The furnace off-gas duct (OGD) connects the smelting furnace with the gas cleaning plant. The process gas generated in the furnace enters the OGD via the furnace stub mounted on the furnace roof and is routed to the first gas cooler of the gas cleaning plant.
Typical conditions of process gas generated in electric arc reduction furnaces are:
- temperature: 350 – 1’800 °C
- dust load: 100 – 500 g/Nm³
- chemical composition: CO 60 – 90 vol.-% dry, H2 5- 40 vol.-% dry (balance CO2 + N2)
- potentially explosive and auto combustible
- highly toxic
Due to these critical gas properties the OGD is subject to special requirements: the design has to ensure permanent gas tightness and heat resistance as well as minimized fouling and wear.
Cooling System of the Furnace Off-Gas Duct
The purpose of the OGD cooling system is not to cool the process off-gas before entering the gas cleaning plant, but to reduce and limit the thermal loading on the OGD to maintain stability.
The OGD has a water cooling system, comprising of external cooling water channels providing cooling of the various pipe sections. This forced water cooling system allows for continuous monitoring of the essential cooling parameters; cooling water flow, temperature and pressure at both, feed and return lines.
The cooling water quality must adhere to usually applied criteria for closed loop cooling water circuits. Typically the OGD cooling system is connected to the water cooling system of the furnace.