Patent Application
20090008487
1. Field of the Invention
The present invention relates to a loading system for a material processing system. Particularly, the present invention is directed to a loading system for a vertical material size reduction system.
2. Description of Related Art
In coal-fired furnaces, for purposes of improved and more efficient ignition, it is preferred to pulverize the coal to a fine powder before introducing it into the furnace for combustion. Coal pulverization involves systematically comminuting coal to a desired, preferably optimum size, e.g. a fine powder, prior to introduction into a coal-fired furnace. Currently, coal pulverization systems include ball tube type mills, high-speed attrition type pulverizers, and vertical roller type mills.
Ball tube type mills are low speed mills that have their origins in the 1930's and 1940's. The ball tube type mill comprises a plurality of hardened steel balls that are disposed in a large, rotatable barrel. While the barrel rotates, coal is introduced into the barrel ends. Through the rotating action of the barrel, the steel balls fall and cascade onto the coal, pulverizing the coal by the impact. The pulverized coal is then removed and fed into a coal-fired furnace. Ball tube type mills are successfully used in conjunction with highly abrasive coal. Ball tube mills rotate at approximately 20 RPM.
A high speed attrition type pulverizer typically, as in the ATRITA® pulverizer available from Riley Power Inc. of Worcester, Mass. (U.S. Pat. Nos. 7,172,146 and 7,028,931) provides three stages of pulverization. Each stage is powered by a common rotary assembly. Coal enters the first (crushing) section where a plurality of rotating and reciprocating swing hammers crush the coal against a grid. The grid deters passage of coal that has not been crushed sufficiently to a preferred nominal size, e.g. about ¼ inch. Once the coal has been reduced to a nominal size, it passes through a grid section and then is introduced into the second section where coal particles are forced to rub together by a set of impellers on a rotating disk, further reducing the coal size. Next, it enters a section where it is forced between a set of high speed rotating pegs and stationary clips. Then the coal exits through a rejecter assembly (while coarse particles are forced back into the previous section for further size reduction), to the final third section. The third section is an exhauster section which transports the fine, pulverized coal in a fluid stream to the coal-fired furnace.
Vertical roller type mills pulverize coal on a rotating grinding table. A plurality of rollers typically cast in abrasion resistant material apply a shearing force downward onto the carrier table and thus apply a grinding pressure to the coal via pressure derived from a set of springs. On the top of the carrier table is mounted a set of segments cast from a similar abrasion resistant material. The pulverized coal is then removed from the mill using a high velocity stream of air and fed into a coal-fired furnace. Vertical pulverizers' rotating tables typically turn at approximately 25 RPM.
Loading the grinding rollers in most vertical coal pulverizers is currently via a set of heavy-duty springs. A set of springs 28 is held between a set of loading and guide frames 26 and 30, as shown in
The main disadvantage with this system is that the spring loading is constant and grinding load cannot be adjusted for lower or higher coal throughput rates. The grinding pressure cannot be reset unless the pulverizer is shut down. Once the pulverizer is shut down, the spring loading can be reset to change the pressure exerted onto the roller wheel assemblies, which must then be locked in place again before the pulverizer can startup. An additional disadvantage with this system is that the pulverizer must be started with the grinding rollers in place on the grinding table, which causes vibration and premature wear of the grinding elements while also shortening the useful life of the electrical motor and gear reducer that drive the pulverizer.
Such conventional methods and systems generally have generally been considered satisfactory for their intended purpose. However, there still remains a continued need in the art for a loading system for vertical material size reduction systems that allows for variable pressure for the grinding rollers, wherein the pressure can be varied as a function of mill throughput. There also remains a need in the art for a loading system that has the ability to raise grinding rollers above the grinding table during mill startup. The present invention provides a solution for these problems.
The purpose and advantages of the present invention will be set forth in and become apparent from the description that follows. Additional advantages of the invention will be realized and attained by the methods and systems particularly pointed out in the written description and claims hereof, as well as from the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the invention, as embodied herein, the invention includes a loading system for a vertical material size reduction system. The system includes a pressure frame configured and adapted to be attached to at least one roller wheel assembly of the vertical material size reduction system. The system also includes at least one hydraulic cylinder operably connected to the pressure frame. The hydraulic cylinder is configured and adapted to apply a variable force to the pressure frame to apply pressure through the at least one roller wheel assembly to a grinding table of the vertical material size reduction system.
In accordance with a further aspect of the invention, the at least one hydraulic cylinder includes a first pressure chamber on one side of a hydraulic piston, and a second pressure chamber on an opposite side of the hydraulic piston. The hydraulic cylinder is configured and adapted to control pressure between the at least one roller wheel assembly and the grinding table based on a pressure differential between the first and second pressure chambers.
The at least one hydraulic cylinder can include a pneumatic element configured and adapted to absorb mechanical shock. The system can further include at least one tensioning rod connecting the at least one hydraulic cylinder to the pressure frame. The at least one tensioning rod can be connected to the pressure frame in a manner that prevents relative rotational movement between the pressure frame and the tensioning rod along a lengthwise axis defined by the tensioning rod. The system can further include a plurality of pendulum adjustment connectors mounted to the pressure frame. The plurality of pendulum connectors can be configured and adapted to attach roller wheel assemblies to the pressure frame and to align the roller wheel assemblies with the grinding table. The at least one hydraulic cylinder can be configured and adapted to raise the at least one roller wheel assembly off from a grinding table during startup of the vertical material size reduction system. The at least one hydraulic cylinder can be configured and adapted to control pressure between the at least one roller wheel assembly and a grinding table in response to coal throughput rates for the vertical material size reduction system. Moreover, the at least one hydraulic cylinder can be configured and adapted to lift the at least one roller wheel assembly from the grinding table.
The invention also includes a vertical pulverizer for pulverizing coal. The vertical pulverizer includes a pressure frame, at least one roller wheel assembly attached to the pressure frame, and a rotatable grinding table configured and adapted to rotate and to grind coal between the grinding table and the at least one roller wheel assembly. The vertical pulverizer further includes at least one hydraulic cylinder operably connected to the pressure frame. The hydraulic cylinder is configured and adapted to apply a force to the pressure frame to apply pressure through the at least one roller wheel assembly to the grinding table of the vertical pulverizer.
In accordance with a further aspect of the invention, the at least one hydraulic cylinder includes a first pressure chamber on one side of a hydraulic piston, and a second pressure chamber on an opposite side of the hydraulic piston. The hydraulic cylinder is configured and adapted to control pressure between the at least one roller wheel assembly and the grinding table based on a pressure differential between the first and second pressure chambers.
The at least one hydraulic cylinder can include a pneumatic element configured and adapted to absorb mechanical shock. The vertical pulverizer can further include at least one tensioning rod connecting the at least one hydraulic cylinder to the pressure frame. The at least one tensioning rod can be connected to the pressure frame in a manner that prevents relative rotational movement between the pressure frame and the tensioning rod along a lengthwise axis defined by the tensioning rod. The vertical pulverizer can further include a plurality of pendulum adjustment connectors mounted to the pressure frame. The plurality of pendulum connectors can be configured and adapted to attach roller wheel assemblies to the pressure frame and to align the roller wheel assemblies with the grinding table. The at least one hydraulic cylinder is configured and adapted to raise the at least one roller wheel assembly off from a grinding table during startup of the vertical pulverizer. The at least one hydraulic cylinder can be configured and adapted to control pressure between the at least one roller wheel assembly and a grinding table in response to coal throughput rates for the vertical pulverizer.
The invention further includes a kit for retrofitting a vertical material size reduction system. The kit includes a pressure frame configured and adapted to be attached to at least one roller wheel assembly of the vertical material size reduction system. The kit also includes at least one hydraulic cylinder configured and adapted to be operably connected to the pressure frame. The hydraulic cylinder being further configured and adapted to apply a force to the pressure frame to apply pressure through the at least on roller wheel assembly to a grinding table of the vertical material size reduction system.
In accordance with a further aspect of the invention, the at least one hydraulic cylinder includes a pneumatic element configured and adapted to absorb mechanical shock. The kit can further include at least one tensioning rod. The at least one tensioning rod can be configured and adapted to connect the at least one hydraulic cylinder to the pressure frame.
The invention also includes a method of retrofitting a vertical pulverizer. The method includes replacing a spring assembly from a vertical pulverizer with a pressure frame configured and adapted to be attached to at least one roller wheel assembly of the pulverizer. The method further includes attaching at least one hydraulic cylinder to the pressure frame. The hydraulic cylinder is capable of applying a varying force to the pressure frame to apply pressure through the at least one roller wheel assembly to a grinding table of the vertical pulverizer.
The invention also includes a method of operating a vertical pulverizer. The method includes grinding material between at least one roller wheel assembly and a grinding table of the vertical pulverizer. The method also includes adjusting grinding pressure between the at least one roller wheel assembly and the grinding table during operation of the vertical pulverizer.
In accordance with another aspect of the invention the step of adjusting includes adjusting grinding pressure as a function of throughput of the vertical pulverizer. The step of adjusting can also include varying grinding pressure over time.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and are intended to provide further explanation of the invention claimed.
The accompanying drawings, which are incorporated in and constitute part of this specification, are included to illustrate and provide a further understanding of the method and system of the invention. Together with the description, the drawings serve to explain the principles of the invention.
Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. The method and corresponding steps of the invention will be described in conjunction with the detailed description of the system.
The devices and methods presented herein may be used for controlling grinding pressure in a material size reduction system during operation. The present invention is also well suited for reducing wear to a material size reduction system during startup.
Referring to the Figures generally, wherein like numerals designate the same element throughout the several drawings,
In preparation to operate pulverizer 10, it is necessary to preload spring loading system 18.
The traditional use of spring loading system 18 has various disadvantages. Since loading frame 26 is locked into position during startup procedures, the pressure on roller wheel assembly 14 cannot be adjusted during operation of pulverizer 10. Another disadvantage is that with existing loading system 18, it is necessary to preload springs 28 prior to starting the rotation of grinding table 16. Thus tire 20 is pressed against grinding table 16 during startup, which leads to vibrations that cause extra wear on the various components.
In accordance with the invention, a loading system for a vertical material size reduction system is provided including a pressure frame configured and adapted to be attached to at least one roller wheel assembly of the vertical material size reduction system. At least one hydraulic cylinder is operably connected to the pressure frame. The hydraulic cylinder is configured and adapted to apply force to the pressure frame to apply pressure through the at least one roller wheel assembly to a grinding table of the vertical material size reduction system.
For purposes of explanation and illustration, and not limitation, a partial view of an exemplary embodiment of the loading system in accordance with the invention is shown in
For purposes of illustration and not limitation, as embodied herein and as depicted in
Referring again to
In accordance with the invention, the hydraulic cylinders of the loading system are configured and adapted to apply a variable force to the pressure frame in response to increased or decreased coal demand, or in response to a change in coal quality. Thus, a variable grinding pressures can be achieved during operation of a vertical material size reduction system.
For purposes of illustration and not limitation, hydropneumatic cylinders 110 can adjustably direct upward or downward forces on pressure frame 102. Thus if pressure frame 102 is unconstrained in the vertical direction, hydropneumatic cylinders 110 can raise or lower the level of pressure frame 102. When roller wheel assemblies 104 attached to pressure frame 102 are in contact with grinding table 106, if hydropneumatic cylinders 110 apply additional force in the downward direction, the pressure between roller wheel assemblies 104 and grinding table 106 is increased. Similarly, if hydropneumatic cylinders 110 have roller wheel assemblies 104 under pressure, hydropneumatic cylinders 110 can be relaxed to relax the pressure on roller wheel assemblies 104. Therefore it is possible to use hydropneumatic cylinders 110 to control the grinding pressure during operation of pulverizer 101.
In order to assure proper grinding and in order to reduce wear, grinding pressure must be determined as a function of pulverizer throughput. Pulverizer throughput includes factors such as variations in coal properties as well as variations in fuel flow demand, if the material being pulverized is coal, for example. Thus if the volume of material to be pulverized is raised or lowered during operation, loading system 100 can be adjusted appropriately without shutting down the pulverizer to adjust the grinding pressure, as required by traditional spring loading system 18.
The ability to vary grinding pressure on the fly provides a significant advantage over traditional spring loading systems (e.g. 18) because grinding pressure can be controlled as a function of pulverizer throughput to reduce wear on grinding components including tires 20 and grinding table 16. Extending the service life of the grinding elements compared to traditional spring loaded systems also shortens outage time required for replacing roller wheel components and table segments of grinding table 106 by approximately 30%. Controlling grinding pressure also helps maintain proper fineness in coal or other materials being pulverized. Adjusting grinding pressure on the fly also enables reduction in electrical power required for reduced load operation. Loading system 100 used in a coal pulverizer, for example, can increase coal throughput at least 20% compared to traditional spring loaded designs.
A further advantage of loading system 101 involves startup of the pulverizer. Hydropneumatic cylinders 110 can raise pressure frame 102 high enough so that roller wheel assemblies 104 clear grinding table 106 completely. Thus, during startup, there is no need for roller wheel assemblies 104 to be pressed against grinding table 106 during the startup of grinding table 106, as there is with traditional spring loading system 18. Raising roller wheel assemblies 104 off from grinding table 106 during startup significantly reduces wear in the grinding elements of pulverizer 101 by reducing vibrations in roller wheel assemblies 104 otherwise experienced between roller wheel assemblies 104 and grinding table 106 as grinding table 106 builds up speed. Raising roller wheel assemblies 104 during startup also extends the life of drive motor 32 (see
In further accordance with the invention, and as shown in
Pressure applied by hydropneumatic cylinders 110 is a function of the differential between pressures within first and second hydraulic piston chambers 124 and 126 of hydropneumatic cylinder 110. One side of a piston, grinding pressure is applied to chamber 124, typically by pressurized hydraulic oil or other suitable liquids as known in the art. On the other side, a counter pressure is similarly applied to chamber 126. The position and/or force acting on tensioning rods 112 is a function of the differential of grinding and counter pressures.
In further accordance with the invention, a kit is provided for retrofitting a vertical material size reduction system. The kit includes a pressure frame configured and adapted to be attached to at least one roller wheel assembly of the vertical material size reduction system. The kit further includes at least one hydraulic cylinder configured and adapted to be operably connected to the pressure frame. The hydraulic cylinder is further configured and adapted to apply a force to the pressure frame to apply pressure through the at least one roller wheel assembly to a grinding table of the vertical material size reduction system.
For purposes of illustration and not limitation, as embodied herein and as depicted in
In further accordance with the invention, a method is provided for retrofitting a vertical pulverizer. The method includes replacing a spring assembly from a vertical coal pulverizer with a pressure frame configured and adapted to be attached to at least one roller wheel assembly of the vertical pulverizer. The method further includes attaching at least one hydraulic cylinder to the pressure frame. The hydraulic cylinder is configured and adapted to apply a force to the pressure frame to apply pressure through the at least one roller wheel assembly to a grinding table of the vertical pulverizer.
For purposes of illustration and not limitation, as embodied herein and as depicted in
While the methods and systems above have been described in the exemplary context of a vertical pulverizer, and particularly a vertical pulverizer for pulverizing coal, those skilled in the art will readily appreciate that the invention is not limited to use with vertical coal pulverizers. The loading system can be used on any suitable material size reduction system without departing from the spirit and scope of the invention.
The methods and systems of the present invention, as described above and shown in the drawings, provide for a loading system for a vertical material size reduction system with superior properties including reduced wear, reduced down time, and reduced power consumption. It will be apparent to those skilled in the art that various modifications and variations can be made in the device and method of the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention include modifications and variations that are within the scope of the appended claims and their equivalents.
