى القسم ده يارب يعجبكم وتشاركونا بآراكم ومواضيعكم
INTRODUCTION


Separators are mechanical devices for removing and collecting liquids from natural gas. A properly designed separator will also provide for the release of entrained gases from the accumulated hydrocarbon liquids. A well stream separator must perform the following:

1. Cause a primary-phase separation of the mostly liquid hydrocarbons from those that are mostly gas.
2. Refine the primary separation by removing most of the entrained liquid mist from the gas.
3. Further refine the separation by removing the entrained gas from the accumulated liquid.
4. Discharge the separated gas and liquid from the vessel and insure that no re-entrainment of one into the other takes place.

If these functions are to be accomplished, the separator design must:

1. Control and dissipate the energy of the well stream as it enters separator.
2. Insure that the gas and liquid flow rates are low enough so that gravity segregation and vapor-liquid equilibrium can occur.
3. Minimize turbulence in the gas section of the separator and reduce velocity.
4. Eliminate re-entrainment of the separated liquid into the gas.
5. Accumulate and control froths and foams in the vessel.
6. Provide outlets for gases and liquids with suitable controls to maintain pre-set operating pressure and liquid levels.
7. Provide relief for excessive pressure in case the gas or liquid outlets should become plugged or valves malfunction.
8. Provide equipment (pressure gauges, thermometers, and liquid-level gauge assemblies to visually check the separator for proper operation.
9. Provide cleanout opening at points where solids will accumulate when solids are present in the inlet stream.



Basic Considerations of Separator Selection:

The goal for ideal separator selection and design is to separate the well stream into liquid-free gas and gas-free liquid. Ideally, the gas and liquids reach a state of equilibrium at the existing conditions of pressure and temperature within the vessel. As it is generally not economically justifiable to separate to the state of true equilibrium, industry consensus standards as to liquid retention time for solution gas break-out and liquid carry-over in the gas have been set. In some cases, the process equipment and conditions downstream of a separator will dictate the necessary degree of separation and the actual design.



Well stream Characteristics:

The following characteristics influence vessel selection, in addition to the obvious quantities of liquids and gas to be separated:

1. Proportions of gas and liquids composing the inlet stream.
2. Differences between the densities of the gas and liquids.
3. Differences between the viscosities of the gas and liquids.
4. Temperature and pressure at which separation is to be made.
5. Particle sizes of liquids in the gas phase or gas in the liquid Phase.
6. Identification of impurities or special conditions such as H2S,CO2, pipe scale, dust,
foam, fogs, etc.
7. Instantaneous flow rates (slugs or heading).
- Applications:-

1. Well streams having large liquid to gas ratios.
2. Well streams having sizable quantities of sand, mud, or other related substances.
3. Areas having horizontal space limitations, but little or no vertical height limitations.
4. Well streams or process flow streams which are characterized by large instantaneous volumes of liquid.
5. Upstream of other process equipment tolerating essentially no entrained liquid droplets in the gas.
6. Downstream of equipment causing liquid formation.
Horizontal Separators:

Horizontal separators are ideally suited to well streams having high gas-oil ratios, constant flow, and small liquid surge characteristics. Horizontal separators are smaller and less expensive than vertical separators for a given gas capacity. Liquid particles in the well stream travel horizontally and downward at the same time as a result of two forces acting upon them-the horizontal force of the gas stream and the downward force of gravity. Therefore, higher gas velocities can be permitted in horizontal separators and still obtain the same degree of separation as in vertical separators. Also, the horizontal separators have a much greater gas-liquid interface area than other types, which aids in the release of solution gas and reduction of foam. A special de-foaming section is used when severe foaming of the inlet stream is anticipated. The horizontal configuration is best suited for liquid-liquid-gas, or three phase separations because of the large interfacial area available between the two liquid phases. In addition to being easier to hook-up,

easier to service, and easier to skid-mount, horizontal separators can be stacked in piggy-back fashion to form stage separation assemblies and minimize horizontal space requirements.
- Applications:-

1. Areas where there are vertical height limitations.
2. Foamy production where the larger liquid surface area available will allow greater gas breakout and foam breakdown.
3. Three phase separation applications for efficient liquid-liquid separation.
4. Upstream of process equipment, which will not tolerate entrained liquid droplets in the gas.
5. Downstream of equipment causing liquid formation.
6. Well streams having a high gas to oil ratio and constant flow with little or no liquid surges.
7. Applications requiring bucket and weir construction for three-phase operation.

Separator Operation:

Like all separators the HLF must perform four distinct functions; inlet momentum control, vapor demisting, liquid retention and liquid outlet control. Normally the inlet is on one end of the horizontal separator and the gas and liquid outlets are on the opposite end. As fluid enters, bulk separation occurs at the inlet device; the phases separate within the liquid retention section and flow to their respective outlets. Demisting, coalescing devices and vortex breakers assist in the phase separation and prevent the re-entrainment of phases.