After experiencing first-hand the benefits of a novel emulsion-breaking technology, ExxonMobil Research & Engineering (EMRE) has signed a marketing agreement with the developer of the technology�Houston-based Imperial Petroleum Recovery Corp. (IPRC)�and is applying the process in varied operational settings, both downstream and upstream.
The process uses electromagnetic radiation in the microwave range to separate stable, difficult-to-break emulsions into oil, water, and solids. ExxonMobil had tested the process on desalter undercarry at its Torrance, Calif., refinery. The application debottlenecked the desalter and enabled the refinery to increase crude throughput significantly. The refinery was so pleased with the results that after the merger between Exxon and Mobil late last year, ExxonMobil took a closer look at MST and decided to carry through with its efforts, together with IPRC, jointly to further develop the technology, apply it internally, and license it externally.
In May, ExxonMobil Research & Engineering Co. completed a worldwide marketing and development agreement with IPRC for the MST technology. In addition to applying the technology to downstream operations, upstream applications are being considered as well. IPRC retains title to the patents related to the process (it has 1 US and 19 international patents).
How it works
MST is a deceptively simple process. The general concept of using microwave energy to separate emulsions is not a new one, says IPRC, but the firm was the first to realize the necessary changes and developments to the technology to apply it effectively in commercial settings. "Lots of people worked on [microwave-based separation technologies], but they couldn't get the energy safely and consistently into the feed," said IPRC Pres. Brent Kartchner.
According to a paper written jointly by engineers from ExxonMobil and IPRC and presented in March 2000 at the American Institute of Chemical Engineers spring national meeting in Atlanta, "The MST has the potential to economically treat a wide range of crude oil emulsions in the upstream, downstream, and chemical sectors. Benefits include desalter and crude unit water and solids-related maintenance and chemical savings; enhanced crude unit energy, yield, and reliability performance; and increased desalter operating flexibility."
The paper was presented by Kenneth Albinson, ExxonMobil, who said, "These emulsions cause multiple problems to operating units, accumulate in refinery tankage, and in many instances have strong negative economics."
The MST process uses a proprietary microwave applicator to destabilize emulsions, facilitating their separation into oil, water, and solids streams. Here's how it works. A transmitter converts electricity to electromagnetic radiation in the microwave range. The units have a 75-kw power rating, says Kartchner, producing radiation with a frequency unlike the one used in a home microwave.
The microwaves then travel through a carefully configured arrangement of wave guides formed into precise shapes and assembled in such a way as to convey the microwaves toward the applicator, where they contact the emulsion feed. The interior of the wave guides is specially coated with material that facilitates propagation of the microwaves, and the system contains what Kartchner calls "aiming mechanisms" and uses precise angles of reflection. (Think of the way a camera uses a series of mirrors to reflect light onto film.)
Stepper motors keep the radiation moving toward the applicator at the correct rate, said Kartchner. The feed rate to a typical MST unit is 15-30 gpm, The water portion of the emulsion absorbs the applied energy preferentially. It is this characteristic that destabilizes the emulsion, says IPRC, because heating promotes flocculation and creaming. The MST process accelerates settling. "Disruption of the droplet interface promotes coalescence," said Albinson.
The energy absorbed by the feed increases its temperature by about 50� F., and the typical outlet temperature is less than 200� F. No further heating is applied after the microwaving step. Operating pressure ranges from 20 psig to 50 psig.
The system is effective on most oil-based emulsions, says IPRC, including so-called "rag layers" (the unseparated mixture that remains between the oil and water layers of an emulsion), slop oil emulsion solids, dissolved air flotation float, API separator sludge, desalter undercarry (the undesirable transport of crude oil out the bottom of the desalter along with the desalter brine), and tank bottoms. The output from the unit can be separated using either a centrifuge or in a settling tank, depending on the speed of separation needed, says IPRC.
IPRC's MST units are mounted on either 10 ft by 40 ft skids or 48 ft by 8 ft trailers, and thus are mobile and have a small footprint. They are fully automated and can be monitored on operator rounds.
The units are controlled by a sophisticated computer system that can be operated independently or run through a site-wide control system, such as a refinery distributed control system. If there is a problem on the system of any sort, an 80 db horn sounds, as does an alarm on the operator's computer monitor.
The Torrance Application
Although Mobil was dewatering its crude feed at the Torrance refinery, said Kartchner, the inefficiency of the operation was causing a reduction in crude unit throughput, "wear" problems with processing equipment, and increased costs associated with additional chemical usage. Mobil decided to review the MST technology and, based on the results of that review, opted for an 8-month test of a trailer-mounted unit.
The results of the Torrance test run were included in the ExxonMobil-IPRC paper presented at AIChE. In a test run, the feed rate to the unit was 629 b/d, consisting of 282 b/d of oil, 317 b/d of water, and 30 b/d of solids. After separation, the oil stream containing 96.5 vol % oil, 2.5 vol % solids, and 1.0 vol % water; the water stream contained 91.5 vol % water, 8.2 vol % solids, and 0.3 vol % oil; and the solids stream contained 46.3 vol % solids, 44.0 vol % oil, and 9.7 vol % water.
"We blast that stuff apart, give them back oil with less than 2% bs&w, so essentially only oil goes back..." to the crude unit, said Kartchner. Beyond the separation efficiency, the results of the test run were successful. By simply debottlenecking the desalter, the refinery has been able to significantly increase oil throughput. "This is because every barrel of water not removed displaces 6 bbl of oil in the crude unit," says Kartchner.
ExxonMobil was so pleased with the results of the extended test that it completed the marketing and development agreement with IPRC and arranged for IPRC to install an MST-1000 (a 1,000 b/d MST unit) at Torrance and operate it for a minimum of 3 years, with an option to extend it for another 3 years.
The unit separates the desalter undercarry feed into solids, water; and clean oil, which is reprocessed.
.The benefits of the MST project are numerous, according to the ExxonMobil-IPRC paper. Aside from significantly increasing crude unit throughput, raising desalter capacity, and enabling desalting of heavier crudes, the benefits are:
� Reduction in bs&w in recovered oil, resulting in increased preflash temperature and decreased pressure in the crude unit.
� Reduction in water in the atmospheric tower overhead stream, resulting in decreased top pressure, increased atmospheric and vacuum tower cut points, and a higher yield of gas oil at the expense of lower resid.
� Reduction in atmospheric tower heater and overhead cooling duty.
� Elimination of dewpoint limits on crude unit cuts.
� Reduction of corrosion, erosion, and fouling in the crude unit.
� Increased desalter operating flexibility and crude unit reliability.
� Potential for processing other refinery slops.
There are other potential benefits downstream of the crude unit, including fewer crude and desalter upsets; reduced chemical costs; decreased fouling and maintenance of downstream equipment; less oil loss to the sewer; reduced wastewater treatment load; less need for contractor emulsion treating; and reduced turnaround downtime.
Torrance sends new feed samples to IPRC in Houston for laboratory testing whenever the refinery's crude slate is changed, or when it wants to test the process on new non-desalter feeds. Refinery tank bottom emulsions have been tested in the unit, with excellent results, says Kartchner.
Expansion of efforts
Remotely controlled, IPRC-owned mobile units are "...generally going to be the direction we'll end up going," said Kartchner, although there will be exceptions to that rule.
Meanwhile, the Houston company is continuing with marketing efforts to other companies, both on its own and together with ExxonMobil. IPRC has about 20 projects pending, most of them downstream.
Marketing Director Marjorie Makielski says she expects the number of US applications to increase as more results come in from upstream applications. The potential benefits of MST at oil production sites, in storage facilities, and in shipping applications include reduced bs&w penalties, decreased chemical costs, less sludge production and storage, and increased wellhead production, according to IPRC. In addition, the process can enable an operator to open shut-in wells or separate oil, water, and solids in offshore applications, says the company.