The importance of desulfurization solution analysis for the control of desulfurization systems

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The laboratory analysis of the desulfurization fluid in the chemical desulfurization units of coking plants is an important task that must be given attention in the operation and management of such units. For the stable operation of these desulfurization units, it is not only crucial to control process parameters, maintain equipment, and manage processes; laboratory analysis of the desulfurization fluid is also something that requires attention. Desulfurization liquid laboratory analysis is akin to diagnosing a desulfurization unit; it can promptly reveal any problems in the operation of the desulfurization system. Since the application of complexed iron technology currently involves direct replacement in existing HPF units, without any specific design or modification tailored for complexed iron, there are significant changes in the operating approaches and concepts. Precise management is required during operation; important control factors such as tower blockage, corrosion, and the formation of by-products need to be adjusted promptly through data analysis. Therefore, after adopting complexed iron technology, the analysis of the desulfurization liquid becomes particularly important. Regarding the key points for analyzing coking complexed iron desulfurization liquid, my personal summary includes the following aspects: 1. Proper sampling method control – The desulfurization site must ensure that the sampling pipes for the desulfurization liquid are unobstructed. When sampling, it is necessary to first drain a small amount of liquid to remove any stagnant fluid before taking a sample; a way to determine whether the sampling was accurate is to check that the sampled liquid is warm. Samples should be properly labeled and documented; a distinction between lean and rich solutions must also be recorded. Additionally, for multiple systems, samples should be taken in separate containers and clearly marked, in accordance with relevant sampling and sample retention standards. 2. Rigorous control of laboratory testing procedures: The analysis of desulfurization solutions should be carried out by the laboratory analysis team at regular intervals, and tests must be conducted in accordance with national standards or the methods provided by professional technicians. Laboratories should regularly compare the analysis results obtained by different teams and different analysts in order to minimize the impact of human factors as much as possible. For test results with significant deviations or substantial discrepancies, retesting should be carried out promptly. 3. Comprehensive analysis and control of indicators: The test results related to desulfurization and liquefaction must be promptly reviewed and analyzed by teams, technical personnel, and managers. Prior to this, technical staff should have a thorough understanding of the meaning of each indicator and make targeted adjustments as necessary. (1) Total iron concentration: The total iron concentration has a significant impact on issues such as desulfurization tower clogging, by-product salt control, and catalyst consumption. It should be regulated in accordance with the requirements specified in the project design; it is necessary to maintain relative stability in both the total iron concentration and the effective iron concentration, while also properly determining the relationship between catalyst consumption, gas load, and process conditions. Total iron concentration analysis is an important indicator in the control of desulfurization using complexed iron, and it needs to be analyzed daily. (2) Content of by-products: The content of by-products directly indicates whether the complexed iron is under effective control; if this content increases too rapidly, it is necessary to pay attention to changes in the total iron concentration in the system as well as other process parameters such as the volume of air used for regeneration and temperature. The frequency of secondary salt content testing can be determined based on testing conditions, but it should be conducted at least 1–2 times per week. (3) Specific gravity: The range of specific gravity is generally 1.1–1.25 g/cm3. Attention should be paid to any increase in specific gravity; a rapid increase indicates that the control of side reactions is insufficient, or that substances such as suspended sulfur are accumulating at a fast pace. Furthermore, the specific gravity also reflects the accumulation of other impurities in the desulfurization solution, such as soluble organic substances like tar and naphthalene; sometimes, the quality of the desulfurization solution can be assessed directly based on changes in specific gravity during operation. (4) pH value and alkalinity: The pH value is generally maintained between 8 and 9, while the alkalinity is usually around 0.3 mol/L. If pH and alkalinity fluctuate significantly, pay attention to the amount of alkali or ammonia added, as well as temperature control; additionally, changes in gas load or hydrogen sulfide concentration also have a rapid impact on pH. Furthermore, an excessively high pH value can also have an adverse effect on the control of by-products; in the case of iron chelation desulfurization, there is no need to rely heavily on alkalis, allowing the pH and alkalinity to be kept at lower levels. (5) Redox potential: The redox potential is primarily used to characterize the redox properties of the desulfurization liquid. This value is mainly influenced by the amount of gas, the concentration of hydrogen sulfide, and the volume of regeneration air. A relatively low potential indicates a high load and insufficient regeneration; this is generally controlled by the amount of air used for regeneration. Redox potential is one of the analytical parameters that is most easily overlooked. (6) Suspended sulfur: The level of suspended sulfur in the lean liquid should generally be kept below 1.5 g/L; when it rises abnormally, it is necessary to check whether the foam overflow volume is normal and whether the desulfurization liquid has good stability. When iron complexation is used for desulfurization, the sulfur content in the rich liquid is generally relatively high; this is related to the reaction properties of the iron complex and is considered a normal phenomenon. Only by mastering the three steps of sampling, testing, and indicator analysis can process control of the desulfurization system be truly ensured, enabling prior understanding, prior treatment, and root-cause analysis.