Desalter Emulsion Separation By Emulsion Recycle (Exxonmobil Research And Engineering)
This utility claims priority to U.S. Provisional Software Ser. No. 61/911,153 filed Dec. Three, 2013, herein included by reference in its entirety.
Discipline OF THE INVENTION
This invention pertains to petroleum desalters and their operation.
Crude petroleum usually incorporates salts that may corrode refinery units; salt is removed from the crude oil by a process often called “desalting”, through which scorching crude oil is blended with water and an acceptable demulsifying agent to kind a water-in-oil emulsion which offers intimate contact between the oil and water, transferring salt into the water. The salty emulsion is then handed into a excessive voltage electric subject inside a closed separator vessel. The electric subject forces water droplets to coalesce, forming larger water droplets. As the water droplet volumes enhance, they settle to the underside of the tank underneath gravitation. The desalted oil forms on the higher layer in the desalter from the place it’s continuously drawn off for distillation. The salty water is withdrawn from the underside of the desalter.
During operation of desalter models, a stable emulsion part (often known as a “rag layer”) of variable composition and thickness types above the interface between the oil-steady part and the water-steady phase at the underside of the desalter. Sure crude oils contain natural surfactants (e.g. asphaltenes and resins) which are likely to kind a barrier around the water droplets within the emulsion, stopping coalescence and stabilize the emulsion in the desalting Toluene Equipment vessel. Finely-divided stable particles in the crude may act to stabilize the emulsion, and it has been found that solids-stabilized emulsions present explicit difficulties. Solids coated with crude oil parts, such as those found in oil sands, are thought to be particularly effective in forming stable emulsions. This emulsion phase might develop into stable and persistent in the desalting vessel. The expansion of stable emulsion layer reduces workable quantity and may short the electric circuit and drive unplanned and expensive desalter shut down. To mitigate the rag layer buildup in some circumstances, emulsion is withdrawn from the unit; alternatively or as well as, pricey demulsifiers may be added to the oil phase upstream of the desalter although with limited success.
Moreover, processing crudes with high rag layer formation tendencies in present desalter configurations may trigger poor desalting (salt removal) effectivity attributable to solids construct up at the bottom of the vessel, and/or a solids-stabilized rag layer leading to erratic level control and insufficient residence time for proper water/oil separation. Solids-stabilized emulsion layers have develop into a significant desalter operating concern, generating desalter upsets, elevated preheat prepare fouling, and deteriorating high quality of the brine effluent and disruption of the operation of the downstream wastewater therapy facilities.
Refinery websites which course of excessive solids-content material crudes (characterized as containing more than one hundred fifty ppm inorganic solids) have probably the most pervasive problems with emulsion formation. Heavy crude oils and bitumens from Western Canada which include elevated levels of small clay fines and different small solids are particularly vulnerable to forming massive volumes of extremely stable emulsion and with such feeds, growth of the rag layer is extra prevalent. These feeds are, nevertheless, being launched to refineries in larger quantities despite two important disadvantages associated to the efficacy of desalting. First, the viscosity of these crudes might be fairly excessive, so transport of water by means of the feed is slower than in excessive API gravity crude. Second, the density mismatch between water and oil is lower, so the gravitational vitality gradient is reduced in comparison with larger API gravity crudes. Progress of the rag layer in the desalter requires both the quantity of crude handed through the desalter is reduced or elimination of the rag layer from the desalting vessel for exterior treatment.
The water content material of the rag layer could range from 20 to 95% water with the stability being hydrocarbon (usually full vary crude oil) and up to 5 weight % inorganic solids. Precipitated asphaltenes, waxes, and paraffins may also be found at elevated levels in the rag layer (in comparison with the incoming crude oil) which combine with particulates (solids), to bind the mixture collectively to form a posh construction that is very stable. Intractable emulsions of this kind comprising oil, water and solids make ample separation and oil recovery troublesome. Typically, these stable emulsions arising from the desalter are periodically discarded as slop streams. This leads to expensive treating or handling procedures or pollution problems in addition to the fact that crude oil is also misplaced with these emulsions and slop streams.
Emulsions should be separated into effectively-outlined oil and water phases earlier than they are often reintroduced to refinery course of items (e.g. crude distillation, coker, and so forth.) or a waste water therapy plant. These stable emulsions might not be completely separated by heating and conventional gravity settling and require specialized separation gear.
Considered one of the commonest industry practices is to separate the stable emulsion into separate water, oil and solids phases using 3-phase centrifuges (decanter centrifuges). The centrifuge separation is usually enhanced with using chemical emulsion breakers, heating and/or depressurizing the emulsion to facilitate the process. US 2012/0024758 (Love) proposes a method through which the emulsion “rag” layer is withdrawn from the separator vessel at a fee that maintains the top of the emulsion layer approximately constant so as to permit withdrawal of the rag layer at a hard and fast level from the vessel. The withdrawn emulsion is then processed exterior the vessel via a stacked disk centrifuge. At present practiced centrifuge separation approach has, nonetheless, quite a few reliability and price drawbacks centering on the separation of the oil and water phases before they can be reintroduced to refinery process models (e.g. crude distillation, coker, and so forth.) or the waste water remedy plant.
As one problem crude oil prices 5 years space arises from the comparatively high viscosity of the emulsions formed from heavy oil feeds, varied proposals for dilution of the emulsions to cut back their viscosity have been made. U.S. Pat. No. 3,396,one hundred (Pettefer), for example, proposes the separation of oil and water in the rag layer by the direct addition of naphtha or kerosene to the rag layer within the separation tank with out withdrawal of the rag layer, the injection of the diluent into the interfacial zone acts to launch the solids otherwise retained within the layer in order that they settle out into the water layer as a residue.
U.S. Pat. No. 4,200,550 (Scherrer) discloses withdrawal of the rag layer that’s examined to find out the amount of stable emulsion, water, and oil. If there may be greater than a specific amount of rag layer in the withdrawn pattern, then a demulsifier is injected instantly into the desalter.
U.S. Pat. No. 5,219,471 (Goyal) discloses dilution of the rag layer with an aromatic hydrocarbon followed by centrifugation to separate the phases.
U.S. Pat. No. 4,824,555 (Paspek) discloses a way in which the stable emulsion is removed from the desalter and a hydrocarbon with a high vapor pressure is added beneath excessive strain in a separate vessel.
U.S. Pat. No. 5,882,506 (Ohsol) describes methodology for treating desalter rag layer emulsions, for the recovery of processable oil values by adding a adequate quantity of a light hydrocarbon diluent to the emulsion to lower its general viscosity and to reduce the specific gravity of the oil part. The diluted emulsions are subjected to flashing at emulsion-breaking circumstances after which the oil is recovered from the various streams created in the flashing steps.
A related course of is described in U.S. Pat. No. 4,938,876 (Ohsol) during which emulsions are rendered more amenable to gravitational and cyclonic separation by inflicting a portion of the normally water-dispersed phase to flash into vapor by abruptly reducing pressure on the emulsion which has been heated by direct contact with superheated water and/or steam. The envelope around each droplet is thus shattered so the dispersed phase can be coalesced and separated by gravity, or enhanced gravity forces, when there’s a enough divergence of specific gravity and a low viscosity. Appropriate anti-emulsion chemicals are sometimes added to forestall re-emulsification. These processes, nonetheless, are vitality-intensive requiring vital quantities of heat in the flash vaporization.
A unique approach is prompt in U.S. Pat. No. Four,722,781(Swartz). A portion of the rag layer is returned to the crude oil feed stream, upstream of water and chemical addition, and without any extra processing. A slip stream comprising the portion which isn’t returned to the crude oil feed is drawn off to keep away from solids contaminant buildup. This slip stream is diluted with a mild hydrocarbon materials to interrupt the emulsion and the oil lowered in solids content is then recovered by settling and decantation. Oil is removed from a tank after the water and oil layers have settled. The oil section and rag layer may be removed together from the desalter and taken to a second vessel in which they are separated.
Co-pending U.S. Provisional Patent Application Ser. No. 61/774,957, filed 8 Mar. 2013 (EM Household No. 2013EM063), describes an improved mode of desalter operation through which for withdrawal of a portion of the emulsion layer is withdrawn from the desalter vessel by means of one or more external withdrawal headers in keeping with the thickness and place of the emulsion layer with the selected withdrawal header(s) being managed by sensors monitoring the place and thickness of the emulsion layer. The withdrawn emulsion layer is then routed as such or with the desalter water effluent to a settling tank or directly to a different unit for separation and reprocessing.
Co-pending U.S. Provisional Patent Utility Ser. No. Sixty one/828,963, filed 30 Might 2013 (EM Family No. 2013EM170), describes an improved mode of desalter operation in which a portion of the emulsion layer from the desalter vessel is withdrawn for treating the emulsion layer withdrawn from the desalter vessel as a way to separate it into its oil and water parts along with any solids introduced along with it. This therapy contains diluting the withdrawn emulsion with added water or oil to destabilize the emulsion and permit its subsequent separation. The desalting technique is operated by forming a settled water layer containing the dissolved salts with a settled supernatant, desalted oil layer and an intervening emulsion layer formed from the oil and the water. A portion of the emulsion is withdrawn through a number of withdrawal ports or headers and diluted with an added fluid, usually water or an added hydrocarbon feedstock, to destabilize the emulsion which is then separated, optionally with the aid of an electrostatic precipitator in a separator vessel which itself may be a desalter kind vessel working with a excessive voltage electric filed to facilitate the separation.
Co-pending U.S. Provisional Patent Software Ser. No. 61/882,358, filed 25 Sep. 2013 (EM Household No. 2013EM259, Brian D. Albert et al.), describes a desalting course of during which the oil/water emulsion layer which forms within the desalter vessel between the settled oil and water layers is separated into the oil and water elements by direct contact with a heated, excessive boiling hydrocarbon performing as a heating medium to switch heat from the heating medium to the emulsion. This has the impact of breaking the emulsion after which at the very least partly vaporizing the water content of the emulsion in a flash drum downstream from the desalter vessel. The popular heating medium is an atmospheric or vacuum resid, each of which have the advantage of being readily accessible and of not introducing extra gentle hydrocarbon vapors into the flash drum together with the water vaporized from the emulsion.
– High of Web page
Based on the current invention, a fluid stream that includes the interface between the effluent water and fluid above is removed from the desalter. Additionally, this fluid may be recycled again to the crude feed into the desalter, ideally to be returned upstream of the combination valve that creates the water-in-oil emulsion earlier than it is sent to the desalting vessel. The fluid that’s withdrawn and taken to recycle consists of fluid extracted from the boundary layer on the interface of the water and the supernatant emulsion including oil-wet solids which stabilize the emulsion layer. The addition of a small amount of rag layer to crude oil and water before emulsification not solely does not inhibit efficiency, it enhances water separation by reusing the trapped demulsifier for higher water resolution. In a single variant of the method, a hydrocarbon diluent is used to help the separation of the oil from the solids within the settler.
In operation, the desalting is carried out by mixing a crude oil to be desalted with water and passing the mixture of oil and water to the desalter vessel. The emulsion enters the desalting vessel between electrodes at a high voltage. Water droplets coalesce within the electric area and settle towards the bottom of the tank below gravitational forces. An crude oil prices 5 years emulsion layer formed from the oil and the water and emulsion-stabilizing solids kinds between the settled water layer and the settled oil layer; water is removed from the water layer through a water outlet conduit at the bottom of the vessel and desalted oil is removed from the oil layer by an oil outlet conduit at the highest of the vessel. An emulsion outlet for removing an emulsion stream from the emulsion layer is offered in the vessel and that is related to an optionally available settling drum interposed between the emulsion outlet of the desalter vessel and the recycle conduit to cut back the amount of non-emulsified water returned to the process.