Application
Coke Oven (CO)
Production coke oven gas, an incredibly “rich” fuel for use throughout plant
Accurate, real-time analysis of caloric value of gas enables better control of processes utilizing the gas as fuel, reduceing electricity costs
Efficiency of gas cleaning plant increased if concentration of environmentally unfriendly compounds is known in realtime, reducing environmental fines
Production coke for use in blast furnace, high quality coke makes blast furnace more efficient
Typical Coke Oven Gases Monitored
Hydrogen (H2) 0-100%
Nitrogen (N2) 0-100%
Methane (CH4) 0-30%
Carbon Monoxide (CO) 0-10%
Carbon Dioxide (CO2) 0-10%
Ethane (C2H4) 0-5%
Ethylene (C2H6) 0-5%
Oxygen (O2) 0-2%
Argon (Ar) 0-1%
Propylene (C3H6) 0-1%
Propane (C3H8) 0-1%
Hydrogen Sulfide (H2S) 0-1%
Blast Furnace (BF)
Real time analysis of top gas provides means of controlling the process tighter to minimize the use of fuel (coke) but maximize production of steel.
Achieved by monitoring the CO2/(CO+CO2) ratio. CO too high indicates using too much coke. CO2 too high indicates chemical reaction is too hot
Safety issue: hydrogen monitoring – especially during blowdowns
Typical Blast Furnace Gases Monitored :
Hydrogen (H2) 0-50%
Nitrogen (N2) 0-75%
Carbon Monoxide (CO) 0-50%
Methane (CH4) 0-30%
Oxygen (O2) 0-1%
Carbon Dioxide (CO2) 0-1%
Argon (Ar) 0-1%
Basic Oxygen Furnace (BOF)
Typical BOF gases measured:
Nitrogen (N2) 0-100%
Carbon Monoxide (CO) 0-10%
Carbon Dioxide (CO2) 0-10%
Oxygen (O2) 0-2%
Argon (Ar) 0-1%
Electric Arc Furnace (EAF)
Monitoring of oxygen concentration is a signal of the complete combustion of CO to CO2. The presence of CO in the sample stream indicates a waste of energy increasing the costs.
Typical EAF Gases Monitored
Hydrogen (H2) 0-100%
Nitrogen (N2) 0-100%
Methane (CH4) 0-30%
Carbon Monoxide (CO) 0-50%
Carbon Dioxide (CO2) 0-1%
Oxygen (O2) 0-1%
Argon (Ar) 0-1%
Process
Coke Oven: Producing Coke from Coal
The production of coke is an integral part of steelmaking as coke is used as a primary fuel for Blast Furnaces. It involves the carbonization of coal at high temperatures (about 1100°C) under an oxygen deficient atmosphere inside a coke oven. The coal-to-coke conversion is intended to produce a carbon-enriched material devoid of chemical impurities normally present in unprocessed coal. Coke production also generates what is called coke oven gas, which consists of hydrogen, methane, nitrogen, carbon monoxide, carbon dioxide, and light hydrocarbons. As it has a high energy content, coke oven gas is conditioned and recycled as a fuel gas for use in other steel processing operations.
Blast Furnace : Producing Molten Iron
The steelmaking process begins at a Blast Furnace, where iron oxide (Fe2O3), a primary component of iron ore, is chemically reduced to molten iron (called pig iron) by reaction with carbon monoxide. The
series of chemical reactions involved in producing molten iron occurs at temperatures between about 850°C and 1500°C. The energy required to achieve these reaction temperatures is obtained from the heat
evolved during exothermic reactions, the heat generated by the combustion of coke in air, and the heat content of the hot (>1000°C) air blasts.
At about 850°C carbon from coke reacts with oxygen in air and forms carbon dioxide. In the next step carbon dioxide is reduced to carbon monoxide in the presence of excess carbon. The reducing (carbon-rich) atmosphere in a BF is achieved by maintaining the required material balance between air and coke. This reaction takes place at about 1100°C. Finally, at about 1300°C the extraction of iron metal from iron ore occurs. Carbon monoxide reacts with iron (III) oxide to yield elemental iron and carbon dioxide. Because the temperature near the bottom of the BF is 1500°C or higher, the iron metal is produced in a molten state and tapped at the bottom as a liquid. The hot metal is about 95% iron and contains residual contaminants such as carbon, sulfur, manganese, phosphorus, and silicon. Iron metal and slag, both in liquid state, are the final products. They collect in two separate layers at the bottom of the furnace; the low-density slag floats on top of the heavier molten iron. The slag and molten iron exit the BF through the tap holes and undergo further refining steps. The molten iron is transported to a BOF where it is refined into different grades of steel.
Basic Oxygen Furnace : Producing Steel
The hot metal (pig iron) that leaves the BF contains about 5% carbon and other trace impurities. The impurities, particularly carbon, impart an undesirable brittleness to the iron; therefore, further processing
is employed to reduce their levels. The charge to a BOF includes hot metal (from the BF), steel scraps and calcium oxide (burnt lime). Typically, the metal charge consists of about 75% BF iron and 25% steel scraps. The refining is initiated by melting the steel scraps with the molten iron. Then pure oxygen is introduced through a lance into the furnace where it reacts with the chemical impurities in the hot metal pool, yielding oxides. During the formation of oxides the impurities are stripped off the metal leaving refined steel. Subsequently, the oxides react with lime (calcium oxide) to produce the BOF slag. At the end of the cycle, the furnace is tilted and molten steel is poured through a taphole into a ladle. At this point the collected steel is ready for casting.
Electric Arc Furnace : Producing Steel
The EAF is used to produce steel primarily from steel scraps. Its basic configuration includes a tiltable furnace, moveable roof for entry of charges, graphite electrodes, tap hole and gas exhaust system. The
EAF operation involves a batch melting process consisting of charging, melting, refining, tapping, and slag handling. A cycle (or batch) takes less than one hour to complete and is referred to as a “heat.”
A heat is started by dumping a charge consisting of steel scraps, carbon and fluxes into the furnace through the furnace’s roof. Then the roof is replaced over the furnace and electrodes are lowered to
strike an arc on the pile of scraps; this starts the melting process. Once all the scraps are melted, pure oxygen is lanced directly into the molten pool of steel to initiate reactions with the impurities present in
the steel. The impurities (aluminum, silicon, manganese, phosphorus, carbon, iron) combine with oxygen to generate metallic oxides, which conglomerate into a slag. Additional carbon may also be injected
during the heat. Carbon reacts exothermally with oxygen to form carbon monoxide (CO). The heat liberated by the formation of CO supplies part of the energy requirement for EAF operation. CO also aids the formation of “foam” in the slag bath. The foam helps bury the arc in the bath, resulting in improved furnace thermal efficiency. In addition, CO aids in removing nitrogen and hydrogen, thereby resulting in better grades of steel. The excess CO either vents to the exhaust handling system or combusts in the furnace. The end product in an EAF operation is refined steel which is tapped into a ladle after the heat is concluded.
Installation notes
Extraction of sample with sample probe. Transport sample to sample conditioning system (Sample Chiller, Coalescing Filter, Transport Pump, Blowback Control, Multiplexing system)
