FI87109B - Procedure and arrangement for utilizing waste-gas residual heat - Google Patents

Description

K,, 87109

METHOD AND APPARATUS FOR RECOVERY OF AFTER HEAT FROM FLUE GASES

FARRING REQUIREMENTS FOR TILLVARATAGANDE AV RESTVÄRME UR AVGASER

The present invention relates to a method and apparatus for recovering the residual heat of flue gases after the actual heat recovery boiler in the chimney and / or immediately before introducing the gases into the chimney.

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The method and device according to the invention are suitable, for example, for recovering the residual heat of gases from a gas turbine, a gas engine or another process. The invention is particularly directed to the placement of a residual heating surface or a condensing heating surface 10 in both a new and an existing boiler. The invention also relates to the collection of condensate water and the control of the thermal power.

The flue gases often have to be led from the boiler 15 to the chimney when unnecessarily hot, at a high temperature. This waste heat cannot be recovered economically, for example in old plants, because the flue gases are, however, low-temperature in terms of heat recovery. Final heat recovery requires good contact between the gas and the heating surfaces.

On the other hand, for example in plants where the chimney is built directly on top of the waste boiler, it has not been possible to allow the flue gases to cool below the dew point in the chimney, because condensate would then flow directly down to the waste boiler.

Various solutions have been proposed for recovering final heat in the chimney. German patent application 30 DE 28 03 403 proposes to recover the final heat with a water jacket fitted inside or outside the chimney or with a tubular heat exchanger fitted inside the chimney, adjacent to the wall. This solution does not achieve optimal heat recovery due to poor heat transfer contact when a large portion of the gases flow past the heating surfaces without cooling. The proposed solution is also not suitable for use directly in a chimney to be built on top of the boiler, as condensate would flow directly down into the boiler.

GB 1 438 499 also proposes a double jacketed chimney for cooling flue gases. The aim is to partially prevent condensate from flowing down into the boiler by arranging the diameter of the barrel to be larger than the diameter of the gas inlet, whereby part of the condensate accumulates in the space around the inlet and can be removed therefrom. In this solution, the transfer of heat-15 between the gas and the surrounding jacket is also not optimal. In addition, some of the condensate from the center of the barrel cannot flow back into the gas inlet direction.

European patent application EP 0 042 129 proposes to place a heat exchange package in a side duct next to the chimney so that the gases are partially or completely led from the lower part of the chimney to the side duct and from there further through the heat transfer package back to the chimney. Thus, two large openings for flue gases have to be made in the side duct side 25 of the side pipe. Due to the heat exchanger fitted to one side only, the gas flow in the barrel will be asymmetrical. Fitting a conventional heat transfer package next to one side of the barrel takes up a lot of space.

On the other hand, EP 0 042 129 also proposes to place a heat transfer package in the middle of the barrel so that the barrel is sawn across and a heat transfer package 35 is arranged between the upper and lower part of the barrel thus formed, through which the gases are passed. The gases are directed tortuously past the heat package. The solution is complex and requires both cutting the barrel and re-supporting the heating surfaces and the barrel.

3 87109

The object of the present invention is to provide a simple arrangement of the final heating surfaces also in an existing barrel without breaking the barrel 5.

It is a further object of the invention to provide an arrangement of heating surfaces which achieves a good optimum speed and heat transfer from the gas to the heat transfer medium.

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It is also an object of the invention to provide a space-saving arrangement of heat transfer surfaces which is suitable for installation in existing plants.

To achieve the above objects, the method according to the invention is characterized in that - the gases are led into a housing surrounding the chimney, in which heat recovery surfaces are arranged to recover the residual heat of the gases, and that the cooled gases are led

Preferably, the gases are first led to the lower part 25 of the chimney and then to the chimney wall through lower openings arranged radially substantially around the entire chimney to the lower part of the housing, where the guide plates distribute the gases evenly over the entire heating surface. In the housing, the gases are directed to travel upwards so that they are in heat exchange contact with the heat exchange surfaces, thus transferring their final heat to the heat transfer medium. From the top of the housing, the gases are led back into the chimney through radially substantially upper openings arranged in the chimney wall substantially around the entire chimney.

The gases are thus preferably passed symmetrically outwards into the lower part of the barrel through openings drilled radially or otherwise made. The outer circumference of the barrel. The gases in the housing preferably also pass symmetrically upwards around the barrel past the symmetrically arranged heat transfer surfaces, giving up their final heat. From the top of the housing, the gases are introduced symmetrically into the barrel, 5 from which the gases are allowed to continue up and out of the barrel. There may be about 4 to 16 openings in the barrel wall on each level.

The condensate generated by the cooling of the gas is collected in the housing 10 and removed through connections arranged in the lower part of the housing.

The device according to the invention is thus characterized in that it comprises a housing which is arranged substantially around the chimney and which at the same time acts as a support structure for the chimney; - first openings for the introduction of flue gases into the housing; - second openings for conducting flue gases from the housing to the chimney; 20 - a heating surface fitted in the housing for recovering the heat of the flue gases.

Preferably, the first openings are arranged radially in the lower part of the chimney for conducting flue gases from the chimney to the housing. The second openings are preferably also arranged radially above the first openings for conducting flue gases from the housing back to the chimney.

Guide plates are preferably arranged in the lower part of the housing radially and / or on top of each other in layers to control the flow of 30 gases in the housing. A shut-off or control damper is preferably arranged inside the chimney, by opening which the flue gases can be directed past the housing directly to the top of the chimney, if necessary. In addition, a trough for collecting and draining condensate is preferably arranged in the lower part of the housing.

Thermal surfaces are arranged in the housing between its vertical wall and the barrel wall to recover heat from the gases. The housing can be, for example, a cylinder, a truncated cone, I; 35 5 87109 in the shape of a rectangle or a polygon, but preferably arranged concentrically with the barrel. The diameter of the housing is substantially larger than the diameter of the barrel.

5 The heating surfaces arranged in the housing can be, for example, pipe heating surfaces wound in a spiral around the barrel so that the flue gases flow evenly past the pipes. The tube heating surfaces can be so-called ribbed tubes or formed of smooth tube coils. Quite large pipe lengths can be utilized in the manufacture of the helical surface 10, whereby the proportion of welding work is reduced, provided that the spiral manufacturing technique does not otherwise cause difficulties. Similar heating surfaces are used in the process industry, e.g. in columns and digesters. The heating surfaces may also consist of radially arranged lamella elements around the barrel.

The heating surfaces of the rectangular housing may consist of straight, ribbed or smooth tubular radiators or 20 lamella elements.

The housing can be constructed to transfer the loads of the barrel to the boiler support structures. The heating surfaces are preferably supported on support members of the barrel or housing.

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A flap damper, for example, is fitted to the part surrounded by the housing, which prevents the gas from flowing completely or at least partially directly through the barrel. The flap can act as a control device that affects the heat output of the heat transfer package and / or the gas temperature after the package. With the damper closed, the gases are directed to pass through the openings in the lower part of the barrel into the housing surrounding the barrel and from there through the openings further upwards back into the barrel, thus bypassing the valve point in the barrel. 35 If necessary, the damper can be opened and the gases allowed to flow directly through the barrel.

The hole field at the bottom of the housing can be equipped with a 6 87109 adjusting device with which the area of the holes can be adjusted. At the same time, the amount of gas and the heat output of the heat transfer package are adjusted.

If desired, the housing can be divided into isolated radial sections, whereby the gas flow is correspondingly divided into sub-streams which are directed to pass through certain housing sections without mixing with each other. The housing can also be formed of parts that can be closed one by one and direct the gas flow to pass past the desired parts and heat transfer surfaces. This allows the gas cooling to be adjusted. The solution according to the invention is well suited for use in recovering the final heat of the gases of existing boilers. Final heat recovery can be achieved without cutting the barrel or other substantial changes. The invention is particularly advantageous compared to other previously known solutions in boilers in which the barrel is placed directly on top of the boiler and in which further cooling of the gas would easily cause condensate to flow down into the boiler. In the housing around the barrel, the condensate can be easily arranged on the bottom of the housing.

In general, the convective heat transfer in the last heating surface of a conventional gas turbine heat recovery boiler is quite poor due to the low flow rate. In the construction according to the invention, the surface can be optimized for a suitable flow rate, which reduces the required heating surface.

The solution according to the invention further achieves e.g. the following advantages: - easy placement of the heating surfaces in existing plants, whereby the heating surfaces can be placed so that they rest directly on the barrel support steels; 35 - the housing can also act as a barrel support structure so that the forces are applied by the housing directly to the steel structure; - the perforated field drilled or otherwise provided by the pipe and the flow distribution plates 7 87109 below the heat exchanger package allow the gas flow to be evenly distributed regardless of the geometry of the housing; - the heat exchanger package is positioned so that any condensed water can be collected and utilized e.g.

5 into the combustion chamber of the gas turbine as injection water to reduce NOx without flowing back into the boiler; - the part of the barrel remaining in the housing can act as a bypass channel to the heating surface, whereby, for example in temporary oil combustion, the residual heating surface can be bypassed unnecessarily and the gas 10 does not cool too much and there is no risk of sulfur corrosion; - the perforated field in the barrel can easily be equipped with a control device to direct the gas to the desired destination in each case.

The invention will now be described in more detail with reference to the accompanying drawings, in which - Figure 1 schematically shows a device according to the invention arranged on a waste heat boiler for recovering final heat from gases; Fig. 2 shows a section along the line A-A in Fig. 1; Figure 3 shows an enlarged view of a second embodiment of a device according to the invention; Fig. 3a shows a section along the line A-A in Fig. 3; Fig. 4 shows a section similar to Fig. 3a of a third embodiment of a device according to the invention; Figure 5 shows a fourth embodiment of a device according to the invention; and Fig. 6 shows a section along the line A-A in Fig. 5.

Figure 1 shows a vertical waste heat boiler 10, from the top of which the flue gases are led to a chimney 12 arranged on the boiler. A device 16 according to the invention for recovering the final heat of the flue gases is arranged around the lower part 14 of the chimney. In the embodiment 35 according to Fig. 1, the device is mainly formed by a frustoconical housing 16 and a heat transfer surface fitted thereto. The housing can also be rectangular or cube-shaped or, for example, cylindrical. In the embodiment according to Fig. 8 87109, the diameter of the lower part of the housing is larger than the diameter of its upper part.

The waste heat boiler is supported by steel beams 18, which also support the barrel 12 and the housing 16. The flue gases are led through an opening 20 to a waste heat boiler, the walls 22 of which are formed of plate structures and / or water pipe panels. In addition, other heat transfer surfaces 23 are arranged in the waste boiler. The flue gases are led from the boiler to the chimney 10 from a gas outlet 24 arranged at the top thereof.

The chimney 12 is arranged on the waste heat boiler parallel to its degassing opening 24, whereby the flue gases first flow from the boiler to the lower part 15 of the chimney 26. The wall 28 of the lower part of the chimney is radially provided with openings 30 through parts. In the housing, the flue gases flow upwards past the heating surfaces 32 arranged in the housing, whereby the final heat of the flue gases 20 is transferred to the heat transfer medium flowing in the heating surfaces. Heat transfer interval The medium can be, for example, feed water, which can be connected to the boiler feed-water system, or district heating water or some other liquid or gaseous heat transfer medium.

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A second row of openings 34 is arranged in the chimney wall substantially radially at the height of the upper part of the housing, from which the flue gases are led back to the chimney. Inside the chimney, a flap valve 36 is arranged between the openings 30 and 34, by means of which the flow of gas inside the chimney is blocked by the part between the openings 30 and 34. In this way, the flue gases can be directed into the bypass duct formed by the housing and they are made to transfer their final heat to the heating surfaces therein.

Figure 2 shows the lower part 14 of the chimney and the housing 16 in section from Figure 1 at A-A. It can be seen from the figure that the openings 34 are equal to each other and arranged 35 symmetrically and equally spaced in the wall 28. The heat transfer surfaces 32 are shown only schematically. The openings 34 do not necessarily have to be equal in size. They may be round, oval, rectangular or the like. They do not have to be symmetrical and do not have to be arranged in the barrel wall at equal intervals.

The lower base 38 of the housing is inclined, so that any water condensing from the flue 10 flows to the lowest point of the base, in this case to the circumference of the housing, from where it can be removed by the joint 40.

Figures 3, 3a and 4 show two embodiments of the invention which are different with respect to the heat transfer surface. In the figures, the same reference numerals as in Figure 1 have been used, where applicable. The heating surfaces 33 placed in the housing in the embodiment according to Figure 4 are formed of lamellar elements and arranged radially around the barrel. In the embodiment shown in Figures 20 3 and 3a, the heating surfaces 32 are formed of a helically wound heat transfer tube 42, whereby large tube lengths can be arranged in a small space with minor welds.

In the lower part of the housing 16, in Fig. 3, overlapping guide plates 44 are arranged to guide the flue gas towards the heat transfer pipes 42 in the desired manner. The baffles 45 can also be arranged radially in the housing as shown in Fig. 4.

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Figures 5 and 6 show an embodiment of the invention with a different housing structure. Also in these figures, where applicable, the same reference numerals as in Figure 1 have been used. In this embodiment, the housing 16 is partially divided into two substantially elongate, rectangular spaces 46 and 48 connected to a chimney on either side thereof.

Arrangements 50 and 52 10 87109 are arranged in the wall of the lower part of the chimney to direct the flue gases to both parts 46 and 48 of the housing. The openings are arranged in two opposite walls of the chimney. The openings do not necessarily have to be arranged evenly over the entire circumference of the barrel. The openings direct the 5 gases mainly to the two opposite sides of the barrel. The openings 50 on the first side of the chimney direct the flue gases to the first part 46 of the housing and the openings 52 on the other side of the chimney direct the flue gases to the second part 48. The housing elongate parts 46 and 48 are provided with heat transfer surfaces 10 which may be heat transfer packages 54 and 56. thus, in the embodiment, ready-made heat transfer packages can be utilized.

In some cases, the housing 15 arranged around the chimney can be positioned so that the flue gases are fed directly from the waste heat boiler to the housing and not through the lower part of the chimney. In this case, it may be necessary to control the flue gases with baffles so that they flow evenly past the heat transfer surfaces.

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The openings fitted in the chimney may be provided with closing devices which allow the open area of the openings to be adjusted as required.

The invention is not intended to be limited to the embodiments described above, but can be applied in the most varied ways within the scope of the inventive idea limited by the appended claims.

Claims (22)

A process for recovering residual heat from hot gases in a chimney or immediately before introducing it into the chimney, characterized in that: - the cooled gases are conducted from the stove into the chimney through radially substantially openings arranged throughout the chimney in the wall of the chimney. Method according to claim 1, characterized in that. 15. the gases are first directed to the lower part of the chimney and thence further through radially substantially radially substantially all around the chimney arranged into the lower part of the chimney in the wall of the chimney; - the gases in the chimney are fed up in heat exchange contact with 20 heat exchange surfaces and, - the gases from the upper part of the chimney are led back to the chimney through radially arranged substantially in the chimney wall around the entire chimney. 25 Method according to claim 1 or 2, characterized by •. that: the condensate sorti condenses from the flue gases collected in the stove and is removed from the stove from its lower part. 1 4. Apparatus for the recovery of residual heat from flue gases according to the actual heat recovery boiler, characterized therein. comprising: - a chute (16,46,48) arranged substantially around the chimney (12); : - 35 - first openings (30,50,52) for introducing the flue gases into the hood; - other openings (34) for introducing the flue gases from the stove into the chimney; 87109 - a heating surface (32,33,42,54,56) arranged in the cap for recovering heat from the flue gases. 5. Apparatus according to claim 4, characterized in that the first openings (30,50,52) of the chimney are provided in the lower part (26) for introducing the flue gases from the chimney into the chimney and that above the first openings are second openings (34). arranged for conducting the flue gases from the stove back into the chimney. 10 Device according to claim 4, characterized in that the first and second openings (30, 34) are arranged radially around the chimney in the wall of the chimney. 7. Apparatus according to claim 4, characterized in that the cover (16) is cylindrical and the space between the cover and the wall (28) of the chimney forms a space in which heating surfaces (32, 33, 42) are arranged. 8. Device according to claim 7, characterized in that the cylindrical casing is arranged around the chimney concentrically therewith. Device according to claim 4, characterized in that the cover (16) is in the form of a truncated cone and is concentrically arranged around the chimney. Device according to claim 4, characterized in that the cover (46, 48) has a square shape. 30. ·. Device according to claim 4, characterized in that the cover is divided into two separate parts (46, 48) and that the openings (50) on one side of the chimney periphery interfere with one part of the cover part (46). ... · 35 and the openings (52) on the other side of the periphery with. the second portion (48) of the cap. 87109 12. Device according to claim 4, characterized in that the cover is divided by guide plates (45) into several different parts, arranged around the periphery of the chimney, and that apertures are provided on the periphery of the chimney, which direct the gases to the different cover parts. 13. Apparatus according to claim 4, characterized in that the bottom (38) of the cover is inclined and a connection (40) is provided at its lowest location for removing the condensate from the flue gas. Device according to claim 4, characterized in that the heating surface (42) arranged in the cap is made of tubular plate. Device according to claim 14, characterized in that. a heating tube (42) is wound in a spiral around the chimney inside the housing. 16. Apparatus according to claim 14, characterized in that the heating surface provided in the cap is a tube plate provided with flanges. 17, Device according to claim 4, characterized in that. that the heating surface provided in the cap consists of smooth tube batteries (54.56). Device according to claim 4, characterized in that. that the heating surface provided in the housing consists of slat elements: (33), which are arranged in the housing radially around the chimney. 30 : 19. Device according to claim 4, characterized in that: ··. that the chimney is arranged on top of a heat recovery boiler so that the flue gases can flow straight up from the boiler to the lower part of the chimney, and that the stove is arranged around the chimney immediately on the heat recovery boiler. Apparatus according to claim 5, characterized in that between the first and second openings (30, 34) arranged inside the chimney is provided an adjustable damper plate (36) which partially or completely prevents the flue gases from flowing through the space between the first and the other openings. 5 21. Apparatus according to claim 4, characterized in that it comprises radial and / or control plates (44) arranged for conducting the gas evenly past the heating surfaces. 22. Device according to claim 4, characterized in that the first and / or the second openings are provided with closing devices by which the open area of the openings can be controlled. 15