JP2892141B2 - Double pressure type waste heat recovery boiler - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention is to generate steam using sensible heat of exhaust gas of a gas turbine using a fuel containing a sulfur component such as heavy oil. Further, the present invention relates to a double-pressure exhaust heat recovery boiler in which a denitration device is incorporated.

(Prior Art) FIG. 3 shows an example of a conventional double-pressure type exhaust heat recovery boiler.
This equipment is of a double pressure type to improve the thermal efficiency of the waste heat recovery boiler.
The superheater 1, the high-pressure evaporator 2, the high-pressure economizer 4, the low-pressure evaporator 5, and the low-pressure economizer 6 are arranged in this order from the upstream side in 20. Further, in order to reduce the amount of NOχ (oxygen nitride) in the exhaust gas, the ammonia injection system 7 is provided with the denitration device 3 upstream of the high-pressure evaporator 2 and upstream of the high-pressure economizer 4. . Note that a chimney 8 for finally discharging exhaust gas to the atmosphere is provided in the exhaust gas duct 20.

By the way, there is a specific problem in the exhaust heat recovery boiler in which the denitration device 3 is incorporated and which recovers heat from gas turbine exhaust gas containing sulfur.

That is, the reaction formula of the denitration by the denitration system is generally expressed by the following formula.

4NO + 4NH ₃ + O ₂ → 4N ₂ + 6H ₂ O (1) However, in order to compensate for the lack of denitration capacity, ammonia more than the amount necessary for the reaction is actually injected into the exhaust gas from the ammonia injection system 7.

Therefore, unreacted ammonia remains on the downstream side of the denitration device 3.
4 reacts with SO ₃ and H ₂ O in the exhaust gas to generate acidic ammonium sulfate.

NH ₃ + SO ₃ + H ₂ O → ← NH ₄ HSO ₄ …… (2) This acidic ammonium sulfate is generally formed at a temperature of about 200 ° C., although it depends on the concentrations of ammonia and SO _{3 in} the exhaust gas.
Therefore, below 200 ° C., liquid or solid acidic ammonium sulfate is present.

FIG. 5 is a temperature diagram of a typical exhaust heat recovery boiler, showing the process of temperature rise and fall due to mutual heat exchange between gas turbine exhaust gas and pipe fluid. From FIG. 5, the gas temperature in the low-pressure evaporator and low-pressure economizer is about 200 ° C.
It turns out that it becomes the following. That is, it is considered that acidic ammonium sulfate is present in the exhaust gas of the low-pressure evaporator 5 and the low-pressure economizer 6.

Therefore, this acidic ammonium sulfate adheres to the outer surfaces of the fin tubes of the low-pressure evaporator 5 and the low-pressure economizer 6 (usually, fin tubes are used as heat transfer tubes for increasing heat transfer efficiency). Foreign matter such as dust in the exhaust gas adheres to and accumulates on the fin tube using the attached acidic ammonium sulfate as a medium. As a result, the heat transfer efficiency of the fin tubes is reduced, which not only causes the performance of the exhaust heat recovery boiler to deteriorate, but also increases the pressure loss of the exhaust gas flowing through the outer jacket of the exhaust heat recovery boiler, leading to a reduction in the performance of the gas turbine. Eventually, the efficiency of the entire plant will be reduced.

Therefore, conventionally, a soot blower (not shown in FIG. 3) is installed at a position immediately upstream of the low-pressure evaporator 5, between the low-pressure evaporator 5 and the low-pressure economizer 6, and immediately downstream of the low-pressure economizer 6. The fin tube was installed at an appropriate position such as a side position, and during operation, the foreign matter attached and deposited on the outer surface of the fin tube was regularly removed. However, this method can cover the design value and the guaranteed value of the exhaust heat recovery boiler efficiency and gas turbine efficiency until a certain operation time, but after the certain operation time, foreign matter adhesion on the fin tube surface increases. , Below the design values and guaranteed values. Therefore, the operation of the exhaust heat recovery boiler or the entire plant is stopped, the outer surfaces of the fin tubes of the low-pressure evaporator 5 and the low-pressure economizer 6 are washed with water or a mechanical method, and after the work is completed, the operation is started again. I have to do it.

Therefore, when designing and planning an exhaust heat recovery boiler that uses gas turbine exhaust gas containing SO ₃ and incorporates a denitration device, as shown in Fig. 4, the possibility of failure due to acid ammonium sulfate may occur. The exhaust heat recovery boiler was composed of only the high pressure section. That is, the gas turbine exhaust gas passage 20
Inside, a superheater 1, a high-pressure evaporator 2, a denitration device and a high-pressure economizer 4 are arranged in this order from the upstream side.
Was installed between the superheater 1 and the high-pressure evaporator 2.

Further, for example, as shown in JP-A-64-8802, in a double-pressure exhaust heat recovery boiler, when the sulfur content is not contained in the gas turbine exhaust gas, the exhaust gas is also supplied to the low-pressure part. Used to generate low-pressure steam,
In the case where the sulfur content is contained in the exhaust gas of the gas turbine, a method of directly discharging the exhaust gas from the high pressure section to the chimney by bypassing the low pressure section in order to avoid the above-described problem in the low pressure section has been proposed.

(Problems to be Solved by the Invention) As described above, in the conventional exhaust heat recovery boiler, even if a denitration device is incorporated, if the sulfur content is contained in the exhaust gas of the gas turbine, the power generation efficiency or If low-pressure steam generation is indispensable for the needs of industrial process steam, the operation of the waste heat recovery boiler will be stopped for a certain period,
Cleaning of the low pressure section had to be carried out. This is a huge loss from the viewpoint of the extremely high power demand and energy demand these days.

The present invention has been made in view of the above points, and the present invention adheres to the outer surface of a fly tube of a low-pressure part (low-pressure evaporator, low-pressure economizer), adheres as an intermediate to the deposited acidic ammonium sulfate, and removes accumulated foreign matter. An object of the present invention is to provide a double-pressure exhaust heat recovery boiler that includes a denitration device that enables complete removal without stopping the operation of the entire recovery boiler, and that recovers exhaust heat from gas turbine exhaust gas containing sulfur. And

[Configuration of the invention]

(Means for Solving the Problems) According to the present invention, a superheater, a high-pressure evaporator, and a high-pressure economizer are sequentially arranged from the exhaust gas upstream side in a duct in which the exhaust gas flows linearly, and further downstream of the high-pressure economizer. The exhaust gas duct is branched into two sub-ducts so that the exhaust gas is divided into two at the side, and a low-pressure evaporator and a low-pressure economizer are sequentially arranged in each sub-duct from the upstream side, and each of the low-pressure evaporators. The present invention relates to a double-pressure exhaust heat recovery boiler in which dampers are arranged immediately upstream of a vessel and immediately downstream of each low-pressure economizer.

(Operation) In the double-pressure type exhaust heat recovery boiler of the present invention, the exhaust gas is discharged to the plurality of low-pressure sides by being configured such that the plurality of downstream sides can be switched and connected to the upstream side by a damper disposed therein. It can be switched to one of the subducts and discharged. As a result, it adheres to the outer surface of the fly
It is possible to remove the deposited foreign matters that have adhered and accumulated using the acidic ammonium sulfate as a medium without stopping the operation of the entire boiler.

(Example) An example of an exhaust heat recovery boiler of the present invention will be described with reference to FIG.

As shown in FIG. 1, in the exhaust gas duct 20, a superheater 1, a high-pressure evaporator 2, and a high-pressure economizer 4 are arranged in this order from the upstream side. The denitration device 3 is arranged between the high-pressure evaporator 2 and the high-pressure economizer 4, and the ammonia injection system 7 is arranged between the superheater 1 and the high-pressure evaporator 2. Incidentally, the denitration device 3 may be installed between the high pressure evaporator 2 itself in two parts depending on its temperature characteristics.

The exhaust gas duct 20 is branched downstream of the high-pressure economizer 4 into low-pressure sections of two sub-ducts 21a and 21b.
In low pressure evaporators 5a, 5a in order from upstream in 21a, 21b
b, Low pressure economizers 6a and 6b are installed. Also each evaporator 5
Immediately upstream of a and 5b, dampers 9a and 9b
Immediately downstream of a and 6b, dampers 10a and 10b are installed, respectively.

Therefore, when operating the exhaust heat recovery boiler normally, the damper
9a and 10a are fully opened, and the dampers 9b and 10b are fully closed. Gas turbine exhaust gas containing sulfur passes through a superheater 1, a high-pressure evaporator 2, a high-pressure economizer 4, a low-pressure evaporator 5a, and a low-pressure economizer 6a, and is finally discharged from the chimney 8 to the atmosphere. You. At this time, the dampers 9b, 10b are fully closed and the low-pressure evaporator 5b,
Exhaust gas does not flow into the low-pressure economizer 6b.

As described above, during the operation of the exhaust heat recovery boiler, the remaining ammonia that has not reacted in the denitration device 3 reacts with SO ₃ in the exhaust gas, and the outer surface of the low-pressure evaporator 5a and the low-pressure economizer 6a has an outer surface. It precipitates as acid ammonium sulfate, and foreign substances such as dust adhere and accumulate using this as an intermediary.
Therefore, the operation of the exhaust heat recovery boiler is continued while the outer surface of the fly tube is periodically cleaned by a soot blower (not shown) so as not to fall below the performance and design guarantee values of the exhaust heat recovery boiler. However, this cleaning method is not perfect, and at a certain time, foreign matters will be deposited on the outer surface of the feed tube so as to fall below the guaranteed value.

Therefore, when such a situation occurs, the dampers 9b and 10b in the sub duct 21b are first fully opened, and then the dampers 9a and 10a in the sub duct 21a are fully closed. As a result, a predetermined low-pressure steam is generated for a certain period by the low-pressure evaporator 5b and the low-pressure economizer 6b having a clean outer surface of the fly tube. On the other hand, at this time, since the dampers 9a and 10a are completely closed and the leak of exhaust gas is zero, the worker enters the inside of the sub duct 21a from a manhole (not shown) and enters the outer surface of the low-pressure evaporator 5a and the low-pressure coal economizer 6a. The deposited foreign matter can be completely removed by washing with water or a mechanical method. After the cleaning is completed, the low-pressure evaporator 5a and the low-pressure economizer 6a are ready for operation again.

During operation, when the accumulation amount of foreign matter on the outer surface of the low-pressure evaporator 5b and the low-pressure economizer 6b increases and reaches the operation limit, the sub-duct is switched in the reverse procedure to the above-described low-pressure section switching. Then, the sub-duct 21a, the low-pressure evaporator 5a, and the low-pressure economizer 6a are utilized to separate the low-pressure evaporator 5b and the low-pressure economizer 6b of the sub duct 21b from operation. In this way, the two low-pressure sections can be switched appropriately.

Although the embodiment described above shows a case where the present invention is applied to a gas horizontal flow type exhaust heat recovery boiler, the same operation can be achieved in a gas vertical flow type exhaust heat recovery boiler.

Another embodiment of the present invention will be described with reference to FIG. 2, which is a plan view of the entire structure of a two-series double-pressure exhaust heat recovery boiler.

In this two-line dual-pressure exhaust heat recovery boiler, the exhaust gas duct is composed of the upstream ducts 20a and 20b and the upstream ducts 20a and 20b.
a and 20b, each of which comprises two downstream ducts 21a and 21b.

The superheaters 1a, 1b, the high-pressure evaporators 2a, 2b, and the high-pressure economizers 4a, 4b are respectively arranged in the upstream ducts 20a, 20b from the exhaust gas upstream side, and the upstream of the high-pressure economizers 4a, 4b. On the side, denitration devices 3a and 3b and ammonia injection systems 7a and 7b are arranged for the purpose of reducing NO2 in exhaust gas. In addition, low-pressure evaporators 5a and 5b, low-pressure economizer 6 are provided in downstream ducts 21a and 21b.
a and 6b are arranged respectively.

Furthermore, in order to achieve the function intended by the present invention, in the present embodiment, the bypass duct 22 interconnects the exhaust gas passages between the respective high-pressure economizers 4a, 4b and the low-pressure evaporators 5a, 5b of the exhaust heat recovery boiler. The bypass duct 22
Is provided with a damper 13. Also, low-pressure ducts 21a, 2
Immediately upstream of the low-pressure evaporators 5a and 5b of 1b, dampers 12a and 12b capable of completely sealing the exhaust gas passage are provided, respectively.

In addition, 8a and 8b are chimneys that discharge exhaust gas to the atmosphere separately in two lines.

On the other hand, 14a and 14b indicate water supply systems, and low-pressure economizers 6a and 6b
Valves 15a and 15b, low-pressure economizers 6a and 6b
Valves 17a and 17b are provided in the water supply line that supplies water to the higher pressure section, and valves are provided in the water supply line that bypasses the low pressure economizers 6a and 6b.
16a and 16b are provided respectively.

Usually, the two series of waste heat recovery boilers are operated independently. That is, with the damper 13 fully closed, the gas turbine exhaust of each system is supplied to each duct 20a, 20b, 21a, 2
Guided to 1b, each heat exchange section, superheaters 1a, 1b, high-pressure evaporator 2a,
2b, heat exchange with the high-pressure economizers 4a and 4b, the low-pressure evaporators 5a and 5b, and the low-pressure economizers 6a and 6b, and are released into the atmosphere from the chimneys 8a and 8b.

On the other hand, in the water supply system, the valves 15a, 15b, 17a, 17b are fully opened,
When the valves 16a and 16b are fully closed, the water supplied from the water supply systems 14a and 14b is supplied to the low-pressure economizers 6a and 6b.
A part is supplied to low-pressure evaporators 5a and 5b (not shown), and the rest is supplied to high-pressure economizers 4a and 4b.

By the way, as already described, the ammonia remaining without reacting in the denitration apparatus reacts with SO ₃ and H ₂ O in the exhaust gas, and the generated acidic ammonium sulfate is reduced in the low-pressure economizers 6a and 6b and the low-pressure evaporator 5a. Foreign matter adheres to and accumulates on 5b, using the acidic ammonium sulfate as a mediator. At this time, these deposits are removed by a soot blower (not shown), but this is not always effective, and as the operation is continued, the accumulation of foreign substances increases, and the performance of the exhaust heat recovery boiler deteriorates. This leads to lower efficiency.

Therefore, when such a situation occurs, the damper 13 is fully opened and the damper 12a is fully closed in order to remove foreign matter from the low-pressure economizer 6a and the low-pressure evaporator 5a. As a result, the exhaust gas guided to the exhaust heat recovery boiler 10a passes through the superheater 1a, the high-pressure evaporator 2a, and the high-pressure economizer 4a, exchanges heat, passes through the bypass duct 22, and is guided to the low-pressure side duct 21b. And low pressure evaporator 5
b, After passing through the low-pressure economizer 6b and exchanging heat, it is released into the atmosphere from the chimney 8b. On the other hand, in the water supply system, the valves 15a and 17a are fully closed and the valve 16a is fully opened, and the water is supplied to the high-pressure economizer 4a by bypassing the low-pressure economizer 6a and the low-pressure evaporator 5a.

As a result, the exhaust heat recovery boiler operates only on the upstream side, that is, the high pressure section to generate steam (not shown), and on the downstream side, that is, the low pressure section, the exhaust gas is discharged because the damper 12a has a complete sealing function. It does not flow at all here, and the operation is stopped.

Therefore, during that time, the worker enters the exhaust gas passage 21a downstream of the manhole (not shown) and adheres to and accumulates on the outer surface of the fin tube of the low-pressure evaporator 5a and the low-pressure economizer 6a. It can be completely removed by washing with water or a mechanical method.

After the removal operation is completed, the sub ducts are switched in the reverse order of the exhaust gas operation, and the normal operation is performed through the low-pressure evaporator 5a and the low-pressure economizer 6a.

Also for the low-pressure evaporator 5b and the low-pressure economizer 6b, the same operation as described above is performed on the downstream duct 21b, so that the foreign matter and the acidic ammonium sulfate on the outer surface of the fin tube can be completely removed.

By the way, in the present embodiment, it is difficult to operate under the same conditions as in the normal operation by bypassing the downstream side. Therefore, during the cleaning period on the downstream side, it is necessary to consider the operation in which the load of the gas turbine is adjusted, or the specification of the heat transfer surface of the exhaust heat recovery boiler corresponding to the bypass operation.

Although the embodiment described above shows a case where the present invention is applied to a gas horizontal flow type exhaust heat recovery boiler, the same operation can be performed in the case of a gas vertical flow type exhaust heat recovery boiler.

Even when the number of series of the exhaust heat recovery boiler is two or more, the same operation can be performed by performing the same configuration.

The same applies to the exhaust heat recovery boiler in the case of a double-pressure type with two or more high-pressure and low-pressure steam.The denitration device is located at another position, such as the position where the high-pressure evaporator is divided into two, and is located upstream of the low-pressure part. The same phenomenon occurs as long as the position is located, and the effect of the present invention is the same.

 Also, various water supply systems can be considered depending on the plant.

〔The invention's effect〕

As described above, the double-pressure exhaust heat recovery boiler of the present invention incorporates a denitration device, and when the sulfur content is contained in the exhaust gas of the gas turbine, furthermore, in terms of power generation efficiency or the need for industrial process steam. Even when low-pressure steam generation is indispensable in terms of the above, the predetermined high-pressure steam and low-pressure steam are always generated without stopping the operation of the entire boiler by appropriately switching and connecting the downstream side to the upstream side. be able to.

Therefore, it is possible to dramatically increase the plant operation rate, and it is possible to sufficiently cope with recently extremely high power demand and energy demand.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an exhaust heat recovery boiler according to an embodiment of the present invention, FIG. 2 is a configuration diagram of an exhaust heat recovery boiler according to another embodiment of the present invention, and FIG. 3 is a conventional double-pressure exhaust heat recovery boiler. Configuration diagram,
FIG. 4 is a configuration diagram of a conventional single-pressure exhaust heat recovery boiler, and FIG. 5 is a diagram showing temperatures and exchange heat amounts of respective components of the double-pressure exhaust heat recovery boiler. 1, 1a, 1b ... superheater, 2, 2a, 2b ... high-pressure evaporator,
3, 3a, 3b ... denitration equipment, 4, 4a, 4b ... high-pressure economizer,
5a, 5b: Low pressure evaporator, 6a, 6b: Low pressure economizer, 7, 7
a, 7b ... ammonia injection system, 8, 8a, 8b ... chimney, 9
a, 9b, 10a, 10b, 12a, 12b, 13 ... damper, 20 ... exhaust gas duct, 20a, 20b ... upstream duct, 21a, 21b ... downstream subduct.

Claims (2)

(57) [Claims] 1. A superheater, a high-pressure evaporator and a high-pressure economizer are arranged in the exhaust gas duct in which the exhaust gas flows in a straight line from the upstream side, and the exhaust gas is divided into two at the downstream side of the high-pressure economizer. The exhaust gas duct is branched into two sub-ducts so as to flow, and a low-pressure evaporator and a low-pressure economizer are sequentially arranged in the respective sub-ducts from the upstream side, and the upstream side of each of the low-pressure evaporators and each of the low-pressure evaporators. A double-pressure exhaust heat recovery boiler with tampers arranged immediately downstream of the economizer. 2. A two-line exhaust gas duct in which exhaust gas flows in a straight line is divided into an upstream duct and a downstream duct connected to each of the upstream ducts, and each of the upstream ducts is heated sequentially from the upstream side. Vessel, a high-pressure evaporator and a high-pressure economizer are arranged, while a low-pressure evaporator and a low-pressure economizer are sequentially arranged in the respective downstream ducts from the upstream side, and the high-pressure economizer and the low-pressure evaporator are arranged. A multi-pressure exhaust heat recovery system comprising a bypass duct for interconnecting the exhaust gas passages between the low pressure evaporator and a damper in the bypass duct, and a damper disposed immediately upstream of each of the low-pressure evaporators. boiler.