Use and Maintenance
Heat exchanger component lifting:
The heat-exchange components provided by Qixing Power generally come in two materials: one is a low-carbon steel plate component with a thickness ranging from 0.5 to 0.6 mm, used on the hot side; the other is an enamel-coated heat-exchange component, with a coating thickness of between 1.15 and 1.2 mm after enameling, used on the cold side. Since these heat-exchange components are all made from thin metal sheets, care must be taken during transportation and lifting to avoid damaging the component ends. Otherwise, issues such as component deformation or enamel peeling may occur. Typically, Qixing Power provides a set of specialized lifting tools specifically designed for handling the heat-exchange component boxes. The use of self-made, ordinary carbon-steel lifting tools is strictly prohibited! This is because carbon steel has poor fatigue resistance and is prone to hook detachment or fracture, which could lead to serious safety hazards.
Heat exchanger component transportation and storage:
During loading and transportation, heat exchange components must be neatly stacked and securely fastened with protective netting and covered with a waterproof tarpaulin. Before unloading, any rain or snow accumulated on the tarpaulin must be shaken off outside the vehicle; it is strictly forbidden to shake or scatter such materials onto the components themselves. The stacking area for heat exchange components must be free of standing water and debris, located on a level concrete surface that is higher than surrounding areas, and protected by a waterproof tarpaulin. Loading and unloading of heat exchange components are prohibited on rainy days, as this could lead to corrosion of the components.
Heat exchanger component installation protection:
When installing the heat exchange components, avoid contact with metal objects such as steel structural columns, electric hoist hooks, and guide chains. During the lifting and placement of the component bins, be sure to check the stability of the supporting steel bars and remove any debris, such as welding slag and edge trimmings. After the components are placed into the bins, lay down asbestos blankets one by one to protect the component ends and prevent damage during subsequent installation procedures!
Component dust and corrosion control:
In practice, nearly all fuels burned in boilers contain sulfur. During the combustion process, 2% to 6% of the sulfur dioxide is converted into sulfur trioxide, which then reacts with water vapor in the flue gas to form ammonium bisulfate—a compound resulting from the escape of ammonia used in denitrification. This ammonium bisulfate deposits as a sticky, wet corrosion product on the surfaces of the cold-end heat-exchange elements. Additionally, fly ash in the flue gas and particulate matter or fragments generated during soot-blowing operations can further damage these elements. As a result, the heat-exchange elements are continuously corroded, their heat-transfer channels become blocked, leading to poor heat-transfer performance, shortened service life, and significant pressure drops.
To effectively control and mitigate corrosion and blockage of the cold-end heat-exchange components, it is essential to keep the ammonia escape rate within a safe limit—typically no higher than 2.3 mg/m³—and ensure that the SO₂/SO₃ conversion rate does not exceed 1% (molar ratio). Additionally, avoid operating the air preheater for extended periods when its “combined cold-end temperature” (flue gas outlet temperature plus air inlet temperature) falls below the recommended minimum value. Furthermore, prevent moisture from leaking into the flue gas due to malfunctions in the economizer or air heater, as such moisture can raise the flue gas dew point. Any pipe leaks should be promptly repaired.
Fire prevention measures:
During ignition, low-load operation, and poor combustion conditions, incompletely burned pulverized coal and oil mist entrained during ignition may undergo secondary combustion. Therefore, it is essential to prevent the deposition of combustible materials on the surface of heat-exchange elements; otherwise, a fire could break out in the air preheater.
Under conditions of ignition, no-load operation, and low load, the air preheater rotor must remain rotating. Regular soot-blowing should be maintained to ensure that the surfaces of the heat-exchange elements are kept clean. Pay close attention to the temperatures of the flue gas and air in the air preheater; if any temperature anomalies occur, promptly investigate and eliminate the cause. In the event of secondary ignition, make sure that the forced-draft fan, induced-draft fan, soot blower, and low-pressure water system are all operating normally. The fire monitoring system must be kept in a normal working state.
Pre- and post-operation checks:
1. Inspect and thoroughly clean the upper part of the air preheater components, as well as temporary platforms, scrap materials, supports, and other debris inside the flue duct.
2. Check whether the welds of the sootblower gun tube supports are firm and reliable. If necessary, take reinforcement measures to prevent the sootblower support from detaching and getting stuck in the rotor.
3. Use the handle to turn the rotor two full revolutions and check whether it can rotate freely.
4. Check whether the high-pressure water and steam pipelines and valves are functioning properly; verify that the condensate drainage in the soot-blowing steam pipeline is normal; and ensure that the pressure and superheat before the soot-blower valve are within the proper range.
5. Check whether the radial, circumferential, and axial sealing clearances, as well as the sealing strip bolts, are in normal condition.
6. Check whether the oil levels in the rotor top and bottom bearings and in the gearbox lubrication system meet the requirements.
7. Check that the inlet and outlet dampers of the air preheater have been closed.
8. Inspect the fire monitoring device and check the local control panel to ensure it is functioning properly.
9. Check to ensure that the rotor stall alarm device is functioning properly.
10. Check whether the operating sounds of the air preheater reducer and the upper and lower bearings are normal.
11. Check whether the drive motor current is normal.
12. Check whether the inlet and outlet temperatures of the air and flue gas in the air preheater are normal.
Dust removal of heat exchange elements:
1. After the air preheater is running normally, perform soot blowing every 8 hours, and strictly follow the operating instructions for the soot blower. Ensure that the operating resistance of the air preheater remains within the design range. Before shutting down the furnace, during boiler startup, and during periods of low unit load, increase the frequency of soot blowing.
2. To prevent condensation on the surface of heat-exchange elements, steam sootblowing should be performed when the temperature of the heat-exchange elements is relatively high. Therefore, sootblowing should be scheduled when the unit has reached a certain load level.
3. To ensure effective soot blowing and prevent any extraneous moisture from entering the air preheater, it is crucial to use superheated steam with a certain level of pressure and temperature, thereby guaranteeing a dry cleaning medium. The temperature of the soot-blowing steam should be maintained between 120℃ and 330℃, and the steam nozzle outlet pressure should be 1.5 MPa. Using steam containing water for soot blowing can exacerbate corrosion of the heat-exchanging components.
4. Ensure that condensate from the steam lines does not enter the sootblower; thorough and effective drainage is required before performing sootblowing.
Water from steam blowdown can cause corrosion of components, increase the adhesion and hardness of deposits on the surface of the air preheater’s heat exchange elements, making it impossible to remove these deposits through steam blowdown, and thereby exacerbating fouling and blockage of the heat exchange elements.
5. During the soot-blowing process, if the cold-end temperature is found to be lower than expected, measures should be taken in advance (such as activating the air heater or reheating the hot air recirculation) to raise the wall temperature at the cold end of the heat-exchange elements, ensuring that the “combined cold-end temperature” of the air preheater remains no lower than the minimum recommended value. (That is, the sum of the cold-end flue gas temperature and the air temperature should not be less than 150℃.)
Heat exchanger component cleaning:
1. During operation, if the resistance of the air preheater exceeds 35%, the unit should be shut down and cleaned using high-pressure water. Under no circumstances is high-pressure water cleaning permitted when the unit is under load, as the instantaneous flushing action of high-pressure water can cause thermal shock to the heat-exchanging elements, resulting in fatal damage to both the enamel coating and the element bodies themselves. If such cleaning is absolutely necessary, it must be carried out after the furnace has been shut down. The high-pressure water pressure should not exceed 15 MPa, and the air heater must be kept running during the cleaning process.
2. When the operating resistance of the air preheater exceeds the design value by more than 25%, low-pressure water flushing should be employed. Once low-pressure water washing is initiated, it must be carried out thoroughly and completely; otherwise, hard deposits will form on the surface of the heat-exchange elements. The ideal temperature for the flushing water is between 50 and 60°C. Water washing is typically performed under low-speed conditions, with the heat-exchange elements maintained at a temperature approximately 35 to 45°C higher than the ambient temperature. Low-pressure water washing yields better results. After cleaning, the components should be dried thoroughly using hot-air blowing.
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