Rebuilding Boiler Feed Pumps for the Wastewater Industry

Author:

Bob Bluse, Hydro East Inc., and Scott Morisi, Passaic Valley Sewerage Commissioners

Publisher:

Pumps & Systems

Date Published:

October, 2009

 

Repairing multistage, segmental diffuser, boiler feed pumps and maintaining the original performance can be difficult and challenging. In this case study, a comprehensive inspection and repair program was applied to rebuilding six boiler feed pumps to improve MTBR and hydraulic performance to meet system demands.

 

Background

The pumps sent for rebuilding played an important role in maintaining plant performance for one of the six largest wastewater treatment plants in the United States, located in northeastern New Jersey. The plant, operated by the Passaic Valley Sewerage Commissioners (PVSC), uses the boiler feed pumps in a wet air oxidation (WAO) process.

The WAO process treats combined thickened waste activated sludge and primary sludge with heat (420 deg F) and high pressure (650 psi) for 30 minutes in a reactor to reduce the volatile solids content, break the chemical bond between the solids and the water, facilitate a high degree of dewaterability, sterilize the sludge and minimize the volume to be removed for beneficial reuse.

 


Facility’s boiler house
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Improving Pump Efficiency to Save Energy and Increase Generating Capacity

Author:

Ross Bertoli, Hydro Australia, and Mark Moerke, International Power Hazelwood

Publisher:

Pumps & Systems

Date Published:

August, 2009

 

As the global demand for energy grows, power companies are working to implement new technologies that would enable them to produce more power from existing stations. The following example demonstrates how International Power’s Hazelwood power station in Australia improved the efficiency of their motor-driven boiler feed pumps to produce a higher megawatt output without burning additional fossil fuels.

 

The Growing Demand for Energy

Built between 1964 and 1971, the Hazelwood Power Station in Victoria’s Latrobe Valley originally planned to have six units producing 200 MW each. However, growing electricity demand in the late 60s prompted the approval of a proposal to add two units to the station to increase generating capacity. The eight-unit power station was producing 1,600 MW output by the early 70s; each unit generated 200 MW of power. In recent years, this power station has moved to improve its output through thermal efficiency gains and increasing each unit’s capacity by 20 MW.

 

Engineered Modifications to Improve Pump Efficiency

Having modified the turbines to use less power, the plant needed to upgrade the 11-stage ring section, boiler feed pumps to meet the newly elevated performance requirements. International Power Hazelwood (IPRH) contacted a pump aftermarket service center in the Latrobe Valley to determine if modifications could be made to seven of these pumps within a two-year time period.

Though the original pump curves implied that the pump would have sufficient head and flow to handle the increased service conditions, several factors were discovered during inspection that would determine the course of action. Due to a vane pass vibration, the diffuser vanes had been machined to correct a vane pass issue that the pump experienced early on in its life. As a result, the hydraulic performance of the diffuser was compromised, and the pump no longer matched the manufacturer’s original design. The motor size also limited the power usage.

 


Rotor Centralization was performed to improve pump efficiency

 

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Engineered Modifications for an Ash Handling Water Pump

Written by: George Harris, Hydro Inc.
Publisher: Pumps & Systems / May, 2009

 

Modifications can be made to many older pumps to improve on their original design. Pump rebuilders with experienced engineering staffs can provide these modifications and upgrades to substantially extend mean time between repair (MTBR) and increase pump longevity. In the following case history, an ash handling water pump that had been experiencing a short operational history was removed from service on an emergency basis because of catastrophic bearing failure caused by poor lubrication.

This pump was shipped to the service center where it was disassembled and inspected. It was observed that the bearings had failed and the rotor had moved axially toward the non-drive end, allowing the second stage impeller to contact the pump casing (see Figure 1).

 

Figure 1

 

Excessive wear was noted at all running clearances. Discussions with the plant subsequently revealed that these pumps have an average MTBR of 18 months. Excess running clearances accompanied by rotor axial movement have resulted in similar failures on sister pumps. Continue reading

Service Center Engineering for a Power Plant

Many pumps in power plants and other heavy industries are designed and custom engineered for specific applications. The repair and servicing of these pumps should also include careful engineering review. Very often, smaller local repair shops attempt to repair these engineered pumps without the input and oversight of an engineer to ensure that the proposed repairs meet the original design’s intent.

When emergencies occur and practical solutions are needed, a service center engineer is invaluable in developing and guiding the pump repair plan. When a plant is down and the pump needs immediate attention, this crucial part of the process may be overlooked or eliminated.

This case history illustrates what can happen when a low-cost repair leads to catastrophic failure and the importance of experienced engineering support from the service center was to return a plant to service.

Circulating Water Pump Fails

Prior to the high-demand summer season, a Midwest plant’s circulating water pump (a 54-in mixed flow pump) failed. When the vertical pump was pulled, it was discovered that both the impeller and suction bell required complete replacement. After checking with the OEM, it was determined that replacing the components would take 8 months. With this pump out of service, the plant was in danger of being derated during the high-demand summer season. The pump had been repaired one year earlier but was no longer under warranty.

At this point, the plant asked a pump service center experienced in engineered pump repairs and upgrades to evaluate the pump and offer a plan for bringing the plant online and running at full rating. The service center’s engineering and operations team evaluated the hydraulic, mechanical, and logistical data and developed a plan to meet the plant’s critical requirements and need for a quick turnaround.

Broken Suction Bell

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