US3318374A - Protectors for heating surfaces of boiler tubes - Google Patents

Description

PROTECTORS FOR HEATING SURFACES OF BOILER TUBES Filed Sept. 17, 1965 F. BLOCK May 9, 1967 5 Sheets-Sheet l Qw Nvm mm 3 NM N GI INVENTOR Frank BLOCK mufiy y ATTORNEYS F. BLOCK 3,318,374

PROTECTORS FOR HEATING SURFACES OF BOILER TUBES May 9, 1967 s Sheets-Sheet 2,

Filed Sept. 17, 1965 INVENTOR Frank BLOCK y 9, 1967 F. BLOCK 3,318,374

PROTECTORS FOR HEATING SURFACES 0F BOILER TUBES Filed Sept. 17, 1965 5 Sheets-Sheet (5 F- F G I5 124 60 INVENTOR Frank BLOCK ATTORNEYS United States Patent 3,318,374 PROTECTORS FOR HEATING SURFACES 0F BOILER TUBES Frank Block, Montreal, Quebec, Canada, assignor to Dominion Bridge Company Limited, Montreal, Quebec,

Canada Filed Sept. 17, 1965, Ser. No. 488,126 8 Claims. (Cl. 165134) This invention relates generally to boilers used for the generation of saturated or superheated steam, or for the general heating of water or any thermal liquid, such boilers being heated by hot waste gases from industrial or chemical processes.

Hot waste gases of this type generally contain varying proportions of abrasive dust, according to the industrial or chemical process from which the gases were produced, and these abrasive gases have highly erosive effects up on the heating surfaces of the boiler tubes over which they pass at varying velocities.

The boiler heating surfaces generally comprise panels of tubes which are bare and in tangent or spaced relation, or the tubes may be finned, or joined together by welding or by membrane arrangements. In order to prevent the abrasive gas stream passing over any parts of the tubes in cross-flow, and thus subjecting the tubes to direct abrasive action, it is conventional to locate the tube bends at the end portions of the panels and to use shielding to cover and protect the tube end surfaces. The shielding devices usually comprise metal plates, but can also comprise metal castings, ceramics, etc., which are wrapped around the tube ends and over which the abrasive gases flow.

However, where the dust-laden gas strikes the leading edge of a shield plate, or other protective device, turbulence is created which rapidly erodes the tubes at this point. It is thus necessary to decrease the velocity of the gas flow in order to decrease such turbulent effects.

It is, therefore, the main object of this invention to provide improved boiler tube protector means for producing gas flow over the leading edges of boiler tube shield plates having negligible turbulence and thus resulting in negligible tube erosion at these points.

This object is achieved by providing tube protectors which are adapted to completely surround the tubes at positions adjacent the leading edge portions of the shield plates and which provide fairing means for improving the gas flow and reducing gas turbulence at these points to negligible amounts.

Numerou tests have shown that if a gas containing an appreciable amount of solid abrasive particles in suspension strikes a solid surface at an angle of impact exceeding the abrasive gas turbulence created by the impact results in erosion of the solid surface. As the velocity of the dust laden gas increases, so the surface erosion increases at a high power of the increase in gas velocity. Increase in the angle of gas impact also increases thp turbulence, and thus the amount of erosion, the maximum erosion occurring with an impact angle of 90, and negligible erosion occurring, even at relatively high gas velocities, when the angle of gas impact is between 0l0.

In the basic form of this invention the tube protectors comprise individual units surrounding each tube adjacent the shield plate leading edges. Each unit comprises a substantially conical thimble extending, in a direction against the direction of gas flow, from a rectangular base adjacent the shield plates, to a narrow or sharp edge annular lip surrounding the tube at a point remote from the shield plates. Thus each protector thimble presents a fairing in the gas flow for reduction of turbulence normally caused by gas flowing over the abrupt edges of the shield plates, and the angle of the conical fairing surface,

relative to the axis of the tube, is arranged to be 10 or less for negligible gas turbulence effects. The protector thimbles may be constructed from ferrous or non-ferrous metals, ceramics, or other suitable materials.

Thus, another object of this invention is to provide boiler tube protector means which will permit the use of higher gas flow velocities over the boiler tubes to obtain more efficient use of the heating surfaces, without incurring rapid erosion of the boiler tubes.

Another object is to provide boiler tube protectors which increase the effective life of the boiler tubes by reducing gas turbulence to negligible amounts and thus reducing tube erosion due to abrasive gas turbulence.

A further object is to provide improved boiler tube protectors which embody the additional function of providing a secure fastening of the shield plate edges without interfering with the thermal expansion of the shield plates.

These and other objects and advantages of this invention will be further apparent by referring to the following detailed specification and figures, in which:

FIGURE 1 is a schematic section through a typical boiler, embodying tube protectors in accordance with this invention.

FIGURE 2 is a section on 22 in FIGURE 1.

FIGURE 3 is a section on 3-3 in FIGURE 1.

FIGURE 4 is a typical section through boiler tube shield plates and tube ends, and illustrating typical tube erosion caused by abrasive dust laden gas turbulence.

FIGURE 5 is a perspective view of a protector thimbio for application to a bare boiler tube of circular cross-section.

FIGURE 6 is a perspective view of a protector thimble for application to a bare boiler tube of rectangular cross-section.

FIGURE 7 is a side view of a protector thimble applied to bare boiler tubes of circular cross-section and having membrane connections.

FIGURE 8 is a section on 88 in FIGURE 7.

FIGURE 9 is section on 9-9 in FIGURE 7.

FIGURE 10 is a side view of a protector thimble applied to bare boiler tubes of circular cross-section and in tangent relation.

FIGURE 11 is a section on 11-11 in FIGURE 10 FIGURE 12 is a section on 12--12 in FIGURE 10.

FIGURE 13 is a side view of a protector thimble and tube, similar to FIGURE 5, but showing the thimble adapted to provide a secure fastening of the shield plate edges, whilst permitting free thermal expansion of the shield plates.

FIGURE 14 is a section on 14-44 in FIGURE 13.

FIGURE 15 is a section on 1515 in FIGURE 13.

Referring now to the figures, and particularly to FIG- URES l3, a typical boiler is schematically illustrated at 20. Boiler 20 comprises a casing 22 and includes a gas inlet 24 and a gas outlet 26 for the flow of hot gases therethrough. Casing 22 is divided into two vertical flow compartments 28 and 30 by dividing wall 32, such that gas will flow through inlet 24 downwardly through flow compartment 28 and upwardly through flow compartment 30, to discharge through outlet 26.

A plurality of boiler tube panels 34- are arranged within boiler casing 22 and provide a plurality of flow passages 36 in the path of the gas flow. In the specific boiler arrangement illustrated in FIGURES 1-3 each panel 34 comprises four boiler tubes 38 which start at the lower end of one side of the panel, follow upwardly and downwardly extending continuous paths axially aligned with the direction of gas flow, and finish at the lower end of the other side of the panel. The ends of the tubes are connected by bend portions 40. Boiler tubes 38 may be of circular or substantially rectangular cross-section and made of ferrous or non-ferrous metal. Each boiler tube 38 contains a thermal liquid, such as water, which is heated by heat transfer from the hot gases flowing over the boiler tubes.

Conventional shield plates 42, of metallic or ceramic material, are arranged to cover the surfaces of bend portions 40 in direct path of the gas flow, to protect these portions from the abrasive effects of the dust laden gases. Shield plates 42 extend on each side of bend portions 40 and provide additional support for boiler tubes 38. Other conventional shielding devices may be substituted for V shield plates 42 as required.

In these schematic figures protector thimbles are illustrated at 44 and comprise, in the basic form, individual units surrounding each tube 38 and positioned adjacent the leading edge portions of shield plates 42 at the out let ends of How passages 36. Protector thimbles 44 are substantially conical in shape and thus serve to promote smooth flow of gas over the abrupt surface transition from tubes to shield plates. vFIGURE 4 shows turbulence 46 in the gas flow caused by the abrupt transition from tube 38 to shield plates 42 in conventional boiler arrangements, and illustrates, at 48,- the tube erosion caused by such turbulence.

It should be noted that the particular boiler arrangeent shown in FIGURES 1-3 is for purposes of illustration only. The basic concept of this invention, the application of protector thimble means to surround tubesat points of abrupt surface transition to promote smooth flow of gas thereover, can be applied to any installation of tube arrangements which are characterized by such erosion problems.

Boiler arrangements may range from a single boiler tube arranged in a plurality of axially aligned passes, with bend portions at-the ends, to form a single tube panel positioned within a single gas flow compartment; to boiler arrangements having a plurality of consecutive flow compartments in which a plurality of tube panels form flow passages and in which each tube panel comprises a plurality of boiler tubes which may start and end at various positions on the panel, as dictated by designconsiderations. Gas may also be arranged to flow horizontally, upwardly, or downwardly through the boilers, or combinatrons of such flows, with the tube panels and flow passages arranged accordingly.

FIGURE 5 shows a perspective view of the basic concept of this invention in which a protector thimble 44 surrounds a bare circular boiler tube 38 and is positioned adjacent shield plates 42. Thimble 44 is substantially conical and extends from a narrow or sharp edge annular I lip surrounding the tube, to a rectangular base 52, dimensionedto be flush with the outside dimension over the leading edges of shield plates 42. The angle of the conical surface is 10 or less to the axis of tube 38, and

' is between 5 and 6 in the preferred execution. Thimble tector thimbles 44B applied to flow tubes 38 arranged in spaced relation and being connected by membranes 54 welded therebetween. In this arrangement protector thimbles 44B are constructed in two halves and attached to tubes 38 from each side of membranes 54. One method for attaching the thimbles to the tubes, is by welding or brazing through holes 56 to form secure spot connections.

' Again the conical surface angles are 10 or less to the 4 tube axes, the preferred angles being 56. thimbles 44B are shown in chain dot lines.

FIGURES 1012 show a side view and sections of protector thimbles 44C applied to boiler tubes 38 arranged in tangent abutting relation. In this arrangement protector thimbles 44C are constructed in two halves and attached to each side of tubes 38 by welding or brazing through holes 56, or other suitable means of attachment. The rectangular base of each thimble 44C is dimensioned to extend, in the direction of the shield plates, from tangent to tangent of the tube. Again the conical surface angles are 10 or less to the tube axes, the preferred angles being 5-6.

FIGURES 13-15 show a side view and sections of a protector thimble and tube, similar to the arrangement in FIGURE 5, but adapted to provide a secure fastening of the shield plate edges whilst permitting free thermal expansion of the shield plates. This is accomplished by providing inwardly and upwardly extending chamfers 58 on the leading edges of shield plates 42A, together with corresponding V-grooves 60 along the edge portions of the undersides of thimbles 44D. Thus thimbles 44D positively and securely locate the edges of shield plates 42A in a dovetail arrangement, preventing the outward movement of the edges of the shield plates 42A whilst permitting downward or sideways movement of the shield plates relative to the thimbles, due to thermal expansion. Chamfers 5S and V-grooves 60 may also be embodied in all the aforegoing thimble and tube executions.

If the thimbles are to be exposed to high temperatures it is necessary that they are arranged to be a tight fit on the tubes, or they may be brazed to the tubes by a heat carrying medium.

Although the illustrated thimble embodiments incorporate conical surfaces of 10 or less to the axes of the tubes, it will be understood that equally effective results may be obtained by using concave tapering surfaces of equivalent angular relationships, or combinations of conical and concave surfaces.

What I claim is:

1. Ina boiler for the generation of steam or like installation wherein hot abrasive gases flow over boiler tubes positioned axially in the path of said gas flow and wherein shield means are positioned on each side of said tubes transverse to the direction of said gas flow and provide abrupt surface transitions to theflow of said gas thereover, tube protector means adapted to substantially sur- Adjacent round said tubes and positioned adjacent said shield plates,

said protector means comprising substantially conical thimbles extending in the direction of gas flow from an annular lipsubstantially surrounding each of said tubes to a substantially rectangular base adjacent the shield means, the conical surface angle of said thimbles lying within the range 010 to the axes of said tubes and providing for the smooth flow of said gas over said abrupt surface transitions.

2. In a boiler as set forth in claim 1 in which said tubes are arranged in spaced relation and aligned in panels, and in which said protector means comprise individual thimble units surrounding each of said tubes, the

substantially rectangular bases of said thimbles extending to abut the substantially rectangular bases of adjacent thimbles.

3. In a boiler as set forth in claim 1 in which said tubes are arranged in abutting relation and aligned in panels, and in which said protector means comprise individual thimble units adapted to surround each of said tubes, the substantially rectangular bases of said thimbles extending to abut the substantially rectangular bases of adjacent thimbles, each of said thimble units being composed of two half units and positioned on each side of said tubes and securely attached thereto to form whole units.

4. In a boiler as set forth in claim 1 in which said tubes are arranged in spaced relation and aligned in panels, the tubes in each panel being connected by membranes extending between the tubes on the axes thereof, and in which said protector thimble means comprise individual thimble units adapted to substantially surround each of said tubes, the substantially rectangular bases of said thimbles extending to abut the substantially rectangular bases of adjacent thimbles, each of said thimble units being composed of two half units and positioned on each side of the membranes and securely attached to said tubes to form whole units.

5. In a boiler as set forth in claim 1 in which said tubes are aligned in panels and in which said shield means comprise plates positioned on each side of said tubes, the edges of said shield plates adjacent said thimbles being located in grooves in the adjacent surfaces of said thimbles to restrain said edges from outward movement.

6. In a boiler as set forth in claim 5 in which said edges of said shield plates are chamfered and securely located in V-grooves in the adjacent surfaces of said thimbles.

7. In a boiler for the generation of steam or like installation including a boiler casing having an inlet and an outlet for the flow of hot abrasive dust laden gases therethrough, a plurality of boiler tubes positioned within said casing and aligned axially in the path of said gas flow to provide gas flow passage means, said tubes having connecting bend portions at the ends thereof, and shield plate means adapted to cover the surfaces of said bend portions in said gas flow and providing abrupt surface transitions to the flow of said gas thereover, tube protector means adapted to surround said tubes and positioned adjacent said shield plate means at the outlets of said flow passage means, said protector means comprising substantially conical thimbles positioned on each tube and extending in the direction of gas flow from an annular lip surrounding each tube to a substantially rectangular base adjacent the leading edge portions of said shield plate means, the substantially rectangular bases of said thimbles extending to abut the substantially rectangular bases of adjacent thimbles, the conical surface angle of said thimbles lying within the range 5 6 to the axes of said tubes and providing for smooth flow of gas over said abrupt surface transitions.

8. In a boiler as set forth in claim 7 in which said tubes are aligned in a plurality of panels and in which said shield plate means comprise plates positioned on each side of said panels, the edges of said shield plates adjacent said thimbles being chamfered and securely located in V- grooves in the adjacent surfaces of said thimbles to restrain said edges from outward movement.

References Cited by the Examiner UNITED STATES PATENTS 2,850,267 9/1958 Guthrie 122--476 X 2,902,264 9/1959 Schick et a1 -434 3,190,352 6/1965 Simpelaar 165134 FOREIGN PATENTS 469,213 12/1928 Germany. 853,080 10/1952 Germany.

ROBERT A. OLEARY, Primary Examiner.

MANUEL A. ANTONAKAS, Examiner.

Claims (1)

1. IN A BOILER FOR THE GENERATION OF STEAM OR LIKE INSTALLATION WHEREIN HOT ABRASIVE GASES FLOW OVER BOILER TUBES POSITIONED AXIALLY IN THE PATH OF SAID GAS FLOW AND WHEREIN SHIELD MEANS ARE POSITIONED ON EACH SIDE OF SAID TUBES TRANSVERSE TO THE DIRECTION OF SAID GAS FLOW AND PROVIDE ABRUPT SURFACE TRANSITIONS TO THE FLOW OF SAID GAS THEREOVER, TUBE PROTECTOR MEANS ADAPTED TO SUBSTANTIALLY SURROUND SAID TUBES AND POSITIONED ADJACENT SAID SHIELD PLATES, SAID PROTECTOR MEANS COMPRISING SUBSTANTIALLY CONICAL THIMBLES EXTENDING IN THE DIRECTION OF GAS FLOW FROM AN ANNULAR LIP SUBSTANTIALLY SURROUNDING EACH OF SAID TUBES TO A SUBSTANTIALLY RECTANGULAR BASE ADJACENT THE SHIELD MEANS, THE CONICAL SURFACE ANGLE OF SAID THIMBLES LYING WITHIN THE RANGE 0*-10* TO THE AXES OF SAID TUBES AND PROVIDING FOR THE SMOOTH FLOW OF SAID GAS OVER SAID ABRUPT SURFACE TRANSITIONS.

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