New Urban Relics
februari 13, 2026
Read moreThis brief overview is a modest attempt to provide some background and context for the several HFB photo series. Don’t expect an in-depth scientific article, as that is not the purpose of this website. Photography remains the key element here.
For those who would like to learn more on the inner workings of a blast furnace, I would advise the Wikipedia article on the subject as a kicking off point.
An Aerial Overview
(1) Blast Furnace – (2) Cokes Facility – (3) Sinter Plant – (4) Carousel – (5) Power Plant – (6) Pump House – (7) Laboratory – (8) Workshop – (9) Charbon 13 – (10) Coal Pulverizer – (11) Kettle House
Basic Principles
If you ever had a look at the structure of a blast furnace, it should be immediately clear that this type of industry is a complex and extensive undertaking. Each individual component provides enough material to warrant a comprehensive essay.
In its most rudimentary form, the blast furnace could be compared to a cooking kettle, where various ingredients are combined to cook a single dish: pig iron. Just as with preparing a dish, it’s crucial that the right ingredients, in the right quantities are introduced to the cooking kettle at the right time. These ingredients include sinter pellets, which are prepared in the sinter plant, coke, pulverized coal, oxygen, and heat.
The diagram above shows how the basic raw materials (sinter pellets and cokes) are introduced into the blast furnace in alternating layers. To stimulate combustion and increase the heat, pulverized coal and oxygen are added.
At the bottom, hot air is added from the Cowper stoves to create explosions (hence the name ‘blast furnace’). Meanwhile the gasses that are produced inside the blast furnace are sent through the ‘dust cyclone’, where unwanted particles are removed, after which the cleaned oven gas is reused inside the Cowper stoves.
Once melted, the pig iron is tapped off at the bottom for processing, and the residue (slag) is removed.
Cokes
Coal is needed to produce molten pig iron in the blast furnace, but it cannot be used directly in the blast furnace. It contains too many harmful or unusable byproducts for the blast furnace process, and it is not strong enough to support the load in the blast furnace. Therefore, the coal is first converted into coke.
A coal mixture is heated in coke ovens to approximately 1,250°C. Since there is no oxygen in these sealed ovens, the coal does not burn. This process is called “dry distillation.” It takes about 18 hours to convert 35 tons of coal into 25 tons of coke. During the distillation process, a large amount of gas and smoke is released, which, after purification, yields coke oven gas and other valuable byproducts, such as tar, sulfur, ammonia, naphthalene, and benzol. The coke produced is used as fuel in the blast furnace and plays a key role in the chemical processes that take place there. The coke oven gas is used internally as fuel.
The coke, brought in from the coke factory located a short distance away, was screened and sorted in this facility, before finding its way to the blast furnace.
Sinter
The main raw material for steelmaking is iron ore. But just like coal, iron ore cannot be used directly in the blast furnace for chemical and physical reasons. Therefore, the iron ore is first converted into sinter. Sinter traditionally represents 90% of the blast furnace charge. The remainder of the charge consists of pellets and calibrated iron ore.
Iron ore, derived from iron mining, arrives in shapeless chunks. These chunks can range in size from a few centimeters to several meters. If these chunks were to be thrown directly into the blast furnace, they could damage the internal structure, for example, by breaking the refractory bricks that form the furnace’s inner lining.
Moreover, large blocks in the blast furnace would create more and larger air pockets, which would ultimately have a poor contact surface with the coke. To prevent this, the iron ore is pretreated in the sinter plant, also known as the ‘agglomeration’. The sinter plant is one of the most complex parts of the blast furnace operation. The iron ore is placed on a belt, mixed with ground coke. The grate belt is a closed chain of grate cars positioned against each other, between which hot air can pass. The mixture of iron ore and coke passes under an ignition hood, which ignites the mixture from above and allows it to burn. As the grate belt moves, the flue gases are extracted through exhaust hoods beneath the grate belt. The heat released during combustion causes the ore to form a homogeneous layer. In other words, the mixture is baked from top to bottom.
At the end of the sinter belt, the sintered hot ore cake falls onto a crushing deck, where it is broken and cooled. This crushing device, consisting of wheels with massive teeth, is called the ‘hedgehog’. The final product appears as shapeless blocks approximately 2 centimeters in size. These sinters form the main component of the blast furnace.
After passing through the hedgehog, the sintered ore is conveyed into hoppers. These are called agglomeration hoppers. They are then transported to the carousel, where they cool further before being transported to the blast furnace.
‘Agglomeration’ is a procedure that produces a lot of carbon monoxide through the combustion of coke. For this reason, the line is equipped with a fume hood to prevent the gases from escaping into the atmosphere and poisoning the workers. Along the way, these gases are purified and later reinjected into the metallurgical process. The sinter plant has a very tall chimney at the inlet and a second at the outlet. The combustion of coke dust produces a large smoke stream, heavily laden with pollutants: dust, carbon monoxide, nitrogen monoxide, and sulfur dioxide. To meet environmental standards, it is increasingly necessary to use expensive smoke control techniques, which entail excessive additional costs.
Carousel
This installation is located at the exit of the sinter plant. It is an aesthetically pleasing, circular structure, resembling a merry-go-round. The sintered ore is sent to this merry-go-round to cool. The installation makes approximately one rotation per hour. The carousel is an open structure with troughs. After the ore has made one rotation, it is sufficiently cooled. It then ends up in a hopper, which directs it onto conveyor belts. The main component of the blast furnace charge is now ready for use.
Pulverized Coal
The biggest drawback to this kind of blast furnace operation is the inevitable production of carbon dioxide from iron reduction processes, which is considered one of the main contributors to global warming. The Pulverized Coal Injection (PCI) method was developed to improve blast furnace operations. This method was developed in the 19th century but only became industrially applicable in the 1970s.
The PCI method is based on the simple concept of primary air (called the ‘carrier gas’) carrying pulverized coal injected through a lance into the tuyere (the lower center inlet of a blast furnace) and then mixed with secondary hot air (called the ‘blast’) supplied through a tuyere and then fed into a furnace. The most remarkable aspect of this method is that it allows cheaper coal to be used in the system, replacing expensive coke, thus significantly reducing costs.
The PCI plant consists of a vertical mill that grinds, dries, and classifies coal. A storage silo uses an inert gas to reduce the risk of fire and dust explosions. A precision weighing system, combined with parallel-mounted pressure vessels, ensures continuous measurement of the coal transport rate and dense-phase transport. Pressurized nitrogen (typically 40 to 50 kg of coal per 1 kg of transport gas) is used to transport the pulverized coal under dense-phase conditions. A powerful long-distance pneumatic conveying system then transports the pulverized coal between the injection vessels and the blast furnace.
The PCI factory on this site is a very (very) dark place, making photography virtually impossible. A similar series about the slightly better lit PCI factory of another blast furnace company, HF4, can be found under the title Brains Tower.
Blast Furnace
In the first section I already briefly introduced you to the general working of a blast furnace. The blast furnace is, of course, the heart of this operation. Everything from the supply of raw materials to the discharge of finished products is focused on ensuring the blast furnace operates optimally. Let’s take a closer look at this part of the operation.
The pre-prepared raw materials—iron ore-bearing sinters, coke, and limestone—are transported to the base of the blast furnace via numerous conveyor belts, where they are collected in silos, ready to be fed into the blast furnace. The raw materials are hoisted up in precise quantities and at precise times via the “skips,” where they are fed into the blast furnace via the “gueulard” (mouth).
The blast furnace charge is fed in alternating layers of sinter and cokes.
At the bottom, at the tuyeres, hot air (approximately 1200°C, preheated in Cowper stoves) and pulverized coal are blown in, possibly enriched with oxygen. The hot air from the Cowpers causes explosions, which raise the temperature in the hearth. The oxygen in the air burns the carbon from the coke and pulverized coal, forming carbon monoxide (CO). The CO gas, which has a temperature of approximately 2200-2400°C, rises through the layers of coke and ore. Under these conditions, the iron oxides in the sinter, pellets, and lump ores are reduced to iron and melted into ‘iron smelt’. This pig iron smelt then percolates down through the coke layers and collects at the bottom of the blast furnace (the so-called blast furnace hearth).
Kilometers of tubes run around the blast furnace. These tubes serve various purposes, including gas supplies, hot air supplies, and cooling water supplies. Two systems are used to cool the walls of the blast furnace: cooling boxes and plate-shaped cooling elements, also known as ‘staves’. The cooling elements used in HFB are made of copper. The purpose of these cooling structures is to allow water to flow into the tank wall. The interior of the blast furnace is lined with staves. Water circulates inside to cool the tank. The copper staves are typically 150 mm thick. Copper staves are usually combined with refractory bricks during assembly. Without cooling, even with refractory bricks, the temperature of the shielding steel would be very high, would be transferred to the ambient air, and would be unbearable for workers around the blast furnace. The goal is to maintain a workable environment for maintenance and to protect the steel itself from near-melting temperatures.
Two examples of the seemingly endless tube structure that almost completely surrounds the blast furnace and which, among other things, provides the supply and circulation of cooling water around the blast furnace shell.
When sufficient pig iron melt has accumulated in the hearth, the blast furnace is drilled open at the bottom, and the pig iron melt flows out through the taphole. There, it is collected in mixers, specially designed rail cars with a torpedo-shaped storage vessel and a refractory lining. These are transported to the steel mill for further processing. Once all the pig iron has been tapped from the blast furnace, the taphole is closed again.
Sinter, pellets, and lump ores contain not only iron oxides but also impurities such as calcium oxide and silicon dioxide. These materials are also melted and form slag, which, along with the pig iron, is extracted and processed in industries such as cement.
The casting floor, or casting hall, is where the molten iron and slag are discharged. The casting time varies, from one hour to three hours or longer. It all depends on the blast furnace speed and the length and diameter of the taphole. Cast iron is distinguished from slag by its color. Only a highly experienced operator can tell the difference. First the cast iron flows, then the slag. The slag is less dense than cast iron, so it falls on top. These molten liquids flow through a channel. At the right moment, an operator lowers a barrier into the channel to redirect the liquid to its intended destination.
The casting hall. The casting floor is located beneath the blower nozzles. From the control room on the right, the barrier is lowered into the exhaust duct. On the left of the photo is a second casting floor and a second control room.
Power Plant
All of the above, of course, requires an enormous amount of energy, which can’t simply be tapped from the grid. An impressive number of machines need to be operated, each consuming a significant amount of power. Therefore, HFB has its own power plant, which generates energy for many of these machines, but also recovers the energy from certain installations and recycles it.
The power plant consists of the boiler house, the power plant itself consisting of two Acec steam generators, an emergency diesel plant, a control station, an electrical control room, the transformers, the laboratory and finally the reserves of hard water and demineralized water.
The power plant has a traditional design. Adjacent to the turbine hall is the boiler room, where water is converted into steam. This steam is then sent to the turbine hall to drive the turbines. Inside the energy room is a pressurized water vapor turbine, which drives a dynamo. After the turbine, the steam is passed through a cooling circuit to condense. The condensed water is reinjected into the boilers. The generated energy is an alternating current (AC). The dynamo is similar to a bicycle dynamo, except it weighs several tens of tons. The voltage is sent to transformers, which increase or decrease the voltage to ensure a continuous power supply to the installations.
The whole process is controlled and monitored from a control room located above the turbine hall.
Pump House
The various installations described above each generate a tremendous amount of heat. This is especially true for the power plant and the blast furnace. They consume a huge amount of water to cool the installations. To feed the cooling system, there is a discrete installation on the northwest side of the site, known as the pump house.
Laboratory
Some of the water pumped from the Meuse River, filtered, and now demineralized, ends up in the power plant, where it is converted into steam in the boiler room to drive the turbines. The quality of a demineralized product is essential for a high-pressure boiler (120 bar, 510°C). The quality of the water used is continuously monitored in this laboratory, located between the boiler room and the turbine hall.
Afterthought
If the photos and texts inspired you to visit this (or another) blast furnace site yourself, always keep in mind that such a visit is not without danger. You might fall off or into something and seriously injure yourself, you could encounter gangs of copper and metal thieves, and of course, you might get caught by security or the police. So be prepared for anything and never visit such a site alone. If a problem arises, it’s helpful to have someone with you who can offer assistance.
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