Glass Furnace Energy-Saving Retrofits Accelerate as All-Electric Melting Gains Ground

Glass melting has long been the largest energy consumer in the glass industry. Much of the energy is wasted in furnace heat loss and in the flue gas from fuel combustion. Entering 2015, with assessment of the 12th Five-Year Plan energy intensity reduction target approaching and tighter constraints on industrial furnace emissions in various regions, furnace energy-saving retrofits became a common choice for many glass producers. Among the many technical routes, the one with the clearest direction is the accelerated penetration of all-electric furnaces from specialty glass into a wider range of applications.

All-Electric Furnaces Show a Clear Thermal Efficiency Advantage

Conventional flame furnaces generally have a thermal efficiency of only 20 to 30 percent, with substantial heat carried away by flue gas and lost through furnace body dissipation. An electric melting furnace works on a completely different principle: current is fed through molybdenum electrodes directly into the resistive glass melt, heat is generated inside the melt, thermal efficiency can usually reach over 70 percent, and there is almost no combustion flue gas at the furnace. Under the dual constraints of energy consumption and emission targets, this gap is enough to push companies toward electric melting, or hybrid fuel-plus-electric boosting, for suitable products.

From Specialty Glass to General Glass

All-electric melting was first applied to high value-added grades such as quartz glass, borosilicate glass and glass microspheres, because these products use small furnaces, demand high melting quality and cannot tolerate refractory contamination. In recent years the picture has been changing: as power supply reliability improves and peak-valley electricity pricing gradually takes shape, some container glass and insulation glass wool producers have also begun trying fuel-plus-electric boosting, or even partial all-electric retrofits, to gain higher melting rates, stable furnace temperature and lower emissions. The electric furnace is no longer a niche process.

Molybdenum Electrodes Are the Core Component of Electric Furnaces

In a glass melt at 1300 to 1500 °C, only a handful of electrode materials can work stably over the long term. With the combined advantages of resistance to glass melt corrosion, no coloring of the glass and the ability to carry a moderate current density, molybdenum electrodes have become the mainstream choice for glass electric melting furnaces. Common electrode arrangements include:

• Bottom and side-entry electrodes, which carry the heating load of the main melting zone with stable current distribution;
• Top-entry electrodes, used for temperature control in the boosting and refining zones;
• Multiple electrode groups arranged to suit the furnace type and mapped one-to-one to power transformer taps, enabling zoned power control.

How to Run the Retrofit Numbers

For a company considering a retrofit, the electric melting option requires a combined assessment of electricity price, peak-valley structure, electrode life and production loss, not just equipment investment. Industry analysis suggests that the pace of electric furnace retrofits directly affects electrode shipments, and furnace builders and electrode suppliers are forming closer supply relationships. The WeiBeam technical team believes that continued energy-saving policy is a clear industry signal, and that the ability to match electrode life with power supply parameters will be the key to the next round of competition in electric melting.