Dominik Fry, P.E., is Engineered Software, Inc.’s business development engineer and has nearly a decade of experience in the energy industry while working on some of the nation’s largest energy projects. Fry earned a Bachelor of Science at Montana State University. For more information, visit www.eng-software.com.
Cutting Maintenance Costs
To project future maintenance savings when evaluating a pumping system, there is 100 hp less power going into the fluid in the system. That extra 100 hp supplied by the pump, due to running at a higher speed, was removed from the fluid by using an over-throttled control valve. This also reduced wear and tear on system components. Another way of looking at the system is the excess power was wasted, pushing more energy than necessary, operating the equipment at a higher threshold, causing more stress on the equipment thereby increasing the maintenance costs.
Lastly, looking at the pump curve, we can see that when the pump is operating at 850 rpm with a flow rate of 2,800 gpm it is operating much closer to the BEP. Running a pump closer to its BEP has been proven to increase pump reliability.
Once the VFD was installed in the system and the pump operated at a lower speed, the vibration on the pump and discharge header were virtually eliminated. One year after operating the pump at the lower speed, the pipe cracking in the discharge header was eliminated along with the need to repair pump seals and bearings. With the loss of the pump vibration, discharge header cracking, pump bearing and seal repairs, a documented $15,000 per year in maintenance savings was realized.
By factoring the documented maintenance savings into the power savings the ROI for the VFD was reduced from 20 months to 10 months. For the past five years, the only maintenance performed on the vat dilution pump had been routine preventative maintenance.
Increasing Plant Up-Time
With the system operating with fewer repairs, there were additional savings due to increases in system uptime. Just like maintenance savings, increases in plant uptime are difficult to project.
In our vat dilution example, once the VFD was installed, the cracking in the pump discharge header and excessive pump maintenance was eliminated, and as a result:
- The vat dilution system was able to operate for longer time periods without breakdowns, resulting in increased plant uptime.
- The cost associated with draining the vat dilution systems for repairs and sending the filtrate for environmental treatment was eliminated.
- Since the number of unplanned outages of the vat dilution system was reduced, the entire plant was able to operate longer and produce products at a higher quality.
Based on actual plant data, the forced shutdowns caused by the problems associated with the vat dilution system cost the plant $400,000/year in lost production. When the cost of the lost production was factored in, the payback for the VFD addition was three weeks.
Remember, this pump system assessment was performed to fix a chronic problem that plant management was tired of dealing with. By evaluating the system, they were able to discover the root cause of the problem, make the necessary improvements, and based on the records they were able to document the savings. This is just one of many systems in an integrated paper mill.
By performing this assessment, the plant had several takeaways:
- Running the pump more efficiently (closer to its BEP) resulted in energy savings, and those savings can be easily calculated.
- Running the pump more efficiently reduces the excess power added to the system. The excess power results in the generation of heat, noise and vibration. Based on this case study, one could make the case that the savings in maintenance costs could be estimated as the same order of magnitude as the savings in power cost.
- If the equipment can run longer between forced shutdowns, more products can be made resulting in increased uptime and plant profitability.
By analyzing the entire system, the plant was able to resolve a long-standing maintenance problem that normal spreadsheets and day-to-day troubleshooting simply did not uncover. Once the operating data became apparent, they were able to quickly resolve the issues, make system improvements and reduce exposure to increased maintenance issues caused by the original problem. Lastly, management had the added benefit of improving their bottom line, coupled with a short ROI on the cost of the improvements making their investment a solid choice.