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Metallurgical Industry

Metallurgical Industry
November 28, 2023


Steel smelting includes many production processes such as ironmaking, steelmaking, and rolling. The smelting process uses combustion gases, inert gases as fuel or protective gases, while also producing a large amount of process gases. Detecting and analyzing the content of these gases is important to optimize production, approve safety control, energy recovery, environmental protection, and energy conservation.


Generally speaking, it takes about 2.1× 107kJ of energy to produce 1 ton of crude steel, which can generate approximately 4.2 × 106kJ blast furnace gas and 1.0 × 104kJ of converter gas. This gas as by-product is approximately 30% -40% of the total energy revenue of steel factory. Therefore, achieving the recycling and reuse of by-product gas can greatly reduce the cost of the steel and metallurgical industry. The value of gas recovery depends on the concentration of energy gases such as CO in the gas, and the online monitoring system for CO and O2 is the key to measuring gas concentration.



Ensure the safety of production

The CO concentration in blast furnace and coke oven gas is relatively high, and its mixed explosion limit in air is 12.5% to 74%. As long as the concentration reaches the explosion limit, it is very easy to explode when encountering open flames. The harmfulness and explosion potential of carbon monoxide are related to its concentration, so gas measurement system must be used for real-time monitoring of CO and O2 in coal gas.


At present, there are more than 20 steel joint factory in China with an annual steel production of 4 to 20 million tons, of which a considerable number of factory have blast furnace gas emissions of 100000 to 300000 m3/H. Based on such emissions, it can be inferred that metallurgical factory can seriously affect the air quality for several kilometers around, causing air pollution. Severe air pollution not only endangers the physical health of surrounding residents, but also deteriorates the ecological environment. In short, the quality of the surrounding environment of metallurgical factory is closely related to the concentration of CO emitted.


Typical metallurgical process flow and process gas monitoring points:


1.  Blast furnace top gas detection system

Blast furnace gas is a byproduct generated during the ironmaking process, with main components including CO20-30%, CO2 15-30%, N2 50-60%, H2 1-3%, CH4, O2, etc. Its calorific value is around 3500kJ/m3. The main function of gas detection is to reduce the emission rate of blast furnace gas, fully utilize blast furnace gas, and is one of the important measures for energy conservation, consumption reduction, and improvement of energy consumption indicators.


2. Online gas analysis system for blast furnace coal injection 


Single point detection and multi-point inspection methods (automatic, manual) can be used.

  • The inlet of waste gas from ball mill in the powder making system Ÿ
  • Bag filter waste gas outlet Ÿ
  • Coal powder silo inlet, etc

The multi-point inspection method can use a set of systems to simultaneously detect points such as bag filters, mills, and coal powder silos.


The function of the online gas analysis system for blast furnace coal injection is to prevent the explosion and combustion of coal powder under three conditions: gas concentration, oxidant (O2 concentration), and ignition source. Controlling the concentration of O2 can greatly reduce the risk of explosion and combustion.


3.  Online gas monitoring system for converter gas recovery

The function of converter gas recovery: The efficiency of converter gas recovery is one of the important parameters for measuring energy conservation and consumption reduction in modern steel factory. The main gases and ranges analyzed for converter gas recovery are CO and O2.

  • Analyzing the effect of CO concentration: To improve the actual efficiency of converter gas recovery, it is generally set to start recovery when the content is greater than 30%
  • Analyzing the role of O2 concentration: ensuring the safety of converter gas recovery, with national standards controlled within 2%



4.  Online gas monitoring system for coke oven gas



Measurement points

Gas and range

Measurement purpose

Before and after electric tar gas capture

O2  0-5%

Production safety

Dry quenching circulating fan outlet

CO 0-10%; H2 0-3%; CO2 0-20%

Waste heat utilization and energy conservation

Gas pressurization station

CO 0-30%; CH4 0-20%; H2 0-80%

Energy Saving

Before and after desulfurization tower

SO2; O2

Environmental protection and process control

Clean gas main pipe


Environmental protection and quality control



5.  EAF arc furnace flue gas monitoring system

During the smelting process of an electric furnace, a large amount of high-temperature dusty flue gas is generated, which carries about 11% of the total energy input into the electric furnace, and some even reach up to 20%. At present, the smoke exhaust treatment facilities inside electric furnaces are still mainly water-cooled, and the waste heat recovery system of electric furnace smoke is still in its initial stage. Both steelmaking electric furnaces and ferroalloy electric furnaces, whether open or closed, use vaporization cooling. In recent years, with the widespread application of waste heat utilization technologies such as high-temperature radiation converter vaporization cooling and heating furnace vaporization cooling in the domestic market, the significant economic and social benefits obtained from the electric furnace flue gas waste heat recovery device will be of great significance for domestic enterprises to save energy, reduce consumption, and improve economic benefits.




Monitoring the gas inside the flue plays an important role in EAF (electric arc furnace) steelmaking process. The following are some main functions: 

  • Safety monitoring: Toxic gases such as carbon monoxide (CO) and sulfur dioxide (SO2) may be generated inside the furnace. By regularly monitoring the concentration of these gases, it is possible to ensure the safety of the working environment and take necessary measures to prevent operators from being exposed to harmful gases.
  • Environmental monitoring: The flue gas may contain some harmful substances to the environment, such as nitrogen oxides (NOx) and dust. By monitoring the emissions of these gases, it is possible to ensure compliance with environmental regulations and reduce negative impacts on the surrounding environment.
  • Production process control: Monitoring of flue gas can also be used to control process parameters inside the furnace. By monitoring the composition and concentration of gases, the operating conditions inside the furnace can be adjusted to optimize the production process and improve the efficiency and quality of steelmaking in the furnace.
  • Energy utilization optimization: Monitoring some components in flue gas, such as carbon monoxide, can help optimize energy utilization. This helps to improve the combustion process, reduce energy waste, and improve the energy efficiency of the furnace.
  • Fault diagnosis: The monitoring of flue gas can also be used to diagnose possible problems inside the furnace. Abnormal gas composition or concentration may indicate faults or abnormal process conditions in the furnace, and timely measures should be taken for maintenance and adjustment.


The main gases that are usually of concern with conducting gas monitoring in the EAF (electric arc furnace) flue,:

  • Carbon monoxide (CO): It is a product of combustion, but excessive CO is toxic. Monitoring CO concentration can ensure sufficient and safe combustion process in the furnace.
  • Sulfur dioxide (SO2): It is the oxidation product of sulfur in the raw materials burned in the furnace. High concentrations of SO2 may pose a threat to the environment and human health.
  • Nitrogen oxides (NOx): A group of gases formed during the combustion process, including nitrogen oxides. High concentrations of NOx may also be harmful to the environment.
  • Particle matter: including smoke and other suspended particles. The monitoring of particulate matter helps to understand the combustion efficiency inside the furnace and its impact on the environment.
  • Oxygen (O2): Monitoring oxygen concentration helps control the combustion process, ensuring sufficient oxygen supply to support combustion, and avoiding the generation of harmful gases from incomplete combustion.
  • Water vapor (H2O): The water vapor content in the flue gas can affect the temperature and efficiency of combustion. Monitoring water vapor helps optimize the process conditions inside the furnace.

Overall, by monitoring the gas inside the EAF flue, real-time control and optimization of the production process can be achieved, ensuring production safety, environmental protection, and improving production efficiency.


SIGAS SGS Metallurgical Process Gas Analysis System


  • Realize simultaneous detection of multiple components, with built-in real-time component interference calibration function to remove cross interference caused by various mixed gases;
  • The infrared gas analyzer adopts industrial high-precision infrared modules to ensure high-precision and high stability gas concentration detection;
  • The infrared gas analyzer is equipped with an automatic calibration function, which greatly reduces maintenance and prevents data drift; Ÿ
  • Configure zero point and full-scale point calibration, and also third point calibration, with the third point calibration value limited to 35% Between 75%, ensuring good linearity; Ÿ
  • The direct extraction sampling method using electric heating temperature control dry method has fewer auxiliary links compared to other methods, high reliability, and shielding against harsh on-site environments such as large dust. Truly reflecting the content of smoke components, with no additional errors, and high measurement accuracy;
  • The pre-treatment completes the purification, dust removal, and dehumidification of the sample gas, with a filtration accuracy of up to 0.1 μ The ultra clean, constant temperature, and stable flow sample gas that meets the requirements of the analytical device is continuously fed into the analytical instrument, ensuring the accuracy and long-term reliability of the analytical device; Ÿ
  • The probe filter adopts a high-efficiency specialized filter manufactured by a special process, which has the characteristics of high strength, good adaptability, and high filtration efficiency. The adoption of high-efficiency filters, reasonable filtering processes, and automatic blowing of sampling pipelines ensure continuous sampling and long-term reliable operation of the system under high dust conditions; Ÿ
  • The entire dry process of the system includes the use of 316L anti-corrosion stainless steel, polytetrafluoroethylene material or special anti-corrosion treatment for the sampler, sampling tube, various pipe joints (in contact with the sample gas), and extraction pump, which improves the system's anti-corrosion performance and ensures its service life; Ÿ
  • The system adopts PLC control and intelligent analytical instruments, with high automation, small maintenance workload, and fast and convenient data processing; Ÿ
  • The analytical instruments in the system have self diagnostic functions and main instrument component fault alarm functions;
  • Advantages of in-situ laser systems: (single sided flange installation)

-      Can withstand a dust concentration of 30g/m3;

-      Purging, fully automatic EPC blowing technology, can obtain the best blowing flow rate ratio to achieve optimal protection;

-      Zero point and self calibration function;

-      Equipped with a zero point reference chamber (reducing light source or circuit noise, improving lower limit measurement reliability and stability);

-      self calibration technology (calibration free), achieving "calibration free" measurement, significantly reducing the frequency of range calibration and reducing standard gas consumption;

-      Probe temperature resistance: -20...+400 ℃;


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