Industrial fans are crucial to the efficient performance of plants of all sizes, from power plants to steel mills and pulp & paper mills. The importance of their job – to direct the flow of air and gases – cannot be overstated. A well-designed, well-maintained mechanical draft fan system will help a plant be maximally efficient.
But when a fan system isn’t designed well, or is using antiquated parts or processes, the entire system can be a drag on a plant’s efficiency. This results in dollars lost in higher energy costs and worse performance overall, which impacts a plant’s bottom line.
Optimizing industrial fans to get the highest efficiency rates as possible can involve either retrofitting an existing system with newer upgrades, or designing a brand-new system to completely replace the legacy system. Whichever one is chosen depends on the ROI calculations, but the ideal end result for either option is more efficiency and better ROI for the entire system.
Finding Maximum Efficiency
Mechanical draft (or draught) fans have a certain “sweet spot” of maximum efficiency. Finding that sweet spot involves careful engineering and testing, not to mention exacting fabrication of the fan components.
The process of finding the sweet spot involves making sure the fan is accurately sized. This depends on a set of performance conditions, such as inlet density, static pressure, and volumetric flowrate, that tell us the proper width-to-diameter ratio. When placed on curves, the peak efficiency point is located just to the right of the peak of the capacity curve. A properly-engineered fan system will have the performance curve and the system resistance curve intersect at that point. The result is maximum efficiency.
Thus, finding the maximum efficiency settings for a mechanical draft fan system involves careful, precise calculations that take into account accurate readings of environmental conditions within the plant itself. Inaccuracy at this stage can result in even well-crafted equipment performing poorly
Obtaining Maximum Efficiency through Industrial Fan Upgrades: A Case Study
One client of ours found that its preheater or kiln ID fans were only operating at 55 percent static efficiency during normal production. That is a woefully small efficiency rate, caused in part by inaccurate calculations involving the required system resistance. Modifications made by the plant to the preheater tower duct system threw the curve off even more, which helped to result in the 55 percent rate.
Additionally, the existing fans were older radial blade designs originally installed in 1980, over 30 years ago. That legacy fan design wouldn’t be used today, due to its inefficiency.
After assessing the situation, the plan our engineers came up with was two-fold:
- Right-size the rotors by re-designing them to get back into the sweet spot of efficiency; and
- Upgrading the rotors to backward curved blades for more efficiency.
When upgrading fans, you can lower costs by trying to fit the new components into existing infrastructure. In this case, costs were lowered by designing the backward curved blades into the existing rotary blade housings. It took special engineering to design an inlet cone that would operate correctly and accommodate the larger backward curved blade rotor. At this stage, it’s crucial to engineer an industrial fan upgrade that will work as preferred within the existing environment; if the specs aren’t up to snuff, then a complete overhaul or fresh install may be necessary. Fortunately, in this case, it wasn’t.
Results of the Efficiency Upgrade
Installing the new rotors took place during a two-phase process beginning in August 2007 and ending in fall 2014. After installation, it was found that the two new rotors saved up to 800 hp (597 kW), which – at a cost of $0.082/kWh – resulted in annual savings of up to $428,800.
These results were achieved through careful, rigorous testing and engineering. Only after all calculations and tests were performed could the equipment itself be designed and manufactured, let alone implemented. The best way to achieve maximum efficiency, then, is to analyze a situation and determine what possible efficiency can be achieved, then find a configuration that can meet the specs and save as much money as possible in the process.
Of course, the upgrade wasn’t without its issues. Material accumulation occurred with the new backward curved blades, which caused unbalance and vibration. This was first noticed in fall of 2007; immediately following, we analyzed the situation using computational fluid dynamic models to discover how a blade stiffener was the culprit as far as causing the material build-up along the back of the blades.
We designed an airfoil-shaped nose bar on the blade’s leading edge, which offered rigidity and eliminated the dam effect from the stiffener. The result was that material accumulation was reduced and overall efficiency was increased by 6.3 percent.
Issues such as these will occur following any successful installation. Constant analysis and maintenance is needed to ensure the successful operation of any industrial fan system, which is well worth the investment given how important a mechanical fan system is to a plant.
Does Your Plant Need an Industrial Fan Upgrade?
Analyzing your plant’s efficiency ratings can tell you if there is potential to boost efficiency and get better results from your equipment as it is today. It can also tell you if better equipment would result in efficiency gains – as long as they’d result in favorable ROI.
As we saw, something as relatively straightforward as replacing radial blade rotors with backward curved blade rotors – i.e. swapping an older design with a newer, more advanced design – can reap benefits. Many plants are fitted with older fan designs that just aren’t as efficient as newer models because they were either installed decades ago or were chosen due to initial cost savings – even though there are better long-term benefits with more efficient models.
The process of deciding on a mechanical fan upgrade or retrofit follows these general steps:
- Determine current efficiency rates
- Calculate potential efficiency savings
- Pre-engineer potential designs that can upgrade efficiency
- Determine if you need a retrofit, upgrade, or replacement
- Perform ROI calculations to justify the cost of the upgrade or replacement
- Analyze the design to ensure it will meet desired specs for performance
- Test the solution before moving to the construction phase
- Implement the solution
By following this process, you can determine if a fan upgrade is a possibility and if it’ll result in net ROI gains through higher efficiency.
ProcessBarron specializes in engineering and implementing industrial fan upgrades for a wide variety of plants across multiple industries. Contact our team for more information about analyzing your current industrial fan configuration and seeing if a retrofit or upgrade makes sense for your facility.
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