Corroded Steel

Fertilizer Focus: Volute Reprofiling Resolves Vane Pass Vibration

A hot potassium carbonate pump at a nitrogen fertilizer plant had been experiencing elevated vibration at vane pass frequency. Recognizing that this vibration likely contributed to shortened equipment life, the end user partnered with Hydro to investigate the root cause of the vibration and modify the pump as necessary to remove it.

When the vibration and performance indicated that it was time to take the pump out of service for refurbishment, it was sent to Hydro’s Chicago service center for inspection and analysis. The inspection showed significant damage caused by component contact and erosion.

After reviewing the inspection data, an engineering analysis was completed on the design to determine what could be done to eliminate the vibration. The engineering team determined that the vane pass vibration was related to shock waves caused by the high energy fluid impacting the volute lip. This was intensified in the first stage, where the 4-vane impeller was discharging into a dual volute. The volute lip was reprofiled to reduce this impact and provide a smoother transition from the impeller exit into the volute passage.

The upgraded design was tested in Hydro’s performance test lab. This gave the end user confidence that the hydraulic performance of the pump had not been negatively affected by the volute lip geometry modification. It also verified that the vibration amplitudes had been reduced. After successful testing, the modified pump was returned to the field, where it continues to run smoothly.

chart, bar chart

1. Reduced Vane Pass Vibration Observed During Testing

Casing Geometry

Fertilizer Focus: Expedited Sourcing for Replacement Casing

A Midwest US fertilizer plant had a boiler feed pump whose casing suffered from significant erosion damage at the packing gland location. The damage to the casing was severe enough that it was unusable. The delivery time and cost for a new pump both exceeded what the plant felt comfortable with, so they looked for alternative means to return the pump to reliable operation.

To provide a solution that reduced cost and lead time, Hydro’s Chicago service center explored various outlets for a used casing that could be refurbished for the service. Fortunately, a casing that matched the original boiler feed pump’s size and number of stages was found and procured.

Understanding the importance of casing geometry for hydraulic and mechanical performance, Hydro’s engineering team performed an extensive analysis of the two cases to verify geometric equivalency. After the engineering analysis concluded that the used case would meet the required hydraulic performance, it was refurbished and brought up to best-in-class tolerances.

Boiler feed pump casing

As a final check to ensure that the refurbished case would operate smoothly and achieve the desired performance, the newly assembled pump was tested at Hydro’s performance test lab. The test lab generated a full performance curve that verified that the pump met the design operating flow and head. Mechanical performance was also assessed to ensure that vibration was acceptable throughout the operating range.

By reusing an old casing instead of purchasing a new pump, the site was able to reduce the cost of the repair. More importantly, the repair was completed in a much shorter timeframe than it would have taken to source a new pump. This greatly reduced the risk to plant production of not having a spare pump available on-site.