Chapter 300 Blast Furnace

The product of the grinding would not right away be taken to its destination, for this product still contained one last impurity.

And to remove this, the cart would be taken to a separate station a bit further from the machine and about fifty workers would scamper into the cart, carrying buckets on their backs, and then start quickly shifting through the crushed ore.

They did this to retrieve the make iron balls that were used to grind the ore and though some balls were inevitably lost, close to 95% retrieval was possible for these expert men.

'Hmmm, I should invent the magnet. I will need it to make the compass anyway,' Alexander made a mental note as he watched the diligent workers shifting through the black coke and turning their faces and hands pitch black in the process.

While this was going on, the empty machine was being filled up in a novel way others had never seen before.

It was being done by placing one end of a hollowed-out log into the center of the machine, while the other end rested atop the scaffolding built much taller.

Using this hollowed-out log like a slide, the iron ores, limestone, or cokes would be easily deposited into the machine, with workers using large wheelbarrows to rapidly transport these commodities.

'So, that's why the machine is slanted and placed so high,' The mystery was made clear to all as the council members continued to observe the complete operations of the ball milling machine.

Once the machine was filled, the necessary amount of iron balls was added, the door pushed closed, the wooden planks reinstated, and the whole cooperation would start again.

"Hahaha, to think one day we would be able to produce so much of anything," Heliptos would sleep in his sleep thinking of all the money that could be made using

"How much can we grind in a day?" The aged Menicus was more interested in their capacity and so pointedly ask.

"....." Harun shot a glance at Alexander and after seeing the nonchalant look on his boss's face, he got the message.

"I'm sorry, my lord. But that is classified." Harun had wondered if Alexander would make an exception for the most senior and powerful council member but it seemed the pasha was adamant about keeping his secrets.

"Enough for the foreseeable future," Alexander decided to at least give this amount of respect to the senior statesman, and it got an understanding nod from Menicus.

The daily capacity of the machine was twenty to twenty-five tons a .day, and there were three such similar machines in workshops similar to this.

And the reason why it was so low compared to those at the cement production which could process a hundred tons (100 tons) a day was because the currents and amount of water in the springs near there were extremely high, allowing for the spinning of much greater loads.

"Now let us go to the actual furnace where iron is made," Harun finally decided to lead the group to the place all these people had come to witness.

The crowd hence moved quickly, ignoring the scores of workers moving about the place like ants with no time to waste, and instead focusing on the huge tower that stood against the skyline, like a proud peacock, Alexander's pride and joy.

The white blast furnace had been made using stone and concrete, with a thick layer of clay lining to resist heating, and was of the same design as the cement kiln, the only difference being that the dimensions were a bit larger.

No, scratch that, a lot larger, particularly the height, reaching close to sixteen meters, as opposed to the cement kiln's measly four.

But it was a lot leaner too, designed as such because many of the reactions needed such a tall design to allow different temperature gradients to appear.

There was also the difference in how the double-action blowers were operated.

Instead of being manually driven by human hands like it was with their sister furnaces, the two enormous blowers were operated using pistons driven by two waterwheels on both sides, these giant wheels themselves spun by water transferred via aqueducts from nearby springs.

"As you can see my lord, this is where the magic happens," Harun did not really need to point out the obvious as everyone had already disregarded the miner's existence and instead focused on the huge, roaring structure whose belly was full of fire and who was connected to a myriad of scaffolding, aqueducts, pipes, and waterwheels.

They could see huge cranes situated next to the blast furnace which were being used to fill the enormous, hungry beast, as the load would be raised using ropes pulled by animals and then the special buckets would be tipped over by the few strong men on the scaffolding around the mouth of the blast furnace.

"We always keep the furnace full, and run the furnace 24/7," Harun added some commentary, but did not reveal in what arrangement the charge inside the blast furnace was kept.

This was to be kept secret under Alexander's order, as the way the charge was introduced into the furnace affected the final production.

The correct way to do it was not to mix the three ingredients, iron ore, coke, and limestone together and then dump it all in, but to do it in layers.

First, a layer of iron ore would be deposited, followed by a layer of coke, and then a layer of limestone, after which the pattern would repeat itself.

And these layers could not just be of equal amount, with the proper proportions being 1.6 tons to 500kg of coke to 150kg of crushed limestone, or any amount maintaining this ratio.

These particular numbers were used because to produce one ton of pig iron, this amount of raw materials formed the perfect balance.

Any less, and some of the numerous reactions that take place in the blast furnace would remain incomplete.

While any more, and the excess would interfere with the reactions taking place during the next phase.

This chain of reactions were vital to steel production, and it all started at the very top.

This was facilitated by the design of the blast furnace which was a counter-current gas/solids reactor in which the descending column of burden materials [iron ore, coke, and limestone reacted with the ascending hot gases and produced the desired products.

These numerous reactions were a continuous process and were kept constantly running by adding new raw materials to the top of the furnace and molten iron and slag being tapped from the bottom of the furnace at regular intervals.

At the very top part of the furnace, any free moisture would be driven off from the burden materials and limestone (CaCO3) would decompose into calcium oxide (CaO).

A bit below, some of the iron oxides would be reduced by carbon monoxide produced due to incomplete combustion of the coke, and this typically occurs at 700-1,000°C.

In the middle part of the furnace, called the bosh, was the place iron starts to soften and melt and where the real smelting took place.

And it was also here that heated, hot air, at around a 1,000 to 1,300 degrees Celsius was blown into the furnace by blowers, combusting the coke and raising the temperature to around 2,000 degrees, making it the hottest place in the furnace.

This heat would cause the iron to finally melt and being denser, it sinks down, causing the less dense pool of impurity formed by various reactions with the limestone, called the slag to float to the top.

The two liquids would have different tap holes and these would be periodically opened and the products extracted to the outside.

That was the basics of a blast furnace, but Alexander did face one large issue while designing this, and that was the tap holes.

This was because whereas in modern times, such access points would be electronically operated by opening and closing the doors, currently he was required to design a kind of manual switch that would be opened and closed repeatedly without having to go too close to the burning inferno.

And after thinking for a while, the solution he came up with a both simple and ingenious.

What he did was design a horizontal L-shaped concrete plug, with the lower part of the letter driven into the plug hole, while the other part of the structure was attached to pillars that connected to large wheels placed on concrete rails.

In this way, draft animals could be used to move the L-shaped plug, thereby opening and closing the tapping holes.

These concrete plugs were not too heavy, as the holes they plugged were really not that large, only about 15cm in diameter or half the shoulder width of an average man and these would be opened for about 30 seconds every two hours, letting out 4 tons of pig iron, along with around 800kg of slag

The slag would be taken away to be used as fertilizers in Alexander's personal estate as the amount of the stuff was nowhere near enough to be useful in large-scale productions, while the molten pig iron would be taken through a concrete channel right below the tapping below into a Bessemer converter situated at an elevation 6m below the blast furnace some distance away to be converted into steel.

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