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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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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