Steel blast furnace

Blast furnaces remain a vital component of the modern steel production industry, and the ProC-TOF industrial gas analyser provides the gas analysis data required for ironmaking. The use of mass spectrometers in blast furnace equipment at steelworks will improve product quality and reduce production costs, as demonstrated in the following areas:

Improved steel production efficiency

Reduced coke consumption

Ensuring consistent quality of primary steel

Ensuring safe operating procedures

The ProC-TOF process mass spectrometer is used to measure CO, CO₂, N₂ and H₂ in top gas. The mass spectrometer analyses top gas continuously, with a reliability of over 98 per cent for blast furnace gas analysis; calibration of the mass spectrometer is fully automated. Its accuracy is routinely checked and compared against calibration standard gases. Gas analysis is used to optimise the blast furnace process, including the rate of coke consumption during the reduction process and temperature control within the furnace. Cooling water leaks can lead to serious damage or even explosions; therefore, the analysis of hydrogen is particularly important.

Results of repeatability tests on instrument gas measurements conducted over several consecutive days. It can be seen that the data for CO and CO₂ measured using process mass spectrometry exhibit a high degree of repeatability. Test results for the linearity of CO and CO₂ measurements at different concentrations, based on single-point calibration using process mass spectrometry. The measured values fall entirely within the tolerance range of the true values of the calibration gases. Gas output rate is a crucial parameter for optimising blast furnace operation. Some mass spectrometry users also insert probes into the blast furnace chimney to take measurements.

Practical experience has demonstrated that the economic value of the energy savings achieved through process optimisation—resulting from reduced coke consumption—can offset the cost of a mass spectrometer within just 3–6 months. The ProC-TOF series can be used for a variety of measurements, such as:

Analysis of reducing gases at several different levels within the blast furnace

Rapid analysis of gas composition at multiple points to enable precise air control

Analytical results that allow plant operators to increase or decrease the flow rate of the inlet air

In addition to gas analysis at the blast furnace top, ProC-TOF industrial process mass spectrometers are frequently used for analysis during blow-off and quenching operations. In addition to monitoring combustion products to indicate the progress of blow-off and proper quenching, hydrogen can also be monitored to ensure that explosive levels are avoided. Analysis in this process results in:

Faster turnaround times due to accurate endpoint detection

Enhanced safety through hydrogen monitoring

Reduced risk of damage to furnace components

Applications of mass spectrometers in blast furnace ironmaking:

I. Improving gas efficiency and reducing coke consumption

During blast furnace production, excessive CO₂ content in the top gas reduces the furnace’s thermal efficiency; conversely, excessive CO concentration leads to low energy utilisation and an increased coke ratio. Under constant direct reduction conditions, every 1 per cent increase in gas efficiency reduces coke consumption by 8 kg per tonne of iron and increases the yield of molten iron by 3.5 per cent. To realise these cost benefits, analysis time must be kept to an absolute minimum to enable rapid feedback on burner combustion conditions from the data points. The use of an in-process mass spectrometer on the blast furnace has reduced this absolute time from 15 minutes to 2–4 minutes.

II. Mass Balance

Analysis of top gas flow is essential for measuring smelting intensity, fuel ratio and pig iron output; uniform molten iron quality is ensured through closed-loop control of furnace temperature. When using discrete analysers, calculations are based on the percentage of nitrogen in the top gas. This is based on the assumption that the nitrogen in the top gas represents the total nitrogen content in the furnace (as nitrogen does not participate in any reactions within the furnace). For nitrogen, a 1 per cent error can lead to a 3 per cent error in the predicted mass balance. Similarly, a 1 per cent error in nitrogen can result in fluctuations of 5 kg/t in the coke ratio and 10,000 m^²/h in blast air flow rate. The nitrogen analysis method provided by the ProC-TOF mass spectrometer effectively reduces errors in the mass balance.

III. Thermal Balance

Gas analysis is a core component of blast furnace thermal control; by analysing the blast furnace thermal balance, the silicon content in the molten iron can be predicted in advance. The fundamental requirement for thermal balance is accurate and repeatable analysis of the top gas. The WU coefficient in thermal balance—that is, the ability to predict silicon content—indicates the available heat associated with molten iron mass parameters (including silicon). The WU value is sensitive to gas composition; consequently, an error of ±1 per cent renders it unsuitable for any high-sensitivity control scheme.

IV. Hydrogen Analysis

An increase in hydrogen content within the furnace indicates water leakage from the furnace cooling system, which has implications for safety and furnace temperature. Water ingress into the furnace during cooling can lead to heat loss and increased fuel consumption. The ProC-TOF mass spectrometer enables continuous and precise control of hydrogen levels during maintenance, thereby preventing the formation of explosive gas mixtures. The mass spectrometer analyses hydrogen composition and provides rapid alerts in the event of a sudden increase in hydrogen levels.

V. Sampling System and System Communication

The ProC-TOF process mass spectrometer is typically located in an analyser room at the base of the furnace and takes samples from the top-off gas, as well as from the upper and lower charge probes. Sampling control signals are output to the sample control system, and the analysis results are transmitted to the DCS for display. Should the process analysis system receive any alarm signal from the system, the transmission of analytical data will cease. The mass spectrometer’s PC may be housed in the analyser room or in a remote control room, communicating with the Distributed Control System (DCS) via analogue and digital input/output (I/O). Communication is achieved via RS232, RS45, Ethernet, and a range of suitable networks and data buses, such as Modbus, Profibus and Allen-Bradley data buses. The use of the ProC-TOF mass spectrometer in blast furnace gas monitoring is essential for calculating gas efficiency and mass balance, as well as for the early detection of leaks, saving users at least 10 kg of coke per metric tonne of iron.