Intro.
In 2025 M HEAVY TECHNOLOGY carried out an audit for a project of switching blast furnaces BF-2, BF-3 and BF-4 at “QARMET” JSC from fuel oil to natural gas. The scope included:
- thermal and material balance calculations,
- CFD – modeling,
- development of hot blast stove operating modes with the use of gaseous fuel.
In addition, the company’s experts carried out a detailed analysis of the project documentation in the process engineering (PE) and automated process control systems (APCS) sections, developed for gasification of the blast furnace shop.
As a result of implementing M HEAVY TECHNOLOGY technical solutions the Client achieved:
1. Cutting hot metal production costs
Savings in coke consumption lead to a significant reduction in smelting costs.
2. Production expansion
Higher productivity without substantial capital investments
3. Confidence in furnace reliability
CFD modeling demonstrates that thermal conditions remain safe.
4. Pre-developed equipment operating modes
Hot blast stoves operate efficiently and ensure the required blast parameters.
The Importance of Gas Supply in Metallurgical Plants.
Gas supply is a critical component of metallurgical plant infrastructure. Reliable natural gas availability ensures stable furnace operation, precise temperature control and continuous combustion. Any disruption can cause production delays, reduced quality, and operational risks.
How Fuel Choice Directly Impacts Operations.
Choosing the right fuel is strategically vital. Different fuels affect:
- Technological Stability
Natural gas provides stable combustion and uniform heat distribution, ensuring consistent blast furnace thermal efficiency.
- Economic Efficiency
It reduces fuel costs, lowers coke consumption and optimizes energy use.
- Environmental Performance
It minimizes CO₂, SO₂ and particulate emissions, supporting sustainable ironmaking and ESG compliance.
Assessment of efficiency of changing over to gas in terms of fuel consumption and productivity.
Scope of Work.
Balance calculations.
We analyzed how changing over from fuel oil to natural gas affects blast furnace operation. To do this, detailed material and heat balance calculations were performed. They showed:
✔ Reduction in coke consumption.
Switching to natural gas reduced coke consumption on average from ~540 to ~465 kg per ton of hot metal. This means a significant fuel saving without changing the burden composition.
✔ Blast furnace productivity gains.
Productivity increases up to 5300 t/day, while the utilization coefficient of the useful volume reaches 0,95, which corresponds to the global performance level of large blast furnaces.
✔ Maintaining the quality of hot metal and slag.
The product composition remains stable:
- Fe in hot metal — about 94%
- Carbon— ~4,18%,
- Manganese and silicon — within standard technological ranges,
- Slag basicity— 1,30–1,36.
✔ Improvement of top gas parameters.
The calorific value of the gas increases to 1100 kcal/m³, making the process more energy-efficient.
Conclusion:
Changing over to natural gas is economically beneficial, technologically stable and does not require changes to the burden composition or final product quality.
Fig. Computational grid model (detail).
Computer simulation of thermal processes inside the furnaces.
M HEAVY TECHNOLOGY carried out detailed CFD modeling of combustion processes in blast furnaces No. 2, 3, and 4 at “QARMET” JSC to assess the impact of replacing fuel oil with natural gas.
CFD analysis of natural gas injection into blast furnace.
Input data:
For calculations we used furnace profile drawings and the results of blast furnace process calculations. Particular attention was paid to the thermal load on the lining and cooling staves when using natural gas instead of fuel oil.
Methods and approach:
A blast furnace is a complex engineering system where chemical and physical processes occur simultaneously.
M HEAVY TECHNOLOGY experts developed a digital model of a blast furnace section, including tuyeres, cooling staves and the porous burden. The model accounted for:
- blast velocity and temperature,
- natural gas consumption,
- distribution of heat flows,
- changes in gas composition.
CFD modeling using the finite element method (FEM) was applied for the analysis.
- The calculation included a furnace sector with two adjacent tuyeres and the upper layer of cooling staves.
- The burden charging zone was modeled as a porous medium, allowing optimization of computational resources without loss of heat transfer accuracy.
- Combustion of methane and fuel oil was modeled using single-step reactions with turbulence taken into account (k–ω model).
- The gas phase was calculated as an ideal gas.
Model features:
The tuyere raceway was formed artificially, with a surrounding zone defined for carbon supply and resistance to gas flow. The counter-current movement of the burden was accounted for through local negative heat fluxes calculated based on the smelting heat balance.
Fig. Geometric 3D design model.
Impact of natural gas on blast furnace thermal efficiency.
- Switching to natural gas does not increase the thermal load on the lining.
- Furnace structures and cooling systems remain within a safe operating range.
- No additional measures for equipment reinforcement or replacement are required.
As a result of CFD modeling the Client received confirmation that replacing fuel oil with natural gas is safe for blast furnaces and enables increased process efficiency without additional capital investment.
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Ensuring stable blast temperature.
To ensure a stable hot blast temperature when switching from fuel oil to an enriched gas mixture M HEAVY TECHNOLOGY experts carried out a comprehensive optimization of blast furnace stove operating modes.
The work included development of optimal “heat–blast” cycles, taking into account the actual condition of the equipment, design features of the hot blast stoves and changes in the fuel balance when using natural gas.
What was taken into account in the calculations?
- target blast temperature of 1100–1200°C,
- gas mixture composition when natural gas is added,
- design features of each type of hot blast stove,
- optimal “heat –blast” cycles.
Adjustment of hot blast stove operating modes when switching to natural gas.
For all types of hot blast stoves at each blast furnace, verification thermal calculations were carried out in two stages:
- Engineering thermal calculation – determination of thermal inertia, heat storage capacity of the checkerwork and permissible cycle parameters.
- CFD modeling – detailed analysis of temperature fields and gas dynamics under transient conditions.
This approach made it possible to base the calculated operating modes not on standard assumptions, but on the actual physical characteristics of the equipment.
Fig. Temperature distribution contour in the tuyere plane.
Step 1.
Comprehensive thermal calculations.
Justification of cycle duration based on the thermal inertia criterion.
Unlike the standard regulatory method, the project applied a reverse calculation approach — based on the mass and heat capacity of the active checkerwork.
As part of the calculation:
- the mass of the active checkerwork was determined based on geometry and specific properties of the brick;
- the heat storage capacity of the regenerators was calculated at the specified blast flow rate;
- duration of the blasting period was determined based on limiting the drop in the average bulk temperature of the checkerwork, ensuring a stable hot blast temperature until the end of the cycle;
- the heating time was calculated taking into account the pairwise-parallel operating mode, valve switching time, and operational reserve.
The result was physically justified cycle time parameters, tailored to each type of hot blast stove.
Heat balances and consumption characteristics.
For the calculated operating modes a heat balance of the “fuel – checkerwork – blast” system was performed.
During the work:
- the amount of heat required to heat the blast to temperatures of 1100…1200°C was determined;
- taking into account the efficiency of the hot blast stoves, the required heat input from fuel combustion was calculated;
- setpoints for fuel gas and combustion air flow rates were established;
- the calculated flow rates were verified for compliance with the technical capabilities of the equipment.
Step 2.
CFD modeling of hot blast stove operation.
Model and problem setup.
CFD modeling was performed for all hot blast stoves under transient conditions and covered two operating stages:
- the combustion process of the blast furnace gas with the addition of natural gas in the combustion chamber;
- heat transfer from the checkerwork to the cold blast.
Three-dimensional models of the hot blast stoves were developed based on the client’s detailed drawings at full scale and included:
✔️ combustion chamber and dome;
✔️ checkerwork block;
✔️ under-checkerwork support structure;
✔️ lining, with consideration of the thickness and thermophysical properties of the materials;
✔️ burner devices of various types:
- burner devices of the “Gipromez” hot blast stove;
- ceramic burner of the “Danieli Corus” hot blast stove;
- dome-mounted burner of the “Kalugin” hot blast stove.
Applied calculation methods.
The calculations used advanced models that adequately describe real processes in hot blast stoves:
- non-premixed combustion — for modeling combustion with separate supply of fuel and oxidizer;
- standard k–ε turbulence model with near-wall resolution;
- ideal gas model for the gas phase;
- coupled heat transfer — convection, conduction, and radiation;
- radiative heat transfer using the Discrete Ordinates (DO) model;
- accounting for flue gas radiation using the WSGGM spectral model for water vapor and CO₂.
This set of models made it possible to reliably assess temperature fields, heat fluxes, and heat transfer efficiency under real operating conditions.
Fig. Heat flux distribution contours on the lining surface (left image: natural gas; right image: fuel oil).
Results and benefits for the client.
As a result of the comprehensive thermal calculations and CFD modeling:
- operating modes of the hot blast stoves using an upgraded gas mixture were developed and validated ;
- achievement and stable maintenance of target hot blast temperatures were ensured:
- “Gipromez” HBS — 1100–1125 °C;
- “Danieli Corus” HBS — stable 1120 °C;
- Kalugin-design stoves — 1180–1200 °C;
- “Gipromez” HBS — 1100–1125 °C;
- possible operation in a pairwise-parallel mode with extended blast cycle durations was confirmed;
- a thermal capacity margin was identified for individual units, enabling flexible control of operating modes;
- higher efficiency of modern hot blast stove designs was demonstrated at comparable fuel consumption levels;
- high consistency between the results of engineering calculations and CFD modeling was achieved.
The developed operating charts are adapted to the actual condition of the equipment and are recommended for industrial implementation.
Preparation of operating instructions and process regulations.
As part of the completed work, process instructions and regulations were developed:
- Technical regulation for natural gas injection into blast furnace tuyere systems.
- Process regulation for mixing blast furnace gas and natural gas for hot blast stoves.
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Conclusions.
The change-over of blast furnaces from fuel oil to natural gas is accompanied by changes in thermal and gas-dynamic operating conditions and requires thorough engineering analysis.
Application of thermal engineering calculations, development of hot blast stove operating modes and CFD modeling of combustion processes made it possible to ensure acceptable thermal loads, reduce operational risks and maintain stability of the blast furnace process.
The use of engineering calculations and CFD modeling methods is a necessary condition for improving energy efficiency and reliability of blast furnaces when modernizing the fuel system.