Ceramic kilns for heat recovery heat exchangers
一, Sources and characteristics of waste heat from ceramic kilns
Ceramic kilns (roller kilns, tunnel kilns, etc.) are high energy consuming equipment, with kiln energy consumption accounting for 30% -50% of total energy consumption, and exhaust heat loss accounting for 35% -40% of total kiln energy consumption. Main source of waste heat:
High temperature flue gas: The exhaust temperature at the kiln tail is 200-500 ℃, containing a large amount of sensible heat.
Cooling section waste heat: The product cooling section discharges hot air at * * 400-450 ℃ * *, which is a high-quality waste heat source.
Kiln body heat dissipation: Heat dissipation from kiln walls, roof, etc. can be recovered and utilized through insulation and radiation.
二, Mainstream heat recovery technology and application
1. Regenerative heat recovery
Principle: Use thermal storage materials (such as ceramic thermal storage bricks) to alternately store high-temperature flue gas heat, and then heat the combustion air/fuel gas to achieve high-temperature preheating.
Application: The regenerative combustion system for roller kilns and tunnel kilns can preheat the combustion air to 800-1000 ℃, saving energy by 20% -40%.
Advantages: High heat transfer efficiency, high temperature resistance, suitable for high flow flue gas.
2. Recuperative wall heat exchange
Principle: Indirect heat transfer between cold and hot fluids is achieved through heat exchangers (tube, plate, heat pipe) without cross contamination.
Mainstream devices
Heat Pipe Heat Exchanger (HPHE): Suitable for medium and low temperature flue gas (150-500 ℃), with a heat transfer efficiency of 70% -85% and an investment payback period of 1-2 years.
Tube/finned tube heat exchanger: used for preheating combustion air and generating hot water/steam.
Application: Cooling section waste heat recovery, flue gas preheating combustion air, heating and drying hot air.
3. Direct reuse of waste heat
Preheating of Combustion Air: Directly heating the combustion air with hot air or waste heat from the cooling section to increase combustion temperature and reduce fuel consumption.
Drying heat source: waste heat hot air is used for body drying and spray drying tower for heat supplement to replace part of fuel.
Kiln circulation: The hot air from the cooling section is returned to the preheating zone to reduce the heat load during firing.
4. Waste heat power generation (ORC/steam turbine)
Principle: High temperature waste heat generates steam/organic working fluid, which drives the turbine to generate electricity.
Applicable to large-scale kilns, scenarios with stable waste heat and high temperatures (≥ 300 ℃), achieving waste heat electrification.
三, Typical heat recovery system scheme
Option 1: Cooling section waste heat+heat pipe heat exchanger (electric porcelain/ceramic tile)
Extract hot air from the cooling section at 400-450 ℃ → heat pipe heat exchanger → heat fresh air to 200-300 ℃ → send it to the drying room to dry the billet; After cooling, the flue gas returns to the kiln as atmospheric air.
Effect: Eliminating steam boilers, improving drying efficiency, and achieving significant annual energy savings.
Plan 2: Flue gas cascade recovery (roller kiln)
High temperature section (350-500 ℃) → preheating combustion air;
Medium temperature range (200-300 ℃) → Heating and drying with hot air;
Low temperature range (150-200 ℃) → producing hot water/heating;
The overall thermal efficiency has been improved by 15% -20%.
Plan 3: Regenerative combustion+comprehensive utilization of waste heat
Recovering waste heat from flue gas in the heat storage chamber → preheating the combustion air to 900 ℃+;
Cooling section waste heat → drying/combustion air supplementary heating;
The exhaust temperature drops below 150 ℃, with a thermal efficiency of over 70%.
四, Benefits and Key Points
1. Core benefits
Energy saving: Fuel consumption is reduced by 15% -40%, and energy consumption per ton of product is reduced by 20% -30%.
Economy: The investment payback period is 1-3 years, saving tens of thousands to millions of fuel costs annually.
Environmental protection: simultaneous reduction of CO ₂ and NO ₓ emissions, in line with dual carbon requirements.
Production: Stabilize kiln temperature, improve product qualification rate, and extend kiln life.
2. Key points of design and operation
Temperature matching: Utilize the waste heat temperature in a cascade manner, with high temperature priority given to preheating the combustion air, and medium and low temperature used for drying/hot water.
Corrosion/blockage resistance: Smoke contains dust and sulfur, and corrosion-resistant and easy to clean heat exchangers (such as heat pipes and wear-resistant pipes) should be selected.
System integration: linked with kiln control, without affecting kiln pressure, atmosphere, and product quality.
Insulation: Strengthen the insulation of waste heat pipelines and equipment to reduce secondary heat dissipation.
五, Application Trends
Efficiency: High temperature heat pipes, honeycomb heat storage bodies, and compact heat exchangers are gradually becoming popular.
Intelligence: The linkage between waste heat recovery and kiln DCS system automatically adjusts air volume, temperature, and heat exchange load.
Integration: waste heat+carbon capture, waste heat refrigeration, distributed energy coupling, to achieve energy closed-loop.
