Overview of Flue Gas Waste Heat Recovery Technologies for Industrial Kilns and Furnaces
China has a vast number of various industrial kilns and furnaces—glass melting furnaces, cement rotary kilns, steel reheating furnaces, ceramic tunnel kilns, non-ferrous metal smelting furnaces, and more. The exhaust gas temperature of these kilns is typically 200–600°C, and exhaust heat loss accounts for 30%–50% of total energy consumption, making them one of the most promising areas for energy savings in industry.
I. Flue Gas Waste Heat Parameters of Various Kilns
| Kiln Type | Exhaust Gas Temp. (°C) | Exhaust Heat Loss (%) | Recommended Recovery Scheme |
|---|---|---|---|
| Glass melting furnace | 400~600 | 35%~55% | Waste heat boiler + power generation |
| Cement rotary kiln | 300~380 | 25%~35% | Waste heat power generation (ORC/steam turbine) |
| Steel reheating furnace | 250~450 | 30%~45% | Air preheater + waste heat boiler |
| Ceramic tunnel kiln | 150~300 | 20%~35% | Air preheating + drying utilization |
| Non-ferrous metal smelting furnace | 200~400 | 25%~40% | Waste heat boiler for steam production |
II. Comparison of Flue Gas Waste Heat Recovery Schemes
Scheme 1: Tubular Air Preheater
- Principle: Flue gas heats combustion air to improve combustion efficiency
- Applicable: Exhaust gas temperature 250–450°C
- Energy-saving rate: 5%–15% (lowering exhaust temperature by 100–200°C)
- Investment: Moderate, 300,000–800,000 RMB/unit
Scheme 2: Heat Pipe Air Preheater
- Principle: Phase-change heat transfer through heat pipes; cold and hot sides completely isolated
- Applicable: Exhaust gas temperature 200–350°C, where flue gas and air require strict isolation
- Energy-saving rate: 8%–18%
- Advantage: Prevents flue gas leakage to the air side; high safety
Scheme 3: Waste Heat Boiler (Steam Type)
- Principle: Flue gas exchanges heat to produce 0.4–1.6 MPa steam for production use
- Applicable: Exhaust gas temperature >350°C, where the plant has steam demand
- Energy-saving rate: 15%–30%
- Steam output reference: Recovering 1 MW of heat produces approx. 1.3 t/h of saturated steam
Scheme 4: Organic Rankine Cycle (ORC) Power Generation
- Principle: Low-temperature flue gas heats an organic working fluid that expands to drive a generator
- Applicable: Exhaust gas temperature 150–300°C, with no steam demand
- Power generation efficiency: 8%–15%
- Investment: High, approx. 8,000–12,000 RMB/kW
III. Decision Logic for Scheme Selection
- Steam demand → Scheme 3 (waste heat boiler), best economic benefit
- Exhaust >350°C + no steam demand → Scheme 4 (ORC power generation)
- Exhaust 200–350°C + need to improve combustion → Scheme 1 or 2 (air preheating)
- Exhaust <200°C → Scheme 1 + space heating/process heating (low-temperature utilization)