A New Zealand scientist is part of a team working on how to eliminate carbon dioxide emissions from steel-making.
Steel is everywhere in our built environment Dr Chris Bumby told Afternoons and comes at significant environmental cost.
Bumby is the MacDiarmid Institute principal investigator and principal scientist at the Robinson Research Institute of Victoria University of Wellington.
File photo. Photo: 123RF
“Steel is really important, steel is everywhere, particularly in New Zealand if you look around our cities - our earthquake resilient high-rise buildings, our steel-framed buildings and steel-reinforced concrete.”
And demand for steel will increase as the global economy transforms to renewables, he says.
“If you look at a wind turbine, the mast of that wind turbine is made of steel, if you look at a hydroelectric dam the concrete inside that dam is all steel reinforced generally, if you look at the pylons we are going to need to transport additional electricity, geothermal power stations, new railway lines all of these fundamental pieces of infrastructure are built on steel.”
But now there is absolutely no way to make steel without carbon dioxide emissions, he says.
“If we just kept making all of this steel we need for these renewables generation without doing something we’ll end up emitting more CO2 than we’re saving.”
The steel-making process is 2500 years old. It mixes coal with rocks, the carbon in the coal reacts with the iron oxide in the rocks to take the oxygen out and to leave the iron metal behind.
“If you want to change that process you have to fundamentally get your hands on this piece of chemistry and change the basic reaction that mankind has been using for 2500 years,” Bumby says.
Steel-making currently contributes 7 percent of the total CO2 emissions across the entire world, Bumby says.
But there is a solution.
“The only other reasonable chemical reagent you can use to replace carbon in this reaction is hydrogen.
“That hydrogen we can use to react with iron oxide and the product of that reaction is water vapour, steam, and iron metal.”
Using hydrogen would entail redesigning reactors so that a gas and a solid could be mixed to form metal, he says.
“We change our reactor into what’s called a direct reduced iron system, so now we’re reacting a gas with a solid and we can pass our hydrogen through a reactor, it reacts with the iron oxide, water vapour comes off the top and we are left with the solid metal behind. We can than pass through to other parts of the process and treat much like we would treat recycled steel.”
They have successfully done this in the lab, he says.
New Zealand’s iron sand, found on the west coast of the North Island, have properties that were once viewed as a hindrance, he says.
“This material is subtly different to what you’d find in global iron ores much of which comes from Western Australia, the Pilbarra mines.
New Zealand iron sands contain not only iron oxide but also a little bit of titanium, he says. And this titanium set back steel making 100 years in New Zealand.
“It doesn’t react in the same way … it forms these very high melting point slags which are basically pottery, even at temperatures of 1500 to 1600 centigrade and so if you then try and process it clogs up your blast furnace and reactor and turns the whole thing into a big terracotta ornament.”
The New Zealand government put a lot of money into over coming this problem in the post war period he says, because steel was viewed a strategically important for economic and military reasons.
“In developing new processed to make steel we can’t rely on the rest of the world to solve the problem for us, it’s our rock and it’s our problem.”
That problematic titanium is proving to be an advantage with this new steel making process, he says.
“One of the reasons that we are doing the work in our lab is that New Zealand iron sand behaves differently, it turns out it does some really cool stuff that actually you can’t do with other types of iron ore and that’s allowing us to look at some processes that aren’t possible using Australian hematite.”
New Zealand’s iron sands are particularly well-suited for this hydrogen reaction, he says
“Were quite optimistic in the medium term there is quite a bright future.”
For this process to be an environmental win the hydrogen must be made from green electricity supply, he says.
“You need about one sixth of the amount of electricity that Tiwai Point does in order to generate enough hydrogen to produce all of the steel that New Zealand requires.
“It’s about 130 megawatts, but it is not an unreasonable amount if you look at what’s going on elsewhere in the country.”
The source iron sands remain abundant in two main supply mines in New Zealand, he says.
“This steel has to come from somewhere and if it doesn’t come from New Zealand iron sand it has to come from a hole somewhere else in the world.”
There is a lot of “fundamental science” to be done before moving to a pilot stage, he says, but believes his team could reach that point in another five years.
