JPH05288301A - Coal firing discharged gas re-igniting combined cycle plant - Google Patents

Abstract

PURPOSE:To improve a combustion stability, simplify a facility, reduce a facility expenditure, decrease a consumption power and further reduce a leaking rate of an air preheater. CONSTITUTION:A primary air duct 15 having a primary air preheater 7 for use in preheating primary air with discharged gas flowing in a boiler discharged gas branching duct 23 branched from a boiler discharged gas duct 17 at an upstream side of a gas cooler 9 arranged in the midway part thereof is connected to a mill 4 connected to a fuel pipe 14 of a boiler 1, a primary blower 5 is arranged at an upstream side and then a primary air preheater bypass duct 24 connecting an upstream side and a downstream side of the primary air preheater 7 is installed. A secondary air preheater 8 for use in preheating secondary air with heat of the discharged gas flowing within the boiler discharged gas duct 17 is arranged in the midway part of the secondary air duct 16 of the boiler 1. A steam type air preheater 11 is arranged in the midway part of the secondary air duct 16 at an upstream side of the secondary air preheater 8 and a forced drafting machine 6 is arranged at an upstream side of it.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coal-fired exhaust gas re-combustion combined cycle plant.

[0002]

2. Description of the Related Art In recent years, a generator is driven by a gas turbine, and unburned oxygen in turbine exhaust gas from the gas turbine is used to burn fuel in a boiler, and the generator is driven by steam generated in the boiler. A coal-fired exhaust gas re-combustion combined cycle plant that heats feed water supplied to the boiler by the boiler exhaust gas has been put into practical use.

A flow mainly composed of a gas system of the coal-fired exhaust gas re-combustion combined cycle plant is shown in FIG. 3, in which 1 is a coal-fired boiler, 2 is a gas turbine, and 3 is a gas turbine.
Is a generator driven by the gas turbine 2, and the boiler 1 is provided with a fuel pipe 14 for supplying pulverized coal as a fuel, and a secondary air duct 16 for supplying secondary air for combustion. And a boiler exhaust gas duct 17 for discharging the combustion exhaust gas from the chimney via an electric dust collector (not shown).

An air preheater 8'for preheating the secondary air by the heat of the exhaust gas flowing in the boiler exhaust gas duct 17 is provided in the middle of the secondary air duct 16 and the upstream side of the air preheater 8 '. A push-in fan 6 is provided in the.

A coal crushing mill 4 is connected to the fuel pipe 14, and the mill 4 is branched from a secondary air duct 16 downstream of the air preheater 8'and a primary blower 5 is provided midway. Is connected to the primary air duct 15.

A gas cooler 9 for heating the feed water fed to the boiler 1 and cooling the exhaust gas is provided in the middle of the boiler exhaust gas duct 17 upstream of the air preheater 8 ', and the primary An exhaust gas introduction duct 18 for introducing the exhaust gas of the gas turbine 2 is connected in the middle of the secondary air duct 16 downstream of the branch portion of the air duct 15, and the exhaust gas introduction branch duct 1 is branched from the exhaust gas introduction duct 18.
9 is connected in the middle of the primary air duct 15, and a boiler bypass exhaust duct 20 that branches from the exhaust introduction duct 18 and bypasses the boiler 1 is connected in the middle of the boiler exhaust gas duct 17 upstream of the gas cooler 9. ..

An air preheater bypass duct 21 that branches from the secondary air duct 16 upstream of the air preheater 8'and bypasses the air preheater 8'is connected to the primary air blower 5 '.
A gas cooler bypass duct 22 connecting the upstream and downstream positions of the gas cooler 9 is provided in the middle of the boiler exhaust gas duct 17 connected to the upstream primary air duct 15.

In the figure, 26 to 32 are dampers that can open and close the ducts.

During the so-called steam power alone operation in which only the boiler 1 is driven, the dampers 28, 29, 30 are closed and the gas turbine 2 is disconnected, and the damper 31 is closed and the damper 32 is opened. Then, the air pressure-fed by the forced draft fan 6 into the secondary air duct 16 is heated by the exhaust gas from the boiler 1 in the air preheater 8 ′ and then flows through the secondary air duct 16 as it is for combustion. While being supplied to the boiler 1 as secondary air, a part of it is branched to the side of the primary air duct 15 and is introduced into the mill 4 as primary air for fuel transportation through the primary air blower 5 and is accompanied by pulverized coal and fuel. The pulverized coal is burned by being supplied from the pipe 14 to the boiler 1.

The exhaust gas after combustion of the pulverized coal flows from the boiler exhaust gas duct 17 through the gas cooler bypass duct 22, bypasses the gas cooler 9 and is introduced into the air preheater 8 ', and the forced draft is blown by the air preheater 8'. After exchanging heat with the air pressure-fed from the machine 6, the air is discharged from the chimney via an electric dust collector (not shown).

Here, when the amount of water in the coal pulverized in the mill 4 is small and it is not necessary to raise the temperature of the primary air so much, the opening degree of the damper 26 of the air preheater bypass duct 21 is adjusted. By doing so, a part of the air before being heated by the air preheater 8 ′ is guided to the primary air duct 15, and the temperature of the primary air is adjusted.

On the other hand, at the time of so-called combined operation in which the boiler 1 and the gas turbine 2 are simultaneously driven, the damper 32 is closed and the damper 31 is opened. In this state, the forced draft fan 6 pressure-feeds the secondary air duct 16 into the secondary air duct 16. When the generated air is heated by the exhaust gas from the boiler 1 in the air preheater 8 ′ and then flows through the secondary air duct 16 as it is to be supplied to the boiler 1 as secondary air for combustion, the secondary air Exhaust gas from the gas turbine 2 is mixed into air through the exhaust gas introduction duct 18.

At the same time, a part of the air that has passed through the air preheater 8'is branched to the side of the primary air duct 15 and the primary fan 5 is blown.
Is introduced into the mill 4 as primary air for fuel transfer via
The pulverized coal is supplied from the fuel pipe 14 to the boiler 1 and is burned.

The exhaust gas after combustion of the pulverized coal flows through the boiler exhaust gas duct 17 and, when passing through the gas cooler 9, is deprived of heat by the feed water supplied to the boiler 1 and cooled, and thereafter, the air preheater. After being introduced into the air preheater 8 ', heat is exchanged with the air fed under pressure from the forced draft fan 6'in the air preheater 8', and then discharged from the chimney via an electric dust collector (not shown).

Here, when the amount of water in the coal pulverized in the mill 4 is small and it is not necessary to raise the temperature of the primary air so much, the opening degree of the damper 26 of the air preheater bypass duct 21 is adjusted. By doing so, a part of the air before being heated by the air preheater 8 ′ is guided to the primary air duct 15, the temperature of the primary air is adjusted, and the amount of water in the coal is very large and the primary air is When it is necessary to further raise the temperature of the gas turbine 2, the damper 26 is closed and the opening degree of the damper 29 of the exhaust introduction branch duct 19 is increased, and the gas turbine 2
The exhaust gas from the air is mixed with the primary air to raise the temperature of the primary air.

[0016]

However, in the coal-fired exhaust gas re-combustion combined cycle plant as described above, when the amount of water in the coal pulverized in the mill 4 during the combined operation is large, the primary air from the gas turbine 2 is discharged. Since the exhaust gas is used, the oxygen concentration of the primary air decreases,
It had a problem of lacking combustion stability.

Further, since the primary air blower 5 is installed on the downstream side of the air preheater 8 ', that is, on the high temperature side, the volumetric flow rate of the primary air passing through the primary air blower 5 increases, and a plurality of mills 4 are provided. In that case, the same number of primary ventilators 5 as that is required, which leads to complication of equipment and an increase in equipment cost, and also increases power consumption.

Furthermore, the gas cooler 9 is used when the steam power is independently operated.
Since the exhaust gas inlet temperature of the air preheater 8'is high and the difference from the air inlet temperature is large because it is not used, the exhaust gas inlet temperature of the air preheater 8'is low because the gas cooler 9 is used during combined operation. Since the difference with the inlet temperature becomes small, the thermal strain generated in the air preheater 8 ′ accompanying the switching between the steam power single operation and the combined operation becomes very large, and the leak rate of the air preheater 8 ′ also becomes high. It was happening.

In view of the above situation, the present invention is a coal-fired fuel which has excellent combustion stability, simplifies the equipment, reduces the equipment cost, reduces the power consumption, and reduces the leak rate of the air preheater. The present invention aims to provide an exhaust gas recombustion combined cycle plant.

[0020]

The present invention provides a boiler with a fuel pipe for supplying pulverized coal as fuel, a secondary air duct for supplying secondary air for combustion, and a combustion exhaust gas. A boiler exhaust gas duct for discharging is connected, a mill for coal crushing is connected to the fuel pipe, and a primary air duct for supplying primary air for fuel transportation to the mill is connected to the primary air. To preheat the primary air with the heat of the exhaust gas flowing in the boiler exhaust gas branch duct branched from the boiler exhaust gas duct in the middle of the duct and the secondary air duct, and to preheat the secondary air with the heat of the exhaust gas flowing in the boiler exhaust gas duct. Of the air preheater, a primary air blower is connected to the primary air duct upstream of the air preheater, and a forced draft fan is connected to the secondary air duct upstream of the air preheater. An air preheater bypass duct that connects the primary air ducts at upstream and downstream positions of the air preheater is provided, and a steam type air preheater is provided in the middle of the secondary air duct between the forced draft fan and the air preheater, and the air preheater is used. In the middle of the boiler exhaust gas duct on the upstream side of the reactor, a gas cooler for heating the feed water fed to the boiler and cooling the exhaust gas is provided, and a gas cooler bypass duct that connects the boiler exhaust gas ducts at the upstream and downstream positions of the gas cooler is provided, A boiler bypass exhaust duct, which is connected to an exhaust introduction duct for introducing exhaust gas of a gas turbine and is branched from the exhaust introduction duct and bypasses the boiler, is connected to the gas cooler in the middle of the secondary air duct downstream of the air preheater. A coal-fired exhaust gas re-combustion combined cycle plant characterized by being connected to the boiler exhaust gas duct on the upstream side It is hunt thing.

In the coal-fired exhaust gas re-combustion combined cycle plant, a steam type air preheater is provided in the middle of the primary air duct between the branch position of the air preheater bypass duct and the air preheater to branch the boiler bypass exhaust duct. A gas cooler for heating the feed water sent to the boiler and cooling the exhaust gas of the gas turbine is provided in the middle of the exhaust introduction duct upstream of the position, and the gas cooler bypass duct is downstream from the connection position of the boiler bypass exhaust duct. Also, a denitration device is installed in the boiler exhaust gas duct upstream of the branch position of the boiler exhaust gas branch duct, and the boiler is branched from the boiler exhaust gas duct midway between the gas cooler and the connection position of the gas cooler bypass duct and upstream of the air preheater. Boiler exhaust gas branch auxiliary duct connected in the middle of the exhaust gas branch duct It may be formed.

[0022]

[Operation] Therefore, during the steam power alone operation, after the air forced into the secondary air duct by the forced draft fan is preheated by the steam type air preheater and then heated by the exhaust gas from the boiler by the air preheater, The air that flows in the secondary air duct is supplied to the boiler as secondary air for combustion, and the air that has been pressure-fed into the primary air duct by the primary air blower is the exhaust gas that flows in the boiler exhaust gas branch duct in the air preheater. After being heated, it is introduced into the mill as primary air for fuel transportation, is supplied from the fuel pipe to the boiler with pulverized coal, the pulverized coal is burned, and part of the exhaust gas after combustion of the pulverized coal is , Flows from the boiler exhaust gas duct through the gas cooler bypass duct, bypasses the gas cooler and is introduced into the air preheater, and the air preheater is pressure-fed from the forced draft fan in the air preheater. Through which heat is exchanged with the preheated air, and the exhaust gas other than that is branched from the boiler exhaust gas duct to the boiler exhaust gas branch duct and introduced into the air preheater, and in the air preheater, the primary blower is introduced. Heat is exchanged with the air pumped from, where the amount of water in the coal crushed in the mill is small, and when the temperature of the primary air does not need to be raised too much, it is heated with an air preheater. A portion of the previous air is introduced into the mill via the air preheater bypass duct and the temperature of the primary air is adjusted.

On the other hand, during the combined operation, the air forced into the secondary air duct by the forced draft fan is not preheated only by passing through the steam type air preheater but is heated by the exhaust gas from the boiler in the air preheater. After that, when it flows in the secondary air duct and is supplied to the boiler as secondary air for combustion, the exhaust gas from the gas turbine is mixed into the secondary air through the exhaust introduction duct, and at the same time, the primary air blower. The air pumped into the primary air duct by the air is heated by the exhaust gas flowing in the boiler exhaust gas branch duct in the air preheater and then introduced into the mill as the primary air for fuel transportation, and from the fuel pipe along with pulverized coal. The pulverized coal is supplied to the boiler and burned, and part of the exhaust gas after combustion of the pulverized coal flows through the boiler exhaust gas duct and is sent to the boiler when passing through the gas cooler. Deprived of heat is cooled, after this,
It is introduced into the air preheater, and in the air preheater, heat is exchanged with the air which is not preheated only by passing under pressure from the forced draft fan and passing through the steam type air preheater. Branches from the upstream high temperature part boiler exhaust gas duct to the boiler exhaust gas branch duct, is introduced into the air preheater, and performs heat exchange with the air pressure-fed from the primary fan in the air preheater, where the inside of the mill When the amount of water in the coal pulverized in is low and it is not necessary to raise the temperature of the primary air so much, part of the air before being heated by the air preheater is passed to the mill via the air preheater bypass duct. Is introduced, the temperature of the primary air is adjusted, and
When the amount of water in the coal is very large and it is necessary to further raise the temperature of the primary air, by guiding a part of the exhaust gas of the gas turbine to the boiler exhaust gas duct through the boiler bypass exhaust duct, the boiler exhaust gas branching is performed. The temperature of the exhaust gas flowing in the duct and introduced into the air preheater is increased.

Further, in the case of adding a denitration device etc., in the steam power independent operation, the air pressure-fed into the secondary air duct by the forced draft fan is preheated by the steam type air preheater and then the air preheater is used. After being heated by the exhaust gas from the air, it flows in the secondary air duct and is supplied to the boiler as secondary air for combustion, and the air that is pressure-fed by the primary air blower into the primary air duct is steam-type air preheat. After being preheated by the furnace, it is heated by the exhaust gas flowing in the boiler exhaust gas branch duct by the air preheater, then introduced into the mill as primary air for fuel transportation, and is supplied to the boiler from the fuel pipe together with pulverized coal, The charcoal is burned, and the exhaust gas after burning the pulverized coal passes through a denitration device to be denitrified, and a part of it is discharged from the boiler exhaust gas duct to the gas cooler bypass duct. Flow, bypassing the gas cooler and introduced into the air preheater, where heat is exchanged with the preheated air that has been pressure-fed from the forced draft fan in the air preheater and passed through the steam air preheater, and The exhaust gas is branched from the boiler exhaust gas duct to the boiler exhaust gas branch duct, introduced into the air preheater, and exchanges heat with the air pressure-fed from the primary fan in the air preheater, where it is pulverized in the mill. When the amount of water in the coal is low and it is not necessary to raise the temperature of the primary air so much, a part of the air before being heated by the air preheater is introduced to the mill through the air preheater bypass duct. The temperature of the primary air is adjusted.

On the other hand, during the combined operation, the air pressure-fed into the secondary air duct by the forced draft fan is not preheated only by passing through the steam type air preheater but is heated by the exhaust gas from the boiler in the air preheater. After that, when the air flows in the secondary air duct and is supplied to the boiler as secondary air for combustion, heat is taken from the water supplied from the gas turbine and sent to the boiler by the gas cooler. Air mixed into the secondary air through the exhaust introduction duct, at the same time, the air pressure-fed into the primary air duct by the primary fan,
After passing through the steam-type air preheater and not being preheated, it is heated by the exhaust gas flowing in the boiler exhaust gas branch duct in the air preheater and then introduced into the mill as the primary air for fuel transportation, and the fuel is accompanied by pulverized coal. It is supplied to the boiler from a pipe, the pulverized coal is burned, and the exhaust gas after combustion of the pulverized coal passes through a denitration device for denitration, flows through the boiler exhaust gas duct, and is sent to the boiler when passing through the gas cooler. It is cooled by the heat supplied to the supplied water, after which part of the exhaust gas is introduced into the air preheater, and in the next air preheater, it is pressure-fed from the forced draft fan and passes through the steam air preheater. Heat exchange with the unpreheated air, and the other exhaust gas is branched from the boiler exhaust gas duct to the boiler exhaust gas branch auxiliary duct, introduced into the air preheater, and then placed in the air preheater. Performing heat exchange with air pumped from the primary ventilator.

Here, when the amount of water in the coal pulverized in the mill is small and it is not necessary to raise the temperature of the primary air so much, part of the air before being heated by the air preheater is air. It is guided to the mill through the preheater bypass duct, the temperature of the primary air is adjusted, and when there is a large amount of water in the coal and it is necessary to raise the temperature of the primary air, it is pumped from the primary fan. Air is preheated by the steam air preheater and then introduced to the air preheater, and part of the hot exhaust gas before passing through the gas cooler is introduced to the air preheater via the boiler exhaust gas branch duct, and the coal When the amount of water in the air is higher and it is necessary to raise the temperature of the primary air further, a part of the gas turbine exhaust is guided to the boiler exhaust gas duct through the boiler bypass exhaust duct, so that the boiler exhaust gas branch duct The temperature of the exhaust gas is increased to be introduced to flow into the air preheater inner, this result, the temperature of the primary air introduced into the mill can be more finely adjusted according to the amount of moisture in the coal.

[0027]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an embodiment of the present invention.
The parts denoted by the same reference numerals as in FIG. 3 represent the same things, and the mill 4 connected to the fuel pipe 14 leading to the boiler 1
Is connected to a primary air duct 15 in which a primary air preheater 7 for preheating the primary air by the heat of exhaust gas flowing in a boiler exhaust gas branch duct 23 described later is provided,
A primary air blower 5 is provided on the upstream side of the primary air preheater 7 of the primary air duct 15, and a primary air preheater bypass duct 24 connecting the upstream and downstream positions of the primary air preheater 7 is provided.

Secondary air duct 16 connected to the boiler 1
A secondary air preheater 8 for preheating the secondary air with the heat of the exhaust gas flowing in the boiler exhaust gas duct 17 is provided on the way, and the secondary air duct 1 upstream of the secondary air preheater 8 is provided.
6. A steam type air preheater 11 is provided on the way, and a forced draft fan 6 is provided on the upstream side of the steam type air preheater 11.

A boiler exhaust gas branch duct 23, which branches from the boiler exhaust gas duct 17 upstream of the gas cooler 9 and is connected to the boiler exhaust gas duct 17 downstream of the secondary air preheater 8, is provided in the middle of the boiler exhaust gas branch duct 23. Is provided with the primary air preheater 7.

In the figure, 33 to 36 are dampers that can open and close each duct.

Next, the operation of the above embodiment will be described.

During the so-called steam alone operation in which only the boiler 1 is driven, the damper 31 is closed and the damper 32 is opened. In this state, the forced draft fan 6 is used to drive the secondary air duct 1
The air pressure-fed into 6 is preheated by the steam type air preheater 11 and then heated by the exhaust gas from the boiler 1 in the secondary air preheater 8 and then flows in the secondary air duct 16 for combustion. While being supplied to the boiler 1 as secondary air,
The air pressure-fed by the primary fan 5 into the primary air duct 15 is transferred to the boiler exhaust gas branch duct 2 by the primary air preheater 7.
After being heated by the exhaust gas flowing in 3, the air is introduced into the mill 4 as primary air for fuel transportation and is supplied to the boiler 1 from the fuel pipe 14 together with the pulverized coal, and the pulverized coal is burned.

Part of the exhaust gas after combustion of the pulverized coal is transferred from the boiler exhaust gas duct 17 to the gas cooler bypass duct 2
2 which flows through the gas cooler 9 and bypasses the gas cooler 9 and is introduced into the secondary air preheater 8 in which air is preheated from the forced draft fan 6 through the steam air preheater 11. Exhaust gas other than that exchanges heat from the boiler exhaust gas duct 17 to the boiler exhaust gas branch duct 23.
And is introduced into the primary air preheater 7, and after exchanging heat with the air pressure-fed from the primary air blower 5 in the primary air preheater 7, it joins the exhaust gas flowing in the boiler exhaust gas duct 17. , Is discharged from the chimney via an electric dust collector (not shown).

Here, when the amount of water in the coal pulverized in the mill 4 is small and it is not necessary to raise the temperature of the primary air so much, the opening degree of the damper 34 of the primary air preheater bypass duct 24 is set. By adjusting, a part of the air before being heated by the primary air preheater 7 is guided to the mill 4, and the temperature of the primary air is adjusted.

On the other hand, at the time of so-called combined operation in which the boiler 1 and the gas turbine 2 are simultaneously driven, the damper 32 is closed and the damper 31 is opened, and in this state, the forced draft fan 6 feeds the compressed air into the secondary air duct 16. The generated air is heated by the exhaust gas from the boiler 1 in the secondary air preheater 8 without passing through the steam type air preheater 11 and is not preheated, and then flows in the secondary air duct 16 for combustion. When the secondary air is supplied to the boiler 1, the exhaust air from the gas turbine 2 is mixed into the secondary air via the exhaust introduction duct 18.

At the same time, the air pressure-fed by the primary fan 5 into the primary air duct 15 is heated by the exhaust gas flowing in the boiler exhaust gas branch duct 23 by the primary air preheater 7 and then used as primary air for fuel transportation. The pulverized coal is introduced into the mill 4 and is supplied from the fuel pipe 14 to the boiler 1 together with the pulverized coal, and the pulverized coal is burned.

A part of the exhaust gas after combustion of the pulverized coal flows through the boiler exhaust gas duct 17 and, when passing through the gas cooler 9, the water supplied to the boiler 1 removes heat and is cooled. It is introduced into the secondary air preheater 8 and in the secondary air preheater 8, heat is exchanged with the air that is not preheated only by passing under pressure from the forced draft fan 6 and passing through the steam type air preheater 11. , The other exhaust gas branches from the boiler exhaust gas duct 17 to the boiler exhaust gas branch duct 23, is introduced into the primary air preheater 7, and exchanges heat with the air pressure-fed from the primary fan 5 in the primary air preheater 7. After that, it joins the exhaust gas flowing in the boiler exhaust gas duct 17, and is discharged from the chimney via an electric dust collector (not shown).

Here, when the amount of water in the coal pulverized in the mill 4 is small and it is not necessary to raise the temperature of the primary air so much, the opening degree of the damper 34 of the primary air preheater bypass duct 24 is adjusted. By adjusting, a part of the air before being heated by the primary air preheater 7 is guided to the mill 4, the temperature of the primary air is adjusted, and the amount of water in the coal is very large, When it is necessary to raise the temperature further, the damper 34 is closed and the damper 30 of the boiler bypass exhaust duct 20 is opened to guide a part of the exhaust gas of the gas turbine 2 to the boiler exhaust gas duct 17, thereby making the boiler exhaust gas branch duct 23 The temperature of the exhaust gas flowing inside and introduced into the primary air preheater 7 is increased.

In this embodiment, even when the amount of water in the coal crushed in the mill 4 during the combined operation is large, the exhaust gas from the gas turbine 2 is not directly used as the primary air but is always fresh. Because air is used,
The oxygen concentration of the primary air does not decrease, and the combustion stability is high.

Further, since the primary air blower 5 is installed upstream of the primary air preheater 7, that is, on the low temperature side, the volumetric flow rate of the primary air passing through the primary air blower 5 does not increase, and a plurality of mills 4 are provided. Even when provided, the same number of primary fans 5 are not required, and the required minimum number (one or two) is sufficient, which simplifies the equipment and reduces the equipment cost, and the power consumption can be reduced.

Furthermore, the gas cooler 9 is used when the steam power is independently operated.
However, since the exhaust gas inlet temperature of the secondary air preheater 8 becomes high, the secondary air introduced into the secondary air preheater 8 is preheated by the steam type air preheater 11 and the secondary air preheater 8 Since the air inlet temperature of the secondary air preheater 8 is increased, the difference between the exhaust gas inlet temperature of the secondary air preheater 8 and the air inlet temperature becomes small, and the secondary air preheater 8 is switched to the secondary air preheater 8 with the switching between the steam alone operation and the combined operation. The generated thermal strain is reduced, and the leak rate of the secondary air preheater 8 can be reduced.
In addition, since the amount of air passing through the secondary air preheater 8 in the case of steam power alone operation is larger than that in the case of combined operation, the steam inlet air preheater 11 is used to increase the air inlet temperature of the secondary air preheater 8. However, the exhaust gas outlet temperature of the secondary air preheater 8 can be made equal to that in the combined operation.

FIG. 2 shows another embodiment of the present invention.
In the figure, the parts denoted by the same reference numerals as in FIG. 1 represent the same things, and the primary air duct 15 between the branch position of the primary air preheater bypass duct 24 and the primary air preheater 7.
A steam type air preheater 12 is provided on the way, and the exhaust gas introduction duct 1 upstream of the branch position of the boiler bypass exhaust duct 20 is provided.
A gas cooler 10 for heating the feed water sent to the boiler 1 and cooling the exhaust gas of the gas turbine 2 is provided in the middle of 8, and is located on the downstream side of the connection position of the boiler bypass exhaust duct 20 and the gas cooler bypass duct 22 and the boiler. A denitration device 13 is provided in the middle of the boiler exhaust gas duct 17 upstream of the branch position of the exhaust gas branch duct 23 to branch from the middle of the boiler exhaust gas duct 17 between the connection position of the gas cooler 9 and the gas cooler bypass duct 22 and to the primary air preheater. 7. A boiler exhaust gas branch auxiliary duct 25 connected to the boiler exhaust gas branch duct 23 upstream of 7 is formed, a damper 38 is provided in the boiler exhaust gas branch auxiliary duct 25, and a connection position of the boiler exhaust gas branch auxiliary duct 25. A damper 37 is provided in the middle of the boiler exhaust gas branch duct 23 on the upstream side. Than it is.

In the case of the embodiment shown in FIG. 2, the dampers 31 and 38 are closed and the dampers 32 and 37 are opened during the steam alone operation, and in this state, the forced draft fan 6 feeds the secondary air duct 16 under pressure. The air is preheated by the steam type air preheater 11 and then heated by the exhaust gas from the boiler 1 by the secondary air preheater 8 and then flows through the secondary air duct 16 to serve as secondary air for combustion as a boiler. Exhaust gas that flows into the boiler exhaust gas branch duct 23 by the primary air preheater 7 after the air that has been supplied to No. 1 and is pressure-fed by the primary air blower 5 into the primary air duct 15 is preheated by the steam air preheater 12. After being heated by the fuel pipe 14, it is introduced into the mill 4 as primary air for fuel transportation, and the fuel pipe 14 is accompanied by pulverized coal.
Is supplied to the boiler 1 and the pulverized coal is burned.

Exhaust gas after combustion of the pulverized coal is denitration device 1
3 through which denitration is performed, a part of which flows from the boiler exhaust gas duct 17 through the gas cooler bypass duct 22, bypasses the gas cooler 9 and is introduced into the secondary air preheater 8, and the secondary air preheater In 8, heat exchange is performed with the air that has been pressure-fed from the forced draft fan 6 and has passed through the steam type air preheater 11 and has been preheated, and the other exhaust gas is branched from the boiler exhaust gas duct 17 to the boiler exhaust gas branch duct 23. Then, after heat exchange with the air introduced into the primary air preheater 7 and being pressure-fed from the primary air blower 5 in the primary air preheater 7, it joins the exhaust gas flowing in the boiler exhaust gas duct 17, Exhaust from the chimney via an electrostatic precipitator not shown.

Here, when the amount of water in the coal pulverized in the mill 4 is small and it is not necessary to raise the temperature of the primary air so much, the opening degree of the damper 34 of the primary air preheater bypass duct 24 is adjusted. By adjusting, a part of the air before being heated by the primary air preheater 7 is guided to the mill 4, and the temperature of the primary air is adjusted.

On the other hand, during combined operation, the damper 3
2, 37 are closed and the dampers 31, 38 are opened. In this state, the air forced into the secondary air duct 16 by the forced draft fan 6 only passes through the steam air preheater 11 and is not preheated. After being heated by the exhaust gas from the boiler 1 in the secondary air preheater 8 and then supplied to the boiler 1 as secondary air for combustion flowing in the secondary air duct 16, the gas cooler is discharged from the gas turbine 2. The exhaust gas, which is deprived of heat by the water supplied to the boiler 1 at 10 and cooled, is mixed into the secondary air through the exhaust introduction duct 18.

At the same time, the air pressure-fed into the primary air duct 15 by the primary air blower 5 passes through the steam type air preheater 12 only and is not preheated. After being heated by the flowing exhaust gas, it is introduced into the mill 4 as primary air for fuel transportation,
The pulverized coal is supplied from the fuel pipe 14 to the boiler 1 and is burned.

The exhaust gas after the combustion of the pulverized coal is the denitration device 1
3, denitration is carried out, flows through the boiler exhaust gas duct 17, and when passing through the gas cooler 9, the water supplied to the boiler 1 removes heat and is cooled. It is introduced into the secondary air preheater 8 and in the secondary air preheater 8, heat is exchanged with the air that is not preheated only by passing under pressure from the forced draft fan 6 and passing through the steam type air preheater 11. The other exhaust gas branches from the boiler exhaust gas duct 17 to the boiler exhaust gas branching auxiliary duct 25 and is introduced into the primary air preheater 7, and the primary air preheater 7
In the above, the heat is exchanged with the air pressure-fed from the primary blower 5, and then the heat is exchanged with the exhaust gas flowing in the boiler exhaust gas duct 17, and is discharged from the chimney via an electric dust collector (not shown).

Here, when the amount of water in the coal pulverized in the mill 4 is small and it is not necessary to raise the temperature of the primary air so much, the opening degree of the damper 34 of the primary air preheater bypass duct 24 is adjusted. By adjusting, a part of the air before being heated by the primary air preheater 7 is guided to the mill 4, the temperature of the primary air is adjusted, and the amount of water in the coal is large and the temperature of the primary air is adjusted. When it is necessary to increase the temperature, the air blown from the primary blower 5 is preheated by the steam type air preheater 12 by closing the damper 34, and then the air is guided to the primary air preheater 7, and the boiler exhaust gas branching assist is also provided. By closing the damper 38 of the duct 25 and opening the damper 37 of the boiler exhaust gas branch duct 23, a part of the high-temperature exhaust gas before passing through the gas cooler 9 is transferred from the boiler exhaust gas branch duct 23 to the primary air. It is guided to the heat unit 7. When the amount of water in the coal is large and it is necessary to further raise the temperature of the primary air, the damper 30 of the boiler bypass exhaust duct 20 is used.
By opening a part of the exhaust gas of the gas turbine 2 to the boiler exhaust gas duct 17,
The temperature of the exhaust gas flowing inside and introduced into the primary air preheater 7 is increased. As a result, the temperature of the primary air introduced into the mill 4 can be adjusted more finely according to the amount of water in the coal.

In the embodiment shown in FIG. 2, as in the embodiment shown in FIG. 1, even when the amount of water in the coal pulverized in the mill 4 during the combined operation is large, the gas turbine 2 is used as the primary air. Since the exhaust air from is not used directly but fresh air is always used, the oxygen concentration of the primary air does not decrease, the combustion stability is high,
In addition, since the primary air blower 5 is installed upstream of the primary air preheater 7, that is, on the low temperature side, the volume flow of the primary air passing through the primary air blower 5 does not increase, and a plurality of mills 4 are provided. Moreover, the same number of primary ventilators 5 is not required, and the required minimum (1 or 2) is required, which helps simplify the equipment and reduces the equipment cost, and also reduces the power consumption. Sometimes the gas cooler 9 is not used, so the exhaust gas inlet temperature of the secondary air preheater 8 rises,
The secondary air introduced into the secondary air preheater 8 is preheated by the steam type air preheater 11 and the air inlet temperature of the secondary air preheater 8 is raised, so the exhaust gas inlet of the secondary air preheater 8 is increased. The difference between the temperature and the air inlet temperature becomes small, the thermal strain generated in the secondary air preheater 8 accompanying the switching between the steam power single operation and the combined operation becomes small, and the leak rate of the secondary air preheater 8 is reduced. You can

Further, in the case of the embodiment shown in FIG. 2, assuming that the steam type air preheater 12 is not provided, in the combined operation, when the amount of water in the coal is small, the primary air preheater 7 is provided with a gas cooler. Since the exhaust gas after passing through No. 9 is introduced, the exhaust gas inlet temperature of the primary air preheater 7 is low and the difference from the air inlet temperature is small, whereas when the water content in the coal is large, the primary air preheater 7 Since the exhaust gas before passing through the gas cooler 9 is introduced into the primary air preheater 7
Since the exhaust gas inlet temperature of the coal is high and the difference from the air inlet temperature is large, the thermal strain generated in the primary air preheater 7 with the change in the amount of water in the coal becomes very large, and the primary air preheater 7
However, when the exhaust gas inlet temperature of the primary air preheater 7 is high, the primary air introduced into the primary air preheater 7 is preheated by the steam air preheater 12,
Since the air inlet temperature of the primary air preheater 7 is raised,
The difference between the exhaust gas inlet temperature and the air inlet temperature of the primary air preheater 7 becomes small, the thermal strain generated in the primary air preheater 7 due to the change of the water content in the coal becomes small, and the leakage of the primary air preheater 7 The rate can be reduced.

Further, in the case of the embodiment shown in FIG. 2, since the exhaust gas of the gas turbine 2 can be appropriately introduced to the upstream side of the denitration device 13, the exhaust gas inlet temperature of the denitration device 13 can be secured.

The coal-fired exhaust gas re-combustion combined cycle plant of the present invention is not limited to the above-mentioned embodiment, and the primary air preheater and the secondary air preheater are integrated twin-flow type air preheaters. It is also possible to install a primary air blower on the downstream side of the forced draft fan, and a part of the air pressure-fed from the forced draft fan may be further boosted by the primary draft fan to be the primary air, etc. Of course, various changes can be made without departing from the scope of the present invention.

[0055]

As described above, the first aspect of the present invention is as described above.
According to the coal-fired exhaust gas re-combustion combined cycle plant described, the combustion stability is excellent, the facility can be simplified and the facility cost can be reduced and the power consumption can be reduced, and the leakage rate on the secondary air side of the air preheater can be reduced. In addition to the above effects, according to the coal-fired exhaust gas re-combustion combined cycle plant of claim 2 of the present invention, the temperature of the primary air introduced into the mill is It is possible to make finer adjustments according to the amount of water, reduce the leak rate on the primary air side of the air preheater, and appropriately introduce the exhaust gas of the gas turbine to the upstream side of the denitration device. The excellent effect that the exhaust gas inlet temperature can be secured can be obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing a gas system according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a gas system according to another embodiment of the present invention.

FIG. 3 is a block diagram showing a gas system of a conventional example.

[Explanation of symbols]

1 Boiler 2 Gas turbine 4 Mill 5 Primary air blower 6 Pushing air blower 7 Primary air preheater (air preheater) 8 Secondary air preheater (air preheater) 9 Gas cooler 10 Gas cooler 11 Steam type air preheater 12 Steam type air Preheater 13 Denitration device 14 Fuel pipe 15 Primary air duct 16 Secondary air duct 17 Boiler exhaust gas duct 18 Exhaust introduction duct 20 Boiler bypass exhaust duct 22 Gas cooler bypass duct 23 Boiler exhaust gas branch duct 24 Primary air preheater bypass duct (Air preheater Bypass duct) 25 Boiler exhaust gas branching auxiliary duct

Claims (2)

[Claims] 1. A fuel pipe for supplying pulverized coal as a fuel to a boiler, a secondary air duct for supplying secondary air for combustion, and a boiler exhaust gas duct for discharging combustion exhaust gas. And a mill for coal crushing is connected to the fuel pipe, and a primary air duct for supplying primary air for fuel transportation to the mill is connected to the primary air duct and the secondary air duct midway. An air preheater for preheating the primary air with the heat of the exhaust gas flowing in the boiler exhaust gas branch duct branched from the boiler exhaust gas duct and for preheating the secondary air with the heat of the exhaust gas flowing in the boiler exhaust gas duct, A primary air blower is connected to the primary air duct upstream of the air preheater, and a forced draft fan is connected to the secondary air duct upstream of the air preheater. An air preheater bypass duct connecting the primary air ducts is provided, a steam type air preheater is provided in the middle of the secondary air duct between the forced draft fan and the air preheater, and a boiler exhaust gas duct upstream of the air preheater is provided. On the way
A gas cooler is provided for heating the feed water sent to the boiler and cooling the exhaust gas, and a gas cooler bypass duct connecting the boiler exhaust gas ducts at the upstream and downstream positions of the gas cooler is provided, and the secondary air downstream of the air preheater is provided. An exhaust gas introduction duct for introducing exhaust gas of the gas turbine is connected in the middle of the duct, and a boiler bypass exhaust duct that branches from the exhaust gas introduction duct and bypasses the boiler is connected to the boiler exhaust gas duct upstream of the gas cooler. A coal-fired exhaust gas re-combustion combined cycle plant characterized by the above. 2. A steam type air preheater is provided in the middle of the primary air duct between the branch position of the air preheater bypass duct and the air preheater, and in the middle of the exhaust introduction duct upstream of the branch position of the boiler bypass exhaust duct. Provide a gas cooler for heating the feed water sent to the boiler and cooling the exhaust gas of the gas turbine, downstream of the connection position of the boiler bypass exhaust duct and upstream of the branch position of the gas cooler bypass duct and the boiler exhaust gas branch duct. Boiler exhaust gas that is installed in the middle of the boiler exhaust gas duct on the side of The coal-fired exhaust gas reburn combined cycle according to claim 1, wherein a branch auxiliary duct is formed. plant.