The HIsarna steelmaking process is a process for primary steelmaking in which iron ore is processed almost directly into steel. The process is based around a new type of blast furnace called a Cyclone Converter Furnace, which makes it possible to skip the process of manufacturing pig iron pellets that is necessary for the basic oxygen steelmaking process. Without the necessity for this preparatory step the HIsarna process is more energy-efficient and has a lower carbon footprint than traditional steelmaking processes[1].
The HIsarna process was developed in stages and with pauses at Koninklijke Hoogovens and Corus IJmuiden, starting in 1986. The final stages were made possible through the Ultra-Low Carbon Dioxide Steelmaking (ULCOS) consortium and cooperation between Corus and the Rio Tinto Group. The latter contributed their HIsmelt technology to the final design of the installation, prompting the name HIsarna for the process ("HI" from HIsmelt and "sarna" from Isarna, a celtic word for iron)[2][3].
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The very first attempts at applying cyclone oven technology in the reduction of iron ore took place at Koninklijke Hoogovens in the 1960s. Cyclone technology had already been used successfully in different industrial, chemical processes and the designers at Hoogovens thought it might be an improvement strategy for their process. However, at the time they couldn't get it to work properly and the experiment was quickly abandoned[1].
The first serious revival came in 1986, when Hoogovens sought a method of producing steel without having to produce pig iron pellets. At that time the desire was mostly a cost-cutting measure in order to make the process cheaper in trying economic times. The trying times did not last however and the project was put on the back burner until the early 1990s.
By the early 1990s a pinch was being felt in the availability of cokes, the raw coal material used to heat iron ore. The problem wasn't a lack of coal (there is plenty of that available), but around that time many of the major distillation facilities in the West that produced cokes from coal were reaching the end of their (economic) life. Heavy environmental restrictions made it unattractive to build new facilities, so steel producers sought ways to reduce the need for cokes; Hoogovens started putting more effort into the cyclone technology as a solution to this problem and a test facility (just the cyclone part) proved capable of producing twenty tons of pig iron per hour. The rest of the process didn't work very well though, so when steel producers massively moved from coke bricks to powdered cokes injection and China started mass-producing cokes, the project lost momentum again. The steep drop in prices of commodities around 1999 landed the whole project back on the shelf[1].
In 2004 however, the European Union brought pressure on the steel industry to reduce its carbon footprint; the ULCOS consortium was founded as a result and in the period 2005-2007 the cyclone technology was selected as one of four high-potential technologies. A theoretical answer was found to the earlier problems of the post-cyclone part of the cyclone furnace and by chance it turned out that the Rio Tinto Group already had industrial-scale experience with the required process, called HIsmelt. An agreement between them and ULCOS added the HIsmelt technology to the cyclone furnace and the result was the HIsarna process[1].
As of September 2010 the first pilot plant for HIsarna is under construction at Corus IJmuiden (now part of Tata Steel). The pilot furnace will be capable (if successful) of producing 60.000 tons of pig iron per year[2][3].
The HIsarna process is a variation of the basic oxygen steelmaking process in which the production of pig iron is drastically altered through the use of a Cyclone Converter Furnace (CCF) rather than a traditional blast furnace.
The normal primary steelmaking process produces steel from iron ore in two separate steps. The last of these is melting pig iron pellets and blasting oxygen through the molten sludge from the bottom to reduce the carbon content; the first is the production of the pig iron pellets by heating iron ore with carbon to reduce it to an iron/carbon sludge which can be cast into the pellets. The production of the pellets is necessary in order to arrive at a material with a very porous structure, sufficiently porous to allow hot gas to be blasted through evenly in order to arrive at uniformly high-grade steel in the end.
By comparison, HIsarna uses a CCF furnace rather than a blast furnace. Where a blast furnace is essentially a large pot with an air-inlet on the bottom, a CCF is shaped more like a wine bottle: a high pot or "bottle" at the bottom and a thin "neck" at the top. The geometry of this furnace causes a hot air cyclone to form in the neck when the furnace is heated. Crushed iron ore (i.e. iron ore powder) is injected into this cyclone together with oxygen (so oxygen is injected at the top rather than at the bottom). The heat of the cyclone causes the initial (partial) reduction reaction to take place that reduces iron ore to iron. Also, the centrifugal force of the cyclone separates the reduced iron from remaining impurities and flings the reduced iron droplets against the wall of the furnace[1].
The molten iron droplets then drip down the furnace wall to the place where the "neck" widens into the "bottle". Here the droplets fall from the wall into the molten iron bath in the bottom of the furnace. On the way down the droplets pass through a second set of heated oxygen injectors and then a set of coal powder cannons. The reduction reaction now continues "as normal" in the bottom of the furnace, with the partially reduced iron ore further reducing to regular pig iron and the whole separating into two molten layers (a top layer of slag and a bottom layer of molten pig iron). Both layers can be tapped individually and the pig iron can be used immediately in the remainder of the basic oxygen steelmaking process[1].
In a technical sense, the advantage of the HIsarna process is that it removes the step of creating pig iron pellets to create a porous material for the blast furnace. In the traditional process one cannot use powdered coal throughout the heating process, since the oily components of coal would turn into sludge and ruin the porous structure of the pig iron. By comparison, in a CCF, the powder form of the coal and ore are an advantage because the increased surface area improves the speed and quality of the reduction reaction in the cyclone[1]. This in turn means that the pig iron that is finally drained from the molten iron bath is also of somewhat better quality.
The main advantages of the process (and the reason that the process is being developed into a pilot plant) are derived from those mentioned above, however: the fact that the separate step of creating pig iron pellets disappears from the process makes the process more energy efficient and (most of all) severely reduces its carbon footprint (estimates from labwork are as high as a 20% carbon footprint reduction)[1][2][3]. This makes the process attractive to steelmakers, who are being pressured to make their processes more environmentally friendly — particularly in Europe, where government regulations are increasingly attaching a financial penalty to high carbon dioxide emissions.