Importance of the Cooling System for Reliable Blast Furnace Operation
The cooling system is one of the main factors of reliable blast furnace operation. Except in emergencies, its failure can result in losses of tens of millions of dollars and a complete production cycle stop.
Energy efficiency is the primary indicator of effective blast furnace stave cooling system operation. Reduction in heat losses leads to a decrease in fuel and energy consumption.
Ecological factors also play an essential role in the system’s operation. It means minimization of water consumption by the blast furnace.
What Is a Cooling System of a Blast Furnace?
Blast furnaces are equipped with cooling systems to protect the furnace shell from excessive overheating and burnouts, which, along with the lining, ensure the furnace’s lifetime.
What does a blast furnace water cooling system consist of?
Cooling water pump house
Systems of utility pipelines
They feed cooling water to the blast furnace and distribute it among the cooling elements.
Cooled elements
As a rule, these are cooling staves located inside the furnace shell. Sometimes, the furnace shell has an outside cooling, known as “external shower cooling,” when water is sprayed onto the outer shell surface and cools it down. In rare cases, so-called “shaft panels” are used as cooled elements. But there is a lot of other process equipment that requires cooling: tuyeres, charging device elements, hoists, charging device elements, measurement and control instrument components, etc.
Outlet cooling system pipelines
They carry heated water away from the furnace to the equipment, where it is cooled, and then to the pump house.
Equipment in which water, heated in the blast furnace, is cooled down:
Cooling towers, various heat exchangers (“water/water,” “water/air” type and others).
Read more on blast furnace equipment.
Blast Furnace Cooling Process
Based on the above, any cooling system operation can be described as follows: through a system of pipelines, water is fed from the pump house to the elements of the blast furnace, which have to be cooled down, where it is heated and then directed to the cooling equipment through a system of outlet pipelines. Afterward, it goes to the pump house again; thus, the cooling cycle is over.
Cooling Staves are Essential Elements of the Blast Furnace Cooling System
They are cooled elements of the blast furnace located inside the furnace shell, protecting it from thermal damage.
M HEAVY TECHNOLOGY has experience in the development and supply of all known types of cooling staves made of:
- Cast iron,
- Copper (horizontal and vertical),
- Steel.
Each type of such stave has advantages and disadvantages, according to which it is decided in what blast furnace areas and under what conditions the corresponding kind of cooling stave should be installed.
An example of the application of all the above-mentioned stave types can be the projects implemented by M HEAVY TECHNOLOGY at blast furnaces No.3 and No.4 of “MK AZOVSTAL” PJSC and blast furnace No.3 of “MK Zaporizhstal” PJSC.
Copper cooling plates
These staves are located in the tuyere zone and have a flat shape without “teeth”.
The staves located in the bosh, belly, and lower rows of the stack have a flat design with a “dovetail” connection type.
All staves are pre-lined with silicon carbide bricks before installation.
Main advantage of copper cooling staves
They have a high thermal conductivity. It makes it possible to take over and transfer maximal thermal loads to the cooling system without their destruction and build up a protective skull layer on the stave surface or lining.
Main disadvantages
High cost and abrasive wear if not protected with refractory materials or a scull layer.
The best areas to use
They should be installed in areas with maximum thermal loads, where all conditions for increasing the skull layer are present and the contact with smelted charge material is minimal.
Cast-iron cooling staves
They are located in the hearth, hearth bottom (except for the tuyere zone), the middle and upper part of the stack, and the furnace top area. Cooling staves with refractory bricks pre-lining and without “teeth” are installed in the hearth and hearth bottom, and “dovetailed” staves are used in the stack.
Main advantage of cast-iron cooling staves
Relatively low cost and high wear resistance.
Main disadvantage
Significantly lower thermal conductivity if compared to copper cooling staves.
The best areas to use
Based on the cast-iron cooling plate characteristics, they should be installed in the zones with allowable heat loads and where contact with solid burden materials is possible.
Steel cooling staves
The main advantage of steel cooling staves over cast-iron ones lies in the specific design feature, where the material of a cooling plate body and coils is the same. During cast sealing of the cooling stave, the cooling coil melts and becomes one piece with the stave body. No gap between the body of the stave and the cooling coil increases the thermal conductivity of the entire stave.
Steel staves have a flat shape with a “dovetail” connection and are pre-lined with silicon carbide bricks.
In the cast-iron type, a gap between the cooling coil and the body significantly reduces the entire stave’s thermal conductivity. It can eventually destroy the stave if thermal loads exceed allowable limits.
Based on the above-mentioned, steel cooling staves are to be installed in a transition zone between copper and cast-iron cooling staves to even the heat flow between the staves with a high and low heat conductivity.
Benefits of an Effective Blast Furnace Cooling System
The benefits of upgrading and using an efficient blast furnace cooling system are:
- Blast furnace operation without stops for major overhauls of the 1st category within 15–20 years, despite the intensification of blast furnace processes under the conditions of PC or hydrogen-containing gas injection technology, operation with a great amount or even 100% of pellets.
- Decrease of coke or any other equivalent fuel consumption. Saving electric power or any other energy resources.
- A modern “closed-loop” system makes it possible to minimize water consumption for the system’s needs. Due to the energy efficiency of modern cooling systems, the carbon footprint decreases, and the “temperature” pollution of the environment is also minimized.
Check out blast furnace design services from M HEAVY TECHNOLOGY.
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Industries
Modern cooling systems find application in all industry branches. They are particularly crucial in metallurgy, mining, and processing works. A well-functioning makes it possible to prevent overheating of cooled elements of devices and, in this way, to extend their service life, minimize thermal losses and environmental impact, and save fuel resources.
What Does Modernization of a Blast Furnace Cooling System Look Like?
M HEAVY TECHNOLOGY has completed dozens of projects on upgrading existing cooling systems. The majority of these projects had a low budget. However, after project implementation, the systems met the requirements of all modern global practices and, in some aspects, were even superior to them.
The primary customer requirements that our company fulfilled during the modernization of the existing systems were:
– To retain the existing shell, maintenance platforms, and other blast furnace elements;
– Minimal modernization costs;
– Minimum possible repair and furnace shutdown time;
– Extending minimal operation time without major first-grade overhauls up to 15÷20 years within the furnace campaign;
– Reduction of coke or equivalent fuel consumption;
– Reduction of water consumption by the blast furnace, minimizing or eliminating water discharge after furnace cooling.
Conversion of evaporative cooling systems with natural circulation to “adaptive” closed-loop ones utilizing chemically purified water, performed by M HEAVY TECHNOLOGY
As part of these modernization projects, the following works have been performed:
- – Replacement of cast-iron cooling staves in the bosh, belly, and bottom rows of the stack with copper staves, with silicon carbide bricks pre-lining, installation of thermocouples for measurements of the cooling stave body temperature;
- – Installation of pumping units with E-motor speed frequency control;
- – Installation of heat exchangers of the “water/water” or “water/air” type;
- – Installation of a new or modernization of the existing automation system for pumping unit speed control, depending on the copper cooling staves temperature;
- – Almost all existing piping lines remained.
Due to these upgrades, the Customer received:
1. The most reliable cooling system, which makes provision for furnace operation without major repairs, of the 1st category for at least 15 ÷ 20 years.
2. An incredible number of backup modes that provide for the system operability under all operating conditions:
- Optimal operation mode with the use of “cold” chemically treated water;
- Operation mode with the use of “hot” chemically treated water in the event of failure of heat exchangers or interruption of the process water supply to heat exchangers of the “water/water” type;
- Evaporative cooling operation mode with natural circulation in the event of a complete loss of power supply, failure of all pumping units, or damage to the main pipelines;
- Operation mode with the use of standby process water if all previous modes do not work.
3. Energy efficiency, a 5-times reduction of thermal losses, resulting in a coke consumption decrease to 55 kg per t/HM, power consumption reduction by the system to 300 kW/h, and minimization of the process or make-up water demand.
An example of performance indicators of two identical blast furnaces at “MK Zaporizhstal” PJSC, with the modernization of the cooling system and installation of an «adaptive» cooling system and without it:
| BF №2 | BF №4 | |
| Cooling | Hot chemically treated water with forced circulation | |
| Lining | Silicon-carbide bricks (λ=17-20 W/mК) | Chamotte brick (λ=1,65 W/mK) |
| Stack cooling staves | Two rows of copper ones (λ=380 W/mK) | Cast iron (λ=38,8 W/mK) |
| Hot metal daily production | Average – 3400 t/day Maximum – 3700 t/day | Average – 3050 t/day |
| Average PC flow rate | 152 kg/t of HM | 135 kg/t of HM |
| Average coke flow rate | 365 kg/t of HM | 420 kg/t of HM |
| Average steam production capacity | Up to 1,8 t/h | Up to 10 t/h |
Conversion of process water cooling systems to “adaptive” closed-loop cooling using chemically treated water
For this task, it was necessary to carry out the entire range of works that are usually performed during evaporative cooling systems modernization, as well as to take the following additional measures:
- To lay a new piping for the connection of the staves;
- To install an expansion tank for chemically treated water or drum separators for feed water.
The benefits are the same as with an evaporative cooling system upgrade. Besides, there is no need to supply process water for the furnace cooling.
Conversion of chemically treated water cooling systems to «adaptive» closed-loop cooling using chemically treated water
In this case, modernization works were minimal:
- Installation of thermocouples in the existing copper cooling staves;
- Installation of E-motor frequency control devices on the existing pumping units;
- Modernization of the existing automation system for speed control of the pumping units depending on the temperature of the cooling stave body.
The benefits of this modernization are similar to the two previous modernizations.
Why Choose Blast Furnace Cooling System of M HEAVY TECHNOLOGY
Team of highly qualified engineers: Many years of experience
The company has implemented dozens of successful projects on creating new and modernizing existing blast furnace cooling systems.
Maximum customer focus
The company finds an optimal solution for each Customer. It is the developer of many proprietary technologies and unique and patented solutions.
Сomprehensive approach and full range of services
The company carries out concept and technology development, engineering, equipment supply, and commissioning to bring the facility to design or warranty performance.
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M HEAVY TECHNOLOGY Cooling System Professionals and Engineers
Case Studies
M HEAVY TECHNOLOGY is the author of “adaptive” blast furnace cooling systems and has performed several successful implementation projects over the past few years.
Experience in implementation of “adaptive” blast furnace cooling systems at Metinvest holding enterprises in Ukraine
The main impetus for the modernization of the cooling systems at “Metinvest” blast furnaces was the introduction of the technology of injecting pulverized coal (PCI) into the BF hearths at the holding enterprises.
Injection of large amounts of PC along with accumulated problems at the enterprises, such as lack of necessary pre-treatment of the charged raw materials, poor quality of burden materials, and no possibility to control the precise distribution of the burden materials on the stockline level, intensification of the of blast furnace smelting process, exceeding the design indicators for daily hot metal production resulted in failures of the cooling systems.
The first “adaptive” cooling systems were implemented at “MK Zaporizhstal” PJSC. At that time, evaporative cooling systems with natural circulation cooled the bosh and BF stack. Modernization was carried out on a staged basis with a minimal impact on the blast furnace structures. All existing blast furnace shells remained, the inlet branches of the new cooling staves were connected to the existing openings in the shell, and practically all piping was kept.
In the first stage, the evaporative cooling system was modified to a system in which “hot” chemically treated water with forced circulation was used.
The main feature of this system is that the use of circulation pumps made it possible to shift the water boiling point from the staves’ cooling channels to the rising headers. Convective heat transfer occurs below the boiling point in the staves’ cooling channels. Conversion from liquid to steam occurs only in the case of pressure drop in the risers, going to the drum separators. The boiling temperature threshold at this pressure level can be adjusted by controlling the water flow rate through frequency converters installed on the E-motors of the circulation pumps.
At this stage, the following modifications were made:
- Installation of vertical copper staves, pre-lined with silicon-carbide bricks, in the bosh and lower stack rows. The staves are equipped with thermocouples for measuring their body temperature;
- Construction of a pump house. Pumping units are equipped with E-motor frequency control devices;
- Automatic process control system enabling you to control the cooling water flow rate depending on the stave body temperature.
In the second stage, the cooling system utilizing “hot” chemically treated water was converted into a system with “cold” chemically treated water. For this purpose, “water/water” heat exchangers were added to the circulation loop of the cooling system.
The main effect obtained from the implementation of these systems:
- Cooling staves resistance in the most heat-loaded zone (bosh, belly, bottom rows of the stack); during the entire period of operation of these systems, not a single failure of a copper stave was detected;
- Reduction of heat losses, in some cases, by five times;
- Reduction of coke flow rate to 55 kg/t of HM;
- Reduction in power consumption, up to 500 kW per one cooling system;
- Possibility to intensify blast-furnace melting processes without the risk of cooling staves burnouts and higher product output.
Modernization of cooling systems at blast furnaces of “МК Azovstal” PJSC
Modernizing cooling systems at the blast furnaces of “Azovstal” PJSC took place as part of more extensive overhauls, so implementing “adaptive” cooling systems was performed in one stage. Also, “water/air” type heat exchangers were used, which made it possible to make these systems truly closed and, as an additional advantage, to eliminate the use of process water.
All other advantages obtained at the furnaces of “MK “Zaporizhstal” PJSC are the same as at the furnaces of “MK “Azovstal” PJSC.
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