CN111828951A - A kind of method and boiler structure to avoid low temperature corrosion of heating surface of boiler tail - Google Patents

Abstract

The invention discloses a method for avoiding low-temperature corrosion of a heated surface at the tail of a boiler, which comprises the following steps: controlling the working medium temperature of the heated surface at the tail of the boiler to ensure that the wall temperature of the metal surface of the heated surface at the tail of the boiler is higher than the highest temperature of low-temperature corrosion, and preventing SO in flue gas₂With water vapour to form H₂SO₃And the water vapor in the flue gas is condensed on the pipe wall after being fused with the water vapor in the flue gas, so that the acidic corrosion is generated. The invention ensures that the wall temperature of the metal surface is higher than the highest temperature of low-temperature corrosion, and avoids SO in flue gas₂With water vapour to form H₂SO₃And the water vapor in the flue gas is condensed on the pipe wall after being fused with the water vapor in the flue gas, so that the acidic corrosion is generated.

Description

A kind of method and boiler structure to avoid low temperature corrosion of heating surface of boiler tail

technical field

The invention relates to a method and a boiler structure for avoiding low-temperature corrosion of a heating surface of a boiler tail, and belongs to the technical field of power station boiler structures.

Background technique

The traditional 130t/h high temperature and high pressure boiler tubular air preheater is arranged at the outlet of the economizer. The flue gas scours the outer surface of the air preheater pipe horizontally. The heated air is pressurized by the blower and circulates in the pipe. After the air, the hot air enters the boiler to support combustion through the primary and secondary hot air systems. However, the temperature of the working fluid on the heating surface at the tail of the boiler is often low. SO ₂ in the flue gas and water vapor form H ₂ SO ₃ , which condense on the tube wall after fusion with the water vapor in the flue gas, resulting in acid corrosion.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a boiler structure that avoids low-temperature corrosion of the heating surface of the boiler tail, so that the wall temperature of the metal surface is higher than the maximum temperature of low-temperature corrosion, so as to prevent SO ₂ and water vapor in the flue gas from forming H ₂ SO ₃ , and The water vapor in the flue gas condenses on the pipe wall after fusion, resulting in acid corrosion.

In order to solve the above-mentioned technical problems, the present invention adopts the following technical scheme:

A method for avoiding low-temperature corrosion of a heating surface at the tail of a boiler, comprising the following methods: controlling the temperature of the working medium on the heating surface at the tail of the boiler, so that the wall temperature of the metal surface of the heating surface at the tail of the boiler is higher than the maximum temperature of low-temperature corrosion, preventing the SO ₂ and water vapor form H ₂ SO ₃ , which condense on the pipe wall after merging with the water vapor in the flue gas, resulting in acid corrosion.

In the aforementioned method for avoiding low-temperature corrosion of the heating surface at the rear of the boiler, the following method is used for controlling the temperature of the working fluid on the heating surface at the rear of the boiler: heat balance calculation is performed on the heating surface at the rear of the boiler, and the water supply system and the air supply system of the boiler are controlled. and flue gas system, so that the metal surface wall temperature of the heating surface of the boiler tail is higher than the maximum temperature of low temperature corrosion.

A boiler structure for avoiding low-temperature corrosion of the heating surface of the boiler tail, comprising an air preheater and a flue gas cooler, the air preheater is installed in an air duct system, the air duct system is located outside the boiler, and the flue gas The cooler is located in the boiler tail flue, and the air duct system communicates with the boiler tail flue. Boiler combustion requires combustion air. In order to ensure the thermal efficiency of the boiler, the combustion air is generally heated to a certain temperature (about 197 degrees) and sent to the furnace. The air preheater is set in the air duct system to heat the cold air into hot air, and the air duct system delivers primary hot air and secondary hot air to the boiler for combustion support.

In the aforementioned boiler structure to avoid low-temperature corrosion of the heating surface of the boiler tail, the flue gas cooler includes a first flue gas cooler, a second flue gas cooler, and a third flue gas cooler that are connected in series along the flow direction of the feedwater. The water inlet of the flue gas cooler is located on the first flue gas cooler, and the water outlet of the flue gas cooler is located on the fifth flue gas cooler.

In the aforementioned boiler structure to avoid low temperature corrosion of the heating surface at the boiler tail, a first economizer and a second economizer are arranged in sequence downstream of the fifth flue gas cooler in the boiler tail flue.

In the aforementioned boiler structure for avoiding low-temperature corrosion of the heating surface at the rear of the boiler, the pipes in the air preheater are spiral finned tubes, the spiral finned tubes are perpendicular to the air circulation direction in the air preheater, and the spiral finned tubes are perpendicular to the air circulation direction in the air preheater. Arranged in rows, and two adjacent rows of spiral fin tubes are staggered.

In the aforesaid boiler structure to avoid low temperature corrosion of the heating surface of the boiler tail, the water velocity in the pipeline in the air preheater is 1-2m/s, and the air velocity in the air preheater is 7.5m/s.

In the aforementioned boiler structure to avoid low-temperature corrosion of the heating surface at the tail of the boiler, the flue gas cooler includes a fin serpentine tube panel, a support plate and an inner guard plate, and the fin serpentine tube panel is installed on the support plate, and the inner The guard plate is located around the finned serpentine tube screen, and the exhaust gas temperature of the boiler is 134℃.

Compared with the prior art, the present invention makes the metal surface wall temperature higher than the maximum temperature of low-temperature corrosion, and avoids SO ₂ in the flue gas and water vapor to form H ₂ SO ₃ , which condense on the pipe after merging with the water vapor in the flue gas. On the wall, acid corrosion occurs. The boiler structure provided by this patent has the following advantages: 1. The original air preheater system has been changed, so that the original flue gas and air have direct convection heat exchange, and become boiler feed water and cold air heat exchange, high temperature flue gas and cooling 2. The air preheater is arranged in the air duct system outside the boiler, and the 5-stage flue gas cooler is arranged in the flue gas outlet area of the economizer. The flue gas cooler adopts Φ38x4 serpentine tubes, which are arranged in series along the flue gas flow direction. 3. The air preheater adopts Φ38x4 serpentine tubes, which are arranged in staggered arrangement along the flow direction of cold air. 4. The serpentine pipes of the flue gas cooler and the air preheater are all finned tubes, which can increase the heating surface of the pipes and save the material consumption of the pressurized pipes. The heating surface at the outlet of the flue at the tail of the boiler designed and manufactured by the method of the invention is not prone to low temperature corrosion, and the service life is greatly prolonged.

Description of drawings

1 is a schematic structural diagram of an embodiment of the present invention;

Figure 2 is a schematic diagram of the internal structure of the boiler tail flue;

Fig. 3 is the structural representation of air preheater;

Fig. 4 is the sectional view of A-A part in Fig. 3;

Figure 5 is a piping diagram of boiler feed water.

Reference numerals: 1- boiler tail flue, 2-air duct system, 3-air preheater, 4-first flue gas cooler, 5-second flue gas cooler, 6-third flue gas cooler , 7- the fourth flue gas cooler, 8- the fifth flue gas cooler, 9- the first economizer, 10- the second economizer, 11- water outlet of the flue gas cooler, 12- flue gas cooling The water inlet of the device, 13-spiral fin tube, 14-inner guard plate, 15-support plate.

The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

Detailed ways

A method for avoiding low-temperature corrosion of a heating surface at the tail of a boiler, comprising the following methods: controlling the temperature of the working medium on the heating surface at the tail of the boiler, so that the wall temperature of the metal surface of the heating surface at the tail of the boiler is higher than the maximum temperature of low-temperature corrosion, preventing the SO ₂ and water vapor form H ₂ SO ₃ , which condense on the pipe wall after merging with the water vapor in the flue gas, resulting in acid corrosion. The following method is used to control the working fluid temperature of the heating surface at the tail of the boiler: the heat balance calculation is performed on the heating surface at the tail of the boiler, and the water supply system, the air supply system and the flue gas system of the boiler are controlled, so that the metal surface wall temperature of the heating surface at the tail of the boiler is controlled. Above the maximum temperature for low temperature corrosion.

The heat balance calculation of the heating surface at the rear of the boiler and the power method of the water supply system, air supply system and flue gas system can be referred to the following table:

Annex 1 Thermal Calculation of Air Preheater System of 130t/h High Temperature and High Pressure Boiler

Form 1 FGC Sections 5-3

Form 2 FGC-2

Form 3 FGC-1

Table 4 Water heating air preheater

Example 1: A boiler structure for avoiding low-temperature corrosion of the heating surface at the rear of the boiler, including an air preheater 3 and a flue gas cooler, the air preheater 3 is installed in the air duct system 2, and the air duct system 2 Located outside the boiler, the flue gas cooler is located in the boiler tail flue, and the air duct system 2 communicates with the boiler tail flue. The flue gas cooler includes a first flue gas cooler 4, a second flue gas cooler 5, a third flue gas cooler 6, a fourth flue gas cooler 7 and a fifth flue gas cooler that are connected in series along the flow direction of the water supply. In the gas cooler 8 , the water inlet 12 of the flue gas cooler is located on the first flue gas cooler 4 , and the water outlet 11 of the flue gas cooler is located on the fifth flue gas cooler 8 .

A first economizer 9 and a second economizer 10 are arranged downstream of the fifth flue gas cooler 8 in the flue of the boiler tail. The pipeline in the air preheater 3 is a spiral finned tube 13. The spiral finned tube 13 is perpendicular to the air circulation direction in the air preheater 3. The spiral finned tube 13 is arranged in rows, and the adjacent two rows of spiral fins are arranged in a row. The sheet tubes 13 are staggered.

Example 2: A boiler structure for avoiding low-temperature corrosion of the heating surface at the rear of the boiler, including an air preheater 3 and a flue gas cooler, the air preheater 3 is installed in the air duct system 2, and the air duct system 2 Located outside the boiler, the flue gas cooler is located in the boiler tail flue, and the air duct system 2 communicates with the boiler tail flue. The flue gas cooler includes a first flue gas cooler 4, a second flue gas cooler 5, a third flue gas cooler 6, a fourth flue gas cooler 7 and a fifth flue gas cooler that are connected in series along the flow direction of the water supply. In the gas cooler 8 , the water inlet 12 of the flue gas cooler is located on the first flue gas cooler 4 , and the water outlet 11 of the flue gas cooler is located on the fifth flue gas cooler 8 .

A first economizer 9 and a second economizer 10 are arranged downstream of the fifth flue gas cooler 8 in the flue of the boiler tail. The pipeline in the air preheater 3 is a spiral finned tube 13. The spiral finned tube 13 is perpendicular to the air circulation direction in the air preheater 3. The spiral finned tube 13 is arranged in rows, and the adjacent two rows of spiral fins are arranged in a row. The sheet tubes 13 are staggered. The water velocity in the pipeline in the air preheater 3 is 1-2 m/S, and the air velocity in the air preheater 3 is about 7.5 m/S. The flue gas cooler includes a finned serpentine tube screen, a support plate 1 and an inner shield 14, the finned serpentine tube screen is mounted on the support plate 1, and the inner shield 14 is located around the finned serpentine tube screen, The exhaust gas temperature of the boiler is 134°C.

As shown in Figure 5, the boiler feed water temperature is 220 °C, and it enters the boiler system through two branch pipes. After the heat balance calculation, branch 1, 58% of the total feed water volume directly enters the economizer inlet header through the bypass of the air preheater system. In the second branch, 42% of the total water supply enters the air preheater inlet header. After passing through the air preheater outlet header, the water temperature drops from 220°C to 90°C. The water flow direction and the air flow direction are countercurrent to each other, increasing the convective heat transfer coefficient. . The feed water enters the inlet header of the flue gas cooler from the outlet header of the air preheater. After the convection heat exchange between the high temperature flue gas and the boiler feed water, the temperature of the boiler feed water at the outlet header of the flue gas cooler rises from 90 degrees to 220 degrees , and merge with branch road 1, and enter into the economizer inlet header. The 5-stage flue gas cooler and air preheater are equipped with bypass pipes respectively.

Claims (8)

1. A method for avoiding low-temperature corrosion of a heated surface at the tail part of a boiler is characterized by comprising the following steps: controlling the working medium temperature of the heated surface at the tail of the boiler to ensure that the wall temperature of the metal surface of the heated surface at the tail of the boiler is higher than the highest temperature of low-temperature corrosion, and preventing SO in flue gas₂With water vapour to form H₂SO₃And the water vapor in the flue gas is condensed on the pipe wall after being fused with the water vapor in the flue gas, so that the acidic corrosion is generated.

2. The method for avoiding the low-temperature corrosion of the heating surface at the tail part of the boiler as claimed in claim 1, wherein the following method is adopted for controlling the working medium temperature of the heating surface at the tail part of the boiler: and carrying out heat balance calculation on the heated surface at the tail part of the boiler, and controlling a water supply system, an air supply system and a flue gas system of the boiler to ensure that the wall temperature of the metal surface of the heated surface at the tail part of the boiler is higher than the highest temperature of low-temperature corrosion.

3. The boiler structure capable of avoiding low-temperature corrosion of the heating surface at the tail part of the boiler comprises an air preheater (3) and a flue gas cooler, and is characterized in that the air preheater (3) is installed in an air duct system (2), the air duct system (2) is located outside the boiler, the flue gas cooler is located in a flue at the tail part of the boiler, and the air duct system (2) is communicated with the flue at the tail part of the boiler.

4. The boiler structure for avoiding the low-temperature corrosion of the heating surface at the tail part of the boiler according to claim 3, wherein the flue gas cooler comprises a first flue gas cooler (4), a second flue gas cooler (5), a third flue gas cooler (6), a fourth flue gas cooler (7) and a fifth flue gas cooler (8) which are sequentially connected in series along the flow direction of feed water, a water inlet (12) of the flue gas cooler is positioned on the first flue gas cooler (4), and a water outlet (11) of the flue gas cooler is positioned on the fifth flue gas cooler (8).

5. The boiler structure for avoiding the low-temperature corrosion of the heated surface at the tail part of the boiler as per claim 4, characterized in that a first coal economizer (9) and a second coal economizer (10) are arranged in sequence at the downstream of a fifth flue gas cooler (8) in a flue at the tail part of the boiler.

6. The boiler structure for avoiding the low-temperature corrosion on the heating surface at the tail part of the boiler as claimed in claim 5, wherein the tubes in the air preheater (3) are spiral fin tubes (13), the spiral fin tubes (13) are perpendicular to the air flowing direction in the air preheater (3), the spiral fin tubes (13) are arranged in rows, and two adjacent rows of spiral fin tubes (13) are arranged in a staggered manner.

7. A boiler structure avoiding low-temperature corrosion of the heated surface at the tail of the boiler, as defined in claim 6, characterized in that the water flow rate in the tubes in the air preheater (3) is 1-2m/S and the air flow rate in the air preheater (3) is 7.5 m/S.

8. The boiler structure for avoiding the low-temperature corrosion on the heating surface at the tail part of the boiler according to the claim 7, characterized in that the flue gas cooler comprises a finned serpentine tube panel, a support plate (1) and an inner guard plate (14), the finned serpentine tube panel is installed on the support plate (1), the inner guard plate (14) is positioned around the finned serpentine tube panel, and the exhaust smoke temperature of the boiler is 134 ℃.

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