FRAME 6 BEST PRACTICE: Plant audit identifies major cost-saving opportunity
J C Rawls, utilities department technology engineer for BASF in Louisiana, accepted the CCJ’s 2015 Best Practices Award at the Frame 6 Users Group annual meeting in Scottsdale, Ariz, June 22-25, recognizing the company’s Geismar facility for re-engineering and modifying its boiler feedwater system to reduce energy consumption and improve plant availability/reliability. BASF Geismar was the only plant powered by a Frame 6B engine recognized by the judges this year.
Recall that the Frame 6B is a popular gas turbine for industrial cogeneration facilities, on the Gulf Coast in particular, because of its durability and “right size.” Process plants use GT/HRSG cogen units for their clean, efficient steam production; electricity is a beneficial byproduct for use onsite and/or sale.
Most engineers familiar with industrial-plant energy systems recognize that infrastructure expands as required by the installation of new process units. Expansions typically do not justify a re-engineering of the existing systems—feedwater, in this case—each time a “customer” is added. The important thing is to have sufficient steam and other utilities available when needed.
Periodic audits point to opportunities for improvements when ROIs are consistent with company financial goals. At Geismar, the installation of two simple piping runs and related valves to connect common infrastructure paid big dividends. Others may find similar benefits from a review of their plant utility systems.
Tom Yura, senior VP for the BASF-Geismar site, Derek Zambo, utilities production manager, and Rawls explained the feedwater-system challenge this way: Two separate sets of pumps were used to supply the boiler feedwater (BFW) header serving two cogen units (Fig 1) and four boilers (Fig 2). One set of three pumps (A1, A2, and A3 at right in Fig 3) pumped condensate returns into the header; the other set of five pumps (B1-B5 at left in the schematic) supplied demineralized makeup from the deaerator to the header.
Five pumps (A1, A2, A3, B4, B5) were kept in service to assure reliable supply of BFW for the site. In recent years, as a result of successful condensate-recovery strategies, the increased rate of condensate returns dictated operation of three condensate pumps, even though each was throttled back somewhat to match the typical condensate flow volume.
Two demin pumps supplied from the deaerator also were operated because of the inconsistency of condensate return flow at this very large chemical complex. Periodically, the required demin flow dictated operating the two pumps at their rated capacity. Typically, however, these pumps were operated at far less than full capacity.
Based on the normal operating scenario described above, this meant the plant operated:
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All three condensate pumps and had no spare, and
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Two of the five demin pumps, leaving three spares.
If one of the condensate pumps was taken out of service for maintenance, returns in excess of the capacity of the two operating pumps was discharged to the sewer, meaning expensive demin water provided the required makeup.
Solution. Knowing the deaerator and condensate collection drum were located at the same elevation, and operated at nearly the same pressure and temperature, engineers proposed the installation of a connecting jumper pipe between the suction lines for the condensate pumps and for the demin pumps. This would create one common suction line for all eight pumps and reduce the number of pumps required in service. The proposed solution was approved. To ensure proper level control in the condensate collection tank, a second cross-connect line was installed between it and the deaerator, allowing the vapor pressures in both tanks to equalize.
Results exceeded expectations. With the demin pumps able to pump condensate, their excess capacity could be used for that purpose, thereby allowing one, or even two, of the condensate pumps to be shut down. Only three pumps total are required at typical loads, so the normal operating lineup now is the following:
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One or two condensate pumps in operation, leaving one or two spares, and
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One or two demin pumps in operation, leaving three or four spares.
Benefits of the modified BFW piping system are the following:
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Capital was saved because the spare condensate pump being considered was no longer needed.
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Significant power savings accrue from operating three pumps instead of five.
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Pump runtime is reduced because only three pumps are now required—not five. The load sharing now possible allows for “resting” some condensate pumps, which previously had operated 24/7.
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When one of the least-efficient pumps in the system was found damaged, it was retired rather than repaired because spare pumps were available.
Additionally, the following unanticipated benefit was realized after the crossover pump suction line was placed in service: Two condensate pumps were forced out of service simultaneously, at a time when demin production was limited because of other operational issues. The crossover line allowed the demin pumps to continue serving the plant by pumping condensate into the BFW header. Had the crossover line not been in place, the loss of condensate supply could not have been made up with the limited amount of demin water available. The result would have been a severe production curtailment, or site outage, in the worst case. CCJ
