Solid material comminution or disintegration – Apparatus – Rolls frictionally driven and supported by relatively moving...
Reexamination Certificate
2001-09-07
2003-08-26
Rosenbaum, Mark (Department: 3725)
Solid material comminution or disintegration
Apparatus
Rolls frictionally driven and supported by relatively moving...
C241S132000
Reexamination Certificate
active
06609669
ABSTRACT:
FIELD AND BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to the field of pulverizers for grinding combustion fuels, such as coal, and, in particular, to a new and useful hydraulic loading system for the top grinding ring of ball and ring pulverizers, such as the type E and EL coal pulverizers made by The Babcock & Wilcox Company.
2. Description of the Related Art
Coal pulverizers are used to grind, dry and classify raw chunks of coal into fine solids which can be fluidized and fed, for example, to burners used in conjunction with industrial or utility boilers or furnaces. E and EL type pulverizers are ball and ring (or ball and race) type pulverizers which employ the ball-bearing principle to grind the coal. Presently known E and EL type pulverizers use a pair of vertical axis, horizontal grinding rings, that surround a number of balls arranged between the rings, to pulverize coal. The lower or bottom grinding ring rotates through connection to a rotating, vertical main shaft, while the upper or top grinding ring remains stationary and is spring loaded to create grinding pressure.
The coal is ground by contact with the upper and lower grinding rings and balls (collectively grinding elements). The lower and upper grinding rings are each provided with a race having a predefined, matching track contour that engages the balls. The force from the upper grinding ring pushes the balls against the coal layer on the lower grinding ring. The grinding rings and the balls are made of abrasion resistant alloys and comprise the major wear parts of the pulverizer. The balls wear evenly and remain spherical, since the balls are free to rotate in all directions within the confines of upper and lower grinding rings. Ground coal is swept from the grinding zone defined by the grinding rings and the balls by air for final particle size classification and subsequent pneumatic transport to one or more coal burners.
FIG. 1
shows a cross section of a B&W type EL pulverizer generally depicted as numeral
2
. This type of pulverizer has a stationary top ring
4
, one rotating bottom ring
6
, and one set of balls
8
that comprise the grinding elements. The pulverizer includes a cylindrical housing
20
. The pressure required for efficient grinding is obtained from externally adjustable, dual purpose springs
10
. The bottom ring
6
is driven by the yoke
12
which is attached to a vertical main shaft assembly
14
of the pulverizer. The top ring
4
is loaded by the dual purpose springs
10
which provide the desired grinding pressure and hold the top ring
4
stationary. Raw coal is fed into the grinding zone where it mixes with partially ground coal that forms a circulating load. Pulverizer air causes the coal to circulate through the grinding elements where some of it is pulverized in each pass through the row of balls
8
. As the coal becomes fine enough to be picked up by the air conveyed into the pulverizer around the perimeter of the bottom ring
6
, it is carried to the classifier where coal of a desired fineness is separated from the stream of air and pulverized coal, and is carried out with the air. Oversized material is returned to the grinding zone.
The pulverizer is driven by bevel gears provided on the underside of the bottom ring
6
which engage corresponding bevel gear teeth on horizontal pinion shaft
16
provided in the base of the pulverizer
2
. Both the vertical main shaft
14
and the horizontal pinion shaft
16
are mounted in roller bearings. Forced lubrication is provided for the entire gear drive by an oil pump submerged in the oil reservoir and gear-driven from the pinion shaft.
For further details of such EL type pulverizers, the reader is referred to Chapter 12 of
Steam/its generation and use,
40
th
Edition, Stultz and Kitto, Eds., Copyright©1992, The Babcock & Wilcox Company, the text of which is hereby incorporated by reference as though fully set forth herein.
One of the main requirements for grinding coal in a pulverizer of this type is adequate loading on the grinding elements. EL pulverizer top grinding rings have historically been loaded, and horizontal/rotational movement restricted, by using up to six single coil, dual purpose springs
10
. The springs
10
apply a predetermined grinding pressure, as dictated by the grindability of the fuel and fineness required, to the non-rotating top ring
4
. The springs
10
also permit vertical movement of the top ring to compensate for variations in size of pieces of fuel and foreign material that pass through the grinding elements. Additionally, the springs
10
prevent rotation of the top ring
4
, and, by eliminating rubbing of contact surfaces, thereby reduce pulverizer maintenance. As the grinding elements wear, the pressure is restored by adjusting screw-down bolts that pass through brackets attached to the top of the housing
20
.
FIG. 2
illustrates a known mechanism for applying a load to the grinding balls
8
of a ball and ring pulverizer
2
as taught in U.S. Pat. No. 2,595,587 to Lester L. Leach and assigned to The Babcock & Wilcox Company, the text of which is hereby incorporated by reference as though fully set forth herein. The mechanism has a set of spring loading assemblies
200
connected to the compression springs
10
for applying the load to the top grinding ring
4
. Individual threaded rods
24
and captive nuts
58
in each of the spring loading assemblies
200
are used to adjust the load applied to each spring
10
. The compression spring
10
of each spring loading assembly
200
is loaded individually by rotating the associated captive nut
58
to move the threaded rod
24
vertically, thereby increasing or decreasing the degree of load applied to each compression spring
10
.
Maintaining the proper load on the grinding elements of ball and ring pulverizers is critical to their operation. As the balls and rings wear, the top ring
4
moves closer to the rotating bottom ring
6
, and the loading spring compression relaxes, reducing the grinding force. The force reduction in turn causes a drop in the pulverizer capacity and coal fineness. With the mechanism described above, the pressure exerted upon the grinding elements can be suitably adjusted to compensate for the ring and ball wear without altering the restraining forces exerted by the springs
10
in a plane normal to the coil axes of springs
10
. Each set of compression springs
10
and spring loading assemblies
200
, however, must be individually loaded and calibrated with the remaining sets to ensure that an even loading is provided on the top grinding ring
4
and balls
8
.
With conventional spring loading assemblies, the pulverizer must typically be shut down in order to reset the compression on the springs
10
and ensure even operation of the pulverizer. Large tools must be used to turn the captive nut
58
and adjust the loading in a time-consuming procedure. The procedure requires workers to be on top of the pulverizer to make some of the adjustments as well, creating a risk of injury to the worker.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an apparatus for rapid and uniform loading of the grinding balls used in a ball and ring coal pulverizer.
It is a further object of the invention to provide a hydraulic loading system having a central control for centrally applying a load to the top grinding ring of a coal pulverizer.
Yet another object of the invention is to provide a loading system for ball and ring pulverizers which accommodates wear of the grinding assembly without lengthy maintenance shutdowns.
Accordingly, a hydraulic loading system for applying a compressive load to the top grinding ring of a ball and ring coal pulverizer is provided. The hydraulic loading system replaces conventional, threaded spring bolt assemblies with linearly loaded, non-threaded spring bolt assemblies. A hydraulic cylinder and piston assembly is mounted above each spring. The high-pressure connections of all the hydraulic cylinder and piston assemblies are piped
Houser David P.
Pifer Rodney C.
Rakocy Michael E.
Grant Kathryn W.
Marich Eric
Rosenbaum Mark
The Babcock & Wilcox Company
LandOfFree
Hydraulic loading system for ball and ring pulverizers does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Hydraulic loading system for ball and ring pulverizers, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Hydraulic loading system for ball and ring pulverizers will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3074032