US2581896A - Vapor generator - Google Patents

Description

VAPOR GENERATOR Filed April 26, 1949 INVENTOR.

ATTORNEY Patented Jan. 8, 1 952 VAPOR GENERATOR Charles H. Woolley, Cranford, N. J., assignor to The Babcock dt Wilcox Company, Rockleigh, N. J., a corporation of New Jersey 7 Application April 26, 1949, Serial No. 89,601

2 Claims.

, 1 This invention relates to vapor generators, and the invention is particularly exemplified in a high pressure and high capacity vapor generating and superheating installation.

v More particularly, the invention is exemplified in a high pressure water tube steam boiler of the radiant type, with a steam superheater incorporated in the same installation.

Extensive experience in the field of steam generation and more particularly in the development 'of modern water tube steam-boilers of the type used in stationary service-to supply steam for the generation of electric power'has demonstrated clearly that certain conditions are necessary in order that the maximum of practical efiiciency may be attained. Relatively high steam pressures 'must be used in the interest of efiiciency, and for turbine use. The steam must not only be superheated to higher temperatures as steampressures rise, but it is of paramount importance that the final or total steam temperature shall be controlled over a wide range of boiler loads. This is particularly important in the operation of large central power stations which are subject to daily peak load demands.

The maintenance of a closely controlled final steam temperature is not only important from the standpoint of protection of the turbine against danger, but it is also-important for the protection of the metal of superheater tubes.

When a convection superheater is employed in the described type of vapor generating andsuperheating installation for safe metal temperatures and for a desired superheat at full load, that superheat will be deficient in superheating capacity at fractional loads, but the factors wh ch require the desired'superheat at full load are still effective at fractional loads. Thisdifiiculty is corrected in the present invention by the provision of a pulverized fuel fired furnace, a superheater gas pass and by-pass, so constructed and associated with the fuel burning means and the gas cooling and Vapor generating wall tubes that the above indicated inherent deficiency in the superheater is corrected by variation in gas flow over the superheater. This arrangementis such that, under conditions requiring an increase in gas flow over the superheater elements, slagging is reduced and a longer flame travel is provided for the furnace gases before the entrance of the superheater gas by-pass is reached.

The invention also accomplishes the above indicated results by an arrangement of elements which eliminates constructions which tend to promote the development of slag accumulations.

The illustrative invention also is characterized by lower gas temperatures at the zone in which dampers are employed to vary the gas fiow for effecting superheat control.

A preferred embodiment of the invention is "illustrated in the accompanying drawings, and other objects of the invention will appear from the following description which refers to that drawing.

The drawing indicates a vertically elongated combustion chamber [0, the walls and other boundary surfaces of which include steam generating wall tubes such as l2 to M, communieating at their upper ends with a steam and water drum l8 and having their lower ends communicating with the water space of that drum by appropriate connections such as the headers 29-43 and downcomer tubessuch as 26 and 28.

The furnace is fired by burners 3G and the resulting'furnace gases pass to the lower part of the furnace and then turn to pass upwardly through a convection section which includes the economizer 34 and the convection superheater 32. These components are disposed mainly in a vertical gas pass formed between the rear wall 36 and an intermediate wall 38. The latter cooperates with the rear furnace wall 40 to provide an upright gas by-pass for superheat control. The intermediate wall includes an inclined section 44 and a vertical section 46 extending across the banks of tubes forming the superheater 34, as clearly indicated inthe drawing.

For controlling superheat the gasfiow through the by-pass 42 is regulated by dampers 48. These may be actuated by devices responsive-to variations in a plurality of factors such as superheat temperatures and steam flow. At full load a predetermined proportion of the gases from the furnace flows through the by-pass '42, and as the load. decreases, this proportion of gas is decreased to prevent substantial variations in the superheat temperature from an optimum value.

In the illustrative installation, it is to be appreciated that as the furnace gases travel through the furnace, and particularly through the lower part thereof, they aresubje'cted to the gas cooling effect of extensive fluid cooled surfaces provided by the furnace wall tubes. After passing to the right at-the bottom of the furnace, the gases pass over at least one of two tubular screens 50 and 52 provided, respectively, by inclined sections of the tubes which define the walls 38 and 40. Thereafter, some of the gases flow upwardly through the main gas pass 54 and are constantly subject to further cooling action in this flow.

It is to be particularly noted that the by-pass' 42 extends across the complete width of the installation, in order to prevent uneven heating.

In the illustrative installation the greatest quantity of gases is by-passed at a predetermined high rate of steam generation, when the gas temperature to the superheater and to the by-pass inlet is at a maximum. These conditions involve the maximum slagging tendency, and the illustrative installation, with its radiant by-pass, instead of a convection by-pass, is particularly advantageous because of its elimination of structures promoting accumulations of the slag.

The amount of by-passed gasesis decreased to control superheat as the load decreases and the control of the b'y-passing may be automatically effected by known control systems by which the dampers 48 may be regulated in. response to variations in steam temperature which may be also modified by variation in other variables such steam flow and air flow.

The superheater tubes have their inlets connectedto a header 64 which, in turn, is in com munication with the steam space of the drum IB by a row of tubes 58. The outlets in the superheater tubes are connected to a header 62 from which the steam may pass through appropriate connections to a point of use.

The construction of the economizer is somewhat similar to the superheater. The economizer tubes are arranged to form two successive banks of return bend tubes 34 connected in series and receiving water from the economizer inlet header 6!]. The outlet ends of the economizer tubes are connected with the header 56 which, in turn is in communication with the Water space of the drum l8 through the tubes 56.

While in accordance with the provisions of the statutes I have illustrated and described herein the best form of my invention nowknown to me, those skilled in the art will understand that changes may be made in the form of the apparatus disclosed without departing from the spirit of the invention covered by my claims, and that certain features of my invention may sometimes be used to advantage without a corresponding use of other features.

I claim; v 1. In a vapor generating and superheating installation, upright vapor generating wall tubes defining the boundary surfaces of a combustion chamber with a gas outlet at its lower part, fuel burning means associated with the upper part of the combustion chamber, wall means including some of said vapor generating tubes defining a main upright gas pass and an upright gas bypass leading in parallel upwardly from the furnace gas outlet to the upper part of the installation, one of the walls formed by said wall means being common to the combustion chamber and the by-pass, the by-pass being disposed intermediate the main upright gas pass and the combustion chamber, some of the tubes of said wall means having parts extending in two groups arranged as tubular screens across which gas flows upwardly to the main gas pass, the gases to the by-pass passing over but one of the screens, said screens extending at an upward inclination from a wall of the combustion chamber to the walls of the by-pass, a convection section including a superheater having a bank of tubes extending across the upward flow of furnace gases in the main gas pass, and damper means at the upper part of one of said passes for proportioning the gas flow between the by-' pass and the main upright gas pass.

2. In a vapor generating and superheating installation, upright vapor generating wall tubes defining the boundary surfaces of a combustion chamber with a gas outlet at its lower part, fuel burning means associated with the upper part of the combustion chamber, wall means including some of said vapor generating tubes defining Walls, a main upright gas pass and an upright gas by-pass leading in parallel upwardly from the furnace gas outlet to the upper part of the installation, a major part of the by-pass walls receiving heat radiantly transmitted from the body of the gases traversing the by-pass, one of the walls formed by said wall means being common to the combustion chamber and the bypass, the by-pass being disposed intermediate the main upright gas pass and the combustion chamber, some of the tubes of said wall means having parts extending in two groups arranged as tubular screens across which gas flows upwardly to the main gas pass, the gases to the by-pass passing over but one of the screens, said screens extending at an upward inclination from a wall of the combustion chamber to the walls of the by-pass, a convection section including a superheater having a bank of tubes extending across the upward flow of furnace gases in the main gas pass, the by-pass and the main gas pass being co-extensive across the width of the installation, and damper means at the upper partof one of said passes for proportioning the gas.

flow between the by-pass and the main upright gas pass.

CHARLES H. WOOLLEY.

REFERENCES CITED The following references are of record in the V file of this patent:

UNITED STATES PATENTS

Images