US3285232A - Steam generating unit - Google Patents

Description

Nov. 15, 1966 E.GRlFFlTH STEAM GENERATING UNIT Filed March 22, 1965 FIG.

LOU/5 E. GRIFFITH INVENTOR.

United States Patent Ofi ice 3,285,232 Patented Nov. 15, 1966 3,285,232 STEAM GENERATING UNIT Louis E. Griffith, Worcester, Mass, assignor to Riley Stoker Corporation, Worcester, Mass., a corporation of Massachusetts Filed Mar. 22, 1965, Ser. No. 441,524 1 Claim. (Cl. 122-481) This invention relates to a fuel-burning apparatus and, more particularly, to apparatus arranged to produce steam by burning fuel in a combustion chamber in the presence of tubes carrying water or steam.

In the generation of steam, two of the major problems are concerned with the conrtol of the final steam superheat temperature and with the problem presented by fouling and coating of the heat exchange elements in the combustion chamber. For instance, when the superheater tube platens become fouled, the temperature at which the super heated steam leaves the unit may change from a preselected value. Since the steam temperature to the turbine must be maintained at a fixed value for effective operation of the turbine, considerable equipment has to be provided to correct this temperature variation. These and other difiiou'lties experienced with the prior art apparatus have been obviated in a novel manner by the present invention.

It is, therefore, an outstanding object of the invention to provide a steam generating unit which is capable of maintaining control of superheat temperature irrespective of load and in which the superheater surfaces are kept relatively clean.

Another object of this invention is tlhe provision of a furnace providing the advantages of the directed-flame method of superheat control while maintaining radiant superheater surface in a clean condition.

A further object of the present invention is the provisilon of a steam generating unit in which the temperature distribution from wall to wall of the furnace is maintained evenly without undue fouling of water-wall tube surfaces.

With these and other objects in view, as will be apparent to those skilled in the art, the invention resides in the combination of parts set forth in the specification and covered by the claims appended hereto.

The charatcer of the invention, however, may be best understood by reference to one of its structural forms, as illustrated by the accompanying drawings in which:

FIG. 1 is a longitudinal vertical sectional view of a steam generating unit embodying the principles of the present invention,

FIG. 2 is a vertical sectional view of the unit taken on the line II-Il 'of FIG. 1, and

FIG. 3 is a somewhat schematic view of the unit showing a condition of operation different from FIG. 1.

Referring first to FIG. 1, wherein are best shown the general features of the invention, the steam generating unit, indicated generally by the reference numeral 10, is shown as consisting of a vertically-elongated combustion chamber 11 formed by a front wall 12, a rear wall 13, side walls 14 and 15, a roof 16, and a bottom 17. The upper part of the rear wall 13 is provided with a nose 18 whose upper edge defines with the roof 16 a gas oiftake 19. This gas ofitake leads to a back pass 21 terminating in a duct 22 which leads, in turn, to a stack (not shown).

At the upper part of the back pass 21 is located a main steam-andwater drum 23 and at the bottom of the pass adjacent the rear Wall 13- is a bottom drum 24, the two drums being joined by downcomer tubes 25. Extending from the bottom drum 24 is a large downcorner 26 leading to headers 27 and 28 located under the bottom 17. Water-wall tubes extend upwardly from the headers 27 and 28 and pass along the walls of the combustion chamber and terminate in the steam-andwater drum in the usual Way.

Located in the front wall 12 adjacent the bottom 17 is an abutment '29 extending horizontally across the front wall and carrying on its undersurface a directionalflame burner 31. A similar abutment 32 extends horizontally across the rear wall ,1? and has on its undersurface a directional-flame burner 33. The burners 31 and '33 are of the inter-tube, directional-flame type shown and described in the patent to Craig No. 2,759,460. Formed on the side wall 14 above the abutments 29 and 32 and extending horizontally thereacross is an abutment 84, while a similar horizontal abutment 35 is formed on the side wall ;15.

Generally speaking, the bottom surface of the upper abutments 34 and 35 leave their respective side walls at approximately the same horizontal plane as the upper surfaces of the abutments 29 and 32 meet their respective front and rear walls. In other words, the abutments 34 and 35 are immediately above the abutments 29 and 32. Located adjacent the side wall 14 above the abutment 34 is a radiant superheater panel 36, while a similar panel 37 is located adjacent the side wall 15 above the abutment 35. Located above the nose in the gas olftake 19 is a convection reheater =38 consisting of spaced panels which are shown particularly well in FIG. 2. The panels for the heater 38 are all spaced well away from the side walls 14 and 15. Finally, in the backpass 21 is located the primary convection superheater 39.

The operation of the invention will now be readily understood in view of the above description. When the steam generating unit is operating, streams of combustion gas will leave the burners 31 and '33 and progress upwardly through the combustion chamber 11. In the arrangement shown in FIG. 1, the vanes of the burners are set so that the stream of gas flows .adjacent the rear wall 13 of the furnace. As is evident in the drawing, the radiant superheaters 36 and 37 are arranged on the side walls 14 and 15, respectively, in such a way that the center of gravity of the area provided by the panel is located closer to the front wall 12 than to the rear wall 13. In other words, each radiant superheater is disposed on its side wall with the major portion of its heating surface closer to the front wall than to the rear wall. Therefore, when the gas mass passes up along the rear wall 13, the heat transfer from the gas to the steam through the radiant superheaters 36 and 37 is at a minimum value. The gas passes outwardly of the combustion chamber around the nose 18 through the gas olft'ake 19 and flows in convective heat exchange with the reheater 38, the superheater 39, and the downcomcrs 25. This is the manner in which the burner would usually operate at high load. It can be seen that the gas flow leaving the burners 33 in FIG. 2 flows upwardly through the combustion chamber 11 and is drawn inwardly by the abutments 34 and 35. This means that the gas flow is maintained away from the side walls 14 and 15 and away from the radiant superheaters 36 and 37 so that it does not foul these elements. This means that, with the gas crowded toward the center of the furnace, the gas passes through the gas ofitake 19 and over the reheater 38. Eventually, it flows over the convection superheater '39 with the gases thoroughly mixed and the temperature from side to side at a very even value. In the past, the tendency has been for the hotter gases to flow up the center of the furnace so that the side walls receive lower temperature gas. This means that, in passing over convection superheater surfaces, the inner parts of the superheater receive hot gas, while the outer parts receive low-temperature gas.

This makes it very difiicult to maintain superheat at a final superheat temperature at a predetermined value. At low loads, there is a tendency for the superheat to drop olf; therefore, at that time, the burners are adjusted in the manner shown in FIG. 3 so that the gas flows adjacent the front wall 12 of the furnace and passes closely adjacent to the radiant supenheater platens 36 and 37. This maintains the temperature of superheat at a high value. At the same time, there is no danger of the heat exchange surfaces of the superheaters 36 and 37 becoming fouled, since the abutments 34 and '35 maintain the flow of gas largely centrally of the furnace, and also provides for thorough mixing of the gases so that the gas temperature pattern from side to side of the furnace is quite even.

An added benefit has been provided by the present construction. To begin with, there is a tendency in the type of furnace using a nose to throw the gases forwardly toward the [front wall. In the past, because of the [fact that there are some cooler gases, particularly adjacent the side walls, there has been a tendency for slag to accumulate on the front wall a little above the level of the nose. By the practice of the present invention, the combustion gases will be thoroughly mixed before they reach this portion of the furnace, so that there will 'be no gas elements suflicientl-y cool to permit condensation .and deposit of slag on any of the walls.

It is obvious that minor changes may [be made in the form and construction of the invention without departing from the material spirit thereof. It is not, however, desired to confine the invention to the exact form herein shown and described, but it is desired to include all such as properly come within the scope claimed.

The invention having been thus described, what is claimed as new and desired to secure by Letters Patent A stream (generating unit, comprising (a) front, rear, and side walls forming a verticallyelongatedcombustion chamber, the chamber having a gas offtake located in the rear wall at the upper end of the chamber and having a horizontal nose extending forwardlly from the rear wall immediately under the :gas olftake,

(b) a horizontal primary abutment extending inwardly from both the front and rear walls adjacent the lower end of the chamber,

(c) burners mounted beneath the abutments, each burner including the vanes which are adjustable about horizontal axes perpendicular to the side walls to permit the regulation of the flame direction,

(d) a horizontal secondary abutment extending inwardly from the side walls at a level located a substantial distance above the primary abutments, and

(e) a radiant vapor heater located on each side wall with the major portion of its heating surface closer to the [front wall than to the rear wall.

References Cited by the Examiner UNITED STATES PATENTS KENNETH W. SPRAGUE, Primary Examiner.

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