The bleach plant was facing downtime issues that could not be ignored. Internally, an energy team determined that nearly two-thirds of the facility’s valves were less than 50 percent open, and many were less than 30 percent open. One key pump system had a capacity of 6,500 gallons per minute (gpm), but the average load was only 2,750 gpm. The peak flow demand was only 5,200 gpm. The pump was heavily throttled, which resulted in chronic stress on pump components and valves, pipe cracks, gasket leaks and frequent downtime. It experienced failures while running and during startup and shutdowns, which occurred more than 10 times per year.
More damage occurs at startup and shutdown than at any other time, primarily because of the large pressure changes and water hammer across the pump system components. However, the initial shock to the system upon startup involved more than pressure. Thermal shock from 220-degree fluid entering the pipes on startup also occurred.
The mill’s reliability engineers had conducted a thorough examination of the system, determining that the installation of automated gate valves and new operating procedures—to open slowly as pipes warmed to avoid thermal shock and cracking—would provide incremental improvements with a reduction in breakdowns. However, the complete elimination of failures was only accomplished when the plant performance services consultant recommended a low-voltage motor and VFD, operated in pressure control mode, for the three vessels that the pump was feeding. The result was markedly increased efficiency plus a pump system modification that paid for itself quickly.
Plant performance services provides plants with expert analysis support services to reduce the total cost of ownership and improve the efficiency of pump operations.
Stabilizing the control loops and reducing pressure inside the system took a pump that failed frequently and turned it into a properly functioning component of the system. The bleach plant witnessed $18,000 USD in energy savings in 2002. Energy savings in the same process had climbed to $32,000 per year in 2010 as energy costs increased. Beyond the efficiency improvement, plant representatives reported that the systems-based solution saved them more than $1 million annually in downtime and repair costs.
Adopting a Systems Approach
Plants are not investing in efficiency quickly enough for several reasons. One is simply a lack of experience with the methods and techniques used to raise efficiency. When components break, operators often buy what they know works to replace them.
Plant operations are risk adverse, and modifying a system to improve efficiency often represents an element of risk. Not making the changes also carries a risk that is usually much greater. When in the process of deciding to modify systems to improve efficiency, it may feel like Catch-22. Nobody wants to interrupt day-to-day operations of the plant to overhaul functioning equipment or systems—especially if they are not necessarily part of the specialized production equipment that is paramount to a plant’s business success and a product’s differentiation in the market.
However, critical subsystem issues in many plants have been ignored for too long. Engineers and suppliers oversize pumps frequently and for many reasons. Sometimes, they prepare for increased demand, imagining future capacity increases that never come. Sometimes, pipe friction losses are overestimated, leaving no doubt that enough head is available when needed. The approach is common but not ordinary.
The main reason for lower than expected investment in high-return energy efficiency projects is a lack of funds set aside specifically for energy efficiency studies and projects. The need to earmark funds in the capital budget must be addressed, because plants will face the imperative to make energy investments in the future. Sustainability is an essential strategy for industrial plant survival.
Though it is often appealing in the short-term to fight fires, this approach can overlook potential design and operating cost-savings that far exceed the implementation cost. A dedicated systems approach to optimizing efficiency can save the industry billions and save plants millions in energy and maintenance costs—while improving process control and plant sustainability—throughout the manufacturing landscape. It is something everyone should be thinking more about—from the plant floor to Washington.
1. ARC Advisory Group, “Strategies to Drive Manufacturing Efficiency on the Production Floor.”