US20130008394A1 - Radiant Superheater - Google Patents
Radiant Superheater Download PDFInfo
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- US20130008394A1 US20130008394A1 US13/178,570 US201113178570A US2013008394A1 US 20130008394 A1 US20130008394 A1 US 20130008394A1 US 201113178570 A US201113178570 A US 201113178570A US 2013008394 A1 US2013008394 A1 US 2013008394A1
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- pass
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- steam
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F22—STEAM GENERATION
- F22G—SUPERHEATING OF STEAM
- F22G1/00—Steam superheating characterised by heating method
- F22G1/06—Steam superheating characterised by heating method with heat supply predominantly by radiation
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F22—STEAM GENERATION
- F22G—SUPERHEATING OF STEAM
- F22G1/00—Steam superheating characterised by heating method
- F22G1/06—Steam superheating characterised by heating method with heat supply predominantly by radiation
- F22G1/08—Steam superheating characterised by heating method with heat supply predominantly by radiation from heated brickwork or the like
Definitions
- the present invention relates to a radiant superheater. More particularly, the present invention relates to a radiant superheater arranged to hang at the upper portion of a furnace of a boiler, especially, of a supercritical or ultra supercritical pulverized coal firing boiler.
- SH superheaters
- heat exchangers in which the temperature of high pressure steam produced in an evaporator is raised above the saturation temperature.
- Superheated steam is then conducted to a high pressure steam turbine to produce steam power.
- Many boilers also comprise a reheater, in which the temperature of lower pressure steam released from the high pressure steam turbine is raised again, in order to produce more power by an intermediate pressure steam turbine.
- reheater in which the temperature of lower pressure steam released from the high pressure steam turbine is raised again, in order to produce more power by an intermediate pressure steam turbine.
- the term “superheater” may refer to either an actual superheater or a reheater.
- supercritical (SC) boiler refers to a boiler having a steam temperature of at least about 550° C.
- USC ultra supercritical
- a power boiler comprises a superheater system consisting of multiple in-series-connected superheater sections, which are located in different parts of the boiler.
- Superheaters are generally called convective superheaters (CSH), into which heat is mainly conducted by hot flue gas, or radiant superheaters (RSH), which dominantly absorb heat by radiation.
- CSH convective superheaters
- RSH radiant superheaters
- Radiant superheaters are arranged at the top of the furnace of a boiler to be in direct visibility to the flames in the furnace.
- the duty of the RSH is substantially greater than that for a supercritical boiler.
- a series RSH arrangement is often used to obtain the required steam enthalpy.
- the metal tube temperature of an RSH depends on the local heat flux and on the temperature of the steam flowing in the tube. The metal temperature can be especially high at the bottom of a radiant SH, facing the flame zone.
- Superheating of saturated steam is usually started in a CHS arranged in the flue gas channel downstream of the furnace.
- the steam usually goes to an RSH arranged at the upper portions of the furnace.
- the RSH may comprise pendant tube coils or hanging panels of tubes, or divisional tubewalls arranged parallel to the flue gas flow.
- Steam leaving the RSH usually goes to an attemperator, where water is sprayed onto the steam, to bring down the steam temperature to its desired value.
- steam finally goes to a pendant superheater (PSH) arranged behind the nose of the furnace or in a horizontal pass immediately downstream of the furnace for further superheating the steam before it leaves to a high pressure (HP) turbine.
- PSH pendant superheater
- Steam exiting the HP turbine may be conducted back to the furnace for being re-superheated to the desired temperature in a reheater (RH). Steam, after being reheated, flows to the intermediate pressure (IP) turbine for further expansion.
- RH is usually arranged in the horizontal pass downstream of the PSH, but it may, as well as the PSH for final superheating, in some cases, also be arranged as a radiant superheater at the top portion of the furnace.
- German Patent No. 1012614 discloses an arrangement in which the tubes of a radiant superheater are protected from overheating by special shield tubes leading steam to a convective superheater.
- Great Britain Patent No. 855,114 discloses a boiler having superheater tubes, closest to the flame in the furnace, protected from radiation by reheater tubes surrounding the superheater tubes. It is also known from U.S. Pat. No.
- An object of the present invention is to provide a radiant superheater by which the problems of the prior art mentioned above are minimized.
- the present invention provides a radiant superheater arranged to hang at the upper portion of the furnace of a boiler, wherein the radiant superheater is substantially planar and comprises a first vertical pass, a first connection pass, a second vertical pass, a third vertical pass, a second connection pass and a fourth vertical pass, each vertical pass comprising an upper end and a lower end.
- the vertical passes are connected in series, so that steam to be superheated enters at the upper end of the first vertical pass and flows through the first vertical pass and from the lower end of the first vertical pass via the first connection pass, to the lower end of the second vertical pass and through the second vertical pass, and from the upper end of the second vertical pass to the upper end of the third vertical pass and through the third vertical pass, and from the lower end of the third vertical pass via the second connection pass to the lower end of the fourth vertical pass and through the fourth vertical pass, to be discharged from the upper end of the fourth vertical pass.
- the first connection pass is arranged below the second connection pass, so as to shield the second connection pass from radiation from the lower portion of the furnace.
- a flow of relatively low temperature steam comes from a primary, convective superheater (CSH), arranged in the flue gas channel to the first vertical pass of the radiant superheater (RSH). Due to the continuous radiant heating of the RSH, the average temperature of the steam is constantly increasing when the steam is flowing from the first vertical pass up to the fourth vertical pass. Therefore, the temperature of the steam in the first connection pass is lower than that of the steam in the second connection pass. Correspondingly, even if the level of radiation at the outer pass is at its maximum, the metal temperature of the outer pass can be maintained at an acceptable level, due to the relatively low temperature of the steam flowing in the first connection pass.
- CSH convective superheater
- RSH radiant superheater
- the first vertical pass and the second vertical pass are arranged to surround the fourth vertical pass and the third vertical pass in a horizontal direction, so as to, in the horizontal direction, shield the fourth vertical pass and the third vertical pass from the radiation.
- the first and second vertical passes and the first connection pass inside of which, flows a relatively low temperature steam
- the third and fourth vertical pass and the second connection pass inside of which, flows a higher temperature steam.
- the most intense radiation from the flames is in all relevant directions directed to the tubes of the first and second vertical passes and of the first connection pass, whereby the peak metal temperature of a radiative superheater is reduced. This is particularly important in an SC or a USC boiler, where steam of an especially high temperature is generated.
- each of the first vertical pass, the first connection pass, the second vertical pass, the third vertical pass, the second connection pass and the fourth vertical pass comprises multiple parallel steam tubes.
- the multiple parallel steam tubes of the first vertical pass, the first connection pass and the second vertical pass preferably form continuous U-tubes, i.e., each of the multiple parallel steam tubes of the first vertical pass are in steam flow connection to one of the multiple parallel steam tubes of the first connection pass, and each of the multiple parallel steam tubes of the first connection pass are in steam flow connection to one of the multiple parallel steam tubes of the second vertical pass.
- the multiple parallel steam tubes of the third vertical pass, the second connection pass and the fourth vertical pass preferably form continuous U-tubes, i.e., each of the multiple parallel steam tubes of the third vertical pass are in steam flow connection to one of the multiple parallel steam tubes of the second connection pass, and each of the multiple parallel steam tubes of the second connection pass are in steam flow connection to one of the multiple parallel steam tubes of the fourth vertical pass.
- the second vertical pass and the third vertical pass are connected in series in such a way that steam flows from the upper end of the second vertical pass via a third connection pass to the upper end of the third vertical pass, in which the third connection pass comprises multiple parallel steam tubes.
- the third connection pass may be arranged above the roof of the furnace, but preferably, it is arranged within the furnace, in order to absorb heat also in the third connection pass.
- each of the multiple parallel steam tubes of the second vertical pass are in steam flow connection to one of the multiple parallel steam tubes of a third connection pass, and each of the multiple parallel steam tubes of the third connection pass are in steam flow connection to one of the multiple parallel steam tubes of the third vertical pass.
- the multiple parallel steam tubes of the second vertical pass, the third connection pass and the third vertical pass form multiple parallel inverted U-tubes.
- the above-mentioned way of connecting the tubes provides the advantage that tubes that are at the outer edge of the second vertical pass, i.e., those that receive the most radiation heat, continue as tubes at the inner edge of the third vertical pass, i.e., they receive the least amount of radiation heat. In this way, the heat pick-up of the tubes is balanced.
- the upper end of each of the multiple parallel steam tubes of the second vertical pass is connected to a first header arranged above the roof of the furnace
- the upper end of each of the multiple parallel steam tubes of the third vertical pass is connected to a second header arranged above the roof
- the first header is in steam flow connection with the second header by a connecting pipe arranged above the roof.
- the connecting pipe comprises a water attemperator, whereby it is possible to adjust the temperature of the steam to a desired level before it enters the third vertical pass.
- the first vertical pass is arranged adjacent to the front end side of the boiler, and the second vertical pass is arranged adjacent to the back end side of the boiler.
- the radiant superheater also partially acts as a convection superheater
- the use of the above-mentioned arrangement provides the advantage that flue gas mainly flowing from the front end side towards an exit at the back end side hits first the first vertical pass, where the steam temperature is the lowest. Thereby, the risk of overheating the second vertical pass is minimized.
- the fourth vertical pass is arranged adjacent to the first vertical pass, and the third vertical pass is arranged adjacent to the second vertical pass.
- the final temperature of the steam is raised. It is also possible, and in some applications, advantageous, to switch the third and the fourth vertical passes, i.e., to arrange the third vertical pass adjacent to the first vertical pass and the fourth vertical pass adjacent to the second vertical pass.
- the radiant superheater is advantageously an intermediate superheater arranged in steam flow direction upstream of a high pressure steam turbine. This means that hot steam from the superheater is led to a finishing superheater before it is conducted to the high pressure steam turbine.
- the superheater may be a finishing superheater, from which the steam is directly conducted to a high pressure steam turbine.
- the radiant superheater is an intermediate or finishing reheater, i.e., a superheater arranged in the steam flow between a high pressure steam turbine and an intermediate pressure steam turbine.
- the present invention relates to a consideration of the metal temperature of a radiant superheater by having the highest local heat flux combined with a relatively low steam temperature inside the tube.
- a new approach is provided based on inserting the second portion of an RSH, i.e., the third and fourth vertical passes and the second connection pass, inside the first portion of the RSH, i.e., inside the first and second vertical passes and the first connection pass.
- the first portion of the RSH is used to protect the second portion of the RSH from radiation from any relevant direction.
- the first portion of the RSH, with relatively colder fluid inside acts as an outer platen
- the second portion of the RSH, with higher temperature fluid inside acts as the inner platen.
- a complete RSH may comprise several parallel elements, each comprising a series of passes, as described above.
- the metal temperatures will be reduced, thus allowing a lower cost tube material, or thinner minimum wall thickness, be used in the RSH.
- the superheating system of a boiler comprises two or more radiant superheaters, as described above, connected in series.
- FIG. 1 is a schematic diagram of a boiler with a radiant superheater according to an embodiment of the present invention.
- FIG. 2 is a schematic diagram of a boiler with a radiant superheater according to another embodiment of the present invention.
- FIG. 1 schematically shows a pulverized coal firing supercritical or ultrasupercritical boiler 10 in accordance with a first embodiment of the present invention.
- the boiler comprises a furnace 12 with water-cooled enclosure walls 14 and a roof 16 .
- burners 18 for firing pulverized coal and producing a flame zone 20 into the furnace 12 .
- From the flame zone 20 is conducted heat by radiation 22 and by hot flue gases 24 .
- the upper portion of the furnace 12 comprises a hanging radiant superheater 26 , in which steam is superheated, to be finally conducted to a steam turbine (not shown) to generate power.
- Horizontal pass 28 immediately downstream of the furnace 12 comprises further hanging superheaters, such as finishing superheaters 30 .
- the radiant superheater 26 comprises one or more substantially planar, in parallel connected superheating elements 32 , each of which comprises a first vertical pass 34 , a first connection pass 36 , a second vertical pass 38 , a third vertical pass 40 , a second connection pass 42 and a fourth vertical pass 44 .
- the first connection pass 36 and the second connection pass 42 are advantageously horizontal, but they may, in some applications, also be of another form, for example, half-circles.
- Steam to be superheated in the radiant superheater 26 is conducted, usually, from a convective superheater (not shown), along a feed pipe 46 to an inlet header 48 , which is arranged at the upper end of the first vertical pass 34 .
- heated steam is conducted via an outlet header 50 , arranged at the upper end of the fourth vertical pass 44 , along a discharge pipe 52 to the next stage.
- the next stage may be a finishing superheater 30 or, if the radiant superheater 26 is a finishing superheater, a steam turbine (not shown).
- the steam turbine is a high pressure steam turbine, but when the radiant superheater 26 is a reheater, the steam turbine is an intermediate pressure steam turbine.
- the steam to be superheated is distributed to multiple parallel steam tubes 54 running as U-tubes through the first vertical pass 34 , the first connection pass 36 and the second vertical pass 38 to an intermediate header, a so-called first header 56 , arranged at the upper end of the second vertical pass 38 .
- first header 56 the steam flows via a connecting pipe 58 to a second header 60 arranged at the upper end of the third vertical pass 40 .
- the connecting pipe 58 advantageously comprises a water attemperator 62 , by which it is possible to adjust the temperature of the steam to a desired level before it enters the third vertical pass 40 .
- the superheating system may comprise further water attemperators 64 upstream or downstream of the radiant superheater 26 .
- the steam is again distributed to multiple parallel steam tubes 66 running as U-tubes through the third vertical pass 40 , the second connection pass 42 and the fourth vertical pass 44 , to the outlet header 50 .
- the second connection pass 42 is arranged above the first connection pass 36 , so that the first connection pass 36 shields the second connection pass 42 from radiation from the lower portion of the furnace 12 .
- the first vertical pass 34 and the second vertical pass 38 are correspondingly arranged to surround the fourth vertical pass 44 and the third vertical pass 40 .
- FIG. 2 shows another critical or supercritical boiler 10 ′ that comprises a radiant superheater 26 ′, which is slightly modified from that shown in FIG. 1 .
- the radiant superheater 26 ′ comprises a first vertical pass 34 , a first connection pass 36 , a second vertical pass 38 , a third vertical pass 40 , a second connection pass 42 and a fourth vertical pass 44 , as the radiant superheater 26 shown in FIG. 1 .
- an inlet header 48 and an outlet header 50 are provided as in the embodiment shown in FIG. 1 , but there are no in intermediate headers therebetween. Instead, the multiple parallel steam tubes of the second vertical pass 38 and the third vertical pass 40 are mutually connected by parallel steam tubes 68 of a third connection pass 70 .
- the third connection pass 70 is here arranged within the furnace 12 , but it may, in some applications, also be located above the roof 16 of the furnace 12 .
- the use of a third connection pass 70 provides the advantage that the outer steam tubes of the second vertical pass 38 are turned as inner tubes of the third vertical pass 40 , which balances the heat absorption in the steam tubes.
- the radiant superheater is advantageously applied in a supercritical or an ultrasupercritical boiler, but it may, if desired, also be applied in a subcritical boiler.
Abstract
A radiant superheater arranged to hang at the upper portion of a furnace of a boiler. The radiant superheater is substantially planar and includes a first vertical pass, a first connection pass, a second vertical pass, a third vertical pass, a second connection pass, and a fourth vertical pass. Each vertical pass includes an upper end and a lower end. The vertical passes are connected in series, so that steam to be superheated enters at the upper end of the first vertical pass and flows through the first vertical pass and from the lower end of the first vertical pass via the first connection pass to the lower end of the second vertical pass and through the second vertical pass and from the upper end of the second vertical pass to the upper end of the third vertical pass and through the third vertical pass and from the lower end of the third vertical pass via the second connection pass to the lower end of the fourth vertical pass and through the fourth vertical pass, to be discharged from the upper end of the fourth vertical pass. The first connection pass is arranged below the second connection pass so as to shield the second connection pass from radiation from the lower portion of the furnace.
Description
- 1. Field of the Invention
- The present invention relates to a radiant superheater. More particularly, the present invention relates to a radiant superheater arranged to hang at the upper portion of a furnace of a boiler, especially, of a supercritical or ultra supercritical pulverized coal firing boiler.
- 2. Description of the Related Art
- In practice, all power boilers of today have superheaters (SH), i.e., heat exchangers, in which the temperature of high pressure steam produced in an evaporator is raised above the saturation temperature. Superheated steam is then conducted to a high pressure steam turbine to produce steam power. Many boilers also comprise a reheater, in which the temperature of lower pressure steam released from the high pressure steam turbine is raised again, in order to produce more power by an intermediate pressure steam turbine. In the following, the term “superheater” may refer to either an actual superheater or a reheater. The term supercritical (SC) boiler refers to a boiler having a steam temperature of at least about 550° C., whereas, for ultra supercritical (USC) boilers, the steam temperature is at least about 600° C. The use of increased superheat and reheat temperatures improves the cycle, and thus, the plant efficiency.
- Usually, a power boiler comprises a superheater system consisting of multiple in-series-connected superheater sections, which are located in different parts of the boiler. Superheaters are generally called convective superheaters (CSH), into which heat is mainly conducted by hot flue gas, or radiant superheaters (RSH), which dominantly absorb heat by radiation. Radiant superheaters are arranged at the top of the furnace of a boiler to be in direct visibility to the flames in the furnace. For SC and USC pulverized coal firing boilers, the duty of the RSH is substantially greater than that for a supercritical boiler. Thus, a series RSH arrangement is often used to obtain the required steam enthalpy. The metal tube temperature of an RSH depends on the local heat flux and on the temperature of the steam flowing in the tube. The metal temperature can be especially high at the bottom of a radiant SH, facing the flame zone.
- Superheating of saturated steam is usually started in a CHS arranged in the flue gas channel downstream of the furnace. From the CHS, the steam usually goes to an RSH arranged at the upper portions of the furnace. The RSH may comprise pendant tube coils or hanging panels of tubes, or divisional tubewalls arranged parallel to the flue gas flow. Steam leaving the RSH usually goes to an attemperator, where water is sprayed onto the steam, to bring down the steam temperature to its desired value. From the attemperator, steam finally goes to a pendant superheater (PSH) arranged behind the nose of the furnace or in a horizontal pass immediately downstream of the furnace for further superheating the steam before it leaves to a high pressure (HP) turbine. Steam exiting the HP turbine may be conducted back to the furnace for being re-superheated to the desired temperature in a reheater (RH). Steam, after being reheated, flows to the intermediate pressure (IP) turbine for further expansion. The RH is usually arranged in the horizontal pass downstream of the PSH, but it may, as well as the PSH for final superheating, in some cases, also be arranged as a radiant superheater at the top portion of the furnace.
- Due to high flame temperature in the furnace, the durability of radiant superheaters may suffer from overheating. German Patent No. 1012614 discloses an arrangement in which the tubes of a radiant superheater are protected from overheating by special shield tubes leading steam to a convective superheater. Great Britain Patent No. 855,114 discloses a boiler having superheater tubes, closest to the flame in the furnace, protected from radiation by reheater tubes surrounding the superheater tubes. It is also known from U.S. Pat. No. 3,101,698 to make a platen superheater behind a furnace nose, in which third and fourth passes are arranged partially in parallel flow, i.e., so that horizontal radiation is directed to tubes of a third pass, which are in flue gas flow upstream of the fourth pass, to prevent overheating of the hotter outlet tube sections.
- The above-mentioned prior art solutions may adversely alter the heat duty among the superheating stages, and thus, lower the thermal efficiency of the boiler, or they address primarily convective dominant heat transfer. Therefore, there still exists a need for an improved radiant superheater.
- An object of the present invention is to provide a radiant superheater by which the problems of the prior art mentioned above are minimized.
- According to one aspect, the present invention provides a radiant superheater arranged to hang at the upper portion of the furnace of a boiler, wherein the radiant superheater is substantially planar and comprises a first vertical pass, a first connection pass, a second vertical pass, a third vertical pass, a second connection pass and a fourth vertical pass, each vertical pass comprising an upper end and a lower end. The vertical passes are connected in series, so that steam to be superheated enters at the upper end of the first vertical pass and flows through the first vertical pass and from the lower end of the first vertical pass via the first connection pass, to the lower end of the second vertical pass and through the second vertical pass, and from the upper end of the second vertical pass to the upper end of the third vertical pass and through the third vertical pass, and from the lower end of the third vertical pass via the second connection pass to the lower end of the fourth vertical pass and through the fourth vertical pass, to be discharged from the upper end of the fourth vertical pass. The first connection pass is arranged below the second connection pass, so as to shield the second connection pass from radiation from the lower portion of the furnace.
- Generally, a flow of relatively low temperature steam comes from a primary, convective superheater (CSH), arranged in the flue gas channel to the first vertical pass of the radiant superheater (RSH). Due to the continuous radiant heating of the RSH, the average temperature of the steam is constantly increasing when the steam is flowing from the first vertical pass up to the fourth vertical pass. Therefore, the temperature of the steam in the first connection pass is lower than that of the steam in the second connection pass. Correspondingly, even if the level of radiation at the outer pass is at its maximum, the metal temperature of the outer pass can be maintained at an acceptable level, due to the relatively low temperature of the steam flowing in the first connection pass.
- According to a preferred embodiment of the present invention, the first vertical pass and the second vertical pass are arranged to surround the fourth vertical pass and the third vertical pass in a horizontal direction, so as to, in the horizontal direction, shield the fourth vertical pass and the third vertical pass from the radiation. Thereby, the first and second vertical passes and the first connection pass, inside of which, flows a relatively low temperature steam, are arranged outside the third and fourth vertical pass and the second connection pass, inside of which, flows a higher temperature steam. Thus, the most intense radiation from the flames is in all relevant directions directed to the tubes of the first and second vertical passes and of the first connection pass, whereby the peak metal temperature of a radiative superheater is reduced. This is particularly important in an SC or a USC boiler, where steam of an especially high temperature is generated.
- Usually, each of the first vertical pass, the first connection pass, the second vertical pass, the third vertical pass, the second connection pass and the fourth vertical pass comprises multiple parallel steam tubes. The multiple parallel steam tubes of the first vertical pass, the first connection pass and the second vertical pass preferably form continuous U-tubes, i.e., each of the multiple parallel steam tubes of the first vertical pass are in steam flow connection to one of the multiple parallel steam tubes of the first connection pass, and each of the multiple parallel steam tubes of the first connection pass are in steam flow connection to one of the multiple parallel steam tubes of the second vertical pass. Correspondingly, the multiple parallel steam tubes of the third vertical pass, the second connection pass and the fourth vertical pass preferably form continuous U-tubes, i.e., each of the multiple parallel steam tubes of the third vertical pass are in steam flow connection to one of the multiple parallel steam tubes of the second connection pass, and each of the multiple parallel steam tubes of the second connection pass are in steam flow connection to one of the multiple parallel steam tubes of the fourth vertical pass.
- According to a first preferred embodiment of the present invention, the second vertical pass and the third vertical pass are connected in series in such a way that steam flows from the upper end of the second vertical pass via a third connection pass to the upper end of the third vertical pass, in which the third connection pass comprises multiple parallel steam tubes. The third connection pass may be arranged above the roof of the furnace, but preferably, it is arranged within the furnace, in order to absorb heat also in the third connection pass. Advantageously, each of the multiple parallel steam tubes of the second vertical pass are in steam flow connection to one of the multiple parallel steam tubes of a third connection pass, and each of the multiple parallel steam tubes of the third connection pass are in steam flow connection to one of the multiple parallel steam tubes of the third vertical pass. Thus, the multiple parallel steam tubes of the second vertical pass, the third connection pass and the third vertical pass form multiple parallel inverted U-tubes. Thus, the above-mentioned way of connecting the tubes provides the advantage that tubes that are at the outer edge of the second vertical pass, i.e., those that receive the most radiation heat, continue as tubes at the inner edge of the third vertical pass, i.e., they receive the least amount of radiation heat. In this way, the heat pick-up of the tubes is balanced.
- According to a second preferred embodiment of the present invention, the upper end of each of the multiple parallel steam tubes of the second vertical pass is connected to a first header arranged above the roof of the furnace, the upper end of each of the multiple parallel steam tubes of the third vertical pass is connected to a second header arranged above the roof, and the first header is in steam flow connection with the second header by a connecting pipe arranged above the roof. Preferably, the connecting pipe comprises a water attemperator, whereby it is possible to adjust the temperature of the steam to a desired level before it enters the third vertical pass.
- According to a further preferred embodiment of the present invention, the first vertical pass is arranged adjacent to the front end side of the boiler, and the second vertical pass is arranged adjacent to the back end side of the boiler. Taking into account that the radiant superheater also partially acts as a convection superheater, the use of the above-mentioned arrangement provides the advantage that flue gas mainly flowing from the front end side towards an exit at the back end side hits first the first vertical pass, where the steam temperature is the lowest. Thereby, the risk of overheating the second vertical pass is minimized.
- According to an advantageous design of the above-mentioned embodiment of the present invention, the fourth vertical pass is arranged adjacent to the first vertical pass, and the third vertical pass is arranged adjacent to the second vertical pass. In this way, due to the role of the radiant superheater as a convection superheater, the final temperature of the steam is raised. It is also possible, and in some applications, advantageous, to switch the third and the fourth vertical passes, i.e., to arrange the third vertical pass adjacent to the first vertical pass and the fourth vertical pass adjacent to the second vertical pass.
- The radiant superheater is advantageously an intermediate superheater arranged in steam flow direction upstream of a high pressure steam turbine. This means that hot steam from the superheater is led to a finishing superheater before it is conducted to the high pressure steam turbine. Alternatively, the superheater may be a finishing superheater, from which the steam is directly conducted to a high pressure steam turbine. It is also possible that the radiant superheater is an intermediate or finishing reheater, i.e., a superheater arranged in the steam flow between a high pressure steam turbine and an intermediate pressure steam turbine.
- The present invention, as described above, relates to a consideration of the metal temperature of a radiant superheater by having the highest local heat flux combined with a relatively low steam temperature inside the tube. For this purpose, a new approach is provided based on inserting the second portion of an RSH, i.e., the third and fourth vertical passes and the second connection pass, inside the first portion of the RSH, i.e., inside the first and second vertical passes and the first connection pass. Thereby, the first portion of the RSH is used to protect the second portion of the RSH from radiation from any relevant direction. In other words, the first portion of the RSH, with relatively colder fluid inside, acts as an outer platen, while the second portion of the RSH, with higher temperature fluid inside, acts as the inner platen.
- If desired, a complete RSH may comprise several parallel elements, each comprising a series of passes, as described above. By using the above-described RSH, the metal temperatures will be reduced, thus allowing a lower cost tube material, or thinner minimum wall thickness, be used in the RSH. It is also possible, when increased RSH duty is desired, that the superheating system of a boiler comprises two or more radiant superheaters, as described above, connected in series.
- The brief description above, as well as further objects, features, and advantages of the present invention will be more fully appreciated by reference to the following detailed description of the currently preferred, but nonetheless illustrative, embodiments of the present invention, taken in conjunction with the accompanying drawings.
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FIG. 1 is a schematic diagram of a boiler with a radiant superheater according to an embodiment of the present invention. -
FIG. 2 is a schematic diagram of a boiler with a radiant superheater according to another embodiment of the present invention. -
FIG. 1 schematically shows a pulverized coal firing supercritical orultrasupercritical boiler 10 in accordance with a first embodiment of the present invention. The boiler comprises afurnace 12 with water-cooledenclosure walls 14 and aroof 16. At theboiler walls 14 are arrangedburners 18 for firing pulverized coal and producing aflame zone 20 into thefurnace 12. From theflame zone 20 is conducted heat byradiation 22 and byhot flue gases 24. Because the radiation heat depends on the fourth power of the absolute temperature, heat conduction by radiation dominates in regions having direct visibility to the hightemperature flame zone 20. The upper portion of thefurnace 12 comprises a hangingradiant superheater 26, in which steam is superheated, to be finally conducted to a steam turbine (not shown) to generate power.Horizontal pass 28 immediately downstream of thefurnace 12 comprises further hanging superheaters, such as finishingsuperheaters 30. - The
radiant superheater 26 comprises one or more substantially planar, in parallel connected superheatingelements 32, each of which comprises a firstvertical pass 34, afirst connection pass 36, a secondvertical pass 38, a thirdvertical pass 40, asecond connection pass 42 and a fourthvertical pass 44. Thefirst connection pass 36 and thesecond connection pass 42 are advantageously horizontal, but they may, in some applications, also be of another form, for example, half-circles. Steam to be superheated in theradiant superheater 26 is conducted, usually, from a convective superheater (not shown), along afeed pipe 46 to aninlet header 48, which is arranged at the upper end of the firstvertical pass 34. Correspondingly, heated steam is conducted via anoutlet header 50, arranged at the upper end of the fourthvertical pass 44, along adischarge pipe 52 to the next stage. The next stage may be a finishingsuperheater 30 or, if theradiant superheater 26 is a finishing superheater, a steam turbine (not shown). Normally, the steam turbine is a high pressure steam turbine, but when theradiant superheater 26 is a reheater, the steam turbine is an intermediate pressure steam turbine. - From the
inlet header 48 of theradiant superheater 26, the steam to be superheated is distributed to multipleparallel steam tubes 54 running as U-tubes through the firstvertical pass 34, thefirst connection pass 36 and the secondvertical pass 38 to an intermediate header, a so-calledfirst header 56, arranged at the upper end of the secondvertical pass 38. From thefirst header 56, the steam flows via a connectingpipe 58 to asecond header 60 arranged at the upper end of the thirdvertical pass 40. The connectingpipe 58 advantageously comprises awater attemperator 62, by which it is possible to adjust the temperature of the steam to a desired level before it enters the thirdvertical pass 40. The superheating system may comprisefurther water attemperators 64 upstream or downstream of theradiant superheater 26. From thesecond header 60 of theradiant superheater 26, the steam is again distributed to multipleparallel steam tubes 66 running as U-tubes through the thirdvertical pass 40, thesecond connection pass 42 and the fourthvertical pass 44, to theoutlet header 50. - In accordance with the present invention, the
second connection pass 42 is arranged above thefirst connection pass 36, so that thefirst connection pass 36 shields the second connection pass 42 from radiation from the lower portion of thefurnace 12. In the embodiment shown inFIG. 1 , the firstvertical pass 34 and the secondvertical pass 38 are correspondingly arranged to surround the fourthvertical pass 44 and the thirdvertical pass 40. -
FIG. 2 shows another critical orsupercritical boiler 10′ that comprises aradiant superheater 26′, which is slightly modified from that shown inFIG. 1 . Theradiant superheater 26′ comprises a firstvertical pass 34, afirst connection pass 36, a secondvertical pass 38, a thirdvertical pass 40, asecond connection pass 42 and a fourthvertical pass 44, as theradiant superheater 26 shown inFIG. 1 . Also, aninlet header 48 and anoutlet header 50 are provided as in the embodiment shown inFIG. 1 , but there are no in intermediate headers therebetween. Instead, the multiple parallel steam tubes of the secondvertical pass 38 and the thirdvertical pass 40 are mutually connected byparallel steam tubes 68 of athird connection pass 70. Thethird connection pass 70 is here arranged within thefurnace 12, but it may, in some applications, also be located above theroof 16 of thefurnace 12. The use of athird connection pass 70, as shown inFIG. 2 , provides the advantage that the outer steam tubes of the secondvertical pass 38 are turned as inner tubes of the thirdvertical pass 40, which balances the heat absorption in the steam tubes. - While the invention has been described herein by way of examples in connection with what are at present considered to be the most preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but is intended to cover various combinations or modifications of its features, and several other applications included within the scope of the invention as defined in the appended claims. For example, the radiant superheater is advantageously applied in a supercritical or an ultrasupercritical boiler, but it may, if desired, also be applied in a subcritical boiler.
Claims (16)
1. A radiant superheater arranged to hang at the upper portion of a furnace of a boiler, wherein the radiant superheater is substantially planar and comprises:
a first vertical pass;
a first connection pass;
a second vertical pass;
a third vertical pass;
a second connection pass; and
a fourth vertical pass,
wherein each vertical pass comprises an upper end and a lower end, the vertical passes are connected in series, so that steam to be superheated enters at the upper end of the first vertical pass and flows through the first vertical pass and from the lower end of the first vertical pass via the first connection pass to the lower end of the second vertical pass and through the second vertical pass and from the upper end of the second vertical pass to the upper end of the third vertical pass and through the third vertical pass and from the lower end of the third vertical pass via the second connection pass to the lower end of the fourth vertical pass and through the fourth vertical pass, to be discharged from the upper end of the fourth vertical pass, and
wherein the first connection pass is arranged below the second connection pass so as to shield the second connection pass from radiation from the lower portion of the furnace.
2. The radiant superheater according to claim 1 , wherein the first vertical pass and the second vertical pass are arranged to surround the fourth vertical pass and the third vertical pass, so as to shield, in a horizontal direction, the fourth vertical pass and the third vertical pass from radiation.
3. The radiant superheater according to claim 1 , wherein each of the first vertical pass, the first connection pass, the second vertical pass, the third vertical pass, the second connection pass and the fourth vertical pass comprises multiple parallel steam tubes.
4. The radiant superheater according to claim 3 , wherein each of the multiple parallel steam tubes of the first vertical pass is in steam flow connection to one of the multiple parallel steam tubes of the first connection pass and each of the multiple parallel steam tubes of the first connection pass is in steam flow connection to one of the multiple parallel steam tubes of the second vertical pass.
5. The radiant superheater according to claim 4 , wherein each of the multiple parallel steam tubes of the third vertical pass is in steam flow connection to one of the multiple parallel steam tubes of the second connection pass and each of the multiple parallel steam tubes of the second connection pass is in steam flow connection to one of the multiple parallel steam tubes of the fourth vertical pass.
6. The radiant superheater according to claim 5 , wherein the second vertical pass and the third vertical pass are connected in series so that the steam flows from the upper end of the second vertical pass via a third connection pass to the upper end of the third vertical pass, and the third connection pass comprises multiple parallel steam tubes.
7. The radiant superheater according to claim 6 , wherein each of the multiple parallel steam tubes of the second vertical pass is in steam flow connection to one of the multiple parallel steam tubes of the third connection pass, and each of the multiple parallel steam tubes of the third connection pass is in steam flow connection to one of the multiple parallel steam tubes of the third vertical pass.
8. The radiant superheater according to claim 3 , wherein the furnace comprises a roof, each of the multiple parallel steam tubes of the second vertical pass is connected to a first header arranged above the roof, each of the multiple parallel steam tubes of the third vertical pass is connected to a second header arranged above the roof, and the first header is in steam flow connection with the second header by a connecting pipe arranged outside the roof.
9. The radiant superheater according to claim 8 , wherein the connecting pipe comprises a water attemperator.
10. The radiant superheater according to claim 1 , wherein the first vertical pass is arranged adjacent to the front end side of the boiler and the second vertical pass is arranged adjacent to the back end side of the boiler.
11. The radiant superheater according to claim 10 , wherein the fourth vertical pass is arranged adjacent to the first vertical pass and the third vertical pass is arranged adjacent to the second vertical pass.
12. The radiant superheater according to claim 1 , wherein the radiant superheater is an intermediate superheater arranged in steam flow direction upstream of a high pressure steam turbine.
13. The radiant superheater according to claim 1 , wherein the radiant superheater is a finishing superheater arranged in steam flow direction upstream of a high pressure steam turbine.
14. The radiant superheater according to claim 1 , wherein the radiant superheater is an intermediate superheater arranged in steam flow direction downstream of a high pressure steam turbine.
15. The radiant superheater according to claim 1 , wherein the radiant superheater is a finishing superheater arranged in steam flow direction downstream of a high pressure steam turbine.
16. The radiant superheater according to claim 1 , wherein the boiler is one of a supercritical boiler and an ultra supercritical boiler.
Priority Applications (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US13/178,570 US20130008394A1 (en) | 2011-07-08 | 2011-07-08 | Radiant Superheater |
PCT/IB2012/053370 WO2013008130A2 (en) | 2011-07-08 | 2012-07-03 | Radiant superheater |
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US13/178,570 US20130008394A1 (en) | 2011-07-08 | 2011-07-08 | Radiant Superheater |
Publications (1)
Publication Number | Publication Date |
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US20130008394A1 true US20130008394A1 (en) | 2013-01-10 |
Family
ID=46584088
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
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US13/178,570 Abandoned US20130008394A1 (en) | 2011-07-08 | 2011-07-08 | Radiant Superheater |
Country Status (2)
Country | Link |
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US (1) | US20130008394A1 (en) |
WO (1) | WO2013008130A2 (en) |
Cited By (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
WO2016147023A1 (en) * | 2015-03-13 | 2016-09-22 | Babcock & Wilcox Vølund A/S | Incineration plant with superheater |
US10495299B2 (en) * | 2016-10-17 | 2019-12-03 | David Fortenbacher | Superheater |
CN114135862A (en) * | 2021-11-30 | 2022-03-04 | 刘杰 | Tube body positioning mechanism of boiler superheater |
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US2947288A (en) * | 1957-08-20 | 1960-08-02 | Kohlenscheidungs Gmbh | Radiant tubular heat exchanger |
US3015319A (en) * | 1958-01-22 | 1962-01-02 | Kohlenscheidungs Gmbh | Radiant tubular heat exchanger |
GB855114A (en) | 1958-04-28 | 1960-11-30 | Brian R Morris & Company Ltd | Improvements in or relating to counting devices |
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2011
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US2851017A (en) * | 1954-02-16 | 1958-09-09 | Combustion Eng | Panel type steam heaters |
US2902010A (en) * | 1957-08-19 | 1959-09-01 | Kohlenscheidungs Gmbh | Radiant tubular heat exchanger |
US2942587A (en) * | 1957-10-25 | 1960-06-28 | Babcock & Wilcox Co | Vapor generator |
US3048131A (en) * | 1959-06-18 | 1962-08-07 | Babcock & Wilcox Co | Method for burning fuel |
US3532079A (en) * | 1967-09-11 | 1970-10-06 | Svenska Maskinverken Ab | Method for starting steam power plants |
US4442800A (en) * | 1982-05-03 | 1984-04-17 | The Babcock & Wilcox Company | Single drum all-welded boiler |
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Publication number | Priority date | Publication date | Assignee | Title |
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WO2016147023A1 (en) * | 2015-03-13 | 2016-09-22 | Babcock & Wilcox Vølund A/S | Incineration plant with superheater |
US10495299B2 (en) * | 2016-10-17 | 2019-12-03 | David Fortenbacher | Superheater |
CN114135862A (en) * | 2021-11-30 | 2022-03-04 | 刘杰 | Tube body positioning mechanism of boiler superheater |
Also Published As
Publication number | Publication date |
---|---|
WO2013008130A2 (en) | 2013-01-17 |
WO2013008130A3 (en) | 2014-01-09 |
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