US3838666A

US3838666A - Fluid heaters

Info

Publication number: US3838666A
Application number: US00319074A
Authority: US
Inventors: P Smith
Original assignee: Stone Platt Crawley Ltd
Current assignee: Stone Platt Crawley Ltd
Priority date: 1972-12-27
Filing date: 1972-12-27
Publication date: 1974-10-01
Anticipated expiration: 1991-10-01

Abstract

In a fluid heater of the kind having a coil box through which a fuel-air combustor is arranged to direct its combustion exhaust gases, the coil box has a hollow peripheral side-wall structure and the path for at least part of the air supply to the combustor is through said hollow peripheral wall structure.

Description

United States Patent Smith 1 Oct. 1, 1974 [54] FLUID HEATERS 2,223,856 12/1940 Price 122/250 2,291,872 8/1942 Brantly 122/D1G. 1 [75] Inventor- Peter Crawley, England 2,582,830 1 1952 Hawley 122/1310. 1 73 Assignee: stoneylafl Crawley Limited 3,351,041 11/1967 Watson et a1 122/250 Crawley Sussex, England 3,398,722 8/1968 Smykal, Jr. et al. 122/250 Filed: 1972 Primary ExaminerKenneth W. Sprague [21] Appl 319 074 Attorney, Agent, or Firm-Fred Philpitt 52 vs. C]. 122/250 R, 122/1310. 1 [57] S T [51] Int. Cl. F22b 27/08 In fluld heater of the kmd having a C91] box through 5 Field f Search 122 250 24 249 DIG 1 which a fuel-air combustor is arranged to direct its combustion exhaust gases, the coil box has a hollow 5 R f r Cited peripheral side-wall structure and the path for at least UNITED STATES PATENTS part of the air supply to the combustor is through said hollow peripheral wall structure. 2,160,644 5/1939 Clarkson 122/250 2,201,625 5 1940 La Mont 122 250 10 Claims, 11 Drawing Figures PATENTEDUBT H 4 3,838.666

mraor' PATENTEUHBT H 1 3338.666

SHEETSUF 6 FIGS? FLUID HEATERS This invention reltaes to fluid heaters. By the term fluid heater" as used in this specification it is intended to embrace boilers, in which a change of state from liquid to vapour takes place, and also heaters in which there is no change in fluid state, for example water heaters.

More particularly this invention is concerned with fluid heaters having a fuel-air combustor for example a gas-air or oi-air combustor to which air is supplied to support combustion and which emits combustion exhaust gases.

The primary object of the invention is to control and inter-relate the air and exhaust gas flows in a more advantageous manner than hitherto.

According to the invention, in a fluid heater comprising a fuel-air combustor, a coil box through which the combustor is arranged to direct its combustion exhaust gases, and coils within the coil box for carrying fluid to be heated and arranged so that they are in heat exchange relationship with the combustion exhaust gases, the coil box has a hollow peripheral side-wall structure and the path for at least part of the air supply to the combustor is through said hollow peripheral wall structure.

The invention will now be further explained with reference to the accompanying drawings, which show examples of fluid heater constructions in accordance with the invention and various modifications which may be made to the heater constructions without departing from the scope of the invention. In the drawings:

FIG. 1 shows a vertical section through one example of heater construction in accordance with the invention,

FIG. 2 shows a modified form of heater construction to that shown in FIG. 1,

FIG. 3 shows a section on the line III-III of FIG. 2,

FIG. 4 shows a perspective view of a form of stub pipe through which combustion gases flow from the coil box to the flue box in the FIG. 1 construction of heater,

FIG. 5 shows a developed view of the cross air-duct arrangement used in the FIG. 2 construction as an alternative to the stub pipe arrangement to the FIG. 1 construction,

FIGS. 6 and 7 show suitable forms of cross air-ducts for the FIG. 2 construction of heater,

FIG. 8 shows a modification of the upper part of the heater construction in FIG. 1,

FIG. 9 shows a flexible sealing arrangement used in the FIG. 1 construction of heater,

FIG. 10 shows an advantageous flue box shaping for the FIG. 1 heater construction, and

FIG. 11 shows an advantageous flue box shaping for the FIG. 2 heater construction.

Referring now more particularly to FIG. 1 of the drawings, the heater comprises a coil box 1 containing

coil packs

2 and 3 disposed one above the other about a vertical axis 4 and supported on a refractory base 5. Disposed above the coil box 1 is an oil-fired combustor 6 centred on axis 4 and having its lower end projecting into the coil box 1. Thus combustion gases are directed downwardly from the combustor 6 into the coil box 1, circulate in heat exchange relationship with the

coil packs

2 and 3 and then pass, in a manner to be described, into the flue box 7 and thence to the stack. A forced air feed to the combustor 6 via air box 8 is provided by fan 9.

The coil box 1 has an outer hollow cylindrical wall 10 formed by spaced inner and outer

cylindrical wall members

12 and 13 defining an annular air space 14 between them. The outer wall member 13 is advantageously made of light gauge steel or aluminum sheet and has a reflective inner surface to reduce heat loss by radiation. The air space 14 forms part of the path for at least part of the conbustion air from the fan 9 to the combustor 6 the fan 9 supplying air into the space 14 via a volute 73. The air passing up the air space 14 to the combustor 6 will pick up heat principally by convection and will be pre-heated prior to entry into the combustor 6 and so improve the thermal efficiency and combustion of the heater. At the same time it will maintain the outside surface of the coil box 1 at an acceptably low temperature so obviating the need for lagging. Also the air space 14 will reduce noise generated by the fan and will prevent gas leaks from the coil box 1 to atmosphere.

If desired secondary heating surfaces, such as tins of thin sheet metal can be provided on both surfaces of the inner wall member 12 to increase the heat transfer from the combustion gas in coil box 1 to the air in space 14. Further, secondary heating surfaces such as fins may be provided on the inner surface of the outer wall member 13 to reduce the temperature of the outer wall member 13 in situations where the temperature of the outer wall member 13 is raised above the temperature of the air in the space 14 by radiation from the inner wall member 13.

Fins or guides may also be placed between the inner and

outer wall members

12 and 13 so that the air is forced to follow a path other than the shortest path .which is parallel to the coil axis 4.

It may be arranged that all the air required for combustion passes through the air space 14. Alternatively a branch path may extend from the fan 9 to the air box 8 so that part of the air is fed directly to the air box 8 and thence to the combustor 6.

FIGS. 2 and 3 show modifications of the FIG. 1 construction. Corresponding parts in FIGS. 1, 2 and 3 have been given the same reference numerals. In FIG. 2 the outer cylindrical wall member 13 is extended downwardly to below the base 5. Further, refractory base 5 is supported on a heavy section metal dish provided with feet 1 12 which raise the dish 110 clear of the base plate 113 so that an air space 114 is provided beneath the base 5 connecting with the annular air space 14. The fan 115 is arranged to'direct its output air flow tangentially into the space 114 as can best be seen from FIG. 3. The air flows from space 114 up the space 14. A helical guide plate 116 is arranged in the space 14 so that the air will follow a helical path in its passage from the space 114 to the combustor 6. The provision of the air space around the base 5 improves heat recovery, adds further to noise insulation and, by virtue of the fact that the whole heater is ,now surrounded with a blanket of air which is slightly above atmospheric pressure improves sealing of the heater so that the leaks flow inwards not outwards.

In order to maintain a reasonably high temperature difference between the combustion gas and the

coil packs

2 and 3, inter alia so that the combustion gases in the heater and stack never fall to a temperature at which condensation of water (which is one of the products of combustion) takes place, it is advisable to have minimum combustion gas temperature of 300 to 400 C. The combustion gas leaving the coil box 1 therefore still has a relatively high temperature as compared with the air entering the combustor 6, which air with an annular air space arrangement as described above would have a typical value of 28 to 30 C. It is therefore possible to extract further heat from the combustion gases and impart it to the combustion air.

In order to achieve this with the FIG. 1 construction a ring of stub pipes extend from the top of the coil box 1 into the flue box 7, the stub pipes passing through a space through which air flows from the annular air space 14 to the air box 8. Thus the hot combustion gases flowing up the stub pipes from the coil box 1 are in heat exchange relationship with the air being fed to the combustor 6 via the air box 8.

In FIG. 1 a single circle of stub pipes 15 has been shown. In an alternative arrangement two or three circles of pipes of smaller diameter and, for example, in staggered formation could be used. Further the pipes may be replaced by non-circular ducts.

The stub pipes 15 may be provided with secondary heat transfer surfaces on both their insides and outsides as shown at 16 and 17 in FIG. 4.

As an alternative to the stub pipe arrangement of FIG. 1, the air can pass from the annular space 14 to the air box 8 via cross airducts 118 passing through the flue box 7 as shown in FIGS. 2 and 5, FIG. 5 shows a developed view of the FIG. 2 construction at the entry to the cross air-ducts 118 from the annular space 14 incorporating the helical guide plate 116.

In FIGS. 2 and 5 the cross ducts 118 are of circular cross-section. Other cross-sectional shapes as shown in FIGS. 6 and 7 may be employed with advantage. 'In FIG. 6 the duct 119 has a rectangular cross-section. The

duct side walls

120 and 121 converging and the duct top wall 122 sloping upwardly in the direction from the air inlet to the air outlet end so that a longer and slimmer rectangular cross-section is provided at the air outlet end than at the air inlet end. The air velocity through the duct can be varied by suitably choosing the cross-sectional areas of the duct at the inlet and outlet ends. If a constant air flow through the duct is desired then the cross-sectional areas at the inlet and outlet ends are made equal. It will be appreciated that, since the circumferential outer wall 123 (FIG. 2) of the flue box 7 is greater than the length of the inner circumferential wall 124, the duct width dimension at the air outlet end of the duct has to be smaller than the duct width dimension at the air inlet end if a large number of cross ducts 119 are to extend across the flue box. This can be readily appreciated from FIG. 14.

As shown in FIG. 6 the cross-duct has secondary heat transfer surfaces 125 on its inside and 126 on its out side.

FIG. 7 illustrates a further form of cross air-duct 128 generally similar to the cross-duct of FIG. 6 but having a triangular instead of a rectangular cross-section.

Two problems associated with forced air heaters such as shown in FIGS. 1 and 2 are as previously stated the noise of the fan which emanates mainly from the fan intake and leakage of fuel vapour and combustion gas, causing contamination of the atmosphere. To provide additional measures for overcoming these problems a dome or hood 18 (FIGS. 1 and 2) oflight construction for example of light gauge steel or aluminium is fitted over the top of the heater. The hood is provided with accoustic baffles 19 and the air space under the hood 18 is ducted to the intake of fan 9, (FIG. 1), (FIG. 2). Combustion air is drawn into the hood 18 via an annular gap 20 between the hood 18 and the outer wall member 13 of the coil box 1, this gap being interrupted at one or two points for the passage of flue ducts 22 to the stack and for other services to the top of the heater. The passage of air through the annular gap 20 causes a small air depression in the space below the hood 18. Any leakages of combustion gas or fuel vapour therefore pass into this low pressure region and are eventually drawn into the fan intake and consumed in the heater.

The annular intake gap 20 can be closed by a debris guard or air intake filter if required. 7

Instead of obtaining the whole of the fan intake air from beneath the hood 18 only a part of it may be so obtained. In this case the hood would be used for creating a small air depression above the combustor 6, so

-that leaks are consumed, and would not be used for suppressing the fan intake noise.

The top of the hood 18 as shown in FIGS. 1 and 2 is provided with a port closed by a lid 23 which is readily removable so that the fuel nozzles of the combustor 6 can, be serviced without removing the hood. Conveniently the lid 23 is transparent to enable viewing of the top of the combustor 6 without removing the hood 18.

As an alternative form of hood, a construction may be used consisting of an expanded plastics or other filler sandwiched between two bonded sheets of light gauge metal. The inner wall surface of the dome would need to be perforated to form a sound absorbent surface. The plastics or other filler material would be noncombustible to satisfy boiler-house requirements. For example an asbestos based material would be satisfactory. With this latter construction the sound absorbing baffles may not be necessary.

Advantageously, if explosion relief doors or ports are provided in the lid of the flue box 7, the hood is not positively bolted or otherwise fixed to the top of the heater but rests under its own weight on the heater and is located for example by locating pegs. Operation of the explosion relief" doors will cause a sudden pressure rise below the hood 18 which can then lift the hood 18 off its locating pegs to vent the excess air and gas mixture without damage.,The parting line of the hood 18 from the heater under such conditions is indicated at 24 in FIG. 1.

If the hood is resting over location pegs only, it may be desirable to provide guides and end stops to limit the vertical travel of the hood and to ensure that it returns correctly under its own weight over its peg locations after it has been lifted.

In FIG. 8 an alternative form of hood construction 25 is shown provided with locating pegs 26. In this construction the hood extends down to below the flue duct 22, a suitable vertical slot being provided in the skirt 27 of the hood to accommodate the flue duct 22. The skirt 27 defines with the outside of the coil box 1 the annular air intake gap 20. A sliding joint 28 is provided between the hood 25 and the air intake of the fan 9.

In FIGS. 1, 2 and 8 the heater is shown arranged on a vertical axis. If however it is arranged on another axis, for example a horizontal axis, gravitational force may be held in place by elastic members. For example the aforementioned guides and limit stops can be provided with light springs.

In conventional once-through coiled tube type heaters, the coil packs are rigidly held and sealed at each end to the coil box. Sealing is necessaryto ensure that all the combustion gas passes through the coil pack and none escapes directly into the flue box. The rigid constraint placed on the coil packs causes stresses to be set up in the tubes and the coil box when these two items reach different temperatures.

In the heater of FIGS. 1 and 2 a flexible sealing ar' rangement is provided at the upper end of the coil packs 2 and 3. This sealing arrangement is illustrated in detail in FIG. 9 and allows this end of the coil packs to float.

The seal comprises a flexible metal diaphragm 29 which as shown in FIG. 1 is of inverted frusto-conical form sealed around its upper rim to the coil box lid 30 and along its lower rim to the annular top plate 32 of the coil packs. The diaphragm 29 is convoluted or corrugated as shown to increase its flexibility.

The upper rim of the diaphragm 29 is sealed to the lid 30 of the coil box 1 by sandwiching it between the lid 30 and a sealing ring 33 which is clamped to the lid by a series of nuts and

bolts

34, 35 extending around the edge of the lid 30.

The lower rim of the diaphragm 29 is similarly clamped in position by a series of nuts and

bolts

34 and 36 extending around the inner periphery of the annular top plate 32 of the coil packs. In addition to clamping the lower rim of the diaphragm 29 the nuts and

bolts

34, 36 also serve to clamp in position through spacer rings 37, 38 and 39, a pair of spaced

annular members

41 and 42. In the space between the

members

41 and 42 is located an annular flange 43 extending from a member having an entry cone 44 and guide ring 45 for the combustor 6 and may also carry air slots surrounding the combustor 6.

The flange 43 forms with the members 41 and 42 a seal between the air box 8 and coil box 1, and the flange 43 is free to move laterally of the heater axis 4 to allow some eccentricity during assembly and subsequent working of the combustor 6 within the air box.

flanges or other pipe fittings which are sufficiently small in diameter to be able to pass through the stub pipes. By this means the complete coil pack or packs can be assembled or dismantled without having to cut pipes or make joints through the coil box wall. The terminations can be either in the flue box as shown at 72 in FIG. 1 or can be brought up to the flue box lid 61. The termination of other services such as, for example, oil pressure and temperature transducers and auxiliary coil feeds such as de-superheater or normaliser feed pipes can also terminate similarly in the flue box or at the flue box lid.

FIG. shows a cross-section of the heater of FIG. 1 in the region of the flue box 7. The flue box 7 receives gas from the flue stub pipes which are equi-spaced on a circumference in the flue box base. However, the.

exit from the box to the stack is at one point only on the circumference through duct 22. In order therefore to maintain a reasonably uniform gas velocity from the stub pipes to the exit it is necessary to vary the cross section of the box 7, the area becoming progressively greater as the efflux from additional stub pipes is added, until the exit duct 22 is reached. This feature is achieved by making the inner wall 74 of the flue box annulus eccentric to the outer wall 75 and enables the complete heater to be manufactured using only plate which is flat or rolled to a constant radius.

It should be noted that the use of two eccentric circles gives only an approximate uniform increase of area of the annulus formed between them with radial position. Closed curves other than a circle and in particular a curve such that the cross sectional area of the annulus increases uniformally from a minimum at one radius to a maximum at a radius which is from the minimum section can be provided by suitable shaping of the

walls

74 and 75. I

The same principle of construction could apply to the heater construction of FIG. 2 in which cross air ducts are used. The cross-section of the heater of FIG. 2 in the region of the flue box would then be as shown in FIG. 11.

I claim:

1. A fluid heater comprising:

a. a fuel-air combustor,

b. heat exchange coils for carrying fluid to be heated by heat exchange with the combustion exhaust gases from the combustor,

c. a coil box housing the heat exchange coils and having a hollow peripheral side-wall structure defining a path for at least part of the air supply to the fuelair combustor, the fuel-air combustor being located in one end of the coil box so that it directs its combustion exhaust gases towards the other end of the coil box,

d. a fan for supplying air to the hollow peripheral side-wall structure at a position adjacent said other end of the coil box, and

e. ducting leading to the inlet of said fan and including a hood covering said fuel-air combustor and said one end of the coil box.

2. A fluid heater according to claim 1, wherein the coil box has a structure defining an air space extending over said other end of the coil box, said air space being in communication with the air path through said sidewall structure and said fan being arranged to direct air tangentially into said air space.

3. A fluid heater according to claim 1, wherein th underside of the hood is provided with accoustic baffles.

4. A fluid heater according to claim 1, wherein the hood and the peripheral side-wall structure define between them an annular air intake.

5. A fluid heater comprising:

a. a fuel-air combustor,

b. heat exchange coils for carrying fluid to be heated by heat exchange with the combustion exhaus gases from the combustor,

c. a coil box housing the heat exchange coils and having a hollow peripheral side-wall structure defining combustion exhaust gases towards the other end of the coil box,

cl. a flue box disposed on said one end of the coil box and through which the combustion exhaust gases pass from the coil box to a flue outlet, and

e. air ducts within the flue box for carrying air over said one end of the coil box from the hollow sidewall structure to the combustor, each of the air ducts being of substantially the same crosssectional area throughout its length but being narrower in width at its air outlet end than at its air inlet end.

6. A fluid heater comprising:

a. a fuel-air combustor,

d. a flue box disposed on said one end of the coil box and through which the combustion exhaust gases pass from the coil box to a flue outlet, the flue box being of annular form and the flue outlet being located at a point on its outer periphery, the width of the annular space within the flue box being narrowest at a position diametrically opposite the flue outlet and increasing gradually to its widest dimension at the flue outlet.

7. A fluid heater according to claim 6, wherein the flue box is formed by two circular sheet members disposed eccentrically of each other.

8. A fluid heater comprising:

a. a fuel-air combustor,

c. a coil box housing the heat exchange coils and hav ing a hollow peripheral side-wall structure defining a path for at least part of the air supply to the fuelair combustor, the fuel-air combustor projecting through one end of the coil box so that it directs its combustion exhaust gases towards the other end of the coil box, and

d. a flexible seal arrangement between said one end of the coil box and the adjacent end of the coils to prevent combustion exhaust gases passing to the outlet of the coil box before coming into heat exchange relationship with the coils.

9. A fluid heater according to claim 8, wherein said flexible seal comprises a frusto-conical diaphragm clamped around its upper rim to said end wall of the coil box to surround an aperture through which the combustor projects and clamped around its lower rim to the adjacent end of the coils.

10. A fluid heater according to claim 9, wherein the clamping arrangement for the lower end of the diaphragm also clamps in position a member having an entry cone and a guide ring for locating the projecting end of the combustor in the coil box.

Claims

1. A fluid heater comprising: a. a fuel-air combustor, b. heat exchange coils for carrying fluid to be heated by heat exchange with the combustion exhaust gases from the combustor, c. a coil box housing the heat exchange coils and having a hollow peripheral side-wall structure defining a path for at least part of the air supply to the fuel-air combustor, the fuel-air combustor being located in one end of the coil box so that it directs its combustion exhaust gases towards the other end of the coil box, d. a fan for supplying air to the hollow peripheral side-wall structure at a position adjacent said other end of the coil box, and e. ducting leading to the inlet Of said fan and including a hood covering said fuel-air combustor and said one end of the coil box.

2. A fluid heater according to claim 1, wherein the coil box has a structure defining an air space extending over said other end of the coil box, said air space being in communication with the air path through said side-wall structure and said fan being arranged to direct air tangentially into said air space.

3. A fluid heater according to claim 1, wherein the underside of the hood is provided with accoustic baffles.

5. A fluid heater comprising: a. a fuel-air combustor, b. heat exchange coils for carrying fluid to be heated by heat exchange with the combustion exhaust gases from the combustor, c. a coil box housing the heat exchange coils and having a hollow peripheral side-wall structure defining a path for at least part of the air supply to the fuel-air combustor, the fuel-air combustor being located in one end of the coil box so that it directs its combustion exhaust gases towards the other end of the coil box, d. a flue box disposed on said one end of the coil box and through which the combustion exhaust gases pass from the coil box to a flue outlet, and e. air ducts within the flue box for carrying air over said one end of the coil box from the hollow side-wall structure to the combustor, each of the air ducts being of substantially the same cross-sectional area throughout its length but being narrower in width at its air outlet end than at its air inlet end.

6. A fluid heater comprising: a. a fuel-air combustor, b. heat exchange coils for carrying fluid to be heated by heat exchange with the combustion exhaust gases from the combustor, c. a coil box housing the heat exchange coils and having a hollow peripheral side-wall structure defining a path for at least part of the air supply to the fuel-air combustor, the fuel-air combustor being located in one end of the coil box so that it directs its combustion exhaust gases towards the other end of the coil box, d. a flue box disposed on said one end of the coil box and through which the combustion exhaust gases pass from the coil box to a flue outlet, the flue box being of annular form and the flue outlet being located at a point on its outer periphery, the width of the annular space within the flue box being narrowest at a position diametrically opposite the flue outlet and increasing gradually to its widest dimension at the flue outlet.

8. A fluid heater comprising: a. a fuel-air combustor, b. heat exchange coils for carrying fluid to be heated by heat exchange with the combustion exhaust gases from the combustor, c. a coil box housing the heat exchange coils and having a hollow peripheral side-wall structure defining a path for at least part of the air supply to the fuel-air combustor, the fuel-air combustor projecting through one end of the coil box so that it directs its combustion exhaust gases towards the other end of the coil box, and d. a flexible seal arrangement between said one end of the coil box and the adjacent end of the coils to prevent combustion exhaust gases passing to the outlet of the coil box before coming into heat exchange relationship with the coils.