GB2068513A

GB2068513A - Fire-tube boiler

Info

Publication number: GB2068513A
Application number: GB8102807A
Authority: GB
Original assignee: DUCOSTO STOOMKETEL MACH BV
Current assignee: DUCOSTO STOOMKETEL MACH BV
Priority date: 1980-01-31
Filing date: 1981-01-30
Publication date: 1981-08-12
Also published as: DE3102941A1; NL8000635A; FR2475187A1

Abstract

A fire-tube boiler for the production of hot water or steam, comprising a shell (2) containing a flue (3) surrounded by a supply of water. At least one additional flue (6, 8) is provided in addition to the first flue (3), the additional flue (6, 8) comprising at least one wide tube, through which a plurality of successive sets of water tubes (11, 12, 13) of relatively large diameter extend transversely to the longitudinal extent of said wide tube. Each set of water tubes consists of one or more successive water tubes having the same orientation and positioned crosswise relatively to the preceding and the next set of water tubes. <IMAGE>

Description

SPECIFICATION Fire-tube boiler This invention relates to a fire-tube boiler for the production of hot water or steam, comprising a housing containing a flue surrounded by a supply of water, and a plurality of water tubes communicating with said supply of water and being in heat-exchange relationship with said flue.

Such a boiler is described, for example, in Dutch patent No. 57935. In this prior boiler, the flue is a single wide tube, through which a plurality of water tubes having a relatively small diameter extend in the transverse direction. This is a socalled one-pass boiler, which has a low efficiency, i.e., the combustion gases leave the boiler at a very high temperature. Furthermore, owing to the relatively small diameter of the water tubes and their location in the back of the flue, the water circulation is not as good as it can be, which does not contribute to a high efficiency either.

In the past, with a view to improving the efficiency, multi-pass boilers have been developed in practice, in which the furnace tube or first flue in the form of a wide tube extends within the housing substantially throughout the entire length thereof, the output end of which wide tube is connected to a combustion chamber, from which, again, a large number of tubes of smaller diameter extend substantially through the entire length of the housing to form a second flue. The second flue may terminate in a smoke box with a stack, or in a reversing box, to which a similar third flue is connected, which terminates in a smoke box.

Such two- or three-pass boilers do indeed give an improvement in efficiency, but the water circulation was still not ideal, especially in the case of hot-water boilers and low-pressure steam boilers, so that short-circuiting was liable to occur, even using a separate circulation pump. Also, in such multi-pass boilers, the exhaust resistance is rather high, so that it is necessary to employ a high-capacity blower.

Furthermore, owing to the large number of closely-spaced parallel tubes, which are secured in corresponding apertures in common tube plates, the construction of the second, and possibly third flue is relatively complicated, which is apparent in particular if, after a number of years service, one or more tubes must be renewed.

It is an object of the present invention to overcome the disadvantages outlined above. For this purpose, according to the invention, a fire-tube boiler of the kind described is characterized by the provision of at least a second flue beside the furnace tube or first flue, said second flue comprising a single wide tube, through which a plurality of water tubes of relatively large diameter extend transversely to the longitudinal extent of said wide tube, in alternating crossing relationship.

Water tubes extending in alternating crossing relationship, as used herein, is intended to include constructions in which some, preferably two, consecutive water tubes have the same orientation and are followed, and preceded, by a few, for example also two, water tubes crossing the water tubes first mentioned.

One embodiment of the invention will now be described, by way of example, with reference to the accompanying drawing.

The figure is a perspective view of an embodiment of a fire-tube boiler according to the invention. The boiler shown is a three-pass boiler but the invention is also applicable to a boiler having a different number of passes, for example, a two-pass boiler.

A frame 1 carries a cylindrical shell 2, depicted as being transparent, which is closed with end walls. Extending through the shell, as viewed in the drawings from left to right, is a wide tube 3, forming the furnace tube or first flue. The first flue is connected on one end through an opening in the end wall to a blower, not shown, which in operation blows hot gases into the flue. The blower is situated at the end of the furnace tube designated by 4.

The other end of the furnace tube terminates in a reversing box 5, sometimes referred to as a combustion chamber, which is situated at the end of the shell remote from the blower. Through the combustion chamber, the hot gases can reach the second flue 6, which extends from the combustion chamber substantially parallel to the furnace tube to a second reversing box 7, also referred to herein as the smoke box or front reversing box 7, which is placed at the end of the blower. In the case of a two-pass boiler, box 7 is connected to a stack. In the embodiment shown, however, a third flue 8 is provided, which extends from box 7 substantially parallel to the second flue, and terminates in a smoke box 9 placed at the opposite end of the shell, and connected to a stack 10.

Around the first, second and third flue, the housing is fully filled with the water to be heated, and provided with inlet and outlet means for the cooled and re-heated water, not shown.

The furnace tube or first flue consists of a wide tube. In the embodiment shown, the second and third flues consist of tubes having a smaller, but still relatively large diameter, in which a plurality of cross-tubes are mounted transversely to the longitudinal direction of the main tubes, which cross-tubes cross each other at substantially right angles alternately in one and in another direction.

In the operative condition, the axes of the crosstubes preferably make an angle of no more than 45 to the vertical.

As stated before, the cross-tubes may also be arranged in alternating groups of a few tubes extending in one direction, followed and preceded by groups of a few cross-tubes extending in a crossing direction.

Thus, in the second flue, as viewed from the end of the blower, the first cross-tube designated by 11 extends from a left-hand bottom position to a right-hand top position at an angle of 45 to the vertical, and a second cross-tube 1 2 extends from a right-hand bottom position to a left-hand top position, also at an angle of 45 to the vertical.

The third tube 13 extends again from the left-hand bottom position to the right-hand top position, etc.

The cross-tubes are welded in corresponding apertures in the walls of tubes 6 and 8, so that the water can circulate through the cross-tubes.

As a result of the position of the cross-tubes as described and shown in the accompanying drawing, a favourable, natural circulation arises in the water, whereby "short-circuits" (a stream of cold water direct from the inlet to the outlet) are prevented and, generally speaking, a separate circulation pump is no longer required.

Experiments have shown that the diameter of the cross-tubes should preferably be'at least 20% of the diameter of the wide tube and still more preferably between 20 and 25% of the diameter of the wide tube.

Furthermore, with the form of the flues as described and shown in the drawing, the exhaust resistance is relatively low, so that the power consumption of the blower with the same, or even a superior efficiency of the heat exchange in the boiler, is less than with prior fire-tube boilers.

Finally, the fire-tube boiler according to the present invention is simpler than an existing boiler from the point of view of production engineering, by virtue of the fact that the flue designed in accordance with this invention produce a saving of approx. 50% on material and man hours. The flues according to the invention can be made separately, and be installed in the boiler as one whole. This latter is also of importance in the case of repairs, as this minimizes idling periods of a boiler being repaired.

Various variations of the embodiment described are possible. As stated before, the principle of the invention can also be applied to two-pass boilers.

Furthermore, experiments have shown that if, in a three-pass boiler in which the second and third flues consist of bundles of parallel fire tubes, e.g.

the second flue is replaced by a flue designed in accordance with the teachings of the present invention, a considerable improvement is obtained.

Flues 6 and 8 need not have the same diameter. As shown in the drawing, the tube 8 of the third flue may have a smaller diameter than the tube 6 of the second flue. This is connected with the lower temperature of the combustion gases in the third flue as compared with the second flue.

Similarly, the cross-tubes may vary in diameter in each flue from the front to the back as viewed in the direction of flow of the flue gases.

Also, it is not strictly necessary for the successive cross-tubes of a flue to cross each other substantially perpendicularly; other positions are conceivable and feasible.

It is finally observed that a flue may also consist of a plurality of parallel wide tubes provided, in the manner described hereinbefore, with crosspositioned water tubes.

Claims

1. A fire-tube boiler for the production of hot water or steam, comprising a shell containing a flue surrounded by a supply of water, and a plurality of water tubes communicating with said supply of water and being in heat exchange relationship with said flue, characterized by the provision of at least a second flue beside the furnace tube or first flue, said second flue comprising at least one wide tube, through which a plurality of successive sets of water tubes of relatively large diameter extend transversely to the longitudinal extent of said tube, each set of water tubes consisting of one or more successive water tubes having the same orientation and positioned crosswise relatively to the preceding and the next set of water tubes.

2. A fire-tube boiler as claimed in claim 1, characterized in that the water tubes cross each other in alternating fashion.

3. A fire-tube boiler as claimed in claim 1 or 2, characterized in that the water tubes have a diameter of at least 20% of the diameter of the wide tube.

4. A fire-tube boiler as claimed in claim 3, characterized in that the diameter of the water tubes ranges between 20% and 25% of the diameter of the wide tube.

5. A fire-tube boiler as claimed in any one of the preceding claims, characterized in that the furnace tube or first flue extends from one end of the shell into a combustion chamber positioned at the other end of the shell, which combustion chamber communicates with the second flue, which extends to said one end of the shell, where it terminates in a reversing box, which in turn communicates with a third flue extending back to a smoke box positioned at said other end of the shell and provided with a stack connection.

6. A fire-tube boiler as claimed in claim 5, characterized in that the third flue comprises at least one wide tube through which a plurality of successive sets of watertubes of relatively large diameter extend transversely to the longitudinal extent of said tube, each set of water tubes consisting of one or more successive water tubes having the same orientation and positioned crosswise relatively to the preceding and the next set of water tubes.

7. A fire-tube boiler as claimed in claim 6, characterized in that the successive water tubes of said third flue cross each other in alternating fashion.

8. A fire-tube boiler as claimed in claim 6 or 7, characterized in that the water tubes of the third flue have a diameter of at least 20% of the diameter of said wide tube.

9. A fire-tube boiler as claimed in claim 8, characterized in that the diameter of the water tubes of the third flue ranges between 20% ad 25% of the diameter of said wide tube.

10. A fire-tube boiler as claimed in any one of the preceding claims, characterized in that the sets of water tubes in each wide tube provided with water tubes cross each other substantially at right angles, and in the operative position each enclose an angle with the vertical of no more than 45 .

1 A fire-tube boiler as claimed in any one of claims 6-10, characterized in that the diameter of said at least one wide tube of the third flue is less than the diameter of said at least one wide tube of the second flue.

12. A fire-tube boiler as claimed in any one of the preceding claims, characterized in that the diameter of the water tubes in the second and/or third flue varies as viewed in the direction of flow of the flue gases.

13. A boiler tube for a fire-tube boiler as claimed in any one of the preceding claims, characterized by a wide tube having mounted therein successive sets of one or more successive, open-ended cross-tubes, said sets being orientated crosswise in alternating fashion.

14. A boiler tube as claimed in claim 13, characterized in that the diameter of the crosstubes is at least 20% of the diameter of the wide tube.

1 5. A boiler tube as claimed in claim 14, characterized in that the diameter of the crosstubes ranges between 20% and 25% of the diameter of the wide tube.

16. A boiler tube as claimed in any one of claims 1 3-1 5, characterized in that the diameter of the cross-tubes varies along the length of the wide tubes.