Patent Publication Number: US-6988452-B2

Title: Tower distributor assembly

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims benefit of U.S. Provisional Patent Application 60/355,676, filed Feb. 7, 2002, the disclosure of which is incorporated by reference herein. 
   BACKGROUND OF THE INVENTION 
   This invention relates generally to fuel burner systems and, more particularly, to solid fuel burner systems. 
   Many industrial processes require the equal distribution of heterogeneous flows to multiple receptors. For example in the electric utility industry, pulverized coal (“PC”) is transported through a pipe (duct) system that connects a grinding mill to one, or more, burners of a furnace. The PC is transported within the pipe system by a carrier gas, e.g., air. Thus, the heterogeneous flow, or stream, is made up of the PC and air (i.e., a two-phase flow or multi-phase flow). Ideally, one grinding mill is capable of supplying one or more such streams to multiple burners (receptors) of the furnace. 
   Unfortunately, as a stream moves through a long length of pipe, the solid particles in the stream tend to concentrate together in a pattern generally characterized as being in the shape of a rope strand. This phenomenon is commonly referred to as roping, or laning. As such, any attempt to further distribute, or split, a stream into multiple streams for transport to respective receptors seldom, if ever, yields equal amounts of PC going to each of the receptors. In other words, when roping occurs in a stream, splitting that stream into multiple streams results in a flow imbalance between the multiple streams. This flow imbalance could be on the order of ±30% between the multiple streams. 
   Likewise, with respect to receptors fed by multiple sources, roping makes it difficult to combine the flows from these multiple sources such that each of the receptors are supplied with equal flows. 
   The prior art has attempted to resolve these problems in several ways. For example, the installation of adjustable orifices to each carrier pipe and adjusting the resistance through each orifice is one method to reduce the range of imbalances in the flow. This method, although helpful, does not provide predictable results in all cases. 
   More recently, on-line flow measurement devices have been developed that can provide real-time information on the relative coal and air flows in each pipe. The use of this monitoring equipment, in combination with the above-mentioned adjustable orifices, permits the measurement and modification of the flows. However, a significant limitation of this method is the requirement for continuous adjustments using complex computer-controlled algorithms. 
   As such, these and other methods are generally ineffective, both in cost, effort, and time, to rectify flow imbalance. Indeed, many methods suffer from the general inability to attain satisfactory flow balance and maintain flow balance over time; the inability to prevent high-pressure drop requiring excessive power consumption; and the inability to prevent nonlinear flow balance as flow quantity changes. 
   SUMMARY OF THE INVENTION 
   In view of the above flow balance problem, and in accordance with an aspect of the invention, a tower distributor assembly for use in a furnace system produces substantially equal multiple heterogeneous streams of solids in a carrier gas from either a single flow source or multiple flow sources. 
   In accordance with an embodiment of the invention, a tower distributor assembly comprises four sections: an inlet section, a mixer section, a recovery section and an outlet section. Illustratively, the inlet section includes a first elongated passageway where one, or more, input streams pass into the tower distributor assembly. The mixer section receives the one, or more, input streams and mixes them together to provide a single, turbulent, well-mixed (or homogeneous) stream to the recovery section. The latter includes a second elongated passageway having a length that is illustratively greater than or equal to one half of a diameter of the second elongated passageway. In particular, the length of the second elongated passageway is selected such that the length of time taken for the single, turbulent, well-mixed stream to travel through the recovery section provides enough time for the turbulent stream to settle such that the well-mixed stream exits the recovery section to the outlet section as a laminar flow. The outlet section divides the single, laminar, well-mixed stream for application to multiple outlet pipes for transport to the ultimate receptors. 
   In another embodiment, a furnace system comprises a grinding mill, a first pipe distribution system, the above-described tower distributor assembly, a second pipe distribution and multiple burners of a furnace. 
   In accordance with another aspect of the invention, a method produces equal well-mixed streams of solids in a carrier gas in a burner system. A first step comprises receiving in a first elongated passageway of an inlet section one, or more, input streams. A second step comprises mixing the received one, or more, input streams in a mixer section to provide a turbulent, well-mixed, stream. A third step comprises receiving the turbulent, well-mixed, stream in a recovery section such that movement of the well-mixed stream through the recovery section provides a single, laminar, well-mixed stream. A fourth step comprises applying the single, laminar, well-mixed stream to an outlet section for splitting the single, laminar, well-mixed stream for distribution to multiple receptors. 
   It is, therefore, an object of the present invention to provide a tower distributor assembly for use in a furnace system that will produce a single, laminar, homogeneous stream. 
   It is also an object of the present invention to provide a method that will produce substantially equal well-mixed streams in a furnace system. 
   Another object of this invention is to improve the distribution of the solid particles in a stream such that a stream is of more nearly equal weight and density. 
   Another object of this invention is to achieve substantially equal outlet streams that are derived from multiple unequal streams. 
   Another object of the present invention is to provide a cost effective means of achieving a single, laminar, homogeneous stream that relies substantially on pipe geometry and aerodynamics to effectively create a laminar homogeneous flow. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an illustrative block diagram of a burner system in accordance with the principles of the invention; 
       FIG. 2  is a side view of an illustrative embodiment of a tower distributor assembly in accordance with the principles of the invention for use in the burner system of  FIG. 1 ; 
       FIG. 3  is another side view of the tower distributor assembly of  FIG. 2 ; 
       FIG. 4  is a top view of the tower distributor assembly of  FIG. 2 ; 
       FIG. 5  is a side view of another illustrative embodiment of a tower distributor assembly in accordance with the principles of the invention; and 
       FIGS. 6 and 7  are other illustrative embodiments of a tower distributor assembly in accordance with the principles of the invention. 
   

   DETAILED DESCRIPTION 
   Other than the inventive concept, the apparatus and methods of a solid-fuel burner system are well known and are not described further herein. For example, other than the inventive concept, a burner may comprise a fuel injector, which is a portion of the combustion equipment that injects the fuels and carrier gas into a combustion zone of a furnace. Also, like numbers on different figures represent similar elements. 
   An illustrative block diagram of a burner system in accordance with the principles of the invention is shown in  FIG. 1 . Burner system  10  comprises a coal mill (fuel preparation plant or grinding mill)  50 , a number of representative feed pipes (or just pipes),  102 - 1  to  102 -N and  103 - 1  to  103 -N, a tower distributor assembly  200 , a number of burners as represented by burners  104 - 1  to  104 -N, and a boiler furnace, of which a portion  60  is shown (hereafter boiler furnace  60 ) having a combustion zone  65 . For simplicity, the inventive concept is described in the context of feed pipes  102 - 1 ,  102 - 2 ,  103 - 1 ,  103 - 2 ,  103 - 3  and  103 -N and burners  104 - 1 ,  104 - 2 ,  104 - 3  and  104 -N. However, the inventive concept is not so limited and may apply to any number and combination of feed pipes and burners. 
   Illustratively a solid fuel, e.g., coal, and a transport medium (or carrier gas) (e.g., air) are provided to a fuel preparation plant as represented by coal mill  50 , which pulverizes the coal for distribution via the carrier gas to a number of burners (or receptors). This distribution initially occurs via feed pipes  102 - 1  to  102 -N. As noted above, as a stream moves through a long length of pipe, the phenomenon of roping occurs. As such, any attempt to further distribute, or split, for example the stream in pipe  102 - 1  to pipes  103 - 1  and  103 - 2  for transport to burners  104 - 1  and  104 - 2 , respectively, will typically result in a flow imbalance between the streams in pipes  103 - 1  and  103 - 2 . Therefore, and in accordance with the principles of the invention, a tower distributor assembly  200  is used to mix the input streams (or input stream, for that matter) such that further division, or splitting, of the input streams into a number of output streams results in substantially equal distribution of the solid fuel among the output streams. That is, the output streams are flow balanced. To this extent, and as described further below, tower distributor assembly  200  illustratively combines and mixes the streams transported by pipes  102 - 1  and  102 - 2 , and then divides the combined mixed stream to provide multiple flow-balanced output streams for transport to burners  104 - 1  to  104 -N, via pipes  103 - 1  to  103 -N, respectively. Burners  104 - 1  to  104 -N provide these output streams to combustion zone  65  of boiler furnace  60  for combustion therein. 
   Turning now to  FIG. 2 , an illustrative side view of tower distributor assembly  200  of  FIG. 1  is shown. Tower distributor assembly  200  comprises four sections: an inlet section  205 , a mixer section  210  (or mixer  210 ), a recovery section  215  and an outlet section  220 . The direction of fuel flow in  FIG. 2  is represented by arrow  201 . Illustratively, the overall shape of tower distributor  200  is generally of a cylindrical form. 
   Inlet section  205  includes a first elongated passageway  206  and a transition section  207 . Inlet section  205  is where one, or more, input streams pass into the tower distributor assembly. The first elongated passage way  206  has a length, L I , in the direction of arrow  201  and a circular cross-section having a diameter D 206  (shown in  FIG. 3 ). The diameter D 206  is also referred to herein as an outlet diameter of the inlet section. Preferably, the length of the first elongated passage way  206  is less than or equal to two times the diameter D 206 . In this example, inlet section  205  is coupled to pipes  102 - 1  and  102 - 2  via transition section  207 . The latter combines the streams from these pipes to provide a single stream to the first elongated passageway  206 . Transition section  207  provides a square, or rectangular, to circular transition to match the circular cross-section of elongated passage way  206  with the typically non-circular connecting pipes. It should be noted that this type of transition section is not required for the inventive concept and merely provides the ability to match different geometries that may be found in the pipe distribution system. To facilitate this transition, a diameter  201  (shown in  FIG. 3 ) of inlet section  205  may be larger, or less than, D 206  of inlet section  205  (a larger diameter is illustrated in  FIG. 3 , while a smaller diameter is illustrated in  FIG. 6 ). The diameter  201  is also referred to herein as an inlet diameter of the inlet section. 
   The mixer section  210  receives the one, or more, input streams and mixes them together to provide a single, turbulent, well-mixed (or homogeneous) stream to the recovery section  215 . Illustratively, mixer section  210  includes a diffuser, which is known in the art. For example, an illustrative diffuser is shown and described in U.S. Pat. No. 6,042,263 issued Mar. 28, 2000 to Mentzer et al. However, other types of turbulence inducing devices or elements can be used in the mixer section. Indeed, it is only necessary in the mixer section to mix the stream. As such, any turbulence inducing device can be used, e.g., an impeller, and the turbulence inducing device may be further determined by cost, size and material considerations. 
   Turning briefly to  FIG. 3 , mixer section  210  comprises a diffuser element  211 , such as that described in the above-mentioned U.S. Pat. No. 6,042,263. Adjacent diffuser element  211  are diffuser regions  212  and  213 . Diffuser element  211  is preferably located midway along a length of diffuser  215  in the direction of arrow  201  such that the lengths of diffuser regions  212  and  213  in the direction of arrow  201  are substantially equal. However, diffuser element  211  may be located anywhere along the length of mixer section  210  and, as such, the lengths of diffuser regions  212  and  213  can vary. Diffuser region  212  receives the single stream from inlet section  205  and provides this single stream to diffuser element  211 . The latter induces turbulence into the stream to provide a single, turbulent, well-mixed stream to diffuser region  213  for application to recovery section  215 . Preferably, a length of mixer section  210  is less than, or equal to, a diameter (not shown), D 210 , of mixer section  210 . 
   It should be appreciated that reference numeral  211  as shown in  FIG. 3  is intended to generically represent various mixing devices other than a diffuser. 
   Turning back to  FIG. 2 , recovery section  215  is located downstream of mixer section  210  and includes a second elongated passageway  216  having a length (in the direction of arrow  201 ), L R , that is illustratively greater than or equal to one half of a diameter, D 216 , of the second elongated passageway  216 . In particular, and in accordance with an aspect of the invention, the length of the second elongated passageway  216  is selected such that the length of time taken for the single, turbulent, well-mixed stream to travel through recovery section  215  provides enough time for the turbulent stream to substantially settle, or substantially subside, such that the well-mixed stream exits recovery section  215  to the outlet section  220  as a substantially laminar flow. It should be noted that the length of diffuser region  213  in the direction of flow may also affect the stream. As such, an effective recovery section length L E  is defined as shown in  FIG. 3  for the second elongated passageway. Length L E  includes the length of recovery section  215 , L R , and a length of diffuser region  213  in the direction of flow. In this case, length L E  is illustratively greater than or equal to one half of D 216 . As such, as used herein the term “length of the recovery section” may also include the length L E . 
   Outlet section  220  separates, splits, or divides the stream (or flow) leaving recovery section  215  into multiple outlets. In this example, outlet section  220  receives the single, laminar, well-mixed stream from recovery section  215  and divides this stream for application to four outlet pipes ( 103 - 1 ,  103 - 2 ,  103 - 3  and  103 -N) for transport to the ultimate receptors (burners  104 - 1 ,  104 - 2 ,  104 - 3  and  104 -N). Since, the stream from recovery section  215  is a laminar, well-mixed (or homogeneous) stream—the splitting of this stream into multiple output streams does not suffer from flow imbalance. Outlet section  220  includes a conical frustrum with internal separators. The internal separators segregate the two-phase flow leaving the recovery section into the desired number of flow streams and channel them into the respective outlet pipes. Preferably, a length of outlet section  220  in the direction of arrow  201  is less than or equal to two times a diameter, D 220 , of outlet section  220  (shown in  FIG. 3 ). The diameter D 220  is also referred to herein as an inlet diameter of the outlet section. Like inlet section  205 , outlet section  220  also serves as a transition section. As such, to facilitate this transition, a diameter  221  of outlet section  220  may be larger, or less than, inlet diameter D 220  of outlet section  220  (illustrated in  FIG. 3 ). As used herein, the diameter  221  is also referred to as the outlet diameter of the outlet section. A top view of outlet section  220  of tower distributor  200  is further illustrated in  FIG. 4 . 
   As described above, a tower distributor assembly receives multiple multi-phase streams, combines them into a single stream, mixes the single stream to provide a turbulent single stream, converts the turbulent single stream into a laminar single stream and then splits the laminar single stream into multiple output streams, where each output stream has substantially the same amount of solid fuel as the other output streams. Thus, avoiding the problem of flow imbalance between streams as described earlier. 
   As can be observed from  FIGS. 1 ,  2  and  3 , the tower distributor assembly receives multiple input streams. However, the tower distributor assembly may also receive a single stream for distribution to multiple receptors. This is illustrated in  FIG. 5  showing single feed pipe  102 - 1  providing an input stream to tower distributor assembly  200 . Like numbers on different figures represent similar elements to those described above and are not described further herein. 
   Other variations of a tower distributor assembly in accordance with the principles of the invention are shown in  FIGS. 6 and 7 . These figures also show some illustrative dimensions (in inches). 
   Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. For example, although the inventive concept was described in the context of a single solid fuel burner system, the inventive concept is also applicable to cofiring burner systems, e.g., having a primary solid fuel and a secondary solid fuel. Also, although the cross-section of the tower distributor assembly was described as being circular for ease and simplicity of manufacture, the cross-section of the tower distributor assembly may have other shapes, such as, but not limited to, a polygon. Similarly, although described in the context of a tower distributor assembly having four sections, there may be additional sections. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.