Why is a blast furnace needed in the Bessemer process? PLEASE HELP!?

Question

When making steel:

First Iron ore (iron oxide) carbon (coke charcoal, etc.) and limestone are mixed in a furnace and air is blow through The limestone is present to remove silicon but the carbon iron oxide and air blast work to generate a high enough temperature that the carbon can rob the iron oxide of its oxygen.

Second the iron in a melted state is subjected to more air flow (atmospheric oxygen to remove the carbon, thereby producing very low carbon iron.

Third, carbon is put back into the nearly pure iron to make high carbon steel.



This process could be summarized as:

· Carbon is used to remove oxygen

· Oxygen is used to remove carbon

· Carbon is added back in.



This seems contradictory! Explain the process and why a blast furnace is needed for the first step and a Bessemer converter might be used in the second case and why after getting all the carbon out the carbon is put back in. Place the development of this process in a a historical context.



Additional information might be found on the internet or in the accompanying booklet.



In reviewing the steel making process, consider that originally, charcoal from biological sources was used in steel making until it was discovered that coal mined from the ground could be turned into coke, and this would provide the carbon much more cheaply. IF we assume that manmade release of carbon dioxide is a significant factor in global warming, since so much carbon is burned in making steel, perhaps we could find a bio-based source so that we are simply recycling atmospheric carbon rather than increasing it. Could we afford to do this? Would we burn down the environment faster than it grows, Could we afford steel?

Answer 1

In the first stage (blast furnace) there is an excess of carbon and it is partially burnt carbon, carbon monoxide which is instrumental in stripping the oxygen from the iron oxide ore. The oxygen in the second stage (the Bessemer Process) is in gaseous form (not bound to iron) and this reacts with the carbon. In the third stage carbon (and other metals) can be added back in in a controlled amount to produce a steel with the desired precise amount of carbon for given properties of the finished steel.

For an historical context see:
http://en.wikipedia.org/wiki/Bessemer_process

Certainly reverting to a biological basis for the carbon used in steel making would require a lot of trees. The better answer may be to develop ways to sequester the CO2 produced. In theory there are a number of ways this can be done - google CO2 sequestration. One North Sea gas platform already injects CO2 impurity extracted from natural gas into an deep underground reservoir.

Answer 2

The basic component of steel is pure iron, and the blast furnace is required to reduce iron ore into pure iron and waste (slag). Simply blasting oxygen through iron ore in a Bessemer converter would not produce the temperatures necessary to separate iron from waste compounds found in iron ore. In addition to the chemical reactions required to separate carbon, oxides and waste elements from iron, a physical separation is required to make the reaction practical (i.e. to keep the pure iron from re-integrating with the wasted elements). A blast furnace is a bit like a giant gravy boat in that molten slag is lighter than liquid iron, and slag is tapped off the blast furnace mixture (the "burden") at a height above that of where the iron is tapped off.
There is one means of removing impurities from iron ore (and steel scrap) that doesn't involve a blast furnace: direct reduction (see reference below).
In terms of a bio-based source of carbon: it's already being done by Nucor Steel. Nucor raises eucalyptus trees on reclaimed land that was formerly subjected to slash and burn agriculture in South America. The growing eucalyptus trees consume CO2 and put forth oxygen. When mature, the eucalyptus trees are turned into charcoal, which Nucor uses to make iron. Making and burning charcoal put some CO2 back into the atmosphere, but at a net oxygen gain for the atmosphere, according to Nucor's website.