Carrie’s Choice
(A Steel Industry Fantasy)

By IonMars

February 1, 2015


It is 2033 and Carrie faces the biggest decision of her life. If she makes the right choice she will make billions of dollars and become the new industrial tycoon of Mars. She will restore her family name to the top of the steel industry, albeit within a new colony on a remote planet. If she makes the right choice she will follow her illustrious forebear, Andrew Carnegie, who established the steel industry in the United States 150 years before, by introducing the Bessemer steelmaking process1.

Carrie CarnegieCarrie Carnegie had already shown her entrepreneurial skill by organizing a startup company, the Carnegie Group. With her partners, Eric and Amahd, she financed an advance expedition to Mars to scout out the sources of iron ore.  As a matter of practicality the group limited themselves to the vicinity of the International Mars Research Station (IMRS), sponsored by a consortium of seven space-faring nations to establish humanity on a second planet2.  This site is where the earliest explorers set up an oxygen and fueling-making plant to supply oxidant and fuel for rockets that return to Earth.

The mini-chemical factory at IMRS was the result of many years of planning by the National Aeronautics and Space Administration (NASA) to develop an In-Situ Resource Utilization (ISRU) plant on Mars3. The early explorers also established habitats and electric power generation at the IMRS with life support systems that could be shared by succeeding crews of explorers or colonists. So when the Carnegie Group laid out their own plans for resource exploration, they contracted with the IMRS administrators to supply oxygen, fuel and electricity for their private venture. This arrangement would reduce their venture costs and also help support the IMRS.

The major decision facing Carrie and her partners is this:  which of three major sources of iron ore should they pursue to achieve the biggest gain for their initial investment? Eric Anderson favored the iron ore hematite, which meant going after the Martian “blueberries,” that were pure hematite4. “If we are to set up a Martian steelmaking plant,” he liked to say, “why not go after the iron ore that propelled the iron making industry in the USA?” Amahd Kamali, on the other hand, liked the idea of sifting the Martian dunes for magnetite regolith, a fine-grained magnetite dust that could be readily separated from non-magnetic sands.5 “I would like to feel a pouch of magnetite powder in my hand,” he said, “it would weigh heavily, like a bag of gold dust.”

But Carrie had her own idea that she brought to their meeting. “The results are in,” she reported. Only two weeks before the group had landed their robots on Mars to carry out a survey of meteorites lying on the surface. Following a strategy proposed by IonMars in 2014, they employed a hovering, rocket-powered survey instrument (HovMag) to conduct their research6. But they went a step further and conducted the investigation entirely by robots. “As planned, we surveyed the area within 1 km of the IMRS,” she said and pointed to the on-screen map. We found 53 meteorites showing on the surface but only a few of real size.”

She looked thoughtfully at the chart showing the size distribution of the meteorites that were found. This many iron chunks would only supply her industry through the first year of operation. Yet one could not be certain that some of these lumps of iron weren’t the tips of much larger submerged meteorites. And more would likely be identified further from the base.


Why Carrie Cares

To appreciate the importance of Carrie’s choice, we need to understand certain iron making and steelmaking processes. On Earth the iron ores hematite (Fe2O3) and magnetite (Fe3O4) are both iron oxides that are useless in their native mineral form. The oxygen components must be removed and the elemental iron (Fe) isolated for further usage. This process is called iron making, which produces pig iron ingots.  Such ingots are an intermediate product to be fed into a steelmaking furnace7.  

In iron making, raw iron ore is mixed with a high-carbon fuel such as coke. A blast furnace is charged with iron ore, coke and limestone flux for removing some of the impurities8. The pig iron product is poured into molds or passed along for additional processing. (In the early blast furnaces the molten iron was poured into sand molds that took the shape of a row of piglets suckling a sow. Thus the nomenclature “pig iron” was coined.) Pig iron has a high carbon content and silica that cause brittleness; it requires further treatment to become useful in construction. Construction steel is an alloy of iron and carbon (up to 2.7 percent) so the next step involves re-melting the pig iron, removing more impurities and adding specific amounts of certain components like carbon that create a strong and durable material. This is steelmaking. 

To operate a traditional iron-making furnace it is necessary to produce coke from coal. Coke production is a dry distillation process that involves the combustion of coal without access to oxygen9. The heart of the process is the coking battery consisting of tall, narrow airtight ovens. The ovens have brick partitions wherein the wall channels are heated by the gas generated in the coking battery itself. The coal inside the ovens is heated until it is in a flowing, plastic form. The unwanted elements to be removed are gasified in about 18 hours and the gas is cleaned in stages so that many raw materials are recovered. Thus the coking plant is a major operation in itself, but is required for the traditional iron-making processes. 

Another operation associated with iron production is the sintering plant. Sintering is a pre-treatment step prior to iron making that produces a charge material called sinter for the blast furnace10. It is made from iron ore fines and other metallurgical wastes from iron and steelmaking such as collected dusts, sludge and mill scale. The original purpose of sintering was just to recycle waste materials, but now the aim is to produce a high quality input to the blast furnace that increases the efficiency of the entire process. Today sinter is the main metallic burden for a large blast furnace. 

Bessemer ConverterTo begin steelmaking, the pig iron from iron making is delivered to a steel mill. In a large operation the two mills are combined into one integrated operation. The traditional Bessemer steelmaking process that was employed by Andrew Carnegie in in the 19th century was the first large-scale industrial process for the inexpensive mass-production of steel from pig iron11. The Bessemer process rapidly removed impurities from the iron by blowing air through the Bessemer converter to oxidize unwanted components such as excess carbon, manganese and silicon. These oxidation reactions also raised the temperature of the iron mass and kept it molten. The resulting oxides either escaped as gas or formed a slag that could be poured off to separate it from the molten metal. 

The refractory lining of the converter also played a role in the chemical conversion. When there was low phosphorous in the molten material a clay (dolomite) lining was used; whereas when the phosphorus content was high limestone  or magnesite linings were sometimes employed. When the conversion reactions were completed other substances could be added to give the steel certain desired properties, such as harness or strength. 

PlantAnother procedure that was begun in the 19th century was the open-hearth furnace.13 The open-hearth method is a batch process wherein each batch is called a "heat". The furnace was charged with light scrap, such as sheet metal or waste metal pieces and was heated by burning natural gas. Once the preliminary charge was melted, heavy materials such as construction scrap or steel milling scrap were added along with pig iron. Once all the iron was melted, slag-forming agents, such as limestone were added. The oxygen from impurities decarburized the pig iron by burning away excess carbon and forming steel. To increase the oxygen content, iron ore was added to the heat.

 The open-hearth process was far slower than that of the Bessemer converter, but was easier to control. Preparing a heat usually took 8 hours to convert all the pig iron into steel. During this time samples were taken frequently to assess the product for quality. In this slower process it was not necessary to burn all the carbon away and it could be terminated at any point when the desired carbon level was reached. But by the 1990s both the open-hearth furnaces and the Bessemer converters had been phased out in favor of newer procedures. 

If traditional iron making were employed for Mars’ iron ores, a blast furnace, sintering plant and coking plant would all be required. One problem with this approach is that the coal-derived coke that is employed on Earth will not be feasible to employ on Mars because coal does not exist on the Red Planet. Coal is a product of the masses of plants that died on Earth during the carboniferous era and were buried under many tons of soil by geological processes.  The plant masses were subjected to high pressure and high heat that eventually transformed it into coal. As far as we know neither plant life nor geological processes occurred on Mars in such a way as to produce coal. Iron making on Mars will necessarily be a process that does not depend on coal or the coke derived from coal. 

Today, alternative processes that do not require coal or coke can be employed to produce iron. Instead of coke, a reducing gas derived from natural gas (mostly methane) can be employed. This gas reduces to hydrogen and carbon monoxide that act as the reducing agents for the process. By this means iron ores in the form of lumps, pellets or fines are treated by the reducing gas to produce a product called direct-reduced iron (DRI), also called sponge iron13. Sponge iron is an easily oxidized form of iron that is usually transported quickly from iron making to a steel-making furnace before it becomes oxidized by exposure to air. 

Flash IronThe DRI method bypasses the conventional routes for making iron and steel, including the sintering plants, and iron blast furnaces. An example of the method is the MidRex technology employed by Siemens Company14. The Tenova HYL15 technology is another DRI process using natural gas. In addition to replacing coal, the DRI process also allows iron and steel to be produced on a smaller scale that is more consistent with the needs a Mars colony. Note that CO and H2 are byproducts of the chemical mini-plant that will be employed on Mars to produce CH4 from the Mars’ atmosphere for use as rocket fuel (See the article “Dr. Sabatier’s Appurtenances” on this website). 

A new technology highlighted by the American Iron and Steel Institute (AISI) and the Department of Energy is called “flash iron making.” This proposed process would apply hydrogen (or methane) as a reducing agent to convert iron ore fines directly into sponge iron16. It would eliminate the need for a coking plant or a sinter plant. If CH4 were used as an input it would introduce carbon into the procedure for a direct iron ore-to-steel process. Such a process would be compatible with the other chemical operations planned for Mars that would produce both H2 and CH4.

If Carrie Carnegie choses to utilize one of the high quality Mars iron ores such as hematite or magnetite, they will likely be treated by one of the iron making operations that are already used on Earth. It could be a DRI process using H2 or CH4 that eliminates the requirement of a coking plant.  Alternatively, a new method could be developed, such as the novel flash iron making process. However, if Carrie chooses the third readily available source of iron on Mars, then all of the iron making problems will disappear because meteoric iron is already an iron-nickel alloy and requires no further treatment. It could be melted and poured directly into molds or it could be delivered directly to a steelmaking operation to produce carbon steel.

 

Implementing Carrie’s Choice

If Carrie discovers enough iron meteorites on or near the surface of Mars then she will want to implement a plan for using them. Whether they are exploited from their native state or converted into carbon steel, iron meteorites will need to be melted as a first step. For the purpose of melting iron metal, the basic oxygen furnace (BOF) and the electric arc furnace (EAF) have replaced the Bessemer converter and the open-hearth furnace. Carrie will need to choose one of these methods to begin a smelting operation on Mars. 

The Basic Oxygen Steelmaking (BOS) process has replaced the open-hearth furnace. It employs a BOF as its central feature, which is an open-top vessel similar to the Bessemer converter that can be tilted. The vessel interior features a magnesia (MgO) refractory lining. This lining is required because of contact with a basic slag, which is the reason for the “B” in BOF. No heating devices are required because the chemical reactions that take place are exothermic and the process is energy self-sufficient17 

Charging ScrapThe following diagrams are adopted from “SteelWorks,” an online publication of the American Iron and Steel Institute. The first steps shown in diagrams 1 and 2 show how a heat begins by charging the vessel with scrap metal followed by charging with “hot metal,” which is melted iron produced in a nearby blast furnace. The hot metal ladle is transported directly from the iron making process to the BOF as part of an integrated iron and steel operation. 

SamplingThe next step is the “main blow,” whereby a long tube called a lance is lowered into the hot metal and scrap iron. At the same time fluxes consisting of lime and dolomite are dumped into the vessel. Then highly purified oxygen is forced through the lance and into the mixture at hypersonic speed, which initiates violent chemical reactions. The fluxes react with various impurities in the molten steel and form slag, which is a lighter, frothy material that migrates to the surface.. After a predetermined amount of time, a sample is taken from the product to test its quality and temperature. 

TappingAfter a satisfactory blow, the molten steel is poured into a ladle through a tap hole. The ladle also receives measured amounts of alloying materials that react with the steel to achieve a final product that exhibits the desired characteristics according to specifications. Then the slag is poured off for disposal or recycling of waste materials. The vessel lining is frequently repaired between blows because of the harsh chemical conditions it encounters. 

A prominent feature of the BOS process is that it is usually executed on a very large scale. BOF heat sizes in are typically around 250 tons, and tap-to-tap times are about 40 minutes. This high rate of production is compatible with the continuous casting of slabs for the construction industry on Earth, but would require massive machinery that is not compatible with the modest requirements of a small Mars colony. Such a huge operation would also introduce huge financial requirements to ship large machinery to Mars. 

The electric arc furnace (EAF) is the other major type of steelmaking process in use today. It is the predominant method for melting and reusing metal scrap. The EAF melting process is a batch procedure whereby each batch of molten steel is known as a “heat.” and the furnace operating cycle is called a tap-to-tap cycle. The steps in the cycle consist of charging, melting, refining, de-slagging, tapping, and furnace turnaround. In a modern furnace the tap-tap cycle takes less than 30 minutes18. 

Each batch operating cycle varies in the type of metal to be melted and the refining steps to be taken. Different formulae are employed to produce the grade of steel required by a particular customer. To begin, the scrap yard operator prepares buckets of selected types of scrap according the requirements for a certain grade of steel. He will layer the materials to aid in the processing and may also add lime and carbon. 

To charge the furnace, the roof and electrodes are raised from the furnace. An overhead crane with a clamshell bucket brings the selected scrap over the top of the furnace and dumps the scrap into it. Two or three buckets may be required to make up a heat. The roof and electrodes then swing back into place over the top and descend into the furnace. A switch is turned to strike an arc on the scrap and begin the melting. 

During the melting period the graphite electrodes provide much of the energy for melting. At first, a moderate voltage is applied to prevent excess energy from damaging the roof of the furnace. Then as the electrode bores into the scrap metal a molten pool is formed. The growing pool of melted iron provides protection for the vessel so a long-arc high voltage can be applied for faster, more efficient melting. 

Electric Arc Furnace

The combustion of natural gas and oxygen supplies a second form of energy for melting.  The gaseous fuel is fed through fuel burners and oxygen is delivered through oxygen lances to supply the oxidizer. Oxygen reacts not only with the gas, but also with unwanted aluminum, silicon, manganese, phosphorous, carbon, and some of the iron in the metal scrap. These reactions are exothermic and provide additional heat for melting. The oxides of these metals become components of the slag that forms during this process. 

The process of refining steel within an EAF consists primarily of reducing the unwanted components in the heat to meet specifications for a particular grade of steel. Much of this takes place during the step called slag foaming. Oxidizing the metals that form slag and then de-slagging goes far towards refining the steel product. Typically, this slag will contain CaO, SiO2, FeO, MgO, MnO, S, P, and other more minor constituents. During slag foaming, carbon may be injected to reduce the iron oxide to metallic iron. At the same time carbon monoxide is produced, which helps to foam the slag. 

Phosphorous and sulfur are particularly troublesome to remove because the chemical and temperature conditions that help remove one will cause the other to dissolve back into the melt. Current practice is to remove some of the slag containing P during the early phase of the melt when the temperature is lower. Later, when the temperature is higher, calcium aluminate is added to form a slag with higher S content, which is then removed during tapping18.

Arc Furnace
To perform de-slagging, the furnace is tilted back and the slag is allowed to pour out the slag door.

Tapping consists of allowing the molten steel to flow out a hole near the bottom of the furnace. Tapping takes place when an analysis of a sample of the product determines that the desired steel composition and temperature have been reached. The previously closed tap-hole is opened, the furnace is tilted, and the steel pours into a transfer ladle. During tapping, additional alloying chemicals are also poured into the ladle for further refining in the ladle itself. De-oxidizers such as ferrosilicon or silicomanganese may be added to lower the oxygen content. Slag forming compounds are also added to the ladle at tap so that a fresh slag cover is formed just prior to transferring molten steel to the ladle. 

The time period following tapping and before the furnace is recharged for the next heat is called turn-around time.. During this period, the electrodes and roof are raised and the furnace lining is inspected for damage. If necessary, repairs are made to the hearth, slag-line, or tap-hole and the tap-hole is plugged with sand. When required, the furnace is repaired using gunned refractories or “mud slingers.” In modern furnaces the furnace bottom is routinely switched out every two to six weeks and repaired off-line. Current practices of furnace operation now allow turn-around time to be reduced to less than 5 minutes.18 

Power on MarsA prominent feature of the EAF is that it requires a prodigious amount of electrical power to melt iron and steel. Theoretically, the energy required for melting scrap metal and then superheating it to tap temperature is 350 to 370 kWh per ton of steel produced. This energy is primarily provided by the electric arc at the anodes, but it is also derived from fuel injection and oxidation of materials. The type and quality of the feedstock, the parameters of the final product and the operating practices for each furnace determine the electrical energy actually utilized. In 1999, actual electricity usage averaged 425 kWh per ton but by 2005 this had been reduced to 350 kWh per ton of steel produced, largely due to improvements in operating practices18. It is still a large energy requirement that can dominate the electrical generating capacity of a electrical generating plant.

 

The Poignant Problem

Carrie’s choice will carry the weight of a multiple billion-dollar expenditure. It will require the development of an entire steelmaking operation scaled to the needs and capabilities of an initial Mars settlement. It will need to be designed in components that can be readily loaded and unloaded from the cargo hold of the Mars Colonial Transporter. The colonists will set up the steel plant while working under the hostile conditions of near zero atmospheric pressure and cryogenic cold where even small forays must be planned in advance. The steel plant must also operate under these conditions and work effectively with little delay in order to justify the expenditure of money and talent. 

Many persons will jump immediately to the EAF as the obvious solution, the operation that is most easily set up and ready to operate. There are many desirable features of an EAF for melting and possibly refining meteoric iron alloy to create a a Mars-based product that can be put to use immediately to build flex houses and steel parts. 

On the other hand, the electrical power requirements of an EAF will raise a difficult issue back on planet Earth. At this time the primary method for generating sufficient power for melting steel in a small Mars settlement is a nuclear fission reactor.  Such a reactor is part of the NASA plan for colonizing Mars, as expressed in the Mars Design Reference Architecture, Version Five3.  

Radioactive SignReasonable people, especially people in the Mars colonization community do not view control of fissionable material as a significant problem, However, it is seen as a huge problem among the leaders of nations who are fighting against small groups of unreasonable people who act with little social regard in order to propagate their ideology. Fanatics yearn to grasp the best and biggest weapons of destruction they can employ and nuclear is the biggest.  Even we colonizing enthusiasts must recognize that control of nuclear materials is an over-riding political problem that we must solve if we are to employ nuclear fission on Mars. We want to colonize Mars, in part, as a safety valve for the survival of humanity in case we manage to destroy our Earth. How ironic it would be if our colonizing efforts were to spark that very destruction. 

With that sobering view in mind, consider further the refining of meteoric iron alloy. The BOF is probably a less desirable alternative for melting and refining iron into steel. On the other hand, it is energy self-sufficient since the reactions that create the steel are exothermic and drive the entire process to completion. If we cannot solve the issue of transporting fissionable materials to Mars in the short run, then the BOF will give us an alternative solution. 

In the long run, there should little doubt that nuclear fission will be employed on Mars. The control of fissionable materials has appeared as an issue when fissionable materials are sent into space. As exploration and colonization proceed, it seems likely that uranium, thorium and other fissionable ores will be found on Mars in sufficient concentration to be put to use. Then the control of nuclear material during transportation will not be an issue. Then a nuclear industry can be built to move Mars toward self-sufficiency, which is the long-term goal. 

Another sobering note is that in the past the iron and steel industry has required a considerable amount of time to develop new systems and procedures. Setting up new machinery, testing a new system, and developing procedures have required many years, even decades to execute. From this point in time where we see humans possibly landing on Mars in the next decade, we have no time to waste. We need to design the systems now, test them here on Earth now, and perfect the steelmaking techniques before Carrie Carnegie ever steps foot on Terra Martia. Cartoon


References

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