Optimizing the seals of the air heaters of the power plant with the brush method
One of the most basic parts of a fossil fuel boiler is the air preheater, whose performance evaluation and optimization play an essential role in the efficiency of the boiler. Reducing internal leaks by using modern sealing systems is effective in combustion air quality, combustion efficiency and proper operation of the air fan. The presence of Jungström in a large boiler has an effect of up to 10% on its efficiency. Jungström’s performance is so critical that if the exhaust gas temperature changes up to c6, it will affect the cost of boiler fuel by hundreds to thousands of dollars per year. Jungström’s main advantage is its low price compared to other heaters. Leaks inside Jungström have the greatest effect on its performance. Jungström’s corrosion and sedimentation, the formation of chemical compounds such as aluminum sulfate, etc., in addition to increasing energy consumption, are effective in increasing the pressure difference on both sides and also limit the air required by the boiler.
History of air heaters
The air preheater for use in boilers was invented in 1925 by the Swedish Frederik Jungström. The first industrial application of Frederick’s design was a 25% reduction in boiler fuel consumption. Today, preheaters do about 20% of the heat transfer rate.
The most effective boiler functions
- excess air;
- unburnt carbon;
- moisture in fuel;
- flue gas temperature;
- Boiler efficiency.
Flue gas temperature and boiler efficiency are related to air heater performance. In the construction of a boiler, Airheater has only 2% investment share, but it has an effect of more than 12% on its efficiency.
general rule: Every 20 degrees decrease in the temperature of the gas leaving the air preheater increases the efficiency of the boiler by 1% and reduces fuel consumption.
Results of proper performance of an APH
- improve the performance of FDF and IDF;
- complete combustion and proper operation of burners;
- increasing boiler production capacity;
- reducing fuel consumption;
- reduction of production costs;
- decreasing air pollution;
- Reducing damage to air measurement systems.
The most important evaluation parameter of an air heater is its leakage rate and thermal efficiency. The leakage rate is related to the settings and performance of the seals, and the efficiency is related to the condition of its baskets.
leak
When the incoming air is inclined towards the smoke coming out of the heater, leakage occurs, the main cause of which is the pressure difference between the air in the heater’s inlet and the smoke coming out of it. This means that the air goes out through the chimney without entering the heater.
Leakage rate index
This index determines the percentage of air entering the heater and its leakage, which is a negative parameter. According to the ASME 4.3PTC standard, this amount should be around 6-10%, and deviation from this amount causes an increase in fuel consumption, a decrease in boiler efficiency, and an increase in production costs.
2.86 tons of carbon dioxide gas is emitted for every ton of unburned coal in every megawatt of production.
The adaptable wire brush sealing system registered by the American Sealeze company has provided a type of adaptable sealing that is more durable and effective and at a lower price than APH seals.
Conventional air-to-gas sealing systems used in rotary air heaters are less complete than the construction of metal bands that were used in the first Janström air heater sealing of the last century. These metal band seals are more suitable for radial, axial and circumferential sealing exposed to corrosive gases and intermittent high temperatures.
The advantage of brush seals over wire seals is their flexibility in terms of compliance. Metal band seals do not bend and break permanently. Because of this, the seal is damaged and this problem can potentially damage the APH and stop the rotor.
The metal band seals shown in the picture on the left are rigid and wear out quickly. Changing a small sealing space to a large one causes excessive leakage. The new brush seal in the right picture shows that only some of its seal brushes have been lost. The flexibility feature of the shown wire brush allows the seal to be deflected in the dimensions of small spaces to ensure sealing in larger spaces and then return to its original position.
Sealeze power company’s adaptable sealing brush seals and holders are made of stainless steel to easily resist corrosion at high temperatures in APH environments. These brushes maintain long-term effectiveness after conventional sealants have been damaged or are essentially gone.
Repeated thermal expansions and buildings with large rotors (often over 20 m long in diameter or more) in APHSs generally result in large irregular sealing spaces. At high temperatures, APHS outer edges may weaken and fail, as much as 3 inches above the cold state. The wear of metal bands (deflection or breaking) is based on the smallest size of the sealing spaces. Therefore, it does not allow the sealing of large spaces. Leakage rates for properly designed and installed seals should be 10% or less. Damaged or worn metal band seals can show this leakage rate of 15 to 20 percent or more. Leakage rates in metal band seals, up to 30%, are not uncommon.
Adaptive brush seals consist of thousands of brush strands of a perfect seal that provide high wear resistance. High degree of resistance, long life and non-return of bending are not found in metal band seals. Each independent and adaptable brush strand can be bent to accommodate any irregularities and changes in the sealing voids and return to the original position. A more effectively maintained seal lasts 2 to 5 times longer than a metal band seal; It means more than the output multiple of its cycles.
The compatibility and coordination of the seal with whistleblowers is quite obvious. The effect of an adaptable wire brush seal after 135 days of use with high-pressure 175 PSI sootblowers is shown in the figure below.
In sealeze’s adaptable wire brush sealing system for rotary APH, stainless steel brush and holder (or other suitable materials) with different options and features are used. Sealeze’s unique holder design allows manufacturers to easily replace existing sealing brushes.
The new brush can be installed without having to readjust the clearance and sealing dimensions inside the holder.
The important advantage of this feature is saving time and the possibility of removing the unevenness of empty spaces.
For sealing the air-to-gas and gas-to-air leakage paths, various types of peripheral, axial, radial and post rotor seals are available. The investigated seals are a suitable choice to replace metal strip seals for peripheral, radial and axial. Each brush is made up of thousands of wires (wires) with metal resistant to corrosion and wear, resistant to high heat, flexible and bendable. Each wire deflects independently and conforms to the irregularities and discrepancies in the sealing voids, then returns to its original state. The inherent tension in the design of the brush reduces the amount of stretching and wear in it due to the stresses of the shape change under the shape change. This brush consists of thousands of flexible stainless steel wires that are independently inside a membrane. These conformable members are designed to deflect and conform to any irregularity and gap differences and return to the original position to ensure a tight seal is maintained. These members increase the sealing power of the brush up to 80% without sacrificing the flexibility of the seal.
Comparison of metal band with brush sealant
Comparing worn metal band sealing with a new brush seal shows that brush seal is flexible and can be adapted to small spaces. This type of sealing can return to its original position for larger spaces. Plain worn metal band seal is not sealed based on the smallest sealing spaces and larger sealing spaces.
Using a flexible brush made for austenitic malleable steel (stainless steel series 300) filled with brush wires reduces leakage by 70-80% without sacrificing flexible sealing.
One of the factors of proper waterproofing design is the necessity of its easy installation. The design made by the company allows quick replacement of worn seals at a lower price than Sealeze.
Sealeze APH wire brush seals are made of stainless steel with less space like OEM seals. The replaceable seal cartridge design allows the seals to be replaced quickly and easily.
Definitely, in the future, the sealing brush can be moved in half the required time compared to the OEM seal and reduce costs. Here, only the brush is moved, not the holder; Because the remaining retainer is lost during the calculated time of the alignment process. With this system, the retainer is in place to install and lock. The quick-locking brush sealing system keeps the sealing brush in place during service, but in APH trips, the brushes are quickly replaced with new ones without losing the settings of the sealing spaces. The necessary tools for replacing the waterproofing brush are a screwdriver and a pair of pliers. Grinding and welding are not needed for this.
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