JP5887216B2 - Cleaning method for heating element of gas-air heater - Google Patents

Description

  The present invention relates to a cleaning method for removing deposits attached to a heating element of a gas-air heater associated with a boiler.

When fuel such as heavy oil, residual oil, and coal is burned, sulfur contained in the fuel is burned, and sulfur dioxide (SO ₂ ) is generated. Further, sulfur dioxide is partially oxidized to sulfur trioxide (SO ₃ ), which reacts with moisture in the exhaust gas to produce sulfuric acid (H ₂ SO ₄ ). In particular, when coal is burned as a fuel, it is known that fly ash generated by burning contains a large amount of aluminum, calcium, iron and the like. Fly ash reacts with sulfuric acid to produce a compound that is difficult to dissolve.

  The boiler is accompanied by a device (gas-air heater) for giving heat of the exhaust gas to the air in order to increase the combustion efficiency of the fuel. In the gas-air heater, the exhaust gas is cooled, so that an acidic component derived from fuel, fly ash, a reaction product of the acidic component and fly ash, and the like easily adhere to the heating element of the gas-air heater. In particular, the adhesion in the temperature range where the temperature of the exhaust gas is lower than the dew point of sulfuric acid becomes remarkable, and the clogging with the deposits occurs. When a pressure loss occurs in the gas-air heater, the stable operation of the boiler is impaired. Therefore, removal of deposits when the pressure loss occurs is indispensable for maintaining a stable operation.

  As a cleaning method for removing deposits adhering to the heating element of the gas-air heater, methods using a cleaning liquid containing sodium hydrogen carbonate have been proposed (Patent Documents 1 to 3).

JP 2001-348689 A International Publication No. 2007/018058 JP 2007-211037 A

According to recent research, when coal is burned as fuel, deposits attached to the heating element of the gas-air heater are generated near silicon dioxide (SiO ₂ ) derived from fly ash and the middle temperature part of the heating element. It is known to be a mixture of reaction products of acidic ammonium sulfate ((NH ₄ ) HSO ₄ ) with aluminum, calcium, iron and the like. In particular, a compound containing aluminum, calcium, and iron tends to adhere firmly to the heating element and is difficult to dissolve.

These compounds containing aluminum, calcium, and iron, especially compounds containing calcium, cannot be sufficiently removed with a conventional cleaning solution containing sodium bicarbonate.
As a cleaning method for heating elements with deposits that are difficult to dissolve, the ultra-high pressure water is sprayed directly onto the heating elements using an ultra-high pressure pump to dissolve the deposits while physically flowing water. A method of removing is known. However, this method requires about 3 days per boiler when cleaning the heating element of the gas-air heater because it takes time to install the high-pressure water injection nozzle and the cleaning area per hour is small. It takes a long time.

  The present invention provides a cleaning method capable of sufficiently removing deposits adhering to a heating element of a gas-air heater in a relatively short time even if a compound containing aluminum, calcium and iron is contained in the deposits. provide.

The heating method of the heating element of the gas-air heater of the present invention comprises 20 to 60 parts by mass of alkali metal bicarbonate (A) and 40 to 80 parts by mass of chelate compound (B) (however, (A) and ( The total of B) is 100 parts by mass.) A cleaning liquid obtained by mixing water and water is brought into contact with the heating element of the gas-air heater to remove the deposits adhering to the heating element. In this method, the chelate compound (B) is tetrasodium ethylenediaminetetraacetate (B1) and sodium gluconate (B2) .

The total concentration of the alkali metal hydrogencarbonate (A) and the chelate compound (B) in the cleaning liquid (100% by mass) is preferably 2 to 5% by mass.
The alkali metal salt hydrogen carbonate (A) is preferably sodium hydrogen carbonate.

Of 40 to 80 parts by weight of the pre-SL chelating compound (B), tetrasodium ethylenediaminetetraacetate (B1) is 20 to 40 parts by weight, sodium gluconate (B2) is preferably 20 to 40 parts by weight .

In the cleaning method of the present invention, the cleaning liquid is preferably sprayed onto the heating element of the gas-air heater at a pressure of 0.3 MPa to 1.0 MPa.
Injection amount of the cleaning solution, 60~300m ³ / h, it is preferable that the element area per 7~20m ³ / h · ^{m 2.}

  According to the method for cleaning a heating element of a gas-air heater according to the present invention, even if a compound containing aluminum, calcium, or iron is contained in the deposit, the deposit adhered to the heating element of the gas-air heater is compared. Can be removed in a short time.

It is a schematic block diagram which shows an example of the equipment which implements the cleaning method of the heating element of the gas-air heater of this invention.

FIG. 1 is a schematic configuration diagram showing an example of equipment for carrying out the method for cleaning a heating element of a gas-air heater according to the present invention.
The facility 10 includes a boiler 12, a denitration device 14 that removes nitrogen oxides contained in the exhaust gas from the boiler 12, and a gas-air heater that exchanges heat between the combustion air used in the boiler and the exhaust gas from the boiler 12. 16, an electrostatic precipitator 18 that removes dust and the like contained in the exhaust gas, a desulfurization device 20 that removes sulfur oxides contained in the exhaust gas, a chimney 22 that discharges the exhaust gas to the outside, and a stirring tank 30 that prepares the cleaning liquid A storage tank 32 for storing cleaning liquid; a stationary upper cleaning device 34 having a plurality of nozzles 33 for injecting cleaning liquid from above to the heating element 24 of the gas-air heater 16; and a heating element of the gas-air heater 16; A stationary lower cleaning device 36 having a plurality of nozzles 35 for injecting a cleaning liquid from below to the fuel 24; and fuel (coal, etc.) boiler 1 A first air flow path 42 for sending combustion air to the gas-air heater 16; a second air flow for sending combustion air heated by the gas-air heater 16 to the boiler 12; A first exhaust gas flow channel 50 for sending exhaust gas from the boiler 12 to the denitration device 14; an ammonia supply flow channel 51 for supplying denitration ammonia (NH ₃ ) in the middle of the first exhaust gas flow channel 40. A second exhaust gas flow channel 52 for sending the exhaust gas from the denitration device 14 to the gas-air heater 16; a third exhaust gas flow channel 54 for sending the exhaust gas from the gas-air heater 16 to the electric dust collector 18; A fourth exhaust gas flow path 56 for sending the exhaust gas to the desulfurization apparatus 20; a fifth exhaust gas flow path 58 for sending the exhaust gas from the desulfurization apparatus 20 to the chimney 22; a first for sending the cleaning liquid of the stirring tank 30 to the storage tank 32 Washing A cleaning liquid flow path 60; a second cleaning liquid flow path 62 that is provided with a pump 61 in the middle and sends the cleaning liquid in the storage tank 32 to the upper cleaning apparatus 34 and the lower cleaning apparatus 36; and a heating element of the gas-air heater 16 A third cleaning liquid flow path 64 for sending the cleaning liquid collected in the cleaning liquid receiver 63 provided below 24 to the storage tank 32; an industrial water supply flow path for sending industrial water to the upper cleaning apparatus 34 and the lower cleaning apparatus 36 66.

(Attachment)
The deposits on the heating element 24 of the gas-air heater 16 associated with the boiler 12 burning with coal as fuel include fly ash (silicon dioxide (SiO ₂ ), calcium oxide (CaO), alumina (Al ₂ O ₃ ). Etc.), sulfur-derived acidic components (sulfuric acid (H ₂ SO ₄ ), acidic ammonium sulfate ((NH ₄ ) HSO ₄ ), etc.) contained in fuel, reaction products of fly ash and acidic components (aluminum ammonium sulfate (Al (NH ₄ ) (SO ₄ ) ₂ )) and the like. These are compounds that exhibit acidity when dissolved in water (hereinafter referred to as acidic compounds). Therefore, an aqueous solution containing an alkali metal hydrogen carbonate is used as the cleaning liquid.

(Alkali metal bicarbonate)
Examples of the alkali metal hydrogen carbonate include sodium hydrogen carbonate and potassium hydrogen carbonate. Since alkali metal bicarbonate has a low pH value when dissolved in water and is weakly alkaline, it does not exceed the regulation value of hydrogen ion concentration stipulated in the Water Pollution Control Law, and Since it can be handled safely, it is suitable as an alkaline component of the cleaning liquid. As the alkali metal hydrogen carbonate, sodium hydrogen carbonate is particularly preferable because it is inexpensive.

  Alkali metal hydrogen carbonate reacts with an acidic compound to generate carbon dioxide gas and foams, so that the deposit on the heating element 24 is chemically dissolved while peeling off by physical action. Iron rust, dust, soot, etc. in the deposit are also peeled off at the same time. The foaming effect of carbon dioxide increases the cleaning effect and shortens the cleaning time. Even if the heating element 24 has a complicated shape and is difficult to clean, it can be cleaned in a short time. Sodium hydrogen carbonate is particularly preferable for cleaning using foaming because of the high carbonate content per unit mass of the substance.

(Chelate compound)
A chelate compound is a component that promotes dissolution of a compound containing aluminum, calcium, iron, or the like that cannot be removed with an alkali metal bicarbonate.

  Chelate compounds include ethylenediaminetetraacetic acid tetrasodium, sodium gluconate, nitrilotriacetic acid, diethylenetriaminepentaacetic acid, hydroxyethyldiaminetriacetic acid, triethylenetetraminehexaacetic acid, hydroxyethyliminodiacetic acid, dihydroxyethylglycine, glycol etherdiaminetetraacetic acid Etc. As the chelate compound, a combination of tetrasodium ethylenediaminetetraacetate and sodium gluconate is particularly preferable because pH adjustment of the solution (cleaning solution) is simple.

(Cleaning solution)
The cleaning liquid is 20 to 60 parts by mass of the alkali metal bicarbonate (A) and 40 to 80 parts by mass of the chelate compound (B) (however, the total of (A) and (B) is 100 parts by mass). And water.

  If the amount of the alkali metal hydrogen carbonate (A) is less than 20 parts by mass, the foaming moment due to the reaction with the acidic compound is weakened, and the effect of peeling off the deposits due to physical action tends to be impaired. When the amount of the alkali metal hydrogen carbonate (A) exceeds 60 parts by mass, the amount of the chelate compound (B) decreases and the chemical cleaning effect is weakened.

  When the chelate compound (B) is less than 40 parts by mass, the effect of promoting dissolution of a compound containing aluminum, calcium, iron or the like is likely to be impaired. When the amount of the chelate compound (B) exceeds 80 parts by mass, the amount of the alkali metal hydrogen carbonate (A) decreases and the physical cleaning effect is weakened.

  When the chelate compound (B) is a combination of tetrasodium ethylenediaminetetraacetate (B1) and sodium gluconate (B2), the washing liquid is 20 to 60 parts by mass of alkali metal hydrogencarbonate (A), ethylenediaminetetraacetic acid tetraacetate. 20-40 parts by mass of sodium (B1) and 20-40 parts by mass of sodium gluconate (B2) (however, the sum of (A), (B1) and (B2) is 100 parts by mass), water, Are mixed.

  When the amount of ethylenediaminetetraacetic acid tetrasodium (B1) is less than 20 parts by mass, the chelating action on calcium is mainly reduced. When the amount of ethylenediaminetetraacetic acid tetrasodium (B1) exceeds 40 parts by mass, the alkalinity becomes strong, and it becomes necessary to neutralize the waste water after washing.

  When the amount of sodium gluconate (B2) is less than 20 parts by mass, the chelating action on iron mainly decreases. When the amount of sodium gluconate (B2) exceeds 40 parts by mass, the chemical oxygen demand of the waste water after washing increases.

  2-5 mass% is preferable and, as for the total density | concentration of the alkali metal hydrogencarbonate (A) and chelate compound (B) in a washing | cleaning liquid (100 mass%), 3-5 mass% is more preferable. When the total concentration of (A) and (B) is less than 2% by mass, the cleaning effect may be low, and the amount of waste water after cleaning increases. If the total concentration of (A) and (B) exceeds 5% by mass, undissolved residue may be generated, and the concentration of insoluble matter derived from the deposit increases during cleaning, and the viscosity of the cleaning solution Density increases.

The pH of the cleaning liquid is preferably 6.5 to 9.0, and more preferably 7.5 to 8.5. If the pH of the cleaning liquid is less than 6.5, the equipment 10 may corrode. When the pH of the cleaning liquid exceeds 8.5, it is necessary to neutralize the waste water after cleaning.
When the cleaning liquid is circulated between the storage tank 32 and the upper cleaning device 34 and the lower cleaning device 36 for cleaning, the pH decreases as the removal of the deposits containing acidic compounds proceeds. When the pH of the cleaning liquid is less than 6.5, it is preferable to add an alkali metal hydrogen carbonate (A) and, if necessary, a chelate compound (B) in a timely manner.

Examples of the method for preparing the cleaning liquid include the following methods (α) to (β), and the method (γ) is preferable because it does not require time and effort for the on-site preparation.
(Α) A method of further adding a chelate compound (B) after adding an alkali metal hydrogencarbonate (A) to water.
(Β) A method of adding an alkali metal hydrogencarbonate (A) after adding the chelate compound (B) to water.
(Γ) A method of adding a mixture of an alkali metal hydrogencarbonate (A) and a chelate compound (B) to water.

Prior to the method (γ), the means for premixing the alkali metal hydrogen carbonate (A) and the chelate compound (B) may be V-type mixers, ribbon mixers, planetary screw type mixers, etc. Examples of various mixing devices that are commonly used.
The order of charging into the mixer during mixing is not particularly limited, and either alkali metal hydrogen carbonate (A) or chelate compound (B) may be charged into the mixer first, and simultaneously charged. May be.

Alkali metal hydrogen carbonate (A) and chelate compound (B) may be charged at a specific ratio in one packaging unit such as a paper bag or a flexible container bag, but the presence in the packaging unit is biased. When the mixture is dissolved in water, undissolved residue may be generated. Therefore, it is preferable to mix as uniformly as possible.
The alkali metal hydrogencarbonate (A) and the chelate compound (B) do not change in quality even when dissolved in water, and may be stored in this state.

(Cleaning method)
The method for cleaning a heating element of a gas-air heater according to the present invention is a method in which a cleaning liquid is brought into contact with the heating element 24 of the gas-air heater 16 to remove deposits attached to the heating element 24.

Examples of the contact method include the following method (a) or method (b), and the method (a) is preferable from the viewpoint of shortening the cleaning time.
(A) A method of injecting the cleaning liquid from the nozzle 33 of the upper cleaning device 34 and the nozzle of the lower cleaning device 36 to the heating element 24.
(B) A method in which the heating element 24 is removed from the gas-air heater 16 and immersed in the cleaning liquid.

  According to the method (a), since the existing apparatus (stationary cleaning apparatus) attached to the gas-air heater 16 is used, it is not necessary to stop the boiler 12 for cleaning preparation, and the cleaning liquid has a large area. Since it can wash | clean efficiently, the stop period of the boiler 12 can be shortened significantly.

The spraying of the cleaning liquid onto the heating element 24 may be carried out by a high-pressure water cleaning apparatus that is usually used for cleaning. However, if the water pressure is increased too much, the heating element 24 may be damaged. Further, in the high-pressure water cleaning apparatus, the cleaning liquid can be injected only at an injection amount of about 25 m ³ / h, and the sprayable range becomes narrow, and the time required for cleaning becomes long. Therefore, in the present invention, it is preferable to use an existing apparatus (stationary cleaning apparatus) attached to the gas-air heater 16 and not a high-pressure water cleaning apparatus.

  In the method (a), the pressure when spraying the cleaning liquid is preferably 0.3 MPa to 10 MPa, more preferably 0.5 MPa to 5 MPa. When the pressure is less than 0.3 MPa, the time required for cleaning becomes long. If the pressure exceeds 10 MPa, the heating element 24 may be damaged.

Injection amount of the cleaning liquid is preferably from ^{60~300m 3 / h, 80~300m 3 /} h is more preferable. When the injection amount is less than 60 m ³ / h, the time required for cleaning becomes long. If the injection amount exceeds 300 m ³ / h, the capacity of the pump 61 attached to the existing device (stationary cleaning device) attached to the gas-air heater 16 may be exceeded.

  The heating element 24 is cleaned while circulating the cleaning liquid between the storage tank 32, the upper cleaning device 34, and the lower cleaning device 36. A conventional cleaning method recommended by a manufacturer that manufactures a gas-air heater is a method in which industrial water is poured until the pH value of the wastewater used for cleaning becomes minus 2 or more of the pH value of industrial water before cleaning. However, the conventional method requires a large amount of industrial water, resulting in a large amount of waste water. On the other hand, according to the cleaning method of the present invention in which the cleaning liquid is circulated, the amount of waste water generated by cleaning the deposits can be greatly reduced.

  After removing the deposit on the heating element 24, it is preferable to remove the reaction product, iron rust, dust, and the like remaining on the surface of the heating element 24 by washing with water. The water washing is performed by pouring new industrial water or the like until the pH of the water after washing becomes 6.0 to 8.0. If the pH of the water after washing is less than 6.0, there is a high possibility that deposits remain. If the pH of the water after washing exceeds 8.0, an alkali metal bicarbonate may remain. The pH of the water after washing is particularly preferably 6.5 to 7.5.

(Function and effect)
In the method for cleaning the heating element of the gas-air heater of the present invention described above, the alkali metal hydrogen carbonate contained in the cleaning liquid is foamed by contact with the deposit on the heating element, so that the cleaning liquid has a diffusion effect. In addition, an effect of physically removing deposits can be obtained. In addition, the chelate compound contained in the cleaning liquid accelerates the dissolution of the compound containing aluminum, calcium, iron, and the like, and an effect of chemically removing deposits can be obtained. As a result, even if a compound containing aluminum, calcium and iron, which is difficult to remove by conventional methods, is included in the deposit, the deposit adhering to the heating element of the gas-air heater can be removed in a relatively short time. And can be removed sufficiently.
Moreover, since the alkali metal bicarbonate and the chelate compound are contained in the cleaning liquid, even if the cleaning liquid is sprayed onto the heating element at a relatively low pressure, the deposits can be efficiently removed.

Examples are shown below, but the present invention is not limited to these examples.
Examples 1 to 5 are reference examples, and Examples 6 to 10 are examples.

[Examples 1 to 5]
A 5 mm thick simulated soil was adhered to an iron plate (1,100 mm × 800 mm) and dried at room temperature for 24 hours to prepare a test piece for a cleaning test.
The simulated dirt was prepared by collecting deposits on the heating element of the actual gas-air heater and mixing 50 parts by mass thereof with 50 parts by mass of water.
An amount of the mixture shown in Table 1 was mixed with water to prepare a cleaning liquid having a mixture concentration of 5% by mass. Each cleaning solution was sprayed onto a test piece for a cleaning test, and the degree of removal of simulated dirt was observed and evaluated according to the following criteria. The results are shown in Table 1.
A: Completely removed,
○: Slightly remained,
Δ: About half remained,
X: Remaining residue occurred.

  From the results of Table 1, it was found that a combination of tetrasodium ethylenediaminetetraacetate and sodium gluconate was effective as the chelate compound.

[Examples 6 to 9]
The following mixture (I) and mixture (II) were prepared using sodium hydrogen carbonate, tetrasodium ethylenediaminetetraacetate and sodium gluconate.
(I) A mixture of 60 parts by mass of sodium bicarbonate, 20 parts by mass of tetrasodium ethylenediaminetetraacetate and 20 parts by mass of sodium gluconate.
(II) A mixture of 20 parts by weight of sodium bicarbonate, 40 parts by weight of ethylenediaminetetraacetic acid tetrasodium and 40 parts by weight of sodium gluconate.

About each of mixture (I) and mixture (II), the mixture and water were mixed and the washing | cleaning liquid whose concentration of a mixture is 2 mass% and 5 mass% was prepared. A test was conducted to clean the deposits on the heating element using each cleaning solution. The results are shown in Table 2.
The details of the cleaning test method are as follows.

Part of the heating element (area 3.2 m) of the gas-air heater (IHI, Rotemulet type heat exchanger, high-temperature layer height: 700 mm, medium-temperature layer height: 1,000 mm, low-temperature layer height: 450 mm) ^A washing test was conducted for ² ).
A flow path capable of injecting the cleaning liquid from the temporary storage tank of the cleaning liquid to the heating element 24 was produced.
First, 4 m ³ of industrial water was sprayed for about 4 minutes and passed between the heating elements 24 to remove deposits that could be easily removed.
Next, 10 m ³ of cleaning liquid was sprayed for about 10 minutes and passed between the heating elements 24 to remove deposits.
Finally, 4 m ³ of industrial water was sprayed for about 4 minutes and passed between the heating elements 24 for rinsing.

Before and after the cleaning test, using a fiberscope, observe the low temperature side of the medium temperature layer from the high temperature layer upper end side of the heating element 24 (a portion that is easily clogged by deposits, about 100 to 150 cm from the upper end of the high temperature layer), The condition of occlusion and removal was evaluated according to the following criteria. The results are shown in Table 2 .
A: Completely removed,
○: The blockage disappeared, but thin rust remained.
Δ: Some obstruction remains
X: Many obstruction | occlusion parts remained.

  From the results of Table 2, it is sufficient that the composition of the mixture is in the range of 20 to 60 parts by mass of sodium bicarbonate, 20 to 40 parts by mass of tetrasodium ethylenediaminetetraacetate, and 20 to 40 parts by mass of sodium gluconate. It was found that the effect is demonstrated. Moreover, it turned out that an effect is fully exhibited by making the density | concentration of a mixture into the range of 2-5 mass%.

[Example 10]
A mixture of 60 parts by mass of sodium hydrogen carbonate, 20 parts by mass of ethylenediaminetetraacetic acid tetrasodium and 20 parts by mass of sodium gluconate was mixed with water, so that the concentration of the mixture was 5% by mass and pH was 8.7. A cleaning solution was prepared. A test was conducted to clean the deposits on the heating element using the cleaning liquid.
The details of the cleaning test method are as follows.

Part of the heating element of the gas-air heater (Alstom Co., Ltd., Jungstrom heat exchanger, 33V type, high temperature layer height: 1,050 mm, medium temperature layer height: 1,500 mm, low temperature layer height: 300 mm) (area: 41m ²⁾ with respect to, first, the injection amount of the industrial water with a stationary cleaning device ^{60 m} 3 / h, pouring and injection at a pressure of 0.7 MPa 20 min, the deposits can be easily removed Removal was performed.
Next, as shown in FIG. 1, a flow path capable of injecting the cleaning liquid from the cleaning liquid storage tank 32 to the heating element 24 is prepared, and the cleaning liquid is injected from the high temperature side with an injection amount of 300 m ³ / h and a pressure of 0.7 MPa. The deposits on the heating element were cleaned by spraying for about 20 minutes, then for about 20 minutes from the low temperature side, and further for about 20 minutes from the high temperature side.
Finally, industrial water was sprayed for 30 minutes at a spraying amount of 60 m ³ / h and a pressure of 0.7 MPa using a stationary cleaning device, and rinsed.
During the cleaning test, the heating element of the gas-air heater was rotated by an air motor at a speed of 0.125 rpm.

Before and after the cleaning test, using a fiberscope, observe the low temperature side of the heating element from the upper end side of the heating layer to the low temperature side of the intermediate temperature layer (place that is likely to be blocked by deposits, about 200 to 250 cm from the upper end of the high temperature layer). The status of cleaning was confirmed. As a result, all of the 24 check points were clogged before cleaning, but after the cleaning, the deposits were removed at all 24 check points.
From the above results, it can be seen that a sufficient effect can be achieved by cleaning the heating element with an injection amount of 300 m ³ / h, a pressure of 0.7 MPa, and an injection amount per element area of 7.3 m ³ / h · m ^2. all right.

  The method for cleaning a heating element of a gas-air heater according to the present invention is useful for removing deposits attached to the heating element of a gas-air heater associated with a boiler that burns coal as fuel.

16 Gas-air heater 24 Heating element

Claims (6)

20 to 60 parts by mass of alkali metal hydrogen carbonate (A) and 40 to 80 parts by mass of chelate compound (B) (however, the total of (A) and (B) is 100 parts by mass), water, A cleaning liquid obtained by mixing the heating element of the gas-air heater with the cleaning liquid in contact with the heating element of the gas-air heater to remove deposits attached to the heating element ,
The method for cleaning a heating element of a gas-air heater, wherein the chelate compound (B) is tetrasodium ethylenediaminetetraacetate (B1) and sodium gluconate (B2) .   2. The gas-air heater according to claim 1, wherein the total concentration of the alkali metal bicarbonate (A) and the chelate compound (B) in the cleaning liquid (100 mass%) is 2 to 5 mass%. Cleaning method for heating element.   The method for cleaning a heating element of a gas-air heater according to claim 1 or 2, wherein the bicarbonate (A) of the alkali metal salt is sodium bicarbonate. Of the 40 to 80 parts by weight of the chelating compound (B), tetrasodium ethylenediaminetetraacetate (B1) is 20 to 40 parts by weight, sodium gluconate (B2) is 20 to 40 parts by weight, claim 1 The cleaning method of the heating element of the gas-air heater as described in any one of -3. The method for cleaning a heating element of a gas-air heater according to any one of claims 1 to 4 , wherein the cleaning liquid is sprayed onto a heating element of the gas-air heater at a pressure of 0.3 MPa to 1.0 MPa. Injection amount of the cleaning liquid, a 60~300m ³ / h, the element area per 7~20m ³ / h · ^{m 2,} gas according to claim 5 - air heater method of heating elements cleaned.

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