Analyzing the importance of desulfurization liquid

Thread Content

During the desulfurization process, the analysis of the components in the desulfurization solution plays a role in supporting and guiding production; it serves as the eyes and ears for normal operations. Therefore, when selecting methods for analyzing the desulfurization solution, it is essential to ensure speed, accuracy, and the use of small sample sizes. The analysis of the desulfurization solution in wet desulfurization mainly includes the following items: the pH value, OPR value, total alkalinity, total iron content, and the analysis of by-products (sodium thiosulfate, sodium sulfate) in the desulfurization solution. Below, the common issues in each type of analysis are listed one by one, along with a brief assessment of the importance of each analysis item. 1. pH value: The pH of the solution increases as the total alkalinity rises, and it also changes with alterations in other cations and anions present in the solution. However, the key factor is the equivalent ratio of sodium bicarbonate to sodium carbonate. When the total concentration of sodium ions in the solution remains constant, a higher carbon dioxide concentration leads to an increase in the mole ratio of sodium bicarbonate, thereby reducing the pH value. Therefore, it is best to keep the pH between 8.0 and 8.5. A too low pH value hinders the absorption of hydrogen sulfide, while a too high pH value causes the formation of by-products, reduces oxygen absorption, and also impedes the aggregation of sulfur. 2. ORP value: The ORP value refers to the potential of the desulfurization solution, and it reflects the redox capacity of the solution. It also gives an indication of the ratio between Fe2+ and Fe3+. This value should be maintained between -125 mV and -250 mV. An excessively high ORP value can lead to the formation of double salts, while an excessively low value can cause the catalyst to become deactivated, reducing its oxidizing capacity; in some cases, FeS precipitates may even form. Therefore, regularly measuring the ORP value allows for a quick assessment of the performance of the desulfurization solution. ORP is measured using a potentiometric agent; the potentiometer works similarly to that used for pH measurement, and may need to be calibrated daily to maintain measurement stability. 3. Total alkalinity: The determination of total alkalinity relies on acid-base neutralization reactions; a standard sulfuric acid solution is used for titration in the presence of an indicator, thereby allowing the calculation of the amounts of sodium carbonate and sodium bicarbonate. From this, the total alkalinity of the desulfurization solution can be determined. The total alkalinity is generally maintained between 0.3 and 0.6. Keeping it at a lower level is highly beneficial for maintaining stable operating conditions, reducing the formation of by-products, lowering resistance, and decreasing the amount of material carried away during regeneration. The importance of determining total alkalinity is self-evident; the addition of alkalis serves as a guide and is directly related to production costs. 4. Total iron: The iron-complexed desulfurization system uses Fe as a catalyst, and the iron ion content is an important parameter. Iron ions are inevitably lost during the production process; if their concentration is too low, hydrogen sulfide in the gas cannot be completely removed, failing to meet the purification requirements. Furthermore, if the total iron concentration is too low, Fe3+ will be reduced to Fe2+ to an excessive extent, which may affect the regeneration process and create a vicious cycle that leads to the collapse of the entire system. Therefore, regular testing of total iron is essential, and atomic absorption spectroscopy is recommended for greater accuracy. 5. Scientifically speaking, in the wet oxidation method for desulfurization, the formation of by-products is inevitable; in other words, it is an inherent phenomenon. No matter what desulfurizing agent is used, it is not possible to eliminate or prevent the formation of such by-products. For example: 2HS- + 2O2 = H2O + S2O32-, 2S2O32- + 5O2 = 4SO42-. Of course, when high-quality and efficient iron-based complexing agents are used, hydrogen sulfide reacts rapidly with these agents, preventing HS- from coming into contact with oxygen and thus avoiding any peroxidation reactions; as a result, almost no by-products are formed. However, the detection of by-products indirectly reflects whether the system is operating stably; therefore, it is essential to regularly check the content of by-products in the desulfurization agent.