PEMEX, Mexico's national petroleum company, contacted VAF Filtration Systems due to excessive sand particulate problems it was having with 11 wells located throughout the community near its refinery in Guanajuato. These wells supply the cooling makeup water for all the cooling towers in the refinery. The cooling tower basins and related equipment in the refinery were being overloaded with debris and sand that was entering the makeup water from these wells.
PEMEX's first attempt at eliminating, or at least reducing, the problem of particulate entering the tower basins was to install centrifugal separators at each of the wells. After a period of five years, PEMEX discovered that something else needed to be done because the centrifugal sand separators were not capable of removing most of the sand particles in one pass as is required in a makeup water line.
The sand that passed by the separators and entered the cooling tower basins resulted in at least four manual basin cleanings per year. Each basin cleaning required “shutting down” the towers, which interrupted the refinery's operation. Hence, the refinery's maintenance costs remained unacceptably high to manually clean the basins, the chillers and the spray nozzles while interrupting the refinery's operations. The centrifugal separators were not meeting PEMEX's expectations or its specifications for water quality, so something had to be done.
PEMEX then contacted VAF Filtration Systems' distributor in Mexico seeking a solution. It was recommended that PEMEX install a “barrier” to all particulate coming from the wells by installing VAF's V-Series automatic self-cleaning screen filter technology at each well. Working with its distributor, VAF engineers determined that the least costly installation would allow the centrifugal separators to remain installed (since they were already paid for) with the screen filter inlet connected to the outlet of the centrifugal separator, which required minimal pipe changes.
Based on years of experience, VAF's engineers proposed to provide a barrier to all particulate 50 micron and larger in size. VAF has found that most well water particulate (depending on the well) is larger than 50 micron in size, so a 50-micron screen barrier would remove more than 95% of the particulate coming from the well. The flow rate at each well is 800 gpm (182 m3/hour), so VAF's engineers recommended a V-1000 filter with a 50-micron screen at each well (Fig. 1).
PEMEX agreed to VAF's recommendations and installed the filters. PEMEX engineers immediately saw results. A water sample was drawn from the water that had passed through the centrifugal separator and would then pass to the screen filter. The water that had passed through the separator was shown to have a high particulate load of more than 250 ppm and appeared very “dirty” from the brown color (Fig. 2). Then a water sample was drawn from the water that had passed through the V-Series automatic self-cleaning screen filter. The water that had passed through the screen filter was shown to have a particulate load of approximately 20 ppm. The result is that the screen filter reduced the particulate load of the water coming from the centrifugal separator by an additional 92%.
The outcome for PEMEX operations was that the cooling towers only required one cleaning every three years, so the return on investment occurred within 16 months, or well before the first cleaning.