Posts Tagged ‘fluid drives’

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Fluid Drive Upgrades

May 14, 2014

Back in 2007, Dr. Mel created a presentation for fluid drive upgrades. This presentation explains how fluid drives are used specifically with boiler feed pumps. The operational history and the changes to the standard practices led to issues for which TRI has engineered solutions.

 

 

 

 

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Fluid Drive Brake Systems

November 22, 2010

The Purpose For The Brake System On A Fluid Drive

by Turbo Research Inc.

There is only one purpose for having a brake on the output shaft of a fluid drive; to aid in the operation of the boiler feed pump by stopping the boiler feed pump shaft and to keep it from rotating when the pump is out of service.

There are certain boiler feed pumps which are designed and built in ways that will cause them to gall and consequently to seize if they rotate for more than a few seconds or a few minutes at low speed with no or low flow through them. Typically, these pumps have stainless steel components that can rub together. They are often the higher performance, higher pressure pumps, but this is not always the case.

There usually is sufficient experience with each boiler feed pump over the years to know if that pump has or has not seized when it was at low speed during those times when a) the pump was out of service and simultaneously, b) the brake is imperative.

For those boiler feed pumps which have not seized when they were operated at low speed for several hours, or for which the manufacturer indicates that no problem will arise by operating at low speed with low/no flow, the brake is not required, and there is no value in using it.

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Sliding PressureĀ Operations

November 16, 2010

“Sliding Pressure” simply mans reducing boiler pressure in proportion to a reduction of MW generation. When “Power Wheeling” is fully effective, clearly those electrical generating units with the lowest cost will operate the most. Overall operating costs, efficiency, and/or “”eat rate”” as well as “turn down ratio” for each turbine-generator unit will be critical.

The “turn down ratio” is the ratio of maximum to minimum load. Those with high ratios are preferred because they can take a big swing from maximum load in the day to minimum load at night. Without coming off line.

“Sliding Pressure” for most sub-critical boilers is usually required to obtain the lowest minimum load a unit can achieve continuously and the maximum efficiency at that minimum load.

For fluid drive applications, a reduction of boiler pressure corresponds to a reduction of the output shaft speed/BFP shaft speed, resulting in increased heat, usually more than the amount for which the unit was designed, and often, high amplitude vibration.

TRI Transmission & Bearing Corp. has proven solutions in hand for fully evaluating and resolving these issues for all sizes and types of fluid drives, in BFP or other applications.

For certain units, during sliding pressure operation, new control valve opening patterns occur, leading to different “nozzle block” forces on the turbine rotors. TRI evaluates the changing rotor vibration conditions which result and makes recommendations, including the benefits provided by TRI Align-A-Pad Ā® bearings and other TRI products for reducing rotor vibration and bearing maintenance.