Temper furnace selection and carbon footprint
What should such a tempering furnace look like? There are two basic solutions. Retort furnace and non-retort furnace with direct batch heating. Those who want to purchase equipment only for tempering should know that a furnace with a retort consumes 30% more energy for the same job, ie for tempering, than a furnace without a retort.
If we calculate the service life of the furnace at 20 years, then the retort furnace consumes extra energy during its life, comparable to its acquisition value. But not only that. Because 0.256 kg of CO2 is created per 1 kWh of energy consumed, a huge amount of CO2 is created during the life of the furnace.
The calculation is simple. The average hourly input of the tempering furnace with a retort, size 600×900 mm, loading 200 kg, is approximately 25 kW. Cycle time 8h. At 80% annual utilization of the equipment, the consumption is 365 * 24 * 0.80 = 7008 Nh * 25 kW = 175 200 kWh. If I temper in a furnace without a retort, the energy consumption will be 30% lower (see diagram), so I will save 52,560 kWh per year. With an energy price of € 0.20 / kWh, this is an annual saving of € 10 512. In the 20 years of the furnace’s life, it is saving of € 210 240.
Fig.1 – Energy consumption by tempering cycle Fig.2 – Unit energy consumption by 1 kg of temperd steel
If we convert this amount to a carbon footprint, then in these 20 years the furnace without retort will reduce the amount of CO2 by 52,560 * 20 * 0.256 = 269,107 kg of CO2. It’s an incredible number.
I understand the importance of retort furnaces where diffusion processes are involved. Nitriding, carbonitriding, etc. There is this irreplaceable solution. But if I really only want this device for tempering, then I make a huge mistake and I’m not sure if I’m always aware of it as an investor.
So if we are not very environmentally friendly, and we don’t care how much extra CO2 we produce, we should in all circumstances think about the economic conditions of heat treatment so that the customer gets its value at a good price. And I’m not really sure if everyone really wants it.
Yours, Jirka Stanislav
