US2821366A - Heating surface condition indicator - Google Patents

Description

Jan. 28, 1958 P. H. KARLSSON HEATING SURFACE CONDITION INDICATOR Filed April 8, 1954 2 Sheets-Sheet 1 0555/? VA T/ON PORT W A A r/ 5 IN V EN TOR.

ATTORNEY Jan. 28, 1958 P. H. KARLSSON HEATING SURFACE CONDITION INDICATOR 2 Sheets-Sheet 2 Filed April 8, 1954 OBSERVA T O INVEN TOR. erflz/m er fir/rron ATTORNEY HEATING SURFACE CONDITION INDICATOR Per Hilmer Karlsson, Wellsville, N. Y., assignor to The Air Preheater Corporation, New York, N. Y., a corporation of New York Application April 8, 1954, Serial No. 421,741

4 Claims. (Cl. 257-6) The present invention relates to heat exchange apparatus and particularly to a novel means for obtaining a visual indication of heat transfer element corrosion and of deposits collecting upon the heat exchange elements of a heat exchanger while the heat exchanger remains in continuous operation.

In the operation of heat exchangers of either the re- United States Patent i generative or recuperative types, difficulties are frequently encountered because of clogging of the flow passageways with dust or ash deposits and corrosion of the heat exchanger elements to a point such that the operating efiiciency of the heat exchanger is impaired. These difliculties most frequently arise when temperature consary to arrange periodic shut-downs of the heat exchange system to enable an operator to partially dismantle and inspect the units in question. Obviously, this is an inefiicient and often expensive method of determining the physical condition of the heat exchange elements, and it is apparent that a system affording continuous indication of conditions within an operating air preheater would be highly desirable.

It is therefore a primary object of this invention to provide an indicator system which permits continuous observation of conditions within an operating heat exchanger.

, By being able to operate the surface condition indicator of this invention under conditions similar to those encountered in the primary heat exchanger, it is possible to observe conditions comparable to those within the primary heat exchanger and prevent such conditions as would bring about clogging of the passages or corrosion of the heat exchanger elements. As long as there are relatively limited deposits on the heat exchange plates, and these deposits are maintained in a dry state, they may be readily removed by conventional methods of cleaning, such as by blowing with steam or air. When however, these deposits become dampened by condens ing vapors, an operator upon observing the surface condition indicator is forewarned that a critical point has been reached and that the temperature level within the primary heat exchanger must be raised to prevent difficulties associated with clogged passageways and corroded heat exchange elements.

In practice the surface condition indicator of the invention comprises a miniature heat exchanger arranged to receive hot exhaust gases from the exit duct of a primary heat exchanger and also a quantity of cooler air to be heated from the inlet duct of the same primary Patented Jan. 28, 1958 'ice heat exchanger. Due to slight transmission losses in the gas and air ducts respectively, the entrance temperature of the gas and air at the miniature heat exchanger will be somewhat lower than the temperature of these fluids at the primary heat exchanger. Relative air and gas temperatures within the miniature preheater which comprises the heating surface condition indicator of this invention, may be varied by regulating the amount of exhaust gas that is drawn from the primary heat exchanger exhaust duct. After gas flow to the heating surface condition indicator has been regulated, conditions therein will be similar to conditions within the primary heat exchanger and any increase or decrease in the gas outlet temperature at the primary heat exchanger will be duplicated at the heating surface condition indicator. If therefore, the gas temperature therein is lowered below the critical dew point, moisture from the gas condenses on the heat exchanger surfaces and is absorbed by the fly ash and deposits clinging to said surfaces to form a highly corrosive coating which cannot be easily removed by conventional cleaning methods. Since conditions within the surface condition indicator are visible through an observation port, it is possible to ascertain at any moment the conditions therein and the corresponding conditions within the primary heat exchanger.

The invention may be best understood upon consideration of the following detailed description of illustrative embodiments thereof, when read in conjunction with the accompanying drawings in which:

Figure 1 is a schematic drawing showing the elements comprising a suggested plant layout including a surface condition indicator in conjunction with a rotary regenerative air preheater.

Figure 2 is a side elevation, partially in section, of the heating surface condition indicator this being a regenerative type of heat exchanger.

Figure 3 is an end elevation, partly in section of the regenerative type heating surface condition indicator.

Figure 4 is a modification showing a recuperative type heating surface condition indicator to be used in conjunction with a recuperative type primary heat exchanger.

The arrangement shown in Figure 1 essentially comprises a primary air preheater 20 having a gas inlet port connected to the flue gas outlet 22 of a boiler 24. Air for combustion in the boiler is supplied by the forced draft fan 26 to the air side of the preheater where it absorbs heat from the gas passing therethrough before it passes on through duct 27 to the boiler.

Before the combustion air reaches the preheater 20, a small portion thereof is taken through a duct 30 to the air side of the heating surface condition indicator 34 where it is placed in heat transfer relationship with a portion of the gas from the gas outlet side of preheater 20. The hot gas from the preheater 20 is drawn to the indicator 34 by an ejector 37 utilizing steam or pressurized air from any convenient source not here shown. Hot gas enters the duct 32 and after traversing the indicator is returned to the main gas exhaust duct 35 through duct 33. As the hot gases and air for combustion meet in heat transfer relationship within the indicator 34 at substantially the same or lower temperatures than encountered in the primary heat exchanger, it is apparent that there will be a near duplication of condensation, corrosion and dust deposit conditions. Therefore, by making the effects of these conditions visible through observation win dows in the indicator housing, an indication of comparative conditions within the primary heat exchanger may be obtained.

Reference to Figure 2 of the drawing discloses more specific detailsof the surface condition indicator 34. The indicator comprises a rotor 38 mounted for rotation with a horizontal shaft 40 which is rotated by the motor 44 acting through the gear box 46 and coupling 48. The rotor 38 carries heat transfer plates like those in the primary heater 20. Bearings 50 support the shaft 40 for rotation about its axis. Surrounding the rotor is a housing 54 having openings at one end for a gas inlet 60 and an air outlet 66, and at the other end openings for a gas outlet 64 and an air inlet 62. In addition to the air and gas openings at each end of the housing, there are glass covered observation ports at 70 and ".72 which afford visual admittance inside the miniature preheater so a visual examination of the rotor 38 may be made to determine when unfavorable conditions arise. The opening 72 is directed into the cold end of the rotor where condensation of the cooled gases first occurs while the opening 70 affords access to the relatively warm end of the rotor, which remains comparatively free from deposits and corrosion.

Additional openings 73 are made in both the air and gas passages of the hot and cold ends of the miniature heat exchanger to receive thermometers or thermocouples to indicate the temperatures at these critical locations. When not used, individual openings may be closed by plugs 74 (Figure 3).

In operation exhaust gases from the boiler 24 are passed to the primary preheater 20 via duct 22 where they are cooled and flow on to the exhaust duct 35 before being exhausted to the atmosphere. Combustion air is taken from the atmosphere by forced draft fan 26 and supplied to the duct 25 leading to the preheater 20 and thence to the duct 27 leading to the air inlet of the boiler 24.

A portion of the exhaust gas leaving preheater 20 is taken from duct 35 through conduit 32 to the gas inlet side 60 of the miniature preheater 34 where it enters the preheater housing and is directed over the heat transfer elements in rotor 38 and thence through the outlet 64 to duct 33 which may lead back into duct 35. Simultaneously a quantity of combustion air from duct 25 is bled off through duct 30 to the air side 62 of the miniature preheater 34 where it is directed over the heating elements to absorb heat therefrom before it is discharged through outlet 66 and enters duct 36 from whence it is vented to the atmosphere.

The heat transfer elements of the heating surface condition indicator 34 are normally at a slightly lower temperature than the elements of the primary heat exchanger; consequently, any condensation within the system is likely to occur on the surfaces of indicator 34 before it occurs on the surfaces of the primary heat exchanger 20. Therefore, it is apparent that a regular inspection of the miniature heat exchanger surface as seen through observation ports 70 or 72 will give a comparative indication of the heat exchange surface Within the primary heat exchanger 20, and at the first indication of condensation or fouling conditions within the heating surface condition indicator, appropriate steps are taken to cause the gas outlet temperature to be increased and fouling conditions entirely obviated. This may be done, for example, by reducing the air flow to heater 20.

Figure 4 shows a modified form of heating surface indicator in which the miniature preheater comprises a recuperative heat exchanger 50 having an air inlet 82 connected to a main air duct 25A and an air outlet 86 vented to atmosphere. The gas inlet 92 draws hot exhaust gas from the main gas duct 35A and exhausts it back to the same duct 35A via outlet 94. As shown, observation windows 96 and 97 permit observation of the tubes 98 within the heat exchanger housing, although it is to be understood that plates or equivalent heat exchanger elements might be used without departing from the spirit of the invention.

What is claimed is:

l. A primary heat exchanger enclosed in a housing having supply and discharge ducts connected thereto for directing the flow of hot gas and cool air between which heat is exchanged over metallic heat transfer elements subject to the effects of corrosive constituents of the gases flowing thereover; the combination therewith of a secondary heat exchanger substantially smaller than said primary heat exchanger and including heat transfer elements as in said primary heat exchanger; a housing enclosing the heat transfer elements and positioned at a distance from said primary heat exchanger; a conduit from the gas discharge duct of said primary heat exchanger to a gas supply duct of said secondary heat exchanger; a conduit from the air supply duct of said primary heat exchanger to an air supply duct of said secondary heat exchanger; and observation ports formed in opposite ends of the secondary heat exchanger housing so arranged that the heat transfer elements within said secondary heat exchanger housing may be observed during periods the interconnected preheaters are in operation.

2. A primary heat exchanger having air and gas supply and discharge ducts connected to a housing for directing relatively hot and cold fluids between which heat is exchanged over heat transfer elements subject to the effects of corrosive constituents of the gases flowing thereover; the combination therewith of a secondary recuperative heat exchanger substantially smaller than said primary heat exchanger and including heat transfer elements as in said primary heat exchanger; a housing enclosing the heat transfer elements positioned at a distance from said primary heat exchanger; a conduit connecting the gas discharge duct of said primary heat exchanger and the gas supply duct of said secondary heat exchanger; a second conduit connecting the air supply duct of said primary heat exchanger and the air supply duct of said secondary heat exchanger; and an observation port formed in the housing of said secondary heat exchanger so arranged that the heat transfer elements may be continuously observed during periods of operation.

3. A first air preheater having a rotor including a cylindrical shell joined to a rotor post by radial partitions forming compartments that carry heat transfer material and a housing surrounding the rotor and provided opposite the ends of the latter with apertures for the supply and discharge of heating gases and air to and from the heat transfer material carried by the rotor; the combination therewith of a relatively secondary preheater substantially smaller than said first preheater and including a .rotor having a cylindrical shell joined to a rotor post by radial partitions forming compartments that carry heat transfer material, and a housing surrounding the rotor and provided opposite the ends of the latter with apertures for the supply and discharge of heating gases and air to and through the heat transfer material carried by the rotor; conduit means connecting the gas discharge aperture of said first preheater and the gas supply aperture of said secondary air preheater, and other conduit means connecting the air supply aperture of said first air preheater and the air supply opening of said secondary air preheater to a common source of air supply.

4. A preheater combination as defined in claim 3 wherein an observation port is arranged in the housing of said secondary preheater to permit observation of the heating elements therein during periods of operation.

References Cited in the file of this patent UNITED STATES PATENTS 1,603,026 Cook Oct. 12, 1926 1,736,304 Benjamin Nov. 19, 1929 FOREIGN PATENTS 688,656 Great Britain Mar. 11, 1953

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