TL-165

Mechanics of the Grand Coulee Dam

incorporated six Vanton sump pumps to

ensure reliability and operation of

three 805 megawatt turbines.

Grand Coulee Dam Uses

Six Cantilever Pumps to

Ensure the Reliability of

Three 805 Megawatt

Turbines

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Power, Energy and Utility

Grand Coulee Dam

Wastewater

SUMP-GARD Thermoplastic Vertical Pump

 

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Reprinted from WATER & WASTES DIGEST

G. Michael Stromback, Senior Mechanical Engineer

 

With an installed capacity of 6,809 megawatts, the Grand Coulee Dam

located on the Columbia River in the state of Washington is the largest

hydro project in North America.

 

For a short time following its completion, it was known as the largest

hydro project in the world. Measuring more than a mile long (1.6

kilometers) and 550 ft tall (167.6 meters), it is the biggest concrete

structure ever built, containing nearly 12 million cubic yards (339,847

cubic meters) of concrete.

 

Lake Roosevelt, which stretches out behind the dam, is approximately

150 miles (241 kilometers) long as it extends up the Columbia River to

the Canadian border and to the Spokane River within 37 miles (60

kilometers) of the city of Spokane. As such, Lake Roosevelt contains

more than five million acre-feet (6,167,409,188 cubic meters) of active

storage capacity.

 

The Grand Coulee Dam releases, on average, 110,000 cubic feet

(3,114.85 cubic meters) of water per second, primarily for generating

electricity. Controlling high volumes of water requires giant-sized

equipment, which can sometimes face giant-sized problems when

problems occur.

 

Three of the 24 turbines are rated at 805 megawatts and are some of the

largest turbines ever built. Making sure they consistently function in a

reliable manner can present significant hurdles for maintenance

engineers and mechanics.

 

Spotlight on the problem

 

Mentioned above, three of the turbines, Units G-22, G-23, and G-24,

each are rated at 805 megawatts. Their main turbine shaft is

approximately eight feet in diameter with shaft seals that consist of a set

of braided packing rings, held in place by a gland within the stuffing

box. Water supplies cooling and lubrication for the packing through a

standard lantern ring located in the middle of the packing set. Leakage

during operation is to be expected.

 

Further, the amount of leakage increases as the packing wears and ages.

This leakage collects in the turbine pit and has to be pumped out

periodically; otherwise it could damage the turbine.

 

The original design for turbine pit drainage provided for two 200-gpm

pumps, one designated as the lead pump and the other as backup.

These pumps were controlled by a multi-step float switch system. If the

leakage became severe, exceeding the ability of the pumps to keep up,

the generator would have to be shut off.

 

Because it is highly undesirable to shut off the generator, maintenance

personnel placed additional, small, submersible pumps to remove water

from the turbine pit. The discharge from the pumps was sent to gravity

drains or to adjacent units with less leakage.

 

The amount of packing leakage varies, depending on the unit load as

well as other variables. Thus, the additional pumps are not needed all

the time. When the water level eventually falls below the pump

impeller, the seal in the suction cavity is broken. All cooling and

lubrication provided by the water stops and the pumps overheat and

burn up. The problem can be exacerbated by the fact that the added

submersible pumps are not always visible to operations personnel.

To make matters worse, the water that comes out of the packing area

mixes with water leaking out of wicket gates and other mechanical

seals. As a result, the water often contains grease, rags and oil that

sometimes clog up the added pumps.

 

One of the mechanics based at the Grand Coulee Dam suggested

replacing one of the small pumps with a bearingless Vanton

cantilever-shaft pump, which was specifically designed to operate under

extended dry-run conditions. Because it incorporated a vortex pump

head configuration to handle foreign objects without clogging, it was

put to the test.

 

The original intent was to use it as a backup pump, which operators

could simply start and leave running when one of the turbine units

experienced severe leakage. To the surprise of the Grand Coulee Dam

operators, the 600-gpm Vanton Sump-Gard® SGK polypropylene pump

quickly drained the entire pit and handled the contaminated water

without any problems and without the risk of damage associated with

dry running conditions.

 

Because of the positive results, the Grand Coulee Dam retrofitted all

three 805 MW turbines to use the cantilever pumps. There are two

Vanton SGK pumps in each of the turbine pits, connected to a

multi-stage float system that alternates running time. Although each

pump is able to completely drain the pit, they are instrumented with

level controls so the idle pump will kick in should the volume of the

water in the pit get too high. These are the specifications for the

installed pumps that have been providing uninterrupted, dependable

service for the past two years.

 

Design specifications

 

To address the problem faced by the water leakage at the Grand Coulee

Dam, various design specifications were indicated. For example,

engineers required a rugged, thermoplastic vertical pump with

cantilevered shaft and dry running capability that had no bearings

immersed in the pump fluid.

 

The pump required a large diameter alloy steel shaft isolated from the

fluid by a thick-sectioned thermoplastic sleeve and heavy-duty external

hall bearings above cover plate, housed in epoxy-coated cast iron

motor bracket to accommodate NEMA, IEC and European standard

motors. All immersed pump parts and hardware were made of

homogeneous thermoplastics so that no metal or thermoset

composites are in fluid contact.

 

Finally, it was required the pump have a dynamically balanced

semi-open impeller with embedded, molded-in stainless steel

reinforcing insert and a vortex pump head to handle foreign objects

without clogging.

 

Close-up of one of the six Thermoplastic

Cantilever SGK sump pumps with dry-run

capability.

Sump-Gard® SGKThermoplastic Cantilever

Bearingless Vertical Pump

Copyright 2016 - Vanton Pumps (Europe) Ltd - All rights reserved

About Us

In the 1950, Vanton developed a revolutionary all-plastic pump for use in conjunction with the first heart-lung device. The design limited fluid contact to only two non-metallic parts: a plastic body block and a flexible liner. This was the birth of our Flex-I-Liner rotary pump. Its self-priming sealless design made it an industry standard for the handling of corrosive, abrasive and viscous fluids as well as those that must be transferred without contaminating the product. Vanton now offers the most comprehensive line of thermoplastic pumps in the industry.

 

 

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