Diseño. "Valorización de Crudo Extra-pesado en Villavicencio, Colombia" Notebook: Diseño Created: 17/03/2020 03:56 p.m. Author: [email protected] Updated: 17/03/2020 06:34 p.m. Diseño. "Valorización de Crudo Extra-pesado en Villavicencio, Colombia" Book Crude Oil Emulsions. (H. Vernon Smith & Kenneth E. Arnold) Date 17 de Marzo de 2020 SUMMARY –––––– "To prevent increased transportation costs, water treatment and disposal costs, and deterioration of equipment purchases of crude oil limit the basic sediments and water (BS&W) content of the oil they purchase. Limits vary depending on local conditions, practices, and contractual agreements and typically range from 0.2 to 3.0%" "Oil-in-water emulsions are generally resolved in the same way as water-in-oil emulsions, except electrostatic treaters cannot be used on oil-in-water emulsions." "The most common range of emulsified water in light crude oil-i.e., oil above 20°API is from 5 to 20 vol%. The most common range of emulsified water in crude oil heavier than 20°API is from 10 to 35%." STABILITY OF EMULSIONS "Generally, crude oils with low API gravity (high density) will form a more stable and higher-percentage volume of emulsion than will oils of high API gravity (low density)." Chemical Demulsifiers "Certain chemical compounds are widely used to destabilize and to assist in coalescence of crude oil emulsions. These are referred to as deshydration chemicals or demulsifiers. This treatment method is popular because the chemicals are easily applied to the emulsion, usually are reasonable in cost, and usually minimize the amount of heat and settling time required." "For actions are required of a chemical demulsifier: Strong attraction to the oil/water interface: The demulsifier must have ability to migrate rapidly through the oil phase to reach the droplet interface where it must counteract the emulsifying agent. Flocculation: The demulsifier must have an attraction for water droplets with a similar charge and bring them together. Coalescence: After flocculation, the emulsifier film is still continuous. If the emulsifier is weak, the flocculation force may be enough to cause coalescence. With the emulsion in a flocculated condition, the film rupture results in growth of water drop size." "If the system is an electrostatic process, where some of the flocculation and coalescing action is accomplished by the electric field, there is need for a quickacting demulsifier" "The optimun chemical is one that will provide the clearest, cleanest separation of water from oil at the lowest temperature in the shortest time at the lowest cost per barrel treated and that will not interfere with subsequent deoiling of the water." "The required concentration of demulsifying chemical may be as high as 8gal/1000bbl (about 200ppm) or as low as 1gal/5000bbl (about 5.0ppm). This is a range of 40 to 1. The most common range of chemical injection is between 10 and 60ppm." Electrostatic Coalescing "When a nonconductive liquid (oil) containing a dispersed conductive liquid (water) is subjected to an electrostatic field, the conductive particles or droplets are caused to combine by one of three physical phenomena: 1. The water droplets become polarized and tend to align themselves with lines of electric force. 2. The water droplets are attracted to and electrode because of an induced electric charge. In an AC field, because of inertia, small droplets vibrate a greater distance than larger droplets, promoting coalescence. In a DC field, the droplets tend to collect on the electrodes, forming larger and larger droplets util eventually the settle by gravity." 3. The electric field tends to distort and thus to waken the film of emulsifier surrounding the water droplets. Water droplets dispersed in oil subjected to a sinusoidal alternating-current field will be elongated along the lines of force as voltage rises during the first half-cycle" "If the quantity of water in the oil is large there is a tendency for the formation of a chain of charged water particles, which may form links between the two electrodes, causing short-circuiting. This is referred to as "chaining" and has been observed in emulsions containing 4% of less water." "If chaining occurs, the voltage gradient is too large (The electric grids of the electrostatic treater are too close together or the voltage is too high) for the amount of water being handled. Small amounts of gas breaking out of solution may also created sufficient turbulence and impede the coalescing process." Water-Washing "The water-wash is more beneficial if the emulsion has been destabilized by addition of a demulsifier and if the water is heated. The effectiveness of a water-wash greatly depends on the ability of the spreader plate or distributor to divide the emulsion into small streams or rivulets and to cause the emulsion to be in maximum intimate contact with the water bath so that the small drops of water can coalesce with the water." "Water from the emulsion to be treated should be used if available. If it is not, extraneous water may be used." EMULSIONS-TREATING EQUIPMENT AND SYSTEMS Horizontal Emulsion Treaters "Flow enters the front section of the treater where gas is flashed. The loquid flows downward to near the oil/water interface where the liquid is waterwashed and the free water is separated. Oil and emulsion rises past the fire tubes and flows into and oil surge chamber. The oil/water interface in the inlet section of the vessel is controlled by and interface-level controller, which operates a dump valve for the free water. The oil emulsion flows through a spreader into the back or coalescing section of the vessel, which is fluid-packed. The spreader distributes the flow evenly through-out the length of this section. Treated oil is collected at the top through a collection device used to maintain uniform vertical flow of the oil. Coalescing water droplets fall counter current to the rising oil. The oil/water interface level is maintained by a level controller and dump valve for this section of the vessel. A level control in the oil surge chamber operates a dump valve on the oil outlet line regulating the flow of oil out the top of the vessel and maintaining a liquidpacked condition in the coalescing section. Gas pressure on the oil in the surge section allows the coalescing section to be liquid-packed. The inlet section must be sized to handle separation of the free water and heating of the oil. The coalescing section must be sized to provide adequate retention time for coalescence to take place and to allow the coalescing water droplets to settle downward countercurrent to the upward flow of the oil." Electrostatic Coalescing Treaters "Two grids of electrodes typically are installed in electrostatic emulsion treaters. One is wired to a source of electric current and the other is grounded. The emulsion flows between these electrodes, which are charged with a very high voltage. The electrodes are installed in the vessel to provide a final stage of coalescence to the emulsion after ir has already been treated to near pipeline quality." "The normal operating spacing between the two grids is usually 4 to 6 in." "In addition to safety controls normally found on emulsion treaters with fireboxes, there are also low-liquid-level safety switches on the electric power being applied when the high-voltage grid is surrounded with gas instead of liquid." "The transformes is normally an 18000-20000V." "The application of electrostatic treaters should be limited to "polishing" of oil to avoid chaining and short-circuiting of the grids. They are particularly effective in reducing the water content of oil to very low levels (less than 0.5 to 1.0%). Electrostatic coalescence may also aid in reducing heat and/or chemicals required to treat crude oil to specific quality." Desalting Crude Oil (Page 26) "Most produced water contains salts, which may cause problems in production and refining processes when the solids precipitate to form scale on heaters, plug ex-changers, etc... This can cause accelerated corrosion in piping and equipment." "Because of the operational problems associated with salts, most refineries buy crude at a salt content of 10 to 20 lbm/1000bbl, then desalt the oil to 1 to 5ppm/1000bbl before charging to crude stills" "Mixing efficiency in a desalting system refers to the fraction of wash water that actually mixes with the produced water. The remainder of the water, in effect, bypasses the desalting stage and is disposed of as free water. A mixing efficiency of 70 to 85% can be considered a reasonable range of attainment. Part of the energy for mixing is obtained from the pressure of the wash water, which should enter the mixer approximately 25psi above the pressure in the vessel." Clarification of Water Produced with Emulsions "These small particles of oil will be suspended in the water and held there by mechanical, chemical, and electrical forces. The amount of oil contained in the untreated produced water in most systems will vary from an average low of about 5.0ppm to an average high of about 2000ppm. In some water systems, oil contents as high as 20000ppm (2%)." OPERATIONAL CONSIDERATIONS FOR EMULSION-TREATING EQUIPMENT Burners and Fire Tubes "API RP 14C, "Analysys, Design, Installation and Testing of Basic Surface Safety Systems for Offshore Production Plataforms" contains a basic description of recommended safety devices needed for fired and exhaust-heated units." "Every gas-fired crude oil heating unit should be provided with fuel gas from which liquids have been "scrubbed". These ful-gas scrubbers are typically 8 to 12in in diameter and 2 to 4ft tall, and contain a float-operated shutoff valve. If liquid enters the fuel-gas scrubber, the float will close a valve and stop gas flow to the burners of the heating unit. This will prevent oil from entering the combustion chamber and possibly prevent a fire." "Most fire tubes trar transfer heat to crude oil or emulsion are sized to transfer 7500Btu/hr - sqft, although some manufacturers use heat-transfer rates as high as 10000btu/hr - sqft." "The temperature controller, fuel control valve, pilot burner, main burner, combustion safety controls, and fuel-gas scrubber for controlling and cleaning the fuel gas for fired treating vessels should be inspected and cleaned periodically as required." Level controllers and Gauges "For heavy crude oils, electronic interface controllers have been very succesful. These operate on the principle of the difference between oil and water electrical conductivity, electrical capacitance, or radio frequency. The most common type called "capacitance probes", they use the dielectric strength of the fluid in which the are immersed." Special Safety Features for Electrostatic Treaters "Because the high voltage and the associated potential hazard to personnel, electrostatic treaters require a positive shutdown switch for the high-voltage transformer. This disconnects the transformer if the fluid levels fall below a predetermined level in the treating vessel. Some manufacturers install an internal grounding device inside the treater that grounds the hot grid if fluid is not present." ECONOMICS OF TREATING CRUDE OIL EMULSIONS
