Building a Better Boiler Feed Pump

Author:

Robert Aronen, Dennis Plaizier and Dave Sinclair, Hydro Scotford Inc.

Publisher:

Pumps & Systems

Date Published:

November, 2007

 

Say goodbye to concerns about pump seizure: By properly applying composite materials to a troublesome boiler feed water pump, this large process facility in Alberta can now run one pump during full-rate operation with very low vibration and higher efficiency.

The reliability and efficiency impacts of close-clearance wear components – wear rings, inter-stage bushings, throat bushings, and pressure-reducing bushings – have been well documented.

In 1985, Bloch and Geitner cited the following potential problems associated with excessive wear ring clearance: efficiency losses, loss of rotor stability, shaft breakage, driver overloading, bearing overheating or failure, unequal load sharing in parallel pump operation, noise and damage typically associated with cavitation, and possible total pump destruction (p. 31-36).

One application for which the wear components are particularly important is boiler feed water. In the typical process plant, the boiler feed water pump is a multistage, horizontally-split, between-bearings design that is heavily dependant upon the wear components for rotor stability. Material selection is very important to ensure long-term reliability in this service.

The value of proper application and installation of modern composites is demonstrated by the results from a 9-stage boiler feed water pump from a large process facility in Central Alberta.

Why Wear Components are Important

The close clearance wear components in a centrifugal pump perform similar functions. They separate high pressure areas within the pump from lower pressure areas via a minimal clearance between a rotating and stationary member.

Due to the differential pressure across these components, there is substantial flow from the high pressure to lower pressure regions of the pump – recirculation flow. If inadequate clearance lies between two metal components, the rotating and stationary elements could possibly seize and lead to substantial pump damage (Bloch, 1988).

Conversely, as the clearance between rotating and stationary components increases, the recirculation flow within the pump increases and efficiency drops (Bloch and Geitner, 1985). Over time, this will become evident to the pump operators as recirculation flow increases to the point where the pump can no longer operate at design capacity.

What the operators may not notice is that the wear components also contribute substantially to rotor stability (Lobanoff and Ross, 1992, p. 440-451). Increased clearance at the wear components can lead to higher vibration, shorter bearing life, and the potential for high-energy failure modes such as shaft breakage.

Furthermore, recirculation flow at the first-stage impeller eye increases the effective inlet fluid temperature, possibly leading to cavitation damage (Lobanoff and Ross, p. 90-97). The net result is that a pump with increased clearance at the wear components is not as reliable or efficient as a pump with reduced clearance.

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Reduce Consumption of Seal Water

Author:

Fluid Sealing Association

Publisher:

Pumps & Systems

Date Published:

October, 2007

 

Two imperatives for many of today’s industrial plants are to reduce the cost of operations through the enhancement of rotating equipment reliability and enhanced energy efficiency of pumping systems.

One place to look for a significant, yet relatively easy “quick win,” is the seal flush water going to packing, single, and double seals. In many industrial plants water is being used to provide lubrication, cooling and/or as a means to exclude a harmful process fluid from the stuffing box or seal chamber.

The means for providing an external water flush or quench are generally described as API/ISO piping plans 32 (ANSI 7332), 54 (ANSI 7354) or 62 (ANSI 7362).

 

 

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Non-OEM Pump Rebuild Shops Part II: Guideline Details

Author:

Heinz P. Bloch, P.E., Jim Steiger, Robert Bluse

Publisher:

Maintenance Technology

Date Published:

September, 2007

 

The first installment of this series highlighted general guidelines regarding the selection of competent non-OEM pump repair facilities. This month, these guidelines are discussed in more detail.

 

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You get what you inspect. That said, a pump user must have a repair specification. It may or may not be identical to the specification used by the non-OEM competent pump repair shop (CPRS). Where the specification or checklist of the CPRS differs from the one of the user/purchaser, the issues need to be explored and the ramifications of any deviations understood. At that time, waivers are issued and details of the understanding are documented.

In any event, unless a process pump manufacturer gives specific and different values or measurements for a particular make, size or model, experience shows the guidelines in this article to be useful”and valid. Even an in-house pump shop would benefit from making it a habit to use and apply the following assembly dimension checklist. Some of the listed diametral clearance and/or interference tolerances will be stricter than what certain pump manufacturers allow (for reasons of internal cost savings, perhaps). But, then again, this simply illustrates the opportunities to improve on some OEM products.

Best-of-Class user shops often make copies, laminate them and either hand them to each of their shop technicians or post them near mechanic/technician workstations. CPRS facilities use similar approaches to disseminate the information in Sidebar 1, Best-of-Class Pump Specifications, to their staffs.

Beyond the actual specifications listed in Sidebar 1, there are other Best-of- Class type guidelines to consider when rebuilding a pump. A CPRS certainly considers them.

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Non-OEM Pump Rebuild Shops Part I: Facts And Considerations

Author:

Heinz P. Bloch, P.E. Process Machinery Consulting, Jim Steiger, HydroAire Inc., Robert Bluse, Pump Services Consulting

Publisher:

Maintenance Technology

Date Published:

July, 2007

 

In light of so many consolidations across the pump industry, is it any wonder that legacy brand experience often is lost? These days, some OEMs may not be able to offer the same engineering competence they once had in the area of pump rebuilding.

Trying to rebuild a vintage process pump to original OEM specifications makes no sense, given current pump rebuilding capabilities and changes to system performance that occur over time. Thus, a qualified independent rebuild shop deploying highly experienced personnel and a full range of state-of-the-art technologies (including balancing and alignment, vibration analysis, ultrasonics, infrared thermography, oil analysis and non-destructive testing techniques, among others) can verifiably offer high-quality upgrades that improve both uptime and efficiency consistent with current system performance requirements.

 

 

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State of the Aftermarket

Author:

George Harris, Hydro Inc.

Publisher:

Pumps & Systems

Date Published:

April, 2007

 

Observations on the changes, trends and challenges that both suppliers and pump users may face in the coming years.

 

Changes

Perhaps the most pronounced change we have experienced is that the customer we serve is no longer a “local” customer, but is increasingly a large national or global organization with locations throughout the world.

These global customers are interested in working with suppliers that can provide a comprehensive range of specialized services with a high degree of professionalism. Because they are interested in reducing the number of suppliers with which they work, they often prefer to deal with suppliers that can effectively service multiple locations.

Over time, this will change the landscape of aftermarket suppliers, with smaller, local organizations being reduced. The aftermarket providers that emerge from this period of change will be larger companies with broader capabilities and services, particularly those that are strong in engineering and technical services and in employing new technologies.

When industrial capital projects in the U.S. were in a slump during the 1980s and 1990s, a dramatic consolidation of pump companies resulted in only a few major broadbased OEMs dominating the industry. Today, the pump industry enjoys resurging demand – new power plants, major refinery expansions, oil sands projects in Canada and so on – that is straining productive capacity, with deliveries for both pumps and replacement parts often exceeding acceptable parameters.

This strain, in turn, creates opportunities for qualified aftermarket parts suppliers.

 

Trends

The focus of our business is no longer the “machine shop,” but rather technological improvements that continue to change and advance the way we operate.

 

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