Application of Siemens online analytical instruments in the steel industry

1. Introduction

The steel industry plays a pivotal role in my country's national economy. As a global manufacturing center, China has great potential for industrial development, and sustained economic growth will provide impetus for the development of the steel industry. Today, China's steel industry is undergoing a process of mergers and reorganizations, elimination of obsolete production capacity, optimization of industrial layout, development of a circular economy, and energy conservation and emission reduction. The healthy and steady development of the steel industry is of great importance.

The steel smelting process is essentially a circulation process of raw materials, fuels and finished products, during which a large amount of gas is generated. Online detection and analysis of these process gases is one of the key technologies essential for optimizing production process control, safety and environmental monitoring in the metallurgical industry. Siemens is a partner of China's steel industry and has been committed to promoting the continuous improvement of the automation level of China's steel industry. Siemens analytical instruments can be applied to various devices such as steelmaking, ironmaking and sintering in the steel industry, playing a very important role in reducing energy consumption and ensuring production safety. They also have a positive effect on increasing the production capacity and improving product quality of steel enterprises.

2. Analyzer Introduction

Siemens analytical instruments cover all kinds of gas analyzer products and can provide customers with a variety of solutions. Siemens analytical instruments include online chromatographs, infrared analyzers, oxygen analyzers, thermal conductivity analyzers and laser analyzers.

Among them, the MAXUM II online chromatograph, with its powerful functions, can be used to analyze and measure the content of various gas components in various complex samples, such as CO, CO2, N2, H2 in blast furnace gas, CO, CO2, H2, CH4, O2, N2 and trace H2S in coke oven gas, etc. Coupled with Siemens' powerful EZChrom chromatography workstation software, it can also be used for laboratory analysis.

The multi-component non-spectral infrared analyzer ULTRAMAT 6/23 obtains the concentration of the measured gas by analyzing the absorption of the measured gas on the measuring beam. Due to its wide light source, it can simultaneously measure multiple components such as CO, CO2, SO2, etc. The OXYMAT 6 magnetic pressure oxygen analyzer obtains the concentration of oxygen in the mixed gas by measuring the volume magnetic susceptibility of the oxygen-containing mixed gas. Its fast response time enables it to be used for safety control and optimization control.

Laser analyzers LDS 6 and SITRANS SL can measure in situ online and obtain data in real time. With low maintenance costs and a minimum response time of 1 second, they gradually replace some traditional analyzers and become the new favorite in the steel industry. The next chapter will specifically introduce the application of these analyzers in various devices in the steel industry.

3. Application of Siemens analyzers in the steel industry

3.1. Application in ironmaking

Blast furnace smelting is the most important ironmaking method in today's ironmaking process. Current detection of the content of each component in blast furnace gas can timely reflect the furnace conditions and guide the operation of the blast furnace, thereby ensuring the stable and smooth operation of the blast furnace. At the same time, it plays a very important role in improving product quality and output.

Siemens MAXUM II chromatograph can detect the content of N2, CO, CO, and H2 in blast furnace gas online, and automatically provide a set of accurate and reliable percentage content of each component in blast furnace gas to the blast furnace control center in each cycle. By calculating the ratio of CO2/ (CO+CO2), the gas utilization rate is judged and the coking coal ratio is controlled. Generally, when the coke load remains unchanged, the ratio decreases, indicating that the gas utilization rate decreases, which indicates that the blast furnace is cooling down; by observing the H2 content, it is judged whether the small set of high-pressure water in the tuyere and the normal-pressure water of the furnace cooling wall are leaking. If the H2 value increases, it means that there is a leak, which needs to be solved as soon as possible to prevent explosion; by detecting the N2 content, the leakage rate of the blast furnace can be inferred. The sampling point is generally selected on the horizontal gas pipeline after the gravity dust collector and before the bag dust collector. Since Siemens chromatograph has many technical advantages such as multiple detectors, parallel chromatography, valveless switching, and electronic pressure control, the response time of the measurement is improved and the reliability of the measurement data is guaranteed. In addition, analytical instruments can help measure the O2 content at the hot blast stove outlet, optimize blast furnace combustion, and improve product quality.

In addition, in order to improve the economic efficiency of ironmaking and reduce costs, many domestic blast furnaces use bituminous coal or sparged bituminous coal to complete the ironmaking process. Since bituminous coal is highly volatile and combustible, when the coal is ground in the coal mill, too much oxygen entering can easily cause an explosion. Therefore, the oxygen content must be tested on the hot air duct in front of the coal mill and after the bag filter after the coal mill. If the oxygen content is too high, an alarm must be sounded. In the pulverized coal bin, the CO content must also be tested. When the CO content is too high, nitrogen must be flushed in time to prevent accidents.

In the application of blast furnace coal injection, Siemens' OXYMAT 6 magnetic pressure oxygen analyzer, ULTRAMAT 6/23 non-dispersive infrared analyzer LDS 6 and SLTRANS SL laser analyzer have all been well applied. Among them, the laser analyzer has its own advantages over the traditional extraction analyzer. First, the laser analyzer is installed in situ and directly installed on the process pipeline, eliminating the sampling probe, sampling pipeline and pretreatment system. Secondly, the laser analyzer is very easy to maintain, which reduces maintenance costs. Finally, the response time of the laser analyzer can be as low as 1 second, providing data for the safety protection system in a timely manner, and can be competent for the measurement of key points. It is worth mentioning that although the laser analyzer has many advantages, it cannot completely replace the traditional analytical instrument. At some measurement points, such as the outlet of the coal mill, the coal powder bin, etc., due to the very large dust content, the transmittance of the laser will be greatly affected, resulting in poor measurement results. At this time, only the traditional extraction analyzer can be used for measurement. [page]

The Pudong Iron and Steel relocation project in Luojing was listed as the second key project of Shanghai's "World Expo" relocation project. It is also the world's first COREX C3000 new ironmaking technology demonstration project with an annual output of 1.5 million tons of molten iron. It has attracted much attention from the industry and the public. In this project, Siemens analytical instruments were used in the measurement of CO content in the pulverized coal bunker and H2 analysis of furnace gas.

In the steel industry, Siemens can provide complete solutions with its comprehensive product line. Figure 1 below shows the application of Siemens analyzers in blast furnace ironmaking process.

Figure 1. Application of Siemens analyzer in ironmaking

3.2. Application in converter gas recovery

The characteristics of converter steelmaking are large throughput, short cycle, and high smelting intensity. A large amount of flue gas is easily generated in converter production, and its main component is coal gas, of which CO accounts for about 60% to 70%. It is a dangerous gas that is toxic, harmful, flammable, and explosive. It is also a good chemical raw material and industrial production energy. Therefore, the purification and recovery of converter gas is an important part of steelmaking that cannot be ignored. In the past, the gas produced by steelmaking was directly released, which not only polluted the atmosphere and destroyed the natural environment, but also wasted a lot of energy. Realizing the maximum recovery of converter gas has huge economic and social benefits for reducing consumption and increasing efficiency, reducing air pollution, and saving energy and protecting the environment.

The analyzer measures the CO/CO2 and O2 values ​​after the secondary dust removal, before the flue gas discharge, and at the gas cabinet outlet and before the electrostatic precipitator. The CO/CO2 detection is to ensure the recovery of the most valuable gas, and the O2 detection is to avoid the excessive oxygen content in the gas, which may cause explosion during recovery or use.

For these two measurement points, LDS 6 and SITRANS SL laser analyzers are a good choice due to their easy maintenance and short response time. Their IP65 protection level, Zone 1 explosion-proof design and automatic calibration function can fully meet the harsh working conditions on site and ensure effective and safe gas recovery.

In the gas recovery of the steel industry, including blast furnace gas, COREX furnace gas, coke oven gas, etc., there are certain requirements for the H2S content in the gas. Another application of the analyzer in gas recovery is to use a chromatographic analyzer to measure the sulfur content in the gas.

3.2.1. Project Introduction

Tianjin Tiantie Metallurgical Group is a large enterprise group supported by Tianjin Municipal Government. It ranks 152nd in the newly released list of China's top 500 enterprises in 2006 and 72nd in the list of China's top 500 manufacturing enterprises. It currently has an annual production capacity of 3.5 million tons of iron, 3.5 million tons of steel billets and 2.57 million tons of steel products, and enjoys a high reputation at home and abroad. In recent years, Tiantie Group has continuously cooperated with world-renowned steel companies to learn advanced technologies. In the hot rolling project and process reconstruction in which Voestalpine participated, Siemens LDS6 laser gas analyzer was used to monitor the content of CO and CO2 in converter gas in real time and participate in process control; as well as oxygen content monitoring related to safety in converter gas recovery.

The "long process" consisting of blast furnace ironmaking, oxygen converter steelmaking, and finally rolling by rolling mill is the main production process in today's steel industry. More than two-thirds of steel is produced by the long process. Iron ore is refined in a blast furnace to form molten iron, which contains a large amount of carbon and impurities (such as sulfur, phosphorus, etc.). In order to obtain high-quality steel, the molten iron must be further processed to remove carbon and impurities. The oxygen converter (BOF) is a common steelmaking equipment. Molten iron is injected into the converter, and high-pressure oxygen is blown into the converter by a water-cooled nozzle. The blown oxygen combines with the carbon in the molten iron through oxidation to form CO and CO2, which are separated from the molten iron and discharged in the form of furnace gas. The entire converter steelmaking process takes about 15 to 20 minutes. CO and CO2 in the furnace gas can be used as a parameter group to reflect the working status of the converter. By monitoring the content of CO and CO2 in the furnace gas, the working efficiency of the converter can be improved. The fast response of LDS6 can accurately determine the end time of the entire process, save a lot of oxygen and energy, and optimize the entire process.

Converter gas contains a large amount of CO, which can be recovered as combustible gas. The recovery and treatment of such high-CO gas requires special attention to explosion-proof safety. Fast, accurate and interference-free measurement is one of the characteristics of the LDS6 in-situ laser gas analyzer. Using LDS6 to monitor the oxygen content in converter recovery gas can enhance safety.

Figure 2. Application of Siemens analyzer in steelmaking[page]

3.2.2. System composition

The LDS6 laser gas analyzer adopts in-situ measurement, without sampling and sample gas processing system, and completes the analysis directly at the installation point. The whole system consists of a central processing unit, a transmitting probe, a receiving probe and a composite optical cable. The laser light source is located in the central processing unit, and the emitted laser is transmitted to the transmitting probe by the optical cable. The laser passes through the measured gas and is detected by the receiving probe. The detection signal is transmitted back to the central processing unit for processing, analysis and display. The central processing unit also assumes the functions of human-machine interface and input and output. The transmitting probe and receiving probe of LDS6 are directly installed on both sides of the on-site analysis pipeline (see Figure 3). Both adopt modular design, and most of the hardware can be interchanged. The Tiantie converter gas monitoring project* uses two sets of LDS6 equipment to monitor CO, CO2, and O2 in the converter gas after electrostatic precipitator. The former is used for the optimization and control of the converter process and the latter is for the purpose of gas recovery safety.

Two sets of LDS6 are used for the measurement of CO, CO2, and O2. The Siemens LDS6 laser analyzer uses optical cables to transmit signals. The optical cable mode selection can be used to further ensure the "purity" of the signal, improve the measurement system's ability to resist electromagnetic interference and adapt to harsh environments. At the same time, the central processing unit uses the twisted pair integrated in the composite optical cable to power the probe, without

The probe is then powered on site. The protective layer on the outside of the optical cable makes it meet the requirements of industrial sites.

Figure 3. Application of laser analyzer LDS 6 in steelmaking

3.2.3. Functions completed by the system

Steelmaking from iron ore requires two steps: blast furnace ironmaking and converter steelmaking. Iron ore is melted into molten iron in a blast furnace. Since the molten iron contains impurities such as oxygen, sulfur, and phosphorus, they need to be further removed. The steelmaking process is decarbonization (degassing), desulfurization and dephosphorization, as well as the subsequent deoxidation and heating process. The most commonly used steelmaking equipment is the oxygen top-blown converter. Oxygen is blown in from a water-cooled nozzle, and the carbon in the molten iron is directly oxidized into CO bubbles in the reaction zone. When the carbon is low, part of the carbon reacts to generate CO2. The converter gas contains a large amount of CO, a small amount of CO2, and trace amounts of other high-temperature gases. The gas analyzer mainly monitors CO and CO2 in the analysis of converter gas. Their content and change trend can be used as important information to directly feedback: (1) the process progress and end time of converter decarbonization; (2) information such as the temperature of the molten steel; and (3) the status of the slag making process. Since the entire converter steelmaking process only takes 15-20 minutes, the analyzer is required to have a fast response time in addition to accurate analysis results. Otherwise, there is no practical significance for the control and optimization of the entire process.

Converter gas contains a large amount of combustible components, which can be recycled for reuse. During the recycling process, attention must be paid to explosion prevention. If the oxygen content in the gas is too high, the gas will easily exceed the lower explosion limit, which is very detrimental to the safety of equipment and personnel. The oxygen content must be monitored at all times during the gas recovery process. Once it exceeds a certain set value, measures must be taken quickly to prevent accidents. The monitoring of oxygen content in the gas must also meet the requirements of accuracy and speed, so that as much gas as possible can be recycled under the premise of production safety, and an alarm can be quickly issued when a dangerous situation occurs to avoid the loss of personnel and material resources.

In the application of converter gas monitoring and recovery of Tiantie, the analyzer is installed after the electrostatic precipitator to analyze the CO, CO2 and O2 content of the converter gas. The CO and CO2 content is used to reflect the decarbonization information of the converter. The CO and O2 content is used as the basis for judging gas recovery, and the analysis results control a three-valve group.

In order to effectively and safely recover converter gas, a three-valve group is installed in front of the gas tank to control the recovery or release of gas. There are three criteria for judgment: (1) The O2 content is less than 2%. Too much oxygen will make the gas in the gas tank close to the lower explosion limit, making the entire gas tank and even the factory area in a very dangerous situation. The oxygen content in the recovered gas must be strictly controlled. Once it is higher than 2%, the three-valve group will release the gas. (2) The CO content is greater than 35%. The purpose of recovering converter gas is to utilize the large amount of combustible components (mainly CO) in it. Analyzing the CO content can ensure that high-quality gas is recovered as secondary energy. (3) There is still space in the gas tank to store gas. For the entire gas recovery control, the analysis results of O2 and CO are crucial and must meet the requirements of accuracy and speed. This is not only from the perspective of process control optimization, but also related to safe production.

The LDS6 in-situ laser gas analyzer directly analyzes the pipeline to be tested, without the need for sampling, sample gas transportation, pretreatment systems, etc., and the response speed can reach 1 second. Figure 4 is a comparison of the analysis results of the traditional extraction infrared analyzer and the LDS6 laser gas analyzer. It is not difficult to find from the figure: (1) The response speed of the LDS6 is much better than that of the extraction analyzer. The difference of tens of seconds makes a world of difference for the entire process (15-20 minutes). (2) The results of the LDS6 can better reflect the details of the changes in gas content during the process. The LDS6 laser gas analyzer is a typical line measuring instrument. The gas in the area where the laser beam passes through is involved in the analysis. It can better reflect the true concentration of the component to be tested than the point sampling method of the traditional extraction analysis. The LDS6 is based on TDLAS (Tunable Diode Laser Absorption Spectros copy) technology, based on the principle of spectral absorption, to achieve fast and high-precision detection. One of the most important characteristics of lasers that distinguishes them from ordinary light sources is their good monochromatic performance. The better the monochromatic performance, the narrower the spectrum line width of the light source. Because of the excellent monochromatic performance of lasers, laser absorption spectrum is also called single-line absorption spectrum, which fundamentally eliminates the possibility of interference from the absorption spectrum of other components in the gas when measuring a certain gas component by traditional gas absorption spectrum technology, and can better reflect the actual content and slight changes of the component to be measured. [page]

Similarly, a fast response and online measurement method that can better reflect the actual concentration of the components to be measured is also of great significance for monitoring the oxygen content in converter gas recovery.

Figure 4. Comparison of response time between laser analyzer and conventional analyzer

The LDS6 analyzer has a built-in calibration unit, which integrates the manual external calibration work often required by analytical instruments into the analyzer. The analyzer automatically performs calibration and correction work once in each measurement cycle. This functional design fundamentally reduces the maintenance workload of the LDS6, and also ensures that the LDS6 is calibrated and corrected at all times, improving the measurement accuracy of the analyzer. Traditional manual calibration is a periodic work (for example: calibration once every three months). Only during each calibration can the user confirm the deviation of the instrument. In the interval between calibrations, the user has no way to verify the deviation of the instrument, which may be a huge error for trace analysis. The LDS6 self-calibrates in each measurement cycle, dozens of times per second. It can ensure that each measurement data is "real". Each historical data can be used for performance comparison research without worrying about the impact of instrument drift. The built-in reference cell self-calibration technology of the LDS6 has been recognized by authoritative organizations such as the German TUV and the US EPA. Accurate and drift-free analysis values ​​are of great significance for real-time monitoring of CO and CO2 content in converter gas, as well as monitoring of O2 content, and other applications involving process optimization control, safety monitoring, etc.

Siemens LDS6 laser analyzer uses automatic gain control (AGC) technology, which can dynamically compensate for dust and is also suitable for applications where gas composition changes dramatically. Whether it is a change in dust content or gas composition, or a certain deviation in probe alignment, AGC technology can automatically control the gain according to the received signal strength, so that the signal received by the central processing unit will not be distorted after transmission through the optical cable, providing a signal of sufficient strength for further signal processing. During the real-time monitoring of converter gas, the content of CO and CO2 changes rapidly and dramatically with the decarbonization process. AGC technology can ensure that the LDS6 laser gas analyzer can fully adapt to the entire converter decarbonization process and the analysis requirements of converter gas recovery.

3.2.4. Project operation

The two LDS6 systems were commissioned and put into operation in April 2007, and the overall operation is good. In the early stage of operation, the purge effect was poor, but after improving the probe purge pipe, the problem has been properly solved. The measurement and analysis results of LDS6 are accurate and the response is fast.

3.2.5. Application experience

Compared with traditional extractive analyzers, the in-situ laser gas analyzer LDS6 has a fast response and accurate measurement. It is very suitable for applications such as converter gas monitoring and coal gas oxygen content monitoring that have high requirements for analyzer response time.

Traditional extractive infrared analyzers are subject to time constraints for sampling, transmission, and preprocessing, and the analysis cycle of the entire system is much longer than that of an in-situ laser analyzer. In applications such as monitoring and recycling of gas in Tiantie converters, the system analysis cycle is required to be less than 20 seconds, which means that the extractive analyzer must be installed nearby, which also means that many factors such as civil engineering and public works must be considered on site, increasing the construction volume and cost from an engineering perspective. The LDS6 laser analyzer probe is installed directly on site, and only nitrogen purge of the probe is required to protect the light-transmitting lens and reduce maintenance. There are no other requirements, which simplifies on-site construction and cost requirements.

Citing the analysis results of LDS6 to participate in process optimization and control can improve efficiency, reduce costs, increase safety and other functions, so that users can obtain tangible benefits. [page]

3.3. Application in coking plants

The electrostatic tar precipitator plays an important role in the recovery system of the coking plant. It can recover the tar in the coke oven gas, which not only brings considerable economic income, but also ensures the normal production of the subsequent process. However, the electrostatic tar precipitator is installed on the blower. In order to ensure its safe operation under negative pressure, the oxygen content in the coke oven gas must be detected online, and the interlock shutdown must be performed when the oxygen content is too high.

In previous applications, the traditional extractive OXYMAT 6 magnetic pressure oxygen analyzer was used. Since coke oven gas contains a large amount of highly viscous and easily crystallized substances such as tar, benzene, and naphthalene, a steam jet pump is generally used to introduce the sample gas, and then wash it with water. The introduction of steam makes it difficult for tar to solidify and block the sampling pipeline, and washing with water can effectively remove various impurities. Finally, the clean sample enters the analyzer to obtain the oxygen content. In practical applications, this type of method has also been widely recognized.

Now, the newly launched SITRANS SL laser oxygen analyzer from Siemens can better meet the real-time requirements of this measurement point due to its fast response time. The actual application point is recommended to be applied to the measurement point after electric coke capture to avoid excessive dust and oil content affecting the accuracy of measurement. Its automatic calibration technology and automatic gain control technology (AGC) can help the analyzer be used in occasions with low light transmittance.

Figure 5. Application of Siemens laser analyzer on coke oven gas

3.4. Other applications

In the steel industry, there are other applications such as air separation measurement of single components, gas power generation measurement of calorific value, etc. In addition, the "Steel Industry Adjustment and Revitalization Plan" (Guofa [2009] No. 6) clearly stated that in the next three years, the steel industry should implement a special project for technological progress and technological transformation in the steel industry, give priority support to circular economy and energy-saving and emission-reduction process technologies such as sintering flue gas desulfurization, and put forward clear indicators and requirements for energy conservation and emission reduction in key large and medium-sized steel enterprises. At present, sulfur dioxide in the steel industry is mainly produced by sintering pellet flue gas, and sulfur dioxide produced by sintering pellet flue gas accounts for more than 70% of the total emissions of steel enterprises, and some enterprises reach about 90%.

Siemens Continuous Emission Measurement System (CEMS) has been widely recognized and applied worldwide, and has achieved good application results in many domestic desulfurization projects, helping to monitor the effect of desulfurization and control the desulfurization process. Therefore, flue gas analysis is also a very important application field.

4. End

This article mainly introduces the application of Siemens analytical instruments in the steel industry, and describes one of the projects in detail. For colleagues who want to know more about analyzers, reading this article can give you a simple understanding. In fact, not only in the steel industry, Siemens analytical instruments are widely used in other industries, especially in the petrochemical and chemical industries. In the future, with the continuous improvement of the automation level of various industries in China, the application of analytical instruments will become more and more. I believe that with Siemens' high-quality products and rich experience, we will be able to achieve greater success and contribute to China's industrial development.