Intro
The blast furnace is a vertically positioned shaft-type furnace, the distinctive feature of its continuous operation throughout the campaign. The duration of the furnace campaign from the start of the smelting process has consistently increased and currently makes 20 to 25 years. The necessity for the continuous operation of the blast furnace, as well as the constant extension of the furnace campaign duration, are fundamental factors having an impact on the characteristics and properties of the blast furnace equipment. All primary equipment and a significant part of auxiliary equipment must be continuously operated without failures or accidents throughout the entire blast furnace campaign, i.e., for 20 – 25 years.
Blast Furnace Process
The process of hot metal smelting in a blast furnace includes several stages:
- Iron ore preparation;
- Charging into the furnace;
- Hot metal smelting;
- Slag separation;
- Hot metal tapping.
- M HEAVY TECHNOLOGY is the author of unique developments for blast furnace design.
Modern blast furnace complex.
Key Components and Their Functions
The key components of the blast furnace complex include equipment or entire technological chains that are directly involved in the process and the failure of which can lead to an accident or a blast furnace process stop. The blast furnace complex can be divided into the following vital subsystems:
Central Unit
It includes the blast furnace proper, which in turn consists of the following parts:
- a shell;
- cooling staves;
- a refractory lining;
- a cooling system;
- a charging device (a bell-type top charger or a bell-less top charger, (usually a chute-type one), a hot blast feeding system (a straight and bustle main and a tuyere stock).
All the blast furnace process’s main redox reactions occur in the central unit.
Cast House
It includes runners responsible for separating hot metal from slag, as well as their transportation to the discharge from the cast house into hot-metal ladle cars and slag cars. The cast house equipment includes taphole opening and ramming machines, runner cover manipulators, and other equipment.
Hot Blast Stoves
They are designed for heating combustion air and consist of a casing, lining, hot-blast stove checkerwork and a sub-checkerwork, a burner, valves, and a bustling main for feeding hot blasts into the furnace.
BFG Gas Cleaning Plant
It is designed for gas purification for further use when heating hot blast stoves and other consumers, such as factory thermal power plants, heating furnaces, etc. The gas cleaning plant is also used to maintain the required top pressure. The gas cleaning plant usually includes a dust catcher or cyclone, a scrubber, a Venturi tube, a demister and a throttle group (for a wet-type gas purification system) or bag filters, a heat exchanger, and a TRT (for a dry-type gas purification system).
BF Charging System
This system is responsible for preparing and supplying material of the required quality and at the required ratio into the blast furnace. It usually consists of storage bins, screens, chutes, feeders, conveyors, or a skip-hoist system for materials.
M HEAVY TECHNOLOGY specialists designed, developed, produced, and supplied equipment for all the above-mentioned vital components.
Role of Auxiliary Equipment
Auxiliary systems of the blast furnace complex include systems that are not directly related to the technological process, but with which the operation of a modern blast furnace seems possible.
Stockhouse and Cast House Dedusting Systems
They are designed to maintain standard indicators of air quality in workplaces and common indicators of emissions into the atmosphere. They include a gas duct system, shelter, draft equipment, and proper filters (bag, electric, or combined). Currently, bag filters are more often used due to environmental standards tightening.
Pumping Stations and Water Supply Systems for Blast Furnace Cooling
They are designed to supply water to the blast furnace cooling system, which maintains necessary thermal conditions in the cooling staves, preventing their burnouts and furnace shell damage. It comprises a pipeline system, fittings, pumping units, and heat exchange equipment.
Utility Networks
They include systems of supply of energy carriers (nitrogen, oxygen, natural gas, compressed air, electricity, etc.), heating, ventilation and air conditioning systems, compressor stations, etc. M HEAVY TECHNOLOGY specialists designed, developed, produced, and supplied equipment for all the above-mentioned auxiliary equipment.
Read more on manufacturing engineering consulting services.
Main Parts of Blast Furnaces
The furnace shell, cooling staves, and lining are the main components of the central unit, where the cooling staves play almost a decisive role in the blast furnace campaign duration. Adequately designed and selected for required zones cooling staves are the basis for the reliable operation of a blast furnace. M HEAVY TECHNOLOGY experts have designed, produced, and supplied all cooling staves.
Cooling staves can be divided into three main types based on their material: cast iron, steel, and copper.
Cast Iron Cooling Staves
This equipment the most commonly used; their main advantage is wear resistance, which is very important in the upper part of the furnace stack and the blast furnace top, where the descending material still needs to be softened and is highly abrasive. Their main disadvantage is relatively low thermal conductivity compared to other types of cooling staves. A cast iron cooling stave is a cast iron plate cast in steel tubes (coils). The coils can be arranged either in one row or in two rows. The surface of the cooling staves facing the fireside of the furnace can be either flat (such staves are used in the lower part of the furnace: hearth, bottom, and tuyere zone) or have teeth, including those having a “dovetail” shape for the possibility of inserting refractory bricks. Such cooling staves are used in a blast furnace’s bosh, belly, stack, and top. When embedding a steel tube into a cast iron cooling stave, there is a gap S = 0.3÷0.8 mm between the outer wall of the tube and the stave body, which appears during the casting process when the marshalite coating of the cooling stave pipes burns out. The multilayer structure of the cooling stave (cast-iron body, steel tube with a wall subjected to the process of carburization during the stave manufacturing) leads to the formation of cracks both in the cooling tubes and in the cast-iron body of the stave under sudden impact of peak thermal loads. This design also reduces the overall thermal conductivity of the stave itself.
Fig. Blast furnace equipment details: Steel coil tube of the cooling stave.
Fig. Cooling staves manufacturing process.
Fig. Cast iron cooling stave with installed silicon-carbide bricks.
Steel Cooling Staves
Incredible plate-type staves made of cast steel have some advantages over cast-iron staves. The technology of embedding cooling pipes into the body of the stave allows for pipe-stave body contact without air gaps and ultimately obtains the following properties: excellent total thermal conductivity, high thermal fatigue resistance, excellent mechanical characteristics, excellent thermal shock resistance, etc. However, steel cooling staves are still significantly inferior to copper staves in thermal conductivity and are in a transition stage. In our blast furnace cooling system projects, we use them as a transition row between the zone with cast-iron staves and the zone with copper staves to smooth out the difference in thermal conductivity between these zones. We also have experience using steel staves as a cheaper option for replacing copper coolers.
Copper Cooling Staves
This type of equipment are the most expensive and modern solution and are used in the most heat-loaded areas of the blast furnace: belly, bosh, the lower part of the stack, and the area around the tapholes. A copper cooling stave is a copper slab with drilled channels to let cooling water pass through. To obtain a high-quality copper stave, high demands are placed on the copper slab:
All copper staves are made of oxygen-free copper plates with increased requirements for their chemical composition and physical and mechanical properties.
Chemical composition:
Cu>99.9%
Physical properties:
Density ρ > 8.93 g/cm 3
Conductivity r > 98% IACS (international standard)
Heat conductivity factor λ > 381.8 W/ (m * К)
Mechanical properties:
Tensile strength Rm > 200 MPa
Flow limit Rp 0.2 > 40 MPa
Stretching А > 40%
Hardness HB > 40
Our company’s cooling system projects use copper staves’ “dovetail” design to insert refractory bricks with high thermal conductivity.
Fig. Copper stave with inserted refractory bricks having high thermal conductivity.
It is worth noting that copper staves can only work if there is protection on the wall facing the fireside of the furnace in the form of refractory materials or skull or refractory materials and skull simultaneously due to their low resistance to abrasive wear.
Fig. Process of manufacturing copper cooling staves.
Fig. Copper cooling staves, pre-lined with silicon carbide bricks before shipping to the customer.
M HEAVY TECHNOLOGY specialists implement all types of blast furnace cooling systems.
The company’s unique development is the creation of an “adaptive” cooling system, the specific feature of which is automatic regulation of the cooling intensity of blast furnace elements depending on changes in the thermal state of the metallurgical unit, which reduces the wear of the lining and helps reduce heat losses and to a decrease in coke consumption.
Factors Influencing Productivity and Production
One of the main factors for optimal blast furnace operation is the correct charging of materials. The most important current solution is using a cone-less top charging device. In this issue, we provide a solution developed in cooperation with our partner, the DHM GROUP company, which supplies unique equipment – the cone-less top charging device HydroMech Top. The design of this blast furnace top equipment is a state-of-the-art solution that fits all blast furnace charging process requirements.
Main advantages of the cone-less top charging device HydroMech Top:
✅️ HydroMech Top fits into all existing blast furnace top structure dimensions without changing the angle of the inclined bridge.
✅️ The charge-distributing chute has the shape of a conical pipe with a range of inclination angles changing from 0° to 53°, which is not provided by any of the existing cone-less top chargers. This range makes it possible to implement directed charging over the entire cross-section of the top as well as maintain a concentrated charge layer precisely in the center.
✅️ All cone-less top charging device components are made without rubber or other non-metallic seals, allowing uncooled sinter operation.
✅️ The design of the chute and axial hole of the distributor is made so that the chute freely passes through the ordinary central charging door of the distributor’s route or the technological opening of the furnace dome. A door can also be made for changing the chute directly in the distributor body.
✅️ The centering device eliminates the influence of intermediate bins’ location with respect to the distributor, regardless of the number of charge routes.
Fig. Cone-less top charging device HydroMech Top
Taphole as a Main Equipment
The main equipment used in blast furnace cast yards is a taphole drilling machine, a taphole ramming machine, and a runner cover’ manipulator. A fundamental feature of modern equipment for cast yard maintenance is the use of hydraulic drives in machines and mechanisms. This feature makes it posible to achieve high technical performance with minimal overall dimensions of the equipment. We also cooperate with our partner, DHM GROUP, for this equipment.
Main advantages of taphole drilling machines of DHM GROUP:
✅️ Opening the tap hole regardless of its length or furnace volume.
✅️ Full automatic control mode with the ability to monitor the taphole length.
✅️ Optimal placement in the cast houses of any configuration.
✅️ Reliable operation with any ramming masses.
✅️ Precise positioning and reliable design allow the drilling of a perfectly smooth taphole channel without damage, significantly increasing the taphole block’s service life.
Fig.Hydraulic taphole drilling machines
Main advantages of taphole opening machines of DHM GROUP:
✅️ Their efficiency and reliability are confirmed by more than 20 years of trouble-free operation at our Customers’ enterprises.
✅️ The use of modern temperature control systems can remarkably reduce tap hole mass consumption.
✅️ A wide range of parameter settings ensures correct operation and guarantees the taphole closing.
✅️ Full automation of hydraulic equipment control processes.
✅️ The forces developed by the machine’s hydraulic drives guarantee well-planned and reliable operation with any modern and high-strength tapping masses.
✅️ The piston design prevents tapping material from getting behind the piston, ensuring uninterrupted operation and extending the equipment’s service life.
Fig. Hydraulic taphole ramming machine
Reducing hot metal temperature losses before draining into a mixer or ladle and efficient aspiration of the cast house when tapping smelt products is ensured by covering the main and transporting runners with stationary and removable covers.
Lifting and moving removable covers is carried out by hydraulic manipulators to provide access for servicing the hot metal taphole using drilling and ramming machines.
The main advantages of the DHM GROUP runner cover manipulator are:
✅️ It is adapted to any blast furnace volume; the load capacity of the manipulator is from 5 to 30 tons.
✅️ Work process safety. Complete coverage of the leading runner increases the safety of the personnel and ensures effective suction of gases and dust.
✅️ Wide range of models. The type of manipulator depends on the characteristics of the Client’s cast house.
✅️ 3 equipment operation modes. The operation can be manual, semi-automatic, or automatic at the operator’s choice
Fig. Runner cover manipulators.
Blast Furnace Equipment Safety Measures
An important factor influencing coke consumption and, consequently, the cost and environmental impact of blast furnace production is maintaining a high hot blast temperature, i.e., using modern hot blast stoves. Currently, many steelmaking plants use blast furnaces with an internal combustion chamber, the main feature of which is the placement of the checkerwork and combustion chamber in one casing in parallel. Also, a “tube-in-tube” burner is used in these hot blast stoves to which blast furnace gas (either pure blast furnace gas or a mixture of blast furnace gas with natural/coke gas) and combustion air from the fan are fed.
These solutions have several disadvantages:
- destruction of lining between the combustion chamber and the checkerwork chamber, which leads to the mixing of cold and hot blasts and, as a consequence, to a decrease of the blast temperature, as well as an increase in the amount of CO in the gases;
- the use of the “tube-in-tube” burner leads to incomplete combustion of CO, uneven distribution of combustion products along the checkerwork, high-temperature creep of refractory bricks in the area of combustion of blast furnace gas under the load of the lining of the combustion chamber, and so on;
- checkerwork blocks with channels with a diameter of 40 mm have a significantly smaller heating surface than used in modern hot blast stoves checker works with channel diameters of 30 and 20 mm;
M HEAVY TECHNOLOGY performs blast furnace modernization projects with minimal changes to the existing equipment (preservation of the current shell, maintenance platforms, fittings, etc.).
A ceramic burner is used as a burner device. This solution has the following advantages:
- a ceramic burner improves the mixing of air and gas to make combustion more complete and the released calorific value higher;
- the flame of a ceramic burner has a strictly vertical trajectory and spreads parallel to the walls of the combustion chamber, which eliminates the possibility of local overheating caused by the uneven temperature of the partition and prevents its burning (short circuit); subsequently, it significantly increases the HBS durability and increases the thermal efficiency;
- the burner works silently, with low gas pressure losses. The flame is well controlled; there are no gas pulsations; the heating is better than «pipe-in-pipe burners.»
To increase the heating surface area of the checkerwork chamber, our company replaced existing checkerwork blocks with cylindrical channel diameters of 40 mm. It replaced checkerwork blocks with conical channel diameters of 30 and 20 mm. These solutions make it possible to increase the heating surface area of the checkerwork almost twice.
An example of a checkerwork block with a conical channel, 30 mm in diameter.
An example of the operating efficiency calculating of different types of checkerwork blocks.
All of the above measures make it possible to maximize the efficiency and durability of the existing hot blast stoves at the lowest possible cost and improve the units’ environmental and economic performance.
Assistance in Blast Furnace Equipment
M HEAVY TECHNOLOGY Experience in Blast Furnace Equipment Modernization or Maintenance
At all blast furnaces, regardless of the subsequent gas purification stages and the use of “wet”- or “dry”- type gas cleaning plants, a dry dust catcher, or an inertial-type cyclone is installed at the first stage.
If a blast furnace dust catcher is installed and not a cyclone at the first stage, its efficiency is at most 40 – 50%. It captures only the coarse fraction of dust (>100 microns).
The main cleaning of blast furnace gases takes place in the subsequent «wet» stages, in which a huge amount of sludge is formed, which requires unique methods of preparation for disposal.
Existing sludge dewatering and disposal technologies are complex and expensive, require large areas for sludge sumps and storage tanks, and have higher operating costs, significantly affecting production profitability. The costs associated with the disposal of sludge (transportation, dewatering, etc.), even with the ineffective dewatering system at the plant, are 8–15 times higher than the costs of dry dust disposal.
How Does Znc Influence Gas-Cleaning
In recent years, even more serious problems have additionally been due to steelmaking waste recycling. They are associated with zinc.
As a sublimated product of smelting, zinc is removed from the blast furnace in gaseous form and is practically not captured in «dry»-type gas cleaning systems. As a rule, the main condensation of zinc occurs only during cooling gases in «wet»-type gas cleaning units, with its subsequent removal in the form of sludge. Thus, different blast furnace gas purification systems effectively separate dust into chemical components such as zinc and lead. According to numerous studies, zinc content in the blast furnace sludge is 120–150 times higher than in dry flue dust from BF dust catchers. The higher the dust-catching ratio of the «dry» cleaning stage is, the higher the separation degree of the above chemical components (zinc, lead). However, the zinc problem has not been resolved. In that case, it will become even more aggravated over time since, with the existing technology, this element is constantly circulating in the system, which leads to its accumulation in circulating products (sludge, agglomerate, etc.) with an inevitable concentration increase. In this case, the degree of the blast furnace gas saturation with zinc vapor can reach such a critical state that it will unpredictably condense on any cooled surface of the furnace lining and gas ducts, destroying the lining and leading to massive clogging of gas lines.
These problems can be solved by partially modernizing the existing blast furnace gas cleaning equipment by radically increasing the efficiency of its first stage – «dry»-type inertial dust catchers.
Currently, the operating efficiency of dust catchers’, operating on the gravitational principle of dust precipitation, does not exceed 40–50%, which is insufficient for the efficient operation of the entire blast furnace gas cleaning system and for the efficient disposal of industrial waste (sludge).
Dust Catcher Design Features
An analysis of the design features of existing blast furnace dust catchers showed that they have all the necessary conditions for converting them into combined inertial-cyclone units, the efficiency of which is much higher than that of the existing ones in terms of output gas dust content.
The main idea of the proposed modernization of blast furnace dust catchers is that two stages of cleaning are conventionally combined in the existing body of this unit:
- the stage of inertial dust precipitation in the central (paraxial) zone of the dust catcher body;
- the stage of centrifugal-vortex dust separation in the dust catcher casing’s peripheral (near-wall) zone.
A schematic diagram of such a modernized dust catcher is shown in Fig. 1.
As we can see from the presented figure, the modernization of the dust catcher is quite simple and consists only of partial re-equipment of its internal filling with complete preservation of the existing structures and auxiliary equipment.
The dust catcher works as follows: the blast furnace gas supply to the dust catcher is carried out according to the existing scheme through a lined gas duct lowered inside the casing. The speed of gases in the duct is ~ 12 – 15 m/s. When leaving the duct, the gas flow enters the dust-settling chamber of the inertial cleaning stage, located in the central (paraxial) zone of the dust catcher body. In this chamber, a sharp expansion of the gas flow occurs with a speed drop to 1.8 m/s and a change in the direction of gas movement by 180°. Here, dust fractions >100 µm are precipitated from the gas flow under the influence of gravitational and inertial forces. Taking into account the dispersed composition of the blast furnace dust, the efficiency of the inertial cleaning stage of a modernized dust catcher will be ~ 40 – 50%.
Blast-furnace gas, initially cleaned from large dust fractions, uniformly enters from the central precipitation chamber, the inter-tube space of the cyclone cleaning stage, located in the peripheral (near-wall) zone of the dust catcher body.
The degree of dust capture at the dust catcher’s second (cyclone) stage will be 80 – 90%. And the overall efficiency of the dust catcher is expected to be 90 – 95%.
The presented design of the modernized blast furnace dust catcher will provide for reliable and efficient operation throughout the entire furnace campaign.
Fig. Modernized blast furnace dust catcher
- Supporting structures
- Block-type multi-cyclone element
- Exhaust pipes
- Dust collecting bin
- Partition shell
How Can M Heavy Technology Help
Our company also has extensive experience developing equipment for preparation and feeding raw materials into a blast furnace, such as bunkers for sinter, coke, additives and other materials, screens, chutes, skips, skip winches, conveyors, etc.
Suppose it is necessary to increase the design performance of a blast furnace. In that case, our company has experience in reconstructing the bin trestle and the system for feeding materials into the blast furnace, incl. increasing the valuable volume of the skip and replacing the existing skip winch with a greater capacity.
Fig. Material supply with two feeders onto one screening machine.
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Conclusion (Summary)
Specific technological processes of blast furnace smelting impose special requirements on equipment for blast furnace production. Many years of experience with M HEAVY TECHNOLOGY specialists in creating and maintaining blast furnace production facilities allows us to provide our Customers with equipment that will improve the reliability of production processes and make them more economical and environmentally efficient.
Author of the article: Tetiana Bondarieva
