JPH0979504A - Cleaning method for exhaust heat recovery boiler - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for cleaning an economic exhaust heat recovery boiler by reducing a temporary facility. SOLUTION: Degreasing agent such as sodium hydroxide of a specified amount is introduced from the manholes of a high-pressure drum 10 and a low- pressure drum 9. Thereafter, a gas turbine 1 is started, and a load operation of a no-load or more is executed. A high-pressure evaporator 5 and a low- pressure evaporator 7 are heated by this operation to generate steams, which are mutually circulated via the drum 9, a low-pressure downflow tube 9a and the generator 7 at the drum 9 side, and via the drum 10, a high-pressure downflow tube 10 and the generator 5 at the drum 10 side. The agent is circulated via the generators 5, 7 and the drums 9, 10 to degrease it by the circulating operation.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a chemical cleaning method for an exhaust heat recovery boiler.

[0002]

2. Description of the Related Art Combined power plants have recently attracted attention as plants most suitable for high-efficiency power generation and intermediate load operation. This plant generates electricity using a gas turbine, and has an exhaust heat recovery boiler that recovers the heat of the exhaust gas discharged from the gas turbine.The steam generated by the exhaust heat recovery boiler drives a steam turbine to generate power. It is. An example of such an exhaust heat recovery boiler will be described with reference to FIG.

FIG. 1 is a system diagram of an integrated power plant.
The combined cycle power plant includes a gas turbine 1 and the gas turbine 1.
Exhaust gas G of generator 2 and gas turbine 1 driven by
And a steam turbine 12 driven by steam from the exhaust heat recovery boiler 3 and the like.

The exhaust heat recovery boiler 3 comprises a superheater 4, a high-pressure evaporator 5, a high-pressure economizer 6, a low-pressure evaporator 7, a low-pressure economizer 8, a low-pressure drum 9 and a high-pressure drum 10. The steam turbine 12 driven by the steam from the superheater 4 of the exhaust heat recovery boiler 3 is connected to the generator 2. The steam discharged from the steam turbine 12 is condensed by the condenser 13, and the condensed water W is supplied to the low pressure economizer 8 by the condensate pump 14. The heated feed water at the outlet of the low-pressure economizer 8 is introduced into the high-pressure economizer 6 by the boiler transfer pump 15 and is mixed with the feedwater to the low-pressure economizer 8 via the flow rate adjusting valve 16.

The drains of the high-pressure evaporator 5, the high-pressure economizer 6, the low-pressure evaporator 7 and the low-pressure economizer 8 are drain pipes 20 to 2 respectively.
3 is discharged to the blow tank 17 and temporarily stored there, and the drain overflowing the blow tank 17 is passed through the drainage pipe 24 and is cooled to a specified temperature (about 60 ° C.) by the in-house water 25 in the desuperheater 18. ,
It is discharged to pit 19.

Further, the high-pressure turbine bypass pipe 26 and the low-pressure turbine bypass pipe 27 are pipes for allowing the steam generated in the exhaust heat recovery boiler 3 to escape to the condenser 13 when the steam turbine 12 cannot receive the steam. .

[0007]

Since the above combined power generation plant is well known, the description of its operation will be omitted, but in the case of the exhaust heat recovery boiler 3 for the combined power generation plant, the exhaust gas temperature of the gas turbine 1 is about Since the temperature is relatively low at 600 ° C., the heat load (heat absorption amount per unit heat transfer area: unit kcal / m ² h) of each heat transfer tube group such as the high-pressure evaporator 5 is small. Therefore, the scale generation rate on the inner surface of the pipe is also small (usually proportional to the heat load to the 1st power to the 2nd power), and the pipe is not overheated or damaged by the scale.
No acid pickling using hydrochloric acid, etc., has been carried out for the chemical cleaning of the inner surface of the pipe.

On the other hand, since oil and fat such as machine oil is used when the exhaust heat recovery boiler 3 is manufactured, the oil and fat remains on the inner surface of the pipe after manufacturing. If oil and fat are present on the inner surface of the pipe, homing (foaming) occurs in the high-pressure drum 10 or the low-pressure drum 9 to increase carryover (outflow from the drums 10 and 9) and corrosion of iron oxide etc. on the inner surface of the pipe. Since it may be a source of the product, degreasing cleaning using sodium hydroxide etc. to remove oil and fat is carried out.

In the case of degreasing cleaning, it is necessary to heat to above 80 ° C. in order to enhance the degreasing effect of chemicals such as sodium hydroxide. In this case, conventionally, as shown in FIG. 6, the high-pressure economizer 6 and the low-pressure economizer 8 have a temporary water injection pipe 30 containing a chemical.
And a temporary pipe 31 for draining water from the high-pressure evaporator 5 and the low-pressure evaporator 7 is installed, and a chemical injection facility 32 including a temporary pure water tank and a chemical tank is provided in the middle of the temporary water injection pipe 30 for heating. It is necessary to provide a mixing heater 33 for injecting auxiliary steam. Further, as shown in FIG. 6, after degreasing and cleaning, a temporary processing tank 34 (about 2
00m ³ × 2 units) must be installed at the same time require more temporary facilities, large arrangement space is also necessary it was very uneconomical.

An object of the present invention is to provide an economical cleaning method for an exhaust heat recovery boiler by reducing temporary equipment.

[0011]

The above object of the present invention can be achieved by the following means. That is, in the exhaust gas flow path from the gas turbine, the water supply system that supplies water to the steam drum through the economizer and the heat transfer tube group of the evaporator to recover the heat of the exhaust gas and generate steam, and the generated steam In a heat recovery steam generator consisting of a steam system that supplies steam from a steam drum to a steam turbine through a superheater, cleaning chemicals are put in the steam drum and the gas turbine is operated under no-load or more load conditions. Exhaust heat recovery boiler cleaning method that cleans the inside of the pipe, or the water supply system that is installed in the exhaust gas flow path from the gas turbine and that supplies water to the steam drum via the economizer and the heat of the exhaust gas in the heat transfer tube group of the evaporator. It is composed of a steam system that collects steam to generate steam, and supplies the generated steam from the steam drum to the steam turbine through a superheater, and then discharges it from the steam drum and steam turbine. In a heat recovery steam generator that has a bypass valve installed in the steam turbine bypass pipe that bypasses the steam turbine, the cleaning chemicals are put in the steam drum and the gas turbine is removed. This is a method for cleaning an exhaust heat recovery boiler, in which the inside of the pipe of the exhaust heat recovery boiler is cleaned while performing a load operation above the load and controlling the drum pressure to a specified value by the steam turbine bypass valve.

In the above-mentioned exhaust heat recovery boiler cleaning method of the present invention, the cleaning waste water after cleaning is chemically treated by using a blow tank for temporarily accumulating each drain of the economizer and the evaporator, or the cleaning. Blow tank drain pipes are used for chemical treatment of post-cleaning wastewater using a wastewater treatment tank that is already installed in the exhaust heat recovery boiler system, or for post-cleaning wastewater chemical treatment. The method of doing may be adopted.

The facility for introducing a chemical into the steam drum may be combined with the facility for introducing a chemical for chemical treatment of the cleaning waste water after cleaning. As a chemical to be added to the steam drum, hydrazine may be added in addition to degreasing in order to form a protective film of magnetite on the inner surface of the tube.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The procedure for degreasing and cleaning an exhaust heat recovery boiler 3 for a combined cycle power plant according to the present invention will be described below with reference to FIG. First, the manhole 35 of the high-pressure drum 10 and the low-pressure drum 9 (a plan view of the high-pressure drum 10 is shown in FIG. 2) is charged with a specified amount of degreasing chemicals such as sodium hydroxide, and the manhole 35 is closed. After that, the gas turbine 1 is started, and a load operation of no load or more is performed. In addition, during no-load operation, the outlet gas temperature of the gas turbine 1 is about 300 ° C., and a temperature of 80 ° C. or higher at which the degreasing effect is obtained is sufficiently secured.

By this operation, the high-pressure evaporator 5 and the low-pressure evaporator 7 are heated to generate steam, and at the low-pressure drum 9 side, the drum 9, the low-pressure downcomer pipe 9a and the low-pressure evaporator 7 are generated.
On the high-pressure drum 10 side, the high-pressure drum 10, the high-pressure downcomer 10a, and the high-pressure evaporator 5 perform natural circulation operation. By this circulation operation, chemicals
7 and drums 9 and 10 are circulated for degreasing.

In recent years, the management of the exhaust heat recovery boiler 3 at the time of manufacture has been improved, so that the amount of oil and fat has been reduced (oil and oil concentration 20 to 3).
0ppm is 2-3ppm), and from the past results,
It is known that most of the oil and fats eluted from the tube group of the exhaust heat recovery boiler 3 and the drums 9 and 10 are the oils and fats attached to the internal device 36 of the drums 9 and 10 shown in FIG.
Therefore, it is sufficient to wash only the high-pressure evaporator 5, the low-pressure evaporator 7, the high-pressure drum 10, and the low-pressure drum 9 as in this embodiment.

Further, since the degreasing chemicals are non-volatile, the chemicals are not contained in the steam generated from the drums 9 and 10. Therefore, the steam turbine 12 or the condenser 13 (in the turbine bypass valves 28 and 29). , When the pressures of the high-pressure drum 10 and the low-pressure drum 9 are controlled to the specified pressures, and the steam flows through the turbine bypass pipes 26 and 27, respectively.

In addition to degreasing, hydrazine may be added to the inner surface of the pipe to form a protective coating on the inner surface of the pipe, and cleaning may be performed by adding hydrazine in a prescribed concentration or more.

After the cleaning is completed, as shown in FIG. 4, the cleaning liquid in the high pressure evaporator 5 and the low pressure evaporator 7 is discharged to the blow tank 17 through the drain pipe 20 and the drain pipe 22, respectively. In this case, as shown in FIG. 4, the blow tank 1
The neutralization reaction treatment liquid is injected into the inside of the container 7 from the chemical tank 32 to neutralize the cleaning liquid.

Since the neutralization reaction occurs instantaneously here, there is no problem in the neutralization process in the blow tank 17. After the neutralization process, the cleaning liquid passes through the drainage pipe 24 and the temperature reducer 18
It is supplied to the pit 19, cooled with on-site water 25, and then poured into the pit 19.

FIG. 5 shows another embodiment of the present invention. The neutralizing agent for the temporary pipe 38 for injection and the blow tank 17 or the drainage pipe 24 for injecting the chemical from the chemical injection device 32 into the drums 9, 10 is shown. The case where the pipe 39 for injecting is also used is shown. For the chemical injection into the drums 9 and 10, for example, a water gauge 4
The detection pipe 41 for 0 or the like is used.

The above embodiment has been described with reference to the example of the double pressure exhaust heat recovery boiler 3, but one or three pressure drums are used.
Of course, the present invention can also be applied to exhaust heat recovery boilers having three or more, and, for example, drainage treatment such as neutralization treatment can be performed not only in the blow tank 17 but also in drainage tanks used in the exhaust heat recovery boiler system. It is possible.

According to the present invention, the temperature required for degreasing cleaning is ensured by operating the gas turbine at a load of no load or more, and the cleaning is performed by the natural circulation operation of the exhaust heat recovery boiler, Since the sum treatment can be done using a blow tank, the temporary equipment is almost unnecessary, and the installation and removal period of the temporary equipment can be shortened by about one month or more, providing a very economical cleaning method. .

[Brief description of drawings]

FIG. 1 is a system diagram of an integrated power plant according to an embodiment of the present invention.

FIG. 2 is a plan view of the high-pressure drum of FIG.

FIG. 3 is a view of the internal device of the high pressure drum or low pressure drum of FIG. 1.

FIG. 4 is a wastewater treatment system diagram of an exhaust heat recovery boiler according to an embodiment of the present invention.

FIG. 5 is a wastewater treatment system diagram of an exhaust heat recovery boiler according to another embodiment of the present invention.

FIG. 6 is a system diagram of conventional boiler chemical cleaning of an exhaust heat recovery boiler.

[Explanation of symbols]

1 Gas Turbine 2 Generator 3 Waste Heat Recovery Boiler 4 Superheater 5 High Pressure Evaporator 6 High Pressure Economizer 7 Low Pressure Evaporator 8 Low Pressure Economizer 9 Low Pressure Drum 10 High Pressure Drum 12 Steam Turbine 13 Condenser 14 Condensate Pump 15 Boiler transfer pump 16 Flow rate control valve 17 Blow tank 18 Desuperheater 25 Water for internal use 26 High pressure turbine bypass pipe 27 Low pressure turbine bypass pipe 32 Chemical tank 35 Manhole 36 Internal device of drum 9, 10 38 Temporary pipe for injection 39 Neutralizing agent Injection pipe 40 Water level gauge 41 Detection pipe

Claims (7)

[Claims] 1. A water supply system which is provided in an exhaust gas flow path from a gas turbine and supplies water to a steam drum through a economizer, and a heat transfer tube group of an evaporator to recover heat of exhaust gas and generate steam, In an exhaust heat recovery boiler consisting of a steam system that supplies the generated steam from a steam drum to a steam turbine via a superheater, cleaning chemicals are put in the steam drum, and the gas turbine is discharged by performing a load operation of no load or more. A method for cleaning an exhaust heat recovery boiler, which comprises cleaning the inside of a heat recovery boiler. 2. A water supply system which is provided in an exhaust gas flow path from a gas turbine and supplies water to a steam drum through a economizer, and a heat transfer tube group of an evaporator to recover heat of exhaust gas and generate steam, It consists of a steam system that supplies the generated steam from a steam drum to a steam turbine through a superheater.The steam drum and the condenser for condensing the steam discharged from the steam turbine are directly connected to each other, and the steam turbine In an exhaust heat recovery boiler equipped with a bypass valve in the steam turbine bypass pipe that bypasses the steam turbine, the cleaning chemicals are put in the steam drum, the gas turbine is operated under no load or more, and the steam turbine bypass valve sets the drum pressure to the specified value. A method for cleaning an exhaust heat recovery boiler, characterized in that the inside of a pipe of the exhaust heat recovery boiler is cleaned while controlling the above. 3. The exhaust heat recovery according to claim 1 or 2, wherein the chemical treatment of the cleaning waste water after cleaning is carried out by using a blow tank for temporarily accumulating each drain of the economizer and the evaporator. Boiler cleaning method. 4. The waste recovery boiler cleaning according to claim 1 or 2, wherein the chemical treatment of the cleaning waste water after cleaning is carried out by using a waste water treatment tank provided in advance in the exhaust heat recovery boiler system. Method. 5. The exhaust heat recovery boiler cleaning method according to claim 1, wherein the cleaning waste water after cleaning is chemically treated by using a blow tank drain pipe. 6. The method for cleaning a waste heat recovery boiler according to claim 1, wherein the equipment for introducing the chemical into the steam drum and the equipment for introducing the chemical for the chemical treatment of the cleaning waste water after cleaning are used together. . 7. The exhaust heat recovery boiler cleaning method according to claim 1 or 2, wherein hydrazine is added as a chemical to be added to the steam drum.