In early 2023, I received a call from a die casting plant in Shanghai. They were running two gas-fired reverberatory furnaces, each with a capacity of 3 tonnes. They melted around 18 tonnes per day of ADC12 alloy. Their energy bill had risen 30% in two years. The plant manager told me, “We cannot keep going like this. We need to cut energy, but we cannot afford new furnaces.”
I spent three days on site. By the end of the following month, their energy consumption per tonne had dropped by 22%. The total investment was less than $8,000. The payback period was just over two months.
This is the story of how we did it — and what you can learn from it.
The Starting Point: Energy Consumption at 1,050 kWh/t
When I arrived, the furnaces were consuming an average of 1,050 kWh per tonne of aluminium melted. That is not unusual for a legacy gas-fired reverb furnace, but it is far above the modern benchmark of 550–650 kWh/t.
I measured three things first:
Flue gas temperature: 920°C after the recuperator (if there was one — there wasn’t).
Oxygen in flue gas: 7.8%. That meant massive excess air.
Furnace shell temperature: Several hot spots at 180–200°C. The lining was losing heat.
The plant manager admitted they had no maintenance schedule for the burners. They had never used a flue gas analyser. They had never checked door seals. The furnaces ran 24 hours a day, six days a week.
I told him: “Your furnaces are not broken. They are just badly tuned. We can fix this without buying new equipment.”
Step 1: Burner Tuning — The Biggest Single Win
The burners were running with 7.8% oxygen. The ideal range is 2–4%. Too much excess air means you are heating nitrogen instead of aluminium. Every 1% reduction in O₂ saves roughly 2–3% of fuel.
We borrowed a portable flue gas analyser and spent a full day tuning both burners. We adjusted the air dampers, cleaned the nozzles, and re-set the gas pressure regulators.
The result: O₂ dropped to 3.2%. CO stayed below 30 ppm. Flame colour changed from yellow to a crisp blue.
That single change reduced gas consumption by 12%. No new parts. Just proper adjustment.
Step 2: Recover Waste Heat — The Second Big Win
The flue gas was leaving the furnace at 920°C. That is money going up the stack.
We installed a simple recuperative burner system on each furnace. The recuperator uses exhaust heat to preheat combustion air. Every 100°C of preheat improves efficiency by about 5%. We achieved 350°C preheat.
The recuperators cost $2,800 each. Installation took two days. The energy saving was another 7%.
I have written about burner efficiency in detail before. The principles are simple: measure, adjust, recover. But most foundries skip the measurement step.
Step 3: Fix Door Seals and Lining Hot Spots
The furnaces had two main heat leaks:
Door seals: Worn flat. We could feel hot air escaping. Replacing them cost $400 per furnace.
Refractory hot spots: The shell was 180°C in two areas. We applied a refractory coating to the affected zones. Cost: $1,200 total.
These fixes reduced heat loss by another 3%. They also made the working environment safer.
A thermal camera is invaluable for this. If you do not have one, borrow one. The hot spots you find will pay for the effort.
Step 4: Change Operating Practice — Free Savings
The operators were making three mistakes:
Charging wet scrap. They stored scrap outdoors. After rain, they charged it wet. Moisture absorbs heat and increases oxidation.
Overcharging. They filled the furnace to 95% capacity. The burner could not melt efficiently.
Holding metal overnight at 750°C. They melted on Friday and held until Monday.
We changed these practices:
Built a simple drying rack under a roof. Scrap dries before charging.
Reduced charge to 80% of capacity. Melt time dropped, and oxidation loss fell.
Adjusted the schedule: melt on Sunday evening for Monday start. Holding temperature reduced to 700°C.
These changes cost nothing. They saved another 2% in energy and reduced metal loss by 0.8%.
Step 5: Install Simple Monitoring
We installed a gas flow meter and a temperature logger on each furnace. The cost was $600 per furnace.
Now the plant manager can see daily gas consumption per tonne. If it rises, he knows something is wrong. He can call me before the problem gets worse.
Data is not a luxury. It is the foundation of control.
The Results After One Month
| Metric | Before | After | Improvement |
|---|---|---|---|
| Energy consumption | 1,050 kWh/t | 819 kWh/t | 22% reduction |
| Flue gas O₂ | 7.8% | 3.2% | Optimised |
| Metal oxidation loss | 3.2% | 2.4% | 0.8% reduction |
| Annual energy cost (18 t/day) | $620,000 | $484,000 | $136,000 saved |
| Investment | — | $7,800 | Payback: 2.1 months |
The plant manager was shocked. He had been told he needed new furnaces. He didn’t. He needed someone to look at the details.
What I Learned — And What You Can Apply
This case is not unique. I have seen similar results in Vietnam, India, Thailand, and the UK. The pattern is always the same:
Most furnaces are running with too much excess air. Tune the burner first. It is the cheapest and biggest win.
Waste heat is free money. A recuperator pays for itself in months.
Small leaks add up. Door seals, lining cracks, and open doors waste more than you think.
Operating habits matter. Wet scrap, overcharging, and unnecessary holding are common and costly.
Measure everything. You cannot improve what you do not measure.
I wrote a detailed guide on how to optimise burner efficiency and a furnace maintenance checklist. If you follow those, you will capture most of these savings yourself.
When to Call an Expert
You can do much of this work yourself. But sometimes an experienced eye finds things you miss. The plant in Shanghai had a maintenance team. They were competent. But they had never been trained on combustion analysis or thermal imaging.
I spent three days on site. The fee was less than 10% of the annual savings. That is a good return.
If your energy bills are rising, and you have not tuned your burners in the last six months, call someone. Or buy a flue gas analyser and learn to do it yourself. Either way, do not wait.
Final Thoughts
Cutting energy costs by 22% did not require new furnaces. It required attention to detail, a few inexpensive parts, and a willingness to change habits.
In my 25 years, I have seen this pattern repeat in foundries across the world. The biggest savings are often hiding in plain sight — in the burner, in the flue, in the door seal, in the charging practice.
If you run a foundry, start with the burner. Then recover the heat. Then fix the leaks. Then train the operators. You will see the difference in your first gas bill.
Internal links: How to Optimize Burner Efficiency in Gas-Fired Aluminium Furnaces, Furnace Maintenance Checklist
About the Author: Hu Shenyue is a veteran aluminium melting furnace expert with 25 years of hands-on experience in China, Southeast Asia, India, the UK, and Europe. He writes practical, experience-based content on furnace selection, maintenance, and optimisation at SmeltPro.
