Coordinating Flue Gas Treatment with Electric Melting in Glass Furnaces

Flue gas treatment in glass furnaces is often treated as an end-of-pipe issue, but in practice the fuel and the melting method determine where the gas comes from and what it contains. As the electric boosting ratio rises, the total volume of combustion products falls, yet batch volatiles and dust remain, so the abatement system cannot simply be designed around the old operating conditions.

In flame furnaces, flue gas comes mainly from fuel combustion, and nitrogen oxides are closely tied to the amount of excess air; once electric boosting carries part of the heat load, fuel consumption falls, the gas volume drops accordingly, and the conditions for NOx formation change. A fully electric furnace has no combustion process and generates even less flue gas, but batch dust, boron or fluorine volatiles, and gases escaping under the slight positive pressure inside the furnace still have to be handled. Electrode configurations for different melting ratios are described on the products and specifications page.

When the Pollutant Sources Change, the System Must Change Too

A lower gas volume affects the operating conditions of both the desulfurization tower and the dust collector: gas velocity falls and residence time increases, which may raise desulfurization efficiency, but the gas distribution inside the tower can also become uneven; the filtration velocity in the dust collector falls and resistance decreases, while the risk of condensation at low temperature rises. A retrofit should recalculate gas volume, temperature and dew point rather than reusing the existing fan and ductwork. Ammonia injection in the DeNOx system must also be adjusted to the NOx concentration to avoid excessive injection and ammonia slip. Abatement route options are covered in furnace environmental and electric melting solutions.

Dust collector selection has to be adjusted as well. After the gas volume falls, running the original filtration area means a low filtration velocity, a dust layer that is difficult to build up, and a cleaning cycle that becomes hard to control; if the gas temperature approaches the dew point, the risk of wet filter bags rises. The retrofit should be rechecked against the new gas volume and temperature curve.

Furnace Pressure and the Temperature Regime Must Be Reviewed Together

Once electric boosting is introduced, the thermal regime inside the furnace changes and furnace pressure tends to fluctuate. If pressure runs high, more gas escapes and crusting accelerates around the electrode ports and sight holes; if pressure runs low, cold air is drawn in and the oxidation risk in the electrode zone rises. Furnace pressure control and electrode power adjustment should be placed under a single operating procedure instead of being handled separately. The induced-draft fan control of the flue gas system and its interlock with furnace pressure should also be checked as part of the retrofit.

Furnace pressure control is also tied to electrode port sealing. If a port is not sealed tightly, outside air is drawn in and molybdenum faces an oxidation risk at high temperature; if the seal is too tight, electrode advance is affected. Port sealing condition should be added to the inspection rounds and judged together with furnace pressure and flue gas oxygen content.

The Order in Which a Retrofit Is Assessed

1. First calculate the post-retrofit gas volume and composition, then determine the capacity of the abatement system.
2. Check the matching of ductwork, fans and stack so that capacity is neither short nor idle.
3. Assess whether waste heat recovery is affected, since a change in gas temperature alters heat exchanger duty.
4. Complete the online monitoring points so that operating data can be compared after the retrofit.
5. Verify the start-up and shutdown sequence of the electrodes and the abatement system to avoid large furnace pressure swings from simultaneous action.

Environmental equipment and the melting process form one system, and changing only one end rarely delivers the expected result. Evaluating gas volume, furnace pressure, temperature regime and electrode load on a single sheet gives a more reliable basis for the retrofit.

Emission requirements and energy conditions differ from region to region, so retrofit plans should not be copied between sites. If you are planning an electric boosting or fully electric project, talk to us about the process details.