The air preheater is a core component of thermal equipment such as boilers and industrial furnaces. Its function is to utilize the waste heat of flue gas to heat the air required for combustion, thereby improving thermal efficiency. However, during operation, dust and sulfides in the flue gas will adhere to the surface of the heat exchange elements, forming ash and scale, leading to a decrease in heat exchange efficiency and increased flue gas resistance. In severe cases, it can cause ash blockage, corrosion, and even boiler shutdown. The **air preheater automatic cleaning system** is an automated cleaning device designed to solve this problem, enabling continuous online cleaning and ensuring stable equipment operation.
I. System Core Components
1. Cleaning Medium Supply Unit
High-pressure water source system: Includes a high-pressure pump, water storage tank, filter, and pressure regulating valve, used to provide high-pressure clean water (pressure generally 10–30 MPa), suitable for conventional ash cleaning.
2. Spraying Execution Unit
Cleaning spray gun: Installed on the outside or inside of the air preheater casing, divided into two types: fixed spray guns and rotating spray guns.
- Fixed spray guns: Arranged in key ash accumulation areas of the heat exchange elements, with the nozzle direction precisely aimed at the heat exchange surface.
- Rotating spray guns: Driven by a motor to rotate, covering a larger cleaning area, suitable for large air preheaters.
- Nozzles: Using fan-shaped or conical atomizing nozzles, which can atomize water or chemicals into fine droplets, improving cleaning coverage and impact force.
- Pipes and valves: High-pressure, corrosion-resistant stainless steel pipes, coupled with electric/pneumatic valves, to control the on/off of the cleaning circuit.
3. Control System
- PLC controller: The core of the system, which can preset cleaning programs (cleaning time, interval, medium pressure, etc.), and can also be connected to the DCS system for remote control.
- Sensors: Equipped with differential pressure sensors (monitoring the flue gas pressure difference at the inlet and outlet of the air preheater to determine the degree of ash accumulation), temperature sensors (monitoring flue gas/air temperature to prevent low-temperature corrosion caused by cleaning), and flow sensors (monitoring the flow rate of the cleaning medium).
- Human-machine interface (HMI): Touch screen displays the system's operating status, supports manual/automatic mode switching, parameter setting, and fault alarms. 4. Waste Liquid Recovery Unit
- The dust-containing and chemical-containing wastewater after cleaning is collected through the collection tank at the bottom of the air preheater. After treatment in a sedimentation tank and filter, it can be recycled or discharged after meeting standards, preventing environmental pollution.
II. Working Principle and Cleaning Modes
1. Working Principle
When the pressure difference between the inlet and outlet of the air preheater reaches a preset threshold (or reaches the set cleaning cycle), the control system automatically starts the cleaning program: the high-pressure pump pressurizes water/chemicals and delivers them to the spray gun; the nozzle sprays a high-speed jet to impact the surface of the heat exchange elements, stripping off accumulated dust and scale; at the same time, the air preheater rotor continuously rotates to ensure that all heat exchange areas are covered by cleaning; the cleaning wastewater is treated by the recovery unit and then recycled or discharged.
2. Cleaning Modes
- Automatic Mode: Based on the feedback from the pressure difference sensor or a preset time cycle, the system automatically starts, runs, and stops without manual intervention, suitable for routine operation and maintenance.
- Manual Mode: Cleaning is manually triggered through the HMI or remote DCS, suitable for emergency cleaning in case of sudden dust blockage or special working conditions.
- Online Cleaning: Cleaning is performed while the air preheater is in normal operation, without affecting the continuous production of the boiler/kiln, which is the most commonly used cleaning method.
- Offline Cleaning: During equipment shutdown and maintenance, it is used in conjunction with manual cleaning for deep cleaning of stubborn dirt.
III. Applicable Scenarios and Advantages
1. Applicable Scenarios
- Boiler air preheaters in thermal power plants and combined heat and power plants
- Waste heat recovery devices for industrial kilns in the steel, cement, and metallurgical industries
- Flue gas heat exchange equipment for waste incinerators and biomass boilers
2. Core Advantages
- Improved equipment efficiency: Timely removal of accumulated dust reduces flue gas resistance, restores heat exchange efficiency, and reduces fuel consumption.
- Extended equipment life: Avoids local overheating, corrosion, and wear caused by dust accumulation, extending the service life of the air preheater heat exchange elements.
- Reduced operation and maintenance costs: Automated operation reduces the workload of manual cleaning and downtime, reducing the labor intensity of maintenance personnel.
- Environmental protection and safety: Wastewater is recovered and treated to prevent pollution; the temperature monitoring function prevents low-temperature corrosion and ensures safe equipment operation.
IV. Selection and Operation and Maintenance Considerations
1. Selection Key Points
- Select the appropriate number of spray guns and pressure parameters based on the air preheater model, heat exchange area, and flue gas conditions (temperature, dust concentration).
- For flue gas environments with high sulfur content, corrosion-resistant materials (such as 316L stainless steel) should be used for pipes and spray guns, and corrosion inhibitors should be added.
2. Operation and Maintenance Considerations
- Regularly check whether the nozzles are clogged, and clean or replace them promptly to ensure effective cleaning.
- During chemical cleaning, strictly control the concentration of chemicals and cleaning time to avoid damaging the heat exchange elements.
- Regularly calibrate the sensors to ensure the accuracy of the control system parameters.
- During winter operation, the water pipelines need to be heated and insulated to prevent freezing and cracking.
