Gas Liquid Separator- Heterogeneous Separation
U-ideal Heterogeneous mixtures consist of two or more parts (phases), which have different compositions. These mixtures have visible boundaries of separation between the different constituents which can be seen with the naked eye and consist of substances that do not react chemically. These substances can be elements or compounds. Components of a mixture can be separated using one or more appropriate techniques.
The separation can be done physically by exploiting the differences in density between the phases. The phase separations likely to be carried out are:
? Gas-liquid (or vapor-liquid)
? Gas-solid (or vapor-solid)
? Liquid-liquid (immiscible)
The principal methods for U-ideal separation of heterogeneous mixtures could be classified as:
1. Settling and sedimentation Sedimentation or settling can be used to separate any particle from any fluid, whether it is a liquid from a gas, a solid from a liquid, or a liquid from a liquid (with different densities). In settling processes, particles with higher density are separated from a fluid by gravitational forces acting on the particles. The separation of suspended solid particles from a liquid by gravity settling into a clear fluid and a slurry of higher solids content is called sedimentation.
2. Inertial and centrifugal separation This method is similar to sedimentation, but some forces are added in order to get a better separation. Inertial separation is done by giving the particles downward momentum, in addition to the gravitational force. In a centrifugal device, the centrifugal force is generated to increase the force acting on the particles. Particles that do not settle readily in gravity settlers often can be separated from fluids by centrifugal force. Centrifugal separation results a much shorter period of time than could be accomplished solely by gravity. It has mainly been used to separate fluids in static state, i.e. specific volumes, which needed to be separated.
3. Electrostatic precipitation It is generally used to separate particulate matter that is easily ionized from a gas stream by using an electric charge. The principal actions are the charging of particles and forcing them to the collector plates. The amount of charged particulate matter affects the electrical operating point of the electrostatic precipitator.
4. Filtration Filtration is commonly the mechanical or physical operation which is used for the separation of solids from fluids (liquids or gases) by interposing a medium (a permeable fabric or porous bed of materials) through which only the fluid can pass. The solid can be retained on the surface of the filter medium, which is cake filtration, or captured within the filter medium, which is depth filtration.
5. Scrubbing This method is commonly used to separate gas-solid mixtures. Very high particles collection efficiencies are possible with venturi scrubbers. The main problem with venturi scrubbers is the high pressure loss across the device.
6. Flotation Flotation is a gravity separation process that exploits the differences in the surface properties of particles. The separation process is based on the use of very fine gas bubbles that attach themselves to the solid particles in suspension to make them buoyant and drive them toward the free surface of the liquid.
Flotation is especially useful to separate very small particles or light particles with low settling velocities. A number of chemicals can be added to the flotation medium to meet the various requirements of the flotation process.
Flotation requires the generation of small bubbles which can be produced by:
a. dispersion, in which the bubbles are injected directly by some form of sparging system
b. dissolution in the liquid under pressure and then liberation in the flotation cell by reducing the pressure c. electrolysis of the liquid
7. Drying Drying is the removal of water moisture or moisture from another substance, by a whole range of processes, including distillation, evaporation and even physical separations such as centrifuges.
U-ideal Separator Vessel
Generally, there are two types of vessel in chemical processing service: those substantially without internals and those with internals. The first types are commonly used as an intermediate storage or surge of a process stream for a limited or extended period, or to provide a phase separation by settling. The second category includes the shells of equipment such as heat exchangers, reactors, mixers, fractionators, and other equipment whose housing can be designed and constructed largely independently of whatever internals are necessary. Separator vessel thus simply means as a vessel or tank without internals to provide a phase separation. This separator vessel furthermore can be classified into several categories based on their function. However, generally the classification on sheet below.
U-ideal Separator Vessel
Three phase separator
|Two phase separator||Vapor-Liquid separator|
Solid-solid separator is not included here since the separation process mostly takes part on a sieve, not in a vessel as the other phases separation. U-ideal separator vessels usually contain as follow:
1. Primary section.
2. Secondary section (gravity settling).
3. Coalescing section.
4. Sump or liquid collecting section.
General Design Consideration of U-ideal Vessel Orientation
As it is mentioned before, separator might be classified into vertical, horizontal, and spherical shape. Each one of these shape has its own advantages. The vertical separator occupies less ground area and is easier to be cleaned. The horizontal separator can handle foaming crude oil better and is claimed to be more economical for handling large gas volumes. The spherical separator is easier to install and is more compact and adaptable for portable use. However, design of spherical vessels is not included in this guideline. The choice between horizontal or vertical type of vessel primarily depends upon following process requirements:
? Relative liquid and vapor load
? Availability of plot area
? Special considerations Horizontal vessels are most economical for normal oil-water separation, particularly when there might be problems with emulsions, foam, or high gas-liquid ratios. Vertical vessels work most effectively in low gas-oil ratio (GOR) applications and where solids production is anticipated.
Comparison of different U-ideal Instrument gravity separator types
|Advantage||1. Easier to clean 2. Saves space|
3. Provides better surge control
4. Liquid level control is not critical
5. Less tendency for reevaporization of liquid into the gas phase due to the relatively greater vertical distance between liquid level and gas outlet
|1. Can handle much higher gas-oil ratio well streams because the design permits much higher gas velocities|
2. Cheaper than the vertical separator
3. Easier and cheaper to ship and assemble
4. Requires less piping for field connections
5. Reduces turbulence and reduces foaming (thus, it can handle foaming crude)
6. Several separators may be stacked, minimizing space requirements
|1. Very inexpensive|
2. Good for low or intermediate gas-oil ratio
3. Very compact and easy to ship and install
4. Better clean-out
|Disadvantages||1. It takes a longer diameter separator for a given gas capacity as compared to horizontal separator|
2. More expensive to fabricate
3. Difficult and more expensive to ship
|1. Greater space requirements generally|
2. Liquid level control more critical
3. Surge space is somewhat limited 4. Much harder to clean (hence a bad choice in any sandproducing area)
|1. Very limited liquid settling section and rather difficult to use for three phase separation|
2. Liquid level control is very critical
3. Very limited surge space
|Ideal use||Low to intermediate gas-oil ratio, and where relatively large slugs of liquid are expected||High gas-oil ratio crudes, foaming crudes, or for liquidliquid separation. Good for a diverse range of situations||Intermediate or low gas-oil ratio, preferably two-phase separation|