US2640468A - Method of superheat control - Google Patents

Description

`June 2, 1953 w. H. ARMAcos-r METHOD OF SUPERHEAT CONTROL Filed Aug. 9. 1945 M/M BUR h. ARMA csr 4 INVENTOR.

BY ATT R//Er Patented June 2, 1953 2,640,468 METHOD OF SUPERHEAT CONTROL Wilbur H. Armaoost, Scarsdale, N. Y., assignor to Combustion Engineering- Superheater, Inc., a

corporation of Delaware Application August 9, 1945, Serial No. '609,956

2 Claims. 1

The present invention relates to superheaters and particularly to improved methods of controlling the iinal temperature of superheated steam in generators of high capacity.

The single figure in the drawingis a schematic view of a power plant including a steam generating boiler in which the temperature of superheated steam is controlled in accordance with the `present invention by effecting the major control through burner adjustment to eiect the major regulation by varying the temperature of the products of combustion passing over the superheater with the nal regulation being attained. through a desuperheating action.

The use of tiltable burners alone for the control of steam temperature has not been entirely satisfactory. The principle of the tiltable burner is to regulate the temperature of hot gases over the superheater surface, and thereby control the heat which is transferred from the gas to the steam so as to obtain the steamv temperature desired.

There is one Outstanding disadvantage in the use of tiltable burners which cannot be corrected by design, and that is the sluggishness in the response. quate response of the control equipment and the burner tilting mechanism, but is due rather to the inertia in -changing the temperature of the large mass of metal embodied in the superheater units I0. In the case of automatic control the It is not so much a question of ade- Ufor'desuperheating is not of good quality, asmall thermocouple l2 which is laffectednby the steam temperature leaving the header I4 calls for a change in the setting of the burners 34. On some installations, it takes less than a minute to change the angle of burner tilt, but a period of fifteen minutes or more is required to effect a change in steam temperature because the residual heat in the large mass of the superheater keeps raising the temperature above the desired point until a suiicient volume of steam has flowed through to carry ofl' the residual heat. A reduction in load may be followed by lowering the temperature of the gases through tilting the burners 34 but even the lower gas temperature tends to keep the steam temperature up and even cause it to rise due to the action of the residual heat of the superheater metal on a smaller steam volume. This phenomenon is inherent in the design of tiltable burner control of steam temperature, and is due to the large mass of the superheater Il). The mass of the superheater cannot be reduced and the present trend in design is to increase it. By the time burner tilting effects the desired change in steam temperature, the

superheater outlet 'of the desired temperature.

need for a change if due to load variations, etc.,

often has passed.

Tiltable burners do have the advantage of effecting relatively large changes in steam temperature at an economical cost. The invention therefore contemplates retaining the advantages 1 of a tilting burner type of steam temperature control and the use of additional controls to Offset the disadvantage of sluggishness to effect a major part of the regulation in steam temperature, and achieve the final regulation by other controls.

The quickest acting control is a spray desuperheater 20 located beyond the superheater outlet I4. range of control-Of about 15 degrees to 25 degrees F. at maximum load on the boiler. used for desuperheating would be drawn from the feed Water heater or feed water itself, if of sufficient purity. A valve 24 in the feed water line 22 is operable in response to the fluctuations in steam temperature at or near the turbine 26 as reflected bya thermostat 28. By proper manipulation the steam temperature at the turbine or engine can be maintained within 2 degrees F. By limiting the range of auxiliary desuperheater control to the nal l5 degrees to 25 degrees F. of regulation the percentage of Water used for this purpose is kept to a minimum.

For .installations in which the water available non-contact desuperheater may be used which would be lplaced in one of the boiler drums. It is possible to design such a desuperheater which can be installed assembled through a standardv manhole opening, and which will have maximum range of control of l5 degrees to 25 degrees FK. With such a design the heat removed from lthe superheated steam would be transmitted through the tubes of the desuperheater into the boiler water. The reaction in response to a change in steam temperature would be many times faster than the reaction obtained solely with tilting burner control in that a considerably less mass of metal would be affected. The response would not be quite as fast as in the case of the spray type of desuperheater.

The small non-contact type of desuperheater would be connected so as to withdraw part of the superheated steam from the outlet header I4. In this respect the connection can be made at the blank end of the outlet header, thereby requiring a slightly smaller outlet header. The part of steam withdrawn would be passed through the desuperheater and its temperature reduced to a Such a spray would be designed to give a The water point so that when returned and mixed with the main steam ow the resultant steam temperature will be that desired.

In boilers equipped with tilting burners regulation is effected by tilting the furnace burners vertically to vary the vertical position A, B, or D of the combustion zone with respect to water Walls or by adjusting burners'horizontally to change*l the size andlocation ofthe combustion zone by altering the size of a circle toward which the flames are directed tangentially and thus in' either case to vary the degree ofcocling oiv the:

gases by the furnace walls prior to reaching the superheater. Such controli arrangements are more fully disclosed in Kreisinger et al'.4 Patent' 2,363,785 issued November 28, 1944, and Kruger Patent 2,243,909, issued June 3,4 1941/, respectively; With such installations the major amount of control may be effected by adjustment of the burners 34 and the final 15 degrees-,to 25 degrees by passing. parti of the steam through: the desuper-v heater 3i?.

What I claim is:

l. The method of: maintaining superheat'ed' steam temperature in asteam'generator in-vvvlfii'ch` the major portion ofthey steam is produced' in` a vertical furnace'lined with steam generating elements exposed to radiant neatV from burning fuel andi Which generators have superheat'ersl of relatively large heat storage capacity, due to the metallic mass-thereof; suflicient to cafuse'- a substantial time l'ag'in the change of'steam4 temperature when the-volume and temperature of' heating' gases passing over the superheater decrease with the f-uel'? burningv rate upon a fall insteam demand, Which comprises: introducing fuel and' air into the furnace in'- such directions so as to create a turbulent gas mass in a zone remote from the furnace outlet; burning said fuel at a rate in accordance With steam demand and absorbing theradia-nt heat therefrom `in the steam generating elements to produce steam to be superheated; passing the steam so generated through the superheater to increase its temperature; controllably altering the angle` of` introduction of fuel and air' to the furnace to lower" the zone-of' combustion with respect to the steam generating elements that absorb radiant'heat so as to increase said absorption and reduce the temperature of gasesv passing over the superheaterto compensate for only the` major part offincreases'above a predetermined value ofisteam temperature leavingthe superheater; and simultaneously subjecting all orv part ofi the super'- heated: steam toa desuperheating action so as to promptly offset the overheating of all of' the steam, during said lag; due to said heat storage in the superheater metal to effect minor adjustments of steam temperature during'a change in load thereby maintaining a substantially constant nal steam temperature.

2. The method of maintaining final temperature of steam in a superheater receiving its heat mainly by convection from gases leaving a furnace provided with water cooled tubes in which the major portion of the steam isiproduced by radiantiabsorption of heat from fuel! burned in the furnace and which generators have superheaters of relatively large heat storage capacity suiiicient to cause a substantial time lag, due to the.metallicmass'thereof, in the change of steam temperature when the volume and temperature `of the heating gases'passing over said super- 151 heater changes with' increase or decrease of the fuel burningrate'upon change in steam demand, which comprisestintroducing fuel and air into the furnace in such directions as to create a turbulent' gas mass in av zone remote from the furnace outlet; burning said fuel at a rate in accordance.- with steam demand' and absorbing radianty hea-t1therefromy in the steam generatingelements to pro-duce steam to be superheated': passing steam so generatedv throughy the superheater. to' increase its temperature; controllabl'y altering the. angle of introductiony of fuel andair.' into the furnace *so as: to`r shift the Zone ofl combustion. toward or away from the furnaceI outlet so as to decreaseor increase, respectively;

the absorption of radiant heat in said steam generating elements and? thereby increaseJ and: reduce, respectively, the temperature ofheat'-4 ing gases passing' over thesuperheater and thus compensate for only the major part of variations from a predetermined value of the steam temperature leaving the superheater; and sub jecting all or part of the superheated steam to' a desuperheating action for promptly offsetting' the overheatingv of allofI the steam, during said lag. due to said heatstorage in the superheaterv metal so as to effect minor adjustments of steaml temperature occurring as a result of increasing and' decreasing the temperature of the gases passing over the superheater thereby maintaining a substantially constant' final steam tem-1 perature.

WILBUR I-I. ARMACOSTL References Citedin the file ofthis. patent UNITED" STATES PATENTS- Number Name Date 2,363,875 Kreisinger et al. Nov. 28,419.44

FOREIGN PATENTS Number Country Date 409275' Germany Feb. 3, 1925 43?;534 GermanyA Nov. 24,1926 482.901 Great Britain Apr. 7, 1938

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