The present invention relates to a reheat boiler including a reheat furnace and a reheater provided downstream of an evaporation tube bank and reducing temperature unevenness of combustion gas near an outlet of the reheat furnace and to a gas temperature controlling method of such a reheat boiler.

Marine boilers including a super heater have been widely used (JP 2002-243106A). Furthermore, reheat boilers including a reheat furnace and a reheater provided downstream of combustion gas in conventional marine boilers have been used.

An exemplary configuration of the conventional marine reheat boiler is illustrated in Fig. 6. Fig. 6 is a schematic of a configuration of the conventional reheat boiler. As illustrated in Fig. 6, this conventional reheat boiler 100 includes: a main boiler 106 including a burner 101, a furnace 102, a front tube bank 103, a super heater (SH) 104, and an evaporation tube bank (rear tube bank) 105; a reheat furnace 108 including a reheat burner 107 provided downstream of the evaporation tube bank 105; and a reheater 109 provided at a combustion gas outlet side. The combustion gas originating from combustion in the burner 101 flows from the furnace 102, passes through the front tube bank 103, the SH 104, and the evaporation tube bank 105, and is mixed with the combustion gas originating from combustion in the reheat burner 107 in the reheat furnace 108. With its heat exchanged with the reheater 109, the gas further flows, and is output from a gas outlet 110. The reheat boiler is thus operated efficiently. In Fig. 6, the numeral 111 indicates a water drum, the numeral 112 indicates a steam drum, the numerals 113, 114 indicate headers, and the numeral 115 indicates a wall tube.

US 3956898 A discloses a reheat boiler arranged for operation in a marine reheat power plant and it includes a main boiler, a reheat furnace, and a reheater provided on an upper side of the reheat furnace. A supplemental reheat burner and an air supply for the burners is provided on the same side of the reheat furnace.

The conventional marine reheat boiler 100 includes the reheat burner 107 on a front wall side of the reheat furnace 108, but not on a rear wall side of the reheat furnace 108. Because of this configuration, as illustrated in Fig. 7, large temperature unevenness of the combustion gas arises between the front wall side (indicated by the letter X in Fig. 7) and the rear wall side (indicated by the letter Y in Fig. 7) of the reheat furnace 108 on the outlet side thereof (indicated by the letter B in Fig. 6).

Temperature unevenness of the combustion gas on the outlet side of the reheat furnace 108 (that is, on the inlet side of the reheater 109) deteriorates heat conductivity of the reheat furnace 108 and the reheater 109, and may also cause high-temperature corrosion of reheater tubes and strength drops of support members in the reheater 109. The letter A in Fig. 7 indicates where the reheat burner is provided, and the letter C indicates the outlet portion of the reheater 109.

In view of the above problems, an object of the present invention is to provide a reheat boiler and a gas temperature controlling method of a reheat boiler that change gas flow patterns of a reheat burner to reduce temperature unevenness of combustion gas on the outlet side of a reheat furnace.

The present invention provides a reheat boiler with the features of claim 1 and a gas temperature controlling method of a reheat boiler with the features of claim 5. According to an aspect of the present invention, a reheat boiler that includes a main boiler in which combustion gas produced by combustion in a burner flows through a super heater and an evaporation tube bank from a furnace, a reheat furnace with a reheat burner provided downstream of the evaporation tube bank, and a reheater provided on an upper side of the reheat furnace, includes a combustion air supply portion that is provided at a position opposite to the reheat burner in the reheat furnace to supply a part of combustion air.

Advantageously, in the reheat boiler, at least two stages of such combustion air supply portions are provided in a height direction of the reheat furnace.

Advantageously, in the reheat boiler, a part of the combustion air is supplied to the combustion air supply portion by a rate of 50% or less.

Advantageously, in the reheat boiler, at least two stages of such combustion air supply portions are provided in a height direction of the reheat furnace, and each stage of the combustion air supply portions supplies a different volume of the combustion air.

According to another aspect of the present invention, a gas temperature controlling method of the above mentioned reheat boiler includes: supplying a part of the combustion air into the reheat furnace from a position opposite to the reheat burner to reduce temperature unevenness of the combustion gas on an outlet side of the reheat furnace.

According to the present invention, by providing the combustion air supply portion at a position opposite to the reheat burner in the reheat furnace to supply a part of the combustion air to the reheat furnace, flow patterns of gas discharged from the reheat burner can be changed. Therefore, temperature unevenness of the combustion gas on the outlet side of the reheat furnace is reduced.

• [Fig. 1A] Fig. 1A is a schematic of the configuration of a reheat furnace and a reheater included in a reheat boiler according to a first embodiment of the present invention.
• [Fig. 1B] Fig. 1B is a sectional view seen in a direction perpendicular to the vertical direction of the reheat furnace illustrated in Fig. 1A.
• [Fig. 2] Fig. 2 is a schematic of the configuration of the reheat boiler according to the first embodiment of the present invention.
• [Fig. 3] Fig. 3 is an illustrative view of the temperature distribution of combustion gas at the outlet of the reheat furnace.
• [Fig. 4] Fig. 4 is a schematic of the configuration of a reheat boiler according to a second embodiment of the present invention, extracting its reheat furnace and reheater alone.
• [Fig. 5] Fig. 5 is an illustrative view of the temperature distribution of combustion gas near the outlet of the reheat furnace.
• [Fig. 6] Fig. 6 is a schematic of an exemplary configuration of a conventional reheat boiler.
• [Fig. 7] Fig. 7 is an illustrative view of the temperature distribution near the outlet of a conventional reheat furnace.

10A, 10B:

reheat boiler

11, 11b-1 to 11b-3:

combustion air

12, 12-1 to 12-3:

combustion air supply portion

101:

burner

102:

furnace

103:

front tube bank

104:

super heater (SH)

105:

evaporation tube bank (rear tube bank)

106:

main boiler

107:

reheat burner

108:

reheat furnace

109:

reheater

110:

gas outlet

111:

water drum

112:

steam drum

113, 114:

header

115:

wall tube

The present invention will be described in detail with reference to the accompanying drawings.

A reheat boiler according to an embodiment of the present invention will now be described with reference to some drawings.

The reheat boiler according to the present embodiment has a similar configuration to that of a conventional reheat boiler as illustrated in Fig. 6 and has an air supply portion provided to a reheat furnace; therefore, like elements have like reference numerals, and repeated descriptions will be omitted.

Fig. 1A is a schematic of the configuration of the reheat furnace and a reheater included in the reheat boiler according to the first embodiment of the present invention, and is a sectional view along the line I-I in Fig. 2. Fig. 1B is a sectional view seen in a direction perpendicular to the vertical direction of the reheat furnace illustrated in Fig. 1A. Fig. 2 is a schematic of the configuration of the reheat boiler according to the first embodiment of the present invention.

In Figs. 1A and 1B, the letter X represents a front wall side of the reheat furnace, and the letter Y represents a rear wall side of the reheat furnace.

Referring to Figs. 1A, 1B, and 2, this reheat boiler 10A according to the present embodiment includes, like the configurations of conventional reheat boilers as illustrated in Fig. 6, the main boiler 106 configured to make combustion gas originating from combustion in the burner 101 flow from the furnace 102 and pass through the SH 104 and the evaporation tube bank 105, the reheat furnace 108 in which the combustion gas is reburned with the reheat burner 107, and the reheater 109 through which the reburned combustion gas passes. Referring to Figs. 1A and 1B, the reheat boiler 10A also includes a combustion air supply portion 12 provided at a position opposite to the reheat burner 107 in the reheat furnace 108 to supply a part of combustion air 11 to be supplied to the reheat burner 107 as combustion air 11b.
According to the present invention, the combustion air 11a refers to combustion air that is a part of the combustion air 11 and is supplied to the reheat burner 107, while the combustion air 11b refers to combustion air that is another part of the combustion air 11 remaining after being allocated to the reheat burner 107 and is supplied to the combustion air supply portion 12.

By providing the combustion air supply portion 12 at the position opposite to the reheat burner 107 in the reheat furnace 108, combustion gas 107a discharged from the reheat burner 107 and the combustion air 11b supplied through the combustion air supply portion 12 collide head-on with each other, which facilitates mixing of the combustion gas 107a with the combustion air 11b. Consequently, temperature unevenness of the combustion gas 107a at the outlet of the reheat furnace 108 can be reduced.

Fig. 3 is an illustrative view of the temperature distribution of the combustion gas at the outlet of the reheat furnace illustrated in Fig. 1A. As indicated in Fig. 3, by providing the combustion air supply portion 12 at the position opposite to the reheat burner 107 in the reheat furnace 108 and supplying the combustion air 11b into the reheat furnace 108, the temperature distribution of the combustion gas 107a near the outlet of the reheat furnace 108 (indicated by the letter B in Figs. 1A and 2) falls within a range from 600 to 800 degrees Celsius, for example. With the average temperature being kept about 700 degrees Celsius, this range is narrower than the temperature distribution of the combustion gas 107a near the outlet of the reheat furnace 108 (indicated by the letter B in Figs. 6 and 7) included in the conventional reheat boiler 100 as indicated in Fig. 7.

By thus supplying the combustion air 11 into the reheat furnace 108 from the position opposite to the reheat burner 107, temperature unevenness near the outlet of the reheat furnace 108 can be suppressed compared with the temperature of the combustion gas 107a near the outlet of the reheat furnace 108 (indicated by the letter B in Figs. 6 and 7) included in the conventional reheat boiler as indicated in Fig. 7.

In the reheat boiler 10A according to the present embodiment, the combustion air 11b that remains after subtracting the combustion air 11a to be supplied to the reheat burner 107 from the combustion air 11 is supplied through the combustion air supply portion 12 preferably by a rate of 50% or less. This is because allocating a majority of the combustion air 11 to the combustion air 11b will cause incomplete combustion of fuel in the reheat burner 107.

In the reheat boiler 10A according to the present embodiment, the combustion gas 107a is first burned with the combustion air 11a supplied into the reheat burner 107 and then with the combustion air 11b supplied through the combustion air supply portion 12 in a step-by-step manner. Burning the combustion gas 107a in two stages with the combustion air 11a and the combustion air 11b can suppress the formation of NO_x.

In the reheat boiler 10A according to the present embodiment, the air volume of the combustion air 11b supplied through the combustion air supply portion 12 is adjusted with, for example, a damper or other air volume adjusters.

In the reheat boiler 10A according to the present embodiment, by supplying the combustion air 11b into the reheat furnace 108 through the combustion air supply portion 12 provided at the position opposite to the reheat burner 107 in the reheat furnace 108, the flow patterns of the combustion gas 107a discharged from the reheat burner 107 can be changed. Accordingly, temperature unevenness of the combustion gas 107a on the outlet side of the reheat furnace 108 can be reduced. This configuration prevents heat conductivity drops of the reheat furnace 108 and the reheater 109 and also prevents high-temperature corrosion of reheater tubes and strength drops of support members in the reheater 109.

A reheat boiler according to a second embodiment of the present invention will now be described with reference to Figs. 4 and 5.

Fig. 4 is a schematic of the configuration of the reheat boiler according to the second embodiment of the present invention, extracting its reheat furnace and reheater alone.

The reheat boiler according to the present embodiment has a similar configuration to that of the reheat boiler according to the first embodiment; therefore, like elements have like reference numerals, and repeated descriptions will be omitted.

Referring to Fig. 4, this reheat boiler 10B according to the present embodiment includes three-staged combustion air supply portions 12-1 to 12-3 disposed at intervals in the height direction of the reheat furnace 108 and at positions opposite to the reheat burner 107 in the reheat furnace 108.

By supplying the combustion air 11b-1 to 11b-3 into the reheat furnace 108 through the air supply portions 12-1 to 12-3, the mixture degrees of combustion gas with the combustion air 11b-1 to 11b-3 can be adjusted desirably, whereby the temperature distribution of the combustion gas near the outlet of the reheat furnace 108 can be controlled.

In the boiler 10B according to the present embodiment, the flow rates of the combustion air 11b-1 to 11b-3 supplied through the air supply portions 12-1 to 12-3, respectively, are adjustable thereby. By adjusting the flow rates of the combustion air 11b-1 to 11b-3 supplied into the reheat furnace 108, the mixture degrees of the combustion gas 107a with the combustion air 11b-1 to 11b-3 can be adjusted, whereby the temperature distribution near the outlet of the reheat furnace 108 can be controlled. For example, by making the air volume of the combustion air 11b-1 relatively large and the air volumes of the combustion air 11b-2 and the combustion air 11b-3 even, the temperature distribution near the outlet of the reheat furnace 108 can be smoothed.

Fig. 5 is an illustrative view of the temperature distribution of the combustion gas near the outlet of the reheat furnace illustrated in Fig. 4. By adjusting the flow rates of the combustion air 11b-1 to 11b-3 supplied through the combustion air supply portions 12-1 to 12-3 as illustrated in Fig. 4, temperature unevenness of the combustion gas 107a on the outlet side of the reheat furnace 108 can be reduced as indicated in Fig. 5.

By thus supplying the combustion air 11b into the reheat furnace 108 in multiple stages, the temperature distribution of the combustion gas 107a near the outlet of the reheat furnace 108 (indicated by the letter B in Fig. 4) falls within a range from 620 to 780 degrees Celsius, for example. With the average temperature being kept about 700 degrees Celsius, this range is narrower than the temperature distribution of the combustion gas 107a near the outlet of the reheat furnace 108 (indicated by the letter B in Fig. 6) included in the conventional reheat boiler 100 as indicated in Fig. 7.

This configuration can achieve a smoother temperature distribution than the temperature distribution of the combustion gas 107a near the outlet of the reheat furnace 108 (indicated by the letter B in Fig. 2) included in the reheat boiler 10A according to the first embodiment as indicated in Fig. 3.

By thus supplying the combustion air 11b-1 to 11b-3 into the reheat furnace 108 from the positions opposite to the reheat burner 107 and finely adjusting the air volumes of the combustion air 11b-2 and the combustion air 11b-3, temperature unevenness near the outlet of the reheat furnace 108 can be suppressed.

Fine adjustment of the flow rates of the combustion air 11b-1 to 11b-3 can in turn adjust temperature, retention time, and other conditions of an area where reduction takes place, thereby suppressing the formation of NO_x. For example, making the flow rate of the combustion air 11b-1 small and the flow rate of the combustion air 11b-3 large to cause a shortage of air in the reheat furnace 108 can suppress the formation of NO_x.

Accordingly, in the reheat boiler 10B according to the present embodiment, by delivering the combustion air 11b-1 to 11b-3 through the combustion air supply portions 12-1 to 12-3 disposed at intervals in the height direction and at the positions opposite to the reheat burner 107 in the reheat furnace 108 and finely adjusting the flow rates of the combustion air 11b-1 to 11b-3 supplied into the reheat furnace 108, the gas flow patterns from the reheat burner 107 can be changed. Consequently, temperature unevenness of the combustion gas 107a on the outlet side of the reheat furnace 108 can be further reduced. This configuration prevents heat conductivity drops of the reheat furnace 108 and the reheater 109 and also prevents high-temperature corrosion of the reheater tubes and strength drops of the support members in the reheater 109.

The mixture degrees of the combustion gas 107a with the combustion air 11b-1 to 11b-3 can be finely adjusted, whereby the temperature distribution at the outlet of the reheat furnace 108 can be controlled. Furthermore, fine adjustment of the air volumes of the combustion air 11b-1 to 11b-3 can in turn adjust conditions of an area where reduction takes place in the reheat furnace 108, thereby suppressing the formation of NO_x.

While three stages of the combustion air supply portions 12-1 to 12-3 are disposed at intervals in the height direction of the reheat furnace 108 in the reheat boiler 10B according to the present embodiment, the present invention is not limited thereto. Three or more stages of such air supply portions 12 may be provided.

With the reheat boilers 10A and 10B according to the present invention, by supplying a part 11b of the combustion air into the reheat furnace 108 from the position(s) opposite to the reheat burner 107 in the reheat furnace 108, the flow patterns of the combustion gas are changed, whereby temperature unevenness of the combustion gas on the outlet side of the reheat furnace 108 can be reduced. Therefore, they are applicable for marine boilers; however, the present invention is not limited thereto.

As described above, the reheat boilers and methods for adjusting the temperature of gas output from a reheat boiler according to the present invention can change the flow patterns of combustion gas by supplying a part of combustion air into a reheat furnace through at least one combustion air supply portion disposed at intervals in the height direction of the reheat furnace and at position(s) opposite to a reheat burner in the reheat furnace. Therefore, they are applicable for marine reheat boilers intended to reduce temperature unevenness of the combustion gas on the outlet side of the reheat furnace.