Normally iron ore is smelted with coal or coke. The carbon steals the oxygen and leaves behind molten iron. What is the feasibility of using hydrogen instead of coal? Would it not give a higher temperature without the carbon and sulfur oxide by-products?
It’s not that simple. Blast furnaces using carbon based fuel do leave a lot of carbon in the molten iron because of the physical contact at high temperatures. However, that iron-carbon alloy produced has a lower melting point than pure iron. Pure iron is not usually the end goal, it’s steel, and that requires further refinement from iron. Modern steel making mostly does that with the introduction of oxygen to molten iron which contains high carbon content. The heat requirements are optimized through the use of reverberatory furnaces which use heat exchangers to minimize fuel costs. If hydrogen was more economically efficient to produce heat it would be in use already.
The steel industry plans to start using natural gas.
No sulfur, and AFAIK, some degree of carbon is ok or even necessary in the finished pig iron anyway.
You need to get the sulphur out somehow. If not combined with oxygen, it isn’t clear what. Adding hydrogen might simply get you hydrogen sulphide, which isn’t a good bargain.
You need to ensure there is no residual hydrogen left dissolved in the metal. Hydrogen leads to cracking of the metal (hydrogen embrittlement) as the diffused atoms recombine into molecules and pockets will form eventually forcing cracks in the metal. Iron and steel can lose significant strength even by just adsorbing hydrogen when they are solids.
Its not the Carbon but the carbon monoxide (Blast Furnace) that steals the oxygen and leaves behind the iron.
Direct Reduction of Iron (DRI) is the reduction of iron ore to steel using Hydrogen, Carbon Monoxide, Methane etc. - its been done for decades now. The two big players in this technology are Midrex and Tenova.
About 73 Million tons of steel was produced in 2015 using DRI.
You can make the Hydrogen from Coal too - by gasification or from petcoke or natural gas.
As a nitpick, the smelting is done with coke not coal. Not all coals are coking coals.
This question does not make sense. DRI processes are usually lower temperature than blast furnace and the product iron is not molten but like a sponge. It is also called sponge iron.
Here is the wikipedia link : Direct reduced iron - Wikipedia