The CANMET Hydrocyclone: An Innovative Technology for the ...

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APPLICATIONS OF THE CANMET HYDROCYCLONETREATMENT OF DESALTER EFFLUENTRefinery desalters generate significant volumes of oily effluents. Depending on the upstream processes andthe initial feed, these effluents may contain significant amounts of oil (up to 10% by volume) and solids (upto 5%), especially during desand operations. High oil contents reduce the separating ability of the skimtanks and significantly lengthen the residence time of the fluid in the tank. Typical retention time of skimtanks ranges from a few hours to a day. Hence, it is highly desirable to utilize a separation technology thatis able to efficiently and effectively separate this effluent, reducing the retention time and hence reducingthe number of skim tanks required. With its low capital cost and virtually no maintenance costs, theCANMET hydrocyclone stands out as the best solution to this problem.A period of successful field testing was conducted at the Husky Energy Lloydminster refinery prior to theinstallation of the commercial CANMET hydocyclone system. The results obtained from the field testingwere very encouraging, as a stream of clean water containing ppm levels of oil and the bulk of the solids(mostly clean with the oil coating stripped off) was produced. From observations of the underflow samplescollected, the solids settled in less than 30 minutes in most cases. Hence, it was anticipated that theunderflow water could be separated in a significantly reduced period of time and would cause minimal orno problems when injected into disposal wells. As a result, a multi-hydrocyclone system with a capacity ofabout 1000 m3/d (shown in Figure 3) was constructed and installed at the Husky refinery. Figure 4 shows afront view of the open CANMET hydrocyclone vessel. The worker is installing a hydrocyclone unit.Excellent results were obtained after the installation of the multi-hydrocyclone system. Oil content analysesof feed, overflow, and underflow streams on various days are shown in Table 1. On some days, make-upwater was added to the effluent stream to meet the minimum processing capacity of the system. In anyevent, the multi-hydrocyclone unit can be set up for a lower processing capacity by replacing some of thehydrocyclone units with blanks. Figure 5 shows samples collected during normal desalter operation. Thefeed contained about 1% oil and 5.6% suspended solids. After the separation, the overflow contained about11% oil (with traces of solids remaining with the oil phase) and was free of settled solids. The underflowwas almost free of oil (on-site colour matching analysis showed oil concentration less than 100 ppm) andall of the solids reported with this stream. Figure 6 shows samples collected during the desanding phase ofoperation. This difficult-to-separate emulsion takes about 4–6 hours (and longer in some cases) to separatein a settling tank. The photograph was taken about 30 minutes after the three samples were collected. Noseparation could be observed in the feed sample. BS&W analysis showed that it contained about 7% oil and6% solids by volume. However, when this same feed was treated using the CANMET hydrocyclonesystem, it was separated into an oil-rich overflow containing about 35 vol% oil and traces of solids (about0.2%). Almost all of the solids in feed reported to the underflow stream with small amounts of residual oil.TREATMENT OF SLOP OILSlop oil is the fluid that is skimmed from deoiling skim tanks. It is a tight emulsion containing significantamounts of water, up to 90% by volume. Slop oil also contains “rag layer”, described by experienced oilfield workers as a solids-containing material found in the interphase region of the oil and water layers in askim tank. Rag layer is relatively viscous and is formed when residues from chemical injections in priorprocesses become attached to solids (fines), water, or oil droplets.A two-stage CANMET hydrocyclone system was set up at the client site to evaluate the performance of theCANMET hydrocyclone to treat slop oil produced during the processing of wellhead production. The testloop, designed and assembled by the AST hydrocyclone team, is shown schematically in Figure 7.The Environment & Energy 2003 Conference 470
Tests were conducted with and without conditioning of the slop oil feed to the hydrocyclone. Slop oilsamples were collected from bottom to the top of the slop tank; oil concentration varied from 15% to 40%by volume. Bench-scale testing (hot spin centrifuge from Alfa Laval was used) showed that these slopsamples, with oil concentrations higher than 15%, would be difficult to separate at temperatures of 50–70°C because of the high viscosity of the oil.Testing Without ConditioningInitial testing was conducted without conditioning the feed stream, at a process temperature of 70°C. Theoil concentration in the feed stream (to the first-stage) varied from 20% to 40% by volume. The operatingparameter settings (pressures and orifice size) predetermined as optimal for these test runs were: feedpressure (P F ) 700 kPa, overflow pressure (P O ) 300 kPa, and underflow pressure (P U ) 500 kPa (maintainingpressure differential ratio [PDR]* of 2, ), and a 2.5-mm overflow orifice.Results from these test runs, shown graphically in Figures 8 and 9 show the dependence of separationefficiency on feed temperature. In summary, for feed containing 15-20% oil at process temperatures from60°C to 75°C, maximum separation efficiency was 35% and oil recovery was 50%.Testing with ConditioningTo improve separation, the slop oil was conditioned by adding water and heating to around 90°C. Thislowered the oil concentration in the feed stream from the 30% range to 10-15%, and also reduced theviscosity. The hydrocyclone operating parameters were the same as for the tests without conditioning.As the graphs in Figure 8 and 9 show, the increase in temperature resulting from conditioning was a majorcontributor to improvements in separation efficiency and oil recovery.A series of tests were conducted at elevated temperatures (80-90°C); the results are given in Table 2. Withthe reduced oil viscosity, the water phase was able to migrate more easily through the oil phase towards theperimeter of the hydrocyclone, while oil droplets coalesced at the central core. As a result, higher oilconcentrations were achieved in the overflow stream. In most of the test runs, as Figure 10 shows, overflowoil concentrations of 65% to 75% were achieved, nearly five times the feed oil concentration. The resultssuggest that separation would be improved further by heating the feed to 95°C or by further reducing theviscosity of the slop oil by conditioning. A photograph of BS&W analysis of feed and product streamsfrom a test is shown in Figure 11SUMMARYIn extensive field testing the CANMET hydrocyclone has proved to be an effective and economicalternative for separating a variety of oily feeds into a concentrated oil stream and a clean water streamsuitable for reuse or disposal.Successful test programs have been conducted using refinery desalter effluent, slop oil, wellheadproduction, and other produced fluids.Compared to conventional treatment schemes, the CANMET hydrocyclone lowers capital and operatingcosts and reduces environmental impacts.* PDR = [P F – P O ] / [P F - P O ]The Environment & Energy 2003 Conference 471
Page 1 and 2: The CANMET Hydrocyclone: An Innovat
Page 3: ENIVIRONMENTAL ADVANTAGESReduced CO
Page 7 and 8: Table 2 - Results from slop oil tes
Page 9 and 10: Figure 4 - Opened from front view o
Page 11 and 12: 807060Separation Efficiency (%)5040

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