Patent Application
20170246643
Technical Field
Embodiments of the invention relate to pulverized coal boilers and, more particularly, to a system, method and apparatus for controlling the flow distribution of coal between outlet pipes of a pulverizer.
Discussion of Art
Coal fired boilers utilize pulverizers to grind coal to a desired fineness so that it may be used as fuel for burners. In a typical pulverized coal boiler, coal particulate and primary air flow from the pulverizers to the burners through an array of coal pipes leading from the pulverizers to the burners. Typically, raw coal is fed through a central coal inlet at the top of the pulverizer and falls by gravity to the grinding area at the base of the mill. Once ground using one or more of a variety of known 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 classifier and rejects cone to prevent coarse coal particles from flowing into the discharge turret of the pulverizer. The centrifugal force field set up in the rejects cone forces the coarse coal particles to drop back down onto the grinding surface to be reground until the desired fineness is met. Once the coal is ground finely enough, it is discharged from the pulverizer and distributed among multiple pulverized coal outlet pipes and into respective fuel conduits where it is carried to the burners.
With reference to
While the swirling flow of pulverized coal is efficient in preventing coarse coal particles from being carried upward to the coal pipes, such swirling flow has also been known to create an imbalance in coal flow distribution between the coal pipes 30. As illustrated by the particle tracking diagrams of
This unbalanced distribution of coal among the coal outlet pipes can adversely affect the performance of each burner and the boiler as a whole and can lead to decreased combustion efficiency, increased potential for tube fouling, furnace slagging, and non-uniform heat release within the combustion chamber. In addition, unbalanced distribution of coal can also result in the inability to control individual burner stoichiometry (i.e., the air-to-coal ratio), which can lead to elevated emissions of nitric oxides, carbon monoxide and the like.
In view of the above, there is a need for a system and method for ensuring a more uniform distribution of coal between the various outlet pipes of a pulverizer in order to improve overall system efficiency and performance.
In an embodiment, a turret is provided. The turret includes a generally frusto-conical shaped body and a plurality of static straightening vanes arranged interior to the body, the vanes dividing the body into a plurality of sections. The vanes are configured to straighten a swirling flow of solid particles as they enter the body, and to divide the swirling flow into a plurality of straightened flows that are communicated to a plurality of coal outlet pipes.
In another embodiment, a method for controlling the output of coal in a plurality of coal outlet pipes in a coal pulverizer is provided. The method includes the steps of modifying, or retrofitting, a portion of a coal pulverizer with a turret, the turret comprising a generally frusto-conical shaped body and a plurality of static straightening vanes arranged interior to the body, the vanes dividing the body into a plurality of sections.
In yet another embodiment, a coal pulverizer is provide. The pulverizer includes a grinding mechanism configured to transform raw coal into pulverized coal, a classifier configured to receive the pulverized coal from the grinding platform and to generate a swirling flow of coal, the classifier being further configured to reject coarse particles of the pulverized coal from the swirling flow, a turret arranged generally above the classifier, the turret having a generally frusto-conical body and a plurality of static straightening vanes arranged interior to the body, the straightening vanes dividing the body into a plurality of sections, and a plurality of coal outlet pipes in fluid communication with the interior of the turret. The straightening vanes within the turret are configured to straighten the swirling flow of coal as it enters the turret, and to divide the swirling flow into a plurality of straightened flows that are communicated to the coal outlet pipes.
The present invention will be better understood from reading the following description of non-limiting embodiments, with reference to the attached drawings, wherein below:
Reference will be made below in detail to exemplary embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference characters used throughout the drawings refer to the same or like parts. While embodiments of the invention are directed to systems and methods for controlling the flow distribution of pulverized coal in a pulverizer and, in particular, for controlling the flow distribution of coal to burner coal pipes on front and rear fired boilers, embodiments of the invention may be also applicable to controlling the flow distribution of coal to burner coal pipes on any type of boiler, and to controlling the flow of solid particles, generally.
As used herein, “operatively coupled” refers to a connection, which may be direct or indirect. The connection is not necessarily being a mechanical attachment. As used herein, “fluidly coupled” or “fluid communication” refers to an arrangement of two or more features such that the features are connected in such a way as to permit the flow of fluid between the features and permits fluid transfer.
Embodiments of the invention relate to a system and method for controlling the flow distribution of solid particles, namely coal, in a pulverizer or mill for a coal fired boiler. As illustrated in
In an embodiment, the classifier 22 is a static classifier. In other embodiments, the classifier 22 may be a dynamic classifier. In an embodiment, the vanes 20 of the classifier 22 may be selectively adjustable in order to control the relative fineness or coarseness of coal particles according to system operating parameters. For example, one or more of the vanes 20 may be pivotable about a vertical axis.
As illustrated in
In an embodiment, the vanes 110 are static vanes, meaning that they are in fixed position within the turret 26 and unable to rotate about any axis. In an embodiment, the number of vanes 110 and sections defined by the vanes 110 corresponds to the number of outlets 36 and coal pipes 30 fluidly coupled to the turret 26. For example, as illustrated in
In operation, raw coal is fed into the coal inlet pipe and by force of gravity falls through the centrally located coal chute 12 until it reaches the grinding platform 14 where the grinding mechanism 16 grinds the coal into fine pieces. Air flows into an air inlet port (not shown) below the grinding platform 14, feeding primary air into the pulverizer 100. This creates a stream of low-velocity air that carries the particles of pulverized coal upward from the grinding platform 14 where they enter the classifier vanes 20 of the classifier 22. These vanes 20 establish a swirling flow within the reject cone 24. The centrifugal force field set up in the classifier and reject cone 24 prevents coarse pieces of coal from entering the discharge turret 26. In particular, coarse pieces of coal fall by force of gravity back into the grinding platform 14, to be reground by the grinding mechanism 16 until they reach a desired degree of fineness. The pulverized coal that is not too coarse, however, is carried by the swirling flow of air upwards through the deflector ring 28 of the classifier 22 and into the turret 26. In particular, the pulverized coal that is not rejected passes upwards into the sections of the turret 26 defined by the vanes 110, and into the coal outlet pipes 30 associated with each section. The pulverized coal may then be fed to one or more burners where it is combusted.
As best shown in
In an embodiment, the use of static flow straightening vanes 110 within the turret 26 may improve pipe-to-pipe coal flow balance to approximately +/− 10% or better, as compared to a pipe-to-pipe imbalance of over 30% in some cases with existing systems. As indicated above, by uniformly distributing the flow of coal among each of outlets 36 in the turret 26 utilizing static, tapered flow straightening vanes 110 within the turret 26, fouling and slagging may be minimized, combustion efficiency increased and emissions decreased, which leads to improved boiler efficiency and better overall performance as compared to existing systems.
Referring back to
This ability to adjust the vertical height of each of the vanes 110 by extending or retracting the sections 112, 114, 116, 118 allows for additional control of the flow distribution of coal in the event that flow distribution between the coal pipes is still not uniform due to, for example, other variables within the system downstream from the pulverizer (such as, for example, differences in pipe lengths and numbers and types of elbows in each fuel line). In particular, in certain instances, even with the flow straightening vanes 110, downstream configurations and conditions may result in certain pressure imbalances between the coal pipes, which can lead to some remaining coal flow imbalance. The height of one or more of the vanes 110, however, may be adjusted in order to compensate for or remedy this imbalance. In an embodiment, the height of one or more of the vanes 110 may be adjusted in dependence upon a measured flow of coal within a coal outlet pipe or fuel line or in dependence upon, for example, measured emissions of a respective burner or boiler.
In an embodiment, the pulverizer 100 may be manufactured with the turret 26 having the vanes 110 installed therein. In other embodiments, the turret 26 having vanes 110 may be manufactured as a separate component that may be retrofit into existing pulverizers. In yet other embodiments, existing pulverizers, and turrets thereof, may be retrofit with static flow straightening vanes 110 for improving the flow distribution of coal to the outlet pipes connected thereto. In this respect, the invention can be integrated into new power plant installations, as well as retrofit into the pulverizers of existing power generation systems. As a result, improved boiler efficiencies and decreased emissions may be realized, regardless of whether a new plant is being brought online, or an existing plant updated or upgraded.
In an embodiment, a turret is provided. The turret includes a generally frusto-conical shaped body and a plurality of static straightening vanes arranged interior to the body, the vanes dividing the body into a plurality of substantially equal sections. The vanes are configured to straighten a swirling flow of solid particles as they enter the body, and to divide the swirling flow into a plurality of straightened flows that are communicated to a plurality of coal outlet pipes. In an embodiment, the number of straightening vanes is equal to the number of coal outlet pipes in the pulverizer. In an embodiment, each of the straightening vanes is selectively extendable and retractable in a vertical direction for adjusting a height of each of the vanes. In an embodiment, the height of each straightening vane is designed to be individually adjusted. In an embodiment, each of the straightening vanes includes four segments. In an extended position the height of a respective vane is substantially equal to a combined height of the four segments. In a retracted position the height of a respective vane is substantially equal to a height of a single segment. In an embodiment, a feed pipe extends through the body, the feed pipe and the body being substantially concentric, wherein each of the straightening vanes extends radially from the feed pipe to an inner peripheral wall of the body. In an embodiment, the plurality of straightening vanes is seven straightening vanes. In an embodiment, the solid particles are pulverized coal particles.
In another embodiment, a method for controlling the output of coal in a plurality of coal outlet pipes in a coal pulverizer is provided. The method includes the steps of modifying, or retrofitting, a portion of a coal pulverizer with a turret, the turret comprising a generally frusto-conical shaped body and a plurality of static straightening vanes arranged interior to the body, the vanes dividing the body into a plurality of substantially equal sections. In an embodiment, the turret is positioned in an upper portion of the pulverizer above a classifier of the pulverizer and is in fluid communication with the classifier. In an embodiment, the method may also include the steps of, within the classifier of the pulverizer, generating a swirling flow of coal, within the turret, dividing the swirling flow of coal into a plurality of flows equal in number to the number of sections within the turret, and, within each of the sections of the turret, straightening the flows of coal. In an embodiment, the method may also include transporting the plurality of flows of coal into the plurality of coal outlet pipes associated with each of the section, wherein the plurality of flows of coal are generally vertical through the turret. In an embodiment, the number of straightening vanes is equal to the number of coal outlet pipes in the pulverizer. In an embodiment, the method may also include the step of adjusting a height of at least one of the straightening vanes in dependence upon a detected coal flow imbalance between the coal outlet pipes. In an embodiment, each of the straightening vanes includes four segments. In an extended position the height of a respective vane is substantially equal to a combined height of the four segments. In a retracted position the height of a respective vane is substantially equal to a height of a single segment. In an embodiment, a feed pipe extends through the turret, the feed pipe and the body of the turret being substantially concentric, wherein each of the straightening vanes extends radially from the feed pipe to an inner peripheral wall of the turret.
In yet another embodiment, a coal pulverizer is provide. The pulverizer includes a grinding mechanism configured to transform raw coal into pulverized coal, a classifier configured to receive the pulverized coal from the grinding platform and to generate a swirling flow of coal, the classifier being further configured to reject coarse particles of the pulverized coal from the swirling flow, a turret arranged generally above the classifier, the turret having a generally frusto-conical body and a plurality of static straightening vanes arranged interior to the body, the straightening vanes dividing the body into a plurality of substantially equal sections, and a plurality of coal outlet pipes in fluid communication with the interior of the turret. The straightening vanes within the turret are configured to straighten the swirling flow of coal as it enters the turret, and to divide the swirling flow into a plurality of straightened flows that are communicated to the coal outlet pipes. In an embodiment, the classifier includes a reject cone that is configured to receive the coarse particles rejected by the classifier and to transport the rejected coal particles to a grinding platform of the pulverizer. In an embodiment, each of the straightening vanes is selectively extendable and retractable in a vertical direction for adjusting a height of each of the straightening vanes. In an embodiment, each of the straightening vanes includes four segments. In an extended position the height of a respective straightening vane is substantially equal to a combined height of the four segments. In a retracted position the height of a respective straightening vane is substantially equal to a height of a single segment.
It is to be understood that the above description is intended to be illustrative, and not restrictive. For example, the above-described embodiments (and/or aspects thereof) may be used in combination with each other. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from its scope. While the dimensions and types of materials described herein are intended to define the parameters of the invention, they are by no means limiting and are exemplary embodiments. Many other embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the invention should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. In the appended claims, the terms “including” and “in which” are used as the plain-English equivalents of the respective terms “comprising” and “wherein.” Moreover, in the following claims, terms such as “first,” “second,” “third,” “upper,” “lower,” “bottom,” “top,” etc. are used merely as labels, and are not intended to impose numerical or positional requirements on their objects. Further, the limitations of the following claims are not written in means-plus-function format and are not intended to be interpreted based on 35 U.S.C. §112, sixth paragraph, unless and until such claim limitations expressly use the phrase “means for” followed by a statement of function void of further structure.
This written description uses examples to disclose several embodiments of the invention, including the best mode, and also to enable one of ordinary skill in the art to practice the embodiments of invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to one of ordinary skill in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.
As used herein, an element or step recited in the singular and proceeded with the word “a” or “an” should be understood as not excluding plural of said elements or steps, unless such exclusion is explicitly stated. Furthermore, references to “one embodiment” of the present invention are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. Moreover, unless explicitly stated to the contrary, embodiments “comprising,” “including,” or “having” an element or a plurality of elements having a particular property may include additional such elements not having that property.
Since certain changes may be made in the above-described system and method without departing from the spirit and scope of the invention herein involved, it is intended that all of the subject matter of the above description or shown in the accompanying drawings shall be interpreted merely as examples illustrating the inventive concept herein and shall not be construed as limiting the invention.
