Furnaces – Utilizing powdered fuel
Reexamination Certificate
2001-07-03
2002-08-27
Lazarus, Ira S. (Department: 3749)
Furnaces
Utilizing powdered fuel
C110S265000, C239SDIG001, C239S502000
Reexamination Certificate
active
06439136
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to firing systems for use with pulverized solid fuel-fired furnaces, and more specifically, to a pulverized solid fuel nozzle tip with a ceramic component for use in such firing systems.
It has long been known in the prior art to employ pulverized solid fuel nozzle tips in firing systems of the type that are utilized in pulverized solid fuel-fired furnaces. By way of exemplification and not limitation in this regard, reference may be had to U.S. Pat. No. 2.895,435 entitled “Tilting Nozzle For Fuel Burner”, which issued on Jul. 21, 1959 and which was assigned to the same assignee as the present patent application. In accordance with the teachings of U.S. Pat. No. 2,895,435, there is provided a tilting nozzle that is alleged to provide substantially uniform distribution of the fuel-air mixture leaving the tilting nozzle and substantially uniform velocity across the discharge opening of the tilting nozzle into the furnace. To this end, the tilting nozzle includes an inner conduit within an outer conduit. Moreover, a plurality of baffles or division walls are provided within the inner conduit arranged in planes substantially parallel to fluid flow and such as to divide the inner conduit into a multiplicity of parallel channels. These baffles or division walls are designed to be operative to correct the concentration of the air-fuel mixture along the deflecting wall of the inner conduit and the resulting relatively unequal pressure there when the titling nozzle is tilted. Thus, the effect is that as the tilting nozzle is tilted, either upwardly or downwardly, the unequal velocities through the tilting nozzle are made substantially equal by restricting the flow in the high pressure zone present at the inlet end of the inner conduit and encouraging the flow in the low pressure zone also present at the inlet end of the inner conduit.
Another prior art form of a pulverized solid fuel nozzle tip that has been employed in firing systems of the type that are utilized in pulverized solid fuel-fired furnaces is depicted in U.S. Pat. No. 4,274,343 entitled “Low Load Coal Nozzle”, which issued on Jun. 23, 1981 and which is assigned to the same assignee as the present patent application. In accordance with the teachings of U.S. Pat. No. 4,274,343, there is provided a fuel-fired admission assembly of the type incorporating a split coal bucket having an upper and a lower coal nozzle pivotally mounted to the coal delivery pipe and independently tiltable of each other. Continuing, a plate is disposed along the longitudinal axis of the coal delivery pipe with its leading edge oriented across the inlet end of the coal delivery pipe so that that portion of the primary air pulverized coal stream having a high coal concentration enters the coal delivery pipe on one side of the plate and that portion of the primary air-pulverized coal stream having a low coal concentration enters the coal delivery pipe on one side of the plate and that portion of the primary air-pulverized coal stream having a low coal concentration enters the coal delivery pipe on the other side of the plate. Moreover, the trailing edge of the plate is orientated across the outlet end of the coal delivery pipe such that that portion of the primary air-pulverized coal stream having a high coal concentration is discharged from the coal delivery pipe through the upper coal nozzle and such that that portion of the primary air-pulverized coal stream having a low coal concentration is discharged from the coal delivery pipe through the lower coal nozzle.
Although the pulverized solid fuel nozzle tips that form the subject matter of the above-noted U.S. patents have been demonstrated to be operative for their intended purposes, there has nevertheless been evidenced in the prior art a need for such pulverized solid fuel nozzle tips to be further improved. In this regard, it has been found that pulverized solid fuel deposits, i.e., coal deposits, on and within the pulverized solid fuel, i.e., coal, nozzle tips are problematic from an operational standpoint. That is, such coal deposits on and within the coal nozzle tip have been found to lead to either premature or catastrophic coal nozzle tip failure, depending primarily upon the tenacity of the formed deposits and the rate at which the deposition occurs. To this end, deposition of coal on or within the coal nozzle tip is believed to be caused by a combination of the following three variables: 1) coal composition/type, i.e., slagging, non-slagging, sulfur/iron content, plasticity, etc.; 2) furance/coal nozzle operational settings, i.e., primary/fuel air flow rate/velocity, tilt position, firing rate, etc.; and 3) coal nozzle tip aerodynamics.
Thus, by way of summary, present designs, i.e., prior art forms, of coal nozzle tips have by and large been found to exacerbate the coal deposition problem through the creation of regions of low or negative velocities, i.e., recirculation, that cause slowly moving, “hot”, coal particles to come in contact with “hot” coal nozzle tip metal surface. Namely, it has been found that as a result of this interaction, and under requisite thermal conditions that are related to the coal's plasticity, some of the coal particulate sticks to the plate, thus initiating the deposition process. Moreover, with specific reference to present designs, i.e., prior art forms, of coal nozzle tips, it has been found that regions of low and negative velocities typically occur along the thickness of the nozzle plane platework and in the sharp corners of the primary air shroud.
There has, therefrom, been evidenced in the prior art a need for a new and improved pulverized solid fuel nozzle tip that would address the deficiencies from which present designs, i.e., prior art forms of pulverized solid fuel nozzle tips have been found to suffer. Namely, there has been evidenced in the prior art a need for a new and improved pulverized solid fuel nozzle tip that would be advantageously characterized in the following respects: 1) would minimize low and negative, i.e., recirculation, velocity regions at the exit plane of the pulverized solid fuel nozzle tip, 2) would reduce available deposition surface on the pulverized solid fuel nozzle tip, and 3) would vary the nozzle tip/solid fuel nozzle thermal conditions to keep the “hot” solid fuel particulate matter from deposition on available metal platework surfaces of the pulverized solid fuel nozzle tip. Such a new and improved pulverized solid fuel nozzle tip accordingly would be effective in controlling the deposition phenomena, from which present designs, i.e., prior art forms, of pulverized solid fuel nozzle tips have been found to suffer. This would be accomplished through the aerodynamic design embodied by such a new and improved pulverized solid fuel nozzle tip coupled with proper adjustment of the controllable operational variables, i.e., fuel air flow rate, etc. As employed herein, the term “controllable” refers to the fact that solid fuel type and furnace load, and in some, notably retrofit, cases primary air flow rate are typically not controllable operational variables for mitigation of the deposition phenomena.
A common material composition for pulverized solid fuel nozzle tips is stainless steels, typically with relatively high temperature ratings such as, for example, 309 stainless steel. While stainless steel has the desirable material properties of ease of effort in incorporating it into the finished product, toughness, durability, high temperature strength, and ductility, certain material properties of conventional pulverized solid fuel nozzle tips comprised of stainless steel often force operators of pulverized solid fuel combustion facilitates to operate their facilities in a less than optimal economic manner to avoid exceeding the physical limits of such conventional pulverized solid fuel nozzle tips.
Two such limiting material properties are the ability of a stainless steel pulverized solid fuel nozzle tip to maintain its structural integrity at a high temperature (i.e
Mann Jeffrey S.
Nowak Ronald H.
Alstom (Switzerland Ltd
Lazarus Ira S.
Reinehart K. B.
Warnock Russell W.
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