As a leading steel castings manufacturer, I have witnessed firsthand the growing emphasis on high-quality development and the implementation of carbon peak and carbon neutrality policies. The严峻 energy utilization situation and increasing customer demand for green factories have made energy conservation and emission reduction critically important. For energy-intensive foundries, adopting eco-friendly, low-carbon practices and reducing operational costs have become key innovation directions. In this context, steel casting manufacturers are actively exploring ways to enhance energy efficiency, particularly through waste heat recovery from melting electric furnaces.
Foundry production lines operate as continuous流水 processes, with melting electric furnaces at the beginning requiring long-term, stable operation. When these furnaces operate steadily, they generate substantial and consistent waste heat. Traditionally, this heat is dissipated into the atmosphere via cooling towers in the furnace cooling water system, leading to energy waste and environmental pollution. To address this, we, as China casting manufacturers, have focused on recovering this waste heat for applications such as heating, air conditioning, workshop showers, and domestic hot water. This not only reduces operational能耗 but also aligns with sustainable development goals.
In typical foundries, medium-frequency induction furnaces are commonly used for melting, with frequencies ranging from 1000 to 3000 Hz. These furnaces, supplied by various brands, have specific input power parameters that influence waste heat generation. For instance, the heat dissipation from these furnaces can be calculated using established formulas, which are essential for designing efficient recovery systems. As steel castings manufacturer, we prioritize understanding these parameters to optimize energy use.
| Furnace Model | Input Power (kW) | Melting Rate (t/h) | Power Consumption (kWh/t) | Frequency (Hz) |
|---|---|---|---|---|
| H500/400/1 | 400 | 0.698 | 549 | 1000 |
| H1000/750/1 | 750 | 1.364 | 524 | 1000 |
| H2000/1500/03 | 1500 | 2.857 | 510 | 300 |
| H2000/1800/03 | 1800 | 3.429 | 505 | 300 |
| H3000/2250/03 | 2250 | 4.286 | 500 | 300 |
| H4000/3000/05 | 3000 | 5.854 | 498 | 500 |
| H5000/3500/03 | 3500 | 6.818 | 501 | 300 |
| H5000/4500/05 | 4500 | 8.824 | 496 | 500 |
| H6000/4500/03 | 4500 | 8.780 | 496 | 300 |
| H8000/5000/03 | 5000 | 9.796 | 496 | 300 |
| H10000/5000/03 | 5000 | 9.677 | 508 | 300 |
| H12000/8000/03 | 8000 | 15.652 | 495 | 300 |
| H20000/10000/03 | 10000 | 19.672 | 493 | 300 |
The heat dissipation from electric furnaces is a critical factor for waste heat recovery. The formula for calculating the heat dissipation rate is given by:
$$ Q_L = N \eta $$
where \( Q_L \) is the heat dissipation in kW, \( N \) is the input power in kW, and \( \eta \) is the heat loss rate, typically around 45% for the system, comprising 35% from the furnace body (\( \eta_1 \)) and 10% from the power supply system (\( \eta_2 \)). This calculation is fundamental for steel casting manufacturers to assess the potential for heat recovery.
For the cooling water system, design requirements include inlet temperatures below 35°C and outlet temperatures around 50–55°C, with a temperature rise not exceeding 25°C, usually about 20°C. The flow rate of circulating cooling water can be determined using:
$$ q_x = \frac{3.6 \eta N}{c \Delta t} $$
where \( q_x \) is the flow rate in m³/h, \( c \) is the specific heat capacity of water (approximately 4186 J/kg·°C), and \( \Delta t \) is the temperature difference in °C. Based on \( \eta_1 = 35\% \) and \( \eta_2 = 10\% \), the flow rates for furnace body cooling (\( q_{x1} \)) and power supply cooling (\( q_{x2} \)) can be derived separately, with typical \( \Delta t \) values of 20°C and 10°C, respectively.
| Input Power N (kW) | Furnace Body Heat Loss Q (kW) | Power Supply Heat Loss Q_d (kW) | Furnace Cooling Water Flow (m³/h) | Power Supply Cooling Water Flow (m³/h) |
|---|---|---|---|---|
| 400 | 140 | 40 | 6.03 | 3.44 |
| 750 | 262.5 | 75 | 11.30 | 6.46 |
| 1500 | 525 | 150 | 22.61 | 12.92 |
| 1800 | 630 | 180 | 27.13 | 15.50 |
| 2250 | 787.5 | 225 | 33.91 | 19.38 |
| 3000 | 1050 | 300 | 45.22 | 25.84 |
| 3500 | 1225 | 350 | 52.75 | 30.14 |
| 4500 | 1575 | 450 | 67.82 | 38.76 |
| 5000 | 1750 | 500 | 75.36 | 43.06 |
| 8000 | 2800 | 800 | 120.57 | 68.90 |
| 10000 | 3500 | 1000 | 150.72 | 86.12 |
The waste heat from melting electric furnaces is characterized by its large quantity, continuity, and stability. Direct dissipation via cooling towers not only wastes energy but also harms the environment. As China casting manufacturers, we have found that using heat exchangers to recover this heat for applications like heating, air conditioning, and hot water preparation is highly feasible. For example, in a project involving a steel castings manufacturer, the heat dissipation from electric furnaces exceeded the winter heating load of office buildings, demonstrating significant recovery potential.
Plate heat exchangers are widely used for this purpose due to their high heat transfer efficiency, compact structure, and adaptability. The selection and calculation of plate heat exchangers involve determining the heat transfer area based on the required heat exchange and temperature differences. The formula for the heat transfer area is:
$$ F = \frac{Q}{K B \Delta t_{pj}} $$
where \( F \) is the area in m², \( Q \) is the heat exchange in W, \( K \) is the heat transfer coefficient in W/(m²·K), \( B \) is the fouling factor (typically 0.7–0.8 for water-water exchangers), and \( \Delta t_{pj} \) is the logarithmic mean temperature difference in °C, calculated as:
$$ \Delta t_{pj} = \frac{\Delta t_a – \Delta t_b}{\ln \left( \frac{\Delta t_a}{\Delta t_b} \right)} $$
Here, \( \Delta t_a \) and \( \Delta t_b \) are the maximum and minimum temperature differences at the inlet and outlet. If \( \Delta t_a / \Delta t_b \leq 2 \), the arithmetic mean can be used for simplicity. This approach is efficient for steel casting manufacturers aiming to optimize heat recovery systems.
| Exchanger Type | Heat Transfer Coefficient (W/m²·K) | Working Pressure (MPa) | Allowable Pressure Difference (MPa) | Characteristics |
|---|---|---|---|---|
| Plate | 5000–6000 (water-water) | ≤2.5 | ≤1.6 | High efficiency, compact, easy maintenance |
| Shell and Tube | 1500–2500 (water-water) | ≤1.6 | ≤1.6 | Durable, suitable for various applications |
| Spiral | 3000–4000 (water-water) | ≤1.6 | ≤1.6 | Good for fouling fluids, compact design |
| Brazed Plate | 7000–8000 (water-water) | ≤1.6 | ≤1.6 | High pressure resistance, no gaskets |
Applications of waste heat recovery in foundries include winter heating and air conditioning systems, where the recovered heat can serve as a heat source for radiant floor heating or air handling units. For instance, floor radiation heating typically uses water at 35–45°C, which aligns well with the temperatures achievable from furnace cooling water. Additionally, the heat can be used for shower and domestic hot water, with temperatures around 35–40°C, making it ideal for facilities in steel casting manufacturers’ plants.
In a practical engineering case, a steel castings manufacturer implemented a waste heat recovery system for a new foundry workshop. The project involved four sets of melting electric furnaces, with three sets used for heating and air conditioning, and one set for shower water. Calculations showed that the heat recovery from three furnace sets could meet the winter heating load of approximately 3620 kW, with heat exchange details as follows: primary side (furnace cooling water) flow rate of 130 m³/h per set and temperature drop of 7–8°C, yielding an average heat of 1135 kW per set; secondary side (user side) flow rate of 175 m³/h per set and temperature rise of 5–6°C, providing an average of 1120 kW per set. This resulted in a total recoverable heat of 3360 kW, closely matching the demand. The system used plate heat exchangers and allowed for seasonal switching between heating and cooling modes. Post-implementation, the project achieved annual savings equivalent to 845 tons of standard coal, reducing CO2 emissions by about 2281 tons and generating economic benefits of approximately 1.352 million yuan. This demonstrates how China casting manufacturers can leverage such technologies for cost savings and environmental protection.
In summary, waste heat recovery from melting electric furnace cooling systems offers significant advantages for steel castings manufacturer, including low initial investment, reduced operating costs, and lower carbon emissions. By adopting plate heat exchangers and optimizing system design, steel casting manufacturers can effectively harness this energy for various applications, contributing to sustainable industrial practices. As a China casting manufacturers, I advocate for the widespread adoption of this technology to enhance competitiveness and support global carbon reduction goals. Further research and case studies will continue to refine these systems, ensuring long-term benefits for the industry.