In high-temperature industrial fields such as steel, metallurgy, and ceramics, the energy consumption of industrial furnaces has always been a core pain point that restricts corporate benefits. According to statistics, the average thermal efficiency of industrial furnaces in my country is only 30%-40%, of which the heat dissipation loss of the furnace lining accounts for as high as 20%-30%. With the advancement of the “dual carbon” goals, how to achieve energy conservation and consumption reduction through material innovation has become a key direction for the industry’s technological upgrade. Lightweight castables are reshaping the technical standards of industrial furnace insulation layers with their unique physical properties.
1.Energy-saving principle of lightweight castables: from heat conduction to thermal optimization
The core advantage of lightweight castables lies in their dual role of low thermal conductivity and lightweight structure. Taking alumina hollow ball castables as an example, its thermal conductivity is only 0.15-0.3 W/(m·K), which is more than 60% lower than that of traditional heavy castables. This difference stems from the microstructure inside the material: lightweight aggregates (such as expanded perlite and vermiculite) form a large number of closed pores, effectively blocking the heat conduction path.
At the thermal engineering calculation level, the heat dissipation loss formula of the furnace lining is:
Q = λ·A·ΔT/δ
(Q is heat dissipation, λ is thermal conductivity, A is surface area, ΔT is temperature difference, δ is insulation thickness)
When lightweight castables are used to replace heavy materials, the λ value decreases significantly, and under the same temperature difference conditions, the heat dissipation can be reduced by 30%-50%. A case study of a heating furnace renovation at a steel company showed that after the furnace roof insulation layer was replaced from heavy castables to lightweight mullite castables, the furnace temperature uniformity increased by ±5°C, the unit energy consumption decreased by 8.2%, and the annual standard coal savings exceeded 2,000 tons.
2.Material selection: temperature classification and scene adaptation
The electric furnace for smelting copper sulfide concentrate and copper-nickel sulfide ore can be rectangular, oval and circular.
In non-ferrous metal smelting, large smelting electric furnaces generally use fixed rectangular closed electric furnaces. Rectangular electric furnaces allow for a larger hearth area and power, are more suitable for transformer configuration, and are conducive to the separation of matte and slag, and are convenient for furnace masonry.
The size of the rectangular electric furnace is 10 to 35.66m long and 4.5 to 10.67m wide. The slag temperature is 1200 to 1380℃, and the final smelting product is copper-nickel matte (which is an alloy of nickel, copper and iron) or copper matte, with a temperature of about 1050 to 1250℃, and production is continuous.
3.Construction specifications: thickness control and structural optimization
The insulation effect of lightweight castables is highly dependent on the construction thickness and structural rationality:
Thickness standard: The thickness of the insulation layer needs to be controlled in the range of 80-150mm. Experimental data show that when the thickness increases from 50mm to 100mm, the heat dissipation loss decreases by 22%; but after exceeding 150mm, the marginal benefit significantly decays.
Composite structure: The “lightweight layer + reflective layer” double-layer design can further improve the energy-saving effect. For example, coating the surface of lightweight castables with a high-temperature coating with an emissivity of ≥0.9 can reduce the comprehensive heat transfer coefficient by 15%.
Anchor system: In view of the low shear strength of lightweight materials, Y-type stainless steel anchors are required, and the spacing is controlled at 200-300mm to ensure the reliable combination of the material and the furnace shell.
Key points for construction quality control:
The mixing time must be strictly controlled within 3-5 minutes to avoid uneven performance caused by aggregate sedimentation;
High-frequency vibrating rods are used during vibration molding to ensure that the material density is ≥90%;
The ambient humidity must be maintained at >60% during the curing stage, and the curing time must be no less than 72 hours.
4.Economic analysis: full life cycle cost optimization
Although the initial purchase cost of lightweight castables is 20%-30% higher than that of heavy materials, its cost advantage over the entire life cycle is significant:
Energy saving: Taking a 100m³ heating furnace as an example, the use of lightweight castables can save about 150,000 yuan in natural gas costs per year;
Maintenance cost: The thermal shock resistance of the material is improved (strength retention rate after 100 cycles of 1000℃→room temperature>90%), which extends the service life of the furnace lining to 8-10 years, 3-5 years longer than traditional materials;
Production capacity improvement: Better insulation effect improves the temperature uniformity in the furnace, and the product qualification rate increases by 5%-8%, indirectly creating economic benefits.
Environmental benefits: A transformation project of an aluminum company shows that the application of lightweight castables reduces carbon emissions per unit product by 12%, which meets the requirements of technical barriers such as the EU carbon tariff (CBAM), and provides technical support for enterprises to expand into the international market.
5.Industry trends: intelligent and functional upgrades
With the advancement of Industry 4.0, lightweight castable technology is developing towards intelligent monitoring and multifunctional integration:
Self-sensing materials: Intelligent castables embedded with fiber grating sensors can monitor temperature field distribution and stress changes in real time, and warn of potential cracking risks;
Phase change energy storage function: By adding microcapsule phase change materials, the castable absorbs/releases heat when the temperature fluctuates, further stabilizing the working conditions in the furnace;
3D printing technology: The robot spraying process can achieve precise molding of complex special-shaped structures, reducing material waste and construction cycle.