REHEAT TYPE EXHAUST GAS BOILER

Abstract: The known reheat type exhaust gas boiler of the type that superheaters and reheaters are disposed in paral­ lel in the most gas upstream portion of an exhaust gas boiler main body, is improved in order to simplify the structure and to achieve recovery of heat from the exhaust gas more effectively. The superheaters and reheaters are divided into a plurality of stages. A high-temperature side superheater (2) and a high-temperature side reheater (3) are disposed in parallel in the most upstream portion of the gas flow. A low-temperature side reheater (5) is disposed on the gas downstream side of the high-temperature side super­ heater (2), while a low-temperature side superheater (4) is dis­ posed on the gas downstream side of the high-temperature side reheater (3). The high-temperature side superheater and the high-temperature side reheater are formed so as to have an identical heat transfer tube outer diameter, an identical tube pitch in the widthwise direction of a flue, an identical tube pitch in the direction of the gas flow and an identical number of tube raws in the direction of the gas flow. Likewise, the low-temperature side reheater and the low-temperature side reheater are formed so as to have an identical heat transfer tube outer diameter, an identical tube pitch in the widthwise direction of the flue, an identical tube pitch in the direction of the gas flow and an identical number of tube raws in the direction of the gas flow.

Description: Field of the Invention: The present invention relates to a reheat type exhaust gas boiler in which superheaters and reheaters are disposed in parallel in the most upstream portion in the direction of an exhaust gas flow within an exhaust gas boiler main body. Description of the Prior Art: Heretofore, an exhaust gas boiler for recovering heat of exhaust gas discharged from various heat generating sources such as gas turbines, diesel engines, cement calcinators or the like have been well known, for instance, those disclosed in Japanese Patent Specification No. 61-186702 (1986) (& EP-A-0 191 415) are known. In these exhaust gas boilers in the prior art, two sets of secondary superheaters 102 and secondary reheaters 103 are disposed in parallel in the most upstream portion in the direction of an exhaust gas flow within an exhaust gas boiler main body 101 through which exhaust gas flows in the horizontal direction as shown in Figs. 3 and 4. And, on the downstream side with respect to gas of the respective secondary superheaters 102 are respectively disposed primary reheaters 104, while on the downstream side with respect to gas of the respective secondary reheaters 103 are respectively disposed primary superheaters 105, and further on the gas downstream side of them is disposed a high-pressure evaporator 106 along the widthwise direction of a flue. On the gas downstream side of this high-pressure evaporator 106 is disposed a high-pressure economizer 107, and on the gas downstream side of this high-pressure economizer 107 are successively disposed a low-pressure superheater 108, a low-pressure evaporator 109 and a low-pressure economizer 110. On the other hand, above the exhaust gas boiler main body 101 are disposed a high-pressure steam drum 111 and a low-pressure steam drum 112. The high-pressure steam drum 111 is connected to an outlet of the high-pressure economizer 107, and also connected to a bottom header 106a of the high-pressure evaporator 106 via a down comer 113. In addition, a top header 106b of the high-pressure evaporator 106 is connected to the high-pressure steam drum 111 via a riser tube 114. Furthermore, a steam section of the high-pressure steam drum 111 is connected to an inlet section of the primary superheater 105 via a steam pipe 115. Whereas, the low-pressure steam drum 112 is connected to an outlet of the low-pressure economizer 110, and also connected to a bottom header 109a of the low-pressure evaporator 109 via a down comer 116. In addition, a top header 109b of the low pressure evaporator 109 is connected to the low-pressure steam drum 112 via a riser tube 117. Furthermore, the low-pressure steam drum 112 is connected to an inlet side of the high-pressure economizer 107 via a feed water pipe 119 provided with a feed water pump 118. And, a steam section of the low-pressure steam drum 112 is connected to an inlet section of the low-pressure superheater 108 via a steam pipe 120. In addition, the inlet of the primary reheater 104 is communicated with a steam turbine not shown through a pipe for returning steam which has done a work in the steam turbine. The outlet the primary reheater 104 is communicated with the secondary reheater 103 through a communication pipe not shown. Likewise, the outlet of the primary superheater 105 is communicated with the secondary superheater 102 through a communication pipe not shown. And, between these superheaters and reheaters disposed in parallel are provided partition walls 121. It is to be noted that in the midway of the above-described communication pipes are provided steam temperature lowerers which rely upon water spray, water injection or the like so that the steam temperature can be regulated. Now description will be made on the operation of the above-described exhaust gas boiler in the prior art. Exhaust gas discharged from a heat generating source flows into the inlet of the exhaust gas boiler main body 101, then during the period when the exhaust gas flow from the side of the secondary superheater 102 and the secondary reheater 103 to the side of the low-pressure economizer 110, heat-exchange is effected with the fluid flowing through the heat transfer tubes in the respective units, and after it has become a low temperature, it flows out through the outlet of the exhaust gas boiler main body 101. On the other hand, feed water (condensate) is sent to the low-pressure economizer 110 by means of a condensate pump not shown, and here it is heated by the exhaust gas. Then, the heated feed water is sent from the low-pressure economizer 110 to the low-pressure steam drum 112. A part of the feed water in the low-pressure steam drum 112 is sent to the low-pressure evaporator 109 via the down comer 116, then it is heated in this low-pressure evaporator 109 by the exhaust gas and becomes steam/water mixture fluid, and it is returned through the riser tube 117 to the low-pressure steam drum 112. This steam/water mixture fluid returned to the low-pressure steam drum 112 is separated into steam and water, the steam is sent through the steam pipe 120 to the low-pressure superheater 108, in which the steam is superheated. On the other hand, another part of the feed water in the low-pressure steam drum 112 passes through the feed water pipe 119, and is boosted in pressure by the pump 118, and after it has become high pressure, it is sent to the high-pressure economizer 107. Then, in this high-pressure economizer 107, the feed water is heated by the exhaust gas and sent to the high-pressure steam drum 111. The feed water sent to the high-pressure steam drum 111 is partly sent to the high-pressure evaporator 106 through the down comer 113, here it is heated by the exhaust gas and becomes steam/water mixture fluid, and it is returned through the riser tube 114 to the high-pressure steam drum 111. Within this high-pressure steam drum 111, the mixture fluid is separated into steam and feed water, the steam is sent through the steam pipe 115 to the primary superheater 105, and in this primary superheater 105 it is superheated by the exhaust gas. Then the superheated steam is sent to the steam temperature lowerer through the above-described communication pipe, after the steam has been controlled into a predetermined temperature in this temperature lowerer, it is sent to the secondary superheater 102, and in this secondary superheater 102 high-temperature high-pressure steam is formed and is sent to the steam turbine. The steam which have done a work in the steam turbine is returned to the primary reheater 104, and it is superheated in this primary reheater 104. Then, this superheated steam is sent through the above-mentioned communication pipe to the steam temperature lowerer, wherein the steam temperature is controlled into a predetermined temperature, and thereafter it is sent to the secondary reheater 103 and is superheated again. In an exhaust gas boiler having reheaters, for the purpose of effectively carrying out recovery of heat from exhaust gas, it is desirable that superheaters and reheaters are disposed in such manner that the gas temperatures at their outlets and inlets and the steam temperatures at their outlets and inlets may be held at the same conditions. To that end, in the prior art, as described above superheaters and reheaters are divided into primary ones and secondary ones, the secondary superheater 102 and the secondary reheaters 103 are disposed in parallel, on the gas downstream side of the secondary superheater 102 is disposed the primary reheater 104, while on the gas downstream side of the secondary reheater 103 is disposed the primary superheater 105, the primary superheater 105 and the secondary superheater 102 are communicated with each other, also the primary reheater 104 and the secondary reheater 103 are communicated with each other, by providing partition walls 121 between the respective superheaters and the respective reheaters disposed in parallel, the gas path is divided and the gas flow is guided so as to form proper gas flows, and thereby the gas temperatures at the downstreams of the primary superheater 105 and the primary reheater 104 can become substantially the same temperature. In such reheat type exhaust gas boiler in the prior art, however, there was a problem that the structure of the exhaust gas boiler became complicated due to the fact that the gas path is divided by providing partition walls between the superheaters and the reheaters disposed in parallel. SUMMARY OF THE INVENTION: It is therefore one object of the present invention to provide an improved reheat type exhaust gas boiler which is free from the above-described shortcomings of the exhaust gas boilers in the prior art. A more specific object of the present invention is to provide a reheat type exhaust gas boiler, which is simple in structure and which can carry out recovery of heat from the exhaust gas more effectively. According to one feature of the present invention, there is provided a reheat type exhaust gas boiler, in which superheaters and reheaters are disposed in parallel in the most upstream portion in the direction of an exhaust gas flow within an exhaust gas boiler main body, and in which the superheaters and the reheaters are respectively divided into a plurality of stages, a high-temperature side superheater and a high-temperature side reheater are disposed in parallel in the most upstream portion of the gas flow, on the gas downstream side of the high-temperature side superheater is disposed a low-temperature side reheater, while on the gas downstream side of the high-temperature side reheater is disposed a low-temperature side superheater, the high-temperature side superheater and the high-temperature side reheater are formed so as to have an identical heat transfer tube outer diameter, an identical tube pitch in the widthwise direction of a flue, an identical tube pitch in the direction of the gas flow and an identical number of tube rows in the direction of the gas flow, and the low-temperature side reheater and the low-temperature side superheater are formed so as to have an identical heat transfer tube outer diameter, an identical tube pitch in the widthwise direction of the flue, an identical tube pitch in the direction of the gas flow and an identical number of tube rows in the direction of the gas flow. With the above-mentioned measure, since the high-temperature side superheater and the high-temperature side reheater disposed in parallel, and the low-temperature side superheater and the low-temperature side reheater disposed in parallel, are respectively constructed so that their heat transfer tube outer diameters, their tube pitches in the widthwise direction of the flue, their tube pitches in the direction of the gas flow and the number of tube raws in the direction of the gas flow are identical to each other, the conditions for the draft losses on the gas side would become identical, and accordingly, there is no need to provide partition walls for distributing gas paths. The above-mentioned and other objects, features and advantages of the present invention will become more apparent by reference to the following description of one preferred embodiment of the invention taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS: In the accompanying drawings: Fig. 1 is a plan system diagram showing one preferred embodiment of the reheat type exhaust gas boiler according to the present invention; Fig. 2 is a side system diagram of the same; Fig. 3 is a plan system diagram showing one example of the reheat type exhaust gas boiler in the prior art; and Fig. 4 is a side system diagram of the same exhaust gas boiler in the prior art. DESCRIPTION OF THE PREFERRED EMBODIMENT: In the following, detailed description will be made on one preferred embodiment of the present invention with reference to Figs. 1 and 2. In Figs. 1 and 2, in the most upstream portion with respect to the direction of the exhaust gas flow within an exhaust gas boiler main body 1 through which exhaust gas flows in the horizontal direction, are disposed a tertiary superheater 2 and a secondary reheater 3 in parallel. And, on the gas downstream side of the tertiary superheater 2 is disposed a primary reheater 5, while on the gas downstream side of the secondary reheater 3 is disposed a secondary superheater 4, and on the further gas downstream side is disposed a primary superheater 6 extending over the entire width of a flue. The secondary reheater 3 and the primary reheater 5 are connected through a communication pipe 22. And the tertiary superheater 2 and the secondary superheater 4 are connected through a communication pipe 21, and the secondary superheater 4 and the primary superheater 6 are connected through a communication pipe 23. On the gas downstream side of the primary superheater 6 are further disposed a high-pressure evaporator 7, a high-pressure economizer 8, a medium-pressure superheater 9, a medium-pressure evaporator 10, a medium-pressure economizer 11, a low-pressure economizer 12 and a low-pressure economizer 13, in sequence. On the other hand, above the exhaust gas boiler main body 1 are installed a high-pressure steam drum 14, a medium-pressure steam drum 15, a low-pressure steam drum 16 and a deaerator 17. Thus, feed water (condensate) is fed from a condensate pump not shown, it enters into the low-pressure economizer 13 through a piping 36, further it is sent to the deaerator 17 through a piping 20 and it is deaerated by steam. The heated steam for deaeration is fed from the low-pressure steam drum 16. A part of the low-pressure steam in the low-pressure steam drum 16 is fed to a low-pressure steam turbine not shown through a piping 37. This low-pressure steam 16 also serves as a water storage tank for the deaerator 17. On the other hand, another part of the water in the low-pressure steam drum 16 flows through a piping 24 into a medium-pressure feed water pump 25 and a high-pressure feed water pump 30. The feed water boosted in pressure by the medium-pressure feed water pump 25 passes through a piping 26 and reaches the medium-pressure economizer 11, and after it has been heated it is sent to the medium-pressure steam drum 15 through a piping 19. And, steam generated in the medium-pressure evaporator 10 is fed to the medium-pressure superheater 9 through a piping 27, and further it flows into the primary reheater 5 via a piping 29. In this case, since exhaust gas (steam) sent from a high-pressure turbine (not shown) is fed to the primary reheater 5, the medium-pressure steam fed through the piping 29 is mixed with the exhaust gas sent from the high-pressure turbine at the gas upstream side of the primary reheater 5, and thereafter it flows into the primary reheater 5. Furthermore, steam is sent to the secondary reheater 3 through the communication pipe 22, and after it has been heated there, it is sent to a medium-pressure turbine. In this case, if necessary, in the midway of the communication pipe 22 is provided a steam temperature lowerer of water spray injection type or the like, and thereby the steam temperature can be regulated. Subsequently, the feed water boosted in pressure by means of the high-pressure feed water pump 30 reaches the high-pressure economizer 8 through a piping 31, and after it has been heated, it is sent to the high-pressure steam drum 14 through a piping 18. And, steam generated in the high-pressure evaporator 7 is sent through a piping 32 to the primary superheater 6, after it has been heated there, it is sent to the secondary superheater 4 via the communication pipe 23, and after it has been heated there, it reaches the tertiary superheater 2 through the communication pipe 21. Steam at the outlet of the tertiary superheater 2 is sent to a high-pressure turbine not shown. In this case, if necessary, in the midway of the communication pipe 21 or 23 is provided a steam temperature lowerer relying upon water spray injection or the like, and thereby the steam temperature can be regulated. It is to be noted that in Fig. 2, reference numeral 28 designates a medium-pressure evaporator bottom drum, numeral 34 designates a high-pressure evaporator bottom drum, and numeral 38 designates a low-pressure evaporator bottom drum. In the above-described construction of the reheat type exhaust gas boiler, according to the present invention the tertiary superheater 2 and the secondary reheater 3 disposed in parallel both have their heat transfer tube outer diameters, their tube pitches in the widthwise direction of the flue, their tube pitches in the direction of the gas flow and their numbers of tube rows in the direction of the gas flow all chosen to be identical, so that along the widthwise direction of the flue their resistances against the gas flow can be held under the identical condition. Likewise, the secondary superheater 4 and the primary reheater 5 disposed in parallel on the gas downstream side of the above-mentioned units also have their heat transfer tube outer diameters, their tube pitches in the widthwise direction of the flue, their tube pitches in the direction of the gas flow and their number of tube rows in the direction of the gas flow all chosen to be identical, so that along the widthwise direction of the flue their resistances against the gas flow can be held under the identical condition. As described above, by arranging the tertiary, i.e., the high-temperature side superheater 2 and the secondary, i.e., the high-temperature side reheater 3 to be disposed in parallel, and the secondary, i.e., the low-temperature side superheater 4 and the primary, i.e., the low-temperature side reheater 5 to be disposed in parallel in such manner that along the widthwise direction of the flue their resistances against the gas flow may be held under the identical condition, a draft loss on the gas side can be held under the identical condition, hence always constant gas flows, and accordingly, there is no need to provide partition walls for specially dividing gas paths between these superheaters and reheaters to be disposed in parallel. It is to be noted that while the exhaust gas boiler was explained to have such construction that it includes the deaerator 17, the low-pressure economizer 13, and further the medium-pressure evaporator 10, the medium-pressure superheater 9 and the primary superheater 6 in the above-described preferred embodiment, these constituent elements are not always the essential formative condition of the present invention. Accordingly, the present invention is applicable equally to an exhaust gas boiler not including the deaerator 17 and the low-pressure economizer 13. Likewise, the present invention can be applied also to an exhaust gas boiler not having the medium-pressure superheater 9. Furthermore, in some case, the primary superheater 6 can be omitted. As described in detail above, according to the present invention, since the gas flow in the region extending in the widthwise direction of the flue of the superheaters and the reheaters disposed in parallel can be always maintained constant without providing partition walls for dividing gas paths between the high-temperature side superheater and the high-temperature side reheater and between the low-temperature side superheater and the low-temperature side reheater which are respectively disposed in parallel in the most upstream portion with respect to the direction of the exhaust gas flow within the reheat type exhaust gas boiler main body, recovery of heat from exhaust gas can be achieved effectively while simplifying the structure of the exhaust gas boiler.

Claims: A reheat type exhaust gas boiler, in which superheaters and reheaters are disposed in parallel in the most upstream portion in the direction of an exhaust gas flow within an exhaust gas boiler main body; said superheaters and reheaters are respectively divided into a plurality of stages, a high-temperature side superheater and a high-temperature side reheater are disposed in parallel in the most upstream portion of the gas flow, on the gas downstream side of said high-temperature side superheater is disposed a low-temperature side reheater, while on the gas downstream side of said high-temperature side reheater is disposed a low-temperature side superheater, characterised in that said high-temperature side superheater and said high-temperature side reheater are formed so as to have an identical heat transfer tube outer diameter, an identical tube pitch in the widthwise direction of a flue, an identical tube pitch in the direction of the gas flow and an identical number of tube rows in the direction of the gas flow, and said low-temperature side reheater and said low-temperature side superheater are formed so as to have an identical heat transfer tube outer diameter, an identical tube pitch in the widthwise direction of the flue, an identical tube pitch in the direction of the gas flow and an identical number of tube rows in the direction of the gas flow. A reheat type exhaust gas boiler as claimed in Claim 1, wherein on the gas downstream side of said low-temperature side superheater and said low-temperature side reheater is provided a primary superheater as traversing an exhaust gas flow path, and an outlet of said primary superheater is connected to an inlet of said low-temperature side superheater.

Inventors: KASHIWAZAKI, MASAMICHI MITSUBISHI JUKOGYO K.K., MOTAI, TOSHIKI MITSUBISHI JUKOGYO K.K.
Applicants: MITSUBISHI JUKOGYO KABUSHIKI KAISHA
Application year: 1989
Main classification: F22G7
IPC codes: F22B37, F22B1, F22G7