How to Dry Fly Ash Using Waste Heat from Power Plant Flue Gas?

Utilizing boiler exhaust gas (120°C–180°C) from a power plant as the heat source for a fly ash dryer is a core strategy for reducing costs in fly ash recovery projects. However, three key issues must be addressed in practice:

1. Material Selection and Low-Temperature Dew Point Corrosion: Power plant flue gas contains sulfides and water vapor. After the gas releases heat during the drying process, if the temperature drops below the acid dew point, condensation readily forms on the equipment's inner walls, causing severe corrosion.

Engineering Countermeasure: Materials such as ND steel (steel resistant to low-temperature sulfuric acid dew point corrosion) or stainless steel must be used instead of ordinary carbon steel in high-risk areas, such as the feed inlet duct and the front section of the dryer drum.

2. Anti-Caking Design for Low-Temperature Heat Sources: Pond ash often has a moisture content as high as 30%–40% and is highly adhesive. Since power plant flue gas is a low-temperature heat source, it cannot achieve instantaneous dehydration like high-temperature furnaces; consequently, wet ash tends to stick to the drum walls, impairing heat exchange efficiency.

Engineering Countermeasure: The system requires a "high airflow, large volume" design to rapidly extract water vapor via high exhaust rates. Additionally, the drum must be equipped with a powerful breaking shaft and anti-caking chains to shatter the material immediately upon entry and disrupt its adhesiveness.

3. System Integration and Airflow Balance/Safety: The drying line must divert flue gas from the power plant's main flue. Improper control of wind pressure—leading to abnormal negative pressure in the main flue—poses a direct threat to the safe operation of the power plant boiler.

Engineering Countermeasure: The flue gas connection point must be equipped with an automated pressure-regulating valve and a bypass system, integrated with the power plant's DCS (Distributed Control System). In the event of a drying line malfunction, the valve must switch back to the original flue within seconds to ensure the safety of the main power generation system.

Parameters for Preliminary Scheme Confirmation

Before coordinating with equipment manufacturers, it is recommended to verify the following three design data points:

1. Available Flue Gas Parameters: The actual temperature, flow rate (m³/h), and pressure of the flue gas that can be diverted from the power plant. 2. Initial moisture content of wet ash: Determine the aggregate moisture content and calculate whether the total heat carried by the flue gas meets the evaporation requirements.

3. Site layout: Consider the physical distance between the drying line and the power plant's main flue; this distance directly impacts costs related to pipeline insulation and heat loss.

Effective waste heat utilization requires rigorous heat balance calculations. Please feel free to contact us if you require a preliminary engineering feasibility assessment.