WO1999028675A1

WO1999028675A1 - A refuse incineration boiler

Info

Publication number: WO1999028675A1
Application number: PCT/DK1998/000487
Authority: WO
Inventors: Gabriel Da Silva Pinto
Original assignee: FLS Miljo AS
Current assignee: FLS Miljo AS
Priority date: 1997-11-11
Filing date: 1998-11-11
Publication date: 1999-06-10
Anticipated expiration: 2000-05-11
Also published as: DK128199A; WO1999028675A9; DK173090B1; AU1144499A

Abstract

The boiler has a flue gas flow passage with a horizontal economizer section containing one or more horizontal 180° bends so that two consecutive parts of the flue gas flow passage, seen in the direction of the flue gas flow, have a joint partition (11, 12).

Description

A refuse incineration boiler

The present invention relates to a refuse incineration boiler with a flue gas flow passage issuing from a combustion chamber and having a radiation part and a convection part, the convection part including a superheater section and a horizontal economizer section defined in the horizontal plane by two side walls, the economizer section containing one or more economizers. In prior-art refuse incineration boilers of the above type, the economizer section is generally very long compared with the economizer section in boilers using, for example, oil or natural gas as the only fuel. This is due to the fact that the flue gas formed by incineration of the refuse has a large ash content tending to deposit on the tubes in the heating surfaces of the economizers and thus being able to block the interspaces between the tubes. To avoid such blockage, the economizers are formed with tube interspaces which are larger than in economizers used in oil or gas-fired boilers. This results in a lower efficiency for the individual economizer, and it is therefore necessary to arrange several economizers consecutively to be able to exploit the heat in the flue gas fully, resulting in the long economizer section mentioned above . To further prevent said blockage, the heating surfaces are provided with vibration or shaking apparatus making the tube banks vibrate, whereby the ash is shaken down from the tubes to underlying ash hoppers. Attempts to increase the efficiency of the economizers by increasing the velocity of the flue gas across the tubes can only be made by reducing the cross-sectional area of the flue gas flow passage. This, however, reduces the area available for arrangement of economizer heating surfaces, and to compensate therefor, the economizer section must be correspondingly extended.

The result of these factors is that because of its length the economizer section takes up a large area and that both the bedplate, sidewalls and ceiling of the flue gas flow passage as well as supply and discharge conduits for, the economizers become long, resulting in high construction and maintenance costs.

DΞ patent publication No. 40 25 252 discloses a refuse incineration boiler of the above type in which the convection, part including superheaters, evaporator tubes and economizers is arranged in parallel with the radiation part so that the two parts are separated by a joint water-cooled wall. This arrangement does not alleviate the above deficiencies, but has the further disadvantage that the heat absorbed in the cooled partition from the radiation part is emitted to the economizer section, which leads to an impaired overall efficiency of the boiler. The DΞ patent publication also shows a modification in which the convection part is divided between two flue gas flow passages both extending in parallel with the radiation part . It is possible in this way to compensate for falling flue gas velocity during partial loads by simply closing the flue gas outlet for one of the two convection parts.

The object of the present invention is to provide an improved refuse incineration boiler in which the above disadvantages are reduced. This object is achieved according to the invention with a refuse incineration boiler of the type mentioned in the introduction in which each economizer comprises several tube banks which are constructed from substantially vertical tubes, are suspended substantially vertically and have upper and lower headers located in the transverse direction of the flue gas flow passage, the side walls of the economizer section of the flue gas flow passage being uncooled, and the part of the flue gas flow passage containing the economizer section including at least one 180° bend positioned in a horizontal plane so that two consecutive parts of the flue gas flow passage seen in the direction of the flue gas flow have a common side wall or partition.

When the flue gas flow passage of the refuse incineration boiler containing the economizer section folds back upon itself in a bend of 180°, the economizer section becomes substantially less space-demanding, and this allows bedplate, tubes, etc., to be concentrated in a smaller area. If the economizer section of the flue gas flow passage comprises two 180° bends, it is possible, for example, to reduce the distance between the flue gas inlet and the flue gas outlet and thus the total length of the economizer section to about one third of the length commonly used so far in prior-art refuse incineration boilers. This provides the further advantage that the exterior surface area of the economizer section is reduced, directly resulting in a reduction of the heat loss to the surroundings.

In a preferred embodiment, adjacent tube banks in said two consecutive parts of the economizer section of the flue gas flow passage may be located in the same transverse plane, and their lower headers may be mechanically interconnected in 'extension of each other through the joint side wall or partition of said part. This means that the number of shaking devices can be heavily reduced, as striking on the free end of one of the mechanically interconnected lower headers for the purpose of loosening any deposited ash from the heating surf ce of the tube bank results in shaking or vibration of the other mechanically interconnected lower headers in the same plane. Instead of each lower header requiring a shaking device, each shaking device in the above embodiment can now service three lower headers, whereby the number of shaking devices can be reduced to a third. Since, as a consequence of their function, shaking devices are exposed to heavy influences and furthermore operate in a corrosive atmosphere, they frequently require repairs, and it is realized that the costs of such repairs can be highly reduced by reducing the number of shaking devices.

In a second embodiment the lower headers mechanically interconnected in extension of each other in each transverse plane may at a free end have a bar adapted for influencing by means of a shaking device, the bar being passed out of the flue gas flow passage through an adjacent outer wall, and in an especially suitable embodiment, all bars may be passed out through the same outer wall. The latter embodiment renders it possible to make use of a shaking device which is movable along said outer wall on a rail.

In a third embodiment, upper headers located in the same transverse plane may be mechanically interconnected in extension of each other through said joint side wall or partition. In an especially simple design, for example, both upper and lower headers may be formed as through tubes extending across the flue gas flow passage from one outer wall to the other. Each of the through headers is blocked inside, for example by means of blind panels welded in alignment with the longitudinal partitions of the flue gas flow passage.

In yet another embodiment, the economizers may be connected as counter-current heat exchangers, which has proved to yield an especially high efficiency in refuse incineration boilers. The invention will now be described in more detail below by means of some embodiments and with reference to the drawing, in which

Fig. l is a vertical longitudinal view through the economizer section of a refuse incineration boiler according to the invention,

Pig. 2 is a sectional view along the line II-II in Fig. 1,

Fig. 3 is a sectional view as in Fig. 2 of another embodiment, of the economizer section,

Fig. 4 is. a sectional view along the line IV-IV in Fig, 3, and

Fig. 5 is a diagram of the piping on the water side of the economizers in the embodiment illustrated in Fig. 2.

The economizer section 1 illustrated very schematically in Figs. 1 and 2 has a ceiling 2 , side walls 3 and 4 and end walls 5 and 6. In the economizer section, the flue gas flow passage is defined by longitudinal partitions 11 and 12. The flue gas flows in through an inlet 15 and, as indicated by arrows in Fig. 2, is forced through two 180° bends before it flows out through an outlet 16, wherefrom it is passed to a flue gas purification plant, not shown, and the chimney. The length of an outer wall of the economizer section, for example the outer wall 3, is only about one third of the length .used in a prior-art economizer section. It appears from Fig. 2 that the flue gas outlet, seen in the longitudinal direction of the economizer section, is displaced sideways in relation to the flue gas inlet.

The outer walls, partitions and ceiling of the economizer are constructed from uncooled steel plate, and the outer walls are insulated to reduce the heat loss to the surroundings. Under the economizer section, ash hoppers 20 are arranged with screw conveyors 21 leading the ashes to an ash outlet 22.

Each economizer 30 is constructed from vertical tubes 32 interconnected at the top across the direction of the flue gas flow passage by means of upper headers 33 and at the bottom by lower headers 34, the lower headers in this case being arranged at two different levels. The lower headers are interconnected across the direction of the flue gas flow passage by bars 35 passed through openings in the partitions 11 and 12.

The free ends of the lower headers adjacent to the outer wall 3 have bars 40 passed through the outer wall 3 so that they can be influenced by a shaking device 41, the arrangement of which is schematically indicated in Fig. 4. The shaking device 41 has a shaft extending in' parallel with the side wall 3. This shaft supports several articulated arms 43 having a hammer 42 at the end. When the shaft rotates, the hammer 42 strikes the bar 40 at the end of the lower header so that deposits and ashes are shaken free of the tubes 32 and fall down into the ash hoppers 20. The arrangement described is enclosed in a housing 44.

The economizer section shown in Figs. 3 and 4 has a ceiling 2, side walls 3 and 4 and end walls 5 and 6. In the economizer section, the flue gas flow passage is defined by three longitudinal partitions 7, 8, 10 and a transverse wall 9. The flue gas flows in through an inlet 15 and, as indicated by arrows in Fig. 3, is forced through four 180° bends before it flows out through an outlet IS, wherefrom it is passed to a flue gas purification plant, not shown, and the chimney. In this embodiment, the flue gas inlet is aligned with the flue gas outlet.

In this embodiment, the economizer section is constructed in the same way as the economizer section described above in connection with Figs . 1 and 2. However, as it appears from Figs. 3 and 4, the upper and lower headers, 37 and 36, respectively, are designed as through tubes extending across the flue gas flow passage from the side wall 3 to the side wall 4 and are blocked internally by a blind (not shown) arranged in alignment with the longitudinal partitions 7, 8 and 10.

The economizers 30 in the embodiment shown in Fig. 2 are connected on the water side as shown in Fig. 5. The cold feed water flows in at the inlet 38 and divides into two parallel circuits to be joined again at the outlet 39 for heated feed water. The tube diagram is to be understood so that the inlet 38 is located at the bottom right corner of Fig. 2, while the outlet 39 is located at the upper left corner of Fig. 2. It appears from Fig. 5 that the water in the first feed water circuit flows through the economizers marked ECO 1,1; ECO 1,2;. ECO 1,3; ECO 1,4; and ECO 1,5 before it flows to the outlet, while the water in the second circuit flows through the economizers ECO 2,1; ECO 2,2; ECO 2,3; and ECO 2,4 whereupon it flows to the outlet. In each economizer, the water supply tube and the water discharge tube are connected to respective upper headers . In this way, the economizer section achieves a more even temperature distribution than if the feed water had been passed from the inlet 38 ^• in series through the economizers ECO 1,1; ECO 2,1; ECO 1,2; ECO 2,2; ECO 1,3; ECO 2,3; ECO 1,4; ECO 1,5; and ECO 2,4. As a consequence of this evening out of the temperatures, the stresses in the tube banks of the economizer caused by temperature differences are reduced.

Claims

P A T E N T C L A I M S

1. A refuse incineration boiler with a flue gas flow passage issuing from a combustion chamber and having a radiation part and a convection part, the convection part including a superheater section and a horizontal economizer section (1) defined in the horizontal plane by two side walls (3,4) , the economizer section containing one or more economizers (30) , c h a r a c t e r i z e d in that each economizer comprises several tube banks which are constructed from substantially . vertical tubes (32) , are suspended substantially vertically and have upper and lower headers (33, 34,-37, 36) located in the transverse direction of the flue gas flow passage, that the side walls (3,4,5,6) of the economizer section (1) of the flue gas low passage are uncooled, and that the part of the flue gas flow passage containing the economizer section (1) includes,at least one 180° bend positioned in a horizontal plane so that two consecutive parts of the flue gas flow passage seen in the direction of the flue gas flow have a joint side wall or partition (11,12;7,8,10) .

2. A ref se incineration boiler according to claim

1, c h a r a c t e r i z e d in that adjacent tube banks in said two consecutive parts of the economizer section (1) of the flue gas flow passage are located in the same transverse plane, and that their lower headers (34;36) are mechanically interconnected in extension of each other through the joint side wall or partition (11,12;7, 8,10) of said section.

3. A refuse incineration boiler according to claim

2, c h a r a c t e r i z e d in that the lower headers (34;36) mechanically interconnected in extension of each other in each transverse .plane at a free end have a bar (40) adapted for influencing by means of a shaking device (41) , the bar being passed out of the lue gas flow passage through an adjacent outer wall (3) .

4. A refuse incineration boiler according to claim 3, c h a r a c t e r i z e d in that all bars (40) are passed out through the same outer wall (3) .

5. A refuse incineration boiler according to any one of the preceding claims, c h a r a c t e r i z e d in that upper headers (33; 37) located in the same transverse plane are mechanically interconnected in extension of each other through said joint side wall or partition (11,12;7,8,10)_J.

6. A refuse incineration boiler according to any^¬ one of the preceding claims, c h a r a c t e r i z e d in that the economizers (30) are connected as counter- current heat exchangers .