Thyssenkrupp in Andernach, Germany is the world’s largest production site for the packaging and production of chromium-coated blackplate. The packaging steel produced by Thyssenkrupp Rasselstein is eventually transformed into cans for food, beverages, aerosols, paints and much more. The company employs approximately 2,400 workers and produces around 1.5 million tons of packaging steel each year.
The exhaust air that is produced from Thyssenkrupp’s production of chromium-coated blackplates is treated prior to its release into the environment in an effort to prevent the release of harmful pollutant emissions. As the limit value for chromium(VI) in exhaust air in Germany is 50 μg/m3, Thyssenkrupp continually works to ensure their compliance with these federal regulations.
In an effort to do so, Thyssenkrupp has recently utilized a fully automated online measurement program that enables the company to optimize their emission content analysis to minimize any possible emissions containing heavy metal concentrations.
Monitoring Chromium(VI) Emissions
In addition to complying with Germany’s regulations on chromium(IV) emissions, the exhaust air released from the chrome coating plant at Thyssenkrupp's Andernach location is also regularly subjected to regulatory inspections regarding its chromium(VI) content.
Sampling of emissions for chromium(IV) concentrations is first conducted by a sampling probe that is used to suction exhaust air from the plant's chimney. Particles are then separated using a filter element. The sample is then sent to an accredited laboratory where the filter residue is eluted and mixed with 1,5-diphenylcarbazide to form an optically active complex with Cr(VI). The formation of this complex enables its determination by photometric analysis, in which results of the analysis are provided to Thyssenkrupp within 2 to 4 weeks after the initial sampling has been conducted.
It is important to note that this type of sampling measurement only provides an integrated value of the Cr(VI) content across the long sampling period. From this value, regulatory officials are unable to determine whether there are concentration peaks during this time that exceed the limit value.
Limiting the Release of Chromium(VI) in Exhaust Air
Regulation of the maximum chromium(VI) content that is present in industrial exhaust air varies from country to country. For example, in Germany, the Federal Immission Control Act (BImSchG) specifies a numerical limit value of 50 μg/m3, whereas in the United States, the Environmental Protection Agency (EPA) sets Maximum Achievable Control Technology (MACT) requirements that are based on the emissions of the best performing facilities in the respective sector of industry.
The Thyssenkrupp Approach to Chromium(IV) Emissions
Thyssenkrupp has recently installed a Metrohm Process Ion Chromatograph (Figure 1) that is placed directly at the chimney of the exhaust air purification system for its chrome coating plant. This ion chromatograph determines the presence of any Cr(VI) traces in a fully automatic method after just 1.5 to 10 minutes of sampling. Once sampling procedure is initiated, results are available in less than 30 minutes.
Figure 1. The Metrohm Process Ion Chromatograph at thyssenkrupp Rasselstein.
The sampling of exhaust air emissions is conducted using a gas sampler that suctions exhaust air a duration of approximately ten minutes, in which the sample is then transferred the Process IC control.
Ten minutes of sampling results in a measuring range of between 0.6 and 6 μg/m3, however this range can be adjusted by changing the sampling period. The suctioned exhaust air sample is then transferred to a solution through a wash bottle containing ultrapure water to allow the Cr(VI) content to be fully absorbed and concentrated here. The sample solution is then transmitted to the analysis system.
Figure 2. The wash bottle, in which the analyte is transferred to a solution.
Fully Automated Results
In the analysis system, chromatographic separation takes place on an anion separation column. Post-column derivitzation with 1,5-diphenylcarbazide is then performed to allow for the detection of Cr(VI) concentrations as a result of the formation of a complex following the interaction of the chromate ions and 1,5-diphenylcarbazide. This complex can be absorbed easily at 538 nm, thereby allowing an accurate recording of its quantity to be assessed by the UV/VIS detector.
The Metrohm Process IC achieves a detection limit of 0.028 μg/L at 95% for the concentration of Cr(VI) present within the absorption solution. By increasing the sampling period, a concentration of up to 0.05 μg/m3 Cr(VI) can be reliably determined in exhaust air by the Metrohm Process IC.
The Cr(VI) concentration in the exhaust air is automatically calculated from the measured concentration in the absorption solution, in which the results of these calculations are exported to the process control system and stored in the database of the Metrohm ProcessLab Manager. This software handles the process communication and overall control of the Metrohm Process IC, thereby enabling single values and trends to be monitored easily and accurately.
With its robust housing with protection class IP65, the Metrohm Process IC is ideally equipped for use in the process. The components included in the Metrohm Process IC include all required reagents that are necessary for the fully automated analysis. From sampling, sample preparation, analysis, evaluation and export of the results, the Metrohm Process IC is equipped to handle all Cr(VI) measurements in a fully automated manner. By using the Metrohm Process IC, Thyssenkrupp Rasselstein evaluates their chemical emissions at least twice a week, however the actual manual work required for these analyses could be reduced to an even greater extent by integrating an ultrapure water system. It should be noted that at least one hour every month is required to replace the pump tubing and restart the system to ensure a continuous operation without any possible problems during analysis.
To achieve a measurement range of 1.2 to 12 μg/m3, the Metrohm Process IC achieves a maximum measuring frequency of 2 analyses per hour, in which only 1.5 to 5 minutes are required for the actual sampling procedure and the analysis time typically requires 17 minutes. Additionally, 5 minutes at the end of the analytical procedure is required for rinsing processes. Therefore, the total analysis time should typically last less than 30 minutes.
Achieving Process Optimization
Thyssenkrupp has implemented the semi-continuous analysis of the Cr(VI) content in an effort to optimize their analytical processes to ensure that their Cr(VI) emissions are reduced. For example, it has been established that the process speed of the production plant and certain settings in the exhaust air purification system have a major impact on the Cr(VI) content in the exhaust air, therefore, by optimizing these parameters, it was possible for the company to achieve significant improvements in their Cr(VI) emissions.
It has also been identified that weather plays an important role in the Cr(VI) emissions. In fact, the Cr(VI) content is subject to a sinusoidal fluctuation with a peak of approximately 30 μg/m3 around the afternoon, whereas a minimum of below 5 μg/m3 is detected during the evening. A systematic investigation of the fluctuation in Cr(IV) emissions in relation to environmental temperature and air pressure shows promise for further improvement potential.
Figure 3. By adapting the mode of operation, lower Cr(VI) emissions are achieved, and these hardly change if the plant speed is increased.
The Benefit of Online Analysis of Cr(VI) Emissions
Thyssenkrupp Rasselstein is already benefiting from the online monitoring of the Cr(VI) content in their emissions. Rather than simply meeting federal limit regulations following random sampling procedures, Thyssenkrupp can now associate any changes in the concentration of Cr(VI) in their emissions to potential causes in their industry. This enables the steel manufacturers to satisfy the highest quality and sustainability standards at its largest production site worldwide.
The continuous online monitoring of emissions conducted at Thyssenkrupp in Andernach has provided useful information on factors that affect their manufacturing procedures. For example, the semi-continuous monitoring showed the company that their Cr(VI) emissions has worsened following repair work performed to the lamella separators on the exhaust air treatment system. Without the Metrohm Process IC, this would not have been determined until the next regulatory inspection, which could have resulted in fines and other penalties to the company. By implementing the Metrohm Process Ion Chromatograph, Thyssenkrupp has detected any increase in their Cr(VI) emissions immediately, as well as determine the source and potential resolution immediately.
This information has been sourced, reviewed and adapted from materials provided by Metrohm AG.
For more information on this source, please visit Metrohm AG.