Guardian in the chemical park
TOC process measurement at Leuna Chemical Park, Germany
As a method of analysis that has been established for decades, the sum parameter TOC (Total Organic Carbon) measures the total contamination of organic components in a matrix in a single analytical run – whether in a laboratory environment or online during an industrial process. This makes the TOC a versatile and universal parameter, as demonstrated by InfraLeuna Chemical Park in Leuna, Germany.
The Leuna Chemical Park, located in the heart of central Germany, stands for dynamism, innovation and maximum efficiency. As an independent operator of the entire infrastructure, InfraLeuna ensures the synergy of the Leuna chemical site and provides the framework for local companies for a cost-effective and efficient production.
The comprehensive offer of InfraLeuna consists of the redundant provision of steam, electricity, fresh water and drinking water as well as sanitation and other services. This also includes complex logistics services. The focus is on the business success for the customers and the further development of the chemical site as a whole.
Analytical monitoring of water quality is an integral part of these services. It is an important tool for safe running of all processes, and protection of equipment and the environment. It is carried out at various points where different water qualities occur, such as waste water, ultrapure water or water vapor.
Analytical monitoring of water quality by TOC measurement is essential for efficient processes in the Leuna Chemical
The TOC
To quickly measure the level of organic component contamination in water, the TOC value is determined. This can be done offline in the lab as well as online during the process. Shimadzu’s TOC-4200 is an example of a TOC process for online monitoring.
An automatic sampling station withdraws process water steadily and feeds it to the analyzer. It is important to adjust the extraction to the respective water quality: If it contains particles, it has to be treated differently than saline particle-free water. Shimadzu offers various sampling modules for this purpose. Up to six different sample streams can be connected to one station and can be measured by a single analyzer.
Important for the determination of the TOC is the differentiation between organic and inorganic carbon. After all, carbonates and bicarbonates can be found in every natural water. The most commonly used method for TOC determination is therefore the so-called NPOC (Non Purgeable Organic Carbon) method. The sample is acidified in order to convert the carbonates and bicarbonates contained to CO2. Subsequently, the resulting carbon dioxide is expelled by a gas stream which is passed through the sample.
This sample preparation is done automatically by the TOC-4200. Once the inorganic carbon is removed, an aliquot is injected automatically onto a 680 °C platinum catalyst where all existing organic compounds are oxidized to carbon dioxide. The resulting CO2 is conducted by a carrier gas flow to a highly sensitive CO2-selective NDIR detector and subsequently measured. Based on an external calibration, the TOC concentration is then calculated.
Wastewater treatment
At the chemical site of Leuna, about 300 m3 per hour of wastewater is produced that needs to be cleaned. For this purpose, the site operates its own multi-stage wastewater treatment plant. In order to protect the biological treatment stage of the sewage treatment plant, the entrance of the biological treatment stage is meticulously controlled. An online TOC system closely monitors the inflow, as excessive amounts of organic load can severely disrupt or even kill the plant’s sensitive biology. In order to detect potential incoming volatile solvent loads, NPOC and also POC (purgeable organic carbons) as option are measured in the feed.
To control the efficiency of the wastewater treatment plant and the clarification process, output of the wastewater treatment plant is also monitored. For this, two streams are analyzed:
- waters from the various purification stages of the sewage treatment plant
- surface waters resulting from precipitation events.
If the appropriate limits are not exceeded, the water may be discharged to the river. To avoid environmental damage, the TOC-4200 systems used for this purpose are connected to a mechanical gate valve system. If the limit value is exceeded, the valve is closed automatically and the water is sent to a containment tank and then returned to wastewater treatment.
Ultrapure water
In many areas of the chemical park, ultrapure water is used, either for chemical processes or for thermal processes in waste heat or boiler plants. InfraLeuna produces about 350 m3 ultrapure water per hour. In this manufacturing process, different techniques are combined. The raw water is first decarbonated, filtered through a gravel filter and a candle filter, then purified by reverse osmosis and desalted by ion exchange.
TOC impurities in ultrapure water can have a negative impact on chemical processes. Especially in the production and processing of high purity chemicals, contamination can have a negative influence on the quality of the product. An important specification of ultrapure water is thereby described by the TOC: it must not contain more than 0.2 mg/L of organic carbon. The ultrapure water is therefore examined continuously before feeding into the supply lines. To perform such sensitive measurements, a special high-sensitivity catalyst is used. The platinum-plated quartz wool of the catalyst enables injection of higher volumes. Detection limits below 50 µg/L TOC are achieved in this combination.
Steam / condensate
One of the most important sources of energy in the Leuna Chemical Park is steam. It is used to heat reactors and is sometimes even part of the manufacturing process. InfraLeuna supplies their customers and their own plants with steam at different pressure levels. The steam is generated with high efficiency, using cogeneration system in a combined cycle power plant.
Contaminants in the water used for steam production can have negative effects on the plant. In addition to inorganic substances such as salts or CO2, organic contaminants can also cause damage. In steam generation, some organic substances are decomposed. Decomposition products, e.g. organic acids, lead to increased corrosion of system components such as heat exchangers or the blades of steam turbines.
In the return condensate, organic substances can accumulate. The condensate is therefore also monitored and only reused if a maximum limit of 0.8 mg/L TOC is met. If the measured TOC concentration is higher, the condensate is treated by suitable procedures before reuse. To protect the system components in the steam-condensate circuit, TOC is carefully monitored.
Recooling Water
For condensation in the water-steam circuit, additional cooling circuits are needed. The cooling towers used for this purpose with their large amounts of water are an open system, in contrast to the closed water-steam circuits. From the outside, various environmental influences affect the water quality of the so-called recooling water. In addition, with temperatures between 20 °C and 40 °C, it presents an ideal breeding ground for microorganisms of all kinds. To reduce microbial contamination, chemicals are added to the recooling water. This water is also monitored continuously for its organic impurity level.
Sampling
At the Leuna chemical site, process TOC devices are used in many places to monitor the water. Sampling, on the other hand, is carried out in all used systems by means of counter flow-extraction. The sampling system consists of a curved overflow pipe into which a sampling capillary is inserted.
The sampling point is located directly behind the pipe bend, so that a turbulent flow of the sample homogenizes a multiphase mixture which may be present. The TOC-4200 draws the flowing sample out of this capillary against its direction of flow, and then washes it back with rinse water. The sampling device thus contains no moving parts or filters and is effectively maintenance free. The flowing medium flushes particles or deposits away from the capillary, so that no blockages can occur.
Conclusion
Many varied fields of application with TOC analysis are in operation in a chemical park such as in Leuna. Whether sewage, rainwater, condensate, ultrapure water or recooling water, whether with or without salts and particles – all waters have their own requirements for analysis, which can be met by appropriate options.
Read for you in Laborpraxis December 2017
