Control system improves ethanol blending precision
Product quality is one of the many objectives of Motiva Enterprises, LLC, which operates the eastern and south-eastern US refining and marketing businesses of Shell Oil and Saudi Refining.
The company operates four refineries with a total capacity of 860000 barrels a day, and it sells fuel to more than 22000 Shell-branded and Texaco-branded gasoline stations. An extensive terminal network is also owned and operated by Motiva with approximately 50 terminals. These terminals, along with another 320 contracted locations where product is stored on behalf of customers, provide a source of gasoline products to several transportation modes including tanker trucks, pipelines, railcars, and marine vessels.
Motiva strives to operate all of those distribution resources at peak performance and within government regulations. In response to governmental mandates to eliminate the use of methyl tertiary butyl ether, or MTBE, as an additive to gasoline, Motiva uses ethanol. This application required blending up to 10percent ethanol by volume by means of injection it into the gasoline stream during truck loading. In different parts of the country, other companies reported problems with the injecting stream resulting from inadequate pressure control.
The pressure control issue was a perfect application for ITT Goulds Pumps PumpSmart control system. PumpSmart is a microprocessor-based variable speed drive, programmed specifically for centrifugal pumps up to 700HP. PumpSmart allows for continuous monitoring and reaction to both pump conditions and systems allow accurate control of virtually any process parameter demands. PumpSmart provides pump users with energy savings in the 30–70percent range because at lower demands, PumpSmart reduces motor speeds, eliminating the extra energy that is used to overcome the pressure drop of control valves. This new model can be applied to any centrifugal pump in a wide range of applications.
Motiva had an earlier experience with PumpSmart on gasoline loading and were sold on PumpSmart’s ability to eliminate cavitation experienced when loading a single truck or operating below minimum flow.
In addition to the pressure control problems in the ethanol injection application, prior to using PumpSmart, Motiva had also experienced the inefficiency of kicking on an additional pump simply because another truck required loading. By keeping a constant pressure on the header and injection system, ethanol could be injected at a rate necessary to obtain the desired blend into each truck from the
multiple-bay loading rack. In addition to enhancing
the injection and blending process, constant pressure control allowed the pump to vary the speed to maintain a set pressure in the main header as the flow fluctuated by the addition or deletion of tank trucks loading.
However, in this ethanol injection application, as the primary pumps reached maximum capacity and the set pressure could no longer be achieved, the PumpSmart would turn on an additional (fixed speed) pump. In response, the PumpSmart unit would serve as the trim pump to balance the supply with the need. Four separate gasoline distribution terminals in the north-east US were equipped with a PumpSmartPS200 to operate two Goulds3996 in-line process pumps in multipump operation using constant slave mode and pressure control. The two pumps were piped in parallel with a pressure transmitter in the common discharge line.
John Booth, Technical Manager, Distribution with Motiva commented on the PumpSmart difference. “In my opinion, PumpSmart will allow a more uniform ethanol flow into the base gasoline. This should help assure a more consistent ethanol content under all operating conditions. We should experience fewer product quality issues, reduce the reliance on other mechanical systems to manage flows as a function of pressure variations and provide a more reliable overall system. The added benefit should be continued cost saving. Since the ethanol must operate at a higher pressure than the base gasoline, we also expect to prevent any line shock problems.”
Motiva experienced improved ethanol injection and blending characteristics by PumpSmart’s ability to maintain constant pressure. Eliminating the possibility of cavitation during times of low demand was an additional benefit and pump life cycle enhancer. Lastly, by balancing the supply with the need, PumpSmart is able to produce significant energy savings compared to fixed speed pumps over the life of the equipment.
For more information, visit www.gouldspumps.com
"