Heat Recovery Efficiency
A brief inroduction to heat recovery efficiency.
Heat Recovery Efficiency
Heat recovery efficiency is a core indicator for evaluating the performance of regenerative heat exchangers, directly reflecting the equipment's ability to recover heat energy from high-temperature flue gas. In industrial furnaces, kilns, and RTOs (Regenerative Thermal Oxidizers), the level of heat recovery efficiency determines the system's energy consumption and operational economy.
Definition
Heat recovery efficiency refers to the percentage of heat recovered through the heat exchanger relative to the input heat. For regenerative systems, it typically refers to the proportion of heat released by the flue gas absorbed by the combustion medium (air, fuel gas, etc.).
Basic Calculation Formula:
η = T<sub>flue gas inlet</sub> − T<sub>air inlet</sub> / T<sub>flue gas inlet</sub> − T<sub>flue gas outlet</sub> × 100%
Where:
η: Heat recovery efficiency (%)
T<sub>flue gas inlet</sub>: Flue gas temperature entering the regenerator (°C)
T<sub>flue gas outlet</sub>: Flue gas temperature exiting the regenerator (°C)
T<sub>air inlet</sub>: Temperature of cold air entering the system (°C)
This formula is based on temperature difference calculations; in actual engineering, factors such as heat loss and air leakage need to be considered and corrected.
Heat Recovery Efficiency in Industrial Equipment
Regenerative Thermal Oxidizer (RTO)
The core function of an RTO is to treat organic waste gas while recovering heat generated from combustion. Its heat recovery efficiency typically reaches over 95%.
Three-chamber RTO: 95%-97%
Rotary RTO: Over 97%
Highly efficient recovery allows the RTO to maintain self-sustaining operation even under low-concentration waste gas conditions, requiring little or no supplemental fuel.
Regenerative Thermal Oxidizer (HTAC)
Used in industrial furnaces such as heating furnaces and heat treatment furnaces, it preheats combustion air to 800-1000℃ through alternating heat absorption and release by a heat regenerator. Heat recovery efficiency reaches 80%-90%, more than 30% higher than traditional heat exchangers, resulting in overall energy savings of 30%-50%.
Influencing Factors
Properties of heat storage materials
Material Parameters | Impact on Efficiency |
Specific Heat Capacity | The higher the specific heat capacity, the greater the heat storage capacity per unit volume, and the higher the efficiency. |
Thermal Conductivity | The better the thermal conductivity, the faster the heat storage and release rate, which is beneficial to improving efficiency. |
Thermal Shock Resistance | Affects long-term operational stability and indirectly affects efficiency maintenance. |
Geometry of the heat storage body
Structural Parameters | Impact on Efficiency |
Specific Surface Area | A larger surface area results in a larger gas-solid heat transfer area and higher efficiency. |
Aperture Ratio | Too high a porosity reduces heat storage capacity; too low a porosity increases pressure drop. |
Wall Thickness | Too thick a wall results in high thermal resistance and slow response; too thin a wall results in insufficient strength. |
Vascular Pattern | Regulated pores provide more uniform heat transfer than disordered packing. |
Reversing Cycle
Too short a cycle: Frequent switching increases airflow scouring losses and reduces efficiency.
Too long a cycle: Heat storage medium temperature saturates, outlet flue gas temperature rises, and efficiency decreases.
Typical reversing cycles are 30-120 seconds, requiring adjustment based on bed heat capacity and flue gas flow rate.
Airflow Distribution
Uneven airflow distribution in the heat storage bed can lead to localized overheating or undercooling, reducing overall efficiency. Influencing factors include:
Inlet distributor design
Bed packing uniformity
Bed height to diameter ratio
Flue gas characteristics
Dust content: Dust deposits clog pores, reducing heat exchange area
Humidity: Water vapor condensation corrodes equipment and affects heat exchange
Corrosive components: Corrode the heat storage medium surface, damaging the structure.
Measures to Improve Heat Recovery Efficiency
Optimize Heat Storage Medium Selection
Select materials with high specific heat capacity and high thermal conductivity (corundum-mullite, silicon carbide)
Adopt a honeycomb structure to increase specific surface area (500-1000 mm²). (m²/m³)
Optimize orifice shape and wall thickness to balance heat storage and pressure drop.
Improve Airflow Distribution
Optimize inlet distributor design.
Layered filling of heat storage media of different specifications (large spheres at the bottom for uniform flow, small spheres in the main layer for heat storage).
Ensure a flat and dense bed to avoid channeling.
Optimize Operating Parameters
Adjust reversing cycle according to operating conditions.
Control flue gas inlet temperature within the design range.
Regularly clean bed ash to keep channels clear.
Improve Sealing Performance
Use ceramic fiber blanket wrapping for sealing.
Ensure tight sealing between modules.
Regularly check for equipment leaks.
Summary
Heat recovery efficiency is a core indicator for evaluating the performance of thermal regenerative equipment, influenced by a combination of factors including materials, structure, operating parameters, and sealing condition. During equipment selection, priority should be given to high specific heat capacity thermal storage materials, regular honeycomb structures, and designs with low air leakage rates. During operation and maintenance, attention should be paid to optimizing reversing cycles, cleaning accumulated dust, and maintaining seals. Through systematic design and management, heat recovery efficiency can be stabilized above 95%, achieving significant energy savings and return on investment. We are a Chinese industrial ceramics manufacturer. For more information, please contact us via email at annayu@169chem.net or WhatsApp at +8618909016373.