US1918311A - Superheat control - Google Patents

Description

July 18, 1933. w R 109:; 1,918,311

SUPERHEAT CONTROL Filed nay 1'7. 1950 W0? BY M/% A TTORNEYS.

Patented July 18, 1933 UNITED sr-Arss W'IIFRED R. WOOD, OF LONDON, ENGLAND, ASSIGNOR TO INTERNATIONAL COMBUS- PATENT OFFICE TION ENGINEERING CORPORATION, OF NEW YORK, N. Y., A CORPORATION OF DELA- WARE SUIPERHEAT CONTROL Application filed May 17, 1930. Serial No. 453,198.

This invention relates to superheat control and is especially useful in connection with high pressure boilers such, for example, as the type in which the boiler is shaped in the form of a box and constitutes its own combustion chamber with the great majority of its tubes subjected to radiant heat and with a relatively small amount of tubes subjeeted to heat by convection; the temperature of the exit gases being reduced to allowable limits by convection surfaces independent of the boiler, such, for example, as reheating surfaces, economizer surfaces, boiling and otherwise, and combustion air preheating surfaces. Such a boiler is shown in the copending application of Wilfred R. Wood, Serial No. 440,883, filed April 2, 1930.

A boiler of this type has high capacity and the steam is generated at a high rate from a relatively small amount of evaporation surface.

()ne of the primary objects of the invention is to make it possible to secure an approximately uniform superheat for a varying load, or to hold the superheat constant if desired, with change in furnace condltions, or to make it possible to use a superheater which is oversize for normal operat-- ing conditions but is adapted to meet peak conditions of operations More specifically it is an object of the invention to provide means for governing the amount of gases sweeping over the superheater without affecting the sweep of the gases over the convection surfaces.

My invention also contemplates the provision of an effective and simple movable baflie arrangement for efi'ecting superheat control.

The foregoing, together with such other objects and advantages. as may hereinafter appear, or are incident to my invention, is illustrated in the preferred form in the accompanying drawing in which the figureis a vertical section through a high pressure, high capacity boiler installation embodying my improvements.

Referring now to the figure, it will be seen that I have herein illustrated what is, in effect, a single drum, high pressure boiler,

the tubes of the boiler being arranged in the form of a six-sided box providing or definlng the combustion space.

This combustion chamber is defined at the rear by a row of tubes 7 rising from the headers 8 and 12 to the drums 9; at the bot tom by the rows of relatively widely spaced tubes 10 and 11 which lead from the header 12 to the headers 13 and 14 respectively; at the front by the row of relatively closely spaced tubes 15 rising from the headers 13 and 14 and delivering to the headers 16 and 17; at the top by three rows of tubes 18 which incline upwardly and rearwardly from the headers 16 and 17 to the rear of the combustion chamber where they bend upwardly and then rearwardly for connection to the drum 9; and at the sides by the row of relatively closely spaced tubes 19 which rise from the headers 20 and 21 and lead to the headers 22 and 23, which latter headers are spaced well above the tubes 18. The headers 20 and 21 are supplied from a header 8 by the tubes 24 and deliver to the drum from the headers 22 and 23 as by means of the tubes 25.

Downcomer tubes 26 supply the header 8 from the drum 9 and downcomer tubes 27 supply the header 12 from the header 9. A bafl'le indicated as a whole by the reference character B is provided and disposed so as to provide a passage 28 which establishes communication between the space 0 between the tubes 18 and the tubes 25 and the ofl'take 29. i

The upper ends of the tubes 18, 7, 26 an 27 are swept by the gases leavingethe space C, these portions of the said tu s largely constituting the convection surface of the boiler proper.

' In the space 0 I provide a superheater D which is preferably over-size to give adequate superheat at normal operating conditions of a high capacity boiler such as used, for example, in a large public utility generating plant. The gaseous products of combustion leaving the combustion spare proper and entering the space C through the spaces between the tubes 18, sweep over the superheater D, then over the portions of the tubes lying in the passage 18 and thence to the reheater E (in this case) and then through the air preheater F into the stack. Part of the baflie B is carried in the tubes 18, this part extending forwardly from the wall which separates thetube's' 7 and26 at the rear of the combustion chamber partway across the outlet from the combustion space proper. At the forward end of the bafile there is an upright bridge portion 31 carried on the tubes 18 and extending vertically to the superheater D. This bridge extends across the furnace. Immediately to the rear of the bridge the baflie is composed of a hinged member 32, preferably made of refractory material. This hinged member is shown in closed position in the figure, in which case all of the gaseous products of combustion pass over the superheater D. By swinging the bafiie upwardly a by-pass is provided to the rear of the bridge through which any desired portion, within limits, of the gaseous products of combustion, is diverted thereby, reducing the volume of gases passingover the superheater, and giving roper superheat under peak conditions 0 operation. This hinge section of the baflle need not be very wide, as, for example, a twelve inch section extending for the full width of the boiler, when full 0 en, will provide about fifteen square feet 0 by-pass outlet.

The hinged section is moved by means of the rod or rods 33 made of high temperature resistant metal and operated either by hand or by a solenoid 'or other automatic device diagrammatically indicated at 34.

It is to be noted that while a portion of I the gaseous products of combustion may be diverted from the superheater D, nevertheless the disposition of the parts is such that none of the gaseous products of combustion are diverted from the convection surface of the boiler proper which, therefore, function with full effectiveness. 7

It will be seen from the foregoing that I have thus provided an effective arrangement whereby it is possible to operate the installation under normal conditions by subjecting the superheater to all of the gases of combustion, getting the desired degree of superheat by diverting a portion of the gases 'under abnormal or extreme heat conditions the boiler otherwise,

- character here involved it is preferable to use a reheater E to reheat the low pressure steam leaving the high pressure engines before its use in the low pressure engines. It is also frequently desirable to provide a control of the volume of gases passing over the reheater as operating conditions vary, to which end I arrange the preheater' as follows. The reheater preferably has an upper section E which extends for the full width of the offtake 29 and is followed by two reheater sections F laterally spaced apart to' provide a central space in which I locate a duct 35 controlled by a damper 36, the position of which determines the volume of gases passing over the sections F of the reheater. This damper may be controlled by automatic apparatus as before, in this case operating under the influence of the temperature of steam leaving the reheater. Since, however, the operation of the member 32 does not affect the gases which sweep over the convection elements, it will be seen that the control of the reheat is not compli cated by antecedent conditions and the control apparatus may be said so secure uniform reheat for varying load or a constant reheat despite change in furnace conditions.

Because of the pulverized fuel firin a deposit collects on the tubes of the com ustion chamber which varies the absorption of heat and, therefore, the temperature of the gases leaving the combustion space. This makes the bypass very useful in this t e of furnace-boiler. The deposit falls 0 on change in operating condltions, reforms, etc.

I claim 1. A furnace-shaped boiler having an upper drum, a superheater at the top of the chamber, a plurality of screening tubes extending between the superheater and the active part of the boiler and rising upwardly at their inner ends to connect with the drum and to be subject to gases leaving the vspace in which the superheater is located,

an off-take including a gas by-pass passage at one side of the superheater, a bafile carried by said tubes and a movable damper forming part of said baflie, located in advance of the inner ends of the tubes below the superheater, and disposed in said 'passag to control the flow therethrough.

2. A furnace-shaped boiler having an up per drum, a superheater at the top of the chamber, a plurality of screening tubes extending between the superheater and the active part of the boiler and rising upwardly at their inner ends to connect with the drum and to be subject to gases leaving the space in which the superheater is located, a baflie carried by said tubes and a movable damper forming part of said baflie and located in advance of the inner ends of the tubes and below the superheater, the front of the baffle being in the form of a brid e rising from said tubes and extending to t e superheater.

3. A furnace-shaped boiler having an upper drum, a superheater at the top of the chamber, a plurality of screening tubes.ex--

tending between the superheater and the active part of the boiler and rising upwardly at their inner ends to connect wlth the drum and to be subject to gases leaving the space in which the superheater is located, a baflie carried by said tubes and a movable damper forming part of said bafiie and located in advance of the inner ends of the boiler subject to radiant heat, an off-take from said chamber, a superheater positioned to be subject to the flow of gases leaving the combustion space to pass to said off-take, said off-take including a gas by-pass passage at one side of said superheater and said boiler tubes including a set thereof disposed between the superheater and the combustion space proper whereby to screen the former from the latter, and adjustable damper means in said by-pass passage for controlling the flow of gases therethrough, whereby a portion of the gases leaving the combustion space may be .by-passed around the WILFRED R. WOOD.

superheater.

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