What Is The Air Leakage Of The Steam Air Preheater?

- Jan 15, 2018-

The air leakage of steam air preheater

1, Analysis of the reasons for air leakage

1) Due to the rotation of the rotor, the air in the cell warehouse will inevitably be brought into the flue gas to form air leakage.

2) Due to the rotation of the rotor, there must be a gap between the motion and the static. The negative pressure on the flue gas side and the positive pressure on the air side make the air leak to the negative pressure side of the flue gas to form a direct air leakage.

① The air preheater air leakage control system (LCS) has been working abnormally. In operation, the hot end fan-shaped sealing baffle can not automatically track the mushroom deformation of the rotor to reduce the air leakage gap, and the fan-shaped seal is severe wear when the gray air leaks to the flue gas side, which further increase the air leakage gap, and the amount of air leakage  is proportional to air leakage area, Therefore, the air leakage surge of the steam air preheater.

② Because of low heat value and high ash content in the boiler, the lean coal and the steam air preheater, especially the low temperature corrosion of the heat exchange element, cause fouling and blockage of ash in the air preheater. The flow resistance increases after the flow channel is blocked, resulting in the increase of the pressure difference between the air side and the flue gas side, and the amount of air leakage is proportional to the square root of the pressure difference. Therefore, the plugging ash aggravates the air leakage.

2, Air leakage control measures

1) Exploration of air leakage control measures. The steam air preheater is equipped with a Leakage Control System (LCS). Because the fan seal baffle can be adjusted, there is a slip sealing strip between the air preset housing and the adjustable fan seal baffle. After a long period of operation, the sealing strips are worn to form a gap, so that air and dust can pass behind the fan-shaped sealing plate, thus increasing air leakage of the air preheater, on the other hand, with the accumulation of dust, Limit the movement of the fan seal baffle. Therefore, the unreliability of the air preheater air leakage control system (LCS) is determined by its working environment. In other words, a large amount of manpower and material resources recovery of the air leakage control system (LCS) is not worth the candle.

In contrast, VRcooler Air Preheater VN design technology eliminates the Leakage Control System (LCS) by welding new slats between the sector seal, the axial seal and the housing, Sealing baffle and axial sealing baffle fixed in a certain position, forming a complete welded structure, thus eliminating the possibility of secondary air leakage. Of course, the position of the fan-shaped seal and the seal of the axial seal should be pre-calculated before fixing to ensure that the fan-shaped seal and the seal can adapt to the thermal deformation of the rotor under any load. At the same time, the use of "dual seal" to enhance the existing air pre-radial and axial seal effect, which is doubted by the radial axial seal plate to achieve the number of sheets. Thus, there is an intermediate pressure between the air flow pressure of the flue gas so that the pressure difference between the two air flows is reduced by half, which can also be understood as a labyrinth-like "double seal". The increased  flow resistance of air flow (leakage to) flue gas side, which can effectively reduce the air leakage rate.

After repeated study and comparison, decided to adopt VRcooler design technology to improve the Junker air preheater sealing system to control the air preheater air leakage.

2) The use of air preheater heat exchange element has reached the service life should be fully replaced by the opportunity, commissioned VRcooler to use its Jun gram-type air preheater VN design technology to the boiler in the burning Guangwang coal and mixed with burning The M CR condition of 4 000 Nm / h natural gas is designed for retrofitting the design basis.

① design parameters before and after transformation comparison 

② changes before and after the transformation of heat exchange elements 

③ Cancel the air leakage control system (LCS), fix all the fan-shaped seal plates and axial seal plates and install the secondary radial partitions to double the radial and axial seal plates;

④ changes according to the rotor compartment selection VRcooler. heat exchanger plate redesigned heat exchanger components dimensions;

⑤ Because of fan-shaped plate and the center of hot end tube sealing plate transferred to the weight of the connecting plate, so cancel four suspension screw, barrel at the center of the hot end seal plate fixed on the connection on board, and the central cylinder seal shaft seal welding.

3) Check the thrust bearing capacity. The air preheater bottom thrust bearing is a 45 BV tilting-padded sliding bearing with a carrying capacity of 263 083 kg, or 263 t. The pre-engineered air preheater rotor weighs 190 t and the modified rotor weighs 200 t, much less than the maximum support weight for thrust bearings, so it does not affect bearing usage.

3, air leakage control economic analysis

Because the fuel and other conditions used in the boiler before and after the transformation are not identical, the following is a rough comparative analysis of the load condition before and after the modification of the air preset.

1) Comparison of the main performance parameters before and after the air pre-reform under full load conditions 

2) The air preheater heat exchanger has reached the end of its useful life, and the spare parts of the heat exchanger in the warehouse have run out. At this time, the air preheater is transformed to transform the sealing device and the heat exchanger is replaced.

3) Decreasing air leakage rate can protect the boiler from burning enough oxygen to reduce the heat loss from incomplete combustion and exhaust heat loss. The exhaust gas temperature is reduced by 19 ℃ and the boiler efficiency is increased by 1% . At the same time, hot air temperature increased by 30 ℃, effectively guarantee the wide prosperous coal ignition and stable combustion.

4) Reduce the air leakage rate, reduce the air and flue gas flow, reduce the blower, induced draft fan power consumption 300kW·h, annual savings of about 1.8 million kW·h, but also to avoid the fan due to insufficient output and affect the entire Unit output.

5) The reduced air leakage rate reduces the flue gas flow at the outlet of the air preheater and reduces the flue gas flow rate, thus increasing the electrostatic precipitator efficiency. At the same time, all the equipment downstream of

the air preset wear down, and its maintenance and maintenance is greatly reduced.

6) For the air preheater itself, the air leakage rate is reduced, the flow rate on the air side leaking to the flue gas side is decreased, the flow rate is reduced, the service life of each wearing part is prolonged, and the workload for maintenance and maintenance is reduced.

7) The elimination of air leakage control system (LCS), radial vane seal, axial positive vane seal, the sealing plate position correction and other maintenance work can be completely canceled, simplifying the maintenance work, while 

reducing the air preheater maintenance workload.