PREHEATER FOR COMBUSTION AIR, AND A POWER PLANT
A preheating device for combustion air in a boiler. First heat exchanger structures fitted in a flue gas duct heat primary air. A first air supply area in the wall of the flue gas duct supplies air to be heated to the first heat exchanger structures. Second heat exchanger structures fitted in a flue gas duct heat secondary air. A second air supply area in the wall of the flue gas duct supplies air to be heated to the second heat exchanger structures. The first air supply area is opposite the second air supply area. Also a power plant.
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The invention relates to a device for preheating combustion air by flue gas in the boiler of a power plant. Furthermore, the invention relates to a power plant comprising a device for preheating combustion air to be supplied into a boiler by means of flue gas.
BACKGROUND OF THE INVENTIONFor preheating combustion air for a solid fuel boiler, flue gas air preheaters (LUVOs) are typically used, in which the heating medium, i.e. flue gas, flows outside heat exchanger pipes, and the medium to be heated, i.e. air, flows inside the heat exchanger pipes. The heat exchanger pipes are placed horizontally in the flue gas duct, and the heat exchanger units on different levels are connected to each other by air ducts outside the flue gas duct. There are also configurations, in which the flue gas flows inside the pipes and the pipes are vertical.
A typical combustion air preheating device 1 is shown in
Now, a solution has been found which enables a more uniform temperature distribution in the terminal part of the flue gas duct.
To achieve this aim, the combustion air preheating device according to the invention is primarily characterized in what will be presented in the independent claim 1. The power plant according to the invention is, in turn, primarily characterized in what will be presented in the independent claim 8. The other, dependent claims will present some preferred embodiments of the invention.
The basic idea of the invention is to form a preheating device for the combustion air of the boiler by providing the flue gas duct with first heat exchanger structures for heating primary air and second heat exchanger structures for heating secondary air. The inlet of the first heat exchanger structure and the inlet of the second heat exchanger structure are placed substantially on the same level, the level being substantially perpendicular to the central line of the flue gas duct.
In an embodiment, the first heat exchanger structures and the second heat exchanger structures are staggered.
In an embodiment, the first heat exchanger structures and the second heat exchanger structures extend at their air supply areas to the central area of the flue gas duct provided with air flow deflecting structures for changing the direction of air flows of the heat exchangers. The deflecting structure may be, for example, a chamber or a bent pipe.
In an embodiment, the first heat exchanger structures and the second heat exchanger structures are formed of pipes by bending so that the straight portions of the pipes extend both parallel to the central line of the flue gas duct and perpendicular to the central line of the flue gas duct.
A power plant according to the basic idea of the invention comprises at least a boiler and a flue gas duct, into which the flue gases exiting the boiler are led. Furthermore, the plant comprises the above-described preheating device for heating the combustion air to be supplied into the boiler. In an advantageous embodiment, the flue gas duct is vertical, and the flue gases from the boiler are introduced from the upper part of the flue gas duct and discharged from the lower part.
In an embodiment, the first air supply area and the second air supply area are placed substantially at the same height.
In an embodiment, the first air supply area and the second air supply area are the lowermost parts of the preheater which are placed in the flue gas duct.
The different embodiments of the above-described configuration, taken separately and in various combinations, provide various advantages. A single embodiment may comprise one or more of the following advantages depending on its implementation:
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- the distortion of the flue gases can be leveled out;
- the temperature difference between the flue gases and the combustion air can be made as great as possible even in the lowermost pipe rows, in both the front and rear parts of the preheating device;
- the material temperature of the pipe of the preheating device can be raised at the location of the air inlet flow;
- the duct arrangements of the plant are simpler than in conventional configurations;
- in the area of the bent pipe element, problems of vibration of the preheating device are possibly reduced, because in one embodiment, the pipes are tied together in the vertical portion;
in one embodiment, the problems of vibration of the preheating device are reduced, because the bundle comprises a primary air pipe and a secondary air pipe adjacent to each other; vibrations possibly caused by blowers on the primary and secondary air side have different frequencies, wherein they do not amplify each other.
One advantageous embodiment has the advantage that the cold bundles of both primary air and secondary air are placed as a single lowermost bundle. Thus, when replacing a damaged bundle is necessary, only a single bundle has to be replaced. Normally, when e.g. a corrosion problem occurs, it is usually necessary to replace both the lowermost primary and secondary air bundles according to a given schedule. It is particularly difficult to replace the lowermost bundle but one.
In an application according to one embodiment of the invention, an air deflecting chamber in the centre of the primary and secondary air bundles increases advantageously the flow rate of the flue gases at the end part of the flow gas duct, improving the heat transfer on the flue gas side. This contributes to raising the material temperature of the pipes of the preheating device in the most critical cold part and thereby reduces the risk of erosion of the pipes by the effect of the acid dew point.
In an advantageous embodiment, the heat transfer surface of the preheating device consists, in its entirety, of a pipe element extending from the bottom to the top. The elements are made, for example, on a bending line for superheater pipes. Of the adjacent elements, one is for primary air and the other for secondary air. The sizes of the pipes may be equal or different, depending on the reciprocal proportions of primary and secondary air. The pipe spacing may be, for example, typical 75×75 mm, or the spacing can be selected to provide a desired flue gas rate. In addition to the advantages presented above, the structure provides, among other things, the following advantages to conventional configurations:
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- the connecting channels between bundles on the air side are totally eliminated, providing significant cost savings in the manufacture of ducts;
- the elimination of the connecting channels saves space in the boiler room;
- the installation of the preheating device becomes faster, because there is no need to install connecting air channels;
- the preheater device is divided into installation units in the width direction of the preheater device;
- the pressure loss on the air side is smaller than in a conventional preheater device, because the inflows and outflows of pipes between bundles are eliminated;
- the single resistance coefficient on the 90° curve is lower than in inflow or outflow of the pipe. This saves the internal consumption of the boiler.
In the following, the invention will be described in more detail with reference to the appended principle drawings, in which
For the sake of clarity, the drawings only show the details necessary for understanding the invention. The structures and details that are not necessary for understanding the invention but are obvious for anyone skilled in the art have been omitted from the figures in order to emphasize the characteristics of the invention.
DETAILED DESCRIPTION OF THE INVENTIONIn the example of
The heat exchanger structures terminating in the air supply areas 5, 6 are, in the flowing direction of the flue gases F, the last ones of the heat exchanger structures of the preheater 1 placed in the flue gas duct 2. In the examples, the flue gas duct 2 is vertical, and the flue gases F flow downwards from an upper level so that the air supply areas 5, 6 are placed lowermost. In the beginning (that is, in the example, on the upper level), the flue gases F are hotter than in the end (in the example, on the bottom), so that the combustion air P, S can be made hotter when it is heated last before the outlet at the upper part of the preheater 1.
A basic idea of the configuration is that the air supply areas 5, 6 are perpendicularly facing each other on the opposite walls of the flue gas duct 2. In the horizontal flue gas duct 2, this means that the air supply areas 5, 6 are opposite each other, substantially at the same height. If the flue gas duct 2 is in another position, the air supply areas 5, 6 are in the same zone, which zone is perpendicular to the central line 2× of the flue gas duct 2.
The primary air P and secondary air S heated with the preheater 1 are guided with suitable channel structures from the upper part of the preheater into the boiler 7. In the example, the primary air P is supplied to the inlet of fluidized air and the secondary air S is supplied to the air supply level on the wall of the boiler 7. In the preheater 1, the combustion air P, S is heated to a temperature of about 150 to 250° C.
The heat exchangers of the preheater 1 consist of one or more units. In this context, a unit refers to an aggregate, in which the ends of the pipes extend from one wall of the flue gas duct 2 to another wall of the flue gas duct. Preferably, a unit in a vertical flue gas duct 2 comprises 20 to 30 pipes on top of each other and about a hundred pipes adjacent to each other.
Furthermore, one unit may consist of one or more subunits connected to each other. Preferably, a unit consists of two or more subunits. The building up of a preheater to be assembled of several subunits is often easier than the building up of a preheater of a single large unit.
The pipes of the same air circulation can be adjacent to each other, wherein the structure is similar to that of
In an application according to an embodiment of the invention shown in
Preferably, the pipe sections parallel to the central line 2× of the flue gas duct 2 are connected to each other, for example by binding. Thus, possible displacement and vibration of the pipes is reduced, and thereby also problems of vibration of the preheating device 1 are reduced.
In the configuration shown in
Furthermore, for cleaning and maintenance of the preheater 1, the device comprises other structures than the above-described units of the preheater. The figures show sooting means 17, service hatches 18 as well as an ash removal opening 19. Furthermore, the device may also comprise other structures and parts which are not shown in the figures.
In the above-presented examples, the flue gas duct 2 is vertical, and the flue gases F flow downwards from an upper level, so that the air supply areas 5, 6 are placed lowermost. The flue gas duct may also be implemented in another way. For example, in
By combining, in various ways, the modes and structures disclosed in connection with the different embodiments of the invention presented above, it is possible to produce various embodiments of the invention in accordance with the spirit of the invention. Therefore, the above-presented examples must not be interpreted as restrictive to the invention, but the embodiments of the invention may be freely varied within the scope of the inventive features presented in the claims hereinbelow.
Claims
1-13. (canceled)
14. A preheating device for combustion air in a boiler, the device comprising:
- first heat exchanger structures fitted in a flue gas duct for heating primary air, the first heat exchanger structures comprising a set of heat exchanger pipes forming a primary air circulation for primary air flow;
- second heat exchanger structures fitted in the flue gas duct for heating secondary air, the second heat exchanger structures comprising a set of heat exchanger pipes forming a secondary air circulation for secondary air flow;
- an inlet of the first heat exchanger structure for supplying primary air to be heated to the primary air circulation; and
- an inlet of the second heat exchanger structure for supplying secondary air to be heated to the secondary air circulation;
- wherein the inlet of the first heat exchanger structure and the inlet of the second heat exchanger structure are placed substantially on a same level, the same level being substantially perpendicular to a central line of the flue gas duct.
15. The preheating device according to claim 14, further comprising:
- a first air supply area in a wall of the flue gas duct for supplying air to be heated to the first heat exchanger structures, the first air supply area comprising the inlet of the first heat exchanger structure;
- a second air supply area in the wall of the flue gas duct for supplying air to be heated to the second heat exchanger structures, the second air supply area comprising the inlet of the second heat exchanger structure; and
- wherein the first air supply area is opposite the second air supply area.
16. The preheating device according to claim 15, further comprising:
- deflecting structures for the air flow for changing the direction of the air flows of the heat exchangers, wherein the deflecting structures are arranged in a central area of the flue gas duct, and wherein the first heat exchanger structures and the second heat exchanger structures extend at the first air supply area and the second air supply area to the central area of the flue gas duct.
17. The preheating device according to claim 14, wherein the first heat exchanger structures and the second heat exchanger structures are staggered.
18. The preheating device according to claim 14, wherein the heat exchanger pipes are bent such that straight portions of the heat exchanger pipes are placed both parallel to the central line of the flue gas duct and perpendicular to the central line of the flue gas duct.
19. The preheating device according to claim 14, wherein the flue gas duct is vertical, whereby the inlet of the first heat exchanger structure and the inlet of the second heat exchanger structure are located at a same height.
20. A power plant, comprising:
- a boiler;
- a flue gas duct to which flue gases exiting the boiler are led;
- a preheating device for heating combustion air to be supplied into the boiler, the preheating device comprising:
- first heat exchanger structures fitted in the flue gas duct for heating primary air, wherein the first heat exchanger structures comprise a set of heat exchanger pipes forming a primary air circulation for primary air flow,
- second heat exchanger structures fitted in the flue gas duct for heating secondary air, wherein the second heat exchanger structures comprise a set of heat exchanger pipes forming a secondary air circulation for secondary air flow,
- an inlet of the first heat exchanger structure, for supplying primary air to be heated to the primary air circulation, and
- an inlet of the second heat exchanger structure, for supplying secondary air to be heated to the secondary air circulation,
- wherein the inlet of the first heat exchanger structure and the inlet of the second heat exchanger structure are placed substantially on a same level, the same level being substantially perpendicular to a central line of the flue gas duct.
21. The power plant according to claim 20, wherein the preheating device of the power plant further comprises:
- a first air supply area in a wall of the flue gas duct for supplying air to be heated to the first heat exchanger structures, the first air supply area comprising the inlet of the first heat exchanger structure;
- a second air supply area in the wall of the flue gas duct for supplying air to be heated to the second heat exchanger structures, the second air supply area comprising the inlet of the second heat exchanger structure; and
- wherein the first air supply area is opposite the second air supply area.
22. The power plant according to claim 20, wherein the flue gas duct is vertical, whereby the inlet of the first heat exchanger structure and the inlet of the second heat exchanger structure are located at a same height.
23. The power plant according to claim 21, wherein the first air supply area and the second air supply area are lowermost parts of the preheater placed in the flue gas duct.
24. The power plant according to claim 21, wherein the first air supply area and the second air supply area are uppermost parts of the preheater placed in the flue gas duct.
25. The power plant according to claim 22, wherein the flue gases from the boiler are introduced into the flue gas duct from an upper part of the flue gas duct and removed from a lower part.
26. The power plant according to claim 22, wherein the flue gases from the boiler are introduced into the flue gas duct from a lower part of the flue gas duct and removed from an upper part.
Type: Application
Filed: May 21, 2010
Publication Date: Mar 15, 2012
Applicant: Metso Power Oy (Tampere)
Inventor: Timo Mero (Nokia)
Application Number: 13/321,957
International Classification: F23L 15/00 (20060101);