US3048152A - Rotatable steam coil air heater - Google Patents

Description

1962 G. HELLWIG 3,048,152

ROTATABLE STEAM COIL AIR HEATER Filed Jari. 9, 1959 FIG.1 FIG.2

I J I l l I I r INVENTOR.

Gijnfer Hellwig BY ATTORNEY United rates This invention relates to a heat exchanger and more specifically to a steam-air preheater disposed in a cold air inlet of an air heater adapted to supply preheated combustion air to a steamgenerator.

It is well known that in tubular air heaters and the like, relatively warm entering air is requried, particularly when wet or high hydrogen content fuels are used to produce the heating gases, in order to avoid condensation. This is because the utilization of relatively cold air produces a reduction below the dew point temperature on the flue gas side of the heat exchange surfaces which results in the condensation of the moisture in the heating gases. Such condensation produces deleterious effects on the air heater such as accelerated wear, pluggage of the channels and corrosion. These conditions are especially aggravated when a steam generator or boiler is operating at low loads, at which time it has a low gas exit temperature.

Heretofore, in order to overcome these difiiculties it was customary to install steam-air preheaters in the cold air inlet to initially preheat the cold air to a point where condensation would not occuigthus avoiding the deleterious effects of corrosion, wear, etc. Since the steam-air heaters are generally installed for approximately 50% of the combustion air quantity at their maximum load, the air flowing in heat exchange relationship therewith will encounter only minor resistance. However, when the steam generator is operated at full load and while it may be possible to shut off the preheater on the steam side, the resistance to air flow resulting from such installation increases quadratically, thus producing such an excessive flow loss on the air side that the blowers forcing the air through the air heater must be operated under overload conditions or must be over-designed.

In order to overcome this problem of the preheater resistance to air flow at full loads, it has been customary to provide the air heater with a by-pass on the cold air inlet side, in which the preheater was positioned. Thus, at low load, the cold air would enter the air heater through the by-pass and the air initially heated as it flowed over the preheater. At full loads when the preheater was not necessarily required the air flow was by-passed around the preheater, thus eliminating the flow loss due to the resistance occasioned thereby. However, such a by-pass arrangement is relatively expensive and complicated because additional duct work and damper controls are required.

Thus, an object of this invention is to overcome the foregoing difliculties by arranging a steam-air preheater in a cold air inlet of an air heater and the like so that at full load operations of the air heater the resistance to air flow occasioned by the preheater is reduced to a minimum, without resorting to a by-pass arrangement.

According to this invention, a steam-air preheater is arranged so as to have a broad face and narrow edge and is installed in the cold air inlet of an air heater or the like in a manner so as to permit rotation of the same. Thus, in one position thereof, i.e. at low loads, the air heater has its broad face presented to or normal to the flow of air through the inlet. Upon attaining boiler half load the preheater may be cut oif on the steam side and rotated 90 to present its narrow edge to the flow of air. As a result, resistance to air flow at more than half boiler atent Patented Aug. 7, 1932 I "a rloads is greatly reduced. If desirm the leading narrow edge portion of the preheater may be provided with means for streamlining the air flow to further reduce the resistance to air flow thereover. In the event the boiler load is exposed to excessive swings, the operation of the preheater can be automatically performed with the controlling impulses being taken from the air temperature at the cold end of the air preheater or from a dew point measuring instrument.

A feature of this invention resides in the provision that it is relatively simple in construction, inexpensive to install and positive in operation.

Other features and advantages will be apparent when considered in view of the drawings and description in which:

FIG. 1 is a sectional side view of a cold air inlet of an air heater illustrating the preheater in accordance with this invention in operative position during low load operation: of a boiler.

FIG. 2. is a sectional side vieW of a cold air inlet similar to that of FIG. 1, but illustrating the preheater rotated out of operative position.

FIG. 3 is a schematic plan view of the preheater in which the solid lines illustrate the operative position thereof and the broken line illustrates the inoperative position thereof.

Referring to the drawings, there is shown a duct 10 defining a cold air inlet to a tubular air heater or the like, not shown, in which the direction of air flow therethrough is indicated by arrow A. Wholly disposed within the inlet is a'steam-air preheater 11 which is arranged to initially heat the air to a temperature which will prevent condensation of the moisture in the heating gases flowing through the air heater at low loads when the air and gases are brought into heat exchange relationship.

According to this invention the steam-air preheater comprises essentially an elongated steam inlet header 1'2 and a corresponding elongated steam condensate outlet header 13, each header having a length which extends across a major portion of the width of the inlet duct 10. Connecting the headers 12 and 13 into fluid circulation is a row of space tubes 14, two such rows being illustrated. Accordingly, the tubes in each of the rows have their longitudinal axes lying in a common plane. Thus it will be noted that with the tubes 14 spaced longitudinally along headers 12 and 13, the arrangement is such that the plane, containing the longitudinal axes of the tubes in a row, presents a broad face, while the ends of the tube rows present a relatively narrow edge to the air flow in operation and inoperative positions, respectively.

According to this invention the preheater 11 is disposed in the inlet duct 10 so as to rotate about a pivot 11A, as diagrammatically illustrated in FIG. 3, as shown. The inlet header 12 intermediate the ends thereof is provided with an entrance nozzle 15 which is rotatably supported in bearing 16. Likewise the outlet header 13 is provided with a condensate discharge nozzle 17 which is rotatably supported in bearing 18. As shown the upper bearing 16 is designed to withstand the internal excess pressure, while the lower bearing 18 is further designed to support the Weight of the preheater 11. In order to provide fluid circulation through the preheater, a flexible conduit 19 connecting with a suitable steam source, not shown, delivers the heating steam to the entrance nozzle 15 of inlet header 12. As the steam flows in heat exchange relationship with the air flowing thereover, when the preheater is operating, the steam is condensed and the condensate is discharged from header 13 through a flexible conduit 21. In addition, the flexible conduits facilitate rotation of the preheater through 90. Thus the preheater is free to pivot about the axis of nozzles 15 and 17.

On starting up or during low load operation when it is desirable to warm. the intake air prior to flowing it I through the air heater, to prevent condensation of'the moisture in the heating gases,-the preheater is rendered operative and is rotated to a position illustrated in FIG. 1. In this position the broad face or plane containing the longitudinal axes of the tubes in row 14 is presented normally to the flow of air passing in heat exchange relationship therewith. Since the quantity and velocity of air flowing through the inlet is relatively low, the resistance to flow occasioned by the interposition of the broad face of the preheater to the air flow is relatively small. If desired the resistance can be further reduced by providing means, such as bafiles, deflectors or the like 20, forming an air foil to the leading edges of the tubes to further streamline the flow of air thereover, Thus, increased efficiency of the over all boiler cycle can be attained due to the reduction in the required tfan'horsepower needed to push the air through the air heater.-

At high loads and with higher gas temperature the problem of condensation is greatly. reduced, if notjeliminated, thus the preheater may be shut down on the steam side. However, as the resistance to air flow increases quadratically as. load increases, the preheater is rotated 90, as shown inFIG. 2, so that the plane common to-the tubes in row is, disposed parallel to the flow of air. Thus, only the narrow edge of the preheater 11 is exposedto offer resistance to air flow.

may be further reduced by providing means in the form of an air foil 20A to streamline the flow of air thereround. t l

While the rotation of the preheater maybe performed manually as the boiler load varies, it may be automatiically operated by suitable control means, notshown,

1. In an air heaterhaving means defining, a relatively cold air inlet, 'a preheater having. 'a broad face with openings therethrough and narrow edge disposed in said inlet forpreheating said. incomingcold to a predetermined temperature so as to avoid condensation of any moisture in the heating gases flowing through said air heater in indirect heat exchange relationto said air,

If desired, the resistance which the edge of. the, preheater presents to the air flow I a preheater has its narrow edge portion presented to the flow. of air through saidinlet, means for circulating a heating fluid through said preheater in heat transfer relationship to the flowing through said inlet, and streamlining means connected to the narrowedge of said preheater for decreasing theresistance to air flow thereover whenin theinope'rative position; r

2. Air heating apparatus comprising an air heater havsaid duct over said tubes and through said intertube spaces in indirect heat transfer relation with the heating medium passing through said tubes, and means for'mountingsaid tubes'for rotation about an axis in an arcuate path. from a position where the broad faces of the air heater and the imaginary plane including the tubes lie normal to the flow of air through said duct to a position Where said broad faces and planelie parallel to the flow ofair through said duct, while-inhibiting movement plurality of channels for the flowof a heating medium means for rotating said preheater in said inlet, about. an 1 axis of revolution which prevents movement ,of said preheater in a direction transversely of said axis so that in operative position said preheater has its broad face presented transversely to the fiow of relatively cool air entering said inlet whereby said air flows through the openings in said face and in inoperative position said and air with metallicwalls therebetween through which heat is transferred from theheating medium to the air and with the air fiovv channels extending between the broad iace'sof the air heater, air duct means containing said channels and constructed andarrangedto distrib -nte. thensupply' of air to beheated uniformly over the cross-sectional area of the duct and to direct the air substantially parallel tothe axis of the duct through said airflow channels in'indirect heat transferrelation with the heating medium, and means for rotatably'mounting said air heater. about :an axis in an arcuate path from a position where the broad/faces of the air heater lie nor-; mal to the flow of airthrough said duct to a position where said broad faces lie parallel to the flow of air through said duct, while inhibiting movement of said air heater in directions parallel to said axis. of rotation.

ReferencesCited in the fiieof patent V UNITED, STATES PATENTS 583,944 Germany a Sept.

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