Gas Measurement in Metal Smelting

The metals industry uses furnaces to melt materials into metals or remelt metals. Air is blown into the furnace as part of the mixture. Foundries can include a holding furnace or reduction furnace where additional materials are added or removed. Smelters use a blast furnace for mixing the coke, iron ore and limestone. A smelter may have additional furnaces for producing specific metals.

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Metal Smelter Gas Metering Applications

Stack Gas
After being filtered, exhaust gas is expelled through the stack. Stack emissions are measured for pollutants so careful monitoring is essential.

Gas Characteristics:
Hot, Particulates, Erratic Flow, High Volume
Combustion Exhaust Gas
Gas exhausted from the smelter may be recirculated back to the burner, to heat exchangers or to power cogeneration. After it has been cycled through the burner sufficiently to minimize unburned compounds it is filtered and sent to the stack.

Gas Characteristics:
Very Hot, Particulates, Corrosive, Errosive
Fuel Gas
Fuel is pumped into the blast furnace in tightly controlled amounts. Careful measurement of fuel ensures a clean and efficient burn. Depending on furnace design fuel gas may be injected at up tp 24 seperate firing ports.

Gas Characteristics:
High Flow Rate, Pressurized, Combustible
Primary Air
Primary Air provides oxygen to the combustion chamber. Precise control of airflow is neccessary to achieve a proper air/fuel ratio and to burn cleanly and efficiently. Air is injected higher in the burner as well to ensure thorough burn of noxious gases.

Gas Characteristics:
High Flow Rate, High Volume

Metal Smelter Gas Metering Instruments

Primary Air

Several specialized types of furnaces are used to melt metal. Metal smelters are powered by a variety of fuels: coal, coke, natural gas or electric arc. Primary air is used to preheat the fuel and provide oxygen to the combustion process. Heated air is blown into the blast furnace to mix with raw ingredients such as coke, ore and limestone. The air provides components needed for the chemical reaction which transforms the raw ingredients into metal. Hot air travels up through the vertical furnace and metal slag travels down to be collected at the bottom. Proper metal smelting requires precise control of the burn temperature and rate. When the system is balanced the greatest quantity of metal can be recovered from the source materials.

Combustion Gas

Excess hot gas is emitted from the top of the furnace and used in many applications in the plant. It may be used to preheat the incoming air, preheat the raw materials, send heat to additional holding or reduction furnaces, power recovery boilers and cogeneration systems. All these systems require combustion gas measurement and control. Air exiting the smelter is very hot and full of debris: particles, corrosive and erosive compounds, sand, dust, metal flakes and moisture. This gas must be cooled and filtered before it is sent to the stack for release. With this dangerous mix of chemicals the stack must be constantly monitored for emissions.

Stack Gas

Flue gases generated in the process of calcination, sintering, blowing and refining often have very high temperatures, a large amount of dust, moisture and gaseous pollutants which create acids. After heat recovery, re-burning and filtration the gas is collected in a tunnel and exhausted through a stack. The numerous noxious compounds present along with dust and grit, metal shavings, unspent fuel and moisture make foundry exhaust an extremely harsh environment.