JP7380309B2 - Boiler chemical cleaning method - Google Patents

Description

The present invention relates to a method for chemically cleaning a boiler, and more particularly to a method for evenly chemically cleaning evaporation tubes arranged in parallel.

Figure 2 shows the schematic configuration of the steam system of a thermal power boiler. Steam generated by burning fuel in the furnace 2 with the burner 1 is supplied to the high-pressure turbine 7 through the steam drum 3, saturated steam pipe 4, superheater 5, main steam pipe 6, and main steam stop valve 6a. . The steam that has done work in the high-pressure turbine 7 is sent to a reheater 9 through a low-temperature reheat steam pipe 8 and heated, and then passes through a high-temperature reheat steam pipe 10 to an intermediate-pressure turbine 11 and a low-pressure turbine 12. Be supplied and do the work. Further, the steam that has done work in the low-pressure turbine 12 is condensed in a condenser 13 and then returned to the furnace 2 through a degassing pipe 14, a boiler feed water pump 15, and a economizer 16.

Note that a drain pipe 6b having a drain valve is connected to the main steam pipe 6.

A nose wall tube 20 is provided on the exit side of the upper part of the furnace wall tube. As shown in FIG. 3, the nose wall tube 20 has a large number of evaporation tubes 21 that are bent to have a nose shape (dog-shaped) when viewed from the side, and project toward the inside of the furnace. The nose wall tube 20 is for preventing combustion gas from flowing in a short-circuit manner to the furnace outlet (Patent Document 1). As shown in FIG. 4, the lower end of the nose wall tube 20 is connected to the nose wall tube inlet header 22, and the upper end is connected to the nose wall tube outlet header 23.

In the steam system of such a thermal power boiler, there is a known method of chemically cleaning the evaporator pipe, steam drum, downcomer pipe, collector header, etc. by circulating a cleaning chemical solution (Patent Documents 2 to 4).

In commercial and general industrial boilers, when chemical cleaning is used to remove scale such as iron oxide that adheres to the inner surface of water-cooled wall evaporation tubes, the flow balance of chemical cleaning fluid may be uneven for each evaporation tube depending on the boiler structure. In the evaporator tube where the flow rate has become uniform and the flow rate has decreased, problems such as an inability to maintain a predetermined temperature due to heat radiation may occur, and there is a concern that scale may remain without being able to be removed.

In particular, in large commercial boilers, the configuration and structure of the boiler evaporator tube is complicated, and canned water is divided into the middle side wall tube and nose wall tube, and the upper water cooling wall tube and nose wall tube in the middle of the evaporator tube. There are some structures that are

During chemical cleaning, circulation cleaning is performed at a smaller flow rate than during boiler operation due to cleaning equipment constraints, and although the flow rate sent to the boiler is controlled, the balance of flow rates flowing to each evaporation pipe after separation cannot be determined. First, a large amount of chemical cleaning liquid passes through some of the evaporation tubes, and insufficient liquid passes through other evaporation tubes, which may result in insufficient cleaning.

For example, in a nose wall tube, approximately 500 evaporation tubes are arranged in a line in one header, and chemical cleaning liquid is supplied from both ends of the nose wall tube inlet header. It is not known whether or not a uniform flow rate is flowing into the evaporation tube in the central part, and there is a risk that the flow rate will become non-uniform as shown in FIG.

In addition, in the horizontal part of the nose wall pipe, if the flow rate is low, carbon dioxide gas generated when organic acids decompose during chemical cleaning, and hydrogen gas generated when the acid reacts with carbon steel, which is the boiler's constituent material, accumulate. Initially, the chemical cleaning solution may eventually stop passing through.

In order to prevent such an event, it is conceivable to install, for example, an ultrasonic flowmeter in each evaporation tube and perform chemical cleaning while controlling the flow rate or flow rate (Patent Document 4). However, installing an ultrasonic flowmeter in each of a large number of evaporation tubes requires a long time, and the cost of the ultrasonic flowmeter increases, making it unsuitable.

In addition, during the temperature raising process in which chemical cleaning liquid is injected into the boiler, when steam is injected into the circulating water, palpation with bare hands is performed at a low temperature of about 40 to 50 degrees Celsius, and the thermocouple of the contact thermometer is evaporated. There is also a method of attaching thermocouples to the evaporation tubes and determining that the chemical cleaning solution is passing through if the evaporation tube temperature is the same as the temperature of the chemical cleaning solution, but a thermocouple is installed on all evaporation tubes. This takes a long time and is costly.

WO2004/023037 publication Japanese Patent Application Publication No. 2006-322672 Japanese Patent Application Publication No. 2015-230150 JP 2019-124412 Publication

In this way, the flow rate (flow velocity) inside the evaporator tube during chemical cleaning cannot be determined, so air or gas accumulates in some evaporator tubes during chemical cleaning, which obstructs the flow of liquid. There was a concern that the chemical cleaning solution would not be able to spread, or that the chemical cleaning solution would not flow uniformly, causing the flow rate of the cleaning solution to decrease and the temperature of the solution to drop due to heat dissipation, potentially making it impossible to remove scale.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for chemically cleaning a boiler in which the flow rate of the evaporator tubes can be easily controlled and each evaporator tube can be chemically cleaned sufficiently.

The chemical cleaning method for a boiler of the present invention is a method for chemically cleaning a boiler having an evaporator panel made up of a plurality of evaporator tubes arranged in parallel, wherein the evaporator panel is obtained by photographing the evaporator tube panel using a thermography. It is characterized by heating and cleaning while controlling temperature distribution.

In one aspect of the present invention, when the temperature distribution becomes uneven beyond a predetermined level, the flow rate of the pump that circulates the chemical cleaning liquid into the boiler is increased, the pump is stopped, or the pump discharge flow rate is increased or decreased. Repeating this will change the flow rate.

In one aspect of the present invention, the thermograph is installed in a boiler furnace, the thermograph is installed in a storage box, and the inside of the storage box is cooled by a cooling means.

In the chemical cleaning method for a boiler of the present invention, the temperature distribution of the evaporator tube panel is managed, and the chemical cleaning liquid is uniformly passed through each evaporator tube while confirming that the temperature distribution of the evaporator tube panel is uniform. Each evaporator tube can be thoroughly chemically cleaned.

According to the present invention, the liquid flows evenly through each evaporation tube during chemical cleaning, thereby avoiding poor liquid flow due to gas or air pockets and temperature drop due to heat radiation, preventing scale from being left behind, and ensuring sufficient chemical cleaning. Can be washed. This will lead to long-term safe operation of the boiler plant.

It is an explanatory view explaining the temperature distribution measurement system of the evaporation pipe panel in the chemical cleaning method of the boiler concerning an embodiment. It is a schematic system diagram of a boiler apparatus. FIG. 3 is a schematic perspective view of a nose wall tube; FIG. 3 is an explanatory diagram of the water flow distribution of the nose wall pipe.

An embodiment will be described below with reference to FIG. The configuration of the boiler to which the cleaning method according to this embodiment is applied is the same as that shown in FIG. 2, and the configuration of the nose wall tube 20 is the same as that shown in FIGS. 3 and 4.

In this embodiment, an infrared camera 30 is used to measure the temperature distribution of the evaporator tube panel (in this example, the nose wall tube 20). The infrared camera 30 is stably held on a tripod or the like.

Specifically, one or more infrared cameras (thermography) 30 are placed near the evaporation tube panel (nose wall tube 20) to be measured. Note that although the infrared camera is held on a tripod in FIG. 1, the present invention is not limited to this. The image output signal of the infrared camera 30 is transmitted to the place where chemical cleaning is managed using a LAN cable 40, etc., and is input into the computer 41 for temperature data management, where the infrared rays emitted from the evaporation tube are analyzed and a heat distribution map is created. By doing so, the temperature distribution can be monitored.

That is, infrared rays emitted from the evaporation tube panel are captured by an infrared camera (thermography), and transmitted as an image signal to an image processing computer to create a temperature distribution image. Depending on the number of tubes in the evaporator panel, it is possible to monitor all evaporator tubes simultaneously by increasing the number of infrared cameras as necessary.

Note that when the infrared camera 30 is installed in a high-temperature boiler furnace, the infrared camera is housed in a cooling jacket and cooling water or cooling air is circulated to protect it from the atmosphere inside the furnace, which becomes high temperature during chemical cleaning. This cools and protects the infrared camera. In FIG. 1, compressed air is cooled by a cooler 32, and the cooled air is supplied into the cooling jacket.

If the temperature distribution of the evaporator panel becomes uneven (for example, if the difference between the temperature of the hottest evaporator tube and the temperature of the coldest evaporator tube exceeds the set value), immediately By repeatedly starting and stopping the temporary circulation pump that circulates the cleaning liquid into the boiler and increasing and decreasing the pump discharge flow rate, the flow rate is changed and the liquid flow through the evaporation pipe is improved.

When chemically cleaning the wall pipes and economizers of this boiler, after the boiler has stopped operating, it is filled with water through a temporary supply pipe, the temporary circulation pump is activated, and heating steam and cleaning chemicals are injected. do. Washing water is circulated through temporary piping, water supply pipes, energy savers, lower wall pipes and upper wall pipes of the furnace, furnace outlet wall pipes or nose wall pipes, manifolds, brackish water separators and drain tanks, and the brackish water is separated between these pipes. The equipment, drain tank, economizer, wall pipes and headers will be chemically cleaned.

After continuing this chemical cleaning for a predetermined period of time, the temporary circulation pump is stopped and the cleaning water is discharged to the drain pipe. In addition, fresh water will be supplied to wash the brackish water separator, drain tank, economizer, wall pipes and headers, and will be drained from the drain pipe.

After extrusion of the cleaning chemicals remaining in the system is completed, rust prevention and blowing are performed, the temporary piping is removed, and normal water flushing and startup operations are performed to resume boiler operation.

According to this cleaning method, by measuring the temperature distribution with an infrared camera and managing the non-uniformity of liquid passage during chemical cleaning, it is possible to avoid poor liquid passage due to gas or air pockets and temperature drop due to heat radiation, and to reduce the scale. It prevents any residue from being left behind and can be thoroughly chemically cleaned. This will lead to long-term safe operation of the boiler plant.

The method of the present invention can be applied both to cleaning the entire boiler and to selectively chemically cleaning only the nose wall tube.

Cleaning agents for dissolving and removing scale include inorganic acids such as hydrochloric acid, hydrofluoric acid, and sulfamic acid, and organic acids such as citric acid, glycolic acid, formic acid, oxalic acid, gluconic acid, maleic acid, malic acid, malonic acid, and acetic acid. For chelate cleaning agents, ethylenediaminetetraacetic acid and its salts are used, and these are mixed with auxiliary agents such as ascorbic acid, erythorbic acid, hydrazine, and corrosion inhibitors as reducing agents. It is desirable to carry out preliminary tests on the chemicals to be applied based on scale components and adhesion conditions to select the most economical chemical composition. The temperature of the cleaning liquid passed through the evaporation tube is preferably about 50°C or higher, particularly about 60°C or higher.

2 Furnace 20 Nose wall tube 30 Infrared camera

Claims (4)

In a chemical cleaning method for a boiler, which chemically cleans the evaporation tube panel by passing a cleaning liquid through the evaporation tube panel of the boiler having an evaporation tube panel consisting of a plurality of evaporation tubes arranged in parallel,
A method for chemically cleaning a boiler in which heating and cleaning are performed while monitoring the temperature distribution of the evaporator tube panel obtained by photographing the evaporator tube panel with an infrared camera , the method comprising:
simultaneously monitoring all evaporator tubes of the evaporator tube panel;
A method for chemically cleaning a boiler, characterized in that the temperature of the cleaning liquid passed through the evaporator tube panel is set to 50° C. or higher . In claim 1, if the temperature distribution becomes uneven beyond a predetermined level, the flow rate of the pump that circulates the chemical cleaning liquid into the boiler is increased, or the pump is started and stopped, or the pump discharge flow rate is repeatedly increased and decreased. A boiler chemical cleaning method characterized by giving a flow rate change. In claim 1 or 2, the infrared camera is installed in a boiler furnace, the infrared camera is installed in a storage box,
A method for chemically cleaning a boiler, characterized in that the inside of the storage box is cooled by a cooling means. The method for chemically cleaning a boiler according to any one of claims 1 to 3, characterized in that a plurality of said infrared cameras are installed to simultaneously monitor all evaporation tubes of said evaporation tube panel.

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