1. Field of the Invention
The present invention relates to coal pulverizers and, more particularly, to the on-line control of the distribution of coal among the pulverized coal outlet pipes in pulverizers using independently adjustable flow control elements installed inside the pulverizer upstream of the entrance to each pulverized coal outlet pipe.
2. Description of the Background
Coal fired boilers utilize pulverizers to grind coal to a desired fineness so that it may be used as fuel for the boilers. Typically, raw coal is fed through a central coal inlet at the top of the pulverizer and falls by gravity to the grinding area. Once ground (different types of pulverizers use different grinding methods), the pulverized coal is transported upwards, using air as the transport medium. The pulverized coal passes through classifier vanes within the pulverizer. These classifier vanes may vary in structure, but are intended to establish a swirling flow within the rejects cone to prevent coarse coal particles from flowing into the discharge turret of the pulverizer. These vanes are often adjustable mechanisms. The centrifugal force field set up in the rejects cone forces the coarse coal particles to drop back down onto the grinding surface until the desired fineness is met. Once the coal is ground finely enough, it enters the discharge turret. From the discharge turret the pulverized coal is distributed among multiple pulverized coal outlet pipes and into respective fuel conduits where it is carried to the burners. Each coal pulverizer is an independent system and delivers fuel (pulverized coal) to a group of burners.
Poor balance of pulverized coal distribution between pulverized coal outlet pipes is commonly experienced in utility boilers. This can be due to various reasons, such as system resistance of each individual fuel conduit, physical differences inside the pulverizer, and coal fineness. Unbalanced distribution of coal among the pulverized coal outlet pipes adversely effects unit performance and leads to decreased combustion efficiency, increased unburned carbon in fly ash, increased potential for fuel line plugging and burner damage, increased potential for furnace slagging, and irregular heat release within the combustion chamber. In addition, it is critical for low NOx (Nitric Oxides) firing systems to precisely control air-to-fuel ratios in the burner zones to achieve low levels of NOx formation.
Therefore, there is a need in the industry for a method and apparatus that provides for on-line balance and control of the distribution of pulverized coal between the multiple pulverized coal outlet pipes of coal pulverizers.
Accordingly, it is the main object of the present invention to provide an improved method and apparatus for the on-line balancing and control of pulverized coal flow into the multiple pulverized coal outlet pipes of a coal pulverizer, thereby improving boiler performance by making it possible to operate the boiler with reduced pollutant levels (e.g. NOx, CO) and increased combustion efficiencies.
It is another object of the present invention to provide an improved method and apparatus for the on-line balancing and control of pulverized coal flow from the discharge turret of a coal pulverizer into multiple pulverized coal outlet pipes and onto connected fuel conduits that does not disturb any pre-existing primary air flow balance among the multiple pulverized coal outlet pipes.
It is a further object of the present invention to provide an improved method and apparatus for the on-line balancing and control of pulverized coal flow from the discharge turret a coal pulverizer into multiple pulverized coal outlet pipes, where the type of pulverizer is a pressurized vertical spindle pulverizer. It is a further object of the present invention that the apparatus can be readily installed within an existing pressurized vertical spindle pulverizer without causing a significant pressure drop.
The objects of the present invention are accomplished by providing a device for balancing and control of pulverized coal distribution to multiple pulverized coal outlet pipes of a coal pulverizer. The device generally comprises a plurality of independently adjustable flow control elements and a means for adjusting the positioning of those flow control elements.
It is a further object of the present invention that each of the multiple flow control elements corresponds to an outlet pipe and controls the flow of pulverized coal into that particular corresponding outlet pipe.
It is a further object of the present invention that each of the multiple flow control elements is positioned within the discharge turret of the coal pulverizer at some appropriate distance upstream from the entrance to its corresponding pulverized coal outlet pipe.
Yet another object of the present invention is to provide a means for independently adjusting the positioning of each of the multiple flow control elements within the discharge turret and thereby, controlling the flow of pulverized coal to the corresponding outlet pipe.
It is a further object of this invention that each adjustment mechanism includes an independently adjustable rod seated in the top or side of the discharge turret of the coal pulverizer and connected to the flow control element for adjusting positioning of the flow control element horizontally or vertically.
The method of the present invention is practiced by monitoring either the pulverized coal flow at the individual pulverized coal outlet pipes or the individual flame characteristics, and then compensating for imbalances in the coal particulate flow or differences between flame characteristics by selectively adjusting the individual flow control elements as needed, thereby balancing and controlling the distribution of pulverized coal and improving combustion efficiency.
Other objects, features, and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiment and certain modifications thereof when taken together with the accompanying drawings in which:
In a conventional coal pulverizer 100 (as shown in
As discussed above, poor balance of pulverized coal 107 distribution between pulverized coal outlet pipes 111 is commonly experienced in utility boilers. This can be due to various reasons, such as system resistance of each individual fuel conduit, physical differences inside the pulverizer, and coal fineness. The unbalanced distribution of coal among the pulverized coal outlet pipes adversely affects the unit performance and leads to decreased combustion efficiency, increased unburned carbon in fly ash, increased potential for fuel line plugging and burner damage, increased potential for furnace slagging, and non-uniform heat release within the combustion chamber. In addition, it is critical for low NOx (Nitric Oxides) firing systems to precisely control air-to-fuel ratios in the burner zones to achieve minimum production of NOx. The relative distribution of coal between the pulverized coal outlet pipes is monitored by either measuring the concentration of pulverized coal flow at the individual pulverized coal outlet pipes or measuring the particular flame characteristics of burning fuel discharged from the each of the outlet pipes.
The method and apparatus of the present invention represent an improvement over the prior art of
Referring to
Generally, each flow control element 10 will be positioned in a horizontal plane at some point directly below (upstream of) the pulverized coal outlet pipes 111, allowing a free flow of pulverized coal into the outlet pipes 111. However, the horizontal and vertical positioning of each individual flow control element 10 may be adjusted by a flow control adjustment mechanism 20 to align the flow control element 10 to some degree in front of the entrance 112 to the corresponding pulverized coal outlet pipe 111 in order to decrease the flow of pulverized coal 107 into that particular outlet pipe 111.
The working principle of adjusting pulverized coal flow balance, by adjusting the positioning of the individual flow control elements 10 relative to the entrance 112 of the particular outlet pipes 111 is based upon creating a pulverized coal particle concentration wake 115 just upstream of each outlet pipe 111 that receives a relatively high pulverized coal particle flow rate (see
Those skilled in the art will recognize that a variety of adjustment mechanisms 20 are suitable for supporting the individual flow control elements 10 within the discharge turret 108 and for easily accessible on-line adjusting of the position of those flow control elements 10 in relation to the outlet pipes 111. For example, as shown in
The shape and dimensions of the flow control elements 10 and the distance between the flow control elements 10 and the outlet pipes 111 are important parameters in outfitting a particular coal pulverizer with the present invention. Specifically, the flow control elements 10 must be positioned within the discharge turret 108 a sufficient predetermined distance from the pulverized coal outlet pipes 111 such that they have a negligible effect on the distribution of primary air flow while coincidentally having a significant effect on the distribution of pulverized coal. The primary air flow distribution 116 should not be disturbed because in most boilers primary air flow is balanced by the use of orifice-type restrictors in the individual pulverized coal outlet pipes 111. Thus, if primary air flow distribution 116 was disturbed, air flow would have to be re-balanced whenever a flow control element 10 was adjusted. The shape of the flow control elements 10 likewise affects the distribution of primary air flow.
To determine the preferred shape of the flow control elements 10 and the preferred distance from the entrance 112 to pulverized coal outlet pipe 111 to position the flow control elements 10, the inventors conducted a series of quantitative experiments. These experiments were conducted on a laboratory scale pressurized vertical spindle mill type pulverizer having four outlet pipes and configured with air foil shaped flow control elements 10 (as shown in
Additionally, referring to
Therefore, in order to practice the method of the present invention and configure the device of the present invention to a particular pulverizer the distance of the flow control elements 10 from the outlet pipes 111 and the dimensions and cross sectional shape of the flow control elements 10 should be predetermined by testing and cataloging the results for that pulverizer, or by a more refined mathematical approach based upon the results of the experiments herein describe, in light of the different dimensions and internal configuration of the particular pulverizer. However, based upon the above-described experiments a user should start with a streamlined coal flow element with a frontal diameter and length of one quarter and one half, respectively, of the diameter of the outlet pipes. The flow control element should be positioned a distance upstream from the outlet pipes within the discharge turret of approximately twice the diameter of the outlet pipes. Then, this configuration should be subjected to trial-and-error adjustments.
One skilled in the art will appreciate that while the above-described positioning of the flow control elements and the shape and dimensions of the flow control elements were made with reference to a pressurized vertical spindle pulverizer with four pulverized coal outlet pipes, depending on the configuration of the particular pulverizer, a variety of flow control element positions and flow control element shapes and dimensions are considered to be within the scope and spirit of the present invention.
For example, one skilled in the art will recognize that for a vertical spindle pulverizer with three outlet pipes, the spacing between outlet pipes is greater than with a four outlet pipe pulverizer and thus the distance between the entrance to the outlet pipes and the flow control elements and the shape and dimensions of the flow control elements might require adjusting in order to minimize the effect on the distribution of primary air flow while maximizing the effect on the pulverized coal flow distribution. Similarly, a coal pulverizer with more than four outlet pipes will result in less of a physical separation between outlet pipes and engender further adjustment of the distance between the entrance to the outlet pipes and the flow control elements and/or the shape and dimensions of the flow control elements.
Having now fully set forth the preferred embodiments and certain modifications of the concept underlying the present invention, various other embodiments as well as certain variations and modifications of the embodiments herein shown and described will obviously occur to those skilled in the art upon becoming familiar with said underlying concept. It is to be understood, therefore, that the invention may be practiced otherwise than as specifically set forth in the appended claims.
The present application derives priority from U.S. Provisional Patent Application No. 60/436,241 for “ON-LINE CONTROL OF COAL FLOW IN PRESSURIZED VERTICAL SPINDLE MILLS” filed by Levy et al. on Dec. 23, 2002.
Number | Name | Date | Kind |
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5819947 | Nardi et al. | Oct 1998 | A |
5873156 | Wark | Feb 1999 | A |
5957300 | Nardi et al. | Sep 1999 | A |
5971302 | Doumet | Oct 1999 | A |
Number | Date | Country | |
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20040188554 A1 | Sep 2004 | US |
Number | Date | Country | |
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60436241 | Dec 2002 | US |