A Salt Lake City refinery recently implemented recommendations that resulted from an innovative energy best practices program.
By implementing the recommendations, the Flying J refinery reduced electrical consumption by 5-6% and lowered purchased natural gas use by 35-40%. That resulted in cost savings of approximately $900,000 in the first year.
A US Department of Energy (DOE) showcase enabled Flying J to combine input from DOE-sponsored energy experts and university personnel with industry-specific insight and recommendations from UOP LLC, resulting in a comprehensive evaluation of plant-wide energy use.
Refinery participation
As a participant in the Utah 2001 Industry Showcase (see box on opposite page), Flying J teamed with DOE and UOP to evaluate plant-wide energy use. The savings proved to be worth the effort.
Flying J, based in Ogden, Utah, operates a 25,000-b/sd refinery in North Salt Lake. The 130-employee refinery processes a combination of crude oils from Utah, Wyoming, and Canada. Refinery products include gasoline, diesel, propane, and wax intermediates. The refinery supplies fuel products to the company's highway travel plazas and fuel stops.
As a participant in the regional showcase, Flying J received access to a selection of technical and financial DOE resources.
DOE resources
In the months before the August 2001 event, Flying J hosted DOE-sponsored groups in an effort to successfully identify plant-wide energy savings opportunities.
•Targeted assessment experts. Five DOE-sponsored experts in industrial energy management best practices provided in-plant technical assistance to help Flying J identify opportunities for increased savings and productivity in industrial energy-use systems.
The experts worked with Flying J to evaluate energy-savings opportunities in its process heating, pumps, steam, insulation, and compressed air systems.
Flying J elected to schedule the targeted, walk-through assessments (lasting 1-3 days) as part of its showcase support agreement with DOE.
•Industrial assessment center team. A team of engineering students and faculty from Texas A&M University conducted a 2-day assessment of Flying J plant operations to identify, evaluate, and recommend opportunities to conserve energy, increase productivity, and prevent pollution.
Texas A&M is one of 26 DOE sponsored, university-based industrial assessment centers around the country. Teams of engineering faculty and students conduct free, on-site industrial assessments (for 1-2 days) at eligible manufacturing facilities.
Typical for showcase plant sites, Flying J received $100,000 from DOE to work with the consultant of its choice in conducting an energy study. Flying J chose UOP's Refinery Profitability Services Group to perform a comprehensive plant energy-systems audit.
UOP audit
UOP kicked off a 4 month, refinery-wide study of Flying J's energy use in April 2001.
The study's scope included the crude and vacuum distillation units, naphtha reformer and isomerization units (including hydrogen pretreater), alkylation unit, diesel desulfurization and dewaxing units, saturated gas plant and butane isomerization unit, and the sulfur plant.
The study did not include the new FCC unit that was under construction.
The study objectives were to:
- Summarize energy consumed in each unit.
- Benchmark energy consumption to industry standards.
- Install a computer-based program that allows for continual energy monitoring.
- Generate a preliminary list of projects to help improve energy efficiency.
Fig. 1 shows the steps to implement this type of study.
In preparation for the study's analysis phase, the project team, including UOP energy specialists and Flying J engineering and operations staff, conducted process unit walk-throughs, held brainstorming sessions, and collected unit operating data.
The project team calculated energy consumption for each process unit. Consumption values were benchmarked against industry-wide standards and against UOP's latest and most efficient designs.
The team also generated a customized "refinery target" for each unit in addition to industry benchmarks. These more refined and adjustable refinery targets were based on the best actual performance recorded during the test period.
Customized benchmarks identified obtainable energy targets for each unit and transient energy losses associated with short-term upsets or control problems.
Figs. 2 and 3 show actual unit energy performance compared to benchmarks and refinery targets.
UOP tracked key energy indicators to establish a connection between unit operating conditions and energy consumption. Examples include heater efficiencies, reflux-feed ratios, and steam-stripping rates.
These indicators helped the team identify why unit energy consumption changed in a specified time frame.
To determine the efficiency loss that can occur from improper turndown, UOP tracked total energy consumed vs. charge rate for each process unit. A linear regression of target energy values showed how closely the unit operates to the refinery target at varying charge rates.
Study findings
The DOE-sponsored experts, industrial assessment center team, and UOP engineers all developed energy-saving recommendations for Flying J to consider for implementation.
Assessments; UOP study
Table 1 shows a summary of savings opportunities that the DOE-sponsored targeted assessment experts identified. Table 2 shows the eight recommendations that the Texas A&M University team identified. Potential savings were $261,000/year.
Total energy consumed in the Flying J refinery averaged 230 MMbtu/hr during the 4-month evaluation period. This value includes steam, fuel, and electricity consumption. This energy cost about $22,000/day.
The UOP target energy consumption was 219 MMbtu/hr, or $21,000/day. Potential refinery-wide cost savings were therefore $1,000/day for normal operations.
Figs. 4 and 5 show the energy and cost variance between the energy consumed in each process unit and the refinery target energy consumption for each unit.
Several process units showed little change in total energy consumption as charge rates varied.
UOP quantified this effect to demonstrate the increase in per-barrel energy costs resulting from equipment underutilization.
UOP's findings suggested where improved controls and instrumentation would help minimize efficiency losses at low throughputs.
Some unit-specific performance findings were:
•Crude unit. The utility breakdown graphs clearly showed the effects of switching between mixed and waxy crude runs. Actual energy consumed was closer to the target during waxy runs, indicating that optimizing feed heat exchange could improve performance during mixed-crude runs.
•Vacuum unit. Unit efficiency markedly improved after a mid-June 2001 shutdown. Two months later, however, the unit was returning to pre-shutdown performance levels.
UOP attributed the decreasing unit efficiency to higher fuel-gas use per barrel of feed.
This, in turn, was due to a loss in heater efficiency (as indicated by increased stack temperatures) and to an increase in column reflux rate.
UOP quantified the cost of this efficiency loss and sent it to Flying J's engineering staff for consideration; several trade-off issues were associated with meeting product specifications.
•Butane isomerization unit. Low energy use in this unit was partially due to the fact that reactor preheat is partially supplied by process-heat integration instead of a direct utility.
A correlation between changes in feed rate and changes in the stabilizer reflux-feed ratio indicated potential steam cost savings with an optimized stabilizer reflux-feed ratio. UOP also found that regeneration equipment might contribute to intermittent efficiency declines.
•Naphtha hydrotreater unit. Improved reactor-effluent heat recovery and a lower reactor feed-effluent hot end approach would yield significant efficiency improvements. Additionally, UOP recommended an operating procedure for setting the fractionator reflux rate.
Reformer and isomerization units. The hot-end approach in the feed-effluent exchanger was higher than similar units in other plants. Fuel and steam use varied in this unit, which possibly indicated changes in feed properties or unmeasured changes in product octane.
•Alkylation unit. Unit conditions were unsteady during the study timeframe due to sharp variations in the feed rate. Stabilizing the charge rate would allow Flying J to fine-tune the operating parameters to improve efficiency.
•Diesel desulfurization and dewaxing units. These units experienced high energy consumption because there are two separate reactor-heater trains sharing a common separator and stripping facilities; however, there was not much day-to-day variation, which indicated good control.
During the study, UOP identified 33 energy improvement projects. A team that included refinery operations staff, refinery engineering staff, and technical specialists at UOP developed these projects.
The team provided sufficient detail to convey the project idea with the understanding that, for several of the projects, additional detailed engineering would be required to bring the project to fruition.
Flying J implementation
Flying J implemented many of the energy-saving recommendations that resulted from the DOE assessments, industrial assessment center team, and UOP energy-usage study.
DOE assessments
Flying J implemented most of the savings opportunities that the DOE experts suggested.
Flying J implemented oxygen control for flue gases in the process heaters.
The refiner also implemented all the pump system recommendations except those for the 250-hp pump, which are still under evaluation.
The steam expert's recommendations resulted in improved boiler efficiency.
Flying J implemented all the insulation recommendations with the exception of the 80,000-bbl storage tank. This project will occur during the next scheduled tank inspection.
Flying J repaired compressed air leaks and partially implemented a central compressed-air drying system.
Industrial team
Of the eight recommendations from the Texas A&M assessment team, Flying J implemented four.
The refiner is still considering the other four projects for future implementation.
Flying J repaired leaking steam traps, insulated reformer unit piping and heat exchangers, rescheduled butane isomerization unit regenerations, and repaired steam leaks.
In the year after receiving the UOP energy study, Flying J implemented 8 of the 33 recommended projects and eliminated approximately 10 of the projects for process reasons unique to the refinery. The other projects are still under consideration.
The eight UOP energy study project recommendations that Flying J implemented were to:
•Optimize crude unit preflash operation. Optimized reflux rate and overhead temperature on the preflash tower improved crude-unit heat recovery.
•Optimize crude unit stripping-steam rates. Ratio control that varies stripping-steam rates based on the rundown flow rate helped minimize excessive stripping. Savings estimates are based on reducing the steam-stripping rate to the crude tower bottoms by 3 lb/bbl, with additional savings on side-cut streams.
•Bypass heavy diesel run-down coolers. Flying J bypassed a run-down cooler to avoid reheating approximately 1,000 b/sd of diesel from storage as feed to the hydrotreater. Consequently, Flying J is saving approximately 1,600 MMbtu/year in heater demand.
•Produce nitrogen on site. On-site nitrogen production replaced liquid nitrogen brought in on trailers. In addition to the avoided cost of purchased nitrogen, on-site nitrogen is generally cheaper than fuel gas; this allows for conversion of fuel gas purges to nitrogen. Nitrogen purges reduce costs and CO2 emissions.
•Insulate hydrotreater-reactor piping. Insulating the reactor bottom elbow saved the refinery approximately $3,000/year.
•Reduce reactor-circuit pressure drop in the reformer. The reformer-reactor pressure drop increased steadily between runs. Benefits from correcting the pressure drop include reduced recycle compressor energy use, increased unit capacity, and increased product yield.
•Reduce water to the sulfur recovery unit. Flying J reduced the sour-water-stripper overhead temperature to 185° F., which minimized water carryover to the sulfur recovery unit.
Less water in the sour-water-stripper offgas reduces the fuel gas use in the sulfur unit. Flying J also optimized the sour water steam-stripping rate using ratio control based on the bottoms flow rate.
Check for leaking relief valves. Flying J conducted a plant-wide survey of more than 75 valves and found four leaks, which they repaired during unit turnarounds.
Relief valve surveys conducted with hand-held acoustic sensors once or twice a year can identify significant fuel gas losses to flare. Typical industry findings show that 80% of the fuel gas losses to flare will occur in 2% of the valves.
The authors
Sabine Molden Brueske is a process engineer at Energetics Inc., Bellingham, Wash. She provides engineering support to the US Department of Energy, Office of Energy Efficiency and Renewable Energy. Brueske holds a degree in chemical engineering from the Colorado School of Mines, Golden, Colo. She is a member of AIChE.
Stuart Smith is a process engineer and energy coordinator at Flying J Inc.'s North Salt Lake, Utah, refinery. He previously served as assistant refinery manager for Inland Refining Inc., Woods Cross, Utah, and as staff engineer for Exxon Research & Development Laboratories, Baton Rouge. Smith holds a BS in chemical engineering from Brigham Young University, Provo, Utah, and an MBA from Louisiana State University, Baton Rouge.
Robert Brasier is a senior consultant in UOP LLC's solutions and services department, Des Plaines, Ill. He holds a degree in chemistry and chemical engineering from the University of Michigan, Ann Arbor, and a masters in chemical engineering from the Illinois Institute of Technology, Chicago.
Utah 2001 Industry Showcase
In August 2001, the U.S. Department of Energy's (DOE) Office of Industrial Technologies and the state of Utah hosted a regional showcase event in Salt Lake City. The showcase provided 400+ attendees with solutions to various energy problems that commonly confront the petroleum refining, mining, and aluminum industries in the western US.
The 4-day event featured plant tours, breakout sessions, an exhibit hall, and a forum with local members of Congress and industry CEOs.
Six industrial plant sites in Salt Lake City demonstrated the savings achievable through energy-management best practices and emerging technologies. The companies were Flying J Inc., ChevronTexaco Corp., Silver Eagle Inland Refining Inc., Magnesium Corp. of America, Kennecott Minerals Co., and Alcoa Inc.
Attendees selected from a number of plant tours, each of which included several tour stops describing the various energy-saving practices and technologies.
Breakout sessions covered such topics as energy supply and quality, combustion simulation, and computational fluid dynamics.
Sen. Orrin Hatch (R-Utah), senior member of the Utah Congressional delegation and ranking member of the US Senate Judiciary Committee, was the keynote speaker. He addressed the importance of Utah's industries to the state and nation.
