EP2009354A1

EP2009354A1 - Horizontal structure in a boiler

Info

Publication number: EP2009354A1
Application number: EP08075573A
Authority: EP
Inventors: Johannes Hermanus Jacobs
Original assignee: Tetra Tube BV
Current assignee: Tetra Tube BV
Priority date: 2007-06-27
Filing date: 2008-06-24
Publication date: 2008-12-31
Also published as: NL1034043C2

Abstract

The invention relates to a horizontal structure in a boiler of for instance an incinerator, which boiler comprises at least two mutually opposite membrane walls, wherein each membrane wall comprises a large number of pipes through which cooling agent flows, wherein at least one pipe of each of the mutually opposite membrane walls is bent out substantially horizontally and extends to the respective opposite membrane wall, and then continues in vertical direction.

Description

The invention relates to a horizontal structure in a boiler of for instance an incinerator, which boiler comprises at least two mutually opposite membrane walls, wherein each membrane wall comprises a large number of pipes through which cooling agent flows. Flowing between these two walls are hot flue gases which relinquish heat to the membrane walls, whereby the cooling agent is heated.
In an incinerator of for instance a waste treatment plant it is important to properly control the combustion process in order to reduce the emission of harmful substances. For this purpose additional air is usually blown in from the top to still enable afterburning of plumes of unburned carbon monoxide. It is important here that the blown-in air is mixed properly with the flue gases in order to obtain an optimal mixing.
It has been found that the impulse alone of blowing in air does not bring about sufficient mixing of the air with the flue gases, and it is therefore necessary to take additional measures in order to improve the mixing of supplied air and flue gases.
This improved mixing can be brought about by obstacles in the boiler. The conditions in a boiler are however particularly aggressive as a result of, among other factors, the high temperature and the chemical constituents present in the not yet fully combusted flue gases. Simply placing a metal beam in the boiler is therefore not an option, since the lifespan thereof will be very limited. Partly for this reason the vertical membrane walls of the boiler are also constructed from pipes through which a cooling agent flows. The temperature of the pipes is thus kept relatively low, which enhances the lifespan of the walls.
It is now an object of the invention to provide a horizontal structure having a lifespan in the same order as the vertical membrane walls of the boiler.
This object is achieved according to the invention in that at least one pipe of each of the mutually opposite membrane walls is bent out substantially horizontally and extends to the respective opposite membrane wall, and then continues in vertical direction in the respective opposite membrane wall.
The use of the pipes from the membrane wall to manufacture a horizontal structure ensures that the same cooling agent flows through the horizontal structure and the lifespan thereof is thus increased.
In an embodiment of the horizontal structure according to the invention a part of at least one pipe of the vertical membrane wall is bent out of the plane of the vertical membrane wall, although a part subsequently runs parallel thereto and is then bent out horizontally.
The advantage of first bending the pipe of the vertical membrane wall out of the plane of the membrane wall and having a part run parallel thereto is that more space is hereby created for the horizontal bending of the pipe, particularly if a plurality of adjacent pipes are bent out.
In another embodiment of the horizontal structure according to the invention a number of adjacent pipes are bent out in order to form the horizontal membrane wall in the boiler. In this way a platform can be formed in the boiler, which for instance disrupts the flue gas flow and thereby causes eddies which improve the mixing of the flue gases.
In a particular embodiment the formed horizontal membrane wall has a roof-like cross-section. The accumulation of fly ash on top of the horizontal membrane wall will hereby be reduced. The construction moreover becomes more rigid due to the roof shape. Because the horizontal membrane wall is constructed from a number of parallel pipes, a roof-like cross-section can be readily created by varying the vertical position of the horizontal pipe parts.
The invention further relates to a boiler of for instance an incinerator, which boiler has a substantially rectangular cross-section and comprises two pairs of mutually opposite membrane walls, wherein each membrane wall comprises a large number of pipes through which cooling agent flows, wherein at least one horizontal structure according to the invention is formed between at least one pair of mutually opposite membrane walls.
An improved mixing is hereby realized due to an abrupt, forced deflection of the gases for mixing. Due to the abrupt change in direction of the gases the mixing action under the horizontal structure is much greater than in the case of a usual, gradual constriction. In addition, the horizontal structure causes the phenomenon 'vena contracta' to occur, whereby the gas flow contracts even further, an intensified difference in speed occurs, and an excellent mixing of gases occurs due to these differences.
A preferred embodiment of the invention comprises two first horizontal structures which each form a horizontal membrane wall and which each lie against a membrane wall of the other pair of membrane walls such that a constriction is formed in the boiler.
A further embodiment of the invention comprises a number of pipes which are bent horizontally out of a membrane wall and which run back again into the same membrane wall and are placed between the two horizontal membrane walls such that the boiler is constricted in two horizontal, orthogonal directions. Such a structure is for instance known from NL-A-1022586 . The substantially rectangular boiler is hereby constricted in both horizontal directions similar to a diaphragm, and this further intensifies the eddies in the flue gasses and improves the mixing.
Another embodiment of the invention further comprises two second horizontal structures which each form a horizontal membrane wall and which each lie against a membrane wall of the other pair of membrane walls and are arranged immediately above the first horizontal structures such that the boiler is constricted in two horizontal, orthogonal directions. In this construction there is a partial overlap of the horizontal membrane walls. A constriction similar to a diaphragm is here also obtained in the boiler.
These and other features of the invention are further elucidated with reference to the accompanying drawings.

Figure 1 shows a perspective view of a schematic representation of an incinerator.
Figure 2 shows a perspective view of a part of the boiler having therein horizontal structures according to the invention.
Figure 3 shows a perspective view of a part of the boiler having therein a second embodiment of the horizontal structures according to the invention.
Figure 4 shows a schematic side view of a third embodiment of the horizontal structures according to the invention.
Figure 5 shows a perspective view of a part of the horizontal structure according to figure 4.
Figure 6 shows a perspective view of a horizontal structure as applied in the boilers according to figures 2 and 3.
Figure 7 shows a fourth embodiment of a horizontal structure according to the invention.

Figure 1 shows an incinerator 1 with a combustion chamber 2 and a boiler 3 arranged thereabove. Arranged in combustion chamber 2 is a grate 4 on which fuel 5 is arranged. Air is supplied below grate 4 in order to enhance the combustion of fuel 5. Arranged on the upper side of combustion space 2 are nozzles 6 which blow in secondary air in order to provide flue gases G with additional air and thereby enable an afterburning of gases contained therein.
Further arranged in boiler 3 is a horizontal structure 7 which forms a diaphragm in boiler 3. Because horizontal structure 7 forms a constriction and is moreover flat, flue gases G are forced through opening 8, whereby considerable turbulence is created in flue gases G.
Figure 2 shows horizontal structure 7 in more detail. The walls of boiler 3 are formed by pipes 9 through which a cooling agent flows. Pipes 9 are alternately bent out horizontally into a horizontal part 10 which runs to the opposite wall and is there taken up into the wall. A horizontal structure is thus created through which cooling agent moreover flows and which therefore has an acceptable lifespan. In order to obtain constriction 18 in both horizontal directions elements 11 bent out of the wall are arranged between the two horizontal membrane wall parts 10. These elements 11 bent out of the wall are pipes 9 which are partially bent out horizontally and then run back again to the same wall. Such as structure is already known from the prior art, i.e. NL-1022586 .
Figure 3 shows a variant 12 wherein horizontal membrane wall parts 13,14 are arranged between each pair of mutually opposite walls. Membrane walls 14 here lie immediately above membrane wall parts 13, thereby creating a constriction 15. Figure 4 shows a third embodiment 16 of a horizontal structure according to the invention. This horizontal structure 16 is shown in perspective view in figure 5.
Pipes 17 bent out of the vertical membrane wall are offset in vertical position relative to each other so that a roof shape is created in cross-section. These horizontal structures 16 lie against walls 18 of the boiler, whereby a constricted opening 19 is created in the centre. The flue gases are forced to pass through constriction 19, whereby a turbulence occurs. The roof shape provides the advantage that less fly ash can accumulate on top of horizontal structure 16, and a more rigid structure is provided.
Figure 6 shows a part of the horizontal structure according to figure 2. It is apparent herefrom that vertical pipes 9, which form part of the membrane walls of the boiler, are bent out horizontally into a horizontal part 10 and cross over to the opposite wall. The pipes are bent alternately out of the membrane wall. The other pipe 19 remains in the vertical membrane wall.
Figure 7 shows a fourth embodiment 20 of a horizontal structure according to the invention. Here a vertical pipe 21 is bent out of the plane of the wall, after which a part 22 continues parallel to this wall. A part 23 is then bent out horizontally and runs to the opposite wall, where it is taken up into the relevant wall. Pipes 24 which are not bent out do not need to be modified in this construction, since the parallel part 22 of bent-out pipe 21 makes it possible to position the horizontal parts such that vertical pipes 24 can continue without modification.

Claims

Horizontal structure in a boiler of for instance an incinerator, which boiler comprises at least two mutually opposite membrane walls, wherein each membrane wall comprises a large number of pipes through which cooling agent flows,
characterized in that
at least one pipe of each of the mutually opposite membrane walls is bent out substantially horizontally and extends to the respective opposite membrane wall, and then continues in vertical direction in the respective opposite membrane wall.
Horizontal structure as claimed in claim 1, wherein a part of the at least one pipe of a vertical membrane wall is bent out of the plane of the vertical membrane wall, a part subsequently runs parallel thereto and is then bent out horizontally.
Horizontal structure as claimed in claim 1 or 2, wherein a number of adjacent pipes are bent out in order to form a horizontal membrane wall in the boiler.
Horizontal structure as claimed in claim 3, wherein the formed horizontal membrane wall has a roof-like cross-section.
Boiler of for instance an incinerator, which boiler has a substantially rectangular cross-section and comprises two pairs of mutually opposite membrane walls, wherein each membrane wall comprises a large number of pipes through which cooling agent flows, wherein at least one horizontal structure as claimed in any of the foregoing claims is formed between at least one pair of mutually opposite membrane walls.
Boiler as claimed in claim 5, comprising two first horizontal structures which each form a horizontal membrane wall and which each lie against a membrane wall of the other pair of membrane walls such that a constriction is formed in the boiler.
Boiler as claimed in claim 6, comprising a number of pipes which are bent out horizontally out of a membrane wall and which run back again into the same membrane wall and are placed between the two horizontal membrane walls such that the boiler is constricted in two horizontal, orthogonal directions.
Boiler as claimed in claim 6, further comprising two second horizontal structures which each form a horizontal membrane wall and which each lie against a membrane wall of the other pair of membrane walls and are arranged immediately above the first horizontal structures such that the boiler is constricted in two horizontal, orthogonal directions.