Steel Scrap Preheating for steel and iron

Steel is by far the most important metal in the world, with global production of 1.12 billion metric tons (MMt) in 2009.In September 2010,the most important steel producers were China (42, 90%),EU-27 (12, 79%),Japan (8, 26%),USA (5, 95%) and India (5, 05%) (World Steel Association,2010), the development of world steel production since 1999.Clearly,China has become a major steel producer.Since steel is an important component of many economies around the world and is the most important metal,it is important to use and produce steel efficiently.The technology described here allows for more efficient use of steel scrap in the production of new steel.Therefore,it is essentially a recycling technology of old steel.The technology reduces energy use in steel production and has several socio-economic and environmental benefits. 

1. According to IPCC (2007) and worldsteel association (2010),three main routes for steelmaking can be distinguished:

2. Main routes.The route,used in nearly fifty countries,primarily uses coke or coal to reduce iron ore to iron in blast furnaces.The iron is then processed into steel.This route accounts for approximately 70% of world steel production.

3. The Direct Reduced Iron (DRI) production route,which accounts for about 5% of worldsteel production.This route uses natural gas to produce direct      reduced iron,which is mainly used as an alternative iron feedstock in electric arc furnaces.Using this route can reduce CO2 emissions by up to      50% compared to the main route of steelmaking .The use of DRI is expected to increase in the future.

4. .The third route,accounting for about 25% of the steel industry,melts steel scrap in an electric arc furnace (EAF) to produce crude steel,which      is then further processed (IPCC, 2007).According to the process uses only 30% to 40% of the energy of the main route.Since the electric furnace process can use up to 100% scrap to produce crude steel, it is the main process for the application of scrap preheating technology.However the primary route can use up to 30% scrap in its process and,as it is the dominant route,scrap preheating technology is also valuable for this route.This description will primarily focus on the EAF process.

The EAF process has four main outputs:

1. Molten steel itself;

2. Cooling loss;

3. Slag and

4. Hot exhaust gas, about 15% to 20% of production.

Essentially,scrap preheating is a technique that uses hot exhaust gases from a furnace to preheat a scrap charge . Scrap charges are the scrap entered into the EAF process.Preheating the scrap with hot exhaust gas reduces the power consumption of the EAF as it does not need to burn fuel to heat the scrap.

Feasibility of technical and operational needs

The three main technologies corresponding to the three main production routes are Basic Oxygen Furnace (BOF), EAF and Hearth Furnace (OHF). Among these technologies,EAF accounts for 30% and 8% of the world,while OBC accounts for 66%, 7%,and OHF accounts for 2.4% .Thus,the breadth of EAF technology itself is evident.Since modern EAFs generate large quantities of hot combustion product gases,accounting for about 15-20% of production,several new scrap preheating systems have been developed .This section discusses three different forms of scrap preheating systems:

a) Traditional scrap drum-charged preheating systems; 

b) Consteel process; 

c) Fuchs shaft furnace.The Consteel and Fuchs processes are the main modes of preheating systems that have reached commercial maturity.Note that there are other preheating systems with other characteristics and operating requirements.Therefore,which preheating system is most suitable for a particular steelmaking facility should be evaluated on a case-by-case basis.

Waste bin charging process

A conventional waste material hopper preheating system of preheating scrap has several advantages: 

a) reduces energy consumption; 

b) removes moisture from scrap; 

c) reduces electrode consumption; 

d) reduces refractory consumption.However,there are some disadvantages in the method of preheating the scrap steel feeding bucket,which limits its use:

 e) scrap steel sticks to the bucket,and the operation is inconvenient;

f) the life of the bucket is short; c) the preheating controllability is poor; d) for small With a tap-to-tap time of 70 minutes,the logistics of this preheating method resulted in minimal energy savings .

Steel process

The Consteel process consists of a conveyor belt that transports the waste through a tunnel and down to the EAF via a heated heel .The technology is at a mature stage with 8 installations and 35 installations worldwide. A conveyor belt continuously conveys the scrap charge to the EAF,while the charge is preheated by the exhaust gases leaving the furnace via the preheating conveyor belt.The continuous feeding of preheated scrap into the EAF is one of the main differences from other methods.

Fox shaft furnace

In contrast to the continuous feed system of the Consteel process,the Fuchs shaft furnace is a batch feed system.Inside the shaft,the scrap is preheated by the low-velocity gas from the EAF and then falls into the EAF.Like Consteel and scrap drum charging,the technology is at a mature stage.