What are the steps for furnace drying in a circulating fluidized bed boiler?

Furnace drying, often also called "oven drying" or "boiler drying-out", is an essential step when commissioning a new circulating fluidized bed (CFB) boiler or after any maintenance that might have introduced moisture into the system. The purpose is to remove moisture, ensure the refractory and insulation materials are dry, and prepare the system for safe ignition and operation.

Here are the general steps involved in furnace drying for a circulating fluidized bed boiler:

Inspection: Before starting the drying process, a thorough inspection of the boiler should be conducted to ensure that all tools and foreign materials have been removed from the furnace and drum. Ensure all inspection doors, manways, and access points are properly sealed.

Ventilation: Ensure that the boiler has adequate ventilation. This is crucial for moisture and any potential gas build-up to escape.

Lighting Up: Use small auxiliary burners or igniters to gradually heat the furnace. The heat source could be oil or gas burners introduced through the burner windbox.

Gradual Heating: The temperature should be increased gradually. A typical schedule might involve holding at low temperatures (around 100°C to 150°C) for an extended period, then slowly ramping up. This ensures even drying and minimizes the risk of damage due to thermal stress.

Monitoring: Monitor the exit gas temperature and ensure that it doesn't rise too quickly. A rapid temperature increase might indicate that the drying process is proceeding too fast, which can damage refractory materials.

Moisture Check: The presence of steam or moisture at the boiler outlets or vents indicates that drying is still in progress. The process should continue until no more moisture is evident.

Cool Down: Once the drying process is complete, allow the boiler to cool down gradually. Avoid sudden cooling as this can introduce thermal stress.

Inspection (Post-Drying): After the boiler has cooled down, perform another inspection to ensure that no damage has occurred during the drying process.

Proceed with Light-Up: Once drying is complete and everything is verified to be in proper order, the boiler can be lighted up for normal operation.

Documentation: Always document the drying process, noting temperatures, durations, and any abnormalities observed. This can be useful for future reference and ensuring adherence to best practices.

It's crucial to remember that these steps might vary based on the specific design of the CFB boiler and the manufacturer's recommendations. Always refer to the boiler manual or consult with the manufacturer or an expert when conducting the drying-out process to ensure safety and the longevity of the boiler system.